1,720,986 research outputs found
Broadcast and Aggregation in BBC
No full textIn this paper we introduce a process calculus BBC that has both forms of communication. For both many-to-one and one-to-many communication, it is often a natural assumption that communication is bounded; this reflects two distinct aspects of the limitations of a medium. In the case of broadcast, the bound limits the number of possible recipients of a message. In the case of collection, the bound limits the number of messages that can be received. For this reason, BBC uses a notion of bounded broadcast and collection. Moreover, the syntax of the calculus introduces an explicit notion of connectivity that makes it possible to represent a communication topology directly. By using a proof technique introduced by Palamidessi we show that even a version of BBC that only uses collection is more expressive than the pi-calculus
Static analyses over weak memory
Get PDFWriting concurrent programs with shared memory is often not trivial. Correctly synchronising the threads and handling the non-determinism of executions require a good understanding of the interleaving semantics. Yet, interleavings are not sufficient to model correctly the executions of modern, multicore processors. These executions follow rules that are weaker than those observed by the interleavings, often leading to reorderings in the sequence of updates and readings from memory; the executions are subject to a weaker memory consistency. Reorderings can produce executions that would not be observable with interleavings, and these possible executions also depend on the architecture that the processors implement. It is therefore necessary to locate and understand these reorderings in the context of a program running, or to prevent them in an automated way. In this dissertation, we aim to automate the reasoning behind weak memory consistency and perform transformations over the code so that developers need not to consider all the specifics of the processors when writing concurrent programs. We claim that we can do automatic static analysis for axiomatically-defined weak memory models. The method that we designed also allows re-use of automated verification tools like model checkers or abstract interpreters that were not designed for weak memory consistency, by modification of the input programs. We define an abstraction in detail that allows us to reason statically about weak memory models over programs. We locate the parts of the code where the semantics could be affected by the weak memory consistency. We then provide a method to explicitly reveal the resulting reorderings so that usual verification techniques can handle the program semantics under a weaker memory consistency. We finally provide a technique that synthesises synchronisations so that the program would behave as if only interleavings were allowed. We finally test these approaches on artificial and real software. We justify our choice of an axiomatic model with the scalability of the approach and the runtime performance of the programs modified by our method
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Fences and Synchronisation Idioms in Weak Memory Models
No full textWe present an axiomatic framework, implemented in the Coq proof assistant, to define weak memory models in terms of several parameters: local reorderings of reads and writes, and visibility of inter and intra processor communications through memory, including full store atomicity relaxation. Thereby, we give a formal hierarchy of weak memory models, in which we provide a formal study of what should be the action and placement of fences to restore a given model such as SC from a weaker one. Finally, we provide formal requirements for abstract locks that guarantee SC semantics to data race free programs, and show that a particular implementation of locks matches these requirements
Fences and Synchronisation Idioms in Weak Memory Models
Get PDFWe present an axiomatic framework, implemented in the Coq proof assistant, to define weak memory models in terms of several parameters: local reorderings of reads and writes, and visibility of inter and intra processor communications through memory, including full store atomicity relaxation. Thereby, we give a formal hierarchy of weak memory models, in which we provide a formal study of what should be the action and placement of fences to restore a given model such as SC from a weaker one. Finally, we provide formal requirements for abstract locks that guarantee SC semantics to data race free programs, and show that a particular implementation of locks matches these requirements
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