Brane Solutions with/without Rotation in PP-wave Spacetime

We present two classes of brane solutions in pp-wave spacetime. The first class of branes with a rotation parameter are constructed in an exact string background with NS-NS and R-R flux. The spacetime supersymmetry is analyzed by solving the standard Killing spinor equations and is shown to preserve the same amount of supersymmetry as the case without the rotation. This class of branes do not admit regular horizon. The second class of brane solutions are constructed by applying a null Melvin twist to the brane solutions of flat spacetime supergravity. These solutions admit regular horizon. We also comment on some thermodynamic properties of this class of solutions.Comment: 17 pages, added references, to be published in Nucl. Phys.

Mechanism of photoinduced charge transfer at MEH-PPV and titanium dioxide nanoparticle interface

1278-1284In this study, we investigated mechanisms of photoinduced electron transfer from a conjugated polymer (poly(2-methoxy-5-(2-ethylhexyloxy) 1,4-phenylenevinylene (MEH-PPV) to titanium dioxide (TiO2) nanoparticles (acceptor) through steady-state photoluminescence (PL) spectroscopy. Since mixed phase TiO2 has better photocatalytic compared to single phase, it is an efficient charge separation process during photoexcitation of polymer nanocomposites by incorporating the mixed phase TiO2 nanoparticles into the MEH-PPV polymer matrix through in situ polymerization. Structural characterization revealed only physical interaction between the polymer matrix and dispersed nanoparticles. The absorbance spectra of nanocomposites also indicated the absence of ground state complex formation. Luminescence quenching of polymer nanocomposites compared to pristine MEH-PVV signifies the charge transfer taking place at the MEH-PPV/TiO2 interfaces. Thus, the MEH-PPV/ mixed phase TiO2 nanocomposite serves as an active layer for photovoltaic application