Combining Monte Carlo methods with coherent wave optics for the simulation of phase-sensitive X-ray imaging

Phase-sensitive X-ray imaging shows a high sensitivity towards electron density variations, making it well suited for imaging of soft tissue matter. However, there are still open questions about the details of the image formation process. Here, a framework for numerical simulations of phase-sensitive X-ray imaging is presented, which takes both particle- and wave-like properties of X-rays into consideration. A split approach is presented where we combine a Monte Carlo method (MC) based sample part with a wave optics simulation based propagation part, leading to a framework that takes both particle- and wave-like properties into account. The framework can be adapted to different phase-sensitive imaging methods and has been validated through comparisons with experiments for grating interferometry and propagation-based imaging. The validation of the framework shows that the combination of wave optics and MC has been successfully implemented and yields good agreement between measurements and simulations. This demonstrates that the physical processes relevant for developing a deeper understanding of scattering in the context of phase-sensitive imaging are modelled in a sufficiently accurate manner. The framework can be used for the simulation of phase-sensitive X-ray imaging, for instance for the simulation of grating interferometry or propagation-based imaging.

Integrating tracking in concentrating photovoltaics using laterally moving optics

In this work the concept of integrating tracking in concentrating photovoltaics is briefly summarized and possible fields of application are classified. A previously proposed system setup relies on the use of two rotational symmetric laterally moving plano-convex lenses to achieve 500× concentration over an angular range of ±24 ◦ . However, the circular lens apertures are less suitable for application in lens array structures. A new design algorithm based on the Simultaneous Multiple Surface algorithm in three dimensions (SMS3D) demonstrates the ability to address this problem. Performance simulations show that the resulting non-rotational symmetric design outperforms its conventional rotational symmetric counterpart

Free-form optics for Fresnel-lens-based photovoltaic concentrators

The Concentrated Photovoltaics (CPV) promise relies upon the use of high-efficiency triple-junction solar cells (with proven efficiencies of over 44%) and upon high-performance optics that allow for high concentration concurrent with relaxed manufacturing tolerances (all key elements for low-cost mass production). Additionally, uniform illumination is highly desirable for efficiency and reliability reasons. All of these features have to be achieved with inexpensive optics containing only a few (in general no more than 2) optical elements. In this paper we show that the degrees of freedom using free-forms allow the introduction of multiple functionalities required for CPV with just 2 optical elements, one of which is a Fresnel lens.

Single process femtosecond microfabrication of key components for integrated optics

We present recent results on femtosecond microfabrication of key components for integrated optics such as highly curved low-loss waveguides in glasses, depressed cladding waveguides in crystals. Details of microfabrication and characterisation are discussed.

Conference Report of the First Meeting of the Native American and Indigenous Studies Association, 21-23 May 2009, Department of American Indian Studies, University of Minneapolis, Minesota, United States of America

Report provided back by Bronwyn Fredericks on her participation at the First Native American and Indigenous Studies Association Meeting held 21-23 May 2009 in Minnesota, United States of America.

Psychopathology during childhood and adolescence predicts delusional-like experiences in adults : a 21-year birth cohort study

Objective: Community surveys have shown that many otherwise well individuals report delusional-like experiences. The authors examined psychopathology during childhood and adolescence as a predictor of delusional-like experiences in young adulthood. ---------- Method: The authors analyzed prospective data from the Mater-University of Queensland Study of Pregnancy, a birth cohort of 3,617 young adults born between 1981 and 1983. Psychopathology was measured at ages 5 and 14 using the Child Behavior Checklist (CBCL) and at age 14 using the Youth Self-Report (YSR). Delusional-like experiences were measured at age 21 using the Peters Delusional Inventory. The association between childhood and adolescent symptoms and later delusional-like experiences was examined using logistic regression. ---------- Results: High CBCL scores at ages 5 and 14 predicted high levels of delusional-like experiences at age 21 (odds ratios for the highest versus the other quartiles combined were 1.25 and 1.85, respectively). Those with YSR scores in the highest quartile at age 14 were nearly four times as likely to have high levels of delusional-like experiences at age 21 (odds ratio=3.71). Adolescent-onset psychopathology and continuous psychopathology through both childhood and adolescence strongly predicted delusional-like experiences at age 21. Hallucinations at age 14 were significantly associated with delusional-like experiences at age 21. The general pattern of associations persisted when adjusted for previous drug use or the presence of nonaffective psychoses at age 21. ---------- Conclusion: Psychopathology during childhood and adolescence predicts adult delusional-like experiences. Understanding the biological and psychosocial factors that influence this developmental trajectory may provide clues to the pathogenesis of psychotic-like experiences.

Limits of spherical blur determined with an adaptive optics mirror

We extended an earlier study (Vision Research, 45, 1967–1974, 2005) in which we investigated limits at which induced blur of letter targets becomes noticeable, troublesome and objectionable. Here we used a deformable adaptive optics mirror to vary spherical defocus for conditions of a white background with correction of astigmatism; a white background with reduction of all aberrations other than defocus; and a monochromatic background with reduction of all aberrations other than defocus. We used seven cyclopleged subjects, lines of three high-contrast letters as targets, 3–6 mm artificial pupils, and 0.1–0.6 logMAR letter sizes. Subjects used a method of adjustment to control the defocus component of the mirror to set the 'just noticeable', 'just troublesome' and 'just objectionable' defocus levels. For the white-no adaptive optics condition combined with 0.1 logMAR letter size, mean 'noticeable' blur limits were ±0.30, ±0.24 and ±0.23 D at 3, 4 and 6 mm pupils, respectively. White-adaptive optics and monochromatic-adaptive optics conditions reduced blur limits by 8% and 20%, respectively. Increasing pupil size from 3–6 mm decreased blur limits by 29%, and increasing letter size increased blur limits by 79%. Ratios of troublesome to noticeable, and of objectionable to noticeable, blur limits were 1.9 and 2.7 times, respectively. The study shows that the deformable mirror can be used to vary defocus in vision experiments. Overall, the results of noticeable, troublesome and objectionable blur agreed well with those of the previous study. Attempting to reduce higher-order aberrations or chromatic aberrations, reduced blur limits to only a small extent.

Effect of optical aberrations on the colour appearance of small lights

Purpose: Small red lights (one minute of arc or less) change colour appearance with positive defocus. We investigated the influence of longitudinal chromatic aberration and monochromatic aberrations on the colour appearance of small narrow band lights. Methods: Seven cyclopleged, trichromatic observers viewed a small light (one minute of arc, λmax = 510, 532, 550, 589, 620, 628 nm, approximately 19 per cent Weber contrast) centred within a black annulus (4.5 minutes of arc) and surrounded by a uniform white field (2,170 cd/m2). Pupil size was four millimetres. An optical trombone varied focus. Longitudinal chromatic aberration was controlled with a two component Powell achromatising lens that neutralises the eye’s chromatic aberration; a doublet that doubles and a triplet that reverses the eye’s chromatic aberration. Astigmatism and higher order monochromatic aberrations were corrected using adaptive optics. Results: Observers reported a change in appearance of the small red light (628 nm) without the Powell lens at +0.49 ± 0.21 D defocus and with the doublet at +0.62 ± 0.16 D. Appearance did not alter with the Powell lens, and five of seven observers reported the phenomenon with the triplet for negative defocus (-0.80 ± 0.47 D). Correction of aberrations did not significantly affect the magnitude at which the appearance of the red light changed (+0.44 ± 0.18 D without correction; +0.46 ± 0.16 D with correction). The change in colour appearance with defocus extended to other wavelengths (λmax = 510 to 620 nm), with directions of effects being reversed for short wavelengths relative to long wavelengths. Conclusions: Longitudinal chromatic aberrations but not monochromatic aberrations are involved in changing the appearance of small lights with defocus.