The interaction of two pairs of solitary waves in a two-fluid system

This paper deals with the interaction of solitary waves in a two-fluid system which consistsof two superimposed incompressible inviscid fluids with a free surface and a horizontal rigidbottom. Under the assumption of shallow water wave, we first derive the basic equationssuitable for the model considered, a generalized form of the Boussinesq equations, then usingthe PLK method and the reductive perturbation method, obtain the second-order approximatesolution for the head-on collision between two pairs of interface and surface solitary waves,and give their maximum amplitudes during the collision and the nonuniform phase shiftsafter the collision which lead to the distortion of the wave profiles.

Cytotoxicity evaluation of three pairs of hexabromocyclododecane (HBCD) enantiomers on Hep G2 cell

Hexabromocyclododecanes (HBCDs) are additive brominated flame retardants mainly used in plastics and textiles. At the present time, these compounds are found in almost all environmental and human samples. In order to evaluate the environmental safety and health risk of HBCDs, the enantiomerically pure alpha-, beta-, and gamma-HBCD were prepared using high performance liquid chromatography (HPLC) on a PM-P-CD column and the cytotoxicities of their enantiomers were evaluated in Hep G2 cells. Results from the 3-(4,5-dimethylthioazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), resazurin reduction and lactate dehydrogenase (LDH) release assays showed a good agreement that the order of cytotoxicity was gamma-HBCD >= beta-HBCD > alpha-HBCD, and that significantly lower cell viability and higher LDH release were observed in all (+)-enantiomers ((+) alpha-, (+) beta- and (+) gamma-HBCD) than the corresponding (-)-forms ((-) alpha-, (-) beta- and (-) gamma-HBCD). Additionally, the formation of reactive oxygen species (ROS) induced by these HBCD enantiomers were detected. The positive correlation between the LDH release and ROS formation demonstrated that the toxic mechanism might be mediated by oxidative damage. These results suggest that environmental and human health risks of HBCDs must be evaluated at the level of individual enantiomers. (C) 2008 Published by Elsevier Ltd.

Entanglement degree of electron pairs out of Andreev reflection

We study the entanglement degree of electron pairs emitted from an s-wave Superconductor, which Couples to two normal leads via a single-level quantum dot. Within the framework of scattering matrix theory. the concurrence is used to quantify the entanglement. And the result shows that the entanglement degree is generally influenced by the initial separation of the two electrons in a Cooper pair and the normal transmission eigenvalues T-1, T-2. But it is only determined by the eigenvalues in the tunnelling limit, T-1. T-2 << 1, what is more. it is measurable. (C) 2008 Elsevier B.V. All rights reserved.

Surface morphology control of strained InAs/GaAs(331)A films: From nanowires to island-pit pairs

We have studied the effect of molecular beam epitaxy growth conditions on the surface morphology of strained InAs/GaAs(331)A films. Our results reveal that InAs nanowires aligned along the [1 (1) over bar0] direction are formed under As-rich conditions, which is explained by the effect of anisotropic buffer layer surface roughing. Under In-rich conditions, however, the surface morphology of the InAs layers is characterized by a feature of island-pit pairs. In this case, cooperative nucleation of islands and pits can lower the activation barrier for domain growth. These results suggest that the surface morphology of strained InAs layers is highly controllable. (C) 2005 American Institute of Physics.

Storage of photoexcited electron-hole pairs in an AlAs/GaAs heterostructure created by electron transfer in real and kappa spaces

The storage of photoexcited electron-hole pairs is experimentally carried out and theoretically realized by transferring electrons in both real and k spaces through resonant Gamma - X in an AlAs/GaAs heterostructure. This is proven by the peculiar capacitance jump and hysteresis in the measured capacitance-voltage curves. Our structure may be used as a photonic memory cell with a long storage time and a fast retrieval of photons as well.

Excitation transfer in vertically self-organized pairs of unequal-sized InAs/GaAs quantum dots

The excitation transfer processes in vertically self organized pairs of unequal-sized quantum dots (QD's), which are created in InAs/GaAs bilayers with different InAs deposition amounts in the first and second layers, have been investigated experimentally by photoluminescence technique. The distance between the two dot layers is varied from 3 to 12 nm. The optical properties of the formed pairs of unequal-sized QD's with clearly discernible ground-state transition energy depend on the spacer thickness. When the spacer layer of GaAs is thin enough, only one photoluminescence peak related to the large QD ensemble has been observed as a result of strong electronic coupling in the InAs QD pairs. The results provide evidence for nonresonant energy transfer from the smaller QDs in the second layer to the larger QD's in the first layer in such an asymmetric QD pair.