太阳风等离子体输出流量的全日面二维结构

本文根据1983年十个 Carrington 周(1733—1742)期间的 K-日冕亮度、行星际闪烁(IPS)观测和光球磁场观测,首次探讨了太阳风等离子体质量、动量和能量输出流量 F_M,F_P 和 F_E 的全日面二维平均结构及其与光球磁场结构的关系.     

Laser ablation from Lithium niobate

Received: 21 May 1997/Accepted: 4 July 1997     

Micelle Effects of Functionalized Surfactants, 1-Cetyl-3-(2-hydroxyiminopropyl)imidazolium Halides,in Reactions with p-Nitrophenyl p-Toluenesulfonate,Diethyl p-Nitrophenyl Phosphate,and Ethyl p-Nitrophenyl Ethylphosphonate

1-Cetyl-3-(2-hydroxyiminopropyl)imidazolium chloride and bromide were synthesized for the first time. These compounds are functionalized zwitterionic surfactants which give rise to micelle formation in aqueous solution. Kinetic and thermodynamic analysis of nucleophilic cleavage of p-nitrophenyl p-toluenesulfonate, diethyl p-nitrophenyl phosphate, and ethyl p-nitrophenyl ethylphosphonate in the presence of 1-cetyl-3-(2-hydroxyiminopropyl)imidazolium halide micelles showed that the latter are powerful nucleophilic reagents whose kinetic behavior can be described in terms of a simple pseudophase distribution model. The efficiency of substrate solubilization with zwitterionic surfactant micelles and the reactivity of the oximate fragment in the micelle phase were estimated on a quantitative level. The observed acceleration of S_N2 reactions with the examined p-nitrophenyl esters relative to analogous reactions of zwitterionic 1-methyl-3-(2-hydroxyiminopropyl)imidazolium halides is, respectively, 12800, 550, and 900 times; it is explained mainly by increased concentration of the reactants in micelles.     

Micellar catalysis of the reaction of 2,4-dinitrofluorobenzene with phenoxide and thiophenoxide ions

The reactions of 2,4-dinitrofluorobenzene with phenoxide and thiophenoxide ion in water are strongly catalyzed by micelles of cetyltrimethylammonium bromide (CTABr) by factors of 230 and 1100 respectively. Nonionic micelles of Brij weakly catalyze the reaction with thiophenoxide ion. Spectral measurements show that phenoxide, and especially thiophenoxide, ions interact strongly with micelles of CTABr which also markedly change the acid dissociation of phenol under given buffer conditions.     

A Common Conformation of Stabilized Triphenyl Phosphonium Ylidic Diesters with Bulky Alkoxy Groups

The phosphonium ylidic diesters, methyl and ethyl isopropyl and, methyl and ethyl t-butyl triphenylphosphoranylidene malonates, 1a,b and 2a,b , respectively, have the syn-anti conformation in solution, as in the crystal, and the bulkier alkoxy group is oriented towards phosphorus. The ¹ H NMR spectra show that in 1a,b , the isopropyl group is oriented towards the face of a phenyl group, consistent with π shielding in the ¹ H signals, and examination of the ¹ H coupled ¹³ C NMR spectra allows assignment of the acyl carbon signals. Computed bond lengths and angles for isolated molecules are similar to those in the crystal, and the geometry and the NMR spectra indicate extensive ylidic resonance. Estimated partial atomic charges on the ester oxygens are more negative when they are oriented towards, rather than away from, phosphorus.     

锂离子电池硅基负极材料的研究进展

硅基材料是新一代高容量锂离子蓄电池负极材料的典型代表,近年来已成为理论研究和应用研究的热点.本文介绍了锂离子电池硅基负极材料的制备方法、电化学性能及其研究现状,分析了硅材料作为锂离子电池负极材料存在的问题;讨论了硅材料作为锂离子电池负极材料的研究前景.并指出若能克服目前存在问题,将有望成为新一代锂离子电池负极材料.     

Effects of Amine Oxide Surfactants on Reactions of Bromide and Hydroxide Ions with Methylnaphthalene-2-Sulfonate

The SN2 reaction of Br- with methylnaphthalene-2-sulfonate (MeONs) in water is accelerated by micelles of tetradecyldialkyl amine oxide (alkyl = methyl, n-propyl) and rates increase sharply in HBr due to increased binding of Br- to the protonated amine oxide. Second-order rate constants at the micellar surface are similar to those at surfaces of trialkylammonium and sulfobetaine micelles. The reaction of OH- with MeONs is weakly inhibited by amine oxide micelles, showing that dispersive, as well as coulombic and charge-dipole, forces play a major role in the association of ions with surfaces of micellar aggregates. Copyright 1999 Academic Press.     

Aromatic nucleophilic substitution in nonionic alkylglucoside micelles

The kinetics and mechanism of the aromatic nucleophilic substitution reaction of 2,4-dinitrochlorobenzene (DNCB) with OH- in nonionic sugar-derived micelles were investigated and compared with those for reaction in polyoxyethylene glycol surfactants. Hydroxyl groups on the sugar headgroups of micellized n-nonyl beta-D-glucopyranoside (C9G1), n-dodecyl beta-D-maltoside (C12G2), and n-dodecyl beta-D-maltotrioside (C12G3) are partially deprotonated by OH- and the alkoxide ions react with DNCB, forming an arene ether. Observation of more than one isosbestic point indicates that more than one intermediate ether is formed, largely at C3 or C4 with micellar stereocontrol. Over time the ethers react with OH- giving 2,4-dinitrophenoxide ion.     

Advances in pulsed-laser atom probe: instrument and specimen design for optimum performance.

The performance of the pulsed-laser atom probe can be limited by both instrument and specimen factors. The experiments described in this article were designed to identify these factors so as to provide direction for further instrument and specimen development. Good agreement between voltage-pulsed and laser-pulsed data is found when the effective pulse fraction is less than 0.2 for pulsed-laser mode. Under the conditions reported in this article, the thermal tails of the peaks in the mass spectra did not show any significant change when produced with either a 10-ps or a 120-fs pulsed-laser source. Mass resolving power generally improves as the laser spot size and laser wavelength are decreased and as the specimen tip radius, specimen taper angle, and thermal diffusivity of the specimen material are increased. However, it is shown that two of the materials used in this study, aluminum and stainless steel, depend on these factors differently. A one-dimensional heat flow model is explored to explain these differences. The model correctly predicts the behavior of the aluminum samples, but breaks down for the stainless steel samples when the tip radius is large. A more accurate three-dimensional model is needed to overcome these discrepancies.