Local Linearization method for the numerical solution of stochastic differential equations

The Local Linearization (LL) approach for the numerical solution of stochastic differential equations (SDEs) is extended to general scalar SDEs, as well as to non-autonomous multidimensional SDEs with additive noise. In case of autonomous SDEs, the derivation of the method introduced gives theoretical support to one of the previously proposed variants of the LL approach. Some numerical examples are given to demonstrate the practical performance of the method.     

Surface and interface analysis at 3rd generation light sources

A third generation of synchrotron radiation facilities is coming on line worldwide, whose brilliance exceeds previous ultraviolet and x-ray light sources by four orders of magnitude. The capabilities at second and third generation light sources are discussed, using examples in surface and interface chemistry and magnetic nanostructures. The authors' experience at the IBM-Tennessee-Tulane-LLNL-LBL undulator beam line will serve as a hands-on guide for work at one of the new facilities.     

Influence of geology and soil particle size on the surface-area/volume activity ratio for natural radionuclides

The radioactive concentrations of²²⁶Ra,²³²Th,²³⁵U and⁴⁰K in surface soil of the province of Cáceres (Spain) were studied as a function of the geology and grain size. The activities of the four radionuclides in granitic and metamorphic soils have normal frequency distributions, with the mean value being significantly higher for the granitic soils than for the metamorphic soils. Sedimentary soils present asymmetric distributions, and their activities lie between the previous two types. The specific activities of the four radionuclides rises as the particle radius decreases. The equationA _e =(P ₁/R)+P ₂ describes the dependence of the specific activityA _e on radiusR, P ₁ andP ₂ being parameters that are related to the surface area and volume activities of the grains. The isotopes²²⁶Ra,²³²Th and²³⁵U accumulate with greater intensity on the surface of the grains than⁴⁰K. This effect is more pronounced in granitic and sedimentary soils than in metamorphic soils.     

Measurement of the enthalpies of vaporization and sublimation of solids aromatic hydrocarbons by differential scanning calorimetry

An experimental procedure is proposed for direct measurement of the heat involved in the vaporization of a solid organic compound above its normal melting temperature. This technique consists on the fusion of a solid aromatic hydrocarbon, which is then vaporized by a sudden decrease of the pressure. The direct register of heat flow as function of time by differential scanning calorimetry allows the quantifying of the enthalpy of vaporization of compounds such as phenanthrene, β-naphthol, pyrene, and anthracene. Enthalpies of vaporization were measured in an isothermal mode over a range of temperatures from 10 to 20 K above the melting temperatures of each compound, while enthalpies of fusion were determined from separate experiments performed in a scanning mode. Enthalpies of sublimation are computed from results of fusion and vaporization, and then compared with results from the literature, which currently are obtained by calorimetric or indirect techniques.     

Studies on the kinetics of the ligand-substitution reaction of the Zinc(II)-4-(4′-methyl-2-́thiazolylazo)-2-methylresorcinol with 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid

Spectrophotometric studies have been carried out on the kinetics of the ligand-substitution reaction of the Zinc(II)-4-(4′-methyl-2′-thiazolylazo)-2-methylresorcinol complex with 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, in the pH range 8.4–9.4 at μ = 0.25 and 25 °C. The reaction rate constant was established to be $\text{?}\text{(d[}\text{ZnR}{}_2\text{]}\text{dt)}\text{= K[}\text{ZnR}{}_2\text{][H}{}^{\mathrm{+}}\text{][Y′]/[HR}{}^{\mathrm{?}}\text{], and}\text{K = 6.88 × 10}{}^4\text{liter · mol}{}^{\mathrm{?1}}\text{· sec}{}^{\mathrm{?1}}$ was obtained.     

Ba(OH)2 as catalyst in organic reactions, part XIV. Michael addition catalyzed by barium complex salts in the homogeneous phase

Michael addition to chalcone is catalyzed by barium complex salts in the homogeneous phase under various conditions. The nature of these intermediates is analyzed. These complex salts are described for the first time. The Michael adduct of malonodinitrile to chalcone is described for the first time.

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Reduction by hydrogen transfer processes, II. Reduction of substituted derivatives of benzaldehyde

In the present paper, date are reported on transfer hydrogenation of aromatic aldehydes with commercial and synthetic Pd catalysts, based on SiO₂–AlPO₄ (2080 mass). Cyclohexenes and ,-unsaturated alcohols have been tested as hydrogen donors. The reaction products obtained upon reduction of benzaldehyde were benzyl alcohol and toluene (hydrogenation) and benzene and formaldehyde (hydrogenolysis), while methyl, ethoxycarbonyl and hydroxyl groups also present are not affected by the reaction. The selectivity towards each product depends on both the hydrogen donor and the catalyst used. When electron-donor substituents exist on the substrate, a decrease of the reaction rate towards the hydrogenolysis products is observed.

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Simultaneous Kinetic Determination of Carbamate Pesticides after Derivatization withp-Aminophenol by Using Partial Least Squares

A method has been developed for the fast spectrophotometric determination of propoxur, carbaryl, and ethiofencarb in water samples using injection analysis in the stopped-flow mode. The method is based on the reaction betweenp-aminophenol and the phenolic compounds obtained from the pesticides, after a previous hydrolysis with 0.05MNaOH at room temperature for 15 min. The partial least-squares treatment of the spectrophotometry kinetic data provides a simultaneous determination of the three carbamate pesticides assayed with a relative accuracy error lower than 5% in complex mixtures also containing formetanate, which is only partially hydrolyzed under the experimental conditions and cannot be determined accurately by the above procedure.