title
list | over_18
list | post_content
stringlengths 0
9.37k
⌀ | C1
list | C2
list | C3
list |
|---|---|---|---|---|---|
[
"How come we can create a 2D picture of IR, visible light, UV and X-ray but we can't create a 2D picture out of radio waves for example?"
] |
[
false
] |
[deleted]
|
[
"You can, it's called ",
". The spatial resolution is determined by the wavelength of the radio waves so can vary from centimeters to 10s of meters. Also, radio waves penetrate/reflect from objects differently from light waves so you 'see' different types of things. It's possible to use radio tomography to 'see' ",
"ore deposits",
" underground and ",
"plasma jets",
" in the atmosphere."
] |
[
"The airforce does this with planes that they want to be difficult to detect on radar before they go out on missions to verify that they won't be detected.",
"Here is an image of a car using radar.\n",
"http://www.sysplan.com/images_content/radar/capabilites/gpu/gpu_saab.jpg"
] |
[
"It depends on what you mean by \"creating a picture\".",
"The reason why \"taking a picture\" in the traditional sense doesn't work for radiowaves is that their wavelength is around 1m, so you cannot resolve objects smaller than that (very roughly speaking). This does work just fine for radioastronomy, where the objects you are taking pictures of are very large.",
"Magnetic resonance imaging in a sense creates a picture using radio waves, however it is more difficult than just pointing a camera/telescope somewhere..."
] |
[
"If you were landing on an alien planet and your instrumentation died on approach, would it be visually impossible to spot your altitude do to geologists fractal nature?"
] |
[
false
] | null |
[
"read the instructions in the comment..."
] |
[
"Hi CaptainJamesTWoods thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"How do I add flair n mobile?"
] |
[
"Since direct current can be positive, negative or off, why not design logic circuits that use base 3 instead of binary?"
] |
[
false
] |
My kid has been learning about different number systems and it got me to thinking.
|
[
"Increased complexity of design and larger component footprints within the ICs. Positive/off systems or negative/off (where 'negative' current is really just positive current with a different assumption made about it) systems are nice and easy because your digital inputs for whatever makes up your logic gates only need to differentiate \"something is flowing\" and \"nothing is flowing\". Turns out this is a whole lot easier than differentiating \"sinking current (current in)\", \"sourcing current (current out)\", and \"high-Z (no current either way)\".",
"In reality people have made such devices but they've been made obsolete by the much easier to design/develop/build binary-based competition. ",
"\"Ternary computing\"",
" is the technical name for such systems but I'm not able to find readily-available references to the few current-based systems I'm aware of.",
"In the end it's simpler to design the smallest components in terms of two binary voltage levels rather than three current levels purely due to physical properties of the materials we implement them with. Contemporary transistor technology ",
" be used to implement three-state systems but there are a large number of technical issues with little projected gain so it's never really taken off.",
"tl;dr: Much easier to build a device that asks \"Is this 0v or X v?\" than \"Is this current -X uA, 0 uA, or X uA?\""
] |
[
"Great question. This is known as ",
"balanced ternary",
". To be honest I can't give you an answer beyond the standard \"ternary is more complex than binary\". The fundamental unit of transistors is the diode, which is designed to work in a single direction of current. Off the top of my head I'm not sure how you would design an IC circuit to work with current moving in multiple directions. ",
"Here's",
" a paper on the topic and ",
"pdf",
". It's been awhile since I've worked directly at the IC/transistor level so I don't totally understand the paper, but the paper seems to argue it's theoretically feasible. "
] |
[
"Edit: See byrel for corrections to what I said.",
"Some circuits do use three values, but one value is a \"Don't care\" value. In content addressable memory (as opposed to your normal random-access memory), you can retrieve values that satisfy a string of 1's,0's, and \"x\"'s, where the x means it can be either 1 or 0. "
] |
[
"Do humans ears \"pop\" if they are aboard a diving submarine?"
] |
[
false
] |
[deleted]
|
[
"No. When flying the cabin isn't airtight, and at 30k feet atmospheric pressure drops inside the cabin to a pressure roughly equivalent to 6-8k feet above sea level. This change in effective pressure in the cabin causes ears to pop. ",
"When diving in a submarine the sub is watertight and there is the same amount of air at depth in the sub as there is while on the surface. With no change in air or sub volume, there's no pressure change. This also means that subs can do emergency surfaces without the crews having to worry about decompression sickness. "
] |
[
"It's basically the exact same pressure at depth. There's an immense amount of steel structure on the interior of a submarine, typically in bulkheads. If there was any compression of the inner hull it would be unevenly distributed due to the bulkheads, and significantly uneven distribution of water pressure at depth would result in the hull being compromised.",
"Anecdotally I can tell you that the only way you notice you're at depth in a submarine vs periscope depth is the boat is much, much more stable."
] |
[
"Are you sure it's the exact same pressure at max dive depth? I thought the water pressure would squeeze the sub a bit. Not crush but squeeze. Maybe not enough for ear popping though. "
] |
[
"How does UV light kill bacteria?"
] |
[
false
] | null |
[
"UV photons have enough energy to break chemical bonds. When UV light hits a bacteria it breaks bonds randomly. The resulting broken molecules are unstable and may further damage other molecules. This results in damage to DNA and RNA and broken or malfunctioning proteins. The bacteria can repair itself if there is not much damage, but exposure to strong UV light destroys so much of the cell that it can't repair itself."
] |
[
"Other replies to this thread are sort of true, but miss the main answer. UVA/UVB light generally isn't powerful enough to ionize atoms and break bonds (at least for the types of bonds present in biomolecules), but it does excite certain bonds and make them reactive. When pyrimidines in DNA get excited, they form ",
"pyrimidine dimers",
". The cell can repair some of these, but if there is enough UV light the repair machinery is overwhelmed and the DNA is damaged enough to cause cell death.",
"UVC light can more easily ionize atoms; for this, the other replies in this thread are more accurate."
] |
[
"I always thought cyclobutane T-T dimers were caused by ionization",
"It's a photochemical [2 + 2] cycloaddition, if you want to get into the mechanistic details. Interestingly, this reaction is reversible in presence of the repair enzyme photolyase.",
"There are also other forms of DNA photoadducts, which are reviewed here: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3010660/",
"Ionizing radiation is generally more damaging to DNA, and can lead to a wide variety of chemical changes, often by radical-based mechanisms. UV light is much more selective in the reactions it causes."
] |
[
"What does the evolutionary timeline of the platypus look like?"
] |
[
false
] |
Every feature about them seems to be taken from other species. 10 sex chromosomes similar to birds, eyes like hagfish, feet/bill like a duck, beaver tail, one of the only mammals to lay eggs, sweats milk instead of having nipples, has venom, electroreceptors like a shark, etc etc.. It seems like nature just clicked the "random" button Thanks.
|
[
"Platypi are (probably) more closely related to birds than any other mammal",
"This is really misleading. I'm aware that ",
"this article",
" says that the platypus' possession of a sex chromosome which is homologous to one of those present in birds suggests that, from their abstract,",
"\"This suggests an evolutionary link between mammal and bird sex chromosome systems, which were previously thought to have evolved independently.\"",
" it's important to note that Synapsids (which mammals are) and Sauropsids (which birds and reptiles are) diverged 320 million years ago. So, every other sauropsid that ever existed is more closely related to birds than platypuses are— every turtle, every lizard, every snake, every icthyosaur, every pterosaur, every skink, every mesosaur, etc. And these animals don't share birds' sex chromosomes.",
"Saying \"the platypus has genes leftover from a common ancestor between reptiles and mammals\" is one thing, \"the platypus is more closely related to birds than any other mammal, which is why they share characteristics\" is another."
] |
[
"Platypi are (probably) more closely related to birds than any other mammal",
"This is really misleading. I'm aware that ",
"this article",
" says that the platypus' possession of a sex chromosome which is homologous to one of those present in birds suggests that, from their abstract,",
"\"This suggests an evolutionary link between mammal and bird sex chromosome systems, which were previously thought to have evolved independently.\"",
" it's important to note that Synapsids (which mammals are) and Sauropsids (which birds and reptiles are) diverged 320 million years ago. So, every other sauropsid that ever existed is more closely related to birds than platypuses are— every turtle, every lizard, every snake, every icthyosaur, every pterosaur, every skink, every mesosaur, etc. And these animals don't share birds' sex chromosomes.",
"Saying \"the platypus has genes leftover from a common ancestor between reptiles and mammals\" is one thing, \"the platypus is more closely related to birds than any other mammal, which is why they share characteristics\" is another."
] |
[
"Monotremes (the Platypus and the Echidna are the only examples I know of) shared a common ancestor with other mammals about 160 million years ago. We can call them our extremely distant cousins (actually, the most distant mammal cousin). "
] |
[
"Do dietary studies normally include the calories of what's leaving the body?"
] |
[
false
] |
There are tons of dietary studies presented to us every day. Quite often there are contradictions, which leads to the question: Are calories in urine, feces etc. measured and subtracted from the intake in dietary studies?
|
[
"It depends on the kind of study, sometimes they do.",
"http://ajcn.nutrition.org/content/94/1/58.long",
"No significant difference was shown in energy excretion in stools between lean and obese subjects who consumed the 2400-kcal/d diet [134.3 ± 48.9 kcal/d (lean) compared with 133.2 ± 44.8 kcal/d (obese) (P = 0.96); 4.9 ± 1.8% compared with 4.8 ± 1.4% (P = 0.87), respectively] or 3400-kcal/d diet [145.1 ± 42.7 kcal/d (lean) compared with 173.7 ± 65.0 kcal/d (obese) (P = 0.21); 3.8 ± 1.1% compared with 4.6 ± 1.8% (P = 0.240), respectively]. However, there was a large interindividual range for the percentage of calories lost in stools (2400-kcal/d diet: 2.1–9.2%; 3400-kcal/d diet: 1.6–7.6%).",
"So between 1.6% and 9.2% of calories consumed are lost in the stool...",
"The change in the percentage of urine calories between the 2400- and 3400-kcal/d diets was not different in either lean or obese subjects [−0.5 ± 0.5% (P = 0.34) and −0.6 ± 0.5% (P = 0.15)]. In addition, calories in urine were not different between lean and obese subjects when expressed as total calories or as the percentage of ingested calories with either the 2400-kcal/d diet [88.4 ± 30.8 kcal/d (lean) compared with 99.3 ± 31.2 kcal/d (obese) (P = 0.48) and 3.2 ± 1.1% (lean) compared with 3.5 ± 1.1% (obese) (P = 0.56)] or the 3400-kcal/d diet [106.0 ± 34.1 kcal/d compared with 112.6 ± 28.4 kcal/d (P = 0.64) and 2.8 ± 0.9% compared with 2.9 ± 0.7% (P = 0.72)].",
"...and between 0.7% and 1.1% of calories consumed are lost in the urine.",
"Assuming I'm reading that correctly."
] |
[
"Short answer: No, they are not.",
"The body should not be shedding calories in the urine. There is caloric content in feces, but it wouldn't be easily quantifiable. If you really wanted to be precise, you would have to separate bioavailable calorie sources from biologically unavailable calorie sources. Every person is going to process every single food source differently, due to variations in intestinal flora, so you would have to measure every stool sample from every subject to obtain reasonably useful data.",
"More importantly, though, is that practically useful data is going to be applicable in the real world. If subjects consumed ",
" calories and evacuated ",
" calories, that is not equivalent to a subject consuming ",
" calories, where ",
" = ",
" - ",
". The reason for this is that consumption of ",
" calories will still lead to evacuation of some caloric content. Probably just less than consumption of ",
" calories. By simply reporting calorie consumption as opposed to absorption, you have a repeatable protocol."
] |
[
"This is done by the release of heat from the body",
"Actually it's done by the release of CO2 from the body. Fatty acids are around 80% carbon by weight, so when you lose weight, it's because your body literally burned some fat, i.e., converted hydrocarbon chains to CO2. A 140 lb person exhales about 1 kg of CO2 per day just from basal metabolism. The same person also inhales about 0.728 kg of O2, for a net loss of 0.272 kg of C.",
"That's about 11 grams lost per hour, and when you exercise this increases by 5 to 10 times, depending on how hard you're working and what kind of shape you're in."
] |
[
"Do gaseous weight figures usually take in account their buoyancy?"
] |
[
false
] |
Just watching a SciSchow clip that mentions astronauts on ISS consumes only 840 grams of O2 a day, and I imagined how gases can be weighed, then wondered if all those metric tons of CO2 figures take in account their buoyancy when the samples were measured...
|
[
"840 grams is a mass. It doesn't depend on buoyancy, or gravity, or anything. You can translate 840 grams to a number of O2 molecules. Same for tonnes of CO2. If you would want to put them on a scale you'll have to take buoyancy into account, but no one measures emissions by putting them on a scale - you measure the concentration in air, or you calculate it from the amount of fuel consumed or whatever."
] |
[
"No they don't take buoyancy into account. Buoyancy varies based on fluid and depth. Mass of gasses refers to the molecular mass. O2 is about 32 g/mol. A mol is a specific amount of atoms (6.022 x 10",
" So in your example they're saying the astronauts breathe 26.25 moles of O2 a day."
] |
[
"I don’t believe they do. Although I’d like to offer an interesting comment. In scuba diving, a full tank weighs more than an empty tank. If you are diving with a standard aluminum tank as opposed to a steel tank, you have to take buoyancy into account as empty aluminum tanks will actually float."
] |
[
"How is water collected?"
] |
[
false
] |
How is water extracted from Oceans and Seas on industrial scales? Or maybe what's the term used for that sort of thing so I can look it up? I wanted to learn about the potential impacts of this behaviour on the environment.
|
[
"If you're talking about potable water used for drinking, nearly all of it comes from freshwater sources (surface waters, underground reservoirs). A typical flow diagram for water collection starting from the source and going through a water treatment plant and then to a home or business looks like this",
"http://cof-cof.ca/wp-content/uploads/2012/03/Surface-Water-Treatment-Plant.gif",
"Desalination of water from oceans and seas is used only when other more conventional options are not feasible for whatever reason. This is due to the much higher costs of reverse osmosis and other desalination methods."
] |
[
"It uses the reverse osmosis process. Osmosis is the net movement of water from high water potential to low water potential through a semi-permeable membrane. ",
"Basically, you \"push\" (insert pressure) the salt water through a barrier where it is semi-permeable (only water can pass through, salt can't because their molecular size is big). ",
"The process is called reverse osmosis because without our intervention, water would flow to the salt water because it has lower water potential than pure water. However, because we \"squeeze\" them, the otherwise happens. ",
"source: ",
"https://en.wikipedia.org/wiki/Reverse_osmosis",
" upper part of the page"
] |
[
"Not really. It's cheaper to use reverse osmosis. However, look up waste heat desalination. Basically uses the heat put off from power plants to boil off and condense water (there's been a lot of research put into utilizing this for small scale generators that could help in the event of a natural disaster)"
] |
[
"When whales and other aquatic animals come out of the water, does their eyesight become blurry like ours do going into the water? How do amphibious animals handle seeing in and out of water?"
] |
[
false
] |
I saw a video the other day of a whale poking it's eye out of the water to get a better look at a boat and it got me to wondering would it make their sight blurry.
|
[
"Ok, it bothered me so I had to check. Whales have a great eyesight in the water contrary to what was long believed. Even dolphins who use echolocation have good eyesight. \nWhen they come out of the water they get nearsighted but correct it with very strong muscles to bend the cornea. I'm only repeating what I read so but the source was pretty serious (French source because I'm French)."
] |
[
"That is an excellent question... I have divergent answers on the net. Some say that it's probable that crocodiles don't smell under water since they close their nostrils, others say that they have olfactory bulbs specially modified. But I don't know how. ",
"However, it seems that they can taste water since they can open their mouth underwater without swallowing water, and they have some very specific captors on their head's skin, which may be able to sense vibrations but also maybe electric fields and probably some chemicals. Almost like smelling through their skin."
] |
[
"How do non-water-breathing animals detect smells in water?"
] |
[
"By what mechanism is a human being able to estimate the passing of time? What happens when this function is disrupted? Can you lose your sense of time passing?"
] |
[
false
] |
[deleted]
|
[
"Just to expand. ",
"Tests have been done showing people in rooms with no time-based environmental cues having significantly inaccurate estimations of time passed. There have been some pretty crazy stories on this subject.",
"Lowered states of consciousness (e.g. Meditation, concussion, sleeping, coma) are also linked to impaired perception of time"
] |
[
"I think OP between the lines asks an interesting question not asked a lot: what areas in our brain handles time? ",
"How do the areas change when faced with a clock in a doctor's room, or a clock when late for a buss. What areas activate when the brain handles \"time\" and what does it mean cognitively? "
] |
[
"Human beings often sense the passage of time via such things as the rotation of the earth around its axis, and the rotation of the earth around the sun (indicated by the amount of sun or starlight visible in the sky, or by the changing of the seasons); as well as watches, and digital or analog clocks.",
"A human can lose their sense of time passing should they lose the ability to view a clock, sky, or other indicators of change of the earth's axis or solar orbit. For instance, if you bury a human deep in a cave with none of the aforementioned means of tracking time, they lose the ability to accurately log the passage of time. ",
"Hope this helps.",
"Cheers."
] |
[
"How many people would there need to be for a good (P>.5) chance that an arbitrarily selected person to have a perfect genetic match?"
] |
[
false
] | null |
[
"Ok. So, basically, every time I try to figure out how to answer this question, I just circle back around to \"yeah, basically not possible\". Two randomly chosen individuals will differ at approximately one out of every thousand sites. There are 6 billion sites in the human genome, so that means we expect a random pair of individuals to differ at approximately 6 million sites. If we assume the distribution on the number of differences between different pairs is Poisson with a mean of 6 million (it's not, but this should give us a conservative estimate), my computer returns the probability of any given pair differing at exactly 0 sites as a whopping 0%, which basically means I'm getting an underflow error, and the probability is no larger than about 10",
", which means that you would need more people than there are atoms in the universe (this is excluding the fact that you might by chance choose a pair of identical twins, although even identical twins aren't exactly identical everywhere, due to new mutations which occur every generation)."
] |
[
"If you look at the Poisson equation, for X=0 it just comes out to e",
" For λ = 6 million, that's about 10",
" .",
"Realistically it's much higher than that, since people who are related have vastly fewer differences, and some people are even identical twins. Even then, I think you're probably not a perfect genetic match due to mutations, but it's vastly more likely to just have no mutations than to have the same DNA by chance."
] |
[
"What exactly do you mean for a person to have a genetic match?"
] |
[
"What are physiological tricks of the human body?"
] |
[
false
] | null |
[
"Not sure how to add the flair"
] |
[
"Not sure how to add the flair"
] |
[
"This question is too broad/ vague."
] |
[
"Why do my LED lights change color near my hotplate?"
] |
[
false
] | null |
[
"LEDs are based on semiconductors which are sensitive to their environment. Semiconductors have something called a bandgap which is the origin of the emitted light. By altering the bandgap the wavelength (color) of the light changes. Not sure about the details of your exact situation but it's possible the heat caused this change."
] |
[
"This is fascinating--a little research shows that AlGaInP is used in the manufacture of both orange and \"traditional green\" wavelength LEDs. My old lab chief described semiconductor doping and manufacture as some arcane wizardry, as far as sensitivity to conditions goes; I wouldn't be surprised if you melted some of the bands that are supposed to separate the electron traps in your diode. What brand of LED was this? I'd like to order a few and test this under more rigorous circumstances...it'd make for a great classroom demo.\n",
"http://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphide"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Why doesn't malaria spread from endemic to non-endemic regions of the world?"
] |
[
false
] |
[deleted]
|
[
"Malaria parasites can’t complete their life cycle in mosquitoes if the temperature falls below about 20 oC (68 oF). That means that in temperate climates, malaria spread is seasonal and inefficient. ",
"Malaria once was common in the US, not all that long ago. The precursor of the CDC was formed to eliminate malaria in the Americas, which it did mainly through surveillance and mosquito control. Unsurprisingly, the modern CDC is extremely aware of malaria’s potential threat, and operates aggressive surveillance for it, so that even when cases are imported (which isn’t unusual) rapid treatment prevents it from exploding. Obviously, the fact that the parasite can only spread seasonally in most of the country is a huge help in control, because there’s an annual window to gets things under control. ",
"CDC pages:",
"CDC and Malaria",
"Malaria Transmission in the United States",
"Malaria Diagnosis & Treatment in the United States"
] |
[
"The same strategy keeps Dengue fever, Chikungunya, and yellow fever in check."
] |
[
"Malaria was common in the UK or at least believed to the cause of marsh fever. ",
"link",
" ",
"When I have traveled from endemic countries to non endemic by plans they sprayed insecticide in the plane before take off. ",
"There are concerns that with global warming it could spread further around the globe and to populations without any natural immunity."
] |
[
"Are human feet any more thermosensitive than human hands?"
] |
[
false
] |
When you submerge your feet in hot bath water, it can sting a lot more than if you just put your hand in. Probably observer bias but worth an ask.
|
[
"So there's a lot of stuff to cover with this. First of all, the stinging you mention, is it just the normal sting of hot water touching your skin (that is at a normal temperature)? Or are you inadvertently referring to the stinging that comes from having cold feet (or cold skin in general) touching something warm/hot?",
"Our hands have a lot more sensory connections than our feet. They are more fine-tuned in various manners. In that respect alone, one might infer that hands are actually more thermosensitive. ",
"But that only covers the first topic of \"stinging.\" If you are inadvertently or purposefully referencing the stinging in relation to your hands/feet already being cold, then we have other things at work. Our body has a way of focusing heat towards our bodies/torsos where they are more necessary for proper functioning. So our extremities (fingers/hands and feet) get colder before the rest of the body might. If your feet are feeling colder than your hands, then they would appear to be more sensitive to the same temperature of some water.",
"Heat to the body is basically dictated by blood flow. If you have \"good circulation\" in a specific area of your body it will not be cold. ",
"This paper",
" shows that our hands regularly get more blood flow than our feet. This basically means that feet are kept slightly colder than hands. Now why does their being cold affect the way they sense temperature? Our thermoreceptors measure both absolute temperature AND relative temperature. The latter means that it measure the difference of temperature between the skin near it and the thing touching it. So if your feet are colder than your hands and you put hot water on both of them, your feet's thermoreceptors will record a larger difference between temperature and tell your brain that the water is hotter. ",
"So I would say that your hands can more accurately tell you the temperature of something (assuming its not already too cold) but your feet will be just slightly more sensitive to hotter temperatures."
] |
[
"Fantastic reply. I never factored the differing temperatures of feet and hands into this, but it makes a lot of sense.",
"Thank you."
] |
[
"I'm glad I could help."
] |
[
"How do stock markets and equity sales benefit a company after the initial offering?"
] |
[
false
] |
So after a public company either has its initial offering or if they float more shares, how do the seconday market sales affect the company? The answer could very well be that it doesn't, but I just wanted an overview of the effects of secondary sales. Thanks!
|
[
"The company only receives money from the IPO or when they create more shares later. However, secondary sales do affect the company in a couple ways. ",
"Since the shareholders are the ones who get to vote in the company, someone completely outside the company could buy up a large chunk of shares and suddenly have huge power in the company without the company being able to do anything about it. If they get a large enough portion and/or can convince enough other shareholders, they can fire the board of directors, fire the CEO, merge the company with another willing company, or dismantle the company into parts. This is often called a hostile takeover.",
"Even more indirect, the current sale price of a company's stock, while it has nothing to do directly with how the company is doing, both reflects and influences the confidence people have in that company."
] |
[
"Many people working within the company, including low & mid-level people, take part of their pay in stock or stock options. It's an incentive for workers to positively contribute to the company. The higher a company's stock price, the more the employees make."
] |
[
"A stock market provides shareholders with liquidity as they can convert their shares into cash.\nFor companies, a stock market gives them ability to raise funds from a larger number of investors in the future through methods such as rights issue "
] |
[
"How much electricity is saved during a widespread blackout like this?"
] |
[
false
] |
[deleted]
|
[
"The average person in the US uses 12,914kWh of electricity per year or 35.4kWh/day. This includes commercial and industrial use - let's assume that in blackout areas 5% of what is normally used is still going on through places with backup power. The latest news article I read said 8 million people were without power. This means that for every day the blackout continues (and with a blackout this big it will last a couple days) 269GWh of electricity use is being avoided. ",
"For comparison, this is more electricity that Afghanistan consumes in a year."
] |
[
"Is there a good way to estimate the extra power that will be used for the rescue/recovery/clean-up efforts? Because in my mind (with no experience or sources, so intuition) these would almost balance out. "
] |
[
"Holy crap! Thanks for the info. ",
"Is this electricity just not being consumed, is it being stored, is it being wasted? "
] |
[
"What is the most common colour in the universe?"
] |
[
false
] |
To Clarify; Mean, Median and Mode.
|
[
"The most common photon in our universe are the photons from the cosmic microwave background radiation which is the afterglow from the big bang. These photons wave a wavelength of around 1 mm which our eyes cannot see. Check out Fig. 4 of this paper,",
"https://arxiv.org/abs/1004.2049",
"However, if you're interested in the optical band which our eyes can actually see, then the color red (~0.7 microns) is the most common color in the universe. The local peak near this wavelength though is firmly in the infrared (near 1 micron) and is referred to as the cosmic optical background (COB or CUVOB if UV is included) radiation. Check out Fig. 5 here,",
"https://arxiv.org/pdf/astro-ph/0011359v1.pdf",
"There are also the cosmic infrared (CIB), x-ray (CXB), radio (CRB) and gamma (CGB) backgrounds. These figures are looking at the aggregate background of light of the whole universe and not just nearby sources which can dominate locally. ",
"Edit1: Here's another couple page describing it, ",
"http://www.astro.ucla.edu/~wright/CIBR/",
" ",
"http://www.ias.u-psud.fr/irgalaxies/SpitzerPR2006/",
"It is also important to note that power distribution is weighted differently than the photon number distribution and that gives quite a bit of perspective. The CMB is much more intense than the COB, but each CMB photon carries substantially less energy than optical/infrared light. If we redrew the plots (which are already in log scale) using photon number, it'd be even more lopsided.",
"Edit2: Here's a review article on the subject of CIB, but has a relatively non-technical section on the COB",
"https://arxiv.org/abs/astro-ph/0105539",
"And a neat Scientific American article on cosmic backgrounds and where they come from, ",
"http://www.scientificamerican.com/article/background-noise-space/"
] |
[
"Correct me if I'm wrong, but given that any colour is derived from light, and black is the absence of that, is black a colour or just an absence? It's a pedantic question, but scientifically is it a colour?"
] |
[
"black objects are objects that tend to absorb all visible wavelengths of light.",
"red objects are objects that tend to absorb all wavelengths but red, or at least absorb enough of other colors to make it reflect mainly red.",
"but neither refer to photons per se, they refer to how certain objects interact with incoming photons to produce outgoing photons.",
"i'm not sure if there's a consensus on what \"color\" \"scientifically\" means.",
"there's no such thing as \"black light\" (barring the colloquial usage of blacklight as UV-dominant light), but there certainly are black objects. non-visible light is simply that, non-visible light."
] |
[
"Is \"the urge to have children\" (AKA \"the biological clock\") partially inherent in people or completely socially constructed?"
] |
[
false
] | null |
[
"Please see research by ",
"Kristin Park",
". Childlessness is deviant from social norms; therefore, there is at least clear social pressure to reproduce. I'm not sure if anyone has done a study on your exact question, but the research shows that having children is a socially constructed activity."
] |
[
"I have removed most responses for being speculation. If no one has a study to cite, then perhaps we can conclude for the time being that \"we don't know\" and this discussion can be resumed in ",
"/r/asksciencediscussion",
", our new-ish sister-sub, which is more focused on speculative and open-ended questions."
] |
[
"The \"ticking biological clock\" refers to the decline in a healthy and normal pregnancy, which occurs naturally as we age; people who want to have kids, or who ",
" want to have kids are essentially racing against that timeframe before things start going wrong."
] |
[
"Why and when did certain natural human functions become something that requires privacy?"
] |
[
false
] | null |
[
"In some cultures where children share a common domicile with their parents, it is indeed common for parents to have sex in the vicinity of their children. Historically it was also normal to engage in sex during the period of wakefulness late at night (between the \"first sleep\" and the \"second sleep\").",
"Reportedly, some African tribesmen who hear of the West's obsession with breasts tend to laugh at us: to them, breasts are for feeding offspring, not for titillating men. Not coincidentally, breasts often aren't considered taboo in these cultures.",
"This is a question that's going to be really difficult (perhaps impossible) to answer in a scientific way. The dynamics of shame and taboo are very difficult to study from a scientific angle. There are very few universal taboos––possibly none at all (even incest and patricide are tolerated in some cultures in some situations)."
] |
[
"The major source for the universality of biphasic sleep appears to be Roger Ekirch, according to whom it was normal in pre-industrial societies for humans to sleep first for four hours following sundown, enjoy an hour or two of wakefulness, then sleep for another few hours until sunrise, with a nap or siesta during the day. His book ",
" pushes this idea. ",
"Here",
" is one paper showing that \"biphasic sleep\" becomes common when the photoperiod ",
" is changed from 16 hours light, 8 hours dark to 10 light, 14 dark.",
"(thanks to ",
"/u/NorthernSparrow",
" for the technical note)"
] |
[
"Can you give more info on first and second sleep? It sounds fascinating."
] |
[
"Does being immune to a similar disease help the immune response to a novel strain?"
] |
[
false
] |
For example, even though most of us had the flu at some point, we are still at risk to get it again every year (or we have to get vaccinated again). This is because the virus has mutated enough that the immune system does not immediately recognize it & know how to deal with it. My question is, does a person who is immune to some kind of flu have an easier time dealing with the new strain than a person who never had the flu? Relating this question to the new coronavirus pandemic: we know that there are multiple strains and that people who had the disease can get sick again. However, I am wondering if people who already had one strain get over the new one easier than people who never had Covid-19?
|
[
"Milkmaids during the smallpox epidemic were found to be immune, having already contracted the weaker variant, cowpox. The immune system is a surprisingly good adaptive system, it just needs something to go on first. This is why we vaccinate as well."
] |
[
"There really are not strains of SARS-CoV-2 yet. (I know there’s a paper that claims there are, but it’s nonsense.). We don’t know, of course, but the guess is that SARS-CoV-2 will change much more slowly than flu, so a vaccine (or immunity to a virus) should last for many years, with luck. ",
"Strains of influenza specifically evolve to avoid the population pressure of immunity, so strains of flu give gradually less and less cross-protection. Typically, flu strains will give solid cross-protection for a few years (say, 2-4), then gradually less over the next few years."
] |
[
"Influenza may seem like a similar disease, but the viruses are completely dissimilar. We wouldn’t expect any crossover immunity from influenza to SARS-CoV-2. ",
"What about from one strain of influenza to another, or from one strain of SARS-CoV-2 to another?"
] |
[
"How do electric guitars transmit sound?"
] |
[
false
] |
[deleted]
|
[
"Let's overly simplify the situation. The metal wire of the guitar attracts a magnet. This magnet is inside of a pickup coil of wire. As the wire vibrates up and down, the magnet vibrates up and down. As the magnet vibrates up and down it generates a current in the pickup coil. ",
"That current is then passed through the various amplification processes or distortion processes that may be wanted, then converted back into sound or recorded."
] |
[
"I'm not precisely sure here. If I'm not mistaken though, each magnet/pickup configuration has a kind of natural frequency it would prefer to vibrate at, so it responds to those frequencies a bit better. Supposedly this was one of Hendrix's great inventions: that he played left handed, but did it by restringing the strings so that the higher strings were on the lower pickups, and the lower strings on higher pickups, mellowing out the overall sound.",
"Anyway a dual pickup (just looked this up and doesn't have anything to do with the above) is about reducing system noise. Ie, the power coming into the guitar has a frequency of its own, and other electrical equipment puts out electromagnetic noise of its own. By using two coils together, you can cancel out the electromagnetic noise to a large degree and only pick up signal from the wire itself."
] |
[
"That's extremely interesting! Thank you for the answer. As a follow-up, how does having humbuckers (dual pickups) differ from having single pickups?"
] |
[
"Is it possible that our solar system is inside of the event horizon of a black hole?"
] |
[
false
] |
From what I understand an observer out side of a black hole looking in on an object moving towards one will appear stretched to infinity, but that to the observer moving into the black hole the rest of the universe appears normal. Is it possible that the observable universe is really the event horizon of a large black hole, but also that the black holes we observe are also inside of this larger black hole? Side question: is it possible for a black hole to exist inside of another black hole?
|
[
"This write up seems to refute the idea - ",
"relevant post by robot roll call"
] |
[
"http://discovermagazine.com/2011/jun/03-our-universe-may-be-a-giant-hologram"
] |
[
"http://discovermagazine.com/2011/jun/03-our-universe-may-be-a-giant-hologram"
] |
[
"Is it necessary for some people to use their vocal chords while sneezing?"
] |
[
false
] |
[deleted]
|
[
"The vocal 'cords' are in the path of a sneeze, and some people have more control over them than others. From a respiratory standpoint, all I can say is that anytime air is able to go through the vocal folds, they can change the sound coming out. This is why anyone with a (unfenestrated) tracheostomy is unable to speak, as the vocal folds are bypassed and air simply escapes through the trachea."
] |
[
"I'm one of those loud sneezers. I can control the sound, but it requires effort and when I do the sneeze doesn't feel as satisfying as with it. So I don't. It's all about feeling good :)"
] |
[
"My father does this loud sneeze. It's more like a shout.\nI have developed this same habit over the years. But I can control it, shouting or not.\nThe louder version clears throat much better and it feels better afters.\nbtw, I have to force the low noise sneeze, but the shouting version comes naturally."
] |
[
"Why is gallium never used by robbers?"
] |
[
false
] | null |
[
"Chemistry"
] |
[
"Chemistry"
] |
[
"or perhaps psychology?"
] |
[
"How do chimpanzees develop so much muscle on a diet of mostly fruit?"
] |
[
false
] | null |
[
"More than that, about ",
"half of chimpanzee diet are one fruit–Figs",
".",
"Actually, the chimp diet is very broad. About 97% of their food are plant sources (about 102 species, probably triple what a human consumes). But they also consume meat (usually other apes) and insects.",
"With such a broad diet, they have a wide variety of protein sources, if you are implying that muscle development requires animal protein only. Remember, chimps eat the whole fruit too, seeds and all. "
] |
[
"Chimpanzees work as a teams to chase other primates into ambushes, where they then kill and eat them."
] |
[
"They don't eat other apes, though they eat other primates. The only other non-chimp apes that chimpanzees are known to coreside with are humans and gorillas. Chimps don't eat chimps, humans or gorillas - instances of cannibalism are very rare indeed.",
"They do eat a lot of red/ black and white colobus monkeys (See various Wrangham) as well as cute little bush babies which they skewer with spears in Fongoli, Senegal (See: Pruetz and Bertolani).",
"<3",
"Edit: Grammar and cannibalization clarification.",
"Edit 2: Probably also worth mentioning, going back to the original post, that not all protein people eat is converted into muscle. If you're not using your arms for, say, habitually climbing through dense canopy, you will likely put on less muscle than some person and/or chimpanzee who is even if you're eating two roast chickens a day...",
"Silverback gorillas are HUGE not because they eat a lot of protein, nor because they habitually use their muscles for fighting off other males, but because ",
" they might need their muscles to fight off other males, so the cost of growth and upkeep is worth it, even on a diet of mainly low-protein leaves.",
"For humans it seems that, unless muscles are being used, it's not worth paying the metabolic cost of keeping them large, no matter how much protean you eat.",
"Just some a-priori rambling..."
] |
[
"Is heating/boiling water more efficient in a microwave or kettle?"
] |
[
false
] |
For a small-ish amount of water - say between one and three cups. The amounts you would use to make a cup of tea or some ramen. Efficiency in terms of lower cost (electricity and gas for a gas stove).
|
[
"http://www.treehugger.com/clean-technology/ask-pablo-electric-kettle-stove-or-microwave-oven.html",
"http://www.scientificamerican.com/article.cfm?id=stove-versus-microwave-energy-use",
"Depends on who you ask? ;) The answer is highly dependent on the EXACT combination of water volume, container used, microwave type, etc.",
"edit: an induction stove should win out over both of these, but an electric plug-in kettle will be close -- maybe even better than induction."
] |
[
"No, not all systems have identical efficiency.",
"Stoves tend to heat the air as well as the water.",
"Microwaves don't convert electricity to microwaves efficiently.",
"The question isn't how much energy goes into the water. That's the same for all systems. The question is how much energy gets used that DOESN'T end up in the water..."
] |
[
"This, from the scientific american article, is your answer. ",
"... the difference in energy saved by using one method over \nanother is negligible: Choosing the most efficient process might save \na heavy tea drinker a dollar or so a year. “You’d save more energy \nover the year by replacing one light bulb with a CFL [compact \nfluorescent lightbulb] or turning off the air conditioner for an hour—\nnot an hour a day, one hour at some point over the whole year,” \nsays consumer advocate Michael Bluejay.\n"
] |
[
"When does my body begin burning fat for energy?"
] |
[
false
] | null |
[
"Your body is burning fat all the time. It's also storing fat all the time.",
"There is also energy stored as glycogen in your muscles and your liver, and energy is constantly floating in and out of this system and your adipose tissue, so there isn't any 'time' when you switch from one to the other - just a gradual change in the ratios of what goes where. It's this ",
"glycogen storage",
" which is at the heart of your question I believe, since it's this system that is why you aren't 'burning fat' the moment your stomach is empty.",
"So, during the day, on an empty stomach, you are using this glycogen store along with adipose tissue, to power yourself. Same as any other time, I suppose. "
] |
[
"That makes sense. Thank you. "
] |
[
"This is a question for your physician, since they will know you better than any of us."
] |
[
"What makes some viruses seasonal?"
] |
[
false
] |
How do we know when something is "seasonal"? Are there any truly seasonal viruses? Is it really human behavior during the seasons that's key, or are some viruses just naturally only able to spread under certain seasonal weather conditions? Thanks for any help in understanding this.
|
[
"Probably the most research about seasonal viruses is based on flu viruses but this same trend holds true for many other respiratory viruses.",
"Although Flu is regarded as seasonal, flu cases happen year-round, they just seem to nearly always peak in December to February. ",
"https://www.cdc.gov/flu/about/season/flu-season.htm",
"The reason for this peak isnt fully understood, but generally its seen that cooler and dryer (lower humidity) conditions favor transmission of the virus.",
"In this study they showed that in a guinea pig model lower humidity and temperature not only allowed for increased spreading of the virus via aerosols, but the guinea pigs themselves also shed more virus for longer periods of time.",
"https://journals.plos.org/plospathogens/article%3Fid%3D10.1371/journal.ppat.0030151",
"There are also other theories regarding human behavior, i.e travel patterns, more crowding indoors when temperatures are lower etc that may also contribute to the seasonality of these viruses."
] |
[
"The winter of each. That is how, in the US, the CDC determines which flu vaccine to administer, by examining the strains of flu present in the flu season in the Southern Hemisphere."
] |
[
"Most of the work has been done on influenza, even though several other viruses are almost equally strongly seasonal. It’s generally assumed that the reasons for seasonality are the same, but it’s not certain. ",
"For influenza, there are lots of explanations, but it's still not completely clear which of them is most right. (Probably, as with most biology, there are many different reasons adding up.) Some of the reasons put forward are:",
"Some of these are more convincing than others (I'm pretty skeptical about nutrition in particular). One of the most convincing explanations is ",
"It's more complicated than humidity alone, since flu still can transmit in tropical regions where it is less seasonal or not seasonal at all, but in temperate climates it's probably a strong influence.",
"Some references:",
"Global Influenza Seasonality: Reconciling Patterns across Temperate and Tropical Regions",
"Influenza Seasonality: Underlying Causes and Modeling Theories",
"Absolute humidity, temperature, and influenza mortality: 30 years of county-level evidence from the United States."
] |
[
"Can atoms give up electrons that are not in the outer layer?"
] |
[
false
] |
[deleted]
|
[
"With enough energy, yes. ",
"For example, X-ray photoelectron spectroscopy (XPS) uses x-rays to eject core electrons and then measures the kinetic energy of the ejected electrons to give an indirect measure of their energy level (binding energy) within the atom.",
"(Since the x-ray energy is known, and the total energy must remain constant, the binding energy is the difference between the measured kinetic energy and the initial energy of the x-ray). ",
"This is typically used for elemental analysis. "
] |
[
"You can fully ionize anything using heat or high-speed collision with metal foil. You can also use a pulse laser to push the electrons away - the nucleus has a very different charge to mass ratio compared to its electrons so an electric field (ie laser) will move the electrons much more than it moves the comparatively heavy nucleus.",
"Stripping an innermost electron can take dozens of times more energy than stripping outer valence electrons. A bare heavy nucleus can exist for as long as you can keep it from slowing down and finding more electrons, which usually isn't long. "
] |
[
"Yes. For starters you can always apply more energy and get more electrons out. Actually this does happen naturally in superheated plasmas. In the case of sodium the second ionization energy is almost 10x higher than the first, so this is extremely endergonic and the resulting Na(2+) is a potent oxidizing agent.",
"http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch7/ie_ea.html",
"Interestingly, you can also blast core electrons out of a non-ionized atom without disrupting the outer shell, most notably in X-ray absorbtion spectroscopy. ",
"https://en.wikipedia.org/wiki/X-ray_absorption_spectroscopy"
] |
[
"Can water be magnetized?"
] |
[
false
] |
I thought if you dissolved magnetite "dust" into water, you could magnetize the water. But then I realized if you put a magnet to it, it would just attract the magnetite. Is there any other way this can be done?
|
[
"Water is ",
"diamagnetic",
", and will generate a magnetic field opposed to an externally applied field."
] |
[
"http://www.youtube.com/watch?v=A1vyB-O5i6E",
"If I understand correctly, the frog is levitated in that video due to the water within the animal being magnetized."
] |
[
"Does anyone mind if I jump in on this question?",
"I was told that to magnetise something, you let it transition from it's liquid state to it's solid state in a strong magnetic field, and voila, all your electrons are pointing the right way and you have a magnet. ",
"So I immediately wondered wether you could create an ice cube using the same method (assuming it's not complete nonsense) and have magnetic ice cubes?"
] |
[
"If coral reefs existed in the past when the earth was hotter why is the hypothesis that today the corals reefs are currently dying because the earth is too hot?"
] |
[
false
] | null |
[
" did the coral reefs exist in the past? And did they have the same organisms as today?",
"Stable temperatures give places where they can form and survive. Changing temperatures changes these places - and currently this change is faster than the formation of coral reefs."
] |
[
"it's a matter of CO2 affecting pH in water, temperature increase is due to atmospheric effects also due to CO2. CO2 is what relates the distinct phenomenon of oceans acidifying and temperatures warming, the latter of which is much less threatening to coral at this point."
] |
[
"Thanks for the explanation. When I looked at this page ",
"https://en.wikipedia.org/wiki/Geologic_temperature_record",
" for temperatures I did not account for the scale not being linear so it made the rate of change look much higher that it was."
] |
[
"[Biology] Carrots contain Falcarinol, which can potentially irreversibly block one of the Cannabinoid receptors. So, by eating carrots, is an individual permanently reducing their ability to feel the effects of cannabis?"
] |
[
false
] |
Falcarinol is found in carrots, celery, and a few other vegetables. And Falcarinol is a covalent inverse agonist to CB1 receptors. From my understanding, this means Falcarinol irreversibly blocks the CB1 receptors. And these receptors are densely packed in the brain on nerve cells, which don’t regenerate/reproduce. So, once a nerve cell’s CB1 receptor is blocked, it will always be blocked? If that is so, then these receptors cannot be bound to cannabinoids after they bind to Falcarinol. So, by eating foods with Falcarinol, would an individual be permanently suppressing the effects of future cannabis use?
|
[
"Oh my gosh, no wonder I can't get high! ",
"Seriously, the cells may not regenerate, but those receptors are constantly turning over. Constantly.",
"Any effects would be temporary, as those receptors turn over you'd see less and less. "
] |
[
"Plus the amount of falcarinol in these plants are too low to cause problems. We'd be suffering from far worse issues if the dose was high enough to block most of the CB1 receptors."
] |
[
"The receptors are internalized and degraded and remade. Receptors are proteins, so we have genes that encode them and those genes will be transcribed regularly.",
"The term irreversible can be misleading sometimes. Some irreversible antagonists can be removed by binding the antagonist off with something else (see pralidoxime in organophosphate poisonings), while others do dissociate off the receptor at very low rates.",
"Also consider if the drug in the carrots can even cross the blood brain barrier. If it can’t, then you won’t feel a difference when you’re exposed to cannabis."
] |
[
"What happens if a person take caffeine and nicotine together? Net vasoconstricter or Net vasodilator?"
] |
[
false
] | null |
[
"As far as I know ( and I could be wrong )The combination is a great vasodilator. In some studies , nicotine actually doubled the rate in which the body gets rid of the caffeine. \nThe combination can trigger anxiety in some individuals."
] |
[
"Caffeine is generally vasodilatory through the production of nitric oxide: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3003984/"
] |
[
"This",
" says it produces cerebral vasoconstriction. This is why it can help treat headaches."
] |
[
"If I'm in a spaceship travelling at near light speeds, does the distance between me and my end goal shrink or expand?"
] |
[
false
] |
I understand when an outside observer views my spaceship it shrinks in the direction of motion. However, how do things look outside from inside the spaceship?
|
[
"Lengths can only contract, they can never be made ",
" than the proper length, in special relativity."
] |
[
"This is matter physically getting ripped apart. It is not a distance getting longer from changing your reference frame."
] |
[
"That's correct. That's why I specified ",
" relativity only. In general relativity, lengths can be shortened or lengthened."
] |
[
"Relativity and speed"
] |
[
false
] |
Hi, this might be a dumb question, it's about relativity. Let's ignore all the news about that neutrino (I didn't read up on it), then according to relativity theory nothing can move faster than light. My question is, relative to what? See, if nothing can move faster than light relative to e.g. the microwave background, then how could something as the LHC work. The LHC, according to get protons "up to about 3 metres per second slower than the speed of light". But the Wikipedia articles about the Sun and the Earth give them at best a speed of about 400 km/s relative to the microwave background, which would give the proton, if it's moving in the right direction (and since the LHC is circular it would at some time) a combined speed of more than c. Does relativity state that nothing can move at the speed of light relative to another? Would that mean that two objects could not move at c/2 from a reference point exactly in between them in opposite directions?
|
[
"The resolution to your puzzle lies in the way that ",
"velocities add in relativity",
". Here's the long and short of it:",
"Let's say you are moving west at a speed c/2 relative to me, and Albert is moving west at a speed of c/2 relative to you. In the land of Galilean/Newtonian theory, we expect that I would observe Albert to be moving west at speed c relative to me. This would violate the \"rule\" that nothing travels at the speed of light (in my reference frame). However, in relativity the transformation equations wind up saying that in my reference frame Albert is moving west at (4/5)c, and is therefore not meeting or exceeding the speed of light.",
"You can actually prove the following statement just using the Lorentz transformations: If body A is moving at speed less than c in reference frame S, and reference frame S' is moving at speed less than c relative to S, then body A will always be moving at less than speed c in reference frame S'. Therefore, if a body is moving at speed less than c in any inertial frame, then it's moving at speed less than c in ",
" inertial frames. This resolves your puzzle."
] |
[
"Nothing can move faster than ",
" relative to ",
". In some situations you can have particles traveling faster than the speed of light in a specific medium, see ",
"Cherenkov Radiationn",
", but the speed of light in a vaccum (c) is the speed limit of the universe.",
"What this means is that it is impossible to observe anything travelling faster than c. The laws of physics are different for relativistic speeds (at any reasonable fraction of c). This is achieved by non-linear ",
"velocity addition",
", length contraction, and time dilation."
] |
[
"Relative to any chosen frame of reference; the speed of light is constant and is the same for any reference frame.",
"The LHC works because the protons are never moving faster than the speed of light; velocity addition does not work the same way for relativistic speeds as it does for small, everyday speeds. For example, if a ball is travelling 4m/s relative to the Earth and the Earth is moving at 30000m/s, relative to the Sun, in the same direction then the total velocity of the ball is 30004m/s. However, velocity addition at relativistic speeds (speeds that are an appreciable fraction of the speed of light) uses a more complicated equation, although I don't know it myself. Perhaps someone else can post the equation and a more detailed explanation behind it."
] |
[
"Why do we get the feeling of \"pins and needles\" when blood-flow is cut to a certain part of the body."
] |
[
false
] |
simple question
|
[
"It is not the blood that is cut off, you are cutting off the nerve. Some cells don't send signals back, so your body does not know what is going on. When you remove the pressure the nerves start to communicate again, but it doesn't happen in an instant. When they are coming back 'on line' is when you get the pins and needles feeling."
] |
[
"While this explains when it happens, it doesn't really explain why. Any more info on that?"
] |
[
"Well, you cut off the ",
"nerve signals",
" from the brain. Once you remove the pressure they are able to start up again. ",
"The technical term is ",
"paresthesia"
] |
[
"Why is Supercritical Water Non-Polar?"
] |
[
false
] |
Edit and Answer Based off the Comments: The individual molecules of water in SCW are still polar. However, in bulk, SCW behaves as if it is non-polar. This is likely (not 100% certain) because with the increased kinetic energy of the molecules, the effect of hydrogen bonding is weakened. Furthermore, the molecules may conglomerate in ways that cancel out the individual molecules' dipoles. Ultimately though, there is still more research needed on this topic. Thank you to everyone who answered and commented. I really appreciate it. Happy Holidays!
|
[
"The answer is simple. It's not non-polar.",
"I'm guessing you or somebody who told you got the idea from the fact that you can use the supercritical state of water to dry things without the capillary pressure destroying their fine structure. The water doesn't become non-polar, but it does stop sticking to itself in the same way it usually does when it's a liquid. As you decrease the pressure it becomes less dense and more like a gas until finally it is gas. This process is used for making ",
"aerogel",
"."
] |
[
"Sorry but you have been misinformed. Just because it acts as a non-polar solvent does not make the molecule itself non-polar. Nothing about the bonding of the molecule changes just because of a change in temperature or pressure. As other have stated, it is only because the polarity of the molecule becomes insignificant enough under high temperatures and pressures that it can interact with non-polar molecules as if it were non-polar."
] |
[
"A professor mentioned that supercritical water is non polar and as such is used to dissolve organic compounds and matter. And it says pretty much everywhere online that it behaves as if it is non polar. I'm simply curious as to why. Thank you though!",
"Edit: Poor phrasing on my part. The individual molecules of water still are polar. But why, as a bulk fluid, does it behave as if it were non-polar?"
] |
[
"Are compressed gasses more buoyant than when they are not compressed?"
] |
[
false
] |
•
|
[
"No. The buoyancy of an object is proportional to its density, so the more compressed a gas is, the more dense it is, and the less buoyant it is."
] |
[
"This is why divers can still go underwater without tying a car to their weight belt"
] |
[
"Hi roh8880 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"How can the North Star appear fixed from any other view point on Earth other than the North Pole?"
] |
[
false
] |
I understand how the sky would appear to rotate around a center point when it's viewed from one of the axis of earth, but If I'm looking at the sky from anywhere else I wouldn't expect to find any fixed points. How can it be that long exposure images of the night sky always seem to have this fixed center?
|
[
"When you are on a merry-go-round and you look at the central pole, it's always in the same position relative to you. The same principle applies here. ",
"Polaris is on the imaginary line around which the Earth spins. And the earth is just a very large merry-go-round, so it behaves exactly as expected."
] |
[
"As long as you're north of the equator, the north star (Polaris) will be above the horizon. Polaris is very close to the celestial pole (an imaginary point in the sky where the Earth's axis of rotation, indefinitely extended, intersects the celestial sphere).",
"At the north pole, Polaris appears to be directly up. As you get closer to the equator, the star appears to be closer to the horizon, but it still represents the point at which the Earth rotates around."
] |
[
"This is wrong! Other than precession, if that's what you mean, it would not \"rotate\" out of position no matter where you were. Imagine a beam extending out of the Earth's axis to the north star. If you are looking up, right at the pole, you see the beam rise above you and touch the star, ",
"If you are standing in Texas, the relative position of the beam will look way different, but you would still see it touch the star. Polaris will ",
" no matter where you are, except for precession. The fact that Polaris is directly above the pole is not an illusion, its physical. "
] |
[
"Why are face transplants so rough?"
] |
[
false
] |
This might seem like kind of a brash question, I don't mean it to be. It seems like with all the advances in plastic surgery, facial transplants should be more convincing than they currently are. What are the reasons it's so difficult to make a convincing facial transplant?
|
[
"There are so many nerve endings. Not like with most plastic surgery, where it's one area of the face that is fixed. This is an ",
". ",
"I would assume there's a lot of tissue damage/tissue death involved as well. It's just a really difficult task."
] |
[
"Also the face has grown to cover a specific bone structure. Putting it on a different bone structure is like wearing someone else's perfectly-tailored suit - it still looks like a suit and it's better than being naked but it doesn't look quite right."
] |
[
"Hi, I'm new to ",
"/r/askscience",
".\nCan we continue asking relevant questions? \nFor instance, what if someone responds to the OP saying \"What could make the job easier? Do you know of any current methods used to partially deal with the issues?\" Or \"are partial skin grafts...\"\nAnd so on... \nI figure someone can help. \nPlease, don't ban. Lol. "
] |
[
"Would I be able to breathe better in a forest than I would in a desert?"
] |
[
false
] |
I feel kind of ridiculous for even asking this but I feel like more trees around = more oxygen. Whether its easier to breathe or not, is there at least a small but significant difference in the oxygen levels?
|
[
"[citation needed]"
] |
[
"askscience is not for educated guesses, it's about facts."
] |
[
"I'm having trouble finding a citation, but I think there must be a small difference. The rainforests are responsible for ~40% of the new oxygen in the atmosphere each year (balancing the use in respiration), so these can serve as a \"source\" and thus have slightly higher oxygen concentrations. \"Sinks\" would include any area where there is a large concentration of animals, but little vegetation. The desert doesn't have a lot of animal life, so maybe the oxygen concentration there is more of a middle value since nothing there is \"using\" it.",
"Now, exactly how big of a change this is, I can't find. Up to now I've only been speculating."
] |
[
"Is a rain (snow?) of carbon dioxide possible in Antarctica?"
] |
[
false
] |
Wikipedia says that temperature in Antarctica can be less than -80 °C. Carbon dioxide boils at -57 °C and melts at -78 °C, but I've never heard anything about such rain (snow). Is it possible or it isn't because of some reasons?
|
[
"It's cold enough, but there is very little CO2 in the atmosphere. You can't look at the sublimination point at 1 atm because the partial pressure of CO2 is much lower. The low partial pressure of carbon dioxide would cause it to subliminate in this environment--some molecules are freezing out, but at the same time others are sublimating and there is no accumulation."
] |
[
"atomfullerene covered your main question, but I'll add that phase transitions are pressure dependent, and carbon dioxide can't exist as a liquid at atmospheric pressure.",
"Phase diagram",
"Note that the liquid area is entirely above 5.11 atmospheres. At 1 atmosphere, it transitions directly from solid to gas... This is why it's called dry ice."
] |
[
"The primary method to find past co2 data for the atmosphere is analyzing air pockets in ice cores.",
"Right, air pockets. CO2 is not precipitating out (as either \"rain\" or \"snow\") of the atmosphere in this case. As Davecasa and atomfullerene explained, it is impossible for many reasons primarily the fact that it is impossible for liquid CO2 to exist at any temperature when the pressure is below about 5 atmospheres."
] |
[
"In what form (or forms) are the thoughts of people who have congenital deafness? Are they purely visual? How is thought constructed?"
] |
[
false
] |
As a hearing person, I have an inner monologue in my own voice and in the imagined voices of others, but I wonder: what is going on in the heads of those who have never heard language? I am fascinated by the notion of this sensory experience of the world, visual, felt on the skin and in the bones (in gesture and proprioceptively). I also wonder: how do people with congenital deafness or profound hearing loss from infancy learn to read?
|
[
"Im not deaf, but unless im frustrated about something my 'inner monologue' isnt in language. Its just concept links and i would assume thats how a deaf person would think in general.",
"Concepts are efficient after all. You can think of \"a guy drinking water at the side of a river\" in one instant. Its a picture or a feeling or a memory. Language just slows thought down"
] |
[
"The memory models defining in that fashion arent wrong. They are correct to the point where letters are a prerequisite for words (in english at least, not true for kanji).",
"Communicating your thoughts requires language. And to an overwhelming extent the majority of the concepts we understand were originally learned via language describing something we had not personally experienced yet. But it really ends at communication. THINKING, only in your head, doesnt require language and is slowed down by it. Doesnt mean most the things you think about werent learned via it, and would be nearly impossible to learn without it. So being a prerequisite is true. As long as you dont require your definition of language to include sound.",
"-edit-",
"Clarification: im not saying language slows down learning. It speeds up learning. It slows down non communicative thought."
] |
[
"The Sapir-Whorf hypothesis is almost certainly wrong in it's strongest forms, and it's unclear the extent to which language is a requirement for thought or whether it simply influences thought. ",
"I also think any study of language is usually confounded by human interaction. In other words, \"natural experiments\" like the case of Genie, a child never really taught to speak, certainly show cognitive deficits, but she was also deprived of typical, loving human contact. Weaker forms of the Sapir-Whorf hypothesis may be true, but I don't think thought is defined by language. Infants begin to mimic adult caregivers as young as 42 days, and this mimicry begins to capture something resembling symbolic representation at 12 months. For example, infants match the rhythm of their mother's voice with movement in their limbs. This is a match in the same dimension, but infants also match across dimensions. It's hard to know what to call this kind of cross-dimensional matching (a baby matching an intense movement from mom with a change in limb rhythm) if not some type of representation. Personally, I think this mimicry and matching are the earliest signs of thought we've observed. They may not be conscious or memorable, but these behaviors are the developments that eventually lead to the cognitive life of adults."
] |
[
"Why can't we point a telescope at the center of another Galaxy and see the warped space that would theoretically surround the black hole at its center?"
] |
[
false
] | null |
[
"The Hubble telescope can see things about .05 arc seconds small. The Andromeda Galaxy is 2,538,000 light years away which means Hubble can see something .624 light years across or 5.9x10",
" Km. The super-massive black hole in our galaxy is a maximum of 6.25 light hours across and applying the Schwarzschild radius gives a radius of 41 light seconds. That's a radius somewhere between 12.2x10",
" and 6.74x10",
" km or between 0.0002% and 0.11% of Hubble's max resolution. Andromeda's black hole is about 30 times larger than ours but this isn't enough to overcome the difference.",
"TL;DR Galaxies are very far away",
"EDIT: Maybe in about 2-3 billion years when Andromeda gets close enough we will be able to see it. I'll set a reminder on my phone."
] |
[
"While ",
"/u/washyleopard",
" is right that the black hole is far too small to be resolved with our telescopes we can see some effects.",
"Gravity is the warping of spacetime, and we can observe stars moving incredibly quickly very near the black hole.",
"This animation shows the motion of stars near Sag A, the Milky Way's black hole, over a period of about 12 years.",
" Sagitarius A is the yellow star shape in the middle of the gif. These stars are travelling around 3 millions miles per hour.",
"This site has a lot of good info too.",
"http://www.astro.ucla.edu/~ghezgroup/gc/journey/smbh.html"
] |
[
"I am not sure, but very likely. from the trajectory it appears to be in front of the plane of the picture."
] |
[
"If a first-world person had to store their own waste (garbage/rubbish, not human waste) instead of sending it to landfill, how much space would it require over a lifetime?"
] |
[
false
] |
Assuming nothing gets recycled, the person is literally just collecting every piece of garbage that would otherwise go to landfill. Would we be talking about a swimming pool sized volume? Or more? The reason I ask is that I'm a little surprised there aren't more landfill sites all over the place considering how many people there are and how much waste we generate.
|
[
"A cubic meter of water weights a metric ton. There is no way your trash is approaching the density of water even if bricked by a compressor, so it would be a lot bigger than that storage vessel. I don't know the average density of garbage so I can't give you a better estimate though."
] |
[
"I think a lot of these answers are missing the point. I just took an Environmental Engineering course on landfills, and here's the data they gave us:",
"A person generates around 5kg of waste per day, which includes a tolerance for industrial waste generated by the products that you use (this would be around half of that; definitely needs to be considered). Over a lifetime, that means around 140 tonnes of waste.\nTypical density of waste varies greatly, but tends to be around 300kg/m",
" before compaction, and up to 600kg/m",
" after.",
"I assume you're more interested in the non-compacted waste, so that results in a landfill of around 450m",
" A smallish house is around 175m",
" so ignoring the ceiling and filling all the way up to the pitched roof, it's about that much.",
"If you don't care about industrial waste, just halve that and you'll have a good idea."
] |
[
"People generate around 2.5 pounds of trash a day, not including around 54% that is recycled. So let's make it an even 5 pounds a day.",
"Multiply that by 365 days a year and around 80 years and you get 146,000 pounds, or 66 tons. That's equivalent to around 66 meters cubed.",
"That can't be right though - seems like a lot...",
"source: ",
"http://postcom.org/eco/facts.about.landfills.htm",
" Right, it's for a ",
", not per year. so it seems about right."
] |
[
"Is hemp really a miraculous plant that could replace dozens of products at a cheaper cost?"
] |
[
false
] | null |
[
"Hemp isn't a 'miraculous' product, per se, but it is useful and could be a cheaper or more effective replacement for a few different materials if grown industrially. The reason people seem to sing its praises and make it sound like a miracle product is because right now in North America you pretty much can't grow it industrially because it has been lumped in with marijuana plants as a controlled substance. People think this is silly because you can't get high using hemp and so they point out that you can make all sorts of products out of it, such as paper, textiles, rope, etc. The reason we can't is political, not based on evidence or reason.",
"Basically, imagine if cows were illegal to raise industrially. You could say 'but they can be used for high-yield production of meat, milk, leather, gelatin, glue, etc. without consequences that are any worse than raising pigs or sheep for similar purposes.' Whether cows are the best choice for any of that is debatable, and also beside the point. The fact that they are (in this hypothetical situation) illegal to raise for reasons that are not based in fact is silly.",
"Whether hemp is indeed the most efficient or effective way of producing some or all of the things you mentioned is debatable. Keeping it as a controlled substance when there is no danger of it being used as a narcotic is less defensible in a lot of people's minds, hence the seemingly hyperbolic claims of its value.",
"The wikipedia article on industrial hemp is quite good and well-referenced: ",
"http://en.m.wikipedia.org/wiki/Hemp",
"TL;DR: Industrial hemp could potentially be used for lots of stuff, but we can't grow it in North America because of arguably dubious policy and thus people sometimes overstate its value as an industrial crop. I make no claims as to the relative efficacy of hemp as an industrial crop vs the alternatives.",
"Edit: I posted this from my phone and didn't realize that this was ",
"/r/AskScience",
". Apologies if my reply isn't up to subreddit standards, I did my best."
] |
[
"This is a friendly reminder from the moderators of AskScience to please refrain from posting a top-level comment to this post unless you have a scientific, evidence based point to contribute. Anecdote and speculation are not welcome, but followup questions certainly are!"
] |
[
"Just to be a nitpicker, in 1998 Canada changed its laws and now allows hemp to be grown for industrial purposes, so we can't grow it in the United States not technically all of North America. "
] |
[
"where does epinephrine comes from? The one used for people with allergies because Google only says It comes from glands so I don't understand if it's donated or sintethized by other means."
] |
[
false
] | null |
[
"Extraction and purification of adrenaline from the adrenal glands of cattle and sheep is one way you can produce it at scale. Since the early 1900’s though synthetic production of epinephrine has been ongoing, and generally involves reacting catechol and chloroacetyl chloride.",
"https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(15)00087-9/fulltext",
"https://pubmed.ncbi.nlm.nih.gov/12806434/"
] |
[
"Well the animals are killed, the adrenal glands sit on top if the kidneys, but you have to keep in mind that cattle and sheep aren’t exactly ",
" used for that. So yes, this harms the animal in that they’re killed, but the environmental impact is the same as raising any livestock, and the animals required to supply adrenaline is a small fraction of the animals raised to be eaten or produce dairy products. ",
"I couldn’t even begin to estimate the environmental impact of synthesis, but as far as I know this isn’t really done at any scale, but if it had to be ramped up… I don’t know."
] |
[
"Epinephrine is a small molecule. It doesn‘t matter where you get it from. If it is pure it is identical.",
"Doesn‘t matter what animal, planet or universe you get it from.",
"Insulin for example is different, because that‘s just a class of peptide hormones, not a specific one. Meaning human insulin is slightly different from say a pigs insulin. It still works the same on insulin receptors, but it‘s different enough that sometimes your immunesystem might go ‚wsit, this doesn‘t look right, let’s destroy it‘.",
"But you can also make human insulin through genetic engineering from E. coli bacteria or yeast, that molecule will be identical to the insulin your body produces.",
"Just modern insulins are modified more heavily, cause actual human insulin only works well if it’s secreted continuously at the correct levels. And not just once you eat food/measure your sugar levels."
] |
[
"Hey guys. I posted this in r/crazyideas but was wondering if it was feasible at all. It involves a remote pair of robotic hands to perform tasks such as mechanic work and surgery."
] |
[
false
] | null |
[
"i hate to be the bearer of bad new",
"Replace gel with finger clamps with resistance and you're about 5 years behind the next big thing in surgery. "
] |
[
"The first remote surgery was performed back in 2001. The robotic \"hands\" however can be made vastly superior in accuracy and range of motion - designed exactly for the task required - than mere human hands can so there's no goo making a model of them."
] |
[
"Check out the ",
"wiki article",
" especially the section on delay in data transfer required to attempt to duplicate instantaneous sensory feedback as well as the section entitled 'limitations'."
] |
[
"Why do we think matter warps space and not that warps in space attract matter?"
] |
[
false
] | null |
[
"It's clear that the presence of mass is always associated with a warping of spacetime. It follows naturally to assume that some invisible matter is causing the extra warping to occur in galaxies. While what you're proposing isn't impossible, it simply isn't the most simple possible explanation for what's occuring. We need to rule out the possibility of dark matter before considering some entirely new force, for which a whole lot of new physics would need to be created to work."
] |
[
"Mass and energy to be more exact. It's certainly ",
" that something else can do it, but I don't think we have any indication that that's the case. "
] |
[
"Because we ran some tests. ",
"Imagine the following experiment: Two spheres attracting each other, negligible friction. Note that iron has way lower density than gold."
] |
[
"Why is it that warming a cold, dead, electronic device will sometimes give it a substantial charge?"
] |
[
false
] |
I have noticed this in the past but it really struck me today when I got into my car and tried to plug my ipod (which had been sitting in freezing weather for several hours) into the speakers. It was totally drained of battery. So, I turned the heat on full blast and set the ipod in the vent for a few minutes and when I plugged the auxiliary cable back into it it played fine for an hour and a half. Why is that?
|
[
"It's also because the battery gives power through the chemical reactions in the battery, which run faster when temperatures are higher. "
] |
[
"It's also because the battery gives power through the chemical reactions in the battery, which run faster when temperatures are higher. "
] |
[
"Yup. It's called electrolytic conduction ;D",
"http://www.google.com/search?hl=en&tbo=d&site=&source=hp&q=what+is+electrolytic+conduction&oq=what+is+electrolytic+condu&gs_l=mobile-gws-hp.1.0.0l2j0i30j0i8i10i30.1988.21937.0.23391.27.19.0.8.8.0.824.4184.10j4j1j5-3j1.19.0.les%3B..0.0...1ac.1.E5l773T3qTo",
" "
] |
[
"How much of our body is made up of other organisms?"
] |
[
false
] |
or other animals' bodies for that matter.
|
[
"I can't comment on the mass of you vs. non-you in/on your body, but I recall in college microbiology learning that the organisms in and on your body outnumber your own cells by an order of magnitude. ",
"Bacteria are normal inhabitants of humans (as well as the bodies of upper animals and insects) including the gastrointestinal tract, where more than 400 bacterial species are found (reviewed by Tannock, 1999): half of the wet weight of colonic material is due to bacterial cells whose numbers exceed by 10-fold the number of tissue cells forming the human body. Normally the stomach contains few bacteria (10",
" colony forming units per 7 ml of gastric juice) whereas the bacterial concentration increases throughout the gut resulting in a final concentration in the colon of 10",
" bacteria/g.",
"Also, here's your wiki link: ",
"http://en.wikipedia.org/wiki/Human_microbiome",
"."
] |
[
"There's some answers here regarding bacteria: ",
"http://answers.google.com/answers/threadview/id/208733.html",
"TLDR answer: typical human has 2-9 pounds of bacteria (which are much smaller than human cells). "
] |
[
"From Wikipedia:",
"\nThere are many species of bacteria and other microorganisms that live on or inside the healthy human body. In fact, 90% of the cells in (or on) a human body are microbes, by number[12][13] (much less by mass or volume). Some of these symbionts are necessary for our health. Those that neither help nor harm us are called commensal organisms.",
"\nAlso, responses like that don't belong in this sub ya dick."
] |
[
"Hard Drives in Space"
] |
[
false
] |
If a spinning HDD were to be put in a small probe or satellite, would its spin have a gyroscopic effect on the probe? If we've ever done this, are compensations needed when designing it? Also, would the disk need to always be spinning because wouldn't stopping it cause a huge change in momentum?
|
[
"If a spinning HDD were to be put in a small probe or satellite, would its spin have a gyroscopic effect on the probe?",
"Yes, it would. In particular, increasing or decreasing the spin rate of the HDD would put some spin on the craft. Generally this would be negligible, but over long time periods you would certainly need to account for it, especially if the craft is thrusting while the HDD is speeding up or slowing down. Additionally, a hard disk actually ",
"needs a certain amount of atmospheric pressure",
" to cushion its rotation, so unless the craft is partially pressurized that wouldn't work. For these reasons, ",
".",
"Also, a lot of early spacecraft had tape recorders for data storage, which spin at a much much lower rate than HDDs (and probably have less mass, though given how bulky some old technology is I wouldn't be sure), and thus have less angular momentum."
] |
[
"If a spinning HDD were to be put in a small probe or satellite, would its spin have a gyroscopic effect on the probe? ",
"Yes, of course.",
"If we've ever done this, are compensations needed when designing it?",
"\nAlso, would the disk need to always be spinning because wouldn't stopping it cause a huge change in momentum? ",
"I don't know if it has ever been done. Although I think you are underestimating the mass of most existing man-made probes/satellite compared to the mass/inertia of a hard disc. According to the Voyager FAQ: \"The Voyager spacecraft weight, including hydrazine, at launch was 815 kg or about 1797 pounds. It was almost the weight and size of a sub-compact car. The current approximate weight of Voyager 1 is 733 kg and Voyager 2 is 735 kg. The difference is in the amount of hydrazine remaining. Hydrazine is being used to control the spacecrafts' attitude.\" ",
"You could compensate by using another hard disc, although if they didn't both constantly spin you'd still have a residual. But my guess is that such an effect would be small enough that you'd compensate via the regular attitude thrusters. ",
"Or simply not use a hard disc drive, and use a robust solid-state memory instead. I would expect that the relatively poor reliability of a mechanical hard disc would make it unsuitable for most space applications. Again, from the Voyager FAQ: ",
"\"There are three different computer types on the Voyager spacecraft and there are two of each kind. Total number of words among the six computers is about 32K. ",
"\"Computer Command System (CCS) - 18-bit word, interrupt type processors (2) with 4096 words each of plated wire, non-volatile memory. ",
"\"Flight Data System (FDS) - 16-bit word machine (2) with modular memories and 8198 words each ",
"\"Attitude and Articulation Control System (AACS) - 18-bit word machines (2) with 4096 words each. \""
] |
[
"I figured solid state drives were preferred because of no moving parts (partly for the momentum and also for reliability and failure rate). What about the computers in the ISS? Were large enough SSD's in existence when it began? Or is the mass becoming large enough that the change in momentum is negligible?"
] |
[
"Can someone explain why the integral of 1/x^2 from 1 to infinity = 1, but 1/x = infinity?"
] |
[
false
] |
[deleted]
|
[
"Note that the region underneath 1/x has an interesting geometric property: If you take the part between x = 1 and x = 10, say, and you flatten it by a factor of 10, and then stretch it horizontally by a factor of 10, then because 1/10 * 1/(x/10) = 1/x, what you get is the same shape as the part between x = 10 and x = 100. Because the flattening decreases the area by a factor of 10 and the stretching does the opposite, these two parts have equal areas. Thus if the integral from 1 to 10 of 1/x is equal to A, then the integral from 10 to 100 is also A. Similarly, the integral from 100 to 1000, from 1000 to 10000, etc. are all equal to A. From this you can see that the integral of 1/x must diverge, as it is made of an infinite sequence of pieces like this, each having the same (positive) area.",
"By way of contrast, if we take 1/x",
", then since at x = 10 the value is 1/100, when we stretch by a factor of 10 we need to flatten by a factor of 100 to get something that looks like another part of the graph. This checks out because 1/100 * 1/(x/10)",
" = 1/x",
". Thus if the area between x = 1 and x = 10 is A, then the area between x = 10 and x = 100 is A/10, the area between x= 100 and x = 1000 is A/100, etc. Therefore the integral of 1/x",
" becomes A + A/10 + A/100 + A/1000 + ..., which is a convergent geometric series."
] |
[
"You can start to see it yourself, just by playing around. ",
"Start adding up a couple terms of the series 1/x",
" vs 1/x, just letting x be the integers. ",
"If you look at 1/x",
" you'll get something like:",
"1 + 1/4 + 1/9 + 1/16 ~= 1.4236",
"And you can play with your calculator and see no matter how many terms you add- you'll never get above 2 (Actually, you'll never get above (pi",
" )/6 ~= 1.64",
"But if you do the same thing with 1/x, you won't be so lucky. If you add a few terms you'll get:",
"1 + 1/2 + 1/3 + 1/4 = 2.0833...",
"And it turns out that no matter how large of a number you choose, if you add enough terms together you'll be able to sum up 1/x to be bigger than that number. For instance, maybe you think that 1/x actually will never get bigger than 3? Well, after summing 12 terms, you'll get 3.0199. OK, maybe a bigger number, like 10? Actually, you can calculate that after 12368 terms, you'll be just a touch over 10. In fact, no matter how large of a number you choose, you can eventually sum enough numbers to get larger than it. But not so with 1/x",
" no matter how many numbers you sum, you'll never get bigger than (pi",
" )/6"
] |
[
"I don't think the difference between convergence and logarithmic divergence is something one can \"see for oneself\" very easily. If you naively set up a computer to add terms one at a time, it's sure going to look like the series is converging. For any computer, there will be a (fairly small) number such that the numerically computed partial sums it spits out never get larger than that. ",
"I think to see for oneself, one has to reason through why it is that, say, doubling the number of summands increases the output by at least a fixed amount."
] |
[
"Does Porn Consumption Have Negative Consequences?"
] |
[
false
] |
[deleted]
|
[
"There was an Italian study done that showed a link between internet porn use from an early age and sexual dysfunction. There's a ",
"Psychology Today Article",
" about it. Basically it can cause desensitization of your brain to ",
" sexual stimuli. Especially if the porn consumption began before sexual interaction with others.",
"There may also be some hard to cope with withdrawal symptoms if one tries to quit cold-turkey.\nNow, I must go masturbate before the shakes set in."
] |
[
"Not as far as anyone can tell. The only major study I know done on it was the 1970 ",
"President's Commission on Obscenity and Pornography",
" which was setup by Congress to give political cover to banning or regulating it. After more than a year of study, they concluded that there was no discernable harm done by it and that it should be mostly unregulated as to access by adults. ",
"This was a politically inconvienent result and was promptly completely rejected by the US Senate with a 60 to 5 vote with 34 abstentions.",
"The 1986 ",
"Meese Report",
" had learned the political lesson of the 1970 report and instead of actually doing research it just made up a heavily biased report catering to the political prejudices of the people sponsoring it. It was quite telling that the Meese report had a budget only a small fraction of the 1970's commission, interviewed only a small number of carefully selected people and reached a conclusion 180 degrees opposite of the previous large and well funded commission research."
] |
[
"There are some preliminary studies that actually show porn may be beneficial and be a cause of lower sex crimes:",
"http://skeptics.stackexchange.com/questions/6656/is-the-increasing-availability-of-high-speed-internet-pornography-reducing-sex-c"
] |
[
"Why is the heat capacity of salt water lower than freshwater?"
] |
[
false
] |
[deleted]
|
[
"Okay, so ice has a lower heat capacity than liquid water. Does that mean ice has fewer hydrogen bonds as well? (It doesn't) Extending the same that rationale to another substance: Covalent bonds store vibrational energy as well, graphite forms fewer bonds per mole than diamond does, thus graphite has a lower heat capacity than diamond? (nope)",
"Also, if salt water is less bonded than pure water, why does it require more energy to vaporize it? The boiling point of salt water is higher. D2O also has a higher boiling point than water. It forms the same number, but stronger hydrogen bonds. Its heat capacity is lower than H2O. ",
"Heat capacities are proportional to the change in entropy with temperature, but your post doesn't refer to entropy - the number of bonds and their strength alone is merely a change in ",
". Entropy is the (logarithm of) how many ways you can distribute the energy, in a sense how flexible the structure is.",
"Salt water is ",
" less bonded. It is structurally more tightly bound than pure water, because the strong ion-water interactions and rigidity of the hydration shells around the ions. This is not just reflected in its higher boiling point, but also its higher viscosity and density. Ice is more rigid than water, diamond more rigid than graphite, and heavy water is more tightly bound than ordinary water. This means fewer ways of distributing the energy as the temperature increases, that is lower dS/dT, meaning lower heat capacity. ",
"The number of hydrogen bonds is not the reason for water's high heat capacity, but ",
"because of their bending modes of vibration",
" that don't exist in ice because it's too rigid, nor in steam as there's no intermolecular bonds."
] |
[
"The hydrogen bonds that form between water molecules can store heat as potential energy of vibration. Salt water forms fewer intermolecular hydrogen bonds (per molar quantity) than regular water because the sodium chloride ions are now interacting with the water molecules. Thus the reduction in heat capacity.",
"Source: ",
"http://en.wikibooks.org/wiki/Structural_Biochemistry/Water#High_Heat_Capacity"
] |
[
"Cool, that makes sense. Follow-up question: salt water has been proven to evaporate more slowly than freshwater. Wouldn't a reduction in heat capacity facilitate more aggressive evaporation?"
] |
[
"How exactly does nutella \"release energy slowly\"?"
] |
[
false
] |
[deleted]
|
[
"http://www.wolframalpha.com/input/?i=100g+peanut+butter",
"http://www.wolframalpha.com/input/?i=100g+nutella",
"Based on that nutritional information, I suggest that peanut butter is healthier than nutella. Far less sugar (8g v 54g per 100g), more vitamins, more protein, etc. However, IANADietician."
] |
[
"It's perfectly plausible that Nutella is fairly low-GI. It has a lot of vegetable oil. Fats and oils are large molecules that take a long time to break down and digest, and also slow down the absorption of everything else: eating sugar+fat will give you a ",
"lower glycemic response",
" than the sugar alone.",
"That does not mean it's healthy, since health is not a function just of glycemic index. Most pure fats will have a negligible GI - fat does not spike blood glycogen levels much. Doesn't mean you should eat lard all day."
] |
[
"Otherwise, Nutella isn't breakfast. Nutella is frosting.",
"Liquid candy bar.",
"http://www.wolframalpha.com/input/?i=100g+nutella",
"http://www.wolframalpha.com/input/?i=100g+snickers+bar"
] |
[
"Why are there massive tornadoes in US, but almost none in South America and Asia or Africa?"
] |
[
false
] | null |
[
"There have been documented tornadoes on every continent EXCEPT Antarctica (figures). But you are correct in that the majority of the earth's tornadoes happen in Tornado Alley in the United States. This is because of a very unique weather system that only the USA sees. ",
" air moves south from Canada and mixes with ",
" air from the Rocky Mountains and this air then meets ",
" air from the Gulf of Mexico (dry air from the Sonoran Desert may also play a part) and the combination of all this leads to atmospheric instability, which then produces strong thunderstorms and crazy tornadoes.",
" Tornadoes happen everywhere except Antarctica, but the unique weather system of the USA leads to a higher frequency of tornadoes than anywhere else in the world."
] |
[
"As a master's student in meteorology, I approve this message."
] |
[
"Here I am. Meteorology Ph.D student, and I approve of all of the above messages."
] |
[
"Could there be anything more fundamental than quarks, bosons and leptons?"
] |
[
false
] |
If we zoomed in on matter even further than the three categories of subatomic particle discovered so far, is it possible that we could see something more fundamental, perhaps something that is a constituent of all three types? Or have these particles been proven to be the most fundamental?
|
[
"Quarks and leptons being composite, as in being bound states of some constituents, is a very disfavoured hypothesis, for a reason I explained ",
"here",
".",
"Gauge boson compositeness does not make a lot of sense, I think. Higgs compositeness instead is still an open question as far as I know.",
"Now it's still possible that particles are extended objects without being composite. That's for example the main point of string theory.",
"Thirdly, even if you still persist in keeping the standard model particles pointlike you can imagine them being quantum superpositions and/or just a subset of a more fundamental and elegant set of degrees of freedom. Since quantum pointlike particles = local quantum field theory, these theories are still all QFTs just like the standard model. This would be the case for supersymmetric extensions of the standard model, grand unification theories, etc."
] |
[
"There could be, but there's no evidence of it, and no real necessity to have that be the case. "
] |
[
"is a very disfavoured hypothesis, for a reason I explained here.",
"I don't think a \"one off\" tuning is a particularly strong argument. If the tuning is radiatively unstable then there is an argument (hence higgs and CC problems)."
] |
[
"What does it mean that a photon has an oscillating magnetic field perpendicular to an oscillating electric field?"
] |
[
false
] |
I’m speaking particularly about the common representation of a photon as two in-phase sine waves at right angles to each other. exactly is oscillating? A couple places said it was the magnitude of each respective field, which I think refers to the strength and length(?) of the field lines “generated” by the field. But what shape do the field lines take? Is it the kind of pattern you would see with, say, iron fillings and a bar magnet? Additionally, the fields are projected in the 3rd dimension right? How can they be rotated at 90% then? Or is it something to do with quantum numbers? When the magnitudes of both waves reaches 0, do the fields diminish to nothing or just stop influencing anything around them? If someone put a magnet near a stream of radio wave with a noticeably long wavelength, could the exertion of forces on the magnet be detected? Sorry I don’t really understand EM waves at all and I’m probably dumb for trying to understand with a cursory knowledge of physics.
|
[
"I’m speaking particularly about the common representation of a photon as two in-phase sine waves at right angles to each other.",
"That's a classical electromagnetic wave which is not the same as a photon which is the quantum of the electromagnetic field. ",
"( ",
"https://physics.stackexchange.com/questions/90646/what-is-the-relation-between-electromagnetic-wave-and-photon",
" ) ",
" exactly is oscillating? A couple places said it was the magnitude of each respective field, which I think refers to the strength and length(?) of the field lines “generated” by the field.",
"It's the magnitude / strength of the electric ",
" and magnetic field ",
". It's not the length of field lines but if anything the density of field lines. ",
"But you can also visualize it a bit by noting that a charge q would feel a Lorentz force ",
" = q(",
" + ",
" x ",
") in an electromagnetic field. ",
"But what shape do the field lines take?",
"The field lines of an electromagnetic wave are closed loops. ",
"Here's an illustration of that",
"Edit: the link doesn't actually work and I'm not allowed to use a link shortener. The image I attempted to post is Figure 16.9 in ",
"this link [cnx.org]",
" (right at the bottom of the page)",
"A similar image (animated version) is on ",
"wikipedia",
"The blue dots and crosses are magnetic field lines pointing into and out of the screen. They are the intersection of closed magnetic field lines with the screen. ",
"Is it the kind of pattern you would see with, say, iron fillings and a bar magnet?",
"That would be a static magnetic field which is something else. ",
"Additionally, the fields are projected in the 3rd dimension right? How can they be rotated at 90% then? Or is it something to do with quantum numbers?",
"Not entirely sure what that means. The electric field is a vector field which means that in every point in space ",
" and at every time t it has a vector value ",
"(t, ",
"), ie a magnitude ",
" a direction. The magnetic field in t and ",
" has a direction perpendicular to that. ",
"When the magnitudes of both waves reaches 0, do the fields diminish to nothing or just stop influencing anything around them?",
"They will then just be zero in one point (and a moment in time), but not everywhere. It's like a node in a water wave. At that point a charge would feel no force. ",
"If someone put a magnet near a stream of radio wave with a noticeably long wavelength, could the exertion of forces on the magnet be detected?",
"Not sure. You'd overlay a static field onto the oscillating field of the wave. The two would just add up. "
] |
[
"Sorry I don’t really understand EM waves at all and I’m probably dumb for trying to understand with a cursory knowledge of physics.",
"Don't worry, the EM field is ",
" hard to visualise and it's very common to get confused when thinking about it. I think one of the main problems is that people imagine something like ",
"this",
" when they think of an EM wave (or just one of E or M in this case). In fact, you should be thinking of something like ",
"this",
", where the brightness of the orange represents the field strength. Note that the wave ",
" -- this thing is not oscillating in some position dimension like a water wave.",
"The confusion generally arises because the electric and magnetic fields are ",
" fields, which means that in addition to the strength (shown in the second image) they also have a direction at each point. This usually leads to a picture like the first one, but that picture is just wrong. The direction doesn't mean the wave actually traces out a wave in space, it's just an abstract property of the field. In general, I wouldn't bother trying to visualise this bit; just remember that it is what leads to the polarisation. For all intents and purposes, the electric and magnetic parts of an EM wave fully overlap: they both trace out the same straight line in space.",
"A couple places said it was the magnitude of each respective field, which I think refers to the strength and length(?) of the field lines “generated” by the field.",
"The magnitude of the field is reflected in the ",
" of the field lines. Look at ",
"this",
" heatmap of the electric field strength of waves in the x-y plane emitted from a point source at the centre of the image. Note that the field along any radial line you draw will look like in the second image above. The field lines here will be a set of concentric circles, more closely spaced near the peaks (more orange parts) and with the arrows swapping direction at each alternate peak (since the sign of the field changes).",
"When the magnitudes of both waves reaches 0, do the fields diminish to nothing or just stop influencing anything around them? If someone put a magnet near a stream of radio wave with a noticeably long wavelength, could the exertion of forces on the magnet be detected?",
"You can set up a standing EM wave between a pair of mirrors, so the position of the field 0 points don't move. In this case, yes, you can very much tell that there's no field at these nodes.",
"photon",
"quantum numbers",
"Probably worth quickly touching on quantum stuff, since all of the above is classical electromagnetism. Basically the thing that gets quantised is the amplitude of the waves -- the size of the maximum field strength. A single photon corresponds to some fundamental amplitude, E0. Then subsequent photons add additional factors of E0, so a wave with N photons has an amplitude N*E0. This is obviously not the full picture, but I think it gives a reasonable intuition of what we mean when we say that light is 'discrete'. It's not really that it's discrete in space (it's still a wave), it's that its amplitude is discrete in some sense."
] |
[
"Thanks for this reply. Would you mind elaborating on what it means for an amplitude to be discrete?"
] |
[
"Why is the energy and mass in quasar accretion disks not simply pulled into the enveloped black hole?"
] |
[
false
] |
I can't understand what forces are at play in quasars. I understand there is a matter pile up and subsequent expelling of that matter due to gravitation and friction but I don't understand the . Why is this all piling up near the event horizon instead of being seamlessly sucked in?
|
[
"Because angular momentum is conserved. Earth doesn't simply fall into the sun because of the very same reason, so those gas particles orbit the black hole in exactly the same fashion, just in a much lower orbit. Only through friction they can slowly lose angular momentum, so they do approach the black hole after all."
] |
[
"That's not really my specialty, but as far as I know, that's not entirely clear. The stuff heats up and becomes a plasma, which induces strong magnetic fields. Hydrodynamics are notorious for their complex equations, but with magnetic fields and relativistic fluids in the mix it becomes a real challenge. It's called relativistic magneto hydrodynamics."
] |
[
"Oh, cool! Clear as day. Cheers for that"
] |
[
"Does science have theories which are non-falsifiable?"
] |
[
false
] |
I would like to refute this statement, which I stumbled across on a forum, if it is untrue: "Science pushes this notion but actually has theories than are not falsifiable, namely The beginnings of the universe(Big bang, ect, ect) and Life from non life(abiogenesis)" So basically I would like to defend science (and learn) from this attack and prove that these things are falsifiable.
|
[
"All scientific theories must be falsifiable, in principle, using new evidence. ",
".",
"Can't be simpler than that.",
"A corollary is that scientific theories cannot ever be proven true, only false. Philosopher John Stuart Mill summarized this outlook best when he said, “No amount of observations of white swans can allow the inference that all swans are white, but the observation of a single black swan is sufficient to refute that conclusion.”",
"The result for scientific theories is that they are always open to further investigation, they are never declared true or proven, and the only ending for a particular theory is that it might be proven false and discarded.",
"More here."
] |
[
"I don't believe that there is a standard accepted theory of abiogenesis. It is an open question.",
"Here is an analogy for the big bang problem:",
"If you come upon the remains of a forest with charred wood and ashes everywhere, you will conclude that there was a forest fire. You can do this because you have lots of experience with fire, and understand that this is what it does to wood. Someone can always come in and argue that there was actually some weird tree-killing fungus that turned it into ashes and char, but everyone knows that to be absurd - unless someone can produce the miraculous fungus. Fire is well understood and it is by far the most likely explanation for what happened.",
"In the case of the universe, one observes galactic red-shift, cosmic microwave background, and a mountain of other evidence. Knowing that the theory of general relativity seems to work very well, one can construct a most likely explanation that the universe was once very concentrated and hot by applying general relativity to this data. ",
"The problem is that while most people have made campfires, not many people have played around with general relativity equations, and so the interpretation of this astronomical data does not appear to obviously lead to only one honest and sane conclusion.",
"If someone wants to combat the theory of the big bang, what they need to do is come up with a theoretical framework that explains all astronomical data better than the current benchmark model of cosmology, because all anyone is saying that the big bang is the most likely explanation given what is known. ",
"In the case of the forest, one can falsify the likely explanation of fire by producing the miraculous fungus that turns wood to ash. ",
"In the case of the universe, one can falsify the likely explanation of the big bang by either showing that general relativity is incorrect, or by finding some sort of new fundamental interaction which changes ones interpretation of the data."
] |
[
"The Big Bang is a falsifiable theory-- if it were demonstrated that the Universe was either static or in a ",
"steady state",
", the Big Bang would have been disproved."
] |
[
"Why is three phosphorylations the limit of Adenosine and not two or four?"
] |
[
false
] |
Totally not procrastinating listening to protein kinase lecture.
|
[
"Well, adenosine di- and tetra- phosphate both exist in biological systems, so tri- is definitely not the limit. Why tetra- isn't used as the 'energy currency' of the cell is beyond me, though I'd hazard a guess that the bond involved in getting that fourth phosphate on there doesn't have as good a payoff as the third phosphate does."
] |
[
"In order for A4P (aka AP4) or A5P (aka AP5) — both of which do exist in biological systems — to be used for energy storage, you'd need a few things to happen.",
"First, they'd need to be sufficiently more efficient to justify the metabolic cost of additional enzymes (A4P synthase and A5P synthase). If they aren't, then using A4P and A5P would incur a reproductive disadvantage. ",
"Second, you'd need to actually evolve those enzymes. There are many good ideas that evolution never invents. ",
"Third, you'd need the existence of A4P and A5P not to interfere with any of the existing molecular mechanisms. However, since at least ",
"A4P appears to act as a signaling molecule in some brain pathways",
", you now have the problem that evolving in that direction might void the warranty on your brain. "
] |
[
"The amount of energy needed to add the next phosphate exponentially increases, due to the strong repulsion of the negative charge. I would hypothesize, the amount of power provided by the atp synthase is insufficient to add a 4th phosphate. If an adenosine-4-phosphate does exist, it is likely from a substrate level phosphorylation event, not mitochondrial or chloroplast driven energy production."
] |
[
"Gravity assist: I'm imagining a planet shaped like a torus, and an object passing through the hole. Does the object acquire orbital velocity if it enters in the direction of the planet's orbit (\"catches up with\" it), and lose velocity if it goes the other way (the planet \"catches up with\" it)?"
] |
[
false
] |
In case I was unclear, I'm trying to understand whether this "donut" model is the same thing as a traditional gravity assist ( ).
|
[
"Relative to the planet, yes. However, the important thing here is the change of the velocity vector. This is exactly how planetary assists in orbital mechanics work. While you exit the planet's sphere of influence with exactly the same speed as you entered, you're pointing in a completely different direction. You can use this to \"speed up\", \"slow down\" or change the plane of the orbit.",
"I use quotes there because of the often counter-intuitive nature of orbital mechanics. Often times, you must decelerate in order to achieve the fastest speeds, and accelerate in order to get slower. So, we can think of a gravity assist as giving energy to an orbit (\"speeding up\"), or taking some away (\"slowing down\").",
"So, energy will be conserved and the speed in equals the speed out of the planet's sphere of influence. But this space craft isn't orbiting the planet...it's orbiting something larger - be it a sun, another planet, or the galactic central point. ",
"So to make things easy, imagine a large circle that is a planet. Down is towards the sun, up is away from it, left is the direction it's orbiting, and right is where it's coming from. The planet's speed along this x-axis is X. A satellite comes traveling around the planet parallel to the y-axis with a speed of Y. Whoever planned for this orbital transition planned for a complete 90 degree turn (parallel to the x-axis). If the satellite is aimed for the right side of the planet, to be sling-shotted around to the left (direction of planetary motion), then the satellite will leave the planet's sphere of influence with the speed of Y, however, it's speed relative to the star is now X+Y. If it was aimed at the front of the planet, then it's speed would be X-Y.",
"This doesn't even take into consideration the effect a vector change of that magnitude (90 degrees) would have in addition to the speed increase - which is substantial. There's a reason planetary assists are used so often for missions past Mars - the added time of transit is far, far cheaper than the price of the fuel needed to do the same mission minus the planetary assists.",
"So let's put this concept in the OP's problem - a torus. Again, let's take a 2-D model for simplification. Now you still have the same x/y axis setup, but instead of one circle in the middle you have two circles offset from one another so that the center of mass is at (0,0). The simplest version of OP's problem is if that satellite is designed to pass exactly through (0,0). In this case, the satellite would exit the planet's sphere of influence parallel to the vector it entered on (since one half of the torus would exert the exact same orbital change and influence as the other half). It's ending vector would then be it's initial vector plus or minus the orbital vector of the planet. If the satellite doesn't pass through exactly the center, then things get way too difficult for my \"had a few beers tonight\" brain to comprehend without really doing some actual math (which I'm way too lazy to actually do right now).",
"*"
] |
[
"So, in layman's terms, and feel free to correct me if I'm wrong, while the craft would speed up due to gravitational attraction in the way in, it would slow down by the same amount on the way out, regardless of direction of travel. Thus making your net speed change zero."
] |
[
"For a gravity assist, you need to enter and leave the planet's influence in different directions, AFAIK."
] |
[
"In the LHC how are protons removed from the nucleus of an atom and kept together?"
] |
[
false
] |
I read somewhere there are billions of protons flowing round the LHC, how are they isolated and kept that way? What happens to the neutrons and the other parts of the atom? Thanks!
|
[
"The proton bundles in the LHC start out as hydrogen. To be more specific, they start out as hydrogen from the bottle shown in ",
"this picture",
".",
"Since a hydrogen atom is just 1 proton and 1 electron, we don't have any pesky neutrons to worry about. So that's easy.",
"What's also useful is that protons and electrons have opposite charge. That means that if you apply an electric field to a hydrogen atom, the protons will want to go left and the electrons will want to go right (it's just like driving a car with my wife). Normally, the attraction between the two is strong enough to keep them together (so far the wife analogy still holds, fortunately!), but yank up the electric field far enough and you can separate the proton from the electron.",
"Afterwards, the protons are redirected to the accelerators. The LHC actually reuses old accelerators as early stages that already speed up the protons before they're finally deposited into the big one. As the protons are moving around, magnetic fields are used to keep them in tight bunches. When a charged particle moves through a magnetic field, it'll feel a force perpendicular to its direction of motion, so magnetic fields can be used for steering, whereas electric fields are used for accelerating. In the LHC, by far the largest part of the ring consists of magnets used to keep the proton bunches going in a circle and only a small part does the actual accelerating.",
"And the electrons? We like to think we're simply discarding them, but in secret they're conspiring to influence decission makers to make the next big experiment an electron-positron accelerator instead of a proton-proton one like the LHC is."
] |
[
"You can also find the picture in this blog post:\n",
"http://backreaction.blogspot.ch/2010/02/lhc-proton-source.html",
"It's a really unimpressive bottle considering the amazing stuff that they do with its contents."
] |
[
"Do you have another link to the image of the \"hydrogen bottle\"? I just get \"Problem loading page\". I'd really like to see what it looks like. "
] |
[
"How does the light emission of a solar cell benefit the efficiency?"
] |
[
false
] | null |
[
"What do you mean by \"light emission of a solar cell\"? Solar cells don't emit light."
] |
[
"They do, but I fail to see how it makes sense that it actually increases the efficiency. I edited the post, hoping its more clear now."
] |
[
"https://arstechnica.com/science/2012/04/solar-cells-must-emit-light-to-attain-perfection-research-suggests/",
" This is an article suggesting so for example"
] |
[
"How many ants would it take to hold up a horizontal human?"
] |
[
false
] | null |
[
"Assuming...",
"mass of ant: 3mg",
"strength of ant: 50 times its body weight --> 150mg",
"length of ant: 10mm",
"width of ant's body: 2mm",
"area of ant: 10x2 --> 20mm",
"density of human: 1.4mg/mm",
"depth of lying human: 100mm",
"mass per unit area: 140mg/mm",
"According to my rough calculations it would be very close. They would definitely be able to get the arms and legs off the ground but the torso not quite. For a child as you mentioned they might not be able to deal with the head but the rest of the body should be okay as they aren't as thick. Also because it is so close if I am off by a factor of 2 with some of my assumptions it could completely change the answer."
] |
[
"Wow! Thank you for your reply! Would it be impossible to calculate roughly how many ants it'd take to lift a small child (or at least attempt)?"
] |
[
"if ants can stand on one another they can lift almost anything. ",
"How? What do you mean?"
] |
[
"How do electron microscopes produce 3D looking images with depth and shadows?"
] |
[
false
] |
If only electrons are being used, how are images like produced. .
|
[
"The 3D images produced by electronic microscopy most likely come from a specialized form called Scanning Electron Microscopy. In SEM, a primary electron beam is used to scan the surfaces of objects, but rather than the beam passing straight through (such as with Transmission Electron Microscopy), particles are emitted from the surface of the specimen upon excitation from the primary electron beam. These secondary electrons are detected by a secondary electron detector, which can then map the various intensities of signals across different sections of the specimen’s surface to give an image with precise topographical features. Therefore, you get the cool ass 3D image you mentioned. "
] |
[
"The image you have posted is from a TEM which I know because it is of such a very small scale (100nm for the scale bar means this is very very tiny, those salt crystals we're probably on the order of 10-100um and were 1000X bigger). In order to take a TEM image you have to slice a piece that is nanometers (nm) thick and you 'read' the electrons that travel through the sample in order to say what the sample is made of & thus what it looks like by layer. The salt crystals were done using a SEM so instead to the electron beam going through the sample, they reflect off the surface of the sample. This means that you see what the surface of the sample looks like instead of what it is made of. (The salt example is actually a really large sample, something you don't necessarily even need an SEM to see, but it still looks cool AF)\nFYI you can get info on what the sample is made of if you collect the electrons that are reflected back out of the material and have a good idea of what those materials were to begin with this is backscatter electrons microscopy.",
"TLDR: the image shown is a 2D sample and the salt was 3D"
] |
[
"Adding to this answer, the 3 dimensionality is inceased because some of the electrons don't bounce back elastically. Some of the electrons penetrate the sample and lose some energy the the atoms in the specimen. They bounce around and can penetrate up to a few microns. If they end up bouncing around and end up leaving the sample again with less energy than they started with they are called secondary electrons. The interaction volume formed as they enter the sample is teardrop shaped (depends on sample and beam energy). The interesction of the teardrop shape and sample surface represents the area that electrons can escape. For a flat surface perpendicular to the beam, thats a small spot. For inclined surfaces the area can increase significantly so edges close to parrallel to the beam generate more secondary electrons and are bright in the image. ",
"It doesn't matter if the surface is towards or away from the secondary electron detector because the detector is biased to attract and collect as many secondary electrons as possible.",
"Backscattered electron detectors are negatively biased to only collect electrons that bounce back with negligible energy loss. These electrons haven't bounced around inside the sample so they don't have this edge highlighting phenomenon. The images look flatter."
] |
[
"If you're standing on Jupiter's moon and jump, do you jump noticeably higher on the side closest to Jupiter than on the side furthest from it?"
] |
[
false
] | null |
[
"The astronaut jumping on Io should be visualized as being similar to the ocean on Earth affected by tides. Your weight is lowest on Io where Jupiter is directly overhead AND on the opposite side of Io, where Jupiter is directly under foot. Your weight will be highest on Io on the circle 90 degrees from those two points.",
"Remember that tidal forces reduce weight on the close and far side, because only the center of Io is in freefall relative to Jupiter's gravity. On the near side, Jupiter's gravity is higher than your orbital acceleration. On the far side of Io, the orbital acceleration is higher than Jupiter's gravity at that point."
] |
[
"The Jovian gravity cancels out with the centrifugal force.",
"This is true for the center of mass of the moon, but not true for every point (hence tidal forces). The surface gravity of Io is 1.8 m/s",
" The difference in gravitational acceleration from Jupiter between Io's surface and its center is ~0.006 m/s",
" which is ~0.3% of the surface gravity. It wouldn't make a large difference jumping, but it would be easily measurable."
] |
[
"As the moon orbits Jupiter, and you are standing on that moon, you will be in an orbit around Jupiter as well. That means both you and the moon are in freefall around Jupiter, and weightless with respect to the planet. There are some tidal forces, but from your perspective, Jupiter doesn't really matter. The only thing that is pulling on you is the moon. The Jovian gravity cancels out with the centrifugal force.",
"EDIT: ",
" Sorry for that. The correct answer is further down the thread."
] |
[
"Why don't particles spontaneously decay?"
] |
[
false
] |
From what i understand of the atomic nucleus, there are two forces at play: the weak and the strong nuclear forces. Generally when you get to the heavier elements, the size of the nucleus becomes such that because the strong force works only in very short distances, the atoms become less stable and you get radioactive elements. My question is to why they don't spontaneously undergo decay? What I am saying is if you graph both the strength of the strong force on the x axis with respect to the diameter of the atom, and the strength of the weak force with respect to the diameter of the atom, at some point they will meet (because we have radioactive decay, this is an oversimplification because i know some elements can be more stable with a longer nuclear diameter than ones with a smaller nuclear diameter). Or is the idea of the nucleus as protons and neutrons held together by the strong force in the nucleus an incorrect assumption and therefore a net force calculation between the weak and strong nuclear forces do not describe reality as evidenced by decay as probabilistic in nature? Could it be that the nucleus acts as a standing wave and when the constructive interference overcomes something not unlike the work function for electrons, the excess energy splits from the atom in the form of alpha beta or gamma decay? I wouldn't be surprised if I were totally off the mark
|
[
"Are you familiar with the concept of quantum tunneling? Basically it's a phenomenon where a particle is in a potential, but has a finite probability of crossing that potential barrier and appearing on the other side, even though classically this would be forbidden. An example would be if you had an egg rolling around in a bowl, but not rolling fast enough to reach the rim of the bowl. Then, suddenly, you see the egg on the counter next to the bowl.",
"Anyway, that is essentially how alpha decay works. You have an egg (alpha particle) rolling around inside a bowl (nucleus), and after a long enough time, the alpha particle will appear outside the nucleus and you will have decay.",
"I'm sorry I couldn't answer your question directly...it confused me."
] |
[
"Remember that everything we're talking about right now is ",
" non-deterministic.",
"You can imagine, if you like, that God has a clock, and that things only happen when the clock ticks, and not in between ticks. Each time the clock ticks, there is a ",
" for an alpha particle to tunnel out of a suitable nucleus. So God rolls his dice or whatever, and if they come up snake-eyes, the alpha particle tunnels out. If they don't, then nothing happens until the next tick of God's clock.",
"Now take the limit — making the time between ticks of the clock shorter and shorter until it's exactly zero — and you have a good idea of how this works. Also, there aren't any actual dice.",
"Every non-deterministic process has an associated expectation value — that is, the value to which you expect the ",
" of a lot of repetitions of that process to converge. Tossing a coin has an expectation value of zero (using the convention that heads is +1 and tails is –1). Rolling a die has an expectation value of 3.5 (if I remember right). Well, the expectation value for a particular type of atom to alpha-decay is going to be such-and-such. That doesn't mean every atom will decay after such-and-such time; it means that if you have a squillion of those atoms, the ",
" time until each atom decays is such-and-such."
] |
[
"Basically the energy height of the potential and the kinetic energy of the particle."
] |
[
"Slightly complicated permutation?"
] |
[
false
] |
Hi, someones comment on a thread claiming that the number of possible combinations of a deck of cards would be doubled if the back of the cards could be used - which I'm pretty sure is wrong, so I guess that is essentially my question. How does one go about calculating a permutation such as this? I would imagine it to be one of 53 possibilities is possible at the start but I'm not sure. It confuses me because there is the option of 52 cards, and the 52 backs of cards. However, when viewed each of these 'back of cards' look identical, so if there is one card at the start, then 50 'back of cards,' followed by another upturned card there are 52*51 combinations. But the main problem arises when considering that for each back of card placed we must use up a card number. I really have no idea how to tackle this question.
|
[
"The problem isn't quite fully specified, so I'll answer the two questions that I think it could be.",
"How many ways can you order a deck with some number of cards are face down, considering the ordering of the facedown cards?",
"In this, a six of hearts face down is filling a position in the sequence, so they could be denoted by a 52 long sequence of the cards paired with a 52 long sequence of face up/face down binary decisions.",
"As ",
"u/fishify",
" says somewhere else in this thread, there's 52! ways to order the deck, and then a binary choice for each card based on whether it is face up or face down. That gives 2",
" *52! = 3.63 * 10",
" possible orderings.",
"How many ways can you order a deck with some number of cards are face down, with the face down cards indistinguishable?",
"In this, all face down cards are only noted as blanks, so they could be denoted by a sequence of 52 cards where some of the cards are replaced by blanks.",
"This is a harder problem, so consider the case where n cards are face down. There's 52! ways to order the deck, 52Cn ways to pick the n cards to be face down. But now for the sequence with n particular cards all down in some particular spots, we've counted it n! times, so we need to divide by that. So that's 52!/n! * 52Cn = (52-n)! (52Cn)",
" = [; (^{52} C_n) (^{52} P_{52-n}) ;] ways with n cards down. This shows we could have thought of this as permuting the 52-n cards and then choosing the n places where blanks go.",
"Then we'd sum that over all the possible n's, for [; \\Sigma_{n=0}^{52} (52-n)! (^{52} C_n)^2 ;] = 1.03 * 10",
" total ways for an unknown number of indistinguishable cards facedown.",
"Both of these are way more than twice 52! =8 * 10"
] |
[
"This assumes that a face down Queen of Spades is distinguished from a face down Seven of Diamonds, which may or may not be appropriate.",
"If the backs of cards aren't distinguishable, this becomes a much harder problem, I think. ",
"If n cards are face down, then there's 52! ways to order the deck, 52Cn ways to pick the n cards to be face down. But now for the sequence with n particular cards all down in some particular spots, we've counted it n! times, so we need to divide by that. So that's 52!/n! * 52Cn = (52-n)! (52Cn)",
" ways with n cards down.",
"Then we'd sum that over all the possible n's, for [; \\Sigma_{n=0}^{52} (52-n)! (^{52} C_n)^2 ;] total ways for some number of indistinguishable cards facedown.",
"Using Wolfram Alpha, I get that as 52!*2",
" =3.63 * 10",
" for distinguished facedowns, and [; \\Sigma_{n=0}^{52} (52-n)! (^{52} C_n)^2 ;]=1.03 * 10",
" for indistinguished facedowns."
] |
[
"Awesome, glad I could help."
] |
[
"Is the energy produced by the sun constant?"
] |
[
false
] |
whether it be on a microsecond by microsecond or hour by hour basis, is the power produced by the sun constant? I know that the sun will eventually run out of fuel but I am really wondering if there are fluctuations.
|
[
"No. In the long-term trend it is gradually getting hotter, in the short-term the solar output fluctuates over an 11-year cycle corresponding to different numbers of active sunspots."
] |
[
"in the short-term the solar output fluctuates over an 11-year cycle",
"To expand on this a bit: ",
"this fluctuation is very small",
". On average we receive 1366 W/m",
" of flux from the Sun, and that only really varies by about ± 1 W/m",
", which in percentage terms is only ± 0.1%.",
"Since I've seen this question come up before when mentioning global warming: if you're wondering how this fluctuation affects the temperature of the Earth, the answer is very little. Just as luminosity scales as the temperature to the fourth power (an object that is twice as hot outputs 16x as much radiation), temperature scales as luminosity to the 1/4 power - to double an object's temperature, it needs to absorb 16x as much radiation.",
"If the average temperature of the Earth is 288 Kelvin, then the total amount the Earth's temperature changes from this 11-year fluctuation will then be:",
"288 K * (1367 W/m",
" / 1366 W/m",
")",
" = 288.053 K",
"288 K * (1365 W/m",
" / 1366 W/m",
")",
" = 287.947 K",
"...or in other words, it will change the global temperature by about ±0.05 degrees."
] |
[
"in the short-term the solar output fluctuates over an 11-year cycle corresponding to different numbers of active sunspots.",
"That is the energy released by the surface of the Sun, not the fusion power (\"produced\") in the core."
] |
[
"Assuming Mars harbors/harbored life, what are the chances that it could contain fossil fuels as we currently know them?"
] |
[
false
] |
... And I suppose a more compelling question would be what other usable resources might Mars contain?
|
[
"Ah, but we DO detect methane in Mars's atmosphere. Interestingly enough the emissions peak during the martian summer and drop off during fall/winter. "
] |
[
"I'd be surprised if there were oil deposits. I think we would have detected methane in the atmosphere if there had been such a large amount of biomass on mars in the past. At least if it were biomass like earth's."
] |
[
"I think that's unlikely because for fossil fuels to form you need a large and thriving ecosystem with huge amounts of biomass that existed for millions of years, coupled with an appropriate active geological system, which seems unlikely to have existed on Mars.",
"In addition, I think that if such things existed underground on Mars today we'd see occasional signs on the surface, sinkholes and occasionally deposits leaking onto the surface.",
"Then again Mars has been geologically dead for a long time, so the dead surface could be deceptive; who's to really say what existed millennia ago, and what's hidden today.",
"I'd be very surprised, but the universe has a knack of surprising us."
] |
[
"Why did the Russian computer, Setun, a ternary computer, offer advantages such as lower electricity consumption and lower production cost over its binary successor?"
] |
[
false
] |
I am a computer science major and I have been taught that memory costs money. That being said wouldn't a ternary computer use more memory? Or have more parts? Was the technology of the time more suited for three valued logic over Boolean logic?
|
[
"Computers can be built using any arbitrary radix. Some early machines were base 10. I can't find much information on Setun, however, nobody would claim the USSR ever had any sort of edge in computing, despite the country's strong reputation for maths. It is possible the limited electronics available in the USSR were more suited to ternary logic, but I cannot see how. ",
"The advantage of binary logic over other radix is that the number of interconnections is significantly reduced. Also, in modern semiconductor computers (i.e. vs. tube) noise margin is important and binary systems have greater noise margin than ternary ones."
] |
[
"I found the concept!",
"It's called radix economy and if you allow non-integers as a radix then ",
" is the best in terms of radix economy. ",
"Base 3 has some marginal advantage overall, in terms of the radix economy, but base 2 has other advantages which have been pointed out by you and other people.",
"http://en.wikipedia.org/wiki/Non-integer_representation#Base_e",
"http://en.wikipedia.org/wiki/Radix_economy"
] |
[
"Possibly. If you have a ternary system you may have attributes such as the transition time which works better. For example, if you define 0 volts as 0, 2.5 volts as 1, and 5 volts as 2 in a ternary system, and 1 as 5 volts in a binary system. At the same switching speed (volts/microsecond) you'd be able to transition from 0 to 1, 1 to 2, 2 to 1, and 1 to 0 faster than if you had a binary system switching 0 to 1 or 1 to 0.",
"However, given the limited information, it is hard to know what the issue was. "
] |
[
"What is the relationship between momentum and kinetic energy"
] |
[
false
] |
they seem so much alike, but totally seperate in all of their uses.
|
[
"To expand a little:",
"Momentum is often designated by \"p\". We'll call kinetic energy KE.",
"From mutatron's first line follows:",
"KE = p",
" / 2m",
"So there's your direct relationship between classical momentum and kinetic energy."
] |
[
"That is the definition that is generally used in grownup physics."
] |
[
"Momentum is m*v, and kinetic energy is 1/2 m*v",
" .",
"You can get the force for stopping something in time ",
" using:",
"F = m*v/t",
"Or you can get ",
"force for stopping something in distance ",
" using",
":",
"F = (1/2 m*v",
" )/d"
] |
[
"Why are there no green stars?"
] |
[
false
] |
Most stars are either blue, white, red, or orange, but why are there no green ones?
|
[
"Because stars radiate roughly a blackbody spectrum. As the temperature increases, the blackbody color changes as red -> orange -> yellow -> practically white -> bluish white. Then it stays bluish white all the way to infinite temperature.",
"It's called the Plankian locus - Wikipedia has a nice diagram:",
"https://en.wikipedia.org/wiki/Color_temperature#/media/File:PlanckianLocus.png"
] |
[
"Oh I see, similar to the colors in normal fire?",
"It's exactly the same thing, because the light from the flame of burning wood or a candle IS black-body radiation. ",
"A yellow flame is caused by glowing soot particles. When the hydrocrabons (like those in wood or wax candles) burn, the combustion reaction (hydrocarbon + oxygen → carbon dioxide + water) isn't prefect. ",
"Incomplete combustion",
" occurs when the supply of air or oxygen is poor. Water is still produced, but carbon monoxide and carbon are produced instead of carbon dioxide. In general, the reaction for incomplete combustion is: hydrocarbon + oxygen → carbon monoxide + ",
" + water. ",
"The carbon is released as ",
"soot",
", a mass of tiny, impure carbon particles, which are carried upward in the flow of hot gases being released by the fire. These soot particles are ",
"heated by the exothermic reaction",
" of the fire, and begin to emit ",
"thermal radiation",
". This is exactly the same sort of glowing you see when a piece of metal is heated in a furnace. These tiny glowing soot particles are what you are actually seeing when you look at a candle flame or a burning log.",
"A blue flame is produced when the combustion is complete and no soot is produced. The high temperature of the flame causes the vaporized fuel molecules to decompose, forming various incomplete combustion products and ",
"free radicals",
", and these products then react with each other and with the oxidizer involved in the reaction. The complete combustion reaction creates enough energy to excite and ionize gas molecules in the flame, leading to a blue appearance.",
"Check out ",
"this simulation",
" (requires Adobe Flash) that shows how the wavelengths of light being emitted by a black body change with temperature. Notice that when the peak wavelength is green, at about 5300 K, there's also a bunch of red and blue light being emitted. This means it would trigger all three kinds of color receptors in your eye, and look white."
] |
[
"Stars emit radiation over a broad range of wavelengths, and the human eye is most sensitive to yellow and green radiation. When a star is green, it is pretty much right in the middle of the visible spectrum. It is radiating strongly at all visible wavelengths, with most of the radiation right in the middle. When we look at the star, then, all these colors are mixed and the result is the color white. So you won't ever see a green-looking star."
] |
[
"Evolutionarily, why would mosquitos change to the point that they are itchy nuisances to their hosts instead of being unnoticeable?"
] |
[
false
] |
My only guess is that humans are the ones who adapted, not mosquitos. Maybe we adapted to get itchy mosquito bites because mosquitos carry disease, and it's better if we avoid them.
|
[
"Mosquito saliva actually contains an anesthetic which prevents you from feeling the bite as it is happening. It only gets itchy later (human immune response) by which time the mosquito is gone."
] |
[
"They are usually unnoticeable. You usually only notice a mosquito bite after the mosquito is long gone and you present no danger to it."
] |
[
"The itch happens after the mosquito is safely away, so it doesn't matter to the bug."
] |
[
"How much does a covid-19 vaccine lower the chance of you not spreading the virus to someone else, if at all?"
] |
[
false
] | null |
[
"Before you can pass the virus on to someone else, you must first become infected.Vaccines reduce this massively, with efficacies between 60 and 90%. ",
"https://www.nature.com/articles/d41586-021-02261-8",
"Once a person is infected, the adaptive immune system means the infection is cleared from the body more quickly in a vaccinated/previously infected person than someone with no existing immunity. This leaves a shorter period of time when the viral load is high enough to infect others. And this is borne out by the data. ",
"https://www.gavi.org/vaccineswork/mounting-evidence-suggests-covid-vaccines-do-reduce-transmission-how-does-work",
"immunisation with either the Pfizer or AstraZeneca vaccine reduced the chance of onward virus transmission by 40-60%",
"Put the two together and a vaccinated person is between 76% and 96% ",
" likely to infect another person than someone unvaccinated.",
"Edit - this is based on the data/studies we have done so far. There's evidence that protection against infection is a bit lower for Delta and a possibility that immunity to ",
" may wane over time. However, it's also been shown that a booster improves the efficacy against Delta.",
"So the takeaway shouldn't the absolute figures, which are prone to margins of error anyway. It's that ",
" as well as protecting individuals against severe outcomes, but it's important that we keep our eye on the ball and be ready to use boosters and new vaccines to maintain our edge in this fight against covid."
] |
[
"Thanks to this sub-thread, I've booked in for my vaccine tomorrow. ",
"I'm not anti-vax (childhood rubella left me deaf), but I had some questions about this one. Finding some of those answers without the name calling and condescension that seems to be the default for any discussion on the topic these days is helpful. ",
"So thanks for the great replies everyone."
] |
[
"When playing the lottery you can either win or not win -- 2 possible outcomes but that does not make the chance 50-50"
] |
[
"Does radioactive decay of an atom cause significant changes in the properties of chemical compounds?"
] |
[
false
] |
I am not asking about the radiation, what I mean is, for instance if F-18, used in Pet scans, decays to oxygen-18, the resulting oxygen will be unsaturated. Will it immediately react with another molecule in its surroundings? What about metals in organometallic complexes, will they instantly change configuration if the new metal center is unstable in the old one?
|
[
"Technically speaking you can refer to either Beta + or Beta - decays, which emit either a positron or an electron respectively. (Yes this was pedantic)"
] |
[
"Perhaps pedantic, but critically important to the application that OP asked about, Positron Emission Tomography. If berry's decay were only electrons, then PET would not be possible. "
] |
[
"Not sure if you're kidding or not, but the detectors for PET don't detect the positrons produced by beta",
" decay themselves, but rather the gamma rays produced by positron-electron annihilations."
] |
[
"Why does solar pressure cause rotations of the JWST instead of just pushing it away uniformly?"
] |
[
false
] |
I've been curious about this for a long time and I expected that when the Aft Momentum Flap was eventually deployed (as it was today), there would be more layman-accessible explanations of this; however, I've not found any. My naive first guess about how solar pressure would affect JWST would be that the force would be uniformly in one direction: outward from the sun, and therefore cause it to move slightly away from the sun over time, but not cause any changes in rotations or orientation. So how, exactly, does solar pressure cause of the JWST instead? So far the only explanation I've found is what it says in NASA's blog, which doesn't explain how solar pressure causes rotations ( ): "The aft momentum flap helps minimize the fuel engineers will need to use throughout Webb’s lifetime, by helping to maintain the observatory’s orientation in orbit. As photons of sunlight hit the large sunshield surface, they will exert pressure on the sunshield, and if not properly balanced, this solar pressure would cause rotations of the observatory that must be accommodated by its reaction wheels. The aft momentum flap will sail on the pressure of these photons, balancing the sunshield and keeping the observatory steady." One explanation that occurred to me is that the telescope is running into more solar wind in the direction of motion (like how a fast runner runs into more rain droplets on their front than their back), is that on the right track? Bonus question: how does the Aft Momentum Flap counteract the force? (Although perhaps the answer will be self-evident after one understands the reason for the rotation.)
|
[
"If the force doesn't act through the center of mass it will induce a torque. If you push sideways on one end of a rod you won't move the whole rod in that direction, you would rotate the rod. The momentum flap provides a counteracting torque to keep the telescope from rotating."
] |
[
"Oh, I see! That makes so much sense, thank you.",
"All we need to do now is build a telescope that is perfectly spherical with uniform density, then we can get rid of that pesky momentum flap. :D"
] |
[
"Project Echo",
" perhaps?"
] |
[
"When our sun turns red giant, will it push all the planets away or suck them all in?"
] |
[
false
] |
the mass of the sun wouldn't change right? so I don't see how it would suck us in. Would it have a slow wake or pressure wave that pushes the orbits of the planets away from itself? all the simulations I've seen on TV just show static planets sitting there waiting for a sun to swallow them, can't see that happening.
|
[
"The Sun shouldn't create too much of an outward force as it expands (by a pressure wave or anything), and as you noted the mass stays the same and so, due to a nice feature of Newtonian gravity, the Sun's gravitational field won't change either. So it's pretty accurate to think the inner couple of planets will just sit there waiting to be sucked in, without too much disruption to the outer solar system."
] |
[
"That's the opposite of weird. What would be weird is if stellar evolution somehow magically caused the sun's gravitation to change in a sufficiently significant way to alter the orbits of the planets."
] |
[
"That works better when you remove \"the opposite of\"."
] |
[
"Why are there no nuclei consisting exclusively of neutrons?"
] |
[
false
] | null |
[
"There are no bound nuclei, but there are resonances like the dineutron. There is also the more controversial tetraneutron.",
"But these systems are unbound, and decay with half-lives on the order of 10",
" seconds.",
"If you take a system of two neutrons at low relative momentum, there is an attractive interaction between them due to the residual strong force. However the attraction is not strong enough to form bound states."
] |
[
"Those are held together by gravity, not the strong force."
] |
[
"No, because the nuclear binding energy is dependent on the total isospin of the system. Helium-4 has isospin 0 in the ground state, but the tetraneutron must have total isospin 2.",
"Or if you think of nucleons occupying some mean-field orbitals, Pauli exclusion means that the extra two neutrons in the tetraneutron would have to occupy higher orbitals, whereas if you have two neutrons and two protons, they can all occupy the lowest single-particle orbitals."
] |
[
"When a child receives an organ transplant (heart, kidneys, etc.), does the transplanted organ grow along with them as they get older? How does it know what speed to grow at?"
] |
[
false
] | null |
[
"The transplanted organs will grow appropriately with the child as they age as they would have in the donor's body as is governed by the normal cell's cycle and physiologic changes. ",
"EDIT: thanks reddit, turns out that children generally above the age of 2 can receive a transplanted kidney from an adult (",
"http://www.aakp.org/aakp-library/Pediatric-transplant",
"). My age cut-off was slightly higher as our center works differently."
] |
[
"It does grow along with them, your bodies growth and all the organs within it are regulated by hormones so they secrete the hormone telling it to grow based upon the need for that organ."
] |
[
"Growth Hormone (GH) dictates gross growth, and is secreted by the pituitary gland. This is the place where a lot of endocrine functions are regulated, to make sure your entire body is listening to only one master system.",
"Also, a lot of organs can undergo cell proliferation (hypertrophy) or cell enlargement(hyperplasia) in accordance to the body's need. This is why partially why the liver regenerates, why the thymus shrinks with age, and why one parathyroid gland is eventually enough for the entire body. They grow in a compensatory fashion, based on other hormonal signals and just plain everyday extensive use of the organ (much like muscles).\nHow much this process is involved in development is unknown, but it is part of normal physiology."
] |
[
"How do scientists know we've only discovered 14% of all living species?"
] |
[
false
] |
EDIT: WOW, this got a lot more response than I thought. Thank you all so much!
|
[
"It's basically extrapolating from data. One way of finding new species is (nowadays, less invasive methods are preferred) to go to the Amazon (or any other biodiverse ecosystem) and find a large tree (which shouldn't prove much of a challenge), spread a large sheet beneath the tree and then gas the whole tree to send every (formerly) living thing flying down onto your nice big sheet. You can then easily classify every animal. Scientists would then find that a large percentage of the animals collected were previously unknown species. This process would be repeated on several other trees in the area, with similar results. From this, we can tell that there are a whole lot of species we don't know about yet"
] |
[
"There have been many different estimates given for the total number of species on planet Earth. Some estimates are mere educated guesses by experts, while others are more grounded in statistics. A famous estimate was provided by Terry Erwin, an entomologist working for the Smithsonian Institute. He sampled beetles from the Amazon basin by pumping insecticides into large rainforest trees and catching the dead insects that rained down into nets (this method is now called 'fogging'). Using these samples, he observed that many species of beetles were only found within a single species of tree. By sampling lots of different species of tree, he found that on average, each species of canopy tree had roughly 160 species of beetle that were only found on a single tree species. So then, estimating that there are about 50,000 species of canopy trees, he simply multiplied 160 x 50,000 to come up with 8 million. Since it is relatively well known that beetles make up approximately 25% of all described species on Earth, he then multiplied 8 million x 4 to come up with 32 million. This estimate received a lot of attention because of how large it was. It also received quite a lot of criticism, given the extrapolations that he used. For example, his estimate of 50,000 Amazon tree species is likely too high, and the number of endemic beetles per tree species is also highly variables from one tree species to the next. Today, most scientists think the Erwin estimate is probably too high.",
"There have thus been many other estimates provided by different groups over the years. A good one that comes to mind is described in a paper by Mora et al. 2011 in PlosONE (",
"http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001127",
"). The authors identify an important relationship that helped them to derive an accurate estimation of global species diversity. That is, there tends to be a linear relationship between the log number of taxonomic units found within different taxonomic hierarchies (i.e., from species, to genus, to family, to order, etc.). While we have a poor idea of the total number of species on Earth, we do have very good estimates for the total number of genera and families, etc. So, using these numbers, the authors simply plotted the number of taxonomic units found within all hierarchies above the species level (i.e., from genera to phylum). Using the linear model obtained from this procedure, they extrapolated their data to the species level and found the model to land on the number 8.7 million. Given the fact that about 1.2 million species have been described, 1.2/8.7 = 14%, bringing us to your original question. ",
"This number is widely regarding as being a fairly accurate estimation of global species richness. Most biologists expect this number to be somewhere between 6 and 12 million now. However, it is important to point out that these estimates ignore microbes! We really don't have a clue what the diversity of prokaryotes looks like, so they are largely left out of these types of estimations. Advances in genomic sequencing will hopefully help us get closer to an answer, but we are still in the very early stages of developing techniques for describing microbial diversity."
] |
[
"Same, I pictured a mad scientist nuking entire Atolls so he could count Ants after"
] |
[
"Solar highways were on the table in 2008. Why haven't they taken off? What are the downsides?"
] |
[
false
] |
explains a really awesome idea for solar paneled highways. Sounds great, and they do a good job selling it, but why haven't we heard anything about it? This video's pretty old. Seeing as they were commissioned by the Department of Transportation to come up with this stuff, why hasn't it taken off? What isn't working?
|
[
"The gentlemen who was doing the solar highway project from the Department of Engineering has moved onto the next level of development. They are looking to build a mile or so of actual product in the real world and test it. They are probably testing or building it right now as I read a long while ago that he had already gotten through the first round of testing.",
"It is coming."
] |
[
"and lastly...sorry for all these replies - I am on their facebook page (",
"http://www.facebook.com/pages/Solar-Roadways/41869107125",
") right now and am going to post a couple of questions about the status of things. It looks like they stay close to Facebook and we might get an answer sooner than later."
] |
[
"http://solarroadways.com/",
" - this is the companies website (which totally sucks)",
"http://solarroadways.com/intro.shtml",
" - this is the info page, I am just starting to read it."
] |
[
"How can all the immense complexity of human organism be coded in only few tens of thousands of genes?"
] |
[
false
] |
Development, immune system, repair mechanisms, brain, eye, language, consciousness, all the tissues and chemicals ... how is it possible that so much information only uses so little code? Where's the compression coming from, if it exists?
|
[
"It's actually not that 'little' of code, if you want to look at it that way. The human genome consists of over 3 billion base pairs - and while we can consider only about 15% of those base pairs to directly code for proteins, the other 85% are slowly being determined to control other things (like protein interactions, stress interactions, cancer etc.) ",
"Broadly speaking, the human genome isn't even as 'compressed' as some other species - bacteria often have multiple proteins that can be coded for by one gene. Also, remember that most proteins do multiple functions. That is, they may have a basic function, but it may be useful in many of the situations you mentioned above. There actually really isn't any compression for the human genome (as far as I know, please correct me if I'm wrong, somebody), because all base-pairs code 3:1 (in other words, 3 base pairs for every 1 amino acid in a protein chain), so there can be no compression. "
] |
[
"To expand on the part about base pairs that do not code for protein, I would add that a big part of complexity comes from when and where genes are expressed in time and space. This can be controlled by regions that control transcription (promoters, enhancers, insulators, etc) by affecting where proteins bind DNA or the way the DNA is organized in 3D space."
] |
[
"In decoding genes, there is a process called transcription, that creates a copy of our genes (which are in the format of DNA) into a much more 'portable format', if you will, which is mRNA. It is known that eukaryotic mRNAs undergo a post-transcriptional process called alternative splicing. ",
"Alternative splicing is a very clever way in creating multiple types of mature proteins, that serve perhaps the same function but for different environment (contrast brain environment with muscle environment), or mature proteins that serve almost different functions etc by splicing out, or omitting parts of the gene coding sequence of the mRNAs. ",
"To illustrate: Imagine this sentence as the whole stretch of a freshly transcribed mRNA.",
"In alternative splicing, the mRNA transcript can either be spliced into ",
" which codes for protein A, or into ",
" which codes for protein B, a slightly different protein in structure but similar in function, or into ",
" which codes for protein X, which may be entirely different in function/structure. ",
"So yeah, just by one simple stretch of bases, can we get 3 or even more combinations of proteins. And this is only alternative splicing. There are other processes in genes like frameshift reading, backward transcription, and others that I my sleepy mind can't think of right now. I just meant to illustrate the huge amount of info our genome holds, and we are just talking about coding regions of genome, which make up less than 50% of our total DNA (other are non-coding sequences, that as we learn about them over the years, actually code for something else that plays many salient roles in maintaining a complex organism such as us humans). "
] |
[
"If you were to release a liquid somehow in a cube shape, what would happen? Would it retain its shape, or spread?"
] |
[
false
] |
Just wondering?
|
[
"It'd splash all over the floor if there was gravity present. But I'm guessing you mean in the absence of gravity? If it's a normal liquid, it has surface tension. So if you released it, it'd contract into a sphere, since that minimizes the surface area. "
] |
[
"Oh right! I've been trying to work out what would happen over the last few days (Not studying science, so I didn't come to a solid conclusion)",
"Thanks!"
] |
[
"Well, 'surface tension' is the macroscopic phenomenon. The way it works at the molecular level is fairly simple though. The molecules in a liquid form intermolecular bonds with each other, they're attracted to each other. So a molecule of a liquid will have the lowest energy when it's surrounded by its fellow liquid molecules, and things 'strive' to be in the lowest possible energy state.",
"Now if you imagine the layer of molecules at the very surface of a liquid, they're in a position they'd rather not be in, since they're only surrounded on ",
" side by the other liquid molecules. They'd lose energy if they could move into the 'interior' of the liquid, the attraction of the other liquid molecules is pulling them in. That force is surface tension. This is balanced by a force in the opposite direction, namely the pressure of the liquid. In other words, the surface contracts to the point where the molecules inside the liquid are pushing outwards as strongly as those on the surface are being pulled inwards. ",
"In the simplest possible terms: Molecules in a liquid attract, and things that attract will lump together as tightly as possible. ",
"Of course, a solid can have just about any shape, since that's the situation where the molecules don't have enough kinetic energy to overcome the attraction and be able to move around. While a gas is when the molecules have so much kinetic energy that the attraction is negligible, so they fly apart and fill whatever container they're in. "
] |
[
"Does \"thinking hard\" burn more calories than normal thought?"
] |
[
false
] | null |
[
"Here's some previous answers:",
"http://www.reddit.com/r/askscience/comments/kjwes/does_thinking_require_calories/",
"http://www.reddit.com/r/askscience/comments/j8lau/is_it_possible_to_burn_calories_as_if_you_were/",
"http://www.reddit.com/r/askscience/comments/fjndk/does_thinking_harder_burn_more_calories_if_so/",
"http://www.reddit.com/r/askscience/comments/f7l0d/does_thinking_hard_use_more_calories/"
] |
[
"I didn't bother searching on that one because I was so certain I was the first to think to ask it. Ohhh the hubris!"
] |
[
"Over what time scale?"
] |
[
"What evidence is there that electrons literally orbit the nucleus?"
] |
[
false
] |
As I understand it, electrons have different energy levels which we call atomic orbitals. How do we know that the electrons are literally moving around the nucleus?
|
[
"They aren't, at least not in the same way the Earth orbits the Sun. It's taught as such because it's a comforting inaccuracy that still allows students of chemistry or physics to make many physically meaningful calculations without mucking about with the insanity that is quantum mechanics.",
"Electrons are a smear of probability whose overall 'shape' of the cloud is defined by the quantum states it occupies. We know this to be the case because it's possible to directly probe atomic structures and make very precise measurements of energy and mass. If you're more interested in how the basic structure of atoms was discovered than I invite you to read upon Rutherford's now-famous gold foil experiment and it's descendants. These experiments solidified the notion that atoms had an extremely small positively-charged core and and nebulous negatively-charged outer structure."
] |
[
"The observation came first, then the theory. ",
"Balmer found that hydrogen emission occurred at specific wavelengths and developed an ",
"empirical formula to describe it",
". Bohr then developed a ",
"model",
" that postulated that electrons circle the nucleus in discrete orbits. Using this he derived a formula that exactly matched Balmer's formula. ",
"We've since learned that thought the electrons have this energy in the orbitals, the actual position of the electron is given by the Schrodinger equation, and are ",
"actually probability clouds",
", rather than specific orbitals. "
] |
[
"The reason the Bohr model works is that it correctly predicted that angular momentum and energy are quantized, even if it didn't quite understand that position and momentum of the electron can't be well defined in the atom. "
] |
[
"Theoretically speaking if we tried to colonize Mars would we succeed and how long will it take until it is habitable for humans, animals and plants?"
] |
[
false
] |
[deleted]
|
[
"No physical limitation, only an engineering problem.",
"I think that could be a motto for the entirety of humanity's scientific and technological accomplishments."
] |
[
"No physical limitation, only an engineering problem."
] |
[
"Problem?"
] |
[
"What is the fireball of a nuclear explosion composed of?"
] |
[
false
] |
I assume it isn't the bomb itself due to the sheer volume of it.
|
[
"The 'fireball' from the explosion is from the surrounding matter which has been vaporised by the energy released from the fission.",
"The nuclear fission releases ",
" energy in gammas and x-rays (and kinetic fission fragments and neutrinos and neutrons). This energy get absorbed by the surrounding matter (rock, air, bomb casing, fission fragments etc) and they become superheated into plasmas ",
" which then rapidly expand (shockwave) and also re-radiate their energy all over the EM spectrum (heat, light)."
] |
[
"Materials scientist here. I wanted to correct you on one thing, a candle is most certainly not a plasma. Plasma is a state of matter in which particles are in a highly energized state (ionized), this typically requires a larger amount of energy that a candle cannot provide.",
"Plasma is electrically conductive, think Spencer's Gifts plasma balls, or the sun; if a candle were truly a plasma, you could put two contacts in a flame to determine if a current is measured.",
"The nuclear parts are largely out of my field of study, I am sure the rest of your post is correct, I just simply needed to inform you of the plasma bit. "
] |
[
"Just another FYI - the reason candle flames glow is not because they create a plasma, but because there is a continuous stream of soot particles that the combustion reaction heats up until they glow due to blackbody radiation. The soot particles continue to react with oxygen and shrink the further away from the wick they get, and so the length of the flame is determined by either how long until the soot cools down too much to glow (resulting in a sooty/smoky flame), or when the soot particles are consumed by the reaction (when it is clean burning)."
] |
[
"What would happen if you forced two opposing magnets together?"
] |
[
false
] |
[deleted]
|
[
"Eventually the magnetic moments of the atoms within the magnets would re-align to make one bigger magnet. You can observe this happen in real time if you hold a really string magnet in the \"opposing\" configuration to a smaller magnet.",
"I don't know exactly what would happen if you had two perfectly symmetrical identical magnets at zero temperature with no external field etc."
] |
[
"Would heat build up? "
] |
[
"That was my thought. Eventually a quantum fluctuation rather than a thermal one breaks the symmetry."
] |
[
"Why is it easy to remember melodies from songs, but not the lyrics sung to the same melody?"
] |
[
false
] | null |
[
"Our brains evolved to recognize and predict patterns in the world around us. The cortex is particularly adept at this and has been the inspiration behind ",
", most often used as pattern recognition systems.",
"Recognizing patterns with a temporal dimension to them is beneficial across most of our senses. If you see a commonly recognized object falling or rotating, your brain uses past experience to fill in the next few \"frames\" of our experience. The same is true of auditory patterns and music signatures. We get better at recognizing, predicting and encoding the memory of a pattern as the signal-to-noise ratio increases. Music is typically a very straightforward pattern with very little random noise, and the melody is effectively the underlying pattern of the music.",
"Another contributing factor is that, for various reasons, memories are better encoded when there is a high emotional response associated with the memory. For reasons we don't truly understand music is fairly pleasant to listen to already, and many songs evoke strong emotional responses. Lyrics can contribute strongly to this as well by providing an emotional context for the pattern.",
"We can and do recognize patterns within words and of words, to recognize and predict spellings, grammar and phrases. However the space of words is so large and varied that we tend not to remember arbitrary combinations. We remember commonly seen combinations like \"Happy ",
"\", \"I love ",
"\", \"I have to go to the ",
"\", \"I need a cup of ",
"\", etc.",
"Songs that strive for novelty, or are verbose, or have largely subjective meanings are difficult to remember because our brains are designed to filter out non-obvious, rare combinations. Have you ever noticed that when song lyrics are strongly rhyming or annoyingly repetitive, it seems impossible to get them out of your head? These lyrics have an inherent pattern that our brains are very good at detecting and encoding."
] |
[
"\"BTW: I claim no authority in the field of psychology, I'm just share an interest in it and formulated a semi-educated assumption.\"",
".... which is precisely what this sub is not for."
] |
[
"\"BTW: I claim no authority in the field of psychology, I'm just share an interest in it and formulated a semi-educated assumption.\"",
".... which is precisely what this sub is not for."
] |
[
"What does the pOH tell you about a solution where there is no hydroxide?"
] |
[
false
] |
Okay, it was hard to make a title for this one, but I'll try to clarify here! If we have the following reaction: HCl + H2O → H3O + Cl Let's say the pH for this solution is 1.7. Using Kw(10 molars ) = [OH ] * [H3O ] log([H3O ] * [OH ]) = log[10 ] log[H3O ] + log[OH ] = log[10 ] -log[H3O ] - log[OH ] = - log[10 ] pH + pOH = 14 I would imagine that pH + pOH = 14 is valid for the reaction above. But is this where I am wrong? If not, I continue. Since the pH is 1.7 we could calculate that the pOH is 12.3. Using this we could calculate the concentration of hydroxide in the water (10 ). But this makes no sense since there is no known concentration of hydroxide in this solution. Where am I thinking wrong?
|
[
"As long as you are working with an aqueous solution, the Kw expression is valid. In another solvent, that wouldn't be true. ",
"However, in the expression above, your determination of the concentration of hydroxide is correct. Even if there is a lot of H",
" around, that doesn't mean there can't also be OH",
" around. Pure[ish] water has a concentration of 55 M H2O. There's plenty of room for both H",
" and OH",
" at any attainable concentration of either of those ions in solution."
] |
[
"Water naturally dissociates into hydronium and hydroxide ions.",
"2 H2O <--> H3O",
" + OH",
"So even if you start with, say, a liter of pure H2O, some of those water molecules steal hydrogen ions from other water molecules, creating hydronium and hydroxide ions. As the concentration of H3O",
" and OH",
" ions increase it becomes more likely for a H3O",
" and OH",
" to come in contact with each other and for the H3O",
" ion to give one of its hydrogens to the OH",
" ion, turning the two of them back into water molecules.",
"The likelihood of any two water molecules swapping a hydrogen and becoming a hydronium and hydroxide ion has some constant probability that increases with temperature. The likelihood of a hydronium and hydroxide ion coming into contact and turning back into water increases with the total concentration of each. At room temperature and starting with pure water, these two processes reach equilibrium when there is very close to 10",
" mol/L of hydronium ions and 10",
" mol/L of hydroxide ions.",
"So basically the hydroxide ions occur naturally from the dissociation of water. They will always be present in any aqueous solution.",
"When you add a strong acid to the water, you add lots of H3O",
" ions. This makes it far more likely for a naturally occurring OH",
" ion to encounter a H3O",
" ion and get turned back into H2O. This lowers the concentration of OH",
" in the solution from 10",
" mol/L to 10",
" mol/L in your example."
] |
[
"Thanks for the clarification!"
] |
[
"Does the insulin/insulin-like signaling pathway have different roles in different organisms or groups of life?"
] |
[
false
] |
Or does it seem to universally perform the same ultimate functions for all life? Insulin-like signaling seems to be a very ancient, conserved, and ubiquitous pathway. I'm wondering what, if any, differences in its function may have arisen in response to the varied environmental pressures that different groups of life were subject to. Any references would be great.
|
[
"To my knowledge insulin and the insulin-like growth factor signalling pathways are strongly conservd across all animals. Here is at least one paper on this",
"https://www.ncbi.nlm.nih.gov/pubmed/11943559",
"Because insulin is critically involved in fat deposition you should expect that insulin functioning is somewhat adapted in animals that have specific fat deposition requirements. Pinnipeds like seals and sealions and ceteans (whales and dolphins) both have a requirement to lay down extensive blubber. Hibernating animals like bears and squirrels also have highly adapted fat deposition mechanisms.",
"This paper has some background on pinniped insulin adaptations",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3814516/",
"I can't really provide much more as comparative mammalian endocrinology isn't really my field but hopefully that is enough to get you started"
] |
[
"Life is so broad that until an expert in the insulin pathway comes along, I'm going to have to supply a limited answer. In Drosophila and C. elegans there is ",
"strong conservation of the pathway, protein structure, and function",
". This already covers a pretty remarkable breadth of animal life. To quote from that review:",
"Molecular and genetic analysis of the insulin signaling pathway in Drosophila has revealed striking conservation at both the structural and functional levels. Recent studies emphasize the central role of insulin in the coordinated regulation of growth, metabolism, reproduction and lifespan. These data suggest that the level of activity of the insulin pathway reflects environmental conditions, in particular, nutrient availability, and serves to adapt many aspects of physiology for optimum survival via modulation of central neuroendocrine pathways.",
"Yeast don't appear to have an insulin pathway ",
", but seem to have a similar sort of ",
"precursor",
" pathway. That review also discusses insulin pathway functional similarities in rodents, nematodes, insects, and humans.",
"That said, there are cases where metabolic intake is linked to something that happens in an organism that doesn't happen in others. Take, for example, Apis mellifera (the honey bee), which has two different castes (queen vs. workers). Apparently, in honey bees, the ",
"insulin pathway is a critical pathway",
" during the differentiation between the castes during development. Clearly, in this case, there is a relationship between food intake and intended caste, and in a sense the insulin pathway is functioning as it would in other organisms -- it is just hooked up to extra pathways that end up determining caste. This is part of what makes your question so complex.",
"Edit:",
"Another example of the interplay between \"conserved function\" and \"species specific outcome\" is in ",
"beetles that have horns",
". The insulin pathway appears to be important for determining the size of the horn while it is being developed by acting as a sensor for larval nutrition. Being a sensor for nutrition and regulating growth/protein synthesis/cell proliferation based on that input is a strongly conserved function of insulin signaling. That said, horn growth is one specific way that a group of organisms has used that sensor."
] |
[
"Like I said to the other guy, thanks for taking the time to respond. Much appreciated."
] |
[
"How are the assembly languages for different processors turned into higher level programming languages like C?"
] |
[
false
] |
I understand the highest level programming languages are written in lower level ones, (ie. java is written in C), but what handles converting C to assembly? Is C rewritten for different processors?
|
[
"A compiler is typically viewed as having three stages:",
"Note that what most compilers generate is machine code, and ",
" assembly. Assembly itself is a language; just simply one that has a roughly 1:1 mapping between assembly instructions and machine code, as a way to make it much easier to program than having the programmer type in a pile of numeric opcodes. It is possible for a compiler to generate assembly code, but few modern compilers do this.",
"A slight correction to your question: languages aren't always written in lower level languages. In fact, many compiler developers aim to produce self-compiling compilers. This process is known as ",
"bootstrapping",
". Indeed, the ",
"(Oracle) Java compiler is itself written in Java",
" (albeit with a small native front-end to make it easier to run from the command line). There are a number of benefits to bootstrapping in this way, not the least of which is that once bootstrapping has been achieved, you don't need developers who are experts in two languages (the one being compiled, and the language for the compiler itself). This is generally done by first creating an initial version of the compiler (using perhaps just a subset of the language) in another language (such as C), and then re-writing it in the language of your compiler, and compiling it with the initial compiler. The Wikipedia article (linked above) has more details on why compiler developers do this, and is worth a read."
] |
[
"A ",
"compiler",
" is what is used and is a complicated subject. When a new computer processor is created, a cross compiler is made that runs on an existing processor which creates the machine code for the new computer processor. Using ",
"the LLVM project",
" it is possible to make dozens of languages work on a new computer processor in one step. Here is the documentation to create a new ",
"LLVM backend",
"."
] |
[
"A correction: Most compilers do always generate assembly code, or a low level representation that is very close to assembly code, but most modern compilers will silently and seamlessly hand that off to the system assembler (and then linker) so the user only has to invoke one program. ",
"For example, GCC produces no less than three successively lower level representations inside the compiler, and still produces assembly language as the final output. It converts the high level input into GIMPLE, then into an abstract syntax tree (AST), and then into register transfer language (RTL), and finally produces assembly as output. Each representation has a different purpose, but by the time you get to the AST you're no longer target-independent, and RTL is an assembly-like, processor-specific representation.",
"The final generated assembly is then passed on to ",
", the standard GCC assembler, and then onto the linker ",
". ",
"One major exception are ",
" that don't want the overhead of producing an intermediate representation or optimizing that representation before executing it.",
"Another major exception are ",
" whose purpose is not to generate an executable program but to convert one high-level representation into another high-level representation. An example of this would be the early C++ compilers, which took C++ and translated that code to C, which could then be compiled but the existing C compilers."
] |
[
"Would spreading sugar on an icy path have the same effect as spreading salt on it?"
] |
[
false
] | null |
[
"Sucrose in anything but nanoparticles dissolves very frustratingly slowly into liquid water at low temperatures, and even slower into ice that it's sitting on the surface of.",
"That said, sucrose-water solutions do lower the freezing point of the solution, and the saturation of the solution controls the amount of that freezing point depression.",
"So, granulated sugar onto an icy sidewalk might take hours to work vs. minutes for NaCl. If you poured syrup (a supersaturated solution) onto the ice, it would work pretty quickly meanwhile. Powdered sugar would probably be somewhere in between."
] |
[
"Do you want ants? Because that’s how you get ants"
] |
[
"This has the advantage of making the surface annoyingly sticky as it dries."
] |
[
"How do antibiotics work and how do doctors know which to prescribe to you?"
] |
[
false
] |
Anyone know?
|
[
"Bigbuddha is correct - different antibiotics have different mechanisms. The broader point is that because bacteria are quite far removed from us evolutionarily, so any chemical that can disrupt essential processes of bacteria without messing up the analogous process in our own bodies is a potential antibiotic.",
"As to your second question, there are a number of factors that doctors consider when prescribing antibiotics. Do you have any known allergies to antibiotics? What type of infection do you have? (the types of bacteria that cause a urinary tract infection might be very different from those that would infect a cut) Is there any risk of antibiotic resistance? How long will you need to be on antibiotics? (some can cause adverse reactions if you're on them for a long time)",
"There are several broad-spectrum antibiotics that can kill many types of infectious bacteria, and depending on your allergies, the first step for a simple infection is usually to use one of these. If there's something special about your infection, or if it doesn't respond to the first course of antibiotics, doctors can take a culture and the lab can analyze it to see what type of bacteria it is and if it has any antibiotic resistances that might require a different treatment."
] |
[
"Its basically depends on the antibiotic or the bacteria.",
"Some antibiotics break down the bacterias cell wall (which causes it to die when it replicates) others prevent them from making energy so they just die from lack of nourishment."
] |
[
"Antibiotics have different mechanism based on the type:",
"The beta-lactams: This includes the penicillins and the cephalosporins as the major groups. These work by preventing the cross-linking of bacterial cell wall components. Since the bacterial cell wall is constantly under construction and deconstruction, preventing cross-linking leads to the breakdown of the cell wall, killing the cell.",
"The ribosomal inhibitors: These include the macrolides, the aminoglycosides, the tetracyclines, and others. These work by inhibiting specifically the bacterial ribosome, which normally translates the bacterial genome into proteins that the bacteria need to survive.",
"The fluoroquinolones: These inhibit bacterial topoisomerase, an enzyme necessary for cell replication. Without this, bacteria can't proliferate.",
"The cell-wall disruptors (bacitracin, vancomycin): These directly break down the cell wall of the bacteria, killing them. ",
"The folate inhibitors (trimethoprim-sulfamethoxazole): These inhibit bacterial use of folate in synthesizing thymine, one of the DNA bases needed for cell replication. ",
"There are other types (including the many drugs used to treat tuberculosis, which are in a class of their own), but I just listed the previous off the top of my head. ",
"As for how to figure out which antibiotic needs to be used, it all depends on the type of bacterial infection and the location of the infection. For example, the tetracyclines are unique in that they accumulate in cells, making them useful against intracellular bacterial infections such as chlamydia and rickettsial infections. Penicillins are mostly only useful against gram-positive infections such as staph and strep (though many strains are now immune to penicillin due to resistance) and syphillis. Macrolides are used to treat atypical pneumonias, and vancomycin to treat MRSA. A lot of this is based on previous trial-and-error to see what works and what doesn't against various infections; these previous trials are clinically tested and determine the standards of antibiotic treatment for various types of infections. "
] |
[
"How much weight can a person lose by fasting for a month?"
] |
[
false
] | null |
[
"Well, if their bmr holds steady at 2,000 calories a day for 30 days, and there's no exercise, that's 60,000 calories in a month / 3500 calories per pound of fat = ~17 lbs.",
"But. the body will not only be degrading fats, there will be loss of muscle as well (which is how the body decreases bmr, after all, by scrapping muscle, so bmr decreases as muscle mass decreases, and so less fat is burned...)"
] |
[
"Please don't tell me you're asking this because you want to try."
] |
[
"Nope. Though a lot of people fast for religious reasons and such."
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.