When I was 9, we packed up our home in Los Angeles and arrived at Heathrow, London on a gray January morning. Everyone in the family settled quickly into the city except me. Without my beloved beaches and endless blue—sky days, I felt at a loss and out of place. Until I made a discovery.

Southbank, at an eastern bend in the Thames, is the center of British skateboarding, where the continuous crashing of skateboards left your head ringing .I loved it. I soon made friends with the local skaters. We spoke our own language. And my favorite: Safe. Safe meant cool. It meant hello. It meant don't worry about it. Once, when trying a certain trick on the beam（横杆）, I fell onto the stones, damaging a nerve in my hand, and Toby came over, helping me up: Safe, man. Safe. A few minutes later, when I landed the trick, my friends beat their boards loud, shouting: " Safe! Safe! Safe!" And that's what mattered—landing tricks, being a good skater.

When I was 15, my family moved to Washington. I tried skateboarding there, but the locals were far less welcoming. Within a couple of years, I'd given it up.

When I returned to London in 2004, I found myself wandering down to Southbank, spending hours there. I've traveled back several times since, most recently this past spring. The day was cold but clear: tourists and Londoners stopped to watch the skaters. Weaving（穿梭）among the kids who rushed by on their boards, I found my way to the beam. Then a rail—thin teenager, in a baggy white T—shirt, skidded（滑）up to the beam. He sat next to me. He seemed not to notice the man next to him. But soon I caught a few of his glances. "I was a local here 20 years ago," I told him. Then, slowly, he began to nod his head. "Safe, man. Safe."

"Yeah," I said. "Safe."

Can a small group of drones（无人机）guarantee the safety and reliability of railways and, at the same time, help railway operators save billions of euros each year? That is the very likely future of applying today's "eyes in the sky" technology to making sure that the millions of kilometres of rail tracks and infrastructure（基础设施）worldwide are safe for trains on a 24/7 basis.

Drones are already being used to examine high-tension electrical lines. They could do precisely the same thing to inspect railway lines and other vital aspects of rail infrastructure such as the correct position of railway tracks and switching points. The more regularly they can be inspected, the more railway safety, reliability and on-time performance will be improved. Costs would be cut and operations would be more efficient（高效）across the board.

That includes huge savings in maintenance costs and better protection of railway personnel safety. It is calculated that European railways alone spend approximately 20 billion euros a year on maintenance, including sending maintenance staff, often at night, to inspect and repair the rail infrastructure. That can be dangerous work that could be avoided with drones assisting the crews' efforts.

By using the latest technologies, drones could also start providing higher-value services for railways, detecting faults in the rail or switches, before they can cause any safety problems. To perform these tasks, drones for rail don't need to be flying overhead. Engineers are now working on a new concept: the rail drones of the future. They will be moving on the track ahead of the train, and programmed to run autonomously. Very small drones with advanced sensors and AI and travelling ahead of the train could guide it like a co-pilot. With their ability to see ahead, they could signal any problem, so that fast-moving trains would be able to react in time.

If you ever get the impression that your dog can "tell" whether you look content or annoyed, you may be onto something. Dogs may indeed be able to distinguish between happy and angry human faces, according to a new study.

Researchers trained a group of 11 dogs to distinguish between images（图像）of the same person making either a happy or an angry face. During the training stage, each dog was shown only the upper half or the lower half of the person's face. The researchers then tested the dogs' ability to distinguish between human facial expressions by showing them the other half of the person's face or images totally different from the ones used in training. The researchers found that the dogs were able to pick the angry or happy face by touching a picture of it with their noses more often than one would expect by random chance.

The study showed the animals had figured out how to apply what they learned about human faces during training to new faces in the testing stage. "We can rule out that the dogs simply distinguish between the pictures based on a simple cue, such as the sight of teeth," said study author Corsin Muller. "Instead, our results suggest that the successful dogs realized that a smiling mouth means the same thing as smiling eyes, and the same rule applies to an angry mouth having the same meaning as angry eyes.”

"With our study, we think we can now confidently conclude that at least some dogs can distinguish human facial expressions," Muller told Live Science.

At this point, it is not clear why dogs seem to be equipped with the ability to recognize different facial expressions in humans. "To us, the most likely explanation appears to be that the basis lies in their living with humans, which gives them a lot of exposure to human facial expressions," and this exposure has provided them with many chances to learn to distinguish between them, Muller said.