Electronic structure and magnetic properties of(Cu,N)-codoped3C-SiC studied by first-principles calculations

The electronic structures and magnetic properties of the Cu and N codoped 3C-Si C system have been investigated by the first-principles calculation.The results show that the Cu doped Si C system prefers the anti-ferromagnetic（AFM） state.Compared to the Cu doped system,the ionicities of C–Cu and C–Si in Cu and N codoped Si C are respectively enhanced and weakened.Especially,the Cu and N codoped Si C systems favor the ferromagnetic（FM） coupling.The FM interactions can be explained by virtual hopping.However,higher N concentration will weaken the ferromagnetism.In order to keep the FM interaction,the N concentration should be restricted within 9.3% according to our analysis.

Statefinder diagnostic and constraints on the Palatini f(R) gravity theories

We focus on a series of f（R） gravity theories in Palatini formalism to investigate the probabilities of producing late-time acceleration for the flat Friedmann-Robertson-Walker（FRW） universe.We apply a statefinder diagnostic to these cosmological models for chosen series of parameters to see if they can be distinguished from one another. The diagnostic involves the statefinder pair{r,s},where r is derived from the scale factor a and its higher derivatives with respect to the cosmic time t,and s is expressed by r and the deceleration parameter q. In conclusion,we find that although two types of f（R） theories：（i） f（R） = R ＋ αR^m-βR^-n and（ii） f（R） = R ＋ α lnR-β can lead to late-time acceleration,their evolutionary trajectories in the r-s and r-q planes reveal different evolutionary properties,which certainly justify the merits of the statefinder diagnostic. Additionally,we utilize the observational Hubble parameter data（OHD） to constrain these models of f（R） gravity. As a result,except for m = n = 1/2 in case（i）,α = 0 in case（i） and case（ii） allow the ΛCDM model to exist in the 1σ confidence region. After applying the statefinder diagnostic to the best-fit models,we find that all the best-fit models are capable of going through the deceleration/acceleration transition stage with a late-time acceleration epoch,and all these models turn to the de Sitter point（{r,s}={1,0}） in the future. Also,the evolutionary differences between these models are distinct,especially in the r-s plane,which makes the statefinder diagnostic more reliable in discriminating cosmological models.

The ROSAT bright source 1RXS J201607.0+251645:an active Algol-type binary

1RXS J201607.0＋251645 is identified as an eclipsing binary. We present preliminary observations in the V band with the 0.6-m telescope for three years and extensive observations in the V and R bands with the 0.8-m telescope for six nights, respectively. The light curve of the system is E13 type. Five light minimum times were obtained and the orbital period of 0.388058^d（±0.00044d） is determined. The photometric solution given by the 2003-version of the Wilson-Devinney program suggests that the binary is a semidetached system with photometric mass ratio 0.895（±0.006）, which is probably comprised of a G5 primary and an oversized K5 secondary. The tess massive component has completely filled its Roche lobe, while the other one almost fills its Roche lobe with a filling factor of 93.4%. The system shows a varying O＇Connell effect in its phase folded diagrams from 2005 to 2007, and is X-ray luminous with log Lx/Lbol - -3.27. Possible mechanisms to account for these two phenomena are discussed. Finally, we infer that the binary may be in thermal oscillation or may evolve into a contact binary.