Laser Guide Star for 3.6m and 8m telescopes: Performances and astrophysical implications

We have constructed an analytical model to simulate the behavior of an adaptive optics system coupled with a sodium laser guide star. The code is applied to a 3.6-m and 8m class telescopes. The results are given in terms of Strehl ratio and full width at half maximum of the point spread function. Two atmospheric models are used, one representing good atmospheric conditions (20 per cent of the time), the other median conditions. Sky coverage is computed for natural guide star and laser guide star systems, with two different methods. The first one is a statistical approach, using stellar densities, to compute the probability to find a nearby reference. The second is a cross-correlation of a science object catalogue and the USNO catalogue. Results are given in terms of percentage of the sky that can be accessed with given performances, and in terms of number of science object that can be observed, with Strehls greater than 0.2 and 0.1 in K and J bands.Comment: 14 pages, 17 figures, accepted for publication in MNRAS. Also available at: http://www-obs.univ-lyon1.fr/~lelouarn

Pressure dependence of the oxygen isotope effect in YBa2_2Cu4_4O8_8

We have carried out measurements of the pressure dependence to 1.2 GPa of the oxygen isotope effect on $T_c$ in the high-$T_c$ superconductor YBa$_2$Cu$_4$O$_8$ using a clamp cell in a SQUID magnetometer. This compound lies close to, but just above, the 1/8$^{th}$ doping point where in La$_{2-x}$Sr$_x$CuO$_4$ marked anomalies in isotope effects occur. Both isotopes show the same very large pressure dependence of $T_c$ with the result that the isotope exponent remains low ($\sim$0.08) but increases slightly with increasing pressure. This is discussed in terms of stripe suppression, a competing pseudogap and the effect of superconducting fluctuations.Comment: 4 pages, 1 figures, submitted to Phys. Rev.

Thermodynamic properties of Bi2Sr2CaCu2O8 calculated from the electronic dispersion

The electronic dispersion for Bi2Sr2CaCu2O(8+d) has been determined from angle-resolved photoelectron spectroscopy (ARPES). From this dispersion we calculate the entropy and superfluid density. Even with no adjustable parameters we obtain an exceptional match with experimental data across the entire phase diagram, thus indirectly confirming both the ARPES and thermodynamic data. The van Hove singularity is crossed in the overdoped region giving a distinctive linear-in-T temperature dependence in the superfluid density there.Comment: 5 pages, 4 figures, submitted to Physical Review Letter

Synthesis of imidazole schiff base ligands, their silver (I) complexes and their activities against candida albicans

The work described in this thesis concerns the synthesis of ca. 50 new imidazole-containing Schiff base ligands, the formation of their Ag(I) complexes and their evaluation as agents for inhibiting the growth of the fungal pathogen, Candida albicans. The synthesis of some Schiff base ligands proved problematic and the products were characterized using standard IR and NMR spectroscopic methods, micro-analysis and, in two instances, by X-ray crystallography. Compared to the synthesis of the ligands the preparation of the Ag(I) complexes was relatively simple and pure products were isolated in moderate to good yields. The Ag(I) complexes were also characterized using standard IR and NMR spectroscopic methods, micro-analysis and, in two cases, by mass spectrometry. All of the Schiff base ligands and their corresponding Ag(I) complexes were tested for their anti-Candida activity. While the metal-free Schiff base ligands were essentially inactive, the corresponding Ag(I) complexes showed excellent activity. The set of Ag(I) complexes based on the Apim (Apim = 1-(3-aminopropyl)imidazole) Schiff base ligands were the most potent. A progressive improvement in activity of the Ag(I) complexes was seen on going from Schiff base ligands derived from 1H-imidazole-2-amine to histamine to Apim, corresponding to the increase in spacer chain length of the respective ligand sets. A notable reduction in activity was observed in the Ag(I) complexes of di-Schiff base ligands derived from 1,2-diaminoethane, 1,3-diaminopropane and 1,4-diaminobutane. The extra imine group in the spacer chain may have had a negative impact on activity and negate any positive effect due to the progressive increase in spacer chain length. The set of Ag(I) complexes containing di-Schiff base ligands derived from 1,2-, 1,3- and 1,4-phenylenediamine had similar activity to those complexes with ligands derived from 1,2-diaminoethane, 1,3-diaminopropane and 1,4-diaminobutane. In this instance, the resulting increase in the level of aromaticity does not appear to affect the anti-Candida activity

Electron pockets and pseudogap asymmetry observed in the thermopower of underdoped cuprates

We calculate the diffusion thermoelectric power of high-Tc cuprates using the resonating-valence-bond spin-liquid model developed by Yang, Rice and Zhang (YRZ). In this model, reconstruction of the energy-momentum dispersion results in a pseudogap in the density of states that is heavily asymmetric about the Fermi level. The subsequent asymmetry in the spectral conductivity is found to account for the large magnitude and temperature dependence of the thermopower observed in underdoped cuprates. In addition we find evidence in experimental data for electron pockets in the Fermi surface, arising from a YRZ-like reconstruction, near the onset of the pseudogap in the slightly overdoped regime.Comment: 6 pages, 7 figures, accepted for publication in EP

Photovoltaic system criteria documents. Volume 3: Environmental issues and evaluation criteria for photovoltaic applications

The environmental issues and evaluation criteria relating to the suitability of sites proposed for photovoltaic (PV) system deployment are identified. The important issues are defined, briefly discussed and then developed into evaluation criteria. System designers are provided with information on the environmental sensitivity of PV systems in realistic applications, background material which indicates the applicability of the siting issues identified, and evaluation criteria are defined to facilitate the selection of sites that maximize PV system operation

Photovoltaic system criteria documents. Volume 1: Guidelines for evaluating the management and operations planning of photovoltaic applications

Guidelines are provided to the Field Centers for organization, scheduling, project and cost control, and performance in the areas of project management and operations planning for Photovoltaics Test and Applications. These guidelines may be used in organizing a T and A Project Team for system design/test, site construction and operation, and as the basis for evaluating T and A proposals. The attributes are described for project management and operations planning to be used by the Field Centers. Specifically, all project management and operational issues affecting costs, schedules and performance of photovoltaic systems are addressed. Photovoltaic tests and applications include residential, intermediate load center, central station, and stand-alone systems. The sub-categories of system maturity considered are: Initial System Evaluation Experiments (ISEE); System Readiness Experiments (SRE); and Commercial Readiness Demonstration Projects (CRDP)