Dissertação (mestrado)—Universidade de Brasília, Instituto de Química, Programa de Pós-Graduação em Química, 2012. / Submitted by Albânia Cézar de Melo (albania@bce.unb.br) on 2013-09-05T16:28:38Z No. of bitstreams: 1 2012_GuilhermeDuarteRamosMatos.pdf: 1464081 bytes, checksum: 60e8692a5bf80bf60620c9964fd2f8bf (MD5) / Approved for entry into archive by Guimaraes Jacqueline(jacqueline.guimaraes@bce.unb.br) on 2013-09-06T11:46:43Z (GMT) No. of bitstreams: 1 2012_GuilhermeDuarteRamosMatos.pdf: 1464081 bytes, checksum: 60e8692a5bf80bf60620c9964fd2f8bf (MD5) / Made available in DSpace on 2013-09-06T11:46:43Z (GMT). No. of bitstreams: 1 2012_GuilhermeDuarteRamosMatos.pdf: 1464081 bytes, checksum: 60e8692a5bf80bf60620c9964fd2f8bf (MD5) / O avanço das metodologias teóricas para a apreciação de fenômenos químicos tem sido bastante acentuado nas últimas décadas. Com o surgimento de métodos cada vez mais refinados, os quais possibilitam em muitos casos resultados mais precisos que os experimentais, surge a impressão equivocada que o entendimento qualitativo de determinados fenômenos deve ser posto de lado visando a obtenção numérica das quantidades em questão. Não obstante, o conhecimento qualitativo de certos fenômenos tem se provado essencial para a predição de seus caminhos completos. Dentro da química o exemplo maior pode ser dado pelos cálculos de estado de transição, nos quais as suposições corretas sobre as interações entre reagentes e produtos são essenciais para o desenvolvimento dos cálculos. Entre os métodos qualitativos, destaca-se a Teoria dos Orbitais Moleculares de Fronteira, desenvolvida por Kenichi Fukui na primeira metade do século XX, que permitiu a racionalização de um grande número de reações químicas. Nesse âmbito, Lionel Salem e Gilles Klopman, independentemente, propuseram uma equação que permitia a identificação imediata das interações presentes entre os substratos de uma reação assim como a caracterização da dominância de uma sobre a outra, sendo um trabalho pioneiro nesse sentido. O objetivo deste trabalho é testar um conjunto de técnicas para predição qualitativa de caminhos de reação, o modelo de Salem-Klopman, a análise por Orbitais de Ligação Naturais (Natural Bond Orbitals, NBO), e as grandezas da Teoria do Funcional da Densidade Conceitual, verificando a coerência de suas predições de sítios de interação entre moléculas reagentes, principalmente no que tange à reações SN2 com nucleófilos ambidentados. Quanto ao estudo de cargas atômicas serão utilizadas três metodologias diferentes de cálculo de cargas atômicas, os métodos de Mulliken, Löwdin - baseados em análise de população eletrônica - e CHELPG (CHarges from Electrostatic Potentials using a Grid based methodology), baseado em análise do potencial eletrostático. Pretende-se, também, com as informações vindas destas metodologias, testar o princípio HSAB de Pearson, que tem sido rediscutido nesses últimos anos. ______________________________________________________________________________ ABSTRACT / The description of chemical phenomena suffered a great enhancement on the last decades. Currently, theoretical methods can hold very accurate results, sometimes even better than experimental ones. This fact creates a paradigm: Is it really necessary to qualitatively predict chemical phenomena since it is possible to perform calculations with such high accuracy? Even though many chemists are tempted to answer negatively this question, it is surely positive. Transition state calculations, for example, depend heavily on qualitatively correct pictures of the interaction between reactants. Among the qualitative methods, it is imprescindible to highlight the Frontier Molecular Orbitals (FMO) theory, developed by Kenichi Fukui in the first thhalf of the 20 century and allowed the description of many chemical reactions. In this context, Lionel Salem and Gilles Klopman, independently, proposed a pioneer approach which used a now-called Salem-Klopman equation. With this formula they could identify interactions present in the system and determine which one dominates over the other, marking the beginning of the qualitative approach of understanding reaction paths. The objective of this work is to test Salem-Klopman’s, Natural Bond Orbital (NBO) analysis and Conceptual DFT quantities for the prediction of interaction sites in SN2 reactions with ambident nucleophiles. Parameters were collected from modern electronic structure calculations, with special attention to three atomic charges methodologies: Mulliken’s and Löwdin’s method based on electronic population analysis and CHELPG (CHarges from Electrostatic Potentials using a Grid based methodology). It is also intended to test Pearson’s HSAB principle whose validity is been called into question recently.

Orientador: Luiz Carlos Dias / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-07-24T20:51:21Z (GMT). No. of bitstreams: 1 Giacomini_RosanaAparecida_M.pdf: 3738514 bytes, checksum: cb023fb9d7224f4133f22c3b4f47edeb (MD5) Previous issue date: 1998 / Mestrado

Ingeniero Civil Químico / Hoy en día las empresas productoras, para sobrevivir y perdurar en el mercado, deben tomar buenas decisiones y así maximizar sus ingresos. Para lograr esto, es necesario que distribuyan sus recursos de manera eficiente, además de identificar con exactitud el precio de sus productos o servicios. Esto último se logra únicamente con la implementación de un sólido sistema de costeo. Dado que en la empresa Clariant, específicamente su planta productiva Oil & Mining Services, ha adquirido un nuevo reactor de vidrio de 16 [m3], se abre la posibilidad de establecer el sistema de costeo para este nuevo equipo, y así determinar las nuevas posibilidades de fabricación con sus respectivos precios unitarios. Entre los costos de producción se conoce el importante rol que juegan los costos asociados a las horas hombre y las horas máquina, los que suman cerca del 60% del costo de producción. En el presente trabajo, además de lo anterior, se incorpora como extensión al proyecto el cálculo del consumo de vapor en cada producción, debido al alto costo invertido en el último tiempo en este ítem, cercano al 12% de los costos de conversión. Luego de determinar la estructura de costos, se proyecta el aumento del tamaño de lote, lo que provoca una disminución de los costos unitarios de fabricación, los cuales no presentan un ahorro significativo al observarlos como costos unitarios, pero al observar esta disminución según el volumen de fabricación presente en la planta se aprecia un ahorro significativo. En el mejor de los casos por ejemplo, la fabricación en el nuevo reactor presenta un ahorro de 25 pesos por kilogramo de producto, pero el producto presenta un volumen de producción de 148 toneladas al mes, esto significa un ahorro de 3,7 millones de pesos al mes. Siendo esta la principal conclusión del trabajo, el ahorro generado es principalmente por la disminución de las horas hombres y horas máquinas. Por otro lado al disminuir el costo unitario de producción mejora el margen de ganancia de la empresa en sus ventas. Con respecto al vapor se compara el consumo medido en planta con los cálculos generados mediante dos metodologías, estimando el coeficiente de transferencia global de energía y, en otro caso, despreciándolo. En función de lo anterior se observa que el consumo al despreciar el coeficiente es menor en comparación con el escenario que lo incluye. Esto se debe a las resistencias que presenta tanto el material de transferencia como los fluidos involucrados en el momento del intercambio, presentando una diferencia del 10 al 20%. En este trabajo se proyecta la estructura de costos para un conjunto de productos que serán producidos en la nueva unidad de Clariant, tomando por referencia la actual estructura de costos en un reactor de menor escala. El escalado de la estructura de costos y el consumo de vapor varían en función del producto analizado, no siendo posible definir una regla general de escalado del servicio de vapor.

Este trabalho tem como objetivo estudar as reações físico-químicas do concreto, principalmente aquelas que interferem direta e indiretamente nas suas variações volumétricas causando a retração - química, autógena e secagem - que tem promovido excessivas patologias em pavimentos rodoviários e industriais. Apresenta um breve resumo da história dos ligantes hidráulicos nos últimos séculos, a fabricação do cimento Portland e o estado da arte das reações de hidratação, bem como das principais adições empregadas nos cimentos brasileiros. Na parte experimental analisa o comportamento quanto a tendência à fissuração de cimentos empregados no sudeste do Brasil, bem como a mitigação dessa patologia. Conclui que a causa dessa excessiva fissuração pode estar ligada diretamente ao teor de gesso dos cimentos e apresenta sugestão para o seu controle.

Orientador: Albert James Kascheres / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-07-23T06:07:34Z (GMT). No. of bitstreams: 1 Moura_PatriciaRibeirode_M.pdf: 5584008 bytes, checksum: 51612470eab6fb8b46167f33c72817ef (MD5) Previous issue date: 1997 / Mestrado

En este trabajo se presenta el diseño e implementación de una grilla (ventana multidimensional) móvil para aproximar numéricamente la solución de la ecuación de Fisher-Kolmogorov (FK), aplicada al modelamiento de frentes de reacciones autocatalíticas de reacción-difusión-advección. Nos apoyaremos en la perspectiva de la físico-química, el análisis numérico y su implementación en computador. Explicaremos concretamente en qué consisten las reacciones autocatalíticas y la importancia del estudio de los frentes de onda en dichas reacciones. Precisamos los fenómenos de reacción-difusión, mencionando los principales valores conocidos de velocidad de los frentes de onda, cuando no existe flujo externo. Mencionamos la dinámica de los sistemas de reacción-difusión-advección, con velocidades externas pequeñas (número de Peclet pequeño ( )), haciendo énfasis en el fenómeno de la dispersión hidrodinámica de Taylor y algunas aproximaciones asociadas. En cuanto al análisis numérico, utilizamos el método de diferencias finitas para aproximar las ecuaciones diferenciales mencionadas anteriormente, convirtiéndolas en relaciones algebraicas, utilizando el método Forward-Time Centered-Space (FTCS), mencionando los criterios de convergencia y estabilidad necesarios. Con ello, formulamos y sustentamos un algoritmo de grilla móvil, implementándolo en Fortran. Con el algoritmo implementado en Fortran, simulamos los frentes de onda, sin advección y con advección, comparando los valores teóricos de velocidades de frentes de onda, con los valores simulados. Al obtener una similitud razonable entre los valores de velocidad de los frentes de onda, para reacciones de orden dos (cuadráticas) y tres (cúbicas), procedimos a realizar predicciones sobre las velocidades de los frentes para reacciones de orden superior, cuatro y cinco. Durante las simulaciones por computadora, hemos conseguido mejorar el procesamiento de datos utilizando procesamiento paralelo y operaciones de bloques de memoria, adaptando nuestras estructuras de datos a la jerarquía de memoria cache del CPU utilizado. El algoritmo de grilla móvil implementado, con su estrategia de procesamiento y adaptación de estructuras de datos, puede ser adaptado fácilmente para estudiar otros fenómenos que admiten un esquema explícito para ser simulados. / Tesis

No description available.

En esta Tesis se ha contribuido al desarrollo metodológico y la aplicabilidad tanto de la Microbalanza Electroquímica de Cuarzo (EQCM) como de la Espectroscopia de Impedancia Electroquímica (EIS).En el análisis de la respuesta de la EQCM, se ha aplicado el uso de la función F(dm/dQ), la cual proporciona una estimación del peso molecular de las especies que intervienen en una transferencia faradaica. De esta manera, se ha profundizado en su aplicación al depósito y disolución del cinc, lo que permite postular la formación de una nueva fase de Zn(I) en la disolución anódica del cinc de distintos tipos de galvanizado. Esta cinética se ha cuantificado mediante la realización de experiencias de EIS y el contraste de dos modelos: a) deducción de la función que explica las impedancias electroquímicas teóricas, elaborada a partir de leyes cinéticas, y b) el uso de circuitos equivalentes. Desde esta perspectiva se han analizado las funciones Z(w), Y(w) y C(w).Además, también se ha profundizado en el sistema electródico ES F PB, por considerarse modelo teórico dentro del estudio de películas electroactivas. / The use of the F(dm/dQ) function has been applied in the analysis of the Electrochemical Quartz Microbalance (EQCM) response, which proportionate a estimation of the atomic weight of the species involved in a faradaic transfer. Thus, it is studied in depth the zinc electrodeposition as well as its anodic dissolution, this one has allowed to postulate the formation of a new phase of Zn(I) in the zinc anodic dissolution process of different galvanized.The dissolution kinetics has been quantified by means of the realization of EIS experiences and the contrast of two models: a) the deduction (from kinetics laws) of the theoretical electrochemical impedances function and b) the use of equivalent circuits. Accordingly, the Z(w), Y(w) and C(w) functions have been analyzed.Furthermore, the electrodic system ES F PB has been studied in depth due to the fact that it is considered a theoretical model in the study of electroactive films.

The coupling of liquid chromatography (LC) to infrared (IR) spectrometry is an interesting analytical tool, because high resolution provided by LC is combined with the non-destructive and molecular specific information of IR spectrometry. However, the potential of on-line LC-IR employing a flow cell interface, characterized by its technical simplicity, cannot yet be fully exploited due to the limited sensitivity of IR detection and difficulties in on-line measurements arising from the dominating absorption of most of the commonly used mobile phase components. Accordingly, the objective of this Thesis was to promote the use of the on-line hyphenation of LC and IR spectroscopy through the development of instrumental and chemometric tools to overcome existing limitations, thus increasing the applicability of this technique. Chapter 2 describes innovations in the field of isocratic separation. A method for the determination of lecithin and soybean oil in dietary supplements using on-line Gel Permeation Chromatography – Attenuated Total Reflectance – Infrared (GPC-ATR-IR) was developed including a simple procedure to select the optimum wavenumber used for the extraction of characteristic elution profiles. For the monitoring of polymerized triglycerides in deep-frying oil, an approach employing on-line GPC-IR spectrometry and the Science Based Calibration (SBC) multivariate approach for chromatogram-extraction were reported. An on-line LC-IR procedure for the determination of glycolic acid in cosmetics employing the rapid scan data acquisition mode was proposed. Chapter 3 deals with different methods for background correction in on-line LC-IR using reference spectra matrices (RSM). The determination of the critical eluent composition for polyethylene glycols using methanol as organic modifier was discussed employing the absorbance ratio as identification parameter for background correction. For the determination of fructose, glucose, sucrose and maltose in beverages employing acetonitrile as organic modifier, again the absorbance ratio was used as identification parameter. A Partial Least Squares (PLS) procedure as well as the application of point-to-point matching algorithms for automated background correction were discussed for background correction in acetonitrile:water gradients using different examples of applications. Chapter 4 deals with the compensation of the background contribution employing column-wise techniques. Polynomial regressions modelling the background absorbance at each wavenumber throughout the gradient run were applied for acetonitrile:water mobile phase gradients. The use of cubic smoothing splines could be demonstrated for background correction under reversed phase gradient conditions employing different alcohols as organic modifiers. In Chapter 5, background correction based on factor analysis and reference spectra matrices was discussed. The contribution of the background absorption to overall LC-IR signals could be compensated using two approaches based on Principal Component Analysis (PCA) and simple-to-use interactive self modeling analysis (SIMPLISMA), obtaining good results in acetonitrile:water systems. Subsequently, multivariate curve resolution-alternating least squares (MCR-ALS) was applied improving peak and spectral resolution and eliminating remaining signal variation due to background absorption and detector drift. The chemometric extraction of ‘analyte-specific’ chromatograms in on-line LC-IR was discussed in Chapter 6. Obtained results confirm that the SBC method is particularly well suited for recovering ‘analyte-specific’ signals from on-line LC-IR chromatograms. The last chapter describes instrumental developments in on-line LC-IR. On-line IR detection in gradient capillary LC using micromachined nanoliter-flow cells was discussed. Four model compounds were separated and identified using an acetonitrile:H2O gradient with limits of detection in the concentration range of 35-94 ng μL-1, representing an increase in mass sensitivity by a factor of approximately 30 as compared to standard LC systems. The last chapter also focuses on the development of LC with on-line dual Quantum Cascade Laser (QC-laser) detection. Compared to state-of-the-art FTIR spectrometers, the use of the developed QC-laser based system provided a significant improvement in both, sensitivity and data acquisition frequency. / The coupling of liquid chromatography (LC) to infrared (IR) spectrometry is an interesting analytical tool, because high resolution provided by LC is combined with the non-destructive and molecular specific information of IR spectrometry. However, the potential of on-line LC-IR employing a flow cell interface, characterized by its technical simplicity, cannot yet be fully exploited due to the limited sensitivity of IR detection and difficulties in on-line measurements arising from the dominating absorption of most of the commonly used mobile phase components. Accordingly, the objective of this Thesis was to promote the use of the on-line hyphenation of LC and IR spectroscopy through the development of instrumental and chemometric tools to overcome existing limitations, thus increasing the applicability of this technique. Chapter 2 describes innovations in the field of isocratic separation. A method for the determination of lecithin and soybean oil in dietary supplements using on-line Gel Permeation Chromatography – Attenuated Total Reflectance – Infrared (GPC-ATR-IR) was developed including a simple procedure to select the optimum wavenumber used for the extraction of characteristic elution profiles. For the monitoring of polymerized triglycerides in deep-frying oil, an approach employing on-line GPC-IR spectrometry and the Science Based Calibration (SBC) multivariate approach for chromatogram-extraction were reported. An on-line LC-IR procedure for the determination of glycolic acid in cosmetics employing the rapid scan data acquisition mode was proposed. Chapter 3 deals with different methods for background correction in on-line LC-IR using reference spectra matrices (RSM). The determination of the critical eluent composition for polyethylene glycols using methanol as organic modifier was discussed employing the absorbance ratio as identification parameter for background correction. For the determination of fructose, glucose, sucrose and maltose in beverages employing acetonitrile as organic modifier, again the absorbance ratio was used as identification parameter. A Partial Least Squares (PLS) procedure as well as the application of point-to-point matching algorithms for automated background correction were discussed for background correction in acetonitrile:water gradients using different examples of applications. Chapter 4 deals with the compensation of the background contribution employing column-wise techniques. Polynomial regressions modelling the background absorbance at each wavenumber throughout the gradient run were applied for acetonitrile:water mobile phase J. Kuligowski | NEW INSTRUMENTAL AND CHEMOMETRIC DEVELOPMENTS FOR THE ON-LINE HYPHENATION OF LIQUID CHROMATOGRAPHY AND INFRARED SPECTROSCOPY II gradients. The use of cubic smoothing splines could be demonstrated for background correction under reversed phase gradient conditions employing different alcohols as organic modifiers. In Chapter 5, background correction based on factor analysis and reference spectra matrices was discussed. The contribution of the background absorption to overall LC-IR signals could be compensated using two approaches based on Principal Component Analysis (PCA) and simple-to-use interactive self modeling analysis (SIMPLISMA), obtaining good results in acetonitrile:water systems. Subsequently, multivariate curve resolution-alternating least squares (MCR-ALS) was applied improving peak and spectral resolution and eliminating remaining signal variation due to background absorption and detector drift. The chemometric extraction of ‘analyte-specific’ chromatograms in on-line LC-IR was discussed in Chapter 6. Obtained results confirm that the SBC method is particularly well suited for recovering ‘analyte-specific’ signals from on-line LC-IR chromatograms. The last chapter describes instrumental developments in on-line LC-IR. On-line IR detection in gradient capillary LC using micromachined nanoliter-flow cells was discussed. Four model compounds were separated and identified using an acetonitrile:H2O gradient with limits of detection in the concentration range of 35-94 ng μL-1, representing an increase in mass sensitivity by a factor of approximately 30 as compared to standard LC systems. The last chapter also focuses on the development of LC with on-line dual Quantum Cascade Laser (QC-laser) detection. Compared to state-of-the-art FTIR spectrometers, the use of the developed QC-laser based system provided a significant improvement in both, sensitivity and data acquisition frequency.

Este documento fue elaborado por el Proyecto Plan Nacional de Implementación del Convenio de Estocolmo Sobre Contaminantes Orgánicos Persistentes en el Perú (GEF-SENASA-CONAM-DIGESA-PNUMA) y ha sido transcrito para adaptarse a esta publicación.  La correspondencia debe ser dirigida a cop@digesa.minsa.gob.pe; mquinones@digesa.minsa.gob.pe o visitar www.copsperu.org.pe; www.digesa.minsa.gob.pe; www.senasa.gob.pe; www.conam.gob.pe.