El presente proyecto está basado en el análisis del siguiente problema: personas que tienen auto y requieren del servicio de mantenimiento, pero cuentan con tiempos limitados por lo que se plantea brindar una alternativa de solución rápida, eficiente y con la confianza necesaria, trasladando el servicio que ofrece un taller automotriz de local fijo, hacia el punto de ubicación del usuario sea este domicilio o trabajo. El monto de inversión inicial que representa el proyecto es de S/ 77 096 soles, como inicio de operaciones aportado por los cuatro socios fundadores de APP MOBILE CAR. En la actualidad presentamos un escenario de mercado automotriz optimista con una industria cada vez más competitiva y dinámica donde la nueva tendencia van de la mano con era digital (App) que van revolucionando el mercado automotriz. Un estudio realizado por la empresa Brandwatch indica lo siguiente: Para el año 2020, un 40% de los nuevos consumidores de automóviles serán millennials. De ellos, un 88% navega por internet, complementando que hasta Abril del presente 2018 el mercado peruano ha crecido un 33.4 %. Esto representa estabilidad, solidez y crecimiento para APP MOBILE CAR donde se refleja optimismo de los consumidores generado por la estabilidad que estamos viviendo. / The present project is based on the analysis of the following problem: people who have a car and require maintenance service, but have limited time for what is proposed to provide a quick, efficient and trustworthy alternative solution, transferring the service which offers a fixed-site automotive workshop, to the point of user's location, whether this address or work. The initial investment amount represented by the project is S / 77 096 soles, as start of operations contributed by the four founding partners of APP MOBILE CAR. Currently we present an optimistic automotive market scenario with an increasingly competitive and dynamic industry where the new trend goes hand in hand with the digital era (App) that are revolutionizing the automotive market. A study conducted by the company Brandwatch indicates the following: By the year 2020, 40% of new car consumers will be millennials. Of these, 88% surf the Internet, complementing that until April of the present 2018 the Peruvian market has grown by 33.4%. This represents stability, solidity and growth for APP MOBILE CAR which reflects the optimism of consumers generated by the stability we are experiencing. / Trabajo de investigación

Eletrocatalisadores de Pt-Sn suportados em carbono de elevada área superficial foram preparados por redução química de precursores metálicos em solução usando como agente redutor o ácido fórmico 0,5 M, 0,1 M e 2 M e caracterizados em termos de estrutura, morfologia e propriedades superficiais para aplicação em células a combustível a etanol direto (DEFC). Os catalisadores foram caracterizados por fluorescência de raios X (XRF), difração de raios X (DRX), espectroscopia de fotoelétrons de raios X (XPS), microscopia eletrônica de transmissão (TEM) e análise termogravimétrica (TGA). Os testes eletroquímicos dos catalisadores foram realizados com o uso de medidas de polarização, voltametria cíclica e linear, testes de estabilidade a potencial constante, e espectroscopia de impedância eletroquímica. A melhor composição atômica superficial, em termos de desempenho eletroquimico foi Pt3Sn1/C. Sobrepotenciais ânodicos são necessários de modo a gerar espécies oxidadas na superfície de platina, desta maneira a reação é favorecida. Em termos de produtos de oxidação, o acetaldeído e o ácido acético foram os principais produtos detectados por HPLC, com um baixo teor de CO2. A seletividade para o ácido acético com respeito ao acetaldeído aumentou com o teor de Sn e diminuiu com a menor concentração do agente redutor utilizado na preparação do catalisador. Estudos de estabilidade com base no catalisador Pt3Sn1/C foram realizados e o efeito de diferentes procedimentos de liga/desconexão da célula investigados. Testes de 250h a 0.4V incluindo tres ciclos de liga/desconexão a 50h, 150h e 200h são apresentados. Na sequência foram analisados os materiais com testes de estabilidade contínuo de 220 h em 0,4 V com recirculação de etanol. Pode-se dizer que no caso de um procedimento contínuo o sitema é menos afetado devido a menor perda em relação a corrosão do material. Análise morfológica e estrutural pós-testes forneceram informações complementares no que diz respeito ao diagnóstico eletroquímico in-situ e sobre o mecanismo de degradação. O aspecto mais crítico em relação às perdas irrecuperáveis aparece estar relacionado com a corrosão de Sn. Com base nos resultados obtidos neste trabalho, o protocolo de liga/desconexão foi o que mais afetou o desempenho geral da célula. / Pt-Sn electrocatalysts supported on carbon having high surface area were prepared by chemical reduction of metal precursors in solution using 0.5 M, 0.1 M and 2 M formic acid. These electrocatalysts used as anode materials for direct ethanol fuel cells (DEFC), have been physico-chemically characterized in terms of structure, morphology and surface properties. The catalysts were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) e Thermogravimetric Analysis (TGA). The electrochemical properties of such electrocatalysts were investigated by using polarization measurement, cyclic and linear voltammetry, potentiostatic lifetime tests and electrochemical impedance spectroscopy (EIS). The best composition, in terms of electrochemical performance was the Pt3Sn1/C sample. High anode overpotentials are required in order to generate oxidized species on the platinum surface, which favor the reaction is favored. Essentially, acetaldehyde and acetic acid were detected as the main reaction products, whereas, a low content of CO2 was detected. The selectivity towards acetic acid with respect to acetaldehyde increased with the increase of the Sn content and decreased by decreasing the concentration of the reducing agent used in the catalyst preparation. Stability tests of a DEFC based on a Pt3Sn1/C catalyst was studied and the effect of different cell shut-down procedures investigated. Tests of 250 h at 0.4 V cell potential which include three intermediate shut-down/start-up cycles at 50, 150 and 200 h were was analyzed. Stability tests of 220 h at 0.4 V with recirculation of ethanol were carried out. In the case of a continuous procedure the system is less affected due to the lower loss compared material. Morphological analysis of structural and post-tests provide additional information regarding the diagnosis and in-situ electrochemical effects on the mechanism of degradation. The most critical aspect in respect of irrecoverable losses appears to be related to the corrosion of Sn. Based on the results obtained in this study, the protocol of start/stop was the one that most affects the overall performance of the cell.

Thesis advisor: Utku Unver / This dissertation is composed of three essays in microeconomic theory. The first and second essays are in the theory of matching, with hierarchical organizations and complementarities being their respective topic. The third essay is in on electoral competition and political polarization as a result of manipulation of public opinion through social influence networks. Hierarchies are a common organizational structure in institutions. In the first essay, I offer an explanation of this fact from a matching-theoretic perspective, which emphasizes the importance of stable outcomes for the persistence of organizational structures. I study the matching of individuals (talents) via contracts with institutions, which are aggregate market actors, each composed of decision makers (divisions) enjoined by an institutional governance structure. Conflicts over contracts between divisions of an institution are resolved by the institutional governance structure, whereas conflicts between divisions across institutions are resolved by talents' preferences. Stable market outcomes exist whenever institutional governance is hierarchical and divisions consider contracts to be bilaterally substitutable. In contrast, when governance in institutions is non-hierarchical, stable outcomes may not exist. Since market stability does not provide an impetus for reorganization, the persistence of markets with hierarchical institutions can thus be rationalized. Hierarchies in institutions also have the attractive incentive property that in a take-it-or-leave-it bargaining game with talents making offers to institutions, the choice problem for divisions is straightforward and realized market outcomes are pairwise stable, and stable when divisions have substitutable preferences. Complementarity has proved to be a challenge for matching theory, because the core and group stable matchings may fail to exist. Less well understood is the more basic notion of pairwise stability. In a second essay, I define a class of complementarity, asymmetric complements, and show that pairwise stable matchings are guaranteed to exist in matching markets where no firm considers workers to be asymmetric complements. The lattice structure of the pairwise stable matchings, familiar from the matching theory with substitutes, does not survive in this more general domain. The simultaneous-offer and sequential-offer versions of the worker-proposing deferred acceptance algorithm can produce different matchings when workers are not necessarily substitutable. If no firm considers workers to be imperfect complements, then the simultaneous-offer version produces a pairwise stable matching, but this is not necessarily true otherwise. If no firm considers workers to be asymmetric complements, a weaker restriction than no imperfect complements, then the sequential-offer version produces a pairwise stable matching, though the matching produced is order-dependent. In a third essay, I examine electoral competition in which two candidates compete through policy and persuasion, and using a tractable two-dimensional framework with social learning provide an explanation for increasing political polarization. Voters and candidates have policy preferences that depend upon the state of the world, which is known to candidates but not known to voters, and are connected through a social influence network that determines through a learning process the final opinion of voters, where the voters' initial opinions and the persuasion efforts of the candidates affect final opinions, and so voting behavior. Equilibrium level of polarization in policy and opinion (of both party and population) increases when persuasion costs decrease. An increase in homophily increases the equilibrium level of policy polarization and population opinion polarization. These comparative static results help explain the increased polarization in both the policy and opinion dimensions in the United States. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.

Os estudos realizados até o momento demonstram que os instrumentos descritos na literatura possuem pouca capacidade de identificar os indivíduos em risco de quedas e portanto, existe a necessidade do desenvolvimento de novos testes ou de uma bateria de testes para essa população. Este estudo teve como objetivo traduzir e validar a Escala de Equilíbrio e Marcha (GABS) para aplicação em pacientes com doença de Parkinson (DP), determinar as características clínicas que estariam associadas ao maior risco de quedas em pacientes com DP e sujeitos saudáveis e analisar a utilidade do teste de Estabilidade Postural para avaliar o risco de quedas nos pacientes com DP. Foram selecionados pacientes do Ambulatório de Distúrbios do Movimento (AEXP) do Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto Universidade de São Paulo, com diagnóstico de DP e controles saudáveis. Os participantes foram avaliados por meio da versão motora simplificada da UPDRS, escalas de HY, SE, FOGQ, FES-I, BBS e GABS. Fizeram parte do estudo 107 pacientes com DP e 80 controles e pode-se verificar que a versão brasileira da GABS mostrou ser válida e confiável, com ótima consistência interna e boa confiabilidade inter e intraexaminador. Além disso, obteve validade convergente consistente, com correlações boas com outros instrumentos que avaliam o mesmo conceito. Somado a esses resultados, a GABS teve boa acurácia, sensibilidade, especificidade, valor preditivo positivo e valor positivo negativo considerável. Quando a GABS foi comparada com a BBS, as duas escalas tiveram resultados semelhantes. Entretanto, a GABS mostrou ser uma escala mais completa que a BBS, pois avalia diversos aspectos relacionados ao risco de quedas, como a instabilidade postural, alterações na marcha, o freezing e o medo de quedas, mostrando ser um instrumento mais interessante de ser utilizado em futuros ensaios clínicos e estudos prospectivos de evolução clínica da doença. Com relação às quedas, o principal ambiente relacionado às quedas nos pacientes com DP foi o doméstico e a marcha a principal causa, já nos controles o principal local das quedas também foi o doméstico e a principal causa de quedas foram os obstáculos presentes no ambiente. Além disso, maior tempo de doença e maior medo de quedas foram os fatores que mais contribuíram para explicar as quedas da população com DP. O teste de Estabilidade Postural conseguiu diferenciar os indivíduos com DP que sofreram quedas dos que não sofreram quedas, obteve correlações significativas com outros instrumentos que avaliam o equilíbrio e teve boa confiabilidade interexaminador. / Most studies to date have shown that the instruments available for the assessment of fall risk are inadequate for the identification of vulnerable individuals. Therefore, new tests assessing fall risk are strongly needed. This study aimed to translate and validate the Gait and Balance Scale (GABS) for use in patients with Parkinson\'s disease (PD), describe the clinical characteristics of a sample of patients with PD and controls that are related to the fall risk and analyze the Postural Stability test and it validity for assessing fall risk in patients with PD. We selected 107 PD patients at the Movement Disorders Outpatient Clinic of the School of Medicine of Ribeirão Preto - Universidade de São Paulo (USP) and 80 healthy controls. Participants were evaluated using the simplified version of the UPDRS motor scale, HY, SE, FOGQ, FES-I, BBS, and GABS. The Brazilian version of the GABS showed to be valid and reliable, with excellent internal consistency and good test-retest reliability. Furthermore, satisfactory convergent validity with other instruments that assess the same construct was found. In addition to these results, the GABS had good accuracy, sensitivity, specificity, positive predictive value, and negative predictive value. When the GABS was compared with the BBS, the two scales had similar results. However, the GABS showed to be more complete and could analyze more aspects related to fall risk in PD, as postural instability, gait deficits, freezing and fear of falling. Among controls, most falls also occurred indoors, however, they were mostly related to environmental hazards, and not gait. Longer disease duration and greater fear of falling were the factors that most contributed to explain falls in the population with PD. The Postural Stability test is able to differentiate individuals with PD who had experienced falls from those who had not, had significant correlation with others balance instruments and had good interexaminer reliability.

Cette thèse porte sur la dynamique de modèles de leucémie myéloïde chronique (LMC). Les modèles qui nous intéressent décrivent les populations de cellules leucémiques dans la moelle osseuse ou le sang, en compétition avec des populations de cellules saines ou avec le système immunitaire. Dans un premier chapitre, nous proposons une version mathématiquement analysable d'un modèle à équations différentielles ordinaires qui décrit l'interaction du système immunitaire avec les cellules leucémiques. Nous caractérisons l'existence d'équilibres et leur stabilité puis nous fournissons une analyse de bifurcation complète en co-dimension 1. Dans un deuxième chapitre, nous confrontons ce modèle à des données cliniques. Dans un troisième chapitre, nous proposons et analysons une version simplifiée d'un modèle d'équations aux dérivées partielles qui décrit la prolifération et la différenciation des cellules souches leucémiques dans la moelle osseuse et l'effet d'un traitement par ITK sur ces cellules. Nous nous intéressons au comportement à long terme des solutions, et à sa dépendance vis à vis du traitement. Dans un quatrième et dernier chapitre, nous nous intéressons à la stabilité des équations différentielles scalaires et autonomes à deux retards, qui apparaissent naturellement dans la modélisation de nombreux phénomènes biologiques ou physiques, comme la LMC / This thesis deals with the dynamics of models of chronic myeloid leukemia (CML). Models of interest describe leukemic cell populations in the bone marrow or in the blood, in competition with healthy cell populations or with the immune system. In a first chapter, we propose a mathematically tractable version of an ordinary differential equation model that describes the interaction of the immune system with leukemic cells. We characterize the existence of steady states and their stability and then we provide a complete bifurcation analysis in co-dimension 1. In a second chapter, we confront this model with clinical data. In a third chapter we propose and analyze a simplified version of a model of partial differential equations that describes the proliferation and differentiation of leukemic stem cells in the bone marrow and the effect of an TKI treatment on these cells. We are interested in the long-term behavior of the solutions, and its dependence on treatment. In a fourth and final chapter, we are interested in the stability of scalar and autonomous differential equations with two delays, which appear naturally in the modeling of many biological or physical phenomena, such as CML

Este trabalho é dedicado ao estudo da estabilidade de arcos, em regime elástico linear, submetidos a carregamentos conservativos. No Capítulo I, desenvolve-se a análise de alguns importantes trabalhos dos últimos 20 anos, sobre estabilidade de arcos, apresentando-se os seus procedimentos e principais resultados. O Capítulo 2 é dedicado aos estabelecimento de conceitos básicos do cálculo tensorial necessários para o desenvolvimento claro da teoria da elasticidade em coordenadas curvilíneas e sua aplicação na formulação variacional da teoria de barras curvas, apresentadas no Capítulo 3. O Capítulo 4 é dedicado à confecção de modelo matemático para o estudo da estabilidade de arco com geometria e carregamentos conservativos quaisquer, envolvendo o estabelecimento da trajetória fundamental de equilíbrio, a determinação da carga crítica e o estabelecimento da trajetória pós-crítica na vizinhança da carga crítica. A formulação adotada é a lagrangiana, a discretização do problema é feita pelo método dos elementos finitos, e as equações não lineares de equilíbrio são resolvidas por uma combinação dos métodos das perturbações e de Newton-Raphson. / This paper deals with the stability of arches in a linear-elastic condition under conservative loads. In Chapter 1, the analysis of some important papers on arch stability written during the last 20 years is developed, together with a presentation of their procedures and main results. Chapter 2 establishes some basic concepts of tensorial calculus, required for the clear development of the elasticity theory on curvilinear coordinates and its application to the variational formulation of the curved beams theory, which are presented in Chapter 3. In Chapter 4, a mathematical model for the study of the stability of arches with any geometry and any conservative loading is presented; it involves the establishment of the fundamental equilibrium trajectory, the determination of the critical loading and the establishment of the post critical trajectory near the critical loading. The Lagrangean formulation is adopted, the problem discretization is made by the finite element method, and the nonlinear equilibrium equations are solved through a combination of the perturbation and the Newton-Raphson methods.

Proposição: O objetivo deste estudo foi avaliar a estabilidade das relações oclusais e da correção do apinhamento anteroinferior em curto e longo prazo, 5 e 35 anos póstratamento. Material e métodos: A amostra constituiu-se de 28 pacientes, sendo 15 Classe I e 13 Classe II, tratados com extrações de 4 pré-molares, com idade inicial média de 12,72 anos (d.p.= 0,99), idade final de 14,74 anos (d.p.=1,26), e um tempo de tratamento médio de 2,02 anos (d.p.=0,66). A idade média em curto prazo póstratamento foi de 20,15 anos (d.p.=1,34), e em longo prazo foi de 49,40 anos (d.p.=4,54). A média do tempo de avaliação em curto prazo pós-tratamento foi de 5,40 anos (d.p.=0,43) e em longo prazo foi de 34,65 anos (d.p.=4,25). Foram avaliados, nos modelos de estudo das fases inicial, final e em curto e longo prazo pós-tratamento, os índices PAR e de irregularidade de Little. Após a realização da estatística descritiva da amostra total, os índices avaliados foram comparados na amostra total entre os 4 tempos avaliados pelo teste ANOVA dependente e de Tukey. Resultados: Houve diferença significante do índice PAR entre as fases inicial, final e em curto e longo prazo pós-tratamento, sem diferença entre as fases em curto e longo prazo pós-tratamento. Houve diferença significante do índice de irregularidade de Little entre todas as fases estudadas, inicial, final, em curto prazo e em longo prazo pós-tratamento. Conclusões: As relações oclusais, avaliadas pelo índice PAR, foram significantemente corrigidas com o tratamento ortodôntico, apresentaram uma recidiva significante em curto prazo e demonstraram permanecer estáveis em longo prazo pós-tratamento. O apinhamento anteroinferior, medido pelo índice de irregularidade de Little, foi significantemente corrigido com o tratamento, apresentou uma recidiva significante em curto prazo, e continuou a sofrer recidiva significante em longo prazo pós-tratamento. / Proposition: The aim of this study was to evaluate the stability of occlusal relationships and correction of mandibular anterior crowding in short and long-term, 5 and 35 years posttreatment. Material and methods: The sample comprised 28 patients, 15 Class I and 13 Class II, treated with 4 premolars extraction, with mean initial age of 12.72 years (s.d.=0.99), final age of 14.74 years (s.d.=1.26) and mean treatment time of 2.02 years (s.d.=0.66). The mean short-term posttreatment age was 20.15 years (s.d.=1.34), and long-term was 49.40 years (s.d.=4.54). The mean time of short-term posttreatment evaluation was 5.40 years (s.d.=0.43) and long-term was 34.65 years (s.d.=4.25). It was assessed, in the dental casts of initial, final and short-term and long-term posttreatment stages, the PAR index and the Little irregularity index. Upon completion of the descriptive statistics of the total sample, these indices were compared for the whole sample among the 4 stages by dependent ANOVA and Tukey tests. Results: There was significant difference among the PAR index in initial, final and short and long-term posttreatment stages, with no difference between the short and long-term posttreatment stages. There was a significant difference in the Little irregularity index among all the stages studied: initial, final, short-term and long-term posttreatment. Conclusions: The occlusal relationships, assessed by PAR index were significantly corrected with orthodontic treatment, showed a significant relapse in the short-term and demonstrated to remain stable in the long-term posttreatment. The mandibular anterior crowding, measured by the Little irregularity index, was significantly corrected with treatment, showed a significant relapse in the short-term, and continued to suffer significant relapse in the long-term posttreatment.

In this thesis I make extensive use of the Lyapunov analysis formalism to unravel fundamental mechanisms of instability in two different systems : the Kuramoto model of globally coupled phase-oscillators and the Lorenz 96 (L96) atmospheric "toy" model, portraying the evolution of a physical quantity along a latitude circle. I start by introducing the relevant theoretical background, with special attention on the main tools I have been using throughout this work : Lyapunov Exponents (LEs), which quantify the asymptotic growth rates of infinitesimal perturbations in a system, and by extension, its degree of chaoticity, and Covariant Lyapunov Vectors (CLVs), which indicate the phase space direction (or the geometry) associated with these growth rates. The Kuramoto model is central in the study of synchronization among oscillatory units characterized by their various natural frequencies, but little is known on its chaotic dynamics in the unsynchronized state. I thus investigate the scaling behavior of the first LE, upon different assumptions on the natural frequencies, and make use of educated structural simplifications to analyze the origin of chaos in the finite size model. On the other hand, the L96 model has been devised to gather the main dynamical ingredients of atmospheric dynamics, namely advection, damping, external (solar) forcing and transfers across different scales of motion, in a minimalist and functional way. It features two coupled dynamical layers : the large scale variables, representing synoptic scale atmospheric dynamics, and the small scale variables, faster and more numerous, associated with convective scale dynamics. The core of the study revolves around geometrical properties of CLVs, in the aim of understanding the processes underlying the observed multiscale chaoticity, and an exhaustive study of a non-trivial ensemble of CLVs featuring relevant projection on the slow subspace.

Suspensões coloidais encontram um grande interesse prático e apresentam aplicações na área de material cerâmico. No processamento deste material, a qualidade do produto final depende das propriedades iniciais da suspensão. Portanto, a desaglomeração e dispersão do pó cerâmico são cruciais para que os defeitos sejam minimizados. Para isto, estabilizantes eficientes devem ser utilizados. A carboximetilquitosana (CMQ) é a uma cadeia macromolecular, que apresenta grupos funcionais (carboximetila e amino) que podem adquirir cargas quando dissolvidos em meio aquoso e, por isso, pode ser usada no controle de propriedades de suspensões em que a presença de grupos com cargas seja importante para os mecanismos de estabilização. Neste trabalho, a CMQ foi preparada pela reação entre quitosana e diferentes proporções de ácido monocloroacético. A reação foi realizada em dois meios, um em que ocorreu previamente a dissolução da quitosana em um sistema de solventes (dimetilacetamida/cloreto de lítio) e outro em meio heterogêneo, no qual o material permaneceu em suspensão. A carboximetilação com prévia dissolução da quitosana pode levar a uma distribuição mais homogênea dos grupos carboximetila, quando comparado à preparação em meio heterogêneo, o que poderá influenciar na eficiência da CMQ como estabilizante. As amostras de CMQ foram caracterizadas pelas técnicas de espectroscopia na região de infravermelho (IV), ressonância magnética nuclear (RMN) e análise termogravimétrica (TGA). A técnica de IV, aplicada também para as amostras na forma ácida, permitiu a determinação do grau de substituição médio (GS ), sendo encontrado valores que variaram de 0,6 a 1,1. A eficiência da CMQ como dispersante foi avaliada por meio de medidas viscosimétricas, de potencial zeta e diâmetro médio de partícula. Em geral, houve uma diminuição da viscosidade da suspensão de alumina com a adição da CMQ, com certo destaque para as amostras com GS em torno de 1,0. As medidas de potencial zeta mostraram um aumento da magnitude das cargas superficiais, quando na presença de CMQ, o que proporciona repulsão eletrostática entre as partículas. As medidas de diâmetro de partícula mostraram que, além da diminuição do valor médio na região do ponto de carga zero (pcz), em que a agregação é máxima, ocorreu uma diminuição na distribuição dos diâmetros das partículas, em todos os pHs considerados. Estes resultados confirmam a eficiência das amostras de CMQ como estabilizantes para suspensões aquosas de alumina. / Colloidal suspensions are of great practical interest, including applications in ceramic materials. In colloidal ceramic processing, the quality of the final product will depend on the properties of the initial powder suspension. Thus, an efficient deagglomeration and dispersion of the ceramic powder in a solvent is crucial for minimizing defects. This requires efficient dispersants. Carboxymethylchitosan (CMCh) corresponds to macromolecular chains containing groups carboxymethyl and amino, that can acquire charges when dissolved in water. Then, it can be used for the control of the properties of surface, when the presence of charged groups is important to the mechanisms of particles dispersion. In this work, carboxymethylchitosan was prepared reacting chitosan and different amount of monochloroacetic acid, in two different media. In the first one, chitosan was previously dissolved in a solvent system (dimethylacetamide/ lithium Chloride) and in the second one, corresponding to heterogeneous media, the reactants and products remained suspended during the whole process. The reaction with previous dissolution of chitosan may generate a more homogeneous distribution of carboxymethyl groups, which in turn can influence the CMCh efficiency as dispersant. The CMCh sample was characterized by infrared spectroscopy (IR), nuclear magnetic resonance (NMR) and thermogravimetric analyses (TGA). The obtainment of IR spectra considering the samples of CMCh in their acid form, also allowed determining the average degree of substitution (DS), that ranged from 0.6 to 1.1. These samples were used as dispersants for aqueous alumina suspensions. In this work the efficiency of the carboxymethylchitosans as stabilizing agents was analyzed considering rheological, zeta potential and average particle size measurements. The addition of CMCh, mainly that with DS near 1.0, led to a suspension with lower viscosity. Zeta potential measurements show that the addition of CMCh results in an increase in the absolute value of zeta potential at the point of zero charge (pzc), what promote the electrostatic repulsion between the particles. The presence of CMCh led also to a suspension with lower average diameter of particles and narrow particle size distribution in all pH values considered in the present work. The results showed that the charged macromolecules (CMCh) obtained from a renewable source (chitosan), present a good performance as deflocculating agents of alumina suspensions.

Proposição: O objetivo deste estudo foi avaliar a estabilidade das relações oclusais e da correção do apinhamento anteroinferior em curto e longo prazo, 5 e 35 anos póstratamento. Material e métodos: A amostra constituiu-se de 28 pacientes, sendo 15 Classe I e 13 Classe II, tratados com extrações de 4 pré-molares, com idade inicial média de 12,72 anos (d.p.= 0,99), idade final de 14,74 anos (d.p.=1,26), e um tempo de tratamento médio de 2,02 anos (d.p.=0,66). A idade média em curto prazo póstratamento foi de 20,15 anos (d.p.=1,34), e em longo prazo foi de 49,40 anos (d.p.=4,54). A média do tempo de avaliação em curto prazo pós-tratamento foi de 5,40 anos (d.p.=0,43) e em longo prazo foi de 34,65 anos (d.p.=4,25). Foram avaliados, nos modelos de estudo das fases inicial, final e em curto e longo prazo pós-tratamento, os índices PAR e de irregularidade de Little. Após a realização da estatística descritiva da amostra total, os índices avaliados foram comparados na amostra total entre os 4 tempos avaliados pelo teste ANOVA dependente e de Tukey. Resultados: Houve diferença significante do índice PAR entre as fases inicial, final e em curto e longo prazo pós-tratamento, sem diferença entre as fases em curto e longo prazo pós-tratamento. Houve diferença significante do índice de irregularidade de Little entre todas as fases estudadas, inicial, final, em curto prazo e em longo prazo pós-tratamento. Conclusões: As relações oclusais, avaliadas pelo índice PAR, foram significantemente corrigidas com o tratamento ortodôntico, apresentaram uma recidiva significante em curto prazo e demonstraram permanecer estáveis em longo prazo pós-tratamento. O apinhamento anteroinferior, medido pelo índice de irregularidade de Little, foi significantemente corrigido com o tratamento, apresentou uma recidiva significante em curto prazo, e continuou a sofrer recidiva significante em longo prazo pós-tratamento. / Proposition: The aim of this study was to evaluate the stability of occlusal relationships and correction of mandibular anterior crowding in short and long-term, 5 and 35 years posttreatment. Material and methods: The sample comprised 28 patients, 15 Class I and 13 Class II, treated with 4 premolars extraction, with mean initial age of 12.72 years (s.d.=0.99), final age of 14.74 years (s.d.=1.26) and mean treatment time of 2.02 years (s.d.=0.66). The mean short-term posttreatment age was 20.15 years (s.d.=1.34), and long-term was 49.40 years (s.d.=4.54). The mean time of short-term posttreatment evaluation was 5.40 years (s.d.=0.43) and long-term was 34.65 years (s.d.=4.25). It was assessed, in the dental casts of initial, final and short-term and long-term posttreatment stages, the PAR index and the Little irregularity index. Upon completion of the descriptive statistics of the total sample, these indices were compared for the whole sample among the 4 stages by dependent ANOVA and Tukey tests. Results: There was significant difference among the PAR index in initial, final and short and long-term posttreatment stages, with no difference between the short and long-term posttreatment stages. There was a significant difference in the Little irregularity index among all the stages studied: initial, final, short-term and long-term posttreatment. Conclusions: The occlusal relationships, assessed by PAR index were significantly corrected with orthodontic treatment, showed a significant relapse in the short-term and demonstrated to remain stable in the long-term posttreatment. The mandibular anterior crowding, measured by the Little irregularity index, was significantly corrected with treatment, showed a significant relapse in the short-term, and continued to suffer significant relapse in the long-term posttreatment.