Showing papers by "James J. Collins published in 1996"

Noise-enhanced information transmission in rat SA1 cutaneous mechanoreceptors via aperiodic stochastic resonance.

Abstract: 1. Aperiodic stochastic resonance (ASR) is a phenomenon wherein the response of a nonlinear system to a weak aperiodic input signal is optimized by the presence of a particular, nonzero level of no...

Aperiodic stochastic resonance.

Abstract: Stochastic resonance (SR) is a phenomenon wherein the response of a nonlinear system to a weak periodic input signal is optimized by the presence of a particular level of noise. Recently, we presented a method and theory for characterizing SR-type behavior in excitable systems with aperiodic (i.e., broadband) input signals [Phys. Rev. E 52, R3321(1995)]. We coined the term aperiodic stochastic resonance (ASR) to describe this general type of behavior. In that earlier study, we demonstrated ASR in the FitzHugh-Nagumo neuronal model. Here we demonstrate ASR in three additional systems: a bistable-well system, an integrate-and-fire neuronal model, and the Hodgkin-Huxley (HH) neuronal model. We present computational and theoretical results for each system. In the context of the HH model, we develop a general theory for ASR in excitable membranes. This work clearly shows that SR-type behavior is not limited to systems with periodic inputs. Thus, in general, noise can serve to enhance the response of a nonlinear system to a weak input signal, regardless of whether the signal is periodic or aperiodic. \textcopyright{} 1996 The American Physical Society.

Information measures quantifying aperiodic stochastic resonance

Abstract: Aperiodic stochastic resonance ~ASR! is a phenomenon in which the response of a nonlinear system to a subthreshold information-bearing signal is optimized by the presence of noise. We have previously characterized this effect by the use of cross-correlation-based measures. Here we apply a measure ~transinformation! that directly quantifies the rate of information transfer from stimulus to response and show that the presence of noise optimizes the information-transfer rate. By considering a nonlinear system ~the FitzHugh-Nagumo model! that captures the functional dynamics of neuronal firing, we demonstrate that sensory neurons could, in principle, harness ASR to optimize the detection and transmission of weak stimuli. @S1063-651X~96!51309-7#

Using chaos control and tracking to suppress a pathological nonchaotic rhythm in a cardiac model.

Abstract: Atrioventricular (AV) nodal alternans is a pathological cardiac condition characterized by a beat-to-beat alternation (period-2 rhythm) in AV nodal conduction time. Here we implement an AV nodal conduction model which undergoes a period-doubling bifurcation into alternans. We show that additive noise can be used to locate the unstable period-1 fixed point which underlies the alternans rhythm. We then use chaos control to suppress alternans by stabilizing the model about its unstable period-1 fixed point. We also show that the period-doubling bifurcation into alternans can be prevented by tracking the period-1 rhythm into its unstable regime. We demonstrate that these techniques are robust to imprecise measurements and experimental noise. Importantly, these methods require no knowledge of the underlying system equations. These findings suggest that chaos control and tracking may be useful for suppressing alternans in a clinical environment. \textcopyright{} 1996 The American Physical Society.

Method and apparatus for improving the function of sensory cells

Abstract: Method and system for enhancing the function of sensory cells are disclosed The method comprises locating a sensory cell area associated with the sensory cell whose function is to be enhanced and inputting a bias signal to the sensory cell area The apparatus comprises a signal processor for producing a bias signal and an input device for inputting the bias signal to a sensory cell area associated with a sensory cell whose function is to be enhanced Inputting the bias signal to a sensory cell area effectively lowers the threshold of sensory cells with which the sensory cell area is associated

Experimental control of high-dimensional chaos: The driven double pendulum.

Abstract: Chaos control techniques exploit the sensitivity of chaos to initial conditions by applying feedback perturbations to an accessible system parameter. Most methods apply only one perturbation per period and are thus susceptible to control failure when applied to highly unstable systems. Here we extend a recently developed model-independent, quasicontinuous chaos control technique to stabilize a high-dimensional chaotic system: the driven double pendulum. \textcopyright{} 1996 The American Physical Society.

Evaluation of mortality and cancer incidence among alachlor manufacturing workers.

Abstract: Alachlor is the active ingredient in a family of preemergence herbicides. We assessed mortality rates from 1968 to 1993 and cancer incidence rates from 1969 to 1993 for manufacturing workers with potential alachlor exposure. For workers judged to have high alachlor exposure, mortality from all causes combined was lower than expected [23 observed, standardized mortality ratio (SMR) = 0.7, 95% CI, 0.4-1.0], cancer mortality was similar to expected (6 observed, SMR = 0.7, 95% CI, 0.3-1.6), and there were no cancer deaths among workers with 5 or more years high exposure and 15 or more years since first exposure (2.3 expected, SMR = 0, 95% CI, 0-1.6). Cancer incidence for workers with high exposure potential was similar to the state rate [18 observed, standardized incidence ratio (SIR) = 1.2, 95% CI, 0.7-2.0], especially for workers exposed for 5 or more years and with at least 15 years since first exposure (4 observed, SIR = 1.0, 95% CI, 0.3-2.7). The most common cancer for these latter workers was colorectal cancer (2 observed, SIR 3.9, 95% CI, 0.5-14.2 among workers). Despite the limitations of this study with respect to small size and exposure estimating, the findings are useful for evaluating potential alachlor-related health risks because past manufacturing exposures greatly exceeded those characteristic of agricultural operations. These findings suggest no appreciable effect of alachlor exposure on worker mortality or cancer incidence rates during the study period.

Real-time and adaptive method and system for suppressing a pathological non-chaotic rhythm

Abstract: Low-dimensional real-world chaotic or non-chaotic dynamical systems are controlled by a model-independent control technique that does not require knowledge of the system's governing equations or a pre-control learning stage. Control is applied to a real-world system by estimating the desired unstable periodic fixed point, determining the value of a perturbation that will be made to a readily-accessible system parameter, entering the perturbation to the system, and adaptively adjusting the control sensitivity in order to force the system toward its unstable periodic fixed point. Control is repeated periodically and maintained indefinitely or for a predetermined length of time.