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Dynamic Phase Transition in Coupled Oscillators under a Periodic Symmetry-breaking Field
최중재,최무영,윤병국 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.6
We study numerically the dynamic responses of a system of globally coupled oscillators driven by periodic symmetry-breaking fields in the presence of noise. We find that the system undergoes a dynamic phase transition as the period or the amplitude of the symmetry-breaking field is varied at sufficiently low noise level. We employ a finite-size scaling analysis to investigate the characteristics of the dynamic transition. The obtained critical exponents turn out to be different from the mean-field values.
최중재,최무영,정문성,윤병국 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.9
We investigate numerically the clustering behavior of a system of phase oscillators with positive and negative couplings under a periodic external driving field with a bimodal distribution of driving phases. The phase distribution and the mean speed of the traveling state, as well as the order parameter for synchronization, are computed as the driving amplitude is varied. We observe that the periodically-driven system can also host traveling states for parameters in the same range as those for the case of a system without a driving field. The traveling speed is found to depend nonmonotonically on the driving amplitude. In particular, oscillators divide into four clusters and move in pairs. Further, depending on the driving amplitude, two kinds of traveling mode arise: pairs of clusters traveling in the same direction (symmetric mode) and in opposite directions (antisymmetric mode). In the latter case (antisymmetric traveling mode), the average phase speed of the whole system apparently vanishes. A phenomenological argument for such behavior is given.
최중재,최무영,윤병국 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.4
We numerically study dynamic responses of a system of globally coupled oscillators driven by periodic symmetry-breaking fields in the presence of noise. Depending on the field amplitude, noise level, and width of the natural frequency distribution, a variety of global ordering, including single-cluster motion and asymmetric or symmetric bi-cluster motion, emerges. Particularly, in appropriate regions, the system exhibits rich resonance-like behavior in the power spectrum at the driving frequency.
Traveling Speed of Clusters in the Kuramoto-Sakaguchi Model
최중재,최무영,윤병국 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.3
We study a variant of the Kuramoto-Sakaguchi model in which oscillators are divided into twogroups, each characterized by its coupling constant and phase lag. Specifically, we consider the casethat one coupling constant is positive and the other negative, and calculate numerically the travelingspeed of two clusters emerging in the system and the average separation between them, as well asthe order parameters for positive and negative oscillators, as the two coupling constants, phase lags,and the fraction of positive oscillators are varied. An expression explaining the dependence of thetraveling speed on these parameters is obtained and is observed to fit the numerical data well. Withthe help of this, we describe the conditions for the traveling state to appear in the system.
Connectedness and strength of biological organisms
윤병국,최중재,최무영 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.6
We study, via extensive Monte Carlo simulations, a model for failures in biological organisms with local load sharing. The qualitative behaviors of the model are found to be similar to those of the global load sharing case, but the system is weaker in the sense that it has smaller values of the critical stress and requires larger healing ability for a transition to the healthy state. When shortcuts or pathways along which load is transferred are introduced, the critical stress, in general, increases with the number of shortcuts present, and the system, thus, becomes stronger, manifesting the importance of connectedness in biological systems.
Time Evolution of Entropy in a Growth Model: Dependence on the Description
Segun Goh,최중재,최무영,윤병국 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.1
Entropy plays a key role in the statistical physics of complex systems, which in general exhibit diverse aspects of emergence on different scales. However, how entropy varies with the coarsegraining level and the description scale still remains not fully resolved. In this paper, we consider a Yule-type growth model, where each element is characterized by its size being either continuous or discrete. Entropy is then defined directly from the probability distribution of the states of all elements, as well as from the size distribution of the system. Probing in detail their relations and time evolutions, we find that heterogeneity, in addition to correlations between elements, can induce loss of information during the coarse-graining procedure. Another revelation is that the expansion of the size space domain depends on the description level, leading to a difference between the continuous and the discrete descriptions.
Quick Detection of Variance Change Point for I.I.D. Data
박경화,송규문,최중재,김태윤 한국데이터정보과학회 2005 한국데이터정보과학회지 Vol.16 No.2
This paper studies quick detection of variance change point for iid data. For development of sensitive and adaptive variance change point detector, moving variance ratio is employed as a variance ratio estimator. It is shown that selection of tuning parameters of detector, (i.e., information and lag tuning parameters) is critical for detector to achieve desirable sensitivity and adaptiveness.Interestingly our simulation result reveals limitations of the commonly used change ratio against the previous day. Our results will provide useful insight when the detector is applied to time series data.
Dynamic Model for Failures in Biological Systems: Criticality and Resonance
최무영,윤병국,조정효,최중재 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.1I
We present a dynamic model for failures in biological organisms, where each cell becomes dead under su±ciently strong stress and is then allowed to be healed with some probability. Revealed is the characteristic time evolution that the system tends to resist the stress longer than a system without healing, followed by a sudden breakdown with some fraction of cells surviving. If we perform Monte Carlo simulations on this model, the rate of cell failure exhibits a 1=f behavior. Under periodic stress, the average fraction of intact cells decays stepwise or exhibits an oscillating behavior, depending on the stress and healing. Under some condition, the power spectrum at the stress frequency at .rst increases with the healing parameter, and then decreases, which may be called a healing resonance. When the healing varies periodically in time, the system undergoes a transition from an unhealthy state to a healthy one as the frequency increases. This suggests a way for adjusting the frequency of medical treatment to the optimum.