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Closure theories with non-Gaussian restarts for truncated two-dimensional turbulence (1994)

Frederiksen, J. S. ; Davies, A. G. ; Bell, R. C.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 6 (1994), S. 3153-3163

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: NonMarkovian closure theories, with and without non-Gaussian restarts, are compared with ensemble averaged direct numerical simulations (DNS) for severely truncated two-dimensional Navier–Stokes flows. Both the closures and DNS are formulated for discrete spectra relevant to flows on the doubly periodic domain allowing unambiguous comparisons between the closure and DNS results. We examine the performance of the direct interaction approximation (DIA), self-consistent field theory (SCFT) and local energy-transfer theory (LET) closures and are particularly interested in the reliability of cumulant update versions of these closures (CUDIA, CUSCFT, and CULET). In the latter, the potentially long time-history integrals are periodically truncated and the closures are restarted using a three-point cumulant as the new non-Gaussian initial conditions, thus yielding computationally much more efficient closures. In 80-day integrations, the DIA replicates the DNS results most faithfully in inviscid, viscous decay and forced dissipative experiments. With an update time of T=10 days, the CUDIA is particularly promising performing nearly as well but with some extra oscillations at intermediate times. The SCFT and particularly LET, have spurious oscillations in inviscid and viscous decay experiments; this is also the case, but to a greater degree, for the CUSCFT and CULET closures.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.868139

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Digitale Medien

Formation, structure and bond dissociation thresholds of gas-phase vanadium oxide cluster ions (2001)

Bell, R. C. ; Zemski, K. A. ; Justes, D. R. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 114 (2001), S. 798-811

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The formation and structure of gas-phase vanadium oxide cluster anions are examined using a guided ion beam mass spectrometer coupled with a laser vaporization source. The dominant peaks in the anion total mass distribution correspond to clusters having stoichiometries of the form (VO2)n(VO3)m(O2)q−. Collision-induced dissociation studies of the vanadium oxide species V2O4–6−, V3O6–9−, V4O8–10−, V5O11–13−, V6O13–15−, and V7O16–18− indicate that VO2, VO3, and V2O5 units are the main building blocks of these clusters. There are many similarities between the anion mass distribution and that of the cation distribution studied previously. The principal difference is a shift to higher oxygen content by one additional oxygen atom for the stoichiometric anions (VxOy−) as compared to the cations with the same number of vanadium atoms, which is attributed to the extra pair of electrons of the anionic species. The oxygen-rich clusters, VxOy(O2)−, are shown to more tightly adsorb molecular oxygen than those of the corresponding cationic clusters. In addition, the bond dissociation thresholds for the vanadium oxide clusters ΔE(V+–O)=6.09±0.28 eV, ΔE(OV+–O)=3.51±0.36 eV, and ΔE(O2V−–O)=5.43±0.31 eV are determined from the energy-dependent collision-induced dissociation cross sections with Xe as the collision partner. To the best of our knowledge, this is the first bond dissociation energy reported for the breaking of the V–O bond of a vanadium oxide anion. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1329643

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Size-Specific Reactivities of Vanadium Oxide Cluster Cations (1999)

Bell, R. C. ; Zemski, K. A. ; Castleman, A. W.

Springer

Journal of cluster science 10 (1999), S. 509-524

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ISSN: 1572-8862

Schlagwort(e): Clusters ; vanadium oxide ; size dependence ; gas phase ; reactivities

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract This article is intended to summarize recent studies on the reactivity and dynamics of gas-phase vanadium oxide cluster cations in terms of their dependence on the size and stoichiometry of the selected clusters. In addition, the effects of coordination, oxidation states of the vanadium atoms, influence of charge, and ionization potentials on the reactivity of these clusters are presented. Reactions of the clusters V3 O 7 + and V5 O 12 + with 1-butene, 1,3-butadiene, and difluoromethane differ significantly from those of similar clusters such as V3 O 6 + and V5 O 11 + . While oxygen transfer and carbon–carbon cracking reactions are observed for the former clusters, the latter primarily associate the neutral reactant species. These differences are largely related to the oxidation states of the vanadium atoms within the cluster, but also display a dependence on the size of the cluster, with the smaller clusters being more reactive than the larger ones. Reactions with carbon tetrachloride display a dependence on the coordination of the clusters, but also display a distinct change in reaction channels from the chloride transfer reaction for the smaller clusters to the oxidative chloride transfer and formation of neutral phosgene for cluster with more than three vanadium atoms. In contrast, the dehydrohalogenation reactions of CH3CF3 display little dependence on the size of the clusters.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1021952907867

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