A nonuniform-shape photonic crystal taper integrated with a single-mode optical fiber and a photonic crystal waveguide for high-efficiency mode coupling is presented. The curvature of the tapering section is varied by the parameter alpha. For values of alpha set to 2 and 0.5, concave and convex tapers are obtained, respectively. Numerical calculations yield an average coupling efficiency greate...

The efficiency of off-axis adaptive astronomical systems is estimated for four astronomical sites: Paranal (Chili), Roque de los Muchachos (Canary Islands), San Pedro Mártir (México) and Observatoire de Haute Provence (France). The efficiency of interest is considered through the Strehl ratio of the corrected image calculated for V, J and K bands and for 8-m class telescopes. The experimental o...

We show that the envelope of the diffraction efficiency of a two-dimensional photonic crystal can exhibit spectral regions of very small diffraction efficiency (,5310), while in other regions, the diffraction efficiency is near unity. The experimental results on higher bands of hexagonal, silicon-based photonic crystals agree well with corresponding numerical calculations and highlight the prom...

By means of first principles calculations we show that both rutile and anatase phases of bulk TiO2 doped by S, Se or Pb can display substantial decreasing in the band gap (up to 50%), while doping by Zr does not sizably affect the band-gap value. Moreover, the absorption edge is shifted (up to 1 eV) to the lower energy range in the case of TiO2 doped by S or Pb that opens a way to enhancin...

The present literature on quantum efficiency is confusing and contains contradictions partly because definitions of efficiency have differed, partly because false assumptions about the working of the eye have been implicit in the method of calculation used, and partly because the experimental results chosen for the calculations were obtained under different conditions. The present paper defines...

BACKGROUND/AIMS Genetic single-nucleotide polymorphism (SNP) data are often analyzed using trend tests that rely on a specific assumption about the way that disease frequency varies across genotypes, but the validity of this assumption is not typically known. We explore the relative efficiency of trend tests in which the assumed model may or may not correspond to the true genetic model. METHO...