• DHARMENDRA KUMAR

      Articles written in Pramana – Journal of Physics

    • Pressure- and orientation-dependent elastic and ultrasonic characterisation of wurtzite boron nitride

      CHANDRESHVAR PRASAD YADAV DHARMENDRA KUMAR PANDEY

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      The present study discloses the evaluation of second-order elastic constants of wurtzite boron nitride(w-BN) at room temperature and at different pressures using the many-body interaction potential model approach. Orientation- and pressure-dependent ultrasonic velocity, thermal relaxation time and other related thermophysical parameters (Debye temperature, Debye average velocity, specific heat and thermal energy density) are also calculated using the evaluated second-order elastic constants. The orientation-dependent thermal relaxation time of w-BN is predominantly affected by the Debye average velocity and is indirectly governed by second-order elastic constants. Thermal relaxation time of w-BN is found to decrease with pressure. Calculated elastic and ultrasonic properties of w-BN are compared with the properties of other wurtzite structured materials for a complete analysis and characterisation of the material.

    • Computational soliton solutions to (2 + 1)-dimensional Pavlov equation using Lie symmetry approach

      SACHIN KUMAR MUKESH KUMAR DHARMENDRA KUMAR

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      In this work, Lie symmetry analysis and one-dimensional optimal system for Pavlov equation are presented. All the possible vector fields, their commutative and adjoint relations are carried out under invariance property of Lie group theory. On the basis of optimal system, similarity reductions of Pavlov equation are obtained. A repeated process of similarity reductions transforms the Pavlov equation into ordinary differential equations, which generate invariant solutions. The obtained invariant solutions are supplemented by numerical simulation toanalyse the physical behaviour. Thus, their parabolic, multisoliton, nonlinear, kink and antikink wave profiles are traced in results and discussions sections.

    • Lie symmetry analysis, abundant exact solutions and dynamics of multisolitons to the (2 + 1)-dimensional KP-BBM equation

      SACHIN KUMAR DHARMENDRA KUMAR HARSHA KHARBANDA

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      In the present article, our main aim is to construct abundant exact solutions for the (2+1)-dimensional Kadomtsev–Petviashvili-Benjamin–Bona–Mahony (KP-BBM) equation by using two powerful techniques, the Lie symmetry method and the generalised exponential rational function (GERF) method with the help of symbolic computations via Mathematica. Firstly, we have derived infinitesimals, geometric vector fields, commutation relations and optimal system. Therefore, the KP-BBM equation is reduced into several nonlinear ODEs under two stages of symmetry reductions. Furthermore, abundant solutions are obtained in different shapes of single solitons, solitary wave solutions, quasiperiodic wave solitons, elastic multisolitons, dark solitons and bright solitons, which are more relevant, meaningful and useful to describe physical phenomena due to the existence of free parameters and constants. All these generated exact soliton solutions are new and completely different from the previous findings. Moreover, the dynamical behaviour of the obtained exact closed-form solutions is analysed graphically by their 3D, 2D-wave profiles and the corresponding density plots by using the mathematical software, which will be comprehensively used to explain complex physical phenomena in the fields of nonlinear physics, plasma physics, optical physics, mathematical physics, nonlinear dynamics, etc.

    • Generalised exponential rational function method for obtaining numerous exact soliton solutions to a (3 + 1)-dimensional Jimbo–Miwa equation

      SACHIN KUMAR DHARMENDRA KUMAR

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      In this work, we apply the generalised exponential rational function (GERF) method on an extended (3+1)-dimensional Jimbo–Miwa (JM) equation which describes the modelling of water waves of long wavelength with weakly nonlinear restoring forces and frequency dispersion. This JM equation is also used to construct modelling waves in ferromagnetic media and two-dimensional matter-wave pulses in Bose–Einstein condensates. The main purpose is to construct analytical wave solutions for the (3+1)-dimensional JM equation by utilising theGERF method with the help of symbolic computations.We have also presented three-dimensional plots to observe the dynamics of obtained results. To understand physical phenomenon through different shapes of solitary waves,we discussed solitons, the interaction of multiwave solitons, lump-type solitons and kink-type solutions.

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