Replica Creation Algorithm for Data Grids

Data grid system is a data management infrastructure that facilitates reliable access and sharing of large amount of data, storage resources, and data transfer services that can be scaled across distributed locations. This thesis presents a new replication algorithm that improves data access performance in data grids by distributing relevant data copies around the grid. The new Data Replica Creation Algorithm (DRCM) improves performance of data grid systems by reducing job execution time and making the best use of data grid resources (network bandwidth and storage space). Current algorithms focus on number of accesses in deciding which file to replicate and where to place them, which ignores resources’ capabilities. DRCM differs by considering both user and resource perspectives; strategically placing replicas at locations that provide the lowest transfer cost. The proposed algorithm uses three strategies: Replica Creation and Deletion Strategy (RCDS), Replica Placement Strategy (RPS), and Replica Replacement Strategy (RRS). DRCM was evaluated using network simulation (OptorSim) based on selected performance metrics (mean job execution time, efficient network usage, average storage usage, and computing element usage), scenarios, and topologies. Results revealed better job execution time with lower resource consumption than existing approaches. This research contributes replication strategies embodied in one algorithm that enhances data grid performance, capable of making a decision on creating or deleting more than one file during same decision. Furthermore, dependency-level-between-files criterion was utilized and integrated with the exponential growth/decay model to give an accurate file evaluation

A fault-tolerant photovoltaic integrated shunt active power filter with a 27-level inverter

This paper introduces a fault-tolerant shunt active power filter (SAPF). The novility in of this work is that it poposes a solutions to increase the reliability of shunt active power filter to maintain its operation under a single-phase open-circuit fault in the SAPF. This will increase the reliability of the whole power system. The SAPF is composed of a 4-leg 27-level inverter based on asymmetric cascaded H-bridge topology. If an open-circuit fault is introduced to the operation of the SAPF, a special control technique will be implemented and the redundant leg of the SAPF will be activated. The fault-tolerant SAPF can do many tasks under healthy operating conditions and post and open circuit fault depending on the state of charge (SOC) of the batteries. It can mitigate harmonics in the power system, improve power factor in the system by injecting reactive power, and inject real power to the system. The proposed SAPF is tested and simulated in MATLAB/Simulink and the results have shown a significant improvement in total harmonics distortion (THD) of the source current from 13.9% to 3.9% under the normal operating condition and from 42% to 8.4% post and open circuit fault

Estimating RVE sizes for 2D/3D viscoplastic composite materials

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Numerical study of creep in two-phase aggregates with a large rheology contrast : implications for the lower mantle

International audienceIt is generally accepted that the Earth's lower mantle is dominated by two minerals, magnesiowustite (Mg, Fe)O (Mw) and (Mg, Fe)SiO3 perovskite (Mg-Pv) which are thought to exhibit very different rheological properties. In order to assess the respective role of those phases in the mechanical properties of the assemblage, we have carried out 3D finite element modelling of a model two-phase aggregate. An isotropic random polycrystal has been built from a Voronoï mosaic. Then each grain has been attributed a “hard” or “weak” behavior in such a way that the hard phase represents a volume fraction of 70%. The creep law introduced for both phases is a simple power law creep without hardening. A contrast of 35 is chosen between the strain rates of both phases under a shear stress of 10 MPa. A representative volume element of 470 grains has been shown to provide a satisfactory description of the mechanical response of the aggregate with a relative precision equal to 3%. Numerical creep experiments conducted under a constant macroscopic shear stress of 10 MPa suggest that the creep rate of lower mantle assemblages would be dominated by the mechanical behavior of the harder phase (Mg-Pv). The finite element model allows one to extract the individual behavior of the two phases within the aggregate. It is shown that during creep, the harder Mg-Pv phase carries most of the stress whereas the softer Mw phase is responsible for most of the accumulated strain. This result should have implications for the development of shape and lattice preferred orientations of Mw within the aggregate, thus for seismic anisotropy of the lower mantle

Prediction of the elastic modulus of the trabecular bone based on X-ray computed tomography

International audienceThis work aims to estimate the apparent Young's modulus of real human trabecular bones using a numerical micro-macro approach. Cylindrical specimens of trabecular bone were extracted from human femur heads, cleaned and scanned using a SkyScan-1072 micro-computed tomography system. 3D volumetric tetrahedral grids were generated from the exploitation of the reconstructed images using original meshing techniques. Numerical compressive tests were simulated, assuming isotropic tissue Young's modulus for all elements. The large size of the volumes implies grids with a high number of nodes, which required the use of a large number of parallel processors in order to perform the finite element calculations. Numerical Young's moduli varied between 1300 MPa and 1600 MPa, with a good agreement with experiments

The impact of audit committee characteristics on corporate voluntary disclosure

The purpose of this study is to investigate the influence of audit committee characteristics on corporate voluntary disclosure of 146 Malaysian listed firms for the year 2009.Based on content analysis of disclosure, the empirical results of multiple regressions reveal that audit committee independence, size and multiple directorships of audit committee members are positively associated with corporate voluntary disclosure.Frequency of meetings and financial expertise of audit committee members are not significantly associated with corporate voluntary disclosure.The results offer evidence to policy makers, investors and accounting professionals on the extent to which audit committee characteristics associated with such committee effectiveness in monitoring corporate reporting processes

Comparative analysis of classification techniques for network fault management

Network troubleshooting is a significant process. Many studies were conducted about it. The first step in the troubleshooting procedures is represented in collecting information. It's collected in order to identify the problems. Syslog messages which are sent by almost all network devices include a massive amount of data that concern the network problems. Based on several studies, it was found that analyzing syslog data (which) can be a guideline for network problems and their causes. The detection of network problems can become more efficient if the detected problems have been classified based on the network layers. Classifying syslog data requires identifying the syslog messages that describe the network problems for each layer. It also requires taking into account the formats of syslog for vendors' devices. The present study aimed to propose a method for classifying the syslog messages which identify the network problem.This classification is conducted based on the network layers. This method uses data mining instrument to classify the syslog messages. The description part of the syslog message was used for carrying out the classification process.The relevant syslog messages were identified. The features were then selected to train the classifiers. Six classification algorithms were learned; LibSVM, SMO, KNN, Naïve Bayes, J48, and Random Forest. A real data set was obtained from an educational network device. This dataset was used for the prediction stage. It was found that that LibSVM outperforms other classifiers in terms of the probability rate of the classified instances where it was in the range of 89.90%-32.80%. Furthermore, the validation results indicate that the probability rate of the correctly classified instances is >70%. © 2020 Turkiye Klinikleri. All rights reserved

Influence de la morphologie tridimensionnelle sur le comportement mécanique de réfractaires électrofondus

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Finite element simulations of the deformation of fused-cast refractories based on X-ray computed tomography

International audienceThis work consists in building a 3D numerical model of the microstructure of a fused-cast refractory (two-phase material)..