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New techniques for the analysis of fine-scaled clustering phenomena within atom probe tomography (APT) data

MICROSCOPY AND MICROANALYSIS 2007年第6期13卷 448-463页

作者： Stephenson, Leigh T. Moody, Michael P. Liddicoat, Peter V. Ringer, Simon P. Univ Sydney Australian Key Ctr Microscopy & Microanal Sydney NSW 2006 Australia Univ Sydney ARC Ctr Design Light Metals Sydney NSW 2006 Australia

Nanoscale atomic clusters in atom probe tomographic data are not universally defined but instead are characterized by the clustering algorithm used and the parameter values controlling the algorithmic process. A new core-linkage clustering algorithm is developed, combining fundamental elements of the conventional maximum separation method with density-based analyses. A key improvement to the algorithm is the independence of algorithmic parameters inherently unified in previous techniques, enabling a more accurate analysis to be applied across a wider range of material systems. Further, an objective procedure for the selection of parameters based on approximating the data with a model of complete spatial randomness is developed and applied. The use of higher nearest neighbor distributions is highlighted to give insight into the nature of the clustering phenomena present in a system and to generalize the clustering algorithms used to analyze it. Maximum separation, density-based scanning, and the core linkage algorithm, developed within this study, were separately applied to the investigation of fine solute clustering of solute atoms in an Al-1.9Zn-1.7Mg (at.%) at two distinct states of early phase decomposition and the results of these analyses were evaluated.

关键词： atom probe tomography solute clustering cluster algorithms nearest neighbors data analysis data mining

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Wang-Landau Multibondic cluster Simulations for Second-Order Phase Transitions

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Physical Review Letters 2007年第4期98卷 040602-040602页

作者： Bernd A. Berg Wolfhard Janke Department of Physics Florida State University Tallahassee Florida 32306 USA School of Computational Science Florida State University Tallahassee Florida 32306 USA Institut für Theoretische Physik and Centre for Theoretical Sciences (NTZ) Universität Leipzig Augustusplatz 10/11 D-04109 Leipzig Germany

For a second-order phase transition the critical energy range of interest is larger than the energy range covered by a canonical Monte Carlo simulation at the critical temperature. Such an extended energy range can be covered by performing a Wang-Landau recursion for the spectral density followed by a multicanonical simulation with fixed weights. But in the conventional approach one loses the advantage due to cluster algorithms. A cluster version of the Wang-Landau recursion together with a subsequent multibondic simulation improves for 2D and 3D Ising models the efficiency of the conventional Wang-Landau or multicanonical approach by power laws in the lattice size. In our simulations real gains in CPU time reach 2 orders of magnitude.

关键词： .energy range canonical cluster algorithms ensemble weights Recursion covered Wang-Landau Second-Order Phase

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Some refinements of rough k-means clustering

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PATTERN RECOGNITION 2006年第8期39卷 1481-1491页

作者： Peters, Georg Munich Univ Appl Sci Dept Comp Sci Math D-80335 Munich Germany

Lingras et at. proposed a rough cluster algorithm and successfully applied it to web mining. In this paper we analyze their algorithm with respect to its objective function, numerical stability, the stability of the clusters and others. Based on this analysis a refined rough cluster algorithm is presented. The refined algorithm is applied to synthetic, forest and microarray gene expression data. (c) 2006 Pattern Recognition Society. Published by Elsevier Ltd. All rights reserved.

关键词： cluster algorithms rough k-means soft computing data analysis forest data bioinformatics data

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Geometric and stochastic clusters of gravitating Potts models

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PHYSICS LETTERS B 2006年第3-4期639卷 373-377页

作者： Janke, Wolfhard Weigel, Martin Heriot Watt Univ Sch Math & Comp Sci Dept Math Edinburgh EH14 4AS Midlothian Scotland Univ Leipzig Inst Theoret Phys D-04109 Leipzig Germany Univ Leipzig Ctr Theoret Sci NTZ D-04109 Leipzig Germany

We consider the fractal dimensions of critical clusters. occurring in configurations of a q-state Potts model coupled to the planar random graphs of the dynamical triangulations approach to Euclidean quantum gravity in two dimensions. For regular lattices, it is well-established that at criticality the properties of Fortuin-Kasteleyn clusters are directly related to the conventional critical exponents, whereas the corresponding properties of the geometric clusters of like spins are not. Recently it has been observed that the latter are related to the critical properties of a tricritical Potts model with the same central charge. We apply the KPZ formalism to develop a related prediction for the case of Potts models coupled to quantum gravity and employ numerical simulation methods to confirm it for the Ising case q = 2. (c) 2006 Elsevier B.V. All rights reserved.

关键词： Potts model Ising model quantum gravity Fortuin-Kasteleyn representation fractal dimensions annealed disorder cluster algorithms

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New approaches to strong coupling lattice QCD

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INTERNATIONAL JOURNAL OF MODERN PHYSICS B 2006年第19期20卷 2714-2723页

作者： Chanrasekharan, Shailesh Duke Univ Dept Phys Durham NC 27708 USA

Efficient cluster algorithms have recently been discovered to solve strong coupling lattice QCD with staggered fermions in the chiral limit from first principles. This allows us for the first time to uncover the universal properties close to chiral phase transitions and make connections with chiral perturbation theory. In this article we will review some of the recent progress and outline some possible directions for future work.

关键词： lattice QCD strong coupling cluster algorithms chiral limit

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Robust Perron cluster analysis in conformation dynamics

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LINEAR ALGEBRA AND ITS APPLICATIONS 2005年第1-3期398卷 161-184页

作者： Deuflhard, P Weber, M Konrad Zuse Zentrum Informat Tech D-14195 Berlin Germany

The key to molecular conformation dynamics is the direct identification of metastable conformations, which are almost invariant sets of molecular dynamical systems. Once some reversible Markov operator has been discretized, a generalized symmetric stochastic matrix arises. This matrix can be treated by Perron cluster analysis, a rather recent method involving a Perron cluster eigenproblem. The paper presents an improved Perron cluster analysis algorithm, which is more robust than earlier suggestions. Numerical examples are included. (C) 2004 Elsevier Inc. All rights reserved.

关键词： Markov chains cluster algorithms Perron cluster analysis conformation dynamics

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Hybrid multicanonical cluster algorithm for efficient simulations of long-range spin models

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COMPUTER PHYSICS COMMUNICATIONS 2005年第1-3期169卷 243-246页

作者： Reynal, S Diep, HT Univ Cergy Pontoise CNRS Lab Phys Theor & Modelisat F-95031 Cergy Pontoise France ENSEA F-95014 Cergy France

An efficient, flat histogram Monte Carlo algorithm is proposed that simulates long-range spin models in the multicanonical ensemble with very low dynamic exponents and drastically reduced computational effort. The method combines a random-walk in energy space with cluster updates, where bond weights depend continuously on the lattice energy. Application to q-state Potts chains with power-law decaying interactions is considered. Lattice sizes as high as 216 spins, unattainable with conventional flat histogram algorithms, are investigated. Numerical results demonstrate the remarkable performance of the method over a wide spectrum of model parameters. (c) 2005 Elsevier B.V. All rights reserved.

关键词： Monte Carlo multicanonical flat histogram long-range interactions cluster algorithms first-order transitions

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A cluster algorithm for lattice gauge theories

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COMPUTER PHYSICS COMMUNICATIONS 2005年第1-3期169卷 370-373页

作者： Alet, F Lucini, B Vettorazzo, M ETH Inst Theoret Phys CH-8093 Zurich Switzerland ETH Computat Lab CH-8092 Zurich Switzerland

A new algorithm for simulating compact U(l) lattice gauge theory in three dimensions is presented which is based on global changes in the configuration space. We show that this algorithm provides an effective way to extract partition functions at given external flux. As an application, we study numerically the finite temperature deconfinement phase transition. (c) 2005 Elsevier B.V. All rights reserved.

关键词： lattice gauge theory Monte Carlo methods cluster algorithms

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A cluster algorithm for lattice gauge theories

A cluster algorithm for lattice gauge theories

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Europhysics Conference on Compuitational Physics

作者： Alet, F Lucini, B Vettorazzo, M ETH Inst Theoret Phys CH-8093 Zurich Switzerland ETH Computat Lab CH-8092 Zurich Switzerland

关键词： lattice gauge theory Monte Carlo methods cluster algorithms

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