Modeling the dynamics of information propagation in the temporal and spatial environment

In this paper, we try to establish a non-smooth susceptible–infected–recovered(SIR) rumor propagation model based on time and space dimensions. First of all, we prove the existence and uniqueness of the solution. Secondly, we divide the system into two parts and discuss the existence of equilibrium points for each of them. For the left part, we define R₀ to study the relationship between R₀ and the existence of equilibrium points. For the right part, we classify many differ...     

Damping of second sound in the critical dynamics of liquid helium belowT λ

We calculate toO(=4 –d) the effect of the small ratiow ^* of the relaxation rates of the order parameter and the entropy on the damping of second sound in the hydrodynamic regime of liquid helium belowT . Forw ^* 1 we find a partial reduction of the previous discrepancy between theory and experiment on the amplitude of second sound damping.On leave from Universität Linz, Austria     

When does coarsening occur in the dynamics of one-dimensional fronts?

Dynamics of a one-dimensional growing front with an unstable straight profile are analyzed. We argue that a coarsening process occurs if and only if the period lambda of the steady-state solution is an increasing function of its amplitude A. This statement is rigorously proved for two important classes of conserved and nonconserved models by investigating the phase diffusion equation of the steady pattern. We further provide clear numerical evidence for the growth equation of a stepped crystal surface.     

Nonlinear dynamics of deformation bands in aluminum–magnesium alloy in the creep test

Various types of plastic instabilities that emerge in intermittent creep have been studied experimentally for AlMg6 aluminum–magnesium alloy. It has been shown that intermittent creep exhibits threshold dynamics. The deformation step on the creep curve of amplitude is ~1–6% and begins when the rate of the preceding continuous creep attains a certain critical value. In the course of evolution of the step, the strain rate varies in the interval that spans more than two orders of magnitude, and transitions occur between different dynamic regimes of type A and B characterized by different stress drop regularity levels in the force response. Nonlinear aspects of the deformation behavior of the alloy in the intermittent creep conditions are considered.     

Collision dynamics of two Bose–Einstein condensates in the presence of Raman coupling

A collision of two-component Bose-Einstein condensates in the presence of Raman coupling is proposed and studied by numerical simulations. Raman transitions are found to be able to reduce collision-produced irregular excitations by forming a time-averaged attractive optical potential. Raman transitions also support a kind of dark soliton pair in two-component Bose-Einstein condensates. Soliton pairs and their remnant single solitons are shown to be controllable by adjusting the initial relative phase between the two colliding condensates or the two-photon detuning of Raman transitions. Received: 5 February 2001 / Published online: 27 April 2001     

Effect of a localized impurity on soliton dynamics in the Bose-Einstein condensates

By using a multiple-scale method,we analytically study the effect of a localized impurity on the soliton dynamics in the Bose-Einstein condensates.It is shown that a dark soliton can be transmitted through a repulsive (or attractive) impurity,while at the position of the localized impurity the soliton can be quasitrapped by the impurity.Additionally,we find that the strength of the localized impurity has an important effect on the dark soliton dynamics.With increasing strength of the localized impurity,the amplitude of the dark soliton becomes bigger,while its width is narrower,and the soliton propagates slower.     

Influence of second sideband excitation on the dynamics of trapped ions in a cavity

We study the dynamics of a trapped ion placed at an antinode of the standing wave inside a high finesse cavity with consideration of the second sideband excitation between the ionic internal levels and the light field. We investigate the entanglement of the three subsystems embodying the ionic internal levels, the vibrational mode of the ion and the cavity field.     

Mössbauer study of the dynamics of iron ions in bipyramidal positions of strontium hexaferrite

The dynamics of Fe³⁺ ions in bipyramidal 2b positions of a type M hexaferrite are studied on single-crystal and polycrystalline SrFe₆Ga₆O₁₉ samples in the paramagnetic temperature range. We show that when the angle between the c axis of the crystal and the direction of -ray emission varies from 0 to 32 the area under the resonance lines corresponding to Fe³⁺ ions in 2b positions increases by a factor of roughly 1.5. The effect is more pronounced upon passing from a single-crystal sample (=0) to a polycrystalline sample. A comparison of the line intensities under different experimental conditions served as a basis for an evaluation of the difference between the mean-square displacements of the Fe³⁺ ions in 2b positions along the c axis in the perpendicular plane.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 5–8, January, 1991.     

Linear entropy dynamics of the field in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation

We present the linear entropy dynamics of the field state in the dispersive cavity in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation, and investigate the influence of dissipation on entanglement between the field and the atoms. We show that the coherence properties of the field are also affected by the cavity when the nonlinear process of the field interacting with the atoms with an intensity-dependent coupling is involved, and find that the dissipation constant, the intensity of the field and the atomic distribution angle have different influence on the coherence properties of the field.     

‘Percolative’ dynamics in the hexagonal lattice

We study a percolative dynamic model for the hexagonal lattice. Random trajectories are generated and their critical behaviour is studied. The critical behaviour corresponds to that of simple percolatio in some of the parameter space, but elsewhere the exponents reveal new universality classes. We calculate the fractal dimension of extended trajectories for different critical points.     

The dynamics of 180° domains in a ferroelectric in the process of polarization reversal and electron emission

A model is proposed to describe the evolution of 180° domains in a ferroelectric. Closed analytic expressions are obtained for the velocity of sideways motion of a 180° domain wall in an electric field and numerical calculations are performed. The connection between polarization reversal and electron emission is discussed.     

Critical dynamics of φ2n with random fields in the tree approximation

In the tree approximation, the critical relaxational dynamics of ²ⁿ with quenched random fields is calculated by renormalization near the upper critical dimensiond _u=4+2/(n–1). Although the relation between the characteristic frequency _c q and the wave-numberq is as usual,unusual results are obtained for the asymptotic decay of the order-parameter correlation functionS(q,t).Dedicated to Prof. Dr. W. Döring on the occasion of his 75th birthday     

Molecular dynamics investigation of the size effect upon the β → α transformation in Zr nanocrystals

The stability of the β phase in cubic zirconium nanoparticles has been calculated as a function of the size r (r varies in the range from 2.5 to 11.5 nm) by the molecular dynamics method with the many-body interatomic interaction potential obtained within the embedded-atom model. It has been demonstrated that the temperature T _k at which the cubic cluster of body-centered cubic zirconium becomes structurally unstable depends nonlinearly on the particle size. The curve T _k (r) exhibits a pronounced maximum in the range r ≈ 4.3−4.7 nm. It has been established that the mechanism of the structural transition from the body-centered cubic phase to the hexagonal close-packed phase depends substantially on the particle size. For particles with sizes in the range from 2.5 to 5.0 nm, there exists a temperature range in which the transition from the body-centered cubic phase to the hexagonal close-packed phase remains incomplete for a long time. In this case, two phases coexist and the initial particle undergoes a strong deformation along the habit plane.     

muSR study of the quantum dynamics in the frustrated S=3/2 kagomé bilayers

We present muSR experiments in the S=3/2 kagomé bilayer compound Ba(2)Sn(2)ZnGa(10-7p)Cr(7p)O22 [BSZCGO(p)] and compare it to the isostructural SrCr(9p)Ga(12-9p)O19 [SCGO(p)], including for the latter new results for p > or =0.89. Quantum-dynamical low energy magnetic excitations are evidenced in this novel compound. We study the evolution of the muon relaxation rate with p, T, and field. A phenomenological model for the muon relaxation based on sporadic dynamics due to spin excitations in a singlet sea proposed by Uemura et al. is extended to all fields and T range. Its connection to the RVB picture is discussed, and we argue that such coherent states might mediate the interactions between "impurities" which induce the spin glass freezing.     

Nonlinear dynamics in sliding processes： the single-particle case

Dynamical behaviours of the motion of particles in a periodic potential under a constant driving velocity by a spring at one end are explored. In the stationary case, the stable equilibrium position of the particle experiences an elasticity instability transition. When the driving velocity is nonzero, depending on the elasticity coefficient and the pulling velocity, the system exhibits complicated and interesting dynamics, such as periodic and chaotic motions. The results obtained here may shed light on studies of dynamical processes in sliding friction.     

Influence of one-dimensional “defects” on the new-phase nucleation dynamics near the first-order transition in magnets

The evolution of a new-phase nucleus near the first-order spin-reorientation phase transition in magnets has been investigated. A strong influence of one-dimensional magnetic anisotropy “defects” on the nucleation dynamics has been shown. The conditions of the localization of the new-phase nucleus in the region of the magnetic anisotropy “defect” have been determined.