Dispersive and non-dispersive transport processes in polymers

2007 ◽  
pp. 35-44 ◽  
Author(s):  
H. Bässler
Keyword(s):  
Transport Processes ◽  
Dispersive Transport

scholarly journals Application of divided convective-dispersive transport model to simulate variability of conservative transport processes inside a planted horizontal subsurface flow constructed wetland

2020 ◽  
Author(s):  
Ernő Dittrich ◽  
Mihály Klincsik ◽  
Dávid Somfai ◽  
Anita Dolgos-Kovács ◽  
Tibor Kiss ◽  
...  
Keyword(s):  
Constructed Wetland ◽  
Dispersion Coefficient ◽  
Transport Model ◽  
Subsurface Flow ◽  
Distribution Functions ◽  
Transport Processes ◽  
Inverse Gaussian ◽  
Dispersive Transport ◽  
Subsurface Flow Constructed Wetland ◽  
Horizontal Subsurface Flow

AbstractThis paper offers a novel application of our model worked out in Maple environment to help understand the very complex transport processes in horizontal subsurface flow constructed wetland with coarse gravel (HSFCW-C). We made tracer measurements: Inside a constructed wetland, we had 9 sample points, and samples were taken from each point at two depths. Our model is a divided convective-dispersive transport (D-CDT) model which makes a fitted response curve from the sum of two separate CDT curves showing the contributions of the main and side streams. Analytical solutions of CDT curves are inverse Gaussian distribution functions. This model was fitted onto inner points of the measurements to demonstrate that the model gives better fitting to the inner points than the commonly used convective-dispersive transport model. The importance of this new application of the model is that it can resemble transport processes in these constructed wetlands more precisely than the regularly used convective-dispersive transport (CDT) model. The model allows for calculations of velocity and dispersion coefficients. The results showed that this model gave differences of 4–99% (of velocity) and 2–474% (of dispersion coefficient) compared with the CDT model and values were closer to actual hydraulic behavior. The results also demonstrated the main flow path in the system.

scholarly journals Exact analytical solutions for contaminant transport in rivers 1. The equilibrium advection-dispersion equation

2013 ◽  
Vol 61 (2) ◽  
pp. 146-160 ◽  
Author(s):  
Martinus Th. van Genuchten ◽  
Feike J. Leij ◽  
Todd H. Skaggs ◽  
Nobuo Toride ◽  
Scott A. Bradford ◽  
...  
Keyword(s):  
Surface Water ◽  
Dispersion Equation ◽  
Contaminant Transport ◽  
Analytical Solutions ◽  
Decay Chain ◽  
Transport Processes ◽  
Dispersive Transport ◽  
Chain Reactions ◽  
Surface Water Hydrology ◽  
Advection Dispersion

Abstract Analytical solutions of the advection-dispersion equation and related models are indispensable for predicting or analyzing contaminant transport processes in streams and rivers, as well as in other surface water bodies. Many useful analytical solutions originated in disciplines other than surface-water hydrology, are scattered across the literature, and not always well known. In this two-part series we provide a discussion of the advection-dispersion equation and related models for predicting concentration distributions as a function of time and distance, and compile in one place a large number of analytical solutions. In the current part 1 we present a series of one- and multi-dimensional solutions of the standard equilibrium advection-dispersion equation with and without terms accounting for zero-order production and first-order decay. The solutions may prove useful for simplified analyses of contaminant transport in surface water, and for mathematical verification of more comprehensive numerical transport models. Part 2 provides solutions for advective- dispersive transport with mass exchange into dead zones, diffusion in hyporheic zones, and consecutive decay chain reactions.

scholarly journals MODELING ESTUARIAL COHESIVE SEDIMENT TRANSPORT

1984 ◽  
Vol 1 (19) ◽  
pp. 199
Author(s):  
E.J. Hayter ◽  
A.J. Mehta
Keyword(s):  
Sediment Transport ◽  
Transport Model ◽  
Cohesive Sediment ◽  
Transport Processes ◽  
Weighted Residual Method ◽  
Dispersive Transport ◽  
Time Step ◽  
Advection Dispersion ◽  
Cohesive Sediment Transport ◽  
Suspended Sediment Concentrations

Cohesive sediment related problems in estuaries include shoaling in navigable waterways and water pollution. A two-dimensional, depth averaged, finite element cohesive sediment transport model, CSTM-H, has been developed and may be used to assist in predicting the fate of sorbed pollutants and the frequency and quantity of dredging required to maintain navigable depths. Algorithms which describe the transport processes of redispersion, resuspenslon, dispersive transport, settling, deposition, bed formation and bed consolidation are incorporated in CSTM-H. The Galerkin weighted residual method is used to solve the advection-dispersion equation with appropriate source/sink terms at each time step for the nodal suspended sediment concentrations. The model yields stable and converging solutions. Verification was carried out against a series of erosion-deposition experiments in the laboratory using kaolinite and a natural mud as sediment. A model application under prototype conditions is described.

scholarly journals Exact Analytical Solutions for Contaminant Transport in Rivers

2013 ◽  
Vol 61 (3) ◽  
pp. 250-259 ◽  
Author(s):  
Martinus Th. van Genuchten ◽  
Feike J. Leij ◽  
Todd H. Skaggs ◽  
Nobuo Toride ◽  
Scott A. Bradford ◽  
...  
Keyword(s):  
Dispersion Equation ◽  
Contaminant Transport ◽  
Analytical Solutions ◽  
Hyporheic Zone ◽  
Decay Chain ◽  
Transport Processes ◽  
Dispersive Transport ◽  
Chain Reactions ◽  
First Order ◽  
Advection Dispersion

Abstract Contaminant transport processes in streams, rivers, and other surface water bodies can be analyzed or predicted using the advection-dispersion equation and related transport models. In part 1 of this two-part series we presented a large number of one- and multi-dimensional analytical solutions of the standard equilibrium advection-dispersion equation (ADE) with and without terms accounting for zero-order production and first-order decay. The solutions are extended in the current part 2 to advective-dispersive transport with simultaneous first-order mass exchange between the stream or river and zones with dead water (transient storage models), and to problems involving longitudinal advectivedispersive transport with simultaneous diffusion in fluvial sediments or near-stream subsurface regions comprising a hyporheic zone. Part 2 also provides solutions for one-dimensional advective-dispersive transport of contaminants subject to consecutive decay chain reactions.

scholarly journals Bacterial density as an unexpected factor regulating decomposition by soil oligotrophs

2020 ◽  
Author(s):  
Alexandre Coche ◽  
Tristan Babey ◽  
Alain Rapaport ◽  
Laure Vieublé Gonod ◽  
Patricia Garnier ◽  
...  
Keyword(s):  
Transport Model ◽  
Transport Processes ◽  
Bacterial Density ◽  
Strong Interactions ◽  
List Type ◽  
Soil Core ◽  
Dispersive Transport ◽  
Density Regulation ◽  
Metabolic Traits ◽  
Ratio Dependent

AbstractBacterial decomposition of organic matter in soils is generally believed to be mainly controlled by the accessibility of bacteria to their substrate. The influence of bacterial metabolic traits on this control has however received little attention in highly heterogeneous spatial conditions under advective-dispersive transport of bacteria and substrates. Here, we develop a biochemical transport model to screen the interactive impacts of dispersion and metabolic traits on mineralization. We compare the model results with two sets of previously performed cm-scale soil-core experiments in which the mineralization of the pesticide 2,4-D was measured under well-controlled initial distributions and transport conditions. Bacterial dispersion away from the source of substrate induced a significant increase in 2,4-D mineralization, revealing the existence of a control of decomposition by the bacterial density, in addition to the accessibility to the substrate. This regulation of degradation by density becomes dominant for bacteria with an efficient uptake of substrate at low substrate concentrations (i.e. oligotrophs). The model output suggests that the distance between bacteria adapted to oligotrophic environments is a stronger regulator of degradation than the distance between substrate source and these bacteria. Such oligotrophs, commonly found in soils, compete with each other for substrate even under remarkably low population densities. The ratio-dependent Contois growth model, which includes a density regulation in the expression of the uptake efficiency, appears more versatile and accurate than the substrate-dependent Monod model. In view of their strong interactions, biochemical and transport processes cannot be handled independently but should be integrated, in particular when biochemical processes of interest are carried out by oligotrophs.Abstract FigureHighlights–Biodegradation in soils results from strong biochemical and transport couplings–Biodegradation depends on bacterial density, in addition to substrate accessibility–Bacterial density regulation counterbalances substrate accessibility regulation–Density regulation is enhanced for oligotrophic bacteria–The ratio-dependent Contois model is relevant to represent this double regulation

Saturn's E, G and F rings: modulated by the plasma sheet

1984 ◽  
Vol 75 ◽  
pp. 597
Author(s):  
E. Grün ◽  
G.E. Morfill ◽  
T.V. Johnson ◽  
G.H. Schwehm
Keyword(s):  
Solar Wind ◽  
Direct Contact ◽  
Transport Processes ◽  
Time Variable ◽  
Dust Particles ◽  
Spatial Diffusion ◽  
Drag Forces ◽  
Orbit Perturbation ◽  
Time Variations ◽  
F Ring

ABSTRACTSaturn's broad E ring, the narrow G ring and the structured and apparently time variable F ring(s), contain many micron and sub-micron sized particles, which make up the “visible” component. These rings (or ring systems) are in direct contact with magnetospheric plasma. Fluctuations in the plasma density and/or mean energy, due to magnetospheric and solar wind processes, may induce stochastic charge variations on the dust particles, which in turn lead to an orbit perturbation and spatial diffusion. It is suggested that the extent of the E ring and the braided, kinky structure of certain portions of the F rings as well as possible time variations are a result of plasma induced electromagnetic perturbations and drag forces. The G ring, in this scenario, requires some form of shepherding and should be akin to the F ring in structure. Sputtering of micron-sized dust particles in the E ring by magnetospheric ions yields lifetimes of 102to 104years. This effect as well as the plasma induced transport processes require an active source for the E ring, probably Enceladus.

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