363 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
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
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
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
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
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
FORGIVENESS AS A MULTIFUNCTIONAL COPING RESOURCE OF A MATURE PERSONALITY
Розглянуто теоретичні концепції ролі готовності пробачати як особистісного фактора, що впливає на ефективність психологічного подолання стресу. Наведено емпіричні дані, що свідчать про наявність розбіжностей між групами досліджуваних із різними рівнями схильності пробачати (себе, інших і загального рівня пробачення) за показниками ефективності копінг-поведінки. З’ясовано, що за високого рівня схильності до самопробачення індивіди характеризуються низьким рівнем звернення до емоційно-фокусованої копінг-стратегії та самоінвалідизації як негативної проактивної копінг-стратегії. Доведено, що за високого рівня готовності пробачати інших спостерігається низький рівень відволікання та наявність тенденції до високого рівня пошуку соціальної підтримки в подоланні стресу. За високого загального рівня готовності до пробачення виявлено високий рівень орієнтації на вирішення проблеми, низький рівень застосування стратегії фокусування на емоціях і низький рівень прояву тенденції до самоінвалідизації.Рассмотрены теоретические концепции роли готовности к прощению в обеспечении эффективности психологического преодоления стресса. Описаны результаты эмпирического исследования, свидетельствующие о наличии различий между группами испытуемых с разными уровнями склонности к прощению в эффективности психологического преодоления стресса. Установлено, что при высоком уровне готовности к самопрощению отмечается низкий уровень обращения к эмоционально-фокусированной стратегии копинг-поведения и самоинвалидизации. Доказано, что при высоком уровне склонности к прощению других наблюдается низкий уровень применения стратегии отвлечения. При высоком общем уровне склонности к прощению зафиксированы высокая вероятность выбора проблемно-ориентированной стратегии психологического преодоления стресса и низкий уровень ориентации на эмоциональное реагирование и самоинвалидизацию.Background. Researchers who study forgiveness have used different theoretical conceptualizations of the construct. Most agree that forgiveness is a complex phenomenon (Enright and Fitzgibbons, 2000), which involves cognitive (Flanigan, 1992), affective (Malcolm & Greenberg, 2000), behavioral (Gordon et al., 2000), motivational (McCullough et al., 1997), decisional (DiBlasio, 1998), and interpersonal (Baumeister et al., 1998) aspects. Forgiveness was also interpreted in terms of coping strategies (Worthington & Scherer, 2004, Strelan & Covic, 2006), though there is no uniform statements as to which types of strategies are likely to be related to forgiveness.Objectives. The aim of the present study was to analyse the multifunctional nature of forgiveness and test the hypothesis that proneness to forgiveness facilitates the ef?cacy of the individual’s coping with stressful situations.Method. For the empirical research we have used Heartland Forgiveness Scale (Thompson, Snyder, Hoffman, 2005), Coping Inventory for Stressful Situations (Endler & Parker, 1990, adapted by T. Kryukova, 2001) and The Self-Handicapping Scale (Jones & Rhodewalt, 1982, adapted by D. Nosenko).Sample. Participants (36 females and 26 males) of the ?rst mature age group (21 – 35 years) were recruited from the population of the university undergraduate and graduate students as well as the university alumni who volunteered to participate as acquaintances of the authors.Results. The research has shown that the individuals with high level of willingness to forgive demonstrate lower frequency of resorting to the emotion-focused coping in comparison with the individuals characterized as unforgiving, lower proneness to self-handicapping as well as the lower tendency to avoidance. Conclusion. The research ?ndings have con?rmed the hypothesis about the existence of the statistically signi?cant differences between the individuals with different levels of willingness to forgive in the ef?cacy of coping (both reactive and proactive)
First direct measurement of optical phonons in 2D plasma crystals
Spectra of phonons with out-of-plane polarization were studied experimentally
in a 2D plasma crystal. The dispersion relation was directly measured for the
first time using a novel method of particle imaging. The out-of-plane mode was
proven to have negative optical dispersion, comparison with theory showed good
agreement. The effect of the plasma wakes on the dispersion relation is briefly
discussed.Comment: submitted to Physical Review Letter
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