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排序方式: 共有193条查询结果,搜索用时 31 毫秒
81.
A study of the mechanism of the catalytic transformation of mixed ethyl acetate (EA) + methyl acetate (MA) (50:50 v/v) to hydrocarbons over HZSM‐5 (Si/Al ratio of 9) catalyst was conducted. The reaction was carried out in a continuous fixed‐bed reactor under atmospheric pressure and in the temperature range 250–390°C and with weight hourly space velocity of 3.2 and 4.6 h?1. The distribution of products including monoaromatics, fused ring aromatics and oxygenates was determined using GC‐MS. The product distribution was controlled by temperature. The oxygenate components (kinetically controlled products) were transformed into aromatics (thermodynamically controlled products) with an increase in temperature. The effluents were benzene‐free or with low content of benzene and toluene. Two intermediates were proposed for this conversion to hydrocarbons over HZSM‐5: cyclobutane‐1,3‐dione and/or acetic acid (AA) as ketene source. Furthermore, AA and mesityl oxide (MO) were selected as potential intermediates in the transformation of mixed EA + MA into hydrocarbons over HZSM‐5. It is suggested that ketene dimerization, the phenolic pool and the condensation reaction between ketene and MO are the probable mechanism routes for AA conversion. Aldol condensation, Michael addition, cracking, isomerization and ketene formation are the presumable pathways for MO conversion over HZSM‐5. 相似文献
82.
Mohammad Navid Soltani Rad Ali Khalafi‐Nezhad Somayeh Behrouz 《Helvetica chimica acta》2009,92(9):1760-1774
The syntheses of some novel carboacyclic nucleosides, 17a – 17o , containing oxiconazole‐like scaffolds, are described (Schemes 1–3). In this series of carboacyclic nucleosides, pyrimidine as well as purine and other imidazole derivatives were employed as an imidazole successor in oxiconazole. These compounds could be prepared in good yields by using two different strategies (Schemes 1 and 2). Due to Scheme 1, the N‐coupling of nucleobases with 2‐bromoacetophenones was attained for 18a – 18e , and their subsequent oximation affording 19a – 19e and finally O‐alkylation with diverse alkylating sources resulted in the products 17a – 17g, 17n , and 17o . In Scheme 2, use of 2‐bromoacetophenone oximes 20 , followed by N‐coupling of nucleobases, provided 19f – 19j whose final O‐alkylation produced 17h – 17m (Scheme 2). For the rational interpretation of the dominant formation of (E)‐oxime ethers rather than (Z)‐oxime isomers, PM3 semiempirical quantum‐mechanic calculations were discussed and the calculations indicated a lower heat of formation for (E)‐isomers. 相似文献
83.
Ammonium acetate and basic alumina catalyzed efficiently the Knoevenagel condensation of aldehydes and ketones with active methylene compounds under solvent-free condition where olefinic products were obtained in high yields. 相似文献
84.
Partially hydrogenated binaphthol monophosphoric acids were prepared via an improved four-step sequence. It is demonstrated that typical protection and deprotection of the phenolic groups are dispensable. The vinyl-substituted derivative has been polymerized to give a novel polymerized organocatalyst. 相似文献
85.
Amrita Mukhopadhyay Christin Grabinski A. R. M. Nabiul Afrooz Navid B. Saleh Saber Hussain 《Applied biochemistry and biotechnology》2012,167(2):327-337
Gold nanoparticles exhibit unique spectral properties that make them ideal for biosensing, imaging, drug delivery, and other therapeutic applications. Interaction of gold nanoparticles within biological environments is dependent on surface characteristics, which may rely on particular capping agents. In this study, gold nanospheres (GNS) synthesized with different capping agents??specifically citric acid (CA) and tannic acid (TA)??were compared for serum protein adsorption and cellular uptake into a lung epithelial cell line (A549). Both GNS samples exhibited noticeable protein adsorption based on surface charge data after exposure to serum proteins. Light scattering measurements revealed that GNS-CA-protein composites were smaller and less dense compared to GNS-TA-protein composites. The cell uptake characteristics of these nanoparticles were also different. GNS-CA formed large clusters and elicited high uptake, while GNS-TA were taken up as discrete particles, possibly through nonendosomal mechanisms. These results indicate that the capping agents used for GNS synthesis result in unique biological interactions. 相似文献
86.
The star graph, as an interesting network topology, has been extensively studied in the past. In this paper, we address some of the combinatorial properties of the star graph. In particular, we consider the problem of calculating the surface area and volume of the star graph, and thus answering an open problem previously posed in the literature. The surface area of a sphere with radius i in a graph is the number of nodes in the graph whose distance from a given node is exactly i. The volume of a sphere with radius i in a graph is the number of nodes within distance i from the given node. In this paper, we derive explicit expressions to calculate the surface area and volume in the star graph. 相似文献
87.
Omidbakhsh N 《Journal of AOAC International》2010,93(6):1944-1951
High-touch environmental surfaces are important in the spread of many nosocomial pathogens. Although such surfaces are routinely disinfected, the testing and label claims of many common disinfectants do not reflect the realities of field use. A study was conducted to determine the influence of several crucial factors on the action of disinfectants in general, and to assess the killing efficiency of selected chemistries against Staphylococcus aureus and Pseudomonas aeruginosa, related to their drying times (i.e., after one application) and label-specified contact times using a quantitative carrier test. The products were also tested for their ability to wet a hydrophobic (epoxy resin) surface. The hard-surface disinfectants (in-use concentration in ppm) tested were: (a) chlorine bleach (500); (b) quaternary ammonium compounds (quat; 600) alone; (c) quat (3000) with 17% isopropanol (v/v); (d) quat (3000) with 60% ethanol (v/v); (e) phenolic (800) alone; (f) quat (2000), phenolic (3000) with 70% ethanol (v/v); and (g) accelerated hydrogen peroxide (AHP; 5000 of H2O2). The arbitrarily set criterion of bactericidal activity was > or = 6 log10 reduction in the viability of both species tested. All surfaces tested with all products dried in < 5 min, with alcohol-based surfaces drying significantly faster. Even though the alcohol-free quat and phenolic claim a contact time of 10 min, they dried in < 4 min after a single application and failed to meet the performance criterion. Bleach (500 ppm) dried in about 3 min and was effective. AHP also dried in about 3 min and met its label claim even at 1 min of contact. Quat (3000) with 17% isopropanol dried at 1 min and was effective. Quat (3000) with 60% ethanol and quat (2000), phenolic (3000) with 70% ethanol dried in < 1 min, and were ineffective. AHP, alcohol-containing quats, and quat-phenolic-alcohol gave acceptable wettability, while quat and phenolic alone, as well as bleach, covered the treated surface unevenly. The findings show that label claims, especially those for contact times, fail to reflect the way many hard-surface disinfectants are used in the field. 相似文献
88.
Zelaya AJ Stough G Rad N Vandervoort K Brelles-Mariño G 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2010,38(12):3398-3403
Bacterial biofilms are more resilient to standard killing methods than free-living bacteria. Pseudomonas aeruginosa PAO1 biofilms grown on borosilicate coupons were treated with gas-discharge plasma for various exposure times. Almost 100% of the cells were inactivated after a 5-min plasma exposure. Atomic force microscopy was used to image the biofilms and study their micromechanical properties. Results show that the adhesiveness to borosilicate and the thickness of the Pseudomonas biofilms are reduced upon plasma treatment. 相似文献
89.
Vahid Chalangaran Hamed Firoozinia Riyaz Kharrat Navid Chalangaran 《Journal of Dispersion Science and Technology》2014,35(3):313-321
The usefulness of the asphaltene deposition envelope (ADE) is that no asphaltene flocculation occurs at conditions outside the envelope. Since artificial neural network (ANN) is best at identifying patterns or trends in data, it is well suited for prediction or forecasting needs. ANN is also capable of addressing case specific problems that may be encountered in the field such as deposition of asphaltene. In this article, the high pressure, high temperature setup used to perform pressure depletion experiments at three different temperatures on one the Iranian live oils and the ADE generated using ANN. 相似文献
90.
Electrospun titania sol–gel‐based ceramic composite nanofibers for online micro‐ solid‐phase extraction with high‐performance liquid chromatography
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Habib Bagheri Hamed Piri‐Moghadam Soroush Rastegar Navid Taheri 《Journal of separation science》2014,37(15):1982-1988
Titanium(IV) tetraisopropoxide was employed as a metal oxide sol–gel precursor to prepare ceramic composite nanofibers by the electrospinning system. To facilitate this process and obtain the desired nanofibers with higher aspect ratios and surface area, poly(vinylpyrrolidone) was added to the sol of titania. Four ceramic nanofibers sheets based on titania were prepared while each sheet contained different transition metals such as Fe‐Mn, Fe‐Ni, Fe‐Co, and Fe‐Mn‐Co‐Ni. The scanning electron microscope images showed good homogeneity for all the prepared ceramic composites with a diameter range of 100–250 nm. The sorption efficiency was investigated by a micro‐solid‐phase extraction setup in online combination with high‐performance liquid chromatography for the determination of naproxen and clobetasol. All the prepared composites exhibited comparable efficiencies for the desired analytes and the type of metal showed insignificant effect. For the selected composite with Fe‐Mn, the linearity of the analytes was in the range of 1–1000 μg/L and the limit of detection values were found to be 2 and 0.3 μg/L for naproxen and clobetasol, respectively. The developed method was extended to the analysis of urine and blood plasma samples and acceptable relative standard deviations were obtained at two concentration levels. 相似文献