A semi-discrete line-free method of monopoles for dislocation dynamics

We develop a semi-discrete particle method for Volterra dislocation currents in which the particles, or monopoles, represent an element of line and carry a Burgers vector. The monopoles move according to mobility kinetics driven by elastic and applied forces. The divergence constraint of Volterra dislocation currents is enforced weakly through mesh-free interpolation and an explicit linear connectivity, or ‘sequence’, between the monopoles need not be defined. In this sense, the method is ‘line-free’, i. e., it sidesteps the need to track dislocation lines. This attribute offers significant computational advantages in terms of simplicity, robustness and efficiency, especially as regards the tracking of complex dislocation patterns, including topological transitions. We illustrate the range and scope of the method, by means of an example of application concerned with the plastic hardening of nano-sized grains under monotonic loading

Glyph reader app: multisensory stimulation through ICT to intervene literacy disorders in the classroom

This article shows the experience in the implementation of a tool called Glyph Reader, which is an application that has two interfaces, Web and Mobile and that responds to the need for an educational and interactive resource whose main objective is the Multisensory stimulation for literacy training in a population with cognitive disabilities and/specific learning disorder. The design of the activities that this application has is based on the theoretical model of multisensory stimulation Orton Gillingham, which seeks the development of basic skills for decoding isolated words based on a phonetic - graphic analysis of them. The techniques within this model use the basic concepts of intersensory integration of simultaneous visual-auditory-kinesthetic- tactile differentiation (VAKT), to which the Glyph Reader application takes full advantage, by including graphic phonetic recognition and training activities of syllables/words (exercises with symphons and exercises with combinations of consonants or working syllables), which pass from basic levels to complex levels of decoding, necessary for the development of literacy skills. The study sample for software validation is 250 students from the Eustorgio Salgar educational institution, in the municipality of Puerto Colombia, in the department of Atlántico – Colombi

Coupled thermoelastic simulation of nanovoid cavitation by dislocation emission at finite temperature

In this work we study the early onset of void growth by dislocation emission at finite temperature in single crystal of copper under uniaxial loading conditions using the HotQC method. The results provide a detailed characterization of the cavitation mechanism, including the geometry of the emitted dislocations, the dislocation reaction paths and attendant macroscopic quantities of interest such as the cavitation pressure. In addition, this work shows that as prismatic dislocation loops grow and move away from the void, the material surrounded by these loops is pushed away from the void surface, giving rise to a flux of material together with a heat flux through the crystal

A Line-free Method of Monopoles for 3D Dislocation Dynamics

We develop an approximation scheme for three-dimensional dislocation dynamics in which the dislocation line density is concentrated at points, or monopoles. Every monopole carries a Burgers vector and an element of line. The monopoles move according to mobility kinetics driven by elastic and applied forces. The divergence constraint, expressing the requirement that the monopoles approximate a boundary, is enforced weakly. The fundamental difference with traditional approximation schemes based on segments is that in the present approach an explicit linear connectivity, or 'sequence', between the monopoles need not be defined. Instead, the monopoles move as an unstructured point set subject to the weak divergence constraint. In this sense, the new paradigm is 'line-free', i. e., it sidesteps the need to track dislocation lines. This attribute offers significant computational advantages in terms of simplicity, robustness and efficiency, as demonstrated by means of selected numerical examples

Atomistic Modeling and Analysis of Hydride Phase Transformation in Palladium Nanoparticles

Palladium-hydrogen (Pd-H) is a prototypical system for studying solute-induced phase transformation in various energy conversion and storage applications. While the behaviors of bulk Pd-H have been studied extensively, the detailed atomic picture of hydride phase transformation within individual Pd nanoparticles is still unclear. In this work, we employ a novel atomistic computational model, referred to as Diffusive Molecular Dynamics (DMD), to characterize the H absorption dynamics in Pd nanoparticles of spherical, octahedral and cubic shapes. The DMD model couples a non-equilibrium thermodynamic model with a discrete diffusion law, which allows it to reach diffusive time scales with atomic resolution. The model is capable of capturing the propagation of an atomistically sharp hydride phase boundary. A remarkable feature of the phase boundary structure that is predicted by the calculations is the emergence of misfit dislocations distributed over the interface. These dislocations relieve the elastic residual stresses induced by the change of volume that accompanies the phase transformation. Shape effects are also investigated in this work. More specifically, in both spherical and octahedral nanoparticles, we observe stacking faults during the H absorption process while the phase boundary in the cubic nanoparticle remains coherent. The spatial distribution of the stacking faults in the spherical sample is investigated in detail using an elastic core-shell model. We also identify the mechanisms that enable the movement of the stacking faults as they track the propagation of the phase boundary. Finally, we find that the rate of H absorption is reduced by the formation and movement of the stacking faults