Deterministic SR in a Piecewise Linear Chaotic Map

The phenomenon of Stochastic Resonance (SR) is observed in a completely deterministic setting - with thermal noise being replaced by one-dimensional chaos. The piecewise linear map investigated in the paper shows a transition from symmetry-broken to symmetric chaos on increasing a system parameter. In the latter state, the chaotic trajectory switches between the two formerly disjoint attractors, driven by the map's inherent dynamics. This chaotic switching rate is found to `resonate' with the frequency of an externally applied periodic perturbation (multiplicative or additive). By periodically modulating the parameter at a specific frequency $\omega$, we observe the existence of resonance where the response of the system (in terms of the residence-time distribution) is maximum. This is a clear indication of SR-like behavior in a chaotic system.Comment: 6 pages LaTex, 4 figure

Statistical mechanics of money: How saving propensity affects its distribution

We consider a simple model of a closed economic system where the total money is conserved and the number of economic agents is fixed. In analogy to statistical systems in equilibrium, money and the average money per economic agent are equivalent to energy and temperature, respectively. We investigate the effect of the saving propensity of the agents on the stationary or equilibrium money distribution.The equilibrium probablity distribution of money becomes the usual Gibb's distribution, characteristic of non-interacting agents, when the agents do not save. However with saving, even for local or individual self-interest, the dynamics become cooperative and the resulting asymmetric Gaussian-like stationary distribution acquires global ordering properties. Intriguing singularities are observed in the stationary money distribution in the market, as function of the ``marginal saving propensity'' of the agents.Comment: 9 pages, 5 figures. Revised version with major changes in the text and figures (to appear in Euro. Phys. Jour. B

Dynamic transitions and hysteresis

When an interacting many-body system, such as a magnet, is driven in time by an external perturbation, such as a magnetic field,the system cannot respond instantaneously due to relaxational delay. The response of such a system under a time-dependent field leads to many novel physical phenomena with intriguing physics and important technological applications. For oscillating fields, one obtains hysteresis that would not occur under quasistatic conditions in the presence of thermal fluctuations. Under some extreme conditions of the driving field, one can also obtain a non-zero average value of the variable undergoing such dynamic hysteresis. This non-zero value indicates a breaking of symmetry of the hysteresis loop, around the origin. Such a transition to the spontaneously broken symmetric phase occurs dynamically when the driving frequency of the field increases beyond its threshold value which depends on the field amplitude and the temperature. Similar dynamic transitions also occur for pulsed and stochastically varying fields. We present an overview of the ongoing researches in this not-so-old field of dynamic hysteresis and transitions.Comment: 30 Pages Revtex, 10 Postscript figures. To appear in Reviews of Modern Physics, April, 199