Efficient calculation of SAMPL4 hydration free energies using OMEGA,SZYBKI, QUACPAC,and Zap TK

Several submissions for the SAMPL4 hydration free energy set were calculated using OpenEye tools, including many that were among the top performing submissions. All of our best submissions used AM1BCC charges and Poisson–Boltzmann solvation. Three submissions used a single conformer for calculating the hydration free energy and all performed very well with mean unsigned errors ranging from 0.94 to 1.08 kcal/mol. These calculations were very fast, only requiring 0.5–2.0 s per molecule. We observed that our two single-conformer methodologies have different types of failure cases and that these differences could be exploited for determining when the methods are likely to have substantial errors.     

Evidence for charge Kondo effect in superconducting Tl-doped PbTe

We report results of low-temperature thermodynamic and transport measurements of Pb1-xTlxTe single crystals for Tl concentrations up to the solubility limit of approximately x=1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature T(K) approximately 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high T(c) values.     

C-terminal processing of yeast Spt7 occurs in the absence of functional SAGA complex

Background  

Spt7 is an integral component of the multi-subunit SAGA complex that is required for the expression of ~10% of yeast genes. Two forms of Spt7 have been identified, the second of which is truncated at its C-terminus and found in the SAGA-like (SLIK) complex.     

Microstructure and transport properties of various 90° grain boundaries in YBa2Cu3O7 thin films

The microstructure and transport properties of various 90° grain boundaries in (103) oriented YBa₂Cu₃O₇(YBCO) thin films grown epitaxially in situ by 90° off-axis sputtering are compared. The (103) films grown on (101) LaAlO₃ and (101) SrTiO₃ substrates have specific sets of 90° grain boundaries in both principal in-plane directions: 90° [010] twist boundaries along the [101] direction, and 90° [010] symmetrical tilt boundaries and 90° [010] basal-plane-faced tilt boundaries along the (301) direction. No weak-link behavior is observed across some of these boundaries by transport critical current density and normalized magnetic field dependence of J _c measurements along both those in-plane directions. High-resolution transmission electron microscopy reveals variations in the structure and microfaceting of the 90° boundaries, which may contribute to the absence of weak-link behavior. These results have important implications for understanding the behavior of step-edge Josephson junctions.     

Optical microscopic,X-ray diffraction,and electrical resistance studies of CuCl at high pressure

Electrical resistance and X-ray diffraction measurements and also optical observations under a polarizing microscope were made on CuCl to pressures in excess of 12.5 GPa at room temperature using a diamond anvil cell. Resistance measurements were also performed in a piston-cylinder apparatus to pressures of approximately 5.5 GPa at room temperature. Three samples of CuCl prepared by different methods were examined. No anomalous pressure dependence in electrical resistance was found in the pressure range studied, and no dramatic changes in optical transmission were observed up to pressures of approximately 10.0 GPa. Optical observations and X-ray diffraction measurements indicate the existence of four phases in the pressure range studied, including a nonconducting black opaque phase which grows with time when CuCl is left for several days at the highest pressures.     

Epitaxial growth of Nb3Ge on Nb3Ir and Nb3Rh

This is a report on a cooperative research carried out in Stanford University to investigate the possibility of using epitaxy to prepare the high T_c superconductor Nb₃Ge in an A15 crystalline structure at the 3:1 stoichiometry.Nb₃Ir polycrystalline films with the A15 structure deposited on sapphire were used as substrates for the epitaxial growth of Nb₃Ge because of the favorable lattice parameter match. The experimental results clearly show that epitaxial growth indeed occurs and helps to extend the range of homogeneity of the A15 phase up to 26.3 at.% Ge as compared with the thermodynamic equilibrium boundary at 19 at.% Ge. We also used Nb₃Rh films as substrates and found them inferior to Nb₃Ir because of the multiphase nature of the films.In addition to extending the A15 phase boundary epitaxy results in a considerable rise in the superconducting transition temperature for Ge-rich samples together with a reduction in the transition width. The work suggests that polycrystalline epitaxy can be an important tool in the synthesis of thin-film intermetallic compounds.