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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A general numerical analysis program for the superconducting quasiparticle mixer

A user-oriented computer program SISCAP (SIS Computer Analysis Program) for analyzing SIS mixers is described. The program allows arbitrary impedance terminations to be specified at all LO harmonics and sideband frequencies. It is therefore able to treat a much more general class of SIS mixers than the widely used three-frequency analysis, for which the harmonics are assumed to be short-circuited. An additional program, GETCHI, provides the necessary input data to program SISCAP. The SISCAP program performs a nonlinear analysis to determine the SIS junction voltage waveform produced by the local oscillator. The quantum theory of mixing is used in its most general form, treating the large signal properties of the mixer in the time domain. A small signal linear analysis is then used to find the conversion loss and port impedances. The noise analysis includes thermal noise from the termination resistances and shot noise from the periodic LO current. Quantum noise is not considered. Many aspects of the program have been adequately verified and found accurate.

Hicks, R. G.↗
NASA NTRS1977

Optimum performance of suppressed carrier receivers with Costas loop tracking

The performance of suppressed carrier receivers with Costas loop tracking is optimized by proper choice of loop arm filter bandwidth. In particular, it is shown that for a variety of passive arm filter types, there exists, for a given data rate and data signal-to-noise ratio, an optimum filter bandwidth in the sense of minimizing the loop's squaring loss. For the linear theory case, this is equivalent to minimizing the loop's tracking jitter. When symbol synchronization is known, it is shown that by replacing the passive arm filters with active filters, i.e., integrate-and-dump circuits, one can achieve an improvement in carrier-to-noise ratio of as much as 4 to 6 dB depending on the passive arm filter type used for comparison and the value of data signal-to-noise ratio.

Simon, M. K.↗
NASA NTRS1987

Theory of Periodic-Binary-Sequence Generators

Algorithms yield feedback shift registers with maximum regularity. Report provides extensive mathematical treatment of new and previous results related to generation of pseudo-noise binary sequences by feedback shift registers. Generator architectures amenable to efficient implementation in very-large-scale integrated (VLSI) circuits. Report includes literature references to applications of such sequences in random-number generation, radar, VLSI testing, data encryption and decryption, algebraic error-detection and error-correction encoding and decoding, and feedback-shift-register synthesis of sequential machines.

Perlman, M.↗
NASA NTRS1978

An investigation for the development of an integrated optical data preprocessor

The successful fabrication and demonstration of an integrated optical circuit designed to perform a parallel processing operation by utilizing holographic subtraction to simultaneously compare N analog signal voltages with N predetermined reference voltages is summarized. The device alleviates transmission, storage and processing loads of satellite data systems by performing, at the sensor site, some preprocessing of data taken by remote sensors. Major accomplishments in the fabrication of integrated optics components include: (1) fabrication of the first LiNbO3 waveguide geodesic lens; (2) development of techniques for polishing TIR mirrors on LiNbO3 waveguides; (3) fabrication of high efficiency metal-over-photoresist gratings for waveguide beam splitters; (4) demonstration of high S/N holographic subtraction using waveguide holograms; and (5) development of alignment techniques for fabrication of integrated optics circuits. Important developments made in integrated optics are the discovery and suggested use of holographic self-subtraction in LiNbO3, development of a mathematical description of the operating modes of the preprocessor, and the development of theories for diffraction efficiency and beam quality of two dimensional beam defined gratings.

Verber, C. M.↗
NASA NTRS1987

Variations in the electrical short-circuit current decay for recombination lifetime and velocity measurements

An improved measurement system for electrical short-circuit current decay is presented that extends applicability of the method to silicon solar cells having an effective lifetime as low as 1 microsec. The system uses metal/oxide/semiconductor transistors as voltage-controlled switches. Advances in theory developed here increase precision and sensitivity in the determination of the minority-carrier recombination lifetime and recombination velocity. A variation of the method, which exploits measurements made on related back-surface field and back-ohmic contact devices, further improves precision and sensitivity. The improvements are illustrated by application to 15 different silicon solar cells.

Jung, Tae-Won↗
NASA NTRS1994

A high-performance constant-temperature hot-wire anemometer

A high-performance constant-temperature hot-wire anemometer has been designed based on a system theory analysis that can be extended to arbitrary order. A motivating factor behind the design was to achieve the highest possible frequency response while ensuring overall system stability. Based on these considerations, the design of the circuit and the selection of components is discussed in depth. Basic operating instructions are included in an operator's guide. The analysis is used to identify operating modes, observed in all anemometers, that are misleading in the sense that the operator can be deceived by interpreting an erroneous frequency response. Unlike other anemometers, this instrument provides front panel access to all the circuit parameters which affect system stability and frequency response. Instructions are given on how to identify and avoid these rather subtle and undesirable operating modes by appropriate adjustment of the controls. Details, such as fabrication drawings and a parts list, are provided to enable others to construct the instrument.

Watmuff, Jonathan H.↗
NASA NTRS1975

Advances in the theory and application of BSF cells

The characteristics and behavior of p(+), p solar cells were investigated. The p(+), p cells were made by the removal of the n(+) surface layers from n(+), p p(+), BSF cells followed by application of a suitable contact to the resultant p(+), p structures. The open circuit voltage of p(+), p cells was found to increase with increasing 'p' bulk resistivity. The measured open circuit velocity-temperature coefficients were positive and increased with increasing resistivity. An outline of prior limitations in solar cell design is presented, and the removal of these limitations through use of BSF effects is pointed out. The study of BSF effects made feasible production of very thin high efficiency silicon cells as well as high resistivity-high efficiency cells, two desirable types of silicon cells which were previously impossible to make.

Mandelkorn, J.↗
NASA NTRS1981

On a theory of temporal fluctuations in the electrostatic potential structures associated with auroral arcs

A possible mechanism is presented for the generation of large-amplitude temporal fluctuations in the structure of the electron energization region associated with auroral arcs. The mechanism is based on the observation that the auroral arc system resembles a laboratory circuit consisting of the series connection of battery, resistance and a forward biased diode containing collisionless plasma in which large-amplitude relaxation oscillations are sometimes observed to be superimposed on the steady-state current. It is shown that in both the laboratory and auroral systems, in which a localized auroral arc dynamo, the ionosphere and the electron energization region are involved, the oscillations are controlled by the times for ions and electrons to traverse the acceleration region, which also characterize the low- and high-frequency structure of the fluctuating waveform. It is demonstrated that a plausible one-dimensional double-layer model of the auroral arc acceleration region exhibits the dynamic negative resistance necessary for the generation of oscillations by the present mechanism. Finally, consideration is given to two kinds of auroral phenomena which might be associated with the mechanism: the 10-Hz quasi-periodic flickering aurora and 10-Hz modulations in the intensity of electrostatic hydrogen cyclotron waves.

Silevitch, M. B.↗
NASA NTRS1991

A model for the scattering of high-frequency electromagnetic fields from dielectrics exhibiting thermally-activated electrical losses

An equivalent circuit model (ECM) approach is used to predict the scattering behavior of temperature-activated, electrically lossy dielectric layers. The total electrical response of the dielectric (relaxation + conductive) is given by the ECM and used in combination with transmission line theory to compute reflectance spectra for a Dallenbach layer configuration. The effects of thermally-activated relaxation processes on the scattering properties is discussed. Also, the effect of relaxation and conduction activation energy on the electrical properties of the dielectric is described.

Hann, Raiford E.↗
NASA NTRS1990

Interferometric Measurement Of Residual Stress

Stress averaged through thickness of plate measured nondestructively. Theory of elasticity combined with laser interferometric technique into technique for measurement of residual stresses in solid objects - usually in thin, nominally-flat plates. Measurements particularly useful in inspection of wafers of single-crystal silicon for making solar cells or integrated circuits, because stresses remaining after crystal-growing process cause buckling or fracture. Used to predict deflections of plates caused by known applied loads under specified boundary condition, or to infer applied loads that cause known deflections. Also used to relate known deflections to residual stresses equivalent to stresses produced by fictitious applied loads.

Danyluk, Steven↗
NASA NTRS1989

Paralleling power MOSFETs in their active region: Extended range of passively forced current sharing

A simple passive circuit that improves current balance in parallelled power MOSFETs that are not precisely matched and that are operated in their active region from a common gate drive are exhibited. A nonlinear circuit consisting of diodes and resistors generates the differential gate potential required to correct for unbalance while maintaining low losses over a range of current. Also application of a thin tape wound magnetic core to effect dynamic current balance is reviewed, and a simple theory is presented showing that for operation in the active region the branch currents tend to revert to their normal unbalanced values even if the core is not driven into saturation. Results of several comparative experiments are given.

Niedra, Janis M.↗
NASA NTRS1971

Gyroscope relativity experiment

A gyroscope test of general relativity theory is proposed. The basic ideas and hardware concepts conceived by the investigators to implement the experiment are discussed. The goal is to measure the extremely small relativistic precession of gyroscopes in an earth-orbiting satellite. The experiment hardware (cryogenic gyroscopes, a telescope and superconducting circuits) is enclosed in a liquid helium dewar. The experiment will operate in orbit for about one year.

Decher, R.↗
NASA NTRS1979

Application of the superposition principle to solar-cell analysis

The superposition principle of differential-equation theory - which applies if and only if the relevant boundary-value problems are linear - is used to derive the widely used shifting approximation that the current-voltage characteristic of an illuminated solar cell is the dark current-voltage characteristic shifted by the short-circuit photocurrent. Analytical methods are presented to treat cases where shifting is not strictly valid. Well-defined conditions necessary for superposition to apply are established. For high injection in the base region, the method of analysis accurately yields the dependence of the open-circuit voltage on the short-circuit current (or the illumination level).

Lindholm, F. A.↗
NASA NTRS1992

Jovian electron transport to the polar heliosphere - An analogy to magnetospheric recirculation

The theory of magnetospheric recirculation for cyclic electron energization and transport may apply in part to heliospheric transport of Jovian electrons if enhanced cross-IMF propagation occurs at heliospheric altitudes near and below the solar wind transition region. Low altitude, ecliptic-to-polar transport would short-circuit conventional interplanetary diffusion, facilitate rapid access to the polar heliosphere with minimal adiabatic energy losses, and provide a seed population for acceleration to 100-1000 MeV energies at the solar wind termination shock and in the heliomagnetotail.

Cooper, J. F.↗
NASA NTRS1992

Quantum-well diode frequency multipliers - Varistor case

Local oscillators for heterodyne receivers at submillimeter wavelengths are typically made using a fundamental source followed by a harmonic frequency multiplier. An investigation of the required circuit embedding conditions for a possible new harmonic generator, the quantum-well resonant-tunneling diode, is summarized. A low-frequency multiplier has been tested that employs the resistive nonlinearity of the device as opposed to the reactive nonlinearity. The results show good agreement between practice and theory.

Batelaan, Paul D.↗
NASA NTRS1995

Mechanically-steered disk antenna for mobile satellite service

This paper describes a low-profile disk antenna for vehicular mounting that accommodates L-Band (1525-1660.5 MHz) mobile satellite service requirements. The antenna uses a rotatable printed circuit array mechanically-steered in azimuth via an external tracking system. A shaped elevation beam inherent to the antenna design provides continuous coverage with a minimum gain of 9 dBic between elevation angles of 25-degrees and 60-degrees measured above the horizon. A brief background on the theory, design, and performance for this antenna is discussed.

McCarrick, Charles D.↗
NASA NTRS1976

High photovoltages in ferroelectric ceramics

The short-circuit currents and photo-emfs were measured for various ceramics including barium titanate, lead metaniobate, and lead titanate. It is suggested that the emfs and currents arise from the presence of photoconductor-insulator sandwiches in the presence of space-charge-produced internal fields. Results are in agreement with the proposed theory and indicate that the ferroelectric ceramics are not only producers of high-voltage photoelectricity but a photo-battery, the polarity and magnitude of which can be switched by application of an electrical signal.

Brody, P. S.↗