Carrier generation and recombination rate in armchair graphene nanoribbons

Armchair graphene nanoribbons (A-GNRs), with a tunable energy gap, are an alternative structure for use in optoelectronic devices. The performance of these optoelectronic devices critically depends on the carrier generation and recombination rates, which have been calculated in this paper. Because of the 1D band structure of A-GNRs, carrier scattering, generation and recombination rates in these structures would be completely different from those in 2D graphene sheets. In this paper, using the tight binding model, and by considering the edge deformation and Fermi golden rule, we find the band structure, and the carrier generation and recombination rates for pure A-GNR due to optical and acoustic phonons, as well as Line Edge Roughness (LER) scatterings. The obtained results show that the total generation and recombination rates increase with increasing A-GNR width and eventually saturate for wide ribbons. These rates increase as the carrier concentration is increased (which has been considered homogenous along ribbon width) and temperature. Also, despite the large LER scattering in narrow ribbons, the generation and recombination rates are less for A-GNRs than for graphene sheets. Using this theoretical model, one can find the suitable A-GNR structure for the design of optoelectronic devices.     

Effects of radiation on mixed convection stagnation-point flow of MHD third-grade nanofluid over a vertical stretching sheet

This paper considers the problem of the two-dimensional mixed convection stagnation-point flow of a magnetohydrodynamic non-Newtonian nanofluid bounded by a vertical stretching sheet. Convective surface boundary and zero surface nanoparticle mass flux conditions are employed. The effects of buoyancy, radiation, Brownian motion, thermophoresis, and viscous dissipation are taken into account. The stretching velocity is assumed to vary linearly with the distance from the stagnation point. The fluid is electrically conducted with uniform magnetic field, and the work done due to deformation is taken into consideration. The three-coupled partial differential boundary layer equations are reduced to ordinary differential equations by using proper similarity transformations. Analytical solution by homotopy analysis method is obtained. Effects of different physical parameters on the dynamics of the problem are analyzed and discussed.

     

Protein Engineering of Bacillus thermocatenulatus Lipase via Deletion of the α5 Helix

Lipases from Bacillus thermocatenulatus are a member of superfamily of α/β hydrolase, but there are structural differences between them. In this work, we focused on the α5 helix of B. thermocatenulatus lipase (BTL2) which is absent in canonical α/β hydrolase fold. In silico study showed that the α5 helix is a region that causes disorder in BTL2 protein. So, the α5 helix (residues 131 to 150) has been deleted from the B. thermocatenulatus lipase gene (BTL2) and the remain (Δα5-BTL2) has been expressed in Pichia pastoris yeast. The α5 deletion results in increase of enzyme-specific activity in the presence of tributyrin, tricaproin, tricaprylin, tricaprin, trilaurin, and olive oil (C18) substrates by 1.4-, 1.7-, 2.0-, 1.2-, 1.75-, and 1.95-fold, respectively. Also, deletion leads to increase in enzyme activity in different temperatures and pHs, whereas it did not significantly affect on enzyme activity in the presence of organic solvents, metal ions, and detergents.     

广义Oldroyd-B流体作MHD旋转流动时的精确解

对充满多孔空间的广义Oldroyd-B流体,研究有滑移时磁流体动力学（MHD）的旋转流动．数学建模时采用了分式积分法．给出平板振荡和周期性压力梯度诱导的3个示例,并得到了每种情况下的精确解．比较了有滑移和没有滑移条件下两种情况的结果．曲线图表表明,滑移对速度分布的影响是巨大的．     

Virtually semisimple modules and a generalization of the Wedderburn-Artin theorem

A widely used result of Wedderburn and Artin states that “every left ideal of a ring R is a direct summand of R if and only if R has a unique decomposition as a finite direct product of matrix rings over division rings.” Motivated by this, we call a module M virtually semisimple if every submodule of M is isomorphic to a direct summand of M and M is called completely virtually semisimple if every submodule of M is virtually semisimple. We show that the left R-module R is completely virtually semisimple if and only if R has a unique decomposition as a finite direct product of matrix rings over principal left ideal domains. This shows that R is completely virtually semisimple on both sides if and only if every finitely generated (left and right) R-module is a direct sum of a singular module and a projective virtually semisimple module. The Wedderburn-Artin theorem follows as a corollary from our result.