No presente trabalho foram estudados alguns aspectos não lineares da catálise da oxidação de etileno glicol (EG) sob platina em meio alcalino (KOH). A dinâmica do sistema foi investigada através de voltametria cíclica, séries temporais de corrente e potencial e por espectroscopia de impedância eletroquímica. (EIE). Os resultados da EIE revelaram a presença de uma região de resistência diferencial negativa escondida nas proximidades o pico principal obtido na voltametria cíclica. De modo geral o sistema se mostrou apto a oscilar tanto sob regime potenciostático quanto galvanostático e por longos períodos de tempo apresentando uma miríade de estados dinâmicos que incluem oscilações harmônicas, de baixa e alta amplitudes, períodos 2, 3, 4 e modos mistos, além da duplicação de período na transição para o caos. A concentração tanto de EG como de KOH tiveram caráter essencial nos padrões temporais observados. A complexidade dos períodos aumenta com o aumento da concentração de EG resultando em 90% do tempo em que o sistema passa oscilando devotado às oscilações caóticas quando a concentração de EG é de 1,6 M. O aumento da densidade de corrente produz um efeito contrário nos padrões, ou seja, quanto mais alta é a corrente mais simples são os períodos. A influência de alguns produtos de oxidação parcial do EG foi estudada em diferentes condições. Os resultados das mudanças de morfologia das oscilações são racionalizados em termos das eventuais conexões com os intermediários de reação formados durante o processo de oxidação que, por sua vez, dependem da concentração do álcool e da densidade de corrente. / In the present work were studied some nonlinear aspects of the catalytic oxidation of ethylene glycol (EG) on platinum electrodes in alkaline media (KOH). The system\'s dynamics was investigated by means of cyclic voltammetry, current and potential time series, and electrochemical impedance spectroscopy (EIS). The EIS results reveal the presence of a hidden negative differential resistance around the main voltammetric peak. Overall, the system was able to oscillate for several periods, displaying a myriad of dynamic states which includes harmonic, small and large amplitude, periods 2, 3, and 4, and mixed-mode oscillations, as well as period doubling transition to chaos. The concentration of both EG and KOH were found to play an essential role in the temporal patterns observed. The complexity of the periods increase with EG concentration resulting in 90% of the oscillating time devoted to chaotic patters when EG concentration is 1.6 M. The increment of the current density produces an opposite behavior of the patters: the higher the applied current the simpler the oscillatory dynamics. The influence of some products of partial EG oxidation was studied under different conditions and compared. The results of the changes in the oscillatory morphology are rationalized in terms of its eventual connection with reaction intermediates formed during the oxidation process that, in turn, depends on the alcohol concentration and on the current density.

Ritmos biológicos são regulados por mecanismos homeostáticos que asseguram a confiabilidade funcional do relógio fisiológico independentemente de mudanças de temperatura no ambiente. Compensação de temperatura, ou a independência do período oscilatório em relação à temperatura, é conhecida por exercer um papel central em muitos ritmos biológicos, mas um fenômeno raro em osciladores químicos. Estudou-se nessa dissertação a influência da temperatura na dinâmica oscilatória durante a oxidação catalítica de ácido fórmico sobre eletrodo de platina policristalina. Os experimentos foram conduzidos em cinco temperaturas diferentes de 5 à 25 ºC, e as oscilações foram estudadas sob controle galvanostático. Resultados experimentais foram comparados a um novo modelo proposto para a eletro-oxidação de ácido fórmico, considerando formato como intermediário ativo e a desidrogenação da água em altos potenciais. Sob condições oscilatórias apenas comportamento anti-Arrhenius foi observado. Sobre-compensação com coeficiente de temperatura (q10, definido como a razão entre a constante de velocidade à temperatura T + 10 ºC e em T) < 1 é achada para a maioria dos casos, exceto em altas correntes aplicadas onde compensação de temperatura, q10 ~ 1 predomina. O comportamento do período e amplitude resulta de uma combinação complexa entre a temperatura e corrente aplicada ou, equivalentemente, a distância do equilíbrio termodinâmico. Altas energias de ativação aparente foram obtidas em condições voltamétricas, não-oscilatórias, as quais implicam que o comportamento anti-Arrhenius observado sob regime oscilatório resulta de um acoplamento entre as rotas reacionais em vez de uma fraca dependência da temperatura nas etapas elementares. Mecanisticamente, os experimentos e o modelo matemático sugerem que o período em regime de (sobre)compensação de temperatura durante a eletro-oxidação de ácido fórmico sobre platina é governado pelo acoplamento entre as taxas reacionais de formação/remoção de monóxido de carbono e formato em condições oscilatórias. / Biological rhythms are regulated by homeostatic mechanisms that assure that physiological clocks function reliably independent of temperature changes in the environment. Temperature compensation, i.e. the independence of the oscillatory period on temperature, is known to play a central role in many biological rhythms, but it is rather rare in chemical oscillators. It was studied in this master thesis the influence of temperature on the oscillatory dynamics during the catalytic oxidation of formic acid on a polycrystalline platinum electrode. The experiments are performed at five temperatures from 5 to 25 ºC, and the oscillations studied under galvanostatic control. Experimental results are compared to a new model proposed for formic acid electro-oxidation, which includes formate as an active intermediate and water dehydrogenation at high potentials. Under oscillatory conditions only non-Arrhenius behavior is observed. Over-compensation with temperature coefficient (q10, defined as the ratio between the rate constants at temperature T + 10 ºC and at T) < 1 is found in most cases, except that temperature compensation with q10 ~ 1 predominates at high applied currents. The behavior of the period and the amplitude result from a complex interplay between temperature and applied current or, equivalently, the distance from thermodynamic equilibrium. High, positive apparent activation energies were obtained under voltammetric, non-oscillatory conditions, which implies that the non-Arrhenius behavior observed under oscillatory conditions results from the interplay among reaction steps rather than from a weak temperature dependence of the individual steps. Mechanistically, the experiments and the mathematical model suggest that the period in temperature (over)compensation regime during electro-oxidation of formic acid at platinum is governed by the coupling among the reaction rates of formation/removal of carbon monoxide and formate coverage in oscillatory conditions.

Orientadores: Carlos Ourivio Escobar, Amir Ordacgi Caldeira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-19T20:52:14Z (GMT). No. of bitstreams: 1 Coelho_JoaodeAbreuBarbosa_D.pdf: 8877509 bytes, checksum: fb8787302605bdb88dd855ddc2b5351f (MD5) Previous issue date: 2012 / Resumo: A oscilação de neutrinos é um modelo muito bem sucedido em explicar uma grande variedade de experimentos. O modelo se embasa na premissa de que os neutrinos que interagem através da força fraca por corrente carregada não são autoestados de massa, mas uma superposição destes. De forma geral, a superposição em sistemas quânticos está sujeita a perda de coerência de forma que estados puros tendem a estados mistos. Esse tipo de evolução não é possível no contexto de sistemas quânticos isolados pois a evolução é unitária e, portanto, invariante por inversão temporal. A quebra da unitariedade permite que uma seta do tempo seja introduzida e o efeito característico para os neutrinos é o amortecimento das oscilações. Investigamos aqui alguns modelos fenomenológicos de descoerência e decaimento que podem ser observados por MINOS, um experimento de oscilação de neutrinos que consiste em medir o uxo de neutrinos produzidos num acelerador de partículas a 735 km de distância. Para esta tese, analisamos o desaparecimento de neutrinos muônicos em MINOS. Informações de outros experimentos são utilizadas para restringir o número de parâmetros de forma que apenas um parâmetro extra é introduzido para cada modelo. Adotamos uma dependência energética em forma de lei de potência para o parâmetro de descoerência. A simulação e software ociais do experimento MINOS são utilizados para obter a sensibilidade do experimento aos efeitos de quebra de unitariedade considerados / Abstract: The neutrino oscillation model is very successful in explaining a large variety of experiments. The model is based on the premise that the neutrinos that interact through the weak force via charged current are not mass eigenstates, but a superposition of them. In general, a quantum superposition is subject to loss of coherence, so that pure states tend toward mixed states. This type of evolution is not possible within the context of isolated quantum systems because the evolution is unitary and, therefore, is invariant under time reversal. By breaking unitarity, an arrow of time is introduced and the characteristic effect for neutrinos is a damping of oscillations. In this thesis, some phenomonological decoherence and decay models are investigated, which could be observed by MINOS, a neutrino oscillation experiment that consists of measuring the neutrino ux produced in a particle accelerator 735 km away. We analyse the disappearance of muon neutrinos in MINOS. Information from other experiments is used to constrain the number of parameters, leaving only one extra parameter in each model. We assume a power law energy dependence of the decoherence parameter. The o-cial MINOS software and simulation are used to obtain the experiment's sensitivities to the eects of unitarity breaking considered / Doutorado / Física / Doutor em Ciências

Orientador: Marcelo Moraes Guzzo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-20T17:05:52Z (GMT). No. of bitstreams: 1 Oliveira_RobertoLeandroNevesde_D.pdf: 2779754 bytes, checksum: a4305b15e2ab247f07cb3cf74146335f (MD5) Previous issue date: 2012 / Resumo: Nesta tese, estudamos algumas consequências fenomenológicas da introdução do fenômeno de dissipação quântica na fenomenologia de oscilações de neutrinos em duas famílias. Utilizando a abordagem de equação mestra to tipo Lindblad-Kossakowski e o critério de completa positividade, descrevemos diferentes modelos para o sistema de oscilação de neutrinos sujeitos aos efeitos dissipativos causados por considerarmos que estes estão abertos a interagirem com o meio a seu redor. Investigamos como incluir os efeitos dissipativos para oscilação de neutrinos no vacuo e para quando os efeitos causados pelo potencial efetivo de matéria também estão incluídos no modelo de oscilação. Por m, aplicamos a fenomenologia estudada ao experimento MINOS como forma de observar como os efeitos dissipativos se comportam frente aos dados experimentais / Abstract: In this thesis, we study the introduction of the quantum dissipation phenomenon and the phenomenological consequences in the model of neutrino oscillations in two families. Using the Lindblad-Kossakowski master-equation approach and the complete positivity condition, we describe different models for the neutrino oscillation system subject to dissipative effects, that are caused when we consider that neutrinos can interact with the environment around them, forming a open quantum system. We investigate as to include the dissipative e ects in neutrino oscillation in vacuum and when the effects of the efective potential of matter are also included in the model of oscillation. Finally, we apply the phenomenology studied to MINOS experiment as a way to observe the behavior of the dissipative e effects from experimental data / Doutorado / Física / Doutor em Ciências

This paper is concerned with the investigation of the nonlinear eigenvalue problem describing the natural oscillations of a plate with a load that elastically attached to it. We study properties of eigenvalues and eigenfunctions of this eigenvalue problem and prove the existence theorem for eigensolutions. Theoretical results are illustrated by numerical experiments.

M.Sc. / The content of this dissertation is directed at a clearer understanding of pulsar behaviour. Pulsars are neutron stars in relatively early stages of their evolution. The intervals between observed arrival times of pulsar beams have been observed to suddenly decrease implying an increase in the star’s angular velocity Ω. This phenomenon is called a glitch. The first observed glitch occurred in the Vela pulsar (PSR 0833 -45) in 1969. The largest observed glitch also occurred in the Vela pulsar and exhibited a relative spin-up, Ω∕Ω~10−6 [1]. These relative pulsar spin-ups generally fall within the range 10−9 to 10−6 [2]. Pulsar glitches occur as a result of the processes in the interior of a neutron star [3]. Thus, a rigorous study of neutron star interiors is justified. Neutron star interiors are composed of hadronic matter: mostly neutrons, with a few per cent of protons (and, of course, non-hadronic electrons to conserve electric charge). The density of a neutron star interior increases with increasing depth as illustrated in 1.1.

Ce travail présente une étude de la dynamique interfaciale de gouttes oscillantes dans une plage étendue de fréquences, en particulier dans le domaine des hautes fréquences. Nous avons développé une méthode de caractérisation de la dynamique des oscillations de gouttes, en présence d’un forçage externe imposé, sous la forme de variations de volume périodiques de faible amplitude sur une goutte attachée à l’extrémité d’un capillaire. Cette méthode permet d’identifier les modes d’oscillation des gouttes et d’en mesurer les fréquences et les taux d’amortissement. Cette méthode a été appliquée à différents systèmes liquide-liquide, en l’absence ou en présence de surfactants. Dans ce dernier cas, elle permet d’évaluer l’effet du comportement viscoélastique des interfaces sur la dynamique des oscillations. Ainsi 3 types d’interfaces ont été identifiés. Pour les interfaces de premier type (heptane/eau sans ajout de surfactant), chaque mode propre est modélisé par un oscillateur linéaire peu amorti. Les fréquences propres et les taux d’amortissement sont bien prédits par la théorie linéaire. Les interfaces de types 2 et 3 sont obtenues en ajoutant du pétrole brut à la phase dispersée. Les surfactants naturellement présents dans le pétrole (asphaltènes, résines) s’adsorbent à l’interface et lui confèrent des propriétés viscoélastiques. Pour les interfaces jeunes (type 2, moins de 20 minutes de vieillissement), les fréquences propres mesurées restent bien prédites par la théorie, qui considère des interfaces non contaminées, tandis que les taux d’amortissement sont de loin supérieurs aux valeurs théoriques. D’autre part, les interfaces vieillies (type 3) présentent des modes propres différents avec des fréquences de résonance supérieures à celles des interfaces jeunes. Dans ce cas, la dynamique de l’interface à haute fréquence est régie par l’élasticité du réseau formé par les espèces amphiphiles du pétrole brut. Les oscillations libres d’une goutte en ascension dans une phase externe stagnante, pour un système liquide-liquide sans ajout de surfactants, ont été étudiées. Les valeurs mesurées de la fréquence d’oscillation des 4 premiers modes sont en adéquation avec la théorie linéaire. Cependant les valeurs mesurées du taux d’amortissement sont très élevées par rapport aux valeurs théoriques, pour une interface non contaminée. En effet, des espèces résiduelles adsorbées à l’interface provoquent l’apparition d’un gradient de tension interfaciale par effet Marangoni et par suite une production de vorticité plus intense dans les couches-limites, ce qui conduit à l’augmentation de l’amortissement des oscillations. / We present an experimental study of oscillating drop interfacial dynamics at a wide frequency range, especially at high frequency. A characterization method of drops oscillation dynamics has been developed. The oscillations are generated by imposing low amplitude periodic variation of volume to a drop which is attached to a capillary tip. The present method is based on the identification of the drop eigenmodes and the determination of their frequencies and damping rates. It has been applied to characterize several liquid-liquid systems. Three types of interface have been identified. For interfaces of type 1 (heptane/water without added surfactant), each eigenmode is modelled by a weakly damped linear oscillator. Eigenfrequencies and damping rates are well predicted by the linear theory. Interfaces of Types 2 and 3 are obtained by adding crude oil to the disperse phase. Oil native surfactants (asphaltenes, resins) adsorb on the drop interface and provide the latter with viscoelastic behaviour. For young interfaces (type 2 with aging time below 20 minutes), eigenfrequencies remain well predicted by the theory, which deals with non contaminated interfaces, whereas the measured damping rates are significantly higher than the theoretical values. On the other hand, aged interfaces (type 3) exhibit different eigenmodes, of which eigenfrequencies are much higher than the resonance frequencies measured for the young interfaces. At high frequency, the dynamics of aged interfaces are governed by the elasticity of the network constituted by the crude oil amphiphilic species, while the dynamics of young interfaces are governed by interfacial tension. Freely decaying oscillations of a rising drop in a liquid at rest without added surfactant were also considered. Measured frequencies for the first four eigenmodes are in good agreement with the linear theory. However, measured damping rates are much higher than the theoretical rates for non contaminated interfaces. In fact, residual adsorbed species at the heptane/water interface induce Marangoni effects and thus gradients of interfacial tension. Therefore, vorticity production within the boundary layers is enhanced, which explains the observed increase of the oscillation damping rates.

Sensory neurons assemble to form networks that process inputs coming from the senses. Through synaptic connections neurons interact and create complex dynamical states in response to these inputs. Networks with different connectivity patterns are thought to display different states and therefore subserve different computational goals. In this thesis, we mainly study brain rhythms, a dynamical state that occurs in various neural structures. Rhythms are emergent oscillations that typically occur in homogeneous recurrent networks, whose neurons have identical properties and are densely interconnected. Many sensory systems comprise neurons with opposite ON and OFF responses to inputs. We show that homogenous recurrent networks fail to sustain rhythms when ON and OFF neurons are present in equal proportions. This happens even when the network is subjected to spatially correlated inputs, which are known to promote synchronized oscillations. In this context, we adapted the so-called linear response theory to include networks containing ON and OFF neurons with different intrinsic properties. In this asymmetric case, oscillations can be recovered. A simpler approach is to segregate the ON and OFF populations, thus producing two oscillating subnetworks. The dynamics of purely feedforward networks are studied next. These networks are composed of two or more populations. The populations are connected in a serial fashion, but neurons are unconnected within the populations. This connectivity scheme is drastically different from the fully recurrent network. Yet, this network is shown to display oscillatorylike properties when subjected to spatially correlated stimulation under certain conditions. We also find that this network can implement various types of gain control, depending on the noise in the system and the strength of synaptic interactions. These results establish some unexpected links between feedforward and recurrent networks. Along the way, we apply our results and conclusions to a well-characterized sensory network, the electrosensory system of weakly electric fish.

Předmětem tohoto studia bylo prozkoumat reologické chování vodných roztoků vysokomolekulárního hyaluronanu. Byl studován vliv zvyšující se koncentrace biopolymeru v roztoku, která se pohybovala v rozmezí od 1 do 3 hmotnostních procent, a také vliv vzrůstající iontové síly rozpouštědla, způsobené přídavkem chloridu sodného, na viskoelasticitu a stabilitu těchto roztoků. Pro obsáhlejší popis viskoelasických vlastností roztoků byla použita, vedle běžných oscilačních měření, také metoda ceepových testů, ze které bylo možno určit důležité veličity, jako je procentuální poměr viskozní a elastické složky vzorku, rovnovážná poddajnost, viskozita při nulovém smykovém napětí a retardační čas. Ty byly následně porovnávány s výstupy z jiných typů měření, jako jsou právě oscilační a tokové křivky, nebo nesly dopňující informace důležité pro detailnější popis viskoelastických vlastností těchto roztoků. Ke studiu stability vzorků během namáhání pak byla použita metoda peak-hold, která ukázala na velmi dobou mechanickou i časovou odolnost roztoků hyaluronanu a naznačila hranice, za kterými už dochází k trvalému poškození struktury a degradaci řetězců hyaluronanu a je s němi proto potřeba při manipulaci s roztoky tohoto biopolymeru pro jejich další použití v aplikacích počítat.

Propofol is one of the most commonly used general anesthetics in the world, and yet precisely how it enables loss of consciousness still eludes us. It exhibits rich spectral characteristics on electroencephalogram (EEG) recordings from human patients, including alpha oscillations (8-14 Hz) and Slow Wave Oscillations (SWO, 0.5-2.0 Hz). Additionally, these two oscillations are phase-amplitude coupled (PAC) in a dose-dependent manner: low doses cause “trough-max” coupling where alpha power is maximal during the trough of the SWO cycle, while high doses cause “peak-max” coupling where alpha power is maximal during the peak of the SWO cycle. These propofol rhythms occur at the same frequencies as sleep spindles and sleep SWO, and likely use the same well-studied thalamocortical circuitry. The study of anesthesia therefore represents a safe method for investigating both how our brains sleep and the much-debated components of consciousness. In this dissertation, I use Hodgkin-Huxley-style computational models of both the thalamus and cortex to explain how the direct and indirect effects of propofol can generate such spectral phenomena. In the first part of this dissertation, I discuss results from a thalamic model. I illustrate how GABAA potentiation by propofol can create sustained alpha oscillations in the hyperpolarized thalamus by utilizing the same mechanisms used by sleep spindles. I then show how the thalamus, under artificial SWO conditions, can output trough-max or peak-max PAC depending on background excitation, GABAA potentiation, and H-current conductance. In the second part of this dissertation, I discuss results from a thalamocortical model. My analysis reveals how, in a simulated EEG signal, trough-max PAC can arise from competition between thalamocortical and intracortical synaptic currents, while peak-max PAC can arise from their cooperation. Furthermore, the coherence of cortical SWO rhythms can directly control whether the system expresses trough-max or peak-max PAC, while the indirect effects of propofol on acetylcholine are required for both PAC states. This culmination of years of work reveals just how complex the inner workings of anesthesia can be in enabling its profound effects.