question stringlengths 3 301 | answer stringlengths 9 26.1k | context list |
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At what point does someone stop sleeping and start being in a coma? | A person is considered to be *comatose* if they, for a period lasting **longer than six hours**, cannot be awakened, don't respond to external stimuli, lack a normal sleep-wake cycle and do not act voluntarily.
(source: Weyhenmyeye, James A.; Eve A. Gallman (2007). Rapid Review Neuroscience 1st Ed. Mosby Elsevier. pp. 177–9. ISBN 0-323-02261-8.) | [
"People may emerge from a coma with a combination of physical, intellectual, and psychological difficulties that need special attention. It is common for coma patients to awaken in a profound state of confusion and suffer from dysarthria, the inability to articulate any speech. Recovery usually occurs gradually. In... |
From an evolutionary standpoint, what is the advantage for trees that have fruit that is sour, like the Lemon, or even poisonous, like the Manchineel? I thought animals eating fruit and defecating the seeds was an important part of plant reproduction. | Some seeds prefer, or even need, specific carriers. Consider this: a mammal chews a fruit and seeds, killing the embryo, whereas a bird would simply swallow and defecate it. To prevent mammals from chewing it's fruit, peppers are spicy. This spicy flavor is undetected by birds but not mammals. | [
"The species is variable because of selection pressure by humans to produce larger, fleshier fruits with a thinner exocarp. The avocado fruit is a climacteric, single-seeded berry, due to the imperceptible endocarp covering the seed, rather than a drupe. The pear-shaped fruit is long, weighs between , and has a lar... |
when jumpstarting your car, why do you connect the black cable to the engine block instead of the black/negative terminal? | Sparks near the battery can cause hydrogen fires. Sparks near the engine block are much safer. That said, modern batteries are sealed and pretty safe, but safer is always better. | [
"As the cars came out of turn four, without any warning, USAC officials suddenly displayed the white and green flag at the starter's stand, and the race was back underway. A startled Luyendyk, running about 85 mph, hastily dropped a gear, and punched the throttle. Almost the entire field was caught off-guard and, t... |
Which non-military event had the biggest impact on the course of World War II? | I think I would go with the death of FDR. With Truman being much less experienced with foreign affairs, the removal of one of the major architects of the Allies' success changed how the war came to a close. Gone would be the issues of how much Truman knew about the atomic bomb, and there would be different questions about how the war ended in the Pacific. Just how it would be different we will never know, but *that* things would have been different is a certainty. | [
"By 1916 a new factor was emerging—a sense of national self-interest and American nationalism. The unbelievable casualty figures in Europe were sobering—two vast battles caused over one million casualties each. Clearly this war would be a decisive episode in the history of the world. Every American effort to find a... |
To what degree (if any) do personal habits (e.g. slouching) attribute to scoliosis, torticollis, etc.? | I'm an instructor for musculoskeletal anatomy, so this question caught my eye! Personal habits such as slouching, leaning, and poor posture in general can most definitely lead to abnormal positioning of the spine/neck/head. In a small percentage of cases, scoliosis, torticollis, kyphosis, lordosis can be due to birth defects, but typically they are not conditions that occur with acute onset. These conditions arise as a result of repetitive sheer loads we place on our spines over long durations (we're talking many months). Basically, if the spine is in a compromised position for a long period of time , the muscles that attach to the spine loosen or tighten and can pull the vertebrae into misalignment. This misalignment can be prevented with regular breaks from slouching (leaning, etc.), exercise, and the conscious effort to sit/stand with good posture.
| [
"Scoliosis, is a medical condition where a person's spine has several irregular curves that are located between the neck and the pelvis. Symptoms of scoliosis in mild cases usually exhibit abnormal posture, back pain, tingling or numbness in the legs and in worse cases can exhibit breathing problems, fatigue, perma... |
Can wifi ever be as fast as fiber? | Fiber has a few advantages over wireless (I'll lump more RF technologies with WiFi, as WiFI is really more intended for local communications) it is not just about speed:
Range- With fiber a 10 miles is no big deal, longer transmission is not much harder although the optics are more expensive. Wireless requires large towers to get similar transmission distances
Reliability- Wireless gets somewhat problematic in poor weather conditions. The only weather concerns I have heard of with fiber is ice crush, and that is easily designed around.
Network equipment capacity- when using a wireless method, generally each node is a repeater. Each repeater has to handle all the traffic, with fiber, individual fibers can be patched, bypassing the active equipment at any given shelter
Network spectrum- Wireless technologies only have so much spectrum allocated, when the traffic fills that spectrum you need more spectrum allocated (FCC) or you are done. With fiber, land is the most expensive part, adding an additional cable is repetitively low cost. Also installed 144 strand fiber cables are not that much more expensive than 12 strand. At least where I work we always install way more fiber than we expect to need in the near future, as it is cheater leave dark fiber than to go back and add more. This also leaves redundancy in case a fiber (or more likely a buffer tube of 12) goes bad.
Security: While there are ways to encrypt wireless signals, it is also possible to intercept wireless signals. Intercepting fiber signals is significantly harder, you need to physically intercept the cable. It reduces on possible point of intrusion.
I am sure there are more but these are the ones that I hear about most often. Reliability is for my by far the biggest reason for fiber.
Source: I design Intelligent Transportation Systems which require remote network connections, including fiber and wireless (we prefer fiber) | [
"In years 2012–2015 the data transfer speeds will be increased, so that the end users connected through the fiber-optic cabling will get speeds up to 2.5 gigabits, those with copper a speed of up to a 100 megabits and those connecting through wireless at either 42 or 100 megabits per second depending on the technol... |
What psychological techniques can be used to counteract procrastination? | Everything you want to know is in this previously, exhaustively explored thread: [Why do humans procrastinate and how can it be beat?](_URL_0_) | [
"Aversives can be used as punishment during applied behavior analysis to reduce unwanted behavior, such as self-injury, that poses a risk of harm greater than that posed by application of the aversive. Aversive stimuli may also be used as negative reinforcement to increase the rate or probability of a behavior by i... |
Why is the Great Leap Forward considered the biggest famine of all time? | You are suffering from a strong mathematical fallacy, based on notation. Rate is the _portion_ of the inititial population that expired from famine. When you use the phrase 'biggest famine' you are talking about raw death _counts_, not the death _rate_. If the only two people on a deserted island starved, by your metric, it would be the greatest famine of all time at a 1000:1000 rate. Instead, it's important to note that the 'size' of a famine refers to the total number dead (ignoring initial population), and not the _percentage_ affected of the initial population. Although other regions may have had higher rates (even through antiquity), the initial _population_ of 1950's China during said famines was high enough to negate the lower decay rate.
**Conclusionary**: Assume two countries/populations, 'Cat' and 'Dog', both have famines. Cat has a death rate of 10:1000, while Dog has a death rate of 50:1000, five times larger. Clearly, Dog has had a far more devastating famine, as a greater _portion_ has died. However, lets assume that Cat initially had a much larger population of 20 million, while Dog has a pop. of two million (1/10). Cat will have suffered 200k deaths, while Dog suffered 100k deaths. Cat had a famine twice as great (numerically), despite having one-fifth the death rate.
Another issue here is that you list a rate for _each year_; they stack! The death rate for 1959 only applies to the people who didn't die in 1958! So lets assume a model population of 1000. The first year, 1958, 11.98 die leaving a pop of 988. The next year, 1959, 1.459% of the _remaining population_ dies, leaving 988 * (100%-1.459%), or 973. Repeating this (iterative) process through your last point, 1961, gives a remaining pop of 935 after the four year period. That means that in the 4 year period, the famine caused a _total_ loss rate of 65:1000! | [
"Benjamin Valentino claims that the Great Leap Forward was a cause of the Great Chinese Famine and the worst effects of the famine were steered towards the regime's enemies. Those labeled as \"black elements\" (religious leaders, rightists and rich peasants) in earlier campaigns died in the greatest numbers because... |
How close was Japan to cracking Navajo code talkers? Was Japan aware Americans were using a Native American language as code? | I did a research project with Navajo sources on this. It sadly never was finished and published, but I was able to use local archives, talk to members of the Navajo community about their verbal histories and study the US military documents regarding the code. I was also studying Navajo Language at time as I am not Navajo or a member of any tribe.
Four separate things kept the Navajo code from being cracked. In order of importance, this was the code itself, the Navajo language, it's use, and the Japanese intelligence community.
The code itself was relatively simple and was a glorified slang with a weird syntax. With applications for the military alphabet. Here is an example of ship names provided by the CIA [_URL_8_](_URL_8_). In English or any other language this could be cracked with time. Imagine a modern US infantry squad calling for "Apache support". To someone without knowledge of US weapon systems, this would seem like a very strange request. However after a few times hearing that and having helicopter gunships show up, the link could be drawn and part of the code could be cracked.
The next step in encryption that kept it safe was the language itself. Navajo is certainly one of the most difficult languages in the world to learn. Very very few non-Navajo have ever been nearly fluent in the language. Navajo heavily relies on inflections of tone and use of nasal noises on vowels, so simple changes in pitch of a vowel mean a completely different word. It is also extremely specific on conjugating verbs, using singular, dual and plural. Among many other complexities.
Navajo was (it's doing much better now due to many programs and educational outreach), a dying language and very few texts on it existed at the time. It's language family is the Athabaskan language, composed of a few other tribal languages in the American SW and several in central and western Canada. This is not a language where one could go pick a book off the shelf.
There was a Navajo POW in Japanese captivity, Joe Kieyoomia, who was not part of the Code Talker program. He was forced to listen to the transmissions by his captors. The Japanese had studied the Navajo transmissions and had narrowed it down through a lengthy process (I cannot understand Japanese so I was unable to read the primary sources on this, sorry for the vagueness), to figure out that it was Navajo. Kieyoomia listened into these transmissions and heard phrases like "Red soil ahead" among all of the organizational information that was also coded. He thought it was complete gibberish, and told the Japanese that it made no sense. The Japanese thought he was lying, and I'll get into their response more to the code later, and tortured him regularly in an attempt to get more information about the Navajo language and code out of him.
Third, the Navajo Code was a tactical, and very rarely strategic code that was only submitted verbally. The Navajo Code was never used in a written form. If it had been, it could have been subjected to the same methods of code breaking that the world was using on operational and strategic codes like Enigma. The Navajo code was far less complex than Enigma and would not have held up well to such attacks. Audio recordings on wax cylinders were expensive and difficult to maintain in the Pacific theater, so even recording the radio messages that the Code Talkers sent was incredibly difficult.
The Navajo Code was not only used on a tactical level, but on a much smaller scale than US operational codes. When the Code Talkers program was under development, it's major selling point wasn't it's heavy encryption, but time. The current way for US forces to communicate on a open level was either "in the clear", i.e. just over the radio, or to use an encoding machine that usually took about an hour to encode and decode messages. The latter wasn't great when you needed fire support, and the former the Japanese heavily exploited with their relatively high percentage of fluent English speakers. They did so both gathering intelligence on American activities and sending false messages to sew confusion and disorder.
Code Talkers on the other hand, could communicate messages to other Code Talkers nearly instantly. Fire support, movements, positions, could all be transmitted nearly "in the clear" in terms of speed. Also, Code Talkers worked like a sort of passcode, or key. With Navajo being so complex and the Code Talkers being such a small group, they were able to absolutely recognize and know each other during transmissions. And once attached units also recognized this, Code Talkers messages were treated as critically important, the Japanese couldn't falsely transmit them. There are cases of false Japanese messages being sent out as if they were American, and then Code Talkers letting everyone know of the real situation. This uniqueness kept the code in the military arsenal (and the Navajo language was classified) until 1965, when frequency hopping radios started to become available and replaced the Code Talkers concept.
Finally, the Japanese Intelligence Community. I again, do not understand Japanese, so none of this is a primary source and I won't go into much detail as it is not my expertise. The Japanese Intelligence Community was an absolute shambles. The Army/Navy rivalry was replicated between the different organizations, resulting in no real clear unified efforts and quite a few efforts to steal glory from each other. There were more focused on American operation codes that were transmitted in text, far more regularly and often and contained more information. It also seems that Kieyoomia's resistance to Japanese efforts also led the Japanese to believe that it really was just the language, and such limited their code breaking efforts there.
The Navajo (and others!) Code Talkers provided a critical role for the Allied war effort. Much of the information on the Code Talkers is still only in verbal histories. There are many issues regarding Tribal Sovereignty around collecting this information and publishing it, so information can be hard to come by. I highly respect those issues and recommend you all do too.
Thanks!
As a post script, the Germans actually sent Anthropologists to the US during the inter-war to study Tribal languages after the success of similar Tribal Code Talkers in WW1. I have been unable to find if this information was ever put to much use, as other tribes' Code Talkers were used in the European Theater.
Edit: Thank you for the gold, but please, please stop. I wrote below about the commodifying of cultural knowledge, and this is exactly what I was speaking about. I give this knowledge freely, and ask that if interested, you all check out Navajo sources for more info! Or just go check out r/Navajo to see what the Navajo Nation is like today!
Also, this wasn't a thesis project or anything big like that, it was just a semester undergrad research project that I really felt a calling to. I apologize for any confusion there.
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Recommended Readings (UPDATED!):
You can read an HTML version of the codebook here: [_URL_6_](_URL_6_)
Code Talker: The First and Only Memoir By One of the Original Navajo Code Talkers of WWII by Chester Nez
Diné Bizaad Bínáhoo’aah: Rediscovering The Navajo Language
Philip Johnston's letter to the USMC on starting the program: [_URL_5_](_URL_5_)
The Rising Sun by John Toland (For a detailed look of how the Japanese fought the war)
A great source of photos of Code Talkers during the war: [_URL_2_](_URL_4_)
A 1979 Article on Code Talkers from The Gallup Independent: [_URL_1_](_URL_0_)
A more recent (2001) article on how the code was developed: [_URL_7_](_URL_7_)
The NAU Cline Library "The Navajo Code Talkers Collection" was extremely helpful in my research you can search through all the primary sources here: [_URL_3_](_URL_3_) | [
"The Japanese tried unsuccessfully to have him decode messages in the \"Navajo Code\" used by the United States Marine Corps, but although Kieyoomia understood Navajo, the messages sounded like nonsense to him because even though the code was based on the Navajo language, it was decipherable only by individuals spe... |
why do i sometimes see ads for the service i'm using to see the ad? | Because self-promotion is a way to retain customers. Also, they're usually ads for Pandora's premium service right? | [
"An ad in the lower third of a TV screen during a show helps to remind people what network they are watching. Called a snipe, this type of promotion targets people, especially younger people, who are used to seeing such items when they look at computer screens or cell phones. Some people have criticized the practic... |
why isn't the remote finder feature common on tvs? | Most TVs use IR (infrared), which require line of sight to the TV - (the remote sends a series of invisible 'blinks', like morse code).
The TV doesn't have a way to send a blink out, and even if it could, the remote is probably lodged inside a couch saying "screw you hippy i'm taking a nap, come and find me, suckah".
If the TV used RF (radio frequency) then it could do that, but then the remote would have to listen for that RF signal, which would eat up the batteries.
| [
"RemoteView is an electronic light table application, initially developed and released commercially by Sensor Systems in 1996. An electronic light table application makes it possible for imagery analysts to review satellite images on a computer instead of examining film or printed photographs. RemoteView was origin... |
how on earth is it a good idea to cross lanes of traffic like this on an overpass? | Cloverleafs are super-expensive to build, and stoplights cause inefficient traffic. In this design, there are only two stoplights (at the crossover), and only two turnabouts. Cars from the surface road don't have to stop at *any* stoplights before getting onto the highway if they're turning right; neither to cars getting off the highway (again, if they're turning right). Cars making left turns only pass one of the stoplights; only through-traffic on the surface road stops at both lights. | [
"Pedestrians may dislike using crossing at intersections for other reasons, such as being uncomfortable dealing with traffic from several directions (whereas a jaywalker at a location distant from an intersection only needs to observe two directions of traffic), or wanting to avoid the extra air emissions generated... |
Did America's founding fathers believe the country would become a super power of the world in the next centuries? | It depends. More than likely, no. The thing about the founding fathers is that none of them ever agreed on anything. George Washington was an adamant isolationist, which is why the US broke their treaty with France to help them during their revolution like they did for us.
After the US gained independence from Great Britain, there were two major ways of thinking, the first being that to maintain and grow our new country we must remain isolated and not get involved in global politics, which is what George Washington wanted. The second was more like "HOLY SHIT WE JUST BEAT THE GREATEST SUPERPOWER IN THE WORLD WE CAN DO ANYTHING LET'S GET INVOLVED IN THE ENTIRE WORLD!" which was more Thomas Jefferson's way of thinking.
In the end, obviously the viewpoint of the President won, and we remained isolated for the time. So my answer would be that no, the founding fathers did not anticipate being a superpower. | [
"The \"American Century\" existed through the Cold War and demonstrated the status of the United States as the foremost of the world's two superpowers. After the Cold War, the most common belief held that only the United States fulfilled the criteria to be considered a superpower. Its geographic area composed the f... |
if cancer is basically a clump of cells that dont want to die, why/how do things like cigarettes, asbestos, and the literal sun trigger it? | Cancer cells result from mutations that disable the things that keep cell growth in check. Those mutations come from incorrect repairs to cell DNA, and those errors happen more frequently the more repairs take place.
Therefore things that cause damage that requires repairs increase the chances of developing cancer, stuff like cigarettes, asbestos, and sun exposure. | [
"Some substances cause cancer primarily through their physical, rather than chemical, effects on cells. A prominent example of this is prolonged exposure to asbestos, naturally occurring mineral fibers which are a major cause of mesothelioma, which is a cancer of the serous membrane, usually the serous membrane sur... |
how is it that the president can have the authority to authorize a nuclear attack but not a travel ban? | He actually does have the authority to implement a travel ban under section 212(B) subsection F of the immigration and nationality act.
_URL_0_
"Whenever the President finds that the entry of any aliens or of any class of aliens into the United States would be detrimental to the interests of the United States, he may by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate."
Judges, however do have the ability to block any law that they deem unconstitutional which is what happened in this case. So from here, the justice department will issue an appeal of the judge's decision, it will move to a higher court and we'll start the process over | [
"Only the president can direct the use of nuclear weapons by U.S. armed forces, through plans like OPLAN 8010-12. The president has unilateral authority as commander-in-chief to order that nuclear weapons be used for any reason at any time.\n",
"In the 115th Congress Lieu introduced H.R. 669 – Restricting First U... |
Plasma Gasification? Thoughts Please | From a chemical standpoint, the biggest problem with plasma gasification is that it makes big assumptions as to the chemical composition of the input waste (i.e. it's not energy-generating if you "feed" it the wrong things.) Beyond that, they are complicated and rely on high temperatures, which means that even if you can (theoretically) have a net energy increase, that won't necessarily offset the large costs of keeping the thing running. | [
"Plasma gasification is an extreme thermal process using plasma which converts organic matter into a syngas (synthesis gas) which is primarily made up of hydrogen and carbon monoxide. A plasma torch powered by an electric arc is used to ionize gas and catalyze organic matter into syngas, with slag remaining as a by... |
can somebody please explain cosmic microwave backgorund radiation? | When the universe was very young—as in, less than 400,000 years old—it was very, very hot. It was so hot, in fact, that matter couldn't exist except in a form called "plasma". This is the kind of stuff the sun is made out of, except the plasma at that time was much hotter than the sun. One of the things about plasma is that light can't travel through it very well. The sun gives off a lot of light, but you can't really see into it, and if you were inside of it you wouldn't be able to see very far at all. So while the universe was in this state, all of the light that existed was sort of trapped and unable to move around freely.
Eventually, the universe cooled down and expanded enough that the plasma turned into an actual gas. When that happened, the light was no longer trapped and could stream out across the universe. This light filled the entire universe at that time. What happened to it? Well, it's still there. Except that the universe has gotten much colder and expanded a lot more since then, so not it's very, very faint. We call that light the "cosmic microwave background radiation": cosmic, because it's related to space; microwave, because that's the kind of light it is; background, because it exists everywhere, kind of in the background underneath any other light you might see; and radiation, because light is a kind of radiation.
What's so important about it? Well, first it was predicted before it was discovered. Some people were thinking about the idea of the Big Bang and realized that if the theory were correct there should be this background radiation, but no one had seen it anywhere. Then, some time later, some people were looking at the information they'd gathered from a telescope and noticed some "noise"—apparent light that shouldn't really be there. They tried a lot of things to get rid of the noise but nothing worked. Then one of them got the idea to see if it matched the light that had been predicted, and it did. Future tests confirmed that it was, indeed, precisely what the Big Bang model had predicted. Thus, it served as evidence that the Big Bang model was correct.
Also, by studying the light very closely and looking at how it changes depending which part of the sky you look at (remember, it's everywhere, so you will see it no matter where you point a telescope that's capable of "seeing" it), we are able to get information about the shape of your universe and the conditions at the time the light was created some 13 billion years ago. | [
"A major recent focus of microwave radio astronomy has been mapping the cosmic microwave background radiation (CMBR) discovered in 1964 by radio astronomers Arno Penzias and Robert Wilson. This faint background radiation, which fills the universe and is almost the same in all directions, is \"relic radiation\" from... |
why did pilgrims wear buckles on their hats? | Contrary to popular myth, capotains never included buckles on the front of them; this image was created in the 19th century. | [
"The capotain is especially associated with Puritan costume in England in the years leading up to the English Civil War and during the years of the Commonwealth. It is also commonly called a Flat Topped Hat and a Pilgrim hat, the latter for its association with the Pilgrims who settled Plymouth Colony in the 1620s.... |
how is fm radio still thriving as much as it supposedly is as a media source? | It's possible but the radio is also an easy way to hear new music. Some people don't want to decide which music to listen to or go out searching for a podcast, most morning radio shows have some music but also a talk show, which is a great way to get news. Add on that radio is free and many blue collar shops (mechanics and the like) still use radios on the work floor, FM has some time left. | [
"The consensus about radio in Canada as well as in most parts of the world is that it is a dying medium. With innovations such as television and the Internet, which have allowed for audio communication paired with visual, there has been less need for radio. Furthermore, the introduction of personalized and portable... |
Double slit experiment: what happens if you move the slits further apart? | Diffraction only happens when the gap is roughly equal to the wavelength of the wave passing through it. If you increase the size of the gap, diffraction just won't happen and the wave would pass through it like it would a doorway. | [
"In the double-slit experiment, the two slits are illuminated by a single light beam. If the width of the slits is small enough (less than the wavelength of the light), the slits diffract the light into cylindrical waves. These two cylindrical wavefronts are superimposed, and the amplitude, and therefore the intens... |
Does a galaxy receding from us at close to the speed of light due to the expansion of space experience time dilation and length contraction from our perspective? | The answer is **yes, at least in some way**. But to fully understand this you have to realize that the insights from special relativity can't be used in the big picture of cosmology. This means, among other things, that the special relativistic doppler formula should not be used to calculate the velocity of distant galaxies. Only **general relativity** can fully describe the picture and eliminate contradictions.
Nonetheless, there are relativistic effects (as predicted by *special relativity*) observable related to your actual question:
The effect of **time dilation** has been observed in **distant supernovae**. When a supernova in a galaxy close to us would take 20 days to decay, the same type of supernova will appear to take 40 days to decay in a distant galaxy with an observed redshift of z=1. ([relevant paper](_URL_0_))
Whether something is moving away from you or the space between you and the object is expanding is merely a choice of coordinates. In the first coordinate system, the spatial position of the galaxy changes which results in a redshift. In the latter one, the distance between fixed points in space would increase over time, again causing a redshift.
**However, if a galaxy recedes from us faster than the speed of light it does not appear to go backwards in time**. It gets more and more redshifted. Even as it appears to travel faster than the speed of light. (Or starts to move close to the speed of light if you include special relativity in your calculation.) If that doesn't really make sense, remember that, as already stated, only general relativity can eliminate these inconsistensies.
edit: formatting | [
"Current evidence suggests that the expansion rate of the universe is accelerating, which means that the second derivative of the scale factor formula_23 is positive, or equivalently that the first derivative formula_24 is increasing over time. This also implies that any given galaxy recedes from us with increasing... |
can someone explain how to start your own company? | I regrettably don't have any first-hand experience, and I also would like to know more about this question, but I can offer what I witnessed from my mother starting her own company:
Know your shit. There's a lot of legal aspects to starting your own business (licensure, permits, documentation, etc.). I'm fairly sure it varies by state, possibly even down to the county level, depending on where you are. I know my mom had to do a LOT to get her business established, and I remember being extremely glad I wasn't the one going through it.
Best of luck, and hopefully someone can provide us with a real answer :-/ | [
"Founders with an early-stage company are faced with the challenge of building a team with minimal people and cost. The process starts by listing out basic functions of a particular company (e.g., engineer, operations, finance) and then stripping down to the abstract job activities and skills that the company must ... |
What are some real world applications of the infinite sum of natural numbers? (1+2+3+...=-1/12) | First, let me stress this: 1+2+3+… does NOT equal -1/12. You can see my explanation in [this thread](_URL_0_).
The application of the regularization technique that has us replace that infinite sum with -1/12 probably rose to attention in recent years due to its appearance in one approach to the calculation of the number of dimensions in which string theory makes sense. What matters in string theory is that a particular symmetry, known as conformal symmetry or Weyl symmetry, must be preserved in order for the theory to be mathematically sensible; this condition leads to the determination of the critical dimension in string theory, and the regularization of the sum 1+2+3+… is required in one standard approach to the relevant calculation.
It is also quite generally useful for calculating [the first quantum corrections](_URL_1_) to classical field theories.
David Tong's [string theory text](_URL_2_) discusses this particular sum. As a warm-up, he uses this regularization result in a treatment of the Casimir energy in one-dimensional systems on pages 38-40 (the Casimir energy is a quantum feature of the vacuum) and then returns to a more careful treatment in Chapter 4, where he shows the relevance to string theory. (This latter treatment is certainly not for the faint of heart.) | [
"In physics, approximations of real numbers are used for continuous measurements and natural numbers are used for discrete measurements (i.e. counting). It is therefore assumed by physicists that no measurable quantity could have an infinite value, for instance by taking an infinite value in an extended real number... |
why do some radios only come with the fm station and not the am | AM (_URL_1_) and FM (_URL_0_) radio are two different ways of encoding audio in a radio signal. the actual mechanics of converting the radio signal into audio you can hear are different, and the two different method require different circuitry or software to decode the signal.
because of it's poorer audio quality, AM radio has fallen into disfavor for most broadcasting, and while it is still very widely used in the US, it's not be as popular, and is more widely used for Talk Radio, where audio fidelity isn't as important as for Music.
Some radios will only include the circuitry for FM radio, because that's all they expect their users to actually listen to. | [
"BULLET::::- \"AM(/FM) only radio\": Before FM radio receivers came to the market, AM receivers were simply just known as radios. However, as AM/FM radios started to include turntables, tape players, CD players, and later on analog AUX inputs, satellite radio and even USB, AM/FM radios without bells and whistles wo... |
Why have so few transdermal medication patches been developed? | This doesn't completely address the question, but transdermal medications can have variable efficacy in elderly patients, as their absorption through the skin is often dependent upon hypodermal fat. As people age, this fatty layer decreases. Considering a bulk of pharmaceutical use is among the elderly, it stands to reason that oral/injectable medications would be more ideal in treating chronic disease in this patient population. | [
"A transdermal patch is a medicated adhesive patch that is placed on the skin to deliver a specific dose of medication through the skin and into the bloodstream. Often, this promotes healing to an injured area of the body. An advantage of a transdermal drug delivery route over other types of medication delivery suc... |
why are all podcast ads for subscription services? | Subscription services are just a very popular startup business model currently, it’s a really successful one as subscription services generate good, solid, predictable, and real cash flows (of course only for those that succeed). Subscriptions are an amazing business to be in for most any company over a la carte sales.
Podcasts offer cheap as hell advertising and they can target their demos well. For new emerging companies it’s a pretty good option compared to far higher priced digital ads on stuff like FB or google | [
"Contemporary talk, music, sports and newscasts are significantly branching out to the internet and Smartphone App choices such as TuneIn Radio. Many independent and liberal talk show hosts offer podcast (digital audio Play-On-Demand recordings, see also iPod) subscriptions in order to support their on-going broadc... |
is it cheaper to automate processes than to outsource them to cheap labour? | It really depends on the product, the process and the size of the run. If you are trying to perhaps, bottle beer, or box cereal, a simple, constant product and process, automation makes sense if demand is high. You really don't want workers putting bottles of beer in six pack holders all day, and then placing them into cartons.
On the other hand, if you are making short run products, 100 of these, 50 of those, then automation becomes less important and flexibility becomes more important. For example, if you only make 20 jet engines a week, but the engines are of four different types than only certain aspects can be automated.
However, if you want to eliminate unskilled labor, like fork lift drives, box closers, packagers, assemblers, and demand for the product will exist for a long period of time, then automation becomes cheaper than unskilled labor. | [
"The machine is able to replace a worker, who works at one specific job with one tool, with a mechanism that accomplishes the same task, but with many similar tools and at a much faster rate. One machine doing one specific task soon turns into a fleet of co-operating machines accomplishing the entire process of pro... |
How does heat travel at an atomic level? | Temperature is a bulk property of matter- it doesn't make sense to talk about a "hot" atom or a "cold" atom- only large collections of atoms have a defined temperature. So, it doesn't really make sense about a "hot" atom coming into contact with a "cold" one.
In general though, when heat flows from one object to another, it is done through kinetic transfer. Faster moving/faster vibrating/etc atoms come into contact with slower moving/slower vibrating/etc atoms and impart to them some of their kinetic energy. | [
"Heat is defined as energy, and as such, it moves from higher levels of energy (i.e., temperature) to low. At the atomic level, heat is the motion of the atoms and electrons that make up a material. The more the particles move, the higher the heat. Excited particles bouncing off each other transfer the heat, moving... |
Why exactly do teeth have nerves? | Your jaw is extremely powerful and if you exerted its full force on your teeth you could shatter them. The nerves give you some indication of the pressure you're applying. | [
"Nerve fibers start to near the tooth during the cap stage of tooth development and grow toward the dental follicle. Once there, the nerves develop around the tooth bud and enter the dental papilla when dentin formation has begun. Nerves never proliferate into the enamel organ.\n",
"Cranial nerves are the nerves ... |
how does a heat pump work? | It's basically air-conditioning in reverse. The compressor increases pressure and concentrates heat on the refrigerant flowing to one coil while a fan moves air through it, heating the air and cooling the coil. This now cooled refrigerant flows to the metering device. These can be as simple as a stopper with a tiny hole or a dynamically adjustable valve. Passing through this restriction drops the pressure and spreads the heat back out, lowering the temperature of the refrigerant as it flows into the second coil. A second fan moves air through this second coil, this time raising the temperature of the coil and cooling the air. The refrigerant now flows back to the compressor, repeating the cycle.
In a heat pump, the first hot coil would be connected to indoor air. And the second cold coil would be using outdoor air. On a standard heat pump unit there is a "reversing valve" which changes the direction of the flow. Making the outdoor coil the hot one and the indoor coil the cool one. This produces air-conditioning.
As you can see in both instances very little heat is actually produced, but rather it's moved. Heat is moved from outside to inside in heat pump mode and the opposite for cooling mode.
Since we are moving heat that's already there, that's why heat pumps struggle to produce enough heat when it's very cold outside. Most units will have a less efficient source of backup heat that actually generates heat rather than moving it. Running this along with the heat pump is "Aux" heat. Emergency is running this backup heat alone.
Source - Former HVAC Service Tech | [
"A heat pump is a device that transfers heat energy from a source of heat to what is called a heat sink. Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses external power to accomplish the work... |
What happens to the mitochondria as an animal ages? Are their fewer per cell? Are mitochondria less efficient? | I would research this more using google, but from the literature that I’ve read, it appears that mitochondrial dysfunction occurs over time, and more mitochondria exist in cells that do not replicate (in G0, so muscle cells for example) as time progresses.
Not sure what the implications for this are, but I’d give this a read: [Mitochondria and the aging heart](_URL_0_) | [
"The ability to ingest other cells enabled ancestral eukaryotes to build a much more complex cell. Once the capacity for consuming other cells was in place, early eukaryotes began to acquire internal membrane-bound organelles that included organelles that were once free-living prokaryotes. Based on phylogenetic and... |
what is happening when i turn off the television and the lights, and the television still looks to be dimly lit? | You mean old CRT TVs? The way those work is the back side of the screen is coated in phosphor. The TV makes images by firing a beam of electrons at the phosphor coating, making it glow. The beam moves from left-to-right and top-to-bottom, redrawing the entire screen many times a second.
When the electron beam stops, the dot stops glowing. It loses *almost* all of its glow in less than a tenth of a second, but it doesn't lose *all* of its glow for a good while. If you're in a completely dark room, and your eyes are adjusted, you can see the residual glow. It's quite dim, even to start with, and loses all its brightness over the course of a few minutes, the same way a glow-in-the-dark toy does. | [
"Many televisions and monitors automatically degauss their picture tube when switched on, before an image is displayed. The high current surge that takes place during this automatic degauss is the cause of an audible \"thunk\" or loud hum, which can be heard (and felt) when televisions and CRT computer monitors are... |
does a baby smell like s mix of its parents or a new smell to an animal with a more sensitive ability to detect odor? | While extensive studies have been done examining the ability for parents and newborns to identify each other VERY quickly after birth, I don't think there's yet been investigation into the similarities of babies to their parents. But given that dog trainers encourage new parents with dogs to first bring a blanket the baby has been wrapped in home for the dog to acclimate to the new smell, the baby's scent is likely to be different *enough* from its parents for dogs to treat it as a new smell. This also makes sense with what we know about the differences in smell that humans undergo as part of puberty: even if babies smelled similar to their parents in some identifiable ways, they wouldn't smell the same because the parents are adults and the baby is not. | [
"Physiological, behavioral and anatomical evidence show that some species may have a functioning olfactory system in utero. Newborn infants respond positively to the smell of their own amniotic fluid, which may serve as evidence for intrauterine olfactory learning. Mammals’ sense of smell becomes mature at an early... |
the marvel cinematic universe and the film rights to their respective characters in the marvel comic universe. more specifically, quicksilver & scarlet witch. | Quicksilver and Scarlet Witch occupy a weird little grey area in the usage rights that Marvel licensed to Fox. They're mutants, children of Magneto, so they're part of the X-Men franchise. So Fox can use them. However, they're *also* long-term Avengers, and -- unlike Spider-Man and Wolverine -- most of their comic book history has *been* as part of the Avengers, and not with the X-Men franchise. So it's natural for Marvel to use them. Marvel and Fox could have had a big brou-ha-ha over who got to use the characters, but instead worked out an arrangement so that each company could use the elements of the character that is relevant to their franchise. That is, Fox can use Scarlet Witch and Quicksilver as mutants and children of Magneto, but cannot reference their history with the Avengers. Marvel Studios can use Scarlet Witch and Quicksilver as members of the Avengers, but cannot reference X-Men or Magneto, and -- probably -- cannot directly call them mutants. (They'll just be people who have their super powers naturally but the reason why is likely to be glossed over.)
I don't know enough about Django's appearance in *A Million Ways to Die in the West* to answer that question. Was Django present as a full character, or just a cameo? If so, was he *actually* Django -- as in, called such by name -- or was he just Jamie Foxx dressed like Django? There's enough room in the difference between the two that it's possible a small usage could skate through, especially given that parody (which I know AMWtD is) is protected speech. (Of course, it's also possible Weinstein just licensed the use of the character to AMWtD.) | [
"Marvel Studios launched the Marvel Cinematic Universe in 2008, focused on the Avengers and their related characters, whose film rights they still owned. Marvel was then bought by Disney in 2009, but could not use the X-Men or their related characters. Quicksilver and the Scarlet Witch were an odd case, as they had... |
Does hair grow at a constant rate or in bursts? | Generally our hair grows fastest in the summer and it is more productive when people reach 15-30 years. After this period, as we become older, the natural hair growth process slows down considerably.
Stress is a major cause of countless health problems and hair is no exception. Constant stress can lead to severe hair loss problems, hampering proper hair growth.
A healthy, balanced diet promotes a better functioning of your cells and hair follicles, thus increasing hair growth. A diet rich in proteins and sulfur optimizes the growth of hair.
Regular workout will improve blood circulation, which delivers nutrients and vitamins to your scalp.
All of the above affect hair growth, and your hair can grow faster/slower at times in accordance with these factors. So, in response to your question, your hair does not always grow at the same rate. | [
"The three stages of hair growth are the anagen, catagen, and telogen phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The rate or speed of hair growth is about 1.25 centimetres or 0.5 inches per month,... |
Katyn Massacre and Nazis | Although only focused specifically on Katyn for a small portion, [this](_URL_0_) will likely be of interest for you. | [
"The Katyn massacre (, \"Katyń crime\"; \"Katynskaya reznya\", \"Katyn massacre\", or , \"Katyn execution by shooting\") was a series of mass executions of Polish military officers and intelligentsia carried out by the Soviet Union, specifically the NKVD (\"People's Commissariat for Internal Affairs\", aka the Sovi... |
Why can't we capture carbon with trees or technology? | Well, we can. And up to a point, we do.
The follow up question which will immediately pop up in your mind, is why it isn't a greater deal, and the short answer to that is that we've just begun looking into it, and of course cost and scale. Yes, it's expensive. And yes, people object to large-scale geo-engineering projects in their back yard (go figure...)
Now:
Trees ... we are currently in an unprecedented time of reforestation. Tens of thousand of previously cultivated square kilometers of land are being returned to fallow or being actively reforested. However, the impact of that in terms of C sequestration is relatively minor as tree growth is slow, and the gain in forest areas is small in relation to the volume of the atmosphere. Potentially more effective, but equally more controversial, would be sequestration in artificially cultivated/fertilised phytoplancton blooms. But there would be concurrently larger side effects to that as well, in terms of anoxia and acidification, if not done right.
A more technological approach currently in use in underground CO2 sequestration in oil/gas reservoirs. The CO2 is injected into a geological reservoir which used to contain hydrocarbons (or even used to push out some more production ... see "economics"), and stored there. Neat, elegant ... and expensive. But it is starting to happen [example](_URL_0_).
see also: _URL_1_
Other approaches are also under study, but are further from being deployed, or are in use at various scales.
See also:
_URL_2_
_URL_3_
| [
"Real or cut trees are used only for a short time, but can be recycled and used as mulch, wildlife habitat, or used to prevent erosion. Real trees are carbon-neutral, they emit no more carbon dioxide by being cut down and disposed of than they absorb while growing. However, emissions can occur from farming activiti... |
why do people on reddit care so much about comment and link karma? | Human brains love being rewarded, even if that reward is just positive feedback (in the form of an upvote or a comment agreeing) from other anonymous users. It creates pleasure to get link and comment karma and displeasure to lose it.
Also if you have low karma it makes it harder (slower) to use the site. | [
"Since 2006, each user has the opportunity to express their opinions on the site, by pressing the '+' or '–' button for comments and posts. In the same way, they can express their attitude to each individual user on their profile page. Depending on the number of the '+/-' entries the user receives, it is shown as a... |
why do i have to be 18 to buy a lighter? | Because that's the legal age to buy tobacco and tobacco paraphernalia? | [
"Disposable lighters sold in Australia, Canada, New Zealand, and the United States (since 1994) must incorporate child-resistant features. The European Union added the same standard in 2010. The inexpensive alterations have resulted in fewer juvenile-set fires and deaths. One firefighter was quoted as saying \"Chil... |
Dual pregnancy by two different men? | Yes, it's possible to have multiple ova fertilized by sperm from different men. Sperm can live for several days, and multiple ova can be released over the course of several days in a single ovulation cycle. That means it's possible for more than one ovum to be fertilized and implant, resulting in a pregnancy of multiples with different paternities (I've only ever heard of this happening with twins, but triplets, etc., aren't impossible).
As DNA testing has become more common case reports have come out verifying the different paternities of twins. [Here](_URL_2_) is an example from the 1970s, and [here](_URL_1_) is one from the 1990s.
The phenomenon of having two ova fertilized in two seperate coital events is often referred to as "superfecundation". It technically refers to any instance in which more than one egg is fertilized in more than one act. Instances where the paternity differs is referred to as "heteropaternal superfecundation". [One study estimated](_URL_0_) that 1 in 12 sets of dizygotic twins born to married white women in the US were the result of superfecundation, while 1 in 400 were the result of heteropaternal superfecundation.
Edited for clarity. | [
"Twins are two offspring produced by the same pregnancy. Twins can be either \"monozygotic\" ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or \"dizygotic\" ('fraternal'), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm c... |
What is the precedent for the 'one phone call' if you are arrested? | Turns out it's just a Hollywood invention, in real life if you're arrested it looks like in some places they aren't even required to grant you a single phone call, and in others it's stipulated as a "reasonable" amount of calls. If you'd like to read more - _URL_0_ | [
"Arrests under English law fall into two general categories—with and without a warrant—and then into more specific subcategories. Regardless of what power a person is arrested under, they must be informed that they are under arrest and of the grounds for their arrest at the time or as soon after the arrest as is pr... |
buddism | This may not be something a 5 year old will 100% understand, but I am explaining a religion here so I'll do my best to keep it simple.
Buddhists believe that:
1. Everything is always changing, nothing stays the same, by accepting this you will no longer hold on to things that cannot last- this helps them accept death etc.
2.There is no self, this is based off Hindu beliefs of finding a self but the Buddha said there is no self or at least no permanent self(relating it to point 1)
3.Buddhism believes that all humans suffer, it is part of the 'human
condition'. - First Noble truth
The cause of this suffering is craving - The 2nd Noble truth
By getting rid of craving you get rid of suffering - 3rd Noble truth
The best way to do this is to live the middle way, between poor and rich, living on what you need, as you see how monks in a temple live.- 4th Noble Truth.
There is then the eightfold path which is ways to live your life, having the right view of things, putting these views into action and holding the correct thoughts(meditation comes into this). There is 8 sections to this path but that's the general gist of it.
All of this helps Buddhists reach enlightenment through helping them think and act the correct way - it helps them be compassionate to others. This will help Buddhists receive good Karma.
Buddhists believe in the wheel of life, it has different realms which vary from good and bad, if you have Good karma you are reborn(not reincarnated, buddhists believe in no self so there is nothing to be reincarnated only your Karma follows on) into a better realm/rebirth, if you gain bad karma you are reborn into a worse realm/rebirth.
However the ultimate goal of Buddhism is enlightenment, which is escaping this wheel of life by getting rid of suffering and realising all the truths of Buddhism.
This is what I know of Buddhism by doing it in my RMPS class in secondary school, if you have any questions about anything I have said just ask and I will see if I can answer them.
TL:DR -Get rid of suffering by getting rid of craving and be compassionate. Through this you will reach Enlightenment.
or a TL:DR for a 5 year old - If you want to feel happy you must stop wanting things and be nice to everyone, then you will feel truly happy.
| [
"Creepersin is an American horror punk/goth rock band that was formed in Orange County, California. Creepersin was known for loud guitars (as in \"Last House on the Left on Mockingbird Lane\") and sleepy vocals (as in \"Proceed with Plan 9\"). Their lyrics are mostly inspired by old horror and exploitation films su... |
Are any of our direct (evolutionary) ancestors alive today? And if so, which is the one that is closest to us? | Your closest evolutionary ancestors are your parents :)
Okay, all kidding aside, it looks like the answer is no. Diagram [here](_URL_0_). Our direct evolutionary ancestors *H. heidelbergensis* died a while ago, and we helped to kill off the *H. neanderthalis* subspecies, so.
Honestly, it isn't surprising that we're the only ones around. Anyone too closely related to *H. sapiens* would be a direct competitor, and you might have noticed we don't deal well with competition. Well, we *do* deal well with competition, we just often annihilate the other competitor in the process. | [
"The RTB claim that all current humans are descended from a specially created couple that lived about 50,000 years ago and that there is no common ancestor between humans and other primates is disputed in a scholarly essay by evangelical geneticist Dennis Venema. There is strong genetic and fossil evidence suggesti... |
why is the force of gravity lower in water then on land? | It's not less, it's exactly the same.
There's just a new force involved, bouncy, that's pushing you up while gravity is pulling you down. It could be argues that bouncy is simply the force of gravity applied differently, but that's not really important for this argument.
| [
"If formula_7, formula_8 is positive though generally much smaller than formula_4. Because water is much more dense than air, the displacement of water by air from a surface gravity wave feels nearly the full force of gravity (formula_10). The displacement of the thermocline of a lake, which separates warmer surfac... |
Why is it apparently accepted that different breeds of cats and dogs have certain personalities, abilities, and levels of aggressiveness, but not different races of humans? | This is really a snakepit of a question and I don't know how to answer it completely.
It's important to note, though, that dog and cat breeds are extensively inbred compared to human races, and are much less genetically diverse. This makes it a lot easier to predict how a puppy will turn out than how a child will turn out, and even then everyone know there's a lot of personality and morphological differences even within breeds. It's not a very accurate comparison.
| [
"Dogs and cats have a range of interactions. The natural instincts of each species lead towards antagonistic interactions, though individual animals can have non-aggressive relationships with each other, particularly under conditions where humans have socialized non-aggressive behaviors. \n",
"Most feline pets in... |
how is braille used/interpreted in cultures with complicated writing systems (arabic, japanese, etc.)? does each language have its own unique braille alphabet? | For [Chinese braille](_URL_0_) see here. It uses "multiple characters" for one sign. | [
"Hebrew Braille () is the braille alphabet for Hebrew. The International Hebrew Braille Code is widely used. It was devised in the 1930s and completed in 1944. It is based on international norms, with additional letters devised to accommodate differences between English Braille and the Hebrew alphabet. Unlike Hebre... |
why does your brain automatically read words and why can’t you stop it from doing so? | Our brains are wired to pattern match. By teaching kids to read, we shortcut the patterns at an early age, and it becomes habit. Try looking at a totally different language and you certainly won’t automatically read it. | [
"More recently, they have turned their attention to how learning to read may depend on a process of \"neuronal recycling\" that causes brain circuits originally evolved for object recognition to become tuned to recognize frequent letters, pairs of letters and words, and have tested these ideas examining brain respo... |
Why do so many American suburbs have the word "Heights" in them? And why is this naming trend not present in other English-speaking countries? | I am not an expert, but I believe it has to do with the fact that the wealthy use to have their homes built on the hills surrounding cities. These would often be called "the heights". So as suburbs developed to give an impression of wealth some would have "heights" in their names.
It could also be that they are developed in areas that had named that spot of land ______-heights. | [
"Much of the term's history evolved from the Appalachian area of Pennsylvania, which includes most of the T and most of the Pittsburgh area. Since the early 1800s, Pittsburgh has been one of America's major cities with a distinct association to the Midwest. Its geographic proximity to Ohio and West Virginia creates... |
south atlantic anomaly | The South Atlantic Anomaly is an area of low earth orbit where radiation is particularly high, due to the shape of Earth's magnetic field. This means that satellites pass through these areas are bombarded by high-energy particles, which cause cumulative damage to electronics.
This damage occurs since electronics such as computer memory (as an example) work by sending very small amounts of electricity through what are basically very small wire packages in a very exact way. How exact this has to be is called "tolerance" - if your electronics no longer deliver the right amount of electricity to the places it needs to go, it's "out of tolerance" and you end up with things like a failure to store/process information properly, or even complete failure of the device.
This happens in two general ways:
1) "Soft-errors," which are temporary, can happen when when some electrons are displaced from their normal path. To put this in ELI5 terms, electricity "flowing" along a wire can be thought of as a chain of people (atoms) passing a ball (an electron) from one person to another, until it reaches some destination. Radiation is "ionizing" which means that it can introduce new balls along this chain, or even knock some balls out of people's hands or give them a permanent ball to hold so they can no longer be part of the chain. Up above I said that some electronics require a very specific amount of electricity to be delivered to some places - the introduction of new electrons into the system messes this up. It is temporary if the amount of radiation is small, because you could move to a place with less radiation and there will be no more interference with the chain and the electron passing will go as normal. Even those people that can no longer pass electrons along in a chain don't really matter, provided that there are a few of them - since we're talking about tiny atoms, there's thousands if not millions of those chains going at once.
2) Permanent damage can happen when the amount of ionizing radiation is so high that there's a great deal of electrons being added to the system. A lot of electronics are built only to handle a certain amount, if they get too much, the excess will be released as heat and you can damage them, literally burn/melt them. Another thing that can happen is that devices that normally let out a certain amount of electricity are changed, so that they might let out a lot more or less. Like a stretched out sweater, it no longer really fits, and whatever its job was, it can't do it anymore.
Satellites (both old and new) have many of these tiny electronics inside. Some of the radiation can be shielded, but the best radiation protection is shielding with heavy metal plates that are harder to send into space. There are other ways to make or design electronics that are more resistant from radiation damage, and some of those techniques do make their way into satellites. On the other hand, older satellites were probably simpler in construction, with larger parts with larger tolerances. Radiation in space has been known for quite some time, so they dealt with it with the technology available at the time. However, nothing will completely shield high levels of radiation - for example immediately after the Chernobyl nuclear disaster, even remotely controlled robots shielded against radiation couldn't last long in that environment (at those levels, the radiation was high enough to degrade plastic insulation in large wires). | [
"The South Atlantic Anomaly (SAA) is an area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface, dipping down to an altitude of . This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher-than-usual levels of radiation.\n",
"... |
why does the greenhouse effect doesn't work both ways? | It’s different wavelengths of light. The sun sends us a broad spectrum of light which warms the earth. The earth radiates back to space light primarily at longer wavelength infrared spectrum. Greenhouse gasses only block infrared light. It’s similar in concept to blue blockers sunglasses which also only filter out a narrow range of light | [
"\"Greenhouse effect\" is actually a misnomer since heating in the usual greenhouse is due to the reduction of convection, while the \"greenhouse effect\" works by preventing absorbed heat from leaving the structure through radiative transfer.\n",
"The anti-greenhouse effect is a mechanism similar and symmetrical... |
Why are haunted housed historically depicted as Victorian-style in pop culture? | The classic Hollywood haunted house from horror movies is French Second Empire style and not the later Victorian/Queen Anne style. The archetypal houses in "Psycho" and "The Addams Family" have clear Second Empire details like a square central tower and mansard roofs.
As to why this became the archetypal "horror" style, after the American Civil War, several state mental hospitals were built in this style, such as the [Athens (Ohio) Lunatic Asylum](_URL_0_) and the [New Jersey State Lunatic Asylum](_URL_1_). | [
"The haunted house as an American cultural icon can be attributed to the opening of the Haunted Mansion in Disneyland on 12 August 1969. Knott's Berry Farm began hosting its own Halloween night attraction, Knott's Scary Farm, which opened in 1973. Evangelical Christians adopted a form of these attractions by openin... |
How do interlocking basalt columns, such as those seen in "The Giant's Causeway" in Northern Ireland, form? | First, you need to form an even layer of hot molten rock. The two best ways of doing that are either a lava flow, or a sill (a sill being an intrusion of magma along a bedding plane between sedimentary rock layers).
That then gives you a hot flat plate of rock, which begins to cool.
Any cooling liquid, given time, will start experiencing convection as hotter parts are more buoyant, while the cooled edges sink. So cold material at the top sinks down, and is replaced by hot material from the inside. This starts off being evenly spread, but given time it formalises into discrete [convection cells](_URL_0_). So we have a core of buoyant material rising, which replaces cold material sinking at the edges of each cell. The cells can only be stable over a scale of a few tens of centimeters wide, because there's lots of other hot buoyant material nearby which also wants to rise. The precise size of the convection cell is controlled by a lot of factors, including things like viscosity, temperature differences, layer thickness, etc.
Now, these cells would typically default to being circular, except that circles don't tesselate. Instead, what forms is the simplest tesselating shape which gives the highest surface area for the lowest circumference; a hexagon.
So each column in a columnar jointed basalt represents an individual convection cell. | [
"It features unusual and impressive basalt columns, the same type which make up the Giant's Causeway, Ireland. As the volcano's lava cooled, it formed distinct columns or pillars with five to eight sides, called columnar basalt. When hit on the tops with a hammer, the columns make musical notes of varying pitch.\n"... |
Is peer review essential? (philosophy of science(?)) | Philosophy time!
As with any useful word in a useful language, "science" is a complex. Certainly an isolated individual can engage in scientific inquiry, so "science" in this sense doesn't require peer review. However, we live in a society with many scientists, and in that society, "science" is a social enterprise. Peer review is essential to this enterprise because it provides distributed arbitration of authority. Individual scientists get by just fine without peer review, but the communication that drives the scientific enterprise as a whole could not. | [
"Peer review is the evaluation of work by one or more people with similar competences as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review methods are used to maintain quality standards, improve performance, and p... |
how do cows pollute so much and why is this happening? | Cows release methane and a lot of it, approximately 70 to 120kg a year. Like carbon dioxide, methane is a greenhouse gas. However the negative effect of methane is much higher than carbon dioxide (what we breath out and what plants breath in to make oxygen), the amount worse methane is for the climate compared to carbon dioxide is debateable but its around 30 times worse. The effect of cows on the environement from pollution is not limited to methane but also includes: carbon dioxide, nitrous oxide, run off, land use, water use, water to grow feed for cows (grain/soy), land to grow feed for cows, the list goes on. The resource's needed to breed cows for food is huge and overlooked by most of society not to mention the environmental effect farming cows has. You have to factor so many things in with farming cows (farming cows is what I assume you are referring to), things often overlooked includes water used to make the feed (soy/grain), feeding/watering the cow from birth to adulthood, transportation of cows/meat, land use (which includes land for feed) that could be used for beneficial things (e.g. a forest which would decrease carbon dioxide emmisions as plants inhale carbon dioxide and exhale oxygen), species extinction due to deforestation and land use, there's many more but I think you get the point. The resources needed for cows not to mention the gases they excrete is vastly overlooked by the general society. The impact of beef/milk farming is far bigger than most think. The fact that always gets me is that animal agriculture is responsible for more greenhouse gas emissions than the combined exhaust from all transportation. Yet all we hear about is "drive less, bike more, catch public transport instead, its better for the environment". I highly recommend you watch the documentary " cowspiracy" its all about this stuff and is extremely interesting. | [
"One reason why cows burp so much is that they are often fed foods that their digestive systems cannot fully process, such as corn and soy. Some farmers have reduced burping in their cows by feeding them alfalfa and flaxseed, which are closer to the grasses that they had eaten in the wild before they were domestica... |
It's 1776, how would I drink beer at home? | In Sweden, most people would brew a dark, cloudy and weak beer (1-3%) at their own farm from their own produced barley. This was stored in kegs or barrels and drunk by everyone (including young children) from wooden tankards or mugs.
Stronger beer, but still dark and cloudy, was brewed by brewers usually close to towns or *bruk* (early industrial sites based around copper or iron mining or work with those metals). Peasants could buy this (or make their own) for special occasions and places that served alcohol would probably be major customers. However, *brännvin* (vodka) was the preferred and most common way to consume alcohol at the time. The fledgling temperance movement was at the time arguing that people should restrict themselves to 6 shots of *brännvin* per day. | [
"Prior to the Revolution, New Englanders consumed large quantities of rum and beer, as maritime trade provided them relatively easy access to the goods needed to produce these items. Rum was the distilled spirit of choice, as the main ingredient, molasses, was readily available from trade with the West Indies. Furt... |
Is it likely that the United States would have invaded Grenada following the October 1983 Beirut barracks bombing even if Maurice Bishop hadn't been deposed earlier that month? | For context:
* Grenada is a small nation, but its alignment with the USSR and Cuba provided strategic advantages to those nations. Grenada was on the opposite side of the Caribbean from Cuba. The construction of an airfield on the island by Cuban soldiers threatened to establish a real strategic threat to commerce and military operations in the Caribbean. A Cuban military presence on Grenada would also allow Cuba to ramp up its military activities in Africa, by shaving over 3,000 miles off a round trip.
* The US government had established a precedent of financial, covert and military intervention (Guatemala, El Salvador, Nicaragua, Colombia) against any Cuba-aligned government in the Americas.
* Several hundred U.S. citizens attended the St. George's University School of Medicine on Grenada, providing a concentrated group of potential hostages.
* Tensions around the world were high in late 1983; the Soviets shot down a civilian airliner on September 1, killing 269 people. President Reagan adopted a belligerent stance in reaction. As a result, the U.S. military deployed forces in the eastern Caribbean to threaten Grenada. (The intervention in Lebanon was a sideshow to the larger confrontation between the superpowers.)
These actions created the crisis of October 1983 in Grenada. Leftist elements within the government pressed Prime Minister Bishop to strengthen the military and invite stronger Cuban support. Bishop refused, fearing this would provoke an intervention. He was removed from power on October 12. Street protests broke out. Loyalists broke Bishop and other members of his government out of house arrest, but the new junta (led by Deputy Prime Minister Bernard Coard and military commander Gen. Hudson Austin) suppressed the loyalist revolt on October 19, killing 10 demonstrators. Later that night, Bishop and seven of his followers were executed. General Austin assumed command of a new military government.
The next day, the Joint Chiefs ordered the deployment of combat-ready troops within striking range of Grenada and the U.S. government shepherded a joint declaration through the Organization of Eastern Caribbean States on October 21, calling for a multinational intervention to restore order. The next day, the British Governor-General of Grenada formally requested an intervention. The same day, Castro ordered his troops on Grenada to fire in self-defense only.
Also that day, President Reagan met with the Joint Chiefs and was informed that Grenada's new military government was calling up 2,000 reservists. The final straw was the new junta's refusal to allow the American students on Grenada to evacuate. Reagan approved the military proposal for a massive attack on October 25.
It wasn't until October 23 that the Beirut barracks was bombed, and preparations for the invasion were not paused as a result.
Would the United States have intervened without Coard and Austin's coup? Unlikely to say the least. There was no broad diplomatic consensus, and if Bishop had stayed in power the Lebanon crisis would have made U.S. decision-makers more gunshy. The United States had other economic measures it could have deployed. For example, tuition from the St. George's medical school represented 10 percent of Grenada's GNP - this was a large part of Bishop's reluctance to adopt a more confrontational posture. Ordering U.S. citizens to evacuate from the school was the American ace in the hole - and in a more prolonged contest it certainly would have been threatened to extract concessions.
Sources:
Cole, Ronald H. *Operation Urgent Fury: The Planning and Execution of Joint Operations in Grenada, 12 October–2 November 1983.* Washington, D.C.: Joint History Office, Office of the Joint Chiefs of Staff, 1997.
Stewart, Richard W., and Edgar F. Raines. *Operation Urgent Fury: The Invasion of Grenada, October 1983.* Washington, D.C.: U.S. Army Center of Military History, 2008.
| [
"The reason given by the U.S. Administration of Ronald Reagan to justify the October 1983 invasion of Grenada was to rescue American medical students at St. George’s University from the danger posed to them by the violent coup, as well as to return the country to its democratic status, that had overthrown Grenada’s... |
what happens when a limb loses and then regains it's feeling? | Hi there, excellent question.
When pressure is placed on a nerve(neuron), this prevents signals from getting through.
There are 4 main types of primary afferent axons:
**A-alpha(I):** Control skeletal muscle. Fancy name is Proprioceptors
**A-beta(II):** Mechanoreceptors of the skin. Innervate touch, hair receptors. Many kinds of dermal receptors for many kinds of stimuli
**A-delta(III):** Nociceptors (pain), temperature
**C(IV):** Temperature, pain, itch. These are the smallest diameter and are not myelin-insulated.
Back to your numb limb. They do need a minute or two for the muscles to get their feeling back, but it is relatively quick since those are controlled by Group I axons. The itchiness, or pins and needles feeling is a result of those much slower Type IV axons getting signals through.
Your brain moves pretty quickly- but the signal cannot travel up and down if the highway is blocked. It could send the signal down the Efferent (ventral) path, but it wouldn't make it. Any signal meant to return to the brain up the Afferent (dorsal) path would be delayed.
I hope I have provided an adequate explanation. Please respond if you need something clarified. It sort of morphed into a ELI25
Source: Neuro student | [
"In the phenomenon of phantom limb sensation, a person continues to feel pain or sensation within a part of their body that has been amputated. This is strangely common, occurring in 60–80% of amputees. An explanation for this is based on the concept of neuroplasticity, as the cortical maps of the removed limbs are... |
Why is the weak nuclear force between 2 protons in the nucleus, 10^-7 times the electromagnetic interaction? | The driving reason for this is that the weak force is carried by massive particles, so the strength of the force drops off exponentially with distance, whereas the electromagnetic force is carried by photons which are massless and hence produce a force that only drops off geometrically.
There's a good discussion of this all [here](_URL_0_). | [
"At short distances (less than 1.7 fm or so), the attractive nuclear force is stronger than the repulsive Coulomb force between protons; it thus overcomes the repulsion of protons within the nucleus. However, the Coulomb force between protons has a much greater range as it varies as the inverse square of the charge... |
Would a bubble be absorbed by the water around it? | Yes - for most gasses, solubility in water increases with pressure. | [
"If a bubble or an object exists which collects gas molecules this collection of gas molecules may reach a size where the internal pressure exceeds the combined surface tension and external pressure and the bubble will grow. If the solvent is sufficiently supersaturated, the diffusion of gas into the bubble will ex... |
How do we know if subatomic particles are spherical? | It's an artist interpretation. The currently accepted model, the standard model (or more generally quantum field theory itself) models fundamental particles (photons, neutrinos, quarks, electrons) as pointlike, i.e. they are mathematical points, so they occupy no volume at all. This might seem weird to your common sense, but there's really nothing illogical about it. There's no law telling us that existing things have to occupy any volume.
Composite particles like the proton (consisting of 3 quarks) of course have some shape, and this shape is not always just a ball but can be deformed into rugby-like shapes and possibly even more exotic shapes (donuts even? I remember reading some pop-sci article about this a while back, I don't know too much about it really) . The proton is a surprisingly elaborate system, since the quarks are interacting strongly which makes understanding it very hard. But this is something we can investigate experimentally in scattering experiments. The same comment applies for fundamental particles being pointlike: we can model what it would look like if they occupied some finite volume and then look for this signal in experiments; and so far we've not seen anything. Of course we can only conclude things down to some finite resolution. And string theory replaces the pointlike particles with 1d strings, so if we believe this then all fundamental particles are really string-shaped. | [
"While the model Eq. () offers a reasonable approximation for almost-spherical particles (e.g. biomass burning aerosols), it no longer provides a viable description for the non-spherical case. Particle shape is known to have substantial effects for the scattering in side- and backward direction. Recent studies show... |
in WW2 was it easier for non-Germans to volunteer for the SS compared to the Wehrmacht. | The SS had the strictest policy about proof of German blood, and needed to get a certificate called "Großer Ariernachweis" (Greater Aryan certificate) with the added information that showed proof of pure Aryan blood back to at least 1750.
| [
"Non-Germans in the German armed forces during World War II were volunteers, conscripts and those otherwise induced to join who served in Nazi Germany's armed forces during World War II. In German war-time propaganda those who volunteered for service were referred to as \"Freiwillige\" (\"volunteers\"). At the same... |
why don't video game industries use sd cards instead of discs? | Compared to SD cards, Blu-ray discs are extremely more cheap to mass produce. Even with DVD's, you as a consumer can buy a 50 pack for pretty cheap. | [
"Nintendo DS and 3DS storage devices are used to store a licensed developer's work-in-progress images, homebrew video games, and downloaded commercial games (since the Nintendo DS is not sold with a rewritable storage medium). Licensed developers, however, can use a blue Intelligent Systems Nitro Emulator box to fl... |
if police officers are not required to tell us when they are undercover, what stops all police offers from just wearing normal clothes and always being undercover? | Why would they?
Clearly marked police presence is a crime deterrent. Very few police activities involve being sneaky and doing undercover stuff (though that's what you see on TV and the movies). A lot of what police do, like helping people, really isn't possible if you don't know who they are. | [
"Undercover agents should not be confused with law enforcement officers who wear plainclothes. This method is used by law enforcement and intelligence agencies. To wear plainclothes is to wear civilian clothes, instead of wearing a uniform, to avoid detection or identification as a law enforcement officer. However,... |
can someone please eli5 why accretion hasn't affected saturn's ring? | Can someone please ELI5 accretion? | [
"The brightness and purity of the water ice in Saturn's rings has also been cited as evidence that the rings are much younger than Saturn, as the infall of meteoric dust would have led to darkening of the rings. However, new research indicates that the B Ring may be massive enough to have diluted infalling material... |
how do ads load on bad service but normal content doesn’t? | Youtube (through Google) have many, many servers across multiple regions of the world to store their data. Very popular content may be hosted on multiple servers to constantly have it closer to the viewer, and on faster servers.
Less popular, more normal content will not necessarily be copied on multiple servers, or stored on very fast servers, making the video load more slowly.
Ads, on the other hand, will be stored in servers geographically close to you, and fast enough to always let them play as smoothly as possible. | [
"Because infomercials may sometimes take a sensational tone, and because some of the products and services sold may be of a questionable nature, consumer advocates recommend careful investigation of the sponsor, the product and the claims before making a purchase. To that end, some stations and networks normally ru... |
what the pirate bay are fighting for and what they hope to achieve in the future | The right to get free copyrighted stuff on the internet so that you don't have to pay content producers. | [
"The Pirate Bay has sparked controversies and discussion about legal aspects of file sharing, copyright, and civil liberties and has become a platform for political initiatives against established intellectual property laws and a central figure in an anti-copyright movement. The website faced several shutdowns and ... |
What is to prevent a spaceship, like the USS Enterprise traveling at "WarpSpeed" from not hitting objects in space while in motion? Granted they are not traveling through wormholes. | Nothing is stopping you from hitting things. But keep in mind a) that space is really really empty, and b) it's science fiction. It's usually explained that they aren't traveling through normal space as such (hyperspace/subspace), so they can't hit things in the way. The problem of seeing where you are going was a major plot point in the Dune universe (spice being used to see the future so they didn't hit things).
However, this would be a major issue with real warp drives, if we could ever create them. | [
"Players control a spaceship which lacks weaponry, instead, having to fight by swinging around a mace made of trash particles that are tethered to their ship. The mace can be controlled using by using the ship's own momentum to drag it along behind, and rapidly changing direction to swing it at enemies and obstacle... |
If energy can't be created, what's happening in this scenario? | It came from separating them in the first place. This resulted in the potential energy that was converted into kinetic energy as the planets attracted each other. | [
"Energy is also transferred from potential energy (formula_8) to kinetic energy (formula_9) and then back to potential energy constantly. This is referred to as conservation of energy. In this closed system, energy cannot be created or destroyed; therefore, the initial energy and the final energy will be equal to e... |
weightlessness scenes in movies | I don't know what they did for the expanse, but Apollo 13 was filmed on the vomit comet, it took several hundred runs according to [IMDB](_URL_0_) | [
"Principal photography took place over 44 days in Thailand. In preparation for the roles, the actors playing the prisoners spent several months losing weight. Since weight gain is accomplished more quickly than weight loss, the film was shot in reverse, with Bale fully regaining his weight during the course of the ... |
the recent cs:go gambling drama with differnt streamers and the website csgo lotto | _URL_0_
this explains a lot. You can't gamble on your own site. You can't advertise for something you own without expressly stating you own it. | [
"\"The Lottery\" pokes fun at the excitement surrounding the lottery held during the fall of 1731. In particular, Fielding mocks both those who sell or rent tickets and those who purchase the tickets. The portrayal of the ticket vendors emphasised the potential for deceit and the amount of scams that were possible.... |
why it took this long to find another planet behind pluto? | The further out you go, the less light planets reflect and the harder it is to see them against the backdrop of the stars. Pluto was only discovered with very painstaking comparison of images of the sky, with it very faintly moving between images (unlike the stars). Modern technology has made this easier and helped us discover very many Pluto-like objects, but we know many more bodies in the Kuiper Belt remain to be discovered, as well. What is special about the recent news is that we think there might be a much larger body, perhaps one that has cleared its orbit (and therefore not a *dwarf* planet).
We haven't "found another planet" yet--however, by tracking some of the dwarf planets we've found and looking at their orbit, some scientists have concluded they are being influenced by a planetary mass. Historically this has sometimes been the first step in the discovery of a new planet--it gives us a clue about where to look, but we don't know that conclusion is correct until we actually spot the planet. Often, the prediction has been wrong. | [
"Exploring Pluto was contemplated since its discovery by Clyde Tombaugh in 1930, but Pluto presents significant challenges for exploration because of its small mass and great distance from Earth. The two probes of the Voyager program, launched in 1977 to explore Jupiter and Saturn, had also the ability for an exten... |
how does gmail's undo a sent email feature work? | they send the mail not instantly, they hold it back for a moment. if you decide not to send the mail it had never left your mailbox. | [
"Gmail allows users to 'archive' emails. Archiving removes a conversation from the inbox and can be accessed via the 'All Mail' section. In Gmail, the 'All Mail' section displays all of a user's emails, excluding the ones in Spam and Bin. Technically, when a message is archived, the 'Inbox' label is removed from it... |
how is beer made | I make beer and wine so I guess I should chime in on this one.
First, let's look at the basic ingredients:
1. Grain
2. Water
3. Hops
4. Yeast
The basic overall concept is to get the yeast to eat what's in the grain and the waste of the yeast is what we use to get tipsy.
In order to do this we first water the grains until they sprout. We do this because inside the grains at first is starch which is form of sugar but not easily digestible by yeast. Grains are seeds and to get them to turn the starch into sugar we wet them to get them to sprout. Enzymes are activated in seeds when they start to sprout and the dormant starch is turned into something more usable by the plant by those enzymes which is sugar. The point at which the sugar is the highest and the starch is the lowest is when the sprout is about a half an inch high (varies per grain). We then stop the seed from continuing it's path to plant-hood by drying it out which kills it after which we shake off the sprouted part. Now you have malt, the same kind of stuff that is put in milk shakes (and if you don't do this, ask for it, it's awesome) and what is Milk Duds (malt balls covered in chocolate).
Now on to brewing! You have the sugar and now you just need some yeast, water and hops. Hops are the buds of a plant closely related to marijuana! They are vary fragrant and are used in beer to add balance, more flavor and longevity. I'll add a neat piece story of beer at the end of this. Before hops were added to beer, the Egyptians and others used various spices.
Now basically you boil the malt in water with the hops after which you have what is called "mash". After it is cooled down to room temperature (so that the heat doesn't kill the yeast) and add the yeast. After the boiling you need to make sure you do everything in a sterile manner so other things don't eat the sugar and your yeast is able to become the dominant power in the war to eat the sugar water you created. Note: There are many different species of yeast, it's best to use ones that are bred for beer though their spores do float around in the air and will naturally introduce themselves. Back before the knowledge of microscopic creatures, people thought spirits (where the nickname for hard alcohol comes from which starts it's process similar to this), gods and other things would transform the liquid!
So long as everything goes to plan your yeast will eat the sugar and poop and pee two things, the gas CO2 and the liquid Ethanol. Ethanol is the toxin that most humans are ok with drinking in moderate quantities! Most of us have enzymes which can convert the ethanol back into sugar! Don't drink things other alcohols, especially Methanol, the human body can not process it and it will do very bad things to you!
Once the sugar is all or mostly eaten up your beer is done! You can get those neat bubbles in your beer by trapping them instead of allowing them to just bubble away! (same thing they do with sparkling wine!)
Neat story time:
During the time of British imperialism, soldiers and others who were stationed in India were used to drinking beer and desired it greatly; especially when they were away from home. The beer would many times go bad on the journey from Great Britain because of the heat especially on those long sea voyages. Since hops are an excellent preserver they just added more hops to make sure the beer would be more palatable when they reached India. This created the style of beer that is known today as IPA or India Pale Ale!
Believe it or not, beer was one of the main things if not the main thing that much of civilization built itself upon! It contained calories so it was almost a meal in itself, all while for most people being much much safer to drink than the local water. It could be traded as it always held a value and of course it was an excellent stress reliever and social lubricant! Of course it helped to keep populations from revolting as well, the people would never quite get mad enough at their horrible situation because they could always fall back on their pain reliever, alcohol!
Wine:
Grapes are pretty damn near perfect to ferment. They already contain sugar and they have the perfect balance of micro-nutrients for the yeast to thrive. Simply: Grow grape vines, pick grapes, crush crapes, add yeast, strain out wine, drink.
Hard alcohol:
Distilling involves taking beer, wine or a similar substance containing ethanol and separating it from a portion of the water it's in. Brandy for instance is made from wine and basically all you are doing is taking the ethanol out of the mixture. Ethanol has a lower boiling point than water so all you are doing is heating it to a point between the boiling point of ethanol and water and the steam that comes off will be mostly ethanol. Instead of it just going away in the air you re-route the steam into a cold environment (usually into tube with water around it), at this point the gas falls in temperature thereby becoming a liquid again and it drips drips drips into a new container as hard alcohol!
Having the drinking age at 21 instead of 18 (or even at all) when you considered an adult is dumb. You can vote, get imprisoned as an adult and be sent to war to get your limbs blown off but you can't decide to consume alcohol into your own body! I know this drinking age is not the same everywhere, but it's like that where I am and it's absolutely silly.
Hope you've enjoyed this! | [
"Beer is produced through steeping a sugar source (commonly malted cereal grains) in water and then fermenting with yeast. Brewing has taken place since around the 6th millennium BC, and archeological evidence suggests that this technique was used in ancient Egypt. Descriptions of various beer recipes can be found ... |
How did the hubble space telescope not move when talking this photo? | The telescope did move. It was in orbit. It was kept pointed on the same area of the sky. At that distance, the difference in the angle from which the area is viewed when the hubble is on one "side" of the earth versus another, and even the much larger movement of the earth itself and the sun relative to the center of the galaxy, were all negligible. So, the image stayed sharp.
BTW, I'm not sure about that photo in particular. But, if the dark area was close to the moon, it was in the plane of the ecliptic. So, it's likely that the 4 month shutter speed is really an aggregate of multiple openings and closings of the shutter. I am not sure about this.
Here's a detailed description for the ultra deep field images. I'm sure the super deep field images were done similarly.
_URL_0_ | [
"After Jimmy passingly mentions the Hubble Space Telescope, a man in the audience dressed head to toe in New York Yankees apparel named Milky J (Bashir Salahuddin) enthusiastically begins listing and showing photos of astronomical features photographed by the telescope, each one punctuated by him yelling \"Hubble g... |
Why don't we use the Saturn V anymore? | We don't use the Saturn V because we can't - we don't know how to build them anymore. Oh sure the plans are still there but every engineer who worked on them and every facility to actually construct them are long dead and long dismantled.
The Saturn V was designed in the 1960's - 50 years ago. It was the masterpiece of [von Braun](_URL_0_), the greatest rocket scientist in the history of man.
Enter then the age of the Space Shuttle where we didn't design a new rocket for nearly 40 years (the Shuttle was designed in the 1970's). That's nearly two generations of rocket scientists who don't exist.
The [Ares V](_URL_1_) was NASA spinning up a new generation of rocket scientists capable of a moon launch to rectify the problem introduced by the lack of institutional knowledge. The Constellation program got canceled by an bean-counter at OMB so now we need to wait for the second generation (The [SLS](_URL_2_)) to spin up before we can get past LEO again.
Hopefully that explains it. If you want more detail go visit Huntsville someday and go through the Space and Rocket center. They do a really good job of explaining it. | [
"The Saturn V-3, also known as the Saturn MLV 5-3, was a conceptual heavy-lift launch vehicle that would have utilized new engines and new stages that were never used on the original Saturn V. The Saturn V-3 was studied by the NASA Marshall Space Flight Center in 1965.\n",
"The baseline for the Saturn II was a Sa... |
What happens in your brain, chemically, when you wake up? | Sleep and wakefulness is regulated by a group of nuclei in the brainstem called the RAS (reticular activating system). These nuclei produce different chemicals. Some nuclei produce GABA and galanin, which promotes sleep. Other nuclei produce noradrenaline, orexin/hypocretin and histamine, which promote wakefulness.
So during hypnopompia (transition from sleep to consciousness), you get an increase in these latter chemicals (mainly orexin/hypocretin). You also get endocrine effects like cortisol spikes. | [
"Large parts of the brain that are activated and sending signals during waking are inactive during NREM sleep and become reactivated during REM sleep. It is based on the fact that the brain and its neural circuitry is plastic and self-regulating, especially in its own activation and inactivation. This was observed ... |
How did the first ever logic gate chip get made? | Well I am a rising junior in computer engineering so I'll give this my best shot! Logic gates are made up of transistors, a device that has been around since about 1925 which you can read here: _URL_0_.
However, production chips are made of silicon transistors which was created in 1954 by a few guys it would go on to be known as Silicon Valley for that reason. As you may know, transistors are the fundamental components of logic and so many And, or nand, xand, xor, xnor chips were created for the purpose of making electronics and eventually the computer. Many companies sprang up for making and selling these chips like TI and IBM. The rest is history.
| [
"The 4004 was the first random logic circuit integrated in one chip using the MOS (metal–oxide–semiconductor) silicon gate technology (SGT). It was the most advanced integrated circuit (IC) design undertaken up until then. Hoff, head of the Application Research department, had formulated an architectural proposal c... |
What Equipment Would a World War Two/ Korean War Tank Crew Have Inside Their Vehicle? | To give you a rough idea, here's a US M4's crew standing next to it's equipment: _URL_2_
Here's someone recounting his experience fighting in WW2 as a tank crewman who trained on an M4 Sherman only to discover he was going to be fighting in an M3 Stuart. With no turret.
_URL_1_
Furthermore, while I'd call into question the accuracy of the physical game, World of Tanks has a running feature where they have one of their military advisers climb around on tanks and show you around called "Inside the Hatch."
_URL_0_
*Most* tanks have machine guns that can essentially be popped off the tank and brought around. While a gun mounted to the top of the turret is usually what everyone thinks of, tanks typically had additional ports on the sides and front of the tank. Not *all* of these could simply be detached though. Some tanks also had a machine gun port mounted to the back of the turret.
Crews were typically equipped with an odd array of small arms. German tanks mid-war made use of pistol ports but as the war dragged on they became less common to cut back on the cost of manufacturing tanks. No one else really made use of pistol ports but the crews were typically armed with *something* so that they weren't completely naked if their tank wasn't operational. US tank crews seemed to have had Thompson SMGs standard, but I can't find anything that confirms this, and it strikes me as a bit lavish- Thompsons were a bit pricy to manufacture.
Early, crude tanks- particularly for the Soviets- often made use of primitive transmission systems that required you use a mallet to hit the gears into place. The point to this was that it was incredibly inexpensive to manufacture, and used the same transmission that many farm tractors from this era would have had. Not many Soviet soldiers had any experience driving a *car* per say, but if you happened to work on a farm you at some point probably had to learn how to work the tractor.
A fair amount of parts and tools were kept inside the tank. While something as involved as overhauling an engine would typically require specialized equipment and time in a shop, crews were expected- typically- to know how to perform repairs on the mechanics of the tank, and take care of the tread system. But sometimes you can't help it when you're German, and your tank weighs 70 tons. There's only so much a crew can do before a specialized piece of equipment needs to be brought in.
The electronics for tanks is something I'm admittedly fuzzy on. I know they were notorious for being a bit unreliable- many countries took to wrapping the wiring in paper or something similar because rubber was simply too important for other applications to be using it to insulate wires. So far as what'd happen if, say, a radio was wrecked, is a bit beyond me. Because of the simplicity of the radios from the time I have to assume they'd be repaired if at all possible, but its honestly something I'm not sure about, and to the best of my knowledge no one would want to send someone with that kind of talent in a tank out to war.
Tanks would be stocked with munitions for both the main gun and machine guns. Because of the fragile nature of the munitions they were stored on racks. Some who were a bit more foolish would take to stuffing additional rounds anywhere they'd fit which would cause problems- particularly for US crews- when those rounds would be struck in combat and fire inside the tank. That's not a good thing and was the main culprit behind the US M4 Sherman gaining a reputation for bursting into flames.
So far as the actual soldiers they had their fatigues, if it involved cold weather they'd have a jacket, they had helmets and generally some form of goggles. And a belt. | [
"The (also known as the Ke-Go) was a light tank used by the Empire of Japan during the Second Sino-Japanese War, at Nomonhan against the Soviet Union, and in the Second World War. It proved sufficient against infantry but, like the American M3 Stuart light tank, was not designed to combat other tanks. Approximately... |
Since our galaxy is spinning, does the night sky as I see it and the position of the stars gradually move over time? | The stars move through our perceived celestial plane, but very very slowly. It's called Proper Motion. Since ancient Egyptian times, Sirius has moved maybe the width of the moon, relative to distance stars.
The star with the greatest proper motion is [Barnard's Star](_URL_1_).
In an extreme case, the stars near the centre of the galaxy move a lot [gif](_URL_0_). | [
"In either hemisphere, observations of the night sky show that the visible stars appear to be moving in circular paths, caused by the rotation of the Earth. This is best seen in a long exposure photograph, which is obtained by locking the shutter open for most of the intensely dark part of a moonless night. The res... |
why is there so much competing information when it comes to fitness? for every weight loss or fitness "fact" you can easily find someone saying the exact opposite, to the point where it's very difficult to find reliable information on fitness/weight loss/diet. | There are a lot of people with very little knowledge or training making a lot of claims. These people, be they famous fitness personalities or just gym trainers, make money by sounding like they know what they're talking about.
In reality, there are a lot of things that we don't know about the human body. | [
"Weight loss and fitness competitions reflect a broader trend in consumer and corporate fitness around using games and money to provide accountability and motivation for health-related activities ranging from weight loss to regular gym use, healthy eating and smoking cessation. A study published in the Journal of t... |
Jewish money-lenders: how did they collect? | Jews were most certainly banned from the use of organized violence, that privilege only belonged to lords or kings. However, because Jewish merchants loaned money to these most powerful groups, they could sometimes call upon them to force dead beats to pay up.
However, violence wasn't the most common way of encouraging repayment. Because the most prolific lenders worked in cartels with other merchant-bankers, the increase of one's interest on a loan was often incentive enough to get people to pay back their debts. It's worth noting that people taking out loans in the middle ages would not usually be from the poorer segments of society, and if they were, they were often personally known by the lender. More often than not, they were merchants themselves, ship captains, or feudal lords/kings who would need good credit for their future livelihood. They were also usually familiar to the lender and could easily be tracked down due to the local nature of the times.
Escaping one's debt would entail leaving one's life behind completely or being a total dick. This last was usually only available to kings and high lords who would either ignore the Jewish lenders asking for repayment or order action be taken against them as heretics. The latter course often took the form of exile or pogroms where Jewish populations were slaughtered en masse. Such occurrences were not uncommon in the Italian states and France between the 13th and 16th centuries.
I apologize for any typos and lack of concrete detail. I'm typing on my phone on a plane, but this information mostly came from Braudel's Mediterranean vol.2 chapter: Societies where there's a long section on Jews
Edit: I should add that using violence was probably not unheard of for collecting debts, but that its use was significantly curtailed by the anti-Semitism of the middle ages. For a Jew to use violence, especially against a Christian would often mean running the risk of death. Though customs, laws, and sentiments obviously varied from place to place, for a Jew to be engaged in violence was not something most local rulers would permit. This the reliance by Jews on local administrators to dole out the beatings or an increase in one's interest rates | [
"This branch was used for robbing the Dutch Jews, mainly living in Amsterdam, of their possessions. Not only bank accounts at other banks were confiscated, Jews were also forced to deposit their art collections, jewels etc. at this bank. If a Jewish family was deported from their home, their possessions were sold. ... |
How did we get 3n+1 and n/2 for the operations in the collatz conjecture? | Because that's the conjecture. If you change them, it's a different conjecture.
Note that they work particularly well because 2 and 3 are relatively prime, and the concept of "even/odd" is well understood, even by those casually familiar with the relevant math. | [
"In the triangle case, the Fermat problem consists in locating a point D with respect to three points A, B, and C in such a way that the sum of the distances between D and each of the three other points is minimized. It was formulated by the famous French mathematician Pierre de Fermat before 1640, and it can be se... |
If samples were brought back from every planet (and including Pluto), what would each one smell like? | I assume you mean their atmosphere:
Mercury: There isn't a substantial atmosphere to sample, so there wouldn't be much of a smell.
Venus: The Venusian atmosphere is mostly carbon dioxide and nitrogen, neither of which can be smelled. However, it is also 0.015% sulfur dioxide, which supposedly smells similar to a recently burned match. Unfortunately, the levels of sulfur dioxide, while certainly capable of being smelled (0.001% is detectable) is about a hundred times greater than is considered safe, and would quickly form sulfuric and sulfurous acid in your lungs, which is unsurprisingly bad for your health.
Earth: Smells like a mixture of feces and Nuts4Nuts.
Mars: The atmosphere is made entirely of inert compounds (CO2, N2, Ar, etc.) so it would not have much of a smell. However, based off of some reading, it sounds like the soil is so rich in various ionic compounds that the surface is bathed in a slightly metallic smell.
Jupiter: The atmosphere is mostly hydrogen and helium, but concentration of hydrogen sulfide is probably high enough that it would smell like a "lethal" fart.
Saturn: The atmosphere isn't very well understood, but it is fairly clear that there is far less heavy compounds like there were in the planets further in. The most distinct smell would probably be that of ammonia, which is in fairly high concentrations in the Saturnian atmosphere.
Uranus: Somewhat ironically, Uranus is likely odorless. The only gases that are visible through current observations are hydrogen, helium, and methane, all of which are odorless.
Neptune: Similar to Uranus, maybe some hydrogen sulfide to give it that far smell. The atmosphere of Neptune isn't very well understood (for instance we aren't sure why it is such a dark blue).
Pluto: It's atmosphere consists of methane, nitrogen, and carbon monoxide. Taking a whiff of it would yield no smell, but probably give you a headache because of the high carbon monoxide concentration.
Final note: Despite the common association between methane and flatulence, methane is completely scentless, and when used as a natural gas, we actually mix hydrogen sulfide (or another sulfur compound) with the methane so we can smell it if there is a leak. | [
"One source of Mars samples is what are thought to be Martian meteorites, which are rocks ejected from Mars that made their way to Earth. Of over 61,000 meteorites that have been found on Earth, 132 were identified as Martian . These meteorites are thought to be from Mars because they have elemental and isotopic co... |
the shape of bread | The split in the top is a line cut into the top by the baker. As the yeast in the bread is warmed, it bursts into activity and releases a bunch of gas causing the bread to rise. As it rises above the edges of the pan, it starts to spill over. If the baker does not put a line down the center, the bread can split in random places causing a misshapen loaf. The line creates a point of least resistance to facilitate the split. | [
"In general, the categories of bread derive from the type of dough (or batter). Some shapes, such as roscas (rings) or cuernos (crescents), may be made with different doughs, but are distinguished by different names. Breads of the same category have the same basic flavor, but differ in shape and additives. Conchas,... |
Why does the human brain contain folds? Are they indicative of something else? | sucli and gyri (the grooves and ridges, respectively) exist to increase surface area of the neocortex. This allows for more grey matter, which is where things like spacial reasoning, decision making, language, and most 'intelligent' behaviors occur within the brain. | [
"The arrangement of these folds differs from human to human, and is believed to account for the differing cognitive abilities of individual humans. It has been found by neuroscientists that the cerebral neocortex accounts for roughly 76% of the human brains total volume . The neocortex is predominately associated w... |
Is there a scientific definition of sentience - and at what age/stage do humans achieve it? | As this is tagged "Psychology", I don't think the field offers a definitive, or close-to-definitive, answer to this question. While Developmental Psychology offers a few different explanations (whether you're a Piaget follower, or a Erickson fan), but one of the most enduring is the concept of Theory of Mind.
Theory of Mind is the idea that the person before you understands that others behave as individuals and have their own beliefs / judgments. The classic example involves sitting a child down, and showing them a situation involving two dolls -- we'll call them Jimmy and Sarah. Sarah comes in, and leaves her keys on an endtable. Sarah then leaves the room, and Jimmy walks in. Jimmy then grabs the keys, and puts them in a drawer across the room. Jimmy leaves, and Sarah walks back in. Then the child is asked: "Where will Sarah look for her keys?" A child that possesses Theory of Mind will point to the endtable (where Sarah initially left her keys). A child that does NOT possess Theory of Mind will point to the drawer the keys are now.
Researchers have demonstrated Theory of Mind in children as young as 18 months (Meltzoff, 1995), but it's normally observed in children from 3-4 years of age. There are even studies that show that chimps and monkeys exhibit behavior similar to Theory of Mind (Premack & Woodruff, 1978).
But this is all hinging on what you define as "sentience". The field does not have consensus on it yet.
**Sources:**
Meltzoff, A. N. (1995). Understanding the intentions of others: re-enactment of intended acts by 18-month-old children. *Developmental psychology*, 31(5), 838.
Premack, D., & Woodruff, G. (1978). Does the chimpanzee have a theory of mind?. *Behavioral and brain sciences*, 1(04), 515-526. | [
"In the philosophy of consciousness, \"sentience\" can refer to the ability of any entity to have subjective perceptual experiences, or as some philosophers refer to them, \"qualia\". This is distinct from other aspects of the mind and consciousness, such as creativity, intelligence, sapience, self-awareness, and i... |
Will plant life feed off of increased CO2 levels in the atmosphere? Is Le Chattelier's principle applicable? | CO2 isn't typically the primary factor determining net ecosystem productivity. Instead, the availability of precipitation, the diurnal temperature range, and soil nutrients set the overall uptake carbon dioxide by the environment. | [
"Elevated atmospheric carbon dioxide affects plants in a variety of ways. Elevated CO increases crop yields and growth through an increase in photosynthetic rate, and it also decreases water loss as a result of stomatal closing The growth response is greatest in C plants, C plants ,are also enhanced but to a lesser... |
I'm aware that Hitler punished the mentally disabled, but did this also include those with mental illnesses such as depression and anxiety? | Generally speaking, no, but that really depends on the severity of the depression or anxiety (or both) in a patient.
Some background: At the time Aktion Tiergartenstraße 4, the programme of euthanasia used on those considered 'handicapped' under the Nazis, was implemented, psychiatry was still limited, coming off of the reinvention of the practise in the late nineteenth century. Most of the patients killed under the euthanasia practises of both Aktion T4 and what came after it were described as severely mentally disabled and not actively contributing to society (which, under the practise of eugenics that was justification for these and all genocides during the Nazi regime, indicated they needed to be euthanised), which indicates that only those with severe depression and anxiety that manifested in a way that would disturb 'normal' life were murdered.
Psychiatric patients were chosen for assessment by psychiatrists on site at asylums, and if they were condemned they were transferred to the specialised asylums where they would be euthanised, so there was a very close relationship between seeking treatment for psychiatric disorders and being killed for seeking treatment. Relatives of patients who were murdered under Aktion T4 were given letters after the fact, giving false, made-up reasons for the deaths of their relatives, which contributed to the end of AT4 when these relatives became suspicious and involved the Catholic Church (which has a very complex role in the Nazi regime).
However, the killings didn't end after Hitler ended T4. They moved on to a second phase, which was less discriminating, as patients often did not have to be moved to a specialised asylum to be euthanised.
It comes down to the definition of psychiatric patients in the 30s and 40s, and what could cause someone to be committed to an asylum. Depression was certainly diagnosed and studied at the time, and there were multiple theories and categorisations (many put forth within Germany post- and including Freud), and it was usually recognised in a patient as more than mourning. There were cases patients admitted to asylums by their families or doctors during major depressive episodes.
Anxiety is less clearly defined and studied during this time period, often categorised as a subset of other mental illnesses, but again, it comes down to the severity of the disorders and whether or not a patient was considered useless in society.
Source (if I need more let me know, this is my primary):
Thorsten Noack M.D. & Heiner Fangerau M.D. (2007) Eugenics, Euthanasia,
and Aftermath, International Journal of Mental Health, 36:1, 112-124 | [
"According to their eugenics policy, the Nazis believed that the disabled were a burden to society because they needed care and were considered an affront to their notion of a society composed of a perfect race. About 375,000 people were sterilized against their will due to their disabilities.\n",
"Margarete Hiel... |
how come we instantly recognize faces (the eyes, nose, and mouth) when we look at a certain arrangement of objects? | Basically our brain is tuned into finding patterns and faces, even where there are none.
Here is the link:
_URL_0_ | [
"Neurobiological research has identified separate areas of the brain responsible for recognizing faces. In humans, identifying unfamiliar faces activates one region of the brain (the Fusiform face area) while recognizing familiar faces also activates another area of the brain (in the lateral midtemporal cortex). A ... |
when an active, obese person gets liposuction and surgery to get rid of the extra skin, are they muscular underneath all the fat because of how much weight they had to carry before? | Probably not. Chances are, the obese person moves everywhere quite slowly and struggles up steps - just like you would if you were carrying an extra 100-200 pounds. Their muscles may be slightly stronger, but it's not significant or enough to generate big muscles just sitting "under" rolls of fat. | [
"In an obese person, excess adipose tissue hanging downward from the abdomen is referred to as a panniculus. A panniculus complicates surgery of the morbidly obese individual. It may remain as a literal \"apron of skin\" if a severely obese person quickly loses large amounts of fat (a common result of gastric bypas... |
Do humans also emit radiation at lower frequencies than infrared? (microwaves, radio, etc) | Yes, humans emit radio waves and microwaves due to thermal emission, but only a very small amount compared to infrared waves. Take a look at these [thermal radiation spectral curves](_URL_0_). The curves just keep going out to longer and longer wavelengths with out every reaching exactly zero. | [
"Since 1962, the microwave auditory effect or tinnitus has been shown from radio frequency exposure at levels below significant heating. Studies during the 1960s in Europe and Russia claimed to show effects on humans, especially the nervous system, from low energy RF radiation; the studies were disputed at the time... |
Is a functioning human brain hot? | Yes, the brain does dissipate around [20 or 25 watts](_URL_1_). It would also be warm because blood from other organs is bringing their heat and taking some away. The whole human dissipates around [100 watts](_URL_0_). | [
"The resting human body generates about two-thirds of its heat through metabolism in internal organs in the thorax and abdomen, as well as in the brain. The brain generates about 16% of the total heat produced by the body.\n",
"Humans and primates use the sudomotor response to cause thermoregulation, or control o... |
Is there a possible scenario where two events, A and B, can occur as: A then B, A and B simultaneously, and B then A, all using three different relativistic frames? | Let's answer this in SR. Forget about GR.
Given two events A and B, we can consider the invariant spacetime interval between them:
> (Δs)^(2) = -(Δt)^(2)+(Δx)^(2)+(Δy)^(2)+(Δz)^(2)
The notation "Δt" means the difference in the time coordinate between the events, and similarly for Δx, Δy, and Δz. The two events can be classified into three categories (assume that A and B are different events):
* timelike separated: (Δs)^(2) < 0
* lightlike separated: (Δs)^(2) = 0
* spacelike separated: (Δs)^(2) > 0
Timelike separated events are those events for which a massive particle can, in principle, travel between them. Lightlike separated events are events connected by a light signal. Spacelike separated events are events so far apart that not even a light signal could have traveled between their spatial locations in the required time. Note that the number (Δs)^(2) is the same in all reference frames. So if A and B are timelike separated in one frame, they are timelike separated in all frames. (Similarly for lightlike and spacelike separated events.)
Now to answer your question:
* The temporal order of A and B is the same in *all* reference frames IF AND ONLY IF the events can be joined by a signal traveling at or below the speed of light.
* It follows that if A and B are timelike or lightlike separated, then their temporal order is the same in all reference frames.
* It follows that if A and B are spacelike separated, then given any temporal order of A and B (A before B, A and B at same time, or A after B), there is a reference frame in which that temporal order occurs.
There are some other interesting properties these events must satisfy:
* If A and B occur at the same space location in the frame *S* (from which it follows that A and B are timelike separated), then their temporal order is the same in all reference frames and the least time separation between A and B occurs in that frame *S*.
* If A and B occur at the same time in the frame *S* (from which it follows that A and B are spacelike separated), then there is no limit on their time separation (it can be any real number) and the least space separation between A and B occurs in that frame *S*. | [
"BULLET::::- Relativity of simultaneity: Suppose two events occur simultaneously () along the x axis, but separated by a nonzero displacement . Then in , we find that formula_16, so the events are no longer simultaneous according to a moving observer.\n",
"Two events are called simultaneous in a chosen reference ... |
why can i go a day without food at home but when i am at school i feel so hungry after a lesson? | Possibly because you are much more active at school/see other kids eating/smelling more food? | [
"A 2012 study undertaken by Netmums found that one in five mothers would regularly miss out on meals so as to be able to save their children from going hungry. Also in 2012, London charity Kids Company named five inner London schools where 70% to 80% of pupils do not always have food at home or do not know how they... |
Is battery technology going to get better anytime soon or should we expect Lithium batteries to be our best option for the next couple decades? | The US DoEnergy has a [project](_URL_2_) to increase automotive batteries' capacity 5-fold, in 5 years and have batteries 1/5 their current cost. A battery researcher in my office says their project is achievable.
Other elements they're looking at are [Sodium](_URL_1_) and [Magnesium](_URL_0_) | [
"Independent reviews of the technology discuss the risk of fire and explosion from Lithium-ion batteries under certain conditions because they use liquid electrolytes. The newly developed battery should be safer since it uses glass electrolytes, that should eliminate short circuits. The solid-state battery is also ... |
why does heartburn become more of an issue when you get older? | It's not so much your increasing age that makes it a problem, it's the recurrence. The longer you suffer from chronic heartburn or GERD, the more damage occurs to your esophagus. As a result this increases your risk of heightened symptoms such as difficultyswallowing, esophageal bleeding, vomiting, and an increased risk of esophageal cancer. | [
"Another factor that may contribute to chronic wounds is old age. The skin of older people is more easily damaged, and older cells do not proliferate as fast and may not have an adequate response to stress in terms of gene upregulation of stress-related proteins. In older cells, stress response genes are overexpres... |
Is it possible for blood type to change? | You should probably get that double checked. | [
"All the common blood types, such as the ABO blood group system, are genetic polymorphisms. Here we see a system where there are more than two morphs: the phenotypes A, B, AB and O are present in all human populations, but vary in proportion in different parts of the world. The phenotypes are controlled by multiple... |
What were some the leading theories on magnets until we learned about electromagnetism? | The pre-Socratic philosopher Thales of Miletus seems to have believed that magnets contained souls because they can move and be moved without any apparent outside force. This was a result of his belief that the soul was a cause of motion.
However, our information is all second hand and it's nearly impossible to separate Thales' actual beliefs from the ones merely ascribed to him. So there's that.
Source: Aristotle, De Anima 405a19-21 | [
"These theories of electricity and magnetism were thought of as two separate phenomena, until Hans Christian Ørsted noticed that a compass needle would deflect from magnetic north when placed near an electric current. This caused him to develop theories that electricity and magnetism were interrelated and could aff... |
What characteristics of a medium affect its permittivity? | Permittivity is related to the polarizability and density of the medium which determines how much how much of a dielectric effect that medium can generate--which is modulated by the effective permittivity. Here's a little write up I did awhile back taking linear polarization on a line into account:
_URL_1_
Here's Richard Feynman doing it correctly (and much better!) for a solid material replicating the Clausius-Mossotti equation:
_URL_0_
If you're interested my derivation stops at equation 32.25 and Feynman continues with the correct solution by including the self-electric field generated by the local polarized molecules. To note, all of this falls apart when considering metals, you need a different approach for those. | [
"In general, permittivity is not a constant, as it can vary with the position in the medium, the frequency of the field applied, humidity, temperature, and other parameters. In a nonlinear medium, the permittivity can depend on the strength of the electric field. Permittivity as a function of frequency can take on ... |
How did miners during the middle ages find metal ore deposits to mine? | Georgius Agricola wrote *De Re Metallica* in the mid-1500s, which is a detailed description of mining practices at the time.
The full text of *De Re Metallica* is available from Project Gutenberg:
_URL_0_
From Book & nbsp;II:
> The miner, after he has selected out of many places one particular spot adapted by Nature for mining, bestows much labour and attention on the veins. These have either been stripped bare of their covering by chance and thus lie exposed to our view, or lying deeply hidden and concealed they are found after close search; the latter is more usual, the former more rarely happens, and both of these occurrences must be explained. There is more than one force which can lay bare the veins unaided by the industry or toil of man; since either a torrent might strip off the surface, which happened in the case of the silver mines of Freiberg (concerning which I have written in Book & nbsp;I. of my work "*De Veteribus et Novis Metallis*"); or they may be exposed through the force of the wind, when it uproots and destroys the trees which have grown over the veins; or by the breaking away of the rocks; or by long-continued heavy rains tearing away the mountain; or by an earthquake; or by a lightning flash; or by a snowslide; or by the violence of the winds: "Of such a nature are the rocks hurled down from the mountains by the force of the winds aided by the ravages of time." Or the plough may uncover the veins, for Justin relates in his history that nuggets of gold had been turned up in Galicia by the plough; or this may occur through a fire in the forest, as Diodorus Siculus tells us happened in the silver mines in Spain; and that saying of Posidonius is appropriate enough: "The earth violently moved by the fires consuming the forest sends forth new products, namely, gold and silver." And indeed, Lucretius has explained the same thing more fully in the following lines: "Copper and gold and iron were discovered, and at the same time weighty silver and the substance of lead, when fire had burned up vast forests on the great hills, either by a discharge of heaven's lightning, or else because, when men were waging war with one another, forest fires had carried fire among the enemy in order to strike terror to them, or because, attracted by the goodness of the soil, they wished to clear rich fields and bring the country into pasture, or else to destroy wild beasts and enrich themselves with the game; for hunting with pitfalls and with fire came into use before the practice of enclosing the wood with toils and rousing the game with dogs. Whatever the fact is, from whatever cause the heat of flame had swallowed up the forests with a frightful crackling from their very roots, and had thoroughly baked the earth with fire, there would run from the boiling veins and collect into the hollows of the grounds a stream of silver and gold, as well as of copper and lead." But yet the poet considers that the veins are not laid bare in the first instance so much by this kind of fire, but rather that all mining had its origin in this. And lastly, some other force may by chance disclose the veins, for a horse, if this tale can be believed, disclosed the lead veins at Goslar by a blow from his hoof. By such methods as these does fortune disclose the veins to us.
>
> But by skill we can also investigate hidden and concealed veins, by observing in the first place the bubbling waters of springs, which cannot be very far distant from the veins because the source of the water is from them; secondly, by examining the fragments of the veins which the torrents break off from the earth, for after a long time some of these fragments are again buried in the ground. Fragments of this kind lying about on the ground, if they are rubbed smooth, are a long distance from the veins, because the torrent, which broke them from the vein, polished them while it rolled them a long distance; but if they are fixed in the ground, or if they are rough, they are nearer to the veins. The soil also should be considered, for this is often the cause of veins being buried more or less deeply under the earth; in this case the fragments protrude more or less widely apart, and miners are wont to call the veins discovered in this manner "*fragmenta*."
>
> Further, we search for the veins by observing the hoar-frosts, which whiten all herbage except that growing over the veins, because the veins emit a warm and dry exhalation which hinders the freezing of the moisture, for which reason such plants appear rather wet than whitened by the frost. This may be observed in all cold places before the grass has grown to its full size, as in the months of April and May; or when the late crop of hay, which is called the *cordum*, is cut with scythes in the month of September. Therefore in places where the grass has a dampness that is not congealed into frost, there is a vein beneath; also if the exhalation be excessively hot, the soil will produce only small and pale-coloured plants. Lastly, there are trees whose foliage in spring-time has a bluish or leaden tint, the upper branches more especially being tinged with black or with any other unnatural colour, the trunks cleft in two, and the branches black or discoloured. These phenomena are caused by the intensely hot and dry exhalations which do not spare even the roots, but scorching them, render the trees sickly; wherefore the wind will more frequently uproot trees of this kind than any others. Verily the veins do emit this exhalation. Therefore, in a place where there is a multitude of trees, if a long row of them at an unusual time lose their verdure and become black or discoloured, and frequently fall by the violence of the wind, beneath this spot there is a vein. Likewise along a course where a vein extends, there grows a certain herb or fungus which is absent from the adjacent space, or sometimes even from the neighbourhood of the veins. By these signs of Nature a vein can be discovered.
Agricola then goes on to discuss in quite a bit of detail the mystical practice of divining for veins, noting that "There are many great contentions between miners concerning the forked twig, for some say that it is of the greatest use in discovering veins, and others deny it." | [
"In the 19th and 20th centuries a lot of mining for metal ores took place in the town, concentrated on lead, silver, zinc and copper. The Romans had already dug for ores using open cast mining, which continued throughout the Middle Ages. The many indentations on Blöskopf Hill bear witness to this period of history.... |
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