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A D V A N C E D

M A T E R I A L S

&

P R O C E S S E S |

N O V E M B E R / D E C E M B E R

2 0 1 5

9

repulsion tomake the hydrogel perform

like a coiled spring.

Researchers exploited their hy-

drogel’s large and rapid thermally in-

duced shape changes by designing an

actuator that walks when exposed to

alternating temperature cycles. Their

L-shaped gel contains two “feet” in

contact with a horizontal, underwa-

ter surface. On heating, the back foot

elongates, propelling the gel forward.

A quick plunge in temperature then

draws the feet back into position for

another kick forward. The team is cur-

rently working on improving material

properties with a view to achieving

their ultimate goal—a new generation

of hydrogel-based artificial organs and

muscles.

For more information: Yasuhi-

ro Ishida, 81.048.462.1111 ext. 6351,

y-ishida@riken.jp

,

www.riken.jp/en.

RARE EARTHS HELP PROBE

PARTICLE PHYSICS

In recent work by Lawrence Liv-

ermore National Laboratory, Calif.,

scientist Michael Hohensee and col-

leagues discovered that the properties

that make rare earth elements so useful

also make them great probes of physics

beyond the Standard

Model of particle phys-

ics—a theory concern-

ing the electromagnet-

ic, weak, and strong

nuclear

interactions,

as well as classifying all

the known subatomic

particles.

According to Ho-

hensee, rare earths

make great magnets

in part because their

valence electrons have

more orbital angular

momentum than other

elements, and because

other electrons form a

shield around the va-

lence electrons. This

shield also helps make

themgood laser media,

as it prevents external

heat and noise from

affecting the laser tran-

sitions,

maintaining

the rare earths’ unique

properties when they

are mixed (or doped)

into a piece of glass or

Each of the National Ignition Facility’s

(NIF) 192 beamlines contains two large

amplifier sections. The amplifiers are

designed to efficiently provide 99.99% of

NIF’s power and energy. Laser amplifier

glass is doped with rare earth ions, which

prevent external heat and noise from

affecting the laser transitions.

crystal. “Thanks to both these proper-

ties, the electronic states of rare earths

doped in a crystal make possible an

electronic equivalent of the Michel-

son-Morley experiment that would be

more sensitive than any other yet per-

formed, helping to validate or rule out

unified theories of gravity and particle

physics,” says Hohensee.

llnl.gov.

Researchers created a muscle-like hydrogel by trapping face-stacked inorganic nanosheets within a polymer network. The repulsive force

between the charged nanosheets becomes greater with increasing temperature, causing the material to elongate in one direction.