900 research outputs found
Shear Flows and Shear Viscosity in a Two-Dimensional Yukawa System (Dusty Plasma)
The shear viscosity of a two-dimensional liquid-state dusty plasma was
measured experimentally. A monolayer of highly charged polymer microspheres,
with a Yukawa interaction, was suspended in a plasma sheath. Two
counter-propagating Ar laser beams pushed the particles, causing shear-induced
melting of the monolayer and a shear flow in a planar Couette configuration. By
fitting the particle velocity profiles in the shear flow to a Navier-Stokes
model, the kinematic viscosity was calculated; it was of order 1 mm^2/s,
depending on the monolayer's parameters and shear stress applied.Comment: all 3 figures are combined in a separate pdf fil
Supersonic dislocations observed in a plasma crystal
Experimental results on the dislocation dynamics in a two-dimensional plasma
crystal are presented. Edge dislocations were created in pairs in lattice
locations where the internal shear stress exceeded a threshold and then moved
apart in the glide plane at a speed higher than the sound speed of shear waves,
. The experimental system, a plasma crystal, allowed observation of this
process at an atomistic (kinetic) level. The early stage of this process is
identified as a stacking fault. At a later stage, supersonically moving
dislocations generated shear-wave Mach cones
Dust interferometers in plasmas
An interferometric imaging technique has been proposed to instantly measure
the diameter of individual spherical dust particles suspended in a gas
discharge plasma. The technique is based on the defocused image analysis of
both spherical particles and their binary agglomerates. Above a critical
diameter, the defocused images of spherical particles contain stationary
interference fringe patterns and the fringe number increases with particle
diameters. Below this critical diameter, the particle size has been measured
using the rotational interference fringe patterns which appear only on the
defocused images of binary agglomerates. In this case, a lower cut-off limit of
particle diameter has been predicted, below which no such rotational fringe
patterns are observed for the binary agglomerates. The method can be useful as
a diagnostics for complex plasma experiments on earth as well as under
microgravity condition
Anisotropic shear melting and recrystallization of a two-dimensional complex (dusty) plasma
A two-dimensional plasma crystal was melted by suddenly applying localized
shear stress. A stripe of particles in the crystal was pushed by the radiation
pressure force of a laser beam. We found that the response of the plasma
crystal to stress and the eventual shear melting depended strongly on the
crystal's angular orientation relative to the laser beam. Shear stress and
strain rate were measured, from which the spatially resolved shear viscosity
was calculated. The latter was shown to have minima in the regions with high
velocity shear, thus demonstrating shear thinning. Shear-induced reordering was
observed in the steady-state flow, where particles formed strings aligned in
the flow direction.Comment: 7 pages, 8 figures, submitted to Physical Review
Quasi-two-dimensional complex plasma containing spherical particles and their binary agglomerates
A new type of quasi-two-dimensional complex plasma system was observed which
consisted of monodisperse microspheres and their binary agglomerations
(dimers). The particles and their dimers levitated in a plasma sheath at
slightly different heights and formed two distinct sublayers. The sys- tem did
not crystallize and may be characterized as disordered solid. The dimers were
identified based on their characteristic appearance in defocused images, i.e.,
rotating interference fringe pat- terns. The in-plane and inter-plane particle
separations exhibit nonmonotonic dependence on the discharge pressure which
agrees well with theoretical predictions
Microstructure of a liquid complex (dusty) plasma under shear
The microstructure of a strongly coupled liquid undergoing a shear flow was
studied experimentally. The liquid was a shear melted two-dimensional plasma
crystal, i.e., a single-layer suspension of micrometer-size particles in a rf
discharge plasma. Trajectories of particles were measured using video
microscopy. The resulting microstructure was anisotropic, with compressional
and extensional axes at around to the flow direction.
Corresponding ellipticity of the pair correlation function or
static structure factor gives the (normalized) shear rate of the
flow.Comment: 5 pages, 6 figure
“Nos temen porque somos Otro”: actitudes hacia las personas con discapacidad en la Rusia moderna
El número de personas con discapacidad en la Rusia postsoviética supera los 13 millones, pero hasta el momento se han realizado muy pocas investigaciones sobre los procesos que se desarrollan dentro de este gran sector de la sociedad. El objetivo de este artículo es abordar las diferentes nociones y estereotipos relacionados con la discapacidad. Desde el abordaje metodológico de la historia oral se realizaron entrevistas en profundidad a 11 hombres y 16 mujeres con discapacidad en tres regiones de Rusia, además de seis entrevistas a expertos en Moscú y Nizhny Novgorod. También fueron incorporados relatos sobre la experiencia de discapacidad publicados en Internet. El análisis de estas fuentes muestra que la percepción de las personas con discapacidad y de la discapacidad en general es ambivalente e impacta en la percepción de la discapacidad y la autoidentificación que tienen las propias personas discapacitadas que forman parte de la sociedad rusa.Although the number of disabled people in post-Soviet Russia exceeds 13 million, research regarding many processes occurring within this large segment of the society remains scant. The objective of this article was to examine the different notions and stereotypes dealing with impairments. Using the qualitative approach of oral history, in-depth interviews with 11 men and 16 women with disabilities were carried out in three regions of Russia, as were interviews with six experts in Moscow and Nizhny Novgorod.
In addition, accounts of disability experience published in online journals were examined. The analysis of these sources shows that the perception of disabled people and disability in general is ambivalent and impacts the perception of disability and selfidentification of disabled people who are also a part of Russian society
Coupling of non-crossing wave modes in a two-dimensional plasma crystal
We report an experimental observation of coupling of the transverse vertical
and longitudinal in-plane dust-lattice wave modes in a two-dimensional complex
plasma crystal in the absence of mode crossing. A new large diameter rf plasma
chamber was used to suspend the plasma crystal. The observations are confirmed
with molecular-dynamics simulations. The coupling manifests itself in traces of
the transverse vertical mode appearing in the measured longitudinal spectra and
vice versa. We calculate the expected ratio of the trace to the principal mode
with a theoretical analysis of the modes in a crystal with finite temperature
and find good agreement with the experiment and simulations.Comment: 4 figures, 5 pages, accepted for publication in PRL Nov 201
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