This dissertation investigates the design of a quarter-wave polarization transformer and presents some options for a high-performance polarizer in both normally incident and obliquely incident cases. Then, a novel concept for investigating polarization transformation is presented. Based on this concept, the broad axial ratio bandwidth polarizer, composed by anisotropic and chiral media, is accomplished using genetic algorithm. For the normally incident case, we present some methods to eliminate the reflection for designing novel high-performance polarizer in two situations. The polarizers provide perfect linear-to-circular polarization transformation without insertion loss at the center frequency. Then, two novel designs are presented for a high-performance quarter-wave polarizer in the obliquely incident case. In these designs, the material parameters of uniaxial media can be arbitrary. The polarizer is achieved by using only one layer of the uniaxial anisotropic medium without conventional anti-reflection coatings because of the unique property of the oblique incidence. The polarizer can produce a perfect linear-to-circular polarization transformation without any insertion loss at the center frequency. The equivalent circuit concept is presented to study polarization transformations. This concept is more convenient when dealing with polarization transformation problems in multiple layers. The anisotropic medium and the chiral medium can be regarded as circuit elements. Specifically, we show that anisotropic media can be seen as transformers and chiral media as transmission lines. Once the equivalent circuits are determined, the microwave network theory can be used to investigate the polarization transformation. An example is used to demonstrate the transformation from the horizontally polarized wave to the circularly polarized wave employing the equivalent circuit concept. Based on the equivalents concept, we present broad axial ratio bandwidth quarter-wave polarizer composed of mutilayered uniaxial anisotropic media and chiral media using genetic algorithm. In our design, the constitutive parameters of materials can be arbitrary. This broadband polarizer can be realized through the adjustment of the thickness of materials. The nearly optimal and suitable thickness of each cell is determined by using a genetic algorithm. Two numerical examples with three and five cells are presented to validate the design. The axial ratio bandwidths of about 84.1% and 92.8% can be achieved, more than double the maximum theoretical bandwidth for the case of the single uniaxial anisotropic slab.

Abstract Anisotropic wet etching is one of the key technologies for the microstructure fabrication in Micro Electro Mechanical Systems (MEMS). Agitation technique is one of the key parameters to affect significantly the quality of silicon anisotropic wet etching, which includes the etch rate and surface roughness. In general, magnetic stirring is used during silicon anisotropic wet etching operation. The ultrasonic agitation and add surfactant have been to replaced and to proceed a series of experiment for KOH solution and TMAH solution in this study. The results show that the ultrasonic agitation can reduce the surface roughness and achieve the high-quality etching surface, its roughness even is only about Ra 47.5Å. Besides, the etch rate is also increased slightly. But it is easily to cause the damage of the microstructure. The addition of anionic surfactant to the KOH solution without any agitation condition can achieve the same at the etching performance of the ultrasonic agitation. The addition of anionic surfactant and nonionic surfactant to the TMAH solution without any agitation condition can achieve the same at the etching performance of the ultrasonic agitation. TMAH solution adds nonionic surfactant not only improves the surface roughness, but also retards the phenomenon of the undercut. Keyword¡Ganisotropic wet etching, magnetic stirring, ultrasonic, surfactant

This dissertation presents the integration of a damage viscoelastic constitutive relationship with a viscoplastic relationship in order to develop a comprehensive anisotropic damage viscoelastic-viscoplastic model that is capable of capturing hot mix asphalt (HMA) response and performance under a wide range of temperatures, loading rates, and stress states. The damage viscoelasticity model developed by Schapery (1969) is employed to present the recoverable response, and the viscoplasticity model developed at the Texas Transportation Institute (TTI) is improved and used to model the irrecoverable strain component. The influence of the anisotropic aggregate distribution is accounted for in both the viscoelastic and viscoplastic responses. A comprehensive material identification experimental program is developed in this study. The experimental program is designed such that the quantification and decomposition of the response into viscoelastic and viscoplastic components can be achieved. The developed experimental program and theoretical framework are used to analyze repeated creep tests conducted on three mixes that include aggregates with different characteristics. An experiment was conducted to capture and characterize the three-dimensional distribution of aggregate orientation and air voids in HMA specimens. X-ray computed tomography (CT) and image analysis techniques were used to analyze the microstructure in specimens before and after being subjected to triaxial repeated creep and recovery tests as well as monotonic constant strain rate tests. The results indicate that the different loading conditions and stress states induce different microstructure distributions at the same macroscopic strain level. Also, stress-induced anisotropy is shown to develop in HMA specimens.

Zr-2.5Nb is used as pressure-tube material in CANDU (CANada Deuterium Uranium) reactors. Under reactor operating conditions, pressure tubes undergo anisotropic dimensional changes, and thermal creep contributes to this deformation. In a previous study, the limited textures available to Zr-2.5Nb significantly restricted the understanding of the relationship between texture and creep anisotropy. Moreover, there has been no research performed to investigate textures and stress states simultaneously for this material, which would provide a valuable resource for developing creep anisotropy models and optimizing textures to improve creep resistance. Cold-worked Zr-2.5Nb fuel sheathing (FS) and micro pressure tubes (MPT) with various textures and microstructures were used as experimental materials. The tubes were machined as thin-wall standard (ratio of axial to transverse stress 0.5) and end-loaded (ratio of axial to transverse stress = 0.25~0.75) capsules and were internally pressurized and sealed. Stress and temperature dependence tests were performed on standard capsules under transverse stresses of 100~325MPa at 300~400°C to establish a regime in which dislocation glide is the likely strain producing mechanism. An average stress exponent vaule of 6.4 was obtained, indicating that dislcation creep is the likely dominant mechanism. Texture and stress state dependence tests were performed on standard and end-loaded capsules under a nominal transverse stress of 300MPa at 350°C. It was evident that creep anisotropy strongly correlates with textures under different stress states. A self-consistent polycrystalline model SELFPOLY7 based only upon crystallographic texture was employed to simulate the creep anisotropy of the tubes. However, the model cannot fit all the experimental data well by using a uniform critical resolved shear stress (CRSS) ratio of the operating slip systems. A modification was made, by taking into account the pre-existing dislocation distributions generated during cold work, and an improvement was achieved. This work provides a valuable resource for understanding the effect of texture, stress states and microstructure on anisotropic creep of cold-worked Zr-2.5Nb tubes. The current research also provides a strategic direction to improve creep anisotropy predictions. The large sets of experimental data supply a database to evaluate and develop improved models. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-08-14 11:16:08.67

This project was designed to investigate the possibility of producing alignment layers for liquid crystal devices by cross-linking thin films containing anisotropic polymer bound chromophores via irradiation with polarised ultra violet light. Photocross-linkable polymers find use in microelectronics, liquid crystal displays, printing and UV curable lacquers and inks; so there is an increasing incentive for the development of new varieties of photopolymers in general. The synthesis and characterisation of two new photopolymers that are suitable as potential alignment layers for liquid crystal devices are reported in this thesis. The first polymer contains the anthracene chromophore attached via a spacer unit to a methacrylate backbone and the second used a similarly attached aryl azide group. Copolymers of the new monomers with methyl methacrylate were investigated to establish reactivity ratios in order to understand composition drift during polymerisation.

Indiana University-Purdue University Indianapolis (IUPUI) / Articular cartilage (AC) is a strong but flexible connective tissue that covers and protects the end of the long bones. Although cartilage has excellent friction and wear properties that allow smooth joint function during daily activities, these properties are not fully understood. Many material properties of cartilage are anisotropic and vary with anatomic location and the composition of the tissue, but whether this is also true for cartilage friction and wear has not been previously determined. Furthermore, cartilage disease and injury are major health concerns that affect millions of people, but there are few available treatments to prevent the progression of cartilage degeneration. Collagen crosslinking may be a potential treatment to reduce cartilage wear and slow or prevent the progression of cartilage disease. The objectives of this thesis were to investigate the relationships between the friction/wear characteristics of cartilage and the orientation of the preferred fiber direction, the anatomic location of the tissue, the composition of the tissue, and exogenous photochemical crosslinking. In the superficial zone, AC has preferential fiber direction which leads to anisotropic material behavior. Therefore, we hypothesized that AC will show anisotropic behavior between longitudinal and transverse direction in an accelerated, in vitro wear test on bovine cartilage in terms of friction and wear. This hypothesis was proven by the quantification of glycosaminoglycans released from the tissue during the wear test, which showed that more glycosaminoglycans were released when the wear direction was transverse to the direction of the fibers. However, the hydroxyproline released from the tissue during the wear test was not significantly different between the two directions, nor was the coefficient of friction. The material properties of AC can also vary with anatomic location, perhaps due to differences in how the tissue is loaded in vivo. We hypothesized that cartilage from a higher load bearing site will give better wear resistance than cartilage from lower load bearing regions. However, no differences in friction or wear were observed between the different anatomic locations on the bovine femoral condyles. The concentration of collagen, glycosaminoglycans, cells and water in the tissue was also quantified, but no significant differences in tissue composition were found among the locations that were tested. Although wear did not vary with anatomic location, variation in the wear measurements were relatively high. One potential source of variation is the composition of the cartilage. To determine whether cartilage composition influences friction and wear, a correlation analysis was conducted. An accelerated, in vitro wear test was conducted on cartilage from bovine femoral condyles, and the tissue adjacent to the wear test specimens was analyzed for collagen, glycosaminoglycan, cell, and water content. Because wear occurs on the cartilage surface, the superficial zone of the cartilage might play an important role in wear test. Therefore, composition of the adjacent cartilage was determined in both the superficial zone and the full thickness of the tissue. A significant negative correlation was found between wear and collagen content in the full thickness of the tissue, and between the initial coefficient of friction and the collagen content in the superficial zone. This correlation suggests that variation in the collagen content in the full thickness of the cartilage partially explains differences in amount of wear between specimens. The wear resistance of cartilage can be improved with exogenous crosslinking agents, but the use of photochemical crosslinking to improve wear resistance is not well understood. Two photochemical crosslinking protocols were analyzed to improve the wear resistance of the cartilage by using chloro-aluminum phthalocyanine tetrasulfonic acid (CASPc) and 670nm laser light. The cartilage treated with the two crosslinking protocols had lower wear than the non-treated group without changing the friction properties of the cartilage.

<p> The semi-classical path-integral method for finding the magnetoconductivity is specialised to cubic one-electron metals having a spherical Fermi surface, isotropic effective mass and anisotropic scattering times. Properties of the conductivity and resistivity tensors are deduced for this special case, in more detail for high magnetic fields. The magnetoconductivity for potassium, and the quantities derived from it - magnetoresistance and induced torque - are calculated as functions of temperature, field strength, impurity concentration and crystal orientation. Comparison is made with experimental results.</p> / Thesis / Master of Science (MSc)

<p> Layers of plasticene lubricated with talcum powder were compressed in directions perpendicular to the layering. Normal kink bands oblique to the principal compression direction were produced. These structures were predicted by Cosgrove (1972) after a theory developed by Biot (1965). Other multilayers, with the layering oblique to the principal compression direction, were compressed and these developed instabilities also. </p> <p> The normal kink bands were analysed geometrically. It was found that variation in layer thickness provided the best description and also provided a statement of the state of strain of the final deformation. </p> / Thesis / Bachelor of Science (BSc)

In recent years, there has been an increasing interest in the study of hydrophobic surfaces. Hydrophobic surfaces have been used in multiple applications in microfluidic devices due to their properties of self-cleaning, and also in deicing products. Conventionally, hydrophobic surfaces were created by laser cutting, self-assembly and other chemical processing methods. However, in most of these methods, hydrophobicity of the surface cannot be maintained for an extended time or restricted to limited set of materials. A low-cost, high-throughput method to generate highly hydrophobic anisotropic surface has been developed in this thesis which uses Computer Numerical Control (CNC) machining employing diamond tools whose tips have been micro-structured using Focused Ion Beam (FIB) built tips. The versatility of this method has been demonstrated by machining both metal and polymeric materials. Significant anisotropic wetting has been observed on the machined surface with the anisotropic contact angle can reach up to 71.6 degree and highly-hydrophobic property with contact angle of 163.1degree on 6061 Aluminum Alloy and 155.7 degree on PMMA surface. / Thesis / Master of Science in Mechanical Engineering (MSME)

This thesis will present the synthesis, characterization and magnetic measurements of lanthanide complexes with varying nuclearities (Ln, Ln2, Ln3 and Ln4). EuIII, GdIII, TbIII, DyIII, HoIII and YbIII have been selected as the metal centers. Eight polydentate Schiff-base ligands have been synthesized with N- and mostly O-based coordination environments which chelate 7-, 8- or 9-coordinate lanthanide ions. The molecular structures were characterized by single crystal X-ray crystallography and the magnetic properties were measured using a SQUID magnetometer. Each chapter consists of crystal structures and magnetic measurements for complexes with the same nuclearity. There are eight DyIII SMMs in this thesis which are discrete molecules that act as magnets below a certain temperature called their blocking temperature. This phenomenon results from an appreciable spin ground state (S) as well as negative uni-axial anisotropy (D), both present in lanthanide ions owing to their f electron shell, generating an effective energy barrier for the reversal of the magnetization (Ueff). The ab initio calculations are also included for the SMMs with high anisotropic energy barriers to understand the mechanisms of slow magnetic relaxation in these systems.