Domain Growth in Random Magnets

We study the kinetics of domain growth in ferromagnets with random exchange interactions. We present detailed Monte Carlo results for the nonconserved random-bond Ising model, which are consistent with power-law growth with a variable exponent. These results are interpreted in the context of disorder barriers with a logarithmic dependence on the domain size. Further, we clarify the implications of logarithmic barriers for both nonconserved and conserved domain growth.Comment: 7 pages, 4 figure

Walking the Talk: A Guide to Assessment Using the CAPRA Community Problem Solving Model

CAPRA is a community problem-solving model with five stages: C = Clients, A = Analysis, P = Partnership, R = Response, and A = Assessment. CAPRA was the problem-solving method used by the Alaska Native and Technical Resource Center (ANTARC). This guide describes the final stage of the CAPRA model—assessment—including the reasons for conducing an assessment, the documentation needed and why it is needed, and methods for evaluation. Discussion is with a particular focus on assessment methods for community problem-solvers in rural Alaska Native villages. Some background about CAPRA is assumed.What is Assessment? / Why do we do Assessment? / Assessment = Documentation + Evaluation / Documentation / Evaluation / How Do We Deal With those Who Object to Assessment? / What DO We Do With Our Assessment? / Conclusio

Bifurcation analysis in an associative memory model

We previously reported the chaos induced by the frustration of interaction in a non-monotonic sequential associative memory model, and showed the chaotic behaviors at absolute zero. We have now analyzed bifurcation in a stochastic system, namely a finite-temperature model of the non-monotonic sequential associative memory model. We derived order-parameter equations from the stochastic microscopic equations. Two-parameter bifurcation diagrams obtained from those equations show the coexistence of attractors, which do not appear at absolute zero, and the disappearance of chaos due to the temperature effect.Comment: 19 page

Instability analysis procedure for 3-level multi-bearing rotor-foundation systems

A procedure for the instability analysis of a three-level multispan rotor systems is described. This procedure is based on a distributed mass elastic representation of the rotor system in several eight-coefficient bearings. Each bearing is supported from an elastic foundation on damped, elastic pedestals. The foundation is represented as a general distributed mass elastic structure on discrete supports, which may have different stiffness and damping properties in the horizontal and vertical directions. This system model is suited to studies of instability threshold conditions for multirotor turbomachines on either massive or flexible foundations. The instability conditions is found by obtaining the eigenvalues of the system determinant, which is obtained by the transfer matrix method from the three-level system model. The stability determinant is solved for the lowest rotational speed at which the system damping becomes zero in the complex eigenvalue, and for the whirl frequency corresponding to the natural frequency of the unstable mode. An efficient algorithm for achieving this is described. Application of this procedure to a rigid rotor in two damped-elastic bearings and flexible supports is described. A second example discusses a flexible rotor with four damped-elastic bearings. The third case compares the stability of a six-bearing 300 Mw turbine generator unit, using two different bearing types. These applications validate the computer program and various aspects of the analysis

Alaska Native Technical Assistance and Resource Center: Final Report

Too often, federal and state justice programs directed at rural, predominately Alaska Native villages do not sufficiently coordinate planning and funding, and are not tailored to fit local cultures and needs. The language and institutional contexts of granting agencies and requests for proposals for grants frame justice problems and their solutions in ways that may or may not relate to the experiences of Alaska Native villages. The Alaska Native Technical Resource Center (ANTARC) was designed as a three-year project to improve village capacity to identify problems and educate the university and granting agencies about the nature of their justice problems and the resources needed to implement solutions. The initial group involved the Justice Center and four rural communities — Gulkana, Kotlik, Wainwright, and Yakutat — with representatives from the communities chosen by village leaders. This report examines ANTARC's evolution, considers its implementation, evaluates the results, and presents recommendations for promoting effective change in Alaska Native villages.Bureau of Justice Assistance, United States Department of Justice Award No. 1999-LB-VX-002Introduction / The Evolution of Antarc / Structure of the Project / Implementation / Evaluating Results / Concluding Recommendations / References / Appendix 1: Proceedings of the March 1999 Antarc Workshop / Appendix 2: Proceedings of the November 1999 Antarc Workshop / Appendix 3: Capra Training Materials / Appendix 4: Evaluation Training Workshop Material

VERITAS Observations of the Coma Cluster of Galaxies

Clusters of galaxies are one of the few prominent classes of objects predicted to emit gamma rays not yet detected by satellites like EGRET or ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs). The detection of Very High Energy (VHE, E > 100 GeV) gamma rays from galaxy clusters would provide insight into the morphology of non-thermal particles and fields in clusters. VERITAS, an array of four 12-meter diameter IACTs, is ideally situated to observe the massive Coma cluster, one of the best cluster candidates in the Northern Hemisphere. This contribution details the results of VERITAS observations of the Coma cluster of galaxies during the 2007-2008 observing season.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008

Path integral Monte Carlo study of the interacting quantum double-well model: Quantum phase transition and phase diagram

The discrete time path integral Monte Carlo (PIMC) with a one-particle density matrix approximation is applied to study the quantum phase transition in the coupled double-well chain. To improve the convergence properties, the exact action for a single particle in a double well potential is used to construct the many-particle action. The algorithm is applied to the interacting quantum double-well chain for which the zero-temperature phase diagram is determined. The quantum phase transition is studied via finite-size scaling and the critical exponents are shown to be compatible with the classical two-dimensional (2D) Ising universality class -- not only in the order-disorder limit (deep potential wells) but also in the displacive regime (shallow potential wells).Comment: 17 pages, 7 figures; Accepted for publication in Phys. Rev.

The influence of the Alfv\'enic drift on the shape of cosmic ray spectra in SNRs

Cosmic ray acceleration in SNRs in the presence of the Alfv\'enic drift is considered. It is shown that spectra of accelerated particles may be considerably softer in the presence of amplified magnetic fields.Comment: 4 pages, 4 figures, poster talk at 4-th Gamma-ray Symposium (Heidelberg, Germany, 7-11th of July 2008

Central engines of Gamma Ray Bursts. Magnetic mechanism in the collapsar model

In this study we explore the magnetic mechanism of hypernovae and relativistic jets of long duration gamma ray bursts within the collapsar scenario. This is an extension of our earlier work [1]. We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state and takes into account the cooling associated with emission of neutrinos and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe solutions with different black hole rotation, mass accretion rate, and strength of progenitor's magnetic field. Some of them exhibits strong explosions driven by Poynting-dominated jets with power up to $12\times10^{51} {erg s}^{-1}$. These jets originate from the black hole and powered via the Blandford-Znajek mechanism. A provisional criterion for explosion is derived. A number of simulation movies can be downloaded from http://www.maths.leeds.ac.uk/~serguei/research/movies/anim.htmlComment: 4 pages, 3 figures, GAMMA08 Heidelberg Symposiu