1,721,250 research outputs found
Distributed Algorithms
No full textThis course intends to provide a rigorous introduction to the most important research results in the area of distributed algorithms, and prepare interested students to carry out independent research in distributed algorithms. Topics covered include: design and analysis of concurrent algorithms, emphasizing those suitable for use in distributed networks, process synchronization, allocation of computational resources, distributed consensus, distributed graph algorithms, election of a leader in a network, distributed termination, deadlock detection, concurrency control, communication, and clock synchronization. Special consideration is given to issues of efficiency and fault tolerance. Formal models and proof methods for distributed computation are also discussed. Detailed information on the course textbook can be found here: Lynch, Nancy A. Distributed Algorithms. San Francisco, CA: Morgan Kaufmann, 1997. ISBN: 1558603484
Timeout Order Abstraction for Time-Parametric Verification of Loosely Synchronized Real-Time Distributed Systems
No full textURL to paper listed on conference site.We present timeout order abstraction (TO-abstraction), a
technique to systematically abstract a given loosely synchronized
real-time distributed system (LSRTDS) into an untimed model. We
define the subclass of LSRTDS’s that we can apply TO-abstraction
using a syntax template that represents a restriction to Tempo,
the primary modeling language of TIOA [7]. The untimed model
obtained from the abstraction is a classical finite state machine, and
thus one can automatically verify temporal properties of the model
using a conventional model-checker. We prove the soundness of the
abstraction using simulation relation. From this result, we guarantee
that any untimed safety property of the untimed model also holds for
the original TIOA model.
We have applied TO-abstraction to a resource-sharing protocol
and the DHCP Failover protocol. We verified untimed abstractions
of them by bounded model-checking up to depth 20. We have also
experimented with effectiveness of bug-finding using our technique by
mutating particular parts of the original code. From this experiment,
we found a complex bad execution that would have been very difficult
to find by human or simulations.National Science Foundation (U.S.) (NSF Award CCF-0702670)National Science Foundation (U.S.) (NSF Award CNS-0614414)United States. Dept. of the Air Force (AFOSR/DOD CAP Funds
Self-stabilizing robot formations over unreliable networks
Full text linkWe describe how a set of mobile robots can arrange themselves on any specified curve on the plane in the presence of dynamic changes both in the underlying ad hoc network and in the set of participating robots. Our strategy is for the mobile robots to implement a self-stabilizing virtual layer consisting of mobile client nodes, stationary Virtual Nodes (VNs), and local broadcast communication. The VNs are associated with predetermined regions in the plane and coordinate among themselves to distribute the client nodes relatively uniformly among the VNs' regions. Each VN directs its local client nodes to align themselves on the local portion of the target curve. The resulting motion coordination protocol is self-stabilizing, in that each robot can begin the execution in any arbitrary state and at any arbitrary location in the plane. In addition, self-stabilization ensures that the robots can adapt to changes in the desired target formation.National Science Foundation (U.S.) (Grant No. CNS-0614993
Dynamic input/output automata: A formal and compositional model for dynamic systems
No full textWe present dynamic I/O automata (DIOA), a compositional model of dynamic systems. In DIOA, automata can be created and destroyed dynamically, as computation proceeds, and an automaton can dynamically change its signature, i.e., the set of actions in which it can participate. DIOA features operators for parallel composition, action hiding, action renaming, a notion of automaton creation, and a notion of behavioral subtyping by means of trace inclusion. DIOA can model mobility, using signature modification, and is hierarchical: a dynamically changing system of interacting automata is itself modeled as a single automaton. We also show that parallel composition, action hiding, action renaming, and (subject to some technical conditions) automaton creation are all monotonic with respect to trace inclusion: if one component is replaced by another whose traces are a subset of the former, then the set of traces of the system as a whole can only be reduced. Keywords: Dynamic systems; Formal methods; Semantics; Automata; Process creation; Mobilit
Special issue on DISC 2010
Full text linkThis special issue of Distributed Computing is based on papers that originally appeared as extended abstracts in the Proceedings of the 24th International Symposium on Distributed Computing (DISC2010), held in Cambridge, Massachusetts on August 13–15, 2010. The papers for the Special Issue were chosen by the Program Committee from the 32 regular papers presented at the Symposium, based on their quality and representation of the spectrum of topics encompassed by the Symposium. In addition to being reviewed, in preliminary form, by the Program Committee, the full papers submitted for the Special Issue were refereed according to the standard practices of Distributed Computing (due to time constrains, some papers could not appear in this volume). We thank the Members of the Editorial Board for their work in editing this issue, and the referees and the authors of these papers for their respective contributions
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Full text linkWe 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
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