A non-traditional view on the modeling of nematic disclination dynamics
Chiqun Zhang Xiaohan Zhang Amit Acharya Dmitry Golovaty Noel Walkington
Nonsingular disclination dynamics in a uniaxial nematic liquid crystal is modeled within a mathematical framework where the kinematics is a direct extension of the classical way of identifying these line defects with singularities of a unit vector field representing the nematic director. It is well known that the universally accepted Oseen-Frank energy is infinite for configurations that contain disclination line defects. We devise a natural augmentation of the Oseen-Frank energy to account for physical situations where, under certain conditions, infinite director gradients have zero associated energy cost, as would be necessary for modeling half-integer strength disclinations within the framework of the director theory. Equilibria and dynamics (in the absence of flow) of line defects are studied within the proposed model. Using appropriate initial/boundary data, the gradient-flow dynamics of this energy leads to non-singular, line defect equilibrium solutions, including those of half-integer strength. However, we demonstrate that the gradient flow dynamics for this energy is not able to adequately describe defect evolution. Motivated by similarity with dislocation dynamics in solids, a novel 2D-model of disclination dynamics in nematics is proposed. The model is based on the extended Oseen-Frank energy and takes into account thermodynamics and the kinematics of conservation of defect topological charge. We validate this model through computations of disclination equilibria, annihilation, repulsion, and splitting. We show that the energy function we devise, suitably interpreted, can serve as well for the modeling of equilibria and dynamics of dislocation line defects in solids making the conclusions of this paper relevant to mechanics of both solids and liquid crystals.
A microscopic continuum model for defect dynamics in metallic glasses
Amit Acharya Michael Widom
To appear in Journal of the Mechanics and Physics of Solids
Motivated by results of the topological theory of glasses accounting for geometric frustration,
we develop the simplest possible continuum mechanical model of defect dynamics in metallic
glasses that accounts for topological, energetic, and kinetic ideas. A geometrical description
of ingredients of the structure of metallic glasses using the concept of local order based on
Frank-Kasper phases and the notion of disclinations as topological defects in these structures is
proposed. This novel kinematics is incorporated in a continuum mechanical framework capable
of describing the interactions of disclinations and also of dislocations (interpreted as pairs of
opposite disclinations). The model is aimed towards the development of a microscopic understanding
of the plasticity of such materials. We discuss the expected predictive capabilities of
the model vis-a-vis some observed physical behaviors of metallic glasses.
[Call for abstracts] 3D Printed Soft Materials, ASME IMECE 2016
Dear Colleagues,
Please be reminded that this year IMECE runs with two abstract submission deadlines.
2017 ASME Congress invitation-Dynamic failure of advanced materials
Dr. Jun Xu and I organize one topic on “Dynamic failure of advanced materials (fatigue failure is included also)” for 2017 ASME Congress. Our keynote speakers include a senior program manager of US Office of Naval Research and a distinguished researcher of US Army Research Laboratory. We would invite you (also your colleagues and group members) to submit a short abstract before ASME’s deadline March 6. More details below:
ASME Conference: Constitutive Modeling of Biological Tissues
Dear Colleagues,
On behalf of the ASME Mechanics for Biology and Medicine Technical Committee and Constitutive Equations Technical Committee, I cordially invite you to submit an abstract to the following track:
12-9 Constitutive Modeling of Biological Tissues
The ASME/IMECE 2016 will be held from November 11 to November 17, 2016 in Phoenix, AZ (https://www.asme.org/events/imece)
Abstract submission deadline: March 07, 2016
Strain-induced programmable half-metal and spin-gapless semiconductor in an edge-doped boron nitride nanoribbon
Shuze Zhu* and Teng Li*, Strain-induced programmable half-metal and spin-gapless semiconductor in an edge-doped boron nitride nanoribbon, Physical Review B, 93, 115401 (2016)
Simpleware Boston Seminars: Wednesday Mar 16 2016
Introduction and Live Demo
3D Image Visualization, Analysis and Model Generation with Simpleware
Date: Wednesday, March 16, 2016
Time / Venue: 10:30am - 12:00pm: Boston Marriott Cambridge, 50 Broadway, Cambridge, MA 02142
Time / Venue: 2:00pm - 3:30pm: Regus Newton, Riverside Center, 275 Grove St #2, Newton, MA 02466
Who should attend