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排序方式: 共有1089条查询结果,搜索用时 15 毫秒
91.
James McGregor Zhenyu Huang Edward P.J. Parrott J. Axel Zeitler K. Lien Nguyen Jeremy M. Rawson Albert Carley Thomas W. Hansen Jean-Philippe Tessonnier Dang Sheng Su Detre Teschner Elaine M. Vass Axel Knop-Gericke R. Schlögl Lynn F. Gladden 《Journal of Catalysis》2010,269(2):329-339
The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes are of significant industrial importance. In this work both carbonaceous material deposited on VOx/Al2O3 catalysts during reaction and unsupported carbon nanofibres (CNFs) are shown to be active for the dehydrogenation of butane in the absence of gas-phase oxygen. Their activity in these reactions is shown to be dependent upon their structure, with different reaction temperatures yielding structurally different coke deposits. Terahertz time-domain spectroscopy (THz-TDS), among other techniques, has been applied to the characterisation of these deposits – the first time this technique has been employed in coke studies. TEM and other techniques show that coke encapsulates the catalyst, preventing access to VOx sites, without a loss of activity. Studies on CNFs confirm that carbonaceous materials act as catalysts in this reaction. Carbon-based catalysts represent an important new class of potential catalysts for DH and ODH reactions. 相似文献
92.
A novel reactive hot melt adhesive was prepared by coating an epoxy resin on maleic anhydride grafted polyethylene (MAPE) powder. This adhesive had markedly improved adhesion power compared with pristine MAPE powder, which is normally used as a hot melt adhesive. The generation of an ester linkage by the reaction between the anhydride group of MAPE and the hydroxyl group of epoxy resin, during the bonding operation at 190°C with the pressure of 22 MPa for 30 min, was confirmed from the FTIR spectra. The bond strength was further improved by a small amount of 1‐methylimidazole, which accelerated the esterification reaction. When the epoxy resin was coated on hydrated MAPE, in which the anhydride group of MAPE was converted into carboxylic acid group by the reaction with water, the esterification reaction was much faster than that of pristine MAPE, and consequently, the bond strength of the adhesive was much higher than that of pristine MAPE coated with epoxy resin. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
93.
In this investigation, chitosan (CS) is modified by propane sultone via a sulfonation reaction to create various degrees of sulfonation. The sulfonated chitosan (SCS) has a pendant alkyl sulfonic group dangling at the side chain, which can improve its hydrophilicity and water solubility. Elemental analysis, Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (13C NMR) were applied to identify the structure by determining the distribution of the substituents in the product. The degree of sulfonation in the SCS can be controlled and the hydrogen bonding interaction can be reduced by varying the degree of sulfonation. A solubility test proved that solubility increased with degree of substitution at over a wide range of pH values. X‐ray diffraction patterns of SCS samples demonstrated that the crystallinity declined as the degree of sulfonation increased. Thermogravimetric analysis and modulated differential scanning calorimetry (MDSC) results indicated that thermal stability fell but water absorbance increased with the degree of sulfonation. More water‐soluble SCS is thus obtained. The controllable different sulfonation degree of the CS polymer suggests new possibilities for the application of CS‐based materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
94.
采用向量式有限元分析,对受火钢结构的非线性响应进行研究。通过与已公布的钢结构试验数据及分析结果相比较,验证数字模型。对Williamstoggle框架和钢框架在地震荷载和火荷载下的非线性性能响应进行研究。数值结果显示:当温度低于临界值时,随着温度增加,Williamstoggle框架的承载力显著增大;然而,当温度高于临界值时,随着温度增加,Williamstoggle框架的承载力显著减少,但当温度达到1000℃时,承载力仍大于室内温度时的弹性屈服强度。此外,随着温度增加,屈服前浅拱向上偏转,而且其挠度远小于同样跨度的梁结构。屈曲后,结构的挠度向下,当重新平衡时,显示出悬链线作用。在地震诱发的火灾中,结构变形受余震、火、结构单元的破坏影响较大。 相似文献
95.
Surface area-normalized rate constants (k(SA)) of reaction between metallic nanoparticles and reducible contaminants, such as chlorinated hydrocarbons, heavy metals, and nitrate, have been reported to be dramatically increased as compared to that of commercial metallic powder. However, k(SA) for individual pollutants in previously published data vary by as much as 1-2 orders of magnitude and much of this variability is due to the effect of various sizes. The size dependence of the reactivity of nanoparticles is not yet fully understood; however, yielding nanoparticles with uniform size and without agglomeration during the period of reaction would demonstrate the effect of varying particle size. In this study, resin-supported zerovalent copper with average particle size of 7, 10, 18, 26, and 29, respectively, were successfully synthesized and evidenced no agglomeration during the reaction period of 10h. The k(SA) of copper nanoparticles (k(n,SA)) was 110-120 times higher than that of powdered copper particles (k(p,SA)) when the copper particle size was about 10nm. However, for diameters of 18-29 nm, the ratio of k(n,SA)/k(p,SA) was around 10-20, indicating that the reactivity of small copper nanoparticles (approximately 10nm) varies discontinuously. Thus, most variability in previous k(SA) is attributed to the presence of small nanoparticles. 相似文献
96.
The aim of this study is to investigate the bioactive components of GABA (γ-aminobutyric acid) tea as compared with green tea produced in Taiwan. Using in total 56 tea samples (28 green tea and 28 GABA tea), moisture content, Hunter L, a and b values, phenolic compounds, amino acids including GABA, fatty acids and ascorbic acid were determined. The results showed that moisture, total free amino acids, crude fat, Hunter L value, total nitrogen, free fatty acids and reducing sugar did not differ significantly between GABA tea and green tea. However, GABA tea had higher Hunter a and b values, while green tea had higher total catechin and ascorbic acid contents (p < 0.05). Of major catechins, epicatechin and epigallocatechin gallate were found to be lower in GABA tea than in green tea. For free amino acids, GABA, alanine, ammonia, lysine, leucine and isoleucine were found to be significantly higher in GABA tea, while the glutamic acid, aspartic acid, and phenylalanine were higher in green tea (p < 0.05). Theanine, tryptophan, valine, threonine and methionine were not found to be different between the two kinds of tea. 相似文献
97.
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99.
The increased use of e-learning techniques as an accepted form of teaching has resulted in a growing volume of academic research
dedicated to their assessment. Despite the importance of the technique, there is little comprehensive knowledge on e-learning,
especially in non-educational fields. Author co-citation analysis (ACA) is an analytical method for identifying the intellectual
structure of specific knowledge domains through the relationship between two similar authors. ACA has been applied to many
fields, such as information retrieval, knowledge management, and strategic management; however, it has not yet been used to
analyze e-learning development. This study examines the intellectual structure of e-learning from the perspective of management
information systems (MIS). By applying the ACA method, we analyze and categorize international and Taiwanese research topics
into clusters. Our results show that Taiwanese authors put more effort into practical studies of business training, while
international authors focus on a users’ psychological reaction to learning context. Altogether, our research provides a clear
intellectual analysis of e-learning practices from 1996 to 2009, enabling us to thoroughly study and understand the influence
of these techniques on modern education. 相似文献
100.