The Experts below are selected from a list of 2646 Experts worldwide ranked by ideXlab platform
Naoki Kawashima - One of the best experts on this subject based on the ideXlab platform.
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modification of directed Loop Algorithm for continuous space simulation of bosonic systems
Physical Review E, 2007Co-Authors: Yasuyuki Kato, Takafumi Suzuki, Naoki KawashimaAbstract:We modify the directed-Loop Algorithm (DLA) to solve the problem that typically arises from large on-site interaction. The large on-site interaction is inevitable when one tries to simulate a Bose gas system in continuum by discretizing the space with small lattice spacings. While the efficiency of a straightforward application of DLA decreases as the mesh becomes finer, the performance of the new method does not depend on it except for the trivial factor due to the increase in the number of lattice points.
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Recent developments of world-line Monte Carlo methods
Journal of the Physical Society of Japan, 2004Co-Authors: Naoki Kawashima, Kenji HaradaAbstract:World-line quantum Monte Carlo methods are reviewed with an emphasis on breakthroughs made in recent years. In particular, three Algorithms – the Loop Algorithm, the worm Algorithm, and the directed-Loop Algorithm – for updating world-line configurations are presented in a unified perspective. Detailed descriptions of the Algorithms in specific cases are also given.
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Coarse-grained Loop Algorithms for Monte Carlo simulation of quantum spin systems.
Physical review. E Statistical nonlinear and soft matter physics, 2002Co-Authors: Kenji Harada, Naoki KawashimaAbstract:Recently, Syljuåsen and Sandvik [Phys. Rev. E. (to be published)] proposed a new framework for constructing Algorithms of quantum Monte Carlo simulation. While it includes new classes of powerful Algorithms, it is not straightforward to find an efficient Algorithm for a given model. Based on their framework, we propose an Algorithm that is a natural extension of the conventional Loop Algorithm with the split-spin representation. A complete table of the vertex density and the worm-scattering probability is presented for the general XXZ model of an arbitrary S with a uniform magnetic field.
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Loop Algorithm for Heisenberg Models with Biquadratic Interaction and Phase Transitions in Two Dimensions
Journal of the Physical Society of Japan, 2001Co-Authors: Kenji Harada, Naoki KawashimaAbstract:We present a new Algorithm for quantum Monte Carlo simulation based on global updating with Loops. While various theoretical predictions are confirmed in one dimension, we find, for S = 1 systems on a square lattice with an antiferromagnetic biquadratic interaction, that the intermediate phase between the antiferromagnetic and the ferromagnetic phases is disordered and that the two phase transitions are both of the first order in contrast to the one-dimensional case. It is strongly suggested that the transition points coincide with those at which the Algorithm changes qualitatively.
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Quantum Monte Carlo Loop Algorithm for the t-J model
Physical Review B, 1998Co-Authors: Beat Ammon, Hans Gerd Evertz, Naoki Kawashima, Matthias Troyer, Beat FrischmuthAbstract:We propose a generalization of the Quantum Monte Carlo Loop Algorithm to the t-J model by a mapping to three coupled six-vertex models. The autocorrelation times are reduced by orders of magnitude compared to the conventional local Algorithms. The method is completely ergodic and can be formulated directly in continuous time. We introduce improved estimators for simulations with a local sign problem. Some first results of finite temperature simulations are presented for a t-J chain, a frustrated Heisenberg chain, and t-J ladder models.
Hiroshi Shinaoka - One of the best experts on this subject based on the ideXlab platform.
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Loop Algorithm for classical antiferromagnetic Heisenberg models with biquadratic interactions
arXiv: Statistical Mechanics, 2011Co-Authors: Hiroshi Shinaoka, Yusuke Tomita, Yukitoshi MotomeAbstract:Monte Carlo simulation using the standard single-spin flip Algorithm often fails to sample over the entire configuration space at low temperatures for frustrated spin systems. A typical example is a class of spin-ice type Ising models. In this case, the difficulty can be avoided by introducing a global-flip Algorithm, the Loop Algorithm. Similar difficulty is encountered in O(3) Heisenberg models in the presence of biquadratic interaction. The Loop Algorithm, however, is not straightforwardly applied to this case, since the system does not have a priori spin-anisotropy axis for constructing the Loops. We propose an extension of the Loop Algorithm to the bilinear-biquadratic models. The efficiency is tested for three different ways to flip spins on a Loop in Monte Carlo simulation. We show that the most efficient method depends on the strength of the biquadratic interaction.
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Extended Loop Algorithm for pyrochlore Heisenberg spin models with spin-ice type degeneracy: application to spin-glass transition in antiferromagnets coupled to local lattice distortions
arXiv: Statistical Mechanics, 2011Co-Authors: Hiroshi ShinaokaAbstract:For Ising spin models which bear the spin-ice type macroscopic (quasi-)degeneracy, conventional classical Monte Carlo (MC) simulation using single spin flips suffers from dynamical freezing at low temperatures ($T$). A similar difficulty is seen also in a family of Heisenberg spin models with easy-axis anisotropy or biquadratic interactions. In the Ising case, the difficulty is avoided by introducing a non-local update based on the Loop Algorithm. We present an extension of the Loop Algorithm to the Heisenberg case. As an example of its application, we review our recent study on spin-glass (SG) transition in a bond-disordered Heisenberg antiferromagnet coupled to local lattice distortions.
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Loop Algorithm for classical Heisenberg models with spin-ice type degeneracy
Physical Review B, 2010Co-Authors: Hiroshi Shinaoka, Yukitoshi MotomeAbstract:In many frustrated Ising models, a single-spin flip dynamics is frozen out at low temperatures compared to the dominant interaction energy scale because of the discrete "multiple valley" structure of degenerate ground-state manifold. This makes it difficult to study low-temperature physics of these frustrated systems by using Monte Carlo simulation with the standard single-spin flip Algorithm. A typical example is the so-called spin ice model, frustrated ferromagnets on the pyrochlore lattice. The difficulty can be avoided by a global-flip Algorithm, the Loop Algorithm, that enables to sample over the entire discrete manifold and to investigate low-temperature properties. We extend the Loop Algorithm to Heisenberg spin systems with strong easy-axis anisotropy in which the ground-state manifold is continuous but still retains the spin-ice type degeneracy. We examine different ways of Loop flips and compare their efficiency. The extended Loop Algorithm is applied to the following two models, a Heisenberg antiferromagnet with easy-axis anisotropy along the z axis, and a Heisenberg spin ice model with the local easy-axis anisotropy. For both models, we demonstrate high efficiency of our Loop Algorithm by revealing the low-temperature properties which were hard to access by the standard single-spin flip Algorithm. For the former model, we examine the possibility of order-from-disorder and critically check its absence. For the latter model, we elucidate a gas-liquid-solid transition, namely, crossover or phase transition among paramagnet, spin-ice liquid, and ferromagnetically-ordered ice-rule state.
Hans Gerd Evertz - One of the best experts on this subject based on the ideXlab platform.
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the Loop Algorithm
Advances in Physics, 2003Co-Authors: Hans Gerd EvertzAbstract:A review of the Loop Algorithm , its generalizations, and its relation to some other Monte Carlo techniques is given. The Loop Algorithm is a quantum Monte Carlo procedure that employs non-local changes of worldline configurations, determined by local stochastic decisions. It is based on a formulation of quantum models of any dimension in an extended ensemble of worldlines and graphs, and is related to Swendsen-Wang Algorithms. It can be represented directly on an operator level, both with a continuous imaginary time path integral and with the stochastic series expansion. It overcomes many of the difficulties of traditional worldline simulations. Autocorrelations are reduced by orders of magnitude. Grand-canonical ensembles, off-diagonal operators, and variance reduced estimators are accessible. In some cases, infinite systems can be simulated. For a restricted class of models, the fermion sign problem can be overcome. Transverse magnetic fields are handled efficiently, in contrast to strong diagonal fiel...
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Quantum Monte Carlo Loop Algorithm for the t-J model
Physical Review B, 1998Co-Authors: Beat Ammon, Hans Gerd Evertz, Naoki Kawashima, Matthias Troyer, Beat FrischmuthAbstract:We propose a generalization of the Quantum Monte Carlo Loop Algorithm to the t-J model by a mapping to three coupled six-vertex models. The autocorrelation times are reduced by orders of magnitude compared to the conventional local Algorithms. The method is completely ergodic and can be formulated directly in continuous time. We introduce improved estimators for simulations with a local sign problem. Some first results of finite temperature simulations are presented for a t-J chain, a frustrated Heisenberg chain, and t-J ladder models.
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A NONLOCAL APPROACH TO VERTEX MODELS AND QUANTUM SPIN SYSTEMS
International Journal of Modern Physics C, 1993Co-Authors: Hans Gerd Evertz, Mihai MarcuAbstract:We discuss the Loop-Algorithm, a new type of cluster Algorithm that reduces critical slowing down in vertex models and in quantum spin systems. We cover the example of the 6-vertex model in detail. For the F-model, we present numerical results that demonstrate the effectiveness of the Loop Algorithm. We show how to modify the original Algorithm for some more complicated situations, especially for quantum spin systems in one and two dimensions, and we discuss parallelization.
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Vertex Models and Quantum-Spin Systems: A Nonlocal Approach
arXiv: Condensed Matter, 1993Co-Authors: Hans Gerd Evertz, Mihai MarcuAbstract:Within a general cluster framework, we discuss the Loop-Algorithm, a new type of cluster Algorithm that reduces critical slowing down in vertex models and in quantum spin systems. We cover the example of the 6-vertex model in detail. For the F-model, we present numerical results that demonstrate the effectiveness of the Loop Algorithm. We discuss how to modify the original Algorithm for some more complicated situations, especially for quantum spin systems in one and two dimensions.
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Cluster Algorithm for vertex models
Physical Review Letters, 1993Co-Authors: Hans Gerd Evertz, Gideon Lana, Mihai MarcuAbstract:We present a new type of cluster Algorithm that strongly reduces critical slowing down in simulations of vertex models. Since the clusters are closed paths of bonds, we call it the Loop Algorithm. The basic steps in constructing a cluster are the breakup and the freezing of vertices. We concentrate on the case of the F model, which is a subset of the six-vertex model exhibiting a Kosterlitz-Thouless transition. The Loop Algorithm is also applicable to simulations of other vertex models and of one- and two-dimensional quantum spin systems
Mihai Marcu - One of the best experts on this subject based on the ideXlab platform.
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A NONLOCAL APPROACH TO VERTEX MODELS AND QUANTUM SPIN SYSTEMS
International Journal of Modern Physics C, 1993Co-Authors: Hans Gerd Evertz, Mihai MarcuAbstract:We discuss the Loop-Algorithm, a new type of cluster Algorithm that reduces critical slowing down in vertex models and in quantum spin systems. We cover the example of the 6-vertex model in detail. For the F-model, we present numerical results that demonstrate the effectiveness of the Loop Algorithm. We show how to modify the original Algorithm for some more complicated situations, especially for quantum spin systems in one and two dimensions, and we discuss parallelization.
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Vertex Models and Quantum-Spin Systems: A Nonlocal Approach
arXiv: Condensed Matter, 1993Co-Authors: Hans Gerd Evertz, Mihai MarcuAbstract:Within a general cluster framework, we discuss the Loop-Algorithm, a new type of cluster Algorithm that reduces critical slowing down in vertex models and in quantum spin systems. We cover the example of the 6-vertex model in detail. For the F-model, we present numerical results that demonstrate the effectiveness of the Loop Algorithm. We discuss how to modify the original Algorithm for some more complicated situations, especially for quantum spin systems in one and two dimensions.
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Cluster Algorithm for vertex models
Physical Review Letters, 1993Co-Authors: Hans Gerd Evertz, Gideon Lana, Mihai MarcuAbstract:We present a new type of cluster Algorithm that strongly reduces critical slowing down in simulations of vertex models. Since the clusters are closed paths of bonds, we call it the Loop Algorithm. The basic steps in constructing a cluster are the breakup and the freezing of vertices. We concentrate on the case of the F model, which is a subset of the six-vertex model exhibiting a Kosterlitz-Thouless transition. The Loop Algorithm is also applicable to simulations of other vertex models and of one- and two-dimensional quantum spin systems
Carlos Gustavo C. Branco - One of the best experts on this subject based on the ideXlab platform.
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A Phase-Locked Loop Algorithm for Single-Phase Systems With Inherent Disturbance Rejection
IEEE Transactions on Industrial Electronics, 2019Co-Authors: Francisco Kleber De A. Lima, Renato G. Araújo, Fernando L. Tofoli, Carlos Gustavo C. BrancoAbstract:This paper presents a phase-locked Loop Algorithm adequate for applications regarding single-phase power grids. The proposed approach is based on the correlation of the input signal with a complex one obtained from an adaptive filter aiming at minimizing computational burden and increasing accuracy when compared with a former Algorithm previously proposed in the literature. Thus, it is possible to obtain high disturbance rejection, especially when dealing with the presence of subharmonics and interharmonics in the frequency spectrum of the supply voltage. Performance is thoroughly evaluated through experimental tests considering both steady-state and dynamic behaviors, while a proper comparison is established with other similar solutions.
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A Phase-Locked Loop Algorithm for single-phase grid-connected systems with sub and interharmonics immunity
2015 IEEE 13th Brazilian Power Electronics Conference and 1st Southern Power Electronics Conference (COBEP SPEC), 2015Co-Authors: Renato G. Araújo, Francisco Kleber A. Lima, João Moor A. Neto, Carlos Gustavo C. BrancoAbstract:This paper proposes a new closed-Loop synchronization Algorithm, PLL (Phase-Locked Loop), for applications in power conditioner systems for single-phase networks. The structure presented is based on the correlation of the input signal with a complex signal generated from the use of an adaptive filter in a PLL Algorithm in order to minimize the computational effort. Moreover, the adapted PLL, due to the use of the adaptive filter, presents a higher level of rejection for two particular disturbances: interharmonic and subharmonic, when compared to the original Algorithm. Simulation and experimental results will be presented in order to prove the efficacy of the proposed adaptive Algorithm. The Algorithm will be exposed to several scenarios. The response of the Algorithm also be compared to the synchronization system based on SOGIFLL.
