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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.

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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Shot-noise in resistive-diode mixers and the attenuator noise model

The representation of a pumped exponential diode, operating as a mixer, by an equivalent lossy network, is reexamined. It is shown that the model is correct provided the network has ports for all sideband frequencies at which (real) power flow can occur between the diode and its embedding. The temperature of the equivalent network is eta/2 times the physical temperature of the diode. The model is valid only if the series resistance and nonlinear capacitance of the diode are negligible. Expressions are derived for the input and output noise temperature and the noise-temperature ratio of ideal mixers. Some common beliefs concerning noise-figure and noise-temperature ratio are shown to be incorrect.

Kerr, A. R.↗
NASA NTRS1979

Optokinetic motion sickness - Attenuation of visually-induced apparent self-rotation by passive head movements

An experimental study was conducted on seven normal subjects to evaluate the effectiveness of passive head movements in suppressing the optokinetically-induced illusory self-rotation. Visual simulation was provided by a servo-controlled optokinetic drum. Each subject participated in two experimental sessions. In one condition, the subject's head remained stationary while he gazed passively at a moving stripe pattern. In the other, he gazed passively and relaxed his neck muscles while his head was rotated from side to side. It appears that suppression of optokinetically-induced illusory self-rotation with passive head movements results from the operation of a spatial constancy mechanism interrelating visual, vestibular, and kinesthetic information on ongoing body orientation. The results support the view that optokinetic 'motion sickness' is related, at least in part, to an oculomotor disturbance rather than a visually triggered disturbance of specifically vestibular etiology.

Teixeira, R. A.↗
NASA NTRS1979

Cumulative slant path rain attenuation statistics associated with the Comstar beacon at 28.56 GHz for Wallops Island, Va.

The paper presents and characterizes the cumulative fade statistics for the 1 April 1977 to 31 March 1978 period for the Wallops Island site on the basis of direct measurements of a beacon signal at 28.56 GHz emanating from the Comstar geosynchronous satellite. Also presented are the month and time of day statistics as well as the rain gage rain-rate distribution. The concept of effective path length using the 28.56-GHz fade and measured rain-rate distributions are employed to predict the 19.04-GHz fade distribution. Predicted distributions for the year period are obtained from disdrometer data and radar results.

Goldhirsh, J.↗
NASA NTRS1980

Noise transmission and attenuation by stiffened panels

An analytical study of noise transmission into semi-cylindrical and rectangular acoustic enclosures due to turbulent boundary layer pressure and propeller noise (prop-fan) is presented. The structural noise transmission models include a single panel, discretely stiffened elastic panel and stiffened viscoelastic sandwich panel. Response characteristics of the stiffened panels are evaluated using a transfer matrix procedure. The interior noise field is determined by a Galerkin-like method. The effect on interior noise due to aerodynamic surface flow, cavity back-up pressure, pressurization, mass, stiffness, and damping addition to the structure is investigated. It is shown that stiffened viscoelastic sandwich panels, while providing the same stiffening benefits as an equivalent elastic panel, could significantly reduce vibration levels and subsequently give similar benefits for interior noise control.

Vaicaitis, R.↗
NASA NTRS1980

Irradiance attenuation coefficient in a stratified ocean - A local property of the medium

The influence of optically important constituents of water on the absorption (a) and scattering (b) coefficients and the backscattering probability is considered, with emphasis placed on measuring the volume scattering function (B/theta/). Two stratification models are examined; one in which the phase function (B(theta)/b) is depth independent and only b/c is allowed to vary with optical depth, and the other in which both b/c and the phase function depend on depth. The results demonstrate that Gordon's (1977) technique of estimating a and b is applicable without change to a stratified ocean.

Gordon, H. R.↗
NASA NTRS1981

Vibration attenuation using magnetic suspension isolation

The paper derives the vibration transfer function for a magnetic suspension in generic form, with specific reference to the Annular Suspension and Pointing System for Shuttle payloads. It is shown that a magnetically suspended pointer can exhibit considerably improved dynamic stability over conventional means, particularly at high frequencies and for transient disturbances. The amount of improvement to be anticipated is quantified to allow first-cut assessments for specific applications.

Hamilton, B. J.↗
NASA NTRS1984

Active attenuation of propeller blade passage noise

Acoustic measurements are presented to show that active cancellation can be used to achieve significant reduction of blade passage noise in a turboprop cabin. Simultaneous suppression of all blade passage frequencies was attained. The spatial volume over which cancellation occurred, however, is limited. Acoustic intensity maps are presented to show that the acoustic input to the fuselage was sufficiently non-localized so as to require more judicious selection of cancellation speaker location.

Zalas, J. M.↗
NASA NTRS1986

Generation of attenuation corrected images from lidar data

The interpretation of data generated by aerosol backscatter lidars is often facilitated by presentation of RHI and PPI images. These pictures are especially useful in studies of atmospheric boundary layer structure where convective elements, stratifications and aerosol laden plumes can be easily delineated. Procedures used at the University of Wisconsin to generate lidar images on a color enhanced raster scan display are described.

Eloranta, E. W.↗
NASA NTRS1986

Differential partition of virulent Aeromonas salmonicida and attenuated derivatives possessing specific cell surface alterations in polymer aqueous-phase systems

Two-polymer aqueous-phase systems in which partitioning of biological matter between the phases occurs according to surface properties such as hydrophobicity, charge, and lipid composition are used to compare the surface properties of strains of the fish pathogen Aeromonas salmonicida. The differential ability of strains to produce a surface protein array crucial to their virulence, the A layer, and to produce smooth lipopolysaccharide is found to be important in the partitioning behavior of Aeromonas salmonicida. The presence of the A layer is shown to decrease the surface hydrophilicity of the pathogen, and to increase specifically its surface affinity for fatty acid esters of polyethylene glycol. The method has application to the analysis of surface properties crucial to bacterial virulence, and to the selection of strains and mutants with specific surface characteristics.

Van Alstine, J. M.↗
NASA NTRS1988

Formulation of a General Technique for Predicting Pneumatic Attenuation Errors in Airborne Pressure Sensing Devices

Presented is a mathematical model derived from the Navier-Stokes equations of momentum and continuity, which may be accurately used to predict the behavior of conventionally mounted pneumatic sensing systems subject to arbitrary pressure inputs. Numerical techniques for solving the general model are developed. Both step and frequency response lab tests were performed. These data are compared with solutions of the mathematical model and show excellent agreement. The procedures used to obtain the lab data are described. In-flight step and frequency response data were obtained. Comparisons with numerical solutions of the math model show good agreement. Procedures used to obtain the flight data are described. Difficulties encountered with obtaining the flight data are discussed.

Whitmore, Stephen A.↗
NASA NTRS1988

Formulaton of a general technique for predicting pneumatic attenuation errors in airborne pressure sensing devices

Presented is a mathematical model, derived from the Navier-Stokes equations of momentum and continuity, which may be accurately used to predict the behavior of conventionally mounted pneumatic sensing systems subject to arbitrary pressure inputs. Numerical techniques for solving the general model are developed. Both step and frequency response lab tests were performed. These data are compared against solutions of the mathematical model. The comparisons show excellent agreement. The procedures used to obtain the lab data are described. In-flight step and frequency response data were obtained. Comparisons with numerical solutions of the mathematical model show good agreement. Procedures used to obtain the flight data are described. Difficulties encountered with obtaining the flight data are discussed.

Whitmore, Stephen A.↗
NASA NTRS1989

Feasibility study using large ribbon parachutes, retrorockets, and hydrodynamic attenuation to recover liquid rocket boosters for the Space Shuttle

A new three-phase approach to recovery of the large liquid rocket boosters being studied for the Space Shuttle is proposed. The concept consists of a cluster of larger ribbon parachutes, retrorockets, and spar mode flotation. The two inert liquid rocket boosters weighing 115,000 lb to 183,000 lb descend from high altitude in a side-on coning attitude to 16,000 ft altitude where a cluster of large ribbon parachutes are deployed. The terminal velocity near water landing is 80 ft/sec. Retrorockets are used to decrease the velocity to about 40 ft/sec. The third phase is opening of the front end of the cylindrical rocket case to allow flooding to cushion impact and allow vertical flotation in the spar mode keeping the four expensive liquid rocket engines dry.

Pepper, William B.↗
NASA NTRS1991

Sound attenuation apparatus

An apparatus is disclosed for reducing acoustic transmission from mechanical or acoustic sources by means of a double wall partition, within which an acoustic pressure field is generated by at least one secondary acoustic source. The secondary acoustic source is advantageously placed within the partition, around its edges, or it may be an integral part of a wall of the partition.

Shepherd, Kevin P.↗