The regulators at America's Food and Drug Administration (FDA) could be forgiven for wanting a cigarette break. They rushed to meet a September 9th deadline to decide whether more than 6.5m e-cigarette products made by over 500 companies can remain on the market.

E-cigarettes have attracted keen government attention in recent years. More and more young people begin vaping (吸电子烟). In 2019 America's surgeon-general called vaping an epidemic (流行病) among you people, animadverting in particular products with "kid-friendly" flavours, such as oranges and grapes. Later that year more than 450 people in America suffered from a mysterious and severe lung illness that was linked to vaping.

Other countries, including Brazil, India and Singapore, have already banned e-cigarettes. So what goes into them, and how bad are they really?

The devices use an electric charge to vaporise (蒸发) a dose of nicotine (尼古丁) (accompanied, often, by various flavouring chemicals) . Nitrosamines, a family of chemicals causing cancers, have been found in e-cigarette vapour. Metallic particles from the device's heating element, such as nickel and cadmium, are also a concern. High exposure to these can increase the risk of cancer. It also contains harmful substances that can damage tissue or DNA, and which are thought to come mostly from flavourings.

Then there is nicotine. Besides being addictive, it is known to have a harmful effect all around the body. Scientists have done research on animals and humans, which suggests that exposure to nicotine at an early age could make users more influenced to other addictive substances later in life.

Scientists at the University of Washington (UW) have come up with an unusual way to help farmers get information about the plants in their fields. 

Farmers already use drones (无人机) to collect information about their crops. But they can only fly for 10 to 20 minutes, and can only travel for a few miles. Last year, the team at UW showed off "RoboFly", a tiny robot that weighed as much as a toothpick and could fly. But it can't fly far at all and it needs a laser (激光) for power. So the scientists began to think about things that already knew how to fly, which led them to the bumblebees (大黄蜂) that fly all day. Compared to many flying insects, bumblebees are so large and strong as to fly carrying almost as much as their own weight.

The UW scientists created a special device with sensors, a small battery, and a way of storing tiny amounts of information. This "backpack" weighs about as much as seven grains of dry rice.

To track the bee, the scientists send radio signals from several spots along the edges of the field where the bee is. The tiny computer on the bee's back uses the strength of the signals to figure out where it is. The backpack records information about the temperature and light. When the bee return s home at the end of the day, a device can wirelessly download the information the bee has collected. Another device can wirelessly recharge the backpack's battery.

In the UW experiment, the scientists cooled the bumblebees down so that they stopped moving, and then glued the backpacks onto the bees. But it would be difficult for farmers to do the same thing for hundreds of bumblebees. Besides, bumblebees don't live long — about a month. Farmers would need to be careful as the bees got older, otherwise the trackers could die while they are out in the field, leaving the electronic litter behind.

In 2007,the African Union announced an ambitious project-to plant the Great Green Wall(GGW),a band of trees that would stretch the length of the Sahel.

The GGW is an ecological restoration project designed by African people for African people. Heavy rains, droughts, wildfires and landslides have all become common throughout the world. But nowhere is quite like the Sahel. In this huge African region, climate change has materialized in a dramatic manner. In some cases, the severe conditions have left people with no option other than to migrate elsewhere to survive. It was with all of this in mind that the extraordinary, but heavily debated project was first put forward.

Fourteen years have passed since the initiative formally kicked off. The stated goal was to create a 15-kilometre-wide, 8,000-kilometre-long green belt of trees and other plants that, by 2030, would span（跨 越）the entire width of the Sahel, from Senegal to Djibouti．Overall, 100 million hectares（公顷）of land would be restored by 2030．Once completed, it was announced, the wall could end up capturing（俘获）250 million tonnes of carbon dioxide, while its creation and upkeep could create ten million jobs in rural areas.

Looking at the project as a whole, there's still a long way to go. According to a status report by the UN Convention to Combat Desertification, about four million hectares of degraded land have been restored. This means that progress towards the 100 million hectares target stands at just four per cent.

"When we started restoring the soil, we realized the area at risk was much wider than we initially thought, "explains Elvis Paul Tankmate African Union's GGW coordinator. "We had few funds to push the initiative as much as we wanted to. There was skepticism among investors, who didn't understand the project, but also among the African states themselves, which needed time to figure out if the GGW was a priority. "