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David Levy

Bio: David Levy is an academic researcher from University of Sydney. The author has contributed to research in topics: Cloud computing & Web service. The author has an hindex of 16, co-authored 93 publications receiving 1222 citations.


Papers
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Journal ArticleDOI
TL;DR: The failure rates of HPC systems are reviewed, rollback-recovery techniques which are most often used for long-running applications on HPC clusters are discussed, and a taxonomy is developed for over twenty popular checkpoint/restart solutions.
Abstract: In recent years, High Performance Computing (HPC) systems have been shifting from expensive massively parallel architectures to clusters of commodity PCs to take advantage of cost and performance benefits. Fault tolerance in such systems is a growing concern for long-running applications. In this paper, we briefly review the failure rates of HPC systems and also survey the fault tolerance approaches for HPC systems and issues with these approaches. Rollback-recovery techniques which are most often used for long-running applications on HPC clusters are discussed because they are widely used for long-running applications on HPC systems. Specifically, the feature requirements of rollback-recovery are discussed and a taxonomy is developed for over twenty popular checkpoint/restart solutions. The intent of this paper is to aid researchers in the domain as well as to facilitate development of new checkpointing solutions.

238 citations

Journal ArticleDOI
TL;DR: In this paper, the quality of the students' experiences of learning through those discussions is investigated in a study using qualitative approaches to investigate the variation in students' understanding of what they were learning through discussions, and how they went about engaging in them.
Abstract: Students studying a third‐year e‐commerce subject experienced face‐to‐face and online discussions as an important part of their learning experience. The quality of the students' experiences of learning through those discussions is investigated in this study. This study uses qualitative approaches to investigate the variation in the students' understanding of what they were learning through discussions, and how they went about engaging in them. Quantitative analyses are used to investigate how the students' experience related to their performance. Key outcomes of the study include that the quality of the students' experience of learning through discussions is positively related to their performance and that face‐to‐face and online discussions have qualitatively different benefits for learning.

84 citations

Journal ArticleDOI
TL;DR: Applying a real-time queuing protocol that is developed recently, this paper is able to limit the sum of the network-induced communication delay and the control computation delay within a control period to compensate for the control packet dropout at the actuator using past control signals.

81 citations

Proceedings ArticleDOI
17 May 2010
TL;DR: A virtual file system, called Trust Store, is prototyped, which allows users to utilize untrusted storage service provider with confidentiality and integrity of the data preserved and is deployed with Amazon S3 to evaluate its performance.
Abstract: The enormous amount of data generated in daily operations and the increasing demands for data accessibility across organizations are pushing individuals and organizations to outsource their data storage to cloud storage services. However, the security and the privacy of the outsourced data goes beyond the data owners' control. In this paper, we propose a service composition approach to preserve privacy for data stored in untrusted storage service. A virtual file system, called Trust Store, is prototyped to demonstrate this concept. It allows users utilize untrusted storage service provider with confidentiality and integrity of the data preserved. We deployed the prototype with Amazon S3 and evaluate its performance.

77 citations

Proceedings ArticleDOI
05 Jul 2010
TL;DR: A novel design to achieve Trustworthy Service Oriented Architecture (TSOA) in the Cloud through enforcing strong accountability is proposed and the testing figure indicates the cost of incorporating the design to SOA in the cloud is acceptable.
Abstract: Computing resource provisioning through the use of the Cloud computing paradigm has triggered revolutions in modern day computing. It is a new paradigm for deploying services on rented machines. On the other hand, Service Oriented Architecture (SOA) has gained wide adoption among organizations due to the importance of collaborations and outsourcing. Therefore the Cloud’s enormous capacity with comparable low cost makes it an ideal platform for SOA deployment. The overall correctness of the SOA deployed in the Cloud depends on the correctness of all individual participants. As the SOA usually spans multiple administration domains, concluding the faulty service and making the provider responsible become a challenging task. In this paper, we propose a novel design to achieve Trustworthy Service Oriented Architecture (TSOA) in the Cloud through enforcing strong accountability. In such system not only the root of a fault can always be concluded to the guilty participant(s), each conclusion is supported with non-disputable evidence. We also implemented a demonstrative system to show its effectiveness in real practice. Our testing figure indicates the cost of incorporating our design to SOA in the cloud is acceptable.

68 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: Barwise and Perry as discussed by the authors tackle the slippery subject of ''meaning, '' a subject that has long vexed linguists, language philosophers, and logicians, and they tackle it in this book.
Abstract: In this provocative book, Barwise and Perry tackle the slippery subject of \"meaning, \" a subject that has long vexed linguists, language philosophers, and logicians.

1,834 citations

Book
01 Jan 1996

1,170 citations

Journal ArticleDOI
TL;DR: E-Moderators are the new generation of teachers and trainers who work with learners online as mentioned in this paper using Computer-Mediated Conferencing (CMC) as a learning tool, regardless of the subject they are teaching.
Abstract: E-Moderators are \"the new generation of teachers and trainers who work with learners online\" (p. viii) using Computer-Mediated Conferencing (CMC) as a learning tool, regardless of the subject they are teaching. They are the focus of E-Moderating, a recent book which provides both a theoretical framework for developing online learning using CMC (part one), and a wealth of practical advice (part two). The book is supported by a Web site. The author, Gilly Salmon, a distance education specialist with the Open University Business School in the UK, provides a five-step model of effective online education, along with copious examples of how the model relates to real-life online learning contexts. Salmon proposes that, by basing learning on a constructivist model, it is e-moderators that can make the difference in online education as they convene, direct, summarize, and archive synchronous and asynchronous discussions.

1,055 citations

Journal ArticleDOI
TL;DR: The main methodologies suggested in the literature to cope with typical network-induced constraints, namely time delays, packet losses and disorder, time-varying transmission intervals, competition of multiple nodes accessing networks, and data quantization are surveyed.
Abstract: Networked control systems (NCSs) have, in recent years, brought many innovative impacts to control systems. However, great challenges are also met due to the network-induced imperfections. Such network-induced imperfections are handled as various constraints, which should appropriately be considered in the analysis and design of NCSs. In this paper, the main methodologies suggested in the literature to cope with typical network-induced constraints, namely time delays, packet losses and disorder, time-varying transmission intervals, competition of multiple nodes accessing networks, and data quantization are surveyed; the constraints suggested in the literature on the first two types of constraints are updated in different categorizing ways; and those on the latter three types of constraints are extended.

989 citations