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排序方式: 共有4520条查询结果,搜索用时 15 毫秒
51.
The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of tartaric acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by energy spectroscopy dispersion (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al2O3 layer.A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium.Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, EDS reveals a good homogeneity and compactness of the film achieved in galvanostatic method. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al2O3/PPy shows a capacitor with future applications. 相似文献
52.
Incorporation and oxidation of fatty acids (FA) were investigated in resident and thioglycolate-clicited (TG-elicited) rat
macrophages (Mϕ). Both cell types presented a time-dependent incorporation of [14C]-labeled palmitic acid (PA), oleic acid (OA), linoleic acid (LA), and arachidonic acid (AA) up to 6h. The total amount of
[14C]-FA incorporated by resident Mϕ after 6 h was: AA>PA=LA>OA. TG-elicited cells presented a 50% reduction in the incorporation
of LA, PA, and AA, whereas that of OA remained unchanged as compared to resident Mϕ. The FA were oxidized by resident Mϕ as
follows: LA>OA>PA>AA. TG elicitation promoted a reduction of 42% in LA oxidation and a marked increase in AA oxidation (280%).
The increased oxidation of AA in TG-elicited cells may account for the lower production of prostaglandins in Mϕ under these
conditions. The full significance of these findings for Mϕ function, however, remains to be examined. 相似文献
53.
This paper describes a kinetic method to predict the z-average molecular mean square radius of gyration of tree-like polymers formed by irreversible reactions, assuming Gaussian chains. It is based on the population balance equations for the two-sided molecular distributions of pendant chains associated with every chemically distinguishable kind of bonds. An automated method for the solution of those equations is valid both before as well as after gelation for complex kinetic schemes. Examples of its use are presented with polycondensation systems leading to hyperbranched polymers, the anionic polymerization of mono- and divinyl monomers and a radical polymerization with terminal branching and transfer to polymer. 相似文献
54.
High surface area Mn-based porous oxides (MANPO) containing additives like Ce, Sr and La were found to be very active and selective materials under 0.67% CH4/0.2% NO/5% O2 lean-deNO
x
conditions in the 200–300°C low-temperature range. These materials perform also impressively in the presence of 4% H2O in the feed stream, where a N2 selectivity of 98% and an excellent stability over 24 h on stream have been observed. The MANPO materials can be considered serious competitors of noble metals for low-temperature lean-deNO
x
applications. 相似文献
55.
Santosh K. Verma Zhe Zhao Theodore K. Courtney Wen-Ruey Chang David A. Lombardi Yueng-Hsiang Huang 《Ergonomics》2014,57(12):1919-1926
Several studies have indicated that slip-resistant shoes may have a positive effect on reducing the risk of slips and falls, a leading cause of injury at work. Few studies, however, have examined how duration of shoe usage affects their slip-resistance properties. This study examined the association between the duration of slip-resistant shoes usage and the self-reported rate of slipping in limited-service restaurant workers. A total of 475 workers from 36 limited-service restaurants in the USA were recruited to participate in a 12-week prospective study of workplace slipping. Of the 475 participants, 83 reported changing to a new pair of shoes at least once during the 12-week follow-up. The results show that slip-resistant shoes worn for less than six months were moderately more effective than those worn for more than six months. Changing to a new pair of shoes among those wearing slip-resistant shoes at baseline was associated with a 55% reduction in the rate of slipping (RR = 0.45, 95% CI = 0.23–0.89). Further research is needed to develop criteria for the replacement of slip-resistant shoes.
Practitioner Summary: The duration of usage impacts the slip-resistance properties of slip-resistant shoes. Slip-resistant shoes worn for less than six months were moderately more effective in reducing slips than slip-resistant shoes worn for more than six months. Shoe use policies should not only encourage or require their use but also include guidance on replacing slip-resistant shoes at regular intervals. 相似文献
56.
A. Calcagnì L. Lombardi E. Pascali 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2014,18(8):1575-1588
LR-fuzzy numbers are widely used in Fuzzy Set Theory applications based on the standard definition of convex fuzzy sets. However, in some empirical contexts such as, for example, human decision making and ratings, convex representations might not be capable to capture more complex structures in the data. Moreover, non-convexity seems to arise as a natural property in many applications based on fuzzy systems (e.g., fuzzy scales of measurement). In these contexts, the usage of standard fuzzy statistical techniques could be questionable. A possible way out consists in adopting ad-hoc data manipulation procedures to transform non-convex data into standard convex representations. However, these procedures can artificially mask relevant information carried out by the non-convexity property. To overcome this problem, in this article we introduce a novel computational definition of non-convex fuzzy number which extends the traditional definition of LR-fuzzy number. Moreover, we also present a new fuzzy regression model for crisp input/non-convex fuzzy output data based on the fuzzy least squares approach. In order to better highlight some important characteristics of the model, we applied the fuzzy regression model to some datasets characterized by convex as well as non-convex features. Finally, some critical points are outlined in the final section of the article together with suggestions about future extensions of this work. 相似文献
57.
G. L. Chen C. Guyon Z. X. Zhang B. Da Silva P. Da Costa S. Ognier D. Bonn M. Tatoulian 《Microfluidics and nanofluidics》2014,16(1-2):141-148
In this paper, tricobalt tetraoxide (Co3O4) catalyst was coated on the polydimethylsiloxane microchannel by the plasma-enhanced metal-organic chemical vapor deposition technology. The obtained Co3O4 film was characterized by SEM, XRD, XPS, and TEM, and the results show that the as-deposited Co3O4 film was initially composed of many cauliflowers-shaped microclusters. Also, the microcauliflower was transformed from an amorphous phase to a crystal phase when the Co3O4 film was treated by Ar and O2 plasma for more than 20 min, and the crystal lattice line occurred on the surface of nano-sized-Co3O4 particles. Meanwhile, the interface of Co3O4 particles with diameter between 3 and 12 nm became obvious and some nano-catkin structures were also formed on the Co3O4 film. The ratio of Co3+/Co2+ in the spinel-type Co3O4 was nearly 2, and the nano-particles predominantly expose their {311}, {111}, and {220} planes. These morphologies and structure characteristics were found to be ideal for increasing the catalytic activity efficiency of Co3O4 for CO oxidation, and the catalytic stability of Co3O4 coated on the organic microreactor lasted nearly 85 h for trace CO oxidation at room temperature. 相似文献
58.
Luis Carlos Ferreira Jr.Marcos A.S. Costa Pedro Ivo C. GuimarãesLuiz Claudio de Santa Maria 《Polymer》2002,43(14):3857-3862
Styrene polymerization was carried out with Ni(acac)2/MAO and Ni(acac)2/SiO2/MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type. 相似文献
59.
A systematic reactivity study of N2O, NO, and NO2 on highly dispersed CuO phases over modified silica supports (SiO2–Al2O3, SiO2–TiO2, and SiO2–ZrO2) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N2O) to selective reductions by hydrocarbons (N2O, NO, and NO2) and oxidation (NO to NO2). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO2–Al2O3 and SiO2–ZrO2, led to a better activity and selectivity of CuO for the reactions of N2O, NO, and NO2 reductions and N2O decomposition than SiO2–TiO2. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values. 相似文献
60.
An optimization strategy has been applied to describe the chemical composition at the furnace bottom in the Kraft recovery boiler of a pulp production process. The concentrations of each involved chemical species were calculated through an optimization approach, minimizing the Gibbs free energy of the system. Various systems were proposed and tested, assuming different chemical species and phases number. Because serious initialization problems were found at this stage for some of the proposed systems, an optimization heuristic method (PSO) was used for the first approach to the problem. Once the appropriate phases number and chemical species in the system were determined, the initialization problems disappeared and the use of a deterministic optimization method (SQP) became viable. The proposed approach has shown to be satisfactory to reproduce industrial data and also data reported in the open scientific literature. 相似文献