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101.
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Hoffmann R Barth C Foster AS Shluger AL Hug HJ Güntherodt HJ Nieminen RM Reichling M 《Journal of the American Chemical Society》2005,127(50):17863-17866
Recent advances in dynamic force microscopy show that it is possible to measure the forces between atomically sharp tips and particular atomic positions on surfaces as a function of distance. However, on most ionic surfaces, the positive and negative ions can so far not be distinguished. In this paper, we use the CaF2(111) surface, where atomic resolution force microscopy has allowed identification of the positions of the Ca2+ and F- ions in the obtained images, to demonstrate that short-range interaction forces can be measured selectively above chemically identified surface sites. Combining experimental and theoretical results allows a quantification of the strength and distance dependence of the interaction of a tip-terminating cluster with particular surface ions and reveals details of cluster and surface relaxation. Further development of this approach will provide new insight into mechanisms of chemical bond formation between clusters, cluster deposition at surfaces, processes in adhesion and tribology, and single atom manipulation with the force microscope. 相似文献
104.
Li WC Lu AH Palkovits R Schmidt W Spliethoff B Schüth F 《Journal of the American Chemical Society》2005,127(36):12595-12600
In this study, we present a synthetic pathway for the fabrication of self-supporting zeolite monoliths consisting of crystallized nanoparticles. A resorcinol-formaldehyde-based organic aerogel is used as a template, and silicalite-1 is used as the zeolite example. The silicalite-1 monoliths obtained consist of individual well-defined zeolite nanocrystals with sizes of 30-40 nm. The monoliths exhibit a high mechanical stability and have hierarchical porosity, with micropores within the zeolite particles, a mesopore system formed by the packing of the nanoparticles, and a macropore system on the monolith level. Such monolithic zeolites show high selectivity typically above 80% to epsilon-caprolactam combined with a high rate of reaction of 0.46 g(caprolactame)/(g(catalyst).h) in the Beckmann rearrangement of cyclohexanone oxime. 相似文献
105.
Lee CK Holmes AB Ley SV McConvey IF Al-Duri B Leeke GA Santos RC Seville JP 《Chemical communications (Cambridge, England)》2005,(16):2175-2177
Suzuki cross-coupling reactions are effected in both conventional organic solvents, under continuous flow conditions at 70 degree C, and in batch mode in supercritical carbon dioxide (scCO2), at temperatures as low as 40 degrees C in the presence of palladium(II) acetate microencapsulated in polyurea [PdEnCat] and tetra-n-butylammonium salts. 相似文献
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107.
K. Wagner R. Lenz H. Gaedike Regina Müller W. Joachim 《Isotopes in environmental and health studies》2013,49(9-10):338-341
Es werden die Ergebnisse von Mischverfahren für Kohlepulver, Pech und andere Komponenten mitgeteilt, die unter Markierungen mit 24Na-Benzoat im Laboratorium (Mischvolumen etwa 1 Liter) und im Betrieb (Mischvolumen etwa 100 Liter) durchgführt wurden. Die Experimente dienten dem Vergleich der Vergleich der Wirksamkeit verschiedener Mischmaschinen, der Ermittlung optimaler Mischzeiten und der Bestimmung des Verhaltens einzelner Komponenten beim Mischprozeβ. Dis mittels Szintillationszählung gewonnenen Meβwerte werden dabei mit einem Ergebnisdrucker registriert und mit Hilfa einer Rechenanlage mathematisch ausfewertet. 相似文献
108.
Regina S. Burachik Alfredo N. Iusem Jefferson G. Melo 《Journal of Optimization Theory and Applications》2013,157(1):108-131
We consider a primal optimization problem in a reflexive Banach space and a duality scheme via generalized augmented Lagrangians. For solving the dual problem (in a Hilbert space), we introduce and analyze a new parameterized Inexact Modified Subgradient (IMSg) algorithm. The IMSg generates a primal-dual sequence, and we focus on two simple new choices of the stepsize. We prove that every weak accumulation point of the primal sequence is a primal solution and the dual sequence converges weakly to a dual solution, as long as the dual optimal set is nonempty. Moreover, we establish primal convergence even when the dual optimal set is empty. Our second choice of the stepsize gives rise to a variant of IMSg which has finite termination. 相似文献
109.
Izabela Regina Cardoso de Oliveira Daniel Furtado Ferreira 《Computational Statistics》2013,28(4):1663-1680
The noncentral gamma distribution can be viewed as a generalization of the noncentral chi-squared distribution and it can be expressed as a mixture of a Poisson density function with a incomplete gamma function. The noncentral gamma distribution is not available in free conventional statistical programs. This paper aimed to propose an algorithm for the noncentral gamma by combining the method originally proposed by Benton and Krishnamoorthy (Comput Stat Data Anal 43(2):249–267, 2003) for the noncentral distributions with the method of inversion of the distribution function with respect to the noncentrality parameter using Newton–Raphson. The algorithms are available in pseudocode and implemented as R functions. To evaluate the accuracy and speed of computation of the algorithms implemented in R, results of the distribution function, density function, quantiles and noncentrality parameter of the noncentral incomplete gamma and its particular case, the noncentral chi-squared, were obtained for the arguments settings used by Benton and Krishnamoorthy (Comput Stat Data Anal 43(2):249–267, 2003) and Chen (J Stat Comput Simul 75(10):813–829, 2005). The implemented routines performed well and, in general, were as accurate than other approximations. The R package denoted ncg is available to download on the CRAN-R package repository http://cran.r-project.org/. 相似文献
110.
Annibal Figueiredo Marcio T. de Castro Regina C.B. da Fonseca Iram Gleria 《Physics letters. A》2013,377(25-27):1571-1581
We investigate which type of diffusion equation is most appropriate to describe the time evolution of foreign exchange rates. We modify the geometric diffusion model assuming a non-exponential time evolution and the stochastic term is the sum of a Wiener noise and a jump process. We find the resulting diffusion equation to obey the Kramers–Moyal equation. Analytical solutions are obtained using the characteristic function formalism and compared with empirical data. The analysis focus on the first four central moments considering the returns of foreign exchange rate. It is shown that the proposed model offers a good improvement over the classical geometric diffusion model. 相似文献