1,721,016 research outputs found
Phase stability of Ni-Al solid solutions
No full textWe have studied the stability of Ni(1-x)-Alxsolid solutions at different stoichiometries (x = 0 25 and x = 0 5) via molecular dynamics simulations of models based on an n-body potential. The face-centred-cubic solid solution with x = 0 25 is stable at room temperature against the ordering transformation which occurs at T = 360°C via the activation of vacancy diffusion with a release of a disordering enthalpy of 8 kJ (g-atom)-1. The results obtained from the simulated model show an intrinsic instability of the x = 0 5 solid solution which is consistent with experimental results that have revealed the direct formation of NiAl (B2) intermetallic phase accompanied by a considerable heat release. © 1993 Taylor & Francis Group, LLC
Two-state theory of single-molecule stretching experiments
No full textWe present a statistical mechanics analysis of the finite-size elasticity of model polymers, consisting of domains which can exhibit transitions between more than one stable state at large applied force. The constant-force (Gibbs) and constant-displacement (Helmholtz) formulations of single molecule stretching experiments are shown to converge in the thermodynamic limit. Monte Carlo simulations of continuous three dimensional polymers of variable length are carried out, based on this formulation. We demonstrate that the experimental force-extension curves for short and long polymers are described by a unique universal model, despite the differences in chemistry and rate-dependence of transition forces
On the electrical activity of sp2-bonded grain boundaries in nanoscrystalline diamond
No full textBy means of tight-binding molecular dynamics simulations we find that the ground-state atomic structure of a typical high-energy grain boundary in diamond is highiy disordered with a large fraction of sp2 bonded atoms. This structure gives rise to localised bands within the band gap. We describe how multiphonon assisted hopping conduction can arise from such electronic states in high-energy grain boundaries, giving in turn a basis for the experimentally observed conductivity and electron field emission in nanocrystalline diamond. Simulated electron-energy-loss spectra indicate correlations between the disordered atomic structure and features of the electronic structure
Correlation between atomic structure and localized gap states in silicon grain boundaries
No full textAdvances in Materials Theory and Modeling - Bridging over multiple length and time scales
No full textResponse to “Comment on ‘Elasticity of flexible and semiflexible polymers with extensible bonds in the Gibbs and Helmholtz ensembles”’ [J. Chem. Phys. 138, 157101 (2013)]
Full text linkNo abstract: this is a "response" to a Comment
Theory and Monte Carlo simulations for the stretching of flexible and semiflexible single polymer chains under external fields
No full textStretching experiments on single molecules of arbitrary length opened the way for studying the statistical mechanics of small systems. In many cases in which the thermodynamic limit is not satisfied, different macroscopic boundary conditions, corresponding to different statistical mechanics ensembles, yield different force-displacement curves. We formulate analytical expressions and develop Monte Carlo simulations to quantitatively evaluate the difference between the Helmholtz and the Gibbs ensembles for a wide range of polymer models of biological relevance. We consider generalizations of the freely jointed chain and of the worm-like chain models with extensible bonds. In all cases we show that the convergence to the thermodynamic limit upon increasing contour length is described by a suitable power law and a specific scaling exponent, characteristic of each model. (C) 2012 American Institute of Physics
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