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Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of GaAsxSb1 – x ternary alloys have been presented and discussed. Density functional theory (DFT) computation based on the full-potential (linearized) augmented plane-wave (FP-LAPW) method has been utilized to calculate the Density of States (DOS) and the band structure of ternary alloys GaAsxSb1 – x (x = 0, 0.25, 0.50, 0.75, 1). The calculations were performed using the exchange-correlation energy functional from Perdew, Burke, and Ernzerhof, a generalized-gradient approximation (GGA-PBE) and Becke–Johnson exchange potential with local-density approximation (BJLDA) available within the framework of WIEN2k code. As compared to PBE, the results obtained from BJLDA are in close agreement with other experimental works. The DOS results show a reduction in bandgap as the Sb fraction is increased in GaAsxSb1 – x ternary alloys. The bandgap obtained by PBE and BJLDA are found to deviate from Vegard's law, i.e., it doesn't vary linearly with composition. However, the bandgap obtained by BJLD is found to closely match Vegard's law when the bowing parameter is considered. [ABSTRACT FROM AUTHOR]

Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of GaAsxSb1 –x ternary alloys have been presented and discussed. Density functional theory (DFT) computation based on the full-potential (linearized) augmented plane-wave (FP-LAPW) method has been utilized to calculate the Density of States (DOS) and the band structure of ternary alloys GaAsxSb1 –x (x = 0, 0.25, 0.50, 0.75, 1). The calculations were performed using the exchange-correlation energy functional from Perdew, Burke, and Ernzerhof, a generalized-gradient approximation (GGAPBE) and Becke-Johnson exchange potential with local-density approximation (BJLDA) available within the framework of WIEN2k code. As compared to PBE, the results obtained from BJLDA are in close agreement with other experimental works. The DOS results show a reduction in bandgap as the Sb fraction is increased in GaAsxSb1 –x ternary alloys. The bandgap obtained by PBE and BJLDA are found to deviate from Vegard's law, i.e., it doesn't vary linearly with composition. However, the bandgap obtained by BJLD is found to closely match Vegard's law when the bowing parameter is considered. [ABSTRACT FROM AUTHOR]

Dependence on petroleum and petrochemical products is unsustainable; it is both a finite resource and an environmental hazard. Biodiesel has many attractive qualities, including a sustainable feedstock; however, it has its complications. The pyrolysis (a process already in common use in the petroleum industry) of biodiesel has demonstrated the formation of smaller hydrocarbons comprising many petrochemical products but experiments suffer from difficulty quantifying the myriad reaction pathways followed and products formed. A computational simulation of pyrolysis using "ab initio molecular dynamics" offers atomic-level detail of the reaction pathways and products formed. Herein, the most prevalent fatty-acid ester (methyl linoleate) from the most prevalent feedstock for biodiesel in the United States (soybean oil) is studied. Temperature acceleration within the atom-centered density matrix propagation formalism (Car–Parrinello) utilizing the D3-M06-2X/6-31+G(d,p) model chemistry is used to compose an ensemble of trajectories. The results are grounded in comparison to experimental studies through agreement in the following: (1) the extent of reactivity (40% in the experimental and 36.1% in this work), (2) the homology of hydrocarbon products formed (wt % of C6–C10 products), and (3) the CO/CO2 product ratio. Deoxygenation pathways are critically analyzed (as the presence of oxygen in biodiesel represents a disadvantage in its current use). Within this ensemble, deoxygenation was found to proceed through two subclasses: (1) spontaneous deoxygenation, following one of four possible pathways; or (2) induced deoxygenation, following one of three possible pathways. [ABSTRACT FROM AUTHOR]

ABSTRACT Downscaled CMIP5 (Coupled Model Intercomparison Project Phase 5) climate projections of maximum daily temperature from the Downscaled CMIP3 and CMIP5 Climate and Hydrology Projections archive are examined regionally over the southeastern United States. Three measures of model skill (means-based, distribution-based, extreme-based) are utilized to assess the ability of 15 downscaled models to simulate daily maximum temperature observations. A new test is proposed to determine statistical significance of the probability density function-based skill measures. Skill scores are found to be generally high for all three measures throughout the study region, but lower scores are present in coastal and mountainous areas. Application of the significance test shows that while the skill scores may be high, they are not significantly higher than could be expected at random in some areas. The distribution-based skill scores are not significant in much of Florida and the Appalachians. The extreme-based skill scores are not significant in more than 90% of the region for all models investigated. The findings suggest that although the downscaled models have simulated observed means well and are a good match to the entire distribution of observations, they are not simulating the occurrence of extreme (above 90th percentile) maximum daily temperatures. [ABSTRACT FROM AUTHOR]

Overlapping soil moisture time series derived from two satellite microwave radiometers (the Soil Moisture and Ocean Salinity (SMOS) and the Advanced Microwave Scanning Radiometer-Earth Observing System) are used to generate a soil moisture time series from 2003 to 2010. Two statistical methodologies for generating long homogeneous time series of soil moisture are considered. Generated soil moisture time series using only morning satellite overpasses are compared to ground measurements from four watersheds in the U.S. with different climatologies. The two methods, cumulative density function (CDF) matching and copulas, are based on the same statistical theory, but the first makes the assumption that the two data sets are ordered the same way, which is not needed by the second. Both methods are calibrated in 2010, and the calibrated parameters are applied to the soil moisture data from 2003 to 2009. Results from these two methods compare well with ground measurements. However, CDF matching improves the correlation, whereas copulas improve the root-mean-square error. [ABSTRACT FROM AUTHOR]