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

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 $\pm 45^{\circ}$ to the flow direction. Corresponding ellipticity of the pair correlation function $g({\bf r})$ or static structure factor $S(\bf{k})$ gives the (normalized) shear rate of the flow.Comment: 5 pages, 6 figure

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

Wave mode coupling due to plasma wakes in two-dimensional plasma crystals: In-depth view

Experiments with two-dimensional (2D) plasma crystals are usually carried out in rf plasma sheaths, where the interparticle interactions are modified due to the presence of plasma wakes. The wake-mediated interactions result in the coupling between wave modes in 2D crystals, which can trigger the mode-coupling instability and cause melting. The theory predicts a number of distinct fingerprints to be observed upon the instability onset, such as the emergence of a new hybrid mode, a critical angular dependence, a mixed polarization, and distinct thresholds. In this paper we summarize these key features and provide their detailed discussion, analyze the critical dependence on experimental parameters, and highlight the outstanding issues

Direct experimental observation of binary agglomerates in complex plasmas

A defocusing imaging technique has been used as a diagnostic to identify binary agglomerates (dimers) in complex plasmas. Quasi-two-dimensional plasma crystal consisting of monodisperse spheres and binary agglomerates has been created where the agglomerated particles levitate just below the spherical particles without forming vertical pairs. Unlike spherical particles, the defocused images of binary agglomerates show distinct, stationary/periodically rotating interference fringe patterns. The results can be of fundamental importance for future experiments on complex plasmas

Direct observation of mode-coupling instability in two-dimensional plasma crystals

Dedicated experiments on melting of 2D plasma crystals were carried out. The melting was always accompanied by spontaneous growth of the particle kinetic energy, suggesting a universal plasma-driven mechanism underlying the process. By measuring three principal dust-lattice (DL) wave modes simultaneously, it is unambiguously demonstrated that the melting occurs due to the resonance coupling between two of the DL modes. The variation of the wave modes with the experimental conditions, including the emergence of the resonant (hybrid) branch, reveals exceptionally good agreement with the theory of mode-coupling instability.Comment: 4 pages, submitted to Physical Review Letter

Nonlinear regime of the mode-coupling instability in 2D plasma crystals

The transition between linear and nonlinear regimes of the mode-coupling instability (MCI) operating in a monolayer plasma crystal is studied. The mode coupling is triggered at the centre of the crystal and a melting front is formed, which travels through the crystal. At the nonlinear stage, the mode coupling results in synchronisation of the particle motion and the kinetic temperature of the particles grows exponentially. After melting of the crystalline structure, the mean kinetic energy of the particles continued to grow further, preventing recrystallisation of the melted phase. The effect could not be reproduced in simulations employing a simple point-like wake model. This shows that at the nonlinear stage of the MCI a heating mechanism is working which was not considered so far.Comment: 6 pages, 4 figure

Retardation of nanoparticles growth by doping

The process of doping of CdS nanoparticles with Mn during colloidal synthesis is analyzed by EPR and optical studies. Analysis of EPR results demonstrated that Mn2+ ions are successfully incorporated into the nanoparticles and occupy the crystal sites both in the bulk of a NP and near the surface of a NP. Optical absorption measurements revealed the retardation of absorption edge shift during the growth for Mn-doped CdS NPs as compared to the undoped CdS NPs. It was concluded that the presence of Mn in the solution leads to the inhibition of NPs growth