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Search Results: 1 - 10 of 301560 matches for " J. Choi "
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Sphalerons in the Standard Model with a real Higgs singlet
J. Choi
Physics , 1994, DOI: 10.1016/0370-2693(94)01654-U
Abstract: Sphaleron energies within the standard model with a real Higgs singlet added on are calculated. The coupled non-linear equations of motion are numerically solved and the sphaleron energy evaluated for a set of parameters in the Higgs potential. I find a small difference in the sphaleron energy compared to the standard model. A slightly stronger constraint on the strength of the first order phase transition thus results for this model.
Stability and ensemble inequivalence in a globally coupled system
M. Y. Choi,J. Choi
Physics , 2003, DOI: 10.1103/PhysRevLett.91.124101
Abstract: We consider a system of globally coupled rotors, described by a set of Langevin equations, and examine stability of the incoherent phase. The corresponding Fokker-Planck equation, providing a unified description of microcanonical and canonical ensembles, bears a few solutions, depending upon the ensemble. It is found that the stability of each solution varies differently with the temperature, revealing the inequivalence between the two ensembles. This also suggests a physical explanation of the quasi-stationarity observed in recent numerical results.
Topological quantization and degeneracy in Josephson-junction arrays
M. Y. Choi,J. Choi
Physics , 2001, DOI: 10.1103/PhysRevB.63.212503
Abstract: We consider the conductivity quantization in two-dimensional arrays of mesoscopic Josephson junctions, and examine the associated degeneracy in various regimes of the system. The filling factor of the system may be controlled by the gate voltage as well as the magnetic field, and its appropriate values for quantization is obtained by employing the Jain hierarchy scheme both in the charge description and in the vortex description. The duality between the two descriptions then suggests the possibility that the system undergoes a change in degeneracy while the quantized conductivity remains fixed.
Stability of thermodynamic and dynamical order in a system of globally coupled rotors
J. Choi,M. Y. Choi
Physics , 2005, DOI: 10.1088/0305-4470/38/25/005
Abstract: A system of globally coupled rotors is studied in a unified framework of microcanonical and canonical ensembles. We consider the Fokker-Planck equation governing the time evolution of the system, and examine various stationary as well as non-stationary solutions. The canonical distribution, describing equilibrium, provides a stationary solution also in the microcanonical ensemble, which leads to order in a system with ferromagnetic coupling at low temperatures. On the other hand, the microcanonical ensemble admits additional stationary and non-stationary solutions; the latter allows dynamical order, characterized by multiple degrees of clustering, for both ferromagnetic and antiferromagnetic interactions. We present a detailed stability analysis of these solutions: In a ferromagnetic system, the canonical distribution is observed stable down to a certain temperature, which tends to get lower as the number of Fourier components of the perturbed distribution is increased in the analysis. The non-stationary solution remains neutrally stable below the critical temperature, indicating inequivalence between the two ensembles. For antiferromagnetic systems, all solutions are found to be neutrally stable at all temperatures, suggesting that dynamical ordering is relatively easy to observe at low temperatures compared with ferromagnetic systems.
On the -Euler Numbers and Polynomials with Weight
T. Kim,J. Choi
Abstract and Applied Analysis , 2012, DOI: 10.1155/2012/795304
Abstract: The purpose of this paper is to investigate some properties of -Euler numbers and polynomials with weight 0. From those -Euler numbers with weight 0, we derive some identities on the -Euler numbers and polynomials with weight 0.
On the -Bernoulli Numbers and Polynomials with Weight
T. Kim,J. Choi
Abstract and Applied Analysis , 2011, DOI: 10.1155/2011/392025
Abstract: We present a systemic study of some families of higher-order -Bernoulli numbers and polynomials with weight . From these studies, we derive some interesting identities on the -Bernoulli numbers and polynomials with weight .
Hybrid Spectral Difference/Embedded Finite Volume Method for Conservation Laws
Jung J. Choi
Mathematics , 2014, DOI: 10.1016/j.jcp.2015.04.013
Abstract: A novel hybrid spectral difference/embedded finite volume method is introduced in order to apply a discontinuous high-order method for large scale engineering applications involving discontinuities in the flows with complex geometries. In the proposed hybrid approach, the finite volume (FV) element, consisting of structured FV subcells, is embedded in the base hexahedral element containing discontinuity, and an FV based high-order shock-capturing scheme is employed to overcome the Gibbs phenomena. Thus, a discontinuity is captured at the resolution of FV subcells within an embedded FV element. In the smooth flow region, the SD element is used in the base hexahedral element. Then, the governing equations are solved by the SD method. The SD method is chosen for its low numerical dissipation and computational efficiency preserving high-order accurate solutions. The coupling between the SD element and the FV element is achieved by the globally conserved mortar method. In this paper, the 5th-order WENO scheme with the characteristic decomposition is employed as the shock-capturing scheme in the embedded FV element, and the 5th-order SD method is used in the smooth flow field. The order of accuracy study and various 1D and 2D test cases are carried out, which involve the discontinuities and vortex flows. Overall, it is shown that the proposed hybrid method results in comparable or better simulation results compared with the standalone WENO scheme when the same number of solution DOF is considered in both SD and FV elements.
Simulation of controlled queuing systems and its application to optimal resource management in multiservice cellular networks
Choi, Jinsung;Silvester, J. A.;
Journal of the Brazilian Computer Society , 1999, DOI: 10.1590/S0104-65001999000100005
Abstract: we consider a controlled queuing model and derive the corresponding markov decision process for simple g/m/1 call admission controller. as an application of the controlled queuing model, we look into an optimal resource management problem arising in the context of multiservice cellular network with reuse partitioning. in particular, we consider a channel borrowing scheme between zones in two-zone reuse partitioning in a two-class cellular network and investigated the performance of various channel borrowing policies via simulation. we also introduce the simulator developed for controlled queuing systems. most importantly, we demonstrate that markov decision processes are well suited to this kind of optimization problem.
Inflammatory cytokines IL-1β and TNF-α regulate p75NTR expression in CNS neurons and astrocytes by distinct cell-type-specific signalling mechanisms
Soyoung Choi,Wilma J Friedman
ASN Neuro , 2009, DOI: 10.1042/an20090009
Abstract: The p75NTR (where NTR is neurotrophin receptor) can mediate many distinct cellular functions, including cell survival and apoptosis, axonal growth and cell proliferation, depending on the cellular context. This multifunctional receptor is widely expressed in the CNS (central nervous system) during development, but its expression is restricted in the adult brain. However, p75NTR is induced by a variety of pathophysiological insults, including seizures, lesions and degenerative disease. We have demonstrated previously that p75NTR is induced by seizures in neurons, where it induces apoptosis, and in astrocytes, where it may regulate proliferation. In the present study, we have investigated whether the inflammatory cytokines IL (interleukin)-1β and TNF-α (tumour necrosis factor-α), that are commonly elevated in these pathological conditions, mediate the regulation of p75NTR in neurons and astrocytes. We have further analysed the signal transduction pathways by which these cytokines induce p75NTR expression in the different cell types, specifically investigating the roles of the NF-κB (nuclear factor κB) and p38 MAPK (mitogen-activated protein kinase) pathways. We have demonstrated that both cytokines regulate p75NTR expression; however, the mechanisms governing this regulation are cytokine- and cell-type specific. The distinct mechanisms of cytokine-mediated p75NTR regulation that we demonstrate in the present study may facilitate therapeutic intervention in regulation of this receptor in a cell-selective manner.
Real Higgs singlet and the electroweak phase transition in the standard model, (UM-P-93/80, OZ-93/20)
J. Choi,R. R. Volkas
Physics , 1993, DOI: 10.1016/0370-2693(93)91013-D
Abstract: The effective potential at finite temperature is constructed within the minimal standard model when a real Higgs singlet is added on. We find that a region of parameter space exists for which one can find a first order transition strong enough to prevent the erasure due to sphalerons of baryon asymmetry, while keeping the mass of the smallest Higgs boson above the experimental lower bound of about 60 GeV.
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