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排序方式: 共有273条查询结果,搜索用时 15 毫秒
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J Buc CL Santini F Blasco R Giordani ML Cárdenas M Chippaux A Cornish-Bowden G Giordano 《Canadian Metallurgical Quarterly》1995,234(3):766-772
A soluble alpha beta complex of nitrate reductase can be obtained from a strain of Escherichia coli that lacks the narI gene and expresses only the alpha and beta subunits. The beta subunit contains four Fe-S centres and the alpha subunit contains the molybdenum cofactor, which is the site at which nitrate is reduced. Despite the lack of the gamma subunit of the complete enzyme, this complex can still catalyse the reduction of nitrate with artificial electron donors such as benzyl viologen, so that it is suitable for studying the transfer of electrons between these two types of redox centre. To examine whether the electrons from reduced benzyl viologen are initially delivered to the Fe-S centres, or directly to the molybdenum cofactor, or both, we have studied the steady-state kinetics and the binding of benzyl viologen to the alpha beta complex and mutants alpha beta* with altered beta subunits. Reduction of the enzyme by reduced benzyl viologen in the absence of nitrate showed that all four Fe-S centres and the molybdenum cofactor could be reduced. Two classes of site with different equilibrium constants could be distinguished. The kinetic results suggest that benzyl viologen supplies its electrons directly to the molybdenum cofactor, at a rate showing a hyperbolic dependence on the square of the concentration of the electron donor. A reaction mechanism is proposed for the reduction of nitrate catalysed by the alpha beta complex of nitrate reductase with artificial electron donors. 相似文献
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Fernando Corvillo Laura Gonzlez-Snchez Alberto Lpez-Lera Emilia Arjona Giovanni Ceccarini Ferruccio Santini David Araújo-Vilar Rebecca J Brown Joan Villarroya Francesc Villarroya Santiago Rodríguez de Crdoba Teresa Caballero Pilar Nozal Margarita Lpez-Trascasa 《International journal of molecular sciences》2021,22(12)
5.
Zdena Tvarůžková Magda Tupá Pavel Jírů Alfonso Nastro Giorgio Giordano Ferruccio Trifiró 《Catalysis Letters》1989,2(6):369-374
The small pore zeolite HLZ 132 exhibits, in comparison with other zeolites, an increased selectivity for the transformation of methanol to ethylene in the reaction temperature range 350–500 °C: the weight ratio of C2H4 to C3H6 in the products ranges between 1 and 4 at WHSV=2 h–1. Besides the effect of the reactant shape selectivity this fact may be interpreted by the participation of the asymmetrical methoxy groups in the surface as well as by proton-donor centres of lower acidity which do not catalyze the oligomerization of ethylene but which do the more basic molecule of propylene, thereby generating polyene-type coke. 相似文献
6.
In this paper, we propose a content-based method the for semi-automatic organization of photo albums based on the analysis of how different users organize their own pictures. The goal is to help the user in dividing his pictures into groups characterized by a similar semantic content. The method is semi-automatic: the user starts to assign labels to the pictures and unlabeled pictures are tagged with proposed labels. The user can accept the recommendation or made a correction. To formulate the suggestions is exploited the knowledge encoded in how other users have partitioned their images. The method is conceptually articulated in two parts. First, we use a suitable feature representation of the images to model the different classes that the users have collected, second, we look for correspondences between the criteria used by the different users. Boosting is used to integrate the information provided by the analysis of multiple users. A quantitative evaluation of the proposed approach is obtained by simulating the amount of user interaction needed to annotate the albums of a set of members of the flickr® photo-sharing community. 相似文献
7.
Antonio Balena Marco Bianco Ferruccio Pisanello Massimo De Vittorio 《Advanced functional materials》2023,33(39):2211773
Two-Photon Lithography, thanks to its very high sub-diffraction resolution, has become the lithographic technique par excellence in applications requiring small feature sizes and complex 3D pattering. Despite this, the fabrication times required for extended structures remain much longer than those of other competing techniques (UV mask lithography, nanoimprinting, etc.). Its low throughput prevents its wide adoption in industrial applications. To increase it, over the years different solutions have been proposed, although their usage is difficult to generalize and may be limited depending on the specific application. A promising strategy to further increase the throughput of Two-Photon Lithography, opening a concrete window for its adoption in industry, lies in its combination with holography approaches: in this way it is possible to generate dozens of foci from a single laser beam, thus parallelizing the fabrication of periodic structures, or to engineer the intensity distribution on the writing plane in a complex way, obtaining 3D microstructures with a single exposure. Here, the fundamental concepts behind high-speed Two-Photon Lithography and its combination with holography are discussed, and the literary production of recent years that exploits such techniques is reviewed, and contextualized according to the topic covered. 相似文献
8.
Clara Comuzzi Giuliano Dolcetti Alessandro Trovarelli Fabrizio Cavani Ferruccio Trifirò Jordi Llorca Richard G. Finke 《Catalysis Letters》1996,36(1-2):75-79
The thermal and structural stability of the Wells-Dawson-type heteropoly compound K6P2W18O62·10H2O was examined by FT-IR spectroscopy, X-ray powder diffraction, thermogravimetric analysis and HRTEM. It was found that calcination at temperatures higher than 850 K led to the formation of a Keggin-type compound K3PW12O40, containing small amounts of an additional phase originated from the high-temperature interaction between potassium phosphate (K3PO4 formed during the decomposition of the K6P2W18O62·10H2O) and the Keggin-type compound itself. The Keggin-type product showed a higher activity in the selective oxidative dehydrogenation of isobutane to isobutene compared to both the Wells-Dawson precursor and to pure, authentic K3PW12O40. This higher activity can be tentatively attributed to the presence of an amorphous layer of unknown stoichiometry at the surface of the thermally rearranged Wells-Dawson compound. 相似文献
9.
Emergent semantics through interaction in image databases 总被引:9,自引:0,他引:9
Santini S. Gupta A. Jain R. 《Knowledge and Data Engineering, IEEE Transactions on》2001,13(3):337-351
In this paper, we briefly discuss some aspects of image semantics and the role that it plays for the design of image databases. We argue that images don't have an intrinsic meaning, but that they are endowed with a meaning by placing them in the context of other images and by the user interaction. From this observation, we conclude that, in an image, database users should be allowed to manipulate not only the individual images, but also the relation between them. We present an interface model based on the manipulation of configurations of images 相似文献
10.
Measurements of the shear viscosity at saturated vapor pressure through the lambda transition indicate a singular behavior of the form |1 – (/)|=A
x
, (where =|1–(T/T
)|, with equal values for the critical exponent on both sides of the transition.Work sponsored by Consiglio Nazionale delle Ricerche, Rome (Italy). 相似文献