8,974 research outputs found
Fluidized-bed reactor modeling for production of silicon by silane pyrolysis
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
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
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 and amplitudes simultaneously. The isoscalar
contribution is also taken exactly into account. From the existing experimental
measurement on doubly polarized thermal neutron capture, it is seen that the
isoscalar 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
contribution at astrophysical energies.Comment: 5 Pages, Latex-2
Standards relevant to transformers – Part III
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
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
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
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