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521.
Ketene as a Reaction Intermediate in the Carbonylation of Dimethyl Ether to Methyl Acetate over Mordenite 下载免费PDF全文
Dominik B. Rasmussen Prof. Jakob M. Christensen Dr. Burcin Temel Dr. Felix Studt Dr. Poul Georg Moses Prof. Jan Rossmeisl Prof. Anders Riisager Prof. Anker D. Jensen 《Angewandte Chemie (International ed. in English)》2015,54(25):7261-7264
Unprecedented insight into the carbonylation of dimethyl ether over Mordenite is provided through the identification of ketene (CH2CO) as a reaction intermediate. The formation of ketene is predicted by detailed DFT calculations and verified experimentally by the observation of doubly deuterated acetic acid (CH2DCOOD), when D2O is introduced in the feed during the carbonylation reaction. 相似文献
522.
523.
Henrik T. Rasmussen Robert McDonough Robert J. Gargiullo Bruce P. McPherson 《Journal of separation science》1996,19(6):359-361
A validated gas chromatographic method for the determination of triclosan in human dental plaque is described. Based on plaque sample weights of 10 mg, the limit of detection (2 × S/N) is 0.5 μg/g. The method is linear (r = 0.9986) from the limit of detection to 50 μg/g. Recoveries from placebos spiked with 2.0, 25, and 50 μg/g of triclosan were 105.6%±7.5%, 107.2%±3.1%, and 99.1%±1.1%, respectively (n = 3 at each level). Twenty replicate preparations and analyses of a homogenized sample, conducted by two operators over the course of 4 days, showed agreement to within 9% RSD. Analyses of dental plaque collected from patients after brushing with dental cream containing triclosan, shows triclosan to be retained in dental plaque at concentrations above the minimum inhibitory concentration (1 μg/g) after 12 h. 相似文献
524.
M.萨哈伊 朱胜江 甘翠云 朱凌燕 杨利明 许瑞清 全明吉 姜卓 张征 J.H.Hamilton A.V.Ramayya B.R.S.Babu J.K.Hwang W.C.Ma J.Komicki J.D.Cole R.Aryaeinejad M.W.Dirgert J.O.Rasmussen M.A 《中国物理 C》2000,24(11):1018-1023
通过对252Cf自发裂变产生的瞬发γ谱的测量,对丰中子奇A核145,147Ce的高自旋态进行了研究,首次识别了145Ce的集体带结构,扩展了147Ce的集体带结构,扩展了147Ce的能级,并新识别了3个边带,粒子–转子模型的计算指出,145,147Ce的晕带可能来自于νi13/2轨道的耦合,145Ce基态起源于(νh9/2νf7/2)组态混合,而147Ce基态则起源于νh9/2轨道.在这两个核中未观测到明显的八极形变带,然而,在147Ce中观测到的一个边带,可能显露出八极关联的迹象. 相似文献
525.
Ole Hassager Jose Manuel Roman Marin Kaijia Yu Henrik Koblitz Rasmussen 《Rheologica Acta》2010,49(6):543-554
We use a transient 3D free surface finite element method to simulate flow of entangled polymer fluids in the dual cylinder
wind-up extensional rheometer. The constitutive equations are K-BKZ integral representations of the Doi–Edwards models with
and without the independent alignment approximation (IA). It is demonstrated that the actual kinematics in this rheometer
is a mixture of planar and uniaxial extension. Moreover, the ratio of planar to uniaxial deformation is highly dependent upon
whether IA is invoked. Without IA, the flow has a tendency toward planar extension, while it tends to be more uniaxial with
IA invoked. As a second illustration of the techniques, we simulate the phenomenon of delayed rupture after rapid extension
of entangled polymer systems. It is demonstrated that this phenomenon can be explained on the basis of the Doi–Edwards model
in terms of a Considere-type instability after chain stretch relaxation. 相似文献
526.
527.
B. K. Annis G. D. Wignall Alan R. Hopkins Paul G. Rasmussen Rafil A. Basheer 《Journal of Polymer Science.Polymer Physics》1997,35(17):2765-2774
The structure of blends of Nylon 6 with deuterated polyaniline emeraldine base (D-PANI-EB) and fully doped D-PANI salts (D-PANI-ES) formed from camphorsulfonic acid (CSA), methanesulfonic acid (MSA), or dodecyl benzenesulfonic acid (DBSA) were investigated by small-angle neutron (SANS) and X-ray scattering. The blends were formed from hexafluoro-2-propanol solutions and had volume fractions of 0.038, 0.20, and 0.40 for D-PANI/CSA, 0.20 and 0.40 for D-PANI/MSA, 0.24 and 0.44 for D-PANI/DBSA, and 0.07, 0.14, and 0.31 for D-PANI-EB. The SANS results are compared with a number of standard models for two-phase systems. No evidence was found for significant molecular mixing. In some cases the inverse power law model is in reasonable agreement with observations, and in the case of the lowest concentration of D-PANI/CSA there is an indication of mass fractal structure. This was not found at the higher concentrations. The results establish that the blends with the smaller more polar dopants CSA and MSA behave similarly and are unlike either the D-PANI/DBSA blends or those with D-PANI-EB. There is evidence that the simple picture of two pure phases is inadequate for these materials. With the exception of the D-PANI/DBSA blend which has a relatively low scattering contrast, the results indicate that the lower limit of volume fraction for application of SANS is a few percent D-PANI-ES in Nylon 6. X-ray scattering was used to demonstrate the presence of Nylon 6 lamellae and residual peaks attributable to the pure components. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2765–2774, 1997 相似文献
528.
Taeseok Jang Paul G. Rasmussen 《Journal of polymer science. Part A, Polymer chemistry》1998,36(14):2619-2629
The 2-(1-methyl-4,5-dicyanoimidazolyl) group was attached to poly(diallylamine) and polyethylenimine, affording polymers containing an electron-withdrawing pendant group. The key to their preparation is high reactivity of 1-methyl-2-fluoro-4,5-dicyanoimidazole (1) toward nucleophilic aromatic substitution (NAS) reactions with aliphatic amines. Cyclic voltammograms of these polymers show reduction waves at −2.6 to −2.7 V vs. Ag/Ag+ but no reoxidation waves, unlike those of monomeric and oligomeric model compounds, which are quasi-reversible. The cyclic voltammetry studies of oligomeric model compounds with different alkyl spacers show that the degree of quasi-reversibility decreases as dicyanoimidazoles are crowded together in a molecule, suggesting that a certain degree of chemical reaction occurs between reduced dicyanoimidazole groups. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2619–2629, 1998 相似文献
529.
Multi-mycotoxin analysis of maize silage by LC-MS/MS 总被引:1,自引:0,他引:1
R. R. Rasmussen I. M. L. D. Storm P. H. Rasmussen J. Smedsgaard K. F. Nielsen 《Analytical and bioanalytical chemistry》2010,397(2):765-776
This paper describes a method for determination of 27 mycotoxins and other secondary metabolites in maize silage. The method
focuses on analytes which are known to be produced by common maize and maize-silage contaminants. A simple pH-buffered sample
extraction was developed on the basis of a very fast and simple method for analysis of multiple pesticide residues in food
known as QuEChERS. The buffering effectively ensured a stable pH in samples of both well-ensiled maize (pH < 4) and of hot
spots with fungal infection (pH > 7). No further clean-up was performed before analysis using liquid chromatography–tandem
mass spectrometry. The method was successfully validated for determination of eight analytes qualitatively and 19 quantitatively.
Matrix-matched calibration standards were used giving recoveries ranging from 37% to 201% with the majority between 60% and
115%. Repeatability (5–27% RSDr) and intra-laboratory reproducibility (7–35% RSDIR) was determined. The limit of detection (LOD) for the quantitatively validated analytes ranged from 1 to 739 μg kg−1. Validation results for citrinin, fumonisin B1 and fumonisin B2 were unsatisfying. The method was applied to 20 selected silage samples and alternariol monomethyl ether, andrastin A, alternariol,
citreoisocoumarin, deoxynivalenol, enniatin B, fumigaclavine A, gliotoxin, marcfortine A and B, mycophenolic acid, nivalenol,
roquefortine A and C and zearalenone were detected. 相似文献
530.
Maurice L. Rasmussen 《International Journal of Non》1970,5(4):687-696
A uniformly valid zeroth-order approximation is obtained for the general equation y + εH(y)y + M(y)y = 0, where ε is a small parameter. The notion of multiple scaling is utilized to set up a systematic approximation scheme. Examples are given for simple polynomials for H(y) and M(y), which lead to results involving elliptic integrals. Further restrictions allow progress to be made in terms of gamma functions. 相似文献