Standing pulses in almost periodic channels

We use variational methods to study the existence of standing pulses in almost periodic channels. Since there is no group of symmetries as in the periodic case for which the functional is invariant, the negative gradient flow will be utilized to generate the convergent Palais–Smale sequences. Starting with suitable initial data, we prove that the infinite number of standing pulses can actually be found out in almost periodic channels.     

Standing pulses in almost periodic channels

We use variational methods to study the existence of standing pulses in almost periodic channels. Since there is no group of symmetries as in the periodic case for which the functional is invariant, the negative gradient flow will be utilized to generate the convergent Palais–Smale sequences. Starting with suitable initial data, we prove that the infinite number of standing pulses can actually be found out in almost periodic channels.     

A relation between the pressure gradient and the flux for the general channel flow problem

In this paper we establish that the pressure gradient and the flux, for a linear stationary Stokes problem for general periodic two-dimensional channels, are related by a simple formula, the same as that for laminar Poiseuille flows.     

Time periodic solutions to the Navier–Stokes equations in the rotational framework

We consider the Navier–Stokes equations in the rotational framework with the time periodic external force. We give sufficient conditions on the size of the external forces for the existence of time periodic solutions in terms of the Coriolis parameter. It follows from our conditions that the unique existence of time periodic solutions is guaranteed for large external forces provided the speed of rotation is sufficiently fast.     

Double scattering channels for 1D NLS in the energy space and its generalization to higher dimensions

We consider a class of 1D NLS perturbed with a steplike potential. We prove that the nonlinear solutions satisfy the double scattering channels in the energy space. The proof is based on concentration-compactness/rigidity method. We prove moreover that in dimension higher than one, classical scattering holds if the potential is periodic in all but one dimension and is steplike and repulsive in the remaining one.     

Organizational growth and hierarchical change in formal structure

Three hypotheses about aggregate change in organizational size (measured as number of employees) and formal structure over time are tested: (1.) the frequency of hierarchical change is higher at lower levels of hierarchy; (2.) periodic pressures for organizational change are translated into periodic changes in organizational size; and (3.) changes in size are more readily translated into increases in structure at lower levels of hierarchy. These hypotheses are tested by using spectral analysis to decompose the variance in the time series of size and structure. The implications of the confirmation of these hypotheses for organizational change over time are discussed.     

Symmetric patterns in the Dirichlet problem for a two-cell cubic autocatalytor reaction model

By using an approach developed by one of the authors, approximate solutions of the soft periodic boundary conditions for a two-cell reaction diffusion model have been obtained. The system is considered with reactant A and autocatalyst B. The reaction is taken cubic in the autocatalyst in the two-cell with linear exchange through A. The formal exact solution is obtained which is symmetric with respect to the mid-point of the container. Approximate solutions are found through the Picard iterative sequence of solutions constructed after the exact one. It is found that the solution obtained is not unique. When the initial conditions are periodic, the most dominant modes initiate to traveling waves in systems with moderate size. Symmetric configurations forming a parabolic one for large time are observed. In systems of large size, spatially symmetric chaos are produced which are stationary in time. Furthermore, it is found the symmetric pattern formation hold irrespective of the condition of linear instability against small spatial disturbance.     

Risk aggregation based on the Poisson INAR(1) process with periodic structure

In this paper, we consider a risk model by introducing a temporal dependence between the claim numbers under periodic environment, which generalizes several discrete-time risk models. The model proposed is based on the Poisson INAR(1) process with periodic structure. We study the moment-generating function of the aggregate claims. The distribution of the aggregate claims is discussed when the individual claim size is exponentially distributed.     

The weak capacity of averaged channels

Summary Coding theorem and weak converse of the coding theorem are proved for averaged semicontinuous stationary channels and for almost periodic discrete channels, whose phases are statistically known. Explicit formulas for the capacities are given. The strong converses of the coding theorems do not hold.     

四边形剖分下的组合多尺度有限元方法求解多尺度椭圆问题（英文）

The combined finite element and multiscale finite element method(FEMsFEM) [W. Deng and H. Wu, Multiscale Model. Simul., 12(2014), pp.1424-1457.]has been introduced for the multiscale elliptic problems. This is accomplished by using the standard finite element method on a fine mesh of the problematic part of the domain and using the oversampling MsFEM on a coarse mesh of the other part. The transmission condition across the FE-MsFE interface is treated by the penalty technique. FE-MsFEM can solve the multiscale elliptic problems with fine and long-ranged high contrast channels very efficiently. However, the detailed convergence analysis reveals that the error generated by the mismatch between the triangulation and the period of the coefficient still exists. A direct approach to reduce this error is to utilize the rectangle mesh for the domain. In this paper,we investigate the FE-MsFEM based on the rectangle mesh for the multiscale elliptic problems. Error estimate is given under the assumption that the oscillating coefficient is periodic. Numerical experiments for the rectangle mesh are carried out on the multiscale problems with periodic highly oscillating coefficient and high contrast channels. Their results demonstrate the efficiency of the proposed method.     

Spectral problem with Steklov condition on a thin perforated interface

A two-dimensional Steklov-type spectral problem for the Laplacian in a domain divided into two parts by a perforated interface with a periodic microstructure is considered. The Steklov boundary condition is set on the lateral sides of the channels, a Neumann condition is specified on the rest of the interface, and a Dirichlet and Neumann condition is set on the outer boundary of the domain. Two-term asymptotic expansions of the eigenvalues and the corresponding eigenfunctions of this spectral problem are constructed.     

Effect of the phase on the dynamics of a perturbed bouncing ball system

The phase control method is a non-feedback control technique which has been used for different purposes in continuous periodically driven dynamical systems. One of the main goals of this paper is to apply this control technique to the bouncing ball system, which can be seen as a paradigmatic periodically driven discrete dynamical system, and has a rather simple physical interpretation. The main idea is to apply a periodic control signal including a phase difference with respect to the periodic forcing of the initial system and to analyze its effect on the dynamics of the bouncing ball system. The numerical simulations we have carried out clearly show the strong effect of the phase of the control signal in suppressing or generating chaotic behavior and in changing the period of a periodic orbit. We have also analyzed the effect of the phase in the phenomenon of the crisis-induced intermittency, showing how the phase enhances the size of the attractor near a crisis and can induce the intermittent behavior. Finally we have analyzed the scaling behavior of the crisis by varying the phase difference between the perturbation and the external forcing.     

A Sharp Existence Theorem for Vortices in the Theory of Branes

In this paper, we investigate the existence of solutions for a system of BPS vortex equations arising from the theory of multiple intersecting D-branes. Using a direct minimization method, we establish a sharp existence and uniqueness theorem for this system over a doubly periodic domain and over the full plane, respectively. In particular, we obtain an explicit necessary and sufficient condition, explicitly expressed in terms of the vortex numbers and the size of the domain, for the existence of a solution of the system in the doubly periodic domain case.     

无限压电体内共线周期裂纹间的相互作用

研究了无限压电体内共线周期裂纹间的相互作用的问题,并且考虑了裂纹尖端的饱和条带作用．应用Stroh理论和保角变换方法,得到了共线裂纹的一般周期解A·D2对应力强度因子和饱和条带尺寸进行了理论推导,详细分析了它们与周期长和半裂纹长的比值h/l之间的关系．数值结果表明:1) 当h/l大于4.0时,裂纹之间的相互作用对应力强度因子影响较小,无限压电体内周期裂纹和单裂纹的值几乎相等．这表明当h大于4.0l时,建立裂纹扩展判据时可以近似忽略裂纹之间的相互作用;2) 周期裂纹的饱和条带尺寸趋近于单裂纹值的速度,取决于无穷远处的电载荷,通常无穷远处的电载荷越大,趋近速度越慢．     

On invariant closed curves for one-step methods

Summary We show that a one-step method as applied to a dynamical system with a hyperbolic periodic orbit, exhibits an invariant closed curve for sufficiently small step size. This invariant curve converges to the periodic orbit with the order of the method and it inherits the stability of the periodic orbit. The dynamics of the one-step method on the invariant curve can be described by the rotation number for which we derive an asymptotic expression. Our results complement those of [2, 3] where one-step methods were shown to create invariant curves if the dynamical system has a periodic orbit which is stable in either time direction or if the system undergoes a Hopf bifurcation.     

Averaging of Neumann problems for nonlinear elliptic equations in regions of framework type with thin channels

TheG-convergence of operators of the Neumann problem is established in regions with framework-type periodic structure with thin channels. A representation of the coefficients of aG-limiting operator is obtained.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 45, No. 11, pp. 1503–1513, November, 1993.     

Averaging of integral functionals related to domains of frame-type periodic structure with thin channels

We establish the Γ-convergence of a sequence of integral functionals related to domains of frame-type periodic structure with thin channels. We obtain a representation for the integrand of a Γ-limit functional.     

Crisis transitions in excitable cell models

It is believed that sudden changes both in the size of chaotic attractor and in the number of unstable periodic orbits on chaotic attractor are sufficient for interior crisis. In this paper, some interior crisis phenomena were discovered in a class of physically realizable dissipative dynamical systems. These systems represent the oscillatory activity of membrane potentials observed in excitable cells such as neuronal cells, pancreatic β-cells, and cardiac cells. We examined the occurrence of interior crises in these systems by two means: (i) constructing bifurcation diagrams and (ii) calculating the number of unstable periodic orbits on chaotic attractor. Bifurcation diagrams were obtained by numerically integrating the simultaneous differential equations which simulate the activity of excitable membranes. These bifurcation diagrams have shown an apparent crisis activity. We also demonstrate in terms of the associated Poincaré maps that the number of unstable periodic orbits embedded in a chaotic attractor suddenly increases or decreases at the crisis.     

Lytic cycle: A defining process in oncolytic virotherapy

The viral lytic cycle is an important process in oncolytic virotherapy. Most mathematical models for oncolytic virotherapy do not incorporate this process. In this article, we propose a mathematical model with the viral lytic cycle based on the basic mathematical model for oncolytic virotherapy. The viral lytic cycle is characterized by two parameters, the time period of the viral lytic cycle and the viral burst size. The time period of the viral lytic cycle is modeled as a delay parameter. The model is a nonlinear system of delay differential equations. The model reveals a striking feature that the critical value of the period of the viral lytic cycle is determined by the viral burst size. There are two threshold values for the burst size. Below the first threshold, the system has an unstable trivial equilibrium and a globally stable virus free equilibrium for any nonnegative delay, while the system has a third positive equilibrium when the burst size is greater than the first threshold. When the burst size is above the second threshold, there is a functional relation between the bifurcation value of the delay parameter for the period of the viral lytic cycle and the burst size. If the burst size is greater than the second threshold, the positive equilibrium is stable when the period of the viral lytic cycle is smaller than the bifurcation value, while the system has orbitally stable periodic solutions when the period of the lytic cycle is longer than the bifurcation value. However, this bifurcation value becomes smaller when the burst size becomes bigger. The viral lytic cycle may explain the oscillation phenomena observed in many studies. An important clinic implication is that the burst size should be carefully modified according to its effect on the lytic cycle when a type of a virus is modified for virotherapy, so that the period of the viral lytic cycle is in a suitable range which can break away the stability of the positive equilibria or periodic solutions.     

Time periodic and almost time periodic solutions to rotating stratified fluids subject to large forces

Consider the 3D incompressible Boussinesq equations for rotating stably stratified fluids. It is shown that this set of equations possesses a unique time periodic or almost time periodic solutions for external forces satisfying these properties, which, however, do not necessarily need to be small. An explicit bound on the size of the external force, depending on the buoyancy frequency N, is given, which then allows for the unique existence of time periodic or almost periodic solutions. In particular, the size of the external forces can be taken large with respect to the buoyancy frequency. The approach depends crucially on the dispersive effect of the rotation and the stable stratification.