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排序方式: 共有88条查询结果,搜索用时 15 毫秒
1.
An accurate method for the determination of inorganic sulphate in synthetic detergents has been developed. After addition of a cationic surface-active agent (cetyl pyridinium chloride) to an anionic detergent, sulphate can be determined by means of indirect titration with EDTA, using a mixture of Metalphthalein and Naphthol Green B as indicator. 相似文献
2.
Tin dioxide SnO2−δ is a pronounced n-type electron conductor due to its oxygen deficiency. This study investigates the rate of chemical diffusion of oxygen in SnO2−δ single crystals, which is a crucial step in the overall stoichiometry change of the material. The chemical diffusion coefficient Dδ was determined from conductivity- and EPR-relaxation methods. The temperature dependence was found to be . The dependence on crystal orientation, dopant content and oxygen partial pressure was below experimental error. The latter observation leads to the conclusion that the chemical diffusion coefficient is close to the diffusion coefficient of oxygen vacancies. Along with the relaxation process resulting from the chemical diffusion of oxygen, additional processes were observed. One of these was attributed to complications in the defect chemistry of the material. The relevance of the results for the kinetics of drift processes of Taguchi sensors is discussed. 相似文献
3.
Stereoselective high-performance liquid chromatographic determination of the enantiomers of ketamine and norketamine in plasma. 总被引:1,自引:0,他引:1
An enantioselective high-performance liquid chromatographic assay for the quantitation of the enantiomers of ketamine and its major metabolite norketamine in human plasma is described (assay I). The procedure involved extraction of the compounds from alkalized plasma into cyclohexane. Stereoselective separation was achieved with a prepacked alpha 1-acid glycoprotein column without any derivatization procedure. A second assay using a conventional reversed-phase column to determine total (racemic) ketamine and norketamine is also described. Because of interfering plasma peaks (assay II) the cyclohexane solution was reextracted into 1 M hydrochloric acid. The detection wavelength was 215 nm for all substances. The limit of quantification of the method was ca. 40 ng/ml in plasma. The assays were sensitive and reproducible. The method was demonstrated to be sensitive for stereoselective pharmacokinetic studies of ketamine after clinical doses. 相似文献
4.
Xiaoyu Zhang Michele E. Lake Adam S. Butterbaugh Kirk A. VanDer Kamp 《液相色谱法及相关技术杂志》2017,40(20):1015-1019
This study demonstrates the first use of a reversed-phase (RP) high-performance liquid chromatography method with a high-pH buffer for the analysis of sodium stearyl fumarate (SSF) from a tablet formulation. After examining the retention time and peak shape using various buffer concentrations, buffer pH, and RP stationary phases, an optimized method was established using the XBridge® BEH C18 at high pH. This column was further evaluated for method specificity, accuracy, precision, linearity, stability, and sensitivity. Finally, the method was successfully used as a convenient and robust analytical procedure to accurately quantitate SSF in stratified tablets from a continuous manufacturing process to confirm the excipient uniformity throughout the process. 相似文献
5.
Dr. Christoph Ludwig Teske Dr. Anna-Lena Hansen Prof. Dr. Richard Weihrich Prof. Dr. Lorenz Kienle Marius Kamp Kasper Pieter van der Zwan Prof. Dr. Jürgen Senker Dr. Carsten Dosche Prof. Dr. Gunther Wittstock Prof. Dr. Wolfgang Bensch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6763-6772
A new preparation route is developed for the synthesis of needle-like crystals of [Au(S2CNH2)2]SCN, which avoids disproportionation of the AuI salt used as a starting material. In the crystal structure, the two crystallographically independent AuIII centers are in a square-planar environment of two S2CNH2 ligands. The Hirshfeld surface analysis reveals the presence of noncovalent intermolecular S⋅⋅⋅S interactions, which are essential for the spatial arrangement of the molecules. Density functional theory (DFT) calculations including dispersion and damping corrections result in a unit cell volume very close to the value determined experimentally. Thermal decomposition in an inert atmosphere generates black needles with lengths of up to 500 μm. X-ray powder diffraction and pair distribution function analyses demonstrate that the needles are composed of nanosized crystals with a volume-weighted average domain size of 20(1) nm. According to results of X-ray photoemission experiments, the black needles are covered by a nitrogen-rich carbon nitride with composition near (CN)2N. 13C solid-state NMR investigations indicate that two different carbon species are present, with signals corresponding well to heptazine units as in melon and triazine units as in poly(triazin imide) type compounds. Scanning transmission electron microscopy tomography evidences that the needles are composed of slightly elongated nanoparticles. 相似文献
6.
We have fabricated electron Y-branch switches (YBS) on modulation doped GaAs/AlGaAs heterostructures. The Y branch consists of a one-dimensional source, which is split along the branching section into two one-dimensional drains. In addition to source drain voltages, external electric fields can be applied via gates along the branches. In the nonlinear transport regime sweeps of the side-gate voltages lead to a voltage difference between the drain reservoirs with gain. This switching gain increases superlinearly with the bias voltage applied between the source and the drains of the YBS. We explain the bias voltage enhanced switching by a capacitive coupling of the branches. 相似文献
7.
C. Kirchner V. Schwegler F. Eberhard M. Kamp K. J. Ebeling
P. Prystawko
M. Leszczynski I. Grzegory S. Porowski 《Progress in Crystal Growth and Characterization of Materials》2000,41(1-4):57-83Epitaxial growth on GaN bulk single crystal substrates sets new standards in GaN material quality. The outstanding properties provide insights into fundamental material parameters (e.g. lattice constants, exciton binding energies, etc.) with a precision not obtainable from heteroepitaxial growth on sapphire or SiC. With metalorganic vapor phase epitaxy (MOVPE) we realized unstrained GaN layers with dislocation densities about six orders of magnitude lower than in heteroepitaxy. By the use of dry etching techniques for surface preparation, an important improvement of crystal quality is achieved. Those layers reveal an exceptional optical quality as determined by a reduction of the low-temperature photoluminescence (PL) linewidth from 5 meV to 0.1 meV and a reduced X-ray diffraction (XRD) rocking curve width from 400 to 20 arcsec. As a consequence of the narrow PL linewidths, new features as, e. g. a fivefold fine structure of the donor-bound exciton line at 3.471 eV was detected. Additionally, all three free excitons as well as their excited states are visible in PL at 2 K.
Dry etching techniques for surface preparation allow morphologies of the layers suitable for device applications. We report on InGaN/GaN multi-quantum-well (MQW)_ structures as well as GaN pn- and InGaN/GaN double heterostructure light emitting diodes (LEDs) on GaN bulk single crystal substrates. Those LEDs are twice as bright as their counterparts grown on sapphire. In addition they reveal an improved high power characteristics, which is attributed to an enhanced crystal quality and an increased p-doping. 相似文献
8.
We investigate the distribution of instanton sizes in the framework of a simplified model for ensembles of instantons. This
model takes into account the non-diluteness of instantons. The infrared problem for the integration over instanton sizes is
dealt with in a self-consistent manner by approximating instanton interactions by a repulsive hard core potential. This leads
to a dynamical suppression of large instantons. The characteristic features of the instanton size distribution are studied
by means of analytic and Monte Carlo methods. In one dimension exact results can be derived. In any dimension we find a power
law behaviour for small sizes, consistent with the semi-classical results. At large instanton sizes the distribution decays
exponentially. The results are compared with those from lattice simulations.
Received: 15 May 2000 / Revised version: 17 July 2000 / Published online: 25 September 2000 相似文献
9.
M. Motyka F. Janiak K. Ryczko G. Sęk J. Misiewicz A. Bauer R. Weih S. Höfling M. Kamp A. Forchel 《Opto-Electronics Review》2011,19(2):137-139
Modulation spectroscopy in its Fourier-transformed mode has been employed to investigate the optical properties of broken
gap ‘W’-shaped GaSb/AlSb/InAs/InGaSb/InAs/AlSb/GaSb quantum well structures designed to emit in the mid infrared range of
3–4 μm for applications in laser-based gas sensing. Besides the optical transitions originating from the confined states in
the type II quantum wells, a number of spectral features at the energy above the GaSb band gap have been detected. They have
been analyzed in a function of InAs and GaSb layer widths and ultimately connected with resonant states in the range of AlSb
tunneling barriers. 相似文献
10.