At least 10 mm per year! Is our city sinking? | Expo Daily

300 million people in my country will be affected by urban subsidence

The soil on the surface of the earth is not a solid block, but soft and elastic with cracks inside. As the buildings on the ground become heavier, the ground will also be pressed down. This is ground subsidence.

With the process of urbanization, a large number of people have poured into cities and high-rise buildings have sprung up, so urban land faces a relatively large risk of land subsidence.

Recently, a research team led by Professor Tao Shengli of Peking University wrote an article in the magazine Science. After analyzing satellite data, they gave a measurement report on land subsidence in various parts of China.

The research paper considered 82 cities with a total population of nearly 700 million. The results showed that 45% of the urban areas analyzed are sinking, and 16% of them are sinking at a rate of 10 mm or more per year . However, "the land subsidence problem in China is not more serious than in other countries and regions," said the authors of the article, researchers Tao Shengli and Hu Xie.

In the study, the sinking of coastal cities such as Tianjin and Shanghai is particularly prominent. Take Shanghai as an example, the ground in Shanghai has sunk by 3 meters in the past century and is sinking further.

If global sea level rise is factored in, the results will be catastrophic: If the rates of land subsidence and sea level rise continue, the area of ​​Chinese cities below sea level could triple by 2120, affecting 128 million residents .

In addition to the weight of buildings causing ground subsidence, groundwater extraction is also one of the factors causing ground subsidence. The increase in urban population, the increase in domestic water demand, and the excessive exploitation of groundwater have led to a decrease in the ground's bearing capacity, exacerbating the ground subsidence.

In response, my country has currently taken active measures to protect groundwater.

Population growth will also bring about an explosive increase in transportation demand, and the vibration caused by vehicles and the excavation of underground tunnels may also be a factor influencing ground subsidence - Beijing's subway and highway areas sink 45 mm each year.

Subsidence can compromise the structural integrity of buildings and critical infrastructure and exacerbate the flooding impacts of climate change, particularly in coastal cities where subsidence can exacerbate sea level rise.

These new results underscore the need for a national response. New satellite measurements are providing new and detailed subsidence data, but this is not enough; it also requires a practical response from urban planners. We need to learn from this experience to address the threat of subsidence, which is more common than currently recognized.

Urban subsidence across the country, brown: fast subsidence; blue: no subsidence or ground rise

Why don’t the curls I get from perming last longer?

Those who often perm their hair know that permed hair will remain curly for several months or even a year, and will not become straight even after being wetted with water. It is permanent. In contrast, hair that is bent due to sleeping or hair that is bent with hair tongs is called "temporary curly hair" and can return to its original shape after being wetted with water. Why is this?

The reason why these curly hairs are different is related to the four main intermolecular bonding modes between keratin proteins in the hair. Arranged from weak to strong, these bonding modes are hydrogen bonds, ionic bonds, disulfide bonds (-SS-, S refers to sulfur), and peptide bonds, among which hydrogen bonds are the most numerous.

When we use a curling iron to curl our hair, except for the peptide bond, the other three bonds in the hair will be cut by the high temperature. At this time, the connection object changes, making the hair curl.

For hair that is curled due to sleeping, only hydrogen bonds are at work. Since the disulfide bonds that can restore the hair to its original shape are not broken, the hydrogen bonds are broken after being soaked in water, and the hair can return to its original shape.

The perm ingredients include hydrogen bonds and chemical agents. The hair is fixed in a bent state by the agent, so the ionic bonds and disulfide bonds will not be broken even if it is soaked in water, and the hair will not easily return to its original shape.

Image source: pexels

From the US and the Soviet Union to the present,

Why are major countries so keen on space stations?

As a manned spacecraft that operates in low-Earth orbit for a long time and is visited and worked and lived by multiple astronauts for a long time, the space station is a product that has evolved from imagination to reality along with human curiosity. After a hundred years, the human dream of space has finally gradually turned from fantasy into reality. The emergence of the space station has made human beings more determined to move towards the stars and the sea , and the feast of the mysteries of the universe is waiting for its grand opening. Click on the video to learn about the history of the space station~

Chicken discerner , a magical profession that even the boss dares not let you work overtime

For the poultry farming industry, if the errors in chicken sex identification reach a certain scale, the production companies will suffer huge economic losses. For example, if you want a chicken to lay eggs, you find out it is a rooster after raising it for half a year.

In order to avoid this kind of loss, in the 1820s, a mysterious profession that required extremely good eyesight and skills came into being - professional chicken identifier. The profession was to identify the gender of newborn chicks .

At present, the main identification methods are feather speed identification and anal protrusion identification . Feather speed identification distinguishes gender by observing the growth rate of feathers, while anal protrusion identification determines gender by observing the characteristics of the chicken's cloaca.

Becoming a professional chicken identifier requires 3 to 6 months of practical training, in order to identify 700 to 800 chicks per hour with an accuracy rate of over 99%. This job is very professional and requires extremely high eyesight and skills from the operator.

Therefore, professional chicken identification experts cannot work for 8 hours continuously or work overtime to avoid fatigue leading to a decrease in identification efficiency. Even a 1% error may cause huge economic losses to the company.

What if the chicken identification expert makes a mistake? In the farm breeding process, the wrong chickens can be found in the middle of the rearing period. The earlier they are found, the less adverse impact on the overall flock. "Fake roosters" or "fake hens" usually need to be eliminated directly because they can no longer adapt to the flock of their original gender.

Smell it, lick it, can your phone taste something?

Smell may be more effective than images in stimulating clear memories and emotions. When you watch the colorful food videos on the Internet, would you like to have a "smell phone"? In fact, scientists have been exploring how to digitize smell and taste.

The core of this technology is to convert the smell into electronic signals, which are then transmitted and re-released through the device. At present, there have been many attempts at devices.

This year, McDonald's in the Netherlands placed a billboard on the roadside that exudes the smell of French fries to attract passers-by to the nearby restaurant. The oPhone Duo platform can send images with scent tags, allowing the recipient to smell the corresponding smell. In terms of personal devices, there have been devices such as iSmell that can be connected to a computer via USB and release specific smells.

"Taste the TV (TTTV)" developed by Japanese scientists allows you to taste the food on the screen by licking the screen. The technology involved is a bit like a tablecloth. TTTV's system can use basic flavors such as sour, sweet, bitter, salty and fresh to create specific flavors, and then spray the seasoning liquid on the film covering the screen to create a specific flavor for the audience to lick. Not only can you taste the flavor, but it can also provide some food tests for chefs. TTTV also has a chat function, so you can even share a "virtual dinner" with friends on the other side of the screen~

The content is compiled from China Science Expo Weibo, Science Academy, Global Science, Science World, and Science Popularization China

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