Walled Cities Of The World

There are numerous historical walled cities across the world, whose walls date back several centuries. These walls were fortification (碉堡), a necessity throughout medieval eras for defense. They have been preserved as historical monuments and popular tourist attractions in the modern time.

York, England

The city of York is a medieval city situated in the north of England. Historically, the city was ruled by the Romans, Angles, and the Vikings before being incorporated as part of the Kingdom of England in 954. Located in the city are walls built in 71 AD which have been restored and extended with time.

Xi’an, China

The city of Xian is one of the oldest cities in China. It prospered economically as the eastern last station of the Silk Road. The existing walls were originally built in 770 BC and reconstructed in the 14th century under the Ming Dynasty. The walls are well preserved and are a major tourist attraction in the city.

Quebec City, Canada

Quebec City was a colonial (殖民地的) town which was fortified by the settling Europeans. The walls began to be built in 1608 under both British and French regimes (政权). A fort was constructed by the British as an additional defensive measure and remains undamaged to date. The city’s fortifications were listed as a UNESCO World Heritage Site in 1985.

Mexico City, Mexico

Historically, the City of Mexico gained importance as the Aztec Capital. The Spanish then drove out the Aztecs and rebuilt it as the Spanish Capital. The walls protecting the city were built in 1521. Mexico City is also home to numerous colonial-era buildings which together with the walls are major tourist attractions in the city.

Amazon recently announced its latest launch, a robot called Astro. Small in size, but with impressive technology, Astro is seemingly similar to Amazon’s popular virtual assistant. With all the same capabilities as Alexa, many critics are asking why there’s a need for Astro.

Answering this question, Amazon’s Vice-President of Products, Charlie Tritschler, highlights some unique features of Astro that make it a different kind of robot. Astro can move on its own and follow people, offering consumers a far broader range of options. Besides, it can monitor home security. Astro uses Artificial Intelligence to learn more about household members by interacting with users. Users can also register themselves and others into its recognition system. When they leave home, they can make an away mode, which means “Sentry (哨兵) Mode”, or “Patrol Mode” start working. If someone who is not recognized enters the house, Astro will follow and record them. Astro’s mobility seems to be the key feature in its technological enhancement, but what appeals to people most is its “unique persona”. Its big, circular, blinking “eyes” displayed on its screen-like head making it look rather cute are a big reason for this.

Years of research show that humans often experience positive emotional connections with robots. According to MIT’s technology review of Astro, it may not fall far from this observation. People have come to love robotic pets, though they are fully aware that the pets are lifeless. Robots at home can play a useful role in helping elderly patients fight loneliness or young children face social anxiety.

Amazon is offering people interested in Astro the chance to sign up for Day 1 Editions, a program giving invitations to Astro as soon as it goes on the market later this year. Tritschler is encouraging people to personalize the robot when it becomes available, and he is confident that users will come up with more ideas and features they will want to see in the robot in the near future to make it even better.

Nocturnal (夜间的) exposure to blue light containing short wavelength emissions (450-500 nm) — the kind of light produced by the screens of many devices raises blood sugar levels and increases sugar intake, according to a study performed on Sudanian grass rats.

“Much of the artificial light we are exposed to comes from LED lights and screens, which emit high levels of blue light,” said Anayanci Masis-Vargas from the Universities of Strasbourg and Amsterdam and his colleagues. According to their study, retinal (网膜的) cells of the eye are sensitive to this blue light and directly convey information to areas of the brain that control appetite.

In the study, the scientists exposed diurnal Sudanian grass rats to nighttime blue light (490 nm) and measured their food consumption and glucose (葡萄糖) tolerance the following day. “In order to better model human light exposure, the rats were diurnal, meaning awake during the day and asleep at night, rather than the typical nocturnal laboratory rats which are awake during nighttime hours,” the researchers explained. They found that after only one hour of nocturnal blue light exposure, glucose tolerance was changed in the rats, a warning sign of pre-diabetes.

To investigate what happens with appetite control and food choice after exposure to blue light at night, in the follow-up study, the rats were given the option to choose among a nutritionally balanced food, water, pig fat, and sugar water. After the exposure to blue light, the study authors observed that the rats preferred sugar water and drank more of it that night than during the nights with no blue light exposure. As the experiment continued, the researchers noticed more exposure to blue light caused rats’ heavier bodies as well.

“Limiting the amount of time that we spend in front of screens at night is, for now, the best measure to protect ourselves from the harmful effects of blue light,” Masis-Vargas said. “In case it is necessary to be exposed to device s at night, I would recommend the night mode features on the devices, which turn the screens more orange and less blue or the use of blue light filtering glasses that are already available in the market.”