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991.
The influence of the new mineral filler Pansil, a natural magnesium silicate (sepiolite), on the properties of SBR vulcanizates is studied and compared with other synthetic silicas and a carbon black N-330 (HAF) at various filler concentrations.A series of dynamic tests was carried out in traction-compression and shear at various frequencies, temperatures and strain amplitudes.The so-called Payne effect was observed as the strain amplitude was increased. The variation of tan with the dynamic deformation was more pronounced in the Pansil filled compounds. The needle-shaped nature and the large internal surface (mesopores) of the new mineral filler may give rise to a high adsorption of rubber chain segments with the subsequent increase in heat generation. However, when the Pansil was treated with a silane coupling agent (Silane A-189) the heat generation decreased.By applying the time-temperature superposition principle, master curves for the storage modulus and loss factor tan were derived over a wide frequency range. 相似文献
992.
Begoña Cano Adolfo González‐Pachón 《Numerical Methods for Partial Differential Equations》2015,31(1):78-104
In this article, it is proved that explicit Lawson methods, when projected onto one of the invariants of nonlinear Schrödinger equation (norm) are also automatically projected onto another invariant (momentum) for many solutions. As this procedure is very cheap and geometric because two invariants are conserved, it offers an efficient tool to integrate some solutions of this equation till long times. On the other hand, we show a detailed study on the numerical performance of these methods against splitting ones, with fixed and variable stepsize implementation. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq31: 78–104, 2015 相似文献
993.
We introduce the notion of radical in Bernstein algebras and prove a splitting theorem, that is an analog of a well-known statement in classical varieties of algebras. Note that in this situation Bernstein algebras are more similar to solvable Lie and Malcev algebras (see [4], [6]) than to associative, Jordan or Binary Lie ones. Throughout the paper all algebras and vector spaces are finite dimensional over an algebraically closed field k of characteristic 0. 相似文献
994.
995.
Luciana P. Assis André L. Maravilha Alessandro Vivas Felipe Campelo Jaime A. Ramírez 《Optimization Letters》2013,7(7):1419-1431
We present an adaption on the formulation for the vehicle routing problem with fixed delivery and optional collections, in which the simultaneous minimization of route costs and of collection demands not fulfilled is considered. We also propose a multiobjective version of the iterated local search (MOILS). The performance of the MOILS is compared with the $\epsilon $ -constrained ( $P_{\epsilon }$ ) ILS, the NSGA-II and the indicator-based multi-objective local search methods in the solution of 14 problem instances containing between 50 and 199 customers plus the depot. The results indicate that the MOILS outperformed the other approaches, obtaining significantly better average values for coverage, hypervolume and cardinality. 相似文献
996.
We address the determination of the second point-to-point shortest simple path in undirected networks. The effective reduced cost concept is introduced to compute the second best solution. This concept is used to prove that a path tree containing the second point-to-point shortest simple path is adjacent to any shortest path tree. Therefore, this result immediately implies a method requiring O(m) time once that the shortest path tree is obtained on an undirected network with n nodes and m edges. 相似文献
997.
Vanessa R. Landaeta Rafael E. Rodríguez-Lugo Eloy N. Rodríguez-Arias David S. Coll-Gómez Teresa González 《Transition Metal Chemistry》2010,35(2):165-175
New imidazolium salts derived from the natural methylated xanthines theophylline, theobromine and caffeine, namely 1,3-dimethyl-9-benzylxanthinium
bromide (tphBzBr, 1a), 3,7-dimethyl-9-benzylxanthinium bromide (tbrBzBr, 2a) and 1,3,7-trimethyl-9-benzylxanthinium bromide (caffBzBr, 3a), are reported. Also, the disubstituted analog of 1a, 1,3-dimethyl-7,9-dibenzylxanthinium bromide (tphBz2Br, 1a′) was identified and characterized by NMR. The coordination chemistry of ligands 1a–3a toward palladium, and some theoretical aspects of the unmodified theophylline, theobromine and caffeine are studied. Our
results prove that the theophylline derivative has the thermodynamic tendency to form N-bonded species, even when an equilibrium
between the Pd–NHC and the “theophyllinate” was observed spectroscopically, due to the anisotropy of the NHC ligand. To confirm
the N-coordination, the solid state structure of the new “theophyllinate” species PdBr2(tphBz-H)2 (4), derived from 1a, was determined by X-ray diffraction. The analog with theobromine, ligand 2a, coordinates to palladium via N1, in an analogous manner to 1a, and a mixture of the cis/trans isomers of its palladium complex is obtained. On the other hand, since there is no possibility
of N-coordination in 3a, this caffeine derivative forms a Pd-NHC compound after deprotonation with a strong base. Both the theoretical results and
the experimental evidence are in accordance, in terms of the predicted coordination sites or possibility of modification of
the selected methylated xanthines to obtain new ligands. 相似文献
998.
Felipe Hernández-Luis Raquel Rodríguez-Raposo Héctor R. Galleguillos Jaime W. Morales 《Fluid Phase Equilibria》2010
The electromotive force of the cell containing two ion-selective electrodes (ISE), K-ISE|KCl(m), PEG 4000(Y), H2O(100 − Y)|Cl-ISE has been measured at temperatures of 288.15, 298.15, and 308.15 K as a function of the weight percentage Y of PEG 4000 in a mixed solvent. Y was varied between 0 and 25 wt.% in five-unit steps and the molality of the electrolyte (m) was between ca. 0.05 mol kg−1 and almost saturation. The values of the standard electromotive force were calculated using routine methods of extrapolation together with extended Debye-Hückel and Pitzer equations. The results obtained produced good internal consistency for all the temperatures studied. Once the standard electromotive force was determined, mean ionic activity coefficients for KCl, Gibbs energy of transfer from the water to PEG 4000 + water mixtures, interaction parameters (gEN, hEN, sEN, cp,EN), salting constants, and the KCl primary hydration number were estimated and comparatively discussed in terms of a model of structural and electrostatic interactions with those of the LiCl and NaCl previously obtained in similar mixtures. 相似文献
999.
Urszula Domanska Maciej Zawadzki Juan Antonio González 《The Journal of chemical thermodynamics》2010,42(4):545-552
(Solid + liquid) equilibrium (SLE) temperatures have been determined using a dynamic method for the systems (1H-imidazole, + benzene, + toluene, + hexane, or + cyclohexane; 1-methylimidazole + benzene, or + toluene, 2-methyl-1H-imidazole + benzene, + toluene, or + cyclohexane, and benzimidazole + benzene). In addition (liquid + liquid) equilibrium (LLE) temperatures have been obtained using a cloud point method for (1H-imidazole, + hexane, or + cyclohexane; 1-methylimidazole + toluene, and 2-methyl-1H-imidazole + cyclohexane). The measured systems show positive deviations from the Raoult’s law, due to strong dipolar interactions between amine molecules related to the high dipole moment of imidazoles. On the other hand, DISQUAC interaction parameters for the contacts present in these solutions and for the amine/hydroxyl contacts in (1H-imidazole + 1-alkanol) mixtures have been determined. The model correctly represents the available data for the examined systems. Deviations between experimental and calculated SLE temperatures are similar to those obtained using the Wilson or NRTL equations, or the UNIQUAC association solution model. The quasichemical interaction parameters are the same for mixtures containing 1H-imidazole, 1-methylimidazole, or 2-methyl-1H-imidazole and hydrocarbons. This may be interpreted assuming that they are members of a homologous series. Benzimidazole behaves differently. 相似文献
1000.