scholarly journals Calculation method for steady-state pollutant concentration in mixing zones considering variable lateral diffusion coefficient

2017 ◽  
Vol 76 (1) ◽  
pp. 201-209 ◽  
Author(s):  
Wen Wu ◽  
Zhouhu Wu ◽  
Zhiwen Song

Prediction of the pollutant mixing zone (PMZ) near the discharge outfall in Huangshaxi shows large error when using the methods based on the constant lateral diffusion assumption. The discrepancy is due to the lack of consideration of the diffusion coefficient variation. The variable lateral diffusion coefficient is proposed to be a function of the longitudinal distance from the outfall. Analytical solution of the two-dimensional advection–diffusion equation of a pollutant is derived and discussed. Formulas to characterize the geometry of the PMZ are derived based on this solution, and a standard curve describing the boundary of the PMZ is obtained by proper choices of the normalization scales. The change of PMZ topology due to the variable diffusion coefficient is then discussed using these formulas. The criterion of assuming the lateral diffusion coefficient to be constant without large error in PMZ geometry is found. It is also demonstrated how to use these analytical formulas in the inverse problems including estimating the lateral diffusion coefficient in rivers by convenient measurements, and determining the maximum allowable discharge load based on the limitations of the geometrical scales of the PMZ. Finally, applications of the obtained formulas to onsite PMZ measurements in Huangshaxi present excellent agreement.

2015 ◽  
Vol 17 (38) ◽  
pp. 25160-25171 ◽  
Author(s):  
Angel Lai ◽  
Qasim Saleem ◽  
Peter M. Macdonald

Theory of CODEX 31P NMR lateral diffusion coefficient measurements on phospholipids in spherical vesicles is described and used to simulate experimental results on DMPC in both the gel and liquid-crystalline phases.


1974 ◽  
Vol 27 (2) ◽  
pp. 195 ◽  
Author(s):  
HR Skullerud

The motion of electrons in a gas in the presence of large electron density gradients has been studied theoretically, starting from the two-term expansion of the Boltzmann equation. The effects of material boundaries have not been considered. An electron swarm released as a b-function in space and with an equilibrium energy distribution is found initially to develop as a spheroid with dimensions determined by the lateral diffusion coefficient. It subsequently passes through a stage involving a slowly decaying pear-shaped deformation, before ultimately becoming an ellipsoid with dimensions determined by the longitudinal and lateral components of the diffusion tensor. Numerical values cited in the literature for the long-term deviations from the mean square widths predicted by the diffusion equation have been found to be in error by factors of 10 or more.


2020 ◽  
Vol 50 (4) ◽  
pp. 965-982 ◽  
Author(s):  
Sarah Ragen ◽  
Marie-Aude Pradal ◽  
Anand Gnanadesikan

AbstractThis study examines the impact of changing the lateral diffusion coefficient ARedi on the transport of the Antarctic Circumpolar Current (ACC). The lateral diffusion coefficient ARedi is poorly constrained, with values ranging across an order of magnitude in climate models. The ACC is difficult to accurately simulate, and there is a large spread in eastward transport in the Southern Ocean (SO) in these models. This paper examines how much of that spread can be attributed to different eddy parameterization coefficients. A coarse-resolution, fully coupled model suite was run with ARedi = 400, 800, 1200, and 2400 m2 s−1. Additionally, two simulations were run with two-dimensional representations of the mixing coefficient based on satellite altimetry. Relative to the 400 m2 s−1 case, the 2400 m2 s−1 case exhibits 1) an 11% decrease in average wind stress from 50° to 65°S, 2) a 20% decrease in zonally averaged eastward transport in the SO, and 3) a 14% weaker transport through the Drake Passage. The decrease in transport is well explained by changes in the thermal current shear, largely due to increases in ocean density occurring on the northern side of the ACC. In intermediate waters these increases are associated with changes in the formation of intermediate waters in the North Pacific. We hypothesize that the deep increases are associated with changes in the wind stress curl allowing Antarctic Bottom Water to escape and flow northward.


Parasitology ◽  
1994 ◽  
Vol 109 (4) ◽  
pp. 469-477 ◽  
Author(s):  
S. F. Lima ◽  
L. Q. Vieira ◽  
A. Hardert ◽  
J. R. Kusel

SUMMARYBy using fluorescent probes the distribution and fluid properties of lipid and saccharide-bound molecules was assessed in the tegument of praziquantel (−) treated Schistosoma mansoni adult male worms. Our results show that higher amounts of glycoproteins and/or glycolipids are exposed in damaged areas of the membrane compared with undamaged ones. At damaged regions these molecules present high lateral diffusion coefficient and mobile fraction values which suggests that after praziquantel(−) treatment they are being shed by the worm into the medium. The lateral diffusion coefficient of the lipid analogue 5'-octadecanoyl aminofluorescein is unchanged in damaged or undamaged areas but the mobile fraction is significantly reduced at damaged areas. The immunological significance of these altered surface properties is discussed.


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