Nonlinear suboptimal filtration of pseudorandom sequences

The critical importance of studies of alternative methods of representation and processing of signals constructed from pseudorandom sequences of maximal period is demonstrated. For the first time, it is proposed that a multidimensional nonlinear finite-difference representation of an arbitrary pseudorandom sequence be employed. A suboptimal algorithm for nonlinear discrete Kalman filtration of a pseudorandom sequence is obtained. A numerical example of filtration of a sequence formed on the basis of a given recurrence rule is considered and its efficiency is demonstrated.     

基于波动方程的聚焦点控制照明叠前深度偏移

 基于波动方程的聚焦点控制照明叠前深度偏移技术借助于差分计算，把速度、密度等介质参数的影响体现在差分计算的矩阵方程中，能够自动适应速度场的任意变化，快速傅里叶变换的使用也加速了波场延拓的计算速度。因此此法兼具有限差分偏移方法和傅里叶偏移方法的优点，既可适应速度场的剧烈变化，又可保证对陡倾地层的成像效果，是目前针对复杂构造最有效的成像方法之一。对于单个聚焦点及其周围的成像步骤为：①采用矩形网格情况下绕射走时的有限差分计算方法生成合成算子；②应用合成算子来合成面炮震源和面波记录；③对合成的面炮震源和面波记录做傅里叶有限差分法波动方程叠前深度偏移，得到该聚焦点及其附近区域的成像结果。按照上述成像步骤，将震源波场和炮集记录依据相应的外推公式进行延拓，最终应用成像条件求取成像值。在地质目标处选取多个聚焦点，可以得到面向目标的控制照明偏移成像，在多个层位上选取多个聚焦点进行控制照明叠前深度偏移，可以得到整块区域的成像。通过对Marmousi模型的试算，取得了较好的效果。     

INTERACTION OF VORTICES WITH A PROGRESSIVE SURFACE WAVE

ＩＮＴＥＲＡＣＴＩＯＮＯＦＶＯＲＴＩＣＥＳＷＩＴＨＡＰＲＯＧＲＥＳＳＩＶＥＳＵＲＦＡＣＥＷＡＶＥＷａｎｇＬｉｎ－ｌｉｎ；ＭａＨｕｔ－ｙａｎｇ（ＧｒａｄｕａｔｅＳｃｕｄｏｆＡｃａｄｅｍｉｃａＳｉｎｉｃａＢｅｉｊｉｎｇ１０００３９Ｐ．Ｒ．Ｃｈｉｎａ）Ａｂ...     

两种群食饵-捕食者模型参数估计的数值微分法

给出了一种基于数值微分的两种群食饵-捕食模型参数估计的两阶段方法。该方法将参数的非线性最小二乘估计,转化为一个数值微分和一个线性最小二乘估计问题,具有计算简单快速的特点。数值算例详细分析了三种常见有限差分数值微分法及非线性最小二乘估计对参数估计精度的影响,结果表明提出的方法是可行的。     

Adjustable transmission properties through ring-shaped nanotube arrays using finite-difference time-domain method

Metallic ring-shaped nanotube arrays are proposed and its optical transmission properties are studied by using finite-difference time-domain （FDTD） method. Compared with the transmission spectra of conventional circular nanotube arrays, two photonic band gaps are emerged in the transmission spectra offing-shaped nanotube arrays, the two band gaps and transmission spectra are adjusted by the length, inner radius, intertube spacing and the dielectric constants of the core and embedding medium, and magnitude modification, redshift and blueshift of the resonance modes are observed. A metallic ring-shaped nanotube arrays for subwavelength band-stop filter in the range of visible light can be achieved. To understand its physical origin, field-interference mechanism was suggested by the field distributions. The proposed nanostructures and results may have great potential applications in subwavelength near-field optics.     

MODELING OF CONTROLLED THERMO-MECHANICAL PROCESSING OF TUBES FOR ENHANCED MANUFACTURING AND PERFORMANCE

1.IntroductionApproximately15milliontonsofsteeltubeandpipeproductsareconsumedintheUnitedStatesannually.Mechanicaltubesarethefeedstocksusedinthemanufactureofrollingelementbearings,hydrauliccylinders,alldagreatvarietyofpowertransmissioncomponents.Steeltubesarealsoemployedinthedrillstringsforoilandnaturalgasexplorationandrecovery.Steelpipesareusedinthetransportofgas,oilandotherfluids.ControlledThermal--MechanicalProcessing(CTMP)involvesprecisecontroloftemperature,mechanicaldeformation,andmicr…     

Numerical modeling of high-temperature corrosion processes

Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element may form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.     

高阶旋转体时域有限差分法

旋转体时域有限差分法(BOR FDTD)是模拟电磁波与旋转对称目标体相互作用的一种高效算法,但目前的BOR FDTD对时间和空间的差分精度均只有二阶.通过把电磁场各分量作泰勒展开,并结合麦克斯韦方程,提出了BOR FDTD的三种高阶算法.相对于目前的BOR FDTD,三种高阶算法均不增加存储量.通过模拟简谐波与介质球的相互作用并和理论值作比较,证实了高阶算法在提高计算精度方面的有效性.此外还分析了三种高阶算法的优、缺点,给出了关于高阶算法应用的建议.     

有限差分法的并行化计算实现

有限差分法是求解偏微分方程近似解的一种重要的数值方法。并行化计算可提高复杂计算问题的效率,二维场中拉普拉斯方程的差分格式非常适合并行化方法的计算。如何将串行部分并行化以提高大规模计算的效率,MPI（消息传递接口）是实现并行程序设计的标准之一。虚拟进程（MPI_PROC_NULL）是MPI中的假想进程,它的引用可简化MPI编程中的通信部分,引入虚拟进程编写代码,可实现有限差分方法的并行化计算。     

黑磷纳米盘-层等离激元系统中的各向异性可调多阶强耦合

黑磷支持各向异性的表面等离激元,可用于设计具备更多功能的原理性器件。用时域有限差分法数值模拟了中红外到远红外波段基于黑磷的层-盘-层系统中不同等离激元模式之间的杂交行为。通过动态调节黑磷中的载流子浓度,可以实现两个晶格方向上强耦合现象的产生与控制。对不同模式间的耦合进行分析并计算,得到吸收光谱中的拉比分裂能最高可达42.9 meV。此外,还计算了偏振角度对各向异性强耦合的影响,其最高可以实现6个吸收频带。该模型可为构建未来在中远红外波段工作的基于二维材料紧凑型各向异性等离激元器件提供基础。