Direct evidence for negative grain boundary potential in Ca-doped and undoped YBa2Cu3O7-x

Using electron holography in a transmission electron microscope, we obtained direct evidence for the reduction of negative charge at grain boundary dislocations in Ca-doped YBa2Cu3O7 (YBCO) when compared to undoped YBCO. Because of the finite width of the valence band in the superconducting CuO2 planes, the negative grain boundary charge can lead to a depletion of electron holes available for superconductivity. A significant reduction in the size of the perturbed region in the Ca-doped samples appears to be the principal mechanism for the improved interfacial superconductivity.     

Synthesis, structure, and reductive elimination chemistry of three-coordinate arylpalladium amido complexes

Four three-coordinate arylpalladium amido complexes with a single hindered phosphine were isolated and structurally characterized. Each possessed a T-shaped geometry. Several of these complexes possessed true three-coordinate structures that lacked any additional coordination by ligand C-H bonds. All of the three-coordinate complexes underwent reductive elimination to form the corresponding triarylamine. A comparison of the rate of reaction of the three-coordinate compounds demonstrated that the rate of elimination from the pentaphenylferrocenyl di-tert-butylphosphine complex were the fastest. A comparison of the rates of reactions between three-coordinate and four-coordinate complexes showed that the rates were much faster from the three-coordinate complexes.     

Synthesis of Amino[2.2]paracyclophanes-Beneficial Monomers for Bioactive Coating of Medical Implant Materials

No Abstract     

Invariance of the non-vanishing specializations of polynomials

This paper resolves a recent conjecture of I. Kaplansky concerning the nonsingularity of linear maps that preserve the set of nonzero specializations of polynomials.     

The crystal and molecular structure of 9-methylphenanthro[4,3-a]dibenzothiophene

The crystal structure of 9-methylphenanthro[4,3-a]dibenzothiophene, C₂₅H₁₆S, M_r = 348.47, has been determined. Monoclinic, P2₁/c, a = 11.364(3), b, = 14.257(3), c = 11.575(2)Å, β = 116.26(2)°, V = 1681.9(7)ų, Z = 4, D_x = 1.38 g/cc, MoKα radiation λ = .71069 Å, F(000) = 728, T = 163K, R = .0458 for 2330 reflections. The structure compares favorably with that of hexahelicene and methylated derivatives. The thiophene moiety increases the helical core radius and decreases the pitch with respect to hexahelicene and its derivatives.