Aerospace medicine and biology: A continuing bibliography with indexes, supplement 197, September 1979

This bibliography lists 193 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1979

Aerospace Medicine and Biology: A continuing bibliography, supplement 216

One hundred twenty reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1981 are listed. Topics include: sanitary problems; pharmacology; toxicology; safety and survival; life support systems; exobiology; and personnel factors

Efficient modeling of sound source radiation in free-space and room environments

Motivated by the need to develop efficient acoustics simulations for sources in different room environments, a modeling procedure has been proposed that consists of two steps in general: (1) the modeling of the free-space radiation of the source based on measurements in a anechoic environment, and (2) the prediction of the sound field in a room environment based on that free-space information. To achieve a high modeling efficiency, i.e., to reduce the number of modeling parameters while still maintaining acceptable accuracy, a Multipole Equivalent Source Model (ESM) with undetermined source locations has been developed for the free-space sound field prediction. In contrast with traditional ESM’s, or acoustical holography methods in general, the model developed in the present work possesses two efficiency improvements: (1) the use of the series of monopoles, dipoles, quadrupoles, etc. as equivalents sources (since in predicting the sound field, the multipole series can be simply represented as closely located monopoles) and (2) the flexibility of using spatially separated sources with undetermined locations. In the inverse parameter estimation process of this method, the calculation of the source strengths is linear while the source locations are determined by a nonlinear optimization procedure. It is shown, by an experimental validation, that the prediction using this method can be accurate for almost the whole audio frequency range. To model the sound field at high frequencies specifically, different types of methods using local-basis functions were developed. At high frequencies, the spatial variation of the sound field is usually large and thus the number of measurements points in space is likely not to be enough to model a relatively complicated source if a traditional equivalent source model is used, and the under-sampling errors from all regions will accumulate to affect the predictions in any particular region. However, if localized basis functions are used to represent the sound field, the under-sampling errors from different regions do not affect each other. Two types of local-basis method are developed in this work: one based on piece-wise polynomial interpolation (which is limited to having only a single source) and the other based on least squares (which can be applied to multiple sources and even to interior problems). Simulation results have shown that these local-basis methods, at very high frequencies, can achieve good overall prediction accuracy with only a loss of some details in the spatial variation of the sound field. In the room acoustics modeling section, the Equivalent Source Method is modified and implemented which, compared with the geometric acoustics models, gives a prediction based on a more rigorous mathematical foundation and, compared with Boundary Element methods, reduces the computational intensity. In this proposed room acoustics ESM, the free-space source radiation is assumed known, and the room component sound field is determined by an ESM. Differing from the free-space ESMs, this room acoustics ESM (1) contains additional equivalent sources representing the incoming waves, and (2) uses impedance boundary conditions on the surfaces instead of the measured sound field, to estimate the source strengths. It is validated by simulations (in both 2D and 3D spaces) and then by experiments that the proposed room acoustics ESM can be used as a reduced order modeling technique in simulating the sound field in a room. It is also shown that the prediction accuracy and the computational load can be flexibly balanced, if Multipole ESMs are used, by selecting an appropriate maximum source order

Aeronautical engineering: A continuing bibliography with indexes (supplement 239)

This bibliography lists 454 reports, articles, and other documents introduced into the NASA scientific and technical information system in April, 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Electrical Characterization of Intrinsic and Induced Deep Level Defects in Hexagonal SiC

Deep level defects in hexagonal SiC were studied using digital deep level transient spectroscopy (DLTS) methods over the temperature range of 100 to 800 deg K. New centers were found in bulk and epitaxial 6H-SiC with ionization energies between 0.38 to 1.3 eV, and levels from 0.2 to 0.856 eV were identified in 4H-SiC epitaxy. Direct correlation between inequivalent lattice sites was identified for energetic pairs associated with both vanadium and ion implanted Mg impurities. Nonradioative carrier capture mechanisms were studied and deep level trapping was found to proceed via lattice relaxation multi-phonon emission, indicating efficient electronic lattice coupling in the wide bandgap material. Junction transport characteristics of 4H-SiC p+/n bipolar devices were observed to be dominated by deep level defects in the epitaxial layers. Significant tunneling conduction in both forward and reverse bias conditions was directly correlated to deep level centers in these devices

Aeronautical engineering: A continuing bibliography with indexes (supplement 289)

This bibliography lists 792 reports, articles, and other documents introduced into the NASA scientific and technical information system in Mar. 1993. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Aeronautical engineering: A continuing bibliography with indexes (supplement 276)

This bibliography lists 705 reports, articles, and other documents introduced into the NASA scientific and technical information system in Feb. 1992. Subject coverage includes: design, construction, and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Aeronautical engineering: A continuing bibliography with indexes (supplement 250)

This bibliography lists 420 reports, articles, and other documents introduced into the NASA scientific and technical information system in February, 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics