The TV science-fiction series Star Trek no longer looked far-fetched (牵强的) as four men and four women in black space-suits locked themselves into a giant hi-tech greenhouse, known as a ‘biosphere', in the Arizona desert yesterday for a two-year study of the environment.

    As dawn broke over the Santa Catalina mountains, the eight waved goodbye to television cameras. Edward Ross, their multibillionaire sponsor from a Texas oil family, closed the door of the $150 million structure, with its mini-ocean, marsh, desert, savanna, rain-forest and 3,800 plant and animal species designed to allow the team to recreate Earth and its ecosystems.

    The so-called Biosphere 2 is the latest of a dozen environmental projects started by the self-titled ‘ecopreneur'. The project's main aim is to set up a self-sustaining community for possible use in a spaceship or on another planet. The crew members must plant, harvest and process their food on a half-acre farm in the seven-storey glass and metal structure, while conducting a series of experiments.

    ‘We will be custodians (监护人) of our new little world,' said Abigail Mayer, aged 31, a US marine biologist on the team, her voice choking with emotion. ‘It is a brave new step.' Many scientists, however, are more than skeptical. They point out that the largest closed ecosystem which survived more than a few days was smaller than a football. It was developed at the University of Miami and contained only shrimp, algae and other micro-organisms.

    Critics have also accused Mr. Ross of being more interested in producing a profitable theme park than in carrying out serious scientific research. Hundreds of tourists visited the site daily in the summer before it was occupied by the team. They paid $9.95 to enter and all stopped at the souvenir shop.

    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.

    For centuries, medical pioneers have refined a variety of methods and medicines to treat sickness, injury, and disability, enabling people to live longer and healthier lives.

    “A salamander (a small lizard-like animal) can grow back its leg. Why can't a human do the same?” asked Peruvian-born surgeon Dr. Anthony Atala in a recent interview. The question, a reference to work aiming to grow new limbs for wounded soldiers, captures the inventive spirit of regenerative medicine. This innovative field seeks to provide patients with replacement body parts.

These parts are not made of steel; they are the real things — living cells, tissue, and even organs.

    Regenerative medicine is still mostly experimental, with clinical applications limited to procedures such as growing sheets of skin on burns and wounds. One of its most significant advances took place in 1999，when a research group at North Carolina's Wake Forest Institute for Regenerative Medicine conducted a successful organ replacement with a laboratory-grown bladder. Since then, the team, led by Dr. Atala, has continued to generate a variety of other tissues and organs—from kidneys to ears.

    The field of regenerative medicine builds on work conducted in the early twentieth century with the first successful transplants of donated human soft tissue and bone. However, donor organs are not always the best option. First of all, they are in short supply, and many people die while waiting for an available organ; in the United States alone, more than 100,000 people are waiting for organ transplants. Secondly, a patient's body may ultimately reject the transplanted donor organ. An advantage of regenerative medicine is that the tissues are grown from a patient's own cells and will not be rejected by the body's immune system.

    Today, several labs are working to create bioartificial body parts. Scientists at Columbia and Yale Universities have grown a jawbone and a lung. At the University of Minnesota, Doris Taylor has created a beating bioartificial rat heart. Dr. Atala's medical team has reported long-term success with bioengineered bladders implanted into young patients with spina bifida (a birth defect that involves the incomplete development of the spinal cord). And at the University of Michigan, H. David Humes has created an artificial kidney.

    So far, the kidney procedure has only been used successfully with sheep, but there is hope that one day similar kidney will be implantable in a human patient. The continuing research of scientists such as these may eventually make donor organs unnecessary and, as a result, significantly increase individuals' chances of survival.

    Growing up, I wanted to be just like my mom. She was kind. People always seemed to feel comfortable in her presence. For years, she was a volunteer in our community. I loved going to the local nursing home with her where she taught a ceramics(制陶技术) class.

    On one summer day, Mama told me to get changed and meet her at the car.

I had planned to spend the day at the lake with friends. Why did she have to ruin everything? I imagined the cool lake water. Irritated，I climbed into the car and slammed the door shut. We sat in silence. I was too upset to make conversation.

    "Tasha, would you like to know where we are going?" Mama asked calmly.

    "No," I said.

    "We are going to volunteer at a children's shelter today. I have been there before and I think it would benefit you," she explained.

    When we reached the shelter, Mama rang the doorbell. Moments later, we were greeted by a woman. She led us to the front room where all of the children were playing. I noticed a baby whose body was scarred with iron marks. I was told it was because she wouldn't stop crying. The majority of the children had noticeable physical scars. Others hid their emotional wounds.

    As I took in my surroundings, I felt a gentle pull on my shirt. I looked down to see a little girl looking up at me. "Hi. You want to play dolls with me?" she asked. I looked over at Mama for reinforcement. She smiled and nodded. I turned back and said, "Sure." Her tiny hand reached up and held mine, as if to comfort me.

    My mom taught me a valuable lesson that summer. I returned to the shelter with her several times. During those visits, some of the children shared their troubled pasts with me and I learned to be grateful for what I had. Today as I try to instill (逐渐灌输) these values in my own child, I reflect back to that experience. It was a time that I will never forget.

    A trip to Paris is not complete without a visit to the Eiffel Tower. To get the most out of your visit read our tips below:

    Visit at Night

    Riding up the Eiffel Tower at night and looking out over the streets of Paris, you'll see why Paris is known as the “City of Light”. At street level, the spotlights on the top of the Tower and the reflections (倒影) of the Tower in the Seine (塞纳河) are sights not to be missed.

    Purchase (购买) Your Ticket in Advance Online

    Avoid the long ticket lines at the Eiffel Tower by purchasing your ticket online from the Eiffel Tower website.

    You'll pick a time to visit and then select whether to print out the ticket or display it on your phone or iPad, a convenient choice if you buy your ticket in Paris without a printer.

    Don't Bring Valuable Objects with You

    Before entering the Eiffel Tower, your bags will be examined by a security officer. If an item you are carrying sets off the metal detector, the officer will take you away from the line for further inspection. Probably you will miss the chance to go up the Eiffel Tower.

    Have Drinks and Snacks at the Eiffel Tower

    If you're like us, after an exciting trip to the Eiffel Tower, you'll be ready to rest your legs and have a relaxing snack and a drink in a Parisian cafe. Across the Seine in the Trocadero area, there are many elegant cafes. The atmosphere is great, but the prices are in the stratosphere (极高水平). Actually, the perfect place for common visitors to eat and drink is on the Eiffel Tower itself.

    Depression and suicidal thoughts have doubled in young Americans, according to a new study from the American Psychological Association.

    Likely triggers? Cell phones and social media.

    "More US adolescents and young adults in the late 2010s, vs the mid-2000s, experienced serious psychological distress, major depression and more attempted suicide (自杀)", says lead researcher Jean Twenge, professor of psychology at San Diego State University. "These trends are weak or non-existent among adults 26 years and over, suggesting a generational shift in mood disorders instead of an overall increase across all ages."

    Twenge believes this trend is partially due to the explosion of digital culture over the past decade, which may have twisted modes of social interaction enough to affect mood disorders.

    The study analyzed data from the National Survey on Drug Use and Health, which tracked drug and alcohol use and mental health issues in more than 200,000 youths aged 12 to 17 from 2005 to 2017 and almost 400,000 adults from 2008 to 2017.

    Major depression in the last 12 months increased by 52 percent in kids from 2005 to 2017 and 63 percent in young adults aged 18 to 25 from 2009 to 2017. There was also a 71 percent jump in young adults experiencing serious psychological distress in the previous 30 days from 2008 to 2017.

    So what's so different now? Twenge says research shows young people just aren't getting as much shuteye as they did in previous generations.

    Whereas older Americans might have established more stability in their lives, sleep-disrupting social stressors are likely at their peak for teens and young adults in this digital era, she says. Older adults are also less likely to let devices interfere (干预) with sleep.

    These results suggest a need for more research to understand how digital communication versus face-to-face social interaction influences mood disorders and to develop specialized interventions for younger age groups.

    Her suggestion? Put your phone down at least an hour before bedtime.