Mesoscale model of dislocation motion and crystal plasticity

A consistent, small scale description of plastic motion in a crystalline solid is presented based on a phase field description. By allowing for independent mass motion given by the phase field, and lattice distortion, the solid can remain in mechanical equilibrium on the timescale of plastic motion. Singular (incompatible) strains are determined by the phase field, to which smooth distortions are added to satisfy mechanical equilibrium. A numerical implementation of the model is presented, and used to study a benchmark problem: the motion of an edge dislocation dipole in a hexagonal lattice. The time dependence of the dipole separation agrees with classical elasticity without any adjustable parameters.Comment: 5 pages, 3 figure

Decisión making and decisión support systems for balancing Socio-Economic and Natural Capital Development.

The paper discusses briefly a hierarchical spatio-temporal framework to study globalization, economics and ecology for better understanding and conceptualization of the balance between biodiversity and Natural Capital (NC) on one side, and the Socio-Economic Systems (SES), on the other side, which was designed based on the recent achievements in the field of Systems Ecology. Based on the conceptual clarification of the dynamic condictions for sustainability and on an extensive review of the most recent literature, there are proposed and discussed the decision support system and decision making model as the operational interface between Natural Capital components and Socio-Economic Systems, which might enable to establish and maintain the balance among them. The identified weaknesses and gaps in the structure and function of the Decision Support System (DSS) show the need for extensive and long term research and integrated monitoring and for development and improvement of the methodology and tools.Sin resume

Classical analogies for the force acting on an impurity in a Bose-Einstein condensate

We study the hydrodynamic forces acting on a small impurity moving in a two-dimensional Bose-Einstein condensate at non-zero temperature. The condensate is modelled by the damped-Gross Pitaevskii (dGPE) equation and the impurity by a Gaussian repulsive potential coupled to the condensate. For weak coupling, we obtain analytical expressions for the forces acting on the impurity, and compare them with those computed through direct numerical simulations of the dGPE and with the corresponding expressions for classical forces. For non-steady flows, there is a time-dependent force dominated by inertial effects and which has a correspondence in the Maxey-Riley theory for particles in classical fluids. In the steady-state regime, the force is dominated by a self-induced drag. Unlike at zero temperature, where the drag force vanishes below a critical velocity, at low temperatures the impurity experiences a net drag even at small velocities, as a consequence of the energy dissipation through interactions of the condensate with the thermal cloud. This dissipative force due to thermal drag is similar to the classical Stokes' drag. There is still a critical velocity above which steady-state drag is dominated by acoustic excitations and behaves non-monotonically with impurity's speed.Comment: 21 pages, 4 figures. Supplementary movies available at: https://cloud.ifisc.uib-csic.es/nextcloud/index.php/s/AFzw6JxNW77DT6

Rotation induced grain growth and stagnation in phase field crystal models

We consider the grain growth and stagnation in polycrystalline microstructures. From the phase field crystal modelling of the coarsening dynamics, we identify a transition from a grain-growth stagnation upon deep quenching below the melting temperature $T_m$ to a continuous coarsening at shallower quenching near $T_m$. The grain evolution is mediated by local grain rotations. In the deep quenching regime, the grain assembly typically reaches a metastable state where the kinetic barrier for recrystallization across boundaries is too large and grain rotation with subsequent coalescence is infeasible. For quenching near $T_m$, we find that the grain growth depends on the average rate of grain rotation, and follows a power law behavior with time with a scaling exponent that depends on the quenching depth.Comment: (4 pages, 4 figures