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131.
Raimund Quint Herbert Boller Herbert Blaha 《Monatshefte für Chemie / Chemical Monthly》1986,117(12):1387-1397
Two different polytypic series (2s and 3s) of layered alkali and alkaline earth thiochromites of formulaM
x(H2O)
y
CrS2 (x=0.2–0.4;y=0.18–0.5) were prepared by topotactic ion exchange in 2H- and 3R- K
x
(H2O)
y
CrS2. The products were studied by TGA and X-ray diffraction techniques. Hydrates with monomolecular (hydrates I) and bimolecular (hydrates II) water layers between the CrS2 slabs were observed. In the 3s series the CrS2 layers are stacked according to 3R (Ib) (hydrates I) and 3R (Ia) (hydrates II) structures. In the 2s series the layer stacking leads to a 2H (Ib) structure and to a new orthorhombic 2 O structure.
Herrn Prof. Dr.K. Komarek zu seinem 60. Geburtstag gewidmet. 相似文献
132.
Raimund Röhl 《Analytica chimica acta》1982,135(1):99-110
Stability constants of individual trace metal complexes form the basis for calculations predicting the distribution of trace metal species in complexing media, such as sea water. In this study, the electrophoretic mobility of radiotracer 210Pb is measured as a function of ligand concentration in chloride and sulfate solutions of constant ionic strength and temperature. A theoretically-derived expression, relating mobility to ligand concentration and complex stability constants, is fitted by the method of least squares to the experimental data to obtain estimates of the conditional stability constants of lead(II) chloro and sulfato complexes at 23°C and ionic strength 0.7 i.e., under conditions resembling those of ocean water. The values obtained are: log β1 = 0.999 ± 0.014, log β2 = 1.037± 0.032, log β3 = 1.250 ± 0.015 for lead(II) chloro complexes, and log β1 = 1.048 ± 0.015 and log β2 = 1.183 ± 0.025 for lead(II) sulfato complexes. Experiments with eight other metal ions [Au(III), Bi(III), Cd(II), Co(II), Cu(II), Hg(II), Ni(II), and Po(IV)] and with sea water as electrolyte indicate the general applicability of the method. 相似文献
133.
134.
Diverging Mechanisms: Cytochrome‐P450‐Catalyzed Demethylation and γ‐Lactone Formation in Bacterial Gibberellin Biosynthesis 下载免费PDF全文
Dr. Raimund Nagel Prof. Dr. Reuben J. Peters 《Angewandte Chemie (International ed. in English)》2018,57(21):6082-6085
Biosynthesis of the gibberellin (GA) plant hormones evolved independently in plants and microbes, but the pathways proceed by similar transformations. The combined demethylation and γ‐lactone ring forming transformation is of significant mechanistic interest, yet remains unclear. The relevant CYP112 from bacteria was probed by activity assays and 18O2‐labeling experiments. Notably, the ability of tert‐butyl hydroperoxide to drive this transformation indicates use of the ferryl‐oxo (Compound I) from the CYP catalytic cycle for this reaction. Together with the confirmed loss of C20 as CO2, this necessitates two catalytic cycles for carbon–carbon bond scission and γ‐lactone formation. The ability of CYP112 to hydroxylate the δ‐lactone form of GA15, shown by the labeling studies, is consistent with the implied use of a further oxygenated heterocycle in the final conversion of GA24 into GA9, with the partial labeling of GA9, thus demonstrating that CYP112 partitions its reactants between two diverging mechanisms. 相似文献
135.
Raimund Quint Herbert Boller Herbert Blaha 《Monatshefte für Chemie / Chemical Monthly》1984,115(8-9):975-985
KCrS2, KCr5S8 and the new compound KCr3S5 were prepared by the reaction of H2S with chromium in K2CO3 melts. KCr3S5 (space group C2/m,a=19.16 Å,b=3.49 Å,c=12.02 Å, β=123.0°) is isotypic with TlCr3S5 having a psilomelane like channel structure. The thermal degradation: $$KCrS_2 \xrightarrow{{ - K_2 S}}KCr_3 S_5 \xrightarrow{{ - K_2 S}}KCr_5 S_8$$ was studied and the topochemical relations between the products are discussed. A new layered phase K0.5(H2O)0.2CrS2 having a 2 H stacking sequence (space group P63/mmc,a=3.36 Å,c=16.83 Å) was prepared from polysulfide melts. The dehydration of this phase was studied by TGA and X-rays. 相似文献
136.
This paper describes the development of an accelerated solvent extraction methodology that is capable of simultaneously extracting organometallic species of As, Sn and Hg in a semi-automated manner. Accelerated solvent extraction (ASE) methods based on previous research on the separate extraction of organotin and -arsenic species in our laboratory were adapted for the co-extraction of six different species from an oyster tissue certified reference material (BCR 710). For the first time, the extraction of MeHg by this technique is also investigated. The proposed ASE conditions employed 50% acetic acid in methanol at a temperature of 100 degrees C with up to five consecutive extraction cycles of 3 minutes. Extraction efficiencies for organoarsenic species ranged from 80% (dimethylarsinic acid, DMA) to 99% for arsenobetaine (AsB). Species of toxicological interest, such as dibutyltin (DBT), tributyltin (TBT) and methylmercury (MeHg), were extracted with mean recoveries of 81, 84 and 76%, respectively. The extracted species were analysed by gas chromatography/inductively coupled plasma mass spectrometry (GC/ICPMS; DBT, TBT and MeHg) and liquid chromatography/inductively coupled plasma mass spectrometry (LC/ICPMS; MMA, DMA, AsB) after ethylation with sodium tetraethylborate or dilution with water, respectively. In addition to those species for which the extraction efficiency was assessed during this study, a further five arsenic species (arsenite, arsenate and three unidentified species), as well as monobutyltin (MBT) and mono-, di- and triphenyltin, could also be extracted from other matrices. The developed ASE method provides a significant improvement over many currently available routine monitoring methods for trace element speciation due to the fact that it is capable of extracting several species of toxicological interest simultaneously and quantitatively. 相似文献
137.
Numerical Approximation of Oscillatory Solutions of Hyperbolic-Elliptic Systems of Conservation Laws by Multiresolution Schemes 下载免费PDF全文
Stefan Berres Raimund Bü rger & Alice Kozakevicius 《advances in applied mathematics and mechanics.》2009,1(5):581-614
The generic structure of solutions of initial value problems of
hyperbolic-elliptic systems, also called mixed systems, of
conservation laws is
not yet fully understood. One reason for the
absence of a core well-posedness
theory for these equations is the
sensitivity of their solutions to the structure of
a parabolic
regularization when attempting to single out an admissible solution
by the
vanishing viscosity approach. There is, however, theoretical
and numerical evidence
for the appearance of solutions that exhibit
persistent oscillations, so-called oscillatory
waves, which are (in
general, measure-valued) solutions that emerge from Riemann data or
slightly perturbed constant data chosen from the interior of the
elliptic region.
To capture these solutions, usually a fine
computational grid is required.
In this work, a version of the
multiresolution method applied to a WENO scheme for systems of
conservation laws is proposed as a simulation tool for the efficient computation of solutions of oscillatory wave type. The
hyperbolic-elliptic $2 \times 2$
systems of conservation laws
considered are a prototype system for three-phase flow
in porous
media and a system modeling the separation of a heavy-buoyant
bidisperse suspension.
In the latter case, varying one scalar
parameter produces elliptic regions of different shapes and numbers of points of tangency with the borders of the phase space, giving
rise to different kinds of oscillation waves. 相似文献
138.
A fully adaptive finite volume multiresolution scheme for one-dimensional strongly degenerate parabolic equations with discontinuous flux modelling an extended clarifier-thickener, is presented. The numerical scheme is based on a finite volume discretization using the approximation of Engquist-Osher for the flux and explicit time stepping. Cell averages multiresolution scheme speeds up CPU time and memory requirements. A particular feature of our scheme is the storage of the multiresolution representation of the solution in a dynamic graded tree. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
139.
F. Allegretti G. Parteder L. Gragnaniello S. Surnev F.P. Netzer A. Barolo S. Agnoli G. Granozzi C. Franchini R. Podloucky 《Surface science》2010,604(5-6):529-534
We report on an interface-stabilized strained c(4 × 2) phase formed by cobalt oxide on Pd(1 0 0). The structural details and electronic properties of this oxide monolayer are elucidated by combination of scanning tunneling microscopy data, high resolution electron energy loss spectroscopy measurements and density functional theory. The c(4 × 2) periodicity is shown to arise from a rhombic array of Co vacancies, which form in a pseudomorphic CoO(1 0 0) monolayer to partially compensate for the compressive strain associated with the large lattice mismatch (~9.5%) between cobalt monoxide and the substrate. Deviation from the perfect 1:1 stoichiometry thus appears to offer a common and stable mechanism for strain release in Pd(1 0 0) supported monolayers of transition metal rocksalt monoxides of the first transition series, as very similar metal-deficient c(4 × 2) structures have been previously found for nickel and manganese oxides on the same substrate. 相似文献
140.