Method of lines with boundary elements for 1‐D transient diffusion‐reaction problems

Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006     

Unified approach to photo-and electro-production of mesons with arbitrary spins

A new approach to identify the independent amplitudes along with their partial wave multipole expansions, for photo-and electro-production is suggested, which is generally applicable to mesons with arbitrary spin-parity. These amplitudes facilitate direct identification of different resonance contributions.      

Nickel peroxide: A more probable intermediate in the Ni(II)‐catalyzed decomposition of peroxomonosulfate

The Ni(II) ion catalyzed thermal decomposition of peroxomonosulfate (PMS) was studied in the pH range 3.42–5.89. The rate is first order in [PMS] and Ni(II) ion concentrations. At pH greater than or equal to 5.23, the reaction becomes zero order in [PMS] and this changeover in the order of the reaction occurs at a higher concentration of nickel ions. The first‐order kinetics in PMS can be explained as a rate‐limiting step and is the transformation of nickel peroxomonosulfate into nickel peroxide. This peroxide intermediate reacts rapidly with another PMS to give oxygen and Ni(II). The formation of nickel peroxide is associated with a small negative or nearly zero entropy of activation. The zero‐order kinetics in [PMS] can be explained by the fact that the hydrolysis of aquated nickel(II) ions into hydroxocompounds is the rate‐limiting step. The turnover number is 2 at pH 3.42 and increases with pH. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 320–237, 2007     

Photon interaction studies using 241Am γ-rays

We have carried out some photon interaction measurements using 59.54 keV γ-rays from a ²⁴¹Am source. These include γ attenuation studies as well as photoelectric absorption studies in various samples. The attenuation studies have been made using leaf and wood samples, samples like sand, sugar etc., which contain particles of varying sizes as well as pellets and aqueous solutions of rare earth compounds. In the case of the leaf and wood samples, we have used the γ-ray attenuation technique for the determination of the water content in fresh and dried samples. The variation of the attenuation coefficient with particle size has been investigated for sand and sugar samples. The attenuation studies as well as the photoelectric studies in the case of rare earth elements have been carried out on samples containing such elements whose K-absorption edge energies lie below and close to the γ-energy used. Suitable compounds of the rare earth elements have been chosen as mixture absorbers in these investigations. A narrow beam good geometry set-up was used for the attenuation measurements. A well-shielded scattering geometry was used for the photoelectric measurements. The mixture rule was invoked to extract the values of the mass attenuation coefficients for the elements from those of the corresponding compounds. The results are consistent with theoretical values derived from the XCOM package.     

Low Reynolds Number Interactions between Colloidal Particles near the Entrance to a Cylindrical Pore

The interaction between stable colloidal particles arriving at a pore entrance was studied using a numerical method for the case where the particle size is smaller than but of the same order as the pore size. The numerical method was adapted from a front-tracking technique developed for studying incompressible, multifluid flow by S. O. Unverdi and G. Tryggvason (J. Comp. Phys. 100, 25, 1992). The method is based on the finite difference solution of Navier-Stokes equation on a stationary, structured, Cartesian grid and the explicit representation of the particle-liquid interface using an unstructured grid that moves through the stationary grid. The simulations are in two dimensions, considering both deformable and nondeformable particles, and include interparticle colloidal interactions. The interparticle and particle-pore hydrodynamic interactions, which are very difficult to determine using existing analytical and semi-numerical, semi-analytical techniques in microhydrodynamics, are naturally accounted for in our numerical method and need not be explicity determined. Two- and three-particle motion toward a pore has been considered in our simulations. The simulations demonstrate how the competition between hydrodynamic forces and colloidal forces acting on particles dictate their flow behavior near the pore entrance. The predicted dependence of the particle flow behavior on the flow velocity and the ratio of pore size to particle size are qualitatively consistent with the experimental observations of V. Ramachandran and H. S. Fogler (J. Fluid Mech. 385, 129, 1999). Copyright 2000 Academic Press.     

Pulsed double resonance in the pure quadrupole regime: off-resonant DRRF technique for detection of rare quadrupolar nuclei

A scheme for the detection of rare quadrupolar nuclei based on off-resonant pulse excitation of the abundant quadrupolar nuclei coupled to the rare ones in the sample has been outlined and demonstrated. Pure quadrupole resonance spectrum of ²³Na in poly-crystalline samples of sodium chlorate has been thus recorded at room temperature. The present double resonance scheme in the pure quadrupole regime is marked by a substantial reduction in spectrometer transmitter power and hardware requirements.     

Estimation of tricalcium silicate through polymorphic transformation

Tricalcium silicate characteristically exhibits the most intense reversible transition at a temperature of about 915. The intensity of this effect can be used to estimate the amount of C₃S in mixtures and to calculate the degree of hydration of C₃S. Low sensitivity forT up to 800 and higher sensitivity between 800 and 1000 enable estimation of both Ca(OH)₂ and C₃S. Interference effects at higher temperatures owing to decarbonation, recrystallization to-wollastonite, and dehydration of the calcium silicate hydrate can be overcome by heating to 1000, cooling to 800, and reheating. A determination of the degree of hydration of C₃S obtained at different periods by DTA correlates well with that using the X-ray method.

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Zusammenfassung Trikalziumsilikat zeigt einen charakteristischen übergang bei einer Temperatur von ungefÄhr 915. Die IntensitÄt dieses Effektes kann zur Bestimmung der Mengen von C₃S in Gemischen und zur Errechnung seines Hydratationsgrades herangezogen werden. Die niedrige Empfindlichkeit fürT bis 800 und die höhere zwischen 800–1000 ermöglicht die Bestimmung von Ca(OH)₂ und C₃S. Interferenzeffekte bei höherer Temperatur, verursacht durch Entkohlung, Rekristallisation von -Wollastonit und Dehydratation von Kalziumsilikathydrat, können durch Glühen auf 1000, Abkühlen auf 800 und erneutes Glühen behoben werden. Die durch DTA erhaltenen Hydratationswerte von C₃S stimmten gut mit den röntgenographisch erhaltenen Ergebnissen überein.

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Résumé Le silicate tricalcique montre une transition réversible, intense et caractéristique à 915 environ. On peut utiliser l'intensité de cet effet pour estimer la teneur en C₃S des mélanges et pour calculer le taux d'hydratation. La sensibilité du signalT, faible jusqu'à 800 et plus élevée entre 800 et 1000 permet d'estimer à la fois Ca(OH)₂ et C₃S. Les effets d'interférence aux températures élevées dus à la décarbonatation, à la recristallisation en -wollastonite, et à la déshydratation du silicate calcium hydraté peuvent Être évités par chauffage à 1000, refroidissement à 800 et nouvel échauffement. La détermination du taux d'hydratation de C₃S par ATD recoupe bien les résultats de l'étude aux rayons X.

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915. C₃S C₃S. 800 800 1000 Ca(OH)₂, C₃S. , , - , 1000, 800 . C₃S, , , .

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The author wishes to thank G. M. Polomark, for experimental assistance.This paper is a contribution from the Division of Building Research, National Research Council of Canada, and is published with the approval of the Director of the Division.     

A new method for the determination of residual piperazine in pharmaceuticals by capillary gas chromatography

A new selective open tubular capillary gas chromatographic method is developed for the determination of trace amounts of piperazine. Piperazine is extracted from pharmaceuticals into cyclohexane and is partitioned with water. The aqueous solution is then injected into a 5% crosslinked Ph-Me silicone column programmed at 50-180 degrees C for 10 min. Piperazine is eluted after 3.18 min under isothermal conditions. The lower limit of determination is 0.4 ppm. This method has been successfully applied for the assay of piperazine in pharmaceutical formulations and its trace determination in fluoroquinolone drugs such as norfloxacin and ciprofloxacin. The method is reproducible and the standard and relative standard deviation for 10 repeated injections of 2 mug piperazine are 0.7 and +/-2.1% respectively.     

Synthesis of homoallylic chiral tertiary alcohols via chelation-controlled diastereoselective nucleophilic addition on alpha-alkoxyketones: application for the synthesis of the C(1)-C(11) subunit of 8-epi-fostriecin

[reaction: see text] Chiral beta-syn-alkoxyhomoallylic alcohols derived from alkoxyallylboration of aldehydes upon oxidation provided the corresponding chiral ketones. Chelation-controlled nucleophilic addition to these ketones occurred in a highly stereoselective manner to afford anti-homoallylic tertiary alcohols. This methodology has been applied for the synthesis of the C(1)-C(11) subunit of C(8)-epi-fostriecin.