Houses fall down. Trees fall over. Large holes form in the ground. Could Alaska be sinking? That's what some villagers in Alaska have been asking themselves recently and scientists think they know why. Warmer temperatures may be causing Alaska's frozen ground to thaw (解冻).

    About 85 percent of Alaska's land surface has permafrost (永久冻结带). Permafrost supports the ground above it—including trees, houses, and roads. But why is the permafrost thawing?

    Some scientists say that human-caused pollution is leading to global warming. And most scientists agree that Alaska has been getting warmer. They say that the warmer temperature is causing permafrost to thaw in some areas. The thawing permafrost can cause problems for people, plants, and animals.

    The collapsing (倒塌) is a problem in the villages in Alaska which are built on permafrost, and some of them may have to move to safer ground, where there is no permafrost.

    The Alaskan town of Glennallen saw its old post office collapse. And, according to James Walters, a permafrost expert at the University of Northern Iowa, house-moving companies have been very busy.

    “Melting permafrost can also destroy trees and forests,” Walters said. “When holes in the ground form, trees fall into them and die. This could turn a forest into a swamp (沼泽), and animals which need the forests will have to move elsewhere.”

    “The melting could cause severe problems.” Walters says, “This could take hundreds of years, but in the end Alaska will look quite different from what it looks like now.”

    A warm drink of milk before bed has long been the best choice for those wanting a good night's sleep. But now a study has found it really does help people nod off（打瞌睡）—if it is milked from a cow at night.

    Researchers have discovered that “night milk” contains more melatonin(褪黑激素), which has been proven to help people feel sleepy and reduce anxiety（焦虑）.The study, by researchers from Seoul, South Korea, involved mice being fed with dried milk powder（奶粉） made from cows milked both during the day and at night. Those given night milk, which contained 10 times the amount of melatonin, were less active and less anxious than those fed with the milk collected during daytime, according to the study published in The Journal of Medicinal Food.

    Night milk quickened the start of sleep and caused the mice to sleep longer.

    While the effect of cow milk harvested at different time has not been tested on humans up to now, taking melatonin drugs has been suggested to those who have trouble falling asleep at night.

    Previous （以前的）studies have also showed that milk can be excellent for helping sleep because of the calcium content, which helps people to relax.

    “Clothes Swapping”has become an increasingly popular activity for women in the United States. The women can give away unwanted clothing at a clothes swap event and get something different in return.

    Recently about 300 women went to a clothes swap at a high school in Springfield, Virginia. It was the largest crowd ever for the area's popular clothing-swapping group.

    Daphne Steinberg was having a good day.“For anyone who knows Ann Taylor LOFT, Ann Taylor is a really nice women's designer and I will totally wear this to work. So I love that, I love that I can equip myself for work, have a good time in doing it, not totally bankrupt myself.”

Sandy Van Dusen likes the idea that clothes are finding new homes instead of being thrown away. “Because it helps to keep the Earth green. There's no point in my opinion in continuing to buy new clothes when we can reuse what's already here. Give it a new home— let somebody else love what you used to love and no longer love.”

    Kim Pratt organized the clothing-swapping event in Springfield. She also organized a money-raising activity for the high school's debate team. It is one of several ways that her group gives to charitable causes. Another is by donating all of the“un-swapped” clothing to shelters for victims of domestic violence.

    “I started doing this four years ago, and we've been doing it for four years, getting bigger and bigger each time we have a swap.”

    She used the social media website meetup.com to help publicize the events. The website has helped her group grow from 30 members to 1,300. Mrs.Pratt says most of the members respect the clothing swap rules. But she say competition for desirable fashion can be strong.

    “We have to tell people sometimes not to hover over the new people coming in with their clothing. As they put it out, some people tend to grab the stuff right out of their hands and it becomes like a free-for-all. We try to avoid that as much as possible.”

    When the fork was stolen off Bart Michiels's mountain bike last summer, he wheeled it nearly three miles from his home in Chelsea to Frank's Bike Shop on the eastern end of Grand Street.

Mr. Michiels passed many other bike shops along the way, including one that offers free coffee. But for 20 years, he has remained devoted(忠实的) to Frank's. “Frank's the man,” he said of Frank Arroyo, the owner. “I don't care where he is in the city — I'll go.”

    Mr. Michiels doesn't have to worry about Mr. Arroyo's relocating (搬迁). The shop has stayed on the Lower East Side of Manhattan for 40 years.

    After Mr. Michiels left, Marvin Priess arrived. A professor of chemistry and math, Mr. Priess wheeled in the Ross 18-speed he had bought at Frank's in 1978 and still rides today, at age 68. Mr. Priess said that over the years, every single part of it that couldn't be repaired had been replaced, sometimes more than once, at Frank's. Customers don't come for the ambience(环境). It's crowded and dirty; buckets of parts and boxes of training wheels line the entryway.

    The store is filled with about 500 bikes and you will find Mr. Arroyo, 72, six days a week. He has been in the bike business since age 14. Born and raised on the Lower East Side, he has employed and taught many young people in the neighborhood. He is also willing to repair bikes in any condition, as well as his neighbors' walkers and wheelchairs.

    English Epps, a lawyer, needed a new seat; his had been stolen. “I've been coming here since I was in the third grade,” he said, adding: “There's a new bike shop on Delancey Street, but everybody comes here.”

    Why do some people live to be older than others? You know the standard explanations: keeping a moderate diet, engaging in regular exercise, etc. But what effect does your personality have on your longevity（长寿）? Do some kinds of personalities lead to longer lives? A new study in the Journal of the American Geriatrics Society looked at this question by examining the personality characteristics of 246 children of people who had lived to be at least 100.

    The study shows that those living the longest are more outgoing, more active and less neurotic (神经质的) than other people. Long-living women are also more likely to be sympathetic and cooperative than women with a normal life span. These findings are in agreement with what you would expect from the evolutionary theory: those who like to make friends and help others can gather enough resources to make it through tough times. Interestingly, however, other characteristics that you might consider advantageous had no impact on whether study participants were likely to live longer. Those who were more self-disciplined, for instance, were no more likely to live to be very old. Also, being open to new ideas had no relationship to long life, which might explain all those bad-tempered old people who are fixed in their ways.

    Whether you can successfully change your personality as an adult is the subject of a longstanding psychological debate. But the new paper suggests that if you want long life, you should strive to be as outgoing as possible.

    Unfortunately, another recent study shows that your mother's personality may also help determine your longevity. That study looked at nearly 28,000 Norwegian mothers and found that those moms who were more anxious, depressed and angry were more likely to feed their kids unhealthy diets. Patterns of childhood eating can be hard to break when we're adults, which may mean that kids of depressed moms end up dying younger. Personality isn't destiny, and everyone knows that individuals can learn to change. But both studies show that long life isn't just a matter of your physical health but of your mental health.

    Hotshot jet pilots are no match for cliff swallows. The birds rocket over bridges and skim over lakes, rushing forward at accelerations that would knock an Air Force. By tracking these contests with high-speed cameras, a new study gives the first, in-depth peek into avian aerodynamics (鸟类空气力学) in the wild. "The findings may even provide insight into how to design better micro air vehicles-tiny drones. This technology will be brilliantly useful," says biomechanics expert Jim Usherwood of the United Kingdom's Royal Veterinary College in Hatfield. "High-resolution field studies like this have never been done before for birds."

    For cliff swallows, the trouble starts when they return from wintering in South America to their summer homes in North America. After arrival, they seek out their old mud nests—usually located under concrete bridges and freeways-and start rebuilding their homes. But rather than hunt down a fresh supply of mud, some swallows prefer stealing supplies from their more hardworking neighbors. Others take things further and will even lay an egg or two in their neighbor's nest before taking off.

    Battles in the air follow if the invaders are caught in the act, and a new study takes advantage of these fights to learn how birds perform high-speed maneuvers (演习). The team placed three cameras along a North Carolina lake crossed by a highway bridge that houses several cliff swallow nests and waited for the battles to commence.

The team was surprised to learn that most of the time, chasers copied the move of fleeing invaders. Swallows also pull very hard turns to escape an enemy, with one extreme case reaching 7.8 gravity. Fighter pilots usually pass out at about 5 or 6 gravity, which is why these experiments have earned interest, and partial funding, from the Office of Naval Research. The Navy may use the findings to build better guidance systems for micro air vehicles. However, the swallows' biomechanics are complex, and now the team is simply trying to collect a few tricks.