A discrete sequential tunneling model is used for studying the influence of the doping density on the dynamical behaviors in weakly coupled GaAs/AlAs superlattices. Driven by the DC bias, the system exhibits self- sustained current oscillations induced by the period motion of the unstable electric field domain, and an electrical hysteresis in the loop of current density voltage curve is deduced. It is found that the hysteresis range strongly depends on the doping density, and the width of the hysteresis loop increases with increasing the doping density. By adding an external driving ac voltage, more complicated nonlinear behaviors are observed including quasi- periodicity, period-3, and the route of an inverse period-doubling to chaos when the driving frequency changes.
The masses of some orbitally and radially excited heavy-light mesons are calculated in Regge phenomenol- ogy. The results are in reasonable agreement with the experimental data and those given in many other theoretical approaches. Based on the calculation, we suggest that the recently observed D（2550）, D（2600） and D（2760） can be assigned as the charmed members of the 21S0, 23S1 and 13D1 multiplets, respectively. D＇1（2700） may be assigned as the charm-strange member of the 23S1 state. The results may be helpful in understanding the nature of current and future experimentally observed heavy-light mesons.
In the framework of factorization, we study direct CP violation in the decays of B（s） → J/φP（V） （P（V） refer to the pseudoscalar （vector） meson）. The CP violation depends strongly on Cabibbo-Kobayashi- Maskawa （CKM） matrix elements and the effective parameter, Nc. The recent experimental data for the branching ratios of B（s） → J/φP（V） are accurate enough and we can give a strong constraint on the range of Arc. We find that the CP violating asymmetry is consistent with the available experiment values for the b→ d transition, and a little smaller than the b→ s transition. We also predict the CP violation of other decay channels for B（s） → J/φP（V）. We expect our results can give valuable guidance for experiments.
The electronic and optical properties of graphene monoxide,a new type of semiconductor material,are theoretically studied by first-principles density functional theory.The calculated band structure shows that graphene monoxide is a semiconductor with a direct band gap of 0.95 eV.The density of states of graphene monoxide and the partial density of states for C and O are given to understand the electronic structure.In addition,we calculate the optical properties of graphene monoxide,including the complex dielectric function,absorption coefficient, complex refractive index,loss-function,reflectivity and conductivity.These results provide a physical basis for potential application in optoelectronic devices.
