Propagation of low power low divergence Gaussian fields in unbiased self-defocusing photorefractive media and their interactions

Many optical networks are limited in speed and processing capability due to the necessity for the optical signal to be converted to an electrical signal and back again. In addition, electronically manipulated interconnects in an otherwise optical network lead to overly complicated systems. Optical spatial solitons are optical beams that propagate without spatial divergence. They are capable of phase dependent interactions, and have therefore been extensively researched as suitable all optical interconnects for over 20 years. However, they require additional external components, initially high voltage power sources were required, several years later, high power background illumination had replaced the high voltage. However, these additional components have always remained as the greatest hurdle in realising the applications of the interactions of spatial optical solitons as all optical interconnects. Recently however, self-focusing was observed in an otherwise self-defocusing photorefractive crystal. This observation raises the possibility of the formation of soliton-like fields in unbiased self-defocusing media, without the need for an applied electrical field or background illumination. This thesis will present an examination of the possibility of the formation of soliton-like low divergence fields in unbiased self-defocusing photorefractive media. The optimal incident beam and photorefractive media parameters for the formation of these fields will be presented, together with an analytical and numerical study of the effect of these parameters. In addition, preliminary examination of the interactions of two of these fields will be presented. In order to complete an analytical examination of the field propagating through the photorefractive medium, the spatial profile of the beam after propagation through the medium was determined. For a low power solution, it was found that an incident Gaussian field maintains its Gaussian profile as it propagates. This allowed the beam at all times to be described by an individual complex beam parameter, while also allowing simple analytical solutions to the appropriate wave equation. An analytical model was developed to describe the effect of the photorefractive medium on the Gaussian beam. Using this model, expressions for the required intensity dependent change in both the real and imaginary components of the refractive index were found. Numerical investigation showed that under certain conditions, a low powered Gaussian field could propagate in self-defocusing photorefractive media with divergence of approximately 0.1 % per metre. An investigation into the parameters of a Ce:BaTiO3 crystal showed that the intensity dependent absorption is wavelength dependent, and can in fact transition to intensity dependent transparency. Thus, with careful wavelength selection, the required intensity dependent change in both the real and imaginary components of the refractive index for the formation of a low divergence Gaussian field are physically realisable. A theoretical model incorporating the dependence of the change in real and imaginary components of the refractive index on propagation distance was developed. Analytical and numerical results from this model are congruent with the results from the previous model, showing low divergence fields with divergence less than 0.003 % over the propagation length of the photorefractive medium. In addition, this approach also confirmed the previously mentioned self-focusing effect of the self-defocusing media, and provided an analogy to a negative index GRIN lens with an intensity dependent focal length. Experimental results supported the findings of the numerical analysis. Two low divergence fields were found to possess the ability to interact in a Ce:BaTiO3 crystal in a soliton-like fashion. The strength of these interactions was found to be dependent on the degree of divergence of the individual beams. This research found that low-divergence fields are possible in unbiased self-defocusing photorefractive media, and that soliton-like interactions between two of these fields are possible. However, in order for these types of fields to be used in future all optical interconnects, the manipulation of these interactions, together with the ability for these fields to guide a second beam at a different wavelength, must be investigated.

Self-assembled multicomponent Pd-6 aggregates showing low-humidity proton conduction

Two Pd-6 molecular aggregates (1 and 2), self-sorted via a template-free three-component self-assembly process, represent new examples of discrete architectures exhibiting very high proton conductivity 0.78 x 10(-3) S cm(-1) (1) and 0.22 X 10(-3) S cm(-1) (2)] at 300 K at low relative humidity (B46%) with low activation energy comparable to that of currently used Nafion in fuel cells.

Demonstration of a self aligned hybrid silicon-plasmonic waveguide with low loss and nanoscale confinement

We demonstrate self-aligned approach for fabricating hybrid silicon plasmonic waveguide. The demonstrated structure provides nanoscale confinement together with propagation length of 100 microns on chip. Near-field measurements of propagation and coupling loss are presented. © 2011 Optical Society of America.

Demonstration of a self aligned hybrid silicon-plasmonic waveguide with low loss and nanoscale confinement

We demonstrate self-aligned approach for fabricating hybrid silicon plasmonic waveguide. The demonstrated structure provides nanoscale confinement together with propagation length of 100 microns on chip. Near-field measurements of propagation and coupling loss are presented. ©2011 Optical Society of America.

Study of self-assembled InAs quantum dots grown on low temperature GaAs epi-layer

InAs self-organized quantum dots (QDs) grown on annealed low temperature GaAs (LT-GaAs) epi-layer were investigated by transmission electron microscopy (TEM) and photoluminescence (PL) measurement. TEM showed that QDs formed on annealed LT-GaAs epi-layer have a smaller size and a higher density than QDs formed on normal GaAs buffer layer. In addition, the PL spectra analysis showed that the LT-GaAs epi-layer resulted in a blue shift in peak energy, and a narrower linewidth in the PL peak. The differences were attributed to the point defects and As precipitates in annealed LT-GaAs epi-layer for the point defects and As precipitates change the strain field of the surface. The results provide a method to improve the uniformity and change the energy band structure of the QDs by controlling the defects in the LT-GaAs epi-layer.

Electrochemical characterization of self-assembled Ferrocene-terminated alkanethiol monolayers on low-index gold single crystal electrodes

We present a voltammetric and in situ STM study of 11-ferrocenyl-1-undecanethiol (FcC11) assembled on low-index single crystal and polycrystalline gold electrodes. The influence of electrode surface structure as well as of structure defects in the self-assembled FcC11 monolayers on the electrochemical response during the oxidation and reduction of the terminal ferrocene group is explored. The nature of the redox peaks is discussed in detail. We identified the coexistence of disordered FcC11 regions with 2D patches of “locally ordered” FcC11 species. We demonstrate that close-packed domains are preferentially formed at atomically flat terraces. Increasing the defect density of the substrate surface leads to a decreasing amount of locally ordered FcC11 molecules.

What constitutes vulnerable self-esteem? Comparing the prospective effects of low, unstable, and contingent self-esteem on depressive symptoms

A growing body of longitudinal studies suggests that low self-esteem is a risk factor for depression. However, it is unclear whether other characteristics of self-esteem, besides its level, explain incremental or even greater variance in subsequent depression. We examined the prospective effects of self-esteem level, instability (i.e., the degree of variability in self-esteem across short periods), and contingency (i.e., the degree to which self-esteem fluctuates in response to self-relevant events) on depressive symptoms in 1 overarching model, using data from 2 longitudinal studies. In Study 1, 372 adults were assessed at 2 waves over 6 months, including 40 daily diary assessments at Wave 1. In Study 2, 235 young adults were assessed at 2 waves over 6 weeks, including about 6 daily diary assessments at each wave. Self-esteem contingency was measured by self-report and by a statistical index based on the diary data (capturing event-related fluctuations in self-esteem). In both studies self-esteem level, but not self-esteem contingency, predicted subsequent depressive symptoms. Self-esteem instability predicted subsequent depressive symptoms in Study 2 only, with a smaller effect size than self-esteem level. Also, level, instability, and contingency of self-esteem did not interact in the prediction of depressive symptoms. Moreover, the effect of self-esteem level held when controlling for neuroticism and for all other Big Five personality traits. Thus, the findings provide converging evidence for a vulnerability effect of self-esteem level, tentative evidence for a smaller vulnerability effect of self-esteem instability, and no evidence for a vulnerability effect of self-esteem contingency.

Illness cognitions and coping self-efficacy in depression among persons with low vision

PURPOSE: To investigate the mediating role of coping self-efficacy (CSE) between two types of illness cognitions (i.e., acceptance and helplessness) and depressive symptoms in persons with low vision.

METHODS: This was a single-group, cross-sectional study. Patients with visual acuity < 6/12 in the better eye and at least minimal depressive symptoms (≥5 on the Patient Health Questionnaire-9 [PHQ-9]) were recruited from vision rehabilitation services and participated in telephone-administered structured interviews at one time point. Measures were the PHQ-9, CSE Scale, and Illness Cognition Questionnaire. Structural equation modeling (SEM) devised the causal flow of illness cognitions and their observed indirect effects on depressive symptoms via the CSE mediators: problem focused, emotion focused, and social support.

RESULTS: The study comprised 163 patients (mean age 62 years; 61% female), most with age-related macular degeneration (26%) and moderate vision impairment (44%, <6/18-6/60). Structural equation modeling indices indicated a perfect fit (χ2 < 0.001, P = 1.00), accounting for 55% of the variance in depressive symptoms. Lower levels of acceptance and higher levels of helplessness illness cognitions were associated with lower self-efficacy in problem-focused coping (β = 0.38, P < 0.001, β = -0.28, P < 0.01, respectively), which in turn was associated with greater depressive symptom severity (β = -0.54, P < 0.001).

CONCLUSIONS: Lack of acceptance and greater helplessness relating to low vision led to a lack of perceived capability to engage in problem-focused coping, which in turn promoted depressive symptoms. Third-wave cognitive-behavioral treatments that focus on acceptance may be efficacious in this population.

Creative self-efficacy and individual creativity in teams:cross-level interactions with team informational resources

We propose a cross-level perspective on the relation between creative self-efficacy and individual creativity in which team informational resources, comprising both shared “knowledge of who knows what” (KWKW) and functional background diversity, benefit the creativity of individuals more with higher creative self-efficacy. To test our hypotheses, we conducted a multi-level study with 176 employees working in 34 research and development teams of a multinational company in 4 countries. In support of our hypotheses, the link between creative self-efficacy and individual creativity was more positive with greater shared KWKW, and this interactive effect was pronounced for teams of high rather than low functional background diversity. We discuss implications for the study of creative self-efficacy in team contexts. (PsycINFO Database Record (c) 2012 APA, all rights reserved).

Computer simulation of miscibility and self-assembly structure for polymer-containing systems with special interactions

The miscibility and structure of A-B copolymer/C homopolymer blends with special interactions were studied by a Monte Carlo simulation in two dimensions. The interaction between segment A and segment C was repulsive, whereas it was attractive between segment B and segment C. In order to study the effect of copolymer chain structure on the morphology and structure of A-B copolymer/C homopolymer blends, the alternating, random and block A-B copolymers were introduced into the blends, respectively. The simulation results indicated that the miscibility of A-B block copolymer/C homopolymer blends depended on the chain structure of the A-B copolymer. Compared with alternating or random copolymer, the block copolymer, especially the diblock copolymer, could lead to a poor miscibility of A-B copolymer/C homopolymer blends. Moreover, for diblock A-B copolymer/C homopolymer blends, obvious self-organized core-shell structure was observed in the segment B composition region from 20% to 60%. However, if diblock copolymer composition in the blends is less than 40%, obvious self-organized core-shell structure could be formed in the B-segment component region from 10 to 90%. Furthermore, computer statistical analysis for the simulation results showed that the core sizes tended to increase continuously and their distribution became wider with decreasing B-segment component.