Modelos multi-estados têm sido utilizados para descrever o comportamento de unidades amostrais cuja principal resposta é o tempo necessário para a ocorrência de seqüências de eventos. Consideramos um modelo multi-estados markoviano, não homogêneo, que incorpora covariáveis cujos efeitos podem variar ao longo do tempo (efeitos dinâmicos), o que permite a generalização dos modelos usualmente empregados. Resultados assintóticos mostram que procedimentos de estimação baseados no método histograma crivo convergem para um processo gaussiano. A metodologia proposta mostra-se adequada na modelagem de dados reais para comparação de desenvolvimento de recém-nascidos pré-termo com os a termo. Estudos com dados gerados artificialmente confirmam os resultados teóricos obtidos. / Multi-state models have been used to describe the behavior of sample units where the principal response is the time needed for the occurrence of a sequence of events. We consider a non-homogeneous Markovian multi-state model that incorporates covariates with time-dependent coefficient (dynamic effects), generalizing models usually employed. The asymptotic results show that the estimators based on the method of histogram sieves converge to a Gaussian process. The proposed methodology revels adequated for modeling data related to the comparison of developement of preterm infants with term infants. The studies with artificially generated data confirm the asymptotic results.

The purpose of this work is to study the effects of boundaries on granular flows down vibrating inclines, on segregation in granular mixtures induced by boundary vibrations, and on flows of granular mixtures through vibrating sieves. In each case, we employ techniques borrowed from the kinetic theory to derive an appropriate set of boundary conditions, and combine them with existing flow theories to calculate the profiles of solid volume fraction, mean velocity, and granular temperature throughout the flows. The boundaries vibrate with full three-dimensional anisotropy in a manner that can be related to their amplitudes, frequencies, and phase angles in three independent directions. At impenetrable surfaces (such as those on the inclines), the conditions derived ensure that momentum and energy are each balanced at the boundary. At penetrable surfaces (such as sieves), the conditions also ensure that mass is balanced at the boundary. In these cases, the momentum and energy balances also are modified to account for particle transport through the boundary. Particular interest in all the applications considered here is in how the details of the boundary geometry and the nature of its vibratory motion affect the resulting flows. In one case, we derive conditions that apply to a monosized granular material that interacts with a bumpy, vibrating, impenetrable boundary, and predict how such boundaries affect steady, fully developed unconfined inclined flows. Results indicate that the flows can be significantly enhanced by increasing the total energy of vibration and are more effectively enhanced by normal vibration than by tangential vibration. Regardless of the direction of vibration, the bumpiness of the boundary has a profound effect on the flows. In a second case, we derive conditions that apply to a binary granular mixture that interacts with a flat, vibrating, penetrable sieve-like boundary, and predict how such boundaries affect the process in which the particles pass through the sieve. In the special case in which the particles are all the same size, the results make clear that energy is more effectively transmitted to the assemblies when either the total vibrational energy or the normal component of the vibrational energy is increased, but that an increase in the energy transferred to the material can sometimes actually decrease the flow rates through the sieve. Consequently, at any instant of time in the sieving process, there is an optimum level of vibrational energy that will maximize the flow rate. For the sieving of binary granular assemblies, the physics associated with the effects of energy transfer on the flow rates still applies. However, in these cases, the flows through the sieve are also profoundly affected by segregation that occurs while the particles reside on sieve before the pass through. For this reason, we also isolate the segregation process from the sieving process by considering the special case in which the holes in the vibrating sieve are too small to allow any particles to pass through. In this case, the results show that under most circumstances the region immediately adjacent to the vibrating surface will be populated almost entirely by the smaller particles or by the more dissipative particles if there is no size disparity, and that the reverse is true in a second region above the first.

In the first part, the mechanisms for the dissociation of TPA are studied under three types of conditions. The unimolecular dissociation is initiated by the breaking of either the N-Calpha and Calpha -Cbeta bonds and leads to many complicated processes. Within the confined space inside neutral zeolite channels, the diffusion of H radicals enhances a cycle of reactions, which accounts for the experimental observation of dipropylamine and monopropylamine. In the presence of an acidic site, the dissociation of TPA goes through catalyzed successive steps to produce ammonia and propylene molecules. / In the last part, two distinct paths are proposed to investigate the carbon nanotube growth mechanism using benzene as the growth seed and propylene as carbon resource. There is an incremental aromatization process, involving both alkylation and dehydrogenation, that leads to linked aromatic rings to form either (3,3) tube or (4,2) tube. Two paths are identified, one via toluene and the other via cumene. The cumene path is more favorable as the barrier is significant lower. / In the second part, A T5 cluster model is used to investigate mechanisms of propylene aromatization to benzene, which involves chemisorption, dimerization, cyclization and dehydrogenation. Propylene can be chemisorbed to form two distinct products, n-propoxide and i-propoxide, which can further be dimerizated to form longer chain olefins 1-hexene and 2-hexene (from n-propoxide), and 4-methyl-1-pentene and 4-methyl-2-penetene (from i-propoxide). Initiated by H2 elimination, these dimerization products can further go through cyclization process to generated either 6-member ring cyclohexene or 5-member ring methyl-cyclopentene. Catalyzed by zeolite, cyclohexene can directly dehydrogenate to form benzene whereas methyl-cyclopentene can dehydrogenate to form fulven, an isomer to benzene. Under acidic zeolite environment, a fulvene can readily be transformed to the thermodynamically more stable benzene. / The growth mechanisms of mono-sized and parallel-aligned single wall carbon nanotube (CNT) in the microporous channels of AlPO4-5 are investigated by density functional theory calculations. Detailed mechanisms are proposed for the decomposition of TPA, the formation of aromatic ring, and the growth of carbon nanotubes. / Liu, Jianwen. / Adviser: Zhifeng Liu. / Source: Dissertation Abstracts International, Volume: 70-09, Section: B, page: . / Thesis submitted in: December 2008. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 98-99). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Modelos multi-estados têm sido utilizados para descrever o comportamento de unidades amostrais cuja principal resposta é o tempo necessário para a ocorrência de seqüências de eventos. Consideramos um modelo multi-estados markoviano, não homogêneo, que incorpora covariáveis cujos efeitos podem variar ao longo do tempo (efeitos dinâmicos), o que permite a generalização dos modelos usualmente empregados. Resultados assintóticos mostram que procedimentos de estimação baseados no método histograma crivo convergem para um processo gaussiano. A metodologia proposta mostra-se adequada na modelagem de dados reais para comparação de desenvolvimento de recém-nascidos pré-termo com os a termo. Estudos com dados gerados artificialmente confirmam os resultados teóricos obtidos. / Multi-state models have been used to describe the behavior of sample units where the principal response is the time needed for the occurrence of a sequence of events. We consider a non-homogeneous Markovian multi-state model that incorporates covariates with time-dependent coefficient (dynamic effects), generalizing models usually employed. The asymptotic results show that the estimators based on the method of histogram sieves converge to a Gaussian process. The proposed methodology revels adequated for modeling data related to the comparison of developement of preterm infants with term infants. The studies with artificially generated data confirm the asymptotic results.

Carbon molecular sieve (CMS) membranes represent the most attractive pure component materials to compete against polymer membranes for high performance gas separations. CMS membranes are formed from the thermal decomposition of polymer precursors and can therefore be formed into continuous defect free membranes with excellent gas separation performance. Over the last 20 years, CMS membranes have been produced in a variety of geometries and have a wide range of separation performance applicable to several important gas separations. Though research into CMS membrane formation is quite extensive, the relationship between synthesis factors and separation performance is still not well understood. The goal of this study was to elucidate the effect of two different synthesis factors on the separation performance of CMS membranes to allow more control over separation performance. The foci of this study were to clarify (1) the effect of pyrolysis atmosphere and (2) the effect of polymer precursor composition. Dense flat CMS membranes were synthesized from 6FDA:BPDA-DAM precursor at 550 oC using several pyrolysis atmospheres including vacuum pyrolysis (<0.05 torr), helium and argon flowing at atmospheric pressure, and helium and argon flowing at reduced pressures. The separation performance of CMS membranes produced under different pyrolysis atmospheres suggests that the amount of oxygen available during pyrolysis has a significant affect on the microstructure of membrane. CMS membranes were produced from 6FDA:BPDA(1:1)-DAM and 6FDA:BPDA(1:1)-DAM under identical pyrolysis conditions to determine the utility of polymer precursor composition as an engineering tool to fine-tune the performance of CMS membranes. In a second study utilizing 6FDA-6FpDA and 6FDA-6FmDA precursors, the separation performance of CMS membranes was shown to be dependent on the intrinsic precursor free volume. These studies have shown that two factors to be considered when choosing a polymer precursor are the intrinsic free volume of the polymer and the composition of the by-products evolved during pyrolysis.

It had been shown that the transport properties of CMS membranes varies as a function of H₂S exposure making the conditioning protocol an important step in identifying the steady state properties of CMS membranes. In this study the conditioning of CMS membranes with H₂S was studied for the determination of the acid gas steady state transport properties. The conditioned steady state has been shown to be the same state for both an extended conditioning protocol using high pressure mixed gas and a rapid conditioning protocol using pure H₂S. The rate of conditioning does vary between the two conditioning protocols as the rapid conditioning protocol takes 48 hours less to reach the conditioned steady state. The results of this study also show that oxygen doping during the formation of the CMS membrane affects the final, conditioned steady state transport properties.

Discovery of mesoporous materials by Mobil researchers in 1992 opened a new field in catalytic applications. The materials designated as M41S family are MCM-41 with one-dimensional hexagonal structure, MCM-48 with three-dimensional cubic structure and MCM-51 with unstable lamellar structure. This family of materials have high surface areas up to 1500 m2/g, narrow pore size distributions with pore sizes varying from 20 to 100 &Aring / . These materials can be activated by incorporation of metals or active compounds into their structures. In this study, copper and nickel incorporated MCM-41 type catalytic materials were synthesized via different methods namely, impregnation, high temperature and low temperature direct synthesis methods. The Cu-MCM-41, and Ni-MCM-41, as well as synthesized MCM-41 were characterized by using XRD, TEM, N2 sorption, SEM, XRF, EDS, AAS and TPR. MCM-41 was synthesized with high temperature direct synthesis method. High surface area values up to 1400 m2/g of MCM-41 mesoporous materials were obtained with high pore volumes up to 1.17 cc/g. Cu-MCM-41 type catalytic materials were synthesized with three different methods. Impregnation and high temperature direct synthesis methods gave better results than those of low temperature direct synthesis method. In impregnation, relatively high surface area values (730 m2/g) were obtained with Cu/Si mole ratio as high as 0.3 in the product. For the case of high temperature direct synthesis products, Cu/Si mole ratios as high as 0.26 were obtained with somewhat smaller surface areas (400 m2/g). Low temperature direct synthesis method is the least favorable method in metal loading. Ni-MCM-41 type of catalytic materials were synthesized by impregnation and high temperature direct syntheses methods. Ni incorporation by high temperature direct synthesis method gave high surface area values (560-930 m2/g) having Ni/Si mole ratios of 0.12-0.28.

Mixed matrix membranes that comprise domains of organic and inorganic components are investigated in this research. Such materials effectively circumvent the polymeric 'upper bound trade-off curve' and show properties highly attractive for industrial gas separations. Nevertheless, lack of intrinsic compatibility between the organic polymers and inorganic fillers poses the biggest challenge to successful fabrication of mixed matrix membranes. Consequently, control of the nanoscale interface between the sieve and polymer has been the key technical challenge to the implementation of composite membrane materials. The overarching goal of this research was to devise and explore approaches to enhance the performance of mixed matrix membranes by properly tailoring the sieve/polymer interface. In an effort to pursue the aforementioned objective, three approaches were developed and inspected: (i) use of silane coupling agents, (ii) hydrophobizing of sieve surface through alcohol etherification reactions, and (iii) a two-step modification sequence involving the use of a Grignard reagent. A comparison was drawn to evaluate these methodologies and the most effective strategy (Grignard treatment) was selected and further investigated. Successful formulation and characterization of mixed matrix membranes constituting zeolite 4A modified via the Grignard treatment are described in detail. Membranes with impressive improvements in gas separation efficiency and mechanical properties were demonstrated. The basis for the improvements in polymer/sieve compatibility enabled by this specific process were proposed and investigated. A key aspect of the present study was illuminating the detailed chemical mechanisms involved in the Grignard modification. Systematic characterization and carefully designed experiments revealed that the formation of distinctive surface structures is essentially a heterogeneous nucleation process, where Mg(OH)2 crystals grow from the nuclei previously extracted from zeolites. In addition to the main work, discovery of sonication-induced dealumination of zeolites was made during the systematic exploration of Grignard chemistry. The new procedure employing sonication can potentially be applied to prepare zeolites with a variety of Si/Al ratios under relatively mild conditions. The last part of this thesis focused on development of a technique to generalize the highly specific Grignard treatment to inorganic materials other than zeolite 4A. This work delivered composite membranes with improved interfacial adhesion. Moreover, research revealed the effect of surface nuclei density on the ultimate morphology of deposited nanostructures and how different surface morphologies influence polymer/filler interaction in composite membranes. Methods were devised to tailor the morphologies of such structures in order to optimize adhesion enhancement. The acquired results demonstrated the potential of extending this modification process to a broad domain of materials and render it a general methodology for interfacial adhesion promotion.

Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2017-05-17T18:25:54Z No. of bitstreams: 1 DissAROF.pdf: 8258056 bytes, checksum: 0a3e4acabf6e7541cfbb0a0d125d2408 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-22T13:54:57Z (GMT) No. of bitstreams: 1 DissAROF.pdf: 8258056 bytes, checksum: 0a3e4acabf6e7541cfbb0a0d125d2408 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-22T13:55:05Z (GMT) No. of bitstreams: 1 DissAROF.pdf: 8258056 bytes, checksum: 0a3e4acabf6e7541cfbb0a0d125d2408 (MD5) / Made available in DSpace on 2017-05-22T13:59:47Z (GMT). No. of bitstreams: 1 DissAROF.pdf: 8258056 bytes, checksum: 0a3e4acabf6e7541cfbb0a0d125d2408 (MD5) Previous issue date: 2016-02-19 / Não recebi financiamento / The master degree work presented is a result of a research conducted together with a group, which has worked on the modification of the synthesis CTA-MCM-41, that silica belongs to the mesoporous materials family (composed by MCM-41, MCM-48 e MCM- 50). The synthesis of silicas was disclosed by Mobil Oil Corporation in 1992 due to processing of higher molecular that the processed for microporous silica. Between the mesoporous silicas, the more studied it’s MCM-41. When the MCM-41 has in their pores the cation (CTA+) it has also basic catalytic sites due to siloxi anion (≡SiO-) associated. In evaluating the basic character of the CTA-MCM-41 in transesterification reactions of monoester, we obtained satisfactory conversions, but when catalyst reused, there was a loss of catalytic due to leaching cations CTA+. Then, the catalyst loses part of the basicity necessary to that reaction. This work has challenged, synthesize hybrid catalysts that are able of keep the same catalytic activity when reused. From the research, the formation of MCM-41, the cocondensation of TEOS with functionalized groups can result in new hybrid materials. These materials offer functional groups connected to wall silica, [Si]– CnH(2n+1), this connection type can create more stability to this form of silica. For this particular research, arose the proposal to use together with TEOS, the hexadecyltrimethoxysilane (silane) or dimethyloctadecyl[3-(trimethoxysilyl) propyl] ammonium chloride (silônio) like fonts of silicas in the synthesis of the MCM-41. The silicas synthesized showed X-ray diffraction characteristic of the MCM-41 and the presence of the silane and the silônio was proven through the technique nuclear magnetic resonance of 29Si and of the termogravimetric analysis. The silicas were evaluated catalytically by transesterification reaction of ethyl acetate in methyl acetate and ethanol. The conversions obtained in the reaction, when compared with the silica synthesized just with TEOS, were lower, due to deposition silônio group on silica surface, hindering the access to basic sites. / O trabalho de mestrado apresentado é resultado de pesquisas realizadas em conjunto com o grupo, que tem trabalhado na modificação da síntese da CTA-MCM-41. A MCM-41 com os poros obstruídos pelo cátion (CTA+), possui sítios catalíticos básicos devido ao ânion siloxi (≡SiO-) associados. Ao avaliar o caráter básico da CTA-MCM-41 em reações de transesterificação de monoésteres, observa-se conversões satisfatórias. Entretanto, o problema do emprego dessa sílica nesta reação é a perda de atividade (ocorre desativação) à medida que é reutilizada, esta desativação tem sido apontada como sendo ocasionada pela lixiviação do cátion CTA⁺. Desta forma, o catalisador perde parte da basicidade requerida para esse tipo de reação. Este trabalho teve como desafio sintetizar catalisadores híbridos que sejam capazes de manter a atividade catalítica mesmo ao serem reutilizados. Para isso, foi levantado uma pesquisa, que durante a formação da MCM-41, a co-condensação do TEOS com nova fonte de sílica que contem grupos funcionalizados, pode resultar em novos tipos de materiais híbridos. Esse tipo de ligação, [Si]-C, pode resultar em uma maior estabilidade dessa sílica. Para esta pesquisa em particular, surge a proposta de utilizar, juntamente com o TEOS, o hexadeciltrimetoxisilano (chamado de silano) ou o cloreto de dimetiloctadecil[3-(trimetoxisilil)propil] amônio (chamado de silônio) como fontes de sílicas na síntese da MCM-41. Os difratogramas de raios X apresentaram, para as sílicas sintetizadas com diferentes teores de silano, estruturas características de materiais mesoporosos e para os materiais sintetizados com diferentes teores de silônio apresentaram estrutura característico da sílica MCM-41. A quantificação e a incorporação preferencial desses compostos nas sílicas sintetizadas foram comprovadas pela ressonância magnética nuclear de 29Si com e sem polarização cruzada com Hidrogênio. As sílicas, ao serem avaliadas cataliticamente na reação de transesterificação, mostraram-se menos ativas quando comparadas com o material sintetizado apenas com TEOS. Para os materiais sintetizados com silônio, as baixas conversões foram devidas a deposição desse grupo na superfície da sílica, dificultando assim o acesso aos sítios básicos.

Made available in DSpace on 2016-06-02T19:55:27Z (GMT). No. of bitstreams: 1 3154.pdf: 5552497 bytes, checksum: 0a1853852321cef9c6280241685ff21d (MD5) Previous issue date: 2010-08-13 / Universidade Federal de Sao Carlos / The investments in the biofuel production have increased a lot in the last years mainly because of smaller damages they cause to the environment in comparison with the derived conventional petroleum fuels. The reaction of biodiesel formation is denominated transesterification and, nowadays that reaction happens in the presence of homogeneous catalyst as the sodium methoxide, sodium hydroxide, (NaOH) or potassium hydroxide (KOH). However, those catalysts create problems such as the possibility of soap formation and they need stages such as the neutralization and washing of the biodiesel. Moreover, the residues of the hydroxides are aggressive to the environment. To eliminate these and other problems, the present work presents a new technology in heterogeneous catalysts with enough basic force to accomplish the transesterification of vegetable oil in tender conditions. For the first time, hybrid catalysts of the type molecular sieves of the family M41S ([CTA]Si-MCM-41, [CTA]Si-MCM-48 and [CTA]Si-MCM-50) were synthesized and used, without modification, in transesterification reactions with monoesters and vegetable oils. The results show that catalysts reach conversions around 96 % in the transesterification of canola oil (1:18) at 79 ºC, however the activity is reduced when the catalyst is reused, due, mainly, to the lixiviation of the CTA+ cation. However, new techniques are being developed in order to increase the catalyst stability. / Os investimentos na produção de biocombustíveis aumentaram significativamente nos últimos anos devido, principalmente, aos menores danos causados ao meio ambiente em comparação aos combustíveis convencionais derivados de petróleo. A reação de formação do biodiesel é denominada transesterificação e, atualmente, essa reação ocorre na presença de catalisador homogêneo como o metóxido de sódio, hidróxido de sódio (NaOH) ou de potássio (KOH). Entretanto, esses catalisadores possuem problemas como possibilidade de formação de sabões e necessitam de etapas como a neutralização e lavagem do biodiesel, além disso, os resíduos dos hidróxidos são agressivos ao meio ambiente. Para eliminar estes e outros problemas o presente trabalho apresenta uma nova tecnologia em catalisadores heterogêneos com força básica suficiente para realizar a transesterificação de óleos vegetais em condições amenas. Pela primeira vez, catalisadores híbridos do tipo peneiras moleculares da família M41s ([CTA]Si-MCM-41, [CTA]Si-MCM-48 e [CTA]Si-MCM-50) foram sintetizados e utilizados, sem modificação, em reações de transesterificação com monoésteres e óleos vegetais. Os resultados mostram que catalisadores atingem conversões em torno de 96 % na transesterificação de óleo de canola (1:18) a 79 ºC, porém a atividade é reduzida no reuso do catalisador, devido, principalmente, à lixiviação do cátion CTA+. Entretanto, novas técnicas estão em desenvolvimento para aumentar a estabilidade dos catalisadores.