Self-similarity of Mean Flow in Pipe Turbulence

Based on our previous modified log-wake law in turbulent pipe ‡flows, we invent two compound similarity numbers (Y;U), where Y is a combination of the inner variable y+ and outer variable , and U is the pure exect of the wall. The two similarity numbers can well collapse mean velocity profile data with different moderate and large Reynolds numbers into a single universal profile. We then propose an arctangent law for the buffer layer and a general log law for the outer region in terms of (Y;U). From Milikan’s maximum velocity law and the Princeton superpipe data, we derive the von Kármán constant = 0:43 and the additive constant B=6. Using an asymptotic matching method, we obtain a self-similarity law that describes the mean velocity profile from the wall to axis; and embeds the linear law in the viscous sublayer, the quartic law in the bursting sublayer, the classic log law in the overlap, the sine-square wake law in the wake layer, and the parabolic law near the pipe axis. The proposed arctangent law, the general log law and the self-similarity law have been compared with the high-quality data sets, with diffrent Reynolds numbers, including those from the Princeton superpipe, Loulou et al., Durst et al., Perry et al., and den Toonder and Nieuwstadt. Finally, as an application of the proposed laws, we improve the McKeon et al. method for Pitot probe displacement correction, which can be used to correct the widely used Zagarola and Smits data set

Effect of Rhodium Distribution on Thermal Stability of Nanoporous Palladium-Rhodium Powders

Nanoporous palladium−rhodium alloys with nonuniform Rh distribution show enhanced thermal stability of pores in Rh-rich regions when the surface is under vacuum in either oxidized or reduced form. However, when heated in the presence of hydrogen, accelerated rearrangement of surface atoms is observed, and pores are less stable

Mechanisms of gold biomineralization in the bacterium Cupriavidus metallidurans

While the role of microorganisms as main drivers of metal mobility and mineral formation under Earth surface conditions is now widely accepted, the formation of secondary gold (Au) is commonly attributed to abiotic processes. Here we report that the biomineralization of Au nanoparticles in the metallophillic bacterium Cupriavidus metallidurans CH34 is the result of Au-regulated gene expression leading to the energy-dependent reductive precipitation of toxic Au(III)-complexes. C. metallidurans, which forms biofilms on Au grains, rapidly accumulates Au(III)-complexes from solution. Bulk and microbeam synchrotron X-ray analyses revealed that cellular Au accumulation is coupled to the formation of Au(I)-S complexes. This process promotes Au toxicity and C. metallidurans reacts by inducing oxidative stress and metal resistances gene clusters (including a Au-specific operon) to promote cellular defense. As a result, Au detoxification is mediated by a combination of efflux, reduction, and possibly methylation of Au-complexes, leading to the formation of Au(I)-C-compounds and nanoparticulate Au(0). Similar particles were observed in bacterial biofilms on Au grains, suggesting that bacteria actively contribute to the formation of Au grains in surface environments. The recognition of specific genetic responses to Au opens the way for the development of bioexploration and bioprocessing tools.Frank Reith, Barbara Etschmann, Cornelia Grosse, Hugo Moors, Mohammed A. Benotmane, Pieter Monsieurs, Gregor Grass, Christian Doonan, Stefan Vogt, Barry Lai, Gema Martinez-Criado, Graham N. George, Dietrich H. Nies, Max Mergeay, Allan Pring, Gordon Southam and Joël Brugge

Effect of Rhodium Distribution on Thermal Stability of Nanoporous Palladium–Rhodium Powders

Powders of nanoporous palladium and palladium alloy particles are of potential value for storage of hydrogen isotopes, as long as the pores remain stable over a useful range of temperatures and chemical environments. Rhodium alloys are known to have enhanced hydrogen storage and improved thermal stability versus pure palladium. However, the distribution of rhodium on pore and particle surfaces is critical to this. Pores are more ordered and thermally stable in rhodium-rich regions. Treatment of particles at elevated temperature under reducing conditions can cause rearrangement of Rh and Pd at the surface, but not a major change in Rh distribution throughout the particle. Heating in the presence of hydrogen causes more rapid pore rearrangement than heating in vacuum subsequent to hydrogen exposure, suggesting a direct chemical influence of hydrogen on mobility of surface atoms. These results provide a clear path to future improvements in the stability of nanoporous metals in reducing atmospheres