Moments of Nucleon Light Cone Quark Distributions Calculated in Full Lattice QCD

Moments of the quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD. Calculations of proton matrix elements of operators corresponding to these moments through the operator product expansion have been performed on $16^3 \times 32$ lattices for Wilson fermions at $\beta = 5.6$ using configurations from the SESAM collaboration and at $\beta = 5.5$ using configurations from SCRI. One-loop perturbative renormalization corrections are included. At quark masses accessible in present calculations, there is no statistically significant difference between quenched and full QCD results, indicating that the contributions of quark-antiquark excitations from the Dirac Sea are small. Close agreement between calculations with cooled configurations containing essentially only instantons and the full gluon configurations indicates that quark zero modes associated with instantons play a dominant role. Naive linear extrapolation of the full QCD calculation to the physical pion mass yields results inconsistent with experiment. Extrapolation to the chiral limit including the physics of the pion cloud can resolve this discrepancy and the requirements for a definitive chiral extrapolation are described.Comment: 53 Pages Revtex, 26 Figures, 9 Tables. Added additional reference and updated referenced data in Table I

Syntheses and reactions of polymer-bound molybdenum complexes and hydrogenolyses of an alkynyl cobalt carbonyl cluster. [Co/sub 3/(CO)/sub 9/CCH/sub 2/CCH/sub 2/C(CH/sub 3/)/sub 3/; cyclopentadienyl-(tricarbonyl) hydridomolybdenum]

Co/sub 3/(CO)/sub 9/CCH/sub 2/C(CH/sub 3/)/sub 3/ reacted with hydrogen in aromatic solvents to yield 3,3-dimethylbutene, 2,2-dimethylbutane, and 4,4-dimethylpentanal. First order decomposition of starting material and a hydrogen pressure dependence for the rate of appearance of total products were indicated. The hydrogenation was inhibited in the presence of carbon monoxide (CO:H/sub 2/, 3.7:3.7 atm, 60/sup 0/C), but at 85/sup 0/ under the same CO/H/sub 2/ atmosphere, aldehyde production became the predominant reaction pathway at the expense of earlier-formed olefin. Incorporation of independently added olefins in the hydrogenation suggested the intermediacy of olefin aldehyde ad alkane production. A polystyrene-attached n/sup 5/-cyclopentadienyl(tricarbonyl)-hydridomolybdenum complex was prepared and its reactions with several THF-soluble bases were investigated. Enolates of ..beta..-dicarbonyl compounds quantitatively deprotonated this complex, giving polymer-bound salts of the corresponding anion. Little change in pKa in THF was induced by binding the molybdenum hydride to the polymer. Even though the polymer-supported partners rendered the reactions heterogeneous, the systems adhered reasonably well to conventional equilibrium behavior. A polymer-bound carboxylic acid and its conjugate base also displayed essentially conventional equilibrium dynamics

Imaging of liquid crystals with tunneling microscopy

We have used the scanning tunneling microscope (STM) to image a wide variety of organic liquid crystal molecules adsorbed onto a graphite substrate. From the images it is apparent that the STM is resolving individual liquid crystal molecules, as well as the different functional groups within the molecules. The high resolution allows direct observation of features that were not previously known, or had to be inferred from X-ray diffraction, neutron scattering, dilatometry, and other means. In this work, we image four diverse examples of liquid crystal molecules, and measure their packing arrangement and internal bond angles. We find that liquid crystal phases occur at the substrate boundary which have a higher degree of order and stability than the corresponding bulk phase. This surface phase remains intact even when heated 10-15 °C above the bulk isotropic transition temperature.Nous avons utilisé un microscope à effet tunnel (STM) pour visualiser une grande variété de molécules de cristaux liquides organiques adsorbées sur un substrat en graphique. D'après les images, on voit que le STM a la résolution correspondant aux molécules individuelles et aux divers groupes fonctionnels à l'intérieur des molécules. La haute résolution permet l'observation directe de détails par encore connus ou qui étaient seulement déduits à partir d'expériences de rayons X, neutrons, dilatométrie, etc... Dans ce travail, nous analysons les images de plusieurs exemples de molécules de cristaux liquides, mesurons leurs arrangement et angles de liaisons. On en déduit que les phases de cristal liquide apparaissant à la frontière du substrat ont un degré d'ordre et une stabilité supérieure à ceux de la phase massique. Cette phase en surface reste intacte, même après un réchauffement de 10 à 15 °C au-dessus de la température de transition isotrope de la phase massique