No description available.

We examine a model of solid-solid phase transitions that includes thermo-elastic effects and an order parameter. The model is derived as a special case of the Gurtin-Fried model posed in one space dimension with a symmetric triple-well free energy in which the relative heights of the wells vary with temperature. We examine the temperature independent case, showing existence of a unique classical solution of a regularized system of partial differential equations using semigroup theory. This is followed by numerical study of a finite element algorithm for the temperature independent model. Finally, we present computational material concerning the temperature dependent model. / Ph. D.

Configuration-bias Monte Carlo simulation is used to investigate the structural property of liquid crystal. Our results show that the surface molecules of the smaller nanoclusters are formed the helical structure, In addition, the morphologies of nanoclusters show a tube-like structure when the surface molecules formed the helical structure; however, as the surface molecules do not form the helical structure, the morphologies of nanoclusters become a ball-like structure. For the tube-like structure, because of the configurations of nanoclusters are simpler, the nanoclusters will show an order structure. In the case of the ball-like structure, the molecules will attract with others, so the nanocluster reveals an ordered structure at local area. According to the result of the averaged order parameters, as the averaged order parameter larger than 0.5, the configuration of nanocluster will be a tube-like structure, while as the averaged order parameters smaller than 0.5, the configuration of nanocluster will form a ball-like structure.

In recent years, technologies using supercritical water have gained considerable attention, mainly due to versatility and uniqueness of water at elevated temperatures and pressures. The physical conditions required to generate supercritical water also make it prone to large intrinsic thermal and density fluctuations, exacerbated if there are impurities present in the system. These fluctuations induce nucleation, the initial stage of a first-order phase transition, and subsequent mixing of the new phase within the original phase. When this new phase reaches its critical size it grows irreversibly to macroscopic proportions, otherwise, tending to disintegrate. The presence of a polydispersed solid phase within the supercritical phase is responsible for unfavorable phenomena such as particle deposition and corrosion of structural components, both of which result in decreased efficiency and reliability of the supercritical water employing process. Molecular Dynamics (MD) simulation method has been the primary tool of investigation. Molecular motions are tracked on the femto and picosecond time-scales which are particularly important for the study of nucleation. Sodium chloride has been chosen in this research since it is computationally tractable and is unavoidably involved in most industrial water based applications. Cluster size distributions, the size of critical nuclei and cluster life-times are reported. The size distribution of emerging clusters shows a very strong dependence on the system’s density, with larger clusters preferentially formed at lower densities. Also, a materials science application is presented where the rapid quenching of hydrothermally formed sodium chloride clusters leads to a variety of nanostructures, characterizable by prominent vibrational modes. And lastly, during the conditions prior to crystallization, water is not only physically adsorbed to the cluster’s surface but also exists in a “confined” state within subsurface regions for several picoseconds during the nucleation process. A mechanism for the sodium chloride hydrolysis reaction is presented as well as showing that asymmetric electrostatic fields generated by the coalescing ions are on the order of 1010 V/m, sufficient to drive the hydrolysis of confined water molecules. The HCl molecule and hydroxide ions are formed, with the latter segregating preferentially to sub-surface regions in the amorphous NaCl particles. Both HCl and hydroxide are implicated in corrosion. / Thesis (Master, Chemistry) -- Queen's University, 2008-11-03 13:54:56.021

Polarized Raman Spectroscopy (PRS) is one of the experimental methods which can be employed to deduce orientational order parameters, e.g. 〈P_200 〉, 〈P_400 〉, in liquid crystals from the experimental depolarization ratio graph via fitting. However, it has long been known that the order parameters deduced from the different vibrational modes are found to be different within the same sample. As a result, only certain vibrational modes can be reliably selected for analysis, limiting the application of PRS. The possible explanations are discussed in this thesis. The first explanation is given by considering a dipole tilt β_0 which is defined as the tilt angle of the dipole vibrational direction and the molecular long axis. A second explanation comes from assuming different vibrational symmetries, i.e. cylindrical or elliptic cylindrical. Molecular biaxial order parameters are introduced in both explanations. A systematic check via calculation shows that a common set of order parameters (including molecular biaxial order parameters) can be obtained with different depolarization ratio graphs when the explanations are considered. Both depolarization ratio graphs can also agree well with that obtained from phenyl and cyano stretching modes experimentally. A supplementary discussion shows that by using the first explanation, 〈P_400 〉 which, in previous fitting, shown an excessive value by using cyano stretching mode is reduced (15% reduced at β_0=15°, 〈P_402 〉=0.0536). PRS is also employed to analyse the order parameters in a bent-core system using a molecular model with the bend angle Ω and tilt angle B_0. The effects of each of the uniaxial and phase biaxial order parameters are considered. With a total Raman tensor generated by the sum of Raman tensor from each arm, reasonable uniaxial order parameters fitting values can be obtained from PRS without considering biaxial order parameters. These results agree well with those deduced from the refractive index measurements, which shows a new approach to the investigation of bent-core systems. However, it is also shown that introducing phase biaxial order parameters can’t provide robust fitting, leading inaccurate fitting values in the end. Several different liquid crystals (5CB, E7, HAT-6 and SSY) have been examined on seeking graphene/graphene oxide dispersions in liquid crystal systems. Unfortunately, no stable dispersion was obtained by applying simple experimental techniques. However, a highlight comes from the test of a lyotropic liquid crystal formed by a discotic molecule in NMP suggesting a possible dispersion medium for graphene. Meanwhile, by using Raman spectroscopy, the interaction between liquid crystal molecules and graphene can be obtained from the peak shift of vibrational modes. The experimental results suggest a stronger interaction in E7 compared to 5CB. No shift in ZLI-1695 indicates the different effects from the rigid core. Further, the discotic liquid crystal (HAT-6) shows a strong interaction with graphene. These facts lead to a conclusion that the interaction still exists in the graphene/liquid crystal dispersion providing a guide on controlling and optimizing the dispersion quality for the future research.

The Kitaev model has become a source of much excitement in the field of condensed matter. It is a two dimensional model of spins ½ on a honeycomb lattice with bond-dependent interactions. Its interesting properties include a quantum spin liquid ground state and anyonic excitations. These properties could lead to exciting applications in quantum computing if materials were found to behave similarly to the Kitaev model. Such materials have been found, however the Kitaev model is too simple to describe these materials and additional interactions must be considered. The Heisenberg interaction is one such additional interaction. As such, we can define the Kitaev-Heisenberg model by combining the Kitaev and Heisenberg interactions. We can now ask ourselves if the quantum spin liquid ground state and anyonic excitations still exist in the Kitaev-Heisenberg model. To answer this question, a non-local string order parameter has been defined which is non-zero inside the quantum spin liquid phase and zero outside of it. This string order parameter was shown to exist and survive the Heisenberg interaction on the 2-leg ladder. In this thesis, we look to expand this result to multileg ladders such as the 3-leg, 4-leg, and 5-leg ladders to see if the string order parameter survives in the Kitaev-Heisenberg model in 2 dimensions. Our results show that the string order parameter does exist in multileg ladders, however the phase space window in which it survives the Heisenberg interaction is narrower than in the 2-leg ladder. / Thesis / Master of Science (MSc)

No description available.

Understanding the mechanisms by which proteins act on membrane surfaces is fundamental if we are to exploit their capabilities or halt the progression of the diseases they are associated with. Arguably, the best way to study these interactions is by using techniques that can obtain molecular-scale information, in real time and under physiologically relevant conditions. Studying supported lipid bilayer systems with high spatial resolution tools, such as atomic force microscopy (AFM), and high temporal resolution techniques, such as polarized total internal reflection fluorescence microscopy (pTIRFM), allows us to meet these requirements [1]. The goal of this project is to use methods that are currently available and further their applications and capabilities to provide insight into the mechanisms by which amyloidogenic and antimicrobial peptides act on membranes.

Understanding the mechanisms by which proteins act on membrane surfaces is fundamental if we are to exploit their capabilities or halt the progression of the diseases they are associated with. Arguably, the best way to study these interactions is by using techniques that can obtain molecular-scale information, in real time and under physiologically relevant conditions. Studying supported lipid bilayer systems with high spatial resolution tools, such as atomic force microscopy (AFM), and high temporal resolution techniques, such as polarized total internal reflection fluorescence microscopy (pTIRFM), allows us to meet these requirements [1]. The goal of this project is to use methods that are currently available and further their applications and capabilities to provide insight into the mechanisms by which amyloidogenic and antimicrobial peptides act on membranes.

Pendant les dernières décennies les chercheurs ont étudié l'interaction entre des inclusions membranaires avec leur environnement et plus particulièrement avec la bicouche lipidique. On trouve dans la litérature beaucoup d'études théoriques et de simulations numériques sur ce sujet mais très peu d'expériences ont été menés là-dessus.Nous avons effectué des études systématiques afin de quantifier le potentiel d'interaction entre deux types d'inclusions au sein de la même couche et entre des couches adjacentes de plusieurs types de membranes ceci en variant surtout la concentration de particules dopantes, mais aussi d'autres paramètres pertinents : le type de tensioactif, l'épaisseur de la membrane, le contenu en cholestérol, la température, le degré d'hydratation. Pour cette fin nous avons utilisé la diffraction des rayons X aux petits angles et nous avons constaté que le potentiel d'interaction peut être décrit par une exponentielle décroissante en fonction de la concentration et de la température d'inclusion et qu'il dépend largement de la teneur en cholestérol et du degré d'hydratation.D'autre part, nous avons étudié l'effet de la gramicidine, un peptitde membranaire, sur l'ordre local des chaînes acyles de lipides et de tensioactifs. Cette étude a été menée en utilisant deux techniques différentes: en premier lieu la résonnance magnétique nucléaire, (DROSS-NMR) qui permet de détecter le changement d'ordre dans l'orientation des chaînes acyles, et en second lieu par diffraction des rayons X aux grands angles afin de déterminer le changement d'ordre dans la position des chaînes acyles. Nous avons trouvé que le dopage de la gramicidine dans les membranes rigidifie les chaînes acyles et dans un cas aussi les têtes polaires et en plus induit une modification de l'ordre local de ces chaînes. / For years scientists have been studying the interaction of membrane inclusions with their environment and more particularly with the lipid bilayer.This field has been based on theoretical approaches and numerical simulation and lack experiments.We performed systematic studies in order to quantify the interaction potential between two types of inclusions within the same layer and between adjacent layers in several kinds of membranes and tried to elucidate the influence of the relevant parameters: the type of lipids or surfactants, the cholesterol content, the hydration degree, the type of inclusions and the membrane thickness using small-angle X-ray scattering. We found that the interaction potential can be described by a decreasing exponential as a function of inclusion concentrations and temperature and depends largely on the cholesterol content and hydration degree.On the other hand, we also studied the effect of the peptide inclusions on the local order of lipid and surfactant acyl chains using two different techniques: DROSS-NMR technique to detect the changes in the orientational order and WAXS technique to detect the changes in the positional order of the acyl chains. We found that inserting these peptides inclusions within the membrane rigidifies the acyl chains and sometimes even the headgroups and modifies their local order.