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  • 1
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    Effect of growth parameters on compositional variations in directionally solidified HgCdTe alloys (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A series of Hg(1-x)Cd(x)Te alloy crystals was grown by directional solidification with compositions ranging from x = 0.2 to x = 0.4. The measured axial compositional profiles were interpreted in terms of an exact numerical solution of the appropriate diffusion equation that takes into account both the variations of the segregation coefficient and solidification rate with composition. The solutions for all growth rates agree generally well with the experimental data, and confirm earlier observations that employed approximate analytical solutions. The effective mass diffusion coefficients showed no significant composition or melt temperature dependence. Slightly higher diffusion coefficients were obtained, however, for the highest growth rates.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Crystal Growth (ISSN 0022-0248); 70; 343-348
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  • 2
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    Theoretical interpretation of thermal arrest data from differential thermal analysis measurements (1985)
    In:  Other Sources
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    Publication Date: 2016-06-07
    Description: A theory was developed to interpret the thermal arrest data of HgCdTe system from differential thermal analysis measurements. A nonlinear regression program is used to model fit the data. The purpose is to obtain a set of parameters which will give the information about average radiation coefficient, latent heat of fussion, and specific heat of the HgCdTe system at various compositions. The liquidus and solidus at various compositions are also obtained. The heat radiation from the furnace, heat radiation from the system, heat capacity from both the system and the quartz tube and the heat of fusion of the system are considered, however, it neglects heat transfer through conduction and convection.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Alabama Univ. Res. Rept.: 1984 NASA/ASEE Summer Faculty Fellowship Program (NASA-CR; 13p
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  • 3
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    Compositional Segregation in Unidirectionally Solidified Solid Solution Crystals (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: A computer program was developed to model compositional segregation in unidrectionally solidified solid-solution-semiconducting crystals. The program takes into account the variations of the interface segregation constant and solidification rate with composition. Calculations are performed for the HgCdTe solid solution system that is compared with experimental data.
    Keywords: SOLID-STATE PHYSICS
    Type: Alabama Univ. Res. Rept.: 1983 NASA(ASEE Summer Faculty Fellowship Program; 32 p
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  • 4
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    Flight test planning and parameter extraction for rotorcraft system identification (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present study is concerned with the mathematical modelling of aircraft dynamics on the basis of an investigation conducted with the aid of the Rotor System Research Aircraft (RSRA). The particular characteristics of RSRA make it possible to investigate aircraft properties which cannot be readily studied elsewhere, for example in the wind tunnel. The considered experiment had mainly the objective to develop an improved understanding of the physics of rotor flapping dynamics and rotor loads in maneuvers. The employed approach is based on a utilization of parameter identification methodology (PID) with application to helicopters. A better understanding of the contribution of the main rotor to the overall aircraft forces and moments is also to be obtained. Attention is given to the mathematical model of a rotorcraft system, an integrated identification method, flight data processing, and the identification of RSRA mathematical models.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 86-9772
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  • 5
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    Investigation of compositional segregation during unidirectional solidification of solid solution semiconducting alloys (1982)
    In:  Other Sources
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    Publication Date: 2016-06-07
    Description: Compositional segregation of solid solution semiconducting alloys in the radial direction during unidirectional solidification was investigated by calculating the effect of a curved solid liquid interface on solute concentration at the interface on the solid. The formulation is similar to that given by Coriell, Boisvert, Rehm, and Sekerka except that a more realistic cylindrical coordinate system which is moving with the interface is used. Analytical results were obtained for very small and very large values of beta with beta = VR/D, where V is the velocity of solidification, R the radius of the specimen, and D the diffusivity of solute in the liquid. For both very small and very large beta, the solute concentration at the interface in the solid C(si) approaches C(o) (original solute concentration) i.e., the deviation is minimal. The maximum deviation of C(si) from C(o) occurs for some intermediate value of beta.
    Keywords: METALLIC MATERIALS
    Type: NASA. Marshall Space Flight Center The 1982 NASA(ASEE Summer Fac. Fellowship Program; 20 p
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  • 6
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    Control strategies (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Techniques for improving the performance of robotic-manipulator path-control systems comprising independent SISO feedback controllers for each joint are discussed and illustrated with block diagrams, reviewing the results of recent analytical investigations. Topics examined include the servo design for a single link, the equations of motion for manipulators, SISO servo design for multiple links, inverse methods, pole placement with compensation of the gravity terms, linear state-feedback control based on the perturbation equations, and adaptive control methods. Consideration is given to variable-structure systems, suboptimal controllers, and the optimal-design-strategy approach.
    Keywords: CYBERNETICS
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  • 7
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    A scalar/vector potential formulation of an airfoil in nonuniform stream (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A recent innovation in aerodynamic calculation techniques is the formulation based upon scalar and vector potentials (Stokes-Helmholtz decomposition) for the velocity field. This technique is presented: an implementation involving classical panel method is studied. The application of interest is to two-dimensional airfoils moving into a nonuniform approach flow. Comparisons with theoretical and numerical results are included. Furthermore the variations of lift and moment coefficients of quasi-steady simulated flight of an airfoil through microburst wind shear data are studied.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 88-0397
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  • 8
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    Anti-Stokes scattering as an XUV radiation source (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Harris (1977) has shown that laser induced scattering from atoms stored in a metastable level may be used to produce an XUV radiation source with several unique properties, including narrow linewidth, tunability, linear polarization, picosecond pulsewidth, and relatively high peak spectral brightness. The present investigation provides a summary concerning the progress made on the use of this radiation source as a unique instrument for XUV spectroscopy, and as a possible flashlamp for a 200 A laser. Zych et al. (1978) demonstrated that the maximum spectral brightness of the source is that of a blackbody with a temperature of the metastable storage level. The peak count rate and peak spectral brightness of the anti-Stokes emission at 569 A are 17 times and 139 times greater than those of the 584 A resonance line. The anti-Stokes process was employed as an external source of radiation for high resolution spectroscopy of the 3p6 shell of potassium. Attention is also given to emission spectroscopy of lithium, metastable levels which are appropriate for storage, and a hollow cathode discharge.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
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  • 9
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    Crystal Growth of HgZnTe Alloy by Directional Solidification in Low Gravity Environment (2002)
    In:  Other Sources
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    Publication Date: 2018-06-12
    Description: An Hg(0.84)Zn(0.16)Te alloy crystal was back-melted and partially re-solidified during the first United States Microgravity Laboratory mission in the Marshall Space Flight Center's Crystal Growth Furnace. The experiment was inadvertently terminated at about 30% of planned completion. Nonetheless, it was successfully demonstrated that a HgZnTe alloy ingot partially grown and quenched on the ground can be back-melted and re-grown in space under nearly steady-state growth conditions. An identical "ground-truth" experiment was performed following the mission and a comparison between the properties of the crystals is described. The results indicate the importance of residual microgravity acceleration (less than or approx. equal to 0.4 micro-grams) even in the sub-microgravity range for the slow solidification velocities and large density gradients.
    Keywords: Geosciences (General)
    Type: Journal of Crystal Growth (ISSN 0022-0248); Volume 234; 487-497
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  • 10
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    Crystal Growth of HgZnTe Alloy by Directional Solidification in Low Gravity Environment (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: A Hg0.84Zn0.16Te alloy crystal was back-melted and partially resolidified during the first United States Microgravity Laboratory (USML-1) mission in the Marshall Space Flight Center's Crystal Growth Furnace. The experiment was inadvertently terminated at about 30% of planned completion. Nonetheless, it was successfully demonstrated that a HgZnTe alloy ingot partially grown and quenched on the ground can be back-melted and regrown in space under nearly steady state growth conditions. An identical "groundtruth" experiment was performed following the mission and a comparison between the properties of the crystals is described. The results indicate the importance of residual microgravity acceleration (approx. less than 0.4 mg) even in the sub-microgravity range for the slow solidification velocities and large density gradients.
    Keywords: Space Processing
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