To prevent the deserts coming near, China has planted billions of trees—to replace destroyed forests and as barriers against the sand. This isn't a cure, though, say experts, as thirsty trees can make the problem worse by taking in groundwater.

    “Planting tress is one way, but it isn't that simple. It doesn't solve the basic issue of water resources,” says Wu Bo, a professor. “We need to calculate how much water the trees will absorb, or else it could have a negative effect.”

    Villagers in Zhengxin have taken on this challenge, with limited success. When the irrigation channels began to run dry, Lu Xianglin switched from wheat to cotton on his land. He also planted trees to protect his fields from sandstorms. He says he still gets good yields（产量） using flood irrigation and earns a good income for his family.

    Other farmers haven't stuck it out（坚持到底）: about one in three have left Zhengxin in the past 10 years after their wheat crops died. Young people who can find jobs in the towns rarely return.

    Last week, Mr Lu joined the other men in his village on a government-arranged trip to see the land that has been set aside for their relocation, nearly 40 miles to the south. The next day, he was back, shaking his head at the plan. The idea of uprooting his family troubles him, as does the idea of giving up the land that fed his forefathers. He prefers to stay and keep up the fight.

    “With enough water, this problem can be solved,” Lu says. “We can plant trees and grass, and they will grow bigger. That will stop the desert.”

    Experts say that farmers could switch to drip irrigation （滴灌）to lessen their water intake for growing crops. Elsewhere in the region, farmers have built brick greenhouses as part of a plan to grow vegetables using less water. Roadside signs urge farmers to “Save Water, Protect the Environment”.

    A German study suggests that people who were too optimistic about their future actually faced greater risk of disability or death within 10 years than those pessimists who expected their future to be worse.

    The paper, published this March in Psychology and Aging, examined health and welfare surveys from roughly 40,000 Germans between ages 18 and 96. The surveys were conducted every year from 1993 to 2003.

    Survey respondents (受访者) were asked to estimate their present and future life satisfaction on a scale of 0 to 10, among other questions.

    The researchers found that young adults (age 18 to 39) routinely overestimated their future life satisfaction, while middle-aged adults (age 40 to 64) more accurately predicted how they would feel in the future. Adults of 65 and older, however, were far more likely to underestimate their future life satisfaction. Not only did they feel more satisfied than they thought they would, the older pessimists seemed to suffer a lower ratio (比率) of disability and death for the study period.

     “We observed that being too optimistic in predicting a better future than actually observed was associated with a greater risk of disability and a greater risk of death within the following decade,” wrote Frieder R. Lang, a professor at the University of Erlangen-Nuremberg.

    Lang and his colleagues believed that people who were pessimistic about their future may be more careful about their actions than people who expected a rosy future.

     “Seeing a dark future may encourage positive evaluations of the actual self and may contribute to taking improved precautions (预防措施),” the authors wrote.

    Surprisingly, compared with those in poor health or who had low incomes, respondents who enjoyed good health or income were associated with expecting a greater decline. Also, the researchers said that higher income was related to a greater risk of disability.

    The authors of the study noted that there were limitations to their conclusions. Illness, medical treatment and personal loss could also have driven health outcomes.

    However, the researchers said a pattern was clear. “We found that from early to late adulthood, individuals adapt their expectations of future life satisfaction from optimistic, to accurate, to pessimistic,” the authors concluded.

    Do you love holidays but hate the increase weight that follows? You are not alone.

    Holidays are happy days with pleasure and delicious foods. Many people, however, are worried about the weight that comes along with the delicious foods.

     With proper planning, it is possible to control your weight. The idea is to enjoy the holidays but not to eat too much. You don't have to turn away from the foods that you enjoy. The following suggestions may be of some help to you.

    Do not miss meals. Before you leave home for a feast, have a small, low-fat snack. This may help to keep you from getting too excited before delicious foods.

    Begin with clear soup, fruit or vegetables. A large glass of water before you eat may help you feel full. Use a small plate; a large plate will encourage you to have more than enough.

    Better not have high-fat foods. Dishes that look oily or creamy have much fat in them.

    Choose lean meat. Fill your plate with salad and green vegetables.

    If you have a sweet tooth, try mints and fruit. They don't have fat content as cream and chocolate.

    Don't let exercise take a break during the holidays. A 20-minute walk after a meal can help burn off excess calories.

    Bees in a colony work with each other to gather food, and they try to find the most nectar (花蜜)in the least amount of time possible. A small number of bees work as searchers, but when a good flower patch (花丛) is found, how do they tell other bees where to find it?

    Bees communicate flower location using special dances inside the hive, where bees live. One bee dances while the other bees watch. The dancing bee smells like the flower patch, and also gives the watching bees a taste of the nectar she has gathered. Smell and taste helps other bees find the correct flower patch. Bees use two different kinds of dances to communicate information: the waggle (摇摆) dance and the circle dance.

    Waggle dance

    The waggle dance tells the watching bees two things about a flower patch's location: the distance and the direction away from the hive.

A. Distance

    The dancing bee waggles back and forth as she moves forward in a straight line, then circlesaround to repeat the dance. The length of the middle line, called the waggle run, shows roughly how far it is to the flower patch.

B. Direction

    Bees know which way is up and which way is down inside their hive, and they use this to show direction. How? Bees dance with the waggle run at a specific angle away from straight up. Outside the hive, bees look at the position of the sun, and fly at the same angle away from the sun.

    Circle dance

    The circle dance tells the watching bees only one thing about the flower patch's location: that it is somewhere close to the hive.

    In this dance, the bee walks in a circle, turns around, then walks the same circle in the opposite direction. Sometimes, the bee includes a little waggle as she's turning around. The duration of this waggle is thought to indicate the quality of the flower patch.

Preparing Cities for Robot Cars

    The possibility of self-driving robot cars has often seemed like a futurist's dream, years away from materializing in the real world. Well, the future is apparently now. The California Department of Motor Vehicles began giving permits in April for companies to test truly self-driving cars on public roads. The state also cleared the way for companies to sell or rent out self-driving cars, and for companies to operate driverless taxi services. California, it should be noted, isn't leading the way here. Companies have been testing their vehicles in cities across the country. It's hard to predict when driverless cars will be everywhere on our roads. But however long it takes, the technology has the potential to change our transportation systems and our cities, for better or for worse, depending on how the transformation is regulated.

    While much of the debate so far has been focused on the safety of driverless cars (and rightfully so), policymakers also should be talking about how self-driving vehicles can help reduce traffic jams, cut emissions (排放) and offer more convenient, affordable mobility options. The arrival of driverless vehicles is a chance to make sure that those vehicles are environmentally friendly and more shared.

    Do we want to copy—or even worsen—the traffic of today with driverless cars? Imagine a future where most adults own individual self-driving vehicles. They tolerate long, slow journeys to and from work on packed highways because they can work, entertain themselves or sleep on the ride, which encourages urban spread. They take their driverless car to an appointment and set the empty vehicle to circle the building to avoid paying for parking. Instead of walking a few blocks to pick up a child or the dry cleaning, they send the self-driving minibus. The convenience even leads fewer people to take public transport—an unwelcome side effect researchers have already found in ride-hailing (叫车) services.

    A study from the University of California at Davis suggested that replacing petrol-powered private cars worldwide with electric, self-driving and shared systems could reduce carbon emissions from transportation 80% and cut the cost of transportation infrastructure (基础设施) and operations 40% by 2050. Fewer emissions and cheaper travel sound pretty appealing. The first commercially available driverless cars will almost certainly be fielded by ride-hailing services, considering the cost of self-driving technology as well as liability and maintenance issues (责任与维护问题). But driverless car ownership could increase as the prices drop and more people become comfortable with the technology.

    Policymakers should start thinking now about how to make sure the appearance of driverless vehicles doesn't extend the worst aspects of the car-controlled transportation system we have today. The coming technological advancement presents a chance for cities and states to develop transportation systems designed to move more people, and more affordably. The car of the future is coming. We just have to plan for it.