载有卟啉的介孔SBA-15表面光电压的性质研究

用表面光电压谱(SPS)和场诱导表面光电压谱(FISPS)技术对比研究了卟啉和介孔SBA-15及载有卟啉的介孔SBA-15的表面光伏特性.固载后同时显示了卟啉和介孔的光电压性质,但是光电压响应强度减弱,这是因为卟啉和介孔之间发生了电子传递的缘故.在外电场诱导下,它们的光伏响应强度随外加正电场光伏响应强度的增加而增强,随外加负电场光伏响应强度的增加而减弱.而装载后的SBA-15在334和425 nm处的光伏响应信号随外加电场的变化而有不同的变化.     

Determination of the Nitrogen Atom Density in the Afterglow of a Nitrogen and Helium,Nonequilibrium, Atmospheric Pressure Plasma

Three methods have been examined for evaluating the concentration of nitrogen atoms in the afterglow of a nonequilibrium, helium-stabilized, atmospheric pressure plasma. These are nitric oxide titration, absolute emission intensity of N₂(B ³_g) and temporal decay of the N₂(B ³_g) emission. To employ the second method, the rate constants for the recombination of N atoms into N₂(B ³_g), at different vibrational levels of the B state, were determined. The third newly developed method has three advantages over the other two techniques: (1) it can predict the N-atom density for the entire afterglow, (2) it does not require calibration of the N₂(B ³_g) emission intensity, and (3) it does not disturb the gas flow. According to these measurements, the atmospheric pressure plasma produced a high density of nitrogen atoms, exceeding 4.0×10¹⁵ cm^–3 at the edge of the discharge for 10 Torr N₂ in 745 Torr He at 375 K and 15.5 W/cm³.     

Strong supramolecular-based magnetic exchange in pi-stacked radicals. Structure and magnetism of a hydrogen-bonded verdazyl radical:hydroquinone molecular solid.

The X-ray crystal structure and magnetic properties of a molecular crystal consisting of 1,5-dimethyl-3-(2-pyridyl)-6-oxoverdazyl radical and hydroquinone (pyvd:hq) are presented. The structure contains a two-dimensional network of hydrogen bonds involving the hydroquinones and the pyridine ring of the pyvd radical. The radicals adopt an unusual head-over-tail (antiparallel) pi-stacked array perpendicular to the hydrogen-bonded planes. The variable-temperature magnetic susceptibility data can be modeled using a one-dimensional antiferromagnetic chain model, with J = -58 cm(-1). The strength of the magnetic coupling is very unusual because there are no close intermolecular radical-radical contacts to provide conventional pathways for magnetic interactions. A pathway for coupling is proposed involving the mediation of magnetic exchange interactions between radical centers by the pyridine rings. Density functional calculations on the pyvd radical, as well as aggregates thereof based on the X-ray structure, have been employed in attempts to understand the possible mechanisms by which the strong magnetic interactions are achieved.     

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Ohne Zusammenfassung     

Partnering a Three-Coordinate Gallium Cation with a Hydroborate Counter-Ion for the Catalytic Hydrosilylation of CO2

A novel β-diketiminate stabilized gallium hydride, (^DippL)Ga(Ad)H (where ( ^Dipp L)={HC(MeCDippN)₂}, Dipp=2,6-diisopropylphenyl and Ad=1-adamantyl), has been synthesized and shown to undergo insertion of carbon dioxide into the Ga−H bond under mild conditions. In this case, treatment of the resulting κ¹-formate complex with triethylsilane does not lead to regeneration of the hydride precursor. However, when combined with B(C₆F₅)₃, (^DippL)Ga(Ad)H catalyses the reductive hydrosilylation of CO₂. Under stoichiometric conditions, the addition of one equivalent of B(C₆F₅)₃ to (^DippL)Ga(Ad)H leads to the formation of a 3-coordinate cationic gallane complex, partnered with a hydroborate anion, [(^DippL)Ga(Ad)][HB(C₆F₅)₃]. This complex rapidly hydrometallates carbon dioxide and catalyses the selective reduction of CO₂ to the formaldehyde oxidation level at 60 °C in the presence of Et₃SiH (yielding H₂C(OSiEt₃)₂). When catalysis is undertaken in the presence of excess B(C₆F₅)₃, appreciable enhancement of activity is observed, with a corresponding reduction in selectivity: the product distribution includes H₂C(OSiEt₃)₂, CH₄ and O(SiEt₃)₂. While this system represents proof-of-concept in CO₂ hydrosilylation by a gallium hydride system, the TOF values obtained are relatively modest (max. 10 h⁻¹). This is attributed to the strength of binding of the formatoborate anion to the gallium centre in the catalytic intermediate (^DippL)Ga(Ad){OC(H)OB(C₆F₅)₃}, and the correspondingly slow rate of the turnover-limiting hydrosilylation step. In turn, this strength of binding can be related to the relatively high Lewis acidity measured for the [(^DippL)Ga(Ad)]⁺ cation (AN=69.8).     

Simulation of three-phase displacement experiments

Three-phase displacement experiments for a water-benzyl alcohol-decane system are simulated. Literature experimental three-phase relative permeabilities for the system are used to describe the relative permeabilities in the three-phase region for different three-phase relative permeability models. Saturation trajectories and elliptical regions are mapped in the three-phase region. Simulations are performed to model displacement experiments including breakthrough and the formation of multiple shocks. The model can be used to predict the results for other displacements. In an experiment where significant gravity segregation is present, the displacement is more accurately modeled by assuming a uniform initial condition than by using the actual vertical saturation and assuming no cross flow. It is shown how different residual saturation values can be measured in the laboratory depending on the initial saturation conditions in the core. The experimental residual saturations can be significantly different than the ‘theoretical’ or model values.     

The evolution of linear viscoelasticity during the vulcanization of polyethylene

The evolution of linear viscoelasticity during the vulcanization of polyethylene is studied through the gel point. The material in the vicinity of the gel point is described by two scaling laws: one characterizes the viscoelasticity at the critical point and a second characterizes the evolution of viscoelasticity near the gel point. Time Resolved Mechanical Spectroscopy is used to observe both scaling phenomena. The material at the gel point displays power law relaxation over five decades of time with a power-law relaxation exponent equal to 0.32. This study conforms with previous findings that this exponent is composition-dependent. The longest relaxation time diverges in the vicinity of the gel point as _max |p _c - p| ^–1/, and we find = 0.2. This result conforms with previous reports that this exponent may be independent of composition. The Arrhenius flow activation energy for this material undergoes three-fold changes during crosslinking up to the gel point. A single-adjustable-parameter stretched-exponential-power law relaxation function is an inadequate representation of crosslinked materials over any significant range of extent of the reaction up to the gel point.     

W-代数W(2,2)的单参数量子形变(英文)

众所周知,泛包络代数的量子形变所对应的量子群结构是依据所给代数的单根系给出的.我们构造了q-形变W代数Wq,并给出其非平凡的量子群结构.