Derivatives of the Arithmetic-Geometric Mean
Developed for theoretical studies of lightning requiring estimates of electric fields in clouds, the technique is expected to reduce computation time and improve accuracy.
Taton, F. B.↗
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Theoretical Problems in Materials Science
Interactions between theoretical physics and material sciences to identify problems of common interest in which some of the powerful theoretical approaches developed for other branches of physics may be applied to problems in materials science are presented. A unique structure was identified in rapidly quenched Al-14% Mn. The material has long-range directed bonds with icosahedral symmetry which does not form a regular structure but instead forms an amorphous-like quasiperiodic structure. Finite volume fractions of second phase material is advanced and is coupled with nucleation theory to describe the formation and structure of precipitating phases in alloys. Application of the theory of pattern formation to the problem of dendrite formation is studied.
Langer, J. S.↗
Aerodynamic data banks for Clark-Y, NACA 4-digit and NACA 16-series airfoil families
With the renewed interest in propellers as means of obtaining thrust and fuel efficiency in addition to the increased utilization of the computer, a significant amount of progress was made in the development of theoretical models to predict the performance of propeller systems. Inherent in the majority of the theoretical performance models to date is the need for airfoil data banks which provide lift, drag, and moment coefficient values as a function of Mach number, angle-of-attack, maximum thickness to chord ratio, and Reynolds number. Realizing the need for such data, a study was initiated to provide airfoil data banks for three commonly used airfoil families in propeller design and analysis. The families chosen consisted of the Clark-Y, NACA 16 series, and NACA 4 digit series airfoils. The various component of each computer code, the source of the data used to create the airfoil data bank, the limitations of each data bank, program listing, and a sample case with its associated input-output are described. Each airfoil data bank computer code was written to be used on the Amdahl Computer system, which is IBM compatible and uses Fortran.
Korkan, K. D.↗
Sound propagation over uneven ground and irregular topography
The development of theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere is discussed. Irregular topography here is understood to imply a ground surface that (1) is not idealizable as being perfectly flat or (2) that is not idealizable as having a constant specific acoustic impedance. The study focuses on circumstances where the propagation is similar to what might be expected for noise from low-altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence.
Pierce, A. D.↗
Convective Evaporation Of Sprayed Liquid
Theoretical model developed to analyze behavior of both dense and dilute clusters of evaporating liquid drops in gas flows. Particularly useful in search for methods of controlling evaporation, ignition, and combustion of fuel sprays.
Bellan, Josette↗
Ground-based observations of the Jupiter plasma torus
The intensity variation of (SIII) 9531 A emission from the hot plasma torus of Jupiter was measured using a scanning Fabry-Perot spectrometer. During the observational period, which covered 43 rotations of Jupiter, the (SIII) intensities showed a periodic variation consistent with a zone of enhanced emission approximately 90 deg in longitude, rotating with a period of 10.2 hours, or 2.8% longer than Jupiter's rotational period. Dessler developed a theoretical model of account for Jovian magnetospheric phenomena that differ in repetition period by 3%. In his model, periodic modulation of magnetospheric phenomena is controlled in part by the spin period of magnetic features below the surface of the planet. The differing observed periods are then due to differential rotation of the subsurface magnetic features at different latitudes. A consequence that follows from this concept of differential rotation of the internal planetary magnetic field is that not all the apparent subcorotational plasma flow in the torus is caused by plasma mass loading, as described by Hill and his associates. As a result, the mass loading required to produce the residual subcorotational flow is less than previously estimated.
Scherb, F.↗
Physics of the inner heliosphere: Mechanisms, models and observational signatures
Selected problems concerned with the important physical processes that occur in the corona and solar wind acceleration region, particularly time dependent phenomena were studied. Both the physics of the phenomena and the resultant effects on observational signatures, particularly spectroscopic signatures were also studied. Phenomena under study include: wave motions, particularly Alfven and fast mode waves; the formation of standing shocks in the inner heliosphere as a result of momentum and/or heat addition to the wind; and coronal transient phenomena where momentum and/or heat are deposited in the corona to produce transient plasma heating and/or mass ejection. The development of theoretical models for the inner heliosphere, the theoretical investigation of spectroscopic plasma diagnostics for this region, and the analysis of existing skylab and other relevant data are also included.
Withbroe, George L.↗
Transition from a planar interface to cellular and dendritic structures during rapid solidification processing
The development of theoretical models which characterize the planar-cellular and cell-dendrite transitions is described. The transitions are analyzed in terms of the Chalmers number, the solute Peclet number, and the tip stability parameter, which correlate microstructural features and processing conditions. The planar-cellular transition is examined using the constitutional supercooling theory of Chalmers et al., (1953) and it is observed that the Chalmers number is between 0 and 1 during dendritic and cellular growth. Analysis of cell-dendrite transition data reveal that the transition occurs when the solute Peclet number goes through a minimum, the primary arm spacings go through a maximum, and the Chalmers number is equal to 1/2. The relation between the tip stability parameter and the solute Peclet number is investigated and it is noted that the tip stability parameter is useful for studying dendritic growth in alloys.
Laxmanan, V.↗
Origin and evolution of X-ray binaries in globular clusters
The theoretical model developed by Grindlay (1984 and 1985) and Grindlay and Hertz (1985) to explain the relative numbers of low-luminosity and high-luminosity X-ray sources in Galactic globular clusters is briefly characterized, and the relevant observational evidence is summarized. In the model, high-rate mass transfer onto white dwarfs in about 1 percent of the low-luminosity binary sources produces neutron stars, which then form compact high-luminosity X-ray binaries (by tidal capture in the dense cluster cores); these in turn evolve into hierarchical triple systems. Evidence considered includes observations of the high-luminosity giant-fed X-ray binary in M 15, the results of searches for CVs in globulars, comparisons of X-ray-binary and host-globular evolution, and indications that GX 17 + 2 is a bound triple.
Grindlay, Jonathan E.↗
Refined Transistor Model For Simulation Of SEU
Equivalent base resistance added. Theoretical study develops equations for parameters of Gummel-Poon model of bipolar junction transistor: includes saturation current, amplification factors, charging times, knee currents, capacitances, and resistances. Portion of study concerned with base region goes beyond Gummel-Poon analysis to provide more complete understanding of transistor behavior. Extended theory useful in simulation of single-event upset (SEU) caused in logic circuits by cosmic rays or other ionizing radiation.
Zoutendyk, John A.↗
Detection of soil erosion with Thematic Mapper (TM) satellite data within Pinyon-Juniper woodlands
Pinyon-Juniper woodlands dominate approximately 24.3 million hectares (60 million acres) in the western United States. The overall objective was to test the sensitivity of the LANDSAT Thematic Mapper (TM) spectral data for detecting varying degrees of soil erosion within the Pinyon-Juniper woodlands. A second objective was to assess the potential of the spectral data for assigning the Universal Soil Loss Equation (USLE) crop management (C) factor values to varying cover types within the woodland. Thematic Mapper digital data for June 2, 1984 on channels 2, 3, 4, and 5 were used. Digital data analysis was performed using the ELAS software package. Best results were achieved using CLUS, an unsupervised clustering algorithm. Fifteen of the 40 Pinyon-Juniper signatures were identified as being relatively pure Pinyon-Juniper woodland. Final analysis resulted in the grouping of the 15 signatures into three major groups. Ten study sites were selected from each of the three groups and located on the ground. At each site the following field measurements were taken: percent tree canopy and percent understory cover, soil texture, total soil loss, and soil erosion rate estimates. A technique for measuring soil erosion within Pinyon-Juniper woodlands was developed. A theoretical model of site degradation after Pinyon-Juniper invasion is presented.
Price, Kevin Paul↗
An exactly solvable model for calculating critical misfit and thickness in epitaxial superlattices. II - Layers of unequal elastic constants and thicknesses
The theoretical model developed by van der Merwe and Jesser (1988) is extended to permit the exact determination of the critical misfit and critical thickness of an epitaxially grown superlattice made up of layers with differing elastic constants and thicknesses. Lateral force balances are maintained by means of an explicit relationship between the homogeneous misfit strains and the thicknesses and moduli. A number of simplifying approximations are introduced, and sample numerical results are presented in graphs.
Jesser, W. A.↗
Characteristics and kinetics of laser-pumped Ti:sapphire oscillators
The experimental performance of a gain-switched Ti:sapphire laser oscillator pumped by a frequency-doubled Q-switched Nd:YAG laser system is presented for a variety of operating conditions. A theoretical model developed for this oscillator predicts well its performance. The observed curved input-output energy plots for the oscillator result from the kinetics of gain switching and fluorescence decay during the gain buildup period. Fluorescence decay also produces observed oscillator thresholds higher than those normally predicted by the standard gain-equals-loss condition. Gain-switched parasitic modes, with a higher threshold but shorter round-trip time than the resonator mode, cause the resonator mode to oscillate only over a finite range of pump energies. Spectroscopic investigations show that the Ti:sapphire cross-section spectrum is well fit by a Poisson distribution, giving a peak cross section of 3 x 10 to the -19th sq cm for the pi polarization.
Eggleston, John M.↗
Heat flow control and segregation in directional solidification: Development of an experimental and theoretical basis for Bridgman-type growth experiments in a microgravity environment
Within the framework of the proposed research, emphasis was placed on application of magnetic fields to semiconductor growth systems. It was found that magnetic fields up to 3 kGauss do not affect the growth behavior nor the macro-segregation behavior in the system Ge(Ga). Applied fields are found to significantlty alter the radial dopant distribution, which is attributed to alterations in the spatial orientation of convective cells. Increasing the magnetic field to 30 kGauss is found to have a fundamental effect on dopant segregation. Emphasis is also placed on the potential of KC-135 flights for preliminary studies on the effects of reduced gravity environments on the wetting behavior of semiconductor systems in growth configuration. The limited number of experiments conducted does not allow any conclusions on the merits of KC-135 flights for semiconductor processing research.
Witt, A. F.↗
Thermosphere dynamics - Recent contributions from Dynamics Explorer-2
This paper discusses results obtained during the period between August 1981, and February 1983, by the instruments aboard the Dynamic Explorer-2 (DE-2) mission, with emphasis placed on the data obtained through the direct measurements of thermospheric vector neutral winds and ion drifts. The DE-2 instrumentation used to obtain the vector neutral-wind observations is described together with the information obtained on the dynamics of the thermosphere. Special consideration is given to the theoretical model development and the ongoing data-theory comparative studies. The progress made during the first five years of the DE mission is summarized.
Killeen, T. L.↗
Hot stars
Theoretical models developed to explain the emission of hot stars are examined, summarizing and analyzing the results of ground-based and space observations obtained at different wavelengths. The physical processes responsible for emission in the radio, IR, visible, UV, and X-ray bands are reviewed, and particular attention is given to observations of OB-star winds, B-emission stars, compact stellar cores, and hot stars in binary systems. The importance of the UV and EUV spectral regions and the need for a space observatory to replace the IUE when it becomes inoperative are stressed.
Snow, Theodore P.↗
Estimation of Boltzmann damping coefficients in beam models
A distributed parameter model of a flexible structure with Boltzmann type viscoelastic damping is discussed. A computational method for the estimation of the damping parameters is developed, and theoretical convergence results are given. An example is presented in which actual experimental data is used, demonstrating the efficacy of the computational method and the plausibility of the model for predicting response in damped structures.
Banks, H. T.↗
The response of helicopter rotors to vibratory airload
The problems of oscillatory and vibratory loading are examined from the perspective of the rotor's structural response. Blade flap, chord, and torsion responses, from flight or wind tunnel tests of eight full-scale rotors are examined and compared for high-speed flight conditions in the absence of blade stall or maneuvers. Some important similarities and differences between rotors are considered, and it is pointed out that these observations are useful in determining the appropriate tests for development of theoretical prediction methods. Among other things, major similarities were found in the dominant flapping vibratory response which occurs at 3/rev, and the root oscillatory chord bending for the CH-34, the SA 349/2, and the UH-60A; differences noted include vibratory chord bending-moment behavior of the rotors, a difference in the damper-induced behavior of CH-53A root oscillatory chord bending, and unique torsion and pitch link loading behavior exhibited by the AH1-G articulated rotor.
Bousman, William G.↗