Flux scaling and plume structure in high Ra - high Sc turbulent convection

The arrangement of brine above water across a micro porous permeable membrane is used to study high Rayleigh Number($10^{11}- 10^{10}$) high Schmidt number(650)turbulent convection. The flux shows 4/3$^{rd}$ scaling with line plume as the near wall coherent structures. Shifting of multiple large scale flow cells result in changing near membrane mean shear directions for large aspect ratios. Lower aspect ratios show single large scale flow cell and constant sense of mean shear.Comment: 7 pages, 7 Figures, Published in Proceedings of the Tenth Asian Congress of Fluid Mechanics 17--21, May 2004, Peradeniya, Srilank

Multifractal nature of plume structure in high Rayleigh number convection

The geometrically different plan forms of near wall plume structure in turbulent natural convection, visualised by driving the convection using concentration differences across a membrane, are shown to have a common multifractal spectrum of singularities for Rayleigh numbers in the range $10^{10}- 10^{11}$ at Schmidt number of 602. The scaling is seen for a length scale range of $2^5$ and is independent of the Rayleigh number, the flux, the strength and nature of the large scale flow, and the aspect ratio. Similar scaling is observed for the plume structures obtained in the presence of a weak flow across the membrane. This common non trivial spatial scaling is proposed to be due to the same underlying generating process of the near wall plume structures.Comment: 11pages, 16 figures Accepted in Journal of Fluid mechanics. Revised version. Added two more figures and related discussion on suggestion of referee

Integral analysis of laminar indirect free convection boundary layers with weak blowing for Schmidt no. ~ 1

Laminar natural convection at unity Schmidt number over a horizontal surface with a weak normal velocity at the wall is studied using an integral analysis. To characterise the strength of the blowing, we define a non-dimensional parameter called the blowing parameter. After benchmarking with the no blowing case, the effect of the blowing parameter on boundary layer thickness, velocity and concentration profiles is obtained. Weak blowing is seen to increase the wall shear stress. For blowing parameters greater than unity, the diffusional flux at the wall becomes negligible and the flux is almost entirely due to the blowing.Comment: 10 pages, published in International Communications in heat and mass transfer,Vol31,No8, 2004, pp 1199 -120

Dynamics of collapse of free-surface bubbles: effects of gravity and viscosity

The rupture of the thin film at the top of a bubble floating at a liquid-gas interface leads to the axisymmetric collapse of the bubble cavity. We present scaling laws for such a cavity collapse, established from experiments conducted with bubbles spanning a wide range of Bond (${10^{-3}<Bo\leq1}$) and Ohnesorge numbers (${10^{-3}<Oh<10^{-1}}$), defined with the bubble radius $R$. The cavity collapse is a capillary-driven process, with a dependency on viscosity and gravity affecting, respectively, precursory capillary waves on the cavity boundary, and the static bubble shape. The collapse is characterised by tangential and normal velocities of the kink, formed by the intersection of the concave cavity opening after the top thin film rupture, with the convex bubble cavity boundary. The tangential velocity $U_t$ is constant during the collapse and is shown to be $U_t=4.5~U_c{\mathcal{W}}_R$, where $U_c$ is the capillary velocity and ${\mathcal{W}}_R(Oh,Bo)={(1-\sqrt{Oh {\mathscr{L}}} )^{-1/2}}$ is the wave resistance factor due to the precursory capillary waves, with $\mathscr{L}(Bo)$ being the path correction of the kink motion. The movement of the kink in the normal direction is part of the inward shrinkage of the whole cavity due to the sudden reduction of gas pressure inside the bubble cavity after the thin film rupture. This normal velocity is shown to scale as $U_c$ in the equatorial plane, while at the bottom of the cavity $\overline{U}_{nb}=U_c(Z_c/R)({\mathcal{W}_R}/ {\mathscr{L}})$, where $Z_c(Bo)$ is the static cavity depth. The total volume flux of cavity-filling, which is entirely contributed by this shrinking, scales as ${Q_T\simeq 2\pi R Z_c U_c}$; remains a constant throughout the collapse.Comment: 22 page

Orientation of heparin-binding sites in native vitronectin. Analyses of ligand binding to the primary glycosaminoglycan-binding site indicate that putative secondary sites are not functional

A primary heparin-binding site in vitronectin has been localized to a cluster of cationic residues near the C terminus of the protein. More recently, secondary binding sites have been proposed. In order to investigate whether the binding site originally identified on vitronectin functions as an exclusive and independent heparin-hinding domain, solution binding methods have been used in combination with MR and recombinant approaches to evaluate ligand binding to the primary site. Evaluation of the ionic strength dependence of heparin binding to vitronectin according to classical linkage theory indicates that a single ionic bond is prominent. It had been previously shown that chemical modification of vitronectin using an arginine- reactive probe results in a significant reduction in heparin binding (Gibson, A., Baburaj, K., Day, D. E., Verhamme, I., Shore, J. D., and Peterson, C. B. (1997) J. Biol. Chem. 272, 5112-5121). The label has now been localized to arginine residues within the cyanogen bromide fragment-(341-380) that contains the primary heparin-binding site on vitronectin. One- and two- dimensional NMR on model peptides based on this primary heparin-binding site indicate that an arginine residue participates in the ionic interaction and that other nonionic interactions may be involved in forming a complex with heparin. A recombinant polypeptide corresponding to the C-terminal 129 amino acids of vitronectin exhibits heparin-binding affinity that is comparable to that of full-length vitronectin and is equally effective at neutralizing heparin anticoagulant activity. Results from this broad experimental approach argue that the behavior of the primary site is sufficient to account for the heparin binding activity of vitronectin and support an exposed orientation for the site in the structure of the native protein

Transcriptomic profile of adverse neurodevelopmental outcomes after neonatal encephalopathy

A rapid and early diagnostic test to identify the encephalopathic babies at risk of adverse outcome may accelerate the development of neuroprotectants. We examined if a whole blood transcriptomic signature measured soon after birth,predicts adverse neurodevelopmental outcomeeighteenmonths after neonatal encephalopathy.We performed next generation sequencing on whole blood ribonucleic acid obtained within sixhours of birth from the first 47encephalopathic babies recruited to the Hypothermia for Encephalopathy in Low and middle-income countries (HELIX)trial. Two infants with blood culture positive sepsis were excluded, and the data from remaining 45 were analysed. A total of 855genes were significantly differentially expressed between the good and adverse outcome groups, of which RGS1and SMC4 werethe most significant. Biological pathway analysis adjusted for gender, trial randomisation allocation (cooling therapy versus usual care) and estimated blood leukocyte proportions revealed over-representation of genes from pathways related to melatoninand polo-like kinase in babieswith adverse outcome. These preliminary data suggest that transcriptomic profiling may be a promising tool for rapid risk stratification in neonatal encephalopathy. It may provide insights into biological mechanismsand identify novel therapeutic targetsfor neuroprotection