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排序方式: 共有144条查询结果,搜索用时 31 毫秒
41.
Qualitative characterization of the diffusion of cationic-modified PVA into the cellulose fiber pores 总被引:1,自引:0,他引:1
Pedram Fatehi Bryce MacMillan Zainab Ziaee Huining Xiao 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,348(1-3):59-63
In this work, the diffusion of cationic poly (vinyl alcohol) (CPVA) with well-defined structures into the pores of bleached kraft fibers was investigated at equilibrium level of adsorption by means of adsorption, solute exclusion technique (SET), and nuclear magnetic resonance (NMR) relaxation method. The results showed that the interaction between CPVA and dextran polymers was weak, which allowed us to use the SET method to investigate the variation in the pore size of fibers upon diffusing CPVAs. Both adsorption and SET methods confirmed the diffusion of CPVA polymers into the fiber pores. However, the NMR technique was unable to reflect the pore size changes. The main reason for such results was probably the error that occurred in removing water between fibers via applying the water retention value (WRV) test prior to the NMR analysis. In fact, not all of the water on the fiber surface, especially on the surface of CPVA-modified fibers, could be removed by the WRV, introducing some error in the NMR analysis. 相似文献
42.
Analysis of a TE011 mode composite sapphire-rutile dielectric resonator has been carried out to study the temperature variation of resonance
frequency, close to the Cs atomic clock hyperfine frequency of 9.192 GHz. The complementary behavior of dielectric permittivity
with temperature of the composite has been exploited to obtain the desired turning point in the resonant frequency. The frequency
of the composite structure is found to be independent of the shield diameter beyond four times the puck diameter. 相似文献
43.
The relative and absolute configurations of long-chain syn- and anti-1,5-, 1,7- and 1,9-glycols were determined from exciton-coupled circular dichroism (ECCD) of the corresponding bis-5-(4'-carboxyl)-5,10,15,20-tetraphenylporphyrin esters measured in uniform (phi = 26 nm), unilamellar liposomes. Long-range transmission of configuration by ECCD is made possible through partial ordering of glycol ester-lipid molecules by liposomal bilayers. 相似文献
44.
Water content profiles with a 1D centric SPRITE acquisition 总被引:1,自引:0,他引:1
Mastikhin IV Mullally H MacMillan B Balcom BJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(1):122-130
The purpose of this work is to develop a rapid MRI method amenable to profiling with minimal or no T(1) relaxation weighting. The behavior of a signal during a centric SPRITE acquisition is analyzed. It is shown that the technique can be made immune to a broad range of T(1) changes. In a properly executed measurement, only T(2)* and proton density parameters define the image intensity. A T(2)* mapping technique can be easily applied, separating T(2)* and proton density contributions to the image. A drying soil sample with low initial water content is experimentally studied as a demonstration of the technique. A characteristic baseline artifact is easily removed from the profiles by a simple operation. 相似文献
45.
C. A. Kennedy S. N. MacMillan M. J. McAlduff D. G. Marangoni 《Colloid and polymer science》2001,279(1):1-7
The micelle formation process for a typical anionic surfactant, sodium dodecyl sulfate, and a typical cationic surfactant,
dodecyltrimethylammonium bromide, has been investigated in a series of mixed solvents consisting of different concentrations
of isomeric hexanediols (1,2-hexanediol and 1,6-hexanediol) in water. The critical micelle concentrations and the degrees
of counterion dissociation of the mixed micelles were obtained from conductance experiments. Luminescence probing experiments
have been used to determine the concentration of micelles in solution and, hence, the micellar aggregation numbers of the
surfactants in the mixed solvent systems. The alcohol aggregation numbers were determined by combining the partition coefficients
(obtained using NMR paramagnetic relaxation enhancement experiments) with the micellar concentrations from the luminescence
probing experiments. All these results are interpreted in terms of the difference in the interaction of the isomeric hexanediols
with the surfactant as a function of the position of the hydroxyl groups on the six-carbon chain of the alcohol.
Received: 28 June 2000/Accepted: 5 July 2000 相似文献
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The enantioselective α-arylation of aldehydes has been accomplished using diaryliodonium salts and a combination of copper and organic catalysts. These mild catalytic conditions provide a new strategy for the enantioselective construction and retention of enolizable α-formyl benzylic stereocenters, a valuable synthon for the production of medicinal agents. As one example, this new asymmetric protocol has been applied to the rapid synthesis of (S)-ketoprofen, a commercially successful oral and topical analgesic. 相似文献
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Direct α‐Arylation of Ethers through the Combination of Photoredox‐Mediated CH Functionalization and the Minisci Reaction
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Dr. Jian Jin Prof. Dr. David W. C. MacMillan 《Angewandte Chemie (International ed. in English)》2015,54(5):1565-1569
The direct α‐arylation of cyclic and acyclic ethers with heteroarenes has been accomplished through the design of a photoredox‐mediated C? H functionalization pathway. Transiently generated α‐oxyalkyl radicals, produced from a variety of widely available ethers through hydrogen atom transfer (HAT), were coupled with a range of electron‐deficient heteroarenes in a Minisci‐type mechanism. This mild, visible‐light‐driven protocol allows direct access to medicinal pharmacophores of broad utility using feedstock substrates and a commercial photocatalyst. 相似文献