Network Information Flow in Small World Networks

Recent results from statistical physics show that large classes of complex networks, both man-made and of natural origin, are characterized by high clustering properties yet strikingly short path lengths between pairs of nodes. This class of networks are said to have a small-world topology. In the context of communication networks, navigable small-world topologies, i.e. those which admit efficient distributed routing algorithms, are deemed particularly effective, for example in resource discovery tasks and peer-to-peer applications. Breaking with the traditional approach to small-world topologies that privileges graph parameters pertaining to connectivity, and intrigued by the fundamental limits of communication in networks that exploit this type of topology, we investigate the capacity of these networks from the perspective of network information flow. Our contribution includes upper and lower bounds for the capacity of standard and navigable small-world models, and the somewhat surprising result that, with high probability, random rewiring does not alter the capacity of a small-world network.Comment: 23 pages, 8 fitures, submitted to the IEEE Transactions on Information Theory, November 200

Informed Network Coding for Minimum Decoding Delay

Network coding is a highly efficient data dissemination mechanism for wireless networks. Since network coded information can only be recovered after delivering a sufficient number of coded packets, the resulting decoding delay can become problematic for delay-sensitive applications such as real-time media streaming. Motivated by this observation, we consider several algorithms that minimize the decoding delay and analyze their performance by means of simulation. The algorithms differ both in the required information about the state of the neighbors' buffers and in the way this knowledge is used to decide which packets to combine through coding operations. Our results show that a greedy algorithm, whose encodings maximize the number of nodes at which a coded packet is immediately decodable significantly outperforms existing network coding protocols.Comment: Proc. of the IEEE International Conference on Mobile Ad-hoc and Sensor Systems (IEEE MASS 2008), Atlanta, USA, September 200

Effective Delay Control in Online Network Coding

Motivated by streaming applications with stringent delay constraints, we consider the design of online network coding algorithms with timely delivery guarantees. Assuming that the sender is providing the same data to multiple receivers over independent packet erasure channels, we focus on the case of perfect feedback and heterogeneous erasure probabilities. Based on a general analytical framework for evaluating the decoding delay, we show that existing ARQ schemes fail to ensure that receivers with weak channels are able to recover from packet losses within reasonable time. To overcome this problem, we re-define the encoding rules in order to break the chains of linear combinations that cannot be decoded after one of the packets is lost. Our results show that sending uncoded packets at key times ensures that all the receivers are able to meet specific delay requirements with very high probability.Comment: 9 pages, IEEE Infocom 200

Seismic Response of Tanks and Vibration Control of their Pipelines

The purpose of this work is to detail some methodologies applied for analysis of the seismic behaviour of existing bottom supported storage tanks and pipelines, under predominantly horizontal seismic actions. Developments on the established finite element method (FEM), permitted to analyse tanks and their liquid contents by two possible approaches: Ritz method coupled with FEM applied to an analytical solution of the tank-liquid system; FEM of the full system by modelling the liquid as a degenerated solid. Both formulations permit to determine seismic response envelopes. Further, some considerations on active control of cylinders by piezoceramic stacks of actuators are outlined, for potential uses in pipelines and tube-like structures

Genome-scale metabolic modelling of an extremophile microbial community

Dissertação de mestrado em BioinformaticsBiomining offers an ecological alternative to the standard mining practices by using ex tremophiles that can endure elevated temperatures and low pH values. Several studies have been performed using Acidithiobacillus caldus SM-1 and Acidimicrobium ferrooxidans DSM 10331, suggesting that these bacteria in a community offer several advantages in bioleaching environ ments. Genome-Scale Metabolic (GSM) models simulate the organisms’ metabolism through constraint based approaches. Therefore, the reconstruction of GSM models for A. caldus and A. ferroox idans and their integration into a community will offer, besides valuable insights into their metabolism, a unique perspective on the potential interaction mechanisms between the two organisms within the community. In this work, we developed manually curated GSM models for A. caldus with 416 genes, 846 reactions and 646 metabolites, and A. ferrooxidans with 408 genes, 817 reactions and 640 metabolites. Both models were reconstructed using the user-friendly software merlin. We performed the functional annotation of both organisms’ genomes to identify their metabolic characteristics, which allowed generating a draft of the metabolic network. Manual curation efforts through literature, genomic information, phylogenetically close organisms and biological databases allowed refining the metabolic network. Furthermore, the models were validated using Cobrapy and Mewpy which allowed analysing flux distribution and interactions in different environmental conditions, and the results were compared with the literature and experimental data. Lastly, the community model was built using the organisms’ validated GSM models. In silico phenotypic simulations of the community model revealed that A. caldus exchanged lipid-production related compounds whilst A. ferrooxidans donated hydrogen sulfide assisting the former with its more complex sulfur metabolism. Moreover, the results suggest a more significant influence of A. ferrooxidans in the community’s growth rate whilst A. caldus assists A. ferrooxidans in biomass production. These models can serve as a starting point to study and model the community’s behaviour in several bioleaching conditions.A biomineração oferece uma alternativa ecológica às práticas de mineração comuns através do uso de extremófilos que são capazes suportar elevadas temperaturas e baixos valores de pH. Vários estudos foram realizados usando os microrganismos Acidithiobacillus caldus SM-1 e Acidimicrobium ferrooxidans DSM 10331 em comunidade, sugerindo várias vantagens em ambientes de biolixiviação. Os modelos metabólicos à escala genómica permitem a modelação do metabolismo através de abordagens baseadas em restrições. Portanto, a construção de uma comunidade com contendo o modelo da A. caldus e outro da A. ferrooxidans poderá oferecer novas perspetivas sobre os seus respetivos metabolismos, assim como sobre os mecanismos de interação entre os dois organismos dentro da comunidade. Neste trabalho, foram reconstruídos dois modelos metabólicos à escala genómica com um elevado nível de curação manual utilizando a ferramenta merlin. O modelo da A. caldus conta com 416 genes e 846 reações enquanto que o da A. ferrooxidans possuí 408 genes e 817 reações. Os modelos foram funcionalmente anotados a fim de identificar as características metabólicas dos organismos, gerando um esboço da rede metabólica. Esta rede metabólica foi depois curada manualmente a fim de a refinar. Para isto foi usado informação presente na literatura, dados genómicos, organismos filogeneticamente próximos e bases de dados biológicas. Posteriormente, os modelos foram validados através de uma análise da distribuição de fluxo com diferentes condições ambientais e os resultados foram comparados com a literatura e dados experimentais. Por fim, o modelo da comunidade foi construído usando os modelos validados dos dois organismos. Simulações fenotípicas in silico do modelo da comunidade revelaram uma troca de compostos relacionados com produção de lípidios por parte da A. caldus, enquanto A. ferrooxidans doou sulfato de hidrogénio, auxiliando o primeiro no seu metabolismo de enxofre mais complexo. Por fim, os resultados sugerem uma maior influência de A. ferrooxidans na taxa de crescimento da comunidade enquanto que A. caldus auxilia o primeiro na produção de biomassa

International, Transnational, and Global Dimensions

UID/HIS/04209/2019 IF/01579/2015 PTDC/EPH-HIS/6964/2014This themed section explores various international and transnational dimensions of the struggle for the decolonisation of Guinea-Bissau and Cape Verde in the 1960s and early 1970s. Its articles analyse how the path to independence of these relatively small West African nations tied into a wide array of interconnected historical processes taking place around the world, from the streets of Paris to the Great Hall of the People, in Beijing. The aim is to shed new light on the circulation of ideas and foreign connections involved in this struggle, especially those of Amílcar Cabral (1924–73), founding leader of the liberation movement PAIGC and widely regarded as a key thinker of African emancipation, alongside Frantz Fanon and Kwame Nkrumah. In particular, this collection of articles examines how the struggle both shaped and was shaped by larger and/or distant trends, including Third World solidarity networks, the spread of the Cold War to Africa, and the impact of tiers-mondisme in the northern world. It thus contributes to assess the impact of African politics beyond the African continent, as well as to highlight the role of the international community in African liberation and in the emergence of postcolonial states.authorsversionpublishe