The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
I'm curious. If it doesn't, I imagine there's some future genetic engineering in the works that will be the delight of young people everywhere, and I imagine it could be very lucrative for street hustlers with biotech qualifications. John Riemann Soong (talk) 02:55, 22 May 2009 (UTC)[reply]
The large leaves have little THC content but still have the herb smell, so I'd say no, the smell is due to other chemical compounds. Of course, that's only what I've heard through my church group, I never touch the stuff. :) One of the attractions of cannabis is that it is a natural plant product that springs from the earth all by itself and delivers a gift of nature - I'm not so sure there is a big market for GMO's in that space. There are already lots of synthetic chemical products to whack your head with if you're so inclined. (I'm not) Franamax (talk) 08:19, 22 May 2009 (UTC)[reply]
THC is not the only compound in weed that gets you high. Many psychopharmocological studies use pure THC in place of cannabis in order to study the effects of the drug, but they lack a certain amount of validity (as the researchers are the first to admit) due to only being about THC, not the cocktail of other compounds that make up herbal cannabis. —Preceding unsigned comment added by 158.223.34.22 (talk) 17:14, 29 May 2009 (UTC)[reply]
If you're thinking of sniffing dogs, I would imagine expect they could be trained to smell THC if they're not already. In any case, removing every single compound likely to be detected by humans is an extremely difficult task. In other words, you could change the smell but it would likely still have a fairly unique smell. Indeed, I would expect the current smell is a combination of a large number of compounds not one single one although some may be more important then others. Most importantly perhaps, removing most of the compounds giving it a smell is likely to result I would expect in a product that doesn't 'taste' as good when the marijuana is smoked or whatever Nil Einne (talk) 08:52, 22 May 2009 (UTC)[reply]
As an analogous scenario, think about decaffeinated coffee. While some enthusiasts insist it's as tasty as regular coffee, I can tell the difference. However, removing the caffeine does not create a colorless, odorless liquid. Many other constituent chemicals contribute to the total flavor and aroma. Nimur (talk) 09:54, 22 May 2009 (UTC)[reply]
Actually I was thinking of splicing the gene complex for THC into other plants. Like say, dandelion. Because THC isn't a protein I imagine there's a slight bit of more complication than say, splicing in a fluorescent protein. Have we identified the genes that are responsible for negative feedback or regulatory genes that would inhibit the production of "too much" THC in a plant? (Like say, hemp?) John Riemann Soong (talk) 02:31, 24 May 2009 (UTC)[reply]
I imagine you meant so that people wouldn't be caught because of the smell! I guess that the smell is caused by terpenes and other secondary metabolites. I don't think anyone will have found the genes - getting funding for that isn't really going to happen. Oh actually, looking at THC#Biosynthesis I'm wrong although there isn't a citation. Cannabinoid#Plant_synthesis seems to tell a different story as well (uncited again). I guess (again) that high THC containing strains have some difference in transcription factors that mean that they express the genes for the biosynthesis more than in Hemp. Smartse (talk) 16:50, 27 May 2009 (UTC)[reply]
Hypermetropia
How to find power of corretive lens? why do we consider normal near point as object distance and the defective near point as image distance while calculating the power of convex corrective lens for Hypermetropic eye? —Preceding unsigned comment added by 61.2.178.70 (talk) 03:10, 22 May 2009 (UTC)[reply]
I assume you are asking this question with some knowledge of lenses and optics. Now consider a hypermetropic eye. The problem is that things too close are not focused on the retina. The objective is to give normal vision, where the least distance of distinct vision (D) is about 25cm. That is, if an object is placed in front of the eye as close as D, even then the eye must be able to see it. That is the limiting case, so if we satisfy for the limiting, we (theoretically at least) satisfy for all cases. So now the object is at D. But the eye can see only its own least distance of distinct vision (d) which is greater than D. Therefore, the image must be formed there. So now applying the lens formula, as you correctly suggested, we consider normal near point as object distance and the defective near point as image distance. Also don't forget to sign your posts by typing four '~'s at the end. Rkr1991 (talk) 05:07, 22 May 2009 (UTC)[reply]
Lilac bushes
I have a few lilac bushes in my front yard. I'd like to have more. Is there an easy way for me to take a cutting from one of the bushes and get another bush out of it? Dismas|(talk)05:15, 22 May 2009 (UTC)[reply]
I have no answer for you (other than talking about all my different-coloured lilac bushes) but I will say that if you're in the northern hemisphere, this is probably the time to clip off some green shoots and test directly. You could also try using a rooting hormone in the water, and while you're at the garden centre buying it, ask one of those helpful people. Franamax (talk) 09:42, 22 May 2009 (UTC)[reply]
Buddleia seeds can be easily bought, where I am at least, and grow into shrubs that look very similar to lilac bushes in my opinion. Perhaps you could harvest some lilac seeds from your bushes and grow those in pots of compost before planted them out. Other shrubs with lots of blossom also exist - I sometimes see for example a shrub that is completely covered in blue, no idea what its name is. Edit: I have looked at The Tree And Shrub Expert by D. G. Hessayon, published in the UK. Buddleia - propagate by sowing seeds in spring or sowing cuttings outdoors in autumn. The blue bush seems to be Ceanothus or 'Californian Lilac' - propagate by planting cuttings in a cold frame in summer. Syringa or 'Lilac' - also propagate by planting cuttings in a cold frame in summer. But as the UK is mostly in hardiness zone 8 or 9, and where the OP comes from is in zone 4 I think, then that advice may not apply. 78.146.162.232 (talk) 11:50, 22 May 2009 (UTC)[reply]
Lilacs grow most successfully from suckers. At the base of every lilac bush you will see shoots emerging. Get a mattack and detach the shoot from the rootstock below the soil level, then put it in a plastic bag until you are able to plant it (don't wait too long though). Then it's easy enough to just plant it and it should grow. And then you will find that, before too long, you want to get rid of said lilac bush because it's about to take over your garden! --TammyMoet (talk) 13:04, 22 May 2009 (UTC)[reply]
BTU'S produced by a conventional 4 or 6 cylinder engine
Can anybody advise how much heat is produced on the exhaust system of a conventioal 4 -6 cylinder engine at the exhaust pipe near the catalytic convertor? —Preceding unsigned comment added by Sustain6996 (talk • contribs) 07:36, 22 May 2009 (UTC)[reply]
Since the heat produced in the catalytic converter comes from reactions involving incomplete combustion products, unburnt hydrocarbons, and nitrogen oxides, I would say it depends heavily on the operation conditions of the engine and the particular fuel/air mixture. Under certain conditions (overly rich fuel/air mix and severe incomplete combustion) it could reach levels comparable to the power output of the engine, but is usually much less. This risk of producing huge amounts of heat is why car manuals have the whole "Do not drive, park, or idle the vehicle over dry grass" warning... 69.140.12.180 (talk) 15:51, 23 May 2009 (UTC)Nightvid[reply]
When you get to the smaller rivers - you start running into the "How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension" problem. When precisely does the river start? Maybe water trickles over some fields before it starts to look like a river? If the river is very crinkly, then issues of fractal dimension start to become a problem. So I doubt very much that you can say with any authority which of those 123 rivers are longer than which others...except for the biggest and most obvious ones - which we've already covered. SteveBaker (talk) 14:27, 22 May 2009 (UTC)[reply]
Eating too little fats
What would be the long term physiological or medical effects of an adult eating say only 10% of their calories as fat, instead of the 25 to 35% that is recommended? I understand that fat-deficiency was a problem in Victorian times, before margarine was invented. 78.146.162.232 (talk) 13:11, 22 May 2009 (UTC)[reply]
See rabbit starvation. It does not discuss the American West in the article, but apparently this was a condition suffered by some pioneers, even though they had a high calorie intake and the native Americans around them on the same diet were not suffering. The difference - the pioneers were discarding the fat from the meat. SpinningSpark13:25, 22 May 2009 (UTC)[reply]
From the lede paragraph of the article: Symptoms include diarrhea, headache, lassitude, a vague discomfort and hunger that can only be satisfied by consumption of fat or carbohydrates, and low blood pressure and heart rate. Are those not physiological effects? SpinningSpark14:49, 22 May 2009 (UTC)[reply]
Thanks again, but those are the symptoms. I'm wondering what physiological pathways are involved, how it might for example affect the nerves or the brain which I understand include a lot of fat, or if something like ketosis or its opposite is involved. 89.242.85.248 (talk) 19:03, 22 May 2009 (UTC)[reply]
See Essential fatty acid. There may also be some links you can track down in the articles on Omega-3 and Omega-6 fatty acids. I'm not convinced that someone taking in only 10% of their calories in fat would have any adverse physiological effects unless the fat source was completely deficient in Omega-3 and Omega-6 fatty acids. The body can otherwise make other lipid molecules it needs. Do you have any references for fat-deficiency in Victorian times? Also, the issue of "rabbit starvation" applies to a special condition of a diet largely composed of "lean meat coupled with a lack of other sources of nutrients" (i.e. presumably also lacking in carbohydrates and certain vitamins) which isn't really directly related to what the OP is asking. --- Medical geneticist (talk) 13:36, 23 May 2009 (UTC)[reply]
Consuming less than twenty percent of calories from fat will almost invariably cause the carbohydrate intake to be too high. Very high carbohydrate diets (such as those obtaining more than two-thirds of calories from carbohydrates) can adversely impact lipid profiles, increasing triglycerides and suppresses HDL cholesterol. The Institutes of Medicine said this in 2005:
The AMDR for fat and carbohydrate is estimated to be 20 to 35 and 45 to 65 percent of energy for adults, respectively. These AMDRs are estimated based on evidence indicating a risk for coronary heart disease (CHD) at low intakes of fat and high intakes of carbohydrate and on evidence for increased risk for obesity and its complications (including CHD) at high intakes of fat. Because the evidence is less clear on whether low or high fat intakes during childhood can lead to increased risk of chronic diseases later in life, the estimated AMDRs for fat for children are primarily based on a transition from the high fat intakes that occur during infancy to the lower adult AMDR. The AMDR for fat is 30 to 40 percent of energy for children 1 to 3 years of age and 25 to 35 percent of energy for children 4 to 18 years of age. The AMDR for carbohydrate for children is the same as that for adults—45 to 65 percent of energy. The AMDR for protein is 10 to 35 percent of energy for adults and 5 to 20 percent and 10 to 30 percent for children 1 to 3 years of age and 4 to 18 years of age, respectively.
(http://books.nap.edu/openbook.php?record_id=10490&page=769)
The Institutes of Medicine talk about the harmful effects of both fats and carbohydrates (see the lengthy chapters beginning here and here).
The USDA says:
A low intake of fats and oils(less than 20 percent of calories) increases the risk of inadequate intakes of vitamin E and of essential fatty acids and may contribute to unfavorable changes in high-density lipoprotein (HDL) blood cholesterol and triglycerides.
"The AHA notes that in the absence of weight loss, diets high in total carbohydrate (e.g., >60% of energy) can lead to elevated triglycerides and reduced HDL cholesterol. These effects do not occur with substitution of monounsaturated or polyunsaturated fats for saturated fat. NCEP suggests that monounsaturated fat
can be up to 20% of total energy and polyunsaturated fat up to 10% of total energy."
(http://www.diabetes.org/uedocuments/ADACardioReview4.pdf)
In reducing fat, it would be better to compensate with calories from protein than carbohydrate. In conclusion, Atkins might not have been right about fats and proteins, but he was right about carbohydrates. There is no doubt that they are bad for you. The only question is whether increasing fat or protein might be worse. They might come with useful nutrients (e.g., minerals or antioxidants), but carbohydrates themselves have no benefit except to meet calorie needs. This list of effects was the best that the FAO could come up with (most of the effects apply to the digestion of fiber, a beneficial carbohydrate that provides few if any calories).
What would happen if a man with a double-barreled name married? What would the woman be named? If they had a child, what would the child be named? 143.238.237.25 (talk) 13:39, 22 May 2009 (UTC)[reply]
It's up to the couple. There may be legal restrictions on what they can choose, though. A German court has recently upheld a ban on triple-barrelled names [2]. --Tango (talk) 13:50, 22 May 2009 (UTC)[reply]
The world population is still increasing, even though not quite as fast as previously forecast. How long will it be using current population projections before the earth can no longer produce enough food for its inhabitants? I heard David Attenborough say on tv that the worlds population was only about 2 billion when he was born rather than the 6 or approaching 7 billion now. A world packed with the maximum number of people would be like hell. 78.146.162.232 (talk) 14:35, 22 May 2009 (UTC)[reply]
You may want to read Malthusian catastrophe. People have been predicting that the Earth won't be able to sustain the growing population for years and we've haven't had a problem so far. Improved agricultural technologies allow increase yields that will probably keep up with population growth until the population levels out. There are plenty of people going hungry in the world but that isn't due to lack of food, it is due to food not getting where it is needed (generally due to politics). --Tango (talk) 14:57, 22 May 2009 (UTC)[reply]
With enough technology applied to the problem I guess we could have many times the current population of the earth fed so if things go on as they are the earth will be utterly and totally devastated and all other non-food species above microbes extinct except as some genes saved in a bank. The earth won't run out of food but there is some very high limit on the ultimate carrying capacity of the earth, certainly 30 billion and possibly much more than a hundred billion. Most food will be grown in vats or in trays and a few cows will be kept to feed the very rich. If the population could be reduced to less than a billion, maybe 500 million, then they would be able to have good lives without constantly worrying about destroying everything. Dmcq (talk) 17:39, 22 May 2009 (UTC)[reply]
"With enough technology applied to the problem" - if that includes artificial fertilizer or fossil fuel products, then they will run out at some time. 89.242.85.248 (talk) 19:18, 22 May 2009 (UTC)[reply]
The crisis is likely to come not from the earth as a whole running out of food, but specific regions. The two greatest danger points, in my opinion, are India and sub-Saharan Africa. In India, the population continues to increase rapidly while the Green Revolution yields diminishing results and the supply of usable land has been pretty much exhausted. In Africa, the population is projected to more than double before stabilizing, and already there are continual flare-ups of famine. Looie496 (talk) 17:41, 22 May 2009 (UTC)[reply]
But a large percentage of people in S-SA are HIV positive as well, which should mitigate a lot of famine potential in the 10-20 year range right? 65.121.141.34 (talk) 19:21, 22 May 2009 (UTC)[reply]
Not necessarily. Plenty of people have children despite being HIV+, so there might not be a significant long term reduction in population. --Tango (talk) 19:57, 22 May 2009 (UTC)[reply]
(EC) With access to certain drugs the chance is greatly reduced. See [3]. Of course for a variety of reasons many pregnancies in sub-saharan Africa don't get such drugs [4]Nil Einne (talk) 21:04, 22 May 2009 (UTC)[reply]
(EC) Another big concern in a number of places including IIRC China, India and sub-Saharan Africa is the diminishing availability of fresh water caused by a variety of reasons including ground water that's being overused (deeper and deeper wheels need to be dug, contamination of water supplies, diminishing reservoir (lakes, rivers etc) levels, climate change. We may be able to partly or completely solve this by engineering crops able to grow in sea water. We may not. Only time will tell. Nil Einne (talk) 21:04, 22 May 2009 (UTC)[reply]
There are other high-tech ways to get fresh water - if you have power, a desalinization plant will work - if you are close to the sea, you could tow a gigantic iceberg into a convenient harbor and 'mine' it for water. If you have enough energy, there isn't much you can't do. SteveBaker (talk) 23:16, 22 May 2009 (UTC)[reply]
I think the 'enough energy' is a big if. I suspect if we really had unlimited energy, terraforming Mars, the moon, or a few other places would be a piece of cake. We could even build giant stations to grow food. In other words, we don't have to restrict ourselves to earth if we don't consider practicalities. While these may be several orders of magnitude more difficult then having sufficient energy to desalinise sufficient water for 7 billion people, the basic issue is the same IMHO. It's pointless talking about possibilities which even if we devote all our current efforts to them we probably couldn't achieve in 50-100 years. Nil Einne (talk) 08:49, 23 May 2009 (UTC)[reply]
By sufficient technology I mean sustainably the world could probably support many many times its current population using solar panels and wave power plus using some fast breeder reactors as backup. Fertilizer can be generated from power and of course suitably treated waste from people would also be used. I wonder what the earth would look like from space with every last spot covered with farm or power machinery of one sort or another Dmcq (talk) 20:55, 22 May 2009 (UTC)[reply]
On the subject of climate change, the area of arable land is forecast to decrease within the century. Although CO2 fertilization may have the effect of temporarily increasing crop productivity, as well as more arable land being produced in Northern Canada and Siberia, major "breadbaskets" today are forecast to decline. For example, the American Midwest is predicted to suffer major desertification with a further warming of just 1C (2F), Southern Mediterranean Europe is forecast to become much drier and hotter, the Kalahari desert is expected to expand south, the Gobi desert to expand east, and the water supplies from the Himalayan glaciers, which support farming in otherwise dry areas, are expected to nearly dissapear before the end of the century. In addition, crop and insect diseases could increase, and major staple grains, especially rice, suffer a dramatic drop in yields above a certain threshold temperature. Population load, once it increases past global supply, reaches the "final point of sustainability". After such, both supply and load must start to decrease, until load decreases sharply below the level of supply, although not everyone predicts this. Clean drinking water supplies could decrease as well, which would hinder farming. ~AH1(TCU)23:13, 22 May 2009 (UTC)[reply]
The answer has a political as well as a scientific component. Many things that are scientifically possible won't be done. Someone would have to allocate the resources. (e.g. money, energy, water, raw materials, medication). In an ideal scenario humans would all be altruistic and distribute those to benefit all. That is unrealistic, though. Despite the fact that there are mass die-offs due to war, pandemics, starvation and drought the human population in general seems to keep multiplying. There is no free lunch, though. Scientific scenarios to feed and water ever increasing numbers come at a cost. Either environmentally or in loss of life or reduced lifespans or quality of life of some populations. The more artificial components the system gets the more fragile it becomes. If you feed your entire population with food grown in vats, one good bug could wipe our a significant portion or them. BTW. Last I checked Egypt had a higher birth rate than sub-Saharan Africa. Just because s.o. is e.g. in the U.S. they should not develop the attitude "It can't happen here." Example: Atlanta, which is in an area with lots of rainfall, has grown so much that in years that have less rainfall there's water rationing. Cases of people dying because they can't pay their water bill are rare, but not unheard of. People in industrialized nations have a higher chance of having their food supply ensured, but there's no guarantee. There is also an inverse relationship between wealth and population increase. 71.236.24.129 (talk) 10:28, 23 May 2009 (UTC)[reply]
I think if we use nuclear energy, it will last a ridiculously long amount of time. Even more so if we use fusion. I'm not sure about the former, but I think with the latter we could keep growing the population until we physically run out of space, which won't be for a very long time. — DanielLC15:59, 23 May 2009 (UTC)[reply]
If the current growth trend (population doubling every 40 years) continues, each person on Earth will have thier own square meter plot of land by 2270. Livewireo (talk) 16:13, 26 May 2009 (UTC)[reply]
The current growth trend is not population doubling every 40 years - we've been sup-exponential for a while now. If growth were exponential, this graph would be completely level (give or take some minor fluctuations). --Tango (talk) 16:39, 26 May 2009 (UTC)[reply]
They are a good way of understanding how an ecosystem fits together. Such understanding is important whenever you have to consider the environmental impact of something, which we have to do quite often. --Tango (talk) 16:36, 22 May 2009 (UTC)[reply]
So you don't grow up like one of the dumb people some on the Internet laugh about, like ones who think food just comes from the supermarket, and who don't understand how the stuff grows and has to be shipped. So you understand the importance of farmers and don't grow up to build huge subdivisions with homes that cost a lot of money, but which deplete the available land to grow food.Somebody or his brother (talk) 18:13, 22 May 2009 (UTC)[reply]
Food web / pyramid does not mean food distribution or even growing, so learning them would have little or no impact on ignorance on such topics. It is a schematic representation of ecological interactions, like cats eat fish eat flies plant eggs in cat corpses/faeces, which can be useful in practical application such as ecological planning (eg, releasing ladyirds to control aphids may simply cause an increase in ladybird predators, if understanding of the food-web is insufficent) and in understandig various food scandals and recomendations (like why heavy metals appear in fish, or why DDT is banned). As with most school sciences, it is essential for anyone undertaking further scientific education, and is the sort of thing that any typically educated person should know.YobMod09:03, 23 May 2009 (UTC)[reply]
All the food that we eat is either the body of a living organism (plant or animal) or the product of a living organism (sugar, milk, honey). The plants and animals in our world must remain healthy so that we may have healthful, nutritious food. Pollutants in the ocean have reduced the quality of seafood. What we eat is affected by food chains and food webs. As a simple example, the livestock eat the grass, and then we eat the livestock. We have to know where our food comes from to ensure that it is safe.71.31.105.41 (talk) 23:29, 24 May 2009 (UTC)[reply]
Phlegm and vocal range
This morning I woke up with a laryngitis, and was able to sing a loud and clear (mf) B♭1, a note I had only been able to sing ppp in Mahler's Eight and the All-Night Vigil. I even could sing down to F1, although that was very hoarse and open to interpretation. Now that I've been up for a while, my lower range has moved up, too, but my electronic tuner still recognizes my A1. Is this because the phlegm acts as a weight on the vocal chords? — Sebastian15:28, 22 May 2009 (UTC)[reply]
Just speculation, but since I'd think that phlegm would be rather mobile when you start singing... It may be the swelling of the mucosae that adds weight to the vocal chords, and causes the frequency to drop. --NorwegianBluetalk18:10, 22 May 2009 (UTC)[reply]
Would swelling of the mucosae be the reason that, the morning after drinking heavily, some people speak in a lower tone of voice and are able to reach lower notes? Tempshill (talk) 21:14, 22 May 2009 (UTC)[reply]
I'm curious how could one most easily calculate the surface area of a person's body? Would men or women have more than the other and would tall, thin people have less than a short, fat person?TheFutureAwaits (talk) 16:30, 22 May 2009 (UTC)[reply]
The easiest way, which should be exact enough for what you need, would be to measure length and average circumference of your body parts - torso, arms, legs, and head - and add them up (neglecting the areas of your feet and the top of your head). Roughly speaking, you can think of your surface as your height times your average circumference. Since girth can easily vary by a factor of 2, while length only varies within a much narrower range, it is easy to see that a short, fat person has more surface than the tall, thin one. — Sebastian16:45, 22 May 2009 (UTC)[reply]
If you have access to a corpse, you could try peeling off a small section of skin, weighing it and measuring its surface area, then weighing the whole skin and scaling up the previous surface area accordingly. Vimescarrot (talk) 19:43, 22 May 2009 (UTC)[reply]
Bottom of feet is much thicker skin then the rest of you. Might be pretty uneven in other places too. Could throw off the calculation. Might be a decent approximation on someone who does not walk, though. I would think that perhaps you could cut up a wetsuit and measure the area of that? Also include some socks with toes and gloves made of a material that is not very stetchy. No cadavers involved. 65.121.141.34 (talk) 20:02, 22 May 2009 (UTC)[reply]
Just as a general principle, the more "spherical" the body shape, the less surface area in proportion to mass. In other words, of two people who weigh the same, the "rounder" one will generally have less skin surface. Looie496 (talk) 21:01, 22 May 2009 (UTC)[reply]
Take a vat of molten chocolate of known volume. Dip subject in vat and remove. Measure the volume lost from vat and the thickness of chocolate adhering to subject - bit of arithmetic and Hilda's your auntie. SpinningSpark00:29, 24 May 2009 (UTC)[reply]
This paper from 1952 used a formula developed by du Bois:-
weight0.425 x height0.725 x 71.84
[Weight in kg, height in m] The original reference is from 1916: DuBois D, DuBois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Medicine. 1916; 17:863-71.
And this paper uses a direct measurement technique it calls "coating and planimetry" (which seems to be surprisingly similar to my "dip in chocolate" scheme above) and makes the claim that this shows all the "formula" methods are wildly innacurate, at least for persons of African descent. SpinningSpark14:03, 25 May 2009 (UTC)[reply]
Hip anatomy
Hi is there any way in which the ilium on either side of the pelvis is referred to differently in a clinical setting? My question is how would you know what side of the ilium someone was talking about if it is only one bone? If there was for example a fracture on one side of the ilium but not the other would doctors talk about the left/right ilium? Hope this makes sense. Is there a similar way of differentiating which side of pubis or ischium someone was talking about? Thanks in advance to anyone who can help! —Preceding unsigned comment added by 139.222.240.161 (talk) 16:53, 22 May 2009 (UTC)[reply]
Take a look at Anatomical terms of location. There is a precise term for each orientation or position (e.g. the anterior distal portion of the ilium). These terms avoid the use of terminology which would be vague based on how somebody is standing/moving the limb, etc. Nimur (talk) 16:57, 22 May 2009 (UTC)[reply]
When did fruit bearing plants first evolve and what was the first fruits?
Evolution of plants doesn't cover this terribly well, but as far as I can tell, the Gingko is a good candidate. According to our articles, the first gingkos evolved around 270 million years ago, and were among the first seed-bearing plants. And having lived next to a female Gingko tree for a few years, I can tell you from unpleasant experience that they do bear fruit. Looie496 (talk) 19:43, 22 May 2009 (UTC)[reply]
According to our article: "The apricot-like structures produced by female ginkgo trees are technically not fruits, but are seeds that have a shell that consists of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta)." --Tango (talk) 19:50, 22 May 2009 (UTC)[reply]
The Wikipedia article on dendritic cells says that these phagocytes are unique to the mammalian immune system. However, things like this and this seem to suggest other groups of animals have DCs as well. Which is right? If other groups of animals have DCs, which have them: all amniotes? all tetrapods? all jawed vertebrates? Thanks a lot. --Leptictidium (mt) 20:12, 22 May 2009 (UTC)[reply]
The adaptive immune response goes back to jawed vertebrates as you suggest, and it seems likely that would be true for dendritic cells. I don't know for how many of the more "primitive" jawed vertebrates they've been demonstrated, though. Your reference for Langerhans cells in reptiles is a good one, though. --Scray (talk) 00:15, 23 May 2009 (UTC)[reply]
Can anyone tell me the amount of pushing power a man who weighs 90 kgs and has 7 inch by 7 inch hands in psi (pounds per square inch) ? my brother says its something like 20psi but that doesnt seem right to me. Is there a way to roughly work this out?
It depends on what they are pushing...the world record for weight-lifting is around 260 kg - and that's over a length of cylindrical bar the width of the guy's hands (let's say 20cm) by maybe 4cm wide...so 260kg over 80cm2 - which is about 46 psi. Obviously that's the world record - I'd say that less than half that is perhaps reasonable. SteveBaker (talk) 23:11, 22 May 2009 (UTC)[reply]
(Edit conflict)Yes, if you first define what "amount of pushing power" really means. Since you've mentioned psi you (or the teachers who set this poorly worded homework question?) are presumably thinking of how much pressure the man can exert through his hands (since psi is pounds per square inch, a measure of pressure).
An accurate figure will depend on how well muscled he is, how he applies the pressure, and in what direction, but let's assume he's moderately strong and can push with flat hands with a total force equal to his own weight - does that sound reasonable? Think of a wrestler holding his opponent above his own head preparatory to a body slam, not an unlikely scenario, and certainly below world-class weightlifting standards.
Now, you know the linear measurements of his (two) hands, so you should be able to work out their area in square inches - you should find that the answer comes close to a round figure useful for approximate calculations. you know how much he weighs in kilos, which we've assumed is about the same as the maximum force he can exert (weight being a force). You need to convert this force to pounds, which I'm sure you can manage. You should find this comes close to another convenient round figure.
Now you need to work out how how that total force is distributed over the total area he's using to push with, how many pounds he's exerting on each square inch. The answer may surprise you, and should show that your brother has made a minor error in his working. 87.81.230.195 (talk) 23:24, 22 May 2009 (UTC)[reply]
If a 200 pound man does a hand stand then he is supporting his whole weight on the area of his two hands, which I reckon is a pressure of about 4 psi. However, as pointed out above, a weighlifter can support the same weight on a much smaller area, so they are exerting a higher pressure. And a 100 pound ballet dancer en pointe is supporting her weight on probably 2 square inches, so she is exerting a pressure of around 50 psi. So pressure is not a useful measure of "pushing power". Gandalf61 (talk) 09:45, 23 May 2009 (UTC)[reply]
Actually, since the original question was actually for pushing power, the correct answer is "power", e.g. force times velocity, or rate of energy expended per second. I think the original questioner may want to review some basic physics terminology like force, energy, power, and pressure, to decide which quantity is actually the one he/she is trying to inquire about. Nimur (talk) 12:06, 23 May 2009 (UTC)[reply]
If the questioner doesn't know whether pressure, force, power, work or energy is the thing that is to be measured - then perhaps we need to ask why the question is being asked? To what use is the answer being put? Very often, these questions are just idle curiosity - but since the numbers don't mean much, it's all rather arbitary. SteveBaker (talk) 15:33, 23 May 2009 (UTC)[reply]
Well, strictly, yes. I was interpreting "power" to just mean "ability", rather than its technical definition in physics. --Tango (talk) 17:15, 23 May 2009 (UTC)[reply]
Fancy Guppy Reproduction
I have a femal fancy guppy and a male gold swordtail, among other things. It appeared that my guppy was pregenant, and seeing no other possible candidate, assumed the swordtail was the father. I took the neccessary steps to prepare, and even moved her to a seperate breeder when I assumed she was close (before it would be to dangerous to move her though). There she sat, for nearly a month. Then one day she was skinny again! There was no evidence of a miscarriage, and there were no babies in the other compartment. The only change is that I was better able to control how much she ate, so she probably cut back on some calories, but if this were the cause, I assume she would have lost weight over time, instead of so suddenly. What happened? And now she's starting to show pregnancy signs again. This is very troubling.DrewSmithWhat I've done23:59, 22 May 2009 (UTC)[reply]
Do fish get phantom pregnancies? I know other mammals (than Humans) do, so could be. I also read that Guppies can store sperm, so can have multiple pregnancies from one mating - but this doesn't explain the spontaenous loss by itself, uness followed by multiple miscarriages.YobMod08:35, 23 May 2009 (UTC)[reply]
Could a low-cost photovoltaic cell mounted to the top or side of an electronic vending machine provide enough power to run it reliably? The machine would be indoors, but in a vestibule with glass double doors and overhead lighting during the evening (at least during the hours when it would need to run). NeonMerlin02:25, 23 May 2009 (UTC)[reply]
One important question is whether this vending machine needs to have a refrigerator in it, as it would if it's vending cold soft drinks. Tempshill (talk) 03:33, 23 May 2009 (UTC)[reply]
There are Mechanical vending machines, condom machines are often just a place to put cash, pull a handle and get your prize. Zero electricity - the room that it is in is already lit up so no need for electricity. Similarly there are apparently 'eco' vending machines but not sure how good they are (from a brief read - not entirely free of grid-electricity use - the link from google is 'blacklisted' but search for 'eco vending machine'). ny156uk (talk) 10:02, 23 May 2009 (UTC)[reply]
If the panels are directly driving the machine - then I'd say no. But if they are charging a battery that operates the machine - then perhaps if the machine is used sufficiently infrequently, it'll have time to recharge fully between 'vends' - in which case you'd be OK. But if you had a whole bunch of kids arrive at once - all wanting to buy trading cards - then you'd run the risk that the battery would go dead. I agree with Ny156uk - there have been plenty of purely mechanical vending machines where the weight of the coin against a spring releases the ratchet on of a wheel - allowing it to rotate. The purchaser drops in the coin - then turns a knob to rotate that wheel and thereby to release the product. When the wheel rotates past a certain point, it reveals a slot through which the coin drops - allowing the ratchet to re-engage against the wheel and prevent it from rotating again until another coin is dropped in. This approach is much more practical than messing around with solar panels and rechargeable batteries. SteveBaker (talk) 15:21, 23 May 2009 (UTC)[reply]
Insect identification
This tree in Bavarian countryside was entirely covered in a kind of web and had caterpillars crawling all over it, yellow to light brown with two dotted black stripes down their backs, thin, about 1.5 - 2 cm long (I think, I didn't measure them). Can anyone tell me what the caterpillars are? N p holmes (talk) 08:25, 23 May 2009 (UTC)[reply]
Thankyou. I looked at some pictures: the Small Tortoiseshell caterpillars look fatter and hairier than these (and the web was only a little thing on a couple of nettle leaves). So I'm slightly doubtful. Any other suggestion? N p holmes (talk) 10:13, 23 May 2009 (UTC)[reply]
If an air vortex has enough force to move a 150lb object 1 foot from 30 foot distance from the launcher. Is there any way to estimate how far it will be able to move the same object from 5 foot? Or is the degredation of force within a vortex unique for each vortex depending on the speed of the spin of the vortex, and the speed which it is traveling?
Some information that may help is that the starting pressure within the vortex is 14,7 psi and the speed is mach 1 and the size of the vortex is 2ft (24 inches) in diametre —Preceding unsigned comment added by 79.68.229.253 (talk) 11:43, 23 May 2009 (UTC)[reply]
Well - the air vortex is going to dissipate sideways - so the pressure will decrease as you get further away at a rate that's proportional to the increase in cross-sectional area. Probably a good estimate would be an inverse-square-law kind of thing - as you double the distance from the source, the pressure decreases by a factor of four. However, it's going to depend critically on the size of the object being moved. For an object who's cross-sectional area is small compared to the diameter of the air vortex, the area over which that pressure is exerted doesn't change as the air flow diameter increases - so the inverse-square drop in pressure equates to an inverse-square decrease in force applied. But for an object that's much larger than the airflow, as the pressure drops off, the area it's exerted onto increases at the same rate - so the force is about the same no matter how far away you are. But in truth, this is a very rough estimate. The details matter a lot. SteveBaker (talk) 15:11, 23 May 2009 (UTC)[reply]
Hmmm that helps a little but wont the slowing down of the air due to the distance decrease the impact as well? If the vortex grows at a very small rate the area effected would not change much, but the air speed would slow due to drag. how much does drag decrease air flow?
The air can really only slow down by spreading out. Think about it...if the air leaving the nozzle is moving at speed X meters per second with a cross-section of Y square meters - then the volume of air coming out of the nozzle is X.Y cubic meters per second. If it then slows down to X/2 - then the air is only moving out of the way at X.Y/2 cubic meters per second...so where does all the extra air go? As the air slows down, it's cross-sectional area has to increase at the same rate - so if the speed drops to X/2 then the cross-sectional area has to go up to 2.Y...unless the pressure is steadily increasing somehow. But if the pressure is bigger than ambient - then the air in the jet can push the ambient air out of the way - so it'll spread out. There is really no avoiding it. SteveBaker (talk) 03:50, 24 May 2009 (UTC)[reply]
Fancy swordcraft and damaged clothing...
I'm guessing not, BUT...
is it actually possible to damage clothing but not the wearer in a controlled manner ala Zorro (or many other films & shows)?
It is possible, but unlikely - especially at the speeds Zorro slashes at. Fine motor skill is handled by small muscles, while quick slashing motions is gross motor skill. The two processes are handled by different parts of the brain and executed by anatomically different muscle and tendon groups. Nimur (talk) 12:13, 23 May 2009 (UTC)[reply]
Ala zorro, very unlikely. Zorro carved complex patterns into another persons clothing; a Z. As stated above, this would take a combination of fine motor and gross motor skills. However, the kind of swordplay often seen in humorous disney films, i.e. peter pan, where peter slashs the belt off of captain hook, and his pants drop, would be a very simple maneuver. The only real difference is that in the animation it shows a slash across, while in real life it would have to be a downward slash, to cut the belt. It is unlikely this would make the pants drop though, unless the target was wearing extremely loose pants.
Calculating oversteer/drift in a car
Hi all. I'm trying to calculate the amount of oversteer of a car, based on one main variable, the centre of mass, and forward velocity.
The main result I want to achieve is to be able to calculate, for a set numbers of degrees of drifting, how the center of mass affects the forward speed and stability of the drift, so the car doesn't slide out.
I've tried to solve it in terms of opposite torques. For the front tires, I've assumed they aren't slipping, so have used the force into the drift as (coeffient of static friction)(normal force of tires)(center of rotation), and taking the centre of rotation as the intersection of the normals of the inside tires (think that's right, haven't derived it.)
The rear tires are where I'm having the most trouble. Assuming they are slipping, the only force I can think to use is mv^2/R, but I don't think that's right because there should be a force straight on, since the car is angled? And I'm not sure what figures to use for R, the center of rotation, and r, the length of the lever arm for the torque equation.
The end result I think I want it (coeffient of static friction)(normal force of tires)(center of rotation) > (mv^2/R(?))(r) so the car doesn't slide out.
On second thoughts, mv^2/R may be not a valid equation for this, instead using the kinetic friction force. But then velocity doesn't come into it at all, and it should... I think I need to use both, on thinking that sounds better.203.206.34.183 (talk) 14:07, 23 May 2009 (UTC)[reply]
I think you are dramatically underestimating the complexity of the system you're trying to analyse. In real cars, the weight is not evenly distributed over the wheels - and as the car accelerates or turns, that weight shifts as the suspension takes up the strain and the car leans or pitches. In some cars, one wheel may actually lift off the road altogether. Chassis flex and the effect of anti-sway bars change this weight shift in complicated ways. Front wheel drive versus rear wheel drive makes a difference. Static versus dynamic friction and side-wall flex in the tires complicates the answer too. This is an insanely complex thing to try to analyse mathematically. SteveBaker (talk) 14:52, 23 May 2009 (UTC)[reply]
Yeah, I know it's a heavy bit of analysis. I was planning on simplifying it by assuming the front and rear wheels are both on live axles, so they can be looked at together. It is viable for me to ignore suspension and roll affects for my problem. Rear wheel drive. Sidewall flex would be insignificant as well. I'm not looking to include every possible force, just the most significant ones. 124.169.20.149 (talk) 00:29, 24 May 2009 (UTC)[reply]
But my point is that these other things are FAR from insignificant. There are 'approximations' that are reasonable - and there is ignoring major features of the system...and you are well into realms of the latter!
I've competed in many Autocross events in my bone stock MINI Cooper'S - and videos taken by spectators clearly showed that in hard cornering (long before 'drift' set in), the inside rear wheel would lift completely off the ground. Just think about that - with that wheel off the ground, the frictional forces on the rear end of the car are halved! Later, I added a stiffer rear antisway bar (going from a 20mm torsion bar to 25mm) - that keeps that inside wheel glued to the road and that added close to a third of a g to my lateral cornering force! That's a SPECTACULAR improvement...not by any means a negligable effect and it's an extremely subtle suspension tweak. Ignoring all of these kinds of effects makes your results all but meaningless. You might just as well save yourself the effort of doing the math and just guess! SteveBaker (talk) 01:57, 24 May 2009 (UTC)[reply]
Today's featured pic
Hi, in todays (23) featured pic, it shows a volcano erupting. There's a curious thing; the smoke from the volcano is drifting to one side, while the clouds around the volcano seem to be drifting to another side. What is the explanation for this? What is happening here? 202.129.232.137 (talk) 13:56, 23 May 2009 (UTC)[reply]
My guess is that the clouds are actually flowing in the same direction as the smoke - and are being constrained by the other two islands. But as the cloud reaches the volcano, the air temperature rises steeply. Since the amount of water that the air can hold increases with temperature, the water vapor in the clouds simply evaporates.
Alternatively - if your theory as to the direction the clouds are travelling is true - then perhaps it's merely that the smoke is at much higher altitude than the clouds - and that perhaps the wind at those altitudes are blowing in a different direction from the winds at lower altitudes.
No - that's not possible. Look at Mount_Cleveland_(Alaska) and you'll see that this is a very steep-sloping stratovolcano. Now, look again at the photo - notice that the mountain isn't casting a shadow - the sun is sufficiently high in the sky that there is no shadow being cast. Next, look at the shadow of the brown stuff - you can see it cast clearly onto the mountainside beneath. With the sun being as steep as it is - that means that there much be considerable vertical distance between the smoke plume and the mountain. Look (for comparison) at the shadows of the clouds - notice that the shadow is MUCH shorter - meaning that the clouds are much closer to the ground than the smoke plume is. It's not close to the ground. SteveBaker (talk) 18:37, 23 May 2009 (UTC)[reply]
But a pyroclastic flow hugs the ground. Look at the picutre at Pyroclastic flow. You see the flow going opposite from the wind plume. Flow is determind by slope and in independent of wind. Also follow the link to pyroclastic surge and read about 'base surge. I do not think the "clouds are an active surge: I think they are the aftermatch of such a surge, basiclaly dust left in the air by teh surge that has not yet fallen out. -Arch dude (talk) 18:48, 23 May 2009 (UTC)[reply]
This image (taken at roughly the same time as the one our OP is asking about) makes it much clearer. Firstly, you can see more clearly how the low altitude clouds are being channeled by the nearby mountains (as I suggested) - which indicates much more clearly how they are moving in the same direction as the dust plume. Secondly, this photo makes it easier to see how high the dust plume is above the terrain. This photo (taken by a satellite one day later) shows that the dust plume is drifting away from the actual volcano (something that would absolutely not be possible with the 'pyroclastic flow' hypothesis...and the photo has that plume clearly labelled "Ash Plume". This video of an eruption about a year later - under very similar-looking cloud conditions makes it even more obvious. QED. SteveBaker (talk) 22:47, 23 May 2009 (UTC)[reply]
Thanks, Steve. I never thought the plume to the SW was a pyroclastic flow or surge. I thought the crescent-shaped billow to the NE might be the aftermath of such a flow or surge. However, thanks to your excellet work we now know that it is merely the leading edge of a very large area of low-lying clouds. -Arch dude (talk) 05:20, 24 May 2009 (UTC)[reply]
Oh! I see what you're saying. Yeah - now I understand where you're coming from, it seems more plausible - but then you'd still have had to explain why it's drifting in the opposite direction to the other plume...but those other photos prove it's just clouds behaving oddly because they are close to the ocean and are being funnelled around these tall mountain/islands. It's a very cool photo though. SteveBaker (talk) 14:24, 24 May 2009 (UTC)[reply]
At some point in the past few weeks I have read a quote by Taiichi Ohno that Lean Production should not be separated and codified as tools, but should be adopted by organisations as a whole system. Now that I'm writing my dissertation I can't find it, and it's driving me bonkers. Can anyone who has read any of Ohno's books identify the quote, and give me a citation for it please? Otherwise I'm going to have to re-write my dissertation in order to not miss the deadline. -- roleplayer13:59, 23 May 2009 (UTC)[reply]
Breaking stength of an extension cord.
Someone at my car club spotted a pickup truck towing an Accura using a yellow extension cord!! I was wondering whether this was really as foolhardy as it sounds. Does anyone have any idea of the breaking strain on one of those things? Some way to get a rough estimate? SteveBaker (talk) 14:23, 23 May 2009 (UTC)[reply]
Human perception has weird effects. When on the road things have a tendency to look smaller than they really are or would look in, for instance, a small room. I suspect the cord could have been far more heavy-duty than it looked, and thus able to hold vehicles together... 69.140.12.180 (talk) 15:59, 23 May 2009 (UTC)Nightvid[reply]
Well, clearly it was able to hold vehicles together, since that's what it was doing. I don't think that's in any doubt. The question is whether it can do so reliably, which isn't really a question of perception... -- Captain Disdain (talk) 16:26, 23 May 2009 (UTC)[reply]
If nothing else there's the danger that there will be damage to the cord that you can't see because it's covered by the outer insulator. APL (talk) 16:37, 23 May 2009 (UTC)[reply]
You can estimate it, but you have to make tons of assumptions. So, lets assume that it is a twisted copper wire. Copper has about 1/3 the tensil strength of steel (from memory - please verify). So, if you assume that it is safe for a 1/4" twisted steel cable to pull a car, then it should be safe for a 3/4" twisted copper cable to pull the car. You can make different assumptions and estimate away. -- kainaw™17:25, 23 May 2009 (UTC)[reply]
You mean sqrt(3)×1/4 = less than 1/2 inch. But anyway, if you've ever cut into an an extension cord you know that most of the material is not solid copper -- most of the cross-sectional area is insulation. --Anonymous, 17:55 UTC, May 23, 2009.
ALthough it is a really stupid thing to do except in a dire emervency, it is possible, using extreme care, to tow a vehicle without placing a lot of strain on the tow rope. Don't go up hill, use extremely low acceleration, and the guy in the towed vehicle must not use the brakes unless the rope is slack. Therefore, your friend may have seen someone actually do this, but it's really dumb. -Arch dude (talk) 19:00, 23 May 2009 (UTC)[reply]
Yes. It gives a tensile strength of 10.9MPa and a breaking strain of 224%. I'm not sure how to turn those into the answer we need, but I imagine someone here can. --Tango (talk) 22:31, 23 May 2009 (UTC)[reply]
Seems like it's "safe", then (this is not hauling advice). A one-ton car accelerated at no more than, say, g/4 (0-60 in 10.9 s), would be 2.45 kN, so a cylinder of radius 8.5 mm of the plastic should be able to support it. --Tardis (talk) 22:44, 26 May 2009 (UTC)[reply]
Hmm — I suppose the real issues are whether the stress is evenly distributed (it isn't, especially where the cord is bent!) and whether several lengths of cord were being used in parallel (as by looping the cord around both attachment points a few times). --Tardis (talk) 22:46, 26 May 2009 (UTC)[reply]
I've looked hard to try to find this - but without luck. The only references to it online are in other places hosting that same video. It's possible that "flying turkey" isn't the name of the creature - just a description this guy gave it in his narration - and it's also quite possible that this is the first and only time it's ever been seen. People who do these kinds of crazy deep dives often report that they see species that are new to science every time they go down. Perhaps someone else will have more luck. SteveBaker (talk) 01:43, 24 May 2009 (UTC)[reply]
I've looked at pictures in the book The Deep and found a plausible match: a sea cucumber called the "deep-sea Spanish dancer"(scientific name Enypniastes eximia). Here's a video of it in action: http://www.youtube.com/watch?v=5PdRt31FqDc 15:43, 24 May 2009 (UTC) —Preceding unsigned comment added by 69.224.113.202 (talk)
I've just read this article about a 'new' DVD technology that could allow up to 300 DVDs to be recorded on a single disk. I've had a look at the article on 5D, but as a layman I cannot understand head nor tail of it. How does this work. What is the 5th dimension and more to the point, why don't we just invent a 700D DVD that could store every movie ever made? russ (talk) 21:18, 23 May 2009 (UTC)[reply]
OK - they call it "five dimensional" but that's not what's really going on. They are saying that they are recording data using five parameters:
How far from the center of the disk are you?
How far around the circumference of this 'track' are you?
What layer are you on (they claim 10 layers)?
What color of light is reflected at this point?
How does this point polarize light if it is reflected by it?
These five numbers are what they are calling dimensions - but that's just marketing-speak. They haven't invented five-dimensional space-time (which is what Fifth dimension is talking about).
Let's examine their claims carefully:
Existing DVD's can be 'multilayer' (two layers on each of two sides - four layers in total) - so they have (1),(2) and (3) above. At each point in that three-dimensional space, there can be something that absorbs laser light or reflects it - representing either a 'one' or a 'zero' - a binary code. So all these guys are proposing is to use polarization plus color to allow each point in that 3D space to represent more than just a 1 or a 0. Contrary to what the article says, a standard 4 layer DVD can already store 17Gbytes (they said 5Gbyte?!?) - the new technology claims 1.6Tbytes - which is actually less than 100 times more than a "standard" DVD - and only 30 times more than a BluRay disk (which can only have 2 layers). So they are getting 5x more than the BluRay disk by having 10 layers instead of 2 - and that leaves only a factor of 6 gain from their fancy color and polarization tricks. So if they could distinguish 2 different colors and 3 different polarization planes (or vice-versa) - then they can reach their claimed capacity. There is no magic going on here - it's just a logical extension of what we already do.
These kinds of fancy high-capacity storage systems are claimed by researchers all the time - but 99% of them fail because they are often unable to actually deliver that in a form that's cheap to manufacture (DVD's cost about 50 cents each to make - and that includes the case, the printed inlays and shrink-wrapping!) - and which withstand the rigor of the mishandling they'll get in daily life. There are also issues of the cost of the players and whether such players will be able to play existing CD's, DVD's and BluRays as well as their new format.
So don't hold your breath waiting for these things!
By "standard DVD" I guess they mean single-layer. That also fits with them saying DVDs are 2D. The article says there are 2 polarisation angles, so I guess there must be 3 colours. While calling it 5D is, in a sense, correct, it is a little misleading since 3 of the dimensions are discrete (have only a finite number of positions). In topology discrete spaces aren't usually counted as dimensions. The article says the "material cost" would be less than 5 cents, I don't know what it would actually cost to make. I think the main flaw in this new design isn't cost, though, it's speed. There is no point having lots of data if you can't access it. Lots of storage space would be great for really high definition movies, but if you can't read 1 second's worth of data per second, it doesn't work and the article suggests data access is pretty slow. I can't think of a real purpose for this technology. I know better than to say no-one will ever find a purpose, but I'm drawing a blank. --Tango (talk) 22:41, 23 May 2009 (UTC)[reply]
Yes - I suppose you could stick 300 movies on it so you could store your entire movie collection on a handful of disks - then when you want to watch a particular movie - you tell the machine to copy the movie (S-L-O-W-L-Y) onto a conventional hard drive so you can watch it later. If the replay mechanism was (say) 10x slower than required - then you'd have to request the movie you wanted the day before you wanted to watch it...which is kinda inconvenient.
Personally, I think we're more likely to be downloading movies in the future - and the storage issue goes away...you need enough space locally to store whatever new movies you want to watch over the next few weeks - the software slowly downloads new ones on demand so you always have enough material to keep you happy. I simply don't see the value of a 1.6Tb non-recordable media. What could you possibly want to buy in one chunk that consumes that much storage space?
But bear in mind that storage capacity isn't really the limiting factor here - the cost of buying a movie is what kills you. They could already sell movies on DVD at $1 each and make a decent profit if the cost of making the movie was low enough. But we pay $20 for a DVD - that's $19.50 for the movie and $0.50 for the disk/box. Even if these things were $0 to make - the cost of the 300 movies that it would hold would still be something like $6,000. NOBODY is going to spend $6,000 on a movie disk - and the movie companies can't afford to drop the price of the actual content to the $0.10 per movie it would take to pack 300 movies onto a $30 disk. You can't even argue form the point of view of convenience. You can already buy 1Tbyte hard drives - 1.7Tbyte are presumably only about a year away. So your hard drive is by far the best place to keep movies...now it's just a matter of how to distribute them - and the Apple iTunes mechanism is by far the more likely way for this to happen. That's possible with today's tech. Take a 1Tbyte drive - with a $50 computer - pack it into a shiney white $200 box with an Internet socket and a TV video output and a little remote controller and you're done. Apple could make a product like that tomorrow if they wanted to - the only issue is pursuading the movie companies to sell their movies that way.
If such a disk format were to have a use, it would be in computer games - in the games business, we're always bumping into the limits of what we can pack onto a DVD. But lack of speed would kill us in that application. SteveBaker (talk) 23:12, 23 May 2009 (UTC)[reply]
You can already get 2TB hard drives. CD style storage media are good for transferring data, not for storing it. I'm not sure if these things are intended to be writeable to on a desktop, but if they aren't then they'll only be useful for when you want to buy a terabyte of data all at once, which no-one is likely to want to do. Games is a possibility, I suppose - you would have to fully install it to a hard drive to play, though, and at those sizes it might be easier just to sell it on a hard drive! --Tango (talk) 23:34, 23 May 2009 (UTC)[reply]
Ah - I wasn't aware that we'd hit the 2Tbyte level with hard drives - but it doesn't surprise me. Anyway - from the way I read that article, it doesn't sound like a writable version is likely...quite how you'd change the orientation of these nanoparticles in order to change the plane of polarisation seems tricky - and changing the chemistry of the particles on the fly to change the color just using a laser seems impossible. Installing a couple of Terabytes onto your hard drive would take HOURS - possibly days if this drive is as slow as we suspect. SteveBaker (talk) 01:40, 24 May 2009 (UTC)[reply]
I've had a quick read through of the actual letter in Nature ([7] subscription probably needed, I'm on a uni network). The only number they offer for speed is the recording speed of up to 1 Gbit/s (and they have an idea for dramatically increasing that), so it seems production is reasonable. They don't say how quickly it can be read, but it sounds like it could actually be quite fast (if I'm reading it right, they have a way of reading all the polarisations and colours at the same time, although I didn't fully understand that). It's a little difficult to understand - it's a scientific paper, not a technical specification, and concentrates more on how they do it rather than what it can actually do. --Tango (talk) 14:36, 24 May 2009 (UTC)[reply]
Well, they've got to be writeable to at some point! I don't know if they could be written to by a desktop drive or if you would need an expensive thing only big manufacturers could afford. It seems they are written to using a single laser, though, so they probably are writeable to at home (how reasonable the cost would be, I don't know). --Tango (talk) 16:22, 24 May 2009 (UTC)[reply]
Not in that sense. Pre-recorded CD's and DVD's are pressed out of plastic just like the old vinyl records were - I suppose that technically that is "writing to them" - but if so, then the entire content of the disk is written in a tiny fraction of a second as the plastic is pressed...it would be meaningless to talk about the "recording speed" in that case. SteveBaker (talk) 22:02, 24 May 2009 (UTC)[reply]
I believe the ability to write them is one of the advantages they are pushing "Holographic methods take all of the information to be recorded and encode it in the form of a graph showing how often certain frequencies arise in it. That means that the recording process is a complex, all-at-once, all-or-nothing approach that would be difficult to implement on an industrial scale. By contrast, 5-D recording is "bit-by-bit", like current CD and DVD writing processes in that each piece of information is read sequentially." They do acknowledege the cost/development issues: "For the moment, Dr Milster says, the equipment needed to write the data would make a commercial system expensive. However, that has not stopped the development of optical storage solutions in the past. "For example, a Blu-ray player is not an easy system to realise; they've got some wonderful optics in there," Dr Milster said. "People thought that would be pretty difficult to do, but others managed to do it." " Nil Einne (talk) 21:55, 27 May 2009 (UTC)[reply]
I have read and re-read this article. Assuming (for sake of arguement) that both an irreststible force and an immovable object did exist (perfectly, of course)and they were to meet or collide, wouldn't they just cancel each other out and the end result would be nil? —Preceding unsigned comment added by 216.154.17.116 (talk) 21:27, 23 May 2009 (UTC)[reply]
Just because you say that such things can exist doesn't mean that they can. Neither irresistable forces nor immovable objects can actually exist - so it's truly meaningless to ask what would happen. Saying "for the sake of argument" doesn't allow you to logically debate illogical impossibilities. There simply is no argument, no paradox, just some meaningless words on a page. SteveBaker (talk) 22:06, 23 May 2009 (UTC)[reply]
The paradox is proof that such concepts are nonsense. That's what paradoxes always are - proof that your assumptions are flawed. --Tango (talk) 22:28, 23 May 2009 (UTC)[reply]
The real point is that, even if both these things could exist (which they can't), they could not exist simultaneously. The existence of an irresistible force means that there's no such thing as an immovable object, because if there were, no force would be irrestistible. That's a logical contradiction. And vice-versa. So they could never exist simultaneously, not even theoretically. -- JackofOz (talk) 02:34, 24 May 2009 (UTC)[reply]
Hmmm - I suppose they could both exist if they were the same thing. An immovable object would require infinite mass (F=ma) - and an irresistable force would require infinite energy - but since E=mc2, our infinite force provider will conveniently have infinite mass...which means it's also an immovable object! Since it can't be moved - there is no paradox. SteveBaker (talk) 03:41, 24 May 2009 (UTC)[reply]
Mathematically speaking, the answer to your question is everything. For example, if an irresistible force is exerted on an immoveable object, Elvis is alive. See the Paradox of entailment for details. — DanielLC05:50, 24 May 2009 (UTC)[reply]
Thanks everyone. I think I'll just stick with "they would cancel each other out leaving nil" cause that is easier for my wee brain to handle! —Preceding unsigned comment added by 216.154.23.87 (talk) 17:56, 24 May 2009 (UTC)[reply]
I answered this question at school when I was five years old. If there were such things as an irresistible force and an immovable object, the source of the irresistible force would end up moving toward the immovable object, attracted by its own force. Totally logical answer to a seemingly impossible question. --KageTora - (영호 (影虎)) (talk) 18:06, 24 May 2009 (UTC)[reply]
A similar paradox is this: a man in Ancient China advertises the most superior weponary; his sword, which will cut down all walls, and his shield, which will defend against attacks of the strongest arrows. A customer then asks him, "what if you put your own sword to your own shield, what will happen?" The answer is that the man advertising this items has to walk away, because if the sword breaks the shield, then the shield is inferior, and if the sword does not penetrate the shield, then the sword is inferior. ~AH1(TCU)20:36, 24 May 2009 (UTC)[reply]
You are not "hit" by them . They pass through the mostly empty space that you inhabit. Sorry. That's a fact, not a personal attack.Julzes (talk) 15:18, 26 May 2009 (UTC)[reply]
The anecdotal "counterexample" (not really the right word) I was given many years ago was: You can no more imagine the I.F. meeting the I.O. than you can imagine two men, each of whom is taller than the other. Hope that helps! --DaHorsesMouth (talk) 02:35, 25 May 2009 (UTC)[reply]
If i was to put a bottle of ice in front of a fan, would the fan blow air over the bottle which would cool, and would then cool down the surroundings? Would the air about a foot in front of the fan be colder with the bottle there than without the bottle? Would it make much difference to the temperature of the air around the fan, or would it be negligible? Thanks.—Preceding unsigned comment added by 86.177.122.34 (talk) 02:47, 24 May 2009 (UTC)[reply]
If the ambient air temperature is above the temperature of the ice (I presume it is) - then the fan will gradually warm up the bottle - eventually melting the ice - and the air blown over the bottle will be cooler than ambient. Heat is moved from the air into the bottle - so the bottle warms up and the air cools down.
Important Note: Fans don't make things colder.
They stir up the air and they make lightly clothed humans feel cooler - but they don't reduce the air temperature at all. The reason that standing in front of a fan makes you feel cooler is because your body produces heat which warms up the air next to your skin. That layer of warm air insulates you somewhat from feeling the ambient air temperature directly. The fan moves that layer of warm air away so that you can feel the cooler air that's all around you - which (because the ambient air temperature is lower than body heat) makes you feel cooler. This is what meteorologists mean when they talk about "wind chill factor".
But when the ambient air temperature is above body temperature - fans don't make you feel cooler - they make you feel hotter! It's like opening an oven door! (I speak from experience - it gets HOT in Texas!) SteveBaker (talk) 03:18, 24 May 2009 (UTC)[reply]
This is all true, except that Steve forgets that air circulation also cools human skin by helping sweat evaporates faster. However, most of it has nothing to do with the question, which is about cooling of the air due to ice as affected by the fan.
The bottle of ice will absorb heat and thus cool the air around it, at a rate which depends on the difference in temperature between the bottle's surface and the air nearby. The surroundings will be cooled as the cooled air in turn cools the air around it. If a fan is mixing the air, it will bring warmer air into contact with the bottle. This increases the difference in temperature and therefore the bottle will absorb heat, and cool the air, faster. So, yes, the fan will promote cooling of the surroundings (until all the ice is gone, which will also happen faster). However, I think the difference would be negligible, perhaps not even enough to make up for the heat added by the fan motor. --Anonymous, edited 04:31 UTC and again 07:27 UTC, May 24, 2009.
"But when the ambient air temperature is above body temperature - fans don't make you feel cooler - they make you feel hotter! It's like opening an oven door! (I speak from experience - it gets HOT in Texas!) "
Are you sure that this is true as a general statement? I would only expect it to be true at near 100% humidity. APL (talk) 07:43, 24 May 2009 (UTC)[reply]
Well, I see where you're coming from - removing the humid air from around the body theoretically gives sweat a better chance to evaporate into drier ambient air...but in the height of summer, it's rarely more than 30% humidity where I live - and fans definitely seem to make matters worse when the temperature hits 100F. Fortunately, we have air conditioned houses, cars, offices and shopping malls...so it's rarely a practical problem! SteveBaker (talk) 14:18, 24 May 2009 (UTC)[reply]
Thanks for the answer. The air conditioning point raises another question. Are most houses in the USA built with air conditioning pre-installed, or do most people have to have it installed afterwards? Are there many places in America where it isnt hot enough to warrant air conditioning in the summer months. Here in the UK we can have summers that have high enough temperatures, but those summers are an exceptional rather than the rule. As it is im sure the vast majority of houses are built without air conditioning because it usually isnt hot enough. My question is how much warmer would the average summer have to be in order for most houses to have air conditioning built-in,as a general rule?
In my personal experience, the existence of central air conditioning depends on several factors:
The age of the house. Back in the day, only large buildings had central air, with most having window-mounted air conditioners. Nowadays the technology's gotten a bit cheaper.
The price of the house. Let's face it: if you're rich, and it gets hot sometimes, you're going to buy a house with central air. If you're not rich, installing the window-mounted units, though a hassle, is worth the cut in cost. From my personal experience, the richer my friend's parents, the more likely they were to have central air.
The size of the house. This is slightly related to factor #3, but important: the bigger the house/building, the harder it would be to cool it with window/wall-mounted air conditioners.
In Texas, all houses less than maybe 20 years old will have central air conditioning. Older - low-budget houses might only have one or two window-mounted units - but very, very few people would have none. We get temperatures over 100F every year - 110F is not all that unusual. I doubt you could sell a car here that didn't have A/C. However, it wasn't always this way. Quite a few people who were born here recall living in houses with "swamp coolers" which is basically a fan blowing over a wet surface - the evaporation of the water cools the air - however it also increases the humidity and promotes unhealthy mold growth in the house - so people wouldn't turn them on unless they absolutely had to. Most of the deaths from high temperatures are amongst the poor and elderly who either don't turn on their A/C because of the cost - or can't afford to get their A/C repaired when it breaks. SteveBaker (talk) 16:13, 24 May 2009 (UTC)[reply]
Cartophilia
Is there an actual cartoneurosis called "cartophilia", or is it some sort of injoke? Ottre 03:52, 24 May 2009 (UTC)
Cooler to wear long sleeves in the sun?
Is it cooler to wear a long sleeved cotton shirt or a short sleeved cotton shirt when it's say 80 or 90 deg F outside in the sun? —Preceding unsigned comment added by 76.25.202.33 (talk) 06:02, 24 May 2009 (UTC)[reply]
Arabs traditionally wear long flowing robes in the desert. Loose long baggy sleeves may keep the heat off the skin, as an umbrella would, and circulating air would remove the heat from the underside of the fabric. 89.243.84.208 (talk) 10:05, 24 May 2009 (UTC)[reply]
I believe that the 'long flowing robes' thing only really works when the air temperature exceeds body temperature - which is not the case at 80 to 90F - so I'd go with short sleeves. However, if you have light colored skin - it may be wise to cover up in strong sunlight order to avoid the risks of skin cancer. SteveBaker (talk) 14:13, 24 May 2009 (UTC)[reply]
I think you are correct, but have your numbers wrong. You don't want core body temperature, you want skin temperature. I think that's about 33C (91F), so at the upper end of the OP's range it might be helpful. Also, if you are in direct sunlight you are being heated by radiation as well as conduction from the air, so being covered from the sun helps you keep cool. Wearing baggy clothes in the shade when the ambient temperature is below skin temperature is probably not a good plan, but either sunlight or high ambient temperature can change that. --Tango (talk) 14:45, 24 May 2009 (UTC)[reply]
AIR, skin temperature depends on the distance from the heart/body core, and at room temperature the extremities are around 25 °C (77 °F). Then again talking about the temperature of a non-equilibrium system is always dicey, with molecular sublayers and the such. I suppose the skin temperature would be highly dependent on the external temperature, which then leads us back to the original question (I swear I intended this as a helpful answer initially :-D).-RunningOnBrains(talk page)15:32, 24 May 2009 (UTC)[reply]
Indeed. I think the 33 degrees value I have stored away in my head from somewhere (possibly that question not long ago about radiating heat in space) was an average. For this question, we actually want the temperature of the arms, which I don't know (does anyone have one of those forehead strip thermometers? Put one of them on your arm and let us know what is says (and give us a rough idea of the ambient temperature where you are, and what you are wearing on your arms)!). --Tango (talk) 16:14, 24 May 2009 (UTC)[reply]
Thirty three degrees appears to be in the right range. According to one study, "the epidermis layer is uniformly effected by the environmental conditions irrespective of its thickness while the subcutaneous part is more influenced by the body core temperature. Also, the skin and subcutaneous tissues thickness play an important role in the temperature regulation under different environmental conditions."152.16.16.75 (talk) 00:16, 25 May 2009 (UTC)[reply]
It seems to me SB is close to being right and Tango is mostly wrong. 33 and 25 degrees C are irrelevant. Your skin temperature is probably NOT going to be that temparature when the air temperature is 36 degrees C for example and you've been out in the open for the past 5 hours. Sweating does help cool you down, but it's not magic. If your skin is exposed to 36 degrees C air it's not likely to end up much lower then that. In other words, while perhaps a bit lower then 37 degrees C, it seems unlikely it'll be that much lower whereby you'll skin temperature will be the same as or hotter then the surrounding air. Radiation obviously has to be considered which I haven't but the temperature of your skin in a cold environment is irrelevant. Obviously in the short term, if you go from an airconditioned room or car then you should consider it but that's only short term. Going from a non airconditioned but sheltered location will add some complexity but I expect it will have to be at the fairly high end, probably past 32-33 degrees C and again, that's only in the short term. Nil Einne (talk) 22:25, 27 May 2009 (UTC)[reply]
Remember that sunlight heats up the surface of the skin, possibly causing it to exceed 90F if exposed, and in addition it heats up the air, usually to several degrees warmer than in the shade, which is where temperature readings taken for weather condition reports are usually located. ~AH1(TCU)20:31, 24 May 2009 (UTC)[reply]
I would say from personal experience the short sleeve shirt. Actually no shirt is probably better. Particularly if there's wind. (And if your under shelter.) As SB says, this may not be a good idea if you have light skin and aren't wearing sun screen however. Note I'm primarily referring to the temperature range of the OP (and high humidity at that). I don't have much experience wiht temperatures much higher thankfully. Nil Einne (talk) 22:11, 27 May 2009 (UTC)[reply]
Strange blue sea creature on NSW coastline
Today I found many strange, shiny blue, frond like sea creatures at the beach. I live on the Central Coast, NSW, Australia. I've attached a picture I took of the creature (it was taken by me, on my iPhone, so sorry if it isn't the best quality). Here is a link to the image: http://img.skitch.com/20090524-874rj2bfh41pb9fn4tq3mhcdph.png
I was wondering if anyone could identify it for me,
Thanks,
Sam. —Preceding unsigned comment added by 58.107.134.227 (talk) 06:39, 24 May 2009 (UTC)[reply]
A link in the article on the G. atlanticus says that they can be "up to 6 cm", whereas the G.marginata is shown as being barely a quarter of that size. It's not clear, but I think that the IP above was probably right, some of the atlanticus specimens in google images are clearly of the size that you mention. Mikenorton (talk) 12:11, 25 May 2009 (UTC)[reply]
Theoretical lower bound of maximum member load in a truss?
We're building a bridge out of popsicle sticks as part of the Undergrad programme and in the design of the trusses I've found that different designs lead to quite different results. In some cases for a 100N load the maximum member load goes up to 200N while others only at 70N. Which led me asking, what is the theoretical lower bound of maximum member load for a given criteria? --antilivedT | C | G09:22, 24 May 2009 (UTC)[reply]
Swimming pigs
A friend of mine was relating the following factoid: pigs can't swim because their front trotters slash across their throats, opening the jugular and killing them. Is there even the slightest bit of truth to this?
That's hilarious, thanks Vimescarrot - I'm sitting here with him now, and just remembered that I myself have seen pigs swimming at the Royal Melbourne Show with little or no evidence of throat-self-slashing. Adambrowne666 (talk) 09:50, 24 May 2009 (UTC)[reply]
When watching a normal "live" broadcast, how long after an event happens before it shows up on my tv screen"?
Since most radio is local, I assume that the delay is very minor. But for a US Cable tv customer watching a "live broadcast from Rome", it might be quite a sizable delay.
I suppose I should clarify-- I'm looking for the actual answer, based on knowing about the electronics involved; I know the time it would take a truly instant broadcast at the speed of light.
The actual answer involves how long does it takes light to enter a camera, be digitized, be broadcast via satellite to New York, be received and altered, and then rebroadcast via satellite to the cable company which travels on wires to my digital cable box to my television which then re-emits the light.
I can only say that it varies by several seconds. My personal experience from switching between two television channels showing the same live events is a difference of up to around 4 seconds between the two channels. This is without a deliberate broadcast delay as far as I know (on European channels with less sensitivity than you Americans). I don't know how big the actual delay on the fastest of the two channels is. PrimeHunter (talk) 11:27, 24 May 2009 (UTC)[reply]
In some situations they actually insert several seconds of deliberate delay in live events in order to give themselves a chance to spot something going horribly wrong in the live feed and be able to cut it before it reaches viewer screens. Radio shows with live phone-ins are particularly careful about this - using up to 10 seconds of delay. SteveBaker (talk) 14:08, 24 May 2009 (UTC)[reply]
Communications satellites are typically 1.334 light-milliseconds (low earth orbit) to 0.1194 light-seconds (geostationary orbit) from the surface of the Earth. Hence there will always be a delay of at least 0.24 s in a communication via geostationary satellite: this delay is just perceptible in a transoceanic telephone conversation routed by satellite.
One satellite broadcasting system sends two carrier signals with 4-second delay between them. This enables the receiver to maintain a large buffer of the audio stream, which, along with forward error correction, helps keep the audio playing in the event that the signal is temporarily lost, such as when driving under an overpass or otherwise losing line-of-sight of any of the satellites or ground repeater stations. Cuddlyable3 (talk) 14:27, 24 May 2009 (UTC)[reply]
From the point of view of the speed of the recording and displaying electronics, you wouldn't notice the delay. If you go to a shop with a video camera display and you step into the view of a camera displayed on a TV ahead of you you'll see a very, very, very short between you moving and the image of you doing the same. Of course cable TV may well be encrypted and be decrypted by cheap hardware in your set top box which can add seconds to the delay. --203.202.43.53 (talk) 06:45, 26 May 2009 (UTC)[reply]
I have to wonder, how long of a delay could they insert before the show is no longer "live" and their claims to the contrary become legally-prosecutable false advertising? I suppose that's very much a subjective judgement call. Dcoetzee06:59, 26 May 2009 (UTC)[reply]
I'm sure the FCC (or whatever governmental broadcasting body you wish) has some sort of regulation about what can and cannot be considered "live." Livewireo (talk) 15:46, 26 May 2009 (UTC)[reply]
Why do humans need fat in their diet?
It is commonplace that humans get fat when they overeat. In other words, they can synthesise fat. Why then do humans need fat in their diet? 89.243.84.208 (talk) 10:28, 24 May 2009 (UTC)[reply]
Also, quite a few of the vitamins we need are 'fat soluable' - they are dissolved into fats that we eat - so if you have a totally fat-free diet, you can suffer rabbit starvation. 14:04, 24 May 2009 (UTC)
Fat is an important energy source. It has nine calories per gram, 2.25 times more than carbohydrates and proteins. Fat is necessary to displace carbohydrates as an energy source, and consuming less than twenty percent of calories from fat will almost invariably cause the carbohydrate intake to be too high. Very high carbohydrate diets (such as those obtaining more than two-thirds of calories from carbohydrates) can adversely impact lipid profiles, increasing triglycerides and suppresses HDL cholesterol.
The AMDR for fat and carbohydrate is estimated to be 20 to 35 and 45 to 65 percent of energy for adults, respectively. These AMDRs are estimated based on evidence indicating a risk for coronary heart disease (CHD) at low intakes of fat and high intakes of carbohydrate and on evidence for increased risk for obesity and its complications (including CHD) at high intakes of fat. Because the evidence is less clear on whether low or high fat intakes during childhood can lead to increased risk of chronic diseases later in life, the estimated AMDRs for fat for children are primarily based on a transition from the high fat intakes that occur during infancy to the lower adult AMDR. The AMDR for fat is 30 to 40 percent of energy for children 1 to 3 years of age and 25 to 35 percent of energy for children 4 to 18 years of age. The AMDR for carbohydrate for children is the same as that for adults—45 to 65 percent of energy. The AMDR for protein is 10 to 35 percent of energy for adults and 5 to 20 percent and 10 to 30 percent for children 1 to 3 years of age and 4 to 18 years of age, respectively.(http://books.nap.edu/openbook.php?record_id=10490&page=769) The Institutes of Medicine talk about the harmful effects of both fats and carbohydrates (see the lengthy chapters beginning here and here).
The USDA says:
A low intake of fats and oils(less than 20 percent of calories) increases the risk of inadequate intakes of vitamin E and of essential fatty acids and may contribute to unfavorable changes in high-density lipoprotein (HDL) blood cholesterol and triglycerides.
"The AHA notes that in the absence of weight loss, diets high in total carbohydrate (e.g., >60% of energy) can lead to elevated triglycerides and reduced HDL cholesterol. These effects do not occur with substitution of monounsaturated or polyunsaturated fats for saturated fat. NCEP suggests that monounsaturated fat can be up to 20% of total energy and polyunsaturated fat up to 10% of total energy."(http://www.diabetes.org/uedocuments/ADACardioReview4.pdf)
Foods that are high in fat tend to be palatable (they taste good) and high in calories per ounce. There are very few foods (with the exception of whole milk) that obtain a huge percentage of their calories from fat and are also high in water. This is why high intakes of fat may be associated with obesity, but studies comparing high-carbohydrate diets have produced conflicting results. Some studies, of course, show that carbohydrates are more likely to cause obesity than fats.75.89.27.94 (talk) 23:13, 24 May 2009 (UTC)—Preceding unsigned comment added by 71.31.105.41 (talk) [reply]
Thank you very much for all that, I shall try to study and comprehend that very carefully. I'm still surprised that its beneficial to eat what seems to me quite a lot of fat - I thought it was sinful in dietry terms. 89.241.155.179 (talk) 18:16, 25 May 2009 (UTC)[reply]
What has changed about agricultural practices to make the dust bowl of the 1930s something that does not seem to happen since then? Years ago the UK fens had the same problem with soil erosion, but that is never reported in the news or media now either. The fens farmers went through a phase of using very deep plowing with powerful double-engined articulated tractors in an unsuccesful attempt to stop the wind erosion, but I do not think such plows are used anymore. 89.243.84.208 (talk) 10:49, 24 May 2009 (UTC)[reply]
If I recall one of the main ecological reasons behind the dust bowl was poor agricultural practices like a lack of crop rotation. I suspect that changing back to more traditional practices will have gone a long way towards that end. I suspect the dust bowl phenomena is one of these exponential tipping-point type things, where once it gets bad it gets worse and worse and worse, but if you keep it from getting bad in the first place then it's not a problem. --98.217.14.211 (talk) 18:31, 24 May 2009 (UTC)[reply]
I'm thinking that the dust bowl occured in the first place due to overfarming; natural vegetation was removed (which holds the soil together) and new crops planted during a period of intense drought. The lore back then was that the "rain follows the plow", but that obviously did not occur, leading to the loose, dry soil blowing away. Today, there are a number of reforestation programs, which have helped to hold the soil together, so that a repeat of the dust bowl does not occur. There is one threat, however, that could cause prolonged dust bowl-like conditions in the near future. One degree Celcius (roughly 2F) of further global warming could turn much of the US Midwest into a semi-desert, meaning that the soil may blow away more easily once again, unless massive irrigation and plantation projects are farther exploited. ~AH1(TCU)20:28, 24 May 2009 (UTC)[reply]
While not quite as bad as the dust bowl, I do recall dust storms in South Dakota about 10 years ago that filled in the roadside ditches with dirt and reduced visibility to about 1/4 mile for 2-3 days. So these storms can still happen on smaller scales. 65.121.141.34 (talk) 13:53, 26 May 2009 (UTC)[reply]
Research indicates that the Raw Egg Eating Meme (REEM) originated circa 1890 with Bernarr Macfadden, the index case. The highly influential Charles Atlas became infected by 1920 and is reguarded by many historians as patient 0. In 1976 REEM went pandemic with the release of Rocky. It is now endemic within bodybuilding community. --Digrpat (talk) 20:33, 24 May 2009 (UTC)[reply]
what are the various aspects of this field instrumentation ? what are the research prospects ? Is instrumentation related to robotics ? if so how? —Preceding unsigned comment added by Srini279 (talk • contribs) 13:00, 24 May 2009 (UTC)[reply]
Instrumentation is a broad term - it can mean anything from TV cameras to little switches that turn on when a robot bumps into something...robotics are heavily dependent on good instrumentation (they'd be more likely to call them "sensors") because the computer inside is blind and deaf without them. With the rise in the applicability of robots, there is considerable research into the sensors they use. Finding novel sensors, making cheaper/lighter/lower-power-consumption/more-robust sensors and finding better ways to interface the sensors to the computer software - these are all hot research topics. SteveBaker (talk) 14:30, 24 May 2009 (UTC)[reply]
I read in this article that Phobos, with its orbit only 3000 miles from Mars and synchronized to always face the planet, is a "natural staging area for manned excursions to Mars." My question is: wouldn't it be difficult for a Phobos colony to be powered by solar energy if Mars completely encompasses the sky? Sappysap (talk) 15:02, 24 May 2009 (UTC)[reply]
One side of the moon always faces Mars - so there are several possibilities:
If you set up camp on the side of Phobos that's nearest Mars - then during your "mid-day", Mars is between you and the Sun and appears as a black disk that's blocking out the sun. During the night - the Sun isn't in your sky. However, there will be times around dawn and dusk when the Sun is low in your sky between the horizon and Mars. However, even during the day - Mars only takes up a quarter of the sky - so you'd get a few hours of sunlight in each 7.5 hour "day". However, even at midnight - Mars would be 2500 times brighter than our moon and 6400 times larger...that's quite a lot of reflected sunlight - so you'd probably get reasonable amounts of power from "marslight"...especially if you made solar panels that were most sensitive to red light.
If you set up camp on the side of Phobos that's furthest from Mars - then Mars is permenantly below the horizon and you get plenty of sunlight during the day (but no marslight at night).
You could also build tall, vertical, rotating solar panels on the North or South poles of Phobos then they would benefit from sunlight for all but maybe an hour a day when Mars gets in the way. Phobos has zero degrees of axial tilt - so unlike here on earth, the sun would never set below the horizon at the poles - the only darkness is when Mars gets in the way.
So - either put fixed solar panels on the equator as far as possible from Mars. You'll get full sunlight for almost 4 hours in every 7.5 hour "day"...or...put them on the poles and make them rotate one revolution every 7.5 hours. That's attractive because you only need to have enough battery storage to cover that one hour of darkness - and keeping the panels at 90 degrees to the incoming sunlight maximises their power production. SteveBaker (talk) 15:59, 24 May 2009 (UTC)[reply]
I believe Phobos' axial tilt it zero with respect to its orbit around Mars, not the Sun. Phobos' orbit is inclined 1 degree to Mars' equator which has an axial tilt of 25 degrees. So, if I'm visualising this correctly, that's equivalent to an axial tilt that varies between 24 and 26 degrees. I don't see how Mars would ever get in the way of the poles, though. Yes, I do! --Tango (talk) 16:09, 24 May 2009 (UTC)[reply]
Being so close to Mars, presumably there is a lot of tidal strain. Could that be used for power? I'm not entirely sure how - there is no ocean or atmosphere, so you would have to use tidal movement in the rock itself, which isn't particularly convenient. --Tango (talk) 16:03, 24 May 2009 (UTC)[reply]
That tidal strain will stress and release the rock, causing it to warm (the way a paperclip warms when you bend it back and forward). The insulated centre of the moon should be warmer than the outside, so that sets up a thermal gradient. You could, in theory, use that to run a heat engine (like an OTEC) but surely the thermal gradient will be so shallow that you wouldn't, in practice, break even. 87.114.167.162 (talk) 19:00, 24 May 2009 (UTC)[reply]
I doubt there is enough tidal strain in Phobos to be of any use given that
a) Mars gravity isn't very strong,
b) Phobos always shows the same face to Mars,
c) Phobos' orbit isn't very eccentric,
d) There isn't any large moon around Mars that could periodically tug on Phobos and steadily transfer energy to Phobos libration which would than be dissipated through tidal friction.
You probably have two lighting loops. It may be that one of those loops is being exposed to rainwater, causing a short circuit. That's a dangerous condition, and you should have an electrician look at it. 87.114.167.162 (talk) 18:46, 24 May 2009 (UTC)[reply]
I'm surprised it hasn't blown a fuze or tripped a circuit breaker - but yeah - this is very dangerous. Somewhere there could be a puddle that'll electrocute you when you step in it...also, as it dries out, there is a good chance of arcing and all sorts of other things that could cause an electrical fire. Definitely get it fixed ASAP. SteveBaker (talk) 21:55, 24 May 2009 (UTC)[reply]
Whoa, don't go overboard here! I mean, yeah, if there's an actual rainwater leak, it's dangerous and needs fixing. But it's common for fluorescent lights to malfunction in rainy weather if they're starting to fail -- my house is full of fluorescents and I see this all the time. Presumably the explanation is increased current leakage through the air when it's humid. Bill probably just needs to do the usual things for non-working fluorescents: check if they're properly in the sockets, change the tubes, check the wiring connections, replace the ballast. The latter two things are the sort of work where some people would say an electrician is necessary and others would say "learn how, then do it yourself"; I'll leave it at that. --Anonymous, 21:07 UT, May 25, 2009.
The intermittent problem could be a leak causing a short in the mains supply, but the lamps would robably keep going until the fuse or breaker interrupted the current. Do you find the fuse/breaker open? They do not, in general, reclose on their own. Absent that, we are left with the ballast, the starter, the socket, or a temporary open in the switching circuit. I doubt it is the lamp itself which is somehow sensitive to humidity or precipitation. If water is leaking into a connection such as a wire nut, insulating crud could build up. A screw terminal or push-in terminal could be loose producing intermittent operation only coincidentally related to rain. There could be an intermittent open in an underground cable, if the feed to the shop is underground, but that would likely affect all the lights. A qualified electrician could check for loose or corroded connections. The circuit should be turned off at the breaker while inspections or repairs are attempted. Edison (talk) 00:53, 26 May 2009 (UTC) Edison (talk) 00:53, 26 May 2009 (UTC)[reply]
prognostic markers
Hi I have been given the task of researching the 'prognostic markers' used in the management of breast cancer. I have no idea what the term 'prognostic markers' even means. Can anyone give me a definition please? Theres no article on them and Wiktionary doesn't seem to have heard of them either. Also if you know of any websites which may be of use for my research I would be grateful to hear about them! Cheers RichYPE (talk) 18:50, 24 May 2009 (UTC)[reply]
We should maintain a distinction between "prognosis" and "prediction" here... Prognosis assumes that a person has a disease, and that we are trying to use "prognostic markers" to tell how well or poorly they are likely to do, or whether they are likely to respond to a particular treatment. Prediction assumes that a person does NOT have a disease and we are trying to use "predictive markers" to tell whether or not they are likely to have the disease at some time in the future. While it is true that prognostication and prediction sometimes use similar assays, these are two VERY different things. --- Medical geneticist (talk) 23:36, 24 May 2009 (UTC)[reply]
Excellent point! I missed that in the prior answers, was focused on the OP. Thanks for pointing that out. --Scray (talk) 02:13, 25 May 2009 (UTC)[reply]
When I was younger, I recall reading a children's book that stated that the planet Saturn was composed of very light elements, and therefore could actually float on a hypothetical ocean that was large enough. I just did a google search, and I actually turned up this http://coolcosmos.ipac.caltech.edu/cosmic_kids/AskKids/saturnfloat.shtml
I guess I'm just looking for confirmation to this claim, because I figure that the dense core might create problems for this hypothetical scenario. ScienceApe (talk) 20:00, 24 May 2009 (UTC)[reply]
It's true. The average density of Saturn, according to Saturn, is 0.687 g/cm³, compared to 1 g/cm³ for water. There is a slight question regarding how you define the edge of a gas giant, but there is enough margin of error there that any reasonable definition will still give it a density less than that of water. --Tango (talk) 20:38, 24 May 2009 (UTC)[reply]
Saturn is mostly hydrogen so it is not surprising that its density is less than water. Jupiter is also mostly hydrogen but has a density greater than 1, but this is because of the great pressure in Jupiter. I expect that water at the same pressure would still have a greater density. As for floating, well no it would not. It is light enough to float, but any body of water large enough to float Saturn in would be larger than the planet. Saturn would lose its separate identity and be gravitationally melded into a new water+hydrogen planet, the combined body possibly being now large enough to ignite nuclear fusion and create a second sun in the solar system. In any case it would be spectacular, not at all like rubber ducks in the bath. SpinningSpark21:23, 24 May 2009 (UTC)[reply]
These kinds of comparisons are always very tortured, approximate and flawed. The problem with a gas giants is that they are kinda soft fuzzy things - and saying how big they are is a bit like asking how big a ball of cotton wool is. So you can come up with all sorts of density numbers depending on where you draw that line. Whether it would actually float is a really silly question - when you consider the gravitational pull of all of that water and of the planet itself - plus the fact that while the outer layers are really light - the core is pretty heavy and would obviously sink...but please - let's not go there! Suffice to say that most authorities say that it's mean density is less than that of water and quietly forget about floating. SteveBaker (talk) 21:52, 24 May 2009 (UTC)[reply]
Well, yes, obviously you can't actually float it in water. That would require the water and Saturn to be inside a gravitational field, which, in order for the whole thing to make sense, would have to be much greater than that generated by Saturn itself (just as when you float at apple at Halloween the apple is far smaller than the Earth). If you put Saturn in that gravitational field it would fall apart since it is only held together by its own gravity. "Would float" in this context just means "has a density less than that of water", it shouldn't be interpreted literally. --Tango (talk) 22:22, 24 May 2009 (UTC)[reply]
Yeah the question wasn't intended to really mean Saturn. The question was just about density, and buoyancy. Obviously, such a scenario can never exist with the real saturn, but that wasn't really the point of the question. ScienceApe (talk) 18:15, 27 May 2009 (UTC)[reply]
As an aside, I always wondered if that figure for density factored in the rings-- which I assume would be included in that bag with the rest of Saturn, even if the planet was in a rather misshapen form as the result of being in the massive gravitational field necessary for this thought experiment. 69.224.113.202 (talk) 04:24, 26 May 2009 (UTC)[reply]
True, but their volume is quite big, especially if you define Saturn as the ball containing the planet with rings. I don't think the rings are included and including them, however you did it, would reduce the density, so you still have it less than that of water for any reasonable definition. --Tango (talk) 11:50, 27 May 2009 (UTC)[reply]
Weird Bug
For the past couple of years I've seen this insect right around springtime, It's fuzzy, fairly large, has a black head and black legs, and the fuzz is mostly a dull yellow with a black stripe running width-wise through the center of his back.
No, a bumblebee does not "walk around" before it grows wings :) . Bumblebees have a complete metamorphosis, so their larvae look nothing like the familiar adult (winged) stage. Now, there are distant relatives of bumblebees called "velvet ants" (Mutillidae). Mutillidae females really do resemble wingless bees, or big fuzzy ants, in their adult stage; males, OTOH, have wings. Is that what you've seen? --Dr Dima (talk) 00:44, 25 May 2009 (UTC)[reply]
Jet fighters sometimes practice following the terrain at an altitude of just a few feet, called 'hedge hopping'. I'm wondering what would happen if such a jet misjudged things and found itself sliding along on its belly on a flat area of wet grass, like a sledge. If it had no significant damage, would it be able to get into the air again?. That suggests another question - why do aircraft have their wheels on poles? 78.146.52.86 (talk) 23:19, 24 May 2009 (UTC)[reply]
To answer your second question first, airplane wheels are setup to hold the airplane some distance (at least a couple feet) from the ground to keep the engines as far as possible from the ground. Propeller planes obviously need this distance to keep from smashing up their propellers. Jets also need this distance to avoid sucking in debris from the ground.
For your first question, you might check out Belly landing. Most planes would not be able to recover from even the softest belly landings under their own power. I'm not sure if a fighter plane could do it, they're supposed to be more rugged and definitely have very powerful engines. I doubt the pilot would attempt it, he would have no way of knowing how bad the damage was. APL (talk) 01:39, 25 May 2009 (UTC)[reply]
You've got to read it carefully - the wings didn't scrape along the ground as the OP is asking - the undercarriage support apparatus evidently worked like skids - protecting the underside of the wings from damage. Still - a pretty amazing happening! SteveBaker (talk) 01:43, 26 May 2009 (UTC)[reply]
What about an aircraft where the wings and underneath of the body formed a flat surface - can a wing lift if it has no air underneath it, but is just sliding along a flat surface? 78.146.108.137 (talk) 13:35, 25 May 2009 (UTC)[reply]
Well, when the wings get within about half their length of the ground, you get a build-up of pressure under the wing (it's called "ground-effect") that actually increases the amount of lift - but if the wings actually hit the ground, there is so much friction that the plane's speed would rapidly drop to the point where flight is impossible...and the damage that's inevitable means it's going nowhere afterwards. SteveBaker (talk) 13:46, 25 May 2009 (UTC)[reply]
(EC) It's called 'nap-of-the-earth' (NOE) flight. In peacetime, they are limited to something like 500 feet above the terrain - but in wartime, they can go much lower - 50 to 200 feet depending on the nature of the terrain and the aircraft type. Most fighters that do this have terrain-following radar - the pilot hands control of the height of the plane over to the computer because human reactions simply aren't good enough to do this at hundreds of miles per hour (and because you often want to do it at night!). Some aircraft avoid using active radar by having accurate digital maps of the terrain instead (I know the Royal Dutch Airforce F16's do this because I worked on that subsystem in a flight simulator we built for them). As for 'belly landings' - if the ground is very smooth - with no large rocks - trees, etc - then it's possible to do a controlled 'wheels-up' landing and not die in the process - but the plane is going to be a write-off. Most fighter pilots would rather eject. SteveBaker (talk) 13:44, 25 May 2009 (UTC)[reply]
Belly landing is a bad idea. Very good chance that you will clip some sort of obstruction or bump in the ground. Even if you don't, the airframe is not designed for that kind of stress. You will weaken your aircraft, and the FAA wouldn't want to re-certify the aircraft and risk it falling apart at 10,000 ft. 65.121.141.34 (talk) 16:07, 27 May 2009 (UTC)[reply]
May 25
Casino Royal Poisoning Scene
In Casino Royal, 007 is poisoned by digitalis and develops V-TACH. That would not occur, as digitalis SLOWS the heart rate. Why don't the movie producers take a few minutes to verify the medical scenes in their movies?
P.S. the poison was probably modeled off atropine, as victims of atropine poisoning exhibit the same symptoms as in the movie.
Interesting. Our page on ventricular tachycardia in popular culture does assert that this was a mistake in the movie. However, that statement is incorrect as far as I know, so I checked the source and found it much less reliable than our usual standard. Here is a reliable source, and here is another, to show that digitalis at high levels can cause ventricular tachycardia. So, I will correct our page. --Scray (talk) 02:05, 25 May 2009 (UTC)[reply]
A movie where the hero saves the world with a lucky draw to an inside straight is probably not one with a whole lot of reality checks. -- Tcncv (talk) 06:39, 25 May 2009 (UTC)[reply]
No, see, Bond was so skilled that he got great cards! Ghh. That whole poker thing was the low point of an otherwise fine movie. Could you perhaps explain this "tell" thing one more time? It's such a complex concept! -- Captain Disdain (talk) 11:53, 25 May 2009 (UTC)[reply]
Are you asking whether someone can get an STD without having sex? The answer is yes—some are spread through alternative means (e.g. HIV in blood transfusions) that may or may not be very likely, but can occur. Are you asking if being celibate by itself will give you diseases? No. --98.217.14.211 (talk) 00:33, 25 May 2009 (UTC)[reply]
I have read (I can't remember where) that because males do not stop making sperm, that a persons testicles could become overful causing a very painful, but if treated harmless, disease.DrewSmithWhat I've done04:27, 25 May 2009 (UTC)[reply]
That's just ridiculous. The idea that all of the sperm just stay alive indefinitely and keep swimming around in the testicles is silly to begin with; no other cells in our body manage to keep from dying, so why would sperm be exempt from this? The body will reabsorb any excess semen. It's not a problem. -- Captain Disdain (talk) 08:56, 25 May 2009 (UTC)[reply]
This is persistent myth, e.g. for the cause of nocturnal emissions. I'm not going to boldly assert that people who never ejaculate have no long-term health differences from those who do so regularly; for all I know it may affect hormone production, with consequent auxiliary effects. But I may assert that there have been no serious experiments one way or the other. Dcoetzee06:54, 26 May 2009 (UTC)[reply]
But that does not imply that not having regular ejaculations causes prostate cancer. Sperm that is not ejaculated is reabsorbed into the body. The idea of huge testicles indicating complete celibacy is a nice idea but untrue. There are cases of enlarged testicles [13](work safe) but the causes are well documented. 86.4.190.83 (talk) 07:36, 25 May 2009 (UTC)[reply]
Nuns and other women who never give birth are more prone to breast cancer, per [14]. It seems to be the giving birth rather than the sexual intercourse that makes the difference. This was documented back in 1713 and confirmed since. Edison (talk) 18:36, 26 May 2009 (UTC)[reply]
Strange aircraft wing
I've recently seem some very strange aircraft, and this article (http://englishrussia.com/?p=2331) says it has huge advantages compared to more classical designs. Obviously, it should have it's flaws, because else nearly every aircraft would be designed lika that. Does anyone have any ideas about this? Besides, it's strange that it has no article here, as Elliptical wing means something completely different. --131.188.3.21 (talk) 09:57, 25 May 2009 (UTC)[reply]
My guess is that this would behave much like a biplane and have the same advantages and disadvatages. Aircraft were originally built as biplanes mainly for structural reasons - a single canvas wing is very difficult to tension - but once aluminium started to be used strong monoplane wings could be built. A biplane has greater lift than a similar sized monoplane but it is not twice as much because the vortex of the two wings tend to cancel in the space in-between the wings. Monoplanes are therefore more efficient in terms of lift per unit area of wing. This elliptical design gets a good separation between the top and bottom aerofoil surfaces so the negative effects may be somewhat lessened. Like a biplane, it is likely to have good manoeuvarability and short takeoff and landing characteristics, but I have not been invited to fly one, so as I say, I am only guessing. SpinningSpark10:55, 25 May 2009 (UTC)[reply]
I have no idea whether that's real or not, but this being the internet, the picture could simply be fake. I suspect it is; the design seems pretty senseless, and I can't find a single YouTube video featuring such a plane, at least not with the words "elliptical wing". In fact, even fairly rigorous Googling only reveals those very same pictures all over the net...
In any case, even if it was real, your logic is a little iffy: saying that the design must be faulty, because otherwise every aircraft would be designed like that presupposes that people instantly arrive to the best solution. I mean, why didn't the Wright brothers build a stable aircraft right from the beginning instead of the flawed contraption they had? Well... you gotta start somewhere, and if you hit upon a design that works (not that the Wright brothers really did, but anyway), it can remain essentially unchanged for a long time simply because it's good enough. (The M1911 pistol is a great example of this: it's still being used by some armed forces, even though the basic design is over a hundred years old. There are far more advanced sidearms out there, but it's a popular classic.) It can take a long time for a genuine innovation to arrive and really make an impact. -- Captain Disdain (talk) 10:57, 25 May 2009 (UTC)[reply]
Oh, I think the photos are real: at least the ones at the top of the page, the bottom two are obvious fakes. What I don't believe is that it has ever got off the ground, and you would be quite foolhardy to take off in something you had bolted together in your back yard and has a side panel that looks like it's been in a car crash. There are no (unfaked) pictures of it actually in the air, although the engine and prop are clearly working. SpinningSpark17:30, 25 May 2009 (UTC)[reply]
For a small aircraft that needs high manouverability, I could imagine this thing being interesting. However, it loses the benefits of 'dihedral' (which imparts inherent stability) - it will be hard to fly (although computerized fly by wire controls could fix that). Who knows what construction difficulties and structural strength this design might impart? The claim for high efficiency comes about because with conventional wings the higher pressure air under the wing tends to 'leak' around the wing-tips into the low pressure air that's on top of the wing. That wastes lift and causes tip-vortices which increase drag. This wing has no tips - but the high pressures under the lower section of the ellipse can still move around to the low pressure over the top section - but that's a much larger vortex. But then the high pressure under the top section will push around into the low pressure over the bottom section - creating a counter-vortex. It's really hard to predict the results of these two counter-acting effects. The 747-400 (see picture at right) has little wing-tip fins that attempt to 'dam' that air. I dunno - it's hard to imagine someone like NASA wouldn't already have tried this if it had widespread benefits...they've tried some pretty weird designs in the past so it's not like there is a lack of effort in innovating wing shapes. SteveBaker (talk) 13:26, 25 May 2009 (UTC)[reply]
Although that particular aircraft has no dihedral, there is no essential reason that wings in that format could not be given dihedral so I don't think that dihedral is an essential drawback to the ellipse-wing. Besides which, stability is not always a good thing. Stability and manoeuvarability are exchangeable and are a compromise on all aircraft; for military fighter aircraft manoeuvarability has overriding importance and for this reason, amongst others, stability is often low. Likewise aerobatic aircraft want manoeuvarability over stability. The Cessna 152, for instance, is so stable that you can put it into a stall, let it start dropping like a stone and then let get of all the controls. The aircraft is so stable that it will pick up speed, start flying again and then level out into straight and level flight all by itself (warning: don't try this at home) as if it had an autopilot. On the other hand, it is no fun to fly, equivalent to exchanging a sports car for a minibus. Likewise with the winglets, there is no essential reason they (or some other wingtip device) could not be fitted to an ellipse-wing, although I am unconvinced that there is a need for them. The smooth shape of the ellipse-wing at the "tip" will encourage laminar flow, removing one of the reasons for them. SpinningSpark15:50, 25 May 2009 (UTC)[reply]
Occasionally there is a reference to "Steam II" as if there are two phases of steam. However even this rather complicated phase diagram of water, which identifies a grand total of eleven different phases of ice, does not mention steam II. Would it be steam in the supercritical region? SpinningSpark11:14, 25 May 2009 (UTC)[reply]
The title of the article that you linked doesn't say quite what it seems to, it's the second part of a two-part article, this is the first [16]. Mikenorton (talk) 13:13, 25 May 2009 (UTC)[reply]
I have asked this question three times before. Each time, there is no answer because the topic is quickly derailed by discussions of artificially colored hair. Therefore, I want to make this clear: I am not in any way interested in any discussion of artificially colored hair.
When hair turns gray, I have always seen a hair that is gray from root to end. My hair is dark brown and my gray hair is actually white. I have no hairs that are brown on the end and white at the root. This makes me wonder... Do hairs turn from natural color to gray? If so, how does the entire hair change color? Do the gray hairs come from a different follicle than the natural colored hair? I'm just wondering why I never see a hair that is brown on one end and white on the other. -- kainaw™15:32, 25 May 2009 (UTC)[reply]
From personal experience, I have come across hairs that are coloured near the end and grey/white at the root, but very few. In those hairs there is a short (~1 cm) transition zone of decreased pigmentation rather than an abrupt loss of pigmentation. I suspect the reason that they are hard to find is that there are so many hairs on your head. Those that are in the midst of losing their pigmentation are hidden among the other hairs. They only become noticeable when you get your hair cut, and cut hairs likely would have removed the coloured bit. -- Flyguy649talk15:52, 25 May 2009 (UTC)[reply]
I am in agreement with Flyguy649, with the additional note that white hairs are often thinner and more brittle than coloured hairs. It could be that the bi-coloured hairs are more likely to break off and be lost due to the tip being to heavy for the white base. Matt Deres (talk) 15:56, 25 May 2009 (UTC)[reply]
Each individual hair is produced by a single folicle. Each folicle loses its ability to produce color at a different age. So, hair produced by a folicle before the loss is colored, and after the loss the new hair is gray. Therefore, the timr it takes for particular hair to becoem completely gray is the time it takes to grow from root to tip, which in turn depends on the length of the hair. Most hairs are eithr all colored aro all gray because the time is relatively short in comparison to the time span over which all your folicles lose their coloring ability. -Arch dude (talk) 20:59, 25 May 2009 (UTC)[reply]
There was a recent article on sciencedaily.com about grey hair here. The gist is that hair goes white because our bodies naturally produce bleach, and as we age we are less able to remove that bleach. The article also says that hair goes white from the inside out. Quietmarc (talk) 22:03, 25 May 2009 (UTC)[reply]
Each hair follicle does not keep producing hair constantly. Instead, there is a cycle of growth, quiescence, hair loss, and then renewed growth. While I don't have anything to show this is the case, I imagine that the color loss may occur during the quiescent to renewed growth phases. In this way each individual hair shaft is either entirely colored or entirely gray. -- 128.104.112.37 (talk) 00:32, 26 May 2009 (UTC)[reply]
I believe 89.242.ip is referring to gorrilas, not guerillas. Often what happens is that individual hairs become white, and as the proportion of that increases, the mas of hair appears more "gray". ~AH1(TCU)01:14, 26 May 2009 (UTC)[reply]
It occurs to me that if you can't get a satisfactory answer from reliable sources, it would be a good idea to ask or look into the situation for a traditionalist/adherent Sikh, Rastafarian or someone else who never cuts their hair Nil Einne (talk) 22:00, 26 May 2009 (UTC)[reply]
As an aside, its probably not a good idea to compare the mechanism of hair colour of other mammals to that of humans. Most mammals have striped hairs - in that there are bands of different colours. For example, of you look at the pelt of a wild mice - that typically looks brown - you will notice that each hair shaft is actually is yellowish at the tip and black nearer the root. The sum of this gives the brown hue to the pelt. This type of hair pattern is called agouti after the eponymous rodent. This is caused by the pulsatile expression of the Agouti signalling peptide around the hair follicle, which switches the production of pigment from black to yellow. ASP is only turned on during the early growth phase of each hair, therefore only the tip of the hair is yellow. By modifying the Agouti gene locus so that that peptide is expressed at different times or in different parts of the body one can get animals of all sorts of hues. The silverback gorilla is likely to use a modified version of this system. However during human evolution, we appear to have lost this signaling system, so we no longer have banded hairs under genetic or hormonal control. In contrast, our hair turns white when the follicular melanocytes die. As others point out above, there may be a few human hairs that "fade to grey" along their length, but the likelihood of finding one is small, due to the timespan it occurs in. Rockpocket06:19, 27 May 2009 (UTC)[reply]
Thanks. I want to note that I've already written a lot about ASP in hedgehogs. Hedgehog quills are normally tri-band. Through inbreeding, there are many mutations that cause a lot of variety in the tri-band colorings. However, none have come out blue yet. -- kainaw™12:34, 27 May 2009 (UTC)[reply]
Racism and science.
Why is racism a scientifically wrong belief? The article on racism doesn't explain it clearly enough.
Thanks in advance,
― Ann ( user | talk )15:49, 25 May 2009 (UTC)[reply]
Because there are no scientifically reliable methods of discriminating races from each other. The methods that can be used (such as using haplo-groups) often have little to do with the conventional races at all. Also, you would need to specify which brand of racism you want to talk about. Most racism has nothing to do with rational thinking in any case. Since science attempts to be rational, the two have little to say to one another. Matt Deres (talk) 16:03, 25 May 2009 (UTC)[reply]
(edit conflict) There is no scientific evidence that can't be explained by differences in culture. It also hasn't been proven that the cause is differences in culture rather than being of different intelligence, so it isn't so much scientifically wrong as just not scientific. If there is a difference, it's not that big, so anything more than mild racism is scientifically debunked. It should be noted that if there is a small difference in the intelligence of different races, that doesn't mean that it's in the direction a lot of people seem to think it is. Also, even if there was a difference, it couldn't easily be said which was better. For example, there is a clear difference in how men and women think, but there's no agreement as to who is more intelligent. — DanielLC16:10, 25 May 2009 (UTC)[reply]
It's also of note that any racial differences are probabilistic over the aggregate of a population. So what you're saying is, "in a given population (defined in some sort of useful way), the average IQ is X." But that doesn't tell you anything about individuals within the population, which is how racism is always practically expressed—you don't get the job not because you don't have the ability, but because you are a member of a population that on the aggregate has different abilities than others. You can illustrate how silly this is by doing the reverse (boosterism)—imagine being asked if someone is a good basketball player on the basis of their race alone. The idea is completely silly—any individual member of a race could be a good or bad basketball player, even if on the whole for a variety of reasons some races might on average produce better basketball players than others.
The definition of "race" is itself scientifically problematic—there are no "pure races" and never have been. The most rigorous scientific definitions are still very probabilistic—people who live in a given area have a certain higher percentage of having certain combinations of genes than people who come from other areas. In reality there is a graduate spectrum of relatedness among the human species.
Lastly, the question can never be is "racism" scientific—racism is a form of social judgment that sits on top of questions of racial difference. Are there racial differences? Obviously some (on average)—some of which are easy to measure (skin tone variations) some of which are hard (intelligence, which is hard to measure even under ideal circumstances). Whether one thinks that justifies discrimination is an entirely non-scientific question (it is a philosophical or political question). --140.247.241.193 (talk) 19:42, 25 May 2009 (UTC)[reply]
One of the problems is the meaning of the word itself. Scientifically, racism means the view that people from different origins have different characteristics besides their look. So, saying that someone from African descent and with dark skin tolerates a hot climate and sunburn better than a Caucasian, and the later tolerates cold and a lack of sunbathing better - which is obviously true - would still be considered racism? The problem with this is that the word "racism" means today just "something very evil" and nearly nothing else, and actually used to discredit some other party even if they didn't mean to discriminate people based only on "racial" descendence. I think this discussion would more likely fit the humanities desk, as the world racism has mostly propagandistic uses. Besides, with this current usage, no one even dares to study or write about racial differences, and writing "racism is scientifically wrong just because it's wrong" is a must, if you do not want to be labeled as someone very evil.
Of course, racism in it's current usage is wrong, as the behavioral differences seen in statistics are caused by cultural, educational or other social heritage, and not by biological makeup.
The interesting, and sad thing is, that forcefully denying the above mentioned behavioral differences (and calling everyone a racist who mentions them) actually leads to increase racism, rather than solve the problem. Of course, saying that these behavioral differences are cause by the genetic profile of that specific group is equally wrong. I prefer referring as racism only to this last example, and not how most politicians tend to use it. --131.188.3.20 (talk) 20:46, 25 May 2009 (UTC)[reply]
Racism is like claiming that within a species, there are breeds that are better at some activity than other breeds. Aren't all horses equally able to run a race or pull a plow? Aren't all dogs equally able to track, pull a sleigh or herd ruminants? Don't all pigeons have the same homing ability? Edison (talk) 00:47, 26 May 2009 (UTC)[reply]
Was the answer to those questions supposed to be no? A Chihuahua can't pull a sleigh nearly as well as a Great Dane. In any case, that's not very scientific. You have to actually check, you can't just say what it should be. — DanielLC05:11, 26 May 2009 (UTC)[reply]
Racism might be more like assuming that dogs of some particular color are more likely to bite you than others. But Temple Grandin, animal scientist, claims that the selective breeding which led to chickens which lay white eggs has left the hens more prone to stress. White lab rats have behavioral differences from wild rats of various fur colors. Minor physical or coloration differences between subgroups of an animal species may correlate to varying extents with behavioral differences. I have heard intelligent and well educated people assert that there simply cannot be any differences in intelligence, aptitudes or physical abilities between races, on the same principle that there should not be discrimination between different races. Edison (talk) 18:30, 26 May 2009 (UTC)[reply]
Yes, clearly there are the possibilities of differences on average between population groups, and anyone who disagrees with that on the face of it is probably doing so for primarily political reasons. But dogs are a very poor comparison—dog breeds are very carefully developed exercises in inbreeding over tens of thousands of generations with relatively small population sizes for specific characteristics that often are at the expense of others. There is nothing comparable in humans, and the differences between human races are really quite slight when compared to differences between dog breeds. (Temple Grandin is careful to point out that what she says about domesticated breeds does not apply to human races, if I recall.) --140.247.251.62 (talk) 18:49, 26 May 2009 (UTC)[reply]
There are two entirely separate things going on here. It is entirely scientific to say that there are races - and that they are different in many ways. We know (for example) that people of African descent are more prone to sickle-cell anaemia...it's a fact - there is no point in denying it. There are LOTS of differences between people of different races. It's scientifically valid (but not entirely politically correct) investigate those differences.
HOWEVER, what is entirely UN-scientific is to discriminate between individuals on the basis of race. The variations between individuals of one race are generally far greater than the differences between races - so to pick one individual and to treat him/her differently because of the color of his/her skin is entirely illogical and unscientific.
Actually, I think that is inaccurate. First, of course, we are all "People of African descent". But secondly, people with a a long ancestry from malaria-prone areas are more prone to sickle-cell anemia. Many Africans are, but then, many are not. By lumping them all together, you are artificially creating a "race" that, quite by accident, shares this property, while the actual cause only applies to a sub-population. "Races" are social constructs with fairly limited predictive power about the non-obvious criteria - in Brazil, for example, your income and life style influence your perceived skin colour... --Stephan Schulz (talk) 07:26, 26 May 2009 (UTC)[reply]
I'm surprised this hasn't already come up but I think this is highly relevant to the discussion race and genetics. A key part IMHO "The 0.1% genetic difference that differentiates any two random humans is still the subject of much debate. The discovery that only 8% of this difference separates the major races led some scientists to proclaim that race is biologically meaningless. They argue that since genetic distance increases in a continuous manner any threshold or definitions would be arbitrary. Any two neighboring villages or towns will show some genetic differentiation from each other and thus could be defined as a race. Thus any attempt to classify races would be imposing an artificial discontinuity on what is otherwise a naturally occurring continuous phenomenon.". While not everyone agrees "However, other scientists disagree by claiming that the assertion that race is biologically meaningless is politically motivated and that genetic differences are significant. Neil Risch states that numerous studies over past decades have documented biological differences among the races with regard to susceptibility and natural history of a chronic disease. Effectively Neil Risch is attempting to redefine "race" for human populations to represent that small proportion of variation that is known to vary between continental populations." I don't think it is fair, or logical to dismiss all scientists who argue that race is biologically meaningless as just letting their political beliefs get in the way. I would say that both sides are likely influenced by their political beliefs but regardless, it doesn't mean there aren't valid scientific reasons to argue both ways about whether race is a meangingful scientific concept. This doesn't mean people dispute that certain genes are more strongly associated with certain groups if you choose to define such a group in some way Nil Einne (talk) 21:53, 26 May 2009 (UTC)[reply]
This is a pretty complicated question. One might reasonably say that, given no other evidence about two people other than their races, you may prefer one over another for a certain job or task, since race conveys limited statistical information about a person. Irrational decisions arise in situations where the statistical information supplied by race is given disproportionate emphasis over the direct information supplied by examining the individual; or over information about the individual that could be easily obtained. Irrational decisions also arise in cases where the statistical information supposed to arise from race has no basis in experiment, or those experiments are procedurally faulty (as in the case of most scientific racism). To give a ludicrous example, young males tend to break bones more often young females; therefore, given a random young male, you'd be more likely to conclude that their leg is broken than when given a random young female. On the other hand, a much better way of determining this is to actually examine their leg. Dcoetzee06:39, 26 May 2009 (UTC)[reply]
casimir effect pressure anomalies
Hello
Alot of talk about zero point or vacuum energy has been passed around lately and its been used to explain everything from telepathy to gravity. Loads of it is complete hocum some is not. I was wondering if you guys could help clear something up for me. I recently read an article that proposes that changes in the state of this vacuum energy either on its own or to cause upsets in air pressure etc could mave objects. Is this possible if not yet proven and what is the view of the general scientific community on this idea. I read it was considered as a means for space propulsion. Note I am not talking about psychic connections, healing, living universe etc, just wether the changes in the vacuum could conceivably move objects.
Do you have a link to the article? Generally speaking it's deeply unclear what ought to count as "vacuum" in modern physics. If there are vacuum disturbances that can exert forces on objects then we're likely to decide to give them some other name than "vacuum", making the vacuum inert by definition. That's pretty much what the known particles and forces are, fluctuations of the vacuum that we've decided to call by different names. Note this includes the Casimir force, which is no more or less an effect of vacuum fluctuations than anything else. -- BenRG (talk) 19:02, 25 May 2009 (UTC)[reply]
The article was on the new scientist and suggested a vacuum energy sail, ill try find a link. Think it suggested a polerization of the vacuum so one side vibrates more and thus exerts more pressure on one side, thus moving it. Like the casimir effect except instead of pushing the two mirrors together only pushing one side.
I haven't had a chance to dig up this particular New Scientist article yet, but I would urge its readers to be particularly cautious when new inventions which (apparently) violate conservation of momentum laws appear. The most recent major screwup – of which I am aware, at least – was in 2006, when they published a very credulous cover story on the EmDrive. TenOfAllTrades(talk) 12:52, 26 May 2009 (UTC)[reply]
Thanks for the link. This doesn't look like reactionless propulsion, it looks like a very roundabout description of a photon drive, i.e. a rocket that emits light for propulsion. In other words, it's a Rube Goldberg flashlight. The whole vacuum-fluctuation angle doesn't make it a better source of photons. For that matter I could probably figure out a way of attributing the operation of an ordinary battery-powered flashlight to vacuum fluctuations. That New Scientist reported on this doesn't mean anything. I think it was once a good physics magazine, but it's pretty cringeworthy these days. They seem to have no knowledgeable physicists on staff and a lot of their articles are basically press releases for kooks. This looks like it's in that category. -- BenRG (talk) 21:20, 26 May 2009 (UTC)[reply]
I agree with that. I wouldn't recomend the New Scientist to anybody that actually wants to learn anything about real science. Scientific American is still a better choice of science-to-the-public magazine than any other I've seen. Dauto (talk) 15:17, 27 May 2009 (UTC)[reply]
the color of protons/nutrons
There are so many different elements and many of them are different colors. Though they are all made of the same things protons nutrons and electrons? How can somthing made from the same things have so many different colors? how can a material be a different collor just because it has a dirrerent amount of nutrons electonrs or protons? So if we could look at a seperat nutron of sepret proton what color would it be?
--76.236.178.7 (talk) 16:27, 25 May 2009 (UTC)[reply]
Your understanding of colour seems to be wrong. I'm not an expert in the area, but the A-level chemistry explanation is that photons from a light source (e.g. the sun) are absorbed by the electrons of an object, which causes excitation of the electrons, so the jump up to a higher "energy state". When the electron falls back to its ground state, an electromagnetic wave is emitted. In chemicals that we see as coloured, this wave is in the "visible light" area of the EM spectrum (between ultraviolet and infrared). Protons and neutrons individually won't have a colour, I believe. --Mark PEA (talk) 16:55, 25 May 2009 (UTC)[reply]
...so many different elements..., actually, most elements are metals, and most of those are some shade of grey/white (with the exception of gold and copper) not many different colours. Or did you mean chemicals rather than element? SpinningSpark17:10, 25 May 2009 (UTC)[reply]
Mark's explanation is a pretty good one - in the case of 'diffuse' reflection (which gives objects their color) - the light is absorbed - kicking an electron up to a new energy level - and re-radiated at a different frequency when the electron gives up that energy. But shiney surfaces use a much more complicated mechanism - requiring 'quantum electrodynamics' to explain how they reflect light (typically without changing it's color). It's a complicated matter - and it's WAY more complicated when you stray from pure elements to chemical compounds where the interaction of lots of different atoms causes the phenomenon of color.
Things as small as electrons, neutrons and protons are far too small to reflect light. A 'wave' of visible light is between about 400 and 700 nanometers - an atom of (say) carbon is around 70 picometers - that's around 10,000 times smaller than the wavelength of light. That's why you can't see individual atoms in a normal microscope. Protons, neutrons and electrons don't have a 'size' at all - they are just infinitely small dots. So when you get into the physics of how light is reflected or refracted, absorbed or radiated, it all gets very complicated. It's wrong to think of things as small as atoms as having a 'color'. SteveBaker (talk) 01:21, 26 May 2009 (UTC)[reply]
Of course, not to confuse the living shit out of the OP, but while protons, neutrons, and electrons do not have a color, quarks do. Well, not really, but they have a property which is not a color, but we call"color" just to confuse the living shit out of people. See Quantum chromodynamics for more living-shit-level confusion of quark color... --Jayron32.talk.contribs00:54, 27 May 2009 (UTC)[reply]
They are sometimes found in caves. Are there caves in Missouri with snakes which have over generations lost the use of their eyes? Edison (talk) 00:43, 26 May 2009 (UTC)[reply]
The question is not so much the number of eyes but the way the brain puts the information together. I think it's going to be hard to make sense of that through human understandings of such things (one big coherent image is sort of what we are used to—imagining it as eight different images is probably not actually how the spider sees it and says more about our understanding of vision than theirs). --140.247.241.193 (talk) 19:58, 25 May 2009 (UTC)[reply]
Yeah - it's really not possible to know. For example - human eyes have a blind spot in each eye - literally, a place in the middle of the retina where you are totally blind. Are you aware of this spot? No! In fact you have to go to considerable trickery to fool yourself into actually noticing it! Are you aware of the continuous vibration of the eyeball that's used to improve spatial resolution...do you notice that? No! Are you aware of not being completely unable to see color in your peripheral vision? Nope? I thought not! Our brains are very good indeed at hiding the deficiencies of the system from our conscious minds. I assume the spider's brain is doing something similar - but perhaps it isn't - we really have no way to know from simply looking at the geometry of the spiders' ocular geometry. Hence we have no clue how the world looks to it. SteveBaker (talk) 01:07, 26 May 2009 (UTC)[reply]
Is it even possible for the human mind to comprehend what a 3D view constructed from eight separate images (making a huge assumption here in suggesting that this is how a spider's visual system actually works) would look like? I guess that a computer might be able to knock one out (in the same way as you can get them to draw multidimensional shapes that make your head hurt if you try to visualise them as meatspace objects)...
(1) On the poor color sensitivity in human peripheral vision - it is true, and well known. AFAIR, it is related both to the low number of cone receptors in the peripheral retina and to how the ganglion cells in the peripheral retina are "wired". Actually, it is also very easy to test. Pick up one color pencil from a set, without looking, and hold it in the outstretched hand at eye level, starting as far back as your hand would go. Now move it very slowly forward. At some stage you will be able to see the pencil out of the corner of your eye. Now ask yourself what color it is. You'll be surprized... (2) On the spider vision - we can not possibly imagine what spider "sees" as it possesses a brain architecture very different from ours. However, if we imagine that all the processing that occurs in the retina and beyond is similar in spider and in human (which is not true), then having additional eyes is not much different from having a rear view mirror in a car, or having several graphic application windows opened at once on your computer monitor. My point is, simply having more eyes is not the main difference between the spider and a human :). Spider visual system is truly unique and truly exquisite, especially in Salticidae, Lycosidae, and some other active hunters. Unfortunately, it is far less well studied than rodent, cat, or primate visual system. Still, googling for "spider vision" returns plenty of fascinating stuff. --Dr Dima (talk) 07:17, 26 May 2009 (UTC)[reply]
The cone cells detect color but the rod cells only detect overall brightness. However, the rods are faster and more sensitive to subtle brightness changes. As cone cell says - the number of cones drops off around the periphery of the retina. Hence, color sensitivity drops to essentially zero at the edges of your field of view...it's like watching a black and white television. The evolutionary reason for this is that you need to be acutely aware of things happening in your peripheral vision where a predator might be sneaking up on you - so you need cells that are fast, responsive to motion and to the subtle brightness changes that come about when a shadow is cast nearby or something. We probably evolved color perception mostly for detecting whether fruit is ripe or not - but for that you can look directly at the fruit and get it in the center of your visual field where color perception works best. But unless you try experiments such as Dr Dima (above) suggests, you're totally unaware of the fact because your brain 'censors' that kind of annoying detail. The color you think you're seeing around the edges of your visual field is guessed or remembered from the last time you looked in that direction. That's why in Dr Dima's experiment, you need to pick a colored pencil at random - and WITHOUT LOOKING AT IT - move it into your peripheral vision. Since your brain can neither guess nor remember the pencil's color - it gives up trying to fool you and you see it in shades of grey. The 'censorship' is so good that User:4.242.147.133 demands documentary proof of something he/she has been looking out for an entire lifetime and never noticed! Is that cool or what?!
So is the spider 'aware' that it has eight eyes? Perhaps...but perhaps not. We really have no way to know what it's visual cortex hides from it's higher brain functions. If you didn't know you had two eyes and had no independent control of your eyelids - it would be pretty hard for you to figure out that you have two of them. Our perception of eyesight isn't two separate pictures - it's one 'fused' image...most of the time. But then think about a chameleon - it's two eyes are steerable in two utterly different directions - does it somehow still see one fused image? If you try to simulate what the chameleon might see by (for example) putting a mirror at 45 degrees in front of one of your eyes and turning it around - you get the impression of two images overlaid on top of each other - not two completely separate pictures. Pilots who fly the Apache helicopter actually have to learn how to see two separate images (like a chameleon presumably does)! That's because the Apache requires you to wear a helmet that has a monocular display that comes from a camera on the front of the aircraft over one eye and straight through, normal vision with the other eye. Normally, the monocule shows an infra-red view that "overlays" your normal vision - but it can be zoomed in and out so the two images don't match anymore - and they still have to be able to fly the helicopter and target weapons at the same time - using one eye for each purpose. Apparently a large fraction of people who try to do this mental trick never manage it and flunk out of Apache-flight-school-101 as a direct result of that.
There is anecdotal evidence (and even videos on youtube) that claim it to be false. There is even a popular book that uses this very question as a title. Most of the people who say that cows can walk down stairs say that the animal has to either be led or otherwise enthused to do it and will not approach a downward set of stairs of its own volition. The same can be said of other animals with similar hind legs such as dogs, horses, donkeys, goats and sheep - all need encouragement or leading but will eventually do it. Nanonic (talk) 17:22, 25 May 2009 (UTC)[reply]
Try going up a flight of stairs on all fours, and you'll find it easy. Try going down a flight of stairs on all fours, and you'll be hesitant at the very least. It can be done, but you have to adjust the way you would 'normally' crawl on all fours. Try it and see. --KageTora - (영호 (影虎)) (talk) 21:06, 25 May 2009 (UTC)[reply]
KageTora, That experiment is faulty. Cow knees bend the opposite way from our knees and elbows. Many four-legged creatures are like that, including dogs and cats. APL (talk) 01:00, 26 May 2009 (UTC)[reply]
I believe that those are not knees, but rather the animal's ankles. The knees are usually located way up the thigh. Look at the flamingo, for example, where the ankles are actually midway between the end of the legs and the torso. ~AH1(TCU)01:03, 26 May 2009 (UTC)[reply]
Fair enough. My point was only that the creature's legs were different than ours, with potentially different capabilities. APL (talk) 01:27, 26 May 2009 (UTC)[reply]
I was actually aware of the difference, but without breaking the OP's legs and arms, there is no practical way to remedy it. In some scientific experiments, you just have to make do with the tools you've got. --KageTora - (영호 (影虎)) (talk) 06:23, 26 May 2009 (UTC)[reply]
The truth is that it's not much fun for cows/horses, but most animals can go down stairs with a bit of coaxing. They much prefer ramps and elevators, however. Some animals, such as mountain goats, are probably even better suited to going down stairs than humans. Dcoetzee06:28, 26 May 2009 (UTC)[reply]
Even Mountain goats would prefer to approach ledges and stair like structures from the side, hitting the ledge at an angle. The design of human stairs won't allow for that. So if you had sufficiently wide stairs your four legged friends might go down them diagonally. 71.236.24.129 (talk) 03:50, 27 May 2009 (UTC)[reply]
Distance That Whale Song Is Audible
According to our article on Whale song, it says that research by Cornell University showed that whale noises travelled 3,000,000 km. Now, how many times around the planet would that be? Considering it would be almost ten times the distance to the moon, I find this hard to believe (I am not saying the sound would get to the moon, for obvious reasons, I am saying the distance cited is ludicrous). Should this be changed? --KageTora - (영호 (影虎)) (talk) 20:52, 25 May 2009 (UTC)[reply]
You're right, it is clearly nonsense. It was vandalism (here), I've reverted it. It should be 3,000km (at least, that's what it was before that edit, I don't have the source to check it is correct). --Tango (talk) 21:06, 25 May 2009 (UTC)[reply]
scientific method and evolution
In reading the article on the scientific method the following is noted:
"Scientific method refers to bodies of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering observable, empirical and measurable evidence subject to specific principles of reasoning.[1] A scientific method consists of the collection of data through observation and experimentation, and the formulation and testing of hypotheses.[2]"
So, my question is: to what extent does the science of the Theory of Evolution adhere to the scientific method? If it does not, then in what way is the exploration/investigation of the Theory of Evolution "scientifically" utilized or based? Are there other legitimate "scientific methods" other than the traditional one? —Preceding unsigned comment added by 69.77.185.91 (talk) 21:04, 25 May 2009 (UTC)[reply]
The scientific method is rather difficult to define. It is applied very differently in different fields. Evolution is certainly scientific, though. It is a theory supported by empirical evidence (from the fossil record, analysis of DNA, etc.). Evolutionary biologists hypothesise about how a certain animal or group of animals evolved and then they go out and find more fossils and see if they match the intermediary stages their hypothesis predicts, refine their hypothesis and then go and find some more fossils and repeat ad infinitum. --Tango (talk) 21:11, 25 May 2009 (UTC)[reply]
The Scientific method is the practical side of the philosophy of science. It is all about formulating and testing hypotheses. The term "Theory" is used of a hypothesis that is of major importance and that has whthstood many tests. (The term has other meansing, but please do not confuse them.) To be useful, a hypothesis must be "falsifiable." That is, a scientist must be able to us the hypothesis to predict the (initially unknow) outcome of an observation or an experiment. If the outcome is not as predicted by the hypothesis (theory,) then the hypothesis (theory) has been shown to be false. The theory of Evolution has been tested in this manner many, many times,and has not been falsified.This is in stark contrast ot (for example) the "theory" tha God created teh earth in seven days: this is not falsifiable, because this theory postulates an omnipotent God, and an omnipotent God can produce anything that we can obaseve. sucn a "theory" has no predictive power, and is therefore not within the purview of science. -Arch dude (talk) 00:57, 26 May 2009 (UTC)[reply]
There is no great mystery about "The Scientific Method" - you have an idea (a 'hypothesis'), you figure out an experiment that would test that hypothesis. If the experiment comes out right - you publish your hypothesis and your experimental technique and the results you got. Other people try the same experiment - and if they agree that you're right - then you have a theory...otherwise you start again with a new hypothesis. Evolution was a hypothesis since the time of the ancient Greeks - but evidence had not been methodically gathered...so it remained a hypothesis. Darwin found his finches and other unusual groupings of animals and that constitutes experimental evidence. Since then, we have countless cases where we have shown either the results of evolution - or in the case of species with very short generations, we've even been able to show it in the lab. The consequences of evolution show up in the need to continually come up with new antibiotics as bacteria evolve immunity to the ones we've been using successfully for years. We can even show evolution in humans by looking at how junk DNA has accumulated in separated populations of humans. Things like adult lactose tolerance can be shown to have evolved in humans over just the last 5000 years or so. So there is plenty of experimental evidence - gathered independantly by people from widely separated disciplines. Evolution frequently stands up to contrary hypothesis - the commonly stated case of the bacterial flagellum, for example...but these challenges have always been successfully and comprehensively deflected. That makes evolution one of the most solidly based scientific laws we have. SteveBaker (talk) 00:45, 26 May 2009 (UTC)[reply]
Well, its not as law, which is to say that it is not a consise description of a single phenomenon, but rather a theory, which is a comprehensive explanitory framework. The terms "law" and "theory" are frequently misunderstood outside of people who study the philosophy of science.
But back to the OP. The most basic understanding of the scientific method is the basic framework of "hypothesis - observation - conclusion" cycle. The basic idea is that an idea is proposed; observations are made which could either confirm or refute the idea, and then determinations are made as to veracity of the original hypothesis. Its not more complicated than that. Its almost a self-evident method of understanding the world around us; indeed though the basics of it were codified by Roger Bacon and Francis Bacon (no relation to each other) and others over the bast few centuries, the basic process has been carried out since people first started getting ideas and testing them out. Even something as simple as "I think my arm is broken. It hurts when I move it this way. Therefore it is probably broken" is basicly using the scientific method.
The deal with evolution is that it is pretty solidly backed by huge amounts of data; and its not just that people have specifically sought out and shown that evolution works; its that we operate on a day-to-day basis assuming that it does, and absolutly nothing that happens refutes that it does. As Steve has mentioned, concepts such as antibiotic resistance or even such basic ideas as dog breeding show that we work within evolution all the time, and it always works. People seeking to refute evolution mistakenly believe that the entire system is built on a few easily refuted ideas, and that if they somehow could come up with an as-to-yet unanswered question, it would come down like a house of cards. The problem with that is a) not every question which could be answered has even been asked yet and b) the occasional unanswered question that does come up is rather quickly answered once anyone bothers to take the time to answer it. The classic case of the flagellum was basically worked out a decade ago, and it started because some anti-evolution types said "Hey, look, evolution can't explain the flagellum! So it must all be wrong". Then someone said... "Hmmph. never noticed that" then they quickly showed how evolution could neatly explain the flaggelum, which sent the anti-evolution types seeking out some other esoteric idea which could not be explained, which would then be quickly explained. The same cycle continues, and only adds to the data that fully supports the theory. It's not just that its a proven theory, in that people have worked out the experiments to specifically back it up sometime in the past; its that its a working theory which we use all the time, and continues to work well. Are the minutae of evolution being tweaked all the time? Yes they are. There are always things which are being changed regarding our understanding of evolution; things we assumed to be true turn out to be false, but these are mostly the small details (for one example, read this month's Scientific American article on synonymous DNA mutations). The basic concept is perfectly sound and works perfectly well as a theory. --Jayron32.talk.contribs04:13, 26 May 2009 (UTC)[reply]
Essays about scientific method seem to assume that there is a ready supply of new hypotheses and therefore that the work of scientists is to test which of these hypotheses wins over the others. That hardly considers real situations where only one hypothesis is proposed and open to analysis. While that is the case, the scientist cannot conclude that the single hypothesis is relatively "good" or "bad" since there is no basis for comparison. (S)he finds that it must be (for now) the overiding theory. However there can be scope for alternative hypotheses within the overiding theory, and these are subject to the scientific method. Cuddlyable3 (talk) 09:38, 26 May 2009 (UTC)[reply]
We have done quite a lot of science now, so we have a pretty good idea of how most things work. That means most new hypotheses are just refinements of existing ones. Major paradigm shifts are few and far between. --Tango (talk) 11:04, 26 May 2009 (UTC)[reply]
Steve, you've been spending too much time with creationists! A law is not a theory that has been proven to a high level of certainty. A law is a simple result, often a simple formula (Ohm's law, Kepler's laws, etc.), that is generally derived empirically. A theory is a framework that attempts to explain why that formula holds and predicts new laws that can be tested. Evolution is a theory, not a law, and will always be a theory. --Tango (talk) 11:04, 26 May 2009 (UTC)[reply]
Of course, it was Stephen J. Gould himself that argued that evolution was both a law and a theory—that the change of species was clearly observable (a law), whereas natural selection is the theory by which it happened (theory). --140.247.251.62 (talk) 17:13, 26 May 2009 (UTC)[reply]
I would disagree. Observing that organisms change gradually over many millennia doesn't allow you to make predictions (at least, not very precise ones). A law needs to have predictive power. Natural selection allows you to make predictions. You know the gradual changes need to have some reproductive benefit so you can work out, for example, what order certain changes are likely to happen in so you can predict what the missing link in the particular evoluntionary sequence would look like (and then you can go fossil hunting and try and test that prediction). --Tango (talk) 17:19, 26 May 2009 (UTC)[reply]
[citation needed] for the claim that Stephen J. Gould has called evolution both a law and a theory. A quick Google on my part doesn't show any evidence of Stephen J. Gould having said that. He has said evolution is both a fact and a theory [19], as does several of our articles (e.g. evolution as theory and fact). This is quite a different thing, because as we have established in this discussion and elsewhere, a 'law' is a poorly defined word in science and is usually avoided in most modern scientific contexts except where it can't be for historic reasons. A good example is Newton's law of universal gravitation which although still called a law, is arguably not entirely correct. The fact of gravitation or evolution though are there even if the theories of them are not entirely correct. And calling them the fact, conveys entirely IMHO the appropriate sense in the modern world without the confusion of calling them by such a poorly defined and poorly used word in science as law. Indeed I've never heard someone call anything in biology a law, it's thankfully IMHO something that never caught on Nil Einne (talk) 21:21, 26 May 2009 (UTC)[reply]
Lest we focus too much on the "test a hypothesis" part of science, we should remember that an important part of the "scientific method" is that someone first needs to make an initial observation, and then have enough curiosity to ask "why?" or "how?". Only then can she/he come up with a plausible explanation (hypothesis) and test it using whatever techniques are available and applicable to the question. Much of what we do in science is actually not "hypothesis driven" (see human genome project, for example) but this doesn't mean that it isn't science just because it doesn't directly test a hypothesis. Rather, it is the new "observation" that now generates new hypotheses or enables other hypotheses to be examined in a different light. --- Medical geneticist (talk) 16:49, 26 May 2009 (UTC)[reply]
Allow me to clarify that - an individual research project can start at any point. Science as a whole has to start with an observation. Forming a hypothesis with no reason behind it is a good way to waste time, but that reason can come from somebody else's work. --Tango (talk) 17:22, 26 May 2009 (UTC)[reply]
If science required observations before it could create hypotheses, much of our current canon of theoretical physics would never have gotten anywhere. (Einstein didn't observe anything when he was re-thinking space and time. Both SR and GR were undertaken primarily for internal theoretical reasons and not in response to specific experiments or observational problems—though in the case of SR it's worth noting there is some historical dispute over whether he paid any attention to experimental data or not. There are many other theories that have started out as purely "what-if?" questions that may or may not be compelling/likely enough to go through actual testing on.) Most scientists and philosophers agree that it really, really, really doesn't matter HOW someone comes to START thinking about something in science. The question is whether you can then confirm it, falsify it, etc. (In the Einstein example, what mattered not is that he was thinking about space and time disconnected from experiment, but that his theories did have testable predictions that could then later be explored.) Trying to put a "method" on to the investigation side of things does not work nor does it matter — what matters is that the follow-up is done correctly. --140.247.251.62 (talk) 18:38, 26 May 2009 (UTC)[reply]
If you trace it back far enough, you get to observations. The "internal theoretical reasons" you mention were issues with previous theories, which had been developed from observations. So someone made an observation, then someone made a theory, Einstein then looked at that theory and found some problems (even though they didn't, at the time, result in testable false predictions) and fixed them. The process started with observations. --Tango (talk) 20:02, 26 May 2009 (UTC)[reply]
If you trace it back far enough, it goes back to theory. Or maybe observations. Or maybe theory. Because in the end, if you trace it "far" enough you end up wherever you want. The fact is, a huge amount of scientific investigation takes place in a purely theoretical realm. Obviously the theoretical and observational feed off of each other—you can't have just one or the other, but giving one of them the ultimate precedence doesn't make much sense either. Science is the interplay of observations and theory, each feeding off of each other, each pushing the other further in its demands (observe this! understand that! repeat!). --98.217.14.211 (talk) 13:05, 29 May 2009 (UTC)[reply]
Oh jeez - Karl Popper! He's a philosopher...and a philosopher who works in a school of Economics at that. <sigh> Philosophers are a waste of quarks. SteveBaker (talk) 19:57, 26 May 2009 (UTC)[reply]
So you're saying that I should put up with them - I can't put them down? I'll try getting on top of that - but to be honest, they are at the bottom of my list. SteveBaker (talk) 16:53, 27 May 2009 (UTC)[reply]
Of course, Steve, I'm sure you are aware that much of what anyone calls the "scientific method" is derived from Popper's particular discussions of it (e.g. the whole falsifiability bit). Other than Robert Merton he is probably the number one person that scientists inadvertently parrot when they discuss things like this, having been somewhat indoctrinated to his general approach to things. --98.217.14.211 (talk) 13:03, 29 May 2009 (UTC)[reply]
Predicting Rainstorms
In London today we had a quick rainstorm. I was speaking to someone on the bus who was telling me they always know that it's going to thunder because insects burrow up from beneath the paving slabs on the pavement. I've noticed this is generally true, and when I got off the bus, there were piles of sand all over the place and ants scurrying round, with a lot of flying insects about. Why is this? Can they sense air pressure? Are they worried about being drowned? Is this just anecdotal evidence or is there a scientific basis for this phenomenon? -russ (talk) 21:19, 25 May 2009 (UTC)[reply]
With regard to thunder, there is a possibility that the insects are detecting voltage changes in the earth, which are an indication that lightning is about to strike? Or perhaps they are truly psychic, not unlike Tyrone Slothrop, and are able to predict where the lighting will strike? Actually, our article on Lightning contains a pretty thorough explanation of how it works; and one could easily propose a reasonably hypothesis about how ants are able to predict thunderstorms based on the information there. --Jayron32.talk.contribs03:52, 26 May 2009 (UTC)[reply]
We assume the insects flying around were swarming ants seeking mates and new nest sites. I have always understood that ants use a simpler method of predicting thunderstorms. It is akin to the method that humans use - increased temperature, increased humidity and a change in atmospheric pressure. The ants I believe are not seeking to save themselves from death by drowning (you won't see this behaviour in autumn or winter)but attempting to use the properties of the thermals generated by thunderstorms to assist their dispersal. Of course the thermals in London at street level are likely to be limited but these creatures are not aware of that and valiantly strive to spread far and wide. Regarding voltage changes in the earth I wonder how all the electrical cabling that threads through London affects the local readings. Richard Avery (talk) 07:36, 26 May 2009 (UTC)[reply]
May 26
Understanding the Michelson-Morley Experiment
From what I Michelson did the experiment thinking that the speed of light was relative to the aether wind, like the speed of sound was relative to the air. But what does it mean the speed of sound is relative to the speed of the air? Does it work like the headwind-tailwind on a plane? If the sound is in an area with a 10 kph wind does that change the speed of the sound?
—Preceding unsigned comment added by 24.171.145.63 (talk) 01:46, 26 May 2009 (UTC)[reply]
As far as what people thought at the time of the Michelson Morley experiment, all speeds (velocities)change with respect to reference frames. For example, on the road, say you move in a car at 20kmph. You see another car moving towards you. By common sense you can tell that the car approaches you faster than if you were not moving, that is the velocities add up. Similarly, it is easily understood that if a car races past you in the same direction as your car, its not moving away from you as fast as it would have if you were standing on the road. This is the Principle of Galilean relativity. This also applies to the speed of sound, cars, and everything which moves at speeds sufficiently lower than that of light. But the Michelson Morley experiment found the speed of light to be same in all directions, even against the hypothetical ether. This violates the Galilean theory. This was resolved when Einstein proposed his Special theory of Relativity, which assumes the speed of light to be constant everywhere in all inertial reference frames. Rkr1991 (talk) 08:30, 26 May 2009 (UTC)[reply]
An alternative interpretation of the null result of the MM experiment that had to be considered is that the speed of light does change for a moving observer but that the universe contracts or expands in the direction of movement so that the light speed (i.e. apparent distance divided by time to traverse it) seems constant. Such a hypothetical contraction or expansion would include the observer so would not be observable. Cuddlyable3 (talk) 10:30, 26 May 2009 (UTC)[reply]
There are Newtonian models of light that are consistent with Michelson–Morley and distinguishable from each other and special relativity, like draggable aether and emission theories. Also, Lorentz–Fitzgerald contraction of the apparatus is enough to make Michelson–Morley produce a null result, you don't also need time dilation. This experiment didn't singlehandedly overthrow Galileo—it needs to be considered together with other experiments that ruled out the other possibilities. -- BenRG (talk) 20:11, 26 May 2009 (UTC)[reply]
Is it to make it more stable/support the weight of the engine or do fat tyres improve acceleration (do they typically increase the coefficient of friction between the tyres and the surface)?
Wider tires produce more contact with the road surface which decreases slippage, and thus improves the ability of the car's engine to push the car forward. If you take it to extremes, imagine trying to drive a car forward using tires as thin as a razor. You'd get almost nowhere. So you want as large of tires as practical, keeping in mind that really large tires also take a lot of power to get moving in-and-of themselves, so there is a tradeoff between being large enough not to slip too much to being too large to move efficiently. --Jayron32.talk.contribs03:46, 26 May 2009 (UTC)[reply]
And to preempt the objections, this is one of many places where the simplified classroom model (surface area doesn't affect friction) is not representative of reality. — Lomn03:55, 26 May 2009 (UTC)[reply]
Both answers above are incorrect. Lomn, the simplified classroom model is actually an excellent model ove a vast range of surface areas and materials. The dragsters tyres are no exception. The real reason the tyres are as big as they are is to keep them from overheating. Jayron is right about one thing, though. There is a tradeoff here and the tyres should be just large enough to avoid overheating but no larger, to minimize drag and inertia. Dauto (talk) 14:11, 26 May 2009 (UTC)[reply]
What?! Where did you get this information? They want the tires to be hot, not cold, for better traction. This is why they do a burnout. And the extra width does indeed improve traction. Friday(talk)18:38, 26 May 2009 (UTC)[reply]
The "high-school theory" is quite good for friction between rigid surfaces. Large tires apply little force to each part of the ground and therefore move it (horizontally) only a little. Thus, the larger the tires and/or the more solid the road, the better the rigid-ground model ought to be. On the other hand, thin tires may at any instant well happen to lie entirely on top of a round pebble and consequently roll whereever. Also, they tend to make deeper grooves into the soil (we're talking about off-road here, right?), during that moving in quite unwanted directions in a quite unpredictable way, not even talking about the energy wasted in digging.—Pt(T)19:41, 26 May 2009 (UTC)[reply]
In fairness to highschool (and college) teachers I recall being specifically taught that this model for friction only applied to theoretical perfectly rigid objects. APL (talk) 19:49, 26 May 2009 (UTC)[reply]
Oh dear - this silly argument again. Dauto is 100% wrong (just like last time - and the time before). The simplified frictional model completely falls apart when it comes to car tyres...as anyone who has ever actually driven a car both before and after putting big fat tyres on it will tell you. Cooling doesn't come into it at all. As Friday says, you really want your dragster to have hot tyres because the hotter they get, the stickier they become. That's why they always do a 'burn out' before they race - it's to get the tyres hot. On Formula 1 tracks, the pit crews actually keep the spare tyres in specially heated jackets specifically to avoid them being cold when the driver comes in to get a new set. I actually race cars for fun (Autocross) - my Mini Cooper has two sets of front tyres (it's a front wheel drive car) one fat pair for track days and one skinny pair for street driving. The 0-60 time is about 2.5 seconds faster on the wide tyres than on the narrow ones. Inertia is certainly an issue - but it's far outweighed by the additional grip. Heating is an issue - but it's the opposite to the way Dauto implies. You actually WANT your tyres to get hot. It's interesting to see the complicated dance Dauto has to go through to explain how come slick tyres (with no tread pattern) have better grip than all-weather tyres that have a tread pattern. The actual reason is because the slicks have more contact area - but the classical/high-school friction equations say that doesn't matter. Pah! SteveBaker (talk) 19:44, 26 May 2009 (UTC)[reply]
Steve, we agree on at least one account, this is a silly argument. Would you care to tell us wheather your fat and skinny pairs of tires are acctually made of the same kind of rubber? I doubt they are. Dauto (talk) 04:03, 27 May 2009 (UTC)[reply]
I can't prove that they are - but they certainly seem very similar. These aren't racing slicks (which are certainly made of softer composition rubber) - they have treads - they are quite safe in wet weather and are claimed to be street-legal. The reason I don't drive on them all the time is that they protrude out of the wheel-wells of my diminuitive car - and that's NOT street-legal in Texas. Also, they are really expensive and I don't want to wear them out with normal driving. But if the traction they delivered only depended on the rubber composition (as you seem to be suggesting), why would they make wide tyres for track use rather than thinner ones with stickier rubber? Your argument is utterly busted. Pick up a book like the amateur racers' bible: "Speed Secrets" by Ross Bentley. It goes into great detail about how tyres work and how racing drivers 'manage' the contact patch, weight distribution, etc - how to choose the right tyres for the right event, etc. Nobody who drives racing cars would give your version(s) of why wide tyres work the time of day...what you are saying is totally laughable. The honest truth is that the way friction is described in Physics 101 is bullshit out here in the real world. It's a fair approximation for some kinds of materials over some ranges of pressure and temperature - but a horribly incorrect not-even-an-approximation for others. Friction is just too complex. SteveBaker (talk) 16:48, 27 May 2009 (UTC)[reply]
As I already said, the high-school (or freshman's) model of friction is in many situations a good approximation! You just must not forget its assumption: you must have two rigid surfaces with no hooks (and the like). Obviously it's well fulfilled for a tram on a railroad (really, a three-cabin tram needs just as long a track to stop as a two-cabin one, although the contact area is much bigger; trains need kilometers for stopping just to avoid excessive forces), but not so well for a car's tires, that are deformed in between the roughnesses and pebbles of the road ("hooks"!). However, don't pour the model entirely down the drain! Another assumption for the simplest formula () is, that the coefficient of friction () is constant throughout the surfaces considered. If it's not, you have to integrate (, where is an element of normal reaction force). Now, if is constant, you get simply the formula, but with the average instead. So, with large tires you achieve an averaged good traction, but with thin ones you are sometimes on a really-good- surface (which you naturally even don't notice), at other times on a small (and there you swear). Even more, there is often a correlation between and : the latter is larger where there's something to push against and thus the former is also bigger. Assuming the simplest, linear correlation, we see that now we're averaging over the square of ! The better it is to have some point on the tire on a bigger- surface, as it contributes even more.—Pt(T)22:29, 27 May 2009 (UTC)[reply]
Another point about tires (specially soft tires used for racing) is that when heated they become sticky partially crossing over from a friction force into adhesion force (which is indeed proportional to the contact area). So, I guess I concede that the physics 101 friction formula is not an excellent model for a dragster's tires. It is still a fairly good model for street tires nevertheless. Dauto (talk) 03:11, 29 May 2009 (UTC)[reply]
The 'd' probably comes from the word "difference" (or its equivalent in whatever language Leibniz liked to work in). --Tango (talk) 10:49, 26 May 2009 (UTC)[reply]
While the sectiondoes try to explain the notation, it seems to do this while going to great lengths not to ever mention the word derivative or link to further reading on the subject; instead the reader is presumed to understand what an "infinitesimally small displacement" is, what an "infinitesimally small length of time" is, and how the one can be divided by the other. I'm not sure this is really productive. —JAO • T • C11:29, 26 May 2009 (UTC)[reply]
Well, I'm not an expert, but i believe the answer comes from gravity. Most planets are very huge(otherwise they aren't called planets) so they have huge mass. Now we all know that because of gravity all masses attract each other, so all the little itsy bitsy particles which make up the planet end up attracting each other, which leads to the planet being under a compressive force, something which pushes itself in from all sides. This results in a spherical shape, as the body then comes under least strain, where all the particles are as close to each other as possible. So, the planets are almost perfect spheres, as other factors also have to be taken into consideration.(I'm guessing the other factors are things like the velocity of the body, the gravity of other bodies, various internal forces, etc.) However, we must note that this does not apply to smaller bodies, like asteroids, which can be seen of almost any shape. This is because the mas is too small for gravity to play a significant role in shaping them, so they are just like chunks of rocks floating around in space.. Also don't forget to sign your posts by placing four '~'s in the end...Rkr1991 (talk) 12:13, 26 May 2009 (UTC)[reply]
Not a very helpful answer, but strictly speaking the correct one: All planets are round because being (roughly) round is part of the definition of a planet! Asteroids are generally not round, because (roughly speaking) they aren't big enough. --Tango (talk) 14:12, 26 May 2009 (UTC)[reply]
Why would you call my answer not very helpful ? If there is any specific flaw i can correct it in all my future posts... Rkr1991 (talk) 14:32, 26 May 2009 (UTC)[reply]
You misunderstand me. My answer wasn't very helpful. If I were replying to your answer I would have indented my response further. --Tango (talk) 14:35, 26 May 2009 (UTC)[reply]
Ceres, the largest of our Solar System's asteroids is also now designated as a dwarf planet because it and only it meets the degree standard for roundness. See List of notable asteroids, and also note that because of rotation and the interaction of other gravitating bodies, the self-gravitation of an astronomical body will generally not result in sphericity, with flattening at the poles and the varying to one degree or another in shape being the total result.Julzes (talk) 15:49, 26 May 2009 (UTC)[reply]
A slap implies a firm strike with an open hand. I cannot envisage any normal circumstances where this needs to happen. A light slap of the face may possibly be used to rouse a person in danger of slipping into an undesired state of unconsciousness. There are procedures available within the UK healthcare system to express concern about such an occurrence. If a child, elderly person or a person with some other form of vulnerability is involved then an urgent explanation of the circumstances is required. If, on the other hand, this it research for a book the answer is still no. Richard Avery (talk) 14:51, 26 May 2009 (UTC)[reply]
No, I only meant in general, for keeping someone awake or wake up someone. I can imagine some situations when it would be useful. Imagine that you find an unconscious person with signs of poisoning. You might try to wake the person up to ask what kind of poison he took.--Mr.K.(talk)15:08, 26 May 2009 (UTC)[reply]
You would generally shake them, rather than slap them, I think. If you want to test someone's response to pain (for example, the work out their score on the Glasgow Coma Scale) the standard way is pressure to the fingernail bed. --Tango (talk) 15:18, 26 May 2009 (UTC)[reply]
I've got an auntie who used to be a nurse. As you may or may not be aware, overworked A+E doctors tend to have a *very* dim view of patients who fake unconsciousness. Apparently, it was not unknown for unnecessary 'needle biopsies' of the fingernail bed to be taken in order to test the malingerer's pain response... --Kurt Shaped Box (talk) 20:33, 26 May 2009 (UTC)[reply]
I've gotten the impression that it used to be customary for doctors to gently slap a baby immediately after its birth to see that it responded properly, i.e. by crying. Was this ever correct and, if so, is it still done? I have no personal experience in the matter. --Anonymous, 16:45 UTC, May 26, 2009.
It is certainly done on TV, and I think it did used to be done in real life as well. As far as I'm aware, it isn't recommended any more. --Tango (talk) 17:04, 26 May 2009 (UTC)[reply]
Yes, but the ends of babies are closer together; and, anyway, if you could be got to let out a loud wail by a potch on your tuchis, while inverted, I'll bet it would clear your airway. Deor (talk) 21:09, 26 May 2009 (UTC)[reply]
Having worked for too many years in mental health care I can assure you that in the UK nobody of any repute slapped a hysterical (what ever that means) patient or used it to get someone out of a psychotic episode (ditto) If it were that easy why we'd all be psychiatrists. Or maybe there's a critical moment to slap them. Nope, Kurt you've watched Airport the movie, too many times. Richard Avery (talk) 14:41, 27 May 2009 (UTC)[reply]
I accept that I may be wrong on this (and I reserve the right to be wrong!) but I do remember reading something somewhere once about the effect of 'percussive therapy' on 'emotional' humans. This would've been way, way, way back if it happened - probably pre 20th Century... --Kurt Shaped Box (talk) 16:29, 27 May 2009 (UTC)[reply]
If I were hysterical and somebody came up and SLAPPED me, I can't imagined that it would help the situation any. And from my experience with individuals having psychotic episodes (which is considerable), if you slapped one of them, he or she would get mad, possibly incorporate you into his or her delusional worldview (there's nothing like an unprovoked assault to play into a persecution complex), and, if he or she were predisposed to violence, possibly hand you your sorry tuchis on a silver platter.
What's so weird is that (although I'm not a health care professional) I almost slapped my friend the other day because I thought she was slipping into a diabetic coma . . . I didn't, but I did shake her and say her name very firmly and loudly and force her to keep responding until the paramedics came. (She's fine.) Funny, I never thought to do fingernail torture, but if she ever scares me like that again . . . ;) -AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 22:57, 29 May 2009 (UTC)[reply]
Bird-flight
How do feathers contribute to bird's ability to fly? I have a general idea, but I am not finding anything about it in the articles. My general idea will send me to fluid mechanics next, but I am thinking it should be prioritized to get this into an article that is obvious to someone less knowledgeable than myself.Julzes (talk) 18:07, 26 May 2009 (UTC)[reply]
The critical thing about feathers is that when you push a feather upwards, it kinda unzips and lets air pass through fairly easily - but when you push them down, the little strips lock together to form a fairly airtight seal. This is a really useful thing because it allows a fairly simple vertical cyclic movement to generate lift. Bird flight is very different from aircraft, bat and insect flight. SteveBaker (talk) 19:31, 26 May 2009 (UTC)[reply]
These are large plates that (as far as I can tell from pictures) stick out sideways from the front of the engine. The purpose is to keep the smoke from obscuring the driver's view. Efficient engine design made them necessary, because it extracted more heat from the smoke as it passed through the boiler, making the smoke heavier. I have very little interest in steam trains, but certain things about smoke deflectors bother me:
Wouldn't they cause serious air resistance, perhaps enough to counteract the efficiency savings that make the smoke heavier?
Wouldn't the plates themselves block the driver's view?
Why not just connect the engine the other way round, so the chimney is at the back?
It would certainly improve the view if the engineer and fireman (for Brits, the driver and ?? [still fireman --Heron (talk) 11:10, 27 May 2009 (UTC)]) were in front of the boiler. But where would the fuel and water be stored? The tender was behind the steam engine, and a short path from the coal supply to the boiler was essential. In an oil fired engine, it would have been possible to have the engineer at the front of the locomotive, as on modern diesels. As for efficient engine design eliminating smoke, there was still steam. Steam locomotives at the end in the 1960's still put up a very impressive cloud of smoke and steam. How much was the increase in ari resistance due to the steam deflectors in addition to that of the locomotive, its cab, and the vertical projections of the steam dome and other features? Steam or smpoke deflectors are not mentioned in the Steam locomotive article.
Do you have a reference to a book which discusses them? Pictures of locomotives show the smokestack way above the cab windows. Why would the smoke go down instead of up where it would be out of the way? There was a blower which gave it extra upward velocity on locomotives. Edison (talk) 22:56, 26 May 2009 (UTC)[reply]
Found the Smoke deflector article. Also Google book search has [20]. The smoke did sometimes drop and obscure the crew's view. Letting the engineer and fireman keep their heads inside the engine and be able to see signals and the track ahead seems a small price to pay for any slight increased drag. Edison (talk) 23:03, 26 May 2009 (UTC)[reply]
Smoke deflectors were placed parallel to the air stream - it's hard to imagine them making the vertical-front of the engine much worse than it already was. The front-view from the engine was never that great...but evidently they felt it was worth the small sacrifice in order to keep the smoke out of the way. I also get the impression that most of these were retro-fitted. SteveBaker (talk) 23:04, 26 May 2009 (UTC)[reply]
Oh, do they go edge-on to the airflow, rather than flat-on? That makes much more sense. It's kind of hard to judge perspective in the various pictures I've seen (which all look pretty much like the ones in our smoke deflector article), I got the impression they stuck out like ears. Well, if your ears stick out like that. Um. Edison's link took me to a copy of Popular Science with a picture of a highly streamlined locomotive with unique highly streamlined smoke deflectors. I feel generally happier about the whole concept now, thank you. 81.131.57.202 (talk) 23:22, 26 May 2009 (UTC)[reply]
Three points. First, the smoke deflectors were typically far enough
ahead of the cab that they didn't block much more of the forward view
than the boiler itself.
Second, while I've never seen actual numbers on this, it makes sense that
it's more efficient to lift the smoke by setting up a diagonal updraft
(using smoke deflectors) than by blasting it up vertically (as the older,
less efficient engines that did not use smoke deflectors did).
Third, there was one important example
of a steam locomotive design with the cab in front of the boiler instead
of behind; this was used on the California-based Southern Pacific Railroad.
As suggested above, these engines were oil-fired, and as the article
indicates, there were some problems with the design, including crew safety
in case of a collision and the effect of fuel leaks on traction. However,
I think the reason most railways kept the cab at the rear even with
oil-fired engines was probably that they wanted them easily convertible
in case they later switched to coal, and perhaps a measure of "that's
the way it's always been done".
There were also a few railways that tried locomotives with
the driving cab in the middle,
part way along the boiler. The man driving then had to work in a
cramped and hot space, and while he had better visibility on one
site, it was even worse on the other side; and he also couldn't
communicate with the fireman. Not a successful idea.
--Anonymous, 23:48 UTC, May 26, 2009.
Freight engines in use in the U.S. in the last days of steam generally did not have the smoke deflectors in place. A crew behind the boiler in a collision would be scalded to death by the steam, and as dead as if they were in front of the boiler, but in a more painful way. Edison (talk) 05:57, 27 May 2009 (UTC)[reply]
In any case, I don't see the advantage in letting the crew think it is safe to have a collision! The driver of that Baltimore & Ohio Railroad camelback appears to have taken his house along for the trip. SpinningSpark07:50, 27 May 2009 (UTC)[reply]
Nobody is saying that it's safe to have a collision! However, if it does happen, you have a better chance of survival with the big mass in front of you than behind you. As for "scalded to death", while that was certainly possible, it was not a likely result of a collision. A locomotive boiler is a pressure vessel that, by the late steam era, regularly contained as much as 20 atmospheres and was tested for more than that; an accident that wasn't violent enough to kill the engine crew by impact would be pretty unlikely to breach it. --Anonymous, 08:54 UTC, May 27, 2009.
A Google book search for locomotive "scalded to death" seems to show that there were more cases of the boiler exploding for reasons such as crown sheet failure and scalding the crew to death than scaldings secondary to wrecks, but some such instances appear. A broken pipe was sufficient to scald one to death, or at least severely. [21], [22], [23], [24], [25], [26], [27]. Steam leaks sufficient to cause severe scalding seem a common consequence of a locomotive wreck, such as a collision or just going off the tracks from a switch error. Then there's the song about the "Wreck of the Old 97" based on a 1903 derailment and crash, where "They found him in the wreck, with his hand on the throttle, scalded to death by the steam." Edison (talk) 23:16, 27 May 2009 (UTC)[reply]
Taken from the cat article: "Cats are classified as obligate carnivores, because their physiology is geared toward efficient processing of meat, and lacks efficient processes for digesting plant matter". Any cat would prefer meat in some form much more than cheese and bread. --131.188.3.20 (talk) 21:20, 26 May 2009 (UTC)[reply]
Though it is worth noting that cats can be pretty picky. I've had cats turn down human food that was obviously something that it theoretically would enjoy. (Dogs seem less finicky in this respect.) I'm not sure my old cat would have gone for burger. --98.217.14.211 (talk) 22:14, 26 May 2009 (UTC)[reply]
Most cats I've known have liked cheese, though. It is, as BenRG points out below, bad for them, though - adult cats, like most adult mammals, are lactose intolerant. --Tango (talk) 22:30, 26 May 2009 (UTC)[reply]
Please don't put this to the test; most cats are lactose intolerant and onion is toxic to cats, and who knows what else goes into a McDonald's hamburger that isn't tested on felines. -- BenRG (talk) 21:38, 26 May 2009 (UTC)[reply]
I think cheese doesn't contain much lactose, because the lactose is in the whey, which is removed. Also there is no mention of their alleged lactose intolerance in the cat article (although there is something about fatty acids), and there is a picture of "a very young cat being fed on milk"; and cats are famously portrayed as drinking milk - have they been given diarrhea all throughout history? - and of course they are mammals - does cat milk not contain lactose? Basically I don't believe you, except the bit about the onion, which I am going to accept unquestioningly and tell to other people. 81.131.57.202 (talk) 22:55, 26 May 2009 (UTC)[reply]
Adult cats are lactose intolerant. Most mammals lose the ability to digest milk after infancy, so there is no need to mention it specifically in the cat article. Humans are the exception to the usual rule, although even we only evolved to keep the ability very recently in evolutionary terms and there are plenty of people that don't have that mutation. --Tango (talk) 23:12, 26 May 2009 (UTC)[reply]
Oh yes, that rings a bell actually, you're right. Lactose intolerant people are not weird, it's those of us who can digest it who are the mutants, supposedly. Bit odd to lose an ability in adulthood, though, for no reason. I can only assume it's a side-effect of gaining some other advantage. 81.131.57.202 (talk) 23:27, 26 May 2009 (UTC)[reply]
The reason mammals lose the ability to digest milk is to ensure that one litter of offspring are properly weaned before the next litter comes along. The mother can only produce so much milk and if older offspring were competing against the newborns, that would be highly detrimental to the younger animals. Hence, all mammals have developed a system that makes them unable to digest milk past a certain age - and to have major discomfort should they try to do so. It is thought that humans were just like all of the others in that regard until perhaps 5000 years ago when we started to farm dairy animals such as sheep, goats and cows. Since we have language and education and societal pressures to ensure that babies are weaned off of their mother's milk soon enough - we no longer need the genetic shutting off of the lactose pathway. To the contrary - if you imagine a family who farm a few goats and who are lactose intolerant - then in times of famine - they'll be tempted to slaughter the goats for meat...and then they are in deep trouble. The family who happen to be lactose tolerant into adulthood can get their nutrition from milk, butter and cheese and keep the goats alive through to the next time of plenty. Guess who does better in the long term? It seems that 5000 years ago, we started to evolve the ability to drink milk in adulthood - but increasing civilisation means that very few people indeed survive preferentially because they can drink milk - so the evolutionary pressure to become lactose-tolerant has gone away - and here we hover, partly evolved, partly not.
Uh-huh. Do lactose-intolerant adult cats like to drink milk? If so, then the inability to digest it clearly doesn't work as a way of getting older kittens to stop suckling, since it doesn't make them actually stop drinking it, just gives them a stomach upset. I'm also unsure what animal rights logic says an animal should be prevented from causing itself harm in a way it apparently enjoys (all of which is anthropomorphic anyway, the harm and the enjoyment). Also, as a third point, "unable to digest" must be shorthand for something a bit more complicated, because we eat things we can't digest all the time, without any problem: when it's called "roughage", we're encouraged to eat it, and there must be indigestible liquids which similarly pass straight through without causing pain. Or indigestible components of otherwise digestible foods. Must happen all the time, harmlessly. 213.122.66.195 (talk) 17:47, 27 May 2009 (UTC)[reply]
Actually that last point is answered below in the question about gulls (and in the lactose intolerance article, which I should have read properly) - it's gut bacteria feasting on the undigested milk-sugar that cause the trouble. 213.122.66.195 (talk) 17:59, 27 May 2009 (UTC)[reply]
The first five of those references might just be echoing a myth, since they just seem to blankly say, in gentler terms, "CATS ARE LACTOSE INTOLERANT ALRIGHT SO STFU", but I like the last one, it looks science-y. I like the term "vetinary technician". Also it confirms that "cow milk has higher levels of lactose than does cat milk", and explains about lactase. Still, none of them mention cheese. I think cheese is OK for cats, by reason of being low in lactose.81.131.57.202 (talk) 23:46, 26 May 2009 (UTC)[reply]
I tried to provide a variety, to suit whatever your doubts were that cats are like all other mammals. The third link, for example, links to advice from the RSPCA. Cheese is lower in lactose than milk; do you have a particular reason for thinking that the levels are low enough not to cause a problem for cats? Like most things, it will vary from cat to cat and by amount of cheese. 80.41.39.25 (talk) 01:06, 27 May 2009 (UTC)[reply]
I would assume that his particular reason for thinking that the levels are low enough to not bother a cat is that because you can get cheeses with zero lactose. It's not even a specialty item. Aged cheddar and sharp swiss are both commonly recommended to people who can't eat lactose, and both would be excellent on a cheeseburger.
Personally, I'd be more concerned about the roll. Does it still count as a cheeseburger if it's not served on a bun? Normally you could depend on a cat to simply eat around a bun, but if it soaked up the grease from a freshly cooked cheeseburger, I wouldn't bet on it. APL (talk) 01:32, 27 May 2009 (UTC)[reply]
You can get cheeses which are zero lactose, so those would probably be fine, but that isn't all cheese. Most cheeseburgers I've seen have come with those processed cheese slices; what are the lactose levels in those? Does it vary depending on the manufacturer and variety? I'm not saying you couldn't carefully construct something that would count as a cheeseburger and which a cat could safely eat, but I'm not convinced a random generic cheeseburger would be a good idea. 80.41.39.25 (talk) 01:43, 27 May 2009 (UTC)[reply]
You're right that American Cheese is probably the most common cheesebuger cheese thanks to McDonalds, Burger King, etc. But most sit-down restaurants (nothing fancy, your local diner will do) that serve cheeseburgers will offer one with cheddar or swiss. You couldn't trust the cheddar, though unless it specifically says "aged cheddar", and I can't seem to find any sources that say whether or not "mild swiss" has any lactose in it, so you'd really have to ask the chef.
But who are we kidding? What kind of diner is going to let your bring a cat? If your heart was set on giving your cat a cheeseburger you'd want to set up the old barbecue grill and do it yourself. Aged cheddar or sharp swiss are perfectly legitimate burger toppings, so I don't feel that's a cheat at all. I don't know what sort of other toppings are safe for cats, but they're purely optional and the cat probably wouldn't appreciate them anyway.
Here is a vet who says that, like with all other mammals, most cats do not retain the ability to digest lactase into adulthood, therefore giving an adult cat milk may lead to diarrhoea. Here is another vet who says the same, with less science. Or how about this? —Preceding unsigned comment added by 80.41.39.25 (talk) 01:16, 27 May 2009 (UTC)[reply]
The humour in "I CAN HAZ CHEEZBURGER" originates from its implication that the depicted cat desires a food that normally humans and not cats desire, in the same way that "INVISIBLE BIKE" is funny because people ride bikes, not cats. Dcoetzee21:46, 26 May 2009 (UTC)[reply]
I wonder how many generations of people cluelessly feeding cats saucers of milk or cream will cause them to gain the ability to digest milk. I have no idea how reliable it is, but I've heard anecdotal evidence that some adult cats are fine with it. I suggest that cat breeders start selecting for those cats so as to bring reality more in line with Tom&Jerry cartoons. APL (talk) 01:21, 27 May 2009 (UTC)[reply]
Unless the cats who do not drink the provided milk die off or breed less, that scenario will never produce a selection pressure. If a statistically significant number of cat owners fed only milk to their cats, only those who adapted would survive and reproduce; and lactose tolerance would evolve into the gene pool. Because most owners only provide milk as a "supplement," this will not happen. When cats choose not to drink milk, it does not impact their capability to breed. Nimur (talk) 01:45, 27 May 2009 (UTC)[reply]
I was imagining the people, in books and cartoons, who leave a saucer outside their back door for the neighborhood stray. But I don't suppose that's anywhere near common enough in real life to be a useful food source powerful enough to cause a selection pressure towards cats that can take advantage. Once again cartoons and books are more interesting than real life. APL (talk) 02:51, 27 May 2009 (UTC)[reply]
It is best to feed pets standard pet food. The standards set up by the AAFCO are light-years better than the way the FDA is geared to handle human food.Julzes (talk) 03:25, 27 May 2009 (UTC)[reply]
Having recently acquired a couple of cats, I noticed that you can buy "cat milk"; I assume there aren't cat dairy farms out there, so it must be synthetic/manufactured from cow's milk. If you were really dedicated to reproducing the meme, you could probably make your own cheese from this. However, according to Cats Protection, the milk is very high in calories ([28]), although that may not be a concern if the cat is eating burgers anyway. --Kateshortforbob11:30, 27 May 2009 (UTC)[reply]
Hahaha! When I first saw my mother feeding 'cat milk' to her moggy, my first response was "They've started commercially milking cats now?"... ;) --Kurt Shaped Box (talk) 12:01, 27 May 2009 (UTC)[reply]
Do you mean to ask which radio frequencies have wavelengths close to the 60 meter band? That would be HF radio or Shortwave. If you want a specific broadcaster, you will need to give a more precise wavelength and/or frequency, and probably a region as well (although shortwave does propagate almost globally). Nimur (talk) 00:13, 27 May 2009 (UTC)[reply]
And if you're hamming, take a look at this FAQ. The NTIA has granted five 2.8 kHz channels, (5332, 5348, 5368, 5373, and 5405 kHz center frequencies), for amateur use in the United States. Regulations may vary in your region. Are these the channels you were asking for? Nimur (talk) 00:17, 27 May 2009 (UTC)[reply]
Adding R-values for bulk ceiling insulation not allowed
I'm having a problem with this. I'm told that laying 2 layers of R 2.0 (S.I units) ceiling insulation wont give R 4.0. I understand this would be the case if the insulation (uncoated polyester) became compressed, or if the batts were not uniform in composition. The reflective value is not an issue as the standard the work is done to in this case is concerned only with heat transfer from the rooms to the roof (i.e winter insulation). The proposed technique is laying the first layer (10 cm thick) between the joists in the ceiling, and the second layer at right angles on the top completely covering the first layer and the joists as well. The joists themselves are rated R 0.6-0.8. The standard (AS 3999 - dont bother looking it up as you have to pay for it) allows R 4.0 (20cm)laid between the joists (not covering them) which I feel certain would give a lesser effective insulation than the cross-laid technique. R 4.0 insulation costs slightly more than two layers of R 2.0 This is a heavily relevant question as the Aust. Government has a massive rebate for ceiling insulation and many people are getting their ceilings done for the first time. I will check for answers here for several months, so late replies very welcome. Polypipe Wrangler (talk) 23:57, 26 May 2009 (UTC)[reply]
As I understood R-value, putting two layers of R 2.0 would yield an equivalent R value of 4.0. Of course, R-values are approximate anyway, within a very wide tolerance of the manufacturing and installation procedure. Nimur (talk) 01:29, 27 May 2009 (UTC)[reply]
I'm not sure of the definition of R-value - but think about how insulation actually works: If you spend $100 on heating bills and one layer of insulation were to (say) halve the heat lost from the room - a second layer would halve the half that the first layer let though - so the first layer would save you $50 - but the second layer only saved $25. Every additional layer would save you less and less. This is a multiplicative effect. If they added - then the second layer would have to block every last drop of heat loss that the first layer missed...and that's just not reasonable. SteveBaker (talk) 03:58, 27 May 2009 (UTC)[reply]
According to US Department of Energy's Insulation fact sheet, "In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added." While this is only an approximation (because of second order effects like compression of the lower layers that reduces their effectiveness), it seems to be a reasonable one. Are the regulatory recommendations any different in Austria (Australia ?), or is it possible that you were just misinformed ? Abecedare (talk) 04:13, 27 May 2009 (UTC)[reply]
Hi, I stumbled upon the article, electrolysis, some of questions were answered but one of them were not.
How is it possible for metals to be solved in mercury? Do metals actually become solved in mercury or do they just form an alloy? How does mercury absorb these metals? -Funper (talk) 01:10, 27 May 2009 (UTC)[reply]
Technically, they form an amalgam. Mercury is a liquid under standard laboratory conditions ("room temperature, atmospheric pressure"). When other metals, like gold or lead are added to it, the result is often a "soft" metal solid. For example, take a look at sodium amalgam. This compound ranges from a liquid to a "spongy gray mass" depending on the amount of mercury present. Nimur (talk) 01:32, 27 May 2009 (UTC)[reply]
MM Experiment
Michelson Morley Experiment- Sorry about this I'm the same guy who asked the earlier question. Anyway, the theory of the aether was that the aether was stationary right? The "wind" was generated by the earth moving through the field of aether, not the aether moving across earth right? Because from what I understand the results they were seeking were made with the assumption the aether speed was 30 km/s (the speed the earth orbits around the sun).
Secondly: (Sorry for this crappy drawing but w/e) Distance from Mirror A to half slivered mirror = Distance from Mirror B to half slivered mirror. BTW these drawing look weird so to better understand what I meant could you go to "Edit Summary" and look at them because I didn't mean for this formatting boxes.
MIRROR A
.
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Light source----- /---- MIRROR B
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.
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Detector
This whole problem is assuming there is an aether wind. I'm trying to understand how Michelson constructed his apparatus, given he thought a wind existed.
Suppose the aether wind is coming down parallel to mirror A (suppose mirror A is the north, imagine the wind is blowing from North to South). Given that there is a wind, shouldn't the beam of light be deflected downward a little coming from the light source to the half slivered mirror (the / in the center)? As it won't strike the center of the mirror but rather a point a little below the center at a different incident angle then 45 degrees. In this case both beams would also be deflected and the light beam would not be split equally.
If this was compensated by angling the light source a little, so that the light went in a straight line from the light source to the half slivered mirror, then the beam of light going from the half slivered mirror to mirror B would be deflected downward a little.
MIRROR A
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.
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Light source----- /-
- DEFLECTED LIGHT BEAM
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- MIRROR B
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Detector
Sorry for asking questions that seem kinda dumb but ever place I looked it up only has a diagram similar to the first one I drew but I can't understand how that would compensate for a wind blowing. —Preceding unsigned comment added by 24.171.145.63 (talk) 02:09, 27 May 2009 (UTC)[reply]
I don't understand why you would think that there should be a deflection of the beam going to mirror B. This is simply not the case. The first diagram is the correct one. Dauto (talk) 05:11, 27 May 2009 (UTC)[reply]
I'm viewing it from the point of view of Michelson, believing that there WOULD be an aether. I understand that there IS NOT an aether and I'm not trying to prove otherwise (obviously...) but I'm trying to understand how Michelson constructed his apparatus. Imagine swimming across a stream. You are swimming straight (suppose North) at a speed of 5 m/s. The current of the river is 3m/s due east. So in reality you are going 4m/s NE. You are not going in a straight line, you are going in a angled line. Michelson believed along these lines I think. He used the same analogy that I used to explain this experiment (or more correctly I'm using the one he did...)(http://galileoandeinstein.physics.virginia.edu/lectures/michelson.html). This site has a pretty good explanation but when you look at its animated experiment (http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htm), they state themselves "we have cheated by not taking into account the effect of the aether wind on the direction of motion of the light, but only including its effect on the speed of the light.". How did Michelson take into account the "effect on the direction of motion". His apparatus, at least every one I look at, looks like my first apparatus, the same one seen in the flashlet. Yet as they themselves state, this apparatus (or at least the animation) doesn't take into account the effect on the direction. How did Michelson compensate? —Preceding unsigned comment added by 24.171.145.63 (talk) 05:33, 27 May 2009 (UTC)[reply]
-EDIT: Damnit I'm confusing myself now. On the wikipedia article it states " the beam reflecting back and forth perpendicular to the flow of ether would have to travel farther than the beam reflecting parallel to the ether". However I was under the impression the experiment was conducted thinking that the beams would TRAVEL THE SAME DISTANCE (not, as the article says, travel FARTHER) but merely at different speeds. Keeping the same analogy as the river (which is explained on the linked site), the man going perpendicular to the river is going at 4 m/s. The man going parallel to the river (also with a swimming speed of 5m/s) goes at 8m/s on way (with the current of 3m/s) and 2m/s against the current. So if the river is 10 m long and one man swims 10 m perpendicular to the current and one man swims parallel to the current, it would take the first man 5 seconds (20m at 4m/s) and the other man 6.25 seconds (10 m at 8m/s and 10 m at 2m/s). Ignoring that the swimmer swimming parallel must angle himself (the basis of my original question), I thought the different times each light beam took would cause the fringe shift? If, in fact it is correct he thought the beam going perpendicular would go farther that would resolve my first question; the beam going perpendicular goes the same horizontal distance as the parallel beam but is deflected so it forms a small right triangle, whose hypotenuse is greater than the horizontal distance alone. However; it still doesn't resolve how he compensated his apparatus for the deflection of perpendicular beam. Right? I know I have some major logical fallacy somewhere I just can't think of it myself for some reason... 05:56, 27 May 2009 (UTC)
The aether wasn't assumed to be stationary as such, just to be moving at a roughly constant speed over a region the size of Earth's orbit. Since Earth's orbital velocity changes by about 60 km/sec in six months, you can be sure of having an aether wind of at least 30 km/sec at least once in the course of a year. Note it makes no difference whether you consider the aether or the Earth to be stationary; the (Galilean) principle of relativity applies here. Also, the paths weren't of equal length (they couldn't achieve that kind of precision), rather, they looked for sinusoidal variation in the fringe shift as they rotated the apparatus. Since you're interested in the detailed experimental setup, I should also mention that the light was not simply reflected back once as shown in most diagrams, but was bounced back and forth numerous times so as to increase the effective path length.
There are several ways to think about the issue of the direction of the light. First, any correction would be very small since the wind speed (~30 km/sec) is around 0.0001c. Second, calibrating the experiment would include fiddling around with the light source and the mirrors until the light goes where you want it to; it's a feedback-driven process that automatically adjusts for any bias in the direction. Keep in mind that any effect would apply equally to every light source in every experiment ever done, whether or not it was intended to detect the aether wind. Third, in fact there is no effect. Consider objects being fired "horizontally" through a tube that's moving vertically downward.
The velocity of each object is diagonal down and to the right, but the line of objects as a whole points horizontally. From the rest frame of the tube, the objects move horizontally despite the "wind". A real object moving in the wind might be blown to one side, especially if it's of low density, but that's just because the analogy is a lousy one. The light is not an object blown by aether wind, it's motion of the aether itself. A better analogy is sound waves in the wind, but most people don't have good intuition for that (I know I don't). The boat analogy can be made to work. Suppose you're trying to row east against some unknown north-south current while staying between parallel barriers (the walls of my tube). After you clear the barriers you continue rowing as you were before; then you will continue moving horizontally. This isn't exactly an airtight argument, and I'm not sure that there wouldn't be, say, some aether-speed-dependent effect on the displacement of the light transmitted by the half-silvered mirror, but I hope this gives you the intuition you were missing.
Whether the difference of travel time is due to distance or speed is a matter of perspective. With respect to the rest frame of the apparatus, the beams travel the same distance at different speeds. With respect to the rest frame of the aether, they travel different distances at the same speed. -- BenRG (talk) 10:19, 27 May 2009 (UTC)[reply]
About two weeks ago, I brought home some cut roses, which were placed in a vase containing tap water and the preservative that came with them. The roses withered slightly as one would expect, but they also seemed to develop small roots below the waterline. Does this happen often, and what might have caused it? Can these cut roses be re-rooted? 69.224.113.202 (talk) 02:25, 27 May 2009 (UTC)[reply]
Cutting (plant) does not specifically mention roses, but this is a common way to breed plants. I have heard it described as a special form of asexual reproduction as it can generate an entirely new organism without going through the standard pollination process. If conditions are right, the plant can survive and be replanted. Nimur (talk) 03:07, 27 May 2009 (UTC)[reply]
Yeah - it's certainly possible to grow plants from cuttings - you can even buy hormonal rooting compound that you dip cut stems into that promotes root growth. I'm a little surprised that roses would do it spontaneously - but it's clearly not beyond the realms of reason! SteveBaker (talk) 03:43, 27 May 2009 (UTC)[reply]
Who could these critters be? They're all over the leaves of this manzanita near Kernville, California, a quarter mile or so from the Kern River. Of course they're the larvae of something, but I couldn't find anything like them on caterpillar identification websites. The green verging on pink is quite pretty; it's like a blend of the green of the manzanita leaves and the red of the stems and bark. --jpgordon∇∆∇∆04:33, 27 May 2009 (UTC)[reply]
To me it looks more like a form of plant desease, since one can see clearly, that the leaves writher up from the sides and then turn the shade of red you described. That also seems to be the reason for mixing colours. Maybe some kind of Rust?--91.6.48.74 (talk) 06:10, 27 May 2009 (UTC)[reply]
I am assuming you did not actually pick off one of theses "critters". I would not disagree with rust but they may be some sort of leaf gall caused by a small mite or fly laying an egg and the larva causes this peculiar damage. If you Google image 'leaf gall' you will see the weird and wonderful shapes and distortions that can occur. Richard Avery (talk) 06:44, 27 May 2009 (UTC)[reply]
Ah-ha! I think they are indeed galls caused by the Manzanita Leaf-gall Aphid (Tamalia coweni). Thanks! (and, no, we didn't try to pick 'em off. Dunno why.) --jpgordon∇∆∇∆07:08, 27 May 2009 (UTC)[reply]
You seem satisfied with that, but if you want more help from local experts, I would suggest contacting the Kern River Preserve. When I lived in the area, I visited the Preserve a few times, and the folks there didn't bite. -- Coneslayer (talk) 17:50, 27 May 2009 (UTC)[reply]
Oh yes. Great place. But I got an answer here faster than I did from Alison (who runs the place.) She sure knows her birds! --jpgordon∇∆∇∆20:06, 27 May 2009 (UTC)[reply]
Yes, it probably would. Helium has an atomic weight of 4 (and is monoatomic). Hydrogen is H2 and has an atomic weight of 2. Both are close enough to ideal gases that this translates to about the same difference in weight per volume. That seems like a lot less lift from Helium, but what provides the lift is the difference to the density of air, which is mostly determined by the molecular weight of of N2 at 28 and O2 at 30. I do think Helium is harder to contain, so you may have a bigger loss of gas due to diffusion over time. On the other hand, it is chemically more benign. --Stephan Schulz (talk) 09:56, 27 May 2009 (UTC)[reply]
I don't think the weight of air makes a difference in this comparison - twice the weight means half the lift. I doubt Zeppelins carried their weight again in ballast, so it's not going to work. You would need to double the volume of your balloon (which requires increasing the linear dimensions by about 26%). --Tango (talk) 11:42, 27 May 2009 (UTC)[reply]
(ec)Yes, Tango is wrong. The uplift for any body in the atmosphere is equal to the weight of the atmosphere it replaces. The net uplift is that minus the weight of the body. For air at sea level, the density is about 1.2 kg/m3. For Helium, its 0.1786 kg/m3 and for H2 its 0.08988 kg/m3. In other words, a cubic meter of Helium (close to standard conditions) provides a net lift of 10 N, and one of Hydrogen one of 10.9 N. For any real vehicle, you also have to take into account the significant weight of the actual structure, so even that difference of 9% overstates the case. --Stephan Schulz (talk) 12:13, 27 May 2009 (UTC)[reply]
As stated above, helium has about 90% of the lifting power of hydrogen, so if lift using hydrogen exceeds the weight of the vehicle by more then 10%, it should work, although your controls might be sluggish. 65.121.141.34 (talk) 13:02, 27 May 2009 (UTC)[reply]
The dirigible USS Los Angeles was built in Germany and used hydrogen as the lifting gas. It was acquired by America as part of the reparations payments made after World War I. The Americans used helium as the lifting gas in this same dirigible. At the time, helium was a rare gas and the USS Los Angeles and the USS Shenandoa (the firsr American-built dirigible) alternately used the same helium gas. It was pumped from one dirigible to the other. At that time, America was the only country that had an appreciable amount of helium, and it refused to sell Germany any of it's increasing supply for Germany's post-war Zeppelin program. – GlowWorm. —Preceding unsigned comment added by 98.16.66.187 (talk) 13:58, 27 May 2009 (UTC)[reply]
Actually, helium is still pretty expensive - prices have gone up by at least a factor of four in just the last decade. This can only get worse. The US still produces 90% of the helium in the world - and that only as a byproduct of natural gas extraction. When global warming remediation seriously kicks in - natural gas will have to be phased out as a fuel - and that will severely impact helium production. Airships are an exceedingly useful technology (albeit very under-utilised right now) - but sooner or later, we're going to have to 'get over' the Hindenburg catastrophy and switch back to hydrogen-filled airships. These can be exceedingly cheap to fill - and with modern safety precautions, we really shouldn't have to worry about catastrophic explosions anymore. SteveBaker (talk) 14:36, 27 May 2009 (UTC)[reply]
This sounds exactly like the owners of the Titanic, who felt that with modern safety precautions they didn't have to worry about liners sinking any more. But the reference desk is not the place for debate, so let's stop that now.
As a point of fact, the Hindenburg did not explode; it burned. For it to have exploded, there would have had to be a significant mixing of air and hydrogen before ignition. The result would then probably have devastated the whole airfield, whereas the actual disaster merely destroyed the airship and killed about 1/3 of the people on board.
As another point of fact, the Hindenburg was originally designed to be lifted using about 65% helium and 35% hydrogen, with the helium cells surrounding the hydrogen ones to minimize the number of places where hydrogen came close to the air. Once the Zeppelin company realized that helium was not going to be available as they had optimistically hoped, they canceled the construction of the inner cells, which saved some weight and cost. Using hydrogen instead of helium for the whole volume also gave about 25,000 pounds more lift -- which was needed, because the airship exceeded its design weight, although my source* does not say by how much. (To put this in proportion, the total dead weight of the Hindenburg as built was 118,000 kg or 260,000 lb; on one transatlantic flight in 1936 that the book describes in detail, it carried an estimated 96,000 kg or 211,500 lb of passengers, crew, supplies, etc.)
*The Golden Age of the Great Passenger Airships: Graf Zeppelin & Hindenburg by Harold G. Dick with Douglas H. Robinson, Smithsonian, 1985, ISBN 0-87474-364-8.
I think the answer to the original poster's question is that it might fly, but its operations would be severely crippled. Most of the gas volume is required just to lift the dead weight and necessary supplies such as fuel; with the loss of about 8-10% of the lifting capacity, the usable payload and/or range would be too limited. Airships work on a pretty small margin of lift.
Also, as a side point, because helium is monatomic (and highly inert), it leaks through membranes and joints more easily than most other gases. Gasbags meant for hydrogen might not be quite good enough for use with helium.
--Anonymous, edited 16:52 UTC, May 27, 2009.
I don't think the Titanic comparison is legit. Titanic could be compared to that original Hindeburg design that you mention (hydrogen surrounded by helium). An all-helium airship sounds more like Titanic with an adamantium hull - sure, you can still have problems, but you're never going to get your ship (going up in flames/sinking with a hole in the side). Vimescarrot (talk) 17:43, 27 May 2009 (UTC)[reply]
Chemically, it is pretty much identical to regular hydrogen. Some of the energy levels are a little different, but I doubt they are different enough to stop it burning. --Tango (talk) 19:05, 27 May 2009 (UTC)[reply]
[edit conflict] Deuterium, being merely an isotope of hydrogen, is chemically identical (although see also Graham's law; the rates of some processes depend on the molecular speeds). It is twice as heavy as hydrogen, so no help there (but see above how this does not mean "half as useful"). --Tardis (talk) 19:14, 27 May 2009 (UTC)[reply]
I stand corrected: This image represents it a lot better, but apparently that gap is very real (and is analogous to another gap around Z=105). I'm not sure if it has a name or not.
Yes, the gap is real. There is also a small gap at Z=43 not clearly visible on that picture. But look for it on that table. The shell model is the model used to explain why some number of protons (or neutrons) lead to more stable nuclei then others. The numbers that lead to more stable nuclei are called "magic numbers". So, I guess we are talking about anti-magic numbers here :). Dauto (talk) 03:01, 29 May 2009 (UTC)[reply]
I think the idea was that it is lighter than helium but might not be as flammable as hydrogen. Regrettably, this is not the case, but it was a nice idea. --Tango (talk) 22:23, 27 May 2009 (UTC)[reply]
How about using a well-mixed blend of hydrogen and helium as a lifting gas, with sufficient helium to prevent explosion deflagration? What would be the proportion of each gas for the minimum use of the more expensive and heavier helium? Would the gases separate due to their difference in weight specific gravity, or would Brownian movement keep them mixed? If they would separate, would a turbulence-creating fan be feasible to keep them mixed? – GlowWorm. —Preceding unsigned comment added by 98.17.40.143 (talk) 23:24, 28 May 2009 (UTC)[reply]
Concave tympanic membrane
When a tympanic membrane is concave does it remain so or does it self-correct over time or require medical intervention? What caused it to become concave? —Preceding unsigned comment added by Nicola Chessher (talk • contribs) 10:48, 27 May 2009 (UTC)[reply]
In general, the TM returns to its "normal" shape after a distorting force is removed. When allowed to move freely, the TM is shaped like a cone pointed inward due to its circumferential attachments to the external auditory canal and central attachment to the malleus, which maintains the TM under tension. When the Eustacian tube is blocked the TM cannot move freely, and fluid may accumulate in the middle ear. When the TM cannot move freely, the TM may be stretched outward or inward as you suggest. Once allowed to move freely, then like an elastic sheet under tension the normal TM will assume the lowest-energy shape given its attachments. --Scray (talk) 21:42, 27 May 2009 (UTC)[reply]
Are gulls lactose intolerant?
Inspired by the question above. From my personal observations when feeding the gulls or watching the local urban gulls scavenging, it would seem that gulls love to eat cheese and butter (in preference to bread, at least - though they go for meat first, if available). In fact, the very first abandoned gull chick I raised when I was a kid was fed on a mixture of gold top milk and mashed tuna - my reasoning at the time being something along the lines of 'the baby needs milk to drink'. She seemed to come out of it absolutely fine. Better than, in fact.
I know now that it's very unlikely that a truly wild gull would ever encounter milk in its diet - but considering that gulls will consume just about anything organic if they're hungry enough, are their digestive systems completely incapable of handling lactose? --Kurt Shaped Box (talk) 12:21, 27 May 2009 (UTC)[reply]
Only mammals have lactase, the enzyme necessary to break down lactose, in their digestive systems. All birds, gulls included, will lack the enzyme. Butter has low levels of lactose and cheese (depending on type) has much less than milk (our article on lactose intolerance say cheddar has only 10% of the amount in milk), so neither of them may be a problem for a gull in small amounts. As to the gold top milk, if you used the 'top of the milk', there would be less lactose than normal milk due to the increased amount of butterfat - lactose being water soluble. Maybe your chick happened to have enough of the right bacteria to help it process the amount of lactose it got. The general advice, according to all the petcare websites I just looked at, is 'don't give your birds milk'. Mikenorton (talk) 13:09, 27 May 2009 (UTC)[reply]
As the article lactose intolerance notes, the symptoms of lactose intolerance aren't really due to the lactose itself, but result from the fermentation of the disaccharide by bacteria in the intestine. Birds, especially wild birds, are likely to have a different set of intestinal flora, as well as different speeds of digestive processes, which might change how lactose will ferment in the intestine. This might make the symptoms from eating lactose worse, better, or even non-existent when compared to a lactose-intolerant human. To be on the safe side, though, I'd agree with the recommendation not to try it. -- 128.104.112.106 (talk) 15:33, 27 May 2009 (UTC)[reply]
Could a human break their own neck simply by unassisted extreme rotation?
No using of the hands, no using contact against another object...
Just, by pure rotation via the existing neck muscles, could you turn so far as to... *crunch* -- paralyze yourself? 61.189.63.185 (talk) 12:23, 27 May 2009 (UTC)[reply]
Its weird thinking about it... You've just given me some pain in the neck !!. Anyway, i think it should be within the limits of the neck muscle power, but it would definitely require a lot of effort, i don't think anybody has committed suicide this particular way..My guess is that there is there is nothing which says you can't do it..Rkr1991 (talk) 12:54, 27 May 2009 (UTC)[reply]
I could not do it either. Maybe the neck and its muscles and pain receptors were intelligently designed, or there is survival value in not being able to inadvertently or intentionally kill yourself that way. Edison (talk) 03:40, 28 May 2009 (UTC)[reply]
Hmm, I wonder if you and Steve really tried hard enough. No one said it would be easy. Could be your commitment is lacking. --Trovatore (talk) 01:01, 29 May 2009 (UTC)[reply]
I doubt it could be done voluntarily. Pain is a pretty good way of stopping you doing stupid things. I guess it could happen with muscle spasms or something, but I've never heard of anything like that. --Tango (talk) 19:03, 27 May 2009 (UTC)[reply]
Different question, but on the same spirit: Could a human stop their own breathing (permanently) simply by unassisted ... well ... will power? No using of the hands, no smothering against another object...no getting into a oxygen-lacking environment. Jay (talk) 12:23, 29 May 2009 (UTC)[reply]
No. Even if you had the willpower to override the intense desire to breathe, you will simply pass out and begin breathing while unconscious. 65.121.141.34 (talk) 13:22, 29 May 2009 (UTC)[reply]
The question i asked before seemed to not really get answers just more questions so I will ask it in a simpler way here. If the casimir effect works by vacuum energy pushing the two plates together( since there is more waves outside the plates than inbetween them) , that would mean that given the right conditions the vacuum can produce pressure, so surely if you could manipulate the vacuum in such a way that it could produce more pressure on one side of an object than another, it would move that object. IS this correct or not?
People answered you last time. May be you didn't like the answer? The answer is no, you can't do that. It would violate conservation of momentum and energy. Dauto (talk) 15:07, 27 May 2009 (UTC)[reply]
The Casimir effect (as beloved by free-energy nuts and science fiction authors) as a means for extracting free energy from vacuum simply doesn't exist. It exists as a force between two VERY close, parallel plates - but force is not energy. We get an AMAZING number of questions here where people confuse force with energy - and I'm starting to believe that this is one of the most misunderstood parts of physics amongst the general public. Vacuum energy is a horribly misleading term. When you have a force between two parallel plates (imagine holding two fridge magnets apart by a tiny distance - you can only 'extract energy' by releasing them and letting them smack together. Once you've done that - there is no more energy to extract. To get them to do it again, you have to pull them apart - and that takes (at best) the same amount of energy as you just gained in letting them smack together. So there is no free lunch - no violation of the laws of Thermodynamics - just an interesting demonstration of quantum effects at the "macro" scale. In the situation that you're thinking of ("if you could manipulate the vacuum...") there is just one plate - that's like just one fridge magnet. There is no force unless there are two parallel plates very close together - and if there are two plates and you let them move then they're going to move about a micrometer then hit each other and stop. You can't make a perpetual motion machine in this (or any other) way. SteveBaker (talk) 16:26, 27 May 2009 (UTC)[reply]
No, it is the articles that are wrong. As I said, the Casimir force is no different from any other force. It is not caused by vacuum fluctuations. It is a relativistic-quantum correction to the electromagnetic force, as these authors point out in their abstract. A repulsive Casimir force is not going to lead to levitation technology, and the authors of course make no such claim. We already have maglev. Universities like Harvard turn these papers into pop-science press releases in the hope of getting free publicity. Newspapers and magazines publish them uncritically because they don't employ anyone who can tell good science from bad and because they think it will entertain their readers. It's a terrible situation that could hurt funding for genuinely important research that doesn't play well as infotainment. Please don't encourage this system. -- BenRG (talk) 22:23, 27 May 2009 (UTC)[reply]
Reliability of Air Armament
What are the methods to ensure correct preservation of Air Armament while under storage? What are the common mistakes made while undertaking storage of Air Armament and how to avoid them?Why should a missile when fired in the air at correct range miss its target?Fighterflyboy (talk) 14:54, 27 May 2009 (UTC)[reply]
This sounds like a series of AFROTC homework questions. Sorry, we do not do homework for you, but we will help if you are stuck on something specific. Please look at the relevant articles ahbd then come back her if you have specific questions that the articles do not answer. -Arch dude (talk) 15:19, 27 May 2009 (UTC)[reply]
Hopefully, the methods to ensure correct preservation of weapons of any type (air armament included) are centered around a competent, highly trained corps of military officers. If Wikipedia is the preferred reference for aforementioned officers, we are all in a lot of trouble. Nimur (talk) 16:05, 27 May 2009 (UTC)[reply]
Actually I would think that the preservation of such weps would be the responsibility of enlisted personnel, since they are the ones who load the aircraft. 65.121.141.34 (talk) 16:14, 27 May 2009 (UTC)[reply]
Any effective military will certainly have well-defined roles for the enlisted and commissioned ranks; let me clarify my previous statement, and just say that weapons policy is rarely decided by an enlisted personnel; execution of that policy is certainly performed by them. Nimur (talk) 16:39, 27 May 2009 (UTC)[reply]
Since alpha particles are the same as a helium nucleus, can one produce helium by alpha decay of Uranium? How do you get electrons into the alpha particles? 65.121.141.34 (talk) 16:01, 27 May 2009 (UTC)[reply]
Yes, an alpha particle is a helium nucleus, so technically it is already helium. It is just very hot, as it is carrying much of the kinetic energy of the nuclear decay (you can think of the decay as "the second half" of an elastic collision between a heavy nucleus and a light alpha particle. The alpha particle goes flying off at high speed). This high kinetic energy needs to be transferred somewhere else, because hot atoms tend to thermally ionize their electrons away. But, if you could get electrons from some other source (or the original atom, which should have released some free electrons as well), electrostatic attraction will eventually reattach them and neutral helium will form. Nimur (talk) 16:18, 27 May 2009 (UTC)[reply]
(EC) Yes, an alpha particle is an ionized helium and it will readily collect any electrons it may find in the enviroment and spontaneously produce a helium atom. Just remember that the radioactive decay does not produce any net charge, so there should be no problem for the helium ion to eventually find electrons for itself. Dauto (talk) 16:19, 27 May 2009 (UTC)[reply]
Well, it won't readily collect electrons, because the nucleus will be at high temperature and will remain as a free ion plasma until its thermal energy decreases to a level that can support stable electron orbitals. Any individual alpha particle might capture an electron, but it would immediately reionize due to the thermal energy. You really do have to find a way to cool the plasma down if you want to form atomic helium. If the experiment is taking place in air (not in vacuum), then thermal collisions with the air might be sufficient to cool the alpha particles within a few centimeters or meters, depending on the decay process. Nimur (talk) 16:24, 27 May 2009 (UTC)[reply]
It's probably worth noting that the amount of helium you could produce by this process would be very small, and there's no way to conceive of it as the basis for an efficient industrial process for the production of helium. Dcoetzee17:48, 27 May 2009 (UTC)[reply]
In fact, that's the way all the helium you see on Earth *was* produced. Helium, being very light and unreactive, quickly makes it's way to the upper atmosphere and is stripped away by the solar winds. There is negligibly little in the atmosphere. The helium we do have is obtained from natural gas wells. The helium is in the natural gas because the low levels of radioactive isotopes in the surrounding rocks decay over millions of years, producing helium which cannot escape because of the geology of the rocks (the helium can't escape for the same reasons the natural gas cannot escape). As Dauto indicates above, there is no net change in charge for radioactive decay, so if an atom of uranium spits out a +2 alpha particle, the thorium particle that's left behind carries a -2 charge (2 electrons). The alpha particle will then grab electrons from the material it passes through (that's why it's called ionizing radiation). The atom which it pulls it from will then pull other electrons to make itself neutral from somewhere else, which will pull electrons from somewhere else, etc. etc. On the other side, the excess electrons on the thorium will get dumped onto some other atom, which will dump them onto another atom, etc. etc. until the positive charges and negative charges eventually meet each other, restoring neutrality (this may take a while). -- 128.104.112.106 (talk) 21:48, 27 May 2009 (UTC)[reply]
Burning fat
Why is it recommended to do cardio to burn fat? When does the body start to burn fat? If a person just do push-up (aka press-ups) will he loose fat, since he needs energy to it?--Mr.K.(talk)16:07, 27 May 2009 (UTC)[reply]
Yes, but very slowly. Push-ups require strength more than energy. Basically, you need to get your heart rate up, it doesn't really matter what kind of exercise you do in order to do that, but cardio is specifically intended for that purpose (hence the name). --Tango (talk) 17:09, 27 May 2009 (UTC)[reply]
@Tango: yes, but strength is energy. The question is that if a person has a balanced diet - in the sense that he whether earns nor looses weight - and he starts to do push-ups (=> more consume of energy) will he loose weight without cardio? The energy/strength has to come from somewhere. Cardio may help you deplete the glucose from your blood and start using your fat, but in the scenario above, isn't it logical to expect to burn fat?Mr.K.(talk)17:50, 28 May 2009 (UTC)[reply]
I think what happens is the body will typically use carbohydrates before it uses fat. Therefore you will probably burn primarily carbohydrates rather than fat when you do some pushups. I believe that is why aerobic exercise is usually recommended to lose fat - once your body consumes the "easy to use" carbohydrates, it will start to look to its fat stores (so you might be running off carbohydrates for the first hour and then start "burning fat"). However, if you build muscle from doing things like pushups, your basal metabolic rate will increase and you will find it easier to keep weight (fat) off. TastyCakes (talk) 17:58, 28 May 2009 (UTC)[reply]
Sure, but the energy expended to do a few pushups is trivial. To burn a significant amount of calories, you need to be doing pushups for a long time (some estimates: http://wiki.answers.com/Q/How_many_calories_are_burned_by_doing_push_ups ~650 kcal/hr] ~500/hr). Doing pushups for an hour is an aerobic exercise, of a rather rubbish variety (the same person should be able to burn more calories running or swimming with much less effort). The real trouble is that, in most people, the muscles in the arms and chest just aren't very big, so their capacity to expend large amounts of energy is pretty limited. Worse, their endurance is very poor (who on earth can do vigorous pushups for an hour?), so even a fit person will have to quit before they've burned very many calories. If you want to expend large amounts of energy then only the big muscles of the legs and lower torso are up to the job. TastyCakes is absolutely right that building muscle through strength training will raise BMR (and thus, given the same diet as a less muscled person, lead to fat loss), which is why most fitness instructors set training plans that include weights, even for people who say they only want to lose weight. 87.114.167.162 (talk) 21:57, 29 May 2009 (UTC)[reply]
I don't understand the question. 2-methyl propanal does have an "alpha" hydrogen; all aldehydes do. Also, the best place to find answers to the questions at the end of the chapter in your chemistry textbook is in the chapter immediately preceding it. --Jayron32.talk.contribs17:08, 27 May 2009 (UTC)[reply]
I'm sorry but the above statement appears erroneous. Not all aldehydes have an alpha hydrogen. For example Benzaldehyde, or 2,2 di-methylpropanal. But 2-methylpropanal does have an alpha hydrogen. The question the OP asks is that despite having an alpha hydrogen, why does this compound also undergo Cannizaro reaction, instead of Aldol reaction, under basic conditions ?
I would say that this compound would indeed undergo Cannizaro, but in only limited amounts. It has only one alpha hydrogen, which is sterically hindered as well. So under strong basic conditions(like 50% NaOH) it might also undergo Cannizaro in competition with Aldol condensation. However, the reaction probably does not take place to a great extent, so it shouldn't be used even for writing conversions on paper, let alone industrially. It yields a mixture of products, but overall the Cannizaro product must be quite a low fraction. Rkr1991 (talk) 02:54, 28 May 2009 (UTC)[reply]
Self-published scientific magazine
What can be called "self-published"? If a faculty has a magazine and this magazine publish many works of its own teachers - and some articles of external researchers - , is it self-published?--Mr.K.(talk)16:14, 27 May 2009 (UTC)[reply]
If the university press publishes such a report, it is not self published. Also, there is an important distinction between self-published and "non-peer-reviewed" research. For example, my research group self-publishes our bi-annual journal, since we maintain and contract our own document management and printing services (rather than the Stanford University Press); but our research is peer reviewed by a consortium of academic and industry experts, sponsors, and collaborators. We also publish other work in academic and industry journals. Nimur (talk) 16:30, 27 May 2009 (UTC)[reply]
Turns out many of the other yellowish pigments in fish appear to be breakdown products or modification of xanthophylls or carotenoids, probably not what you are looking for. However, another type of yellowish pigment is ceroid, also known as lipofuscin, and the yellow pigments found in many insects are pteridine derivatives such as Xanthopterin. Rockpocket17:08, 28 May 2009 (UTC)[reply]
calluses on fingers
I'm an electric bass player--I regularly get blisters then calluses from my playing
BUT THEN! the calluses peel off! How do I keep those calluses strong and firm without peeling off after a while.
If you're getting blisters, then you're playing too much. And what you're calling calluses is just skin that's grown as part of the healing to the damage you've done, not a callus. So quit playing until your fingers are back to normal, and then return to playing gradually. When your fingertips hurt, stop for the day. Do a little more each day, and real calluses will gradually form (my fretting fingertips look almost identical to the other hand; no cracking or peeling here, but with tougher skin nevertheless). Ignore that Ted Nugent "play til your fingers bleed" nonsense. 87.114.167.162 (talk) 19:49, 27 May 2009 (UTC)[reply]
This happened to me for a while (like a year) when I started playing, but eventually my fingers realized that I wasn't going to stop playing the guitar. There are two things that happened to me over time. First, my callouses became more permanent, and the blister-peel cycle stopped. Second, my finger tips just became less sensitive to it; I wouldn't say that my fingers are numb, I just learned to "play through the pain". I don't even notice it anymore. Other than that, I would agree with the above. Don't play until you bleed, but always play a little each day. You're body will eventually change. --Jayron32.talk.contribs19:52, 27 May 2009 (UTC)[reply]
Drumming your fingertips on wood might help a bit. (OR note: Side effect of driving those around you crazy might be undesirable, depending on your age:-) It gets the skin stressed over a wider area than just the string/fret and may help with building Calluses instead of blisters.71.236.24.129 (talk) 07:50, 28 May 2009 (UTC)[reply]
i found that the skin under the peeled callouses is a little stronger than before the callous formed. Eventually you will have slightly harder skin on your fingertips but no callouses and no pain. Dont play with sore fingers however! —Preceding unsigned comment added by ThrobbingTrousers (talk • contribs) 00:12, 29 May 2009 (UTC)[reply]
Spelling note: The original poster got it right. Callus is a noun; callous is an adjective. Cuddlyable3's reference to callous skin is just barely possible, though it makes one think of skin that doesn't take others' feelings into account. The other uses of callous above are wrong.
Similar pairs are mucus / mucous and phosphorus / phosphorous. Rule of thumb is that mucous is almost always wrong unless followed by membrane or secretion; phosphorous is almost always wrong unless followed by acid. --Trovatore (talk) 01:30, 29 May 2009 (UTC)[reply]
Passage of matter through descendents
This is kind of a weird question, but I was looking over my family tree and wondering: are any of the molecules that were present in my great, great great etc. grandmother present in ME? Or are fetuses entirely produced on matter taken in by the mother from outside the body? 58.161.196.113 (talk) 17:41, 27 May 2009 (UTC)[reply]
Wierd, yes, but also a very intriguing question. I would seriously doubt that any molecules from your distant ancestors are still present in you, since each embryo starts from a single fertilized egg, meaning that any direct molecular contribution from your parents is limited to the contents of 2 cells, which then becomes diluted over the course of multitudes of cell divisions (the materials for which must come from external sources). There's quite a bit of cellular turnover throughout development and life. So, statistically speaking I'd guess that there's basically no chance that you actually have any of the same molecules that came from your distant ancestors. Unless, of course, you happen to grow and eat food from an area nearby where your ancestors were buried, in which case it's certainly possible that their molecules were recycled into the soil and somehow made their way into your body that way. It sure gets spooky when you start to think about what your molecules were doing before you occupied them! --- Medical geneticist (talk) 18:23, 27 May 2009 (UTC)[reply]
I agree that the chance of any molecules being directly inherited is pretty much zero, however there are so many molecules in you and were so many in your great-great-great-...-grandmother that there is actually a pretty good chance that just by pure coincidence some of the ones from her are in you. This kind of thing is usually formulated as questions like "Are their any atoms of oxygen in me that there exhaled in Julius Caesar's last breath?". If you go back far enough there is almost complete mixing of the atmosphere over that time so the chances end up being pretty high. It's a similar issue with your question, although slightly complicated by the fact that you haven't specified a time - most molecules don't stay in your body for your entire life (some in your bones might, I think that's about it). --Tango (talk) 18:49, 27 May 2009 (UTC)[reply]
I think that particular thought experiment has more to do with the concept of equal ratios, in this case molecules/breath and breaths/atmosphere, and the two equal each other suggesting that supposing all the molecules from his last breath are still around, the average Caesars-last-breath molecule inhalation rate is 1. I would be inclined to agree with the 'plausible' camp in this "hereditary atoms/molecules myth", at least along the maternal line. Since a woman's eggs are all produced very close to the beginning of her life, she is much more likely to make them out of some of the molecules from her predecessor. Conversely, for men, since sperm are produced in an ongoing basis, the later in a man's life he produces offspring the less likely he will be to contribute any of his predecessor's molecules to it.--66.195.232.121 (talk) 20:31, 27 May 2009 (UTC)[reply]
Is it close to 1? I know it works out to be at least 1, but I think it is mostly a thought experiment to do with just how many atoms there are in a small amount of air, rather than the ratios. Your argument suggests that it is quite likely for someone to contain molecules from their maternal grandmother, but it doesn't suggest anything about longer lines - the chance of having molecules from your great-grandmother would still be extremely low. --Tango (talk) 22:19, 27 May 2009 (UTC)[reply]
If the turnover time for cellular is something like five years, then individual atoms might get passed over a century. There are ~10^14 atoms in a cell (give or take), which would be ~45 half-lifes before the expectation drops to zero for any matter still being there. If cellular matter, on average, persists for years, then things might get passed around 2 centuries or so. Of course one has to worry about dilution and mixing and other effects, but I wouldn't rule out direct passage of a few atoms from your grandparents, etc. Dragons flight (talk) 19:01, 27 May 2009 (UTC)[reply]
The chances of an atom being transmitted from egg>egg>egg for however many generations without it leaving the body is remote (this is a crude calculation):
There are 7x1027 atoms in an average body, and ~5x1013 cells. Each egg cell will contain ~1.4x1014 atoms. The number of atoms from that egg that get into the next egg to be produced would be around 1 (1.4x1014/5x1013) but that one atom is likely to have been lost at some point over 20 or 30 years anyway.But take a look at this - it calculates that everytime we breath in, we breathe five molecules that Leonardo da Vinci breathed out in his dying breath! I'd guess that if this was expanded to all the atoms that have ever passed through your ancestors there's a good chance there will be some in you now. Perhaps someone can do the maths. It is even more likely that one atom that passed through your ancestors at some point has also passed through you. Smartse (talk) 22:13, 27 May 2009 (UTC)[reply]
That's a good start as an approximation, but you're neglecting the vast number of cells that are produced and die over the lifespan of an individual. Think first about the embryo itself. At the time that the fertilized egg has undergone enough cell divisions to approximate a small hollow sphere only a fraction of the cells will actually become part of the embryo proper. The rest of the cells go on to form parts of the placenta which will not significantly contribute molecules to the adult organism. A few cells from the inner cell mass are the primordial germ cells which will migrate to the site of the gonads and divide a large number of times during the process of gametogenesis. As noted above, the likelihood of any molecules remaining in the egg or sperm depends on the number of cell divisions required for production (more divisions for sperm than eggs). The rest of the cells of the body are just a vehicle for the germ cells to be able to ultimately reproduce. Keep in mind that while all of this is going on, every cell is constantly breaking down and building up cellular components, which means that even basic molecules are likely to be reduced to waste (carbon dioxide and urea) and excreted. So, it isn't inconceivable that your egg contained some molecules from your mother's parents, or even your mother's maternal grandparents. Just highly unlikely... --- Medical geneticist (talk) 23:47, 27 May 2009 (UTC)[reply]
It's worth noting that a fetus acquires many cells directly from its mother, particularly those used for immune defense, and continues to receive them after birth via breast milk. The question of whether these cells are really "part" of the mother is sometimes fuzzy, but many of them actively served a biological function in the mother before their conveyance. In fact, you continue to receive cells from the bodies of people in your environment on a routine basis, for example by inhaling or eating particles of dead skin and hair. Dcoetzee22:24, 27 May 2009 (UTC)[reply]
Could you point me toward a good source that shows many cells from the mother's immune system are preserved in the newborn, either before or after birth? Certainly, antibodies are passed from mother to child, but I seriously doubt many cells are transferred and survive, particularly from breast milk. --Scray (talk) 01:06, 28 May 2009 (UTC)[reply]
I'm afraid this is a meaningless question in most cases because small molecules lose their identity completely in a homogeneous fluid. It's quite meaningless to ask whether a molecule removed at a later time is the same as one you put in earlier. Larger objects like cells do have individual identities, and atoms fixed in some solid part of the cell might retain an identity for some period of time. I don't know if any could be traced from parent to child, but I guess probably not since they all end up floating through cytoplasm at some point. At any rate it's a totally different calculation from the classical one with billiard balls. In the case of Caesar's last breath it's much simpler: quantum mechanics says unequivocally that there's no answer. -- BenRG (talk) 23:38, 27 May 2009 (UTC)[reply]
The finite amount of water on Earth is continually being recycled through people, animals, sea and atmosphere. I think the statistics show it to be very unlikely that any two people have not employed the same water molecule. Cuddlyable3 (talk) 10:31, 28 May 2009 (UTC)[reply]
Again, there's no such thing as "the same water molecule" in this situation. The ocean only has a total water molecule (or ion) count; it doesn't have individual molecules of water! Having n molecules of water is the same as having k liters of water, except that quantum field theory constrains n to be a nonnegative integer. But it only constrains it to an integer, it doesn't partition the water into n pieces each of which is one molecule. Sometimes n = 1 and in that case you can say that you have a single, isolated molecule of water. But when n = 2 you don't have this one and that one, you just have two. -- BenRG (talk) 20:03, 29 May 2009 (UTC)[reply]
There would be no advantage to having specific matter from ones ancestors, rather than duplicates, unless someone can think of a specific scenario where passing material is simpler and more logical. On a reverse sort of notion, women who have been pregnant may have an immune or other advantage compared with men and women who haven't because of what passes back to the mother through the placenta.Julzes (talk) 19:00, 29 May 2009 (UTC)[reply]
Genetic crossing notation
I'm trying to understand a paper about genetic manipulations performed with Drosophila; it describes a cross in the form:
AB+; CD1118;[PQR][STU];[VW][XYZ]/blah X AB+; +;[CD+cheese]
I changed the genes for simplifcation. Can someone explain what is being described in this notation? Sometimes I also see things like blah::blahblah - what does the :: mean? Thanks in advance :) --94.212.39.7 (talk) 23:04, 27 May 2009 (UTC)[reply]
I'm afraid that changing the gene names didn't really simplify the question. It might be better to just write out the cross that you're confused about. In any case, with regard to the "blah::blahblah" notation, I've seen that done for fusion proteins, for example when a particular protein is hooked up to green fluorescent protein it might be written "GFP::Mygene". The other parts of your notation seem to relate to particular genetic variants but I can't really be sure. --- Medical geneticist (talk) 01:17, 28 May 2009 (UTC)[reply]
Do cats enjoy chilled water in their bowl? My observation is that they do not, even on hot days. Is there a reason for this? Thanks. Viriditas (talk) 02:26, 28 May 2009 (UTC)[reply]
Maybe it is a matter of taste. Try putting identical amounts of room temp and refrigerated water in bowls, and check an hour later how much is left in each. Repeat the next day to make sure. Then try intermediate temps to find the ideal. Maybe someone can make sure that cats are not somehow harmed by cold water. Edison (talk) 03:37, 28 May 2009 (UTC)[reply]
Googling for 'cat cold water' finds stuff like this, with some cats demanding ice water from their human slaves. If you see evidence to the contrary then a matter of taste it must be. 62.78.198.48 (talk) 08:01, 28 May 2009 (UTC)[reply]
Water from the fridge usually has less oxygen in it than agitated water. If you keep it in a jug, shake the jug before pouring the water. On the other hand some cats prefer mud-puddle water to both tap and bottled water. They usually prefer their food an drink at room temp. Very cold food can upset their stomachs. That is why you shouldn't store cat food in the fridge. (..and don't reheat it in the microwave because that can harden cartilage and collagen pieces in the food and also upset their stomach.) Most of the time, all that will happen is that they'll throw up. They do that without much sign of later discomfort. (Also in case of hairballs.) Cleanup in aisle 2 :-) 71.236.24.129 (talk) 08:00, 28 May 2009 (UTC)[reply]
Even when our cat has a bowl full of water, he calls us to open up the kitchen door to allow him to go outside and drink rain water. (That cat is full of surprises...) - Mgm|(talk)09:57, 29 May 2009 (UTC)[reply]
I'm wondering how many cats the OP has observed. My experience with cats and dogs is that they are, like humans, individuals. The soup that my father calls too hot, my friend calls just right; my father once ridiculed me when I said that I didn't think lukewarm water was as thirst-quenching as cold water. It probably isn't any different with pets. They have food preferences (Precious my hot dog loves salmon, Obi my cool dog shares apples with me, and Houdini the dog of my heart utterly adored bananas), so why not temperature preferences as well? As long as what you're giving your cat isn't reheated or so cold as to cause stomach upset, as mentioned above, there's no reason you shouldn't indulge your pet's individuality as long as it's convenient for you. —Preceding unsigned comment added by 66.215.227.218 (talk) 22:34, 29 May 2009 (UTC)[reply]
I assume your link is to transverse wave. Sound waves always need some kind of elastic media to travel in. There is no error in the Sound article about waves being transverse or longitudinal. I added to the Sound article information that transverse waves are at right angle to the direction of propagation. I hope that helps to clarify. Cuddlyable3 (talk) 10:07, 28 May 2009 (UTC)[reply]
(ec):Transverse or shear sound waves are possible in elastic solids. For example, in an earthquake the first seismic waves to arrive are the compressional (known as primary) P-waves followed by the slower transverse (known as secondary) S-waves. S-waves, however, do not pass through liquids and this property has allowed them to be used to show that the earth's Outer core is in a liquid state. Mikenorton (talk) 10:14, 28 May 2009 (UTC)[reply]
Yes, I agree. However, there can exist a transverse wave in a gas when the gas (plasma) is at least partially ionized and a magnetic field is present. It is called Alfvén wave. It is not a sound in the conventional sense, though. An ion sound wave (more generally, a magnetosonic wave) can also exist under the same conditions, but it is longitudinal rather than transverse. See Waves in plasma and follow the links for more details. --Dr Dima (talk) 18:02, 28 May 2009 (UTC)[reply]
Maximum optical zoom
Is there a limitation for the optical zooming, assuming vacuum case? And what is the maximum practical optical zoom ever made (For examples for telescope and camera purposes)? The reason I ask this question is because of some very high resolution imaging satellites. Thanks again for your help in advance --Email4mobile (talk) 10:15, 28 May 2009 (UTC).[reply]
To begin with, you seem to be making the common mistake of misusing the word zoom. The focal length of a lens is (among other things) what determines how large the things you're photographing will appear in the photograph. With a short focal length, or a "wide-angle lens", you might take in a whole landscape. With a long focal length lens, which is often a telephoto lens, you can fill the frame with a small songbird from some distance away.
A zoom lens is simply a lens that can change its focal length. You can have zoom lenses that are entirely wide-angle. Telescopes and earth-imaging satellites are not generally "zoom" optical systems. I think you want to know about upper limits on focal lengths, or the ability to resolve fine detail.
As you increase the focal length of an optical system, you also need to increase the diameter of the lens or mirror to maintain a reasonable f-number, or else you will end up with a very faint image. Increasing the diameter gets harder and harder the bigger you get; first there's the obvious expense of manufacturing a big lens or mirror, but there are also the engineering challenges of getting the lens or mirror to support its own weight without bending (which would ruin the optical quality), or the costs of launching all that weight in the case of orbiting telescopes or imaging satellites.
Furthermore, even if you increase the focal length and diameter, your ability to resolve fine detail when looking at space from the ground, or looking at the ground from space, is limited by atmospheric seeing. Have you ever seen some wavy distortion when you look over a hot grill? A similar phenomenon limits the images from telescopes. Looking up from the ground, your angular resolution is not likely to be much better than 1 arcsecond no matter how big your telescope, unless you use advanced technologies like adaptive optics. Looking down from space, the same phenomenon limits resolution on the ground to about 5 cm. -- Coneslayer (talk) 11:48, 28 May 2009 (UTC)[reply]
You do not need adaptive optics: lucky imaging works just as well. Combining several images of the same thing would also improve image quality: this is often used in digital photography, I forget the names of the techniques. Using just ultra-violet could improve resolution more. So if things like this could improve the resolution by - complete guess - ten times, then you are down to a resolution of .5cm. I suppose you would see faces at this resolution, perhaps identify people. The article about the 5cm resolution was written in 1966 - technology will have improved since then. 78.146.211.210 (talk) 23:40, 29 May 2009 (UTC)[reply]
Fisrt I'd like to thank you very much for correcting my wrong information about optical zoom; and second awfull thanks for all the valuable explanation summerized in your text :) Coneslayer --Email4mobile (talk) 12:00, 28 May 2009 (UTC).[reply]
No problem... it's a complicated subject, and I glossed over a lot in the above discussion. You could spend all day reading the articles I linked to, and the related articles they link to. Feel free to stop back with follow-up questions. -- Coneslayer (talk) 12:15, 28 May 2009 (UTC)[reply]
Military satellites are known to be able to resolve down to 10cm - it is believed that they are able to recognise individual human faces, and there were claims in the 1970's that a satellite from that era could read license plates on cars...which I think means we're down to a centimeter or so. However, the very best stuff is classified - so the best we KNOW they can do is 10cm...which is about what you get on Google Maps in their high res city centers (although in that case the high-rez pictures come from Aerial photography - not satellites). SteveBaker (talk) 14:02, 28 May 2009 (UTC)[reply]
A limit comes from diffraction on the aperture. The larger your front lens is, the better is the limit resolution. Assuming a circular aperture (diameter ) and looking at objects close to the optical main axis, the Rayleigh's criterion (see the same link; its use is subjective and the limit is not rigid) says that from distance the smallest resolvable object can be wide. is the wavelength, thus, you can see sharper in blue than in red. With your eye's and green, from you can resolve two points up to apart (try it, I have!). From a satellite's and with a reasonable (the same ), we get , which really is about the resolution of the Google Earth satellite images: the better ones have already likely been taken from airplanes.—Pt(T)14:25, 28 May 2009 (UTC)[reply]
I would expect even the 20cm ones have been taken from planes. 20cm resolution from satellites is achievable, but it's not easy. --Tango (talk) 17:04, 28 May 2009 (UTC)[reply]
Respondents have assumed the OP is asking about the limit of a fixed telephoto lens. However zooming means changing the focal length of a lens while keeping the scene in focus. A limit to the ratio of a zoom lens is the increasing complexity of its design. Here is The World's First Triple Digit Zoom LensCuddlyable3 (talk) 10:32, 29 May 2009 (UTC)[reply]
Live Google Maps
With the current technology, is it possible to have a live Google Maps kind of thing, where we can zoom in on any part of planet earth to see people walking, birds flying, river flowing, traffic moving and sharks swimming? Is there any such service already in existence? I guess not, at least to such extreme level of precision. If not, when can we expect such thing (if ever) and how difficult is it to get there in comparison to where we are today. Thanks - DSachan (talk) 12:27, 28 May 2009 (UTC)[reply]
No, it isn't possible. The true-color images we see in Google Earth come from the imagery of a finite number of satellites, and (as I was surprised to learn) aerial photography. In order to have a "Live" Google Earth, you would need millions, if not billions, of satellites, all sending immense amounts of data per second, to be integrated and stitched in short enough time to be considered "live". I'm not sure that this will even be possible, never mind practical or worth the tremendous cost, for more than 100 years.
Now, if you're willing to sacrifice some spatial resolution, in a way we already have what you speak of: the GOES satellites send imagery at a resolution of a few kilometers every 15 minutes, and together have coverage of the entire planet (though the resolution declines as you approach the poles). I see no reason why in the near future we couldn't have near-real-time views at this spatial resolution, although I'm not sure anyone would be able to justify the cost.-RunningOnBrains(talk page)12:47, 28 May 2009 (UTC)[reply]
(edit conflict) Not now, and not likely. Imagery satellites are typically in orbits where they only pass over a particular point on the earth for a brief period, typically every few days. They cannot provide persistent motion imagery, nor image a particular location whenever you want. I was surprised to see in Satellite_imagery#Moving_images that a company planned to put an imaging satellite in geosynchronous orbit to provide ongoing live video; note, however, that because of the high orbit, the resolution would be very poor (250 meters). That's not good enough to see the kinds of things you're asking about. -- Coneslayer (talk) 12:52, 28 May 2009 (UTC)[reply]
Also - satellite photography has to be done on a more or less cloudless day - and if you want it to look any good, sometime close to midday. But the highest resolution commercial satellites produce really terrible spatial resolution - 5 meters, I believe. You can buy imagery from the Russian military at perhaps 1 meter accuracy. US military satellites can reach 10cm or better...but that imagery isn't for sale! There is a 'gentlemans agreement' amongst satellite photography sources not to sell better than 1 meter accuracy data to anyone other than government agencies because of the obvious privacy issues. (They chose that number because it makes recognition of individual humans impossible).
Aerial photography is therefore the only way to get high resolution imagery - and it's expensive.
So certainly, we're nowhere near even close to being able to do this. But even if we were - consider the bandwidth requirements. Most of the high res stuff in Google maps is about 10cm resolution. The surface of the earth covers 510,072,000 square kilometers - even if we ignore the oceans, that's still 148,940,000 square kilometers. At 10cm resolution, that's 14,894,000,000,000,000 pixels. About 8,000 of the largest hard drives you can buy. If we updated it every second, that's something like 24,000 terabytes per second! There is no known transmission medium that could possibly get even a tiny fraction of that from satellite down to the earth! This is so far away from being possible! Consider satellite TV - they typically have about 1.6 Gbits/second (per satellite) of down-stream bandwidth. It would take about a quarter of a million satellites of that kind of performance to transmit the data down to us...for the land alone. If you wanted to do the oceans too - you'd need a million satellites!
You would need to make it on-demand - the satellites only transmit the data that is wanted at that moment (that would increase latency slightly, but not too much). The bandwidth isn't really a problem, it's the sheer number of satellites you would need to have constant global coverage. You could use fewer satellites by having them higher, but that would lower the resolution. Getting 10cm resolution from a geostationary satellite, for example, would require technology well beyond current level - you're probably talking decades until we can manage that. --Tango (talk) 14:06, 28 May 2009 (UTC)[reply]
Really what you want is to have access to security cameras, then in a place like Britain you could check on people all day long and with the need be secure against terrorism we'll hopefully soon have cameras and microphones inside the houses too, except for politicians of course because what they do is so sensitive. We could start with a law that all webcams are permanently accessible to the security forces at lease though you really need other people like for instance schools to be able to use them to make certain people are applying from the appropriate area. The more eyes are watching the less chance they have to get away with their crimes. RIPA details the advances Britain has made along these lines. Dmcq (talk) 15:33, 28 May 2009 (UTC)[reply]
You joke, but I remember a news story a year or two ago about a town (in the UK, I believe) that started broadcasting its CCTV on a local TV channel (so, CCTV is a misnomer, I guess!) so residents could help spot crimes as they occurring and inform the police. I don't know how successful it was or if the scheme is still running and can't find it now. --Tango (talk) 16:14, 28 May 2009 (UTC)[reply]
I think its dreadful that in some northern UK town - Middlesborough? - they have a tannoy system where the security droids can bark out commands at the public. I'm surprised that nobodies rioted about that yet, they would do in the south. Its truely 1984. Spy satellites - a few years ago I remember reading something about them. Many or most of them see in the ultraviolet, because that has least distortion through the atmosphere, as far as I recall. They can see fag packets. Most observation satellites see in various wavelengths and create false-colour images. True-colour visual wavelength images may be in the minority. I expect the cleverest satellites could use astronomy techniques in reverse, such as lucky imaging. 78.147.139.18 (talk) 23:09, 28 May 2009 (UTC)[reply]
Does heat contribute to production or increase in PCB's (Polychlorinated Biphenyls)
Can intense heat cause production of, or, an increase in the amount of
Polychlorinated Biphenyls (PCBs) in new Non-PCB transformer oil over time?209.26.182.3 (talk) 14:52, 28 May 2009 (UTC)[reply]
Seems unlikely, but the chemists on the board can weigh in on the possiblity of PCB being created from the heating of mineral oil or silicone coolant. If a transformer once had PCB contaminated oil in it, but was flushed until it tested PCB-free, I supposed that operation at high temperature could free up a bit more PCB from the windings. There was a time when utilities allowed PCB to contaminate mineral oil cooled transformers by the common use of tanks and filter presses, so there were so many parts per billion of PCB found in equipment which did not start out with PCB or "Askarel" (trade-name). High temperatures reportedly caused PCB to turn to dioxin, which was supposed to be worse than PCB. Edison (talk) 19:06, 28 May 2009 (UTC)[reply]
No. As far as I know, no commonly-used transformer oil type (mineral, silicone, or fluorocarbon) contains any chlorine. It is therefore impossible for any chemcal reaction involving the oil to generate a polychlorinated biphenyl. TenOfAllTrades(talk) 19:23, 28 May 2009 (UTC)[reply]
What is needed to heal Humanity's ills?
Say by some great miracle, all religious/tribal/political countries/factions/groups in the world agreed to a 5 year truce with each other. Meaning, no violence, retaliation, nothing. What can humankind do during this time of peace to get reduce of world hunger, make education and healthcare more available to everyone?
For instance, what should the US do first in this opportunity? I always thought that if everyone was well fed, had access to healthcare and all types of education, this world would be a very different place meaning less violence and more social awareness and a reduction of the human population. --Reticuli88 (talk) 16:35, 28 May 2009 (UTC)[reply]
Of course, from where do you get food, health care, or education? Those things require people to do work in order to provide people with them. Farmers need to grow food; truckers need to transport goods around, teachers have to, well, teach. So how do you recompense those people? Plus, if people receive food, shelter, education, and healthcare for absolutely no cost at all, then what is the motivation to work? Why should I be a teacher if I don't need any money to buy my own food and put my own kids through college? Why be a farmer if I have no motivation because I am so well taken care of I have no reason to work hard? See? Sometimes its not all that easy. --Jayron32.talk.contribs16:53, 28 May 2009 (UTC)[reply]
Teachers and farmers are not doing it for the money. The motivation for work, real work, not digging ditches and cleaning toilets, comes from within. The concept that people are motivated to work hard because there is a carrot dangling in front of them doesn't address the fundamental problem. People like Abraham Maslow have addressed some aspects of this motivation, and John Neulinger proposed creating a society that was based not on work as we know it, but on work redefined as leisure, where leisure is pursued for its intrinsic reward. But the question proposed by the editor is flawed, since fear and "violence" from "religious/tribal/political countries/factions/groups" is encouraged at every level of society, and governments want their citizens to have as many people as possible to increase the tax base. We know that the higher the population density the more social and ecological problems result, from crime to mental illness, to pollution and resource extraction. In a world where people are treated as "consumers" (a recent invention of the last century) and where accumulating wealth is the highest human value, scarcity will be the result. The kind of "peace" that Reticuli88 talks about is an important issue for psychology. See also inner peace. Viriditas (talk) 21:00, 28 May 2009 (UTC)[reply]
Some teachers and farmers are not doing it for the money. At least, its easy for them to say that when they are recieving a living wage AND still have real pressures to do SOMETHING for work. The neat thing is that someone did the experiment and we actually have data on this. See Kolkhoz for what happened when farmer's WERE'NT doing it for the money any more. Strangely enough, the stopped farming really well, and an entire nation starved. People in collective (that is, on average) will only work as hard as they have to and no more. Individual, anecdotal examples exist of a person working harder just for the sheer joy of it. But in the bulk, people don't do that. --Jayron32.talk.contribs00:37, 29 May 2009 (UTC)[reply]
Most teachers are not doing it for the money. They do it because they are interested in education and they tend to be "idealistic and altruistic" about why they teach.(Goodlad 2004:171-173) As for farmers in the modern world, "economic considerations now make it difficult for farmers to earn a living at farming, because farm costs have been rising much faster than farm income." For farmers in the United States, "the lifestyle was highly valued by older generations", and "people used to expect no more of a farm than to produce enough to feed themselves."(Diamond 2006:57-60) So it wasn't about money, it was about feeling good about your work and being able to be self-sufficient and raise your family. This is true for any profession. Why do mathematicians work hard at math? For the money? Of course not. They do it because they love it. Viriditas (talk) 03:21, 29 May 2009 (UTC)[reply]
You appear to be asking for a discussion about what might happen if some other rather impossible event were to occur. This is not a discussion forum. This is a reference desk. If you have a question that might possibly be something that has been studied and reported on in a respectable resource, please ask. If all you want is a discussion, please use one of the thousands of discussion forums available on the Internet. -- kainaw™17:02, 28 May 2009 (UTC)[reply]
Absolutely. We can refer you to a variety of philosophical, economic, and political theories, but this is not the place for a long and drawn-out discussion. Maybe you can start with utopia. That article is a great introduction and is full of links to numerous theories spanning the gamut from communism to fascism, feminism to individualism to mass annihilation. Personally, my favorite quote regarding utopia comes from an unlikely source, "The Khmer Rouge leadership boasted over the state-controlled radio that only one or two million people were needed to build the new agrarian communist utopia. As for the others, as their proverb put it, "To keep you is no benefit, to destroy you is no loss."" (Let me be clear - I don't condone this statement or the genocidal actions it represents - but I feel that it succinctly summarizes the problem that one man's utopia is not necessarily the same as the next). For virtually every atrocity historians can attribute to human activity, somebody thought it was a good idea.Nimur (talk) 17:11, 28 May 2009 (UTC)[reply]
It seems unlikely that poverty and crime would disappear with the end of war and conflict, even places that have known peace for many decades (Sweden?) have crime and poverty. In many places people do have free access to education and healthcare, but are still afflicted by the problems you mention to some degree (although hunger has been stamped out even among the poor among most of the industrialized world). I think historically urbanisation has reduced human birth rates much more effectively than eliminating war or reducing poverty. I think it should also be remembered that the well being of the world's people is improving, as described in this TED talk. To me, rather than an end to wars what the world really needs is good government. I would define that as largely transparent with as little corruption as possible, and being responsive to the populace without pandering to short sighted populism that is a problem even in the first world (like in, say, California). In my opinion a mostly free economic system is also paramount, as well as means for people to improve their status in society and better themselves, education as the great equaliser and all that. But while I think a world without wars is possible, a world without violence and theft is not, they seem to me inseperable from the human condition. TastyCakes (talk) 17:04, 28 May 2009 (UTC)[reply]
I agree with TastyCakes, corruption is the main thing to get rid of. If you achieve that, then I think hunger would all but disappear. Growing enough food to support the current world population isn't difficult, the problem is getting it where it is needed. Getting rid of hunger and poverty isn't likely to reduce violence, though. While some people are violent because they need to be to get the essentials to live, most people do it for reasons of power. There is always going to be a finite amount of power available so people will always fight over it (at all scales of existence - domestic violence is to do with power in a family, gangs fighting in the streets is about power in a particular sector of society, civil wars are about power in a country, regular wars are about power in a region, or even the world). --Tango (talk) 17:13, 28 May 2009 (UTC)[reply]
How is this a science question? Seems like a forum topic anyway - i don't think anyone in the world could answer this, let alone the reference desk.YobMod17:16, 28 May 2009 (UTC)[reply]
That some people who have approached philosophical questions happen to have had scientific backgrounds does not make the question about science. All we have is speculation - where are the testable hypotheses? The consequences of an impossible situation can not be scientifically explored. Eg, Stevebaker's reply after this suggests people reproduce more after a war. It may be true , but with only one example and absolutely no controlled studies, it is not a scientific answer (not that he claimed it to be, except by putting it on the science ref desk). I predict that world-peace would inspire an hysterical epidemic of religiosity, resulting in a huge drop in birth-rate as people prepare for the Rapture. The fact that i have 2 degrees in sciences does not make that a scientific prediction.YobMod12:53, 29 May 2009 (UTC)[reply]
Let's try to find some generalities that might apply to this hypothetical situation: When wars end - people make more babies. The present 'baby boomer' generation are the consequences of the end of the second world war. So I'd expect one consequence of the end of all of these conflicts would be a jump in world population. That's really not a good thing. SteveBaker (talk) 21:52, 28 May 2009 (UTC)[reply]
I suspect if there really were a five year truce, many people would use this period to, well, stockpile weapons, train armies, and spy on their enemies. Otherwise, when the five years are up, they're going to get trampled by their enemies who have been busy doing the same. Dcoetzee21:59, 28 May 2009 (UTC)[reply]
As to why Dcoetzee's answer is probably the best one, see Game theory. There are four outcomes here: Both nations disarm, Nation A does and Nation B does not; Nation A does not and Nation B does, and no one disarms. This is a classic Nash equilibrium whereby the best possible outcome (all countries disarm) cannot be reached because two of the three other outcomes (one country disarming while the other does not) is so catastrophic for the peacenik nation that the fourth option (both countries stockpile weapons) is the only stable equilibrium. Its a classic case of the prisoner's dilemma. See also Balance of terror for the classic application of the prisoner's dilemma to military strategy. --Jayron32.talk.contribs00:31, 29 May 2009 (UTC)[reply]
The problem is that this is NOT a prisoner's dilemma situation. At worst, it's a "Continuously iterated prisoner's dilemma" - the same test happens over and over and you can learn from what happened in previous rounds. At best, it's not a prisoner's dilemma at all - because the players can communicate. That radically shifts the results. SteveBaker (talk) 01:54, 29 May 2009 (UTC)[reply]
Except that the communication is meaningless. You can TELL the other nation you want to reduce your armaments together, but do you TRUST your enemy? If you don't trust what they tell you, its just as good as not talking at all. And the net result is ultimately the same; the payoff matrix for the "Do we build weapons or not" game is identical to the prisoner's dilemma payoff matrix, and you ultimately always end up with the same equilibrium result. Both look like this:
NO!!!!!! it's not like that! You've completely failed to understand what the prisoner's dilemma teaches us.
In the true prisoner's dilemma you have no information about how the other person is behaving right now or is likely to behave in the future. So you have no information on which to make your decision. It's also an all-or-nothing thing. In the disarmament scenario - you can slowly ramp down your arms production and watch to make sure that the other guy does the same thing - every round of defense-funding decision-making becomes another game of prisoner's dilemma. Hence it's an ITERATED version - and game theory predicts utterly different conclusions under those situations (read the article AGAIN!). In an iterated system, your chart looks like this:
Reduce armaments by 1%
Increase armambents by 1%
Reduce armaments by 1%
Win a modest amount/Win a tiny amount
Win a tiny amount/Lose a tiny amount
Increase armaments by 1%
Lose a tiny amount/Win a tiny amount
Lose a tiny amount/Lose a tiny amount
You can even look back at how the other guy has been doing in the past. If he rearms a bit when he says that he won't - you can arm yourself a little more as 'punishment' in the next round. In this "iterated" prisoner's dilemma, there is a clear strategy that always works - as demonstrated by a very famous computer simulation/game (which you can find out about in the article). "Tit for Tat". You start out as "Mr Nice Guy" - but if/when the other guy screws you over - you punish him on the following round - then you go back to being Mr Nice Guy. That stategy is utterly unbeatable over the longer term when there is no communication between players other than the game results. But even more than that - if you have communication, you can try to make it clear the rules by which you are playing - with openness in your processes (everyone can see your military expenditure budget BEFORE that gets turned into weapons manufacture) - then it becomes clear that you are playing Mr Nice Guy - and your opponents can benefit by doing the same.
So this is NOT the classic Prisoner's Dilemma - unless you play the game like North Korea currently is (which is closer to the classical version of the game - and has results that are probably going to play out very soon). North Korea's government see this as a one-off event because their stability is at risk and they know that if they screw up - the could be deposed and there is no second chance...their insular policies and closed borders mean that there is none of the information flow needed for a communicative/iterative version of Prisoner's Dilemma - and the consequences are exactly as game theory predicts.
When people cooperate and are open - you get things like the de-escalation towards the end of the cold war. But that only happens if you talk to each other and regard it as an iterated game and not a one-off. That requires a stable political system - and explains why stable/open governments spend less time at war than unstable/closed governments.
I can picture in my mind a world without war, a world without hate. And I can picture us attacking that world, because they'd never expect it.[32]. TastyCakes (talk) 20:18, 29 May 2009 (UTC)[reply]
"An excess of virtue is to be feared more than an excess of vice because only the latter is subject to the moderation of conscience." I devoutly hope not to see the so-called great miracle that the OP anticipates would give an opportunity to impose a US-centric one-size-fits-all ideology on everyone. But a "reduction of the human population" can be done in many ways, few of them nice. Cuddlyable3 (talk) 10:08, 29 May 2009 (UTC)[reply]
Well there you have it, I think the consensus is we should have a big war or preferably a plague that decimates us. Perhaps I'll build a huge robot that goes WARNING!!! WARNING!!! CRUSH!!! KILL!!! DESTROY!!! as it goes about its work. Dmcq (talk) 15:13, 29 May 2009 (UTC)[reply]
The trouble, Reticuli88, is that just about any good-hearted person basically knows what we would all have to do to cut the nonsense and play nice (and basically, it consists of everyone, well, deciding to cut the nonsense and play nice) - but getting everyone to implement the solution all at once? Impossible. - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 22:15, 29 May 2009 (UTC)[reply]
My car's owners manual recommends using 10W-30 grade. I have a case of 10W-40 which I would like to blend with another grade so the mix is approximate to 10W-30. Can I do this? What other grade do I need to buy, and what proportions do I need to use? —Preceding unsigned comment added by 75.36.216.34 (talk) 18:46, 28 May 2009 (UTC)[reply]
With very rare exception, it is always best to follow the owner's manual's reccommendation. Is it possible to simply return the oil to the place of pruchase and exchange it for the correct weight? That would easier and less costly than buying more oil and then having to mix the two. cheers, 10draftsdeep (talk) 19:01, 28 May 2009 (UTC)[reply]
In general, you can't just mix different grades of commercial motor oils and expect them to work appropriately. We have information on the grades of motor oil at Motor oil#Grades. One difficulty you'd face in mixing oils is that oils with designations such as 10W-30 or 10-W40 are multi-grade oils, meaning that they have special additives which allow them to perform like different oil grades at different temperatures. Matching the exact performance characteristics at differing temperatures would thus be very difficult. Even matching a single weight oil wouldn't be trivial, as the number designations are based on the kinematic viscosity of the oil, which isn't going to be linearly additive (that is, mixing equal part 10 weight oil and 30 weight oil is not going to get you the equivalent of 20 weight oil), especially when potential non-newtonian fluid behavior is taken into account. Leave motor-oil mixing to the professionals, who have proper test lab facilities. -- 128.104.112.106 (talk) 19:37, 28 May 2009 (UTC)[reply]
All of that is technically correct, as it should be in an encyclopedia. That said, though, the odds of negative consequences from tossing one quart of 10W40 into your engine now and then are "slim to nil".
10W40 will be slightly more viscous when hot. If you have an old enough engine, where you're actually burning through a quart of oil periodically, then a bit more viscosity is not a bad thing. At the other end of the calendar, the 10W components are "close enough" for winter use.
So, it's a case of theory vs practice. Theoretically, don't do it. Practically, it don't make much difference.
Drain the old oil and do a proper full oil change using, if you want, your supply of 10W-40. Your engine will thank you. That is better than experimenting blindly with a mix of two oils that become increasingly different in viscosity as the engine heats, and they might not even stay blended. Change the oil filter too.Cuddlyable3 (talk) 09:54, 29 May 2009 (UTC)[reply]
I have mixed different oil viscosities several times, with no perceptible harm to my engine. Oil grades cover a range of viscosities... some 10W30 oils are a bit thicker/thinner than others. Your engine will not grenade if you are a little bit off in your mixing skills. That said, the simplest solution would be to return the oil for the proper grade if possible. If not, adding a quart or two of 10W40 to each oil change should be quite safe. 75.157.28.248 (talk) 20:15, 29 May 2009 (UTC)[reply]
Poor TV picture improves a lot when VCR on
I live in an area with a low signal strength. I have a 20db (as far as I recall) signal amplifier between the tv and the aerials coaxil cable. Even so, sometimes the image becomes very hazy and difficult to see - it looks exactly as I would expect from a low signal strength. But when I press the appropriate button on my remote, the TV takes the aerial input via a VCR, and the picture becomes perfect, crystal clear! So the signal goes aerial - 20db amplifier - VCR - scart lead - tv. Yes, I still have and use a VCR.
My question is - is this simply due to the VCR adding some extra amplification to the 20db amplifier? Or could there be some other reason? Could I get the same result by buying an even more powerful signal amplifier, or by putting two in series? I assume that although the signal is weak, the signal/noise ratio must be good. It is several times cheaper to buy a new amplifier than upgrade the tv aerial. A subsidary question is why the signal seems to be much worse for several minutes at a time, and then improve again? 78.147.151.201 (talk) 21:25, 28 May 2009 (UTC)[reply]
Does your aerial go into your VCR or tv first? I would expect that whichever is the system that gets the 'mains' aerial would be the one that gets the best reception. Also are you definitely taking the signal from the best location? I know where I am I can get a couple of different signals - my strongest one being from Emley Moor. It may be that you should check that to make-sure as well. Perhaps your VCR has better decoding/system than your tv? My old digi-box is much worse than my new one, even though the aerial hasn't changed. ny156uk (talk) 22:57, 28 May 2009 (UTC)[reply]
The aerial goes into the VCR first, and then there is another short coaxil cable from the VCR to the TV, as well as a scart cable that is in use when the VCR is on. But you still get a picture when the VCR is turned off. I thought the aerial signal just went straight though the VCR without being changed in any way. The aerial is definately pointed at the nearest and best transmitter, which is some way away. I have not bought a digital radio because the signal is not good enough, and the tv signal is not good enough for digital tv either. 78.147.139.18 (talk) 23:37, 28 May 2009 (UTC)[reply]
So you have the coax from the aerial going through a splitter with one output going to your TV and the other going to your VCR? I'm betting a poor quality splitter. It's pretty common for cheap splitters to give a better signal to one output than to the other. Especially the old fashioned T shaped ones. APL (talk) 01:11, 29 May 2009 (UTC)[reply]
No, the signal goes to the VCR, then through the VCR to the TV. I imagine there is merely a plain connection between the in and out coaxial sockets. It still functions when the VCR is off. The same thing happened when I used other VCRs. 84.13.164.142 (talk) 09:10, 29 May 2009 (UTC)[reply]
Not to be picky on this, but do you live in an area that is undergoing mandatory transfer to Digital TV? In the U.S. for example, all over-the-air analog televison will cease on June 12, 2009. I believe the UK and Canada have 2-3 more years; but it may be something to think on as analog TV becomes less and less availible. --Jayron32.talk.contribs00:22, 29 May 2009 (UTC)[reply]
I am well aware that this area will convert to digital tv in the future. But that does not have any bearing on the current problem. As I mentioned, the TV signal is currently too weak to allow recieving digital tv. I think the signal strength is going to be increased when the digital switchover occurs in this region, so hopefully I will be able to get it then. TV is not very important to me. 84.13.164.142 (talk) 09:34, 29 May 2009 (UTC)[reply]
Geolocate puts this poster in Liverpool. (Which brings to mind a different question: Does the UK still have television police? I recall years ago seeing a story where authorities were tossing televisions out of second-story windows if the owner didn't have the proper paperwork.) -- Tcncv (talk) 01:22, 29 May 2009 (UTC)[reply]
Well - you're exaggerating wildly...but the essentials are true. In the UK, the free (and advert-free) BBC television and radio stations (probably the highest quality broadcast anywhere in the world) are funded by the "Television License" - effectively a tax. If you have a television - you have to buy a license. I forget how much it is - but we're talking over 100 pounds a year. It's not funded from central government taxation because the BBC is required to be independant from the government in order that they may criticize them and hold politicians feet to the fire without being concerned about having their funding withdrawn. Hence, lots of people don't pay the license fee.
In order to enforce the system, there are 'Television detector vans' that drive around to houses that don't have TV licenses and they use a directional antenna to pick up secondary radio waves created in the process of decoding the TV signal. They can detect to a fair degree of accuracy where the TV is in the house. Armed with this information, they can come to your door and demand to see your TV license - and if you don't have one, you get fined. I suppose it's possible that they might be empowered to confiscate your TV if you continually break the law - but that's not a common thing. No - they certainly don't toss your TV out of second floor windows!! And no, they aren't police officers - they are tax collectors.
Americans are frequently horrified at this concept. But I should explain that the process is essentially no different from the car taxes you pay in the USA for the privilege of driving on the public roads. If you get stopped for not having your car tax paid up to date - you get fined...same deal if you get caught operating a TV without a license in the UK. It's arguably unfair that you pay the same car tax whether you drive 100 miles a year in a tiny MINI Cooper or 100,000 miles a year in a honking great SUV. It's arguably unfair that you pay the same TV license no matter how much you watch the BBC...but that's life. Having experienced US "free" television - I can tell you that the TV license is an absolute bargin. SteveBaker (talk) 01:42, 29 May 2009 (UTC)[reply]
Well, there's a difference, though. When you're driving on public roads, you are, not to belabor the point, driving on the public roads. You're taking up space that could be used by other drivers. When you're just sitting in your private space, intercepting the EM radiation that the government shoots through you whether you like it or not, it's hard to argue that you're putting any burden on that resource. --Trovatore (talk) 03:08, 29 May 2009 (UTC)[reply]
As with many things American, SteveBaker, "your mileage may vary" as the expression goes. In Michigan, your classic MINI (pre-1983) would have a license fee based on weight but your new one would have been charged based on MSRP price. I don't know of any states that charge by mileage yet although I have heard of such proposals. Rmhermen (talk) 05:54, 29 May 2009 (UTC)[reply]
...but if everyone use that as an argument then a much greater burden is placed upon the people that are willing to pay. It's more about fairness than about whether you are using a finite resource. --antilivedT | C | G03:58, 29 May 2009 (UTC)[reply]
Not being allowed to listen to electromagnetic radiation that someone sends through your residence is a bit like not being allowed to listen to a loud argument by the couple living in the next apartment, or not being allowed to read a flyer thrust through your mail slot. If they don't want you to enjoy the broadcast, they should not send it into your property. (Just a Yank view of things.) Edison (talk) 04:42, 29 May 2009 (UTC)[reply]
Edison - If the BBC encoded the signal and charged you a monthly/annual fee for use of a decoder/their decoding algorithm would that be better? Essentially that's what pay satellite tv companies such as Sky tv do. Seems that the bbc method is better in my view (though obvious sky is through satellites but they work to receive signals in much the same way). ny156uk (talk) 07:39, 29 May 2009 (UTC)[reply]
In my opinion, yes, the encryption option is much better. For one thing, if you wanted to use your TV only to watch private stations, and not the BBC at all, you could do that and not pay for the BBC. (There are private TV stations in Britain, right? I haven't been there in a couple decades and I don't think I watched any TV while I was there, but I thought I had heard that by now there were private stations. If not, well, you could watch Dutch or French TV.) --Trovatore (talk) 10:13, 29 May 2009 (UTC)[reply]
The worst thing about the current BBC license system is that if you do not watch tv, do not have any tv in the house, do not watch it on the internet either, and thus are not required to pay the license fee, then you still get frequently and truely harrassed by many threatening letters commanding you with threats to buy a liscense. The letters really are upsetting and even when you tell the licensing people that you do not have a license, then the threatening and hysterical letters keep on coming. 84.13.164.142 (talk) 09:16, 29 May 2009 (UTC)[reply]
Yes, we Americans have the pleasure of watching 12–15 minutes of commercials every hour. I actually think there are advantages to the British system. Several shows are rebroadcast on our PBS stations or are picked up on some of our cable networks. I especially like the science and technology coverage. Most of the best are of British origin. And it is refreshing to see a comedy that is based on wit rather than the slapstick, and dramas that don't feel compelled to lead with some sexually suggestive scenario as if there were no other way to get the audiences attention. Of course I realize that what we see is a non-representative fraction of British broadcasting. I'm sure you have your trashy shows too. But in general, I can see there are advantages to the pay system – more emphasis on quality that there would be in the pursuit of the advertising dollar. (POV alert!) We on the other hand have Lost – a drag-u-drama with no apparent plot, that seems made up from week to week, but for some reason has a huge loyal following. (Diving for cover now.)
Oh, and I do clearly remember seeing a television tossed from a window, bouncing off a porch (?) roof, and crashing to the sidewalk below. Likely part of some high publicity enforcement back in the 70's. They had the electronic detection trucks then too. -- Tcncv (talk) 05:27, 29 May 2009 (UTC)[reply]
The OP's TV takes its signal at its aerial connector when the VCR is off and at its SCART connector when the VCR is on. Possibly the tuner or i.f. signal amplifier stages in the TV (which are bypassed by a SCART input) are failing. Older TVs with mechanical tuners, and the dual-standard 405/625 TVs once sold in the UK, are plagued by unreliable switch contacts. Cuddlyable3 (talk) 09:45, 29 May 2009 (UTC)[reply]
Tuner - that's an interesting point. Could it be that the VCRs tuner is more tuned in than the TVs tuner is? That the problems are caused by the Tvs tuning drifting off? When listening exclusively to one channel only on FM radio, the tuner often seems to need adjusting. Perhaps the tuning is affected by day or night. 84.13.164.142 (talk) 12:15, 29 May 2009 (UTC)[reply]
Problem probably solved. The coxial cable socket on the Durabrand tv seems to have a loose connection with the internal circiutry, and I can reproduce the bad picture if I wriggle it around. So I will take the back off and see if I can tighten something up without electrocuting myself from the capacitors. 78.146.211.210 (talk) 21:05, 29 May 2009 (UTC)[reply]
determining diet via feces
It is my understanding that biologists can determine an animal's diet via examining it's feces (I'm sure it is a bit more complicated than that). What I'm wondering is if scientists can tell if an animal is a herbivore, carnivore or omnivore by examining fossilized feces? In other words can we tell what the diet of a dinosaur was based on it's fossilized poop? —Preceding unsigned comment added by 69.77.185.91 (talk) 21:27, 28 May 2009 (UTC)[reply]
One could certainly can make some good inferences about diet, as long as its possible to match the poop with the pooper. Inevitably, we have an article about fossilized poop, better known as coprolite, or see this article for more details. Rockpocket00:06, 29 May 2009 (UTC)[reply]
See Scatology. It works for whales and elephants. Can't remember reading of a dinosaur study. Rockpocket objection that you wouldn't be able to determine the origin probably has a lot to do with that. Teeth usually are a pretty good indicator. They do sometimes mix up scavengers and hunters though. 71.236.24.129 (talk) 02:08, 29 May 2009 (UTC)[reply]
In order to make determinations about an animal's diet by examining its feces, it's usually necessary to do some poking and prodding. (Well, if you've been eating a lot of corn . . . never mind.) Since a coprolite (like any fossil) is, regardless of what it used to be, currently a rock (however interesting), that would be difficult. I suppose you could slice it up and examine the inside, but I doubt that we know enough about what plant and animal materials of various kinds look like after they've been through digestion AND fossilization to get anything useful out of it. - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 22:08, 29 May 2009 (UTC)[reply]
Mix rice varieties to reduce clumping?
I have some red rice and some white Basmati rice. Both tend to stick together in clumps when cooked separately. Will they clump less if cooked as a mixture? NeonMerlin22:32, 28 May 2009 (UTC)[reply]
Are you rinsing the rice through before you cook it? Basmati rice normally isn't 'sticky' (at least not in my experience of cooking with it). Not sure how much impact mixing rice will have but rinsing through before with cold-water and then after with boiling water (and fluffing up with a fork) are the things i'd recommend (though i'm by no means a rice expert). ny156uk (talk) 22:47, 28 May 2009 (UTC)[reply]
I'd second ny156uk's assessment. Rice does not have any gluten per se, but the starches like amylopectin that adhere to the outside of the kernel can undergo some gluten-like polymerization which will lead to the "stickiness". Glutinous rice (aka Sushi rice) is known for its high amylopectin content and takes advantage of this. Rinsing the rice in cold water prior to cooking should reduce this in rice varieties for which this is not a desirable property. Mixing the rices will have no effect on this, as each rice likely produces amylopectin and will stick to each other just as well as it will stick to itself. Just rinse well, and you should be fine. --Jayron32.talk.contribs00:17, 29 May 2009 (UTC)[reply]
Note that Sushi rice is not the same thing at glutinous rice. Also there are ways you can cook the rice to reduce the clumping effect, although I consider such rice to be disgusting so don't know how to do it personally Nil Einne (talk) 08:54, 29 May 2009 (UTC)[reply]
You can usually vary the amount of stickiness by just changing the amount of water you put in, and generally less sticky rice require less water too. --antilivedT | C | G03:25, 30 May 2009 (UTC)[reply]
two questions about force, motion , and displacement
1st question:
If you can push a 165 pound weight 1 foot in a straight line, with x amount of force, how much further will it be displaced if pushed at the perfect arc angle (such as is used by cannons for optimum range) with the same amount of force. dont need an exact just a general answer (2feet/ 3feet/ 4 feet etc) general guess?
2nd question:
Does anyone know the power to displacement equasion in its most basic form, using to example above again if X force moves 165 pounds 1 foot, how far will double the amount of force be able to move it, twice the distance, triple the distance? again just basic guesses would be fine, just need a general idea.
Thanks for your help I dont know much about these type of things.
The question is unclear. What do you mean by "pushing in a straight line"? Sitting on the ground? Accelerated at shoulder level parallel to the ground? Also, "force" is of limited interest - you need energy (force times distance) for this calculation (although you can do some simple substitutions and use time). If you use the usual abstractions (a spherical cow of uniform density on a flat planet with no air resistance and a uniform gravity field), and use the same angle to the ground (45 degrees for optimal range in that case), I think twice the energy will give you twice the range. But it's 2 am here, so my thinking may be of limited value. --Stephan Schulz (talk) 00:02, 29 May 2009 (UTC)[reply]
Ok what i meant was put simply, when i push my brother directly forward in the chest he moves 1 foot, if i push upwards and forwards he moves further. I wanted to know why this was?
So it is double the energy, double the distance of displacement then?
Well, in that case its a very hard problem. Your brother is actively resisting being pushed. I suspect if you push him from a different angle, you may throw him more off-balance. It is doubtful if you can transfer enough energy to actually make him go ballistic (except in the figurative sense). --Stephan Schulz (talk) 00:32, 29 May 2009 (UTC)[reply]
There are so many layers of confusion here. We have to start by answering the basic, underlying principles...and that means Sir Isaac Newton. Newtons' laws of motion say that when an object is in motion - it will keep moving at the same speed - in the same direction until some other force acts upon it. So if you push your 165lb weight - it can only stop moving (ever!) if some other force acts on it. Out in deep space, the smallest, gentlest nudge would send your 165lb weight off on an infinite journey. But in our common experience, things stop moving because of friction, gravity and air resistance. So the only reason your 165lb weight stops AT ALL is because of some combination of those three things. So the first part of your first question doesn't contain enough information for us. We need to know why it stopped - what OTHER force than the one you used to get it moving caused it to stop so quickly.
Now - if you'd told us that (and let's suppose it's just friction with the floor) - we have to move on to the object moving in a curve. Again - that nice Mr Newton had something to say here - objects move in a straight line - unless acted on by some other force. So now, for your weight to move in a curve - there needs to be some other force. If you fire a cannonball up at (say) a 45 degree angle - then gravity is what bends the path into a curve - as air resistance slows it down. But if you simply push a weight across the floor - friction slows it down - but nothing bends the motion into a curve. So answering your question requires some indication of what bends that straight line motion into an arc.
Worse still - a force has to operate over some distance. When you push something with your hands - you have to actually make your hands move forwards for a while as you exert force on the object. Force times distance is Energy...and (as is increasingly irritating here on the science desk) lots of people confuse force and energy.
Now for the second part of your question: Power is yet a different thing from force and energy. Power is the rate at which energy can be delivered. So the amount of power you need depends on how fast you need to move your object. If you expend some amount of energy very quickly, you need more power than if you expend it slowly. A sports car can get up to 60mph faster than a rusted out VW bug because it's engine produces more power - but the amount of energy the two cars need to get up to 60mph is roughly the same.
So we can't answer either part of your question because they simply don't mean anything without understanding all of the forces involved, the time these things take to happen and so forth.
Well i personally think the first question at least can be answered with some meaning. In all common sense, we can assume the damping force to be friction, the force which causes curved motion to be gravity, the angle of projection to be 45 degrees, the coefficient of friction to be some unknown, say k, and no air resistance. I think i also need another constant, the e value, for when the body bounces off the ground, we need to know how much energy is lost in the collision. So with all these assumptions and the knowledge of the two constants e and k, this becomes a pretty well defined problem, and e and k shouldn't be so hard to find anyway, provided the OP tells us what is the body and what surface he is using, and some clever guesswork. Of course, if he is pushing his brother, e is 0 and k...hmm... you have to take a guess...So now the problem can easily be approached... see projectile motion.. we just plug in the formula for maximum range..., and when you push the object along the ground you can also calculate the distance it moves, using energy conservation. But i think i forgot the biggest assumption we should make... that when we push the body, we just give an impulse... that is a force for a very short amount of time essentially giving it a constant kinetic energy... You might think this is just crap... too much approximations, but i think its not so bad, it should give you a reasonable idea of the number we are looking for... Will get back to you after doing the calculation bit...provided someone tells me what i can choose k...Rkr1991 (talk) 04:47, 29 May 2009 (UTC)[reply]
By invoking a coefficient of friction k are you supposing that the OPs brother slides 1 to 4 feet? If so, how can the brother move further when pushed at an "optimum cannon" angle ?Cuddlyable3 (talk) 09:21, 29 May 2009 (UTC)[reply]
Yes, i suppose that the OP does something (like pushing or striking) his brother to give him some kinetic energy, with which he slides along for some distance. See, when he is launched at an angle, he will fall at the same angle (provided the floor is flat. Now, he can either bounce up and do another projectile motion, or since he has some horizontal component of velocity, slide along for some more distance. This depends on the coefficient of restitution, which is zero if the body in question is the OP's brother. SO for the brother problem, we just take the horizontal component of velocity and its like the sliding part all over again, we just add the result to the range. If, however, the object is something like a ball, where the value of e is not zero. then we must make an infinite sum of the ranges caused by repeated bouncing. If the collision is perfectly elastic, then the distance traveled is, of course, infinity, which can never happen. SO for the brother problem i need to know what friction coefficient i can take, to give a decent figure. Rkr1991 (talk) 10:41, 29 May 2009 (UTC)[reply]
Hmmm this is getting too complicated for me, I just wanted a simple explanation for why when you push something both up and forward at the same time (i used the analogy of a cannon since they are never fired strait when they want to hit something far away, they are fired both up and forward), it is moved further than if you just pushed it strait on, I know for a fact that I can push something further this way, I just wanted to know why.
Also wanted to know if, under the same conditions, double the amount of force applied to an object makes it move twice as far, or more than twice.
Thanks again, also please bare in mind that I know little of physics, hence why I am asking here.
Well, if i assume you are applying a constant force for a short period of time while pushing (just ignore it, its for the geeks) then double the force means the distance goes up by square root of 2 times, that is, force is proportional to the square of the distance, not the distance. The energy you give is proportional to the distance, that is, if you double the energy you give, the object moves twice the distance. If you want to compare it with throwing it, then please hold on, i'll get back to you with just a number as soon as i can find a suitable value of k to assume, cause i have no idea. Rkr1991 (talk) 11:04, 29 May 2009 (UTC)[reply]
Thank you, so if you double the force you double the distance, put basically. now I just need to know why pushing something up and forward moves it further than just pushing forward.
Well, if you push something up and away, you also reduce the weight on the ground and hence the amount of friction. But in the case of your brother (not, I hope, an inanimate object), he will not really slide significantly on normal floors. If you push him, he will be off-balance. To recover, he will typically take a step to move his legs under his center of mass again. So this is at least partially an active movement. If you push him up and away, you may cause his center of gravity to rise, so he will be more off balance before he can recover. With an living, acting object that presumably never fully leaves the ground its really very hard to determine exactly what happens. --Stephan Schulz (talk) 11:20, 29 May 2009 (UTC)[reply]
Okay Rob, a simple explanation for why pushing something both up and forward at the same time moves that thing further than just pushing forward. Let's use your cannon example.
If a cannon fires a cannonball straight forward, that ball keeps going forward until it hits the ground, then it stops (let's ignore rolling for now!). If the cannon fires a cannonball straight up, it goes straight up slower and slower until it starts coming down again, hits the ground and stops. If a cannon fires a cannonball both up and forward, the cannon ball will go forward until it hits the ground and stops, but it will also go up until it starts coming down again. This 'going up' keeps it away from the ground for longer, so takes longer before it hits the ground. This means it can go further forwards before hitting the ground.
If you want to get slightly more complicated, you can think about what angle gets you furthest.
When it comes to you pushing your brother, it's likely that other things are involved, like what muscles you use to push straight forwards compared to pushing up and forwards. I know that if I push something up and forwards, my legs are more involved than if I just push forwards, and I can push back against the ground more (rather than just relying on my own weight). Think about how you position yourself, what parts of your body you're using, what way you're bending, etc. 80.41.31.27 (talk) 11:27, 29 May 2009 (UTC)[reply]
It was confusing to hear about pushing your brother if you really want to discuss firing a cannon. When a cannon is fired at an angle the speed of the ball leaving the muzzle has two parts: the horizontal velocity and the vertical velocity. The vertical velocity is initially upwards but gravity will turn it around and the ball will hit the ground at the same velocity but going downwards. The vertical velocity is what determines the time the ball is in the air. The horizontal velocity is constant (air friction modifies it slightly but you specified a vacuum) as long as the ball flies. The distance the ball flies is the product of its horizontal velocity and time in the air. For simplicity assume the ball hits something at the same height as the cannon and that it doesn't bounce or roll any further after the impact.
Consider 3 cases. 1) The cannon is aimed horizontally. Result: the ball has no vertical velocity so it drops "like a stone" i.e. the time for it to hit the ground is short. The horizontal velocity has no time to take it more than a short distance. You have already observed this. 2) The cannon is aimed straight up. Result: the ball has lots of vertical velocity and stays up in the air for a long time. But the horizontal velocity is zero so the ball doesn't go anywhere. Duck and cover or protect your head with a helmet! 3) The cannon is aimed at an angle somewhere between horizontal and vertical. Result: the ball has both horizontal and vertical velocities and can go far. There is an article about calculating how far. In short the distance the ball flies is proportional to the square of its speed leaving the cannon. So if you double the speed of the ball it flies 2x2 = 4 times as far. Cuddlyable3 (talk) 11:33, 29 May 2009 (UTC)[reply]
Thank you both for the simple explanation, I asked about my borther being pushed and trajectories, because I saw a video of dummies getting throw backwards by a shockwave from an explosion, (as i understand it like a really innifecient cannonball) and noticed that the dummies that where thrown up and away were thrown really far. And was wondering if the angle had anything to do with this. Thanks for your answers they really helped.
Clouds form on dust etc particles, fog also. So is there any difference between fog and cloud (apart from the height) ? If so, what is it? —Preceding unsigned comment added by 79.75.108.190 (talk) 23:56, 28 May 2009 (UTC)[reply]
See our article on Fog: "Fog is a cloud bank that is in contact with the ground. A cloud may be considered partly fog; for example, the part of a cloud that is suspended in the air above the ground is not considered fog, whereas the part of the cloud that comes in contact with higher ground is considered fog. Fog is distinguished from mist only by its density, as expressed in the resulting decrease in visibility: Fog reduces visibility to less than 1 km, whereas mist reduces visibility to no less than 2 km." Rockpocket00:00, 29 May 2009 (UTC)[reply]
Yes, this is just conventional terminology. In some cases, precise standard definitions apply (for example, in weather statistics or aviation forecasts); in most common usage, the distinction is sort of ... cloudy.Nimur (talk) 14:57, 29 May 2009 (UTC)[reply]
May 29
Time quickens?
Thank you for always answering my questions.
Does time ever quicken in special relativity?
Lorenz transformations shows transformation of coordinates in a reference frame S to another reference frame S'. The time is transformed from t for S to t' for S' as follows.
where v is the velocity of S' and x seems to be the distance of the event in the direction of x-axis for S.
If v and x have the same sign, that is, if the origin of S' approaches the event (The origins of S nad S' are at the same point at time 0), t' will be less than , and if, for example, x =vt, t' will be even less than t ( if t is positive).
where v is the velocity of the source, is the observed direction of the light ( It seems to be from the observer to the source), and is the direction of emission of the light (It seems to be from the source to the observer),
if the light is emitted at an angle or , the light is observed as coming form where , that is, from the hemisphere at opposite side to v.
If two plane sources are at both side of the observer parallel to each other and to the axis of v, and if the source is approaching the observer, at the time the wavefront is supposed to be in head to head if at rest, they seem to have already crossed each other in the direction opposite to v.
Special relativity applies to observers who are moving at a constant velocity relative to one another (and where the effects of gravity are either uniform or negligible). Each observer sees time passing more slowly for the other observer - this is a symmetric observational effect. If the observers want to compare the actual duration that they each experience between two events, they will have to both become stationary in the same frame of reference, so that they have a common definition of simultaneity (see relativity of simultaneity). To achieve this, one or the other (or both) will have to accelerate, which takes us out of the realm of special relativity and into general relativity. In general relativity, there are asymmetric time dilation effects due to non-uniform gravitational fields or, equivalently, relative accelerations. So when the two observers compare the actual duration that they have experienced between events, one observer may find that they have experienced a longer duration than the other. Informally, we can say that time has passed "more quickly" for one observer than for the other. See time dilation and twin paradox for more details. Gandalf61 (talk) 12:50, 29 May 2009 (UTC)[reply]
Gandalf, your explanation is essentially correct, except at the moment when you said "will have to accelerate, which takes us out of the realm of special relativity and into general relativity." Special relativity can deal with accelerated objects within flat Minkowsky space-time. See Rindler coordinates. Dauto (talk) 14:33, 29 May 2009 (UTC)[reply]
Looking at a moving image of relativity of simultaneity, it seems like, if the relative inertial motion is resolved, that is, if the two observers become stationary to each other, the effect of special relativistic time dilation vanishes. To achieve this, accelaration is needed, but if the accelarations are symmetric, and general relativistic time dilations are the same, observers can see the resoluion of special relativistic time dilation between them? And if so, is the resolution attributed to accelaration? (Then, for an observer, the other's accelaration must look differently from his, even though they are the same.)
If the accelerations are the same, both observers will experience the same amount of time lapse. Note that there is no need to use general relativity to understand that problem since it is assumed that the two observers are moving within flat space-time. Dauto (talk) 15:15, 29 May 2009 (UTC)[reply]
I know this is a "standard" view of special relativity that's taught in classrooms, but I strongly recommend ignoring it, I think it will just confuse you. The emphasis on disagreeing observers is backwards. There's only one world, and a bunch of equivalent descriptions of it in terms of different coordinates, and the Lorentz transformation is just a translation between different coordinate systems. It's the same as
x' = cos θ (x + y tan θ)
y' = cos θ (y − x tan θ)
for converting between different Cartesian coordinate systems that are at a relative angle of θ. I've deliberately written that in an unusual way to emphasize the similarity to the Lorentz transformation as it's usually written. With y = ct, v/c = tan θ and γ = cos θ, the analogy is very close. The coordinates (x,t) describe an event, i.e. something happening at a given place and time. The Lorentz transformation turns that into (x',t') which is the location of the same event with respect to a different coordinate system.
When you write down just the t' part of the Lorentz transform, it's the same as writing down just the y' part of the Cartesian rotation. That's likely to get you into trouble, because the y' coordinate is nearly meaningless without its corresponding x'. You could say that it describes the "horizontal" line through the point represented by (x',y'), but "horizontal" in this sense is a coordinate-dependent concept. In different coordinates you would have gotten a different line, and your choice of coordinates was arbitrary, so this line is meaningless. It's very tempting to imagine that t has independent meaning, because it does in Newtonian physics, but in relativity you'll frequently get into trouble it you treat it as though it does.
Okay, think of a line with evenly spaced dots on it, and a rotation of that line:
*
|
| *
* /
| *
| /
* *
I did the best I could in ASCII—the line segments are supposed to be the same length and the * spacing is supposed to be the same in both. The point is that the stars on the diagonal line are "more compressed in the vertical direction" than the stars on the vertical line. The rotation has compressed the dots, if you like, though it's a strange notion of compression that's tied specifically to the y or y' coordinate. A rotation won't always compress the dots, sometimes it will uncompress them. For example, if you take the diagonal line and rotate it the same amount counterclockwise, you'll get the vertical line again. This is the geometric meaning of your observation that the Lorentz transformation sometimes makes t' larger than t and sometimes smaller. There is no "quickening of time" exactly in special relativity, just as no rotation can increase the y-coordinate spacing of the dots beyond the vertical case, but there are rotations that increase the spacing.
So obviously this vertical dot compression doesn't really mean anything—the two lines are the same, our definition of "vertical" is arbitrary. But can we make the compression mean something? Yes, if we're willing to bend one of the lines and make a triangle, like this:
*
|\
| *
* >
| *
|/
*
That looks awful, but I hope the point is clear: "because of the compression", if you like, there are three star spacings' worth of distance from bottom to top on the bent line, only two on the straight line. Is this a paradox? After all, the compression was a meaningless coordinate artifact a moment ago. It's not a paradox because this is really a different setup, and it's not even clear it ought to have the same name. Before we had two symmetrical lines, now we have an asymmetrical arrangement, and it's the asymmetry that determines which path is longer.
Moving along to your intersecting wavefronts. This requires at least two spatial dimensions and one time dimension, which makes it harder to visualize. Let's say that, with respect to some arbitrary inertial frame S with coordinates (x,y,t), your wavefronts are moving straight up (in the +y direction) and straight down (in the −y direction) and intersect all along the x axis at t = 0. The events where the wave fronts appear are then given by y = ±ct (+ for the upward-moving one, − for the downward). If you now replace t by a third Cartesian coordinate, z, and plot y = ±cz for some constant c, the result is an "extruded X", like this:
\\\\\///////////// ^ z
\\\///////////// |
... \///////////// ... |___\ x
/\\\\\\\\\\\\\ /
///\\\\\\\\\\\\\
/////\\\\\\\\\\\\\
with the x and z axes as shown and the y axis pointing into the page. Now, rotate this shape clockwise in the plane of the page by a small angle so that the part to the right tilts down. First, the crossing of the wavefronts (i.e. the former x axis) no longer happens "at the same time" (i.e. at the same z coordinate). Points farther to the right are now at lower values of z or at "earlier times". Second, this is hard to visualize, but if you take slices of the figure in the xy plane, representing the wavefronts "at a given instant", they are no longer parallel. Rather, they are both inclined to the left by an amount that depends on how much you rotated the figure. That's aberration.
This analogy can only be taken so far. Many things end up with the wrong sign (in special relativity there are fewer clock ticks along the non-straight path, not more). And there's no analogue to the speed of light or the distinction between past and future in Euclidean geometry. But the analogy is still very helpful for understanding what the Lorentz transformation and "observers" are really about. People talk it up to be a subtle, even mystical thing, but it really, really isn't. When people talk about "observers" they are talking about planar slices through the world, and, just as in Cartesian geometry, those slices have no special meaning. You can slice a cube one way and get squares, or a different way and get equilateral triangles and hexagons, but it's just a cube any way you slice it. There is a tendency to do far too much slicing in relativity because people don't want to let go of the Newtonian world where there really was such a thing as "the state of the universe at a given moment". To really understand relativity you need to give up the idea that, in the tilted extruded X, the wavefront crossing events happen "at different times" just because they have different z (or t) coordinates. That's a Newtonian idea and it will lead you astray. -- BenRG (talk) 18:36, 29 May 2009 (UTC)[reply]
I don't know if I have understood what you (Mr. or Ms.BenRG) say, but I think I do understand that two events which occur at the same place at rest will always be observed to occur with larger time interval if in relative motion. Now it might have been better to ask if an event can be observed at an earlier time in relative motion than at rest. And I think the answer is "yes"?.
(Additionally, I have been suspecting that, if an event occurs later in relative motion than at rest, the event which has already been observed could be something not yet has occured at the time. But this is solved, if I admit that c is the ultimate speed.)
What do these actually do? Mine are encased in plastic and I cannot see what any circuity inside them is, if they have any. Does it make any difference which sockets of the Y you put the input and output cables?
I am running three tvs off one aerial. Sometimes all three tvs may be on at once. The aerial signal goes through an amplifier and then is split into a TV and cable2. Cable2 goes to another part of the house, then it is split into a tv and cable3. Cable3 feeds another tv. It is not possible to provide seperate cables, but as I imagine the TV aerial sockets are all joined up in parallel rather than in series, then it should not make any difference. Is there any way of doing this better while not going to the expense of more or better aerials please, or drilling new cables through walls and floors? 84.13.164.142 (talk) 10:11, 29 May 2009 (UTC)[reply]
The key consideration with splitters is that each split reduces signal quality. Based on the architecture you describe, TV 1 is getting a better signal than TV 2 and TV 3. As a result, you should consider putting your best / most-watched TV on the TV 1 line (or switching the splitters such that the best TV becomes the TV 1 line). In my personal experience, though, TVs are rarely affected by this sort of thing -- at least with normal numbers of splitters. More critical is something like a cable modem, which should always be placed as close to the incoming signal as possible. — Lomn15:19, 29 May 2009 (UTC)[reply]
We have a splitter article, from which it's pretty obvious the thing is a hybrid coil. From that article, you can learn that that the inner electrical component is really just a small transformer. Impdendence-balancing is pretty important for high-quality RF signal handling. While 1→2 splitters are common, there are also 1→3 and others. For your configuration, that would let you do it all at once instead of a second split on one output of the first split (see Lomn's comments for why). DMacks (talk) 15:28, 29 May 2009 (UTC)[reply]
According to the article, a hybrid coil is a kind of transformer. These splitters are small and very light, so I very much doubt they have a tranformer in them. Perhaps they have no electronics at all. 78.146.211.210 (talk) 21:00, 29 May 2009 (UTC)[reply]
Transformers needn't be large nor heavy. A power transformer usually is because it needs to handle a lot of current, be insulated against a large voltage, and/or it has an iron metal core. But for low-voltage high-frequency RF applications you can have an air core and just a few windings. DMacks (talk) 21:53, 29 May 2009 (UTC)[reply]
Why are cockroaches such a pest in the US but not in the UK?
While coackroaches seem to be a common pest in the US, I've never heard of any cockroach problems in the UK. Yet in the UK we have far milder winters than in places like New York, so they would find it easier to survive the cold, and we also have central heating. Is it simply that cockroaches are not a native species in the UK? 84.13.164.142 (talk) 10:58, 29 May 2009 (UTC)[reply]
I have had cockroach issues in Glasgow (so they do exist), but you're right that they seem to be pretty mild in the UK. I'm curious too as to why; my auntie in Germany had some pretty horrific cockroach infestations, which really doesn't have a greatly different climate to Scotland. 87.114.167.162 (talk) 11:02, 29 May 2009 (UTC)[reply]
I don't know where your auntie in Germany is, but Frankfurt is about 5 C hotter in summer[33][34] which is not an insignificant difference. Most sources[35] say cockroaches are originally tropical, and Glasgow is much colder and further north (even if you take into account house heating). —Preceding unsigned comment added by Maltelauridsbrigge (talk • contribs) 11:25, 29 May 2009 (UTC)[reply]
My experience - mild winters make for a reasonably nice summer. When we get a hard cold freeze that doesn't thaw until Spring, the cockroach problem is much worse. Our exterminator claims that this is because the eggs and larvae and such can survive being frozen quickly, but not being slowly frozen. Where I live (at least for the next week or so), the problem is compounded by the addition of palmetto bugs (flying cockroaches). I've fogged the trees that overhang my house and it is rather scary how many palmetto bugs fall out - hundreds of them. So, we have cockroaches on the ground and palmetto bugs in the trees and almost nothing to keep their populations in check. -- kainaw™12:21, 29 May 2009 (UTC)[reply]
It is also because America is a land of opportunities.
I don't know about the UK, but when apartments in New York don't have roaches, it's often because they have mice who are eating the roaches. 207.241.239.70 (talk) 04:32, 30 May 2009 (UTC)[reply]
Automatic train control
Building a computer/sensor system which could replace a human driver for a car or an airplane is exceedingly difficult and probably not possible today (especially not if operational safety is taken into account), although we are actively working on getting there. However, at first glance, I would have thought trains would be a lot more feasible. Several subway/metro systems in the world (eg Toulouse Metro) already do this. However, from the list of driverless trains, it looks like this has never been implemented for long-distance mainline trains (ie beyond a metro system serving a city). Is there a reason for this? Is there something that make automatic control of long-distance trains more difficult / less feasible than for metro systems? Thanks! — QuantumEleven11:06, 29 May 2009 (UTC)[reply]
I think small, closed systems like the Toulouse Metro and the Docklands Light Railway are workable because the automatic controller totally "owns" the system - it knows where all the trains are (and the system is heavily instrumented to support that). Most existing long-distance train networks are a lot more ad-hoc (a lot more like the road) with a variety of trains, tracks, signalling systems, and vexing things like level crossings. I'm sure if you built a new, modern, fully grade-separated long distance railway then an automatic system would be quite workable. 87.114.167.162 (talk) 12:50, 29 May 2009 (UTC)[reply]
(ec) I'd say that the anon above me has hit the major points. I'll also add that there are challenges associated with the time and distance to an engineer in the event of a problem. For existing systems, you can have a couple of guys with pagers at head office downtown who can be anywhere in the metro system in under an hour. A train with some sort of impending mechanical failure can often coast as far as the next station to disembark its passengers.
Long-distance routes typically have stations which are much more widely separated than those of a city metro/subway/light rail system. It is possible to strand passengers in the 'middle of nowhere', potentially between multiple working tracks. Head office can't send help for hours, so you need to have widely dispersed response teams. The line remains blocked until the train receives assistance; this can have a ripple effect on all rail service across a country. It's sometimes remarkably useful to have a 'man on the scene'. TenOfAllTrades(talk) 13:24, 29 May 2009 (UTC)[reply]
It is probably cheaper to hire people to run the trains then it would be to install the hardware and develop the software to run such a system on the current rail networks. 65.121.141.34 (talk) 13:09, 29 May 2009 (UTC)[reply]
Plus there's a comfort factor in knowing there's a person up front "in control" even if they're really not, or if the computers do a better job overall anyway. Ask an A-380 or 777 pilot who's doing most of the flying up front, for example. ArakunemTalk13:28, 29 May 2009 (UTC)[reply]
Yep - on a typical transatlantic flight, the pilot actually flies the plane for less than three minutes. However, if you lose both engines in a freak bird-strike accident and have to land on a handy river...you probably want a pilot on board. This could probably be solved by having a handful of well-qualified pilots stading by on the ground who could take over and fly the plane by remote control at short-notice in the event of an emergency...but the public might find that hard to swallow. SteveBaker (talk) 14:16, 29 May 2009 (UTC)[reply]
Aye, there's the rub. That darn pattern recognition in humans is still hard to beat when it comes to picking a nice soft landing spot out of an urban jungle. :) Of course with trains, your options are much simpler: Go, Go faster, Go slower, Stop. ArakunemTalk14:20, 29 May 2009 (UTC)[reply]
I used to think that too. I used to design flight simulators for a living - so I know a lot about what pilots have to do. But one time we had a shot at building train simulators too (we actually delivered a bunch of them to Burlington Northern Railroads). That was quite an eye-opener. While it's true that you pretty much have just the one control - what you do with it is pretty tricky. It's such a high-skilled job that the average train driver in the US earns more than the average airline pilot - which surprised me quite a bit too! There are many subtleties with driving a train that are not at all obvious to the layperson. For example - suppose you have a long train and a series of hills to go up and down. One's natural instinct is to gun the throttle to get up the hill and sit on the brakes on the way back down again - but often, as the locomotive crests the top of the hill - the majority of the train has not yet reached the bottom of the hill - so you often actually need more power rather than less - as you reach the bottom of the hill and start going up the next one - you tend to want to apply more power - but with the rest of the train stretching back a few miles behind you, most of the weight is still rolling downhill and you may well be applying the brakes whilst simultaneously heading up a steep hill! Also, when your train is going around a curve, it has a tendancy to want to straighten out (like pulling on the ends of a piece of string) - which would derail the cars in the middle of the train - so keeping your the tensions in the couplings between cars fairly slack (which means no acceleration) is important when going around curves. When you stop, it's essential not to come to a nice slow, gentle stop - you actually want to stomp on the brakes fairly abruptly...what that does is to cause all of the slack in the couplings to be taken out as each carriage runs into the one in front with a nice thump. If you don't do that - so that all of the couplings are stretched out tight - then when you try to accelerate away, the locomotive has to overcome the static friction and accelerate all 100 or so carriages at once...which it probably can't do. If the couplings are all squashed up - then the engine only has to start one carriage moving at a time - which is much easier. If you see a train backing up and then starting off rolling forwards - that's a sure sign that the driver screwed up and stopped too gently! Then, locomotive drivers are responsible for keeping a lookout for things around the track that need maintenance or are in a dangerous state - this requires them to be alert throughout the entire trip - even if they are going 100 miles across a dead flat desert at a constant speed. There are loads more things like that. It's surprising how much complexity there is in such a seemingly simple system. Even though it's essentially a one-dimensional system - it's a lot tougher than driving a car OR flying a plane. SteveBaker (talk) 22:11, 29 May 2009 (UTC)[reply]
I would think that pilots only actually flying the aircraft for 3 minutes on TA flights would be a bad idea, because then when there is an actual emergency the computers can not handle, the pilot will be out of practice and will not perform optimally. 65.121.141.34 (talk) 14:42, 29 May 2009 (UTC)[reply]
Eh, I doubt this is as relevant as you consider it. What does the pilot need to practice? Takeoffs and landings in adverse conditions. What is all but 3 minutes of a TA flight? Stable level operation. Pilots need to keep sharp, yes, but they'll do that better in a good sim that provides emergency conditions than by doing nothing at 35000 feet. — Lomn15:11, 29 May 2009 (UTC)[reply]
What keeps them sharp is definitely the simulator time. The landing on the Hudson river was fairly impressive - but the guy would have trained hard at looking for suitable landing spots in busy areas after unexpected engine failures - and would have also trained for water landings - it was really just a matter of putting the two things together. And even with all that training, there was one critical switch that they forgot to throw (it's right there in the landing-over-water procedures manual) that would have made the plane sink more slowly and given people more time to get off. Airline pilots don't spend a lot of time in the simulator - but when they do - they get all of the problems thrown at them at once. You're on approach...it's night - and it's foggy - and at the last minute you're switched to a parallel runway and...oh...your undercarriage didn't come down...and wouldn't you know it - there is another plane converging on your position - and your left engine is only producing half power...GO!!! SteveBaker (talk) 22:11, 29 May 2009 (UTC)[reply]
Protective relaying takes a year or 2 of study,after getting an electrical engineering degree, and cannot be conveyed in a few words. Have you studied a standard text such as "Protective relaying theory and applications" by Walter Elmore, ABB, (2004) which sells for $100? It has examples such as you seek. The setting should be sensitive and selective, both terms of art. It should trip for faults but generally not for heavy loads. It should be able to carry normal and emergency loads, with tap settings and current transformer taps correctly chosen. This is one of the simpler applications, protecting a radial feeder. I have not used this particular relay. The manufacturer's brochure shows it to be a flexible relay capable of acting as device 50, 50N, 51, 51N, and 50 breaker protection. Do you know what these mean? You could take a simple example, and set it to trip for a fault on the feeder it protects, based on the calculated fault current, such that the backup protection does not operate. It should trip for the lowest current phase to phase or phase to ground fault, at the remote end of the feeder, perhaps "buried in" the remote transformer (so that you do not leave a bit of feeder unprotected at the remote end). It should not trip before downstream fuses or other devices have a chance to clear faults downstream from them: that is coordination. If used as a 50, the operating time would be substantially constant, like a CO-6 relay. This would allow fast clearing, and might be used on an undergrounfd feeder. The 51 application would mean the operating time decreases as the amount of fault current increases, like a CO-7 relay, or a GE IAC-51. Edison (talk) 14:35, 29 May 2009 (UTC)[reply]
My protection coordination course was only two hours instead of two years, but shouldn't the relay be set to trip before any downstream fuses, to give it a chance to clear a line-to-line fault? I seem to remember basing the relay settings on the time-current curves of downstream fuses—the strategy was to have the relay re-close twice, then stay closed long enough to blow the fuse, and finally trip and stay open.—eric15:42, 29 May 2009 (UTC)[reply]
Pork
I heard that Americans extensively use Pork in their daily diet,but there is a common belief that Pig is a host to many disease causing agents like the Tapeworm!!!!!It is also said that these agents may be destroyed by high temperatures but the ova doesnt get destroyed even at such temperatures.But lot of people still eat it without any fear of infection!!!!What makes them still consume Pork extensively???? —Preceding unsigned comment added by 59.165.84.9 (talk) 14:29, 29 May 2009 (UTC)[reply]
Tapeworms such as Taenia solium are not transmitted by eating cooked pork. Only the ingestion of uncooked pork, or contaminated human vomit and faeces transmit the worms. Once proper hygiene standards are adhered to, there's little to worry about. Same as any meat, really. Fribbler (talk) 14:35, 29 May 2009 (UTC)[reply]
Taste and price? Bacon is immense, and it's not particularly expensive. Pork chops are great and not baldy priced either. Sausages are commonly pork as well. Essentially the taste, price and availability of the meat are major factors on how much of it is eaten (though the amount that sells will have impacts on price and availability too of course). Also my understanding is that Pigs can survive in quite a lot of environments thus making them a good animal to farm which helps too. 194.221.133.226 (talk) 14:33, 29 May 2009 (UTC)[reply]
Americans and many other humans also smoke, which is proven to be bad for you. Just because it might be harmful, does not stop everyone from participating in said activity. Also, I have been eating pork for many years, and have never gotten a tapeworm to my knowledge, so I can infer that the risk of eating properly prepared pork to be low enough to justify the reward. mmmmmmmmmm bacon. 65.121.141.34 (talk) 14:39, 29 May 2009 (UTC)[reply]
I think, larvae remain alive only when the pork is undercooked and not all pigs harbor tapeworm larvae. Also FYI, pork is one of the world's most commonly consumed meats. So, it is not just USA but the other part of the world also consumes it including Europe, China or India. [36] - DSachan (talk) 14:41, 29 May 2009 (UTC)[reply]
Tapeworms and trichina are rare in pork in the United States, and we usually eat our pork fully cooked, which further reduces the risk. On the other hand, outbreaks of Escherichia coli O157:H7 from beef occur with some frequency, and a high percentage of chickens are contaminated with salmonella. Your statement that "there is a common belief that Pig is a host to many disease causing agents" probably reflects more on your own culture than either the beliefs or reality of US food production. -- Coneslayer (talk) 14:46, 29 May 2009 (UTC)[reply]
Chill dudes!!!!Even I like Pork but my muslim friend abused it so much that even I started feeling lethargic towards it....He also said that even if Pigs are reared in most hygienic environments they will not forget their inherent practice of eating each others faecal matter!!!!That was the reason I posted this question...actually I wanted to ask whether Pig is really a fit to be eaten animal or not??? —Preceding unsigned comment added by 59.165.84.9 (talk) 17:22, 29 May 2009 (UTC)[reply]
Religious taboos are generally not scientifically based; religious taboos established over a millennium ago are even less likely to be scientifically based. --jpgordon∇∆∇∆18:16, 29 May 2009 (UTC)[reply]
Plenty of the answers have shown that pigs are clearly a hygienic enough animal to eat. They are widely eaten around the world, and according to this site (http://www.gan.ca/animals/pigs.en.html) and many others they are reasonable clean and intelligent animals (that is clean in a hygiene senese, not religious). ny156uk (talk) 17:57, 29 May 2009 (UTC)[reply]
In terms of hygiene, cows routinely get just as dirty as pigs when they are in feed lots. And chickens will be scavenge their own dead. 65.121.141.34 (talk) 18:31, 29 May 2009 (UTC)[reply]
Indeed, there is nothing particularly unique about pigs vis-a-vis other animals in terms of how hygenic eating it is. Swine and cattle and poultry and sheep and any animal can be kept under clean or dirty conditions; the meat can be properly handled or it can be contaminated by improper butchering techiniques. In terms of the risk of disease from pork vs. other meats, there is no difference at all. If you eat beer or lamb or chicken or turkey then these are no more or less risky to eat than pork is. --Jayron32.talk.contribs20:19, 29 May 2009 (UTC)[reply]
Just skimming this makes me so glad I'm a vegetarian! I don't advocate eating any sentient being, but strictly sticking to the scientific nitty-gritty, the greatest risk with any kind of meat comes not from the kind of animal it's from, but from the conditions in which the animal lived and died and how the body was handled after death. If the environment was reasonably clean and the meat was properly handled at the right temperature with clean instruments, contamination is unlikely. The more the situation deviates from this ideal, the greater the risk there is that the end result will be unsuitable for consumption. - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 21:57, 29 May 2009 (UTC)[reply]
A comment to the vegetarian: Humanity has eaten meat for ten thousands of years, even before we could be considered "humanity". Obviously this works nicely even in very unclean environments and with animals that were far from living a sterile life, so "unsuitable for consumption" is a very...cultural expression. Today our nice big brain with all the cultural ideas in it may find it "unsuitable", but our ancestors certainly ate what meat they could get, and lived fine with it. Sure, they sometimes got sick, but our immunesystem is really capable of handling most of the insults that nature has thrown at us. I don't say you should eat every meat under every circumstance, but, believe it or not, not many (biological) things you can eat will kill you. This is really only western luxury thinking. --TheMaster17 (talk) 22:26, 29 May 2009 (UTC)[reply]
Somewhat of a side-issue, but I should point out that "humans have done it for 1000s of years so it must be ok/healthy enough" is not really a valid argument. The human life expectancy for most of its history has been ~30 years, and almost doubled in the 20th century after public health improvements were introduced. So during those 1000s of years of early history,
many people did die of what we would now consider to be avoidable causes (food poisoning and various gastrointestinal diseases),
the short lifetimes meant most people didn't live long enough to develop and subsequently die from chronic conditions like cancer, heart disease, diabetes etc; and so we cannot assess (based on historical evidence) if their habits and lifestyles increased the risk of developing such conditions.
Again, I am not arguing against your conclusion (that eating meat is not necessarily unhealthy); just your justification for it. Abecedare (talk) 01:01, 30 May 2009 (UTC)[reply]
beer freezing
Water freezes at 32F. What temperature will a can of beer freeze? I understand that the alcoholic content would make a significant difference and lower the freezing point, but would a 5% alchohol content lower the freezing point by 1 degree, or more on the order of 10 degrees? Would this be overridden by the higher pressure found inside the can?
I know, a lot of questions, but I don't have the equipment to test this observationally. 65.121.141.34 (talk) 14:33, 29 May 2009 (UTC)[reply]
In countries with a very cold climate, I think freezing is used as an informal way to concentrate alcohol to produce a kind of spirit, instead of distillation. 84.13.52.104 (talk) 15:15, 29 May 2009 (UTC)[reply]
He might have a point. Fractional freezing might be effected by pressure. And I assume that the can is pressurized and the vat is not? 65.121.141.34 (talk) 19:00, 29 May 2009 (UTC)[reply]
Coming back to the original question: Ethanol freezes at -174F, so the answer has to lie somewhere between 32F and -174F :-) I think we need a theoretical chemist here who can give a melting point formula for solutions. I have no clue if the relationship is linear. If this was the case, the freezing point would be lowered by 5% of 32F-(-174F)=5% of 206F which is roughly 10F, so it would freeze at 22F (without fractionated freezing, which would be irrelevant if the whole can freezes and is melted again (without taking out frozen solid). Hmm, but this is all considering normal pressure. I can't remember my physics lessons concerning pressure and melting point any more. Chemists? Physicists? Anyone? --TheMaster17 (talk) 23:09, 29 May 2009 (UTC)[reply]
It's certainly not a linear relationship. Due to the phenomenon called freezing point depression, the freezing point of a solution (in this case, water and ethanol) can be lower than the freezing point of either of the two substances alone. The freezing point of water is 0°C and the freezing point of ethylene glycol is −13°C, but when mixed in the proper ratio (as in automobile antifreeze) the freezing point can be lowered to about −50°C. See, for example, [37]. (I failed to find a good explanation of this in a Wikipedia article, though.) —Bkell (talk) 02:50, 30 May 2009 (UTC)[reply]
Best solvent for a blocked printer head?
My colour cartridge printer head is partly blocked. This comment here http://www.pcguide.com/vb/showthread.php?t=49543 suggests other solvents: "Since it's dried hard you need a more powerful solvent than plain water cold or hot. Try Windex. If that does'nt work use straight household amonia. Clorox Bleach will remove the ink no matter how hard it is. Don't bleach too long or it will dissolve other parts of the cartrige as well. Heat will help, but I would not exceed 180 deg F."
What would be the best solvent for dissolving dried ink without dissolving the plastic-and-copper ink cartridge? I have a number of solvents available: water, white sprit, nail varnish remover, bleach, RugDoctor Traffic Cleaner which I think contains glycol - the same chemical used as a solvent in gloss paint. Would anything be better than water?
I am from the UK, so what would the UK equivalent of Windex be? Is ammonia available here - I've never seen any for sale? And is "Clorox Bleach" just the same as "bleach"? The cartridge is an HP78. Thanks. 84.13.52.104 (talk) 15:28, 29 May 2009 (UTC)[reply]
Windex in the US is a window cleaner and is usually blue. I would imagine the standard window cleaner in the UK will be chemically the same. 65.121.141.34 (talk) 16:32, 29 May 2009 (UTC)[reply]
If a pregnant woman is put under general anesthesia, will the fetus be anesthetized as well, or would the placenta filter out too much of the anesthetic to make a difference? —Preceding unsigned comment added by 66.215.227.218 (talk) 21:48, 29 May 2009 (UTC)[reply]
The Skylark (rocket) can lift 440 pounds to 357 miles. Could it in theory be used to put a person into space for a brief time? Would there be so much of a problem with re-entry heating if it was not moving at an orbital speed but just going straight up and straight down? In any case, does the final stage of the rocket burn up or not as it falls to earth? 78.146.211.210 (talk) 23:14, 29 May 2009 (UTC)[reply]
I would think the payload's volume would be too small to make this feasible... But it's not given so I don't know. Clearly the available space for life support would be minimal, and I think heat shielding alone is likely to make 440 lbs too little. TastyCakes (talk) 23:24, 29 May 2009 (UTC)[reply]
Even if you could fit in the life support (not a great deal needed for just a few minutes) and heat shield (not much needed for a sub-orbital craft compared to a Space Shuttle or similar), you would need some impressive parachutes and they aren't light. --Tango (talk) 23:44, 29 May 2009 (UTC)[reply]
Taking the Project Mercury capsules as a baseline, the article says their launch weight was 4,265 lb. However, nearly half of this is fuel for the retro-engine burn to get the thing out of orbit - this would not be needed in the case of a straight-up-straight-down flight. The landing weight was 2,241 lb. A good deal of this would be engines, also not needed, and also the remains of the heatshield can be subtracted and most of the life-support. After taking all that off you might just about be getting into the right ballpark of 440 lb, but it is probably right on the limit of what can be achieved. But remember, space actually starts a lot lower than 357 miles, it is 62.1 miles by one definition. Skylark could easily achieve a manned mission to this height since payload is much greater for a lower altitude mission. SpinningSpark01:14, 30 May 2009 (UTC)[reply]
pH change at river mouth?
I was just wondering, at the mouth of a river, would the pH change with water depth?
I know that the water containing the lower salt concentrations would remain floating up the top (usually the river water)and that the ocean water (containg more salt ions) would remain down the bottom. but does the pH vary with water depth at the mouth of the river where this water seperation occurs? if so, why?
The caterpillars.
The tree.
Another view.
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