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1.
A hybrid heuristic method for combinatorial optimization problems is proposed that combines different classical techniques such as tree search procedures, bounding schemes and local search. The proposed method enhances the classic beam search approach by applying to each partial solution corresponding to a node selected by the beam, a further test that checks whether the current partial solution is dominated by another partial solution at the same level of the search tree. If this is the case, the latter solution becomes the new current partial solution. This step allows to partially recover from previous wrong decisions of the beam search procedure and can be seen as a local search step on the partial solution. We present here the application to two well known combinatorial optimization problems: the two-machine total completion time flow shop scheduling problem and the uncapacitated p-median location problem. In both cases the method strongly improves the performances with respect to the basic beam search approach and is competitive with the state of the art heuristics. 相似文献
2.
3.
Nicola Arcozzi Enrico Casadio Tarabusi Fausto Di Biase Massimo A. Picardello 《Transactions of the American Mathematical Society》2006,358(6):2781-2798
We establish a potential theoretic approach to the study of twist points in the boundary of simply connected planar domains.
4.
In this work, the NP-hard maximum clique problem on graphs is considered. Starting from basic greedy heuristics, modifications and improvements are proposed and combined in a two-phase heuristic procedure. In the first phase an improved greedy procedure is applied starting from each node of the graph; on the basis of the results of this phase a reduced subset of nodes is selected and an adaptive greedy algorithm is repeatedly started to build cliques around such nodes. In each restart the selection of nodes is biased by the maximal clique generated in the previous execution. Computational results are reported on the DIMACS benchmarks suite. Remarkably, the two-phase procedure successfully solves the difficult Brockington-Culberson instances, and is generally competitive with state-of-the-art much more complex heuristics. 相似文献
5.
M. Piana M. Arrabito S. Bodoardo A. D'Epifanio D. Satolli F. Croce B. Scrosati 《Ionics》2002,8(1-2):17-26
Solid State Reaction was employed to prepare phospho-olivines LiMPO4 (where M=Fe, Co) as pure phase and LiNiPO4 in presence of foreign phases, as cathodic materials for lithiumions batteries. The relationship between structural, morphological
and electrochemical properties were investigated in the case of LiFePO4. Structural investigation has been carried out by means of X-ray powder diffraction (XRPD) and Rietveld refinement. The influence
on the morphology of annealing temperature, different flowing gas mixture and addition of ascorbic acid during the synthesis,
has been analysed via scanning electron microscopy. The electrochemical cycling performances on LiFePO4 showed to be positively affected by the modifications of the experimental conditions. Cyclic voltammetry showed a good reversibility
during insertion-extraction mechanism, in particular in presence of additives. LiCoPO4 and LiNiPO4 are interesting as high voltage cathode materials for Li-ion batteries and have been taken into account, but their electrochemical
operating conditions are still to be optimised. In the case of LiNiPO4 it is very difficult to obtain, by solid state synthesis, suitable purity powders, having a grain size small enough to exploit
it usefully as cathodic material for Li-ion cells.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2000. 相似文献
6.
Leibniz agebras are a generalization of Lie algebras, where no symmetry properties of the bracket are required. In this Letter we introduce a notion of R-matrices for this structure and the related Yang–Baxter equations, and discuss some of their basic properties. 相似文献
7.
Roughness effect on the heat transfer and pressure loss performances of microscale tubes and channels are investigated through a finite element CFD code. Surface roughness is explicitly modelled through a set of random generated peaks along the ideal smooth surface. Different peak shapes and distributions are considered; geometrical parameters are representative of tubes in the diameter range from 50 to 150 μm. The use of a fine enough mesh allows the direct computation of tube performances under the assumption of incompressible fully developed flow. As a result, a significant increase in Poiseuille number is detected for all of the configurations considered, while the effect of roughness on heat transfer rate is smaller and highly dependent on the tube shape. 相似文献
8.
Tight control of flux loci in 2D testing of soft magnetic laminations is realized by a method based on the principle of contraction mapping. It is implemented through digital control of the currents supplying a three-phase yoke magnetizer and the use of circular samples. Faithful realization of the prescribed loci and good measuring accuracy are demonstrated in grain-oriented and non-oriented Fe–Si laminations. 相似文献
9.
In this paper some synthetic procedures to obtain (η6-arene)metal derivatives are reviewed. The metal-atom-arene-vapor co-condensation technique is the most appropriate to generate complexes of polycyclic aromatic hydrocarbons or heterocycles. As far as the aluminium halide-mediated synthesis is concerned, two classes of reaction are observed. When AlX3 is used with a metal halide in the presence of an aromatic hydrocarbon in the absence of any reducing agent, AlX3 can function as a dehalogenating agent, to give ionic compounds of general formula [M(η6-arene)n](AlX4)m, or it can add across the M---X bond with formation of M(μ-X)nAlX4−n systems. In both cases the metal displays its typical oxidation state. However, the use of AlX3 in combination with aluminium (the Fischer-Hafner reducing system) affords ionic or covalent low-oxidation-state metal(η6-arene) complexes. Attention is focused on our most recent results concerning the synthesis, properties and reactivity of η6-arene derivatives of Group 4 and 5 elements, showing, inter alia, the first example of a tetraarylborate anion behaving as a 12-electron donor to one metal atom and low-valent η6-arene compounds as useful reagents in the inorganic and coordination chemistry of the corresponding metal in nonaqueous systems. 相似文献
10.
Marta Elena Díaz-García Fausto Alava-Moreno Alfredo Sanz-Medel 《Mikrochimica acta》1994,113(3-6):211-222
A new optical sensor phase for potassium ions has been developed based on the immobilization of the pH-dependent fluorogenic crown ether 4-acryloylamidobenzo-18-crown-6 on the non-ionic polymeric resin Amberlite XAD-2.Two different optical designs, a flow-through sensor and a fibre optic probetype sensor (optrode), have been constructed and their analytical performance characteristics have been evaluated. The resulting fluorimetric sensors for K+ ions exhibited detection limits of 0.4 or 0.8 M of K+ (16 g/l or 31 g/l), depending on the design, while the linear response occurred from 1 to 25 M of the metal concentrations. The precision, evaluated as the relative standard deviation of measurements of K+ levels at around ten times the detection limit (e.g. 5 M), turned out to be around ±2%.Advantageous features of this fluorimetric sensing phase and optrode include ease of construction, simplicity of use, reversibility, short response times (ca. 1 min full scale deflection) selectivity and operational stability, suitable for sensing potassium at low levels in complex matrices such as biological fluids.The fluorimetric optical sensor has been successfully applied to the direct determination of potassium in clinically important samples (serum and urine) and in natural waters. Very good accuracy has been obtained just using adequate synthetic aqueous potassium standards for calibration. 相似文献