Plane-strain discrete dislocation plasticity incorporating anisotropic elasticity

The increasing application of plane-strain testing at the (sub-) micron length scale of materials that comprise elastically anisotropic cubic crystals has motivated the development of an anisotropic two-dimensional discrete dislocation plasticity (2D DDP) method. The method relies on the observation that plane-strain plastic deformation of cubic crystals is possible in specific orientations when described in terms of edge dislocations on three effective slip systems. The displacement and stress fields of such dislocations in an unbounded anisotropic crystal are recapitulated, and we propose modified constitutive rules for the discrete dislocation dynamics of anisotropic single crystals. Subsequently, to handle polycrystalline problems, we follow an idea of O’Day and Curtin (J. Appl. Mech. 71 (2004) 805–815) and treat each grain as a plastic domain, and adopt superposition to determine the overall response. This method allows for a computationally efficient analysis of micro-scale size effects. As an application, we study freestanding thin copper films under plane-strain tension. First, the computational framework is validated for the special case of isotropic thin films modeled by means of a standard 2D DDP method. Next, predictions of size dependent plastic behavior in anisotropic columnar-grained thin films with varying thickness/grain size are presented and compared with the isotropic results.     

Convergence of fundamentalists and chartists’ expectations: An alarm for stock market crash

We construct a network of the Tehran stock market based on the cross-correlation of trading volume of stocks both for fundamentalists and chartists. In order to investigate the dynamics of expectations of fundamentalists and chartists over time we introduced a homogeneity coefficient. Our results show that in the Tehran Stock Exchange (TSE) which is an emerging market, chartists in comparison with fundamentalists more strongly believe the stocks’ co-movements. We also found that in a bull market (booming period), the optimism of fundamentalists and chartists about the similarity of stocks’ performance diverge from each other while in a bear market (recession period) both groups of traders have approximately same level of pessimism about the simultaneous collapse of stock prices.     

Dispersive solid-phase extraction of risperidone from plasma samples using graphene oxide aerogels and determination with liquid chromatography

A graphene oxide-based aerogel was synthesized and applied to the extraction and the determinations with the high-performance liquid chromatography-ultraviolet detector. After the characterization of the produced graphene-aerogel, it was utilized as a dispersive solid-phase extraction sorbent for risperidone extraction from plasma samples. Aerogels are materials with a large surface area-to-mass ratio and plenty of core with functional groups which can easily attach to the analytes to extract them to the second phase. The suggested method determined risperidone in plasma samples in the wide dynamic range from 20 ng/ml to 3 μg/ml. The limits of detection and quantification of the developed method were calculated as 2.4 and 8.2 ng/ml, respectively. As a novel feature, the developed method has no need to precipitate plasma proteins, improving the analytical performance of the analysis. Also, for the first time, the produced materials were utilized for the extraction of risperidone from the plasma samples. The obtained results revealed that the developed approach could be employed as an accurate method for the quantification of risperidone in real plasma samples.