Houses fall down. Trees fall over. Large holes form in the ground. Could Alaska be sinking? That's what some villagers in Alaska have been asking themselves recently and scientists think they know why. Warmer temperatures may be causing Alaska's frozen ground to thaw (解冻).

    About 85 percent of Alaska's land surface has permafrost (永久冻结带). Permafrost supports the ground above it—including trees, houses, and roads. But why is the permafrost thawing?

    Some scientists say that human-caused pollution is leading to global warming. And most scientists agree that Alaska has been getting warmer. They say that the warmer temperature is causing permafrost to thaw in some areas. The thawing permafrost can cause problems for people, plants, and animals.

    The collapsing (倒塌) is a problem in the villages in Alaska which are built on permafrost, and some of them may have to move to safer ground, where there is no permafrost.

    The Alaskan town of Glennallen saw its old post office collapse. And, according to James Walters, a permafrost expert at the University of Northern Iowa, house-moving companies have been very busy.

    “Melting permafrost can also destroy trees and forests,” Walters said. “When holes in the ground form, trees fall into them and die. This could turn a forest into a swamp (沼泽), and animals which need the forests will have to move elsewhere.”

    “The melting could cause severe problems.” Walters says, “This could take hundreds of years, but in the end Alaska will look quite different from what it looks like now.”

    See a cellphone cover that you like on Taobao? Forget about placing an order, paying the bill online and waiting for days for it to be delivered to you. In the near future, you'll be able to get it in minutes just by hitting “print” on your computer.

    You might find it hard to believe that you could actually “print” an object like you would a picture. But it is not that hard to understand how it would work. Just as a traditional printer sprays ink onto paper line by line, modern 3D printers spread material onto a surface layer by layer, from the bottom to the top, gradually building up a shape.

    Instead of ink, the materials the 3D printer uses are mainly plastic, resin(树脂) and certain metals. The thinner each layer is—from a millimetre to less than the width of a hair—the smoother and finer the object will be.

    This may sound like a completely new technology, but the truth is that 3D printing has been around since the late 1980s. Back then, it was barely affordable for most people, so few knew about it.

    Last year, though, saw a big change in the 3D printing industry—printers became much cheaper. For example, 10 years ago a desktop 3D printer might have cost ￡20，000, while now they cost only about ￡1，000, according to the BBC.

    Taken out of the factory and introduced to more diverse and common uses, 3D printing can create just about anything you can think of—flutes , bikinis, jewelry, aircraft parts and even human organs. In fact, scientists from Cornell University in New York have just made an artificial ear using a 3D printer, according to Science Daily. The fake ear looks and acts exactly like a natural one.

    However, as 3D printing becomes more common, it may bring about certain problems—such as piracy. “Once you can download a coffee maker, or print out a new set of kitchen utensils (餐具) on your personal 3D printer, who will visit a retail  store again？” an expert in 3D printing told Forbes News. Even more frightening, what if anyone in the world could use a 3D printer to print out a fully functioning gun?

    Is there a magic cutoff period when offspring become accountable for their own actions? Is there a wonderful moment when parents can become spectators (旁观者) in the lives of their children and shrug, "It' s their life," and feel nothing?

    When I was in my twenties, I stood in a hospital corridor waiting for doctors to put a few stitches in my son's head. I was asked, "When do you stop worrying?" A nurse said, "When they get out of the accident stage." My mother just smiled faintly and said nothing.

    When I was in my thirties, I sat on a little chair in a classroom and heard how one of my children talked incessantly, disrupted (打断) the class, and was headed for a career making license plates. As if to read my mind, a teacher said, "Don't worry. They all go through this stage, and then you can sit back, relax, and enjoy them." My mother listened and said nothing.

    When I was in my forties, I spent a lifetime waiting for the phone to ring and the cars to come home, the front door to open.

    My friends said that when my kids got married I could stop worrying and lead my own life. I wanted to believe that, but I was haunted by my mother' s wan ( 淡淡的 ) smile and her occasional words, "You look pale. Are you all right? Call me the minute you get home."

    Can it be that parents are sentenced to a lifetime of worry? Is concern for one another handed down like a torch to blaze the trail of human frailties and the fears of the unknown? Is concern a curse? Or is it a virtue that elevates us to the highest form of life?

    One of my children became quite irritable recently, saying to me, "Where were you? I've been calling for three days, and no one answered. I was worried!!!"

    I smiled a wan smile.

    It's not often you get information about a destination from a heavy metal band, but in Debrecen, Hungary's second largest city, locals are used to having to make a noise to get heard.

    Just off the historic center, Roncs bar is a pub that also hosts live music.  It has the atmosphere of a student party in an old building that might soon be knocked down.

    Roncs is owned by Hungary's best-known heavy metal rock band, Tankcsapda. Sometimes referred to as the “Hungarian Metallica", the band has taken a type of music that is famous worldwide and-through lyrics, album covers, and an annual New Year's party and concert-made it all about their home city.

    It's perhaps fitting that Tankcsapda should be seen as ambassadors for Debrecen-the city sometimes needs loud heavy metal rock music to get noticed. “Foreigners think that Hungary is Budapest and there's nothing else,” is a familiar saying on Debrecen's:streets.

    Debrecen has, at times, been more important than the current seat of power, with locals claiming it takes over in times of trouble.

    That doesn't quite add up.

    Debrecen survived an attack from the Mongols in the 13th century, the Black Death, 150 years of struggle against the Ottomans and numerous conflicts, and yet it has still only briefly been the country's capital twice. This happened for the first time after a short-lived revolution in 1849, and for a second time at the end of World War II.

    Today, Debrecen may not be well known to tourists, but that only adds to the charm of this relaxed city. It's a small place; the historical center is sized for strolling (散步) and regular cafe stops. There's also a view of Debrecen's mix of architectural styles, a result of the frequent large fires that back in the 19th century led the city's students to form one of Europe's first-ever fire brigades (消防队).

    You can also see traditional weathercocks from the rooftops, featuring Islamic star and crescent moon symbols that once advertised to Ottoman invaders that the city preferred trading to fighting.

    Trade meant that Debrecen's skilled people became very successful and the city became famous for-among other things-fine foods, hats and clay pipes. In the early 19th century, 10 million clay pipes were reportedly made a year, with thousands bought for Britain's navy.

    Most people know that Marie Curie(居里夫人) was the first woman to win the Nobel Prize, and the first person to win it twice. However, few people know that she was also the mother of a Nobel Prize winner.

    Born in September, 1887, Irene Curie was the first of the Curies' two daughters. Along with nine other children whose parents were also famous scholars, Irene studied in their own school, and her mother was one of the teachers. She finished her high school education at the College of Sévigné in Paris. Irene entered the University of Paris in 1914 to prepare for a degree in mathematics and physics. When World War I began, Irene went to help her mother, who was using X-ray facilities（设备） to help save the lives of wounded soldiers. Irene continued the work by developing X-ray facilities in military hospitals in France and Belgium. Her services were recognized in the form of a Military's Medal by the French government.

    In 1918, Irene became her mother's assistant at the Curie Institute. In December 1924, Frederic Joliot joined the Institute, and Irene taught him the techniques required for his work. They soon fell in love and were married in 1926. Their daughter Helene was born in 1927 and their son Pierre five years later.

    Like her mother, Irene combined family and career. Like her mother, Irene was awarded a Nobel Prize, along with her husband, in 1935. Unfortunately, also like her mother, she developed leukemia because of her work with radioactivity（辐射能）. Irene Joliot-Curie died from leukemia on March 17, 1956.

After years of travel it was bound to happen. Waiting by the moving belt, I watched the suitcases make mocking(嘲弄的) rounds. My companions, exhausted after16hours in the plane, were sympathetic and relieved. They were all thinking: at least it wasn't me. Any moment now, I told myself, swearing at the happy vacationers busy collecting their things. What about my necessities (必需品)?

For millions of travelers a year, it happens. Their missing bags stolen, sold in blind auctions(拍卖), or gone forever without any explanation. Today it was my turn, in a crowded Indian airport, as far from home as I'd ever been.

So, while the airline hunted for my belongings with no any order or plan and asked whether I would rather have $200– I found myself wandering the hot streets of Delhi in an orange dress and a pair of blister-producing ballet flats. Equipped with my carry-on (contents: eyeglasses, a paperback, an ancient tube of Chapstick), I was forced to "manage".

Day two, good news. The bag had been found! Bad news: it is still sitting in Toronto. Did it miss me as much as I missed it?

But then, a twist. I survived. By day three, I was secretly enjoying myself. What to wear? Hello, orange. Make-up today? Not an option. With almost nothing, I found better things: a new understanding of necessity, a short break from my obsession(痴迷) with stuff, stuff and more stuff, and a new appreciation for what does matter (the Taj Mahal) , when my bag finally made its way back to me.

That's right, my jam-packed blue suitcase resurfaced – on day four – and I suddenly had a rainbow of ten dresses to choose from. I decided to wear my orange dress once more, for good luck. It worked: nothing went missing on my journey home.