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41.
M. Del C. Ruiz J. A. González J. B. Rivarola 《Metallurgical and Materials Transactions B》2004,35(3):439-448
The mechanism and kinetics of β-Ta2O5 chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature
range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray
diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters
was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method,
and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature
has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is
144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the
order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable
mechanism for the carbochlorination of β-Ta2O5 is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta2O5, (3) oxidation of carbon, and (4) recrystallization of β-Ta2O5. 相似文献
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This paper reports the findings of a detailed study of Web-based systems design (WBSD) practices in Ireland based on data
collected over a 3-year period (2002–2005), the objectives of which were to (1) contribute towards a richer understanding
of the current “real-world” context of WBSD by characterising the profile of a typical project (team size, timeframe, nature
of requirements, etc.) and identifying the key challenges, constraints, and imperatives (i.e. “mediating factors”) faced by
Web-based system designers, and (2) understand how those contextual parameters and mediating factors influence the activity
of WBSD as regards the selection and enactment of whatever design practices are therefore engaged (i.e. the use of methods,
procedures, etc.). Data was gathered through a survey which yielded 165 usable responses, and later through a series of semi-structured
qualitative interviews. Using grounded theory, an explanatory conceptual framework is derived, based on an extension of the
“method-in-action” model, the application of which to WBSD has not been previously investigated in depth. It is proposed that
this framework of WBSD issues is valuable in a number of ways to educators, researchers, practitioners, and method engineers. 相似文献
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Caterina Dinnella Gaetano Lanzarini Andrea Stagni Claudio Palleschi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(3):237-241
Endopectinlyase (EC 4.2.2.10) from Aspergillus japonicus was immobilized on to γ-alumina. Adsorption performed at pH 5·0 and a subsequent cross-linking phase using 0·1% glutaraldehyde were the chosen immobilization conditions. The comparison between the main biochemical parameters of the immobilized and free form of the enzyme showed that the immobilization procedure used did not affect the enzyme biochemical properties. The interactions between the carrier and the enzyme are essentially secondary bonding. In fact they depend on the pH and on the presence of phosphate ions in the medium. A tentative chemical model of the biocatalytic matrix thus obtained is proposed. 相似文献
49.
Study on the Role of Vitamin E as Nitrite Scavenger and N-Nitrosamine Inhibitor N-nitrosamine are known for their powerful carcinogenicity. They may be formed under acidic conditions by interaction of nitrosable amino substrates and nitrosating agents such as nitrite, nitrate and nitroso gases. Several of recent investigations demonstrate that certain micronutrients such as vitamin A, C, and E and trace elements selenium and zinc play an important role in cancer prevention. Because of their strong antioxidative, nitrite scavenging and free radical quenching properties, vitamin C and E are capable of inhibiting the peroxidation and nitrosation reaction. This paper summarizes the research work done up to date in the field of inhibition of N-nitrosamine formation by vitamin E. It also includes the latest results of our in vitro study on the inhibitory influence of vitamin E and a mixture of tocopherols as well as the cumulative effect of vitamin C and E on the formation of N-nitroso-N-methylaniline (NMNA). α-tocopherol and the mixture of tocopherols are capable of reducing nitrite concentration in hydrophilic reaction medium and thus inhibits the formation of N-nitrosamine. Both vitamins together have a stronger nitrite scavenger effect than either of them alone. The results of research work done up to date strongly suggest that both vitamins may play an important role in reducing the health hazard of some carcinogenic N-nitroso compounds. 相似文献
50.
Keng Siau 《Requirements Engineering》2007,12(4):199-201