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[
"How much speed does the jet engine of an F-18 Super Hornet add to the USS Kitty Hawk [image relevant]"
] |
[
false
] |
[deleted]
|
[
"Using values found online for thrust (63.3kN) and mass of the carrier (~80000t), I calculate that the carrier will gain an additional acceleration of ~0.0008m/s",
" without accounting for drag."
] |
[
"Basic F = ma equation, rearranged to F/m = a and plugged in the numbers to get acceleration."
] |
[
"Basic F = ma equation, rearranged to F/m = a and plugged in the numbers to get acceleration."
] |
[
"Do our bodies send a signal to our brain to wake up when we are cutting off circulation to an arm or leg while sleeping?"
] |
[
false
] |
I've woken up more than once with completely 'dead' limbs. Does the body know what is happening?
|
[
"Yes, and no. Let's consider your hand \"falling asleep\". When a body part falls asleep, what is happening is that there is pressure on the nerve innervating that body part. You sleep on your elbow, and can compress the ulnar nerve at the elbow, and the medial part of your hand falls asleep. ",
"Now, the interesting part. Pressure is a selective nerve block. It blocks larger diameter nerves first. These are motor nerves, so you begin to lose motor function first. Next largest are the low threshold sensory fibers controlling proprioception and touch. You lose these next. Pain fibers are the last to go. ",
"When you are in that intermediate state, when pain is still there but touch is gone, you experience paresthesias. These are numbness and tingling in the medial hand. These could easily wake you up. If not, however, and the pressure continues, the sensation will be completely lost. ",
"When the sensation begins to return, the paresthesias come back first. They occur, specifically, because touch fibers have a modest tendency to inhibit pain fibers. If you have a lot of touch input and a little pain input, it is not perceived as painful. You need a stronger balance of pain to touch to make something feel painful. ",
"When your arm falls asleep, that inhibition is lifted, and even the most modest inputs are felt as burning pain. ",
"Hope this helps. If you have questions, ask. I did my PhD on the sense of touch a little more than 20 years ago, and the concepts in this post are a small section of lectures I give to medical students each year. "
] |
[
"Is there any detriment or chance of permanent damage to sleeping on your arm like that?"
] |
[
"If the numbness goes away in a few minutes after the pressure is relieved, not really. If it lingers, you need a decompression procedure. But remember, this is not medical advice, this is reddit ;)"
] |
[
"Why aren't archaea human pathogens?"
] |
[
false
] |
I'm an undergraduate microbiology student, but I am still pretty mystified by archaea. I realize archaea weren't discovered until relatively recently, but why aren't they more important from a human perspective? Do you think they will eventually be seen as important as bacteria? What's the freakin' deal with archaea?!
|
[
"That is an EXCELLENT question, and unfortunately there is not a very good answer yet. It's not fully known, but there are some ideas.",
"It has been proposed that because Archaea use different cofactors in their metabolism, eukaryotes don't provide a good \"food source.\" But this isn't completely satisfactory, as they do use some factors. To make this even less likely, some Archaea do act as commensals in humans, and \"host as a food source\" is not the only advantage to pathogenesis. So that's kind of out. It may be ",
" factor, but it's not ",
" factor.",
"One recent idea has to do with the genetics of pathogenogenesis (not a typo...refers to how pathogens are generated). One of the big ways a nonpathogen becomes a pathogen is via horizontal gene transfer of pathogenic genetic material. A friendly bug picks up a T3S or a Type II pilus gene (biochemical systems used by pathogens to injure host cells). That gene infers some kind of advantage to the friendly bug, and it starts to use it...BANG, pathogen.",
"A big source of these is mobile genetic elements, like phages. This is Dawkin's selfish gene; eukaryotic viruses (like the common cold) infect eukaryotic cells and thereby increase their number. Prokaryotic pathogenogenic phages ",
" bacteria, which are in turn induced to invade and colonize eukaryotic hosts and thereby increase the range of the phage genes. From the gene (phage) perspective, this not only gives benefit via direct replication, but also through more opportunities for further transduction. The commensals in the eukaryote are fertile ground, with unsullied genomes.",
"And therein lies the reason (maybe): It is known that bacterial phages, on the whole, don't infect Archaea and Archaean phages don't infect Bacteria. This largely has to do with specific molecular differences between the two Domains. The result is that there isn't a good way to get those genes to jump from pathogenic bacteria into Archaea. The Arachaens don't have access to the pathogenogenic genetic information accumulated by Bacteria. Or, more accurately, the genetic information in the bacteria doesn't have access to the Archaean genomes.",
"OK, so why haven't the Archaens developed their own pathogenic mechanisms? Where's the Archaean version of T3S? That's even less known. Maybe it's because Archaens did a lot of early evolutionary development in the absence of eukaryotes, more so than Bacteria. Whatever paths they took are somehow inhibitory or exclusive to pathogenic development. Due to early evolutionary commitments, they are forever excluded from independently developing the pathogenic lifestyle. ",
"Maybe it's just because the development of this complex system of mobile gene elements takes a lot of evolutionary steps, and Archaea just never have done the correct combination. (Implying that they could, but they've been around eukaryotes just as long as bacteria have. If they can, have had enough time to, yet haven't, why haven't they?)",
"Maybe it's because there aren't as many Archaean commensals as there are Bacterial, and any putative Archaean pathogenogenic phage that gets in has a hard time finding the Archaean needle in the Bacterial haystack to carry it's genes.",
"Or, maybe it's a combination of those things (this is where I'd put my money).",
"EXCELLENT question, though.",
"(edited for some typos...got a little excited while typing and accidently a fw lttrs words)"
] |
[
"Although many extremophiles are archaea, not all archaea are extremophiles. This isn't a good reason for the lack of archaeal pathogens."
] |
[
"Wow, thanks for the awesome answer! I didn't even know Archaean phages existed. Time to do some reading!"
] |
[
"If a patrticle is executing uniform circular motion under gravitational fprce, then why does it not fall to the center?"
] |
[
false
] |
So if a particle is executing uniform circular motion, then it will accelerate and acceleration means that it will radiate energy and then come closer to the center and finally fall into it or become a part of it. Why does this not happen?
|
[
"It does radiate energy. It just radiates so little energy that it's almost impossible to detect, and so little that it would take many lifetimes of the universe before the Earth would fall into the Sun (in fact, the Sun will likely engulf the Earth in its red giant phase before you'd ever notice the orbital decay). In fact, it is predicted to take about 10",
" Billion years for the Earth to fall into the Sun due to gravitational radiation. ",
"Gravitational Radiation is also called ",
"Gravity Waves",
", and we attempt to detect them, but gravity is so weak, it's hard to detect. One of the most promising is the ",
"Hulse-Taylor binary",
" where two neutron stars are orbiting at essentially one solar radius apart, which should make gravitational waves which are about 10",
" larger than the ones made from the Earth/Sun system."
] |
[
"Quick caveat, it's gravitational waves -- gravity waves are a type of wave in fluids, and are important in atmospheres. It's quite annoying when you work on gravity waves and people mostly think you mean gravitational waves XD"
] |
[
"Gravitational Radiation is also called Gravity Waves",
" waves. ",
"Gravity waves",
" are things like water waves.",
"We had many successful detections of black hole mergers and a few neutron star mergers. ",
"Wikipedia has a list",
"."
] |
[
"Why are there drug effects in nature?"
] |
[
false
] |
Why can some plants be refined to give hallucinigenic, depressant or stimulant effects? How is this a defensive attribute for any plant? I know that we must refine, combine or cause a reaction in plant chemicals to obtain the effects, but why do the chemicals exist in the first place?
|
[
"Some of the chemicals are toxins used by the plant to defend themselves. Those can have hallucigenic effects for a human, but might not for an animal that happens to eat the plant."
] |
[
"Evolutionarily speaking, things like poisons and whatnot work from the ground up. If a plant usually gets eaten by a certain bug and over time develops some sort of a poison mechanism, it only has to be poisonous to that bug, the effects it has on other organisms doesn't matter.",
"In a sense, nature likes to cut corners. Why make the plant poisonous to everything when you don't have to? :P ",
"TRIVIA: The one poison I can think of that kills almost all life is arsenic. Jus' sayin"
] |
[
"In addition to toxic effects (like caffeine's natural insecticide effect), many plants may naturally produce chemicals for their own needs, which just so happen to have psychotropic or similar effects in people. ",
"As plants and humans have vastly different body structures, we are affected differently by chemicals."
] |
[
"If the circuit is broken, does the capacitor still hold charge/pd?"
] |
[
false
] |
if the circuit is set up like this, where the open end is a fly lead which could connect to the other side of the battery, before it does, is there a charge on the plates? is it half the maximum charge (i'm just guessing that the p.d halves and so the charge does too, idk) thanks Battery------Capacitor-------open end
|
[
"Theoretically, with an ideal capacitor, yes.",
"Practically, no. Capacitors undergo a phenomena called the leakage effect, or bucket effect.",
"Imagine you have a bucket with a tiny hole in the bottom. You start filling the bucket with water, and the hole really doesn't matter because water is constantly coming into this bucket if any falls out. However, when you turn the water off, the water level decreases because there is no water coming back in to fill it back up, and eventually all the water leaks from the hole.",
"Now think of water as charge, and the bucket as a capacitor."
] |
[
"Yes. If its discharged and in an open circuit, it will not charge back up"
] |
[
"thank you very much! i have an a level physics practical in a couple days and its about capacitors and this really helps!! So if i want to discharge a capacitor and leave it discharged, i can discharge by putting a wire across it and then leave it with one side attached to the source?"
] |
[
"Is it possible to have animals that are taught skills, teach those skills to their offspring?"
] |
[
false
] |
Not really sure what to flair this as, but I guess psychology? Like say you teach a bird to use a tool or item to do something useful, will they teach other birds they like and/or their offspring? Or do those learned skills disappear once they're gone.
|
[
"Orca whales have ",
"learned to hunt seals on icebergs",
" by capsizing the icebergs. They then pass that on to their offspring. ",
"Capuchin monkeys in Brazil are something like ",
"3000 years",
" into their own stone age, again suggesting that these learned skills are passed on.",
"I'm not sure what would happen if it's taught by a human or conditioned in a lab and then sent back out into the wild, but chances are if it's something observable and beneficial, there would be a good chance of it being passed on. Some of this obviously depends on the species as well - some species can learn more complex behaviors, and some species learn well through observation (vs. something like, I dunno, a banana slug or butterfly that may struggle to \"teach\" others). You also have to keep the reinforcement coming – that is, if it's a rare event, or if it rarely pays off it's harder to teach, and harder to not just extinguish naturally. I know that we can rehabilitate some animals to feed themselves in the wild (like orphaned sea lions who never learned to hunt) by training them in \"lab\" settings; again, beneficial and observable, so good chance of being passed own."
] |
[
"Some animals will copy each other, some won't. So maybe but not for all species. Crows for example learn to break nuts by droppibg them on the road for cars to drive over them.",
"It's a big difference between dogs and wolves too. If you take 2 wolves and make them solve it but first you show them so solution, for one by another wolf, for the other by a human, the one that saw another wolf do it will solve it faster. On the other hand a dog who saw a human will solve it faster than one who saw a dog."
] |
[
"Not sure if we're making a distinction between ",
"- the offspring just learn the skills",
"or ",
"- the parents ",
" the skills.",
".",
"Milk used to be delivered to people's homes every morning. It came in glass bottles with foil or cardboard caps, and was left outside the front door. ",
"Birds learned to remove or peck holes in the tops and drink whatever of the milk they could reach, ",
"and this behavior spread to whole flocks. ",
"- ",
"https://www.birdspot.co.uk/bird-behaviour/blue-tits-and-milk-bottle-tops",
" ",
"- ",
"https://theconversation.com/milk-bottle-raiding-birds-pass-on-thieving-ways-to-their-flock-34784",
" ",
"(Famous - you can find lots of articles about this)",
".",
"There's a type of macaque monkey that lives in Japan. Researchers studying them left food on the beach to attract the monkeys to the area. ",
"One of the monkeys started washing the sand off her food. Eventually most of the other monkeys learned to do this. ",
"- ",
"http://alfre.dk/monkeys-washing-potatoes/",
" ",
"(Very famous, many articles, but unfortunately some are New Age sources about how the monkeys \"learned by telepathy\" or something. Watch for those.)",
"- ",
"https://en.wikipedia.org/wiki/Hundredth_monkey_effect",
" ",
".",
"Washoe (c. September 1965 – October 30, 2007) was a female common chimpanzee who was the first non-human to learn to communicate using American Sign Language (ASL) as part of a research experiment on animal language acquisition.[1]",
"Washoe learned approximately 350 signs of ASL,",
"[2] also teaching her adopted son Loulis some signs.[3][4][5] ",
"- ",
"https://en.wikipedia.org/wiki/Washoe_(chimpanzee)",
" ",
"Washoe and 3 other chimpanzees (Tatu, Dar, and Moja) were raised as if deaf human children and acquired American Sign Language. The chimpanzees regularly use the hand signals to communicate with each other and humans. Loulis is the only chimpanzee in the family who was not cross-fostered (he wasn't raised by humans but rather Washoe and the other chimpanzees).",
"After eight days with Washoe, Loulis learned his first sign. For the first five years of his life, Loulis's human handlers only used seven signs around him (the signs used were who, which, want, where, name, that, and sign). ",
"Loulis was able to acquire what he learned of ASL from Washoe.",
"- ",
"https://en.wikipedia.org/wiki/Loulis",
" ",
"."
] |
[
"Why does scalding hot water feel so orgasmically good on poison ivy or hives?"
] |
[
false
] | null |
[
"It's the same feeling you get when run hot water on mosquito bites. Basically you are stimulating the nerves and overloading them with the hot water. ",
"Source: ",
"http://www.peoplespharmacy.com/2009/08/01/hot-water-for-itchy-bug-bites/",
"Usually you stimulate the nerves through scratching, although that isn't as intense and is more localized than hot water all over your skin. The reason scratching is bad for you is because the friction tears your skin and can damage it more. Hot water has the same effect but no tear damage."
] |
[
"I can confirm the same for eczema (atopic dermatitis). Awesomeness aside, my dermatologist pointed out the heat is damaging to the skin and can do more damage to the skin (depending on temperature and duration of course)."
] |
[
"The way you guys are describing this almost makes me want to do it on purpose... :/"
] |
[
"Is it possible to use a commercial motion sensor aimed at mirrors to activate? Given any type of commercial sensor"
] |
[
false
] |
I've always wondered if the light reflected off a mirror can trigger some of these sensors. You could extend the range or improve on the detection angle quite easily.
|
[
"Motion detectors might be using ultrasound, where a mirror is of course useless. A detector using Infrared will detect motion in the reflected view, but with the following caveats:",
"transmission of IR light through the coating and glass layer. If the glass absorbs too much IR, range of detection in the reflected view is diminished.",
"reflection characteristics of your metallic mirror behind the glass. Just because it reflects all visible wavelengths does not mean it will reflect IR, but it usually will.",
"So, yes it generally will work, but depending on your mirror, it might see not as far through the mirror as it would if there were no mirror."
] |
[
"Actually, ultrasound-based detectors will probably reflect off a glass surface in much the same way. "
] |
[
"It will reflect off the surface diffusely, just as from most other hard surfaces, so unless you want to use the mirror to look into an opening with a huge open space all around, your acoustic signal would bounce off other walls just as well and you don't need a special surface for reflection."
] |
[
"I've never been very good with electronic hardware. Is there any chance that I could get an explanation of these circuits?"
] |
[
false
] |
I'd really like to simple know what's going on in layman's terms. Thanks, in advance.
|
[
"A) Differential amplifier, gain is determined by the left hand R",
"B) Inverting amplifier, gain=-1",
"C) ",
"http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html"
] |
[
"B) Inverting amplifier, gain=-1",
"Iff ",
"R2 == R1",
". More generally the gain will be ",
"-(R2/R1)",
" ."
] |
[
"i'd look for circuit design software, that would allow you to figure out the working of any design. There's some links on this page for example: ",
"http://www.electronics-lab.com/downloads/schematic/index.html"
] |
[
"How do we know the half-life of things that have the half life of thousands of years?"
] |
[
false
] |
Im trying to wrap my head around half life, and i trying to understand how do we know that radium has the half life of 1600 years? I understand smaller times (countable times) like time/days (average blahblah) but how is it tested for thousands of years??
|
[
"How do you check the speed of a car in km/hr if you don't measure it for a full hour? You measure it for a much shorter period of time and extrapolate, assuming the speed is constant.",
"Likewise, you can measure how much material has decayed over a much shorter period of time, and extrapolating it on an ",
"exponential curve",
" assuming a fixed rate constant.",
"The half-lives of some isotopes may be too long or too short to experimentally measure, so it is predicted via theoretical calculations."
] |
[
"This answer is incomplete. The measurement is far more difficult than that. Things with short half lives (less than a few years) are easy to measure. Once you get into the longer half lives, things are more difficult. Your sample will not have a large change in activity over time. Thus, the normal way of measuring an exponential does not work. In that case, you need to measure the actual activity of the sample and measure the mass very accurately to get the half life. "
] |
[
"Radioactive decay follows something known as ",
"first order",
" kinetics, which takes essentially the same form as compound interest. The net result of that is that the rate of decay is really only dependent on one variable, which is the so-called decay constant (which you can convert into a half-life). The upshot of that is, it's conceptually pretty straightforward to figure out the half-life. All you really need to do is take a known amount of the isotope in question, and measure the number of decays coming off of it every second. This is doable for long half-lives because for even modestly sized samples there are ",
" atoms that measurable amounts of decays occur every second."
] |
[
"Where does food go when it “goes down the wrong pipe”?"
] |
[
false
] | null |
[
"Very interesting! So is it possible for a small piece of food to actually make it down the trachea into the lungs?"
] |
[
"A little anatomy lesson here, bear with me. In your throat there is a little flap called the epiglottis. The epiglottis closes off your windpipe (trachea) whenever you swallow or eat. (Hence not being able to swallow and breathe). This prevents food and other objects from entering your lungs. (Only want air going in there nothing else). Sometimes, it doesnt close off fast enough or other reasons and a foreign object gets stuck in the trachea and it causes it to become irritated and making you cough because it is in the trachea and not in the esophagus. This makes the feeling of \"going down the wrong pipe\". This is also the cause of choking. When the foreign object completely occludes the trachea and the victim cannot breathe, cough, or anything else."
] |
[
"Yep! When anything enters the lungs that's not supposed to, it's called aspiration. The consequence is often pneumonia.",
"Check out more ",
"here",
"."
] |
[
"Where do photons go after they enter your eyes?"
] |
[
false
] |
What happens to them after they enter your eyes? I assume they hit the retina (or whatever part of the eye absorbs light), but then what?
|
[
"A photon enters your eye and strikes a protein called ",
"rhodopsin",
". The energy of the photon is absorbed and used to cause a chemical change in the structure of the protein. This chemical change kicks off a biological pathway that ultimately results in vision. Ultimately, energy in photochemical systems like this is typically dissipated as molecular vibration (heat)."
] |
[
"More details at ",
"http://www.reddit.com/r/askscience/comments/ofv7o/what_happens_to_photons_after_they_reach_my_eye/"
] |
[
"No prob!"
] |
[
"How does oxygen affect the environment? Is there any way is does other than keeps things alive through breathing ?"
] |
[
false
] |
[deleted]
|
[
"Many ways. It reacts with iron to produce rust aka iron oxide, it gets split by sunlight and reacts to form ozone in the atmosphere. The ozone layer is important for shielding the planet from uv radiation. When somethings burns aka combustion it is reacting with oxygen to form co2 and water."
] |
[
"It has shaped the course of history. Because Iron reacts to form Iron oxide, it is not found as pure usable metal but rather as iron ore. If Iron could exist as pure metal than the iron age probably would have occurred much earlier because there would be no need for people to have developed the necessary process and equipment to refine iron. The bronze preceded the iron age because copper and tin, the components of bronze were much easier to refine from ore to useable metal. Still today, refining iron ore (iron oxides) into iron is a significant industrial process that takes resources and creates pollution."
] |
[
"It has shaped the course of history. Because Iron reacts to form Iron oxide, it is not found as pure usable metal but rather as iron ore. If Iron could exist as pure metal than the iron age probably would have occurred much earlier because there would be no need for people to have developed the necessary process and equipment to refine iron. The bronze preceded the iron age because copper and tin, the components of bronze were much easier to refine from ore to useable metal. Still today, refining iron ore (iron oxides) into iron is a significant industrial process that takes resources and creates pollution."
] |
[
"Why do British singers seem to lose their accent?"
] |
[
false
] |
I've heard that this has something to do with old English sounding more like American English today - is that true?
|
[
"Singing is not the same as speaking. If you take classes on how to sing they teach you to open your mouth certain ways and to breath certain ways. There are more efficient ways to make sound when singing and these are pretty much universal.",
"It's not so much that British singers sound more American, it's that all singers lose their accents when singing. Whether you're American, British, Chinese, Russian... good singing produces similar sounds."
] |
[
"Too true.",
"For those who have not had training though you often see the same effect. Many pop/rock singers historically have not had a ton (or any) vocal training but have learned by example.",
"For example, the excuse put for by the Beatles was that they learned rock & roll by listening to Elvis and other American artists. For them, that's what rock sounded like."
] |
[
"Or even better, listen to some non-English pop songs. The sounds of the words themselves will sound very familiar to you (though of course the lyrical content will be unintelligible). Whether you're listening to Korean-pop, Ukrainian disco, or Billy Idol, each singer uses basically the same uniform ideal vowel and consonant pronunciations while singing, even though their languages sound much different from each other while spoken.",
"Ninja edit for clarity."
] |
[
"A few questions about entropy on a cosmological scale"
] |
[
false
] |
[deleted]
|
[
"Heat death doesn't mean the temperature is approaching zero, it means that the temperature of the universe would become totally \"uniform\". More precisely, there is no energy available to do work (aka free energy).",
"If we consider (global) entropy increase as a fundamental law, yes, the entropy of the universe is presently greater than just after the big bang. ",
" the big bang might be a different story, since quantum system can locally break this law, and the universe at very early times(and thus very small, quantum scale distances) may have different behavior with regards to entropy. Until we have a theory that can handle the length/energy scales involved in the birth of the universe, it is difficult to talk about \"the entropy of the big bang\".",
"Edit: clarity"
] |
[
"Cool! Thank you, so then, does the question \"what is the temperature of the Heat Death\" have no real meaning?"
] |
[
"Heat death doesn't necessarily imply that the temperature of the universe is ",
" uniform, just that there is no ",
". So no, the question is a bit ill-defined. Generally heat death is just considered the maximum entropy state (by definition)."
] |
[
"How did the early astronomers know which planets were closer and further from the sun and in what order?"
] |
[
false
] |
[deleted]
|
[
"Annual parallax doesn't actually work with the planets, because they move drastically over a year. You can do parallax with multiple observers or using the rotation of the Earth, but I don't know if that's the way it was done."
] |
[
"Well, Mercury and Venus never stray very far from the sun in the sky and are thus typically visible during twilight hours (in daytime it being too bright to see them). Whereas Mars, Jupiter, and Saturn seem to move around the whole sky over the course of several months – half the time they’re on the ”near side” of the sky relative to the sun and half the time on the ”far side”."
] |
[
"Once you develop heliocentric theory:",
"Planets closer to the sun from Earth can never be seen at \"opposition\" to the Sun, because Earth will never be between them and the Sun. You can never see Mercury or Venus at midnight, only in the early morning before sunrise or in the early evening after sunset.",
"Planets further from the sun than Earth ",
" be seen at solar opposition, because Earth ",
" fall between them. As such, there ",
" times of year when Mars, Jupiter, Saturn, etc. will be visible at midnight.",
"As for the order:",
"Venus can get further away from the Sun than Mercury can, and it takes longer to reach successive conjunctions (directly behind - or, for a planet closer to the Sun than Earth, also in front of - the Sun)",
"For the outer planets, the longer it takes them to complete a lap around the circuit of the \"fixed\" stars (specifically, the zodiac signs, astronomy and astrology being enmeshed with each other back then). If it takes Mars only two months to get through, say, Aries, while it takes Jupiter a year and Saturn two and a half years, and they're all orbiting the Sun, then Mars must be closer than Jupiter, which is in turn closer than Saturn."
] |
[
"I've always wondered, if the External Tank on the Space Shuttle was jettisoned after the Shuttle had already achieved a stable preliminary orbit, how did it re-enter the atmosphere to burn up?"
] |
[
false
] | null |
[
"The final orbit wasn't achieved using the main engines but the ",
"Orbital Maneuvering System",
" instead (they are also used for deorbiting). They are the two smaller cones above the three big main engine cones at the rear of the shuttle. At the point where the external tank is jettisoned, the space shuttle is on a trajectory that would take it back to the upper atmosphere and thus re-entry, which is also what happens to the external tank. The final orbit is achieved when the OMS engines are used later to raise the orbit. This was done partly also due to safety as the shuttle is already on a return trajectory if the OMS engines malfunction. See ",
"the wiki page",
" for more."
] |
[
"I had absolutely no idea. Thank you.",
"Wikipedia says those boosters had only 300 m/s of potential delta/v in them. If I've learned anything from Kerbal Space Program, that isn't very much at all. Is the orbit just so low that only a little burn takes them into the atmosphere, which does the rest of the work for re-entry?"
] |
[
"300 m/s is a fair amount of delta-v for on orbit maneuvering. Dropping from a 400 km orbit (ISS altitude) to something low enough to reenter the atmosphere needs less than 100 m/s delta-v.",
"Yes, the atmosphere does nearly all the work getting you down from LEO velocities to standing still on the ground. This is why it's much easier to land on a planet that has an atmosphere than on one without."
] |
[
"Why are fevers cyclical?"
] |
[
false
] |
Sometimes when fighting off a virus, bacteria, injury, etc., the body fluctuates between elevated temperature (fever) and normal temperature. This causes a cycle of chills, sweats, chills, sweats,… Why does the body not maintain an elevated temperature until the “problem” is resolved.
|
[
"as your body fights off the virus the viral load drops, the fever reduces, the body becomes more hospitable for the virus again, the virus is reproducing in cells teh whole time, the cells burst, the viral load shoots up again, the body responds with more fever. I'm sure someone will explain it in more detail but as i understand it thats pretty much it. viral load goes up and down which causes symptoms to be cyclic."
] |
[
"To add to this, from the perspective of someone with biology training but not medical…",
"It is entirely possible that this is an evolutionary response. Fevers kill the disease and, if they go on long enough, the host. ",
"It makes complete sense that a cycling fever provides the most likely survival of the host and that individuals that don’t cycle fevers simply don’t survive."
] |
[
"It's also worth mentioning that the human immune system is an insane rube goldberg machine where almost every pathway has multiple mechanisms of negative feedback regulation. It's almost universal that when your cells sense a cytokine produced by a viral infection, like interferon gamma, they respond to it (inflammation, fever, antiviral gene transcription, etc), but they also up-regulate genes that serve to dampen the cell's response to interferon. If you put a cell in a steady state amount of cytokine, it will usually have a strong initial response, followed by a damping of the signal. There are a lot of mechanisms by which this happens (down-regulating the receptor, up-regulating the inhibitors of the receptor, etc.)"
] |
[
"Does the velocity of a photon change?"
] |
[
false
] |
When a photon travels through a medium does it’s velocity slow, increasing the time, or does it take a longer path through the medium, also increasing the time.
|
[
"I'm of the mind that the term \"the speed of light in a medium\" should be forever abolished. Light does not travel at all through a medium. Rather, an EM wave incident on the boundary between the vacuum and a material INDUCES A POLARIZATION WAVE in the material. It is this polarization wave that is making the journey through the material, not the original light.",
"What is meant by polarization? Atoms have a positively charged nucleus surrounded by negatively charge electrons. Their net charge is zero and if left alone the average position or \"center\" of their negative charge and the center of their positive charge lie on top of one another/are at the same point (the center of the nucleus) even though the electrons and nucleus are in spatially separate places. However an electric field pulls negative charges one way and positive charges the other, and thus when an electric field is applied to an atom, the centers of its negative charge and positive charge are slightly pushed apart from one another and the atom acquires a net dipole moment (a dipole is a positive charge q and an equal in magnitude negative charge -q that are slightly displaced in position from one another resulting in a net electric field even though one has charge neutrality overall). This dipole moment produces its own field which acts against the applied field. This whole action is called polarization and how a material is polarized for a given applied field is a material dependent property depending on what is made out of and the crystal structure it adopts.",
"So the true object is a composite excitation that is the net \"thing\" that comes out of this competition from the applied electric field (by this we mean the incident vacuum EM wave) and the polarization response of the material. An EM wave never travels anything but the speed of light, but this net composite object has a material dependent character and can make its way across the material at a slower speed than the inciting EM wave.",
"Also, just a few final comments. If anyone ever told you light is slowed in a material because it makes a pinball path, that is utter BS. One can understand this pretty readily as, if that were true, the path of light would be random when leaving the material, rather than refracted by a clear, material dependent, angle theta. If someone told you that it's gobbled up by atoms and then re-emitted randomly and this produces a pinball path, that's even more wrong. If that were the case then clearly \"the speed of light in a medium\" would depend on the capture and emission times and decay times of electron states of atoms, it doesn't.",
"does it take a longer path through the medium, also increasing the time.",
"It is possible to derive Snell's law, the law saying how much incident light curves due to refraction, by simply finding the path of least time given the \"speed of light\" in each medium (again, I don't like this term).",
"EDIT: For those with the appropriate background, Feynman's lecture on this is pretty great:",
"http://www.feynmanlectures.caltech.edu/I_31.html"
] |
[
"This is just one way of modeling the system. There are various other ways to model it, such as the polariton model where a photon plus some atoms together make up a particle (well, quasiparticle) called a polariton. That particle has mass and thus travels slower than c. Here is a nice youtube video with explanations of the phenomenon:",
"https://www.youtube.com/watch?v=CiHN0ZWE5bk"
] |
[
"I mention a polariton description in one of the comments but honestly one should really only talk about such a description in certain circumstance. A classical EM wave is not at all a quantum mechanical object, in the language of quantum electrodynamics it's what is called a \"coherent state\", which is a state that has no notion of \"number of photons\" and is in essence a weighted superposition of all states with different numbers of photons. So light from say a laser or a light bulb which is incident on a material boundary is not really very well described as a stream of photons. Furthermore, a polariton is a valid quasi-particle description of a material system only SOMETIMES. Specifically, in what is called the \"strong coupling\" limit. ",
"So it may seem attractive to say \"it's a photon that becomes a polariton that becomes a photon\", which I discuss a bit in this response I gave to ",
"/u/hobopwnzor",
" :",
"https://www.reddit.com/r/askscience/comments/8d4y5x/does_the_velocity_of_a_photon_change/dxkdeta/",
"But you're really doing some pretty lazy alchemy in saying that. Laser light isn't, like \"a million photons at energy E\", it's a fairly different object, and a polariton is only \"quasiparticle-y\" under a certain set of conditions and scenarios."
] |
[
"How far does a million dollars go in your field of science?"
] |
[
false
] | null |
[
"A lot of post-docs. There's not really much equipment to buy in math."
] |
[
"\"Adding to that, we'll fund your dig for another 5 years..\" - Hammond"
] |
[
"That's probably about how much it cost to set up our lab."
] |
[
"Why does milk go bad after only a few weeks, but butter can stay edible for months or even a year refrigerated?"
] |
[
false
] |
Butter is just churned cream, so I wouldn't think there would be any preservatives acting to keep it fresh that milk does not have (other than possibly salt?).
|
[
"Water content and salt. Butter doesn’t enough water in it for microbes to comfortably live in there. Salting butter also helps to preserve it by increasing the osmotic pressure on any microorganisms that try to get a foothold. ",
"The bigger issue with butter (and other fats) is oxidation. The unsaturated fatty acids will react with oxygen to form compounds that taste rancid. That’s why the water rimmed butter bells help it to last longer."
] |
[
"Butter doesn’t enough water in it for microbes to comfortably live in there.",
"Butter is approximately 10-20% water, so plenty left. However, the water is emulsified - spread evenly throughout the fat as tiny globules - so not readily available for microbiota. Furthermore, it has a low carbohydrate and protein content, and fats tend to degrade slowly, so there isn't much easily consumable food for microbiota."
] |
[
"Interesting, I hadn't thought about the oxidation aspect. Thanks for the explanation!"
] |
[
"Since color and sound are both observed as waves, would it be possible to create intervals of color \"harmonies\" (combinations of colors that look good together) in the same way one manipulates tones?"
] |
[
false
] |
[deleted]
|
[
"No, not in the same sense as harmonies in sound exists. While there are colors that go well together in the sense that they are aestethically pleasing, this has nothing to do with \"harmonies\".",
"Harmonies in sound stem from harmonics (",
"http://en.wikipedia.org/wiki/Harmonic",
"), i.e. multiples of a frequency oscillating together.",
"Now there are two problems when bringing this to optics:",
"While light can be represented as a wave, it does not excite an oscillation with the frequency of light in the eye, so there cannot be a superposition of these frequencies.",
"The visible range does not even cover one octave (in terms of frequencies) so harmonies would not be very interesting even if seeing worked that way."
] |
[
"We do have that. Take out a color wheel and pick a color along it. The color on the opposite side is called that colors complement. This premise is used all the time in design(take a look at movie posters. Many will use orange and blue because those are complementary colors)."
] |
[
"The color wheel has little to do with frequencies. Blue is near to red, where frequencywise they should be at opposing ends.",
"In that sense, this is not at all like harmonies in sound."
] |
[
"Could all three stars in systems that Gliese 667 C or HR 8832 are a part of be visible from their planets at the same time?"
] |
[
false
] |
I'm a writer, and I like to have some realism and credibility when developing space-faring systems. I'm asking because dual star systems are visible from the planets. I was wondering, if that was the case, then would all three of a tri-star system would be in the sky at the same time or would it depend on where the planet was at any given time in relation to the stars?
|
[
"This",
" is probably a pretty accurate representation of what the view would be from Gliese 667Cc. The red dward this planet orbits would appear a little larger than our sun appears on Earth, and the other two stars would be bright enough to be seen in the day, but very small in the sky."
] |
[
"Thank you! That was exactly what I was looking for. "
] |
[
"Okay, thank you. That also really helps! Sometimes I find really good info online but it's aimed at professionals not at laymen, so clarification on where they'd be during what time of the year is super great info because it helps me plan storylines. "
] |
[
"How can birds sit on the uninsulated cables on power lines without dying?"
] |
[
false
] |
in our neighborhood there are two uninsulated live wires and then some other insulated cables below them on the power poles. How are birds and squirrels able to touch the uninsulated ones without being shocked?
|
[
"Because they are not grounded. For electricity to flow, it has to have a pathway to ground or be in the path of a full circuit. When a bird sits on a wire, it's at the same voltage potential as the wire, so no electricity flows. ",
"Check out this video of a lineman who was dropped off on some high voltage wires to do repairs. If he were to touch the wires AND a grounded pole or support for the whole wiring system, he'd be toast. ",
"https://www.youtube.com/watch?v=_cx-eOUjNPE"
] |
[
"There is no potential difference (voltage difference).",
"For electricity to flow, there has to be a potential difference. In the case of your electric plug at home (if you are in the US), one side is at 120 Volts AC and the other is neutral (0 Volts). The ground is also 0 volts, by definition. ",
"If hypothetically you stuck your finger into the 120V side and you were not touching the ground or perfectly insulated from the ground, you would not be electrocuted. You would simply take on the 120V potential. The moment you touch the ground and the hot wire, now there is a potential difference of 120 V between the wire and the ground, and current can begin to flow leading to potential electrocution. ",
"However, ground is not the only case that causes a potential difference. In a 240V circuit in the US, one side has a potential of +120V and the other side has a potential of -120V. This is a 240V potential difference if you touch both sides, or only 120V if you touch one side and a ground. If for some reason, you had two wires, one at 80 volts and one at 100 volts, touching both would give you a potential difference of 20 volts.",
"In addition, the potential difference has to be able to power enough current to do damage. In the case of household AC wires, there's a lot of power coming through from the generator at the power company, but if you build up a static charge during the winter and touch a doorknob, that's a few thousand volts but not enough current to fry you.",
"The bird is only touching the 120 V wire, so it has a potential of 120V, but since it is not touching anything else such as a ground wire, there's no potential difference, much less enough power to fry it.",
"This is also how linemen can fly up in helicopters to perform maintenance on high-tension (high-voltage) power lines. They just have to make sure everything, including the helicopter, is at that high voltage before they begin working, and that nothing contacts anything that is at another voltage or else there could be a deadly potential difference. (You can actually see the electrical arc as they come up to the same voltage in videos like ",
"this one",
")"
] |
[
"In basic terms, yes, although it can be a little more complicated with things like arcing through air because of high voltages. I found this link that says more about the subject: ",
"https://en.wikipedia.org/wiki/Live-line_working"
] |
[
"What happened to Acid Rain? Is it still a problem in the developed world? Third World?"
] |
[
false
] |
Just wondering if Acid Rain is still a problem or have we put measures in place to solve the problem?
|
[
"Environmental engineer here working in air quality and pollution control. I can cover at least the history of the issue in America. ",
"Acid rain is caused by the release of specific gases (SO2 and NOx) during combustion, mainly the burning of coal. Before the Clean Air Act and the EPA, regulation of these pollutants were mostly left to the states. The problem was when these gases were emitted by one state, for example a power plant in Kentucky, they would move over another state and cause acid rain. This is one reason federal regulations were created. ",
"The capture of SO2, the main cause of acid rain, was a fairly simple one. (If you want a long explanation if how these control devises work I could go into that). One popular scrubber used is an electrostatic precipitator. This device can remove both particular are matter and SO2 from the power plant emissions. The device does cost energy, but the emissions captures can be sold to subsidize this cost. Also, those industries that don't follow the regulations are fined, which can be very expensive. ",
"So, because of those fines, along with the captured emissions being a profitable product itself, it became economically feasible to remove upwards of 99% of SO2 from coal fired power plant emissions. This has drastically lower the amount of SO2 in the air and decreases the occurrence of acid rain across America. NOx is still an issue, but doesn't have as large of an impact. ",
"The decrease of acid rain, along with lead, is one big success story of the EPA and one that should not be forgotten when people claim that states alone can be responsible for air quality and the EPA should be eliminated.",
"Edit: grammar"
] |
[
"Worth mentioning the reduction of sulfur in gasoline/diesel/fuel oils. Here in Sweden there aren't any coal plants (other stuff is burned though, including household waste), but smokestack scrubbers and lower-sulfur fuel has reduced the total SO2 emissions by over 95% since 1980. Despite the relatively low emissions, it's been quite a problem since a lot of our water systems are naturally weakly acidic and have a poor buffering capacity. Upwards of 200 million SEK are still spent every year on dumping chalk in lakes to combat the effects. ",
"The emissions from Germany and Poland, who are major coal-consumers are really the bigger problem (e.g. Poland has about 4x the population of Sweden and 25x the SO2 emissions). So on a similar note, that's where EU regulations and EU membership for former-East Bloc nations have had a significant impact. "
] |
[
"Sure, and this still happens today. But who pays the imposed fine? The state? The industries of the state? Which state upstream and which polluter in that state is most responsible for the acid rain that fell hundreds of miles down stream? A case like this will be difficult to prove and easy to defend. So, by having a fine upfront, it causes industry to find technologies that lower their emissions. It is a preemptive solution instead of an after the fact one. There would be little insensitive to lower emissions if all it takes to get out of paying a fine is a good legal team. "
] |
[
"Why do organisms who naturally eat rotting food not get sick?"
] |
[
false
] |
Obviously the bacteria aren't eating one another, but why don't, for example, ants get sick from eating bacteria that would kill us? For that matter why don't mammalian scavengers or vultures?
|
[
"I know Vultures have highly corrosive stomach acid that neutralizes bacteria like botulism.",
"They also pee down their legs to kill off the bacteria accumulated from standing on rotting bodies.",
"I'm also going to guess that organisms like Maggots, Vultures etc.. have highly evolved immune systems that take care of bacteria commonly found in their food."
] |
[
"Many things that are harmful to one organism are not harmful to another. Simply because rotting flesh is harmful to us, does not make it so for other animals."
] |
[
"They also pee down their legs",
"Well that's my favorite new thing I've learned today."
] |
[
"AskScience AMA Series: We have made the first successful test of Einstein's General Relativity near a supermassive black hole. AUA!"
] |
[
false
] |
We are an international team led by the Max Planck Institute for extraterrestrial physics (MPE) in Garching, Germany, in conjunction with collaborators around the world, at the Paris Observatory-PSL, the Universite Grenoble Alpes, CNRS, the Max Planck Institute for Astronomy, the University of Cologne, the Portuguese CENTRA - Centro de Astrofisica e Gravitacao and ESO. Our observations are the culmination of a 26-year series of ever-more-precise observations of the centre of the Milky Way using ESO instruments. The observations have for the first time revealed the effects predicted by Einstein's general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the centre of the Milky Way. You can read more details about the discovery here: Several of the astronomers on the team will be available starting 18:30 CEST (12:30 ET, 17:30 UT). We will use the ESO account* to answer your questions. Ask Us Anything! *ESO facilitates this session, but the answers provided during this session are the responsibility of the scientists.
|
[
"Thank you so much for being here to answer our questions. It's very much appreciated.",
"What are the most surprising findings after all these years of hard work? ",
"What effects are the black hole having on the Milky Way?"
] |
[
"In some sense it is always surprising how well the theory and the preditions of Einstein's General Relativity work.",
"\nEven close to one of the most extreme objects we can imagine, a supermassive black hole, the laws of physics work and govern the motion of the stars. Despite beeing 100 years old, Einstein's theory so far has passed all tests with flying colors. ",
"The effects of a black hole on its host Galaxy are the matter of intensive research. There seems to be a connection between the growth of the central parts of a Galaxy and the Black Hole. "
] |
[
"Did the results rule out any alternative gravity theories or parameter spaces?"
] |
[
"Do neurons respond to certain states, or to changes in states?"
] |
[
false
] |
I heard somewhere that neurons do not respond to states, but instead to the transitions between states. I googled the question, but I am not really sure what I am looking for. If this factoid is true I would love some more info/sources. I am partucularly curious what the implications of this would be vs. a state based system. Thanks!
|
[
"Both. Some neurons are excited by a static stimulus (like an image of a face), while some neurons respond to \"changes in state\", like the neurons that detect motion. "
] |
[
"There are neurons specialized for both. Search for onset and sustained response neurons. There are many examples in the auditory and visual systems."
] |
[
"Thanks! That seems like what I was looking for."
] |
[
"Why is the standard (or most common, at least) tuning fork tuned to A, and is it just a coincidence that the frequency (440hz) is such an even number?"
] |
[
false
] |
[deleted]
|
[
"The relevant Wikipedia article is ",
"this one",
"."
] |
[
"Our perception of what sounds sharp/flat is heavily influenced by our cultural upbringing. Western music is primarily based on the 12 tone scale (C, C#/Db, E, etc.) while eastern music cultures such as Bulgarian, Indian, and Chinese often use scales with more notes or smaller spacings. These scales sound flat or sharp at times to our western ears. There has been some research done that suggests that like with language there is a critical acquisition period for music. That is, our perception of what sounds right vs wrong is based on the music we hear during development. ",
"With that said there are commonalities between musical systems worldwide. For example, certain intervals show up in many musical systems such as the perfect fifth, the perfect fourth, and the major third. My guess is that these intervals are present in the overtone series and could thus be derived regardless of cultural influence. ",
"Sorry for the lack of citations, I responded on my phone. "
] |
[
"We needed a standard, so it got set to something nice and even. It's an arbitrary number."
] |
[
"If a container of saltwater is placed in an electric field, will the positive and negative ions all move the the edges?"
] |
[
false
] | null |
[
"Yeah, you can read about it here: ",
"http://en.wikipedia.org/wiki/Double_layer_(interfacial)"
] |
[
"The simplest way to think of it is that positive moves one way and negative moves another, but you're correct. In systems of charged colloids (like charged beads in salt water), the layer of ions around the charge negates it."
] |
[
"Oh in that case a paper detailing stationary electric fields in ionic gels says that there will be a gradient that forms as a result of the field, as expected this gradient is exponential and crosses through a neutral area in the middle",
"But I think that was already said ",
"http://journals.jps.jp/doi/abs/10.1143/JPSJ.61.4085",
"Sorry if I'm misinterpreting the paper"
] |
[
"Why is beet juice a good addition to de-icers from a chemical stand point?"
] |
[
false
] |
I want to ask why the addition of beet juice to de-icers is beneficial from a chemical point of view, for example adding it the calcium chloride and salt brine then spreading it on roads to keep them clear of ice.
|
[
"It's not quite what you'd get out of a juicer that is being mixed with salt. It's more like molasses that's obtained by boiling down sugar beet extract. Sugar, just like salt is capable of lowering the freezing point of water. It is sticky, so it has the advantage of not running off roads quite as much as salt would after the snow begins to melt. All the information I can find about this technique looks like marketing material for the company that sells \"Beet Heet\", so it remains to be seen if this is a good, long-term solution."
] |
[
"That's right. Freezing point depression is one of the colligative properties. Basically you could add anything to water and it will lower its freezing point. Salt is used most often because it's very cheap and will actually lower the freezing point a little bit more. Hope this helps!"
] |
[
"Thanks for you're insight on the matter, so would the extra sugars cause water to freeze at a lower temp because of the addition of extra molecules?"
] |
[
"If the Earth's core is as hot as the sun, why does Earth melt?"
] |
[
false
] |
Last night I was explaining to my girlfriend the article in the science subreddit yesterday about the Earth's core being out of sync. One of the comments in the thread said the Earth's core is as hot as the sun which I told my girlfriend. She then asked why doesn't Earth melt if it's that hot. I couldn't explain it.
|
[
"The earths outer core ",
" molten. That's why the inner core is able to rotate at a different rate to the rest of the planet - the liquid outer core provides the decoupling. The inner core is solid because of tremendous pressure, the mantle and crust are solid due to decreasing temperature and a change in chemistry."
] |
[
"The inner core is as hot as the surface of the sun (the center of the sun is much ",
" hotter).",
"As a matter of fact, the earth is melted inside (",
"https://en.wikipedia.org/wiki/Structure_of_the_Earth",
"), at least partly. The inner core is under so much pressure, that it is solid despite the temperature. The outer core, however, is liquid. However, the temperature of the earth is not uniform and the surface is cooler.",
"The surface loses heat by radiation to space and is heated by the core and the sun. The (rather cold) surface temperature we experience stems from the equilibrium between these processes."
] |
[
"There is melting, but the mantle is largely silicate, and generally an excellent thermal insulator.",
"The way to look at it is more like the Earth started off completely molten, and the heat inputs have reduced over time, so it is becoming increasingly cooler and therefore solid."
] |
[
"Electricity in a Maze?"
] |
[
false
] |
Simple question, probably not too hard to set up experimentally, but I thought I'd ask: If one did the following: Question: Would the electricity "choose" the shortest route through the maze? Let's say we introduce iron filings to the conductive gel. Would we see electromagnetic changes in only those filings which were in the shortest route? "Help me, Mr. Wizard! You're our only hope!"
|
[
"The electricity would flow along ",
" paths between the entrance and exit, with more current traveling through shorter paths of less resistance."
] |
[
"This may be of interest to you: ",
"http://www.youtube.com/watch?v=ap7j2cwApmc"
] |
[
"In a real maze (paths with non-zero thickness) there will be a small amount of current flowing out to the end and back in the dead end paths. The net current flow through any surface across a dead-end path will be zero, but that doesn't mean there will be no current flow at all in dead-end paths."
] |
[
"How far has gene therapy come? Has it successfully treated or cured anything? What?"
] |
[
false
] | null |
[
"What do you mean by how? Are you asking how gene therapy works?"
] |
[
"Well, there are various methods now, but classical gene therapy is done using viruses.",
"Viruses work by infecting cells and introducing their own genetic material for the cells to make proteins from. Normally the genes viruses carry only code for genes to make more viruses- however we can now engineer these viruses to carry whatever genetic material we want.",
"One particular virus of note used in gene therapy are retroviruses. These are a class of viruses (fun fact: HIV belongs to this type of virus) that use RNA as their genetic material, but once they infect a cell, will use reverse transcriptase (just an enzyme that makes a copy of DNA from RNA) to make a DNA copy of the viral genes, and then will integrate these viral genes into the native cell's genome. In other words, when this virus enters a cell, it inserts its own genes into your DNA.",
"Now if we have a genetic defect in a gene, we can use these viruses to deliver a copy of a functional, normal gene by splicing this gene into the virus's genetic material. Then, when these viruses infect cells, they will deliver the gene we want into the patient cell's DNA. For instance, in colorblindness you are missing one of your three color opsins- we can make a virus that delivers this missing opsin into cells in your retina.",
"Once the DNA is there, the cells will start making the gene product (as long as we include the proper promoter elements to make sure the gene is actually expressed), because after all, to the cell, it's just DNA.",
"That's just the canonical gene therapy- nowadays there are a lot more types of viruses used and other methods used, but this is the basic idea. For instance, we also can try to remove genes or modify genes instead of simply adding new ones, using things like zinc-finger nucleases, which cut out specific sections of DNA."
] |
[
"Bacteriophages infect bacteria, and not mammalian cells, so no, although they do serve a similar purpose in transferring genes.",
"The cancer-causing problems of gene therapy arise with the viral DNA integration step. When the viral DNA inserts its DNA into that of the host cell, the insertion location is random- the DNA does not care where it inserts itself. Because this integration is completely random, there is a very small possibility that it will integrate into the middle of a pre-existing gene or its regulatory elements. This often disrupts and inactivates the gene, as the gene now has a fat chunk of foreign DNA in the middle of it. Since these insertional mutations are rare, for the most part this doesn't cause an issue. However, in the event that the mutated gene is a tumor-supressor gene or a gene that regulates the cell division cycle, these mutations can lead to loss of regulation of cell division, and can lead the cell to become cancerous.",
"Since this is probabilistic, not everyone who has gene therapy will get cancer. However, it is very much a threat, since you only need a few mutations to cause cancer, and there will be lots of chances for this to happen.",
"There are ways around this, for example, using viruses like adeno-associated viruses (AAVs) that do not integrate into the genome, and thus does not have this possibility of carcinogenic mutations. However, since the DNA from these viruses do not integrate into the genome, it is not replicated and will be lost after cell division. For this reason AAVs really can only be used for things like retinal gene therapy, like the colorblindness, because their target are neurons which do not divide anyway."
] |
[
"[Meme] AskScience Memes! The next generation in Science Education."
] |
[
false
] |
Here at we're always on the forefront of teaching, education, and science outreach. We are known as being one of the more heavily moderated subs out there. This effort keeps the discussion here on point and scientific. However, as I have taken over this subreddit I've realized that we're losing out with younger kids because we are less 'hip' than other subs. Luckily, as the top moderator I can make changes to bring us up to speed with today's dank internet culture. For years we've provided a place for all netizens to ask about everything from chromosomes to black holes to Monty Hall to Sadly, one topic has been woefully underrepresented in scientific discourse. exploded to the forefront of internet culture, but which has received little attention from the academic community: memes. We want to change that. Because of their popularity and obvious educational value, if you have a question about science and want the use of memes, use the tag [meme] in the title. If not please add [serious] to the title so our panelists can craft the kind of answer you want.
|
[
"Are the mods going to remove memes that aren't dank enough? I think it's important that we continue to maintain the quality of comments in ",
"/r/askscience",
"."
] |
[
"That brings up an interesting point"
] |
[
"In order to preserve the quality of posts and prevent reposts of memes, I think we should institute a peer-review process for memes to determine if they are indeed dank enough. "
] |
[
"Why can’t mules reproduce?"
] |
[
false
] |
[deleted]
|
[
"A mule has 32 horse chromosomes and 31 donkey chromosomes. A total of 63 chromosomes. Normally, an organism would have two copies of one chromosome, one from the mother and the other from the father. However, for mules, they will get two different sets of chromosomes since the mother is a horse, and the father is a donkey. These genes will not exactly be matched sets, but they are still relatively similar (enough to produce the mule offspring in the first place). To reproduce, a process called meiosis will happen, in order to get one copy of each chromosome into the sperm or egg. During this process, the chromosomes will need to “match up” to another. Unfortunately, the donkey and horse chromosome are not similar enough to pair. Additionally, the mule will also have an extra unmatched horse chromosome, so sperm or eggs are unable to be made."
] |
[
"It should be noted that there are organisms where populations differ in their karyotype while still being compatible. This is quite common among rodents, where population of the same species can be easily identified with their karyotype, but still produce viable and fertile offspring.",
"So I don't know enough about this particular case to say where exactly is the problem, but just having a different number of chromosomes isn't such a barrier as people often make. Yet, it is still likely related because chromosomes represent organisational units. During meiosis, there are multiple steps where the material is divided. An unequal distribution might possibly be the cause, but again I don't know enough about this particular case and I would have to speculate."
] |
[
"Mules ",
" reproduce - it's just ",
" uncommon (only 60 cases recorded in the last 500 years). But, that being said, the other responses re: the genetic component fill you in on why that's the case. ",
"https://www.npr.org/2007/07/26/12260255/befuddling-birth-the-case-of-the-mules-foal"
] |
[
"Why does it become increasingly more difficult to fold a single piece of paper in half?"
] |
[
false
] |
It is often said that you can't fold a piece of A4 paper in half more than 7 times. Why is this ? Would it be easier with a piece of paper the size of a football field ?
|
[
"Because every time you fold it, the thickness increases by a factor of two. Thus, after the first fold it's twice as thick as a single piece of paper. Then it's four times as thick, then eight, then sixteen, then thirty-two, then sixty-four, then after the seventh fold it's one-hundred twenty-eight times the thickness of your standard piece of paper. That's a little over 1.25 centimeters.",
"But you've also been decreasing the area by a factor of two each time, so now your A4 sheet of paper has an area of only about 5 cm",
" . This means that your paper is about half as thick as it is wide.",
"Now let's say you fold it one more time. The result would have a surface area of only 2.4 cm",
" , but a thickness of 2.6 cm. Your piece of paper would now be ",
" than it is wide. But that's a problem, because it means that if you try to actually fold it that way, you won't have enough paper on one side of the fold to actually reach the other side."
] |
[
"Here's",
" a cool link about the mathematics involved in folding a piece of paper in half."
] |
[
"Great reply ! The Einstein quote \"If you can't explain it simply, you don't understand it well enough\" comes to mind! Thanks."
] |
[
"Can 10 individual 5-watt speakers create as many decibels of sound as one 50-watt speaker?"
] |
[
false
] | null |
[
"In simplistic terms, yes. Speaker coupling can yield a decibel gain but individual driver efficiencies and the enclosure design will also come in to play. The principle is that you can get an overall db gain by aligning the drivers in a plane. This is why sound reinforcement systems use arrays of aligned drivers. "
] |
[
"This question is incomplete, you can make a single speaker with 5 watts going through it be as loud as a speaker with 50 watts going through it. What matters there is sensitivity of the speaker. That is the measurement that specifies dB/W @ 1m. A speaker rated at 93db/W @ 5 W will be just as loud as a speaker rated at 84dB/W @ 40W."
] |
[
"Not quite.",
"Every 10 decibels is perceived as being twice as loud, but is actually ten times as much energy.",
"Want to make it sound twice as loud? You need 10 times as much power!"
] |
[
"Hive insects - How do they evolve?"
] |
[
false
] |
If most of the worker ants and bees don't pass on their genes through the queen, then how do they evolve to their specialized tasks? How did these hive species begin in the first place? I know the entire hive acts like an organism and the success or failure of a hive depends on the abilities of the workers, but is there something else going on? Some ant colonies have big ants that can't even feed themselves and require smaller ants to put food in their mouths, it's hard to imagine how this came about.
|
[
"I'm sorry to be the \"link to wikipedia\" guy, but I'm not in the mood to compose a thorough enough explanation, and I can't let you go with just a 2 or 3 sentence answer.",
"The prevailing theory for years has been ",
"kin selection",
", but Martin Nowak and EO Wilson (a very famous sociobiologist) have recently (in the last 5 years) begun to argue very strongly in favor of the old ",
"group selection",
" hypothesis. ",
"From what I can tell, the majority of the field thinks they're nuts, and is sticking with kin selection. I still haven't fully been able to wrap my head around how group selection would work, so I'm inclined to stick with kin selection as well."
] |
[
"I can't speak to how insect colonies evolved highly specific job roles, but I do know a little bit about insect genetics, which might help answer a portion of your question.",
"Many insect species are categorized as having a ",
"Haplodiploid sex-determination system",
". Female workers are derived from a fertilized egg (with a full set of chromosomes = diploid) while male drones are derived simply from an unfertilized egg (half a set of chromosomes = haploid)",
"So the next step is to look at how individuals relate to each other genetically in these Haplodiploid systems. In the case of a female worker, she shares 50% of her genes with her mother (the queen) and 50% of her genes with her father (the drone). However due to the Haplodiploid system, a female worker actually shares 75% of her genes on average with her full sisters. So it actually benefits her ",
"reproductive fitness",
" wise to help raise full sisters, as they are more genetically similar to her, than it would be to give birth to her own children.",
"A final note on how this compares with humans, we are diploid, so each person, both male and female contain a full set of chromosomes (22 pairs of autosomes, and 1 pair of sex chromosomes). So a human shares 50% of their genes with their mother, their father, any full sibling, and any child."
] |
[
"damnit, for months i wait for this question to be asked so i can whip out my haplodiploidy knowledge. foiled again... However, i have heard that when you actually look at the genetics, haplodiploidy is not enough to explain the eusocial behavior (not sure on the specifics, just something i heard in a lecture awhile back) in hymenopterids (bees, wasps, and ants, which are haplodiploid). I believe the leading hypothesis is that haplodiploidy predisposes a species to eusocial behavior, but it must interact with the correct environmental factors in order to produce this behavior. ",
"another interesting topic is termites. eusocial creatures, which are completely diploid. I have heard that termites evolved eusocial behavior because due to the hostility of the environments they originate from it is nearly impossible for a termite to be successful on its own, however i am not sure on the specifics.",
"There are even mammals (naked mole rats) which exhibit eusocial behavior. With these animals it is believed that a combination of severe inbreeding (we are talking like 80% coefficient of relatedness on average for \"hive\" members) and a hostile environment together favored eusociality.Mole rats for whatever reason are extremely tolerant of inbreeding, much more than humans. "
] |
[
"What parameters about the gas decide it’s compressibility?"
] |
[
false
] | null |
[
"The compressibility is defined by κ = -(1/V)(dV/dP), but you have to be careful about what quantities are being held constant when you take the partial derivative dV/dP.",
"The simplest kind of gas is the ideal gas, obeying PV = NkT. We can find the isothermal compressibility by letting T be a constant and differentiating to get (dV/dP)",
" = -NkT/P",
".",
"Then plugging that in to the previous equation, we find κ",
" = NkT/VP",
" = 1/P. So the isothermal compressibility of an ideal gas depends only on its pressure, not on any intrinsic properties of the gas.",
"We can do the same thing for the adiabatic compressibility. For an adiabatic process, PV",
" is a constant, where γ is the ratio of specific heats at constant pressure and constant volume. Differentiating this with respect to volume gives PγV",
" + V",
"(dP/dV) = 0, or (dV/dP)",
" = -V/γP, implying that κ",
" = 1/(γP). So it’s smaller than the isothermal compressibility by a factor of γ (which is greater than 1). Now it doesn’t only depend on the pressure, but also the properties of the gas. Namely, its heat capacities."
] |
[
"Thanks a lot for your answer! This was really interesting."
] |
[
"If you're asking from an applied aerodynamics sense, that would depend primarily on the Mach number, which in aerospace contexts is generally taken as anything above ~ Mach 0.3 as a rule of thumb.",
"This is actually quite closely related to the previous comment, as the speed of sound is directly related to the partial derivative of pressure with respect to density. ",
"In the applied context, compressiblity or not is primarily judged based on whether there is a large enough effect for the result to change if compressibility is taken into account - and for very low Mach numbers having a zero change in density results in an undefined speed of sound which pretty thoroughly breaks numerical simulations that assume compressible flow."
] |
[
"Does logarithm of negative numbers have any meaning?"
] |
[
false
] |
I know that there is no real solution to logarithm of negative numbers, but I understand one could define log of natural number using the Euler's identity, as exemplified by ln (-1) = (pi)*i. Does this kind of definition have any physical/mathematical meaning at all, or is it useful to solve certain problems? Thanks a lot
|
[
"Physicist here, we use complex exponentials when representing the amplitude and phase of a wave of light. It is based off Euler's formula and can help make solving problems involving light much easier to calculate.",
"When finding the phase of the light we have to take the logarithm of a complex number. In the special case it is a real negative number the phase is simply pi +/- 2(pi)n as the phase is cyclic. ",
"In the more general case we use the Euler formula to find the phase given the wave state or vice versa."
] |
[
"Physicist here. I would add that phases also play a big part in calculating on anything quantum, not just in the (classical) theory of light.",
"The thing about phases (say we have a phase p) is that we never observe them directly, we only ever observe their effect through the exponential e",
". As freakyemo correctly writes, that means we can only ever determine them up to a constant multiple of 2*pi.",
"Because of this, we may as well choose to say that all phases lie in the interval [0,2",
"pi enough times to make it fit within this interval -- It won't ever impact our results anyway!\nOnce you've chosen to say that phases only ever lie in the interval [0,2",
"pi[.\nPhysicists would call choosing a=0 choosing a particular gauge.",
"Now this is where interesting things start to happen.\nYou could have chosen ",
" a. So when you make a new theory that deals with phases, any predictions of the theory cannot depend on your choice of a.\nThis is a strong restriction on which mathematical expressions you can use to make a theory!",
"This very simple yet powerful idea is used extensively in Quantum Field Theory (with more quantities than just the phase) to figure out how new theories could look like -- And in fact most of modern physics is based on this principle.",
"So, in a roundabout way, asking what ln(-1) is, is a very powerful question."
] |
[
"As others have mentioned, you can interpret the logarithms of non-positive numbers in terms of Euler's identity, up to an ambiguity in the complex part. That is, e",
" is unchanged when you replace t with t + 2 pi.",
"Now the logarithm is the inverse of the exponential, but when dealing with functions we need to be clear about both the domain and range. The domain is the set of inputs of the function, and the range is the set of outputs.",
"The reason we care about the \"logarithm of negative numbers\" has to do with the very definition of angles. If you look very carefully at the definition of angles, you find that they are actually rather strangely defined. It is with reference to the \"length\" of a curve (if you use radians), but of course it's hard to nail down exactly what the length of a curve even means. At some point, you need to use transcendental functions like the logarithm or the sine in order to determine these values, and if you're going to use these kinds of functions you need to be clear about certain ambiguities in their definition. This ambiguity about multiples of 2 pi in the definition of an angle is a very important example of a more general phenomenon that occurs when you study holomorphic functions.",
"Generally, holomorphic functions are best understood as mappings between ",
"Riemann surfaces",
". These are surfaces that look 'locally' like the complex plane (in a precise sense), but may look quite different globally. A useful analogue is how a sphere looks locally like a plane, but globally has quite different properties from a plane. If you take the complex plane as the domain of the logarithm, the Riemann surface corresponding to the range is ",
"rather interesting",
". If you can wrap your head around the Riemann surface of the logarithm, and Riemann surfaces in general, you will be far less mystified by concepts such as the ",
"Residue Theorem",
"."
] |
[
"Can I kill termites in wood by baking it in the oven? If so, how hot should it be?"
] |
[
false
] |
A couple years ago me and my niece cut down a cedar tree to use as a Christmas tree. I kept it inside the workshop and have been using it to make various projects, but I've used almost all of it. So I went out and cut off the 3 or 4 foot stump that was still in the ground and found that it has termites in it (not bad, but still). My question is, if I bake small chunks of the wood in the oven (at say 350 degrees) will that kill the termites inside and make the wood safe to use? The holes they chewed aren't a problem. There's few and I can patch them so they're hardly visible, but I don't want to bring termites into my house or send them to someone else. If they're able to survive such extreme heat (I know paper burns at 451 degrees Fahrenheit, so I imagine 350 degrees would be a safe temp), is there anything else I can do or is that wood only fit for burning in a trashpile?
|
[
"A quick search turned up this article: ",
"http://www.beyondpesticides.org/alternatives/factsheets/Termite%20Control.pdf",
"It lists the temperature used in commercial microwave devices for killing termites to be 190 Fahrenheit. Termites on their own would definitely cook in an oven at 350, but the wood (and any water in it) will keep the temperature down... I would bore a hole in that you can stick a meat thermometer (or any probe thermometer) down and be sure that the center has passed 200.",
"By the way, the actual autoignition temperature of paper is 450 Celsius, not Fahrenheit; Bradbury changed it because he thought the incorrect version sounded better as a title."
] |
[
"**",
"**",
"Wood will begin to char as low as 250º F and certainly the loss of water from extended time in the oven will ruin the wood.",
"Please don't risk burning your house down to save a few dollars.",
"http://www.tcforensic.com.au/docs/article10.html"
] |
[
"I only regret that I have but one upvote to give for this answer. Thanks a lot. I tried googling it with no luck but didn't spend a whole lot of time searching since it didn't seem like a very conventional thing to do. That's exactly what I needed to know. And of course, you're right about Bradbury's book \"Fahrenheit 451\" being where I got that incorrect temperature (it's one of my top 20 favorite books)."
] |
[
"If fish all poop in the ocean, why is the ocean not a huge bacterial cesspool, unsafe to swim in?"
] |
[
false
] | null |
[
"The ocean IS a huge bacterial pool. That said remember that your body has more bacterial cells than it does \"human\" cells. Not all bacteria are dangerous to human/animal life. "
] |
[
"This is true, but it's only by number, certainly not mass."
] |
[
"Have you ever pooped outside? I have. Flies swarm within seconds."
] |
[
"Where do four dimensional objects exist?"
] |
[
false
] |
We obviously live in a three dimensional world and can only perceive objects in three dimensions (or lower). But there is a fourth dimension, in regards to space and not time. Where are these four dimensional objects?
|
[
"The simple answer would be that 4 dimensional objects are in the fourth dimension. I know this doesn't really answer the question that you are asking and I imagine you are wondering why we cannot not perceive these objects. The answer to this question is that from a lower dimension you simply cannot perceive a higher dimension. \nThink about a 2 dimensional object trying to perceive a 3 dimensional object passing through its plane (if that where possible). The 2 dimensional object could not perceive a 3 dimensional object, just as a 3 dimensional object can not perceive a 4 dimensional object. The interesting part is that we, as humans believe we can perceive a lower(2d) object when in fact all we can do is conceptualize a 2d object. So look at your computer screen, right now you are conceptualizing a 2d image, when really what you are looking at is a 3d object. We cant possibly perceive a 2d object in the 3rd dimension because we are stuck in the third dimension.\nThis same concept applies upwards except with one little difference. We can conceptualize 4d (and higher) geometric shapes. But what we conceptualize is either a 2d or 3d rendition of what this object would look like passing through a lower plane ",
"check",
". It isn't the actually object itself because it is only a rendition. ",
"double check",
".\nSide note: we can conceptualize the entirety of a 2d object easily, but to conceptualize a 3d object in its entirety is very hard(look at cubism). If we apply this concept upwards, from the fourth dimension it would be easy to see all sides of a 3d object easily. "
] |
[
"Not sure I agree. If there is a 4th spatial dimension, and it is not a \"curled up\" dimension but rather has near infinite extent like our 3 spatial dimensions, then objects can exist in the 4th dimension, pass through ours, and we would see them while they intersected our 3D dimension. If a 4D sphere went whizzing through our dimension at right angles to it, it would appear as a point, grow to its diameter, then shrink back down to a point and be gone. If it was not moving perfectly at right angles to us, it would also visibly translate through our space as it grew and contracted.",
"It is unlikely, however, that 4D objects with mass are floating around outside our 3D space, beyond our perception. If they were, they would exert a gravitational force on the objects we see, and our objects would translate at right angles to our universe, out of our perception.",
"Also, if a 2D object existed, we could see it and interact with it. If we happened to be precisely looking at it edge on, it would be difficult to see due to its thinness, but at any other angle it would look like a thin object. A 2D disk would look like a line edge on, or a thin disk at right angles. Now it may be the case that our garden variety 3D photons could not interact with it, which may raise issues of perception, but if it had mass, we could detect and influence it (dark matter, anyone?) The edges of such an object would also be incredibly sharp, as long as its internal structure could withstand the lateral forces (e.g. try cutting a loaf of bread with a sheet of paper - the paper just buckles)"
] |
[
"Can a reference be given regarding the claim that \"there is a fourth dimension?\" As I understand, dimensions in physics have been developed as mathematical tools, but I do not know of any physical experiments which would give rise to the existence of 4d objects in our universe. For example, 10 dimensions in string theory is simply (as I understand) a mathematical convenience, not a physical realization. ",
"From a mathematician's standpoint, dimension should be understood as \"degrees of freedom\" rather than \"direction.\" For example, the stock market can be thought of as a huge dimensional object. Each stock can change independently of the others (we assume for simplicity). In a model each dimension is simply a degree of change we need to take into account."
] |
[
"Are universal constants really \"just the way they are\"?"
] |
[
false
] |
I ran across this article: Basically, the idea I get is that there's no point in considering changing or overcoming or using anything that is a "constant" when it comes to considering science. Is this correct, or am I misunderstanding? Is there no point to considering how to exceed the speed of light, or manipulate gravity, or… whatever else there may be?
|
[
"It is possible that fundamental 'constants' do, in fact, vary from place to place (i.e. throughout the universe: we only measure most of these on Earth) but we have no reason to believe that's true. If the fundamental constants are, in fact, constants then there is no reason to try and 'break' them: but that is at odds with the pillars of science. Even fundamental constants must be tested continuously to verify that they are, in fact, constants.",
"It is extremely unlikely that anyone will find a way to exceed the speed of light, but in testing the 'universal speed limit' they may be able to provide a better estimate for the correct speed of light, or even find some new phenomenon. Fundamental constants should not stymie scientific ingenuity. ",
"A perfect example of why you shouldn't let fundamental constants prevent scientific inquiry is Bohr's experience with spin. He insisted that angular momentum be quantized in units of h, and thus refused to accept h/2 for spin: which later turned out to be true. The same can be said for the fundamental unit of charge, e, which can be as small as e/3."
] |
[
"But you have to keep in mind e is the fundamental unit of charge purely for historical reasons. They didn't know about quarks and their silly charges when they decided the electron charge was the fundamental unit."
] |
[
"Yes, my point exactly. If they didn't bother to look because they reasoned that quarks had fractional charge and therefore are impossible: then we'd never have discovered them."
] |
[
"Why is the triangular inequality at the heart of the definition of a distance function?"
] |
[
false
] |
There was a post earlier today about distance functions. I could not understand why the triangular inequality is absolutely necessary to define a distance function... can somebody explain this in not-too-advanced terms? I'm eager to learn, but I'm no math major.
|
[
"\"distance from X to Y\" should be thought of as \"the length of the shortest path from X to Y,\" where things like \"length\" and \"path\" need to be defined. All three properties of a metric fall from this heuristic starting point.",
"There is no such thing as a path of negative length, and a path can only have zero length if it stops where it started (and didn't move anywhere else).",
"Moving along a path backwards doesn't give a different length than moving forwards.",
"if I could get from x to y faster by stopping at z along the way, then that's a path I should have considered to begin with when deciding what the distance from x to y was."
] |
[
"A distance function should measure the best way to move from point a to point b. If there is another point c such that d(a,b)>d(a,c)+d(b,c) then there is a path from a to b through c that is shorter that the distance d(a,b), so what useful information did d(a,b) really give you about the distance from a to b?"
] |
[
"Think about what would happen if the triangle inequality didn't hold. You would have an example of where the distance from A to C, d(A,C), is greater than the distance from A to B plus the distance from B to C, d(A,B) + d(B,C). It doesn't make sense that you can find a shorter route by including an extra point.",
"If you can take a flight from Los Angeles to Dallas (1252 miles) and then from Dallas to New York (1372 miles). Then the triangle inequality says the distance from LA to NY must be less than (or possibly equal to) 1252+1372 = 2624 miles (which is true, a direct route is 2464 miles). If this property doesn't hold, then it just doesn't make sense to call it a distance function."
] |
[
"What is the solid residue that forms on my tongue whenever I drink certain sweet drinks like lemonade and cranberry?"
] |
[
false
] |
I noticed this happens with only a few drinks, not the majority. Does anyone know what I'm talking about/ is this caused by a specific additive? Thanks
|
[
"So that's why I always feel like I'm coated with a layer of grease whenever I drink Coca Cola. (And incidentally, it's why I never buy sugary drinks anymore.)"
] |
[
"biofilm and broken down carbs",
"lemonade and cranberry have among the highest sugar contents"
] |
[
"I know what you're talking about, but I've been told by my doctor that it was just sugars that mix with my saliva/other fluids inside my mouth to make it more viscous. Also that the small food particles in my mouth and tongue catch the sugar, making me feel it more. "
] |
[
"Does solar activity leave terrestrial records?"
] |
[
false
] |
For example, would a massive solar flare leave any record of itself? Radiation in rocks, or that sort of thing? Is there any way to know about the history of solar flares or increased solar activity other than written human records?
|
[
"Oh, so much to tell.",
"The short answer is yes, via so-called cosmogenic isotopes produced by cosmic rays in the atmosphere and recorded in natural archives.",
"One example, radiocabon (C-14) gets involved into the carbon cycle after production. You can probe tree trunks and find radiocarbon atoms there. Their abundance plus ability to date samples using tree rings allow to reconstruct the solar activity back to the past quite well up to 11 thousands years.",
"Another example, beryllium-10. It gets attached to aerosols in the atmosphere and falls down sooner or later. It can fall down with snow in polar regions, where is preserved in ice sheets. If you drill an ice core, you can date the ice along it and measure the content of Be-10, and thus, reconstruct the solar activity in the past.",
"Recently, in 2012, there was a paper published in Nature. Fusa Miyake and her colleagues discovered a strange bump in the C-14 record around 775 AD. There was quite intensive discussion in the community what it could be. Finally, it was ruled out (edit: read \"proved\", not \"ruled out\" ) that it is a large (no, HUGE!) solar energetic particle storm that left its footprint in radiocarbon records. After this discovery, there were several more solar extreme events found and confirmed. This is a quite hot topic now.",
"Feel free to ask more questions if you have them. I did my PhD on this topic and continue working in the field of cosmogenic isotopes and reconstruction of solar activity as a researcher."
] |
[
"It should be clarified for readers outside the discipline that ",
" cosmogenic isotopes are produced by interactions with extrasolar cosmic rays, not those from our sun."
] |
[
"How does it feel when someone posts a question in your key expertise?"
] |
[
"Can batteries absorb power from vinegar?"
] |
[
false
] |
[deleted]
|
[
"Just your imagination. Electric toothbrushes charge via ",
"induction",
" because there are no wires / contacts for the sake of remaining water resistant. There's no way for the vinegar to do anything to the battery."
] |
[
"no, not at all. The bottom of the toothbrush is entirely inert, the only way to interact with the battery is via an electric or magnetic field. Look at the bottom of your toothbrush - it should be all plastic. There are no physical contacts for the battery to have any interaction there"
] |
[
"no, not at all. The bottom of the toothbrush is entirely inert, the only way to interact with the battery is via an electric or magnetic field. Look at the bottom of your toothbrush - it should be all plastic. There are no physical contacts for the battery to have any interaction there"
] |
[
"Do drinks with caffeine dehydrate you?"
] |
[
false
] | null |
[
"This came up in a thread recently. Here's what I posted then:",
"I really disagree. Caffeine is a diuretic, but I have never seen any evidence that it's diuretic effect continues with long-term use and that your own physiologic stimulation of ADH in a dehydrated state will not overpower caffeine's effect. I think the available evidence, based on this ",
"metaanalysis",
", is that caffeine does have an acute diuretic effect, but that people quickly gain tolerance. "
] |
[
"Caffeine is a diuretic"
] |
[
"It depends on the caffeine content. I drink strong coffee and it definietely dehydrates me.",
"I can drink coffee all day and be gagging for water by the 3rd or 4th cup"
] |
[
"Are all physical objects moving through spacetime at the same speed?"
] |
[
false
] |
What is this speed and what is its unit? I know that a point in spacetime can be described by a 4-vector. We measured the maximum speed through space to be c. How do we know what the maximum "speed" through time is? Lots of questions, hope you can help :)
|
[
"All objects have the same magnitude of 4-velocity: u",
"u",
" is the derivative of 4-position x",
" with respect to proper time τ (time elapsed in the rest frame of the object).",
"i.e. u",
" = ∂x",
"/∂τ",
"The magnitude of 4-velocty (4-speed?) is an invariant quantity.",
"|u",
"|",
" = u",
"u",
"μ",
" = (u",
")",
" – (u",
")",
" – (u",
")",
" – (u",
")",
" = "
] |
[
"Someone will chime in and say it's due to scattering or absorption and re-emission, which is a complete and utter myth.",
"I can't really explain it any better than ",
"this video",
".",
"Essentially, light as photons is only valid in a vacuum. In a material made of atoms (which have their own electromagnetic fields), photons combine with the collective excitations that exist in matter – quasiparticles such as phonons and excitons – to form a quasiparticle called a polariton, which has a non-zero effective mass."
] |
[
"By convention, 0 is time and 1, 2 and 3 are space.",
"Also x",
" = ct, so the units are of regular velocity"
] |
[
"What Are These Things in the Arctic?"
] |
[
false
] |
I noticed them on Google Maps a while ago but was never really sure what they are. They're like tons of little lakes/ponds. Here's a picture for reference or you can just look at the Northern coast of Alaska and Russia.
|
[
"All the following information can be found in either ",
"Permafrost: A Guide to Frozen Ground in Transition",
" by Neil Davis or in ",
"Land of Extremes: A Natural History of the Arctic North Slope of Alaska",
" by Alex Huryn and John Hobbie.",
"These are ",
"thermokarst",
" lakes and are an ubiquitous ",
"permafrost",
" feature found all across the arctic tundra along with ",
"pingos",
", ",
"palsas",
", ",
"ice wedges",
", ",
"poygonal ground",
", and beaded streams. These thermokarst lakes are often termed oriented lakes since most seem to be found elongated 90 degrees to the prevailing wind. They are quite shallow, never exceeding 3 m. Those less than 2 m freeze to the bottom every year. They also reduce the thickness of permafrost around and beneath them ( In bare ",
"tundra",
" near Point Barrow, permafrost can be as much as 400 m thick whereas under these lakes it may only be 60 m ). ",
"Since these lakes are often associated with poylygonal ground, it is thought they originate with these structures. Ice wedge polygons often form raised relief, which with the extremely flat tundra prevents drainage. Water tends to stay as it doesn't evaporate very efficiently due to cold temperatures, low sun angle, and short summers despite most of the arctic receiving less than 300 mm of precipitation per year. Consequently, these polygons form small shallow ponds. If there is enough relief, these ponds may connect and form beaded streams. Otherwise, they remain disjoint. ",
"It is thought from these small polygonal ponds, these thermokarst lakes form. Wind blowing across the surface may promote preferential erosion on one side of the small pond, growing and elongating it. This erosion removes the thin active layer (the thin layer of earth that that thaws every summer) insulating the permafrost below. This removal of insulation promotes thawing of the permafrost at the borders of the pond, allowing the pond to continue eroding its banks and melting more permafrost. The pond deepens, widens, and subsides linking up nearby polygonal ponds and forming a basin, allowing it to capture more water and continue growing each summer. They can become quite large such as ",
"Teshekpuk Lake.",
"These lakes rarely host fish. They typically host grasses and a small selection benthic inverbrates. They make great summer habitat for migrating birds and of course mosquitos."
] |
[
"This answer is more likely than the lakes being distorted kettles. Kettles are bigger and more differentiated. "
] |
[
"They may be streched kettles. Ice blocks were dragged onto the shore somehow and broken into a lattice. Those were buried. They melted. At some point there was another ice overlay that dragged the surface around.",
"There seem to be a few processes here. There were round lakes that formed in melted ice blocks that were buried. Another ice movement occured that stirred up the dirt and allowed it to be streched.",
"Edit: its the activation of the soil that's the tricky part. Its usually stirred up before kettles are set. That often happens with subglacial outbursts when high velocity stream flow drains the lakes under ice caps."
] |
[
"Can seismologists differ an underground nuclear test from blowing up the equivalent amount of TNT?"
] |
[
false
] |
With North Korea's nuclear testing activity despite the astonishing backwardness of the country I started wondering -- is it possible for them to just blast kilotonnes of TNT underground to fake a nuclear test?
|
[
"They can't fake the seismograph. Nuclear weapons have a distinct signature."
] |
[
"They can't fake the seismograph. Nuclear weapons have a distinct signature.",
"Could you expand on that? Is it simply that they determine that there was no earthquake where they got a hit, or that the frequency and/or amplitude is actually quite different from what a natural earthquake generates? In ",
"this PopSci article",
" they discuss how in 2006 \"...the USGS detected a 4.3 magnitude earthquake 45 miles north of Kimchaek, North Korea.\""
] |
[
"Well first off, the signal on the seismograph looks different than an earthquake. I don't know where to find a picture of it, but it is based on both the s and p waves. Also, multiple stations can triangulate the location, and if it is in an area not known for earthquakes, it does help. Especially if it is in an area where nuclear work is suspected."
] |
[
"For the cells that have been in my body since birth, do they contain the exact same atoms as at the time of my birth?"
] |
[
false
] |
I know that over time, our body replaces tissues, but some things aren't replaced, liked cerebral cortex neurons. Does this mean they contain the same atoms as I had at birth? Additionally, while the majority of my bone mass has formed as a result of food I've eaten while growing up, I did have bones as a baby. Are some of the atoms in my bones therefore the same atoms I had at birth? I've just been wondering how much of our bodies is actually made up of stuff we were born with.
|
[
"Yes, your body is made up of some of the atoms you were born with. I think the concentration of these \"original\" atoms would be moderately low since the body not only replaces cells, but also repairs cells continuously. This means that a cell could persist, but its constituents may have been replaced slowly over time."
] |
[
"The universe doesn't keep track of particles well enough for your question to be answerable. It only keeps track of the state and configuration of all the particles, and not the particles themselves (we know this because of quantum mechanics' empirical results - if two particles in the same state were somehow different, we wouldn't get the experimental data that we do)."
] |
[
"Except in practice that doesn't matter, since you can just look at it statistically. You're right that you might not be able to know whether any ",
" carbon atom is new or old, by quantum indistinguishability, but you could still look at, I dunno, the ratio of carbon-14 to carbon-12 atoms (or something) in a chunk of tissue and get an answer for on average how long ago the carbon was laid down there."
] |
[
"Is there a speed of a field?"
] |
[
false
] |
If an infinite negative charge appeared in the universe, would all electrons/matter instantly be repelled, or would there be delay in the charge appearing and other charges being affected? Does the same apply to gravitational and magnetic fields?
|
[
" Yes, there is a delay for information to propagate in quantum fields. The maximum speed information can propagate is the speed of light, so you're always feeling and seeing the universe with something of a delay. ",
" You're seeing the light from the sun with an 8 minute delay. You're feeling the gravity of Andromeda based on its position and shape 2.5 million years ago. If some particles are pair-produced 30 meters from you, perhaps an electron and a positron, you won't feel their electric field for 100 nanoseconds. If those same particles are pair-produced a light year from you, then you won't feel their electric field until a year later. ",
"In order to ",
" or ",
" something, you need to receive information from it. Since fields make particles, the speed of those particles can be thought of as the speed of the field. ",
"The electromagnetic field and gravitational field are 'massless fields,' meaning that the particles they make are massless (i.e. the photon, and hypothetical graviton). Since massless particles travel at the speed of light, information travels at the speed of light in those fields. The massive fields (or matter fields) will produce particles which are necessarily slower than the speed of light. ",
"There is a good Kurz Gesagt video from last month which illustrates some of the mechanics of this."
] |
[
"You're seeing the light from the sun with an 8 minute delay. You're feeling the gravity of Andromeda based on its position and shape 2.5 million years ago. You're feeling the gravity of Andromeda based on its position and shape 2.5 million years ago",
"Just a small follow-up, because I think this is an important point to clarify. As I wrote in ",
"a bit more detail below",
", while changes to the velocity of an object would only affect an object after a time delay set by the speed of light, uniform motion is updated in \"real time.\" So for example, even though it takes light from the Sun 8 minutes to reach us, we are feeling the gravity of the Sun as though the Sun were in its true instantaneous position, not the position it was in 8 minutes ago.",
"One way to make sense of this mess is to divide the potential into two parts, a \"static\" part and a \"delayed\" part. The static part accounts for the uniform motion of the body and effectively projects this uniform motion in the future. In contrast the delayed (also called the retarded) component accounts for ",
" to this uniform motion (e.g. acceleration), and it only kicks in after the delay (called the ",
"retarded time",
") needed for the information about the change to reach the observer. ",
"A weird consequence of this result is that if the Sun exploded, we would continue to feel its gravity as though the Sun was continuing to move uniformly as before, but only for 8 minutes when we would essentially receive the information about the explosion and the fields would \"correct\" themselves. "
] |
[
" Many things travel at that speed, and photons are a tiny part. Light is just the first one we thought about.",
"It should really be called \"the speed of causality\". All those fields and particles that are unconstrained by having inertia, happen to be limited to the speed of causality.",
"If we changed the name to something more accurate, you wouldn't have this question, right OP?"
] |
[
"How does the drop height of a marble affect the wave length of the waves in a water tray?"
] |
[
false
] |
[deleted]
|
[
"How can a wave simultaneously have both a larger wavelength and frequency? (Assuming larger means ",
" wavelength and ",
" frequency.) Shouldn't these have an inverse relationship. That is, unless the speed of the wave propagation through the water is also affected."
] |
[
"This relationship is called the ",
"Dispersion Relation",
" and for deep water it is approximately:",
"(Phase) Speed = 2*(gravitational acceleration) / (",
"angular frequency",
")",
"Though the group speed is the actual speed at which peaks and troughs will propogate, and it is half the phase speed."
] |
[
"Thanks for explaining :)"
] |
[
"How does fat travel through your body and get deposited everywhere?"
] |
[
false
] |
I understand the basic digestive system with how food travels through your body, gets absorbed in the intestines, and then gets pooped out. But when you have excess food (ie gain weight/get fat), how is food transformed into fat and how does it travel through your body to get deposited everywhere?
|
[
"(1) How is food transformed into fat? Well, food already contains fat. It's in the form of ",
"triglycerides",
" (TGs). Body fat also consists of triglycerides deposited inside fat cells (adipocytes).",
"TGs can't cross a cellular membrane, so they are broken down into their constituent ",
"fatty acids",
" and reassembled as needed. However, free fatty acids is not how most dietary fats are absorbed in the intestine. Instead, the TGs are packaged into ",
"chylomicrons",
" which are then absorbed and delivered to tissues.",
"In addition, dietary carbohydrate can indeed be transformed into body fat. This pathway is known as ",
", and it occurs in the liver as well as in adipose tissue.",
"(2) Fat is transported to tissues in the bloodstream, either as triglycerides within ",
"lipoproteins",
" or as free fatty acids bound to ",
"albumin",
".",
"Did this clear things up?"
] |
[
"Fat is absorbed through the intestines and collected into chylomicrons and are taken to the liver through specialized lymphatic tissue called lacteals. "
] |
[
"There are plenty of particles floating around in the bloodstream. See ",
"here",
".",
"what is the step before fats are sent via the bloodstream throughout your body?",
"My answer was admittedly a little dense so let's try this again.",
"In the intestine, dietary fats (triglycerides) are first broken down into fatty acids. These molecules come in various lengths, and this aspect dictates how they are absorbed.",
"Short- and medium-chain fatty acids can be absorbed as such, but most dietary fat consists of long-chain molecules that are too big for direct absorption into the bloodstream. Therefore, they are reassembled into triglycerides. The TGs in turn are put in transporter particles called chylomicrons. All of this happens in intestinal cells called ",
"enterocytes",
". The chylomicrons are then ejected from the enterocytes into the ",
"lymphatic system",
" and from there they are eventually released into the bloodstream."
] |
[
"Why does rubbing alcohol burn and why doesn't hydrogen peroxide?"
] |
[
false
] |
I was cleaning my cartilage piercing when I began to wonder. Is rubbing alcohol a better cleaner? Or was I wrong in assuming that because it hurt, it was cleaning better? Would hydrogen peroxide clean just as well?
|
[
"Household dilutions of hydrogen peroxide are not recognized as an effective disinfectant; rubbing alcohol and salt water are more lethal to bacteria. All peroxide does is clean; it's effective at removing dead skin cells.",
"Also, FIY, ",
"using hydrogen peroxide on wounds can disrupt normal healing.",
" This is why you don't use it to clean piercings.",
"The vast majority of advice on cleaning piercings tells you to use a plain salt water solution, which is quite effective at killing bacteria and doesn't sting so badly, and also doesn't irritate the raw areas and possibly inhibit healing the way rubbing alcohol does. "
] |
[
"\"",
"\"",
"How does that not support \"hydrogen peroxide on wounds can disrupt normal healing\"? I'd define \"normal\" as \"scarless\".",
"Article on wound healing from a hospital.",
" \""
] |
[
"OIC what you're saying, k. ",
"It still remains that hydrogen peroxide is not recommended for using on wounds, which is what the OP was asking."
] |
[
"How can doctors/labs tell what type of cancer a person has? And how can they tell what stage the cancer is at?"
] |
[
false
] |
For example, when a biopsy is done, what is being looked for? Is it a certain type of cell or cell growth? If they cant do a biopsy, can they tell just by looking at size and location of a tumor? It seems like there are so many types of cancers out there, how can they tell which one a person has?
|
[
"To add to this, it's a very complex question that can't really be answered without multiple textbooks-worth of text. Because it's different for each cancer.",
"When we biopsy, we're looking for malignant features. The pathologist is looking for telltale signs that the cells under the microscope are malignant. You can look for mitotic figures indicative of rapid replication, ugly looking cells that appear dysplastic, etc. And then there will be different signs for each type of cancer. For example, by looking at the cell types involved, you can differentiate between types of thyroid carcinomas. ",
"If a biopsy cannot be done, we cannot definitively give you a histologic diagnosis. But based on the location of the tumor and its appearance on imaging, we can in some cases give a reasonable guess as to what it is. For example, an ugly heterogenous tumor in the kidney with variable enhancement in a smoker is probably a renal cell carcinoma. But to know for sure, have to biopsy it. ",
"As to what kind of cancer, there are only so many cancers that arise in specific locations. For example, if there's a lung cancer, there really are only a couple subtypes that are primary lung cancers: small cell and non-small cell. The latter category consists of squamous cell, adenocarcinoma, large cell carcinoma, and probably a few others that I'm forgetting. You can reasonably guess which ones they might be or might not be by location - squamous and small cell tend to be central - and whether there are any other symptoms, i.e. small cell is associated with quite a few different paraneoplastic syndromes."
] |
[
"It seems like no one has answered several hours after you asked this so I'll give the broad answer, because I don't know any significant specifics.",
"Stage is usually a medical term describing the extent/size of the tumor and whether it has metastasized.",
"The type of cancer will be determined by pathologist, taking into account the tissue it was found in, the type of cells that appear to be involved, the growth pattern of the tumor, and molecular markers (usually proteins) which can be stained for by immunohistochemistry or similar.",
"Cancer can be graded usually a generalized system where increasing from grade 1-4 based on how abnormal the cells and their organization look for the tissue they're found in, and particularly how close they move to an undifferentiated (ie unspecialized) state. In other cases there is a similar, cancer-specific grading system that is more specific to the structures of the tissue in question, and might incorporate molecular markers. Ki67, for example, can be stained for by immunohistochemistry and is a common indicator of the relative level of proliferation within a tumor. In many cases this sort of approach is also used to identify e.g. hormone or growth factor receptors that might be involved in driving the cancer and determining therapy.",
"Sometimes cancers can be graded by e.g. MRI, taking into account morphological features/textures, diffusion, blood flow, contrast enhancement, etc. I think these grading systems are typically distinct from histological grading, but some might be interchangeable. In most cases histology is preferred."
] |
[
"It's different for different types of cancer. For a lot of blood cancers, you can do flow cytometry to look for specific markers. For others you can tell from imaging (at least to a reasonable extent) and then you biopsy and look at the pathology."
] |
[
"How quickly is stellar fusion depleting the hydrogen in the universe? When will there be more heavy elements than hydrogen?"
] |
[
false
] |
Question in title
|
[
"Not very fast at all. Less than 10% of the mass of a star undergoes fusion during its entire lifetime. A lot of people have that misconception about stars and the sun. It is not a giant ball that is constantly undergoing fusion. Only a very small part of the core is, and the high energy output is only due to the sheer amount of mass there is at the core, but the number of fusions per unit volume even at the core is very low."
] |
[
"The problem there is we don't have the advantage of the insane pressure and temperature from all the mass of a star. For fusion to actually create more energy that we use to create conducive conditions, the rate we have to make here on Earth has to be much higher."
] |
[
"The problem there is we don't have the advantage of the insane pressure and temperature from all the mass of a star. For fusion to actually create more energy that we use to create conducive conditions, the rate we have to make here on Earth has to be much higher."
] |
[
"Why do we consider that a e- n=3 in hydrogen atom has more energy than in n=1, when in reality the energy needed ionize the eletron is more in n=1 than in n=3? Why do eletrons have tendecy to go to lower states of energy? What do you consider a lower state of energy?"
] |
[
false
] |
So.. what its bugging my mind is this.. N=3 has is suppose to be a higher energy leve than n=1 right?However in this level the ionization energy is lower than it is for n=1.As such shouldn´t it be that n=3 is a lower energy level than n=1? And how come eletrons have tendecy to go to a lower energy level?And what do you consider to be a low energy level? Do you consider a low energy level when eletrons are only subject to Zef?Like i can´t stop thinking about this.. What is a lower energy level.. I know schrodinger equation and all that stuff and how he gets it there mathematically.. i just want to understand though
|
[
"Why do we consider that a e- n=3 in hydrogen atom has more energy than in n=1, when in reality the energy needed ionize the eletron is more in n=1 than in n=3?",
"The premise of this question is incorrect. It takes more energy to free a bound n = 1 electron than it does to free a bound n = 3 electron.",
"Why do eletrons have tendecy to go to lower states of energy?",
"This is true of ",
" in nature. Particles in nature prefer to minimize their potential energy.",
"What do you consider a lower state of energy?",
"In the case of the hydrogen atom, ignoring perturbations, the energies of bound states depend only on the radial quantum number (n). The energies are given by",
"E",
" = - [13.6 eV]/n",
".",
"This is an increasing function of n, meaning that if n",
" > n",
", then E",
" > E",
". So a state of lower energy is just a state of lower n."
] |
[
"E",
" is the total energy (kinetic and potential) of the electron. Using the virial theorem for a 1/r potential, we know that <T> = -<V>/2, where T is the kinetic energy and V is the potential energy.",
"Since <T> + <V> = E, it follows that",
"E = <V>/2, and E = -<T>.",
"Note that the potential and total energies are negative and the kinetic is positive.",
"So as you increase E, you increase the potential energy and decrease the kinetic energy, at least in terms of expectation values."
] |
[
"And how come eletrons have tendecy to go to a lower energy level?",
"Let's for the moment make the assumption you have one atom (and let's just consider ground state and one excited state) with no surrounding environment. There is only one possible configuration where the electron is excited in that one particular state it initially is in, but there plenty of different modes into which the atom could radiate a photon in order to get into its ground state. Because there are so many configurations with the electron in the ground state and a photon in some mode, but just one configuration with an excited atom and no photon, the first is more likely than the latter."
] |
[
"Would a circular 2d object in space that has two equally strong opposing thrusters oriented tangentially on its side start and stop rotating if the thrusters are pulsed sequentially, or would it begin to move as a whole?"
] |
[
false
] |
[deleted]
|
[
"One thruster would obviously induce a rotation. However, it would not just induce a rotation around the circles center.",
"Assume you give a very short pulse to one thruster you would send the object spinning and going forward.",
"If you pulsed the thrusters alternatingly, on average the disk would not rotate. However, it would go less fast than with a simultaneous burn and would not go straight ahead from its original orientation.",
"The exact trajectory would depend on the timing of the burns. If you alternate quickly enough that the disk has barely time to turn, you would notice hardly any difference. If you alternate pulses so that the disk does a quarter turn between pulses you would get a net movement 45° from your original orientation. ",
"edit: above only holds true if the starting condition is that one thruster gives of a half pulse and then they always alternate with full pulses. In that case the average rotation speed is 0 (alternates between ritation in one and then in the other direction). If one of the thrusters starts with a full pulse, the average rotation won't be zero and the trajectory of the object will be a wobbly circle (or worse)"
] |
[
"Not at all! The translational displacement can be quite comparable or much larger than the angular displacement depending on the frequency of your pulses. Let's look at Newton's 2nd Law for a system of particles (and continuous objects, such as the disk in this problem).",
"Σ",
" / m = ",
"Note that for a system of particles, ",
" is the acceleration of the center of mass.",
"Given a quick pulse, the center of mass of the disk will accelerate in the opposite direction the exhaust gases of the thruster are pointed at. There will be a rotational component to this motion, but there will be translation motion. Let's call this translational velocity ",
". If the left thruster's exhaust fired first and was pointed downward, the center of mass of the disk will now be moving up with speed v.",
"Let's say, after a quarter turn (90 degree turn), the right thruster fires in exactly the same way as the other thruster did: same force, same impulse. This will now stop the rotation, but it will give the disk a velocity component towards the right. This component has magnitude v as well, but now our overall velocity vector is",
" = v",
" + v",
" where ",
" and ",
" denote the unit vectors pointing to the right and up, respectively. So now the disk is traveling translationally, but it is not rotating.",
"Let's wait the same amount of time again before firing the left thruster again. After the left side fires again, we get another boost towards the right.",
" = 2v ",
" + v ",
"Now the disk is rotating again. and etc.",
"You can fix the frequency of pulses so the time between burns is shortened so the disk does not change direction very much, and each pulse will add to your translational velocity vector. You can also change how the pulses are initially fired to get a more or less \"straight\" path (fire the very first pulse half as strong as the rest of the pulses).",
"And about something converting the rotational kinetic energy to translational kinetic energy: In this scenario, the only forces at play are the forces from the thrusters, and this force comes from the pressure the exhaust gases push on the thrusters when they are burned out. When bringing the disk's rotation to a stop, that rotational kinetic energy leaves mostly with the gases (since they are the much lighter particles). Some of that energy will be given to the disk in the form of translational kinetic energy, but not a majority of the energy."
] |
[
"Not at all! The translational displacement can be quite comparable or much larger than the angular displacement depending on the frequency of your pulses. Let's look at Newton's 2nd Law for a system of particles (and continuous objects, such as the disk in this problem).",
"Σ",
" / m = ",
"Note that for a system of particles, ",
" is the acceleration of the center of mass.",
"Given a quick pulse, the center of mass of the disk will accelerate in the opposite direction the exhaust gases of the thruster are pointed at. There will be a rotational component to this motion, but there will be translation motion. Let's call this translational velocity ",
". If the left thruster's exhaust fired first and was pointed downward, the center of mass of the disk will now be moving up with speed v.",
"Let's say, after a quarter turn (90 degree turn), the right thruster fires in exactly the same way as the other thruster did: same force, same impulse. This will now stop the rotation, but it will give the disk a velocity component towards the right. This component has magnitude v as well, but now our overall velocity vector is",
" = v",
" + v",
" where ",
" and ",
" denote the unit vectors pointing to the right and up, respectively. So now the disk is traveling translationally, but it is not rotating.",
"Let's wait the same amount of time again before firing the left thruster again. After the left side fires again, we get another boost towards the right.",
" = 2v ",
" + v ",
"Now the disk is rotating again. and etc.",
"You can fix the frequency of pulses so the time between burns is shortened so the disk does not change direction very much, and each pulse will add to your translational velocity vector. You can also change how the pulses are initially fired to get a more or less \"straight\" path (fire the very first pulse half as strong as the rest of the pulses).",
"And about something converting the rotational kinetic energy to translational kinetic energy: In this scenario, the only forces at play are the forces from the thrusters, and this force comes from the pressure the exhaust gases push on the thrusters when they are burned out. When bringing the disk's rotation to a stop, that rotational kinetic energy leaves mostly with the gases (since they are the much lighter particles). Some of that energy will be given to the disk in the form of translational kinetic energy, but not a majority of the energy."
] |
[
"Why is it that the majority of humans are right handed?"
] |
[
false
] | null |
[
"To be completely honest, I think scientists still could not explain why majority of us are right-handed. Concordance rates for handedness in monozygotic and dizygotic twins are low, suggesting there are more important players than genetics. From evolutionary perspective, there are some evidence pointing that the Neanderthals are right-handed, although the reason remains unknown. Some people think right hand is better for cooperation, or whatnot.\nThere is a ",
"study",
" published in 2013 suggesting that L/R handedness are influenced by genes that also involved in Left-Right asymmetry.",
"EDIT: ",
"/u/FalsifyH1",
" pointed out that I made a mistake here. I said concordance rate between MZ and DZ twins are low, this is incorrect. It was meant to say that DZ concordance rate is lower than MZ, although as s/he pointed out, the rate of concordance is higher than chance in both MZ and DZ."
] |
[
"I'm surprised that no one in here has said coincidence. Some evolutionary traits aren't because they were necessarily adaptive, but rather because they weren't maladaptive. For example, the ",
"laryngeal nerve in giraffes",
" is likely not optimal, but it wasn't sufficiently maladaptive (and/or the correct mutation never occurred to change it). ",
"So, maybe we just became primarily right handed at some point, and it never changed, because why would it? "
] |
[
"What do you mean by «right hand is better for cooperation»? Do you mean it's better for our specie's cooperation to have a big majority using one hand over the other instead of a 50-50 divide or is there some objective difference between a right hand and a left hand?"
] |
[
"Is any of the following homeopathy trials rigorous?"
] |
[
false
] |
I have a friend trying to convince me to try homeopathic remedies for my illness and I, in turn, have being trying to convince her to stop taking them for hers. At the beginning, all she provided was anecdotal evidence, but this link goes further than that. I'm still of the opinion that homeopathic remedies don't work, but I'm having a hard time refuting the evidence in that link. Help?
|
[
"On the contrary, the more independent trials you look at, the higher the probability that there will be a few that came up \"significant\" just by chance. Even in a well-designed trial, there is always a small probability that you will get a Type I error just by chance (Type I errors are when the data seem to indicate there is a real effect, just by chance, when there truly isn't an effect). Suppose there are 100 trials testing homeopathy, all using good designs, all using classic statistics with p<0.05 as the significance threshold. Even if homeopathy has no real effect you'd still expect 5 of those 100 trials to show significance just due to chance.",
"So when evaluating a set of studies you must bear in mind the overall number of studies performed. The best way to do this is NOT to cherrypick single studies, as it appears that site has done, but rather to look for a good review paper that surveys the entire literature.",
"This is also why it's so important to publish negative results. (Imagine if the 95 trials that showed no effect did not get published, and only the 5 that showed an effect got published.) "
] |
[
"The question you (and everyone else) should be asking is not 'does homeopathy work'; it is 'does homeopathy work better than similarly administered placebo'. From what I see in the writings you linked, none of them attempt to demonstrate that homeopathy works better than placebo."
] |
[
"I only read a few paragraphs down, and scanned the rest, due to typos making it hard to understand (red flag #1)",
"My $0.02: It seems the author has prepared a literature review of some 307 scientific papers that (according to the author) support the idea that homeopathy \"works\". Most of these papers are from relatively obscure journals.",
"The search term \"homeopathy\" in google scholar gets ",
"58,000 hits",
"In pubmed, ",
"14,000 hits",
"307 vs 58k or 14k. What do the other 13k-57k articles say on the subject?",
"It seems to me (again, having literally not read a single article pro or con) that the author of the page may just be cherry picking articles that support his/her pre-concieved ideas, and ignoring the ones that don't. ",
"This is the same way that many climate-change denialists and anti-evolution folks still have careers publishing their ideas; even if 99% of practicing scientists agree on something, if its controversial, the 1% will always be able to get a few papers out. When this 1% makes 100s of papers, they can cite each other and ignore the 99%. It still doesn't mean they are right."
] |
[
"Why do these gifs give a vivid impression of 3D, while video doesn't?"
] |
[
false
] |
link was just posted over in /offbeat. It has gifs of stereoscopic photographs with the image quickly alternating between the two perspectives. This gives me a very vivid impression of being 3D, while a shot from a film with a camera moving around the scene doesn't, though I'd have thought the cues that my brain is picking up on to form a 3D image would be the same in each case. Why the difference?
|
[
"What you're seeing is called ",
"structure from motion",
". Your brain uses the motion in 2D (along your retina) and the assumption that the world is fairly rigid and static (the complex motion doesn't come from weird warps in space) to infer vection (movement of the viewer) or object motion in 3D. This 3D motion information allows you to understand the structure of the objects in the scene.",
"The motion in the images is actually fairly fast. When you have similarly fast panning/rotating shots in a video, you get a similarly strong 3D affect. ",
"What comes to mind is the view from a ",
"helicopter-mounted cam flying through a canyon",
". Notice that the faster the movement, the stronger the 3d effect."
] |
[
"It's a ",
"stereoscope"
] |
[
"It's because video doesn't shake back and forth like that. It would look 3D if it did. ",
"The feeling of 3D appears when each eye sees a slightly different picture, that's how you can feel distance. With picture moving like that you can see the angle of the photo and the distance between objects in it, as objects further away move a bit more than objects closer to the camera."
] |
[
"Why do I feel so tired when I'm doing something boring?"
] |
[
false
] |
Let's say I'm at work or in some classes I feel tired like I'm literaly falling asleep, but when class or work is over I feel like I can run a marathon.
|
[
"This article",
" gives a pretty succinct explanation:",
"People have an embedded sleep–wake cycle regulator controlled by a combination\nof two internal influences: circadian pacemakers and homeostasis [4], [6]. Environmental factors such as stress, noise,\nlight, excitement, anger, pain, and sleep fragment are known\nto affect the sleep–wake cycle as well. However, in contrast\nwith common belief, they do not cause us to sleep, but simply\nunmask any tendency to fall asleep that is already present. It is\nfrequently misunderstood that boredom can cause sleepiness. It\nmay unmask sleep in a human who is either originally sleepdeprived or in circadian sleep peaks, but itself does not cause\nsleepiness [6]. Masking is a critical concept for understanding\nsleep in terms of the sleep–wake cycle. It is common that\npeople with chronic sleep deprivation can mask their level of\nsleepiness at their workplace. However, when they sit still and\nare deprived of external stimuli, sleep is unmasked and quickly\narises [7].",
"I also find ",
"this",
" speaks to your question. Although it is an article on the subject of \"excessive daytime sleepiness\" (a pathology) specifically, rather than the type of feeling tired that you're describing, it does address some of the same topics in the course of its discussion:",
"Johns [3, 8] has proposed a new conceptual model of sleep and wakefulness in which there is a major influence on sleep propensity from the integrated effects of all sensory inputs to the central nervous system. That includes exteroceptive inputs from the environment, (visual input,the direct effect of light, noise, hot and cold sensation, etc) as well as enteroceptive sensory inputs from within the subject’s body and brain. The latter arise from many sources, such as the afferent nerves associated with stretch receptors and spindles in muscles and joint capsules that are activated by the tonic activity of postural muscles and the phasic activity of muscles and joints during body movements, as well as from vestibular inputs from the ears, baroreceptor inputs from stretch receptors in the aortic arch, and central inputs related to ongoing cognitive and affective mental activity. This new conceptual model invokes separate neuronal systems within the central nervous system that provide two drives, a wake drive and a sleep drive, that interact with each other by mutual inhibition.",
"Edit: I would like to note that although I believe the OP's question is wrt ",
", I admit to being a little confused that neither of these articles references hypocretin/orexin in the regulating of sleep vs. wakefulness. I would love to have some clarification from an expert on how orexin fits into the above explanations (if at all)?"
] |
[
"TIL, thanks."
] |
[
"No problem. I know slightly more than the average Joe about sleep and wakefulness due to having narcolepsy with cataplexy and researching my own condition, but am not a bona fide ",
" as such."
] |
[
"Can mountain and lowland gorillas interbreed?"
] |
[
false
] |
If so, has this ever happened? What would the result be like?
|
[
"They are considered subspecies, not different species, so they can interbreed. I don't know if it's ever happened, hoping someone else can answer that. But the result would be a healthy intermediate gorilla. They live in troops, so I think the end result would depend on a lot of different factors. Does the troop accept both parent gorillas?(Probably Not) Do they accept the baby?(Probably) Are they separated from the troop?(Probably Not) Etc etc."
] |
[
"Humans are actually very closely related! One of the main reasons is a bottleneck in the gene pool about 70,000 years ago. It only takes a few genes to be expressed differently to have drastic changes in looks.",
"The issue is that classification is always difficult. Deciding on species, subspecies, variant etc. It's a gradient, not an exact line in between. It could be argued that races could be considered subspecies. But that still doesn't mean there are huge genetic differences between individuals. "
] |
[
"Serious question.",
"If this is the case for gorillas and many other animal species, then why arnt humans, with sometimes more extreme morphological differences, considered as sub-species?",
"A number of vets and zoologists I have asked this before were adamant human population groups can be clearly defined as sub species (if not complete species) by the definitions applied to other animals."
] |
[
"[Astronomy] Say I had the land and resources to launch a teeny, tiny probe into space (Earth's orbit), all by myself, for purely scientific/personal achievement reasons. What's the legality of this? Presumably NASA would need to know, in case it interferes with other satellites. Am I even allowed?"
] |
[
false
] | null |
[
"Such questions are better suited for our new-ish sister sub ",
"/r/asksciencediscussion",
". Please consider reposting there instead."
] |
[
"Please delete!"
] |
[
"Duly noted. Would you like me to delete this post? Or just repost there? :)"
] |
[
"Is there an upper or lower limit on the wavelength of light?"
] |
[
false
] |
Is there anything beyond gamma or radio waves? What would generate them?
|
[
"On the low-frequency end of the electromagnetic spectrum, nothing interesting happens. You just get closer and closer to static fields, which can be thought of as an EM wave with a frequency of zero. There is not really a fundamental lower limit, since static EM fields are perfectly valid and perfectly normal. ",
"On the high-frequency end of the spectrum, things get more interesting. Classical electromagnetics (Maxwell's equations) says there is no upper limit on frequency. But classical electromagnetics is not completely accurate. As you go to higher and higher frequencies, you go to higher and higher energies, and the EM waves act more and more like particles, and you really need quantum electrodynamics. According to QED, photons with high enough energy can decay into particles with mass, but they don't have to, so that's not necessarily a limit. At high enough energy densities, photons can form black holes, so you could see that as an upper limit. I think before we can say anything conclusive about an upper limit on photon energy/frequency, we need a valid theory of quantum gravity.",
"Note that the the phrase \"gamma rays\" applies to all high-energy photons. There is nothing \"beyond gamma\" for the simple reason that the word \"gamma\" is defined to apply to all high-energy photon frequencies all the way up to infinite frequency. Similarly, the phrase \"radio wave\" extends all the way down to zero frequency, so that there cannot be anything below radio waves by definition."
] |
[
"All photons have all energies, frequencies, and wavelengths; it just depends on what reference frame they're being examined in. There might be an upper limit though depending on how quantum gravity works."
] |
[
"I'm pretty sure that a 'single photon' cannot collapse into a black hole, regardless of its energy. After all, the energy of the photon will be dependent on the frame of reference of the observer; I don't think it would be possible for it to be a black hole in one frame while not in another."
] |
[
"What's the deal with beer bellies?"
] |
[
false
] |
There's definitely a distinctly round belly that is often associated with drinking lots of beer, but why? I know you can't work out certain parts of your body to target your weight loss, I assume you can't target your weight gain either. Maybe I'm just not very observant, but I don't know if I've ever seen a woman with a beer belly. Is this an exclusively male thing?
|
[
"I don't believe it has anything to do with energy from beer being stored differently than other forms of food (that's the part I'm not sure about). Men have a greater biological pressure for fat to be stored in their belly than women, who have fatty tissue stores in varying composition vs. men.",
"Just to give some midwestern flavor; the guys i know that have beer bellies have put in a lot of work balancing their diets with excessive bratwurst, cheese and other high calorie foods. So don't blame just the beer! It's a whole team effort."
] |
[
"Chronic alcohol abuse causes one’s body to overproduce corticosteroids. This comes as an adaptation to dehydration and hypoglycemia, as well a consequence of alcohol interfering with the brain’s control of the endocrine system. Alcohol detoxification in the liver also slows the metabolism of cortisol, which allows it to accumulate. ",
"These hormones cause water retention and alter fat storage, leading to a puffy distended look in the gut and face. This is well known among alcoholics. ",
"It’s sometimes referred to as a pseudo-Cushing’s syndrome. "
] |
[
"There are primary and secondary areas of fat storage. The belly is primary. Secondary storage areas like the arms and face are the first to burn off. Girls can have beer bellies, but they also hold more fat in other areas than men, like thighs, hips, breasts etc.."
] |
[
"What's the newest on bipolar type 2?"
] |
[
false
] | null |
[
"Hello,",
"This would be more appropriate for ",
"/r/AskScienceDiscussion",
".",
"Best."
] |
[
"Ok\nBut why?"
] |
[
"The question is open-ended."
] |
[
"How is it that I can type without looking, but if asked to recall the position of the keys on a keyboard I would not be able to do so?"
] |
[
false
] |
This is something I'm not sure is unique to me. Though with that said I do have some problems with my memory and I suspect it could be linked to that (and I mention that incase there's some interesting related nugget of information that we can discuss/ I can stop worrying about this as a symptom of my wierd memory!). Many thanks.
|
[
"Why couldnt you just simulate where your fingers are going and recite from that? (This is actually what I do, I'm a programmer and can type very quickly but like you can't recite the keys without moving my fingers)",
"The obvious answer is it's a reflex from repetitively doing it and your brain modeling the physical locations.",
"I think an apt analogy for being able to recite where the keys are is akin to knowing the speed a ball is being thrown at (generally something most people couldn't do because they've not practiced it) while being able to throw at the right speed to hit a moving target is something many people could do even know they'd have no idea how fast it's going.",
"The point I'm trying to convey is that both knowing where the keys are consciously and being able to physically determine the space they are in are 2 different modeling scenarios in your head, if you practiced picturing where the keys are as often as you practiced typing you could easily remember and recite their positions. ",
"It's entirely feasible for you to recite where the keys are and yet without sufficient practice lack the coordination for your fingers to hit the right keys. It's probably been a long time since you started typing and have forgotten how much you had to look down to even make sure your fingers are in the right resting spot...which is important because finding all the other keys is based relatively on where your fingers rest."
] |
[
"This is because your memory for skill originates in a different part of your brain (the basal ganglia) than your memory for knowledge (the cortex).",
"You've probably heard of people with devastating memory loss. These people usually have trouble with their hippocampi. If you consider your memories as details, you can consider the hippocampus as the brain area that contextualizes these details. For instance, your ability to remember 'yesterday' as a series of related events is dependent on your hippocampus.",
"People with damage to their hippocampi can still learn skills. They won't remember learning them. They'll probably be surprised they're doing so well.",
"This is because the learning is taking place in an 'unconscious' part of the brain. It's the part of the brain that automaticizes behavior. Riding your bike, driving, and other motor skills are all dependent on the basal ganglia.",
"Damage to the basal ganglia is damage to your skill memory. Parkinson's disease involves the death of neurons in an area known as the substantia nigra. The substantia nigra produces dopamine used by the basal ganglia. This neuromodulator (dopamine) is needed for the basal ganglia to function properly.",
"So it's not a problem that you can type without looking while you can't remember the positions of the keys consciously--these are two different problems for the brain and are processed in different areas of it."
] |
[
"I honestly have no idea. I can type just fine and find certain words, but I'd have to do it a word at a time and try to cover the whole keyboard that way!",
"Thanks for explaining this though and that's really a great analogy with the throwing. ",
"What's funny is that this whole 'feel' for the keyboard has become precise enough that, as long as one of my hands is in the correct resting position, the other can just come in and line up based on it's distance to the other pre-rested hand!"
] |
[
"Why is December 21 the shortest day of the year but the coldest in February?"
] |
[
false
] |
Assuming you're in the northern hemisphere... What causes the big delay?
|
[
"It's called ",
"seasonal lag",
"."
] |
[
"Basically, it takes time for the heat absorbed by the land and sea to dissipate. The Winter Solstice marks the decline of the Northern Hemisphere receiving large amounts of direct sunlight, but it takes some time for all the heat absorbed by the planet to finally go away. This is the same reason that the coldest part of the day is just before dawn, even though the Sun set hours earlier."
] |
[
"Its similar to the way that a driven RC circuit works (if you're familiar with electronics). The sun is like a driving voltage, each day it deposits some amount of energy that we can reasonably estimate as dE. This is similar to a voltage powering a resistor and capacitor in series. The capacitor is the \"stuff\" (air, ground, water) in the area. They absorb energy from the sun. The resistor is the heat that is radiated to the surrounding area and back out to space and the cooling that goes on at night. In a system like this, the peak voltage on the capacitor lags behind the driving voltage by some amount depending on the resistance and size of the capacitor. In the same way, the temperature in the area lags behind the peaks (and valleys) in energy input depending on the materials in the area and how much heat it radiates out during times that it doesn't have sunlight."
] |
[
"Why is it that our teeth will rot fairly quickly if we don't brush them, yet other animals eat nasty stuff all the time with no problem?"
] |
[
false
] | null |
[
"The \"nasty stuff\" that animals eat isn't full of sugar."
] |
[
"This ",
"has been asked",
" a few ways before ",
"But a couple short answers are:",
"We eat way more sugar and complex carbs(that break down to sugar) than our ancestors. Sugar is what turns to acid and plaque to cause cavities. The high level of sugars we normally consume do not happen in natural foods.",
"We drink more acidic drinks (coffee, soda, etc) that wear away our teeth",
"People are living longer than they used to (I don't like this explanation as there are elder people who still have their teeth)",
"For an example: If you look at some societies around the world that have more primitive diets with less processed foods (which means a lot less sugar) they may have wonderful teeth without brushing at all.",
"EDIT: grammararar"
] |
[
"So basically, the bacteria that causes cavities needs refined sugars to create plaque. There are three requirements for cavities",
"Sugar",
"Acid",
"Time",
"If you don't get enough of any one of these things, you don't get a cavity. Also, unlike carnivores, our teeth are close together and have the ability to trap food between them (this is the most likely place for cavities in adults). Look at your dog's or cat's teeth, they have gaps between them.",
"One last point. Not many animals live as long as we do, yet their enamel and dentin is just as thick as ours is, ie. it will take the same amount of time to get a cavity that will destroy the tooth."
] |
[
"Why does it feel warmer when it's snowing?"
] |
[
false
] |
Is it actually warmer? Or am I just imagining the difference in temperature?
|
[
"It can only snow within a certain temperature range, if it's too cold there won't be any moisture in the air. A warm front bringing moisture in will warm the air up some and lend enough moisture for snow to form. "
] |
[
"Around here (Boston), it ",
" warmer when it snows. Recall that the air can't hold much water below 20F, so when it snows it warms up from 15F to 25F or more, then snows. "
] |
[
"It can only snow within a certain temperature range, if it's too cold there won't be any moisture in the air. ",
"This is misleading; It can ",
" be too cold to snow, but it can can be too dry to snow. So yeah, a cold front has to meet up with a moist air front and therefore it's warm but insinuating \"It can only snow within a certain temperature range...\" is false."
] |
[
"Are defibrillators portrayed accurately in movies and TV?"
] |
[
false
] |
I have a couple questions about defibrillators. First, it always seems like it's just up to the doctor how many times to try using them before deciding to give up. In real life, is there a guideline about when to stop and declare the person dead? Can a doctor get in trouble for trying too many times, or not trying enough? Also, when it does work, there's always a delay of a few seconds between administering the shock and the flatline on the monitor turning into a heartbeat. Is this just done for suspense, or is there such a delay in reality? What causes that delay?
|
[
"American Heart Association's latest guidelines for defibrillation",
"Overview with flowchart"
] |
[
"There are ",
"guidelines",
", but the number of shocks actually given will depend on the situation. Most newer AED's actually have a telemetry monitor built in and will check to see if the heart has returned to normal sinus rhythm, then recommend the next step (another shock or CPR). There is a delay, but not nearly as long as what is shown on TV. I'll leave an explanation of why to someone with more cardiac knowledge..."
] |
[
"Defibrillators are probably the most misused items in tv and movies second only to handguns. A doctor cannot overuse the defibrillator because the machine will not deliver a shock in the current machines unless a shock is warranted. The heart has to be in fibrillation before the machine will administer a shock. If the heart is stopped, the machine will tell the user to administer CPR. If the heart is beating normally, the machine will tell the user to transport for further medical care. ",
"Doctors could be the person to use the defibrillator, but currently, anyone who understands basic English can use one (or whatever language the machine is programmed to speak.) If a heart goes into fibrillation near a doctor, the casualty has no better chance of surviving than if any other trained user is administering the shock. ",
"If the doctor happens to be a cardiac surgeon, the doctor can try an open chest massage or try to implant a pacemaker. If not, CPR will continue until brain death occurs or the doctor decides any additional life saving methods are useless. ",
"The reason there is a pause is because you need to wait for the machine to test for a normal beat. When you use the defib, the heart is still beating, it just isn't beating efficiently enough to move blood around. The pause gives the machine enough time to check the heart rate and depth. "
] |
[
"Does the moon have any appreciable color?"
] |
[
false
] |
From here on Earth it appears white/gray. The moon landings were, from what I can tell, mostly in black and white or very desaturated. If I was to be standing on the moon, would I see any colors in the rocks, soil, etc.?
|
[
"Assuming it is grey, and rephrasing the question, why is space dust/are space rocks gray? Why not brown, white, green, red, etc. from what we have here?"
] |
[
"The moon is actually rather colorful if slight hued grey is colorful.. ",
"http://www.rc-astro.com/photo/id1018.html"
] |
[
"It's quite dark, but apparently the complete picture is complicated. ",
"The Moon has an exceptionally low albedo, giving it a similar reflectance to coal.",
"- ",
"http://en.wikipedia.org/wiki/Moon",
" - ",
"- ",
"http://web.archive.org/web/20080523151225/http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm",
" - ",
"- ",
"http://en.wikipedia.org/wiki/Lunar_soil",
" - "
] |
[
"After an animal dies, do chemical reactions and processes continue in their body?"
] |
[
false
] |
I'd always imagined that when a person or animal dies that all processes in their body would stop immediately, but this seems unlikely. I'm 17 but I've studied a fair amount of biology, so I'm guessing that respiration would become anaerobic fairly quickly. Does food continue to be digested, do processes like osmosis and cell growth/division still occur? Just curious.
|
[
"Things change rapidly, like you mentioned with respiration. However, interesting proceses still occur, such as that which produces ",
"rigor mortis",
".",
"I think of metabolism, and life processes in general, as those which combat thermodynamic equilibrium. When those processes stop, what is left is the progression towards equilibrium dependent on the kinetics of the process in question. Certainly stomach acid will not stop acting on gut contents, but I wouldn't really call that a continuation of \"digestion\"."
] |
[
"Osmosis isn't a chemical reaction, fyi.",
"However, ",
" processes still occur. The body has only a small amount of available energy though, so things start slowing down, and stopping almost immediately."
] |
[
"I only said it was a process, but sorry if I implied otherwise. I assumed that would be the case, but it just seems counter-intuitive to the idea I have of death. Life isn't that abstract though, I realise."
] |
[
"How does flyspray (i.e. Raid) work and do insects experience pain when they are killed by it?"
] |
[
false
] | null |
[
"I'm no insect physiologist, so I can't answer your second question, but I'll be glad to tackle the first.",
"Depending on what you're trying to kill, the spray will contain varying types of insecticides. However, in household products, you will generally see a group of chemicals known as ",
", which includes permethrin, cypermethrin, and imiprothrin. These compounds are neurotoxins and work as such:",
"Compound penetrates the insect's exoskeleton and locates a neuron",
"Prevents the sodium channels from closing",
"The nerve is unable to \"de-excite,\" which leads to paralysis. ",
"To ensure lethality, synergists will often be added to the spray. In particular, we would probably see something like piperonyl butoxide, which inhibits detoxification enzymes and prevents the insect from actively clearing its system of the insecticide."
] |
[
"Just adding a little to Funkentelechys answer, the way it was explained to me that insects control their movements with a vast array of on/off switches, and the control comes from switching on and off the right things at the right time.\nSo when the Sodium channels can't close, you are effectively telling the flies brain to switch everything to the \"On\" position, and that's why they spaz out and buzz around on the floor in circles. It would be like you trying to run,punch, scream and do all the other actions your muscles do, all at once. A seizure pretty much.",
"They then slowly die of exhaustion, fortunately they don't have a central nervous system because it sounds like an awful way to die!"
] |
[
"Flies certainly have a central nervous system. They are also ",
"capable of feeling pain,",
" though it's probably a more primal response (in other words, they don't have a high enough consciousness to feel pain as we do, but have nociceptors that will tell them to avoid something)."
] |
[
"How do parasites that reside in the intestines avoid being unceremoniously pooped out?"
] |
[
false
] |
It seems like there are several kinds of parasites that inhabit the lower digestive tract of many animals, and it's certainly in their best interest to remain there and feed. So how do they keep their real estate and avoid being discharged with the feces?
|
[
"Hooks and suckers."
] |
[
"and pseudomembranes and some burrowing."
] |
[
"Pretty much the same way our normal flora stays in there. We have over 400 different identified species of bacteria that live in our colon at any given time, and bacterial cells outnumber human cells in our body approximately 10:1. That normal flora helps prevent pathogenic organisms from finding a site to attach, but when we take antibiotics, it opens up new niches for parasites to make a home. C. diff is a common infection that uses this opportunistic method to get in. Amoebae and bacteria have special appendages that allow them to hold tight to areas that seem hostile. Think of H. pylori... It secretes a urease that cleaves urea and neutralizes nearby acid, allowing it to live in our stomachs. If there's a niche, something will evolve to fill it. As far as worm parasites, yeah, it's pretty much hooks and suckers that allow them to hold on. A lot of them also from cysts that conceal them from the immune system, which has a HEAVY presence in the gut."
] |
[
"Is it a myth or a fact that dogs can \"sniff\" cancer?"
] |
[
false
] |
Ive heard of it a long time ago, that dogs are able to detect/sniff/smell cancer but never knew whether that is true or if so where it originated from. Does anybody know? Im personally no expert with animals and biology but I doubt that dogs have the ability to do that.
|
[
"They're not perfect, but neither is traditional screening for early detection. Use of sniffer dogs is promising enough that we've worked on it since 1989. There are a lot of studies on it (use key words \"sniffer dogs cancer\" on Google Scholar), but the quality of those studies varies immensely. As ",
"/u/ondulation",
" has pointed out, some may use a very limited amount of person-specific samples and the dog may simply learn to recognize the person/sample. Approaches that focus on isolated biomarkers may be more promising, but an issue is that we struggle to find biomarkers that are exclusive to cancer. The markers may appear based on someone's diet, other mundane health issues or even genetics.",
"Also, while dogs are cheaper than some traditional techniques, they're still expensive. Just like with using rats to detect landmines, ",
"sniffer mice",
" and ",
"sniffer bees",
" for cancer are emerging options.",
"Here's a recent systematic review on dogs: ",
"https://doi.org/10.1016/j.jveb.2017.03.004",
"An overview of sniffer animal prospectivity: ",
"https://doi.org/10.1016/j.jveb.2017.05.002",
"On a similar topic, the ",
"somewhat famous case",
" of a woman who was able to \"smell Parkinson's disease\" (even in a control participant who was assumed healthy in the study and whom she diagnosed in the process!) lead to the discovery of such a biomarker: ",
"https://doi.org/10.1021/acscentsci.8b00879",
"Edit: found a better link, words"
] |
[
"It seems like total BS upon hearing it.",
"But it turns out its true, dogs can smell certain kind of odor signatures that cancer makes. ",
"https://www.medicalnewstoday.com/articles/323620",
"I wasnt sure about the source but i checked them aparently they're good.",
"https://www.google.com/amp/s/mediabiasfactcheck.com/medical-news-today/%3famp"
] |
[
"I think it is likely that dogs can be trained to detect some smells specific to cancers. But there also seem to be weaknesses in the studies cited. In ",
"one cited article",
" it seems like the dog was trained on samples from the same patients that were used for testing. If that is correct, the dog may “just” have learned to discriminate between the 113 individuals, instead of generally separating cancer from non-cancer smells.",
"As the method has been discussed for decades but is not in regular use I guess there are serious weaknesses. For example, a too high rate of false negatives (cancer which is not detected) would be a show stopper for real world use."
] |
[
"Why do immunities from vaccinations not pass from mother to child in vitro?"
] |
[
false
] |
[deleted]
|
[
"To have immunity you need to have your own cells that are making new antibodies as needed. Antibodies only last for a short time. Their half-lives range from 1-3 weeks, so they should be completely out of your body in the matter of a few months. You only get the cells producing the antibodies by an exposure to the antigens (vaccine or actual bug) when your immune system is mature enough to respond.",
"I think you mean in vivo (within the living) as opposed to in vitro (in the glass (test tube/petri dish))."
] |
[
"If nothing else, I have learned a lesson in Latin today."
] |
[
"Our genes do not change every time we encounter a new antigen(foreign microbes) but the cells that are made from our genes do change as they replicate to adapt to new antigens we encounter. We have the genes to make a basic types of immune cells and it is what happens to the cell after it has been made that determines immunity to a bacteria/virus/other microbe. Vaccinations work to enhance the function of already produced immune cells thus no change is made to the genome and cannot be passed from mother to child.",
"Immunity can be passed from mother to child though. IgA(a type of antibody) is secreted into breast milk and does serve to provide new borns with some immunity to diseases. This again does not mean vaccinations can pass from mother to child since vaccinations elicit a repines in a different type of antibodies."
] |
[
"What is the audible click I hear when I electrically discharge and get \"shocked\"?"
] |
[
false
] |
What is producing this sound I hear when I, or anything, electrically discharge to a piece of metal?
|
[
"Thunder caused by lightning is produced by the rapid expansion through heating of the air through which the electricity arcs, causing a shock wave to propagate from the area of discharge. Static discharges are the same thing on a much smaller scale."
] |
[
"A good way to think of it is to remember what sound is. It is a pressure wave that travels through air (although technically it could travel through any medium, but air is the most common medium in through which our ears detect the sound wave). The spark produced in a \"shock\" rapidly heats the air around it, creating a pressure wave in the air. Since the pressure wave is a sound wave, we hear sound."
] |
[
"An interesting result of this is that it is possible to use this effect to create a \"plasma speaker\". Below is an explanation based on my understanding of how it works. If anyone else knows better, please chime in!: ",
"To do this, two conductors are placed near each other with an air-gap. A high voltage is created (usually using a flyback transformer circuit), enough to have dielectric breakdown of the air - the same thing that a static spark is. This voltage is switched on and off rapidly, (say 50KHz or more), creating a series of sparks that looks like a single spark, but has no noticeable sound. The reason we can't hear the sound from the series, is that the frequency of pressure waves is above the human threshold for hearing. The input voltage level is then oscillated by inputing the sound wave (e.g. from a speaker output). This creates a secondary wave, varying the intensity of the 50KHz pulses, which we can hear as the sound wave caried into the circuit."
] |
[
"Do Prime numbers change with base?"
] |
[
false
] |
E.G., we use Base-10, but would there be different prime numbres in base 12? 20? 99?
|
[
"A prime is a prime no matter which base you use to represent it. The fact of being prime or composite is just a property of the number itself, regardless of the way you write it or the symbol you use for it. 15 and F and Roman numeral XV all mean the same number, which is 3×5, so it is composite.",
"Let's take as an example base 13, where the base ten number 13 will be represented as \"10\" in that system, but \"10\" will still be a prime, because you cannot find two numbers other than 1 and \"10\" that will multiply together to make \"10\"."
] |
[
"Being prime is a property of the quantity, so it does not depend on the langage I speak. ",
"Example : The number of symbols x in the expression \"xxxxxxxxxxxxxxxxx\" is a certain quantity. To say that this quantity is prime is to say that you cannot decompose this quantity of \"x\" into G groups of equal size S (where G and S are bigger than 1). In this example you can convince yourself that it is prime (without counting explicitly the number) by simply trying to decompose into groups of 2, 3, 4 ... elements and checking that you will always have some leftovers.",
"So it is clear that the sequence of symbols that I use to represent this quantity has absolutely no influence on the fact that it is prime or not.",
"For example, the quantity can be represented as \"17\" if I'm talking in base ten, as \"dix-sept\" if I'm talking in french, as \"10001\" in base two, or as \"10\" in base seventeen. Translating into a different langage (base) doesn't change the quantity itself, and hence it doesn't change the primality of the number.",
"Note that (almost) all interesting properties of numbers are independent of the base we use (being rational/irrational, algebraic/transcendental, prime, composite, perfect, etc ...). "
] |
[
"You have 13 cookies. There is no way to fairly divide them up other than giving one to thirteen people. Or be a glutton and eat them all yourself. Regardless if you use base 10 or base 2, you are in the same predicament. The base is just how you describe it, 13 in base 10 and 1101 in base 2."
] |
[
"Science, approximately what percentage of humans that have ever lived are alive today?"
] |
[
false
] | null |
[
"6.38%",
" in 2009, probably more today."
] |
[
"It should decrease into the 22nd century through declining birth rates from increased education."
] |
[
"Will we ever get to the point where we see that percentage decrease?"
] |
[
"How did scientists of the late 1700s and early 1800s prove that meteors were rocks that fell out of the sky?"
] |
[
false
] |
Of course, there are plenty of religious and other objects that are claimed to have fallen out of the sky, and which are venerated, etc. but proving that they came out of the sky, to the satisfaction of all skeptics, is not the easiest thing. Especially given the state of the scientific arts at the time.
|
[
"Speculating here, will confirm on Wikipedia after.",
"With the discovery of Ceres and other asteroids, astronomers became aware of objects orbiting in paths between the orbits of Earth, Mars, and Jupiter. They could then presume that there were smaller objects that they could not yet detect, which might come close enough to Earth to collide. ",
"edit:",
"The astronomer Denison Olmsted made an extensive study of this storm, and concluded it had a cosmic origin. After reviewing historical records, Heinrich Wilhelm Matthias Olbers predicted its return in 1867, which drew the attention of other astronomers. Hubert A. Newton's more thorough historical work led to a refined prediction of 1866, which proved to be correct.[29] With Giovanni Schiaparelli's success in connecting the Leonids (as they are now called) with comet Tempel-Tuttle, the cosmic origin of meteors was now firmly established. Still, they remain an atmospheric phenomenon, and retain their name \"meteor\" from the Greek word for \"atmospheric\".[31]",
"So basically they linked meteor showers to points in the Earth's rotation."
] |
[
"For the longest time, they denied it. Any witnesses to meteors falling were from the lower classes, so their testimony was automatically suspect and thus discarded.",
"I wasn't until one was witnessed by an educated member of the upper classes that they were taken seriously.",
"See: ",
"http://en.wikipedia.org/wiki/Wold_Cottage_%28meteorite%29"
] |
[
"So occam's razor meant that rocks did not fall out of the sky unless witnessed by the appropriate authorities.",
"interesting"
] |
[
"Can cross pollination occur between different plant species?"
] |
[
false
] |
In my Agricultural Science class today we were discussing how “superweeds”, weeds that are resistant to total pesticides, can be formed when a GMO crop (pesticide resistant) cross pollinates with a weed. I was wondering whether or not it is actually possible for this to occur? Isn’t it like trying to cross a dog and a cat? Same kingdom, two completely different organisms? If not, how do weeds actually develop resistance to pesticides?
|
[
"If the evolutionary ancestor or closely related species(same genus) of the domesticated plant is a) present in the area and b) considered a weed, then yes it’s possible.",
"You also have to consider it the resistance mechanism is actually beneficial in a context outside of the farm. There’s no ecological issue if there’s a detriment to having the resistance gene(s).",
"There’s always freak horizontal gene transfer events but that’s quite rare and there’s no guarantee that the resistance gene(s) are the genes transferred."
] |
[
"Cross pollination can occur between species, this is hybridization and occurs reasonably frequently between plants. Domestic wheat itself is a result of several hybridization events, for example. ",
"You can hypothetically get superweeds if a weed species is similar enough to a crop species...don't think \"dog and cat\" think \"dog and wolf\" or \"dog and coyote\". For example there are both crops and weeds in the ",
" genus"
] |
[
"In evolutionary biology, there is a core concept called \"selection pressure\". \n",
"https://en.wikipedia.org/wiki/Evolutionary_pressure",
"In short - its the process where some \"pressure\" on a population, making individuals with certain genes more likely to reproduce. ",
"For pesticides, you have a chemical which strongly harms or kills most plants. If there is a plant which doesn't die, but instead just gets really sick and limps by - that will be the only one to reproduce. Soon you will have more plants that can barely survive. From there, plants that do a \"little better\" with the chemical will produce more offspring, and so on. ",
"Superweeds exist because we are basically grooming plants to be this way. Those that can survive move into the field and multiply. Each generation gets stronger against the chemical, because any plant with a random mutation that makes them 0.1% stronger against the chemical thrives more.",
"Modern farming has a bad relationship with evolution. Look at a field. It has been plowed, so it is completely disrupted. There is ZERO competition there, no other plants to fight against. The ground is soaked with nitrogen and phosphorous. The only thing keeping weeds out is chemical pressure. To truely fight weeds, farmers need to look at how they prepare fields. If they stop creating the absolute perfect growth bed for weeds (highly fertilized and disrupted ground with zero competition), things would change."
] |
[
"Everyone knows lead is toxic, but are there any technically positive effects on the body?"
] |
[
false
] |
Obviously any benefits are going to outweigh the toxicity of lead but after searching I didn't find any studies mentioning it. I did read that lead is absorbed into bones when other minerals are low so I wondered if it's actually giving some structure when that happens. We know some things that are generally bad for us sometimes have positive aspects and that the complete elimination of them might be even worse. A very broad example is alcohol where the relaxing and social effects of an occasional drink on a person's mental health might outweigh the negative effects on the body. Free radicals are known to cause cancer and human disease but are also needed by the immune system. Has there even been research done on lead like this? If there was a way to remove all lead particles (I realize that's basically impossible) would that also have any known negative impacts?
|
[
"Lead, and many other toxic metals like mercury, cadmium, thallium, and uranium, have no known role in the human body. Our biochemistry is not equipped to deal with them at all so any amount will cause harm. The only safe level of exposure to these metals is zero."
] |
[
"Yes. This is the secret of life. It's unsafe and in continuos danger but it doesn't care and continues its run!"
] |
[
"People tried all sorts of crazy things with heavy metals in the 1800s - there are no positive effects.",
"It's possible you could maybe build some kind of drug that contains lead and is useful under ",
" conditions, like a chemotherapy agent. People have done similar things with metals like platinum. ",
"But the crazy toxicity of lead makes this really unlikely. You'd probably have to put it into a bioavailable organic compound in order to have the effect you want, and organic lead is the kind of thing that kills you with a very small dose. ",
"How did we figure out something as toxic as arsenic for example could be used to kill parasites?",
"Lots of dead lab mice. ",
"Also, it's not arsenic itself but rather a molecule that contains one atom of arsenic.",
" Plain old arsenic has no positive effects. Even the drug is a thing of last resort - it gives permanent brain damage to 5-10% of patients and kills half of those."
] |
[
"How can we measure the absolute speed of something?"
] |
[
false
] |
[deleted]
|
[
"There is no absolute speed, only relative speed."
] |
[
"I'm seeing some quick/not fully explained answers here, so here is a link to a series of askscience questions related to special relativity. ",
"A good summary of the simple questions about special relativity"
] |
[
"No, velocities aren't additive. The formula is (v+u)/(1+v*",
"u/c",
" ). This is ~ v+u at low speeds, but the difference becomes significant at higher speeds. If you do the math you can see that as v and u approach c, the result also approaches c."
] |
[
"Can the principles for binding energy be applied to quarks?"
] |
[
false
] |
So in nuclear fission, large atoms are split and part of their binding energy gets turned into kinetic energy. Quarks are held together to form hadrons using the strong nuclear force the same way atomic nuclei are held together, with (from what I’ve researched) hundreds of times the amount of energy. I know from what we currently understand trying to break the strong nuclear force keeping quarks together is used to create more quarks, but would there theoretically be any way a quarks’s chromodynamic binding energy within a nucleon can be released?
|
[
"The potential that binds nucleons to each other is localized, meaning that the potential asymptotically approaches some value as the distance goes to infinity. So a particle with an energy larger than that asymptotic value of the potential energy has enough energy to escape to infinity.",
"But the static quark potential doesn't do that, it increases linearly with distance forever, or at least until the energy in the system is large enough to simply produce new quarks.",
"The binding energy of a system of particles is the difference in energy between the case where they're all bound together, and the case where they're all free particles, infinitely far away, with no kinetic energy.",
"But for quarks, you can't have free quarks infinitely far away from each other, the potential energy of that system would be infinite.",
"So because the quark-quark interaction is fundamentally different than most other interactions you hear about (the nucleon-nucleon potential, the Coulomb potential, Lennard-Jones, etc.), the concept of binding energy doesn't really apply there."
] |
[
"That makes a lot of sense, thank you for answering all my questions!"
] |
[
"The comment above is about today's universe where everything is \"cold\" and bound in hadrons. In a quark gluon plasma both quarks and gluons are free. Again the concept of a binding energy is problematic, but this time because things are not bound. You could ask about the energy to remove them from the plasma, but that's irrelevant at a time when the whole universe is a quark gluon plasma (or something even more exotic maybe, but certainly hot enough)."
] |
[
"Why isn't Asexual reproduction more common in the animal world?"
] |
[
false
] | null |
[
"Asexual reproduction does not allow for genetic diversity, so an organism that reproduces asexually is essentially making clones of itself. This has two major implications, one being susceptibility to disease. Entire populations of animals with the same genotype can be wiped out by a single virus. Also, since there is no genetic diversity, the organism would not be able to adapt to different habitats or niches, so there would be no divergent evolution.\nDivergent evolution is when a new species arises through accumulated genetic differences between two (or more) populations of the same initial species, usually due to the populations being isolated from each other. In asexual species, since the genotype can only change through mutations, this process would be extremely slow, so new species arising from an asexual species would be extremely unlikely."
] |
[
"asexual reproduction ultimately reduces variation in populations. This is due to asexual reproduction creates genetically identical offspring(apart from any mutations that arise). This means that over time populations that use asexual reproduction will be less adaptive to environmental change, as there is less variation in populations. This can be quite harmful to populations that have low birth rates. ",
"http://www.pbs.org/wgbh/evolution/library/01/5/l_015_03.html"
] |
[
"Also, it's not fun."
] |
[
"How is heat dissipated from Earth and its atmosphere into space?"
] |
[
false
] |
For whatever reason, I was contemplating global warming from a heat transfer perspective on my commute home today. We have an enormous number of BTUs entering the Earth's atmosphere everyday; and, we have the vacuum of space surrounding us, and therefore no matter for the heat to dissipate to, the perfect thermal insulator. Yet, we expect the overall temperature of the planet to remain constant. So, finally getting to my question I suppose, does this mean that nearly all of the energy entering the 'system' of Earth must get radiated out in the form of light (visible and otherwise)? Disclaimer: certainly not challenging the science and evidence behind global warming. Just curious.
|
[
"It's all radiation, incoming and outgoing. If you want to be a pedant, you can look at miniscule amounts of particles from the solar wind entering the atmosphere at high speed and heating it up a bit and likewise gas molecules leaving the atmosphere cooling it down ever so slightly."
] |
[
"The atmosphere is quite opaque for thermal radiation from the earth's surface, so it is the upper atmosphere that radiates into space (but also down towards the surface - this is the greenhouse effect). It has a temperature of about 255 kelvin. "
] |
[
"Also to clarify radiation in this context doesn't mean ionizing radiation. Electromagnetic radiation with a roughly black-body spectrum is emitted from earths surface, most of this heads away into space which is at a temperature of 3K. "
] |
[
"Does air sink in water at the bottom of challenger deep?"
] |
[
false
] |
Weird question, but I was reading that the water pressure that deep down is over 1000 times that at the surface level. So a bubble of air would be compressed to 100x the density, correct? Air is 1.29g/L, while seawater is 1.04 /L. At that depth the density should make the air heavier than the water, and sink, correct?
|
[
"100*1.29 [g/L]=129 [g/L]=0.129[kg/L]. Air would still be less dense than water there. The required pressure to make air the same density of water is 827 atm. However, air will probably dissolve into the water before reaching that pressure."
] |
[
"Pressure and density are only proportional for ideal gases. At sea level pressure that's a good approximation, at 1000 times that pressure it is not. It's in a supercritical state, which is a state between a gas and a liquid. ",
"This page",
" says nitrogen has a density of 0.3 g/cm",
" at the critical point. I don't find data for 1000 times the atmospheric pressure, but it's likely the density doesn't exceed the density of liquid nitrogen (~0.8 g/cm",
"), so it would still rise. The 20% oxygen content shouldn't change that, even though liquid oxygen has a higher density than water."
] |
[
"Air is much more compressible",
" than ",
"water is",
".",
"2000bar is 200Mpa, the units are different on those charts, but by 10,000 bar air will be more dense than water at around 20C.",
"E: I extrapolated poorly, read the response to ",
"/u/Origin_of_Mind",
" ",
"looks like these are the wrong charts and below 1Gpa water will always be more dense."
] |
[
"Why can I not draw exactly what I visualize in my mind?"
] |
[
false
] |
Say I want to draw a dog. In my head I can see the dog and descriptions of the dog simultaeniously, but when I tell my arm and hand to start drawing the resulting image is barely a shadow of what I saw. So what's stopping me from becoming art famous? oh yea, my hand has no idea what's on.
|
[
"While muscle memory is important, the difference between a good artist and a bad one is, in fact, what he knows. There's a picture dictionary in your head that your brain uses to quickly figure out what an object is. Each picture is called a \"schema\". How do you know what a house is if no two houses are the same? Your brain takes in fragments (front door, windows, etc) and pieces them together to match a schema.",
"Schemas are the first roadblock that new artists have to overcome. They are accustomed to drawing what the brain knows, and not what the eye sees. They have to clear out everything they think they know and learn ",
" to draw.",
"But here's where it gets interesting. At a certain point, it's almost as if an artist relearns schemas. However, this time around, the schema isn't an image so much as it is a behavior. The artist has learned enough about what an eye looks like to be able to draw whatever kind of eye he wants. He can predict that an eye in 3/4 view will look rounder than an eye viewed from the front because he knows how the eye will behave. ",
"To see this, ask an artist to draw a picture with his non-dominant hand. The picture will be sloppy, yes, because of poor muscle control, but it will be anatomically correct, providing the artist is good at what he does.",
"I'll admit, that was mostly from my own observations with art, but I would like to direct you to ",
"Lowenfeld's Stages of Artistic Development",
". Most people don't make it beyond dawning realism because they never treat art as an emotional outlet. The connection between art and artist is what makes people want to learn how to draw beyond basic skills."
] |
[
"Former art student here.",
"The important thing to understand when drawing is that what you SEE is not what you PERCEIVE, and you have to draw what you SEE.",
"The example we were given in class was a simple children's wooden block. When we look at it, from a given angle, we see both broad and flat angles, and we see different angles as we move around. Our brain integrates all these viewpoints and angles to PERCEIVE that all of the angles are actually square, even though we might never have viewed it from an point where any of the square angles actually appeared square.",
"When a new artist tries to draw that simple cube, even with it right in front of them for comparison, they have a tendency to flatten the sharp angles and narrow the broad angles because they're trying to draw the cube they PERCEIVE (with all of its square corners) rather than the angles they are actually SEEING from their current point of view. That is, their brain is lying to them about what they're seeing to the point where they can't accurately draw a simple shape that's right in front of their eyes. ",
"When you see artists holding out their pencil/pen/whatever and squinting while looking at their model, they're using their pencil as a measuring stick so they can accurately judge ratios or angles to keep their perception of the object from interfering too much with their attempt to draw what they're actually seeing.",
"Addressing the OP's question a little more closely, though, take a step back to what I was talking about assembling the mental cube from the various viewpoints. The brain is VERY GOOD at assembling the mental model of a cube, or a dog, taking in various cues and clues...but it does it subconsciously. It doesn't TELL you what cues are used to let you know the snout is kinda cylindrical, that the head is rounded, it just slaps the pieces together into a 3d model and discards the cues that let it determine the shape. To be fair, the cues will vary due to lighting, but the shape itself is relatively unchanging, so it's more important to remember the shape than the variable light cues that helped you determine the shape. The problem arises when you want to draw that dog, and even if you realize that the snout is roughly a cylinder or the skull is roughly a sphere, your brain doesn't tell you what marks you need to add to the paper to make the appearance of a cylinder, or the appearance of a sphere, other than the most basic. It READS the cues natively, but needs to learn how to also WRITE them; writing those cues is a separate, acquired skill.",
"These were the two most important parts of learning to draw: learning to draw what you are seeing and not what you are perceiving, and learning to analyze what you see to find the cues that tell you what you're actually looking at and replicate them. There's plenty to be learned about how to use a particular medium to draw, sketch, or paint, but these skills are necessary for accurate renditions regardless of medium.",
"tl;dr You can't draw that dog in your head because your brain is a filthy liar."
] |
[
"The same reason you can imagine exactly what you need to do to hit a home-run, yet strike out. You need to be physically coordinated and skilled enough to draw it which is more about \"muscle memory\" and acquired dexterity through training than simple imagination. The brain is very good at dreaming images up- but it is the body's ability to put those dreams on paper that makes it a work of art.",
"TL;DR- Your imagination doesn't control your drawing hand, your muscles do."
] |
[
"Are there any workable theories for 'quick' and low energy deceleration of space craft?"
] |
[
false
] |
I realize that modern designs for space craft's speed means the 'top speed' can only be reached for a certain time, with the rest of the trip spent slowing the craft down again. Are there any theories on ways to speed up the slowing down processes and/or use considerably less energy to do so?
|
[
"That sounds horrifically iffy to me. ",
"That's like the stereotypical \"catching a bullet in your teeth\". ",
"the types of speeds needed to make interstellar travel feasible",
"Voyager 1 is currently leaving our solar system. It's both the fastest thing that we've ever built, and traveling at extremely slow speeds for interstellar travel. -",
"Voyager 1 is the farthest human-made object from Earth in the Universe, traveling away from both the Earth and the Sun at a relatively faster speed than any other probe.",
"Voyager 1's current relative velocity to the sun is 17,060 m/s (",
"; 38,200 mph). [17 kilometers per second, 10 miles per second]",
"- ",
"http://en.wikipedia.org/wiki/Voyager_1",
" - ",
"Compare with the Falcon Hypersonic Test Vehicle 2 (HTV-2) that was just in the news:",
"The Falcon Hypersonic Test Vehicle 2 (HTV-2) - capable of reaching any target in the world in less than an hour - began a test flight from atop a rocket on Thursday.",
"The HTV-2 is designed to travel at 13,000 mph (",
").",
"- ",
"http://www.bbc.co.uk/news/world-us-canada-14497641",
" - ",
"The Falcon HTV-2 is designed to fly ",
" for an atmospheric craft, and the Voyager is traveling ",
" for an interstellar craft, and the Voyager's speed is three times that of the Falcon.",
"With any realistic numbers for \"speeds needed to make interstellar travel feasible\", the situation would be much worse. ",
"(Obviously, you want to slow your interstellar craft down when approaching a planet [",
" down], and ",
" aerobrake.)"
] |
[
"I'm not sure what the virtue is of spending time thinking about how to ",
" from that kind of speed when it isn't possible to accelerate something to that kind of speed in the first place."
] |
[
"Except that wouldn't actually work. The premise is based on the idea of a completely mythical material that can turn gamma rays into mechanical work without ablating."
] |
[
"Do plants need to 'sleep'?"
] |
[
false
] |
Could you keep plants permanently under sunlight/similar light? Or do they need a period of non-photosynthesis, like animals seem to?
|
[
"To properly develop, they usually require 8 (?) hours of near or total darkness per 24 hour period.",
"EDIT: Also, animals do not have photosynthesis. Darkness has nothing to do with sleep, it's just convenient for diurnal predators and gatherers."
] |
[
"Largely incorrect. Most plants that I have tested (dozens under different conditions) grow just fine under 24 hour lighting in the early vegetative stage of a plant's life. There's distinct advantages to 24 hour lighting in the early stage of plant development such as reduced stem elongation.",
"It's flowering where darkness in most cases is required. Even then, some plants such as certain pole beans will flowering and produce fruit under 24 hour lighting.",
"Some ",
"animals",
" indeed do use photosynthesis."
] |
[
"I mean animals in general."
] |
[
"How do hackers get information from unsecure sites?"
] |
[
false
] |
I was sent to an 'Apple' refund page. Logged in using apple id. Was surprised b/c I always forget the password. Then it started asking for sensitive information and it became clear that the page was not secure. Plus there's the little box in the corner on Chrome. My concern is that I started typing in info. I did not submit once I realized this, but my concern is whether they can get the info simply because I typed it, rather than from me hitting submit.
|
[
"Websites can indeed read individual keystrokes. Think of how Google will autocomplete with search suggestions as you're still typing. They couldn't do that if they couldn't intercept your key presses before you hit the \"submit\" button.",
"In Javascript, for example, there is the OnKeyPress event. ",
"As others have said, you'd be safest to assume that anything you typed in has been compromised. "
] |
[
"The website can indeed be configured in either way. Recording keystrokes is a bit more sophisticated and less trivial to implement than simple HTML form methods, but nothing crazy. A little bit of JavaScript will do. Hopefully you didn’t put in any real sensitive information. I think that if Apple asked for your SSN then there would have been a red flag before typing that one out."
] |
[
"Yeah that was the red flag. I'm thinking like wtf. And then I realize it's a scam. I didn't finish typing it out, but stuff like date of birth and address. SSN wasn't blacked out, so that also stopped me. I don't think I typed the full thing, but I am somewhat concerned. And there's basically nothing I can do. "
] |
[
"What prevents a tower crane from toppling over?"
] |
[
false
] |
I’m just astounded by the engineering marvel of cloud-breaching skyscraper construction and the assisting tower cranes that make it possible. Hoisting significantly heavy materials from ground to top level, and such a skinny build, what are the design measures that balance it? What balances the center of mass?
|
[
"So... For one thing, they have a big 'ol counterweight on the back end of the crane, so that when they lift heavy things, the heavy things put less stress on the metal truss structure that holds the train. They also make said truss structure super sturdy so that it can withstand the tremendous forces it is subjected to. Lastly, heir bases have long legs that reach out in all directions to maintain their balance as weight shifts."
] |
[
"The bases are actually pretty small, but well anchored to the building foundation. Maybe 30-40 feet square, but made from massive beams. The steel company I work for has made a lot of them, and we usually get them back afterwards since the GC has no more use for them, so it's win/win for us. They pay for it, and then give it back and we can scrape it, since they're pretty much a single use item"
] |
[
"You don't know how heavy that counterweight is, or how heavy the load they're intending to lift with the crane is. The simple balance for any crane is that the counterweight times the distance from the counterweight to the center has to be equal to the load weight times the distance from the load to the center. This means there is zero torque about the top of the crane so it doesn't tilt and fall over."
] |
[
"Are our bodies optimized for a certain elevation (specifically breathing)?"
] |
[
false
] |
[deleted]
|
[
"Our bodies are able to dynamically alter their respiratory efficiency, so we're sort of optimized for lots of elevations, really. ",
"One basic way that we do this is to change the number of red blood cells in circulation; increasing the number means more oxygen can be extracted from the air, and decreasing the number means less can be extracted. Some competitive runners actually use this phenomenon to give them an advantage in races without using banned chemicals by either training at high altitudes or spending lots of time in chambers with low-oxygen air. Either will increase their red blood cell count and thus allow them to be more efficient than other runners when they return to run in standard oxygen conditions. ",
"So, to answer your question, the body would basically adjust itself homeostatically if left at low or high elevations for a long enough time to allow you to respire in a way that is similar to standard elevations. Of course, there would be limits on how much the body can adjust and I have no idea what the high/low elevation cut offs would be."
] |
[
"Your blood has a system of regulators to it that help adjust what level of oxygen pressure in the air will result in it being absorbed by the blood.",
"There are multiple mechanisms used to adjust this system, each being used for different degrees of extremity. ",
"When you change elevations dramatically you need to take time to allow your body to adjust and get used to the new conditions. A simple analogy is when you arrive at a high altitude location (high up in the mountains) you will find it hard to breath the first few days, but won't notice the effect after a week. This is because your body has adjusted to the lower pressure.",
"Depending on the degree of change (if you went to the grand canyon, vs. the Himalayas, vs. mount Everest) you need to spend a different amount of time adjusting as the processes required to regulate your hemoglobin take time to occur. Different amounts of time are required depending on how much lower the air pressure (or rather how high the altitude). ",
"Like any system of 'regulators' this system has a limit to how much it can accommodate. If you climb the Everest at some point you ",
" carry an oxygen tank. No amount of waiting and physiological adjustments will be sufficient for you to be able to breath at that low pressure. ",
"I apologize for not going into the details of the various mechanisms used to regulate hemoglobin, my biochemistry is pretty rusty so i will leave that to someone else. ",
"While i do not know the answer if there is an upper limit of air density/pressure our bodies can handle, i do know that at the lowest point of elevation on the planet (The Dead Sea) people have no problem breathing, and usually do not experience any adjustment period either. This is of course from Personal Experience only."
] |
[
"I think ",
"yes",
".",
"Research on humans at high-altitudes contributes to understanding the processes of human adaptation to the environment and evolution. The unique stress at high altitude is hypobaric hypoxia caused by the fall in barometric pressure with increasing altitude and the consequently fewer oxygen molecules in a breath of air, as compared with sea level. The natural experiment of human colonization of high-altitude plateaus on three continents has resulted in two—perhaps three—quantitatively different arterial-oxygen-content phenotypes among indigenous Andean, Tibetan and Ethiopian high-altitude populations. This paper illustrates these contrasting phenotypes by presenting evidence for higher hemoglobin concentration and percent of oxygen saturation of hemoglobin among Andean highlanders as compared with Tibetans at the same altitude and evidence that Ethiopian highlanders do not differ from sea-level in these two traits. Evolutionary processes may have acted differently on the colonizing populations to cause the different patterns of adaptation. Hemoglobin concentration has significant heritability in Andean and Tibetan samples. Oxygen saturation has no heritability in the Andean sample, but does among Tibetans where an autosomal dominant major gene for higher oxygen saturation has been detected. Women estimated with high probability to have high oxygen saturation genotypes have more surviving children than women estimated with high probability to have the low oxygen saturation genotype. These findings suggest the hypothesis that ongoing natural selection is increasing the frequency of the high saturation allele at this major gene locus."
] |
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