1,721,082 research outputs found
Computation of the normalising constant for product-form models of distributed systems with synchronisation
Full text linkPerformance evaluation of large distributed systems plays a pivotal role in the design of Internet of Things (IoT) applications, or Big Data analysis, where high scalability and low response times are required. However, this performance assessment requires models, methodologies and tools tailored for this type of systems. Product-form queueing networks have been widely adopted for the analysis of sequential computations thanks to the availability of efficient algorithms for the computation of the average performance indices. However, this formalism has strong limitations since it does not allow one to model fork-join constructs or batches of jobs. Product-form stochastic Petri nets partially overcome these limitations but, on the other hand, general algorithms for the computation of the expected performance indices are not known or require strong assumptions on the model structure. In this paper, we define a new algorithm for the analysis of product-form stochastic Petri nets which works under much less restrictive assumptions than those previously proposed. The idea is that, in many cases, the entire state space of the model can be stored in memory thanks to multi-valued decision diagrams and the computation of the net's performance indices can take advantage of the tree structure that characterises this representation. Finally, we present a case study and several examples that will be used to study the performance of the algorithm for realistic scenarios
Picosecond pulse amplification in AlGaAs flared amplifiers
No full textIEEE JOURNAL ON SELECTED TOPICS IN QUANTUM ELECTRONIC
Analysis of high-power semiconductor laser amplifiers in pulsed regime
No full textWe present a dynamical beam propagation method for modelling pulse propagation in flared semiconductor laser amplifiers, including all the main effects involved such as diffraction, gain saturation, self-focusing, gain dispersion and refractive index dispersion up to the second order. We applied the model to different devices in order to compare the performances of various guiding techniques and geometric shapes of the amplifiers. We obtain the result that linearly flared gain-guided devices give the best results with nearly-Gaussian output pulses, which should be more easily coupled to other optical device
A Mixed PS-FCFS Policy for CPU IntensiveWorkloads
No full textRound robin (RR) is a widely adopted scheduling policy in modern computer systems. The scheduler handles the concurrency by alternating the run processes in such a way that they can use the processor continuously for at most a quantum of time. When the processor is assigned to another process, a context switch occurs. Although modern architectures handle context switches quite efficiently, the processes may incur in some indirect costs mainly due to cache overwriting. RR is widely appreciated both in case of interactive and CPU intensive processes. In the latter case, with respect to the First-Come-First-Served approach (FCFS), RR does not penalise the small jobs. In this paper, we study a scheduling policy, namely PS-FCFS, that fixes a maximum level of parallelism N and leaves the remaining jobs in a FCFS queue. The idea is that of exploiting the advantages of RR without incurring in heavy slowdowns because of context switches. We propose a queueing model for PS-FCFS allowing us to: (i) find the optimal level of multiprogramming and (ii) study important properties of this policy such as the mean performance measures and results about its sensitivity to the moments of the jobs' service demands
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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