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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Hesitations in continuous tracking induced by a concurrent discrete task

Subjects performed a continuous visually-guided pursuit tracking task with the right hand. From time to time (intervals averaging 30 sec) an auditory tone appeared signaling the subjects to perform a discrete response with the left hand. The presence of this tone was frequently associated with a hesitation in right-hand tracking which lasted 1/3 sec or longer. The rate of occurrence of these hesitations was about the same when the left-hand response involved a choice between competing responses as when the left hand responded in a predetermined direction. Hesitations occurred for three different mechanical tracking manipulanda using different controlling muscles, and appeared to be due to freezing rather than to relaxation of muscular action. The rate of occurrence of hesitations declined with practice, and this improvement in right-hand performance was accompanied by an improvement in performance of the concurrent left-hand response. The presence of hesitations, and their reduction with practice, can be interpreted within several viewpoints.

Klapp, Stuart T.↗
NASA NTRS1985

Effect of conductivity and concentration on the sample stream in the transverse axis of a continuous flow electrophoresis chamber

The resolution of continuous flow electrophoresis systems is generally measured by the spread of the sample bands in the direction of the electrophoretic migration. This paper evaluates the cross section of the sample bands in the plane perpendicular to the flow and shows that the spread in the direction perpendicular to the migration increased significantly with the applied electric field. Concentrated samples of monodisperse latex particles and vinyltoluene T-butylstyrene particles in sample buffers of different electrical conductivities were used to map the shape of the sample bands relative to the zero electric field case. As the electric field was applied, the sample band spread from an initial diameter of only one-third the chamber thickness until it approached the chamber walls where electroosmosis significantly reduced the resolution of separation. It can be shown, however, that it is possible to minimize these distortions by careful sample preparation and experiment design.

Miller, Teresa Y.↗
NASA NTRS1988

Adjustable, Audible Continuity Tester For Delicate Circuits

Unit adjustable to resistances up to 35 ohms. Adjustable, audible electrical-continuity tester gives audible indication. Used safely on circuit boards in which semiconductor components installed, and on complementary metal oxide/semiconductor integrated circuits. Tester compact and circuit simple. Built from inexpensive standard components.

Mcalister, William B.↗
NASA NTRS1988

Performance of a small, graphite electrode, multistage depressed collector with a 500-W, continuous wave, 4.8- to 9.6-GHz traveling wave tube

A small, isotropic graphite multistage depressed collector (MDC) and a short permanent magnet refocuser were designed, fabricated, and evaluated in conjunction with a 500-W, continuous-wave (CW), 4.8 to 9.6 GHz traveling wave tube (TWT). A novel performance optimization system and technique were used to optimize the TWT-MDC performance for saturated broad-band operation. The MDC performance was evaluated in both four- and three-stage configurations. Average TWT overall and four-stage collector efficiencies of 43.8 and 82.6 percent, respectively, were obtained for saturated octave-bandwidth operation. The isotropic graphite electrode material performed well, and shows considerable promise. However, considerably more test experience is required before definitive conclusions on its suitability for space and airborne TWT's can be made.

Ramins, Peter↗
NASA NTRS1988

Aeronautical engineering: A cumulative index to a continuing bibliography

This bibliography is a cumulative index to the abstracts contained in NASA SP-7037(210) through NASA SP-7037(221) of Aeronautical Engineering: A Continuing Bibliography. NASA SP-7037 and its supplements have been compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). This cumulative index includes subject, personal author, corporate source, foreign technology, contract number, report number, and accession number indexes.

Source record↗
NASA NTRS1988

A direct-execution parallel architecture for the Advanced Continuous Simulation Language (ACSL)

A direct-execution parallel architecture for the Advanced Continuous Simulation Language (ACSL) is presented which overcomes the traditional disadvantages of simulations executed on a digital computer. The incorporation of parallel processing allows the mapping of simulations into a digital computer to be done in the same inherently parallel manner as they are currently mapped onto an analog computer. The direct-execution format maximizes the efficiency of the executed code since the need for a high level language compiler is eliminated. Resolution is greatly increased over that which is available with an analog computer without the sacrifice in execution speed normally expected with digitial computer simulations. Although this report covers all aspects of the new architecture, key emphasis is placed on the processing element configuration and the microprogramming of the ACLS constructs. The execution times for all ACLS constructs are computed using a model of a processing element based on the AMD 29000 CPU and the AMD 29027 FPU. The increase in execution speed provided by parallel processing is exemplified by comparing the derived execution times of two ACSL programs with the execution times for the same programs executed on a similar sequential architecture.

Carroll, Chester C.↗
NASA NTRS1988

Strain intensity factor approach for predicting the strength of continuously reinforced metal matrix composites

A method was previously developed to predict the fracture toughness (stress intensity factor at failure) of composites in terms of the elastic constants and the tensile failing strain of the fibers. The method was applied to boron/aluminum composites made with various proportions of 0 to + or - 45 deg plies. Predicted values of fracture toughness were in gross error because widespread yielding of the aluminum matrix made the compliance very nonlinear. An alternate method was developed to predict the strain intensity factor at failure rather than the stress intensity factor because the singular strain field was not affected by yielding as much as the stress field. Strengths of specimens containing crack-like slits were calculated from predicted failing strains using uniaxial stress-strain curves. Predicted strengths were in good agreement with experimental values, even for the very nonlinear laminates that contained only + or - 45 deg plies. This approach should be valid for other metal matrix composites that have continuous fibers.

Poe, C. C., Jr.↗
NASA NTRS1988

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Johnson, W. S.↗
NASA NTRS1987

Continuous-wave operation of a room-temperature, diode-laser-pumped, 946-nm Nd:YAG laser

Single-stripe diode-laser-pumped operation of a continuous-wave 946-nm Nd:YAG laser with less than 10-mW threshold has been demonstrated. A slope efficiency of 16 percent near threshold was shown with a projected slope efficiency well above a threshold of 34 percent based on results under Rhodamine 6G dye-laser pumping. Nonlinear crystals for second-harmonic generation of this source were evaluated. KNbO3 and periodically poled LiNbO3 appear to be the most promising.

Fan, T. Y.↗
NASA NTRS1987

OH and CH continuous opacity in solar and stellar atmospheres

Continuous absorption cross sections of OH and CH have been computed for the temperature range 1000 K to 9000 K. Both OH and CH produce significant ultraviolet opacity in the sun and cool stars. CH is also significant in the visible at 400 nm.

Kurucz, Robert L.↗
NASA NTRS1987

Status of the NASA continuing investigation of catastrophic balloon failures

The findings and status of the continuing NASA investigation of catastrophic balloon failures, conducted following the adoption in 1984 of a new material specification, are reported on. Current efforts include a microstructual analysis, balloon stress studies, and seal investigations. Attention is given to the Recovery Plan, a program to demonstrate the use of the existing film and to develop an improved film is discussed. No specific cause for the increased occurrence of catastrophic failures has been identified.

Needleman, H. C.↗
NASA NTRS1987

Continuous flow electrophoretic separation of proteins and cells from mammalian tissues

This paper describes an apparatus for continuous flow electrophoresis (CFE), designed to separate macromolecules and cells at conditions of microgravity. In this CFE, buffer flows upward in a 120-cm long flow chamber, which is 16-cm wide x 3.0-mm thick in the microgravity version (and 6-cm wide x 1.5-mm thick in the unit-gravity laboratory version). Ovalbumin and rat serum albumin were separated in space (flight STS-4) with the same resolution of the two proteins achieved at 25 percent total w/v concentration that was obtained in the laboratory at 0.2 percent w/v concentration. Rat anterior pituitary cells, cultured human embryonic kidney cells, and canine Langerhans cells were separated into subpopulations (flight STS-8) more effectively than in unit gravity, with comparable resolution having been achieved at 100 times the concentration possible on earth.

Hymer, W. C.↗
NASA NTRS1987

Numerical tests of a modified full implicit continuous Eulerian (FICE) scheme with projected normal characteristic boundary conditions for MHD flows

A numerical method has been developed based on a modified full implicit continuous Eulerian (FICE) scheme and projected normal characteristic boundary conditions for simulating MHD flows which undergo a long process of evolution. An astrophysical flow is chosen for illustration of this procedure, and numerical tests are made to verify the computational stability and physically realistic solution. Three computational tests have been accomplished; they are tests of solving methods, characteristic boundary condition, and time steps. The tests show that the program from the modified FICE scheme with proper boundary conditions and time steps can be made numerically stable for a time long enough to obtain physically plausible solutions.

Wu, S. T.↗
NASA NTRS1988

On the stability, storage capacity, and design of nonlinear continuous neural networks

The stability, capacity, and design of a nonlinear continuous neural network are analyzed. Sufficient conditions for existence and asymptotic stability of the network's equilibria are reduced to a set of piecewise-linear inequality relations that can be solved by a feedforward binary network, or by methods such as Fourier elimination. The stability and capacity of the network is characterized by the post synaptic firing rate function. An N-neuron network with sigmoidal firing function is shown to have up to 3N equilibrium points. This offers a higher capacity than the (0.1-0.2)N obtained in the binary Hopfield network. Moreover, it is shown that by a proper selection of the postsynaptic firing rate function, one can significantly extend the capacity storage of the network.

Guez, Allon↗
NASA NTRS1989

Continuously-Variable Vernier Scale

Easily fabricated device increases precision in reading graphical data. Continuously-variable vernier scale (CV VS) designed to provide greater accuracy to scientists and technologists in reading numerical values from graphical data. Placed on graph and used to interpolate coordinate value of point on curve or plotted point on figure within division on each coordinate axis. Requires neither measurement of line segments where projection of point intersects division nor calculation to quantify projected value. Very flexible device constructed with any kind of scale. Very easy to use, requiring no special equipment of any kind, and saves considerable amount of time if numerous points to be evaluated.

Miller, Irvin M.↗
NASA NTRS1988

Local-global analysis of crack growth in continuously reinforced ceramic matrix composites

The development is described of a mathematical model for predicting the strength and micromechanical failure characteristics of continuously reinforced ceramic matrix composites. The local-globe analysis models the vicinity of a propagating crack tip as a local heterogeneous region (LHR) consisting of spring like representation of the matrix, fibers and interfaces. This region is embedded in an anisotropic continuum (representing the bulk composite) which is modeled by conventional finite elements. Parametric studies are conducted to investigate the effects of LHR size, component properties, interface conditions, etc. on the strength and sequence of the failure processes in the unidirectional composite system. The results are compared with those predicted by the models developed by Marshall et al. (1985) and by Budiansky et al. (1986).

Ballarini, Roberto↗