In 1922, Thomas Edison publicly introduced his latest invention—a new type of money, a commodity-backed currency that he believed was the long-term solution to America's monetary woes. “I want to cast the variable out of money. This gold money is not good enough. It's a fiction” he boldly proclaimed (New York Times 1922).

X-Ray Absorption Spectroscopy (XAS) and Photoelectron Spectroscopy (PES) have been performed upon highly radioactive samples, particularly Plutonium, at the Advanced Light Source in Berkeley, CA, USA. First results from alpha and delta Plutonium are reported as well as a detailed analysis of sample quality.

The stationarity conditions for an autoregressive (AR) process in general are reduced to a remarkably simple inequality if the lag coefficients are restricted to be identical. The condition is not only analytically elegant but also applicable in checking the validity of the stationarity conditions for such a restricted AR process of any order.We are deeply indebted to Professor Paolo Paruolo, NP co-editor of Econometric Theory, and anonymous referees for constructive comments and suggestions that led to significant improvements. Errors, if any, are solely ours.

The electronic structure of δ-phase Pu metal and the Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Excellent agreement between calculation and experiment defines a path forward for understanding electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. A comparison is made between the photoemission data and five computational schemes for δ-Pu. The results for δ-Pu and PuCoGa5 indicate 5f electron behavior on the threshold between localized and itinerant and a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.

We have used the embedded-atom method (EAM) to perform molecular-dynamics (MD) simulations of iron films grown on Cu (111). The iron atoms were randomly deposited, one at a time, above the surface just within the force range of the nearest surface atom. The growth mode is discussed by following the iron film coverage for an incident-atom energy ranged from 0.5eV to 15eV. A transition from island to layer by layer growth is observed as a function of incident energy. The effect of deposition rate is also studied.

Epitaxial PbZr0.5Ti0.5O3 (PZT) thin films were grown on top of a SrRuO3 epitaxial electrode layer on a (100) SrTiO3 substrate by the chemical solution deposition method at 600 °C. The microstructure of the PZT thin film was investigated by x-ray diffraction and transmission electron microscopy, and the ferroelectric properties were measured using the Ag/PZT/SRO capacitor structure. The PZT thin film has the epitaxial orientational relationship of (001) [010]PZT ║ (001) [010]SRO ║ (001) [010]STO with the substrate. The remnant (Pr ) and saturation polarization (Ps) density were measured to be Pr ~ 51.4 µC/cm2 and Ps ~ 62.1 µC/cm2 at 5 V, respectively. Ferroelectric fatigue measurements show that the net-switching polarization begins to drop (to 98% of its initial value) after 7 × 108 cycles.

We discuss the implementation of classical molecular dynamics simulations on Single- Instruction Multiple-Data computers with two-dimensional mesh connectivity. Specific timing results are given for the MasPar MP-1, complemented by a general time complexity analysis. Our main interest is in simulations with a number of particles N that is comparable to the number of processors P. In particular, we discuss results for large Si-clusters with up to 2000 particles, using a Stillinger-Weber potential. Particular attention is paid to the problem of handling in an efficient way the calculation of the three-body potential and force.

We have calculated the effective cluster interactions (ECI) which govern the ordering of Ir adatoms on the Ir(111) surface. The computations are based on a tight-binding Hamiltonian in which no adjustable or experimentally determined parameters were introduced. Both atoms adsorbed in ‘bulk’ sites (i.e. continuing the fee lattice) and those in ‘surface’ sites (i.e. producing hep stacking) are considered. We use this formalism to determine the relative stability of various adsorption sites and cluster shapes at zero temperature. The overall trends are in excellent agreement with the experimental results found by Ehrlich and co-workers. Next, we employ these ECI in Monte Carlo simulations of the kinetics of domain growth and evolution. Specifically we analyze the effect of diffusion barriers and the competition between the ordering tendencies of the system and entropic effects. Typical ‘snapshots’ in a range of temperatures and coverages are discussed.

We report the results of Monte Carlo simulations of the kinetics of surface segregation at the (001) face of CuNi and MoW alloys. These two systems were selected because they are based on different lattice structures and show contrasting segregation behavior: CuNi exhibits a monotonie profile, while that of MoW is oscillatory. To describe the energetics we have determined a set of effective cluster interactions (ECI) which govern the ordering or clustering tendencies of these alloys. The ECI were obtained by means of tight-binding electronic structure calculations in which no adjustable or experimentally determined parameters were used. Equilibrium segregation profiles are calculated and a series of quenches are performed. The layer concentrations are studied as a function of time and the existence of metastable phases in the surface region is investigated.

Results from a multicomponent Monte Carlo simulation of the deposition and growth of YBa2Cu3O7 are presented and discussed. In particular, a detailed examination of the growth modes active during different morphological growth conditions is performed. At higher deposition rates, both [001] and [100] epitaxial variants (‘c’ and ‘a’ type growth, respectively) are observed to grow by modes attributed to the classic Volmer-Weber mechanism. At very low deposition rates, the film is observed to grow in a distinct, cyclic, multi-stage process. Small islands of [001] epitaxy nucleate and grow to one unit cell height followed by primarily horizontal growth or “ledge extension” until one unit cell layer has formed. This process then repeats. Simulated RHEED amplitude data from this growth process compares favorably to experimentally obtained data.

Using large-scale molecular dynamics simulation on a massively parallel computer, we have studied the initiation of cracking in a Monel-like alloy of Cu-Ni. In a low temperature 2D sample, fracture from a notch starts at a little beyond 2.5% critical strain when the propagation direction is perpendicular to a cleavage plane. We discuss a method of characterizing crack tip position using a measure of area around the crack tip.

We report the results of computer simulations of phase transitions in noble-gas clusters. The calculations were performed on a MasPar MP-l massively parallel computer with 8,192 processing elements (PE's). We discuss the efficient implementation of molecular dynamics algorithms for small clusters on this type of architecture. The simulations are based on a classical Lennard-Jones pair potential and follow the temporal evolution of the system by numerically integrating Newton's equations of motion using the Gear algorithm. Because the number of particles is much smaller than the number of PE's, optimal partitioning of the processing element array is an essential and non-trivial task.

Algorithmic considerations regarding the implementation of various materials science applications of the Monte Carlo technique to single instruction multiple data (SIMD) computer architectures are presented. In particular, implementation of the Ising model with nearest, next nearest. and long range screened Coulomb interactions on the SIMD architecture MasPar MP-1 (DEC mpp-12000) series of massively parallel computers is demonstrated. Methods of code development which optimize processor array use and minimize inter-processor communication are presented including lattice partitioning and the use of processor array spanning tree structures for data reduction. Both geometric and algorithmic parallel approaches are utilized. Benchmarks in terms of Monte Carlo updates per second for the MasPar architecture are presented and compared to values reported in the literature from comparable studies on other architectures.

The finite temperature properties of a two-dimensional flux lattice are studied by Monte Carlo simulation, with particular attention to the effects of twin-boundaries. The parameters selected are appropriate for the YBa 2 Cu 3 O 7 high-temperature superconducting system. The intrinsic properties of the vortex state are investigated by monitoring system evolution at fixed temperature and applied magnetic field. By varying the temperature, the loss of type-II superconductivity via fluxoid lattice melting is also examined. The introduction of model defects induces the creation of metastable and glassy states which reduce overall hexatic order but are found to enhance system resistance to flux-lattice melting.

The results of systematic computer simulations of the deposition and growth of Y-Ba-Cu-0 thin films is reported. The deposition process is modeled by means of a three-step Monte Carlo simulation incorporating one sorption deposition mode and two modes of film annealing addressing surface and bulk diffusion. The simulation is used to investigate the evolution of surface morphology and film microstructure, growth rate anisotropy, and the dependence of film texture on deposition parameters. Characteristic defects and surface morphologies observed by simulation are found to be in good agreement with those observed experimentally. It is observed that surface kinetics can dominate the evolution of film microstructure.

High resolution transmission electron microscopy (HRTEM) is used to investigate the transformation mechanism responsible for the occurrence of the many stable layered phases in the pseudo-binary Y2Ba4Cu6+xO14+x system. In particular, HRTEM results are compared with microstructural configurations generated by an earlier theoretical study which modeled this transformation by means of an intercalation mechanism. HRTEM images of partially transformed Y-Ba-Cu-O reveal that the predominant structural change is limited to the CuO planes. The location of the transformation front, revealed in the micrographs by the presence of these partial dislocations, suggests that the transformation is nucleated at grain boundaries and internal surfaces within the material. The observation of local CuO layer ordering along the [001] direction is taken as evidence for the presence of longer range interactions. A two-dimensional approximation to the bulk Monte Carlo simulation incorporating long range screened Coulomb [001] interactions is used to investigate the possibility and nature of local, transient stage orderings.

High resolution electron microscopy is used to investigate the effect of electron irradiation induced oxygen loss on the states of partial order in YBa2Cu3Oz. Contrast effects visible in the [001] zone image as a result of the degree of the out-of-plane correlation of these ordered states are investigated. Using statistical simulations to aid in the analysis of the HREM images, an interpretation based on a kinetically limited evolution of the variation of long range [001] ordering is proposed.

We have performed a number of first principles electronic structure calculations for YBa 2Cu 3O7_y with different oxygen orderings and concentrations. The resulting total energies have been used to assess the applicability of some of the proposed models for oxygen ordering in this system. We find that the results are consistent with an Ising-like model with asymmetric next-neighbor interactions between oxygen sites. We determine effective interaction parameters from the first principles calculations and use them to compute the phase diagram for the system, which is in excellent agreement with experiment for the tetragonal-orthorhombic I transition.