Mirko Kovac, using collective building methods inspired by natural builders like bees and wasps, has developed a way to improve the flexibility of 3D printing. A typical 3D printer is limited by the range of its nozzle (喷头), and can only make objects smaller than itself. Dr Kovac’s team has removed these restrictions by giving the printer nozzle wings.

Writing in the latest edition of Nature, Dr Kovac describes a system of flying robots that is composed of two types of drones (无人机): builders and scanners. The builders carry the 3D-printing nozzle. The scanners are robots equipped with cameras that are responsible for monitoring the progress of the builders.

The building process alternates between builders and scanners, layer by layer; Printing and adjusting, until a structure is complete. First,a builder hovers(盘旋)over its area of operation and begins to release a jet of the building material as it moves along its flight path. The choice of material is important — it must be lightweight enough for the drones to carry but powerful enough to hold the subsequent layers that will be built on top.

Once the builder robot has sprayed a layer of material, the scanner robot flies over and inspects the progress. The system then computes the next layer that the builder should make, while also correcting for any errors that might have been discovered in what has already been built. These could be errors made by the builder-drones or imperfections in the expansion of the building material.

While these robots have been shown to be capable of manufacturing by passing some tests with flying co-lours, Dr Kovac says their bread and butter will probably be, initially, in repair, fixing building parts in dangerous or otherwise inaccessible places. Nevertheless, thinking more long term, Dr Kovac even sees a potential future for his construction robots, building on the surfaces of the Moon or Mars.

Next month, I’m traveling to a remote area of Central Africa and my aim is to know enough Lingala — one of the local languages — to have a conversation. I wasn’t sure how I was going to manage this — until I discovered a way to learn all the vocabulary I’m going to need. Thanks to Memrise, the app I’m using. It feels just like a game.

“People often stop learning things because they feel they’re not making progress or because it all feels like too much hard work,” says Ed Cooke, one of the people who created Memrise. “We’re trying to create a form of learning experience that is fun and is something you’d want to do instead of watching TV.”

Memrise gives you a few new words to learn and these are “seeds” which you plant in your “greenhouse”. When you practice the words, you “water your plants”. When the app believes that you have really remembered a word, it moves the word to your “garden”. And if you forget to log on, the app sends you emails that remind you to “water your plants”.

The app uses two principles about learning. The first is that people remember things better when they link them to a picture in their mind. Memrise translates words into your own language, but it also encourages you to use “mems”. For example, I memorized motele, the Lingala word for “engine”, using a mem I created — I imagined an old engine in a motel (汽车旅馆) room.

The second principle is that we need to stop after studying words and then repeat them again later, leaving time between study sessions. Memrise helps you with this, because it’s the kind of app you only use for five or ten minutes a day.

I’ve learnt hundreds of Lingala words with Memrise. I know this won’t make me a fluent speaker, but I hope I’ll be able to do more than just smile when I meet people in Congo. Now, I need to go and water my vocabulary!

Winters are long and cold in Finland. That’s why new technology that stores summer heat in a giant sand battery (电池) is used to keep homes warm in the winter. The sand battery can store the heat for months so the energy that was generated by solar power in the summer can be used in the winter to heat homes. Researchers in Finland have installed (安装) the first fully-functioning“sand battery”. They believe it could solve the country’s year-round crisis (危机) in power supply, which is a significant issue for green energy.

The sand battery was installed in the Vatajankoski power plant that runs the heating system for the houses in the area. It works by heating the sand, circulating the heat generated in the sand using a heat exchanger. Researchers used low-grade sand to charge (充电) the devices with heat from cheap electricity coming from either solar or wind energy. The sand battery can store energy and heat up to 500 degrees Celsius, which can be used to warm homes during winter when large amounts of energy were consumed (消耗).

It is a cost-effective method because when the battery releases the hot air, it warms the water for the district heating system that is pumped around homes, offices, and the local swimming pool. Sand is an ideal material because it is cheap and readily available everywhere. While other inexpensive items like water can store heat, sand can be heated to much higher temperatures. The sand used is of the lowest quality so it cannot be used in construction thus making it a sustainable choice. Besides, sand-based batteries last longer than other batteries. According to a study, researchers obtained silicon using quartz sand to create a battery that lasts three times longer than lithium-ion (锂离子) batteries.

“This innovation is a part of the smart and green energy transition. Heat storage systems can significantly help to increase intermittent renewables in the electrical grid,” said Markku Ylönen, co-founder of Polar Night Energy. “At the same time, we can make full use of the heat waste to keep the city warm. This is a logical step towards combustion-free (无燃烧) heat production.”