Intermediates, Catalysts, Persistence, and Boundary Steady States

For dynamical systems arising from chemical reaction networks, persistence is the property that each species concentration remains positively bounded away from zero, as long as species concentrations were all positive in the beginning. We describe two graphical procedures for simplifying reaction networks without breaking known necessary or sufficient conditions for persistence, by iteratively removing so-called intermediates and catalysts from the network. The procedures are easy to apply and, in many cases, lead to highly simplified network structures, such as monomolecular networks. For specific classes of reaction networks, we show that these conditions for persistence are equivalent to one another. Furthermore, they can also be characterized by easily checkable strong connectivity properties of a related graph. In particular, this is the case for (conservative) monomolecular networks, as well as cascades of a large class of post-translational modification systems (of which the MAPK cascade and the $n$-site futile cycle are prominent examples). Since one of the aforementioned sufficient conditions for persistence precludes the existence of boundary steady states, our method also provides a graphical tool to check for that.Comment: The main result was made more general through a slightly different approach. Accepted for publication in the Journal of Mathematical Biolog

Intermediates and Generic Convergence to Equilibria

Known graphical conditions for the generic or global convergence to equilibria of the dynamical system arising from a reaction network are shown to be invariant under the so-called successive removal of intermediates, a systematic procedure to simplify the network, making the graphical conditions easier to check.Comment: Added theorem 1 and corrected an error in the proof of theorem

Nanofluids for heat exchanger improvement: a numerical approach

Mestrado em Engenharia MecânicaNo panorama industrial, as últimas décadas ficaram marcadas pelo aparecimento do conceito de sustentabilidade, consequência da crescente escassez de recursos e o desaparecimento de ecossistemas. Os resultados da poluição excessiva têm sido notórios, como o buraco do ozono ou a intensificação de fenómenos meteorológicos adversos comprovam. Cientes da aproximação a um ponto de irreversibilidade, governos e indústrias perseguem o objectivo comum de proteger o ambiente e racionalizar consumos energéticos, com vista a garantir a sobrevivência das gerações futuras. Permutadores de calor desempenham um papel fundamental no aquecimento, arrefecimento e recuperação energética, tendo também sido alvo da implementação de medidas que promovem o aumento da sua eficiência com vista a contribuir para a sustentabilidade dos sistemas térmicos nos quais operam. A principal limitação dos actuais permutadores é o baixo desempenho calorífico dos fluidos operantes tipicamente empregues, como óleo, glicóis ou água. De forma a preencher esta lacuna, surgiram recentemente os nanofluidos, suspensões de nanopartículas, possuidores de melhores propriedades de transferência de calor, em fluidos comuns. Estes revelam aumentos substanciais no desempenho, permitindo antever um aumento da eficiência dos dispositivos quando aplicado. De momento, o desconhecimento dos parâmetros mais influentes para a transferência anómala de calor, está a restringir a sua aplicabilidade industrial. Para o estudo da transferência de calor, por convecção, de um nanofluido, composto por água destilada e nanotubos de carbono, um modelo numérico é proposto e validado com base em dados experimentais. As propriedades mais relevantes dos fluidos em estudos desta natureza, o coeficiente de convecção e o número de Nusselt, são obtidos através da análise ao escoamento no interior de um tubo aquecido (aço inox). Os dados obtidos para o nanofluido são posteriormente comparados aos valores correspondentes para a água destilada e às correlações teóricas comuns. Propõe-se, adicionalmente, o estudo e debate do contributo de alguns dos mecanismos comuns à transferência de calor, por intermédio de testes paramétricos individuais.In the industrial panorama, the last decades have been marked by the advent of the concept of sustainability, consequence of growing resource scarcity and ecosystem destruction. Excessive pollution has led to notorious concerns, such as ozone layer depletion or severe climatic events. In order to guarantee the safety of future generations, governments and industries share the common goal of environment preservation and rational energy expenditure, before a point of no return is reached. Heat exchangers perform an important role in heating, cooling and heat recovery, having also been subjected to the implementation of measures that promote efficiency in order to ultimately contribute to the sustainability of the systems in which they operate. The main limitation of current exchangers is the poor heat transfer behaviour of common operating fluids, such as oil, glycols or water. In order to fulfil the requirement of improved fluid heat transfer, the recent advent of nanofluids, high heat transfer nanoparticle suspensions in base fluids, has taken place. These have displayed substantial heat transfer performances, allowing to foresee increases in device efficiency once applied. At present the mechanisms, responsible for the anomalous enhancements, remain unknown, thus restricting industrial applicability. For the convective heat transfer study of a nanofluid, with carbon nanotubes suspended in deionized water, a numerical model is proposed and validated based on experimental data. The relevant fluid properties used for such investigations, the heat transfer coefficient and the Nusselt number, are obtained for fluid flow through a heated tube (stainless steel). The acquired results for the nanofluid are then compared to the matching data for deionized water and to common theoretical correlations. Additionally, a study and debate concerning the contribution of typical heat transfer mechanisms, evaluated individually under parametric testing, is proposed

Tariff policy and sustainability of public transport in Curitiba/PR

This work discusses the concept of sustainability in the public transport system. Specifically, it seeks to discuss how the concept fits into the public transport fare policy. The working hypothesis is that the tariff policy is not an instrument of sustainable urban development, as the costs of the system are mostly covered by users. The methodological procedures are based on a bibliographic review of the concepts, explaining their dimensions and pointing out the absences and presences in the research object (Integrated Transport Network). As provisional conclusions of the research, it is advanced that sustainability is presented only as specific actions, such as the introduction of vehicles with sustainable technologies and the use of biodiesel, which represent an important step towards sustainable urban mobility; however, the social and economic dimensions are not fully addressed. Keywords: sustainability, sustainable urban mobilty, Curitiba’s public transport, sustainable urban developmentDiscute o conceito de sustentabilidade no sistema de transporte público. Especificamente, discute como o conceito se insere na política tarifária do transporte público coletivo. A hipótese de trabalho é que a política tarifária não é um instrumento de desenvolvimento urbano sustentável, pois os custos do sistema são cobertos em sua grande maioria pelos usuários. Os procedimentos metodológicos se baseiam em revisão bibliográfica dos conceitos, explicitando suas dimensões e apontando as ausências e presenças no objeto de pesquisa (Rede Integrada de Transporte). Como conclusões provisórias da pesquisa, adianta-se que a sustentabilidade apresenta-se através de ações pontuais, como a introdução de veículos com tecnologias sustentáveis e o uso de biodiesel, que representam um passo importante para mobilidade urbana sustentável; entretanto, as dimensões sociais e econômicas não são contempladas em sua plenitude. Palavras-chave: sustentabilidade, mobilidade urbana sustentável, transporte público de Curitiba, desenvolvimento urbano sustentável.Peer Reviewe

Avaliação da aptidão e actividade física associadas à saúde em adolescentes do 3º ciclo do ensino básico de diferentes níveis socioeconómicos

Projeto de investigaçãoA Actividade Física tem efeitos benéficos sobre a saúde, sendo a idade escolar o período mais adequado para a aquisição de hábitos saudáveis e promoção da saúde. Pretende-se conhecer e avaliar os níveis de aptidão e actividade física dos alunos do 9º ano de diferentes níveis socioeconómicos de escolas da zona norte de Portugal. Para avaliação será utilizada a bateria de testes do Fitnessgram e acelerómetros. Será aplicado ainda um questionário para caracterizar a sua situação socioeconómica.Fundação para a Ciência e a Tecnologia (FCT) - unidade de investigação 31

An investigation of EPO as a tissue protective agent in human kidney transplantation

Ischaemia-reperfusion injury (IRI) has been identified as a major contributor to both short and long term kidney transplant failure. Experimental evidence from the literature suggests that Erythropoietin (EPO) is tissue protective, reducing both inflammation and apoptosis following IRI. We performed a randomised, double blind, placebo controlled trial examining the tissue protective effect of high dose EPO (100,000iu over 3 days) in 39 recipients of an extended criteria donor kidney or a non-heart-beating donor kidney. The primary endpoints of the study were difference in plasma and urinary biomarker levels (NGAL, IL-18 and KIM-1) in addition to changes in gene expression. Secondary endpoints included safety, clinical data and differences in metabolomics profiles. There was no difference detected between the treatment groups in terms of biomarkers, gene expression, metabolomics profiling or clinical parameters. No adverse events related to EPO therapy were recorded. In addition, we developed a cell model of kidney transplantation using primary tubulo-epithelial cells and HMEC-1 cells, with which to confirm the protective effects of EPO. Treatment with 50U/ml one hour prior to undergoing cold hypoxia resulted in the maximum degree of tissue protection, as measured using an MTT and an LDH assay. No evidence of EPO toxicity was demonstrated. Tubulo-epithelial cells expressed EPOR mRNA and protein. No CD131 receptor could be demonstrated. In summary, EPO confers tissue protection in a cell model of kidney transplantation but this has not been shown to occur in a clinical trial using high dose EPO in recipients of marginal donor kidneys.EThOS - Electronic Theses Online ServiceDepartment of Renal Medicine, Manchester Royal InfirmaryGBUnited Kingdo

Evolutionary history of the Pectoral Sparrow Arremon taciturnus : evidence for diversification during the Late Pleistocene

We focus on reconstructing a spatiotemporal scenario of diversification of a widespread South American species, the Pectoral Sparrow Arremon taciturnus (Aves: Passerellidae). This species is widely distributed in both the humid and the dry forests of South America and therefore provides an interesting model for understanding the connection between different biomes of South America. We examined nucleotide sequences of the mitochondrial genes Cytochrome b (cyt-b) and NADH subunit 2 (ND2) from 107 specimens, and one nuclear marker (intron 7 of the beta-fibrinogen gene) from a subset of samples collected across the distribution ranges of A. t. taciturnus and A. t. nigrirostris. Six major lineages were recovered in the phylogenies that displayed high levels of variance of allele frequencies and corresponded to distinct geographical locations. The estimation of divergence times provided evidence that diversification of the six lineages of the Pectoral Sparrow occurred throughout the Late Pleistocene across major cis-Andean biomes and Amazonian interfluves. Our dataset for A. taciturnus provides further evidence that rivers in Amazonia constitute barriers promoting allopatric speciation, with occasional sharing of alleles among lineages, particularly those with adjacent distributions.Peer reviewe