Analysis of semiconductors with field-dependent mobility
Using the time domain analysis of Lagrangian approach, the small-signal behavior of a semiconductor with field-dependent mobility under various contact conditions is analyzed. A generalized closed form solution for an impulse current response is derived when the carrier velocity characteristic is expressed by a piecewise linear function. This result gives an accurate description of the transient performance of the device and can provide good insight into device operation. Numerical examples are given for a negative differential mobility GaAs crystal, considering the conditions under which negative resistances occur. A generalized small-signal impedance of the semiconductor is given, from which previous results reported for particular devices can be obtained as special cases.
Wave propagation and profile inversion in lossy inhomogeneous media
Using the Lagrangian approach, a time-domain analysis of wave propagation in an inhomogeneous lossy medium is described. We consider a half-space problem (x ≥ 0) in which the medium is plane stratified in the direction of propagation and can be modeled by a piecewise uniform lossy transmission line. A method of profile inversion which is based directly upon quantities measured in time at the sending end boundary is presented. The problem of uniqueness is discussed. For a given medium, computer simulation results obtained by using the known reflected waves at the boundary x = 0 are shown.
Health-care practices of the rural aged.
1. One of the primary concerns of the rural aged is the maintenance of their physical health so that they may function independently and remain in their own homes. 2. The findings of this study indicate that most older rural adults do not regularly have positive health-care practices. This may be due to the unavailability of health-care providers or health promotion programs in isolated rural areas. 3. Implications of this study include the need to make health promotion programs relevant to the concerns of the rural aged rather than those of the urban elderly.