37,499 research outputs found

    Fluctuation-enhanced electric conductivity in electrolyte solutions

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    In this letter we analyze the effects of an externally applied electric field on thermal fluctuations for a fluid containing charged species. We show in particular that the fluctuating Poisson-Nernst-Planck equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation, result in enhanced charge transport. Although this transport is advective in nature, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity. We calculate the renormalized electric conductivity by deriving and integrating the structure factor coefficients of the fluctuating quantities and show that the renormalized electric conductivity and diffusion coefficients are consistent although they originate from different noise terms. In addition, the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye-Huckel-Onsager theory, and provides a quantitative theory that predicts a non-zero cross-diffusion Maxwell-Stefan coefficient that agrees well with experimental measurements. Finally, we show that strong applied electric fields result in anisotropically enhanced velocity fluctuations and reduced fluctuations of salt concentrations.Comment: 12 pages, 1 figur

    Neural Relax

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    We present an algorithm for data preprocessing of an associative memory inspired to an electrostatic problem that turns out to have intimate relations with information maximization

    Euclidean mirrors: enhanced vacuum decay from reflected instantons

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    We study the tunneling of virtual matter-antimatter pairs from the quantum vacuum in the presence of a spatially uniform, time-dependent electric background composed of a strong, slow field superimposed with a weak, rapid field. After analytic continuation to Euclidean spacetime, we obtain from the instanton equations two critical points. While one of them is the closing point of the instanton path, the other serves as an Euclidean mirror which reflects and squeezes the instanton. It is this reflection and shrinking which is responsible for an enormous enhancement of the vacuum pair production rate. We discuss how important features of two different mechanisms can be analysed and understood via such a rotation in the complex plane. a) Consistent with previous studies, we first discuss the standard assisted mechanism with a static strong field and certain weak fields with a distinct pole structure in order to show that the reflection takes place exactly at the poles. We also discuss the effect of possible sub-cycle structures. We extend this reflection picture then to weak fields which have no poles present and illustrate the effective reflections with explicit examples. An additional field strength dependence for the rate occurs in such cases. We analytically compute the characteristic threshold for the assisted mechanism given by the critical combined Keldysh parameter. We discuss significant differences between these two types of fields. For various backgrounds, we present the contributing instantons and perform analytical computations for the corresponding rates treating both fields nonperturbatively. b) In addition, we also study the case with a nonstatic strong field which gives rise to the assisted dynamical mechanism. For different strong field profiles we investigate the impact on the critical combined Keldysh parameter. [...]Comment: 54 pages, 23 figures, revised, restructured to improve readability, matches journal versio

    Relativistic length agony continued

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    An attempt is made to remedy confusing treatments of some basic relativistic concepts and results in recent papers by Franklin (2010 {\it Eur. J. Phys.} {\bf 31} 291-8) and by McGlynn and van Kampen (2008 {\it Eur. J. Phys.} {\bf 29} N63-N67). The authors' misconceptions are recurrent points in the literature

    Universality of Electron Mobility in LaAlO3_3/SrTiO3_3 and bulk SrTiO3_3

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    Metallic LaAlO3_3/SrTiO3_3 (LAO/STO) interfaces attract enormous attention, but the relationship between the electron mobility and the sheet electron density, nsn_s, is poorly understood. Here we derive a simple expression for the three-dimensional electron density near the interface, n3Dn_{3D}, as a function of nsn_s and find that the mobility for LAO/STO-based interfaces depends on n3Dn_{3D} in the same way as it does for bulk doped STO. It is known that undoped bulk STO is strongly compensated with N5×1018 cm3N \simeq 5 \times 10^{18}~\rm{cm^{-3}} background donors and acceptors. In intentionally doped bulk STO with a concentration of electrons n3D<Nn_{3D} < N background impurities determine the electron scattering. Thus, when n3D<Nn_{3D} < N it is natural to see in LAO/STO the same mobility as in the bulk. On the other hand, in the bulk samples with n3D>Nn_{3D} > N the mobility collapses because scattering happens on n3Dn_{3D} intentionally introduced donors. For LAO/STO the polar catastrophe which provides electrons is not supposed to provide equal number of random donors and thus the mobility should be larger. The fact that the mobility is still the same implies that for the LAO/STO the polar catastrophe model should be revisited.Comment: 4 pages and 1 figur
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