Generating heavy quarkonia in a perturbative QCD cascade

We present an implementation of heavy quarkonium production within a perturbative QCD cascade based on the Color Dipole Cascade model. We consider the processes most relevant in the context of the ψ′ surplus at the Tevatron; g → ψ′ and c → ψ′ in the color-singlet model and g → ψ′ through the color-octet mechanism. Our implementation is, however, easily extendible to other quarkonia and other production mechanisms. Where comparison is possible we find good agreement with analytical calculations. We present some suggestions for measurements at the Tevatron that would be sensitive to the shape of the fragmentation functions. Our calculations indicate that such measurements could be used to test the color-octet mechanism solution to the ψ′ surplus at the Tevatron.     

Convergence of subdivision and degree elevation

This paper presents a short, simple, and general proof showing that the control polygons generated by subdivision and degree elevation converge to the underlying splines, box-splines, or multivariate Bézier polynomials, respectively. The proof is based only on a Taylor expansion. Then the results are carried over to rational curves and surfaces. Finally, an even shorter but as simple proof is presented for the fact that subdivided Bézier polygons converge to the corresponding curve.     

Surface and bulk core level binding energy shifts in PtAu alloys

The surface core level shift of the $\text{4}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ level in a Pt2%Au and a Pt15%Au alloy has been investigated using high resolution synchrotron radiation excited photoelectron spectroscopy. The bulk and surface components in the recorded spectra have been extracted using a curve fitting procedure. The chemical shifts and the bulk-to-surface intensity ratios are consistent with a strong enrichments of Au to the alloy surfaces. The chemical shifts on nonsegregated surfaces have been measured on these alloys and on a Pt90%Au alloy using conventional XPS.     

Multicomponent structure in x-ray photoelectron spectroscopy of transition metal compounds

This paper is a summary of work in progress on a comprehensive study of the nature of satellite lines in x-ray photoelectron spectroscopy. The work can be broken down into three principal areas: (1) The satellite structure arising from photoionization in the K shell of transition metal compounds has been measured using CuKα x rays. From these data the relative importance of electron shake up and multiples splitting has been ascertained. (2) A systematic study of the satellite structure following photoionization in the 2p subshell of the metal ion for first row transition metal halides, hexacyano complexes, acetyl acetonates and other miscellaneous compounds. The data can be explained in terms of monopole excitation involving either charge exchange between ligand and metal orbitals or excitation of electrons in the 3d orbital. (3) A study of multiplet splitting in the 3s subshell of nickel for a series of NiFe_xCr _2-xO₄ alloys has been carried out and compared with measurements on the hyper field interactions from Mössbauer experiments.     

The response of an elastomer filled with soft ferrite to mechanical and magnetic influences

The behaviour of a ferrite-elastomer composite is studied under the combined influence of changing elastic stresses and magnetic fields. The instruments used are described, and the results obtained are presented in a series of graphs. The composite behaves erratically unless subjected to a “shake-down” procedure. In a quasi-stable state, previously unknown magnetomechanical effects are exhibited and described.     

Structure of the aqueous electron: assessment of one-electron pseudopotential models in comparison to experimental data and time-dependent density functional theory

The prevailing structural paradigm for the aqueous electron is that of an s-like ground-state wave function that inhabits a quasi-spherical solvent cavity, a viewpoint that is supported by numerous atomistic simulations using various one-electron pseudopotential models. This conceptual picture has recently been challenged, however, on the basis of results obtained from a new electron-water pseudopotential model that predicts a more delocalized wave function and no well-defined solvent cavity. Here, we examine this new model in comparison to two alternative, cavity-forming pseudopotential models. We find that the cavity-forming models are far more consistent with the experimental data for the electron's radius of gyration, optical absorption spectrum, and vertical electron binding energy. Calculations of the absorption spectrum using time-dependent density functional theory are in quantitative or semiquantitative agreement with experiment when the solvent geometries are obtained from the cavity-forming pseudopotential models, but differ markedly from experiment when geometries that do not form a cavity are used.     

Effect of n-alkanes and peptides on the phase equilibria in phosphatidylcholine—water systems

Abstract

The phase equilibria in phosphatidylcholine (PC)-n-alkane-²H₂O systems have been studied to elucidate the driving forces for the transition between a lamellar liquid-crystalline (L _α) phase and a reversed hexagonal (H _II) phase. A tentative phase diagram for the system dioleoyl-PC (DOPC)-n-dodecane-²H₂O was determined. DOPC forms an L _α phase up to at least 90°C in excess water. However, an H _II phase was formed at room temperature at both low and high water concentrations in DOPC-n-dodecane-²H₂O mixtures. The phase equilibria were also studied in PC-n-dodecane-²H₂O systems containing PC with different degrees of acyl chain unsaturation. The water and dodecane concentrations required to induce the formation of an H _II (or isotropic) phase increase in the order dilinoleoyl-PC ～ DOPC < 1-palmitoyl-2-oleoyl-PC < dipalmitoyl-PC. The effect of n-alkanes with different chain lengths (C₈–C₂₀) on the phase equilibria in DOPC-n-alkane-²H₂O mixtures was studied. Although the number of alkane carbon atoms added per DOPC molecule was kept constant, the ability of the alkanes to promote the formation of an H _II phase was strongly chain length dependent; the ability decreased when going from octane to eicosane. Finally, some PC-peptide-²H₂O systems were investigated. Gramicidin (hydrophobic) had a similar influence on the phase equilibria as the alkanes. Melittin (amphiphilic) induced the formation of an isotropic phase, while insulin and duramycin (water soluble) had no, or a very limited, ability to induce a non-lamellar phase, respectively. Our results are discussed in the light of simple physical models dealing with the self-assembly of amphiphiles.     

The first branching point in porphyrin biosynthesis: a systematic docking, molecular dynamics and quantum mechanical/molecular mechanical study of substrate binding and mechanism of uroporphyrinogen-III decarboxylase

In humans, uroporphyrinogen decarboxylase is intimately involved in the synthesis of heme, where the decarboxylation of the uroporphyrinogen-III occurs in a single catalytic site. Several variants of the mechanistic proposal exist; however, the exact mechanism is still debated. Thus, using an ONIOM quantum mechanical/molecular mechanical approach, the mechanism by which uroporphyrinogen decarboxylase decarboxylates ring D of uroporphyrinogen-III has been investigated. From the study performed, it was found that both Arg37 and Arg50 are essential in the decarboxylation of ring D, where experimentally both have been shown to be critical to the catalytic behavior of the enzyme. Overall, the reaction was found to have a barrier of 10.3 kcal mol(-1) at 298.15 K. The rate-limiting step was found to be the initial proton transfer from Arg37 to the substrate before the decarboxylation. In addition, it has been found that several key interactions exist between the substrate carboxylate groups and backbone amides of various active site residues as well as several other functional groups.