Effects of aminoperimidine on electrolyte transport across amphibian skin

The effect of aminoperimidine (AP)on transepithelial Na+ transport and Cl- conductance (G(Cl)) of isolated amphibian skin (Bufo viridis and Rana esculenta) was analyzed using transepithelial and intracellular electrophysiological techniques. AP, applied at concentrations between 30 and 100 mu M from the mucosal side, stimulated Na+ transport rapidly and reversibly by more than 30% of the control value due to an increase in apical membrane Na+ permeability. Influence of AP on basolateral membrane conductance and effective driving force for Na+ were negligible. Voltage-activated G(Cl) of toad skin, but not the resting, deactivated conductance, as well as spontaneously high G(Cl) in frog skin was rapidly inhibited by AP in a concentration-dependent manner. The half-maximal inhibitory concentration of 20 mu M is the highest hithero reported inhibitory power for G(Cl) in amphibian skin. The effect of AP on G(Cl) was slowly and incompletely reversible even after brief exposure to the agent. Serosal application of AP had similar, albeit delayed effects on both Nai and Cl- transport. AP did not interfere with the Cl- pathway after it was opened by 100-300 mu M CPT-cAMP, a membrane-permeable, nonhydrolyzed analogue of cAMP. Inhibition of the voltage-activated G(Cl) by AP was attenuated or missing when AP was applied during voltage perturbation to serosa-positive potentials. Since AP is positively charged at physiological pH, it suggests that the affected site is located inside the Cl- pathway at a certain distance from the external surface. AP affects then the Na+ and Cl- transport pathways independent of each other. The nature of chemical interference with AP, which is responsible for the influence on the transport of Na+ and Cl-, remains to be elucidated

Agent-Based Demand-Modeling Framework for Large-Scale Microsimulations

Microsimulation is becoming increasingly important in traffic demand modeling. The major advantage over traditional four-step models is the ability to simulate each traveler individually. Decision-making processes can be included for each individual. Traffic demand is the result of the different decisions made by individuals; these decisions lead to plans that the individuals then try to optimize. Therefore, such microsimulation models need appropriate initial demand patterns for all given individuals. The challenge is to create individual demand patterns out of general input data. In practice, there is a large variety of input data, which can differ in quality, spatial resolution, purpose, and other characteristics. The challenge for a flexible demand-modeling framework is to combine the various data types to produce individual demand patterns. In addition, the modeling framework has to define precise interfaces to provide portability to other models, programs, and frameworks, and it should be suitable for large-scale applications that use many millions of individuals. Because the model has to be adaptable to the given input data, the framework needs to be easily extensible with new algorithms and models. The presented demand-modeling framework for large-scale scenarios fulfils all these requirements. By modeling the demand for two different scenarios (Zurich, Switzerland, and the German states of Berlin and Brandenburg), the framework shows its flexibility in aspects of diverse input data, interfaces to third-party products, spatial resolution, and last but not least, the modeling process itself

Concordance of knots in S1×S2S^1\times S^2

We establish a number of results about smooth and topological concordance of knots in $S^1\times S^2$. The winding number of a knot in $S^1\times S^2$ is defined to be its class in $H_1(S^1\times S^2;\mathbb{Z})\cong \mathbb{Z}$. We show that there is a unique smooth concordance class of knots with winding number one. This improves the corresponding result of Friedl-Nagel-Orson-Powell in the topological category. We say a knot in $S^1\times S^2$ is slice (resp. topologically slice) if it bounds a smooth (resp. locally flat) disk in $D^2\times S^2$. We show that there are infinitely many topological concordance classes of non-slice knots, and moreover, for any winding number other than $\pm 1$, there are infinitely many topological concordance classes even within the collection of slice knots. Additionally we demonstrate the distinction between the smooth and topological categories by constructing infinite families of slice knots that are topologically but not smoothly concordant, as well as non-slice knots that are topologically slice and topologically concordant, but not smoothly concordant.Comment: 25 pages, 19 figures, final version, to appear in Journal of London Mathematical Societ

Breakup of Air Bubbles in Water: Memory and Breakdown of Cylindrical Symmetry

Using high-speed video, we have studied air bubbles detaching from an underwater nozzle. As a bubble distorts, it forms a thin neck which develops a singular shape as it pinches off. As in other singularities, the minimum neck radius scales with the time until breakup. However, because the air-water interfacial tension does not drive breakup, even small initial cylindrical asymmetries are preserved throughout the collapse. This novel, non-universal singularity retains a memory of the nozzle shape, size and tilt angle. In the last stages, the air appears to tear instead of pinch.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figures. Revised for resubmissio

Vibrations and diverging length scales near the unjamming transition

We numerically study the vibrations of jammed packings of particles interacting with finite-range, repulsive potentials at zero temperature. As the packing fraction $\phi$ is lowered towards the onset of unjamming at $\phi_{c}$, the density of vibrational states approaches a non-zero value in the limit of zero frequency. For $\phi>\phi_{c}$, there is a crossover frequency, $\omega^{*}$ below which the density of states drops towards zero. This crossover frequency obeys power-law scaling with $\phi-\phi_{c}$. Characteristic length scales, determined from the dominant wavevector contributing to the eigenmode at $\omega^{*}$, diverge as power-laws at the unjamming transition.Comment: Submitted to PRL, 4 pages + 7 .eps figure

Still water: dead zones and collimated ejecta from the impact of granular jets

When a dense granular jet hits a target, it forms a large dead zone and ejects a highly collimated conical sheet with a well-defined opening angle. Using experiments, simulations, and continuum modeling, we find that this opening angle is insensitive to the precise target shape and the dissipation mechanisms in the flow. We show that this surprising insensitivity arises because dense granular jet impact, though highly dissipative, is nonetheless controlled by the limit of perfect fluid flow.Comment: 5 pages, 5 figures, submitted to Physical Review Letter

Structural signatures of the unjamming transition at zero temperature

We study the pair correlation function $g(r)$ for zero-temperature, disordered, soft-sphere packings just above the onset of jamming. We find distinct signatures of the transition in both the first and split second peaks of this function. As the transition is approached from the jammed side (at higher packing fraction) the first peak diverges and narrows on the small-$r$ side to a delta-function. On the high-$r$ side of this peak, $g(r)$ decays as a power-law. In the split second peak, the two subpeaks are both singular at the transition, with power-law behavior on their low-$r$ sides and step-function drop-offs on their high-$r$ sides. These singularities at the transition are reminiscent of empirical criteria that have previously been used to distinguish glassy structures from liquid ones.Comment: 8 pages, 13 figure