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71.
Motif patterns consisting of sequences of intermixed solid and don’t-care characters have been introduced and studied in connection with pattern discovery problems of computational biology and other domains. In order to alleviate the exponential growth of such motifs, notions of maximal saturation and irredundancy have been formulated, whereby more or less compact subsets of the set of all motifs can be extracted, that are capable of expressing all others by suitable combinations. In this paper, we introduce the notion of maximal irredundant motifs in a two-dimensional array and develop initial properties and a combinatorial argument that poses a linear bound on the total number of such motifs. The remainder of the paper presents approaches to the discovery of irredundant motifs both by offline and incremental algorithms. 相似文献
72.
Alberto Ros Ricardo Fernández-Pascual Manuel E. Acacio José M. García 《Journal of Parallel and Distributed Computing》2008
In glueless shared-memory multiprocessors where cache coherence is usually maintained using a directory-based protocol, the fast access to the on-chip components (caches and network router, among others) contrasts with the much slower main memory. Unfortunately, directory-based protocols need to obtain the sharing status of every memory block before coherence actions can be performed. This information has traditionally been stored in main memory, and therefore these cache coherence protocols are far from being optimal. In this work, we propose two alternative designs for the last-level private cache of glueless shared-memory multiprocessors: the lightweight directory and the SGluM cache. Our proposals completely remove directory information from main memory and store it in the home node’s L2 cache, thus reducing both the number of accesses to main memory and the directory memory overhead. The main characteristics of the lightweight directory are its simplicity and the significant improvement in the execution time for most applications. Its drawback, however, is that the performance of some particular applications could be degraded. On the other hand, the SGluM cache offers more modest improvements in execution time for all the applications by adding some extra structures that cope with the cases in which the lightweight directory fails. 相似文献
73.
Visual Navigation for Mobile Robots: A Survey 总被引:4,自引:0,他引:4
Francisco Bonin-Font Alberto Ortiz Gabriel Oliver 《Journal of Intelligent and Robotic Systems》2008,53(3):263-296
Mobile robot vision-based navigation has been the source of countless research contributions, from the domains of both vision
and control. Vision is becoming more and more common in applications such as localization, automatic map construction, autonomous
navigation, path following, inspection, monitoring or risky situation detection. This survey presents those pieces of work,
from the nineties until nowadays, which constitute a wide progress in visual navigation techniques for land, aerial and autonomous
underwater vehicles. The paper deals with two major approaches: map-based navigation and mapless navigation. Map-based navigation has been in turn subdivided in metric map-based navigation and topological map-based navigation. Our outline to mapless navigation includes reactive techniques based on qualitative characteristics extraction, appearance-based
localization, optical flow, features tracking, plane ground detection/tracking, etc... The recent concept of visual sonar has also been revised.
This work is partially supported by DPI 2005-09001-C03-02 and FEDER funding. 相似文献
74.
Yolanda Blanco-Fernndez Jos J. Pazos-Arias Alberto Gil-Solla Manuel Ramos-Cabrer Martín Lpez-Nores Jorge García-Duque Ana Fernndez-Vilas Rebeca P. Díaz-Redondo Jesús Bermejo-Muoz 《Knowledge》2008,21(4):305-320
Recommender systems arose with the goal of helping users search in overloaded information domains (like e-commerce, e-learning or Digital TV). These tools automatically select items (commercial products, educational courses, TV programs, etc.) that may be appealing to each user taking into account his/her personal preferences. The personalization strategies used to compare these preferences with the available items suffer from well-known deficiencies that reduce the quality of the recommendations. Most of the limitations arise from using syntactic matching techniques because they miss a lot of useful knowledge during the recommendation process. In this paper, we propose a personalization strategy that overcomes these drawbacks by applying inference techniques borrowed from the Semantic Web. Our approach reasons about the semantics of items and user preferences to discover complex associations between them. These semantic associations provide additional knowledge about the user preferences, and permit the recommender system to compare them with the available items in a more effective way. The proposed strategy is flexible enough to be applied in many recommender systems, regardless of their application domain. Here, we illustrate its use in AVATAR, a tool that selects appealing audiovisual programs from among the myriad available in Digital TV. 相似文献
75.
Roberto Bruttomesso Alessandro Cimatti Anders Franzen Alberto Griggio Roberto Sebastiani 《Annals of Mathematics and Artificial Intelligence》2009,55(1-2):63-99
Most state-of-the-art approaches for Satisfiability Modulo Theories $(SMT(\mathcal{T}))$ rely on the integration between a SAT solver and a decision procedure for sets of literals in the background theory $\mathcal{T} (\mathcal{T}{\text {-}}solver)$ . Often $\mathcal{T}$ is the combination $\mathcal{T}_1 \cup \mathcal{T}_2$ of two (or more) simpler theories $(SMT(\mathcal{T}_1 \cup \mathcal{T}_2))$ , s.t. the specific ${\mathcal{T}_i}{\text {-}}solvers$ must be combined. Up to a few years ago, the standard approach to $SMT(\mathcal{T}_1 \cup \mathcal{T}_2)$ was to integrate the SAT solver with one combined $\mathcal{T}_1 \cup \mathcal{T}_2{\text {-}}solver$ , obtained from two distinct ${\mathcal{T}_i}{\text {-}}solvers$ by means of evolutions of Nelson and Oppen’s (NO) combination procedure, in which the ${\mathcal{T}_i}{\text {-}}solvers$ deduce and exchange interface equalities. Nowadays many state-of-the-art SMT solvers use evolutions of a more recent $SMT(\mathcal{T}_1 \cup \mathcal{T}_2)$ procedure called Delayed Theory Combination (DTC), in which each ${\mathcal{T}_i}{\text {-}}solver$ interacts directly and only with the SAT solver, in such a way that part or all of the (possibly very expensive) reasoning effort on interface equalities is delegated to the SAT solver itself. In this paper we present a comparative analysis of DTC vs. NO for $SMT(\mathcal{T}_1 \cup \mathcal{T}_2)$ . On the one hand, we explain the advantages of DTC in exploiting the power of modern SAT solvers to reduce the search. On the other hand, we show that the extra amount of Boolean search required to the SAT solver can be controlled. In fact, we prove two novel theoretical results, for both convex and non-convex theories and for different deduction capabilities of the ${\mathcal{T}_i}{\text {-}}solvers$ , which relate the amount of extra Boolean search required to the SAT solver by DTC with the number of deductions and case-splits required to the ${\mathcal{T}_i}{\text {-}}solvers$ by NO in order to perform the same tasks: (i) under the same hypotheses of deduction capabilities of the ${\mathcal{T}_i}{\text {-}}solvers$ required by NO, DTC causes no extra Boolean search; (ii) using ${\mathcal{T}_i}{\text {-}}solvers$ with limited or no deduction capabilities, the extra Boolean search required can be reduced down to a negligible amount by controlling the quality of the $\mathcal{T}$ -conflict sets returned by the ${\mathcal{T}_i}{\text {-}}solvers$ . 相似文献
76.
Guilherme T. de Assis Alberto H. F. Laender Marcos André Gonçalves Altigran S. da Silva 《World Wide Web》2009,12(3):285-319
Focused crawlers have as their main goal to crawl Web pages that are relevant to a specific topic or user interest, playing
an important role for a great variety of applications. In general, they work by trying to find and crawl all kinds of pages
deemed as related to an implicitly declared topic. However, users are often not simply interested in any document about a
topic, but instead they may want only documents of a given type or genre on that topic to be retrieved. In this article, we
describe an approach to focused crawling that exploits not only content-related information but also genre information present
in Web pages to guide the crawling process. This approach has been designed to address situations in which the specific topic
of interest can be expressed by specifying two sets of terms, the first describing genre aspects of the desired pages and
the second related to the subject or content of these pages, thus requiring no training or any kind of preprocessing. The
effectiveness, efficiency and scalability of the proposed approach are demonstrated by a set of experiments involving the
crawling of pages related to syllabi of computer science courses, job offers in the computer science field and sale offers
of computer equipments. These experiments show that focused crawlers constructed according to our genre-aware approach achieve
levels of F1 superior to 88%, requiring the analysis of no more than 65% of the visited pages in order to find 90% of the
relevant pages. In addition, we experimentally analyze the impact of term selection on our approach and evaluate a proposed
strategy for semi-automatic generation of such terms. This analysis shows that a small set of terms selected by an expert
or a set of terms specified by a typical user familiar with the topic is usually enough to produce good results and that such
a semi-automatic strategy is very effective in supporting the task of selecting the sets of terms required to guide a crawling
process. 相似文献
77.
Thomas Silverston Olivier Fourmaux Alessio Botta Alberto Dainotti Antonio Pescapé Giorgio Ventre Kavé Salamatian 《Computer Networks》2009,53(4):470-484
The Internet is currently experiencing one of the most important challenges in terms of content distribution since its first uses as a medium for content delivery: users from passive downloaders and browsers are moving towards content producers and publishers. They often distribute and retrieve multimedia contents establishing network communities. This is the case of peer-to-peer IPTV communities.In this work we present a detailed study of P2P IPTV traffic, providing useful insights on both transport- and packet-level properties as well as on the behavior of the peers inside the network. In particular, we provide novel results on the (i) ports and protocols used; (ii) differences between signaling and video traffic; (iii) behavior of the traffic at different time scales; (iv) differences between TCP and UDP traffic; (v) traffic generated and received by peers; (vi) peers neighborhood and session duration. The knowledge gained thanks to this analysis is useful for several tasks, e.g. traffic identification, understanding the performance of different P2P IPTV technologies and the impact of such traffic on network nodes and links, and building more realistic models for simulations.1 相似文献
78.
Degree-Optimal Routing for P2P Systems 总被引:1,自引:0,他引:1
Giovanni Chiola Gennaro Cordasco Luisa Gargano Mikael Hammar Alberto Negro Vittorio Scarano 《Theory of Computing Systems》2009,45(1):43-63
We define a family of Distributed Hash Table systems whose aim is to combine the routing efficiency of randomized networks—e.g.
optimal average path length O(log 2
n/δlog δ) with δ degree—with the programmability and startup efficiency of a uniform overlay—that is, a deterministic system in which the overlay network is transitive and greedy routing is optimal. It is known that Ω(log n) is a lower bound on the average path length for uniform overlays with O(log n) degree (Xu et al., IEEE J. Sel. Areas Commun. 22(1), 151–163, 2004).
Our work is inspired by neighbor-of-neighbor (NoN) routing, a recently introduced variation of greedy routing that allows us to achieve optimal average path length in randomized networks. The advantage of our proposal is that of allowing
the NoN technique to be implemented without adding any overhead to the corresponding deterministic network.
We propose a family of networks parameterized with a positive integer c which measures the amount of randomness that is used. By 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 for routing with asymptotically 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 routing schemes for any c.
This work was partially supported by the Italian FIRB project “WEB-MINDS” (Wide-scalE, Broadband MIddleware for Network Distributed
Services), . 相似文献
79.
月球探测(车)机器人技术的发展与展望 总被引:1,自引:0,他引:1
简述当前国内外探月研究进展及月球探测(车)机器人研究发展情况.基于月球的复杂环境特征,对比轮式运动与步行式运动月球探测(车)机器人的优势与缺陷,重点介绍了一种新型六轮腿式月球探测机器人方案.该方案具有高机动性,越障能力强,容错性好等特点,对该方案主要技术性能、本体结构、运动系统、轮腿切换机构工作原理等关键技术进行了探讨. 相似文献
80.
Migliorini Sara Gambini Mauro Quintarelli Elisa Belussi Alberto 《Knowledge and Information Systems》2023,65(10):3967-3994
Knowledge and Information Systems - In the era of massive sharing of information, the term social provenance is used to denote the ownership, source or origin of a piece of information which has... 相似文献