Optimizations of Pt/SiC and W/Si multilayers for the Nuclear Spectroscopic Telescope Array

The Nuclear Spectroscopic Telescope Array, NuSTAR, is a NASA funded Small Explorer Mission, SMEX, scheduled for launch in mid 2011. The spacecraft will fly two co-aligned conical approximation Wolter-I optics with a focal length of 10 meters. The mirrors will be deposited with Pt/SiC and W/Si multilayers to provide a broad band reflectivity from 6 keV up to 78.4 keV. To optimize the mirror coating we use a Figure of Merit procedure developed for gazing incidence optics, which averages the effective area over the energy range, and combines an energy weighting function with an angular weighting function to control the shape of the desired effective area. The NuSTAR multilayers are depth graded with a power-law, d_i = a/(b + i)^c, and we optimize over the total number of bi-layers, N, c, and the maximum bi-layer thickness, d_(max). The result is a 10 mirror group design optimized for a flat even energy response both on and off-axis

W/SiC x-ray multilayers optimized for use above 100 keV

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard x-ray reflective coatings operating in the energy range 100-200 keV. Grazing-incidence x-ray reflectance at E = 8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W/SiC structures, whereas synchrotron radiation was used to measure the hard x-ray reflectance of a depth-graded multilayer designed specifically for use in the range E ~150-170 keV. We have modeled the hard x-ray reflectance using newly derived optical constants, which we determined from reflectance versus incidence angle measurements also made using synchrotron radiation, in the range E = 120-180 keV. We describe our experimental investigation in detail, compare the new W/SiC multilayers with both W/Si and W/B4C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard x-ray nuclear line telescope

Analysis of Regional Mechanics in Canine Lung Injury Using Forced Oscillations and 3D Image Registration

Acute lung injury is characterized by heterogeneity of regional mechanical properties, which is thought to be correlated with disease severity. The feasibility of using respiratory input impedance ($Z_{rs}$) and computed tomographic (CT) image registration for assessing parenchymal mechanical heterogeneity was evaluated. In six dogs, measurements of ($Z_{rs}$) before and after oleic acid injury at various distending pressures were obtained, followed by whole lung CT scans. Each ($Z_{rs}$) spectrum was fit with a model incorporating variable distributions of regional compliances. CT image pairs at different inflation pressures were matched using an image registration algorithm, from which distributions of regional compliances from the resulting anatomic deformation fields were computed. Under baseline conditions, average model compliance decreased with increasing inflation pressure, reflecting parenchymal stiffening. After lung injury, these average compliances decreased at each pressure, indicating derecruitment, alveolar flooding, or alterations in intrinsic tissue elastance. However, average compliance did not change as inflation pressure increased, consistent with simultaneous recruitment and strain stiffening. Image registration revealed peaked distributions of regional compliances, and that small portions of the lung might undergo relative compression during inflation. The authors conclude that assessments of lung function using ($Z_{rs}$) combined with the structural alterations inferred from image registration provide unique but complementary information on the mechanical derangements associated with lung injury

Refugees & Violent Group Grievance

Do refugee inflows have an effect on state fragility? In this article I examine whether refugee inflows, commonly associated in the literature with economic and cultural pressures, result in a more fragile state by means of increased violent group grievance. Violent group grievance captures a distinct form of intrastate violence, specifically small-scale hate crimes and ethnic group clashes associated with powerlessness and discrimination. The main hypothesis in this paper is that refugee inflows may increase violent group grievance. I examine the effect of refugee inflows on the level of domestic violent group grievance using quantitative analyses based on original large-N datasets and cross-sectional longitudinal models to fill gaps in the literature on state fragility. This study controls for alternative explanations and covers the time period between 2006 and 2014. The analysis results confirm the main hypothesis of this paper

Optical constants for hard x-ray multilayers over the energy range E = 35 - 180 keV

We have determined experimentally optical constants for eight thin film materials that can be used in hard X-ray multilayer coatings. Thin film samples of Ni_(.97)V_(.03), Mo, W, Pt, C, B_4C, Si and SiC were deposited by magnetron sputtering onto superpolished optical flats. Optical constants were determined from fits to reflectance-vs-incidence angle measurements made using synchrotron radiation over the energy range E=35-180 keV. We have also measured the X-ray reflectance of a prototype W/SiC multilayer coating over the energy range E=35-100 keV, and we compare the measured reflectance with a calculation using the newly derived optical constants

Lay and Expert Knowledge in a Complex Society: The AFS Teagle Foundation Project

The Teagle FoundationHow Do You Know What You Know? 2-3, Jay Mechling; Lay and Expert Knowledge in the Community College 4-5, Sean Galvin; Teaching to Live with Moving Horizons of Knowledge: Folklore Studies and New Social Problems 6-7, Jason Baird Jackson; Confronting Alternative Realities 8-9, Howard Sacks; Knowledge Gaps, Lay Experts and Feedback Loops 10-11, Sabina Magliocco; Fostering Critical Engagement through Experiential Learning 12-13, Danille Elise Christensen; Documenting Community Knowledges in Houston 14-15, Carl Lindahl; The knowledge gap as it relates to the concept of expert and lay knowledge 16-17, Tom Mould; What can student vets teach the teachers? An observer's perspective 18-19, Dorothy Noye

X-ray study of W/Si multilayers for the HEFT hard x-ray telescope

This paper outlines an in-depth study of the W/Si coated mirrors for the High Energy Focusing Telescope (HEFT). We present data taken at 8, 40 and 60 keV obtained at the Danish Space Research Institute and the European Synchrotron Radiation Facility in Grenoble. The set of samples were chosen to cover the parameter space of sample type, sample size and coating type. The investigation includes a study of the interfacial roughness across the sample surface, as substrates and later as coated, and an analysis of the roughness correlation in the W/Si coatings for N = 10 deposited bilayers. The powerlaw graded flight coating for the HEFT mirrors is studied for uniformity and scatter, as well as its performance at high energies

Strongly aligned gas-phase molecules at Free-Electron Lasers

We demonstrate a novel experimental implementation to strongly align molecules at full repetition rates of free-electron lasers. We utilized the available in-house laser system at the coherent x-ray imaging beamline at the Linac Coherent Light Source. Chirped laser pulses, i. e., the direct output from the regenerative amplifier of the Ti:Sa chirped pulse amplification laser system, were used to strongly align 2,5-diiodothiophene molecules in a molecular beam. The alignment laser pulses had pulse energies of a few mJ and a pulse duration of 94 ps. A degree of alignment of \left = 0.85 was measured, limited by the intrinsic temperature of the molecular beam rather than by the available laser system. With the general availability of synchronized chirped-pulse-amplified near-infrared laser systems at short-wavelength laser facilities, our approach allows for the universal preparation of molecules tightly fixed in space for experiments with x-ray pulses.Comment: 10 pages, 5 figure