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61.
Isomerization of eugenol can be efficiently performed using 2.2 mol. equiv. of KOtBu and catalytic amount of transfer agent in the absence of solvent. The best conditions (94% within 18 minutes) were obtained in a focused open-vessel Maxidigest MX 350 microwave reactor. 相似文献
62.
63.
Hang T. T. Phan Kaizheng Zhu Anna-Lena Kjøniksen Bo Nyström 《Colloid and polymer science》2011,289(9):993-1003
Temperature-induced interchain association and contraction of species in aqueous solutions of charged (MHEC(−)-g-PNIPAAM) and uncharged (MHEC-g-PNIPAAM) modified hydroxyethylcellulose-graft-poly(N-isopropylacrylamide) copolymer have been studied with the aid of turbidimetry and dynamic light scattering (DLS). It was
shown that by attaching PNIPAAM chains to the backbone of a hydrophilic cellulose derivative, a strongly temperature-responsive
copolymer could be prepared. The results show an intriguing interplay between interchain association and contraction of the
multichain species. The transition zone for compression is narrow, and the compaction effect is promoted by a low polymer
concentration and charges on the polymer moieties. The findings from DLS revealed two populations of species, namely molecularly
dispersed molecules or small clusters and interchain complexes, which exhibit temperature-induced collapse. The magnitude
of the cluster contraction can be modulated by changing the polymer concentration and charge density of the copolymer. 相似文献
64.
Summary A variant of the boundary element method, called the boundary contour method, offers a further reduction in dimensionality.
Consequently, boundary contour analysis of 2-D problems does not require any numerical integration at all. In a boundary contour
analysis, boundary stresses can be accurately computed using the approach proposed in Ref. [1]. However, due to singularity,
this approach can be used only to calculate boundary stresses at points that do not lie at an end of a boundary element. Herein,
it is shown that a technique based on the displacement/velocity shape functions can overcome this drawback. Further, the approach
is much simpler to apply, requires less computational effort, and provides competitive accuracy. Numerical solutions and convergence
study for some well-known problems in linear elasticity and Stokes flow are presented to show the effectiveness of the proposed
approach.
This research was supported in part by the 2004 Ralph E. Powe Junior Faculty Enhancement Award from Oak Ridge Associated Universities
and by the University of South Alabama Research Council. 相似文献
65.
Numerical simulations of a spherical particle sedimenting in circular, triangular and square conduits containing a viscous, inertialess, Newtonian fluid were investigated using the Boundary Element Method (BEM). Settling velocities and pressure drops for spheres falling along the centre-lines of the conduits were computed for a definitive range of sphere sizes. The numerical simulations for the settling velocities showed good agreement with existing experimental data. The most accurate analytic solution for a sphere settling along the axis of a circular conduit produced results which were almost indistinguishable from the present BEM calculations. For a sphere falling along the centre-line of a square conduit, the BEM calculations for small spheres agreed well with analytic results. No analytic results for a sphere falling along the axis of a triangular conduit were available for comparison. Extrapolation of the BEM predictions for the pressure drops, to infinitely small spheres, showed remarkable agreement with analytic results. For the circular conduit, the sphere's settling velocity and angular velocity were computed as a function of drop position for small, medium and large spheres. Excellent agreement with a reflection solution was achieved for the small sphere. In addition, end effects were investigated for centre-line drops and compared where possible with available experimental data and analytic results.Los Alamos National Laboratory, Los Alamos, New Mexico, USA. 相似文献
66.
Organocatalyzed Asymmetric Conjugate Addition of Heteroaryl and Aryl Trifluoroborates: a Synthetic Strategy for Discoipyrrole D
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Jiun‐Le Shih Thien S. Nguyen Prof. Jeremy A. May 《Angewandte Chemie (International ed. in English)》2015,54(34):9931-9935
Bis‐heteroaryl or bis‐aryl stereocenters were formed by an organocatalytic enantioselective conjugate addition using the respective trifluoroborate salts as nucleophiles. Control studies suggested that fluoride dissociation is necessary in the anhydrous conditions. This strategy is applicable to the synthesis of discoipyrrole D, an inhibitor of BR5 fibroblast migration. 相似文献
67.
68.
Schmidt S Liu T Rütten S Phan KH Möller M Richtering W 《Langmuir : the ACS journal of surfaces and colloids》2011,27(16):9801-9806
Charged poly(N-isopropylacrylamide-co-methacrylic acid) [P(NiPAM-co-MAA)] microgels can stabilize thermo- and pH-sensitive emulsions. By placing charged units at different locations in the microgels and comparing the emulsion properties, we demonstrate that their behaviors as emulsion stabilizers are very different from molecular surfactants and rigid Pickering stabilizers. The results show that the stabilization of the emulsions is independent of electrostatic repulsion although the presence and location of charges are relevant. Apparently, the charges facilitate emulsion stabilization via the extent of swelling and deformability of the microgels. The stabilization of these emulsions is linked to the swelling and structure of the microgels at the oil-water interface, which depends not only on the presence of charged moieties and on solvent polarity but also on the microgel (core-shell) morphology. Therefore, the internal soft and porous structure of microgels is important, and these features make microgel-stabilized emulsions characteristically different from classical, rigid-particle-stabilized Pickering emulsions, the stability of which depends on the surface properties of the particles. 相似文献
69.
Droplet synthesis of well-defined block copolymers using solvent-resistant microfluidic device 总被引:1,自引:0,他引:1
Well-defined diblock copolymers were synthesized via an exothermic RAFT route by a droplet microfluidic process using a solvent-resistant and thermally stable fluoropolymer microreactor fabricated by a non-lithographic embedded template method. The resulting polymers were compared to products obtained from continuous flow capillary reactor and conventional bulk synthesis. The droplet based microreactor demonstrated superior molecular weight distribution control by synthesizing a higher molecular weight product with higher conversion and narrow polydispersity in a much shorter reaction time. The high quality of the as-synthesized block copolymer PMMA-b-PS led to a generation of micelles with a narrow size distribution that could be used as a template for well-ordered mesoporous silica with regular frameworks and high surface areas. 相似文献
70.
Nguyen Le Hoang Anh Phan Quoc Khanh 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(6):2358-2379
We develop elements of calculus of variational sets for set-valued mappings, which were recently introduced in Khanh and Tuan (2008) [1] and [2] to replace generalized derivatives in establishing optimality conditions in nonsmooth optimization. Most of the usual calculus rules, from chain and sum rules to rules for unions, intersections, products and other operations on mappings, are established. Direct applications in stability and optimality conditions for various vector optimization problems are provided. 相似文献