非线性自回归模型的几何非常返性

本文研究了非线性自回归模型的随机稳定性.通过建立恰当的Foster-Lyapunov条件,得到了非线性自回归模型几何非常返的充分条件.     

A probability distribution for precipitation data analysis

Hydrologic design is often based on assessments of large return interval measures; it is vital to be able to conclude them as precisely as possible. Henceforth, the selection of a probability distribution is very crucial for such cases. In view of this scenario, we propose and study a pliant probability distribution for precipitation data analysis. Some mathematical and statistical properties are analyzed. In order to make stronger predictions and judge the realistic return period, we have also characterized the model via Laplace transformation. We have estimated its parameters via the maximum likelihood estimation and constructed its information matrix for developing the confidence belt of population parameters. Moreover, a real-life setup is also considered by applying the model over precipitation data of diverse regions, including Jacksonville, Florida (USA), Barkhan (Pakistan), British Columbia (Canada), and Alexandria (Egypt). This investigated study is based on various statistical parametric and nonparametric tests, which indicates that the proposed model is one of the better strategies for precipitation data analysis when compared with the famous three-parameter Kappa model.     

氢键准则在DMSO水溶液中应用的评价

利用分子动力学模拟方法, 分别采用几何准则和能量准则分析了不同浓度下的二甲基亚砜(DMSO)水溶液的氢键统计和动力学等特性. 结果显示, 两种氢键准则可以很好地反映出溶液的氢键性质随浓度的变化趋势. 通过分析比较发现, 由于几何准则不能有效地排除具有弱对势能的分子对, 因此其统计的氢键数量要大于能量准则的结果.此外, 能量准则对于分子间相对取向的区分存在不足, 进而引起氢键寿命的计算结果偏大.因此,为使氢键分析更加准确, 本文建议使用几何-能量混合型氢键准则.     

On the determination of the point of fracture initiation by the load separation criterion in J-testing of ductile polymers

The application of an experimental approach based on the load separation criterion for the determination of the point of fracture initiation in a fracture test on a ductile polymer was critically examined. To this aim, the fracture process outlined by the application of this method was related to that described by the visual analysis of the fracture surfaces obtained in fracture tests on nominally identical specimens, in which different levels of crack extension were produced. The material examined was an acrylonitrile-butadiene-styrene (ABS) resin, and the fracture tests were performed at low loading rate on single-edge notched in bending specimens.The results demonstrated that this load separation criterion based methodology is a promising approach for the determination of the point of fracture initiation, and for material fracture resistance, J_Ic, evaluation. The method also has experimental simplicity and a high degree of repeatability.     

Electric field distribution in biased GaAs microstructures with field-pinning layers

Field-pinning layers are an approach to improve the homogeneity of the electric field in a biased semiconductor structure of length above the Kroemer criterion. Building a THz Bloch oscillator with such a structure requires superlattice regions. Nevertheless, GaAs layers are investigated here. We compare different periodic structures (alternating transit and field-pinning layers) via simulating the field distribution. It is shown that the development of propagating Gunn domains is suppressed when field-pinning layers are included, but the homogeneity of the field is still not satisfying for the purpose of building a Bloch gain THz source. Depending on the temperature, intra- and inter-period inhomogeneities occur.     

斜磁场作用下碰撞电负性等离子体鞘层的玻姆判据

采用流体模型研究了外加斜磁场作用下的碰撞电负性等离子体鞘层的玻姆判据, 讨论了负离子和磁场对鞘层玻姆判据的影响. 研究结果表明: 在电负性鞘层中, 正离子更容易进入鞘层, 负离子的存在只能影响离子马赫数取值的下限; 而外加磁场可以使离子马赫数的取值范围整体发生移动.     

Some regularity criteria for the 3D incompressible magnetohydrodynamics

In this paper, we consider regularity criterion for the three-dimensional incompressible magnetohydrodynamic equations. We present some sufficient integrability conditions on some components of the velocity and magnetic fields for the regularity of the weak solutions.     

Control and synchronize a novel hyperchaotic system

The control and hybrid projective synchronization (HPS) strategies for a novel hyperchaotic system are investigated. Firstly, the novel hyperchaotic system is controlled to the unsteady equilibrium point or limit cycle via only one scalar controller which includes two state variables. Secondly, based on Lyapunov’s direct method HPS between two novel hyperchaotic systems is studied. A new nonlinear feedback vector controller is designed to guarantee HPS, which can be simplified ulteriorly into a single scalar controller to achieve complete synchronization between two novel hyperchaotic systems. Finally, numerical simulations are given to verify the effectiveness of these strategies. The proposed methods have certain significances for reducing the cost and complexity for controller implementation.     

A regularity criterion for the density‐dependent magnetohydrodynamic equations

In this paper, regularity criterion for the 3‐D density‐dependent magnetohydrodynamic equation is considered. It is proved that the solution keeps smoothness only under an integrable condition on the velocity field in multiplier spaces. Hence, it turns out that the velocity field plays a dominant role in the regularity criteria of the weak solutions to this nonlinear coupling problem even with density. Copyright © 2009 John Wiley & Sons, Ltd.