Replica Monte Carlo Simulation (Revisited)

In 1986, Swendsen and Wang proposed a replica Monte Carlo algorithm for spin glasses [Phys. Rev. Lett. 57 (1986) 2607]. Two important ingredients are present, (1) the use of a collection of systems (replicas) at different of temperatures, but with the same random couplings, (2) defining and flipping clusters. Exchange of information between the systems is facilitated by fixing the tau spin (tau=sigma^1\sigma^2) and flipping the two neighboring systems simultaneously. In this talk, we discuss this algorithm and its relationship to replica exchange (also known as parallel tempering) and Houdayer's cluster algorithm for spin glasses. We review some of the early results obtained using this algorithm. We also present new results for the correlation times of replica Monte Carlo dynamics in two and three dimensions and compare them with replica exchange.Comment: For "Statistical Physics of Disordered Systems and Its Applications", 12-15 July 2004, Shonan Village Center, Hayama, Japan, 7 page

Propagation loss on a Si-Slab Waveguide: Simulation revisited

Slab waveguide is one of the simplest types of optical waveguide, the confinement factor is only determined by the thickness of one side so that the propagation of light passing through it will be confined in the material. The slab waveguide is built from Si as the core material and SiO2 as the substrate. The use of various optical waveguides is very dependent on the objectives to be achieved in its application, for it is very important to know the characteristics of each optical waveguide. In this paper the writer wants to know the characteristics of a slab waveguide, specifically with regard to propagation loss. The simulation results show that the propagation loss in the slab waveguide design that the authors propose is around 0.1dB / mm in TE mode conditions. The occurrence of propagation loss in the simulation is likely due to imperfections in determining the effective material index in the design of the slab waveguide

The Percolation Signature of the Spin Glass Transition

Magnetic ordering at low temperature for Ising ferromagnets manifests itself within the associated Fortuin-Kasteleyn (FK) random cluster representation as the occurrence of a single positive density percolating network. In this paper we investigate the percolation signature for Ising spin glass ordering -- both in short-range (EA) and infinite-range (SK) models -- within a two-replica FK representation and also within the different Chayes-Machta-Redner two-replica graphical representation. Based on numerical studies of the $\pm J$ EA model in three dimensions and on rigorous results for the SK model, we conclude that the spin glass transition corresponds to the appearance of {\it two} percolating clusters of {\it unequal} densities.Comment: 13 pages, 6 figure

An Algorithm for Probabilistic Alternating Simulation

In probabilistic game structures, probabilistic alternating simulation (PA-simulation) relations preserve formulas defined in probabilistic alternating-time temporal logic with respect to the behaviour of a subset of players. We propose a partition based algorithm for computing the largest PA-simulation, which is to our knowledge the first such algorithm that works in polynomial time, by extending the generalised coarsest partition problem (GCPP) in a game-based setting with mixed strategies. The algorithm has higher complexities than those in the literature for non-probabilistic simulation and probabilistic simulation without mixed actions, but slightly improves the existing result for computing probabilistic simulation with respect to mixed actions.Comment: We've fixed a problem in the SOFSEM'12 conference versio

Critical behavior of the random-anisotropy model in the strong-anisotropy limit

We investigate the nature of the critical behavior of the random-anisotropy Heisenberg model (RAM), which describes a magnetic system with random uniaxial single-site anisotropy, such as some amorphous alloys of rare earths and transition metals. In particular, we consider the strong-anisotropy limit (SRAM), in which the Hamiltonian can be rewritten as the one of an Ising spin-glass model with correlated bond disorder. We perform Monte Carlo simulations of the SRAM on simple cubic L^3 lattices, up to L=30, measuring correlation functions of the replica-replica overlap, which is the order parameter at a glass transition. The corresponding results show critical behavior and finite-size scaling. They provide evidence of a finite-temperature continuous transition with critical exponents $\eta_o=-0.24(4)$ and $\nu_o=2.4(6)$. These results are close to the corresponding estimates that have been obtained in the usual Ising spin-glass model with uncorrelated bond disorder, suggesting that the two models belong to the same universality class. We also determine the leading correction-to-scaling exponent finding $\omega = 1.0(4)$.Comment: 24 pages, 13 figs, J. Stat. Mech. in pres

Ergonomic Simulation Revisited Using Parametric Virtual Humans in the Biomechanical Framework

The conventional CAD/CAM approach to design does not show the essential spatial relationships between user and product that are crucial for intuitive design analysis. As populations age and the home appliance market stagnates, Universal Design principles implemented with computerized virtual worlds become more important for meeting the ergonomic problems of heterogeneous populations that are increasingly difficult to adequately test with real-world subjects. Digital Human Modelling (DHM) is an emerging area that bridges computer-aided engineering design, human factors engineering and applied ergonomics. The most advanced forms of this technology are being used by many researchers for practical applications, including ergonomic analysis. However, a state of the art model of this technology has never been conceived for the conceptual design stage of a product development cycle as most conventional DHM techniques lack real time interaction, require considerable user intervention, and have inefficient control facilities and non-adequate validation techniques, all contributing to slow production pipelines. They have also not addressed the needs of the growing ageing population in many societies across the globe. The focus of this dissertation is to introduce a complete framework for ergonomic simulation at the conceptual design stage of a product development cycle based on parametric virtual humans in a prioritized inverse kinematics framework while taking biomechanical knowledge in to account. Using an intuitive control facility, design engineers can input a simple CAD model, design variables and human factors in to the system. The evaluation engine generates the required simulation in real-time by making use of an Anthropometric Database, Physical Characteristic Database and Prioritized Inverse Kinematics architecture. The key components of the total system are described and the results are demonstrated with a few applications such as kitchen, wash-basin and bath-tub. By introducing a quantitative estimation of ageing algorithm for anthropometric digital human models, products can be designed from the start to suit the ergonomic needs of the user rather than the biases and assumptions of the designer. Also, by creating a tool that can be used intuitively by non-specialists in a dynamic, real-time environment, designers can stop relying on specialists to test the safety of their ideas and start to effectively use data about populations to discover designs that can be used more easily by more people. Results have been validated with real human subjects indicating the practical implication of the total system as an ergonomic design tool for the conceptual design stage of a product development cycle