3,583 research outputs found
Rolamite - A new mechanical design concept
Rolamite, a mechanical suspension system, provides substantial reductions in friction in the realm of extremely low bearing pressures. In addition, rolamite devices are easily microminiaturized, are extremely tolerant of production variations and are inherently capable of virtually all functions to construct most electromechanical devices
Clues to Quasar Broad Line Region Geometry and Kinematics
We present evidence that the high-velocity CIV lambda 1549 emission line gas
of radio-loud quasars may originate in a disk-like configuration, in close
proximity to the accretion disk often assumed to emit the low-ionization lines.
For a sample of 36 radio-loud z~2 quasars we find the 20--30% peak width to
show significant inverse correlations with the fractional radio core-flux
density, R, the radio axis inclination indicator. Highly inclined systems have
broader line wings, consistent with a high-velocity field perpendicular to the
radio axis. By contrast, the narrow line-core shows no such relation with R, so
the lowest velocity CIV-emitting gas has an inclination independent velocity
field. We propose that this low-velocity gas is located at higher
disk-altitudes than the high-velocity gas. A planar origin of the high-velocity
CIV-emission is consistent with the current results and with an accretion
disk-wind emitting the broad lines. A spherical distribution of randomly
orbiting broad-line clouds and a polar high-ionization outflow are ruled out.Comment: 5 Latex pages, 1 figure, accepted for publication in ApJ Letter
Terahertz emitters based on microcavity dipolaritons
We propose the use of dipolaritons -- quantum well excitons with large dipole
moment, coupled to a planar microcavity -- for generating terahertz (THz)
radiation. This is achieved by exciting the system with two THz detuned lasers
that leads to dipole moment oscillations of the exciton polariton at the
detuning frequency, thus generating a THz emission. We have optimized the
structural parameters of a system with microcavity embedded AlGaAs double
quantum wells and shown that the THz emission intensity is maximized if the
laser frequencies both match different dipolariton states. The influence of the
electronic tunnel coupling between the wells on the frequency and intensity of
the THz radiation is also investigated, demonstrating a trade-off between the
polariton dipole moment and the Rabi splitting.Comment: 4 pages, 4 figures. This article has been submitted to Applied
Physics Letter
Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei
Emission-line variability data on NGC 5548 argue strongly for the existence
of a mass of order 7 x 10^7 solar masses within the inner few light days of the
nucleus in the Seyfert 1 galaxy NGC 5548. The time-delayed response of the
emission lines to continuum variations is used to infer the size of the
line-emitting region, and these determinations are combined with measurements
of the Doppler widths of the variable line components to estimate a virial
mass. The data for several different emission lines spanning an order of
magnitude in distance from the central source show the expected V proportional
to r^{-1/2} correlation and are consistent with a single value for the mass.Comment: 9 pages, 2 Figures. accepted by ApJ Letter
Development of an improved protective cover/light block for multilayer insulation
The feasibility of using a scrim-reinforced, single metallized, 4-mil Tedlar film as a replacement for the Teflon coated Beta-cloth/single metallized 3-mil Kapton film presently used as the protective cover/light block for multilayer insulation (MLI) on the Orbiter, Spacelab, and other space applications was demonstrated. The proposed Tedlar concept is lighter and potentially lower in cost. Thermal analysis with the proper concept was much simpler than with the present system. Tests have already demonstrated that white Tedlar has low alpha (adsorption) degradation in space from U.V. The proposed concept was 4400 percent cheaper with nominal weight savings of 50 percent
The Student Gaze
It is a commonplace for campuses to extol the virtues of ‘International Experience’, to encourage higher levels of engagement in Study Abroad programs, and to try to draw more international students to their campuses. In this article, I give an account of my own experience as a Fulbright Program Advisor and Study Abroad faculty member
The Space of the Social
This is chapter two of the Jane Austen book-length project, Social Jane. Landscape, houses and estates form the backdrop to much of what happens in the Austen novels, and Austen is entirely familiar with the theories of landscape of her time. She sets about debunking Whig improvers, while decimating the pretensions of the Tory do-nothings she saw around her. Benign and cautious progress seems to be her preferred model of land management. The chapter rehearses the social and architectural theories of her time, shows her use of these theories in her characters and in her work, and tries to liberate her from her reputation as a simple lickspittle of the Tory hierarchy
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