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61.
The reactivity with air moisture of finely divided crystals of Na β and Li+-containing β-aluminas is analyzed with thermogravimetric and X-ray techniques. For Na β-alumina two distinct water intake processes are evident: 1) a fast one, controlled by the elastic interactions among water molecules near the crystal boundaries; 2) a slow one, driven by water diffusion away from the boundaries. For finely divided crystals of Li β-alumina the two processes cannot be distinguished but the slow one is observable in crystals of macroscopic dimensions. The water intake is generally accompanied by an expansion of the c-axis. However, the relationship between water content and c-parameter is highly non-linear and the c-axis length at room temperature depends upon the thermal history of the sample. Our results confirm previous reports suggesting that β-aluminas absorb about one water molecule per cation of the conducting plane. 相似文献
62.
Franco Faustini Sergio De Munari Achille Panzeri Vittoria Villa Carmelo A. Gandolfi 《Tetrahedron letters》1981,22(45):4533-4536
In the reaction of α-aminoacids with excess NaNO2 in polyhydrogen fluoridepyridine, stereospecific substitution(i.e. retention of configuration) is observed with C6H11CH2CHNH2COOH, while a stereospecific rearrangment occurs in the case of phenylalanine. 相似文献
63.
64.
Edoardo Cesarotti Patrizia Antognazza Marco Pallavicini Luigi Villa 《Helvetica chimica acta》1993,76(6):2344-2349
A number of 3-O-substituted 1,3-dihydroxypropan-2-ones have been synthesized in view of their potential use as prochiral precursors of optically active glycerols. Indeed, the oxo-ethers have been reduced to the corresponding 3-O-substituted glycerols via chiral Ru complexes derived from (S)-binap, ( =(?)-(S)-2,2′-bis(diphenylphosphino)-1,1′-binaphthalene) with enantiomeric excesses up to 93%. The steric course of the catalytic reduction appears to be essentially dependent on the steric encumbrance of the substituents; indeed, a dramatic increase of the enantiomeric excess is observed when the bulky trityl group is substituted by the less encumbering benzyl or octadecyl groups. 相似文献
65.
Wang D Villa A Porta F Su D Prati L 《Chemical communications (Cambridge, England)》2006,(18):1956-1958
Single phase bimetallic Au/Pd catalyst was prepared and characterised by TEM techniques. The high activity in the selective liquid phase oxidation of glycerol towards glycerate is unambiguously attributed to the synergistic effect of alloy. 相似文献
66.
The Yule–Simon distribution is usually employed in the analysis of frequency data. As the Bayesian literature, so far, has ignored this distribution, here we show the derivation of two objective priors for the parameter of the Yule–Simon distribution. In particular, we discuss the Jeffreys prior and a loss-based prior, which has recently appeared in the literature. We illustrate the performance of the derived priors through a simulation study and the analysis of real datasets. 相似文献
67.
In data envelopment analysis (DEA) an inefficient unit can be projected onto an efficient target that is far away, i.e. reaching
the target may demand large reductions in inputs and increases in outputs. When the inputs and outputs modifications planned
are large, it may be troublesome to carry them out all at once. In order to help an inefficient unit reach a distant target,
a strategy of gradual improvements with successive, intermediate targets has been proposed. This paper extends such approach
to the variable returns to scale (VRS) case. In the VRS scenario we distinguish between units that are technical efficient
and those that are not. On the one hand, for those units that are not technical efficient the proposed approach determines
successive intermediate targets leading to the technical efficiency frontier, i.e. the priority for those units is to attain
technical efficiency. On the other hand, for those units that are technical efficient but not scale efficient the proposed
approach computes a sequence of targets ending in the global efficiency frontier, i.e. when technical efficiency is guaranteed
the goal is then to attain global efficiency. In both cases, the successive targets are obtained by iteratively solving specific
DEA models that take into account given bounds on the rates of change in inputs and outputs that the unit can implement in
each step. 相似文献
68.
Hoimin Jung Mannkyu Hong Marianna Marchini Marco Villa Philipp S. Steinlandt Xiaoqiang Huang Marcel Hemming Eric Meggers Paola Ceroni Jiyong Park Mu-Hyun Baik 《Chemical science》2021,12(28):9673
The mechanism of [2 + 2] cycloadditions activated by visible light and catalyzed by bis-cyclometalated Rh(iii) and Ir(iii) photocatalysts was investigated, combining density functional theory calculations and spectroscopic techniques. Experimental observations show that the Rh-based photocatalyst produces excellent yield and enantioselectivity whereas the Ir-photocatalyst yields racemates. Two different mechanistic features were found to compete with each other, namely the direct photoactivation of the catalyst–substrate complex and outer-sphere triplet energy transfer. Our integrated analysis suggests that the direct photocatalysis is the inner working of the Rh-catalyzed reaction, whereas the Ir catalyst serves as a triplet sensitizer that activates cycloaddition via an outer-sphere triplet excited state energy transfer mechanism.The mechanism of [2 + 2] cycloadditions activated by visible light and catalyzed by bis-cyclometalated Rh(iii) and Ir(iii) photocatalysts was investigated, combining density functional theory calculations and spectroscopic techniques. 相似文献
69.
In this paper, we introduce a novel objective prior distribution levering on the connections between information, divergence and scoring rules. In particular, we do so from the starting point of convex functions representing information in density functions. This provides a natural route to proper local scoring rules using Bregman divergence. Specifically, we determine the prior which solves setting the score function to be a constant. Although in itself this provides motivation for an objective prior, the prior also minimizes a corresponding information criterion. 相似文献
70.
Dr. Katherine Villa Dr. Jan Vyskočil Dr. Yulong Ying Dr. Jaroslav Zelenka Prof. Martin Pumera 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(14):3039-3043
Yeasts play a key role in the production of alcoholic beverages by fermentation processes. However, because of their continuous growth, they commonly cause spoilage of the final product. Herein, we introduce dual magnetic/light-responsive self-propelled microrobots that can actively move in a beer sample and capture yeast cells. The presence of magnetic nanoparticles on the surface of the microrobots enables their magnetic actuation under fuel-free conditions. In addition, their photoactivity under visible-light irradiation leads to an overall enhancement of their swimming and yeast removal capabilities. It was found that after the application of the microrobots into a real unfiltered beer sample, these micromachines were able to remove almost 100 % of residual yeasts. In addition, these microrobots could also be added at the initial step of the fermentation process without altering the final beer properties, such as alcohol level, color, and pH. This work demonstrates the potential of using externally actuated microrobots as an innovative and low-cost solution for avoiding yeast spoilage in complex liquid environments, such as alcoholic beverages. Therefore, these autonomous self-propelled microrobots open new avenues for future applications in the food industry. 相似文献