【推荐2】The number of buses, taxis and other vehicles on Kenya’s roads is growing every day. Now, the country’s first electric-powered motorbikes are coming onto the market. The bike is designed to cut down on pollution and aimed at low-income communities. Most motorbikes used in Kenya depend on gasoline, but not this new motorbike.

Three university students developed the new ecotran bike. It catches the sun’s energy, stores it in batteries and uses it to charge (充电) the electric motor. Robert Achoge is one of the student inventors. “Our hope is that by the fifth year, we will be able to cover the whole of Kenya with the electric motorcycle so as to protect the environment and provide affordable transport.”

The students have set up a charging station for the motorbikes in Nairobi. The small battery can run for 70 kilometers when fully charged. Once the power is used up, the motorbike has to return to the station while another charged battery is connected to the bike. The U.S. African Development Foundation (ADF) is helping set up two solar-powered charging stations in the port of Kisumu.

Each ecotran bike costs about $700. One taxi operator says the new motorbike costs less to operate than that running on traditional gasoline. “When it comes to buying gasoline, there’s no need. It’s basically good for various things. As long as you won’t take quite a heavy load (装载), you can go with it anywhere. Otherwise, it may break down halfway. But now people still have a preference to the gas-powered bikes.”

A Nairobi businessman Kennedy Kusimba is selling the ecotran bikes. He hopes they will become popular. “We also know they are more reliable compared to the gas-powered bikes. They are more efficient (效率高的) and they will last longer.”

【推荐3】Batteries can power anything from small sensors to large systems. While scientists are finding ways to make them smaller but even more powerful, problems can arise when these batteries are much larger and heavier than the devices themselves. University of Missouri（MU) researchers are developing a nuclear energy source that is smaller, lighter and more efficient.

“To provide enough power,we need certain methods with high energy density（密度)", said Jae Kwon, assistant professor of electrical and computer engineering at MU. ''The radioisotope（放射性同位素）battery can provide power density that is much higher than chemical batteries ."

Kwon and his research team have been working on building a small nuclear battery, presently the size and thickness of a penny, intended to power various micro systems（MNEMS）. Although nuclear batteries can cause concerns, Kwon said they are safe.

“People hear the word ‘nuclear' and think of something very dangerous." he said. "However, nuclear power sources have already been safely powering a variety of devices, such as pace-makers, space satellites and underwater systems."

His new idea is not only in the battery's size, but also in its semiconductor（半导体). Kwon's battery uses a liquid semi conduct or rather than a solid semiconductor.

“The key part of using a radioactive battery is that when you harvest the energy, part of the radiation energy can damage the lattice structure（晶体结构）of the solid semiconductor." Kwon said, “By using a liquid semiconductor, we believe we can minimize that problem."

Together with J. David Robertson, chemistry professor and associate director of the MU Research Reactor, Kwon is working to build and test the battery. In the future, they hope to increase the battery's power, shrink its size and try with various other materials. Kwon said that battery could be thinner than the thickness of human hair.