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Joshi Y.M.,Indian Institute of Technology Kanpur
Annual Review of Chemical and Biomolecular Engineering | Year: 2014

Many household and industrially important soft colloidal materials, such as pastes, concentrated suspensions and emulsions, foams, slurries, inks, and paints, are very viscous and do not flow over practical timescales until sufficient stress is applied. This behavior originates from restricted mobility of the constituents arrested in disordered structures of varying length scales, termed colloidal glasses and gels. Usually these materials are thermodynamically out of equilibrium, which induces a time-dependent evolution of the structure and the properties. This review presents an overview of the rheological behavior of this class of materials. We discuss the experimental observations and theoretical developments regarding the microstructure of these materials, emphasizing the complex coupling between the deformation field and nonequilibrium structures in colloidal glasses and gels, which leads to a rich array of rheological behaviors with profound implications for various industrial processes and products. © 2014 by Annual Reviews.

Upadhyay S.,Indian Institute of Technology Kanpur
Annals of Physics | Year: 2015

We consider effective actions of the cosmological Friedmann-Robertson-Walker (FRW) models and discuss their fermionic rigid BRST invariance. Further, we demonstrate the finite field-dependent BRST transformations as a limiting case of continuous field-dependent BRST transformations described in terms of continuous parameter κ. The Jacobian under such finite field-dependent BRST transformations is computed explicitly, which amounts an extra piece in the effective action within functional integral. We show that for a particular choice of a parameter the finite field-dependent BRST transformation maps the generating functional for FRW models from one gauge to another. © 2015 Elsevier Inc.

Upadhyay S.,Indian Institute of Technology Kanpur
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

The BRST quantizations of worldsheet gravity corresponding to final more acceptable derivative gauge and the standard conformal gauge are studied. We establish a mapping between these two gauges utilizing FFBRST formulation in standard way. Therefore, we are able to declare that the problems associated with Virasoro constraints are the gauge artifact. © 2014 The Author.

Mahesh S.,Indian Institute of Technology Kanpur
International Journal of Plasticity | Year: 2010

A model of a rigid-plastic rate-independent polycrystalline aggregate wherein sub-aggregates are represented as the nodes of a binary tree is proposed. The lowest nodes of the binary tree represent grains. Higher binary tree nodes represent increasingly larger sub-aggregates of grains, culminating with the root of the tree, which represents the entire polycrystalline aggregate. Planar interfaces are assumed to separate the sub-aggregates represented by nodes in the binary tree. Equivalence between the governing equations of the model and a standard linear program is established. The objective function of the linear program is given by the plastic power associated with polycrystal deformation and the linear constraints are given by compatibility requirements between the sub-aggregates represented by sibling nodes in the binary tree. The deviatoric part of the Cauchy stress in each sub-aggregate is deduced as linear combinations of the Lagrange multipliers associated with the constraints. It is shown that the present model allows a generalization of Taylor's principle to polycrystals. The proposed model is applied to simulate tensile, compressive, torsional, and plane-strain deformation of copper polycrystals. The predicted macroscopic response is in good agreement with published experimental data. The effect of the initial distribution of the planar interfaces separating the sub-aggregates represented by the binary tree on the predicted mechanical response in tension, compression and torsion is studied. Also, the role of constraints relaxation in simulations of plane strain compression is investigated in detail. © 2009 Elsevier Ltd. All rights reserved.

Chowdhury D.,Indian Institute of Technology Kanpur
Physics Reports | Year: 2013

A molecular motor is made of either a single macromolecule or a macromolecular complex. Just like their macroscopic counterparts, molecular motors "transduce" input energy into mechanical work. All the nano-motors considered here operate under isothermal conditions far from equilibrium. Moreover, one of the possible mechanisms of energy transduction, called Brownian ratchet, does not even have any macroscopic counterpart. But, molecular motor is not synonymous with Brownian ratchet; a large number of molecular motors execute a noisy power stroke, rather than operating as Brownian ratchet. We review not only the structural design and stochastic kinetics of individual single motors, but also their coordination, cooperation and competition as well as the assembly of multi-module motors in various intracellular kinetic processes. Although all the motors considered here execute mechanical movements, efficiency and power output are not necessarily good measures of performance of some motors. Among the intracellular nano-motors, we consider the porters, sliders and rowers, pistons and hooks, exporters, importers, packers and movers as well as those that also synthesize, manipulate and degrade "macromolecules of life". We review mostly the quantitative models for the kinetics of these motors. We also describe several of those motor-driven intracellular stochastic processes for which quantitative models are yet to be developed. In part I, we discuss mainly the methodology and the generic models of various important classes of molecular motors. In part II, we review many specific examples emphasizing the unity of the basic mechanisms as well as diversity of operations arising from the differences in their detailed structure and kinetics. Multi-disciplinary research is presented here from the perspective of physicists. © 2013 Elsevier B.V.

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