Numerical research is reported on the propagation of short microwave pulses into living, biological materials. These materials are dispersive, and data on the dielectric constant and conductivity for these materials follow a Debye model. A Fourier-series calculation is presented that predicts the occurrence of Brillouin precursors when the incident pulses have sufficiently short rise times. These transients are attenuated with increasing propagation distance but are attenuated more slowly than the carrier frequency of the pulse, which is attenuated exponentially with distance. An analysis of the numerical error resulting from truncation of the Fourier series is giv-in. Upperbound estimates of truncation error show good series convergence., -
The quantitative interrogation of the human body or environmental s m c t m s such as plants or soils using electromagnetic or acoustic waves and solutions to inverse problems appears promising in clinical and environmental medicine. This paper reviews applications and methods of inverse electromagnetic and acoustic scattering.
Most non-metallic materials have frequency-dependent reflectivity functions, that is, they reflect electromagnetic energy in a manner that depends on frequency. Pulsed-chirped synthetic aperture radar and other multispectral radar systems do not generally take into account the frequency dependence of material reflections in forming scenes or making other inferences. In this report, we introduce a simple mathematical approach to using existing pulsed chirp synthetic aperture systems in a manner which results in a determination of a frequency-dependent reflectivity function for each pixel in a computed scene. Our analysis of collected data suggests that the method may be useful to distinguish disturbed from non-disturbed earth, and to detect chemicals on the surface of the earth. The method we have developed provides the analyst with a vector above each pixel with each vector component referencing a frequency band. This additional information may be useful for considering surface texture, subsurface layering and materials identification.
Monitoring the hearing of persons who routinely work in potentially hazardous noise areas serves to identify changes, or shifts, in hearing that may be attributed to excessive exposures. Since October 1956 (21 years) medical personnel of the US Air Force have used threshold shifts (current annual audiogram compared against individual reference) to identify persons who may be acquiring a sensorineural loss of hearing due to noise. Fortunately, this procedure has proven of extreme value since it identifies the occurrence of a noise-induced hearing loss during the earliest stages and thus, when combined with proper medical management, prevents the occurrence of significant amounts of hearing loss in the speech hearing range. The authors describe the results of a study of the relative effectiveness of 22 different criteria (or methods) that could be used to identify shifts in hearing (significant threshold shifts, STS) that may be attributed to excessive noise. A total of 56,678 military and civilian employees was selected for this study. The proportions of the total sample that would be identified using the different STS criteria are given; proportions ranged from 7.18% to 65.19%. Median hearing level for the total sample, as well as hearing levels for each of the groups identified by the 22 STS criteria are also reported.
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