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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Radio wave emitted by an extensive air showers in 10KHz to 1MHz region

The importance of radio waves in a frequency range of less than 1MHz in an EAS shower is discussed. Estimates of radio intensities at 10KHz, 100KHz and 1MHz in EAS showers made on the basis of the Kahn-Lerche theory. Negative charge excess in a shower is the main source of low frequency radio emission, in spite of the importance of the contribution of transverse current in the geomagnetic field in a higher frequency range. An estimate is also made for radio intensity produced when the shower hits the ground. The contribution of this process seems to be important at a large distance, i.e., beyond 1km from the shower axis.

Nichimura, J.↗
NASA NTRS1985

Search for long-lived massive particles in extensive air showers

Air showers containing delayed sub-showers which may be produced by a long-lived massive particle have been investigated by using twelve detectors. Ten events have been selected out as the candidates. However, a definite conclusion cannot be reached at the present time.

Kawamoto, M.↗
NASA NTRS1984

Extension of constrained incremental Newton-Raphson scheme to generalized loading fields

This paper develops numerical strategies which enable the constrained incremental Newton-Raphson scheme to handle the static response of structure to loading fields with completely generalized histories. This is made possible through the use of specially warped hyperelliptic constraint surfaces which control successive or clustered load steps in the vicinity of loading events with specific timing schedules. Such an approach enables improved convergence and stability characteristics. Due to the generality of the methodology, pre- and postbuckling behavior caused by both kinematic and material nonlinearity can be handled. To demonstrate the scheme, the results of several bench-mark problems are also presented. These include situations involving nonlinear kinematics as well as highly history-dependent elastic-plastic and thermoelastic-plastic material behavior.

Padovan, J.↗
NASA NTRS1985

Extension of long wavelength response by modulation doping in extrinsic germanium infrared detectors

A new concept for infrared detectors based on multilayer epitaxy and modulation doping has been investigated. This permits a high doping concentration and lower excitation energy in the photodetecting layer as is necessary for longer wavelength response, without incurring the detrimental effects of increased dark current and noise as would be the case with conventional detector designs. Germanium photodetectors using conventional materials and designs have a long wavelength cutoff in the infrared at 138 microns, which can only be extended through the inconvenient application of mechanical stress or magnetic fields. As a result of this approach which was arrived at from theoretical considerations and subsequently demonstrated experimentally, the long wavelength cutoff for germanium extrinsic detectors was extended beyond 200 microns, as determined by direct infrared optical measurements.

Hadek, V.↗
NASA NTRS1985

Extension of ground-based testing for large space structures

A major concern for future large space structures is the ability to verify their dynamic characteristics by ground test. This article presents the results of the multiple boundary conditions test (MBCT) approach, which provides a complete ground test of a large structure that will provide, in turn, the data necessary to construct a test-verified final mathematical model. Theoretical studies indicate that this approach can provide a better final model than a ground test of the full-scale very flexible structure in a 1-g field. The approach is demonstrated by a mathematical simulation.

Wada, B. K.↗
NASA NTRS1985

A new reeling technique for very long extension scanning in the stratosphere

A balloon-borne winching system has been developed for extending a very long tether with payload down into the stratosphere and recovering it, this has been flight proven by being carrried to an altitude of 40 km, lowering a 62-kg stratospheric photochemistry experiment 12 km at a descent velocity of about 6-8 m/sec and recovering it at comparable velocities. During the first flight, the data gave no evidence of dynamic instabilities due to the system or the stratospheric interactions. The future utility of this payload is discussed with attention to the design factors that bound the range of performance of this type of system.

Hazen, N. L.↗
NASA NTRS1985

Extension of Ostwald Ripening Theory

The objective is to develop models based on the mean field approximation of Ostwald ripening to describe the growth of second phase droplets or crystallites. The models will include time variations in nucleation rate, control of saturation through addition of solute, precipitating agents, changes in temperature, and various surface kinetic effects. Numerical integration schemes have been developed and tested against the asymptotic solution of Liftshitz, Slyozov and Wagner (LSW). A second attractor (in addition to the LSW distribution) has been found and, contrary to the LSW theory, the final distribution is dependent on the initial distribution. A series of microgravity experiments is being planned to test this and other results from this work.

Baird, J.↗
NASA NTRS1984

Extensions of the Ritz-Galerkin method for the forced, damped vibrations of structural elements

The Ritz-Galerkin methods were used to obtain approximate solutions for free undamped, vibration problems. It is demonstrated that these same methods may be used straightforwardly to analyze forced vibrations with damping without requiring the free vibration eigenfunctions. It was shown that the Galerkin method is an effective technique for these types of problems. The Ritz method has the advantage that it does not need to satisfy the force-type boundary conditions, which is particularly important for plates and shells. Proper functionals representing the forcing and damping terms were developed. Two types of damping--viscous and material (hysteretic) are discussed. Distributed and concentrated exciting forces are treated. Numerical results are obtained for cantilevered beams and rectangular plates. The rates of convergence of the solutions are shown. Approximate solutions from the present methods are compared with the exact solutions for the cantilever beam.

Leissa, A. W.↗
NASA NTRS1986

Extensions of the concept of suction analogy to prediction of vortex lift effect

Flow field data for a double delta wing at low speed were used to determine the location of a vortex action point. The result was found to be consistent with what was determined for a delta wing. In supersonic flow, the action point location was determined empirically. For a wing with rounded leading edges, an assumption for initial vortex separation was shown to be equivalent to initial leading edge bubble separation for airfoils. A theoretical formulation by the section analogy to determine the delayed vortex separation on a cambered wing with rounded leading edges was presented. The method of suction analogy was further shown to be applicable to predicting the body vortex lift.

Lan, C. E.↗
NASA NTRS1986

Recent extensions to the free-vortex-sheet theory for expanded convergence capability

A new version of the free vortex sheet formulation is presented which has greatly improved convergence characteristics for a broad range of geometries. The enhanced convergence properties were achieved largely with extended modeling capabilities of the leading edge vortex and the near field trailing wake. Results from the new code, designated FVS-1, are presented for a variety of configurations and flow conditions with emphasis on vortex flap applications.

Luckring, J. M.↗
NASA NTRS1984

On the extension of the MCSCF/CI method

Research conducted during this period was focused on two main areas: (1) bonding in transition metal oxides; and (2) adsorption of CO on Al and Ni. In both of these theoretical studies a major interest was to obtain a better understanding of the nature of the bonding in transition metal containing systems. The studies used self consistent field (SCF), multi-configuration self cosistent field (MCSCF) and configuration interaction (CI) methods in the treatment of the transition metal oxides and only the SCF method in the adsorption studies. The reports of three principle investigators who contributed to this work during the tenure of the project are presented along with associated published papers.

Bauschlicher, C., Jr.↗
NASA NTRS1984

A final report on the extension of the MCSCF/CI method

For the period of July 1982 through January 1983, the research carried out focused on the nature of metal adsorbate bonding. Two main areas were investigated in detail: (1) the adsorption of CO on Al, Na, Mg and Ni; and (2) bonding in transition metal oxides, CuO, CrO and MoO. These theoretical studies have lead to a new understanding of CO-metal bonding as well as to a better understanding of the d involvement in the bonding in transition metal oxides. Four areas associated with cluster model studies are discussed in detail: hybridization and changing in cluster model studies, the adsorption of CO on metals (Al, Na, Mg), the adsorption of CO on Ni, and finally the use of effective core potentials (ECP) in cluster models.

Nelin, C. J.↗
NASA NTRS1985

Io: Mountains and crustal extension

It is argued that there is good reason to conclude that mountains on Io, like those on Earth, are subject to growth and decay. The decay of mountains will be assisted by the ability of SO sub 2 to rot silicate rock and by explosive escape of sub-surface SO sub 2 from aquifers (Haemus Mons is seen to be covered by bright material, presumably fallout from a SO sub 2 rich plume which had been active on the mountain flanks). On the west side of the massif at 10 degrees S, 270 degrees W a rugged surface consists of long ridges running perpendicular to the downslope direction, suggesting tectonic denudation with crustal blocks sliding down the mountain flank. Tectonic denudation may be assisted, as in the case of the Bearpaw Mountains, Montana by overloading mountain flanks with volcanic products. The surfaces of some massifs exhibit a well developed, enigmatic corrugated terrain, consisting of complex ridge systems. Ridges may bifurcate, anastomose to form closed depressions and form concentric loops. Taken together, observations of morphology, heat flux, surface deposits and styles of volcanism may point to the existence of lithosphere domains with distinct compositions and tectonic regimes.

Heath, M. J.↗
NASA NTRS1985

Heat and detachment in core-complex extension

It is proposed here that the Miocene to Recent structural and volcanic features of the Basin and Range Province can be explained by a single thermotectonic process acting through time. This process consists of a thermal pulse resulting in a high-temperature regime that includes a steep thermal front moving first up toward the topographic surface, then down owing to cooling induced by a combination of convection and conduction. Within the front is a condition defining a critical surface that separates brittle from ductile behavior, and is marked by a nearly horizonal detachment fault. The most prominent and structurally highest position of the detachment results from interaction between the critical surface and a hydrothermal system near the topographic surface. These various features can be superposed on older ones through thermal remobilization or structural reactivation.

Lucchitta, I.↗
NASA NTRS1986

Extensive air showers (HE-4)

Ultra high energy (UHE) gamma ray astronomy is an exciting area which has added a new sense of purpose to ground based array work. There is much to be done before UHE gamma ray showers can be understood properly and it is important to remain conservative with claims while the properties of such showers are still not clear. The muon content is only one of the properties that needs to be clarified. It remains to be seen how well progress occurs on the second order problem of detailed interaction parameters once the gross features are clarified. The shower disk thickness has become an area of intense study with interest in Linsley's technique for measuremnts of giant showers and in the study of structure near the core for improving fast timing and studying delayed subshowers. Perhaps the most significant area of promise for the future is individual shower develpments with Cerenkov and, particularly, air fluorescence techniques. The importance and potential of having relatively complete information on a complete set of individual showers can hardly be overestimated. A complete understanding of the observation process is needed to determine whether or not the recorded data set is complete at a given energy, apparent core distance, and zenith angle.

Clay, R. W.↗
NASA NTRS1986

Generalization and extension of the law of acoustic energy conservation in a nonuniform flow

An exact conservation equation is derived which generalizes the familiar acoustic energy equations. The new relation is valid for arbitrary disturbances to a viscous, compressible flow. It is suggested by a development of the acoustic energy equation by means of a regular perturbation expansion of the general energy equation of fluid mechanics. A perturbation energy density and flux are defined and identified as the exact physical quantities whose leading order perturbation representations are the usual acoustic energy density and flux. The conservation equation governing the perturbation energy quantities is shown to yield previously known results for several special cases.

Myers, M. K.↗