2,012 research outputs found
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/
Estimativa contínua e tolerante a faltas de funções distribuição cumulativa em redes de larga escala
Em ambientes descentralizados de larga escala como é o caso das redes de sensores sem fios, P2P e outras, a recolha de dados é praticável apenas se houver agregação dos mesmos. No estado da arte actual, as estratégias de resolução desta questão não são satisfatórias dado exigirem que os protocolos sejam reiniciados sempre que os valores iniciais mudam ou quando o rácio de entrada/saída de nodos é não nulo. Acresce que nenhuma estratégia satisfaz a estimativa de CDFs (funções de dis- tribuição cumulativa). A abordagem apresentada neste trabalho mostra como é possível o cálculo de funções de distribuição cumulativa em redes distribuídas, permitindo o seguimento dinâmico dos valores amostrados, sem que seja necessário reiniciar o protocolo em condições adversas de funcionamento da rede (perda de mensagens, entrada/saída de nodos). Esta abordagem é baseada num protocolo de averaging tolerante a faltas. Com este trabalho pretende-se também contribuir com uma estratégia que reduz o custo de comunicação entre nodos, com base em decisões locais e sensível à taxa de variação de estimativas. Os resultados de simulação mostram a resiliência deste protocolo, permitindo a estimativa contínua de CDFs em presença de dinamismo (perda de mensagens, alteração de valor amostrado, churn). Mostram também a convergência rápida na estimativa de CDFs para diferentes configurações de rede
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