Kinetics of the cis,cis to trans,trans isomerization of 1,1,2,2,5,5,6,6-octamethyl-1,2,5,6-tetrasilacycloocta-3,7-diene

The kinetics of the ruthenium-promoted cis,cis to trans,trans isomerization of 1,1,2,2,5,5,6,6-octamethyl-1,2,5,6-tetrasilacycloocta-3,7-diene were investigated. Incubation of a ruthenium alkylidene complex, (Cy(3)P)RuCl(2)(==CHPh)Ru(p-cymene)Cl(2), in CD(2)Cl(2) for 5 days at 40 degrees C afforded a catalytically active ruthenium species that was shown to be responsible for promoting the isomerization. The isomerization was observed to proceed in two steps: (1) conversion of the starting cis,cis isomer to a proposed cis,trans intermediate and (2) subsequent conversion of the intermediate to the product trans,trans isomer. Kinetic studies demonstrated that the two steps are first-order with respect to the concentrations of the cis,cis isomer, the intermediate, and the ruthenium alkylidene complex. The data were further consistent with a mechanism involving bimolecular hydride addition-elimination during the two isomerization steps.     

FPGA-Implemented Fractal Decoder with Forward Error Correction in Short-Reach Optical Interconnects

Forward error correction (FEC) codes combined with high-order modulator formats, i.e., coded modulation (CM), are essential in optical communication networks to achieve highly efficient and reliable communication. The task of providing additional error control in the design of CM systems with high-performance requirements remains urgent. As an additional control of CM systems, we propose to use indivisible error detection codes based on a positional number system. In this work, we evaluated the indivisible code using the average probability method (APM) for the binary symmetric channel (BSC), which has the simplicity, versatility and reliability of the estimate, which is close to reality. The APM allows for evaluation and compares indivisible codes according to parameters of correct transmission, and detectable and undetectable errors. Indivisible codes allow for the end-to-end (E2E) control of the transmission and processing of information in digital systems and design devices with a regular structure and high speed. This study researched a fractal decoder device for additional error control, implemented in field-programmable gate array (FPGA) software with FEC for short-reach optical interconnects with multilevel pulse amplitude (PAM-M) modulated with Gray code mapping. Indivisible codes with natural redundancy require far fewer hardware costs to develop and implement encoding and decoding devices with a sufficiently high error detection efficiency. We achieved a reduction in hardware costs for a fractal decoder by using the fractal property of the indivisible code from 10% to 30% for different n while receiving the reciprocal of the golden ratio.     

Application of Chromium-Containing Silica for Synthesising Functional Glasslike Materials by the Sol–Gel Method

A new variant of the sol–gel method for synthesising silica glasses and optical composites containing nanoparticles of chromium oxide has been designed. Monolithic gels are produced by mixing preformed silica modified with chromium oxide (Cr₂O₃/SiO₂), with a sol–gel solution containing Si(OC₂H₅)₄, and gelation catalyst ((CH₂)₆N₄ or NH₃). Highly dispersed Cr₂O₃/SiO₂ samples were synthesised through a step-by-step controlled adsorption of vapours of CrO₂Cl₂ and C₆H₁₄ on the surface of fumed silica (A-300) and a subsequent thermal decomposition. With increasing chromium concentration in samples from 0.9 to 5.1 wt.%, the size of chromium oxide nanoparticles increases from 10 to 46 nm. XRD, DTA, TG, IR-spectroscopy and measurements of specific surface area have been used to investigate structural and physico-chemical properties of Cr₂O₃/SiO₂ and xerogels during the course of their thermal transformations up to formation of glasses. A study has also been carried out of optical properties of transparent samples (distribution of refractive index values through cross section of a preform). The glasses synthesised with the aid of Cr₂O₃/SiO₂ have a more uniform distribution of doping constituents and exhibit a larger refractive index in comparison to glasses synthesised through impregnation of silica matrices with a solution of (NH₄)₂Cr₂O₇.     

A TPD‐MS study of the interaction of coumarins and their heterocyclic derivatives with a surface of fumed silica and nanosized oxides CeO2/SiO2, TiO2/SiO2, Al2O3/SiO2

The interactions between coumarins and the surface of fumed SiO₂, CeO₂/SiO₂, TiO₂/SiO₂ and Al₂O₃/SiO₂ were assessed by means of temperature‐programed desorption mass spectrometry. The different stages of the thermolysis of coumarin were identified and an analysis of the underlying reactions was performed. The kinetic parameters of the involved reactions were thus obtained. The decomposition of thiazolyl‐substituted coumarins was found to proceed through a ‘thiazole–thiazine’ ring expansion in the adsorbed state. A linear correlation between the sigma constants (Σσ) of the coumarin substituents and the activation energy of CO₂ formation was obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

The catalytic efficiency of Fe-containing nanocomposites based on highly dispersed silica in the reaction of CO2 hydrogenation

Research on Chemical Intermediates - Oxide Ni(80)Fe(20)/SiO2, Co(93)Fe(7)/SiO2, and Ni(19)Co(77)Fe(4)/SiO2 nanocomposites (NCs) were prepared using highly dispersed silica. It was modified by...     

Study of Water,Methanol And Isopropanol Adsorption on The Surface of Titanosilicas of Different Structure

The adsorption of water, methyl and i-propyl alcohol vapours has been studied on the surface of titanosilicas produced by various methods, as well as on the surface of pure silicon and titanium oxides. Based on findings of the studies, it was concluded that the presence on the surface of pyrogenic titanosilicas (TAS) of hydrolytically unstable Si-O-Ti bonds is responsible for their increased adsorption activity towards water molecules. A dissociative adsorption of H₂O on titanosiloxane bridges is accompanied by an appearance of additional groups ≡SiOH and ≡TiOH, which, in turn, become sites of adsorption of subsequent water molecules. This revised version was published online in August 2006 with corrections to the Cover Date.