1,721,027 research outputs found
Middleware per servizi evoluti su sistemi distribuiti wired-wireless di grandi dimensioni
No full textNel campo delle reti e del netputing si assiste a due forti spinte, una tecnologica ed una applicativa, che hanno fatto venir meno gran parte delle premesse su cui si è fondata Internet fino ad ora. La naturale conseguenza è l'aumento di insiemi di utenti che condividono analoghi interessi, obiettivi e requisiti, non soddisfatti dalle attuali infrastrutture. Una sfida chiave della ricerca riguarda quindi lo sviluppo di nuovi servizi telematici che sfruttino al meglio le future tecnologie e la creazione di infrastrutture atte a soddisfare i requisiti che tali servizi comportano. In particolare, è possibile focalizzarsi sul concetto di "comunità virtuali", costituite da insiemi di utenti e relativi dispositivi che si registrano presso un "content provider" per ottenere un insieme di servizi con requisiti prefissati. E' ormai accettata l'idea che la rete stessa diventi il fornitore (distribuito) di servizi integrati a supporto di comunità. I campi applicativi sono i più vari: gruppi di interesse già esistenti, teleformazione, aspetti di e-government, business-to-business, teleconferenze, spettacoli o eventi sportivi, monitoraggio e aggiornamento software.
Giovanni Chiola e' il coordinatore nazionale. Renzo Davoli e' il coordinatore del gruppo di ricerca di Bologna
Optimizing the finger table in Chord-like DHTs
No full textThe Chord protocol is the best known example of implementation of logarithmic complexity routing for
structured peer-to-peer networks. Its routing algorithm, however, does not provide an optimal trade-off
between resources exploited (the size of the ‘finger table’) and performance (the average or worst-case
number of hops to reach destination). Cordasco et al. showed that a finger table based on Fibonacci
distances provides lower number of hops with fewer table entries. In this paper we generalize this result,
showing how to construct an improved finger table when the objective is to reduce the number of hops,
possibly at the expense of an increased size of the finger table. Our results can also be exploited to
guarantee low routing time in case a fraction of nodes fails
Stochastic Well-Formed Coloured Nets for Symmetric Modelling Applications
No full textThe class of stochastic well-formed colored nets (SWN's) was defined as a syntactic restriction of stochastic high-level nets. The interest of the introduction of restrictions in the model definition is the possibility of exploiting the symbolic reachability graph (SRG) to reduce the complexity of Markovian performance evaluation with respect to classical Petri net techniques. It turns out that SWN's allow the representation of any color function in a structured form, so that any unconstrained high-level net can be transformed into a well-formed net. Moreover, most constructs useful for the modeling of distributed computer systems and architectures directly match the “well-formed” restriction, without any need of transformation. A nontrivial example of the usefulness of the technique in the performance modeling and evaluation of multiprocessor architectures is include
Overlay networks with class
No full textWe define a family of distributed hash table systems whose aim is to combine routing efficiency of the randomized networks - i.e. average path length O(log n/log log n) vs. the O(log n) average path length of the deterministic system - with the programmability and startup efficiency of a uniform system - that is a system in which the overlay network is transitive, and greedy routing is optimal. It is known that Ω(logn) is a lower bound to the average path length for uniform systems with O(log n) degree. The proposed family is parameterized with a positive integer c which measures the amount of randomness that is used. Indeed, edges are partitioned into c equivalence classes. Varying the value c, the system goes from the deterministic case (c=1) to an "almost uniform" system. Increasing c to relatively low values allows routing with optimal average path length while retaining most of the advantages of a uniform system, such as easy programmability and quick bootstrap of the nodes entering the system. We also provide a matching lower bound for the average path length of the family of routing schemes for any c. Moreover, we show how to extend the result to other overlay networks
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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