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排序方式: 共有66条查询结果,搜索用时 15 毫秒
1.
Surface effects in metallic iron nanoparticles 总被引:1,自引:0,他引:1
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Rikard Westbom Sune Sporring Louise Cederberg Lars-Ola Linderoth Erland Bj?rklund 《Analytical sciences》2008,24(4):531-533
A selective pressurized liquid extraction procedure (SPLE) was developed for a fast determination of polychlorinated biphenyls in sediment. The final method was performed at 100 degrees C with heptane/dichloromethane (90:10, v/v) as extraction solvent for 2x5 min. Sulfuric acid impregnated silica was placed downstream of the sample in the extraction cell to remove interfering components. This simultaneous extraction/clean-up was performed in 20 min, with an average congener recovery of 92% compared to a classical 24 h Soxhlet methodology and 2 h of external manual clean-up. 相似文献
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Knudsen MM Kalashnyk N Masini F Cramer JR Lægsgaard E Besenbacher F Linderoth TR Gothelf KV 《Journal of the American Chemical Society》2011,133(13):4896-4905
Chiral self-assembled structures formed from organic molecules adsorbed on surfaces have been the subject of intense investigation in the recent decade, owing both to relevance in applications such as enantiospecific heterogeneous catalysis or chiral separation as well as to fundamental interest, for example, in relation to the origin of biomolecular homochirality. A central target is rational design of molecular building blocks allowing transfer of chirality from the molecular to the supramolecular level. We previously studied the surface self-assembly of a class of linear compounds based on an oligo(phenylene ethynylene) backbone, which were shown to form a characteristic windmill adsorption pattern on the Au(111) surface. However, since these prochiral compounds were intrinsically achiral, domains with oppositely oriented windmill motifs and related conformational surface enantiomers were always realized in equal proportion. Here we report on the enantioselective, high yield chemical synthesis of a structurally related but intrinsically chiral compound in which two peripheral tert-butyl substituents are replaced by sec-butyl groups, each containing an (S) chiral center. Using scanning tunneling microscopy under ultrahigh vacuum conditions, we characterize the adsorption structures formed from this compound on the Au(111) surface. The perturbation introduced by the modified molecular design is found to be sufficiently small so structures form that are closely analogous to those observed for the original tert-butyl substituted compound. However, as demonstrated from careful statistical analysis of high-resolution STM images, the introduction of the two chiral (S)-sec-butyl substituents leads to a strong preference for windmill motifs with one orientation, demonstrating control of the chiral organization of the molecular backbones through rational molecular design. 相似文献
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Masini F Kalashnyk N Knudsen MM Cramer JR Laegsgaard E Besenbacher F Gothelf KV Linderoth TR 《Journal of the American Chemical Society》2011,133(35):13910-13913
It is demonstrated by scanning tunneling microscopy that coadsorption of a molecular chiral switch with a complementary, intrinsically chiral induction seed on the Au(111) surface leads to the formation of globally homochiral molecular assemblies. 相似文献
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We investigate the quality of solutions obtained from sample-average approximations to two-stage stochastic linear programs
with recourse. We use a recently developed software tool executing on a computational grid to solve many large instances of
these problems, allowing us to obtain high-quality solutions and to verify optimality and near-optimality of the computed
solutions in various ways.
Research supported by the Mathematical, Information, and Computational Sciences Division subprogram of the Office of Advanced
Scientific Computing Research, U.S. Department of Energy, under Contract W-31-109-Eng-38, and by the National Science Foundation
under Grant 9726385.
Research supported by the Mathematical, Information, and Computational Sciences Division subprogram of the Office of Advanced
Scientific Computing Research, U.S. Department of Energy, under Contract W-31-109-Eng-38, and by the National Science Foundation
under Grant DMS-0073770.
Research supported by the Mathematical, Information, and Computational Sciences Division subprogram of the Office of Advanced
Scientific Computing Research, U.S. Department of Energy, under Contract W-31-109-Eng-38, and by the National Science Foundation
under Grants 9726385 and 0082065. 相似文献
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We present effective linear programming based computational techniques for solving nonconvex quadratic programs with box constraints (BoxQP). We first observe that known cutting planes obtained from the Boolean Quadric Polytope (BQP) are computationally effective at reducing the optimality gap of BoxQP. We next show that the Chvátal–Gomory closure of the BQP is given by the odd-cycle inequalities even when the underlying graph is not complete. By using these cutting planes in a spatial branch-and-cut framework, together with a common integrality-based preprocessing technique and a particular convex quadratic relaxation, we develop a solver that can effectively solve a well-known family of test instances. Our linear programming based solver is competitive with SDP-based state of the art solvers on small instances and sparse instances. Most of our computational techniques have been implemented in the recent version of CPLEX and have led to significant performance improvements on nonconvex quadratic programs with linear constraints. 相似文献
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Weigelt S Schnadt J Tuxen AK Masini F Bombis C Busse C Isvoranu C Ataman E Laegsgaard E Besenbacher F Linderoth TR 《Journal of the American Chemical Society》2008,130(16):5388-5389
The adsorption of octylamine on Au(111) under ultrahigh vacuum conditions is investigated. The molecules surprisingly undergo a thermally activated chemical reaction, resulting in formation of trioctylamine as confirmed both by X-ray photoelectron spectroscopy (XPS) and by comparison to the scanning tunneling microscopy (STM) signature of trioctylamine deposited directly onto the surface. 相似文献