Intercalated smectic-A structures in a new class of laterally branched substances

X-ray, DSC and optical studies of a new class of substances with aromatic rings in the lateral branches are reported. The thermal behaviour of the substances is discussed. The X-ray measurements lead to a structural model of the SA phases consisting of layer structures with intercalating molecules.     

Solvent Effect on the Photocatalytic Activity of g-C3N4/BiOBr and its Effect on Degradation of Acetochlor

Russian Journal of Physical Chemistry A - g-C3N4/BiOBr composites were obtained via solvothermal method. XRD, SEM, FTIR, UV–Vis DRS, BET, and BJH methods were used to characterize the...     

Eclipsed M2X6 compounds exhibiting very short metal-metal triple bonds

The preparation, characterization, and electronic structure of homoleptic complexes of molybdenum and tungsten bridged by bis(alkylamido)phenylboranes, M(2)[RN-B(Ph)-NR](3) (M = Mo, R = Et (1), (i)Pr (2); M = W, R = Et (3), (i)Pr (4)), are described. These triple metal-metal bond species (i) exhibit a nearly eclipsed ligand geometry and (ii) possess the shortest metal-metal bonds of neutral dimolybdenum and ditungsten M(2)X(6) complexes observed to date (d(Mo-Mo) = 2.1612(6) A (1); d(W-W) = 2.2351(7) A (4)).     

Polarized neutron imaging: A spin-echo approach

Polarized neutron imaging has recently been introduced as an efficient method to three-dimensionally visualize and measure magnetic fields even in the bulk of massive objects. Here we introduce a spin-echo approach for polarized neutron imaging, which has the potential to overcome some drawbacks of the first attempts, namely to deal with strong fields, arbitrary field directions and quantification. Furthermore our novel approach increases the efficiency of quantitative studies due to relaxed monochromatisation requirements for spin-echo neutron imaging and with respect to additional information available in the recorded images, which allows for straightforward quantification in many cases.     

Rheology of molten polystyrene with dissolved supercritical and near-critical gases

The viscosities of polystyrene melts containing three different dissolved gases, carbon dioxide, and the refrigerants R134a (1,1,1,2-tetrafluoroethane) and R152a (1,1-difluoroethane) are investigated at pressures up to 20 MPa. These pressures reach near-critical and supercritical conditions for the three gas components, and produce polymer–gas solutions containing up to 10 wt % gas. The measurements are performed in a sealed high-pressure capillary rheometer at 150 and 175°C, and at shear rates ranging from 1–2,000 s⁻¹. Very large reductions in melt viscosity are observed at high gas loading; at 150°C, 10 wt % R152a reduces the Newtonian viscosity by nearly three orders of magnitude relative to pure polystyrene. The viscosity data for all three polystyrene–gas systems follows ideal viscoelastic scaling, whereby the set of viscosity curves for a polymer-gas system can be scaled to a master curve of reduced viscosity vs. reduced shear rate identical to the viscosity curve for the pure polymer. The viscoelastic scaling factors representing the effect of dissolved gas content on rheological behavior are found to follow roughly the same variation with composition for all three polystyrene gas systems. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2771–2781, 1999     

The electronic spectrum of tantalum hydride and deuteride

The diatomic molecule tantalum hydride (TaH) and its isotopologue tantalum deuteride (TaD) have been detected for the first time by laser excitation spectroscopy. The gas-phase molecules were produced in a hollow cathode discharge. Two red-degraded bands, one arising from TaH at 636 nm and the other from TaD at 635 nm, have been recorded at sub-Doppler resolution by intermodulated fluorescence spectroscopy. A rotational analysis shows that both bands are Ω = 2←2 in character, with well-resolved Ω-doubling in the upper state of TaH. Analysis of the ¹⁸¹Ta magnetic dipole and electric quadrupole hyperfine structure reveals that the lower X³Φ₂ electronic state of the two transitions arises from a σ²πδ electronic configuration, in agreement with previous theoretical calculations. The bond length in the TaH X³Φ₂ (v = 0) level is found to be 1.756960(4) Å.     

Dynamical quark effects on light quark masses

Light quark masses are calculated in lattice QCD with two degenerate flavors of dynamical quarks. The calculations are made with improved actions with lattice spacing a = 0.22-0.11 fm. In the continuum limit we find m(M&Smacr;)(ud)(2 GeV) = 3.44(+0.14)(-0.22) MeV using the pi and rho meson masses as physical input, and m(M&Smacr;)(s)(2 GeV) = 88(+4)(-6) MeV or 90(+5)(-11) MeV with the K or straight phi meson mass as additional input. The quoted errors represent statistical and systematic combined, the latter including those from continuum and chiral extrapolations, and from renormalization factors. Compared to quenched results, two flavors of dynamical quarks reduce quark masses by about 25%.     

Imaging with polarized neutrons

While polarized neutrons have long proved to be an outstanding tool for the investigation of magnetic structures by scattering, we report on their potential for real space investigations of magnetic fields on a macroscopic scale by neutron imaging. Due to the ability of neutrons to penetrate thick layers of matter and their high sensitivity to magnetic fields owed to their magnetic moment, neutron imaging enables the investigation of magnetic fields even in bulk samples of condensed matter. We demonstrate how neutrons provide images of magnetic fields trapped in or expelled by superconductors or even reveal the path of electric currents due to the corresponding magnetic fields.