GaAs (AlGaAs)/CuInSe2 tandem solar cells. Technology status and future directions

Mechanically stacked, high efficiency, lightweight, and radiation resistant photovoltaic cells based on a GaAs thin film top and CuInSe2 thin film bottom cells were developed, and are considered one of the most promising devices for planar solar array applications. The highest efficiency demonstrated so far using the 4 sq cm design is 23.1 pct. AM0, one sun efficiency when measured in four-terminal configuration. The current status of the GaAs(AlGaAs)/CuInSe2 tandem cell program is presented and future directions that will lead to cell efficiencies higher than 26 pct. Air Mass Zero (AM0). A new 8 sq cm cell design developed for a two terminal and voltage matched configuration to minimize wiring complexity is discussed. Optimization of the GaAs structure for a higher end-of-life performance and further improvement of tandem cells by utilizing AlGaAs as an top absorber are described. Results of environmental tests conducted with these thin film GaAs/CuInSe2 tandem cells are also summarized

The Adequacy of Retirement Saving

macroeconomics, saving, retirement

Implementation of a Z-matrix approach within the SIESTA periodic boudnary conditions code and its application to surface adsorption

We implement a flexible Z-matrix approach in the density functional theory (DFT) periodic boundary conditions code, SIESTA. This allows a mixture of Z-matrix and Cartesian coordinates to be used for geometry specification and optimisation. In addition, geometry constraints in the form of fixed coordinates and fixed linear relationships between coordinates can be specified. A Z-matrix approach in condensed phase calculations can be advantageous, for example in studying molecular adsorption onto a surface, both in terms of flexibility and efficiency.We demonstrate our implementation for the case of thiol adsorption on the Au(111) surface

Progress in GaAs/CuInSe2 tandem junction solar cells

Much more power is required for spacecraft of the future than current vehicles. To meet this increased demand for power while simultaneously meeting other requirements for launch, deployment, and maneuverability, the development of higher-efficiency, lighter-weight, and more radiation resistant photovoltaic cells is essential. Mechanically stacked tandem junction solar cells based on (AlGaAs)GaAs thin film CLEFT (Cleavage of Lateral Epitaxial Film for Transfer) top cells and CuInSe2(CIS) thin film bottom cells are being developed to meet these power needs. The mechanically stacked tandem configuration is chosen due to its interconnect flexibility allowing more efficient array level performance. It also eliminates cell fabrication processing constraints associated with monolithically integrated multi-junction approaches, thus producing higher cell fabrication yields. The GaAs cell is used as the top cell due to its demonstrated high efficiency, and good radiation resistance. Furthermore, it offers a future potential for bandgap tuning using AlGaAs as the absorber to maximize cell performance. The CuInSe2 cell is used as the bottom cell due to superb radiation resistance, stability, and optimal bandgap value in combination with an AlGaAs top cell. Since both cells are incorporated as thin films, this approach provides a potential for very high specific power. This high specific power (W/kg), combined with high power density (W/sq m) resulting from the high efficiency of this approach, makes these cells ideally suited for various space applications

Modifications of the Rho Meson from the Virtual Pion Cloud in Hot and Dense Matter

The modification of the rho-meson self-energy due to the coupling to in-medium pions is calculated consistently at finite baryon density and temperature, keeping the full 3-momentum dependence in a gauge invariant way. As a function of nucleon density, the rho-meson spectral function is strongly enhanced in the invariant mass region M < 650 MeV, while the maximum, i.e. the pole mass, is slightly shifted upwards. As a function of temperature, for fixed nucleon density, the imaginary part of the self-energy increases further due to Bose-enhancement. At the same time the mass shift from the real part becomes very large. As a consequence of these medium effects, the dilepton rate in the low-mass region M < 650 MeV increases strongly, while the peak at M = 770 MeV disappears.Comment: 18 pages, 9 figures; resonance contributions adde

Retaining nurses in metropolitan areas: insights from senior nurse and human resource managers.

AIM: To investigate the views of senior nurse and human resource managers of strategies to retain hospital nurses in a metropolitan area. BACKGROUND: Against a global shortage, retaining nurses is a management imperative for the quality of hospital services. METHOD: Semi-structured interviews, thematically analysed. RESULTS: Metropolitan areas have many health organisations in geographical proximity, offering nurses choices in employer and employment. Senior nurse and human resource managers recognised the complexity of factors influencing nurse turnover, including those that 'pulled' nurses out of their jobs to other posts and factors that 'pushed' nurses to leave. Four themes emerged in retaining nurses: strategy and leadership, including analysis of workforce and leavers' data, remuneration, the type of nursing work and career development and the immediate work environment. CONCLUSIONS: In contexts where multiple organisations compete for nurses, addressing retention through strategic leadership is likely to be important in paying due attention and apportioning resources to effective strategies. IMPLICATIONS FOR NURSING MANAGEMENT: Aside from good human resource management practices for all, strategies tailored to different segments of the nursing workforce are likely to be important. This metropolitan study suggests attention should be paid to strategies that address remuneration, progressing nursing careers and the immediate work environment

Signal-Jamming in a Sequential Auction

In a recurring auction early bids may reveal bidders’ types, which in turn affects bidding in later auctions. Bidders take this into account and may bid in a way that conceals their private information until the last auction is played. The present paper analyzes the equilibrium of a sequence of ?rst-price auctions assuming bidders have stable private values. We show that signal-jamming occurs and explore the dynamics of equilibrium prices

Low mass dimuons within a hybrid approach

We analyse dilepton emission from hot and dense hadronic matter using a hybrid approach based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model with an intermediate hydrodynamic stage for the description of heavy-ion collisions at relativistic energies. Focusing on the enhancement with respect to the contribution from long-lived hadron decays after freeze-out observed at the SPS in the low mass region of the dilepton spectra (often referred to as "the excess"), the relative importance of the emission from the equilibrium and the non-equilibrium stages is discussed.Comment: Proceedings of Hot Quarks 2010, 21-26 June 2010 Las Londe Les Maures; v2: Corrected typos and added a commen

Aspects of meson properties in dense nuclear matter

We investigate the modification of meson spectral densities in dense nuclear matter at zero temperature. These effects are studied in a fully relativistic mean field model which goes beyond the linear density approximation and also includes baryon resonances. In particular, the role of N*(1520) and N*(1720) on the rho meson spectral density is highlighted. Even though the nucleon-nucleon loop and the nucleon-resonance loop contribute with the opposite sign, an overall reduction of rho meson mass is still observed at high density. Importantly, it is shown that the resonances cause substantial broadening of the rho meson spectral density in matter and also induces non-trivial momentum dependence. The spectral density of the a0 meson is also shown. We study the dispersion relations and collective oscillations induced by the rho meson propagation in nuclear matter together with the influence of the mixing of rho with the a0 meson. The relevant expression for the plasma frequency is also recovered analytically in the appropriate limit.Comment: 19 pages, 17 figure

Interferometry of direct photons in Pb+Pb collisions at 158 AGeV

We present final results from the WA98 experiment which provide first measurements of Bose-Einstein correlations of direct photons in ultrarelativistic heavy ion collisions. Invariant interferometric radii were extracted in the range $100<K_T<300$ MeV/c and compared to interferometric radii of charged pions. The yield of direct photons for $100<p_T<300$ MeV/c was extracted from the correlation strength parameter and compared to the yield of direct photons measured in WA98 at higher $p_T$ with the statistical subtraction method, and to predictions of a fireball model.Comment: 4 pages, 3 figures, proceedings for Quark Matter 200