Extended aqueous systems, crystalline ice and liquid water, are studied computationally to investigate their ground state and excited state properties. Methods from solid state physics and quantum chemistry are combined to shed light on some of the unusual properties of water and ice. For the ground state of crystalline ice, density functional theory (DFT) calculations are compared to an ab initio incremental ansatz that utilizes periodic Hartree-Fock together with localized electron correlation calculations. It is shown that the many-body decomposition of the electron correlation converges very fast, allowing the achievement of excellent agreement with experimental data even when limiting correlation energy contributions to two-body terms only. The incremental method is utilized by a computer program that combines the periodic and localized calculations, and allows for structural optimization of the system of interest. The adsorption of water molecules on the surface of ice is studied using DFT. Adsorption is found to be favoured on non-crystallographic adsorption sites, and a slight tendency towards the formation of rough surfaces is reported. The localization of excess electrons at the surface of ice is facilitated by coadsorbed water molecules. For a correct theoretical description of the latter, a self-interaction correction scheme for the excess electron has to be used. However, it is sufficient to limit the self-interaction correction to the excess electron only, since the neutral ice surface itself is well described within conventional DFT. The self-interaction correction scheme is incorporated into a commonly used DFT program package. Optical excitations of crystalline ice are calculated using many-body perturbation theory. Solving the two-particle Bethe-Salpeter equation yields optical spectra in excellent agreement with experimental data. Based on this agreement, an embedding model is developed that reduces the hydrogen bond network to its most important contribution. The model is applied to crystalline ice, where it reproduces the experimental spectral features, and to microscopic liquid water structures obtained from molecular dynamics simulations, where it reproduces the energy shift of the first absorption peak and gives overall good agreement with experiment. The driving force of water’s anomalous optical behaviour is identified.

Dans un superréseau, le confinement modifie les états électroniques et la réduction de symétrie produit une forte anisotropie des propriétés optiques. Dans les super-réseaux GaAs/AlAs cette anisotropie, avec en plus les effets non-linéaires dans les propriétés optiques de GaAs, est un élément essentiel pour la réalisation des convertisseurs de fréquence. Dans mon travail de thèse, j'ai étudié le tenseur diélectrique statique et les spectres d'absorption des superréseaux (GaAs)p/(AlAs)p en fonction de leur période p. Le calcul de ces quantités a été commencé à l'aide de techniques semi-empiriques à l'Université de Pavia, sous la direction du Prof. L.C. Andreani. En particulier, J'ai développé un code pour appliquer la méthode «linear combination of bulk bands» au calcul des structures de bande et des fonctions diélectriques des héterostructures (superréseaux et nanofils). Dans la suite j'ai passé 12 mois au LSI sous la direction du Dr. Lucia Reining, pour réaliser des calculs ab-initio dans le cadre de la théorie de la fonctionnelle de la densité dépendante du temps. Nous avons réussi à bien décrire l'effet du confinement sur les spectres. L'anisotropie de la réponse diélectrique, mesurée par la biréfringence, est déterminée par les contributions du confinement et des champs locaux cristallins : si on tient compte des deux effets, on peut reproduire les données expérimentales. Les ultérieurs effets à N-corps ne donnent que des corrections quantitatives. La comparaison entre les résultats des calculs ab-initio et semi-empiriques, ainsi qu'avec les données de l'expérience, nous a permis de détecter les mécanismes physiques essentiels qui contribuent à l'anisotropie des propriétés optiques et, de plus, de déterminer les limites de validité de la méthode semi-empirique et de l'approche classique des milieux effectifs.

<p>The determination of the optical properties of biological tissue is an important issue in laser medicine. The optical properties define the tissue´s absorption and scattering behaviour, and can be expressed by quantities such as the albedo, the optical thickness and the anisotropy coefficient. During this project, a measurement system for the determination of the optical properties was built up. The system consists of a double integrating sphere set-up to perform the necessary reflection and transmission measurements, and a computer algorithm to calculate the optical properties from the measured data. This algorithm is called Inverse Adding Doubling method, and is based on a one-dimensional transport model. First measurements were conducted with the system, including measurements with phantom media (Intralipid-ink solutions) and with cartilage samples taken from the human knee joint. This work also includes an investigation about the preparation of tissue samples for optical measurements.</p>

<p>In many materials, changes in chemical composition, pressure or temperature can induce metal to insulator transitions. It is recently observed in yttrium hydride, for example, changes from a shiny mirror (YH₂) to a transparent window (YH₃), which has important technological application in optical devices. We have tuned the above transition by choosing <i>pressure</i> instead of composition. Our predicted finding is confirmed by recent experiments and opens a new way to design optical switches.</p><p>The unique role that gold plays in society is to a large extent related to the fact that it is the most <i>noble</i> of all metals.We have studied the noble nature of gold by choosing <i>pressure</i> as tool. Our prediction shows that gold transforms from a face centered cubic to an hexagonal closed packed phase above 200 GPa whereas platinum, another noble metal, does not show any phase transition up to 500 GPa. This prediction has also been confirmed by experiments suggesting that platinum is more noble than gold.</p><p>The growing concern about climate change and fossil fuel availability, the direct conversion of solar irradiation into electricity appears to be an ideal alternative to conventional energy sources. Power generation by solar cells is a direct method of solar energy conversion. We report a new cubic phase of TiO₂ which can be stabilized at ambient conditions. This phase has an absorption three or four orders of magnitude larger than the conventional state-of-the-art solar cell based on anatase TiO₂. Therefore, we are introducing a well established material with a new structure for future generation solar cells. The same effect is also observed in cubic SnO₂.</p><p>Electronic and optical properties of other materials such as Be_xZn_1-xTe, RuO₂ and IrO₂ are also studied in present thesis. In particular, for Be_xZn_1-xTe, we have used composition as a tool to tune the optical properties.</p>

<p>Part I of this thesis is a theoretical background to parts II and III.</p><p>Part II treats the phenomenon of decreased visibility through a glazing due to external water condensation, dew, on the external surface. Some simulations are presented where it is shown that under certain circumstances condensation can be expected. A combination of coatings on the external surface is suggested to overcome the problem of external condesation. It consists of both a coating which decreases the emissivity of the surface and a hydrophilic coating which reduces the detrimental effects to the view through the window.</p><p>Fresnel calculations of the optical properties are used to discuss the feasibility of using different coatings. A new test box was used to verify that the proposed window coatings perform as expected.</p><p>Part III is a study on the angular dependence of solar absorptance in windows. Optical properties vary with the angle of incidence of the incoming light. The variation is different from one window pane to another. </p><p>A model is proposed to approximate the angular variation of the solar absorptance in window panes. The model is semi-empirical and involves dividing the wide range of windows into nine groups. To which group a window belongs, depends on how many panes it has and on the features of the outer pane. The strength of the model is that it can be used without knowing the exact optical properties of each pane of the window. This makes it useful in the many cases when these data are not given by the manufacturer and Fresnel calculations to get the optical properties of the window are not feasible. The model is simple and can be added as an appendix to existing standards for measuring optical properties of windows.</p>

The thermal denaturation of proteins has been extensively studied using several methods including differential scanning calorimetry (DSC). A custom-built optical system was used to study thermal effects on protein as an alternative method to DSC measurements. It was used to investigate the thermal stability of bovine serum albumin (BSA) with a focus on comparisons with published DSC data. In the first study, the effect of protein concentration on the thermal denaturation (Td) of BSA was determined and validated using published DSC data for bovine serum albumin (BSA). The optical rotation (OR) and transmitted light (TL) signals indicating protein conformational changes and gel formation, respectively, were collected during the heating of BSA solutions at ~6��C/min from room temperature to ~85��C. The experiments were performed on 1, 2.5 and 5% (w/v) BSA in 0.01 M phosphate buffer at pH 7 and ionic strength (IS) 0.08. BSA���s Td values obtained from this investigation were consistent with published values and had low experimental variability (CV<2.5%). In agreement with some but not all published data, increasing BSA concentration did not affect its thermal stability. Protein gel formation, however, increased with protein concentration. In the second study, changes in the OR and TL signal of BSA in 0.01 M phosphate buffer at pH 6.1, 7 and 7.9 with IS maintained at 0.04, 0.08 and 0.16 were recorded during the heating of BSA solutions at ~6��C/min from room temperature to ~85��C. BSA showed a maximum and minimum thermostability at pH 7 and 7.9, respectively, consistent with published values determined by DSC. BSA formed opaque gel at pH 6.1 approaching the BSA���s pI values. Increasing IS level did not have a significant effect on BSA���s Td value but promoted gel formation. In the third study, the optical method was applied to investigate the heat stability of BSA as affected by low concentrations of sucrose, trehalose or sorbitol. BSA solutions (2.5% w/v) in the presence of 0 5% sucrose, trehalose and sorbitol were heated at ~6��C/min from ambient temperature to ~85��C. In contrast with published work on the thermal stability of BSA in the presence of higher sugar concentrations, this study showed that increasing sugar concentration did not enhance the thermal stability of this protein. Also, the ability to promote protein stability among sucrose, trehalose and sorbitol were not significantly different. The significance of these studies is that they demonstrate that the custom-built optical methods here developed can be used to study heat-induced protein denaturation and the effect of environmental conditions. Future studies will examine other proteins such as ��-lactoglobulin or ��-lacactalbumin. A further advantage of optical systems is their ability to conduct real-time measurements which could be used for food processing control. / Graduation date: 2007

The objective of this thesis is to provide an initial demonstration of the feasibility of constructing highly transparent active electronic devices. Such a demonstration is successfully achieved in the fabrication of ZnO-based thin film transistors (TFTs) exhibiting transparency greater than ~90% in the visible portion of the electromagnetic spectrum and prototypical n-channel, enhancement mode TFT characteristics. Electrical characterization studies of these ZnO-based transparent TFTs and of CuYO��� / ZnO / ITO p-i-n heterojunction diodes serve to elucidate the mechanisms responsible for the behavior of these devices in particular, and of transparent electronic devices in general. Energy band analysis of the degenerate semiconductor / insulator heterojunction yields insight into the phenomenon of charge injection into an insulator, with important implications for the analysis of devices containing heterojunctions of this nature. Finally, a novel technique for simultaneously characterizing carrier injection into an insulator and interface channel formation, the capacitance-(voltage, frequency) [C-(V,f)] technique, is proposed and employed in the characterization of ZnO-based TFT structures. / Graduation date: 2003

No description available.

In many materials, changes in chemical composition, pressure or temperature can induce metal to insulator transitions. It is recently observed in yttrium hydride, for example, changes from a shiny mirror (YH2) to a transparent window (YH3), which has important technological application in optical devices. We have tuned the above transition by choosing pressure instead of composition. Our predicted finding is confirmed by recent experiments and opens a new way to design optical switches. The unique role that gold plays in society is to a large extent related to the fact that it is the most noble of all metals.We have studied the noble nature of gold by choosing pressure as tool. Our prediction shows that gold transforms from a face centered cubic to an hexagonal closed packed phase above 200 GPa whereas platinum, another noble metal, does not show any phase transition up to 500 GPa. This prediction has also been confirmed by experiments suggesting that platinum is more noble than gold. The growing concern about climate change and fossil fuel availability, the direct conversion of solar irradiation into electricity appears to be an ideal alternative to conventional energy sources. Power generation by solar cells is a direct method of solar energy conversion. We report a new cubic phase of TiO2 which can be stabilized at ambient conditions. This phase has an absorption three or four orders of magnitude larger than the conventional state-of-the-art solar cell based on anatase TiO2. Therefore, we are introducing a well established material with a new structure for future generation solar cells. The same effect is also observed in cubic SnO2. Electronic and optical properties of other materials such as BexZn1-xTe, RuO2 and IrO2 are also studied in present thesis. In particular, for BexZn1-xTe, we have used composition as a tool to tune the optical properties.

This thesis is geared towards using hydrogel nanoparticles in various biotechnological applications. The polymer that was used in making these nanoparticles was poly(N-isopropylacrylamide), which is a thermoresponsive polymer. These particles were used in making fast responsive polymer films, which can be used in optics. It was observed that the rate of deswelling increased as the concentration of the nanoparticles in the film was increased. These particles were also used in making photoresponsive materials. In this case a photoresponsive dye (malachite green) was conjugated to these nanoparticles and in presence of light of appropriate wavelength the particles undergo a phase transition. A core/shell construct was synthesized where the core was composed of degradable cross-links and the shell of composed of non-degradable cross-links. The degradable cross-linker had vicinal diols, which can be cleaved by sodium periodate. Hence after degrading the core, hollow particles were obtained. Zwitterionic particles were made by incorporating a cationic and anionic comonomer. These microgels go from a positively charged state to zwitterionic to negatively charged state on increasing the pH. One of the important potential applications for these microgels is drug delivery. Microgels were used for targeting cancer cells. Folic acid was used as the targeting ligand. The microgels were conjugated with folic acid and were able to target cells that overexpress folate receptors. In one other application core/shell microgels were made which exhibit pore-size dependent permeation of proteins.