Wooseop Kwak

First-order phase transition and tricritical scaling behavior of the Blume-Capel model: A Wang-Landau sampling approach.

We investigate the tricritical scaling behavior of the two-dimensional spin-1 Blume-Capel model by using the Wang-Landau method of measuring the joint density of states for lattice sizes up to 48×48 sites. We find that the specific heat deep in the first-order area of the phase diagram exhibits a double-peak structure of the Schottky-like anomaly appearing with the transition peak. The first-order transition curve is systematically determined by employing the method of field mixing in conjunction with finite-size scaling, showing a significant deviation from the previous data points. At the tricritical point, we characterize the tricritical exponents through finite-size-scaling analysis including the phenomenological finite-size scaling with thermodynamic variables. Our estimation of the tricritical eigenvalue exponents, yt=1.804(5), yg=0.80(1), and yh=1.925(3), provides the first Wang-Landau verification of the conjectured exact values, demonstrating the effectiveness of the density-of-states-based approach in finite-size scaling study of multicritical phenomena.

Application of Wang–Landau sampling to a protein model using SMMP

Abstract We apply Wang–Landau sampling to the continuous energy model of a protein using Simple Molecular Mechanics for Protein (SMMP). We also tried to parallelize the Wang–Landau sampling method and compare our results with previous results derived from the multicanonical and parallel tempering methods.

Agent-Based Approach for Revitalization Strategy of Knowledge Ecosystem

We conceptualize knowledge as an intellectual infrastructure that helps to maximize efficiency from the viewpoint of ecosystems. The knowledge ecosystem includes people and organizations that participate in the production, distribution, and consumption of this knowledge and information, as well as interactions between participants. We built the agent-based computational model of the ecosystem and induced seven key revitalization conditions from the perspective of complexity science and ecosystem management. We analyzed the effects of these conditions on the knowledge ecosystem based by the simulation of the agent-based model. Our results suggest that the proper implementation of seven revitalization conditions, focusing on the recovery of the positive feedback loop in the knowledge ecosystem, is crucial for sustainable development.

Critical behavior of the XY model on static scale-free networks

The critical behaviors of the equilibrium model on correlated and uncorrelated networks are known to differ, and the critical behavior of the XY model on correlated scale-free networks has been examined. Here, we study the XY model on uncorrelated scale-free networks with various degree exponents λ of the power law degree distribution P(k)~k- λ, where the degree k is the number of neighborhood. For λ>5, we find that the critical exponents of the XY model on uncorrelated networks are identical to those of the standard mean field. These results vary from those derived from correlated networks.

Optimization of consensus time by combining the voter and the majority voter models on scale-free networks

We introduce a spin model combining the majority voter model with probability p and the voter model with probability 1-p and then measure its consensus time on scale-free networks with various degree exponents γ. We find that consensus time depends on both p and γ. When all spins follow either the voter model or the majority voter model, it takes much greater time to reach consensus. On the other hand, when spins may alternate between the majority voter model and the voter model, consensus time is shortened. We find via numerical calculation that the optimized ratio to minimize consensus time is around p=0.72.

Optical coherence tomography in material deformation by using short pulse laser irradiation

We demonstrate the feasibility of OCT imaging for the investigation of samples, which are processed by the short pulse laser. The use of short pulse lasers in various material processing have provided the advantages such as a high peak power and a small heat affected zone over conventional methods based on mechanical treatment. However, due to the improper application of the lasers, the unwanted surface or structural deformation of materials and the thermal damages around an irradiation spot can be caused. Thus, the real-time monitoring/evaluation of laser processing performance in-situ is needed to prevent the excessive deformation of the material and to determine optimal processing conditions. As a standard method to investigation of the material processing by using the lasers, the scanning electron microscopy (SEM) or the transmission electron microscopy (TEM) observation of a physically cleaved surface is used although sample damages are given during the cleaving and polishing process. In this paper, we utilized the OCT advantages such as high resolution and non-invasive investigation to evaluate the laser processing performance. OCT images for the deformation monitoring of the ABS plastic present correlation with images obtained from conventional investigation methods. OCT images of the maxillary bone clearly show the difference in the pit formation of the biological sample at different irradiation conditions. We prove the potential of OCT for the evaluation of laser-processed various samples. Integrating OCT system into a laser processing system, we can visualize the effect of laser-based treatments in clinical and industrial fields.

Critical behavior of the XY model on uncorrelated and correlated random networks

We numerically study the critical behavior of the XY model on the Erd?s?R?nyi random graph and a growing random network model, representing the uncorrelated and the correlated random networks, respectively. We also checked the dependence of the critical behavior on the choice of order parameters: the ordinary unweighted and the degree-weighted magnetization. On the Erd?s?R?nyi random network, the critical behavior of the XY model is found to be of the second order with the estimated exponents consistent with the standard mean-field theory for both order parameters. On the growing random network, on the contrary, we found that the critical behavior is not of the standard mean-field type. Rather, it exhibits behavior reminiscent of that in the infinite-order phase transition for both order parameters, such as the lack of discontinuity in specific heat and the non-divergent susceptibility at the critical point, as observed in the percolation and the Potts models on some growing network models.

Study of the Antiferromagnetic Blume-Capel Model on kagomé Lattice

We study the anti-ferromagnetic (AF) Ising model and the AF Blume-Capel (BC) model on the kagome lattice. Using the Wang-Landau sampling method, we estimate the joint density functions for both models on the lattice, and we obtain the exact critical magnetic fields at zero temperature by using the micro-canonical analysis. We also show the patterns of critical lines for the models from micro-canonical analysis.

Phase transitions of 2D triangular antiferromagnetic Ising model in a uniform magnetic field near h=0 and T=0

Using a microcanonical magnetization-energy (ME) diagram, this paper describes all the possible phase transitions of a 2D triangular antiferromagnetic (TAFM) Ising model in a uniform external magnetic field. In particular, we investigate the detailed phase boundary shape of the TAFM near h = 0 and T = 0 using staggered susceptibility.

3Microcanonical entropy as a function of energies for the Triangular-Lattice Blume-Capel magnetic system

The triangular-lattice Blume-Capel magnetic system is investigated using efficient Wang-Landau Monte Carlo algorithm. From extensive Wang-Landau Monte Carlo simulations with massive large-scale computing, the microcanonical entropy as a function of energy variables, the most fundamental quantity in statistical thermodynamics, for the triangular- lattice Blume-Capel ferromagnet and antiferromagnet at the same time is evaluated for the first time. The important properties of the microcanonical entropy as a function of energy variables are discussed for the triangular-lattice Blume-Capel magnetic system.