<p>The magnetic properties of the heavy rare earth titanium oxides RTiO₃, R=Tb, Dy, Ho, Er, Tm, Yb and Lu, have been investigated. The RTiO₃ develop a spontaneous magnetization below critical temperatures ranging from 28 K to 64 K. Both the rare earth and titanium moments order at the same temperature. The field dependence of the magnetization at 4.2K indicates that the magnetocrystalline anisotropy is very large. The paramagnetic susceptibility of the materials formed with R=Tb-Tm is analyzed with molecular field theory to obtain the molecular field coupling constants λTi-Ti, λR-Ti and λR-R. The magnetic structures are determined for RTiO₃, R=Tb-Tm with the technique of neutron diffraction. The erbium and thulium moments form a ferromagnetic array along the orthorhombic c cxis and the terbium, dysprosium and holmium moments have both ferromagnetic and antiferromagnetic components in the ab plane, giving rise to a canted structure. The titanium moments are in a ferromagnetic array which is directed antiparallel to the ferromagnetic component of the rare earth moment. The preferred direction of the rare earth magnetization with respect to the orthorhombic c axis is discussed in terms of the interaction between 4f electrons on the rare earth and the crystalline environment. Calculations are presented which support this hypothesis.</p> / Doctor of Philosophy (PhD)

<p>The investigation of the feasibility of a bone mineral measurement technique based on coherent scattering of gamma rays was performed using a HPGe detector.</p> <p>Considerations of detector efficiency and resolution, absorbed dose to bone, spectral separation between coherent and Compton peaks, variation of differential coherent cross section and scattering volume with scattering angle led to the selection of a photon soruce energy of 103.2 keV (Sm153) and a scattering angle of 40 degree.</p> <p>Bone phantoms (aqueous solutions of K2HPO4) were used to examine how the coherent intensity emanating from a scattering volume at the centre of an object varied with object dimensions and solution effective atomic number. Simulation and experimental measurements with solutions in cylindrical polyethylene containers of varying sizes indicated that the ratio of the coherent count rate to the transmission count rate was independent of container dimensions (at least up to 7 cm diameter). For ease of comparison, all the ratios at different concentrations were normalised to that of water obtained in an identical measurement geometry. The normalised coherent-to-transmission ratios were related to solution effective atomic number by a power function with a exponent of 3.30 plus minus 0.15.</p> <p>When the rate of change of the normalised ratio with effective atomic number is used as an indicator of the sensitivity of the technique, the coherent-to-transmission method is almost twice as sensitive as a coherent-to-Compton technique.</p> <p>In-citro bone mineral measurements were made in the calcaneus (heel bone), an easily accessible site in which 90% of bone mineral is trabecular. Prior to the measurements the spatial distribution of mineral was investigated with a Norland 278-A single photon absorptiometry (SPA) machine in slices of several calcanei. Cortical bone was restricted to a thin peripheral region of the calcaneus.</p> <p>Three whole calcanei, one of which had its calcium content deliberately reduced by soaking overnight in hydrochloric acid, were selected for measurement using the coherent-to-transmission technique. For the first measurement each bone was submerged in water only. For the second measurement the trabeculae were filled with corn oil, to simulate marrow fate, and again each bone were submerged in water. The latter measurements were about 50% lower than the first, indicating a large "marrow fat" effect. However, both sets of results can by explained by assuming a power relationship between the normalised coherent-to-transmission ratio and the effective atomic number of the scattering volume contents.</p> <p>Cuboid samples of side approximately 16 mm were cut out of the posterior region of each calcaneus and ashed. A plot of the normalised coherent-to-transmission ratio versus the ashed weight per unit volume (bone mineral density) of the three calcanei yielded a straight line. While this indicates that the normalised coherent-to-transmission ratio is an indicator of bone mineral, a larger number of samples will be required to establish a robust calibration curve.</p> / Doctor of Philosophy (PhD)

<p>An all-pervading feature of the work presented in this thesis is the study of ultrafast dynamics, both theoretically and experimentally, in terms of time-dependent wave functions (wave packets).</p><p>We have experimentally, by pump-probe fluorescence spectroscopy, examined spin-orbit interactions, by time-tracing molecular wave packets on excited states of diatomic rubidium, and the main channels causing the fast predissociation from one of those states is revealed.</p><p>The time evolution of wave packets and their extension in space, in addition to varying transition dipole moment is of specific interest in the semiclassically derived expressions for the total ion signal, in the context of pump-probe ionization spectroscopy on diatomic molecules.</p><p>We have experimentally, by pump-probe fluorescence spectroscopy, addressed a previously derived theoretical prediction about level interactions between atomic levels with all angular momentum quantum numbers equal but different principal quantum numbers. Hence, the ultrafast progression of atomic radial wave packets are disclosed in terms of quantum beat frequencies and explained theoretically in the context of pump-probe fluorescence spectroscopy.</p><p>Preliminary fluorescence up-conversion experiments are as well treated in this thesis with the aim to reveal further experimental knowledge on the previously derived theoretical prediction on the specific level interactions mentioned above.</p>

The research is concerned with atmospheric chemistry & physics, and analyzing the environment with respect to the quantity of molecules is in the air we breathe. Fourier Transform Infrared Spectroscopy is used to identify the IR active molecules in our atmosphere. FTIR Spectrometer determines the intensity loss for molecules that have absorbed IR light. The FTIR spectroscopy is performed using the light from the sun or a carbon rod light source in the lab. A Sun-tracking device was employed to direct the sunlight into the spectrometer. Open-path measurements were made using multiple mirror reflections of the carbon rod light source over the top of the SERF (Science and Engineering Research Facility) building. From the Open-path measurements it was determined that the CO and N2O change concentrations during the day and night. Two different open path setups were employed with good success. Time-dependence of the IR spectra for many of the greenhouse gases are presented. In addition, we have performed Gaussian 03 calculations of the IR spectra for many of the greenhouse gases as well as for the nitroethane molecule.

An all-pervading feature of the work presented in this thesis is the study of ultrafast dynamics, both theoretically and experimentally, in terms of time-dependent wave functions (wave packets). We have experimentally, by pump-probe fluorescence spectroscopy, examined spin-orbit interactions, by time-tracing molecular wave packets on excited states of diatomic rubidium, and the main channels causing the fast predissociation from one of those states is revealed. The time evolution of wave packets and their extension in space, in addition to varying transition dipole moment is of specific interest in the semiclassically derived expressions for the total ion signal, in the context of pump-probe ionization spectroscopy on diatomic molecules. We have experimentally, by pump-probe fluorescence spectroscopy, addressed a previously derived theoretical prediction about level interactions between atomic levels with all angular momentum quantum numbers equal but different principal quantum numbers. Hence, the ultrafast progression of atomic radial wave packets are disclosed in terms of quantum beat frequencies and explained theoretically in the context of pump-probe fluorescence spectroscopy. Preliminary fluorescence up-conversion experiments are as well treated in this thesis with the aim to reveal further experimental knowledge on the previously derived theoretical prediction on the specific level interactions mentioned above.

A new challenging application for Li-ion battery has arisen from the rapid development of micro-electronics. Powering Micro-ElectroMechanical Systems (MEMS) such as autonomous smart-dust nodes using conventional Li-ion batteries is not possible. It is not only new batteries based on new materials but there is also a need of modifying the actual battery design. In this context, the conception of 3D nano-architectured Li-ion batteries is explored. There are several micro-battery concepts that are studied; however in this thesis, the focus is concentrated on one particular architecture that can be described as the successive deposition of battery components (active material, electrolyte, active material) on free-standing arrays of nano-sized columns of a current collector. After a brief introduction about Li-ion batteries and 3D micro-batteries, the electrodeposition of Al through an alumina template using an ionic liquid electrolyte to form free-standing columns of Al current collector is described. The crucial deposition parameters influencing the nucleation and growth of the Al nano-rods are discussed. The deposition of active electrode material on the nano-structured current collector columns is described for 2 distinct active materials deposited using different techniques. Deposition of TiO2 using Atomic Layer Deposition (ALD) as active material on top of the nano-structured Al is also presented. The obtained deposits present high uniformity and high covering of the specific surface of the current collector. When cycled versus lithium and compared to planar electrodes, an increase of the capacity was proven to be directly proportional to the specific area gained from shifting from a 2D to a 3D construction. Cu2Sb 3D electrodes were prepared by the electrodeposition of Sb onto a nano-structured Cu current collector followed by an annealing step forcing the alloying between the current collector and Sb. The volume expansion observed during Sb alloying with Li is buffered by the Cu matrix and thus the electrode stability is greatly enhanced (from only 20 cycles to more than 120 cycles). Finally, the deposition of a hybrid polymer electrolyte onto the developed 3D electrodes is presented. Even though the deposition is not conformal and that issues of capacity fading need to be addressed, preliminary results attest that it is possible to cycle the obtained 3D electrode-electrolyte versus lithium without the appearance of short-circuits.

The work in this thesis is focused on molecules that are able to self-assemble on different surfaces by forming two-dimensional templates stabilised via double or triple hydrogen bonding. In particular, assemblies of molecules such as melamine, perylene tetra-carboxylic di-imide (PTCDI), perylene tetra-carboxylic di-anhydride (PTCDA), naphthalene tetracarboxylic-dianhydride (NTCDA) and naphthalene tetracarboxylic diimide (NTCDI) are studied in detail. The aim is to give a complete characterisation of the supramolecular networks, taking into account the balance between the molecule-molecule and molecule-substrate interactions. All our assembly calculations are done within the gas phase approximation, i.e. without taking into account the surface, which is a good approximation assuming that the molecules are quite mobile on the surface. Using a systematic method based on considering all possible hydrogen bond connections between the molecules we investigate planar superstructures that organic molecules can form in one and two dimensions. The structures studied are based on two or more molecules per unit cell and all structures considered, assemble in flat periodic patterns. Most of the calculations are performed using the density functional theory method. We show that the calculated lattice parameters of the structures considered compare well with those measured experimentally. To specifically check the applicability of the gas-phase approximation, we systematically investigated the adsorption of the molecules on the Au(111) metal surface with the particular attention being paid to the characterisation of the potential energy surface of our molecules on this surface. We performed these calculations using both a conventional functional (PBE) which does not include the dispersion interaction, and the newly developed vdW-DF method which does. We find that the adsorption energies of these flat molecules on the metal surface calculated with the vdW-DF method are effected significantly by the dispersion interaction and depend linearly on the size of the molecules. While the PBE method predicts very weak adsorption energies which do not depend on the sizes of the molecules, the vdW-DF method gives strong binding entirely due to the dispersion interaction. We found that both PBE and vdW-DF methods predict a very small corrugation of the total energy of the molecules on gold. These results support our main assumption of the molecule-surface interaction changing little laterally and resulting in a mobility of the molecules at room temperature on the surface, i.e. the gas-phase modelling is a good approximation for the Au(111) surface.

The mechanical breakage of tobacco mosaic virus (TMV) due to the action of acoustic transients has been investigated. The acoustic transients were produced by transient heating of a Prussian blue dye solution (attenuation coefficient of 1000 per cm) when a ruby laser light (20 x 106 watts) was incident on the dye surface. A quartz piezoelectric transducer was used to determine the amplitude and form of the acoustic wave. The production of acoustic waves by transient heating is discussed, and the theoretical form of the acoustic wave determined for various boundary and initial conditions are compared to the experimentally measured values. The electron microscope was used to compare particle length distributions of control TMV solutions and solutions exposed to the acoustic transients. Two conditions of exposure have been studied by varying the boundary conditions of the TMV solutions. In one case the TMV solution was exposed to a single acoustic transient whereas in the other case the solution was exposed to an acoustic transient which was reflected within the solution. Significantly greater breakage was produced in the latter case demonstrating the importance of boundary conditions in the biological effects of pressure transients. Calculations were made of the magnitude of hydrodynamical forces producing tensions in the TMV particle. A laser intensity of 1.6 x 108 watts per cm2 incident on the absorbing dye solution was found to be sufficient to cause significant breakage at the 5 percent level (Kolmogorov-Smirnov test). The corresponding tension on the TMV particle was calculated to be 6.3 x 10-5 dynes.

A visible and Infrared (IR) range dual beam frequency comb Fourier transform spectrometer was developed. Using dual mode-locked Ti:Sapphire lasers a comb-interferogram was generated in the visible range. This spectrum was calculated and used to measure the transmittance of a Nd-doped crystal. The system was further developed to generate an IR interferogram by Difference Frequency Generation (DFG) using a Gallium Selenide (GaSe) crystal placed in the mode-locked pump beam. Numerical work was done to calculate the expected DFG spectrum confirming the necessary IR range can be reached. This has been conducted in support of an IR holographic spectroscopic microscopy spatial and spectral resolving platform for applications in cell biology and biomedical applications.

Intensity modulated proton therapy (IMPT) in the form of pencil beam scanning (PBS) has shown improvement in treatment plan quality as compared to conventional proton and photon-based radiotherapy techniques. However, in IMPT maintaining a sharp lateral dose falloff is crucial for sparing organs at risk (OARs), especially when they are in close proximity to the target volume. The most common approach to improve lateral dose falloff is through the use of physical beam shaping devices, such as brass apertures or collimator-based systems. This work has shown that IMPT can be further improved by implementation of advanced spot placement techniques by moving away from traditional grid-based placements to boundary contoured techniques. We have developed a new optimized spot placement algorithm that provides robust spot distributions inside the target volume by making use of various geometric construction techniques in other fields and developed a unique spot placement technique that provides both high conformality and uniformity in a robust manner for arbitrarily complex target geometries. This approach achieves the boundary conformity of a recently proposed concentric-contours based approach and uses a fast-iterative method to distribute the interior spots in a highly uniform fashion in an attempt to improve both the lateral dose falloff and uniformity. We performed the treatment plan quality comparison for five spot placement techniques using customized homogeneous phantoms. These include two grid-based (rectilinear/hexagonal) and three boundary-contoured (concentric-contours, hybrid and optimized) techniques. Treatment plans were created for two different target volumes, (conical and spherical). An optimal set of planning parameters was defined for all treatment plans and the impact of spot placement techniques on the plan quality was studied in terms of lateral & distal dose falloff, normal tissue sparing, conformity & homogeneity of dose distributions, and total number of spots. For grid-based spot placement techniques, dose conformity is dependent on the target cross sectional shape, which changes for each proton energy. This variable conformity problem is shown to be mitigated by using boundary contoured techniques. However, in the case of concentric contours, the conformity is improved but at the cost of decreased homogeneity. Hybrid and optimized spot placement techniques show more uniform dose distributions while maintaining the improved dose conformity. The optimized spot placement technique is shown to provide robust treatment plans with improved target coverage, homogeneity of dose, and minimal spots count. These results highlight that plan quality in PBS proton therapy may be improved for many patients, without the need for expensive delivery equipment updates, simply by providing additional spot placement techniques in commercial treatment planning software (TPS).