SEARCH · Search NASA

Results for “Bistability”

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.

SourceResearch connectionFrom yearThrough year

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

At least 163 records · Page 9

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Thermal and dynamical effects of pair production on two-temperature accretion flows

The two-temperature criterion for quasi-spherical (ion-pressure supported) accretion onto a black hole, including the effects of electron-positron pair production is studied. For an interesting range of accretion rates, Coulomb interactions between protons and pairs can cool the innermost regions of the accretion flow. The cooled plasma, assumed to possess some angular momentum, will collapse onto the equatorial plane, forming an optically thick annulus. Hysteresis effects involved in the cooling criterion are expected to lead to bistability or time dependence, which may be associated with variability in certain classes of active galactic nuclei (AGNs). Radiation from the annulus may be responsible for the EUV/soft X-ray excess observed in some AGNs.

Begelman, Mitchell C.↗

NASA NTRS1987

Problems and possible solutions involved in hard target calibration of coherent Doppler lidar

The field of radiometry is surveyed with reference to coherent light, since the surfaces to be considered here are irradiated with coherent, polarized light. Definitions of some concepts are modified. In light of these modifications calibration problems are analyzed and solutions suggested. The most important task was to develop hard targets exhibiting minimal specular reflection (mirror-like and retroreflection) and following closely a Lambertian scattering curve. Bistable reflectometer experiments and integrating sphere measurements are used to physically characterize the targets. Optical and electron microscopy are used to physically characterize the targets. Since the BRDF matrix is not measured, this capability must be developed preferably for both bistatic and monostatic reflectometer measurements. The equipment is expensive and not yet developed. Calibration can be simplified if it can be proved that the BRDF matrix is diagonal for a diffuse scatterer.

Anderson, Richard↗

NASA NTRS1987

Novel optoelectronic devices; Proceedings of the Meeting, The Hague, Netherlands, Mar. 31-Apr. 2, 1987

The present conference on novel optoelectronics discusses topics in the state-of-the-art in this field in the Netherlands, quantum wells, integrated optics, nonlinear optical devices and fiber-optic-based devices, ultrafast optics, and nonlinear optics and optical bistability. Attention is given to the production of fiber-optics for telecommunications by means of PCVD, lifetime broadening in quantum wells, nonlinear multiple quantum well waveguide devices, tunable single-wavelength lasers, an Si integrated waveguiding polarimeter, and an electrooptic light modulator using long-range surface plasmons. Also discussed are backward-wave couplers and reflectors, a wavelength-selective all-fiber switching matrix, the impact of ultrafast optics in high-speed electronics, the physics of low energy optical switching, and all-optical logical elements for optical processing.

Adams, Michael J.↗

NASA NTRS1989

Effects of space radiation on electronic microcircuits

The single event effects or phenomena (SEP), which so far have been observed as events falling on one or another of the SE classes: Single Event Upset (SEU), Single Event Latchup (SEL) and Single Event Burnout (SEB), are examined. Single event upset is defined as a lasting, reversible change in the state of a multistable (usually bistable) electronic circuit such as a flip-flop or latch. In a computer memory, SEUs manifest themselves as unexplained bit flips. Since latchup is in general caused by a single event of short duration, the single event part of the SEL term is superfluous. Nevertheless, it is used customarily to differentiate latchup due to a single heavy charged particle striking a sensitive cell from more ordinary kinds of latchup. Single event burnout (SEB) refers usually to total instantaneous failure of a power FET when struck by a single particle, with the device shorting out the power supply. An unforeseen failure of these kinds can be catastrophic to a space mission, and the possibilities are discussed.

Kolasinski, W. A.↗

NASA NTRS1989

Optical systems for digit-serial computation

High-accuracy optical systems for implementing digit-serial computations are discussed which incorporate parallelism and carry-free addition to achieve high processing speed. Employing on-line arithmetic, parallel calculations can be performed by the concurrent execution of operations. The algorithms are shown to be problem invariant and step invariant. Architectures using optical bistable devices and optical interconnects are discussed which can implement digit-serial addition, subtraction, multiplication, and division algorithms via the present approach.

Perlee, Caroline J.↗

NASA NTRS1989

2060 Chiron - CCD and electronographic photometry

R-band observations conducted for 2060 Chiron using CCD photometry in November-December 1986 and March 1988 are discussed. While the 1986 observations exhibit neither periodic nor nonperiodic brightness changes ascribable to comet-like activity, the 1988 observations show an 0.6 + or - 0.1 mag brightening that confirms the Tholen et al. (1988) findings and is consistent with the 1978 electronographic photometry presented. The lightcurve amplitudes appear, however, to have remained unchanged from 1978 to 1988, and the image profiles from 1978 are indistinguishable from the stars in 1986 and 1988. It is suggested that Chiron has either been varying nonasteroidally of late, on a 1-2 month timescale, or its intrinsic brightness has been bistable over the past decade.

Bus, Schelte J.↗

NASA NTRS1989

The effect of asymmetric vortex wake characteristics on a slender delta wing undergoing wing rock motion

An experimental investigation into the fluid mechanisms responsible for wing rock on a slender delta wing with 80 deg leading edge sweep has been conducted. Time history and flow visualization data are presented for a wide angle-of-attack range. The use of an air bearing spindle has allowed the motion of the wing to be free from bearing friction or mechanical hysteresis. A bistable static condition has been found in vortex breakdown at an angle of attack of 40 deg which causes an overshoot of the steady state rocking amplitude. Flow visualization experiments also reveal a difference in static and dynamic breakdown locations on the wing. A hysteresis loop in dynamic breakdown location similar to that seen on pitching delta wings was observed as the wing was undergoing the limit cycle oscillation.

Arena, A. S., Jr.↗

NASA NTRS1990

Analytical study of the origin and behavior of asymmetric vortices

An hypothesis advanced originally to explain computational observations is supported by theoretical considerations: The asymmetric mean flow observed on bodies of revolution at moderate to high angles of attack is the result of a convective instability of an originally symmetric flow to a time-invariant space-fixed disturbance. Additionally, the time-dependent fluctuations characteristic of the flow at higher angles of attack (up to 90 deg) are the result of an absolute instability of an originally steady flow to a small temporal disturbance of finite duration. Within a common domain, the instability mechanisms may coexist. The experimentally confirmed existence of bistable states, wherein the side-force variation with nose roll angle approaches a square-wave distribution, is attributed to the dominant influence of a pair of trailing vortices from the ogival forebody. Their existence is made possible by the appearance of foci of separation in the skin-friction line pattern beyond a critical angle of attack. The extreme sensitivity of the asymmetric flow orientation to nose geometry, demonstrated experimentally, is attributed to the presence of an indeterminate phase in the family of possible solutions for the three-dimensional wave system.

Tobak, Murray↗

NASA NTRS1990

Asymmetric vortices on a slender body of revolution

The symmetric and asymmetric leeward-side flow fields on an inclined ogive-cylinder have been investigated using a number of experimental techniques. Naturally occurring and perturbed flow fields were studied at a moderate Reynolds number and at many incidence angles. By close examination of the steady side force behavior at different roll orientations of the tip, it has been established that micro-variations in the tip geometry of the model have a large influence on the downstream development of the flow field. Under certain conditions, a bistable flow field was observed.

Zilliac, G. G.↗

NASA NTRS1991

Heavy-ion induced single-event upset in integrated circuits

The cosmic ray environment in space can affect the operation of Integrated Circuit (IC) devices via the phenomenon of Single Event Upset (SEU). In particular, heavy ions passing through an IC can induce sufficient integrated current (charge) to alter the state of a bistable circuit, for example a memory cell. The SEU effect is studied in great detail in both static and dynamic memory devices, as well as microprocessors fabricated from bipolar, Complementary Metal Oxide Semiconductor (CMOS) and N channel Metal Oxide Semiconductor (NMOS) technologies. Each device/process reflects its individual characteristics (minimum scale geometry/process parameters) via a unique response to the direct ionization of electron hole pairs by heavy ion tracks. A summary of these analytical and experimental SEU investigations is presented.

Zoutendyk, J. A.↗

NASA NTRS1991

Numerical, experimental, and theoretical study of convective instability of flows over pointed bodies at incidence

A study is conducted to investigate whether the behavior of the asymmetric mean flow observed on pointed bodies of revolution at incidence remains consistent with the presence of a convective instability of an original symmetric flow, even in the incidence range where virtually bistable behavior of the asymmetric flow is observed. By means of a retractable wire located near the tip, it is determined experimentally that for all angles of attack tested (30 to 60 degs), changing the size or location of the controlled disturbance results in a finite change in the asymmetric flow field, even to the extent of reversing the sign of the side force or becoming almost symmetric. The process is reversible; returning the wire to an original position likewise restores the corresponding flow field and mean side force. The effect of wire location (roll angle and distance from the tip) as well as angle of attack and flow conditions are evaluated experimentally by means of flow visualization and side-force measurements for a generic ogive-cylinder model in a low-speed wind tunnel. Evaluation of the results in the light of computational observations and theoretical considerations yields an affirmative answer to the question posed.

Degani, David↗

NASA NTRS1990

Study of mid IR fiber transmission and mode patterns under laser induced stimulated Brillouin scattering

Mid IR fiber transmission and exit radiation mode patterns at various incident CO2 laser power levels appear to be effective diagnostic tools for monitoring laser induced stimulated Brillouin scattering in various mid IR fibers. Such processes are deemed to be essential mechanisms for fiber-optic amplifiers and switches as potential replacements of current repeaters and bistable devices.

Yu, C.↗

NASA NTRS1991

Reynolds number effects on supersonic asymmetrical flows over a cone at high angle of attack

The supersonic viscous flow over a 5-degree half-angle cone at an angle of attack of four times the cone half-angle is studied computationally using both the conical and the three-dimensional Navier-Stokes equations. The numerical solutions were obtained with an implicit, upwind-biased algorithm. Asymmetrical flowfields of the absolute-instability type are found using the conical-flow equations which agree with published results. However, the absolute instabilities of the originally symmetric flow found with the conical equations do not occur in the three-dimensional simulations, although spurious asymmetric three-dimensional flows for symmetric bodies arise if the grid resolution is insufficient in the nose region. The asymmetric flows computed with the three-dimensional equations are convective instabilities and are possible if the local Reynolds number exceeds a critical value and a fixed geometric asymmetry is imposed. A continuous range of asymmetries can be developed, depending on the size of the disturbance and the Reynolds number. As the Reynolds number is increased, the asymmetries demonstrate a bistable behavior at levels of side force consistent with those predicted using the conical equations. Below a certain critical Reynolds number, any flow asymmetries arising from a geometrical asymmetry are damped with increasing distance downstream from the geometrical asymmetry.

Thomas, J. L.↗

NASA NTRS1992

Surface flow patterns on an ogive-cylinder at incidence

A set of photographs has been obtained which documents the oil-imaged surface flow patterns of an ogive-cylinder at angles-of-attack between 30 and 85 deg, and Reynolds number of 26,000. Attention is given to the possibility that the bistable nature of the flow within the 50-65 deg angle-of-attack range is linked to the coincident appearance of foci in the surface flow patterns, in view of the suggestion that these foci act as the anchor points allowing the forebody vortical structures to roll up and form the forebody's trailing vortex system.

Degani, David↗

NASA NTRS1992

Experimental study of controlled tip disturbance effect on flow asymmetry

The effect on the asymmetric mean flow observed on pointed bodies of revolution at incidence of changing the size and location of a controlled disturbance as well as changes in angle of attack and flow conditions are evaluated experimentally. Flow visualization and side-force measurements are carried out for a generic ogive-cylinder body inclined at high angle of attack in a low-speed wind tunnel. For all angles of attack tested (30-60 deg), minute changes in the size or location of the controlled disturbance result in finite changes in the asymmetric flow field, even to the extent of reversing the sign of the side force or becoming almost symmetric. The process is reversible; returning the wire to an original position likewise restores the corresponding flow field and mean side force. The variation of side force with continuous variation of a perturbation's size or location remains continuous and single valued, even in the incidence range of 50 to 60 deg, where 'bistable' behavior of the asymmetric flow field is observed.

Degani, David↗

NASA NTRS1993

Crystal growth of ZnSe and related ternary compound semiconductors by physical vapor transport

The materials to be investigated are ZnSe and related ternary semiconducting alloys (e.g., ZnS(x)Se(1-x), ZnTe(x)Se(1-x), and Zn(1-x)Cd(x)Se). These materials are useful for opto-electronic applications such as high efficient light emitting diodes and low power threshold and high temperature lasers in the blue-green region of the visible spectrum. The recent demonstration of its optical bistable properties also makes ZnSe a possible candidate material for digital optical computers. The investigation consists of an extensive ground-based study followed by flight experimentation, and involves both experimental and theoretical work. The objectives of the ground-based work are to establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low gravity environment and to obtain the experimental data and perform the analyses required to define the optimum parameters for the flight experiments. During the six months of the Preliminary Definition Phase, the research efforts were concentrated on the binary compound ZnSe - the purification of starting materials of Se by zone refining, the synthesis of ZnSe starting materials, the heat treatments of the starting materials, the vapor transport rate measurements, the vapor partial pressure measurements of ZnSe, the crystal growth of ZnSe by physical vapor transport, and various characterization on the grown ZnSe crystals.

Su, Ching-Hua↗

NASA NTRS1995

High Density Memory Based on Quantum Device Technology

We explore the feasibility of ultra-high density memory based on quantum devices. Starting from overall constraints on chip area, power consumption, access speed, and noise margin, we deduce boundaries on single cell parameters such as required operating voltage and standby current. Next, the possible role of quantum devices is examined. Since the most mature quantum device, the resonant tunneling diode (RTD) can easily be integrated vertically, it naturally leads to the issue of 3D integrated memory. We propose a novel method of addressing vertically integrated bistable two-terminal devices, such as resonant tunneling diodes (RTD) and Esaki diodes, that avoids individual physical contacts. The new concept has been demonstrated experimentally in memory cells of field effect transistors (FET's) and stacked RTD's.

vanderWagt, Paul↗

NASA NTRS1997

Microgravity Processing and Photonic Applications of Organic and Polymeric Materials

Some of the primary purposes of this work are to study important technologies, particularly involving thin films, relevant to organic and polymeric materials for improving applicability to optical circuitry and devices and to assess the contribution of convection on film quality in unit and microgravity environments. Among the most important materials processing techniques of interest in this work are solution-based and by physical vapor transport, both having proven gravitational and acceleration dependence. In particular, PolyDiAcetylenes (PDA's) and PhthaloCyanines (Pc's) are excellent NonLinear Optical (NLO) materials with the promise of significantly improved NLO properties through order and film quality enhancements possible through microgravity processing. Our approach is to focus research on integrated optical circuits and optoelectronic devices relevant to solution-based and vapor processes of interest in the Space Sciences Laboratory at the Marshall Space Flight Center (MSFC). Modification of organic materials is an important aspect of achieving more highly ordered structures in conjunction with microgravity processing. Parallel activities include characterization of materials for particular NLO properties and determination of appropriation device designs consistent with selected applications. One result of this work is the determination, theoretically, that buoyancy-driven convection occurs at low pressures in an ideal gas in a thermalgradient from source to sink. Subsequent experiment supports the theory. We have also determined theoretically that buoyancy-driven convection occurs during photodeposition of PDA, an MSFC-patented process for fabricating complex circuits, which is also supported by experiment. Finally, the discovery of intrinsic optical bistability in metal-free Pc films enables the possibility of the development of logic gate technology on the basis of these materials.

Frazier, Donald O.↗