Spatial relationships between snow contaminant content, grain size, and surface temperature from multispectral images of Mt. Rainier, Washington (USA)

We use multispectral MODIS/ASTER Airborne Simulator (MASTER) data collected at Mt. Rainier, Washington (USA) to map spatial covariance between snowpack properties and to evaluate techniques for quantitative estimation of reflectance, grain size, and temperature. The late-August MASTER images reveal a distinct pattern of snow contaminant content, grain size, and temperature related to a recent snowfall and late-summer melting. Spatial correlation between grain size and temperature patterns suggests that rapid destructive metamorphism of the fresh snow occurred when temperatures were near 0 °C. We use 10 specific locations to evaluate hemispherical-directional reflectance factor (HDRF), grain size, and temperature retrievals. We map relative snow contaminant content using visible (0.4-0.8 μm) HDRF spectra. Atmospheric correction and topographic modeling limit the accuracy of HDRF estimates. We use MASTER-derived spectra near 1.8 and 2.2 μm to estimate optical grain size (by comparison to modeled layers of ice spheres) and physical grain size (by comparison to measured spectra with known physical grain size and by correlation to ground measurements). Estimated physical grain sizes were less than estimated optical grain sizes. Differing definitions of optical and physical grain sizes could contribute to this discrepancy. Limitations at 1.8 and 2.2 μm, including reduced discrimination between larger grain radii (>∼500 μm physical, >∼200 μm optical) and low signal-to-noise ration with atmospheric effects and decreasing solar irradiance, suggest that grain size retrieval may be improved at other wavelengths (e.g., 1.1 μm). Accounting for uncertainty in emissivity, atmospheric correction, and detector noise, we estimate systematic errors in our radiant temperatures at <1.8 °C. This study shows both strengths and limitations for coregistered visible, short-wave infrared, and thermal infrared images to estimate snowpack properties and reveal their spatial coherence.     

Fabrication and cathodoluminescent properties of the ZnO‐Cu,Ga and ZnS‐Cu,Ga film phosphors

Abstract— A novel technique for cathodoluminescent screen fabrication using a new method of film phosphor doping has been developed. The crystalline structure and morphology of the films were investigated. Cathodoluminescence spectra were measured at different excitation levels and temperatures (300 and 77 K). The luminance is 200 cd/m² for ZnS:Cu, Ga and 1100 cd/m² for ZnO:Cu, Ga films at a temperature of 300 K and 3700 cd/m² for ZnO:Cu, Ga film at a temperature of 77 K. The films show more saturated green color than commercial phosphors.     

Electronic,electrical and thermodynamic properties of Ca5Si3 by first principles calculations and low temperature experimental techniques

A combined experimental and computational study of the Ca₅Si₃ phase is presented. Its’ electronic structure and lattice stability are investigated by first principles methods: four different crystal lattices have been investigated by means of density functional theory (DFT) calculations and pseudopotentials within the generalized-gradient approximation using the VASP code. The Ca₅Si₃ phase is predicted to undergo an high pressure transition: the lattice transition tI32(Cr₅B₃-type) → tI32(W₅Si₃-type) has been predicted by DFT to occur at 14.9 GPa. The electronic and band structure of the tI32 Cr₅B₃-type lattice is calculated and discussed. The Ca₅Si₃ phase ground state structure is predicted to be a metal with a peaked density of states below the Fermi energy and a sharp minimum right above it. Experimentally the low temperature resistivity and heat capacity of the Ca₅Si₃ phase have been measured between 2 and 300 K and discussed in view of our computational predictions and available literature. The Ca₅Si₃ tI32(Cr₅B₃-type) standard pressure polymorph exhibits a metallic temperature dependence of the electric conductivity in agreement with the DFT predictions.