Many years ago, people relied on the sun, the moon and stars to find their way around. Later, the compass was introduced. And now, we have satnav（卫星导航）systems to guide us. A satnav system uses groups of satellites to show the user's location. They send information to a receiver, such as a smartphone, to show us where we are.

    The earliest built satnav system is the Global Positioning Satellite System, which belongs to the US. Then there is Russia's Global Navigation Satellite system，the European Union's Galileo and China's own satellite navigation system, Beidou.

On October 18, 2017, an ARJ21-700 plane, which was the first domestically（国内地） produced jet equipped with the Beidou navigation system, successfully completed a test flight. The results showed the performance of the system developed by China matches that of similar systems produced abroad, according to the Commercial Aircraft Corporation of China.

    Since its introduction in 2000, the Beidou navigation system has been increasing numbers of applications linked to everyday life, from shared bikes to farming.

When it comes to shared bikes, smart locks that support Beidou chips offer more accurate positioning than others, making it easier to find a bike.

    Farmers can use Beidou-enabled tractors to plow（犁）the soil and use unmanned aircraft with Beidou to sow seeds, which can improve efficiency and make better use of resources. Beidou's farming applications have spread from Heilongjiang Province to Beijing, Liaoning, Shanxi, Hubei and other regions across China.

    With its many uses, the Beidou navigation system is even playing a big role in the Belt and Road Initiative（一带一路）. “To date, the Beidou system has covered most parts of the Asia-Pacific region, as well as countries along the Silk Road Economic Belt and the 21^st Century Maritime Silk Road,” said Yang Changfeng, chief designer of the Beidou system.

    Today, there are more than 20 Beidou satellites above our heads, and China plans to launch even more this year to expand the Beidou network to better serve the Belt and Road Initiative.

    “As Beidou expands its overseas reach, it will be increasingly popular in the logistics（物流） industry,” said Miao Qianjun, Secretary General of the navigation services association. “Ships, for example, can use it to position themselves while sailing across oceans to European countries, no longer limited to Southeast Asian regions in the near future.

    A California family drives a car that could help protect the environment. When Jon and Sandy go to the store or to their daughters' soccer games, they drive in high-tech style. They drive a $1 million, fuel-cell-powered car. It may be the world's most expensive car and one of the most environmentally friendly cars. The FCX is the first fuel-cell-powered car to be used by a family anywhere in the world. The FCX uses hydrogen and oxygen for fuel. Car makers have been working to develop vehicles that are better for the environment. They are developing cars that use fuel other than gasoline.

    And then what is fuel cell technology? Fuel cell technology works by changing the chemicals hydrogen and oxygen into water. This process produces electricity, and water vapor which comes out of the exhaust pipe. Most cars release dangerous gases such as carbon monoxide and carbon dioxide. Many scientists say these gases are major contributors to global warming. “The FCX is driven just like any other vehicle on the road, but without the gases which pollute the environment,” scientists say. Fuel cell technology has been around since the 1800s, but scientists have yet been to perfect it. They say it may take years before the technology is ready for widespread use. Another earth-friendly car is already on the market. Hybrid cars use both gasoline and an electric motor. They are becoming more popular with customers because they cut pollution and improve fuel efficiency.

    Some colors people see late at night could cause signs of clinical (临床的) depression. That was the finding of a study that builds on earlier study findings. They show that individuals who live or work in low levels of light overnight can develop clinical depression. Doctors use the word "clinical depression" to describe severe form of depression. Signs may include loss of interest or pleasure in most activities, low energy levels and thoughts of death or suicide.

    In the new study American investigators designed an experiment that exposed hamsters (仓鼠) to different colors. The researchers chose hamsters because they are nocturnal which means they sleep during the day and are active at night.

    The animals were divided into four groups. One group of hamsters was kept in the dark during their night-time period. Another group was placed in front of a blue light a third group slept in front of a white light while a fourth was put in front of a red light.

    After four weeks the researchers noted how much sugary water the hamsters drank. They found that the most depressed animals drank the least amount of water.

    Randy Nelson heads the Department of Neuroscience at Ohio State University. He says animals that slept in blue and white light appeared to be the most depressed. "What we saw is that these animals didn't show any sleep uneasiness at all but they did mess up biological clock genes and they did show depressive sign while if they were in the dim (微弱) red light they did not."

    He notes that photosensitive (感光) cells in the eyes have little to do with eyesight. He says these cells send signals to the area of the brain that controls what has been called the natural sleep-wake cycle.

    He says there's a lot of blue in white light. This explains why the blue light and white light hamsters appear to be more depressed than the hamsters seeing red light or darkness.

    Since we've headed into the snowy part of the year, it seems like a good time to solve a language puzzle that Eskimos have a huge number of words for snow. The idea was popularized by the now well-known expert Benjamin Lee Whorf in the 1940s. His number was approximately five Eskimo words for snow, but somehow the story was so wide spread and romantic that it got out of control and grew bigger and bigger.

    There are two problems with the concept of Eskimos having tons of words for snow.

    First, Eskimos speak at least two different languages—Inuit and Yupik. Just as we have talked about how English and many other languages developed from a common language called Proto-Indo-European, Inuit and Yupik come from a different common language called Eskimo-Aleut. So saying Eskimos have 100 words for snow is like saying Europeans have 100 words for kings or queens. It might be telling you something broad about culture, but it isn't really telling you much about language.

    The second problem is "What is a word?” The Inuit and Yupik languages make words in different ways from how we make words in English. For example, the West Greenlandic word 'siku,' (sea ice), is used as the root for 'sikursuit (pack ice), 'Sikuliaq (new ice), and 'sikurluk (melting ice). But it's not that West Greenlandic has so many more words for describing snow than English, it's just that West Greenlandic expresses ideas by combining meaningful units of language together into one word while English uses more phrases and compounds. We express all the same ideas; we just do it a little differently because of the way our language is built.

    So you're probably still wondering, "If it's not 50 or 100 or 400 words, how many is it?" Well, Woodbury lists 15 that are present in a Yupik dictionary published in 1984, but he says that depending on how you look at it this is not an exact number. It could be 12; it could be 24. But it's certainly not 100.

    Sometimes, the "hundred words for snow" puzzle is used to argue that because Eskimos have so many words for snow, they think about snow in ways that we can't even begin to imagine—that your language decides or limits your thoughts. Languages are just different. They don't decide what we are able to think about or are not able to think about. I can think about snow floating on water even if we don't have a word for that in English.

    So when you're out skiing or snowboarding or just shoveling your driveway this winter, don't believe the people who try to tell you that Eskimos have 100 words for snow.

We are all stuck in the thought of having satisfying relationships, which bring some meaning to our lives and make us happy. We are so busy in finding true happiness that we often forget true happiness lies within us.

You have to love yourself first in order to love someone else. We have heard in countless inspiring speeches that self-love is the basis of a happy life. Have you ever wondered that with so many people advertising self-love, why haven't we been able to love ourselves?

One of the reasons for our failure to love ourselves is that we have been taught to be selfless from the start of time. The minute we start thinking about ourselves, everyone around us makes it their personal mission to remind us of how selfish we are. However, there is nothing wrong with putting your needs and yourself first. Self-love is not selfish. It only helps us better understand which sacrifices (牺牲) are worth making!

Actually, self-love and healthy relationships cannot be separated. Self-love is the very core of any healthy relationship. Now you might wonder how my love for myself is going to make me able to have a healthy relationship. Isn't a healthy relationship all about giving? Honestly, No.

When you know your worth, you know what you are willing to accept in a relationship and what not. You will know where to draw boundaries because you value your own opinions. You will have a clear understanding of what you need, what are your values and your limits. From now on, you should realize that true happiness lies within you and you shouldn't waste time and effort searching for peace and joy in the world outside.

Upon the release of the publication "The Mountain People" by the American ethnologist Colin Turnbull in the year 1972, he characterized the subjects of his study—a Ugandan tribe known as the Ik—as "a populace devoid of affection." Turnbull, after a period of two years spent in observation, concluded that the Ik exemplified the primal tendencies of mankind: deceit, larceny, and a callous indifference to the suffering of others. However, when Athena Aktipis and her associates from the Human Generosity Project delved more profoundly into the matter, they discovered a society that engaged in the communal sharing of all resources. "Turnbull's observations coincided with a calamitous famine in Uganda. What he witnessed was merely a reflection of the dire circumstances that arise when individuals are gripped by hunger," Aktipis remarks. Yet, her research team uncovered that, despite the oppressive conditions they faced, the Ik held in high esteem the act of mutual assistance whenever it was within their means to do so.

Aktipis posits that the phenomenon of selflessness is more pervasive and advantageous than the field of evolutionary social science has historically acknowledged. "The prevailing assumption was that individuals are inherently inclined to act solely in their own interests or those of their kin," she states. By examining the distinctive and unselfish behaviors that have enabled nine communities across the globe to persist, the scholars from the Project aim to demonstrate that humanity is indeed capable of extensive collaboration.

The Maasai populace in Kenya offers a principal illustration of the Project's findings. They depend on reciprocal friendships to secure necessities such as sustenance or hydration during times of scarcity, with no expectation of reciprocation. Similarly, in the distant locale of New Mexico, while individuals frequently render aid in the transportation of livestock and receive support in kind, they will also provide assistance gratuitously in instances of adversity, such as personal injury or the bereavement of a cherished one.

Aktipis is convinced that the theoretical models she has refined through the study of these communities can be broadly applied to any interdependent systems. Her overarching ambition is to devise social-welfare frameworks that offer sustenance to all members of society. Take, for instance, the market-driven insurance models prevalent in the United States: They are priced according to individual risk factors, including health profiles and geographic location, which results in millions of Americans being priced out of coverage. In contrast, a system founded on the principles of communal support and pooled financial resources would distribute the burden equitably during collective trials, such as natural catastrophes and pandemics.