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排序方式: 共有490条查询结果,搜索用时 15 毫秒
1.
Mariia Svyntkivska Tomasz Makowski Ewa Piorkowska Marek Brzezinski Agata Herc Anna Kowalewska 《Molecules (Basel, Switzerland)》2021,26(5)
Electrospun nonwovens of poly(L-lactide) (PLLA) modified with multiwall carbon nanotubes (MWCNT) and linear ladder-like poly(silsesquioxane) with methoxycarbonyl side groups (LPSQ-COOMe) were obtained. MWCNT and LPSQ-COOMe were added to the polymer solution before the electrospinning. In addition, nonwovens of PLLA grafted to modified MWCNT were electrospun. All modified nonwovens exhibited higher tensile strength than the neat PLA nonwoven. The addition of 10 wt.% of LPSQ-COOMe and 0.1 wt.% of MWCNT to PLLA increased the tensile strength of the nonwovens 2.4 times, improving also the elongation at the maximum stress. 相似文献
2.
Let G=(V,E) be a undirected k-edge connected graph with weights ce on edges and wv on nodes. The minimum 2-edge connected subgraph problem, 2ECSP for short, is to find a 2-edge connected subgraph of G, of minimum total weight. The 2ECSP generalizes the well-known Steiner 2-edge connected subgraph problem. In this paper we study the convex hull of the incidence vectors corresponding to feasible solutions of 2ECSP. First, a natural integer programming formulation is given and it is shown that its linear relaxation is not sufficient to describe the polytope associated with 2ECSP even when G is series-parallel. Then, we introduce two families of new valid inequalities and we give sufficient conditions for them to be facet-defining. Later, we concentrate on the separation problem. We find polynomial time algorithms to solve the separation of important subclasses of the introduced inequalities, concluding that the separation of the new inequalities, when G is series-parallel, is polynomially solvable. 相似文献
3.
The objective of this paper is to analyze under what well-known operations the class of quasipolyhedral convex functions,
which can be regarded as an extension of that of polyhedral convex functions, is closed. The operations that will be considered
are those that preserve polyhedral convexity, such that the image and the inverse image under linear transformations, right
scalar multiplication (including the case where λ=0+) and pointwise addition.
相似文献
4.
In this paper, we examine a variant of the uncapacitated lot-sizing model of Wagner–Whitin that includes fixed charges on the stocks. Such a model is natural in a production environment where stocking is a complex operation, and appears as a subproblem in more general network design problems.
Linear-programming formulations, a dynamic program, the convex hull of integer solutions and a separation algorithm are presented. All these turn out to be very natural extensions of the corresponding results of Barany et al. (Math. Programming Stud. 22 (1984) 32) for the uncapacitated lot-sizing problem. The convex hull proof is based on showing that an extended facility location formulation is tight and by projecting it onto the original space of variables. 相似文献
5.
Through arylsulfonyl activation of thiourea, efficient synthesis of oligomeric guanidines can be achieved in either solution or solid-phase. Incorporation of TFA-sensitive arylsulfonyl groups, such as Pbf, during the synthesis greatly simplifies deprotection procedures for obtaining the final oligomeric guanidine products. 相似文献
6.
Thermal behaviour of a polyhedral oligomeric silsesquioxane with epoxy resin cured by diamines 总被引:1,自引:0,他引:1
Ramírez C. Abad M. J. Barral L. Cano J. Díez F. J. López J. Montes R. Polo J. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):421-429
A new material belongs to the family of polyhedral oligomeric silsesquioxanes, the 1-(3-glycidyl) propoxy-3,5,7,9,11,13,15-isobutylpentacyclo-[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxane
(glycidylisobutyl-POSS) is characterized by differential scanning calorimetry, thermogravimetric analysis and atomic force
microscopy. Epoxy systems based on diglycidyl ether of bisphenol A (DGEBA) cured with the diamines, 4,4'-diamine-diphenylmethane
(DDM) and 1,4-phenylenediamine (pPDA), were kinetically studied by differential scanning calorimetry in isothermal and dynamic
modes. The thermal behaviour of these systems as the glycidylisobutyl-POSS was added, is discussed later.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
TMSOTf-catalyzed intramolecular condensation for catechin and epicatechin units are described. A potential electrophile and a nucleophile were connected with diester linkers and TMSOTf-catalyzed condensation was examined. In comparison with intermolecular catechin and catechin condensation, the intramolecular condensation required high reaction temperature and reversed 3,4-cis product was obtained. The condensed product was transformed into the natural 3,4-cis (+)-catechin-(4β→8)-(+)-catechin dimer. 相似文献
8.
《Operations Research Letters》2022,50(2):122-128
The max-cut problem is a fundamental combinatorial optimisation problem, with many applications. Poljak and Turzik found some facet-defining inequalities for the associated polytope, which we call 2-circulant inequalities. We present a more general family of facet-defining inequalities, an exact separation algorithm that runs in polynomial time, and some computational results. 相似文献
9.
El Houssaine Aghezzaf Thomas L. Magnanti Laurence A. Wolsey 《Mathematical Programming》1995,71(2):113-126
Given a treeG = (V, E) and a weight function defined on subsets of its nodes, we consider two associated problems. The first, called the rooted subtree problem, is to find a maximum weight subtree, with a specified root, from a given set of subtrees.The second problem, called the subtree packing problem, is to find a maximum weight packing of node disjoint subtrees chosen from a given set of subtrees, where the value of each subtree may depend on its root.We show that the complexity status of both problems is related, and that the subtree packing problem is polynomial if and only if each rooted subtree problem is polynomial. In addition we show that the convex hulls of the feasible solutions to both problems are related: the convex hull of solutions to the packing problem is given by pasting together the convex hulls of the rooted subtree problems.We examine in detail the case where the set of feasible subtrees rooted at nodei consists of all subtrees with at mostk nodes. For this case we derive valid inequalities, and specify the convex hull whenk 4.Research supported in part by Nato Collaborative Research Grant CRG 900281, Science Program SC1-CT91-620 of the EEC, and contract No 26 of the programme Pôle d'attraction interuniversitaire of the Belgian government. 相似文献
10.
Dmitry S. Perekalin Pavel V. Petrovskii Bohumil Štíbr Alexander R. Kudinov 《Journal of organometallic chemistry》2005,690(11):2775-2779
The reaction of the tricarbollide salt Tl[7-tBuNH-7,8,9-C3B8H10] (Tl1) with [(cod)Rh(THF)x]+ gives the rhodium complex [1-(cod)-12-tBuNH-1,2,4,12-RhC3B8H10] in almost quantitative yield. Analogous reactions of Tl1 with [(ring)M(THF)x]2+ ((ring)M = Cp*Rh and (1,3,5-C6H3Me3)Ru) afford the corresponding metallatricarbollides [1-(ring)-12-tBuNH-1,2,4,12-MC3B8H10] in ca. 50% yield. Refluxing Tl1 with [Mn(CO)3(MeCN)3]+ in THF give the tricarbollide analogue of cymantrene, [1,1,1-(CO)3-12-tBuNH-1,2,4,12-MnC3B8H10], the structure of which was determined by single-crystal X-ray diffraction analysis. In all cases, the formation of the metallatricarbollide complexes is accompanied by polyhedral rearrangement leading to the maximum separation of the cage carbon atoms. 相似文献