arXiv subjects

Rajarshi Roy

Publications and source records attributed to Rajarshi Roy.

79 records · Page 5Linked to original sources

arXiv2009

Adaptive synchronization of coupled chaotic oscillators

We experimentally demonstrate and numerically simulate a new adaptive method to maintain synchronization between coupled nonlinear chaotic oscillators, when the coupling between the systems is unknown and time-varying (e.g., due to environmental parameter drift). The technique is applied to optoelectronic feedback loops exhibiting high dimensional chaotic dynamics. In addition to keeping the two systems isochronally synchronized in the presence of a priori unknown time-varying coupling strength, the technique provides an estimate of the time-varying coupling.

nlin.CD↗

arXiv2009

Complex Dynamics and Synchronization of Delayed-Feedback Nonlinear Oscillators

We describe a flexible and modular delayed-feedback nonlinear oscillator that is capable of generating a wide range of dynamical behaviours, from periodic oscillations to high-dimensional chaos. The oscillator uses electrooptic modulation and fibre-optic transmission, with feedback and filtering implemented through real-time digital-signal processing. We consider two such oscillators that are coupled to one another, and we identify the conditions under which they will synchronize. By examining the rates of divergence or convergence between two coupled oscillators, we quantify the maximum Lyapunov exponents or transverse Lyapunov exponents of the system, and we present an experimental method to determine these rates that does not require a mathematical model of the system. Finally, we demonstrate a new adaptive control method that keeps two oscillators synchronized even when the coupling between them is changing unpredictably.

nlin.CD↗

arXiv2008

Using Synchronization for Prediction of High-Dimensional Chaotic Dynamics

We experimentally observe the nonlinear dynamics of an optoelectronic time-delayed feedback loop designed for chaotic communication using commercial fiber optic links, and we simulate the system using delay differential equations. We show that synchronization of a numerical model to experimental measurements provides a new way to assimilate data and forecast the future of this time-delayed high-dimensional system. For this system, which has a feedback time delay of 22 ns, we show that one can predict the time series for up to several delay periods, when the dynamics is about 15 dimensional.

nlin.CD↗

arXiv2007

Consistency in the driven butterfly

We study the consistency of the responses in the chaotic Lorenz model driven by chaotic and colored-noise signals. A measure is introduced for the consistency of the response in the system for repeated applications of the same drive signal, starting at different initial conditions of the response system. The convergence of responses is analyzed in dynamical phase space in terms of the local conditional Lyapunov exponent. The dependence of the local conditional Lyapunov exponent on drive signal, and the existence of multiple basins of consistency depending on strength of drive signal, are shown.

nlin.CD↗

arXiv2006

Isochronal synchrony and bidirectional communication with delay-coupled nonlinear oscillators

We propose a basic mechanism for isochronal synchrony and communication with mutually delay-coupled chaotic systems. We show that two Ikeda ring oscillators (IROs), mutually coupled with a propagation delay, synchronize isochronally when both are symmetrically driven by a third Ikeda oscillator. This synchronous operation, unstable in the two delay-coupled oscillators alone, facilitates simultaneous, bidirectional communication of messages with chaotic carrier waveforms. This approach to combine both bidirectional and unidirectional coupling represents an application of generalized synchronization using a mediating drive signal for a spatially distributed and internally synchronized multi-component system.

nlin.CD↗

arXiv2006

Delayed-mutual coupling dynamics of lasers: scaling laws and resonances

We consider a model for two lasers that are mutually coupled optoelectronically by modulating the pump of one laser with the intensity deviations of the other. Signal propagation time in the optoelectronic loop causes a significant delay leading to the onset of oscillatory output. Multiscale perturbation methods are used to describe the amplitude and period of oscillations as a function of the coupling strength and delay time. For weak coupling the oscillations have the laser's relaxation period, and the amplitude varies as the one-fourth power of the parameter deviations from the bifurcation point. For order-one coupling strength the period is determined as multiples of the delay time, and the amplitude varies with a square-root power law. Because we allow for independent control of the individual coupling constants, for certain parameter values there is an atypical amplitude-resonance phenomena. Finally, our theoretical results are consistent with recent experimental observations when the inclusion of a low-pass filter in the coupling loop is taken into account.

nlin.CD↗

arXiv2003

Taylor expansions in chemical potential

Properties of QCD at finite chemical potential are extracted using Taylor series expansions. The continuum limits of lattice results are presented. The result of expanding the free energy density, ie, the pressure, to 6th order in the expansion is shown. The Taylor coefficients of the chiral condensate are also shown. Relations between various Taylor coefficients are demonstrated. All this information is utilised to remove various lattice artifacts from the determination of the Wroblewski parameter in strangeness production.

nucl-th↗