Search

A series of chiral donor-acceptor helicenes have been designed using the molecular engineering of organic nonlinear optical materials. The geometries of donor-acceptor helicenes 1, 2, 3, 4, 5 are optimized using density functional theory (DFT-B3LYP) method at the 6-31g (d, p) basis set level. Based on the obtained stable molecular configuration, we adopt the TDHT/PM3 method and time-dependent density-functional theory (TD-DFT) to calculate the nonlinear optical (NLO) properties and electronic spectra of these molecules. Results show that molecule 4 has the largest static hyperpolarizability βμ of 40.4×10-30esu, which is enhanced by its two charge transfer orientations. In molecule 2, there exists two competitive charge transfers that weaken the second-order nonlinear optical effect of D-π-A structures greatly. The structural type of molecule 3, 4 and 5 are expected to be more efficient to achieve large β values.

A lot of branching ratios of the exclusive c → d / s l + ν l ( l = e , μ ) decays have been quite accurately measured by CLEO-c, BELLE, BABAR, BES(I, II, III), ALEPH and MARKIII Collaborations. We probe the R-parity violating supersymmetric effects in the exclusive c → d / s l + ν l decays. From the latest experimental measurements, we obtain new upper limits on the relevant R-parity violating coupling parameters within the decays, and many upper limits are obtained for the first time. Using the constrained new parameter spaces, we predict the R-parity violating effects on the observables, which have not been measured yet. We find that the R-parity violating effects due to slepton exchange could be large on the branching ratios of D d / s → e + ν e decays and the normalized forward-backward asymmetries of D u / d → π / K l + ν l as well as D s → K l + ν l decays, and the constrained squark exchange couplings have negligible effects in the exclusive c → d / s l + ν l decays. Our results in this work could be used to probe new physics effects in the leptonic decays as well as the semileptonic decays, and will correlate with searches for direct supersymmetric signals at LHC and BESIII.

The plane-wave pseudo-potential method within the framework of first-principles is used to investigate the structural and elastic properties of Mg 2 Si in its low pressure phase (Fm-3m) and intermediate pressure phase (Pnma). The high-pressure lattice constants, the elastic constants, the elastic moduli and the anisotropy factors of the anti-cotunnite Mg 2 Si are presented and discussed. The results show that our system is mechanically stable. The reversible phase transition from anti-fluorite to anti-cotunnite structure is successfully reproduced through the quasi-harmonic Debye model. The phase boundary can be described as P =4.06826−6.95×10 −3 T +5.08838×10 −5 T 2 −4.24073×10 −8 T 3 . To complete the fundamental characteristics of these compounds we have analysed the thermodynamic properties such as thermal expansion, bulk modulus, isochoric heat capacity and Debye temperature in a pressure range 0–21 GPa and a temperature range 0–1200 K. The obtained results tend to support the experimental data when available. Therefore, the present results indicate that the combination of first-principles and quasi-harmonic approximations is an efficient scheme to simulate the high-temperature behaviours of semiconductors like Mg 2 Si.

Recently, the CDF and D{\O} collaborations have claimed that the CP violating phase in $B_s^0-\bar{B}_s^0$ mixing is large, which is contrary to the expectations in the Standard Model. Such a large phase suggests New Physics contributions to $B_s^0-\bar{B}_s^0$ mixing. Motivated by this, we reevaluate the constraints on R-parity violating contributions, including baryon number violating couplings not considered before, to the mixing mass matrix element $M^s_{12}$ from the recent measurements of $B_s^0-\bar{B}_s^0$ mixing. We show that present data allow us to put quite strong constraints on both the magnitudes and the weak phases of the R-parity violating parameters. Some of these bounds are better than the exciting ones, and some bounds are obtained for the first time. Near future experiments at the Tevatron, the LHC and B-factories can shrink or reveal the relevant parameter spaces of R-parity violating couplings., Comment: 18 pages, 4 figures. Three figures and some discussions improved, matches published version