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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Thermal diffusivity measurements for superconducting YBa,Cu,O,-and BizSr,CaCu,O, are reported over the temperature range from 50 to 300 K. The results were obtained using frequency-modulated time-delay photopyroelectric spectrometry (FM-TDPS), which consists of chirped laster excitation of the sample and detection of the associated impulse by a thin-film pyroelectric detector.

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The current through the residential grounding circuit is an important source for magnetic fields; field variations near the grounding circuit accurately track fluctuations in this ground current. In this paper, a model is presented which permits calculation of the range of these fluctuations. A discrete network model is used to simulate a local distribution system for a single street, and a statistical model to simulate unbalanced currents in the system. Simulations of three-house and ten-house networks show that random appliance operation leads to ground current fluctuations which can be quite large, on the order of 600%. This is consistent with measured fluctuations in an actual house.