arXiv subjects

Seung Ki Baek

Publications and source records attributed to Seung Ki Baek.

At least 55 records · Page 3Linked to original sources

arXiv2015

Interrupted coarsening in the zero-temperature kinetic Ising chain driven by a periodic external field

If quenched to zero temperature, the one-dimensional Ising spin chain undergoes coarsening, whereby the density of domain walls decays algebraically in time. We show that this coarsening process can be interrupted by exerting a rapidly oscillating periodic field with enough strength to compete with the spin-spin interaction. By analyzing correlation functions and the distribution of domain lengths both analytically and numerically, we observe nontrivial correlation with more than one length scale at the threshold field strength.

cond-mat.stat-mech↗

arXiv2015

Nash equilibrium and evolutionary dynamics in semifinalists' dilemma

We consider a tournament among four equally strong semifinalists. The players have to decide how much stamina to use in the semifinals, provided that the rest is available in the final and the third-place playoff. We investigate optimal strategies for allocating stamina to the successive matches when players' prizes (payoffs) are given according to the tournament results. From the basic assumption that the probability to win a match follows a nondecreasing function of stamina difference, we present symmetric Nash equilibria for general payoff structures. We find three different phases of the Nash equilibria in the payoff space. First, when the champion wins a much bigger payoff than the others, any pure strategy can constitute a Nash equilibrium as long as all four players adopt it in common. Second, when the first two places are much more valuable than the other two, the only Nash equilibrium is such that everyone uses a pure strategy investing all stamina in the semifinal. Third, when the payoff for last place is much smaller than the others, a Nash equilibrium is formed when every player adopts a mixed strategy of using all or none of its stamina in the semifinals. In a limiting case that only last place pays the penalty, this mixed-strategy profile can be proved to be a unique symmetric Nash equilibrium, at least when the winning probability follows a Heaviside step function. Moreover, by using this Heaviside step function, we study the tournament by using evolutionary replicator dynamics to obtain analytic solutions, which reproduces the corresponding Nash equilibria on the population level and gives information on dynamic aspects.

physics.soc-ph↗

arXiv2015

Anomalous response in the vicinity of spontaneous symmetry breaking

We propose a mechanism to induce negative AC permittivity in the vicinity of a ferroelectric phase transition involved with spontaneous symmetry breaking. This mechanism makes use of responses at low frequency, yielding a high gain and a large phase delay, when the system jumps over the free-energy barrier with the aid of external fields. We illustrate the mechanism by analytically studying spin models with the Glauber-typed dynamics under periodic perturbations. Then, we show that the scenario is supported by numerical simulations of mean-field as well as two-dimensional spin systems.

cond-mat.stat-mech↗

arXiv2015

Quantum Isothermal Reversible Process of Particles in a Box with a Delta Potential

For an understanding of a heat engine working in the microscopic scale, it is often necessary to estimate the amount of reversible work extracted by isothermal expansion of the quantum gas used as its working substance. We consider an engine with a movable wall, modeled as an infinite square well with a delta peak inside. By solving the resulting one-dimensional Schrödinger equation, we obtain the energy levels and the thermodynamic potentials. Our result shows how quantum tunneling degrades the engine by decreasing the amount of reversible work during the isothermal expansion.

cond-mat.stat-mech↗

arXiv2015

Theory of fads: Traveling-wave solution of evolutionary dynamics in a one-dimensional trait space

We consider an infinite-sized population where an infinite number of traits compete simultaneously. The replicator equation with a diffusive term describes time evolution of the probability distribution over the traits due to selection and mutation on a mean-field level. We argue that this dynamics can be expressed as a variant of the Fisher equation with high-order correction terms. The equation has a traveling-wave solution, and the phase-space method shows how the wave shape depends on the correction. We compare this solution with empirical time-series data of given names in Quebec, treating it as a descriptive model for the observed patterns. Our model explains the reason that many names exhibit a similar pattern of the rise and fall as time goes by. At the same time, we have found that their dissimilarities are also statistically significant.

cond-mat.stat-mech↗

arXiv2014

Zero-one-only process: a correlated random walk with a stochastic ratchet

The investigation of random walks is central to a variety of stochastic processes in physics, chemistry, and biology. To describe a transport phenomenon, we study a variant of the one-dimensional persistent random walk, which we call a zero-one-only process. It makes a step in the same direction as the previous step with probability $p$, and stops to change the direction with $1-p$. By using the generating-function method, we calculate its characteristic quantities such as the statistical moments and probability of the first return.

physics.data-an↗

arXiv2014

Stochastic resonance in the two-dimensional q-state clock models

We numerically study stochastic resonance in the two-dimensional q-state clock models from q = 2 to 7 under a weak oscillating magnetic field. As in the mean-field case, we observe double resonance peaks, but the detailed response strongly depends on the direction of the field modulation for q >= 5 where the quasiliquid phase emerges. We explain this behavior in terms of free-energy landscapes on the two-dimensional magnetization plane.

cond-mat.stat-mech↗

arXiv2014

Nonequilibrium steady state of the kinetic Glauber-Ising model under an alternating magnetic field

When periodically driven by an external magnetic field, a spin system can enter a phase of steady entrained oscillations with nonequilibrium probability distribution function. We consider an arbitrary magnetic field switching its direction with frequency comparable with the spin-flip rate and show that the resulting nonequilibrium probability distribution can be related to the system equilibrium distribution in the presence of a constant magnetic field of the same magnitude. We derive convenient approximate expressions for this exact relation and discuss their implications.

cond-mat.stat-mech↗

arXiv2014

Surname statistics - Crossing the boundary between disciplines

Regarding "Surname distribution in population genetics and in statistical physics" by Rossi, we add comments on the following two points: One is a difference in his renormalization-group formulation from the traditional one in statistical physics despite apparent similarity. The other is the potential importance of the entropy maximization principle under constraints governing the evolution of surname statistics.

physics.soc-ph↗

arXiv2014

Universal statistics of the knockout tournament

We study statistics of the knockout tournament, where only the winner of a fixture progresses to the next. We assign a real number called competitiveness to each contestant and find that the resulting distribution of prize money follows a power law with an exponent close to unity if the competitiveness is a stable quantity and a decisive factor to win a match. Otherwise, the distribution is found narrow. The existing observation of power law distributions in various kinds of real sports tournaments therefore suggests that the rules of those games are constructed in such a way that it is possible to understand the games in terms of the contestants' inherent characteristics of competitiveness.

physics.soc-ph↗

arXiv2014

Internal energy density of the critical three-state Potts model on the kagome lattice

It has been conjectured that the internal energy density of the Potts model on a semi-infinite strip with a width $L$ does not have any finite-size corrections at the critical point $K=K_c$. By factorizing the transfer matrix for the kagome lattice with larger widths, we have found that this conjecture is not correct in that the internal energy density slightly varies with $L$ at the critical point. From this size dependence of the internal energy density, we obtain an upper bound as $K_c < 1.0565615$, which is close to a recent estimate $K_c^{\rm JS} = 1.0565600(7)$ by Jacobsen and Scullard [arXiv:1204.0622]. We also obtain a lower bound as $K_c > 1.0560$ by calculating the correlation length along the strips.

cond-mat.stat-mech↗

arXiv2013

Residual discrete symmetry of the five-state clock model

It is well-known that the $q$-state clock model can exhibit a Kosterlitz-Thouless (KT) transition if $q$ is equal to or greater than a certain threshold, which has been believed to be five. However, recent numerical studies indicate that helicity modulus does not vanish in the high-temperature phase of the five-state clock model as predicted by the KT scenario. By performing Monte Carlo calculations under the fluctuating twist boundary condition, we show that it is because the five-state clock model does not have the fully continuous U(1) symmetry even in the high-temperature phase while the six-state clock model does. We suggest that the upper transition of the five-state clock model is actually a weaker cousin of the KT transition so that it is $q \ge 6$ that exhibits the genuine KT behavior.

cond-mat.stat-mech↗

arXiv2013

Faster is More Different: Mean-Field Dynamics of Innovation Diffusion

Based on a recent model of paradigm shifts by Bornholdt et al., we studied mean-field opinion dynamics in an infinite population where an infinite number of ideas compete simultaneously with their values publicly known. We found that a highly innovative society is not characterized by heavy concentration in highly valued ideas: Rather, ideas are more broadly distributed in a more innovative society with faster progress, provided that the rate of adoption is constant, which suggests a positive correlation between innovation and technological disparity. Furthermore, the distribution is generally skewed in such a way that the fraction of innovators is substantially smaller than has been believed in conventional innovation-diffusion theory based on normality. Thus, the typical adoption pattern is predicted to be asymmetric with slow saturation in the ideal situation, which is compared with empirical data sets.

physics.soc-ph↗

arXiv2013

Phase transition in a coevolving network of conformist and contrarian voters

In the coevolving voter model, each voter has one of two diametrically opposite opinions, and a voter encountering a neighbor with the opposite opinion may either adopt it or rewire the connection to another randomly chosen voter sharing the same opinion. As we smoothly change the relative frequency of rewiring compared to that of adoption, there occurs a phase transition between an active phase and a frozen phase. By performing extensive Monte Carlo calculations, we show that the phase transition is characterized by critical exponents β=0.54(1) and ν =1.5(1), which differ from the existing mean-field-type prediction. We furthermore extend the model by introducing a contrarian type that tries to have neighbors with the opposite opinion, and show that the critical behavior still belongs to the same universality class irrespective of such contrarians' fraction.

physics.soc-ph↗

arXiv2012

Bounds of percolation thresholds on hyperbolic lattices

We analytically study bond percolation on hyperbolic lattices obtained by tiling a hyperbolic plane with constant negative Gaussian curvature. The quantity of our main concern is $p_{c2}$, the value of occupation probability where a unique unbounded cluster begins to emerge. By applying the substitution method to known bounds of the order-5 pentagonal tiling, we show that $p_{c2} \ge 0.382 508$ for the order-5 square tiling, $p_{c2} \ge 0.472 043$ for its dual, and $p_{c2} \ge 0.275 768$ for the order-5-4 rhombille tiling.

cond-mat.stat-mech↗

arXiv2012

Vortex interaction on curved surfaces

The vortex-excitation energy on a sphere can be obtained by using the stereographic projection. By applying this method, we calculate the energy needed to create a vortex on a surface with a constant negative curvature. It is found that the energy is a linear function of the radius of the vortex. In accordance with this result, the interaction energy between a pair of vortices is also found to change linearly with the vortex separation distance. Explicit vortex configurations are obtained numerically with this interaction.

cond-mat.stat-mech↗

arXiv2012

Cluster-size heterogeneity in the two-dimensional Ising model

We numerically investigate the heterogeneity in cluster sizes in the two-dimensional Ising model and verify its scaling form recently proposed in the context of percolation problems [Phys. Rev. E 84, 010101(R) (2011)]. The scaling exponents obtained via the finite-size scaling analysis are shown to be consistent with theoretical values of the fractal dimension $d_f$ and the Fisher exponent $τ$ for the cluster distribution. We also point out that strong finite-size effects exist due to the geometric nature of the cluster-size heterogeneity.

cond-mat.stat-mech↗

arXiv2012

Double stochastic resonance in the mean-field $q$-state clock models

A magnetic system with a phase transition at temperature $T_c$ may exhibit double resonance peaks under a periodic external magnetic field because the time scale matches the external frequency at two different temperatures, one above $T_c$ and the other below $T_c$. We study the double resonance phenomena for the mean-field $q$-state clock model based on the heat-bath-typed master equation. We find double peaks as observed in the kinetic Ising case ($q=2$) for all $q\ge 4$, but for the three-state clock model ($q=3$), the existence of double peaks is possible only above a certain external frequency since it undergoes a discontinuous phase transition.

cond-mat.stat-mech↗