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61.
Leop Lenz 《Fresenius' Journal of Analytical Chemistry》1889,28(1):441-443
Ohne Zusammenfassung 相似文献
62.
Lars Lauterbach Hongxin Wang Marius Horch Leland B. Gee Yoshitaka Yoda Yoshihito Tanaka Ingo Zebger Oliver Lenz Stephen P. Cramer 《Chemical science》2015,6(2):1055-1060
Hydrogenases are complex metalloenzymes that catalyze the reversible splitting of molecular hydrogen into protons and electrons essentially without overpotential. The NAD+-reducing soluble hydrogenase (SH) from Ralstonia eutropha is capable of H2 conversion even in the presence of usually toxic dioxygen. The molecular details of the underlying reactions are largely unknown, mainly because of limited knowledge of the structure and function of the various metal cofactors present in the enzyme. Here, all iron-containing cofactors of the SH were investigated by 57Fe specific nuclear resonance vibrational spectroscopy (NRVS). Our data provide experimental evidence for one [2Fe2S] center and four [4Fe4S] clusters, which is consistent with the amino acid sequence composition. Only the [2Fe2S] cluster and one of the four [4Fe4S] clusters were reduced upon incubation of the SH with NADH. This finding explains the discrepancy between the large number of FeS clusters and the small amount of FeS cluster-related signals as detected by electron paramagnetic resonance spectroscopic analysis of several NAD+-reducing hydrogenases. For the first time, Fe–CO and Fe–CN modes derived from the [NiFe] active site could be distinguished by NRVS through selective 13C labeling of the CO ligand. This strategy also revealed the molecular coordinates that dominate the individual Fe–CO modes. The present approach explores the complex vibrational signature of the Fe–S clusters and the hydrogenase active site, thereby showing that NRVS represents a powerful tool for the elucidation of complex biocatalysts containing multiple cofactors. 相似文献
63.
Our work presents extensions of multi layered composite sphere models known from the literature to temperature-dependent elastic effects accompanied by curing. In particular, volumetric effective properties are obtained by homogenization for a representative unit cell (micro-RVE) on the heterogeneous microscale for thermo-chemo-mechanical coupling within linear elasticity. To this end, an analytical solution for an n-layered composite sphere model is derived. In a numerical study for a (3)-phase matrix it is demonstrated that the effective elastic and thermal properties lie within Voigt and Reuss bounds, whilst for the chemical part of the model an analogous result is obtained for the effective strains. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
64.
The water adsorption capacity of a dough consisting of wheat flour was increased linearly by the addition of water-insoluble hemicelluloses (xylane, mannane etc.) extracted from beech-wood pulp using soda lye (a by-product of viscose fiber production). The investigation of this finding by viscosity measurements revealed two reasons for the higher water uptake: 1) a higher kneading resistance of the dough, and 2) a gel-regeneration of the kneaded dough during the dough-rest.
Herrn Prof. Dr. Josef Schurz zum 60. Geburtstag gewidmet. 相似文献
65.
Methane hydrates with the three clathrate structures I, II, and H are studied by quantum-chemical methods. Hybrid density-functional theory B3LYP computations using periodic boundary conditions are combined with force-field methods for the thermal energy effects to calculate energetic, thermodynamic, and structural properties. The pressure dependencies for the crystal structures, lattice energies, and guest molecule interactions are derived. The quantum-chemical geometry optimizations predict too small cell volumes as compared to experimental data, but by including zero-point energy and thermal energy effects, we find the cell volumes increase and the correct densities are obtained. The phase transition from MH-I to ice Ih and methane was computed and found to occur at about 9.7 MPa. 相似文献
66.
A FLUORESCENCE IMAGING DEVICE FOR ENDOSCOPIC DETECTION OF EARLY STAGE CANCER – INSTRUMENTAL and EXPERIMENTAL STUDIES 总被引:1,自引:0,他引:1
R. Baumgartner H. Fisslinger D. Jocham H. Lenz L. Ruprecht H. Stepp E. Unsold 《Photochemistry and photobiology》1987,46(5):759-763
Abstract Visible detection of early stage cancer labelled with the fluorescing porphyrin mixture of dihematoporphyrin-ether and dihematoporphyrin-ester (DHE) is often limited by a high and inhomogeneously distributed level of autofluorescence. A new imaging method for reducing autofluo-rescence is described. The method uses alternating fluorescence excitation with laser light in the violet and blue spectral ranges. Subtraction of the corresponding fluorescence images results in contrast enhancement due to an effective reduction in the autofluorescence contribution. A prototype version of a highly sensitive fluorescence imaging device including a modified krypton ion laser, an image-intensified solid-state TV-camera, a digital image-processing system, and video recording and monitoring has been developed.
Experiments performed with this fluorescence imaging system on a tumorous dog bladder showed that a dose of 0.2 mg DHE kg−1 body wt, which is far below the dose administered for photodynamic therapy (2-5 mg kg− 'body wt), is sufficient to give a high-contrast fluorescence image. The corresponding excitation power density was about 1 W m−2 . Photobleaching of DHE was observed during fluorescence detection at excitation power densities exceeding 1 kW m−2 . At these high excitation levels DHE fades out nearly completely within 0.25 min. 相似文献
Experiments performed with this fluorescence imaging system on a tumorous dog bladder showed that a dose of 0.2 mg DHE kg
67.
We prove quantum dynamical lower bounds for one-dimensional continuum Schrödinger operators that possess critical energies for which there is slow growth of transfer matrix norms and a large class of compactly supported initial states. This general result is applied to a number of models, including the Bernoulli–Anderson model with a constant single-site potential. 相似文献
68.
L. Corradi S. J. Skorka U. Lenz K. E. G. Löbner P. R. Pascholati U. Quade K. Rudolph W. Schomburg M. Steinmayer H. G. Thies G. Montagnoli D. R. Napoli A. M. Stefanini A. Tivelli S. Beghini F. Scarlassara C. Signorini F. Soramel 《Zeitschrift für Physik A Hadrons and Nuclei》1990,335(1):55-72
Double differential cross sections of all prominent transfer channels have been measured in the systems33S +99,91,92Zr at two energies close to the nominal Coulomb barrier. In addition the fusion excitation functions of these systems have been measured below and around the barrier. The angular- andQ-distributions of the most important transfer reactions have been analysed in the framework of a simple semiclassical formalism. Particularly the two-nucleon transfer angular distributions exhibit strong multi step coupling effects which manifest themselves in reduced cross sections at large angles corresponding to close distances. From the angular distributions at forward angles, where a single step character of the transfer reaction can be assumed, approximate form factors have been extracted employing a first order perturbation theory. Within the uncertainties of a schematic coupled channels calculation the isotopic differences of the sub-barrier fusion enhancement can be understood on the basis of the isotopic differences of the transfer form factors andQ-values. 相似文献
69.
We study strictly ergodic Delone dynamical systems and prove an ergodic theorem for Banach space valued functions on the associated
set of pattern classes. As an application, we prove existence of the integrated density of states in the sense of uniform
convergence in distribution for the associated random operators.
Dedicated to J. Voigt on the occasion of his 60th birthday
Research partly supported by the DFG in the priority program Quasicrystals. 相似文献
70.