Search NASA⌕ Search

SEARCH · Search NASA

Results for “Compact”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The gasdynamics of compact relativistic jets

The gasdynamics of compact relativistic jets is explored by analyzing a specific idealized flow problem using the method of characteristics. The basic flow pattern of the gas and pressure waves within a jet experiencing a drop in external pressure is calculated, with analytic expressions given for many of the important parameters. Scaling laws which relate the intrinsic properties of the jet to the pressure of the surrounding medium are obtained and discussed. The physical properties of the jet depend critically on the value and abruptness of the decrease in external pressure, as well as on the initial Lorentz factor of the flow. A variety of the flow patterns can result, including jets of oscillating cross section, jets with standing shocks, and broad, nearly hollow beams which can break up into multiple jets. These results are discussed in relation to the observed characteristics of superluminal radio sources in general and the superluminal quasar 4C 39.25 in particular.

Daly, Ruth A.↗
NASA NTRS1988

An exceptionally bright, compact starburst nucleus

Observations are reported of a remarkably bright (V about 13) starburst nucleus, 0833 + 652, which has been detected at radio, infrared, optical, ultraviolet, and X-ray wavelengths. Despite an observed flux at each of these wavelengths which is comparable to that of NGC 7714, often considered the 'prototypical' example of the starburst phenomenon, 0833 + 652 appears to be a previously uncataloged object. Its ease of detectability throughout the electromagnetic spectrum should make it useful for a variety of problems in the study of compact emission-line galaxies.

Margon, Bruce↗
NASA NTRS1988

Compact wide-aperture hyperbolic analyzers

Compact electrostatic analyzers that employ a new geometry are described. They accept collimated beams of ions through relatively wide (non-slit-like) inlet apertures and focus them at various locations, depending on the ion energy per charge, along rectangular position-sensing detectors. Each analyzer has a dynamic range of 10 or more for a fixed deflection voltage. The focal line width at a given energy is a small fraction of the inlet aperture width, and the focal lines are approximately coplanar.

Curtis, C. C.↗
NASA NTRS1989

Blue compact dwarf galaxies in the Virgo Cluster - H I and IRAS data and upper limits on proto-dwarf galaxies

Correlations between various properties of blue compact dwarf (BCD) galaxies in the Virgo Cluster were studied. It was found that, at constant mass, BCD galaxies are comparable to non-BCD irregulars in both blue luminosity and H I flux. About one-third of the BCDs were detected by IRAS at 60 or 100 microns, mostly at intensities just above the threshold sensitivity.

Hoffman, G. Lyle↗
NASA NTRS1989

A dual chamber Gregorian subreflector system for compact range applications

A dual-chamber compact range configuration is proposed wherein the main reflector and target zone are located in the main chamber and an oversized Gregorian subreflector and associated feed assemblies in the other. The chambers are isolated by an absorber fence except for a small coupling aperture which is used to transmit signals between them. The absorber fence prevents diffraction by the subreflector and spillover by the feed from illuminating the main reflector and target zone. System performance is analyzed with and without the absorber fence to show how the coupling aperture should be shaped to minimize diffractions.

Pistorius, Carl W. I.↗
NASA NTRS1988

Compact high-order schemes for the Euler equations

An implicit approximate factorization (AF) algorithm is constructed which has the following characteristics. In 2-D: the scheme is unconditionally stable, has a 3 x 3 stencil and at steady state has a fourth order spatial accuracy. The temporal evolution is time accurate either to first or second order through choice of parameter. In 3-D: the scheme has almost the same properties as in 2-D except that it is now only conditionally stable, with the stability condition (the CFL number) being dependent on the cell aspect ratios, delta y/delta x and delta z/delta x. The stencil is still compact and fourth order accuracy at steady state is maintained.

Abarbanel, Saul↗
NASA NTRS1989

Radio structure at 8.4 GHz in Sagittarius A, the compact radio source at the Galactic center

VLBI observations of the compact, nonthermal radio source at the Galactic center show it to be elongated at 8.4 GHz along a position angle of 82 + or - 6 deg. The source has an axial ratio of 0.53 + or - 0.10 with a major axis of 17.4 + or - 0.5 mas. Examination of VLA maps of the Galactic center region indicate no obvious alignment with this smaller-scale elongation of the nuclear region, nor is the nuclear position angle aligned with the axis of Galactic rotation. Comparison with the size measured at frequencies from 1 to 22 GHz shows that the size follows very closely the lambda-squared dependence expected from interstellar scattering. The alongated nature of the source implies either that the scattering medium is anisotropic or that some remnant of the intrinsic structure remains visible through the scattering medium.

Jauncey, David L.↗
NASA NTRS1989

Optical identifications of southern compact radio sources

Optical identifications are presented for 158 radio sources, mostly from the Southern Hemisphere, based on the coincidence between the position of the optical object and the compact milliarcsecond radio nucleus. Radio positions with an accuracy of typically 0.3 arcsec rms were measured from the observed delay and fringe rate of VLBI observations at 2.29 GHz on an Australia-to-South Africa baseline. Optical identifications and positions were measured from the UK Schmidt Telescope deep IIIa-J Southern Sky Survey plates, where available.

Jauncey, David L.↗
NASA NTRS1988

Experiments and analysis of a compact electrothermal thruster

The description and experimental performance of a compact microwave electrothermal thruster are presented. Experimental tests using N and He propellants with input power levels of 200 W - 1.5 kW are presented. Experimental results produced energy efficiencies of 20-60 percent and specific impulse of 250-450 sec.

Asmussen, Jes↗
NASA NTRS1989

Frequency stability of a tunable diode laser mounted in a compact Stirling cycle cooler

A tunable diode laser (TDL) has been operated with a compact lightweight closed-cycle Stirling cooler. The laser linewidth has been measured near 80 K and found to be about half of that when using more massive closed-cycle coolers. Novel applications include balloon-borne and aircraft-adapted instruments, where size, weight, and power requirements place stringent demands on necessary TDL cooling systems.

Durso, Santo S.↗
NASA NTRS1990

Compact, Broadband Infrared Spectrometer

Large-aperture, wide-angle, broad-band infrared spectrometer compact and light in weight. Based on double-pass version of Schmidt optical system that acts as both collimator and camera. Because optical system contained in piece of solid glass, it is mechanically and thermally stable. System made of water-free fused silica to minimize absorption of infrared radiation. Although in principle made from single, solid piece, in practice made in two pieces cemented together. Fabrication easier and simpler if more cemented surfaces used so each optical surface grounded and polished like single lens element.

Page, Norman A.↗
NASA NTRS1990

Compact Analyzer/Controller For Oxygen-Enrichment System

System controls hypersonic air-breathing engine tests. Compact analyzer/controller developed, built, and tested in small-scale wind tunnel prototype of the 8' HTT (High-Temperature Tunnel). Monitors level of oxygen and controls addition of liquid oxygen to enrich atmosphere for combustion. Ensures meaningful ground tests of hypersonic engines in range of speeds from mach 4 to mach 7.

Puster, Richard L.↗
NASA NTRS1990

Compact Pinch Welder

Compact resistance-welding pinch gun lets one operator do jobs formerly needing two workers. Light in weight and produces repeatable, high-quality weld joints. Welding-electrode head rotates for easy positioning. Lever at top of handle activates spring to pinch electrodes together at preset welding force. Button at bottom of handle activates welding current. Cables supply electrical power.

Starck, Thomas F.↗
NASA NTRS1990

An analysis of the viscous flow through a compact radial turbine by the average passage approach

A steady, three-dimensional viscous average passage computer code is used to analyze the flow through a compact radial turbine rotor. The code models the flow as spatially periodic from blade passage to blade passage. Results from the code using varying computational models are compared with each other and with experimental data. These results include blade surface velocities and pressures, exit vorticity and entropy contour plots, shroud pressures, and spanwise exit total temperature, total pressure, and swirl distributions. The three computational models used are inviscid, viscous with no blade clearance, and viscous with blade clearance. It is found that modeling viscous effects improves correlation with experimental data, while modeling hub and tip clearances further improves some comparisons. Experimental results such as a local maximum of exit swirl, reduced exit total pressures at the walls, and exit total temperature magnitudes are explained by interpretation of the flow physics and computed secondary flows. Trends in the computed blade loading diagrams are similarly explained.

Heidmann, James D.↗
NASA NTRS1990

Design and test of a compact optics system for the pool boiling experiment

The experiment described seeks to improve the understanding of the fundamental mechanisms that constitute nucleate pool boiling. The vehicle for accomplishing this is an investigation, including tests to be conducted in microgravity and coupled with appropriate analyses, of the heat transfer and vapor bubble dynamics associated with nucleation, bubble growth/collapse and subsequent motion, considering the interrelations between buoyancy, momentum and surface tension which will govern the motion of the vapor and surrounding liquid, as a function of the heating rate at the heat transfer surface and the temperature level and distribution in the bulk liquid. The experiment is designed to be contained within the confines of a Get-Away-Special Canister (GAS Can) installed in the bay of the space shuttle. When the shuttle reaches orbit, the experiment will be turned on and testing will proceed automatically. In the proposed Pool Boiling Experiment a pool of liquid, initially at a precisely defined pressure and temperature, will be subjected to a step imposed heat flux from a semitransparent thin-film heater forming part of one wall of the container such that boiling is initiated and maintained for a defined period of time at a constant pressure level. Transient measurements of the heater surface and fluid temperatures near the surface will be made, noting especially the conditions at the onset of boiling, along with motion photography of the boiling process in two simultaneous views, from beneath the heating surface and from the side. The conduct of the experiment and the data acquisition will be completely automated and self-contained. For the initial flight, a total of nine tests are proposed, with three levels of heat flux and three levels of subcooling. The design process used in the development and check-out of the compact photographic/optics system for the Pool Boiling Experiment is documented.

Ling, Jerri S.↗
NASA NTRS1990

Compact scheme for systems of equations applied to fundamental problems of mechanics of continua

Compact scheme formulation was used in the treatment of boundary conditions for a system of coupled diffusion and Poisson equations. Models and practical solutions of specific engineering problems arising in solid mechanics, chemical engineering, heat transfer and fuid mechanics are described and analyzed for efficiency and accuracy. Only 2-D cases are discussed and a new method of numerical treatment of boundary conditions common in the fundamental problems of mechanics of continua is presented.

Klimkowski, Jerzy Z.↗
NASA NTRS1989

Compact finite volume methods for the diffusion equation

An approach to treating initial-boundary value problems by finite volume methods is described, in which the parallel between differential and difference arguments is closely maintained. By using intrinsic geometrical properties of the volume elements, it is possible to describe discrete versions of the div, curl, and grad operators which lead, using summation-by-parts techniques, to familiar energy equations as well as the div curl = 0 and curl grad = 0 identities. For the diffusion equation, these operators describe compact schemes whose convergence is assured by the energy equations and which yield both the potential and the flux vector with second order accuracy. A simplified potential form is especially useful for obtaining numerical results by multigrid and alternating direction implicit (ADI) methods. The treatment of general curvilinear coordinates is shown to result from a specialization of these general results.

Rose, Milton E.↗
NASA NTRS1990

A compact, rugged, high repetition rate CO2 laser incorporating catalyst

The principal design features and operating characteristics of a high repetition rate CO2 laser are outlined. The laser is a compact, rugged unit, completely sealed and incorporating an unheated solid catalyst. Stable operation has been successfully demonstrated over a temperature range of -35 C to 65 C.

Schwarzenberger, P. M.↗