Children's lives have changed greatly over the last 50 years. But do they have a happier childhood than you or I did?

    It's difficult to look back on one's own childhood without some element of nostalgia (怀旧的). I have four brothers and sisters, and my memories are all about being with them. Playing board games on the living room floor, or spending days in the street with the other neighborhood children, racing up and down on our bikes, or exploring the nearby woods. My parents scarcely appear in these memories, except as providers either of meals or of severe blame after some particularly risky adventure.

    These days, in the UK at least, the nature of childhood has changed dramatically. Firstly, families are smaller, and there are far more only children. It is common for both parents to work outside the home and there is the feeling that there just isn't time to bring up a large family, or that no one could possibly afford to have more than one child. As a result, today's boys and girls spend much of their time alone. Another major change is that youngsters today tend to spend a huge amount of their free time at home, inside. More than anything this is due to the fact that parents worry far more than they used to about real or imagined dangers, so they wouldn't dream of letting their children play outside by themselves.

    Finally, the kind of toys children have and the way they play is totally different. Computer and video games have replaced the board games and more interesting activities of my childhood. The irony (令人啼笑皆非的事情) is that so many ways of playing games are called “interactive”. The fact that you can play electronic games on your own further increases the sense of loneliness felt by many young people today.

    Do these changes mean that children today have a less relaxing childhood than I had? I personally believe that they do, but perhaps every generation feels exactly the same.

    Like all big cities, Paris has a traffic problem: lots of cars, lots of traffic jams and lots of pollution from exhaust fumes (废气). So the city began a project to improve the situation.

    Under the Velib project ('Velib' comes from velo liberty, or 'bicycle freedom') people can take a bicycle, use it for as long as they want, and then leave it at the same or another bicycle station. The first half-hour on the bike is free, but if you don't return it after 30 minutes, you have to pay. But it's only €1 a day or €29 a year! The bicycles are heavy (25 kg), and they are all gray and have baskets. There are about 20,000 of them in the city, and around 1,450 bicycle stations. So there are a lot more Velib stations than the 298 subway stations!

    Paris is not the first city to have a project like this. But not everybody thinks it's a great idea. One Parisian said, “These bicycles are only for short journeys. If people want to travel across the city, they won't use a bicycle - they'll still use their cars.”

    A city spokesman said, “The bicycle project won't solve all our traffic problems, of course. But it might help reduce air pollution. Traffic, together with factory fumes, is a big problem. There aren't any simple answers to traffic problems and pollution in cities. But unless we do something now, there will be more traffic jams and temperatures will continue to rise, so the problems in our environment will get worse. The bikes might help people to lead a healthier life, too.”

    Getting stuck in a traffic jam is one of the most boring problems for people living in big cities. The fact that you're moving so slowly leads too stress, anger and the wish that your car could just fly over the traffic like an airplane.

    Soon, however, that wish could come true .On May 8, US car-renting company Uber showed off what it described as "the transportation mode of the future: on-demand air transport," reported ABC News.

    According to Nikhill Goel, head of products for Uber Air, the company's air taxi service may launch test flights in the US cities of Dallas and Los Angeles, as well as Dubai in the United Arab Emirates, as early as 2020. If everything goes according to plan, passengers will be able to fly to work by 2023.

    When the Olympics comes to Los Angeles in 2028. Uber "expects to have hundreds, if not thousands, of its aircraft in the skies." Goel told Newsweek.

    So what would Uber's flying vehicles be like?

    They are small, electric aircraft that take off and land vertically (垂直地) , and they give off zero emissions (排放) and are quiet enough to operate in cities .

    Just like an airplane, the vehicles will have fixed wings to help them glide. But while a helicopter has just one big fixed rotor (定量). Uber's vehicles will have multiple rotors , which will help increase fuel efficiency (效率) while reducing emissions and noise.

    Because of these fixed wines and multiple rotors. Uber's flying taxis "should be quieter and safer than a helicopter." reported ABC News.

    However, the service still has a long way to go before it's ready to accept passengers. For example, to avoid any potential accidents. Uber is working with NASA to study air traffic control problems associated with low-flying aircraft. But just as Dubai's Mayor Betty Price said in a news release. "This program is revolutionary and future -oriented (面向未来的)."

    American families are accustomed to settling in faraway places, which has been a national phenomenon. Decades of data, including a more recent Gallup study, characterizes the US as one of the most geographically mobile countries in the world. "About one in four US adults(24 percent) has reported moving within the country in the past five years." the reported noted. With the exception of Finns(23 percent) and Norwegians(22 percent), Americans move considerably more than their European peers.

    Though some may move for love or family, the major reason why Americans choose to move around is, unsurprisingly, related to work. Citing data from the Current Population Survey, a post on the blog of the New York Fed noted that between 1998 and 2013, "slightly more than half of interstate(州际的) migrants said they moved for employment­related reasons—a category that includes moves undertaken for new jobs, job transfers, and easier commutes(通勤)."

    The seeking of opportunity, particularly for an immigrant nation, is a national mythology(神话) as well as an emotional attachment to work. A new working paper analyzed by Ben Steverman at Bloomberg suggests that workers in the US now" put in almost 25 percent more hours than Europeans" in a given year. This figure has steadily risen since the 1970s, when the hours logged by workers in Western Europe and the US were roughly the same.

    There are, of course, some internal factors. The US is much vaster than most European countries, plus it boasts(拥有) a common language. It is considered to be a sign of an efficient labor market that US workers can be persuaded to move to regions where there is a steady growth in jobs, such as the Sun Belt in recent years. And while American workers often have fewer labor protections than their European counterparts, as a report by the World Bank noted in 2012, American "labor laws give employers the power to fire, hire, or relocate(重新安置) workers according to their needs", a flexibility that is thought to aid economic growth. The World Band report added that the occupation of the average US employee in 2006 was 4 years, compared to 10 years in the European Union.

    Nevertheless, while Americans remain excessively mobile, FaithKarahan and Darious Li at the New York Fed are the latest to note that US workers are moving around less than before. During the 1980s, 3 percent of working­age Americans relocated to a different state each year; that figure had been cut in half by 2010." While part of the decline can be attributed to the Great Recession," the authors suggest," thisphenomenon took place over the course of several decades and is not necessarily related to the economic conditions."

    So what accounts for this phenomenon? A round­up of theories by Brad Plumer at The Washington Post included the aging of the US workforce, the further rise of two­income households, the burdens of real estate, evolving workplace culture, as well as the flat line of wages, which makes moving away for a job, on average, a less rewarding financial proposition.

    Karahan and Li put much stock in the effects of an aging workforce, to which they attribute at least half of the decline in interstate migration. "In short, a young individual today is moving less than a young person did in the 1980s because of the higher presence of older workers," they write, suggesting that employers have shifted their employment tactics(策略) to adapt to the changing demographics(人口统计数据) of the workforce. Needless to say, movies about this era in American life, in which fewer people set out to start lives in wide­ranging places, will probably be much less exciting.

The Mona Lisa is the famous Leonardo da Vinci painting of a woman with a mysterious smile. This week, the painting gave up a secret.

Scientists used X-rays to examine the chemical organization of an extremely small part of the more than 500-year-old painting. The researchers discovered a technique Leonardo used in the work. A team in France and Britain discovered an oil paint used for the Mona Lisa was a special, new chemical mixture. It suggests that the Italian artist may have been in an experimental mood when he set to work on the painting early in the 16th century.

"He was someone who loved to experiment, and each of his paintings is completely different technically," said Victor Gonzalez. He is the study's lead writer. "In this case, it's interesting to see that indeed there is a specific technique for the ground layer of the Mona Lisa," he said in an interview with The Associated Press. Specifically, the researchers found a rare compound, plumbonacrite (水蛭石), in Leonardo's first layer of paint. The discovery, Gonzalez said, proved that da Vinci most likely used lead oxide to thicken and help dry his paint.

The scientists looked into its atomic structure using X-rays in a synchrotron (同步加速器). The machine moves particles at close to the speed of light, permitting researchers to look deeper into the paint structure. "Plumbonacrite is really a fingerprint of his recipe," Gonzalez said. "It's the first time we can actually chemically prove it."

Dutch artist Rembrandt may have used a similar mixture when he was painting in the 17th century. Gonzalez and other researchers have found plumbonacrite in his work, too. "It also tells us that those recipes were passed on for centuries," Gonzalez said. "It was a very good recipe."

But the Mona Lisa and additional works by Leonardo still have other secrets to tell. "There are plenty, plenty more things to discover," Gonzalez said. "What we are saying is just a little brick more in the knowledge."

Four Best Shows for Toddlers (学步的孩童)

Peppa Pig

If you're looking for a British TV show for toddlers, look no further than Peppa Pig. This charming series will have your little one love Peppa and her family as they start their adventures through life in a colorful world.

Each episode of Peppa Pig is like a colorful storybook, combining five parts into 25 minutes of pure joy. Not only is it entertaining, but it also teaches essential social skills, such as kindness, loyalty, and thoughtfulness, making it an ideal choice for young kids and preschoolers.

Sesame Street

If you have fond memories of watching Sesame Street back in the day, why not pass on some of that magic to your little one? The show now is in its 54th season, which is the longest running program of the four shows, and the whole group is still bringing the fun. Not only is the 30-minute program still a crash course in all things smart, with numbers and words on the menu, but there's also wonderful music.

Daniel Tiger's Neighborhood

Step into the interesting world of Daniel Tiger, the lovable star of this show that's a popular offshoot (分支) of the timeless Mr. Roger's Neighborhood. With a runtime of 30 minutes, this show offers plenty of learning opportunities through engaging stories and catchy musical numbers.

Curious George

If you have fond memories of your parents reading Curious George books, you're in for a treat! The beloved stories were transformed into a charming lively series on PBS in 2006, ideal for toddlers. Each episode clocks in at a solid 30 minutes, and it's all about encouraging kids to be as curious and eager to explore as George himself.