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61.
Ohne Zusammenfassung 相似文献
62.
Menard LD Gao SP Xu H Twesten RD Harper AS Song Y Wang G Douglas AD Yang JC Frenkel AI Nuzzo RG Murray RW 《The journal of physical chemistry. B》2006,110(26):12874-12883
The synthesis and characterization of the clusters Au13[PPh3]4[S(CH2)11CH3]2Cl2 (1) and Au13[PPh3]4[S(CH2)11CH3]4 (2) are described. These mixed-ligand, sub-nanometer clusters, prepared via exchange of dodecanethiol onto phosphine-halide gold clusters, show enhanced stability relative to the parent. The characterization of these clusters features the precise determination of the number of gold atoms in the cluster cores using high-angle annular dark-field scanning transmission electron microscopy, allowing the assignment of 13 gold atoms (+/-3 atoms) to the composition of both cluster molecules. Electrochemical and optical measurements reveal discrete molecular orbital levels and apparent energy gaps of 1.6-1.7 eV for the two cluster molecules. The electrochemical measurements further indicate that the Au13[PPh3]4[S(CH2)11CH3]2Cl2 cluster undergoes an overall two-electron reduction. The electrochemical and spectroscopic properties of the two Au13 cluster molecules are compared with those of a secondary synthetic product, which proved to be larger Au thiolate-derivatized monolayer-protected clusters with an average core of Au180. The latter shows behavior fully consistent with the adoption of metallic-like properties. 相似文献
63.
The rate of crystal nucleation of colloids and globular proteins can be enhanced by critical density fluctuations. It has been argued that a closely related phenomenon influences the rate of intramolecular "crystallization" of single-chain polymers. We report Monte Carlo simulations of the free-energy barrier that separates the crystalline state of a homopolymer chain from the disordered state. The simulations show that the barrier for nucleation of the ordered state is drastically lowered as the disordered state changes from a coil to a globule. We discuss the relation of the present findings to intramolecular nucleation of heteropolymers, such as proteins. 相似文献
64.
We report grand-canonical Monte Carlo simulations of an equimolar mixture of hard colloids coated with long polymers that have a complementary functionalization. Such systems have the potential to function as self-healing materials. Under conditions where the complementary polymer ends are strongly associated, we observe a first-order vapor-liquid transition from a dilute gas of colloidal dimers to a dense, liquid-like phase. This transition is driven exclusively by the increase in entropy associated with bond disorder-an effect that was predicted theoretically by Zilman et al. [Phys. Rev. Lett. 91, 015901 (2003)10.1103/PhysRevLett.91.015901]. Our simulations rationalize experimental observations by Schmatko et al. [Soft Matter 03 (2007) 703.]. 相似文献
65.
In this paper we show that the Kazhdan-Lusztig polynomials (and, more generally, parabolic KL polynomials) for the groupS
n coincide with the coefficients of the canonical basis innth tensor power of the fundamental representation of the quantum groupU
q
k
. We also use known results about canonical bases forU
q
2 to get a new proof of recurrent formulas for KL polynomials for maximal parabolic subgroups (geometrically, this case corresponds
to Grassmannians), due to Lascoux-Schützenberger and Zelevinsky. 相似文献
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This paper considers an aging multi‐state system, where the system failure rate varies with time. After any failure, maintenance is performed by an external repair team. Repair rate and cost of each repair are determined by a corresponding corrective maintenance contract with a repair team. The service market can provide different kinds of maintenance contracts to the system owner, which also can be changed after each specified time period. The owner of the system would like to determine a series of repair contracts during the system life cycle in order to minimize the total expected cost while satisfying the system availability. Operating cost, repair cost and penalty cost for system failures should be taken into account. The paper proposes a method for determining such optimal series of maintenance contracts. The method is based on the piecewise constant approximation for an increasing failure rate function in order to assess lower and upper bounds of the total expected cost and system availability by using Markov models. The genetic algorithm is used as the optimization technique. Numerical example is presented to illustrate the approach. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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