Quasi-equilibrium optical nonlinearities in spin-polarized GaAs

Semiconductor Bloch equations, which microscopically describe the dynamics of a Coulomb interacting, spin-unpolarized electron-hole plasma, can be solved in two limits: the coherent and the quasi-equilibrium regime. These equations have been recently extended to include the spin degree of freedom, and used to explain spin dynamics in the coherent regime. In the quasi-equilibrium limit, one solves the Bethe-Salpeter equation in a two-band model to describe how optical absorption is affected by Coulomb interactions within a spin-unpolarized plasma of arbitrary density. In this work, we modified the solution of the Bethe-Salpeter equation to include spin-polarization and light holes in a three-band model, which allowed us to account for spin-polarized versions of many-body effects in absorption. The calculated absorption reproduced the spin-dependent, density-dependent and spectral trends observed in bulk GaAs at room temperature, in a recent pump-probe experiment with circularly polarized light. Hence our results may be useful in the microscopic modelling of density-dependent optical nonlinearities in spin-polarized semiconductors.Comment: 7 pages, 6 figure

Doxorubicin resistant choriocarcinoma cell line derived spheroidal cells exhibit stem cell markers but reduced invasion

Cell cycle-specifc cancer chemotherapy is based on the ability of a drug to halt, minimise or destroy rapidly dividing cells. However, their efcacy is limited by the emergence of a self-renewing cell pool called “cancer stem cells” (CSC). Choriocarcinoma is a tumour of trophoblastic tissue. We, in this study, analysed whether spheroids generated from doxorubicintreated and non-treated choriocarcinoma cell lines exhibit markers of stem cells. Two choriocarcinoma cell lines, namely JEG-3 and BeWo, were used in this study. Spheroids were generated from doxorubicin-treated cells and the non-treated cells under non-adherent condition, followed by analysis of stem-cell markers’ expression, namely NANOG, OCT4 and SOX2. Immunofuorescence analysis suggested a general increase in the markers’ concentration in spheroids relative to the parental cells. RT-qPCR and immunoblots showed an increase in the stem-cell marker expression in spheroids generated from doxorubicin-treated when compared to non-treated cells. In spheroids, Sox2 was signifcantly upregulated in doxorubicintreated spheroids, whereas Nanog and Oct4 were generally downregulated when compared to non-treated spheroids. Both 2D and 3D invasion assays showed that the spheroids treated with doxorubicin exhibited reduced invasion. Our data suggest that choriocarcinoma cell lines may have the potential to produce spheroidal cells, yet the drug-treatment afected the invasion potential of spheroids

Minimal inhibitory concentrations of sulbactam/ampicillin against drug sensitive and drug resistant isolates of Mycobacterium tuberculosis

A total of 92 isolates of Mycobacteriurn tuberculosis consisting of equal numbers of sensitive and resistant strains was tested for their susceptibility to sulbactam and ampicillin (in the ratio of 1:2) on Lowenstein-Jensen (LJ) and 7H11 agar media. The geometric mean MIC was 63.97 μg/ml for the drug sensitive strains and 65.92 μg/ml for the resistant strains, and the overall mean was 65.01 μg/ml. The high MIC on LJ medium could be attributed to the higher protein content which resulted in greater binding of sulbactam/ampicillin. On the other hand, the geometric mean MIC on 7H11 medium was 26.73 μg/ml for sensitive strains and 23.82 μg/ml for resistant strains; the overall mean being 25.23 μg/ml. Although these MlCs of sulbactamampicillin are higher than those reported earlier, they can be easily achieved in serum. Further studies on experimental tuberculosis and in humans will be needed to prove the efficacy of sulbactam/ampicillin in the treatment of patients with multidrug resistant tuberculosis