Third-order relativistic many-body calculations of energies and lifetimes of levels along the silver isoelectronic sequence

Energies of 5l_j (l= s, p, d, f, g) and 4f_j states in neutral Ag and Ag-like ions with nuclear charges Z = 48 - 100 are calculated using relativistic many-body perturbation theory. Reduced matrix elements, oscillator strengths, transition rates and lifetimes are calculated for the 17 possible 5l_j-5l'_{j'} and 4f_j-5l_{j'} electric-dipole transitions. Third-order corrections to energies and dipole matrix elements are included for neutral Ag and for ions with Z60. Comparisons are made with available experimental data for transition energies and lifetimes. Correlation energies and transition rates are shown graphically as functions of nuclear charge Z for selected cases. These calculations provide a theoretical benchmark for comparison with experiment and theory.Comment: 8 page

High efficiency InGaAs solar cells on Si by InP layer transfer

InP/Si substrates were fabricated through wafer bonding and helium-induced exfoliation of InP, and InGaAs solar cells lattice matched to bulk InP were grown on these substrates using metal-organic chemical-vapor deposition. The photovoltaic characteristics of the InGaAs cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epiready InP substrates, thus providing a demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications

Impact of remotely sensed soil moisture and precipitation on soil moisture prediction in a data assimilation system with the JULES land surface model

We show that satellite-derived estimates of shallow soil moisture can be used to calibrate a land surface model at the regional scale in Ghana, using data assimilation techniques. The modified calibration significantly improves model estimation of soil moisture. Specifically, we find an 18 % reduction in unbiased root-mean-squared differences in the north of Ghana and a 21 % reduction in the south of Ghana for a 5-year hindcast after assimilating a single year of soil moisture observations to update model parameters. The use of an improved remotely sensed rainfall dataset contributes to 6 % of this reduction in deviation for northern Ghana and 10 % for southern Ghana. Improved rainfall data have the greatest impact on model estimates during the seasonal wetting-up of soil, with the assimilation of remotely sensed soil moisture having greatest impact during drying-down. In the north of Ghana we are able to recover improved estimates of soil texture after data assimilation. However, we are unable to do so for the south. The significant reduction in unbiased root-mean-squared difference we find after assimilating a single year of observations bodes well for the production of improved land surface model soil moisture estimates over sub-Saharan Africa

The FERRUM project: laboratory-measured transition probabilities for Cr II

Aims: We measure transition probabilities for Cr II transitions from the z ^4H_J, z ^2D_J, y ^4F_J, and y ^4G_J levels in the energy range 63000 to 68000 cm^{-1}. Methods: Radiative lifetimes were measured using time-resolved laser-induced fluorescence from a laser-produced plasma. In addition, branching fractions were determined from intensity-calibrated spectra recorded with a UV Fourier transform spectrometer. The branching fractions and radiative lifetimes were combined to yield accurate transition probabilities and oscillator strengths. Results: We present laboratory measured transition probabilities for 145 Cr II lines and radiative lifetimes for 14 Cr II levels. The laboratory-measured transition probabilities are compared to the values from semi-empirical calculations and laboratory measurements in the literature.Comment: 13 pages. Accepted for publication in A&

Relativistic fine structure oscillator strengths for Li-like ions: C IV - Si XII, S XIV, Ar XVI, Ca XVIII, Ti XX, Cr XXII, and Ni XXVI

Ab initio calculations including relativistic effects employing the Breit-Pauli R-matrix (BPRM) method are reported for fine structure energy levels and oscillator strengths upto n = 10 and 0.leq. l .leq.9 for 15 Li-like ions: C IV, N V, O VI, F VII, Ne VIII, Na IX, Mg X, Al XI, Si XII, S XIV, Ar XVI, Ca XIII, Ti XX, Cr XXII, and Ni XXVI. About one hundred bound fine structure energy levels of total angular momenta, 1/2 .leq. J .leq. 17/2 of even and odd parities, total orbital angular momentum, 0 .leq L .leq. 9 and spin multiplicity (2S+1) = 2, 4 are considered for each ion. The levels provide almost 900 dipole allowed and intercombination bound-bound transitions. The BPRM method enables consideration of large set of transitions with uniform accuracy compared to the best available theoretical methods. The CC eigenfunction expansion for each ion includes the lowest 17 fine structure energy levels of the core configurations 1s^2, 1s2s, 1s2p, 1s3s, 1s3p, and 1s3d. The calculated energies of the ions agree with the measured values to within 1% for most levels. The transition probabilities show good agreement with the best available calculated values. The results provide the largest sets of energy levels and transition rates for the ions and are expected to be useful in the analysis of X-ray and EUV spectra from astrophysical sources.Comment: 16 pgs., to appear in Astronomy and Astrophysic

Laser cooling of trapped ytterbium ions with an ultraviolet diode laser

We demonstrate an ultraviolet diode laser system for cooling of trapped ytterbium ions. The laser power and linewidth are comparable to previous systems based on resonant frequency doubling, but the system is simpler, more robust, and less expensive. We use the laser system to cool small numbers of ytterbium ions confined in a linear Paul trap. From the observed spectra, we deduce final temperatures < 270 mK.Comment: submitted to Opt. Let

Photocurrent enhancement in In_(0.53)Ga_(0.47)As solar cells grown on InP/SiO_2/Si transferred epitaxial templates

InP/Si engineered substrates formed by wafer bonding and layer transfer have the potential to significantly reduce the cost and weight of III-V compound semiconductor solar cells. InP/Si substrates were prepared by He implantation of InP prior to bonding to a thermally oxidized Si substrate and annealing to exfoliate an InP thin film. Following thinning of the transferred InP film to remove surface damage caused by the implantation and exfoliation process, InGaAs solar cells lattice-matched to bulk InP were grown on these substrates using metal-organic chemical vapor deposition. The photovoltaic current-voltage characteristics of the InGaAs cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epi-ready InP substrates, and had a ~20% higher short-circuit current which we attribute to the high reflectivity of the InP/SiO_2/Si bonding interface. This work provides an initial demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications