For teenagers, it's great fun to explore new places and it feels like an adventure, even when you know you're not the first to have been there. But to make sure not to get lost or waste time going round in circles, the following tips may be helpful.

    ◆Do the map reading if you're being driven somewhere. It'll be easier if you keep the map following the direction you are traveling in. Keep looking ahead so that you can give the driver lots of warning before having to make a turn, or you'll have to move to the back seat.

    ◆Get a group of friends together and go exploring. You'll need a good map, a compass, a raincoat, a cell phone to call for help in case you get lost, and a bit of spare cash for emergencies. Tell someone where you're going before you set out and let them know what time you expect to be back. The purpose of the activity is in not getting lost, not in seeing how fast you can go, so always stick together, waiting for slower friends to catch up.

    ◆See if your school or a club organizes orienteering(越野识途比赛) activities, in which you need a map and a compass to find your way. This can be done as a sport, with teams trying to find the way from A to B(and B to C, etc. ) in the fastest time, or simply as a spare-time activity. It enables you to be familiar with the use of maps and compass and gain some special skills. In some way, it's not only good fun, but also a great way to keep fit.

    There was good news last week for people who struggle to get eight hours of sleep a night: they may not need so much shut-eye after all.

    Researchers from UCLA and elsewhere looked at sleep habits of remote hunter-gatherers in Tanzania, Namibia and Bolivia — groups with pre-industrial lifestyles whose sleep patterns are believed to reflect those of ancient humans. The researchers found that, on average, members of each group sleep a bit less than six and a half hours a night.

    The study, published in the academic journal Current Biology, indicates that “natural” sleep is less than eight hours a night and that modern society's numerous electronic distractions (分心) aren't necessarily to blame for people getting just six or seven hours of sleep.

    “The story that often gets out is that if you sleep for less than seven hours, you're going to die early,” he told me. “That's not true.”

    Yet Americans are addicted to getting more sleep — and on turning to medical shortcuts to help them.

    According to the Centers for Disease Control, as many as 70 million U.S. adults suffer from sleep disorders or sleeplessness. Only a third of Americans get the government's recommended seven to nine hours of sleep a night.

    About 9 million American adults use sleeping pills to help get a good night's rest, the CDC found. Siegel said the number of people relying on medicines “has gone up rather rapidly since then.”

    Industry consulting firm Global Data estimates that worldwide sales for sleeplessness medicines will run about $1.4 billion next year and reach $1.8 billion by 2023, recovering from lower sales in recent years because of cheaper generics(仿制药) hitting the market.

    Dr. Roy Artal, a sleep specialist in West Los Angeles, said it's understandable that busy people in today's go-go world would turn to medicines to speed up the sleep process. But all they're doing is building a reliance on powerful drugs for relatively little improvement.

    “There's no magic pill that makes us sleep when we want and wake up when we want,” Artal said. “The effects of sleeping pills tend to be modest.”

    He and other experts say the answer to sleeplessness isn't to be found in a pill bottle. It's in what's called “sleep hygiene (保健).”

    THURSDAY, July 9 (Health Day News) — A new study that found that a lower calorie diet slowed the aging process in monkeys could be the best proof yet that restricted diets might do the same for humans.

    “The big question in aging research is, ‘Will caloric restriction in species closely related to humans slow aging？'” said Richard Weindruch, senior author of a paper appearing in the July 10 issue of Science. This is the first clear demonstration that, in a primate species, we' re inducing a slowdown of the aging process — showing increased survival, resistance to disease, less brain atrophy and less muscle loss.

    “This predicts humans would respond similarly，” added Weindruch, professor of medicine at the University of Wisconsin and an investigator at the Veterans Hospital in Madison. Another expert noted that, despite some highly publicized studies in certain species, the link between restricted eating and longer lifespan has been far from proven.

    “The idea that dietary restriction extends lifespan in all species is not true. Many strains of rats and mice do not respond. In some strains, it's actually deleterious,” explained Felipe Sierra, director of the biology of aging program at the US National Institute on Aging (NIA), which supported the new study. “The fact that it doesn't work in some mice but it does seem to work in monkeys is surprising and it gives us hope.”

    But there's a larger question: how to change humans' increasingly careless eating habits. “This finding doesn't give me hope that humans are going to go into dietary restriction,” added Marianne Grant, a registered dietitian at Texas A&M Health Science Center Coastal Bend Health Education Center in Corpus Christi.

    Dry Ice is a unique substance which has many uses. Essentially, dry ice is frozen CO2. The first report of what we now call dry ice came from the French chemist Charles Thilorier in 1834. In 1924, the Drylee Corporation of America named the solid form of CO2 as "Dry Ice", which is what it is popularly called today.

    At normal atmospheric pressure, CO2changes directly from solid to gas. It skips the liquid phase（阶段）which makes regular ice wet. Frozen CO2is also much colder than regular ice. But regular ice freezes at 32 degrees Fahrenheit, CO2 changes from gas to solid at -109.3 degrees Fahrenheit. This extremely cold temperature makes it very dangerous to handle with bare hands. It can cause frostbite in a very short period of time.

    Dry ice has been used for a variety of purposes throughout the past century. Its primary use is to refrigerate food when electrical refrigeration isn't available. Through the process of sublimation (when CO2 changes from solid to gas), it can maintain cold food for a long time.

    If you've ever been to a play and seen heavy fog on the ground, it is likely that you have seen dry ice in action. This effect can be achieved because CO2 is heavier than air, so evaporated （挥发的）CO2 will sink and accumulate on the ground.

    Another interesting use for this substance is to bait（诱杀）insects like mosquitoes. These insects have sensors which guide them to CO2. They find the high concentration of CO2 in dry ice quite attractive.

    Mars has long been a mystery for human beings. We have been looking for evidence of life on Mars. In the 1960s scientists guessed that the polar ice cap of Mars was made of frozen CO2. More recent observations have shown that while the topmost layer consists of frozen CO2, the most of it is probably regular frozen water.

    Something very strange and mysterious was going on in Sesemann's house. Every morning, when the servants went downstairs, they found the front door wide open. During the first few days that this happened, every room and corner was searched in great alarm to see if anything had been stolen, but not a thing in the house had been touched. The door was doubly locked at night, and for further security the wooden bar was fastened across it; but it was no good – next morning the door again stood open. One servant even claimed he had seen a white figure standing at the top of the steps and then all in a minute it disappeared.

    Mr. Sesemann told his old friend, a doctor, what had happened in his house. That evening they decided to wait for the ghost. One o'clock struck. There was not a sound. Suddenly the doctor lifted his finger. "Hush! Don't you hear something?" They both listened, and they distinctly heard the bar softly pushed aside and then the key turned in the lock and the door opened. They stepped into the hall.

    "Who is there?" thundered the doctor in a voice that echoed through the hall, as the two men advanced with lights and weapons towards the figure. It turned and gave a low cry. There stood Heidi, with bare feet, staring with wild eyes and trembling from head to foot. The two men looked at one another in surprise. "Child, why did you come down here?" said Sesemann. White with terror, and hardly able to make her voice heard, Heidi answered, "I don't know." The doctor gently took the child by the hand upstairs.

    Then the doctor sat down besides her and asked her some questions in a kind voice. Later he went downstairs. "Sesemann," he said, "let me first tell you that the child is a sleep-walker; secondly, the child is consumed with homesickness. Something must be done at once."

    The Children's Groundwater Festival, first organized by the Groundwater Foundation 19 years ago, is celebrated every year in Nebraska, a state of the central United States in the Great Plains. After organizing the festival for 16 years, the foundation passed the program on to the local community of Grand Island, Nebraska. The festival is an annual event for fourth and fifth graders of Nebraska. It is an interesting and energetic day filled with hands­on education. Water magic, folk singers and musicians, storytellers, and bird shows add to the happy atmosphere during the festival. There are also some educational activities:

    Gooey Garbage: Children build a landfill (废物填埋场) and learn how a properly­built landfill can protect groundwater.

    Water Races: Children learn about water pollution by racing a drop of water through a model.

    Well in a Cup: By building a small aquifer (蓄水层) in a cup, children learn about aquifers and drinking water wells.

    Taster's Choice: Children drink different types of water, from tap water to bottled water. Then they are taught about the treatment process of each type of water.

    There's No New Water: Students are taught to make a special glass container and learn about the water cycle.

    The Children's Groundwater Festival not only has a great influence on Nebraska's people. So far, similar festivals have been held in nearly 40 American states, Mexico City, several provinces in Canada, and New Delhi, India. People everywhere are realizing the importance of educating young people to learn and care about groundwater.

    For more information about this festival, remember to watch our program tomorrow evening. I'll be waiting for you.