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Ion
About: Ion is a research topic. Over the lifetime, 107590 publications have been published within this topic receiving 2004746 citations.
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TL;DR: A voltage-dependent block of sodium channels by hydrogen ions is explained, which shifts the responses of sodium channel "gates" to voltage, probably by altering the surface potential of the nerve.
Abstract: Increasing the hydrogen ion concentration of the bathing medium reversibly depresses the sodium permeability of voltage-clamped frog nerves. The depression depends on membrane voltage: changing from pH 7 to pH 5 causes a 60% reduction in sodium permeability at +20 mV, but only a 20% reduction at +180 mV. This voltage-dependent block of sodium channels by hydrogen ions is explained by assuming that hydrogen ions enter the open sodium channel and bind there, preventing sodium ion passage. The voltage dependence arises because the binding site is assumed to lie far enough across the membrane for bound ions to be affected by part of the potential difference across the membrane. Equations are derived for the general case where the blocking ion enters the channel from either side of the membrane. For H+ ion blockage, a simpler model, in which H+ enters the channel only from the bathing medium, is found to be sufficient. The dissociation constant of H+ ions from the channel site, 3.9 x 10-6 M (pKa 5.4), is like that of a carboxylic acid. From the voltage dependence of the block, this acid site is about one-quarter of the way across the membrane potential from the outside. In addition to blocking as described by the model, hydrogen ions also shift the responses of sodium channel "gates" to voltage, probably by altering the surface potential of the nerve. Evidence for voltage-dependent blockage by calcium ions is also presented.
1,516 citations
01 Jan 1986
TL;DR: In this article, an expression for the probability of tunnel ionization in an alternating field, of a complex atom and of an atomic ion that are in an arbitrary state, was derived in the quasiclassical approximation n* $1.
Abstract: An expression is derived for the probability of tunnel ionization, in an alternating field, of a complex atom and of an atomic ion that are in an arbitrary state. The expression for the tunnel-ionization probability is obtained in the quasiclassical approximation n* $1. Expressions are also obtained for states with arbitrary values of I at arbitrary ellipticity of the radiation. A quasiclassical approximation yields results up to values n * ~ 1, with accuracy up to several percent.
1,504 citations
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TL;DR: In this article, a method for determination of intrinsic ionization and complexation constants of oxide surface sites from potentiometric titration data is reported using these experimental properties and the stoichiometry of surface reactions, surface charge, σo, adsorption density, Γi, and diffuse layer potentials, ψd, at the oxide/water interface.
1,493 citations
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TL;DR: In this paper, the evolution of the intensity ratio between the G band (1585 cm−1) and the disorder-induced D band (1345 cm −1) with ion dose is determined, providing a spectroscopy-based method to quantify the density of defects in graphene.
1,488 citations
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TL;DR: In this paper, an attempt is made to explain the physical process present that will explain the presence of these energetic protons, as well as explain the number, energy, and angular spread of the protons observed in experiment.
Abstract: An explanation for the energetic ions observed in the PetaWatt experiments is presented. In solid target experiments with focused intensities exceeding 1020 W/cm2, high-energy electron generation, hard bremsstrahlung, and energetic protons have been observed on the backside of the target. In this report, an attempt is made to explain the physical process present that will explain the presence of these energetic protons, as well as explain the number, energy, and angular spread of the protons observed in experiment. In particular, we hypothesize that hot electrons produced on the front of the target are sent through to the back off the target, where they ionize the hydrogen layer there. These ions are then accelerated by the hot electron cloud, to tens of MeV energies in distances of order tens of μm, whereupon they end up being detected in the radiographic and spectrographic detectors.
1,485 citations