According to sociologists(社会学家), every modern industrial society has some form of social stratification(阶层). Class, power and status are important in deciding people's rank in society.

    Class means a person's economic position in society. A commonly used classification is lower class, middle class and upper class. While sociologists disagree on how these terms should be exactly defined, they do describe societies like the United States quite well. One study shows that 53% of Americans belong to the lower class, 46% the middle class, and 1% the upper class. Interestingly, a surgeon earning $500,000 a year and a bus driver earning $50,000 a year both regard themselves as the middle class!

    Power refers to the amount of control a person has over other people. Obviously, people in positions of great power (such as governors) exercise(行使)big power, but people who take orders from others have less power. Power and class do not always go hand in hand, however. For example, the governor of a state has great power, but he or she may not belong to a corresponding (相应的)economic class. Generally, however, there is a relationship between power and class. To our knowledge, there aren't too many people who aren't millionaires in the U．S. Senate!

    Status is the honor or respect attached to a person's position in society. It can also be affected by power and class, but not necessarily so. For example, a university professor may have a high status but not belong to a high social class or have a lot of power over others.

    We get it: You're tired. You're busy. And your shoes are away over there. Excuses are OK sometimes, but not every day—and especially not today. So put on your sneakers, get up off the couch, and let us kick your excuses to the curb (路边).

    “I…dislike…panting !”

    Being really out of breath may mean you're trying too much too soon, which will kill your confidence. But you don't have to be huffing and puffing to get a workout. Being active doesn't have to mean high-intensity. It's just about moving.

    “I hate exercise.”

    It may seem unbearable, but you just have to get started. Exercise releases endorphins (your brain's own feel-good chemicals), which can be habit-forming. What' s the best exercise? The one you'll do regularly. So you may hate running. Don't run! Ride your bike or just dance. Even cleaning your room is active. As long as you're moving and getting your blood pumping, it counts. So get creative.

    “I don't have time.”

    You may not have lots of time to spare when you're busy with schoolwork, but we bet you can find 10 minutes. Bonus: An activity break will send oxygen to your brain, making you super-alert and more creative too. Famous thinkers like Aristotle and Steve Jobs liked “walking meetings," and you can follow in their footsteps by moving around while you brainstorm about a tough task or memorize your English vocabulary.

    “I never see results!”

    Even if you train with the help of a professional, you won't see results right away. But you will feel them almost immediately. Don't focus on how your body looks—focus on how you feel. Keep a journal of when you exercise (or don't) and how you feel that day: Stressed? Focused? Tired? When you start noticing the amazing effects of exercise, you'll have no excuses.

    Enough sleep is important to health. The amount of sleep needed depends on the age of the person and the conditions in which sleep takes place. The young may need more sleep than the old, but usually eight hours are enough for the health of grown-ups. Some can do with less than this amount, but others may need more. Every person knows his own need. It is then a matter of good judgement to satisfy his need. Sleep should always be enough to make one bring back his strength and get ready for a day's work.

    Fresh air is necessary to sound sleep. It is not without reason for some people to think that it is practicable to sleep in the open air. When one can keep himself warm, out-of-door sleeping probably gives the body its most complete relaxation (放松).

    Ability (能力) to sleep lies largely in habit. The conditions referred to only lead to sleep. Out-of-door exercises, a good habit of regular hours and the avoidance (避免) of late eating and worry, which are largely within the control of any person, are all helpful to sound sleep.

    A bath at bedtime, neither hot nor cool but of body temperature may be helpful to sleep. Sleep-producing drug (药) should never be taken except when suggested by a doctor.

    There's a good chance something you've bought online has been in the hands of a "picker" first. These are the workers in warehouses(仓库)who pick, pack and ship all those things we're ordering.

    At Amazon and other companies, they're working side by side with robots. Experts say while the robots are replacing some human workers, the machines aren't quite ready to take over completely.

    When a robot finds its storage unit, it slides underneath, lifts it up and then delivers it to a worker 一 they're called pickers. On a recent day, the computer told a picker to grab what looked like a fantasy board (棋盘)game. The picker found it, canned it and placed it on the conveyor belt.

    ^"In a traditional fulfillment center where the associate would walk to the different items, it can take hours to fulfill a customer order." Robinson says.

    Now, with the help of robots, that task takes minutes 一 and fewer humans.

So is this a sign we're entering a new industrial revolution?

    "It's definitely going to take over a lot of jobs." says Karen Myers, a scientist at SRI, one of Silicon Valley's oldest research centers.

    At the same time, she says, we're running against the limits of technology. Take "the picker" at the Amazon fulfillment center. Myers says those skills are proving to be uniquely human.

    "Our fingers are incredibly flexible and the current generation of robotic operators, they're getting much_, much better," she says. "But they're just not quite there yet."

    There's also the robot's brain.

    Remember that board game the Amazon worker was looking for? She could barely see the box filled into the storage bin — but she could tell it was a board game. Robots can't do that.

    Technologists say that, increasingly, humans will work side by side with robots — instead of robots working alone.

    Amazon says robots and humans enabled the Tracy warehouse to fulfill customer orders faster. That means more customers and more human workers.

    In the 1960s, while studying the volcanic history of Yellowstone National Park, Bob Christiansen became puzzled about something that, oddly, had not troubled anyone before: he couldn't find the park's volcano. It had been known for a long time that Yellowstone was volcanic in nature—that's what accounted for all its hot springs and other steamy features. But Christiansen couldn't find the Yellowstone volcano anywhere.

    Most of us, when we talk about volcanoes, think of the classic cone (圆锥体) shapes of a Fuji or Kilimanjaro, which are created when erupting magma (岩浆) piles up. These can form remarkably quickly. In 1943, a Mexican farmer was surprised to see smoke rising from a small part of his land. In one week he was the confused owner of a cone five hundred feet high. Within two years it had topped out at almost fourteen hundred feet and was more than half a mile across. Altogether there are some ten thousand of these volcanoes on Earth, all but a few hundred of them extinct. There is, however, a second les known type of volcano that doesn't involve mountain building. These are volcanoes so explosive that they burst open in a single big crack, leaving behind a vast hole, the caldera. Yellowstone obviously was of this second type, but Christiansen couldn't find the caldera anywhere.

    Just at this time NASA decided to test some new high-altitude cameras by taking photographs of Yellowstone. A thoughtful official passed on some of the copies to the park authorities on the assumption that they might make a nice blow-up for one of the visitors' centers. As soon as Christiansen saw the photos, he realized why he had failed to spot the caldera; almost the whole park-2.2 million acres—was caldera. The explosion had left a hole more than forty miles across—much too huge to be seen from anywhere at ground level. At some time in the past Yellowstone must have blown up with a violence far beyond the scale of anything known to humans.

    Scientists have created a scent(气味)-delivery system that releases a pleasant fragrance when you sweat. Apply it to your skin, and the more you sweat, the better you'll smell. That's because the perfume only gets released upon contact with moisture(湿气).

Chemists from Harvard University combined two compounds to create their new system. One chemical is alcohol-based. This is the nice-smelling perfume. The other chemical is an ionic liquid(离子性液体), which is a type of salt that is liquid at room temperature. Ionic liquids are made of ions—molecules(分子) that have lost or gained one or more electrons(电子). If the molecule loses electrons, it will have a positive charge(正电荷). If it gains electrons, it gets a negative charge. Ionic liquids contain the same number of positive and negative ions, which makes them neutral, with no overall electric charge. In general, ionic liquids have no smell.

    When the perfume and ionic liquid are mixed together, a chemical reaction occurs. This bonds the molecules to each other. The reaction also temporarily inactivates the perfume's molecules. So when applied to the skin, the new perfume has no scent in the beginning. But adding water or sweat breaks the bond between the molecules. That releases the scent into the air.

    "The rate of the release of the fragrance depends on how much you sweat, in other words, how much water is available," explains chemist Nimal Gunaratne from Harvard University, who led the research. "Sweat is like the command to let the fragrance go."

    Christian Quellet is a chemist who has worked in the perfume industry for a long time. He is now an independent consultant based in Switzerland. "Gunaratne's perfume opens the door to new developments and applications of fragrance controlled-release systems," he says. Controlled-release systems allow small quantities of some compounds that they hold to enter the environment slowly.

    The system also traps some chemicals in sweat that are responsible for the bad sweat smell. These compounds are called thiols (硫醇). Just as water does, thiols break apart the bond that ties the perfume to the ionic liquid. When this happens, the thiols attach to the ionic liquid and their bad scent is inactivated as the perfume had been. This means the water in sweat and its thiols are both able to release the fragrance from the newly developed perfume.