【推荐3】Owls are so famous for their nighttime activities that the phrase “night owl” is used to describe people who stay up late.     1    . That’s because some owls are active daytime hunters. During the daytime, the northern hawk owl and the northern pygmy owl are hunting for meals, making them diurnal—that is, active during the daytime. Moreover, it’s not uncommon to spot a snowy owl or burrowing owl during the day, depending on the season and food availability. Still others hunt during both the day and night, as well as daybreak and nightfall.

    2    . For instance, the northern pygmy owl has a preference for songbirds, which are awake during the day. The northern hawk owl, which hunts during the day, as well as at day-break and nightfall, eats small birds and other diurnal animals.

As the northern hawk owl’s name implies, it looks quite hawkish.     3    . However, it’s unclear whether the common ancestor they shared was diurnal, like the hawk, or nocturnal—that is, active at night, like most owls.

However, nocturnal owls certainly get advantages from their nighttime activities.     4    , both of which help them excel at nighttime hunting. Besides, the cover of darkness helps nocturnal owls avoid predators, as well as attack prey, principally because their feathers hardly make any noise when they fly.

Whether owls are nocturnal or diurnal, experts credit their success to the birds’ flexibility and adaptability. “Some hunt specific prey at a specific time, day or night.     5    ,” an expert said.

【推荐1】Long-term exposure to low-frequency noise can cause many health problems, but the solution may be found in an unexpected object, a ping-pong ball. Conventionally thought of as the plastic balls that speed through the air during a fast-speed game of table tennis, with a few changes, ping-pong balls can help absorb the city noise.

Low-frequency noise is everywhere in cities, near roads, and by airports. Though potentially heard as background in the acoustic (声学的) landscape, it can lead to earaches, breathing problems and other long-term harmful effects. Because it is produced by a range of sources and is less affected by structures than higher-frequency sound, low-frequency noise can be challenging to avoid.

In Journal of Applied Physics, researchers from the University of Lille and the National Technical University of Athens describe an acoustic metasurface (超表面) that uses ping-pong balls to prevent sound passing through.

“Ping-pong balls are well-known, everyday objects, present in large numbers all over the world,” said author Robine Sabat. “Our motivation was to use these easily accessible objects to create a low-frequency soundproof panel structure. Ping-pong balls therefore present a suitable alternative to sound insulators.”

Acoustic metasurfaces are materials specially engineered to handle sound waves. This metasurface uses ping-pong balls with small holes, acting as Helmholtz resonators (共振器). More resonant frequencies meant the device was able to absorb more sound. At the success of two coupled resonators, the researchers added more, until their device looked like a square sheet of ping-pong balls covered with holes, multiplying the number of resonant frequencies that could be absorbed.

By adjusting the number of balls, number of holes, and hole sizes, the researchers could change the metasurface’s acoustic properties, proving it is possible to design a sound absorption panel without expensive materials.

“The potential of this metasurface extends beyond sound absorption,” said Sabat. “It can be broadened to achieve various functions similar to other metasurfaces. These functionalities include sound focusing, unconventional sound reflection and more.”

【推荐3】In 1802, 31-year-old Beethoven paced through the countryside around Vienna. Rays of sunshine pierced through the trees, the hard soil crunched beneath his feet and birds conducted their own orchestra. But Beethoven wasn’t amazed at these details. Some years earlier, he had started to lose his hearing. He still persevered with his work, and went on creating timeless music. But he found little joy in the process.

Today, 466 million people worldwide have disabling hearing loss, and over 900 million are expected to have it by 2050, according to the World Health Organization. Its impact is often underestimated compared with other disabilities, and people with hearing loss constantly experience communication difficulties in their everyday lives. They often mishear the speech and find it very difficult to follow conversations. The miscommunication can lead individuals to feel isolated as they struggle to take part in social interactions, and ultimately lead them to withdraw from society. As Helen Keller once wrote: Blindness cuts us off from things, but deafness cuts us off from people.

To this day, there is still no cure for sensorineural (感觉神经性的) hearing loss (the most common type, and the one Beethoven had). We have advanced technological devices that strengthen the sound, such as hearing aids and cochlear implants (人工耳蜗), but these still don’t restore hearing. Scientists have been studying the regeneration process of hair cells in non-mammals, and they have identified various genes and proteins that have central roles. These can be targeted at stimulating support cells in the cochlea to create more hair cells and replace those that died. Some of these cell therapies have been successful in restoring the hearing of mice and guinea pigs: a breakthrough! If it works, such a scientific advance could transform hearing health care.

When Beethoven lost his hearing, he separated himself from society, but one thing that gave him strength was the hope that his hearing could be regained one day. But each medical remedy he attempted failed. In 1802, he wrote: But thinking that for six years now, I have been hopelessly afflicted, made worse by senseless physicians, from year to year cheated by hopes of improvement, and finally forced to face a lasting disease (whose cure will take years or perhaps be impossible).