Fabrication and Characterization of Monolithically Fused Wavelength-Independent 1 × 4 Couplers

A new method for the fabrication of a monolithic 1 × 4 single-mode fused coupler is described together with details of its performance in terms of coupling ratio, spectral response and polarization sensitivity. The fabricated device exhibits ultra-broadband performance with low polarization dependent loss. The coupling pattern exhibits identical coupling to all interacting fibers, enabling an easy control on fabrication parameters of the device.     

Preparation,Characterization, and X-Ray Structure Analysis of 1,4-Diazabicyclo-2,2,2-octane (DABCO) and Ammonium Cation with Tetrathiomolybdate Anion

The reaction of H₂S gas with an aqueous solution of ammonium heptamolybdate in the presence of 1,4-diazabicyclo-2,2,2-octane (DABCO) led to the formation of a red colored complex. The complex was recrystallized in hot water and characterized by elemental analysis and UV-Visible, FT-IR, and ¹H NMR spectroscopy. The single sharp peak in the ¹H NMR spectrum has revealed that all the methylene protons are equivalent due to the hydrogen resonating between the two nitrogens in the DABCO cation. The complex crystallizes in a cubic system with space group P2₁3, a = 10.9482(9) Å, α = 90°, V = 1325.3(7) ų, R ₃ = 0.0154, wR ₂ = 0.038, Z = 4. The structure consists of the tetrahedral tetrathiomolybdate anions, which form an extended three-dimensional network in the solid state involving Mo-S...H-N hydrogen bonding interactions with DABCO and the ammonium cation.Original Russian Text Copyright © 2004 by S. Pokhrel, K. S. Nagaraja, B. Varghese__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 945–949, September–October, 2004.     

New allene synthesis via carbocupration-zinc carbenoid homologation and beta-elimination sequence

[reaction: see text] Polysubstituted propadienes are obtained in good to excellent yields by the consecutive carbocupration-homologation-beta-elimination reactions on the easily accessible alkynyl sulfoxides or sulfones. This one-pot reaction also allows the preparation of functionalized allenes.     

Liesegang patterns: Estimation of diffusion coefficient and a plausible justification for colloid explanation

The Liesegang phenomenon is interpreted as a moving boundary problem. The existing time law, spacing law, and width law are revisited and reformulated on the basis of the new scenario. A better understanding of the basic facts associated with pattern formation is made possible with the new concept. The phenomenon is explained on the basis of colloidal kinetics. Diffusion coefficients of the outer electrolyte in the gel for various experiments in the literature are calculated. The diffusion coefficients so calculated range from 1.792-5.996᎒^-10 m² s^-1. It is suggested that such values confirm the fast colloidal dynamics during the process of periodic precipitation pattern formation.     

Thermal Decomposition Studies of Neodymium Praseodymium Oxalate Decahydrate Crystals

Neodymium praseodymium oxalate decahydrate crystals were grown using silica gel technique by the controlled reaction of rare earth nitrates with oxalic acid. The grown crystal were characterized using X-ray powder diffraction and thermogravimetric analysis. The thermal decomposition process of the crystals is in good agreement with the proposed crystal structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polydimethylsiloxane–cristobalite composite adhesive system for aerospace applications

The effect of phase‐pure cristobalite (a high temperature crystalline polymorph of silica) on the adhesive characteristics of hydroxyl terminated polydimethylsiloxane (PDMS) was studied. The potential advantages of PDMS/cristobalite composite system as an adhesive for aerospace applications are also discussed. A PDMS/cristobalite composite adhesive system containing different filler contents (0–46 volume percentage, vol%) was prepared. The filler material, phase‐pure cristobalite, was synthesized by the pyrolysis of fused silica at 1400°C. The mechanical, rheological, and thermal characteristics of the composites were studied. A high yield stress (0.151 Pa), shear‐thinning index (1.051), and fast recovery rate were observed for ～34 vol% cristobalite loading, which indicate that PDMS retains its excellent adhesive and flow characteristics even at high filler loading with enhanced mechanical characteristics. Thermal analysis shows the onset of degradation of PDMS shifts to higher temperatures, 372–438°C and 317–417°C in nitrogen and air atmosphere respectively, which shows excellent thermal stability. The residual component yields after thermal degradation of PDMS/cristobalite composite system in nitrogen and air atmosphere show different degradation mechanisms. Copyright © 2008 John Wiley & Sons, Ltd.     

Ferroelectric polymer nanocomposite alignment layer in twisted nematic liquid crystal devices for reducing switching voltage

Twisted nematic liquid crystal device (TNLCD) was fabricated using a ferroelectric zinc oxide (ZnO)-doped polyimide alignment layer. The ferroelectric nanoparticle can produce a local electric field, which can trigger the orientation of liquid crystal molecule and reduces the switching voltage. The uniform dispersion of ferroelectric ZnO nanoparticles in the alignment layer was studied using field emission scanning electron microscopy and atomic force microscopy. The ferroelectric property of ZnO-doped polyimide was investigated using dynamic contact electrostatic force microscopy. An increased local electric field due to the presence of nano ZnO was confirmed with the help of scanning tunnelling microscopy. An augmentation of capacitance was observed with an increase in concentration, which substantiates the reduction of switching voltage of TNLCD with the modification of ferroelectric nanoparticle-doped alignment layer.     

Oligo(p‐phenylene‐ethynylene)‐Derived Super‐π‐Gelators with Tunable Emission and Self‐Assembled Polymorphic Structures

Linear π‐conjugated oligomers are known to form organogels through noncovalent interactions. Herein, we report the effect of π‐repeat units on the gelation and morphological properties of three different oligo(p‐phenylene‐ethynylene)s: OPE3 , OPE5 , and OPE7 . All of these molecules form fluorescent gels in nonpolar solvents at low critical gel concentrations, thereby resulting in a blue gel for OPE3 , a green gel for OPE5 , and a greenish yellow gel for OPE7 . The molecule–molecule and molecule–substrate interactions in these OPEs are strongly influenced by the conjugation length of the molecules. Silicon wafer suppresses substrate–molecule interactions whereas a mica surface facilitates such interactions. At lower concentrations, OPE3 formed vesicular assemblies and OPE5 gave entangled fibers, whereas OPE7 resulted in spiral assemblies on a mica surface. At higher concentrations, OPE3 and OPE5 resulted in super‐bundles of fibers and flowerlike short‐fiber agglomerates when different conditions were applied. The number of polymorphic structures increases on increasing the conjugation length, as seen in the case of OPE7 with n=5, which resulted in a variety of exotic structures, the formation of which could be controlled by varying the substrate, concentration, and humidity.