NONPARAMETRIC TESTS FOR COMPARING SURVIVAL DATA WITH NONPROPORTIONAL HAZARDS: EXPLORATION OF A NEW WEIGHT FUNCTION

For survival data with nonproportional hazards, the weighted log-rank tests with a proper weighting function are expected to be more sensitive than the simple log-rank statistics for comparing survival data with random effects. A series of simulations were carried out to investigate how much better the weighted log-rank test performs under these situations. The nonproportional hazards data were generated by changing the hazard ratios and piecewise exponential functions. Our Monte Carlo simulation study shows the test with a newly developed weight function has an overall better sensitivity (statistical power) than the simple log-rank test and Harrington-Fleming's weighted log-rank test in detecting the difference between two survival distributions when populations become more homogeneous as time progresses (early difference). For the datasets with middle difference, the test with the new weight function has better sensitivity than that of Harrington-Fleming's weighted log-rank test, similar to that of the simple-log rank test. For late difference, all three tests have similar sensitivity. The new weight function can be used in testing the survival data with nonproportional hazards in public health relevance applications

Half-Metallic Silicon Nanowires: Multiple Surface Dangling Bonds and Nonmagnetic Doping

By means of first-principles density functional theory calculations, we find that hydrogen-passivated ultrathin silicon nanowires (SiNWs) along [100] direction with symmetrical multiple surface dangling bonds (SDBs) and boron doping can have a half-metallic ground state with 100% spin polarization, where the half-metallicity is shown quite robust against external electric fields. Under the circumstances with various SDBs, the H-passivated SiNWs can also be ferromagnetic or antiferromagnetic semiconductors. The present study not only offers a possible route to engineer half-metallic SiNWs without containing magnetic atoms but also sheds light on manipulating spin-dependent properties of nanowires through surface passivation.Comment: 4 pages, 5 figure

News on PHOTOS Monte Carlo: gamma^* -> pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma)

PHOTOS Monte Carlo is widely used for simulating QED effects in decay of intermediate particles and resonances. It can be easily connected to other main process generators. In this paper we consider decaying processes gamma^* -> pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma) in the framework of Scalar QED. These two processes are interesting not only for the technical aspect of PHOTOS Monte Carlo, but also for precision measurement of alpha_{QED}(M_Z), g-2, as well as pi pi scattering lengths.Comment: 6 pages, 11 figures, proceedings of the PhiPsi09, Oct. 13-16, 2009, Beijing, Chin