On the concept of complexity in random dynamical systems

We introduce a measure of complexity in terms of the average number of bits per time unit necessary to specify the sequence generated by the system. In random dynamical system, this indicator coincides with the rate K of divergence of nearby trajectories evolving under two different noise realizations. The meaning of K is discussed in the context of the information theory, and it is shown that it can be determined from real experimental data. In presence of strong dynamical intermittency, the value of K is very different from the standard Lyapunov exponent computed considering two nearby trajectories evolving under the same randomness. However, the former is much more relevant than the latter from a physical point of view as illustrated by some numerical computations for noisy maps and sandpile models.Comment: 35 pages, LaTe

Local Rigidity in Sandpile Models

We address the problem of the role of the concept of local rigidity in the family of sandpile systems. We define rigidity as the ratio between the critical energy and the amplitude of the external perturbation and we show, in the framework of the Dynamically Driven Renormalization Group (DDRG), that any finite value of the rigidity in a generalized sandpile model renormalizes to an infinite value at the fixed point, i.e. on a large scale. The fixed point value of the rigidity allows then for a non ambiguous distinction between sandpile-like systems and diffusive systems. Numerical simulations support our analytical results.Comment: to be published in Phys. Rev.

Reseñas

Obra ressenyada: Freddy TIMMERMANN, El Gran Terror. Miedo, emoción y discurso. Chile, 1973-1980 . Santiago de Chile: Copygraph., 2014

What is the temperature of a granular medium?

In this paper we discuss whether thermodynamical concepts and in particular the notion of temperature could be relevant for the dynamics of granular systems. We briefly review how a temperature-like quantity can be defined and measured in granular media in very different regimes, namely the glassy-like, the liquid-like and the granular gas. The common denominator will be given by the Fluctuation-Dissipation Theorem, whose validity is explored by means of both numerical and experimental techniques. It turns out that, although a definition of a temperature is possible in all cases, its interpretation is far from being obvious. We discuss the possible perspectives both from the theoretical and, more importantly, from the experimental point of view

The influence of allochthonous leaf detritus on the occurrence of crustacean detritivores in the soft-bottom macrobenthos of the Po River delta area (northwestern Adriatic Sea)

Core samples were examined quarterly at two coastal sites (S1 and S2) and at an offshore station (S3) located in the Po River delta area (northwestern Adriatic Sea). Analyses focused on (i) occurrence of coarse detritus of allochthonous origin in the sedimentary matrix and (ii) the relative influence of macrodetritus enrichment and other environmental factors on the vagile macrofauna. Plant debris occurred in site S1 sediments only in summer and autumn, in contrast, fragments of the phanerogams Cymodocea nodosa and Zostera spp. were found in site S2 sediment throughout the sampling period. Sediments from the offshore site S3 were characterized by negligible plant material, even though in summer and autumn samples debris of continental origin was observed. Even though leaf detritus occurrence at site S2 was similar to5-fold higher compared to the other coastal site S1, it did not influence the total organic matter and its distribution among grain-size classes. Conversely, the specific organic content of dimensional fractions provided an effective assessment of detritus enrichment processes occurring at the two coastal sites. A group of brackish-originated crustaceans (i.e. the amphipods Gammarus insensibilis and G. aequicauda and the isopod Idotea baltica) was the main determinant of among-site multivariate differences in the vagile macrofauna; depositivorous ophiuroids accounted for the residual differences observed during the study period. The analysis of taxa abundance and individual body size indicated that in both site S1 and S3 macrodetritus advection to the benthic system corresponded with passive dispersal of brackish crustaceans, that provided a negligible contribution to the macrobenthic production. In contrast, in site S2 allochthonous inputs from marginal environments could have represented the key factor for the persistence of an authochthonous population of Gammarus insensibilis. The amphipod provided a considerable (19.4%) contribution to the total macrobenthic production of the site, dominated by filter-feeding bivalves and tubicolous deposit feeders. The potential effects of detritivorous crustaceans on soft-bottom macrobenthic assemblages of the northern Adriatic Sea are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved

Sediment structural properties mediating dominant feeding types patterns in soft-bottom macrobenthos of the Northern Adriatic Sea

In sediments sampled in Northern Adriatic Sea invertebrate benthic macrofauna was examined in comparison with both substratum bulk parameters (average grain size, sorting, total organic matter content) and attributes of grain size classes (specific organic matter content of dimensional fractions). The aims were: 1) to determine whether variations of community overall parameters (total spatial density, number of taxa) and in numerically dominant feeding types (deposit-feeders and suspension-feeders) patterns were related to changes in sediment general properties; 2) to evaluate whether the observed patterns of abundance for deposit- and filter-feeders had more valid correlates in specific properties of substratum dimensional fractions. Number of taxa and animal spatial density resulted conventionally related to substratum bulk parameters while feeding types patterns in comparison with sediment total organic matter content exibited a reciprocal negative effect; only when both feeding types and sediment structure were resolved to their specific attributes in terms of prevalence of tubicolous taxa among deposit-feeders and organic matter richness of single dimensional fractions, the analysis emphasized patterns unequally affected by specific size fractions abundance and organic matter content: deposit feeders demonstrated to be related to the presence in the substrate of intermediate grain size classes necessary for tube-building. Those intermediate fractions proved to be more adequate descriptors than average grain size or other overall sediment parameters per se of relations actually established between feeding types and the complex nature of bottom sediments. Our results emphasize that for Northern Adriatic Sea benthic communities, sediment organic matter content may represent a factor of minor importance in comparison with other substrate attributes, for which it may be necessary a detailed analysis of sediment structure. Thus, we concluded that the complexity of soft-bottom communities may defy any simple paradigm relating macrobenthic patterns to any single sediment bulk attribute, and we propose a shift in focus towards an higher resolution of both functional groups in macrobenthic associations las already suggested in other investigations) and of substratum structural description

Characterization of chaos in random maps

We discuss the characterization of chaotic behaviours in random maps both in terms of the Lyapunov exponent and of the spectral properties of the Perron-Frobenius operator. In particular, we study a logistic map where the control parameter is extracted at random at each time step by considering finite dimensional approximation of the Perron-Frobenius operatorComment: Plane TeX file, 15 pages, and 5 figures available under request to [email protected]

Taxonomy and analysis of IP micro-mobility protocols in single and simultaneous movements scenarios

The micro-mobility is an important aspect in mobile communications, where the applications are anywhere and used anytime. One of the problems of micro-mobility is the hand-off latency. In this paper, we analyse two solutions for IP micro-mobility by means of a general taxonomy. The first one is based on the Stream Control Transmission Protocol (SCTP), which allows the dynamic address configuration of an association. The second one is based on the Session Initiation Protocol (SIP), which is the most popular protocol for multimedia communications over IP networks. We show that for the SCTP solution, there is room for further optimisations of the hand-off latency by adding slight changes to the protocol. However, as full end-to-end solution, SCTP is not able to handle simultaneous movement of hosts, whose probability in general cannot be neglected. On the other hand, the SIP can handle both single and simultaneous movements cases, although the hand-off latency can increase with respect to the SCTP solution. We show that for a correct and fast hand-off, the SIP server should be statefull

Desafios e possibilidades para a Inclusão Digital da Terceira Idade. Opportunities and challenges for digital inclusion in the Third Age

Este artigo discute desafios e oportunidades da Inclusão Digital da Terceira Idade com base em uma pesquisa empírica, que teve como objetivo analisar a formação para a Inclusão Digital oferecida em um Curso de Informática de uma Universidade Aberta da Terceira Idade. A pesquisa, de cunho qualitativo, contou com 26 participantes (23 alunos, dois professores e um coordenador de curso) e utilizou uma combinação de métodos de coleta de dados (observação participante, questionários, entrevistas, grupos focais e fontes documentais) e a análise de conteúdo. O texto sugere que, apesar de possuir diversas limitações estruturais e organizacionais, o curso promove uma forma básica de inclusão digital, a qual, embora limitada em relação às possibilidades do ciberespaço e da cibercultura, tem enorme valor para seu público. This paper discusses opportunities and challenges that arise with respect to the digital inclusion of the elderly. It is based on a piece of empirical research that investigated a computer course offered by a University of the Third Age. This qualitative study used a combination of data collection methods (participant observation, questionnaires, interviews, focal groups, and documental sources) and content analysis. The group of participants included 23 elderly learners, two lecturers, and a course coordinator. The text suggests that, despite the various structural and organizational shortcomings, the course promotes a basic form of digital inclusion which is of great value to its audience, although limited compared to the possibilities offered by cyberspace and cyberculture

About the use of generalized forms of derivatives in the study of electromagnetic problems

The use of non-local operators, defining Riemann–Liouville or Caputo derivatives, is a very useful tool to study problems involving non-conventional diffusion problems. The case of electric circuits, ruled by non-integer derivatives or capacitors with fractional dielectric permittivity, is a fairly natural frame of relevant applications. We use techniques, involving generalized exponential operators, to obtain suitable solutions for this type of problems and eventually discuss specific problems in applications