日批在线视频_内射毛片内射国产夫妻_亚洲三级小视频_在线观看亚洲大片短视频_女性向h片资源在线观看_亚洲最大网

Download

Chinese scientists have built the world's first prototype testing platform for an ultra-high-speed vacuum maglev train, which theoretically could hit speeds up to 2,900 km per hour, or almost three times the speed of a passenger jet, researchers confirmed on Wednesday.

Running the maglev train in a near-vacuum environment is the best way to ensure the comfort and energy economy of an ultra-high speed train, said Deng Zigang, head of the project team based in Southwest Jiaotong University in Sichuan's capital Chengdu.

When a train's speed reaches 400 km per hour or above, Deng said, more than 83 percent of the traction is wasted to offset air resistance and the aerodynamic noise is over 90 db, higher than the 75 db set by design standards.

Southwest Jiaotong University developed the initial high temperature superconducting magnetic levitation test loop in March 2013, and the latest model had the vacuum pipe that became the world's first evacuated tube transport system.

When the train runs in the tube, the pressure inside is 10 times lower than outside and the train can use more power for driving at high speed, Deng said.

From the point of design, the vacuum ultra-high-speed maglev train uses two different technologies to increase the speed of the train, said Zhao Lin, an associate research fellow of the National Lab for Superconductivity, Institute of Physics at the Chinese Academy of Sciences.

The first is magnetic levitation, which uses superconductors to produce powerful magnets to elevate the train above the track, thus remove the friction with the track and enhance the speed.

"The reason that an aircraft moves faster than any vehicle on the ground is similar - the friction from the air is much smaller than the ground," Zhao explained.

The concept of maglev transportation was first presented in the mid-20th century and the first commercial maglev train line was put into operation at Birmingham Airport in Britain in 1984, which had a speed of only 42 km per hour because of the technology at that time.

Currently, China and Japan are actively developing such technology, and the maglev train connecting the Bund and Pudong Airport in Shanghai is the world's fastest commercial line with speeds up to 431 km per hour.

The second technology used to speed up the train is to put it into a vacuum tube to reduce air resistance, which is the only source of friction for a magnetic levitation train.

"Compared with conventional superconductors, the high-temperature superconductors require less stringent environmental demands, and thus reduce the cost of the train," Zhao said.

For example, the conventional superconductors used on Japan's levitation trains need to stay at about -270 C to keep their superconducting state, which needs liquid helium cooling.

In contrast, high-temperature superconductors of the maglev train running in Pudong Airport can keep the superconducting state at -180 C to -200 C, which can be refrigerated with liquid nitrogen, a cooling agent one hundred times cheaper than liquid helium.

However, there are major technological problems to resolve before the train could be put in to use.

"For example, the train would need a vacuum tube that extends hundreds of kilometers. And it is challenging to maintain such a large vacuum system," Zhao said.

"Also, there could be external impacts like earthquakes that could pose a threat to the system. And the braking system of the train at such high speed also needs non-traditional designs."

Questions:

1. What university is the project team based at?

2. What year was the first commercial maglev train put into operation?

3. How fast does the world’s fastest maglev train travel?

Answers:

1. Southwest Jiaotong University.

2. 1984.

3. 431 km/hr.

（中國日報網(wǎng)英語點津 Helen 編輯）

About the broadcaster:

Lance Crayon is a videographer and editor with China Daily. Since living in Beijing he has worked for China Radio International (CRI) and Global Times. Before moving to China he worked in the film industry in Los Angeles as a talent agent and producer. He has a B.A. in English from the University of Texas at Arlington.