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VOA慢速英语2013 Sleeping and Dreaming of Comets

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Sleeping and Dreaming of Comets

From VOA Learning English, this is Science in the News. I’m Jim Tedder1.

And I’m Caty Weaver2. Today, we tell how sleep helps to keep our brains healthy. We have a report about what South African researchers are calling Earth’s first-ever  comet strike. And we take you to an American aquarium3 where visitors pay to swim with sharks!

SLEEPING HELPS OUR BRAINS

Ever wonder why we need sleep? Scientists have and now they seem to have found an answer to this age-old question. That answer may lead to new treatments for nerve- related disorders4 such as Alzheimer’s or Parkinson’s disease.  While we sleep, our brains do much more than just rest. American researchers say our brains could also  be doing away with harmful waste. They studied the brains of mice that had had fluorescent5 dye injected into their cerebral6 spinal7 fluid.

Maiken Nedergaard led the study. She is a neurologist with the University of Rochester in New York State. She says our brains have two very different activities.

“When we are aware, the brain cells are working very hard at processing all the information about our surroundings. Whereas when during sleep, really work very, very  hard on removing all the waste that builds up when we are awake.”

The researchers say that waste includes toxins8 – substances responsible for Alzheimer’s disease and other disorders of the nervous system. They also found that  during sleep the brain’s cells shrink, permitting waste to be removed more effectively. Doctor Nedergaard says it all ends up in the liver where the toxins are broken  down.

“So our study suggests that we need to sleep because we have a macroscopic cleaning system that remove many of the toxic9 waste product from the brain.”

The brain’s cleaning system could be studied only by using a new imaging technology because the test animal must be alive to observe this process. Doctor Nedergaard  says the next step is to find out if the human brain has a similar cleaning system.

The results demonstrate how important sleep is in the areas of health and disease. They may lead to treatment to prevent or undo10 neurological disorders.

WORLD FOOD PRIZE WINNERS RECOGNIZED

The World Food Prize was recently awarded to three developers of genetically12 modified crops, or GMOs. Mary Dell Chilton, Marc van Montagu and Rob Fraley received the  award last month.

The award praises the technology they created for being able to increase the quantity and availability of food. It also says GMOs help deal with a growing world  population and changes in weather patterns. But the selection of the three scientists has been criticized by people who question the safety and value of GMOs.

Genetic11 engineering can add information to plants to produce different kinds of things, such as a protein that kills insects.

Farmers quickly accepted and supported the new technology, first used in 1996. Nearly all the corn and cotton grown in the United States is made with GMOs.

The World Food Prize organization in the American state of Iowa says 17 million farmers worldwide grew GMO crops in 2012. It says the technology increased production  and reduced the usage of harmful chemicals on crops.

But opposition13 to GMOs has been spreading. In the Philippines, protesters destroyed test fields of rice that had been genetically engineered to produce vitamin A.

EVIDENCE OF FIRST KNOWN COMET STRIKE RECOVERED 

South African researchers say they have found conclusive14 evidence of Earth's first-ever known comet strike. The researchers say this exciting find in rural Egypt could  help explain more secrets of the universe.

They say the evidence suggests the comet struck the earth about 28-million years ago, over a desert in western Egypt. They say the small particles of glassy black rock  found there are comet fragments.

The South African scientists presented their findings last month at the University of the Witwatersrand in Johannesburg.

David Block is a professor at the university. He says meteor and asteroid15 strikes are fairly common on Earth. But a comet strike, he says, is rare and exciting.

“Because a comet is this dirty snowball of not only rock, but rock mixed with ice. And the point is that atoms, life-giving atoms of carbon, of oxygen, of nitrogen,  of argon, of neon, of krypton, are encoded within this little chemical factory from beyond the solar system. …. These are grains of cosmic dust which existed prior to  our solar system forming. So they contain unique secrets of the chemical compo ((composition)) of the cloud of gas and dust which collapsed16 to form our sun and the  planets around it.”

Some scientists say it may have been a comet strike that killed the dinosaurs17 65 million years ago. But, there is no strong evidence of this.

Marco Andreoli is with the South African Nuclear Energy Corporation. He says no one has seen a comet hit and lived to tell about it. That is because comets usually  burn every living thing in their path to ashes. But Professor Andreoli says the evidence of this comet strike is clear to him.

“We are looking at something of … an astronomical18 phenomenon.”

Jan Kramers of the University of Johannesburg says the scientific community is divided on his team’s findings that the rock fragment was a comet. But he says the  evidence of this comet strike is clear to him.

“It is probably part of a comet, because it can’t be anything else. Coming from the outermost19 reaches in the solar system, traveling in the gravity of the sun and  hitting the Earth by chance. What it did tells you something more. What it did when it hit the atmosphere, it exploded. And that is what comets do when they hit the  atmosphere. And this explosion produces an incredible amount of heat which can account for the Libyan desert glass that we found in that region.”

The researchers say they hope additional study of the comet fragments will help them learn more about the beginnings of our universe.

SWIMMING WITH SHARKS!

For many people, nothing compares to the excitement of swimming with sharks in the wild. Tour boat operators in South Africa, Mexico and the Caribbean offer such  experiences. They also provide cages to protect swimmers from the animals.

Now, several public aquariums20 in the United States are letting visitors pay to swim with sharks in enclosed areas. Reporter Tom Banse recently visited one such  aquarium in the city of Tacoma, Washington. Today we have his report.

On this day, more than 900 people have already asked permission to take a swim in a tank full of sharks. It is all in a day’s work for Heidi Wilken, an employee at  the Point Defiance21 Zoo and Aquarium in Takoma. She tells reporter Tom Banse not to worry as he prepares for his turn.

“We've never had any instances of aggression22 from our sharks. We've done thousands of dives in this exhibit. So I would say you're very safe.”

“When were the sharks fed last?”

“They are fed twice a week - Tuesdays and Saturdays. And you know, we are not prey23 items for them. In most cases when there are shark bites, it's a case of mistaken  identity.”

With those words, aquarium employees help get Tom Banse into a dry suit – special clothing that keeps the person wearing it dry. The large saltwater tank holds 17  sharks of six different species, and a number of smaller fish.

“Walk down that ladder, nice and slow...”

 A swim ladder leads divers24 into an underwater cage. There is enough space for up to four people. Cage divers breathe air from the surface through long tubes.

“Put that in your mouth. Put your face in the water. Take a couple of breaths...”

The water in the tank is warm. Sharks swim slowly by, some as close as two arm lengths away. Before diving, Heidi Wilken told Tom Banse to keep his arms inside the  enclosure. “No petting the sharks,” she says.

Then a guide opens the underwater cage doors, wide open. A sand tiger shark with large teeth swims by, looking closely at the group of humans. The biggest shark in the  tank is a two and one half meter-long, 200-kilogram lemon shark. This animal makes repeated passes. Less frightening sharks swim nearby.

“...You can see, our sand tiger shark is coming very slowly towards us...”

Aquarium visitors can watch all of this through underwater observation windows. The dive ends after about 20 minutes.

John Houck is deputy director of the Point Defiance Zoo and Aquarium. He hopes shark dives create publicity25 and eventually turn a profit for the aquarium. But he also  says a main goal for doing this is to create a better understanding of the environment and the overharvesting of sharks.

“Many people think that sharks are threatening, obviously. But we believe that it is the sharks who are threatened by us and our practices of harvesting in the  oceans.”

Aquariums on America’s East Coast were among the first to offer the chance to swim with sharks. The Georgia Aquarium in Atlanta lets visitors swim with its whale  sharks, the largest fish on earth. There are zebra and black-tip reef sharks at the Florida Aquarium in Tampa, Florida. And the Long Island Aquarium in New York offers  a swim with sand tigers and nurse sharks. There, as in Takoma, education is an important part of the experience, and divers are urged to help protect sharks in the  wild.

This Science in the News was written by Milagros Ardin and June Simms, who was also our producer. I’m Caty Weaver.


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点击收听单词发音收听单词发音  

1 tedder 2833afc4f8252d8dc9f8cd73b24db55d     
n.(干草)翻晒者,翻晒机
参考例句:
  • Jim Tedder has more. 吉姆?特德将给我们做更多的介绍。 来自互联网
  • Jim Tedder tells us more. 吉姆?泰德给我们带来更详细的报道。 来自互联网
2 weaver LgWwd     
n.织布工;编织者
参考例句:
  • She was a fast weaver and the cloth was very good.她织布织得很快,而且布的质量很好。
  • The eager weaver did not notice my confusion.热心的纺织工人没有注意到我的狼狈相。
3 aquarium Gvszl     
n.水族馆,养鱼池,玻璃缸
参考例句:
  • The first time I saw seals was in an aquarium.我第一次看见海豹是在水族馆里。
  • I'm going to the aquarium with my parents this Sunday.这个星期天,我要和父母一起到水族馆去。
4 disorders 6e49dcafe3638183c823d3aa5b12b010     
n.混乱( disorder的名词复数 );凌乱;骚乱;(身心、机能)失调
参考例句:
  • Reports of anorexia and other eating disorders are on the increase. 据报告,厌食症和其他饮食方面的功能紊乱发生率正在不断增长。 来自《简明英汉词典》
  • The announcement led to violent civil disorders. 这项宣布引起剧烈的骚乱。 来自《简明英汉词典》
5 fluorescent Zz2y3     
adj.荧光的,发出荧光的
参考例句:
  • They observed the deflections of the particles by allowing them to fall on a fluorescent screen.他们让粒子落在荧光屏上以观察他们的偏移。
  • This fluorescent lighting certainly gives the food a peculiar color.这萤光灯当然增添了食物特别的色彩。
6 cerebral oUdyb     
adj.脑的,大脑的;有智力的,理智型的
参考例句:
  • Your left cerebral hemisphere controls the right-hand side of your body.你的左半脑控制身体的右半身。
  • He is a precise,methodical,cerebral man who carefully chooses his words.他是一个一丝不苟、有条理和理智的人,措辞谨慎。
7 spinal KFczS     
adj.针的,尖刺的,尖刺状突起的;adj.脊骨的,脊髓的
参考例句:
  • After three days in Japan,the spinal column becomes extraordinarily flexible.在日本三天,就已经使脊椎骨变得富有弹性了。
  • Your spinal column is made up of 24 movable vertebrae.你的脊柱由24个活动的脊椎骨构成。
8 toxins 18c3f40d432ba8dc33bad8fb82873ea8     
n.毒素( toxin的名词复数 )
参考例句:
  • The seas have been used as a receptacle for a range of industrial toxins. 海洋成了各种有毒工业废料的大容器。
  • Most toxins are naturally excreted from the body. 大部分毒素被自然排出体外。 来自《简明英汉词典》
9 toxic inSwc     
adj.有毒的,因中毒引起的
参考例句:
  • The factory had accidentally released a quantity of toxic waste into the sea.这家工厂意外泄漏大量有毒废物到海中。
  • There is a risk that toxic chemicals might be blasted into the atmosphere.爆炸后有毒化学物质可能会进入大气层。
10 undo Ok5wj     
vt.解开,松开;取消,撤销
参考例句:
  • His pride will undo him some day.他的傲慢总有一天会毁了他。
  • I managed secretly to undo a corner of the parcel.我悄悄地设法解开了包裹的一角。
11 genetic PgIxp     
adj.遗传的,遗传学的
参考例句:
  • It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
  • Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。
12 genetically Lgixo     
adv.遗传上
参考例句:
  • All the bees in the colony are genetically related. 同一群体的蜜蜂都有亲缘关系。
  • Genetically modified foods have already arrived on American dinner tables. 经基因改造加工过的食物已端上了美国人的餐桌。 来自英汉非文学 - 生命科学 - 基因与食物
13 opposition eIUxU     
n.反对,敌对
参考例句:
  • The party leader is facing opposition in his own backyard.该党领袖在自己的党內遇到了反对。
  • The police tried to break down the prisoner's opposition.警察设法制住了那个囚犯的反抗。
14 conclusive TYjyw     
adj.最后的,结论的;确凿的,消除怀疑的
参考例句:
  • They produced some fairly conclusive evidence.他们提供了一些相当确凿的证据。
  • Franklin did not believe that the French tests were conclusive.富兰克林不相信这个法国人的实验是结论性的。
15 asteroid uo1yD     
n.小行星;海盘车(动物)
参考例句:
  • Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
  • It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小,但这样的危险还是存在的。
16 collapsed cwWzSG     
adj.倒塌的
参考例句:
  • Jack collapsed in agony on the floor. 杰克十分痛苦地瘫倒在地板上。
  • The roof collapsed under the weight of snow. 房顶在雪的重压下突然坍塌下来。
17 dinosaurs 87f9c39b9e3f358174d58a584c2727b4     
n.恐龙( dinosaur的名词复数 );守旧落伍的人,过时落后的东西
参考例句:
  • The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
  • Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》
18 astronomical keTyO     
adj.天文学的,(数字)极大的
参考例句:
  • He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
  • Houses in the village are selling for astronomical prices.乡村的房价正在飙升。
19 outermost w4fzc     
adj.最外面的,远离中心的
参考例句:
  • He fired and hit the outermost ring of the target.他开枪射中了靶子的最外一环。
  • The outermost electron is shielded from the nucleus.原子核对最外层电子的作用受到屏蔽。
20 aquariums 82747d9c1d5a367d4d227b28ed8cf5c6     
n.养鱼缸,水族馆( aquarium的名词复数 )
参考例句:
  • Biotope aquariums represent the natural environments of ornamental fish. 生态鱼缸表现出观赏鱼的自然生活环境。 来自互联网
  • There are aquariums in many cities in the world. 世界上好多城市有水族馆。 来自互联网
21 defiance RmSzx     
n.挑战,挑衅,蔑视,违抗
参考例句:
  • He climbed the ladder in defiance of the warning.他无视警告爬上了那架梯子。
  • He slammed the door in a spirit of defiance.他以挑衅性的态度把门砰地一下关上。
22 aggression WKjyF     
n.进攻,侵略,侵犯,侵害
参考例句:
  • So long as we are firmly united, we need fear no aggression.只要我们紧密地团结,就不必惧怕外来侵略。
  • Her view is that aggression is part of human nature.她认为攻击性是人类本性的一部份。
23 prey g1czH     
n.被掠食者,牺牲者,掠食;v.捕食,掠夺,折磨
参考例句:
  • Stronger animals prey on weaker ones.弱肉强食。
  • The lion was hunting for its prey.狮子在寻找猎物。
24 divers hu9z23     
adj.不同的;种种的
参考例句:
  • He chose divers of them,who were asked to accompany him.他选择他们当中的几个人,要他们和他作伴。
  • Two divers work together while a standby diver remains on the surface.两名潜水员协同工作,同时有一名候补潜水员留在水面上。
25 publicity ASmxx     
n.众所周知,闻名;宣传,广告
参考例句:
  • The singer star's marriage got a lot of publicity.这位歌星的婚事引起了公众的关注。
  • He dismissed the event as just a publicity gimmick.他不理会这件事,只当它是一种宣传手法。

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