S. Santucci

PHASE-SHIFTS IN BISTABLE EPR SYSTEMS AT STOCHASTIC RESONANCE

Abstract The stochastic resonance phenomenon in a periodically modulated bistable EPR system is discussed with focus on the phase-shift ΔΦ between the periodic forcing term and the system response. A theoretical interpretation of the experimental observations is proposed.

Extraction of periodic signals from a noise background

Abstract A simple technique for extracting periodic signals from a noise background is proposed and tested. A selective amplifier circuit has been realized accordingly, which is capable of resolving low-frequency periodic components in short signal samples.

Thermally activated escape controlled by colored multiplicative noise

Abstract Thermally driven escape over a barrier which fluctuates with Gaussian statistics is studied by means of analog simulation. The phenomenon of resonant activation [C.R. Doering and J.C. Gadoua, Phys. Rev. Lett. 69 (1992) 2318] occurs when the correlation-time of the barrier fluctuations is increased without changing the amplitude. The dependence of the relevant escape time on the fluctuation variance exhibits a number of properties, independent of the potential shape, which eluded previous investigations.

STOCHASTIC RESONANCE WITHOUT SYMMETRY-BREAKING

Abstract Stochastic resonance in a bistable potential is characterized as a resonant synchronization effect of the random hopping mechanism. Most notably, synchronization may occur even in the absence of a coherent drive.

Switch-phase distributions and stochastic resonance

Abstract The de-synchronization mechanism that occurs for noise intensities above stochastic resonance is analyzed in terms of switch-time and switch-phase distributions. In particular, we observed that (i) the switch-time distributions exhibit thicker peak structures with maxima at the multiples (both odd and even) of the half forcing period; (ii) the switch-phase distributions are doubly peaked, being dominated by the in-phase and π out-of-phase events. The appearance of these properties of the switch statistics is discussed on the grounds of numerical simulations.

Statistical properties of nonlinear systems driven by band-limited noise

Abstract Stochastic relaxation in a strongly nonlinear one-dimensional potential driven by band-limited noise is investigated by means of analogue simulation. On suitably high-pass filtering the stochastic process under study, intermittent bursts become observable. Most statistical properties related with this phenomenon appear to be universal, i.e. independent of the noise statistics, over a wide frequency range.

A new definition of stochastic resonance

SummaryStochastic resonance in a bistable potential is characterized as a syncronization effect of the hopping mechanism induced by the external periodic bias. Most notably, syncronization is shown i) to attain a maximum with increasing the forcing frequency close to the relevant switching rate, thus revealing abona fide resonant process; ii) to occur even in the absence of symmetry breaking by the periodic forcing term.

Stochastic Resonance in Paramagnetic Resonance Systems

Experimental evidence of the stochastic resonance phenomenon in an electron paramagnetic resonance (EPR) system is reported. The amplitude and phase response of the EPR system operating in bistable conditions are measured for increasing values of the noise intensity. Theoretical predictions based on a simple dynamical model for the relevant system observables are shown to be in good agreement with experimental results.

Intermittency in nonlinear stochastic systems

Abstract A nonlinear system driven by band-limited Gaussian noise is shown to exhibit intermittent dynamics. The existence of intermittent bursts is revealed by high-pass filtering the system response with cut-on frequency where the random force vanishes. The statistics of stationary intermittency, i.e. the amplitude and time distribution of the bursts, is determined in detail by analogue simulation of a simple monostable system, the quartic oscillator, in the limit of strong nonlinearity.

Escape rates in underdamped bistable potentials driven by coloured noise

Abstract The brownian motion in a quartic double-well potential driven by coloured noise is investigated in the low-viscosity limit by means of analogue simulation. The dependence of the escape rate on the noise correlation-time τ is determined for the conditions simulated: the escape rate decreases exponentially with increasing τ 2 . The relevant law is derived theoretically in the limit of vanishingly small viscosity and high potential barriers.