一种改进的高性能Lorenz系统构造及其应用

Lorenz系统是一种最具有代表性、典型性的混沌模型之一, 一直被众多学者深入研究和广泛应用.为了获取结构和动力学行为更为复杂的混沌吸引子, 不断改善Lorenz系统已成为混沌动力系统研究中的重要课题之一. 为此, 本文提出了一个具有复杂系统动力学行为的改进的Lorenz系统, 并将其用于图像信息安全保护. 在现有各种改进的Lorenz系统的基础上, 首先通过增加Lorenz系统的控制参数和改变非线性项相结合的方法构造出一种新的Lorenz 混沌系统; 其次采用微分动力系统方法深入研究该系统并获得与Lorenz系统、Bao系统、Tee系统和Y系统等具有相似的耗散性、对称性、稳定性, 以及更加复杂的混沌特性和动力学行为, 同时分析该系统所产生随机序列具有良好的相关性和复杂性; 最后将其所产生的离散伪随机序列用于图像置乱和扩散加密, 通过对图像加密结果的相邻像素相关性分析、灰度空间相关特性不确定性分析、抗差分攻击以及密钥敏感性测试, 表明本文所构造的改进的Lorenz系统应用于图像加密能获得相对较高的安全性.     

An improved dynamic subgrid-scale model and its application to large eddy simulation of rotating channel flows

Rotating turbulence occurs extensively in nature and engineering circumstances. Meanwhile, understanding physical mechanisms of the rotating turbulence is important to the fundamental research of turbulence. The turbulent flow in rotating frames undergoes two kinds of Coriolis force effects. First, a secondary flow is induced in the case that there is a mean vorticity component perpendicular to the rotating axis. Second, there are augmenting or suppressing effects on the turbulence if there i…     

An improved shooting algorithm and its application to high-power fiber lasers

An improved shooting algorithm for high-power fiber laser is proposed based on the relation of the two-end boundary laser powers. By the improved shooting algorithm, the evolutions of the pump and laser powers along the fiber position for Yb-doped and Tm-doped high-power double-clad fiber lasers with the laser scattering loss are analyzed. The results prove that the improved shooting algorithm can be efficient even if the pump power is up to kilowatt level, and the initial value can all be fast convergent as long as the initial guessed laser power is smaller than the truth value. So, this improved shooting algorithm can be used in high-power double-clad fiber lasers efficiently.     

An improved calculation for the inner-shell ionization problems

A calculation for the inner-shell ionization problems is made in a new approach. Results are compared with measured values for doubly and triply differential cross sections and improvements are noticed.     

An improved acoustical wave propagator method and its application to a duct structure

The pseudospectral time-domain method has long been used to describe the acoustical wave propagation. However, due to the limitation and difficulties of the fast Fourier transform (FFT) in dealing with nonperiodic problems, the dispersion error is inevitable and the numerical accuracy greatly decreases after the waves arrive at the boundary. To resolve this problem, the Lagrange-Chebyshev interpolation polynomials were used to replace the previous FFT, which, however, brings in an additional restriction on the time step. In this paper, a mapped Chebyshev method is introduced, providing the dual benefit of preserving the spectral accuracy and overcoming the time step restriction at the same time. Three main issues are addressed to assess the proposed technique: (a) Spatial derivatives in the system operator and the boundary treatment; (b) parameter selections; and (c) the maximum time step in the temporal operator. Furthermore, a numerical example involving the time-domain evolution of wave propagation in a duct structure is carried out, with comparisons to those obtained by Euler method, the fourth-order Runge-Kutta method, and the exact analytical solution, to demonstrate the numerical performance of the proposed technique.     

Impulsive control for Takagi--Sugeno fuzzy model with time-delay and its application to chaotic system

A control approach where the fuzzy logic methodology is combined with impulsive control is developed for controlling some time-delay chaotic systems in this paper. We first introduce impulses into each subsystem with delay of the Takagi--Sugeno (TS) fuzzy IF--THEN rules and then present a unified TS impulsive fuzzy model with delay for chaos control. Based on the new model, a simple and unified set of conditions for controlling chaotic systems is derived by the Lyapunov--Razumikhin method, and a design procedure for estimating bounds on control matrices is also given. Several numerical examples are presented to illustrate the effectiveness of this method.     

An improved memristor model for brain-inspired computing

Memristors, as memristive devices, have received a great deal of interest since being fabricated by HP labs. The forgetting effect that has significant influences on memristors' performance has to be taken into account when they are employed. It is significant to build a good model that can express the forgetting effect well for application researches due to its promising prospects in brain-inspired computing. Some models are proposed to represent the forgetting effect but do not work well. In this paper, we present a novel window function, which has good performance in a drift model. We analyze the deficiencies of the previous drift diffusion models for the forgetting effect and propose an improved model. Moreover,the improved model is exploited as a synapse model in spiking neural networks to recognize digit images. Simulation results show that the improved model overcomes the defects of the previous models and can be used as a synapse model in brain-inspired computing due to its synaptic characteristics. The results also indicate that the improved model can express the forgetting effect better when it is employed in spiking neural networks, which means that more appropriate evaluations can be obtained in applications.     

An artificial neural networks approach to model and predict the relationship between the grounding resistance and length of buried electrode in the soil

This paper presents a technique based on the development of an artificial neural network (ANN) model for modeling and predicting the relationship between the grounding resistance and length of an electrode buried in the soil based on experimental data. The results indicate the strong agreement between the model prediction and experimental values. The statistical analysis shows that the R² values were 0.995 and 0.925 for the training and testing sets, respectively.     

离散Arnold变换改进及其在图像置乱加密中的应用

为了改善传统二维Arnold变换用于图像置乱加密的效果,提出了离散Arnold变换的改进方法,并将其用于图像置乱加密测试研究.该方法利用现有离散标准映射的构造思想,将传统离散二维Arnold变换表达式中第一个变换表达式所对应变换结果非线性融入第二个变换表达式,实现经典离散二维Arnold变换的非线性去拟仿射化修改,以便快速改善图像置乱加密效果.数学证明改进方法不再保持现有离散二维Arnold变换所具有的拟仿射不变性,但是改进变换仍是一种具有周期性的可逆映射,将其用于图像置乱加密时,利用其周期性或逆变换能恢复置乱前原图像.大量实验结果表明,本文所建议的改进方法是有效的,相比现有的离散Arnold变换更具有实用价值意义.     

An improved algorithm and its parallel implementation for solving a general blood-tissue transport and metabolism model

Fast algorithms for simulating mathematical models of coupled blood-tissue transport and metabolism are critical for the analysis of data on transport and reaction in tissues. Here, by combining the method of characteristics with the standard grid discretization technique, a novel algorithm is introduced for solving a general blood-tissue transport and metabolism model governed by a large system of one-dimensional semilinear first order partial differential equations. The key part of the algorithm is to approximate the model as a group of independent ordinary differential equation (ODE) systems such that each ODE system has the same size as the model and can be integrated independently. Thus the method can be easily implemented in parallel on a large-scale multiprocessor computer. The accuracy of the algorithm is demonstrated for solving a simple blood-tissue exchange model introduced by Sangren and Sheppard [W.C. Sangren, C.W. Sheppard, A mathematical derivation of the exchange of a labeled substance between a liquid flowing in a vessel and an external compartment, Bull. Math. Biophys. 15 (1953) 387–394], which has an analytical solution. Numerical experiments made on a distributed-memory parallel computer (an HP Linux cluster) and a shared-memory parallel computer (a SGI Origin 2000) demonstrate the parallel efficiency of the algorithm.     

Performance of a PIV system for a combusting flow and its application to a spray combustor model

The performance of PIV system for combusting flow was evaluated by using artificial images generated from computer graphics and experimental data. The influences of shutter speed, filter, laser power and the PIV algorithms on the measurement uncertainty were studied for optimizing the performance of the PIV system. This system was applied to the spray combustor model for boiler, and the flow patterns with and without combustion were elucidated. Results showed that the burner flow generates complex three-dimensional flow pattern, which contributes to highly mixed fuel flow in the combustor. Although the flow pattern with and without combustion is similar, the growth of burner flow area and an increase in velocity magnitude are found in the flow field by the influence of chemical reactions in combustion.     

Triangular approximation for Ising model and its application to Boltzmann machine

When we consider a problem in information processing, it is convenient to formulate the problem by using a random Ising model in statistical physics. However, a kind of computational difficulty arises in a case that the number of nodes becomes large. Hence approximation schemes such as a mean field approximation and a Bethe approximation have been used extensively for overcoming the difficulty. When frustration is essential in some problems, the Bethe approximation gives unfavorable results. In those problems, more advanced approximation schemes are needed beyond the Bethe approximation. In the present paper, we present explicitly the triangular approximation, which is the next approximation to the Bethe approximation. We apply the obtained approximation scheme to a Boltzmann machine in order to investigate the validity of the triangular approximation.     

一种改良的啁啾变换算法及其应用

快速啁啾算法引入两次快速傅里叶变换（FFT）及一个解析高斯核,计算复杂度低于卷积算法.通过对啁啾算法实现过程进行的改进,避免了该算法在实现过程中存在的一些问题,比如输出窗口小、信号丢失、计算复杂度稍大等缺点. 把算法用于简单的可求得解析解的系统并与之做比较. 对高斯函数,最大误差通常在10^-15数量级,而对矩形函数,由于受FFT算法计算精度的影响,误差在10^-3数量级,但这并不影响算法的性能. 最后把算法用于一种典型的标量衍射系统及分数傅里叶变换的计算,获得了很好的结果. 关键词： 快速啁啾算法 啁啾Z变换 菲涅耳变换 分数傅里叶变换     

An improved design for Al Ga N solar-blind avalanche photodiodes with enhanced avalanche ionization

To enhance the avalanche ionization, we designed a new separate absorption and multiplication AlGaN solarblind avalanche photodiode(APD) by using a high/low-Al-content AlGaN heterostructure as the multiplication region instead of the conventional AlGaN homogeneous layer. The calculated results show that the designed APD with Al_(0.3)Ga_(0.7)N/Al_(0.45)Ga_(0.55)N heterostructure multiplication region exhibits a 60% higher gain than the conventional APD and a smaller avalanche breakdown voltage due to the use of the low-Al-content Al_(0.3)Ga_(0.7)N which has about a six times higher hole ionization coefficient than the high-Al-content Al_(0.45)Ga_(0.55)N. Meanwhile, the designed APD still remains a good solar-blind characteristic by introducing a quarter-wave AlGaN/AlN distributed Bragg reflectors structure at the bottom of the device.     

A collisional-radiative model for helium and its application to a discharge plasma

For the collisional-radiative model applied to helium, two alternative formulations are presented in which non-linear process such as ionization due to metastable-metastable collisions may be included. The atomic data, including dielectronic,recombination, employed in the calculations are summarized. The collisional-radiative calculation is applied to a positive-column plasma for which both the nonlinear processes and radiation trapping are taken into account. The calculated population densities of excited levels for a low-pressure and low-current discharge plasma show good agreement with a measurement made using the hook method. The population density distribution among excited levels is interpreted in terms of excitation-ionization mechanisms in the plasma. This leads to a grouping of the excited levels into two phases for the discharge plasma considered: the corona phase applies to the lower-lying levels and the quasi-saturation phase to the higher-lying levels. The importance of the ladder-like excitation-ionization mechanism is noted for this class of plasmas.     

An improved effective liquid drop model for cluster radioactivity

The effective liquid drop model(ELDM) is improved by introducing an accurate nuclear charge radius formula and an analytic expression for assaulting frequency. Within the improved effective liquid drop model(IMELDM), the experimental cluster radioactivity half-lives of the trans-lead region are calculated. It is shown that the accuracy of the IMELDM is improved compared with that of the ELDM. At last, the cluster radioactivity half-lives that are experimentally unavailable for the trans-lead nuc...     

An improved car-following model with consideration of the lateral effect and its feedback control research

A car-following model is presented, in which the effects of non-motor vehicles on adjacent lanes are taken into ac- count. A control signal including the velocity differences between the following vehicle and the target vehicle is introduced according to the feedback control theory. The stability condition for the new model is derived. Numerical simulation is used to demonstrate the advantage of the new model including the control signal; the results are consistent with the analytical ones     

An order-N electronic structure theory with generalized eigenvalue equations and its application to a ten-million-atom system

A linear algebraic theory called the 'multiple Arnoldi method' is presented and realizes large-scale (order-N) electronic structure calculations with generalized eigenvalue equations. A set of linear equations, in the form of (zS - H)x = b, are solved simultaneously with multiple Krylov subspaces. The method is implemented in a simulation package ELSES (www.elses.jp) with tight-binding-form Hamiltonians. A finite-temperature molecular dynamics simulation is carried out for metallic and insulating materials. A calculation with 10(7) atoms was realized by a workstation. The parallel efficiency is shown up to 1024 CPU cores.