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

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

Liquid crystal films on curved surfaces: An entropic sampling study

The confining effect of a spherical substrate inducing anchoring (normal to the surface) of rod-like liquid crystal molecules contained in a thin film spread over it has been investigated with regard to possible changes in the nature of the isotropic-to-nematic phase transition as the sample is cooled. The focus of these Monte Carlo simulations is to study the competing effects of the homeotropic anchoring due to the surface inducing orientational ordering in the radial direction and the inherent uniaxial order promoted by the intermolecular interactions. By adopting entropic sampling procedure, we could investigate this transition with a high temperature precision, and we studied the effect of the surface anchoring strength on the phase diagram for a specifically chosen geometry. We find that there is a threshold anchoring strength of the surface below which uniaxial nematic phase results, and above which the isotropic fluid cools to a radially ordered nematic phase, besides of course expected changes in the phase transition temperature with the anchoring strength. In the vicinity of the threshold anchoring strength we observe a bistable region between these two structures, clearly brought out by the characteristics of the corresponding microstates constituting the entropic ensemble.Comment: 14 pages, 5 figure

Computer simulations of hard pear-shaped particles

We report results obtained from Monte Carlo simulations investi- gating mesophase formation in two model systems of hard pear-shaped particles. The first model considered is a hard variant of the trun- cated Stone-Expansion model previously shown to form nematic and smectic mesophases when embedded within a 12-6 Gay-Berne-like po- tential [1]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k = 3, glassy behaviour is seen at high pressures, whereas for k = 5 several bi-layer-like domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalised Gay-Berne formalism, results are presented for particles with elongation k = 3; 4 and 5. Here, the systems with k = 3 and 4 fail to display orientationally ordered phases, but that with k = 5 shows isotropic, nematic and, unusually for a hard-particle model, interdigitated smectic A2 phases.</p

Long-range correlation and multifractality in Bach's Inventions pitches

We show that it can be considered some of Bach pitches series as a stochastic process with scaling behavior. Using multifractal deterend fluctuation analysis (MF-DFA) method, frequency series of Bach pitches have been analyzed. In this view we find same second moment exponents (after double profiling) in ranges (1.7-1.8) in his works. Comparing MF-DFA results of original series to those for shuffled and surrogate series we can distinguish multifractality due to long-range correlations and a broad probability density function. Finally we determine the scaling exponents and singularity spectrum. We conclude fat tail has more effect in its multifractality nature than long-range correlations.Comment: 18 page, 6 figures, to appear in JSTA

Nematic liquid crystal alignment on chemical patterns

Patterned Self-Assembled Monolayers (SAMs) promoting both homeotropic and planar degenerate alignment of 6CB and 9CB in their nematic phase, were created using microcontact printing of functionalised organothiols on gold films. The effects of a range of different pattern geometries and sizes were investigated, including stripes, circles and checkerboards. EvanescentWave Ellipsometry was used to study the orientation of the liquid crystal (LC) on these patterned surfaces during the isotropic-nematic phase transition. Pretransitional growth of a homeotropic layer was observed on 1 ¹m homeotropic aligning stripes, followed by a homeotropic mono-domain state prior to the bulk phase transition. Accompanying Monte-Carlo simulations of LCs aligned on nano-patterned surfaces were also performed. These simulations also showed the presence of the homeotropic mono-domain state prior to the transition.</p

Saliva-based colorimetric test as an index of gingival inflammation in epidemiologic studies

– There is a pressing need for a reliable, low-cost method of assessing the gingival and periodontal status of large population groups. Existing indexes, despite their value in dental public health, are still too subject to examiner variability for use by uncalibrated examiners. This study describes an evaluation of a quick, inexpensive, extraoral colorimetric test for gingival inflammation, based on a reaction between saliva and the test material. It could probably be applied by non-professional personnel. In this study, the test was applied to a population of elementary schoolchildren, denial hygiene students and faculty, and adult inmates of two correctional institutions. These populations were chosen on the assumption that they would exhibit varying intensities of gingival inflammation. Values obtained from the colorimetric test carried out by one researcher were compared with Gingival Index (GI) scores observed by a different examiner. Results suggest that the colorimetric test may be a valid, reliable means of detecting major differences in the prevalence of gingival inflammation in most adult populations, although having little, if any, useful application among children at the mixed dentition stage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73489/1/j.1600-0528.1978.tb01169.x.pd

EVALUATION OF DENTAL HEALTH EDUCATION IN A SCHOOL DENTAL CARE PROGRAM

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65546/1/j.1752-7325.1978.tb03715.x.pd

Self – perceived and clinically diagnosed dental and periodontal health status among young adults and their implications for epidemiological surveys

BACKGROUND: Clinical (normative) and subjective (self-assessment) evaluation of caries and periodontal diseases have been reported to demonstrate a significant disparity. The dental public health team is obligated to recognize and understand this gap. The objectives of the study were to investigate the practical values of using questionnaires (self–perceived assessment) as compared to clinical examinations (normative assessment) and to evaluate the implications of the results in understanding the public's perception of oral health. METHODS: The investigation was performed on 4920, 21 year-old Israeli adults upon release from compulsory military service between 1996 and 1998. Participants were asked to fill in a questionnaire inquiring how they would rate their personal dental and periodontal health levels. Clinical examinations, employing the DMFT and CPITN indices, were performed to determine normative oral health status. Perceived and normative assessments were compared for sensitivity, specificity, positive and negative predictive values and overall proportions using the clinical examinations as a gold standard. RESULTS: The sensitivity (disease perception) for dental status was found to be 0.34, while the specificity (health perception) was found to be 0.83. The positive predictive value for perceived dental status was found to be 0.68, whereas the negative predictive value was found to be 0.54. The sensitivity for perceived periodontal status was found to be 0.28, while the specificity was found to be 0.83. The positive predictive value for perceived periodontal status was found to be 0.05, whereas the negative predictive value was found to be 0.97. Regarding the overall proportions, a large discrepancy was found between self–assessment and professional assessment for both dental and periodontal health status. CONCLUSIONS: Self-assessment questionnaires were of low value in evaluating oral health status both in the individual and public levels, though perception levels of health were higher than that of disease. Findings reflects a low level of awareness of the public that may influence care-seeking behavior and highlight the importance of oral health promotion and the crucial need for public health action

Spatial and Spectral Coherent Control with Frequency Combs

Quantum coherent control (1-3) is a powerful tool for steering the outcome of quantum processes towards a desired final state, by accurate manipulation of quantum interference between multiple pathways. Although coherent control techniques have found applications in many fields of science (4-9), the possibilities for spatial and high-resolution frequency control have remained limited. Here, we show that the use of counter-propagating broadband pulses enables the generation of fully controlled spatial excitation patterns. This spatial control approach also provides decoherence reduction, which allows the use of the high frequency resolution of an optical frequency comb (10,11). We exploit the counter-propagating geometry to perform spatially selective excitation of individual species in a multi-component gas mixture, as well as frequency determination of hyperfine constants of atomic rubidium with unprecedented accuracy. The combination of spectral and spatial coherent control adds a new dimension to coherent control with applications in e.g nonlinear spectroscopy, microscopy and high-precision frequency metrology.Comment: 12 page