8,680 research outputs found
Channeling of particles and associated anomalous transport in a 2D complex plasma crystal
Implications of recently discovered effect of channeling of upstream extra
particles for transport phenomena in a two-dimensional plasma crystal are
discussed. Upstream particles levitated above the lattice layer and tended to
move between the rows of lattice particles. An example of heat transport is
considered, where upstream particles act as moving heat sources, which may lead
to anomalous heat transport. The average channeling length observed was 15 - 20
interparticle distances. New features of the channeling process are also
reported
Wake-mediated propulsion of an upstream particle in two-dimensional plasma crystals
The wake-mediated propulsion of an "extra" particle in a channel of two
neighboring rows of a two-dimensional plasma crystal, observed experimentally
by Du et al. [Phys. Rev. E 89, 021101(R) (2014)], is explained in simulations
and theory. We use the simple model of a pointlike ion wake charge to reproduce
this intriguing effect in simulations, allowing for a detailed investigation
and a deeper understanding of the underlying dynamics. We show that the
nonreciprocity of the particle interaction, owing to the wake charges, is
responsible for a broken symmetry of the channel that enables a persistent
self-propelled motion of the extra particle. We find good agreement of the
terminal extra-particle velocity with our theoretical considerations and with
experiments.Comment: 7 pages, 4 figures, PRL (https://journals.aps.org/prl/), updated
version with correct author affiliation
Nonlinear structures of strongly coupled complex plasmas in the proximity of a presheath/sheath edge
The formation of a steady-state nonlinear potential structure of a double-layer type near the presheath/sheath edge of a plasma discharge is theoretically investigated in complex plasmas containing Boltzmann electrons, cold fluid ions and strongly coupled microparticles. Equilibrium of the particles is provided by the electrostatic force and an effective 'dust pressure' associated with electrostatic interactions between the highly charged grains. The results are of importance for complex plasma experiments in microgravity conditions, for thermophoretically levitated configurations and for processing plasmas loaded by nanometer-sized microparticles
Nucleosynthesis and the variation of fundamental couplings
We determine the influence of a variation of the fundamental ``constants'' on
the predicted helium abundance in Big Bang Nucleosynthesis. The analytic
estimate is performed in two parts: the first step determines the dependence of
the helium abundance on the nuclear physics parameters, while the second step
relates those parameters to the fundamental couplings of particle physics. This
procedure can incorporate in a flexible way the time variation of several
couplings within a grand unified theory while keeping the nuclear physics
computation separate from any model-dependent assumptions.Comment: 8 pages, no figure
Instability of ion kinetic waves in a weakly ionized plasma
The fundamental higher-order Landau plasma modes are known to be generally
heavily damped. We show that these modes for the ion component in a weakly
ionized plasma can be substantially modified by ion-neutral collisions and a dc
electric field driving ion flow so that some of them can become unstable. This
instability is expected to naturally occur in presheaths of gas discharges at
sufficiently small pressures and thus affect sheaths and discharge structures.Comment: Published in Phys. Rev. E, see
http://link.aps.org/doi/10.1103/PhysRevE.85.02641
Network analysis of 3D complex plasma clusters in a rotating electric field
Network analysis was used to study the structure and time evolution of driven
three-dimensional complex plasma clusters. The clusters were created by
suspending micron-size particles in a glass box placed on top of the rf
electrode in a capacitively coupled discharge. The particles were highly
charged and manipulated by an external electric field that had a constant
magnitude and uniformly rotated in the horizontal plane. Depending on the
frequency of the applied electric field, the clusters rotated in the direction
of the electric field or remained stationary. The positions of all particles
were measured using stereoscopic digital in-line holography. The network
analysis revealed the interplay between two competing symmetries in the
cluster. The rotating cluster was shown to be more cylindrical than the
nonrotating cluster. The emergence of vertical strings of particles was also
confirmed.Comment: 9 pages, 9 figures; corrected Fig.4 and typo
Semiclassical theory of the emission properties of wave-chaotic resonant cavities
We develop a perturbation theory for the lifetime and emission intensity for
isolated resonances in asymmetric resonant cavities. The inverse lifetime
and the emission intensity in the open system are
expressed in terms of matrix elements of operators evaluated with eigenmodes of
the closed resonator. These matrix elements are calculated in a semiclassical
approximation which allows us to represent and as sums
over the contributions of rays which escape the resonator by refraction.Comment: 4 pages, 2 color figure
Non-thermal processes in colliding-wind massive binaries: the contribution of Simbol-X to a multiwavelength investigation
Several colliding-wind massive binaries are known to be non-thermal emitters
in the radio domain. This constitutes strong evidence for the fact that an
efficient particle acceleration process is at work in these objects. The
acceleration mechanism is most probably the Diffusive Shock Acceleration (DSA)
process in the presence of strong hydrodynamic shocks due to the
colliding-winds. In order to investigate the physics of this particle
acceleration, we initiated a multiwavelength campaign covering a large part of
the electromagnetic spectrum. In this context, the detailed study of the hard
X-ray emission from these sources in the SIMBOL-X bandpass constitutes a
crucial element in order to probe this still poorly known topic of
astrophysics. It should be noted that colliding-wind massive binaries should be
considered as very valuable targets for the investigation of particle
acceleration in a similar way as supernova remnants, but in a different region
of the parameter space.Comment: 4 pages, 2 figures, to appear in Proc. of the Second Internqtionql
Simbol-X Symposium, held in Paris (France
The status of shark and ray fishery resources in the Gulf of California: applied research to improve management and conservation
Seasonal surveys were conducted during 1998–1999 in Baja California, Baja California Sur, Sonora, and Sinaloa to determine the extent and activities of artisanal elasmobranch fisheries in the Gulf of California. One hundred and forty–seven fishing sites, or camps, were documented, the majority of which (n = 83) were located in Baja California Sur. Among camps with adequate fisheries information, the great majority (85.7%) targeted elasmobranchs during some part of the year. Most small, demersal sharks and rays were landed in mixed species fisheries that also targeted demersal teleosts, but large sharks were usually targeted in directed drift gillnet or, to a lesser extent, surface longline fisheries. Artisanal fishermen were highly opportunistic, and temporally switched targets depending on the local productivity of teleost, invertebrate, and elasmobranch fishery resources. Major fisheries for small sharks ( 1.5 m, “tiburón”) were minor components of artisanal elasmobranch fisheries in Sonora and Sinaloa, but were commonly targeted during summer and early autumn in Baja California and Baja California Sur. The pelagic thresher shark (Alopias pelagicus) and silky shark (Carcharhinus falciformis) were most commonly landed in Baja California, whereas a diverse assemblage of pelagic and large coastal sharks was noted among Baja California Sur landings. Rays dominated summer landings in Baja California and Sinaloa, when elevated catch rates of the shovelnose guitarfish (Rhinobatos productus, 13.2 individuals/vessel/trip) and golden cownose ray (Rhinoptera steindachneri, 11.1 individuals/vesse/trip) primarily supported the respective fisheries. The Sonoran artisanal elasmobranch fishery was the most expansive recorded during this study, and rays (especially R. productus) dominated spring and summer landings in this state. Seasonal catch rates of small demersal sharks and rays were considerably greater in Sonora than in other surveyed states. Many tiburón populations (e.g., C. leucas, C. limbatus, C. obscurus, Galeocerdo cuvier) have likely been overfished, possibly shifting effort towards coastal populations of cazón and rays. Management recommendations, including conducting demographic analyses using available life history data, determining and protecting nursery areas, and enacting seasonal closures in areas of elasmobranch aggregation (e.g., reproduction, feeding), are proposed. Without effective, enforceable management to sustain or rebuild targeted elasmobranch populations in the Gulf of California, collapse of many fisheries is a likely outcome. (PDF contains 243 pages
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