Researchers have long imagined small flying robots dealing with difficult tasks. However, fitting the heavy electronics into the robot has been challenging. Now, there is hope, thanks to RoboBee X-Wing — the world’s lightest flying machine that can fly without being equipped (配备) with a power source.

Made public by Harvard researchers on June 26, 2019, the robot only weights 259 milligrams and has a wingspan of 3.5 centimeters. Its four tiny wings, which can flap (振翅) up to 170 times a second, are controlled by motors that work when the current passes through them. Six small solar cells, fitted above the wings to prevent them influencing the flight, provide the power.

To test its flying ability, the team, led by postdoctoral fellow Noah Jafferis and PhD student Elizabeth Helbling, exposed (显露) the robot’s solar cells to a combination of halogen and LED lighting. To their joy, the robot’s wings began to flap, and it rose, lasting about half a second. Though the robot lost its flight ability as soon as the power source was turned off, its short flight was regarded as a hug milestone for the future of tiny flying robots.

However, though the robot is a step in the right direction, RoboBee X-Wing is far from perfect. It requires light three times brighter than the sun to operate. In addition, RoboBee X-Wing is not equipped to resist even a slight wind, let alone the strong one it is likely to meet as it goes about performing important tasks. But Jafferis and Helbling, who published their research in the journal Nature, are not not downcast. The team is already working on a new and improved robot — one that is 25 percent bigger and needs light just 1.5 times brighter than the sun to work.

Several companies have begun creating paper bottles to replace glass and plastic ones. Paper bottles are easy to recycle, and also weigh less than glass or plastic, meaning they'll require less energy to produce and move around.

A company called Paboco has been working with other companies to develop paper bottles. The companies are creating their own bottle designs, but they're sharing what they learn to promote the development of paper bottle technology

One of the biggest challenges is preventing a paper bottle leaking（泄漏）. The inside of the bottle needs a special coating to make sure the liquid doesn't leak through. Many companies are lining（做衬垫）their bottles with a thin sheet of plastic. Though bottle makers may say this liner can be recycled, many recycling programs don't have the right machines to handle these liners.

A Danish beer company called Carlsberg is working with Paboco on a paper bottle called the "Green Fiber Bottle". Currently the bottle uses a plastic liner. In the future the company hopes to use a "bio-plastic" that will break down naturally over time, And a company named Diageo just announced the first paper bottle whose inside uses a non-plastic coating.

But even without the plastic, paper bottles aren't perfect. Most paper bottles use wood pulp（纸浆）, meaning trees need to be cut down. To solve this problem, Frugalpac, a company from the United Kingdom, has created wine bottles made of recycled paper. Frugalpac still uses a plastic liner, though.

Companies will need to see how long liquids can be stored in the paper bottles and make sure the bottles don't affect the taste. But with so many companies working toward the same goal, it's likely that we can expect to see paper bottles on store shelves in the near future.