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51.
Given a family of subsets of an arbitrary groundsetE, acover of is any setC E having non-empty intersection with every subset in.
In this paper we deal with thecovering polytope, i.e., the convex hull of the incidence vectors of all the covers of. In Section 2 we review all the known properties of the covering polytope. In Sections 3 and 4 we introduce two new classes of non-Boolean facets of such a polytope. In Sections 5 and 6 we describe some non-sequential lifting procedures. In Section 7 a generalization of the notion ofweb introduced by L.E. Trotter is presented together with the facets of the covering polytope produced by such a structure.Moreover, the strong connections between several combinatorial problems and the covering problem are pointed out and, exploiting those connections, some examples are presented of new facets for the Knapsack and Acyclic Subdigraph polytopes. 相似文献
52.
53.
We present a new Lagrangian-based heuristic for solving large-scale set-covering problems arising from crew-scheduling at the Italian Railways (Ferrovie dello Stato). Our heuristic obtained impressive results when compared to state-of-the-art codes on a test-bed provided by the company, which includes instances with sizes ranging from 50,000 variables and 500 constraints to 1,000,000 variables and 5000 constraints. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Corresponding author.This research was performed while the author was affiliated with IASI, CNR and Dipartimento di Informatica e Sistemistica, Università di Roma, La Sapienza, Italy.This research was partially supported by National Research Program Metodi di Ottimizzazione per le Decisioni, MURST, Roma, Italy. 相似文献
54.
55.
Andrea Nobili Angelo Marcello Tarantino 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(1):137-160
In this paper, the deformation of a composite hard ferromagnetic-elastic beam-plate structure is investigated. A sandwich
structure, composed of two thin hard ferromagnetic layers, with a linear elastic layer in between, is considered. The deformation
is due to the self generated magnetic field (magnetostriction). The aim is to assess the interaction forces among the perfectly
bonded layers, through a consistent application of the classical nonlinear magneto-elastic theory. Once the general mechanical
model is stated, the analysis is specialized to study longitudinal elongation, given its great relevance in technical applications.
Owing to the non-local character of the magnetic action, a nonlinear integro-differential equation is derived. Some qualitative
properties of the solution are pointed out and the asymptotic behavior near the end sections is examined in detail. A finite
differences approach allows writing an approximating nonlinear system of equations in the non asymptotic part of the solution,
which is solved through a Newton’s iterative scheme. The numerical results are discussed and it is shown how the asymptotic
part of the solution well approximates the full behavior of the structure. Furthermore, the longitudinal interaction force
density is found to be singular at the end cross-sections, regardless of the assumed bonding type. 相似文献
56.
Enrico Falcone Germano Nobili Michael Okafor Olivier Proux Giancarlo Rossi Silvia Morante Peter Faller Francesco Stellato 《Angewandte Chemie (International ed. in English)》2023,62(25):e202217791
The redox activity of Cu ions bound to the amyloid-β (Aβ) peptide is implicated as a source of oxidative stress in the context of Alzheimer's disease. In order to explain the efficient redox cycling between CuII-Aβ (distorted square-pyramidal) and CuI-Aβ (digonal) resting states, the existence of a low-populated “in-between” state, prone to bind Cu in both oxidation states, has been postulated. Here, we exploited the partial X-ray induced photoreduction at 10 K, followed by a thermal relaxation at 200 K, to trap and characterize by X-ray Absorption Spectroscopy (XAS) a partially reduced Cu-Aβ1–16 species different from the resting states. Remarkably, the XAS spectrum is well-fitted by a previously proposed model of the “in-between” state, hence providing the first direct spectroscopic characterization of an intermediate state. The present approach could be used to explore and identify the catalytic intermediates of other relevant metal complexes. 相似文献
57.
P. Barois F. Heidelbach L. Navailles H. T. Nguyen M. Nobili M. Petit R. Pindak C. Riekel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):455-462
We report the first X-ray scattering investigation of spatial variations of the q-fold quasicrystalline symmetry (so-called commensurability) of well-aligned samples. A spatial resolution of was achieved using the ESRF microfocus beamline. The liquid crystal samples, contained between glass plates which were either
parallel or in a wedge geometry, were scanned in order (i) to probe the mosaicity and (ii) to continuously change the balance
between surface and volume effects. In the case of parallel plate cells, commensurability was observed everywhere throughout
the sample, hence ruling out possible effects of mosaicity to explain the q-fold symmetry of the diffraction patterns previously reported when probed with a spatial resolution of mm2 in rotating anode experiments. In the case of wedge cells, the evolution of X-ray patterns with thickness suggested that
commensurate lockin occurs for sufficiently thick samples with a width that is statistical.
Received 18 January 1999 相似文献
58.
Antunes Staffolani Hamideh Darjazi Gilberto Carbonari Fabio Maroni Serena Gabrielli Francesco Nobili 《Molecules (Basel, Switzerland)》2021,26(14)
Composite anode material based on Fe3O4 and reduced graphene oxide is prepared by base-catalysed co-precipitation and sonochemical dispersion. Structural and morphological characterizations demonstrate an effective and homogeneous embedding of Fe3O4 nanoparticles in the carbonaceous matrix. Electrochemical characterization highlights specific capacities higher than 1000 mAh g−1 at 1C, while a capacity of 980 mAhg−1 is retained at 4C, with outstanding cycling stability. These results demonstrate a synergistic effect by nanosize morphology of Fe3O4 and inter-particle conductivity of graphene nanosheets, which also contribute to enhancing the mechanical and cycling stability of the electrode. The outstanding capacity delivered at high rates suggests a possible application of the anode material for high-power systems. 相似文献
59.
Walter Meyer H. Vigreux T. Kariyone K. Ohkura H. Patzsch H. Jeglinski L. Nobili J. Büchi M. Ruszkowski J. Herzog H. Tietz A. B. Layons G. Bümming J. D. Booth und W. Zimmermann 《Fresenius' Journal of Analytical Chemistry》1935,101(7-8):306-312
Ohne Zusammenfassung 相似文献
60.
The relation of time indexed formulations of nonpreemptive single machine scheduling problems to the node packing problem
is established and then used to provide simple and intuitive alternate proofs of validity and maximality for previously known
results on the facial structure of the scheduling problem. Previous work on the facial structure has focused on describing
the convex hull of the set of feasible partial schedules, schedules in which not all jobs have to be started. The equivalence
between the characteristic vectors of this set and those of the set of feasible node packings in a graph whose structure is
determined by the parameters of the scheduling problem is established. The main contribution of this paper is to show that
the facet inducing inequalities for the convex hull of the set of feasible partial schedules that have integral coefficients
and right hand side 1 or 2 are the maximal clique inequalities and the maximally and sequentially lifted 5-hole inequalities
of the convex hull of the set of feasible node packings in this graph respectively.
Received: September 10, 2000 / Accepted: April 20, 2002 Published online: September 27, 2002
Key words. scheduling – node packing – polyhedral methods – facet defining graphs – lifted valid inequalities – facet inducing inequalities} 相似文献