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The wind-energy (WE) industry relies on numerical weather prediction (NWP) forecast models as foundational or base models for many purposes, including wind-resource assessment and wind-power forecasting. During the Second Wind Forecast Improvement Project (WFIP2) in the Columbia River Basin of Oregon and Washington, a significant effort was made to improve NWP forecasts through focused model development, to include experimental refinements to the High Resolution Rapid Refresh (HRRR) model physics and horizontal grid spacing. In this study, the performance of an experimental version of HRRR that includes these refinements is tested against a control version, which corresponds to that of the operational HRRR run by National Oceanic and Atmospheric Administration/National Centers for Environmental Protection at the outset of WFIP2. The effects of horizontal grid resolution were also tested by comparing wind forecasts from the HRRR (with 3-km grid spacing) with those from a finer-resolution HRRR nest with 750-m grid spacing. Model forecasts are validated against accurate wind-profile measurements by three scanning, pulsed Doppler lidars at sites separated by a total distance of 71 km. Model skill and improvements in model skill, attributable to physics refinements and improved horizontal grid resolution, varied by season, by site, and during periods of atmospheric phenomena relevant to WE. In general, model errors were the largest below 150 m above ground level (AGL). Experimental HRRR refinements tended to reduce the mean absolute error (MAE) and other error metrics for many conditions, but degradation in skill (increased MAE) was noted below 150 m AGL at the two lowest-elevation sites at night. Finer resolution was found to produce the most significant reductions in the error metrics. [ABSTRACT FROM AUTHOR]

Annually and seasonally averaged wind profiles from three Doppler lidars were obtained from sites in the Columbia River basin of east-central Oregon and Washington, a major region of wind-energy production, for the Second Wind Forecast Improvement Project (WFIP2) experiment. The profile data are used to quantify the spatial variability of wind flows in this area of complex terrain, to assess the HRRR–NCEP model's ability to capture spatial and temporal variability of wind profiles, and to evaluate model errors. Annually averaged measured wind speed differences over the 70-km extent of the lidar measurements reached 1 m s−1 within the wind-turbine rotor layer, and 2 m s−1 for 200–500 m AGL. Stronger wind speeds in the lowest 500 m occurred at sites higher in elevation, farther from the river, and farther west—closer to the Cascade Mountain barrier. Validating against the lidar data, the HRRR model underestimated strong wind speeds (>12 m s−1) and, consequently, their frequency of occurrence, especially at the two lowest-elevation sites, producing annual low biases in rotor-layer wind speed of 0.5 m s−1. The RMSE between measured and modeled winds at all sites was about 3 m s−1 and did not degrade significantly with forecast lead time. The nature of the model errors was different for different seasons. Moreover, although the three sites were located in the same basin terrain, the nature of the model errors was different at each site. Thus, if only one of the sites had been instrumented, different conclusions would have been drawn as to the major sources of model error, depending on where the measurements were made. [ABSTRACT FROM AUTHOR]

We present a systematic study on the influence of the miscut orientation on structural and electronic properties in the homoepitaxial growth on off-oriented β-Ga2O3 (100) substrates by metalorganic chemical vapour phase epitaxy. Layers grown on (100) substrates with 6° miscut toward the [00 1 ¯ ] direction show high electron mobilities of about 90 cm2 V−1 s−1 at electron concentrations in the range of 1–2 × 1018 cm−3, while layers grown under identical conditions but with 6° miscut toward the [001] direction exhibit low electron mobilities of around 10 cm2 V−1 s−1. By using high-resolution scanning transmission electron microscopy and atomic force microscopy, we find significant differences in the surface morphologies of the substrates after annealing and of the layers in dependence on their miscut direction. While substrates with miscuts toward [00 1 ¯ ] exhibit monolayer steps terminated by ( 2 ¯ 01) facets, mainly bilayer steps are found for miscuts toward [001]. Epitaxial growth on both substrates occurs in step-flow mode. However, while layers on substrates with a miscut toward [00 1 ¯ ] are free of structural defects, those on substrates with a miscut toward [001] are completely twinned with respect to the substrate and show stacking mismatch boundaries. This twinning is promoted at step edges by transformation of the (001)-B facets into ( 2 ¯ 01) facets. Density functional theory calculations of stoichiometric low index surfaces show that the ( 2 ¯ 01) facet has the lowest surface energy following the (100) surface. We conclude that facet transformation at the step edges is driven by surface energy minimization for the two kinds of crystallographically inequivalent miscut orientations in the monoclinic lattice of β-Ga2O3. [ABSTRACT FROM AUTHOR]

We present a comprehensive ab initio study of all non fully symmetric Γ point lattice vibrations in CaV2O5. The characteristics of CaV2O5 are a half-filled upper electron band and a ladder-like crystal structure. Adopting the frozen-phonon approach we calculate and analyze in detail the phonon eigenfrequencies and eigenvectors. The corresponding spectra of inelastic light scattering are computed for all Raman-active modes, including their resonance behavior as a function of incoming light. Our results allow for a qualitative and quantitative understanding of the phonon-related features in experimental optical excitation spectra. The theoretical data are employed to discuss available measurements and provide an improved assignment of the observed modes with respect to symmetry and displacement patterns. Electron hopping parameters and spin-spin exchange matrix elements are evaluated from the electronic bands. The changes in these parameters upon atomic displacements along the phonon eigenvectors are analyzed semiquantitatively, yielding the effect of lattice vibrations on charge and spin degrees of freedom. It is discussed how all the obtained results differ from the ones in the quarter-filled NaV2O5 compound due to differences in the electron band structure and in the chemistry. [ABSTRACT FROM AUTHOR]

Here we report the electronic π-band structure of sexithiophene obtained from 6T(010) oriented films. The angle-resolved valence band photoemission results taken parallel and perpendicular to the molecular axis are compared to those of sexiphenyl and interpreted in terms of intra- and inter-molecular band dispersion. We show that the strong photoemission intensity variations with emission angle parallel to the molecular axis are well reproduced by the Fourier transforms of the molecular orbitals of the isolated molecules. These results imply that ARUPS can yield quite detailed information about molecular geometry, both in terms of molecular orientation and internal structure. [ABSTRACT FROM AUTHOR]

To understand the link between doping and electronic properties in the high-temperature superconductors, we have performed first-principles calculations for several representatives of high Tc compounds. In the single-layer cuprate HgBa2CuO4 the excess oxygen attracts electrons from the CuO2 plane leading to an increase of the hole concentration in this building block, where the maximum amount of holes is reached when the dopant oxygen shell is closed. The usage of supercells allows to study the inhomogeneous charge distribution as a function of doping, i.e. from the underdoped up to the overdoped regime. Comparison is made with other compounds like Ba-doped La2CuO4 and oxygen-deficient YBa2Cu3O7− x. The effects of our findings on superconductivity are discussed. [ABSTRACT FROM AUTHOR]

We consider changes in the electron-phonon coupling in high- T c cuprates caused by site-selective oxygen isotope substitution. Contrary to the total substitution, the site-selective replacement influences the coupling constant for each phonon mode due to the induced changes in the phonon eigenvectors. The relative changes for some modes can be larger than 100%. The measured properties sensitive to these changes are discussed. [ABSTRACT FROM AUTHOR]

We consider in detail Raman scattering by vibration of the apical oxygen ions in the RBa2Cu3O7 superconducting cuprates. The scattering intensity is very sensitive to the ratio of diagonal and off-diagonal matrix elements of electron-phonon coupling, bandstructure, and carrier concentration. Our results show a large quantitative difference between the results of frozen-phonon and perturbational approach to the Raman process. The discrepancy becomes especially large when interband transitions to the states near the Fermi level are close to resonance with the incident light. The calculation of phonon-induced ion charge fluctuations shows an analogous discrepancy. The reason for these effects is the possibility of carrier redistribution between different parts of the Fermi surface arising in the frozen-phonon approximation. Our results show that Raman scattering in superconducting superlattices is very sensitive to the properties of the states near the Fermi level. For this reason experiments performed on the superlattices can help to resolve the discrepancy. [ABSTRACT FROM AUTHOR]

With the aim of establishing a relationship between the electronic structure and the site occupancy within the Cu-O chains, we perform total energy calculations for the sub-stoichiometric compound Yba2 Cu3 O6.5 for various patterns of vacancy ordering. Supercells containing up to four formula units are considered. The effective interactions of O(1) atoms are extracted from the total energies by means of the cluster expansion technique. The most stable configuration is found to be the experimentally observed ortho-II structure. This finding is confirmed by Monte-Carlo simulations for a rigid lattice using the pair interactions. Thermal disorder effects are studied. The influence of vacancy ordering on the total and partial densities of states is discussed. [ABSTRACT FROM AUTHOR]