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October 6[edit]

The Origin of Gunpowder.[edit]

It is commonly known that an explosive substance such as gunpowder was invented in the Middle Ages. But the Chinese, who were the original inventors of gunpowder, had mixed sulfur, saltpeter (potassium nitrate), and charcoal together to create an elixir of immortality. But mixing sulfur, saltpeter, and charcoal together had created something in the opposite: GUNPOWDER. It is also known that an explosive material such as gunpowder must be invented 1st before inventing firearms (guns) in the Middle Ages. In Wikipedia's article about gunpowder, the first sentence of the third paragraph says " Gunpowder was, according to prevailing academic consensus, invented in the 8th century in China". But other sources say that Gunpowder was invented in the 9th century AD. It is also said that gunpowder was invented in the year 850 AD, which was in the 9th century AD. So here is my question: Did the Chinese invent gunpowder in the 8th century or the 9th century? By Wikipedia user, Mjfantom

No answers have been provided, so here is my take: you're looking for precision where no precision exists. This is because you're probably trained to think of history as a series of proven and indisputable facts laid out in a dramatic narrative, with specific characters fulfilling exact roles at exact times and places!

Humans have been burning stuff for millenia. Humans have burned wood since the earliest hominids learned to control fire; humans have made and used charcoal since the paleolithic era; sulfur and saltpeter were known pyrogens in Greece and Egypt for most of recorded antiquity; and iron has been refined and used since, well, the Iron Age.

At some point in history, people put all this junk together and burned it. Historians can and do quibble about when that first occurred. This was not a specific event that happened one exact time; it is a continuum of evolving processes that have been blurred into a continuous spectrum: people have burned all kinds of combinations of things, and sometimes the results have had practical or military utility. Our article highlights the current state of historical knowledge: it is believed that the first modern formation of what we could really call black powder took place around the ninth century. The most famous documentation, if you're looking for one specific item to cite, is the 武经总要. This is a specific historical document that explicitly describes one form of gunpowder. It was published much later: circa 1044 AD. Historians can say with strong certainty that the first invention must have occurred "a long time before" this publication.

Particularly because of the way that inventors were glorified in Western Europe during the Enlightenment Era, a lot of people are trained to think that there was one guy and he invented the thing. We've been indoctrinated to recall Bell and his telephone; Edison and his lightbulb; Fulton and his steam thingie. So it seems to fit with the narrative: there's gotta be some Chinese guy and his gunpowder formula, and it happened on one specific day (and it just so happened that the press was around to document it perfectly for the history books)! That's not how real life works! Thousands of humans contributed to these inventions and they evolved slowly over a long period of time. Particularly because the historical records of medieval China were not written by western Europeans, it's not easy to accurately stuff the historical facts into the western/European style narrative.

Nimur (talk) 16:09, 6 October 2014 (UTC)[reply]

Every time I start reading a glorious post on this page, I skip down to check who wrote it. Nine times out of ten it's Nimur. Thank you sir. 188.167.32.16 (talk) 18:05, 6 October 2014 (UTC)[reply]

Another thing to consider is semantics. The formula for what we call "gunpowder" was probably developed in the 8th century, but not used as "gun powder" (explosive force to propel projectiles from a tube) until guns were invented probably in the 12th century.[1] See also: History of gunpowder —71.20.250.51 (talk) 16:43, 6 October 2014 (UTC)[reply]

I agree with Nimur, this was likely a gradual process - someone got a little bit of sulphur and/or saltpeter mixed into a large pile of charcoal and got a slightly more energetic combustion...successive people would play with different mixtures and get progressively better or worse results. At no single point in this process did the resulting concoction suddenly become something new. SteveBaker (talk) 17:36, 6 October 2014 (UTC)[reply]

Fea[edit]

If you're doing finite element analysis to study the effect of variable x on variable y, should you do a mesh convergence of variable y after you've decided on a critical figure for variable x or before? In addition, if you're finding a third variable is it necessary to repeat the mesh convergence or does the mesh convergence only ever need to be done once? — Preceding unsigned comment added by Clover345 (talk • contribs) 15:59, 6 October 2014 (UTC)[reply]

A wise reference desk contributor once said, you're looking for precision where none exists. How can we possibly provide you with a binary answer to such a complex, broad question? The simplistic yes/no answer may exist for any specific instance, but it's not a universal truth. If you are actually performing this study, you need to use a little bit of critical thinking, perhaps guided by a literature survey to see what others have done in the past. Nimur (talk) 16:12, 6 October 2014 (UTC)[reply]

By their very nature, mesh convergence studies and plots are an empirical technique to assess the effect of mesh size on the accuracy of a solution to an FEA. If you have little idea of how well your mesh is approximating your continuous system, you should do mesh convergence for various values of input parameters until you become confident of the mesh sizes that will approximate your system well. Depending on the system, just performing local mesh refinement in critical areas may improve convergence with slowing down the calculation too much. --Mark viking (talk) 18:51, 6 October 2014 (UTC)[reply]

solar eclipse viewing[edit]

There is a partial eclipse of the Sun later this month. Information from several sources says that shade #14 (or higher) welder's goggles will protect your eyes. I have a piece of that and I've used it before. But I can't find out how much of the light #14 cuts out. I want to put filters on my camera, and the glass I have won't work on it. Is cutting down the light by a factor of 1000 enough? Bubba73 ^{You talkin' to me?} 19:05, 6 October 2014 (UTC)[reply]

No, it is not. Radiation with wavelengths <780 nm (i.e. UV and visible light) needs to be cut by a factor of 10,000 for safe viewing. For wavelengths between 780 and 1400 nm, 1000 is enough. See this website, which has a graph of the transmittance of a shade 14 Welder's filter. Note however that these figures apply strictly just to the human eye; the ideal filter for a specific camera will depend on the lens and sensor of your camera (although obviously it is highly unlikely that light which is safe for viewing with the naked eye will be harmful to a camera) - Lindert (talk) 20:39, 6 October 2014 (UTC)[reply]

Resolved

Thank you. A very informative link - exactly what I needed to know. Bubba73 ^{You talkin' to me?} 21:11, 6 October 2014 (UTC)[reply]

evolution[edit]

Doesn't the fact that the lion is faster than the zebra disprove evolution? — Preceding unsigned comment added by 202.91.78.234 (talk) 20:36, 6 October 2014 (UTC)[reply]

Don't know if this is a serious question, but the fact that zebras are still around and not extinct is proof that they are well adapted to survival in their habitat. The same can be said of the lion. Lions catch enough zebras (and other prey) to survive, and zebras reproduce fast enough to compensate for the few that fall victim to lions. -Lindert (talk) 20:46, 6 October 2014 (UTC)[reply]

Coevolution. Also see "Predator-Prey Relationships" at this NECSI site: http://necsi.edu/projects/evolution-old/co-evolution/pred-prey/co-evolution_predator.html Justin15w (talk) 20:50, 6 October 2014 (UTC)[reply]

Who says that "the lion is faster than the zebra"? From all the evidence I've seen (i.e. video), lions (or more often lionesses, who do most of the hunting) put a great deal of effort into trying to creep up on their prey, and are rarely successful in catching healthy adult zebra without an element of surprise, even when working as a group. They also run the risk of serious injury from a kick - there is more to predation than outrunning prey. If one looks at a big cat that specialises in speed, the cheetah, it is fairly obvious that as an evolutionary pathway it has its downsides - though they can sprint fast, they tire rapidly. And they are vulnerable to attack from lions (or hyenas), which may be slower, but are much tougher, and band together. AndyTheGrump (talk) 20:57, 6 October 2014 (UTC)[reply]

Aside (not directed at Andy): Speaking of cheetahs, worth noting that some of the old tales we have all heard about their hunting limitations, are just that. Abecedare (talk) 23:57, 6 October 2014 (UTC)[reply]

(EC) :To understand what's going on, start with the Red_Queen_hypothesis, which applies to many predator-prey interactions. The idea is that selective pressure is applied to both predator and prey, and this can lead to speciation and adaptation, and a sort of 'arms race' between two agonistic species. I assume you are asking in good faith, but please be aware that this might read as a loaded question to some respondents, because you seem to have assumed that evolution is not a valid explanation for the diversity of live on earth, despite the fact that it has been the scientific consensus for at least a century. Finally, I don't think lions are faster than zebras. The lion is an ambush predator, and relies on stealth and better agility to catch a zebra. In a straight-line race, a zebra would be faster.

In short, the answer to your question is "No" -- no more than the fact that there was a colder than normal winter last year where I live disproves global warming. While specific hypotheses about evolution should be falsifiable, there isn't really any way that the entire body of knowledge that we call "evolutionary theory" can be disproven. SemanticMantis (talk) 21:01, 6 October 2014 (UTC)[reply]

Lions have to be fast enough to catch some zebras, or they would die out --- that's not even evolution in any grand sense, just that you won't have lions in your preserve for long if they can't eat. Zebras don't actually have to be fast enough to escape from lions - at some low density, in theory, they could simply hope to get lucky, and if there were no other game in that environment to keep lion numbers up, the lions would get too scarce to find them often enough to matter. But in practice, that "if" on the environment can be a problem, just ask the dodo. But because zebras can hide/get lucky/etc. maybe they can be a little slower than they would otherwise, especially of course the newborns. Still, the main reason is the classic "the lion is just running for his lunch, the zebra is running for his life." Zebra evolution will outpace lion evolution if it really comes down to a straight evolutionary arms race between the two, first because the lions might have other food sources that blunt the push to greater speed, second because the zebras have a larger population size hence a deeper gene pool to call upon. What gets interesting is... what happens on a species level over time? I would think that zebras could evolve to become poisonous to lions, or to jump away at super speed, or otherwise deny the lions every last opportunity to cull out the sicker or slower members of the herd. But then deleterious mutations might build up over time, until they can't evade any more; in theory, you could have an ecosystem full of poisonous zebra couch potatoes sluggishly crawling around on the grass, then a new predator comes in that isn't affected by the poison and wipes them out. Is there a way that evolution fights back against such scenarios? (Say, fast zebras ostracize and kick out slower zebras to give them a competitive disadvantage anyway) Do such things simply happen now and then? (Say, sloths continue to thrive until one day something suitable invades their forests and kills them all?) To what degree are invasive species like we see now from human intervention actually a driving force in which evolutionary tactics have and haven't worked in the past? Hmmm. Wnt (talk) 21:12, 6 October 2014 (UTC)[reply]

Not sure if you really meant to be replying to me, but invasive species absolutely present novel challenges for native populations, and evolutions starts to sort things out. Here's an interesting example from an acquaintance of mine "Lizards Evolving Rapidly to Survive Deadly Fire Ants" [2], you can get to the research articles using her name and fire ants. I don't see the similarity between hypothetical zebra self-culling and hypothetical novel sloth predators... Anyway, assessing long-term stability of an ecological niche is very difficult even in specific cases, and the general theory is still a very active area of research. When we try to account for evolution and ecological processes acting on similar time scales, it gets even harder yet! SemanticMantis (talk) 14:00, 7 October 2014 (UTC)[reply]

A lion doesn't have to outrun all zebras, just one. This preserves the forces of evolution, by culling the slower or weaker animals from the zebra herd. This is really nature's variation on the story of two guys running from a bear. The one guy says to the other, "I don't have to outrun the bear, I just have to outrun you!" ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:23, 6 October 2014 (UTC)[reply]

You realize that just happened in New Jersey, with the first Rutgers student to be killed by a black bear in over 150 years? The other students ran in different directions. μηδείς (talk) 02:56, 7 October 2014 (UTC)[reply]

From the source you provided, I don't think it's clear that the unfortunate student was the slowest. It could easily be when the five students went in different directions and the bear "randomly" (there must have been one or a host of reasons, but we'll never know what they were) chose one of them. Actually this story highlights a flaw in the joke. Logically, if you're the slower you'll run in a different direction from the faster runner and hope the bear chooses the other person even if they're faster. The faster runner could try and follow you, but you can't properly follow someone if you're ahead and trying could easily lead to you being behind. It's possible that the relative speeds may be one factor in who the bear decided to chase, but there could easily be many other factors (particularly if the speed difference isn't that much). While this may seem unfortunate for the faster runner, it's worth considering if they were running in the same direction, that while the bear will probably stop after taking down one, or at least the faster one can make a get away while it's doing so, there's no guarantee so and but being in a different direction probably does make it unlikely you'll get caught after the first person, if the bear does choose to chase them instead of you. Nil Einne (talk) 14:45, 8 October 2014 (UTC)[reply]

Good point! I was originally thinking of this in a simpler context, but herding does provide a way to promote a faster animal even when it's not fast enough on its own. Wnt (talk) 21:56, 6 October 2014 (UTC)[reply]

The question doesn't even make sense. Even if the lion was faster than the zebra, how would that disprove evolution? Many species have been wiped out by other species (even not counting humans). Introduced species in particular, (which can also happen naturally) can completely "out compete" another species to the point of extinction, either by out running and eating all of them, or taking over their habitat and consuming all the resources. Nothing about any of that "disproves" evolution. Vespine (talk) 00:16, 7 October 2014 (UTC)[reply]

He could just as easily have said, "Doesn't the fact that the lion is faster than the zebra disprove the Pythagorean Theorem?" ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:20, 7 October 2014 (UTC)[reply]

No, our OP is clearly reasoning that if evolution worked, then the zebra would evolve to become faster than the lion...but it's not...so evolution is busted. The trouble with that is that if the reverse were the case, and the zebra WAS faster than the lion, then the same simplistic reasoning would lead you to wonder why the lion didn't evolve to be able to catch the zebra by outrunning it. In fact, the only way to avoid this critique would be if all zebras and lions ran at the exact same speed..but even that wouldn't avoid the critique because other animals are also hunted by lions...so by this simplistic view, all animals that hunted zebra and all animals that were hunted by lions would be running at the same speed...but then there are the animals like leopards that also hunt the same things that lions hunt - so by extension, our OP would only be satisfied if all living things ran at the exact same speed. The reason this situation doesn't occur is because the world is just more complicated than that. Zebras all run at different speeds, depending on age, nutrition, general health...and genetics...and so do lions. So long as some zebra can evade some lions - and most lions can catch enough zebra, everything keeps working. These animals have to evolve to do much more than just catch/evade each other - they also need to be able to reproduce effectively, to find enough food to survive, to be able to withstand the temperatures of the open plains, to be able to go without water for long enough, to migrate...all sorts of things. Perhaps a faster zebra would be more likely to break a leg - or perhaps would require more nutritious grasses to fuel that speed...so while fewer might die in lion attacks, more of them would fail to reproduce for other reasons. Lions are more able to pick off Zebra when they become sick - so perhaps it's more important that a Zebra evolves disease resistance than it is to get better running speeds. Evolution tends to find the best compromise across ALL of the functions the animal has to perform. SteveBaker (talk) 16:55, 8 October 2014 (UTC)[reply]

The relevant phenomenon is called a biological arms race. μηδείς (talk) 00:56, 11 October 2014 (UTC)[reply]

Type of mutation in Fragile X syndrome[edit]

What type of mutation that occur in Fragile X syndrome?All reference I found state that it is "alteration" of gene or "repetition" of CGG codon.But what is the mechanism of the repetition actually,is it insertion mutation or substitution mutation?or perhaps something else? — Preceding unsigned comment added by 210.48.219.7 (talk) 23:40, 6 October 2014 (UTC)[reply]

Our Fragile X syndrome article appears to have all these answers. DMacks (talk) 02:45, 7 October 2014 (UTC)[reply]