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2.Metals are deliberately mixed to produce hundreds of new substances with desirable qualities not otherwise available.

3.While small generators frequently have revolving armatures,large machines usually have stationary armatures and revolving fields.

4.With afterburners,fuel is injected behind the combustion section and ignited to increase thrust at the expense of high fuel consumption.

5.Bacteria cannot make their own food,so that they must live on living or dead animals and plants.

6.In vacuum tube radios,a great quantity of heat is produced so that a part of electric power is wasted.

7.Although energy can be changed from one form into another,it can neither be created nor destroyed.

8.As the moon’s gravity is only about 1/6 the gravity of the earth,a 200-pound man weighs only 33 pounds on the moon.

9.Any body above the earth will fall unless it is supported by an upward force equal to its weight.

10.Steel parts are usually covered with grease for fear that they should rust.

（II）篇章翻译练习

1.The powerful lithium-based batteries used in electric vehicle systems,laptops and cell phones are prone to overheating and even blowing up,but adding less than a gram of a new substance could keep both temperatures and costs down,federal researchers say.

The molecule,developed by researchers Khalil Amine and Zonghai Chen at Argonne National Laboratory,is being tested as an additive in the electrolyte of lithium batteries to keep cell voltage from going too high.

The batteries used in hybrid and electric vehicles typically consist of 200 to 400 small cells,strung together into one powerful whole.Individual cells sometimes overcharge,emitting heat when they reach too high a voltage and pushing neighboring cells past the breaking point to set off a runaway thermal reaction.

Because electric and hybrid vehicles are constantly discharging and recharging during normal driving,overcharging problems are not confined to the garage but pose a real operational hazard.

In the lab,Amine and Chen discovered they could make a molecule based on boron and fluorine and add a tiny amount of it to each cell to control charging.When the cell exceeds the safe voltage level,Amine explained,the molecule picks up electrons and keeps the cell charge from going up.

Currently,expensive electronic controls are used to regulate each individual cell in a battery and shut it down if the voltage gets too high.But the control systems are expensive,making up as much as 20 percent of a battery’s cost,and the electronics are prone to failing.

Amine said the new approach offers several advantages over current technologies.In addition to the lower cost,the molecule is more reliable,he said.Other systems that use some kind of molecule in a similar way cannot control more than one overheating cycle,he said,while his molecule will soak up extra voltage through 500 or more cycles.

The material is not easy to make,but only a small amount is needed—2 to 3 percent of the electrolyte by weight.Today,it costs about $1,000 per kilogram,but Amine said battery company EnerDel is leasing the technology and using an Energy Department grant to scale up the fabrication process.He believes that making large batches should bring the cost down to about $100 per kilogram.

The molecule could save $100 to $200 per battery,Amine said.Battery makers today are targeting a total price of $500 to $1,000 per battery.

One more advantage of the new molecule is that unlike the sophisticated electronic control systems,adding a new chemical to the battery pack is quick and easy.“The electrolyte is the last thing you fill in,so it’s an immediate adaptation.Just add this 2 percent and you’re ready to go,” Amine said.（474 words）

2.The primary fuels now used in auto-mobiles,namely gasoline and diesel,are essentially derived from crude oil (petroleum).And using various technologies available today,it is also possible to produce liquid fuels having the same or very similar chemical and physical properties as natural gas,coal and other carbonaceous fuels.Examples of these liquids—such as Fischer-Tropsch Diesel,a mixture of hydrogen and carbon monoxide—are often referred to as “alternative” fuels,but they do not require a major shift from current automobile design.So to address this question,we will assume that “alternative” refers to those fuels that are produced from a nonfossil source or to those fuels (fossil or otherwise) that would require substantial changes in automobile design or in the distribution and marketing infra-structure.

Over the years,industry experts have proposed a number of compounds—including methanol,ethanol,hydrogen,compressed natural gas (CNG),liquefied petroleum gas (LPG),socalled biodiesel and hydrogen—as alternative fuels to meet one or more of the following objectives: decrease dependence on petroleum,which is an imported,nonrenewable resource; reduce air emissions associated with combustion products; and increase overall fuel utilization efficiency.

Ethanol and biodiesel are generally produced by using corn or other renewable agricultural products,thus meeting the first objective.But they are more expensive than the petroleum-based products they displace (gasoline and diesel,respectively).

The technology exists today to operate automobiles on CNG and LPG,which would meet the second objective.In fact,buses and trucks in many urban areas of Asia and Europe operate on CNG and LPG.Expansion of the use of clean-burning gaseous fuels (CNG,LPG and hydrogen) for private automobiles,however,has been slow.Among the obstacles to overcome are low energy storage density (total miles driven per filling of fuel tank),poor economics (the low price of petroleum-based products have historically not provided much incentive for turning to these alternatives) and major engineering challenges in adapting the current internal combustion engine to these fuels.Switching to the gaseous fuels will further require a new infrastructure for fuel stations,which will undoubtedly undergo greater scrutiny in design,construction and environmental safety,as compared with current gasoline and diesel filling stations.

Despite these significant impediments,the situation is changing.New emission regulations in sulfur in gasoline and diesel coming in 2006—and our desire to reduce our dependence on imported crude oil—are driving automobile technology toward cleaner-burning alternative fuels and higher-efficiency (in terms of miles per gallon obtained) drivetrains.The internal-combustion engine may be replaced with a drivetrain consisting of fuel cells that operate on hydrogen,combined with an electric motor.Technologies are being developed for converting gasoline into hydrogen to feed these fuel cells and utilize the existing gasoline pumping station infrastructure.In fact,it is not inconceivable that automobiles would be fueled directly with hydrogen at pumping stations.Significant use of these alternative fuels,however,is not expected before 2010.(481 words)