arXiv subjects

Yong Xu

Publications and source records attributed to Yong Xu.

496 records · Page 28Linked to original sources

arXiv2013

Structure of two-component Bose-Einstein condensates with respective vortex-antivortex superposition states

We investigate the phase structure of two-component Bose-Einstein condensates (BECs) with repulsive intra- and interspecies interactions in the presence of respective vortex-antivortex superposition states (VAVSS). We show that different winding numbers of vortex and antivortex and different intra- and interspecies interaction strengths may lead to different phase configurations, such as fully separated phases, inlaid separated phases, asymmetric separated phase, and partially mixed phases, where the density profile of each component displays a petal-like (or modulated petal-like) structure. A phase diagram is given for the case of equal unit winding numbers of the vortex and antivortex in respective components, and it is shown that conventional criterion for phase separation of two-component BECs is not applicable for the present system due to the VAVSS. In addition, our nonlinear stability analysis indicates that the typical phase structures of two-component BECs with VAVSS allow to be detected in experiments. Moreover, for the case of unequal winding numbers of the vortex and antivortex in respective components, we find that each component in any of the possible phase structures is in a cluster state of vortices and antivortices, where the topological defects appear in the form of singly quantized visible vortex, or hidden vortex, or ghost vortex, depending on the specific parameters of the system. Finally, a general rule between the vortex-antivortex cluster state and the winding numbers of vortex and antivortex is revealed.

cond-mat.quant-gas↗

arXiv2013

Stability of $p$-orbital Bose-Einstein condensates in optical checkerboard and square lattices

We investigate $p$-orbital Bose-Einstein condensates in both the square and checkerboard lattice by numerically solving the Gross-Pitaevskii equation. The periodic potential for the latter lattice is taken exactly from the recent experiment [Nature Phys. 7, 147 (2011)]. It is confirmed that the staggered orbital-current state is the lowest-energy state in the $p$ band. Our numerical calculation further reveals that for both lattices the staggered $p$-orbital state suffers Landau instability but the situation is remarkably different for dynamical instability. A dynamically stable parameter region is found for the checkerboard lattice, but not for the square.

cond-mat.quant-gas↗

arXiv2013

Bright solitons in spin-orbit-coupled Bose-Einstein condensates

We study bright solitons in a Bose-Einstein condensate with a spin-orbit coupling that has been realized experimentally. Both stationary bright solitons and moving bright solitons are found. The stationary bright solitons are the ground states and possess well-defined spin-parity, a symmetry involving both spatial and spin degrees of freedom; these solitons are real valued but not positive definite, and the number of their nodes depends on the strength of spin-orbit coupling. For the moving bright solitons, their shapes are found to change with velocity due to the lack of Galilean invariance in the system.

cond-mat.quant-gas↗

arXiv2013

Stochastic Averaging Principle for Dynamical Systems with Fractional Brownian Motion

Stochastic averaging for a class of stochastic differential equations (SDEs) with fractional Brownian motion, of the Hurst parameter H in the interval (1/2, 1), is investigated. An averaged SDE for the original SDE is proposed, and their solutions are quantitatively compared. It is shown that the solution of the averaged SDE converges to that of the original SDE in the sense of mean square and also in probability. It is further demonstrated that a similar averaging principle holds for SDEs under stochastic integral of pathwise backward and forward types. Two examples are presented and numerical simulations are carried out to illustrate the averaging principle.

math.DS↗

arXiv2012

Lévy Noise Induced Switch in the Gene Transcriptional Regulatory System

Gene transcriptional regulatory is an inherently noisy process. In this paper, the study of fluctuations in a gene transcriptional regulatory system is extended to the case of Lévy noise, a kind of non-Gaussian noises which can describe unpredictable jump changes of the random environment. The stationary probability density is given to explore the key roles of Lévy noise in the gene regulatory networks. The results demonstrate that the parameters of Lévy noise, including noise intensity, stability index and skewness parameter can induce switches between distinct gene-expression states. A further concern is the switching time (from the high concentration state to the low concentration one or from the low concentration state to the high concentration one), which is a random variable and often referred to as the mean first passage time. The effects of Lévy noise in expression time and degradation time is studied by computing the mean first passage time in two directions and a number of different peculiarities of non-Gaussian Lévy noise compared with Gaussian noise are observed.

physics.bio-ph↗

arXiv2012

Lévy Noise-Induced Stochastic Resonance in a Bistable System

Stochastic resonance phenomenon induced by non-Gaussian Lévy noise in a second-order bistable system is investigated. The signal-noise-ratio for different parameters is computed by an efficient numerical scheme. The influences of the noise intensity, stability index of Lévy noise and amplitude of external signal on the occurrence of stochastic resonance phenomenon are characterized. This implies that a high amplitude of signal not only enhances the output power spectrum of system but also promotes stochastic resonance, and a proper adjustment of Lévy noise intensity in a certain range enlarges the peak value of output power spectrum which is significant for stochastic resonance. Moreover, with the optimal damping parameter, lowering the stability index leads to larger fluctuations of Lévy noise, and further reduces the chance of the stochastic resonance.

cond-mat.stat-mech↗

arXiv2009

Intrinsic anisotropy of thermal conductance in graphene nanoribbons

Thermal conductance of graphene nanoribbons (GNRs) with the width varying from 0.5 to 35 nm is systematically investigated using nonequilibrium Green's function method. Anisotropic thermal conductance is observed with the room temperature thermal conductance of zigzag GNRs up to ~ 30% larger than that of armchair GNRs. At room temperature, the anisotropy is found to disappear until the width is larger than 100 nm. This intrinsic anisotropy originate from different boundary condition at ribbon edges, and can be used to tune thermal conductance, which have important implications for the applications of GNRs in nanoelectronics and thermoelectricity.

cond-mat.mes-hall↗

arXiv2008

Nonequilibrium Green's function method for phonon-phonon interaction and ballistic-diffusive thermal transport

Phonon-phonon interaction is systematically studied by nonequilibrium Green's function (NEGF) formulism in momentum space at finite temperatures. Within the quasi-particle approximation, phonon frequency shift and lifetime are obtained from the retarded self-energy. The lowest order NEGF provides the same phonon lifetime as Fermi's golden rule. Thermal conductance is predicted by the Landauer formula with a phenomenological transmission function. The main advantage of our method is that it covers both ballistic and diffusive limits and thermal conductance of different system sizes can be easily obtained once the mode-dependent phonon mean free path is calculated by NEGF. As an illustration, the method is applied to two one-dimensional atom chain models (the FPU-βmodel and the ϕ^4 model) with an additional harmonic on-site potential. The obtained thermal conductance is compared with that from a quasi-classical molecular dynamics method. The harmonic on-site potential is shown to remove the divergence of thermal conductivity in the FPU-βmodel.

cond-mat.mes-hall↗

arXiv2006

A Genetic Algorithm Approach to the Grooming of Dynamic Traffic in Tree and Star Networks with Bifurcation

Traffic grooming is widely employed to reduce the number of ADM's and wavelengths. We consider the problem of grooming of dynamic traffic in WDM tree and star networks in this paper. To achieve better results, we used the bifurcation techniques to the grooming of arbitrary dynamic traffic in a strictly non-blocking manner in networks. Three splitting methods, including Traffic-Cutting, Traffic-Dividing and Synthesized-Splitting were proposed. A genetic algorithm (GA) approach based on these methods was proposed to tackle such grooming problems in tree and star networks. The performance of these algorithms was tested under different conditions in star and tree networks. Computer simulation results showed that our algorithm is efficient in reducing both the numbers of ADM's and wavelengths.

cs.NI↗

arXiv2006

Grooming of Dynamic Traffic in WDM Star and Tree Networks Using Genetic Algorithm

The advances in WDM technology lead to the great interest in traffic grooming problems. As traffic often changes from time to time, the problem of grooming dynamic traffic is of great practical value. In this paper, we discuss dynamic grooming of traffic in star and tree networks. A genetic algorithm (GA) based approach is proposed to support arbitrary dynamic traffic patterns, which minimizes the number of ADM's and wavelengths. To evaluate the algorithm, tighter bounds are derived. Computer simulation results show that our algorithm is efficient in reducing both the numbers of ADM's and wavelengths in tree and star networks.

cs.NI↗