Correction to Rotton, Tikofsky, and Feldman.

Reports an error in the original article by Rotten et al (Journal of Applied Psychology. Vol 67(2) Apr 1982, 230-238). The receipt date was incorrectly listed as May 11, 1982. The article was actually received on May 11, 1981.(The following abstract of this article originally appeared in record 1982-20688-001) In Exp I, 42 Ss (mean age 30.4 yrs) tracked a moving target and monitored lights after receiving sublingual drops that contained either water, sodium nitrate (4.5, 45, 450, or 4,500 ppm), or sodium fluoride (.1, 1, 10, or 100 ppm). Dosage levels equaled, exceeded, or fell below those of municipal waters. In Exp II, 20 females performed this task after receiving sublingual drops of the same test substances in a repeated measures design; dosage levels equaled or exceeded levels found in municipal waters by 100 or 500 times. Neither type nor amount of chemical affected primary task performance; however, after receiving sublingual drops in Exp I, Ss paid less attention to lights on their right. In Exp II, Ss made more errors and had longer response latencies after they received moderate and very high concentrations of test substances. It is concluded that challenge testing is a safe but effective technique for provoking and studying reactions to chemicals when combined with a sensitive measure of sensorimotor performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Efficient simulation of periodically forced reactors with radial gradients

The aim of this paper is to present a limited memory iterative method, called the Broyden Rank Reduction method, to simulate periodically forced processes in plug-flow reactors with radial gradients taken into account. The simulation of periodically forced processes in plug-flow reactors leads to the development of partial differential equations that are normally solved in time using dynamical simulation. Depending on the convergence properties of the system at hand, the number of cycles that needs to be computed up to a cyclic steady state is reached can be large. Therefore direct iterative methods are essential in order to capture the long time dynamics of such systems. In order to overcome severe memory constraints many authors have reverted to pseudo-homogeneous 1D models and to coarse grid discretization, which renders such models inadequate or inaccurate. The results that we present show that the long time dynamics actually depends on the radius of the reactor and, hence, the full 2D model is essential in order to simulate periodically forced processes in plug-flow reactors accurately.     

Simulation of multipolar fiber selective neural stimulation usingintrafascicular electrodes

A realistic, quantitative model is presented for the excitation of myelinated nerve fibers by intrafascicular electrodes. It predicts the stimulatory regions of any configuration of any number of electrodes, positioned anywhere inside the fascicle. The model has two parts. First, the nerve fiber is represented by a lumped electrical network and its response to an arbitrary extracellular potential field is calculated. Second, assuming a cylindrical geometry of the nerve bundle and its surroundings, an analytical expression for this field is derived. With realistic parameters, the model is applied to two cases: monopolar stimulation by a single cathode and stimulation by a specific tripolar configuration. It is shown that tripolar stimulation has the better spatial selectivity. Also tripolar stimulation is less sensitive to the conductivity of the medium surrounding the nerve and yields a more natural recruitment order.