Materials which flow like fluids, but possess anisotropic properties like molecular crystals, are called 'liquid crystals'. Studies of liquid crystals contribute to our understanding of how molecular orientation influences macroscopic properties. This thesis presents experimental and theoretical investigations of molecular order and dynamics in nematic liquid crystal systems. First, deuterium nuclear magnetic resonance is used to determine the degree of orientational order of both components of a liquid crystal mixture simultaneously. The temperature dependence of the four order parameters is interpreted using a newly developed mean field theory of nematic binary mixtures composed of biaxial molecules. Next, mean field theory is applied to predict the phase behavior of arbitrarily shaped nematogens. For single component liquid crystals, the four order parameters needed to quantify orientational order of biaxial molecules in a biaxial nematic phase are calculated as a function of temperature for both rod-like and plate-like liquid crystals. For binary mixtures, temperature-concentration phase diagrams for a variety of molecular shapes are calculated. These theoretical predictions suggest that binary mixtures of highly asymmetric molecules with opposite shape anisotrophies may display stable biaxial nematic phases. Last, deuterium nuclear magnetic spin relaxation rates are measured as a function of temperature to investigate the molecular motion of a liquid crystal and a liquid crystal binary mixture. These experimental results are interpreted using an anisotropic viscosity model of molecular reorientation. The temperature dependence of the correlation times for the molecular motions is examined and discussed. It is demonstrated that mixing probe molecules into a liquid crystal has a profound effect on the molecular motion of the liquid crystal.

In this dissertation we study the development of microwave and RF near-field potentials for use with atom chip trapped atomic gases. These potentials are inherently spin-dependent, able to target individual spin states simultaneously. In contrast with traditional atom chip potentials, these RF traps can be operated at arbitrary bias magnetic field strengths and thus be combined with magnetic Feshbach resonances. Furthermore, these potentials can strongly suppress the potential roughness that plagues traditional atom chip potentials. We present a dual chamber atom chip apparatus for generating ultracold 87Rb and 39K atomic gases. The apparatus produces quasi-pure Bose-Einstein condensates of 104 87Rb atoms in an atom chip trap that features a dimple and good optical access. We have also demonstrated production of ultracold 39K and subsequent loading into the chip trap. We describe the details of the dual chamber vacuum system, the cooling lasers, the magnetic trap, the multi coil magnetic transport system, and the atom chip. The apparatus is well suited for studies of atom-surface forces, quantum pumping and transport experiments, atom interferometry, novel chip-based traps, and studies of one-dimensional many-body systems.

This investigation was undertaken in order to confirm and to extend earlier studies of processes whereby energy and angular momentum are transferred from external to internal degrees of freedom in low velocity collisions between ions and atoms. Specifically, this investigation sought to verify the proper functioning of a device designed to study low velocity atomic and molecular collisions, to confirm results obtained in an earlier study of spectra produced by collisions of He+ions with argon atoms, and to extend the energy and wavelength ranges of this study to 1500 eV and 6200 Å, respectively. The data was in the form of stripchart recordings taken at five beam energies, 600 eV, 800 eV, 1000 eV, 1250 eV, and 1500 eV. A basic analysis of this data was carried out; i.e., lines were identified, their wavelengths determined, and intensities calculated. In addition, the energy dependencies of the emission cross sections of twelve fully resolved lines were plotted and a partial Grotian diagram was drawn. The apparatus was frund to be functioning properly at energies about 609 eV but not a lower energies. Lipeles' energy and wavelength ranges were extended successfully, and in several instances his findings were confirmed (cf. Lipeles 1971). The visible Ar II spectrum was quite rich with twenty-nine lines being observed, six of which had not been detected previously. In addition, a single line was observed from neutral argon and a single band from molecular nitrogen, a contaminant in the argon target gas.

An electron microscope with electrostatic lenses was used for high resolution studies of magnetic domains in thin iron films. Observation methods used to determine the directions of local magnetization in iron thin films were the Lorentz method and the Foucault method. We studied how Bloch line-crosstie pairs and crosstie main walls behave in applied, in-plane magnetic fields. We found that crosstie main walls remain unchanged until crosstie density goes nearly to zero when the field is applied perpendicular to the main wall. A twisted type of domain appears where crossties disappear.

The concept of rendering an object invisible, once considered unfathomable, can now be deemed achievable using artificial metamaterials. The ability for these advanced structures to refract waves in the negative direction has sparked creativity for future applications. Manipulating electromagnetic waves of all frequencies around an object requires precise and unique parameters, which are calculated from various mathemat- ical laws and equations. We explore the possible interpretations of these parameters and how they are implemented towards the construction of a suitable metamaterial. If carried out correctly, the wave will exit the metamaterial exhibiting the same behavior as when it had entered. Thus, an outside observer will not be able to recognize any abnormal changes in wave frequency or direction. This paper will survey studies and technologies from the past 20 years to arrive at a concise mathematical examination of the possibilities and inherent issues under the umbrella of modern ”cloaking.”

The concept of rendering an object invisible, once considered unfathomable, can now be deemed achievable using artificial metamaterials. The ability for these advanced structures to refract waves in the negative direction has sparked creativity for future applications. Manipulating electromagnetic waves of all frequencies around an object requires precise and unique parameters, which are calculated from various mathemat- ical laws and equations. We explore the possible interpretations of these parameters and how they are implemented towards the construction of a suitable metamaterial. If carried out correctly, the wave will exit the metamaterial exhibiting the same behavior as when it had entered. Thus, an outside observer will not be able to recognize any abnormal changes in wave frequency or direction. This paper will survey studies and technologies from the past 20 years to arrive at a concise mathematical examination of the possibilities and inherent issues under the umbrella of modern ”cloaking.”

Classical methods of analyzing heat capacity data for the characteristic moments of the frequency distribution are applied to iridium and rhodium. Impurity moments are determined from high and low temperature f values. These moments are combined by modern theory to estimate the magnitude of the host-host to host-impurity force constant ratio. Ratios of the various host moments are also examined.

No description available.

<p>Molecular dynamics (MD) simulations performed on two-phase simulation cells were used to compute the Austenite (FCC) / Ferrite (BCC) boundary mobility in pure iron (Fe) over the temperature range of 600K - 1400K. An embedded atom method interatomic potential was used to model Fe and the driving force for interface motion is the free energy difference between the two phases, which was computed as a function of temperature using a thermodynamic integration technique. For low index FCC/BCC crystallographic orientations, no interface motion was observed. But for slight misorientations steps were introduced at the interphase and sufficient mobility was observed over MD time scales. A new interphase mechanism was found that instead of the moving of structure disconnection by diffusion control, growing of misfit dislocations in each steps were observed (interphase control). The interphase velocity could reach 2 m/s and the mobility at 1000K was approximately 0.001 mol-m/J-s. In agreement with previous MD studies of grain boundary mobility, we found that the activation energy for the austenite-ferrite boundary mobility was much lower than the values found from previous experiments.</p> / Master of Applied Science (MASc)

<p>In this thesis, the ripple formation at the interface of SiO2 and Si were studied in a systematic fashion by irradiating the SiO2-Si samples with ultrashort laser pulses under a broad variety of experimental conditions. They consist of di↵erent irradiating laser wavelengths, incident laser energies, translation speeds, translation directions, spot sizes of the laser beam, as well as oxide thicknesses. The ripples produced by laser irradiation are examined using various microscopy techniques in order to characterize their surface morphology, detailed structures, crystalline properties, and so on. For the experiments carried out at ! = 800 nm, the ripples formed on the SiO2-Si sample with an oxide thickness of 216 nm were first observed under optical microscopy and SEM. After removing the oxide layer with HF solution, the surface features of the ripples on the Si substrate were investigated using SEM and AFM techniques. Subsequently, by means of TEM and EDX analysis, the material composition and crystallinity of the ripples were determined. It is concluded that the ripples are composed of nano-crystalline silicon. In addition to the 216 nm oxide thickness, other oxide samples with di↵erent oxide thicknesses, such as 24, 112, 117, 158 and 1013 nm, were also processed under laser irradiation. The ripple formation as a function of the laser energy, the translation direction and the spot size is discussed in detail. Furthermore, the ripples created at the SiO2-Si interface are compared with</p> <p>the LIPSS created on pure silicon samples that were processed under similar laser irradiation conditions. The spatial periodicities of the ripples were evaluated to be in the range of between 510 nm and 700 nm, which vary with the oxide thickness and other laser parameters. For the experiments using the ! = 400 nm laser pulses, it is found that ripples can also be formed at the SiO2-Si interface, which have spatial periodicities in the range of between 310 nm and 350 nm depending on the oxide thickness. The ripple formation at this 400 nm wavelength as a function of the laser energy, the translation speed, and translation direction is considered as well. For the case of ! = 400 nm irradiation, a comparison is also made between the interface ripples on the SiO2-Si samples and the LIPSS on a pure Si sample. Through FIB-TEM and EDX analysis, it confirmed that the ripples were produced in the substrate while the oxide layer maintained its structural integrity. In addition, the ripples are composed of nano-crystalline silicon whose crystallite sizes are on the order of a few nanometers. Apart from irradiating oxide samples with femtosecond laser pulses, which applies to the two cases of ! = 800 and 400 nm mentioned above, oxide samples with an oxide thickness of 112 nm were irradiated with picosecond laser pulses at ! = 800 nm whose pulse durations are 1 ps and 5 ps, respectively. However, no regular ripples can be produced at the SiO2-Si interface while maintaining the complete integrity of the oxide layer.</p> / Master of Applied Science (MASc)