3 . Language as a System of Symbols (符号)

Of all systems of symbols, language is the most highly developed. It has been pointed out that human beings, by agreement, can make anything stand for anything. Human beings have agreed, in the course of centuries of mutual dependency, to let the various noises that they can produce with their lungs, throats, tongues, teeth, and lips systematically stand for certain happenings in their nervous systems. We call that system of agreements language.

There is no necessary connection between the symbol and that which it stands for. Just as social positions can be symbolized by feathers worn on the head, by gold on the watch chain, or by a thousand other things according to the culture we live in, so the fact of being hungry can be symbolized by a thousand different noises according to the culture we live in.

However obvious these facts may appear at first glance, they are actually not so obvious as they seem except when we take special pains to think about the subject. Symbols and the things they stand for are independent of each other, yet we all have a way of feeling as if, and sometimes acting as if, there were necessary connections. For example, there are people who feel that foreign languages are unreasonable by nature; foreigners have such funny names for things, and why can’t they call things by their right names? This feeling exhibits itself most strongly in those English and American tourists who seem to believe that they can make the natives of any country understand English if they shout loud enough. Like the little boy who is reported to have said, “Pigs are called pigs because they are such dirty animals, ” they feel that the symbol is inherently connected in some way with the things symbolized.

4 . It is an honor for me to deliver this speech and on behalf of the graduating students, welcome you to this special ceremony 2020.

This is a unique moment. We are stepping up to another phase of our lives at a time of great hardship and global difficulties. Hope this ceremony will help erase sad memories, refresh beautiful ones and add more splendid memories into our lives.

I was born in the middle of war, which caused my family to move to Serbia for three years. When the war ended, we returned to Bosnia. My mother, who is and will ever be my heroine, was the only figure who guided me, provided for me and kept me on the right track, in the hope for a better life. I owed her so much as she is responsible for huge part of my success. I will always remember her teachings “to complain less and always find solutions at the price of whatever it takes” ， which brought me to China, an ancient land of new hopes.

During the COVID-19 outbreak, I got the best opportunity to understand China. I saw millions of people united with one goal-to win the battle against this epidemic. I have never seen such a collective dedication from a nation, turning things for the better by sacrificing personal convenience on a grand scale. China's governance and health care system proves to be one of the most efficient in the world. With a population of 1.4 billion, China not only has successfully controlled the transmission of the corona-virus but also assisted many other countries across the globe.

Everyone has a role to play in the battle against the virus. In Tsinghua, I played a tiny but necessary role: Staying on campus, studying online, cooperating during temperature checks and respecting social distancing measures. The rules set by the university and Chinese government had everyone's health and safety as first priority. This made me feel safe and confident that China was on the right track towards victory. Throughout this time, despite the immense challenges, Tsinghua has facilitated many online conferences, which helped me nurture more skills in my field of study.

Friends, we are now graduating from one of the world’s most prestigious universities. Tsinghua has been like a mother to us over the past months and years, guiding and nurturing us along the way, providing us with great vision and placing on us high expectations. So what comes next? Actions speak louder than words. Let us accept new challenges, think beyond our limits and keep in mind the ethics of life.

Let's undertake everything we can for the sake of unity, humanity and the international community. Let's work together for a more promising future and prosperous world.

5 . Hardware in general, and smartphones in particular, have become a huge environmental and health problem in the Global South’s landfill sites(垃圾填埋场).

Electronic waste (e-waste) currently takes up 5 percent of all global waste, and it is set to increase rapidly as more of us own more than one smartphone, laptop and power bank. They end up in places like Agbogbloshie on the outskirts of Ghana’s capital, Accra. It is the biggest e-waste dump in the world, where 10,000 informal workers walk through tons of abandoned goods as part of an informal recycling process. They risk their health searching for the precious metals that are found in abandoned smartphones.

But Agbogbloshie legally should not exist. The Basel Convention, a 1989 treaty, aims to prevent developed nations from unauthorized dumping of e-waste in less developed countries. The e-waste industry, however, circumvents regulation by exporting e-waste labelled as “secondhand goods” to poor countries like Ghana, knowing full well that it is heading for a landfill site.

A recent report found Agbogbloshie contained some of the most dangerous chemicals. This is not surprising: smart phones contain chemicals like mercury(水银), lead and even arsenic(砷). Reportedly, one egg from a free-range chicken in Agbogbloshie contained a certain chemical which can cause cancer and damage the immune system at a level that’s about 220 times greater than a limit set by the European Food Safety Authority (EFSA). Most worryingly, these poisonous chemicals are free to pollute the broader soil and water system. This should concern us all, since some of Ghana’s top exports are cocoa and nuts.

Some governments have started to take responsibility for their consumers’ waste. For example, Germany has started a project that includes a sustainable recycling system at Agbogbloshie, along with a health clinic for workers. However, governments cannot solve the problem alone, as there is an almost limitless consumer demand for hardware, especially when governments’ green policies are focused on issues like climate change.

Only the manufacturers can fix this. A more economically sustainable and politically possible solution is through encouraging hardware manufacturers to make the repair, reuse and recycling of hardware profitable, or at least cost-neutral.

6 . The brain has a powerful ability to remember and connect events separated in time. And now, in that new study in mice published in Neuron, scientists at Columbia’s Zuckerman Institute have cast light on how the brain can form lasting links.

The hippocampus-a small, seahorse-shaped region buried deep in the brain-is an important headquarters for learning and memory. Previous experiments in mice showed that disruption (中断) to the hippocampus leaves the animals with trouble learning to associate two events separated by tens of seconds.

“The traditional view has been that cells in the hippocampus keep up a level of continuous activity to associate such events,” said Dr. Ahmed, co-first author of the study. “Turning these cells off would thus disrupt learning.”

To test this view, the researchers imaged parts of the hippocampus of mice as the animals were exposed to two different stimuli (刺激物): a neutral (神经的) sound followed by a small but unpleasant puff of air. A fifteen-second delay separated the two events. The scientists repeated this experiment across several trials. Over time, the mice learned to associate the sound with the soon-to-follow puff of air. Using advanced microscopy, they recorded the activity of thousands of neurons (神经元) , a type of brain cell, in the animals’ hippocampus over the course of each trial for many days.

“We expected to see continuous neural activity that lasted during the fifteen-second gap, an indication of the hippocampus at work linking the auditory sound and the air puff,” said computational neuroscientist Stefano Fusi, PhD. “But when we began to analyze the data, we saw no such activity.” Instead, the neural activity recorded during the fifteen-second time gap was sparse (稀少的). Only a small number of neurons worked, and they did so seemingly at random.

To understand activity, they had to shift the way they analyzed data and use tools designed to make sense of random processes. Finally, the researchers discovered a complex pattern in the randomness: a style of mental computing that seems to be a remarkably efficient way that neurons store information.

“We were happy to see that the brain doesn’t maintain ongoing activity over all these seconds because that’s not the most efficient way to store information,” said Dr. Ahmed. “The brain seems to have a more efficient way to build this bridge.”

In addition to helping to map the circuitry involved in associative learning, these findings also provide a starting point to more deeply explore disorders, such as panic and post-traumatic stress disorder.

7 . Mathew White, an environmental psychologist, is on a mission to give Mother Nature the respect he thinks she deserves when it comes to human health. For decades, scientists and health-care professionals have recognized that exposure to green spaces, such as public parks or forests, is linked with lower risks of all sorts of illnesses common in the world. Experimental work has demonstrated various physiological responses that occur when people spend time in natural environments: blood pressure drops, heart rate decreases, immune function improves, and the nervous system directs the body to rest and digest.

As humans increasingly populate urbanized areas, they are spending less and less time in natural environments. But before doctors can start advising their patients to head to the nearest park, there is an important outstanding question, says White: How much time in nature do you need to generate these apparent benefits? Most of the research that has linked health outcomes with exposure to the natural world didn’t use frequency or duration of park visits, but rather the amount of green space within a certain distance of a person’s home, White says. But “it’s not so much where you live; it’s whether you use it or not.”

So he collected data to estimate what dose（剂量） of nature was needed to show benefits to a person’s health. White’s group found the answer he was after: Spending at least two hours in nature per week was strongly correlated with self-reports of being in good health or having high wellbeing. “I was very surprised, to be honest,” says White, who had been expecting a much longer time. “We had no idea that such a clear threshold of time per week would emerge from the data.”

He was further surprised to learn that it didn’t seem to matter how many trips to a park people took, so long as they got in their two hours per week. It could be a long visit one day, a couple of hour-long trips, three visits of 40 minutes, or four half-hour excursions. He and his colleagues speculate that, if nature’s apparent health benefits are a result of being able to de-stress, then whatever pattern of green space exposure fits one’s schedule is probably the best way to achieve that goal.

Health-care recommendations for people to spend time in nature are probably years away, but the movement has begun. Several organizations around the world are working to promote awareness of nature’s contribution to health. Some researchers have used the term “a dose of nature” to evaluate the amount of exposure needed to gain benefits. “That was kind of the deliberate medicalization of the language around nature and health,” says White.

8 . Though people have discussed the relationship between science and nature for many years, there is no consensual(统一的) explanation. While some view science as a powerful tool in ______ nature’s source of power, others view it as a danger. One example is Barry Commoner’s article, Unraveling(解开) the DNA Myth, which explains the recent developments in DNA technology and expresses ______. Another example is Nathaniel Hawthorne’s short story, The Birthmark. It is a tale about a famous scientist, Aylmer, who seems to be unraveling nature’s deepest secrets one by one. Despite all of his ______ and vast understanding of science, Aylmer is unable to direct that knowledge into ______ free from nature’s grasp. He was unable to rid his wife of her birthmark and, in the end, killed her.

Despite the different presentations of the concepts, though time separated the two men, both pieces express a similar view on the relationship between science and nature. Both pieces suggest that nature is ______ and holds wonders, secrets, and powers that many scientists constantly dream about discovering. Although there is a gap of one hundred and sixty years, Commoner still shares and gives evidence to Hawthorne’s beliefs that there is a unique ______ in nature that cannot be discovered or understood through science and that the ______ to uncover nature’s secrets are ______ and can lead to disaster. According to Commoner, nature’s universal power continues to prevent and control their discoveries. Commoner criticizes and ______ doubt on the true power of science.

As Commoner’s article suggests, nature only allows science to have limited power and success. Both men believe that complete trust in science is ______, however wonderful and groundbreaking some scientific discoveries are. Commoner believes that people only seem to focus on the few achievements, while avoiding and ignoring all of the laws. For example, “most clones exhibit developmental failure before or soon after birth”. By stressing all of the ______ and shortcomings of science, he conveys the notion that nature’s secrets are well kept and far from being understood and ______ by man. The government and private companies have invested billions of dollars in mapping the human genome, but we still have no ______ for it. Such a discovery is useless, however interesting it might be.

Commoner’s article clearly represents science as weak and useless, but more importantly, dangerous. It gives evidence to support the suggested dangers ______ with science’s attempts to discover nature’s power. If the result is not ______ dangerous, it can still have harmful side effects.

9 . We love letters. Just as John Donne, a poet, _________ it, “Letters, to me and my friends mean _________ greetings; they get souls together. Thanks to letters, friends who are _________ speak.” He wrote these words nearly 400 years ago. Today, in the age of instant text message, social media, and email, they _________ ring truer than ever, because writing or receiving a letter has become such a _________ event.

A UK-wide survey undertaken by Sunday Times suggests that one in four of us has not _________ a letter for at least 10 years. That’s ten years without the bitter-sweet _________ of pacing the floor waiting for the _________; ten years without recognizing the handwriting on the envelope and eagerly _________ the letter to read its content.

We ____________ not get them any more, but we still love handwritten letters. In the same survey, one third of ____________ people interviewed say that they ____________ the content of sentimental (充满情感的) letters. Shouldn’t we make ____________ to give our friends and families what they will treasure forever? Ann Bickley went online in 2013 and offered to handwrite a letter to anyone who ____________ her. Her website received 50,000 ____________ in its first three months. Five years later, she is still the main ____________ behind one-million-lovely-letter.com and has personally written 4,000 letters offering hope and ____________ to strangers.

The thought behind a letter ____________ as much as its contents. “I never tell anyone that ____________ is going to be OK,” Ann Bickley says, “I am letting someone know that there is someone in the world who ____________ them.”

Who wouldn’t love to receive a letter like that? Let’s get writing!