Cascadic Multigrid in a Spectral-Element Context

Current research in computational fluid dynamics focuses on high-order methods, which offer a significant reduction of the computational effort for a given error bound. In low-order methods optimal complexity solvers for elliptic equations, e.g. the Helmholtz equation, are readily available, but for high-order methods these are still an area of research. This work evaluates the effectiveness of the Cascadic Multigrid Method in the context of spectral elements, comparing it to a standard Krylov subspace solver. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

CH Functionalization of Phenols Using Combined Ruthenium and Photoredox Catalysis: In Situ Generation of the Oxidant

A combination of ruthenium and photoredox catalysis allowed the ortho olefination of phenols. Using visible light, the direct C? H functionalization of o‐(2‐pyridyl)phenols occurred, and diverse phenol ethers were obtained in good yields. The regeneration of the ruthenium catalyst was accomplished by a photoredox‐catalyzed oxidative process.     

Comparison of isotropic and anisotropic subgrid scale models in Large Eddy Simulations of a backward-facing step and square duct flow

The present paper employs the anisotropic explicit algebraic subgrid-stress model (EASM), proposed by Marstorp et al. J. Fluid. Mech. 639, 403 - 432 (2009), developed in the spirit of an earlier explicit algebraic RANS-model for statistical closures. The EASM in its elementary, computationally efficient non-dynamic version is used for Large Eddy Simulation of three-dimensional flows over a backward-facing step at a bulk Reynolds number of 4805 and a square duct at 2205. Its performance is assessed by comparison with experimental data and an own Direct Numerical Simulation. Furthermore, a set of eddy-viscosity models, including the recent σ-model, is employed for comparison. Various statistical quantities are evaluated to assess the respective performance of the different models showing, that the anisotropic EASM compares favorably to the other models. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Desorption and photopolymerization behavior of mixed and multilayered styrene-pyrrole nanofilms

The molecular arrangement and polymerization of adsorbed styrene-pyrrole films were explored using two different dosing schemes: simultaneous dosing to form an intimately mixed film of the two monomers and sequential dosing to form films with distinct layers of styrene and pyrrole. It was found that the desorption of pyrrole was delayed until 175 K when either simultaneously dosed with styrene or in the presence of an overlying styrene layer, whereas it normally desorbs at 165 K when dosed alone. No such effects were observed with styrene in any dosing configuration. The polymerization rate of pyrrole was unaffected in the films when present as the top layer and was observed to decrease by 50% when beneath a styrene layer. Moreover, the rate of polymerization increased by two orders of magnitude in the case of the intimately mixed film. The rate of styrene polymerization was not found to change in any of the explored geometries. These effects are explained by considering the proximity of the components and the potential for screening UV radiation based on their molecular structure.     

Photooxygenations of 1-naphthols: an environmentally friendly access to 1,4-naphthoquinones

Dye sensitized photooxygenations of 1-naphthols were investigated with soluble and solid-supported sensitizers and moderate to excellent yields of the corresponding 1,4-naphthoquinones were achieved in relatively short irradiation times. The mild and environmentally friendly reaction conditions made this application particularly attractive for ‘Green Photochemistry’. Consequently, the photooxygenation of 1,5-dihydroxynaphthalene was studied with non-concentrated and moderately concentrated sunlight and 5-hydroxy-1,4-naphthoquinone (Juglone) was obtained in yields up to 71%.