• A N Njah

      Articles written in Pramana – Journal of Physics

    • Synchronization and basin bifurcations in mutually coupled oscillators

      U E Vincent A N Njah O Akinlade

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      Synchronization behaviour of two mutually coupled double-well Duffig oscillators exhibiting cross-well chaos is examined. Synchronization of the subsystems was observed for coupling strength $k > 0.4$. It is found that when the oscillators are operated in the regime for which two attractors coexist in phase space, basin bifurcation sequences occur leading to $n + 1$, $n \geq 2$ basins as the coupling is varied – a signature of Wada structure and final-state sensitivity. However, in the region of complete synchronization, the basins structure is identical with that of the single oscillators and retains its essential features including fractal basin boundaries.

    • Global chaos synchronization of coupled parametrically excited pendula

      O I Olusola U E Vincent A N Njah

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      In this paper, we study the synchronization behaviour of two linearly coupled parametrically excited chaotic pendula. The stability of the synchronized state is examined using Lyapunov stability theory and linear matrix inequality (LMI); and some sufficient criteria for global asymptotic synchronization are derived from which an estimated critical coupling is determined. Numerical solutions are presented to verify the theoretical analysis. We also examined the transition to stable synchronous state and show that this corresponds to a boundary crisis of the chaotic attractor.

    • Collision frequency of Lennard–Jones fluids at high densities by equilibrium molecular dynamics simulation

      G A Adebayo B C Anusionwu A N Njah O J Adeniran B Mathew R S Sunmonu

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      Detailed classical molecular dynamics simulation of transport coefficients and collision frequencies at high densities in rare gases are presented in this paper with a view to investigate the likely cause of discrepancy between theory and experiments. The results, when compared with experiments, showed an underestimation of the viscosity calculated through the Green–Kubo formalism, but the results are in agreement with some other calculations performed by other groups. The origin of the underestimation was considered in the present work. Analyses of the transport coefficients showed a very high collision frequency which suggested that an atom might spend much less time in the neighbourhood of the fields of force of another atom. The distribution of atoms in the systems adjusts itself to a nearly Maxwellian type that resulted in a locally and temporarily slowly varying temperature. We showed that during collision, the time spent by an atom in the fields of force of other atoms is so small compared with its relaxation time, leading to a possible reduction in local velocity autocorrelation between atoms.

    • Function projective synchronization of identical and non-identical modified finance and Shimizu–Morioka systems

      S R Kareem K S Sojo A N Njah

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      In this paper, function projective synchronizations (FPS) of identical and non-identical modified finance systems (MFS) and Shimizu-Morioka system (S-MS) are studied via active control technique. The technique is applied to construct a response system which synchronizes with a given drive system for a desired function relation between identical MFS, identical S-MS and between MFS and S-MS. The results are validated via numerical simulations.

    • Comparison of backstepping and modified active control in projective synchronization of chaos in an extended Bonhöffer–van der Pol oscillator

      K S Ojo A N Njah S T Ogunjo

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      In this article, projective synchronization of double–scroll attractor of an extended Bonöffer–van der Pol oscillator (BVPO) is considered via the backstepping and active control techniques. In each synchronization scheme, a single control function is designed to achieve projective synchronization between two Bonhöffer–van der Pol oscillator evolving from different initial conditions. To obtain a single control function via the active control, the coefficient of the error dynamics is chosen such that the number of control functions is reduced from three to one, thereby, reducing control function complexity in design. The results show that the transient error dynamics convergence and synchronization time are achieved faster via the backstepping than that of the active control technique. However, the control function obtained via the active control is simpler with a more stable synchronization time and hence, it is more suitable for practical implementation. Numerical simulations are presented to confirm the effectiveness of the analytical results.

    • Increased-order generalized synchronization of chaotic and hyperchaotic systems

      K S Ojo S T Ogunjo A N Njah I A Fuwape

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      This paper presents increased-order generalized synchronization (GS) of chaotic and hyperchaotic systems with different order based on active control technique. By this technique, we design suitable control functions to achieve GS between (i) a new three-dimensional (3D) chaotic system and four-dimensional (4D) hyperchaotic Lorenz system and (ii) four-dimensional hyperchaotic Lorenz system and five-dimensional (5D) hyperchaotic Lorenz system. The corresponding numerical simulation results are presented to verify the effectiveness of this technique.

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