On multilevel voting

Summary In a distributed system mutual exclusion is often used to maintain consistency when restricted operations are performed. Mechanisms guaranteeing mutual exclusions should be both resilient and efficient. Resiliency implies high resource availability in the face of failures, while efficiency implies low overhead incurred by performing restricted operations. In this paper, we propose and study a general paradigm, called multilevel voting, which provides a general framework to assist in the design of resilient and efficient mutual exclusion mechanisms. The proposed method uses multiple level quorum consensus. Unlike another method based on the use of multiple quorum consensus, the proposed model only contains one type of integrity constraints. This has the benefit of being conceptually simple and easy to reason about. The strong resemblance with the traditional quorum consensus makes it easy for the proposed paradigm to embed any technique based on traditional quorum schemes. We show that the proposed model represents the exact class of coteries. This means that not only does it have all the power of coteries, but also all schemes under the model are correct. Thus, should the need arise, we can interchange two schemes freely without using any extra mechanisms to ensure correctness. We study a number of issues that have impact on performance such as the degree of a multilevel scheme and the order of a coterie. We explain how the model can be extended also to model the schemes for the synchronization of read and write of replicated data. We provide algorithms for the design of multilevel schemes in the context of mutual exclusion and that of read and write of replicated data. J. Tang received the M.S. degree in computer science from the University of Iowa in 1983 and the Ph.D degree in computer science from the Pennsylvania State University in 1988. Since 1988, he has been an assistant professor with the Department of Computer Science, Memorial University of Newfoundland, St. John's, Newfoundland, Canada. His current research interests include distributed computing, fault tolerance in distributed systems, database modeling and multidatabase systems.This work was supported in part by the Natural Sciences and Engineering Research Council of Canada, individual operating grant OGP0041916     

Multiscale analysis of the influence of the triplet helicoidal geometry on the strain state of a Nb3Sn based strand for ITER coils

A theoretical model of a beam of unidirectional composites—based on the homogenisation theory and a refined kinematical hypothesis—is used for the analysis of the influence of the helicoidal geometry of a superconducting strand triplet on its strain state. The triplet is the first cabling stage of the superconducting cables used to wind the coils of ITER fusion reactor. The multiscale modelling strategy is presented, for which a finite element code has been developed. A triplet of Nb₃Sn based strands subjected to an axial stretch is analysed, and the resulting complete 3D strain state in the Nb₃Sn filament is recovered. An “extra” strain is found due to the helicoidal geometry of the triplet. Discussion of the results concludes the paper.     

多级安全关系数据库系统审计功能的设计

本文简要地介绍了多级安全关系数据库系统和计算机系统的审计，强调指出了多级安全关系数据库系统审计功能的设计必须遵循多级安全策略，并就审计粒度的选择，审计开关和阈值的设置，审计日志的维护和查询等方面的设计作了详细的讨论。     

DECOMPOSITION THEOREM AND k-HYPERCONNECTION EXPRESSIONS FOR GENERAL k-ORDER COFACTORS

Two k-hyperconnection expressions of a general k-order cofactor Y_((i,j)) are presentedfor the indefinite parameter matrix Y of a linear system by applying directed hypergraph theory,and based on it a decomposition theorem of Y_((i,j)) is derived.By this theorem,the multi-leveltearing and analysis can be carried out easily for any linear large system.This is a new mul-tilevel topological analysis method.Using proposed method the scale of systems which can betopologically analysed by a computer will be enlarged.     

多电平变换器SVPWH策略

论文针对多电平变换器的特点,介绍了基于两电平SVPWM、60°坐标系、虚空间矢量、神经网络以及虚坐标系等多种多电平变换器SVPWM的算法,分析这些算法的优缺点。     

Harmonic elimination in diode-clamped multilevel inverter using evolutionary algorithms

This paper describes two evolutionary algorithms for the optimized harmonic stepped–waveform technique. Genetic algorithms and particle swarm optimization are applied to compute the switching angles in a three-phase seven-level inverter to produce the required fundamental voltage while, at the same time, specified harmonics are eliminated. Furthermore, these algorithms are also used to solve the starting point problem of the Newton-Raphson conventional method. This combination provides a very effective method for the harmonic elimination technique. This strategy is useful for different structures of seven-level inverters. The diode-clamped topology is considered in this study.     

Adjusting electronic structure coupling of Fe–Ni2P (NiFeP-MOF) multilevel structure for ultra-activity and durable catalytic water oxidation

Efficient electrocatalyst for alkaline oxygen evolution reaction is the critical core to the wide application of metal-air energy storage and water electrolysis hydrogen energy. Therefore, appropriate design of highly active and stable non-noble metal oxygen evolution electrocatalyst with good electronic structure and multilevel structure is both a goal and a challenge. Here, we report a Fe–Ni₂P electrocatalyst (NiFeP-MOF) with multilevel structure, which was obtained by anion exchange on the basis of Fe–Ni(OH)₂ (NiFe-MOF) grown on nickel foam in situ by solvothermal method. As expected, Fe substitution regulates the Ni oxidation state in the NiFeP-MOF and realizes electronic structure coupling, showing a highly active and stable oxygen evolution reaction (OER) in alkaline electrolyte solution. Specifically, the NiFeP-MOF demonstrates an ultralow overpotentials (232 mV, 10 mA cm^?2; 267 mV 100 mA cm^?2), respectively, an extremely small Tafel slope (34 mV dec^?1). Separately, the electrocatalyst shows an excellent cycle stability at 10 mA cm^?2 for 12 h (43,200 s). More importantly, this work come up with an available policy for the preparation of excellent alkaline hydrolysis electrolysis catalysts and air cathodes with excellent performance.     

A multilevel calibration technique for an industrial robot with parallelogram mechanism

This paper presents a multilevel calibration technique for improving the absolute accuracy of an industrial robot with a parallelogram mechanism (ABB IRB2400). The parallelogram structural error is firstly modeled based on the partial differential of the position function of a general four-bar linkage and the linearization of the position constraints of the parallelogram mechanism, the model coefficients are fitted from experimental data. Secondly, an absolute kinematic calibration model is established and resolved as a linear function of all the kinematic parameters, as well as the base frame parameters and tool parameters. Finally, contrary to most other similar works, the robot joint space (rather than Cartesian space) is divided into a sequence of fan-shaped cells in order to compensate the non-geometric errors, the positioning errors on the grid points are measured and stored for the error compensation on the target points. After the multilevel calibration, the maximum/mean point positioning errors on 284 tested configurations (evenly distributed in the robot common workspace) are reduced from 1.583/0.420 mm to 0.172/0.066 mm respectively, which is almost the same level as the robot bidirectional repeatability.     

Viewpoint: Information systems research strategy

This article^1,2 has two aligned aims: (i) to espouse the value of a strategic research orientation for the Information Systems Discipline; and (ii) to facilitate such a strategic orientation by recognising the value of programmatic research and promoting the publication of such work. It commences from the viewpoint that Information Systems (IS) research benefits from being strategic at every level, from individual researcher, to research program, to research discipline and beyond. It particularly advocates for more coordinated programs of research emphasising real-world impact, while recognising that vibrant, individual-driven and small-team research within broad areas of promise, is expected to continue forming the core of the IS research ecosystem. Thus, the overarching aim is the amplification of strategic thinking in IS research – the further leveraging of an orientation natural to the JSIS community, with emphasis on research programs as a main strategic lever, and further considering how JSIS can be instrumental in this aim.