The African elephant, the largest land animal remaining on earth , is of great importance to African ecosystem(生态系统). Unlike other animals, the African elephant is to a great extent the builder of its environment. As a big plant-eater, it largely shapes the forest-and-savanna(大草原)surroundings in which it lives, therefore setting the terms of existence for millions of other animals that live in its habitat(栖息地).

    It is the elephant's great desire for food that makes it a disturber of the environment and an important builder of its habitat. In its continuous search for the 300 pounds of plants it must have every day, it kills small trees and underbushes, and pulls branches off big trees. This results in numerous open spaces in both deep tropical forests and in the woodlands that cover part of the African savannas. In these open spaces are numerous plants in various stages of growth that attract a variety of other plant-eaters.

    Take the rain forests for example. In their natural state, the spreading branches overhead shut out sunlight and prevent the growth of plants on the forest floor. By pulling down trees and eating plants, elephants make open spaces, allowing new plants to grow on the forest floor. In such situations, the forests become suitable for large hoofed plant-eaters to move around and for small plant-eaters to get their food as well.

    What worries scientists now is that the African elephant has become an endangered species. If the elephant disappears, scientists say, many other animals will also disappear from vast areas of forest and savanna, greatly changing and worsening the whole ecosystem.

    According to a team of researchers, an animal's ability to perceive(感知) time is linked to their pace of life.

    “Our results lend support to the importance of time perception in animals where the ability to perceive time in a very short time may be the difference between life and death for fast moving creatures.” commented lead author Kevin Healy from Trinity College Dublin.

    The study was done with a variety of animals using phenomenon based on the maximum speed of flashes of light an individual can see before the light source is seen as constant. Dogs, for example, have eyes with a refresh rate higher than humans.

    One example of this phenomenon at work, the authors say, is the housefly and its ability to avoid being hit. The research showed flies “observe motion in a shorter time than our own eyes can achieve,” which allows them to avoid being hit.

    Professor Graeme Ruxton of the University of St Andrews in Scotland, who worked jointly on the research project, said in a statement, “Having eyes that send updates to the brain at much higher frequencies than our eyes do is of no Value if the brain cannot process that information equally quickly. Thus, this work highlights the impressive abilities of even the smallest animal brains. Flies might now be deep thinkers, but they can make good decisions very quickly.”

    In comparison, the tiger beetle (虎甲虫) runs faster than its eyes can keep up, basically becoming blind, which requires it to stop periodically to re-evaluate its prey's(猎物) position.

    Our results suggest that time perception offers an as yet unstudied dimension along which animals can specialize and there is considerable range to study this system in more detail.

    One of the hardest parts of living abroad is being away from your loved ones, especially your family. While my friends are so important to me, I've personally found it more difficult being away from family.

    However, I was fortunate that my mum and sister recently found the time to see me. Both my sister and I have major birthdays this year as she's tuming 18 and I'll be 21. My sister is a very big music fan and this year, I created my status as the best older sister by keeping an eye out for music concerts in Paris. In our home town of Leicester, we don't regularly get many well-known artists playing in our city. But in Paris, I managed to get the best 18th birthday present of all: tickets for all three of us to see my sister's favorite American rapper, Angel Haze.

    I will try to visit for my sister's actual birthday in June, the chance for my sister and my mum to visit became a birthday treat. The experience of finding our way together to the concert or getting to show them around the Paris sites such as the Eiffel Tower,the Arc du Triomphe and even my favorite ice cream place,Amorino, was an amazing memory for us all !Despite the fact that I felt the slight pressure to make sure the weekend went smoothly,even the heavy rain failed to dampen our mood.

    Therefore, while it can be difficult being away from home and potentially missing big family moments,there are ways to avoid the sadness and find a way to make the best of your situation to create an unforgettable memory. Just like the continuing rain while we went up the Eiffel tower, every cloud has a silver lining, because then we got the funniest photos ever!

    Four years ago your friends congratulated you and your father talked big continuously. Four years ago you walked among the gothic towers and weathered traditions that sew our community together. But what's next, will I make friends, or I will measure up? And maybe you quietly wondered why a place like Yale, a place that sparked the drive of presidents, a place that raised the world-famous scholars, a place that trained Pulitzer Prize winners, would ever want you? I hope you had these questions because otherwise I might have embarrassed myself. I admit I asked all of these and more.

    I took an unconventional path to Yale. Five years ago I was working the evening shift at a clothing store in the suburbs of Virginia. My family had moved every year for the past five years and our finances were so consumed that retirement was not a possibility. Worse yet, my son was a junior at an Ivy League college in New Jersey and hearing about his privileged friends often reminded me of all the things I wanted to give him but couldn't.

    When I told him this he relied, “If you really want to spoil me, spoil yourself. ”Then he took my hands and told me I had a brilliant mind and deserved better than everything I had ever known.

    That summer I started community college while working full-time. Education was my second chance. I awoke my curiosity, vitality( 活力) and dignity that I never knew I could feel. When I read Eliot, Miller and Morrison, it was as if I were the first person to have ever read them, as if they were secret insights into the human soul and situations and I knew I couldn't stop.

    Walking among these gothic towers, among these traditions, and among this brilliant, vibrant and unapologetically eclectic Class of 2014 has been inspiring. Whether debating issues in class, or chatting over coffee, I have enjoyed, learned and loved every moment I have shared with you. You have made me a better person and I only hoped I have helped in some way to do the same for you.

    And yet even now this is dreamlike. Four years ago I was convinced no one would want me, I wouldn't measure up and as far as knowing what was next, I supposed I had resigned myself to more of the same. But I've come to learn that nothing great can really be accomplished without a healthy dose of terror. No one ever wrote epic(史诗般的) poems, built monuments or told bedtime stories about people who played it safe.

    I was terrified when I came to Yale. A big part of me thought I wasn't good enough. But a big part of life is ignoring the naysayers(反对者) especially the one inside you. Most people are stopped from doing great things by no one but themselves. I learned to tell myself to shut up. Sometimes in the mirror in the morning and others times in the dark before I went to bed. I came to realize once I could overcome my own fear I could overcome just about anything. If you haven't felt this yet I recommended it: it's the greatest joy you'll ever know.

    You've likely all met your own fear and misgivings(担忧、害怕). I charge you to tell that voice to shut up when necessary because in the end your greatness will not be about IQ but about the sincerity of your ambitions, the toughness of your character and your unwillingness to compromise in the face of difficulty, fear and uncertainty.

    And should someone tell you that it can't be done, or you're not good enough or it's not worth the trouble? Should others ask you to take the safe route, or stick to the path of least resistance? Should people say it's too late or your dreams are impractical? Look them in the eye, laugh a little and let them know “Nothing is impossible”.

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    In our twenties, we find it funny when we can't remember our neighbor's cat's name or a handsome actor who starred in a famous movie. In our thirties, we jokingly call it "brain freeze". In our forties, we laugh it off as a" senior moment" and follow up with one of these old age jokes. But the reality is that there comes a point when being forgetful stops being funny and starts to seem a bit dreadful. You think, "Am I losing it？"Or worse, "Is this a sign of Alzheimer's disease（老年痴呆症）？"

    Well, don't worry. The fact that you recognize your own forgetfulness may be a very good sign, at least in terms of the possibility of your developing Alzheimer's disease（AD）. The researchers in a new study show that it's not forgetfulness but not being aware that we're forgetful that we should fear.

    The researchers began with the assumption that one common feature of Alzheimer's dis-ease is a damaged awareness of illness. And they wanted to prove their theory that the lack of awareness can be used to predict whether someone with" mild cognitive（认知的）damage" will progress to full-on AD. For the study, "mild cognitive damage" was defined as someone whose mental state was considered healthy but who had either complained of memory loss or had suffered objective memory loss.

    The researchers used existing data for 1, 062 people between the ages of 55 and 90 that had been recorded over a 12-year period. The data included brain scans, which the researchers used to look for visual signs of reduced glucose uptake（葡萄糖吸收）.It is an objective marker of the sort of reduced brain function that goes along with AD.As expected, glucose uptake was reduced in those with AD. What the researchers also discovered was that glucose uptake was reduced in those with mild cognitive damage who also showed evidence of reduced illness awareness. Finally, the researchers found that those who had reduced illness awareness were more likely to develop AD than those without.