1,581 research outputs found
Ion-acoustic solitary waves and shocks in a collisional dusty negative ion plasma
We study the effects of ion-dust collisions and ion kinematic viscosities on
the linear ion-acoustic instability as well as the nonlinear propagation of
small amplitude solitary waves and shocks (SWS) in a negative ion plasma with
immobile charged dusts. {The existence of two linear ion modes, namely the
`fast' and `slow' waves is shown, and their properties are analyzed in the
collisional negative ion plasma.} {Using the standard reductive perturbation
technique, we derive a modified Korteweg-de Vries-Burger (KdVB) equation which
describes the evolution of small amplitude SWS.} {The profiles of the latter
are numerically examined with parameters relevant for laboratory and space
plasmas where charged dusts may be positively or negatively charged.} It is
found that negative ion plasmas containing positively charged dusts support the
propagation of SWS with negative potential. However, the perturbations with
both positive and negative potentials may exist when dusts are negatively
charged. The results may be useful for the excitation of SWS in laboratory
negative ion plasmas as well as for observation in space plasmas where charged
dusts may be positively or negatively charged.Comment: 13 pages, 9 figures; To appear in Physical Review
On a phase-field model for electrowetting and other electrokinetic phenomena
In three space dimensions, we present existence results for weak solutions to a novel two-phase model for various electrokinetic phenomena, including in particular dynamic electrowetting with electrolytes. The model is thermodynamically consistent. It combines Navier-Stokes- and Cahn-Hilliard-type phase-field equations with Nernst-Planck equations for ion density-evolution and with an elliptic transmission problem for the electrostatic potential. As physical energy estimates guarantee only boundedness of ion densities in the Llog L-Orlicz class uniformly with respect to time, an iteration method is proposed to establish higher regularity and integrability results of these quantities. In an appendix, the derivation of the model is sketchedThis work was supported by DAAD, Ministerio de Educación y Ciencia through the program Acciones Integradas Hispano Alemanas, project D/06/12788, and by Dr. Hertha und Helmut Schmauser-Stiftung
One year of Galileo dust data from the Jovian system: 1996
The dust detector system onboard Galileo records dust impacts in circumjovian
space since the spacecraft has been injected into a bound orbit about Jupiter
in December 1995. This is the sixth in a series of papers dedicated to
presenting Galileo and Ulysses dust data. We present data from the Galileo dust
instrument for the period January to December 1996 when the spacecraft
completed four orbits about Jupiter (G1, G2, C3 and E4). Data were obtained as
high resolution realtime science data or recorded data during a time period of
100 days, or via memory read-outs during the remaining times. Because the data
transmission rate of the spacecraft is very low, the complete data set (i. e.
all parameters measured by the instrument during impact of a dust particle) for
only 2% (5353) of all particles detected could be transmitted to Earth; the
other particles were only counted. Together with the data for 2883 particles
detected during Galileo's interplanetary cruise and published earlier, complete
data of 8236 particles detected by the Galileo dust instrument from 1989 to
1996 are now available. The majority of particles detected are tiny grains
(about 10 nm in radius) originating from Jupiter's innermost Galilean moon Io.
These grains have been detected throughout the Jovian system and the highest
impact rates exceeded . A small number of grains has been
detected in the close vicinity of the Galilean moons Europa, Ganymede and
Callisto which belong to impact-generated dust clouds formed by (mostly
submicrometer sized) ejecta from the surfaces of the moons (Kr\"uger et al.,
Nature, 399, 558, 1999). Impacts of submicrometer to micrometer sized grains
have been detected thoughout the Jovian system and especially in the region
between the Galilean moons.Comment: accepted for Planetary and Space Science, 33 pages, 6 tables, 10
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Estimating the contribution of assembly activity to cortical dynamics from spike and population measures
The hypothesis that cortical networks employ the coordinated activity of groups of neurons, termed assemblies, to process information is debated. Results from multiple single-unit recordings are not conclusive because of the dramatic undersampling of the system. However, the local field potential (LFP) is a mesoscopic signal reflecting synchronized network activity. This raises the question whether the LFP can be employed to overcome the problem of undersampling. In a recent study in the motor cortex of the awake behaving monkey based on the locking of coincidences to the LFP we determined a lower bound for the fraction of spike coincidences originating from assembly activation. This quantity together with the locking of single spikes leads to a lower bound for the fraction of spikes originating from any assembly activity. Here we derive a statistical method to estimate the fraction of spike synchrony caused by assemblies—not its lower bound—from the spike data alone. A joint spike and LFP surrogate data model demonstrates consistency of results and the sensitivity of the method. Combining spike and LFP signals, we obtain an estimate of the fraction of spikes resulting from assemblies in the experimental data
Existence of solutions for a higher order non-local equation appearing in crack dynamics
In this paper, we prove the existence of non-negative solutions for a
non-local higher order degenerate parabolic equation arising in the modeling of
hydraulic fractures. The equation is similar to the well-known thin film
equation, but the Laplace operator is replaced by a Dirichlet-to-Neumann
operator, corresponding to the square root of the Laplace operator on a bounded
domain with Neumann boundary conditions (which can also be defined using the
periodic Hilbert transform). In our study, we have to deal with the usual
difficulty associated to higher order equations (e.g. lack of maximum
principle). However, there are important differences with, for instance, the
thin film equation: First, our equation is nonlocal; Also the natural energy
estimate is not as good as in the case of the thin film equation, and does not
yields, for instance, boundedness and continuity of the solutions (our case is
critical in dimension in that respect)
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