Catálogo de publicaciones - revistas

<jats:p>A local algorithm is a distributed algorithm that runs in constant time, independently of the size of the network. Being highly scalable and fault tolerant, such algorithms are ideal in the operation of large-scale distributed systems. Furthermore, even though the model of local algorithms is very limited, in recent years we have seen many positive results for nontrivial problems. This work surveys the state-of-the-art in the field, covering impossibility results, deterministic local algorithms, randomized local algorithms, and local algorithms for geometric graphs.</jats:p>

<jats:p>This article addresses the<jats:italic>online exact string matching problem</jats:italic>which consists in finding<jats:italic>all</jats:italic>occurrences of a given pattern<jats:italic>p</jats:italic>in a text<jats:italic>t</jats:italic>. It is an extensively studied problem in computer science, mainly due to its direct applications to such diverse areas as text, image and signal processing, speech analysis and recognition, information retrieval, data compression, computational biology and chemistry.</jats:p><jats:p>In the last decade more than 50 new algorithms have been proposed for the problem, which add up to a wide set of (almost 40) algorithms presented before 2000. In this article we review the string matching algorithms presented in the last decade and present experimental results in order to bring order among the dozens of articles published in this area.</jats:p>

<jats:p>Grids designed for computationally demanding scientific applications started experimental phases ten years ago and have been continuously delivering computing power to a wide range of applications for more than half of this time. The observation of their emergence and evolution reveals actual constraints and successful approaches to task mapping across administrative boundaries. Beyond differences in distributions, services, protocols, and standards, a common architecture is outlined. Application-agnostic infrastructures built for resource registration, identification, and access control dispatch delegation to grid sites. Efficient task mapping is managed by large, autonomous applications or collaborations that temporarily infiltrate resources for their own benefits.</jats:p>

<jats:p> Numerous practical systems based on network coding have been proposed in recent years demonstrating the wide range of benefits of network coding, such as increased throughput, reliability, and energy efficiency. However, network coding systems are inherently vulnerable to a severe attack, known as <jats:italic>packet pollution</jats:italic> , which presents a key obstacle to the deployment of such systems. Several cryptographic schemes have been proposed to defend against pollution attacks. </jats:p> <jats:p>We conduct a detailed analysis and an experimental evaluation in a realistic wireless network coding setting of a set of representative cryptographic defenses against pollution attacks. Our analysis identifies severe limitations of asymmetric-based schemes, which impose high communication overhead by placing constraints on the basic network coding parameters and high computation overhead by relying on numerous operations over large fields. Our analysis also shows that symmetric cryptographic schemes, while having better performance than asymmetric cryptographic-based schemes, impose prohibitive overhead in the presence of multiple byzantine adversaries. We further evaluate these schemes by using a set of typical network coding system parameters on a realistic topology. Our experimental evaluation shows that all the schemes we compare induce a throughput degradation that negates the performance benefits of network coding in the presence of multiple colluding adversaries.</jats:p>

<jats:p>Compilers commonly translate an input program into an intermediate representation (IR) before optimizing it and generating code. Over time there have been a number of different approaches to designing and implementing IRs. Different IRs have varying benefits and drawbacks. In this survey, we highlight key developments in the area of IR for imperative compilers, group them by a taxonomy and timeline, and comment on the divide between academic research and real-world compiler technology. We conclude that mainstream compilers, especially in the multicore era, could benefit from further IR innovations.</jats:p>

<jats:p> VoIP calls are sensitive to several impairments, such as delay and packet loss. One way to overcome these problems is by adaptively adjusting application-layer parameters to keep a minimum speech quality level. At the heart of self-adaptive systems lies a <jats:italic>feedback loop</jats:italic> , which consists of four key activities: monitoring, analysis, planning, and execution. Nevertheless, the existing adaptive approaches to QoS control of VoIP do not explicitly exhibit this feedback loop. Bringing it to surface can help developers in designing more robust and human-independent VoIP systems. This survey presents a comprehensive review of the current state-of-the-art research on speech quality adaptation of VoIP systems at the application layer and some research challenges on this subject. </jats:p>

<jats:p>This article surveys the current state of phase-change memory (PCM) as a nonvolatile memory technology set to replace flash and DRAM in modern computerized systems. It has been researched and developed in the last decade, with researchers providing better architectural designs which address the technology's main challenges—its limited write endurance, potential long latency, high energy writes, power dissipation, and some concerns for memory privacy. Some physical properties of the technology are also discussed, providing a basis for architectural discussions. Also briefly shown are other architectural alternatives, such as FeRAM and MRAM. The designs surveyed in this article include read before write, wear leveling, write cancellation, write pausing, some encryption schemes, and buffer organizations. These allow PCM to stand on its own as a replacement for DRAM as main memory. Designs for hybrid memory systems with both PCM and DRAM are also shown and some designs for SSDs incorporating PCM.</jats:p>

<jats:p>“Exploration and exploitation are the two cornerstones of problem solving by search.” For more than a decade, Eiben and Schippers' advocacy for balancing between these two antagonistic cornerstones still greatly influences the research directions of evolutionary algorithms (EAs) [1998]. This article revisits nearly 100 existing works and surveys how such works have answered the advocacy. The article introduces a fresh treatment that classifies and discusses existing work within three rational aspects: (1) what and how EA components contribute to exploration and exploitation; (2) when and how exploration and exploitation are controlled; and (3) how balance between exploration and exploitation is achieved. With a more comprehensive and systematic understanding of exploration and exploitation, more research in this direction may be motivated and refined.</jats:p>

<jats:p>Virtualization is a powerful technology for increasing the efficiency of computing services; however, besides its advantages, it also raises a number of security issues. In this article, we provide a thorough survey of those security issues in hardware virtualization. We focus on potential vulnerabilities and existing attacks on various virtualization platforms, but we also briefly sketch some possible countermeasures. To the best of our knowledge, this is the first survey of security issues in hardware virtualization with this level of details. Moreover, the adversary model and the structuring of the attack vectors are original contributions, never published before.</jats:p>

<jats:p>As computer systems continue to grow in complexity, the possibility of failure increases. At the same time, the increase in computer system pervasiveness in day-to-day activities bring along increased expectations on their reliability. This has led to the need for effective and automatic error-recovery techniques to resolve failures. Transactions enable the handling of failure propagation over concurrent systems due to dependencies, restoring the system to the point before the failure occurred. However, in various settings, especially when interacting with the real world, reversal is not possible. The notion of compensations has been long advocated as a way of addressing this issue, through the specification of activities which can be executed to undo partial transactions. Still, there is no accepted standard theory; the literature offers a plethora of distinct formalisms and approaches.</jats:p><jats:p>In this survey, we review the compensations from a theoretical point of view by (i) giving a historic account of the evolution of compensating transactions; (ii) delineating and describing a number of design options involved; (iii) presenting a number of formalisms found in the literature, exposing similarities and differences; (iv) comparing formal notions of compensation correctness; (v) giving insights regarding the application of compensations in practice; and (vi) discussing current and future research trends in the area.</jats:p>