Dolphins(海豚) live in a dark underwater world. It's often impossible to see each other or anything else around them, so sound plays an important role in their survival. To communicate with each other, dolphins produce all kinds of sounds.

    Only other dolphins understand what the sounds mean. Scientists haven't uncovered their secret communication, except for one kind of whistle. It might last less than a second, but this whistle is a big deal. Why? Because these whistles are actually names of dolphins - and every dolphin has one. Scientists call these sounds a “signature whistle.” When other dolphins hear the whistle, they know which dolphin is calling.

    Dolphins often hunt by themselves but still need to stay connected to the group. Since they can't always see each other, dolphins use their signature whistles to check in with other dolphins hundreds of yards away. “In coastal areas, dolphins exchange whistles even when they're a third of a mile apart,” says Greg Campbell, who studies animals. That means dolphins shout out to group members that might be nearly five football fields away.

    What's amazing is who names the baby dolphin. Not the mother. Not an auntie dolphin or another group member. Scientists believe the baby dolphin itself comes up with the signature whistle. Like human babies, a baby dolphin plays with sounds throughout its first year. While testing its sound skills, a baby dolphin is doing something amazing. It's creating or figuring out its signature whistle. How or why it chooses its signature whistle is not clear. Studies show that most of the time the signature whistle is nothing like its mother's or group members' whistles.

    When the baby dolphin is about a year old, its signature whistle is set. It repeats it often so the other dolphins learn to recognize it.

    Deciphering(破译) dolphin names is just the beginning of figuring out what dolphins communicate about. Do they chat about sharks? Discuss the tides? Maybe they even have a name for people. Someday scientists are to decipher the rest of dolphins' communication.

    Gadgets that make study fun

    Now in a world piled high with smart phones, tablets and e-readers, technology has entered the classroom in ways unimaginable. Taking classes can be fun too. All you have to do is swipe your fingers on your phone screen and download some apps, which can make your study more fun and efficient. Balancing study and play in a college setting has never been easy-and with the following few apps, it'll be tough to tell the two apart.

    Evernote

    Use: note-taking

    Can be used on: Phone/iPad/iPod touch, Android, BlackBerry, Palm OS and     Windows, Phone 7

    Price: free

It's hard to imagine that with all the magical gadgets, the eager, studious types would still take out a notepad, a pencil, and a highlighter—and take notes in class. While it's not an actual planner or a calendar App, if you take notes to stay organized, then Evernote is for you．The main thing about Evernote is that all of your notes are automatically sent into the cloud—and then you can access them from any web-connected computer via the Evernote app or a web browser. Evernote also supports audio and photo notes-rather handy if you want to record your lecture or take photos of any projected notes. But, of course, ask for permission first.

    Wikipanion

    Use: research database

    Can be used on: iPhone/iPad/iPod touch

Price :free ( Wikipanion Plus for $4.99,or 31.87 yuan )

    Now, you don't necessarily have to go to a library or anywhere with computer services to do research work for your paper anymore. You can get access to the research databases just on your smart phone or tablet. Wikipanion gives you a simplified version of Wikipedia without leaving out any of the site's extra features. The normal links that you'd see to each section of an article are no longer on the main screen. Instead, there's small icon located at the bottom of the App, which can be used to access all the sections of an article. You can also open the links in Safari(苹果浏览器). According to the developers' site, loading Wikipedia pages with Wikipanion is a lot faster than accessing the Wikipedia site from the iPhone's browsers. To be honest, we agree.

    Conquering Bilingual News Listening in 7 Days

    Use: English learning application

    Can be used on: iPhone/iPad/iPod touch

    Price: For a limited time you can get the App for only $0.99—half price.

    Still learning English with a workbook? If so, you are behind the times. Get 21st Century Newspaper's new iPhone App, “Conquering Bilingual News Listening in 7 Days”. When you download the App on your iPhone, you can listen to the hottest bilingual news selected from the newspaper's official website (w. w. w. i2lst. cn) and read by native speakers. User can enjoy the audio bilingual news with synchronized subtitles and fantastic pictures while immersed in an authentic language environment. With a simple tap, the sentence you choose will be repeated. “Conquering Bilingual News Listening in 7 Days” has ranked No 1 on the Chinese education App list.

    Floods are second only to fire as the most common of all natural disasters.They occur almost everywhere in the world,resulting in widespread damage and even death.Consequently,scientists have long tried to perfect their ability to predict floods.So far,the best that scientists can do is to recognize the potential for flooding in certain conditions. There are a number of conditions,from deep snow on the ground to human error,which cause flooding.

    When deep snow melts it creates a large amount of water.Although deep snow alone rarely causes floods,when it occurs together with heavy rain and sudden warmer weather it can lead to serious flooding.If there is a fast snow melt on top of frozen or very wet ground,flooding is more likely to occur than when the ground is not frozen.Frozen ground or ground that is very wet cannot absorb the additional water created by the melting snow.Melting snow also contributes to high water levels in rivers and streams.

    Rivers that are covered in ice can also lead to flooding.When ice begins to melt,the surface of the ice cracks and breaks into large pieces.These pieces of ice move and float down the river,They can form a dam in the river,causing the water behind the dam to rise and flood the land upstream.If the dam breaks suddenly,then the large amount of water held behind the dam can flood the areas downstream too.

    Broken ice dams are not the only dam problems that can cause flooding.When a large human-made dam breaks or fails to hold the water collected behind it,the results can be devastating.Dams contain such huge amounts of water behind them that when sudden breaks occur,the great force of the water is like a great tidal wave.The dam waters can travel tens of kilometres,cover the ground in metres of mud and litter,and drown and crush every thing and creature in their path.

    Although scientists cannot always predict exactly when floods will occur,they do know a great deal about when floods are probably going to occur.Deep snow,ice-covered rivers,and weak dams are all strong conditions for potential flooding.

    Many people wrongly think that cities don't have farms and fruits and vegetables are only grown in the country. Believe it or not, there are more urban farms popping up in cities all over the world.

    Alexandra Sullivan, a food systems researcher in New York, studies urban agriculture. Urban agriculture is another name for farming and gardening in a city environment. Ms. Sullivan studies everything from tiny gardens in empty lots between buildings to bigger fields that have been planted and grown. According to Ms. Sullivan, “Urban agriculture has existed since cities have, across the world.”

    The number of humans living in urban areas, or cities, is increasing. The amount of people who wanted to garden in urban areas is also rising. Ms. Sullivan says, “In small gardens, on rooftops and indoors, city residents grow fruits, vegetables, grains, and herbs, and raise animals to produce milk, eggs, honey, and meat. City residents use these foods as supplements to food produced by rural agriculture.” Even though some people who live in urban areas grow crops, urban residents still need to rely on food grown in rural areas. This is because a city doesn't have enough space to grow enough food for everyone living in it.

    In New York City, urban farmers have come up with many different ways to grow their own produce, even though there isn't a lot of room. For example, Brooklyn Grange is a farming operation that has two rooftop vegetable farms in New York City. All together, the farms are made up of 2.5 acres of rooftop space. This makes Brooklyn Grange one of the largest rooftop farming operations in the world.

    Brooklyn Grange grows all kinds of things. The farming company sells its vegetables to local residents and restaurants. And because the farms are on rooftops, they are specially adapted to their urban location. They use available space that is not needed for anything else. As more urban farmers find ways to grow food in cities, urban residents will be better able to get fresher materials for their meals.

    What's small, buzzes here and there and visits flowers? If you said bees or hummingbirds, you got it. You wouldn't be the first if you mixed the two up. Now a group of researchers even say we should embrace our history of considering the two together in the same group. The way scientists study bees could help them study hummingbird behavior, too.

    Scientists first compared the two back in the 1970s when studying how animals search for food. The idea is that animals use a kind of math to make choices in order to minimize the work it takes to earn maximum rewards. Researchers at the time focused on movement rules, like the order in which they visited flowers, and where flowers were located relative to others .It was “almost like an algorithm（算法）”for efficient searching, said David Pritchard, a biologist at the University of St. Andrews in Scotland. Hummingbirds and bees had similar solutions.

    As the field of animal cognition（认知）appeared, hummingbird and bee research parted. Neuroscientists and behavioral ecologists developed ways to study bee behavior in naturalistic settings. Hummingbird researchers compared hummingbirds to other birds and borrowed methods from psychology to study their ability to learn in the lab. To be fair, hummingbirds and bees differ. For example, hummingbirds have more advanced eyes and brains than bees. Honeybees and bumblebees are social; hummingbirds typically aren't.

    But however they perceive（感知）or process information, they both experience similar information, Dr. Pritchard said. In day-to-day searching for food, for example, hummingbirds may rely on more of a bee's-eye view than a bird's-eye view. Like other birds, they rely on landmarks, distances and directions to make maps when travelling long distances, but they don't use these cues to find flowers. Move a flower just an inch or so away from where a hummingbird thought it was and it will hover over the flower's original location. Dr. Pritchard is investigating if, like bees, hummingbirds engage in view matching — hovering, scanning snapshots of a place to its memory and using those as references later.

    Philadelphia offers a ton of attractions that are suitable for people of every age and here are some family—friendly attractions．

    Spruce Street Harbor Park

    Spruce Street Harbor Park，one of the best urban beaches in American，is an outdoor heaven on the Delaware River waterfront．Visitors can relax in a hammock，play on the playgrounds，and play games like table tennis and giant chess．Don't miss out on the park at night，when colorful LED lights hanging from treetops make the entire area bright.

    Blue Cross RiverRink

    Offering ice skating in the winter and roller skating in the summer，Blue Cross RiverRink creates a fun，outdoor experience for the whole family．Visitors can play on the nine-hole mini-golf course during the summer，and enjoy eats and drinks from the on-site(现场的)bar and restaurant all year round．

    Sesame Place

    Big Bird，Elmo and the other stars of Sesame Street come out and play at Sesame Place，the only theme park in the nation starring the popular TV show's most lovable characters．A water park，interactive activities，parades，fireworks and shows add to the fun．

    Once Upon a Nation Storytelling Benches

    On summer days，uniformed and professional storytellers at 13 storytelling benches throughout Philadelphia's Historic District entertain visitors with true，free，three-to-five minute tales about the colonial(殖民的)era as part of Once Upon a Nation．Children can pick up a Story Flag at any storytelling bench，and then collect a star from every storyteller on their journeys．Flags with all the stars can get free rides on the Parx Liberty Carousel at Franklin Square．