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排序方式: 共有159条查询结果,搜索用时 31 毫秒
81.
A highly diastereoselective Ugi reaction involving a chiral cyclic imine, two enantiomerically pure isocyanides and various carboxylic acids was employed for the synthesis of polyfunctionalized pyrrolidines. Both chiral substrates have been efficiently prepared by chemoenzymatic methodologies from readily available achiral substrates. This highly convergent approach can find an application in the fragment-based drug discovery process. 相似文献
82.
Ruy Alberto Pisani Altafim Ruy Alberto Corrêa Altafim Xunlin Qiu Sebastian Raabe Werner Wirges Heitor Cury Basso Reimund Gerhard 《Applied Physics A: Materials Science & Processing》2012,107(4):965-970
Ferro- or piezoelectrets are dielectric materials with two elastically very different macroscopic phases and electrically charged interfaces between them. One of the newer piezoelectret variants is a system of two fluoroethylenepropylene (FEP) films that are first laminated around a polytetrafluoroethylene (PTFE) template. Then, by removing the PTFE template, a two-layer FEP structure with open tubular channels is obtained. After electrical charging, the channels form easily deformable macroscopic electric dipoles whose changes under mechanical or electrical stress lead to significant direct or inverse piezoelectricity, respectively. Here, different PTFE templates are employed to generate channel geometries that vary in height or width. It is shown that the control of the channel geometry allows a direct adjustment of the resonance frequencies in the tubular-channel piezoelectrets. By combining several different channel widths in a single ferroelectret, it is possible to obtain multiple resonance peaks that may lead to a rather flat frequency-response region of the transducer material. A phenomenological relation between the resonance frequency and the geometrical parameters of a tubular channel is also presented. This relation may help to design piezoelectrets with a specific frequency response. 相似文献
83.
84.
Gianpaolo Ghiani Pasquale Legato Roberto Musmanno Francesca Vocaturo 《Computational Optimization and Applications》2007,38(1):133-145
This paper addresses the problem of optimizing a function over a finite or countable infinite set of alternatives, whenever
the objective function cannot be evaluated exactly, but has to be estimated via simulation. We present an iterative method,
based on the simulated annealing framework, for solving such discrete stochastic optimization problems. In the proposed method,
we combine the robustness of this metaheuristic method with a statistical procedure for comparing the solutions that are generated.
The focus of our work is on devising an effective procedure rather than addressing theoretical issues. In fact, in our opinion,
although significant progresses have been made in studying the convergence of a number of simulation–optimization algorithms,
at present there is no procedure able to consistently provide good results in a reasonable amount of time. In addition, we
present a parallelization strategy for allocating simulation runs on computing resources. 相似文献
85.
Andrea Attanasio Antonio Fuduli Gianpaolo Ghiani Chefi Triki 《Journal of Mathematical Modelling and Algorithms》2007,6(1):77-85
In this paper we examine a consolidation and dispatching problem motivated by a multinational chemical company which has to
decide routinely the best way of delivering a set of orders to its customers over a multi-day planning horizon. Every day
the decision to be made includes order consolidation, vehicle dispatching as well as load packing into the vehicles. We develop
a heuristic based on a cutting plane framework, in which a simplified Integer Linear Program (ILP) is solved to optimality.
Since the ILP solution may correspond to a infeasible loading plan, a feasibility check is performed through a tailored heuristic
for a three-dimensional bin packing problem with side constraints. If this test fails, a cut able to remove the infeasible
solution is generated and added to the simplified ILP. Then the procedure is iterated. Computational results show that our
procedure allows achieving remarkable cost savings.
相似文献
86.
The poly(dimethylamino methacrylate) (PDMAEMA) brush‐modified indium tin oxide (ITO) electrode was used to test the switch properties of interfacial activity caused by bioelectrochemical signals. The swelling of the polymer brushes increased when the medium’s pH changed from alkaline to acid after glucose was added to the system. A pH change generated in situ by means of biocatalytic reactions enabled bioelectrocatalytic interface’s reversible activation. 相似文献
87.
Carlos L. P. Carone Geraldo L. Crossetti Nara R. S. Basso Álvaro G. O. Moraes João H. Z. dos Santos Rubens Bisatto Griselda B. Galland 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5199-5208
The catalyst DADNi(NCS)2 (DAD = (ArN?C(Me)? C(Me)?ArN); Ar = 2,6‐C6H3), activated by methylaluminoxane, was tested in ethylene polymerization at temperatures above 25 °C and variable Al/Ni ratio. The system was shown to be active even at 80 °C and when supported on silica. However, catalyst activity decreased. The catalyst system was also tested in ethylene and 10‐undecen‐1‐ol copolymerization at different ethylene pressures. The best activities were obtained at low polar monomer concentration (0.017 mol/L), using triisopropylaluminum (Al‐i‐Pr3) to protect the polar monomer. The incorporation of the comonomer increased with the increase of polar monomer concentration. According to 13C NMR analyses, all the resulting polyethylenes were highly branched and the polar monomer incorporation decreased as ethylene pressure increased. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5199–5208, 2007 相似文献
88.
89.
Rizzi L Braschi M Colombo M Vaiana N Tibolla G Norata GD Catapano AL Romeo S Prosperi D 《Organic & biomolecular chemistry》2011,9(8):2899-2905
Amphiphilic bile acids linked through an oligoethylene glycol to a biotin moiety were synthesized and shown to create micellar structures in aqueous environment, interact with avidin and be efficiently incorporated into hepatocyte cells, suggesting their potential as a drug delivery system against liver diseases. 相似文献
90.
Alan Patrick da SilvaGisele de Freitas Gauze Tiago Araújo MatiasVagner Roberto de Souza Thiago de Castro RozadaErnani Abicht Basso 《Tetrahedron letters》2011,52(39):5043-5046
Complexation between the Schiff base N4-tetradentate N,N′-bis(7-methyl-2-pyridylmethylene)-1,3-diiminopropane (bpydip) and ion Ru(II) occurs only in trans geometry. However, it is known that the most complex of these ligands with ruthenium present predominantly cis geometry. In order to clarify the effects that drive the formation of the complex [Ru(bpydip)Cl2], we performed a new experimental study of the reaction and a complete theoretical investigation of their transition states. The results showed that nonformation of the cis isomer could be explained by the difference in relative stability of the reaction products and the transition states proposed. 相似文献