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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 89-98 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The occurrence of instabilities in chemically reacting systems, resulting in unsteady and spatially inhomogeneous reaction rates, is a widespread phenomenon. In this article, we use nonlinear signal processing techniques to extract a simple, but accurate, dynamic model from experimental data of a system with spatiotemporal variations. The approach consists of a combination of two steps. The proper orthogonal decomposition [POD or Karhunen-Loève (KL) expansion] allows us to determine active degrees of freedom (important spatial structures) of the system. Projection onto these “modes” reduces the data to a small number of time series. Processing these time series through an artificial neural network (ANN) results in a low-dimensional, nonlinear dynamic model with almost quantitative predictive capabilities.This approach is demonstrated using spatiotemporal data from CO oxidation on a Pt (110) crystal surface. In this special case, the dynamics of the two-dimensional reaction profile can be successfully described by four modes; the ANN-based model not only correctly predicts the spatiotemporal short-term behavior, but also accurately captures the long-term dynamics (the attractor). While this approach does not substitute for fundamental modeling, it provides a systematic framework for processing experimental data from a wide variety of spatiotemporally varying reaction engineering processes.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1794-1803 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Time-dependent viscous flows driven by capillarity act to minimize the surface area of a fluid bounded in a plane geometry with initial gradients in surface curvature. These free-surface flows are solved by a finite-element model applied to describe the viscous sintering of two-dimensional ceramic particles. The numerical model is validated by comparison to the analytical solution obtained by Hopper (1990) for the coalescence of two infinite cylinders of equal cross section and is applied to several other geometries pertinent to the study of particle sintering for which analytical results are not available. Details of the flow fields and morphological evolution lend insight to the physical behavior of these systems and provide a basis for the more complete understanding of viscous sintering phenomena.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Four ethylene- 1 -butene copolymers of about the same comonomer content but obtained with different supported Ziegler-Natta catalyst systems have been studied. The effects of the catalyst and the crystallization conditions on the morphological structure have been analyzed. These two factors'clearly affect the melting endotherms and the most probable crystallite thickness of the copolymers, although no important differences were found in the crystalline contents. The catalyst system influences the melting pattern due to changes in the chemical composition distribution, i.e., variations in the comonomer content between chains of different molecular weight.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 404-409 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this work we report the emulsion copolymerization of styrene and acrylic acid using a cationic (cetyltrimethylammonium bromide or CTAB) or an anionic (sodium dodecylsulfate or SDS) emulsifier. Latexes were stable and monodisperse with spherical particles of ∼100 nm for the CTAB latex and of ∼70 nm for the SDS latex. However, a random copolymer was produced with CTAB whereas a “blocky” copolymer was obtained with SDS. Here we propose a mechanism to explain these structural differences in terms of the relative reactivities of styrene and acrylic acid and of their initial location and distribution in the SDS and CTAB emulsions.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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