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  • 1990-1994  (11)
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  • 1
    Digitale Medien
    Digitale Medien
    Thermal decomposition of 2, 3-dimethyl butane: Experiments and mechanistic modelling (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 241-251 
    Details
    ISSN: 0930-7516
    Schlagwort(e): Chemistry ; Industrial Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Pyrolysis of 2,3-dimethyl butane (DMB) was carried out in a quartz flow reactor in the temperature range from 740 to 1032 K at normal pressure. The input concentration of DMB was 3.3 × 10-3 mol/1 using argon as diluent. Reaction time ranged between 3.1 and 3.9 s. The following products were analyzed by two-column gas chromatography: hydrogen, methane, ethene, propane, propene, butenes, butadiene, 2-methyl-2-butene, isoprene, benzene and toluene. Compared to thermal decomposition of n-hexane under similar experimental conditions, the main difference concerned the formation of ethylene, ethane and branched alkanes. A reaction model, based on elementary reactions, was developed to predict the experimental results and to verify our data basis of elementary reactions under different conditions. The model gives a quantitative description of the complex chemistry of the process. In addition, an algorithm is presented for model reduction.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/ceat.270130133
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  • 2
    Buch
    Buch
    Adaptive Linienmethoden für nichtlineare parabolische Systeme in einer Raumdimension. Zugl. Berlin, Freie Univ., Diss., 1994; TR 93-14 (1993)
    Berlin :Konrad-Zuse-Zentrum,
    Details
    Titel: Adaptive Linienmethoden für nichtlineare parabolische Systeme in einer Raumdimension. Zugl. Berlin, Freie Univ., Diss., 1994; TR 93-14
    Autor: Nowak, Ulrich
    Verlag: Berlin :Konrad-Zuse-Zentrum,
    Erscheinungsjahr: 1993
    Seiten: 177 S.
    Serie: Technical Report TR 93-14
    Materialart: Buch
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    ZIB Katalog
    Zuse-Institut Berlin get availability status
  • 3
    facet.materialart.
    Unbekannt
    Prognoserechnung zur AIDS-Ausbreitung in der Bundesrepublik Deutschland (1994)
    Details
    Publikationsdatum: 2014-02-26
    Beschreibung: Die Autoren sind sich dar{ü}ber im klaren, daß zahlreiche Imponderabilien die Ergebnisse der vorgelegten Modellrechnungen beeinflussen k{ö}nnen. Immerhin repräsentiert jedoch das vorgelegte mathematische Modell die Summe unserer derzeitigen Kenntnisse zur Fragestellung AIDS--Epidemie; neu hinzukommende Erkenntnisse lassen sich rasch einarbeiten und in ihren Konsequenzen überschauen. Die Entwicklung neuer effizienter numerischer Methoden spielte eine Schlüsselrolle bei der tatsächlichen Simulation dieses umfangreichen realitätsnahen mathematischen Modells.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: reportzib , doc-type:preprint
    Format: application/postscript
    Format: application/pdf
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  • 4
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    Die Ausbreitung von HIV/AIDS in Ballungsgebieten. (1991)
    Details
    Publikationsdatum: 2014-03-06
    Beschreibung: The rapidly increasing number of AIDS cases requires a realistic estimation of the future development of the HIV/AIDS disease. For that purpose we develop a large system of coupled nonlinear differential equations describing simultaneously the dynamics of the development of the disease, the population size, the gender and age structure. A set of 1650 coupled equations are linked by balanced parameters. The balancing procedure is described by a set of (formally) 2,178,000 additional algebraic conditions. As the considered system is stiff, it requires new special extrapolation methods combined with techniquees of dynamical sparsing for the solution of sparsely filled systems. According to our simulations we expect 19,0,000 deaths caused by AIDS in the Federal Republic of Germany (former territories) in the year 2000. Such an epidemical spread would tie up about 4-7 percent of the actual health care workers.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: reportzib , doc-type:preprint
    Format: application/pdf
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  • 5
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    Unbekannt
    Adaptive Linienmethoden für nichtlineare parabolische Systeme in einer Raumdimension. (1993)
    Details
    Publikationsdatum: 2014-02-27
    Beschreibung: A new method for the numerical solution of highly nonlinear, coupled systems of parabolic differential equations in one space dimension is presented. The approach is based on a classical method of lines treatment. Time discretization is done by means of the semi--implicit Euler discretization. Space discretization is done with finite differences on non--uniform grids. Both basic discretizations are coupled with extrapolation techniques. With respect to time the extrapolation is of variable order whereas just one extrapolation step is done in space. Based on local error estimates for both, the time and the space discretization error, the accuracy of the numerical approximation is controlled and the discretization stepsizes are adapted automatically and simultaneously. Besides the local adaptation of the space grids after each integration step (static regridding), the grid may even move within each integration step (dynamic regridding). Thus, the whole algorithm has a high degree of adaptivity. Due to this fact, challenging problems from applications can be solved in an efficient and robust way.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
    Format: application/postscript
    Format: application/pdf
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  • 6
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    Recent Developments in Chemical Computing (1990)
    Details
    Publikationsdatum: 2020-12-14
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 7
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    Recent Developments in Chemical Computing. (1990)
    Details
    Publikationsdatum: 2014-02-26
    Beschreibung: The paper surveys three aspects of chemical computing, which seem to play a role in recent developments. First, extrapolation methods for the numerical treatment of differential- algebraic equations are introduced. The associated extrapolation code LIMEX has reached a certain level of sophistication, which makes it a real competitor to the elsewhere widely used multi-step code DASSL of Petzold. Second, adaptive methods of lines for partial differential equations such as those arising in combustion problems are treated. Both static and dynamic regridding techniques are discussed in some detail. Finally, some new ideas about the treatment of the kinetic equations arising from polymer reactions are presented. The new feature of the suggested approach is the application of a Galerkin procedure using sets of orthogonal polynomials over a discrete variable (which, of course, in the case of polymer reactions is the polymer degree). The new approach may open the door to a new reliable low dimensional treatment of complex polymer reactions.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
    Format: application/pdf
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  • 8
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    Dynamic Sparsing in Stiff Extrapolation Methods. (1992)
    Details
    Publikationsdatum: 2014-02-26
    Beschreibung: Based on a simple stability analysis for the semi--implicit Euler discretization a new dynamic sparsing procedure is derived. This procedure automatically eliminates ``small'' elements of the Jacobian matrix. As a consequence, the amount of work needed to handle the linear algebra within a semi--implicit extrapolation integrator can be reduced drastically. Within the course of integration the sparsing criterion, which decides what ``small'' means, is dynamically adapted to ensure stability of the discretization scheme. Thus, stepsize restrictions due to instability can be avoided. Numerical experiments for quite different problems show robustness and efficiency of this dynamic sparsing technique. The techniques developed here in the context of stiff extrapolation integrators can, in principle, be applied to W--methods, where exact Jacobians may be replaced by ``sufficiently good'' approximations. {\bf Keywords:} Large scale integration, extrapolation methods, stiff ODEs, W--methods, sparse matrix techniques.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
    Format: application/postscript
    Format: application/pdf
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  • 9
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    MEXX - Numerical Software for the Integration of Constrained Mechanical Systems. (1992)
    Details
    Publikationsdatum: 2020-11-16
    Beschreibung: MEXX (short for MEXanical systems eXtrapolation integrator) is a Fortran code for time integration of constrained mechanical systems. MEXX is suited for direct integration of the equations of motion in descriptor form. It is based on extrapolation of a time stepping method that is explicit in the differential equations and linearly implicit in the nonlinear constraints. It only requires the solution of well--structured systems of linear equations which can be solved with a computational work growing linearly with the number of bodies, in the case of multibody systems with few closed kinematic loops. Position and velocity constraints are enforced throughout the integration interval, whereas acceleration constraints need not be formulated. MEXX has options for time--continuous solution representation (useful for graphics) and for the location of events such as impacts. The present article describes MEXX and its underlying concepts.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
    Format: application/pdf
    Format: application/postscript
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  • 10
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    GIANT - A Software Package for the Numerical Solution of Very Large Systems of Highly Nonlinear Equations. (1990)
    Details
    Publikationsdatum: 2014-02-26
    Beschreibung: This report presents the final realization and implementation of a global inexact Newton method proposed by Deuflhard. In order to create a complete piece of software, a recently developed iterative solver (program GBIT) due to Deuflhard, Freund, Walter is adapted and serves as the standard iterative linear solver. Alternative linear iterative solvers may be adapted as well, e.g. the widely distributed code GMRES. The new software package GIANT (Global Inexact Affine Invariant Newton Techniques) allows an efficient and robust numerical solution of very large scale highly nonlinear systems. Due to the user friendly interface and its modular design, the software package is open for an easy adaptation to specific problems. Numerical experiments for some selected problems illustrate performance and usage of the package.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
    Format: application/postscript
    Format: application/pdf
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