Twn different approaches, the direct simulation Monte Carlo II)SMC) method based nn molecular gasdynamics, and a finite-volume approximation of the Navier-Stokes equations, which are based on continuum gasdynamies, are employed in the analysis of a low-density gas flnw in a small converging-diverging nozzle. The fluid experiences various kinds of flow regimes including continuum, slip, transition, and free-molecular. Results from the two numerical methods are compared with Rothe's experimental data, in which density and rotational temperature variations along the centerline and at various locations inside a law-density nozzle were measured by the electron-beam fluorescence technique. The continuum approach showed gt_d agreement with the experimental data as far as density is concerned. The results from the I)SMC method showed good agreement with the experimental data, both in the density and the rotational temperature. It is also shown that the simulation parameters, such as the gas/surface interaction model, the energy exchange model between rotational and translational modes, and the viscnsity-temperature exponent, have substantial effects on the results of the DSMC method.

Magnetic properties are calculated for a spin one-half Heisenberg ferromagnet in which the exchange interactions deviate randomly in strength from the mean interaction,, Disorder produces a low-energy peak and a high-energy tail in the density of spin-wave states for a simple-cubic geometry. The ferromagnetic Curie temperature is shown to decrease linearly with disorder; the temperature-dependent magnetization is not otherwise markedly altered.

The direct simulation Monte Carlo method was applied to the analysis of low-density nitrogen plumes exhausting from a small converging-diverging nozzle into finite ambient pressures. Two cases were considered that simulated actual test conditions in a vacuum facility. The numerical simulations readily captured the complicated flow structure of the overexpanded plumes adjusting to the finite ambient pressures, including Mach disks and barrelshaped shocks. The numerical simulations compared well to experimental data of Rothe.

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