Dependability in Aggregation by Averaging

Aggregation is an important building block of modern distributed applications, allowing the determination of meaningful properties (e.g. network size, total storage capacity, average load, majorities, etc.) that are used to direct the execution of the system. However, the majority of the existing aggregation algorithms exhibit relevant dependability issues, when prospecting their use in real application environments. In this paper, we reveal some dependability issues of aggregation algorithms based on iterative averaging techniques, giving some directions to solve them. This class of algorithms is considered robust (when compared to common tree-based approaches), being independent from the used routing topology and providing an aggregation result at all nodes. However, their robustness is strongly challenged and their correctness often compromised, when changing the assumptions of their working environment to more realistic ones. The correctness of this class of algorithms relies on the maintenance of a fundamental invariant, commonly designated as "mass conservation". We will argue that this main invariant is often broken in practical settings, and that additional mechanisms and modifications are required to maintain it, incurring in some degradation of the algorithms performance. In particular, we discuss the behavior of three representative algorithms Push-Sum Protocol, Push-Pull Gossip protocol and Distributed Random Grouping under asynchronous and faulty (with message loss and node crashes) environments. More specifically, we propose and evaluate two new versions of the Push-Pull Gossip protocol, which solve its message interleaving problem (evidenced even in a synchronous operation mode).Comment: 14 pages. Presented in Inforum 200

Spectra: Robust Estimation of Distribution Functions in Networks

Distributed aggregation allows the derivation of a given global aggregate property from many individual local values in nodes of an interconnected network system. Simple aggregates such as minima/maxima, counts, sums and averages have been thoroughly studied in the past and are important tools for distributed algorithms and network coordination. Nonetheless, this kind of aggregates may not be comprehensive enough to characterize biased data distributions or when in presence of outliers, making the case for richer estimates of the values on the network. This work presents Spectra, a distributed algorithm for the estimation of distribution functions over large scale networks. The estimate is available at all nodes and the technique depicts important properties, namely: robust when exposed to high levels of message loss, fast convergence speed and fine precision in the estimate. It can also dynamically cope with changes of the sampled local property, not requiring algorithm restarts, and is highly resilient to node churn. The proposed approach is experimentally evaluated and contrasted to a competing state of the art distribution aggregation technique.Comment: Full version of the paper published at 12th IFIP International Conference on Distributed Applications and Interoperable Systems (DAIS), Stockholm (Sweden), June 201

ID generation in mobile environments

This work is focused in the ID generation problem in mobile environments. We discuss the suitability of traditional mechanisms and techniques to generate IDs in mobile environments. Based on the “Birthday Problem”, we deduced some formulas to evaluate the ID trust that is directly related to the number of entities in the system. The estimation of the system size revels to be the main problem of our approach. To deal with it, we develop a recursive schema that needs to be evaluated. Alternatively, we also design an aggregation algorithm to estimate the system size, which results are currently been analyzed

Fault-tolerant aggregation for dynamic networks

Data aggregation is a fundamental building block of modern distributed systems. Averaging based approaches, commonly designated gossip-based, are an important class of aggregation algorithms as they allow all nodes to produce a result, converge to any required accuracy, and work independently from the network topology. However, existing approaches exhibit many dependability issues when used in faulty and dynamic environments. This paper extends our own technique, Flow Updating, which is immune to message loss, to operate in dynamic networks, improving its fault tolerance characteristics. Experimental results show that the novel version of Flow Updating vastly outperforms previous averaging algorithms, it self adapts to churn without requiring any periodic restart, supporting node crashes and high levels of message loss

Doctor of Philosophy

dissertationBoron's energy potential as a combustion fuel can be harnessed by using nanosize solid particulates. In this study, functionalized boron nanoparticles were produced through highyield ball milling techniques. The organic surface coating protected oxide-free boron nanoparticles from air oxidation and at the same time promoted dispersion in polar and nonpolar liquid fuels. For dispersion in hydrophobic fuels, oleic acid was used as ligand, and its interaction with boron nanoparticles was studied using XPS, FTIR, 13C-NMR and TGA. Results show that oleate species bonded to boron nanoparticles through a bridging bidentate interaction. Furthermore, undissociated oleic acid molecules persisted on the surface which may be anchored through intercalation with covalently bonded oleate species. Hydrogenation of boron through H 2 gas milling provides an alternative pathway of increasing ignitability and specific impulse of boron nanoparticles. It was also used to alkylate boron nanoparticles for dispersion in liquid hydrocarbon fuels. Boron nanoparticles were also milled with hypergolic ionic liquids to increase their energy density. Spectroscopic experiments that probed interactions of boron with 1-methyl-4-amino-1,2,4-triazolium dicyanamide([MAT][DCA]) and 1-butyl-3-methyl-imidazolium dicyanamide([BMIM][DCA]) suggest that a possible B-N binding exist between the amino substituent of [MAT][DCA] and the dicyanamide anion of both ILs

Enacting Enaction-Enaction Enacted: Experiments With and Through Enactive Ontologies

Over the last three decades the enactive approach to life, mind and nature has exerted an impressive amount of influence across a broad range of disciplines and varied research topics. At the core of the enactive approach is a thorough rejection of a number of modernist ideals and tenets; from anthropocentrism, determinism and reductionism to a host of deeply entrenched dualisms found across academia and beyond. This work brings this rejection of certain modernist tenets – qua ‘enactive matters of concern’ – into dialogue with Bruno Latour’s analysis of modernity. This is done primarily as a means to explore, to think-with and through, how and where certain enactive theorists not only reject these modernist tenets but also often reproduce them. Drawing from work in science and technology studies (STS), feminist science studies and anthropology, this work then attempts to ‘bring to light’ the different contrasting worlds enacted by certain enactive theorists. It explores how, in and through the development of ‘autopoietic enactivism’, these contrasting worlds are enacted in relation to key aspects of modernist thought and practice

Development and testing of a dual accelerometer vector sensor for AUV acoustic surveys

This paper presents the design, manufacturing and testing of a Dual Accelerometer Vector Sensor (DAVS). The device was built within the activities of theWiMUST project, supported under the Horizon 2020 Framework Programme, which aims to improve the efficiency of the methodologies used to perform geophysical acoustic surveys at sea by the use of Autonomous Underwater Vehicles (AUVs). The DAVS has the potential to contribute to this aim in various ways, for example, owing to its spatial filtering capability, it may reduce the amount of post processing by discriminating the bottom from the surface reflections. Additionally, its compact size allows easier integration with AUVs and hence facilitates the vehicle manoeuvrability compared to the classical towed arrays. The present paper is focused on results related to acoustic wave azimuth estimation as an example of its spatial filtering capabilities. The DAVS device consists of two tri-axial accelerometers and one hydrophone moulded in one unit. Sensitivity and directionality of these three sensors were measured in a tank, whilst the direction estimation capabilities of the accelerometers paired with the hydrophone, forming a vector sensor, were evaluated on a Medusa Class AUV, which was sailing around a deployed sound source. Results of these measurements are presented in this paper.European Union [645141]info:eu-repo/semantics/publishedVersio

Elementos para uma sociografia das mulheres jornalistas em Cabo Verde

Dissertação apresentada à Escola Superior de Comunicação Social como parte dos requisitos para obtenção de grau de mestre em Jornalismo.Esta dissertação tem como principal objetivo fazer uma primeira sociografia das mulheres no jornalismo cabo-verdiano. Embora haja registos de jornais antes da independência, é a partir de 5 de Julho de 1975 que se inica o processo de institucionalização da profissão. Se até a década 1990, a presença das mulheres nas redações era muito diminuta, a partir do começo do novo século, essa situação tem vindo a alterar-se de forma significativa devido, fundamentalmente, ao aumento da escolarização feminina e também à abertura dos cursos superiores de jornalismo/comunicação social em algumas universidades no país. Em todos os órgãos de comunicação (agência noticiosa nacional, jornais nacionais e televisão), a sua presença numérica tem vindo a crescer de forma constante, embora tal realidade ainda não tenha correspondência ao nível da sua presença em cargos de direção e chefias intermédias. A nível do jornalismo os dados disponibilizados pelos diversos órgãos de comunicação social mostram que existe uma tendência de feminização das redações, quer na imprensa escrita, quer na audiovisual.ABSTRACT: This dissertation’s main purpose is to make the first sociography of women in Cape Verdean Journalism. Although there are records of newspapers before the Independence, it is only after July 5th 1975 that the process of institutionalization of this profession begins. Up until the early 1990’s the presence of women in newsrooms was minimal, as of the beginning of the new century, that situation has been going through significant changes, mostly due to female schooling and also the availability of undergraduate degrees in journalism/media in some of the Cape Verdean universities. In all the Media (national news agency, Newspapers and Television), their numbers have been rising at a steady pace although this is not mirrored at the level of management or even middle management positions. The data made available by the different media show that there is a tendency towards the feminization of the newsrooms in newspapers and radio and television.N/

Flow updating: fault-tolerant aggregation for dynamic networks

Documento submetido para revisão pelos pares. A publicar em Journal of Parallel and Distributed Computing. ISSN 0743-7315Data aggregation is a fundamental building block of modern distributed systems. Averaging based approaches, commonly designated gossip-based, are an important class of aggregation algorithms as they allow all nodes to produce a result, converge to any required accuracy, and work independently from the network topology. However, existing approaches exhibit many dependability issues when used in faulty and dynamic environments. This paper describes and evaluates a fault tolerant distributed aggregation technique, Flow Updating, which overcomes the problems in previous averaging approaches and is able to operate on faulty dynamic networks. Experimental results show that this novel approach out performs previous averaging algorithms; it self-adapts to churn and input value changes without requiring any periodic restart, supporting node crashes and high levels of message loss, and works in asynchronous networks. Realistic concerns have been taken into account in evaluating Flow Updating, like the use of unreliable failure detectors and asynchrony, targeting its application to realistic environments.This work was partially funded by FCT PhD grant SFRH/BD/33232/2007 and by project Norte-01-0124-FEDER- 000058, co-financed by the North Portugal Regional Operational Program (ON.2 O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF)