Person: Tiwari, Mukesh
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Mukesh Tiwari
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079-68261614
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Nonequilibrium statistical mechanics and Nonlinear dynamics
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Mukesh Tiwari is currently working as an Associate Professor at DA-IICT. He joined the institute in 2009. Before this, he completed his M.Sc. in Physics from the Indian Institute of Technology, Delhi, and PhD from the University of New Mexico, working with Nitant Kenkre. His primary research interest is in complex networks, nonequilibrium statistical mechanics, and nonlinear dynamics. His current research directions focus on interdisciplinary sciences. He uses models and techniques originating in physics to understand phenomena and processes in social systems and complex time series arising in finance and physiology. His research also involves studying the properties of highly nonlinear waves in granular systems and transport phenomena in quantum and classical systems.
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Publication Metadata only Decorated Granular Layers for Impact Decimation(Spinger, 01-08-2016) Tiwari, Mukesh; Mohan, T R Krishna; Sen, Surajit; Tiwari, Mukesh; DA-IICT, GandhinagarWe present dynamical simulations and simple mechanics arguments to propose a system of stacked blocks of square lattices of elastic spheres that can be used to decimate an incident impulse. Mass mismatch between adjacent blocks is accomplished by making the sphere radius in the upper block twice that of the lower block. The system decimates impact energies by converting the initial impulse into two solitary waves and then progressively into many smaller amplitude solitary waves. We also show that near perfect impact decimation capability can be realized with increased mass mismatch between adjacent blocks by creating sandwiched structures in which a block with smaller density spheres is surrounded on both sides with blocks of denser spheres. The proposed systems are expected to be scalable down to spheres of�100�nm and work for solid and hollow spheres.Publication Metadata only Approach to equilibrium of a nondegenerate quantum system: decay of oscillations and detailed balance as separate effects of a reservoir(Springer, 01-04-2014) Kenkre, V M; Tiwari, Mukesh; DA-IICT, GandhinagarThe approach to equilibrium of a nondegenerate quantum system involves the damping of microscopic population oscillations, and, additionally, the bringing about of detailed balance, i.e. the achievement of the correct Boltzmann factors relating the populations. These two are separate effects of interaction with a reservoir. One stems from the randomization of phases and the other from phase space considerations. Even the meaning of the word �phase� differs drastically in the two instances in which it appears in the previous statement. In the first case it normally refers to quantum phases whereas in the second it describes the multiplicity of reservoir states that corresponds to each system state. The generalized master equation theory for the time evolution of such systems is here developed in a transparent manner and both effects of reservoir interactions are addressed in a unified fashion. The formalism is illustrated in simple cases including in the standard spin-boson situation wherein a quantum dimer is in interaction with a bath consisting of harmonic oscillators. The theory has been constructed for application in energy transfer in molecular aggregates and in photosynthetic reaction centers.Publication Metadata only Energy exchange calculations in a simple mechanical system to investigate the origin of friction(World Scientific, 30-03-2022) Iglesias, Maria Luján; Tiwari, Mukesh; Kenkre, V M; Gonçalves, Sebastian; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarThe microscopic origin of friction is an important topic in science and technology. To date, noteworthy aspects of it remain unsolved. In an effort to shed some light on the possible mechanisms that could give rise to the macroscopic emergence of friction, a very simple 1D system of two particles is considered, one of them is free but moving with an initial velocity, and the other confined by a harmonic potential. The two particles interact via a repulsive Gaussian potential. While it represents in a straightforward manner a tip substrate system in the real world, no analytic solutions can be found for its motion. Because of the interaction, the free particle (tip) may overcome the bound particle (substrate) losing part of its kinetic energy. We solve Newton�s equations of the two particles numerically and calculate the net exchange of energy in the asymptotic state in terms of the relevant parameters of the problem. The effective dissipation that emerges from this simple, classical model with no�ad hoc�terms shows, surprisingly, a range of rich, nontrivial, behavior. We give theoretical reasoning which provides a satisfactory qualitative description. The essential ingredient of that reasoning is that the transfer of energy from the incoming particle to the confined one can be regarded as the source of the emergent dissipation force the friction experienced by the incoming particle.Publication Metadata only Modeling the nonlinear effects of opinion kinematics in elections: A simple Ising model with random field based study(Elsevier, 15-11-2021) Tiwari, Mukesh; Yang, Xiguang; Sen, Surajit; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarInspired by partisan competitions and contentious elections in democratic countries, we numerically explore the effect of campaign strategies and related factors on the opinion of an electorate. The nature of the electorate is modeled through agents with different behaviors, such as, being conformist, contrarian or inflexible. The agents are assumed to take discrete opinion values that depend on both internal and external influences. The inhomogeneity of external influence on individuals is modeled as a random field. Two types of electorates have been considered. In an electorate with only conformist agents short-duration high impact campaigns are highly effective. These are, however, also sensitive to perturbations at the local level modeled as inflexibles and/or absentees. In electorates with both conformist and contrarian agents and varying level of dominance due to local factors, short-term campaigns are effective only in the case of fragile dominance of a single party. Strong local dominance is relatively difficult to influence and long term campaigns with strategies aimed to impact local level politics are seen to be more effective.Publication Metadata only Foreword to this special issue(World Scientific, 30-03-2022) Giuggioli, Luca; Tiwari, Mukesh; Sen, Surajit; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarThis foreword is to introduce the reason for this special issue of the journal. Professor Vasudev Mangesh (Nitant) Kenkre has had a distinguished career as a statistical physicist, teacher, educator and a magnet for a great many statistical physicists from around the world across nearly five decades. This volume is to celebrate Nitant�s work. The contributors are mostly his former students, friends and collaborators. This foreword captures a fraction of what Nitant means to us.Publication Metadata only Identification of topological measures of visibility graphs for analyzing transitions in complex time series(World Scientific, 30-03-2022) Tiwari, Mukesh; Wong, Yiu-Man; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarWe present a super-resolution technique where the 3-D shape preservation is used as a constraint while super-resolving a scene. Given the observations under different illuminant positions, we combine these observations to obtain the super-resolved image and the spatially enhanced scene structure simultaneously. The use of shape cue in the form of photometric measurements, instead of the motion cue, eliminates the need for image registration with a sub-pixel accuracy. We model the high-resolution image, the structure, and the albedo of the surface as separate Markov random fields and super-resolve them using a suitable regularization scheme. Results of the experimentation on real data are presented.Publication Metadata only Impact Dispersion Using 2D and 3D Composite Granular Packing(KONA, 01-07-2017) Sen, Surajit; Mohan, T R Krishna; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarWe present a study of efficient dispersion of an impact onto structured and potentially scalable granular beds. We use discrete element method based dynamical simulations of shock wave propagation and dispersion in 2D and 3D arrangements of granular spheres. The spheres are geometrically packed in a nested columnar structure, which leads to the severe attenuation and spreading of the incident energy within the structure. We further show that by incorporating inhomogeneity in material properties, or by introducing layers of a dissimilar material in the middle of the arrangement, impact mitigation can be enhanced significantly. Such an arrangement can therefore be useful in the design of effective impact decimation systems. Using a 2D arrangement we first show the basic idea behind impact dispersion in such an arrangement. With this understanding the system is scaled to 3D. The influence of the system size and material properties on the wave propagation within the packing is also presented. Fullsize ImagePublication Metadata only Resonance effects in the nonadiabatic nonlinear quantum dimer(Springer, 04-05-2011) Tiwari, Mukesh; Seletskiy, D V; Kenkre, V M; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarThe quantum nonlinear dimer consisting of an electron shuttling between two sites and in�weak�interaction with vibrations, is studied numerically under the application of a DC electric field. A field-induced resonance phenomenon between the vibrations and the electronic oscillations is found to influence the electronic transport greatly. For initial delocalization of the electron, resonance has the effect of a dramatic increase in the transport. Nonlinear frequency mixing is identified as the main mechanism that influences transport. A characterization of the frequency spectrum is also presented.Publication Metadata only Drag-force regimes in granular impact(APS Publishing, 01-12-2014) Tiwari, Mukesh; Mohan, T R Krishna; Sen, Surajit; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarWe study the penetration dynamics of a projectile incident normally on a substrate comprising of smaller granular particles in three-dimensions using the discrete element method. Scaling of the penetration depth is consistent with experimental observations for small velocity impacts. Our studies are consistent with the observation that the normal or drag force experienced by the penetrating grain obeys the generalized Poncelet law, which has been extensively invoked in understanding the drag force in the recent experimental data. We find that the normal force experienced by the projectile consists of position and kinetic-energy-dependent pieces. Three different penetration regimes are identified in our studies for low-impact velocities. The first two regimes are observed immediately after the impact and in the early penetration stage, respectively, during which the drag force is seen to depend on the kinetic energy. The depth dependence of the drag force becomes significant in the third regime when the projectile is moving slowly and is partially immersed in the substrate. These regimes relate to the different configurations of the bed: the initial loose surface packed state, fluidized bed below the region of impact, and the state after the crater formation commences.Publication Metadata only Impact decimation using alignment of granular spheres(World Scientific, 01-04-2017) Tiwari, Mukesh; Mohan, T R Krishna; Sen, Surajit; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; Tiwari, Mukesh; DA-IICT, GandhinagarSolitary waves in alignment of elastic beads have been an important area of study. An important and rich area has been the behavior of solitary waves at a boundary, where features such as localization, anomalous behavior in scattering and transmission, quasiequilibrium phase, etc. are being studied. An application area of significance is the design of artificial granular alignments for shock decimation and dispersion. In this review article, we first present a summary and background of these unique features, and some designs in 1D which exploit these features. We further discuss some extensions to higher dimensional systems and their impact decimation ability.