Temperature-Graduated Nickel-Silica Catalysts for Photothermal Steam Reforming of Methane

Photothermal steam reforming of methane (PTSRM) is a promising catalytic technology for converting stable methane and water into hydrogen utilizing solar energy. In the present study, the photothermal catalytic activity of silica-supported nickel (Ni/SiO₂) catalysts was investigated using a gas-flow reactor under concentrated visible/near-infrared light irradiation with various experimental parameters to obtain insight into factors affecting the activity and selectivity. In the thermal SRM at 773 K in the dark, the CH₄ conversion reached near-equilibrium with all four Ni/SiO₂ catalysts, while there was a significant difference in activity between the catalysts in the PTSRM reaction under light irradiation. These results indicate that PTSRM activity was affected by both thermodynamic and kinetic aspects. The conversion–selectivity relationship revealed that the product selectivity in PTSRM was different from the values in thermal SRM in the dark and calculated thermodynamic equilibrium. We proposed that concentrated light irradiation created the highest temperature zone in the centre of the reactor and the lower temperature zone downstream, and the consecutive water gas shift reaction and CO hydrogenation occurred in the lower temperature zone, thus resulting in the characteristic product selectivity. This study shows the potential of PTSRM systems with controllable selectivity by the temperature gradients formed under concentrated sunlight irradiation

The r-Process in Supersonic Neutrino-Driven Winds: The Roll of Wind Termination Shock

Recent hydrodynamic studies of core-collapse supernovae imply that the neutrino-heated ejecta from a nascent neutron star develops to supersonic outflows. These supersonic winds are influenced by the reverse shock from the preceding supernova ejecta, forming the wind termination shock. We investigate the effects of the termination shock in neutrino-driven winds and its roll on the r-process. Supersonic outflows are calculated with a semi-analytic neutrino-driven wind model. Subsequent termination-shocked, subsonic outflows are obtained by applying the Rankine-Hugoniot relations. We find a couple of effects that can be relevant for the r-process. First is the sudden slowdown of the temperature decrease by the wind termination. Second is the entropy jump by termination-shock heating, up to several 100NAk. Nucleosynthesis calculations in the obtained winds are performed to examine these effects on the r-process. We find that 1) the slowdown of the temperature decrease plays a decisive roll to determine the r-process abundance curves. This is due to the strong dependences of the nucleosynthetic path on the temperature during the r-process freezeout phase. Our results suggest that only the termination-shocked winds with relatively small shock radii (~500km) are relevant for the bulk of the solar r-process abundances (A~100-180). The heaviest part in the solar r-process curve (A~180-200), however, can be reproduced both in shocked and unshocked winds. These results may help to constrain the mass range of supernova progenitors relevant for the r-process. We find, on the other hand, 2) negligible roles of the entropy jump on the r-process. This is a consequence that the sizable entropy increase takes place only at a large shock radius (~10,000km) where the r-process has already ceased.Comment: 11 pages, 7 figures, submitted to ApJ, revised following referee's comments,Accepted for publication in Ap

Effect of an Inhibitor of Glucosylceramide Synthesis on Cultured Human Keratinocytes

Glucosylceramide (GlcCer) is a major glycosphingolipid component of epidermis, which is thought to be related to the barrier function of skin permeability. However, the role of glycosphingolipids in keratinocyte growth and differentiation has not been fully clarified. It has been reported that D‐threo‐1‐phenyl‐2‐decanoylamino‐3‐morpholino‐1‐propanol (PDMP), an inhibitor of GlcCer synthase (EC 2.4.1.80), depletes cells of glycosphingolipids. This inhibitor has been used as a tool for elucidating their functions. In the present study, the effect of PDMP on cultured normal human keratinocytes was investigated. The cells were treated with various concentrations of PDMP. Forty‐eight hours later cell growth, thymidine incorporation, and lipid content were studied. The cell growth and the incorporation of thymidine into cells were inhibited by PDMP in a dose dependent manner. The synthesis of GlcCer was strongly inhibited by PDMP treatment, whereas no significant changes in ceramide level were observed. We concluded that GlcCer in epidermis may play an important role in regulating epidermal growth and suggested that PDMP may be beneficial for treating proliferative skin disorders in the future.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111117/1/jde02353.pd

Numerical Study on Acoustic Oscillations of 2D and 3D Flue Organ Pipe Like Instruments with Compressible LES

Acoustic oscillations of flue instruments are investigated numerically using compressible Large Eddy Simulation (LES). Investigating 2D and 3D models of flue instruments, we reproduce acoustic oscillations excited in the resonators as well as an important characteristic feature of flue instruments – the relation between the acoustic frequency and the jet velocity described by the semi-empirical theory developed by Cremer & Ising, Coltman and Fletcher et al. based on experimental results. Both 2D and 3D models exhibit almost the same oscillation frequency for a given jet velocity, but the acoustic oscillation as well as the jet motion is more stable in the 3D model than in the 2D model, due to less stability in 3D fluid of the rolled up eddies created by the collision of the jet with the edge, which largely disturb the jet motion and acoustic field in the 2D model. We also investigate the ratio of the amplitude of the acoustic flow through the mouth opening to the jet velocity, comparing with the experimental results and semi-empirical theory given by Hirschberg et al.