scholarly journals Determining rates of epithelial solute transport by optical measurement of fluorochrome concentration gradients in the unstirred layer

2012 ◽  
Vol 215 (17) ◽  
pp. 2945-2949
Author(s):  
S. Seabrooke ◽  
M. J. O'Donnell
Keyword(s):  
Solute Transport ◽  
Optical Measurement ◽  
Unstirred Layer ◽  
Concentration Gradients

scholarly journals Study of Pollutant Transport in Environmental Flows Using Depth-Averaged Random Walk Method

10.29007/gd96 ◽  
2018 ◽  
Author(s):  
Xuefei Wu ◽  
Fan Yang ◽  
Dongfang Liang
Keyword(s):  
Random Walk ◽  
Solute Transport ◽  
Analytical Solutions ◽  
Environmental Flows ◽  
Concentration Gradients ◽  
Bed Elevation ◽  
Numerical Predictions ◽  
Parametric Studies ◽  
Transport Problems ◽  
Sharp Concentration

A depth-averaged random walk scheme is applied to investigate the process of solute transport, including advection, diffusions and reaction. Firstly, the model is used to solve an instantaneous release problem in a uniform flow, for which analytical solutions exist. Its performance is examined by comparing numerical predictions with analytical solutions. The advantage of the random walk model includes high accuracy and small numerical diffusion. Extensive parametric studies are carried out to investigate the sensitivity of the predictions to the number of particles. The result reveals that the particle number influences the accuracy of the model significantly. Finally, the model is applied to track a pollutant cloud in the Thames Estuary, where the domain geometry and bed elevation are complex. The present model is free of fictitious oscillations close to sharp concentration gradients and displays encouraging efficiency and accuracy in solving the solute transport problems in a natural aquatic environment.

scholarly journals Preferential Pathways for Fluid and Solutes in Heterogeneous Groundwater Systems: Self-Organization, Entropy, Work

2021 ◽  
Author(s):  
Erwin Zehe ◽  
Ralf Loritz ◽  
Yaniv Edery ◽  
Brian Berkowitz
Keyword(s):  
Fluid Flow ◽  
Steady State ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Energy Input ◽  
Self Organization ◽  
Saturated Porous Media ◽  
Concentration Gradients ◽  
Transport Pathways ◽  
Preferential Pathways

Abstract. Patterns of distinct preferential pathways for fluid flow and solute transport are ubiquitous in heterogeneous, saturated and partially saturated porous media. Yet, the underlying reasons for their emergence, and their characterization and quantification, remain enigmatic. Here we analyze simulations of steady state fluid flow and solute transport in two-dimensional, heterogeneous saturated porous media with a relatively short correlation length. We demonstrate that the downstream concentration of solutes in preferential pathways implies a downstream declining entropy in the transverse distribution of solute transport pathways. This reflects the associated formation and downstream steepening of a concentration gradient transversal to the main flow direction. With an increasing variance of the hydraulic conductivity field, stronger transversal concentration gradients emerge, which is reflected in an even smaller entropy of the transversal distribution of transport pathways. By defining "self-organization" through a reduction in entropy (compared to its maximum), our findings suggest that a higher variance and thus randomness of the hydraulic conductivity coincides with stronger macroscale self-organization of transport pathways. While this finding appears at first sight striking, it can be explained by recognizing that emergence of spatial self-organization requires, in light of the second law of thermodynamics, that work be performed to establish transversal concentration gradients. The emergence of steeper concentration gradients requires that even more work be performed, with an even higher energy input into an open system. Consistently, we find that the energy input necessary to sustain steady-state fluid flow and tracer transport grows with the variance of the hydraulic conductivity field as well. Solute particles prefer to move through pathways of very high power, and these pathways pass through bottlenecks of low hydraulic conductivity. This is because power depends on the squared spatial head gradient, which is in these simulations largest in regions of low hydraulic conductivity.

scholarly journals SPH Simulations of Solute Transport in Flows with Steep Velocity and Concentration Gradients

Water ◽  
2017 ◽  
Vol 9 (2) ◽  
pp. 132 ◽  
Author(s):  
Yu-Sheng Chang ◽  
Tsang-Jung Chang
Keyword(s):  
Solute Transport ◽  
Concentration Gradients

scholarly journals Preferential pathways for fluid and solutes in heterogeneous groundwater systems: self-organization, entropy, work

2021 ◽  
Vol 25 (10) ◽  
pp. 5337-5353
Author(s):  
Erwin Zehe ◽  
Ralf Loritz ◽  
Yaniv Edery ◽  
Brian Berkowitz
Keyword(s):  
Fluid Flow ◽  
Steady State ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Energy Input ◽  
Self Organization ◽  
Saturated Porous Media ◽  
Concentration Gradients ◽  
Transport Pathways ◽  
Preferential Pathways

Abstract. Patterns of distinct preferential pathways for fluid flow and solute transport are ubiquitous in heterogeneous, saturated and partially saturated porous media. Yet, the underlying reasons for their emergence, and their characterization and quantification, remain enigmatic. Here we analyze simulations of steady-state fluid flow and solute transport in two-dimensional, heterogeneous saturated porous media with a relatively short correlation length. We demonstrate that the downstream concentration of solutes in preferential pathways implies a downstream declining entropy in the transverse distribution of solute transport pathways. This reflects the associated formation and downstream steepening of a concentration gradient transversal to the main flow direction. With an increasing variance of the hydraulic conductivity field, stronger transversal concentration gradients emerge, which is reflected in an even smaller entropy of the transversal distribution of transport pathways. By defining “self-organization” through a reduction in entropy (compared to its maximum), our findings suggest that a higher variance and thus randomness of the hydraulic conductivity coincides with stronger macroscale self-organization of transport pathways. Simulations at lower driving head differences revealed an even stronger self-organization with increasing variance. While these findings appear at first sight striking, they can be explained by recognizing that emergence of spatial self-organization requires, in light of the second law of thermodynamics, that work be performed to establish transversal concentration gradients. The emergence of steeper concentration gradients requires that even more work be performed, with an even higher energy input into an open system. Consistently, we find that the energy input necessary to sustain steady-state fluid flow and tracer transport grows with the variance of the hydraulic conductivity field as well. Solute particles prefer to move through pathways of very high power in the transversal flow component, and these pathways emerge in the vicinity of bottlenecks of low hydraulic conductivity. This is because power depends on the squared spatial head gradient, which is in these simulations largest in regions of low hydraulic conductivity.

On the structural organization of biological pumps and channels

1984 ◽  
Vol 42 ◽  
pp. 138-141
Author(s):  
G. Zampighi ◽  
M. Kreman
Keyword(s):  
Active Transport ◽  
Transport System ◽  
Plasma Membranes ◽  
Transport Proteins ◽  
Molecular Organization ◽  
Passive Transport ◽  
Concentration Gradients ◽  
Cell Functions ◽  
Natural Concentration ◽  
Active Transport System

The plasma membranes of most animal cells contain transport proteins which function to provide passageways for the transported species across essentially impermeable lipid bilayers. The channel is a passive transport system which allows the movement of ions and low molecular weight molecules along their concentration gradients. The pump is an active transport system and can translocate cations against their natural concentration gradients. The actions and interplay of these two kinds of transport proteins control crucial cell functions such as active transport, excitability and cell communication. In this paper, we will describe and compare several features of the molecular organization of pumps and channels. As an example of an active transport system, we will discuss the structure of the sodium and potassium ion-activated triphosphatase [(Na+ +K+)-ATPase] and as an example of a passive transport system, the communicating channel of gap junctions and lens junctions.

Control of Rate of Solute Transport in Newly Developed Portable Agar Gel Blood Purification System

1998 ◽  
Vol 2 (1) ◽  
pp. 67-70
Author(s):  
Akihiro C. Yamashita ◽  
Ryoichi Sakiyama ◽  
Hiroyuki Hamada ◽  
Kakuji J. Tojo
Keyword(s):  
Solute Transport ◽  
Blood Purification ◽  
Agar Gel ◽  
Purification System
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