广义解调时频分析方法中的若干问题探讨

基于广义解调的时频分析方法是一种新的信号处理方法,本文在详细地介绍广义解调时频分析方法的基础上,采用广义解调时频分析方法对仿真信号进行了分析,同时和其它时频分析方法进行了比较,结果表明了广义解调时频分析方法的有效性.重点对广义解调时频分析方法应用范围、相位函数的选择等问题进行了讨论,得出了相应的结论.     

茶叶中维生素分析方法概述

在查阅1907年以来国内外所有关于茶叶维生素分析方法研究文献的基础上,该文介绍了茶叶中的维生素及其分析方法现状,对脂溶性维生素和水溶性维生素的主要分析方法进行了系统地阐述,对微生物法、分光光度法、荧光法、高效液相色谱法、毛细管电泳法和流动注射化学发光法等主要分析方法进行了评述,并提出了应建立对茶叶中维生素的测定方法.     

氨基酸分析方法的进展

氨基酸分析方法的研究是绿色工业、绿色农业和生命科学中的比较重要的课题.综述了氨基酸的分析方法,重点介绍了分析测定氨基酸的分光光度法、色谱法和电化学法,展望了氨基酸分析方法的发展趋势.     

茶叶中糖类物质分析方法综述

在全面检索1907年以来国内外所有关于糖类物质分析方法研究文献的基础上,介绍了茶叶中的糖类物质及其分析方法现状,对糖类物质的主要分析方法进行了系统地介绍,并对化学分析法、气相色谱法、离子交换色谱法、凝胶色谱法、高效液相色谱法、毛细管电泳法、质谱法等主要分析方法进行了评述,并提出了用高效液相色谱法建立茶叶中糖类物质测定的标准方法。     

时域模态分析方法的研究及软件研发

时域模态分析方法是当前国内外热门的课题.本文对主要的几种时域模态分析方法进行了研究总结.指出了时域模态分析方法的特点和存在的问题,以及编程中的一些要点和在使用时域模态分析方法时的一些要领,同时给出了时域法和频域法的对比以及仿真计算结果.如果时域模态分析方法的软件设计合理,使用得当,就能得到可靠的分析结果,使得时域模态分析方法不需要已知激励力、识别密集模态效果好等优点充分展示出来.     

河流泥沙颗粒分析方法品质衡量和标样体系

河流泥沙颗粒分析方法品质衡量需要统一的指标因子和计算方法;用于分析方法品质衡量和日常分析工作质量监督的标样需要建立相应的标准体系。为此,本文中提出了河流泥沙颗粒分析方法统一品质衡量指标和建立标样体系的设想,并对泥沙颗粒分析方法品质、分析方法品质衡量指标、标样制作和标样体系的建立等方面进行了详细的论述。文中提出的河流泥沙颗粒分析方统一品质衡量指标和建立标样体系的设想,具有科学、合理和普遍适用性及可操作性。     

氨气体污染物的分析方法

本文叙述了氨气体污染物的危害和目前国内各类标准对氨污染物的限量控制,针对其现状,对氨气体的高精度分析方法进行了调研和逐一介绍,并配制了钢瓶装氨气体标准物质,对仪器分析方法之一的声光分析方法进行实验,着重考查了该方法的重复性、稳定性和线性响应等指标,并给出了分析方法的关键注意事项。     

磷酸酯分析方法研究

本文对磷酸酯几种分析方法进行了分析讨论。目前运用的分析方法主要包括：混合指示剂法、电位或电导滴定法、31P-NMR波谱法、薄层色谱法等。同时指出多种分析方法的结合应用是磷酸酯分析方法的应用和发展方向。     

茶叶中生物碱的分析方法概述

在查阅1907年以来国内外所有关于茶叶生物碱分析方法研究文献的基础上,结合茶叶中的生物碱及其分析方法现状,对茶叶中咖啡碱、可可碱、茶碱等生物碱的主要分析方法进行了系统地介绍,并对分光光度法、近红外光谱法、薄层色谱法、高效液相色谱法、毛细管电泳法和质谱法等主要分析方法的特点进行了评述,提出对茶叶中生物碱测定方法实行标准化,是实现茶叶生物碱准确定量分析和提高茶叶品质质量的重要途径与保证.     

金属声发射信号三种时频域分析的比较研究

本文首先介绍了短时傅立叶变换、小波变换、二次型时频分布等三种时频域分析方法,并利用这三种分析方法分别对金属裂纹声发射信号进行了分析处理,对比研究了这三种时频域分析方法对金属裂纹声发射信号处理上的不同特点.     

具多变时滞中立型奇异微分系统的稳定性(英文)

本文讨论了中立型奇异泛函微分系统的稳定性问题.利用V泛函方法和差分算子的稳定性获得具变时滞中立型奇异微分系统的渐近稳定性判据.所得结果被描述为矩阵等式或者矩阵不等式,在计算上是可行和有效的,并给出例子说明了所得结果.     

钢筋混凝土结构材料本构模型参数的在线识别

为保证子结构拟动力试验中数值子结构的可靠性,模型参数在线识别与更新方法逐渐受到关注。对于钢筋混凝土结构,当采用纤维模型建立数值子结构时,混凝土材料本构模型参数的选择具有较大不确定性。因此,该文提出了基于隐性卡尔曼滤波器在线识别混凝土材料本构模型参数的方法。首先,对材料本构模型参数进行分类,定义了本构参数与非本构参数,提出了约束混凝土与非约束混凝土的一致本构方程。然后,针对观测量为混凝土应力的情况进行数值仿真分析,验证了此方法的可行性。最后,通过修改OpenSees源代码,实现了此方法在观测量为构件恢复力情况下的应用。研究结果表明该文提出的方法具有较好的稳定性与较高的精度,从而在很大程度上提高了数值模型的可靠性。     

Stability analysis of arbitrary shape landslope by variational calculus and finite difference method

Abstract

In this paper, a method of numerical analysis is presented, which is suitable for the stability analysis of arbitrary shape landslope, and can be used for the stability analysis of both general artificial landslope and arbitrary natural landslope. The mathematical model of stability analysis is based on the theory of the calculus of variations and using Janbu's simplified model. The governing equations are a system of integro‐differential equations which consist of Euler's equations together with the transversality, continuity and boundary conditions. Applying the concept of finite difference method, we set up the numerical procedure for this system. The numerical procedure presented in this paper is powerful for determining the critical sliding surface of arbitrary shape landslope without the necessity of guessing its shape. Furthermore, it gives the actual safety factor of the landslope and consequently obtains a more complete knowledge of the safety of arbitrary shape landslope. For comparison, the proposed numerical method is applied to analyze two problems which have analytic solutions. The numerical results have shown highly accurate. Some examples including the double rectilinear and arbitrary natural landslopes are analyzed inorder to illustrate the applicability of this numerical method.     

Higher derivative explicit one step methods for non-linear dynamic problems. Part I: Design and theory

A new higher order explicit one step scheme is presented for use in the solution of a certain class of non-linear problems in structural dynamics. The generalized scheme covers some recently developed multistep algorithms as well as some new one step methods with improved numerical properties. A weighted residual approach is used which contains new aspects for design of single step algorithms. Accuracy and stability are investigated for linear and non-linear systems. Algorithms with higher accurary than the central difference method are developed and optimized to minimize the reduction in the stability limit.     

Radial point interpolation based finite difference method for mechanics problems

A radial point interpolation based finite difference method (RFDM) is proposed in this paper. In this novel method, radial point interpolation using local irregular nodes is used together with the conventional finite difference procedure to achieve both the adaptivity to irregular domain and the stability in the solution that is often encountered in the collocation methods. A least‐square technique is adopted, which leads to a system matrix with good properties such as symmetry and positive definiteness. Several numerical examples are presented to demonstrate the accuracy and stability of the RFDM for problems with complex shapes and regular and extremely irregular nodes. The results are examined in detail in comparison with other numerical approaches such as the radial point collocation method that uses local nodes, conventional finite difference and finite element methods. Copyright © 2006 John Wiley & Sons, Ltd.     

A Fully Discrete Spectral Method for Fisher’s Equation on the Whole Line

A generalised Hermite spectral method for Fisher’s equation in genetics with different asymptotic solution behaviour at infinities is proposed, involving a fully discrete scheme using a second order finite difference approximation in the time. The convergence and stability of the scheme are analysed, and some numerical results demonstrate its efficiency and substantiate our theoretical analysis.     

阻尼弹性结构动力计算的显式差分法

本文在时域有限元离散的基础上,导出了集中质量阻尼弹性结构动力模型的显式差分法,数值稳定条件同中心差分法。文中还分析了用中心差分法结合单边差方法的不足之处。     

未知输入下的复合反演研究

回顾了近年来未知输入情况下的结构参数识别算法,并针对未知输入情况下的复合反演算法做了深入研究,总结归纳了这类算法的特点和应用条件,并在此基础上提出了能够用于具有多个未知输入组合下的复合反演算法。此方法是基于最小二乘原则并结合统计平均思想的一类迭代算法,对于在多个未知输入情况下的结构(例如在地震动和风荷载共同作用下等),可以用来识别结构参数并同时反演多个未知输入。与仅适用于具有一个未知输入情况下的复合反演算法相比,本文方法具有更广泛的应用背景,最后以一个4层剪切型结构为例来验证本文方法。有噪声情况下和无噪声情况下的识别结果显示本文方法具有一定适用性。     

Numerical Analysis of Novel Coronavirus (2019-nCov) Pandemic Model with Advection

Recently, the world is facing the terror of the novel corona-virus, termed as COVID-19. Various health institutes and researchers are continuously striving to control this pandemic. In this article, the SEIAR (susceptible, exposed, infected, symptomatically infected, asymptomatically infected and recovered) infection model of COVID-19 with a constant rate of advection is studied for the disease propagation. A simple model of the disease is extended to an advection model by accommodating the advection process and some appropriate parameters in the system. The continuous model is transposed into a discrete numerical model by discretizing the domains, finitely. To analyze the disease dynamics, a structure preserving non-standard finite difference scheme is designed. Two steady states of the continuous system are described i.e., virus free steady state and virus existing steady state. Graphical results show that both the steady states of the numerical design coincide with the fixed points of the continuous SEIAR model. Positivity of the state variables is ensured by applying the M-matrix theory. A result for the positivity property is established. For the proposed numerical design, two different types of the stability are investigated. Nonlinear stability and linear stability for the projected scheme is examined by applying some standard results. Von Neuman stability test is applied to ensure linear stability. The reproductive number is described and its pivotal role in stability analysis is also discussed. Consistency and convergence of the numerical model is also studied. Numerical graphs are presented via computer simulations to prove the worth and efficiency of the quarantine factor is explored graphically, which is helpful in controlling the disease dynamics. In the end, the conclusion of the study is also rendered.     

Boundary layer refinements in convective diffusion problems

The paper outlines a numerical procedure for the finite element solution of convective diffusion problems with significant convective terms using conventional (not upwinded) Galerkin methods in connection with ‘boundary-layer type’ elements. The underlying argument in the sequel is that the poor stability properties of conventional Galerkin methods are caused by the insufficient approximation of eigensolutions. These are located at some sections of the boundary and are only present within a generally very thin layer. Consequently, the identification of these layers and the satisfactory approximation of the eigensolutions are necessary and totally sufficient for a satisfactory solution. In the following we intend to present this procedure, its theoretical background and selected numerical results.