Browsing by Author "Roy, S."
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Item A Multiscale Model to Study the Enhancement in the Compressive Strength of Multi-Walled CNT Sheet Overwrapped Carbon Fiber Composites(Elsevier Ltd) Ravindranath, P. K.; Roy, S.; Unnikrishnan, V.; Wang, X.; Xu, Tingge; Baughman, Ray H.; Lu, Hongbing; 0000-0001-5845-5137 (Baughman, RH); Xu, Tingge; Baughman, Ray H.; Lu, HongbingThe high tensile strength of polymer matrix composites is derived primarily from the high strength of the carbon fibers embedded in the polymer matrix. However, their compressive strength is generally much lower due to the fact that under compression, the fibers tend to fail through micro-buckling well before compressive fracture occurs. In this work, we consider multi-walled carbon nanotube (MWNT) sheets wrapped around carbon fiber at room temperature to improve fiber/matrix interfacial properties which, in turn, influences compressive strength of the composite. To investigate the effect of the wrapping of MWNT sheet on composite strength, Molecular Dynamics simulations were performed on an atomistic model of the interface region between the epoxy, carbon fiber and the scrolled MWNT sheets. The compressive strength of the unidirectional composite was computed using a novel hierarchical multi-scale model comprising of the rule of mixtures at the microscale, and the modified Argon's formula for composites at the macroscale. Model predictions were benchmarked through comparison with experimental data for different volume fractions of MWNT sheet. ©2019 Elsevier LtdItem Landau Levels, Bardeen Polynomials, and Fermi Arcs in Weyl Semimetals: Lattice-Based Approach to the Chiral Anomaly(American Physical Society) Behrends, J.; Roy, S.; Kolodrubetz, Michael H.; Bardarson, J. H.; Grushin, A. G.; 0000-0001-5628-3300 (Kolodrubetz, M); Kolodrubetz, Michael H.Condensed matter systems realizing Weyl fermions exhibit striking phenomenology derived from their topologically protected surface states as well as chiral anomalies induced by electromagnetic fields. More recently, inhomogeneous strain or magnetization were predicted to result in chiral electric E₅ and magnetic B₅ fields, which modify and enrich the chiral anomaly with additional terms. In this Rapid Communication, we develop a lattice-based approach to describe the chiral anomaly, which involves Landau and pseudo-Landau levels and treats all anomalous terms on equal footing, while naturally incorporating Fermi arcs. We exemplify its potential by physically interpreting the largely overlooked role of Fermi arcs in the covariant (Fermi level) contribution to the anomaly and revisiting the factor of 1/3 difference between the covariant and consistent (complete band) contributions to the E₅·B₅ term in the anomaly. Our framework provides a versatile tool for the analysis of anomalies in realistic lattice models as well as a source of simple physical intuition for understanding strained and magnetized inhomogeneous Weyl semimetals. ©2019 American Physical Society.