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Progress Seen Toward Making Objects Invisible迅雷专用高速下载 VOICE ONE:This is SCIENCE IN THE NEWS in VOA Sp
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 Progress Seen Toward Making Objects Invisible


迅雷专用高速下载

VOICE ONE:

This is SCIENCE IN THE NEWS in VOA Special English. I'm Bob Doughty.

VOICE TWO:

And I'm Barbara Klein. This week, we will tell about evidence that some people can be both fat and healthy. We will also tell about brain aneurysms(动脉瘤) -- a rare but deadly disorder. And, we will tell about materials that could help make objects seem to disappear.

(MUSIC)

VOICE ONE:

Two studies are suggesting that some overweight people do not always face an increased risk of developing heart disease. Researchers also found that some normal body weight individuals have an increased risk of the disease.

Being overweight does increase your risk of medical problems. But the studies found that not all heavy people are less healthy than thin people.

VOICE TWO:

In one study, American researchers examined medical records from more than five thousand men and women. Each person had taken part in a separate study from nineteen ninety-nine to two thousand four.

The researchers found that about fifty-one percent of the subjects were overweight or obese. About thirty-two percent were obese, but considered metabolically healthy. This means they had no evidence of problems in tests for high blood pressure or other measures linked to heart disease.

However, more than twenty-three percent of people who were at a healthy weight had two or more unhealthy measurements in the tests.

VOICE ONE:

Judith Wylie-Rosett helped supervise the American study. She is a professor at the Albert Einstein College of Medicine at Yeshiva University in New York. Professor Wylie-Rosett says the findings show that an obese person can still be healthy. She believes that having body fat is not as important to health as where the fat is found on body.

America's Centers for Disease Control and Prevention notes that two-thirds of Americans are considered overweight or obese.

VOICE TWO:

A second study is suggesting that fat in the liver may be important to health risks. Norbert Stefan and his team work at Germany's University of Tubingen. They closely examined three hundred fourteen people. They measured how much body fat each person had, and where it was on the body. To do this, they used medical imaging tests. They too discovered that obese people could have healthy hearts. Their results suggest that fat in the liver is more dangerous than fat in other areas.

The results of both studies were published recently in the Archives of Internal Medicine.

VOICE ONE:

Professor Wylie-Rosett says the findings do not mean that people should not be concerned about becoming obese. Experts say there are several diseases linked to obesity that make it more dangerous to be fat than thin. They say that people should see their doctor to learn what health risks they may be facing and what behaviors should be changed to improve health.

(MUSIC)

VOICE TWO:

We often hear the term brain aneurysm. Joseph Biden had two brain aneurysms twenty years ago. Doctors saved his life. Recently, the senator from Delaware was named the vice presidential choice of the Democratic Party.

Ohio's first black congresswoman was not so lucky, however. Representative Stephanie Tubbs Jones died last month within hours after a brain aneurysm burst. Doctors said she may have had no warning.

VOICE ONE:

A brain aneurysm is a weak or thin area along an artery wall in the brain. It can become so thin that it ruptures and bleeds.

The most common form looks like a small, round berry hanging from the artery. The Mayo Clinic in Minnesota says as many as fifteen million people in the United States, or five percent, have a berry aneurysm. Fewer than thirty thousand will ever suffer a rupture.

The National Institute of Neurological Disorders and Stroke says forty percent of victims die within twenty-four hours. Another twenty-five percent die within six months.

VOICE TWO:

People may live a long and healthy life and never know they have an aneurysm. But sometimes, if it gets big enough, it can cause pain or other problems that lead to its discovery.

In Senator Biden's case, his neck hurt for several weeks. Doctors thought he had a pinched nerve and a virus. But in February of nineteen eighty-eight, tests showed a leaking artery at the base of his brain. Doctors operated successfully, and again three months later for an aneurysm in another area.

Experts say most brain aneurysms happen in people born with an abnormality in an artery wall. Other causes can include head injuries, high blood pressure, infections, tobacco use and use of stimulant drugs.

(MUSIC)

VOICE ONE:

For years, scientists have dreamed of someday guiding or directing light in unusual ways. If they could, objects might seem to disappear. The objects would be invisible -- hidden from sight.

Now, scientists in the United States have produced materials that may help to make invisibility possible. Researchers at the University of California in Berkeley performed the experiments. Their study took steps toward "cloaking", or appearing to hide, objects.

The Lawrence Berkeley National Laboratory also took part in the experiments. Support for the work came from America's National Science Foundation and the United States military.

VOICE TWO:

Before now, invisibility experiments succeeded in guiding light around only very thin objects of two dimensions. Such objects had length and width, but no depth. The new study marks the first time experiments have been successfully done in three dimensions using visible light, or light that can be seen.

We normally see objects because light strikes them. Then our eyes receive some of the light from the objects. To make an object seem to disappear, it is necessary to direct the light so it hides the object.

The California researchers successfully did this by using materials called metamaterials. Metamaterials are small almost beyond human imagination. They are made with a process called nanoengineering.

VOICE ONE:

It was thought that directing light with natural materials was not possible. But with nanoengineered materials, the researchers were able to build a special prism. Normally, a prism has many flat surfaces. It divides white light into colors. A nanoengineered prism does the opposite. It creates white light from colors.

Results of the experiment were reported in "Science" magazine. Results with the other metamaterial appeared in the publication "Nature." University of California Professor Xiang Xhang led the research teams that developed both materials. They contained substances including metals, earthenware and fiber.

VOICE TWO:

The researchers designed one metamaterial like a net used to trap fish. It was made of silver nanowires. Each wire was about ten thousand times thinner than a human hair. The other metamaterial used twenty-one grids of silver and magnesium fluoride. The box-like grids formed lines. They were also unimaginably small.

Two years ago, two other researchers also reported on invisibility experiments. But they used microwaves instead of visible light. The two men were David Smith of Duke University in the United States and John Pendry of Imperial College in London.

Last year, scientists at America's Purdue University reported success in guiding light around objects placed in a design. The design employs small needles called – you guessed it – nanoneedles. Mister Pendry, Mister Smith and David Schurig developed some of the required mathematics for that research. At the same time, so did Ulf Leonhardt of the University of Saint Andrews in Scotland.

VOICE ONE:

All this recent interest in invisibility is not surprising. People have been talking about making things invisible for thousands of years. In Plato's "Republic", there is an invisible ring. In the last century, "The Shadow" was a popular radio program. It told of a man who could become invisible. That meant he could defeat all evil.

More recently, the British secret agent of many films, James Bond, had an invisible car. And Harry Potter, hero of many books and films, sometimes had a magic cloak. He was able to protect himself by wearing it.

(MUSIC)

VOICE TWO:

This SCIENCE IN THE NEWS program was written by Jerilyn Watson, Caty Weaver and Brianna Blake, who also was our producer. I'm Barbara Klein.

VOICE ONE:

And I'm Bob Doughty. We would like to hear from you. You can read and listen to our programs at 51voa.com. Join us again next week for more news about science in Special English on the Voice of America.

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