Some inventions are so useful, but seem so simple, that we wonder why no one thought of them long ago. Post-it Notes, the pieces of paper that you can stick almost anywhere and then remove without leaving any sign that they are there, are an example of such an invention.

Post-it Notes were invented about twenty years ago by Art Fry, a scientist at 3M Corporation. The idea for the product came from an upsetting experience he often had while singing in his church choir. Fry used pieces of paper as bookmarks to mark the places in his book of songs, but these bookmarks were always falling out. He knew he needed a bookmark that would stay where he put it, but that he could remove without damaging the pages.

Around that time, Fry heard about a new adhesive(粘合剂) that a colleague, Dr. Spence Silver had created. This adhesive was special because it was sticky, but not too sticky. It was strong enough to hold papers together, but weak enough not to tear the paper when it was removed. Fry saw that the new adhesive could help solve his bookmark problem. One morning, Fry put some of the adhesive on the edge of a piece of paper. Just as he hoped, it made a perfect bookmark.

A short time later, Fry realized that his new invention had even more uses than being a great bookmark. He came to this realization when he wrote a note on one of his new “bookmarks” and attached it to a report he was going to give to a colleague. Soon, co-workers were asking Fry for more sample of his invention so that they could use the new type of notes themselves.

Fry and some other people at 3M believed so much in the new product that they persuaded the company to give away thousands of the sticky pieces of paper for trial use. When some salespeople at 3M went to offices and showed workers just how helpful the new type of notes could be, they immediately received many orders. As more and more people discovered how useful Post-it Notes could be, the product took off.

Since the 1970s, scientists have been searching for ways to link the brain with computers. Brain-computer interface(BCI) technology could help people with disabilities send commands to machines.

Recently, two researchers, Jose Milan and Michele Tavella from the Federal Polytechnic school in Lausanne, Switzerland, demonstrated (展示) a small robotic wheelchair directed by a person’s thoughts.

In the laboratory, Tavella operated the wheelchair just by thinking about moving his left or right hand. He could even talk as he watched the vehicle and guided it with his thoughts.

“Our brain has billions of nerve cells. These send signals through the spinal cord (脊髓) to the muscles to give us the ability to move. But spinal cord injuries or other conditions can prevent these weak electrical signals from reaching the muscles,” Tavella says. “Our system allows disabled people to communicate with external world and also to control devices.”

The researchers designed a special cap for the user. This head cover picks up the signals from the scalp (头皮) and sends them to a computer. The computer interprets the signals and commands the motorized wheelchair. The wheelchair also has two cameras that identify objects in its path. They help the computer react to commands from the brain.

Prof. Milan, the team leader, says scientists keep improving the computer software that interprets brain signals and turns them into simple commands. “The practical possibilities that BCI technology offers to disabled people can be grouped in two categories: communication, and controlling devices. One example is this wheelchair.”

He says his team has set two goals. One is testing with real patients, so as to prove that this is a technology they can benefit from. And the other is to guarantee that they can use the technology over long periods of time.

Long before metal oven racks (架子) were invented, many people would place the things that they wanted to bake onto stones to keep them from burning in ovens or even directly on heat. 【小题1】 However, there are actually many applications for its use in baking.

Typical baking stones can be made of various materials, and tend to be either round or rectangular in shape. The clay stone is popular, but some people like marble. Some have a shiny surface and others don’t have. 【小题2】 Some people suggest that heading to the local kitchen supply store to purchase a baking stone is a waste of time and instead they purchase tiles (瓦片) from kitchen or gardening stores. 【小题3】 They may contain high amounts of lead and cooks would need to test them for the presence of lead before using them to cook.

【小题4】 Baking stones absorb and keep heat very well, so when you put them in the oven and allow the oven to run for a while, the stones heat up. They transfer heat directly to the bottom of your bread or other goods, as the goods can be placed directly on the stone so they never start out on a cold surface. This allows bread to bake more evenly all over, resulting in a much nicer crust (酥皮)—particularly for artisan bread.

There are many benefits of using a baking stone to cook pizza or bread. 【小题5】 For another, the stone is also praised for its ability to evenly heat the crust and lessen chances that pizza or other bread will burn.