Long ago, writing was done on parchments- -thin, dried animal skins specially prepared for writing. But the parchment wasn't easy to make and it wasn't cheap. Then, ancient people removed the original writing from a parchment and then used it again for another piece of writing. That's what creates a palimpsest.

The writing removed from the parchment can't be seen directly. Generally , finding hidden writing on very old documents is so unusual, but for scientists,it is just the opposite because they have learned ways to use special lighting to discover it. For young college students , doing this is a different matter. Last year , some students at the Rochester Institute of Technology( RIT) took part in a class that brought together many students from different areas to do a project as a group, which was to build a special camera system that could take pictures by using different kinds of light. But just as the students were finishing up their project together ,COVID-l9 hit and the students could no longer work on the project in person. Instead , they broke into smaller groups to try to finish parts of the project remotely. Although they met many tough problems, they communicated , sometimes fiercely , with each other timely online to settle them.

Over the summer , they got special permission to continue working on the camera system , and they managed to finish it. Then they borrowed several old parchments from the collection at the school's Cary Graphic Arts Collection. When they put one of the pages under their camera system with ultraviolet( UV) light( 紫外銭) , the hidden writing appeared suddenly. The students are even more excited because even though the parchment is no longer part of a book , the students know where 29 other pages from the same book are. They hope that these , too , will have hidden writing.

It takes a certain quickness to pick a strawberry or a salad. While crops （农作物）like wheat and potatoes have been harvested by machine for decades, many fruits and vegetables have proved resistant （有抵抗的）to automation. They are too easily damaged, or too hard for heavy farm machinery to locate.

But recently, technological developments and advances in machine learning have led to successful trying of more sensitive and skillful robots, which use cameras and artificial intelligence （Al） to locate ripe fruit and handle it carefully and exactly.

Developed by engineers at the University of Cambridge, the Vegebot is the first robot that can identify and harvest iceberg lettuce - bringing hope to farmers that one of the most demanding crops for human pickers could finally be automated.

First, a camera scans （扫描）the lettuce and, with the help of a machine learning calculation trained on more than a thousand lettuce images, decides if it is ready for harvest. Then a second camera guides the picking cage on top of the plant without breaking it. Sensors feel when it is in the right position, and pressed air drives a blade through the stalk （柄）at a high force to get a clean cut.

Its success rate is high, with 91% of the crop accurately classified, according to a study published in July. But the robot is still much slower than humans, taking 31 seconds on average to pick one lettuce. Researchers say this could easily be sped up by using lighter materials.

Such adjustments would need to be made if the robot was used commercially （商业地）. "Our goal was to prove you can do it, and we've done it,” Simon Birrell, co-author of the study, tells CNN Business. "Now it depends on somebody taking the baton （指挥棒）and running forward," he says.

To solve a big environmental problem, chemists have been thinking small. Really small: a new mini robot with the purpose of helping clean up tiny plastic polluting water across the globe.

The new micro-robots, each of which is no bigger than the tip of a pencil, are magnetic (磁性的) and shaped like four-pointed stars. When the sunlight shines on them, they can swim in a specific direction; when the sunlight disappears, they stop moving. Finding a piece of plastic, they hold onto it, produce chemical reactions and start to break it down.

The project is led by chemist Martin Pumera, a researcher who also studies ways to build micro-robots at the Czech University in Prague. About ten years ago, he noticed the micro-plastic was everywhere, from the bottom of the ocean to the ice on the top of mountains. It even turned up in drinking water, both bottled and tap water. Just think about how much plastic you encounter every day. It doesn't easily degrade (降解), which is a big problem. Therefore, Pumera chose to focus on the problem of water pollution caused by micro-plastic.

The researchers tested the micro-robots on four types of plastic in the lab. After a week, all four began degrading, losing between 0.5 and 3 percent of their weight, which indicated they were breaking down. The robots also turned the plastic's smooth surface into rough. Finally, they could be collected for reuse along with the plastic waste without causing new pollution.

In fact, Pumera says they still have a long way to go. These micro-robots are unlikely to succeed in degrading all types of plastic. They'll also need a lot of tests to show that they're safe in open waterways, such as at sea. But he thinks that these challenges can be overcome. Someday, the micro-robots will play a big role in a worldwide cleanup effort.