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Dynamics in orientationally disordered solidsMartínez García, Julio César 15 July 2011 (has links)
The key features of dynamics of ultraslowing glass forming systems are their universality in diversity. Its
origin is recognized as one of the greatest challenges of condensed matter physics and materials
engineering in the XXI century. Similar phenomena are observed on approaching the glass transition in
low molecular weight supercooled liquids, polymers, colloidal fluids as well as in solids, for instance in
orientationally disordered crystals, spin glass-like magnetic, vortex glasses. Pre-vitreous dynamics is also
proposed as a general reference for the category of complex liquids/soft matter systems.
The upsurge of the primary relaxation time or related dynamical properties is the basic physical
phenomena of the still mysterious previtreous behavior. This means a much more pronounced slowing
down than the Arrhenius pattern observed far above the glass transition temperature. Portraying this
behavior constitutes one of key checkpoints for theoretical models developed to unwind the glass
transition puzzle. However, none of the aforementioned features can answer the understanding that
governs the increase of relaxation time in liquids upon cooling.
In this thesis we focus on the above questions studying the dynamics of some materials for which their
molecules can retain a translational order being orientationally disordered between them upon cooling,
which are referred to plastic phases or orientationally disordered (OD) crystalline phases. The work
presented in this thesis potentially extends the knowledge of dynamics of OD phases and orientationally
glasses (OG), a research topic which has gained interest during the last decades.
Through this study, especial attention has been devoted to the phenomenological equations accounting
to the temperature dependence of the mean relaxation time describing the orientational dynamics .The
study was carried out by the use of BDS as well as two complementary experimental techniques. We
show distortion-sensitive and derivative-based empirical analysis of the validity of leading equations for
portraying the previtreous evolution of primary relaxation time. A new method for studying the dynamics of
glass forming systems is introduced and the minimization procedure is validated and discussed.
We present the results divided in two topics, the dynamics of the pure compounds and mixed crystals and
the derivative analysis through different existing models.
In the first topic we focus on the dynamics of the pure compounds and mixed crystals formed between
cycloheptanol and cyclooctanol as well as the a-relaxation dynamics of 1-cyano-adamantane and its
mixtures with 1-chloro-adamantane. The second topic is divided in two groups of models, linearized and
non-linearized models. In the linearized models we show the application of the derivative based,
distortion-sensitive analysis to liquid crystals (LC) and OD phases. We also discuss the results concerning
to the cases of the olygomeric liquid epoxy resin (EPON828), neopentylalcohol and neopentylglycol
mixture, isooctylcyanobiphenyl and propylene carbonate. The possible empirical correlations between one
of the linearized models with the universal pattern for the high frequency wing of the loss curve for primary
relaxation time for LCs and OD phases is also shown.
In the final part we show that the form of the equation recently introduced by Mauro et al. does not allow a
similar straightforward linearization procedure. Unlike the previous models, the involved parameters are
not correlated with the slope and the intercept of a linear function. In order to solve this problem, we have
introduced the concept of the enthalpy space.
The evidences of the existence of crossovers as well as quantitative descriptions are discussed. We show
also a new procedure for detecting the crossover in a very easy way. A new kind of crossovers which
seems to be impossible to be detected by the classical Stickel transformation is presented. / La principal característica de la dinámica de sistemas vítreos viscosos, es su universalidad en la
diversidad. Su origen es uno de los mayores desafíos de la física de la materia condensada y de la
ingeniería de materiales en el siglo XXI. La fenomenología típica de las fases vítreas se observan cerca de
la transición vítrea en líquidos subenfriados de bajo peso molecular, polímeros, fluidos coloidales, así
como en los sólidos con fases orientacionalmente desordenadas. La imposibilidad de explicar las causas
del gran aumento del tiempo de relajación al enfriar un líquido, constituye uno de los problemas más
importantes no resueltos en materia condensada. Con el objetivo de dar respuesta a dicha interrogante, se
han propuesto modelos termodinámicos y dinámicos que han resultado inconsistentes.
En esta tesis nos centramos en dicha problemática, estudiando la dinámica orientacional de algunos
materiales que al ser enfriados pueden conservar un orden traslacional mientras que se conserva el
desorden orientacional de las moléculas que los forman. Dichas fases se conocen como fases plásticas u
orientacionalmente desordenadas (OD).
El trabajo presentado en esta tesis amplía el conocimiento de la dinámica de dichas fases, un tema de
investigación cuyo interés ha aumentado durante las últimas décadas.
Se ha dedicado una atención especial a las ecuaciones fenomenológicas que describen la dependencia del
tiempo de relajación con la temperatura. El estudio se ha llevado a cabo mediante el uso de espectroscopía
dieléctrica de banda ancha, así como mediante el uso de técnicas experimentales complementarias. Se ha
introducido un nuevo método para el estudio de la dinámica de los sistemas que dan lugar a fases vítreas.
El método ha sido validado y discutido.
Los resultados de esta tesis se presentan divididos en dos temas, por un lado, la dinámica de compuestos
puros y de los cristales mixtos y, por otro, el análisis mediante el método derivativo aplicado a los
diferentes modelos físicos existentes. En el primer tema nos centramos en la dinámica de los compuestos
puros y los cristales mixtos formados por cicloheptanol y ciclooctanol, así como la dinámica de la
relajación alfa en 1-ciano-adamantano y sus mezclas con 1-cloro-adamantano. El segundo tema se divide
en dos grupos de modelos, los modelos lineales y no lineales. En los modelos lineales se muestra la
aplicación del procedimiento de derivativo en los cristales líquidos (CL) y las fases OD. También se
discuten los resultados relativos a los casos de la resina líquida (EPON828), la mezcla neopentil-alcohol y
neopentil-glicol, el carbonato de propileno, así como el CL isooctilcianobifenil. Se discute también la
existencia de posibles correlaciones empíricas entre uno de los modelos lineales con el patrón universal
para la parte de alta frecuencia de la curva de pérdidas dieléctricas de la relajación primaria para las fases
CL y OD.
En la parte final se muestra que la forma de la ecuación introducida recientemente por Mauro et al. no
permite la linearización mediante el método derivativo. A diferencia de los modelos anteriores, los
diferentes parámetros no están correlacionados con la pendiente y el origen de coordenadas de una función
lineal. Para resolver este problema, hemos introducido el concepto del espacio entálpico.
Se analiza también la existencia de cambios de comportamiento dinámicos y se aportan descripciones
cuantitativas. Se muestra también un nuevo procedimiento para detectar los cambios dinámicos de una
manera fácil, que permite incluso detectar aquéllos que son obviados mediante el método clásico de
Stickel.
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Potencial das imagens hiperespectrais orbitais na detecção de componentes opticamente ativos no reservatório de ItupararangaEnnes, Rejane [UNESP] 23 May 2008 (has links) (PDF)
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ennes_r_me_prud.pdf: 1370679 bytes, checksum: eb4f2a4378f82b93f832cc48f75c59ef (MD5) / Os recentes avanços na tecnologia de Sensoriamento Remoto proporcionaram o desenvolvimento de sensores orbitais com altíssima resolução espectral, capazes de fornecer medidas radiométricas em bandas estreitas e contínuas para cada pixel da imagem, definindo curvas espectrais com potencial de discriminar diferentes componentes da matéria. Diante disso, o objetivo geral deste trabalho foi de avaliar a contribuição de imagens hiperespectrais na identificação de componentes opticamente ativos presentes em um corpo d’água, considerado de boa qualidade. Para tanto, uma imagem hiperespectral Hyperion foi adquirida simultaneamente com variáveis limnológicas coletadas em alguns pontos georreferenciados no reservatório de Itupararanga. Após a correção atmosférica da imagem, extraíram curvas espectrais nos locais geográficos dos pontos, nos quais se aplicaram técnicas de análise de espectros, tais como, remoção do contínuo, razão de bandas e análise derivativa. Os dados hiperespectrais originais e os resultantes da aplicação de técnicas foram correlacionados com algumas variáveis limnológicas... / The recent improvements in the technology of Remote Sensing are providing the development of sensors with high spectral resolution that can supply radiometric measurements in narrow and continuous bands for each pixel of the image, defining spectral curves with potential of separating several components of the matter. Due to that, the general objective of this work was evaluating the contribution of hyperspectral images in the identification of optically active constituents present in a body of water, considered good quality. To reach the proposed objective, a hyperspectral imagery of EO-1/Hyperion orbital sensor was acquired simultaneously with limnological variables collected in some points in the body of water. After correcting the atmospheric effects, in the geographical locations of those points, spectral curves of the hyperspectral image were extracted, in which techniques of spectral analysis were applied, such as, continuum removal, derivative analysis and ratio analysis. The hyperspectral original data and the resultants of the application of techniques were correlated with some limnological variables. Of the applied techniques, the derivative analysis provided better differentiation among the optically active constituents... (Complete abstract, click electronic access below)
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Potencial das imagens hiperespectrais orbitais na detecção de componentes opticamente ativos no reservatório de Itupararanga /Ennes, Rejane. January 2008 (has links)
Orientador: Maria de Lourdes Bueno Trindade Galo / Banca: Renata Ribeiro de Araújo Rocha / Banca: Waterloo Pereira Filho / Resumo: Os recentes avanços na tecnologia de Sensoriamento Remoto proporcionaram o desenvolvimento de sensores orbitais com altíssima resolução espectral, capazes de fornecer medidas radiométricas em bandas estreitas e contínuas para cada pixel da imagem, definindo curvas espectrais com potencial de discriminar diferentes componentes da matéria. Diante disso, o objetivo geral deste trabalho foi de avaliar a contribuição de imagens hiperespectrais na identificação de componentes opticamente ativos presentes em um corpo d'água, considerado de boa qualidade. Para tanto, uma imagem hiperespectral Hyperion foi adquirida simultaneamente com variáveis limnológicas coletadas em alguns pontos georreferenciados no reservatório de Itupararanga. Após a correção atmosférica da imagem, extraíram curvas espectrais nos locais geográficos dos pontos, nos quais se aplicaram técnicas de análise de espectros, tais como, remoção do contínuo, razão de bandas e análise derivativa. Os dados hiperespectrais originais e os resultantes da aplicação de técnicas foram correlacionados com algumas variáveis limnológicas... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The recent improvements in the technology of Remote Sensing are providing the development of sensors with high spectral resolution that can supply radiometric measurements in narrow and continuous bands for each pixel of the image, defining spectral curves with potential of separating several components of the matter. Due to that, the general objective of this work was evaluating the contribution of hyperspectral images in the identification of optically active constituents present in a body of water, considered good quality. To reach the proposed objective, a hyperspectral imagery of EO-1/Hyperion orbital sensor was acquired simultaneously with limnological variables collected in some points in the body of water. After correcting the atmospheric effects, in the geographical locations of those points, spectral curves of the hyperspectral image were extracted, in which techniques of spectral analysis were applied, such as, continuum removal, derivative analysis and ratio analysis. The hyperspectral original data and the resultants of the application of techniques were correlated with some limnological variables. Of the applied techniques, the derivative analysis provided better differentiation among the optically active constituents... (Complete abstract, click electronic access below) / Mestre
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