• SANJAY KUMAR

      Articles written in Pramana – Journal of Physics

    • Computer calculation of positron drift velocities in He, Ne and Ar

      P S Grover Sanjay Kumar K V Sinha

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      The drift velocities of positrons in rare gases, He, Ne and Ar have been calculated at various temperatures. The drift velocity depends quite sensitively on the strength of the electric field and temperature.

    • Cosmological models consistent with supersymmetric compactiflcation of superstring theories

      Sanjay Kumar S Mahajan A Mukherjee N Panchapakesan R P Saxena

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      The compactification of 10-dimensional supergravity, coupled to super Yang-Mills theory, to curved 4-dimensional spacetimes is investigated. The requirement of unbroken supersymmetry leads to a set of consistency conditions. These are fairly restrictive, but nevertheless permit some nontrivial solutions, including the Milne universe. More general time-dependent metrics are also not ruled out.

    • Surface adsorption and collapse transition of linear polymer chains

      Yashwant Singh Sanjay Kumar Debaprasad Giri

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      The critical behaviour of surface adsorption and collapse transition of a flexible self-attracting self-avoiding polymer chain is examined. Depending upon the underlying lattice and space dimensionality, phase diagrams that exhibit many different universality domains of critical behavior are found. We discuss these phase diagrams and the values of the critical exponents found from different theoretical methods.

    • Multifractal behaviour of n-simplex lattice

      Sanjay Kumar Debaprasad Giri Sujata Krishna

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      We study the asymptotic behaviour of resistance scaling and fluctuation of resistance that give rise to flicker noise in an n-simplex lattice. We propose a simple method to calculate the resistance scaling and give a closed-form formula to calculate the exponent, βL, associated with resistance scaling, for any n. Using current cumulant method we calculate the exact noise exponent for n-simplex lattices.

    • Brief report: Volume dependence of Grüneisen parameter for solids under extreme compression

      SANJAY KUMAR S K SHARMA O P PANDEY

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      The Nie expression is amended in such a way that the expression follows the infinite pressure behaviour, i.e., P → ∞or V → 0. A new empirical relationship is developed to predict the values of volume dependence of Grüneisen parameter. NaCl and ε-Fe have been employed to test the suitability of the expression.The results obtained reveal that the relationship is reliable as there is a good agreement between the calculated and the experimental data

    • Perturbation method for calculating impurity binding energy in an inhomogeneous cylindrical quantum dot with dielectric mismatch

      NILANJAN SIL NIBEDITA DARIPA ACHINT KAPOOR SANJAY KUMAR DEY

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      In the present paper, we have studied the binding energy of the shallow donor hydrogenic impurity, which is confined in an inhomogeneous cylindrical quantum dot (CQD) of $\rm{GaAs-Al_{x}Ga_{1−x}As}$. Perturbation method is used to calculate the binding energy within the framework of effective mass approximation and taking into account the effect of dielectric mismatch between the dot and the barrier material. The ground-state binding energy of the donor is computed as a function of dot size for finite confinement. The result shows that the ground-state binding energy decreases with the increase in dot size. The result is compared with infinite dielectric mismatch as a limiting case. The binding energy of the hydrogenic impurity is maximum for an on-axis donor impurity.

    • Study of chaos in chaotic satellite systems

      AYUB KHAN SANJAY KUMAR

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      In this paper,we study the qualitative behaviour of satellite systems using bifurcation diagrams, Poincaré section, Lyapunov exponents, dissipation, equilibrium points, Kaplan–Yorke dimension etc. Bifurcation diagrams with respect to the known parameters of satellite systems are analysed. Poincaré sections with different sowing axes of the satellite are drawn. Eigenvalues of Jacobian matrices for the satellite system at different equilibrium points are calculated to justify the unstable regions. Lyapunov exponents are estimated. From these studies, chaosin satellite system has been established. Solution of equations of motion of the satellite system are drawn in the form of three-dimensional, two-dimensional and time series phase portraits. Phase portraits and time series display the chaotic nature of the considered system.

    • Analysis and time-delay synchronisation of chaotic satellite systems

      AYUB KHAN SANJAY KUMAR

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      In this paper, we analyse the chaotic satellite system using dissipativity, equilibrium points, bifurcation diagrams, Poincare section maps, Lyapunov exponents and Kaplan–Yorke dimension. We obtain the equilibrium points of chaotic satellite system and at each equilibrium point, we obtain the eigenvalue of Jacobian matrix of the satellite system to verify the unstable region.We calculate the Kaplan–Yorke dimension, which ensures the strange behaviour of the system. We observe closely the three-dimensional (3D) phase portraits of the satellite system at different parameter values. We plot the Lyapunov exponent graphs corresponding to every 3D phase portrait of satellite systems, to verify the chaoticity of satellite systems. We establish time-delay synchronisation for twoidentical satellite systems. The simulated and qualitative results are in an excellent agreement.

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