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.

    A Spanish company Siesta &Go has opened the first public napping (小睡) space in Madrid. It promises people a quiet rest in the middle of the city's business center.

    Napping spaces are nothing new; places to rest are already set up in other big cities in the world. But the idea would appear to work well with the culture of Spain, where people traditionally take an afternoon nap, called siesta.

    The Madrid nap space recently opened with 19 beds. People can use them by the minute or by the hour, and they can also choose either a private or shared room. An hour of napping inside a private room costs about $ l5.

    Siesta &GO provides all bedding, clean nightshirts and other materials. Nippers can request to be woken up when their time is up. It also offers areas to work, with armchairs, newspapers and coffee for those not wishing to sleep.

    Philip &Go is one happy customer. Marco says he gets tired during the day because of hard work. He says a siesta is the perfect way to build up energy. “I come for about 30 minutes or something like that. That is usually enough for me to be full of energy.”

    While many Spanish people love their naps, others like Carlos Villarroja say they are just too busy to keep the tradition. “It's a Spanish tradition, but I think it's more of a legend (传说) than a tradition. Because of the lifestyle and the working hours, we have very little free time for a siesta at least during the week.”

    But many health experts believe there is evidence that taking a short nap can be very good for the body and mind. Scientific studies show that taking a siesta can also prevent illness and lower blood pressure.

    Advances in artificial intelligence and the use of big data are changing the way many large companies recruit (招募) entry level and junior management positions. These days, graduates' CVs may well have to impress an algorithm (算法) rather than an (human resources) manager.

    While algorithms supposedly treat each application equally, experts are divided about whether so-called robo-recruitment promises an end to human prejudice in the selection process —or whether it may in fact add to it.

    “AI systems are not all equal,” says Loren Larsen, chief technology officer for HireVue, which has developed an automated video interview analysis system. “I think you have to look at the science team behind the work,” says Mr Larsen.

    The problem, experts say, is that to find the best candidates an algorithm has first to be told what “good” looks like in any given organization. Even if it is not given criteria that seem discriminatory, a powerful machine-learning system will quickly be able to copy the characteristics of existing workers. If an organization has favoured white male graduates from well-known universities, the algorithm will learn to select more of the same.

    The growing dependence on automation to judge suitability for everything from a loan to a job worries Yuriy Brun, an associate professor specializing in software engineering. “It takes a lot of the time for a company to put out software but it doesn't know if it is discriminatory” he says. Prof Brun explains that, considering the use of big data, algorithms will unavoidably learn to discriminate.

    Many of those working with robo-recruiters are more optimistic. Kate Glazebrook, the leader and co-founder of Applied, a hiring platform, says her task is to encourage hiring manager to move away from such indicators of quality as schools or universities and move to more evidence-based methods. When candidates complete tests online, Applied hides their names and shows the tests the candidates have completed, question by question, to human assessors. Every stage of the process has been designed to remove prejudice.

    With the same aim, Unilever decided in 2016 to switch to a more automated process for its graduate-level entry programme. Unilever worked with HireVue, Amberjack, which provides and advises on automated recruitment processes, and Pymetrics, another high volume recruitment company, which developed a game-based test in which candidates are scored on their ability to take risks and learn from mistakes, as well as on emotional intelligence. Unilever says the process has increased the ethnic diversity of its listed candidates and has been more successful at selecting candidates who will eventually be hired.

    “The things that we can do right now are impressive, but not as impressive as we're going to be able to do next year or the year after,” says Mr Larsen.

    Still, robo-recruiters must be regularly tested in case prejudice has occurred without anyone realizing it, says Frida Polli, the leader and co-founder of Pymetrics. “The majority of algorithmic tools are most likely causing prejudice to continue existing. The good ones should be examined.”

    You can tell a lot about a country from its passport. Color is the first give-away. Nations tend to pick colors that reflect their national character. New Zealand decorates its famous rugby team, its airline and its passports in the nation's favorite color—black. Many Islamic countries have green passports because of the importance of the color in the Muslim faith.

    But as well as a statement of national identity, color can show international cooperation. The British passport was originally a navy blue. But after Britain joined the European Union in 1973, it switched to burgundy red（酒红色）like other EU countries. The common color was supposed to make European passports instantly recognizable.

    But since colors can't be patented（专利）, nothing stops others with the same idea. A number of countries that long to join the EU have changed their passports to burgundy too. Meanwhile Britain has decided to leave the club. Its government has announced that the UK passports will return to navy blue after Breit（脱欧）.

    If you have a passport from Singapore or South Korea, you are in possession of one of the most powe3rful travel documents on earth. Passport power is measured by the number of countries the holder can access visa-free. Currently sharing first place in the power rankings, Singaporean and South Korean passports provide visa-free access to 162 countries each. British passport holders share fourth place in the power ranking with six other nations, each accessing 159 countries visa-free. Americans ranked fifth with access to 158. Somalia, Syria, Pakistan and Iraq are among the world's least powerful passports. Afghanistan is the lowest ranking of all, with visa0free access to just 26 countries.

    Having to get a visa is not a piece of cake. First there is the never-ending form. Then there are lengthy appointments and expensive fees. Some visas also require travelers to pre-booked flights to prove that they intend to return home.

    But there are unexpected advantages to some of the world's weaker passports. Middle-ranking Namibia is one of just a handful of countries, whose citizens can enter Angola visa-free. India is one of only three countries, whose citizens have visa-free access to Bhutan.

    A low-ranking passport limits your choices, but not your sense of adventure.

    Last year, three experienced storm chasers were killed in a tornado(龙卷风)in the US, but despite this the number of people going in search of tornadoes is growing. What drives them to take risks and look for danger? The man at the wheel glanced in the back-view mirror and then slowly turned around. "Don't put this in your program." he said. His wife in the passenger seat laughed. He lowered the window and killed the engine. The wind rushed in from surrounding wheat fields.

    Then, from behind, the sound of footsteps approached on the dirt road. It was a moment of peace after hours of speedy racing through the American grassland. There had been excited shouts about where a tornado might form and how we would be there if it did. We were crazy on the trail a moment ago. But now, everyone was very cool. A Kansas state trooper(骑警) introduced himself through the window. There was pretended surprise when he said how fast we had been going. Really? Wow, sorry.

    Val Cator handed over his driver's license. His wife, Amy, took the registration out of the glove box. Val explained they were storm chasers with Channel 9 News out of Oklahoma City—though it was hardly necessary. Their huge black truck has lightning bolts(闪电)and Storm Tracker 9 painted on the sides.

    Val pointed to the radar on the laptop open next to him and said those red and green dots suggested a tornado could form this afternoon. The state trooper was untouched. "I've got that in my car too." he said. People here keep a close eye on the weather. It's part of living in the tornado alley. Every year some town or other is blown off the map by tornadoes that can reach 300 miles an hour.

    Val and Amy are just two of hundreds of possibly thousands of trackers who speed around with computers and cameras hoping to catch one of these beautiful, deadly storms. I'd joined them to learn why the number of trackers keeps growing. Why are people taking real risks—beyond the steady diet of rest-stop junk food—to watch weather?

    Last year, a tornado killed three of the most experienced storm chasers. It picked up and threw their car as easily as you would a piece of paper. Dozens of other chasers were hurt in the same storm. They were crowded on a few roads when the tornado suddenly expanded and ate them. Val and Amy were there that day but still, in their words, chase aggressively.

    Back in 1988, I was working at the University of Bonn in Germany as a research fellow. I took some time off in early May to visit a friend, who was the director of a museum in Viterbo, in central Italy. I set out by train, which crossed the Swiss border to reach Zurich, winding through valleys and along hillsides, and entering tunnels and making its way through the Swiss Alps. The scenery was so beautiful.

    The train then crossed the Italian border before passing through Milan and Florence, then finally stopping in Rome. I was lucky, as my hotel was close to the railway station. The next morning, I had a coffee at a nearby café and eagerly set out to visit as many of the famous Roman landmarks as possible.

    The following day I headed back to the train station, intending to take a short train ride to Viterbo to meet up with my friend. When I arrived at the station and attempted to locate the correct platform, I quickly realized that the station was closed for an upgrade (升级). For a moment my mind went blank and did not know what to do. My biggest problem was my luggage—my suitcase and hand luggage were so heavy that I couldn't move about easily. As I don't speak Italian, I could not ask anyone for instructions. I dragged my suitcase about 100 meters to a nearby motor mechanics. A tall, strong man of about 50 years of age was working there and I excused myself and asked where the nearest station was. I am sure that he did not understand me properly but he could easily guess that I was looking for a station. He replied, but I did not understand.

    He smiled, wiped his hands and said something, which I guessed to mean "come along". So I dragged my suitcase along and followed him. He opened the door of his car, motioned to me to get in and then drove for a few minutes to the next station. I got out, unloaded my luggage, then shook his hand with thanks. He smiled back and drove away.

    There was no time to hug or exchange names  I understood he was busy and in the middle of his work. I was moved so much by his generosity that I have never forgotten him.