37,499 research outputs found
Fluctuation-enhanced electric conductivity in electrolyte solutions
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
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
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
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 LaAlO/SrTiO and bulk SrTiO
Metallic LaAlO/SrTiO (LAO/STO) interfaces attract enormous attention,
but the relationship between the electron mobility and the sheet electron
density, , is poorly understood. Here we derive a simple expression for
the three-dimensional electron density near the interface, , as a
function of and find that the mobility for LAO/STO-based interfaces
depends on in the same way as it does for bulk doped STO. It is known
that undoped bulk STO is strongly compensated with background donors and acceptors. In intentionally doped
bulk STO with a concentration of electrons background impurities
determine the electron scattering. Thus, when it is natural to see
in LAO/STO the same mobility as in the bulk. On the other hand, in the bulk
samples with the mobility collapses because scattering happens on
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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