Absolute rate constants for hydrogen abstraction from hydrocarbons by the trichloromethylperoxyl radical

Absolute rate constants have been measured for the reactions of trichloromethylperoxyl radicals with cyclohexane, cyclohexene, and hexamethylbenzene. The CCl₃O₂ radicals were produced by pulse radiolysis of air-saturated CCl₄ solutions containing various amounts of the hydrocarbons. The rate constants were determined by competition with the one-electron oxidation of metalloporphyrins, using the rate of formation of the metalloporphyrin radical cation absorption to monitor the reaction by kinetic spectrophotometry. The rate constants for hydrogen abstraction from cyclohexane, cyclohexene, and hexamethylbenzene were found to be 1 × 10³, 1.0 × 10⁵, and 7.5 × 10⁴ M^?1 s^?1, respectively.     

Galerkin finite element method for one nonlinear integro-differential model

Galerkin finite element method for the approximation of a nonlinear integro-differential equation associated with the penetration of a magnetic field into a substance is studied. First type initial-boundary value problem is investigated. The convergence of the finite element scheme is proved. The rate of convergence is given too. The decay of the numerical solution is compared with the analytical results.     

Large time behavior of solutions to a nonlinear integro-differential system

Asymptotic behavior of solutions as t→∞ to the nonlinear integro-differential system associated with the penetration of a magnetic field into a substance is studied. Initial-boundary value problems with two kinds of boundary data are considered. The first with homogeneous conditions on whole boundary and the second with non-homogeneous boundary data on one side of lateral boundary. The rates of convergence are given too.     

One-electron oxidation and demetalation of metalloporphyrins and chlorophyll a in dichloroethane solutions as studied by pulse radiolysis

Formation of cation radicals by pulse radiolysis of metalloporphyrins and chlorophyll a in 1,2-dichloroethane is reported Demetalation of the metalloporphyrin by radiolytically produced HC1 is also observed. Rate constants for demetalation of ZnTPP and Chl a are 1 1 × 10⁸ and ≈ 3 × 10⁸ M^?1 S^?1. Oxidation of Chl a by ZnTPP⁺ has a rate constant of ≈ 4× 10⁹ M^?1S^?1.     

Osmotic backwash mechanism of reverse osmosis membranes

A new osmotic backwash (BW) model for reverse osmosis (RO) membranes was developed for conditions of no applied pressures across the membrane. This analytical model has one adjustable parameter representing the coefficient of a linearized convection term in the general convection–diffusion equation. An experimental RO/BW system was used for 12 data sets to verify the proposed BW model and illustrate its predictability. Results show deviations of the model from the data within a range of 5–15%. The described dilution mechanism of the feed concentration polarization (CP) layer is based on RO originated concentrated layer detachment from the membrane surface followed by its gradual dilution.The understanding gained in this research may be applied to automatic RO/BW cleaning cycles. A dominant RO parameter of the BW process is the RO initial driving force—the concentration difference across the membrane. Other RO process parameters – applied pressure and feed flow rate – have lesser effects. Both theoretical and experimental methods provide quantitative relationships between RO and BW variables that enable an understanding and control of the BW process.     

Aluminum electrodeposition from a non-aqueous electrolyte—a combined computational and experimental study

Electrodeposition of aluminum (Al) from an organic non-aqueous electrolyte of ethylbenzene containing aluminum bromide is demonstrated. It is offered as a simple method for the preparation of Al coatings. This work employs distinct electrochemical techniques and explores the effects of the experimental parameters on the kinetics of the process and the quality of the final coatings. The process presented here enables deposition of pure and crystalline Al at room temperature and facilitates the production of uniform Al coatings on various metallic substrates. Morphological studies establish that the growth of Al deposits follows an island mode, and thus, the most noteworthy effect of the substrate over the morphology of the deposits originates from its impact over the nucleation stage, and the density of islands. This study is complemented by theoretical modeling for the adsorption of Al atoms at the different surfaces. Corrosion evaluation determines the dissolution mechanisms of each of the studied substrates in the examined electrolyte. These findings further corroborate the claim that this electrolyte enables the reversible electrodeposition of Al.

     

Extending a Tandem Mass Spectral Library to Include MS<Superscript>2</Superscript> Spectra of Fragment Ions Produced In-Source and MS<Superscript>n</Superscript> Spectra

Tandem mass spectral library searching is finding increased use as an effective means of determining chemical identity in mass spectrometry-based omics studies. We previously reported on constructing a tandem mass spectral library that includes spectra for multiple precursor ions for each analyte. Here we report our method for expanding this library to include MS² spectra of fragment ions generated during the ionization process (in-source fragment ions) as well as MS³ and MS⁴ spectra. These can assist the chemical identification process. A simple density-based clustering algorithm was used to cluster all significant precursor ions from MS¹ scans for an analyte acquired during an infusion experiment. The MS² spectra associated with these precursor ions were grouped into the same precursor clusters. Subsequently, a new top-down hierarchical divisive clustering algorithm was developed for clustering the spectra from fragmentation of ions in each precursor cluster, including the MS² spectra of the original precursors and of the in-source fragments as well as the MSⁿ spectra. This algorithm starts with all the spectra of one precursor in one cluster and then separates them into sub-clusters of similar spectra based on the fragment patterns. Herein, we describe the algorithms and spectral evaluation methods for extending the library. The new library features were demonstrated by searching the high resolution spectra of E. coli extracts against the extended library, allowing identification of compounds and their in-source fragment ions in a manner that was not possible before.

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High‐order boundary conditions for linearized shallow water equations with stratification,dispersion and advection

The two‐dimensional linearized shallow water equations are considered in unbounded domains with density stratification. Wave dispersion and advection effects are also taken into account. The infinite domain is truncated via a rectangular artificial boundary ??, and a high‐order open boundary condition (OBC) is imposed on ??. Then the problem is solved numerically in the finite domain bounded by ??. A recently developed boundary scheme is employed, which is based on a reformulation of the sequence of OBCs originally proposed by Higdon. The OBCs can easily be used up to any desired order. They are incorporated here in a finite difference scheme. Numerical examples are used to demonstrate the performance and advantages of the computational method, with an emphasis is on the effect of stratification. Published in 2004 by John Wiley & Sons, Ltd.