Influence of the height-to-diameter ratio on turbulent mixed convection in vertical cylinders

Turbulent mixed-convection mass transfer in vertical cylinders was measured using a sulfuric acid–copper sulfate electroplating technique. The Grashof numbers ranged from 5.3?×?10⁹ to 6.9?×?10¹⁰, the Reynolds numbers ranged from 4,000 to 14,000, and the Schmidt numbers were approximately 2,000. The test results under buoyancy-aided and buoyancy-opposed flow conditions successfully reproduced typical turbulent mixed-convection heat-transfer behavior and agreed well with existing studies performed by Ko et al. and Parlatan et al. Previous studies have used the cylinder diameter as the characteristic length for the buoyancy coefficient; however, this study focused on the influence of the cylinder height on the mixed-convection mass-transfer rates because the height determines the buoyancy. The tests performed for various heights with a fixed diameter or for various diameters with a fixed height demonstrated the influence of the height-to-diameter ratio on the mass-transfer rate, revealing that the height of the cylinder should be considered as a length scale. A new empirical correlation was derived for turbulent mixed-convection mass transfer that includes the influence of the height-to-diameter ratios.     

Successive ionic layer adsorption and reaction of ZnSe shells for ZnO nanowire-based dye-sensitized solar cells

Thin ZnSe layers were deposited on ZnO nanowires by a novel successive ionic layer adsorption and reaction technique in order to solve recombination problems in ZnO nanowire-based dye-sensitized solar cells (DSSCs). Cell efficiency increased from 0.1 to 1.3–1.4% with the deposition of a 9- to13-nm-thick ZnSe shell on ZnO nanowires due to a large increase in J_SC. The dramatic increase in J_SC and cell efficiency is due to the facilitation of electron transfer related to ambipolar diffusion by the formation of a type II band alignment and the suppression of recombination in the presence of the ZnSe shell.     

Spontaneous initiation and development of hydrogen–oxygen detonation with ozone sensitization

This work studies numerically the spontaneous initiation and sustenance of a detonation wave from a hot spot with a nonuniform initial temperature embedded within an H₂O₂ mixture with and without O₃ addition. For the case with either no or just a small amount of O₃ addition, a weak reaction wave is auto-ignited at the hot spot, accelerates and then transitions to a pulsating detonation, which propagates along the temperature gradient and quenches as it runs into the cold fresh mixture. However, with increasing O₃ addition, the possibility of sustenance of a developing detonation within the gradient is significantly enhanced as it enters the cold mixture. Furthermore, the reduced induction time by O₃ addition leads to earlier appearance of the spontaneous reaction wave and detonation formation in the cold mixture, demonstrating that quenching of the detonation is largely related to the instability property of the mixture because the shortened induction time reduces substantially the instability. It is also noted that, for 5%O₃ addition, a low-temperature flame produced by the O₃ reactions is present in front of the spontaneous reaction wave, inducing a local pressure wave, which facilitates spontaneous initiation and sustains the detonation entering the cold mixture. Moreover, O₃ addition renders the critical temperature to induce the minimum spontaneous wave speed higher than the crossover temperature, while they are very close for the case without O₃.     

Electron‐transfer transparency of graphene: Fast reduction of metal ions on graphene‐covered donor surfaces

The mechanism of charge transfer through nanomaterials such as graphene remains unclear, and the amount of charge that can be transferred from/to graphene without damaging its structural integrity is unknown. In this communication, we show that metallic nanoparticles can be decorated onto graphene surfaces as a result of charge transfer from the supporting substrate to an adjoining solution containing metal ions. Au or Pt nanoparticles were formed with relatively high yield on graphene‐coated substrates that can reduce these metal ions, such as Ge, Si, GaAs, Al, and Cu. However, metal ions were not reduced on graphene surfaces coated onto non‐reducing substrates such as SiO₂ or ZnO. These results confirm that graphene can be doped by exploiting charge transfer from the underlying substrate; thus graphene is not only transparent with respect to visible light, but also with respect to the charge transfer. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A fast method to generate collisional excitation cross-sections of highly charged ions in a hot dense matter

A method to compute collisional excitation cross-sections in jj-averaged configuration sets is presented in the framework of plane-wave Born approximation using Dirac–Hartree–Slater wave functions with appropriate low-energy corrections. When averaged into the ls configuration or hydrogenic superconfiguration sets, the results are found to compare with distorted wave calculations well within 30% on average. The cross-sections are averaged into hydrogenic cross-sections and fitted using the Gaunt factor formalism. We present analytic fit coefficients of Gaunt factors for 12 atoms of Z between 5 and 79 for hydrogenic transitions.     

3‐Formylpyrroles from 3‐Furfurylamines by Bromine Oxidation Reaction

Oxidation of 3‐furfurylamines 3a‐e with bromine in acetone‐water solution gave N‐substituted 3‐formylpyrroles 4a‐e in good yields. A reaction mechanism via the Clauson‐Kaas reaction followed by the cis‐trans isomerization of the 2‐ene‐1,4‐diones 13 and 14 was proposed to account for the formation of the pyrroles 4a‐e .