We generalize the classical Rayleigh–Faber–Krahn inequality to the case of the Dirichlet Laplacian with a drift. We also solve some optimization problems for the principal eigenvalue of the operator in a fixed domain with a control of the drift v in . To cite this article: F. Hamel et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005).相似文献
The structure of ansatrienin A () and B () is assigned by spin decoupling experiments and chemical reactions. The ansatrienins are unique members among the ansamycin-antibiotics because of their substituent pattern in the ansa bridge. 相似文献
E896 has measured Lambda production in 11.6A GeV/c Au-Au collisions over virtually the whole rapidity phase space. The midrapidity p(t) distributions have been measured for the first time at this energy and appear to indicate that the Lambda hyperons have different freeze-out conditions than protons. A comparison with the relativistic quantum molecular dynamics model shows that while there is good shape agreement at high rapidity the model predicts significantly different slopes of the m(t) spectra at midrapidity. The data, where overlap occurs, are consistent with previously reported measurements. 相似文献
We have used helium-3 nuclear reaction analysis to measure the interdiffusion of linear polystyrene into a film of crosslinked
polystyrene and the intradiffusion of polystyrene in polystyrene networks. The interdiffusion is compared with that predicted
from the Kramer-Sillescu theory, and is found to be considerably faster. This is attributed to the relaxation of inhomogeneities
in the network. The molecular weight and crosslinking dependence of the intradiffusion coefficients of free polystyrene chains
trapped inside networks is discussed in terms of the simple tube model and provides reasonably good agreement with that predicted
from reptation theory.
Received 2 August 2000 and Received in final form 6 November 2000 相似文献
Carbon monoxide dehydrogenase from Oligotropha carboxidovorans catalyzes the aerobic oxidation of carbon monoxide to carbon dioxide, providing the organism both a carbon source and energy for growth. The active site of the native enzyme is a unique binuclear molybdenum- and copper-containing center. Here we show that silver can be substituted for copper in the active site to yield a functional enzyme. The characteristic hyperfine coupling of the I = ? nucleus of Ag is evident in the EPR signal of the binuclear active site observed upon reduction with CO, indicating both the incorporation of silver into the active site and, remarkably, retention of the catalytic activity. The silver-substituted enzyme is reduced by CO with an observed limiting rate constant of 8.1 s(-1), which can be compared with the value of 51 s(-1) for the wild-type enzyme. Steady-state kinetics for the Ag-substituted enzyme yielded k(cat) = 8.2 s(-1) and K(m) = 2.95 μM at pH 7.2. 相似文献
We describe herein formal syntheses of the indole alkaloids cis‐trikentrin A and herbindole B from a common meso‐hydroquinone intermediate prepared by a ruthenium‐catalyzed [2+2+1+1] cycloaddition that has not been used previously in natural product synthesis. Key steps include a sterically demanding Buchwald–Hartwig amination as well as a unique C(sp3)?H amination/indole formation. Studies toward a selective desymmetrization of the meso‐hydroquinone are also reported. 相似文献
Quantum dots (QDs) have a number of unique optical properties that are advantageous in the development of bioanalyses based on fluorescence resonance energy transfer (FRET). Researchers have used QDs as energy donors in FRET schemes for the analysis of nucleic acids, proteins, proteases, haptens, and other small molecules. This paper reviews these applications of QDs. Existing FRET technologies can potentially be improved by using QDs as energy donors instead of conventional fluorophores. Superior brightness, resistance to photobleaching, greater optimization of FRET efficiency, and/or simplified multiplexing are possible with QD donors. The applicability of the Förster formalism to QDs and the feasibility of using QDs as energy acceptors are also reviewed.