一种新的带参数双三次有理插值样条的有界性与点控制

文[19]中,作者构造了一种基于函数值的带参数的分子为双三次、分母为双二次的二元有理插值样条.本文进一步研究该种二元有理插值样条的有界性,给出插值的逼近表达式,讨论插值曲面形状的点控制问题.在插值条件不变的情况下,插值区域内任一点插值函数的值可以根据设计的需要通过对参数的选取修改,从而达到插值曲面局部修改的目的.     

Runge-Kutta-Nystrm方法的若干新性质

本文研究了由Runge-Kutta(RK)方法Φ生成Runge-Kutta-Nystr(?)m(RKN)方法Φ_N的伴随西Φ~*_N的两种途径,证明了由这两条途径生成的西Φ~*_N是相同的;讨论了具有辛性,对称性或P-稳定性的Φ,Φ_N,Φ~*_N之间的一些关系;并表明通过辛(或对称)RK方法可构造辛(或对称) RKN方法.     

基于偏振度椭球的PMD补偿的前馈信息提取方法

通过建立一个简单的模型推导了偏振模色散与偏振度椭球的关系式,可以直接从偏振度椭球的长轴和短轴得到偏振模色散的大小.将得到的一阶偏振模色散大小与理论上从琼斯矩阵中计算的结果进行比较,发现在差分群时延小于20 ps时,模拟结果与理论计算值较好相符.分析了如何从偏振度椭球的长轴判断偏振模色散矢量的方向.因此,从得到的偏振模色散矢量的大小和方向信息可以为一阶偏振模色散补偿提供前馈信息.     

The combination of QoS,aggregation and RTS/CTS in Very High Throughput IEEE 802.11ac networks

We consider a single WiFi cell in which multiple mobile stations transmit multiple QoS constrained Application flows to the Access Point. We investigate the efficiency of using RTS/CTS in the face of the QoS constraints, in various Access Categories that are defined in the WiFi standard, in a number of transmitting stations and in various amounts of aggregation. We show that using RTS/CTS is efficient in terms of Throughput, when there are collisions and the time to recover these collisions is within the Delay/Loss constraints of the Application flows. It turns out that RTS/CTS is most efficient in the Video and Voice Access Categories and Delay constrains in the order of several tens of milli-seconds. For smaller Delay constraints it is more efficient without RTS/CTS. Thus, we show the existence of cross-points: In Delay constraints smaller than the cross points it is more efficient without RTS/CTS and beyond the cross-points the opposite is true.     

Positive almost periodic solution of discrete nonlinear survival red blood cells model with feedback control

In this paper, we consider a discrete survival red blood cells system with feedback control. Assuming that the coefficients in the system are almost periodic sequences, by using Lyapunov functional approach, we obtain the existence and uniqueness of the almost periodic solution which is uniformly asymptotically stable.     

A robust chaotic algorithm for digital image steganography

This paper proposes a new robust chaotic algorithm for digital image steganography based on a 3-dimensional chaotic cat map and lifted discrete wavelet transforms. The irregular outputs of the cat map are used to embed a secret message in a digital cover image. Discrete wavelet transforms are used to provide robustness. Sweldens’ lifting scheme is applied to ensure integer-to-integer transforms, thus improving the robustness of the algorithm. The suggested scheme is fast, efficient and flexible. Empirical results are presented to showcase the satisfactory performance of our proposed steganographic scheme in terms of its effectiveness (imperceptibility and security) and feasibility. Comparison with some existing transform domain steganographic schemes is also presented.     

Stagnation point flow and heat transfer over a non-linearly moving flat plate in a parallel free stream with slip

An analysis is presented for the steady boundary layer flow and heat transfer of a viscous and incompressible fluid in the stagnation point towards a non-linearly moving flat plate in a parallel free stream with a partial slip velocity. The governing partial differential equations are converted into nonlinear ordinary differential equations by a similarity transformation, which are then solved numerically using the function bvp4c from Matlab for different values of the governing parameters. Dual (upper and lower branch) solutions are found to exist for certain parameters. Particular attention is given to deriving numerical results for the critical/turning points which determine the range of existence of the dual solutions. A stability analysis has been also performed to show that the upper branch solutions are stable and physically realizable, while the lower branch solutions are not stable and, therefore, not physically possible.     

Abundant bursting patterns of a fractional-order Morris–Lecar neuron model

In this paper, a fractional-order Morris–Lecar (M–L) neuron model with fast-slow variables is firstly proposed. The fractional-order M–L model is a generalization of the integer-order M–L model with fast-slow variables, where the fractional-order derivative is used to characterize the memory effect and power law of membranes. Then the bursting patterns of the new model are investigated by using the bifurcation theory of fast-slow dynamical systems. Numerical simulation shows that the new model exhibits some bursting patterns that appear in some common neuron models with properly chosen parameters but do not exist in the corresponding integer-order M–L model. Further, on the basis of a comparison of the nonlinear dynamics between the fractional-order M–L model and the integer-order M–L model, we show that the fractional-order derivative can activate the slow potassium ion channel faster and play an important role to modulate the firing activity of the new model.