Properties of Ni-Al under shock loading

New models for the dynamic response of materials will be based increasingly on better understanding and representation of processes occurring at the microstructural level. These developments require advances in diagnostics and models which can be applied explicitly to microstructural response. Various phenomena occur at the microstructural level which are generally ignored or averaged out in continuum-level models. One example of such 'irregular hydrodynamics' is the roughness imparted to a shock wave as it propagates through a polycrystalline material. We have developed imaging techniques to study spatial variations in shock propagation through polycrystalline materials. In order to interpret spatially-resolved data from polycrystal samples, we need to compare with simulations which represent the microstructure. Here we describe work undertaken to develop a model of the dynamic response of individual grains. The material chosen was Ni-Al alloy, because it exhibits a relatively large degree of elastic anisotropy, and it is relatively easy to manufacture

Enhanced sensitivity for hyperspectral infrared chemical detection

The sensitivity of imaging, hyperspectral, passive remote sensors in the long-wavelength infrared (LWIR) spectral region is currently limited by the ability to achieve an accurate, time-invariant, pixel-to-pixel calibration of the elements composing the Focal Plane Array (FPA). Pursuing conventional techniques to improve the accuracy of the calibration will always be limited by the trade-off between the time required to collect calibration data of improved precision and the drift in the pixel response that occurs on a timescale comparable to the calibration time. This paper will present the results from a study of a method to circumvent these problems. Improvements in detection capability can be realized by applying a quick, repetitive dither of the field of view (FOV) of the imager (by a small angular amount), so that radiance/spectral differences between individual target areas can be measured by a single FPA pixel. By performing this difference measurement repetitively both residual differences in the pixel-to-pixel calibration and l/f detector drift noise can effectively be eliminated. In addition, variations in the atmosphere and target scene caused by the motion of the sensor platform will cause signal drifts that this technique would be able to remove. This method allows improvements in sensitivity that could potentially scale as the square root of the observation time

Dynamic response of materials on sub-nanosecond time scales, and beryllium properties for inertial confinement fusion

During the past few years, substantial progress has been made in developing experimental techniques capable of investigating the response of materials to dynamic loading on nanosecond time scales and shorter, with multiple diagnostics probing different aspects of the behavior. these relatively short time scales are scientifically interesting because plastic flow and phase changes in common materials with simple crystal structures--such as iron--may be suppressed, allowing unusual states to be induced and the dynamics of plasticity and polymorphism to be explored. Loading by laser ablation can be particularly convenient. The TRIDENT laser has been used to impart shocks and isentropic compression waves from {approx}1 to 200GPa in a range of elements and alloys, with diagnostics including surface velocimetry (line-imaging VISAR), surface displacement (framed area imaging), x-ray diffraction (single crystal and polycrystal), ellipsometry, and Raman spectroscopy. A major motivation has been the study of the properties of beryllium under conditions relevant to the fuel capsule in inertial confinement fusion: magnetically-driven shock and isentropic compression shots at Z were used to investigate the equation of state and shock melting characteristics, complemented by laser ablation experiments to investigate plasticity and heterogeneous response. These results will help to constrain acceptable tolerances on manufacturing, and possible loading paths, for inertial fusion ignition experiments at the National Ignition Facility. Laser-based techniques are being developed further for future material dynamics experiments, where it should be possible to obtain high quality data on strength and phase changes up to at least 1TPa

Stand Out in Class: restructuring theclassroom environment to reducesedentary behaviour in 9–10-year-olds—study protocol for a pilot clusterrandomised controlled trial

Background: Sedentary behaviour (sitting) is a highly prevalent negative health behaviour, with individuals of allages exposed to environments that promote prolonged sitting. Excessive sedentary behaviour adversely affects health inchildren and adults. As sedentary behaviour tracks from childhood into adulthood, the reduction of sedentary time inyoung people is key for the prevention of chronic diseases that result from excessive sitting in later life. The sedentaryschool classroom represents an ideal setting for environmentalchange, through the provision of sit-stand desks. Whilstthe use of sit-stand desks in classrooms demonstrates positiveeffects in some key outcomes, evidence is currently limitedby small samples and/or short intervention durations, withfewstudiesadoptingrandomisedcontrolledtrial(RCT)designs. This paper describes the protocol of a pilot cluster RCT of a sit-stand desk interventioninprimaryschoolclassrooms.Methods/Design:A two-arm pilot cluster RCT will be conducted in eight primary schools (four intervention, four control)with at least 120 year 5 children (aged 9–10 years). Sit-stand desks will replace six standard desks in the interventionclassrooms. Teachers will be encouraged to ensure all pupils are exposed to the sit-stand desks for at least 1 h/dayon average using a rotation system. Schools assigned to the control arm will continue with their usual practice, noenvironmental changes will be made to their classrooms. Measurements will be taken at baseline, beforerandomisation, and at the end of the schools’academic year. In this study, the primary outcomes of interest will beschool and participant recruitment and attrition, acceptability of the intervention, and acceptability and complianceto the proposed outcome measures (including activPAL-measured school-time and school-day sitting, accelerometer-measured physical activity, adiposity, blood pressure, cognitive function, academic progress, engagement, andbehaviour) for inclusion in a definitive trial. A full process evaluation and an exploratory economic evaluation willalso be conducted to further inform a definitive tria

Stranded assets: environmental drivers, societal challenges, and supervisory responses

Environment factors, particularly those related to climate change, are stranding or could strand assets across different sectors and geographies with significant implications for economies, companies, financial institutions, communities, and workers. In this review, we focus on physical climate change, biodiversity loss, and litigation related to environmental factors as causes of stranded assets. We also review the emerging literature on the consequences of asset stranding for society before turning to some of the key supervisory responses that are emerging to ensure that stranded assets are measured and managed, particularly by financial institutions. These are among the areas of the stranded assets literature that have been growing most rapidly since 2015, and we focus on the literature produced since then

Laser-induced breakdown spectroscopy for the real-time analysis of mixed waste samples containing Sr

In this report, the use of Laser-induced breakdown spectroscopy to analyze mixed waste samples containing Sr is discussed. The mixed waste samples investigated include vitrified waste glass and contaminated soil. Compared to traditional analysis techniques, the laser-based method is fast (i.e., analysis times on the order of minutes) and essentially waste free since little or no sample preparation is required. Detection limits on the order of pmm Sr were determined. Detection limits obtained using a fiber optic cable to deliver laser pulses to soil samples containing Cr, Zr, Pb, Be, Cu, and Ni will also be discussed

Huygens-Fresnel wave-optics simulation of atmospheric optical turbulence and reflective speckle in CO2 differential absorption LIDAR (DIAL)

The measurement sensitivity of C02 differential absorption lidar (DIAL) can be affected by a number of different processes. We have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these processes: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of C02 DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, we briefly review a description of our model including the limitations along with previous simulations of individual effects. The performance of our modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, advanced studies have been performed to demonstrate the utility of our model in assessing the effects for different lidar geometries on RMS noise and correlation "size" in the receiver plane.U.S. Department of EnergyW-7405-ENG-3

Magnetic and Magnetocaloric Properties of the A 2 LnSbO 6 Lanthanide Oxides on the Frustrated fcc Lattice

Frustrated lanthanide oxides are promising candidates for cryogen-free magnetic refrigeration due to their suppressed ordering temperatures and high magnetic moments. While much attention has been paid to the garnet and pyrochlore lattices, the magnetocaloric effect in frustrated face-centered cubic (fcc) lattices remains relatively unexplored. We previously showed that the frustrated fcc double perovskite Ba2GdSbO6 is a top-performing magnetocaloric material (per mol Gd) because of its small nearest-neighbor interaction between spins. Here we investigate different tuning parameters to maximize the magnetocaloric effect in the family of fcc lanthanide oxides, A2LnSbO6 (A = {Ba2+, Sr2+} and Ln = {Nd3+, Tb3+, Gd3+, Ho3+, Dy3+, Er3+}), including chemical pressure via the A site cation and the magnetic ground state via the lanthanide ion. Bulk magnetic measurements indicate a possible trend between magnetic short-range fluctuations and the field-temperature phase space of the magnetocaloric effect, determined by whether an ion is a Kramers or a non-Kramers ion. We report for the first time on the synthesis and magnetic characterization of the Ca2LnSbO6 series with tunable site disorder that can be used to control the deviations from Curie–Weiss behavior. Taken together, these results suggest fcc lanthanide oxides as tunable systems for magnetocaloric design