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41.
H. Hartkamp 《Fresenius' Journal of Analytical Chemistry》1959,169(5):339-342
Zusammenfassung Die photometrische Bestimmung des Vanadiums mit Wasserstoffperoxyd wird weitgehend unabhängig von den in der Probenlösung vorliegenden Gehalten an Wasserstoffperoxyd und Schwefelsäure, wenn man die photometrische Messung bei der Wellenlänge des isosbestischen Punktes, =405 m, vornimmt.Ich danke Fräulein Annette Schenkedehl für die experimentelle Mitarbeit. 相似文献
42.
We have investigated two-photon resonant up conversion of 375 to 159 nm coherent radiation using the four-frequency process 159=2375+1040 in cadmium vapour, where the ir component (1040 nm) is internally generated by the 375 nm pump tuned to the Cd two-photon transition 5s
2
1
S
05s6s
1
S
0. Scaling laws and tuning behaviour of both the 159 and 1040 nm output power were measured up to 1×108 W cm–2 pump intensity and 2×1017 cm–3 Cd number density. The results are compared to numerical calculations based on semiclassical theory in a stationary perturbation approximation up to third order. Here, in accordance with experimental results, the ir component was assumed to originate from a superposition of stimulated emission and parametric generation. The observed saturation effects turned out to be mainly due to population changes of the atomic levels involved and are qualitatively reproduced by calculations. Discrepancies with respect to absolute output levels are discussed in terms of the approximations in the theoretical formalism. 相似文献
43.
Two methods based on gel permeation chromatography (GPC) [size exclusion chromatography] for the analysis of traces (ng/kg)
of nitrogen and phosphorus containing pesticides (like triazines or phosphothionates) from marine sediment samples are compared:
A macro GPC with Biobeads SX-3 and a chromatography on a high-performance (HP-GPC) column with UV-detection. Results for eight
triazine herbicides, two triazine metabolites, the phenylurea derivative linuron, two acetanilides and two organophosphorus
compounds are given. Concentrations obtained with the HP-GPC are compared with those obtained with a macro GPC approach in
an earlier study.
Received: 4 October 1996/Revised: 20 December 1996/Accepted: 24 December 1996 相似文献
44.
45.
Heinrich Wefelscheid 《Journal of Geometry》1977,9(1-2):127-133
A characterisation of those (B*G)-Geometries (in the sense of Benz) is given, which can be constructed with the help of nearfields F, char F 2, in which the multiplicative group F*(·) has a subgroup A with index [F*:A]=2.
Werner Burau zum 70. Geburtstag gewidmet 相似文献
Werner Burau zum 70. Geburtstag gewidmet 相似文献
46.
47.
48.
Mohamed El-Sayed Hardy Müller Gerd Rheinwald Heinrich Lang Stefan Spange 《Monatshefte für Chemie / Chemical Monthly》2003,50(11):361-370
N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments
by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of νmax is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is
described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel
entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular
hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing
an unprecedented bathochromic shift. 相似文献
49.
C. M. Wai M. E. Dysart M. Blander R. R. Heinrich M. C. Oselka 《Journal of Radioanalytical and Nuclear Chemistry》1988,124(1):21-32
A lanthanum fluoride precipitation method for the separation of18F produced from the18O(p,n)18F reaction in alkali halide salts is described. This radiochemical separation method minimizes interferences from other positron emitters produced by proton bombardment and makes the accurate determination of ppm-level18O in complex alkali halide systems feasible. The interference from the19F(p,d)18F reaction is eliminated by keeping the proton energy less than 8.2 MeV. Applications of this technique to studies of dissolved oxide species in molten alkali halide salts are discussed. 相似文献
50.
Cyclic Silicic Acid Derivatives By reaction of SiCl4 with oxygen at elevated temperatures a number of chlorsiloxanes consisting of more or less fused rings can be prepared of which those components of low molecular weight can be separated by combining distillation and crystallization. Methyl and ethyl esters of silicic acids are obtained by reaction with methyl or ethyl nitrite, resp. The compounds are characterized by silicon n.m.r. and mass spectroscopy. 相似文献