Salt flux in a laboratory model estuary

Motivated by recent field observations, a laboratory model estuary experiment was conducted for the study of its flow and stratification. We find that a small inflow of cold freshwater, on top of warm saline water can lead to a large counter flow in the lower layer. This counter flow is part of a large aspect ratio convective cell driven by the horizontally varying diffusive cooling from above. Particle Image Velocimetry (PIV) measurement of the Reynolds stresses associated with transient tilted plumes embedded in this convective cell show that the viscous dissipation of the large-scale cellular flow is largely balanced by the Reynolds stress divergence of the tilted plumes. Using Optical Rotation measurements along with the PIV derived mean flow we find that the internal “salt” flux has Nusselt number (the ratio of convective to diffusive transport) of order 103. Although the convection is vertically forced, the flow is essentially horizontal, and there is very little vertical mixing across the interface between the two layers

Does certification work in emerging markets? evidence from the Indian IPO market

There is inconclusive evidence regarding the economic value of certification in the context of IPOs in developed markets. Using a natural experiment of regulator mandated IPO grading requirement, we examine the effects of third-party certification in the Indian IPO market. We summarize our empirical results below. First, underpricing is unaffected by the grading process. Second, stock price informativeness as proxied by idiosyncratic volatility increases significantly due to IPO grading process. Third, retail and institutional subscription levels are significantly positively associated with IPO grades after controlling for other certification mechanisms such as underwriter reputation, group affiliation, analyst recommendation and venture capital backing. Finally, using a pseudo grading process we conclude that IPO grades are not mechanically derivable from publicly available information. In a nutshell, we use our unique setting to examine the usefulness of certification in emerging markets with institutional voids

Double-diffusive convection with imposed vertical mass flux

Vertical advection and double-diffusive convection are both processes affecting the stratification of the oceans. The effect of vertical advection on double-diffusive convection is investigated by considering the situation in which a horizontal layer of fluid has imposed upon it a destabilizing vertical temperature gradient, a stabilizing vertical salinity gradient and a uniform vertical mass flux. The effect of the imposed vertical mass flux is to remove the stabilizing salt gradient, but not the destabilizing temperature gradient over most of the depth of the layer. This arises from the fact that heat diffuses much more quickly than does salt. The Peelet numbers γT = Wod/κT and γS = Wod/κS where κT and κS are the molecular diffusivities of heat and salt respectively, d is the depth of the layer, Wo the imposed vertical velocity, are dimensionless measures of the relative importance of advection and diffusion. Both the linear stability theory and the laboratory experiments show a decrease in the critical value of the Rayleigh number for the onset of oscillatory convection when |γS| \u3e 0, over that when γS = 0. The calculation is valid for |γS| ≤ 1. The laboratory experiments were conducted for 0 ≤ |γS| ≤ 3.2, where Rc was found to be reduced by as much as 20%

Plume motion and large-scale circulation in a cylindrical Rayleigh-B\'enard cell

We used the time correlation of shadowgraph images to determine the angle $\Theta$ of the horizontal component of the plume velocity above (below) the center of the bottom (top) plate of a cylindrical Rayleigh-B\'enard cell of aspect ratio $\Gamma \equiv D/L = 1$ ($D$ is the diameter and $L \simeq 87$ mm the height) in the Rayleigh-number range $7\times 10^7 \leq R \leq 3\times 10^{9}$ for a Prandtl number $\sigma = 6$. We expect that $\Theta$ gives the direction of the large-scale circulation. It oscillates time-periodically. Near the top and bottom plates $\Theta(t)$ has the same frequency but is anti-correlated.Comment: 4 pages, 6 figure

Wind reversals in turbulent Rayleigh-Benard convection

The phenomenon of irregular cessation and subsequent reversal of the large-scale circulation in turbulent Rayleigh-B\'enard convection is theoretically analysed. The force and thermal balance on a single plume detached from the thermal boundary layer yields a set of coupled nonlinear equations, whose dynamics is related to the Lorenz equations. For Prandtl and Rayleigh numbers in the range $10^{-2} \leq \Pr \leq 10^{3}$ and 10^{7} \leq \Ra \leq 10^{12}, the model has the following features: (i) chaotic reversals may be exhibited at Ra $\geq 10^{7}$; (ii) the Reynolds number based on the root mean square velocity scales as \Re_{rms} \sim \Ra^{[0.41 ... 0.47]} (depending on Pr), and as $\Re_{rms} \sim \Pr^{-[0.66 ... 0.76]}$ (depending on Ra); and (iii) the mean reversal frequency follows an effective scaling law \omega / (\nu L^{-2}) \sim \Pr^{-(0.64 \pm 0.01)} \Ra^{0.44 \pm 0.01}. The phase diagram of the model is sketched, and the observed transitions are discussed.Comment: 4 pages, 5 figure

A note on the phlobatannins of kino and Butea gums

This article does not have an abstract

Restructuring surface tessellation with irregular boundary conditions

In this paper, the surface tessellation problem is explored, in particular, the task of meshing a surface with the added consideration of incorporating constructible building components. When a surface is tessellated into discrete counterparts, certain unexpected conditions usually occur at the boundary of the surface, in particular, when the surface is being trimmed. For example, irregularly shaped panels form at the trimmed edges. To reduce the number of irregular panels that may form during the tessellation process, this paper presents an algorithmic approach to restructuring the surface tessellation by investigating irregular boundary conditions. The objective of this approach is to provide an alternative way for freeform surface manifestation from a well-structured discrete model of the given surface

Geothermal Heating and its Influence on the Meridional Overturning Circulation

The effect of geothermal heating on the meridional overturning circulation is examined using an idealized, coarse-resolution ocean general circulation model. This heating is parameterized as a spatially uniform heat flux of 50 mW m-2 through the (flat) ocean floor, in contrast with previous studies that have considered an isolated hotspot or a series of plumes along the mid-Atlantic ridge. The equilibrated response is largely advective: a deep perturbation of the meridional overturning cell on the order of several Sv is produced, connecting with an upper-level circulation at high latitudes, allowing the additional heat to be released to the atmosphere. Risingmotion in the perturbation deep cell is concentrated near the equator. The upward penetration of this cell is limited by the thermocline, analogous to the role of the stratosphere in limiting the upward penetration of convective plumes in the atmosphere. The magnitude of the advective response is inversely proportional to the deep stratification; with a weaker background meridional overturning circulation and a less stratified abyss, the overturning maximum of the perturbation deep cell is increased. This advective response also cools the low-latitude thermocline. The qualitative behavior is similar in both a single hemisphere and double hemisphere configuration.The anomalous circulation driven by geothermal fluxes is more substantial than previously thought. We are able to understand the structure and strength of the response in the idealized geometry and further extend these ideas to explain the results of Adcroft et al. [2001], where the impact of geothermal heating was examined using a global configuration

The energy budget in Rayleigh-Benard convection

It is shown using three series of Rayleigh number simulations of varying aspect ratio AR and Prandtl number Pr that the normalized dissipation at the wall, while significantly greater than 1, approaches a constant dependent upon AR and Pr. It is also found that the peak velocity, not the mean square velocity, obeys the experimental scaling of Ra^{0.5}. The scaling of the mean square velocity is closer to Ra^{0.46}, which is shown to be consistent with experimental measurements and the numerical results for the scaling of Nu and the temperature if there are strong correlations between the velocity and temperature.Comment: 5 pages, 3 figures, new version 13 Mar, 200