1,720,976 research outputs found
Fault-tolerant rate-monotonic first-fit scheduling in hard-real-time systems
No full textHard-real-time systems require predictable performance despite the occurrence of failures. In this paper, fault tolerance is implemented by using a novel duplication technique where each task scheduled on a processor has either an active backup copy or a passive backup copy scheduled on a different processor. An active copy is always executed, while a passive copy is executed only in the case of a failure. First, the paper considers the ability of the widely-used Rate-Monotonic scheduling algorithm to meet the deadlines of periodic tasks in the presence of a processor failure. In particular, the Completion Time Test is extended so as to check the schedulability on a single processor of a task set including backup copies. Then, the paper extends the well-known Rate-Monotonic First-Fit assignment algorithm, where all the task copies, included the backup copies, are considered by Rate-Monotonic priority order and assigned to the first processor in which they fit. The proposed algorithm determines which tasks must use the active duplication and which can use the passive duplication. Passive duplication is preferred whenever possible, so as to overbook each processor with many passive copies whose primary copies are assigned to different processors. Moreover, the space allocated to active copies is reclaimed as soon as a failure is detected. Passive copy overbooking and active copy deallocation allow many passive copies to be scheduled sharing the same time intervals on the same processor, thus reducing the total number of processors needed. Simulation studies reveal a remarkable saving of processors with respect to those needed by the usual active duplication approach in which the schedule of the non-fault-tolerant case is duplicated on two sets of processors. © 1999 IEEE
Gest Editorial: Special Issue on Algorithmic Solutions for Wireless, Mobile, Ad Hoc and Sensor Networks
No full textCo-editor Special Issu
TIME SLOT ASSIGNMENT IN SS/TDMA SYSTEMS WITH INTERSATELLITE LINKS
No full textThe time slot assignment problem in clusters of SS/TDMA satellite systems interconnected through intersatellite links is studied. The authors show that the problem of finding an assignment which minimizes the total transmission time is NP-complete, i. e. , computationally intractable, even for quite restricted intersatellite link patterns and simplified system models. Successively, they focus attention on clusters of two satellites, proposing a branch-and-bound optimal algorithm and two fast heuristic algorithms. They investigate the performance of the proposed heuristic algorithms both by a theoretical worst case bound and by simulation trials showing that the produced solutions are close to the optimal on the average
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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