A hybrid algorithm for reducing matrix bandwidth

A hybrid algorithm for reducing the bandwidth of symmetric matrices is described in terms of a finite element grid. The new algorithm produces significantly lower bandwidths than either the commonly-used Gibbs–Poole-Stockmeyer (GPS) or Cuthill–McKee (CM) algorithms, with run times comparable to the original CM algorithm. The new hybrid algorithm uses the GPS algorithm as a preprocessor to provide a good initial node numbering for the author's node-shuffling algorithm, which accounts for variable degrees-of-freedom per node (DOF/node). The hybrid algorithm was tested on the 30 benchmark problems that were compiled by Everstine, and on 10 supplemental problems with variable DOF/node. Bandwidths and CPU times are presented for all problems.     

基于带宽借贷的EPON动态带宽分配算法

针对以往以太网无源光网络(EPON)动态带宽算法中存在的带宽分配不公平性问题,提出了基于带宽借贷机制的动态带宽算法LLR和LWR,其基本思想为当某光网络单元(ONU)有空余带宽时,光线路终端(OLT)将此ONU多余带宽借贷给重负载ONU,当债权ONU遇到带宽不足的情况时,OLT将会安排负债ONU偿还其未满足请求部分带宽.通过在正常使用和存在"贪婪"用户的两种情况下的仿真,分析了这两种算法的平均时延和丢包率特性.仿真结果表明这两种算法能为正常使用用户提供有保障的公平性服务,消除了以往算法在若干用户过量使用的情况下所有用户都受影响的问题,使动态带宽分配更加公平.     

A simplified expression for low cleavage probability calculation

This article describes an analysis made to develop a simplified stress-based criterion for brittle fracture focussed on the lowest probability of failure. For that, on the basis of fine numerical interpretation of two series of fracture-tests on 16MND5 reactor vessel steel, a number of variables were proposed:

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A stress threshold σ_th below which cleavage cannot occur. This stress is determined by testing on notch tensile specimen at low temperature.

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A minimum toughness K_min(T) required to make a crack unstable. The originality is here to consider this parameter depends on temperature.

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For K_J > K_min(T), a volume susceptible to cleavage, defined as the volume of material subjected to stress exceeding the threshold stress and noted V_th, representative of the fracture probability.

These three variables are explained in the article then used to establish a tentative criterion for expressing the risk of brittle fracture, in the presence or absence of a crack.     

Analytical models of blocking probability for multi-granularity cross-connect-based optical networks

Multi-granularity optical cross-connect (MG-OXC)-based optical network is a promising optical network architecture as it is capable of flexible switching at different granularity levels. In MG-OXC-based optical networks, wavelength conversion (WC) capability and the number of usable add/drop ports of the nodes are two key factors affecting its performance. Two analytical models of blocking probability for MG-OXC-based optical networks both without WC capability and with sparse WC capability are proposed, exploiting Erlang?s loss formula and birth?death process. Based on the models and simulation, the impact of WC capability and the number of add/drop ports on the blocking probability are investigated. Three kinds of granularities (i.e. fibre, waveband and wavelength) are considered in MG-OXC nodes to reduce the complexity and size of switch fabric. Both the analytical and simulation results are given on two network topologies under dynamic traffic patterns. Simulation results show that the proposed models are accurate and effective for the analysis of blocking probability in MG-OXC-based optical networks.     

稀疏波长变换的WDM光网络阻塞率的分析与计算

本文主要对具有稀疏波长变换的WDM全光网的阻塞率进行分析,首先提出一种模型分析了无波长变换器的L跳路径端到端阻塞率,接着对部分波长变换器的L跳路径的阻塞率进行求解,随后分析了全网的平均阻塞率。研究得到的主要结论是,波长变换器使用的有效性取决于网络的连接度。     

A new mode renumbering algorithm for bandwidth reduction

A new algorithm is presented for automatic renumbering of systems of interconnected nodes so as to minimize the bandwidth of the connectivity matrix. This is necessary to reduce storage requirements for banded matrix solution techniques. The method is based on those due to Cuthill and McKee¹ and Gibbs, Poole and Stockmeyer.² Under test against several other algorithms on a range of 20 examples of various types it always performed at least as well as, and in most cases better than, the best of the other methods. Seven examples are given in the paper, comparing final bandwidths with those produced by seven other algorithms.     

基于矢量DSP的并行化卷积算法

为了提场卷积算法在矢量!字信号处理器(DSP)上的执行效率,提出了一种高效的并行化卷积算法——基2并行短卷积(PSC R2)算法。该算法采用了基2短卷积运算结构,摆脱了传统并行化卷积算法的直接结构,从而有效降低了算法的循环次!。基于该算法结构,还提出了矢量DSP专用指令以匹配卷积的运算结构,保障算法执行效率。通过实际评估,证明了该算法在时间复杂度上仅为传统的内循环矢量化(VIL)算法的43%,为外循环矢量化(VOL)算法的55%,并且在存储空间开销上能够与传统算法基本持平。利用该算法,可以大幅降低移动通信和数字信号处理中的卷积、相关、滤波运算的时间复杂度。     

Clustering clinical departments for wards to achieve a prespecified blocking probability

OR Spectrum - When the number of available beds in a hospital is limited, it can be beneficial to cluster several clinical departments such that the probability of not being able to admit a patient...     

An improved harmony search algorithm with dynamically varying bandwidth

The present work demonstrates a new variant of the harmony search (HS) algorithm where bandwidth (BW) is one of the deciding factors for the time complexity and the performance of the algorithm. The BW needs to have both explorative and exploitative characteristics. The ideology is to use a large BW to search in the full domain and to adjust the BW dynamically closer to the optimal solution. After trying a series of approaches, a methodology inspired by the functioning of a low-pass filter showed satisfactory results. This approach was implemented in the self-adaptive improved harmony search (SIHS) algorithm and tested on several benchmark functions. Compared to the existing HS algorithm and its variants, SIHS showed better performance on most of the test functions. Thereafter, the algorithm was applied to geometric parameter optimization of a friction stir welding tool.     

Analysis of effect of load-based excess bandwidth reservation on performances of differentiated services in E-PON

Performances of differentiated services in the upstream transmission of Ethernet passive optical network (E-PON) are affected by bandwidth reservation algorithm of an optical network unit, since data packets can be transmitted to an optical line termination only during the reserved transmission window. The effects of time-slot reservation on differentiated services are analysed and an adaptive class-based excess bandwidth reservation algorithm, called service quality pre-engagement (SQP), which reserves a time-slot based on the backlog queue and traffic arrival pattern of class is proposed. SQP applies the prediction-based bandwidth reservation to selected forward reservation classes (FRCs) which are determined by the introduced dynamic FRC selection. The proposed short-term service work-based time-slot reservation and long-term adaptive FRC selection optimise time-slot reservation according to traffic load of class. Analytic and simulation results show that this approach improves the performance of differentiated services, especially in terms of system buffer size, light-load penalty and service fairness, while guaranteeing high link utilisation and throughput     

双光纤波分复用网阻塞率研究

研究了双光纤波分复用互联网在不同网络容量使用率时的阻塞率,主要对单光纤网络使用波长变换器和双纤网络在波长数不同时对网络阻塞率的改善情况做了仿真比较,结果表明仅仅在低阻塞率时波长变换器给网络所带来的增益非常有限,双纤网络可以达到其效果。     

Reservation signalling mechanism for reducing blocking probability in optical burst switching networks with limited wavelength conversion capabilities

First, the optical burst switching (OBS) network with limited wavelength conversion capability (LWCC) is decomposed into multiple wavelength continuous segments according to the position of wavelength converters. Based on the decomposed network model, two reservation signalling mechanisms for OBS-LWCC networks, namely wavelength-amend-on-demand (WAoD) and contention-based limited signalling protocol (CLSP), are proposed to reduce the blocking probability in the OBS-LWCC networks. In WAoD, the congested node sends a feedback message to the closest upstream switch with wavelength conversion capability. The notified switch will change the burst wavelength to the one assigned by the congested node to avoid collision in advance. Extensive simulation results indicate that by applying the wavelength reconfiguration method to the core nodes without wavelength conversion capability, the proposed WAoD scheme can improve the blocking performance in the OBS-LWCC networks significantly. Furthermore, CLSP, which combines the burst time-slot reconfiguration with the wavelength reconfiguration of WAoD, always has the lowest burst loss probability when compared with both the conventional and the proposed reservation mechanisms.     

EPON上行接入动态带宽分配算法的研究

以太无源光网络的上行方向需要一种多址接入技术来防止以太数据包的碰撞。时分多址技术应用广泛,而波分多址技术极具潜力,是发展的方向。基于时分多址技术,提出了一种改进的动态带宽分配算法,结合了轮询机制和申请的优先级。通过建模仿真,证明了该算法可以取得较小的平均包延时和较高的带宽利用率。     

适合于HC-MAC协议的感知信道动态预留算法

针对基于HC-MAC协议的认知无线电系统提出了一种感知信道动态预留算法,以解决系统用户较多时可用频谱不能被充分利用的问题.该算法通过在感知开始前为认知用户预留一些信道,使得认知用户可以同时感知信道,从而减少了认知用户等待感知可用信道的时间,提高了频谱利用率.为了使该算法更具实用性,根据实时类业务和尽力服务类业务两类常见...     

Estimation of distribution algorithm with path relinking for the blocking flow-shop scheduling problem

This article presents an effective estimation of distribution algorithm, named P-EDA, to solve the blocking flow-shop scheduling problem (BFSP) with the makespan criterion. In the P-EDA, a Nawaz–Enscore–Ham (NEH)-based heuristic and the random method are combined to generate the initial population. Based on several superior individuals provided by a modified linear rank selection, a probabilistic model is constructed to describe the probabilistic distribution of the promising solution space. The path relinking technique is incorporated into EDA to avoid blindness of the search and improve the convergence property. A modified referenced local search is designed to enhance the local exploitation. Moreover, a diversity-maintaining scheme is introduced into EDA to avoid deterioration of the population. Finally, the parameters of the proposed P-EDA are calibrated using a design of experiments approach. Simulation results and comparisons with some well-performing algorithms demonstrate the effectiveness of the P-EDA for solving BFSP.     

A study using Monte Carlo Simulation for failure probability calculation in Reliability-Based Optimization

In this study, a Reliability-Based Optimization (RBO) methodology that uses Monte Carlo Simulation techniques, is presented. Typically, the First Order Reliability Method (FORM) is used in RBO for failure probability calculation and this is accurate enough for most practical cases. However, for highly nonlinear problems it can provide extremely inaccurate results and may lead to unreliable designs. Monte Carlo Simulation (MCS) is usually more accurate than FORM but very computationally intensive. In the RBO methodology presented in this paper, limit state approximations are used in conjunction with MCS techniques in an approximate MCS-based RBO that facilitates the efficient calculation of the probabilities of failure. A FORM-based RBO is first performed to obtain the initial limit state approximations. A Symmetric Rank-1 (SR1) variable metric algorithm is used to construct and update the quadratic limit state approximations. The approximate MCS-based RBO uses a conditional-expectation-based MCS, that was chosen over indicator-based MCS because of the smoothness of the probability of failure estimates and the availability of analytic sensitivities. The RBO methodology was implemented for an analytic test problem and a higher-dimensional, control-augmented-structure test problem. The results indicate that the SR1 algorithm provides accurate limit state approximations (and therefore accurate estimates of the probabilities of failure) for these test problems. It was also observed that the RBO methodology required two orders of magnitude fewer analysis calls than an approach that used exact limit state evaluations for both test problems.     

Sample regeneration algorithm for structural failure probability function estimation

An efficient strategy to approximate the failure probability function in structural reliability problems is proposed. The failure probability function (FPF) is defined as the failure probability of the structure expressed as a function of the design parameters, which in this study are considered to be distribution parameters of random variables representing uncertain model quantities. The task of determining the FPF is commonly numerically demanding since repeated reliability analyses are required. The proposed strategy is based on the concept of augmented reliability analysis, which only requires a single run of a simulation-based reliability method. This paper introduces a new sample regeneration algorithm that allows to generate the required failure samples of design parameters without any additional evaluation of the structural response. In this way, efficiency is further improved while ensuring high accuracy in the estimation of the FPF. To illustrate the efficiency and effectiveness of the method, case studies involving a turbine disk and an aircraft inner flap are included in this study.     

视网膜机理启发的尺度空间卷积模板构造算法

针对多尺度模板构造,论述形成人眼视觉尺度现象的两个因素并探讨了感受器与节细胞间的空间信息组合模型。基于人眼视觉机理启发,提出了一种新的多尺度滤波模板构造方法。该方法根据标准高斯曲线的采样率变化生成尺度空间模板族。经过时域、频域分析和滤波图例的实验,验证了该算法的普适性、规范性和有效性。与传统高斯尺度空间模板构造方法相比,具有简单、规范等特点。     

New block properties for flowshop scheduling with blocking and their application in an iterated greedy algorithm

This paper proposes new block properties for the flowshop scheduling problem with blocking to minimise makespan. A pruning procedure based on these proposed properties is used in the construction phase of an iterated greedy algorithm to decrease the total number of solutions to be examined to find an optimal schedule. Computational results using Taillard’s benchmark problem instances show that the new block properties help to eliminate more ‘unpromising’ solutions than the classic properties. In addition, the effectiveness of the proposed algorithm is verified by comparison with some high-performing algorithms for the considered problem.