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91.
C. Meier M. Volkmer J. Lieschke M. Fink N. Böwering 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,30(2):183-187
Relative elastic differential cross sections for scattering of 1 keV electrons from CF3H, CF4, CF3Cl, CH3F and CH3Cl molecules were measured for momentum transfer from 3 Å?1 to 29 Å?1. The oscillatory residuals remaining after substraction of the atomic scattering and the molecular interference contributions calculated in the independent atom model are ascribed to the influence of intramolecular multiple scattering. The data reflect the dominant contributions of the CF3-group and show larger oscillations than obtained from triple scattering calculations according to the method of Liu and Bonham using the second Born approximation. 相似文献
92.
The amorphous aluminum silicate (Al2O3)2(SiO2) [AS2] is investigated by means of large scale molecular dynamics computer simulations. We consider fully equilibrated melts in the temperature range 6100 K> or =T> or =2300 K as well as glass configurations that were obtained from cooling runs from T=2300 to 300 K with a cooling rate of about 10(12) K/s. Already at temperatures as high as 4000 K, most of the Al and Si atoms are fourfold coordinated by oxygen atoms. Thus, the structure of AS2 is that of a disordered tetrahedral network. The packing of AlO4 tetrahedra is very different from that of SiO4 tetrahedra in that Al is involved with a relatively high probability in small-membered rings and in triclusters in which an O atom is surrounded by four cations. We find as typical configurations two-membered rings with two Al atoms in which the shared O atoms form a tricluster. On larger length scales, the system shows a microphase separation in which the Al-rich network structure percolates through the SiO2 network. The latter structure gives rise to a prepeak in the static structure factor at a wave number q=0.5 A(-1). A comparison of experimental x-ray data with the results from the simulation shows good agreement for the structure function. The diffusion dynamics in AS2 is found to be much faster than in SiO2. We show that the self-diffusion constants for O and Al are very similar and that they are by a factor of 2-3 larger than the one for Si. 相似文献
93.
The quantitation of thiopental in human serum and plasma was investigated using high-performance capillary electrophoresis (HPCE) in a micellar configuration and the results were compared with reversed-phase high-performance liquid chromatography (HPLC). Thiopental and an internal standard (carbamazepine for HPCE and thiamylal for HPLC) were extracted from serum or plasma using pentane and a phosphate buffer (pH 6.4). HPCE analysis took place in a phosphate-borate buffer with 50 mM sodium dodecyl sulphate using an automated instrument and HPLC was performed with a C8 column and a mobile phase of phosphate buffer-acetonitrile (65:35, v/v). HPCE and HPLC data from 66 patient samples compared well based on linear regression analysis. However, estimates obtained with the inclusion of the internal standard were lower than those based on the sample peak only. This example allows the elucidation of the advantages of using HPCE as an assay methodology for the therapeutic monitoring of thiopental and other drugs. 相似文献
94.
A titration unit for automatic analysis systems is described. The titrator performs different titrations specified by strings of digital parameters. It has 4 independent titration stations with individual electrode systems. A multiburette with 20 cylinders provides all stations with the necessary reagents. End-point titrations, and incremental and equilibrium titrations are controlled by a microcomputer. In combination with a sample transport and a desk calculator, the titrator can be used to process automatically samples of different natures which require different treatment. 相似文献
95.
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97.
(PPh4)2[WO2Cl3]2 · 2 CH2Cl2. Synthesis, Vibrational Spectrum, and Crystal Structure Depending on the stoichiometry and the solvent, dichloromethane or 1.2-dichloroethane, WO2Cl2 reacts with tetraphenylphosphonium chloride affording (PPh4)2[WO2Cl4] or (PPh4)2[WO2Cl3]2, respectively. Both compounds are easily soluble in dichloromethane, from which they can be crystallized under incorporation of two molecules CH2Cl2 per formula unit. The crystalline compounds have been characterized by their IR and Raman spectra. According to the X-ray crystal structure analysis, (PPh4)2[WO2Cl3]2 · 2 CH2Cl2 crystallizes in the triclinic space group P1 with one formula unit per unit cell (986 independent observed reflexions, R = 0.061). Lattice constants: a = 1100.2, b = 1116.9, c = 1238.4 pm, = 69.40, = 80.46 and = 85.62°. The crystals consist of PPh4⊕ ions, centrosymmetric [WO2Cl3]22? anions and CH2Cl2 molecules. In the anions, the tungsten atoms are linked via two oxo bridges with WO distances of 184 and 252 pm. The distorted octahedral coordination around each tungsten atom is completed by three terminal chloro and one terminal oxo ligand (WO bond length 166 pm), the latter being in trans position to the longer WO bridging bond. (PPh4)2[WO2Cl4] · 2 CH2Cl2 also forms triclinic crystals that are isotypic with (PPh4)2[WOCl5] · 2 CH2Cl2 and in which the anions must have orientational disorder. 相似文献
98.
The marine triquinane sesquiterpene Δ9(12)-capnellene () was synthesised from 2,2,5-trimethyl-5-hexenal () by a sequence of all synthetic operations in 5% overall yield. The key steps 3 → 4 → 5 → 6 involve two intramolecular type-I-“Mg-ene” processes. 相似文献
99.
Sun G Kappl M Pakula T Kremer K Butt HJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8030-8034
Forces across polymer melts are poorly understood despite their importance for adhesion and fabricating composite materials. Using an atomic force microscope (AFM), this interaction was measured for poly(dimethyl siloxane) (PDMS). The structure of the polymer at the surface changed during the first approximately 10 h. Afterward, short-range attractive forces were observed with short-chain PDMS (M(w) = 4200 g/mol). Using PDMS with a molecular weight (M(w) = 18 000 g/mol) above the entanglement limit, we measured a monotonically decaying repulsive force, which indicates that a quasi-immobilized layer had formed at the solid surface. Due to the small radius of curvature of the tip, forces could be measured in equilibrium. 相似文献
100.
Three fractions of SiC platelets were characterized using polarizing microscopy, X-ray diffraction, high resolution Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA) and scanning electron microscopy with energy dispersive analysis (SEM/EDX). The chemical analysis of the three fractions is given. The determination of the SiC polytypes (4H, 6H, 15R, 3C) was done and has been correlated with the chemical analysis. The results of the X-ray diffraction investigations confirm the polarizing microscopy observations. Using microanalytical techniques important conclusions about the impurity elements (e.g. B, Al, Fe) and their local distribution could be drawn. Most of them were found to be present on the outermost surfaces of the platelets. Some conclusions concerning the processing of the platelets are suggested.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday 相似文献