Last year DeepMind's AlphaGo programme took on and beat two of the world's best players of the Chinese game of Go（围棋）-an unbelievable achievement seen as a milestone in the development of artificial intelligence (A). That programme was trained by first giving it vast amounts of data from amateur and professional games.

    The new AlphaGo Zero began with a blank board and nothing but the rules of Go and set about playing against itself. Within three days it was so advanced that it took on the previous version, which had taken months to develop, and defeated it by a hundred games to zero.

    DeepMind says that creating knowledge from first principles without learning from human expertise（专门技能）is an important step in developing artificial intelligence. The company's founder Demis Hassabis said this breakthrough could help in real world problems such as designing new drugs or discovering new materials.

    In 1997, Garry Kasparov was defeated by Deep Blue, a computer program written by IBM, running on a supercomputer. This was the first time that a ruling world chess champion was defeated by a computer program in tournament conditions. Superficially, AlphaGo's win against Lee Sedol can be compared to Deep Blue's win against Gary Kasparov, which happened almost 20 years ago. So: what's the big deal? We have to understand the differences between chess and Go.

    In chess, each player begins with 16 pieces of six different types. Each piece of type moves differently. The goal of the game is to seize the other player's king. Go starts with an empty board. The goal of the game is to gain as much territory（领地）as possible.

    Although the rules of Go might appear simpler than those of chess, the complexity of Go is higher. Also, games usually last longer for lots of moves. A typical game in Go might last for 150 moves vs.80 in chess.

    When Nancy Flexer opened the door to her classroom near the end of her final school year, all 41 years of her career as a beloved first-grade teacher came to life right in front of her.

    Cole Elementary School in Tennessee surprised Flexer with a memorable and emotional retirement party featuring former students of all ages, dating back to the first class she taught in the 1973-74 school year. A video of the event shows an overwhelmed Flexer being moved to tears as she hears former students who are now adults tell her how much she affected their lives.

    "I'm one of the luckiest people in this world," Flexer said. "I remember I opened the door to the classroom thinking no one was in there, and it was wall-to-wall people and banners and everything. It was the coolest thing that could've ever happened in my life. How many times do we really realize the lives we've touched, the manner in which we've touched them, and that these are memories that stay with them for life?"

    Despite being young when they were taught by Flexer, students easily recalled the heartwarming notes she wrote them on report cards, the ways she helped them overcome shyness and awkwardness, and how she inspired them to future academic success to earn scholarships and advanced degrees.

Even though Flexer hadn't seen some of the former students for decades, she instantly remembered the names of every single one there.

    A scrapbook(剪贴簿) of her career was presented to her as one student after another recalled the effect Flexer had on his or her life.

    “I've had many opportunities to move to a school closer to my home, but I said 'Cole gave me so much in my life that when I retire, I will retire from Cole school and give back what's been given to me.” Flexer said. “My career could've taken me nowhere that would have made me happier. I think of it as a blessing.”

    Bus Tours in Washington DC

    The Lights Night Tour in Washington DC

Duration: 3 hours $56.33

    Highest-rated Night Tour in DC! The ONLY DC Night Tour where the Tour Guides

    HOP OFF with you at each stop and tell you about each monument and attraction. Hop aboard the Lights Night Tour! The best time to take a tour of Washington DC is at, night.

    Best Mount Vernon & Arlington Cemetery Tour from Washington DC

    Duration: 6 hours. $78.96.

    See Arlington Cemetery, Old Town Alexandria and George Washington's Mount

    Vernon Estate on this small group bus tour from Washington DC. Your tour guide will accompany you through Mount Vemon, telling you about all of the attractions there and the history of George Washington's home on the Potomac River.

    The Best Minibus Tour in Washington DC.

    Duration: 3 hours $ 46.92

    See all the key attractions DC has to offer in a 3-hour format. You will learn all about the history and trivia that surrounds Washington and visit the major monuments and attractions DC has to offer.

    Please Note: Rates for this tour vary by day of the week. When you choose your specific date on the availability calendar, the rates for that date will be displayed.

    The Blossoms Tour in Washington DC.

    Duration: 3 hours $ 56.99

    BEST WAY to Experience the Cherry Blossoms! Each year from mid March to mid April, see the beautiful Cherry Blossoms in Washington DC and get great photos because you'll be led to all the best spots by the best guides. The annual spring bloom in DC is a magical time and this tour promises to provide the very best tour opportunity for you!

    It is irrefutable: Parents, who talk to, read and engage with their very young children as often as possible, help them build literacy (读写能力) skills at an early age.

    Also certain: Parents of very young children usually have to do a lot of laundry. And low-income families tend to bring their kids with them to public laundromats (洗衣房).

    Those truths appear once a week at select neighborhood laundromats in Chicago. That's when librarians lay down colorful mats and oversized board books beside the industrial washing machines.

    Inside one of about 14 laundromats in the city's low-income neighborhoods, the librarians gather all available children for Laundromats Story Time (LST), a Chicago Public Library (CPL) program.

    With the noise of the washers and dryers, anywhere between a handful to more than a dozen children hear stories, sing songs and play games designed to help their brains develop. The event also aims to instruct parents on how to repeat the experience for their kids, working to raise poor literacy rates in underserved communities.

    "We read books, we sing songs, we do plays," says Becca Ruidl, the CPL's STEAM Team early learning manager, who runs the LST program. "We kind of keep it going so parents can walk in adn join in at any time. But a big part of what we do is model literacy skills for parents so they can do it at home with their kids."

    While a laundromat seems an unlikely place to engage with children, "we really wanted to meet people in the community where they're. "Ruidl says.

    And it clearly meets a need: Library officials say the program is in increasing demand, while Ruidl says families have adjusted their household's laundry day to suit the librarians' laundromat visits. At the same time, LST's co-sponsors—including a laundry industry trade group and Libraries Without Borders, an organization fighting poverty through literacy—have worked with the CPL to draft an instruction handbook to help expand the concept to other U.S. cities.

    Elizabeth and I are 18 now, and about to graduate. I think about our elementary school friendship, but some memories have blurred(模糊). What happened that day in the fifth grade when Beth suddenly stopped speaking to me? Does she know that I've been thinking about her for seven years? If only we could go back, and discover what ended our relationship.

    I have to speak with Beth. I see her sometimes, and find out school is "fine". It's not the same. It never will be. Someone says that she's Liz now, what happened to Beth?

    I can't call her. Should I write? What if she doesn't answer me? How will I know what she's thinking?

    Yes, I'll write her a letter. These things are easier to express in writing. "Dear Be-," no, "Dear Li-" no, "Dear Elizabeth," I begin. The words flow freely, as seven-year-old memories are reborn. I ask her all the questions that have been left unanswered in my mind, and pray she will answer. I seal my thoughts in the perfect white envelope, and imagine Beth looking into the mailbox. Will she know why I'm writing? Maybe she once thought of writing the same letter.

    As the mailman takes my envelope from me forever, I wonder if I've made the right decision. Do I have the right to force myself into Beth's life again? Am I simply part of the past? I have taken the first stop. Beth has control of the situation now.

    One day has passed. Are my words lying on the bottom of the post office floor.

    Two days are gone. I'm lost in thought and don't even hear the phone ring.

    "Hello? It's Elizabeth"

    Born in the 1950s, shopping malls were once the symbol of the U.S. consumer culture, but many are now dying out.

    Dying shopping malls can be found across the United States, often in middle-class suburbs. Economic decline in certain areas together with an upward trend towards online shopping and new forms of urban shopping centers have pushed the once seemingly unbeatable shopping malls into decline. It is estimated that 15 to 50 percent of shopping malls may close in the coming decades.

    American shopping culture follows its housing culture. Numerous shopping malls were therefore born after the Second World War, as Americans with cars and fat wallets moved to the suburbs. U.S. shopping malls were built at a rapid pace as shoppers fled cities, peaking in the mid-1990s when they were being built at a rate of 140 a year. Thus, too many shopping malls are left though construction has gradually decreased since then.

    Currently, there are around 1,500 shopping malls across the U.S. Most share a handful of similar feature. They usually contain two or three stories of stores separated by walkways. Food courts serve pizza and other fast food. Parking lots are big enough to easily misplace a car.

    Shopping malls in Europe might contain grocery stores or childcare centers, while those in Japan are often built around mass transit (交通枢纽). But the suburban American shopping malls are hard to get to and mainly sell clothes and gifts.

    As many shopping malls became redundant (过剩的), leaders in many U.S. towns who once fought for malls now struggle with how to transform them to new uses. Highland Mall in Texas is being transformed into a community college campus, and Lakeland Mall in Florida now houses a megachurch (大型教会). Others have been redeveloped to include housing, offices and even green space. However, it is hard to imagine every shopping mall meeting the demands for such transformations.