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排序方式: 共有385条查询结果,搜索用时 15 毫秒
1.
An increase in hydrogen evolution from the hydrogen-evolving enzyme in the actinomycete Frankia was recorded in the presence of nickel. Immunogold localisation analysis of the intracellular distribution of hydrogenase proteins indicated that they were evenly distributed in the membranes and cytosol of both hyphae and vesicles. In addition, molecular characterisation of the hydrogen-evolving enzyme at the proteomic level, using two-dimensional gel electrophoresis combined with mass spectrometry, confirmed that the Frankia hydrogen-evolving enzyme is similar to the cyanobacterial bidirectional hydrogenase of Anabena siamensis. 相似文献
2.
Name resolution using the Domain Name System (DNS) is integral to today’s Internet. The resolution of a domain name is often dependent on namespace outside the control of the domain’s owner. In this article we review the DNS protocol and several DNS server implementations. Based on our examination, we propose a formal model for analyzing the name dependencies inherent in DNS. Using our name dependency model we derive metrics to quantify the extent to which domain names affect other domain names. It is found that under certain conditions, more than half of the queries for a domain name are influenced by namespaces not expressly configured by administrators. This result serves to quantify the degree of vulnerability of DNS due to dependencies that administrators are unaware of. When we apply metrics from our model to production DNS data, we show that the set of domains whose resolution affects a given domain name is much smaller than previously thought. However, behaviors such as using cached addresses for querying authoritative servers and chaining domain name aliases increase the number and diversity of influential domains, thereby making the DNS infrastructure more vulnerable. 相似文献
3.
Silicon - The primary purpose of this work is to study the effect of symmetric and asymmetric variation of underlap regions both on source and drain side of 3D SOI n-FinFET. Underlap length is... 相似文献
4.
Isomorphously substituted cobalt(II) hexagonal mesoporous aluminophosphate (CoHMA) molecular sieves were synthesized hydrothermally and characterized by various analytical and spectroscopic techniques. It was deduced that cobalt ions exhibit a divalent oxidation state in tetrahedral coordination in mesoporous aluminophosphates. Further, unlike cobalt-containing microporous aluminophosphate molecular sieves, Co(II) ions remain in a tetrahedral geometry even after calcination. The catalytic activity of CoHMA was tested for the cyclohexane oxidation reaction under mild conditions. Remarkable substrate conversion and product (cyclohexanol) selectivity were obtained compared to several previously reported heterogeneous catalysts. 相似文献
5.
Arun K. Ray Mamata Jenamani Pratap K.J. Mohapatra 《Expert systems with applications》2011,38(5):4689-4697
Behavioral uncertainty of a supplier is a major challenge to a buyer operating in e-procurement setting. Modeling suppliers’ behavior from past transactions, estimation of possible future performance and integrating this knowledge with the winner determination process can bring a new dimension to procurement process automation. We propose a states-space model to capture the uncertainty involved in long-term supplier behavior. The states represent the performance level of a supplier. This behavioral aspect is then integrated with the winner determination process of a multi-attribute reverse auction for efficient supplier selection using parallel MDP. We also propose an implementation framework to collect the feedback on supplier, generate an aggregate performance score and integrate it with the winner determination process. The performance aggregation and winner determination with help of Markov decision process effectively uses the past performance information. In addition, it updates performance information in regular invervals and allevates the problem of maintaining a long history. We compare the MDP-based selection with that of performance score-based selection through a simulation experiment. It is observed that our scheme gives better buyer utility, selects best suppliers and fetches better quality product. The benefits realized through these attributes to the buyer increases the efficiency of the MDP-based selection process. 相似文献
6.
To investigate the effect of nonhydrostatic pressure distribution, dam-break flows are simulated by numerically solving the one-dimensional Boussinesq equations by using a fourth-order explicit finite-difference scheme. The computed water surface profiles for different depth ratios have undulations near the bore front for depth ratios greater than 0.4. The results obtained by using the Saint Venant equations and the Boussinesq equations are compared to determine the contribution of individual Boussinesq terms in the simulation of dam-break flow. It is found that, for typical engineering applications, the Saint Venant equations give sufficiently accurate results for the maximum flow depth and the time to reach this value at a location downstream of the dam. 相似文献
7.
The effect of citrate, oxalate, acetate, silicate and phosphate on stability of synthetic arsenic-loaded ferrihydrite and Al-ferrihydrite 总被引:2,自引:0,他引:2
Mohapatra D Singh P Zhang W Pullammanappallil P 《Journal of hazardous materials》2005,124(1-3):95-100
The effect of the organic species oxalate, citrate and acetate and the inorganic species silicate and phosphate on release of As(V) from synthetic arsenic-loaded ferrihydrite and Al-ferrihydrite in the pH range 4-8 was investigated. For ferrihydrite, the organic species increased %As(V) extraction in the order: acetatePO4(3-). Competitive adsorption of the investigated organic and inorganic species on ferrihydrite and Al-ferrihydrite could explain the enhanced release of As(V) into solution. However, disproportionate adsorption of other species relative to amount of As(V) release occurs, suggesting that mechanisms other than competitive adsorption are also operative. The results could best be explained in terms of combination of competitive adsorption and processes involving pH-dependent dissolution of ferrihydrite/Al-ferrihydrite, formation of various complex ionic species involving Al(III), Fe(III), As(V), SiO3(2-), PO4(3-), OH-, H+ and organic species: acetate, oxalate and citrate. 相似文献
8.
Sandeep Panda Pradeep Chandra Rout Chinmaya Kumar Sarangi Srabani Mishra Nilotpala Pradhan Umaballav Mohapatra Tondepu Subbaiah Lala Behari Sukla Barada Kanta Mishra 《Korean Journal of Chemical Engineering》2014,31(3):452-460
Bioleaching studies for chalcopyrite contained ball mill spillages are very scarce in the literature. We developed a process flow sheet for the recovery of copper metal from surface activated (600 °C, 15 min) ball mill spillage through bio-hydrometallurgical processing route. Bioleaching of the activated sample using a mixed meso-acidophilic bacterial consortium predominantly A. ferrooxidans strains was found to be effective at a lixiviant flow rate of 1.5 L/h, enabling a maximum 72.36% copper recovery in 20 days. Mineralogical as well as morphological changes over the sample surface were seen to trigger the bioleaching efficiency of meso-acidophiles, thereby contributing towards an enhanced copper recovery from the ball mill spillage. The bio-leach liquor containing 1.84 g/L Cu was purified through solvent extraction using LIX 84I in kerosene prior to the recovery of copper metal by electrowinning. Purity of the copper produced through this process was 99.99%. 相似文献
9.
The dielectric behavior of sol-gel derived Ba0.80Sr0.20(ZrxTi1−x)O3 (0.0 ≤ x ≤ 0.50) thin films is studied. A relaxor behavior is observed for x ≥ 0.35. The degree of relaxation increases with Zr content. The frequency dependence of the polar regions follows Vogel-Fulcher relation with a characteristic cooperative freezing at freezing temperature (Tf). Below Tf, a long range polarization ordering is likely to take place. The plausible mechanism of the relaxor behavior of BSZT thin films with Zr contents ≥ 0.35 has been proposed based on the measured temperature as well as frequency dependent dielectric data. The solid solution system is visualized as a mixture of Ti+ 4 rich polar regions and Zr+ 4 rich regions; with the increase in Zr content the volume fraction of the polar regions is progressively reduced. At and above 35.0 at.% Zr substitution the polar regions exhibit typical relaxor behavior. 相似文献
10.
The present paper deals with the extraction of cobalt from a solution containing cobalt and nickel in a sulphate medium similar
to the leach liquor obtained by the dilute sulphuric acid pressure leaching of the Pacific Ocean nodules matte followed by
copper extraction. The commercial extractant Cyanex 272 (bis (2, 4, 4-trimethylpentyl) phosphinic acid) is used for this purpose.
The leach liquor used for the present study contains Co =1.78 g/L and Ni=16.78 g/L. Before cobalt extraction, impurities,
such as copper and iron, are removed from the leach liquor by the precipitation method. Increasing the concentration of Cyanex
272 increased the extraction percentage of cobalt due to the increase of equilibrium pH. Cobalt extraction efficiency of >99.9
% is achieved with 0.20 M Cyanex 272 in two counter-current stages at an aqueous: organic (A:O) phase ratio of 1.5∶1. Complete
stripping of cobalt from the loaded organic containing 2.73 g/L Co was carried out at pH 1.4 by a synthetic cobalt spent electrolyte
in two stages at an A:O ratio of 1∶2. The enrichment of cobalt during extraction and stripping operations was about 3.5 times.
A complete process flowsheet for the separation and recovery of cobalt is presented. 相似文献