Finite element solution of the unsteady Navier-Stokes equations by a fractional step method

A finite element method is presented for the numerical simulation of time-dependent incompressible viscous flows. The method is based on a fractional step approach to the time integration of the Navier-Stokes equations in which only the incompressibility condition is treated implicitly. This leads to a computational scheme of extremely simple algorithmic structure that is particularly attractive for cost-effective solutions of large-scale problems. Numerical results indicate the versatility and effectiveness of the proposed method.     

On the consistency of Bayesian function approximation using step functions

We consider the problem of estimating a step function with an unknown number of jumps under noisy observations on a grid. Under mild assumptions, the Bayesian approach is shown to produce a consistent estimate, even when the underlying true function is not piecewise constant. A simple prior is constructed to illustrate our assumptions.     

Well-balanced schemes versus fractional step method for hyperbolic systems with source terms

Abstract The paper is devoted to the analysis of the true accuracy of different schemes when computing a simple hyperbolic model with source terms, which describes the motion of two-phase flows including source terms. The strategy of upwinding the source terms is investigated and compared with the standard fractional step method. A first scheme relies on the usual fractional step approach. A second scheme applies for upwinding of source terms. It, however, does not provide satisfactory results when computing certain specific unsteady cases. This behaviour can be easily explained. It thus motivates us to introduce a third scheme, which is similar to the previous but aims at providing an increased accuracy on coarse meshes when computing highly unsteady flows. This latter scheme requires us to define a cell scheme which computes the void fraction with the help of a modified governing equation, while using the same interface solver. A detailed numerical study which includes a measure of the L ¹ norm of the error completes the work.     

One-stage Rosenbrock method with complex coefficients and automatic selection of the time step

The article presents generalization of the well-known one-stage Rosenbrock scheme with complex coefficients. The obtained method preserves all the advantages of its previous version (A stability and L damping), provides a simple estimation of the local error and facilitates the easy selection and correction of the integration step. The strategy of the selection of the step and the new method is tested both on the basis of known and original nonlinear equations and sets of nonlinear equations, as well as of the nonlinear equation of thermal conductivity.     

Model approximation of multiple delay transfer function models using multiple-point step response fitting

Compared with model approximation for general SISO transfer function models with or without a single constant delay, the approximation problem for SISO transfer function models with multiple delays has received much less attention. In this paper, we attack this problem and thus present a multiple-point step response fitting based approximation method to derive the reduced models. A simple frequency-domain weighted recursive least squares (RLS) algorithm is proposed to determine a set of parameters so that the reduced models can approximate the original models by minimizing the defined frequency-domain squared-error between the step responses of the original and the reduced model. Numerical examples have demonstrated that the proposed approximation approach can not only introduce less dynamic approximation error, but also yield zero steady-state error.     

Synchronizing characteristics of a step motor

Based on the analogy between the equation of motion of a step motor and that of a simple pendulum with viscous damping, the paper develops the necessary criteria for synchronization when the motor is subjected to a series of steps. The problem is first analyzed ignoring the discrete nature of the input leading to approximate determination of the critical stepping rates. This is followed by a more accurate analysis. The results of these analyses are presented in nondimensional form and can be used for the design of the motor.     

Image enlargement based on a step edge model

In compiling a multimedia document we often need to enlarge the size of an image. The traditional pixel repetition method tends to make the edges jagged. On the other hand, the interpolation-based methods tend to make the edges blurry in the enlarging process. In this paper we propose an image magnification method based on a step edge model. Using the model, we are able to define a straight step edge segment with four parameters. In enlarging a digital image, we first derive the parameter values for its step edge segments. This is like extracting the step edges in the corresponding continuous image. Then we re-digitize the step edges in the continuous image with a finer grid to obtain an enlarged image. In this way, the step edges are able to stay well defined after they are enlarged. The experiments show that in both visual comparison and quantitative analysis, the results produced by the suggested step edge model-based approach are consistently and significantly better than that produced by pixel repetition and bilinear interpolation.     

步长自适应ICA在地震信号去噪中的应用

提出一种基于改进相对梯度独立分量分析（ICA）的叠前地震信号去噪方法。建立ICA的步长函数与信号相依性测度之间的非线性关系,根据信号的分离状态自适应调节步长函数;在分离矩阵的更新公式中引入动量项,削弱步长函数快速减小对分离矩阵更新的影响;将改进ICA模型应用于叠前地震信号去噪处理中。实验结果表明,改进的变步长ICA算法可以有效地压制叠前地震记录中的随机噪声,并且能很好地保护有效地震信号。     

A step towards unification of syntactic and statistical pattern recognition

The problem of pattern recognition is discussed in terms of single-entity representation versus multiple-entity representation. A combined syntactic-semantic approach based on attributed grammars is suggested. Syntax-semantics tradeoff in pattern representation is demonstrated. This approach is intended to be an initial step toward unification of syntactic and statistical approaches to pattern recognition.     

Single step micro‐patterned liquid crystal photoalignment by patterned quarter‐wave plate

In this article, a method for fabricating the patterned liquid crystal photoalignment structures, in a single step, is proposed. A patterned quarter‐wave plate formed by a photoaligned liquid crystalline polymer film is used as a photomask to generate photoaligned micro‐patterns. Whereas other existing alternatives include complicated fabrication scheme, the proposed method provides an edge with simple one‐step alignment. Moreover, the proposed method offers highly accurate, high resolution, multi micro‐pattern alignment with great repeatability and therefore could find application in wide range of photonic and display devices demanding the micro‐patterned, single of multi domain, alignment. In addition, the structure could be used for optical polarization information storage and patterned alignment structure storage, which could easily be reproduced.     

Identification from step responses with transient initial conditions

Over the last few years there have been some interesting developments in system identification from step and step-like responses. New methods have been proposed to simultaneously estimate model parameters and the delay from step responses that require the process to be at steady state when the step is applied. To deal with transient initial conditions, methods based on pulse responses and the so called piece-wise step tests and iterative algorithm based on a single step response have also been proposed. In this article we propose a new method to estimate model parameters and the delay from a single step response in the presence of transient initial conditions, which does not require iteration. The performance of the proposed procedure is demonstrated through simulations as well as applications on experimental data from a continuous heating tank process and a mixing process.     

冲突证据分步合成的合理性及改进合成算法

针对证据分步合成问题,给出了多证据分步合成结果的一般表达式,对分步合成方法理论上的合理性以及合成结果的收敛性进行了研究。针对高度冲突证据的分步合成问题,提出一种将Dempster合成公式与加权平均法混合使用的分步合成算法;根据预设的冲突阈值,选用相应的合成公式。对比仿真结果表明该算法比国内外一些代表性改进方法合成计算过程更为简捷,合成结果的收敛效果更好。     

Implementation design for databases: the `forgotten' step

Most methodologies for database analysis and design specify conceptual, logical, and physical design as the three major design steps. However, although this three-step approach is popular, there is no consensus on when to use implementation design techniques, such as table partitioning and denormalization. Consequently, these techniques are treated as substeps in one of the three main design steps. This inconsistent treatment may be why many designers frequently rely on their intuition in applying implementation design techniques. Clearly, this ad hoc practice shouldn't continue. Ad hoc anything is not a good idea when designing a complex system. To resolve this problem, the author proposes that we extend the three-step methodology to include a fourth major step: implementation design. In this methodology, implementation design is the process of modifying an “ideal” logical data model (relational or object-oriented) to produce a more machine-efficient, “pragmatic” model: the implementation model. The implementation model, in turn, serves as input to the physical design step. This four-step method will encourage practitioners to resist the ad hoc approach and simplify the other design steps. It will also help in addressing the additional complexity associated with advanced database architectures, such as distributed and parallel databases and data warehouses     

Revisiting the Ziegler–Nichols step response method for PID control

The Ziegler–Nichols step response method is based on the idea of tuning controllers based on simple features of the step response. In this paper this idea is investigated from the point of view of robust loop shaping. The results are: insight into the properties of PI and PID control and simple tuning rules that give robust performance for processes with essentially monotone step responses.     

Performance analysis of evolutionary optimization with cumulative step length adaptation

Iterative algorithms for continuous numerical optimization typically need to adapt their step lengths in the course of the search. While some strategies employ fixed schedules, others attempt to adapt dynamically in response to the outcome of trial steps or the history of the search process. Evolutionary algorithms are of the latter kind. A control strategy that is commonly used in evolution strategies is the cumulative step length adaptation approach. This paper presents a theoretical analysis of that adaptation strategy. The analysis includes the practically relevant case of noise interfering in the optimization process. Recommendations are made with respect to choosing appropriate population sizes.     

Iterative identification and two step control design for partially unknown unstable plants

In this paper we shall extend the applications of iterative identification and control design to partially unknown unstable plants. We show that by employong a two step approach, where an unstable plant is first stabilized by a parallel feedback stabilizer, it is possible to design systematically an overall closed-loop system that has good step responses with little overshoots by using the iterative identification and control design methodology. Furthermore, this approach easily preserves the simplicity of an IMC design through tuning the overall designed closed-loop bandwidth with a single design parameter. Specifically, similarly to situations where the plant is stable (apart from possibly including a simple integrator), we can design a system with a small initial overall designed closed-loop bandwidth (after the plant is stabilized by a known parallel feedback stabilizer) such that high frequency unmodelled dynamics of the plant are not overly excited. Through iterative applications of a control-relevant closed-loop system identification procedure and the standard IMC design method to the stabilized plant, the overall designed closed-loop bandwidth of the system can be widened progressively while maintaining good step responses with little overshoots. Two simulation examples are employed to illustrate the method. These examples show that, irrespective of the presence of adverse unstable real pole-zero structures, the expected results are achievable by the method described.     

Decentralized closed-loop parameter identification for multivariable processes from step responses

This paper presents a novel technique for on-line decentralized closed-loop parameter identification of multivariable processes from step responses. Based on simple sequential step tests, the coupled closed-loop n-inputs and n-outputs (n × n) multivariable process is decoupled equivalently into n² independent single open-loop processes with an unit step input signal acting on the n² transfer functions. By using virtual step response signals, the parameters of each element in the transfer function matrix can be directly identified by the well-developed least squares methods. The significance of the proposed method is that it relaxes most restrictions of existing multivariable process identification methods, it is universally applicable to closed-loop identification for cross-coupling multivariable processes. Simulation examples are given to show both effectiveness and practicality of the identification method for a wide range of multivariable processes.     

Step by step filter based program for calculations of highly informative derivative curves

We have developed a microcomputer program, based on a recently described approach called step by step filter (SBSF), for calculation of derivative curves directly from spectra recorded as a function of wavelength. This program avoids the long wavelength attenuation featured at conventional method for derivative curves calculation, and in this extent could be very helpful for daily spectroscopy practice. The features of the SBSF program include: easy treatment of data through a windowed environment, calculating of both conventional and step by step filter derivatives, possibilities for selection of the mathematical conditions for smoothing and differentiation simultaneous plotting of the original curve and its derivative and a mouse pointer. Several examples from different branches of the molecular spectroscopy (absorption UV-VIS, CD and fluorescence) are provided and discussed in the terms of advantages of SBSF.     

Copyright reform step zero

‘A reasonable person might well think it's a fool's errand to contemplate a [copyright] reform project of any sort.’ The US Copyright Act of 1976 and its subsequent amendments is contained in over 200 pages of incomprehensible, sometimes inconsistent, and highly technical provisions. Attempts to reform this law are doomed from the start. They are doomed not because they lack merit, but because of the way copyright law is made. This article argues that before any meaningful copyright reform is passed, the institutional framework that makes copyright law must be changed. It proposes delegating substantive rulemaking authority to the US Copyright Office as part of that change. The article explores the benefits and drawbacks to this approach and concludes that without the type of institutional reform envisioned by this proposal, copyright law will continue to become increasingly unable to keep up with technological and other challenges while also becoming increasingly resistant to reform efforts.     

一种新的去相关变步长LMS算法及其应用

在一种变步长算法基础上,从语音信号相关性的角度出发,提出了一种新的去相关变步长LMS算法(DCL—NLMS)。该算法结构简单,收敛速度快,稳态失调小,计算量与NLMS算法相当。仿真结果表明,该算法在处理强相关性信号时,不仅收敛速度明显快于其余算法,而且稳态失调特性也有很大优势。