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Chang, S.-H.

Publications and source records attributed to Chang, S.-H..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

An embedding method for the steady Euler equations

Certain difficulties arise in connection with the numerical solution of a direct finite difference representation of the steady Euler equations. Johnson (1979, 1981, 1982) has, therefore, proposed a surrogate-equation technique, in which the first-order steady Euler equations are embedded in a certain second-order system of equations. The present paper is concerned with the theoretical justification for such an embedding approach. For the numerical solution of the two-dimensional steady Euler equations, it is shown that, under a continuity restriction, it is possible to solve a second-order embedded system together with appropriate additional boundary conditions. The result indicates that a more direct and potentially more efficient approach to the steady solutions exists than the alternative of solving the unsteady equations.

Chang, S.-H.↗
NASA NTRS1981

Remote mineralogical analysis using a high-resolution airborne spectroradiometer - Preliminary results of the Mark II system

The 1500-2500-nm region is of particular interest for remote mineralogical analysis since hydroxyl-bearing minerals, such as clays, alunite, muscovite, and pyrophyllite, which are associated with hydrothermally altered rocks, have diagnostic absorption features in this region. The development and successful flight testing of the Mark II instrument are seen as making possible the acquisition of the necessary high-spectral-resolution data for evaluating this approach to the remote sensing of geological features. Preliminary results of an analysis of data gathered in October 1980 using the Mark II system for selected test sites in Nevada are presented. Even though field and laboratory analyses of the data are only in the initial stages, the results are seen as indicating that this system can be used to detect the most diagnostic spectral features of several economically important minerals.

Collins, W.↗
NASA NTRS1978

Stellar model chromospheres. VII - Capella /G5 III +/, Pollux /K0 III/, and Aldebaran /K5 III/

Data from high-resolution SEC vidicon spectroscopy with a ground-based telescope (for the Ca II K line) and from spectral scans made with the BUSS ultraviolet balloon spectrograph (for the Mg II h and k lines) are used to derive models of the chromospheres and upper photospheres of three G-K giants. The models are based on partial-redistribution analyses of the Ca II K line wings and cores and on the fluxes in the Mg II lines. The photospheres thus computed are hotter than predicted by radiative-equilibrium models. The minimum-to-effective temperature ratio is found to decrease with decreasing effective temperature, while the mass column density at the top of the chromosphere increases with decreasing stellar surface gravity. The computed pressure at the chromosphere top in the primary member of the Capella spectroscopic binary system is 70 times smaller than the transition-region pressure derived by Haisch and Linsky (1976), which suggests that additional terms must be included in the transition-region energy equations for giant stars. Estimates of the Ca II and hydrogen column densities are made for the circumstellar envelope of Aldebaran.

Kelch, W. L.↗