To CG or to HDG: A Comparative Study

Hybridization through the border of the elements (hybrid unknowns) combined with a Schur complement procedure (often called static condensation in the context of continuous Galerkin linear elasticity computations) has in various forms been advocated in the mathematical and engineering literature as a means of accomplishing domain decomposition, of obtaining increased accuracy and convergence results, and of algorithm optimization. Recent work on the hybridization of mixed methods, and in particular of the discontinuous Galerkin (DG) method, holds the promise of capitalizing on the three aforementioned properties; in particular, of generating a numerical scheme that is discontinuous in both the primary and flux variables, is locally conservative, and is computationally competitive with traditional continuous Galerkin (CG) approaches. In this paper we present both implementation and optimization strategies for the Hybridizable Discontinuous Galerkin (HDG) method applied to two dimensional elliptic operators. We implement our HDG approach within a spectral/hp element framework so that comparisons can be done between HDG and the traditional CG approach.     

几种复合型数值方法的算法模拟与性能比较

浅水波问题的数值模拟一直是计算数学、计算流体力学的研究热点之一,采用低阶方法和高阶方法相复合的数值方法引起了人们的注意,并在水力学的数值模拟中取得了很大的成功。文中对三种复合型的数值方法,即Lax-Wendroff(LW)格式与Lax-Friedrichs(LF)格式的复合算法,Upwind格式与Lax-Wendroff(LW)格式的复合算法,WENO格式与LW格式的复合算法,进行了分析比较和改进,并就计算流体力学中的一维浅水波方程的两个算例分别做了数值对比试验,在解的光滑性、锐利性,计算速度等几个方面做了比较,模拟结果表明三种方法均能准确捕捉激波又不产生非物理震荡。     

几种复合型数值方法的算法模拟与性能比较

浅水波问题的数值模拟一直是计算数学、计算流体力学的研究热点之一,采用低阶方法和高阶方法相复合的数值方法引起了人们的注意,并在水力学的数值模拟中取得了很大的成功.文中对三种复合型的数值方法,即Lax-Wendroff(LW)格式与Lax-Friedrichs(LF)格式的复合算法,Upwind格式与Lax-Wendroff(LW) 格式的复合算法,WENO格式与LW格式的复合算法,进行了分析比较和改进,并就计算流体力学中的一维浅水波方程的两个算例分别做了数值对比试验,在解的光滑性、锐利性,计算速度等几个方面做了比较,模拟结果表明三种方法均能准确捕捉激波又不产生非物理震荡.     

OBS网络中QoS方案的对比研究

本文讨论在光突发交换OBS网络中支持QoS的两种机制：基于偏置时间的QoS方案和比例QoS方案。前者从OBS的基本协议JET出发,具有简单性、可行性,但存在不公平等问题;后者解决了此问题,但在许多方面仍需改进。仿真结果及分析对两种方案在几种主要性能上进行了对比。     

Multi-Service Dynamic QoS Routing Schemes with Call Admission Control: A Comparative Study

In this paper we consider wide-area backbone networks where multiple connection-oriented guaranteed services with differing bandwidth/flow requirements are offered. Specifically, we consider the case where each service requires a quality-of-service (QoS) peak rate bandwidth/flow allocation (different rate for different services) for the duration of the connection in a loss network environment. We present several dynamic routing schemes in such multi-service settings along with an admission control policy. The routing schemes cover issues such as crankback, periodicity of computation of routing, what type of information is to be used in routing decision, and whether to use centralized or decentralized computation. We present results for various measures, i.e., in addition to well-known call blocking performance, we also address and quantify measures such as signaling loads impact due to alternate routing, crankback impact, and revenue impact, and provide a comparative evaluation of various dynamic routing schemes in multi-service settings.     

变系数线性模型参数的递推估计

变系数线性模型参数的递推估计胡峰（西安卫星测控中心７１００４３）关键词递推估计,最小二乘法,变系数线性模型１引言在工程数据的综合处理中,特别是在卫星及运载工具的动态目标跟踪与精密定位时自从Ｂｒｏｗｎ［‘’提出最佳弹道自校准估计（ＥＭＢＥＴ）技术以来,...     

离线开关变换器中混沌调制技术的比较研究

论文研究了混沌调制技术在实用开关变换器中抑制电磁干扰的效果。所研究的混沌调制技术包括混沌脉冲宽度调制和定占空比混沌载频调制两种模式。从实用化的角度出发,建立了双管正激变换器的元件级电路仿真模型,通过对两种混沌调制模式与周期PWM模式下信号频谱的分析比较说明,混沌调制技术能有效降低谐波峰值,改善了电磁兼容性。此外,文章还分析了混沌调制对输出电压纹波的影响。研究表明在开关变换器中应用混沌调制技术具有实际应用前景。     

Robustness Comparative Study of Two Control Schemes for 3-DOF Flexible Manipulators

This article describes a comparative study of two control schemes designed for a new three-degree-of-freedom flexible arm. This arm has been built with light links, has most of its mass concentrated on the tip, and its special mechanical configuration uncouples tip motions in spherical coordinates. This special configuration simplifies the dynamic modeling and control of the arm. A compliance matrix is used to model the oscillations of the structure. A consequence of this simple dynamics is that minimum sensing effort is required (only direct motor and tip measurements), and the use of complex observers is avoided because the state of the system can be very easily obtained from these measurements; then its control becomes very simple. Two two-nested control loop schemes are used to control the tip position, by using a joint position and tip acceleration feedback, measured with accelerometers placed at the tip (first control scheme), or tip deflexions feedback, measured with strain gauges placed at the bars of the mechanism near the joints (second control scheme). Both control systems can be considered as equivalents when nominal payload is used for designing them. It can be proved that the use of strain gauges is more robust than the use of accelerometers as tip sensors if the tip mass differs from the nominal one. Simulated results are presented for both control schemes and different payload conditions. Comparative results between the controlled and non-controlled tip responses are also shown.     

Quadratic Stabilization of Switched Uncertain Linear Systems: A Convex Combination Approach

We consider quadratic stabilization for a class of switched systems which are composed of a finite set of continuoustime linear subsystems with norm bounded uncertainties. Under the assumption that there is no single quadratically stable subsystem, if a convex combination of subsystems is quadratically stable, then we propose a state-dependent switching law, based on the convex combination of subsystems, such that the entire switched linear system is quadratically stable. When the state information is not available, we extend the discussion to designing an output-dependent switching law by constructing a robust Luenberger observer for each subsystem.      

Comparative Study of Different Decoupling Schemes for TITO Binary Distillation Column via PI Controller

This paper presents a comparative study of different decoupling control schemes for a two-input, two-output (TITO) binary distillation column via proportional-integral (PI) controller. The key idea behind this paper is designing two novel fuzzy decoupling schemes that depend on human knowledge, instead of the system mathematical model used in conventional decoupling schemes. Based on conventional and inverted decoupling schemes, fuzzy and inverted fuzzy decoupling schemes are developed. The control effect is compared using simulation results for the proposed two schemes with conventional decoupling and inverted decoupling. The proposed fuzzy decoupling schemes are easy to realize and simple to design, besides they have a good decoupling capability. Two methods are used to prove asymptotic stability of each loop and the entire closed-loop system by applying the proposed fuzzy decoupling-based PI controller. The Wood and Berry model of a binary distillation column is used to illustrate the applicability of the proposed schemes.      

A Comparative Study Of Global Optimization Approaches To Meg Source Localization

It is well-known that the problem of MEG source localization can be cast as an optimization problem. So far, there have been many works in which various optimization methods were adopted for source localization. In this paper, we compare the performance of three typical and widely used optimization techniques for a specific MEG source localization problem. We first introduce a hybrid algorithm by combining genetic and local search strategies to overcome disadvantages of conventional genetic algorithms. Second, we apply the tabu search, a widely used optimization method in combinational optimization and discrete mathematics, to source localization. To the best of our knowledge, this is the first attempt in the literature to apply tabu search to MEG/EEG source localization. Third, in order to further compare the performance of the above algorithms, simulated annealing is also applied to MEG source localization problem. The computer simulation results show that our local genetic algorithm is the most effective approach to dipole localization, and the tabu search method is also a very good strategy for this problem.     

Parallel Control for Continuous-Time Linear Systems: A Case Study

In this paper, a new parallel controller is developed for continuous-time linear systems. The main contribution of the method is to establish a new parallel control law, where both state and control are considered as the input. The structure of the parallel control is provided, and the relationship between the parallel control and traditional feedback controls is presented. Considering the situations that the systems are controllable and incompletely controllable, the properties of the parallel control law are analyzed. The parallel controller design algorithms are given under the conditions that the systems are controllable and incompletely controllable. Finally, numerical simulations are carried out to demonstrate the effectiveness and applicability of the present method.      

Empirical Optimization for a Sparse Linear Solver: A Case Study

This paper describes initial experiences with semi-automated performance tuning of a sparse linear solver in LS-DYNA, a large, widely used engineering application. Through a collection of tools supporting empirical optimization, we alleviate the burden of performance tuning for mapping today’s sophisticated engineering software to increasingly complex hardware platforms. We describe a tool that automatically isolates code segments to create benchmark subsets for the purposes of performance tuning. We present a collection of automatically generated empirical results that demonstrate the sensitivity of the application’s performance to optimization parameters. Through this case study, we demonstrate the importance of developing automatic performance tuning support for performance-sensitive applications.     

To FLIP or not to FLIP: Comparative case study in higher education in Turkey

The purpose of this study was (1) to investigate the effectiveness of the flipped-classroom approach, when coupled with problem-based learning and cooperative learning, compared to that of a traditional classroom; (2) to investigate the effects of watching videos and of doing homework on achievement in a physics course; and (3) to evaluate students’ perception of the use of the flipped-classroom format in a physics course. In this study, both qualitative and quantitative data were collected. A pre-test/post-test quasi-experimental method with a control group was used. The results showed that homework performance and the amount of video watched (preliminary work before class) were significantly more effective for student achievement in the flipped-classroom. Moreover, although students struggled to adapt to the new system at the beginning, students who know and feel responsible for their own learning can close the gap with more individual and group activities and can achieve higher grades.     

Improved ADI Scheme for Linear Hyperbolic Equations: Extension to Nonlinear Cases and Compact ADI Schemes

This paper studies the Galerkin finite element approximation of time-fractional Navier–Stokes equations. The discretization in space is done by the mixed finite element method. The time Caputo-fractional derivative is discretized by a finite difference method. The stability and convergence properties related to the time discretization are discussed and theoretically proven. Under some certain conditions that the solution and initial value satisfy, we give the error estimates for both semidiscrete and fully discrete schemes. Finally, a numerical example is presented to demonstrate the effectiveness of our numerical methods.     

Optimality Criteria for Fixture Layout Design: A Comparative Study

Fixtures are devices used in manufacturing systems to locate, immobilize, and hold workpieces. There are many different numerical measures proposed in the literature to quantify the locating accuracy of a fixture, and its capability in firmly holding the workpiece in the presence of external loads. These numerical measures are useful in fixture layout design and the related area of grasp synthesis. As a number of numerical measures are available, a user may face the problem that how to choose an appropriate one as the optimality criterion in practice for fixture design. In this paper, we present a comparative study on several widely used optimality criteria, based on both theoretical analysis and simulation studies. First, we establish a set of inequalities, which describe the relations between several widely used numerical measures. Second, comparisons between optimality criteria are demonstrated by numerical examples.