[en] We present a parallel decomposition of the tight-binding fictitious Lagrangian algorithm for the Intel iPSC/860 and the Intel Paragon parallel computers. We show that it is possible to perform long simulations, of the order of 10 000 time steps, on semiconducting clusters consisting of as many as 512 atoms, on a time scale of the order of 20 h or less. We have made a very careful timing analysis of all parts of our code, and have identified the bottlenecks. We have also derived formulas which can predict the timing of our code, based on the number of processors, message passing bandwidth, floating point performance of each node, and the set up time for message passing, appropriate to the machine being used. The time of the simulation scales as the square of the number of particles, if the number of processors is made to scale linearly with the number of particles. We show that for a system as large as 512 atoms, the main bottleneck of the computation is the orthogonalization of the wave functions, which consumes about 90% of the total time of the simulation

[en] An n-fold-way algorithm for the Ising model in a square lattice with anisotropic interactions is discussed. This algorithm shows an improved computational performance at low temperature

[en] The physics departments of a consortium of higher education in Western Massachusetts, the Five Colleges Incorporated, are developing an advanced undergraduate laboratory course. The participating institutions are Amherst College, Mount Holyoke College, Smith College, and the University of Massachusetts. The course is designed to expose students to a variety of state-of-the-art equipment that would normally exceed reasonable financial commitments and faculty expertise of a single institution. The course is divided into experimental modules, one of which is the cosmic ray muon decay module developed at Smith College. The module is designed to investigate the dependence of the muon lifetime as a function of the medium in which it decays. Useful background information and a description of the module is given in this article

[en] The putative ability of cosmic strings to act as seeds for galaxies depends on the efficiency of a number of processes that produce an initial network of strings and then allow them to evolve to a population that can act as condensation centers. Here the classical field theory of the interaction of cosmic strings is studied. A limited survey of numerical evolutions has been carried out. Calculations have been carried out showing parallel string--string repulsion; string--antistring (i.e., antiparallel string) annihilation with initial velocity v = 0 and v = 0.75; string--string collision at right angles with v/c = 0.1, 0.5, 0.75, 0.85, 0.9c, with v/c = 0.75 at θ = π/4 and at θ = 3π/4, and with v/c = 0.9 at θ = 7π/8; and string--string and string--antistring collisions with v/c = 0.9 and v/c = 0.95. Intercommutation occurs in all situations so far investigated except that string--antistring collision with v/capprox. >0.90 apparently leads to reemergence, i.e., no intercommutation. All simulations have a ''sombrero'' potential V (phi) = λ(chemical bondphichemical bond²-σ²)² and a gauge field coupling e. (The numerical results are obtained with λ = 0.01, e = 0.2, giving the gauge field a slightly longer scale length than that of the scalar field.)

[en] We present an elementary introduction to the boundary element method (BEM). We use the BEM to calculate the electromagnetic field enhancements in the vicinity of metallic wires of arbitrary cross-section. The local electric field shows resonant peaks, as a function of the frequency of incident radiation, at the natural frequencies of the electronic plasma in the wires. We consider the effect of the shape of the cross-section of the wire on the resonant frequency, the proximity effect due to neighboring wires, and the influence of a substrate. The calculations are performed using enhanced continuity conditions at the boundaries. We discuss the advantages of such an approach. The field enhancements are predicted for a number of geometries. copyright 1996 American Institute of Physics

[en] A hybrid Monte Carlo simulation method consisting of kinetic and equilibrium moves is presented. The method is applicable to any system involving N different processes whose rates may vary by orders of magnitude. We show that the method easily permits the propagation of the system through macroscopic time scales by application to a study of chemical vapor deposition diamond-film growth. The application is an off-lattice simulation utilizing CH₃ as the growth species on a diamond [111] surface, and incorporating a computationally expensive, many-body potential surface. We show that, by using our method, it is possible to simulate a continuous system of several thousand atoms, with no underlying grid and with a realistic potential for times on the order of milliseconds. The growth rate of the simulated surface is consistent with experimental growth rates, and the simulation sheds light on possible morphologies during the early stages of diamond film formation. copyright 1996 American Institute of Physics

[en] A Mathematica notebook for describing the time evolution and decay of the hydrogen n=2 states in the presence of a weak external electric field is presented. The work involves (1) solving a set of differential equations coupled by the Hamiltonian of the external electric field and (2) deriving a set of formulas for a complete description of the polarization state of the emitted photons. It is demonstrated how problems with such complexity can be treated with ease and in an error-free manner by using symbolic software such as Mathematica. copyright 1996 American Institute of Physics

[en] This paper shows how to use the symbol manipulator MACSYMA to do arbitrarily long calculations and how to translate the typically lengthy results into FORTRAN so that they can be tested, appreciated, and used. This procedure is illustrated by its application to the task of writing the code for a noncompact lattice simulation of a nonabelian gauge theory

[en] Algorithms are given for comformational optimization of proteins. The protein folding problems is regarded as a problem of global energy mimimization. Since proteins have hundreds of atoms, finding the lowest-energy conformation in a many-dimensional configuration space becomes a computationally demanding problem.copyright American Institute of Physics

[en] A computer program for calculating fundamental properties of nuclei in the face-centered-cubic (fcc) nuclear model is presented. The program generates nucleon coordinate values in agreement with the empirical build-up sequence and then calculates three nuclear properties for any specified nucleus: the rms radial value, the total Coulomb repulsion, and the total binding energy