I went to the Tsavo National Park in northern Kenya for a film. We set off early for a distant water hole. A huge elephant covered with dry mud, drank calmly and deeply. He might have traveled 50 km to reach the water. He wasn't going to hurry now. We thought he'd drink a while and rest in the shade, and then drink again. What actually happened was that he drank deeply and stepped away. Then he suddenly fell down. Within minutes he was dead.

    We called animal doctor Jeremiah Poghon immediately. He removed the head of a poisonous arrow (箭) from the elephant's body, and let out over 100 liters of drug—the result of the elephant's meeting with a poacher (偷猎者) months before.

    Today's poacher fires an arrow, covered with poison, into the body of an elephant. If the poacher is lucky, the elephant might die in an hour or two; if not, he might have to follow the elephant for days before it dies. Often the arrow head fails to kill the elephant at once—it doesn't mean the poison won't finally kill the elephant, but it will be a slow death.

    Living in Tsavo through these times, I could see the results of poaching from time to time. When I think about the death of that elephant, what stays with me is the great silence after the shocking sound of his body hitting the ground. I couldn't escape the feeling that with the death of such a large animal, the world seemed to be a poorer and emptier place.

    Gabby Douglas stood beneath the Rio Olympic Arena, still in her Team USA leotard, trying hard to understand how she had become the most unpatriotic athlete in Rio. Tears filled in her eyes. She tried hard to talk but no words came out. Her pauses were long and uncomfortable.

    “I've been trying to stay off the Internet because there's so much negativity,” she said. The attacks against her have been everywhere these last few days. The bullies blamed her for not putting her hand over her heart while the US national song played. Besides, some other people attacked her for not jumping up and cheering hard enough for team-mates at the all-around final. All of this prompted her mother, Natalie Hawkins, to tell Reuters this weekend, that Douglas is “heartbroken”.

    It showed on Sunday, in Douglas's final performance of this Olympics and maybe in the Games ever. Douglas finished sixth in the uneven bars, far from the medal stand she owned four years ago in London, and shook her head, confused. What had she done wrong? Nothing made sense.

    “I mean, you do [Olympics] for your country, and you do it for yourself, how have I offended them? What have I done? I was standing in respect for USA. I'm coming out there representing them to the best of my abilities, so how would I be in disrespect?

    Feeling sad is an important part of human nature.

    Jerome Wakefield, a professor at New York University, mentions that feeling down after your heart is broken is normal and may even be beneficial. Recently, Wakefield's students have been coming up to him because their parents are pressuring them to get help for their sadness; often the kids want no part of it. Rather than “listen to medicine,” they want to listen to their hearts. He believes these students' reaction represents an important part of human nature.

    Professor Diener, who has studied happiness for a quarter century, finds that the Scots and many other peoples like being sad, and don't appreciate being told they should be happier. “They say too much happiness might not be such a good thing, no matter where it comes from,” says Diener. He believes it's wrong for the “happiness industry” to send the message that not only can we all be happier, but we have a duty to be so. He argues that what is considered normal sadness is something we shouldn't avoid.

    Eric Wilson, a professor at Wake Forest University, made every effort to smooth out his habitual frown and wear a sunny smile, since a happy expression can lead to happy feelings. He even tried to be enthusiastic. When neither of these made him happy, he concluded that such a happiness movement was no good for him at all. Americans, love for happiness, he writes, creates an environment where sadness is not valued.

    These researchers believe the problem of continuous, extreme happiness should not be surprising, since negative emotions developed for a reason. Fear warns us against the presence of danger, for instance. Sadness, too, seems to be part of our DNA: monkeys, dogs and elephants all display something that looks like sadness. Being “up” all the time can cause you to play down very real threats.

    They believe that only by experiencing sadness can we experience the fullness of the human condition. Their studies show that when you are in a negative frame of mind, you become more logical and more creative. Abraham Lincoln was not limited by his dark moods, and Beethoven composed his later works in a sad state. Vincent van Gogh, Emily Dickinson and other artistic giants saw the world through a glass darkly.

    People who are somewhat unhappy are more motivated to improve both their own lot and the lot of their community. In contrast, people at the top of the happiness charts feel no such urgency. “If you're totally satisfied with your life,” says Diener, “you don't feel like working for change. Be careful when people tell you that you should be happier.”

    Exposing living tissue to subfreezing temperatures for long can cause permanent damage. Microscopic ice crystals (结晶体) cut cells and seize moisture (潮气), making donor organs unsuitable for transplantation. Thus, organs can be made cold for only a few hours ahead of a procedure. But a set of lasting new antifreeze compounds (化合物)—similar to those found in particularly hardy (耐寒的) animals—could lengthen organs' shelf life.

    Scientists at the University of Warwick in England were inspired by proteins in some species of Arctic fish, wood frogs and other organisms that prevent blood from freezing, allowing them to flourish in extreme cold. Previous research had shown these natural antifreeze molecules (分子) could preserve rat hearts at -1.3 degrees Celsius for up to 24 hours. But these proteins are expensive to extract (提取) and highly poisonous to some species. “For a long time everyone assumed you had to make synthetic (人造的) alternatives that looked exactly like antifreeze proteins to solve this problem, ”says Matthew Gibson, a chemist at Warwick who co-authored the new research. “But we found that you can design new molecules that function like antifreeze proteins but do not necessarily look like them.”

    Most natural antifreeze molecules have a mixture of regions that either attract or repel water. Scientists do not know exactly how this process prevents ice crystal formation, but Gibson thinks it might throw water molecules into push-pull chaos that prevents them from tuning into ice. To copy this mechanism, he and his colleagues synthesized spiral-shaped molecules that were mostly water-repellent—but had iron atoms at their centers that made them hydrophilic, or water-loving. The resulting compounds were surprisingly effective at stopping ice crystals from forming. Some were also harmless to the roundworm Caenorhabditis elegans, indicating they might be safe for other animals.

    “These compounds are really cool because they are not proteins—they are other types of molecules that nonetheless can do at least part of what natural antifreeze proteins do, ”says Clara do Amaral, a biologist at Mount St. Joseph University, who was not involved in the research. Gibson's antifreeze compounds will still need to be tested in humans, however, and may be only part of a solution. “We don't have the whole picture yet,”do Amaral adds. “It's not just one magical compound that helps freeze-tolerant organisms survive. It's a whole suite of adaptations.

    For many, music is as important to the human experience as eating and breathing. We hear music everywhere—at home, the gym, parties and stores. But what kind of music do we prefer to listen to, and when and why do our musical preferences change?

    The relationship between the change of seasons and musical preferences was the focus of a study led by psychologist Terry Pettijohn. He and his team based their research on a previous study that examined the relationship between popular music preferences and the Environmental Security Hypothesis(假设). The results showed that over time, when social and financial conditions were more risky, the songs of the year that were slower, longer, more comforting and serious were most popular. And during periods in which social and financial conditions were generally stable, the result was opposite.

    Building on these findings, Pettijohn and his team wondered if the Hypothesis could also be applied to the change of seasons. For college students, the participants in this study, autumn begins at the start of the school year. Gone are the carefree days of summer, when school is out. Winter means colder temperatures, shorter days, and, in many places in the country, snow. Spring, however, is a different story. It represents a fresh start and when clocks spring forward, we gain an extra hour of daylight. As students walk into summer, they're absorbed in the sunshine and social activities—and enjoy a break from school.

    But do changing seasonal conditions influence musical preferences? To answer this question, the researchers designed two studies. What did they find? Both groups of college students favored more serious music during the seasons of fall and winter, and more active and energetic music during the spring and summer seasons. And these findings, Pettijohn argues, have practical significances.

    Check out our tsunami (海啸) facts and lean some interesting information related to these great walls of water that can cause so much destruction. Find out what causes tsunamis and read about some notable recent examples of tsunamis that have occurred around the globe.

    Tsunamis are huge waves of water that are usually caused by earthquakes or volcanic eruptions.

    As a tsunami approaches the shore, water may move back from the coast. If it is shallow enough, the water may be pulled back hundreds of meters. If you are in the area, observing this is a good indication that a tsunami is on the way.

    Regions in tsunami danger zones often have warning systems in place to give people as much time to evacuate (撤离) as possible.

    When tsunamis hit shallow water (often near the coast), they slow down but increase in height.

    An earthquake in the Indian Ocean off Indonesia in December 2004 caused a tsunami that killed over 200, 000 people in 14 countries.

    In March 2011, the Tohoku earthquake off the eastern coast of Japan caused a tsunami that was a major factor in the death of over 15, 000 people.

    The tsunami waves created by the Tohoku earthquake reached heights of over 40 metres (131feet) in mine areas, wiping out coastal towns and causing a number of nuclear accidents.

    The Japanese word "tsunami" literally means "harbour wave".

    Tsunamis are sometimes referred to as tidal waves but this term has fallen out of favour because tsunamis are not related to tides.