question stringlengths 3 301 | answer stringlengths 9 26.1k | context list |
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Why does my skin look different under different lighting conditions? | Different kinds of lights are composed of different wavelengths of light. That is some lights have more red others more blue etc. When these reflect off your skin which reflects different colors differently you get different colors. It has nothing to do with x-rays. | [
"Skin-lightening products are still prevalent in many parts of the world. This may be due to aesthetic or social-standing reasons, in areas where a lighter skin tone is considered to be a sign of wealth or beauty.\n",
"Often restaurants, bars and other social gathering places will dim lighting to maximise amber s... |
if the polar ice caps were developed during the last ice age, why is it so bad that they are melting now? isn’t that more of a return to where we were rather than an anomaly? | The earth doesn't give a shit what's happening to it. You do along with all the things that live on it because they've adapted to the conditions that existed after the last ice age and they don't want to adapt again to rapidly changing conditions because that means a lot of them and their offspring are going to die. | [
"Earth's polar caps have changed dramatically over the last 12,000 years. Seasonal variations of the ice caps takes place due to varied solar energy absorption as the planet or moon revolves around the Sun. Additionally, in geologic time scales, the ice caps may grow or shrink due to climate variation. If the polar... |
With the massive influx of gold miners immigrating to California during its gold rush, was there enough food and water grown locally for them? Was food sent in? The miners obviously weren’t growing their own food. | Water was usually not a problem - the California Gold Country has plenty of streams and rivers. During the drier times, miners had to wait for enough flow to "wash dirt" - the method used to expose gold, but there was always enough to drink.
Miners spent a lot of time hunting. I co-edited the [letters of the Grosh Brothers](_URL_0_) - placer miners in the California Gold Rush. They described how two of their group would wash dirt while one or two others would go hunting. They would then share everything that each was able to produce during the day - food and gold. That was the typical approach for the first miners in the Gold Country.
There were also those who farmed. The Grosh Brothers gave up mining at some points and took up agriculture, but the lure of gold always brought them back (and they eventually died in the effort). There was also a great deal imported to California. Ships were repeatedly making the trip to Mexico and South American, bringing back passengers (and the mail!), but also a great deal of food grown in those areas. Costs were inflated in Gold Rush-era California, but acquiring food was not difficult.
As the Gold Rush went through its cycle of initial rush, depletion of gold, and then retreat from the Gold Country, infrastructure improved and more people were involved in agriculture, exploiting the rich natural resources of Northern California, which continue to feed the nation. Acquiring food was never that big of a problem; the real question was a matter of distribution and cost, but since the first years were "flush" with gold, money was no object. | [
"During the California Gold Rush there were many new immigrants who were familiar with fishing. There was a large demand for fresh food including fresh fish and shellfish among the rapidly increasing California population. Providing fresh food products were one of the most wanted and lucrative trades that developed... |
How have the eyes of animals that need clear vision in and out of water evolved to cope with the varying refractive indices? | Anableps fish just have eyes that are half-and-half divided, with the top half working well out of water and the bottom working well in. It's _weird_.
Seal pupils contract in the bright light of the surface, and their eyes focus better in air. In dim light (like they experience underwater) the pupils expand and the eyes focus better underwater. But at night on land, their pupils expand and their eyes can't cope well with seeing through air, giving them terrible night vision. It's apparently pretty entertaining to walk around a beach where they have hauled out at night....they know you are there but can't actually see you well at all. | [
"Aquatic animals must rely entirely on their lens for both focusing and to provide almost the entire refractive power of the eye as the water-cornea interface does not have a large enough difference in indices of refraction to provide significant refractive power. As such, lenses in aquatic eyes tend to be much rou... |
why, when most people orgasm, they instinctively want to vocalize their excitement/expressions? | No scientific answer here, but I can only assume it is like any other "unexpected" rush of emotions or feeling. When you step on a nail, you shriek. When you burn your hand, you shriek. Just like anonoman925 said, it is probably an involuntary reaction to too much stimulus.
TL;DR: Too much stimulus = Involuntary reaction. | [
"Normally, a human being is able to feel pleasure from an orgasm. Upon reaching a climax, chemicals are released in the brain and motor signals are activated that will cause quick cycles of muscle contraction in the corresponding areas of both males and females. Sometimes, these signals can cause other involuntary ... |
What would happen if a MAGLEV train lost power? | They have wheels. | [
"The train started moving at 09:53. 57seconds later emergency braking was recorded. Approximately half a second and 25metres later the maglev train hit the maintenance vehicle at a speed of 162km/h. The aerodynamic design of the transrapid caused it to dive under the heavy (60 tonne) maintenance vehicle, ripping of... |
how would the space agencies respond if they detect an incoming asteroid large enough to cause damages? | The space agencies would report it to the public. They are in no position to keep anything like that a secret and in no position to do anything about it. The only thing they can do is warn people the best they can in the hopes that people might get to safety. The only thing anyone might be able to do about it is to launch a nuclear ICBM against it in the hope that it will break up and cause a number of smaller less dangerous meteorites. The space agencies does not have ICBMs as they are used by the military but the space agencies will hopefully be able to help in such an event. We have not tried such a thing either and have no idea if an ICBM can fly the radically different flight path needed or what a nuclear device does to an asteroid. | [
"Sub-150m impacting asteroids would not cause global damage but are still locally catastrophic. They can, by contrast to larger ones, only be detected when they come very close to the Earth, which in most cases only happens during their final approach. Those impacts therefore will always need a constant watch and t... |
how are news outlets and online articles able to be so misleading and sometimes downright wrong with their stories? | Back up a bit and imagine a government body who's job is to decide what is and isn't true, and to censor or fine news agencies that it believes are wrong.
A) It would be incredibly unconstitutional, as freedom of the press is a critical right that we all have.
B) Consider the possibility of abuse. Is it staffed by people? If yes, then its entirely possible that they'll bring in their own biases, and start shutting down points of view that they disagree with.
C) What is true or false. We can all think of blatant examples, as that's easy. Where do you draw the line. Could an organization be punished for a mistake? How about a matter of opinion, which much of the news media focuses on. Are you willing to give a government agency the ability to silence reporters because their opinions are "wrong," or because the person they're interviewing is wrong about something.
Such a thing could never be safely or effectively implemented in a free country. | [
"Because news organizations and websites hotly compete for viewers, there is a need for great efficiency in releasing stories to the public. News media companies broadcast stories 24 hours a day, and break the latest news in hopes of taking audience share from their competitors. News is also produced at a pace that... |
why do injuries tend to hurt more in winter than in summer? | Generally speaking, we feel more pain in the cold because there is a relationship between blood circulation and nerve pain. When its cold outside and you aren’t dressed up for it, it’s very difficult for your body to heat itself because your heart rate slows in the cold as a way to survive. Our nerves are a network that send signals to the brain -ouch- that hurt! As circulation and heat increase our nerves calm down. The cold is more painful because it increases pressure on our nerves and stiffens soft tissues- such as your muscles. This in itself can increase your likelihood of injury (which is why runners do warm ups and wear sweats!) | [
"During the summer rains are common in the late afternoon. Temperatures at this time are always very high. In the winter the arrival of polar air masses that drop and cause frost. In this time of year the relative humidity is too low, and causes discomfort to the population.\n",
"Rising temperatures have two oppo... |
How can moons get "captured" by planetary bodies without having done a "retrograde burn"? | Triton is Neptune's captured moon. To go into orbit, Triton still had to lose momentum somehow, just as you do a burn to get captured by Duna (or, perhaps get your orbit adjusted by Ike). In KSP, the moons and planets are all on rails, but in real space, you would transfer some of your momentum to Ike to get captured by Duna. Your orbit will still intersect Ike's, so you'll either get ejected or eventually settle into a resonance.
Neptune probably didn't have a large moon for Triton to transfer momentum to -- but Triton, like Pluto and many other outer solar system bodies, was probably a binary object. So Triton's partner got sped up as Triton slowed down, letting Triton get captured by Neptune while its partner got boosted to higher-energy orbit. | [
"The mission to Meta is postponed when the crew seemingly contract a virus, later dying on (although the cause of death is subsequently revealed to be \"magnetic radiation\" emanating from nuclear waste disposal areas on the Moon's far side). With the arrival of a back-up crew, preparations for launch resume, but b... |
How did the Merchant Republics in Italy arise in isolation while the rest of Europe seems steeped in Feudalism? | I'm not sure the question as it's posed will yield a satisfactory answer. Feudalism and a republic aren't mutually exclusive, as the former isn't a type of government. Besides, the republics present in Italy weren't the kinds of republics we think of today. They were essentially city-states dominated by elites and ruled by particular noble families (e.g. the de'Medicis in Florence). The Dutch republic and the state of Novgorod functioned in much the same way.
For more info, I'd check out Daniel Waley and Trevor Dean, [_The Italian City-Republics_](_URL_1_) and Perry Anderson's [_Passages from Antiquity to Feudalism_](_URL_0_).
| [
"During the Early Middle Ages, Italy endured sociopolitical collapse and barbarian invasions, but by the 11th century, numerous rival city-states and maritime republics, mainly in the northern and central regions of Italy, rose to great prosperity through trade, commerce and banking, laying the groundwork for moder... |
what causes that characteristic "grandma scent?" | technically it's described as:
* floral
* aldehydic (a sub category of floral, think soapy and citrusy)
* musky
* powdery
To ELI5, it's typically Chanel No 5 with a slight baby powder note. | [
"Phantosmia (olfactory hallucinations), smelling an odor that is not actually there, and parosmia (olfactory illusions), inhaling a real odor but perceiving it as different scent than remembered, are distortions to the sense of smell (olfactory system) that, in most cases, are not caused by anything serious and usu... |
what would happen if you took laxatives for an entire week? | Former laxative abuser here. Assuming you are talking about stimulant laxatives, while continuing a normal diet, the only weight loss would come from holding less waste in your body and dehydration, as your body still digests the food normally. You may experience severe muscle cramps, intestinal bloating from inflammation, joint pain, a sore raw butthole, and headaches from the dehydration. Continued prolonged laxative abuse will also cause nausea, weakness, and can lead to seizures from electrolyte imbalance. Not to mention the normal intestinal cramping from the laxatives itself. There were instances where the nausea and pain were so intense that I would also throw up while having a bowel movement. While taking the laxatives, bowel movements can also become unpredictable, and experiencing random "leaking" is very common, which is usually triggered around half an hour after eating. Your body can also get used to the dose you have been taking, and to continue having the desired effect, you may have to up your dose. Aside, taking stimulant laxatives regularly without continuing to eat can cause you to poop stomach bile, which burns like the fires of hell all the way out. Once you stop taking them after such a period of time, you will experience constipation, as your body has come to rely on the effect of the stimulant laxative to eliminate waste. The constipation will last anywhere from a few days to weeks depending on the individual's response to detoxing from the laxatives. | [
"Methods of prevention include gradually decreasing the dose among those who wish to stop, though it is possible for symptoms to occur with tapering. Treatment may include restarting the medication and slowly decreasing the dose. People may also be switched to the long acting antidepressant fluoxetine which can the... |
if we can't see atoms how did ibm make a movie with them? | Those are Carbon Monoxide molecules.
For that note, electron microscopes can operate pretty much on an atomic scale. | [
"Scientists at IBM used a scanning tunneling microscope to single out and move individual atoms which were used to make characters in \"A Boy and His Atom\". This was the tiniest scale stop-motion video made at that time.\n",
"In 1980, he produced \"The Atomic Alphabet\" – a giant, poster-sized hand-colored litho... |
were little old people always little or do they shrink as they age? | Most people do shrink as they get older and their bodies degenerate.
The very little old people you're thinking of were short to begin with and shrivel up more. | [
"Depending on sex, genetic and environmental factors, shrinkage of stature may begin in middle age in some individuals but tends to be universal in the extremely aged. This decrease in height is due to such factors as decreased height of inter-vertebral discs because of desiccation, atrophy of soft tissues and post... |
Why do some places show a long-term decline in sea level and others a rise? | Measuring sea level is actually tricky business and we're not really *that* good at it currently.
Additionally, there's global sea level and local sea level. Global sea level is mostly affected (at least on human time scales) by the volume and temperature of the ocean (which is mostly affected by melting of surface ice). But the land on Earth is not static, so local sea level ends up being even more complicated with a lot more factors going into it. A major factor around river mouths, for example, is subsidence. The land there is soft, and it settles over time (to simplify) so even if nothing about the ocean changed the water depth at a particular point in a river delta might get deeper over time. Similarly, material deposition can have the opposite effect.
An important factor today is that the Earth only recently, in geological terms, came out of an ice age. For a period of about a hundred thousand years vast ice sheets covered much of the northern land masses. The current location of Boston would have been under more than a kilometer of ice, for example. Those ice sheets were, of course, massive and the water that made them up came out of the oceans, which is why the sea levels were lower during that period. Additionally, the weight of those ice sheets pushed down the continents, which float on the solid but plastic mantle. When the ice sheets retreated with the end of the ice age about ten thousand years ago the water raised the global sea level significantly (flooding a lot of low lying areas) but it also reduced the force that was weighing down the areas of the continents where the ice sheets were. As a consequence many northern land masses have been experiencing a long period of "post-glacial rebound", as slow geologic forces push them toward a different equilibrium elevation than when they were weighed down by glaciers.
This movement is actually large enough to be measurable, and it's highest in places like Norway and Northern Canada. And, of course, Alaska. Southern Alaska is rebounding at a rate of several millimeters per year. Global sea level rise is smaller than this movement so local sea level change in regions still experiencing post-glacial rebound is negative, the sea seems to be going down (though in fact the land is going up). You can see the same thing in [Oslo, Norway](_URL_0_) for example.
But if you look at areas that never had local glaciation and aren't experiencing post-glacial rebound, like [Mumbai, India](_URL_1_), you see a different trend, one of increasing sea level. However, if you look at the sea level trends for a lot of different port cities at low latitudes you'll find that the rates of sea level increase are all over the place, from just a single mm/year up to several mm/year. A lot of that is due to different rates of subsidence. The land moves (both up and down), so trying to measure one moving thing from another moving thing is a very challenging problem.
We've been measuring the sea level with satellites for decades, but even that is not without it's fair share of problems. The main one being that we can't seem to calibrate the measurements of the satellites sufficiently well to actually have much confidence in the exact values of the trend data. We can be fairly certain that there's a global sea level rise but it may be as low as 0.5 mm/year or as high as 2-3 mm/year, it's hard to be certain. | [
"Superimposed on the global rise in sea level, is strong regional and decadal variability which may cause sea level along a particular coastline to decline with time (for example along the Canadian eastern seaboard), or to rise faster than the global average. Regions that have shown a rapid rise in sea level during... |
How do we measure gas levels of an exoplanet's atmosphere? | Molecules have characteristic absorption lines in the electromagnetic spectrum. The width of these absorption lines depends on the optical thickness of the gas. Meaning, with more gas in our line of sight we will have a stronger (wider) absorption band.
In order to measure the atmosphere of a planet, the planet needs to orbit infront of the star. Then some light of the star will pass through the planets atmosphere. We can then compare the spectrum of the star with the planet and without. The difference between the two spectra allows us to see the effect of the atmosphere of the exo planet on the spectrum. By using some sophisticated data and error analysis it is theoretically possible to estimate the content of the atmosphere. However in order to reliably do this you need very high resolution spectrographs and you need to be able to estimate all the other parameters that can also broaden the spectral lines. This could be thermal doppler broadening of atmospheric molecules, broadening due to the rotation of the planet, shifts due to the motion of the planet around its host star, pressure broadening, etc. etc. It is not a trivial process and this kind of technology is not very far yet. However our technology improves every year and we make theoretical advances every year so soon we should be able to characterise exoplanet atmospheres more reliably. | [
"The first exoplanet whose atmospheric composition was determined is HD 209458b, a gas giant with a close orbit around a star in the constellation Pegasus. Its atmosphere is heated to temperatures over 1,000 K, and is steadily escaping into space. Hydrogen, oxygen, carbon and sulfur have been detected in the planet... |
Education in post war Germany? | > How valued were their qualifications?
In West Germany the folks behind the racial science of the nazi regime [kept teaching their subjects](_URL_0_) using their skills to, for example, measure the skulls of the Canary Islanders. The continuity of West German elites would be a major issue both to East Germany and in the West German public.
> But what happened after the war to everyone who had been socialised into believing this?
what was done to "reeducate" or "denazify" Germans has been asked before so here's a primary source on the opinions immediately thereafter:
> Report No.12 (28 June 1946)
> ATTITUDES OF SOME BAVARIAN SCHOOLCHILDREN
> Sample:250 schoolchildren between the ages of 12 and 18 in
Regensburg, Weilheim, Pirkensee, and Burglengenfeld
Interviewing dates:not specified. (6 pp.)
Although 88 per cent of the children had belonged to Nazi youth
organisations, only 12 per cent were members of a new youth
organisation. Thirty-seven per cent of their parents had belonged
to the NSDAP,a figure about average for the American zone. Eightyfour per cent of the youth were Catholic. Most (48%) would vote
for the CSUif they were old enough, 18 per cent for the SPD, and
three per cent for the KPD. Almost a third (29%), however, said
they would not vote even if they could.
> Their principal concern was obtaining food. Thirty per cent said
that the type of aid Germany needed most was food, and 26 per
cent reported that their greatest wish was for more food. They also
desired peace and freedom for their brothers who were prisoners
of war. Their secondary concern were jobs, clothing, and shoes.
The children seemed to be in good health. Reading, sports, and
handicrafts provided recreation.
> Almost all the children (98%) claimed to like school. Most (66%)
thought themselves to be average students. About one-third
considered themselves to be good students. Only a few (3%)
admitted that they were bad students. Although they were interested
in a wide variety of subjects, they liked best mathematics, German,
geography, history, biology, and English. Seventy-four per cent
preferred to learn English rather than some other foreign language.
The employment aspirations of the youth were generally low.
The girls wanted to be saleswomen, dressmakers, clerks, teachers,
or hairdressers. The boys wished to be bakers, electricians, or
carpenters. None of the boys wanted to teach. More girls (7%)
than boys (3%) hoped to become physicians or dentists.
The most common reason given (36%) for Germany’s loss of
the war was the overpowering strength of the enemy. Second
(30%) was Germany’s lack of material. When asked to name the
three greatest Germans, about ten per cent named Hitler, a
quarter mentioned monarchs, and a third poets. When
questioned as to what the respondent would do if he alone knew
the secret of the atom bomb, the most common answer given
(36%) was to keep it a secret. Democracy to these youths meant
freedom for the people (23%) and government by the people
(10%). Forty-eight per cent, however, had no opinion when
asked what democracy meant.
> Almost as many (35%) liked the American soldier as disliked
him (39%). More than half of those who disliked the American
soldier mentioned his general behaviour as a reason.
Most of the youth expected a good, lasting, or just or wise peace
from the Allies. Fifty-nine per cent did not expect another war
soon. Of the 41 per cent who did expect war, most thought it would
be with the Soviet Union. | [
"After the defeat in World War II, the Allied occupation government set education reform as one of its primary goals, to eradicate militarist teachings and convert Japan into a pacifist democracy. Nine years of education was made mandatory, with six years in elementary education and three in junior high as an emula... |
Can house flies, fruit flies, or other insects see the microscopic organisms or bacteria on stuff that we can't see? | I don't believe they can. Their eyes, [compound eyes](_URL_1_), are not intended to see high detail images because their largest threats are larger than they are (ie, a cow's tail or your hand trying to swat them). Instead, they are intended to see fast movements over a large angular resolution, they can see movements from more angles than we can (again, the cow's tail or your hand coming in from a weird angle) however, their eyes lack [visual acuity](_URL_0_). | [
"BULLET::::- Insect stages - \"Some larvae, nymphs and adult insects that live in freshwater.\" \"A UK-based web site with microscopic photos of various insects and other microorganisms as well as biological information.\"\n",
"Micro-animals are animals so small that they can be visually observed only under a mic... |
why do some people enjoy massages but it causes pain for others? | There is a huge difference between massages just for the feeling of someone rubbing your back with some more force in it and massages for relaxing muscles. I have a rather high pain tolerance, but if my muscles are really tense, having them massaged hurts *a lot*. I can't give you a good explanation for that (any physicians/medicine-students around here?), but this is one reason why a lot of people do not enjoy massages meant for really relaxing the muscles. And if my muscles are really tense, even slightly pressing them will hurt, so maybe your neck is just ridiculously tense? In this case I'd recommend going to get a medical massage. I've known folks running around with muscles that were never really relaxed for years. They didn't even know what a relaxed back feels like, so they didn't miss it.
Massages for relaxing the muscles are generally made harder, so they might even hurt slightly if your muscles are not tense and you are not "used to it" (meaning your pain tolerance to this kind of pain is very low). Another possibility: The guys giving you a massage didn't know, what they were doing. A wrong massage hurts too, but it will only tense your muscles even more. | [
"People state that they use massage because they believe that it relieves pain from musculoskeletal injuries and other causes of pain, reduces stress and enhances relaxation, rehabilitates sports injuries, decreases feelings of anxiety and depression, and increases general well being.\n",
"All types of massage, i... |
When was the highest % of the global population enslaved and did ancient societies with more slaves have an economic advantage over their rivals? | Follow-up: Did areas with high percentages of slaves have poor freemen angry over economic woes? It seems like there would be a shortage of paying jobs when the wealthy could simply buy slaves to fill almost every role from farmhands to pedagogues. | [
"According to the \"Encyclopedia of African History\", \"It is estimated that by the 1890s the largest slave population of the world, about 2 million people, was concentrated in the territories of the Sokoto Caliphate. The use of slave labor was extensive, especially in agriculture.\" The Anti-Slavery Society estim... |
why is it easy to pick up a child that weighs 40 to 50 kilograms but very difficult to pick up a 40 to 50 kilogram weight? | The weight of the child is spread out over a large area compared to the relatively small area of the weight, making the child appear easier because it uses more muscles. | [
"For instance, the factor \"153,552,935\" (5 turns around a capstan with a coefficient of friction of 0.6) means, in theory, that a newborn baby would be capable of holding (not moving) the weight of two supercarriers (97,000 tons each, but for the baby it would be only a little more than 1 kg). The large number of... |
If an Amnesia victim has lost their memories for a significant amount of time and recovers their memories, will they regain their original personality or keep the amnesia personality? | What we observe as personality is the product of variance in regions of the brain- this study, for example, shows the correlation between neuroticism and amygdala variance- _URL_0_ . An individual's personality is quite stable over the long run- see here _URL_1_ and here _URL_2_ .
Amnesia, specifically in your case retrograde amnesia, impacts the brains ability to utilize its episodic memory system. From the wikipedia article on amnesia- "This type of amnesia first targets the patient's most recent memories, the amount of memories lost depends on the severity of the case. The person may be able to memorize new things that occur after the onset of amnesia (unlike in anterograde amnesia), but is unable to recall some or all of their life or identity prior to the onset. The effects of retrograde amnesia (RA) occurs on fact memory on a lower degree than its affects on autobiographical memory, which can be affected over the whole lifespan of the patient by RA."
So, to answer the question, personality wise, they would be the same throughout. If their memories returned, their personality wouldnt change- all that would change is their ability to recall the memories they had "lost". | [
"The form of amnesia that is linked with recovered memories is dissociative amnesia (formerly known as psychogenic amnesia). This results from a psychological cause, not by direct damage to the brain, and is a loss of memory of significant personal information, usually about traumatic or extremely stressful events.... |
can alcohol turn you into a different person? | In my experience, alcohol just loosens inhibitions. So people who "get mean" when they drink are just mean people who usually keep it together. Just like I get really sentimental when I drink; I'm a sentimental guy, it's just normally under the surface. | [
"To produce a spiritual conversion necessary for sobriety and sanity, alcoholics needed to realize that they couldn't conquer alcoholism by themselves—that surrendering to a higher power and working with another alcoholic were required. Sober alcoholics could show drinking alcoholics that it was possible to enjoy l... |
Like Google Maps...but for History | The website [GeoCron](_URL_1_) is a good place to start. You can skip to any year and it will show you roughly what the world looked like. It is not entirely accurate at some points, like sometimes the author just places a circle and the name of the civilization where he may not have much information. However, it is a good place to start and gives a good visual of empires, the first civilizations, and the such.
Of course, more detailed maps can be used in collaboration with GeoCron to give your students a better understanding. I have found [Euratlas](_URL_0_) to be a decent sources for maps of different European regions in 100 year increments. So a bit of big stretches between maps, but decent if it has one near the year you are interested in. | [
"BULLET::::4. Google Maps beginning as a \"thought bubble\" and a series of random scribbles on a white board in 2004 by Noel Gordon, one of the four men who founded the Sydney-based software company Where 2 Technologies. Google Earth developed separately in the US around the same time while Google Street View foll... |
modulo | Mod is basically the remainder of a division problem.
50mod7 is 1 because 50/7 = 7 with a remainder of 1. 7*7 = 49. 49 + 1 = 50. 50mod7 = 1.
39mod5 = 4
100mod12 = 4
92mod3 = 2 | [
"\"Modulo\" is mathematical jargon that was introduced into mathematics in the book \"Disquisitiones Arithmeticae\" by Carl Friedrich Gauss in 1801. Given the integers \"a\", \"b\" and \"n\", the expression \"a\" ≡ \"b\" (mod \"n\") (pronounced \"\"a\" is congruent to \"b\" modulo \"n\"\") means that \"a\" − \"b\" ... |
Why have no new phyla developed since the Cambrian Explosion? | This is because of the way that phyla (and other taxonomic groups) are defined. Phyla are essentially arbitrarily-defined groups, and there is no particular amount of structural or genetic divergence that causes us to classify a particular group as a phylum. However, like other taxonomic groups, scientists do strive to make phyla represent monophyletic groups (groups of organisms that contain a common ancestor and all of its descendants). This means that in order for a new phylum to be recognized, we would have to split up a currently recognized phylum, possibly into several groups. | [
"In the 1970s there was already a debate about whether the emergence of the modern phyla was \"explosive\" or gradual but hidden by the shortage of Precambrian animal fossils. A re-analysis of fossils from the Burgess Shale lagerstätte increased interest in the issue when it revealed animals, such as \"Opabinia\", ... |
Before French and Latin, has there been any other lingua franca? | Greek! The Romans themselves were Grekophiles, and most well-educated Romans would be expected to know Greek. Greek was the lingua franca of the eastern Mediterranean (and was also widely spoken in many western mediteranean settlements like Massalia and Emporion) and continued to be the primary language of communication there up to the fall of the Byzantine Empire. [You can read more here](_URL_0_). | [
"The term \"lingua franca\" derives from Mediterranean Lingua Franca, the pidgin language that people around the Levant and the eastern Mediterranean Sea used as the main language of commerce and diplomacy from late medieval times, especially during the Renaissance era, to the 18th century. At that time, Italian-sp... |
Why does it spread germs/illnesses to leave a bathroom with hands unwashed, yet oral-genital contact is not regarded as a surefire way to get the same illnesses? | Washing your hands after using the bathroom is not just about the germs gathered during the time using the bathroom. Ingraining that habit into people while they are at a sink with water gets them to clean away other germs they may have picked up without having to make a special trip to wash.
Human fecal matter is the real germ problem, not the human genitals. The genitals themselves, if clean should carry no more germs than the rest of the skin. Ineffective wiping however leaves fecal matter, and potentially it ends up on the hands. Washing removes it. In reality a male standing to pee, or either gender who doesn't wipe at all shouldn't be gaining any more germs on their hands than from any other activity. Its just easier to train people to always wash after a bathroom event so the bases are covered. It has the added benefit of removing other germs gathered before the bathroom event. | [
"General sanitary hygiene is the most important method of preventing sapovirus. This can be done by thoroughly washing hands after using the restroom and before eating/preparing food. Contaminated surfaces should be cleaned with disinfectant and or solutions containing bleach. Other preventative measures include av... |
how can i invest and grow my money without knowing how to invest? | The market overall is down right now, so it makes sense that you lost some money. The three main things you need to know: Investment gains are slow; it wouldn't be a surprise for it to take a year or so before you make $10 on $500. The safest way to invest is to diversity; buying shares of an index fund or an ETF will let you invest in hundreds of stocks at once rather than putting all of your cash into one or two companies. Third thing to consider is what pre-tax investment options you have. See if your work offers a 401k plan; any money you put into that wont get taxed until you take it out, and some employers will give you extra money for contributions you make to it. | [
"By investing \"directly\" in an institution, rather than purchasing stock, an investor is able to create a greater social impact: money spent purchasing stock in the secondary market accrues to the stock's previous owner and may not generate social good, while money invested in a community institution is put to wo... |
what is the difference between the various semi-automatic gun mechanisms? | The most simple form is straight blowback
Straight blowback works by having an unlocked bolt behind the round in the chamber. when the gun is fired the gas pressure exerts a force on the bolt and it is forced away from the chamber. As it moves rearwards the empty case is pulled out. When the bolt reaches the rear of it's travel it moves forward again using the force stored in the recoil spring. On the way forwards it strips a new round from the magazine and pushes it into the chamber ready to fire again. The main disadvantage of blowback firearms is that the only thing keeping the bolt in battery (against the chamber) is the inertia of the bolt. In order to be safe the case needs to be supported in the chamber until the pressure in the chamber has dropped (after the bullet has left the barrel). As the power of the round being fired increases the mass of the bolt must increase.
Delayed blowback is similar in operation except there will be some mechanism that will increase the inertia of the bolt without adding mass. For example the roller delayed blowback system used in the HK MP5 sub machinegun and G3 rifle or the lever delayed system used in the FAMAS rifle. The mechanism generally works by having a two part bolt having some method of forcing one half to move faster than the bolt face thus giving the bolt assembly more inertia than a one piece bolt of the same mass.
Blow forward is the opposite of blowback. The bolt is in a fixed position and the drag of the bullet travelling through the barrel pulls the barrel forwards off the empty case. As the barrel reaches the end of it's forward travel the empty case is ejected and the barrel returns under spring pressure. As it travels back it collects a new round and chambers it. This method of operation is extremely rare and was only used in a few firearms
Recoil operation means that when the gun is fired the bolt and barrel both move backwards together. This gives the bullet more time to leave the barrel than a blowback design. There are two main types of recoil operation: short recoil and long recoil.
Short recoil operation means that the barrel and bolt are locked together when in battery and only travel a short distance before the barrel unlocks from the bolt. After this happens the barrel stops and the bolt continues. The empty case is ejected and the bolt returns forward collecting a new round and chambering it. The bolt gets to the barrel and moves it forward into the locked position ready to fire again. Most semi-auto pistols use a short recoil action with a browning tilting barrel design which works by locking the barrel into the slide via locking lugs above the chamber. As the barrel moves rearward it drops down which disconnects it from the slide. For example see the 1911. Other short recoil systems include the toggle locked (luger pistol) and rotating barrel (gsh18, beretta px4).
Long recoil operation means that when the gun is fired both the bolt and barrel travel all the way to the end of travel. At this point the bolt stays at the rear and the barrel returns to the forward position. When the barrel slides off the empty case which is held by the bolt the case is ejected and the bolt then moves forward collecting a new round and chambering it. An example of this is the Browning A5 shotgun.
Gas operated firearms use tap some gas from a port in the barrel and use it to operate the gun. Gas operated firearms can be put into 2 categories: direct impingement and piston operated.
Direct impingement firearms work by blowing gas directly at the bolt carrier which then moves rearward unlocking the bolt and ejects a round. For example the AG m/42 rifle.
An alternative is the system used in the AR10 and AR15 rifle which is where gas is tapped off the barrel and directed into the bolt carrier via the gas key. Once inside the carrier it expands in the space behind the bolt (which has a gas piston and rings at the rear) causing the bolt carrier to move rearward and unlock the bolt and then carry it the the rear. If memory serves this system was originally called an "expanding gas system" but is usually called direct impingement now.
Gas piston systems work by directing gas from the barrel and using it to push a piston which moves the bolt carrier to operate the firearm.
There are two types: short stroke and long stroke systems.
Short stroke is where the piston only travels a short distance just enough to give the bolt carrier a kick which sets it into motion. Examples of this are the HK G36 rifle, FN SCAR rifle and the Steyr Aug Rifle.
Long stroke is where the piston is attatched to the bolt carrier and travels all the way to the rear and all the way forward again. For example the AK47 rifle and M1 Garand rifle.
Two different ways that the bolt can unlock are by tilting or rotating. All the rifles I mentioned previously as examples of gas piston systems all have rotating bolts. Examples of tilting bolts are the VZ58 rifle and the FN FAL.
Other actions exist too, I forget the name but there is a gun that used a combination blow forward/blow back action. Also check out the Mateba auto revolver. | [
"The language surrounding automatic, semi-automatic, self-loading, etc., often causes confusion due to differences in technical usage between different countries and differences in popular usage. For example, the term \"automatic pistol\" technically refers to a machine pistol which is capable of firing multiple ro... |
sound. yes i get that is a wave but how is a wave able to encode so much variety (voice, instruments, sound effects)? | If it were a single wave, it would not convey so much. But sounds like you describe are a series of waves, spread out over time and interpreted by an excellent computer -- your brain. | [
"Wave Sequences were first introduced on Korg's Wavestation synthesizer, released in 1990. Wave Sequences allow a single note to play through a list of samples, one after the other, with or without crossfades, with other associated parameters changing for each sample, as listed below. This can create smooth, evolvi... |
Is this any intuitive way to think about normal distribution function ? | The gaussian distribution is e^-x^2. It is the heart to the shape that is called the normal distribution. The pis, the sigmas, the various other values are just adjustments.
The constant term in front of the exponential is just a multiplier to make the area under the curve equivalent to 1 (so that the sum of the probabilities is 100%.))
The x-a term in the exponent is to shift the function right or left. Ie if you set a to 5, the function would peak at 5.
The sigma is widening the curve. | [
"In mathematics, a distribution function is a real function in measure theory. From every measure on the algebra of Borel sets of real numbers, a distribution function can be constructed, which reflects some of the properties of this measure. Distribution functions (in the sense of measure theory) are a generalizat... |
How different were the peoples of northern Spain culturally, linguistically etc from people in southern Spain during the rule of the Umayyads? | So what you're talking about here is a really long period. I happen to have a decent source that discusses this topic at length in some parts, but I might wander a bit here and there.
So to the beginning. If we look at the early days of conquests in the 8th century, even then the actual conquering force of al-Andalus wasn't uniform ethnically at all. When they crossed the straits of Gibraltar in 711 the troops were mainly composed of Arabs and Berbers, being ruled from Damascus by the (Umayyad) Caliph. They were *very* much a Berber-dominated force, and Maribel Fierro (p8) reports that the number of actual Arabs among them was pretty small, and they had a fairly privileged status being Arabs. At that time there was a fairly strong link between being Muslim and being Arab which was broken down over the years, but in those days it was still quite strong. This meant that people who weren't arabs adopted the status of clients (mawali) of an Arab tribesman or of another convert who already had a patron. Freed slaves were clients as well. So in these days islamicization went hand in hand with arabicization but there were still distinct Berber and Arab cultures.
In 739 there was a pretty big Berber rebellion in northern Africa and the Caliph sent some troops to put an end to it. Without getting too much into detail about this - it led to a big influx of Arabs around Ceuta as a Syrian commander named Balj ibn Bishr al-Qushayri, initially refused passage, managed to negotiate with an Andalusi military governor who was attempting to deal with his own Berber rebellions. I could go on and on about the political consequences of al-Qushayri arriving in al-Andalus for an entire post , but suffice to say they brought their division of Qays and Yemen (northern and southern) arabs with them, although the precise meaning of this conflict in the islamic world back then is still debated. Again, without going into too much detail they were settled (with a lot of argument and dispute) in Granada (Elvira), Seville & Niebla, Malaga, Jaen, Algeciras, Sidonia, Beja and Tudmir.
So the Berbers also had their own culture and existence and how arabicised & islamicised they were depended on whether they were urban or not. So the real cultural divide at that point wasn't necessarily *just* northern/southern, but also urban/rural. The Berbers did however mostly settle in tribal groups in rural areas along the frontier. Please remember that when I say "frontier" here it's in the context of the early 8th century, where the frontier was in what we would consider to be fairly southern in modern Iberia. From what we understand they were mostly autonomous although it's difficult to pull the details out of obscurity with limited archaeological work. But for example, Fierro points out that some patterns of irrigation we find can potentially be linked to Berber tribal organisation, and the existence of these tribal, autonomous Berbers in the northern rural regions is highlited whenever they rebelled against the Cordoban ruler or representatives below him.
Some of these tribal berbers in al-Andalus actually continued their existence well into the Umayyad era of al-Andalus and actually outlived it - some of the taifas after the fitna of al-andalus (the huge civil war that caused the Cordoba Caliphate to collapse from around 1009-1031) were ruled by those who gained power because of Berber tribal military resources & organisation - i.e. the Zirid taifa formed by Zawi bin Ziri. From what I understand, most of these guys survived even the reconquista and the inquisition and although they eventually lost their unique cultural identities, their descendants still live in Spain & Portugal today. But, if you were an urban Berber, you were much more likely to have been a state administrator or a scholar and thus very arabicised and islamicised.
Now, if we look briefly at the christians - sometimes you see them called in secondary sources as "mozarabs" (as arabicised christians) but really I don't like this term, especially because they certainly didn't identify as this and afaik none of the actual Andalusi literature ever uses that term. This term appears in the very late Christian sources as a term they used for Christians who emigrated to the north of Iberia but who spoke Arabic and culturally resembled Arabs rather than those with Visigoth ancestry. But it's not an accurate label as it lumps them all together culturally and linguistically, when in reality a lot of them didn't really share those histories or backgrounds.
Anyway, the vast majority of the Andalusi Christians, like the Berbers, lived in rural areas with fairly limited contact with the Arab settlers & conquerors. Ibn Hawqal in the 10th century, translated by Fierro, wrote an interesting section about these relatively autonomous Christian Andalusis:
> In al-Andalus there is more than one agricultural property on which dwell thousands of people who know nothing of urban life and who are Hispano-Romans professing the Christian religion. There are periods in which they rebel and some of them take refuge in fortresses. They put up a stiff fight, for they are fierce and stubborn. When they cast off the yoke of obedience, it is hard to make them return to it, unless they are exterminated and that is a difficult, prolonged process.
Something I'd like to point out about the "extermination" here that needs to be understood with context is that the history of al-Andalus is also the history of a series of governments dealing with a long series of rebellions. These included arab muslim rebellions, tribal berber rebellions, and many others - so they weren't trying to 'exterminate' Christians per se, Ibn Hawqal is more referring to rebels that can't be negotiated with and so must be defeated by conquest.
Now, Ibn Hawqal doesn't speak about what language the rural Christian spoke but it was likely a Romance language descended from Latin since the local Andalusis weren't monolingual until the mid-to-late 11th century, and even then it wasn't truly monolingual demographically until the 12th century. So yes, between urban and rural areas, and the south to the frontier, there were certainly linguistic divides - with Romance/Arabic bilingualism being common for Christians. Indigenous Christian converts were often called muwalladun - in the way it was used then it referred mainly to people who weren't Arabs ethnically, but were born into Arabic culture and were raised as Arabs. That could be anybody, without a specific indication of religion. Jews in al-Andalus were also very arabicised and in their case, it enabled them to flourish and also paradoxically to preserve their language and ethnic identity.
Despite the rural/urban divides in culture and language throughout the early centuries of al-Andalus, by the time of the establishment of the Caliphate of Cordoba under the reign of Abdul Rahman III, an era that was one of stabilising and unifying the region, a common Andalusi identity finally emerged through the work of scholars but also through the fierce advocacy of the muslim traditions of egalitarianism which Abdul Rahman III was a particularly big supporter of. In those days there was a concerted attempt to eradicate the idea of Arab supremacy (particularly in politics), although it was an uphill battle and never quite manifested in the way that was hoped and muwallads hardly ever managed to maintain the power or positions that they were given by Abdul Rahman III in place of ethnic Arabs.
This is already a pretty damn long post, so I'm going to cut it off here. I would close by saying that yes, the frontier - that changed over time - certainly did see an impact culturally but I would argue that just as big was the divide was between rural and urban areas. | [
"In time Islamic migrants from places as diverse as North Africa to Yemen and Syria and Iran invaded territories in the Iberian peninsula. The Islamic rulers called the Iberian peninsula \"Al-Andalus\". That was the root for the name of the present-day region of Andalusia, the southernmost region of Spain.\n",
"A... |
This Week's Theme: The 14th Century, AD |
**Current**: 14th Century AD
**On Deck:** Resistance and Conformity
**In the Hole**: Propaganda | [
"The 15th century is part of the High Middle Ages, the period from the coronation of Charlemagne in 800 to the close of the 15th century, which saw the fall of Constantinople (1453), the end of the Hundred Years War (1453), the discovery of the New World (1492), and thereafter the Protestant Reformation (1515). It ... |
Do the descendants of the major Japanese clans (Tokugawa, Oda, etc) still have influence or command respect? Are their any clans that still 'exist', so to speak? | After the Meiji restoration, the clans were [converted into noble families](_URL_1_), along the lines of European nobility. Their domains were [converted into prefectures](_URL_0_), with a centralized authority, though they were allowed to keep 10% of the province's revenue. If you're interested in this time period, there's a great biography of Saigo called (unfortunately, due to the horrible Tom Cruise Movie) *The Last Samurai*, by Mark Ravina. It's a really good read.
The nobility was finally eliminated in 1947, though their descendents continued to do pretty well for themselves. ([This book](_URL_2_) is pretty much exactly what you're looking for.) After WWII, they maintained an elitist status, referring to non-former-nobles who became rich as *nariagari* (upstarts) or *narikin* (nouveau riche). They were criticized for being ostentatious with their wealth (austerity was a virtue in old money families, with many boasting their maids wore better kimono than their own daughters). | [
"The was a powerful \"daimyō\" family of Japan. They nominally descended from Emperor Seiwa (850–880) and were a branch of the Minamoto clan (Seiwa Genji) by the Nitta clan. The early history of this clan remains a mystery. Members of the clan ruled Japan as \"shōguns\" from 1603 to 1867.\n",
"The was a prominent... |
Ionized water | Could you be more specific? In general, anyone claiming to make "ionized" water is running a scam, but depending on what device they're selling, it may produce any of a number of things. | [
"Although the exact ion formation mechanism is not clear, water can be ionized directly by Penning ionization. Another proposal is that water is ionized by the same mechanism that has been proposed for atmospheric pressure chemical ionization\n",
"A water ionizer (also known as an alkaline ionizer) is a home appl... |
why do i get these rashes on my throat after i've shaved? | A few years back I switched to a brush+lather shave and never looked back. Canned shave gel is total garbage.
This made all the difference in the world to me. That and picking up a safety razor. | [
"After a hair has been shaved, it begins to grow back. Curly hair tends to curl into the skin instead of straight out the follicle, leading to an inflammation reaction. PFB can make the skin look itchy and red, and in some cases, it can even look like pimples. These inflamed papules or pustules can form especially ... |
what is tickling? why do we have places like on our sides and armpits that makes us laugh out of panic when there is no real danger? | This is just a short explanation based on the video at the end of my comment:
Small tickling (like from a feather) is called knismesis. It makes you scratch/touch places. This is to make us get rigd of insects, spiders and other stuff we don't want to have on our skin. Many animals are ticklish too so it shows us our evolutionary history.
The more rough version (e.g. from fingers poking you) is called Gargalesis. It is something all primates have and might be there to teach each other self defence without hurting each other. It makes you react to something that might hurt your most vulnerable parts.
Source: SciShow about this topic.
_URL_0_ | [
"A third, hybrid hypothesis, has suggested that tickling encourages the development of combat skills. Most tickling is done by parents, siblings and friends and is often a type of rough-and-tumble play, during which time children often develop defensive and combat moves. Although people generally make movements to ... |
Why does some music just sound... Old? Is it recording quality, or were instruments constructed differently? | Can you shoot some examples of what recorded music you're thinking of? | [
"Vintage musical equipment is older music gear, including instruments, amplifiers and speakers, sound recording equipment and effects pedals, sought after, maintained and used by record producers, audio engineers and musicians who are interested in historical music genres. While any piece of equipment of sufficient... |
why is nuclear fusion considered the "holy grail" of nuclear power compared to fission? | > but I fail to understand why fusion is safer
Because it requires extremely specific circumstances to occur. The second those conditions are lost, the reaction can't physically happen. If you don't have enough heat in the system, the fuel won't have enough energy in it to fuse.
> cleaner
It doesn't use radioactive fuel and the radioactive byproducts are extremely minimal.
> produces more energy
This is the same system that powers the sun. You're using E=mc^2 basically. Fission is just using the radioactive release of heavy elements to heat water. Fusion converts the entire atom to energy (well not exactly but that's not important for this discussion).
> I thought fusion required very high energy input to even occur
It does initially but the hope is that once you get it running the power output is larger than the input. And NO this does NOT break physics, the input merely allows for the output to occur, it doesn't magically double itself or whatever.
Another bonus: Fuel is easy to come by. It uses light elements, which are the most common in the universe. There's enough hydrogen in the ocean to last us beyond the heat-death of the universe.
_URL_0_
| [
"As a source of power, nuclear fusion is expected to have several theoretical advantages over fission. These include reduced radioactivity in operation and little high-level nuclear waste, ample fuel supplies, and increased safety. However, achieving the necessary temperature/pressure/duration combination has prove... |
why are white americans not called european americans? similar to asian americans and african americans. | We should not use any of these segregating terms.
We should simply use the term Americans instead. | [
"The term is used by some to emphasize the European cultural and geographical ancestral origins of Americans, in the same way as is done for African Americans and Asian Americans. A European American awareness is still notable because 90% of the respondents classified as white in the U.S. Census knew their European... |
why were trains invented so much earlier than cars? it seems like trains would be harder to manufacture and create. | Imagine a car running a steam engine, burning coal in a furnace, using the heat to heat up water, pump that water, and turn the wheels. Also storage for coal to be able to go hundreds of miles.
This is easier to go in a 200 tonne stab of metal than a tiny box with people inside.
Also no need for steering, just turn wheels and drive forward. | [
"In the early 20th century, when automobiles were still new technology, their production levels were low enough that they could be shipped in sufficient quantities in boxcars. Two to four automobiles would usually fit into one boxcar. But as the automobile industry grew in size, railroads found that they needed to ... |
what's the difference between cs (computer science), cis (computer information science, and it (information technology? | **Computer Science** : It’s the science (mathematics) of how computers inherently work. It would have an answer to this question: If I had a bunch of random numbers, what would be the fastest way to sort them, is it the fastest way? And why is it the fastest way. It often requires writing code but only to verify and quantify an idea.
**CIS**: I’ve got this gigantic set of numbers and letters and words and other data. CIS will answer this question (amongst many other): How can I make sense of this data to find how they’re interrelated
**IT**: I’ve got a business to run that requires selling lemonade. But because I’m a genius lemonade maker and the biggest one in town, I’ve set up many lemonade stands around town that are completely automated. IT answers this question: How can I effectively tie in all these lemonade machines to work seamlessly and serve customers without a moments delay? What computers do I need? How shall I set up my storage? What’s the ideal internet connection to use?
Edit: well shit, good morning to me. Glad this is my most upvoted comment! And thank you for the gold and silver!
Edit 2: Because some of y'all asked me to ELI5 some more, so here's my take:
**Software Engineering**: The customers of Lemonade Inc. need an app to order their favorite kind of lemonade right to their door step. A software engineer would be able to: Make an app that's easy to use, and can be installed on the customer's phone.
**Data Science**: Data science is (amongst other things) using lots of data to draw conclusions about a specific topic. If Bob opened the app made by the software engineer, given his previous purchases, which lemonade flavor can I suggest to him that he is most likely to buy? Also, can I perhaps make him buy another one by showing his wife's favorite lemonade right next to his so he would remember to buy her one as well?
**Computer Engineering**: Computer Engineering deals with actually making the physical computer that will physically run the programs made by the computer scientist or software engineer. Example: Hey computer science guy! I hear you want to run that new number sorting method on a set of 1,873,347,234,123,872,193,228 numbers! Oh, are current processors too slow because they need to do 10x more work than required for this specific task? Ok let me see what your method is, and let me perhaps build a custom processor for you to efficiently do everything in as much time as you expect. (Warning: this is a gross oversimplification of computer engineering, and they dont go around making new custom processors for everyone. I've tried to keep it simple and in line with the examples above!) | [
"Information and computer science (ICS) or computer and information science (CIS) (plural forms, i.e., \"sciences\", may also be used) is a field that emphasizes \"both\" computing and informatics, upholding the strong association between the fields of information sciences and computer sciences and treating compute... |
Historical Fencing in the US of A | Matthew J. O'Rourke, a captain of volunteers on the Union side during the Civil War, published a treatise on the use of the saber in 1872, which was adopted as the Army's standard. You can get a free ebook of the manual here: _URL_0_
The first half of the the book is "the Manual," regulations for how to draw a sword on parade, etc. The Part you're probably interested is the second half, "the Exercise," which contains the actual fencing. If you're familiar with other 19th century military sabre systems, say from the U.K., its fairly similar, but with a few differences.
| [
"Many people self-identify as classical fencers, but do not share the concept of classical fencing described in this article, preferring the early to mid-20th-century style of competitive fencing (which, in the United States, was formalized and governed by the American Fencing League, or AFL) to the more classical ... |
In high and late medieval Europe, German & Yiddish-speaking Jews had very high rates of literacy. However, was this isolated to Hebrew literature or could most Jewish people also read the Latin alphabet? | Gotz Aly (Why the Germans, why the Jews) explained that having extremely limited opportunities, European Jews invested heavily in and prioritized education. Whether their own religious education or secular education. As a result, they often had a mastery or at least understanding of multiple languages.
Being persecuted and discriminated against, Jewish people needed the ability to communicate with the Non Jews they were living with. Accordingly, they had to be able to read and talk in the language of their neighbours. | [
"By the Middle Ages, large numbers of Jews lived in the Holy Roman Empire and had assimilated into German culture, including many Jews who had previously assimilated into French culture and had spoken a mixed Judeo-French language. Upon assimilating into German culture, the Jewish German peoples incorporated major ... |
what does the death of kim jong-il mean for north korea/the rest of the world? | It's very hard to say at this point. There is very little information out about Kim Jong-un and we have no clue whether the regime will be better or worse under him. One of the many problems that analysts have outlined is that it isn't just the outside world that is unfamiliar with Kim Jong-un. Most North Koreans, outside of his name, aren't familiar with the successor either. Analysts say that this could lead to the government making drastic moves in order to make the North Korean people embrace the new ruler and the most obvious way in which a North Korean leader can gain approval is through aggression towards South Korea. Another cause for concern is the issue of having a power vacuum in a state possessing nuclear weapons. No one is sure as of right now whether North Korea is even dealing with a power vacuum as Kim Jong-Il's illness was well known and Kim Jong-un was being prepared to succeed his father. However, if there is, this situation could lead to disaster as potentially, many people could have access to these nuclear weapons.
EDIT: Another interesting note that may or may not be important in predicting what Kim Jong-un's regime will be like is the fact that he was educated at an international school in Berne, separating him from his NK-educated father and grandfather. This could mean that he will have more western principles and as a result, he might not be as radical as his predecessors. | [
"Kim Jong-il's funeral took place on 28 December in Pyongyang, with a mourning period lasting until the following day. South Korea's military was immediately put on alert after the announcement and its National Security Council convened for an emergency meeting, out of concern that political jockeying in North Kore... |
what the suds in dish soap do and how they work. | Dish soap is made out of special molecules are both polar (slight charge) and non-polar. This property allows them to form a microscopic "bubble" called a [micelle](_URL_0_) around non-polar molecules (such as fat and oils) which can then be dissolved in water. The reason it is so hard to get things like oil off of your hands without soap is because they are non-polar and do not dissolve in water. Using a soap helps to dissolve the oils and they can then be washed off of your hands with water. | [
"A soap dish is a shallow, open container or platform where a bar of soap may be placed to dry after use. Soap dishes are usually located in or near a sink, shower, or bathtub. Most soap dishes are made from waterproof materials such as plastic, ceramic, metal, or glass, though some are made from bamboo. A china sa... |
Atlatls VS bows in the Americas | [This post](_URL_0_) has it that bows and arrows emerged between 3-4 thousand years ago, probably independently, in a number of locations in North America. To my knowledge, atlatls were widely spread throughout North America both before and after bows were in use.
| [
"The spear-thrower was used by early Americans as well. It may have been introduced to America during the immigration across the Bering Land Bridge, and despite the later introduction of the bow and arrow, atlatl use was widespread at the time of first European contact. Atlatls are represented in the art of multipl... |
What is the limiting factor in human eyesight? | At some point, the eye will be diffraction limited (see Rayleigh Criterion and Angular Resolution [here](_URL_0_)). Even if your eye was physically perfect/ideal in every way, your vision is still limited by the size of the circular aperture of the eye.
I actually did a presentation on this for a lower division physics class and can send it to you if interested, but I can't do that until tomorrow (have to get the file from a lab computer).
EDIT: [Link to said small presentation](_URL_1_). Only three slides, and only one really discusses the physics.
Second edit: I do remember attending a talk where the speaker discussed using a clever algorithm to combine input from multiple lenses (i.e. two eyes) to beat the diffraction limit, but it didn't provide a huge increase in resolution by any means. Will try to hunt down the abstract. | [
"In anatomy, an eyestalk (sometimes spelled as eye stalk or known as an ommatophore) is a protrusion that extends the eye away from the body, giving the eye a better field of vision. It is a common feature in nature and frequently appears in fiction.\n",
"The external limiting membrane (or outer limiting membrane... |
is it true that the 1960's-1970's middle east was super civilized and progressive, and if so, what the hell happened? | Pakistani here!
In the 60s, we were very progressive. Free market economy, thriving banking sector, largely secularist (Alcohol, clubbing and everything was part of society). Then the cold war happened.
In the mid 70s Prime Minister Bhutto, a socialist, was forced to outlaw alcohol by pressure from the Islamic clergy. He gave in to several other of their demands and that's when the left begun to fall. Bhutto was also anti American, opting to ally himself with the Soviets and China. So naturally, when the Shah (Pro US) was overthrown in Iran by the Shia religious faction (Anti US and Saudi), it was time for Bhutto to bite the dust. The US helped the then Chief of Army Zia ul Haq to take power and ousted Bhutto. Bhutto was hanged shortly afterwards.
Now Zia was super Islamist and nationalist. And the US wanted to deter Soviet influence in the then Socialist Republic of Afghanistan. So then came the Afghan Jihad. The US and Pakistan Army started the Al Qaeda and the Taliban to fight the Soviets in Afghanistan. To strengthen this, massive nationalistic and Islamist propaganda and policies were introduced. This included lashing in public, making it mandatory to wear Islamic clothing (people wore western before the 80s), making it mandatory to learn government dictated Islamic studies and Pakistan studies (wasn't even a subject in school before this) and all sorts of policies to radicalize the masses. He also introduced heavy Islamic laws such as blasphemy and sharia. Basically, Pakistan went from being bad to worse in the 80s to pump propaganda and control the masses. The cold war ended, the US left and in the 90s, Pakistan was left in shambles with a radicalized public and a poor economy.
When Musharraf came to power in 1999, he introduced liberal and free market policies. Bless that man otherwise Pakistan would be a complete shithole like Iraq or Afghanistan now. Today, urban Pakistan is progressive and liberal whilst rural Pakistan is still Islamist and radicalized. Issue is, it's difficult to de-radicalize two generations of people indoctrinated with religious and nationalistic propaganda in the rural areas while it was very easy to do so in the urban areas within a decade where people have access to free media and western education. So there's a rift in Pakistan now. Rural folks see urban folks as *shameless* and westernized whilst urban folks look at them as backward and blame them for pulling the country back. | [
"The modern Middle East was shaped by three things: departure of European powers, the founding of Israel, and the growing importance of the oil industry. These developments led increased U.S. involvement in Middle East. The United States was the ultimate guarantor of the region's stability as well as the dominant f... |
What are some good books about US Armored Forces in WWII | More generally Band of Brothers and Citizen Soldier are two great books if you want more of a narrative than a by-the-numbers historical account. Do realize that with books by Steven Ambrose you would do well to research what may or may not have been plagiarized. The core message is still solid even if Ambrose had sticky literary fingers.
Steven Zaloga (being lazy, linking wikipedia for a book list here _URL_1_) is a good source for discussion of US tank tactics and strategy in WW2.
Forty too. _URL_0_
To elaborate a bit on the M4 and the M26, Patton personally had very little to do with the delay- he was no stranger to the inadequacy of the M4 and even ordered his own troops to engage in on-field modifications to effectively upgrade M4's to their Jumbo Sherman counterpart. He wasn't even in a position to decide what did and didn't get built.
Unfortunately US tank doctrine was decided by a career artilleryman, and intended as a reaction to Blitzkrieg tactics; dedicated tank fighting groups were separate from the main US forces and intended to move from fire fight to fire fight (which explains why the US was the only major nation in WW2 building tank destroyers with very light armor, fully operational turrets *and* open tops) while the M4 Sherman was intended as an infantry support tank. In that sense it was a fantastic tank- it excelled at the same role that the Panzer 4 was intended for (the soviets and the British had no clear contemporary tanks) but was grossly inadequate at fighting late war tanks like panthers and tigers. That was a job intended for the M10, M18 and M36.
US tank doctrine was largely inflexible because everything had to be shipped 3000 miles from US factories to the European front. Which is why the M26 joins a laundry list of potent tanks that never made it past prototype phases or saw only limited production. | [
"At the end of World War II, two 6th Armored Division G3 officers, Majors Paul L. Bogen and Clyde J. Burke along with Aide-de-Camp Captain Cyrus R. Shockey, compiled a \"Combat Record of the Sixth Armored Division in the European Theatre of Operations 18 July 1944-8 May 1945\". The official history by George F. Hof... |
I'm interested in the history of the addition of Hawaii to the United States. What was the reasoning behind it? Did the people accept it with open arms? | Hawaii was a major importer of sugar to the United States in the mid and late 19th century. However, after the McKinley Tariff (1890), which raised taxes on imports significantly, the sugar growers realized that they could bypass the costly tariff by becoming annexed into the US. They staged a rebellion against the local regent, Queen Luliokalani (who was staunchly against foreign influence in Hawaii), and with the help of US marines, forced her to abdicate. President Grover Cleveland, however, had not authorized the action, and after various inquiries into the legitimacy of the uprising (and as something of an anti-imperialist), refused to annex the ripe territory. Hawaii, despite pressure from the US to reinstate Luliokalani to the throne, remained the Republic of Hawaii (ruled essentially by the American sugar plantation owners) until in 1898 William McKinley signed an annexation treaty, largely motivated by Hawaii's usefulness as a staging area in the Spanish-American War. Hawaii remained a US territory until 1959 when Eisenhower signed it into the union as a state, and the residents of Hawaii accepted accepted the referendum nearly unanimously. | [
"Upon the inauguration of William McKinley as the 25th President of the United States on March 4, 1897, the Republic of Hawaii resumed negotiations for annexation, which continued into the summer of 1898. In April 1898, the United States went to war with Spain, and Republic of Hawaii declared its neutrality. In pra... |
why do (most) countries have a tomb of the unknown soldier? | It's mainly just a respect thing. War leaves a lot of dead bodies that no one can identify. I think the British or the French started the tradition around WW1. | [
"Many countries have buried an unidentified soldier (or other member of the military) in a prominent location as a form of respect for all unidentified war dead. The United Kingdom's Tomb of the Unknown Warrior is in Westminster Abbey, France's is buried underneath the Arc de Triomphe, Italy's is buried in the Monu... |
the perceived animosity of the nypd towards bill de blasio. | The mayor has repeatedly come across as being in support of those who are angry with the police, even in instances where that anger is not justified. The mayor isn't seen as being on the side of his police force. | [
"Under Mayor Bloomberg, Kelly's NYPD also incurred criticism for its handling of the protests surrounding the 2004 Republican National Convention, which resulted in the City of New York having to pay out millions in settlement of lawsuits for false arrest and civil rights violations, as well as for its rough treatm... |
Where does the energy go when particle-antiparticle pairs spontaneously appear and annihilate? | The energy doesn't go anywhere, because there was zero energy to begin with and zero energy after.
The particle-antiparticle pairs you're referring to are called *virtual particles*. They aren't real particles, and they don't actually exist. They're mathematical tools that are used in calculations, but they fail to have many of the properties of real particles. In particular, *real* particles have a relationship between their mass, energy, and momentum: E^2 = p^2 c^2 + m^2 c^4. In particular, their (mass+kinetic) energy is always positive. That relationship is not true for virtual particles, and one of the pair of virtual particles just has negative energy (so the pair has total energy zero).
But--just to reiterate because this causes so much confusion--virtual particles aren't real. They're just a mathematical tool. | [
"If a particle and antiparticle are in the appropriate quantum states, then they can annihilate each other and produce other particles. Reactions such as + → + (the two-photon annihilation of an electron-positron pair) are an example. The single-photon annihilation of an electron-positron pair, + → , cannot ... |
How many molecules wide are the sharpest blades? | Obisidian blades can be mere molecules thick, the preferred tool of optometrists. I'm not sure if its the SHARPEST but it is practically impossible to not cut yourself on one
Source: History of art professor, the first hand experience.
[and wikipedia as source](_URL_0_)
Edit: as others pointed out its actually Ophthalmologists | [
"Saw blades come in many different thicknesses and the choice of blade will depend on the material being sawn and nature of the work being done. For very fine delicate work, and for cutting very thin material use a finer blade, and for general purpose cutting a heavier blade. Saw blades have a range of sizes, from ... |
how is it possible to have a hole in your heart, and not die of internal bleeding? | Its not an expression, it is literally referring to a hole somewhere in the heart that there isn't supposed to be. Now bear in mind this doesn't mean there's a hole straight through the heart, or that the hole leads to the exterior of the heart. What it usually entails is that there is a defect in the walls that separate the chambers in the heart, or between the major vessels leading out of the heart.
I presume your curiosity was piqued because of that AMA about the kid and his hole-in-the-heart. Without knowing the exact details of his condition, basically the kid has a hole in the wall between one of his atrium and the adjacent ventricle (there are four chambers in your heart, two atrium and two ventricles). In a healthy heart, the atrium contracts and pushes blood into the ventricle, and then ventricle contracts and pushes the blood out of your heart (either to your lungs or the other organs). The hole between the atrium and ventricle means that when the ventricle contracts, some of that blood gets pushed backwards, back into the atrium.
You can have holes elsewhere in the heart, but the results are usually the same. The flow of blood is disrupted as some of it backflows through the defect.
These are always congenital defects. | [
"When there are holes in the septum that divide the four chambers of the heart the oxygen-rich blood and oxygen-poor blood mix this creates more stress on the heart to pump blood to where oxygen is needed. As a result, you get enlargement of the heart, heart failure (being unable to adequately supply body with need... |
Is there a scientific reason that the hexagon is 'nature's shape'? | Hexagons represent the shape with the lowest possible energy when nested / packed. If you imagine a soap bubble, it pulls itself into a sphere for the same reason - the sphere is the least possible surface area which contains the maximum volume - the lowest energy shape. If you subsequently nest soap bubbles together, the membranes between cells pull themselves into straight walls forming hexagons, as this is the lowest energy configuration. Similarly, this is why bees evolved to construct honeycomb cells in their hives. The close packed hexagons use the least amount of wax in their construction than any other possible shape, conserving energy. | [
"Very similar to the Spiral Chart, the Hexagon Chart is also a matrix of consecutive natural numbers, but the difference is that it starts with 0 in the central point, and the numbers spiral out in the form of a hexagon instead a square. The spiral direction in Gann's original course is also counterclockwise, becau... |
how do airlines know the exact departure and arrival times for flights months out in advance? | Plane routes don't change often. The same flight goes from NYC to LA everyday and comes back everyday. To do the same thing tomorrow. Pretty much only time schedules change is when some airline starts a new route. Or shuts down a route | [
"Time of arrival (ToA, also time of flight) is the amount of time a signal takes to propagate from transmitter to receiver. Because the signal propagation rate is constant and known (ignoring differences in mediums) the travel time of a signal can be used to directly calculate distance. Multiple measurements can be... |
why are all of our fingers different lengths? | [I made a quick video to answer your question](_URL_0_)
If you prefer reading here is what I ran over:
- That it's due to evolution, we need it to improve our grip. We started using tools millions of years ago and we need the grip to use them! We still need the grip to date obviously, for items such as pens, tools and even phones. Try and grab an orange yourself and you will find that you can grip it so well due to the curvature of your fingers, and how because of the different length of each finger you end up holding it in various places which makes for great grip.
- We also need different length fingers to make fists to use as a defensive weapon. We wouldn't be able to make a fist if all our fingers were the same length!
Take it easy! | [
"In the classical Akkadian Empire system instituted in about 2250 BC during the reign of Naram-Sin, the finger was one-thirtieth of a cubit length. The cubit was equivalent to approximately 497 mm, so the finger was equal to about 17 mm. Basic length was used in architecture and field division. \n",
"The digit or... |
During the decolonization of Africa, was there any serious discussion/suggestions for the redrawing of colonial borders? (3rd try) | I touched on this answer in [this thread](_URL_3_), and I discussed the [OAU charter and Cairo Declaration here](_URL_2_). [This thread](_URL_4_) focuses mainly on the formation and adjustment of borders in french Africa, but I do touch on origins of anti-colonial nationalism in the WW2 era.
Those answers amount to this observation: the leadership of newly independent African states were interested in either promoting a coherent Nigerian or Tanzanian & c. national identity, or were interested in a pan-african unionist project. By and large, political leaders feared and opposed "tribalism" and sought to equate it with backwardness, while multi-ethnic nation-state and cross-ethnic national solidarity were vehicles to modernity.
At the same time, Marxist or Maoist revolutionaries also condemned tribalism or ethnic chauvinism. For example, here is a Muleleist manifesto from _les Cahiers de Gamboma_, from 1965:
> Tribalists think, more or less consciously, that the men and women of
their tribe and clan are superior to others, and that as a result the others
should serve and obey them. The tribalist tries to impose the hegemony,
the predominance ol his tribe and his clan. In practice, tribalist ideas and
feelings are used most often to create a clientele who can help them to
satisfy their selfish interests and ambitions. Tribalism is expressed in
different forms, of which the following the main ones:
> 1 The tribalist constantly exaggerates and boasts about the qualities,
merits and good deeds ofthe people ofits tribe and its clan; on the
other hand he refuses to recognise their faults,and even tries
systematically to hide them. With respect to other tribes, exactly the
opposite attitude prevails [...].
> 2 The tribalist indulges freely in liberalism and favouritism towards the people of his tribe and his clan [...]. By contrast, he is in general very
sectarian towards people of other tribes and other clans [...].
> 3 The tribalist tries to grant all the privileges and posts of responsibility
to the people of his tribe and his clan [...].
> 4 Conversely, the tribalist seeks to exempt his own people from their
duties and obligations, from any difficult work, or from the most
dangerous, difficult or humiliating missions
> 5 The tribalist practises this favouritism in the division of material
benefits and the distribution of services [...].
> 6 Occasionally, the tribalist even believes that those who are not of his
tribe and his clan are too rich and fortunate to deserve his help [...]
> 7 Some extend tribalism as far as preferring marriage between black
women and white men to marriage between tribes [...].
> 8 In politics, the supreme expression of tribalism consists of demanding
the formation of so-called independent republics which in fact have a
tribal basis; failing this, tribalists demand ‘federation with regional
autonomy’ with the distribution of political and administrative power following tribalist lines.
So, you have both Nationalist leadership and Marxist/Maoist revolutionaries condemning tribalism as obstacle in the path towards liberal nationalist or socialist modernity (respectively).
Nationalist leaders adopted a variety of strategies to contain or channel ethnic consciousness. For example, colonial Northern Rhodesia the territory of the Lozi monarch (Barotseland) was treated as a protectorate, associated with Northern Rhodesia but granted substantial autonomy. When Northern Rhodesia gained independence in 1964, President Kenneth Kaunda quickly negotiated the Barotseland treaty of 1964 which amounted to continuing recognition of autonomy of Barotseland.
On the other hand, in Algeria, the 1962 constitution declared the national language to be Islam. This led to a systematic program of enforcing Arab language education in schools, and use of Arab language in public life. This program led to the "Arabization" of the substantial Berber minority, and a backlash in the 1980s with the rise of Berber rights movement.
---
So, all of this is to say that despite efforts of Liberal Nationalist, Maoist or Marxist Leninist governments to get beyond tribalism, and encourage people to think in terms of national or class consciousness; ethnicity continued to have a political logic. With the ratification of the OAU charter and Cairo declaration, national governments pledged themselves to the principle of only adjusting national borders through mutual agreement from the respective states involved. No military conquest to adjust borders.
In that scenario, the process of negotiating border adjustments to either bring the territory of an ethnic group into the state, or to cede territory (thus excluding an ethnic group from your state); would have been seen by the public through the lens of ethnic political calculus.
To use a hypothetical example: the state of Cameroon entered independence with a heavily Muslim population in the north, and a Christian or Animist population in the south of the country. At independence, leaders from the Northern, muslim portion of the country had power in the country.
Now, let's imagine that the [Fang population](_URL_1_) in the south of Cameroon would like to live in a state with kinsmen in Equatorial Guinea and Gabon. Gabon and Equatorial Guinea are on board to adjust the borders.
However, the non-Fang population in the south, and their politicians, all oppose the deal in Cameroon. They decry it as a trick by Northern politicians to weaken the southern opposition, and castigate their Fang colleagues for leaving them out in the cold.
The deal goes through, but now with a politically weaker Southern population, the [Baka and Gur](_URL_5_) also want to exercise the "exit option" and become part of the Central African Republic. But let's imagine that the government of Central African Republic is uninterested in negotiating, because Baka and Gur are opponents of the current government and that would strengthen Baka and Gur power.
What are the Baka and Gur to do now? Do they secede? OAU and Cairo declaration pledge African states to oppose secessionism. And there is some doubt about how viable such a small secessionist state could be.
Or, from a completely different perspective. What are we to make of populations like the Fula/Fulani? They are primarily herders, and their populations and herds move, and cross borders. Ditto, the Tuareg exist across borders in Mauritania, Mali, Algeria and Niger.
There is also the issue of what to do about ethnic diasporas who live in cities. Immediately before the start of the Nigerian Civil War, there were pogroms against Igbo bureacrats and merchants who lived in the Middle Belt and in northern Nigeria. In an imagined scenario where Biafra seceded peacefully, what would be done about this Igbo commercial diaspora living outside Biafra? Would they be repatriated? We can look to the historical example in Uganda and Tanzania where South Asian merchant communities were persecuted or forced into exile for being "outsiders" who threatened African merchant enterprise.
---
So, that is the logic of the Cairo declaration of accepting existing borders, and many African leaders probably supposed that seeking border adjustments might inflame tribalist sentiments.
However, there is the example of Somalia, which is the big exception. Somalia sought to encourage secessionist movement of ethnic Somalis in northeast Kenya from 1964-1967 in the Shifta war. Later, in 1977 Somalia invaded Ethiopia in order to annex the Ogaden region which had an ethnic Somali population. Both of these actions were in pursuit of the idea of [Greater Somalia](_URL_0_). However, these actions managed to anger Kenya and Ethiopia over Somali expansionism and drove those two countries into alliance with each other to thwart Somali aims.
Both Kenya and Ethiopia wished to keep Northwest Territory and Ogaden region as part of their states, despite viewing the Somali population of these regions as subversive elements. Partly this was a concern with natural resources in the region, partly it was a belief that the population *could* be Kenyan or Ethiopian as long as they kept in line. Partly it was a matter of national honor, where Haile Selassie or Jomo Kenyatta would not want their respective countries to be smaller. In the case of the Derg in Ethiopia in 1978, their Marxist-Leninist reaction to socialist Somalia invading was 1) feeling of betrayal that a socialist neighbor would put the Derg's nascent revolution in danger by invading. 2) that Siad Barre was a national chauvinist who would suborn the greater goal of spreading socialism in East Africa to the lesser goal of creating a larger Somali state. In the Derg's analysis, nationalist chauvinism was a deviation from the goal of transcending ethnicity and achieving socialism for all. | [
"The decolonisation of Africa took place in the mid-to-late 1950s and 1960s, with sudden and radical regime changes on the continent as colonial governments made the transition to independent states; this was often quite unorganized and marred with violence and political turmoil. There was widespread unrest and org... |
What did Lucifer, as a Roman God, represented for the people of Rome? | Lucifer was not a Roman god. | [
"In the Middle Ages, the Cathars, practitioners of a dualistic religion, were accused of worshipping Satan by the Catholic Church. Pope Gregory IX stated in his work \"Vox in Rama\" that the Cathars believed that God had erred in casting Lucifer out of heaven and that Lucifer would return to reward his faithful. On... |
Plate Tectonics on Venus | Interesting explanation here: _URL_0_
Essentially, it doesn't have Earth like plate tectonics because it's too hot. It's a definitions issue, not a process one. | [
"BULLET::::- The typical signs of terrestrial plate tectonics - continental drift and basin floor spreading - are not evident on Venus. The planet's tectonics is dominated by a system of global rift zones and numerous broad, low domical structures called coronae, produced by the upwelling and subsidence of magma fr... |
why do anesthetic needles hurt so much when numbing a nerve? | Because they fairly directly poke the nerve (or very close to it) before injecting. Poking a nerve directly tends to hurt. | [
"Local anesthetic toxicity is indicated by numbness and tingling around the mouth, metallic taste, or ringing in the ears. Additionally, this may lead to seizures, arrhythmias, and may progress to cardiac arrest. This reaction may stem from an allergy, excessive dose, or intravascular injection. Other complications... |
why do addicts of hard drugs tend to lose many of their teeth? | Drug addicts don't typically have the best hygiene. Depending on the drug of choice, they may have no appetite and end up malnourished. | [
"The intense desire to recapture the initial high is what is so addictive for many users. On the other hand, Reinarman et al. wrote that the nature of crack addiction depends on the social context in which it is used and the psychological characteristics of users, pointing out that many heavy crack users can go for... |
Why are bike wheels so big? | It is partly because mechanically it offers the opportunity of higher road speeds on a pedal bike without having to pedal furiously or without the need of excessive gearing.
Also, larger wheels traditionally were used before bike had suspension to try to smooth out the uneven roads that bikes were used on when they were first invented.
surface area is a factor in dynamic friction because the surface area of the wheel determines the shear strength of the surface of the wheel, so a thinner/smaller wheel will skid easier, whereas a wide wheel will skid and leave marks less easily, which is why rear wheel drive sports cars and motorbikes have larger rear tires.
but not all bike wheels have a large diameter, city bikes that pack up into a suitcase have much smaller wheels for obvious reasons. | [
"Following the growing trend in 29-inch wheels, there have been other trends in the mountain biking community involving tire size. One of the more prevalent is the new, somewhat esoteric and exotic 650B (27.5 inch) wheelsize, based on the obscure wheel size for touring road bikes. Some riders prefer to have a large... |
why do public women's toilets have lids if they're never going to be lifted up? | Standard parts for efficient manufacturing. | [
"Toilet seats often have a lid. This lid is frequently left open. It can be closed to prevent small items from falling in, to reduce odors, for aesthetic purposes or to provide a chair in the toilet room. Some people also close the lid to prevent the spread of aerosols on flushing (\"toilet plume\").\n",
"BULLET:... |
what is isis trying to accomplish with the beheading incidents and how do they release the videos? | ISIS believes that they can punish the US for conducting air strikes against itself, by executing American citizens who are so unfortunate as to fall into their hands, and that when America sees that it has been punished for its crimes, it will feel suitably remorseful and will then refrain from its criminal activities in order to avoid further punishment. I would say that this is a misreading of American psychology which is not generally inclined to surrender to extortion.
Releasing the videos is not difficult. A large fraction of the world's population has the means to release videos if they so desire, and ISIS has many sympathizers around the world who would assist in such a release. | [
"In addition to beheading videos, ISIS has released videos of their members doing nonviolent acts. For example, Imran Awan described one such instance in his article \"Cyber-Extremism: Isis and the Power of Social Media\" where one video showed members of the Islamic State were seen helping people and visiting hosp... |
how do frogs, toads and other amphibians know how and where to find new bodies of water? | Amphibians explore and migrate during cool moist weather. They can cover a lot of distance that way, especially if they can find damp places to take shelter in between stages of their journey.
Most animals (including us) are also perfectly capable of smelling water from a good distance. Wind blowing across a body of water will have more moisture in its air than the surrounding air. An exploring frog that smells water on the wind will likely come to check it out. | [
"The first \"Brachycephalus\" species was identified in 1824, but most of the frog species were discovered since the year 2000. The discovery of new frog species is difficult. Field work requires climbing steep mountain trails to the sites where the frogs live.\n",
"The frog was originally discovered by Dr. Willi... |
How easy was to get new identity and "vanish" at the end of WW2? | Follow up: If there were people that did this and were caught, what would the punishment be? | [
"That list has been adapted in that the persons who simply disappeared after the war, who were eliminated by the resistance during the war or who committed suicide before being convicted, have been taken off the list.\n",
"The surnames of those noted lost in the First World War are Lacey, Hind, Middleton, Herapat... |
how effective medical marijuana is. is it actually useful compared to other meds? or is it just used to get people to see the good side to marijuana | Hey! I have Crohn's disease, which is essentially a disease of the gastrointestinal system that has varying effects on the people afflicted. For me, when my Crohn's "flares" as my wife calls it, I am unable to properly digest anything. As a result, I have severe diarrhea, stomach cramps, and a loss of appetite. These symptoms started around 15 years of age, but symptoms weren't really severe until I was in college.
Prior to trying marijuana, I would have no appetite during my flare ups. It was not uncommon for me to lose 30 pounds in 2 weeks, simply because while you're stomach is in intense pain, food just is not palatable. I live in a state where it is not medicinal yet, though it will be on the ballot this fall, and I was really hesitant because of the illegality. Three years later, I am glad I did. It saved my life because it saved my friendships and my marriage.
There are a few medications on the market for Crohn's, from corticosteroids to immune modifiers to dietary supplements... though none of them are as effective for me as marijuana, and all of them presented different side effects that were equally troublesome as the Crohn's to my everyday life. For example, the steroids gave me increased blood pressure and occasional, serious mood swings.
For me, weed doesn't solve my stomach problems. I still have diarrhea, I still have cramps and stomach pain. What weed does is something more beneficial than any other medication I've been exposed to; it removes my pain from my focus. I am still in pain, but I don't mind it. I still gush water out of my asshole and, eventually, end up showering instead of wiping because my ass is raw, but my mind ignores the pain more easily because I'm focused on whatever else I am doing. It also gives me an appetite, not enough of one that I can't control myself, but just enough to make food taste enough that I don't get nauseous trying to swallow it. | [
"In 2003, the American Academy of Ophthalmology released a position statement stating that cannabis was not more effective than prescription medications. Furthermore, no scientific evidence has been found that demonstrates increased benefits and/or diminished risks of cannabis use to treat glaucoma compared with th... |
To what extent can parents' DNA be reverse-engineered from their child's DNA? | research engineer here:
A haplotype (haploid genotype) is a group of genes in an organism that are inherited together from a single parent.
As the human genome consists of two homologous sets of chromosomes, understanding the true genetic makeup of an individual requires delineation of the maternal and paternal copies or haplotypes of the genetic material.
Recognizing the importance of haplotypes, several groups have sought to expand our understanding of haplotype structures at the level of both populations and individuals. Initiatives such as the International Hapmap Project and the 1000 Genomes Project have attempted to systematically reconstruct haplotypes through linkage disequilibrium measures based on populations of unrelated individuals. However, the average length of accurately phased haplotypes generated using this approach is limited to ~300 kb. Alternatively, genotyping parent-child trios can determine whole-genome haplotypes in the child, but such methods are constrained by their higher cost and the sample availability of the two biological parents.
Numerous experimental methods have also been developed to facilitate direct haplotype phasing of an individual, including long-fragment-read sequencing, mate-pair sequencing, fosmid sequencing, and dilution-based sequencing. At best, these methods can reconstruct haplotypes ranging from several kilobases to about a megabase, but none can achieve chromosome-spanning haplotypes. Whole-chromosome haplotype phasing has been achieved by sequencing based on fluorescence-activated cell sorting, chromosome-segregation followed by sequencing and chromosome microdissection–based sequencing. However, these methods only phase a fraction of the heterozygous variants in an individual, and more importantly, they are technically challenging to perform or require specialized instruments. Recently, whole-genome haplotyping has been performed using genotyping from sperm cells; however, this approach is not applicable to the general population and requires the deconvolution of complex meiotic recombination patterns.
Computational analysis has shown that an important factor in haplotype reconstruction from DNA shotgun sequencing methods is the length of the sequenced genomic fragment. For example, longer haplotypes can be obtained using mate-pair sequencing (fragment or insert size, ~5 kb) compared with conventional genome sequencing (fragment or insert size ~500 bp) (Supplementary Fig. 1a). However, it is technically difficult to isolate and sequence DNA fragments that are longer than what is already obtained using fosmid clones. Hence, using existing shotgun sequencing approaches, it is difficult to generate haplotype blocks longer than 1 million bases, even at ultra-deep sequencing coverage.
In the human cell line, ...they obtained chromosome-spanning haplotypes at ~81% resolution with an accuracy of ~98% using just 17× coverage of genome sequencing. These results establish the utility of proximity ligation and sequencing for haplotyping in human populations.
[source 1](_URL_0_)
source 2: I've modeled genetics and complex protein interactions for my job | [
"The replication of damaged DNA before cell division can lead to the incorporation of wrong bases opposite damaged ones. Daughter cells that inherit these wrong bases carry mutations from which the original DNA sequence is unrecoverable (except in the rare case of a back mutation, for example, through gene conversi... |
If you shine a white light through a blue filter, does it actually change the wavelength of the color? | Filters *remove* certain colors from the light beam. White light has all the colors mixed together: the blue filter removes everything but blue.
If the color isn't there to begin with, the filter can't add it. You can test this by getting a red laser pointer (which is *only* red) and shining it through a colored liquid like, say, apple juice or Mountain Dew. It'll change the brightness of the laser, but it'll stay red. | [
"The filter on a colorimeter must be set to red if the liquid is blue. The size of the filter initially chosen for the colorimeter is extremely important, as the wavelength of light that is transmitted by the colorimeter has to be same as that absorbed by the substance.\n",
"The blue filter is centered around 450... |
Do certain activities increase/decrease brain activity during sleep? | One of the main functions of sleep and dreaming is to consolidate (new) memories and reorganise the brain's neural architecture accordingly. Because of this, dream experience seems to have a strong relation with what you have experienced and encoded in waking life.
It is not entirely clear if there are reliable causes of more intense dreams, but some possibilities might be inferred. Firstly, one could argue that the novelty, emotional valence, and arousal related to your novel experience could translate to a necessarily more 'thorough' reorganisation, and vivid dream experience, if the emotion and arousal of episodic events are co-activated during dreaming.
Secondly, one could argue that especially meaningful experiences could lead to more vivid dreams, if we assume meaningful experience to translate to more diverse and informative connections with existing memories/information in the brain.
The latter is based partly on the perspective that consciousness -and thus dream consciousness too- is dependent on a state of integrated information, which is still well possible during dreaming (as 'proven' by the fact that there's a subjective dream experience). To emphasize though, the above are not scientific knowledge, but a hypothesised answer based on it!
Hope the answer was satisfying, happy dreaming!
Sources:
Stickgold, R. (2005). Sleep-dependent memory consolidation. Nature, 437(7063), 1272-1278.
Tononi, G. (2008). Consciousness as integrated information: a provisional m
Wamsley, E. J., & Stickgold, R. (2011). Memory, sleep, and dreaming: Experiencing consolidation. Sleep medicine clinics, 6(1), 97-108. | [
"The function of sleep is not fully understood; however, there is evidence that sleep enhances the clearance of metabolic waste products, some of which are potentially neurotoxic, from the brain and may also permit repair. Evidence suggests that the increased clearance of metabolic waste during sleep occurs via inc... |
how do you enter a gas giant? | > but is there a uniform boundary or is it just Space and then the planet kinda just "starts"?
Atmospheres tail off roughly exponentially as you go up in height. Earth's does too - there's no sharp "you're suddenly in space" line for Earth, either. | [
"Within the gas giant is the Helix, a Suliban aggregate structure composed of hundreds of Suliban ships, which the \"Enterprise\" crew scan to find Klaang. Using the grappler, \"Enterprise\" successfully grabs an attacking Suliban ship, the pilot ejecting. After studying the captured ship and its controls, Archer a... |
what does the f/stop in a camera do? | Building on the other two responses...
The F/stop works with the shutter speed to get the appropriate amount of light on the film. The smaller the F/stop number, the more light is being let in at once, and the larger fraction on the shutter speed, the longer time the light is allowed to reach the film.
So if you turn the F/stop up (closing the aperture more) you need to turn the shutter speed down to keep the same amount of light on the film (the same exposure). And if you turn the shutter speed up, you need to turn the F/stop down (opening the aperture) to keep the same exposure.
For fast moving objects, you'll want a fast shutter speed to cut down on blur, so that means you'll need a wide open aperture to match.
But the more open the aperture, the shallower depth of field you have. Depth of field is how far in front of and behind what you're focusing on is also in focus. If you have a very shallow depth of field, pretty much only the specific thing you're focusing on is sharp; everything else is fuzzy. If you have a deep depth of field, things are in focus for a long distance before and behind your subject.
So you need to decide how much you want in focus for how big you want your aperture, which affects the shutter speed you need. And you have to take into account how fast you need to take your picture for motion blur, which affects the F/stop you can use. It can be a frustrating dance. | [
"The stop-down lever at the right-hand camera front also operates the self-timer. Pushing the lever towards the lens activates the stop down match-needle meter, while pulling in the opposite direction winds the timer. As with the Canon FX and FP, the camera back is opened turning a key at the base. The film speed i... |
Is there such a thing as space coordinates? | There aren't any absolute coordinates in the universe. However, you can broadcast our location relative other parts of the universe. For example, if you wanted to send a message within our [local group](_URL_1_), such as communicating our location to a civilization in the Andromeda galaxy, you could send our galaxy's location relative to others in the local group, [like this](_URL_0_). Then you could include a second message communicating our location within our own galaxy. | [
"Coordinates systems are often used to specify the position of a point, but they may also be used to specify the position of more complex figures such as lines, planes, circles or spheres. For example, Plücker coordinates are used to determine the position of a line in space. When there is a need, the type of figur... |
What is the probability of a couple having identical non-twins? | Here's [my answer](_URL_0_) to this question from about a month ago. The figures I give are for the probability of being unrelated (or rather of being substantially less related than the expectation), but the calculation is symmetric, so those probabilities are the same for the other half of the distribution.
It's not explicitly impossible, but the probability is so low that it basically won't even happen. | [
"More generally, it applies to any exchangeable sequence—it only relies on the fact that for any pair, 01 and 10 are \"equally\" likely: for independent trials, these have probabilities formula_105, while for an exchangeable sequence the probability may be more complicated, but both are equally likely.\n",
"Addit... |
why do people stand along roads holding signs to promote sales of some stores? (e.g. furniture stores, stores going out of business, etc.,.) is there a law against posting signs? | Generally yes it is illegal in many towns to post signs and flyers because no one ever removes the signs later and they usually become trash in the streets, but that is not why they do it. They do it because people like you notice them. How many signs and posters do you stop to read that are posted to telephone poles and taped to windows? Unlike those signs that you don't even see any more, sign spinners get noticed, commented on and even talked about. Being noticed boots sales.
They, like most other simple jobs get payed minimum wage. | [
"There have often been complaints about road signs and infrastructure not being up to date in some parts of the country, with a traffic report in 2008 disclosing that local governments in many cases have not addressed damaged, vanished or outdated road regulatory signs. In Lahore alone, the report estimated that at... |
how / why water goes "bad" when you leave it out but is fine in bottles? | Actually, water in plastic bottles CAN and does go bad (look at the expiration date!)
Exposed water will have dust settle in it, it will have smells and other floating stuff fall in to it, etc. Bacteria might get in it and start to multiply.
Bottled water will stay fresher longer, but since plastic does have very small pores/holes in it, eventually contaminants with find their way through the plastic in to the water (over the span of several years). | [
"Reusable bottles can hold bacteria. Drinking from a reusable bottle can transfer bacteria from a person's mouth to the beverage it contains, which can contaminate both bottle and water. Contamination can cause bacterial or fungal growth in the liquid while it's stored. It is recommend that users clean reusable dri... |
why does a doughnut get nice and fluffy after 20 seconds in the microwave but hard after 40 seconds? | Microwaves act by making water molecules bounce around faster (increasing its kinetics)
The energy from this movement is released through the form of heat and it is dispersed evenly through the body of what you are heating.
If you overdo it you just completely dry out the object of the microwaves. Your doughnut becomes dehydrated. | [
"The production of puff pastry dough can be time-consuming, because it must be kept at a temperature of approximately 16 °C (60 °F) to keep shortening from becoming runny, and must rest in between folds to allow gluten strands time to link up and thus retain layering.\n",
"Many people believe it was the Dutch who... |
why do i have horrendous farts after a night of drinking? | You have bugs in your stomach that like to eat carbohydrates. When they eat they produce gas. Alcohol contains carbs. The diarrhea is probably a side effect of not eating as well as you should while drinking.
If this happens every time you drink, you should see a doctor. | [
"After drinking it, the person will get cramps and loose motion are caused which ultimately will clean the bowels. This was a primitive method for purging and treating intestinal cleansing as well as worms. Now this practice is almost given up owing to access to health facility of allopathic medicines and lethargy ... |
how are digital devices functional in an mri room? how do they operate the mri in that strong magnetic field? | For the most part, magnetic fields are not as bad to electronics as people would lead you to believe. Specifically, magnetism isn't an important thing in the operation of electronics, and it doesn't somehow stop them from working. Really traditional hard drives are the only thing in a modern computer that has any meaningful sensitivity to magnets.
Electronics however do use electricity, and current is directly tied to magnetism, specifically a change in current by definition generates a change in the magnetic field, and a change in a magnetic field generates a change in current (that could have a huge effect on electronics). In an EMP, there is a rapid change in magnetic fields, and that's how an EMP destroys electronics. In an MRI though, it's really just one big constant magnetic field, never changing. A magnetic field that doesn't change really has a minor effect on electronics.
And finally to mitigate whatever sensitivity is left, we use [Mu-Metal](_URL_0_), basically you can make a case of metal, and the magnetic field lines will go through the case, not inside it (letting you make a hole of low magnetic field, inside a stronger one). Stop just put your computer inside a case made of Mu-Metal and it's thousands of times less sensitive to magnetic fields. | [
"An MRI gantry remains fixed, and contains strong electromagnets and radio receivers that manipulate hydrogen atoms in the human body via proton nuclear magnetic resonance. The machine then receives and processes the signals given off by the hydrogen atoms in order to produce a 3D image of the interior of the patie... |
Stem Cells for Rejuvenation | Cells from your body (eg your skin) can be manipulated and turned into [induced pluripotent stem cells](_URL_1_). These cells are, in theory, stem cells that can become any other type of cell in your body. Under the proper conditions, they can be induced to become neurons, blood cells, or any other cell type.
In theory, this technology could be used to produce organs (hearts, kidneys, livers) that could replace your organs as they became worn out over time. This would be difficult to do for complex organs that have multiple types of cells (the heart must contain muscle cells, blood vessels, nerves, etc.) This is the end goal of current research- however, this branch of research is still in its infancy, and it will be some time before it is ready for clinical application.
If your question is whether stem cells themselves can be injected into a patient and have them 'do their own thing' at the site of injection, it is unclear whether this will work or not. Wikipedia has a good [article](_URL_0_) describing potential treatments, although this line of research is also in its preliminary stages, and may or may not be successful in practice. It is currently being attempted for spinal regeneration and a few other areas.
If your question is whether the injection of a whole bunch of stem cells could rejuvenate someone in terms of reversing the aging process, this is unlikely. Stem cells, in general, do not have properties that are related to 'youth'- they are capable of becoming any type of cell, and they are capable of dividing infinitely, but they have no intrinsic properties that would remove wrinkles, restore cartilage, remove cholesterol buildup, etc. | [
"Under defined conditions, embryonic stem cells are capable of self-renewing indefinitely in an undifferentiated state. Self-renewal conditions must prevent the cells from clumping and maintain an environment that supports an unspecialized state. Typically this is done in the lab with media containing serum and leu... |
when an app crashes and i send a report, what exactly does that do, and how is it used? | It tells the developer that the app has crashed, first of all.
But it can also tell the developer what you were doing, what screen you were viewing, what data you were using, what route you took to get to that screen, and so on.
All of this can help fix the bug. Obviously the developer needs to know what screen you're looking at. But it's not uncommon to find find bugs where the app crashes every time you enter a " character, for example. By sending the data to the developer, the developer can look at the report from dozens or even hundreds of similar crashes, and can realise that the " character is the common denominator.
Obviously this has privacy issues - it's up to you to decide whether your privacy is worth sacrificing in order to help make the app better. If you use the app for banking or drug dealing, then probably not. If you use it for looking at pictures of cats you might be happy to share this data. | [
"Crash Reporting creates detailed reports of the errors in the app. Errors are grouped into clusters of similar stack traces and triaged by the severity of impact on app users. In addition to automatic reports, the developer can log custom events to help capture the steps leading up to a crash. Before acquiring Cra... |
Why do trash cans smell even after they've been washed? | I can only speak in generalities -- but I think it's pretty reasonable that those smell molecules have simply diffused into the plastic. At the molecular level, the plastic will be quite porous. | [
"Some types of cans may have interior coatings containing chemicals such as Bisphenol A. Reusing containers originally holding paints and other types of chemicals may be injurious to the health of the user if the can is not properly cleaned and decontaminated.\n",
"Similarly, trash cans that are used inside and t... |
why does closing a credit card account hurt your credit? | Actually, to build great credit you want to have as much available credit (and **debt**) as possible.
Your credit score is a reflection of how trustworthy you are with credit. It's based on how **reliably you pay off your debt**, not how little debt you have. If you have a lot of credit cards, you use them all, and you pay the recommended amount on the recommended time schedule without fail, you are building your credit score.
Closing a credit card account means you're willingly lowering your maximum credit and debt situation, which tells lenders that you don't want that credit/debt, which hurts your overall ability to lend in the future. | [
"A simple solution to this problem is to call the credit card company, request a new card with a different account number, and cancel the previous account. They will transfer the debt amount from the old account to the new account. This makes companies that have the credit card information unable to continue chargi... |
why aren't there bigger pushes to abandon the political party system? | Originally there were no parties. Like- minded individuals formed parties organically.
If they got rid of the current parties the only thing that would happen is new ones would form, officially or othrwise it doesn't matter. | [
"By-elections can be crucial when the ruling party has only a small majority. In parliamentary systems, party discipline is often so strong that the governing party can only lose a vote of no confidence after losing enough by-elections for it to become a minority government. Examples are the Labour government of Ja... |
where does energy go in a short-circuited battery? | It all turns into heat. Short out a battery, and it'll heat up and get warm, hot, or even on fire.
All batteries have internal resistance. That is to say, the inside of the battery isn't superconducting. So even if you had a superconducting wire shorting the battery, it would still get hot. | [
"A secondary cell, commonly referred to as a \"rechargeable battery\" is an electrochemical cell that can be run as both a galvanic cell or as an electrolytic cell. This is used as a convenient way to store electricity, when current flows one way the levels of one or more chemicals build up (charging), while it is ... |
why does falling down hurt more/ longer when you get older | As you get older, you get taller. As you get taller, more of your body gets farther away from the ground. As they get farther from the ground, they have farther to fall.
Knock a three year old over.
Then hold that same three year old up to where his head is level with yours and drop him.
Don't actually do that unless you record it. For science. | [
"Falls in older adults are a significant cause of morbidity and mortality and are an important class of preventable injuries. The cause of falling in old age is often multifactorial, and may require a multidisciplinary approach both to treat any injuries sustained and to prevent future falls. Falls include dropping... |
why are salmon from the pacific prone to parasites while salmon from the atlantic safe to eat raw? | I don't believe this is actually a thing? Atlantic Salmon also frequently have warnings put out about parasite risks. [The NHS publishes warnings in the UK](_URL_0_) about it.
Now you can get sushi-grade fish, of course, but that's fish that has been flash frozen to kill any potential parasites in the fish. That can also be done with Pacific salmon. | [
"Many Atlantic salmon escape from cages at sea. Those salmon that further breed tend to lessen the genetic diversity of the species leading to lower survival rates, and lower catch rates. On the West Coast of North America, the non-native salmon could be an invasive threat, especially in Alaska and parts of Canada.... |
how can a spinning top stay upright while it's rotating? | When something spins, it has inertia just like an automobile and just like an automobile, it is very easy to move it in certain directions in respect to the direction of the movement and difficult in other directions. The trick is that with a top, the inertia isn't all in one direction, it is in all directions along a plane. Shifting that plane up, down, or to the side takes very little energy, but turning the orientation of it requires disrupting the inertia, so you will experience a force if you try to do so. As long as the force which tends to topple the top is less than the force resisting it, the top will stay up. | [
"When a tippe top is spun at a high angular velocity, its stem slowly tilts downwards more and more until it suddenly lifts the body of the spinning top off the ground, with the stem now pointing downward. Eventually, as the top's spinning rate slows, it loses stability and eventually topples over, like an ordinary... |
does my breastmilk have healthier properties if i eat healthier food? | Regarding healthy and unhealthy fats:
generally speaking: the membranes of your cells always feflect the stuff you eat. Of course the body has its own fattyacid metabolism and can contribute here. but regarding the fats the general rule applies: you are what you eat.
On the other hand: the milk you produce contains still certain healthy components eitherway. like omega3 fats that are important for the brain of the baby. Thats a propriety of breastmilk that should not be influenced by diet. | [
"The increasing trend to enrich foods with polyunsaturated acyl groups entails the potential risk of enriching the food with some OαβUAs at the same time, as has already been detected in some studies carried out in 2007. PUFA-fortified foods available on the market have been increasing since epidemiological and cli... |
is it possible to have a mind like sherlock holmes? | That doesn't really happen in the BBC series so much. Deductive reasoning is a real thing. I'm sure you're not seriously asking if you can slow down time with your mind though. | [
"Sherlock Holmes and Dr. Watson find themselves in a university town when a tutor and lecturer of St Luke's College, Mr. Hilton Soames, brings him an interesting problem. Soames had been reviewing the galley proofs of an exam he was going to give when he left his office for an hour. When he returned, he found that ... |
Did any groups still cling to the Roman deities after the fall of Rome? | The Roman Empire was of course not entirely Christian by the end of the fifth century, but it was pretty close. Pagans were never wiped out, but pretty much all our sources for this period and later were written by Christians, so we can't be entirely sure if they are accurate in their accounts of surviving pagans or not. I've written fairly detailed answers on paganism in the later Roman Empire and the early Byzantine empire [here](_URL_1_) and [here](_URL_0_), outlining in broad terms the evidence for pagans in a Christian empire. If you have any questions, I'll do my best to answer them :) | [
"After some 1200 years of independence and nearly 700 years as a great power, the rule of Rome in the West ended. Various reasons for Rome's fall have been proposed ever since, including loss of Republicanism, moral decay, military tyranny, class war, slavery, economic stagnation, environmental change, disease, the... |
How did the ancient Romans think of what we today call race? | Some previous answers to this question while we wait for any further answers:
from /u/cleopatra_philopater -
_URL_3_
And another from cleopatra_philopater with further links to the origins of race perception -_URL_0_
From /u/medieval_pants -
_URL_2_
And some consolidated links from the FAQ - _URL_1_ | [
"The modern concept of race emerged as a product of the colonial enterprises of European powers from the 16th to 18th centuries which identified race in terms of skin color and physical differences. This way of classification would have been confusing for people in the ancient world since they did not categorize ea... |
Can someone explain the dark trail in front of a plane in the sky? | It's the contrail creating a shadow in the low haze.
_URL_0_ | [
"A flash of light is seen, accompanied by severe turbulence, although the captain thinks it might be something else. There is no apparent damage to the aircraft. Still unable to contact anyone on the ground, and at the risk of potential collision with other aircraft, Farver finally decides to descend below the clou... |
When an atom emits a photon, is it one blob of energy shot out like a bullet? Or is it a radiating wavefront coming from any one side of the atom? Or does the wave carry in a full sphere around the atom? Does the nucleus cause an eclipse? | The photon at atomic scales can be thought of like a blob of energy, representing an excitation in the [discrete nature of the electromagnetic field](_URL_0_). It's only at larger scales that light appears to behave like a classical wavefront. | [
"If a single photon approaches an atom which is receptive to it, the photon can be absorbed by the atom in a manner very similar to a radio wave being picked up by an aerial. At the moment of absorption the photon ceases to exist and the total energy contained within the atom increases. This increase in energy is u... |
Why were siege engines not used more often in ancient times? | Siege engines were expensive in terms of expertise to design, materials to gather for construction and (for some types) ammunition, time to build, and men to operate. They were also difficult to move and ranges were limited. [This interview with Peter Vemming](_URL_1_) discusses his work recreating a 22-ton trebuchet that was expected at the time to have a range of about 300m (about 328 yards). His was not the first attempt to recreate a medieval trebuchet, either, suggesting that despite our knowledge, authentic trebuchets required a great deal of knowledge to build properly.
On the topic of the range, a siege engine in the wrong place might be targeted by archers either trying to pick off crew or to damage or destroy the siege engine. CJ Longman wrote in 1894 of [attempts to replicate claims of longbow ranges above 300 yards](_URL_0_), and while he never quite reached it, he opined that a trained longbowman could probably reach 350 yards. Add in a little more distance due to shooting from a height (either a wall or a tower) and the range of the trebuchet suddenly becomes a potential problem. | [
"Siege engines are fairly large constructions—from the size of a small house to a large building. From antiquity up to the development of gunpowder, they were made largely of wood, using rope or leather to help bind them, possibly with a few pieces of metal at key stress points. They could launch simple projectiles... |
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