Kaiserslautern, Rheinland-Pfalz, Germany

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Department of Computer Science
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Department of Physics
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Department of Mathematics
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  • [Show abstract] [Hide abstract]
    ABSTRACT: O-Acyl derivatives of 3-hydroxy-gamma-butyrolactone are formed in up to 20% yield as by-products from 1-alkyl- and 1-phenyl-substituted 4-pentenols and tert-butyl hydroperoxide (TBHP) in vanadium-catalyzed synthesis of (tetrahydrofuran-2-yl)-methanols. The lactones are secondary products formed from (tetrahydrofuran-2-yl)-methanols via hydrogen atom abstraction in positions 4 and 5, as derived from experiments starting from deuterium-labeled alkenols. Stereocenters at tetrahydrofuran carbon 2 and the proximate hydroxyl carbon of the alkanol side chain retain configuration in the course of oxidative tetrahydrofuran conversion. In an atmosphere of nitrogen or argon, no gamma-butyrolactone formation occurs, pointing to dioxygen as terminal oxidant for the secondary oxidation. Adding cyclohexa-1,4-diene or gamma-terpinene to a solution of a 4-pentenol, TBHP, and a vanadium catalyst exposed to air inhibits formation of gamma-butyrolactones. A third approach to prevent gamma-butyrolactones from being formed in oxidative 4-pentenol cyclization uses cis-2,6-bis-(methanol)-piperidine instead of N-salicylidene-ortho-aminophenol as tridentate auxiliary for the vanadium catalyst.
    ChemInform 12/2014; 70(34):5321–5331. DOI:10.1002/chin.201449104
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    ABSTRACT: We continue the complexity analysis of parametric definite and indefinite integration given by Daun and Heinrich (2013). Here we consider anisotropic classes of functions, including certain classes with dominating mixed derivatives. Our analysis is based on a multilevel Monte Carlo method developed in Daun and Heinrich (2013) and we obtain the order of the deterministic and randomized nn-th minimal errors (in some limit cases up to logarithms). Furthermore, we compare the rates in the deterministic and randomized setting to assess the gain reached by randomization.
    Journal of Complexity 12/2014; DOI:10.1016/j.jco.2014.04.002
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    ABSTRACT: In this work, we consider the limited fitness for practical use of the Lattice Boltzmann Method for non-Newtonian fluid flows. Several authors have shown that the LBM is capable of correctly simulating those fluids. However, due to stability reasons the modeled viscosity range has to be truncated. The resulting viscosity boundaries are chosen arbitrarily, because the correct simulation Mach number for the physical problem is unknown a priori. This easily leads to corrupt simulation results. A viscosity adaption method (VAM) is derived which drastically improves the applicability of LBM for non-Newtonian fluid flows by adaption of the modeled viscosity range to the actual physical problem. This is done through tuning of the global Mach number to the solution-dependent shear rate. We demonstrate that the VAM can be used to accelerate LBM simulations and improve their accuracy, for both steady state and transient cases.
    Journal of Computational Physics 11/2014; 276:681–690. DOI:10.1016/j.jcp.2014.08.008


  • Address
    Gottlieb-Daimler-Str., 67653, Kaiserslautern, Rheinland-Pfalz, Germany
  • Head of Institution
    Prof. Dr. Helmut J. Schmidt
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Top publications last week by downloads

Food and Chemical Toxicology 02/2002; 40(2-3):193-236. DOI:10.1016/S0278-6915(01)00118-1

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