Tyrosine hydroxylase (TyrH) catalyzes the rate-limiting step in the synthesis of the catecholamine neurotransmitters dopamine, epinephrine, and norepinephrine. Phosphorylation of Ser40 of rat TyrH activates the enzyme by decreasing the affinity for catecholamines. In humans, there are four different TyrH isoforms with varying lengths for the regulatory domain. DOPA and dopamine binding studies were performed on the phosphorylated and unphosphorylated human isoforms. The Kd for DOPA was increased two times upon phosphorylation of hTyrH1, but no change was seen for hTyrH4; the Kd value decreased with the increase in the size of regulatory domain. The small effect on the Kd value for DOPA upon phosphorylation of hTyrH suggests that DOPA does not regulate the activity of hTyrH. Dopamine binds very tightly and upon phosphorylation the affinity for dopamine is decreased. This Kd value decreases with the increase in the length of the regulatory domain. The crystal structures of substrate complexes of the homologous enzyme phenylalanine hydroxylase (PheH) show a large movement of a surface loop (residues 131-155) upon amino acid binding. The corresponding loop residues (175-200) in TyrH play an important role in DOPA formation. This conformational change in TyrH loop was studied with fluorescence anisotropy. Three tryptophan residues in the TyrH, at positions 166, 233, and 372, were mutated to phenylalanine, and Phe184 was mutated to tryptophan. An increase in anisotropy was observed in the presence of phenylalanine and 6-methyl-5-deazatetrahydropterin (6M5DPH4), but the magnitude of the change of anisotropy with 6M5DPH4 was greater than that with phenylalanine. Further characterization of the sole tryptophan in the loop showed a decrease in the amplitude of the local motion only in the presence of 6M5DPH4 alone. The conformational change in wild type TyrH was examined by H/D exchange LC/MS spectroscopy in the presence of the natural ligands. Time-course dependent deuterium incorporation into the loop in the presence of ligands indicated that the pterin alone can induce the conformational change in the loop irrespective of whether iron is reduced or oxidized. From these results, one can conclude that the loop undergoes a conformational change upon pterin binding, making the active site better for amino acid binding.

Rubbing alignment is widely used in display industry, Rubbing cause anisotropy in rubbed polyimide thin film influence the alignment of Liquid Crystal. The major part of this article is to analyze surface optical anisotropy of rubbed polyimide thin film. RAS signals and surface free energies of rubbed polyimide thin film with different rubbing strength are measured, and relationship between anisotropy of surface and rubbing strength is discussed. The mechanism of alignment can be understood by this work. Reflection Anisotropy Spectroscopy (RAS) has been used in Semiconductor as a tool to monitor crystal growth for many years. RAS is a non-contact and non-destructive measurement method. It only measures the difference of two orthogonal complex reflection signals and optical anisotropy of surface. It¡¦s very sensitive to the anisotropy of surface. In the current studies, RAS has been used to detect surface anisotropy of rubbed polymer. We measured the surface free energy of the rubbed polyimide thin films. It has been found that surface free energy is of anisotropy due to the application of mechanical rubbing to the polymer surface. Pretilt angle influences the alignment of liquid crystals. The molecule orientation of PI surface and anisotropy of rubbed PI surface effect pretilt angle¡CPretilt angles measured by pretilt angle measurement system compare with RAS signals. RAS signals, anisotropy of surface free energies, and pretilt angles are increasing with increasing rubbing strength.

Rutting is one of the major distresses in asphalt pavements and it increases road roughness and traps water, which leads to wet-weather accidents due to the loss of tire-pavement friction and hydroplaning. The fundamental mechanisms of rutting have not been well addressed because of the complexity of asphalt mixtures. A comprehensive characterization of the asphalt mixtures in compression was accomplished by mechanistically modeling the inherent anisotropy, viscoelasticity, viscoplasticity and viscofracture of the material. The inherent anisotropy due to preferentially oriented aggregates was characterized by a microstructural parameter (i.e., modified vector magnitudes) which could be rapidly and accurately measured by lateral surface scanning tests and physically related to anisotropic modulus ratio. The anisotropic viscoelasticity was represented by complex moduli and Poisson's ratios in separate orthogonal directions that were determined by an efficient testing protocol. Master curve models were proposed for the magnitude and phase angle of these complex variables. The viscoplasticity were intensively modeled by an anisotropic viscoplastic model which incorporated 1) modified effective stresses to account for the inherent and stress-induced anisotropy; 2) a new model to provide a smooth and convex yield surface and address the material cohesion and internal friction; 3) a non-associated flow rule to consider the volumetric dilation; and 4) a temperature and strain rate dependent strain hardening function. The viscofracture resulting from the crack growth in compression led to the stress-induced anisotropy and was characterized by anisotropic damage densities, the evolution of which was modeled by the anisotropic pseudo J-integral Paris' laws. Results indicated that the undamaged asphalt mixtures were inherently anisotropic and had vertical to horizontal modulus ratios from 1.2 to 2.0 corresponding to the modified vector magnitudes from 0.2 and 0.5. The rutting would be underestimated without including the inherent anisotropy in the constitutive modeling. Viscoelastic and viscoplastic deformation developed simultaneously while the viscofracture deformation occurred only during the tertiary flow, which was signaled by the increase of phase angle. Axial and radial strain decomposition methods were proposed to efficiently separate the viscoplasticity and viscofracture from the viscoelasticity. Rutting was accelerated by the occurrence of cracks in tertiary flow. The asphalt mixture had a brittle (splitting cracks) or ductile (diagonal cracks) fracture when the air void content was 4% and 7%, respecitvely. The testing protocol that produced the material properties is efficient and can be completed in one day with simple and affordable testing equipment. The developed constitutive models can be effectively implemented for the prediction of the rutting in asphalt pavements under varieties of traffic, structural, and environmental conditions.

No description available.

The purpose of this thesis is to study the relation between surface optical anisotropy of polyimide thin film with different rubbing strength and liquid crystal alignment by means of reflection anisotropy spectroscopy (RAS). We discuss the surface properties of rubbed polyimide thin film by measuring the surface roughness, surface free energy and pretilt angle. RAS is a non-contact optical probe of surfaces. It measures the difference in reflectance of normal incidence linearly polarized light between two orthogonal directions in the surface plane, and we can obtain the surface character of sample by analyzing the signals. It is isotropic of polyimide thin film surface without rubbing, and reflection anisotropy (RA) signal is zero. The non-zero RA signal, i.e. anisotropic of surface, is revealed because of rubbed polyimide thin film surface. The RA signal is increasing with an increase in rubbing strength. In the results, we found that the pertilt angle is increasing with a decrease in surface free energy, and discovered the correlation between RA signal strength of characteristic wavelength and pretilt angle of liquid crystal at the rubbed polyimide thin film.

In our earlier research, we found the MOKE signal incident from 45 degree would cause perpendicular signal to couple with the longitudinal one. To distinguish the signal from one to another, we arranged 45 degree and 0 degree optical setup for the measurement of longitudinal and perpendicular respectively. However, hysteresis loops are only observed in the longitudinal direction. To measure smaller signal in our experiment, we reduced the noise level by one order and thus improved the signal to noise ratio. It¡¦s ten times better then previous result. Under smaller signal or worse S/N ratio condition, we still measured the MOKE signal. In order to quantitatively analyze the current-induced field, we made a metal coil and try to measure the bias produced by the field. And we injected the reverse current-induced field, , try to counteract the bias of hysteresis loop which is induced by sample current. Besides, we also dosed oxygen on the sample and measured the MOKE signal. There was no change comparing with which is measured in gas-free condition. But we found the coercivity became larger after annealing to 300K, and the current-induced bias in oxygen become smaller.

The hot-workability of Titanium (Ti) alloys is of current interest to the aerospace industry due to its widespread application in the design of strong and light-weight aircraft structural components and engine parts. Motivated by the need for accurate simulation of large scale plastic deformation in metals that exhibit macroscopic plastic anisotropy, such as Ti, a constitutive model is developed for anisotropic materials undergoing plastic deformation coupled with ductile damage in the form of internal cavitation. The model is developed from a rigorous micromechanical basis, following well-known previous works in the field. The model incorporates the porosity and void aspect ratio as internal damage variables, and seeks to provide a more accurate prediction of damage growth compared to previous existing models. A closed form expression for the macroscopic yield locus is derived using a Hill-Mandel homogenization and limit analysis of a porous representative volume element. Analytical expressions are also developed for the evolution of the internal variables, porosity and void shape. The developed yield criterion is validated by comparison to numerically determined yield loci for specific anisotropic materials, using a numerical limit analysis technique developed herein. The evolution laws for the internal variables are validated by comparison with direct finite element simulations of porous unit cells. Comparison with previously published results in the literature indicates that the new model yields better agreement with the numerically determined yield loci for a wide range of loading paths. Use of the new model in continuum finite element simulations of ductile fracture may be expected to lead to improved predictions for damage evolution and fracture modes in plastically anisotropic materials.

The aggregate base layer is a vital part of the flexible pavement system. Unlike rigid pavements, the base layer provides a substantial contribution to the load bearing capacity in flexible pavements, and this contribution is complex: stress dependent, moisture dependent, particle size dependent, and is anisotropic in nature. Furthermore, the response of the aggregate layer in the pavement structure is defined not only by resilient properties of the base layer but also by permanent deformation properties of the aggregate layer. Before the benefits of revolutionary changes in the typical pavement structures, such as deep unbound aggregate base (UAB) layers under thin hot mix asphalt surfaces and inverted pavement systems can be justified, an accurate assessment of the UAB is required. Several researchers identified that in order to properly assess the contribution of the UAB in the pavement structure, it is necessary to consider not only the vertical modulus but also the horizontal modulus as this substantially impacts the distribution of stresses within the pavement structure. Anisotropy, which is defined as the directional dependency of the material properties in unbound granular bases, is inherent even before the aggregate layer is subjected to traffic loads due to random arrangement of particles upon compaction. Distribution of particle contacts is dominated by the geometry of the aggregates as well as the compaction effort at the time of construction. Critical pavement responses and therefore performance of flexible pavements are significantly influenced by the level of anisotropy of aggregate layers. There are several ways to characterize the level of anisotropy in unbound aggregate systems. Previous research at Texas A&M University suggests functions of fitting parameters in material models (kvalues) as characterizers of the level of anisotropy. In the realm of geotechnical engineering, the ratio of the horizontal modulus to vertical modulus is commonly referred to as the level of anisotropy. When the vertical and horizontal moduli are equal, the system is isotropic, but when they differ, the system is anisotropic. This research showed that the level of anisotropy can vary considerably depending on aggregate mix properties such as gradation, saturation level, and the geometry of the aggregate particles. Cross anisotropic material properties for several unbound and stabilized aggregate systems were determined. A comprehensive aggregate database was developed to identify the contribution level of aggregate features to the directional dependency of material properties. Finally a new mechanistic performance protocol based on plasticity theory was developed to ensure the stability of the pavement foundations under traffic loads.

The influence of elastic anisotropy on seismic wave propagation is often neglected for the sake of simplicity. However, ignoring anisotropy may lead to significant errors in the processing of seismic data and ultimately in a poor image of the subsurface. This is especially true in wide-aperture Vertical Seismic Profiles where waves travel both vertically and horizontally. Anisotropy has been neglected in wavefront construction methods of seismic ray-tracing until Gibson (2000), who showed they are powerful tools to simulate seismic wave propagation in three-dimensional anisotropic subsurface models. The code is currently under development using a C++ object oriented programming approach because it provides high flexibility in the design of new components and facilitates debugging and maintenance of a complex algorithm. So far, the code was used to simulate propagation in homogeneous or simple heterogeneous anisotropic velocity models mainly designed for testing purposes. In particular, it has never been applied to simulate a field dataset. We propose here an analytical method involving little algebra and that allows the design of realistic heterogeneous anisotropic models using the C++ object oriented programming approach. The new model class can model smooth multi-layered subsurface with gradients or models with many dip variations. It has been used to model first arrival times of a wide-aperture VSP dataset from the Gulf of Mexico to estimate the amount of anisotropy. The proposed velocity model is transversely isotropic. The anisotropy is constant throughout the model and is defined via Thomsen's parameters. Values in the final model are epsilon = 0.055 and delta = -0.115. The model is compatible with the a priori knowledge of the local geology and reduces the RMS average time difference between measured and computed travel times by 51% in comparison to the initial isotropic model. These values are realistic and are similar to other measurements of anisotropy in the Gulf of Mexico.

This dissertation presents the development of a method for quantitative integration of seismic (elastic) anisotropy attributes with reservoir performance data as an aid in characterization of systems of natural fractures in hydrocarbon reservoirs. This new method incorporates stochastic Discrete Feature Network (DFN) fracture modeling techniques, DFN model based fracture system hydraulic property and elastic anisotropy modeling, and non-linear inversion techniques, to achieve numerical integration of production data and seismic attributes for iterative refinement of initial trend and fracture intensity estimates. Although DFN modeling, flow simulation, and elastic anisotropy modeling are in themselves not new technologies, this dissertation represents the first known attempt to integrate advanced models for production performance and elastic anisotropy in fractured reservoirs using a rigorous mathematical inversion. The following new developments are presented: . • Forward modeling and sensitivity analysis of the upscaled hydraulic properties of realistic DFN fracture models through use of effective permeability modeling techniques. . • Forward modeling and sensitivity analysis of azimuthally variant seismic attributes based on the same DFN models. . • Development of a combined production and seismic data objective function and computation of sensitivity coefficients. . • Iterative model-based non-linear inversion of DFN fracture model trend and intensity through minimization of the combined objective function. This new technique is demonstrated on synthetic models with single and multiple fracture sets as well as differing background (host) reservoir hydraulic and elastic properties. Results on these synthetic control models show that, given a well conditioned initial DFN model and good quality field production and seismic observations, the integration procedure results in convergence of both fracture trend and intensity in models with both single and multiple fracture sets. Tests show that for a single fracture set convergence is accelerated when the combined objective function is used as compared to a similar technique using only production data in the objective function. Tests performed on multiple fracture sets show that, without the addition of seismic anisotropy, the model fails to converge. These tests validate the importance of the new process for use in more realistic reservoir models.