Performance and modeling of advanced Ti:LiNbO3 digitaloptical switches

High-performance Y-branch digital optical switches realized in Ti:LiNbO₃ are presented. Their switching response functions have been optimized in terms of switch voltage and crosstalk ratio. The optimization is based on analyzing different types of waveguide shaping and switching arrangements using coupled mode theory and computer simulations. Excellent switching characteristics are achieved with devices exploiting a specially shaped waveguide branch in a dilated switch arrangement. Demonstrated performances include switching voltage as low as 9 V with crosstalk suppression better than 45 dB and fiber-to-fiber losses as low as 4 dB. Polarization independence with crosstalk suppression better than 40 dB over a 1520- to 1570-nm wavelength range is achieved for any applied switch voltage greater than 18 V. These optimized digital optical switches have further demonstrated the capability to reshape electrical input signals at switching rates of several hundred megahertz     

Synthesis, 1H−NMR and Electronic Absorption Spectra,and Halochromic Properties of Bis(2-methyl-1-phenyl-3-isoindolyl)-(het)arylmethane Dyes

Several bis(2-methyl-1-phenyl-3-isoindolyl)-(het)arylmethane perchlorate dye salts have been synthesised, the (het)aryl substituent representing the acceptor systems 2-benzothiazolyl, 1-methyl-2-benzimidazolyl, 4-quinolyl, 4- and 2-pyridyl as well as phenyl.The constitution of these green dye salts was supported by their ¹H-NMR spectra. The variation of the electronic absorption maxima of this dye series was in accord with theoretical considerations based on SCF-CI and PMO calculations. They give rise to the statement that the bathochromic effect of the varied (het)aryl group is essentially due to a LUMO-LUMO interaction with the di-isoindolylmethane cyanine moiety, i.e. a second-order perturbation, enlarging the bathochromic shift caused by the increased twist angles inflicted on the central bonds by the bulkiness of the (het)aryl substituents (a first-order perturbation). The halochromic properties of these dyes are explicable on the same basis.The dissociation constants pK^★ and pK^★_R+ were measured and compared with analogous di-indolyl- (1) and di-indolizinyl-hetaryl-methane dyes (4), showing little difference with regard to the former and the distinct sequence indolizinyl > indolyl > isoindolyl dye series for the latter.     

Is Chlorogenic Acid Bitter?

Chlorogenic acid at 5° published threshold concentration (100 mg/ L) in aqueous 0.2% potassium acid tartrate was not significantly more bitter than aqueous 0.2% potassium tartrate alone when evaluated by taste panel.     

Low-threshold, high-power zero-order lateral-mode DQW-SCH metal-clad ridge waveguide (AlGa)As/GaAs lasers

Metal-clad ridge waveguide (MCRW), double quantum well, separately confined heterostrucuture (DQW-SCH) lasers have been fabricated having continuous-wave (CW) threshold currents of 10?12 mA and external differential quantum efficiencies of 41?46% per uncoated facet. Light/current characteristics are linear to >70 mW, and zero-order lateral mode operation was measured at 56 mW. The CW burn-off power density is nearly double the best previously reported value.     

Convergence of genetic algorithms

The mean convergence of various versions of a genetic algorithm are considered. A number of convergence statements are formulated and relevant estimates are obtained. A hypothesis concerning the form of these estimates under variation of the structure of a genetic algorithm is put forward. Roman Riviyanovich Sharapov. Born 1981. Graduated from the Faculty of Mechanics and Mathematics, Ural State University, in 2003. Presently, a postgraduate at the Department of Mathematical Economics at the same university. Scientific interests: genetic algorithms, neural networks, and financial mathematics. Aleksandr Vyacheslavovich Lapshin. Born 1980. Graduated from the Faculty of Mechanics and Mathematics, Ural State University, in 2003. Presently, a postgraduate at the Department of Mathematical Economics at the same university. Scientific interests: financial mathematics, genetic algorithms, and neural networks.     

Synthesis, Characterization, and Formation Process of Na-X Zeolite from Coal Fly Ash

Using the SiO₂ and Al₂O₃ components of the amorphous phase in coal fly ash (Fa), Fa was converted to Na-X zeolites in NaOH-NaAlO₂ solutions by stirring at 35°C for 72 hr and then aging at 85°C for a given period. The molar ratio SiO₂/Al₂O₃ of the starting materials was controlled from 2.0 to 13.2. The resulting materials were characterized by various means. Increasing the SiO₂/Al₂O₃ ratio of the starting material increased the degree of crystallinity of faujasite, exhibiting a maximum at SiO₂/Al₂O₃ = 8.0. The faujasite formed was identified as Na-X zeolite with Si/Al = 1.20. The amorphous phase in Fa was dissolved during the stirring to form a precursor of zeolite, such as amorphous aluminosilicate. The Na-X zeolite was formed by aging for 24 hr, and the degree of crystallinity of this material was increased with the increasing aging period. The cation exchange capacity and specific surface area were increased with the increasing degree of crystallinity of the Na-X zeolites.     

Optimization of Automated Synthesis of 2-[18F]Fluoro-2-deoxy-D-glucose Involving Base Hydrolysis

Synthesis of 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) involving base hydrolysis was optimized. Fluorine-18 was isolated from irradiated water to more than 90% by sorption of [^{1 8}F]fluoride on QMA anion-exchange resin, which was followed by elution with a 96 : 4 (by volume) acetonitrile-water mixture containing Kryptofix 2.2.2 and potassium carbonate (molar ratio 2 : 1). This composition is the best for preparing the complex [K/K2.2.2]^{+ 18}F^- used in nucleophilic fluorinations. No additional azeotropic drying is required. Base hydrolysis under optimized conditions (40-45°C), followed by neutralization with HCl, removal of traces of the solvent, and purification of the final product on a combined SCX/Alumina N column, yielded [^{1 8}F]FDG of high radiochemical (>99%) and chemical purity with minimal product loss. With an RB-86 robotic system (Anatech, Sweden), the synthesis time was 38 min. The procedure is used in the Institute of Human Brain, Russian Academy of Sciences for routine synthesis of FDG; the radiochemical yield of the product by the end of synthesis (EOS) is reproducibly high: 63±3% (n = 40).     

Top-Seeded Melt-Growth of YBa2Cus3Ox Crystals for Neutron Diffraction Studies

We have grown cubic centimeter-size crystals of YBa₂Cu₃O _x suitable for neutron studies, by a top-seeded melt-growth technique. Growth conditions were optimized with an eye toward maximizing phase purity. It was found that the addition of 2% Y₂BaCuO₅ and 0.5% Pt (by mass) were required to prevent melt loss and to obtain the highest crystallinity. A neutron diffraction study on a mosaic of six such crystals found that the final Y₂BaCuO₅ concentration was 5%, while other impurity phases comprised less than 1% by volume. The oxygen content was set to x = 6.5, the crystals were detwinned, and then carefully annealed to give the well-ordered ortho-II phase. The neutron study determined that 70% of the mosaic's volume was in the majority orthorhomic domain. The neutron (006) and (110) rocking curve widths were ～1° per crystal and ～2.2° for the mosaic, and the oxygen chain correlation lengths were >100 Å in the a- and b-directions and ～50 Å in the c-direction.     

Equal-channel angular extrusion of beryllium

The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions have been successfully completed on Ni-canned billets of Be at approximately 425°C. No cracking was observed in the billets, and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed for a singlepass extrusion, including evidence of <c> and <c+a> dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation processing technique and the underlying physical processes which sustain the deformation. S.R. AGNEW, formerly with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115 This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.