Full Closures Research Articles

Emergency Evacuation Planning with Microscopic Traffic Simulation

A microscopic simulation model (MITSIMLab) for evaluating emergency evacuation plans was developed for the Los Alamos National Laboratory (LANL). MITSIMLab was used as the microscopic traffic simulator to model traffic operations. The study area consisted of the entire region that includes all technical areas within the LANL and the towns of White Rock and Los Alamos, New Mexico. Evacuation planning is a critical component of overall security planning. The approach adopted presents a laboratory-like setup to evaluate a large range of evacuation scenarios including no evacuation. Five evacuation scenarios are considered in LANL evacuation planning. The scenarios, developed in consultation with the Emergency Management Office of LANL, include full or partial closures of various roads, limited access to some special facilities, and security delays at certain locations. Performance measures for evaluating an evacuation plan include the total time to achieve a complete evacuation, the time needed for a partial evacuation in which the population within certain areas is at risk, and the percentage of the population in affected zones as a function of time.

A nonlinear stress–strain model for wall-bounded turbulent flows

A nonlinear stress–strain model, derived from the modeled Reynolds stress transport equation, is modified to account for the near wall effects in wall-bounded turbulent flows. Since it is known that wall reflection of the turbulent pressure field modifies the pressure–strain correlation, the approach taken is to introduce a correction to the coefficients in the closure for the pressure–strain correlation purely based on ideas for full Reynolds stress closures. The stress–strain relation is implemented in the context of the k– ϵ model with a variable C μ . Results are presented for plane channel flow and both zero and adverse pressure gradient boundary layers. Favorable results for the anisotropies in the Reynolds stresses are obtained by the new model as validated by comparisons against direct numerical simulation (DNS) and experimental data.

Gating kinetics of E. coli poly-3-hydroxybutyrate/polyphosphate channels in planar bilayer membranes.

Nonproteinaceous calcium channel complexes from Escherichia coli, composed of poly-(R)-3-hydroxybutyrate (PHB) and inorganic polyphosphate (polyP), exhibit two distinct gating modes (modes 1 and 2) in planar lipid bilayers. Here we report the kinetic characterization of the channel in mode 2, a mode characterized by two well-defined conductance levels, a fully open state (87 +/- 3 pS), and a major subconductance state (56 +/- 2 pS). Other subconductance states and full closures are rare (<0.5% of total time). Several kinetic properties of the channel showed asymmetric voltage-dependence indicating an asymmetry in the channel structure. Accordingly, single channels responded to potential change in one of two mirror-image patterns, postulated to arise from opposite orientations of the asymmetrical channel complex in the bilayer. The fraction of time spent in each conductance level was strongly voltage-sensitive. For channels reported in this study, presumably all oriented in the same direction, residence time in the fully open state increased as clamping potentials became more positive whereas residence time in the major subconductance state increased at more negative potentials. Analysis of open time distributions revealed existence of two kinetically distinct states for each level. The shorter time constants for both conductance states exhibited weak voltage-sensitivity; however, the longer time constants were strongly voltage-sensitive. A kinetic scheme, consistent with the complex voltage dependence of the channel, is proposed.

Nonlinear Kinetic Fluid Equations

Fluid equations are derived that describe wave-particle resonances, which usually require kinetic theory. Unlike previous such efforts the closure is not linearized, and so retains many nonlinear wave-particle effects never before described by fluid equations. To demonstrate utility, we show that the new equations can retain trapping, time reversibility, and rectify a discrepancy between full kinetic theory and linear kinetic fluid closures.

Explicit algebraic stress model of turbulence with anisotropic dissipation

During the past few years, explicit algebraic stress models have been developped that are formally consistent with full second-order closures in the limit of homogeneous turbulence in equilibrium. These models allow for the solution of complex turbulent flows with a substantially reduced level of computation compared with full second-order closures, since they constitute two-equation models.The purpose of the present note is to show how the effects of anisotropic dissipation can be systematically incorporated into these explicit algebraic stress models by a simple readjustmentof the coefficients.

Aerodynamic Evidence for Articulatory Overlap in Korean

Abstract Aerodynamic evidence indicates the existence of overlapped labial//velar sequences in Korean. Oral pressure readings for [ipku] show a brief rarefaction in oral pressure during the consonantal sequence, indicating that tongue retraction during a front-back vowel sequence occurs simultaneously with full closures at the labial and velar places of articulation. This confluence of phenomena results in the observed pressure rarefaction due to expansion of the sealed oral cavity. Similarly, pressure readings for [upki] show a brief, marked increase during the consonantal sequence, indicating that tongue advancement during a back-front vowel sequence temporally overlaps with full closures at both the labial and velar places of articulation. This results in a pressure increase due to contraction of the sealed oral cavity. To our knowledge, the present study is the first to demonstrate consonant coproduction in terms of oral pressure, and to report on coarticulatory effects involving four sequenced segments.

Calculation of Developing Turbulent Flows in a Rotating Pipe

Internal rotating boundary-layer flows are strongly influenced by large circumferential strain and the turbulence field is anisotropic. This is especially true in the entry region of a rotating pipe where the flow is three dimensional, the centrifugal force due to fluid rotation is less important, and the circumferential strain created by surface rotation has a significant effect on the turbulence field near the wall. Consequently, viscous effects cannot be neglected in the near-wall region. Several low-Reynolds-number turbulence closures are proposed for the calculation of developing rotating pipe flows. Some are two-equation closures with and without algebraic stress correction, while others are full Reynolds-stress closures. It is found that two-equation closures with and without algebraic stress correction are totally inadequate for this three-dimensional flow, while Reynolds-stress closures give results that are in good agreement with measurements over a wide range of rotation numbers.

Tetrodotoxin block of single germitrine‐activated sodium channels in cultured rat cardiac cells.

1. The open time of single Na+ channels in excised (outside-out) patches from cultured late-fetal rat ventricular myocytes was prolonged to several minutes by germitrine (0.5 mM) in order to analyse tetrodotoxin (TTX) blocking kinetics. 2. The germitrine modification appeared during depolarizing pulses that activated normal Na+ channels. Following repolarization to -100 mV, the modified Na+ channel remained activated for 136 +/- 186 s (mean +/- S.D., n = 54) with an open-channel current amplitude of -0.5 pA. The predominant open state with a mean open time of 0.13 s was interrupted by brief closing events lasting for milliseconds. Replacing extracellular Na+ by Cs+ decreased the current amplitude to -0.1 pA. 3. Extracellular superfusion with TTX (3 x 10(-7) M) of a single germitrine-activated Na+ channel induced full channel closures lasting seconds (blocked events) separated by channel reopenings (unblocked events) that were indistinguishable in terms of amplitude and gating kinetics from the germitrine-activated state in the absence of TTX. 4. Cumulative probability histograms of blocked and unblocked events (n greater than 140) collected during long-lasting germitrine modifications at 10(-7) and 3 x 10(-7) M-TTX are well described by single exponentials. The 3-fold increase in [TTX] decreased the time constant of the unblocked state, tau o, from 11.9 to 4.7 s, while the time constant of the blocked state, tau c, was not significantly altered from 8.6 to 9.7 s. A microscopic association rate constant of 7.7 x 10(5) M-1 s-1, dissociation rate constant of 0.11 s-1, and equilibrium dissociation constant of 1.4 x 10(-7) M (at -100 mV) were calculated (20 degrees C). 5. Increasing [TTX] to 10(-5) M decreased tau o to 86 ms. This argues against the existence of a slower conformational step interposed between the binding of TTX to an open channel and the resultant channel closure. 6. Setting the membrane potential to -50 or 0 mV subsequent to a germitrine modification at -100 mV did not significantly alter TTX (3 x 10(-7) M) blocking kinetics: tau o was 6.7 s at -50 mV and 5.2 s at 0 mV; tau c was 8.9 and 8.1 s, respectively. 7. These results suggest that blocked events correspond to the random times that a TTX molecule resides on the Na+ channel before it dissociates, and unblocked events correspond to the random waiting times of an unoccupied channel before it binds another toxin molecule.(ABSTRACT TRUNCATED AT 400 WORDS)

Fast events in single‐channel currents activated by acetylcholine and its analogues at the frog muscle end‐plate.

The fine structure of ion-channel activations by junctional nicotinic receptors in adult frog muscle fibres has been investigated. The agonists used were acetylcholine (ACh), carbachol (CCh), suberyldicholine (SubCh) and decan-1,10-dicarboxylic acid dicholine ester (DecCh). Individual activations (bursts) were interrupted by short closed periods; the distribution of their durations showed a major fast component ('short gaps') and a minor slower component ('intermediate gaps'). The mean duration of both short and intermediate gaps was dependent on the nature of the agonist. For short gaps the mean durations (microseconds) were: ACh, 20; SubCh, 43; DecCh, 71; CCh, 13. The mean number of short gaps per burst were: ACh, 1.9; SubCh, 4.1; DecCh, 2.0. The mean number of short gaps per burst, and the mean number per unit open time, were dependent on the nature of the agonist, but showed little dependence on agonist concentration or membrane potential for ACh, SubCh and DecCh. The short gaps in CCh increased in frequency with agonist concentration and were mainly produced by channel blockages by CCh itself. Partially open channels (subconductance states) were clearly resolved rarely (0.4% of gaps within bursts) but regularly. Conductances of 18% (most commonly) and 71% of the main value were found. However, most short gaps were probably full closures. The distribution of burst lengths had two components. The faster component represented mainly isolated short openings that were much more common at low agonist concentrations. The slower component represented bursts of longer openings. Except at very low concentrations more than 85% of activations were of this type, which corresponds to the 'channel lifetime' found by noise analysis. The frequency of channel openings increased slightly with hyperpolarization. The short gaps during activations were little affected when (a) the [H+]o or [Ca2+]o were reduced to 1/10th of normal, (b) when extracellular Ca2+ was replaced by Mg2+, (c) when the [Cl-]i was raised or (d) when, in one experiment on an isolated inside-out patch, the normal intracellular constituents were replaced by KCl. Reduction of [Ca2+]O to 1/10 of normal increased the single-channel conductance by 50%, and considerably increased the number of intermediate gaps. No temporal asymmetry was detectable in the bursts of openings. Positive correlations were found between the lengths of successive apparent open times at low SubCh concentrations, but no correlations between burst lengths were detectable. The component of brief openings behaves, at low concentrations, as though it originates from openings of singly occupied channels.(ABSTRACT TRUNCATED AT 400 WORDS)