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Nonequilibrium Phase Transition in Spin-S Ising Ferromagnet Driven by Propagating and Standing Magnetic Field Wave

Communications in Theoretical Physics 2017年第11期67卷 600-610页

作者： Ajay Halder Muktish Acharyya Department of Physics Presidency University

The dynamical response of spin-S(S=1, 3/2, 2, 3) Ising ferromagnet to the plane propagating wave, standing magnetic field wave and uniformly oscillating field with constant frequency are studied separately in two dimensions by extensive monte carlo simulation. Depending upon the strength of the magnetic field and the value of the spin state of the Ising spin lattice two different dynamical phases are observed. For a fixed value of S and the amplitude of the propagating magnetic field wave the system undergoes a dynamical phase transition from propagating phase to pinned phase as the temperature of the system is cooled down. Similarly in case with standing magnetic wave the system undergoes dynamical phase transition from high temperature phase where spins oscillate coherently in alternate bands of half wavelength of the standing magnetic wave to the low temperature pinned or spin frozen phase. For a fixed value of the amplitude of magnetic field oscillation the transition temperature is observed to decrease to a limiting value as the value of spin S is increased. The time averaged magnetisation over a full cycle of the magnetic field oscillation plays the role of the dynamic order parameter. A comprehensive phase boundary is drawn in the plane of magnetic field amplitude and dynamic transition temperature. It is found that the phase boundary shrinks inwards for high value of spin state *** in the low temperature(and high field) region the phase boundaries are closely spaced.

关键词： Ising model dynamic phase transition monte-carlo algorithm propagating wave standing wave

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Impact of Brillouin Backscattering on Signal Distortions in Single-Fiber Diversity Loop Based Polarization-Insensitive FOPAs

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2017年第19期35卷 4137-4144页

作者： Jazayerifar, Mahmoud Sackey, Isaac Elschner, Robert Richter, Thomas Molle, Lutz Berenguer, Pablo Wilke Schubert, Colja Jamshidi, Kambiz Petermann, Klaus Tech Univ Dresden Inst Nachrichtentech D-01069 Dresden Germany Heinrich Hertz Inst Nachrichtentech Berlin GmbH Fraunhofer Inst Telecommun D-10587 Berlin Germany ADVA Opt Networking North Amer Inc Norcross GA 30071 USA Tech Univ Berlin Fachgebiet Hochfrequenztech D-10587 Berlin Germany

We both experimentally and numerically investigate the impact of Brillouin backscattering in single-fiber-loop-based polarization-insensitive fiber-optical parametric amplifiers. We show that the loop configuration can cause distortions in the pump spectra due to Brillouin interactions of the counter-propagating pumps. This can result in significant distortions for amplified data signals at high gain when conventional highly nonlinear fibers are used. We thoroughly investigate the effect in experiments and derive a numerical model. This allows us to compare the results from system experiments with 28 GBd quadrature-phase shift keying signals to system simulations showing a good agreement on the system. Based on the model, we finally estimate that a large gain (similar to 20 dB) with a low optical signal-to-noise ratio penalty (0.15 dB at bit error rate of 1 x 10(-4)) for the amplified data signal should be possible in a single-fiber loop with Brillouin-suppressed highly nonlinear fibers.

关键词： Brillouin scattering coherent detection four-wave mixing monte-carlo algorithm nonlinear optics optical amplifiers optical fiber communication

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Construction and Analysis of Lattice Boltzmann Methods Applied to a 1D Convection-Diffusion Equation

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ACTA APPLICANDAE MATHEMATICAE 2014年第1期131卷 69-140页

作者： Dellacherie, Stephane CEA Commissariat Energie Atom & Energies Alternat DEN STMFDM2S F-91191 Gif Sur Yvette France

To solve the 1D (linear) convection-diffusion equation, we construct and we analyze two LBM schemes built on the D1Q2 lattice. We obtain these LBM schemes by showing that the 1D convection-diffusion equation is the fluid limit of a discrete velocity kinetic system. Then, we show in the periodic case that these LBM schemes are equivalent to a finite difference type scheme named LFCCDF scheme. This allows us, firstly, to prove the convergence in L (a) of these schemes, and to obtain discrete maximum principles for any time step in the case of the 1D diffusion equation with different boundary conditions. Secondly, this allows us to obtain most of these results for the Du Fort-Frankel scheme for a particular choice of the first iterate. We also underline that these LBM schemes can be applied to the (linear) advection equation and we obtain a stability result in L (a) under a classical CFL condition. Moreover, by proposing a probabilistic interpretation of these LBM schemes, we also obtain monte-carlo algorithms which approach the 1D (linear) diffusion equation. At last, we present numerical applications justifying these results.

关键词： Convection-diffusion equation Lattice Boltzmann method D1Q2 lattice Chapman-Enskog expansion Hilbert expansion LFCCDF scheme Du Fort-Frankel scheme Stability and convergence in L-infinity Discrete maximum principle monte-carlo algorithm

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Analyzing energy landscapes for folding model proteins

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JOURNAL OF CHEMICAL PHYSICS 2006年第20期124卷 4714-1-4714-1页

作者： Cox, Graham A. Johnston, Roy L. Univ Birmingham Sch Chem Birmingham B15 2TT W Midlands England

A new benchmark 20-bead HP model protein sequence (on a square lattice), which has 17 distinct but degenerate global minimum (GM) energy structures, has been studied using a genetic algorithm (GA). The relative probabilities of finding particular GM conformations are determined and related to the theoretical probability of generating these structures using a recoil growth constructor operator. It is found that for longer successful GA runs, the GM probability distribution is generally very different from the constructor probability, as other GA operators have had time to overcome any initial bias in the originally generated population of structures. Structural and metric relationships (e.g., Hamming distances) between the 17 distinct GM are investigated and used, in conjunction with data on the connectivities of the GM and the pathways that link them, to explain the GM probability distributions obtained by the GA. A comparison is made of searches where the sequence is defined in the normal (forward) and reverse directions. The ease of finding mirror image solutions are also compared. Finally, this approach is applied to rationalize the ease or difficulty of finding the GM for a number of standard benchmark HP sequences on the square lattice. It is shown that the relative probabilities of finding particular members of a set of degenerate global minima depend critically on the topography of the energy landscape in the vicinity of the GM, the connections and distances between the GM, and the nature of the operators used in the chosen search method. (c) 2006 American Institute of Physics.

关键词： COLONY OPTIMIZATION algorithm CHAIN GROWTH algorithm monte-carlo algorithm GENETIC algorithmS SIMULATIONS SPACES CODES 2D

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A probabilistic proof of the Perron-Frobenius theorem

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NAVAL RESEARCH LOGISTICS 2023年第5期70卷 443-453页

作者： Glynn, Peter W. Desai, Paritosh Y. Stanford Univ Dept Management Sci & Engn Stanford CA 94305 USA Target Corp Sunnyvale CA USA

The Perron-Frobenius theorem plays an important role in many areas of management science and operations research. This article provides a probabilistic perspective on the theorem, by discussing a proof that exploits a probabilistic representation of the Perron-Frobenius eigenvalue and eigenvectors in terms of the dynamics of a Markov chain. The proof recovers conditions in both the finite-dimensional and infinite-dimensional settings under which the Perron-Frobenius eigenvalue and eigenvectors have been shown to exist by other methods. In addition to providing new insights, the probabilistic representations that arise can be used to produce a monte-carlo algorithm for computing the Perron-Frobenius eigenvalue and eigenvectors that will be explored elsewhere.

关键词： Markov population decision monte-carlo algorithm Perron-Frobenius theorem

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Evaluation of small-angle x-ray scattering data of a Raney-type Ni catalyst with computer simulation

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JOURNAL OF CHEMICAL PHYSICS 2004年第21期121卷 10634-10640页

作者： Tóth, G Körmendi, K Vrabecz, A Bóta, A Eotvos Lorand Univ Dept Theoret Chem H-1518 Budapest Hungary Budapest Univ Technol & Econ Inst Phys Chem H-1521 Budapest Hungary

A reverse monte carlo-type simulation method was developed for the evaluation of anomalous small-angle x-ray scattering data of a Raney-type Ni catalyst. Based on other experimental data the catalytic Ni particles were modeled as small crystalline cylinders dispersed in the matrix. The average size of the Ni particles and their pair-correlation function were determined. Despite the unknown density of the catalyst, it is shown that each particle has about 2 neighbors in the first neighboring shell independent of the modeling density, and the position of the first peak of the pair-correlation function does not depend on the modeling density. A method was elaborated to get reasonable performance of the Reverse monte carlo-type simulation. The scattered intensity was calculated on the basis of probe scattering atoms put inside the cylinders. The effects of the omission of the real number of the atoms, the unknown density, the lack of normalization and the uncertainties in the cross sections were unified in two constants that were determined during the simulation. The method can be used for nanoparticles with other shape, where analytic form factors are complicated, and it may be powerful in the investigation of the usually neglected or simplified inter-particle structure of these systems. (C) 2004 American Institute of Physics.

关键词： BLOCK-COPOLYMER MICELLES monte-carlo algorithm NEUTRON-SCATTERING SYSTEM COLLOIDS DENSITY

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A hierarchical energy management strategy for interconnected microgrids considering uncertainty

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INTERNATIONAL JOURNAL OF ELECTRICAL POWER & ENERGY SYSTEMS 2019年 109卷 597-608页

作者： Bazmohammadi, Najmeh Tahsiri, Ahmadreza Anvari-Moghaddam, Amjad Guerrero, Josep M. KN Toosi Univ Technol Dept Elect Engn Tehran Iran Aalborg Univ Dept Energy Technol DK-9220 Aalborg Denmark

Coordinating the operation of neighboring microgrids is a promising solution for the problem of growing penetration of renewable-based microgrids into the power system. In this paper, a hierarchical stochastic energy management system is proposed for operation management of interconnected microgrids. At the upper-level, a central entity is responsible for coordinating the operation of microgrids. Based on the energy scheduling made at this level, the power reference values to be exchanged within the microgrids network and between the microgrids and the main grid are calculated and communicated with the local energy management systems. At the lower-level, a decision making approach based on chance-constrained model predictive control is adopted for local operation management of each microgrid taking into account different sources of uncertainties. The results show that the proposed strategy provides the microgrids with the opportunity of exploiting maximum available capacity in the network. Consequently, the microgrids dependency on the main grid will be reduced and some important performance indices such as multi-microgrid system cost and real-time power deviations will be improved.

关键词： Energy management Multi-microgrid system Chance-constrained model predictive control Uncertainty management monte-carlo algorithm

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Safeguard management for operation security in nuclear power plants (NPPs)

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ANNALS OF NUCLEAR ENERGY 2011年第2-3期38卷 167-174页

作者： Woo, Tae-Ho Lee, Un-Chul Seoul Natl Univ Dept Nucl Engn Seoul 151742 South Korea

Safeguard modeling is conducted for the successful operations in the nuclear power plants (NPPs). The characteristics of the secure operation in NPPs are investigated using the network effect method which is quantified by the monte-carlo algorithm. Fundamentally, it is impossible to predict the exact time of a terror incident. So, the random sampling for the event frequency is a reasonable method, including the characteristics of network effect method such as the zero-sum quantification. The performance of operation with safeguard is the major concern of this study. There are three kinds of considerations as the neutronics, thermo-hydraulics, and safeguard properties which are organized as an aspect of safeguard considerations. The result, therefore, can give the stability of the operations when the power is decided. The maximum value of secure operation is 12.0 in the third month and the minimum value is 1.0 in the 18th and 54th months, in a 10 years period. Thus, the stability of the secure power operation increases 12 times higher than the lowest value according to this study. This means that the secure operation is changeable in the designed NPPs and the dynamical situation of the secure operation can be shown to the operator. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Nuclear power plants Safeguard Power uprate Network effect monte-carlo algorithm

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Revealing the theoretical assumptions of the trap-depth distribution model in the thermoluminescence theory

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THIN SOLID FILMS 2020年 714卷 138390-138390页

作者： Sadek, A. M. Natl Inst Stand NIS Ionizing Radiat Metrol Dept PO 136 Giza 12211 Egypt

The theoretical assumptions of the analytical expressions characterizing the thermoluminescence glow-peak arising from a continuous trap-depth distribution have been investigated. The sets of the differential equations governing the electrons' transitions within a continuous trap-depth distribution during the irradiation and heating stages have been numerically solved. The analytical expressions are essentially based on a theoretical assumption that correlates the concentrations of the trapped electrons with the distribution of the trap depths in the bandgap. This correlation could not be considered in the numerical solution, since the irradiation stage is entirely independent of the trap depth. Thus, the final values of the instantaneous trap-filling functions of the irradiation stage do not depend on the trap depth, but rather on the trap capacity and the trapping probability coefficient. Consequently, in the numerical solution, the distribution of the trap depths and the distribution of the trapped electrons are independent. This inconsistency between the numerical solution and the analytical expression has led to differences in the shape of the thermoluminescence glow peaks resulting from the same trap-depth spectrum.

关键词： Trap-depth distribution Thermoluminescence models monte-carlo algorithm

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Auto-tune of PVT data using an efficient engineering method: Application of sensitivity and optimization analyses

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FLUID PHASE EQUILIBRIA 2018年 473卷 70-79页

作者： Zarifi, Abdolhadi Daryasafar, Amin NISOC Dept Petr Engn Ahvaz Iran

In reservoir simulation, it is crucial to have a physical model of the reservoir fluid that can give the properties and behavior of the fluid at different conditions. Phase behavior of a reservoir hydrocarbon is modeled through an equation of state (EOS) by adjustment of some of the parameters in EOS so as to reproduce measured data of the mixture. Since the EOSs have some inherent deficiencies which may cause erroneous predictions, these models have to be tuned against experimental data. Conventionally, the methods and algorithms that have been proposed for tuning EOS models are tedious and really time consuming;therefore, a simple and accurate algorithm that can find the best match between EOS and measured data, automatically is really needed. For this purpose, a generalized auto-tune procedure based on monte-carlo and genetic algorithms is proposed in this study. In the presented method, first of all, the matching parameters for regression process are found in an automatic manner by using monte-carlo sensitivity analysis. Then, the selected parameters are fed to the PVT analyzer coupled with genetic algorithm and therefore, the best EOS model is searched and found. Three fluid samples (one gas condensate and two black oils) were used in order to test the proposed method and the matches were found by using Peng-Robindon (PR) EOS. The results illustrated the surprising high performance of the developed algorithm in matching the experimental data. The main advantages of this method is its high speed in finding the best EOS model, working automatically, reducing costs and also having the possibility of evaluating the model at different conditions. (C) 2018 Elsevier B.V. All rights reserved.

关键词： PVT match EOS model Sensitivity analysis Genetic algorithm monte-carlo algorithm

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