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At least 613 records · Page 34

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NASA NTRS1980

Minimum fuel control of a vehicle with a continuously variable transmission

The design and evaluation of a control system for a sedan with a heat engine and a continuously variable transmission, is considered in a effort to minimize fuel consumption and achieve satisfactory dynamic response of vehicle variables as the vehicle is driven over a standard driving cycle. Even though the vehicle system was highly nonlinear, attention was restricted to linear control algorithms which could be easily understood and implemented demonstrated by simulation. Simulation results also revealed that the vehicle could exhibit unexpected dynamic behavior which must be taken into account in any control system design.

Burghart, J. H.↗

NASA NTRS1981

Continuously variable transmission: Assessment of applicability to advance electric vehicles

A brief historical account of the evolution of continuously variable transmissions (CVT) for automotive use is given. The CVT concepts which are potentially suitable for application with electric and hybrid vehicles are discussed. The arrangement and function of several CVT concepts are cited along with their current developmental status. The results of preliminary design studies conducted on four CVT concepts for use in advanced electric vehicles are discussed.

Loewenthal, S. H.↗

NASA NTRS1980

Liquid-phase epitaxy grown PbSnTe distributed feedback laser diodes with broad continuous single-mode tuning range

Distributed feedback (DFB) pulsed laser operation has been demonstrated in stripe geometry Pb(1-x)Sn(x)Te double-heterostructures grown by liquid-phase epitaxy. The grating structure of 0.79 micron periodicity operates in first order near 12.8 microns and was fabricated prior to the liquid-phase epitaxial growth using holographic exposure techniques. These DFB lasers had moderate thresholds, 3.6 kA/sq cm, and the output power versus current curves exhibited a sharp turn-on free of kinks. Clean, single-mode emission spectra, continuously tunable over a range in excess of 20 per cm, centered about 780 per cm (12.8 microns), and at an average rate of 1.2 per cm-K from 9 to 26 K, were observed. While weaker modes could at times be seen in the spectrum, substantially single-mode operation was obtained over the entire operating range and to over 10 times threshold.

Hsieh, H.-H.↗

NASA NTRS1981

A continuous-vorticity panel method for lifting surfaces

A continuous-vorticity panel method is developed and utilized to predict the steady aerodynamic loads on lifting surfaces having sharp-edge separation. Triangular panels with linearly varying vorticity are used. The velocity field generated by an individual element is obtained in closed form. An optimization scheme is constructed for finding the vorticity at the nodes of the elements. The method is not restricted by aspect ratios, angles of attack, planforms, or camber. Rectangular and delta wings are presented as numerical examples. The numerical results are in good agreement with the experimental data for incompressible flows.

Yen, A.↗

NASA NTRS1981

Modeling the human controller in environments that include continuous and discrete tasks

In complex environments where the human operator is a supervisor, he must allocate his attention between different kinds of tasks for satisfactory overall performance. When a portion of the future reference trajectory for a continuous control task is available for preview, scheduling various other discrete activities is possible. A model has been developed for this situation using dynamic programming to solve an optimal control problem. An experiment was conducted where subjects controlled an airplane symbol over a map, shown a fixed distance into the future. Discrete tasks were introduced as data entry tasks. Results showed that the model compared favorably with experimental results.

Govindaraj, T.↗

NASA NTRS1981

Fabrication and wear test of a continuous fiber/particulate composite total surface hip replacement

Continuous fiber woven E-glass composite femoral shells having the ame elastic properties as bone were fabricated. The shells were then encrusted with filled epoxy wear resistant coatings and run dry against ultrahigh molecular weight polyethylene acetabular cups in 42,000 and 250,000 cycle were tests on a total hip simulator. The tribological characteristics of these shells atriculating with the acetabular cups are comparable to a vitallium bal articulating with an ultrahigh molecular weight polyethylene cup.

Roberts, J. C.↗

NASA NTRS1980

Design study of a continuously variable roller cone traction CVT for electric vehicles

Continuously variable ratio transmissions (CVT) featuring cone and roller traction elements and computerized controls are studied. The CVT meets or exceeds all requirements set forth in the design criteria. Further, a scalability analysis indicates the basic concept is applicable to lower and higher power units, with upward scaling for increased power being more readily accomplished.

Mccoin, D. K.↗

NASA NTRS1980

Continuous Czochralski growth: Silicon sheet growth development of the large area sheet task of the low cost silicon solar array project

The growth of 100 kg of silicon single crystal material, ten cm in diameter or greater, and 150 kg of silicon single crystal material 15 cm or greater utilizing one common silicon container material (one crucible) is investigated. A crystal grower that is recharged with a new supply of polysilicon material while still under vacuum and at temperatures above the melting point of silicon is developed. It accepts large polysilicon charges up to 30 kg, grows large crystal ingots (to 15 cm diameter and 25 kg in weight), and holds polysilicon material for recharging (rod or lump) while, at the same time, growing crystal ingots. Special equipment is designed to recharge polysilicon rods, recharge polysilicon lumps, and handle and store large, hot silicon crystal ingots. Many continuous crystal growth runs were performed lasting as long as 109 hours and producing as many as ten crystal ingots, 15 cm with weights progressing to 27 kg.

Johnson, C. M.↗

NASA NTRS1981

A broadband RF continuously variable time delay device

A method for implementation of continuously variable time delay of broadband RF signals is described. The method uses Bragg Cell and optical heterodyne technology. The signal to be delayed is applied to the Bragg Cell acoustic transducer, and the delay time is the acoustic transit time from this transducer to the incident light beam. By translating the light beam, the delay is varied. Expressions describing the Bragg Cell diffraction, lens Fourier transformation, and the optical heterodyne processes are developed. Specifications for the variable delay including bandwidth, range of delay, and insertion loss are provided. Applications include radar signal processing, spread spectrum intercept, radar ECM, and adaptive array antenna processing.

Freyre, F. W.↗

NASA NTRS1981

Viking lander imaging investigation during extended and continuation automatic missions. Volume 2: Lander 2 picture catalog of experiment data record

Images returned by the two Viking landers during the extended and continuation automatic phases of the Viking Mission are presented. Information describing the conditions under which the images were acquired is included with skyline drawings showing the images positioned in the field of view of the cameras. Subsets of the images are listed in a variety of sequences to aid in locating images of interest. The format and organization of the digital magnetic tape storage of the images are described. A brief description of the mission and the camera system is also included.

Jones, K. L.↗

NASA NTRS1981

Results of continuous synchronous orbit testing of sealed nickel-cadmium cells

Test results from continuous synchronous orbit testing of sealed nickel cadmium cells are presented. The synchronous orbit regime simulates a space satellite maintaining a position over a fixed point on earth as the earth rotates on its axis and revolves about the sun. Characteristics of each lot of cells, test conditions, and charge control methods are described.

Harkness, J. D.↗

NASA NTRS1982

A cumulative index to Aeronautical Engineering: A continuing bibliography

This bibliography is a cumulated index to the abstracts contained in NASA SP-7037(132) through NASA SP-7037(143) 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, contract, and report number indexes.

Source record↗

NASA NTRS1979

Flow and thermal effects in continuous flow electrophoresis

In continuous flow electrophoresis the axial flow structure changes from a fully developed rectilinear form to one characterized by meandering as power levels are increased. The origin of this meandering is postulated to lie in a hydrodynamic instability driven by axial (and possibly lateral) temperature gradients. Experiments done at MSFC show agreement with the theory.

Saville, D. A.↗

NASA NTRS1981

Solute partitioning under continuous cooling conditions as a cooling rate indicator

A model of solute partitioning in a finite body under conditions of continuous cooling is developed for the determination of cooling rates from concentration profile data, and applied to the partitioning of zirconium between ilmenite and ulvospinel in the Apollo 15 Elbow Crater rocks. Partitioning in a layered composite solid is described numerically in terms of concentration profiles and diffusion coefficients which are functions of time and temperature, respectively; a program based on the model can be used to calculate concentration profiles for various assumed cooling rates given the diffusion coefficients in the two phases and the equilibrium partitioning ratio over a range of temperatures. In the case of the Elbow Rock gabbros, the cooling rates are calculated from measured concentration ratios 10 microns from the interphase boundaries under the assumptions of uniform and equilibrium initial conditions at various starting temperatures. It is shown that the specimens could not have had uniform concentrations profiles at the previously suggested initial temperature of 1350 K. It is concluded that even under conditions where the initial temperature, grain sizes and solute diffusion coefficients are not well characterized, the model can be used to estimate the cooling rate of a grain assemblage to within an order of magnitude.

Onorato, P. I. K.↗

NASA NTRS1981

Improved formula for continuous-wave measurements of ultrasonic phase velocity

An improved formula for continuous-wave ultrasonic phase velocity measurements using contact transducers is derived from the transmission line theory. The effect of transducer-sample coupling bonds is considered for measurements of solid samples even though it is often neglected because of the difficulty of accurately determining the bond thickness. Computer models show that the present formula is more accurate than previous expressions. Laboratory measurements using contacting transducers with the present formula are compared to measurements using noncontacting (hence effectively correction-free) capacitive transducers. The results of the experiments verify the validity and accuracy of the new formula.

Chern, E. J.↗

NASA NTRS1981

Chronic exposure of a honey bee colony to 2.45 GHz continuous wave microwaves

A honey bee colony (Apis mellifera L.) was exposed 28 days to 2.45 GHz continuous wave microwaves at a power density (1 mW/sq cm) expected to be associated with rectennae in the solar power satellite power transmission system. Differences found between the control and microwave-treated colonies were not large, and were in the range of normal variation among similar colonies. Thus, there is an indication that microwave treatment had little, if any, effect on (1) flight and pollen foraging activity, (2) maintenance of internal colony temperature, (3) brood rearing activity, (4) food collection and storage, (5) colony weight, and (6) adult populations. Additional experiments are necessary before firm conclusions can be made.

Westerdahl, B. B.↗

NASA NTRS1981

Stratospheric measurements of continuous absorption near 2400 per cm

Measurements of continuous absorption near 2400 per cm by N2 and CO2 over long path lengths in the lower stratosphere are presented. The continua were measured in a stratospheric solar spectrum obtained during sunset with a balloon-borne Michelson interferometer in the 2380-2500 per cm region, and transmittances were calculated by ratioing the amplitudes to those of a high-sun spectrum in order to eliminate the wavelength dependence of the measured flux. Comparison of the measured transmittances with those calculated for a multilayered atmospheric model using laboratory absorption measurements results in a fair agreement, and reveals the primary component of the absorption throughout most of the range to be N2, with the CO2 contribution equal to that of N2 only at the CO2 band head. In this region, the shape of the continuum is very sensitive to the sub-Lorentzian line shape assumed in the calculations, and so, if the shape of the N2 continuum at low temperatures can be determined through laboratory measurements, may be used to infer air-broadened far-wing CO2 line shape.

Rinsland, C. P.↗

NASA NTRS1980

The fluid mechanics of continuous flow electrophoresis in perspective

Buoyancy alters the flow in continuous flow electrophoresis chambers through the mechanism of hydrodynamic instability and, when the instability is supressed by careful cooling of the chamber boundaries, by restructuring the axial flow. The expanded roles of buoyancy follow upon adapting the size of the chamber and the electric field so as to fractionate certain sorts of cell populations. Scale-up problems, hydrodynamic stability and the altered flow fields are discussed to show how phenomena overlooked in the design and operations of narrow-gap devices take on an overwhelming importance in wide-gap chambers

Saville, D. A.↗