3,494 research outputs found
Initial '80s Development of Inflated Antennas
State of the art technology was considered in the definition and documentation of a membrane surface suitable for use in a space reflector system for long durations in orbit. Requirements for a metal foil-plastic laminate structural element were determined and a laboratory model of a rigidized element to test for strength characteristics was constructed. Characteristics of antennas ranging from 10 meters to 1000 meters were determined. The basic antenna configuration studied consists of (1) a thin film reflector, (2) a thin film cone, (3) a self-rigidizing structural torus at the interface of the cone and reflector; and (4) an inflation system. The reflector is metallized and, when inflated, has a parabolic shape. The cone not only completes the enclosure of the inflatant, but also holds the antenna feed at its apex. The torus keeps the inflated cone-reflector from collapsing inward. Laser test equipment determined the accuracy of the inflated paraboloids
Strong Effort Manipulations Reduce Response Caution:A Preregistered Reinvention of the Ego-Depletion Paradigm
Optical alignment and spinning of laser-trapped microscopic particles
Light-induced rotation of absorbing microscopic particles by transfer of
angular momentum from light to the material raises the possibility of optically
driven micromachines. The phenomenon has been observed using elliptically
polarized laser beams or beams with helical phase structure. But it is
difficult to develop high power in such experiments because of overheating and
unwanted axial forces, limiting the achievable rotation rates to a few hertz.
This problem can in principle be overcome by using transparent particles,
transferring angular momentum by a mechanism first observed by Beth in 1936,
when he reported a tiny torque developed in a quartz waveplate due to the
change in polarization of transmitted light. Here we show that an optical
torque can be induced on microscopic birefringent particles of calcite held by
optical tweezers. Depending on the polarization of the incident beam, the
particles either become aligned with the plane of polarization (and thus can be
rotated through specified angles) or spin with constant rotation frequency.
Because these microscopic particles are transparent, they can be held in
three-dimensional optical traps at very high power without heating. We have
observed rotation rates in excess of 350 Hz.Comment: 4 pages, 4 figure
Optical microrheology using rotating laser-trapped particles
We demonstrate an optical system that can apply and accurately measure the
torque exerted by the trapping beam on a rotating birefringent probe particle.
This allows the viscosity and surface effects within liquid media to be
measured quantitatively on a micron-size scale using a trapped rotating
spherical probe particle. We use the system to measure the viscosity inside a
prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction
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