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91.
The defect structure model in the wustite phase is considered involving the 4:l cluster as a basic defect structure unit. Interactions between defects are considered in terms of the Debye-Hückel theory for strong electrolytes. It has been shown that the available data on wustite nonstoichiometry fit well the 4:l cluster model. Above 1173 K the degree of ionization of the cluster is −5. The equilibrium constant of the cluster formation determined in this work is K c = [(( V Fe )4 Fe i )5− ][h]5 [FeFe ]−6 [V i ]−1 PO2 −3/2 f 6 ± = 1.07 × 10−14 exp[396.7 (kJ)/ RT ]. The equilibrium constant is quite consistent with such thermodynamic parameters as partial molar enthalpy and entropy of oxygen in Fe1- y O within the entire stability range of the wustite phase. 相似文献
92.
We investigate the thermoelectric transport properties of carbon atomic clusters connected with two Al electrodes using the first-principles density functional analysis combined with the non-equilibrium Green’s function approach. We find that due to the quantum interference the thermopower S changes sign for even-odd number of carbon atoms. The thermal conductance κ is always positive with a similar oscillation between even- and odd-number of carbon atoms. Due to the orthogonalization of the wave functions of the atomic electrodes and the carbon clusters, the electric conductance G is very small for certain range of chemical potentials. Giant thermopower is found in this region. Our results show that the thermopower and thermal conductance are sensitively related to the distance d between the carbon atomic cluster and the Al electrodes. Oscillatory behaviors of S and κ are found as d is varied. 相似文献
93.
Research on science-based industries has shown that it is important for organisations to be active in interorganisational networks. Cluster policy has been developed as a means to stimulate the development of these networks and thereby the success rate of these industries. Cluster policy is however not a common policy instrument in the energy sector. In this paper, we focus on three self-declared clusters active in hydrogen-related R&D in the Netherlands and address several characteristics of these clusters. We conclude that cluster policy is a useful addition to existing energy R&D policies but that monitoring whether self-declared clusters actually function as clusters and what their contribution is to the overall system is pivotal in reaping the benefits of cluster policy. 相似文献
94.
Sandro Montresor 《Industry and innovation》2008,15(3):321-346
The paper aims to investigate how innovations cluster in different technological systems (TSs) when their “techno‐economic”, rather than “territorial” space, is considered. Innovation clusters of economic sectors are identified by referring to the innovation “potential” represented by their R&D expenditure and by applying social network analysis to the intersectoral R&D flows matrices of 15 OECD countries in the mid‐1990s. Different clusterization models are first tested in order to detect the way sectors group on the basis of the embodied R&D flows they exchange. Actual clusters are then mapped in the different TSs by looking for intersectoral relationships which can be qualified to constitute “reduced TSs” (ReTSs). In all the 15 TSs investigated the techno‐economic space appears organized in hierarchies, along which its constitutive sectors grouped into clusters with different density and composition. Once ReTSs are looked for, the 15 TSs display highly heterogeneous structures, but with some interesting similarity on the basis of which different clusters of TSs can be identified in turn. 相似文献
95.
Embedded quantum cluster and Mott-Littleton techniques are used to study defects in MgO, UO2 , and FeO. Through these calculations we illustrate the importance of lattice relaxation and provide evidence that the quantum cluster methodology is both compatible with and complementary to a Born-like ionic model. We discuss the limitations of both methods. Within the Mott-Littleton framework we consider the derivation of effective pair potentials, region sizes, and the application to complex systems. For embedded quantum cluster calculations we investigate basis sets and discuss effective embedding procedures. 相似文献
96.
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98.
Pd clusters were formed on highly dispersed Au nanoparticles (∼3.5 nm in diameter) using a seed-mediated growth process. The structural information and electrocatalytic activities of these Pd clusters on Au nanoparticles were confirmed by high-resolution-transmission-electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The resulting nanoparticles, which had a uniform size (<5 nm in diameter), were highly dispersed on carbon particles, and Pd clusters (<0.44 nm in size, <2 atomic layers) were formed selectively on Au nanoparticles. XPS results show that the Pd 3d5/2 peak shifted to lower binding energies and that the amount of surface oxide decreased as the Pd content was decreased on the Au nanoparticles. In formic acid electro-oxidation, these Pd clusters exhibit enhanced electrocatalytic activity relative to that of carbon-supported Pd nanoparticles. These results may be due to the modified electronic and geometric structure of the Pd clusters on the Au nanoparticle substrate. 相似文献
99.
Fumitaka Kudo Dr. Atsushi Motegi Kazutoshi Mizoue Dr. Tadashi Eguchi Prof. Dr. 《Chembiochem : a European journal of chemical biology》2010,11(11):1574-1582
FD‐891 is a 16‐membered cytotoxic antibiotic macrolide that is especially active against human leukemia such as HL‐60 and Jurkat cells. We identified the FD‐891 biosynthetic (gfs) gene cluster from the producer Streptomyces graminofaciens A‐8890 by using typical modular type I polyketide synthase (PKS) genes as probes. The gfs gene cluster contained five typical modular type I PKS genes (gfsA, B, C, D, and E), a cytochrome P450 gene (gfsF), a methyltransferase gene (gfsG), and a regulator gene (gfsR). The gene organization of PKSs agreed well with the basic polyketide skeleton of FD‐891 including the oxidation states and α‐alkyl substituent determined by the substrate specificities of the acyltransferase (AT) domains. To clarify the involvement of the gfs genes in the FD‐891 biosynthesis, the P450 gfsF gene was inactivated; this resulted in the loss of FD‐891 production. Instead, the gfsF gene‐disrupted mutant accumulated a novel FD‐891 analogue 25‐O‐methyl‐FD‐892, which lacked the epoxide and the hydroxyl group of FD‐891. Furthermore, the recombinant GfsF enzyme coexpressed with putidaredoxin and putidaredoxin reductase converted 25‐O‐methyl‐FD‐892 into FD‐891. In the course of the GfsF reaction, 10‐deoxy‐FD‐891 was isolated as an enzymatic reaction intermediate, which was also converted into FD‐891 by GfsF. Therefore, it was clearly found that the cytochrome P450 GfsF catalyzes epoxidation and hydroxylation in a stepwise manner in the FD‐891 biosynthesis. These results clearly confirmed that the identified gfs genes are responsible for the biosynthesis of FD‐891 in S. graminofaciens. 相似文献