Serap nedir? | what is a mirage?


Hiç sıcak bir havada düz bir yol boyunca baktınız ve var olmayan bir su birikintisi gördünüz mü? Bu bir seraptır. Bu soğuk hava tabakasının altında bulunan, sıcak hava tabakası nedeniyle meydana gelir. Soğuk hava, sıcak havadan, daha kalındır. Bu hava tabakaları içinden geçen ışığın kırılmasına neden olur. Bu kırılma, su hayalini verir, ya da manzaranın bir görüntüsünü kilometrelerce uzağa gönderir.
Seraplar, çoğunlukla çöllerde meydana gelir. Aslında kumdan başka hiç birşey bulunmayan yerlerde göller görünür. Ve bazen palmiyelerin ve kasabaların hayali görünür ve susamış gezginle alay eder. Havada yüzen hayalet gemiler göründüğünde, aynı şey denizde olur.
Bir serabı, gerçek bir şeyden ayırmak kolaydır, çünkü içindeki cisimlerin, hepsi başaşağıdır. Bu, güneş ışınlarının kırılması nedeniyledir.




Have you ever looked along a smooth road in hot weather and seen what appears to be a stretch of water where none exists? This is a mirage. It is caused by the air being heated in such a way that hot layers of air lie under cold layers. The cold air is thicker than the hot air and this causes light passing trough the layers to be bent. This bending gives the illusion of water, or even sends a picture of the scene many miles away.
Mirages often occur in the desert. Lakes are seen where there is really nothing but sand. And sometimes images of towns and palm trees appear and taunt the thirsty traveller. The same thing happens at sea, when ghostly ships are seen floating in the sky.
It is easy to tell a mirage from the real thing, however, because the objects in it are all upside down. This is caused by the way the rays of light are bent.

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Do supplements really do any good?

By Emily Anthes
Posted Wednesday, Jan. 6, 2010, at 12:31 PM ET Deciding what to eat for dinner can be mind-bending. How do we keep track of the ever-evolving recommendations for what to put on, and leave off, the plate? Red meat might cause cancer! But don't replace it with tofu—soy concoctions might be carcinogenic, too! Don't even try to figure out where carbs stand this week. And the verdict on coffee, chocolate, and alcohol changes faster than you can order a mocha martini.
Vitamins—with their promise to bridge the gap between the nutrients our bodies need and those they get—have always seemed reassuringly simple: Just pop a multivitamin and let your body soak in those extra nutrients. But not any longer. During the past few years, study after study has raised doubts about what, if any, good vitamins actually do a body. They could even pose some real medical risks.
Half of all American adults take some sort of nutritional supplement. But research on a wide variety of patient populations and medical conditions has failed to find much evidence that multivitamins, the most commonly used of the lot, prevent major chronic diseases in healthy people. The most recent knock came this spring, when a study of more than 160,000 post-menopausal women, published in the Archives of Internal Medicine, found that the all-in-one pills did not prevent cancer, heart attacks, or strokes and did not reduce overall mortality. 
Individual vitamins and minerals haven't fared much better under scientific scrutinywith research debunking some of the reputed benefits of vitamin B6, calcium, niacin, and others. In 2006, the National Institutes of Health convened an independent panel of experts to evaluate the evidence that vitamins could prevent chronic disease. The scientists ultimately issued a report stating that studies "do not provide strong evidence for beneficial health-related effects of supplements taken singly, in pairs, or in combinations." 
The news on antioxidants, the darlings of the vitamin menagerie, is even more troubling. These compounds, which include vitamins A, C, and E, selenium, beta carotene, and folate, fight free radicals, unstable compounds thought to damage cells and contribute to aging. But not only do antioxidant supplements fail to protect against heart disease, stroke, and cancer; they actually increase the risk of death, according to a 2007 analysis of research on more than 232,000 people, published in the Journal of the American Medical Association, as well as other studies
Exactly why they might increase mortality is unclear, but doctors at prominent research institutions—including New York's Memorial Sloan-Kettering Cancer Center and Seattle's Fred Hutchinson Cancer Research Center—have highlighted some unsettling connections between supplemental antioxidants and an increased risk of a variety of cancers. Popping certain kinds of antioxidant pills can feed latent cancersgrowing in the body, for instance, and reduce the effectiveness of chemotherapy. These observations make a certain intuitive sense, since vitamins and minerals play an important role in the replication of healthy cells—why shouldn't they be doing the same for cancerous cells? (Feeding mice a diet poor in antioxidants, on the other hand, can actually help shrink their brain tumors.) Scientists are also beginning to suspect that the body may actually need free radicals—which help kill cancer cells, ensure optimal immune function, and regulate blood sugar, among other things—so we shouldn't necessarily be mopping them all up.