7,313 research outputs found
An improved dual-frequency technique for the remote sensing of ocean currents and wave spectra
A two frequency microwave radar technique for the remote sensing of directional ocean wave spectra and surface currents is investigated. This technique is conceptually attractive because its operational physical principle involves a spatial electromagnetic scattering resonance with a single, but selectable, long gravity wave. Multiplexing of signals having different spacing of the two transmitted frequencies allows measurements of the entire long wave ocean spectrum to be carried out. A new scatterometer is developed and experimentally tested which is capable of making measurements having much larger signal/background values than previously possible. This instrument couples the resonance technique with coherent, frequency agility radar capabilities. This scatterometer is presently configured for supporting a program of surface current measurements
Hybrid propulsion technology program: Phase 1, volume 1
A number of booster propulsion system concepts are being considered for the next generation of manned and unmanned space launch vehicles. The one propulsion system concept that has potential for reducing costs with increased safety, reliability, and performance is hybrid propulsion (HP). A HP system may be thought of as a liquid propulsion system with solid fuel or a solid propulsion system with a liquid oxidizer. The liquid propulsion features that are most attractive are the higher specific impulse, clean exhaust, separated propellants, and oxidizer loading just prior to launch. The most attractive solid propulsion features includes low life cycle costs, no rotating machinery, compact size, and a robust case. In addition, a HP system has a robust LO2 tank; provides thrust control for ignition, to alleviate flight loads, and for thrust termination; and uses an inert grain that is not sensitive to anomalies such as cracks, voids, and separations. The object is to develop the technology to enable the application of HP to manned and unmanned space launch vehicles. This program will identify the necessary technology, acquire that technology, and demonstrate that technology. This volume is the executive summary
Hybrid propulsion technology program: Phase 1. Volume 3: Thiokol Corporation Space Operations
Three candidate hybrid propulsion (HP) concepts were identified, optimized, evaluated, and refined through an iterative process that continually forced improvement to the systems with respect to safety, reliability, cost, and performance criteria. A full scale booster meeting Advanced Solid Rocket Motor (ASRM) thrust-time constraints and a booster application for 1/4 ASRM thrust were evaluated. Trade studies and analyses were performed for each of the motor elements related to SRM technology. Based on trade study results, the optimum HP concept for both full and quarter sized systems was defined. The three candidate hybrid concepts evaluated are illustrated
Comparison of Josephson vortex flow transistors with different gate line configurations
We performed numerical simulations and experiments on Josephson vortex flow
transistors based on parallel arrays of YBa2Cu3O(7-x) grain boundary junctions
with a cross gate-line allowing to operate the same devices in two different
modes named Josephson fluxon transistor (JFT) and Josephson fluxon-antifluxon
transistor (JFAT). The simulations yield a general expression for the current
gain vs. number of junctions and normalized loop inductance and predict higher
current gain for the JFAT. The experiments are in good agreement with
simulations and show improved coupling between gate line and junctions for the
JFAT as compared to the JFT.Comment: 3 pages, 6 figures, accept. for publication in Appl. Phys. Let
Measurement of ocean wave spectra using polarimetric AIRSAR data
A polarimetric technique for improving the visibility of waves, whose propagation direction has an azimuthal component, in RAR (real aperture radar) or SAR (synthetic aperture radar) images has been investigated. The technique shows promise as a means of producing more accurate 2-D polarimetric RAR ocean wave spectra. For SAR applications domination by velocity-bunching effects may limit its usefulness to long ocean swell. A modification of this technique involving measurement of polarization signature modulations in the image is useful for detecting waves in SAR images and, potentially, estimating RMS wave slopes
The Management and Use of Social Network Sites in a Government Department
In this paper we report findings from a study of social network site use in a
UK Government department. We have investigated this from a managerial,
organisational perspective. We found at the study site that there are already
several social network technologies in use, and that these: misalign with and
problematize organisational boundaries; blur boundaries between working and
social lives; present differing opportunities for control; have different
visibilities; have overlapping functionality with each other and with other
information technologies; that they evolve and change over time; and that their
uptake is conditioned by existing infrastructure and availability. We find the
organisational complexity that social technologies are often hoped to cut
across is, in reality, something that shapes their uptake and use. We argue the
idea of a single, central social network site for supporting cooperative work
within an organisation will hit the same problems as any effort of
centralisation in organisations. We argue that while there is still plenty of
scope for design and innovation in this area, an important challenge now is in
supporting organisations in managing what can best be referred to as a social
network site 'ecosystem'.Comment: Accepted for publication in JCSCW (The Journal of Computer Supported
Cooperative Work
Immunologic properties of purified epidermal Langerhans cells: Distinct requirements for stimulation of unprimed and sensitized T lymphocytes
Inaba, K., Schuler, G., Witmer, M., Valinsky, J., Atassi, B., and Steinman, R.M. Immunologic properties of purified epidermal Langerhans cells: Distinct requirements for stimulation of unprimed and sensitized T lymphocytes. J. Exp. Med. 164: 605-613, 1986.https://digitalcommons.rockefeller.edu/historical-scientific-reports/1019/thumbnail.jp
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