2,644 research outputs found
Spacecraft antenna systems Final engineering report, Oct. 1963 - Jan. 1966
Spacecraft communication system with reliable, beam-steering antenn
High-gain self-steering microwave repeater, volume 1 Final engineering report, Jan. 1966 - Apr. 1969
Engineering model of high gain self steering microwave transponder and application to satellite communication link
Novel Symmetry of Non-Einsteinian Gravity in Two Dimensions
The integrability of -gravity with torsion in two dimensions is traced
to an ultralocal dynamical symmetry of constraints and momenta in Hamiltonian
phase space. It may be interpreted as a quadratically deformed
-algebra with the deformation consisting of the Casimir operators of
the undeformed algebra. The locally conserved quantity encountered in the
explicit solution is identified as an element of the centre of this algebra.
Specific contractions of the algebra are related to specific limits of the
explicit solutions of this model.Comment: 17 pages, TUW-92-04 (LaTeX
Advanced microwave radiometer antenna system study
The practicability of a multi-frequency antenna for spaceborne microwave radiometers was considered in detail. The program consisted of a comparative study of various antenna systems, both mechanically and electronically scanned, in relation to specified design goals and desired system performance. The study involved several distinct tasks: definition of candidate antennas that are lightweight and that, at the specified frequencies of 5, 10, 18, 22, and 36 GHz, can provide conical scanning, dual linear polarization, and simultaneous multiple frequency operation; examination of various feed systems and phase-shifting techniques; detailed analysis of several key performance parameters such as beam efficiency, sidelobe level, and antenna beam footprint size; and conception of an antenna/feed system that could meet the design goals. Candidate antennas examined include phased arrays, lenses, and optical reflector systems. Mechanical, electrical, and performance characteristics of the various systems were tabulated for ease of comparison
Electronically steerable millimeter wave antenna techniques for space shuttle applications
A large multi-function antenna aperture and related components are described which will perform electronic steering of one or more beams for two of the three applications envisioned: (1) communications, (2) radar, and (3) radiometry. The array consists of a 6-meter folded antenna that fits into two pallets. The communications frequencies are 20 and 30 GHz, while the radar is to operate at 13.9 GHz. Weight, prime power, and volumes are given parametrically; antenna designs, electronics configurations, and mechanical design were studied
Hawking Radiation for Non-minimally Coupled Matter from Generalized 2D Black Hole Models
It is well known that spherically symmetric reduction of General Relativity
(SSG) leads to non-minimally coupled scalar matter. We generalize (and correct)
recent results to Hawking radiation for a class of dilaton models which share
with the Schwarzschild black hole non-minimal coupling of scalar fields and the
basic global structure. An inherent ambiguity of such models (if they differ
from SSG) is discussed. However, for SSG we obtain the rather disquieting
result of a negative Hawking flux at infinity, if the usual recipe for such
calculations is applied.Comment: 8 page
Comment on: ``Trace anomaly of dilaton coupled scalars in two dimensions''
The trace anomaly for nonminimally coupled scalars in spherically reduced
gravity obtained by Bousso and Hawking (hep-th/9705236) is incorrect. We
explain the reasons for the deviations from our correct (published) result
which is supported by several other recent papers.Comment: 2 page
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