8,771 research outputs found

    Fluidized-bed reactor modeling for production of silicon by silane pyrolysis

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    An ideal backmixed reactor model (CSTR) and a fluidized bed bubbling reactor model (FBBR) were developed for silane pyrolysis. Silane decomposition is assumed to occur via two pathways: homogeneous decomposition and heterogeneous chemical vapor deposition (CVD). Both models account for homogeneous and heterogeneous silane decomposition, homogeneous nucleation, coagulation and growth by diffusion of fines, scavenging of fines by large particles, elutriation of fines and CVD growth of large seed particles. At present the models do not account for attrition. The preliminary comparison of the model predictions with experimental results shows reasonable agreement. The CSTR model with no adjustable parameter yields a lower bound on fines formed and upper estimate on production rates. The FBBR model overpredicts the formation of fines but could be matched to experimental data by adjusting the unkown jet emulsion exchange efficients. The models clearly indicate that in order to suppress the formation of fines (smoke) good gas-solid contacting in the grid region must be achieved and the formation of the bubbles suppressed

    Radiative capture of polarized neutrons by polarized protons

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    A model-independent irreducible tensor approach to p(n,gamma)d is presented and an explicit form for the spin-structure of the matrix for the reaction is obtained in terms of the Pauli spin-matrices for the neutron and the proton. Expressing the multipole amplitudes in terms of the triplet --> triplet and singlet --> triplet transitions, we point out how the initial singlet and triplet contributions to the differential cross section can be determined empirically.Comment: Revised version; typeset using RevTeX4; 6 pages, no figure

    Deuteron photodisintegration with polarized photons at astrophysical energies

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    Following precise experimental studies at the Duke Free-Electron Laser Laboratory, we discuss photodisintegration of deuterons with 100% linearly polarized photons using a model independent theoretical approach taking together M1M1 and E1E1 amplitudes simultaneously. The isoscalar M1sM1_s contribution is also taken exactly into account. From the existing experimental measurement on doubly polarized thermal neutron capture, it is seen that the isoscalar M1sM1_s contribution could be of the same order of magnitude as the experimentally measured cross sections at energies relevant to Big Bang Nucleosynthesis (BBN). Therefore appropriate measurements on deuteron photodisintegration are suggested to empirically determine the M1sM1_s contribution at astrophysical energies.Comment: 5 Pages, Latex-2

    Mel Greaves: Cancer through the Lens of Evolution

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    Standards relevant to transformers – Part III

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    CIGRÉ counts more than 3,500 experts from all around the world working together to optimise the existing equipment and power systems, including transformers

    Standards relevant to transformers – Part IV

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    Last three parts of this series covered the evolution of Standards / Technical Brochures related to Power Transformers under IEC, IEEE and CIGRE and listed current standards issued by them. Now we see the evolution of transformer standards in Britain and the current position of European Standards (EN) on Transformers

    Standards relevant to transformers – Part I

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    Standards are formulated to meet the generally recognised demands, minimum performance and safety requirements, as well as to make sure that the product from different manufacturers is similar and consistent. A survey is done on the evolution of national standards for transformers and of the range of IEC / IEEE standards available today for transformer engineers. Of course, standards are dynamic and are under continuous revisions and additions. Hence, no claim is made that the listings provided are the latest or include all relevant standards connected with transformers. A listing of standards, if made, as in this contribution in groups – viz. Application guides, Specification, Testing, Transformer Oil, Accessories, Raw Materials, Installation, Operation, Maintenance and Protection, with relevant IEC and IEEE standard numbers for each subject – will be useful as a quick reference for transformer engineers engaged in the selection, procurement, manufacturing, testing, installation, operation, maintenance, and protection of transformers. A list of CIGRE technical brochures relevant to transformers is also included