Browsing by Author "Alexeeva, Nora"

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    The direct scattering study of the parametrically driven nonlinear Schrödinger equation
    (2013) Olivier, Carel Petrus; Alexeeva, Nora
    Includes abstract. Includes bibliographical references.
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    Solitons, spatiotemporal chaos and synchronization in arrays of damped driven nonlinear oscillators
    (2008) Robinson, William Michael Lewin; Barashenkov, Igor; Alexeeva, Nora
    Simulating the homogeneous chain, we demonstrate the existance of periodically oscillating solitons, the period-doubling sequence of transitions to temporal chaos and the degeneration into spatiotemporal chaos for larger driving strengths. Next, we explore the effect of introducing weak disorder in the simplest form, a single impurity, into the chain. We describe how a long impurity can induce a pinned soliton to form and prevent spatiotemporal chaos, synchronizing the oscillators in the chain. Lastly we study chains with several impurities in various configurations.
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    Solitons,spatiotemporal choas and synchronization in arrays of damped driven nonlinear oscillators
    (2008) Robinson,WML; Barashenkov, Igor; Alexeeva, Nora
    We explore periodic and chaotic motion in a soliton-bearing chain of nonlinear oscillators and study the effect of disorder on the spatiotemporal chaos. The chain we consider consists of torsionally coupled, damped, parametrically driven pendulums. We show that the amplitudes of the pendulums satisfy a system of equations in slow time, the "nonlinear Schrodinger (NLS) oscillators". The evolution of the chain of NLS oscillators is simulated numerically. Simulating the homogeneous chain, we demonstrate the existence of periodically oscillating solitons, the period-doubling sequence of transitions to temporal chaos and the degeneration into spatiotemporal chaos for larger driving strengths. ~ext, we explore the effect of introducing weak disorder in the simplest form, a single impurity, into the chain. We describe how a long impurity can induce a pinned soliton to form and prevent spatiotcmporal chaos, synchronizing the oscillators in the chain. Lastly, we study chains with several impurities in various configurations. Cases considered include chains with multiple impurities of different strengths, equal equidistant impurities (both long and short), and equal impurities which are positioned randomly along the chain. vVe show that all the previously reported features of the continuous NLS equation are reproduced in the dynamics of the discrete chain. Our results indicate that the dominant structures of the spatiotemporal chaos are unstable solitons. We show how spatiotemporally chaotic motion can be suppressed by disordering the chain through the inclusion of one or more impurities, synchronizing the oscillators. A comprehensive analysis of chains with identical equidistant long impu- rities reveals an unexpectedly complex relationship between the number and strength of impurities and the dynamics observed. As a result of disordering the positions of impurities, we find that oscillatiug solitons form between impurities when the gaps are large enough. The oscillations may be periodic or chaotic. Equidistant short impurities may also stabilize the chain. We conclude that for a 8et of irnpuritie8 to prevent spatiotemporal chaos from emerging in the array, the intervals between the impurities should be sufficiently small, and the stre11gth of the impuritic8 should be sufficiently large. The required number and strength of impurities depends on the oscillator parameters and the initial condition of the chain.
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