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Systems of atoms have their kinetic energy distributed between three parts: translation, rotation and vibration. These are usually kept about the same following a Maxwell distribution, but under certain circumstances, this equilibrium might break. This would lead to, for example, ice melting anisotropically. In this report, it was determined if ice experiences anisotropic movement when it is exposed to a laser pulse in the form of an electric field. If ice experiences anisotropy, a time frame from when ice moves anisotropically until the movement is isotropic was established. This was done through molecular dynamics simulations using the GROMACS program on a system of solid ice crystals with multiple levels of field strengths. The simulations showed that anisotropy clearly exist in a solid ice structure when affected by the pulse, no matter if it's melting or not. The time period for when anisotropy existed in the ice was normally until the system had melted, which is about a minimum of 40 ps. / Varje system av atomer har tre delar som utgör deras kinetiska energi: translation, rotation och vibration. Dessa brukar hållas jämna i atomsystemen i en Maxwell fördelning, men under visa omständigheter kan detta brytas. Detta skulle leda till att t.ex. is smälts anisotropt. I denna rapport  undersöktes det ifall is som utsätts för en laserpuls, uttryckt med ett elektriskt fält, fluctuerar anisotropt. Om isen smältes anisotropt bestämdes en tidsram från när isens rörelse var anisotropt till när rörelsen blev isotrop.  Detta gjordes genom molekyldynamik simuleringar i programmet GROMACS på ett system med fasta iskristaller med varierande fältstyrka. Det som simuleringarna visade var att det tydligt finns anisotropi i isen när den blivit påverkad av en laser puls, oavsett om den var smältande eller inte. Tidsperioden denna isotropi i isen varade var till när systemet fullständigt smällt, vilket brukade ta minst 40 ps.

<p>Globular clusters have linear sizes (tidal radii) which are theoretically de- termined by their mass and by the gravitational potential of their host galaxy. However observationally, cluster sizes are simply a determination of where the cluster’s surface brightness profile becomes zero. This distance is also known as the limiting radius. While it is commonly assumed that the tidal radius and the limiting radius of a globular cluster are the same thing, it has yet to be validated. The purpose of this thesis is to explore the assumption that cluster tidal radii and limiting radii are equal by comparing the tidal radii of an observed and simulated globular cluster population.</p> <p>An established link between cluster tidal radii and limiting radii will yield new methods of utilizing globular clusters as tools for studying galaxies. If cluster sizes are truly imposed by the tidal field of the host galaxy, then tidal radii measurements can be used to trace the mass distribution within a galaxy, including the dark matter halo. Additionally, as we will demonstrate in this thesis, cluster sizes can also be used a tracer for the orbital anisotropy profile of a galaxy.</p> <p>To explore the assumption that tidal radii and limiting radii are equal, we utilize the globular cluster population of the Virgo giant M87. Unusually deep, high signal-to-noise images of M87 are used to determine the radius for approximately 2000 globular clusters. To compare with these observations, we simulate a globular cluster population that has the same characteristics to the observed M87 cluster population. These characteristics include cluster radial distribution, mass distribution, central concentration distribution and line of sight velocity dispersion. Placing these simulated clusters in the well-studied tidal field of M87, the orbit of each cluster is solved and the theoretical tidal radius of each cluster is determined. We compare the predicted relationship between cluster size and projected galactocentric distance found in our sim- ulation to observations in order to test whether a cluster’s tidal radius and limiting radius are equal. We find that for an isotropic distribution of cluster velocities, theoretical tidal radii are approximately equal to observed limiting radii. The simulation predicts the observed increase in cluster size with galac- tocentric distance, which is expected if tidal radii are dependent on the tidal field. Additionally, simulated cluster sizes are of the same order of magnitude as observed cluster sizes. However the simulation does underestimate cluster sizes in the inner regions of M87. To minimize the discrepancy between theory and observations, we further explore the effects of orbital anisotropy on cluster sizes, and suggest a possible orbital anisotropy profile for M87 which yields the best fit between theory and observations. Finally, we suggest multiple future studies which will aid in our understanding of tidal theory and in establishing a stronger link between tidal radii and limiting radii.</p> / Master of Science (MSc)

Velocity anisotropy is present at a point in a medium if the seismic velocity in one direction in general differs from that in another direction. The problems associated with the determination of subsurface velocity in anisotropic media by the use of surface seismic reflection data are analyzed. Previous studies of anisotropy in exploration seismology required bore-hole data as well as surface data to detect the presence of velocity anisotropy. Three special types of wave propagation are of interest in reflection seismology, in addition to the general case. The theory of isotropic media is commonly utilized in exploration seismology. Elliptical anisotropy has been the method for handling anisotropic media in the past. The theory of transversely isotropic media is studied in detail since this is a reasonable anisotropy model for exploration use. Layered periodic isotropic structures are considered because of the relationships between the elastic coefficients that yield transverse isotropy in the limiting case for which the isotropic lavers are thin in comparison to the wavelength of a propagating disturbance. Synthetic common-depth-point reflection seismic traces were generated for a uniformly anisotropic halfspace, a model with seismic velocity increasing linearly with depth, velocity increasing stepwise with depth, a buried anisotropic interval in an otherwise isotropic section, and models characterized by the dip varying continuously with depth. Correlation methods (velocity analysis) are developed for the determination of rms velocity vs. two-way reflection time for both isotropic and anisotropic (transversely isotropic) media. These methods are applied to the models discussed above for varying amounts of anisotropy for each model. When the surfaces defined by the velocity analysis correlation matrices are integrated to determine the volume under the surface, it is possible to determine within about one percent the degree of anisotropy in a uniformly anisotropic medium. In a medium of varying anisotropy, it does not appear possible to obtain the same degree of accuracy as for the uniform case. Two isotropic dipping layer models were studied to determine the effects of dip on velocity analysis. The effects of dip are such that the analysis methods yield erroneous results for dips in excess of about 10-12 degrees for the models studied. Random noise degrades the velocity analysis (i.e., the magnitudes of the correlation peaks), but does not affect the accuracy of the results. Lateral velocity gradients appear to have no discernible effects on a velocity analysis for the models studied. Results of this study indicate that the compressional wave data normally used in reflection seismic work may not be useful for the detection of velocity anisotropy. Shear wave (SV) data, on the other hand, are ideally suited to this purpose. Hmvever, the necessity of shear wave data for the detection of anisotropy may limit these methods strictly to land use. This study indicates that the probability of detecting anisotropy by using surface methods is sufficiently high to warrant field testing. / Ph. D.

Thermoelectric phenomenon describes the relationship between the flow of heat and electricity. Two main categories encompassed in thermoelectric theory are the Seebeck and Peltier effects. The Seebeck effect is the generation of a voltage in a device that consists of two different materials in the presence of a temperature gradient, while the Peltier effect is the generation of a temperature gradient across a device of two different materials in the presence of an electrical current. This project focuses on the first of these two phenomena, where the Seebeck effect is used in a novel heat flux sensor that is transverse in nature. Transverse thermoelectric devices are characterized by their anisotropy, meaning that a temperature gradient generated across a device will be perpendicular to the flow of electricity through the device. This orthogonal arrangement allows for the manipulation of material properties, device arrangement, and construction methods for device optimization. This project characterizes the heat flux sensing capabilities of an artificially anisotropic transverse thermoelectric device via experimental and theoretical methods. The device tested is constructed out of bismuth telluride and titanium grade 5. Bismuth telluride is a standard thermoelectric material, while the titanium is used because of its high melting point and good electrical conductivity. The device is constructed by alternating rectangular pieces of these two materials. These pieces are bonded together at a given angle to simulate anisotropy. Several devices are constructed in a range of angles from 59 to 88°. These devices are each tested in a vacuum chamber where a heater heats one side of the device. This heat flux into the device creates a temperature gradient across the device and the device generates a voltage perpendicular to this temperature gradient. Steady state data are collected for both the temperature difference between the two sides of the device and the voltage generated by the device. This procedure is repeated on each device for a range of heat fluxes from 0 to 2.6 W/cm². This range generates voltage signals up to 14341 µV for an angle of 59°. Data collected are then used to generate a linear trend line that describes the devices response to a given heat flux. These experimental results are compared to theoretical predictions using thermoelectric theory. The results indicate that the device does exhibit transverse thermoelectric characteristics and the experimental data follow the predicted trends. This thesis documents the process of constructing, testing, and analyzing this device. / Master of Science

A Magnetic Heating Coil (MHC) has been designed, which has the potential to interact with magnetic Nanoparticles (NPs) to produce local temperature changes. The aim is to design a device capable of studying medically targeted magnetic-fluorescent core-shell NPs (with potential applications in cancer therapy via hyperthermia). Very little is known about how the magnetic-fluorescent NPs respond to magnetic fields and the effect this would have on their optical properties, therefore, considerable work is still required in order to understand the detailed interactions. Several modelling and simulations of the MHC were conducted besides developing the MHC that was designed and built for small samples of NPs (1-10ml volumes). Two different heating coil geometries were examined (coil A and coil B), where the former operates at 83 kHz and the latter operates at 125 kHz. Several tests for fluorescent emission, lifetime and anisotropy with several different NPs samples were conducted. We found that as the temperature increased from 5 °C to 45 °C, the fluorescence lifetime dropped from 3.8 ns to 3.6 ns. Also, the correlation time of the fluorescence in dilute solutions with varying temperatures from 20 °C to 40 °C was investigated, and it was found that decreased from 0.9 ns to 0.6 ns showing that the rotational diffusion of the dye increased and the molecules become more mobile. The MNPs were found to quench the fluorescent emission at high concentrations. Also, the MNPs induce only a small change in a lifetime from 3.9 ns to 3.4 ns. / Libyan Higher Ministry of Education

The 2D honeycomb lattice started as a theoretical construct, until its realization in a crystalline system enabled the study of a host novel exotic phenomena arising from its unique electronic structure. Since the isolation of graphene, the search for crystalline materials hosting interesting electronic structures has only increased with the excitement of correlated phenomena that can arise in the two-dimensional limit. This dissertation details the characterization of a van der Waals (vdW) material that realizes a novel flat band lattice model via frustrated hopping. Chapter 1 starts with an introduction into vdW materials and the electronic structure of frustrated lattices. Chapter 2 goes through some of the characterization methods that will be mentioned in this dissertation. Chapter 3 introduces the material that will be the subject of investigation in this thesis and establishes its as arising from a novel flat band lattice model via frustrated hopping. Chapter 4 discusses the electronic properties of newly synthesized analogs of this material. Chapter 5 introduces potential applications of this material in plasmonics. Chapter 6 covers a research story that is independent of the rest of this dissertation. It goes through the optical properties that arise from in-plane structural anisotropy in a superatomic vdW material.

Three test methods were employed to characterize the response of unidirectional Boron/Aluminum metal matrix composite material under monotonic and cyclic loading conditions, namely: Iosipescu Shear, Off-Axis Tension and Compression. The characterization of the elastic and plastic response includes the elastic material properties, yielding and subsequent hardening of the unidirectional composite under different stress ratios in the material principal coordinate system. The elastic response is compared with the prediction of the transformation theory, based on the far field stress ōₓₓ, the Pagano-Halpin Model, and finite element analysis. Yield loci were generated for different stress ratios and were compared for the three different test methods, taking into account residual stresses and specimen geometry. The yield locus for in-plane shear was compared with the prediction of an analytical micromechanical model. The influence of the scatter in the experimental data on the predicted yield surface was also analyzed. Likewise the experimental material strength in tension and compression was compared with the Maximum Stress and the Tsai-Wu failure criterion. / M.S.

Nuclear energy is a proven large-scale, emission-free, around-the-clock energy source. As part of improving the nuclear energy efficiency and safety, a significant amount of effort is being expended to understand how the microstructural evolution of nuclear fuels affects the overall fuel performance. Grain growth is an important aspect of microstructural evolution in nuclear fuels because grain size can affect many fuel performance properties. In this work, the anisotropy of grain boundary energy and mobility, which are two important properties for grain growth, is examined for the light water reactor fuel uranium dioxide (UO₂) by molecular dynamics simulations. The dependence of these properties on both misorientation angle and rotation axis is studied. The anisotropy in grain boundary energy is found to be insignificant in UO₂. However, grain boundary mobility shows significant anisotropy. For both 20º and 45º misorientation angles, the anisotropy in grain boundary mobility follows a trend of M₁₁₁>M₁₀₀>M₁₁₀, consistent with previous experimental results of face-centered-cubic metals. Evidences of grain rotation during grain growth are presented. The rotation behavior is found to be very complex: counterclockwise, clockwise, and no rotation are all observed. / M.S. / Energy needs in the world increase year after year. As part of the effort to address these increasing needs, an increasing effort is needed to study each aspect of energy generation. For energy generated via nuclear fission, i.e., nuclear energy, many things need to be understood to gain maximum efficiency with maximum safety. At the core of a nuclear reactor, transport of energy generated by nuclear fission is heavily dependent on the microscopic structure (microstructure) of the materials being used as fuel. Thus, this work examines the microstructure of the most common nuclear fuel, uranium dioxide (UO₂). The microstructure changes based on at least two properties: grain boundary energy, and grain boundary mobility. This work examines how these properties change based on the orientation of individual crystallites within the polycrystalline material. An additional aspect of microstructural evolution, namely grain rotation, is briefly discussed.