单选题{{B}}第三篇{{/B}}
{{B}}Winged Robot Learns to Fly{{/B}} Learning how to fly took
nature millions of years of trial and error --but a winged robot has cracked it
in only a few hours, using the same evolutionary principles.
Krister Wolff and Peter Nordin of Chalmers University of Technology (CUT)
in Gothenburg, Sweden, built a winged robot and set about testing whether it
could learn to fly by itself, without any pre-programmed data on what flapping
is or how to do it. To begin with, the robot just twitched and
jerked erratically. But, gradually, it made movements that gained height.
At first, it cheated -- simply standing on its wing tips was one early short
cut. After three hours, however, the robot abandoned such methods in favor of a
more effective flapping technique, where it rotated its wings through 90 degrees
and raised them before twisting them back to the horizontal and pushing
down. "This tells us that this kind of evolution is capable of
coming up with flying motion," says Peter Bentley, who works on evolutionary
computing at University College London. But while the robot had worked out how
best to produce lift, it was not about to take off. "There's only so much that
evolution can do," Bentley says. "This thing is never going to fly because the
motors will never have the strength to do it," he says. The
robot had metre-long wings made from balsa wood and covered with a light plastic
film. Small motors on the robot let it move its wings forwards or backwards, up
or down or twist them in either direction. The team attached the
robot to two vertical rods, so it could slide up and down. At the start of a
test, the robot was suspended by an elastic band. A movement detector measured
how much lift, if any, the robot produced for any given movement. A computer
program fed the robot random instructions, at the rate of 20 per second, to test
its flapping abilities. Each instruction told the robot either to do nothing or
to move the wings slightly in the various directions. Feedback
from the movement detector let the program work out which sets of instructions
were best at producing lift. The most successful ones were paired up and
"offspring" sets of instructions were generated by swapping instructions
randomly between successful pairs. These next-generation instructions were then
sent to the robot and evaluated before breeding a new generation, and the
process was repeated.
单选题She
all but
fainted when she heard the news.
单选题Take
vigorous
exercise for several hours a week.
单选题Light Night, Dark Stars Thousands of people around the globe step outside to gaze at their night sky. On a clear night, with no clouds, moonlight, or artificial lights to block the view, people can see more than 14,000 stars in the sky, says Dennis Ward, an astronomer with the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo. But when people are surrounded by city lights, he says, they're lucky to see 150 stars. If you've ever driven toward a big city at night and seen its glow from a great distance, you've witnessed light pollution. It occurs when light from streetlights, office buildings, signs, and other sources streams into space and illuminates the night sky. This haze of light makes many stars invisible to people on Earth. Even at night, big cities like New York glow from light pollution, making stargazing difficult. Dust and particles of pollution from factories and industries worsen the effects of light pollution. "If one city has a lot more light pollution than another," Ward says, "that city will suffer the effects of light pollution on a much greater scale." Hazy skies also make it far more difficult for astronomers to do their jobs. Cities are getting larger. Suburbs are growing in once dark, rural areas. Light from all this new development is increasingly obscuring the faint light given off by distant stars. And if scientists can't locate these objects, they can't learn more about them. Light pollution doesn't only affect star visibility. It can harm wildlife too. It's clear that artificial light can attract animals, making them go off course. There's increasing evidence, for example, that migrating birds use sunsets and sunrises to help find their way, says Sydney Gauthreaux Jr., a scientist at Clemson University in South Carolina "When light occurs at night," he says, "it has a very disruptive influence." Sometimes birds fly into lighted towers, high-rises, and cables from radio and television towers. Experts estimate that millions of birds die this way every year.
单选题Tom"s wife succeeded in
persuading
him into giving up smoking.
单选题Smoking Can Increase Depressive Symptoms in Teens While some teenagers may use cigarettes to "self-medicate" (自我治疗) against the blues (忧郁), scientists at the University of Toronto and the University of Montreal have found that smoking may actually (51) depressive symptoms in some teens. "This observational study is one of the few to examine the perceived (52) benefits of smoking among teens, "says lead researcher Michael Chaiton, a research associate at the Ontario Tobacco Research Unit of the University of Toronto. " (53) cigarettes may appear to have self-medicating effects or to improve mood, in the long (54) we found that teens who started to smoke reported higher depressive symptoms. " As part of the study, some 662 high school teenagers completed up to 20 questionnaires about their use of cigarettes to (55) mood. Secondary schools were selected to provide a mix of French and English participants, urban and rural schools, and schools (56) in high, moderate and low socioeconomic neighbourhoods. Participants were divided into three (57) : never smokers; smokers who did not use cigarettes to self-medicate, improve mood or physical (58) : smokers who used cigarettes to self-medicate. Depressive symptoms were measured using a scale that asked how often participants felt too tired to do things; had (59) going to sleep or staying asleep; felt unhappy, sad, or depressed; felt hopeless about the future; felt anxious or tense; and worried too much about things. "Smokers who used cigarettes as mood (60) had higher risks of elevated (提升) depressive symptoms (61) teens who had never smoked, " says co-researcher Jennifer O'Loughlin, a professor at the University of Montreal Department of Social and Preventive Medicine. "Our study found that teen smokers who reported emotional benefits from smoking are (62) higher risk of developing depressive symptoms. "The (63) between depression and smoking exists (64) among teens that use cigarettes to feel better. "It's (65) to emphasize that depressive symptom scores were higher among teenagers who reported emotional benefits from smoking after they began to smoke, "says Dr. Chaiton.
单选题Cement was
seldom
used in buildings of the Middle Ages.
单选题Hersheypark began Uintegrating/U recycling into its public information programs more than five years ago.
单选题I realized to my {{U}}horror{{/U}} that I had forgotten the present.
单选题Young Adults Who Exercise Get Higher IQ Scores
Young adults who are fit have a higher IQ and are more likely to go on to university, reveals a major new study
1
out at the Sahlgrenska Academy and Sahlgrenska University Hospital.
The results were recently published in the Proceedings of the National Academy of Sciences (PNAS). The study
2
1.2 million Swedish men doing military service who were born between 1950 and 1976. The research group analyzed the
3
of both physical and IQ tests the youngsters took right after they started serving the army.
The study shows a clear link
4
good physical fitness and better results for the IQ test. The strongest links are for
5
thinking and verbal comprehension. But it is only fitness that plays a
6
in the results for the IQ test, and not strength. "Being fit means that you also have good heart and lung
7
and that your brain gets plenty of oxygen," says Michael Nilsson, professor at the Sahlgrenska Academy and chief physician at the Sahlgrenska University Hospital. "This may be one of the reasons why we can see a clear link with fitness, but not with muscular
8
. We are also seeing that there are growth factors that are important."
By analyzing data for twins, the researchers have been
9
to determine that it is primarily environmental factors and not genes that
10
the link between fitness and a higher IQ.
"We have also shown that those youngsters who
11
their physical fitness between the ages of 15 and 18 increase their performance," says Mafia berg, researcher at the Sahlgrenska Academy and physician at a health centre. "This being the case, physical education is a
12
that has an important place in schools, and is an absolute must
13
we want to do well in math and other theoretical subjects."
The researchers have also compared the results from fitness tests during national service
14
the socioeconomic status of the men later in life. Those who were fit at 18 were more
15
to go into higher education, and many secured more qualified jobs.
单选题Tom"s wife succeeded in
persuading
him into giving up smoking.
单选题UApart from/U one or two minor mistakes, I thought the concert was excellent.
单选题People have to change their jobs from time to time.
单选题The word "vandalizing" in Line 17 means
单选题She is a
highly
successful teacher.
单选题The
caliber
of F. Scott Fitzgerald"s writing was reassessed by literary critics in the 1950"s.
单选题These are their{{U}} motives{{/U}} for doing it-
单选题Crayfish, small freshwater crustacean similar to lobsters, are consumed by inhabitants of the Mississippi River Basin.
单选题Accidents caused by car doors being opened into the path of oncoming vehicles or cyclists are common in cities. But these incidents could become a thing of the past, if doors that react to potential impacts catch on. …… The current prototype looks like a normal ear door, but an extra metal bar runs through its centre and connects to the ear's flame between the hinges. In normal mode, the bar moves freely and doesn't affect the door's movement. However, if sensors detect a nearby obstacle at the same time as an accelerometer (加速度讲; 加速仪) detects an attempt to open the door, the door's swing is restricted by a linear motor attached to the bar. The design of the intelligent door is designed in such a way that the door becomes hard to open whenA. there is an obstacle nearby.B. there is something wrong with the accelerometer.C. there is something wrong with the sensors.D. there is an accelerometer in the car.
单选题There should be laws that prohibit smoking around children. A. forbid B. advocate C. inherit D. withdraw