Computer simulation of bistable switching in a nematic device containing pear-shaped particles

We study the microscopic basis of bistable switching of a confined liquid crystal via Monte Carlo simulations of hard pear-shaped particles. Using both dielectric and dipolar field couplings to this intrinsically flexoelectric fluid, it is shown that pulsed fields of opposing polarity can be used to switch between the vertical and hybrid aligned states. Further, it is shown that the field-susceptibility of the surface polarisation, rather than the bulk flexoelectricity, is the main driver of this switching behaviour.</p

High-Precision Spectroscopy with Counter-Propagating Femtosecond Pulses

An experimental realization of high-precision direct frequency comb spectroscopy using counter-propagating femtosecond pulses on two-photon atomic transitions is presented. Doppler broadened background signal, hampering precision spectroscopy with ultrashort pulses, is effectively eliminated with a simple pulse shaping method. As a result, all four 5S-7S two-photon transitions in a rubidium vapor are determined with both statistical and systematic uncertainties below 10$^{-11}$, which is an order of magnitude better than previous experiments on these transitions.Comment: 5 pages, 4 figures. Accepted to PR

Using particle shape to induce tilted and bistable liquid crystal anchoring

We use Monte Carlo simulations of hard Gaussian overlap (HGO) particles symmetrically confined in slab geometry to investigate the role of particle-substrate interactions on liquid crystalline anchoring. Despite the restriction here to purely steric interactions and smooth substrates, a range of behaviours are captured, including tilted anchoring and homeotropic-planar bistability. These macroscopic behaviours are all achieved through appropriate tuning of the microscopics of the HGO-substrate interaction, based upon non-additive descriptions for the HGO-substrate shape parameter.</p

Coherent control and high-precision spectroscopy with an optical frequency comb

Eikema, K.S.E. [Promotor]Witte, S.M. [Copromotor

Entropy-driven formation of the gyroid cubic phase

We show, by computer simulation, that tapered or pear-shaped particles, interacting through purely repulsive interactions, can freely self-assemble to form the three-dimensionally periodic, gyroid cubic phase. The Ia3d gyroid cubic phase is formed by these particles both on compression of an isotropic configuration and on expansion of a smectic A bilayer arrangement. For the latter case, it is possible identify the steps by which the topological transformation from non-intersecting planes to fully interpenetrating, periodic networks takes place</p

Computer simulation of confined and flexoelectric liquid crystalline systems.

In this Thesis, systems of confined and flexoelectric liquid crystal systems have been studied using molecular computer simulations. The aim of this work was to provide a molecular model of a bistable display cell in which switching is induced through the application of directional electric field pulses. In the first part of this Thesis, the study of confined systems of liquid crystalline particles has been addressed. Computation of the anchoring phase diagrams for three different surface interaction models showed that the hard needle wall and rod-surface potentials induce both planar and homeotropic alignment separated by a bistability region, this being stronger and wider for the rod-surface varant. The results obtained using the rod-sphere surface model, in contrast, showed that tilted surface arrangements can be induced by surface absorption mechanisms. Equivalent studies of hybrid anchored systems showed that a bend director structure can be obtained in a slab with monostable homeotropic anchoring at the top surface and bistable anchoring at the bottom, provided that the slab height is sufficiently large and the top homeotropic anchoring is not too strong. In the second part of the Thesis, the development of models for tapered (pear-shaped) mesogens has been addressed. The first model considered, the truncated Stone expansion model, proved to be unsuccessful in that it did not display liquid crystalline phases. This drawback was then overcome using the alternative parametric hard Gaussian overlap model which was found to display a much richer phase behaviour. With a molecular elongation k = 5, both nematic and interdig-itated smectic A2 phases were obtained. In the final part of this Thesis, the knowledge acquired from the two previous studies was united in an attempt to model a bistable display cell. Switching between the hybrid aligned nematic and vertical states of the cell was successfully performed using pear shaped particles with both dielectric and dipolar couplings to an applied field. Also, a parameter window was identified, for values of the electric field, dielectric susceptibility and dipole moment, for which directional switching is achievable between the bistable states

Annual Narrative Report of Home Demonstration Agent in Yavapai County, March 1, 1943 - March 31, 1943, June 1, 1943 - August 31, 1943

Bound typescripts of agents reports, including photographs, charts, clippings, and examples of publications, 1942 to 1943. Also includes statistical summaries for 1942-43.This material from the University of Arizona Agricultural Extension Service is made available by University of Arizona Libraries, Special Collections. Contact us at [email protected], or (520) 621-6423

Annual Narrative Report of Mrs. Flossie Wills Barmes, Home Demonstration Agent, Graham County, Arizona, From November 31, 1935 - December 1, 1936

Bound typescripts of agents reports, including photographs, charts, clippings, and examples of publications, 1935 to 1936. Also includes statistical summaries for 1935-36.This material from the University of Arizona Agricultural Extension Service is made available by University of Arizona Libraries, Special Collections. Contact us at [email protected], or (520) 621-6423