Central elements of the elliptic monodromy matrix algebra at roots of unity

The central elements of the algebra of monodromy matrices associated with the R-matrix are studied. When the crossing parameter w takes a special rational value , where N and n are positive coprime integers, the center is substantially larger than that in the generic case for which the “quantum determinant” provides the center. In the trigonometric limit, the situation corresponds to the quantum group at roots of unity. This is a higher rank generalization of the recent results by Belavin and Jimbo.     

Positive solutions for ratio-dependent predator-prey interaction systems

In this paper, we study the dynamics of predator-prey interaction systems between two species with ratio-dependent functional responses. First we provide sufficient and necessary conditions for positive steady-state solutions, and then we investigate the relationships between positive equilibria and positive solutions of the system over a large domain. Furthermore, we deal with the uniqueness and the stability of positive steady-states solutions with some assumptions. In addition, we discuss the extinction and the persistence results of time-dependent positive solutions to the system.     

Preparation of a reflective‐type electrochromic device based on monodisperse,micrometer‐size‐range polymeric microspheres and viologen pendants

A reflective electrochromic device (ECD) based on polymeric microspheres was proposed, and its feasibility for a display was investigated. The viologen moiety was introduced onto the surface of chloro‐functionalized polymeric microspheres via refluxing in toluene. The existence of the viologen pendants was confirmed with X‐ray photoelectron spectroscopy, and their redox reactions were examined with cyclic voltammetry. The ECD had an inherent white background without an applied potential because the micrometer size range of the substrate particles scattered the light, whereas a deep violet color appeared when 3.0 V was applied to the cell. This color change could have been caused by the reduction of viologen pendants on the surface of the polymeric microspheres. The reflectance values of the ECD were observed with a spectrophotometer, and the response times and cyclic stability of the ECD, depending on the potential, were also examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6562–6572, 2005     

Thermal Stabilization of EDFA gain by hybrid concatenation of antimony-doped silica EDF

Sb-doped silica EDF showed an opposite temperature dependent gain profile compared to Al-doped silica EDF. Concatenation of those two EDFs showed a gain variation less than ± 0.4 dB over 40nm of C-band with the 15dB gain, in the temperature range of - 40 to + 80℃.     

Synthesis and characterization of fluorene‐based low‐band gap copolymers containing propylenedioxythiophene and benzothiadiazole derivatives for bulk heterojunction photovoltaic cell applications

The following noble series of soluble π‐conjugated statistical copolymers was synthesized by palladium catalyzed Suzuki polymerization: poly[(9,9‐dioctylfluorene)‐alt‐(4,7‐bis(3′,3′‐dihepyl‐3,4‐propylenedioxythienyl)‐2,1,3‐benzothiadiazole)] (PFO‐PTBT) derived from poly(9,9‐dioctylfluorene) (PFO) and poly[(4,7‐bis(3′,3′‐dihepyl‐3,4‐propylenedioxythienyl)‐2,1,3‐benzothiadiazole)] poly(heptyl₄‐PTBT). The structure and properties of these polymers were characterized using ¹H‐, ¹³C‐NMR, UV–visible spectroscopy, elemental analysis, GPC, DSC, TGA, photoluminescence (PL), and cyclic voltammetry (CV). The statistical copolymers, PFO‐PTBT (9:1, 8.4:1.6, 6.5:3.5), were soluble in common organic solvents and easily spin coated onto indium‐tin oxide (ITO) coated glass substrates. The weight‐average molecular weight (M_w) and polydispersity of the PFO‐PTBT ranged from (1.0–4.2) × 10⁴ and 1.5–2.3, respectively. Bulk heterojunction photovoltaic cells with an ITO/PEDOT/PFO‐PTBT:PCBM/LiF/Al configuration were fabricated, and the devices using PFOPTBT (6.5:3.5) showed the best performance compared with those using PFO‐PTBT (9:1, 8.4:1.6). A maximum power conversion efficiency (PCE) of 0.50% (V_oc = 0.66 V, FF = 0.29) was achieved with PFO‐PTBT (6.5:3.5). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6175–6184, 2008     

Minimization of wafer bowing in GaN-based vertical light-emitting diodes by selective area growth using metal-organic chemical vapor deposition

The effect of selective area growth (SAG) on wafer bowing of GaN-based light-emitting diodes (LEDs) is investigated. The SAG of LED structures was carried out on a silicon dioxide (SiO₂) mask pattern with periodic 1000×1000 μm openings, along the sapphire 〈1?1 0 0〉 and 〈?1?1 2 0〉 directions. The morphology of a selectively-grown n-GaN epilayer was examined in relation to various growth parameters such as temperature, pressure, and V/III ratio. Under optimized growth conditions, formation of a ridge-shaped epilayer with a v-pit free smooth surface was realized. Furthermore, the ridge-shaped vertical LED structure, after the removal of the sapphire substrate by laser lift-off (LLO) showed less wafer bowing compared with conventional vertical LED structures. This is attributed to the suppression of lateral strain and dislocations during the site-selective growth process, due to a reduction in the lateral dimensions.     

Quantized rotation of atoms from photons with orbital angular momentum

We demonstrate the coherent transfer of the orbital angular momentum of a photon to an atom in quantized units of variant Planck's over 2pi, using a 2-photon stimulated Raman process with Laguerre-Gaussian beams to generate an atomic vortex state in a Bose-Einstein condensate of sodium atoms. We show that the process is coherent by creating superpositions of different vortex states, where the relative phase between the states is determined by the relative phases of the optical fields. Furthermore, we create vortices of charge 2 by transferring to each atom the orbital angular momentum of two photons.