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991.
Eduardo Rodriguez-Tello Jin-Kao Hao Jose Torres-Jimenez 《European Journal of Operational Research》2008
In this paper, a simulated annealing algorithm is presented for the bandwidth minimization problem for graphs. This algorithm is based on three distinguished features including an original internal representation of solutions, a highly discriminating evaluation function and an effective neighborhood. The algorithm is evaluated on a set of 113 well-known benchmark instances of the literature and compared with several state-of-the-art algorithms, showing improvements of some previous best results. 相似文献
992.
Arnal Josep; Migallon Violeta; Penades Jose; Szyld Daniel B. 《IMA Journal of Numerical Analysis》2008,28(1):143-161
993.
Bejoy Francis Sabu Thomas R. Sadhana Nicole Thuaud R. Ramaswamy Seno Jose V. Lakshmana Rao 《Journal of Polymer Science.Polymer Physics》2007,45(17):2481-2496
Bisphenol‐A‐based difunctional epoxy resin was modified with poly(ether ether ketone) with pendent tert‐butyl groups (PEEKT). PEEKT was synthesized by the nucleophilic substitution reaction of 4,4′‐difluoro benzophenone with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone. Blends with various amounts of PEEKT were prepared by melt‐mixing. All the blends were homogeneous in the uncured state. The glass transition temperature of the binary epoxy/PEEKT blends was predicted using several equations. Reaction‐induced phase separation was found to occur upon curing with a diamine 4,4′‐diaminodiphenyl sulfone. The phase morphology of the blends was studied using scanning electron microscopy. From the micrographs, it was found that PEEKT‐rich phase was dispersed in a continuous epoxy matrix. The domain size increased with the amount of PEEKT in the blends. The increase in domain size was due to the coalescence of the domains after phase separation. Dynamic mechanical analysis of the blends gave two peaks corresponding to epoxy‐rich phase and thermoplastic‐rich phase. The tensile strength and modulus of the blends remained close to that of the unmodified resin, while the flexural properties decreased with the addition of PEEKT to epoxy resin. The fracture toughness of the epoxy resin increased with the addition of PEEKT. Investigation of the fracture surfaces revealed evidences for local plastic deformation of the matrix, crack pinning, crack path deflection, and ductile tearing of PEEKT‐rich phase. Thermogravimetric analysis revealed that the initial decomposition temperature of the blends were close to that of the unmodified resin. Finally, the properties of the blends were compared with other modified PEEK/epoxy blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2481–2496, 2007 相似文献
994.
The Asymptotic Distributions of Sums of Records 总被引:3,自引:0,他引:3
LetX
1,X
2... be a sequence of i.i.d. random variables and let
be the associated (upper) record sequence. Resnick (1973) identified the class of all possible limit distributions for
. Here we focus on sums of records,
. We describe three cases in which T
n can be normalized to have a non-trivial limiting distribution. The problem of identifying all possible limit laws for normalized sums of records remains open. 相似文献
995.
Alekseevsky Dmitri V. Cortés Vicente Devchand Chandrashekar Proeyen Antoine Van 《Communications in Mathematical Physics》2003,238(3):525-543
BPS solutions of 5-dimensional supergravity correspond to certain gradient flows on the product M×N of a quaternionic-Kähler manifold M of negative scalar curvature and a very special real manifold N of dimension n0. Such gradient flows are generated by the ``energy function' f=P2, where P is a (bundle-valued) moment map associated to n+1 Killing vector fields on M. We calculate the Hessian of f at critical points and derive some properties of its spectrum for general quaternionic-Kähler manifolds. For the homogeneous quaternionic-Kähler manifolds we prove more specific results depending on the structure of the isotropy group. For example, we show that there always exists a Killing vector field vanishing at a point pM such that the Hessian of f at p has split signature. This generalizes results obtained recently for the complex hyperbolic plane (universal hypermultiplet) in the context of 5-dimensional supergravity. For symmetric quaternionic-Kähler manifolds we show the existence of non-degenerate local extrema of f, for appropriate Killing vector fields. On the other hand, for the non-symmetric homogeneous quaternionic-Kähler manifolds we find degenerate local minima.
This work was supported by the priority programme ``String Theory'of the Deutsche Forschungsgemeinschaft. 相似文献
996.
Merino P Tejero T Laguna M Cerrada E Moreno A Lopez JA 《Organic & biomolecular chemistry》2003,1(13):2336-2342
The cycloaddition reaction of N-benzyl C-(2-pyridyl) nitrone with allylic alcohol has been carried out to obtain the corresponding 2-benzyl-3-(2-pyridyl)-5-hydroxymethylisoxazolidine. The influence of Lewis acids in the reaction has been studied and a complete 3,5-regioselectivity and cis diastereoselectivity was observed when the reaction was carried out with 1.0 equiv of AgOTf, [Ag(OClO3)(PPh2Me)] or Zn(OTf)2. Insight into the mechanism of the reaction has been obtained by isolating and characterizing (X-ray) the intermediate complexes. Also, a model based on both experimental and theoretical results is proposed. 相似文献
997.
Pérez-Balderas F Ortega-Muñoz M Morales-Sanfrutos J Hernández-Mateo F Calvo-Flores FG Calvo-Asín JA Isac-García J Santoyo-González F 《Organic letters》2003,5(11):1951-1954
[reaction: see text] The construction of multivalent neoglycoconjugates is efficiently achieved by the regiospecific catalytic cycloaddition of alkynes and azides using the organic-soluble copper complexes (Ph(3)P)(3).CuBr and (EtO)(3)P.CuI. The simultaneous use of microwave irradiation shortened notably the reaction times. 相似文献
998.
Osornio YM Cruz-Almanza R Jiménez-Montaño V Miranda LD 《Chemical communications (Cambridge, England)》2003,(18):2316-2317
Novel and efficient radical alkylation of several heterocyclic systems including pyrroles, indoles, furan and thiophenes is described using xanthate based radical chemistry. The present methodology could be used to provide rapid access to various nonsteroidal antiinflammatory drugs. 相似文献
999.
Interpolation of Vector-Valued Real Analytic Functions 总被引:2,自引:0,他引:2
Let Rd be an open domain. The sequentially complete DF-spacesE are characterized such that for each (some) discrete sequence(zn) , a sequence of natural numbers (kn) and any family the infinite system of equations
has an E-valued real analytic solution f. 相似文献
1000.
Vicente Rodríguez-Gonzlez Eric Marceau Michel Che Claude Pepe 《Journal of solid state chemistry》2007,180(12):3469-3478
Synthesis of neutral complexes of Ni2+ with amino acids has often been reported on a qualitative basis, with a lack of information on the parameters involved in the dissolution of the nickel-containing solid precursor. This paper reports on a systematic study of the reactivity of Ni(OH)2 toward glycine in aqueous solution. The crystallinity and size of hydroxide particles are found to be key parameters in the rapid glycine-promoted dissolution of the hydroxide and synthesis of [Ni(glycinate)2(H2O)2]. These parameters derive from the nature of the salt used to prepare the hydroxide. Ni(II) chloride leads to the most reactive solid precursor, because of the presence of defects in the Ni(OH)2 sheets arrangements, assigned to the substitution of Cl− ions to OH− ions at the edges of the particles. The reaction between this hydroxide and glycine at 80 °C is quantitative after 7 min and similar rates of dissolution are obtained with other amino acids, alanine or histidine, the reaction with serine being slower. When the hydroxide contains nitrate or carbonate ions, a glycinato complex with composition similar to [Ni(glycinate)2(H2O)2], but with a different crystal structure, is also formed. Spectroscopic results may suggest a structure involving bridging ligands. 相似文献