The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Why didn't natives of North America have fermented alcoholic beverages (except pulque)? It puzzles me because some groups such as the Iroquois had more than adequate supplies of readily fermentable materials like corn and maple syrup. If you've come across any literature on the subject please do point me to it. Thanks!
74.12.208.131 (talk) 00:47, 22 December 2007 (UTC)[reply]
The theory I've heard is that nomadic tribes weren't big on alcohol because the long time associated with the distillation process made travelling prohibitive. The agricultural revolution allowed people to settle down and wait for their booze. This is just what I was told by a teacher years ago! (Admittedly, he was a very intelligent teacher whom I respect greatly -- but it wouldn't be the first time someone was misinformed by the public education system.) 99.245.89.152 (talk) 14:59, 22 December 2007 (UTC)[reply]
North American Native Americans were mostly agricultural and settled -- at the very least those with corn were. I don't know why fermented alcohol was not used. I know corn is commonly distilled into spirits today, but perhaps it doesn't ferment into something you'd want to drink? I can't recall ever hearing of "corn beer". Pfly (talk) 19:05, 22 December 2007 (UTC)[reply]
No idea about the North American ones but according to Alcoholic beverage "By the time the Europeans reached the Americas in the 15th century, several native civilizations had developed alcoholic beverages. According to a post-Conquest Aztec document, consumption of the local "wine" (pulque) was generally restricted to religious ceremonies, but freely allowed to those over 70 years old. The natives of South America manufactured a beer-like product from cassava or maize (cauim, chicha), which had to be chewed before fermentation in order to turn the starch into sugars.". It's easily possible there may have been more but a lot of it was lost due to the destruction of large parts of Native American culture after the arrival of the Europeans. Oh and perhaps other stimulants such as coca and tobacco were a substitute for alcohol for some of them? (They also had other stuff like Cacao of course) Nil Einne (talk) 07:57, 23 December 2007 (UTC)[reply]
Isn't there some genetic problem with Native Americans and alcohol metabolism? Might this have dissuaded them from routinely producing alcoholic drinks? SteveBaker (talk) 14:19, 24 December 2007 (UTC)[reply]
Are you thinking of Alcohol flush reaction? This predominantly occurs in East Asians and after reading the article, isn't that common in Native Americans. In any case when I first thought of this I dismissed it as at best a minor cause at best since it doesn't seem to have stopped the Japanese, Koreans or Chinese from producing alcohol. Nil Einne (talk) 10:57, 25 December 2007 (UTC)[reply]
Some time ago I used a laser interferometer at work to make fine measurements, and recently I've been using a home-grade laser level in some household projects. In both cases I noticed the same thing: Where the light emitted by the laser strikes an object it puts a red spot (or a thin line), but instead of a uniform solid red spot I see what appears like a very finely mottled spot. For example, the laser level is aimed at a wall in my house, so I can affix a shelf to the wall. The spot of laser light isn't a smoothly uniform red spot, but appears mottled or "grainy" in some way. What causes this? 71.112.136.40 (talk) 03:10, 22 December 2007 (UTC)[reply]
What happens when an LED is dead or blown off?..Will it make a short across the line by closing or may it open and give a break in the line?..How do we overcome or predict such problems and be sure about the condition how led's behave?...I often end up with blowing LED or making LED to glow with less intensity by using improper resistance.so please tell me how can we calculate the amount of voltage that the led takes if 'x' resistance is added to it's VCC of say 5V?...Thanks —Preceding unsigned comment added by Balan rajan (talk • contribs) 11:06, 22 December 2007 (UTC)[reply]
An LED can short or open. A short will often quickly become an open because of heating. (It's been my experience that they are usually found dead open.) See Light-emitting diode#Failure modes.
A diode will drop a more-or-less fixed voltage once it is forward biased (see Light-emitting diode#Considerations in use). You have to look at the specification sheet for your diode to find out what that voltage is. The specs will also show maximum current. Choose a current near the low end of the range, and calculate a voltage divider with the calculated drop across the resistor at that current and the given drop across the diode at that current. Say the diode drops 1V at 20 ma. The resistor will have to drop 4V at 20 ma, making it 200ohm. I'd put a small linear pot in place of the resistor and crank for desired light output, checking the result against the calculation so as not to stress the diode long-term. Shield your eyes. --Milkbreath (talk) 13:48, 22 December 2007 (UTC)[reply]
Adding to Milkbreath's point, LEDs pushed far beyond their ratings will ultimately end up "failed open" because the bond wire that connects the exposed side of the LED chip to the lead frame is a very, very fine wire and it will blow like an electrical fuse. LEDs can also fail shorted, but they can only remain in that state if the rest of the circuitry is still properly limiting the current.
We have seen in many racing games like the ones from EA-NFS series which repeatedly introduces the nitreous oxide upgrades for it's cars in the In-game option. So is this nitreous oxide really existing?.If so then how can we get such a boost of power?.Immediate accelaration wouldn't damage the spare parts in the car like the gear shaft or the flywheel for eg?.I have never seen such cars fitted with such things around anywhere here. Also i heard it has the risk of exploding at some circumstances if mishandled. So what is this all about?.... —Preceding unsigned comment added by Balan rajan (talk • contribs) 11:10, 22 December 2007 (UTC)[reply]
We acutally have a whole article on Nitrous systems. Yes, nitrous can wreak havoc with engine parts - this image shows an engine piston which has been cracked and dented by the pressures created when nitrous is used. When heated, nitrous oxide decomposes to release oxygen, and this extra oxygen allows the fuel to burn harder. It's only used in very high-end racing cars (commonly dragsters, which need all the acceleration they can get), because it is expensive, damages the engine, and most people have no need for the kind of acceleration provided by NO2 anyway (a turbocharger or supercharger would be far more effective anyway - Nitrous just squeezes the last bits of acceleration out of the fuel). Laïka12:33, 22 December 2007 (UTC)[reply]
Just a nit -- nitrous oxide is N2O, not the far more corrosive NO2. NO2 is a major pollutant and contributor to lung damage; N2O they give you to breathe on purpose (mixed with oxygen of course) at the dentist's office. On the other side of the coin, N2O is explosive under certain conditions. --Trovatore (talk) 23:05, 22 December 2007 (UTC)[reply]
Science/Sound waves
Hey Steve, thanks for the reply!
I have another question for you- Why is it that the speed of sound is very different in water than what it is in air? Does it have anything to do with the intermolecular forces or intermolecular attraction between the water and air molecules? —Preceding unsigned comment added by GK ROCKS (talk • contribs) 13:46, 22 December 2007 (UTC)[reply]
Ignoring economies of scale, should wholemeal bread be cheaper to produce than white/brown not-wholemeal bread? --[[User:Seans Potato Business|S[[File:[[File:--223.186.79.214 (talk) 18:07, 16 September 2011 (UTC)Example.jpg[reply]
The short answer is that that wholemeal bread costs more to make. Here's a more detailed answer below:
Wholemeal is more commonly known as Whole grain. Since we're ignoring economies of scale, I won't figure in the cost difference between whole wheat and bleached, or other type of wheat flour. The process of making bleached flour is more expensive than to make whole wheat, due but due to its greater demand, bleached flour is cheaper to buy. And additionally whole grain flour is more expensive to store, due to it being susceptible to Rancidification. But we won't factor that extra cost in for this question.
It is actually simpler to make bread from flour that has been processed (such as bleached flour) than whole wheat flour. This is due to the fact that the whole wheat flour contains a lot of Cellulose (sometimes called Dietary fiber) from the outer shell of the wheat kernel. This prevents much of the inner starchy Endosperm to be easily broken down during the process of making the bread dough. In white bread this is not a problem, since all of the dietary fiber has been removed, making it so that the dough is more quickly turned into a form in which it can be ready for baking.
Besides the cellulose issue, there's also the issue concerning Gluten content. Gluten is the protein found in many grains, and it is what makes bread dough "sticky" when it is kneaded. The kneading process breaks the flour particles down, releasing the gluten protein from within the wheat flour particles, and then as the protein molecules start adhering to each other, this produces the stickiness. The more gluten present in bread dough, the stickier it is. When it is baked, this stickiness will be what binds the bread together, creating a firm loaf with pleasing texture for the typical human palate. Different types of wheat flour have different levels of gluten present. It depends on what kind of wheat one is using, as well as additional factors that are described in the article on Flour.
If you've ever eaten whole wheat bread that is dry, crumbly, and texturally unappealing, it is because it was prepared in such a way that the cellulose was not broken down in the dough, and/or there was not enough gluten present before it was placed into the oven to bake. This is the biggest reason that whole wheat bread is not as popular as white - it takes more preparation to make it as appealing to the palate of the typical consumer.
So, how does one take whole wheat flour and make it so that the cellulose is broken down, thus creating better quality bread? There are several considerations to take into account. First, you have to have good quality whole wheat flour. By that I mean, it must be considered to be at least as good as "bread flour", which contains at least 11% gluten. To achieve this, the flour must come from a high-gluten wheat, it must be ground in a mill that will break down the cellulose to a very fine texture, and the dough must be properly prepared to allow further breaking down of the flour to allow the gluten to be able to be freed when it is kneaded.
This last step is important. The best way to prepare whole wheat bread is to combine all the ingredients - except the yeast - and then to allow the dough to sit for at least 24 hours before adding the yeast and preparing it for baking. This 24 hour period allows the cellulose to be broken down further, releasing the gluten. When the dough is first made, it should be mixed and kneaded, and then as it sits, it should be kneaded every 8 hours. This also helps the breakdown process. After the 24 hours is up, bring the dough to a temperature that will optimize yeast growth (30° - 37° C, or 86° - 99° F), add the yeast mixture (yeast, water and sugar, which has been allowed to "start"), and then knead the leavened dough two or three more times before baking.
There are plenty of bakeries who try to short-cut this process, and you can immediately tell by sampling their product that they produce an inferior quality whole wheat bread. A good quality loaf of whole wheat will be firm, moist and have a nice flaky crust - however, it will never be possible to achieve the same level of quality as a very good white bread loaf. That's the trade-off of good health, I suppose. Now, as to how much all these extra steps will cost, I'll leave that to you to figure out. I will, though, include a recipe that I have used myself to make quite good loaves that I sold to customers when I did this sort of thing:
Whole Wheat Bread (three 2-pound or four 1.5-pound loaves)
12 cups unsifted whole wheat flour
1/2 cup raw sugar, honey or molasses
1/3 cup cooking oil or melted shortening
2 Tablespoons salt
5 to 6 cups milk or potato water - if fresh (raw) milk is used, scald first)
2 packages (Tablespoons) of bakers yeast
1 teaspoon sugar
Mix well and let stand overnight 24 hours, kneading every 8 hours, at room temperature. Bring the dough up to a temperature of around 90° F (you can place it in the oven with the setting on Warm). When the dough is warm, mix the yeast and sugar into one cup of water that is between 86° - 99° F and allow it to rest undisturbed in a warm place for about 10 minutes until the yeast begins to work (it will be frothy). Add the yeast to the dough and knead. Allow it to rest for 10 minutes. Now the dough must be kneaded constantly for at least 10 minutes. Do not add flour during the kneading process, even though the dough will become very sticky and almost soupy. If kneading by hand grease may be added a couple of times to the kneading board and one's hands, but not flour.
Put the dough back in a covered pan and set in oven to rise at a temperature of 80° to 85° F for one hour, or until it doubles in bulk. Remove the dough and knead constantly for another 10 minutes. Divide the dough into loaves, but let it rest while you grease the baking pans. Shape the loaves so that you tuck the ends in neatly and then lay the loaf into the pan so that the fold of the dough is on the bottom. Lightly grease the top of the loaf with shortening or margarine (not butter, as it will dissipate). Set the loaves in the warmed oven to rise for 15 to 20 minutes at 80° to 85° to allow them to rise to not quite double. Then raise the temperature of the oven to 325° and bake for 70 to 80 minutes.
I used to add a cup of coarsely ground (cracked) soy beans to the dough, which gave the bread an added texture, and provided addictional amino acids for people who were vegetarians. If done right, the end product of this recipe will produce nice, firm, moist loaves. -- Saukkomies07:50, 23 December 2007 (UTC)[reply]
two slits, QED and light
I'm trying to write a gentle math-less explanation of quantum electrodynamics (or quantum field theory, somewhere in between really, it's mainly based on Feynman's QED book). The problem is, I'm doing so after a series of lectures that were just as gentle and light on mathematics, so I may understand certain things, but I don't have the rigorous education required to know for sure whether my intuitive understanding is actually correct. Since I do need to write about it, I'd like to ask you if I've understood the basic ideas.
As I understand it a photon traveling from A to B does so, not in a straight line, but along all paths (each with an associated probability amplitude). These amplitudes can be represented as arrows, where the length of each arrow is (about) equal, and it's the angle of the arrow that increases as the length of the path increases (I think this is Feynman's way of saying that amplitudes are represented by complex numbers, right?). I understand how this means that paths in a small neighbourhood far away from the shortest path cancel each other out, whereas paths in the neighbourhood around the shortest do not, as much, and therefore the closer a path is to the shortest path, the more it contributes to the probability function of the foton's location, which thus becomes essentially a sharp peak along the shortest line from A to B. I also understand that when the foton passes through a narrow enough slit, the probability function on the other side of the slit will spread out like a handfan (mimicing a wave passing through a slit).
The thing I'm uncertain about, and that I would like to see affirmed is the reason for the wave character of the probability function/wave function. If I want to explain the double-slit experiment in these terms, it isn't enough that the slits spread the wave function out, the peaks of the waves also need to come from somewhere. The way I understand it now, is that as the paths I talked about earlier are lines in spacetime, not just the path of the foton varies slightly around the shortest path, the speed of the foton also varies slightly around the shortest path in space-time, ie. the maximum speed. Each foton has a small probability of traveling a bit faster than lightspeed or traveling a bit slower, just like they have a small probability of deviating slightly from the shortest path (so far I'm just paraphrasing Feynman). This makes the probability function of the foton a tiny blob around the point that travels in a straight line at lightspeed, or a fuzzy circle, spreading out, if we don't know where the photon ends up. Is it this 'blob' that creates the peaks in the probability function, that corresponds to the peaks in EM waves in the classical model?
Is there anything to criticize about this view of things (feel free to nitpick, I can always add footnotes, to say I cheated a bit to simplify). risk (talk) 19:08, 22 December 2007 (UTC)[reply]
The first thing to understand about the path-integral approach to wave mechanics (the one where you have a particle taking all possible paths) is that it's not specific to quantum mechanics. You can formulate classical wave theories (linear ones, at least) in the same terms. With the exception of the use of the word "photon", what you've written above is essentially classical, and a good part of QED (the book) is classical as well, including the whole discussion of reflection, refraction and diffraction. A photon taking all possible paths doesn't just mimic a wave, it is a wave. I think Feynman comes on way too strong with the claim that light is made of particles and not waves.
The path-integral approach has advantages and disadvantages over the wave-equation approach, and one of the disadvantages is that it's not easy to see where the wave-like behavior comes from. One way to understand the connection is to think about triple, quadruple, quintuple... slit experiments, and how you'd calculate the pattern on the screen. It should be obvious that you just add contributions from each slit. Now add a second barrier in front of the first one, and put slits in that as well; now you have to add contributions from every pair of slits in the two screens (a total of nm terms if there are n slits in one screen and m in the other). As the number of barriers and the number of slits goes to infinity, the barriers effectively disappear, and the pattern on the screen is a sum of terms for every possible path between the source and the screen. -- BenRG (talk) 21:06, 22 December 2007 (UTC)[reply]
Quote: "Thus, the number of nucleons modulo 4 is preserved across any decay chain." - what does that mean? Is the word modulo being used correctly? Checked the modulo page but still don't understand this sentence. --SeansPotato Business22:17, 22 December 2007 (UTC)[reply]
It just means except for differences of whole number multiples of 4, the number of nucleons is maintained throughout a decay chain. I haven't looked at the disambig page, but it satisfies Merriam-Webster's (2000 edition) definition of modulus (1 c) "the number (as a positive integer) or other mathematical entity (as a polynomial) in a congruence that divides the difference of the two congruent members without leaving a remainder" It's certainly a more concise way of putting it, if not the most easily understandable. Someguy1221 (talk) 22:23, 22 December 2007 (UTC)[reply]
And funnily enough, it just hit me that it's completely and utterly incorrect, as radioactive nuclei can emit individual protons, neutrons, or whole other nuclei. Someguy1221 (talk) 22:36, 22 December 2007 (UTC)[reply]
Yes, but the nuclei that decay by those processes all have tiny half-lives, so they never occur naturally. All natural decay chains obey the mod 4 rule. —Keenan Pepper19:30, 23 December 2007 (UTC)[reply]
Is there a limit to how far back one can remember in their life? I have a memory that I'm sure is not false that occurred when I was 1 and half, is that farther back than normal? Imaninjapiratetalk to me23:59, 22 December 2007 (UTC)[reply]
It would very from person to person, but it typically somewhere between 1 and 2, probably more towards the 2 end. Until a certain point, a child does not distinguish between him/herself and everything he/she can perceive that is not him/herself. It's only when that realisation dawns that memories of the "outside world" start being collected. It's quite possible to have a memory from the age of one and a half, although most people don't. -- JackofOz (talk) 00:22, 23 December 2007 (UTC)[reply]
I can believe that verbal coding is the key to retrieving most memories, so the acquisition of language would therefore limit the reach. Persons who are advocates of Repressed memory speak of "body memories;" not sure what they are. I have heard people tell of memories of persons or places which would place the memory before age 2, while others say nothingcan be remembered before age 5 or 6. Might have to do with verbal intelligence. Animals (specifically elephants and pigeons) have demonstrated long term memories, so words are not always necessary. I certainly believe adults could remember things from age 1 1/2 years, but experiments have shown that memories are suggestible: college students could be convinced they remembered seeing a Donald Duck costumed character in a visit to Disneyland, but no such character ever appeared there.
I have very clear memories from age 3, and more vague ones dating back to a time when the age or date was not clear, but was very likely before 2. Edison (talk) 01:11, 23 December 2007 (UTC)[reply]
(Fixed your link. --Anon, 04:37 UTC, December 23.)
Hi. I think I have memories from, like, a few months after birth, however I'm not going to describe them in detail because I consider it personal info. Anyway, I have far more memories from say, when i was 1 or 2 than from when I was 0. However, most of the memories have rusted, and for some of the memories as much as half or maybe all of it is false. For example, one memory that I think may be false was when I supposedly saw Jupiter and Saturn closely in the sky as big and bright as the full moon. That's next to impossible. I have other memories of going to bed, doing math, reading a book, looking in the mirror, watching TV, eating, talking, etc, from as far back as 3 or 2 or even 1. However, I don't think a lot of people would be able to recall their actual birth for various reasons. I think that memories may be partially the result or one's parents telling them about when they were little, thus adding supposedly "memorised" detail to the memory.
I think it helps when you're trying to recall long-ago memories if you have a photographic memory. Some people even claim to have memories of previous lives, although there isn't really any real proof. I even remeber some of my actual dreams from my early childhood, but only in vague detail. As you age, it is easier to forget your memories of early childhood, as they rust more and more. Hope this helps. Thanks. ~AH1(TCU)01:56, 23 December 2007 (UTC)[reply]
It's not in his page, but ISTR Isaac Asimov claiming to remember his own circumcision. My own memories don't go back before about the age of about two, but I know several people who have no recollection of their own childhood, so there's obviously a lot of latitude from person to person. For my own part, I see no reason why our memories could not stretch back to within the womb at least theoretically or (more likely) from birth - our brains are designed to retain knowledge after all. Consider this - a child of two has already memorized several words and phrases, even if they cannot articulate them as speech; obviously their noggins are already soaking up memories of some kind. Matt Deres (talk) 02:52, 23 December 2007 (UTC)[reply]
Isaac Asimov described his earliest memory when he was about 59; like most of the others mentioned here, it was from when he was 2 years old, not a few days. This is in Chapter 4, Section 2, of In Memory Yet Green.
I have only one memory of this early period of my life. It is the vague impression of a book. I recall sitting in a chair, turning the pages of a book, and loving it. Then I seem to recall wanting the book again, and looking about for it vaguely, but not finding it and wondering where it was.
Years later, I told this to my mother in an effort to place the memory and she said, "I remember the book. You were two years old at the time and you loved it."
I said, "But where did it go? I remember turning the pages and then I couldn't find it."
"Sure," she said, "because every page you turned you tore out."
--Anonymous Asimov fan, 04:37 UTC, December 23, 2007.
I have a memory from when I was probably around 18 months old. I know this because my father was in the Air Force and we moved around a lot when I was little, so that the details of my memory describe a place where we lived between when I was 12 months to 18 months old (my mother verified the details of this later). The memory was of laying in a crib in a room with an open window, looking out to a back yard and a forest beyond. No real events took place - it was just the impression of the place. -- Saukkomies08:00, 23 December 2007 (UTC)[reply]
The memory I have is from a few different times on one day. I was ,according to my mom about 1 and a half, and I first remember the lady at the daycare telling me to put away a toy truck, but I ignored her. We then went for a walk on bike tracks outside the daycare and I all of a sudden saw my dad. He was working on building some new road. I suppose I remember this because it was the first time I found out my parents had a life outside of my house. Imaninjapiratetalk to me17:20, 23 December 2007 (UTC)[reply]
My earliest memory: I was lying in my cot one night. I decided to push my eiderdown off to feel what the cold was like (although I'm doubtful I reasoned all this out in words - and I should explain this was in an unheated room in the 1950s). I must have fallen asleep, because when I woke up again later that night I was warm. Someone had put the eiderdown back over me while I slept. 80.0.124.1 (talk) 23:36, 23 December 2007 (UTC)[reply]
What you say about a general recollection, but not specific, of something is where I think one needs to look, too, when considering earliest memory. My earliest memory of a specific event of several minutes in length, not just a "snapshot," which I know when it happened was when I was 6 - I'd gotten my first hearing aid shortly before, and we were on vacation in Florida. I heard the squawking seagulls from the bathroom window of our motel, and I asked my mom excitely why the birds were so close!
But, I can recall general thingswalking around the block to my great-grandmas, a story I made up about one stuffed dog with a pattern of flowers on his back (rolling in a flwoerbed on the way there), and so on, from well before then. I even baguely recall my great grandpa, the husband of the one who lived near us, who died when I was 3 and a few months. However, that may be tied to my mom telling me about him or looking through pictures.
I think the one at 6 shows the ability to grasp an entire scene and all that is going on, and describe it in pretty good detail. That may vary from person to person, but I dont' think it comes till a bit later, like 4-7. Other memories may be snapshots - the story I made up about the stuffed dog, or yours about the truck - but without much background. Others may be generalities that I recall becuase they "often happened" and are recorded in there because nothing of major import occurred, but the repetition ingrained them.Somebody or his brother (talk) 01:22, 24 December 2007 (UTC)[reply]
My earliest definitely datable memory is my 4th birthday. But like John Prine said, "often remembered / so many times that my memories are worn" — I suspect that most of my early memories by now are really memories of remembering and telling of those early events. I have many holes in memory of events, even of my teens. —Tamfang (talk) 03:42, 24 December 2007 (UTC)[reply]
December 23
Red spot on an Egg Yolk
What's the red spot on some egg yolks? I've heard this called a "blood spot," but I'm not sure it's really blood, nor would that seem to make any sense. Someguy1221 (talk) 00:51, 23 December 2007 (UTC)[reply]
An early-stage chicken embryo? On occasion, I've cracked open eggs and found embryos large enough to discern the developing features. Heh, my grandma boiled an egg last year and discovered a near-fully grown chicken foetus upon shelling it. --Kurt Shaped Box (talk) 01:00, 23 December 2007 (UTC)[reply]
It appears that the red spot is not an embryo, but rather from a blood-vessel bursting on the surface of the yolk during egg-production, and is a sign of freshness. [1]. DuncanHill (talk) 01:05, 23 December 2007 (UTC)[reply]
Apparently, it used to be that if you were Jewish and keeping Kosher you could not eat an egg with a red spot. In fact, you were supposed to break your eggs into a separate glass and examine them before adding them to a recipe because one bad egg could make the whole recipe not-Kosher. But I guess things have changed. Thanks factory farming! I guess if you are Jewish and prefer organic eggs you still have to be on the lookout? Saudade714:30, 29 December 2007 (UTC)[reply]
Your source goes into some detail and is interesting. But note that it says Therefore, the requirement to check each egg remains in effect, as does the requirement to dispose of eggs containing actual blood spots. So a careful person is required to check every egg, even if it is known to be commercial and hence unfertilized; and at the same time, if the person eating (not cooking) the eggs knows they were commercial, it is permitted to eat them even if he is unsure they were checked. Crazy stuff. Rpresser (talk) 19:09, 31 December 2007 (UTC)[reply]
Airplane safety
If impact and fire are the two major cause of death in a plane crash, why plane maker doesn't build a plane with large cushion and heat insulator that cover the cabin? Are they doing enough for the safety of passengers? roscoe_x (talk) 00:58, 23 December 2007 (UTC)[reply]
A lot that doesn't go into planes is due to weight considerations. Planes are fairly light for their volume, in fact. Good heat insulation to cover the entire cabin would be pretty heavy, I'd imagine, and a large cushion would be quite unaerodynamic. Further, a large cushion wouldn't help at all if the plane is plumetting toward the earth at full speed. And if you're willing to wait for it, I'm sure SteveBaker will give a response that will dwarf mine in both substance and length. Someguy1221 (talk) 01:02, 23 December 2007 (UTC)[reply]
The answer is of course money. If its to expensive, its not practical. Far more people die on the roads than in planes, but we don't increase car safety because its not practical. It could be done, but no one will pay $100,000 for a plane ticket.--Dacium (talk) 10:56, 23 December 2007 (UTC)[reply]
Well we do increase car safety - improved headlights, air-bags, impact bars, crumple zones things like that. As for planes...large cushions would do little to stop most impacts - though they could plausibly introduce airbags into seats/curtain airbags - injuries/deaths can occur due to damaged landings/emergency landings. Fire-wise they could skip heat-insulation and have some sort of sprinkler system - obviously it would need to be advanced enough not to just make the situation worse (e.g. water on electrical fires is a bad thing). As the above note, weight is a big issue - as is cost. The number of deaths in commercial aviation annually is very low as I understand it. ny156uk (talk) 11:13, 23 December 2007 (UTC)[reply]
Gah—sprinkler system on an airplane...too much weight! Water is heavy stuff. Carrying a couple of tons of it around on the aircraft everywhere it flies...ugh. 'Dry' systems that use carbon dioxide or other gaseous fire suppressants would pose a risk of asphyxiation to passengers and crew. Materials used in aircraft construction (particularly in the cabin) are required to be fire-retardant; they burn poorly anyway, if at all. The insurmountable obstancle is that you're lifting off with a hundred tons of fuel on board, and if you break open some fuel tanks in a crash, then there's going to be fuel everywhere. Putting out those sorts of fires takes professional firefighters with heavy equipment. (Attempts have been made to make jet fuel safer in a crash; these attempts have not been successful.) For what it's worth, many of the mechanical spaces on aircraft – the place where in-flight fires are likely to start – do contain fire bottles filled with fire suppressants. In the event of fire, these bottles are triggered automatically or manually from the cockpit. (I have also seen small, automated fire bottles built into airplane washroom waste receptacles, presumably to handle butts from careless, covert smokers.)
On the subject of crumple zones, the legs of airline seats are designed to collapse in a controlled manner to cushion the occupant in the event of a crash. Airbags, meanwhile, are unlikely to appear on commercial aircraft for a number of reasons. First, it would mean putting rather a lot explosive material in the aircraft cabin—something that regulators are understandably twitchy about. Second, there's no good, automated way to figure out when the airbags should go off in an airplane crash. What if you're just on the first bounce? Third, detonating all those airbags in a relatively airtight cabin could force oxygen out of the passenger compartment. TenOfAllTrades(talk) 15:43, 23 December 2007 (UTC)[reply]
Also, the accelerations a body is exposed during a crash are incredible. The report into the Swissair Flight 111 crash off Nova Scotia in 1998 suggested that the occupants were subjected to forces at least 350 g, [3] which is well beyond the limits of human survivability. It is likely impossible to create a system that will protect occupants at loads like that while still being flyable or affordable. -- Flyguy649talk17:47, 23 December 2007 (UTC)[reply]
How much of a sphere can you see from one point?
Particulary to do with planets. I have always assumed it is 50% but I started thinking about it and I thought that it surely must be less, at some point the surface of the sphere will be paralel with your direction of vision. Is there some mathematical relationship that any one could write that would describe this?
Cheers, Shniken1 (talk) 05:10, 23 December 2007 (UTC)[reply]
Let be the distance between the observer and the center of the sphere. Let be the radius of the sphere. Then the apex angle of the visible spherical cap is .?? Using the formula found in the solid angle article, the solid angle of the cap is . Since the full solid angle of the sphere is , it means that the visible surface area is . If , this ratio approaches . - Sikon (talk) 07:15, 23 December 2007 (UTC)[reply]
All of it... provided it's completely lit with nothing obscured, and you use a few mirrors. Of course, that's assuming mirrors are not disallowed in your question. Though, if we're talking planets, those giant mirrors can get expensive. (Sorry, couldn't resist.) -- HiEv10:09, 23 December 2007 (UTC)[reply]
Well, you could do it with smaller mirrors and use a telescope. It does raise an interesting side question though: how many mirrors would you need? (I'm guessing 2, but possibly 3?) --SB_Johnny | talk14:07, 23 December 2007 (UTC)[reply]
If the mirror is large enough and you are far enough away from the sphere, you can do it with ONE mirror. The maximal case is where your viewpoint is at zero inches from surface of the objective sphere, and the reflecting mirror constitutes another sphere that completely encircles both you and the objective sphere. The minimal case is where you are infinitely far away from the objective sphere, using an infinite magnification telescope, and the reflecting mirror is barely larger than the radius of the objective sphere.
If you take general relativity into account, you can do it with NO mirrors. Just have a black hole at the center of the sphere being viewed, and put the observer at the photon sphere.
The "conventional" solution would be to have three mirrors, each one convex in shape, placed at the axes of a tetrahedron with the viewer at the fourth axis, the objective at the center, and all four of you positioned at I think 2R from the center of the objective sphere (R = radius of objective sphere).
All this is back-of-the-envelope drawing, no math used :=) 19:05, 31 December 2007 (UTC)
When I'm out flying in my spaceship, I always measure the angle that the planet covers from my point of view and the distance to the surface. That way, I get the planet radius as
Oils have very distinct tastes depending on what their made out of. Just because it's an oil, it doesn't mean they're all going to taste the same. An analogy could be made to different types of nut butters (i.e. peanut butter, cashew butter, almond butter, etc.) -- MacAddct 1984(talk • contribs)16:14, 23 December 2007 (UTC)[reply]
Hi. What causes snow to turn different colours, say pink, green, or blue? Is it bacteria? Chemical reactions? Minerals? I heard that pink snow was called watermelon snow, I saw green snow on a probably-salted outdoor staircase, and I saw blue snow while building a snowball while the temperature was above freezing. What other colours are there, besides yellow caused by dog pee, and brown caused by road ploughed snow? Thanks. ~AH1(TCU)15:32, 23 December 2007 (UTC)[reply]
Some commercially available ice-melting salts have dyes added to let you see where you've spread it. I've seen magenta, blue and green. -- Flyguy649talk21:26, 23 December 2007 (UTC)[reply]
With regard to light-blue snow, you might enjoy our article Color of water.
telescope aperture required to view astronomical objects
Hi. Can you use the brightness in apparent magnitude of an object, the surface brightness at the site, the surface brightness of the actual night sky at the location of the observing site, the atmospheric conditions, how high an object is in the sky, the capability of the person's eyes, etc, to calculate the effective aperture of a telescope required to actually see and recognise an object apart from the background sky? If possible, please give a relatively simple understandable formula that directly takes the numbers of the factors and uses the numbers to directly calculate to a specific aperture that can be calculated using a scientific calculator and all algebraic symbols must be explained as to what it stands for and the formula can be used to provide an answer in the calculator withought confusion? If you have a formula, also please provide the units that each number is in. If you don't have a direct formula, can you use the numbers to do a simple estimation that isn't exact but uses the numbers directly? Also, as a side note, is the formula for the area of an oval π(sR * lR), where the symbol on the left is pi, and sR is half the shortest diameter and lR is half the longest diameter? If it's something else, can it be found on the article for oval? Thanks. ~AH1(TCU)19:01, 23 December 2007 (UTC)[reply]
If you mean an ellipse, then your formula is correct. Not every oval is an ellipse.
Considering the telescope aperture, I don't know a detailed formula for all the factors, but maybe this formula for the maximal magnitude helps you:
where magmax,eye is the maximal magnitude you can see with your eyes, d is the aperture, deye is your eye's aperture (maximally 4 mm) and lg is the logarithm on base 10. This assumes the object to be point-like.
Gravity gets weaker the further away from the sun (or earth) you are. Tidal effects come about as a result of the difference in the strength of gravity because one side of the orbiting body is further away than the other. That difference stretches the moon or planet slightly in the direction of the tidal force - if the body rotates, it is continually pulled and squashed by the tides (here on earth we can see the effects of that in the tides from our oceans - but it applies to solid rock too). This 'kneading' of the material requires energy and the energy comes from gradually slowing down the rotation of the object. Eventually, the body loses all of it's rotation and winds up with one face pointing towards the center of the orbit...typically the heaviers side, as you might expect.
The reason the earth isn't tidally locked - but the moon is, is because the Earth is about 150 million kilometers from the sun - but it's only around 13,000 km across. So as a percentage of 150 million km, the diameter is tiny - just one part in 10,000 - so there is very little difference in the sun's gravity between the two sides of the planet - and hence, very little tidal forces. The moon, is about 400,000 km from the earth and 1,700 km across one part in 300. So the difference in gravitational force between the two sides of the moon is large - but the difference across the earth is tiny. The moon's gravity has a much bigger tidal effect than the sun's (because we are much closer) - but the moon's gravity is only one sixth of the earth's - and the earth has much more rotational inertia. Eventually, even that tiny effect will cause the earth to be tidally locked so that one side of the planet will face towards the moon which will always appear in the exact same place in our sky.
That will result in the earth rotating just once a month - so our "day" would be a whole month long. But that's going to take a long time. Pluto and it's moon, Charon have already arrived at this exact situation because they are much closer to each other and they are of much more equal sizes than Earth and the Moon. As a result. they are both tidally-locked to each other.
There are two details to add in the above, both of which strengthen Steve's point. First, 1/6 is the strength of gravity at the Moon's surface in proportion to that at the Earth's surface. The relevant number here is 1/81, which is the mass of the Moon in proportion to the Earth. (Gravity at the same distance from the center of the respective bodies will be in this proportion.) And second, gravity doesn't just diminish with distance, it diminishes as the square of the distance. When you consider this in combination with the explanation above, it works out that tidal effects diminish as the cube of the distance. (Or using calculus: the derivative of 1/r² is proportional to 1/r³.) --Anonymous, 05:43 UTC, December 24, 2007, Earth.
battery
The battery of an electronic device originating in China opened (poor quality glue). The sticker claims that it is a Li-ion but it looks like it might not be. The highlighted part on the right is a weight which was glued inside the battery casing, and the highlighted part on the left is weird strip that appears to short-circuit that battery cells - it's silver at the terminals but black along its length. Any idea what that strip is? --SeansPotato Business22:59, 23 December 2007 (UTC)[reply]
what makes you think it's not a li-ion cell? Could you post a clearer picture? Is the strip conductive? Does it actually connect to both terminals? Is the other terminal actually at the bottom of the battery? Furmanj (talk) 00:57, 24 December 2007 (UTC)[reply]
It looks like it's a 2 cell battery. Get a multimeter and measure the voltage. If the battery measures > 4V, then it's Li-Ion. Li-ion BTW in cylinderical form looks no different then regular batteries except for it's size. Lithium ion polymer are the ones that comes in flat retangular shapes. I can't tell for certain from your picture but it does look like li-ions. The hint is the little device at the top, it should be a protection/charge circuit. Regular alkaline battery would not need this. Are you sure the black strip is not a piece of wire? You would need to connect both end of the battery to use it. The black strip looks like it's the negative wire. NYCDA (talk) 19:29, 24 December 2007 (UTC)[reply]
Number of animals consumed during a human lifetime
I recently read a novel about vampires who had to kill someone for food every night. This made me think that in a way, non-vegetarian humans are like vampires - we kill to live. We eat animals, and also use leather. I'm not a vegetarian, and I wonder how many animal deaths I will be indirectly responsible for during my life? I often eat tinned sardines which have three or four lives in them. On the other hand eating a portion of bacon, which I never eat, only requires a small fraction of a whole animal. Does anyone know what my likely total score of animal deaths will be during my lifetime please? If I turn up at the pearly gates and find that God's a vegetarian or gives equal worth to animal souls, then I'm in trouble! This is not a pro-vegetarian rant, I'm just curious. 80.2.209.76 (talk) 23:50, 23 December 2007 (UTC)[reply]
Okay, so it's one of those 'I heard it somewhere' stats - but apparently your average human will inadvertently consume 1lb of insects (or parts thereof) in a lifetime. --Kurt Shaped Box (talk) 00:42, 24 December 2007 (UTC)[reply]
I think it's higher than that. I used to room with an agriculture major, and if I recall correctly, the USDA allows ground flour and other processed grains to be as much as a few grams insect parts per kilogram of product. Dragons flight (talk) 00:56, 24 December 2007 (UTC)[reply]
If one reckons lives like Renfield in Bram Stoker's Dracula, then he must total up not only the creatures he consumes, but the creatures they consumed as well, and the creatures consumed by them, etc. We eat few carnivorous mammals,(perhaps an occasional barbecued raccoon) but birds (including fowl) like to eat insects and worms. Many fish are also little predators. Edison (talk) 05:24, 24 December 2007 (UTC)[reply]
But what about all of the microscopic animals that we ingest all the time without even realising it? Those must amount to vastly more than the number of large mammals, fish, birds, etc. SteveBaker (talk) 14:15, 24 December 2007 (UTC)[reply]
Unless you're counting 1 cow equaling 5 steaks or something, the number of individual animals killed, it's way higher than 1000 or even 6000. If you have, let's say on average, 2 different kinds of meat a day. That's 700 animals a year alone. That's a pretty low estimate, considering a hamburger, made from ground beef, is a collection of a whole bunch of different cows. Or chicken fingers, which are processed from a whole bunch of different chicken. -- MacAddct 1984(talk • contribs)17:21, 24 December 2007 (UTC)[reply]
It all depends on how you count things. The question is, does the tiny bit of meat from each animal count as a whole animal, or are you allowing "fractional animals"? For example, if you have something like sausage it may be made up of meats from many different animals (though they may all be the same type of animal). If even microscopic amounts add another animal to your total, then breathing in or inadvertently eating pet dander from your pets counts towards your total. That makes your count ridiculously high, and impossible to measure. Also, it's not like you're consuming the whole animal yourself either, so this inflates the "death total" since one animal is recounted for every person who eats even a tiny part of it.
If, on the other hand, we use "fractional animals" instead, then any meat you consume counts towards the average amount of edible meat made from that kind of animal. If, for example, the average pig has 50 units (lbs/kg/whatever) of edible meat made from it, then you would only count up by one pig after you've eaten 50 units of ham/pork chops/etc., even though you may have eaten meat from many different pigs. This way, a pepperoni pizza only adds a tiny fraction of an animal to your animal total, as opposed to many animals. This gives you a much more realistic and countable measurement.
Finally, if the Judeo-Christian God exists, then there are numerous passages in the Bible that say that some meats are OK while others aren't (for example, see Leviticus 11), so that god isn't a vegetarian. Heck, according to the Bible the reason why God favored Able over Cain is that Able (a shepherd) sacrificed animals to Him, while Cain (a farmer) only brought plants (see Genesis 4:2-5). God also finds the smell of burning animal flesh pleasing (see Leviticus 3:3-5 & 3:14-17). I don't believe in gods myself, but if you're worried about that one then your problem isn't the number of animals, but the type, portions, and method of preparation. -- HiEv04:47, 25 December 2007 (UTC)[reply]
The number of individual lifeforms in one mouthful of a microbial culture such as cheese staggers the imagination. Do they count? If God cares about the numbers, I wouldn't worry about the cows when you get to Heaven - it's the quadrillions of bacterial deaths you've caused in your lifetime that you'll be responsible for. 74.12.208.131 (talk) 17:00, 25 December 2007 (UTC)[reply]
Just last holiday week I probably ate 4 dozen raw oysters, a couple dozen snails, some mussels and some squids and shrimps, some frog's legs, salmon, foie gras...that gives me a kill-rate of almost 100 animals in 7 days. As for the people who eat beef and determining what counts as a "kill" cow-wise - that reminds me of those problems in Analytic philosophy and possible-world theory where they ask you to determine "The mereological sum of all cats in all possible worlds" and then tell you that there are X worlds where there are only cat tails! Saudade714:17, 29 December 2007 (UTC)[reply]
December 24
Ugh! What the hell is this?
I ran across an image out there in the great wide Interweb, of a closeup of the index and middle fingers of a man who appears to be suffering what can only be a very uncomfortable condition (Warning: rather disturbing image: http://ninjapants.org/files/index.php?image=goodmorning.jpg) All of the detail of the image lead me to suspect that the image is authentic, but I'm at a complete loss at to the condition from which this poor person may be suffering. Does anybody have any ideas? – ClockworkSoul05:32, 24 December 2007 (UTC)[reply]
I'd say without too much hesitation, and apologies for any disappointment, that this image has been altered. There are several clues that hint towards this. Firstly the bizarre image of an apparent serious medical condition is presented with a desktop and mouse in the background. If it had been photographed in some sort of 'medical' context it would look more realistic. Second off, the image shows some odd anomalies that indicate some sort of photographic manipulation. Look at the fingerprint whorl on the finger on the left, it appears completely misplaced. Whorls are normally, but not exclusively, on the pad of the digit. There are also some other signs of post-production manipulation around the edges of the 'what-ever-they-ares'. There is a complete absence of any inflammation around these peculiar 'wounds': it is conceivable that if they were long duration injuries they may not have visible signs of inflammation, but in my experience they would. Next, the inside of the finger pulp does not look like that (unless you are some sort of alien), the image shows the matrix of possibly some sort of fruit or vegetative specimen. Finally, the whole medical appearance looks entirely improbable, what are those white 'teeth' looking bits, where have they come from and what is keeping them there. As you say the rest of the images on this site seem to be authentic, some pretty odd, but not manipulated. I would be very pleased if someone could demonstrate with a reasonable degree of authority that this is some sort of traumatic condition, but for the moment I am not any bit convinced.Richard Avery (talk) 10:31, 24 December 2007 (UTC)[reply]
Just trying to find out the difference. Ive read alot of lorcets are with tylenol and lortabs are with aspirin but none of these sources are doctors or nurses or pharmacists that definitly know the answer. so please anyone that is knowledgeable in this feild answer only and let me know if what info i have dug up myself is correct. thanx.
http://www.druglib.com is a good place to go to look up the ingredients of common drugs. Our article Hydrocodone lists the active ingredients of Lorcet and Lortabs - but notice that there are many variations of both product with different dosages, etc. There appears to be only one variation ("Lortab ASA") that contains asperin - all of the other Lortab/Lorcet varients contain acetaminophen (also called "paracetamol" outside the USA). Acetaminophen is also the active ingredient of Tylanol but it would not be strictly true to say that either Lorcet or Lortab contains Tylanol - although the result may well be the same. For a definitive answer, you should read the ingredients on the actual medication bottle and for medical advice in general, you should see a doctor. SteveBaker (talk) 14:05, 24 December 2007 (UTC)[reply]
Is it possible that we are all floating in a big black hole? Is there a way you can tell when you are in a black hole? Is it possible that whole observable universe is floating in very big black hole? If is possible, how big must it be?
I disagree with Mysid. If the black hole is large enough, tidal forces are small at the event horizon. The Schwarzschild radius is proportional to the mass m, while tidal forces are proportional to 1/r3; therefore, tidal forces at the event horizon are proportional to 1/m3. Icek (talk) 13:02, 24 December 2007 (UTC)[reply]
Indeed - Mysid is way off the mark. With a sufficiently large black hole, there would be negligable tidal forces - even within the event horizon. SteveBaker (talk) 13:51, 24 December 2007 (UTC)[reply]
Some strange thought that I just had: Could the expansion of the universe be described by the whole observable universe undergoing tidal forces? Viewed in the frame of a resting observer at different distances from 3/2 * rS to rS from the black hole's center, the circumference around the black hole gets larger the nearer you come to the event horizon (where it diverges). This provides for the expansion in 2 dimensions, while tidal forces explain the expansion in the remaining direction. But I've not done the math yet, and it's of course not the same for the falling observer. Icek (talk) 13:09, 24 December 2007 (UTC)[reply]
What do you mean by "floating in a big black hole"? We couldn't be inside a black hole—the pressures would be far too high to support anything like life. Could we be floating around a black hole, in orbit? Sure, but you'd really be asking "is our solar system rotating around a black hole at the center of the galaxy", which is, if I recall, what they think is at the center of the Milky Way (see Sagittarius A*). --24.147.86.187 (talk) 16:00, 24 December 2007 (UTC)[reply]
Wouldn't we be seeing some really weird effects, like everything that's between us and the center is completely still, and everything outward is accelerated? Of course, if the radial difference is in a different dimension then it might not be quite as obvious, but a few smart apples would be able to tell what's going on. Also, it would have to be a GIANT black hole for us to still be alive right now. --ffroth20:14, 24 December 2007 (UTC)[reply]
There's no exact mathematical definition of what a black hole is, so there's no right answer to this question. The interior portion of the Schwarzschild solution makes a plausible cosmological model, and I'm sure it was considered for that role at some point in the history of modern cosmology. It's even homogeneous (the singularity is in the future, not in a particular spatial location). But it's a terrible fit to observation in other respects, and the other standard black hole solutions aren't any better. For example, they're all contracting in two spatial dimensions and expanding in one -- or vice versa if you use the time-reversed white hole solution -- so they predict redshift in some directions in the sky and blueshift in others (I think).
Contrary to what some people have said, the Schwarzschild interior is perfectly inhabitable in principle if m is large enough. How large? Er, I don't know, but it needs to be at least circa (c3/G)t, where t is the amount of time you want to survive before hitting the singularity. For t on the order of the age of the universe, that comes out to about the mass of the observable universe. But don't read anything into that -- it was bound to happen because of dimensional analysis alone.
In the big crunch scenario the ultimate fate of all the matter in the universe is to hit a black hole singularity. Since a black hole event horizon is the boundary between stuff that necessarily hits the singularity and stuff that doesn't, you could argue that everything in the universe is already inside the event horizon of this final black hole. But this is a dubious use of the word "inside", since there's no outside (and no event horizon/boundary either). I'd tend to say that this pathological case shouldn't count as a black hole interior. The traditional big crunch scenario is ruled out in any case. it's possible that the quintessence might cause a recollapse (depending on what the quintessence actually is), but I don't know how much this recollapse would resemble black hole solutions.
I'm also tempted to answer "humbug". Black holes get way more press than they deserve. The universe is pretty interesting whether or not it resembles a black hole. -- BenRG (talk) 07:33, 25 December 2007 (UTC)[reply]
Was there a solar eclipse in Ukraine on 12 August 1654?
I am reading a historical account of a battle and there is a claim of one, but the account is old and I'd like to verify it before putting in into the article; I'd assume we have means of calculating and verifying if a solar eclipse could have occurred in a specific region on a specific date? I couldn't find a comprehensive list or how to in our articles on Wikipedia, unfortunately. --Piotr Konieczny aka Prokonsul Piotrus| talk 17:56, 24 December 2007 (UTC)[reply]
Yes, this one is marked as a NASA map, and for the other one here it says, "Permission is freely granted to reproduce this data when accompanied by an acknowledgment: 'Eclipse Predictions by Fred Espenak and Jean Meeus (NASA's GSFC).'" MilesAgain (talk) 08:13, 26 December 2007 (UTC)[reply]
Tuning
How do you, electrically, take an analog input and isolate only the signal that's on a certain frequency? This seems like a fundamental component of radio recievers, but I can't decipher our extremely-technical radio articles to figure out how it works. Just what is happening when I turn the dial on an old radio? --ffroth20:01, 24 December 2007 (UTC)[reply]
You use a filter. The LC circuit is an example of this. How it works is that energy is alternatively exchanged between a current with magnetic field in the inductor, and a charge with electric field in the capacitor. This happens at a particular frequency. When you add a loss this does not oscillate for ever, and instead you get a filter that roughly lets through a range of frequencies. There are also crystals that ring like a bell and also allow only a narror range of frequencies. Graeme Bartlett (talk) 20:28, 24 December 2007 (UTC)[reply]
Makes sense. But where in this do you connect the actual signal wire? And how do you set the frequency? Are the capacitors/inductors somehow powered separately from the LC circuit? --ffroth20:35, 24 December 2007 (UTC)[reply]
The resonant frequency is a function of the magnitudes of both the inductor and the capacitor. Make either variable and you can vary the resonant frequency (and so, pick your station). Most radios use a variable capacitor; older automobile radios often used variable inductors. Nowadays with electronically-tuned radios, the variable capacitor is more often a varicap than a physically-adjustable capacitor.
(edit conflict) Resonance is the key. Here's an over-simplified rendition:
There are basically three sections in an old radio that deal with higher-than-audio frequencies, in this order: the RF (radio frequency) amplifier, the mixer, and the IF (intermediate frequency) amp(s). The RF amp does nothing more than amplify (add power to) the signal from the antenna, amplifying the whole mess of jumbled frequencies across the band it's designed to receive. We'll come back to the mixer. The IF section is tuned to pass only one frequency, the intermediate frequency, which becomes the new carrier for the actual audio signal to be detected later.
The real magic happens in the mixer. Two signals are fed into the mixer: the output of the aforementioned RF amp, and the output of the local oscillator. These beat together, producing harmonics all over the place. The local oscillator sits there the whole time ringing at a single frequency determined by where you have the knob set. It is designed to oscillate at a frequency different from the frequency of the station you want to tune by a difference equal to the intermediate frequency. The mixer and IF effectively perform an analogue subtraction, and the difference is the IF. The IF stage can only pass the intermediate frequency, so it acts like a filter. A side benefit is that the IF is a lot lower than the RF and is therefore easier to control and contain. Darned clever, eh? Some inventions are obvious once somebody's done it, but this ain't one of them.
To answer the other question, when you turn the knob you are rotating a row of semi-circular aluminum discs such that they interleave to a greater or lesser extent with similar fixed semi-circular discs, thereby changing the capacitance between them. This capacitance dictates the resonant frequency of the local oscillator. --Milkbreath (talk) 20:43, 24 December 2007 (UTC)[reply]
Grr, that doesn't make any sense. How can you use analog interference to change frequencies? That would be utterly destructive! --ffroth03:28, 25 December 2007 (UTC)[reply]
The "magic" of heterodyning is that this mixing in the frequency domain does not destroy the signal in question. Instead of destroying the signal, it demodulates it. Nimur (talk) 08:03, 25 December 2007 (UTC)[reply]
Nothing gets demodulated in the mixer stage. When you beat two frequencies together, you get interference. It's just like the way you get a "beat" note when two musical notes clash. If you and another person whistle the same note, and one of you lets his note go slightly sharp or flat, you will hear the beat, which is the difference frequency. The difference frequency is explained here. Only the difference frequency that is equal to the IF will pass. The original modulation is obviously retained. --Milkbreath (talk) 13:38, 25 December 2007 (UTC)[reply]
Your explanation is incorrect. Beating happens when two signals (of similar frequencies) are combined additively. A mixer works by combining two signals multiplicatively. --72.94.50.57 (talk) 16:05, 25 December 2007 (UTC)[reply]
Hey, I'm no physicist, I'm an ex–First Phone and repair tech. I figure the guy who wrote the Shrader knows more than anybody here, and it says: "...mixing, beating, or heterodyning one frequency with another in a non-linear circuit... The result is always at least four output frequencies: (1) one of the original frequencies, (2) the other original frequency, (3) the sum of the two frequencies, (4) the difference between the two frequencies." (author's italics) (Electronic Communication. Robert L. Shrader. McGraw-Hill:New York. 1975. p.396) Suffice it to say that interference happens, and a difference frequency is produced. --Milkbreath (talk) 19:08, 25 December 2007 (UTC)[reply]
One quick comment: An RLC circuit is the electronic equivalent of a mechanical dampedharmonic oscillator. The inductor provides the inertia (it resists changes in current just like inertia resists changes in momentum), the capacitor provides the restoring force (it stores energy when displaced from equilibrium, like a spring), and the resistor provides the damping. So if you can see why a mechanical harmonic oscillator has a resonant frequency, it's not that hard to see why an RLC circuit has a resonant frequency. Instead of a mass moving back and forth periodically, it's charge carriers flowing back and forth. —Keenan Pepper02:46, 25 December 2007 (UTC)[reply]
I just want to make sure.. in event of apocalypse or zombie invasion, does anyone actually know how this stuff works? I thought radios were super simple, this is insanely deep stuff --ffroth07:22, 26 December 2007 (UTC)[reply]
Well, no, we don't know. Does anybody know what's going on when a magnet makes a paper clip jump up and stick to it, or what's keeping my ass in this chair right now? To paraphrase Heinlein, have you ever put salt on the tail of a wavicle? Sometimes the lemmings stay put, and their holes migrate. There is math that accurately describes a lot of this, and there are models that predict things pretty well, but it's all a mystery at the base level. --Milkbreath (talk) 13:01, 26 December 2007 (UTC)[reply]
We certainly can't explain why things like fundamental forces exist (and hence, at the deepest level, we don't know "why" a magnet attracts a paperclip) - but we certainly understand what's going on when you demodulate an AM radio signal. That's just simple math. Ptolomy (and later, Euler) figured out that:
cos(y) is just a phase-shifted version of sin(y) - so you can demodulate a signal (x) by multiplying it by a 90 degree phase-shifted version of the carrier frequency (y). You'll end up with sin(x-y) - which is your recovered audio signal and sin(x+y) which is too high in frequency for the subsequent amplifier stages to deal with, so it's rejected. Crappy analog multipliers (aka transistors or vacuum tubes) allow some of the original signal through too - hence Schrader's assertion that there are FOUR signals present in the output rather than the two you wanted - but those are also way too high in frequency and are effectively rejected by the audio stage amplifiers or by the inertia of the electromechanical loudspeaker. QED
Basic AM radios are extremely simple. When you tune an old radio, you are changing the capacitance. The LC circuit is connected in parallel. In this configuration, it's a band stop circuit. It stops the frequency the LC circuit is tuned to and allows all other frequencies to pass thru. Basically it shorts out all the other frequencies and you are left with only the frequency it's tuned too. You are left with an amplitude modulated signal at the stage. A simple diode and capicitor is needed to demodulate this into audio signal. You now have a crystal radio. It is a fully functional AM radio requiring NO power source. Get a crystal radio kit to learn more. FM works similar but demodulation is more complex. NYCDA (talk) 16:55, 26 December 2007 (UTC)[reply]
As for whether or not this stuff is "simple" or not, it depends what you are trying to do with it and how deep a knowledge of it you require. Remember that it took a gigantic laboratory (the Rad Lab) of top scientists to adapt radio waves for military use during World War II. Aspects of it are classical-physics simple, while other parts delve very deep into the quantum mechanical. --24.147.86.187 (talk) 19:30, 27 December 2007 (UTC)[reply]
Please don't double-post. Hint: The more electronegative atom formally receives a electron from the less electronegative atom when forming a covalent bond. Now It's a matter of counting the bonds. Icek (talk) 15:23, 25 December 2007 (UTC)[reply]
My mother was given this plant as a Christmas present and we are trying to identify it. It has a lot of tall thin shoots that put me in mind if miniaturised bamboo, with lots of leaves branching off from the main stalk. It also appears to have a bunch of bulblike things around the bottom, but I'm not entirely sure if they're part of the plant or just decoration. There is no identifying marks on the bowl or the plant other than a label for the store from which it was purchased.
At first sight it looks like a number of avocado stones have been planted together and these are the resultant young avocado treelets. The round things at the 'soil' surface are the stones from avocado pears, they have split to permit the shoot to emerge. If this is so then you have a bit of a problem in a couple of years because these trees grow up to 3 or 4 metres tall. My only doubt is that a dozen or so of these stones should be planted together in a single pot. Here [4] is a site that shows how to grow avocados. Have a Happy Christmas! Richard Avery (talk) 09:15, 25 December 2007 (UTC)[reply]
About Plant's Cells
Tell how can I know about mechanism of plant's cells (specially root), their performances ,in different situations do they do instinctive or intelligently? In their inside construction how organs work and how chemical processes and electricity... are involve? Is there any perfect articles, links or references?Flakture (talk) 15:10, 25 December 2007 (UTC)[reply]
I don't think that the words instinct or intelligent can be applied to any discussion about plants. Their cells just function in the way that they're "programmed" according to their DNA and epigenetic arrangement and extracellular (i.e. from other cells or the environment) incoming signals. --SeansPotato Business22:44, 25 December 2007 (UTC)[reply]
Exactly. Plants don't have brains or brain-analogs, so the terms "intelligence" and "instinct" don't really apply to them (except perhaps in the broadest and least meaningful sense of those terms). In addition to that, plants only have a few organs. If you're talking about plant cells perhaps you meant "organelles"? You should probably reword your question based on these comments so we'll have a better idea of what you're looking for. -- HiEv01:51, 26 December 2007 (UTC)[reply]
Is a person's reaction after smoking cannibis at all genetic (e.g. Red, eyes, paranoia, sense of floating). Only asking because a friend of a friend of a roommate of one of my distant cousins said he noticed this. Thanks, schyler (talk) 00:30, 26 December 2007 (UTC)[reply]
Of course I can't speak for any specific symptoms, but according to this study, certain individuals have a genetic predisposition toward becoming psychotic as a result of cannabis use; so yes, genetics can affect your reaction to cannabis. And you might want to tell your "roommate's friend's friend's distant cousin" to stop hitting the stuff or see a doctor if the effects are starting to worry him. Someguy1221 (talk) 03:00, 26 December 2007 (UTC)[reply]
The question related some symptoms and then said "What could be the cause of this?" - that is clearly a request for a diagnosis - and is therefore not an acceptable question for the reference desk. The fact that the questioner asked for a reply in the form of some links rather than some inline explanation doesn't change that in the slightest. It is the question that is disallowed - not the form of the answer. If the questioner had asked for a reply in the form of an interpretive tapdance routine, that wouldn't be OK either. Please take further discussion to the talk page. SteveBaker (talk) 15:25, 26 December 2007 (UTC)[reply]
I find it disruptive when reference desk participants assume bad faith and bite new visitors. If we intend to interpret any description of personal health issues as not being welcome here then we should list that as a rule at the top of this page where people can see it before they edit the page. "Please take further discussion to the talk page" <-- I'm trying to repair the damage that has been done here, on this page, to a Wikipedia visitor. I do not see how that can be done effectively on some other page. If the person who started this thread comes back I want them to see that it is Wikipedia policy to welcome and help new visitors. --JWSchmidt (talk) 16:20, 26 December 2007 (UTC)[reply]
To the question asker - you should seek the advice of a doctor for medical/health issues you have as they are the people who are qualified and trained to help you in such matters. If you are too shy, you may want to seek out a female doctor or whoever you will feel comfortable asking. Bear in mind that in nearly all cases doctors are ethically bounded to keep any thing you tell them confidential. Nil Einne (talk) 16:57, 26 December 2007 (UTC)[reply]
It's that time of the year again... (science edition)
Ok, I'm bored, on vacation and my pending image projects don't look very exciting at the moment. Do you guys have any suggestions for cool science images, especially animations, for me to create? Especially physics, but any suggestion is welcome. Drop them here and I'll see what I can do. :) By the way, merry belated xmas! — Kieff | Talk06:03, 26 December 2007 (UTC)[reply]
The Atom page is the the science COTM and would probably be great with some sort of animation. maybe some sort of energy in --> excited state --> return to ground state with emission of a photon or a matter/antimatter annihilation? Cheers! Furmanj (talk) 09:38, 26 December 2007 (UTC)[reply]
Interesting. But how far can artistic freedom go with such a thing? It can't be too conceptual, or there would be misunderstandings. — Kieff | Talk14:06, 26 December 2007 (UTC)[reply]
Personally I think the Tokamak page could use some nicer illustrations. Currently there is only one low-res explanatory graphic and it's not all that explanatory in my opinion. --24.147.86.187 (talk) 17:47, 26 December 2007 (UTC)[reply]
I'm still hoping for a geology and biome map of the the terrain underneath North Carolina. I had hoped I would be skilled enough to create this diagram but I am not. I'm thinking a nice isometric cutaway to reveal the soil and rock forms of the three regions of the state (Appalachian Mountains, Piedmont, and Coastal Plain); then, on top, a sort of schematic representation of the flora and fauna for each region. Post on my Talk Page if you're interested - I can expound in great depth! Nimur (talk) 19:35, 26 December 2007 (UTC)[reply]
The average temperature continues to fall as large bodies of air and water radiate heat into space. Not until those later months to they start gaining net heat. As Cecil Adams put it in this edition of The Straight Dope which I found as an external link in Season, "The period of max temperature in the mid-latitudes always lags about 25 to 30 days behind the period of max daylight, due to the fact that the earth heats up and cools off relatively slowly." MilesAgain (talk) 08:18, 26 December 2007 (UTC)[reply]
The OP clearly said "IF the shortest day is in December..." - so this is quite clearly a hypothetical question which (in practical terms) relates only to the Northern hemisphere. SteveBaker (talk) 17:00, 26 December 2007 (UTC)[reply]
Well, this is of no such importance to start a discussion, in any case. If we go logical, though, the shortest day is in December is an undecidable proposition, if a point of reference is not adjointed. I think this is an issue that relates to the whole planet, for in the Southern hemisphere a similar situation arises, with cold being replaced by warm, I guess. Pallida Mors18:56, 26 December 2007 (UTC)[reply]
Yes but does the OP there is a difference? Some people don't and the OP gave no clear indication he or she does in his or her question so I saw no harm in pointing that out. Note that if could be taken in two ways. It could be taken to mean 'if the shortest day is in December' (like it is in the Northern hemisphere) or 'if the shortest day is in December' (i.e. Since we all know the shortest day is in December). Both are easily as likely. For example, in my above sentence I presumed at the time that it would be clear I knew the difference between the southern hemisphere and northern hemisphere since I included the smiley. NYCDA clearly didn't understand that though and rereading my sentence it was easily posible I was using the smiley because I was poking fun at what I thought was a mistake on the part of the OP rather so it was perfectly resonable for NYCDA to assume I might not know the difference (although I think the a far greater of people in the southern hemisphere particularly those from English speaking countries are since they are exposed to the northern hemisphere a lot) Nil Einne (talk) 14:11, 28 December 2007 (UTC)[reply]
Digital to analog convertor IC sampling Vs settling time confusion
HI everybody, I am not sure if this is the right place to ask this but just asking with hope.If anybody knows then please just reply. I have seen a DAC IC(DAC 9238) indicating that it gives 125MSPS(million samples per sec) or 125MHz speed in updating the digital data to analog signal in its datasheet. But for dac's, the settling time is important(time taken to convert digital data to analog signal). For this dac the settling time is 30ns(I found this value somewhere inside). So this gives a data update rate of only 33 MHz. So what does 125MHz here mean?.The adds show this 125MHz in huge size fonts but looking at the settling time,it can't even exceed 33MHz.I hope you can understands what I'm trying to say.If anybody gets a click in their mind,plz do reply. Thanks for your time. —Preceding unsigned comment added by 122.164.63.100 (talk) 10:55, 26 December 2007 (UTC)[reply]
Settling time should be quoted to a certain accuracy. So it may settle to within 1% @ 33 MHz, but to within 10% @ 125 MHz. Therefore it can still be used at 125 MHz but with reduced accuracy. BTW 125MPS is equivalent to 62.5 MHz.--TreeSmiler (talk) 11:21, 26 December 2007 (UTC)[reply]
62.5 MHz is the maximum bandwidth of a bandwidth-limited signal that can theoretically be reproduced faithfully given a sampling rate of 125 MHz. However, uses of DACs are not limited to reproducing sampled waveforms. I don't think it is strictly correct to equate 125 MSPS to 62.5 MHz without considering the application. --71.162.233.225 (talk) 16:57, 26 December 2007 (UTC)[reply]
OK Say you had a sine wave at 62.5 MHz. THis can be digitized (just about) By taking 2 samples per cycle (ie a sampling rate of 125MS/s). DA conversion followed by a low pass filter with a cutoff just above 62.5 MHz would reconstitute the sine wave. Agree?--TreeSmiler (talk) 22:44, 26 December 2007 (UTC)[reply]
Thanks for your replies. I understood. Anyway, how can we reconstruct using just 2 samples using a LP filter?...I thought that I may gonna need atleast some 20 samples of digital data for one sinewave inorder to reconstruct using a dsp or mcu through dac... —Preceding unsigned comment added by 122.164.61.94 (talk) 11:31, 27 December 2007 (UTC)[reply]
Return protocol for Michael Collins
If during the Apollo 11 mission, there had been an accident which would have left Armstrong and Aldrin stranded on the Moon with no chances of being rescue, would it have been possible for Michael Collins to make it back to Earth alone? Was there even any special plan prepared for such an eventuality? -- Danilot (talk) 13:35, 26 December 2007 (UTC)[reply]
The recent film "In The Shadow Of The Moon" includes the text of a speech for Nixon, in case Armstrong and Aldrin were stranded on the moon. Collins would have returned to Earth. I remember the Apollo 11 mission well. A few days before, the Soviet Union lauched Luna 15 but the West didn't know that it was a robot sampler. The press speculated it might have been a lifeboat to enable the Apollo astronauts to return in case there was an accident.--80.176.225.249 (talk) 14:34, 26 December 2007 (UTC)[reply]
I have been reading on nasa's web site about stellar evolution and some questions have came up that I could not find an answer for. I am currious but not well educated so if you can answer my questions please use small words. Q- if iron evolves inside stars and the end result of this star is a black hole, that not even light can escape, then how do we have iron on our tiny little planet? Q- what is the process that causes gas to colapse into a star. I thought that a gas would dissipate evenly into its surroundings.
Answer 1: Black holes are not the only possible end for a star. It can also become a white dwarf or a neutron star. Both can trigger a supernova in different ways, therefore spreading iron and many more elements into space.
Answer 2: Gravity is the key. An initial smooth distribution of matter will eventually collapse and cause the hierarchy of structures, such as clusters of galaxies, stellar groups, stars and planets. So gas stays in clouds until other forces are unable to compensate for gravity, and mass starts to collapse inwards. -- Danilot (talk) 17:16, 26 December 2007 (UTC)[reply]
On the behalf of every high school athlete out there - does "saving yourself" ; ) before a game or meet actually do anything? If so, how long should one hold off? I've gotten so much conflicting advice, and I think the RD is the place to put this to rest. Thanks. - Anonymous
This is just my opinion: I have no experience of such matters. BUT, if one were not to expend much energy during the act (ie making it an extreme quickie), I dont see how it could affect your performance in the sport. In fact it might be beneficial, because it gets those feelings out and allows you to concentrate on the game etc.--TreeSmiler (talk) 03:24, 27 December 2007 (UTC)[reply]
I was going to ask TreeSmiler if the absence of experience is referred to sexual or athletic activity. But then I refrained. That is so personal. The amount of athletic activity he/she has is none of our business. ;) Pallida Mors14:32, 27 December 2007 (UTC)[reply]
I am not an athlete so I wouldnt know the effect of pre performance sex! The important point is that if you spent all night lovemaking, it takes a lot of energy and you are going to be tired in the morning. I assume the original questioner is male so I think pulling off a 1 minute quickie just before (not during) the game would not affect performance unduly.--TreeSmiler (talk) 17:12, 27 December 2007 (UTC)[reply]
Most of what I can find online (e.g. [5][6]) seems to say there is no direct link. However, a more important factor is being well-rested and avoiding extra psychological stress. So, if sex causes you anxiety and/or is keeping you from sleeping, then perhaps you should abstain. If instead you find sex is satisfying and it is timed not to interfere with sleep, then perhaps it is a good thing to continue. In either case, I would encourage you and other high school athletes to consistently practice safe sex when you choose not to abstain. Dragons flight (talk) 15:59, 27 December 2007 (UTC)[reply]
Or possibly somebody who knows where to look. Have a bit of a wander round here [7]and there is a fair bit about the anatomy of the chest and what the aorta is attached to. You might even be able to find some pictures.Richard Avery (talk) 23:09, 26 December 2007 (UTC)[reply]
Gray's Anatomy is free at Bartleby. This link takes you to a page that describes the attachments. It seems that the deep fascia of the neck hold the whole business up, and that a pair of ligaments, the superior and inferior sternopericardiac ligaments, anchor the pericardium in front. There's more. --Milkbreath (talk) 00:15, 27 December 2007 (UTC)[reply]
Stainless steel, nickle, pulled by magnet
Is it true if an alloy stainless steel has no nickel, it is pulled by a magnet, whereas if an alloy of stainless steel has nickel in it, then it is not pulled by a magnet? William Ortiz (talk) 23:15, 26 December 2007 (UTC)[reply]
I'm nearsighted. When I look at a light-to-dark transition (say, a dark door against a white wall) with my glasses off, I don't see a smooth transition, but rather two or three distinct edges. Why is this? --67.185.172.158 (talk) 02:08, 27 December 2007 (UTC)[reply]
Two distinct edges is easily explained if your two eyes are failing to fuse a stereo image into a single image - or if (for example) one eye is focussing the image differently from the other. Three distinct images would be very tough to explain though...are you SURE you ever see three distinct images? SteveBaker (talk) 07:10, 27 December 2007 (UTC)[reply]
As you would know, unfocused vision causes what should be a dot to spread out into a circle of confusion. This has a definite size that depends on the amount of the focusing defect. If you look at a sharp black/white boundary, you will see the white penetrate into the black by an amount equal to the radius of the circle of confusion, forming a dark gray stripe; and (less obviously) the black penetrates into the white by the same amount, forming a light gray stripe. But you can also perceive the boundary in its true position to some extent (as a boundary between the light and dark gray), because some part of the misfocused light is offset parallel to the boundary or nearly so, and doesn't impair your detection of it. This can create the effect of a triple image.
I'm myopic and in some circumstances I can see this type of triple image with one eye closed, although sometimes not all three boundaries are visible, so then I get a double image. In addition, if your eyes are myopic to different degrees, the circles of confusion for the same object will be different sizes, which may also cause the appearance of additional images of the boundary: logically there could be as many as five, although I have not seen this. --Anonymous, 10:15 UTC, December 27, 2007.
A Mach band
Ah - I see what you're getting at. I don't like your explanation though. If you can see this effect with one eye alone then I think you are seeing a phenomenon called Mach banding (see image at right - sadly, our article on the phenomenon is rather weak). The deal is that if you plotted a graph of brightness versus X coordinate of this defocussed edge, the real world looks like this:
____White
|
Black_________|
but with somewhat blurry vision, it would look something like:
____White
/
Black________/
The human brain is very attuned to the nature of colour brightness transitions and tends to interpret shading as shape. In order to do that, discontinuities in the derivative of the light function are accentuated in our minds to make the changes look more prominant. That's the cause of Mach banding. Look at the image at right which has a brightness-versus-X curve like this:
Light Grey____
\
\_______Dark grey
But it looks to us mere humans like this:
Light Grey__|\
\
\ _____Dark grey
\|
So you see a brighter line just before the colour transition and a darker line just afterwards. This would be a mechanism that would produce these 'double edges' with just one eye.
It's also possible for a particular kind of optical defocus to cause a third discontinuity in the derivative in the middle of the ramp between dark and light that would produce a third 'edge'.
I don't like your not liking my explanation, because I think we're both right. I'm talking about where the transition comes from and you're explaining why it might be perceived as a sharper edge than otherwise. --Anon, 21:35 UTC, December 27.
I found something among the comments to the video. The fifth page of the comments, post by one ' thelaughingjackle'. Awesome video by the way. --Ouro (blah blah) 11:28, 27 December 2007 (UTC)[reply]
In case anyone doesn't want to page all the way to "thelaugingjackle"'s response, here's the process that was described (I'm paraphrasiong what was said to avoid possible copyright issues):
1. The two halves of the grape become charged with negative and positive electromagnetic poles as soon as the microwave is turned on.
2. Immediately, the water contained in the grape starts to go through a process of electrolysis, which breaks the water molecule down into oxygen and hydrogen atoms, which then accumulate at either magnetic pole.
3. As soon as hydrogen gas is relased, A tiny electrical spark is created by the grape being excited by the microwaves. This spark then ignites both the hydrogen and oxygen gases being released, producing a plasma fire above the grape.
4. The hydrogen gas burns as an orange red, and the oxygen gas burns as a blue.
One thing for sure, that is indeed a very cool video! -- Saukkomies10:34, 27 December 2007 (UTC)[reply]
My unresearched guess would be that it was to do with a larger percentage of water in grapes and less porous skin. More water means it absorbs more energy from the microwaves. A less porous skin means that the electrolyzed gases can't simply pass through the skin, creating a build up of flammable gases. Fructose being easier to burn than complex starches may or may not also be a factor. EvilCouch (talk) 04:33, 28 December 2007 (UTC)[reply]
How does Morphine achieve its pain killing effects. All sources I cheacked say that it does this by blocking the opioid receptors. But they never mention who that helps. Does the blockage obstructs pain signals to the brain, or allows the brain to ignore it or what?
is there any good links I can read up on? —Preceding unsigned comment added by 99.240.203.201 (talk) 14:28, 27 December 2007 (UTC)[reply]
The short answer to your question is that the Morphine does block the pain signal to the brain. It does this by plugging up opioid receptors between the nerve cells (called Neurons) in the body, so that signals from a part of the body that indicate pain is occurring are not passed on from one nerve cell to the next - and thus no signal reaches the brain. The way these signals are passed between nerve cells is based on chemistry - there are specific chemicals called neurotransmitters that are in the tip of each nerve cells' little branches, called Axons - and which travel the short distance from one nerve cell to the next when excited to do so (when the cell gets a signal to pass on to the brain). The special message centers located on the end of the nerve cell's branches are called Synapses. When a synapse receives a message to pass on to the next nerve cell's synapse, it releases a flood of neurotransmitters which travel the short distance between the two nerve cells. There are specific receptors to which the neurotransmitters need to go in order for the receiving cell to know to pass the signal on up the chain to the brain. Different receptors are chemically constructed to allow only specific chemicals to fit - sort of like having the precise key to fit into the precise lock. If the receptors are all clogged up with another chemical that is similar to the neurotransmitter being sent by the sending nerve cell, then there's no way for the neurotransmitter chemical to attach itself to the receiving nerve cell's surface - and this blocks the message from being passed on from one nerve cell to the next. Morphine happens to have a similar chemical structure to the "Mu" neurotrasmitter that passes on many of the pain signals that the body sends to the brain. So when someone has morphine introduced to their body, it spreads around and plugs up these nerve receptors, and this blocks the pain signals from reaching the brain. The reason morphine, and all other opiates, are so highly 'tolerant" is because the body compensates for all these plugged receptors by creating more of them on the ends of the nerve cells. This in turn means that a person needs to take more and more of the opiate (morphine) to achieve the same results - it's the body's way to overcome the need for the brain to receive pain messages. -- Saukkomies11:05, 27 December 2007 (UTC)[reply]
Well, the simplest way is to calculate the net torque from the forces you have. The equation for that is the second one in the article:
Then you can use the first equation: (torque = force x distance - which applies when there are two equal and opposite forces, each acting at some distance that are acting as a couple). Since there are an infinite number of possible force/distance values that satisfy your criteria, either pick a fixed distance and use the equation to calculate the force - or pick a force and calculate the distance.
Ok, so when my question says "the equivalent couple" (with no other qualifying info), it really just means "an equivalent couple". Thanks, Laïka20:00, 27 December 2007 (UTC)[reply]
My understanding is that the couple is measured in units of torque, so there is a unique value (distance X force). If you so choose to decompose this into a force and a distance, then as SteveBaker has mentioned, selecting either will define the other. Nimur (talk) 01:54, 28 December 2007 (UTC)[reply]
What is amitotic?
My question for the reference desk is:
In your article on "Glial cells" I found the word "amitotic". When I searched for amitotic I got the message No page with that title exists.
I also searched Wiktionary and got the same results.
The linked abstract was about neurons, not about glial cells, so I'm not sure that the change was correct. Sorry, didn't read our article properly, and thought amitotic was supposed to refer to glia cels, which made no sense. The change was justified. --NorwegianBluetalk17:47, 27 December 2007 (UTC)[reply]
Free basic chemistry textbook?
I'm looking for a free, online basic chemistry textbook. I know about wikibooks, but the General chemistry book is quite a bit from being finished. Any advice? It should start out simple with describing atoms, protons, electrons etc, and move on to the periodic table, bonds, reactions etc. Thanks in advance! Aeluwas (talk) 16:30, 27 December 2007 (UTC)[reply]
Hey Aeluwas, I just finished taking chemistry, these sites may be of interest to you: [12] and [13]. If you really want to learn chemistry, use your book, practice, and don't be afraid to ask a teacher or [teaching assistant] --n1yaNt00:30, 28 December 2007 (UTC)[reply]
I just knew it was going to be a Japanese invention before clicking on the link. They appear to be on the forefront of robotics and related areas particularly in relation to the elderly. As for the second question, what do you mean 'cleanest' way? You could soak them in some kind of acid but you'd end up killing the person as well. Nil Einne (talk) 13:16, 28 December 2007 (UTC)[reply]
The Japanese are furthest ahead in this regard because they have a shrinking population coupled with a sharp increase in life-spans. They realise that in time, care of the elderly will become very difficult because of a shortage of younger people to look after them. The drive to find robotic assistants for the elderly is therefore a significant stimulus for their industry to carry out this kind of research. SteveBaker (talk) 14:51, 28 December 2007 (UTC)[reply]
I know that heating values are usually used for fuels, but in real-world applications, many fuels are not pure but actually have some nitrogen absorbed in them. In particular, I'm trying to calculate out the BTU/standard cubic feet (megajoule/normal cubic meter would be fine, too) for various compositions of natural gas depending on how much nitrogen is added or removed post-production. So my questions:
What is the heating value of Nitrogen?
Am I correct that if I know the BTU/scf of the pre-processed gas, then all I need to know is the % of Nitrogen added or removed and the Heating value of Nitrogen, and I can do a simple ratio calculation to get the BTU/scf of the post-processed gas?
In the conditions found in a residential or commercial heating furnace, Nitrogen will not react and therefore has no heating value. It is possible to obtain nitrous oxide which will serve as an oxidizer (not as a fuel), but this is an extremely unlikely component of your natural gas. As far as your second question, you can probably assume the Nitrogen will not react in any way in your setup, so you can simply neglect it in the calculations (assuming that an inert gas does not affect a reaction is a common first-pass approach, and as long as the percent quantity is low, is very accurate). Simply calculate how much actual fuel (natural gas) you have present. Nimur (talk) 01:49, 28 December 2007 (UTC)[reply]
If nitrogen is burnt to form various nitrogen oxides, it actually consumes energy. If you burn the natural gas with air, the air will provide far more nitrogen (78% of the air) than the natural gas. Nitrogen oxides are only created at high temperatures and you can probably neglect them. You can look up thermochemical data in the NIST Chemistry Webbook; e. g. formation of 1 mole NO2 consumes 33.1 kJ. Icek (talk) 20:38, 28 December 2007 (UTC)[reply]
What is the least damaged ecosystem/biome?
That is, what biome has the largest percentage of its original area remaining? (I assume the Antarctic ice cap would be the answer, but I mean besides that...)
Maybe the ocean, although fishing and whaling threaten many species. I think your question leaves a lot of vagueness - do you mean to equate "undamaged" directly to "least loss of area"? That approach has limited applicability, as human encroachment does not necessarily mean total destruction and replacement of a biome. Nimur (talk) 01:43, 28 December 2007 (UTC)[reply]
If said ecosystem is "completely isolated", how did the cave's discoverer find it, and the film crew get to it and and film it? No, THAT ecosystem has now had a wide array of microbes introduced to it, courtesy of the discoverers and the film crew. Perhaps, if it is somehow sealed away from further visits, and the last visitors left some kind of automated remote-sending equipment, we can see what effects there are without any more visits. -SandyJax (talk) 17:46, 28 December 2007 (UTC)[reply]
You're all right - I worded the question badly. Let's see: Of the major land habitat types (tropical rainforest, temperate deciduous forest, grassland, desert, tundra, etc.), which has the smallest percentage of its original land area converted by farming, ranching, logging, oil extraction, or urbanization?
This can go both ways. There's a general rule in medicine that "tumors love blood," so anything that broadly impedes blood flow is unlikely to assist in tumor growth. Beyond tumor growth, however, cancer can benefit from blood clotting; studies have shown that metastasis of cancer cells may be aided by blood clotting, which may help malignant cells settle down inside a blood vessel (cancer cells have even been observed to generate chemicals that promote coagulation). Just keep in mind that is entirely related to the spread of cancer, not the appearnce of it. Further, blood clotting may be a side affect of certain cancer treatments, or a side-effect of drugs used to treat anemia, which can itself be a side-effect of certain cancer treatments. Someguy1221 (talk) 04:13, 28 December 2007 (UTC)[reply]
Don't know for sure, but I suspect it's the same reason that the Southern Hemisphere gets shorter summers than the north. Something to do with the shape of our orbit. --Psud (talk) 12:09, 28 December 2007 (UTC)[reply]
First of all, you're more likely to get a solar eclipse in your hemisphere's summer. (From your POV on the earth, a solar eclipse has to happen when the sun is up, and it's up longer in the summer. From the sun's POV, the visible half of the earth is dominated by the hemisphere that's in summer.) Now, you know that by remarkable coincidence, the apparent size of the sun and moon are almost exactly the same; the moon can just barely cover the sun. Since the earth's orbit around the sun and the moon's orbit around the earth are both slightly elliptical, the apparent sizes of the moon and sun can vary a bit, as they get closer and farther from us. In some cases, the moon appears slightly smaller than the sun, and the result is an annular eclipse instead of a total eclipse—there's a ring (annulus) of sun sticking out from behind the moon. During the southern hemisphere summer—when the southern hemisphere is most likely to see an eclipse—the earth is closest to the sun, and so the sun is at its largest apparent size. This means that you're more likely to get an annular eclipse instead of a total eclipse, compared to the northern hemisphere summer, when the sun is at its smallest apparent size. -- Coneslayer (talk) 13:34, 28 December 2007 (UTC)[reply]
Another contributory factor is simply the way that particular map was drawn. Because it's using a Mercator projection, the north and south poles are disproportionately large compared to equatorial regions. Most of the 'gaps' in the eclipse coverage map are in the south polar region and while they seem like massive holes in the map, they are in reality quite small compared to the ones nearer the equator. So, while there are undoubtedly more gaps in the southern hemisphere, they are much smaller than they appear and the discrepancy is nothing like as big as the map implies at first glance. SteveBaker (talk) 14:46, 28 December 2007 (UTC)[reply]
That is really going to vary a great deal from coffee to coffee. Coffee#Caffeine content gives the common masses of caffein in various coffee-like beverages (which is the major factor), but doesn't give the density of the coffee. So, it's easy enough you want a mass/volume ratio. In espresso, for example, you have 30 mg of caffein in 30 ml of espresso, so you have 0.1% caffein (mass/volume). The mass/mass ratio shouldn't be too far off, as most water-based solutions have a density pretty close to 1mg/ml. Someguy1221 (talk) 07:19, 28 December 2007 (UTC)[reply]
This is really unscientific but I used to wait tables and the packets we used said that regular coffee had 3% caffeine while "decaf" coffee was 98% caffeine free. To me, bad at math, this seems to say that there is only a 1% difference between decaf and regular. And that rationalising always made me feel not so bad when giving people the wrong kind of coffee when I was "in the weeds". There - since I am not Catholic (or religious at all) my confessional is the Wikipedia:Reference desk/Science! Saudade720:33, 28 December 2007 (UTC)[reply]
The '98% caffeine free' statement is intended to mean that 98% of the caffeine has been removed, leaving just 2% of the original concentration. Note that the 3% number is much too high under any sensible measuring scheme—as Someguy notes, the correct figure is less than 0.1%. (This page suggests that an eight-ounce (225 mL) cup of coffee contains between 80 and 175 mg of caffeine; that's a concentration between 0.03 and 0.08%. Espresso, with its smaller volume, has a caffeine concentration closer to 0.2%. For comparison, a cup of decaf coffee contains 2 to 4 mg of caffeine—roughly 98% less than the regular. TenOfAllTrades(talk) 21:23, 28 December 2007 (UTC)[reply]
That's cool. Like I said it was unscientific! That's just what the individual brewing packets said! But I totally see your reasoning and it sounds right to me! Thanks for being Math-ier than I! Saudade723:11, 28 December 2007 (UTC)[reply]
Snail mail
Where I am (Canberra, Australia) we've just passed summer solstice, and the weather's warming. Temperatures are sitting in the mid 20s (Celcius), occasionally touching 30. We've also had loads of rain. As a result, snail populations are booming.
Coincident to that, letters in my mailbox started to appear eaten, with up to about 15% of each envelope, and occasionally a bit of the enclosed letters gone. With about 5 letters arriving a day, that's quite an appetite.
Investigation turned up a colony of snails - about 10 in the letter box, and another dozen or so clustered around the base of the post on which the box stands. The snails seemed healthy, and the chickens enjoyed eating them, but I can't see how a snail could live on such un-nutritious food as bills and bank statements. Is there really enough in paper (predominately blue and white paper) to support a snail family? Or were they simply snacking on the paper while making a meal out of the nearby plants? Note that the letter box stands on a post a little less than a metre tall and is about half a metre from any greenery.
The snails I'm familiar with seem to live on a cellulosic diet, so I'd imagine that the cellulose in paper isn't all too far off of the cellulose they'd normally consume from living plant matter. In the long run, they might lack some essential nutrients, but in the short run, there goes your mail. Maybe you can train them to just eat the bills and adverts?
You seem to have been running a popular little snail snack bar. What you need to do now is recycle the envelopes and junk mail to grow more snails to feed your chickens. Richard Avery (talk) 14:11, 28 December 2007 (UTC)[reply]
Can't speak to specifics in your case, but you should be aware of our article on Drying oils. A large number of oils will turn solid after exposure to air, due to oxidation. This is the basis of oil painting - the paint goes on "wet" and then "dries" solid. -- 128.104.112.236 (talk) 20:59, 28 December 2007 (UTC)[reply]
Paper tearing question
At work I've been tearing up old bills that are approximately 8.5x5.5 (half the size of a normal piece of paper) into 4ths. So I tear them half down the length then tear each resulting portion into half. I've found that it's much easier to tear the paper on the sides that were factory cut rather than the side that resulted from my previous tearing. Why is this? I have some suspicions but I don't see why any one of them would necessarily be the case.--droptone (talk) 17:28, 28 December 2007 (UTC)[reply]
I suspected this sort of answer. But I wondered about why this would be different than the changes in the grain of the paper after it is cut to the various sizes (A4, etc, etc). Would it be because the device that cuts the paper into those sizes would have a much smaller distribution of energy than the imprecise motion of my hands?--droptone (talk) 19:37, 28 December 2007 (UTC)[reply]
Let's be clear. Are you saying:
it's harder to tear the paper in the side-to-side direction than in the up-and-down direction?
it's harder to tear the paper (in any direction) when starting at a freshly-torn edge, than when starting from a factory-cut edge?
If #1, it's definitely the grain. If #2, I'm quite surprised. There are some materials (notably plastic films and plasticized paper) that are very difficult to start tearing from a clean edge, but are quite easy to tear once they've begun tearing. Often, to tear these at all requires starting a cut with a knife or scissors. But since a torn edge contains all sorts of jaggies and other irregularities, I'd expect tearing from a torn edge to be easier, not harder. —Steve Summit (talk) 22:22, 28 December 2007 (UTC)[reply]
2 is what I was trying to describe. I don't think it matters that these papers have residue from a type of carbon paper but it is worth mentioning.--droptone (talk) 22:56, 28 December 2007 (UTC)[reply]
animals living on humans
I was talking with my 5yo the other day about how there are lots of bacteria on and in our bodies which are either helpful or at least not harmful (generally). Someone else said that there were also animals, and mentioned dust mites as one example. I see from dust mite that sunlight kills them, so it seems that dust mites don't live on people for very long, just on our stuff. Are there other animals that live on or in us, but are not parasites? That is, I know we can have various kinds of worms, lice, fleas, etc., and I'm wondering about microscopic or symbiotic situations. Let me know if I'm not making sense, and I'll try to elaborate. Ingrid (talk) 18:45, 28 December 2007 (UTC)[reply]
Your gut flora (mostly but not entirely bacteria) provide an invaluable job in digestion - that's surely the strongest symbiotic relationship we have with any (modern) organism. But if you're looking for something really cool, consider the endosymbiotic theory, which hypothesises that mitochondria (vital structures present in almost all cells) were once independent creatures that have becoming inextricably symbiotically linked to us. -- Finlay McWalter | Talk18:56, 28 December 2007 (UTC)[reply]
Not to stray off topic but rather to reveal a better understanding of the development of such relationships consider what individual humans are to larger "organisms" such as corporations. Multimillionaire (talk) 20:47, 28 December 2007 (UTC)[reply]
As sulfuric acid has two titratable protons per mole, the (effective) concentration of hydroxide ion in 0.5 M NaOH is the same as the (effective) concentration of hydrogen/hydronium in 0.25 M H2SO4. Equal volumes of the two will thus neutralize each other, resulting in no net gain or loss of hydrogen ions (and thus no shift in pH). You should be aware, however, that there is a difference between molarity and normality - Normality takes into account the difference in titratable hydrogen numbers. One volume of 1 N base will neutralize one volume of 1 N acid. So if the sulfuric acid is 0.25 normal versus 0.25 molar, you would need two volumes of 0.25 N H2SO4 to neutralize one volume of 0.5 N NaOH. - But that doesn't explain the 70 mL answer, either. -- 128.104.112.236 (talk) 20:50, 28 December 2007 (UTC)[reply]
Psychological basis for racial prejudice
Apart from the difficulty of others being able to visually detect dark soil on dark skin, can one basis for racial prejudice be traced and attributed to negative outcome or consequence for the offspring or descendants of racial mix, such as the inheritance of Crohn's and other genetic anomalies or defects? Multimillionaire (talk) 19:57, 28 December 2007 (UTC)[reply]
Sure. Why not? Humans are great at rationalizing. As a reference desk, you need to specify if you are looking for studies on this topic or just references in journals and books. This is not a soapbox or discussion forum for tossing around opinions. -- kainaw™20:19, 28 December 2007 (UTC)[reply]
There is differences in opinion about the genetic basis of race see What We Know and What We Don’t Know: Human Genetic Variation and the Social Construction of Race by Joseph L. Graves and other excellent essays for an overview. However, any systematic negative outcome observed from inter-racial breeding these daysis almost certainly a social consequence and not a genetic one. If you believe race is a good correlate for genetic differences then one would generally expect the opposite, due to heterosis, though of course there will always be examples of outbreeding depression also (and obvious example, to use genetic parlance, would be how lighter skin from a black/white cross could be disadvantageous in Equatorial Africa, compared to a black/black cross). If you don't buy a strong race/genetics association, then using race as a basis for anything biological is a rather artificial construct. Rockpocket20:54, 28 December 2007 (UTC)[reply]
I've noticed that on all articles I can find on toe-walking, it says it should be treated. If it's not related to any other conditions and is most comfortable for the person, why should it be treated? SprayTape (talk) 20:41, 28 December 2007 (UTC)[reply]
Electronic Circuit for Generating a Gaussian Signal
Is there a basic circuit that will create a Gaussian (e^-x^2) signal? I would like to send a constant voltage for a fixed amount of time through the circuit, and receive (as closely as possible) a Gaussian as output (either voltage or current).
Thanks! 99.135.13.90 (talk) 22:42, 28 December 2007 (UTC) -Craig Calcaterra[reply]
Per a document that Tektronix wrote ages ago, a large number of cascaded RC circuits will approximate a Gaussian response. I don't remember whether or not the RCs needed to be isolated by amplifiers. They designed their oscilloscope vertical amplifiers to display this characteristic.
I'm running a role-playing game that I'm trying to keep as "hard science fiction" as possible, despite my ridiculous concepts. A certain element of the back story involves a large asteroid being stopped by a force field via friction - which sets the atmosphere on fire, and I have the following
questions about such an activity:
1. Is it even possible to set the atmosphere on fire?
2. If it is possible, can friction provide enough heat for ignition?
3. What would happen after such an ignition? Would the surface of the Earth be affected much? (i.e. Would the crust melt slightly or anything?)
4. Is it possible for the planet to somehow regain its atmosphere over time (and how long would it take), or would it take an outside source (e.g. technological terraforming)?
Before the Trinity nuclear test, it was debated whether the atomic blast would be sufficient to ignite the atmosphere (burning the nitrogen and oxygen into various nitrogen oxides). This might be an interesting starting point for your reseach.
I was wondering: are áll my cells replaced by new ones after a period of time? If so, are these new ones produced with completely new molecules or with waste of the old ones? Thanks 217.136.141.199 (talk) 23:42, 28 December 2007 (UTC)[reply]
Operating Department Practitioners
Hi there, I am considering taking a DipHE course at university in ODP but can't seem to find a lot of information on the job. I know that there are 3 areas, but I mean, are ODPs allowed to administer oral and IV drugs etc, can I do other jobs like.. that aren't regular ODP jobs such as working in A+E Departments, and I read something about working in helicopter emergencies etc. What would that entail? Finally, would I use a stethoscope and are there any courses in scotland that allow me to then study to become a nurse in an accelerated programme?
Any help would be greatly appreciated!
Christopher
[[File:--223.186.79.214 (talk) 18:07, 16 September 2011 (UTC)Example.jpg
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