Researchers at MIT are developing new technology for converting heat into light and then into electricity that could eventually save fuel in vehicles by replacing less-efficient alternators and allowing electrical systems to run without the engine idling. The technology, called thermophotovoltaics, uses gasoline to heat a light-emitting material, in this case tungsten. A photovoltaic cell then converts the light into electricity. The idea has been around since the 1960s, says John Kassakian, MIT electrical engineering and computer science professor. But until now, the light emitters for the photovoltaics produced inefficient and very costly systems. Improvements in the materials used in these latest devices—possible in part because researchers can modify the material structure at the nano-scale—are now making much more efficient systems, Kassakian says. According to Kassakian, the system could potentially be a more efficient way to power electrical systems in a vehicle than the current alternator-based one, which wastes energy in two stages: the internal combustion engine converts only about 30 percent of the energy in fuel into movement, and then the alternator is only 50 percent efficient in converting the mechanical energy into electricity. He says a small prototype thermophotovoltaics device that could confirm the system’s improved efficiency might be ready in a year. The researchers modified the surface structure of the light emitter, etching into it nano-sized pits to tune the wavelengths of light emitted to precisely those a photovoltaic cell can convert most efficiently into electricity. They further refined the device with the use of filters that allow the desired wavelengths of light to pass through to the photovoltaic cells, but reflect other wavelengths back to the light emitter. The reflected light carries energy that helps keep the emitter hot, reducing the amount of fuel needed. In addition to replacing the alternator with a thermophotovoltaic module, says Kassakian, the technology could be part of an air-conditioning system for vehicles that doesn’t require a compressor. Because this would significantly decrease the load on an engine, it could make it possible to turn off the engine when the vehicle stops in traffic and easily restart it. Today’s hybrids use this technique to save gas, but require large batteries to provide electricity for the radio and lights, and to restart the engine, and they have to turn the engine back on when the battery charge runs out. In the new MIT system, these batteries wouldn’t be necessary.

6. Ms. Smith voted against the investment proposal in that district, since it involved too great a risk and uncertainty. 7. Although Jeff has less intelligence than others, he is one of the best students in the university. 8. It’s not the drama students that built all the scenery for the play, but a carpenter made it according to their designs. 9. Tony treated Barbara so generously that he bought her a beautiful necklace. It really cost him an arm and a leg! 10. Following the buffet will be an important speech made by the chief financial officer from our headquarters in Paris. Ms. Smith believed that the investment proposal would help. Ms. Smith was not in favor of the investment proposal. Ms. Smith was afraid that she might fail. Ms. Smith did not think that her vote was a great risk.

W: Hey Nick, now that the midterms are over, a bunch of us are getting away for the weekend to go canoeing. Wanna come along? M: Well, uhm, it’d be great to get away, but I’ve never done it before. W: None of the others have either except for me. I went once last fall. But there’ll be an instructor in each canoe the first day. M: I don’t know. W: Oh, come on. This is our last chance to take a break before finals. The scenery is beautiful, and if it gets too hot we can dive in whenever we feel like it. The river’s really calm this time of the year, no rapids to deal with. M: That’s a relief. What would I have to bring? W: Let’s see. Tom’s bringing food for the Friday night cookout for everyone. And the people who run the trip have tents set up and they supply food and drinks for all day Saturday. On the way back Sunday morning we’ll stop somewhere for breakfast. So, you have to bring a bathing suit and a sleeping bag. M: Well, I do love camping and sleeping out. Where is this place? W: Well, it’s about an hour and a half to the place where we meet the trip leaders. We leave our car there and they drive us and the canoes up river to the place where we start canoeing. M: And who’s driving us to the meeting place? W: Well, I was hoping we could take your car. Mine’s in the shop again. M: Oh, I see. It’s not me you want, it’s my car. W: Don’t be silly. So what would you say? M: Oh, why not! W: Great. I’ll give you a call when I find out when everyone wants to leave on Friday. 11. Why does the woman call the man? 12. What does the man have to bring? 13. According to the man, what does he enjoy doing? 14. Why does the woman need to call the man later? To convince him to go on a canoe trip. To invite him to a cookout. To ask if she can borrow his car. To tell him about a trip she took.

It’s great to see so many of you interested in this series on survival in outer space. Tonight I’m going to talk about the most basic aspect of survival—the space suit. When most of you imagine an astronaut, that’s probably the first thing that comes to mind, right? Well, without space suit, it would not be possible for us to survive in space. For example, outer space is a vacuum. There’s not gravity or air pressure. Without protection, a body would explode. What’s more, we’d cook in the sun or freeze in the shade with temperature’s ranging from a toasty 300 degrees above to a cool 300 degrees below zero Fahrenheit. The space suit that NASA has developed is truly a marvel. This photo enlargement here is a left side’s image of an actual space suit worn by astronauts on the last space shuttle mission. This part is the torso. It’s made of seven extremely durable layers. This thick insulation protects against temperature extremes and radiation. Next is what they call a bladder of oxygen. That’s an inflatable sack filled with oxygen to simulate atmospheric pressure. This bladder presses against the body with the same force as the earth atmospheric sea level. The innermost layers provide liquid cooling and ventilation. Despite all the layers, the suit is flexible allowing free movement, so we can walk. Another really sophisticated part of the space suit is the helmet. I brought one along to show you. Can I have a volunteer come and demonstrate? 15. What will cause an unprotected human body to explode in outer space? 16. Where is the bladder of oxygen located? 17. What does the speaker show the audience as he describes the main part of the space suit? 18. What will probably happen next? The lack of air pressure. The extremely hot or cold temperatures. Exposure to radiation. An inadequately ventilated space suit.

W: St. Louise College. This is Roger speaking, can I help you? M: Good morning, I’d like some information about the college. My name is Michael Vaughn. I have a friend in Italy who’s interested in applying for a place at one of the colleges. There are one or two questions which she’d like me to ask you. W: Go ahead. M: Thanks. The first one is: What language is used for normal lessons? W: Well, the main language of instruction in all the colleges is English. But some subjects are taught in French and some in Italian. M: Right. Her next question is about fees. Is it expensive to go to one of the colleges? W: Students’ parents don’t have to be rich, if that’s what you mean. There are scholarships for all colleges, but we do ask parents to help by paying what they can afford. M: Good, she’ll be glad to hear that. Now she wants to know something about getting into a college. Does she have to get high marks in her exams? W: Ah, yes, well, she will have to do well, but academic ability is not the only thing that’s important. We also look at personal qualities. M: What sort of things do you mean? W: Maturity, the ability to get on well with people from different countries, that sort of thing. M: Of course. I understand what you mean. Her last question is about her other interests. Can she do painting and modern dancing, for example? W: Yes, probably. It depends on the staff at the college she enters. Each college has its own special activities, such as theatre studies or environmental work, in which students can take part. M: Good. I think that’s all. Thank you very much for your help. W: You’re welcome. I hope your friend sends in an application. M: I’m sure she will. Thanks again. Goodbye. W: Goodbye. 27. Where does the conversation most probably take place? 28. What does the man want to know? 29. What’s the main language used for normal lessons? 30. What does “personal qualities“ refer to? In a school. On the phone. At an education fair. In a street.

(1)Information superhighway is a large-scale nationwide, or worldwide, electronic communications network system, capable of transmitting just about any form of recorded data. (2)According to the statistics from the housing authority, prices of China’s houses averaged at 2,226 yuan a square meter last year, 6% up over the year before. (3)Intel will provide China with technological guidance and standards on the production of personal computers equipped with a Pentium IV processor. (4)Many businesses in the United States are conducted on the telephone. The average businessman spends much of his time on the telephone making business contacts. (5)The Chinese Spring Festival is a wonderful and joyous occasion in our whole year, and I wish all present here a relaxing and delightful evening.

Planning to lease a car because you don’t think you can afford to buy? Think again. Leasing can end up being just as expensive as buying—and you don’t even get to keep the car. Most people who are thinking about leasing are attracted to this option because they believe it will cost them less money. And they’re right—it is cheaper, but only in the short term. For example, if you were to lease a brand-new Subaru Forester with $4,000 down, you might pay $300 per month for the car. If you were to buy the same car with $3,000 down, you would pay closer to $400 per month. Over a three-year lease, that’s $3,600—a big savings. But after your lease is over, you have to give the car back. If you want to keep driving, you’ll either have to put another down-payment on another lease, or, if you have the option to buy the car, you’ll have to pay thousands of dollars to purchase the vehicle—dollars that won’t be spread out in more manageable monthly payments. Many people want to lease because they can drive a more up-market car than they might otherwise be able to afford. For example, if your monthly budget allowed you to spend $300 on a car, you might be able to lease a brand new Ford Explorer. For the same price, you might have to buy an Explorer that was two or three years old with 50,000 miles, or buy a new but considerably less expensive make and model. A lease, therefore, allows you to drive the latest models of more expensive cars. But when your lease is over, you will have to return that Explorer. Whatever car you can afford to buy, you get to keep it, and it will always have a resell or trade-in value if you want to later upgrade to a newer car. Furthermore, people who lease cars are often shocked and appalled by how much they must pay when the lease is over. Most leases limit you to a certain number of miles, and if you go over that allotment, you must pay for each mile. As a result, at the end of a lease, you may end up paying thousands of dollars in mileage fees. For example, if your lease covers you for 25,000 miles over three years, but you drive 40,000, that’s an extra 15,000 miles. At $11 per mile, that’s $1,650 you’ll have to pay. And you still won’t have a car. In addition, when you lease, you still have to pay for regular maintenance and repairs to the vehicle. Since you must return the car when your lease expires, you are paying to repair someone else’s car. If you own the car, however, you would know that every dollar you spend maintaining or repairing the car is an investment in a real piece of property—your property, not someone else’s. By now, the benefits of buying over leasing should be clear. But if you’re still not convinced, remember this fundamental fact: If you lease, when your lease is up, and after you’ve made all of your monthly payments, paid for extra mileage, and paid for repairs, you must give the car back. It isn’t yours to keep, no matter how much the lease cost you. Whatever make or model you can afford to buy, it is yours to keep after you make the payments. There’s no giving it back, and that makes all the difference.

The city of Wuxi, in east China’s Jiangsu province, was hit by a serious ecological disaster this week. A large bloom of blue-green algae in Taihu Lake caused water quality to deteriorate severely. Despite the local water department’s attempts at mitigating the crisis, the water supply to a great number of households was contaminated, the water becoming putrid and very unpleasant to drink. Degradation of water quality led to tremendous inconvenience to local inhabitants. In response, the Wuxi city government used their website to tell residents to come together and surmount the crisis, which they described as a “natural disaster“ . While it is crucial to help others in the face of a crisis, labelling the algae bloom a natural disaster was completely inaccurate. Taihu Lake has suffered from low water levels this year, and the weather has been hot— with little rain—all of which will have contributed to the algae bloom. However, the local government announced that “the water quality problem is in no way caused by manufacturing or any other human activity“, when in fact there were local factors causing the algae bloom. In particular: the serious eutrophication of Taihu Lake, caused by the great volume of pollutants discharged into the water.

1. It cost William a fortnight to finish the scientific research project. 2. Gee! Your new tie looks so nice and it goes well with your new shirt. 3. Wow, nice weather today, but a little chilly. 4. If he had realized it earlier, he wouldn’t have made the suggestion at the committee meeting last Wednesday. 5. The play was scheduled to begin at 7:30 pm, but due to a minor problem, it was delayed for one hour and a half. William spent 14 days on the project. William spent 10 days on the project. William spent a night on the project. William spent 4 nights on the project.

Our electric car is the way of the future. Automobile manufactures are under the pressure to develop cars that do not pollute. One powerful motive is a California law requiring that by the year 2000, 10% of the new car sales in the states be so-called zero emission vehicles. These cars must put no pollutants whatsoever into the atmosphere. California is a huge market for the automobile companies. So they are working hard to meet these standards. So far the electric car seems to be the best alternative. So the biggest advantage of electric cars is that they don’t pollute. However they will be in competition with gas-powered cars. And that’s where the weaknesses come out. The big problem is that the batteries in electric cars weigh a lot relative to the amount of kilograms and they provide enough energy to go 250km before recharging, which takes 8 hours. Compare that to a moderately fuel efficient conventional car it can go 400-700km on a tank of gas. And refilling takes just minutes. If there are other drains on an electric car’s batteries beside a motor, headlight, air-conditioning or a heater, its already limited range would be significantly reduced. So automobile engineers are trying to make more powerful batteries that would increase the car’s range and make them more attractive to buyers. 23. What is the talk mainly about? 24. What is the main advantage of electric cars over gas-powered cars? 25. What is the main disadvantage of an electric car? 26. How do engineers increase electric cars’ range? Automobile safety. Increasing fuel efficiency. California’s pollution laws. Electric-powered cars.

Researchers at MIT are developing new technology for converting heat into light and then into electricity that could eventually save fuel in vehicles by replacing less-efficient alternators and allowing electrical systems to run without the engine idling. The technology, called thermophotovoltaics, uses gasoline to heat a light-emitting material, in this case tungsten. A photovoltaic cell then converts the light into electricity. The idea has been around since the 1960s, says John Kassakian, MIT electrical engineering and computer science professor. But until now, the light emitters for the photovoltaics produced inefficient and very costly systems. Improvements in the materials used in these latest devices—possible in part because researchers can modify the material structure at the nano-scale—are now making much more efficient systems, Kassakian says. According to Kassakian, the system could potentially be a more efficient way to power electrical systems in a vehicle than the current alternator-based one, which wastes energy in two stages: the internal combustion engine converts only about 30 percent of the energy in fuel into movement, and then the alternator is only 50 percent efficient in converting the mechanical energy into electricity. He says a small prototype thermophotovoltaics device that could confirm the system’s improved efficiency might be ready in a year. The researchers modified the surface structure of the light emitter, etching into it nano-sized pits to tune the wavelengths of light emitted to precisely those a photovoltaic cell can convert most efficiently into electricity. They further refined the device with the use of filters that allow the desired wavelengths of light to pass through to the photovoltaic cells, but reflect other wavelengths back to the light emitter. The reflected light carries energy that helps keep the emitter hot, reducing the amount of fuel needed. In addition to replacing the alternator with a thermophotovoltaic module, says Kassakian, the technology could be part of an air-conditioning system for vehicles that doesn’t require a compressor. Because this would significantly decrease the load on an engine, it could make it possible to turn off the engine when the vehicle stops in traffic and easily restart it. Today’s hybrids use this technique to save gas, but require large batteries to provide electricity for the radio and lights, and to restart the engine, and they have to turn the engine back on when the battery charge runs out. In the new MIT system, these batteries wouldn’t be necessary.

20 Things You Do Not Know about Leonardo da Vinci 1. Leonardo was the love child of Caterina, a peasant, and Ser Piero, a lawyer and landlord. He was homeschooled and lacked a formal education in Greek and Latin. 2. He was an accomplished lyre player. When he was first presented at the Milanese court, it was as a musician, not an artist or inventor. 3. Leonardo narrowly beat a sodomy rap—possibly involving one of his male models—brought against him by Florentine officials. 4. Mona Lisa theory #1: Her smile means she was secretly pregnant. 5. Theory #2: She was amused by the musicians and clowns who entertained her while Leonardo painted her.(Another theory says the Mona Lisa is a portrait of Leonardo himself, slyly disguised. But you’d heard that one before, hadn’t you?) 6. Columbia University art historian James Beck retorts, “As sure as the moon is not made of green cheese, this is not Da Vinci in drag.“ 7. Then again, unusual for a painter, Leonardo left no definitive image of himself. 8. Of course, that was before she saw the picture: Researchers at the University of Amsterdam and the University of Illinois used face-recognition software to determine that the Mona Lisa is 83% happy, 9% disgusted, 6% fearful, and 2% angry. 9. Bill Gates bought the Codex Leicester in 1995 for $30 million. This manuscript, the only one not held in Europe, includes Da Vinci’s studies on hydraulics and the movement of water. 10. And Leonardo loved water: He developed plans for floating snowshoes, a breathing device for underwater exploration, a life preserver, and a diving bell that could attack ships from below. In case one had to. 11. Leonardo was the first to explain why the sky is blue.(It’s because of the way air scatters light.) 12. And he figured out why the entire moon is dimly visible when it is a thin crescent. Its nightside is lit by light reflected from Earth, which appears 50 times brighter from the moon than the full moon appears here. 13. An ambidextrous, paranoid dyslexic, Leonardo could draw forward with one hand while writing backward with the other, producing a mirror-image script that others found difficult to read—which was exactly the point. 14. The Louvre recently spent $5.5 million rehanging the Mona Lisa inside a display case set into a wall, six feet behind a wooden barrier. 15. In August 2003, Da Vinci’s Madonna of the Yarnwinder, valued at $65 million, was stolen from Drumlanrig Castle in Scotland by two men posing as tourists. They escaped in a Volkswagen Golf. 16. Leonardo designed an armored car, a scythed chariot, a pile driver, a revolving crane, a pulley, a lagoon dredge, and a flying ship. 17. In December 2000, skydiver Adrian Nicholas landed in South Africa using a parachute built from one of Leonardo’s designs. 18. I wonder what happens if... After dissecting cadavers, Leonardo replaced the muscles with strings to see how they worked. 19. Sometimes he could be such a person: He was a big fan of puns and word games, and Folio 44 of his Codex Arundel contains a long list of playful synonyms. 20. He crushed intelligent design before anyone even thought of it: His studies of river erosion convinced him that the Earth is much older than the Bible implies, and he argued that falling sea levels—not Noah’s Flood—left marine fossils on mountains.

以往几个世纪人口的增长并不能证明人口会无限地直线向上增长直到毁灭的地步。相反地，人口统计史料证明人口的增长完全不是稳定的。若技术革新的成果开始减少，从250到350年前就在西方开始出现的并且目前还在继续的人口迅速增长可能也会放慢。当然，当前的知识革命也许会持续下去而无法预见其未来。无论如何，与那种认为人口以几何级数持续增长的观点相反，从长远的观点来说，人口可望受到生产力的调节。接受了这一观点，人口的增长就可以被看成是经济进步和人类胜利的标志，而不是社会衰败的标志。

People who want to avoid weight gain have to balance the number of calories they eat with the number of【C1】______. To lose weight, you can reduce the number of calories you【C2】______, or increase the number you use, or both. Experts at the National Institutes of Health say【C3】______, a person should do an hour of moderate to intensive physical activity most days of the week. This could include【C4】______, sports or strength training. You should also follow a 【C5】______and take in fewer calories than your body uses each day. A recent study【C6】______four of the most popular dieting plans in the United States. Researchers at Stanford University in California studied more than【C7】______ women, mostly in their thirties and forties. Each woman【C8】______one of the four plans: Atkins, The Zone, Ornish or LEARN. The women attended diet classes and received【C9】______about the food plans. At the end of a year, the women on the Atkins diet【C10】______the most, more than four and one-half kilograms【C11】______. They also did better on tests including cholesterol levels and 【C12】______. Christopher Gardner led the study, reported in the Journal of the American Medical Association. He says the Atkins diet may be【C13】______because of its simple message to lower intake of sugars. Also, he says 【C14】______increase protein in the diet leads to more【C15】______meals. He says there was not enough money to also study men, but that men would probably have【C16】______. But last week, another report suggested that only【C17】______people have long-term success with dieting. The report in the journal American Psychologist was based on【C18】______studies. Researchers at the University of California, Los Angeles, medical school found that most dieters【C19】______their lost weight within five years. And often they gained back even more. But those who【C20】______generally were the ones who exercised.People who want to avoid weight gain have to balance the number of calories they eat with the number of calories they use. To lose weight, you can reduce the number of calories you take in, or increase the number you use, or both. Experts at the National Institutes of Health say to lose weight, a person should do an hour of moderate to intensive physical activity most days of the week. This could include fast walking, sports or strength training. You should also follow a nutritious eating plan and take in fewer calories than your body uses each day. A recent study looked at four of the most popular dieting plans in the United States. Researchers at Stanford University in California studied more than three hundred overweight women, mostly in their thirties and forties. Each woman went on one of the four plans: Atkins, The Zone, Ornish or LEARN. The women attended diet classes and received written information about the food plans. At the end of a year, the women on the Atkins diet had lost the most, more than four and one-half kilograms on average. They also did better on tests including cholesterol levels and blood pressure. Christopher Gardner led the study, reported in the Journal of the American Medical Association. He says the Atkins diet may be more successful because of its simple message to lower intake of sugars. Also, he says the advice to increase protein in the diet leads to more satisfying meals. He says there was not enough money to also study men, but that men would probably have similar results. But last week, another report suggested that only a small minority of people have long-term success with dieting. The report in the journal American Psychologist was based on thirty-one studies. Researchers at the University of California, Los Angeles, medical school found that most dieters regained their lost weight within five years. And often they gained back even more. But those who kept the weight off generally were the ones who exercised.

M: We continue with the World of Investigation. Susan, an identical twin, has agreed to contribute to our investigations. I must apologize for the fact that Susan’s twin cannot be here tonight. And I’d like to tell you, Susan, how sorry we are. You and your sister are very close, aren’t you? W: Of course we are. M: Interesting! You said “of course“. Don’t you think there are quite a few sisters who aren’t close? W: Brenda and I aren’t just sisters. We’re identical twins. M: I take your point. How identical are you, in fact? W: Both blonde, with brown eyes. Same height, same weight, same size. Even shoes. M: As you’re the same in size, have you always dressed alike? W: Oh yes. I’m told it started when we were babies. Mum made a feature of her twins. And then we got into the habit of buying two of everything. M: And you’ve never minded having a double identity? I mean...another person exactly like you? W: Brenda isn’t exactly like me. We may look identical, but...I remember our boyfriends couldn’t tell us apart. M: Didn’t that cause problems? W: For them, perhaps. Not for us. We couldn’t stop laughing. M: I think you said you and Brenda weren’t exactly alike? Just what did you mean by that? W: Brenda has a well-fed happy husband and four healthy children. When she was washing up, I was learning to type. When she was knitting, I was writing articles for the school newspaper. When she was having her second child, I was in Panama, doing my first job Dolphine Credit. See what I mean? M: And haven’t you got a healthy husband and happy children? W: You must be joking. There’s never been the time...or the inclination. M: Susan, you’ve made some very interesting points. I gather that you don’t feel that behavior is purely genetic... that there might be some element of environment or choice or even perhaps... W: Shall I conclude? Brenda and I are identical twins in appearance...in appearance, that is...but it’s a fact that life has presented us with different opportunities, so we’ve led very different lives. 19. Where does the interview most probably take place? 20. What’s the relationship between Susan and Brenda? 21. In what ways are Susan and Brenda identical? 22. Which of the following statements is correct? On the phone. In the laboratory. On the radio. In the classroom.

The late 1980s found the landscape of popular music in America dominated by a distinctive style of rock and roll known as Glam Rock or Hair Metal—so called because of the over-styled hair, makeup, and wardrobe worn by the genre’s ostentatious rockers. Bands like Poison, Whitesnake and Motley Crue popularized glam rock with their power ballads and flashy style, but the product had worn thin by the early 1990s. Just as superficial as the 1980s, glam rockers were shallow, short on substance, and musically inferior. In 1991, a Seattle-based band called Nirvana shocked the corporate music industry with the release of its debut single, “Smells Like Teen Spirit“, which quickly became a huge hit all over the world. Nirvana’s distorted, guitarladen sound and thought-provoking lyrics were the antithesis of glam rock, and the youth of America were quick to pledge their allegiance to the brand-new movement known as grunge. Grunge actually got its start in the Pacific Northwest during the mid-1980s. Nirvana had simply mainstreamed a sound and culture that got its start years before with bands like Mudhoney, Soundgarden, and Green River. Grunge rockers derived their fashion sense from the youth culture of the Pacific Northwest: a melding of punk rock style and outdoors clothing like flannels, heavy boots, worn-out jeans, and corduroys. At the height of the movement’s popularity, when other Seattle bands like Pearl Jam and Alice in Chains were all the rage, the trappings of grunge were working their way to the height of American fashion. Like the music, the teenagers were fast to embrace the grunge fashion because it represented defiance against corporate America and shallow pop culture. The popularity of grunge music was ephemeral: by the mid-to late-1990s, its influence upon American culture had all but disappeared, and most of its recognizable bands were nowhere to be seen on the charts. The heavy sound and themes of grunge were replaced on the radio waves by boy bands like the Backstreet Boys, and the bubblegum pop of Britney Spears and Christina Aguilera. There are many reasons why the Seattle sound faded out of the mainstream as quickly as it rocketed to prominence, but the most glaring reason lies at the defiant, anti-establishment heart of the grunge movement itself. It is very hard to buck the trend when you are the one setting it, and many of the grunge bands were never comfortable with the fame that was thrust upon them. Ultimately, the simple fact that many grunge bands were so against mainstream rock stardom eventually took the movement back to where it started: underground. The fickle American mainstream public, as quick as they were to hop on to the grunge bandwagon, were just as quick to hop off and move on to something else.

Imagine a bacterium that, when injected into the bloodstream, would travel to the site of a tumor, insert itself into the cancer cell, and then produce a cancer-killing compound. That’s exactly what scientists at the University of California, Berkeley(UCB)and University of California, San Francisco(UCSF)have set out to do. Traditional cancer therapies are limited for two key reasons: little of the drug actually reaches the tumor and the drug is toxic to both cancerous and healthy tissues. Bacteria, however, have the potential to precisely target cells. “In a way, bacteria are the ultimate in smart drugs,“ says George Church, a geneticist at Harvard Medical School in Boston(he was not involved in the current work, but will collaborate on the project in the future). “It’s hard to pack a lot of intelligence into a small molecule or protein: but bacteria can have sensors and actuators and can drill into a cell, like a submarine.“ To build a cancer-killing bacterium, biologists must create organisms that can perform a series of complicated functions—namely, when in the bloodstream, they have to sense and respond to the tumor environment. Once inside the tumor, the bacteria must infiltrate the cancer cell, and then—and only then—start producing a tumor-killing toxin. The researchers plan to engineer such super-organisms by co-opting parts from different types of bacteria and inserting them into Escherichia coli, a bacterium commonly used in research. Tumor tissue has unique characteristics, including lower oxygen and higher lactic acid concentrations than surrounding tissue. To create a bacterium that can sense a tumor, Christopher Anderson, a postdoctoral researcher at UCB and UCSF, and colleagues took an oxygen sensor from E. coli and linked it to a special protein, called invasin, from another type of bacteria, which allows the organism to invade cancer cells. In a paper published earlier this year in the Journal of Molecular Biology, the researchers showed in a test tube that the engineered bacterium selectively invades tumor cells. Anderson and colleagues are now working on making the system even more specific. To ensure that the bacteria invade only tumor cells, they will create a genetic mechanism that allows the invasin protein to be expressed only when two conditions are met, such as when both the oxygen and lactic acid concentrations are at a certain level. Essentially, it’s a genetic version of what’s known in engineering terms as an AND gate—a regulatory circuit that’s turned on only if two conditions are met. “By using multiple cues, we can garner a great deal of specificity,“ says Adam Arkin, a bioengineer at UCB and the Lawrence Berkeley National Laboratory, a TR100 recipient in 1999, and one of the senior scientists on the project. “After the bacteria sense the cues, they turn on the rest of the apparatus to do the job.“

Well-preserved wrecks abound in the Baltic, where low salinity and cold water slow down decay. These include the Vasa, which sank on her maiden voyage in 1628 and was raised from Stockholm Harbour in 1961. Another is the Kronan, which blew up and sank during a battle with the Dutch in 1676. Not all wrecks are now under water. Many have been found in reclaimed parts of Holland’s Zuider Zee, after the land has been drained. At Skuldelev in Denmark a group of five Viking ships, sunk to form a blockage at the entrance to a fjord. Although they have to work in a hostile environment, underwater archaeologists follow the same principles as their counterparts on land. A site must first be surveyed. This is done with tape-measures and grids using simple geometry, supplemented by photography, video, and geophysics. The aim is to produce an analytical map so that the wreck can be assessed. Often this will enable archaeologists to record the site and interpret its significance without having to disturb it. Only in exceptional cases are historic shipwrecks excavated, and their contents recovered. Well-preserved wrecks have usually reached a state of equilibrium with their environments. Having survived for centuries in this state, they will probably remain in much the same condition for centuries to come. But if they are disturbed, the stability which has protected them will be broken. Archaeologists normally excavate shipwrecks only if they are under some kind of threat—a shift in the environmental balance, perhaps, or plans to dredge a harbor entrance where historic sites are known to lie. An example of this kind of “rescue“ excavation is provided by the Cromwellian warship Swan wrecked in 1653 off Mull, which is now threatened by seabed erosion. Very occasionally archaeologists excavate wrecks which are not under threat to recover them and their contents for public exhibition. Examples of these include the Swedish warship Vasa at Stockholm(1628)and the Mary Rose at Portsmouth(1545). In such cases the damage to their archaeological integrity is offset by careful records made by the archaeologists, the conservation of the ships and their contents, and subsequent publication and display. Parts of the hull tell the marine archaeologist how the ship was designed and built. Tool-marks reveal woodworking techniques used by the shipwrights. Fragments of rigging and rope—sometimes even pieces of sails—help to show how the ship was operated by its crew. Other finds throw light on activities such as navigation, medical care, everyday crafts, food storage, cooking, and domestic routines. If the ship was a merchant vessel parts of its cargo may have survived, perhaps revealing where it came from. Warships contain evidence of the weapons they carried. Above all, items of clothing and personal possessions bring us into immediate contact with people who lived and died long ago.

Which of the following expressions is closest in meaning to “idling“ in paragraph 1?

Which of the following statements best summarizes the main idea of the passage?

Which of the following statements best summarizes the weakness of current alternator-based systems in terms of energy waste?

Why did scientists etch nano-sized pits into the light emitter surface?

Why does the author mention hybrids in the last paragraph?