Fractional statistics in the fractional quantum Hall effect

A microscopic confirmation of the fractional statistics of the {\em quasiparticles} in the fractional quantum Hall effect has so far been lacking. We calculate the statistics of the composite-fermion quasiparticles at $\nu=1/3$ and $\nu=2/5$ by evaluating the Berry phase for a closed loop encircling another composite-fermion quasiparticle. A careful consideration of subtle perturbations in the trajectory due to the presence of an additional quasiparticle is crucial for obtaining the correct value of the statistics. The conditions for the applicability of the fractional statistics concept are discussed.Comment: Phys. Rev. Lett., in pres

Gallium Nitride Super-Luminescent Light Emitting Diodes for Optical Coherence Tomography Applications

The role of biasing of absorber sections in multi-contact GaN ~400nm SLEDs is discussed. We go on to assess such devices for OCT applications. Analysis of the SLED emission spectrum allows an axial resolution of 6.0μm to be deduced in OCT applications

Berry phases for composite fermions: effective magnetic field and fractional statistics

The quantum Hall superfluid is presently the only viable candidate for a realization of quasiparticles with fractional Berry phase statistics. For a simple vortex excitation, relevant for a subset of fractional Hall states considered by Laughlin, non-trivial Berry phase statistics were demonstrated many years ago by Arovas, Schrieffer, and Wilczek. The quasiparticles are in general more complicated, described accurately in terms of excited composite fermions. We use the method developed by Kjonsberg, Myrheim and Leinaas to compute the Berry phase for a single composite-fermion quasiparticle, and find that it agrees with the effective magnetic field concept for composite fermions. We then evaluate the "fractional statistics", related to the change in the Berry phase for a closed loop caused by the insertion of another composite-fermion quasiparticle in the interior. Our results support the general validity of fractional statistics in the quantum Hall superfluid, while also giving a quantitative account of corrections to it when the quasiparticle wave functions overlap. Many caveats, both practical and conceptual, are mentioned that will be relevant to an experimental measurement of the fractional statistics. A short report on some parts of this article has appeared previously.Comment: 14 pages, 9 figure

Casimir force between sharp-shaped conductors

Casimir forces between conductors at the sub-micron scale cannot be ignored in the design and operation of micro-electromechanical (MEM) devices. However, these forces depend non-trivially on geometry, and existing formulae and approximations cannot deal with realistic micro-machinery components with sharp edges and tips. Here, we employ a novel approach to electromagnetic scattering, appropriate to perfect conductors with sharp edges and tips, specifically to wedges and cones. The interaction of these objects with a metal plate (and among themselves) is then computed systematically by a multiple-scattering series. For the wedge, we obtain analytical expressions for the interaction with a plate, as functions of opening angle and tilt, which should provide a particularly useful tool for the design of MEMs. Our result for the Casimir interactions between conducting cones and plates applies directly to the force on the tip of a scanning tunneling probe; the unexpectedly large temperature dependence of the force in these configurations should attract immediate experimental interest

Symptoms and severity of visual stress in nursing students: implications for education and healthcare settings

Visual Stress reportedly affects 5-12% of the general population and 20-30% of people with dyslexia. Symptoms are characterized by visual discomfort and perceptual distortions when viewing lines of text, and can be exacerbated by fluorescent lighting and bright paper. In this study, nursing students reported their levels of visual discomfort while reading text on contemporary (ultra-white) paper and on beige-coloured paper, under either standard classroom-lighting (600 lux; n = 31) or reduced illumination(400 lux; n = 25). Under the standard lighting, 10(28%) of subjects reported notable levels of Visual Stress (scoring ≥15 on a visual discomfort scale of 1-30). When reading from the beige-coloured paper the group reported less discomfort across all six symptoms. These differences were statistically significant for five of the six symptoms and the total discomfort score. The results were similar but less pronounced for the group in the reduced illumination condition. This study found that Visual Stress-related reading discomfort can also affect capable readers and, moreover, that simple adjustments to lighting and/or visual media can alleviate such symptoms. The implications of these findings for organisational practice in education and healthcare settings are discussed. El estrés visual puede afectar del 5 al 12% de la población general y del 20 al 30% de las personas con dislexia. Los síntomas se caracterizan por incomodidad visual y distorsiones de la percepción visual en la lectura, y pueden agravarse con la iluminación fluorescente y el papel brillante. En este estudio, estudiantes de enfermería expresan niveles de incomodidad visual al leer texto en papel ultrablanco y en papel de color beige, ya sea con iluminación estándar del aula (600 lux; n = 31) o con iluminación reducida (400 lux ; n = 25). Bajo la iluminación estándar, 10 (28%) de los sujetos informaron niveles notables de estrés visual (puntuación ? 15 en una escala de1 a 30). Al leer en color beige, el grupo presentó menos malestar en los síntomas. Estas diferencias fueron estadísticamente significativas para cinco síntomas y el total de malestar. Los resultados fueron menos pronunciados para el grupo en la condición de iluminación reducida. Encontrándose que la incomodidad de lectura relacionada con estrés visual también puede afectar a lectores expertos y, además, que simples ajustes a la iluminación y/o medios visuales pueden reducirla. Se discuten las implicaciones para la práctica en entornos educativos y sanitarios

Caregiver responses to symptoms of first-onset psychosis: A comparative study of Chinese-and Euro-Canadian families

Considerable evidence suggests that ethnic Chinese families in Canada are reluctant to seek psychiatric treatment for a relative with mental illness. The following hypotheses were investigated: (a) longer delay in seeking treatment among Chinese versus Euro-Canadians; (b) greater burden among Chinese versus Euro-Canadians; and (c) more negative conceptions of mental illness among Chinese versus Euro-Canadians. The sample consisted of 18 Chinese Canadians and 36 Euro-Canadians experiencing a first episode of psychosis; each participant recruited a parent or sibling who responded to measures of perceived family burden and attitudes toward mental illness. Results confirmed all three hypotheses. Chinese care-givers were particularly more likely to endorse the practice of keeping mental illness a secret from others, as well as withdrawal from individuals with mental illness. These findings suggest that Chinese caregivers were more affected by the stigma of mental illness than were Euro-Canadian caregivers

OCT-Documented Incision Features and Natural History of Clear Corneal Incisions Used for Bimanual Microincision Cataract Surgery

Use of anterior segment OCT to identify features and natural history of bimanual incisions used only for phacoemulsification and a main incision used only for intraocular lens insertion

Ethnopharmacology and chemotaxonomy of essential oil yielding Australian plants

The first of three main focal points of this study was to uncover commercially viable natural products, particularly essential oils, complemented with information related to cultivar requirements and biological activity. Emphasis was subsequently placed on 'Eremophila longifolia', which produced a range of geographically specific chemotypes. To investigate potential factors related to this variability a ploidy analysis was performed, which revealed that the high yielding isomenthone diploid chemotype of 'E. longifolia' from western New South Wales is genetically different from all other chemotypes in Australia, which are normally tetraploid, except of course the diploid phenylpropanoid chemotype occupying a small geographic range on the north-west coast of Western Australia. With moderate to high antimicrobial activity of essential oils the isomenthone chemotype is therefore judged to be the best choice for cultivation

Gallium nitride light sources for optical coherence tomography

The advent of optical coherence tomography (OCT) has permitted high-resolution, non-invasive, in vivo imaging of the eye, skin and other biological tissue. The axial resolution is limited by source bandwidth and central wavelength. With the growing demand for short wavelength imaging, super-continuum sources and non-linear fibre-based light sources have been demonstrated in tissue imaging applications exploiting the near-UV and visible spectrum. Whilst the potential has been identified of using gallium nitride devices due to relative maturity of laser technology, there have been limited reports on using such low cost, robust devices in imaging systems. A GaN super-luminescent light emitting diode (SLED) was first reported in 2009, using tilted facets to suppress lasing, with the focus since on high power, low speckle and relatively low bandwidth applications. In this paper we discuss a method of producing a GaN based broadband source, including a passive absorber to suppress lasing. The merits of this passive absorber are then discussed with regards to broad-bandwidth applications, rather than power applications. For the first time in GaN devices, the performance of the light sources developed are assessed though the point spread function (PSF) (which describes an imaging systems response to a point source), calculated from the emission spectra. We show a sub-7μm resolution is possible without the use of special epitaxial techniques, ultimately outlining the suitability of these short wavelength, broadband, GaN devices for use in OCT application