3,473 research outputs found

    Enzymatic biosensors for spermidine amperometric determination

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    Polyamines (PA) detection has been shown of great interest as biomarkers for various analytical purposes, such as freshness of fish, fruit and vegetables and cancer control. Various methods have been developed for separation and quantification of biogenic amines and among then all, electrochemical biosensors. These types of biosensors, particularly the ones involving the screen-printing technology, which combine construction simplicity with biological recognition through enzyme specificity, have been reported as a good and cheap alternative to the traditional techniques. Screen-printing technology offers design flexibility, process automatization and good reproducibility in the transducers fabrication, as well as the possibility of using a wide choice of materials. In this work, Monoamine Oxidase (MAO) and Diamine Oxidase (DAO) based biosensors using screen-printed carbon electrodes have been attempted for the determination spermidine. The enzymes have been immobilized onto the working electrode by means of glutaraldheyde and chronoamperometric variables (applied potential and solution pH) adjusted for better reply as experimental variables can affect biosensor chronoamperometric response. One form of screen-printed electrodes (SPEs) modification consists of the incorporation of metallic nanoparticles on the working electrode surface. Due to their reduced size, metallic nanoparticles exhibit important physical and electrical properties which make them very useful for the construction of more sensitive electrochemical biosensors. Silver and gold nanoparticle-modified carbon SPEs show important advantages when they are used as working electrodes in electrochemical techniques. Thus, different experiments were performed using modified nanoparticles DAO/MAO biosensors in order to evaluate nanoparticles influence on detection limit, sensibility, repeatability and reproducibility. Isothermal titration microcalorimetry (ITC) may be used as a tool for obtaining overall apparent molar enthalpy for catalytic reactions and enzyme kinetic constants. ITC is useful, in this regard, since it directly measures the heat change as catalysis proceeds and this is proportional to the rate of the reaction. ITC is a well established, powerful, versatile and high-sensitivity technique that is widely used for measuring the thermodynamics of equilibrium association reactions. In addition, well designed experiments can yield an approximate value for the equilibrium association constant for the enzyme-substrate complex (KA) when product formation is the limiting step, as well as the reaction stoichiometry (n). Thus, this technique has been tried to study MAO activity when immobilized on a non-modified SPE.Presentemente, diversos trabalhos t√™m demonstrado a utilidade das poliaminas (PA) como biomarcadores em v√°rias t√©cnicas de an√°lise para a avalia√ß√£o da qualidade dos alimentos (peixe, fruta e vegetais) e tamb√©m no controlo do cancro. V√°rios m√©todos t√™m sido desenvolvidos para a separa√ß√£o e quantifica√ß√£o de aminas biog√©nicas, destacando-se de entre eles, o uso dos biosensores electroqu√≠micos. Este tipo de biosensores, particularmente os que envolvem a tecnologia de electrodos serigrafados, combinam a simplicidade de constru√ß√£o com o reconhecimento biol√≥gico atrav√©s da especificidade enzim√°tica. A tecnologia de electrodos serigrafados oferece ainda flexibilidade de design, processos de produ√ß√£o automatizados, boa reprodutibilidade, e a possibilidade de uso de diversos materiais. Neste trabalho, usando el√©trodos de carv√£o serigrafados (SCE) imobilizados com oxidase da monoamina (MAO) ou oxidase da diamina (DAO) tentou-se construir um biosensor capaz de detectar espermidina. A imobiliza√ß√£o das enzimas sobre o el√©trodo de trabalho foi realizada por cross-linking usando glutaralde√≠do. Para uma melhor resposta eletroqu√≠mica, procedeu-se ao ajuste das vari√°veis cronoamperom√©tricas (potencial aplicado e pH da solu√ß√£o) dado saberse que estas podem interferir com a resposta electroqu√≠mica. Uma forma de modifica√ß√£o dos SPE consiste na incorpora√ß√£o de nanopart√≠culas met√°licas na superf√≠cie do el√©trodo de trabalho. Devido ao seu reduzido tamanho, as nanopart√≠culas met√°licas exibem propriedades el√©tricas e f√≠sicas importantes que as tornam vantajosas para a constru√ß√£o de biosensores eletroqu√≠micos mais sens√≠veis. SCE modificados com nanopart√≠culas de prata e ouro apresentam vantagens importantes quando s√£o usados como el√©trodos de trabalho em t√©cnicas eletroqu√≠micas. Assim, diversas experi√™ncias usando biosensores MAO/DAO modificados com nanopart√≠culas, foram realizadas, para avaliar a sua influ√™ncia no limite de dete√ß√£o, na repetibilidade e na reprodutibilidade do m√©todo. A t√©cnica de titula√ß√£o microcalorim√©trica (ITC) pode ser usada como uma ferramenta na obten√ß√£o da entalpia molar aparente total de rea√ß√Ķes catal√≠ticas e na obten√ß√£o dos par√Ęmetros cin√©ticos das enzimas. Neste sentido, a ITC √© √ļtil, uma vez que mede diretamente a varia√ß√£o de calor durante a cat√°lise, valor esse proporcional √† velocidade de rea√ß√£o. A ITC √© uma t√©cnica, bem estabelecida, sens√≠vel, vers√°til e poderosa, que √© amplamente usada na determina√ß√£o da termodin√Ęmica de rea√ß√Ķes associadas ao equil√≠brio. Al√©m disso, atrav√©s de experiencias bem programadas pode-se obter um valor aproximado da constante de equil√≠brio de associa√ß√£o para o complexo enzima-substrato (KA) quando o produto formado √© o passo limitante, bem como a estequiometria da rea√ß√£o (n). Portanto, tentou-se estudar a atividade enzim√°tica da MAO quando imobilizada num SCE n√£o modificado com nanoparticulas

    Software Engineering for Millennials, by Millennials

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    Software engineers need to manage both technical and professional skills in order to be successful. Our university offers a 5.5 year program that mixes computer science, software and computer engineering, where the first two years are mostly math and physics courses. As such, our students' first real teamwork experience is during the introductory SE course, where they modify open source projects in groups of 6-8. However, students have problems working in such large teams, and feel that the course material and project are "disconnected". We decided to redesign this course in 2017, trying to achieve a balance between theory and practice, and technical and professional skills, with a maximum course workload of 150 hrs per semester. We share our experience in this paper, discussing the strategies we used to improve teamwork and help students learn new technologies in a more autonomous manner. We also discuss what we learned from the two times we taught the new course.Comment: 8 pages, 9 tables, 4 figures, Second International Workshop on Software Engineering Education for Millennial

    Dynamics of financial markets : study of an agent-based model

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    Mestrado em Matem√°tica FinanceiraNas √ļltimas d√©cadas, o mercado financeiro mundial tem enfrentado v√°rios problemas e colapsos que motivaram anos conturbados para a economia real e para as fam√≠lias. Os sistemas din√Ęmicos apareceram na literatura de matem√°tica financeira para ajudar a compreender melhor as caracter√≠sticas √ļnicas destes mercados financeiros e a din√Ęmica do pre√ßo ao longo do tempo. Este trabalho consiste principalmente numa aproxima√ß√£o estat√≠stica ao sistema din√Ęmico de modelo de mercado com um ponto de descontinuidade introduzido por Tramontana, Westerhoff e Gardini (2010). Usando uma vers√£o do modelo que produz √≥rbitas ca√≥ticas, podemos observar, para par√Ęmetros espec√≠ficos, distribui√ß√Ķes estacion√°rias. Por outras palavras, o sistema din√Ęmico pode ser ca√≥tico do ponto de vista do estudo das √≥rbitas, por√©m, em termos estat√≠sticos, √© assintoticamente previs√≠vel, isto √©, a maioria das trajet√≥rias converge para um atractor que n√≥s conseguimos descrev√™-lo estatisticamente. Ainda, para os par√Ęmetros apropriados, o modelo pode projetar um comportamento absolutamente err√°tico, mesmo numa aproxima√ß√£o estat√≠stica. Para este √ļltimo, n√≥s conclu√≠mos que a previs√£o do pre√ßo √© imposs√≠vel uma vez que s√≥ conseguimos restringir os nossos progn√≥sticos a um intervalo invariante suficientemente grande que cont√©m toda a din√Ęmica do pre√ßo.Over the past few decades, the global financial market has been facing multiple distresses and crashes which led to troubled years for the real economy and families. Dynamical systems emerged in the mathematical finance literature to help comprehending better the unique characteristics of these financial markets and the price dynamics over the time. This work consists mainly of a statistical approach of the one discontinuity point dynamical system market model introduced by Tramontana, Westerhoff and Gardini (2010). Using a model's version that produces chaotic orbits, we can observe stationary distributions under specific parameters. In other words, the dynamical system can be chaotic in a point-wise perspective, however, from a statistical approach, it can be asymptotically predictable, that is, most trajectories converge to an attractor which we can describe statistically. Still, under the proper parameters, the model may project an absolute erratic behavior, even in the statistical approach sense. For the latter, we conclude the price forecast is impossible because we can only restrict our prognoses to an invariant set sufficient large whose contain the whole price dynamic

    Hybrid Threat? Societal Security and the Russians in the Baltics

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    Uma larga percentagem dos habitantes dos Estados B√°lticos t√™m origens Russas. As recentes interven√ß√Ķes militares por parte da Federa√ß√£o Russa refor√ßaram preocupa√ß√Ķes com a seguran√ßa em todo o espa√ßo p√≥s-sovi√©tico. Gra√ßas √† efici√™ncia da opera√ß√£o de anexa√ß√£o da Crimeia, a aplica√ß√£o de longo termo da estrat√©gia apelidada de guerra hibrida, que instrumentaliza a identidade como ferramenta para ganhos geopol√≠ticos, √© considerada um desafio a uma resposta militar atempada pelos aliados militares dos Estados B√°lticos, do qual o contingente militar √© comparativamente marginal. Isto leva √† necess√°ria aplica√ß√£o de um novo paradigma de seguran√ßa humana e estatal, como m√©todo de dissuas√£o contra a estrat√©gia de guerra h√≠brida, sendo importante questionar quais as op√ß√Ķes de dissuas√£o dispon√≠veis para os Estados B√°lticos contra a guerra h√≠brida. A relev√Ęncia do conceito de seguran√ßa societ√°ria √© explorada, alicer√ßada numa estrutura conceptual para o seu desenvolvimento no contexto B√°ltico, questionando ainda como pode a seguran√ßa societ√°ria ser desenvolvida nos Estados B√°lticos. Concluiremos com a pertin√™ncia do conceito para a seguran√ßa da regi√£o.A large percentage of the inhabitants of the Baltic States are of Russian origins. The recent military interventions by the Russian Federation have raised security concerns all across the post-soviet space. Thanks to the efficiency of the annexation operation of Crimea, the long-term application of the strategy named as hybrid warfare, which instrumentalises identity as a tool for political gains, is considered a challenge to a timely military response by the military allies of the Baltic States, whose military contingent is comparatively marginal. This leads to the necessary application of a new paradigm of human and state security, as a dissuasion method against the strategy of hybrid warfare, leading to the questioning on the dissuasion options available to the Baltic States against hybrid warfare. The relevance of the concept of societal security is explored, and embedded into a conceptual structure for its development within the Baltic context, further exploring on how societal security can be developed in the Baltic States. We will conclude on the pertinence of the concept for the security of the region

    Realistic vulnerability injections in PHP web applications

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    Tese de mestrado em Seguran√ßa Inform√°tica, apresentada √† Universidade de Lisboa, atrav√©s da Faculdade de Ci√™ncias, 2011A injec√ß√£o de vulnerabilidades √© uma √°rea que recebeu relativamente pouca aten√ß√£o da comunidade cient√≠fica, provavelmente por o seu objectivo ser aparentemente contr√°rio ao prop√≥sito de fazer as aplica√ß√Ķes mais seguras. Esta pode no entanto ser usada em variadas √°reas que a fazem merecedora de ser investigada, tais como a cria√ß√£o autom√°tica de exemplos educacionais de c√≥digo vulner√°vel, testar mecanismos de seguran√ßa em profundidade, e a avalia√ß√£o de detectores de vulnerabilidades e de equipas de seguran√ßa. Esta tese prop√Ķe uma arquitectura para uma ferramenta de injec√ß√£o de vulnerabilidades gen√©rica que permite a inser√ß√£o de vulnerabilidades num programa, e aproveita a vasta investiga√ß√£o existente sobre detec√ß√£o de vulnerabilidades. A arquitectura √© tamb√©m extens√≠vel, suportando a adi√ß√£o de novas vulnerabilidades para serem injectadas. Foi tamb√©m implementado e avaliado um prot√≥tipo baseado nesta arquitectura por forma a perceber se a arquitectura era implement√°vel. O prot√≥tipo consegue injectar a maior parte das vulnerabilidades da class taint-style, desde que em aplica√ß√Ķes web desenvolvidas em PHP. Esta tese cont√©m tamb√©m um estudo sobre as vulnerabilidades presentes nas √ļltimas vers√Ķes de algumas aplica√ß√Ķes PHP bem conhecidas, que permite perceber quais os tipos de vulnerabilidade mais comuns. Este estudo conclui que as vulnerabilidades que o prot√≥tipo permite j√° incluem a maioria das vulnerabilidades que aparecem habitualmente em aplica√ß√Ķes PHP. Finalmente, v√°rias aplica√ß√Ķes PHP foram usadas na avalia√ß√£o. O prot√≥tipo foi usado para injectar diversas vulnerabilidades sobre estas aplica√ß√Ķes, e ap√≥s isso as injec√ß√Ķes foram analisadas √† m√£o para verificar se uma vulnerabilidade tinha sido criada ou n√£o. Os resultados mostram que o prot√≥tipo consegue n√£o s√≥ injectar uma grande quantidade de vulnerabilidades mas tamb√©m que estas s√£o atac√°veis e realistas.Vulnerability injection is a field that has received relatively little attention by the research community, probably because its objective is apparently contrary to the purpose of making applications more secure. It can however be used in a variety of areas that make it worthy of research, such as the automatic creation of educational examples of vulnerable code, testing defense in depth mechanisms, and the evaluation of both vulnerability scanners and security teams. This thesis proposes an architecture for a generic vulnerability injection tool that allows the insertion of vulnerabilities in a program, and leverages from the vast work available on vulnerability detection. The architecture is also extensible, supporting the addition of new vulnerabilities to inject. A prototype implementing the architecture was developed and evaluated to analyze the feasibility of the architecture. The prototype targets PHP web applications, and is able to inject most taintstyle type vulnerabilities. The thesis also contains a study on the vulnerabilities present in the latest versions of some well known PHP applications, providing a better understanding of which are the most common types of vulnerabilities. This study shows that the vulnerabilities that the prototype is able to inject already includes the majority of the vulnerabilities that appear in PHP web applications. Finally, several PHP applications were used in the evaluation. These were subject to injections using the prototype, after which they were analyzed by hand to see whether a vulnerability was created or not. The results show that the prototype can not only inject a great amount of vulnerabilities but that they are actually attackable

    The role of telomeric DNA damage, mitochondria biogenesis and mTOR signalling in cellular senescence

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    PhD ThesisCellular senescence is a state of enduring cell-cycle arrest characterised by a persistent DNA damage response, elevated Reactive Oxygen Species (ROS), mitochondrial dysfunction and a senescence-associated secretome. Senescence impacts in vivo not only by acting as a tumour suppressor mechanism but also hindering tissue repair and regeneration. Senescent cells build-up with age in many tissues from humans, baboons and mice, and clearance of senescent cells in mice has been demonstrated to ameliorate age-related pathologies. The mTOR (mechanistic target of rapamycin) is a primeval and conserved pathway among eukaryotes. Inhibition of the mTOR pathway has been shown to extend lifespan of model organisms, to be beneficial against cancer progression and to ameliorate several age-related diseases. While reports suggest that mTOR plays a role in cellular senescence, it is still incompletely understood how it contributes to the phenotype. Mitochondria sit on the crossroad of many cell fate decisions including apoptosis, differentiation and metabolism. Despite requirement for the aforementioned processes, the role of this organelle in cellular senescence has not been fully elucidated. In this thesis, I describe potential mechanisms by which mTOR may impact on cellular senescence, given its roles in regulating the DNA damage response and mitochondrial homeostasis. Additionally, I inspect the role of mitochondrial biogenesis during induction and maintenance of cellular senescence. Finally, I study the impact of mTOR inhibition by rapamycin and, the effects of compromised mitochondrial biogenesis in liver senescence with age in mice
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