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排序方式: 共有679条查询结果,搜索用时 31 毫秒
671.
We present a new and complete analysis of the n-bounce resonance and chaotic scattering in solitary-wave collisions. In these phenomena, the speed at which a wave exits a collision depends in a complicated fractal way on its input speed. We present a new asymptotic analysis of collective-coordinate ordinary differential equations (ODEs), reduced models that reproduce the dynamics of these systems. We reduce the ODEs to discrete-time iterated separatrix maps and obtain new quantitative results unraveling the fractal structure of the scattering behavior. These phenomena have been observed repeatedly in many solitary-wave systems over 25 years. 相似文献
672.
673.
Ikeda H Hoshi Y Namai H Tanaka F Goodman JL Mizuno K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(33):9207-9215
Photoinduced single-electron-transfer promoted oxidation of 2,5-diphenyl-1,5-hexadiene by using N-methylquinolinium tetrafluoroborate/biphenyl co-sensitization takes place with the formation of an intense electronic absorption band at 476 nm, which is attributed to the 1,4-diphenylcyclohexane-1,4-diyl radical cation. The absorption maximum (lambda(ob)) of this transient occurs at a longer wavelength than is expected for either the cumyl radical or the cumyl cation components. Substitution at the para positions of the phenyl groups in this radical cation by CH(3)O, CH(3), F, Cl, and Br leads to an increasingly larger redshift of lambda(ob). A comparison of the rho value, which was obtained from a Hammett plot of the electronic transition energies of the radical cations versus sigma(+), with that for the cumyl cation shows that the substituent effects on the transition energies for the 1,4-diarylcyclohexane-1,4-diyl radical cations are approximately one half of the substituent effects on the transition energies of the cumyl cation. The observed substituent-induced redshifts of lambda(ob) and the reduced sensitivity of lambda(ob) to substituent changes are in accordance with the proposal that significant through-space and -bond electronic interactions exist between the cumyl radical and the cumyl cation moieties of the 1,4-diphenylcyclohexane-1,4-diyl radical cation. This proposal gains strong support from the results of density functional theory (DFT) calculations. Moreover, the results of time-dependent DFT calculations indicate that the absorption band at 476 nm for the 1,4-diphenylcyclohexane-1,4-diyl radical cation corresponds to a SOMO-3 --> SOMO transition. 相似文献
674.
675.
West KR Ludlow RF Corbett PT Besenius P Mansfeld FM Cormack PA Sherrington DC Goodman JM Stuart MC Otto S 《Journal of the American Chemical Society》2008,130(33):10834-10835
A simple water-soluble naphthalenedithiol building block is converted quantitatively into a series of octameric [2]-catenanes, composed of two interlocked molecular squares. When this mixture is re-equilibrated in the presence of an adamantyl ammonium guest, the catenanes disassemble into their macrocyclic components that bind the guest with nanomolar affinity in water. 相似文献
676.
Mathew M. Simpson Ching Ching Lam Prof. Jonathan M. Goodman Prof. Shankar Balasubramanian 《Angewandte Chemie (International ed. in English)》2023,62(26):e202304756
The epigenetic modification 5-methylcytosine plays a vital role in development, cell specific gene expression and disease states. The selective chemical modification of the 5-methylcytosine methyl group is challenging. Currently, no such chemistry exists. Direct functionalisation of 5-methylcytosine would improve the detection and study of this epigenetic feature. We report a xanthone-photosensitised process that introduces a 4-pyridine modification at a C(sp3)−H bond in the methyl group of 5-methylcytosine. We propose a reaction mechanism for this type of reaction based on density functional calculations and apply transition state analysis to rationalise differences in observed reaction efficiencies between cyanopyridine derivatives. The reaction is initiated by single electron oxidation of 5-methylcytosine followed by deprotonation to generate the methyl group radical. Cross coupling of the methyl radical with 4-cyanopyridine installs a 4-pyridine label at 5-methylcytosine. We demonstrate use of the pyridination reaction to enrich 5-methylcytosine-containing ribonucleic acid. 相似文献
677.
Catalytically active gold on ordered titania supports 总被引:1,自引:0,他引:1
Almost two decades have passed since supported Au nanoparticles were found to be active for CO oxidation. This discovery inspired extensive research addressing the origin of the unique properties of supported Au nanoparticles, the design and synthesis of potentially technical Au catalysts, and the extension of Au catalysis to other reactions. This tutorial review summarises the current understanding of the origin of the unique properties of titania-supported Au catalysts for carbon monoxide oxidation. The key issues of catalysis by nanostructured Au, effects of oxide support and active site/structure, especially those provided from model studies are discussed in detail. The successful synthesis of a highly catalytically active gold bilayer may lead to the design and synthesis of practically active Au nanofilm catalysts. 相似文献
678.
Melissa D. Goodman Kathryn A. Dowsland Jonathan M. Thompson 《Journal of Heuristics》2009,15(4):351-379
This paper is concerned with the application of a GRASP approach to a nurse-scheduling problem in which the objective is to
optimise a set of preferences subject to a set of binding constraints. The balance between feasibility and optimality is a
key issue. This is addressed by using a knapsack model to ensure that the solutions produced by the construction heuristic
are easy to repair. Several construction heuristics and neighbourhoods are compared empirically. The best combination is further
enhanced by a diversification strategy and a dynamic evaluation criterion. Tests show that it outperforms previously published
approaches and finds optimal solutions quickly and consistently. 相似文献
679.
Frederick M. Goodman 《Journal of Algebra》2009,321(11):3299-3320
We show that cyclotomic BMW algebras are cellular algebras. 相似文献