Proton source size measurements in the eA-->e'ppX reaction

Two-proton correlations at small relative momentum q were studied in the eA(3He,4He,C,Fe)-->e(')ppX reaction at E(0)=4.46 GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on A and on the proton momentum. The size of the two-proton emission region for He was measured in eA reactions for the first time.     

Photoproduction of the omega meson on the proton at large momentum transfer

The differential cross section, dsigma/dt, for omega meson exclusive photoproduction on the proton above the resonance region (2.6相似文献   

Nuclear hyperfine coupling interactions in the rotational spectra of the linear and bent isomers of HF-N2O

The rotational spectra of six isotopomers of the linear and bent isomers of HF-N₂O have been collected in the 7-18 GHz region with a Fourier transform microwave spectrometer. The nuclear hyperfine structure in the spectra produced by HF spin-spin coupling interaction and nuclear quadrupole coupling interactions due to the D nucleus of DF and the nuclei of N₂O have been resolved and analyzed. In the linear isomer, H in HF is bonded to the terminal N in N₂O. The NF bond lengths are 2.9808(2) Å for the HF-containing isotopomers and 2.9732(2) Å for the DF-containing isotopomers. The zero point angles are 23.1° for HF and 31-34° for N₂O. The hyperfine constants suggest that the HF bond is lengthened by 0.0105 Å upon complexation and that the electric field gradients of the two nitrogen nuclei in N₂O are perturbed differently in the complex. In the bent isomer, the hydrogen bond is formed between HF and O in N₂O. The intermolecular distances are 3.4942(2) Å for the HF-containing isotopomers and 3.4436(2) Å for the DF-containing isotopomers, with HF and N₂O forming angles of 34° and 46°, respectively, with the intermolecular axis. The nuclear quadrupole coupling constants of the two nitrogen nuclei do not indicate electric field gradient perturbation in this isomer.     

Measurement of the proton spin structure function g1(x,Q2) for Q2 from 0.15 to 1.6 GeV2 with CLAS

Double-polarization asymmetries for inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH3 target in the CLAS detector. The polarized structure function g(1)(x,Q2) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q(2)=0.15-1.64 GeV2. The contributions to the first moment Gamma(1)(Q2)= integral g(1)(x,Q2) dx were determined up to Q(2)=1.2 GeV2. Using a parametrization for g(1) in the unmeasured low x regions, the complete first moment was estimated over this Q2 region. A rapid change in Gamma(1) is observed for Q2<1 GeV2, with a sign change near Q(2)=0.3 GeV2, indicating dominant contributions from the resonance region. At Q(2)=1.2 GeV2 our data are below the perturbative QCD evolved scaling value.     

The ep -->e'p eta reaction at and above the S11(1535) baryon resonance

New cross sections for the reaction e p-->e p eta are reported for total center of mass energy W = 1.5--1.86 GeV and invariant momentum transfer Q2 = 0.25--1.5 (GeV/c)(2). This large kinematic range allows extraction of important new information about response functions, photocouplings, and eta N coupling strengths of baryon resonances. Newly observed structure at W approximately 1.65 GeV is shown to come from interference between S and P waves and can be interpreted with known resonances. Improved values are derived for the photon coupling amplitude for the S11(1535) resonance.     

New ultrasonically prepared Co-based catalysts for Fischer-Tropsch synthesis

An extensive study of different preparation methods for Co/SiO2 catalysts is reported in this paper. In addition to the conventional impregnation, other more innovative methods are used including ultrasound. The prepared samples are fully characterized and tested in the CO hydrogenation (Fischer-Tropsch synthesis). The best catalytic performance, both as CO conversion and hydrocarbons selectivity, is shown by one of the sample prepared using ultrasound.     

Three different β‐cyclodextrins direct the emulsion copolymerization of a highly fluorinated methacrylate toward distinctive nanostructured particle morphologies

Stable colloidal dispersions of nanostructured semifluorinated acrylic particles with an unfluorinated core and an outer layer consisting of copolymers of the highly hydrophobic and lipophobic heptadecafluorodecyl methacrylate (FMA) were successfully synthesized with the assistance of three different cyclodextrins as phase‐transfer catalysts: β‐cyclodextrin (β‐CD), hydroxypropyl β‐cyclodextrin (HpCD), and methyl β‐cyclodextrin (MeCD). While all the cyclodextrins form a stable inclusion complex (IC) with FMA, only the ICs with the more hydrophilic HpCD and MeCD are soluble in water. Nevertheless, incorporation of FMA in the particle shell copolymer could be achieved also when using β‐CD. On the other hand, the morphology of the nanostructured particles was characterized by a “patchy” fluorinated shell dependent on the cyclodextrin used, the best results being obtained with MeCD. A monomer‐starved semicontinuous emulsion polymerization procedure was essential to favor the CD‐mediated incorporation of FMA into the copolymer structure and to achieve a stable colloidal dispersion even in the presence of small amounts of mixed anionic–nonionic surfactants. The thermal and surface properties of the latex films showed a good correlation with the shell composition and patchy nanostructured morphology of the particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of octahedral zirconium complex bearing [NHC?O] ligands,and its behavior as catalyst in the polymerization of olefins

The synthesis and characterization of a zirconium complex, having two alkoxide functionalized N‐heterocyclic carbene ligands, and its behavior as catalyst in the polymerization of ethylene and propylene, have been reported. NMR analysis showed that more than one species was obtained during synthesis. These data were confirmed by ethylene polymerization that gave rise to a linear polyethylene having a high Molecular weight and a polydispersity index (MDI) > 2 and often bimodal. The same catalytic system was able to produce highly isotactic polypropylene together with an atactic fraction. DFT studies on the complex stereoisomer stability gave indications on the species possibly involved in the polymerizations. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Determination of β-glucosidase activity in soils with a bioanalytical sensor modified with multiwalled carbon nanotubes

Soil microorganisms and enzymes are the primary mediators of soil biological processes, including organic matter degradation, mineralization, and nutrient recycling. They play an important role in maintaining soil ecosystem quality and functional diversity. Moreover, enzyme activities can provide an indication of quantitative changes in soil organic matter. β-Glucosidase (β-Glu) activity has been found to be sensitive to soil management and has been proposed as a soil quality indicator because it provides an early indication of changes in organic matter status and its turnover. The aims of the present study were to test and use a simple and convenient procedure for the assay of β-Glu activity in agricultural soil. The method described here is based on the enzymatic degradation of cellobiose by β-Glu present in the soil sample and the subsequent determination of glucose produced by the enzymatic reaction using screen-printed carbon electrodes modified with multiwalled carbon nanotubes (SPCE-CNT) equipped with coimmobilized glucose oxidase and horseradish peroxidase enzymes. The potential applied to the SPCE-CNT detection was −0.15 V versus a Ag/AgCl pseudo-reference electrode. A linear calibration curve was obtained in the range 2.7–11.3 mM with a correlation coefficient. In the present study, an easy and effective SPCE-CNT-modified electrode allowed an improved amperometric response to be achieved and this is attributed to the increased surface area upon electrode modification.