2 . On paper, hydrogen（H2）looks like a dream fuel. Coal, oil, and natural gas produce carbon dioxide, which warms the earth when burned, Hydrogen produces pure water. Hydrogen packs more energy into less space than a battery（but certainly less than petrol）. Also, empty tanks（燃料箱）can be refilled with hydrogen much faster than refilling empty batteries with electricity.

While in practice, things are trickier. Storing a meaningful amount of hydrogen gas requires pressing it several hundred-fold. Changing it into the liquid form is another option, but it should be cooled to-253C. Both processes require a heavy and strong tank. While a 700 bar tank is acceptable for a city bus or a truck, adapting it for use in small vehicles is very difficult because the pressure during refilling would be too great.

The solution? Powerpaste.

A German team of researchers, led by Marcus Vogt, have come up with an interesting "powerpaste", which can store hydrogen energy at atmospheric pressure, ready for release when needed. It is so named because it comes in tubes and looks like toothpaste（牙膏）, not in its traditional form of gas.

The main ingredient（原料）of the paste is magnesium hydride, a substance that reacts with water to form hydrogen. The escaped hydrogen can then be directed into a fuel cell, where it reacts with oxygen from the air to produce electric power.

Refueling is very simple, as instead of going to a filling station, drivers and riders can simply replace an empty tube with a new one and refill the water tank.

Given that powerpaste only begins to break down at temperatures of around 250℃ it remains safe even when a vehicle stands in the baking sun for hours.

However, we will have to be patient. Just because researchers have succeeded in developing a new fueling way does not mean that we can expect to see such vehicles on the road anytime soon. It will indeed be several years before this concept is turned into reality.

3 . Many people have long   dreamed of being able to fly around as simply as riding a bicycle.

Yet the safety and strength of a flying bike was always a big problem. Over the past 10 years’ developments in technology have moved the dream of personal flying vehicle closer to reality. Now, two groups of inventors say such vehicles may be available very soon .

Grant Stapleton from Malloy Aeronautics says the Hoverbike, which is able to get in and out of small spaces very quickly, will be a truly personal flying vehicle. " It can be moved across continents very quickly because it can be folded and packed, " he adds.

Mr. Stapleton says safety was the company's main concern when developing the Hoverbike, He says the designers solved the safety issue by using overlapping rotors （折叠旋翼）to power the vehicle. The company is testing both a one-third size model and a full-size prototype （原型)）of the Hoverbike.

Inventors say their Hovebike will most likely be used first by the police and emergency rescue teams.

In New Zealand, the Martin Aircraft Company is also testing a full-size prototype of its personal flying bike, called Jetpack. It can fly for more than 30 minutes, up to 1,000 meters high and reach a speed of 74 kilometers per hour.

Peter Coker is the CEO of Martin Aircraft Company. He said Jetpack " is built around safety from the start ” In his words, reliability is the most important part of it. We have safety built into the actual structure itself very similar to a Formula One racing car."

Jetpack uses a gasoline-powered engine that produces two powerful jet streams. Mr. Coker says it also has a parachute （降落伞）that can be used should there be an emergency.

"It opens at a very low altitude and actually saves both the aircraft and the pilot in an emergency," he adds.