题目内容
Eta Carinae
As possibly the galaxy's (银河) most massive star, Eta Carinae is now engaging in some very unusual behaviour. Australian astronomers, being in the Southern Hemisphere (半球), are able to observe it clearly.
In the 19th century, Eta Carinae was for a time the third brightest star in the sky. It has now become less bright so that binoculars (双筒望远镜) are needed to see it. "It seems to be brightening and becoming less bright over a period of many years", said Dr Bob Duncan from the Australia Telescope National Facility.
While it is not unusual for stars to vary in brightness, the period is usually much shorter. "Since 1992 it has become four times brighter, and then last year it began to drop dramatically," he said.
The problem in observing Eta Carinae is that it has been surrounded by a cloud of gas and dust, making it hard to see the star directly. However, radio waves and infrared light (红外线) can pass through this cloud, so telescopes that receive these wavelengths can observe what is occurring.
Eta Carinae is of particular interest to astronomers because it seems to be in its death throes (剧痛). Being so large it will end up as a supernova (超新星). There has not been a supernova in our galaxy since the invention of the telescope. While a 1987 explosion in a nearby galaxy gave astronomers plenty of valuable data, they are hungry for an even closer look.
Eta Carinae has other unique features, and is the only star known to produce an ultraviolet (紫外线) laser that is brighter than that produced by the Sun. Lasers have been observed in other frequencies from a few stars.
第 31 题 Eta Carinae is now engaging in
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A．appeared B．carriedC．published D．contributed
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The International Science Olympiads are held once every two years.
"Salty" Rice Plant Boosts Harvests
British scientists are breeding a new generation of rice plants that will be able to grow in soil containing salt water. Their work may enable abandoned farms to become productive once more.
Tim Flowers and Tony Yeo, from Sussex University's School of Biological Sciences, have spent several years researching how crops, such as rice, could be made to grow in water that has become salty.
The pair have recently begun a three-year programme, funded by the Biotechnology and Biological Sciences Research Council, to establish which genes enable some plants to survive salty conditions. The aim is to breed this capability into crops, starting with rice.
It is estimated that each year more than 10m hectares (公顷) of agricultural land are lost because salt gets into the soil and stunts (妨碍生长) plants. The problem is caused by several factors. In the tropics, mangroves (红树林) that create swamps (沼泽) and traditionally formed barriers to sea water have been cut down. In the Mediterranean, a series of droughts have caused the water table to drop, allowing sea water to seep (渗透)in. In Latin America, irrigation often causes problems when water is evaporated (蒸发) by the heat, leaving salt deposits behind.
Excess salt then enters the plants and prevents them functioning normally. Heavy concentrations of minerals in the plants stop them drawing up the water they need to survive.
To overcome these problems, Flowers and Yeo decided to breed rice plants that take in very little salt and store what they do absorb in cells that do not affect the plants' growth. They have started to breed these characteristics into a new rice crop, but it will take about eight harvests before the resulting seeds are ready to be considered for commercial use.
Once the characteristics for surviving salty soil are known, Flowers and Yeo will try to breed the appropriate genes into all manners of crops and plants. Land that has been abandoned to nature will then be able to bloom again, providing much needed food in the poorer countries of the world.
第 41 题 Which of the following statements about Flowers and Yeo is true？
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