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31.
Ferdinando Mancini Evgeny Plekhanov Gerardo Sica 《Central European Journal of Physics》2012,10(3):609-614
In this paper we study a generalization of the Hubbard model by considering spin-spin interactions described by the exchange constant J. An external magnetic field his also taken into account. In the narrowband limit and for the 1D case, we present the exact solution obtained in the framework of the Green’s function formalism, using the Composite Operator Method. We report the T = 0 phase diagram for both ferro (J > 0) and anti-ferro (J < 0) couplings. The competition of the different energy scales (U, J, and h; being U the local charge interaction) generates a variety of phases and different charge and spin orderings. 相似文献
32.
Maria Antonia Iat Rosalba Saija Arianna Giusto Paolo Denti Ferdinando Borghese Cesare Cecchi-Pestellini 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,100(1-3):157-164
We calculate the energy density distribution in the ultraviolet within small spheres containing concentric cavities, aimed at simulating interstellar dust grains. We explore the dependence on chemical composition by progressively changing, in an arbitrary way, the refractive index of the sphere material. We conclude that a significant fraction of the energy of the impinging radiation is trapped throughout the particle interior. 相似文献
33.
This paper presents a computationally effective heuristic method which produces good-quality solutions for large-scale set
covering problems with thousands of constraints and about one million variables. The need to solve such large-scale problems
arises from a crew scheduling problem of mass transit agencies where the number of work shifts required has to be minimized.
This problem may be formulated as a large-scale non-unicost set covering problem whose rows are trips to be performed while
columns stand for round trips. The proposed method is mainly based on lagragian relaxation and sub-gradient optimization.
After the reduction of the number of rows and columns by the logical tests, “greedy” heuristic algorithms provide upper and
lower bounds which are continuously improved to produce goodquality solutions. Computational results, regarding randomly generated
problems and real life problems concerning crew scheduling at Italian Railways Company, show that good-quality solutions can
be obtained at an acceptable computational cost.
This work was supported by the project “Progetto Finalizzato Transporti 2” of National Research Council of Italy (C.N.R.)
contract No. 94.01436PF74 and by “Ferrovie dello Stato S.p.A.” 相似文献
34.
35.
Guido Perboli Ferdinando Pezzella Roberto Tadei 《Mathematical Methods of Operations Research》2008,68(2):361-382
This paper presents EVE-OPT, a Hybrid Algorithm based on Genetic Algorithms and Taboo Search for solving the Capacitated Vehicle
Routing Problem. Several hybrid algorithms have been proposed in recent years for solving this problem. Despite good results,
they usually make use of highly problem-dependent neighbourhoods and complex genetic operators. This makes their application
to real instances difficult, as a number of additional constraints need to be considered. The algorithm described here hybridizes
two very simple heuristics and introduces a new genetic operator, the Chain Mutation, as well as a new mutation scheme. We
also apply a procedure, the k-chain-moves, able to increase the neighbourhood size, thereby improving the quality of the solution with negligible computational
effort. Despite its simplicity, EVE-OPT is able to achieve the same results as very complex state-of-the art algorithms. 相似文献
36.
Michael R. Martinez Sylwia Dworakowska Adam Gorczyński Grzegorz Szczepaniak Ferdinando De Luca Bossa Krzysztof Matyjaszewski 《Journal of polymer science. Part A, Polymer chemistry》2022,60(12):1887-1898
The photoinduced energy/electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerizations of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA, also known as poly[ethylene glycol] methyl ether methacrylate, PEGMA) and isomeric methyl 2-(oligo(ethylene oxide) methyl ether)acrylate (2OEOAM) macromonomers with OEO average degree of polymerization of 22 or 45 were conducted in aqueous media to provide insight into the effect of monomer structure on grafting-through RAFT of 1,1-disubstituted acrylic macromonomers. The polymerizations of all four monomers reached nearly quantitative conversion. The longer macromonomers polymerized faster than the shorter ones within the same monomer class. The OEO side chain at the α (i.e., 2-) position of isomeric acrylates significantly slowed RAFT polymerization in comparison with OEO ester side chain of methacrylates. 相似文献
37.
Summary This paper discusses the dynamic loading of rigid-perfectly plastic structures by adopting a structural model discretized with constant stress finite elements. This assumption together with the hypothesis of small displacements and of a piecewise linear yield surface leads to the formulation of a problem in linear inequalities, which is, implicitly, time discretized. It is shown how the non linearity of the associated plastic flow laws leads to an equivalent extremal formulation. A numerical algorithm for solving the problem is directly derived from the mechanical statements. Numerical examples illustrate this approach. In the appendix an approximate technique is developed, which takes into account the influence of the strain-hardening and the strain rate sensitivity of material.
Research supported by the National Research Council (C.N.R. - P.A.d.I.S.) of Italy. 相似文献
Sommario Il problema del caricamento dinamico delle strutture rigido-plastiche viene affrontato attraverso un modello discretizzato per elementi finiti a stato di sollecitazione costante. Tale assunzione insieme alle ipotesi di superficie di plasticizzazione lineare a tratti e di piccoli spostamenti, conduce alla formulazione di un problema retto da diseguaglianze lineari che si presenta discretizzato, implicitamente, nel tempo. Si mostra che la non linearità delle leggi del flusso plastico associato conduce ad una equivalente formulazione di estremo.È esposto un algoritmo risolvente affatto aderente alla formulazione meccanica. Alcuni esempi illustrano il procedimento. Una proposta di adattamento al caso di materiali incrudenti e sensibili alle velocità di deformazione è presentata in appendice.
Research supported by the National Research Council (C.N.R. - P.A.d.I.S.) of Italy. 相似文献
38.
An innovative route to prepare a number of variously substituted new biphenyl derivatives is presented here. The protocol avoids the use of a catalyst, an organic solvent, and dry conditions. [reaction: see text] 相似文献
39.
Caliendo Giuseppe Fiorino Ferdinando Grieco Paolo Perissutti Elisa Albrizio Stefania Giordano Marialuisa Santagada Vincenzo Santini Antonello 《Structural chemistry》1998,9(2):121-127
With the aim of discovering new molecules with K+ channel modulating properties, we have synthesized analogues of cromakalim, an important molecule which shows specific affinity toward the K+ channels, by replacing the benzopyrane ring with a benzoxazine moiety. As a part of this study, we have synthesized and characterized, in solution and in the solid state as well, the compound ethyl [2,2-dimethyl-6-(2-thiazolin-2-yl)-4H-l,4-benzoxazin-3-one-4-yl]butyrate (V). This compound exhibits in the solid state the following parameters: molecular formula C19H24N2O4S, triclinic, space group
, Mw = 376.5, a = 12.581(3) Å, b = 5.485(4) Å, c = 14.612(2) Å, = 91.85(2), = 108.9(3), = 82.04(4), V = 944.7 Å3, Z = 2, d = 1.323 g·cm–3. We describe here the synthesis and discuss the solid-state conformation of this new molecule; when tested on rat aorta ring precontracted with phenylephrine, the compound showed a concentration-dependent relaxation comparable to that measured for cromakalin taken as reference drug. 相似文献
40.
Ernest Wenkert Ming Guo Ferdinando Pizzo Kishore Ramachandran 《Helvetica chimica acta》1987,70(5):1429-1438
Furans with side-chains at C(2) of various lengths terminating in diazomethyl keto groups are shown to undergo Rh2(OAc)4-catalyzed furan unravelling with the production of 2-cyclopentenone, 2-cyclohexenone, and 2-cycloheptenone to each of whose olefinic C(β) is attached an acrylaldehyde unit. Interposition of a cyclohexane or a methylaminomethylene moiety between the furan and diazoketo functions leads to the formation of a hydroindenone and pyrrolone, respectively. Replacement of the diazomethylketo terminus by an α-diazoethylketo system or a α-diazo-β-keto-ester function produces 2-substituted 2-cycloalkenones. A furan with a C4, diazo-methylketo-terminating side-chain at C(3) is described to be transformed into a 4-formylmethylidene-2-cyclohe-xenone. 相似文献