110,195 research outputs found
Explicit soliton-black hole correspondence for static configurations
We construct an explicit map that transforms static, generalized sine-Gordon
metrics to black hole type metrics. This, in particular, provides for a further
description of the Cadoni correspondence (which extends the
Gegenberg-Kunstatter correspondence) of soliton solutions and extremal black
hole solutions in 2D dilaton gravity.Comment: Submitted to Phys Rev D, 7 pages, no figure
Sources of sound in fluid flows
Some features of a flow that produce acoustic radiation, particularly when the flow is turbulent and interacting with solid surfaces such as turbine or compressor blades are discussed. Early theoretical ideas on the subject are reviewed and are shown to be inadequate at high Mach number. Some recent theoretical developments that form the basis of a description of sound generation by supersonic flows interacting with surfaces are described. At high frequencies the problem is treated as one of describing the surface-induced diffraction field of adjacent aerodynamic quadrupole sources. This approach has given rise to distinctly new features of the problem that seem to have bearing on the radiating properties of relatively large aerodynamic surfaces
A design and implementation methodology for diagnostic systems
A methodology for design and implementation of diagnostic systems is presented. Also discussed are the advantages of embedding a diagnostic system in a host system environment. The methodology utilizes an architecture for diagnostic system development that is hierarchical and makes use of object-oriented representation techniques. Additionally, qualitative models are used to describe the host system components and their behavior. The methodology architecture includes a diagnostic engine that utilizes a combination of heuristic knowledge to control the sequence of diagnostic reasoning. The methodology provides an integrated approach to development of diagnostic system requirements that is more rigorous than standard systems engineering techniques. The advantages of using this methodology during various life cycle phases of the host systems (e.g., National Aerospace Plane (NASP)) include: the capability to analyze diagnostic instrumentation requirements during the host system design phase, a ready software architecture for implementation of diagnostics in the host system, and the opportunity to analyze instrumentation for failure coverage in safety critical host system operations
System for interference signal nulling by polarization adjustment
A receiving system for automatically selecting a desired one of two approximately orthogonally polarized signals occupying the same bandwidth, is described. Received signals are provided by any orthomode antenna system at a pair of output ports, i.e., right hand and left hand circular polarizations or two linear polarizations. The received signals are then applied to the inputs of a hybrid junction to produce sum and difference signals. The resulting sum signal at one output port comprises components of the undesired one of two orthogonally polarized signals and is used to coherently detect and dynamically balance out the undesired signal components that are included at the difference signal port. The desired one of two orthogonally polarized signals is thereby provided at the difference port of the hybrid junction. Feedback loops are used to effect dynamic balancing
Multibeam-antenna feed system to isolate orthogonally polarized beams
System is polarization tracker and comprises variable polarizer, polarization control, and receiver servo loop. System simultaneously receives desired signal and undesired signal which are approximately orthogonal. They can be either paired as left and right circular polarizations or as cross-linear polarizations
Automatic water inventory, collecting, and dispensing unit
Two cylindrical tanks with piston bladders and associated components for automatic filling and emptying use liquid inventory readout devices in control of water flow. Unit provides for adaptive water collection, storage, and dispensation in weightlessness environment
Chandra discovery of the intracluster medium around UM425 at redshift 1.47
We report on a discovery of a candidate cluster of galaxies at redshift
z=1.47 based on Chandra observations in the field of quasars UM425 A & B. We
detect with high significance diffuse emission due the intracluster hot gas
around the quasar pair. This is the second highest redshift cluster candidate
after 3C294 at z=1.786. The diffuse emission is elliptical in shape with about
17" extent. If indeed at z=1.47, this corresponds to a physical size of 140
h_{70}^{-1} Kpc and 2--10 keV luminosity of about 3 times 10^{43} erg/s. The
cluster is unlikely to be the long sought gravitational lens invoked to explain
unusual brightness of UM425 A and the close quasar pair. Coexistence of the
quasars with the cluster suggests a link of activity to cluster environment.
The unusual brightness of UM425 A may then be due to a higher accretion rate.
We also comment briefly on the X-ray spectra of UM 425 A & B which also happen
to be broad absorption line quasars. We argue that present evidence suggests
that the quasars are just a pair and not lensed images of the same quasar.Comment: Submitted to ApJ Letter
Investigation of Tantalum Wet Slug Capacitor Failures in the Apollo Telescope Mount Charger Battery Regulator Modules
This investigation describes the capacitor failures and to identify the cause of the failure mechanism. Early failures were thought to have happened because of age and/or abuse since the failed capacitors were dated 1967. It is shown that all 1967 capacitors were replaced with 1972 capacitors
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