【推荐3】Scientists have found too much leisure time might not be good for people’s sense of subjectively well-being (主观幸福感). While levels of well-being initially rise as free time increases, the trend does not necessarily hold for very high levels of leisure.

“The sweet spot is a moderate amount of free time,” said Dr. Marissa Sharif, a co-author of the study from the University of Pennsylvania. “We found that having too much time was associated with lower subjective well-being due to a lacking sense of productivity and purpose.” The study found that although subjective well-being rose with the amount of free time up to about two hours, it began to drop once it lasted more than five hours.

Meanwhile, data from the National Study of the Changing Workforce, carried out between 1992 and 2008, revealed that beyond a certain point, having more free time was no longer linked to greater subjective well-being, but it did not drop — possibly because few of the participants reported having more than five hours of free time a day. Nevertheless, it is suggested that people who have too little free time should not quit all of their obligations, but instead try to find a couple of leisure hours a day. Meanwhile those with empty days should try spending their time with purpose, connecting with others or doing something productive.

Andrew Oswald, a professor of economics and behavioral science at the University of Warwick, welcomed the research. “This is a valuable study because it provides all sorts of statistical evidence for a very easily understandable idea; human beings like having spare time for leisure, home chores, hobbies, etc. — in their day but not too much of it,” he said, “It’s a Goldilocks principle — just the right amount.”

【推荐1】For a lot of people, age-related cognitive decline (认知衰退) follows “gradually, and then suddenly”. At first, the loss of mental sharpness is difficult to detect. But one day you may find that your memory and other mental muscles have grown noticeably, frustratingly weak.

Research has found cognitive decline may begin as early as your 20s. “Typically, a person peaks out around their 30th birthday,” says Michael Merzenich, a former director of the Keck Center for Integrative Neuroscience at the University of California. Each decade thereafter, the average person’s mental sharpness steadily drops off.

The brain’s toolset usually grows rusty (生锈的) as a result of disuse—not because of unpreventable degradation but due to taking your brain offline. “Offline” refers to autopilot activities. “This means doing the same things—relying on the abilities or skills you acquired at a younger age,” he explains. During the first few decades of your life, this sort of cognitive coasting isn’t really possible. But once you’ve settled into adulthood—into a set of routines—your day-to-day life may not ask much of your brain’s executive (决策的) functions, which are the high-level operations helping you solve complex problems. The older you get, the more difficult for you to change your habitual routine.

Fortunately, constantly engaging your brain’s learning machinery with skills or activities that are new makes it possible to prevent age-related cognitive decline.

More of Merzenich’s research has shown that “targeted” brain training can help people strengthen their memories, concentration, and high-level processing capabilities. Even among people with mild brain injury, cognitive damage is often reversible with proper training. He recommends adopting a new hobby—something that forces you to learn a new set of skills. “The goal is to expand your understanding in a new way,” he says.

Like your body, your brain requires exercise to stay healthy. Challenging it with new hobbies and learning opportunities may be the best way to maintain its fitness.

【推荐3】Plastic is nearly everywhere — in shoes, clothes, refrigerators and construction materials. But this highly useful material can have a major defect. Made from oil and slow to break down, conventional plastic is not environmentally friendly. Today, researchers discuss inventing what they say should be a safer, biodegradable (可生物降解的) alternative made from fish waste— heads, bones and skin— that would otherwise likely be thrown out.

If developed successfully, fish-oil-based plastic could help meet the considerable need for more sustainable plastic, says Francesca Kerton, the project’s investigator. Previously, others have developed new plastic using plant-based oils. However, this too comes with a disadvantage: the crops that produce these oils require land that could otherwise be used to grow food.

Leftover fish struck Kerton as a promising alternative. Salmon (鲑鱼) farming is a major industry for coastal Newfoundland, where her university is located. After the fish are processed, leftover parts are often thrown away. Kerton and her colleagues developed a process for turning this fish oil into a plastic-like material. But does the plastic smell fishy? “When we start the process with the fish oil a slight kind of fish smell, but as we go through the steps, that smell disappears,” Kerton says.

In other experiments, they have begun examining how quickly the new material would likely break down once its useful life is over. Kerton put pieces of it in water, and to speed up the degradation for some pieces, she added a chemical capable of breaking down fats like those in the fish oil. Under a microscope, she later saw microbial (微生物的）growth on all of the samples, even those that had been in plain water, an encouraging sign that the new material might biodegrade quickly, Kerton says.

Kerton now intends to study the material’s physical properties to see how it might in real-world applications, such as in packaging or fibers for clothing.