Molecular Layer Deposition of Ultrathin Polyester Films

Molecular Layer Deposition (MLD) is an attractive vapour-phase technique to deposit organic thin films with thickness control at the subnanometer level. Thus far, a large deal of research has been dedicated to study MLD on flat substrates. However, MLD on particle substrates is becoming increasingly relevant since depositing organic films is highly sought for several applications, such as controlled release of pharmaceutical and food products and protection of pigments. This project focuses on the MLD growth of polyester films on both inorganic, TiO2, and organic particles, proteins. The deposition is executed in atmospheric-pressure fluidized bed reactors for a wide range of number of cycles, from 5 to 50, using either malonyl chloride or diethyl succinate as reactant, and either 1,2-butanediol or 1,4-butanediol as coreactant. To verify the success of the process, the photocatalytic activity of MLD-coated TiO2 and the dissolution behaviour of MLD-coated protein are tested. FTIR and TGA show that the MLD growth on TiO2 using malonyl chloride and 1,2- butanediol evolves linearly with the number of cycles, thus confirming one of the main characteristics of MLD. However, the film deposited with these precursors is not effective in suppressing the photocatalytic activity as the model pollutant is adsorbed by the coating. The MLD growth using diethyl succinate, independently of the diol, stops after a few cycles. Nonetheless, the photocatalytic activity of TiO2 is reduced by one-half. Regarding proteins, the MLD growth using malonyl chloride potentially leads to denaturation and thus to structural changes of the proteins, which affect the inherent dissolution behaviour. Therefore, no clear conclusion can be drawn by the comparison of the dissolution profiles of uncoated and MLD-coated proteins. The results show that the only successfulMLD approach for the deposition of polyesters involves the use of an acid dichloride (e.g. malonyl chloride) and a diol. However, it can only be applied to chemically stable particles as TiO2. Nonetheless, malonyl chloride changes the colour and thus the intrinsic photocatalytic properties of TiO2

Multipacket reception in LTE femtocell networks

Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de ComputadoresDriven by the growing demand for high-speed broadband wireless services, LTE technology has emerged and evolve, promising high data rates to the demanding mobile users. Based on the 3rd Generation Partnership Project (3GPP) speci cations,Long Term Evo- lution Advanced (LTE-A) telecommunication services predict the existence of macro base stations, Enhanced Node B (eNB) and micro stations HeNB with low power that complements the network's coverage. This dissertation studies the complementary use of HeNBs (femtocells 3GPP terminology) to provide broadband services. It is essential to maintain the networks performance with the network densi cation phenomenon, which brings signi cant interference problems and consequently more collisions and lost packets. The use of SC-FDE in the downlink of a LTE-A femtocell network - speci cally multipacket reception (MPR), with an IB-DFE receiver employing Multipacket Detection (MPD) and SIC techniques is proposed. A new telecommunications concept named GC emerged with the increasing environmental concerns. This dissertation shows the performance results of an iterative MPR and proposes a green association algorithm to change the network layout according to the mobile users demands reducing the Base Station (BS)'s negative contribution to the network total energy consumption. The overall results show that the technologies employed are a solution to achieve a favorable trade-o between performance and Energy E ciency (EE), responding to the global demands (high data rates) and concerns (low energy consumption and carbon footprint reduction). Keywords: Long Term Evolution(LTE), Single Carrier with Frequency Domain Equalization (SC-FDE), Iterative Block-Decision Feedback Equalizer (IB-DFE), Home enhanced Node B (HeNB), Successive Interference Cancellation(SIC),Multipacket Reception(MPR), Green Communications (GC)FCT/MEC Femtocells(PTDC/EEATEL/120666/2010), OPPORTUNISTIC CR(PTDC/EEA-TEL/115981/2009) and ADIN(PTDC/EEI-TEL/2990/2012) project

Inflation driven by 3-form fields

Tese de mestrado em Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2015Inflação primordial foi um curto período de expansão acelerada no universo primitivo (10 -36 a 10 -33s). É uma teoria que foi introduzida por Alan Guth com o objectivo de dar resposta a alguns problemas do modelo standard da Cosmologia. Nesta tese estudo a inflação a partir de campos tensoriais, em particular, campos 3-forma. Começarei por lembrar ao leitor alguns conceitos básicos e necessários de cálculo tensorial. Apresento resumidamente o modelo padrão da cosmologia e explico o que é a inflação primordial, porque é necessária e como é maioritariamente estudada na literatura a partir de um campo escalar a interagir com o seu potencial. Escrevo os modelos standard para uma e para múltiplas 3-formas, já estudadas na literatura. Apresento um modelo para inflação conduzida por dois campos 3-forma acopladas onde calculo as equações de evolução, equações do movimento, tensor energia momento e alguns constrangimentos. Introduzindo quatro variáveis adimensionais úteis, reescrevo as equações do movimentos para os campos, com estas novas variáveis, sob a forma de um sistema de equações diferenciais de primeira ordem o qual resolvo numericamente. Calculo os parâmetros de slow roll e impondo as condições para termos inflação (condições de slow roll) consigo obter as condições iniciais para o sistema dinâmico. Estudo a dinâmica, os pontos críticos e estabilidade destes pontos para dois tipos de potenciais, quadrático e exponencial. Foco-me no papel do acoplamento em comparação com o caso desacoplado, já estudado na literatura, mostrando a sua influência na modificação das equações e na dinâmica inacionária. Em particular, mostro que um acoplamento da ordem de ~ 10 -4 tem a influência de estender a duração da inflação entre 20 a 30 e-folds. Proponho uma forma geral para o Lagrangiano de N campos 3-forma acoplados introduzindo um novo termo que contém os acoplamentos onde imponho algumas restrições de forma a não termos repetições nos potenciais e mostro as respectivas equações do movimento. Familiarizo o leitor com o modelo extra-dimensional Randall-Sundrum II, proposto por Lisa Randall e Raman Sundrum em 1999, onde o nosso universo está confinado a uma 3-brane de 4 dimensões embebido numa quinta dimensão (bulk) cuja geometria é Anti de Sitter. Apresento um modelo inacionário conduzido por um campo 3-forma, confinado à brana, onde deduzo as equações do movimento e respectivos constrangimentos. Uma vez mais, introduzo variáveis adimensionais e reescrevo as equações do movimento sob a forma de um sistema dinâmico. Impondo as condições de slow roll para inacção, estudo a dinâmica, os pontos críticos do sistema e sua estabilidade para diferentes formas do potencial. Em particular foco-me na influência da quinta dimensão em comparação com o caso padrão a quatro dimensões. Calculo a evolução das perturbações escalares e tensoriais perturbando a métrica e a 3-forma. Usando a forma da velocidade do som, deduzo os parâmetros cosmológicos, mais especificamente, a razão entre a amplitudes das perturbações tensorias-escalares e os índices espectrais ns e nT . Por fim comparo as previsões cosmológicas do modelo considerado com os recentes resultados do satélite Planck e observo como são sensíveis à quinta dimensão quando se altera o valor da tensão da brana. Encontro um limite inferior para a tensão da brana para um caso particular do potencial.Throughout this thesis I study primordial inflation, which was a period of accelerated expansion in the early universe, through models of tensorial fields, more specifically 3-form fields. I explore the dynamics of two coupled 3-form fields in the standard four dimensional case and compare it to the uncoupled model already addressed in the literature. I focus on the role of the coupling, in contrast with the uncoupled case, and see how it affects inflationary scenarios for two different forms of the potential. I follow to deduce the evolution equations and the equations of motion which I numerically solve. I propose a general form for the Lagrangian of N coupled 3-form fields and provide the respective equations of motion. I present a single 3-form field model in a five dimensional braneworld, called the Randall-Sundrum II model, in which our universe in confined to a four dimensional 3-brane embedded in a five dimensional AdS bulk. The braneworld effects modify the evolution equations so I focus on the main differences from the five dimensional and the standard four dimensional case. Once again, I calculate the equations of motion and follow to rewrite these in the form of a system of first order differential equations which I numerically solve. I present inflationary solutions for different forms of the potential and study the dynamics, the critical points and their stability, and show the influence of the fifth dimension on these quantities. I follow to calculate the speed of sound for this model and present the evolution of scalar and tensorial perturbations by perturbing the 3-form and the metric. Finally, by calculating the cosmological parameters, tensor to scalar ratio and spectral index, I show how my inflationary setting fits the recent Planck data and see how is it sensible to the value of the brane tension where in a particular case I find a lower bond for it

An exotic Universe : from dark energy to wormholes

This thesis deals with extensions of General Relativity and their application to Cosmology and Gravitation. The introduction and main motivations of this essay can be found on Chapter 1. The second chapter proposes a dark energy model driven by a scalar field kinetically coupled to matter. The dynamics of the system are analysed through dynamical systems techniques. The background is evolved and the solutions are meticulously studied, focusing on the influence of the coupling on the cosmological parameters. Through the Planck constraints, it is derived anupper bound on the coupling parameter. Chapter three is devoted to the analysis of a conformally coupled quintessence model in which the background expansion is set to mimic a CDM evolution. Both the background and linear perturbations are analysed. The growth of structures is tested against redshift space distortions data. The spherical collapse and cluster number counts are explored, and we shed some light on the possibility to distinguish between theoretical models with regard to two surveys. An alternative formulation of General Relativity, where gravity is mediated by nonmetricity, on a flat and torsion free spacetime is exposed on the fourth Chapter. The background dynamics are set to follow the same evolution as in the standard model of Cosmology. The linear matter perturbations are evolved and the f 8 parameter is tested against large scale observations in the late Universe. Chapter five introduces a 3-form field to the Einstein-Hilbert action in the context of gravitation. Specifically, it is found wormhole solutions where the ordinary matter fields are able to coexist throughout spacetime without violating the classical energy conditions. On such scenario, the 3-form field is responsible for holding the throat of the wormhole open. On Chapter six the gravitational Lagrangian for modified Gauss-Bonnet gravity is reconstructed, such that the Friedmann equation of a bouncing Universe is recovered

Acceleration patterns in the perception of biological motion

A lot of natural stimuli are characterized by acceleration patterns. However, available studies are inconclusive about the importance of these patterns on visual perception. Empirical findings seems to both sustain that acceleration patterns might have, or might have not, a significant role on visual perception [Runeson, 1974 Psychological Research 37 3-23; McIntyre et al, 2001 Nature Neuroscience 4(7) 693-694]. In a recent study Chang and Troje [2009 Journal of Vision 9(1) 19-17] stressed the role of acceleration patterns for the perception of biological motion. Nevertheless, we have a limited understanding about the implications of these patterns for translational stimuli. The present study aimed to investigate how acceleration patterns influence the perception of biological translational motion. We manipulated the velocity of the translational component (maintaining spatial characteristics). This allowed us to create a continuum of stimuli that ranged from natural motion to constant velocity. When two stimuli are presented simultaneously participants are asked to choose which appears more natural. Data shows that subjects choose the stimulus closest to the natural motion—biological motion. Results reveal a great accuracy in detecting the stimulus closest to biological motion, which suggests that acceleration patterns are important in the perception of translational biological motion.Fundação para a Ciência e a Tecnologia (FCT

Ecologia e selecção de habitat em crustáceos zooplanctónicos de lagos pouco profundos

Doutoramento em BiologiaApesar das evidências de que os lagos Mediterrânicos pouco profundos possuem características ecológicas distintas, o conhecimento sobre estes sistemas é limitado. Este facto é agravado pela invasão globalizada de peixes alienígenas em lagos mais quentes, cujos efeitos sobre as interacções tróficas são praticamente desconhecidos. Com o intuito de diminuir o grau de incerteza associado à ecologia destes sistemas em Portugal, foi estudada a ecologia do zooplâncton na Lagoa da Vela (Quiaios, Figueira da Foz), um lago natural pouco profundo e eutrófico que apresenta dominância de peixes alienígenas. O objectivo da investigação foi compreender os mecanismos que moldam a comunidade zooplanctónica, com particular enfoque nas suas interacções com os peixes planctívoros, dada a importância deste elo trófico de charneira. Numa primeira fase, foram caracterizadas as comunidades de zooplâncton e peixes durante um ano. A lagoa revelou ser altamente produtiva e turva, exibindo níveis elevados de sólidos em suspensão, nutrientes e clorofila a. Foi observado um contraste evidente entre o período de água transparente, dominado por Daphnia, e o resto do ano, dominado por zooplanctontes de pequenas dimensões, incapazes de controlar o crescimento algal. A pressão predatória revelou ser uma força determinante do funcionamento da lagoa, a par com o nível de partículas em suspensão. Os peixes alienígenas exibiram um grau substancial de omnivoria, com o zooplâncton a constituir um dos principais componentes da dieta. A perca-sol (Lepomis gibbosus) foi o principal peixe planctívoro, exibindo populações muito densas, sobretudo no Verão, como resultado de um recrutamento contínuo de Julho a Setembro. A predação exercida por perca-sol e outros planctívoros contribuiu para o colapso da população de Daphnia (e consequente redução da transparência), mas o desaparecimento dos dafníideos durante o Verão e Outono não pode ser explicado sem recurso a outras variáveis ambientais para além da predação. A segunda fase do estudo pretendeu avaliar as estratégias utilizadas pelos zooplanctontes para minimizar a pressão predatória a que estão sujeitos. Na Lagoa da Vela, o zooplâncton exibiu uma distribuição espacial heterogénea (no plano horizontal e vertical) dependente da transparência da água. Os padrões observados são consistentes com o evitamento de predadores visuais (i.e. peixes). A amplitude reduzida do refúgio no plano vertical e a ausência de refúgio proporcionada pela vegetação aquática tornam os zooplanctontes (sobretudo Daphnia) particularmente susceptíveis à predação. Em ambiente laboratorial, Daphnia reagiu a sinais químicos de duas espécies de peixes alienígenas presentes na lagoa através de incremento reprodutivo e redução do tamanho corporal, evidenciando uma estratégia que maximiza o seu desempenho ante predadores selectivos, conforme documentado para outras espécies de peixes planctívoros.Few studies have focused on Mediterranean shallow lakes, although there is evidence of their distinctive features. This is particularly aggravated by the widespread invasion of alien fish predators in warmer lakes, whose effects on the trophic interactions largely remain unknown. To address the uncertainty associated with the ecology of these systems in Portugal, we studied the zooplankton ecology in a shallow polymictic lake (Lake Vela, Figueira da Foz), which is dominated by alien fish species and suffers from high nutrient loading (eutrophication). The purpose of the research was to understand the mechanisms shaping the zooplanktonic community, with particular emphasis on its interactions with planktivorous fish, given the importance of this pivotal trophic link. In a first stage, surveys on the zooplankton and fish assemblages were conducted for a one-year period. Lake Vela was highly productive and turbid, displaying high levels of suspended solids, nutrients and chlorophyll a. An evident contrast was observed between a clear water phase, dominated by Daphnia, and the rest of the year, dominated by small-sized zooplankters, unable to control algal biomass. Predatory pressure was found to be a key determinant of the lake’s condition and function, along with the level of suspended particles. Alien fish displayed a substantial degree of omnivory, where zooplankton was a main component in the diet. Pumpkinseed sunfish (Lepomis gibbosus) was the main planktivore, attaining very dense populations, mostly in the summer, as a consequence of continuous recruitment from July to September. Predation exerted by pumpkinseed and other planktivores contributed to the population collapse of Daphnia (and consequent reduction in transparency), but the disappearance of the daphniids during summer and autumn cannot be explained unless environmental variables other than predation are considered. The second stage of this work intended to study how zooplankters cope with high predation pressure from the alien benthi-planktivorous fish. Zooplankton displayed a heterogeneous spatial distribution (both horizontal and vertically) in Lake Vela, which was directly dependent on transparency. The observed patterns were consistent with avoidance of visual predators (i.e. fish). The reduced amplitude of refuge in the vertical plane and the absence of refuge in aquatic vegetation make zooplankters particularly susceptible to predation. Under laboratorial environment, Daphnia responded to chemical cues from two alien fish species present in the lake by maximizing reproduction and reducing body size, as an anti-predator defence mechanism against size-selective predation, as reported for most fish taxa.FCT - SFRH/BD/6417/2001FS

Using Common Features to Investigate Common Growth Cycles for BRICS Countries

This paper examines the short and long-term co-movement of large  emerging market economies -- the BRICS countries -- by applying the  econometric techniques and the tests proposed in the common-feature literature. Despite their dissimilarities, given the rising trade linkages among the BRICS over the last 20 years one should expect their cycles to be  synchronized. Our empirical findings fully support this hypothesis. The evidence holds also for the co-movement between the BRICS and developed  economies, the US and the Eurozone, which may reflect the effects of  globalization