Photoacoustic frequencydomain depth profiling of continuously inhomogeneous solids. Theory and quantitative profilometry of octyleyanobiphenyl (8CB) liquid crystals An application is presented of the Hamilton-Jacobi formulation of thermal-wave physics [A. Mandelis, J. Math. Phys. 26, 2676( 1985] to the problem of photoacoustic depth profiling of inhomogeneous solids with arbitrary, continuously varying thermal diffusivity profiles. Simple expressions for the modulation frequency dependence of the photoacoustic signal in the case of exponential thermal diffusivity profiles are obtained, and a working general method for solving the inverse problem and obtaining arbitrary diffusivity depth profiles is demonstrated through computer simulations. The method was found to possess excellent profile reconstruction fidelity.
A model has been developed that permits assessment of residential exposure to 60-Hz magnetic fields emitted by appliances. It is based on volume- and time-averaging of magnetic-dipole fields. The model enables the contribution of appliances in the total residential exposure to be compared with that of other sources in any residence under study. Calculations based on measurements reported in the literature on 98 appliances revealed that appliances are not a significant source of whole-body exposure, but that they may be the dominant source of exposure of the body's extremities.
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