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　　In the atmosphere, carbon dioxide acts rather like a one-way mirror or the glass in the roof of a greenhouse which allows the sun's rays to enter but prevents the heat from escaping．

　　According to a weather expert' s prediction, the atmosphere will be 3℃warmer in the year 2050 than it is today, if man continues to burn fuels at the present rate．If this warming up took place, the ice caps in the poles would begin to melt, thus raising sea level several metres and severely flooding coastal cities．Also, the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere(北半球), possibly resulting in an alteration of the earth's chief food growing zones．

　　In the past, concern about a man-made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet．But the weather experts are now paying more attention to West Antarctic, which may be affected by only a few degrees of warming, in other words, by a warming on the scale that will possibly take place in the next fifty years from the burning of fuels．

　　Satellite pictures show that large areas of Antarctic ice are already disappearing．The evidence available suggests that a warming has taken place．This fits the theory that carbon dioxide warms the earth．

　　However, most of the fuel is burnt in the northern hemisphere, where temperatures seem to be falling．Scientists conclude , therefore, that up to now natural influences on the weather have gone beyond those caused by man．The question is：Which natural cause has most effect on the weather?

　　One possibility is the variable behavior of the sun．Astronomers at one research station have studied the hot spots and "cold" spots(that is, the relatively less hot spots)on the sun．As the sun rotates(使旋转), every 27.5 days, it presents hotter or "colder" faces to the earth, and different aspects to different parts of the earth．This seems to have a considerable effect on the distribution of the earth's atmospheric pressure, and consequently on wind circulation．The sun is also changeable over a long term：its heat output goes up and down in cycles, the latest trend being downward．

　　Scientists are now finding shared relations between models of solar weather interactions and the actual climate over many thousands of years, including the last Ice Age．The problem is that the models are predicting that the world should be entering a new Ice Age and it is not．One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia(惯性)of the earth's climate．If this is right, the warming effect of carbon dioxide might thus be serving as a useful opposed balance to the sun's fading heat．

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　　Remember how great exercise was when you were a little kid?Back then, racing around the playground or skipping rope for hours, you weren't thinking fitness, you were thinking entertainment．But in this age of high-tech home equipment and underused gym memberships, the simple joy of jumping rope has been forgotten, Rediscovering it will give you a total-body exercise you can find．

　　Although considered an excellent form of exercise, jumping rope has never gained widespread acceptance because of two fundamental reasons．First, most people recognize jumping rope as an excellent form of cardiovascular(心血管的)exercise, but they also believe that it is simply too difficult．In other words, they don't think they'll be able to continue jumping for the near 20 minutes that it takes to achieve a beneficial physical outcome．Second, many view it as somewhat boring and overly repetitive not as something fun or enjoyable．

　　As a matter of fact, jumping rope can be great fun if you find a proper way to practice it．Instead of doing the usual two-foot bounce over and over again, people good at rope-jumping often change their pattern every 10 or 20 jumps．A single bounce, a double-bounce, a skip, a knee-up, side swings, as well as a variety of other easy-to-learn free-style rope-jumping．

　　Now researchers are learning that jumping rope also prepares the brain for learning．It is an exercise allowing both brain hemispheres to perform in parallel to each other．In short, jumping rope can be a life-long activity requiring little equipment, time and space, yet leading to a much healthier life．

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　　Since we are social beings, the quality of our lives depends in large measure on our interpersonal relationships．One strength of the human condition is our possibility to give and receive support from one another under stressful conditions．Social support makes up of the exchange of resources among people based on their interpersonal ties．Those of us with strong support systems appear better able to cope with major life changes and daily hassles(困难)．People with strong social ties live longer and have better health than those without such ties．Studies over types of illnesses, from depression to heart disease, show that the presence of social support helps people fend off(挡开)illness, and the absence of such support makes poor health more likely．

　　Social support cushions stress in a number of ways．First, friends, relatives and co-workers may let us know that they value us．Our self-respect is strengthened when we feel accepted by others in spite of our faults and difficulties．Second, other people often provide us with informational support．They help us to define and understand our problems and find solutions to them．Third, we typically find social companionship supportive．Taking part in free-time activities with others helps us to meet our social needs while at the same time distracting(转移注意力)us from our worries and troubles．Finally, other people may give us instrumental support－money aid ,material resources, and needed services－that reduces stress by helping us resolve and cope with our problems．

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　　Is the recession(经济衰退)destroying Americans'health in addition to their incomes?

　　“Yes, for some”, says a recent study led by health economists at Yale University, which found that job losses can make the fat fatter and the drinkers drunkards．

　　The study focused on workers above 50, who have been figuring prominently among the laid-off in recent decades and make up an older group for whom heavy eating and drinking is more likely to have serious health consequences．

　　For this group, results showed the body mass of the average laid-off food-lover increasing by the equivalent of more than seven pounds for a 5-foot, 10-inch man weighing 180 pounds during unemployment．Similarly, frequent drinkers on average doubled their daily alcohol intake after losing their jobs and before finding another one．

　　Lay-offs don't necessarily send people reaching for the beer bottle or digging into the potato-chip bag, explain the authors．In some cases, they make people healthier by reducing the income they would otherwise spend on alcohol and junk food or allowing more time for physical exercise and outdoor activities．

　　In fact, research focusing on the impact of layoffs and recessions on health has provided no evidence that the health of the average American declines as a result of acquiring unhealthy, stress-induced habits．

　　“While there is evidence from animal, preclinical and clinical studies that stress leads to overeating and excessive drinking, economic research on stress suggests substantial heterogeneity(极大的差异性)．”write the authors．In other words, losing one's job can be more or less stressful for different people and different bodies cope differently with stress-induced behavior．

　　But Yale's William T．Gallo, Padmaja Ayyagari, Jason M．Fletcher and Jody L．Sindelar, and Partha Deb, from the City University of New York, found that layoffs among older workers tend to harm the health of those with a pre-existing unhealthy fondness for food and drink．

　　Across all age groups, widespread loss of employer-provided health coverage is another way in which this recession is destroying the health of laid-off Americans, as many decide to “go without treatment or tests,” the Journal reports．

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　　You're rushing to work and a man ahead of you collapses on the sidewalk．Do you stop to help?In a study of by-standers, it was found that some people avert their gaze and keep on walking rather than stop and get involved．

　　“There is a tendency to decide that no action is needed．” says a psychologist．“The first thoughts that pop into your mind often keep you from offering help．In order to take action, you have to work against them．” Here are some common thoughts that might prevent you from helping：

　　●Why should I be the one?I'm probably not the most competent person in this crowd．You might think someone older or with more medical knowledge should offer assistance．

　　●What if he doesn't really need my help?The fear of embarrassment is powerful; no one wants to risk looking foolish in front of others．

　　●No one else looks concerned-this must not be a problem．We can follow the people around us- but most people tend to hold back their emotions in public．

　　“If you spot trouble and find yourself explaining inaction, force yourself to stop and evaluate the situation instead of walking on,” says the psychologist．“Then retry to involve other people; you don't have to take on the entire responsibility of being helpful．Sometimes it's just a matter of turning to the person next to you and saying, ‘It looks like we should do something．' Or asking someone if an ambulance has been called and, if not, to call for one．Once you take action, most people will follow you．”

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　　You might say that one reason Barack Obama is president of the US is because he knows how to give a good speech．

　　Since 2004, Obama has written and delivered thousands of speeches．These are usually praised for two reasons：he treats the audiences like intelligent adults, and he is able to express complicated ideas in a straightforward, natural way．

　　Before becoming president, Obama was a lawyer, a college professor, and a successful writer-his two memories have become best-sellers．The skills he needed to succeed in his previous jobs have also contributed to his success as a speechmaker．

　　What's more, he has some secret weapons．

　　Teleprompter：Obama doesn't go anywhere without his Teleprompter．The textbook-sized panes of glass holding the president's prepared remarks follow him wherever he goes to speak．

　　Writing team：Obama has a team of people who write his speeches．The writers chat with Obama for hours about what he wants to say．They listen to recordings of past presidential addresses and seek advice from advisers．Obama usually edits and rewrites the drafts several times．

　　Tricks for lighthearted speeches：

　　Make fun of the guests：Obama starts his speech by gently teasing his guests．His opening lines grab the audience's attention while giving them an opportunity to relax and laugh at themselves and each other．

　　Make fun of yourself：A good rule for speechmakers：If you're going to make a joke about someone else, be sure to make one about yourself, too．Obama mocks his own poor choices for filling the position of Commerce Secretary, saying, “No president in history has ever named three Commerce Secretaries this quickly．” In fact, his first two nominees(被提名人)for the position withdrew their names for different reasons．In a process that had otherwise gone smoothly, the Obama Administration was tripped up by the problem of filling the Commerce seat．

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　　Forget Miami, Los Angeles and New York．The next big Latin music explosion is on its way in secondary markets across the United States, and the numbers are there to back it up．Among all genres(种类),Latin music was the only one registering growth in 2005．From tiny Vero Beach in northern Florida to Des Moines, Iowa, in the heart of the Midwest, from Charlotte, N．C．to Salt Lake City, Latin music sales are skyrocketing．

　　Wilson says there are two major reasons for the increase．One is simply the Hispanic(说西班牙语国家的)population's increase in specific areas, which encourages stores to carry Latin product for the first time．Second, and perhaps more important, is the fact that major companies－whether dealing in music or not－are addressing the Latin consumer at a corporate(公司的)level, creating Latin departments and hiring Latin ad agencies．One of Handleman's suburban Detroit stores, for example, has expanded its Latin section four times in the last two years．Cities like Milwaukee and Des Moines are now stocking Latin product．

　　Besides, it also results from economic development．It goes something like this：More often than not, a city or country with a seeming important Hispanic population will suddenly expand its construction or offer affordable housing to those working in larger, neighboring cities．This attracts lower-income workers, many of whom are Latin．Small shops and groceries begin to stock a small selection of music．When the Latin population numbers reach a critical mass, the local mass merchant, if there is one, begins stocking the product．Sooner or later, a local radio station follows; first AM, then FM．Sometimes it's a cable TV show or a small TV station．

　　Of course, there are other driving forces that should not be forgotten, for example, regional Mexican music．

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　　When writing for A Journal for Physical and Sport Educators, authors should consider that the journal's aim is to provide information to our physical educators and coaches that will help them in their daily work．We look for articles that find out a problem and offer concrete, step-by-step solutions, or describe " best practices" for typical coach activities or responsibilities．A Journal for Physical and Sport Educators does not publish research studies or theoretical treatment of topics, but does welcome compositions that explain how research or theory can be put into practice．Authors are encouraged to review recent issues of A Journal for Physical and Sport Educators for content and form before presenting, or contact the editor for further information．

　　Write in an informal, conversational and straightforward tone, and minimize formal or technical language．Ideas should be clear, simple and logical．Give practical examples, and when possible, include photos, tables or charts to explain your ideas．Have a partner review your article for content and clarity of presentation before you send it out．

　　All accepted articles are edited by the editors．Experts in fields related to sport and physical education will be invited to submit articles on selected topics．However, solicited articles are subject(经受)to the same review process, and publication is based on positive recommendations by reviewers．

　　A Journal for Physical and Sport Educators welcomes photos for publication．Photos for covers must be high quality, glossy color photos in vertical(垂直)format．If digital, photos must be no less than 1200 DPI．Photos with articles must be high quality black/white or color glossy．If digital, photos must be at least 300 DPI．

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　　He was killed 45 years ago．Since then his memory has been clouded by dark tales of affairs with the likes of Marilyn Monroe(玛莉莲·梦露), and links with the Mafia(黑手党)．

　　But the myth(神话)of John F．Kennedy, the 35th President of the US, will not disappear．As America marked the anniversary of his death in Dallas, Texas ,on November 22,1963 ,questions were still being asked．

　　The official conclusion was that Lee Harvey Oswald, who worked at a Dallas book storehouse, murdered Kennedy．But all kinds of other ideas have been put forward as to what happened and why．

　　Some people believe Oswald was a madman, who spent some time in Russia and was an admirer of Fidel Castro, president of Cuba．It is said he was inspired by James Bond's spy novels and killed Kennedy as a gift for Castro．

　　But Oswald's brother thought he was a sad and lonely man who murdered the president to get attention and show off his shooting skills．

　　Meanwhile, some experts said that Oswald was really aiming for Texas Governor John Connally．He was said to have been angry with Connally, who was also secretary of the navy, over how he had been forced to leave the service．

　　A large number of people think the truth has been covered up on purpose ;even now, surveys show that more than half of Americans believe that Oswald was not working alone．An investigation(调查)found that four shots were fired ,with one shot coming from the building that Oswald was in．

　　But two days after the murder, Oswald himself was killed by Jack Rubinstein, a night-club owner．Rubinstein had Mafia connections and this has led to the theory that they were actually responsible for killing Kennedy．

　　Lyndon Johnson, who became president after Kennedy, has also been accused of being behind it all．According to reports, Johnson was sworn in(宣誓就职)even before Kennedy's death was announced．"We have a really tough decision that we don't want to face．There was a conspiracy(合谋)and people want an answer, " said Barr McClellan, who has written a book about the murder．

　　"The myth is very powerful," said Robert Dallek, a historian at Boston University, who has just published a book about Kennedy．"He was the first president to appear on television．He is frozen in our minds aged 46, forever young, energetic and charming．"

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　　I stole your dog today．No, I didn't set a foot on your house, but from the condition of your dog, I can imagine what it looks like, the word "rubbish " comes to mind．

　　I found her along a road, with a heavy chain wrapped around her neck, still attached to rotten boards from her doghouse．Not only did I know that most of the town people had already ignored her, judging by where I found her, but I knew that if she had gotten into the woods, the "cross" that she dragged behind her would have wrapped around a tree until starvation or thirst killed her．

　　She has a beautiful name now．Already in the first week she has come to look more like she should．Her eyes sparkle and she has learned to wag her tail in greeting．She has stopped flinching(畏缩)when I make a sudden movement, because she knows now that I won't beat her, in fact, she rarely leaves my side．She's even become brave enough to bark at a cat and today I watched from the window as she attempted to play with the other dogs．No, it's clear she does not miss you or her former life on a chain．

　　It's not clear yet whether she'll remain here or whether I'll find her a loving home where she can count on more individual attention than I can give her, but one thing is certain ,this is one bit of stolen "property" who is never returning to you, so sue me, accuse me, plead with the courts that she is rightfully yours．I'm convinced this is the best " crime" I've ever committed．Hardly anything has pleased me more than the day I stole your dog．I need only look into her beautiful brown eyes to know that she'd defend my decision with her life．If we have one prayer, it is that you will not replace her, and if we have one special day to celebrate together, it is the day I stole your dog and the day she stole my heart．