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Triple Points (triple + point)
Selected AbstractsEquation of state for the viscosity of Lennard-Jones fluids,AICHE JOURNAL, Issue 2 2006Leslie V. Woodcock Abstract A one-parameter model constitutive transport equation for the viscosity of the Lennard-Jones (L-J) fluid that is accurate for all equilibrium states of liquid and gas is proposed: The form of this equation is based upon the soft-sphere scaling laws for the residual density-dependent viscosity discovered originally by Ashurst and Hoover and uses their empirical coefficient (CAH). Enskog's density-independent limit theoretical term (,0) is included to reproduce the viscosity in the limit of zero density accurately. Remaining discrepancies at low temperatures, for both gas and liquid densities, are largely removed when the linear-density Rainwater-Friend coefficient is added. The equation is comparable in accuracy to the 24-parameter empirical equation of state proposed by Rowley and Painter. Comparison with this correlation and previous MD results reveals a discrepancy near the triple point. To test the equation, new MD data for three fluid states are reported. Here, the viscosity is computed from time correlation functions resolved into the single-particle auto- and cross-correlation terms. It is found that, at high density (,* > 0.8), the cross,correlations extend beyond 7, (molecule diameters) and oscillate in sign. This explains the wide scatter of previous MD viscosities for small L-J systems. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Normal and Lateral Deformation of Lyotropically Ordered Polymer BrushMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006Alexey A. Polotsky Abstract Summary: Planar polymer brush formed by semirigid chains of freely jointed rigid segments and immersed into a solvent is considered. Brush collapse induced by deterioration of the solvent quality and its deformation by external normal or lateral force is studied. It is demonstrated that these three different situations can be described in the framework of the common approach. It is shown that the collapse is accompanied by liquid-crystalline (LC) ordering within the brush. The LC transition can be jump-like (the first order) or continuous, depending on the segment's aspect ratio and grafting density. Transition point is investigated in detail, the corresponding phase diagrams are calculated. It is shown that the phase diagrams of a normally deformed brush have different structures, with a narrow ,leg' in the good solvent region for sparsely grafted brush, with two coexistence regions and a triple point, in addition, for shorter segment length or without these features if the chains are densely grafted. For the laterally deformed brush, phase diagrams have similar structures with a critical point in the good solvent regime. Polymer brush subjected to deformation by normal (top) and lateral (bottom) external force. [source] Creep failure mechanisms of a Ti-6Al-4V thick plateFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2001F. J. Seco The creep failure operating mechanisms of a 17-mm thick plate of a Ti,6Al,4V alloy in various heat treating conditions have been investigated. Specimens in the as-received, mill-annealed, condition (50 min maintenance at 720 °C and air cooled as the final step of the thermomechanical process) showed the lowest creep resistance and their metallographic analysis revealed that the temperature-activated dislocation climb was the mechanism responsible for the failure and that observed holes were generated by plastic deformation, rather than by creep cavitation. Conversely, maximum times to failure were recorded in beta-annealed specimens (1030 °C for 30 min, air cooled and aged for 2 h at 730 °C). The fracture surfaces of these broken specimens exhibited an intergranular morphology that was attributed to grain boundary sliding along the former beta grains. Finally, alpha,beta field-annealed samples (940 °C 4 h, and furnace cooled to 700 °C) possessed intermediate lives between those of mill-annealed and beta-annealed specimens and the failure operating mechanism was diffusional creep by the nucleation and coalescence of the creep cavities generated at the alpha,beta interfaces and the triple points. [source] Superplasticity of a Fine-Grained TZ3Y Material Involving Dynamic Grain Growth and Dislocation MotionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Guillaume Bernard-Granger Superplastic deformation of a fully dense TZ3Y material, having a starting grain size around 135,145 nm and depleted of any amorphous phase at grain boundaries, has been investigated using compressive creep tests in air in the temperature range of 1100°,1300°C and the real stress range of 50,100 MPa. The key parameters of the creep law have been determined by performing temperature changes at a fixed stress and stress jumps at a fixed temperature. From such experiments, an average value for the apparent stress exponent of around 3 is obtained when the applied stress varied from 50 to 100 MPa and the temperature was kept constant in the range of 1100°,1300°C. The apparent activation energy of the mechanism controlling the creep deformation is evaluated at 577±75 kJ/mol in the temperature range of 1200°,1300°C, for a real stress of 70 MPa. The values of the apparent grain size exponent can be calculated from the initial grain size in the as-sintered samples and the grain size in the crept samples. In all cases, it was determined to be around 2. Observation of the microstructure of the crept samples, using scanning electron microscopy, reveals grain growth but does not show any significant elongation of the elemental grains. Transmission electron microscopy of a sample crept under 100 MPa at 1300°C reveals clear intragranular dislocation activity. This dislocation activity seems to be mainly confined in folds emitted at triple points. Because the creep parameters (experimental and calculated using a simple geometric model) and the microstructure observed are in good agreement, we propose that the creep mechanism involved is grain boundary sliding accommodated by dynamic grain growth and the formation of triple-point folds. [source] Microstructural Morphology and Electrical Properties of Copper- and Niobium-Doped Tin Dioxide Polycrystalline VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Chun-Ming Wang The influence of a Nb2O5 additive on the densification, microstructural morphology, and nonlinear electrical properties of the CuO-doped SnO2 -based varistors was investigated. It was found that copper oxide significantly improves the densification of the SnO2 ceramics. The effects of Nb2O5 on tin dioxide varistors were analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and capacitance,voltage measurements, as well as impedance spectroscopy. Copper oxide segregates at the grain boundaries and precipitates at triple points, and niobium makes the tin dioxide grain semi-conductive. The copper oxide intergranular insulating layer separates two semi-conductive tin dioxide grains and forms the barriers. The reason for the nonlinearity of SnO2 -based ceramics was explained. [source] The Hubbard model extended by nearest-neighbor Coulomb and exchange interaction on a cubic cluster , rigorous and exact resultsANNALEN DER PHYSIK, Issue 6 2010R. Schumann The Hubbard model on a cube was revisited and extended by both nearest-neighbor Coulomb correlation W and nearest-neighbor Heisenberg exchange J. The complete eigensystem was computed exactly for all electron occupancies and all model parameters ranging from minus infinity to plus infinity. For two electrons on the cluster the eigensystem is given in analytical form. For six electrons and infinite on-site correlation U we determinded the groundstate and the groundstate energy of the pure Hubbard model analytically. For fixed electron numbers we found a multitude of ground state level crossings depending on the various model parameters. Furthermore the groundstates of the pure Hubbard model in dependence on a magnetic field h coupled to the spins are shown for the complete U-h plane. The critical magnetic field, where the zero spin groundstate breaks down is given for four and six electrons. Suprisingly we found parameter regions, where the ground state spin does not depend monotonously on J in the extended model. For the cubic cluster gas, i.e. an ensemble of clusters coupled to an electron bath, we calculated the density n (,, T, h) and the thermodynamical density of states from the grand potential. The ground states and the various spin-spin correlation functions are studied for both attractive and repulsive values of the three interaction constants. We determined the various anomalous degeneration lines, where n (,, T = 0, h = 0) shows steps higher than one, since in this parameter regions exotic phenomena as phase separation are to expect in extended models. For the cases where these lines end in triple points, i.e. groundstates of three different occupation numbers are degenerated, we give the related parameter values. Regarding the influence of the nn-exchange and the nn-Coulomb correlation onto the anomalous degeneration we find both lifting and inducing of degeneracies depending on the parameter values. [source] | ||||||||||