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71.
Cobalt catalysts supported on silica aerogel have been prepared using sol–gel chemistry followed by drying under supercritical ethanol conditions. Three different loadings of cobalt were synthesized: 2, 6, and 10% by weight. Transmission electron micrographs indicate that the metallic cobalt exists as discrete particles 50–70 nm in diameter for the 2 and 6% loadings. The 10% catalyst shows long needles of cobalt. BET and BJH measurements indicate that the catalysts retain the silica aerogel properties of high surface area (∼800 m2/g), large pore volume (∼5 cm3/g), and an average pore diameter in the mesoporous regime (∼25 nm). The catalysts were evaluated for Fischer–Tropsch activity in a laboratory-scale packed bed reactor. All three catalysts were active with the 10% Co catalyst achieving more than 20% CO conversion which corresponds to a rate of 1.53 g CO per g-cat per hour. The catalysts were selective for the C10+ hydrocarbons with more than 50% of the carbon contained within this fraction. A significant portion of the C9–C15 hydrocarbon product was observed as 1-olefins which reflects the enhanced mass transport within the very porous aerogel support. 相似文献
72.
This paper addresses the problem of designing controllers that are robust to a great uncertainty in a time constant of the plant. Plants must be represented by minimum phase rational transfer functions of an arbitrary order. The design specifications are: (1) a phase margin for the nominal plant, (2) a gain crossover frequency for the nominal plant, (3) zero steady state error to step commands, and (4) a constant phase margin for all the possible values of the time constant (T): 0<T<∞. We propose a theorem that defines the structure of the set of controllers that fulfil these specifications and show that it is necessary for these robust controllers to include a fractional-order PI term. Examples are developed for both stable and unstable plants, and the results are compared with a standard PI controller and a robust controller designed using the QFT methodology. 相似文献
73.
Marko Ukrainczyk 《Powder Technology》2007,171(3):192-199
The production of precipitated calcium carbonate, PCC, by a semicontinuous process of slaked lime carbonation was performed in a bench-scale chemical reactor, fully controlled by means of custom built electronics and software for the personal computer. Calcite crystals, with different characteristic morphologies (rhombohedral, truncated prismatic, scalenohedral, spheroidal or chain-like agglomerates) were produced by varying a range of process parameters, like temperature, supersaturation, gas mixture flow rate, stirring rate and mass concentration of Ca(OH)2 suspension. In order to identify the effects of the chosen process parameters on the PCC morphology and on the related specific surface area, as well as on the extent of CO2 conversion, an empirical approach based on the experimental design techniques was employed. A multiple correlation analysis of the obtained data suggests that temperature and conductivity significantly influence the PCC morphology, while CO2 conversion is principally influenced by stirring rate, conductivity and gas mixture flow rate. 相似文献
74.
蝗虫中黄酮的含量及提取工艺研究 总被引:1,自引:0,他引:1
蝗虫含有丰富的黄酮,不同品种之间和同一品种不同地域之间有很大差异。稻蝗的黄酮含量最高,为2014.9mg/100g,内蒙黄胫小车蝗的含量最低。为293.2mg/100g。采用有机溶剂提取法对内蒙黄胫小车蝗所含黄酮提取工艺进行了研究,结果表明,甲醇具有很好的提取效果,其最佳提取工艺条件为:提取时间24h。料液比1:30,黄酮的提取量为293.2mg/100g。 相似文献
75.
76.
The purpose of this investigation was to study the origin of the differences in paper‐to‐paper friction of linerboards based on old corrugated containers (OCC). The sheets were subjected to two extraction stages and analyzed with respect to, surface roughness, and their content of low‐molecular‐mass lipophilic compounds (LLC). Friction was measured using a friction tester based on the horizontal plane principle. The surface roughness was measured using a Perthometer profiler and the low molecular mass lipophilic constituent of the paper sheets was determined by gas chromatography‐mass spectroscopy. The sheets were imaged using environmental scanning electron microscopy (ESEM), and the relative compositions of inorganic ions on the paper surfaces were determined by energy dispersive X‐ray spectroscopy (EDS). The results showed that a high amount of LLC in the sheets lead to low friction, due to lubrication. It was also observed that large CaCO3 particles on the surface had a friction‐increasing effect, and that there was no relationship between the surface roughness and the friction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1511–1520, 2002 相似文献
77.
Material characterization has become increasingly important with the adoption of simulation‐based workflow for microwave electronics design. This article focuses on the characterization of printable electronics materials using transmission‐line measurements and demonstrates the capability of the multiline characterization method to separate dielectric and conductor losses when line geometry and material properties vary between the lines. The effects of multiline algorithm, number of line standards, and methods for selecting optimal line lengths are demonstrated. Consistent characterization results are obtained from inkjet‐printed transmission lines on two different substrate materials. In addition, local conductor thickness variations are demonstrated as an effective way to decrease losses. Finally, the simulation‐based procedure for determining the material properties is outlined and applied to printable electronics characterization. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:177–183, 2014. 相似文献
78.
研究了不同老化方式对沥青低温性能的影响,分3个阶段,对不同老化方式的试验结果进行了比较.阶段1研究表明,沥青在压力老化容器(PAV)中100℃条件下老化20 h后的低温性能与在1.01×105Pa、60℃条件下老化38 d后的低温性能相差无几.阶段2研究表明,可以通过58℃、10 r/s时的高温因子G*/sinδ来修正低温性能分级,从而可以利用短期老化来代替长期老化试验.阶段3研究表明,沥青的低温性能会随着老化时间改变而变化.当老化时间较短时,低温性能分级由劲度指标控制;当老化时间较长时,低温性能分级将转变为由蠕变速率控制. 相似文献
79.
80.
根据国家教育部精品视频公开课拍摄制作技术标准(2013年版),将拍摄精品视频公开课过程中前期准备策划工作、摄像机的机位设置和拍摄角度、视频后期制作等问题进行分析。 相似文献