网格环境下的混杂副本管理拓扑结构

在网格中,数据常常由于性能和可用性等原因进行复制.如何有效地管理网格环境中的各副本是网格系统中需要解决的重要问题.提出了一种可扩展及动态自适应的副本管理拓扑结构——混杂网格副本管理拓扑结构（HGRMT）.HGRMT将传统树状的网格逻辑结构中的各节点,在不同层次上又连接成环状,并在此基础上提出了层间与组内不同的副本创建算法.实验表明,HGRMT有较好的可扩展性、可靠性和自适应性.     

k-Dense communities in the Internet AS-level topology graph

In this paper we investigate the structure of the Internet by exploiting an efficient algorithm for extracting k-dense communities from the Internet AS-level topology graph. The analyses showed that the most well-connected communities consist of a small number of ASs characterized by a high level of clusterization, although they tend to direct a lot of their connections to ASs outside the community. In addition these communities are mainly composed of ASs that participate at the Internet Exchange Points (IXPs) and have a worldwide geographical scope. Regarding k-max-dense ASs we found that they play a primary role in the Internet connectivity since they are involved in a huge number of Internet connections (42% of Internet connections). We also investigated the properties of three classes of k-max-dense ASs: Content Delivery Networks, Internet Backbone Providers and Tier-1s. Specifically, we showed that CDNs and IBPs heavily exploit IXPs by participating in many of them and connecting to many IXP participant ASs. On the other hand, we found that a high percentage of connections originated by Tier-1 ASs are likely to involve national ASs which do not participate at IXPs.     

Dynamic hybrid replication effectively combining tree and grid topology

Effective data management is an important issue in a large-scale distributed environment such as distributed DBMS, Peer-to-Peer System (P2P), data grid, and World Wide Web (WWW). This can be achieved by using a replication protocol, which efficiently decrease the communication cost and increase the data availability. The Tree Quorum protocol is one of the representative replication protocols allowing low read cost in the best case but it has some drawbacks such as that the number of replicas grows rapidly as the level increases and root replica is a bottleneck. The Grid protocol requires fixed operation cost regardless of failure condition. In this paper we propose a new replication protocol called Dynamic Hybrid protocol, which efficiently improves the existing protocols. The proposed protocol effectively combines the grid and tree structure so that the overall topology can be flexibly adjusted using three configuration parameters; tree height, number of descendants and grid depth. For high read availability, the height of tree and number of descendants are decreased and depth of grid is increased. For high write availability, the height of tree and the depth of grid are decreased, while the number of descendant is increased. We present an analytical model of read/write availability and the average number of nodes accessed for each operation. We also employ computer simulation to estimate the throughput and communication overhead. The proposed protocol always allows much smaller communication and operation cost than earlier protocols.     

: a toolset for creating customized interfaces for grid user communities

is a comprehensive set of tools for creating customized graphical user interfaces (GUIs). It draws from the concept of computing portals, which are here seen as interfaces to application-specific computing services for user communities. While was originally designed for the use in computational grids, it can be used in client/server environments as well.Compared to other GUI generators, is more versatile and more portable. It can be employed in many different application domains and on different target platforms. With , application experts (rather than computer scientists) are able to create their own individually tailored GUIs.     

Modelling opinion formation driven communities in social networks

In a previous paper we proposed a model to study the dynamics of opinion formation in human societies by a co-evolution process involving two distinct time scales of fast transaction and slower network evolution dynamics. In the transaction dynamics we take into account short range interactions as discussions between individuals and long range interactions to describe the attitude to the overall mood of society. The latter is handled by a uniformly distributed parameter α, assigned randomly to each individual, as quenched personal bias. The network evolution dynamics is realised by rewiring the societal network due to state variable changes as a result of transaction dynamics. The main consequence of this complex dynamics is that communities emerge in the social network for a range of values in the ratio between time scales. In this paper we focus our attention on the attitude parameter α and its influence on the conformation of opinion and the size of the resulting communities. We present numerical studies and extract interesting features of the model that can be interpreted in terms of social behaviour.     

融合拓扑和安全及稳定的电力网脆弱性评估

提出了一种融合拓扑和安全及稳定的静态电力网脆弱性评估方法。先从依赖物理规律的不同程序提取出评估电力网脆弱性的三个主导指标：拓扑脆弱性指标、安全脆弱性指标、稳定脆弱性指标。基于邻接矩阵构建了拓扑脆弱性指标的度量方法。结合线路热极限和功角稳定极限,分别给出了安全脆弱性指标和稳定脆弱性指标的度量方法。计及三个主导脆弱性指标影响电力网脆弱性方式的差异,提出了三合一脆弱性指标的融合模型,并给出了脆弱性指标的算法。示例仿真结果表明,提出的三合一脆弱性指标方法对评估电力网脆弱性有效、可行。     

A critical review of established methods of structural topology optimization

The aim of this article is to evaluate and compare established numerical methods of structural topology optimization that have reached the stage of application in industrial software. It is hoped that our text will spark off a fruitful and constructive debate on this important topic. This article is an extended version of a paper presented at the WCSMO-7 in Seoul in 2007.     

基于海量运行数据挖掘的电网拓扑关系分析及应用

针对电网中GIS系统与用电信息采集等系统中停电数据不一致问题,本文利用大数据分析技术对停电运行数据与拓扑关系的规律进行数据挖掘,构建变压器停电信息与GIS等系统的拓扑优化关系模型.从GIS系统、用电信息采集系统抽取数据,以GIS系统中线路-变压器关系表为基准,以变压器停电信息为校验数据,通过变压器停电与GIS拓扑关系的...     

基于分层约简模型的接地网故障诊断软件设计

在文献[11]提出的接地网分层约简模型和文献[9]提出的多激励迭代最小二乘故障诊断方法的基础上,利用MATLAB完成了一套接地网腐蚀故障诊断的软件设计。详细论述了分层约简模型的自动生成方法、接地网可测性分析的软件实现、不确定支路组及其原形自动分解的软件实现和不确定支路电阻范围估计的软件实现,并以一个60支路的实验接地网为例进行了说明,结果表明提出的方法是可行的。     

A critical comparative assessment of differential equation-driven methods for structural topology optimization

In recent years, differential equation-driven methods have emerged as an alternate approach for structural topology optimization. In such methods, the design is evolved using special differential equations. Implicit level-set methods are one such set of approaches in which the design domain is represented in terms of implicit functions and generally (but not necessarily) use the Hamilton-Jacobi equation as the evolution equation. Another set of approaches are referred to as phase-field methods; which generally use a reaction-diffusion equation, such as the Allen-Cahn equation, for topology evolution. In this work, we exhaustively analyze four level-set methods and one phase-field method, which are representative of the literature. In order to evaluate performance, all the methods are implemented in MATLAB and studied using two-dimensional compliance minimization problems.     

A critical analysis of Building Information Modelling systems used in construction projects

Building Information Modelling (BIM) is now a global digital technology which is widely believed to have the potential to revolutionise the construction industry. This has been mainly a result of worldwide government initiatives promoting BIM uptake to improve efficiency and quality in delivering construction projects. This push has been accompanied by the release of a tremendous amount of BIM software systems which are now available in the market. Although this can be seen as a positive development, one cannot ignore how it has overwhelmed many professionals who cannot easily distinguish between the uses of these software systems. Previous studies about different BIM systems have generally been limited in scope focusing predominantly on operational issues. This study aims to conduct a comprehensive and critical appraisal of a wide range of BIM software systems currently being used in managing construction project information. To achieve this, five main methods are adopted. These include a systematic review of the literature, a structured questionnaire survey, action learning, focus group discussions and email surveys. It has to be noted that, although it is impossible to examine the totality of BIM systems, the study adopts a holistic approach looking at most of the major BIM system categories and 122 application examples which are common in the architecture, engineering and construction (AEC) industry.     

Business customer communities and knowledge sharing: exploratory study of critical issues

Businesses in knowledge intensive industries must appropriately engage with their customers in order to produce goods and services that are desired and valued in the marketplace. Engagement with customers calls for exchanging information and knowledge with customers and fostering exchanges between customers. Recent developments in the area of information and communication technologies (ICTs) have radically increased the variety of opportunities for improving customer engagement. In this paper, we will examine the use of ICTs to build Business Customer Communities (BCCs) to help an organization foster knowledge exchanges between its professional and institutional customers. We define BCCs as groups of business customers, which are deliberately enabled by a firm and share a long-term need to exchange work related knowledge through online and offline interaction. The objectives of this study are (1) to describe BCCs and outline their attributes and features, and (2) to contribute to the understanding of challenges associated with the enabling of BCC formation and how firms can overcome these challenges. As such, a contribution is made to the discussion of knowing in practice in customer communities, which rely in large part on ICT.     

Formalization of a normalization theorem in simplicial topology

In this paper we present a complete formalization of the Normalization Theorem, a result in Algebraic Simplicial Topology stating that there exists a homotopy equivalence between the chain complex of a simplicial set, and a smaller chain complex for the same simplicial set, called the normalized chain complex. Even if the Normalization Theorem is usually stated as a higher-order result (with a Category Theory flavor) we manage to give a first-order proof of it. To this aim it is instrumental the introduction of an algebraic data structure called simplicial polynomial. As a demonstration of the validity of our techniques we developed a formal proof in the ACL2 theorem prover.     

Building a production grid in Scandanavia

Innovative middleware solutions are key to the NorduGrid testbed, which spans academic institutes and supercomputing centers throughout Scandinavia and Finland and provides continuous grid services to its users.     

Flow topology in a steady three-dimensional lid-driven cavity

We present in this paper a thorough investigation of three-dimensional flow in a cubical cavity, subject to a constant velocity lid on its roof. In this steady-state analysis, we adopt the mixed formulation on tri-quadratic elements to preserve mass conservation. To resolve difficulties in the asymmetric and indefinite large-size matrix equations, we apply the BiCGSTAB solution solver. To achieve stability, weighting functions are designed in favor of variables on the upstream side. To achieve accuracy, the weighting functions are properly chosen so that false diffusion errors can be largely suppressed by the equipped streamline operator. Our aim is to gain some physical insight into the vortical flow using a theoretically rigorous topological theory. To broaden our understanding of the vortex dynamics in the cavity, we also study in detail the longitudinal spiralling motion in the flow interior.     

Task cluster scheduling in a grid system

Effective load distribution and resource management is of great importance in designing complex distributed systems as grid. This pre-assumes the capability of partitioning the arriving jobs into independent tasks that can be executed simultaneously, assigning the tasks to processors and scheduling the task execution on each processor. A simulation model, consisting of two homogeneous clusters, is considered to evaluate the performance for various workloads. The Deferred policy is applied to collect global system information about processor queues. This paper proposes a special scheduling method referred to as task clustering method. We examine the efficiency of two task routing policies – one static and one adaptive – and six task scheduling policies, which rearrange processor queues regarding to a criterion. Our simulation results indicate that the adaptive task routing policy in conjunction with SGFS-ST scheduling algorithm, which uses more efficiently the task clustering method, leads to a significant performance improvement.     

Independent checkpointing in a heterogeneous grid environment

The EU-funded XtreemOS project implements an open-source grid operating system based on Linux. In order to provide fault tolerance and migration for grid applications, it integrates a distributed grid-checkpointing service called XtreemGCP. This service is designed to support various checkpointing protocols and different checkpointer packages (e.g. BLCR, LinuxSSI, OpenVZ, etc.) in a transparent manner through a uniform checkpointer interface. In this paper, we present the integration of a backward error recovery protocol based on independent checkpointing into the XtreemGCP service. The solution we propose is not checkpointer bound and thus can be transparently used on top of any checkpointer package.To evaluate the prototype we run it within a heterogeneous environment composed of single-PC nodes and a Single System Image (SSI) cluster. The experimental results demonstrate the capability of the XtreemGCP service to integrate different checkpointing protocols and independently checkpoint a distributed application within a heterogeneous grid environment. Moreover, the performance evaluation also shows that our solution outperforms the existing coordinated checkpointing protocol in terms of scalability.     

When smart grid meets PHEVs: a smart load distribution mechanism in smart grid

Along with the increasing popularity of electric vehicles caused by economic and environmental incentives, the penetration of plug-in hybrid electric vehicles (PHEVs) poses a great threat to the power grid, especially to the aggregated load in the power system. Motivated by this observation, in this paper, we analyze the impact of large-scale usage of PHEVs and address the load distribution problem by solving a decentralized optimization problem and smoothening the peak load with pricing strategies in the power grid. We also investigate the influence of charging time and charging mode on load distribution, as the charging price varies with the changes of these two factors. Our simulation study on PJM’s data warehouse shows that the proposed strategies can well smooth the peak load by pricing on the charging time and mode. The results also indicate that our strategies always distribute the load in a smoother manner at a smaller load fluctuation compared with other schemes (e.g., First Come First Service and PMCS) and thus improving the stability and reliability of the power grid.     

Investigations of an improved PV system topology using multilevel boost converter and line commutated inverter with solutions to grid issues

A photovoltaic (PV) system using multilevel boost converter (MBC) and line commutated inverter (LCI), operating in both grid-connected mode and stand-alone mode has been analysed. This proposed system extracts and feeds the maximum power to a single phase utility grid and stand-alone system simultaneously. The duty ratio of the MBC is estimated from the theoretical analysis of the proposed system, for extracting maximum power from PV array. The proposed system tracks the maximum power with the determined duty ratio which remains the same for all irradiations, for a fixed firing angle of LCI. The flexibility of supplying required proportion of extracted power to grid and stand-alone load and the elimination of a separate MPPT controller are the major benefits of the proposed system under normal grid conditions. In addition to it, the grid issues like voltage swell, blackout and brownout are considered and necessary remedial measures have been taken in the proposed system. Based on the issues, either the firing angle of LCI is adjusted or LCI is disconnected and replaced by a battery. Simulation studies have been carried out and the dynamic response of the system is observed. A laboratory prototype is built and experimental investigations have also been carried out. The theoretical analysis, simulation and experimental results are found to be closely associating with each other proving the efficacy of the proposed configuration.