An improved optical TE-TM mode splitter and modulator using a Ti-LiNbO3 Y-junction waveguide

An optical TE-TM mode splitter and modulator with an improved design using a Y-junction waveguide by Ti-diffusion in a Y-cut LiNbO₃ substrate has been fabricated and characterized. Improvements in fabrication and measurement techniques are discussed. Experimental results on the device characteristics are presented.     

Evaluation of time correlation functions from a generalized Enskog equation

Numerical results for the density and current correlation functions in dense hard-sphere fluids are obtained from a kinetic equation which is the extension of the linearized Enskog equation to finite wavelengths in order to demonstrate the convergence of the method of solution. Comparison is made to a previously proposed approximate solution.This work was performed in part under the auspices of the U.S. Department of Energy by the Lawrence Livermore Laboratory under contract number W-7405-ENG-48 and in part supported by the National Science Foundation.     

Field deformation and polarization change in a step-index optical fibre due to bending

The field distribution and polarization state of waveguide modes propagating around a curved dielectric optical fibre are investigated analytically by using a first-order perturbation theory. It is shown that the polarization direction of all modes except the HE_1m modes changes due to bending. Field distributions are also deformed and the shift in the field maximum, which takes place in the plane of curvature, is clarified for the dominant HE₁₁ mode.     

Congruence and Conjunctivity of Matrices

Congruence of arbitrary square matrices over an arbitrary field is treated here by elementary classical methods, and likewise for conjunctivity of arbitrary square matrices over an arbitrary field with involution. Uniqueness results are emphasized, since they are largely neglected in the literature. In particular, it is shown that a matrix S is congruent [conjunctive] to S₀⊕S₁ with S₁ nonsingular, and that if S₁ here is of maximal size among all nonsingular matrices R₁ for which R₀⊕R₁ is congruent [conjunctive] to S, then the congruence [conjunctivity] class of S determines that of S₁. Partially canonical forms (most of them already known) are derived, to the extent that they do not depend on the field. Nearly canonical forms are derived for “neutral” matrices (those congruent or conjunctive with block matrices $\text{O}\text{N}\text{M}\text{O}$ with the two zero blocks being square). For a neutral matrix S over a field F,the F-congruence [F-conjunctivity] class of S is determined by the F-equivalence class of the pencil S+tS' [S+tS¹] and, if the pencil is nonsingular, by the F[t]-equivalence class of S+tS' [S+tS¹].     

A Symmetric Function Resolution of the Number of Permutations With Respect to Block-Stable Elements

We consider a question raised by Suhov and Voice from quantum information theory and quantum computing. An element of a partition of {1, ..., n} is said to be block-stable for if it is not moved to another block under the action of π. The problem concerns the determination of the generating series for elements of with respect to the number of block-stable elements of a canonical partition of a finite n-set, with block sizes k₁, ..., k_r, in terms of the moment (power) sums p_q(k₁, ..., k_r). We also consider the limit subject to the condition that exists for q = 1, 2,.... Received January 31, 2006     

GaN-nanowire-based dye-sensitized solar cells

GaN nanowires typically exhibit high electron mobility and excellent chemical stability. However, stability of GaN is detrimental for successful attachment of dye molecules and its application in dye-sensitized solar cells (DSSCs). Here we demonstrate DSSCs based on GaN/gallium oxide and GaN/TiO _x core–shell structures, and we show that coating of GaN nanowires with a TiO _x shell significantly increases dye adsorption and consequently photovoltaic performance. The best cells exhibited short circuit current density of 1.83 mA/cm² and power conversion efficiency of 0.44% under AM 1.5 simulated solar illumination.     

Preparation and characterization of carbon nanotubes/epoxy resin nano-prepreg for nanocomposites

The surface carbon nanotubes (CNTs) were modified to generate functional reactors by using the sonicication method to distribute CNTs evenly among epoxy resin, which was prepared into nano-prepreg with carbon fibers. Additionally, based on various proportions of modified and unmodified CNTs, the mechanical properties and conductivities of the composite, as well as, the characteristics of material subjected to various temperature conditions were investigated. Experimental results indicate that increasing CNT content enhances the mechanical strength and electrical properties. At various temperatures, the mechanical strength drops with increase in temperature because different expansion coefficients differ between fiber and epoxy resin. Finally, the failure surface of nanocomposite was examined using scanning electron microscopy (SEM). Finally we provide a discussion of the failure mechanism of the material.     

Assessing the heterogeneity of a disease spread through a community

A multivariate non-parametric test and a semi-parametric regression model via counting process are proposed for detecting the heterogeneity of a disease spread through a community. The infection rates are allowed to depend on time in an arbitrary manner. Infectious data usually are not completely observed, nevertheless only partial information of the epidemic is needed for the suggested methods. The testing procedures and the associated methods of analysis are illustrated with reference to epidemics of respiratory disease on the Island of Tristan da Cunha in the South Atlantic