[en] In this work a transient model of a Cs-Ba diode is developed, and a series of experiments is performed using a diode equipped with Langmuir probes. The Langmuir probe data show that the electron energy distribution is non-Maxwellian at low discharge currents, indicating the presence of an electron beam from the emitter. Experimental results also showed that the plasma properties are non-homogeneous across the 1 mm diode gap; the electron temperature and plasma potential were higher near the emitter and the plasma density was higher near the collector. Experimental evidence is presented to show that the discharge contracts to a filament below the maximum thermal emission current

[en] A model recently introduced by Ianiro and Lebowitz is shown to have a global solution for initial data having a finite H-functional and belonging to L/sub v/¹ (L/sub x//sup infinity/). Methods previously introduced by Tartar to deal with discrete velocity models are used

[en] The authors construct an operator for the equivalent impedance of a rough surface which bounds a layered medium, and discuss the physical approach by which it is generated. They give an example of the application of this operator in computing the attenuation of eigenmodes of an integrated optical waveguide with a rough substrate

[en] The semiclassical interpretation of the experimentally confirmed computational discovery of the resonances for the collinear interaction of the fluorine atom with the hydrogen molecule as action-quantizing classical trajectories is extended to the J = 0 3D reaction in a successful attempt to recover the analogous quantum calculation of the resonance eigenvalues. Confirmation of the semiclassical analogues for both collinear and 3D reactions is then strengthened through a successful construction of stationary-state wave functions when compared to the full quantum calculation, using a time-dependent approach to semiclassical dynamics requiring such action-quantizing trajectories. Extension to future studies are initiated by constructing outgoing scattering states through a semiclassical adiabatic formalism with which the width of the resonance peaks may then be computed. Discoveries incidental to the major objectives required inspection to address the ambiguities associated with multiple semiclassical analogues and were satisfactorily resolved through linear stability analysis and computation of Lyapunov exponents for quasi-periodic trajectories. Successful generalizations for the quantization of the alternative analogues were developed with resultant unification of bound-trajectory initial-position loci on the V = E potential-energy surface

[en] The authors consider the relaxation dynamics of two quantum levels coupled to a stochastic bath. We emphasize that even if the matrix elements of the fluctuating Hamiltonian are Gaussian, a second-order cumulant truncation is not exact. For various stochastic models, including the case of a spin-1/2 particle in a fluctuating magnetic field, we calculate 1/T₁, the population relaxation rate, and 1/T₂, the phase relaxation rate, up to fourth order in perturbation theory. We show that unlike the commonly accepted second-order result that 1/T₂ ≥ 1/2T₁, when fourth-order terms are included, in some instances 1/T₂ < 1/2T₁

[en] The authors determine the zero-temperature properties of a one-dimensional lattice gas of particles that interact via a nearest neighbor exclusion potential and are subject to a random external field. The model is a special limiting case of the random field Ising chain. We calculate (1) the energy and density of the ground state as well as the local energy-density correlation and (2) the pair correlation function. The latter calculation gives access to all higher order correlations. The structure factor is shown to be a squared Lorentzian. The authors also compare the ground state to the quenched state obtained by sequentially filling the lowest available energy levels

[en] The general path-integral formalism for real-time dynamics for a quantum system in a fermionic environment proposed previously is investigated by using a new method called local adiabatic transformation. This method is based on the observation that in the long-time limit (the time scale of the system is much larger than that of the environment, typically characterized by the inverse of the cutoff frequency of the environment), most degrees of freedom of the environment will follow the dynamics adiabatically. This feature is utilized by transforming the original problem of coordinate coupling into a problem of velocity coupling. This is achieved by making some simple unitary transformation on the fermion field (before path-integrating out of that field). By doing perturbations on the new problem, all the previous important results are recovered. Furthermore, generalizations to more realistic situations (for example, a particle traveling over a large distance and coupled to a Fermi gas through the phase factor exp(ik x R) (the coupling may involve many channels of angular momentum)) are considered and significant results obtained

[en] The authors present some new results on the region in the βべーた-h plane where the + spins percolate for the nearest neighbor Ising model. In particular, it is shown that in high enough dimensions d there is percolation of the minority spins at inverse temperatures βべーた < β/sub +/ with some β/sub +/ > βべーた/sub c/, for which βべーた/sub +//βべーた/sub c/ ≥ 1/2 log(cd), c a constant

[en] The authors study analytically the approach to equilibrium in a simple zero-temperature model for phase separation in a binary alloy, in which nearest neighbor interchange can occur only if the portion of AB bonds is thereby decreased. The approach to equilibrium is found analytically. Because of the existence of infinitely many possible stationary states, the asymptotic distribution of AB pairs depends on the details of the initial state and must be obtained by a recursion method

[en] Aharonov and Anandan have recently reformulated and generalized Berry's phase by showing that a quantum system which evolves through a circuit C in projective Hilbert space acquires a geometrical phase βべーた(C) related to the topology of the space and the geometry of the circuit. We present NMR interferometry experiments in a three-level system which demonstrate the Aharonov-Anandan phase and its topological invariance for different circuits