Number 660, November 4, 2003
by Phillip F. Schewe, Ben Stein, and James Riordon
Micro-Origami Fabricated Micromirrors
Microelectromechanical systems (MEMS) are becoming increasingly important
as researchers develop miniaturized mechanical devices for communications,
biotechnology, and a variety of measurement applications. Often these
machines include hinged parts that must be set in place before operation,
which can lead to challenging and time consuming manual manipulation
of components at ever decreasing scales. Recently, researchers from
the ATR Adaptive Communications Research Laboratories in Japan proposed
a technique that they call micro-origami to fabricate MEMS devices that
automatically move into position. The group has now tested the technique,
in collaboration with researchers at Konan University and Osaka City
University, by creating hinged micromirrors that lift themselves up
following the final fabrication stage. The key to the micro-origami
technique is to manufacture hinges out of a pair of material layers
with slightly different atomic spacings. This lattice mismatch causes
a stress that in turn bends the hinge (see
figure) and, in this case, raises a mirror above the substrate.
(The effect is reminiscent of the bimetallic strips in some thermostats,
which consist of bonded layers of metals that expand at different rates
when heated, leading to stresses that bend the strips as temperatures
change.) Once a mirror was in place, the researchers could move it on
its hinge by illuminating the mirror with a high power argon laser.
It is not yet entirely clear what mechanism caused the illuminated mirror
to move; the force due to radiation pressure, in particular, was too
small and in the wrong direction to account for the effect. Nevertheless,
the researchers (Jose M. Zanardi
Ocampo, 81-774-95-1582) were able to use the motion of the micromirror
to control the position of a reflected helium-neon laser beam. Potentially,
the micro-origami mirror could lead to optical MEMS switches or other
small devices that automatically pop into place without human or mechanical
intervention, dramatically speeding and simplifying construction of
miniature machines. (J.
M. Zanardi Ocampo et al., Applied Physics Letters, 3 November
2003)
Acceleration Disrupts Quantum Teleportation
Acceleration disrupts quantum teleportation, a new study has shown
(Paul Alsing, University of
New Mexico, 505-277-9094). In quantum teleportation (see PNU
#350), researchers create a pair of particles (such as photons)
and cause them to interact so their properties become interrelated (a
process called "entanglement").
Subsequently, after the particles go their separate ways, one can send
the first particle of the entangled pair and a new, third particle to
a detector simultaneously, and make a "joint" measurement
of the particles' properties (such as the directions their electric
fields are wiggling). Measuring these particles disturbs them, so as
to reduce the amount of information that an experimenter can obtain
about their properties. The measurement therefore produces just a limited
amount of ordinary, "classical" information.
But since the two entangled particles are interlinked, the measurement
also affects the properties of the second, remote particle in the entangled
pair. This "nonlocal" effect can be understood as a transfer
of "quantum" information from the first to second particle.
When the experimenter who handled the first particle contacts the experimenter
handling the second particle with the limited "classical"
information that he or she obtained from the measurement (a process
that can take place only at light speed or slower), the latter experimenter
has enough information to manipulate the second particle in just the
right way as to produce the exact quantum properties of the (now destroyed)
third particle.
This process of transference of quantum properties between particles,
by means of quantum measurement and classical communication, even if
the particles are light years apart, is called quantum teleportation,
and intimately relies upon the fact that the pair of particles are interlinked
or "entangled" through the unusual rules of quantum physics.
Quantum teleportation is different from Star Trek teleportation in that
real-life physicists are only teleporting a particle's properties, rather
than the particle itself.
Drawing from the example above, a new analysis has shown that quantum
teleportation would malfunction if the receiver of the second particle
is accelerating relative to the third particle. (Coincidentally, spaceships
in Star Trek usually don't teleport crew members when they accelerate
into warp drive.)
The disruption to quantum teleportation arises from the Davies-Unruh
effect (see Physical
Review Focus article),
in which acceleration, even in empty space, creates a bath of hot particles
resulting from the energy of the acceleration. This thermal bath of
particles inextricably disrupts the receiver's ability to perfectly
recreate (with the second accelerated particle) the properties of the
third (unaccelerated) particle that have been teleported from the sender.
While this effect is small for typical accelerations in Earthly labs
the result shows an interesting relationship between the effects of
space-time motion and the quantum world. (Alsing
and Milburn, Physical Review Letters, 31 October 2003)
A Close Look at Hagfish Slime
Hagfish are primitive, eel-like fish that are nearly blind and lack
jaws or true vertebrae, but they have the unnerving capability of producing
copious amounts of slime when disturbed.
Researchers from the Cambridge Polymer Group in Boston and the University
of British Columbia are now taking a close look at Hagfish slime, in
an attempt to understand how the slime protects the fish in nature and
to help determine if the slime could lead to practical materials for
industry or medicine.
Hagfish slime is a concoction of mucus and threadlike fibers, and is
produced in concentrated form from a series of pores that line the sides
of the fish's body. Upon contact with seawater, the concentrated slime
expands rapidly into a sticky gel that can ensnare and sometimes suffocate
an attacker.
Unlike the mucous produced by the membranes of humans and other animals,
which become more rigid, viscous gels at and below ambient body temperatures,
the researchers (Gavin Braithwaite, 617-629-4400, gavin@campoly.com;
Douglas Fudge, dfudge@interchange.ubc.ca) found that Hagfish slime is
much less elastic, even at high concentrations, than its human counterpart.
In addition, over the ranges of temperatures encountered by the hagfish,
the gel strength is relatively temperature independent. The insensitivity
to temperature perhaps ensures that slime is an effective defense in
a variety of conditions. In addition, artificial materials that mimic
Hagfish slime chemistry might make good space-filling gels.
One potential application for such gels, explain the researchers, is
as a way to curtail bleeding in an accident victim or during surgery.
In addition, studying the slime may help us understand how mucins, the
components of mucous, function in our own bodies and elsewhere.
There is currently some debate regarding the relative importance of
the fibers and the mucous in the material properties of Hagfish slime.
The recent research, which was presented earlier this month at the 75th
Annual Society of Rheology meeting in Pittsburgh, focused on characterizing
the properties of the mucous after the fibers had been removed from
the slime.
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