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

Quantifying prehension in persons with stroke post rehabilitation

This study describes the analysis of reaching and grasping abilities of the hemiparetic arm and hand of patients post stroke after a series of interactive virtual reality (VR) simulated training sessions and conventional physical therapy of similar intensity. Six subjects participated in VR training and five subjects in clinical rehabilitation for two weeks. Subjects’ finger joint angles were measured during a kinematic reach to grasp test using CyberGlove® and arm joint angles were measured using the trackSTARTM system prior to training and after training. Downward force applied to the object during grasping was assessed using Nano17TM, a force/torque sensor system that is added to the reach to grasp test paradigm for the VR trained subjects. Results from total movement time, grasping time, and average applied force show that subjects significantly decreased their average kinematic times and force applied to object during reaching and grasping tasks. Classification of hand postures using Linear Discriminant Analysis (LDA) during the reaching phase of movement shows an improvement in subjects’ accuracies and abilities to preshape their fingers post training in both groups. A system utilizing magnetic trackers, a data glove, and a force sensor is sensitive to changes in motor performance elicited by a robotically facilitated, virtually simulated motor intervention and physical therapy of similar intensity

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

A case of post dural puncture headache following labour epidural analgesia, managed by sphenopalatine ganglion block

Postpartum headache is a common complaint faced by most obstetricians, with over 39% of women having headache in the first postpartum week. With the increasing use of labour epidural analgesia, the incidence of postdural puncture headache (PDPH) due to inadvertent dural puncture is 0.5-1%. Most treatment modalities relieve the symptoms of PDPH by minimizing compensatory cerebral vasodilatation, or by sealing the dural puncture site. Treatment options include, conservative, pharmacological, and the gold standard, epidural blood patch (EBP). EBP is invasive and may result in rare however, severe complications. Sphenopalatine ganglion block (SPGB) has been proposed as a non-invasive intervention for PDPH, which has minimal adverse effects, which can be performed bedside. Here we are reporting a case of PDPH, following labour epidural analgesia which was effectively managed by a sphenopalatine block.

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