This thesis investigates the use of two-photon polymerisation direct laser writing (2PP-DLW) in liquid crystal materials, with an emphasis on the development of applications in photonics. 2PP-DLW is ...a 3D printing technique employed in the fabrication of multi-dimensional structures with micro- and nano-scale dimensions. As a maskless microfabrication method, it is typically used as a rapid-prototyping tool for solid polymer objects. However, there is increasing interest in the technique as a way to manufacture functional materials and devices that cannot be produced via other means. Crucial to this effort is the development of smart resins, whereby the physical properties of a resin can be varied and controlled in-situ during the fabrication process. In this thesis, liquid crystal mixtures containing reactive mesogens are shown to be a promising smart resin material due to their anisotropic physical properties and ability to respond to external electric fields. Stabilisation of the voltage-dependent states of the nematic Fréedericksz cell via the fabrication of polymer micropillars with 2PP-DLW is described and analysed. The polymer structures are studied with polarised optical microscopy and an electrically-tunable visibility phenomenon is characterised and explained. By synchronising the fabrication of polymer features with the application of different voltages, reconfigurable images are inscribed into liquid crystal devices. Potential applications are explored with a demonstration of a prototype anti-counterfeiting security marking. Topological defects in nematic liquid crystal pi-cells are fabricated and electrically-controlled via the fabrication of topologically discontinuous polymer structures using 2PP-DLW. A control system for electrical-tuning of defects is developed and advanced concepts for confinement of disclination lines are demonstrated. The transport of a microparticle by a defect is presented with the potential for applications in defect templates for micro/nano assembly. Switchable diffractive optical elements (DOEs) are fabricated with 2PP-DLW in liquid crystals and their diffractive behaviour is characterised. A model of a laser-written diffraction grating is developed using a continuum theory approach to director simulations and a wave-optics approach to the diffraction of light. The 3D capabilities of 2PP-DLW are exploited to fabricate switchable bilayer DOEs and computer-generated holograms. This work in this thesis has important technological implications in both the development of smart resins for 2PP-DLW as well as in the development of advanced alignment and control techniques for liquid crystal devices.
Surgery remains dangerous, and accurate knowledge of what is presented to the surgeon can be of great importance. One technique to automate this problem is non-rigid tracking of time-of-flight camera ...scans. This requires accurate sensors and prior information as well as an accurate non-rigid tracking algorithm. This thesis presents an evaluation of four algorithms for tracking and semantic labeling of deformable tissues for medical applications, as well as additional studies on a stretchable flexible smart skin and dynamic 3D bioprinting. The algorithms were developed and tested for this study, and were evaluated in terms of speed and accuracy. The algorithms tested were affine iterative closest point, nested iterative closest point, affine fast point feature histograms, and nested fast point feature histograms. The algorithms were tested against simulated data as well as direct scans. The nested iterative closest point algorithm provided the best balance of speed and accuracy while providing semantic labeling in both simulation as well as using directly scanned data. This shows that fast point feature histograms are not suitable for nonrigid tracking of geometric feature poor human tissues. Secondary experiments were also performed to show that the graphics processing unit provides enough speed to perform iterative closest point algorithms in real-time and that time of flight depth sensing works through an endoscope. Additional research was conducted on related topics, leading to the development of a novel stretchable flexible smart skin sensor and an active 3D bioprinting system for moving human anatomy.
Using data collected in the region of the $\Upsilon(4S)$ resonance with the CLEO-II detector, the first observation of exclusive decays of the B meson to final states with a charmed baryon is ...reported which is essential in understanding the mechanism for baryon production from the weak decays of the B-meson. We have measured the branching fractions to be ${\cal B}(\bar B\sp-\to\Lambda\sbsp{c}{+}\bar p\pi\sp-)=(0.62\sbsp{-0.20}{+0.23}\pm 0.11\pm0.10)\times10\sp{-3}$ and ${\cal B}(\bar B\sp0\to\Lambda\sbsp{c}{+}\bar p\pi\sp+\pi\sp-)=(1.33\sbsp{-0.42}{+0.46}\pm0.31\pm0.21)\times10 \sp{-3}.$ In addition, we report upper limits for the final states $\bar B\sp0\to\Lambda\sbsp{c}{+}\bar p$ and $B\sp-\to\Lambda\sbsp{c}{+}\bar p\pi\sp+\pi\sp-.$ The two-body decay, $\bar B\sp0\to\Lambda\sbsp{c}{+}\bar p,$ is suppressed in disagreement with theoretical predictions.
Isotactic and syndiotactic polymethacrylic acids (PMA * s) have been prepared and studied by pH titration, enthalpy titration and interaction with copper(II). The syndiotactic polyacid (85% ...syndiotactic triads by NMR of the derived polymethyl methacrylate) is similar to ordinary PMA (57% syndiotactic). Isotactic PMA (90% iso tactic triads) is insoluble at low degrees of neutralization (alpha); it is a weaker acid by about 0.4 pK independent of alpha and level of neutral salt, and binds copper(II) about three times as strongly (equilibrium dialysis). The alpha dependence of the copper binding ratio indicates that there are two carboxylate ions in the syndiotactic complex, one in the isotactic. The visible and ultraviolet absorbancies of the copper- PMA complex are quite sensitive to tacticity, especially at high pH where the possibility of a tacticity index is indicated. Microcalorimetric determination of the heat of neutralization as a function of alpha shows that tacticity in fluences acidity primarily through the dissociation enthalpy. The dissociation enthalpy decreases with increasing alpha, more rapidly in water than in salt solution, the concomitant increase in the free energy of dissociation being due to the rapid decrease in entropy of dissociation. In the presence of copper(II) there are large effects on the heat of reaction with base, corresponding, in general, with the alpha regions of large pH effect. The reaction of syndiotactic PMA with copper(II) is endothermic to the ex tent of about 8 kcal per mole of copper. The experimental results have been interpreted in terms of a helical structure analogous to that of crystalline, stereoregular polymethyl methacrylate; in the syndiotactic helix the carboxyl groups are associated in physically distinct pairs separated by similar pairs of alpha methyl groups; in the isotactic chain the carboxyl and methyl groups alternate. Solubility differences are attributed to differences in hydrogen bonding capacities in accord with this conformation. The titration curves of "atactic" and isotactic poly acrylic acids were only marginally different; there are indications that in this system, the "atactic" polyacid is predominantly isotactic. Crosslinking of polyacrylic acid (microsol copolymer with divinylbenzene) causes a "parallel" shift in the titration curve without change of shape. The tacticity of PMA’s prepared from the monomer by gamma ray initiation in water at various alphas indicates that charge favors syndiotactic placement to about the same extent that would be predicted from the effect of tacticity on the free energy of dissociation. From the effect of polymerization temperature on tacticity, the enthalpy and entropy of activation for iso tactic placement are estimated to be greater than for syndiotactic placement by 1.2 kcal/mole and 1.5 e.u. respectively in the absence of charge. An attempt to study the proton NMR spectra of PMA’s in D2O failed for lack of signal strength and resolution under conditions which gave good spectra of structurally similar monomeric acids.
