Biomedical subjects
Publications and source records attributed to Ronald F. Fox.
Gibbs entropy is invariant for the Baker map. A Jordan basis spectral decomposition of the Baker Frobenius-Perron operator suggests that any initial density evolves to the stationary density that has maximal entropy. This entropy conundrum is resolved by considering the difference between weak and strong convergence. A binary representation is used to make these points transparent. (c) 1998 American Institute of Physics.
The Jordan canonical form basis states for an invertible chaotic map, the Baker map, are constructed. A straightforwardly obtained recursion formula is presented for construction of the Jordan states and of the spectral decomposition of the Frobenius-Perron evolution operator. Comparison of this method with earlier, subdynamics techniques demonstrates that it is much more direct and simpler. The physical significance of the Jordan states is approached from the point of view of an entropy evolution equation. The method is also applied to the Bernoulli map, yielding its eigenstates more straightforwardly than done previously. (c) 1997 American Institute of Physics.
Simple chaotic maps are used to illustrate the inherent instability of trajectory solutions to the Frobenius-Perron equation. This is demonstrated by the difference in the behavior of delta-function solutions and of extended densities. Extended densities evolve asymptotically and irreversibly into invariant measures on stationary attractors. Pointwise trajectories chaotically roam over these attractors forever. Periodic Gaussian distributions on the unit interval are used to provide insight. Viewing evolving densities as ensembles of unstable pointwise trajectories gives densities a stochastic interpretation. (c) 1995 American Institute of Physics.
A detailed study of the effects of quantum fluctuations in a chaotic single mode laser is presented. It has been well established that the linear noise approximation eventually becomes invalid for the case of chaotic dynamics. A more accurate description of the laser is achieved through use of nonlinear Langevin equations. Simple expressions for the time evolution of the phases of the electric field and polarization are derived. These expressions predict that chaotic dynamics will greatly enhance phase diffusion. This prediction is verified through numerical simulations. A quantitative method, for determining the amount of amplification of quantum noise by chaos is discussed. This method makes use of a metric introduced in symbolic dynamics. The fluctuations are shown to have been amplified by over two orders of magnitude, making them macroscopically visible.
Macroscopic systems (e.g., hydrodynamics, chemical reactions, electrical circuits, etc.) manifest intrinsic fluctuations of molecular and thermal origin. When the macroscopic dynamics is deterministically chaotic, the intrinsic fluctuations may become amplified by several orders of magnitude. Numerical studies of this phenomenon are presented in detail for the Lorenz model. Amplification to macroscopic scales is exhibited, and quantitative methods (binning and a difference-norm) are presented for measuring macroscopically subliminal amplification effects. In order to test the quality of the numerical results, noise induced chaos is studied around a deterministically nonchaotic state, where the scaling law relating the Lyapunov exponent to noise strength obtained for maps is confirmed for the Lorenz model, a system of ordinary differential equations.