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排序方式: 共有149条查询结果,搜索用时 15 毫秒
1.
This paper proposes a perturbation-based heuristic for the capacitated multisource Weber problem. This procedure is based on an effective use of borderline customers. Several implementations are considered and the two most appropriate are then computationally enhanced by using a reduced neighbourhood when solving the transportation problem. Computational results are presented using data sets from the literature, originally used for the uncapacitated case, with encouraging results. 相似文献
2.
Abstract New N-substituted 4-arylidene-isoquinoline-1,3-dione derivatives were obtained as one geometrical isomer by aldol condensation of the appropriate aldehyde and the corresponding N-substituted homophthalimides. The structural elucidation of compounds 3a–h was established by infrared and NMR spectroscopy including 1 H, 13 C, CH CORR, and distortionless enhancement by polarization transfer measurements. Compounds 3d–h were evaluated for their antibacterial activity against some strains of bacteria using the disc diffusion method and microdilution tests. 相似文献
3.
Mixed ammonium-transition metal salts with formula of (NH4)xMyHzPMo12O40 (M = Ni2+, Co2+ or Fe 3+) denoted as MPMo12 have been investigated for the oxidation of propane, with molecular oxygen, at temperature range between 380℃ and 420℃ after in-situ pre-treatment performed at two heating rate of 5 or 9℃/min. They were characterized by BET method, XRD, UV-Vis and IR techniques. The catalysts were found to be active in the propane oxidation and selective to propene or acrolein, in particular for samples pre-t... 相似文献
4.
Chiral α-bromonitriles were prepared with good chemical and optical yields starting from natural α-amino acids by dehydrating the corresponding α-bromoamides with thionyl chloride. The combined system α-bromonitriles/hydrogen peroxide was examined for the enantio- and diastereoselective oxidation of N-alkylimines in basic media at room temperature. The oxidation of N-tertiobutylarylimines leads to optically active oxaziridines with moderate enantiomeric excess. However, the oxidation of (S)-1-phenylethylarylimines affords the corresponding oxaziridines with good diasteromeric excess up to 97/3 as proved by gaseous-phase chromatography. 相似文献
5.
We solve the vertex p-centre problem optimally using an exact method that considers both upper and lower bounds as part of its search engine. Tight upper bounds are generated quickly via an efficient three-level heuristic, which are then used to derive potential ‘lower bounds’ accordingly. These two pieces of information when used together make our chosen exact method more efficient at obtaining optimal solutions relatively quickly. The proposed implementation produced excellent results when tested on the OR Library data set. This integrated approach can be adopted for those exact methods that consider both upper and lower bounds within their search engine and hence provide a wider spectrum of applicability in other hard combinatorial problems. 相似文献
6.
The concept of ‘nested methods’ is adopted to solve the location-routeing problem. Unlike the sequential and iterative approaches, in this method we treat the routeing element as a sub-problem within the larger problem of location. Efficient techniques that take into account the above concept and which use a neighbourhood structure inspired from computational geometry are presented. A simple version of tabu search is also embedded into our methods to improve the solutions further. Computational testing is carried out on five sets of problems of 400 customers with five levels of depot fixed costs, and the results obtained are encouraging. 相似文献
7.
Kemmitt T Al-Salim NI Gainsford GJ Bubendorfer A Waterland M 《Inorganic chemistry》2004,43(20):6300-6306
Aqueous titanium citrate solutions were prepared from the reaction of citric acid with titanium 2-propoxide in a range of molar ratios. Solutions containing two or fewer citrates per titanium resulted in the slow crystallization of an insoluble titanium oxo-citrate complex. Single-crystal X-ray analysis identified the species as Ti(8)O(10)(citrate)(4)(H(2)O)(12).14H(2)O.3HOPr(i)(), crystallized in the tetragonal space group I4(1)/a, with a = 30.775(7) A, c = 14.528(7) A, V = 13 759(8) A(3), and Z = 8. The trianionic citrate ligands supply both carboxylate and alkoxide coordination and stabilize the structure using simultaneous chelating and bridging modes of attachment. The compound is a neutral species, exhibiting titanium in three contrasting environments. Laser Raman microscopy and (13)C CPMAS solid-state NMR data were consistent with those of the X-ray crystal structure. When exposed to air, the crystals rapidly lost water and became a powder. The dehydrated powder was noncrystalline to X-rays and insoluble, but (13)C NMR results demonstrated retention of the carboxylate linkages. 相似文献
8.
B. Ortaç A. Hideur M. Brunel T. Chartier M. Salhi H. Leblond F. Sanchez 《Applied physics. B, Lasers and optics》2003,77(6-7):589-594
The properties of an ytterbium-doped double-clad fiber laser, passively mode-locked by nonlinear polarization rotation are investigated in this work. Cartographies of mode-locking regime versus halfwave plates orientations are presented for several values of the total cavity dispersion and for different pump powers. Bistability between the continuous and the mode-locking regimes is pointed out. The effect of the total group velocity dispersion is described with a master mode-locking equation. PACS 42.55.Wd; 42.65.Re 相似文献
9.
The multisource location-allocation problem in continuous space is investigated. Two constructive heuristic techniques are proposed to solve this problem. Both methods are based on designing suitable schemes for the generation of the initial solutions. The first considers the furthest distance rule and is enhanced by schemes borrowed from tabu search such as constructing the forbidden regions and freeing strategy. The second considers the discrete solutions found when solving the p-median problem. Some results on existing test problems are presented. 相似文献
10.
Tim Kemmitt Graeme J. Gainsford Najeh I. Al‐Salim 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(2):m42-m43
The title compound, octa‐tert‐butoxybis[μ3‐2,2′‐(N‐methylimino)diethanolato]di‐μ‐oxo‐tetratitanium(IV), [Ti2O{(OCH2CH2)2(NCH3)}{(CH3)3CO}4]2 or [Ti4(C5H11NO2)2(C4H9O)8O2], lies about an inversion centre, and displays the less usual zigzag configuration. One O atom of the N‐methyldiethoxoamine ligand bridges the symmetry‐related Ti atoms, while the other bridges the two independent Ti atoms, with the N atom binding to give a facial configuration. Four tBuO− ligands and a bridging oxide complete the respective five‐ and sixfold coordination of the two Ti atoms. The Ti—O bond lengths range in a self‐consistent fashion from 1.7624 (17) to 2.0878 (18) Å, while the Ti—N bond length is 2.374 (2) Å. 相似文献