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Decomposition Step (decomposition + step)
Selected AbstractsA domain decomposition method for modelling Stokes flow in porous materialsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2002Guangli Liu Abstract An algorithm is presented for solving the Stokes equation in large disordered two-dimensional porous domains. In this work, it is applied to random packings of discs, but the geometry can be essentially arbitrary. The approach includes the subdivision of the domain and a subsequent application of boundary integral equations to the subdomains. This gives a block diagonal matrix with sparse off-block components that arise from shared variables on internal subdomain boundaries. The global problem is solved using a biconjugate gradient routine with preconditioning. Results show that the effectiveness of the preconditioner is strongly affected by the subdomain structure, from which a methodology is proposed for the domain decomposition step. A minimum is observed in the solution time versus subdomain size, which is governed by the time required for preconditioning, the time for vector multiplications in the biconjugate gradient routine, the iterative convergence rate and issues related to memory allocation. The method is demonstrated on various domains including a random 1000-particle domain. The solution can be used for efficient recovery of point velocities, which is discussed in the context of stochastic modelling of solute transport. Copyright © 2002 John Wiley & Sons, Ltd. [source] The combined use of Patterson and Monte Carlo methods for the decomposition of a powder diffraction patternJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006Angela Altomare The success of ab initio crystal structure solution by powder diffraction data is strictly related to the quality of the integrated intensity estimates. A new method that is able to improve the pattern decomposition step has been developed. It combines the inversion of a suitably modified Patterson map with the use of the Hamming codes [13,10] and [40,36] in order to explore more decomposition trials. The new approach has been introduced in EXPO2005, an updated version of EXPO2004, and successfully applied to a set of known organic and inorganic structures. [source] Modified headspace-SPME-GC device for sampling volatile compounds in acidic mediumJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2003W. A. Araújo Abstract Most of the existing analytical methods for determining dithiocarbamate pesticide residues utilize an acid decomposition step, which promotes the release of carbon disulfide from the pesticide molecule. After release, the CS2 is sampled by static headspace techniques using gas-tight syringes and analyzed by gas chromatography with flame photometric detection (GC-FPD). In our search for faster analytical methodologies for sampling of volatile compounds we have used solid phase microextraction (SPME). However, evaluation of the commercially available SPME system for the analysis of CS2 obtained by decomposing dithiocarbamates showed it to be unsuitable for analysis in an acidic environment. The present communication reports the development of an appropriate device for sampling volatile compounds in an acidic environment by static headspace-SPME followed by GC-FPD. On examining the limitations of using a standard metal needle in HS-SPME sampling of analytes in acidic medium, a corrosion process was observed in both needle and fiber. A new double-needle device which avoids such corrosion problems was developed and built. The successful application of this device to the analysis of mancozeb in water samples is described. [source] Influence of the Composition on Crystal Phase and Thermal Behavior of trans -1,4-Butadiene/Isoprene CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 23 2007Fabio Bertini Abstract Butadiene/isoprene copolymers were prepared using the catalyst system V(acac)3 -MAO. The structure of the comonomers is trans -1,4 and the butadiene and isoprene units are statistically distributed along the polymer chain. The attitude of the butadiene sequences to crystallize in the monoclinic form and to evolve in the hexagonal form is preserved in the copolymer for a certain range of composition. The temperature interval between the two endothermic events is progressively reduced by increasing the isoprene content. The monoclinic/hexagonal transition produces a considerable increase in the lamellar thickness of the polymers. Thermal degradation of the copolymers is influenced by the composition and takes place in two different stages: a series of cyclization and cross-linking reactions occur before the decomposition step. [source] Estimation of Flame Retardancy Effect by Thermal Analysis Using Kinetic Parameters Obtained under Non-Isothermal Conditions in AirCHINESE JOURNAL OF CHEMISTRY, Issue 10 2009Gabriela Vlase Abstract A series of compounds obtained from urea, phosphoric acid and inorganic salts of Zn, Ni and Ca, were tested in respect of their flame-retardancy behavior. The estimation criteria were the kinetic parameters obtained in air, under non-isothermal conditions, on a Perkin-Elmer Diamond device, at heating rates of 5, 10, 12 and 15 deg·min,1. The flame-retardancy effect was assigned to the significant endothermic decomposition at relatively low temperature (150,200°C). The quantitative estimation of the thermal behavior was performed by comparison of the kinetic data obtained by Flyn-Wall-Ozawa, Friedman and NPK (Sempere-Nomen) methods. The kinetic homogeneity and a very good quality of the model are arguments in favour of the NPK method. The Ni containing material exhibited the best flame-retardancy behavior, i.e. higher activation energy and mass loss, respectively a single decomposition step with both physical and chemical processes. The results were validated by fire resistance tests. [source] | ||||||||||