The first ever 3D-printed steel bridge has opened in Amsterdam, the Netherlands. It was created by robotic arms using welding torches (焊枪) to place the structure of the bridge layer by layer, and was made of 4,500 kilograms of stainless steel.

The 12-metre-long MX3D Bridge was built by four commercially available industrial robots and took six months to print. The structure was transported to its location over the Oudezijds Achterburgwal canal in central Amsterdam last week. Now it is open to walkers and cyclists.

More than a dozen sensors attached to the bridge after the printing was completed will monitor pressure, movement, shakiness and temperature across the structure as people pass over it and the weather changes. This data will be fed into a digital model of the bridge.

Engineers will use this model to study the properties of the unique material and will employ machine learning to spot any trends in the data that could indicate maintenance is necessary. They also hope it will help designers understand how 3D-printed steel might be used for larger and more complex building projects.

Mark Girolami at the University of Cambridge, who is working on the digital model with a team at the Alan Turing Institute in London, says that investigations into bridge failures often display deterioration (退化) that was missed. Constant data feedback may have been able to prevent these failures by providing an early warning, he says.

Girolami says that early indications for the strength of 3D-printed steel are positive. “One of the things that we found is that the strength characteristics are dependent on the directions of the printing. But what was in some sense surprising was that the baseline strength was what you would expect of just rolled steel, and it actually increased in some directions.”

Every year, 1.5 million kids around the world die as a result of not getting vaccines (疫苗). This is partly because transporting (运送) and storing medicines can be a huge challenge in some countries.

Anurudh Ganesan, 17, knows this firsthand. When he was a baby in India, his grandparents carried him 10 miles to a health clinic in a remote village to receive a vaccine. But by the time they arrived, the vaccines were no longer usable because they had been overheated.

Vaccines, Anurudh later learned, must be kept cool to stay effective. But refrigerating (冷藏) them requires electricity (电) or ice—valuable things that many developing countries lack (缺少).

Although Anurudh received the vaccine he needed in the end, his experience as a baby and the sad reality that so many other children aren’t as lucky motivated (激发) him to take action. The high school student invented Vaxxwagon, a portable (轻便的) vaccine-carrying device (装置) that produces its own power to keep lifesaving medicines cool as they’re delivered to remote areas around the world.

Anurudh first got his idea for Vaxxwagon in 2014. He read several textbooks to learn everything he could about refrigeration, and then he did research online to learn more about vaccines. Rather than depending on electricity or ice, Anurudh worked out a way to use wheels to power a refrigeration system for about eight hours. The entire rechargeable (可再充电的) cooling system can be pulled to areas in need of vaccines by a bicycle, a car, or an animal. Eventually, Anurudh took his design to professors at Johns Hopkins University for advice. Not only did they think Vaxxwagon could work, but they offered him funding to help build it.

Anurudh was rewarded with the 2015 Google Science Fair LEGO Education Builder Award for his invention. Anurudh says his final goal is to start selling Vaxxwagon to relief organizations, so it can be used to help people around the world.

Anurudh, who plans to pursue engineering degree in college, says, “Don’t give up on your ideas. But always try to help others with your projects. That’s the point of engineering—to help people.”

By the mid-nineteenth century, the term “icebox” had entered the American language, but ice was still only beginning to affect the diet of ordinary citizens in the United States. The ice trade grew with the growth of cities. Ice was used in hotels, pubs, and hospitals, and by some forward-looking city dealers in fresh meat, fresh fish, and butler. After the Civil War (1861-1865), as ice was used to refrigerate freight cars(货车), it also came into household use. Even before 1880, half the ice sold in New York, Philadelphia, and Baltimore, and one-third of that sold in Boston and Chicago, went to families for their own use. This had become possible because a new household convenience, the icebox, a precursor（前身）of the modem refrigerator, had been invented.

Making an efficient icebox was not as easy as we might now suppose. In the early nineteenth century, the knowledge of the physics of heat, which was essential to a science of refrigeration, was undeveloped. The common belief that the best icebox was one that prevented the ice from melting was of course mistaken, for it was the melting of the ice that performed the cooling. Nevertheless, early efforts to economize ice included wrapping the ice in blankets, which kept the ice from doing its job. Not until near the end of the nineteenth century did inventors achieve the delicate balance of insulation(绝缘) and circulation needed for an efficient icebox.

But as early as 1803, an intelligent Maryland farmer, Thomas Moore, had been on the right track. He owned a farm about twenty miles outside the city of Washington, for which the village of Georgetown was the market center. When he used an icebox of his own design to transport his butter to market, he found that customers would pass up the rapidly melting butter of his competitors to pay an extra price for his butter, still fresh and hard in neat, one-pound bricks. One advantage of his icebox, Moore explained, was that fanners would no longer have to travel to market at night in order to keep their produce cool.