Showing papers by "James J. Collins published in 1997"

Noise-mediated enhancements and decrements in human tactile sensation

Abstract: Recently, it has been shown that noise can enhance the detection and transmission of weak signals in certain nonlinear systems. Here we demonstrate noise-mediated improvements in human sensory perception. We show that the ability of an individual to detect a subthreshold tactile stimulus can be significantly enhanced by introducing a particular level of noise. We demonstrate that this effect is robust over time. We also show that the ability of an individual to detect a suprathreshold tactile stimulus can be degraded by the presence of noise. These findings indicate that noise can serve as a ``negative masker'' for the perception of weak stimuli and a ``positive masker'' for the perception of strong stimuli. We discuss the possibility of developing a noise-based technique for improving tactile sensation in humans.

Dynamic control of cardiac alternans

Abstract: A dynamic control technique was used to suppress a cardiac arrhythmia called an alternans rhythm ina piece of dissected rabbit heart. Our control algorithm adapted to drifting system parameters, makingit well suited for the control of physiological rhythms. Control of cardiac alternans rhythms may haveimportant clinical implications since they often precede serious cardiac arrhythmias and are a harbingerof sudden cardiac death. [S0031-9007(97)03337-1]

Stochastic Resonance in Ensembles of Nondynamical Elements: The Role of Internal Noise

Abstract: While many examples of noise-induced signal enhancement have been reported, the role of internal noise has received little attention. Here we study aperiodic stochastic resonance in parallel arrays of nondynamical elements with internal noise. Ensembles of both threshold and threshold-free elements are studied, and the model is applied to two-state ion channels. In finite systems where the input signal controls the probability of discrete events, we demonstrate that the internal noise is modulated by both the applied signal and the external noise. We also show that the internal noise plays a constructive role in information transfer through such systems via an increase in external noise.

Understanding Tolowa Histories: Western Hegemonies and Native American Responses

Abstract: Developing a multi-leveled historical inquiry of the Native Tolowa of the US, James Collins explores the linguistic and political dynamics of place-claiming and expropriation as well as the relation between otherness and subjugation.

Cancer mortality among workers with benzene exposure.

Abstract: We updated a cohort mortality study of 4,172 workers at a chemical plant to examine cancer mortality among workers exposed to low levels of benzene. Overall mortality [standardized mortality ratio (SMR) = 1.0; 95% confidence interval (CI) = 0.9-1.1] and cancer mortality (SMR = 1.0; 95% CI = 0.8-1.3) rates were at expected levels for production workers with benzene exposure. We observed elevated, albeit imprecise, rates of leukemia (SMR = 2.3; 95% CI = 0.7-5.3) and multiple myeloma (SMR = 2.3; 95% CI = 0.7-9.4) in this group of workers. The leukemias and multiple myelomas occurred predominantly among workers 20 or more years after first exposure. The leukemias were not restricted to acute myelogenous subtypes, and they occurred predominantly among workers hired before 1950 at exposure levels lower than previously reported. Leukemia (SMR = 1.3; 95% CI = 0.6-2.4) and multiple myeloma (SMR = 1.2; 95% CI = 0.3-2.9) rates were at expected levels among maintenance workers with intermittent high exposure to benzene. These findings provide evidence on both sides of the debate about whether low benzene exposure increases the risk of multiple myeloma and all types of leukemia.

Real-time experimental control of a system in its chaotic and nonchaotic regimes

Abstract: Current model-independent control techniques are limited, from a practical standpoint, by their dependence on a precontrol learning stage. Here we use a real-time, adaptive, model-independent (RTAMI) feedback control technique to control an experimental system --- a driven magnetoelastic ribbon --- in its nonchaotic and chaotic regimes. We show that the RTAMI technique is capable of tracking and stabilizing higher-order unstable periodic orbits. These results demonstrate that the RTAMI technique is practical for on-the-fly (i.e., no learning stage) control of real-world dynamical systems.

Real-time, adaptive, model-independent control of low-dimensional chaotic and nonchaotic dynamical systems

Abstract: Current model-independent control techniques are limited, from a practical standpoint, by their dependence on a precontrol learning stage. Here we develop a model-independent control technique, for chaotic and nonchaotic low-dimensional dynamical systems, that operates in real-time (i.e., it does not require a learning stage). We show that this technique is adaptive to system nonstationarities, robust to noise, and capable of stabilizing higher-order unstable periodic orbits. Because this technique is real-time, adaptive, and model-independent, it is practical for real-world systems.

Design factors in epidemiologic cohort studies of work-related low back injury or pain

Abstract: The connection between work-related exposures and the onset of back injury or pain is complex and not clearly understood. This paper raises design issues related to the planning and conduct of cohort studies of industrial low back pain (or injury)(LBP), with care given to definition and measurement of exposure and outcome events. These issues include sample size, outcome definition, study biases, and practical considerations when seeking and maintaining company collaboration with a research effort. Without resolving these issues, the authors conclude: (1) cohort studies of worksite-based LBP are needed to elucidate the causal associations between work tasks and LBP onset, (2) both acute and cumulative exposures should be assessed as risk factors for low back injury or pain, and (3) attention should be paid to the planning of such studies and minimization of potential biases that can limit the validity of the results. These design issues will benefit researchers and companies engaged in the planning and conduct of cohort studies of industrial LBP.

Control of chaos in excitable physiological systems: A geometric analysis

Abstract: Model-independent chaos control techniques are inherently well-suited for the control of physiological systems for which quantitative system models are unavailable. The proportional perturbation feedback (PPF) control paradigm, which uses electrical stimulation to perturb directly the controlled system variable (e.g., the interbeat or interspike interval), was developed for excitable physiological systems that do not have an easily accessible system parameter. We develop the stable manifold placement (SMP) technique, a PPF-type technique which is simpler and more robust than the original PPF control algorithm. We use the SMP technique to control a simple geometric model of a chaotic system in the neighborhood of an unstable periodic orbit (UPO). We show that while the SMP technique can control a chaotic system that has UPO dynamics which are characterized by one stable manifold and one unstable manifold, the success of the SMP technique is sensitive to UPO parameter estimation errors. (c) 1997 American Institute of Physics.