Sky Variability in the y Band at the LSST Site

We have measured spatial and temporal variability in the y band sky brightness over the course of four nights above Cerro Tololo near Cerro Pachon, Chile, the planned site for the Large Synoptic Survey Telescope (LSST). Our wide-angle camera lens provided a 41 deg field of view and a 145 arcsec pixel scale. We minimized potential system throughput differences by deploying a deep depletion CCD and a filter that matches the proposed LSST y_3 band (970 nm-1030 nm). Images of the sky exhibited coherent wave structure, attributable to atmospheric gravity waves at 90 km altitude, creating 3%-4% rms spatial sky flux variability on scales of about 2 degrees and larger. Over the course of a full night the y_3 band additionally showed highly coherent temporal variability of up to a factor of 2 in flux. We estimate the mean absolute sky level to be approximately y_3 = 17.8 mag (Vega), or y_3 = 18.3 mag (AB). While our observations were made through a y_3 filter, the relative sky brightness variability should hold for all proposed y bands, whereas the absolute levels should more strongly depend on spectral response. The spatial variability presents a challenge to wide-field cameras that require illumination correction strategies that make use of stacked sky flats. The temporal variability may warrant an adaptive y band imaging strategy for LSST, to take advantage of times when the sky is darkest.Comment: 8 pages, 5 figures, accepted to PASP. Minor changes from referee report and editor's revisions

Soft Gamma-ray Detector for the ASTRO-H Mission

ASTRO-H is the next generation JAXA X-ray satellite, intended to carry instruments with broad energy coverage and exquisite energy resolution. The Soft Gamma-ray Detector (SGD) is one of ASTRO-H instruments and will feature wide energy band (40-600 keV) at a background level 10 times better than the current instruments on orbit. SGD is complimentary to ASTRO-H's Hard X-ray Imager covering the energy range of 5-80 keV. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield where Compton kinematics is utilized to reject backgrounds. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) sensors. Good energy resolution is afforded by semiconductor sensors, and it results in good background rejection capability due to better constraints on Compton kinematics. Utilization of Compton kinematics also makes the SGD sensitive to the gamma-ray polarization, opening up a new window to study properties of gamma-ray emission processes. The ASTRO-H mission is approved by ISAS/JAXA to proceed to a detailed design phase with an expected launch in 2014. In this paper, we present science drivers and concept of the SGD instrument followed by detailed description of the instrument and expected performance.Comment: 17 pages, 15 figures, Proceedings of the SPIE Astronomical Instrumentation "Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray

A NEW DEVICE AND METHOD FOR MEASURING VOLATILE COMPOUNDS IN MONITORING WELLS

Accurate, timely measurement of chlorinated solvents and other volatile contaminants in groundwater is crucial to support responsible environmental management. Traditionally, two distinctly different paradigms have been explored to meet this need--fixed laboratory analysis and ''real-time'' sensors. While these alternatives remain important, field based and field screening tools represent a potentially useful intermediate approach that balances some of the advantages and disadvantages of the traditional ''endmember'' paradigms. The value of accurate, in-field measurements during characterization was recognized in recent sampling/decision methods, such as the TRIAD approach (ITRC, 2003). Strategies that support gathering accurate data on the timescales representative of the rate of change of the system (e.g., months to years, not seconds to minutes) is key for long-term monitoring for chlorinated solvent plumes in which attenuation based remedies are being considered. A team of researchers developed a down-well sampling device that, when used in combination with field gas analysis tools, provides data in the field. The test results indicate this tool, as configured, will provide accurate measurements (as compared with laboratory methods) at concentrations in the hundreds of ppb or higher range, but require confirmatory traditional sampling with laboratory analysis at concentrations approaching 20 ppb and less. The logistics and costs of the sampling device were somewhat complex. The results of the study, while equivocal, generally suggest that future development of this type of in-field technique may be warranted

The effects of maximising the UK's Tobacco Control Score on inequalities in smoking prevalence and premature coronary heart disease mortality: a modelling

Background Smoking is more than twice as common among the most disadvantaged socioeconomic groups in England compared to the most affluent and is a major contributor to health-related inequalities. The United Kingdom (UK) has comprehensive smoking policies in place: regular tax increases; public information campaigns; on-pack pictorial health warnings; advertising bans; cessation; and smoke-free areas. This is confirmed from its high Tobacco Control Scale (TCS) score, an expert-developed instrument for assessing the strength of tobacco control policies. However, room remains for improvement in tobacco control policies. Our aim was to evaluate the cumulative effect on smoking prevalence of improving all TCS components in England, stratified by socioeconomic circumstance. Methods Effect sizes and socioeconomic gradients for all six types of smoking policy in the UK setting were adapted from systematic reviews, or if not available, from primary studies. We used the IMPACT Policy Model to link predicted changes in smoking prevalence to changes in premature coronary heart disease (CHD) mortality for ages 35–74. Health outcomes with a time horizon of 2025 were stratified by quintiles of socioeconomic circumstance. Results The model estimated that improving all smoking policies to achieve a maximum score on the TCS might reduce smoking prevalence in England by 3 % (95 % Confidence Interval (CI): 1–4 %), from 20 to 17 % in absolute terms, or by 15 % in relative terms (95 % CI: 7–21 %). The most deprived quintile would benefit more, with absolute reductions from 31 to 25 %, or a 6 % reduction (95 % CI: 2–7 %). There would be some 3300 (95 % CI: 2200–4700) fewer premature CHD deaths between 2015–2025, a 2 % (95 % CI: 1.4–2.9 %) reduction. The most disadvantaged quintile would benefit more, reducing absolute inequality of CHD mortality by about 4 % (95 % CI: 3–9 %). Conclusions Further, feasible improvements in tobacco control policy could substantially improve population health, and reduce health-related inequalities in England

Studies of active galactic nuclei with CTA

In this paper, we review the prospects for studies of active galactic nuclei (AGN) using the envisioned future Cherenkov Telescope Array (CTA). This review focuses on jetted AGN, which constitute the vast majority of AGN detected at gamma-ray energies. Future progress will be driven by the planned lower energy threshold for very high energy (VHE) gamma-ray detections to ~10 GeV and improved flux sensitivity compared to current-generation Cherenkov Telescope facilities. We argue that CTA will enable substantial progress on gamma-ray population studies by deepening existing surveys both through increased flux sensitivity and by improving the chances of detecting a larger number of low-frequency peaked blazars because of the lower energy threshold. More detailed studies of the VHE gamma-ray spectral shape and variability might furthermore yield insight into unsolved questions concerning jet formation and composition, the acceleration of particles within relativistic jets, and the microphysics of the radiation mechanisms leading to the observable high-energy emission. The broad energy range covered by CTA includes energies where gamma-rays are unaffected from absorption while propagating in the extragalactic background light (EBL), and extends to an energy regime where VHE spectra are strongly distorted. This will help to reduce systematic effects in the spectra from different instruments, leading to a more reliable EBL determination, and hence will make it possible to constrain blazar models up to the highest energies with less ambiguity.Comment: invited review article, 15 pages, 9 figures, Astroparticle Physics, Special Issue on Physics with the Cherenkov Telescope Array, in pres

The LSST Camera Overview

The LSST camera is a wide-field optical (0.35-1um) imager designed to provide a 3.5 degree FOV with better than 0.2 arcsecond sampling. The detector format will be a circular mosaic providing approximately 3.2 Gigapixels per image. The camera includes a filter mechanism and, shuttering capability. It is positioned in the middle of the telescope where cross-sectional area is constrained by optical vignetting and heat dissipation must be controlled to limit thermal gradients in the optical beam. The fast, f/1.2 beam will require tight tolerances on the focal plane mechanical assembly. The focal plane array operates at a temperature of approximately -100 C to achieve desired detector performance. The focal plane array is contained within an evacuated cryostat, which incorporates detector front-end electronics and thermal control. The cryostat lens serves as an entrance window and vacuum seal for the cryostat. Similarly, the camera body lens serves as an entrance window and gas seal for the camera housing, which is filled with a suitable gas to provide the operating environment for the shutter and filter change mechanisms. The filter carousel can accommodate 5 filters, each 75 cm in diameter, for rapid exchange without external intervention

Prenatal exome sequencing in anomalous fetuses: new opportunities and challenges

We investigated the diagnostic and clinical performance of exome sequencing (ES) in fetuses with sonographic abnormalities with normal karyotype, microarray and, in some cases, normal gene specific sequencing

Relative Bioavailability and Bioaccessibility and Speciation of Arsenic in Contaminated Soils

Background: Assessment of soil arsenic (As) bioavailability may profoundly affect the extent of remediation required at contaminated sites by improving human exposure estimates. Because small adjustments in soil As bioavailability estimates can significantly alter risk assessments and remediation goals, convenient, rapid, reliable, and inexpensive tools are needed to determine soil As bioavailability

The guider and wavefront curvature sensor subsystem for the Large Synoptic Survey Telescope

The Large Synoptic Survey Telescope instrument include four guiding and wavefront sensing subsystems called corner raft subsystems, in addition to the main science array of 189 4K x 4K CCDs. These four subsystems are placed at the four corners of the instrumented field of view. Each wavefront/guiding subsystem comprises a pair of 4K x 4K guide sensors, capable of producing 9 frames/second, and a pair of offset 2K x 4K wavefront curvature sensors from which the images are read out at the cadence of the main camera system, providing 15 sec integrations. These four guider/wavefront corner rafts are mechanically and electrically isolated from the science sensor rafts and can be installed or removed independently from any other focal plane subsystem. We present the implementation of this LSST subsystem detailing both hardware and software development and status.Astronom

A framework for modeling the detailed optical response of thick, multiple segment, large format sensors for precision astronomy applications

Near-future astronomical survey experiments, such as LSST, possess system requirements of unprecedented fidelity that span photometry, astrometry and shape transfer. Some of these requirements flow directly to the array of science imaging sensors at the focal plane. Availability of high quality characterization data acquired in the course of our sensor development program has given us an opportunity to develop and test a framework for simulation and modeling that is based on a limited set of physical and geometric effects. In this paper we describe those models, provide quantitative comparisons between data and modeled response, and extrapolate the response model to predict imaging array response to astronomical exposure. The emergent picture departs from the notion of a fixed, rectilinear grid that maps photo-conversions to the potential well of the channel. In place of that, we have a situation where structures from device fabrication, local silicon bulk resistivity variations and photo-converted carrier patterns still accumulating at the channel, together influence and distort positions within the photosensitive volume that map to pixel boundaries. Strategies for efficient extraction of modeling parameters from routinely acquired characterization data are described. Methods for high fidelity illumination/image distribution parameter retrieval, in the presence of such distortions, are also discussed. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.Astronom