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排序方式: 共有149条查询结果,搜索用时 15 毫秒
71.
Marta González Roi Álvarez Rodríguez Maria Magdalena Cid Carlos Silva López 《Journal of computational chemistry》2012,33(13):1236-1239
The mechanism of the acetylene homologation procedure accidentally discovered and further developed by Crabbé and coworkers is unknown. Kinetic isotope effect (KIE) experiments, however, suggest that an intramolecular hydrogen shift is the key step of the transformation. In this work, we present a computational study of this mechanism. We found that the reaction proceeds via an unexpected stepwise retro‐imino‐ene rearrangement. This mechanism justifies the role of Cu(I) as a reaction catalyst and is also compatible with the KIE experiments reported. © 2012 Wiley Periodicals, Inc. 相似文献
72.
73.
This is a companion paper to our polyhedral study [1] of the Vertex Separator (VS) Problem. Given an undirected graph G, the VS problem consists in identifying a minimum-weight vertex set whose removal disconnects G, subject to bounds on the size of the resulting components. In this paper, we describe versions of a branch-and-cut algorithm based on the results of that polyhedral study. It uses two families of cuts, symmetric and asymmetric, for which we develop polynomial-time greedy separation routines. A heuristic to generate feasible separators is also used. A computational experiment on several data sets from the literature compares the performance of three versions of our algorithm to that of the commercial MIP solver XPRESS. This experiment throws a sharp light on the role of cut density, known to software developers but never before documented in the literature. It convincingly shows that the practical usefulness of cuts in integer programming depends not only on their strength, but also on their sparsity: everything else being equal, the smaller the cut support, the better. The power of the inequalities proposed here is well illustrated by the computational tests on dense graphs. This is in accordance with the previous observation, since the support of these cuts tends to decrease with graph density.Research supported by the Brazilian agencies FAPESP (grant 01/14205–6), CAPES (grant BEX 04444/02–2) and CNPq (grants 302588/02–7 and Pronex 664107/97–4).Research supported by the National Science Foundation through grant #DMI-0098427 and by the Office of Naval Research through contract N00014-97-1-0196. 相似文献
74.
A potassium iodide catalysed method for the selective N-monoalkylation anilines with alkylhalides and alkyltosylates under microwave irradiation is described. The corresponding N-alkylanilines are obtained in good yields with only minor quantities of dialkylation by-products. 相似文献
75.
C. González J. I. Gutiérrez J. R. González-Velasco A. Cid A. Arranz J. F. Arranz 《Journal of Thermal Analysis and Calorimetry》1998,52(3):985-989
The aim of this work was to study the thermal transitions of several manganese oxides (MnO, MnOOH, Mn2O3, Mn3O4 and MnO2) under reducing conditions. Differential scanning calorimetry (DSC) was used to analyse the transitions of some oxides into
others. A comparison of the behavior of the synthetic samples with that of a natural manganese dioxide demonstrated that DSC
is a quick tool for the distinction of natural manganese dioxide from synthetic γ-MnO2 from other manganese oxides.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
In this paper we use Tarski's fixed point theorem to extend in a systematic way the existence of extremal solutions from scalar initial value problems to boundary value problems for infinite quasimonotone functional systems of differential equations.
77.
R. Perrin E. Cid S. Cazin A. Sevrain M. Braza F. Moradei G. Harran 《Experiments in fluids》2007,42(1):93-109
The near wake of a circular cylinder at high Reynolds number is investigated by means of 2D-PIV and stereoscopic PIV. Phase-averaged
measurements of the instantaneous fields have been performed. The linear stochastic estimation (LSE) has been adapted to estimate
the phase-averaged quantities. This avoids the long time acquisition and the large storage needed for phase averaging. A good
comparison is achieved between the results of the conditional sampling and those of LSE. Therefore, the estimation has been
applied to the three-component datas and allowed evaluation of the whole phase-averaged turbulent stress tensor. 相似文献
78.
Dr. Sandra Míguez-Lago Dr. Bettina D. Gliemann Prof. Dr. Milan Kivala Prof. María Magdalena Cid 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(53):13352-13357
Chirality, a characteristic tool of molecular recognition in nature, is often a complement of redox active systems. Scientists, in their eagerness to mimic such sophistication, have designed numerous chiral systems based on molecular entities with cavities, such as macrocycles and cages. In an attempt to combine chirality and redox-active species, in this contribution we report the synthesis and detailed characterization of a chiral shape-persistent molecular cage based on the combination of enantiopure diethynylallenes and electron-rich bridged triarylamines, also known as N-heterotriangulenes. Its ability for chiral recognition in solution was revealed through UV/vis titrations with enantiopure helicenes. 相似文献
79.
A Combined Experimental–Computational Investigation to Uncover the Puzzling (Chiro‐)optical Response of Pyridocyclophanes: One‐ and Two‐Photon Spectra 下载免费PDF全文
80.
Random fiber laser 总被引:1,自引:0,他引:1
de Matos CJ de S Menezes L Brito-Silva AM Martinez Gámez MA Gomes AS de Araújo CB 《Physical review letters》2007,99(15):153903
We investigate the effects of two-dimensional confinement on the lasing properties of a classical random laser system operating in the incoherent feedback (diffusive) regime. A suspension of 250 nm rutile (TiO2) particles in a rhodamine 6G solution was inserted into the hollow core of a photonic crystal fiber generating the first random fiber laser and a novel quasi-one-dimensional random laser geometry. A comparison with similar systems in bulk format shows that the random fiber laser presents an efficiency that is at least 2 orders of magnitude higher. 相似文献