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1.
Tahya Bamine Edouard Boivin Christian Masquelier Laurence Croguennec Elodie Salager Dany Carlier 《Magnetic resonance in chemistry : MRC》2020,58(11):1109-1117
7Li, 31P, and 19F solid-state nuclear magnetic resonance (NMR) spectroscopy was used to investigate the local arrangement of oxygen and fluorine in LiVPO4F1-yOy materials, interesting as positive electrode materials for Li-ion batteries. From the evolution of the 1D spectra versus y, 2D 7Li radiofrequency-driven recoupling (RFDR) experiments combined, and a tentative signal assignment based on density functional theory (DFT) calculations, it appears that F and O are not randomly dispersed on the bridging X position between two X–VO4–X octahedra (X = O or F) but tend to segregate at a local scale. Using DFT calculations, we analyzed the impact of the different local environments on the local electronic structure. Depending on the nature of the VO4X2 environments, vanadium ions are either in the +III or in the +IV oxidation state and can exhibit different distributions of their unpaired electron(s) on the d orbitals. Based on those different local electronic structures and on the computed Fermi contact shifts, we discuss the impact on the spin transfer mechanism on adjacent nuclei and propose tentative signal assignments. The O/F clustering tendency is discussed in relation with the formation of short VIVO vanadyl bonds with a very specific electronic structure and possible cooperative effect along the chain. 相似文献
2.
Isolation and Total Synthesis of Kirkamide,an Aminocyclitol from an Obligate Leaf Nodule Symbiont 下载免费PDF全文
Simon Sieber Dr. Aurélien Carlier Dr. Markus Neuburger Dr. Giselher Grabenweger Prof. Leo Eberl Prof. Dr. Karl Gademann 《Angewandte Chemie (International ed. in English)》2015,54(27):7968-7970
The new C7N aminocyclitol kirkamide ( 1 ) was isolated from leaf nodules of the plant Psychotria kirkii by using a genome‐driven 1H NMR‐guided fractionation approach. The structure and absolute configuration were elucidated by HRMS, NMR, and single‐crystal X‐ray crystallography. An enantioselective total synthesis was developed, which delivered kirkamide ( 1 ) on a gram scale in 11 steps and features a Ferrier carbocyclization and a Pd‐mediated hydroxymethylation. We propose that kirkamide is synthesized by Candidatus Burkholderia kirkii, the obligate leaf symbiont of Psychotria kirkii. Kirkamide ( 1 ) was shown to be toxic to aquatic arthropods and insects, thus suggesting that bacterial secondary metabolites play a protective role in the Psychotria/Burkholderia leaf nodule symbiosis. 相似文献
3.
Il Ayranc Guillaume Pinguet Dany Escudi Nevin Seluk Rodolphe Vaillon Frdric Andr 《Experimental Thermal and Fluid Science》2007,31(8):839-847
Measurement of particle concentration by laser Doppler anemometry (LDA) is studied on a vertical air jet seeded by a powder disperser with controlled particle and air flow rates. Particle arrival rate is utilized to retrieve particle number densities from conventional LDA operation. The effect of polydisperse nature of the particles is assessed. Comparisons between measured and estimated particle number densities suggest that only a certain portion of the particle population with a particle size to fringe spacing ratio around unity can be detected. Results indicate that reliable measurement of absolute particle concentration is possible for a particle population of narrow size distribution with an average diameter equivalent to fringe spacing. Present number density measurement technique which is useful for practical purposes with conventional LDA systems is found to yield physically reasonable profiles in both laminar and turbulent regimes. 相似文献
4.
A reliable Pd-catalyzed amination protocol is described for the synthesis of N-alkyltacrines and analogs. The Josiphos ligand CyPFtBu was found to provide optimum yields: 16 examples are given. Compared to the typical high-temperature nucleophilic aromatic substitution (NAS) routes, Pd-catalyzed aminations proceed at significantly lower reaction temperatures, and enable the synthesis of otherwise inaccessible products. 相似文献
5.
The paper deals with algorithms for applying classical list scheduling to a project scheduling problem where the units of resources are produced or consumed at the occurrence of precedence-related events. It is shown that the feasibility variant of the project scheduling problem is NP-complete. Moreover, polynomial-time scheduling algorithms are devised for the three cases where the occurrence time sequence of all events or the consuming events or the producing events is given in advance. By enumerating these sequences (called linear orders), one obtains a list-scheduling based algorithm for minimizing the makespan of a project scheduling problem with production and consumption of resources. 相似文献
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In this work we propose and evaluate two variational data assimilation techniques for the estimation of low order surrogate experimental dynamical models for fluid flows. Both methods are built from optimal control recipes and rely on proper orthogonal decomposition and a Galerkin projection of the Navier Stokes equation. The techniques proposed differ in the control variables they involve. The first one introduces a weak dynamical model defined only up to an additional uncertainty time-dependent function whereas the second one, handles a strong dynamical constraint in which the dynamical system’s coefficients constitute the control variables. Both choices correspond to different approximations of the relation between the reduced basis on which is expressed the motion field and the basis components that have been neglected in the reduced order model construction. The techniques have been assessed on numerical data and for real experimental conditions with noisy particle image velocimetry data. 相似文献
9.
Jacques Carlier Mohamed Haouari Mohamed Kharbeche Aziz Moukrim 《European Journal of Operational Research》2010,202(3):859
This study investigates an optimization-based heuristic for the robotic cell problem. This problem arises in automated cells and is a complex flow shop problem with a single transportation robot and a blocking constraint. We propose an approximate decomposition algorithm. The proposed approach breaks the problem into two scheduling problems that are solved sequentially: a flow shop problem with additional constraints (blocking and transportation times) and a single machine problem with precedence constraints, time lags, and setup times. For each of these problems, we propose an exact branch-and-bound algorithm. Also, we describe a genetic algorithm that includes, as a mutation operator, a local search procedure. We report the results of a computational study that provides evidence that the proposed optimization-based approach delivers high-quality solutions and consistently outperforms the genetic algorithm. However, the genetic algorithm delivers reasonably good solutions while requiring significantly shorter CPU times. 相似文献
10.
Summary. We describe an algorithm to approximate the minimizer of an elliptic functional in the form on the set of convex functions u in an appropriate functional space X. Such problems arise for instance in mathematical economics [4]. A special case gives the convex envelope of a given function . Let be any quasiuniform sequence of meshes whose diameter goes to zero, and the corresponding affine interpolation operators. We prove that the minimizer over is the limit of the sequence , where minimizes the functional over . We give an implementable characterization of . Then the finite dimensional problem turns out to be a minimization problem with linear constraints.
Received November 24, 1999 / Published online October 16, 2000 相似文献