Navajo was the perfect choice for a secret language. It is very complex. One vowel (元音）can have up to ten different pronunciations, changing the meaning of any word. In the 1940s, Navajo was unwritten language. No one outside of the reservation could speak it or understand it.

    The Navajo Code team had to invent new words to describe military equipment. For example, they named ships after fish: lotso-whale (battleship), calo-shark (destroyer), beshloiron-fish (submarine). When a Code Talker received a message via radio, he heard a series of unrelated Navajo words. He would then translate the words into English and use the first letter of each English word to spell the message. The Navajo words tsah (needle), wol-la-chee (ant), ah-kh-di-glini (victor), and tsah-ah-dzoh (yucca) spelled NAVY.

    The Code Talker kept the code a secret. They memorized everything. There were no code books. As a result, no ordinary Navajo soldiers, if captured by the enemy, could understand the code. More than 3,600 Navajos served in World War II, but only 420 were Code Talkers with the US Marines. They coded and decoded battlefield messages better and faster than any machine. They could encode, transmit, and decode a three-line English message in 20 seconds. Machines of the time required 30 minutes to perform the same job.

    Even after the war the code remained top secret. When they were asked about their role, Code Talkers just said: “I was a radioman.” War movies and histories came out without mentioning them. The code was never used again and was finally declassified in 1968. Only then did the secret came out.

    In its early history, Chicago had floods frequently, especially in the spring, making the streets so muddy that people, horses, and carts got stuck. An old joke that was popular at the time went something like this：A man is stuck up to his waist in a muddy Chicago street. Asked if he needs help, he replies, "No, thanks. I've got a good horse under me."

    The city planner decided to build an underground drainage （排水） system, but there simply wasn't enough difference between the height of the ground level and the water level. The only two options were to lower the Chicago River or raise the city.

    An engineer named Ellis Chesbrough convinced the city that it had no choice but to build the pipes above ground and then cover them with dirt. This raised the level of the city's streets by as much as 12 feet.

    This of course created a new problem: dirt practically buried the first floors of every building in Chicago. Building owners were faced with a choice: either change the first floors of their buildings into basements, and the second stories into main floors, or hoist the entire buildings to meet the new street level. Small wood-frame buildings could be lifted fairly easily. But what about large, heavy structures like Tremont Hotel, which was a six-story brick building?

    That's where George Pullman came in. He had developed some house-moving skills successfully. To lift a big structure like the Tremont Hotel, Pullman would place thousands of jackscrews （螺旋千斤顶） beneath the building's foundation. One man was assigned to operate each section of roughly 10jackscrews.At Pullman's signal each man tured his jackscrew the same amount at the same time, thereby raising the building slowly and evenly. Astonishingly, the Tremont Hotel stay open during the entire operation, and many of its guests didn't even notice anything was happening.

    Some people like to say that every problem has a solution. But in Chicago's early history, every engineering solution seemed to create a new problem. Now that Chicago's waste water was draining efficiently into the Chicago River, the city's next step was to clean the polluted river.

    As free as they make us, mobile phones still need to stay close to a power source. Soon that may change with "green" power.

    Three Chilean students got the idea for a plant-powered device(装置) to charge（使……充电） their cellphones, while sitting in their school's outdoor courtyard during a break from exams, with dead mobile phones. Then, one of them had an "aha" moment.

    “It occurred to Camila to say about plants,” said inventor Evelyn Aravena. “'Why don't you have a socket, if there are so many plants? 'After that, we thought, 'why don't they have a charging outlet（插座）? Because there are so many plants and living things that have the potential to produce energy, why not?'”

    Their invention—a small biological circuit called E-Kaia—uses the energy plants to produce during photosynthesis(光合作用). A plant uses only a small part of that energy and the rest goes into the soil, and that's where the E-Kaia collects it. The device plugs into the ground and then into your phone.

    "It's the most amazing project I've ever seen in my life, plain and simple. They brought this original model, and it worked — and that's when it all changed, at least from my personal point of view and I began to support them." said Mauricio Cifuentes.

    The device solved two problems for the engineering students — they needed an idea for a class project, and an outlet to plug in their phones.

    "Looking for a place to charge the notebook, which had no power, and the mobile phones, we weren't able to find anything because all the other students were in the same state of madness trying to find a place to charge their devices," said Aravena.

    But plants are everywhere, and the bio－circuit makes good use of their excess(过多的) power.

    The E-Kaia doesn't carry much charge but it's powerful enough to completely recharge a mobile phone in less than two hours.

    The student inventors have applied for patents（专利） on their technology, and expect the E-Kaia to go on sale in the near future.

    A new study, a project of the researchers from the University of Pittsburgh in Pennsylvania, finds the fitness tracker probably does not help with weight loss.

    The devices are designed to record your physical activity. They are usually worn around the wrist, where they measure a person's heart rate. The research team looked at two groups of individuals. The first wore a fitness tracker and took part in health counseling (咨询) with experts to consider the best weight-loss plan. The researchers compared this group with people who only got health counseling.

    The study found that those only speaking with the health experts lost nearly 6 kilograms, but those using a fitness tracker lost only 3.5 kilograms. John Jakicic, the lead researcher, questioned the use of electronic devices for weight control in place of "effective behavioral counseling for physical activity and diet."

    The study involved 470 subjects aged between 18 and 35. Some of them were overweight, while others were considered obese (肥胖的). Over three fourths of the subjects were women. All the subjects were told to increase physical activity and start on a low-calorie diet. They had their weight measured once every six months. After six months, researchers divided the group into two parts: one continued with monthly counseling, while members of the other group were given a fitness tracker. Eighteen months later, both groups "showed significant improvements in fitness, physical activity, and diet," with no major difference between groups. However, when it came to losing weight, the people who only spoke with experts lost nearly twice as much weight.

    Jakicic said, "the study's findings are important because effective long-term treatments are needed to address America's obesity." More information is needed, he added, to learn how to best use these devices to change "physical activity and diet behaviors" in adults who want to lose weight.

    If you wear glasses, chances are you are smarter. Research published in the famous British journal Nawre Conurunications has found — people who displayed higher levels of intelligence were almost 30 percent more likely to wear glasses.

    The scientist, studied the genes of thousands of people between the ages of 16 and 102. The study showed intelligence can be connected to physical characteristics. One characteristic was eyesight. In out of 10 people who were intelligent, there was a higher chance they need glasses. Scientists also said being smarter has other benefits. It is connected to better health.

    It is important to remember these are connections which are not proven causes. Scientists call this correlation. Just because something is connoted to something else does not mean one of those caused the other. And it's worth noting that what constitutes (构成)intelligence is subjective and can be difficult, if not impossible, to measure.

    Forget genes thought. Plenty of proof shows wearing glasses makes people think you are more intelligent, even if you do no, need glasses. A number of studies have found people who wear glasses are seen as smarter, hard-working and honest. Many lawyers this idea to help win their cases. Lawyer Harvey Slovis explained this. "Classes soften their appearance," he said. Sometimes there has been a huge amount of proof showing that people he was defending broke the law. He had them wear glasses and they weren't found guilty.

    Glasses are also used to show someone is intelligent in movies and people who wear glares have begun to shift. People who do not need glasses sometimes wear them for fashion only. They want to look worldly or cool. But not everyone is impressed by this idea, thought. GQ magazine said people who wear glasses for fashion are trying too hard to look smart and hip(时髦的). However, that hasn't stopped many celebrities (名人) from happily wearing glasses even if they do not need them. Justen Bieber is just one high - profile fen of fashion glasses.

    I'd done it before, and so I had no reason to believe that this time would be any different. I was sure that when I returned home from my mission trip. As always, I'd bring back nothing more some mud on my boots. A hole or two in my jeans and, of course, a lot of great memories.

    The summer before my high school graduation, I went to West Virginia with others as volunteers to repair the homes of those in need. Arriving at our destination, my group was assigned the task of rebuilding sections of a home that had been damaged by fire. No sooner had we parked on the home's dirt driveway than we saw an excited little girl, no more than six years old, standing in the doorway of the family's temporary home. Shoeless and wearing dirty clothes and the biggest smile I'd ever seen, she yelled, "Ma, Ma, they really came!" I didn't know it then, but her name was Dakota, and four more days would pass before she'd say another word near me.

    Behind Dakota was a woman in a wheelchair — her grandmother, we'd soon learn. I also discovered that my job that week would be to help change a fire-damaged dining room into a bedroom for this little girl. Grabbing our tools, we went to work. Over the following days, I noticed Dakota peeking at us every now and then as we worked. A few times, I tried talking with her, but she remained shy and distant, always flying around us like a tiny butterfly but keeping to herself.

    By our fifth and final day, however, this was about to change.

    Before I went to work on her home on that last morning, I spoke for a moment or two with the grandmother. I was especially pleased when she told me how much Dakota loved her new room — so much, in fact, that she'd begged to sleep in it the previous night, even though it wasn't quite ready. As we talked, I noticed something I hadn't seen before — Dakota was hiding behind her grandmother.

    Cautiously, she stepped into view, and I could see that just like her clothes, her face was still dirty. But no amount of soil could hide those bright blue eyes and big smile. She was simply adorable. I wanted so much to hug her, but respecting her shyness, I kept my distance.

    Slowly, she began walking toward me. It wasn't until she was just inches away that I noticed the folded piece of paper in her tiny hand. Silently, she reached up and handed it to me. Once unfolded, I looked at the drawing she'd made with her broken crayons on the back of an old coloring book cover. It was of two girls — one much taller than the other — and they were holding hands. She told me it was supposed to be me and her, and on the bottom of the paper were three little words that instantly broke my heart. Now almost in tears, I couldn't control myself anymore — I bent down and hugged her. She hugged me, too. And for the longest time, neither of us could let go.

    By early afternoon, we finished Dakota's bedroom, and so I gladly used the rare free time to get to know my newest friend. Sitting under a tree away from the others, we shared a few apples while she told me about her life. As I listened to her stories about the struggles she and her family went through daily, I began to realize how boring various aspects of my own life were.

    I left for home early the next morning. I was returning with muddy boots and holes in my Jeans. But because of Dakota, I brought back something else, too-a greater appreciation for all or the blessings of my life. I'll never forget that barefoot little butterfly with the big smile and dirty face. I pray that she'll never forget me either.