Global instabilities in diverging channel flows

A global stability study of a divergent channel flow reveals features not obtained hitherto by making either the parallel or the weakly non-parallel (WNP) flow assumption. A divergent channel flow is chosen for this study since it is the simplest spatially developing flow: the Reynolds number is constant downstream, and for a theoretical Jeffery?CHamel flow, the velocity profile obeys similarity. Even in this simple flow, the global modes are shown to be qualitatively different from the parallel or WNP. In particular, the disturbance modes are often not wave-like, and the local scale, estimated from a wavelet analysis, can be a function of both streamwise and normal coordinates. The streamwise variation of the scales is often very different from the expected linear variation. Given recent global stability studies on boundary layers, such spatially extended modes which are not wave-like are unexpected. A scaling argument for why the critical Reynolds number is so sensitive to divergence is offered.     

Effects of Lewis Number on Scalar Variance Transport in Premixed Flames

The influences of differential diffusion rates of heat and mass on the transport of the variances of Favre fluctuations of reaction progress variable and non-dimensional temperature have been studied using three-dimensional simplified chemistry based Direct Numerical Simulation (DNS) data of statistically planar turbulent premixed flames with global Lewis number ranging from Le?= 0.34 to 1.2. The Lewis number effects on the statistical behaviours of the various terms of the transport equations of variances of Favre fluctuations of reaction progress variable and non-dimensional temperature have been analysed in the context of Reynolds Averaged Navier Stokes (RANS) simulations. It has been found that the turbulent fluxes of the progress variable and temperature variances exhibit counter-gradient transport for the flames with Lewis number significantly smaller than unity whereas the extent of this counter-gradient transport is found to decrease with increasing Lewis number. The Lewis number is also shown to have significant influences on the magnitudes of the chemical reaction and scalar dissipation rate contributions to the scalar variance transport. The modelling of the unclosed terms in the scalar variance equations for the non-unity Lewis number flames have been discussed in detail. The performances of the existing models for the unclosed terms are assessed based on a-priori analysis of DNS data. Based on the present analysis, new models for the unclosed terms of the active scalar variance transport equations are proposed, whenever necessary, which are shown to satisfactorily capture the behaviours of unclosed terms for all the flames considered in this study.     

Purification,Characterization and Kinetic Studies of a Novel Poly(β) Hydroxybutyrate (PHB) Depolymerase PhaZ<Subscript><Emphasis Type="BoldItalic">Pen</Emphasis></Subscript> from <Emphasis Type="Italic">Penicillium citrinum</Emphasis> S2

A fungal isolate, identified as Penicillium citrinum S2, produced ≈1 U/mL of PHB depolymerase by 72 h when grown in BHM containing 0.2%, w/v PHB, pH 6.0 at 30 °C. Partial purification of an extracellular poly(-β-)hydroxybutyrate (PHB) depolymerase PhaZ _Pen from P. citrinum S2 by two steps using ammonium sulphate (80% saturation) and affinity chromatography using concanavalin A yielded 16.18-fold purity and 21.53% recovery of protein. The enzyme was composed of three polypeptide chains of 66, 43 and 20 kDa, respectively, as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. All the three bands stained positive for glycoprotein by PAS staining. Optimum enzyme activity was detected at pH 6.0 and 50 °C. The enzyme was stable between pH 4.0 and 7.0 at 50 °C, 2 h. β-hydroxybutyrate monomer was detected as the major end product of PHB hydrolysis. The enzyme also showed distinct behaviour towards different inhibitors tested, which suggests the role of serine, serine residue, carboxyl group, tyrosine and sulfhydryl groups in its active site.     

Generating hydrogen gas from methane with carbon captured as pure spheroidal nanomaterials

Energy production by using hydrogen gas as a feedstock is considered to be one of the keys to creating clean energy, with the proviso that the gas is generated in a sustainable way with no emissions. A simple, self-sustaining process generating hydrogen gas from methane using inexpensive stainless steel wire-mesh catalysts at elevated temperatures (800 °C) is reported. A theoretical analysis of the production of electricity by this process revealed peak chain energy efficiencies up to 21% (emission free) when using a percentage of the produced hydrogen (approximately 40% of purified yield) as the heat source. In addition, a practical method has been developed to purify the carbon byproduct, affording essentially pure highly graphitic spheroidal carbon for advanced materials applications.     

Effect of macromolecular crowding on the rate of diffusion-limited enzymatic reaction

The cytoplasm of a living cell is crowded with several macromolecules of different shapes and sizes. Molecular diffusion in such a medium becomes anomalous due to the presence of macromolecules and diffusivity is expected to decrease with increase in macromolecular crowding. Moreover, many cellular processes are dependent on molecular diffusion in the cell cytosol. The enzymatic reaction rate has been shown to be affected by the presence of such macromolecules. A simple numerical model is proposed here based on percolation and diffusion in disordered systems to study the effect of macromolecular crowding on the enzymatic reaction rates. The model qualitatively explains some of the experimental observations.      

Large Eddy Simulation of a Bluff Body Stabilised Premixed Flame Using Flamelets

Large Eddy Simulations of an unconfined turbulent lean premixed flame, which is stabilised behind a bluff body, are conducted using unstrained flamelets as the sub-grid scale combustion closure. The statistics from the simulations are compared with the corresponding data obtained from the experiment and it is demonstrated that the experimental observations are well captured. The relative positioning of the shear layers and the flame brush are analysed to understand the radial variations of the turbulent kinetic energy at various streamwise locations. These results are also compared to confined bluff body stabilised flames, to shed light on the relative role of incoming and shear driven turbulence on the behaviour of the flame brush and the turbulent kinetic energy variation across it.     

Simultaneous Harvesting of Multiple Hot Holes via Visible-Light Excitation of Plasmonic Gold Nanospheres for Selective Oxidative Bond Scission of Olefins to Carbonyls

Using visible photoexcitation of gold nanospheres we successfully demonstrate the simultaneous harvesting of plasmon-induced multiple hot holes in the complete oxidative scission of the C=C bond in styrene at room temperature to selectively form benzaldehyde and formaldehyde, which is a reaction that requires activation of multiple substrates. Our results reveal that, while extraction of hot holes becomes efficient for interband excitation, harvesting of multiple hot holes from the excited Au nanospheres becomes prevalent only beyond a threshold light intensity. We show that the alkene oxidation proceeded via a sequence of two consecutive elementary steps; namely, a binding step and a cyclic oxometallate transition state as the rate-determining step. This demonstration of plasmon-excitation-mediated harvesting of multiple hot holes without the use of an extra hole transport media opens exciting possibilities, notably for difficult catalytic transformations involving multielectron oxidation processes.