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971.
In this work, we present some results on the distribution of Lee–Yang zeros for the ferromagnetic Ising model on the rooted Cayley Tree (Bethe Lattice), assuming free boundary conditions, and in the one-dimensional lattice with periodic boundary conditions. In the case of the Cayley Tree, we derive the conditions that the interactions between spins must obey in order to ensure existence or absence of phase transition at finite temperature (T0). The results are first obtained for periodic interactions along the generations of the lattice. Then, using periodic approximants, we are also able to obtain results for aperiodic sequences generated by substitution rules acting on a finite alphabet. The particular examples of the Fibonacci and the Thue-Morse sequences are discussed. Most of the results are obtained for a Cayley Tree with arbitrary order d. We will be concerned in showing whether or not the zeros become dense in the whole unit circle of the fugacity variable. Regarding the one-dimensional Ising model, we derive a general treatment for the structure of gaps (regions free of Lee–Yang zeros) around the unit circle. 相似文献
972.
The apparent molar volumes and adiabatic compressibilities of 18-Crown-6, 15-Crown-5, 12-Crown-4, tetraglyme, and triglyme were measured at 25°C in H2O and D2O. The contribution of the -CH2CH2O- group to the limiting partial molar volumes and compressibilities of cyclic and open-chain ethers in both solvents are compared and solvent isotope effects calculated. It is concluded, based on the compressibility results, that there is a subtle difference between the hydration of the ethene oxde group in cyclic and open-chain ethers and that this difference persists in D2O. These results indicate that the calculation of limiting apparent molar compressibilities using additivity schemes will have to account for whether the group is in a cyclic or open-chain compound. 相似文献
973.
Francisco Martínez-Boza Pedro Partal Francisco J. Navarro Críspulo Gallegos 《Rheologica Acta》2001,40(2):135-141
The viscous and linear viscoelastic properties of different asphalt binders have been analyzed in this paper. Thus, an unmodified
bitumen, a polymer-modified (SBS) bitumen, a commercial synthetic binder, and two model synthetic binders with different polymer
(SBS) concentrations have been studied. The mechanical spectra of these binders are quite different, mainly influenced by
SBS concentration. Thus, up to three regions may be observed for a synthetic binder with high polymer concentration. The temperature
dependence of the zero-shear-rate-limiting viscosity is described by an Arrhenius-like equation, in a temperature range that
depends on binder composition. These results have been discussed taking into account the development of a polymer-rich phase
in SBS-modified bitumen and model synthetic binders.
Received: 6 February 2000 Accepted: 8 August 2000 相似文献
974.
Rui P. S. Fartaria Fernando M. S. Silva Fernandes Filomena F. M. Freitas Pedro C. R. Rodrigues 《International journal of quantum chemistry》2001,84(3):375-387
A first‐principles intermolecular potential recently proposed by Pacheco and Ramalho [Phys Rev Lett 1997, 79, 3873–3876] has been used with the Gibbs ensemble and Gibbs–Duhem integration Monte Carlo methods to simulate the vapor–liquid and fluid–solid coexistence properties of C60. The critical properties were calculated by fitting the results to the laws of rectilinear diameters and order parameter scaling. The triple‐point properties were determined from the limiting behavior of the Gibbs ensemble vapor–liquid simulations at the lowest temperature range. A stable liquid phase is predicted for temperatures between 1570±20 and 2006±27 K and densities between 0.444±0.003 and 1.05±0.01 nm?3. The estimated critical and triple‐point pressures are, respectively, 35±6 and 5±16 bars. We show for the first time, to our knowledge, that it is possible, strictly by computer simulation, to estimate a triple point for C60 in accordance with the predictions of theoretical methods and the basic concepts of thermodynamics. The liquid and fluid radial distribution functions indicate the presence of solid or glasslike features. This may support the suggestion of a more cooperative interaction of clusters in C60. A comparison of our results with the data obtained by other authors is presented and discussed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 375–387, 2001 相似文献
975.
Luis Cataño Carmen Albano Arquímedes Karam Rosestela Perera Pedro Silva 《Macromolecular Symposia》2007,257(1):147-157
Summary: The thermal stability of a polyamide-6/low linear density polyethylene blend (PA6/LLDPE) was studied using thermal analysis techniques. The thermogravimetric studies carried out showed that when a diethyl maleate grafted styrene- ethylene/butadiene-styrene terpolymer (SEBS-g-DEM) is added to the PA6/LLDPE blend there is an actual enhancement of the thermal stability due to the increase in the interfacial area within the blend. The Invariant Kinetic Parameter method (IKP) proved to be a qualitative technique unfolding the type of degradation mechanisms taking place in the material vicinity. Nucleation and phase boundary reactions are the kinetic models of thermal decomposition with the most significant probability of occurring. 相似文献
976.
In multiobjective optimization there is often the problem of the existence of a large number of objectives. For more than two objectives there is a difficulty with the representation and visualization of the solutions in the objective space. Therefore, it is not clear for the decision maker the trade-off between the different alternative solutions. Thus, this creates enormous difficulties when choosing a solution from the Pareto-optimal set and constitutes a central question in the process of decision making. Based on statistical methods as Principle Component Analysis and Cluster Analysis, the problem of reduction of the number of objectives is addressed. Several test examples with different number of objectives have been studied in order to evaluate the process of decision making through these methods. Preliminary results indicate that this statistical approach can be a valuable tool on decision making in multiobjective optimization. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
977.
We report on a result establishing plain convergence for conforming adaptive finite elements under relatively general assumptions on problem class and adaptive algorithm. Moreover, we indicate some applications and give a sketch of the proof. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
978.
Carlos B. da Silva Pedro Neto José C. F. Pereira 《Theoretical and Computational Fluid Dynamics》2009,23(4):287-296
Direct and large-eddy simulations (DNS/LES) of accelerating round jets are used to analyze the effects of acceleration on
the kinematics of vortex rings in the near field of the jet (x/D < 12). The acceleration is obtained by increasing the nozzle jet velocity with time, in a previously established (steady)
jet, and ends once the inlet jet velocity is equal to twice its initial value. Several acceleration rates (α = 0.02–0.6) and Reynolds numbers (Re
D
= 500–20000) were simulated. Acceleration maps were used to make a detailed study of the kinematics of vortex rings in accelerating
jets. One of the effects of the acceleration is to cause a number of new primary and secondary vortex merging events that
are absent from steady jets. As the acceleration rate α increases, both the number of primary merging events between rings
and the axial position where these take place decreases. The statistics for the speed of the starting ring that forms at the start of the acceleration phase for each simulation, agree well with the statistics for the “front” speed
observed by Zhang and Johari (Phys Fluids 8:2185–2195, 1996). Acceleration maps and flow visualizations show that during the
acceleration phase the near field coherent vortices become smaller and are formed at an higher frequency than in the steady
jet, and their (mean) shedding frequency increases linearly with the acceleration rate. Finally, it was observed that the
acceleration decreases the spreading rate of the jet, in agreement with previous experimental works.
相似文献
979.
芳胺和芳酮所形成的希夫碱在无水三氯化铝或二异丙胺锂与氯化锌乙醚溶液存在下和腈类化合物加成,制备了一些文献中未报导过的3-氨基-2-烯亚胺,并经元素分析、1H NMR,13C NMR和MS确证. 相似文献
980.
Pedro H. Ferri Carlito Lariucci Leon I. B. Homar Raquel F. Santos Elaine R. Maia Lourivaldo S. Santos Ivo Vencato 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):118-120
The crystal structure and absolute configuration of the title compound, C17H21BrO8, have been determined by X‐ray analysis. They confirmed the 1′R absolute configuration at the 1′‐bromoethyl moiety which has been assigned previously on the basis of chemical and spectroscopic data. Cohesion of the crystal can be attributed to weak intermolecular C—H?O and van der Waals interactions. 相似文献