No abstract

Nuclear magnetic-resonance studies of the groups IV, V, and VI transition-metal diborides show that the boron nuclei have a small quadrupole coupling constant, and negative frequency shift of the order of 10—4. The V51 resonance in VB2 provides a measure of the quadrupole coupling constant for V51 as 2.35 Mc/sec and a frequency shift of —3.37×10—3. The frequency shifts are enhanced at low temperatures. These data are explained within the framework of a suggested metal—boron donor—acceptor bonds by proposing s—d exchange polarization and diamagnetic ``ring current'' contributions to the field at the nucleus.

No abstract

The yttrium oxide emission produced in the photoablation of Y203, YCls, and YBazCu307-x in oxygen is investigated. Chemiluminescence from the B 22-X28 and the Ld 'II-X "L: YO electronic states, produced by the reaction Y +02, is measured. The intensity of the A 2113,2 band is monitored as a function of pressure, distance from the target, and laser fluence. Hydrodynamic effects have a significant influence on the spatial and temporal evolution of the YO emission in the plume, which is governed by the dynamics of the shock wave generated in the excimer ablation. This shock wave compresses the ambient oxygen and leaves a trough of rarefied oxygen in its wake. 7810

Abstract. We present a framework for optical tomography based on a path integral. Instead of directly solving the radiative transport equations, which have been widely used in optical tomography, we use a path integral that has been developed for rendering participating media based on the volume rendering equation in computer graphics. For a discretized two-dimensional layered grid, we develop an algorithm to estimate the extinction coefficients of each voxel with an interior point method. Numerical simulation results are shown to demonstrate that the proposed method works well.