As a language learning enthusiast, I’ve come up with the best apps for learning English from the thousands of mobile apps out there.

Best for Pronunciation: ELSA Speak

ELSA Speak is probably the best mobile app around for helping you improve your English pronunciation. The app’s greatest strength is its intensive AI feedback, but ELSA also provides mini-training sessions to really perfect your pronunciation. The AI analyzes your recordings based on pronunciation, intonation and fluency then points out exactly which parts sound inaccurate.

Best for Immersing in English Videos: FluentU

FuentU is a language learning app that teaches you English through authentic videos like news reports, movie scenes and interviews, with learner tools for all levels. Each clip has interactive subtitles so if you’re not sure what a word means, you can hover over it and get in explanation. The app also gives video examples for each word so you can learn vocabulary in context.

Best for Practical Topics: Babbel

Babbel has you learn and practice English with realistic conversations that surround things that you’re personally interested in. Lessons are short and consist of written and audio versions of the grammar featured in the lessons. Then you are able to complete practice exercises to solidify your understanding.

Best for Fun Beginner Lessons: Lingodeer

Lingodeer uses games and short exercises to teach beginner and intermediate English learners. Lingodeer takes a gamified approach to language learning with a goal-oriented curriculum consisting of structured lessons and regular reviews. Lingodeer’s lessons are arranged according to themes, such as sports, weather, parts of the body and shopping.

For anyone trying to lose weight, there’s a truth we can all universally acknowledge that better health is often positioned as a numbers game. Hit the right number, and all your health problems will magically resolve, so the logic goes. Yet increasingly, science is revealing that losing weight may not be a silver bullet after all. In a mouse study published in the journal Science, looking specifically at an inflammatory(炎症的) eye condition linked to obesity called macular degeneration(黄斑退化), researchers found the struggle for better health doesn’t necessarily begin and end with weight loss.

Researchers conducted experiments on mice that were fed a high-fat diet for 11 weeks, making them gain weight. The mice were then put on a diet of low-fat food for 9 weeks, making them lose weight. Another group of mice only ate the low-fat diet as a control. Researchers shot lasers into the eyes of both the yo-yo dieter mice and the control mice to encourage atypical blood vessel(非典型性血管) growth, a mark of macular degeneration.

Among the mice that had gained and then lost weight, there was about 40 percent more atypical blood vessel growth than their stable diet peers. Driving the growth appeared to be macrophages(巨噬细胞). In the yo-yo dieter mice, these cells had been reprogrammed to cause inflammation. Taken together, these cells appeared to have an outsize role in atypical blood vessel growth in the eyes. Meanwhile, in the mice fed only a low-fat diet, inflammatory changes were absent. The results suggest that eating a high-fat diet that causes weight gain, even if followed by weight loss, leaves an inflammatory mark on mouse macrophages.

The research comes during a period of renewed interest in anti-obesity drugs. But medicines that help people shed pounds do not treat inflammation linked to a history of weight gain. “How to engage these findings with medicine interventions is a challenge,” says Bapat, head of the research.

A new kind of solar panel, developed at the University of Michigan, has achieved high efficiency in transforming water into hydrogen and oxygen—imitating a crucial step in natural photosynthesis(光合作用). The outdoor version of the experiment, with less reliable sunlight and temperature, achieved 6.1% efficiency at turning the energy from the sun into hydrogen fuel. However, indoors, the system achieved 9% efficiency.

But the biggest benefit is driving down the cost of sustainable hydrogen. This is enabled by reducing the size of the semiconductor(半导体), typically the most expensive part of the device. The team’s self-healing semiconductor withstands concentrated light equivalent to 160 suns.

“We believe that artificial photosynthesis devices will be much more efficient than natural photosynthesis, which will provide a path toward carbon neutrality,” said Zetian Mi, U-M professor of electrical and computer engineering who led the study reported in Nature.

The new technology has two advances. The first is the ability to concentrate the sunlight without destroying the semiconductor that traps the light. “We reduced the size of the semiconductor by more than 100 times compared to some semiconductors only working at low light intensity,” said Peng Zhou, U-M research fellow in electrical and computer engineering and first author of the study. “Hydrogen produced by our technology could be very cheap.”

And the second is using both the higher energy part of the solar spectrum(光谱) to break down water and the lower part of the spectrum to provide heat that encourages the reaction. The magic is enabled by a semiconductor catalyst(催化剂) that improves itself with use, resisting the degradation(降解) that such catalysts usually experience when they trap sunlight to drive chemical reactions.

The next challenges the team intends to tackle are to further improve the efficiency and to achieve superhigh purity hydrogen that can be directly fed into fuel cells.