Magnets firm up this metamaterial
Magnetism transforms a weird new material from soft to rigid
in a split second. This metamaterial — a synthetic structure that
behaves in ways natural materials don’t — comprises a gridlike
network of plastic tubes filled with fluid that becomes more
viscous in a magnetic field, causing the tubes to firm up,
researchers report December 7 in Science Advances.
Christopher Spadaccini, a materials engineer at Lawrence
Livermore National Laboratory in California, and colleagues
3-D printed lattices of plastic struts 5 millimeters long and
injected them with a mixture of tiny iron particles and oil. In
the absence of a magnetic field, the iron microparticles remain
scattered, so the liquid is runny. But near a magnet, the iron
microparticles align into chains along the magnetic field lines,
making the fluid viscous and the lattices stiffer.
Building tubular structures that are mostly open space, rather
than solid microparticle-filled hunks, makes the material light-
weight and less expensive, says coauthor and
engineer Julie Jackson of Lawrence Livermore.
A structure was 62 percent stiffer when it was
one centimeter away from a magnet versus eight
material could help
make more adaptable
robots or body armor.
— Maria Temming C L O
Many Americans don’t sleep enough
Nearly one-third of American adults sleep less than six hours
each night, a broad new survey shows.
That’s not enough. At least seven hours of sleep per night is
recommended, according to the American Academy of Sleep
Medicine and the Sleep Research Society.
Among nearly 400,000 respondents to the National Health
Interview Survey, 32. 9 percent reported this short sleep in
2017 — up from 28. 6 percent in 2004, when researchers began
noticing a drop in sleep time. That’s a 15 percent increase, says
Connor Sheehan, a sociologist at Arizona State University
Analysis of the annual survey results — accounting for the
U.S. population’s age distribution as well as respondents’
marital status, income, employment and lifestyle — suggests
the decline in sleep really picked up from 2013 onward, especially in black adults, Sheehan and colleagues report online
November 17 in Sleep. In 2017, 40.9 percent of black Americans
were likely to report short sleep, as were 30. 9 percent of whites
and 32. 9 percent of Hispanics, the researchers calculate.
Not getting enough sleep can increase the risk of accidents or
of developing conditions such as obesity and diabetes.
Researchers have found
dozens of shallow water
coral species in the deep
ocean off Australia.
Corals living in the
deep may be
Corals are abundant in the deep
Nearly 200 species of Great Barrier Reef corals have a
second home in the deep ocean. That’s six times as many
species as previously thought to be living in the dark, cold
waters off northeastern Australia, researchers report in
the Dec. 12 Proceedings of the Royal Society B.
“The deep reef is a lot more diverse and interesting than
we thought,” says coral biologist Paul Muir of the Museum
of Tropical Queensland in Townsville, Australia.
From 2010 to 2016, Muir and colleagues looked at
museum specimens and sampled 1,263 corals at depths of
30 to 125 meters in the ocean’s mesophotic zone, which
receives little sunlight. The team counted 195 coral
species in this zone, most of which had been thought to
inhabit only shallow waters. — Cassie Martin
Percent of people, by race or ethnicity,
likely to sleep less than six hours a night
Black 34.4 0.9
0 50 40 30 20 10
ZZZ force Americans were more likely in 2017 to report sleeping less
than six hours a night than in 2004. Black and Hispanic people were most
likely to be missing shut-eye. SOURCE: C. SHEEHAN ET AL/ SLEEP 2018
A magnetically tunable metamaterial contains many “unit
cells” (one shown) made of
plastic tubes filled with bits
of iron and oil.
Respondents could be snoozing even less than they
reported, since people tend to overestimate how much they
sleep, the authors say. The study did not explain why some
people are sleeping less now than 13 years ago, though stress
may be a factor. Smartphone overuse, which has been linked
to poor sleep and stress (SN Online: 1/23/17), may also play a
role. In the last decade, the number of adults who own a smartphone more than doubled.
“Staring at a bright smartphone screen and getting anxious
news is definitely not going to help you go to bed,” Sheehan
says. — Rodrigo Pérez Ortega