Biomedical subjects
Publications and source records attributed to C Nicolis.
The principal signatures of a deterministic dynamics in the statistical properties of extreme events are identified. Explicit expressions are derived for generic classes of dynamical systems giving rise to quasiperiodic, strongly chaotic, and intermittent chaotic behaviors.
The early stages of the microphysics of the electrification process within a cloud are considered using a two-dimensional lattice model. Using insights generated from Monte Carlo simulations and the theory of finite Markov processes, the mean walk length statistics of the particles, the instantaneous electric potential and electric field profiles, the time evolution of electrostatic energy and their dependence on system size are studied. Some unexpected features of the kinetics of electrification and of the statistics of crossings of the threshold for an electric discharge to occur are brought out.
The response of a bistable dynamical system to a deterministic forcing is studied with emphasis on the kinetics of the passage across the barrier separating the two states, and compared to classical Kramers' theory describing the response to a Gaussian white noise forcing. The existence of nontrivial thresholds for the occurrence of transitions is established. Analytic results complemented by numerical simulations are derived for the characteristics of these transitions for periodic and chaotic forcings. The probabilistic properties of the response are finally addressed and some connections are established with the universal stable distributions of probability theory.
We study the dynamics of the first two moments and of threshold crossings by the stochastic trajectory in dichotomous diffusion x=xi(t), where xi(t) is a dichotomous Markov process. The transition rate of the latter is regarded as a control parameter and allowed to have specified time variations. The stabilizing or destabilizing effect of this variation is demonstrated, and qualitative changes in the statistical properties of the system are shown to occur. The analysis is then extended to linear dichotomous flow, and to a generalization of dichotomous diffusion in which x is driven by a multilevel Markov noise.
A bistable system subjected to noise and a slow increase of the parameter controlling the instability is studied, with emphasis on the kinetics of the transitions across the barrier separating the stable states. It is shown that the presence of a ramp in the control parameter may considerably affect the distribution of probability mass on the two sides of the barrier as compared to the predictions of the classical Kramers theory.
INTRODUCTION AND OBJECTIVES: Intracavernosal injection (ICI) of vasoactive agents has been successfully used in the treatment of erectile dysfunction (ED). The authors' pharmacologic erection program, using a fixed combination of prostaglandin E1 (PGE1) and papaverine, is notable for its simplicity and acceptance by patients who have suffered spinal cord injuries (SCIs). METHODS: Patients undergo baseline questionnaire, physical examination, and hormone profile followed by instruction and injection of a fixed combination of PGE1 and papaverine. On successive visits, the patient injects himself and the dosage is titrated until a satisfactory erection is obtained. Patients who do not respond to injection of 1.0 cc are considered treatment failures. Patients return periodically for routine follow-up. RESULTS: From May 1994 to March 1997, 37 patients with SCI underwent initial evaluation and 28 (76%) responded to injection therapy and were successfully using self-injection therapy at 3-month follow-up. Twenty-three patients are still on injection therapy. Five patients have dropped out for several reasons including a lack of a current sexual partner (60%) and pain with injection (40%). Patient age ranges from 24 to 72. The dosage range was 0.10 to 0.50 cc (mean = 0.29 cc). The average duration of erection was 43 minutes. At 3-month follow-up, 85% of the patients rated their erections as good or excellent. Forty-three percent of patients are using ICI 1 or more times per week. Seventy-seven percent of patients are moderately or extremely satisfied with their treatment and 89% said that they would recommend this program to a friend. CONCLUSIONS: This simplified pharmacologic erection program offers safe, well accepted, and effective therapy for ED to a SCI population with very high patient satisfaction.
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The oxygen isotope record of the last million years, as provided by a deep sea core sediment, is analyzed by a method recently developed in the theory of dynamical systems. The analysis suggests that climatic variability is the manifestation of a chaotic dynamics described by an attractor of fractal dimensionality. A quantitative measure of the limited predictability of the climatic system is provided by the evaluation of the time-correlation function and the largest positive Lyapounov exponent of the system.
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