Settle a bet. Is there anyone, somewhere in the world, who harvests and distributes cat milk? (For any purpose whatsoever, including but not limited to human consumption, infant feline consumption, or the hell of it.) Or, if you don't know, do you know where I might find out? Black Carrot00:18, 24 June 2007 (UTC)[reply]
That page reads almost like satire to me, I have no idea if it is real or not. For feeding kittens, cat milk formula is widely used [1], though I know of some scientific studies that have used feline milk, the scientists collected it themselves rather than buy it. Rockpocket02:37, 24 June 2007 (UTC)[reply]
I'm pretty sure that the cat milk website is a joke - "In the dairy industry it has long been observed that cats have double the teats of cows, hence twice the source of pure cat milk." And Pussy Whip? Come on. For feeding kittens, it's usually kitten milk replacer that is used, which has cow milk as its source. I've never heard of any products actually containing cat milk. But as Rockpocket said above, you can find articles on nutritional and disease studies involving cat milk, for instance PMID17307374. --Joelmills03:00, 24 June 2007 (UTC)[reply]
Just to be sure, I gathered some reference material (a cat whose belly was recently shaved, and whose teats are therefore prominent), and can tell you with some confidence that your standard-issue housecat has 4, same as a cow. —Tamfang05:35, 24 June 2007 (UTC)[reply]
Yeah, that first site is really obviously a joke. That aside, so far it sounds like my worthy opponent is in the lead. Her stance was that anyone who wanted to feed their kitten kitty-breastmilk would use a synthetic, and your info seems to be bearing that out. I figured that would be the case, it seems the most practical course. I'm more expecting to find it in exotic food, some kind of weird religious tradition, or maybe just an internet niche market of some kind to people who want it for unspecified purposes. Black Carrot07:08, 24 June 2007 (UTC)[reply]
There are reliable sources for lab cats getting milked [2]. In that study it was simply done by hand. Many years ago I read about researchers who had built a mouse milking machine for some study of nutrition or whatever.It is done sometimes with a syringe [3] [[4]]. Rats also get milked [5]. I am a bit surprised there is not the availability of milk of various mammals, like the meat of exotic and game animals and the eggs of various unlikely species are sold. Some people drink goats' milk, which tastes nothing like cows milk. Beef cattle farmers have told me that beef cows produce milk, but in lower quantities than dairy cattle. On the Wagon Train tv series, one week they tried to milk a buffalo to feed a starving infant, with rather violent results. Then there is the old joke from the Bible wherein it is claimed per (American Standard Version) Genesis 22:23 that it takes 8 men to milk a bear ("These eight did Milcah bear.." Edison16:04, 25 June 2007 (UTC)[reply]
The "cross-hair-like thingie" is due to diffraction by the struts that hold the telescope's secondary mirror. See the diagram at Newtonian telescope. The telescope used for your image used four struts to hold its secondary mirror, hence the four-fold symmetry of the diffraction effects. --mglg(talk)04:34, 24 June 2007 (UTC)[reply]
Sometimes the effect is even added to astronomical images in post-production to add aesthetic appeal. I am sort of disappointed by the artistic liberties that have become commonplace in astronomical photography; it is one thing to make a pretty picture, but it is another to pass it off as a scientific image. Nimur07:37, 24 June 2007 (UTC)[reply]
Please, provide sources to your claims. It seems highly unlikely that artifacts would be added to pictures just to make them pretty. Oh, and please, don't confuse channel mixing with photo manipulation. — Kieff | Talk09:11, 24 June 2007 (UTC)[reply]
Here's the first that comes to mind... this goes well beyond false color - [6], all created from this source image from Cassini.
No - that example isn't one of exaggeration for aesthetic reasons - read the article that goes along with the photos! It quite clearly says that by exaggerating the contrast they could find details in the data that were not obvious in the unenhanced image: "In such views, imaging scientists have noticed color variations across the diffuse rings that imply active processes sort the particles in the ring according to their sizes.". Image processing is absolutely necessary - and a quite valid scientific approach to finding more information from the available data. It may be that this is sometimes done for aesthetic reasons (after all, don't astronomers have the right to make pretty posters to hang on their walls too?) - but this is categorically not an example of that. SteveBaker13:22, 24 June 2007 (UTC)[reply]
Perhaps this example was less than stellar. I'm not opposed to image processing, but I think there is a threshold that can be crossed, when more information is due to the post-processing than due to the source measurement. But this is a complaint which can be levied across the board against all of experimental science - "massaging the data" until it looks the way it "should." I'm probably making gross generalizations; most scientists use good technique and have integrity with respect to their data. So, I'll rescind my previous comments. Nimur02:04, 25 June 2007 (UTC)[reply]
Calling the jpeg the source isn't altogether accurate of course... the source image would look similar to it by our eyesight and as far as the monitor could render the colours. I know nothing about digital photography, but isn't it possible that there was hidden data in the form of infrared and ultraviolet that had to be compressed into the visible spectrum? The labelled colours are, afterall simply blue and red with nought in between. Bendž|Ť21:20, 24 June 2007 (UTC)[reply]
I strongly object to User:Nimur's characterisation of how science processes images. Certainly in astronomy - and in many other sciences too - there is no such thing as the "real" image that you can see with your eyes. All we really have is a series of spatially separated numbers representing the count of the numbers of photons hitting the detector within some waveband. Turning those into a picture for human eyes to view is for the most part an entirely arbitary process. To accuse the scientist of "massaging" the data is ridiculous. You can't see in the infrared (or whatever waveband it was) - you can't see things that faint (and certainly not in full colour). Unless you want a completely black picture, you'll never see what your eyes might have 'really' seen. You have to accept a heavy amount of numerical work on the data. Firstly we have to map the photon counts in the detectors into a range of brightnesses that you can see - then we have to shift the frequencies we measured into human frequency ranges. Worse than that - our eyes can only see about three or so orders of magnitude of brightness - and computer monitors and printers can only display a couple of orders of magnitude. If the sensors are detecting five orders of magnitude - then if you do a simple 1:1 mapping then you'll miss much of the subtlety in the data. It's all entirely arbitary - all of it. You are in no position to say what is a 'legitimate' image enhancement and what is 'over manipulation' - there never was a 'true' or 'real' image in the first place. It's purely a matter of the math of how you get this range of brightnesses and frequencies into the human range of perception. SteveBaker02:55, 25 June 2007 (UTC)[reply]
SteveBaker, that is the difference between an "photograph" and all of the other things we call plots, charts, contour maps, data visualizations, etc. But I have already rescinded my comments as overgeneralizations. I understand your point about "arbitrary" visualization. More effort should be made to convince the general public that "this isn't what it would look like if you were looking at this object with your eyes." Nimur06:07, 25 June 2007 (UTC)[reply]
Alright, so it was just a benign generalisation. I'd like to know of a single case where a scientist has used "more information due to the post-processing than due to the source measurement" without being defrocked of his labcoat. This instance is from an academic paper where a "planets may look smaller/darker/duller/less-inspiring-to-E.T.-ologists than they appear" disclaimer would be insulting. If it's in an elementary science textbook, they do just that. Bendž|Ť13:29, 25 June 2007 (UTC)[reply]
This is an interesting discussion. I really think astronomical visualisation techniques and principles deserve an article! JH-man08:39, 27 June 2007 (UTC)[reply]
It's not just astronomy though - all sorts of scientific visualisations require enhancement technologies...and are potentially the subject of abuse if not treated correctly. Think about a "photograph" taken with an electron microscope for example - there is no light coming from the object being photographed - and the machine has to convert the image formed by the electrons into an image we can see and understand - and the processes involved can be identical to the kinds of things we do to data captured with a telescope. In that case, it's pretty obvious how to display the data - so any 'manipulation' of it might come in for these kinds of criticism (unnecessarily so IMHO). But imagine taking the raw data from an X-ray diffraction machine and visualising the crystal structure from the raw data! In that case, the 'enhancement' isn't just shifting colours and brightness ranges around - it's a full-scale reconstruction. So I don't think we need an astronomy-specific article - we need something about scientific data visualisation in general...and we have that in Scientific visualization, Visualization (graphic) and Knowledge visualization. SteveBaker15:27, 27 June 2007 (UTC)[reply]
Several mammals, such as Grizzly bears, prey on fish. Could this evolutionary pressure push certain bony fish towards having more bones, or sharper, peskier bones? Which earlier studies have looked into this speculation? Best, Lior05:53, 24 June 2007 (UTC)[reply]
It's possible that fish might evolve that way. The question would be whether the losses due to bear predation were more damaging to the fish than the wasted energy or other disadvantages of having more annoying bones. If so, then it's possible that they could evolve that way (and in fact, the present shape of their bones is very likely to reflect the best balance between annoying the bears and getting on with life). SteveBaker13:14, 24 June 2007 (UTC)[reply]
Note that the bear must have a way of guessing the shape of the bones without killing the fish, or else this evolutionary development could only occur as group selection which is generally less effective than selection on smaller units like individuals or genes. Icek14:27, 24 June 2007 (UTC)[reply]
Yeah, along the lines of Icek, there really is no mechanism that would allow such an evolutionary event to occur. A bear would only know what kind of bones exist in the fish after/while eating it. At which point, it has already been selected against, regardless of its bone structure. And also, group selection doesn't happen, and is no longer viewed as a possible mode of evolution. --Cody.Pope15:16, 24 June 2007 (UTC)[reply]
Thank you for your fascinating answers. According to your explanation, I fail to grasp how Hebeloma crustuliniforme could have developed its nauseating properties. This mushroom has to be consumed, at least partially, for its naive consumer to feel sick. So how could it be selected for without group selection coming into play? Once I grasp that, the speculative bear hypothesis will be easier to rule out. I guess bears alone do not lay enough pressure over them fish, but let bears represent the total mammalian (or soft-palated) pressure for this matter. By the way, perhaps group selection should be adapted to conform with Cody's last remark. Lior16:28, 24 June 2007 (UTC)[reply]
Erg, learning is what allows for Hebeloma crustuliniforme-like systems to exist. But a bear grabbing fish in a river is a rather hap-hazard endeavor. I was more or less assuming that the act of catching killed the fish and also that the act was random, so that learning couldn't play a huge role. Especially with poisonous animals/plants/fungi, learning plays a big role in avoidance. Also, I haven't looked at group selection, but will when I have the energy. --Cody.Pope17:05, 24 June 2007 (UTC)[reply]
Erg and also, I've looked at the group selection article, it's more or less fine. The thing is is that the cited Wilson paper discusses some extreme social systems, whose evolutionary histories aren't super well understood. When group selection is viewed in systems of high relatedness (like ants or the mole rat), then individual selection can appear to be group selection, when it really isn't (but that's a point of contention). I guess I should amend my comment about group selection to say that the mode is a highly contentious, which is what the article says. --Cody.Pope17:14, 24 June 2007 (UTC)[reply]
As far as I could tell from watching Grizzly Man, Grizzly bears seem to be rather selective fish catchers. Then again, watching the film to this point requires a considerable degree of mental fatigue that precludes fair judgement. I take your answers to imply that fish might only become peskier if their dominant predators can learn that, and that studies on this matter are not widely known. Cheers, Lior19:03, 24 June 2007 (UTC)[reply]
Group selection is just a way of looking at natural selection, but of course, fundamentally, the gene is what is selected for or against. Most damage-inducing predation deterrents work with a warning signal, as there's no use making your grizzley die from tetanus resulting from mouth wounds caused by your pesky rib cage if the rest of you is sitting in its gut. Armour or spikes are more probable solutions as they can be seen and will save your hide. Batesian mimicry is worth a shot if you share your habitat with similar species to you that are poisonous with cautionary bright colours, but don't want to expend resources synthesising poisons yourself. Bendž|Ť21:46, 24 June 2007 (UTC)[reply]
Electroblotting
Why is the reason for the need to pre-soak the PVDF membrane in methanol before transfer? Is it because methanol aids in the binding of proteins to membrane? If so, how does methanol aid in the binding of proteins to membrane? Or, if not, could you please tell me why?
Reading from here: "it is there to stop the gel swelling due to heating, and to keep proteins denatured for attachment to the membrane." Someguy122120:02, 24 June 2007 (UTC)[reply]
Which city in the U.K are you most likely to find Rats?
There are undoubtedly significant rat populations in every city in the UK - quite possibly in every city in the world. So I guess the question is either: Which cities are most likely to bring you into contact with the rats? Or: Which city has the most rats? Or: Which city has the largest ratio of rats to humans? The second question is probably the same as asking "Which is the largest city in the UK?" - which would be London. For the other two - I have no idea. SteveBaker13:06, 24 June 2007 (UTC)[reply]
Einsteins General theory states that things cant travel faster than the speed of light. And if they did, "anything" travelling faster than the speed of light will become more massive. Is ths how the first matter was created? And if this is so, when the universe began what was the "anything" it stated with? WAs it light? DId light travelling faster than light become massive enough to be matter? Was it dust? and if so presumable there was no dust at the beginnig of the universe. And if the universe was created in the process of the big bang can we assume that the big bang acelerated faster than the speed of light, and it was that which created the "first" matter?
Would like an answer to this question that doesnt include "dark matter" please. Dark matter seems to be some recently invented nonsense that seems nothing more than a desperate attempt to force the universe to fit into our common sense notion that there must be stuff out there. Im sure there was an established theory of my question before "dark matter" and I'd liek to be reminded of what what was.
Also note that while dark matter may in fact be nonsense, it enjoys significant support by astronomers because every other theory explaining the available observations is worse. --TotoBaggins15:16, 24 June 2007 (UTC)[reply]
One clarification: Our questioner said: "anything" travelling faster than the speed of light will become more massive" - that's not what Einstein said. He said that it's not possible to travel faster than light at all. Things get more massive as they get closer to the speed of light. I think it's dangerous for someone outside of the field of cosmology/astronomy (especially someone who appears to be clueless about relativity) to declare dark matter to be nonsense. Whilst it's not an entirely proven theory, it fits the facts perfectly and there is no evidence to disprove it. The only really viable theories that don't include dark matter require new forces that we have not observed or modifications of the laws of gravity that we don't see in reality. All of the theories are 'out there' - and dark matter is probably the least unbelievable. Let's leave the experts to figure out whether it's true or not. At any rate - I recommend that our questioner read Big bang. SteveBaker17:15, 24 June 2007 (UTC)[reply]
As far as I know it doesn't follow from Einsteins theory that it wouldn't be possible for anything to travel faster than light. Only thing is that anything traveling slower than light cannot be accelerated to or above the speed of light. 84.160.217.15421:17, 25 June 2007 (UTC)[reply]
Oh...groan...the whole tachyon thing. I think that's been pretty carefully busted as a thoery (as our article explains). There are other theories out there that permit them - but we're not talking about them - we're talking about Einstein. According to him, tachyons would experience time and space distortions that follow the Lorentz factor: - go ahead - plug in any value for v that's greater than c and you'll discover that you're taking the square root of a negative number...the mass, time contraction, distance measures - all become imaginary numbers! You can't have imaginary numbers popping up in the real world - so no going faster than c according to Einstein. SteveBaker02:16, 26 June 2007 (UTC)[reply]
OMG! That's utter nonsense!! Jeez! If you're going to answer questions on the science desk, you should probably learn a little high school math! What you can prove with the equation for the surface of a sphere is that no point on the surface of a sphere of radius 1 (which is what that equation describes) can have a coordinate such that (x2+y2)> 1 because that would result in an imaginary z coordinate. But since no point on the surface of an idealised spherical earth violates that constraint, there is no problem. Australia's negative Z coordinate (in the southern hemisphere) is perfectly fine because the square root of a positive number can be either positive or negative - so there is no difficulty whatever. The problem with v>c in the example above is that (1-v2/c2) is NEGATIVE - and you can't take the square root of a negative number without getting an imaginary result - that's totally different from the situation with the equation of a sphere and Australia! Please learn the following facts about square roots: The square root of a positive number can be either positive or negative - but the square root of a negative number is imaginary. Imaginary distances, times and masses are not allowed - so NO!!!! per Einstein, you are not allowed to travel faster than 'c'. Sorry. SteveBaker15:14, 26 June 2007 (UTC)[reply]
Well, maybe that second link isn't the best. There are several related links about protoplanetary this and that and I'm not sure what's best. But anyway, I think the answer is that a sphere is the shape that any blob of fluid tends to take when the forces of its own gravity dominate other forces. --Allen16:18, 24 June 2007 (UTC)[reply]
Right - and the deviation from an idealised sphere comes about because the earth is spinning - so ceentrifugal force makes it bulge a bit at the equator and is squashed/flattened a little at the poles. SteveBaker17:02, 24 June 2007 (UTC)[reply]
And then, tectonics gives a very minute variation (mountains, valleys, and oceans) on top of the geoid. Cumulatively, these are very small variations of a few kilometers; comparatively, earth radius is roughly 6350 km. Nimur02:11, 25 June 2007 (UTC)[reply]
Yes, these things seems like they're big to us, but on the scale of the Earth they are very small. A nice analogy I've heard is that if put on the same scale, the surface of the Earth would be smoother than a billiard ball. --jjron05:06, 25 June 2007 (UTC)[reply]
I've read that too but I've never quite believed it. Even on such a minute scale, the Himalayas would hardly be that indistinguishable from coastal areas - would they? Maybe indistinguishable by sight, but I doubt by touch. -- JackofOz12:32, 25 June 2007 (UTC)[reply]
Five micrometers? That's right on the edge of what you can distinguish by touch. The Himalayas will show up as a rough patch on your billiard-ball Earth. --Carnildo22:48, 26 June 2007 (UTC)[reply]
I've never quite believed it, either, but according to our Earth article, it's true. Though the rough patch may be detectable, it won't disqualify the billiard ball from being officially acceptably smooth. —Steve Summit (talk) 12:17, 15 July 2007 (UTC)[reply]
In short, gravity. Even rock has a point at which it won't hold more weight above it. For instance, note that Mars, being smaller then the Earth, has bigger mountains before gravity makes them fall down. And that asteriods, or Phobos and Deimos, are small eough to be randomly shaped. Gzuckier14:47, 25 June 2007 (UTC)[reply]
Sure gravity is very important and essentially sets an upper limit, but erosion by wind, water, etc also plays a significant role in this as well. Obviously more significant on Earth than these other places. --jjron23:40, 25 June 2007 (UTC)[reply]
Gravity is the main answer to the question, though. It acts globally to make the planet more or less spherical. Erosion just smooths out some of the bumps and hollows. --Anonymous, June 26, 2007, 21:30 (UTC).
I don't understand the debate between gravity and erosion here. If we're talking about relatively small-scale things like mountains (as opposed to the flattening of the poles and the bulging of the equator), you can't say which effect is in charge. Think about it for a moment: Without bits being knocked off the rocks due to erosion, gravity would have no part to play because the rocks would just sit there in whatever odd shape they were at to start with. Without gravity, erosion could knock bits off the rocks - but they wouldn't settle into hollows to make a more spherical planet, they'd just float off into space somewhere. It's only the two effects taken together that explains the tendency towards a more accurate approximation to a sphere.
But on the other hand: Gravity can cause lighter materials to be pushed upwards to make room for heavier ones beneath - so gravity can cause surface irregularities to appear in a previously smooth surface (think about volcanic islands appearing in the middle of the ocean for example)...and erosion doesn't always make things more smooth and spherical either - look at the deep valleys cut by rivers and glaciers in otherwise flat plains. (The Grand Canyon in the USA for example). So there isn't an 'either/or' debate here. You need both of them to attain smoothness - yet both of them are also causing irregularities. SteveBaker15:15, 27 June 2007 (UTC)[reply]
The question was only one sentence, so we sort of have to guess what the original poster had in mind, and I guess the "debate" is really about that. When I saw "irregular shape" mentioned in this context, it made me think of bodies like the smaller asteroids and moons that are not even close to spherical... and this is possible because they don't have much gravity. However, the question also used the word "exact", which does bring to mind the fine-tuning of the shape due to erosion. --Anonymous, June 27, 22:56 (UTC).
The early responses seemed to form a "hierarchy" or spectrum of (roughly) coarse to fine adjustments to the earth's shape; planetary formation and gravity shape the mass into a sphere; rotational motion squishes it into an oblate spheroid; tectonics and geology encourage mountain ranges and plateaus; and small-scale erosion creates river valleys, glacial canyons, etc. On the most microscopic scale, tiny irregularities can be caused by animal, plant, and human activity. Nimur00:57, 28 June 2007 (UTC)[reply]
Polyester
How to check carbon content in polyester black fibre by an instrument
We have chemical method which takes too much time
—Preceding unsigned comment added by 59.95.205.125 (talk • contribs) 17:28, 24 June 2007
For school I and several other students had to analyse the results for a FACS and figure out what the patient was suffering from. Now you could basically make up anything you'd want. So we setteled on immunosupressed and we know the teacher will be happy with it. Something really stumped me though. If my calculations are correct our patient has a very low T cell count (9%) and an even lower Tcyt count (0.8%) (thus the idea that the patient is immunosupressed). But the patiënt has many cells that express CD8 but not CD3. Aren't cytotoxic T-cells supposed to express CD3 and CD8 at the same time?
So my question is: Are there cells that only express CD8? And if not, how can I (for my own sanity) explain the apperantly rather large amount of cells solely expressing CD8 and not CD3?PvT18:24, 24 June 2007 (UTC)[reply]
No need to go off the deep end :)... there are a number of possible explanations. The cumulative effect of loosing CD3 expression would indeed be immunosupression. And, yes, normal CTLs express CD3 and CD8, but in tumor infiltrating T cells, abundant evidence has shown that a down-modulation of TCR-CD3 (specifically the ζ (zeta) chain) occurs, and possibly contributes to suppression antigen-specific T-cell responses against the tumor.[8] Loss of CD3 expression has also been observed during viral infection (like HIV) and in several autoimmune diseases. In all three situations the loss of CD3 expression is not (usually) accompanied by a loss of CD8 expression[9][10] and could explain the large population of CD3-/CD8+ cells you are seeing. It is worth mentioning that, in a normal immune reaction, CD3 is transiently down-regulated during T-cell stimulation, but this wouldn't usually result in a profound loss. --DO11.1007:05, 30 June 2007 (UTC)[reply]
Circular orbits -- Saturn's rings?
I'm writing a blurb on conic sections for a science museum (in Guatemala City). I want to use orbits as one example. It's easy to find examples of elliptical and hyperbolic orbits, but what about circular ones? I thought maybe I could use Saturn's rings. It seems obvious just from looking at some of the better pictures that some (frictional?) process has all but eliminated any eccentricity from the rings - I'd wager that in general they're as perfectly circular as just about any precision-machined doodad, and that any deviations are more like ripples from the moons than like elliptical eccentricity. Can anyone back me up (or shoot me down) on this? --Homunq21:38, 24 June 2007 (UTC)[reply]
It seems from a bit of Googling that the rings are mostly circular, although the individual particles have elliptical orbits ([11]). Apparently the F Ring and the Titan Ringlet are elliptical exceptions. --Allen22:37, 24 June 2007 (UTC)[reply]
Are leg cramps statistically related to heart attacks in some way and if so are they related to any imbalance, excess or lack of minerals or other constituents of the blood? 71.100.3.13203:08, 25 June 2007 (UTC)[reply]
Have you read the article on cramp, in particular the section on causes and treatment? It covers most of this pretty well. It doesn't really say anything about the heart attacks, and I don't know about that, perhaps someone else has information on that aspect. --jjron05:29, 25 June 2007 (UTC)[reply]
By the way, my English was really bad at the time of that thread, and I hadn't learnt how to properly use prepositions. A.Z.04:59, 25 June 2007 (UTC)[reply]
I can think of several ways they can be harmful:
1) Some produce an unpleasant bluish-white light, which is unnatural and annoying, possibly having a negative psychological effect on people. A side effect is that they make people look "ugly", making varicose veins and acne more visible, for example. Newer models provide more natural light.
Note that colour temperature preference various between countries. In I believe most of the Western world, 'hot' yellowish/red light is generally preferred while in East Asian preference (& perhaps SEA) preference are more variable and whiter or bluer light is sometimes preferred. Note also that the Western colour temperature preference is 'hotter' (i.e. a lower temperature) then daylight (although closer to traditional artificial sources like incandescent light bulbs and fire) so I would question whether either colour preferences could emperically be called 'natural' Nil Einne11:53, 26 June 2007 (UTC)[reply]
Quick follow up, our colour temperature article doesn't explain how the colour temperatures corelate to natural light very well but I found this [12]. Note the D65 article also supports the idea that 6500 K is close to a bright temperate western hemisphere summer day. I think some confusion may arise because of the difference between 'Average Summer Sunlight (plus blue skylight) at 6500 K' and 'Average Summer Sunlight at Noon (Washington DC) at 5400 K'. From what I can tell from my searches, the latter is simply taking into account the colour temperature of the light from the sun, e.g. if you have a ray shining into your room. Whereas the former is the actual colour temperature you will experience out in the open on a cloudless blue day. It is bluer due to the effect of the blueish light from the sky. To me 6500 K is the more 'natural' colour (as it's what you experience out in the open) but AFAIK the preferred temperature in the western hemisphere is lower, around 5000 K or less (which is below the pure 5400 K of simple sunlight). Of course, as you can tell a very wide range can be called natural since it will be experienced in certain conditions of daylight. It's perhaps better to just say people have different colour temperature preferences rather then argue one is more 'natural' then the other Nil Einne12:13, 26 June 2007 (UTC)[reply]
2) When some start to go bad they flicker (at first, imperceptibly) in a way that can cause headaches or possibly trigger seizures in epileptics.
3) Since fluorescent lighting is cheap, businesses tend to overlight some areas, making computer screens difficult to read, causing eye strain and headaches. People may compensate by turning up the brightness on the monitor and sitting closer, both of which increase their radiation exposure (at least for CRT monitors).
4) In cases where incandescent lighting was replaced with fluorescent, the HVAC system may have been designed for the thermal load of the incandescents, and may need to be retuned for the cooler fluorescents. Failure to do so could result in some rooms, with lots of new flourescents, being cold, and others, with few new flourescents, being hot.
Note that all of these issues can be addressed, and the lower power usage of fluorescent lights means less fossil fuel is burnt, resulting in less global warming, less air pollution, etc. So, my conclusion is that fluorescent lights should be used properly, not abandoned. StuRat17:04, 25 June 2007 (UTC)[reply]
Can we note that A.Z. asked for scientific evidence. As best I can tell everything mentioned above is anecdotal evidence. Please read the talk page that he originally directed us to for the reason behind this...
Re this topic, the Australian government has recently announced (see here for example) that it is banning incandescent light bulbs within three years. Presumably other countries may follow suit if this does go ahead. --jjron23:52, 25 June 2007 (UTC)[reply]
I read about this and thankfully the incandescent light bulb article already covers it resonably. Preceeding the Australian move, the European Union had already been considering banning the incandescent light bulbs. Following the Australian annoucement, some European countries, New Zealand and some Canadian provinincial governments annouced that they are also considering or planning such moves. Several proposals have also been made in some US states. It seems likely that most developed countries will have limitation of these sort within 10 years so I expect A.Z. will have to limit him/herself the parts of the US and the developing countries without such limitations (some of which will probably have such limitations) Nil Einne11:53, 26 June 2007 (UTC)[reply]
Politicians shouldn't be allowed to decide about such important matters. I hope a scientist tests human beings and other animals under the influence of fluorescent lighting. Unfortunately, it seems that this has never been done before. A.Z.22:37, 26 June 2007 (UTC)[reply]
I must admit this move has torn me apart - a part of me agrees with any reasonable action to reduce greenhouse emissions, but a part of me simply cannot abide fluorescent lighting in homes, particularly in kitchens. I'll just have to stop eating, I guess. For the record, Australia is not banning incandescent lights per se - it's not as if their use will become illegal - but the ultimate effect of the move will be to severely reduce their availability through the usual outlets. But there's always eBay. And there's always people power; if the demand for incandescent globes does not lessen, the supply will surely be maintained. -- JackofOz00:50, 27 June 2007 (UTC)[reply]
That's really good to know! I could already picture Australia turning into a big drug store (or a hospital, or a mall, or a prison). Restaurants, hotels, people's houses, all of them would become a sickening place because the government told so. There are truly reasonable actions to reduce greenhouse emissions. Using fluorescent lighting is not one of them: I feel that it's not only unpleasant, but can be truly harmful to your health. Any more information is still welcome. A.Z.03:40, 27 June 2007 (UTC)[reply]
Not much more I can tell you, A.Z. But surely there are options other than fluorescent if incandescent is unavailable. -- JackofOz03:57, 27 June 2007 (UTC)[reply]
Whenever I travel by flight, I get a feeling that the body of the plane is not parallel to the ground (Even at the cruising altitude, I feel that the nose of the plane is pointing up, as in climbing). Is it just my feeling or it it an illusion or is it really the case ? -- WikiCheng | Talk04:59, 25 June 2007 (UTC)[reply]
I don't have an answer, but that's interesting, I get the same sensation. I've actually assumed it was for real, and had rationalised it as the plane overcoming it's tendency to be pulled down by gravity (in very simple terms), so still having to point up, even when flying at a fixed altitude (sort of like how you have to keep the engines going to maintain a fixed a speed). I'd be interested if someone knows more about this. --jjron05:47, 25 June 2007 (UTC)[reply]
How would pointing the nose of the plane up help you overcome the tendency to be pulled down by gravity? A.Z.05:49, 25 June 2007 (UTC)[reply]
It might just be that you feel like this because this is often the case in short flights- you spend a lot of the time climbing, then the plane points up when it lands as well. It could also be the air pressures on the plane- keep in mind a lot of the sensation of "which way is up" that we have is from our ears (at least, last I checked), so the cabin's air pressure could very well mess that up. It could also be caused by the way cargo is loaded, although I imagine any amount of luggage holding the plane down like that would make it extremely difficult and dangerous to fly. -- Phoeba WrightOBJECTION!05:59, 25 June 2007 (UTC)[reply]
The angle of attack of a plane is not always horizontal. It depends on many factors, including prevailing weather, aircraft design, speed, and atitude. You can check the attitude by suspending a pendulum (a piece of string with a weight); provided the aircraft is not accelerating, the string will point towards "down," and you can compare it to the normal vector of the floorboards. Nimur06:10, 25 June 2007 (UTC)[reply]
Just a little tip, a tennis shoe makes a good pendulum for things such as this. take one off, and dangle it by one of the strings. You can also use it to get a basic idea of how much gforce there is in one turn compared to other turns in a car trip if you're bored -- Phoeba WrightOBJECTION!06:17, 25 June 2007 (UTC)[reply]
Good idea, but you won't detect any downward pointing force and when turning, I think they try to position the airplane so that the resulting force (from gravity and turn) will point downward. If not for other reasons, so at least because it's the most comfortable things for the passengers. —Bromskloss12:14, 25 June 2007 (UTC)[reply]
(edit conflict)This is OR but planes DON'T fly to parallel to the ground even when it's cruising. Based on the PMDG 737NG on Flight Simulator 2004 it's currently cruising from Auckland to Sydney at 33000 feet at Mach 0.81 and the nose is pointing about 5 degrees up. The angle of attack is 2.2 degrees and if the plane flew parallel to the tangent of the ground then it would be descending quite fast. --antilivedT | C | G06:13, 25 June 2007 (UTC)[reply]
Well, I'm confused by this. I can think of several disadvantages if a commercial aircraft has to maintain 5 degrees nose up attitude in level flight, and not a single advantage. If you didn't have to design a commercial aircraft with this attribute, then why would you ? Gandalf6112:49, 25 June 2007 (UTC)[reply]
Thanks for your answers. Can we conclude that the plane needs to keep going up (or actually keep trying to go up) so as to compensate for the gravity ?. If it tried to fly horizontally, it would actually be pulled down (say at a rate of 10 m per sec). Hence the plane has to try to keep climbing 10 m per sec so that it flies horizontally. It would be a good idea to hang a pendulum to the seat, note down the position while it is on the ground and then see if there is any difference when the plane is cruising without acceleration. If any of you are frequent fliers and find time to do this, please leave a note on my talk page :-) -- WikiCheng | Talk13:45, 25 June 2007 (UTC)[reply]
No, that's not necessary. It's the angle of the wings to the air, the airspeed, the ambient pressure, and the wing geometry that determine lift. For a given cruising altitude and velocity, one could certainly design a plane such that the body is horizontal even if it meant tilting the wings relative to the body. Now, it could be that planes aren't designed to be horizontal when cruising (perhaps because it makes them easier to fly or allows for more lift under other conditions, or something) but being not horizontal is not a fundemental requirement of flight. Dragons flight15:13, 25 June 2007 (UTC)[reply]
Note that it isn't necessary to tilt either the fuselage or wings upward to provide lift, as an airfoil provides lift even when horizontal. However, tilt may be needed to prevent the plane from pitching forward, although placing the wings farther forward would likely do this, as well, but might have other negative consequences. As far as perceptions go, having a large flat area in front of you is important for many people to accurately determine "up" and "down". For the pilots this can be a severe problem, and they sometimes end up flying the plane sideways when it's too dark to get visual clues as to the plane's orientation. Instruments, if working properly, can provide the missing visual information. StuRat16:10, 25 June 2007 (UTC)[reply]
The question has arisen why someone would design a commercial plane to this specification. The crucial information to answer this is that ambient conditions such as pressure and temperature change the available lift (not to mention passenger loading - just a dozen passengers weigh upwards of a ton!). Few aircraft have movable wings, so the only way to change the lift given by a static wing design is to change the attitude of the plane. Finally, it is not necessarily true that a zero-degree pitch would be more fuel efficient, more safe, or any other "obvious" benefit. Nimur16:22, 25 June 2007 (UTC)[reply]
slats and flaps
When you say "Few aircraft have movable wings" - we must be very careful to qualify that by pointing out that almost all aircraft have flaps and almost all large commercial aircraft have slats and specialised aircraft may even have LEX's, blown flaps and slots too. Those things most definitely change the shape of the wing - and therefore the amount of lift it generates! They are typically used during landing and takeoff for precisely that purpose. They also change the trim of the aircraft because the center of pressure will shift as these various gizmos are deployed. It'll generally fly at a different angle to the horizontal depending on how those controls are set. If you get a window seat just behind the trailing edge of the wings the next time you fly in a big commercial plane - just watch the wing as you come into land. You'd swear you were riding in a transformer because the wing seems to completely disassemble itself! So - pretty much all aircraft have wings that move and reshape themselves in one way or another. SteveBaker18:22, 25 June 2007 (UTC)[reply]
Okay, I am not a pilot, but I have done a bit of research on this, and my understanding is that once an aircraft reaches its cruising altitude and speed, the pilot then sets the elevator controls to trim the aircraft so that it is level (see elevator (aircraft) and tailplane). A commercial aircraft is designed to be very stable when properly trimmed. While I don't doubt that it is possible to cruise with 5 degrees of nose up pitch, and their may be reasons why this attitude would be maintained for short periods, I really can't see why a properly flown commercial aircraft would cruise with significant nose up pitch for a long period. Gandalf6109:51, 26 June 2007 (UTC)[reply]
Trim got nothing to do with reducing required pitch, it merely serve as sort of a zero adjustment for the yoke, allowing you to fly without touching the yoke (other than using autopilot). You will be flying at exactly the same pitch when you have neutral trim and holding the stick back to maintain the attitude as to trimmed and flying with no force on the stick. I don't know why they couldn't rotate the wings 5 degrees up so the fuselage can maintain horizontal in cruise but that's just the way it is. The cruise pitch goes up when I climb to say 11000 meters and reduces when I descend to 9000 meters so air density also play a part, maybe it's just that the air is so thin at cruising altitude that you need a higher angle of attack to produce enough lift, and yet having a higher-lift wing is not possible/advantageous than flying at 5 degrees pitch up. --antilivedT | C | G05:45, 27 June 2007 (UTC)[reply]
The relevant parameter is the loss angle, also expressed as the loss tangent. It describes the degree of internal damping (energy loss) in a material. is the complex phase angle of the complex young's modulus. Essentially, if you push on a material with a sinusoidally time-varying force, the resulting deformation will be phase-delayed by relative to the applied force due to energy loss in the material. The loss angle is typically frequency dependent. When your coin is struck, it starts to oscillate (and thus radiate sound); the oscillation amplitude decays with time. The number of oscillation cycles before the amplitude has decayed by a factor e is called the quality factor Q, which equals for small . Copper has a small loss angle and a high quality factor, so a copper coin will ring for a long time, whereas zinc has a moderate loss tangent (around 0.01 at a range of frequencies [13]), so a zinc coin will damp out much faster. --mglg(talk)07:32, 25 June 2007 (UTC)[reply]
The speed of light in air is very close to the speed in vacuum. Sound is made of vibrations in the medium it travels through, so it cannot exist in vacuum. The speed of sound in air you can look up for yourself. :-) (Oh, and is you name taken from Crimson Skies? I played the game and love the setting with airships and airlplanes taking off from it!) —Bromskloss12:01, 25 June 2007 (UTC)[reply]
Ah..I forgot about the fact that soun cannot travel in a vacuum, its what I'm learning currently in school. Thanks. But I did not get my name from the game. Its from the anime Naruto, where a big red demon fox is sealed in the bod of the protagonist. Thanks again! Cheers!!!! -Zacharycrimsonwolf12:15, 25 June 2007 (UTC)[reply]
I recall a sci-fi movie where astronauts, on the moon, in an air-filled plastic dome got into a fight and one fired a machine gun at the other. You heard the first several shots, but as the air leaked into space from the shredded dome the last many shots were silent. A gun should work in vacuum because the oxidizer is contained in gunpowder in the cartridge. Edison15:36, 25 June 2007 (UTC)[reply]
You can feel light without a solar sail - just stick your finger into a suitably high powered laser...you'll definitely feel it! ...and of course you can feel sunlight falling onto your skin to. SteveBaker16:03, 25 June 2007 (UTC)[reply]
You can not smell light, but you can smell the results of ionizing radiation (which could be loosely categorized as light, by some definitions). One such product is ozone, and it has a distinctive smell that is often described as "electric". Nimur16:24, 25 June 2007 (UTC)[reply]
Are Boots the Chemist,uk,toiletries tested on animals? How do they test them? Pol51
Boots is a UK retailer that sources its products from a number of manufacturers, some of whom will have tested their products on animals. Animal testing is the norm in the pharmaceutical and cosmetics industries. Try somewhere like The Body Shop if you wish to avoid such products. For the second part of your question, see animal testing.--Shantavira|feed me07:16, 26 June 2007 (UTC)[reply]
Boots Group (the side of Boots that makes the toiletries) claim on their website that "No animal testing of any kind is undertaken or commissioned by Boots Group PLC or its subsidiary businesses...[however] some animal tests will be carried out by others, to meet regulatory requirements and protect public health. These safety tests may involve ingredients used in products manufactured and sold by our subsidiary businesses". Generally, toiletries not tested on animals will say so somewhere on the packaging, often accompanied by a picture of a rabbit. Laïka07:59, 26 June 2007 (UTC)[reply]
Scientific names Iulus maximus and Everyx myron
The following work:
Hertwig, Richard (1909). A Manual of Zoology. New York: Henry Holt and Company. p. 577.
contains illustrations for Iulus maximus and Everyx myron. However I don't seem to be able to locate the appropriate family/genus/whatever for these binomial names. (I suspect it's because they have since been renamed, but I haven't had much luck trying to track them down.) The captions read:
Fig. 540.--Iulus maximus. (After Schmarda.)
Fig. 536.--Everyx myron. (From Riley.)
The former resemble a millipede-like creature and the later looks like a moth. Can anybody tell me their modern names? I'd like to upload them onto the commons and use an appropriate category. Thank you! — RJH (talk) 20:46, 25 June 2007 (UTC)[reply]
You might want to try Julus Maximus for Iulus maximus, some casual searching hasn't turned up anything more recent than your text on the alternative spelling, though, although I have found some references to "Great Jülus" (both with and without the umlaut. Donald Hosek21:49, 25 June 2007 (UTC)[reply]
Update: A bit of digging indicates that Julus is an active genus according to [14]. Not sure if Julus maximus has been moved to a new genus or not... Donald Hosek21:53, 25 June 2007 (UTC)[reply]
Yes you're right: Iulus is listed as an alternate spelling of Julus on the Ascanius page. It looks like the Millipede page has an "Order Julida [Brandt, 1833]" down in the classification section. So then the Iulus maximus perhaps belongs under there.[15] Thanks! — RJH (talk) 14:36, 26 June 2007 (UTC)[reply]
As for Everyx myron, I suspect that it might be Quasimellana myron although I'm basing this strictly on the fact that it shares a latin species name and is in the right general area of the taxonomic tree. Donald Hosek22:00, 25 June 2007 (UTC)[reply]
We have an article on Richard Hertwig. It doesn't help for this question, but the 1909 book appears to be a translation of a later edition of a textbook first published in German in 1891. We can also guess that the species name for Everyx myron is the name of the discoverer. We also have a Darapsa myron -Arch dude23:21, 25 June 2007 (UTC)[reply]
Update: From there, a google for Everyx Darapsa gets us to a google books scan of "Transactions of the American Entomological Society for 1888", page 78, which discusses a name change involving the two words, but I cannot understand what the heck they are talking about. -Arch dude23:48, 25 June 2007 (UTC)[reply]
What are the byproducts of mixing Sodium Bicarbonate with Aqueous Chlorine?
Specifically, I'm referring to the aqueous chlorine solution you would find in the salt brine tank from a (partially) completed electrolysis via the chloralkali process and a membrane cell. If Sodium bicarbonate is poured into the post-electrolysis chlorinated brine, a) What is the chemical reaction, and b) What chemicals are produced as a result? As a bonus, if anyone knows, could the electrolysis be performed using NaHCO3 instead of NaCl, to possibly clean up the chlorine as it happens? Many thanks in advance. 97.82.254.21322:45, 25 June 2007 (UTC) -Kelaniz[reply]
I went along and tried it. :-) Well, I think. I took some chlorine bleach, though I'm not sure what it contains (chlorine, chlorine dioxide?), and sprinkled over baking soda. There were bubbles, as usual with baking soda, and a smell of swimming pool. Not sure what reactions took place, so it's not much of an answer. (And I was hoping for an explosion or something else spectacular.) —Bromskloss14:44, 26 June 2007 (UTC)[reply]
Well, chlorine bleach would be sodium hypochlorite (NaClO), which I'm guessing would be a different reaction. I'm referring to chlorine gas dissolved in a NaCl brine. After the electrolysis, I'm left with a large tub of this waste, and I've seen lots of references to using NaHCO3 to remove/alter the chlorine to make it safer for dumping. When I did this, I got a lot of gas bubbling (not flammable, apparently) and salty sludge and what looked to be a few carbon granules on the bottom of the tank. So, I don't know. My original guess was that a mix of CO2 H2O and NaCl are formed, but I think that I'm one H atom short, so I'm probably wrong on that. I wish someone would answer this, or point me in the right direction. Even though I don't know the answer, I know it's not a difficult question. Bromskloss: sorry to disappoint you on the explosion thing. :) No bomb making here. I was just creating a NaOH solution and some Hydrogen to experiment with Hydrogenation of oils, among other boring things. :) 97.82.254.21301:10, 27 June 2007 (UTC) - kelaniz[reply]
Got an answer this morning from chemicalforums.com:
Cl2 + H2O = HCl + HOCl
HCl + NaHCO3 = NaCl + CO2 + H2O
Chlorine partially dissolves in water, then reacts according the first reaction. Also, apparently the electrolysis can be performed with NAHCO3. Water and H2, CO2 gases are produced. I'm still not sure whether sodium is formed at the cathode, or something else happens to the hydronium ions.
Can static charges be deliberately accumulated and then discharged into a storage device?
E.G. If bundles of fibreglass fronds are placed in an open air test bed and allowed to collect a charge, could it be then periodically discharged in useful ways?
Static electricity comes in unpredictable amounts, making it probably financially unrealistic to try and harvest it and put it to practical use as we can solar energy. Some of the older books on electricity have sections on using static electricity to cause mechanical motion. An example is "Elements of Static Electricity with Full Description of the Holtz and Töpler Machines..." by Philip Atkinson , 1887, which can be viewed free at Google Books [16]. On pages 102-107 it describes how to have a set of 3 chimes operate from static electricity, how to generate a breeze, and how to make a rotor spin. The book also describes Leyden jars (CAUTION! Static electricity stored in a Leyden jar or any capacitor can cause painful or fatal shocks! Do not experiment with it!). Edison15:27, 26 June 2007 (UTC)[reply]
It's well known that about 70% of the Earth's surface area is covered with water. How does that break down by hemisphere? Most of the land is in the Northern Hemisphere. What percent of the northern hemisphere is water? -GTBacchus(talk)04:54, 26 June 2007 (UTC)[reply]
It's interesting to look at the diagram in our Antipodes article. There is amazingly little overlap between land on one side of the planet and that on the opposite side. SteveBaker03:56, 27 June 2007 (UTC)[reply]
Notch is capitalized in scientific literature because it is a particular family of proteins and genes, and I believe that the style rules for journals always capitalizes those names, like you'd see for trademarks or brand names in other literature. Other examples: Hox genes. -- JSBillings12:18, 26 June 2007 (UTC)[reply]
I'd disagree with above. In Drosophila, a captilized first letter for a classical gene is due to the fact that the first allele was dominant. David D.(Talk)07:34, 27 June 2007 (UTC)[reply]
David D makes a valid point. It used to be, when classical alleles were named from their mutant phenotypes, that a leading cap indicated the allele was dominant and no leading cap meant the allele was recessive (e.g. the mouse agouti allele resulted in a black mouse, while the Agouti allele resulted in a brown mouse). However, more recently in the post-genomic age, fewer genes are named for alleles or phenotypes, instead the gene sequence is named. For reasons better known to the diverse scientific communities and the stubborn people within, gene symbols from different species have different nomenclature rules. Last I heard (and they sometimes change) mouse, rat, Drosophila and most other species' genes have a leading cap (Mc1r), plant and human genes are all caps (MC1R), zebrafish genes have no caps (mc1r). The default tends to be the leading cap. I should add this is the nomenclature for the gene symbols (the abbreviations) the full names all tend to have different rules. Notch is an old skool allele named for the wing phenotype of a mutant, but like many of the old skool names, it is now used to describe the gene itself, and the cap no longer generally used in a manner that indicates dominance. See the following links for the rules for humans, flies and mice. Rockpocket08:20, 27 June 2007 (UTC)[reply]
Cowper's Glands
I am weak and my Cowper's Glands release much Precum when I love with my wife and I become weaker. I was affected with Hepatitis C few years ago but now its ok. Please any doctor tell me if I remove my Cowper's Glands, what it will effect on my health or fertality or erection etc? Thanks — Preceding unsigned comment added by 203.135.56.10 (talk • contribs) 06:57, 26 June 2007
As stated at the top of this page, Wikipedia cannot, indeed must not, give you medical advice. See your doctor. Do not attempt to remove your Cowper's gland! Try a love position that is more relaxing for you.--Mrs Wibble-Wobble08:11, 26 June 2007 (UTC)[reply]
As your question suggests that you already know, the cowper's glands secrete pre-ejaculate. The purpose of this fluid is (among other things, undoubtedly) to lubricate the urethra and create a favorable environment for healthy sperm to travel down the urethra and into the vagina. (There appear to be many factors which collectively create this favorable environment: pH, lubrication, inactive spermatids, binders etc.). Therefore it follows logically that removal of the cowper's glands would result in decreased fertility. The Biblical, Chi Kung, Hindu, and Buddhist notions that semen and its storage is related to energy is nonsense. The production of sperm is a natural and continuous process in all healthy adult males. Sperm is not stored in any long-term sense, and is reabsorbed after a short period. The energy used to create semen is not significant in the lifestyle of a healthy man. Bluntly, there is no reason to suspect that by creating more semen, under normal circumstances, one is draining one's energy. However there are pathologies related to excess seminal fluid production, and if you suspect that there is anything abnormal about your sexual function or energy reserves, you should consult a physician. Tuckerekcut14:55, 26 June 2007 (UTC)[reply]
Speed of turbulent incompressible flow
I am trying to develop a model of fluid flow through a pipe, and am using Coulson and Richardson, Chemical Engineering vol. 1. This has a nice discussion of predicting the total flow rate through a circular pipe for a turbulent Newtonian liquid, and gives an approximate equation: volume flow rate = 49 * pi * radius^2 * (maximum speed) / 60. However, I have been unable to find information about predicting the maximum / central speed of flow through the pipe, is it possible to calculate this theoretically? 84.12.252.21008:11, 26 June 2007 (UTC)[reply]
For a fully developed turbulent flow, the empirical relationship (from [18]) should give you an approximate result. n is a function of Reynolds number, and should be between 6 and 10. Keep in mind this is empirical, rather than theoretical. - anonymous649422:34, 26 June 2007 (UTC)[reply]
Thanks a lot, this is seriously helpful. The equation you gave is in the book I am using, however it assumes from the start that n=7 with no explanation (I think my 49/60 should have been . I think I may be being incredibly stupid, but this equation still doesn't allow me to calculate the actual speed through the centre of the pipe, it just gives the relative distribution of speeds, doesn't it? Does the speed through the centre need to be known empirically? I really need to get hold of the book you mentioned... 84.12.252.21008:20, 27 June 2007 (UTC)[reply]
I don't have the book in front of me, but I believe you're looking for , and at the center of the pipe . is the radius of the pipe, and , the mean flow velocity, is trivial to compute given the flow rate and pipe dimensions. -anonymous649414:46, 27 June 2007 (UTC)[reply]
I apologise for being repeatedly awkward, but I only know the flow rate through the pipe by integrating your equation across the cross section of the pipe, so I only know the flow rate in terms of the speed at the centre of the pipe... wait, I'm confused. By the mean flow velocity, do you mean the average over the cross section of the pipe, or the average over time at a distance r from the centre of the pipe? If it is the first, your equation doesn't seem to make sense, if it is the second then I don't see how it can be trivially calculated except in terms of . My head is starting to hurt, I think I need a trip to the library to find a decent fluid mechanics textbook. Yes, I will (go to a library), I've decided I need to look up lots of other stuff now. Please don't go out of your way to reply again, even if you can make any sense of my train of thought. :) Thanks for your help! 84.12.252.21015:22, 27 June 2007 (UTC)[reply]
Boeing 747 Vs Airbus 340
How are they different between Boeing 747 and Airbus 340 [also A330 & A300]? And I'd like to know what better one is in your opinion.
Acually, I have already searched them in This website, but i don't know exactly how to contrast them. So, i need your good experienced suggestion and i'll take the suggestions to do Airline report to present my teacher.
I would appreciate if you could answer my question
To contrast the aircraft you can compare them along any number of dimensions - size, capacity, engine power, speed, range, cost, number sold etc. etc. Our articles, which you have already seen, should provide all the raw data that you might need. As far as which aircraft is the best, then your teacher doesn't want our opinions - he wants to know your opinion (maybe with some arguments that back it up). So we can't help you with that one. Gandalf6110:40, 26 June 2007 (UTC)[reply]
I've noticed that the wheel nuts on some large vehicles (particularly large trucks) are augmented by a teardrop shaped plastic object (which is often yellow). It's not clear to me whether these are some kind of washer (in which case I don't understand the purpose of the triangular part that sticks out) or whether they're just clipped around the already fitted wheel nut (in which case I really can't see any purpose for them). They're not always present (some wheels have some with them, and some without), and their angle doesn't appear to have any pattern to it. I'm sure they're not just for decoration. I've looked in the likely Wikipedia articles (nut, bolt, bolted joint, wheel nut, lug nut), and I don't see any mention. It's not a nyloc nut, although if the plastic thing really is in the joint like a washer, perhaps it's part of a similar locking mechanism. I've failed to google anything worthwhile about it (and I can't find a clear photo of on on Google Images). Does anyone know what these things are? -- Synthetic element14:29, 26 June 2007 (UTC)[reply]
Sometimes I've seen these all pointing toward the wheel center, I've also seen them point erratically as you describe. I don't know if theyre supposed to point to the center, or if it's just aesthetic. I'd love to know what they are too. 213.48.15.23414:38, 26 June 2007 (UTC)[reply]
AFAIK, they're just indicators, fitted to the nuts after tightening. When the nuts are torqued up, the tabs are fitted over in pairs with the tips facing each other. Since loosening the nuts would cause the tips to move in opposite directions, it's obvious at a glance if one or other of the nuts has worked loose. If they're pointing at "erratic" directions, that suggests that whoever's responsible for checking them isn't doing a very good job! This is all speculation on my part but it seems the most likely purpose for them. --YFB¿14:47, 26 June 2007 (UTC)[reply]
Well done, thanks. Like 213.48.15.234 I think I've seen too many that point at jaunty angles, so maybe the wheels quite literally are about to come off the European transport industry. Ideally Wikipedia would have an article about these - the generic term seems to be loose wheel nut indicator. -- Synthetic element14:57, 26 June 2007 (UTC)[reply]
Hmmm - these yellow gizmo's wouldn't have helped there - the problem with the busses was that the nuts had been over-tightened and snapped the bolts off. The things we're talking about here are to help indicate when a nut has worked loose...quite a different problem. Havn't those guys ever heard of a torque wrench?! SteveBaker03:52, 27 June 2007 (UTC)[reply]
Cat bite
I have been biten by my beloved cat while I was doing what he probably considers hard core water torture. Anyway the bite has swelled a bit and I was wondering what signs should give me the warning to stop entertaining myself while my body heals it's self and look out for one of the men in white? Bastard Soap16:03, 26 June 2007 (UTC)[reply]
medical advice removed
Please see a professional if you're looking for medical advice. We're not qualified or competent to give medical exams over the internet. (Visit a local walk-in clinic, see your family physician, call your local 'telehealth' phone number, or speak to your local pharmacist/chemist.) TenOfAllTrades(talk) 17:20, 26 June 2007 (UTC)[reply]
Yeah, do so. But make sure ask the person on the line if they are a Wikipedian, because then they are apparently not competent! —Bromskloss18:01, 26 June 2007 (UTC)[reply]
If someone who is allergic to an animal is bitten by that animal, a prominent weal will commonly develop. This is the same mechanism of reaction as an allergist provokes when doing a skin test to identify possible allergies. Please note that this comment is an explanation, and offers no advice whatsoever on treating cat bites.
A danger signal of infection needing immediate medical care is red streaking from the point of the wound, visible through the skin. Gzuckier20:13, 26 June 2007 (UTC)[reply]
Same goes for this comment (not medical advice) - cat bites, especially of the hand, have a high rate of infection. One of the signs of infection is swelling. See PMID 7625323 and see a doctor. --Joelmills20:12, 26 June 2007 (UTC)[reply]
cat bites on the hand are notoriously dangerous, because [1] cats have normal flora in their mouths that cause severe infection in humans (e.g., unusual organisms such as the NO-1, Actinomyces, Porphyromonas & Pasteurella sp., or more common ones like Staph), and [2] because the hand is a "closed space" within which such infections, especially anaerobic ones, easily spread. If unchecked the infections may require surgery for drainage. Most physicians would prescribe antibiotics early rather than wait for complications. It would be a very good idea for you to visit your doctor to provide them with that opportunity. The swelling you already have is a sign that you should do so. - Nunh-huh00:06, 27 June 2007 (UTC)[reply]
As far as I understand, "Dark energy" is just a convenient term for the cosmological constant, which can be expressed in units of mass or energy per unit volume, but inherently pervades space in a uniform manner. Clearly, all of this is subject to revision as new theories emerge, but I am not aware of any current theories which would allow a local concentration of dark energy for any purpose. (By the way, wormholes are purely theoretical, something allowed by the mathematics of general relativity but never observed. It is possible that the theory does not apply at the scales necessary, and it is also possible that they are stable but nonexistent, ie, that there is no way to create them.) --Homunq20:22, 26 June 2007 (UTC)[reply]
Well, very little is known about dark energy. It's true that if w = -1, then dark energy acts like a cosmological constant, but people don't necessarily assume this, WMAP3 gives w = -1.02 ± 0.02, if I recall correctly. Dark energy might just be some substance with P = -E, or pressure equal to negative the energy density. The short answer is - nobody knows that. WilyD20:27, 26 June 2007 (UTC)[reply]
Quintessence is the theory of "corpuscular" dark energy that would allow it to be arranged and concentrated. A cosmological constant is preferred theoretically, but both possibilities are consistent with observations. Whether quintessence is useful for wormholes, I have no idea. Dragons flight20:27, 26 June 2007 (UTC)[reply]
omega 3 or omega minus 3?
Chemists and biochemists: is this true?
Actually, they are "Omega minus 3" fatty acids. The term omega-3 (aka "n-3", "ω-3") signifies that the first double bond exists as the third carbon-carbon bond from the terminal methyl end (ω) of the carbon chain. [22], which I interpret as meaning that you are actually counting up three from the "bottom" of the chain.
The folks editing the Omega_3 article would like to know. Thanks. Gzuckier16:11, 26 June 2007 (UTC)[reply]
Right! But why you ask for an artikle from answers.yahoo.com and not the original much better wikipedia article? The saying: "from alpha to omega" meaning from beginning to end states clearly that omega is a synonyme for the end of the chain. Better use the delta or the normal en nomenclature for these kind of substances, because this naming convention is not used by chemists anymore. It contradicts the counting rules of IUPAC. The food and nutrition manufacturers use this naming convention because it sound good.--17:13, 26 June 2007 (UTC)
(edit conflict) Apparently it is[23], according to the University of Utah, although it's a moot point, as "Omega plus three" would not be possible (you would have to count down from the bottom!). I suppose if you wanted to count from the start, you could use the alpha point, but there would probably be no need, given the wide use of the omega system. Laïka17:22, 26 June 2007 (UTC)[reply]
Electrical resistance of the earth
What is the resistance of the earth? If I stick two metal probes in the ground and apply a DC voltage between them what level of current would flow? Would the current decrease if I put the probes further apart? What if I put the probes thousands of miles apart, would a current still be discernible for practical voltages ( e.g. <1000V ) ? Even if there was nothing but miles of rock and dry desert in between?
Do all the possible parallel routes between the probes need to be considered? For example, in the extreme case, current traveling away from the other probe and going right round the world before reaching the other probe from the other direction. Is there a path straight down through the center of the earth?
The reason I ask is that I have been reading about early telegraph cables that used the earth to complete the electric circuit between transmitter and receiver, and wondering how this is possible. My intuition would be that the resistance of 1000s of miles of desert would make such a system impractical. The article on earth (electricity) seems to suggest this, but I thought telegraph communications were routinely possible back then, despite what the article says.
And what about earth connections used for wireless transmission? E.g. If I build a simple radio transmitter and a radio receiver, such as a crystal set, I believe they will both need earth connections. Is this to provide a common reference voltage between them? That is, are both sets' earth connections are at the same potential? How does this work across dry ground? Should I drive the earth connector so deep that it meets the water table, where the ground will be much more conductive?
TIA
Alf Boggis16:46, 26 June 2007 (UTC)[reply]
I can answer only a few little bits. Probes further apart will make the current smaller, yes. All possible paths need to be considered, as I imagine the current will spread out as it leaves the source and collect toward the target. You do not need a common ground for radio transmission. Your mobile phone obviously isn't connected to the ground, for example. —Bromskloss17:48, 26 June 2007 (UTC)[reply]
Radio antennas need two elements that are energized with an electrically-opposite polarity. For very small radiowaves, these two elements can be concealed within the same physical antenna. For larger radio waves, a "ground reference"/ground plane commonly acts like a sort of "mirror" to provide the other electrical pole of the antenna. In the case of cell phones, you are commonly the ground reference (because you are much bigger than the radio wave). For old-fashioned AM/medium wave transmitting towers, a large array of copper cables is buried out in the ground in a radial fashion extending from the antenna. Moist ground makes this a lot easier; it's no accident that the New Jersey Meadowlands are full of AM broadcasting stations as the swampy ground there makes it very easy to set up an effective ground plane. See also dipole antenna, monopole antenna, whip antenna, and image antenna.
It's absolutely not true to assume that two earth connections at geographically distinct places will provide a reference ground - as Ground loop (electricity) notes "electrical potential at different points on the surface of the Earth can vary by thousands of volts". Note also that not only can signal be transmitted with an earth return, even power can - see Single wire earth return and Single-wire transmission line. Now it's my understanding that this all works because the Earth can be looked at as an infinite repository of both positive and negative charge. So if there is a wire between us, we can both measure the potential between it and the earth (it won't be the same, but so long as it doesn't change we don't care). If I then wobble my potential a bit (by briefly attaching my voltatic stack) you should see a wobble too. You're really correct, there really is a returning ground path, and it does (in a theoretic way) follow a big fat footprint through the earth (the entire Earth, I suppose) - but the effect your and my little circuits will have will be so dwarfed by all that geoelectric flux that you can't really ascribe any given current flow through the earth to us. This ground-earth return thing worked, for a while, but the telegraph switched to two-wire (i.e. they provided their own return), I think because the impedance of the whole circuit was too high to prevent higher frequency transmissions (or reliable transmissions over very long lines). Britannica has an article about this, but I think Wikipedia doesn't (that I can find). -- Synthetic element17:50, 26 June 2007 (UTC)[reply]
This is the answer I was looking for, thanks. I think I understand your infinite repository idea. I just need to get my head around how a bit of metal stuck into the soil can draw on infinite amounts of charge, when it probably doesn't make a very good connection to the earth. Does it rely on water in the soil, and whatever electrolytes are dissolved in it? Alf Boggis19:13, 26 June 2007 (UTC)[reply]
Although the resistance of the earth is high, there are so many paths that, after the resistance near the exit and entrance, everything else becomes quite small. It is common for part of an electric circuit to be grounded, which would be pointless if it was so difficult to get electricity through there. — Daniel18:42, 26 June 2007 (UTC)[reply]
Another way to look at it: the resistance of a wire is inversely proportional to the cross-sectional area. This "cross sectional area" for two electrodes sufficiently far apart would be the area of successively larger subterranean hemispheres centered at the electrodes. Thus the resistance would be an integral of 1/r^2, starting with an r that gives the area of the electrode surface and going to infinity, and multiplied by some "constant" for local rock/soil/groundwater properties (and for the 2*pi/3 area of the hemisphere). As has been pointed out, you'd also have to put a voltage term in that leg of the circuit too, generated by the earths magnetic field or whatever, not to mention impedance/capacitance. This model is too rough for real calculation, but it gives an idea of the relevant variables - the one you control is the surface area of your electrode, ie, how deep you drive your grounding rod. With a deep enough rod (or various rods spaced more than their depth apart), you can get essentially arbitrarily small resistance. --Homunq19:31, 26 June 2007 (UTC)[reply]
A pair of ground rods many thousands of miles apart would be able to source or sink an amount of DC current from a single wire connecting them and a source of current which depended on the resistance achieved in the grounds and of course the internal resistance and voltage of the power source. The resistance of a ground rod depends on the soil conditions and the depth to which it is driven. Sand or rock make for high resistance, and soil (especially if damp) makes for lower resistance. Utilities use stainless steel rods which they drive into the ground, then screw on another, and keep going until the required low resistance is achieved. 30 feet deep is common to get the resistance below ten ohms. (The following is presented only as an illustration; do not try anything like this at home, because of the danger of electric shock). So if you had 2 ten ohm ground rod installations, and a 1200 volt DC source, and another 100 ohms resistance in the connecting line (and the voltage source, such as a generator or battery) the current would be 1200 volts divided by (10+10+100)ohms = 10 amps. Increase the voltage to 12,000 volts and you would get 100 amps. Etc. This could of course increase the rate of corrosion of metal objects in the ground near one of the ground rods, and it might heat up the ground rods unless they consisted of several in parallel. It might also dry out the ground and increase the resistance, or it might set up a ground potential causing dangerous shocks if someone stood near the rod, something like lightning hitting a tree and killing someone standing near it. Electric utility installations use a great number of ground rods spread around the facility and bonded together. There are also earth currents of electricity caused by sunspots and other phenomena which can cause large currents under certain conditions. Between two rods the current takes every possible path. Dirt (or rocks, or sand) has a certain resistivity, so more parallel paths just means lower resistance. Inventors such as Samuel Morse and Nathan Stubblefield used rods stuck in the ground to send and receive wireless telegraph and telephone messages respectively, in the 19th century. Edison21:47, 26 June 2007 (UTC)[reply]
To my knowledge, both have been proven to work, but not necessarily on the wide range of claims or on the kind of scale some practitioners claim. In particular, hypnosis is more like a combination of deep meditation and increased suggestibility, rather than some kind of mind controlling power. Confusing Manifestation22:48, 26 June 2007 (UTC)[reply]
It's pretty clear that to the degree that acupuncture does work, it's operating by the placebo effect. It's kinda hard to do a controlled experiment though - merely pretending to stab people repeatedly with needles as a control is a bit tricky! However, the placebo effect is undoubtedly a real, scientifically proven thing - and harnessing that effect with all of the theatre and drama associated with sticking needles in just the right place appears to benefit some people with some conditions. It's pseudo-science because it claims to work in ways that it cannot possibly - but that doesn't stop it from working anyway! Hypnosis is a bit more controversial - I'm not sure what to think. SteveBaker03:30, 27 June 2007 (UTC)[reply]
Saying that something doesn't work in ways some claim it works, because "it cannot possibly" do so, sounds a trifle unscientific. Isn't the scientific approach to observe things that have actually occurred, and explain them? Just because the placebo effect is well described doesn't necessarily mean that that's what's at work with acupuncture. I've no doubt that's the operative agent in some cases, but does it explain all cases? -- JackofOz04:04, 27 June 2007 (UTC)[reply]
Well, this strengthens even more my statement that everyone is ambiguous about this topic. Since intelligent people aren't sure about whether they are scientific or not, I'll have to guess that both are a pile of unscientific trash. --Taraborn11:54, 27 June 2007 (UTC)[reply]
Acupuncture claims that the needles need to be stuck into acupuncture points or on the meridians for the effect to work properly. Now presumably one scientific test you could do to test the placebo effect would be to apply the same technique, preferably in a double blind trial, to places other than the acupuncture points or meridians and see whether or not you got the same effect.
Note that results of this test would not necessarily be conclusive. For example the acupuncture points may have actually been chosen in a prescientific scientific type way through repeated trial and error to find what points on the body had the greatest effect; they could say be close to underlying nerves and thus stimulate those nerves more directly if an acupuncture point rather than a random point is used. Some ancient memory tells me I have heard of this test being done, and there being no difference found in the efficacy of treatment, but I have no references for this and it could just be my preferred memory of the results.
There's also the point (despite the preceding unreferenced claim from Bibliomaniac) that acupuncture, when it does work, is most effective in treating relatively mild pain. A simple explanation for this could be that sticking needles into your body leads to the release of natural endorphins (which of course it would) and that is the explanation for any effect noticed.
I've written enough, so I won't comment at length on the hypnosis side of the question. Conman's statement about it being a state of hypersuggestibility seems to be quite accurate. Though it can have some uses if done properly, consider for example the significant role of hypnosis in false memory syndrome. --jjron07:14, 28 June 2007 (UTC)[reply]
The problem with the natural endorphin theory of acupuncture is that it also appears (or is widely claimed) to be effective for making people give up smoking. Those endorphins would be flushed out of your system very soon after the 'treatment' - they can't explain any effect that lasts more than a few hours. SteveBaker21:16, 28 June 2007 (UTC)[reply]
I'm sorry, I don't regard 'widely claimed' as scientific evidence of efficacy. Any proof from a reputable study that this is anything but the placebo effect, if in fact there is any effect at all? See smoking cessation that claims that's all it is. And perhaps if this is the method for quitting smoking that they are relying on in China, that would explain why China is now one of the largest and fastest growing markets for smoking. --jjron09:51, 29 June 2007 (UTC)[reply]
bentonite
Does anyone know how to remove trace amounts of bentonite from oil? Essentially, I need something that will bond with the bentonite molecule to make it heavy enough to be removed with a centrifuge.
Thanks
facial gymnastics and face lifting
is facial gymnastics a valid 'treatment' and is it true that current facial plastic surgeons use it in the recovery process?
or does it not work at all? i can't find much info online.thank u!
To expand this: is there an evolutionary reason why flowers smell good to humans, or is it just an evolutionary accident? A.Z.22:43, 26 June 2007 (UTC)[reply]
I don't have a reference, but it seems sensible that things that smell good are things you might try eating, whereas things that taste good are things you'll keep eating. So it makes sense that more stuff would smell good than would taste good. Friday(talk)23:02, 26 June 2007 (UTC)[reply]
One simple reason is that when you taste something, you're also smelling it.
(Which is why things don't taste right when your nose is blocked.)
--Anonymous, June 26, 2007, 23:33 (UTC).
When we "smell" something, we are detecting a volatile molecule by activation of our olfactory epithelium. Volatile molecules tend to be small and if something isn't vaporised, we can't smell it. However, molecules that we taste do not need to be volatile, since our taste buds can come into direct contact with non-vaporised compounds. Therefore since the molecules we are actually detecting can be very different, its not surprising that things that smell "good" do not always necessarily taste "good". Of course, even if we are detecting the same chemicals through both modalities (and in some cases we are), then it doesn't follow that the same molecule gives the same general emotional response. This is because taste receptors and olfactory receptors are different, and they project to different brain regions.
However, you are correct in noting that things that taste good generally smell good, but the opposite less so. This is because what you are calling taste is more complex that you may think. In fact, when you say something "tastes good" a large proportion of that sensory signal is actually smell, though you may not realize it. So when something tastes good, that in itself is because it smells good. Consider the difference between the flavor and the basic taste of a substance.
As for A.Z.'s question about evolution, well, thats a good question to which we don't know the answer. In animals, certain natural plant odors appear to activate the vomeronasal organ (VNO), which appears to control hardwired, innate responses. In this paradigm, one could hypothesize that there is an evolutionary reason that these animals respond to pleasant smelling plants in a positive way i.e. that the odors are kairomones. However, humans don't have a VNO, and we don't appear to have the same mechanism to permit us to respond to odors in an innate manner (there is no strong evidence for human pheromones). So when we detect odors the signal is is projected to areas of the brain where we can process, associate and attribute information, rather that simply react to it in a pre-programmed way. Indeed, one would imagine it would be entirely possible that some people do not enjoy the smell of flowers, because their brain associates it with something unpleasant. So, the interesting question is why is it that, in general, some smells do appear to be pleasant to the population at large. Is it innate, or just associative? If its the former, how does the neuronal circuitry mediate such a response? These are questions that are very interesting to the olfactory research community, because smell is such an emotionally meaningful sense that having the ability to understand how we can generate such powerful attractive stimuli would make someone a lot of money indeed. Rockpocket07:46, 27 June 2007 (UTC)[reply]
Eyes Very Sensitive to Bright Light
Over two years ago I underwent the Lasik eye procedure to correct severe nearsightedness. It worked pretty well for what it was intended, but ever since then my eyes have been very sensitive to light from the sun and unshielded lightbulbs and even the computer monitor. Going outside without dark sunglasses on for more than fifteen minutes results in a pounding headache, and even with the glasses I find it painful to face the sun with my eyes closed. I have tried to ignore this in the hopes it would go away eventually, but it has become obvious that if I don't do something I'm going to have a headache most days for the rest of my life.
I know we're not supposed to ask for medical advice here, so I was just wondering if anybody knows of a type of vitamin or nutritional supplement that can help alleviate this problem somewhat. Even a little help would be appreciated.
I really doubt there is any nutrient or vitamin that can address that problem specifically. If anything oral could, it would be a drug or an eye drop... and I currently only know ones that dialate the pupil to let in more light (which is the opposite of what you need) and Wikipedians are generaly not qualified to prescribe such a product to you anyway. I suggest you go back to the doctor who performed the surgury. Post-operative care is usualy included in the operation price, however I don't know about 2 years later. Anyway, why haven't you addressed this problem earlier? Hasn't it been like this since 3-6 months after the surgury? (3-6 months is usualy quoted as when your eyes have completed recovering from surgury)? 209.53.181.3002:47, 27 June 2007 (UTC)[reply]
If you don't like putting your shades on and off maybe you should invest in transition lenses that automatically dim according the ammount of light they are exposed to. Then again, you probably got the surgury done to free you from eyewear... 209.53.181.3002:49, 27 June 2007 (UTC)[reply]
Have you considered tinted contact lenses? They may be available in a null curve, to act as a sort of permanent shade for your eyes. This is not medical advice and you should surely see a doctor for more information. In a more creative approach, maybe you should consider moving to a region known for cloudy days? --Jmeden200016:30, 28 June 2007 (UTC)[reply]
So survival of the fittest has been going on for a while, and it's still going on today, so today I wondered about a über-fit animal that could be the product of said proccess. The animal would be able stay alive by getting food and avoiding being eaten, killed by competitors, or hurt in an accident. Any ideas of attributes this theoretical animal would have? - AMP'd23:04, 26 June 2007 (UTC)[reply]
I'm not sure there is any such thing as "über-fitness". First, the things you mention mostly require lots of energy to be done extra well. That means that a creature that could do them well would probably need lots of food, which would, in one sense, make it less fit. Second, in the context of evolution, "fitness" does not necessarily mean that individuals are good at surviving. Rather, it means that the species survives. One way to do this is to make individuals good at surviving. Another way way is to make lots of relatively fragile individuals that reproduce quickly and in large numbers. (Consider insects.) --Tugbug23:23, 26 June 2007 (UTC)[reply]
Take a look at the herring gull. It's an excellently-'designed' beast. It's strong, it's incredibly fast, it's smart, it's aggressive, it has excellent eyesight, it's large and formidable enough for most predators to decide give it a miss and look for an easier meal, it's long-lived, it can fly (both strong, powered flight and gliding), it can swim, it can run, it can hunt, it can scavenge, it can eat just about anything organic - even decaying matter filled with toxins, it can survive drinking salt water, it can breed just about anywhere - *and* it's sussed out how to exploit humans without ever becoming too trusting. I get a feeling that if anything bad ever happened to the world, there would still be herring gulls left standing at the end of it all. --Kurt Shaped Box23:26, 26 June 2007 (UTC)[reply]
To a certain extent, being fit is relative to current environmental conditions. Not being specifically familiar with any given species, the gene pool may be susceptible to attack by a certain disease, and there are other concerns as well. Succession is an ongoing process that can turn today's winners into tomorrow's losers in any given habitat or ecosystem. –Pakman04423:41, 26 June 2007 (UTC)[reply]
Just to give a good example, and explain further, you also have to look out for the odd population bottleneck, like a meteor impact. Show me a mutation that will make an uber-fit animal survive that. And similar to above, after such an event, nice genes to have might be ones for being able to travel long distances (to someplace that didn't just have its ecosystem wiped out by the heavens), and subsequently being able to eat different foods. Similar to being able to resist a particular strain of disease, some of these genes can be completely independent of ones that made them "fit" in their prior environment. Modern human examples of such genes (alleles, or whathaveyou) would be the sickle cell trait (increased resistance to malaria), and cystic fibrosis (increased resistance to cholera, hypothesized but not confirmed). In the absence of rampant infection by these two diseases (and especially before modern medicine), the accompanying mutations would normally be considered to decrease ones "fitness." Someguy122102:58, 27 June 2007 (UTC)[reply]
Flying is an energy-intensive activity, requiring easy availability of high-energy-density foods. If the world's supply of food energy were to drop (say, from a meteor-impact dust cloud), your gulls would have a hard time. Either they'd switch over to swimming and running, which leaves them vulnerable to energy-conserving ambush predators, or they continue flying and starve to death. --Carnildo22:15, 27 June 2007 (UTC)[reply]
It's a mistake (and a common one) to assume that evolution is a process that slowly makes better and better plants and animals without end. That's really not true. At any given time, it's more or less true that all of the animals and plants are the best that they can possibly be for the environment they are in. In environments where the conditions don't change much, the species stay pretty much stable. Evolution happens surprisingly quickly when conditions change - but the evidence is that each lifeform fits into it's environment as best it can in short order. So it's possible that a future sudden change in the environment (global warming maybe) might result in adaptations, the creatures that result might well not be suited to our present situation - and we not to theirs. SteveBaker03:07, 27 June 2007 (UTC)[reply]
Bottom line is that a major survival feature is adaptability. If something is so good any changes are weeded out, then when the environment changes, their descendants will be disadvantaged. Of course, the retroactive proof by evolution comes into play here; after a billion years, if we haven't seen anything superior to what is alive now, then there probably can't be anything superior to what is alive now, given this need to be able to further evolve from here. Gzuckier14:32, 27 June 2007 (UTC)[reply]
To really do what Amp'd asked would require an organism that could control its environment, essentially produce food at will, be largely unaffected by extremes of weather, destroy or control any natural predators or competitors, be able to avoid injury or disease, or mend itself if it was injured or became sick. I'd suggest to achieve this, rather than typical physical attributes we think about, rather it would need a very big brain to allow it to adapt to changes and come up with solutions to problems that it faced very quickly. Now, it just so happens that such an animal has evolved once in the Earth's history, and we call them humans. --jjron07:37, 28 June 2007 (UTC)[reply]
Timekeeping
Why didn't an ancient Roman or Greek simply create a pendulum out of a string and a weight and have a slave swing it and count the oscillations?
Because they didn't think of it? Or maybe someone did, but didn't think it interesting enough to make public, so we never heard about it. I mean, it's not as if there weren't hourglasses and sundials and things if it was so important to know what time it was. And a pendulum wouldn't be very accurate if a human had to keep swinging it. --Anonymous, June 26, 2007, 23:36 (UTC).
I think you've got it. When you don't have rapid long distance communication ("I'll call you at 3:00") or travel ("The stagecoach leaves at 4:00"), exact timekeeping isn't nearly as important. As it is, I know the time to (if I wish) a precision of much less than a second but I still can't tell you when the traffic will let me get home for dinner.
As I recall, it was Galileo who first noted that the period of oscillation was independent of the arc of the swing, so it's possible they didn't do it because they thought it would be inaccurate. - Akamad00:52, 27 June 2007 (UTC)[reply]
Right - before Galileo, nobody realised that the period of swing of a pendulum is independent of how hard or how far you swing it...it is a little surprising that this is the case. So they simply didn't realise that this was a good way to make a clock. It's surprising that such a simple observation had never been made before (or if it had - that nobody tried to make pendulum clocks) - but they didn't. They had quite accurate water clocks as well as hourglasses and sundials. SteveBaker02:59, 27 June 2007 (UTC)[reply]
It isn't independent; that's just an approximation. See pendulum (the bit where the date 1673 is mentioned). This doesn't matter too much for clock purposes because the pendulum (or balance wheel) is driven by a mechanism, which can be designed to deliver a fixed force. Before this design feature was developed, though, spring-driven clocks would change speed as the spring ran down and the pendulum was driven less far. --Anonymous, June 27, 2007, 04:56 (UTC).
Among other things, having detailed knowledge of the time wouldn't have been all that useful, especially compared to the various other labors a slave might do. Dragons flight07:59, 27 June 2007 (UTC)[reply]
I was thinking that it would be quite charming to have a (modern) "clock" making use of a scantily clad model, as a promotion for a business. I would have thought that the ancients would have liked the idea, too, for the same, reason.
A recent issue of the New Yorker magazine had an article about the Antikythera mechanism. The article explored the general topic of ancient technology, pointing out how we don't really know much about it. We know that the ancient technology included apparently sophisticated mechanical automatons, and there are surviving references to technical texts and devices, but essentially none survive. The common assumption is that the ancients had various kinds of "crude" technology, but not things like clockwork-precise toothed metal gears. And certainly not spring-driven gear trains that could be used to build things like mechanical clocks. But, at least according to this article, these assumptions have been increasingly questioned, with the Antikythera mechanism being a fragment example of the kind of gear train technology known. The article goes into reasons why other ancient technology of this kind has not survived. Also mentioned is the theory that the ancients did not use machines for "practical" purposes but rather for "amusement", because with slave labor there was little incentive for "useful" machinery. This theory is, of course, just speculation. The point is that the ancient Greeks and Romans may well have had good clocks and other such devices. In ancient Athens there was apparently something called the Tower of the Winds, which is generally assumed to have been some kind of water clock, but we really don't know what kind of a clock it was. It must have been a water clock because the ancients did not have mechanical clocks, right? Finally, after the fall of the Roman Empire it seems that whatever sophisticated clockwork tech knowledge there was, it was lost in Europe. But in the Islamic world there are known examples of mechanical clocks and other devices dating back practically to ancient times (see Clock#Early mechanical clocks). There is a theory that ancient clockwork tech survived in the eastern Roman empire and the Islamic world that replaced it; and that the Renaissance-era European "inventions" of precise gears and clockwork were essentially transmissions of technical knowledge from the Islamic world, similar to how ancient philosophical texts were transmitted to Renaissance Europe via Arabic.
On a trip to Peres river, I saw plentiful aphids on the thistly plants of the kind pictured here, but none on adjacent flora. A similar phenomenon has been observed at my window box with a different specie of aphids - there were about a trillion of them on the invasive Hedera helix, but none on nearby plants. What makes invasive plants so attractive, or detracts aphids off local vegetation? Thanks, Lior02:10, 27 June 2007 (UTC)[reply]
It may be that the aphids prefer to hide amongst the spikes of the thistles so as to avoid predators such as birds that might not want to be pricked. SteveBaker02:55, 27 June 2007 (UTC)[reply]
maybe as is the danger with any introduced species, since the local species evolved with the aphids they adapted to a balance with both species in check, where as the introduced species has no natural protection against the aphids and is therefore overwhelmed, a similar thing could possibly happen if that aphid was then introduced into that plant's native environment, but possibly the habit there is in other ways inhospitable to the aphid. Vespine03:30, 27 June 2007 (UTC)[reply]
Chief Executive Officers
What are the names of the past Chief Executive Officers of The Prince of Wales Hospital in Hong Kong?
Would there be any science history enthusiast able to contribute somehow to the explanation of when did the term “direct current” appeared first in English, who proposed or introduced the term, and what actually the word “direct” suppose to imply in this context, meaning why and when did scientists started calling it “direct“ current instead of Galvanic current?
Was it because the graph is a straight line (cannot see any connotation), or because it is directly (!) from a battery (I doubt), or was it unfortunate mistranslation from Latin or other foreign language at the time, or is there some other explanation?
I am of electrical background and I know what direct current is, what I am after is the historical trace of the term “direct current” and its supposed meaning. I have spent many hours in libraries and on internet searching for answers, but with no luck at all. Many thanks in advance to anyone who can contribute or point in the right direction.
Did the term “alternating” current appeared about the same time?
At Google books if you specify full view you will be able to search books about electricity from the 19th century. I did not see a distinction of AC versus DC in the writings of Faraday in the 1840's or De La Rive from the 1850's. Once dynamos were invented and used for arc lighting, some were AC and some were DC. Early uses of the term "direct current {De La Rive, 1850's) were used to distinguish the battery current from the induced current, showing that the term did not then have the present sense. In 1884 I find the same Siemens dynamo described by one writer as a "constant current" machine and by another as a "direct current" machine. Further complicating things is that "constant current" often meant a DC generator with excitation such that the current stayed the same as the load was varied. I found the term "alternating current " popping up before the modern usage of "direct current." Both terms were probably known to physicists and electrical inventors in the 1870's. As Vespine said, the two terms were widely used by the war of the currents in the early 1880s. Similarly, 78rpm records were not called that until 33 1/3 rpm records were introduced; they were just called "records". DC electricity was just called "electricity" or "current electricity" to distinguish it from static electricity until AC gained some usage with transformers for sending current to distant locations. Edison05:45, 27 June 2007 (UTC)[reply]
I'm on Edison's side here. I suspect that transformers created a distinction between direct current (a galvanic connection) and indirect current (through magnetic induction). But I have no reference to support my claim. Atlant12:52, 27 June 2007 (UTC)[reply]
The Oxford English Dictionary (online subscription required) provides a quote from the Journal of the Society of Telegraph Engineers (XV p. 193): "I am glad that people are beginning to use the term ‘direct’ when they mean a current which does not alternate."; this quote dates to 1886, implying that the wide use of the term 'direct current' in the sense that we understand it today started to take hold sometime in that decade. (As others have noted, the first use of the term may well be quite a bit older.) The term was sufficiently established by 1889 to appear in Edward J. Houston's book A dictionary of electrical words, terms and phrases. TenOfAllTrades(talk) 15:20, 27 June 2007 (UTC)[reply]
Our sister project - the Wiktionary says: From Latin directus, past participle of dirigere ‘straighten, direct’, from di- + regere ‘make straight, rule’. - so it seems reasonable to use 'straight' as an antonym of 'alternating'. It also provides a meaning: 1. Straight, constant, without interruption. - also a reasonable use of the word. But I agree that it is almost certainly the other meaning: "directly from the battery - not indirectly through a dynamo" because early sources of AC would have come indirectly from some ultimate DC source. SteveBaker16:29, 27 June 2007 (UTC)[reply]
Thank you guys, especially to Edison for the tip about Goggle books.
I have searched back to 1750, when Goggle gave up on me. Here is what I have found;
•Some US Government document published in1777 states: ….”direct and alternating current feeder wires shall be installed as follows:” …
•“The Discovery” published in 1763 refers to both the … “a.c. current from there to the receiver”… and further …”Low voltage alternating current is supplied”…
•“The Skipper” published 1753 provide interesting insight; …”alternating current generator, or alternator …’as is’ (my assumption)… presently called (meaning then in 1753)”….and further …. “The system is 12 volt and current is generated by what is termed a “three phase” Wico alternator.”
All this shifts the discussion a century back. It appears that both the direct and alternating current terms were well established in the mid 1700. Now, I hope there is still someone there who could dig deeper into the history and put further insight to this fascinating story? BrightSpark09:21, 28 June 2007 (UTC)[reply]
A strong cautionary note here: Google books very frequently gets the date of a book wrong by hundreds of years, since apparently there is very little quality control of the people doing the data input. There is also the problem that when something is in "snippet view" you can't see the entire article to see the puiblication data. 1763 might be when "The Discovery's" first issue was published, and then Google shows you a sentence from something published 150 years later. This is shown by the supposed 1777 reference from "The Skipper" referring to "direct and alternating current feeder wires " because nothing like that existed in the world in that century, and the "US government" was more concerned with repelling the Redcoats than in a hypothetical electric power system for a hundred years or more later. As "history detectives" we may observe that it refers to the "volt" which was not a term in use until long after 1800 when Volta invented the battery. I would assign it 150 years or more later than the year you might infer from the snippet view. Another very poor feature of Google Books is that if you click onthe link to find the journal "The Skipper", apparently about sailing, at a library, it takes you to libraries that carry "Skipper" which is a different German magazine started in 2004 which is about lesbians. Likewise if you click on the link to find libraries with "Discovery: A Monthly Popular Journal of Knowledge" Google Books directs you to University of Arizona and a different journal called "Discovery." which was only puiblished from 1943-1966. All this is why I strongly encourage using only "full view" search for old public domain books to research 19th century technology. Edison16:01, 28 June 2007 (UTC)[reply]
Thanks a lot Edison, after my last post I thought about all this and got to the same conclusion; something must be wrong, the language appears too modern. So, I agree fully with you, the conclusion was premature. BrightSpark05:24, 29 June 2007 (UTC)[reply]
What is a 'return vector'?
Hi all. I was wondering what a 'return vector' is. I've heard the term in reference to 'coordinating points' (I'm not sure exactly what that means either!). It seems like a scientific term (I do know what a vector is), so I was hoping you could help me out. Much help appreciated ! Xhin Give Back Our Membership! 08:03, 27 June 2007 (UTC)
It may be the vector from Point B back to Point A (assuming that the vector from Point A to Point B is the original vector). Nimur16:12, 27 June 2007 (UTC)[reply]
Hmm, so it could be seen as the vector that would provide a means of getting from somewhere back to wherever the source of the original vector was? Xhin Give Back Our Membership! 00:21, 28 June 2007 (UTC)
hi,
why is that calling a mobile from a landline so much more expensive than calling another landline? Also, whilst phone companies (at least in the UK) are falling over themselves to make calling landlines free, the cost of calling mobiles doesnt seem to move- any ideas? (also, my informants tell me that this isn't the case in the US - why?) thanks..87.194.21.17710:47, 27 June 2007 (UTC)[reply]
Mobile phone networks are much more expensive to run than fixed line. Both need the same back-office equipment and trunk networking, but the mobile guys also need lots of cell towers and associated infrastructure, which have a per-user cost that's much higher than the cost of running a copper wire to your house. But moreover the mobile carriers paid crazy sums of money (in the UK, the US, and many other developed countries) to buy radio spectrum for 3G - an investment that they're struggling to pay back.
The cost differential between the US and the UK is a function of how cellphone billing is done. In the UK mobiles have their own area codes (077xx, etc.), while in the US cellphones are tied to regular area codes (212 for New York Cty, for example). If you call a mobile in the UK (something you can tell because of its area code) you pay more than calling a land line. In the US you can't tell you're calling a mobile, and the additional burden is paid by the mobile subscriber receiving the call. -- Synthetic element13:04, 27 June 2007 (UTC)[reply]
As to why you can get free or nearly free landlines in the UK - really, you can't. You can get free or freeish phone service if you buy broadband and TV (a "triple play") from them, with the addition of mobile phone service too (a "quad play"). They do this because voice telephony is a commoditised, low-margin, cost-plus business (so there's not much to be gained from competing hard on it) while broadband, cableTV, and mobile telephony carry bigger profits and have much more opportunity for growth - so they compete on those, and chucking in telephony doesn't cost them much. For cable TV (Virgin) telephony is pretty cheap for them to provide - they own the last-mile cable and they own or lease lots of trunk network (mostly for the broadband service) so telephony is a drop in their bucket. Much the same is true for BT. Sky Broadband is really just a DSL service on a BT line, so they're having to buy the telephony function whole from someone else (either purely from BT or BT+someone's trunk). -- Synthetic element15:21, 27 June 2007 (UTC)[reply]
Actually, according to one article I read, it's not true that "mobile phone networks are much more expensive to run than fixed line" or that they have "a per-user cost that's much higher than the cost of running a copper wire to your house". They can actually be substantially cheaper. In fact, according to this article, a lot of developing countries are skipping widespread deployment of land lines and leapfrogging straight to wireless.
Due to mass production of microelectronics, wireless phone handsets are cheap -- not much more expensive than conventional, wired telephones, these days. But stringing copper wires all over the landscape is fantastically expensive. Sure, cell phone towers cost money, too, but -- how many of them do you need?
If you're using wired lines, you need to string wires to everyone's house who wants to talk. And even if not everyone wants to sign up for phone service at first, you still have to run wires down the streets of everyone who might want to talk, because new subscribers won't be willing to pay for more than the drop from the street to their house. And this model only works for relatively densely-populated areas. Even in the U.S., it was close to 100 years after the invention of the telephone before everybody in rural areas had access to phone service, -- and there are still remote areas without it.
Using a wireless network, on the other hand, if your towers have decent range, you only have to build as many of them to take care of the number of people who are talking on the phone at a given time. At first, when you have few subscribers, you won't need very many towers. (Or even if you have kind of a lot of subscribers, but they haven't gotten into the swing of things yet, where they're gabbing on the phone or messaging each other constantly.) As your subscriber base and usage grows, you can build more towers incrementally, and only where they're needed. So it's easier and cheaper to build a wireless network incrementally, as opposed to a wired network, where nobody can talk to anybody until you first sink the huge capital expense to crisscross every populated area with wires. —Steve Summit (talk) 23:53, 27 June 2007 (UTC)[reply]
Plus, when stringing a lot of copper wire through unpopulated areas, you have to deal with people who steal and resell the copper wire on the black market. -- JSBillings14:24, 28 June 2007 (UTC)[reply]
Yeast Infection
For Candidiasis, does anyone know why or how the yeast overgrowth (or undergrowth) can be resistant to conventional over the counter treatments?
The same basic principles as all other instances of antimicrobial resistance apply. Profligate use of antifungals lead to selection of resistant strains, increasing the probability that the species causing any given infection is resistant to the most widely used treatments. If you were asking about specific mechanisms of resistance: [1] resistance to polyene antifungals involves changes in the ergosterol content of the fungal membrane; while [2] resistance to azole antifungals involve alteration of 14-demethylase, decreased intracellular drug accumulation, and loss of function of the enzyme 5,6-desaturase. - Nunh-huh22:37, 27 June 2007 (UTC)[reply]
Mars Direct
I find Mars Direct to be a very efficent way of getting to Mars, but my only problem is the Methane Rocket technology involved in the ERV. Have methane rockets been tested or is the propulsion system still too young?67.126.240.20817:59, 27 June 2007 (UTC)[reply]
Why would spot or arc welding not electrocute someone holding non-insulated metal?
I've seen this a lot, usually on the Science Channel show How It's Made. A factory worker will hold two metal parts with ungloved hands while an automated spot welder fuses the parts. The weld is performed by the two copper alloy electrodes pressing against opposite sides of the part. I've also seen a robotic arc welder repair one end of a steel I-beam, while an operator standing at the other end steadies the beam, again with ungloved hands. Then there's the spot welding performed in a dentist's office. I've read that spot welding is typically low voltage while arc welding is much higher.
But in any arc welding literature I've read, safety concerns listed are blindness and chemical toxicity, but not electrocution. You're passing current through metal, butt here's no risk of shock? So, what am I missing? Bonus question. If spot welding takes one volt, how come you can't hook two copper electrodes up to an AA battery, touch them to two intersecting metal strips, and form a weld? What's the difference? 97.82.254.21322:36, 27 June 2007 (UTC)[reply]
An arc welder is a powerful device which can supply a huge amount of energy, often high amperage and fairly low voltage. but enough power to melt ferrous metal or to make a heavy piece of steel red hot. An AA battery has internal resistance which prevent very much current from being drawn from it. It might just be able to spot weld small pieces of metal (That said, I must say don't try it, because hot things can burn you or start fires). As to why the people don't get electricuted, I will leave that to a welding expert, but I would look at the areas of grounding, of how the current would divide between the metal pieces and the person touching it (that is draw the circuit diagram), and at the voltage which the machine is putting out. That said, there are many different types of welding equipment and there are probably setups where a person could in fact get shocked. Edison23:07, 27 June 2007 (UTC)[reply]
When you're arc welding, the workpiece is grounded and the high-voltage arc is struck between the electrode and the workpiece. (Actually it's often not such a high voltage, after all, but that needn't concern us.) So the only way to get shocked would be to touch the electrode -- but you don't want to touch that, anyway.
There's lots of current flowing through the workpiece back to the place where the welding machine's ground electrode is connected, but that current would much rather flow through that nice, low-resistance metal than jump out and shock you.
Basically, you get shocked when some part of your body bridges between two spots that are at different voltages. Usually, one spot is at 0 volts ("ground"), and one spot is at some other voltage. Most of the world is grounded, and most much of the time, you are, too, so most of the time, touching anything that's at a voltage significantly different from 0 will give you a shock. But if you touch something that's at a voltage of 0, you don't get a shock, even if that something is carrying lots of electric current.
The story is slightly different for spot welders. They use very high currents (at low voltages), and the current is injected very close to the point that it's collected. Away from that spot, there's very little current flowing at all. (And at any rate, the voltage is too low to shock you anyway.)
Finally, as Edison already explained, an AA battery is simply incapable of supplying enough current/power/energy to do any spot welding. You need hundreds or thousands of amps to make a spot weld, while I think an AA battery is capable of supplying mere milliamps. —Steve Summit (talk) 23:23, 27 June 2007 (UTC)[reply]
A AA alkaline battery can put out several amps, and I think it might be able to cause a very thin piece of iron wire to weld to another.Don't try this, because the battery might explode. Edison03:43, 28 June 2007 (UTC)[reply]
I said "most of the time, you're grounded", but that was a little too strong. If you've wearing a pair of robber-soled shoes, and not touching anything, you're effectively insulated from ground, up to a potential of a couple of hundred volts. (That is, you could probably touch a 120V wire and not get shocked. But if you tried to touch a 1000V wire, the voltage would be high enough that it would probably punch through your shoes and electrocute you.)
This is significant because there are sort of two different ways to get electrocuted. One is to be grounded and to touch a live wire, but the other way is to be in contact with a live wire, and then touch something that's grounded.
If I were wearing a pair of rubber-soled shoes, and holding a bare, live, 120V wire in my hand, I would not get a shock. My body would be raised to a potential of 120 volts, but there would be no place for the current to flow. But then, if I reached out and touched a metal water pipe with my other hand, then I'd get a nasty (potentially fatal) shock. Or if you walked up, barefoot, and touched me, we'd both get a shock. (From my point of view, I'm in contact with a live wire but ungrounded until I touch you. From your point of view, you're grounded, and touching me is like touching a live wire. Now cue Psycho Killer by Talking Heads: "Don't touch me, I'm a real live wire.") —Steve Summit (talk) 23:35, 27 June 2007 (UTC)[reply]
Whoah, careful! You mean, I take it, a 120V direct current source. Many American houses have 120V 60-cycle alternating current; that'll give you a nasty shock even in your rubber boots. The reason is that your body has significant capacitance -- the current will flow into you from the wire and then back out into the wire, over and over again, and it doesn't need an outlet on the other side. --Trovatore00:38, 28 June 2007 (UTC)[reply]
Hmm, how sure are you? (I do know about capacitance, and AC current may flow into and out of you and give you a nasty shock, but I can assure you -- true OR confession here -- it doesn't do that to me!) —Steve Summit (talk) 00:43, 28 June 2007 (UTC)[reply]
Well, I suppose I'm not terribly sure. I have gotten shocked; I don't really recall exactly what I was wearing on my feet. But I don't plan to experiment. --Trovatore01:11, 28 June 2007 (UTC)[reply]
I turn off the circuit breaker before I touch a line-wire; even then, I only touch one wire at a time in case of residual capacitance or unexpected voltage. I think it's a bad idea to touch an live AC line even if you are wearing thick rubber boots. Nimur01:21, 28 June 2007 (UTC)[reply]
If you want to work on dead electric wires safely, the most important thing is to make sure they're dead. This sounds like a tautology, but the sad truth is that many people are killed by touching wires that they only thought were dead.
Neon test lamp Get yourself a neon test lamp (right), and use it religiously. Also, unless you're working in a single-family residence where you can be sure that you're the only one who'll be messing around with the fusebox, put a note right on the fuse/breaker. The last thing you want is for some enterprising person to wonder why the lights are out, and to find the right breaker and "helpfully" turn it back on, just when you're grabbing the wire. (Professional electricians in industrial settings don't just use notes for this purpose, they use padlocks.) —Steve Summit (talk) 11:36, 29 June 2007 (UTC)[reply]
Yeah, I got shocked by sticking my finger into a US 120V electrical outlet when I was 6 years old (on a dare, I'm not stupid or anything.. *ahem*) and I had thick rubber-soled shoes on. I assumed the shock was possible because my fingernail was touching the conductor while another part of my finger was touching the wall plate. Wow. I didn't expect so many answers on this. The welding-related ones do make sense. Sorta. I understand what you're saying, but the idea that 500A could be dumped into a girder, and I could hold barehanded onto that girder a few feet away and live just seems bizarre. It's like an electrolysis setup. Current flows all over, but some does get to each point. I'd figure at the least, there'd be enough current to give you a shock.
Think about it this way: instead of contemplating whether there's enough current to give you a shock, ask whether there's enough voltage.
Whether that steel girder is carrying 1 amp, or 10 or 100 or 1000, or 0 -- as long as its potential with respect to ground is zero volts, no current is going to flow from it to another grounded object, i.e. you. And if the resistance of the girder is low enough that the voltage drop induced by the current it's carrying is near 0, then if one point of the girder is at ground potential, all of it will be. —Steve Summit (talk) 04:49, 29 June 2007 (UTC)[reply]
While we're on the subject, is there a law or rule that specifies what combinations of amperage/voltage are possible? If a static electricity shock can be thousands of volts, but has little amperage, is the opposite also true? That spot welding description would seem to say so. Can you really have a 1V source that, when touched, could dump 1kA and turn you to crispy human bacon? I posted a question about that before. Specifically, I can't fathom why two revisions of the same consumer product would have vastly different power requirements (12v 500mA vs. 6v 2000mA). 97.82.254.21304:41, 28 June 2007 (UTC)[reply]
Any combination of current (amperage) and voltage is possible. The most obvious everyday examples:
Low current, low voltage: most electronics
Low current, high voltage: static shock
High current, low voltage: car starter
High current, high voltage: lightning
Starters draw up to about 1,000 amperes and are typically powered at 12 V. A higher voltage would be more convenient (lighter-weight wiring could be used), but the power source is a battery and that produces low voltage. In fact, 6 V was quite common a few decades ago. --Anonymous, June 28, 2007, 07:06 (UTC).
Well guys you are right and you are wrong. How could that be? OK, there are situations where for whatever critical reasons the maintenance or repair have to be done on live electrical equipment, and sometimes at much, much higher voltages than 120V. In these situations maintenance crew will use special (!) safety (!) equipment; rubber boots, rubber gloves and special mats and platforms, not to mention strict procedures and compulsory presence of a co-worker during the procedure. All this is exactly for the reason you mention, to isolate the person from the ground or earth potential so the current that develops through the serviceman body and the protective equipment is so insignificant that the person can work safely.
Where you go wrong is assuming that wearing any (!) rubber boots will always (!) protect you. At 120V, it may or may not, and the fact that it protected you once does not really mean it will maintain the protection the next time. Electrical safety equipment is made from special (!) rubber like materials, using special design and manufacturing processes, and for that reason it is usually quite expensive. The fact that something is made of rubber or plastic does not automatically mean it is electrically safe! Dielectric properties of such materials vary significantly, though they may look alike. On top of that, all electrical safety equipment is subjected to strict safety tests, is rated at specific maximum voltage it will provide the protection and is given an attest; you may see that electrician’s screwdrivers or cutters, or the multimeters are all marked accordingly, usually 1000V. Further more the equipment is subject to regular maintenance and tests regime during its service life to ensure that its protective ability did not deteriorate over the time or due to accidental damage.
The rubber boots you buy at you local hardware shop are not intended for that purpose. They may possibly protect you at 120V when new and dry but I would not dare to test their ability at any voltage. With time and wear the insulating properties will change significantly. The thickness of the sole will reduce, micro-cracks will develop and moisture from perspiration will accumulate; all this will reduce significantly its protective ability and suddenly the current will find its way to the earth exactly the same way as lightning finds its way from a cloud to the earth; you may be unpleasantly surprised if not harmed. So here is where you go wrong.
I too think, it is a bad idea to touch a live AC line even if you are wearing thick rubber boots, and I am saying this from my past experience. To ensure safety more than that is needed. It is not that I am in any way giving you support but if you ever consider, for whatever reason, to do such an exercise ensure that you have someone responsible with you at all times. Such a person must know where and how to isolate quickly the right circuit and what to do should the unthinkable happened, and without exposing any one to further danger. Live wires are dangerous and there are good reasons for all the warnings.
And, on the other issues mentioned earlier;
Generally, international standards quote the “Extra Low Voltage” limits as being 120V for DC and 50V for AC (mind you the 50V is RMS value). Voltages below and up to the above limits are generaly considered safe to touch under normal conditions!!! (You do not stand barefoot on a wet floor in the bathroom or in the rain; you do not have cuts to you fleshy tissue where you touch the wire, etc. under such abnormal conditions you can be assured you won’t be safe). These limits are summary of statistical tests and the limits may be slightly different in various standards or countries..
Typically human body under normal dry conditions have adequate resistance (primarily due to the dry skin which acts to our fleshy tissue like an insulation on a wire) so the current that develops through you body when you touch voltages below the above limit is so insignificant that it won’t affect you.
Safety standards further quote current limits for what is known as “Threshold of Perception” (lowest current which causes any sensation to a person through which it passes). These are 0.5mA for AC and 2 mA DC. Further more there is another yet limit called “Threshold of “let-go” (highest current at which a person holding electrodes can let go of the electrodes). These are about 10 mA for AC and approximately 300 mA for DC.
These figures are based on statistical data and are not absolute limits. Different people will respond differently under different circumstance, and there are many factors that affect this. So, one must be knowledgeable to interpret them. I have quoted them here to give you some understanding while you can safely touch the car battery or welding equipment, but should not touch the mains at 120V AC.
With the AA battery, yes it will give you a spark, but it will be so minute that you will be lucky to spot it in a dark room. It acts the same way as the arc welder. It simply does not have ability to maintain the current long enough; it wasn’t designed for that purpose. You will probably have more luck with a car battery. Remember however, such experiment is likely to damage the battery due to long term rapid discharge, especially repeated; again this battery was not intended to be subjected to such a torture. And one more, never ever leave a battery short circuited, even the AA. It will overheat due to excessive short circuit current and may explode!!!
And final one; the body capacitance is really of no consequence at 50 or 60 Hz and the theory expressed there appears to be confused.
Um, I wasn't confused, just (apparently) wrong. I hadn't done the actual calculations (and still haven't, but assuming the ones given here are correct then) that wasn't the reason I got the shock. But it could have been, in principle. --Trovatore06:32, 29 June 2007 (UTC)[reply]
According to [26] the capacitance of the human body is 60 to 300 picofarads. Static electricity to as much as 15,000 volts can be stored in this capacitance just by walking across a carpet on a dry day. The electrostatic discharge when you then touch a grounded object or a metal pobject at a lower potential can amount to "tens of millijoules" of power, with a peak current of 7.5 amps and a peak power of kilowatts. An IEEE paper[27] gives 100-150 picofarad as the measured human body capacitance tested with an AC bridge and higher for static electricity, 200-400 picofarads. These amounts of capacitance, with 120 volt electricity at 60 Hertz would produce a very small amount of capacitive current, so the hazard would be conduction from the source of electricity through the body, to a grounded object or another conductor. Capacitive current would be (voltage)*2 π*frequency*capacitance. Now to calculate the current for 120 volts, 60 hertz and for 240 volts 50 hertz, since these are found in most residences of the world (remember this is capacitive current only, and the electrical conduction is a great hazard beside this).
120 volts, 60 Hz, capacitive current for a 300 picofarad person= 14 microamperes
240 volts, 50 Hertz, capacitive current for a 300 picofarad person= 23 microamperes.
(This is presented for discussion only and is not to be relied on for any safety related matters such as doing electrical wiring or experimentation. Do not try the experiment because any inadvertent contact with a grounded object or conductor could be fatal while in contact with something electrified). Edison15:56, 28 June 2007 (UTC)[reply]
I've been zapped when I tried to do TIG welding without wearing a glove. The voltage is somewhere below 110, so you live, but you remember to wear a glove.
You can't get zapped from just one pole of the AC line, body capacitance or not. Both theoretically, and practically. In my stupid youth I had occasion to work on the electrical system of apartments where I didn't have access to the circuit breakers, involving occasional skin contact with one side of the line, and nothing happened.
There are websites which describe how to weld with car batteries.
There was a case years back where an electrical lineman was electrocuted, despite wearing insulating gloves. Turned out a nearly invisible pinhole in the glove was directly over his wedding ring, and when he grabbed the conductor with that glove so that the hole was proximate, that was it.
Let me clarify, I don't want to try welding with a battery or car starter. That was just a hypothetical example given for comparison. BrightSpark's answer was very informative, but one point given confused me. Specifically, the section about the “Threshold of “let-go”. If the let-go threshold for DC is 300mA, does that mean if one were to clip the plug off a puny 3.5V 500mA AC power adapter adapter (or any standard wall wart), strip the wires and grab them, they wouldn't be able to release? Similarly, the anonymous post before BrightSpark said "Starters draw up to about 1,000 amperes and are typically powered at 12 V" Does that also mean that if one were to grab those leads, the car starter would instantly kill them?
I'll break in here to answer that point. If you broke open the starter circuit while the starter was in operation, you might get an impressive arc, but once the gap was opened wide enough, the arc would stop and then there would be zero current flowing. If you then "grabbed the leads" and put yourself in the place of the starter, which I think is what you mean, that would be a different circuit with a much large resistance in it, namely your body. The current that would now flow would be determined by the 12 volts and the resistance of the skin contact and your body in that configuration (plus the internal resistance of the battery, and the restistance of the wiring, but those are both too small to matter). In a worst case it might still be enough to hurt or kill you; this I can't say. But I can say it would be just about 1/10 of the amount of current you'd get if you grabbed two leads that were live with a 120 V household power supply, so the chance of it being lethal would be less. --Anonymous, June 28, 2007, edited 23:50 (UTC).
To the other two points:
You can certainly weld with a car battery. A few years ago, some friends of mine built a go-kart powered by car batteries and starter motors. The fancy high-current solid-state motor controller they'd bought, the one whose specs said it could theoretically handle the currents involved, fried the very first time they used it. So they were reduced to using a little accelerator-pedal-like strip of metal which you pressed with your foot to complete the circuit. Trouble was, it tended to weld itself in place, so while you were zipping around in this thing, trying to not steer into trees or telephone poles or anything, you'd be madly trying to pry the "accelerator pedal" back up with the side of your foot...
A "puny 3.5V 500mA AC power adapter adapter" can supply a maximum of 500 mA. It's not some magical device that shoves 500mA through anything it touches. (Though there are constant-current supplies which try to do this; more on them later.) —Steve Summit (talk) 04:43, 29 June 2007 (UTC)[reply]
I've seen conflicting posts that state the threshold for death is 2A, or around 60mA (I think. Could have been 600mA) across the heart. The former was on Wikipedia, and the latter was on the TV show Mythbusters. Anyway, the arc welding and rubber boots explanations make sense now, though it is a difficult concept for me to wrap my brain around. I do a lot of work with electronics, and always try to make safety a priority. But these simple parts of EE theory always manage to elude my understanding. For example, If I were designing a DC electrical device, and assuming the components could handle it, what would be the difference in supplying 6VDC @ 200mA or 12VDC @ 100mA? Isn't the output identical? As another example, what would happen if a consumer electronic device came with a 12VDC 1250 mA AC adapter, but it was swapped with, say, a 30V 500mA AC adapter? Isn't the output also identical? If not, that's what I just don't get; that there's more than one way to accomplish the same output, but those other ways fail. I know there's a way I can understand this. As I said before, I'm definitely not stupid. Hell, I once quit Mensa. :) 97.82.254.21321:52, 28 June 2007 (UTC)[reply]
If you think that 12 volts at 1250 mA should be the same as 30V at 500mA, ask yourself this: if the recipe says to bake for 30 minutes in a 350 degree oven, does that mean you could also cook it for 350 minutes in a 30 degree oven? (This isn't an exact analogy, but it has the same, er, flavor.) —Steve Summit (talk) 01:10, 29 June 2007 (UTC)[reply]
The "3.5V 500mA" rating means that it will provide a nominal voltage of 3.5 volts, and a maximum of 500 milliamps. To determine the actual current, you divide the voltage by the resistance of the load across the terminals. Since intact human skin has a fairly high resistance, the actual current flowing will be under a milliamp.
If, on the other hand, you were to connect a one-ohm resistor across the terminals of the power supply, it would try to provide 3500 milliamps, overheat, and catch fire. --Carnildo22:58, 28 June 2007 (UTC)[reply]
As I recall, the lethal current directly through the heart muscle is down in the tens or low hundreds of milliamps. And for this reason, pedants are find of saying, "It's not the voltage that kills you, it's the current." But this is a terribly misleading statement. The implication is that a 1 milliamp power supply wouldn't kill you, but that a 1 amp supply would. But you very rarely find true 1 milliamp or 1 amp power supplies. So what we need to understand is why a 12 volt battery almost certainly won't kill you, and a 120V wall socket might, and a 1000 volt power line almost certainly will.
Let's suppose that the resistance across your body is 1000 ohms. (I think that's about right, if you overcome the higher resistance of normally dry skin. Perhaps your hands are wet, or you're applying the electrodes to open wounds.) Suppose further that if you pass a current from one hand to the other, across your chest, one tenth of the current flows through your heart, and the other nine tenths flow through other parts of your chest. (This is a number I just made up; I have no idea what the real current distribution through your chest might be. But this is just a thought experiment; we're not going to try this or anything; we're just getting a rough feel for what the numbers might look like, to mix a metaphor.)
Suppose you touch the two posts of a 12V car battery, one with each hand. Ohm's law says that a current of 12V ÷ 1000Ω flows, or 12 milliamps. If one tenth flows through your heart, that's 1.2 milliamps. Not enough to kill you.
Suppose you put yourself across 120V. Now the current is 120V ÷ 1000Ω, or 120 milliamps. A tenth of that is 12 milliamps, and we're definitely in the danger zone.
Now suppose the voltage is 1000 volts, or one kilovolt. The total current is 1000V ÷ 1000Ω = 1 amp, and a tenth of that is 100 milliamps, and you're probably dead. —Steve Summit (talk) 04:43, 29 June 2007 (UTC)[reply]
P.S. A 500 milliamp power supply that's trying to source 3.5 amps will "overheat and catch fire" only if it's poorly made. Most power supplies limit their output current to their safe limit somehow (perhaps with a fuse), since short circuits are so easy to accidentally complete.
Sounds like you need to consider the difference between voltage and current. The total power might be the same, but a small amount of flow with a lot of force behind it is quite different from a large flow with very little force. Sometimes it's better to be shot by a BB gun vs caught in a car crusher, however, a water jet cutter can cut stone but Hoover Dam is just a giant stone holding up a lake. DMacks22:38, 28 June 2007 (UTC)[reply]
There's one more point that's worth making, although we've drifted pretty far afield from the original question about arc and spot welders.
Some of you may be wondering, why is there this asymmetry between voltage and current when it comes to power supplies? Why does a five volt, 1 amp power supply always try to give exactly five volts, but is perfectly happy delivering any current less than 1 amp?
The answer is that we're talking about constant-voltage power supplies, which are by far the most popular kind. But there is such a thing as a constant-current power supply, and for those, the situation is exactly reversed. The supply will do whatever it takes to make sure that the desired current flows, regardless of the resistance of the load. The higher the resistance of the load, the higher the supply's output voltage goes. But constant-current supplies have a maximum voltage they're capable of delivering. If the output resistance goes so high that it would take more voltage than the rated maximum to induce the requested current, the supply ends up breaking its promise, and supplying less current than requested. —Steve Summit (talk) 04:58, 29 June 2007 (UTC)[reply]
From the information I can find on the different species on Wikipedia - they are all pink (subject to diet and age), but the Andean Flamingo has yellow legs. DuncanHill00:33, 28 June 2007 (UTC)[reply]
In zoos you'll often see whitish flamingos, since artificial dyes turning them pink are costly. Normally the dye is made from carrot oil and a substance derived from shrimp skins. bibliomaniac15BUY NOW!02:45, 28 June 2007 (UTC)[reply]
OK, so the explanation for the color of flamingos has to do with their diet...I suppose, similar to why salmon are colored the way they are? --HappyCamper04:48, 28 June 2007 (UTC)[reply]
In a zoo in Hungary they feed the flamingos with paprika to keep them pink because they can't afford shrimp. They looked fairly white to me though. —Pengo16:20, 28 June 2007 (UTC)[reply]
Bird first aid
I have a cat and occasionally need to rescue birds or mice that she has caught and brought into the apartment. I want to do something to help the injured ones before releasing them back outdoors, but at the same time, I don't really want to do more than the minimum. I have an injured bird in a cage (actually a hamster carrier) and intend to release it as soon as it seems able to fly. Any suggestions on simple (i.e. inexpensive) things that might help a convalescing bird? Peter Grey05:01, 28 June 2007 (UTC)[reply]
There is some advice from the RSPB here, but its prospects of returning successfully to the wild are not good and if you can reduce or prevent injuries, for example by putting a bell on the cat, the birds will fare much better.--Shantavira|feed me08:07, 28 June 2007 (UTC)[reply]
I mis-read your userpage, you are in Ontario. The Ontario Society for the Prevention of Cruelty to Animals has some factsheets, see Guidelines for helping wildlife
Clicks on a link are AFAIK much less rivalrous than cash.
Even if and once nobody was going to click any more recruit links ever, the game could still be succeeded at by the newer players. Although the players who had gotten the clicks would have a substantial advantage, this is probably true in most MMOGs anyway for the established players versus the new ones.
Can anyone tell me when is the production of FGF in the body increase, ie other words, under what conditions? Also, where is FGF produced. Thanks for helping me out.
hi,
For a long time I have bitten my finger nails excessively to the stage where now, the distance from my cuticles to the end of my nail doesnt reach the end of my finger, not even close. its pretty ugly. anyway, i'm trying to give up but have a niggling question. On perfect nails, the red bit (apologies for not knowing any medical terms) extends to the end of the finger and the "over hanging" nail is white. Now, on my nails when i allow the nail to grow it is also that white colour, but as my nails grow longer, will the red bit grow longer as well? or will i end up with ridiculous looking nails where the nail is normal length but half of it is white as opposed to just the end bit like most people. if this is the case, is there any, um, corrective surgery? basically, i want non-repulsive nails, how can i best acheive this. thanks! 130.88.243.22714:29, 28 June 2007 (UTC)[reply]
The line between red and white on your nail is governed entirely by where your nail loses contact with the flesh below. For instance, after some injury that pulls the flesh and nail apart (thus turning red bit into white bit) the nail color will go back to normal not long after flesh and nail are back together. Even when an entire nail needs to be removed, it grows back normal. So I would expect your nails to eventually look perfectly normal once they grow back out. — Laura Scudder☎21:35, 28 June 2007 (UTC)[reply]
I wouldn't be so sure, after years and years of nail biting, the bit that used to be red would now be completely healed over, your nails may not go back to normal, or it may take a long time before they do, at any rate, having a slightly longer white bit then other people doesn't make you a freak. if you've stopped biting your nails, then they will get better, if you keep biting your nails they can only get worse.Vespine00:07, 29 June 2007 (UTC)[reply]
toxic/ heavy metals
I need the introduction of toxic/ heavy metals.
Also i need the literature on method of separation toxic/ heavy metals by liquid membranes.
A lot of the 'toxic heavy metals' are found in computers, so here's a good place to start. Just click on each of the elements, see if they are heavy metals, and read about the ones that are. I was shocked to learn that about 90% of an old-style CRT monitor's weight is comprised of lead. Yuck!Vranak
The lead shielding was there to protect you from the radiation generated by the elecron gun/beam. So it's a good thing. Lead's also beneficial for optical quality--they use a small amount in eyeglasses.[31] — RJH (talk) 22:44, 28 June 2007 (UTC)[reply]
Einstein's Concept of relativity....
Hai Master minds.... I have a doubt in Einstien's Concept of relativity.I find that in my textbook,Under the heading Non Inertial FramesI find the following wordings
"A frame of reference is said to be a non inertial frame,when a body not acted upon by an external force,is accelerated".
Is this correct,and how can a body be accelerated without an external force?
It means accelerated relative to the frame. So for example, in a car turning a corner, you feel pushed outwards. There is no force pushing you, but in the frame of the car you are being accelerated (i.e. if the car could see it would see you being accelerated and not know why.) Therefore a rotating frame (the turning car) is non-inertial. An accelerating frame (i.e. one not moving in a constant speed and direction) is non-inertial. This outwards 'force' you feel is called centrifugal force and is often said not to exist, or to be virtual, as it results not from a real force but from the movement of the car, and is only seen from the car's point of view. Hope that helps. Cyta16:58, 28 June 2007 (UTC)[reply]
Yeah, like he/she said. You seem to have the correct instinct, i.e. that in a normal well-behaved frame of reference that can't happen; a non-inertial frame has to be funky is some way. Typically, it's because the frame of reference is being accelerated, like being rotated, or falling down a gravitational field. You can see how from the point of view of whoever is being accelerated, an object that is just sitting there looks like it's being accelerated the other direction. Gzuckier17:47, 28 June 2007 (UTC)[reply]
Bohr Model
I'm wondering how the Bohr Model of the atom explains the reactivity of the alkali metals. I have already read the article on bohr model and alkali metals.
Is it something to do with the electrons?
Thanks 217.41.217.2416:53, 28 June 2007 (UTC)[reply]
Yes chemistry is all to do with electrons! Basically atoms are stable with a full shell of electrons, the alkali metals need only lose one electron to get a full shell, so they are very reactive. There reactivity increases as you go down the group as the electron you lose is further from the positive nucleus attracting it, which is also shielded by the electrons in between. This makes it easier for the outer electron to be lost. That's obviously a very basic description, but it should explain the main features. The reactvity can be explained using this shell picture, but strictly speaking the Bohr model is a mathematical model referring to hydrogen. It is also requires a full quantum mechanical model to make any numerical predictions about reactivity (quantum chemistry might cover this.) Cyta17:03, 28 June 2007 (UTC)[reply]
Our solar system.
Does our solar system have a name of its own, other than "our solar system"?
We already call them "The XXX system" where 'XXX' is the name of the star. So, if we found planets orbiting Alpha Centauri, we'd talk about "The Alpha Centauri System". SteveBaker21:04, 28 June 2007 (UTC)[reply]
Science fiction frequently uses Earth and Terra for our planet, and Sol for our sun; and hence "Solar" would probably refer to the system around Sol (presumably other star systems are not "solar systems" at all). However, since these are fictional works, there is significant room for artistic license. Nimur18:07, 28 June 2007 (UTC)[reply]
I suspect the reason SciFi uses "Terra" is because the name of the people who live here can be "Terrans" - which is much nicer than "Earthlings" which somehow makes us sound small and weak (like "Ducklings" or something!). The word "Sol" is widely used outside of SciFi - go to NASA's Mars rover web site for example - they talk about "Sols" - meaning one solar day on Mars. To complete the set - we now often call our moon "Luna" to distinguish it from other moons. This is a good way to think about things because if we ever do end up living on a planet orbiting another star, we're going to want to talk about "Sunshine" and "Sunrise" and not have to get into messes like "AlphaCentaurishine" or "Starshine". I doubt that people living on mars will talk about burying things in "regolith" - they'll still say "earth" (lowercase) as a synonym for "soil". I suspect that wherever humans live we'll end up talking about "The Sun" and "The Moon" as being the ones in the sky of wherever we live. But it's hard to guess what might happen that far into the future. SteveBaker21:04, 28 June 2007 (UTC)[reply]
Maybe in the centuries it will take to perfect interplanetary / interstellar spaceflight, we'll make progress towards a universal language that makes sense. I've been a little disappointed with the effortssofar. Nimur05:23, 29 June 2007 (UTC)[reply]
The our in our solar system is redundant. We call the nearest star as Sun (or Sol). Solar system refers to the planetary system around Sun. The planetary systems around other stars wouldn't be called solar systems. I agree with SteveBaker ("the XXX system") -- WikiCheng | Talk05:10, 29 June 2007 (UTC)[reply]
Twin paradox
this is a spesific example of the twin paradox...
Specific example
Consider a space ship travelling from Earth to the nearest star system: a distance d = 4.45 light years away, at a speed v = 0.866c (i.e., 86.6% of the speed of light). The round trip will take t = 2d / v = 10.28 years in Earth time (i.e. everybody on earth will be 10.28 years older when the ship returns). Those on Earth predict the aging of the travellers during their trip will be reduced by the factor \epsilon = \sqrt{1 - v^2/c^2}, the reciprocal of the Lorentz factor. In this case ε = 0.5 and they expect the travelers to be 0.5×10.28 = 5.14 years older when they return.
The ship's crew members also calculate how long the trip will take them. They know that the distant star system and the earth are moving relative to the ship at speed v during the trip, and in their rest frame the distance between the earth and the star system is εd = 0.5d = 2.23 light years ("length contraction"), for both the outward and return journeys. Each half of the journey takes 2.23 / v = 2.57 years, and the round trip takes 2×2.57 = 5.14 years. Their calculations show that they will arrive home having aged 5.14 years, in complete agreement with the calculations of those on Earth.
If a pair of twins were born on the day the ship left, and one went on the journey while the other stayed on earth, the twins will meet again when the traveller is 5.14 years old and the stay-at-home twin is 10.28 years old. This outcome is predicted by Einstein's special theory of relativity. It is a consequence of the experimentally verified phenomenon of time dilation, in which a moving clock is found to experience a reduced amount of proper time as determined by clocks synchronized with a stationary clock. Examples of the experimental evidence can be found at Experimental Confirmation of Time dilation.
My question is, wouldn't the people in the spaceship age twice as fast as the people on earth if one looked at the relative roles in reverse?(say that earth is moving at .866E and that the ship is stationary)
Im just curious as to why this situation cannot have reversed motion/benchmarks like other ones can./ cant the same thing apply to the people on earth making them age 10 years and those on the spaceship 5?
It could be reversed if everyone was initially on the ship and then some hopped out and got on the Earth and then the Earth fired rocket blasters and accelerated off into space and returned 10 years later. The problem you are having is that you feel it is fine to jump from one point of reference to another. That makes it difficult. Instead, simply ask - which object has energy added to it? The ship is the one with the added energy for acceleration. The Earth stays the same. So, the ship is the one in which time slows down. -- Kainaw(what?)19:34, 28 June 2007 (UTC)[reply]
Special relativity talks about how the world behaves as seen from an inertial reference frame, i.e., one that doesn accelerate. We can do calculations with quantities (lengths and times) as measured from Earth since it is not accelerating (not very much at least). The spaceship, on the other hand, has to accelerate to get up to speed, turn around at the destination and slow down when it comes back. The formulas of special relativity can therefore not be expected to yield correct results, which is the reason we cannot simply swap the roles. —Bromskloss19:41, 28 June 2007 (UTC)[reply]
Both are properties of chemical elements? Both are numbers? There are patterns to each, but no easy relationship or trend between these two properties. See our article about the Periodic table to learn about trends of various properties, and the atomic radius and List of elements by melting point for actual numbers to look for anything of interest. DMacks22:43, 28 June 2007 (UTC)[reply]
But why for the alkali metals does the melting point decrease as the atomic radius increases?
I'm making a guess here and assuming someone credible has stated to you that there IS a relationship. With a large atomic radius, the electrons in the outermost shell are less strongly bound to the atom. This may mean covalent bonds between atoms are more easily broken up, lowering the melting point. But this is just a guess EverGreg08:37, 29 June 2007 (UTC)[reply]
Audubon copyrights
Are images of Audobon birds and animals now in the public domain since they are so old? Or has the Audobon family kept up with the copyright and owns all the images? I want to use a few audobon images in my artwork, but want to make sure its legal. thanks for your help with this.
This is a legal question, which we're not supposed to answer. I will anyway; use this information at your own risk. John James Audubon died in 1851 and that means the copyright in the U.S. on any work he did in the U.S. has expired long ago. Other countries have their own rules but I haven't heard of any ordinary copyrights lasting that long.
By the way, please include a title so your questions are separated from the one before. I've added one for you. --Anonymous, June 29, 2007, 00:00 (UTC).
Hello, I own one of those plasma bulb things, (you know what I'm talking about) and I noticed a really strange effect with it that doesn't make sense to me. If you turn on a plasma bulb and put something on it that can conduct electricity (metal works best) anything that touches the metal and can also conduct electricity has a static shock/charge with the metal. I was wondering if whether the electrons in the plasma bulb flow through the metal and jump to another object or if the plasma bulb negatively/positively charges the metal and it creates a charge similar to that of Lightning but on a much much smaller scale. Thanks for your time!- User:ECH3LON
hydrometallurgy in situ leaching
Eskall02:19, 29 June 2007 (UTC)What are the environmental or other hazards or risks, e.g. health and safety, associated with in situ leaching in mining operations?[reply]
Largest cow
Which is the biggest cow and cow race in the world? In terms of height, length, mass... I'm aware about the massive Piedmontese and Belgian Blue but was wondering if others were even larger though less muscular. --Taraborn06:50, 29 June 2007 (UTC)[reply]
I have heard a saying that goes something like this: if a butterfly flaps its wings in Mexico, that creates a hurricane in Japan (or something like that). Is there any truth to that, or is it an old wives tale / urban legend? If it is true, can you please explain the science behind it (in elementary terms). If it is not true, what is the origination of that saying and why does it persist? Or is it just a metaphor for something else? If so, what? Thanks. (JosephASpadaro07:37, 29 June 2007 (UTC))[reply]
What you are referring to is the so-called butterfly effect. It is an expression which should by no means be taken literally, but the story is that the atmosphere is such a complex fluid environment that something as minor as the flap of a butterfly could determine (some time later, mind you) whether or not a major storm system will develop. This phenomenon is known as chaos, or extreme sensitivity to initial conditions, first discovered by meteorologist Edward Lorenz in the 1960s. In a nutshell (sorry if I use too much math language), some systems (such as the earth's atmosphere) are governed by non-linear differential equations. In an ideal mathematical situation, where you know the conditions at all points in a situation, it is possible to predict its future behavior accurately. However, since the supercomputers which simulate the weather take data from weather stations which are spread far apart, they must estimate the conditions between weather stations, and so do not know the exact conditions of the earth's atmosphere. Because the atmosphere is chaotic, the small difference between the actual atmosphere and the computer simulation compound to become large differences as the simulation wears on, making even rough weather prediction more than 10-14 days in advance practically impossible. One estimate is that even if we had weather monitoring stations every 1 meter in all directions, feeding data simultaneously into an infinitely powerful supercomputer, that computer could still not predict the weather with any certainty 30 days later. Hope I've helped, feel free to ask for clarifications! -RunningOnBrains07:50, 29 June 2007 (UTC)[reply]
We have an article on the Butterfly effect which covers this, but it may be somewhat too technical. In short, for a complex, non-linear system like the weather, a very small change (a butterfly flapping its wings) may be magnified over time to a huge effect (a hurricane). --Bob Mellish07:48, 29 June 2007 (UTC)[reply]
One way of thinking about chaos is to imagine a steep hill that comes to a ball precariously balanced at the very top. The slightest difference in the way you touch it will send it on its way downhill to a much different destination. So too with a butterfly's wings and the hurricane. Is it likely? No. Is it possible? Yes. Clarityfiend08:19, 29 June 2007 (UTC)[reply]
I think we can say it's literally true that a butterfly flap may influence when and where a future hurricane or tornado starts and where it's heading. This takes into account conservation of energy. There's a whole lot of energy in a hurricane and that energy would have had to go somewhere, regardless of the butterfly flapping or not. EverGreg08:31, 29 June 2007 (UTC)[reply]
My understanding of it is that every major event is underpinned by so many seemingly unconnected albeit equally prerequisite minor events that there is no way of determining what they all are as an exact science, hence chaos theory. Some may wonder whether if Franz Ferdinand had been shot, would there ever have been two world wars at all, but think of all the minutest changes in events preceeding that day in 1914 that may have spared his life and changed the course of the twentieth century. A butterfly perching on his shoulder, distracting him enough to move his jugular out of the bullet's trajectory perhaps? Bendž|Ť08:45, 29 June 2007 (UTC)[reply]
Well that's a more philosophical approach, I think Bendzh, and many would argue the long term causes of war would have been sparked by some other incident. But the real point is the mathematical one, that small changes in initial conditions lead to large changes in outcome. One problem is that the relation between accuracy of input (i.e. measurement of initial conditions) and accuracy of prediction are logarithmically linked. Which basically means (roughly) that increasing your accuracy of input by a factor 10, may only improve your predicition by a factor 2, increasing it by a factor 100 might only improve your prediction by a factor 3. We'll never know if an individual hurricane was caused by a butterfly Rather like global warming, although the tendency is to blame every bit of extreme weather on climate change, all we can really see are long term trends. 137.138.46.15511:42, 29 June 2007 (UTC)[reply]
The Flight of the Bumblebee
When I was younger, I was told that aerodynamically speaking, a bumblebee should (theoretically) be unable to fly (due to some physics principles and the anatomy of the bee). Yet, bumblebees do in fact fly. Is there any truth to the statement that theoretically their anatomy should render flight impossible? Or is this an old wives tale / urban legend? If the statement is theoretically true, have scientists reconciled that with the reality that the bees do fly? How so? Please keep the science / physics explanations at an elementary level. Thanks. (JosephASpadaro07:37, 29 June 2007 (UTC))[reply]
