Have you ever wanted to travel back in time? What about traveling into the future? There's an easy way to do it. One way you can make a time travel journey is by writing a letter to your future self to be opened in the future. To your future self, the letter will be a visit from the past. 

    What can be gained by writing a letter to yourself? Depends on how good your letter is. You have the chance to say something to your future self. What would you want to say? You'll be able to talk to yourself 5,10,15 years down the road. There may be instructions for your future self, or you may have goals that you will want to reach.

    There are a lot of things you could include in your letter or letters to yourself. The more you include, the better the letter will be to you. Be creative with what you put in your letter. Include a picture of yourself or family to show the period from which the letter came.

    You can store your letter in many different ways. You can give your letter to a friend or family member to keep and mail to you. If you can get others to take part, have them write letters to themselves as well and ask someone to be the letter holder until it's time to send the letters. You can also use a service online to store your letter and e-mail it to you. Ready to write to yourself two and a half years down the road?

    Here is an astonishing and significant fact：Mental work alone can't make us tire. It sounds absurd．But a few years ago, scientists tried to find out how long the human brain could labor without reaching a stage of fatigue(疲劳). To the amazement of these scientists, they discovered that blood passing through the brain, when it is active, shows no fatigue at all!

    If we took a drop of blood from a day laborer, we would find it full of fatigue toxins (霉素) and fatigue products. But if we took blood from the brain of an Albert Einstein, it would show no fatigue toxins at the end of the day.

    So far as the brain is concerned, it can work as well and swiftly at the end of eight or even twelve hours of effort as at the beginning. The brain is totally tireless. So what makes us tired?

    Some scientists declare that most of our fatigue comes from our mental and emotional (情绪的)attitudes. One of England's most outstanding scientists, J. A. Hadfield, says, “The greater part of the fatigue from which we suffer is of mental origin. In fact, fatigue of purely physical origin is rare. ”Dr. Brill, a famous American scientist, goes even further, He declares, “One hundred percent of the fatigue of sitting worker in good health is due to emotional problems.”

    What kinds of emotions make sitting workers tired? Joy? Satisfaction? No! A feeling of being bored, anger, anxiety, tenseness, worry, a feeling of not being appreciated— those are the emotions that tire sitting workers. Hard work by itself seldom causes fatigue. We get tired because our emotions produce nervousness in the body.

    A new study of 8,000 young people in the journal of Health and Social Behavior shows that although love can make adults live healthily and happily，it is a bad thing for young people. Puppy love（早恋）may bring stress for young people and can lead to depression. The study shows that girls become more depressed than boys, and younger girls are the worst of all.

    The possible reason for the connection between love and higher risk of depression for girls is “loss of self”. According to the study, even though boys would say “lose themselves in a romantic relationship”, this “loss of self” is much more likely to lead to depression when it happens to girls. Young girls who have romantic relationships usually like hiding their feelings and opinions. They won't tell that to their parents.

    Dr Marianm Kaufman, an expert on young people problems, says 15% to 20% young people will have depression during their growing. Trying romance often causes the depression. She advises kids not to jump into romance too early. During growing up, it is important for young people to build strong friendships and a strong sense of self. She also suggests the parents should encourage their kids to keep close to their friends, attend more interesting school activities and spend enough time with family.

    Parents should watch for signs of depression—eating or mood changes—and if they see signs from their daughters or sons，they need to give help. The good news is that the connection between romance and depression seems to become weak with age. Love will always make us feel young, but only maturity(成熟) gives us a chance to avoid its bad side effects.

    We're surrounded by chemistry in everyday life. Sometimes it is easy to see, like when your science teacher conducts a big experiment in class. At other times, it can be extremely hard to see everyday chemistry at work, but nearly everything you touch or use has some element of chemistry in it.

    Something as simple as toothpaste contains at least three chemicals, if not more. It is the mixture of them and its chemical reaction that keeps your teeth clean. Other things you use every day are created by chemistry, such as hair products, shampoo and soap. Adding detergent (洗涤剂) to water involves chemistry. Without chemistry, we would never have realized that we need soap to get the oil out of clothes or skin.

    Chemistry not only helps us make products for use, but it also helps us understand the world around us. Chemistry helps us understand what the ozone layer (臭氧层) is and how it protects us. Chemistry also gives us sunscreen to protect us from the sun. Thanks to chemistry, we know bleach (漂白剂) can't be mixed with vinegar, because it can produce poisonous gas. Without chemistry, we wouldn't have had fireworks displays on important days like the Spring Festival.

    Chemistry plays a big role in food preparation. Cooking food causes it to go through a chemical change. That is why cooked food often tastes different from raw (生的) food. Baking is a great example of chemistry. Too much or too little of any ingredient makes a difference to the result of baking, for example, the dough (面团) won't rise or the cake will be flat.

    Chemistry isn't something that just lives in a lab; it's something that you come across hundreds of times every day. If you know how chemistry works, you will get a greater comprehension of the science behind some of the simplest looking things.

Teen Volunteers

    The zoo supports future conservation by having the youth involved in voluntary jobs. We have popular summer year-round programs that are designed to be fun and educational while building job readiness skills and inspiring youth to appreciate, care for, and conserve nature.

    ◆Zoo Crew

    Volunteer on a team to restore wildlife habitat at Lake Merced and Mountain Lake in San Francisco.

    Ages11-14

    Program runs: September through June

    Hours: One Saturday per month, form 10 a. m. to 12 p. m.

    The Zoo Crew will hold a necessary training for all prospective volunteers in August at the Zoo.

    ◆Nature Trail

    Nature Trailers work in close proximity (接近) to the Zoo's ambassador animal collection, and teach guests about adaptations and conservation. Nature Trailers will learn to handle a few small mammals and reptiles.

    Ages 12-14 (must be 12 by Memorial Day)

    Program runs: Memorial Day to Labor Day

    Hours: 2 days per week, 10 a. m. to 4: 45 p. m.

    ◆Talk on the Wild Side

    Learn to handle amazing animals like livestock and arthropods (节肢动物) while giving informational talks to zoo visitors. Use biofact carts to educate the public.

    Ages 14-17

    Program runs: Memorial Day to Labor Day

    Hours: 2 days per week, 9: 30 a. m. to 4: 30 p. m.

    ◆Zoo Teacher Assistant

    Help kids explore the world of animals through zoo tours, crafts, games and assist Zoo Camp teachers with activities. Gain practical work experience with children.

    Ages14-17

    Program runs: mid-June through mid-August

    Hours: A daily half-day or full-day shift for a minimum of four weeks over the course of the summer.

    It was only a dollar. Belscher noticed it on the floor as he sat at the back of his English class. When the school day ended, Belscher wandered back to the classroom. The old bill was still there. He could easily have pocketed it without thinking twice. Instead, he picked it up and brought it to his English teacher, Mattison.

    "It wasn't my money," Belscher says. Mattison was a little surprised he'd turned the dollar in, knowing a lot of people would have just kept it. She suggested that Belscher tape(贴) it to the whiteboard at the front of the classroom, where she always puts lost things.

    Rose, another student, was in English class after break when he spotted the dollar on the whiteboard. After class, he asked Mattison why it was there. She was still waiting for the original owner to claim it, so she replied, "I don't know." Rose took the tape from Mattison's desk and taped a second dollar to the board.

    That got it rolling. The sight of the two dollar bills, side by side, started something in Mattison's students. They started asking about the purpose of the money, to which Mattison always gave the same answer: She didn't know. At that point, it was true.

    More students, curious, taped up single dollar bills. Mattison started to leave the tape on the tray of the whiteboard. The effort snowballed. Even with no clear purpose, many students wanted to be part of whatever this was. The amount continued to grow over several weeks, until it reached $175.76.

    That left Mattison to make the best decision. She kept thinking about her brother-in-law, Jack Hains. Eight years earlier, Jack had died of amyotrophic lateral sclerosis (ALS), a rare and devastating neurological disease(神经疾病).

    Mattison explained to her classes that Jack had raised money every spring for the ALS Therapy Development Institute, established to seek a cure for the disease. She asked the teens whether they minded if she donated the dollars in their names in honor of Jack.

    Their answer was to tape enough money to the whiteboard over the next few days to push the amount to $321.06. Mattison, choking back tears as she recalls the moment, says she carefully picked the cash off the board and made the donation just before the beginning of May, which is National ALS Awareness Month. That was Saturday. By Monday afternoon, eight more dollars had been taped to the board.