Bahr, J.M.
1990-01-01
This paper extends a four-step derivation procedure, previously presented for cases of transport affected by surface reactions, to transport problems involving homogeneous reactions. Derivations for these classes of reactions are used to illustrate the manner in which mathematical differences between reaction classes are reflected in the mathematical derivation procedures required to identify kinetically influenced terms. Simulation results for a case of transport affected by a single solution phase complexation reaction and for a case of transport affected by a precipitation-dissolution reaction are used to demonstrate the nature of departures from equilibrium-controlled transport as well as the use of kinetically influenced terms in determining criteria for the applicability of the local equilibrium assumption. A final derivation for a multireaction problem demonstrates the application of the generalized procedure to a case of transport affected by reactions of several classes. -from Author
Bahr, Jean M.; Rubin, Jacob
1987-01-01
Modeling transport of reacting solutes in porous media often requires a choice between models based on the local equilibrium assumption (LEA) and models involving reaction kinetics. Direct comparison of the mathematical formulations for these two types of transport models can aid in this choice. For cases of transport affected by surface reaction, such a comparison is made possible by a new derivation procedure. This procedure yields a kinetics-based formulation that is the sum of the LEA formulation and one or more kinetically influenced terms. The dimensionless form of the new kinetics-based formulation facilitates identification of critical parameter groupings which control the approach to transport behavior consistent with LEA model predictions. Results of numerical experiments demonstrate that criteria for LEA applicability can be expressed conveniently in terms of these parameter groupings. The derivation procedure is demonstrated for examples of surface reactions including first-order reversible sorption, Langmuir-type kinetics and binary, homovalent ion exchange.
Choi, J.; Harvey, J.W.; Conklin, M.H.
2000-01-01
The fate of contaminants in streams and rivers is affected by exchange and biogeochemical transformation in slowly moving or stagnant flow zones that interact with rapid flow in the main channel. In a typical stream, there are multiple types of slowly moving flow zones in which exchange and transformation occur, such as stagnant or recirculating surface water as well as subsurface hyporheic zones. However, most investigators use transport models with just a single storage zone in their modeling studies, which assumes that the effects of multiple storage zones can be lumped together. Our study addressed the following question: Can a single-storage zone model reliably characterize the effects of physical retention and biogeochemical reactions in multiple storage zones? We extended an existing stream transport model with a single storage zone to include a second storage zone. With the extended model we generated 500 data sets representing transport of nonreactive and reactive solutes in stream systems that have two different types of storage zones with variable hydrologic conditions. The one storage zone model was tested by optimizing the lumped storage parameters to achieve a best fit for each of the generated data sets. Multiple storage processes were categorized as possessing I, additive; II, competitive; or III, dominant storage zone characteristics. The classification was based on the goodness of fit of generated data sets, the degree of similarity in mean retention time of the two storage zones, and the relative distributions of exchange flux and storage capacity between the two storage zones. For most cases (> 90%) the one storage zone model described either the effect of the sum of multiple storage processes (category I) or the dominant storage process (category III). Failure of the one storage zone model occurred mainly for category II, that is, when one of the storage zones had a much longer mean retention time (t(s) ratio > 5.0) and when the dominance of
Technology Transfer Automated Retrieval System (TEKTRAN)
Many or most subsurface pollution problems at the field scale involve such simultaneous processes as water flow, multicomponent solute transport, heat transport and biogeochemical processes and reactions. Process-based models that integrate these various processes can be valuable tools for investiga...
Abbott, Geoffrey W.; Tai, Kwok-Keung; Neverisky, Daniel; Hansler, Alex; Hu, Zhaoyang; Roepke, Torsten K.; Lerner, Daniel J.; Chen, Qiuying; Liu, Li; Zupan, Bojana; Toth, Miklos; Haynes, Robin; Huang, Xiaoping; Demirbas, Didem; Buccafusca, Roberto; Gross, Steven S.; Kanda, Vikram A.; Berry, Gerard T.
2014-01-01
Na+-coupled solute transport is crucial for the uptake of nutrients and metabolic precursors, such as myo-inositol, an important osmolyte and precursor for various cell signaling molecules. Here, we found that various solute transporters and potassium channel subunits formed complexes and reciprocally regulated each other in vitro and in vivo. Global metabolite profiling revealed that mice lacking KCNE2, a K+ channel β subunit, showed a reduction in the myo-inositol concentration in cerebrospinal fluid (CSF) but not in serum. Increased behavorial responsiveness to stress and seizure susceptibility in Kcne2−/− mice were alleviated by injections of myo-inositol. Suspecting a defect in myo-inositol transport, we found that KCNE2 and KCNQ1, a voltage-gated potassium channel α subunit, colocalized and coimmunoprecipitated with SMIT1, a Na+-coupled myo-inositol transporter, in the choroid plexus epithelium. Heterologous coexpression demonstrated that myo-inositol transport by SMIT1 was augmented by coexpression of KCNQ1 but inhibited by coexpression of both KCNQ1 and KCNE2, which form a constitutively active, heteromeric K+ channel. SMIT1 and the related transporter SMIT2 were also inhibited by a constitutively active mutant form of KCNQ1. The activity of KCNQ1 and KCNQ1-KCNE2 were augmented by SMIT1 and the glucose transporter SGLT1, but suppressed by SMIT2. Channel-transporter signaling complexes may be a widespread mechanism to facilitate solute transport and electrochemical crosstalk. PMID:24595108
NASA Astrophysics Data System (ADS)
Harvey, J. W.; Packman, A. I.
2010-12-01
Surface water and groundwater flow interact with the channel geomorphology and sediments in ways that determine how material is transported, stored, and transformed in stream corridors. Solute and sediment transport affect important ecological processes such as carbon and nutrient dynamics and stream metabolism, processes that are fundamental to stream health and function. Many individual mechanisms of transport and storage of solute and sediment have been studied, including surface water exchange between the main channel and side pools, hyporheic flow through shallow and deep subsurface flow paths, and sediment transport during both baseflow and floods. A significant challenge arises from non-linear and scale-dependent transport resulting from natural, fractal fluvial topography and associated broad, multi-scale hydrologic interactions. Connections between processes and linkages across scales are not well understood, imposing significant limitations on system predictability. The whole-stream tracer experimental approach is popular because of the spatial averaging of heterogeneous processes; however the tracer results, implemented alone and analyzed using typical models, cannot usually predict transport beyond the very specific conditions of the experiment. Furthermore, the results of whole stream tracer experiments tend to be biased due to unavoidable limitations associated with sampling frequency, measurement sensitivity, and experiment duration. We recommend that whole-stream tracer additions be augmented with hydraulic and topographic measurements and also with additional tracer measurements made directly in storage zones. We present examples of measurements that encompass interactions across spatial and temporal scales and models that are transferable to a wide range of flow and geomorphic conditions. These results show how the competitive effects between the different forces driving hyporheic flow, operating at different spatial scales, creates a situation
Small agricultural impoundments affect pollutant transport
NASA Astrophysics Data System (ADS)
Balcerak, Ernie
2013-03-01
Reservoirs created by dams intercept runoff from upslope areas and thus are often sinks for fertilizers and other pollutants that would otherwise flow downstream. Most studies of solute transport through impoundments have focused on large, long-lived systems. However, small impoundments, such as those created for irrigation or livestock watering, are common in agricultural regions, and their total global surface area is comparable to that of large reservoirs. As these small systems mature, the impoundments fill with sediment, creating ecosystems with wetland-like characteristics. Because dams that create these small impoundments are more likely to be degraded, poorly maintained, or removed by their owners, it is important to understand how changes in such systems may affect pollutant transport.
Transport solutions for cleaner air.
Kelly, Frank J; Zhu, Tong
2016-05-20
In cities across the globe, road transport remains an important source of air pollutants that are linked with acute and chronic health effects. Decreasing vehicle emissions--while maintaining or increasing commuter journeys--remains a major challenge for city administrators. In London, congestion-charging and a citywide low-emission zone failed to bring nitrogen dioxide concentrations under control. In Beijing, controls on the purchase and use of cars have not decreased transport emissions to a sufficient extent. As cities continue to grow, not even zero-emission vehicles are the solution. Moving increasingly large numbers of people efficiently around a city can only be achieved by expanding mass transit systems. PMID:27199415
Solute transport at fracture intersections
NASA Astrophysics Data System (ADS)
Mourzenko, V. V.; Yousefian, F.; Kolbah, B.; Thovert, J.-F.; Adler, P. M.
2002-01-01
A numerical study of three-dimensional solute transportat fracture intersections by using a particle tracking technique is presented.Two models of orthogonal fracture intersection are considered, namely, twoparallel-walled channels and two rough-walled Gaussian fractures. The fluidvelocity is calculated by solving the three-dimensional Stokes equation withno-slip boundary condition at the solid wall. Examples of individual trajectoriesof particles are first given in order to illustrate the main features of thephenomenon. Solute mass partitioning between outgoing fracture branches isconsidered for various transport regimes, characterized by the local Pécletnumber, and for various ratios of the flow rates in the intersecting channels.Generally speaking, it can be said that at dominant diffusion the influenceof the flow rates ratio is weak, while it is important in the opposite situation.Validity of the classical models of solute mixing, stream tube routing, andperfect mixing is analyzed by comparing their predictions with the numericaldata. Preliminary recommendations are made for the use of these results inlarge-scale modeling.
Coupled Fluid Energy Solute Transport
Energy Science and Technology Software Center (ESTSC)
1992-02-13
CFEST is a Coupled Fluid, Energy, and Solute Transport code for the study of a multilayered, nonisothermal ground-water system. It can model discontinuous as well as continuous layers, time-dependent and constant source/sinks, and transient as well as steady-state flow. The finite element method is used for analyzing isothermal and nonisothermal events in a confined aquifer system. Only single-phase Darcian flow is considered. In the Cartesian coordinate system, flow in a horizontal plane, in a verticalmore » plane, or in a fully three-dimensional region can be simulated. An option also exists for the axisymmetric analysis of a vertical cross section. The code employs bilinear quadrilateral elements in all two dimensional analyses and trilinear quadrilateral solid elements in three dimensional simulations. The CFEST finite element formulation can approximate discontinuities, major breaks in slope or thickness, and fault zones in individual hydrogeologic units. The code accounts for heterogeneity in aquifer permeability and porosity and accommodates anisotropy (collinear with the Cartesian coordinates). The variation in the hydraulic properties is described on a layer-by-layer basis for the different hydrogeologic units. Initial conditions can be prescribed hydraulic head or pressure, temperature, or concentration. CFEST can be used to support site, repository, and waste package subsystem assessments. Some specific applications are regional hydrologic characterization; simulation of coupled transport of fluid, heat, and salinity in the repository region; consequence assessment due to natural disruption or human intrusion scenarios in the repository region; flow paths and travel-time estimates for transport of radionuclides; and interpretation of well and tracer tests.« less
Reactive solute transport in acidic streams
Broshears, R.E.
1996-01-01
Spatial and temporal profiles of Ph and concentrations of toxic metals in streams affected by acid mine drainage are the result of the interplay of physical and biogeochemical processes. This paper describes a reactive solute transport model that provides a physically and thermodynamically quantitative interpretation of these profiles. The model combines a transport module that includes advection-dispersion and transient storage with a geochemical speciation module based on MINTEQA2. Input to the model includes stream hydrologic properties derived from tracer-dilution experiments, headwater and lateral inflow concentrations analyzed in field samples, and a thermodynamic database. Simulations reproduced the general features of steady-state patterns of observed pH and concentrations of aluminum and sulfate in St. Kevin Gulch, an acid mine drainage stream near Leadville, Colorado. These patterns were altered temporarily by injection of sodium carbonate into the stream. A transient simulation reproduced the observed effects of the base injection.
Simulation models for conservative and nonconservative solute transport in streams
Runkel, R.L.
1995-01-01
Solute transport in streams is governed by a suite of hydrologic and chemical processes. Interactions between hydrologic processes and chemical reactions may be quantified through a combination of field-scale experimentation and simulation modeling. Two mathematical models that simulate conservative and nonconservative solute transport in streams are presented. A model for conservative solutes that considers One Dimensional Transport with Inflow and Storage (OTIS) may be used in conjunction with tracer-dilution methods to quantify hydrologic transport processes (advection, dispersion, lateral inflow and transient storage). For nonconservative solutes, a model known as OTEQ may be used to quantify chemical processes within the context of hydrologic transport. OTEQ combines the transport mechanisms in OTIS with a chemical equilibrium sub-model that considers complexation, precipitation/dissolution and sorption. OTEQ has been used to quantify processes affecting trace metals in two streams in the Rocky Mountains of Colorado, USA.
Solute transport by a volatile solvent
NASA Astrophysics Data System (ADS)
Brown, Glenn O.; McWhorter, David B.
1990-05-01
In relatively dry porous media, water is transported as both liquid and vapor. Exact knowledge of this two-phase transport, and the phase transfer of water associated with it, is required for the prediction of solute transport. Combined liquid and vapor transport is examined starting from basic principles. An analytic solution is presented for the case of isothermal, transient, one-dimensional sorption of water with constant liquid content boundaries. A relation is also obtained for the evaporation and condensation within the flow field. A numerical solution for the solute transport is obtained which takes maximum advantage of the analytical flow solution. Using the properties of Lurgi retorted oil shale, several special cases are examined which show the relative importance of the separate phases in the total transport of water, the effects on the phase transfer, and the solute transport. It is expected that these methods and results can be applied to other problems in multiple phase transport, such as hazardous waste disposal and pesticide transport.
Mammalian ion-coupled solute transporters.
Hediger, M A; Kanai, Y; You, G; Nussberger, S
1995-01-01
Active transport of solutes into and out of cells proceeds via specialized transporters that utilize diverse energy-coupling mechanisms. Ion-coupled transporters link uphill solute transport to downhill electrochemical ion gradients. In mammals, these transporters are coupled to the co-transport of H+, Na+, Cl- and/or to the countertransport of K+ or OH-. By contrast, ATP-dependent transporters are directly energized by the hydrolysis of ATP. The development of expression cloning approaches to select cDNA clones solely based on their capacity to induce transport function in Xenopus oocytes has led to the cloning of several ion-coupled transporter cDNAs and revealed new insights into structural designs, energy-coupling mechanisms and physiological relevance of the transporter proteins. Different types of mammalian ion-coupled transporters are illustrated by discussing transporters isolated in our own laboratory such as the Na+/glucose co-transporters SGLT1 and SGLT2, the H(+)-coupled oligopeptide transporters PepT1 and PepT2, and the Na(+)- and K(+)-dependent neuronal and epithelial high affinity glutamate transporter EAAC1. Most mammalian ion-coupled organic solute transporters studied so far can be grouped into the following transporter families: (1) the predominantly Na(+)-coupled transporter family which includes the Na+/glucose co-transporters SGLT1, SGLT2, SGLT3 (SAAT-pSGLT2) and the inositol transporter SMIT, (2) the Na(+)- and Cl(-)-coupled transporter family which includes the neurotransmitter transporters of gamma-amino-butyric acid (GABA), serotonin, dopamine, norepinephrine, glycine and proline as well as transporters of beta-amino acids, (3) the Na(+)- and K(+)-dependent glutamate/neurotransmitter family which includes the high affinity glutamate transporters EAAC1, GLT-1, GLAST, EAAT4 and the neutral amino acid transporters ASCT1 and SATT1 reminiscent of system ASC and (4) the H(+)-coupled oligopeptide transporter family which includes the intestinal H
Electrofuels: Versatile Transportation Energy Solutions
2010-07-01
Electrofuels Project: ARPA-E’s Electrofuels Project is using microorganisms to create liquid transportation fuels in a new and different way that could be up to 10 times more energy efficient than current biofuel production methods. ARPA-E is the only U.S. government agency currently funding research on Electrofuels.
Can Solution Supersaturation Affect Protein Crystal Quality?
NASA Technical Reports Server (NTRS)
Gorti, Sridhar
2013-01-01
The formation of large protein crystals of "high quality" is considered a characteristic manifestation of microgravity. The physical processes that predict the formation of large, high quality protein crystals in the microgravity environment of space are considered rooted in the existence of a "depletion zone" in the vicinity of crystal. Namely, it is considered reasonable that crystal quality suffers in earth-grown crystals as a result of the incorporation of large aggregates, micro-crystals and/or large molecular weight "impurities", processes which are aided by density driven convective flow or mixing at the crystal-liquid interface. Sedimentation and density driven convection produce unfavorable solution conditions in the vicinity of the crystal surface, which promotes rapid crystal growth to the detriment of crystal size and quality. In this effort, we shall further present the hypothesis that the solution supersaturatoin at the crystal surface determines the growth mechanism, or mode, by which protein crystals grow. It is further hypothesized that protein crystal quality is affected by the mechanism or mode of crystal growth. Hence the formation of a depletion zone in microgravity environment is beneficial due to inhibition of impurity incorporatoin as well as preventing a kinetic roughening transition. It should be noted that for many proteins the magnitude of neither protein crystal growth rates nor solution supersaturation are predictors of a kinetic roughening transition. That is, the kinetic roughening transition supersaturation must be dtermined for each individual protein.
Performance Analysis of Solution Transportation Absorption Chiller
NASA Astrophysics Data System (ADS)
Kiani, Behdad; Hamamoto, Yoshinori; Akisawa, Atsushi; Kashiwagi, Takao
Thermally activated advanced absorption cycles are considered promising candidates to replace CFCs, HCFCs and HFCs for residential and commercial applications. In such absorption systems, it is desirable to utilize the waste heat from industries for heating and cooling applications in commercial and residential sectors. For this purpose, it is necessary to transport energy over some distance because the waste heat source and demand are generally located apart from each other. Transportation of steam, hot water or chilled water requires high construction costs for insulation. There is an efficient method of energy transportation using absorption system called “ Solution Transportation Absorption System (STA)”. The solution is transported at an ambient temperature so that tube-insulations not required. This paper shows the simulation of the abovementioned system and the optimal result, using mathematical optimization. The optimum system with industry‧s waste heat utilization is obtained. At the end, the effect on the pollution emission and energy conservation is obtained.
Future variability of solute transport in a macrotidal estuary
NASA Astrophysics Data System (ADS)
Robins, Peter E.; Lewis, Matt J.; Simpson, John H.; Howlett, Eleanor R.; Malham, Shelagh K.
2014-12-01
The physical controls on salt distribution and river-sourced conservative solutes, including the potential implications of climate change, are investigated referring to model simulations of a macrotidal estuary. In the UK, such estuaries typically react rapidly to rainfall events and, as such, are often in a state of non-equilibrium in terms of solute transport; hence are particularly sensitive to climate extremes. Sea levels are projected to rise over the 21st century, extending the salinity maximum upstream in estuaries, which will also affect downstream solute transport, promoting estuarine trapping and reducing offshore dispersal of material. Predicted 'drier summers' and 'wetter winters' in the UK will influence solute transport further still; we found that projected river flow climate changes were more influential than sea-level rise, especially for low flow conditions. Our simulations show that projected climate change for the UK is likely to increase variability in estuarine solute transport and, specifically, increase the likelihood of estuarine trapping during summer, mainly due to drier weather conditions. Future changes in solute transport were less certain during winter, since increased river flow will to some extent counter-act the effects of sea-level rise. Our results have important implications for non-conservative nutrient transport, water quality, coastal management and ecosystem resilience.
Multilevel transport solution of LWR reactor cores
Jose Ignacio Marquez Damian; Cassiano R.E. de Oliveira; HyeonKae Park
2008-09-01
This work presents a multilevel approach for the solution of the transport equation in typical LWR assemblies and core configurations. It is based on the second-order, even-parity formulation of the transport equation, which is solved within the framework provided by the finite element-spherical harmonics code EVENT. The performance of the new solver has been compared with that of the standard conjugate gradient solver for diffusion and transport problems on structured and unstruc-tured grids. Numerical results demonstrate the potential of the multilevel scheme for realistic reactor calculations.
Solute transport through a deforming porous medium
NASA Astrophysics Data System (ADS)
Peters, Glen P.; Smith, David W.
2002-06-01
Solute transport through a porous medium is typically modelled assuming the porous medium is rigid. However, many applications exist where the porous medium is deforming, including, municipal landfill liners, mine tailings dams, and land subsidence. In this paper, mass balance laws are used to derive the flow and transport equations for a deforming porous medium. The equations are derived in both spatial and material co-ordinate systems. Solute transport through an engineered landfill liner is used as an illustrative example to show the differences between the theory for a rigid porous medium, and small and large deformation analysis of a deforming porous medium. It is found that the large deformation model produces shorter solute breakthrough times, followed by the small deformation model, and then the rigid porous medium model. It is also found that it is important to include spatial and temporal void ratio variations in the large deformation analysis. It is shown that a non-linear large deformation model may greatly reduce the solute breakthrough time, compared to a standard transport analysis typically employed by environmental engineers.
Linear transport models for adsorbing solutes
NASA Astrophysics Data System (ADS)
Roth, K.; Jury, W. A.
1993-04-01
A unified linear theory for the transport of adsorbing solutes through soils is presented and applied to analyze movement of napropamide through undisturbed soil columns. The transport characteristics of the soil are expressed in terms of the travel time distribution of the mobile phase which is then used to incorporate local interaction processes. This approach permits the analysis of all linear transport processes, not only the small subset for which a differential description is known. From a practical point of view, it allows the direct use of measured concentrations or fluxes of conservative solutes to characterize the mobile phase without first subjecting them to any model. For complicated flow regimes, this may vastly improve the identification of models and estimation of their parameters for the local adsorption processes.
Solute transport in heterogeneous porous formations
NASA Astrophysics Data System (ADS)
Demmy, George Gary, Jr.
1999-10-01
This work quantifies relationships between the spatial, or Eulerian, distribution of the properties of a chemically and physically heterogeneous porous medium and those as observed along the natural, or Lagrangian, trajectories that a fluid particle traces in a steady and irrotational flow. From these relationships, expressions that relate the transport of solutes through the porous medium along the natural trajectories to the aforementioned Eulerian distributions are developed. The effects of injection mode upon global measures of transport as reflected by the temporal moments of breakthrough curves and spatial moments of a solute plume are developed. The coupled effects of correlation of a linear equilibrium sorption to the underlying log hydraulic conductivity field and injection mode on the evolving temporal moments of mass breakthrough curve and the coupled effects of correlation of a first-order decay coefficient and injection mode upon the spatial moments of a solute plume are examined.
Probing Nanoscale Thermal Transport in Surfactant Solutions
Cao, Fangyu; Liu, Ying; Xu, Jiajun; He, Yadong; Hammouda, B.; Qiao, Rui; Yang, Bao
2015-01-01
Surfactant solutions typically feature tunable nanoscale, internal structures. Although rarely utilized, they can be a powerful platform for probing thermal transport in nanoscale domains and across interfaces with nanometer-size radius. Here, we examine the structure and thermal transport in solution of AOT (Dioctyl sodium sulfosuccinate) in n-octane liquids using small-angle neutron scattering, thermal conductivity measurements, and molecular dynamics simulations. We report the first experimental observation of a minimum thermal conductivity occurring at the critical micelle concentration (CMC): the thermal conductivity of the surfactant solution decreases as AOT is added till the onset of micellization but increases as more AOT is added. The decrease of thermal conductivity with AOT loading in solutions in which AOT molecules are dispersed as monomers suggests that even the interfaces between individual oleophobic headgroup of AOT molecules and their surrounding non-polar octane molecules can hinder heat transfer. The increase of thermal conductivity with AOT loading after the onset of micellization indicates that the thermal transport in the core of AOT micelles and across the surfactant-oil interfaces, both of which span only a few nanometers, are efficient. PMID:26534840
Probing Nanoscale Thermal Transport in Surfactant Solutions
NASA Astrophysics Data System (ADS)
Cao, Fangyu; Liu, Ying; Xu, Jiajun; He, Yadong; Hammouda, B.; Qiao, Rui; Yang, Bao
2015-11-01
Surfactant solutions typically feature tunable nanoscale, internal structures. Although rarely utilized, they can be a powerful platform for probing thermal transport in nanoscale domains and across interfaces with nanometer-size radius. Here, we examine the structure and thermal transport in solution of AOT (Dioctyl sodium sulfosuccinate) in n-octane liquids using small-angle neutron scattering, thermal conductivity measurements, and molecular dynamics simulations. We report the first experimental observation of a minimum thermal conductivity occurring at the critical micelle concentration (CMC): the thermal conductivity of the surfactant solution decreases as AOT is added till the onset of micellization but increases as more AOT is added. The decrease of thermal conductivity with AOT loading in solutions in which AOT molecules are dispersed as monomers suggests that even the interfaces between individual oleophobic headgroup of AOT molecules and their surrounding non-polar octane molecules can hinder heat transfer. The increase of thermal conductivity with AOT loading after the onset of micellization indicates that the thermal transport in the core of AOT micelles and across the surfactant-oil interfaces, both of which span only a few nanometers, are efficient.
Probing Nanoscale Thermal Transport in Surfactant Solutions.
Cao, Fangyu; Liu, Ying; Xu, Jiajun; He, Yadong; Hammouda, B; Qiao, Rui; Yang, Bao
2015-01-01
Surfactant solutions typically feature tunable nanoscale, internal structures. Although rarely utilized, they can be a powerful platform for probing thermal transport in nanoscale domains and across interfaces with nanometer-size radius. Here, we examine the structure and thermal transport in solution of AOT (Dioctyl sodium sulfosuccinate) in n-octane liquids using small-angle neutron scattering, thermal conductivity measurements, and molecular dynamics simulations. We report the first experimental observation of a minimum thermal conductivity occurring at the critical micelle concentration (CMC): the thermal conductivity of the surfactant solution decreases as AOT is added till the onset of micellization but increases as more AOT is added. The decrease of thermal conductivity with AOT loading in solutions in which AOT molecules are dispersed as monomers suggests that even the interfaces between individual oleophobic headgroup of AOT molecules and their surrounding non-polar octane molecules can hinder heat transfer. The increase of thermal conductivity with AOT loading after the onset of micellization indicates that the thermal transport in the core of AOT micelles and across the surfactant-oil interfaces, both of which span only a few nanometers, are efficient. PMID:26534840
Conditions and processes affecting radionuclide transport
Simmons, Ardyth M.; Neymark, Leonid A.
2012-01-01
Understanding of unsaturated-zone transport is based on laboratory and field-scale experiments. Fractures provide advective transport pathways. Sorption and matrix diffusion may contribute to retardation of radionuclides. Conversely, sorption onto mobile colloids may enhance radionuclide transport.
Solute transport along preferential flow paths in unsaturated fractures
Su, G.W.; Geller, J.T.; Pruess, K.; Hunt, J.R.
2001-01-01
Laboratory experiments were conducted to study solute transport along preferential flow paths in unsaturated, inclined fractures. Qualitative aspects of solute transport were identified in a miscible dye tracer experiment conducted in a transparent replica of a natural granite fracture. Additional experiments were conducted to measure the breakthrough curves of a conservative tracer introduced into an established preferential flow path in two different fracture replicas and a rock-replica combination. The influence of gravity was investigated by varying fracture inclination. The relationship between the travel times of the solute and the relative influence of gravity was substantially affected by two modes of intermittent flow that occurred: the snapping rivulet and the pulsating blob modes. The measured travel times of the solute were evaluated with three transfer function models: the axial dispersion, the reactors-in-series, and the lognormal models. The three models described the solute travel times nearly equally well. A mechanistic model was also formulated to describe transport when the pulsating blob mode occurred which assumed blobs of water containing solute mixed with residual pools of water along the flow path.
Compositional transport in solidifying aqueous binary solution
NASA Astrophysics Data System (ADS)
Zhong, Jin-Qiang; Yin, Zuo-Chao; Xue, Qiwei; Wettlaufer, John
2013-11-01
We observe the formation of double-diffusive layers adjacent to mushy layers that form during the directional solidification of aqueous ammonium chloride. The plumes emerging from chimney's in the mushy layers continuously supply a buoyancy flux in the (finite) liquid region above, driving downward motion of double-diffusive layers. The downward velocity of the layers is found to be in good agreement with a filling box model that captures the crucial hydrodynamics of the entraining buoyant plumes and compositional transport. We demonstrate that the buoyancy flux through the system decays according to a similarity solution. We note that the experimental findings provide some insight into the brine transport in growing sea ice.
Space Weather affects on Air Transportation
NASA Astrophysics Data System (ADS)
Jones, J. B. L.; Bentley, R. D.; Dyer, C.; Shaw, A.
In Europe, legislation requires the airline industry to monitor the occupational exposure of aircrew to cosmic radiation. However, there are other significant impacts of space weather phenomena on the technological systems used for day-to-day operations which need to be considered by the airlines. These were highlighted by the disruption caused to the industry by the period of significant solar activity in late October and early November 2003. Next generation aircraft will utilize increasingly complex avionics as well as expanding the performance envelopes. These and future generation platforms will require the development of a new air-space management infrastructure with improved position accuracy (for route navigation and landing in bad weather) and reduced separation minima in order to cope with the expected growth in air travel. Similarly, greater reliance will be placed upon satellites for command, control, communication and information (C3I) of the operation. However, to maximize effectiveness of this globally interoperable C3I and ensure seamless fusion of all components for a safe operation will require a greater understanding of the space weather affects, their risks with increasing technology, and the inclusion of space weather information into the operation. This paper will review space weather effects on air transport and the increasing risks for future operations cause by them. We will examine how well the effects can be predicted, some of the tools that can be used and the practicalities of using such predictions in an operational scenario. Initial results from the SOARS ESA Space Weather Pilot Project will also be discussed,
Numerical error in groundwater flow and solute transport simulation
NASA Astrophysics Data System (ADS)
Woods, Juliette A.; Teubner, Michael D.; Simmons, Craig T.; Narayan, Kumar A.
2003-06-01
Models of groundwater flow and solute transport may be affected by numerical error, leading to quantitative and qualitative changes in behavior. In this paper we compare and combine three methods of assessing the extent of numerical error: grid refinement, mathematical analysis, and benchmark test problems. In particular, we assess the popular solute transport code SUTRA [Voss, 1984] as being a typical finite element code. Our numerical analysis suggests that SUTRA incorporates a numerical dispersion error and that its mass-lumped numerical scheme increases the numerical error. This is confirmed using a Gaussian test problem. A modified SUTRA code, in which the numerical dispersion is calculated and subtracted, produces better results. The much more challenging Elder problem [Elder, 1967; Voss and Souza, 1987] is then considered. Calculation of its numerical dispersion coefficients and numerical stability show that the Elder problem is prone to error. We confirm that Elder problem results are extremely sensitive to the simulation method used.
Analytical solutions for anomalous dispersion transport
NASA Astrophysics Data System (ADS)
O'Malley, D.; Vesselinov, V. V.
2014-06-01
Groundwater flow and transport often occur in a highly heterogeneous environment (potentially heterogeneous at multiple spatial scales) and is impacted by geochemical reactions, advection, diffusion, and other pore scale processes. All these factors can give rise to large-scale anomalous dispersive behavior that can make complex model representation and prediction of plume concentrations challenging due to difficulties unraveling all the complexities associated with the governing processes, flow medium, and their parameters. An alternative is to use upscaled stochastic models of anomalous dispersion, and this is the approach used here. Within a probabilistic framework, we derive a number of analytical solutions for several anomalous dispersion models. The anomalous dispersion models are allowed to be either non-Gaussian (α-stable Lévy), correlated, or nonstationary from the Lagrangian perspective. A global sensitivity analysis is performed to gain a greater understanding of the extent to which uncertainty in the parameters associated with the anomalous behavior can be narrowed by examining concentration measurements from a network of monitoring wells and to demonstrate the computational speed of the solutions. The developed analytical solutions are encoded and available for use in the open source computational framework MADS (http://mads.lanl.gov).
Willis, Catherine; Rubin, Jacob
1987-01-01
In this paper we consider examples of chemistry-affected transport processes in porous media. A moving boundary problem which arises during transport with precipitation-dissolution reactions is solved by three different numerical methods. Two of these methods (one explicit and one implicit) are based on an integral formulation of mass balance and lead to an approximation of a weak solution. These methods are compared to a front-tracking scheme. Although the two approaches are conceptually different, the numerical solutions showed good agreement. As the ratio of dispersion to convection decreases, the methods based on the integral formulation become computationally more efficient. Specific reactions were modeled to examine the dependence of the system on the physical and chemical parameters.
Modeling flow and solute transport in irrigation furrows
Technology Transfer Automated Retrieval System (TEKTRAN)
This paper presents an internally coupled flow and solute transport model for free-draining irrigation furrows. Furrow hydraulics is simulated with a numerical zero-inertia model and solute transport is computed with a model based on a numerical solution of the cross-section averaged advection-dispe...
Analytical Solutions for Sequentially Reactive Transport with Different Retardation Factors
Sun, Y; Buscheck, T A; Mansoor, K; Lu, X
2001-08-01
Integral transforms have been widely used for deriving analytical solutions for solute transport systems. Often, analytical solutions can only be written in closed form in frequency domains and numerical inverse-transforms have to be involved to obtain semi-analytical solutions in the time domain. For this reason, previously published closed form solutions are restricted either to a small number of species or to the same retardation assumption. In this paper, we applied the solution scheme proposed by Bauer et al. in the time domain. Using available analytical solutions of a single species transport with first-order decay without coupling with its parent species concentration as fundamental solutions, a daughter species concentration can be expressed as a linear function of those fundamental solutions. The implementation of the solution scheme is straight forward and exact analytical solutions are derived for one- and three-dimensional transport systems.
Ground-water solute transport with hydrogeochemical reactions
Garcia-Delgado, R.A.; Koussis, A.D.
1997-03-01
Chemical contamination of ground water is typically associated with multicomponent solutions of reactive substances, the mobility of which is affected by their reactivity. In predicting geochemical transport, it is therefore important that the liquid and solid phase reactions be modeled, along with the flow-controlled processes. This demanding task is typically carried out on powerful computers. Frequently, however, field data are available for a limited number of species, or, a small number of species suffices to characterize ground-water quality. In such cases it is desirable to be able to model the transport on a widely available class of inexpensive computers. The authors report on the development of a 2-D model for the transport of reactive species that runs efficiently on PCs. The model follows a modified one-step procedure that adopts total (aqueous and adsorbed) concentrations and aqueous concentrations of components, and accounts for aqueous complexation and for competitive sorption via isotherms or selectivity coefficients. The use of principal directions of transport coordinates, dimensional splitting, and a specialized algorithm for handling advection-dominated transport render it compact and efficient. Mass conservation is satisfied with high accuracy.
Variables Affecting Two Electron Transport System Assays
Burton, G. Allen; Lanza, Guy R.
1986-01-01
Several methodological variables were critical in two commonly used electron transport activity assays. The dehydrogenase assay based on triphenyl formazan production exhibited a nonlinear relationship between formazan production (dehydrogenase activity) and sediment dilution, and linear formazan production occurred for 1 h in sediment slurries. Activity decreased with increased time of sediment storage at 4°C. Extraction efficiencies of formazan from sediment varied with alcohol type; methanol was unsatisfactory. Phosphate buffer (0.06 M) produced higher activity than did either U.S. Environmental Protection Agency reconstituted hard water or Tris buffer sediment diluents. Intracellular formazan crystals were dissolved within minutes when in contact with immersion oil. Greater crystal production (respiration) detected by a tetrazolium salt assay occurred at increased substrate concentrations. Test diluents containing macrophyte exudates produced greater activity than did phosphate buffer, U.S. Environmental Protection Agency water, or ultrapure water diluents. Both assays showed decreases in sediment or bacterial activity through time. PMID:16347067
A quasilinear model for solute transport under unsaturated flow
Houseworth, J.E.; Leem, J.
2009-05-15
We developed an analytical solution for solute transport under steady-state, two-dimensional, unsaturated flow and transport conditions for the investigation of high-level radioactive waste disposal. The two-dimensional, unsaturated flow problem is treated using the quasilinear flow method for a system with homogeneous material properties. Dispersion is modeled as isotropic and is proportional to the effective hydraulic conductivity. This leads to a quasilinear form for the transport problem in terms of a scalar potential that is analogous to the Kirchhoff potential for quasilinear flow. The solutions for both flow and transport scalar potentials take the form of Fourier series. The particular solution given here is for two sources of flow, with one source containing a dissolved solute. The solution method may easily be extended, however, for any combination of flow and solute sources under steady-state conditions. The analytical results for multidimensional solute transport problems, which previously could only be solved numerically, also offer an additional way to benchmark numerical solutions. An analytical solution for two-dimensional, steady-state solute transport under unsaturated flow conditions is presented. A specific case with two sources is solved but may be generalized to any combination of sources. The analytical results complement numerical solutions, which were previously required to solve this class of problems.
BiP negatively affects ricin transport.
Gregers, Tone F; Skånland, Sigrid S; Wälchli, Sébastien; Bakke, Oddmund; Sandvig, Kirsten
2013-05-01
The AB plant toxin ricin binds both glycoproteins and glycolipids at the cell surface via its B subunit. After binding, ricin is endocytosed and then transported retrogradely through the Golgi to the endoplasmic reticulum (ER). In the ER, the A subunit is retrotranslocated to the cytosol in a chaperone-dependent process, which is not fully explored. Recently two separate siRNA screens have demonstrated that ER chaperones have implications for ricin toxicity. ER associated degradation (ERAD) involves translocation of misfolded proteins from ER to cytosol and it is conceivable that protein toxins exploit this pathway. The ER chaperone BiP is an important ER regulator and has been implicated in toxicity mediated by cholera and Shiga toxin. In this study, we have investigated the role of BiP in ricin translocation to the cytosol. We first show that overexpression of BiP inhibited ricin translocation and protected cells against the toxin. Furthermore, shRNA-mediated depletion of BiP enhanced toxin translocation resulting in increased cytotoxicity. BiP-dependent inhibition of ricin toxicity was independent of ER stress. Our findings suggest that in contrast to what was shown with the Shiga toxin, the presence of BiP does not facilitate, but rather inhibits the entry of ricin into the cytosol. PMID:23666197
Innovative Solutions to Challenges in Pupil Transportation.
ERIC Educational Resources Information Center
Ross, Jonathan; Burkybile, Sharon
2000-01-01
States have had to budget increasing amounts for mandated pupil-transportation services as their state transportation aid has been slashed dramatically. Among school districts, cooperation and coordination through shared services (consortia) have resulted in safer, more reliable, and more efficient transportation. Implementation advice is…
Solute transporters in plant thylakoid membranes
Schoefs, Benoît
2010-01-01
Plants utilize sunlight to drive photosynthetic energy conversion in the chloroplast thylakoid membrane. Here are located four major photosynthetic complexes, about which we have great knowledge in terms of structure and function. However, much less we know about auxiliary proteins, such as transporters, ensuring an optimum function and turnover of these complexes. The most prominent thylakoid transporter is the proton-translocating ATP-synthase. Recently, four additional transporters have been identified in the thylakoid membrane of Arabidopsis thaliana, namely one copper-transporting P-ATPase, one chloride channel, one phosphate transporter, and one ATP/ADP carrier. Here, we review the current knowledge on the function and physiological role of these transporters during photosynthesis and light stress in plants. Subsequently, we make a survey on the outlook of thylakoid activities awaiting identification of responsible proteins. Such knowledge is necessary to understand the thylakoid network of transporters, and to design strategies for bioengineering crop plants in the future. PMID:20585503
Waniewski, Jacek; Antosiewicz, Stefan; Baczynski, Daniel; Poleszczuk, Jan; Pietribiasi, Mauro; Lindholm, Bengt; Wankowicz, Zofia
2016-01-01
During peritoneal dialysis (PD), the peritoneal membrane undergoes ageing processes that affect its function. Here we analyzed associations of patient age and dialysis vintage with parameters of peritoneal transport of fluid and solutes, directly measured and estimated based on the pore model, for individual patients. Thirty-three patients (15 females; age 60 (21-87) years; median time on PD 19 (3-100) months) underwent sequential peritoneal equilibration test. Dialysis vintage and patient age did not correlate. Estimation of parameters of the two-pore model of peritoneal transport was performed. The estimated fluid transport parameters, including hydraulic permeability (LpS), fraction of ultrasmall pores (α u), osmotic conductance for glucose (OCG), and peritoneal absorption, were generally independent of solute transport parameters (diffusive mass transport parameters). Fluid transport parameters correlated whereas transport parameters for small solutes and proteins did not correlate with dialysis vintage and patient age. Although LpS and OCG were lower for older patients and those with long dialysis vintage, αu was higher. Thus, fluid transport parameters--rather than solute transport parameters--are linked to dialysis vintage and patient age and should therefore be included when monitoring processes linked to ageing of the peritoneal membrane. PMID:26989432
Waniewski, Jacek; Antosiewicz, Stefan; Baczynski, Daniel; Poleszczuk, Jan; Pietribiasi, Mauro; Lindholm, Bengt; Wankowicz, Zofia
2016-01-01
During peritoneal dialysis (PD), the peritoneal membrane undergoes ageing processes that affect its function. Here we analyzed associations of patient age and dialysis vintage with parameters of peritoneal transport of fluid and solutes, directly measured and estimated based on the pore model, for individual patients. Thirty-three patients (15 females; age 60 (21–87) years; median time on PD 19 (3–100) months) underwent sequential peritoneal equilibration test. Dialysis vintage and patient age did not correlate. Estimation of parameters of the two-pore model of peritoneal transport was performed. The estimated fluid transport parameters, including hydraulic permeability (LpS), fraction of ultrasmall pores (αu), osmotic conductance for glucose (OCG), and peritoneal absorption, were generally independent of solute transport parameters (diffusive mass transport parameters). Fluid transport parameters correlated whereas transport parameters for small solutes and proteins did not correlate with dialysis vintage and patient age. Although LpS and OCG were lower for older patients and those with long dialysis vintage, αu was higher. Thus, fluid transport parameters—rather than solute transport parameters—are linked to dialysis vintage and patient age and should therefore be included when monitoring processes linked to ageing of the peritoneal membrane. PMID:26989432
Coupling of solute transport and cell expansion in pea stems
NASA Technical Reports Server (NTRS)
Schmalstig, J. G.; Cosgrove, D. J.
1990-01-01
As cells expand and are displaced through the elongation zone of the epicotyl of etiolated pea (Pisum sativum L. var Alaska) seedlings, there is little net dilution of the cell sap, implying a coordination between cell expansion and solute uptake from the phloem. Using [14C] sucrose as a phloem tracer (applied to the hypogeous cotyledons), the pattern of label accumulation along the stem closely matched the growth rate pattern: high accumulation in the growing zone, little accumulation in nongrowing regions. Several results suggest that a major portion of phloem contents enters elongating cells through the symplast. We propose that the coordination between phloem transport and cell expansion is accomplished via regulatory pathways affecting both plasmodesmata conductivity and cell expansion.
Biological solutions to transport network design.
Bebber, Daniel P; Hynes, Juliet; Darrah, Peter R; Boddy, Lynne; Fricker, Mark D
2007-09-22
Transport networks are vital components of multicellular organisms, distributing nutrients and removing waste products. Animal and plant transport systems are branching trees whose architecture is linked to universal scaling laws in these organisms. In contrast, many fungi form reticulated mycelia via the branching and fusion of thread-like hyphae that continuously adapt to the environment. Fungal networks have evolved to explore and exploit a patchy environment, rather than ramify through a three-dimensional organism. However, there has been no explicit analysis of the network structures formed, their dynamic behaviour nor how either impact on their ecological function. Using the woodland saprotroph Phanerochaete velutina, we show that fungal networks can display both high transport capacity and robustness to damage. These properties are enhanced as the network grows, while the relative cost of building the network decreases. Thus, mycelia achieve the seemingly competing goals of efficient transport and robustness, with decreasing relative investment, by selective reinforcement and recycling of transport pathways. Fungal networks demonstrate that indeterminate, decentralized systems can yield highly adaptive networks. Understanding how these relatively simple organisms have found effective transport networks through a process of natural selection may inform the design of man-made networks. PMID:17623638
Solute Transport Across a Contact Interface in Deformable Porous Media
Ateshian, Gerard A.; Maas, Steve; Weiss, Jeffrey A.
2012-01-01
A finite element formulation of neutral solute transport across a contact interface between deformable porous media is implemented and validated against analytical solutions. By reducing the integral statements of external virtual work on the two contacting surfaces into a single contact integral, the algorithm automatically enforces continuity of solute molar flux across the contact interface, whereas continuity of the effective solute concentration (a measure of the solute mechano-chemical potential) is achieved using a penalty method. This novel formulation facilitates the analysis of problems in biomechanics where the transport of metabolites across contact interfaces of deformable tissues may be of interest. This contact algorithm is the first to address solute transport across deformable interfaces, and is made available in the public domain, open-source finite element code FEBio (http://mrl.sci.utah.edu/software). PMID:22281406
Solute transport across a contact interface in deformable porous media.
Ateshian, Gerard A; Maas, Steve; Weiss, Jeffrey A
2012-04-01
A finite element formulation of neutral solute transport across a contact interface between deformable porous media is implemented and validated against analytical solutions. By reducing the integral statements of external virtual work on the two contacting surfaces into a single contact integral, the algorithm automatically enforces continuity of solute molar flux across the contact interface, whereas continuity of the effective solute concentration (a measure of the solute mechano-chemical potential) is achieved using a penalty method. This novel formulation facilitates the analysis of problems in biomechanics where the transport of metabolites across contact interfaces of deformable tissues may be of interest. This contact algorithm is the first to address solute transport across deformable interfaces, and is made available in the public domain, open-source finite element code FEBio (http://www.febio.org). PMID:22281406
Transport of Organic Solutes in Clay Formations
The research is a pilot investigation for the SERDP (Strategic Environmental Research and Development Program, DoD) founded project, Impact of Clay-DNAPL Interactions on Transport and Storage of Chlorinated Solvents in Low Permeability Zones, from 2010-2012. The report tries to s...
Nanoparticle characteristics affecting environmental fate and transport through soil.
Darlington, Thomas K; Neigh, Arianne M; Spencer, Matthew T; Nguyen, Oanh T; Oldenburg, Steven J
2009-06-01
Nanoparticles are being used in broad range of applications; therefore, these materials probably will enter the environment during their life cycle. The objective of the present study is to identify changes in properties of nanoparticles released into the environment with a case study on aluminum nanoparticles. Aluminum nanoparticles commonly are used in energetic formulations and may be released into the environment during their handling and use. To evaluate the transport of aluminum nanoparticles, it is necessary not only to understand the properties of the aluminum in its initial state but also to determine how the nanoparticle properties will change when exposed to relevant environmental conditions. Transport measurements were conducted with a soil-column system that delivers a constant upflow of a suspension of nanoparticles to a soil column and monitors the concentration, size, agglomeration state, and charge of the particles in the eluent. The type of solution and surface functionalization had a marked effect on the charge, stability, and agglomeration state of the nanoparticles, which in turn impacted transport through the receiving matrix. Transport also is dependent on the size of the nanoparticles, although it is the agglomerate size, not the primary size, that is correlated with transportability. Electrostatically induced binding events of positively charged aluminum nanoparticles to the soil matrix were greater than those for negatively charged aluminum nanoparticles. Many factors influence the transport of nanoparticles in the environment, but size, charge, and agglomeration rate of nanoparticles in the transport medium are predictive of nanoparticle mobility in soil. PMID:19175296
Effects of Soil Behavior on Solute Transport in Groundwater
NASA Astrophysics Data System (ADS)
Jeng, Dong-Sheng; Zhang, Huijie
2010-05-01
The evaluation of solute transport in groundwater is particularly important for environmental engineers involved in the design of urban environments. In general, the simulation of solute transport in porous medium has been linked with fluid flow, which has commonly based on Darcy law. Unlike previous work, we use a more generalized fluid flow model with poro-elastic theory, in which Darcy model is one of its special cases. The new feature of the new model is the inclusion of soil characteristics and behavior in the prediction of solute transport in aquifers. Based on the new model, numerical example demonstrates significant influence of poro-elastic soil behavior on the movement of zone of peak concentration of solute in groundwater.
Lewis, F.M.; Voss, C.I.; Rubin, J.
1987-01-01
Methodologies that account for specific types of chemical reactions in the simulation of solute transport can be developed so they are compatible with solution algorithms employed in existing transport codes. This enables the simulation of reactive transport in complex multidimensional flow regimes, and provides a means for existing codes to account for some of the fundamental chemical processes that occur among transported solutes. Two equilibrium-controlled reaction systems demonstrate a methodology for accommodating chemical interaction into models of solute transport. One system involves the sorption of a given chemical species, as well as two aqueous complexations in which the sorbing species is a participant. The other reaction set involves binary ion exchange coupled with aqueous complexation involving one of the exchanging species. The methodology accommodates these reaction systems through the addition of nonlinear terms to the transport equations for the sorbing species. Example simulation results show (1) the effect equilibrium chemical parameters have on the spatial distributions of concentration for complexing solutes; (2) that an interrelationship exists between mechanical dispersion and the various reaction processes; (3) that dispersive parameters of the porous media cannot be determined from reactive concentration distributions unless the reaction is accounted for or the influence of the reaction is negligible; (4) how the concentration of a chemical species may be significantly affected by its participation in an aqueous complex with a second species which also sorbs; and (5) that these coupled chemical processes influencing reactive transport can be demonstrated in two-dimensional flow regimes. ?? 1987.
Moridis, George J.
2001-10-10
In this paper, semianalytical solutions are developed for the problem of transport of radioactive or reactive solute tracers through a layered system of heterogeneous fractured media with misaligned fractures. The tracer transport equations in the non-flowing matrix account for (a) diffusion, (b) surface diffusion, (c) mass transfer between the mobile and immobile water fractions, (d) linear kinetic or equilibrium physical, chemical, or combined solute sorption or colloid filtration, and (e) radioactive decay or first-order chemical reactions. The tracer-transport equations in the fractures account for the same processes, in addition to advection and hydrodynamic dispersion. Any number of radioactive decay daughter products (or products of a linear, first-order reaction chain) can be tracked. The solutions, which are analytical in the Laplace space, are numerically inverted to provide the solution in time and can accommodate any number of fractured and/or porous layers. The solutions are verified using analytical solutions for limiting cases of solute and colloid transport through fractured and porous media. The effect of important parameters on the transport of {sup 3}H, {sup 237}Np and {sup 239}Pu (and its daughters) is investigated in several test problems involving layered geological systems of varying complexity.
George J. Moridis
2001-10-01
In this paper, semianalytical solutions are developed for the problem of transport of radioactive or reactive solute tracers through a layered system of heterogeneous fractured media with misaligned fractures. The tracer transport equations in the non-flowing matrix account for (a) diffusion, (b) surface diffusion, (c) mass transfer between the mobile and immobile water fractions, (d) linear kinetic or equilibrium physical, chemical, or combined solute sorption or colloid filtration, and (e) radioactive decay or first-order chemical reactions. The tracer-transport equations in the fractures account for the same processes, in addition to advection and hydrodynamic dispersion. Any number of radioactive decay daughter products (or products of a linear, first-order reaction chain) can be tracked. The solutions, which are analytical in the Laplace space, are numerically inverted to provide the solution in time and can accommodate any number of fractured and/or porous layers. The solutions are verified using analytical solutions for limiting cases of solute and colloid transport through fractured and porous media. The effect of important parameters on the transport of {sup 3}H, {sup 237}Np and {sup 239}Pu (and its daughters) is investigated in several test problems involving layered geological systems of varying complexity.
Field monitoring of water flow and solute transport under different manure amendments.
Technology Transfer Automated Retrieval System (TEKTRAN)
Organic matter (OM) affects water flow and solute transport in the vadose zone. The main objective of this work was to study the effects of different OM types (dairy and chicken manure), rates (O, 168, 336, and 672 kg/ha total equivalent Nitrogen), and levels (one and two time applications) on water...
End-Member Formulation of Solid Solutions and Reactive Transport
Lichtner, Peter C.
2015-09-01
A model for incorporating solid solutions into reactive transport equations is presented based on an end-member representation. Reactive transport equations are solved directly for the composition and bulk concentration of the solid solution. Reactions of a solid solution with an aqueous solution are formulated in terms of an overall stoichiometric reaction corresponding to a time-varying composition and exchange reactions, equivalent to reaction end-members. Reaction rates are treated kinetically using a transition state rate law for the overall reaction and a pseudo-kinetic rate law for exchange reactions. The composition of the solid solution at the onset of precipitation is assumed to correspond to the least soluble composition, equivalent to the composition at equilibrium. The stoichiometric saturation determines if the solid solution is super-saturated with respect to the aqueous solution. The method is implemented for a simple prototype batch reactor using Mathematica for a binary solid solution. Finally, the sensitivity of the results on the kinetic rate constant for a binary solid solution is investigated for reaction of an initially stoichiometric solid phase with an undersaturated aqueous solution.
Insights into non-Fickian solute transport in carbonates
Bijeljic, Branko; Mostaghimi, Peyman; Blunt, Martin J
2013-01-01
[1] We study and explain the origin of early breakthrough and long tailing plume behavior by simulating solute transport through 3-D X-ray images of six different carbonate rock samples, representing geological media with a high degree of pore-scale complexity. A Stokes solver is employed to compute the flow field, and the particles are then transported along streamlines to represent advection, while the random walk method is used to model diffusion. We compute the propagators (concentration versus displacement) for a range of Peclet numbers (Pe) and relate it to the velocity distribution obtained directly on the images. There is a very wide distribution of velocity that quantifies the impact of pore structure on transport. In samples with a relatively narrow spread of velocities, transport is characterized by a small immobile concentration peak, representing essentially stagnant portions of the pore space, and a dominant secondary peak of mobile solute moving at approximately the average flow speed. On the other hand, in carbonates with a wider velocity distribution, there is a significant immobile peak concentration and an elongated tail of moving fluid. An increase in Pe, decreasing the relative impact of diffusion, leads to the faster formation of secondary mobile peak(s). This behavior indicates highly anomalous transport. The implications for modeling field-scale transport are discussed. Citation: Bijeljic, B., P. Mostaghimi, and M. J. Blunt (2013), Insights into non-Fickian solute transport in carbonates, Water Resour. Res., 49, 2714–2728, doi:10.1002/wrcr.20238. PMID:24223444
Larsen, Erik Hviid; Sørensen, Jakob Balslev; Sørensen, Jens Nørkær
2000-01-01
A mathematical model of an absorbing leaky epithelium is developed for analysis of solute coupled water transport. The non-charged driving solute diffuses into cells and is pumped from cells into the lateral intercellular space (lis). All membranes contain water channels with the solute passing those of tight junction and interspace basement membrane by convection-diffusion. With solute permeability of paracellular pathway large relative to paracellular water flow, the paracellular flux ratio of the solute (influx/outflux) is small (2–4) in agreement with experiments. The virtual solute concentration of fluid emerging from lis is then significantly larger than the concentration in lis. Thus, in absence of external driving forces the model generates isotonic transport provided a component of the solute flux emerging downstream lis is taken up by cells through the serosal membrane and pumped back into lis, i.e., the solute would have to be recirculated. With input variables from toad intestine (Nedergaard, S., E.H. Larsen, and H.H. Ussing, J. Membr. Biol. 168:241–251), computations predict that 60–80% of the pumped flux stems from serosal bath in agreement with the experimental estimate of the recirculation flux. Robust solutions are obtained with realistic concentrations and pressures of lis, and with the following features. Rate of fluid absorption is governed by the solute permeability of mucosal membrane. Maximum fluid flow is governed by density of pumps on lis-membranes. Energetic efficiency increases with hydraulic conductance of the pathway carrying water from mucosal solution into lis. Uphill water transport is accomplished, but with high hydraulic conductance of cell membranes strength of transport is obscured by water flow through cells. Anomalous solvent drag occurs when back flux of water through cells exceeds inward water flux between cells. Molecules moving along the paracellular pathway are driven by a translateral flow of water, i.e., the model
Solute transport in eroded and rehabilitated prairie landforms. 1. Nonreactive solute.
Papiernik, Sharon K; Koskinen, William C; Yates, Scott R
2009-08-26
Information regarding solute and water transport as affected by soil properties, topography, and climatic conditions is required to improve and validate transport models. This study evaluated the dissipation of bromide applied to the soil surface in the fall and spring to undisturbed (eroded) and rehabilitated landforms, in which topsoil was moved from depositional areas to the eroded upper slope. Despite large changes in soil properties, the amount and center of mass of bromide remaining in the top 1 m of soil was the same in undisturbed and rehabilitated plots. Approximately 60% of the fall-applied bromide was lost during the winter and early spring, presumably due to leaching and runoff. The center of mass of spring-applied bromide remained at depths of <30 cm. At the end of the experiment, 33% of the spring-applied bromide was detected in soil and 56% in corn plants. These results suggest that little bromide was leached out of the root zone in the spring and that plant uptake was a major route of bromide dissipation during the growing season. PMID:19653694
Molecular level water and solute transport in reverse osmosis membranes
NASA Astrophysics Data System (ADS)
Lueptow, Richard M.; Shen, Meng; Keten, Sinan
2015-11-01
The water permeability and rejection characteristics of six solutes, methanol, ethanol, 2-propanol, urea, Na+, and Cl-, were studied for a polymeric reverse osmosis (RO) membrane using non-equilibrium molecular dynamics simulations. Results indicate that water flux increases with an increasing fraction of percolated free volume in the membrane polymer structure. Solute molecules display Brownian motion and hop from pore to pore as they pass through the membrane. The solute rejection depends on both the size of the solute molecule and the chemical interaction of the solute with water and the membrane. When the open spaces in the polymeric structure are such that solutes have to shed at least one water molecule from their solvation shell to pass through the membrane molecular structure, the water-solute pair interaction energy governs solute rejection. Organic solutes more easily shed water molecules than ions to more readily pass through the membrane. Hydrogen-bonding sites for molecules like urea also lead to a higher rejection. These findings underline the importance of the solute's solvation shell and solute-water-membrane chemistry in solute transport and rejection in RO membranes. Funded by the Institute for Sustainability and Energy at Northwestern with computing resources from XSEDE (NSF grant ACI-1053575).
Technology Transfer Automated Retrieval System (TEKTRAN)
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 t...
Analytical model of solute transport by unsteady unsaturated gravitational infiltration.
Lessoff, S C; Indelman, P
2004-08-01
Penetration of reactive solute into a soil during a cycle of water infiltration and redistribution is investigated by deriving analytical closed form solutions for fluid flux, moisture content and contaminant concentration. The solution is developed for gravitational flow and advective transport and is applied to two scenarios of solute applications encountered in the applications: a finite pulse of solute dissolved in irrigation water and an instantaneous pulse broadcasted onto the soil surface. Through comparison to simulations of Richards' flow, capillary suction is shown to have contrasting effects on the upper and lower boundaries of the fluid pulse, speeding penetration of the wetting front and reducing the rate of drying. This leads to agreement between the analytical and numerical solutions for typical field and experimental conditions. The analytical solution is further incorporated into a stochastic column model of flow and transport to compute mean solute concentration in a heterogeneous field. An unusual phenomenon of plume contraction is observed at long times of solute propagation during the drying stage. The mean concentration profiles match those of the Monte-Carlo simulations for capillary length scales typical of sandy soils. PMID:15240168
Sasabe, Hiroyuki; Shimokawa, Yoshihiko; Shibata, Masakazu; Hashizume, Kenta; Hamasako, Yusuke; Ohzone, Yoshihiro; Kashiyama, Eiji; Umehara, Ken
2016-06-01
Delamanid (Deltyba, OPC-67683) is the first approved drug in a novel class of nitro-dihydro-imidazooxazoles developed for the treatment of multidrug-resistant tuberculosis. Patients with tuberculosis require treatment with multiple drugs, several of which have known drug-drug interactions. Transporters regulate drug absorption, distribution, and excretion; therefore, the inhibition of transport by one agent may alter the pharmacokinetics of another, leading to unexpected adverse events. Therefore, it is important to understand how delamanid affects transport activity. In the present study, the potencies of delamanid and its main metabolites as the substrates and inhibitors of various transporters were evaluated in vitro Delamanid was not transported by the efflux ATP-binding cassette (ABC) transporters P-glycoprotein (P-gp; MDR1/ABCB1) and breast cancer resistance protein (BCRP/ABCG2), solute carrier (SLC) transporters, organic anion-transporting polypeptides, or organic cation transporter 1. Similarly, metabolite 1 (M1) was not a substrate for any of these transporters except P-gp. Delamanid showed no inhibitory effect on ABC transporters MDR1, BCRP, and bile salt export pump (BSEP; ABCB11), SLC transporters, or organic anion transporters. M1 and M2 inhibited P-gp- and BCRP-mediated transport but did so only at the 50% inhibitory concentrations (M1, 4.65 and 5.71 μmol/liter, respectively; M2, 7.80 and 6.02 μmol/liter, respectively), well above the corresponding maximum concentration in plasma values observed following the administration of multiple doses in clinical trials. M3 and M4 did not affect the activities of any of the transporters tested. These in vitro data suggest that delamanid is unlikely to have clinically relevant interactions with drugs for which absorption and disposition are mediated by this group of transporters. PMID:27021329
Influence of surfactants on unsaturated water flow and solute transport
NASA Astrophysics Data System (ADS)
Karagunduz, Ahmet; Young, Michael H.; Pennell, Kurt D.
2015-04-01
Surfactants can reduce soil water retention by changing the surface tension of water and the contact angle between the liquid and solid phases. As a result, water flow and solute transport in unsaturated soil may be altered in the presence of surfactants. In this study, the effects of a representative nonionic surfactant, Triton X-100, on coupled water flow and nonreactive solute transport during unsaturated flow conditions were evaluated. Batch reactor experiments were conducted to measure the surfactant sorption characteristics, while unsaturated transport experiments were performed in columns packed with 40-270 mesh Ottawa sand at five initial water contents. Following the introduction of surfactant solution, the rate of water percolation through the sand increased; however, this period of rapid water drainage was followed by decreased water percolation due to the reduction in soil water content and the corresponding decrease in unsaturated hydraulic conductivity behind the surfactant front. The observed changes in water percolation occurred sequentially, and resulted in faster nonreactive solute transport than was observed in the absence of surfactant. A one-dimensional mathematical model accurately described coupled water flow, surfactant, and solute transport under most experimental conditions. Differences between model predictions and experimental data were observed in the column study performed at the lowest water content (0.115 cm3/cm3), which was attributed to surfactant adsorption at the air-water interface. These findings demonstrate the potential influence of surfactants additives on unsaturated water flow and solute transport in soils, and demonstrate a methodology to couple these processes in a predictive modeling tool.
Scott, D.T.; Gooseff, M.N.; Bencala, K.E.; Runkel, R.L.
2003-01-01
The hydrologic processes of advection, dispersion, and transient storage are the primary physical mechanisms affecting solute transport in streams. The estimation of parameters for a conservative solute transport model is an essential step to characterize transient storage and other physical features that cannot be directly measured, and often is a preliminary step in the study of reactive solutes. Our study used inverse modeling to estimate parameters of the transient storage model OTIS (One dimensional Transport with Inflow and Storage). Observations from a tracer injection experiment performed on Uvas Creek, California, USA, are used to illustrate the application of automated solute transport model calibration to conservative and nonconservative stream solute transport. A computer code for universal inverse modeling (UCODE) is used for the calibrations. Results of this procedure are compared with a previous study that used a trial-and-error parameter estimation approach. The results demonstrated 1) importance of the proper estimation of discharge and lateral inflow within the stream system; 2) that although the fit of the observations is not much better when transient storage is invoked, a more randomly distributed set of residuals resulted (suggesting non-systematic error), indicating that transient storage is occurring; 3) that inclusion of transient storage for a reactive solute (Sr2+) provided a better fit to the observations, highlighting the importance of robust model parameterization; and 4) that applying an automated calibration inverse modeling estimation approach resulted in a comprehensive understanding of the model results and the limitation of input data.
The secret to successful solute-transport modeling.
Konikow, Leonard F
2011-01-01
Modeling subsurface solute transport is difficult-more so than modeling heads and flows. The classical governing equation does not always adequately represent what we see at the field scale. In such cases, commonly used numerical models are solving the wrong equation. Also, the transport equation is hyperbolic where advection is dominant, and parabolic where hydrodynamic dispersion is dominant. No single numerical method works well for all conditions, and for any given complex field problem, where seepage velocity is highly variable, no one method will be optimal everywhere. Although we normally expect a numerically accurate solution to the governing groundwater-flow equation, errors in concentrations from numerical dispersion and/or oscillations may be large in some cases. The accuracy and efficiency of the numerical solution to the solute-transport equation are more sensitive to the numerical method chosen than for typical groundwater-flow problems. However, numerical errors can be kept within acceptable limits if sufficient computational effort is expended. But impractically long simulation times may promote a tendency to ignore or accept numerical errors. One approach to effective solute-transport modeling is to keep the model relatively simple and use it to test and improve conceptual understanding of the system and the problem at hand. It should not be expected that all concentrations observed in the field can be reproduced. Given a knowledgeable analyst, a reasonable description of a hydrogeologic framework, and the availability of solute-concentration data, the secret to successful solute-transport modeling may simply be to lower expectations. PMID:21039449
A fracture network model for water flow and solute transport
Robinson, B.A.
1989-01-01
This paper summarizes code development work and sample calculations for FRACNET, a two-dimensional steady state simulator of fluid flow and solute transport in fractured porous media. The model analyzes flow and transport by generating a fracture network based on statistical characteristics of fractures obtained from well logs and other data. After a network is generated, flow and tracer transport are computed for appropriate boundary conditions and wellbore source/sink terms. In addition, for a given realization, the code can be used to indicate whether the medium can be treated as an equivalent porous medium. 18 refs., 7 figs.
Transport solutions of the Lamé equations and shock elastic waves
NASA Astrophysics Data System (ADS)
Alexeyeva, L. A.; Kaishybaeva, G. K.
2016-07-01
The Lamé system describing the dynamics of an isotropic elastic medium affected by a steady transport load moving at subsonic, transonic, or supersonic speed is considered. Its fundamental and generalized solutions in a moving frame of reference tied to the transport load are analyzed. Shock waves arising in the medium at supersonic speeds are studied. Conditions on the jump in the stress, displacement rate, and energy across the shock front are obtained using distribution theory. Numerical results concerning the dynamics of an elastic medium influenced by concentrated transport loads moving at sub-, tran- and supersonic speeds are presented.
A gravimetric experiment was undertaken to identify the factors affecting solvent evaporation from analytical reference standard solutions and to establish the magnitude of the resultant solvent evaporation. The evaporation of organic solvent from standard solutions is affected b...
Insights into non-Fickian solute transport in carbonates
NASA Astrophysics Data System (ADS)
Bijeljic, Branko; Mostaghimi, Peyman; Blunt, Martin J.
2013-05-01
We study and explain the origin of early breakthrough and long tailing plume behavior by simulating solute transport through 3-D X-ray images of six different carbonate rock samples, representing geological media with a high degree of pore-scale complexity. A Stokes solver is employed to compute the flow field, and the particles are then transported along streamlines to represent advection, while the random walk method is used to model diffusion. We compute the propagators (concentration versus displacement) for a range of Peclet numbers (Pe) and relate it to the velocity distribution obtained directly on the images. There is a very wide distribution of velocity that quantifies the impact of pore structure on transport. In samples with a relatively narrow spread of velocities, transport is characterized by a small immobile concentration peak, representing essentially stagnant portions of the pore space, and a dominant secondary peak of mobile solute moving at approximately the average flow speed. On the other hand, in carbonates with a wider velocity distribution, there is a significant immobile peak concentration and an elongated tail of moving fluid. An increase in Pe, decreasing the relative impact of diffusion, leads to the faster formation of secondary mobile peak(s). This behavior indicates highly anomalous transport. The implications for modeling field-scale transport are discussed.
Continuous time random walk analysis of solute transport in fractured porous media
Cortis, Andrea; Cortis, Andrea; Birkholzer, Jens
2008-06-01
The objective of this work is to discuss solute transport phenomena in fractured porous media, where the macroscopic transport of contaminants in the highly permeable interconnected fractures can be strongly affected by solute exchange with the porous rock matrix. We are interested in a wide range of rock types, with matrix hydraulic conductivities varying from almost impermeable (e.g., granites) to somewhat permeable (e.g., porous sandstones). In the first case, molecular diffusion is the only transport process causing the transfer of contaminants between the fractures and the matrix blocks. In the second case, additional solute transfer occurs as a result of a combination of advective and dispersive transport mechanisms, with considerable impact on the macroscopic transport behavior. We start our study by conducting numerical tracer experiments employing a discrete (microscopic) representation of fractures and matrix. Using the discrete simulations as a surrogate for the 'correct' transport behavior, we then evaluate the accuracy of macroscopic (continuum) approaches in comparison with the discrete results. However, instead of using dual-continuum models, which are quite often used to account for this type of heterogeneity, we develop a macroscopic model based on the Continuous Time Random Walk (CTRW) framework, which characterizes the interaction between the fractured and porous rock domains by using a probability distribution function of residence times. A parametric study of how CTRW parameters evolve is presented, describing transport as a function of the hydraulic conductivity ratio between fractured and porous domains.
Effect of proteolytic enzymes on transepithelial solute transport
Niewoehner, D.E.; Sinha, A.A.; Rice, K.; Cadman, S.; Wangensteen, D.
1986-10-01
The effects of proteases on air-space clearance (AC) of small ((/sup 14/C)sucrose, 342 daltons) and large (/sup 125/I-neutral dextran, 70,000 daltons) solutes were studied in isolated, fluid-filled hamster lungs that were perfused in a nonrecirculating system. When instilled into the air spaces, porcine pancreatic elastase (0.1-0.4 mg/ml) and bovine pancreatic trypsin (BPT) (0.5-2.0 mg/ml), but neither Clostridium histolyticum collagenase (5.0 mg/ml) nor phenylmethylsulfonyl fluoride-inactivated BPT caused large increases in the AC of both tracer molecules. BPT-induced solute clearance was further characterized functionally and morphologically. The functional characteristics of solute AC under steady-state conditions did not indicate that transepithelial transport was diffusion-limited. Inhibition by millimolar concentrations of Zn/sup 2 +/ and by lung cooling, along with electron microscopic studies employing horseradish peroxidase as a macromolecule tracer, were consistent with epithelial solute transport by a vesicular mechanism (transcytosis). Solute transport from the interstitial compartment to the lung exterior was shown to occur via two pathways. By unknown mechanisms BPT caused small amounts of water to flow through an incompletely identified, extravascular pathway. In BPT-exposed lungs efflux of /sup 125/I-dextran 70 occurred almost exclusively through this pathway, whereas (/sup 14/C)sucrose was transported to the lung exterior partly through this same pathway and partly through the vasculature. The large differences in the diffusion coefficients of the two tracers may have accounted for these observed patterns of solute efflux from the lung. The possible significance of our findings to the pathogenesis of experimental emphysema are discussed.
Simulation of transportation of low enriched uranium solutions
Hope, E.P.; Ades, M.J.
1996-08-01
A simulation of the transportation by truck of low enriched uranium solutions has been completed for NEPA purposes at the Savannah River Site. The analysis involves three distinct source terms, and establishes the radiological risks of shipment to three possible destinations. Additionally, loading accidents were analyzed to determine the radiological consequences of mishaps during handling and delivery. Source terms were developed from laboratory measurements of chemical samples from low enriched uranium feed materials being stored at SRS facilities, and from manufacturer data on transport containers. The transportation simulations were accomplished over the INTERNET using the DOE TRANSNET system at Sandia National Laboratory. The HIGHWAY 3.3 code was used to analyze routing scenarios, and the RADTRAN 4 code was used to analyze incident free and accident risks of transporting radiological materials. Loading accidents were assessed using the Savannah River Site AXAIR89Q and RELEASE 2 codes.
Modeling reactive geochemical transport of concentrated aqueous solutions
NASA Astrophysics Data System (ADS)
Zhang, Guoxiang; Zheng, Zuoping; Wan, Jiamin
2005-02-01
Aqueous solutions with ionic strength larger than 1 M are usually considered concentrated aqueous solutions. These solutions can be found in some natural systems and are also industrially produced and released into accessible natural environments, and as such, they pose a big environmental problem. Concentrated aqueous solutions have unique thermodynamic and physical properties. They are usually strongly acidic or strongly alkaline, with the ionic strength possibly reaching 30 M or higher. Chemical components in such solutions are incompletely dissociated. The thermodynamic activities of both ionic and molecular species in these solutions are determined by the ionic interactions. In geological media the problem is further complicated by the interactions between the solutions and sediments and rocks. The chemical composition of concentrated aqueous solutions when migrating through the geological media may be drastically altered by these strong fluid-rock interactions. To effectively model reactive transport of concentrated aqueous solutions, we must take into account the ionic interactions. For this purpose we substantially extended an existing reactive transport code, BIO-CORE2D©, by incorporating a Pitzer ion interaction model to calculate the ionic activity. In the present paper, the model and two test cases of the model are briefly introduced. We also simulate a laboratory column experiment in which the leakage of highly alkaline waste fluid stored at Hanford (a U.S. Department of Energy site, located in Washington State) was studied. Our simulation captures the measured pH evolution and indicates that all the reactions controlling the pH evolution, including cation exchanges and mineral dissolution/precipitation, are coupled.
Heterogeneous solute transport in a tile-drained field
NASA Astrophysics Data System (ADS)
Basile, A.; Comegna, A.; Coppola, A.; Hassan, S.; Haikal, M. A.; Kassab, M.; Lamaddalena, N.
2009-04-01
Preferential flow and its diverse attributes: i) macropore flow; ii) fingered flow; iii) funnel flow, cannot be described by a single process hypothesis and are unpredictable from a priori analysis of field characteristics due to the inability of sampling methods to capture minute features triggering such flows. Most solute transport techniques are expensive and require extensive soil disturbance. Moreover, solute transport in heterogeneous porous media cannot always be conceptualized as being either a convective-dispersive or a stochastic-convective process. One approach to predict subsurface leaching could be the coupling of near surface measurements with a generalized transport model. A steady state field tracer experiment was conducted on a tile-drained "Terra Rossa" plot located in Valenzano (Bari - Italy), to test whether TDR BTCs measured 1 m a part along a transect of 40 m can be used in such a way for accurate prediction of tile's BTC. A Generalized Transfer Function (GTF) (Zhang, 2000) was fitted to the observed concentration a three depths for each site along the transect to identify the transfer function parameters. To account for vertical transport in the unsaturated zone and lateral divergence near the tile, these parameters were used in a 2D model (Utermann, 1990) to predict earlier breakthrough of tile flux concentration. The 2D model predictions of the flux concentrations were similar to the observed values, nearly reproducing the channel-like nature of solute flow.
Conservative and reactive solute transport in constructed wetlands
Keefe, S.H.; Barber, L.B.; Runkel, R.L.; Ryan, J.N.; McKnight, Diane M.; Wass, R.D.
2004-01-01
The transport of bromide, a conservative tracer, and rhodamine WT (RWT), a photodegrading tracer, was evaluated in three wastewater-dependent wetlands near Phoenix, Arizona, using a solute transport model with transient storage. Coupled sodium bromide and RWT tracer tests were performed to establish conservative transport and reactive parameters in constructed wetlands with water losses ranging from (1) relatively impermeable (15%), (2) moderately leaky (45%), and (3) significantly leaky (76%). RWT first-order photolysis rates and sorption coefficients were determined from independent field and laboratory experiments. Individual wetland hydraulic profiles influenced the extent of transient storage interaction in stagnant water areas and consequently RWT removal. Solute mixing and transient storage interaction occurred in the impermeable wetland, resulting in 21% RWT mass loss from main channel and storage zone photolysis (10%) and sorption (11%) reactions. Advection and dispersion governed solute transport in the leaky wetland, limiting RWT photolysis removal (1.2%) and favoring main channel sorption (3.6%). The moderately leaky wetland contained islands parallel to flow, producing channel flow and minimizing RWT losses (1.6%).
Hydrogeochemistry and simulated solute transport, Piceance Basin, northwestern Colorado
Robson, S.G.; Saulnier, G.J., Jr.
1981-01-01
Oil-shale mining activities in Piceance basin in northwestern Colorado could adversely affect the ground- and surface-water quality in the basin. This study of the hydrology and geochemistry of the area used ground-water solute-transport-modeling techniques to investigate the possible impact of the mines on water quality. Maps of the extent and structure of the aquifer were prepared and show that a saturated thickness of 2,000 feet occurs in the northeast part of the basin. Ground-water recharge in the upland areas in the east, south, and west parts of the basin moves down into deeper zones in the aquifer and laterally to the discharge areas along Piceance and Yellow Creeks. The saline zone and the unsaturated zone provide the majority of the dissolved solids found in the ground water. Precipitation, ion-exchange, and oxidation-reduction reactions are also occuring in the aquifer. Model simulations of ground-water pumpage in tracts C-a and C-b indicate that the altered direction of ground-water movement near the pumped mines will cause an improvement in ground-water quality near the mines and a degradation of water quality downgradient from the tracts. Model simulations of mine leaching in tract C-a and C-b indicate that equal rates of mine leaching in the tracts will produce much different effects on the water quality in the basin. Tract C-a, by virtue of its remote location from perennial streams, will primarily degrade the ground-water quality over a large area to the northeast of the tract. Tract C-b, by contrast, will primarily degrade the surface-water quality in Piceance Creek, with only localized effects on the ground-water quality. (USGS)
Hydrogeochemistry and simulated solute transport, Piceance Basin, northwestern Colorado
Robson, Stanley G.; Saulnier, George J.
1980-01-01
Oil-shale mining activities in Piceance basin in northwestern Colorado could adversely affect the ground- and surface-water quality in the basin. This study of the hydrology and geochemistry of the area used groundwater solute-transport-modeling techniques to investigate the possible impact of the mines on water quality. Maps of the extent and structure of the aquifer were prepared and show that a saturated thickness of 2,000 feet occurs in the northeast part of the basin. Ground-water recharge in the upland areas in the east, south, and west parts of the basin moves down into deeper zones in the aquifer and laterally to the discharge areas along Piceance and Yellow Creeks. The saline zone and the unsaturated zone provide the majority of the dissolved solids found in the ground water. Precipitation, ion-exchange, and oxidation-reduction reactions are also occurring in the aquifer. Model simulations of groundwater pumpage in tracts C-a and C-b indicate that the altered direction of groundwater movement near the pumped mines will cause an improvement in groundwater quality near the mines and a degradation of water quality downgradient from the tracts. Model simulations of mine leaching in tract C-a and C-b indicate that equal rates of mine leaching in the tracts will produce much different effects on the water quality in the basin. Tract C-a, by virtue of its remote location from perennial streams, will primarily degrade the groundwater quality over a large area to the northeast of the tract. Tract C-b, by contrast, will primarily degrade the surface-water quality in Piceance Creek, with only localized effects on the groundwater quality. (USGS)
Solute transport in dual-permeability porous media
NASA Astrophysics Data System (ADS)
Leij, Feike J.; Toride, Nobuo; Field, Malcolm S.; Sciortino, Antonella
2012-04-01
A dual-advection dispersion equation (DADE) is presented and solved to describe solute transport in structured or layered porous media with different nonzero flow rates in two distinct pore domains with linear solute transfer between them. This dual-permeability model constitutes a generalized version of the advection-dispersion equation (ADE) for transport in uniform porous media and the mobile-immobile model (MIM) for transport in media with a mobile and an immobile pore domain. Analytical tools for the DADE have mostly been lacking. An analytical solution has therefore been derived using Laplace transformation with time and modal decomposition based on matrix diagonalization, assuming the same dispersivity for both domains. Temporal moments are derived for the DADE and contrasted with those for the ADE and the MIM. The effective dispersion coefficient for the DADE approaches that of the ADE for a similar velocity in both pore domains and large values for the first-order transfer parameter, and approaches that of the MIM for the opposite conditions. The solution of the DADE is used to illustrate how differences in pore water velocity between the domains and low transfer rates will lead to double peaks in the volume- or flux-averaged concentration profiles versus time or position. The DADE is applied to optimize experimental breakthrough curves for an Andisol with a distinct intra- and interaggregate porosity. The DADE improved the description of the breakthrough data compared to the ADE and the MIM.
Stochastic analysis of transport of conservative solutes in caisson experiments
Dagan, G.
1995-02-01
The Los Alamos National Laboratory has conducted in the past a series of experiments of transport of conservative and reactive solutes. The experimental setup and the experimental results are presented in a series of reports. The main aim of the experiments was to validate models of transport of solutes in unsaturated flow at the caisson intermediate scale, which is much larger than the one pertaining to laboratory columns. First attempts to analyze the experimental results were by one-dimensional convective-dispersion models. These models could not explain the observed solute breakthrough curves and particularly the large solute dispersion in the caisson effluent Since there were some question marks about the uniformity of water distribution at the caisson top, the transport experiments were repeated under conditions of saturated flow. In these experiments constant heads were applied at the top and the bottom of the caisson and the number of concentration monitoring stations was quadrupled. The analysis of the measurements by the same one-dimensional model indicated clearly that the fitted dispersivity is much larger than the pore-sole dispersivity and that it grows with the distance in an approximately linear fashion. This led to the conclusion, raised before, that transport in the caisson is dominated by heterogeneity effects, i.e. by spatial variability of the material Such effects cannot be captured by traditional one-dimensional models. In order to account for the effect of heterogeneity, the saturated flow experiments have been analyzed by using stochastic transport modeling. The apparent linear growth of dispersivity with distance suggested that the system behaves like a stratified one. Consequently, the model of Dagan and Bresier has been adopted in order to interpret concentration measurements. In this simple model the caisson is viewed as a bundle of columns of different permeabilities, which are characterized by a p.d.f. (probability denasity function).
Generic transport coefficients of a confined electrolyte solution.
Yoshida, Hiroaki; Mizuno, Hideyuki; Kinjo, Tomoyuki; Washizu, Hitoshi; Barrat, Jean-Louis
2014-11-01
Physical parameters characterizing electrokinetic transport in a confined electrolyte solution are reconstructed from the generic transport coefficients obtained within the classical nonequilibrium statistical thermodynamic framework. The electro-osmotic flow, the diffusio-osmotic flow, the osmotic current, as well as the pressure-driven Poiseuille-type flow, the electric conduction, and the ion diffusion are described by this set of transport coefficients. The reconstruction is demonstrated for an aqueous NaCl solution between two parallel charged surfaces with a nanoscale gap, by using the molecular dynamic (MD) simulations. A Green-Kubo approach is employed to evaluate the transport coefficients in the linear-response regime, and the fluxes induced by the pressure, electric, and chemical potential fields are compared with the results of nonequilibrium MD simulations. Using this numerical scheme, the influence of the salt concentration on the transport coefficients is investigated. Anomalous reversal of diffusio-osmotic current, as well as that of electro-osmotic flow, is observed at high surface charge densities and high added-salt concentrations. PMID:25493746
Generic transport coefficients of a confined electrolyte solution
NASA Astrophysics Data System (ADS)
Yoshida, Hiroaki; Mizuno, Hideyuki; Kinjo, Tomoyuki; Washizu, Hitoshi; Barrat, Jean-Louis
2014-11-01
Physical parameters characterizing electrokinetic transport in a confined electrolyte solution are reconstructed from the generic transport coefficients obtained within the classical nonequilibrium statistical thermodynamic framework. The electro-osmotic flow, the diffusio-osmotic flow, the osmotic current, as well as the pressure-driven Poiseuille-type flow, the electric conduction, and the ion diffusion are described by this set of transport coefficients. The reconstruction is demonstrated for an aqueous NaCl solution between two parallel charged surfaces with a nanoscale gap, by using the molecular dynamic (MD) simulations. A Green-Kubo approach is employed to evaluate the transport coefficients in the linear-response regime, and the fluxes induced by the pressure, electric, and chemical potential fields are compared with the results of nonequilibrium MD simulations. Using this numerical scheme, the influence of the salt concentration on the transport coefficients is investigated. Anomalous reversal of diffusio-osmotic current, as well as that of electro-osmotic flow, is observed at high surface charge densities and high added-salt concentrations.
Technology Transfer Automated Retrieval System (TEKTRAN)
Traditionally, a two-parameter partial differential equation has been used to describe the one-dimensional convective-dispersive transport of chemicals in field soils. The parameters in this equation include the dispersion coefficient and a distribution coefficient, the latter accounting for interac...
Scaling and predicting solute transport processes in riverine ecosystems
NASA Astrophysics Data System (ADS)
Gonzalez-Pinzon, R.; Haggerty, R.; Camacho Botero, L. A.
2012-12-01
In the last three decades, research on solute transport and nutrient processing has revealed complex interactions between landscapes and stream ecosystems, and numerous attempts to scale and predict these processes have been primarily limited by the difficulty of measuring and extrapolating hydrodynamic and geomorphic characteristics. We hypothesize that there should be predictable patterns in the way that streams interact with their landscapes, because those interactions are in the form of energy, mass and momentum, which are conservative and interrelated properties. Therefore, despite local hydrogeomorphic characteristics define the actual extent of solute transport processes in a given riverine ecosystem, the physical imprints marked-up in breakthrough curves (BTCs) should have scaling properties. To evaluate our hypothesis we created an extensive database that includes 133 BTCs from conservative tracer experiments conducted under different hydrologic conditions (1 lt/s to 1197 m3/s), different experimental conditions (10s of meters to 10s of kilometers), different geographic positions (South and North America, Europe, Australia, Antarctica), and different types of lotic environments, i.e., urban manmade channels, forested headwater streams, desert-like streams, hyporheic wells, and major rivers. We investigated the existence of patterns in conservative solute transport using a model-independent approach, i.e., temporal moments of the histories of tracer experiments. Our results show that the normalized first absolute moment is correlated with the second and third moments with R2>0.99 for all riverine ecosystems. Most importantly, the first central temporal moment of the distributions (mean travel time) is correlated with the second (variance) with an R2>0.93, and the correlation between the second central moment and the third central moment (skewness) takes the form of the coefficient of skewness (CSK) with an R2>0.98, defining a statistically averaged CSK= 1
Radial reactive solute transport in an aquifer-aquitard system
NASA Astrophysics Data System (ADS)
Wang, Quanrong; Zhan, Hongbin
2013-11-01
Radial reactive transport is investigated in an aquifer-aquitard system considering the important processes such as advection, radial and vertical dispersions for the aquifer, vertical advection and dispersion for the aquitards, and first-order biodegradation or radioactive decay. We solved the coupled governing equations of transport in the aquifer and the aquitards by honoring the continuity of concentration and mass flux across the aquifer-aquitard interfaces and recognizing the concentration variation along the aquifer thickness. This effort improved the averaged-approximation (AA) model, which dealt with radial dispersion in an aquifer-aquitard system by excluding the aquitard advection. To compare with our new solution, we expanded the AA model by including the aquitard advection. The expanded AA model considerably overestimated the mass in the upper aquitard when an upward advection existed there. The rates of mass change in the upper aquitard from the new solution and the AA model solution increased with time following sub-linear fashions. The times corresponding to the peak values of the residence time distributions for the AA model, the expanded AA model, and the new model were almost the same. The residence time distributions seemed to follow the Maxwell-Boltzmann distribution closely when plotting the time in logarithmic scale. In addition, we developed a finite-element COMSOL Multiphysics simulation of the problem, and found that the COMSOL solution agreed with the new solution well.
EFFECTIVE POROSITY IMPLIES EFFECTIVE BULK DENSITY IN SORBING SOLUTE TRANSPORT
Flach, G.
2012-02-27
The concept of an effective porosity is widely used in solute transport modeling to account for the presence of a fraction of the medium that effectively does not influence solute migration, apart from taking up space. This non-participating volume or ineffective porosity plays the same role as the gas phase in single-phase liquid unsaturated transport: it increases pore velocity, which is useful towards reproducing observed solute travel times. The prevalent use of the effective porosity concept is reflected by its prominent inclusion in popular texts, e.g., de Marsily (1986), Fetter (1988, 1993) and Zheng and Bennett (2002). The purpose of this commentary is to point out that proper application of the concept for sorbing solutes requires more than simply reducing porosity while leaving other material properties unchanged. More specifically, effective porosity implies the corresponding need for an effective bulk density in a conventional single-porosity model. The reason is that the designated non-participating volume is composed of both solid and fluid phases, both of which must be neglected for consistency. Said another way, if solute does not enter the ineffective porosity then it also cannot contact the adjoining solid. Conceptually neglecting the fluid portion of the non-participating volume leads to a lower (effective) porosity. Likewise, discarding the solid portion of the non-participating volume inherently leads to a lower or effective bulk density. In the author's experience, practitioners virtually never adjust bulk density when adopting the effective porosity approach.
Some Exact Solutions in Energy Dependent Transport Theory
NASA Astrophysics Data System (ADS)
Williams, M. M. R.
1980-01-01
Some exact solutions are obtained for energy dependent slowing down problems with energy dependent cross sections. The transport equation is solved using the backward-forward model of Fermi. Also studied is the energy dependent diffusion equation. Using these models, and a novel technique involving difference equations, it has been possible to find explicit, and numerically useful, solutions for slowing down from a plane, monoenergetic source in an infinite medium. The slowing down density and the energy deposition function are obtained which are of value in reactor physics and radiation damage calculations.
NASA Astrophysics Data System (ADS)
Bodin, Jacques
2015-03-01
In this study, new multi-dimensional time-domain random walk (TDRW) algorithms are derived from approximate one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) analytical solutions of the advection-dispersion equation and from exact 1-D, 2-D, and 3-D analytical solutions of the pure-diffusion equation. These algorithms enable the calculation of both the time required for a particle to travel a specified distance in a homogeneous medium and the mass recovery at the observation point, which may be incomplete due to 2-D or 3-D transverse dispersion or diffusion. The method is extended to heterogeneous media, represented as a piecewise collection of homogeneous media. The particle motion is then decomposed along a series of intermediate checkpoints located on the medium interface boundaries. The accuracy of the multi-dimensional TDRW method is verified against (i) exact analytical solutions of solute transport in homogeneous media and (ii) finite-difference simulations in a synthetic 2-D heterogeneous medium of simple geometry. The results demonstrate that the method is ideally suited to purely diffusive transport and to advection-dispersion transport problems dominated by advection. Conversely, the method is not recommended for highly dispersive transport problems because the accuracy of the advection-dispersion TDRW algorithms degrades rapidly for a low Péclet number, consistent with the accuracy limit of the approximate analytical solutions. The proposed approach provides a unified methodology for deriving multi-dimensional time-domain particle equations and may be applicable to other mathematical transport models, provided that appropriate analytical solutions are available.
Scaling of geochemical reaction rates via advective solute transport.
Hunt, A G; Ghanbarian, B; Skinner, T E; Ewing, R P
2015-07-01
Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture. PMID:26232976
Scaling of geochemical reaction rates via advective solute transport
NASA Astrophysics Data System (ADS)
Hunt, A. G.; Ghanbarian, B.; Skinner, T. E.; Ewing, R. P.
2015-07-01
Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture.
In dealing with problems related to land-based nuclear waste management, a number of analytical and approximate solutions were developed to quantify radionuclide transport through fractures contained in the porous formation. t has been reported that by treating the radioactive de...
SOLUTIONS APPROXIMATING SOLUTE TRANSPORT IN A LEAKY AQUIFER RECEIVING WASTEWATER INJECTION
A mathematical model amenable to analytical solution techniques is developed for the investigation of contaminant transport from an injection well into a leaky aquifer system, which comprises a pumped and an unpumped aquifer connected to each other by an aquitard. A steady state ...
SOLUTIONS APPROXIMATING SOLUTE TRANSPORT IN A LEAKY AQUIFER RECEIVING WASTEWATER INJECTION
A mathematical model amenable to analytical solution techniques is developed for the investigation of contaminant transport from an injection well into a leaky aquifer system, which comprises a pumped and an unpumped aquifer connected to each other by an aquitard. teady state gro...
Hydrophilic solute transport across the rat blood-brain barrier
Lucchesi, K.J.
1987-01-01
Brain capillary permeability-surface area products (PS) of hydrophilic solutes ranging in size from 180 to 5,500 Daltons were measured in rats according to the method of Ohno, Pettigrew and Rapoport. The distribution volume of 70 KD dextran at 10 minutes after i.v. injection was also measured to determine the residual volume of blood in brain tissue at the time of sacrifice. Small test solutes were injected in pairs in order to elucidate whether their transfer into the brain proceeds by diffusion through water- or lipid-filled channels or by vesicular transport. This issue was examined in rats whose blood-brain barrier (BBB) was presumed to be intact (untreated) and in rats that received intracarotid infusions to open the BBB (isosmotic salt (ISS) and hyperosmolar arabinose). Ohno PS values of {sup 3}H-inulin and {sup 14}C-L-glucose in untreated rats were found to decrease as the labelling time was lengthened. This was evidence that a rapidly equilibrating compartment exists between blood and brain that renders the Ohno two-compartment model inadequate for computing true transfer rate constants. When the data were reanalyzed using a multi-compartment graphical analysis, solutes with different molecular radii were found to enter the brain at approximately equal rates. Furthermore, unidirectional transport is likely to be initiated by solute adsorption to a glycocalyx coat on the luminal surface of brain capillary endothelium. Apparently, more inulin than L-glucose was adsorbed, which may account for its slightly faster transfer across the BBB. After rats were treated with intracarotid infusions of ISS or hyperosmolar arabinose, solute PS values were significantly increased, but the ratio of PS for each of the solute pairs approached that of their free-diffusion coefficients.
Biotic controls on solute distribution and transport in headwater catchments
NASA Astrophysics Data System (ADS)
Herndon, E. M.; Dere, A. L.; Sullivan, P. L.; Norris, D.; Reynolds, B.; Brantley, S. L.
2015-01-01
Solute concentrations in stream water vary with discharge in patterns that record complex feedbacks between hydrologic and biogeochemical processes. In a comparison of headwater catchments underlain by shale in Pennsylvania, USA (Shale Hills) and Wales, UK (Plynlimon), dissimilar concentration-discharge behaviors are best explained by contrasting landscape distributions of soil solution chemistry - especially dissolved organic carbon (DOC) - that have been established by patterns of vegetation. Specifically, elements that are concentrated in organic-rich soils due to biotic cycling (Mn, Ca, K) or that form strong complexes with DOC (Fe, Al) are spatially heterogeneous in pore waters because organic matter is heterogeneously distributed across the catchments. These solutes exhibit non-chemostatic "bioactive" behavior in the streams, and solute concentrations either decrease (Shale Hills) or increase (Plynlimon) with increasing discharge. In contrast, solutes that are concentrated in soil minerals and form only weak complexes with DOC (Na, Mg, Si) are spatially homogeneous in pore waters across each catchment. These solutes are chemostatic in that their stream concentrations vary little with stream discharge, likely because these solutes are released quickly from exchange sites in the soils during rainfall events. Differences in the hydrologic connectivity of organic-rich soils to the stream drive differences in concentration behavior between catchments. As such, in catchments where soil organic matter (SOM) is dominantly in lowlands (e.g., Shale Hills), bioactive elements are released to the stream early during rainfall events, whereas in catchments where SOM is dominantly in uplands (e.g., Plynlimon), bioactive elements are released later during rainfall events. The distribution of vegetation and SOM across the landscape is thus a key component for predictive models of solute transport in headwater catchments.
Technology Transfer Automated Retrieval System (TEKTRAN)
Upland soils in the Midwestern US often undergo reducing conditions when soils are temporally flooded during the spring and remain water saturated for days or weeks. Short-term reducing conditions change the chemistry of the soil and may affect soil structure and solution chemical transport. The eff...
Analytical solution of two-dimensional solute transport in an aquifer-aquitard system.
Zhan, Hongbin; Wen, Zhang; Huang, Guanhua; Sun, Dongmin
2009-07-21
This study deals with two-dimensional solute transport in an aquifer-aquitard system by maintaining rigorous mass conservation at the aquifer-aquitard interface. Advection, longitudinal dispersion, and transverse vertical dispersion are considered in the aquifer. Vertical advection and diffusion are considered in the aquitards. The first-type and the third-type boundary conditions are considered in the aquifer. This study differs from the commonly used averaged approximation (AA) method that treats the mass flux between the aquifer and aquitard as an averaged volumetric source/sink term in the governing equation of transport in the aquifer. Analytical solutions of concentrations in the aquitards and aquifer and mass transported between the aquifer and upper or lower aquitard are obtained in the Laplace domain, and are subsequently inverted numerically to yield results in the real time domain (the Zhan method). The breakthrough curves (BTCs) and distribution profiles in the aquifer obtained in this study are drastically different from those obtained using the AA method. Comparison of the numerical simulation using the model MT3DMS and the Zhan method indicates that the numerical result differs from that of the Zhan method for an asymmetric case when aquitard advections are at the same direction. The AA method overestimates the mass transported into the upper aquitard when an upward advection exists in the upper aquitard. The mass transported between the aquifer and the aquitard is sensitive to the aquitard Peclet number, but less sensitive to the aquitard diffusion coefficient. PMID:19477033
JOVIAN STRATOSPHERE AS A CHEMICAL TRANSPORT SYSTEM: BENCHMARK ANALYTICAL SOLUTIONS
Zhang Xi; Shia Runlie; Yung, Yuk L.
2013-04-20
We systematically investigated the solvable analytical benchmark cases in both one- and two-dimensional (1D and 2D) chemical-advective-diffusive systems. We use the stratosphere of Jupiter as an example but the results can be applied to other planetary atmospheres and exoplanetary atmospheres. In the 1D system, we show that CH{sub 4} and C{sub 2}H{sub 6} are mainly in diffusive equilibrium, and the C{sub 2}H{sub 2} profile can be approximated by modified Bessel functions. In the 2D system in the meridional plane, analytical solutions for two typical circulation patterns are derived. Simple tracer transport modeling demonstrates that the distribution of a short-lived species (such as C{sub 2}H{sub 2}) is dominated by the local chemical sources and sinks, while that of a long-lived species (such as C{sub 2}H{sub 6}) is significantly influenced by the circulation pattern. We find that an equator-to-pole circulation could qualitatively explain the Cassini observations, but a pure diffusive transport process could not. For slowly rotating planets like the close-in extrasolar planets, the interaction between the advection by the zonal wind and chemistry might cause a phase lag between the final tracer distribution and the original source distribution. The numerical simulation results from the 2D Caltech/JPL chemistry-transport model agree well with the analytical solutions for various cases.
Konikow, L.F.; Hornberger, G.Z.
2003-01-01
This report describes modifications to a U.S. Geological Survey (USGS) threedimensional solute-transport model (MODFLOWGWT), which is incorporated into the USGS MODFLOW ground-water model as the Ground- Water Transport (GWT) Process. The modifications improve the capability of MODFLOW-GWT to accurately simulate solute transport in simulations that represent a nonzero flux across an aquifer boundary. In such situations, the new Boundary Flux Package (BFLX) will allow the user flexibility to assign the flux to specific cell faces, although that flexibility is limited for certain types of fluxes (such as recharge and evapotranspiration, which can only be assigned to the top face if either is to be represented as a boundary flux). The approach is consistent with that used in the MODPATH model. The application of the BFLX Package was illustrated using a test case in which the Lake Package was active. The results using the BFLX Package showed noticeably higher magnitudes of velocity in the cells adjacent to the lake than previous results without the BFLX Package. Consequently, solute was transported slightly faster through the lake-aquifer system when the BFLX Package is active. However, the overall solute distributions did not differ greatly from simulations made without using the BFLX Package.
Role of ABC and Solute Carrier Transporters in the Placental Transport of Lamivudine.
Ceckova, Martina; Reznicek, Josef; Ptackova, Zuzana; Cerveny, Lukas; Müller, Fabian; Kacerovsky, Marian; Fromm, Martin F; Glazier, Jocelyn D; Staud, Frantisek
2016-09-01
Lamivudine is one of the antiretroviral drugs of choice for the prevention of mother-to-child transmission (MTCT) in HIV-positive women. In this study, we investigated the relevance of drug efflux transporters P-glycoprotein (P-gp) (MDR1 [ABCB1]), BCRP (ABCG2), MRP2 (ABCC2), and MATE1 (SLC47A1) for the transmembrane transport and transplacental transfer of lamivudine. We employed in vitro accumulation and transport experiments on MDCK cells overexpressing drug efflux transporters, in situ-perfused rat term placenta, and vesicular uptake in microvillous plasma membrane (MVM) vesicles isolated from human term placenta. MATE1 significantly accelerated lamivudine transport in MATE1-expressing MDCK cells, whereas no transporter-driven efflux of lamivudine was observed in MDCK-MDR1, MDCK-MRP2, and MDCK-BCRP monolayers. MATE1-mediated efflux of lamivudine appeared to be a low-affinity process (apparent Km of 4.21 mM and Vmax of 5.18 nmol/mg protein/min in MDCK-MATE1 cells). Consistent with in vitro transport studies, the transplacental clearance of lamivudine was not affected by P-gp, BCRP, or MRP2. However, lamivudine transfer across dually perfused rat placenta and the uptake of lamivudine into human placental MVM vesicles revealed pH dependency, indicating possible involvement of MATE1 in the fetal-to-maternal efflux of the drug. To conclude, placental transport of lamivudine does not seem to be affected by P-gp, MRP2, or BCRP, but a pH-dependent mechanism mediates transport of lamivudine in the fetal-to-maternal direction. We suggest that MATE1 might be, at least partly, responsible for this transport. PMID:27401571
Phononic heat transport in the transient regime: An analytic solution
NASA Astrophysics Data System (ADS)
Tuovinen, Riku; Säkkinen, Niko; Karlsson, Daniel; Stefanucci, Gianluca; van Leeuwen, Robert
2016-06-01
We investigate the time-resolved quantum transport properties of phonons in arbitrary harmonic systems connected to phonon baths at different temperatures. We obtain a closed analytic expression of the time-dependent one-particle reduced density matrix by explicitly solving the equations of motion for the nonequilibrium Green's function. This is achieved through a well-controlled approximation of the frequency-dependent bath self-energy. Our result allows for exploring transient oscillations and relaxation times of local heat currents, and correctly reduces to an earlier known result in the steady-state limit. We apply the formalism to atomic chains, and benchmark the validity of the approximation against full numerical solutions of the bosonic Kadanoff-Baym equations for the Green's function. We find good agreement between the analytic and numerical solutions for weak contacts and baths with a wide energy dispersion. We further analyze relaxation times from low to high temperature gradients.
Coarse grained modeling of transport properties in monoclonal antibody solution
NASA Astrophysics Data System (ADS)
Swan, James; Wang, Gang
Monoclonal antibodies and their derivatives represent the fastest growing segment of the bio pharmaceutical industry. For many applications such as novel cancer therapies, high concentration, sub-cutaneous injections of these protein solutions are desired. However, depending on the peptide sequence within the antibody, such high concentration formulations can be too viscous to inject via human derived force alone. Understanding how heterogenous charge distribution and hydrophobicity within the antibodies leads to high viscosities is crucial to their future application. In this talk, we explore a coarse grained computational model of therapeutically relevant monoclonal antibodies that accounts for electrostatic, dispersion and hydrodynamic interactions between suspended antibodies to predict assembly and transport properties in concentrated antibody solutions. We explain the high viscosities observed in many experimental studies of the same biologics.
Seismic reflection characteristics of naturally-induced subsidence affecting transportation
Miller, R.D.; Xia, J.; Steeples, D.W.
2009-01-01
High-resolution seismic reflections have been used effectively to investigate sinkholes formed from the dissolution of a bedded salt unit found throughout most of Central Kansas. Surface subsidence can have devastating effects on transportation structures. Roads, rails, bridges, and pipelines can even be dramatically affected by minor ground instability. Areas susceptible to surface subsidence can put public safety at risk. Subsurface expressions significantly larger than surface depressions are consistently observed on seismic images recorded over sinkholes in Kansas. Until subsidence reaches the ground surface, failure appears to be controlled by compressional forces evidenced by faults with reverse orientation. Once a surface depression forms or dissolution of the salt slows or stops, subsidence structures are consistent with a tensional stress environment with prevalent normal faults. Detecting areas of rapid subsidence potential, prior to surface failure, is the ultimate goal of any geotechnical survey where the ground surface is susceptible to settling. Seismic reflection images have helped correlate active subsidence to dormant paleofeatures, project horizontal growth of active sinkholes based on subsurface structures, and appraise the risk of catastrophic failure. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.
Solute transport in solution conduits exhibiting multi-peaked breakthrough curves
NASA Astrophysics Data System (ADS)
Field, Malcolm S.; Leij, Feike J.
2012-05-01
SummarySolute transport in karst aquifers is primarily constrained to solution conduits where transport is rapid, turbulent, and relatively unrestrictive. Breakthrough curves generated from tracer tests are typically positively-skewed and may exhibit multiple peaks. In order to understand the circumstances under which multi-peaked positively skewed breakthrough curves occur, physical experiments utilizing single- and multiple-flow channels were conducted. Experiments also included waterfalls, short-term solute detention in pools, and flow obstructions. Results demonstrated that breakthrough curve skewness nearly always occurs to some degree but is magnified as immobile-flow regions are encountered. Multi-peaked breakthrough curves occurred when flow in the main channel became partially occluded from blockage in the main channel that forced divergence of solute into auxiliary channels and when waterfalls and detention in pools occurred. Currently, multi-peaked breakthrough curves are fitted by a multi-dispersion model in which a series of curves generated by the advection-dispersion equation are fitted to each measured peak by superimposing the measured breakthrough curve to obtain a combined model fit with a consequent set of estimated velocities and dispersions. In this paper, a dual-advection dispersion equation with first-order mass transfer between conduits was derived. The dual-advection dispersion equation was then applied to the multi-peaked breakthrough curves obtained from the physical experiments in order to obtain some insight into the operative solute-transport processes through the acquisition of a consequent set of velocities, dispersions, and related parameters. Successful application of the dual-advection, dispersion equation to a tracer test that exhibited dual peaks for a karst aquifer known to consist of two connected but mostly separate conduits confirmed the appropriateness of using a multi-dispersion type model when conditions warrant.
NASA Astrophysics Data System (ADS)
Mohammadi, Mohammad Hossein; Vanclooster, Marnik
2012-05-01
Solute transport in partially saturated soils is largely affected by fluid velocity distribution and pore size distribution within the solute transport domain. Hence, it is possible to describe the solute transport process in terms of the pore size distribution of the soil, and indirectly in terms of the soil hydraulic properties. In this paper, we present a conceptual approach that allows predicting the parameters of the Convective Lognormal Transfer model from knowledge of soil moisture and the Soil Moisture Characteristic (SMC), parameterized by means of the closed-form model of Kosugi (1996). It is assumed that in partially saturated conditions, the air filled pore volume act as an inert solid phase, allowing the use of the Arya et al. (1999) pragmatic approach to estimate solute travel time statistics from the saturation degree and SMC parameters. The approach is evaluated using a set of partially saturated transport experiments as presented by Mohammadi and Vanclooster (2011). Experimental results showed that the mean solute travel time, μt, increases proportionally with the depth (travel distance) and decreases with flow rate. The variance of solute travel time σ2t first decreases with flow rate up to 0.4-0.6 Ks and subsequently increases. For all tested BTCs predicted solute transport with μt estimated from the conceptual model performed much better as compared to predictions with μt and σ2t estimated from calibration of solute transport at shallow soil depths. The use of μt estimated from the conceptual model therefore increases the robustness of the CLT model in predicting solute transport in heterogeneous soils at larger depths. In view of the fact that reasonable indirect estimates of the SMC can be made from basic soil properties using pedotransfer functions, the presented approach may be useful for predicting solute transport at field or watershed scales.
Modeling solute transport by DLA in soils of northeastern Egypt.
Hamed, Yasser Ahmed; Yasuda, Hiroshi; Persson, Magnus; Berndtsson, Ronny; Wang, Xin-ping
2015-01-01
Arid soils in Egypt display large variability in solute transport properties, causing problems in soil management. To characterize this variability, dye infiltration experiments were conducted on four plots representing three main soil types in northeastern Egypt. The plots represented both cultivated and uncultivated land use. The observed dye patterns displayed a large variability and especially the clay soils indicated a high degree of preferential flow. The loamy sand and sandy soils displayed a more uniform dye distribution indicating more homogeneous soil properties. The observed dye patterns were modeled using a diffusion limited aggregation (DLA) model. The DLA is a random walk model where model parameters can be optimized using genetic algorithms (GA). The DLA model reproduced the observed dye patterns for all soils in an excellent way. The best fit was obtained with a specific combination of directional random walk probabilities Pu, Pd, Pr, and Pl for each plot (correlation 0.97-0.99). To account for soil layers with different hydraulic properties a two layer DLA model was developed. For all plots the Pu (upward random walk probability) was higher for the upper more homogeneous soil layer. The overall results showed that spatial variability resulting from solute transport for the investigated soils can be modeled using a DLA approach. PMID:25790463
Modeling Solute Transport by DLA in Soils of Northeastern Egypt
Hamed, Yasser Ahmed; Yasuda, Hiroshi; Persson, Magnus; Berndtsson, Ronny; Wang, Xin-ping
2015-01-01
Arid soils in Egypt display large variability in solute transport properties, causing problems in soil management. To characterize this variability, dye infiltration experiments were conducted on four plots representing three main soil types in northeastern Egypt. The plots represented both cultivated and uncultivated land use. The observed dye patterns displayed a large variability and especially the clay soils indicated a high degree of preferential flow. The loamy sand and sandy soils displayed a more uniform dye distribution indicating more homogeneous soil properties. The observed dye patterns were modeled using a diffusion limited aggregation (DLA) model. The DLA is a random walk model where model parameters can be optimized using genetic algorithms (GA). The DLA model reproduced the observed dye patterns for all soils in an excellent way. The best fit was obtained with a specific combination of directional random walk probabilities Pu, Pd, Pr, and Pl for each plot (correlation 0.97–0.99). To account for soil layers with different hydraulic properties a two layer DLA model was developed. For all plots the Pu (upward random walk probability) was higher for the upper more homogeneous soil layer. The overall results showed that spatial variability resulting from solute transport for the investigated soils can be modeled using a DLA approach. PMID:25790463
Impact of 3D root uptake on solute transport: a numerical study
NASA Astrophysics Data System (ADS)
Schröder, N.; Javaux, M.; Vanderborght, J.; Steffen, B.; Vereecken, H.
2011-12-01
Plant transpiration is an important component of the hydrological cycle. Through root water uptake, plants do not only affect the 3D soil water flow velocity distribution, but also solute movement in soil. This numerical study aims at investigating how solute fate is impacted by root uptake using the 3D biophysical model R-SWMS (Javaux et al., 2008). This model solves the Richards equation in 3D in the soil and the flow equation within the plant root xylem vessels. Furthermore, for solute transport simulations, the 3D particle tracker PARTRACE (Bechtold et al., 2011) was used. . We generated 3D virtual steady-state breakthrough curves (BTC) experiments in soils with transpiring plants. The averaged BTCs were then fitted with a 1D numerical flow model under steady-state conditions to obtain apparent CDE parameters. Two types of root architecture, a fibrous and a taprooted structure, were compared in virtual 3D experiments. The solute uptake type or the transpiration rate were also modified and we analyzed how these parameters affected apparent disperisivity and velocity profiles. Our simulation results show, that both, apparent velocity and dispersivity length are affected by water and solute root uptake. In addition, under high exclusion processes (slight or no active uptake), solute accumulates around roots and generates a long tailing to the breakthrough curves, which cannot be reproduced by 1D models that simulate root water uptake with solute exclusion. This observation may have an important impact on how to model pollutant mass transfer to groundwater at larger scales. Javaux, M., T. Schröder, J. Vanderborght, and H. Vereecken. 2008. Use of a three-dimensional detailed modeling approach for predicting root water uptake. Vadose Zone J. 7:1079-1088.doi: 10.2136/vzj2007.0115. Bechtold, M., S. Haber-Pohlmeier, J. Vanderborght, A. Pohlmeier, P.A. Ferre, and H. Vereecken. 2011. Near-surface solute redistribution during evaporation. Submitted to Geophys. Res. Lett
Soil properties and preferential solute transport at the field scale
NASA Astrophysics Data System (ADS)
Koestel, J. K.; Luong, N. M.; Nørgaard, T.; Vendelboe, A. L.; Moldrup, P.; Jarvis, N. J.; Lamandé, M.; Iversen, B. V.; Wollesen de Jonge, L.
2012-04-01
An important fraction of water flow and solute transport through soil takes place through preferential flow paths. Although this had been already observed in the nineteenth century, it had been forgotten by the scientific community until it was rediscovered during the 1970s. The awareness of the relevance of preferential flow was broadly re-established in the community by the early 1990s. However, since then, the notion remains widespread among soil scientists that the occurrence and strength of preferential flow cannot be predicted from measurable proxy variables such as soil properties or land management practices (e.g. Beven, K., 1991, Modeling preferential flow - an uncertain future, Preferential Flow, 1-11). In our study, we present evidence that disproves this notion. We evaluated breakthrough curve experiments under a constant irrigation rate of 1 cm/h conducted on 65 soil columns (20 cm diameter and 20 height) which had been sampled from an approximately 1 ha large loamy field-site in Silstrup, Denmark. We show that the holdback factor, which is an indicator for the strength of preferential transport, is strongly correlated to the bulk density, which in turn is correlated to the organic matter content. By applying multiple linear regression in a bootstrapping framework, we could estimate the holdback factor from the bulk density and the very fine sand fraction with a coefficient of determination of 0.65. Our results raise hopes that it is indeed possible to establish pedotransfer functions for soil susceptibility to preferential flow and transport.
Polymer Dynamics Effects on Solute Transport in Hairy Nanoparticle Membranes
NASA Astrophysics Data System (ADS)
Buenning, Eileen; Bilchak, Connor; Durning, Christopher; Benicewicz, Brian; Sokolov, Alexei; Kumar, Sanat
Molecular transport measurements in matrix-free grafted nanoparticle (MFGNP) films have shown remarkable enhancement of permeability and ideal selectivity of small condensable molecules and simple gases over the neat polymer melts and conventional, dispersed nanoparticle composites. Films comprised of covalently-attached poly(methyl acrylate) PMA chains to the surface of 14nm silica particles self-assemble into ordered arrays, and we postulate this structure plays an important role in regulating solute transport. This self-assembly creates interstitial spaces between the nanoparticle cores, which the polymer chains can only fill by stretching. Here we use small-angle neutron scattering (SANS), broadband dielectric spectroscopy (BDS), rheology and temperature-modulated differential scanning calorimetry (TMDSC) to probe polymer chain and segmental dynamics and investigate this hypothesis of chain stretching in MFGNP materials. We found that grafting slows both chain and segmental relaxation, and increases fragility, indicating that the chains are more ``frustrated'' in the grafted systems. We propose that the effects of the chain/surface interactions on chain dynamics leads to an increase in available free volume and thus enhances transport properties in MFGNP systems. Special thanks to the NSF GRFP and the DOE SCGSR programs.
Technology Transfer Automated Retrieval System (TEKTRAN)
Analytical solutions of the advection-dispersion solute transport equation remain useful for a large number of applications in science and engineering. In this paper we extend the Duhamel theorem, originally established for diffusion type problems, to the case of advective-dispersive transport subj...
NASA Astrophysics Data System (ADS)
Frampton, Andrew; Destouni, Georgia
2016-04-01
In cold regions, flow in the unsaturated zone is highly dynamic with seasonal variability and changes in temperature, moisture, and heat and water fluxes, all of which affect ground freeze-thaw processes and influence transport of inert and reactive waterborne substances. In arctic permafrost environments, near-surface groundwater flow is further restricted to a relatively shallow and seasonally variable active layer, confined by perennially frozen ground below. The active layer is typically partially saturated with ice, liquid water and air, and is strongly dependent on seasonal temperature fluctuations, thermal forcing and infiltration patterns. Here there is a need for improved understanding of the mechanisms controlling subsurface solute transport in the partially saturated active layer zone. Studying solute transport in cold regions is relevant to improve the understanding of how natural and anthropogenic pollution may change as activities in arctic and sub-arctic regions increase. It is also particularly relevant for understanding how dissolved carbon is transported in coupled surface and subsurface hydrological systems under climate change, in order to better understand the permafrost-hydrological-carbon climate feedback. In this contribution subsurface solute transport under surface warming and degrading permafrost conditions is studied using a physically based model of coupled cryotic and hydrogeological flow processes combined with a particle tracking method. Changes in subsurface water flows and solute transport travel times are analysed for different modelled geological configurations during a 100-year warming period. Results show that for all simulated cases, the minimum and mean travel times increase non-linearly with warming irrespective of geological configuration and heterogeneity structure. The travel time changes are shown to depend on combined warming effects of increase in pathway length due to deepening of the active layer, reduced transport
Bencala, K.E.
1984-01-01
Solute transport in streams is determined by the interaction of physical and chemical processes. Data from an injection experiment for chloride and several cations indicate significant influence of solute-streambed processes on transport in a mountain stream. These data are interpreted in terms of transient storage processes for all tracers and sorption processes for the cations. Process parameter values are estimated with simulations based on coupled quasi-two-dimensional transport and first-order mass transfer sorption. Comparative simulations demonstrate the relative roles of the physical and chemical processes in determining solute transport. -from Author
A comparison of solute-transport solution techniques based on inverse modelling results
Mehl, S.; Hill, M.C.
2000-01-01
Five common numerical techniques (finite difference, predictor-corrector, total-variation-diminishing, method-of-characteristics, and modified-method-of-characteristics) were tested using simulations of a controlled conservative tracer-test experiment through a heterogeneous, two-dimensional sand tank. The experimental facility was constructed using randomly distributed homogeneous blocks of five sand types. This experimental model provides an outstanding opportunity to compare the solution techniques because of the heterogeneous hydraulic conductivity distribution of known structure, and the availability of detailed measurements with which to compare simulated concentrations. The present work uses this opportunity to investigate how three common types of results-simulated breakthrough curves, sensitivity analysis, and calibrated parameter values-change in this heterogeneous situation, given the different methods of simulating solute transport. The results show that simulated peak concentrations, even at very fine grid spacings, varied because of different amounts of numerical dispersion. Sensitivity analysis results were robust in that they were independent of the solution technique. They revealed extreme correlation between hydraulic conductivity and porosity, and that the breakthrough curve data did not provide enough information about the dispersivities to estimate individual values for the five sands. However, estimated hydraulic conductivity values are significantly influenced by both the large possible variations in model dispersion and the amount of numerical dispersion present in the solution technique.Five common numerical techniques (finite difference, predictor-corrector, total-variation-diminishing, method-of-characteristics, and modified-method-of-characteristics) were tested using simulations of a controlled conservative tracer-test experiment through a heterogeneous, two-dimensional sand tank. The experimental facility was constructed using randomly
Nutrient transport as affected by rate of overland flow
Technology Transfer Automated Retrieval System (TEKTRAN)
Little information is currently available concerning the effects of varying flow rate on nutrient transport by overland flow. The objective of this study was to measure the effects of overland flow rate on nutrient transport following the application of beef cattle or swine manure to plots containin...
Technology Transfer Automated Retrieval System (TEKTRAN)
Understanding and modeling transport of solutes in porous media is a critical issue in the environmental protection. Contaminants from various industrial and agricultural sources can travel in soil and ground water and eventually affect human and animal health. The parabolic advective-dispersive equ...
Effects of isotope selection on solution convergence in HZE transport
NASA Technical Reports Server (NTRS)
Kim, Myung-Hee Y.; Wilson, John W.; Kiefer, Richard L.; Thibeault, Sheila A.
1994-01-01
A fragmenting iron ion produces hundreds of isotopes during nuclear reactions. These isotopes are represented in the solution of the transport problem. A reduced set of isotopes is selected to minimize the computational burden but introduces error in the final result. A minimum list of 122 isotopes is required for adequate representation of the mass and charge distributions of the secondary radiation fields. A reduced set of 80 isotopes is sufficient to represent the charge distribution alone and represents reasonably well the linear energy transfer properties of the iron beam. Because iron fragmentation produces nearly every isotope lighter than iron, the resulting 122-isotope list should be adequate for ion beams with charges equal to or less than 26.
Uncertainty and Sensitivity Analyses of Model Predictions of Solute Transport
NASA Astrophysics Data System (ADS)
Skaggs, T. H.; Suarez, D. L.; Goldberg, S. R.
2012-12-01
Soil salinity reduces crop production on about 50% of irrigated lands worldwide. One roadblock to increased use of advanced computer simulation tools for better managing irrigation water and soil salinity is that the models usually do not provide an estimate of the uncertainty in model predictions, which can be substantial. In this work, we investigate methods for putting confidence bounds on HYDRUS-1D simulations of solute leaching in soils. Uncertainties in model parameters estimated with pedotransfer functions are propagated through simulation model predictions using Monte Carlo simulation. Generalized sensitivity analyses indicate which parameters are most significant for quantifying uncertainty. The simulation results are compared with experimentally observed transport variability in a number of large, replicated lysimeters.
An exact solution of solute transport by one-dimensional random velocity fields
Cvetkovic, V.D.; Dagan, G.; Shapiro, A.M.
1991-01-01
The problem of one-dimensional transport of passive solute by a random steady velocity field is investigated. This problem is representative of solute movement in porous media, for example, in vertical flow through a horizontally stratified formation of variable porosity with a constant flux at the soil surface. Relating moments of particle travel time and displacement, exact expressions for the advection and dispersion coefficients in the Focker-Planck equation are compared with the perturbation results for large distances. The first- and second-order approximations for the dispersion coefficient are robust for a lognormal velocity field. The mean Lagrangian velocity is the harmonic mean of the Eulerian velocity for large distances. This is an artifact of one-dimensional flow where the continuity equation provides for a divergence free fluid flux, rather than a divergence free fluid velocity. ?? 1991 Springer-Verlag.
Hierarchical Adaptive Solution of Radiation Transport Problems on Unstructured Grids
Dr. Cassiano R. E de Oliveira
2008-06-30
Computational radiation transport has steadily gained acceptance in the last decade as a viable modeling tool due to the rapid advancements in computer software and hardware technologies. It can be applied for the analysis of a wide range of problems which arise in nuclear reactor physics, medical physics, atmospheric physics, astrophysics and other areas of engineering physics. However, radiation transport is an extremely chanllenging computational problem since the governing equation is seven-deimensional (3 in space, 2 in direction, 1 in energy, and 1 in time) with a high degree of coupleing betwen these variables. If not careful, this relatively large number of independent variables when discretized can potentially lead to sets of linear equations of intractable size. Though parallel computing has allowed the solution of very large problems, avaliable computational resources will always be finite due to the fact that every more sophisticated multiphysics models are being demanded by industry. There is thus the pressing requirement to optimize the discretizations so as to minimize the effort and maximize the accuracy.
Improved parallel solution techniques for the integral transport matrix method
Zerr, Robert J; Azmy, Yousry Y
2010-11-23
Alternative solution strategies to the parallel block Jacobi (PBJ) method for the solution of the global problem with the integral transport matrix method operators have been designed and tested. The most straightforward improvement to the Jacobi iterative method is the Gauss-Seidel alternative. The parallel red-black Gauss-Seidel (PGS) algorithm can improve on the number of iterations and reduce work per iteration by applying an alternating red-black color-set to the subdomains and assigning multiple sub-domains per processor. A parallel GMRES(m) method was implemented as an alternative to stationary iterations. Computational results show that the PGS method can improve on the PBJ method execution by up to {approx}50% when eight sub-domains per processor are used. However, compared to traditional source iterations with diffusion synthetic acceleration, it is still approximately an order of magnitude slower. The best-performing case are opticaUy thick because sub-domains decouple, yielding faster convergence. Further tests revealed that 64 sub-domains per processor was the best performing level of sub-domain division. An acceleration technique that improves the convergence rate would greatly improve the ITMM. The GMRES(m) method with a diagonal block preconditioner consumes approximately the same time as the PBJ solver but could be improved by an as yet undeveloped, more efficient preconditioner.
Soltanian, Mohamad Reza; Ritzi, Robert W; Dai, Zhenxue; Huang, Chao Cheng
2015-03-01
Physical and chemical heterogeneities have a large impact on reactive transport in porous media. Examples of heterogeneous attributes affecting reactive mass transport are the hydraulic conductivity (K), and the equilibrium sorption distribution coefficient (Kd). This paper uses the Deng et al. (2013) conceptual model for multimodal reactive mineral facies and a Lagrangian-based stochastic theory in order to analyze the reactive solute dispersion in three-dimensional anisotropic heterogeneous porous media with hierarchical organization of reactive minerals. An example based on real field data is used to illustrate the time evolution trends of reactive solute dispersion. The results show that the correlation between the hydraulic conductivity and the equilibrium sorption distribution coefficient does have a significant effect on reactive solute dispersion. The anisotropy ratio does not have a significant effect on reactive solute dispersion. Furthermore, through a sensitivity analysis we investigate the impact of changing the mean, variance, and integral scale of K and Kd on reactive solute dispersion. PMID:25532767
NASA Astrophysics Data System (ADS)
Unc, Adrian; Goss, Michael J.; Cook, Simon; Li, Xunde; Atwill, Edward R.; Harter, Thomas
2012-06-01
Organic waste applications to soil (manure, various wastewaters, and biosolids) are among the most significant sources of bacterial contamination in surface and groundwater. Transport of bacteria through the vadose zone depends on flow path geometry and stability and is mitigated by interaction between soil, soil solution, air-water interfaces, and characteristics of microbial surfaces. After initial entry, the transport through soil depends on continued entrainment of bacteria and resuspension of those retained in the porous structure. We evaluated the retention of bacteria-sized artificial microspheres, varying in diameter and surface charge and applied in different suspending solutions, by a range of sieved soils contained in minicolumns, the transport of hydrophobic bacteria-sized microspheres through undisturbed soil columns as affected by waste type under simulated rainfall, and the field-scale transport of Enterococcus spp. to an unconfined sandy aquifer after the application of liquid manure. Microsphere retention reflected microsphere properties. The soil type and suspending solution affected retention of hydrophilic but not hydrophobic particles. Retention was not necessarily facilitated by manure-microsphere-soil interactions but by manure-soil interactions. Undisturbed column studies confirmed the governing role of waste type on vadose-zone microsphere transport. Filtration theory applied as an integrated analysis of transport across length scales showed that effective collision efficiency depended on the distance of travel. It followed a power law behavior with the power coefficient varying from ˜0.4 over short distances to >0.9 over 1 m (i.e., very little filtration for a finite fraction of biocolloids), consistent with reduced influence of soil solution and biocolloid properties at longer travel distances.
NASA Technical Reports Server (NTRS)
1976-01-01
Papers on major issues and trends that affect the future of intercity transportation are presented. Specific areas covered include: political, social, technological, institutional, and economic mechanisms, the workings of which determine how future intercity transporation technologies will evolve and be put into service; the major issues of intercity transportation from the point of view of reform, including candidate transporation technologies; and technical analysis of trends affecting the evolution of intercity transportation technologies.
TRANSPORT OF NEUTRAL SOLUTE IN ARTICULAR CARTILAGE: EFFECT OF MICROSTRUCTURE ANISOTROPY
Zhang, Le; Szeri, Andras Z.
2008-01-01
Due to the avascular nature of articular cartilage, solute transport through its extracellular matrix is critical for the maintenance and the functioning of the tissue. What’s more, diffusion of macromolecules may be affected by the microstructure of the extracellular matrix in both undeformed and deformed cartilage and experiments demonstrate diffusion anisotropy in the case of large solute. However, these phenomena have not received sufficient theoretical attention to date. We hypothesize here that the diffusion anisotropy of macromolecules is brought about by the particular microstructure of the cartilage network. Based on this hypothesis, we then propose a mathematical model that correlates the diffusion coefficient tensor with the structural orientation tensor of the network. This model is shown to be successful in describing anisotropic diffusion of macromolecules in undeformed tissue and is capable of clarifying the effects of network reorientation as the tissue deforms under mechanical load. Additionally, our model explains the anomaly that at large strain, in a cylindrical plug under unconfined compression, solute diffusion in the radial direction increases with strain. Our results indicate that in cartilage the degree of diffusion anisotropy is site specific but depends also on the size of the diffusing molecule. Mechanical loading initiates and/or further exacerbates this anisotropy. At small deformation, solute diffusion is near isotropic in a tissue that is isotropic in its unstressed state, becoming anisotropic as loading progresses. Mechanical loading leads to an attenuation of solute diffusion in all directions when deformation is small. However, loading, if it is high enough, enhances solute transport in the direction perpendicular to the load line, instead of inhibiting it. PMID:17889882
Modeling colloid and microorganism transport and release with transients in solution ionic strength
Technology Transfer Automated Retrieval System (TEKTRAN)
The transport and fate of colloids, microorganisms, and nanoparticles in subsurface environments is strongly influenced by transients in solution ionic strength (IS). A sophisticated dual-permeability transport model that is capable of simulating exponential, hyperexponential, uniform, and nonmonot...
Product Lifecycle Management and the Quest for Sustainable Space Transportation Solutions
NASA Technical Reports Server (NTRS)
Caruso, Pamela W.
2009-01-01
This viewgraph presentation reviews NASA Marshall's effort to sustain space transportation solutions through product lines that include: 1) Propulsion and Transportation Systems; 2) Life Support Systems; and 3) and Earth and Space Science Spacecraft Systems, and Operations.
NASA Astrophysics Data System (ADS)
Zhang, Hua; Harter, Thomas; Sivakumar, Bellie
2006-06-01
Facies-based geostatistical models have become important tools for analyzing flow and mass transport processes in heterogeneous aquifers. Yet little is known about the relationship between these latter processes and the parameters of facies-based geostatistical models. In this study, we examine the transport of a nonpoint source solute normal (perpendicular) to the major bedding plane of an alluvial aquifer medium that contains multiple geologic facies, including interconnected, high-conductivity (coarse textured) facies. We also evaluate the dependence of the transport behavior on the parameters of the constitutive facies model. A facies-based Markov chain geostatistical model is used to quantify the spatial variability of the aquifer system's hydrostratigraphy. It is integrated with a groundwater flow model and a random walk particle transport model to estimate the solute traveltime probability density function (pdf) for solute flux from the water table to the bottom boundary (the production horizon) of the aquifer. The cases examined include two-, three-, and four-facies models, with mean length anisotropy ratios for horizontal to vertical facies, ek, from 25:1 to 300:1 and with a wide range of facies volume proportions (e.g., from 5 to 95% coarse-textured facies). Predictions of traveltime pdfs are found to be significantly affected by the number of hydrostratigraphic facies identified in the aquifer. Those predictions of traveltime pdfs also are affected by the proportions of coarse-textured sediments, the mean length of the facies (particularly the ratio of length to thickness of coarse materials), and, to a lesser degree, the juxtapositional preference among the hydrostratigraphic facies. In transport normal to the sedimentary bedding plane, traveltime is not lognormally distributed as is often assumed. Also, macrodispersive behavior (variance of the traveltime) is found not to be a unique function of the conductivity variance. For the parameter range
Long range transport of colloids in aqueous solutions
NASA Astrophysics Data System (ADS)
Florea, Daniel; Musa, Sami; Huyghe, Jacques M. R. J.; Wyss, Hans M.
2013-03-01
Colloids in aqueous suspensions can experience strong, extremely long range repulsive forces near interfaces such as biological tissues, gels, ion exchange resins or metals. As a result exclusion zones extending over several millimeters can be formed. While this phenomenon has been previously described, a physical understanding of this process is still lacking. This exclusion zone formation is puzzling because the typical forces acting on colloidal particles are limited to much shorter distances and external fields that could drive the particles are absent. Here we study the exclusion zone formation in detail by following the time and distance-dependent forces acting on the particles. We present a simple model that accounts for our experimental data and directly links the exclusion zone formation to an already known physical transport phenomenon. We show that the effect can be tuned by changing the zeta potential of the particles or by varying the species present in the aqueous solution. We thus provide a direct physical explanation for the intriguing exclusion zone formation and we illustrate how this effect can be exploited in a range of industrial applications.
Nüsing, Rolf M.; Schweer, Horst; Fleming, Ingrid; Zeldin, Darryl C.; Wegmann, Markus
2007-01-01
We investigated the effects of epoxyeicosatrienoic acids (EETs) on ion transport in the polarized renal distal tubular cell line, MDCK C7. Of the four EET regioisomers (5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET) studied, only apical, but not basolateral, application of 5,6-EET increased short circuit current (Isc) with kinetics similar to those of arachidonic acid. The ion transport was blocked by preincubation with the cyclooxygenase inhibitor indomethacin or with the chloride channel blocker NPPB. Further, both a Cl−-free bath solution and the Ca2+ antagonist verapamil blocked 5,6-EET-induced ion transport. Although the presence of the PGE2 receptors EP2, EP3, and EP4 was demonstrated, apically added PGE2 was ineffective and basolaterally added PGE2 caused a different kinetics in ion transport compared to 5,6-EET. Moreover, PGE2 sythesis in MDCK C7 cells was unaffected by 5,6-EET treatment. GC/MS/MS analysis of cell supernatants revealed the presence of the biologically inactive 5,6-dihydroxy-PGE1 in 5,6-EET-treated cells, but not in control cells. Indomethacin suppressed the formation of 5,6-dihydroxy-PGE1. 5,6-epoxy-PGE1 the precursor of 5,6-dihydroxy-PGE1, caused a similar ion transport as 5,6-EET. Cytochrome P450 enzymes homolog to human CYP2C8, CYP2C9, and CYP2J2 protein were detected immunologically in the MDCK C7 cells. Our findings suggest that 5,6-EET affects Cl-transport in renal distal tubular cells independent of PGE2 but by a mechanism, dependent on its conversion to 5,6-epoxy-PGE1 by cyclooxygenase. We suggest a role for this P450 epoxygenase product in the regulation of electrolyte transport, especially as a saluretic compound acting from the luminal side of tubular cells in the mammalian kidney. PMID:17494091
Nüsing, Rolf M; Schweer, Horst; Fleming, Ingrid; Zeldin, Darryl C; Wegmann, Markus
2007-07-01
We investigated the effects of epoxyeicosatrienoic acids (EETs) on ion transport in the polarized renal distal tubular cell line, Madin-Darby canine kidney (MDCK) C7. Of the four EET regioisomers (5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET) studied, only apical, but not basolateral, application of 5,6-EET increased short-circuit current (I(sc)) with kinetics similar to those of arachidonic acid. The ion transport was blocked by preincubation with the cyclooxygenase inhibitor indomethacin or with the chloride channel blocker NPPB. Furthermore, both a Cl(-)-free bath solution and the Ca(2+) antagonist verapamil blocked 5,6-EET-induced ion transport. Although the presence of the PGE(2) receptors EP2, EP3, and EP4 was demonstrated, apically added PGE(2) was ineffective and basolaterally added PGE(2) caused a different kinetics in ion transport compared with 5,6-EET. Moreover, PGE(2) synthesis in MDCK C7 cells was unaffected by 5,6-EET treatment. GC/MS/MS analysis of cell supernatants revealed the presence of the biologically inactive 5,6-dihydroxy-PGE(1) in 5,6-EET-treated cells, but not in control cells. Indomethacin suppressed the formation of 5,6-dihydroxy-PGE(1). 5,6-Epoxy-PGE(1), the precursor of 5,6-dihydroxy-PGE(1), caused a similar ion transport as 5,6-EET. Cytochrome P-450 enzymes homolog to human CYP2C8, CYP2C9, and CYP2J2 protein were detected immunologically in the MDCK C7 cells. Our findings suggest that 5,6-EET affects Cl(-) transport in renal distal tubular cells independent of PGE(2) but by a mechanism, dependent on its conversion to 5,6-epoxy-PGE(1) by cyclooxygenase. We suggest a role for this P450 epoxygenase product in the regulation of electrolyte transport, especially as a saluretic compound acting from the luminal side of tubular cells in the mammalian kidney. PMID:17494091
NASA Astrophysics Data System (ADS)
Liang, Ching-Ping; Hsu, Shao-Yiu; Chen, Jui-Sheng
2016-09-01
It is recommended that an in-situ infiltration tracer test is considered for simultaneously determining the longitudinal and transverse dispersion coefficients in soil. Analytical solutions have been derived for two-dimensional advective-dispersive transport in a radial geometry in the literature which can be used for interpreting the result of such a tracer test. However, these solutions were developed for a transport domain with an unbounded-radial extent and an infinite thickness of vadose zone which might not be realistically manifested in the actual solute transport during a field infiltration tracer test. Especially, the assumption of infinite thickness of vadose zone should be invalid for infiltration tracer tests conducted in soil with a shallow groundwater table. This paper describes an analytical model for interpreting the results of an infiltration tracer test based on improving the transport domain with a bounded-radial extent and a finite thickness of vadose zone. The analytical model is obtained with the successive application of appropriate integral transforms and their corresponding inverse transforms. A comparison of the newly derived analytical solution against the previous analytical solutions in which two distinct sets of radial extent and thickness of vadose zone are considered is conducted to determine the influence of the radial and exit boundary conditions on the solute transport. The results shows that both the radial and exit boundary conditions substantially affect the trailing segment of the breakthrough curves for a soil medium with large dispersion coefficients. Previous solutions derived for a transport domain with an unbounded-radial and an infinite thickness of vadose zone boundary conditions give lower concentration predictions compared with the proposed solution at late times. Moreover, the differences between two solutions are amplified when the observation positions are near the groundwater table. In addition, we compare our
Semianalytical Solutions of Radioactive or Reactive Tracer Transport in Layered Fractured Media
G.J. Moridis; G. S. Bodvarsson
2001-10-01
In this paper, semianalytical solutions are developed for the problem of transport of radioactive or reactive tracers (solutes or colloids) through a layered system of heterogeneous fractured media with misaligned fractures. The tracer transport equations in the matrix account for (a) diffusion, (b) surface diffusion (for solutes only), (c) mass transfer between the mobile and immobile water fractions, (d) linear kinetic or equilibrium physical, chemical, or combined solute sorption or colloid filtration, and (e) radioactive decay or first order chemical reactions. Any number of radioactive decay daughter products (or products of a linear, first-order reaction chain) can be tracked. The tracer-transport equations in the fractures account for the same processes, in addition to advection and hydrodynamic dispersion. Additionally, the colloid transport equations account for straining and velocity adjustments related to the colloidal size. The solutions, which are analytical in the Laplace space, are numerically inverted to provide the solution in time and can accommodate any number of fractured and/or porous layers. The solutions are verified using analytical solutions for limiting cases of solute and colloid transport through fractured and porous media. The effect of important parameters on the transport of {sup 3}H, {sup 237}Np and {sup 239}Pu (and its daughters) is investigated in several test problems involving layered geological systems of varying complexity. {sup 239}Pu colloid transport problems in multilayered systems indicate significant colloid accumulations at straining interfaces but much faster transport of the colloid than the corresponding strongly sorbing solute species.
Semianalytical solutions of radioactive or reactive tracer transport in layered fractured media
Moridis, G.J.; Bodvarsson, G.S.
2001-10-10
In this paper, semianalytical solutions are developed for the problem of transport of radioactive or reactive tracers (solutes or colloids) through a layered system of heterogeneous fractured media with misaligned fractures. The tracer transport equations in the matrix account for (a) diffusion, (b) surface diffusion (for solutes only), (c) mass transfer between the mobile and immobile water fractions, (d) linear kinetic or equilibrium physical, chemical, or combined solute sorption or colloid filtration, and (e) radioactive decay or first order chemical reactions. Any number of radioactive decay daughter products (or products of a linear, first-order reaction chain) can be tracked. The tracer-transport equations in the fractures account for the same processes, in addition to advection and hydrodynamic dispersion. Additionally, the colloid transport equations account for straining and velocity adjustments related to the colloidal size. The solutions, which are analytical in the Laplace space, are numerically inverted to provide the solution in time and can accommodate any number of fractured and/or porous layers. The solutions are verified using analytical solutions for limiting cases of solute and colloid transport through fractured and porous media. The effect of important parameters on the transport of {sup 3}H, {sup 237}Np and {sup 239}Pu (and its daughters) is investigated in several test problems involving layered geological systems of varying complexity. {sup 239}Pu colloid transport problems in multilayered systems indicate significant colloid accumulations at straining interfaces but much faster transport of the colloid than the corresponding strongly sorbing solute species.
A Functional-Phylogenetic Classification System for Transmembrane Solute Transporters
Saier, Milton H.
2000-01-01
A comprehensive classification system for transmembrane molecular transporters has been developed and recently approved by the transport panel of the nomenclature committee of the International Union of Biochemistry and Molecular Biology. This system is based on (i) transporter class and subclass (mode of transport and energy coupling mechanism), (ii) protein phylogenetic family and subfamily, and (iii) substrate specificity. Almost all of the more than 250 identified families of transporters include members that function exclusively in transport. Channels (115 families), secondary active transporters (uniporters, symporters, and antiporters) (78 families), primary active transporters (23 families), group translocators (6 families), and transport proteins of ill-defined function or of unknown mechanism (51 families) constitute distinct categories. Transport mode and energy coupling prove to be relatively immutable characteristics and therefore provide primary bases for classification. Phylogenetic grouping reflects structure, function, mechanism, and often substrate specificity and therefore provides a reliable secondary basis for classification. Substrate specificity and polarity of transport prove to be more readily altered during evolutionary history and therefore provide a tertiary basis for classification. With very few exceptions, a phylogenetic family of transporters includes members that function by a single transport mode and energy coupling mechanism, although a variety of substrates may be transported, sometimes with either inwardly or outwardly directed polarity. In this review, I provide cross-referencing of well-characterized constituent transporters according to (i) transport mode, (ii) energy coupling mechanism, (iii) phylogenetic grouping, and (iv) substrates transported. The structural features and distribution of recognized family members throughout the living world are also evaluated. The tabulations should facilitate familial and functional
PROCESSES AFFECTING SUBSURFACE TRANSPORT OF LEAKING UNDERGROUND STORAGE TANK FLUIDS
The document focuses solely on the process affecting migration of fluids from a leaking tank and their effects on monitoring methodologies. Based upon the reviews presented, soil heterogeneities and the potential for multiphase flow will lead to high monitoring uncertainties if l...
Younes, A; Delay, F; Fajraoui, N; Fahs, M; Mara, T A
2016-08-01
The concept of dual flowing continuum is a promising approach for modeling solute transport in porous media that includes biofilm phases. The highly dispersed transit time distributions often generated by these media are taken into consideration by simply stipulating that advection-dispersion transport occurs through both the porous and the biofilm phases. Both phases are coupled but assigned with contrasting hydrodynamic properties. However, the dual flowing continuum suffers from intrinsic equifinality in the sense that the outlet solute concentration can be the result of several parameter sets of the two flowing phases. To assess the applicability of the dual flowing continuum, we investigate how the model behaves with respect to its parameters. For the purpose of this study, a Global Sensitivity Analysis (GSA) and a Statistical Calibration (SC) of model parameters are performed for two transport scenarios that differ by the strength of interaction between the flowing phases. The GSA is shown to be a valuable tool to understand how the complex system behaves. The results indicate that the rate of mass transfer between the two phases is a key parameter of the model behavior and influences the identifiability of the other parameters. For weak mass exchanges, the output concentration is mainly controlled by the velocity in the porous medium and by the porosity of both flowing phases. In the case of large mass exchanges, the kinetics of this exchange also controls the output concentration. The SC results show that transport with large mass exchange between the flowing phases is more likely affected by equifinality than transport with weak exchange. The SC also indicates that weakly sensitive parameters, such as the dispersion in each phase, can be accurately identified. Removing them from calibration procedures is not recommended because it might result in biased estimations of the highly sensitive parameters. PMID:27182791
NASA Astrophysics Data System (ADS)
Comunian, Alessandro; De Micheli, Leonardo; Lazzati, Claudio; Felletti, Fabrizio; Giacobbo, Francesca; Giudici, Mauro; Bersezio, Riccardo
2016-03-01
The fine-scale heterogeneity of porous media affects the large-scale transport of solutes and contaminants in groundwater and it can be reproduced by means of several geostatistical simulation tools. However, including the available geological information in these tools is often cumbersome. A hierarchical simulation procedure based on a binary tree is proposed and tested on two real-world blocks of alluvial sediments, of a few cubic meters volume, that represent small-scale aquifer analogs. The procedure is implemented using the sequential indicator simulation, but it is so general that it can be adapted to various geostatistical simulation tools, improving their capability to incorporate geological information, i.e., the sedimentological and architectural characterization of heterogeneity. When compared with a standard sequential indicator approach on bi-dimensional simulations, in terms of proportions and connectivity indicators, the proposed procedure yields reliable results, closer to the reference observations. Different ensembles of three-dimensional simulations based on different hierarchical sequences are used to perform numerical experiments of conservative solute transport and to obtain ensembles of equivalent pore velocity and dispersion coefficient at the scale length of the blocks (meter). Their statistics are used to estimate the impact of the variability of the transport properties of the simulated blocks on contaminant transport modeled on bigger domains (hectometer). This is investigated with a one-dimensional transport modeling based on the Kolmogorov-Dmitriev theory of branching stochastic processes. Applying the proposed approach with diverse binary trees and different simulation settings provides a great flexibility, which is revealed by the differences in the breakthrough curves.
NASA Astrophysics Data System (ADS)
Younes, A.; Delay, F.; Fajraoui, N.; Fahs, M.; Mara, T. A.
2016-08-01
The concept of dual flowing continuum is a promising approach for modeling solute transport in porous media that includes biofilm phases. The highly dispersed transit time distributions often generated by these media are taken into consideration by simply stipulating that advection-dispersion transport occurs through both the porous and the biofilm phases. Both phases are coupled but assigned with contrasting hydrodynamic properties. However, the dual flowing continuum suffers from intrinsic equifinality in the sense that the outlet solute concentration can be the result of several parameter sets of the two flowing phases. To assess the applicability of the dual flowing continuum, we investigate how the model behaves with respect to its parameters. For the purpose of this study, a Global Sensitivity Analysis (GSA) and a Statistical Calibration (SC) of model parameters are performed for two transport scenarios that differ by the strength of interaction between the flowing phases. The GSA is shown to be a valuable tool to understand how the complex system behaves. The results indicate that the rate of mass transfer between the two phases is a key parameter of the model behavior and influences the identifiability of the other parameters. For weak mass exchanges, the output concentration is mainly controlled by the velocity in the porous medium and by the porosity of both flowing phases. In the case of large mass exchanges, the kinetics of this exchange also controls the output concentration. The SC results show that transport with large mass exchange between the flowing phases is more likely affected by equifinality than transport with weak exchange. The SC also indicates that weakly sensitive parameters, such as the dispersion in each phase, can be accurately identified. Removing them from calibration procedures is not recommended because it might result in biased estimations of the highly sensitive parameters.
Mc Mahon, Brenda; Andersen, Sofie B; Madsen, Martin K; Hjordt, Liv V; Hageman, Ida; Dam, Henrik; Svarer, Claus; da Cunha-Bang, Sofi; Baaré, William; Madsen, Jacob; Hasholt, Lis; Holst, Klaus; Frokjaer, Vibe G; Knudsen, Gitte M
2016-05-01
Cross-sectional neuroimaging studies in non-depressed individuals have demonstrated an inverse relationship between daylight minutes and cerebral serotonin transporter; this relationship is modified by serotonin-transporter-linked polymorphic region short allele carrier status. We here present data from the first longitudinal investigation of seasonal serotonin transporter fluctuations in both patients with seasonal affective disorder and in healthy individuals. Eighty (11)C-DASB positron emission tomography scans were conducted to quantify cerebral serotonin transporter binding; 23 healthy controls with low seasonality scores and 17 patients diagnosed with seasonal affective disorder were scanned in both summer and winter to investigate differences in cerebral serotonin transporter binding across groups and across seasons. The two groups had similar cerebral serotonin transporter binding in the summer but in their symptomatic phase during winter, patients with seasonal affective disorder had higher serotonin transporter than the healthy control subjects (P = 0.01). Compared to the healthy controls, patients with seasonal affective disorder changed their serotonin transporter significantly less between summer and winter (P < 0.001). Further, the change in serotonin transporter was sex- (P = 0.02) and genotype- (P = 0.04) dependent. In the patients with seasonal affective disorder, the seasonal change in serotonin transporter binding was positively associated with change in depressive symptom severity, as indexed by Hamilton Rating Scale for Depression - Seasonal Affective Disorder version scores (P = 0.01). Our findings suggest that the development of depressive symptoms in winter is associated with a failure to downregulate serotonin transporter levels appropriately during exposure to the environmental stress of winter, especially in individuals with high predisposition to affective disorders.media-1vid110.1093/brain/aww043_video_abstractaww043_video
Technology Transfer Automated Retrieval System (TEKTRAN)
Solute transport in soils and sediments is commonly simulated with the parabolic advective-dispersive equation, or ADE. In the last decades, it has been reported that this model cannot take in account several important features of solute movement through soil. Recently, a new model base on the assu...
Processes affecting transport of uranium in a suboxic aquifer
Davis, J.A.; Curtis, G.P.; Wilkins, M.J.; Kohler, M.; Fox, P.; Naftz, D.L.; Lloyd, J.R.
2006-01-01
At the Naturita site in Colorado, USA, groundwaters were sampled and analyzed for chemical composition and by culture and culture-independent microbiological techniques. In addition, sediments were extracted with a dilute sodium carbonate solution to determine quantities of labile uranium within the sediments. Samples from the upgradient portion of the contaminated aquifer, where very little dissolved Fe(II) is found in the groundwater, have uranium content that is controlled by U(VI) adsorption and few metal-reducing bacteria are observed. In the extreme downgradient portion of the aquifer, where dissolved Fe(II) is observed, uranium content of the sediments includes significant quantities of reduced U(IV) and diverse populations of Fe(III)-reducing bacteria were present in the subsurface with the potential of reducing U(VI) to U(IV). ?? 2006 Elsevier Ltd. All rights reserved.
Essays on alternative energy policies affecting the US transportation sector
NASA Astrophysics Data System (ADS)
O'Rear, Eric G.
This dissertation encompasses three essays evaluating the impacts of different policies targeting the greenhouse gas (GHG) emissions, fuel demands, etc. of the transportation sector. Though there are some similarities across the three chapters, each essay stands alone as an independent work. The 2010 US EPA MARKAL model is used in each essay to evaluate policy effects. Essay 1 focuses on the recent increases in Corporate Average Fuel Economy (CAFE) standards, and the implications of a "rebound effect." These increases are compared to a carbon tax generating similar reductions in system-wide emissions. As anticipated, the largest reductions in fuel use by light-duty vehicles (LDV) and emissions are achieved under CAFE. Consideration of the rebound effect does little to distort CAFE benefits. Our work validates many economists' belief that a carbon tax is a more efficient approach. However, because the tax takes advantage of cheaper abatement opportunities in other sectors, reductions in transportation emissions will be much lower than what we observe with CAFE. Essay 2 compares CAFE increases with what some economists suggest would be a much more "efficient" alternative -- a system-wide oil tax internalizing some environmental externalities. Because oil taxes are likely to be implemented in addition to CAFE standards, we consider a combined policy case reflecting this. Our supplementary analysis approximates the appropriate tax rates to produce similar reductions in oil demands as CAFE (CAFE-equivalent tax rates). We discover that taxes result in greater and more cost-effective reductions in system-wide emissions and net oil imports than CAFE. The current fuel tax system is compared to three versions of a national vehicle miles traveled (VMT) tax charged to all LDVs in Essay 3. VMT taxes directly charge motorists for each mile driven and help to correct the problem of eroding tax revenues given the failure of today's fuel taxes to adjust with inflation. Results
Demonstrations in Solute Transport Using Dyes: Part II. Modeling.
ERIC Educational Resources Information Center
Butters, Greg; Bandaranayake, Wije
1993-01-01
A solution of the convection-dispersion equation is used to describe the solute breakthrough curves generated in the demonstrations in the companion paper. Estimation of the best fit model parameters (solute velocity, dispersion, and retardation) is illustrated using the method of moments for an example data set. (Author/MDH)
Technology Transfer Automated Retrieval System (TEKTRAN)
An analytical solution describing the fate and transport of pesticides applied to soils has been developed. Two pesticide application methods can be simulated: point-source applications such as a hot-gas injection method and a shank-source application method that includes a vertical pesticide distr...
FRACTIONAL SOLUTE TRANSPORT EQUATION EVALUATED WITH THE MISCIBLE DISPLACEMENT EXPERIMENTAL DATA
Technology Transfer Automated Retrieval System (TEKTRAN)
A new solute transport model has been recently developed assuming that the movements of solute particles in hierarchically-structured porous media belongs to the family of Lévy motions rather than to the Brownian motion. The one-dimensional fractional advective-dispersive transport equation, or FADE...
An exploration of coupled surface-subsurface solute transport in a fully integrated catchment model
NASA Astrophysics Data System (ADS)
Liggett, Jessica E.; Partington, Daniel; Frei, Sven; Werner, Adrian D.; Simmons, Craig T.; Fleckenstein, Jan H.
2015-10-01
Coupling surface and subsurface water flow in fully integrated hydrological codes is becoming common in hydrological research; however, the coupling of surface-subsurface solute transport has received much less attention. Previous studies on fully integrated solute transport focus on small scales, simple geometric domains, and have not utilised many different field data sources. The objective of this study is to demonstrate the inclusion of both flow and solute transport in a 3D, fully integrated catchment model, utilising high resolution observations of dissolved organic carbon (DOC) export from a wetland complex during a rainfall event. A sensitivity analysis is performed to span a range of transport conditions for the surface-subsurface boundary (e.g. advective exchange only, advection plus diffusion, advection plus full mechanical dispersion) and subsurface dispersivities. The catchment model captures some aspects of observed catchment behaviour (e.g. solute discharge at the catchment outlet, increasing discharge from wetlands with increased stream discharge, and counter-clockwise concentration-discharge relationships), although other known behaviours are not well represented in the model (e.g. slope of concentration-discharge plots). Including surface-subsurface solute transport aids in evaluating internal model processes, however there are challenges related to the influence of dispersion across the surface-subsurface interface, and non-uniqueness of the solute transport solution. This highlights that obtaining solute field data is especially important for constraining integrated models of solute transport.
Zhang, Yong; Green, Christopher T; Tick, Geoffrey R
2015-01-01
This study evaluates the role of the Peclet number as affected by molecular diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numerical experiments show that 1) the Peclet number affects both the duration of the power-law segment of tracer breakthrough curves (BTCs) and the transition rate from anomalous to Fickian transport by determining the solute residence time for a given low-permeability layer, 2) mechanical dispersion has a limited contribution to the anomalous characteristics of late-time transport as compared to molecular diffusion due to an almost negligible velocity in floodplain deposits, and 3) the initial source dimensions only enhance the power-law tail of the BTCs at short travel distances. A tempered stable stochastic (TSS) model is then applied to analyze the modeled transport. Applications show that the time-nonlocal parameters in the TSS model relate to the Peclet number, Pe. In particular, the truncation parameter in the TSS model increases nonlinearly with a decrease in Pe due to the decrease of the mean residence time, and the capacity coefficient increases with an increase in molecular diffusion which is probably due to the increase in the number of immobile particles. The above numerical experiments and stochastic analysis therefore reveal that the Peclet number as affected by molecular diffusion controls transient anomalous transport in alluvial aquifer-aquitard complexes. PMID:26001981
Zhang, Yong; Green, Christopher T.; Tick, Geoffrey R.
2015-01-01
This study evaluates the role of the Peclet number as affected by molecular diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numerical experiments show that 1) the Peclet number affects both the duration of the power-law segment of tracer breakthrough curves (BTCs) and the transition rate from anomalous to Fickian transport by determining the solute residence time for a given low-permeability layer, 2) mechanical dispersion has a limited contribution to the anomalous characteristics of late-time transport as compared to molecular diffusion due to an almost negligible velocity in floodplain deposits, and 3) the initial source dimensions only enhance the power-law tail of the BTCs at short travel distances. A tempered stable stochastic (TSS) model is then applied to analyze the modeled transport. Applications show that the time-nonlocal parameters in the TSS model relate to the Peclet number, Pe. In particular, the truncation parameter in the TSS model increases nonlinearly with a decrease in Pe due to the decrease of the mean residence time, and the capacity coefficient increases with an increase in molecular diffusion which is probably due to the increase in the number of immobile particles. The above numerical experiments and stochastic analysis therefore reveal that the Peclet number as affected by molecular diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes.
Xu, Chenghao; Zhu, Ling; Chan, Ting; Lu, Xiaoxi; Shen, Weiyong; Gillies, Mark C.; Zhou, Fanfan
2015-01-01
Diabetes mellitus is a chronic metabolic disorder that significantly affects human health and well-being. The Solute carrier transporters (SLCs), particularly the Organic anion/cation transporters (Oats/Octs/Octns), Organic anion transporting polypeptides (Oatps) and Oligopeptide transporters (Pepts) are essential membrane proteins responsible for cellular uptake of many endogenous and exogenous substances such as clinically important drugs. They are widely expressed in mammalian key organs especially the kidney and liver, in which they facilitate the influx of various drug molecules, thereby determining their distribution and elimination in body. The altered expression of SLCs in diabetes mellitus could have a profound and clinically significant influence on drug therapies. In this study, we extensively investigated the renal and hepatic expression of twenty essential SLCs in the type 1 diabetic Ins2Akita murine model that develops both hyperglycemia and diabetes-related complications using real-time PCR and immunoblotting analysis. We found that the renal expression of mOatp1a1, mOatp1a6, mOat1, mOat3, mOat5, mOct2 and mPept2 was decreased; while that of mPept1 was increased at the mRNA level in the diabetic mice compared with non-diabetic controls. We found up-regulated mRNA expression of mOatp1a4, mOatp1c1, mOctn2, mOct3 and mPept1 as well as down-regulation of mOatp1a1 in the livers of diabetic mice. We confirmed the altered protein expression of several SLCs in diabetic mice, especially the decreased renal and hepatic expression of mOatp1a1. We also found down-regulated protein expression of mOat3 and mOctn1 in the kidneys as well as increased protein expression of mOatp1a4 and mOct3 in the livers of diabetic mice. Our findings contribute to better understanding the modulation of SLC transporters in type 1 diabetes mellitus, which is likely to affect the pharmacokinetic performance of drugs that are transported by these transporters and therefore, forms the
Water flow and solute transport in floating fen root mats
NASA Astrophysics Data System (ADS)
Stofberg, Sija F.; EATM van der Zee, Sjoerd
2015-04-01
be very similar and likely functionally related. Our experimental field data were used for modelling water flow and solute transport in floating fens, using HYDRUS 2D. Fluctuations of surface water and root mat, as well as geometry and unsaturated zone parameters can have a major influence on groundwater fluctuations and the exchange between rain and surface water and the water in the root mats. In combination with the duration of salt pulses in surface water, and sensitivity of fen plants to salinity (Stofberg et al. 2014, submitted), risks for rare plants can be anticipated.
NASA Astrophysics Data System (ADS)
Gotovac, Hrvoje; Srzic, Veljko
2014-05-01
Contaminant transport in natural aquifers is a complex, multiscale process that is frequently studied using different Eulerian, Lagrangian and hybrid numerical methods. Conservative solute transport is typically modeled using the advection-dispersion equation (ADE). Despite the large number of available numerical methods that have been developed to solve it, the accurate numerical solution of the ADE still presents formidable challenges. In particular, current numerical solutions of multidimensional advection-dominated transport in non-uniform velocity fields are affected by one or all of the following problems: numerical dispersion that introduces artificial mixing and dilution, grid orientation effects, unresolved spatial and temporal scales and unphysical numerical oscillations (e.g., Herrera et al, 2009; Bosso et al., 2012). In this work we will present Eulerian Lagrangian Adaptive Fup Collocation Method (ELAFCM) based on Fup basis functions and collocation approach for spatial approximation and explicit stabilized Runge-Kutta-Chebyshev temporal integration (public domain routine SERK2) which is especially well suited for stiff parabolic problems. Spatial adaptive strategy is based on Fup basis functions which are closely related to the wavelets and splines so that they are also compactly supported basis functions; they exactly describe algebraic polynomials and enable a multiresolution adaptive analysis (MRA). MRA is here performed via Fup Collocation Transform (FCT) so that at each time step concentration solution is decomposed using only a few significant Fup basis functions on adaptive collocation grid with appropriate scales (frequencies) and locations, a desired level of accuracy and a near minimum computational cost. FCT adds more collocations points and higher resolution levels only in sensitive zones with sharp concentration gradients, fronts and/or narrow transition zones. According to the our recent achievements there is no need for solving the large
Wexler, Eliezer J.
1989-01-01
Analytical solutions to the advective-dispersive solute transport equation are useful in predicting the fate of solutes in groundwater. Analytical solutions compiled from available literature or derived by the author are presented in this report for a variety of boundary condition types and solute-source configuration in one-, two-, and three-dimensional systems with uniform groundwater flow. A set of user-oriented computer programs was created to evaluate these solutions and to display the results in tabular and computer-graphics format. These programs incorporate many features that enhance their accuracy, ease of use, and versatility. Documentation for the programs describes their operation and required input data, and presents the results of sample problems. Derivations of select solutions, source codes for the computer programs, and samples of program input and output also are described. (USGS)
Wexler, Eliezer J.
1992-01-01
Analytical solutions to the advective-dispersive solute-transport equation are useful in predicting the fate of solutes in ground water. Analytical solutions compiled from available literature or derived by the author are presented for a variety of boundary condition types and solute-source configurations in one-, two-, and three-dimensional systems having uniform ground-water flow. A set of user-oriented computer programs was created to evaluate these solutions and to display the results in tabular and computer-graphics format. These programs incorporate many features that enhance their accuracy, ease of use, and versatility. Documentation for the programs describes their operation and required input data, and presents the results of sample problems. Derivations of selected solutions, source codes for the computer programs, and samples of program input and output also are included.
NASA Astrophysics Data System (ADS)
Krezoski, John R.; Robbins, John A.; White, David S.
1984-09-01
presence of biogenically reworked sediments (with pelletized materials and remnant burrow structures) did not affect solute transport. In cells with live Stylodrilus, penetration of 22Na within the feeding zone was considerably more rapid, implying an apparent De twice as high as in cells without worms. Inferences based on the particle reworking results were used to develop an illustrative transport model that includes advective as well as diffusive terms. Advective transport arises from the incorporation of 22Na into pore fluids moved downward as a result of conveyor-belt feeding. The model indicates that within the feeding zone, solute transport is dominated by advection and that the apparent enhancement of De in pure diffusion models is really the result of solute flow induced by particle reworking. In cells with Pontoporeia, De is approximately twice that in control cells. In these cells, 22Na profiles may be treated theoretically without advection.
Houseworth, J.E.
2004-09-16
Exact analytical solutions are presented for solute transport in an unsaturated fracture and porous rock matrix. The problem includes advective transport in the fracture and rock matrix as well as advective and diffusive fracture-matrix exchange. Linear sorption in the fracture and matrix and radioactive decay are also treated. The solution is for steady, uniform transport velocities within the fracture and matrix, but allows for independent specification of each of the velocities. The problem is first solved in terms of the solute concentrations that result from an instantaneous point source. Superposition integrals are then used to derive the solute mass flux at a fixed downstream position from an instantaneous point source and for the solute concentrations that result from a continuous point source. Solutions are derived for cases with the solute source in the fracture and the solute source in the matrix. The analytical solutions are closed-form and are expressed in terms of algebraic functions, exponentials, and error functions. Comparisons between the analytical solutions and numerical simulations, as well as sensitivity studies, are presented. Increased sensitivity to cross-flow and solute source location is found for increasing Peclet number. The numerical solutions are found to compare well with the analytical solutions at lower Peclet numbers ,but show greater deviation at higher Peclet numbers.
Broshears, R.E.; Bencala, K.E.; Kimball, B.A.; McKnight, D.M.
1993-01-01
In 1986, the U.S. Geological Survey began an investigation to characterize within-stream hydrologic, chemical, and biological processes that influence the distribution and transport of hazardous constituents in the headwaters of the Arkansas River. The report describes the results of tracer-dilution experiments and associated solute-transport simulations for a 1804-meter stretch of Saint Kevin Gulch, a stream affected by acid mine drainage in Lake County, Colorado. The report describes transient changes in tracer (lithium chloride) concentration at six instream sites.
VERIFICATION OF TRANSPORT CODES BY THE METHOD OF MANUFACTURED SOLUTIONS: THE ATTILA EXPERIENCE
S. D. PAUTZ
2001-03-19
We extend the Method of Manufactured Solutions (MMS) to the verification of transport codes. We derive analytic fixed sources required by the MMS procedure for several types of transport problems and apply the method to the Attila transport code. By means of this method we discover and correct several coding mistakes in Attila and ultimately verify its correct implementation for the problems studied. Our studies reveal that the MMS procedure is a useful tool for transport code development.
Simulating water, solute, and heat transport in the subsurface with the VS2DI software package
Healy, R.W.
2008-01-01
The software package VS2DI was developed by the U.S. Geological Survey for simulating water, solute, and heat transport in variably saturated porous media. The package consists of a graphical preprocessor to facilitate construction of a simulation, a postprocessor for visualizing simulation results, and two numerical models that solve for flow and solute transport (VS2DT) and flow and heat transport (VS2DH). The finite-difference method is used to solve the Richards equation for flow and the advection-dispersion equation for solute or heat transport. This study presents a brief description of the VS2DI package, an overview of the various types of problems that have been addressed with the package, and an analysis of the advantages and limitations of the package. A review of other models and modeling approaches for studying water, solute, and heat transport also is provided. ?? Soil Science Society of America. All rights reserved.
NASA Astrophysics Data System (ADS)
Kudo, Susumu; Ikezawa, Kenji; Ikeda, Mariko; Tanishita, Kazuo
Endothelial cells (ECs) that line the inner surface of blood vessels are barriers to the transport of various substances into or from vessel walls, and are continuously exposed to shear stress induced by blood flow in vivo. Shear stress affects the cytoskeleton (e.g., microtubules, microfilaments, intermediate filaments), and affects the transport of macromolecules. Here, the relationship between the microtubule network structure and this transport process for albumin uptake within cultured aortic endothelial cells affected by shear stress was studied. Based on fluorescent images of albumin uptake obtained by using confocal laser scanning microscopy (CLSM), both the microtubule network and albumin uptake in ECs were disrupted by colchicine and were affected by shear stress loading.
Computer model of two-dimensional solute transport and dispersion in ground water
Konikow, Leonard F.; Bredehoeft, J.D.
1978-01-01
This report presents a model that simulates solute transport in flowing ground water. The model is both general and flexible in that it can be applied to a wide range of problem types. It is applicable to one- or two-dimensional problems involving steady-state or transient flow. The model computes changes in concentration over time caused by the processes of convective transport, hydrodynamic dispersion, and mixing (or dilution) from fluid sources. The model assumes that the solute is non-reactive and that gradients of fluid density, viscosity, and temperature do not affect the velocity distribution. However, the aquifer may be heterogeneous and (or) anisotropic. The model couples the ground-water flow equation with the solute-transport equation. The digital computer program uses an alternating-direction implicit procedure to solve a finite-difference approximation to the ground-water flow equation, and it uses the method of characteristics to solve the solute-transport equation. The latter uses a particle- tracking procedure to represent convective transport and a two-step explicit procedure to solve a finite-difference equation that describes the effects of hydrodynamic dispersion, fluid sources and sinks, and divergence of velocity. This explicit procedure has several stability criteria, but the consequent time-step limitations are automatically determined by the program. The report includes a listing of the computer program, which is written in FORTRAN IV and contains about 2,000 lines. The model is based on a rectangular, block-centered, finite difference grid. It allows the specification of any number of injection or withdrawal wells and of spatially varying diffuse recharge or discharge, saturated thickness, transmissivity, boundary conditions, and initial heads and concentrations. The program also permits the designation of up to five nodes as observation points, for which a summary table of head and concentration versus time is printed at the end of the
Numerical solution of the radiation transport equation in disk geometry
NASA Technical Reports Server (NTRS)
Spagna, George F., Jr.; Leung, Chun Ming
1987-01-01
An efficient numerical method for solving the problem of radiation transport in a dusty medium with two dimensional (2-D) disk geometry is described. It is a generalization of the one-dimensional quasi-diffusion method in which the transport equation is cast in diffusion form and then solved as a boundary value problem. The method should be applicable to a variety of astronomical sources, the dynamics of which are angular-momentum dominated and hence not accurately treated by spherical geometry, e.g., protoplanetary nebulae, circumstellar disks, interstellar molecular clouds, accretion disks, and disk galaxies. The computational procedure and practical considerations for implementing the method are described in detail. To illustrate the effects of 2-D radiation transport, some model results (dust temperature distributions and IR flux spectra) for externally heated, interstellar dust clouds with spherically symmetric and disk geometry are compared.
Light-driven solute transport in Halobacterium halobium
NASA Technical Reports Server (NTRS)
Lanyi, J. K.
1979-01-01
The cell membrane of Halobacterium halobium exhibits differential regions which contain crystalline arrays of a single kind of protein, termed bacteriorhodopsin. This bacterial retinal-protein complex resembles the visual pigment and, after the absorption of protons, translocates H(+) across the cell membrane, leading to an electrochemical gradient for protons between the inside and the outside of the cell. Thus, light is an alternate source of energy in these bacteria, in addition to terminal oxidation. The paper deals with work on light-driven transport in H. halobium with cell envelope vesicles. The discussion covers light-driven movements of H(+), Na(+), and K(+); light-driven amino acid transport; and apparent allosteric control of amino acid transport. The scheme of energy coupling in H. halobium vesicles appears simple, its quantitative details are quite complex and reveal regulatory phenomena. More knowledge is required of the way the coupling components are regulated by the ion gradients present.
Boundary effects on solute transport in finite soil columns
NASA Astrophysics Data System (ADS)
Schwartz, R. C.; McInnes, K. J.; Juo, A. S. R.; Wilding, L. P.; Reddell, D. L.
1999-03-01
This study investigates the influence of inlet and outlet disturbances and formulated boundary conditions on the estimation of the dispersion coefficient and retardation factor for short soil columns. Unsaturated miscible displacement experiments utilizing a Br- tracer were carried out on undisturbed columns of a fine-textured Ultisol. Solutions were applied using either a fritted plate or an array of dispensing tips that produced droplets at a prescribed flow rate. One- and two-layer analytical solutions of the advective-dispersive equation were fitted to effluent concentrations using nonlinear least squares parameter optimization. Comparison of two-layer simulations with experimental data indicated that the analytical solution with a semi-infinite interface boundary best approximated effluent concentrations under the conditions of this study. This solution corresponds to a continuous flux concentration and a macroscopically discontinuous resident concentration at the interface between the soil and porous plates. Parameter estimates were not significantly different with respect to the application method used at the inlet. This may be attributed to a less uniform distribution of solution onto the soil surface by the drip apparatus and/or by the presence of stagnant regions within the inlet reservoir and hence increased dispersion within the inlet platen apparatus. Two-layer simulations indicated that the dispersion coefficient was underestimated by 14-27% when the influence of the inlet and outlet apparatus were not included in the fitted solution of the advective-dispersive equation. In addition, use of one-layer analytical solutions caused the retardation factor to be overestimated by no more than the fractional increase in pore volume imparted by the platen apparatus.
A dual-porosity model for simulating solute transport in oil shale
Glover, K.C.
1987-01-01
A model is described for simulating three-dimensional groundwater flow and solute transport in oil shale and associated geohydrologic units. The model treats oil shale as a dual-porosity medium by simulating flow and transport within fractures using the finite-element method. Diffusion of solute between fractures and the essentially static water of the shale matrix is simulated by including an analytical solution that acts as a source-sink term to the differential equation of solute transport. While knowledge of fracture orientation and spacing is needed to effectively use the model, it is not necessary to map the locations of individual fractures. The computer program listed in the report incorporates many of the features of previous dual-porosity models while retaining a practical approach to solving field problems. As a result the theory of solute transport is not extended in any appreciable way. The emphasis is on bringing together various aspects of solute transport theory in a manner that is particularly suited to the unusual groundwater flow and solute transport characteristics of oil shale systems. (Author 's abstract)
Influence of spatial and temporal flow variability on solute transport in catchments
NASA Astrophysics Data System (ADS)
Selroos, Jan-Olof; Destouni, Georgia
2015-04-01
The present study quantifies the separate and combined effects of spatial and temporal variability of waterborne solute transport through catchments. The questions addressed are whether, when and why different types of variability may dominate catchment-scale transport. We utilize a versatile numerical solute transport code with a particle-based Monte Carlo time domain random walk method to simulate waterborne transport through a generic catchment. The methodology is exemplified by performing simulations using data on spatiotemporal flow and transport variability from direct stream discharge observations and independently calculated advective solute travel time distributions for catchments within the water management district Northern Baltic Proper (NBP) in Mid-Eastern Sweden. A main conclusion of the study is that projections of catchment mass loading based on spatial variability alone are robust estimates of long-term average solute transport development. This is especially true when annually aggregated mass load rather than finer temporal resolution of mass flux is considered. Temporal variability yields short-term fluctuations around the long-term average solute breakthrough development, and earlier or later arrival than the latter, depending on the timing and duration of solute input relative to the temporal flow variability. The exact temporal characteristics of future solute breakthroughs are thus fundamentally uncertain but their statistical expectation may be well quantified by only spatial variability account.
Dykhuizen, R.C.
1988-03-01
A numerical model is presented to represent the transport of solutes through a highly fractured unsaturated, porous medium. To accomplish this, the solute is tracked separately in two flow systems a matrix pore flow system and a fracture network, with interaction terms. Compatible hydraulic equations for such a dual system are also presented to enable solution of the solute trasport. The hydraulic equations chosen use the equivlaent porous media concept. These equations can also be applied to a saturated medium without modification. However, many of the transport terms will be negligible for such an application. A brief sample calculation illustates the method. 11 refs., 4 figs.
KINEMATIC MODELING OF MULTIPHASE SOLUTE TRANSPORT IN THE VADOSE ZONE
The goal of this research was the development of a computationally efficient simulation model for multiphase flow of organic hazardous waste constituents in the shallow soil environment. Such a model is appropriate for investigation of fate and transport of organic chemicals intr...
CHANGING GEARS: A SUSTAINABLE TRANSPORTATION SOLUTION FOR UCSC
The University of California, Santa Cruz campus sees traffic in/out of campus that averages 22,576 vehicle trips per day. When examining the costs of automobile usage to the UC, students, and the environment it is clear that the primary mode of transportation of students and f...
Impact of thin aquitards on two-dimensional solute transport in an aquifer
NASA Astrophysics Data System (ADS)
Rezaei, Abolfazl; Zhan, Hongbin; Zare, Mohammad
2013-09-01
The influence of aquitards on solute transport in an aquifer is an important and often overlooked process for subsurface contaminant transport. In particular, slow advection (leakage) into an aquitard is often neglected in previous analytical treatment of solute transport, making such analytical solutions unsuitable for benchmarking numerical simulations of transport when aquitard leakage exists. In this study, a semi-analytical solution to the two-dimensional conservative solute transport in an aquifer bounded by thin aquitards is derived in the Laplace domain. The governing equation in the aquifer (not aquitard) incorporates terms accounting for advection, longitudinal dispersion, and transverse vertical dispersion. Both one-dimensional vertical advection and molecular diffusion are considered for aquitard transport. The solutions are derived under conditions of steady-state flow and the first- and third-type transport boundary conditions in the aquifer along with assuming the continuity of concentration and vertical mass flux at aquifer and aquitard interfaces. The solutions in the real time domain are obtained by numerically inverting the solutions in the Laplace domain using the Stehfest (1970) algorithm. The semi-analytical solutions are compared with those from Zhan et al. (2009b), which considered aquitard leakage in infinitively thick aquitards. The concentration profiles, breakthrough curves and distribution profiles in the aquifer are different from those of Zhan et al. (2009b) at small ratios of the aquitard/aquifer thickness; whereas, the results of both are consistent for thick bounding aquitards. This study reveals that the residence time distribution (RTD) in the main aquifer is related to the aquitard/aquifer thickness ratios, Peclet numbers and porosities of adjacent aquitards. The results also suggest that MT3DMS (a commonly applied transport code) cannot successfully simulate solute transport at the aquifer-aquitard interfaces. The presented
Impact of thin aquitards on two-dimensional solute transport in an aquifer.
Rezaei, Abolfazl; Zhan, Hongbin; Zare, Mohammad
2013-09-01
The influence of aquitards on solute transport in an aquifer is an important and often overlooked process for subsurface contaminant transport. In particular, slow advection (leakage) into an aquitard is often neglected in previous analytical treatment of solute transport, making such analytical solutions unsuitable for benchmarking numerical simulations of transport when aquitard leakage exists. In this study, a semi-analytical solution to the two-dimensional conservative solute transport in an aquifer bounded by thin aquitards is derived in the Laplace domain. The governing equation in the aquifer (not aquitard) incorporates terms accounting for advection, longitudinal dispersion, and transverse vertical dispersion. Both one-dimensional vertical advection and molecular diffusion are considered for aquitard transport. The solutions are derived under conditions of steady-state flow and the first- and third-type transport boundary conditions in the aquifer along with assuming the continuity of concentration and vertical mass flux at aquifer and aquitard interfaces. The solutions in the real time domain are obtained by numerically inverting the solutions in the Laplace domain using the Stehfest (1970) algorithm. The semi-analytical solutions are compared with those from Zhan et al. (2009b), which considered aquitard leakage in infinitively thick aquitards. The concentration profiles, breakthrough curves and distribution profiles in the aquifer are different from those of Zhan et al. (2009b) at small ratios of the aquitard/aquifer thickness; whereas, the results of both are consistent for thick bounding aquitards. This study reveals that the residence time distribution (RTD) in the main aquifer is related to the aquitard/aquifer thickness ratios, Peclet numbers and porosities of adjacent aquitards. The results also suggest that MT3DMS (a commonly applied transport code) cannot successfully simulate solute transport at the aquifer-aquitard interfaces. The presented
Biochar pyrolyzed at two temperatures affects Escherichia coli transport through a sandy soil.
Bolster, Carl H; Abit, Sergio M
2012-01-01
The incorporation of biochar into soils has been proposed as a means to sequester carbon from the atmosphere. An added environmental benefit is that biochar has also been shown to increase soil retention of nutrients, heavy metals, and pesticides. The goal of this study was to evaluate whether biochar amendments affect the transport of Escherichia coli through a water-saturated soil. We looked at the transport of three E. coli isolates through 10-cm columns packed with a fine sandy soil amended with 2 or 10% (w/w) poultry litter biochar pyrolyzed at 350 or 700°C. For all three isolates, mixing the high-temperature biochar at a rate of 2% into the soil had no impact on transport behavior. When added at a rate of 10%, a reduction of five orders of magnitude in the amount of E. coli transported through the soil was observed for two of the isolates, and a 60% reduction was observed for the third isolate. Mixing the low-temperature biochar into the soil resulted in enhanced transport through the soil for two of the isolates, whereas no significant differences in transport behavior were observed between the low-temperature and high-temperature biochar amendments for one isolate. Our results show that the addition of biochar can affect the retention and transport behavior of E. coli and that biochar application rate, biochar pyrolysis temperature, and bacterial surface characteristics were important factors determining the transport of E. coli through our test soil. PMID:22218181
NASA Astrophysics Data System (ADS)
Ward, Adam S.; Gooseff, Michael N.; Fitzgerald, Michael; Voltz, Thomas J.; Singha, Kamini
2014-09-01
The transport of solutes along hyporheic flowpaths is recognized as central to numerous biogeochemical cycles, yet our understanding of how this transport changes with baseflow recession, particularly in a spatially distributed manner, is limited. We conducted four steady-state solute tracer injections and collected electrical resistivity data to characterize hyporheic transport during seasonal baseflow recession in the H.J. Andrews Experimental Forest (Oregon, USA). We used temporal moment analysis of pixels generated from inversion of electrical resistivity data to compress time-lapse data into descriptive statistics (mean arrival time, temporal variance, and temporal skewness) for each pixel. A spatial visualization of these temporal moments in the subsurface at each of five 2-D transects perpendicular to the stream was interpreted to inform transport processes. As baseflow recession progressed we found increasing first arrival times, persistence, mean arrival time, temporal variance, and coefficient of variation, and decreasing skewness. These trends suggest that changes in hydrologic forcing alter the relative influence of transport phenomena (e.g., advection vs. other transport processes such as dispersion) along flowpaths. Spatial coverage obtained from electrical resistivity images allowed for qualitative comparison of spatial patterns in temporal moments both at an individual cross-section as well as between cross sections. We found that geomorphologic controls (e.g., bedrock confinement vs. gravel wedge deposits) resulted in different distributions and metrics of hyporheic transport. Results of this study provide further evidence that hyporheic transport is highly variable both in space and through the baseflow recession period. Geophysical images differentiate advection-dominated flowpaths from those that are more affected by other transport processes (e.g., dispersion, mobile-immobile exchange).
Pulse exposure of cultured rat neurons to aluminum-maltol affected the axonal transport system.
Kashiwagi, Y; Nakamura, Y; Miyamae, Y; Hashimoto, R; Takeda, M
1998-08-01
Although chronic aluminum neurotoxicity has been well established, the mechanism of the toxicity has not been elucidated yet. In order to simplify the study of the aluminum neurotoxicity, we employed the pulse exposure of cultured rat cortical neurons to 250 microM aluminum-maltol for 1 h at the early stage (6 h after plating), which resulted in abnormal distribution of neurofilament L (NFL) and fast axonal transported proteins, whereas the axonal transport of tubulin, actin, and clathrin were not impaired. Otherwise, the pulse exposure of neurons at the late stage (4 days after plating) to the same concentration of aluminum-maltol did not affect the cell morphology and the distribution of NFL. The pulse exposure of cultured neurons to aluminum-maltol at the early stage might affect the axonal transport system of NFL and fast axonal transported proteins. PMID:9756345
Krügel, Undine; Veenhoff, Liesbeth M; Langbein, Jennifer; Wiederhold, Elena; Liesche, Johannes; Friedrich, Thomas; Grimm, Bernhard; Martinoia, Enrico; Poolman, Bert; Kühn, Christina
2008-09-01
The plant sucrose transporter SUT1 from Solanum tuberosum revealed a dramatic redox-dependent increase in sucrose transport activity when heterologously expressed in Saccharomyces cerevisiae. Plant plasma membrane vesicles do not show any change in proton flux across the plasma membrane in the presence of redox reagents, indicating a SUT1-specific effect of redox reagents. Redox-dependent sucrose transport activity was confirmed electrophysiologically in Xenopus laevis oocytes with SUT1 from maize (Zea mays). Localization studies of green fluorescent protein fusion constructs showed that an oxidative environment increased the targeting of SUT1 to the plasma membrane where the protein concentrates in 200- to 300-nm raft-like microdomains. Using plant plasma membranes, St SUT1 can be detected in the detergent-resistant membrane fraction. Importantly, in yeast and in plants, oxidative reagents induced a shift in the monomer to dimer equilibrium of the St SUT1 protein and increased the fraction of dimer. Biochemical methods confirmed the capacity of SUT1 to form a dimer in plants and yeast cells in a redox-dependent manner. Blue native PAGE, chemical cross-linking, and immunoprecipitation, as well as the analysis of transgenic plants with reduced expression of St SUT1, confirmed the dimerization of St SUT1 and Sl SUT1 (from Solanum lycopersicum) in planta. The ability to form homodimers in plant cells was analyzed by the split yellow fluorescent protein technique in transiently transformed tobacco (Nicotiana tabacum) leaves and protoplasts. Oligomerization seems to be cell type specific since under native-like conditions, a phloem-specific reduction of the dimeric form of the St SUT1 protein was detectable in SUT1 antisense plants, whereas constitutively inhibited antisense plants showed reduction only of the monomeric form. The role of redox control of sucrose transport in plants is discussed. PMID:18790827
Modeling solute transport in distribution networks with variable demand and time step sizes.
Peyton, Chad E.; Bilisoly, Roger Lee; Buchberger, Steven G.; McKenna, Sean Andrew; Yarrington, Lane
2004-06-01
The effect of variable demands at short time scales on the transport of a solute through a water distribution network has not previously been studied. We simulate flow and transport in a small water distribution network using EPANET to explore the effect of variable demand on solute transport across a range of hydraulic time step scales from 1 minute to 2 hours. We show that variable demands at short time scales can have the following effects: smoothing of a pulse of tracer injected into a distribution network and increasing the variability of both the transport pathway and transport timing through the network. Variable demands are simulated for these different time step sizes using a previously developed Poisson rectangular pulse (PRP) demand generator that considers demand at a node to be a combination of exponentially distributed arrival times with log-normally distributed intensities and durations. Solute is introduced at a tank and at three different network nodes and concentrations are modeled through the system using the Lagrangian transport scheme within EPANET. The transport equations within EPANET assume perfect mixing of the solute within a parcel of water and therefore physical dispersion cannot occur. However, variation in demands along the solute transport path contribute to both removal and distortion of the injected pulse. The model performance measures examined are the distribution of the Reynolds number, the variation in the center of mass of the solute across time, and the transport path and timing of the solute through the network. Variation in all three performance measures is greatest at the shortest time step sizes. As the scale of the time step increases, the variability in these performance measures decreases. The largest time steps produce results that are inconsistent with the results produced by the smaller time steps.
A transportronic solution to the problem of interorbital transportation
NASA Technical Reports Server (NTRS)
Brown, William C.
1992-01-01
An all-electronic transportation system described by the term 'transportronics' is examined as a means of solving the current problem of the high cost of transporting material from low-Earth orbit (LEO) to geostationary orbit (GEO). In this transportation system, low cost electric energy at the surface of the Earth is efficiently converted into microwave power which is then efficiently formed into a narrow beam which is kept incident upon the orbital transfer vehicles (OTV's) by electronic tracking. The incident beam is efficiently captured and converted into DC power by a device which has a very high ratio of DC power output to its mass. Because the mass of the electric thruster is also low, the resulting acceleration is unprecedented for electric-propelled vehicles. However, the performance of the system in terms of transit times from LEO to GEO is penalized by the short time of contact between the beam and the vehicle in low-Earth orbits. This makes it necessary to place the Earth based transmitters and the vehicles in the equatorial plane thus introducing many geopolitical factors. Technically, however, such a system as described in the report may out-perform any other approach to transportation in the LEO to GEO regime. The report describes and analyzes all portions of the beamed microwave power transmission system in considerable detail. An economic analysis of the operating and capital costs is made with the aid of a reference system capable of placing about 130,000 kilograms of payload into GEO each year. More mature states of the system are then examined, to a level in which 60,000 metric tons per year could be placed into GEO.
NASA Astrophysics Data System (ADS)
Hamamoto, S.; Arihara, M.; Kawamoto, K.; Nishimura, T.; Komatsu, T.; Moldrup, P.
2014-12-01
Subsurface warming driven by global warming, urban heat islands, and increasing use of shallow geothermal heating and cooling systems such as the ground source heat pump, potentially causes changes in subsurface mass transport. Therefore, understanding temperature dependency of the solute transport characteristics is essential to accurately assess environmental risks due to increased subsurface temperature. In this study, one-dimensional solute transport experiments were conducted in soil columns under temperature control to investigate effects of temperature on solute transport parameters, such as solute dispersion and diffusion coefficients, hydraulic conductivity, and retardation factor. Toyoura sand, Kaolin clay, and intact loamy soils were used in the experiments. Intact loamy soils were taken during a deep well boring at the Arakawa Lowland in Saitama Prefecture, Japan. In the transport experiments, the core sample with 5-cm diameter and 4-cm height was first isotropically consolidated, whereafter 0.01M KCl solution was injected to the sample from the bottom. The concentrations of K+ and Cl- in the effluents were analyzed by an ion chromatograph to obtain solute breakthrough curves. The solute transport parameters were calculated from the breakthrough curves. The experiments were conducted under different temperature conditions (15, 25, and 40 oC). The retardation factor for the intact loamy soils decreased with increasing temperature, while water permeability increased due to reduced viscosity of water at higher temperature. Opposite, the effect of temperature on solute dispersivity for the intact loamy soils was insignificant. The effects of soil texture on the temperature dependency of the solute transport characteristics will be further investigated from comparison of results from differently-textured samples.
Solute transport and retention in three-dimensional fracture networks
NASA Astrophysics Data System (ADS)
Cvetkovic, Vladimir; Frampton, Andrew
2012-02-01
Resolving the hydrodynamic control of retention is an important step in predictive modeling of transport of sorbing tracers in fractured rock. The statistics of the transport resistance parameter β [T/L] and the related effective active specific surface area sf [1/L] are studied in a crystalline rock volume on a 100 m scale. Groundwater flow and advective transport are based on generic boundary conditions and realistic discrete fracture networks inferred from the Laxemar site, southeast Sweden. The overall statistics of β are consistent with statistics of the water residence time τ; the moments of β vary linearly with distance, at least up to 100 m. The correlation between log τ and log β is predominantly linear, however, there is significant dispersion; the parameter sf strongly depends on the assumed hydraulic law (theoretical cubic or empirical quadratic). Fast and slow trajectories/segments in the network determine the shape of the β distribution that cannot be reproduced by infinitely divisible model over the entire range; the low value range and median can be reproduced reasonably well with the tempered one-sided stable density using the exponent in the range 0.35-0.7. The low percentiles of the β distribution seems to converge to a Fickian type of behavior from a 50 to 100 m scale.
Burnard, C L; Pitchford, W S; Hocking Edwards, J E; Hazel, S J
2015-08-01
An understanding of the perceived importance of a variety of factors affecting the ease of handling of sheep and the interactions between these factors is valuable in improving profitability and welfare of the livestock. Many factors may contribute to animal behaviour during handling, and traditionally these factors have been assessed in isolation under experimental conditions. A human social component to this phenomenon also exists. The aim of this study was to gain a deeper understanding of the importance of a variety of factors affecting ease of handling, and the interactions between these from the perspective of the livestock transporter. Qualitative interviews were used to investigate the factors affecting sheep behaviour during handling. Interview transcripts underwent thematic analysis. Livestock transporters discussed the effects of attitudes and behaviours towards sheep, helpers, facilities, distractions, environment, dogs and a variety of sheep factors including breed, preparation, experience and sex on sheep behaviour during handling. Transporters demonstrated care and empathy and stated that patience and experience were key factors determining how a person might deal with difficult sheep. Livestock transporters strongly believed facilities (ramps and yards) had the greatest impact, followed by sheep experience (naivety of the sheep to handling and transport) and breed. Transporters also discussed the effects of distractions, time of day, weather, dogs, other people, sheep preparation, body condition and sheep sex on ease of handling. The concept of individual sheep temperament was indirectly expressed. PMID:25874817
Coupling of hydrologic transport and chemical reactions in a stream affected by acid mine drainage
Kimball, B.A.; Broshears, R.E.; Bencala, K.E.; McKnight, Diane M.
1994-01-01
Experiments in St. Kevin Gulch, an acid mine drainage stream, examined the coupling of hydrologic transport to chemical reactions affecting metal concentrations. Injection of LiCl as a conservative tracer was used to determine discharge and residence time along a 1497-m reach. Transport of metals downstream from inflows of acidic, metal-rich water was evaluated based on synoptic samples of metal concentrations and the hydrologic characteristics of the stream. Transport of SO4 and Mn was generally conservative, but in the subreaches most affected by acidic inflows, transport was reactive. Both 0.1-??m filtered and particulate Fe were reactive over most of the stream reach. Filtered Al partitioned to the particulate phase in response to high instream concentrations. Simulations that accounted for the removal of SO4, Mn, Fe, and Al with first-order reactions reproduced the steady-state profiles. The calculated rate constants for net removal used in the simulations embody several processes that occur on a stream-reach scale. The comparison between rates of hydrologie transport and chemical reactions indicates that reactions are only important over short distances in the stream near the acidic inflows, where reactions occur on a comparable time scale with hydrologic transport and thus affect metal concentrations.
Fractional Advective-Dispersive Equation as a Model of Solute Transport in Porous Media
Technology Transfer Automated Retrieval System (TEKTRAN)
Understanding and modeling transport of solutes in porous media is a critical issue in the environmental protection. The common model is the advective-dispersive equation (ADE) describing the superposition of the advective transport and the Brownian motion in water-filled pore space. Deviations from...
Technology Transfer Automated Retrieval System (TEKTRAN)
The transport of solutes and colloids in porous media is influenced by a variety of physical and chemical nonequilibrium processes. A combined physical–chemical nonequilibrium (PCNE) model was therefore used to describe general mass transport. The model partitions the pore space into “mobile” and “i...
The Governor's Challenge: "Building a Stronger Virginia Today": Transportation Visions and Solutions
NASA Technical Reports Server (NTRS)
Baker, Susan
2008-01-01
Using STM(Science, Technology, Engineering, Math) education, this emerging workforce will have the chance to creatively solve one of Virginia's biggest challenges: TRANSPORTATION. - Students will be asked to develop alternative transportation systems for the state. This competition will enable teams to work with business mentors to design creative solutions for regional gridlocks and develop other transportation systems to more easily and expediently reach all parts of the Commonwealth.
NASA Astrophysics Data System (ADS)
Zhu, Yonghui; Zhan, Hongbin; Jin, Menggui
2016-08-01
This study deals with the problem of reactive solute transport in a fracture-matrix system using both analytical and numerical modeling methods. The groundwater flow velocity in the fracture is assumed to be high enough (no less than 0.1 m/day) to ensure the advection-dominant transport in the fracture. The problem includes advection along the fracture, transverse diffusion in the matrix, with linear sorption as well as first-order reactions operative in both the fracture and the matrix. A constant-concentration boundary condition and a decay source boundary condition in the fracture are considered. With a constant-concentration source, we obtain closed-form analytical solutions that account for the transport without reaction as well as steady-state solutions with different first-order reactions in the two media. With a decay source, a semi-analytical solution is obtained. The analytical and semi-analytical solutions are in excellent agreement with the numerical simulation results obtained using COMSOL Multiphysics. Sensitivity analysis is conducted to assess the relative importance of matrix diffusion coefficient, fracture aperture, and matrix porosity. We conclude that the first-order reaction as well as the matrix diffusion in the fractured rock would decrease the solute peak concentration and shorten the penetration distance into the fracture. The solutions can be applied to assess the spatial-temporal distribution of concentrations in the fracture and the matrix as well as to assess the contaminant mass stored in the rock matrix. All of these are useful for designing remediation plans for contaminated fractured rocks or for risk assessment of contaminated fracture-matrix systems.
Impact of biofilm-induced heterogeneities on solute transport in porous media
NASA Astrophysics Data System (ADS)
Kone, T.; Golfier, F.; Orgogozo, L.; Oltéan, C.; Lefèvre, E.; Block, J. C.; Buès, M. A.
2014-11-01
In subsurface systems, biofilm may degrade organic or organometallic pollutants contributing to natural attenuation and soil bioremediation techniques. This increase of microbial activity leads to change the hydrodynamic properties of aquifers. The purpose of this work was to investigate the influence of biofilm-induced heterogeneities on solute transport in porous media and more specifically on dispersivity. We pursued this goal by (i) monitoring both spatial concentration fields and solute breakthrough curves from conservative tracer experiments in a biofilm-supporting porous medium, (ii) characterizing in situ the changes in biovolume and visualizing the dynamics of the biological material at the mesoscale. A series of experiments was carried out in a flow cell system (60 cm3) with a silica sand (Φ = 50-70 mesh) as solid carrier and Shewanella oneidensis MR-1 as bacterial strain. Biofilm growth was monitored by image acquisition with a digital camera. The biofilm volume fraction was estimated through tracer experiments with the Blue Dextran macromolecule as in size-exclusion chromatography, leading to a fair picture of the biocolonization within the flow cell. Biofilm growth was achieved in the whole flow cell in 29 days and up to 50% of void space volume was plugged. The influence of biofilm maturation on porous medium transport properties was evaluated from tracer experiments using Brilliant Blue FCF. An experimental correlation was found between effective (i.e., nonbiocolonized) porosity and biofilm-affected dispersivity. Comparison with values given by the theoretical model of Taylor and Jaffé (1990b) yields a fair agreement.
The Mechanism of Field-Scale Solute Transport: An insight from Numerical Simulations
NASA Astrophysics Data System (ADS)
Russo, David
2014-05-01
Field-scale transport of conservative (chloride) and reactive (nitrate) solutes was analyzed by means of two different model processes for the local description of the transport. The first is the classical, one-region advection dispersion equation (ADE) model, while the second is the two-region, mobile-immobile (MIM) model. The analyses were performed by means of detailed three-dimensional (3-D), numerical simulations of the flow and the transport considering realistic features of the soil-water-plant-atmosphere system, pertinent to a turf field located in the Glil Yam site, Israel, irrigated with treated waste water (TWW). Simulated water content and concentration profiles were compared with available measurements of their counterparts. Results of the analyses suggest that the behavior of both the conservative and the reactive solutes in the Glil Yam site is quantified better when the transport on the local scale is modeled as a two-region, MIM model, than when a single-region, ADE model is used. Reconstruction of the shape of the measured solute concentration profiles using the MIM transport model, required relatively large immobile water content fraction and relatively small mass transfer coefficient. These results suggest that in the case of initially non-zero solute concentration profile (e.g., chloride and nitrate), the 3-D ADE transport model may significantly overestimate the groundwater contamination hazard posed by the solutes moving through the vadose zone, as compared with the 3-D MIM transport model, while the opposite is true in the case of initially zero solute concentration profile (e.g., carbamazepine). These findings stem from the combination of relatively large immobile water content fraction and relatively small mass transfer coefficient taken into account in the MIM transport model. In the first case, this combination forces a considerable portion of the solute mass to remain in the immobile region of the water-filled pores, while the opposite
General solution of a fractional diffusion-advection equation for solar cosmic-ray transport
NASA Astrophysics Data System (ADS)
Rocca, M. C.; Plastino, A. R.; Plastino, A.; Ferri, G. L.; de Paoli, A.
2016-04-01
In this effort we exactly solve the fractional diffusion-advection equation for solar cosmic-ray transport and give its general solution in terms of hypergeometric distributions. Numerical analysis of this equation shows that its solutions resemble power-laws.
Technology Transfer Automated Retrieval System (TEKTRAN)
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-w...
Technology Transfer Automated Retrieval System (TEKTRAN)
It has been reported that this model cannot take into account several important features of solute movement through soil. Recently, a new model has been suggested that results in a solute transport equation with fractional spatial derivatives, or FADE. We have assembled a database on published solu...
Solute transport through a pine-bark based substrate under saturated and unsaturated conditions
Technology Transfer Automated Retrieval System (TEKTRAN)
An understanding of how dissolved mineral nutrient ions (solutes) move through pine bark substrates during the application of irrigation water is vital to better understand nutrient transport and leaching from containerized crops during an irrigation event. However, current theories on solute transp...
Derivation of the macroscopic solute transport equation for homogeneous, saturated, porous media
Chu, S.Y.; Sposito, G.
1980-06-01
The macroscopic transport equation for a conservative solute in a homogeneous, water-saturated porous medium is derived on the basis of a rigorous cumulant expansion applied to the equation of mass balance. The essential physical conept underlying the derivation is that of a local volume-averaged solute velocity which fluctuates on a time scale that is orders of magnitude smaller than its autocorrelation time scale, which, in turn, is much smaller than the time scale of interest in a typical solute transport experiment. This clear separation of the scales is illustrated with representative data on solute transport in homogeneous, water-saturated soils and is employed to justify the truncation of an exact cumulant expansion of the divergence of the volume-averaged solute mass flux density. With the cumulant expansion terminated at first order in the ratio of the solute velocity autocorrelation time to the macroscopic solute transport time interval, an expression for the macroscopic solute mass flux density is produced which is the same as Fick's law extended to porous media. 26 references.
Reilly, Thomas E.; Franke, O. Lehn; Buxton, Herbert T.; Bennett, Gordon D.
1987-01-01
Analysis of solute transport in groundwater systems involves a complex, multi-discipline study that requires intensive and costly investigation. Groundwater contamination, particularly from point sources, has been growing in importance in recent years. This report examines the physical mechanisms of solute transport, advection and dispersion, and explains how they relate to one another and the scale of study. The approach uses a preliminary analysis prior to collection of new data to focus on the technical problems to be addressed and to direct the initial collection of new data if warranted. The field investigation (collection of new data) progresses in stages that use the new knowledge and understanding gained from the preceding data collection to aid in further data collection as the study proceeds. A major premise of the approach is that the foundation of any analysis is a detailed quantitative definition of: (1) the groundwater flow field in three dimensions, and (2) the distribution of solutes in the contaminant plume in three dimensions at one point in time, or preferably at more than features of the groundwater flow field, and is an important tool for analysis. However, the scale of analysis for solute transport studies is usually much finer than the scale of analysis for groundwater flow alone. Therefore, an increase in detail of the velocity field is needed to provide for accurate calculations of pathlines in three-dimensional heterogeneous groundwater systems. (Lantz-PTT)
Chen, Cheng; Lau, Boris L.; Gaillard, J.-F.; Packman, A.I.
2010-01-22
Deposition of colloidal particles is one of many processes that lead to the evolution of the structure of natural porous media in groundwater aquifers, oil reservoirs, and sediment beds. Understanding of the mechanisms and effects of this type of structural evolution has been limited by a lack of direct observations of pore structure. Here, synchrotron X-ray difference microtomography (XDMT) was used to resolve the temporal evolution of pore structure and the distribution of colloidal deposits within a granular porous medium. Column filtration experiments were performed to observe the deposition of relatively high concentrations of colloidal zirconia (200 mg/l of particles having diameter {approx}1 {micro}m) in a packed bed of glass beads (diameters 210-300 {micro}m). Noninvasive XDMT imaging of the pore structure was performed three separate times during each column experiment. The structural information observed at each time was used to define internal boundary conditions for three-dimensional lattice Boltzmann (LB) simulations that show how the evolving pore structure affects pore fluid flow and solute transport. While the total deposit mass increased continuously over time, colloid deposition was observed to be highly heterogeneous and local colloid detachment was observed at some locations in a low ionic strength medium. LB simulations indicated that particle accumulation greatly reduced the permeability of the porous medium while increasing the tortuosity. The colloidal deposits also increased the spatial variability in pore water velocities, leading to higher dispersion coefficients. Anomalous dispersion behavior was investigated by simulation at the scale of the experimental system: weak tailing was found in the clean bed case, and the extent of tailing greatly increased following colloid deposition because of the development of extensive no-flow regions. As a result of this coupling between pore fluid flow, colloid accumulation, and the pore geometry
An Evaluation of Conditioning Data for Solute Transport Prediction
Scheibe, Timothy D.; Chien, Yi-Ju
2003-03-01
The large and diverse body of subsurface characterization data generated at a field research site near Oyster, Virginia provides a unique opportunity to test the impact of conditioning data of various types on predictions of flow and transport. Bromide breakthrough curves (BTCs) were measured during a forced-gradient local-scale injection experiment conducted in 1999. Observed BTCs are available at 140 sampling points in a three dimensional array within the transport domain. A detailed three-dimensional numerical model is used to simulate breakthrough curves at the same locations as the observed BTCs under varying assumptions regarding the character of hydraulic conductivity spatial distributions, and variable amounts and types of conditioning data. We present comparative results of six different cases ranging from simple (deterministic homogeneous models) to complex (stochastic indicator simulation conditioned to cross-borehole geophysical observations). Quantitative measures of model goodness-of-fit are presented. The results show that conditioning to a large number of small-scale measurements does not significantly improve model predictions, and may lead to biased or overly confident predictions. However, conditioning to geophysical interpretations with larger spatial support significantly improves the accuracy and precision of model predictions. In all cases, the effects of model error appear to be significant in relation to parameter uncertainty.
Implicitly causality enforced solution of multidimensional transient photon transport equation.
Handapangoda, Chintha C; Premaratne, Malin
2009-12-21
A novel method for solving the multidimensional transient photon transport equation for laser pulse propagation in biological tissue is presented. A Laguerre expansion is used to represent the time dependency of the incident short pulse. Owing to the intrinsic causal nature of Laguerre functions, our technique automatically always preserve the causality constrains of the transient signal. This expansion of the radiance using a Laguerre basis transforms the transient photon transport equation to the steady state version. The resulting equations are solved using the discrete ordinates method, using a finite volume approach. Therefore, our method enables one to handle general anisotropic, inhomogeneous media using a single formulation but with an added degree of flexibility owing to the ability to invoke higher-order approximations of discrete ordinate quadrature sets. Therefore, compared with existing strategies, this method offers the advantage of representing the intensity with a high accuracy thus minimizing numerical dispersion and false propagation errors. The application of the method to one, two and three dimensional geometries is provided. PMID:20052050
Transport of water, solutes and nutrients from a pasture hillslope, southwestern Brazilian Amazon
NASA Astrophysics Data System (ADS)
Biggs, Trent Wade; Dunne, Thomas; Muraoka, Takashi
2006-08-01
A conceptual model of water and solute transport pathways was developed and applied to a pasture hillslope in the southwestern Brazilian Amazon basin using select field measurements. Infiltration-excess or Horton overland flow (HOF), saturation overland flow (SOF), and groundwater in both the near-stream zone and upslope were sampled on a hillslope draining a 3.9 hectare pasture for a total of ten storms during the first half of the rainy season (October-November) in 2002. A Soil Conservation Service SCS curve number model of HOF and an annual water balance of both upslope and near-stream zones were used to calculate the contribution of each flowpath to solute export. HOF occurred in rainstorms greater than 5 mm and accounted for 8% of annual rainfall. Flow generated in the near-stream zone was 8% of annual rainfall. Sub-surface flow from upslope groundwater dominated annual runoff (19-30% of annual rainfall). Solutes fell into three categories according to flowpath. HOF from upslope positions dominated the export of total phosphorus (TP) and total dissolved phosphorus (TDP, 51-72% of total annual export). The near-stream zones controlled the export of K (58-65%), total dissolved nitrogen (TDN, 76-80%), and total nitrogen (TN, 75%) owing to relatively high solute concentrations and the large volume of water that flowed through the near-stream zone. Na and Si export was via groundwater from upslope (50-67% of annual export). The flux calculations were based on a small number of storms and are preliminary estimates designed to identify broad patterns in solute export via different hydrologic pathways. Additional processes, especially N removal at the groundwater-stream interface and in the stream channel, may affect actual export rates at the watershed scale. Whereas HOF production is negligible in Amazon forests, it represents a significant pathway for additional loss of elements, especially phosphorus, from mature pasture systems. The evidence presented here shows
Effect of antidiuretic hormone on human small intestinal water and solute transport
Soergel, Konrad H.; Whalen, George E.; Harris, John A.; Geenen, Joseph E.
1968-01-01
The effect of i.v. Pitressin (ADH) in a dose of 1 U/hr on permeability characteristics and on absorptive capacity of the normal human small intestine was investigated. The method of continuous intestinal perfusion was employed with polyethylene glycol 4000 as a nonabsorbable marker. Unidirectional flux rates of Na and H2O were calculated from the disappearance of 22Na and of 3HOH from isotonic saline solution within the intestinal lumen. Each study consisted of two successive perfusion periods: one while the subject was hydrated, the other during ADH infusion or while the subject was dehydrated. Water and sodium absorption from isotonic NaCl occurred in the hydrated state and was abolished by ADH as well as by dehydration in the jejunum. In some instances, net gain of water and sodium in the lumen occurred. In the ileum, ADH and dehydration caused a decrease in water and sodium absorption rate. By contrast, unidirectional flux into the intestinal lumen of water and sodium, as well as dextrose and D-xylose diffusion, remained unchanged by ADH. During perfusions with hypertonic urea solutions the rates of sodium and water entry into the intestine were greatly increased during i.v. ADH infusion, whereas urea loss from the study segment remained constant. ADH in the dosage used did not affect human intestinal motility. The results suggest that circulating ADH in physiologic concentrations affects the small intestine in one of two ways: increased secretion of water and salt into the lumen or direct interference with the active sodium transport mechanism. PMID:5645853
Prolonged river water pollution due to variable-density flow and solute transport in the riverbed
NASA Astrophysics Data System (ADS)
Jin, Guangqiu; Tang, Hongwu; Li, Ling; Barry, D. A.
2015-04-01
A laboratory experiment and numerical modeling were used to examine effects of density gradients on hyporheic flow and solute transport under the condition of a solute pulse input to a river with regular bed forms. Relatively low-density gradients due to an initial salt pulse concentration of 1.55 kg m-3 applied in the experiment were found to modulate significantly the pore-water flow and solute transport in the riverbed. Such density gradients increased downward flow and solute transport in the riverbed by factors up to 1.6. This resulted in a 12.2% increase in the total salt transfer from the water column to the riverbed over the salt pulse period. As the solute pulse passed, the effect of the density gradients reversed, slowing down the release of the solute back to the river water by a factor of 3.7. Numerical modeling indicated that these density effects intensified as salt concentrations in the water column increased. Simulations further showed that the density gradients might even lead to unstable flow and result in solute fingers in the bed of large bed forms. The slow release of solute from the bed back to the river led to a long tail of solute concentration in the river water. These findings have implications for assessment of impact of pollution events on river systems, in particular, long-term effects on both the river water and riverbed due to the hyporheic exchange.
NASA Astrophysics Data System (ADS)
Zhao, Gang; Takamatsu, Hiroshi; He, Xiaoming
2014-04-01
A new model was developed to predict transmembrane water transport and diffusion-limited ice formation in cells during freezing without the ideal-solution assumption that has been used in previous models. The model was applied to predict cell dehydration and intracellular ice formation (IIF) during cryopreservation of mouse oocytes and bovine carotid artery endothelial cells in aqueous sodium chloride (NaCl) solution with glycerol as the cryoprotectant or cryoprotective agent. A comparison of the predictions between the present model and the previously reported models indicated that the ideal-solution assumption results in under-prediction of the amount of intracellular ice at slow cooling rates (<50 K/min). In addition, the lower critical cooling rates for IIF that is lethal to cells predicted by the present model were much lower than those estimated with the ideal-solution assumption. This study represents the first investigation on how accounting for solution nonideality in modeling water transport across the cell membrane could affect the prediction of diffusion-limited ice formation in biological cells during freezing. Future studies are warranted to look at other assumptions alongside nonideality to further develop the model as a useful tool for optimizing the protocol of cell cryopreservation for practical applications.
Zhao, Gang; Takamatsu, Hiroshi; He, Xiaoming
2014-01-01
A new model was developed to predict transmembrane water transport and diffusion-limited ice formation in cells during freezing without the ideal-solution assumption that has been used in previous models. The model was applied to predict cell dehydration and intracellular ice formation (IIF) during cryopreservation of mouse oocytes and bovine carotid artery endothelial cells in aqueous sodium chloride (NaCl) solution with glycerol as the cryoprotectant or cryoprotective agent. A comparison of the predictions between the present model and the previously reported models indicated that the ideal-solution assumption results in under-prediction of the amount of intracellular ice at slow cooling rates (<50 K/min). In addition, the lower critical cooling rates for IIF that is lethal to cells predicted by the present model were much lower than those estimated with the ideal-solution assumption. This study represents the first investigation on how accounting for solution nonideality in modeling water transport across the cell membrane could affect the prediction of diffusion-limited ice formation in biological cells during freezing. Future studies are warranted to look at other assumptions alongside nonideality to further develop the model as a useful tool for optimizing the protocol of cell cryopreservation for practical applications. PMID:25316951
NASA Astrophysics Data System (ADS)
Li, Weiyao; Huang, Guanhua; Xiong, Yunwu
2016-04-01
The complexity of the spatial structure of porous media, randomness of groundwater recharge and discharge (rainfall, runoff, etc.) has led to groundwater movement complexity, physical and chemical interaction between groundwater and porous media cause solute transport in the medium more complicated. An appropriate method to describe the complexity of features is essential when study on solute transport and conversion in porous media. Information entropy could measure uncertainty and disorder, therefore we attempted to investigate complexity, explore the contact between the information entropy and complexity of solute transport in heterogeneous porous media using information entropy theory. Based on Markov theory, two-dimensional stochastic field of hydraulic conductivity (K) was generated by transition probability. Flow and solute transport model were established under four conditions (instantaneous point source, continuous point source, instantaneous line source and continuous line source). The spatial and temporal complexity of solute transport process was characterized and evaluated using spatial moment and information entropy. Results indicated that the entropy increased as the increase of complexity of solute transport process. For the point source, the one-dimensional entropy of solute concentration increased at first and then decreased along X and Y directions. As time increased, entropy peak value basically unchanged, peak position migrated along the flow direction (X direction) and approximately coincided with the centroid position. With the increase of time, spatial variability and complexity of solute concentration increase, which result in the increases of the second-order spatial moment and the two-dimensional entropy. Information entropy of line source was higher than point source. Solute entropy obtained from continuous input was higher than instantaneous input. Due to the increase of average length of lithoface, media continuity increased, flow and
Addition of simultaneous heat and solute transport and variable fluid viscosity to SEAWAT
Thorne, D.; Langevin, C.D.; Sukop, M.C.
2006-01-01
SEAWAT is a finite-difference computer code designed to simulate coupled variable-density ground water flow and solute transport. This paper describes a new version of SEAWAT that adds the ability to simultaneously model energy and solute transport. This is necessary for simulating the transport of heat and salinity in coastal aquifers for example. This work extends the equation of state for fluid density to vary as a function of temperature and/or solute concentration. The program has also been modified to represent the effects of variable fluid viscosity as a function of temperature and/or concentration. The viscosity mechanism is verified against an analytical solution, and a test of temperature-dependent viscosity is provided. Finally, the classic Henry-Hilleke problem is solved with the new code. ?? 2006 Elsevier Ltd. All rights reserved.
CFEST Coupled Flow, Energy & Solute Transport Version CFEST005 Theory Guide
Freedman, Vicky L.; Chen, Yousu; Gupta, Sumant K.
2005-11-01
This document presents the mathematical theory implemented in the CFEST (Coupled Flow, Energy, and Solute Transport) simulator. The simulator is a three-dimensional finite element model that can be used for evaluating flow and solute mass transport. Although the theory for thermal transport is presented in this guide, it has not yet been fully implemented in the simulator. The flow module is capable of simulating both confined and unconfined aquifer systems, as well as constant and variable density fluid flows. For unconfined aquifers, the model uses a moving boundary for the water table, deforming the numerical mesh so that the uppermost nodes are always at the water table. For solute transport, changes in concentration of a single dissolved chemical constituent are computed for advective and hydrodynamic transport, linear sorption represented by a retardation factor, and radioactive decay. Once fully implemented, transport of thermal energy in the groundwater and solid matrix of the aquifer can also be used to model aquifer thermal regimes. Mesh construction employs “collapsible”, hexahedral finite elements in a three-dimensional coordinate system. CFEST uses the Galerkin finite element method to convert the partial differential equations to algebraic form. To solve the coupled equations for momentum, solute and heat transport, either Picard or Newton-Raphson iterative schemes are used to treat nonlinearities. An upstream weighted residual finite-element method is used to solve the advective-dispersive transport and energy transfer equations, which circumvents problems of numerical oscillation problems. Matrix solutions of the flow and transport problems are performed using efficient iterative solvers available in ITPACK and PETSc, solvers that are available in the public domain. These solvers are based on the preconditioned conjugate gradient and ORTHOMIN methods for symmetric and a nonsymmetric matrices, respectively.
D4Z - a new renumbering for iterative solution of ground-water flow and solute- transport equations
Kipp, K.L.; Russell, T.F.; Otto, J.S.
1992-01-01
D4 zig-zag (D4Z) is a new renumbering scheme for producing a reduced matrix to be solved by an incomplete LU preconditioned, restarted conjugate-gradient iterative solver. By renumbering alternate diagonals in a zig-zag fashion, a very low sensitivity of convergence rate to renumbering direction is obtained. For two demonstration problems involving groundwater flow and solute transport, iteration counts are related to condition numbers and spectra of the reduced matrices.
NASA Astrophysics Data System (ADS)
Seggewiss, G.; Dickson, S. E.
2013-12-01
Groundwater is becoming an increasingly important water source due to the ever-increasing demands from agricultural, residential and industrial consumers. In search of more secure sources, wells are routinely finished over large vertical depths in bedrock aquifers, creating new hydraulic pathways and thus increasing the risk of cross contamination. Moreover, hydraulic pathways are also being altered and created by increasing water withdrawal rates from these wells. Currently, it is not well understood how biological contaminants are transported through, and retained in, fractured media thereby making risk assessment and land use decisions difficult. Colloid transport within fractured rock is a complex process with several mechanisms affecting transport and retention, including: advection, hydrodynamic dispersion, diffusion, size exclusion, adsorption, and decay. Several researchers have investigated the transport of bacteria, bacteriophage, and microspheres (both carboxylated and plain) to evaluate the effects of surface properties and size on transport and retention. These studies have suggested that transport is highly dependent on the physico-chemical properties of the particle, the fracture, and the carrying fluid. However, these studies contain little detail regarding the specific mechanisms responsible for transport beyond speculating about their existence. Further, little work has been done to compare the transport of these particulate materials through the same fracture, allowing for direct observations based on particulate size and surface properties. This research examines the similarities and differences in transport and retention between four different particles through two different laboratory-scale, saturated fractures. This work is designed to explore the effects of particle size, surface properties, ionic strength of the carrying solution, and aperture field characteristics on transport and retention in single, saturated fractures. The particulates
Flow dynamics and solute transport in unsaturated rock fractures
Su, G. W.
1999-10-01
Rock fractures play an important role in flow and contaminant transport in fractured aquifers, production of oil from petroleum reservoirs, and steam generation from geothermal reservoirs. In this dissertation, phenomenological aspects of flow in unsaturated fractures were studied in visualization experiments conducted on a transparent replica of a natural, rough-walled rock fracture for inlet conditions of constant pressure and flow rate over a range of angles of inclination. The experiments demonstrated that infiltrating liquid proceeds through unsaturated rock fractures along non-uniform, localized preferential flow paths. Even in the presence of constant boundary conditions, intermittent flow was a persistent flow feature observed, where portions of the flow channel underwent cycles of snapping and reforming. Two modes of intermittent flow were observed, the pulsating blob mode and the rivulet snapping mode. A conceptual model for the rivulet snapping mode was proposed and examined using idealized, variable-aperture fractures. The frequency of intermittent flow events was measured in several experiments and related to the capillary and Bond numbers to characterize this flow behavior.
Molecular cell biology and physiology of solute transport
Caplan, Michael J.; Seo-Mayer, Patricia; Zhang, Li
2010-01-01
Purpose of review An enormous body of research has been focused on exploring the mechanisms through which epithelial cells establish their characteristic polarity. It is clear that under normal circumstances cell–cell contacts mediated by the calcium-dependent adhesion proteins of the intercellular adhesion junctions are required to initiate complete polarization. Furthermore, formation of the tight, or occluding, junctions that limit paracellular permeability has long been thought to help to establish polarity by preventing the diffusion of membrane proteins between the two plasmalemmal domains. This review will discuss several selected kinases and protein complexes and highlight their relevance to transporting epithelial cell polarization. Recent findings Recent work has shed new light on the roles of junctional complexes in establishing and maintaining epithelial cell polarity. In addition, work from several laboratories, suggests that the formation of these junctions is tied to processes that regulate cellular energy metabolism. Summary Junctional complexes and energy sensing kinases constitute a novel class of machinery whose capacity to generate and modulate epithelial cell polarity is likely to have wide ranging and important physiological ramifications. PMID:18695392
Stochastic models of solute transport in highly heterogeneous geologic media
Semenov, V.N.; Korotkin, I.A.; Pruess, K.; Goloviznin, V.M.; Sorokovikova, O.S.
2009-09-15
A stochastic model of anomalous diffusion was developed in which transport occurs by random motion of Brownian particles, described by distribution functions of random displacements with heavy (power-law) tails. One variant of an effective algorithm for random function generation with a power-law asymptotic and arbitrary factor of asymmetry is proposed that is based on the Gnedenko-Levy limit theorem and makes it possible to reproduce all known Levy {alpha}-stable fractal processes. A two-dimensional stochastic random walk algorithm has been developed that approximates anomalous diffusion with streamline-dependent and space-dependent parameters. The motivation for introducing such a type of dispersion model is the observed fact that tracers in natural aquifers spread at different super-Fickian rates in different directions. For this and other important cases, stochastic random walk models are the only known way to solve the so-called multiscaling fractional order diffusion equation with space-dependent parameters. Some comparisons of model results and field experiments are presented.
Solute Transport in Eroded and Rehabilitated Prairie Landforms. 2. Reactive Solute
Technology Transfer Automated Retrieval System (TEKTRAN)
Information regarding the impact of varying soil, landscape, and climate conditions on the off-site transport of pesticides is critical to the development of improved pesticide management practices. We quantified the rate of S-metolachlor dissipation after fall and spring application in eroded and r...
Automodel solutions for Lévy flight-based transport on a uniform background
NASA Astrophysics Data System (ADS)
Kukushkin, A. B.; Sdvizhenskii, P. A.
2016-06-01
A wide class of non-stationary superdiffusive transport on a uniform background with a power-law decay at large distances of the step-length probability distribution function (PDF) is shown to possess an approximate automodel solution. The solution for the Green’s function is constructed using the scaling laws for the propagation front (relevant-to-superdiffusion average displacement) and asymptotic solutions far beyond and far in advance of the propagation front. These scaling laws are determined essentially by the long-free-path carriers (Lévy flights). The validity of the suggested automodel solution is proved by its comparison with numerical solutions in the one-dimensional (1D) case of the transport equation with a simple long-tailed PDF with various power-law exponents and in the 3D case of the Biberman–Holstein equation of the resonance radiation transfer for various (Doppler, Lorentz, Voigt and Holtsmark) spectral line shapes.
Mackenzie, S M; Brooker, M R; Gill, T R; Cox, G B; Howells, A J; Ewart, G D
1999-07-15
The white, brown and scarlet genes of Drosophila melanogaster encode proteins which transport guanine or tryptophan (precursors of the red and brown eye colour pigments) and belong to the ABC transporter superfamily. Current models envisage that the white and brown gene products interact to form a guanine specific transporter, while white and scarlet gene products interact to form a tryptophan transporter. In this study, we report the nucleotide sequence of the coding regions of five white alleles isolated from flies with partially pigmented eyes. In all cases, single amino acid changes were identified, highlighting residues with roles in structure and/or function of the transporters. Mutations in w(cf) (G589E) and w(sat) (F590G) occur at the extracellular end of predicted transmembrane helix 5 and correlate with a major decrease in red pigments in the eyes, while brown pigments are near wild-type levels. Therefore, those residues have a more significant role in the guanine transporter than the tryptophan transporter. Mutations identified in w(crr) (H298N) and w(101) (G243S) affect amino acids which are highly conserved among the ABC transporter superfamily within the nucleotide binding domain. Both cause substantial and similar decreases of red and brown pigments indicating that both tryptophan and guanine transport are impaired. The mutation identified in w(Et87) alters an amino acid within an intracellular loop between transmembrane helices 2 and 3 of the predicted structure. Red and brown pigments are reduced to very low levels by this mutation indicating this loop region is important for the function of both guanine and tryptophan transporters. PMID:10407069
NASA Technical Reports Server (NTRS)
Gatsonis, Nikos A.; Alexandrou, Andreas; Shi, Hui; Ongewe, Bernard; Sacco, Albert, Jr.
1999-01-01
Crystals grown from liquid solutions have important industrial applications. Zeolites, for instance, a class of crystalline aluminosilicate materials, form the backbone of the chemical process industry worldwide, as they are used as adsorbents and catalysts. Many of the phenomena associated with crystal growth processes are not well understood due to complex microscopic and macroscopic interactions. Microgravity could help elucidate these phenomena and allow the control of defect locations, concentration, as well as size of crystals. Microgravity in an orbiting spacecraft could help isolate the possible effects of natural convection (which affects defect formation) and minimize sedimentation. In addition, crystals will stay essentially suspended in the nutrient pool under a diffusion-limited growth condition. This is expected to promote larger crystals by allowing a longer residence time in a high-concentration nutrient field. Among other factors, the crystal size distribution depends on the nucleation rate and crystallization. These two are also related to the "gel" polymerization/depolymerization rate. Macroscopic bulk mass and flow transport and especially gravity, force the crystals down to the bottom of the reactor, thus forming a sedimentation layer. In this layer, the growth rate of the crystals slows down as crystals compete for a limited amount of nutrients. The macroscopic transport phenomena under certain conditions can, however, enhance the nutrient supply and therefore, accelerate crystal growth. Several zeolite experiments have been performed in space with mixed results. The results from our laboratory have indicated an enhancement in size of 30 to 70 percent compared to the best ground based controls, and a reduction of lattice defects in many of the space grown crystals. Such experiments are difficult to interpret, and cannot be easily used to derive empirical or other laws since many physical parameters are simultaneously involved in the process
An implicit dispersive transport algorithm for the US Geological Survey MOC3D solute-transport model
Kipp, K.L., Jr.; Konikow, L.F.; Hornberger, G.Z.
1998-01-01
This report documents an extension to the U.S. Geological Survey MOC3D transport model that incorporates an implicit-in-time difference approximation for the dispersive transport equation, including source/sink terms. The original MOC3D transport model (Version 1) uses the method of characteristics to solve the transport equation on the basis of the velocity field. The original MOC3D solution algorithm incorporates particle tracking to represent advective processes and an explicit finite-difference formulation to calculate dispersive fluxes. The new implicit procedure eliminates several stability criteria required for the previous explicit formulation. This allows much larger transport time increments to be used in dispersion-dominated problems. The decoupling of advective and dispersive transport in MOC3D, however, is unchanged. With the implicit extension, the MOC3D model is upgraded to Version 2. A description of the numerical method of the implicit dispersion calculation, the data-input requirements and output options, and the results of simulator testing and evaluation are presented. Version 2 of MOC3D was evaluated for the same set of problems used for verification of Version 1. These test results indicate that the implicit calculation of Version 2 matches the accuracy of Version 1, yet is more efficient than the explicit calculation for transport problems that are characterized by a grid Peclet number less than about 1.0.
Op Den Buijs, Jorn; Lu, Lichun; Jorgensen, Steven M.; Dragomir-Daescu, Dan; Yaszemski, Michael J.
2009-01-01
The objective of this study was to investigate the influence of pore geometry on the transport rate and depth after repetitive mechanical deformation of porous scaffolds for tissue engineering applications. Flexible cubic imaging phantoms with pores in the shape of a circular cylinder, elliptic cylinder, and spheroid were fabricated from a biodegradable polymer blend using a combined 3D printing and injection molding technique. The specimens were immersed in fluid and loaded with a solution of a radiopaque solute. The solute distribution was quantified by recording 20 μm pixel-resolution images in an X-ray microimaging scanner at selected time points after intervals of dynamic straining with a mean strain of 8.6 ± 1.6% at 1.0 Hz. The results show that application of cyclic strain significantly increases the rate and depth of solute transport, as compared to diffusive transport alone, for all pore shapes. In addition, pore shape, pore size, and the orientation of the pore cross-sectional asymmetry with respect to the direction of strain greatly influence solute transport. Thus, pore geometry can be tailored to increase transport rates and depths in cyclically deformed scaffolds, which is of utmost importance when thick, metabolically functional tissues are to be engineered. PMID:19196145
Bolshov, L.; Kondratenko, P.; Matveev, L.; Pruess, K.
2008-09-01
In this study, new elements were developed to generalize the dual-porosity model for moisture infiltration on and solute transport in unsaturated rocks, taking into account fractal aspects of the percolation process. Random advection was considered as a basic mechanism of solute transport in self-similar fracture systems. In addition to spatial variations in the infiltration velocity field, temporal fluctuations were also taken into account. The rock matrix, a low-permeability component of the heterogeneous geologic medium, acts as a trap for solute particles and moisture. Scaling relations were derived for the moisture infiltration flux, the velocity correlation length, the average velocity of infiltration, and the velocity correlation function. The effect of temporal variations in precipitation intensity on the infiltration processes was analyzed. It showed that the mode of solute transport is determined by the power exponent in the advection velocity correlation function and the dimensionality of the trapping system, both of which may change with time. Therefore, depending on time, various transport regimes may be realized: superdiffusion, subdiffusion, or classical diffusion. The complex structure of breakthrough curves from changes in the transport regimes was also examined. A renormalization of the solute source strength due to characteristic fluctuations of highly disordered media was established.
A finite-volume ELLAM for three-dimensional solute-transport modeling
Russell, T.F.; Heberton, C.I.; Konikow, L.F.; Hornberger, G.Z.
2003-01-01
A three-dimensional finite-volume ELLAM method has been developed, tested, and successfully implemented as part of the U.S. Geological Survey (USGS) MODFLOW-2000 ground water modeling package. It is included as a solver option for the Ground Water Transport process. The FVELLAM uses space-time finite volumes oriented along the streamlines of the flow field to solve an integral form of the solute-transport equation, thus combining local and global mass conservation with the advantages of Eulerian-Lagrangian characteristic methods. The USGS FVELLAM code simulates solute transport in flowing ground water for a single dissolved solute constituent and represents the processes of advective transport, hydrodynamic dispersion, mixing from fluid sources, retardation, and decay. Implicit time discretization of the dispersive and source/sink terms is combined with a Lagrangian treatment of advection, in which forward tracking moves mass to the new time level, distributing mass among destination cells using approximate indicator functions. This allows the use of large transport time increments (large Courant numbers) with accurate results, even for advection-dominated systems (large Peclet numbers). Four test cases, including comparisons with analytical solutions and benchmarking against other numerical codes, are presented that indicate that the FVELLAM can usually yield excellent results, even if relatively few transport time steps are used, although the quality of the results is problem-dependent.
Reactive solute transport in streams. 1. Development of an equilibrium- based model
Runkel, R.L.; Bencala, K.E.; Broshears, R.E.; Chapra, S.C.
1996-01-01
An equilibrium-based solute transport model is developed for the simulation of trace metal fate and transport in streams. The model is formed by coupling a solute transport model with a chemical equilibrium submodel based on MINTEQ. The solute transport model considers the physical processes of advection, dispersion, lateral inflow, and transient storage, while the equilibrium submodel considers the speciation and complexation of aqueous species, precipitation/dissolution and sorption. Within the model, reactions in the water column may result in the formation of solid phases (precipitates and sorbed species) that are subject to downstream transport and settling processes. Solid phases on the streambed may also interact with the water column through dissolution and sorption/desorption reactions. Consideration of both mobile (water-borne) and immobile (streambed) solid phases requires a unique set of governing differential equations and solution techniques that are developed herein. The partial differential equations describing physical transport and the algebraic equations describing chemical equilibria are coupled using the sequential iteration approach.
Analytically-derived sensitivities in one-dimensional models of solute transport in porous media
Knopman, D.S.
1987-01-01
Analytically-derived sensitivities are presented for parameters in one-dimensional models of solute transport in porous media. Sensitivities were derived by direct differentiation of closed form solutions for each of the odel, and by a time integral method for two of the models. Models are based on the advection-dispersion equation and include adsorption and first-order chemical decay. Boundary conditions considered are: a constant step input of solute, constant flux input of solute, and exponentially decaying input of solute at the upstream boundary. A zero flux is assumed at the downstream boundary. Initial conditions include a constant and spatially varying distribution of solute. One model simulates the mixing of solute in an observation well from individual layers in a multilayer aquifer system. Computer programs produce output files compatible with graphics software in which sensitivities are plotted as a function of either time or space. (USGS)
Pore connectivity effects on solute transport in rocks
Hu, Qinhong; Ewing, Robert P.
2001-11-30
Retardation of nuclear contaminants in rock matrices can lead to long retention times, allowing substantial radionuclide decay prior to eventual release. Imbibition and diffusion into the rock matrix can move contaminants away from an active fracture, thereby contributing to their retardation. However, diffusive transport in some rocks may behave anomalously because of their sparsely connected porespace, in contrast to diffusion in rocks with denser pore connections. We examined imbibition of weakly sorbing tracers into welded tuff and Indiana sandstone, and water imbibition into metagraywacke and Berea sandstone. Tuff samples were initially equilibrated to 12% and 76% water (v/v) within controlled humidity chambers, while the other rocks were air-dried. For imbibition, one face was exposed to water, with or without tracer, and uptake was measured over time. Following imbibition, tracer concentration measurements were made at fine (1 mm) increments. Three anomalous results were observed: (1) Indiana sandstone and metagraywacke showed mass of imbibed water scaling as time{sup 0.26}, while tuff and Berea sandstone showed the more classical scaling with time{sup 0.5}; (2) tracer movement into dry (2% initial saturation) Indiana sandstone showed a dispersion pattern similar to that expected during tracer movement into moist (76% initial saturation) tuff; and (3) tracer concentrations at the inlet face of the tuff sample were approximately twice those deeper inside the sample. The experiment was then modeled using random walk methods on a 3-D lattice with different values of pore coordination. Network model simulations that used a pore coordination of 1.49 for Indiana sandstone and 1.56 for metagraywacke showed similar temporal scaling, a result of their porespace being close to the percolation threshold. Tracer concentration profiles in Indiana sandstone and tuff were closely matched by simulations that used pore coordinations of 1.49 and 1.68, respectively, because of
NASA Astrophysics Data System (ADS)
Faghaninia, Alireza; Ager, Joel W.; Lo, Cynthia S.
2015-06-01
Accurate models of carrier transport are essential for describing the electronic properties of semiconductor materials. To the best of our knowledge, the current models following the framework of the Boltzmann transport equation (BTE) either rely heavily on experimental data (i.e., semiempirical), or utilize simplifying assumptions, such as the constant relaxation time approximation (BTE-cRTA). While these models offer valuable physical insights and accurate calculations of transport properties in some cases, they often lack sufficient accuracy—particularly in capturing the correct trends with temperature and carrier concentration. We present here a transport model for calculating low-field electrical drift mobility and Seebeck coefficient of n -type semiconductors, by explicitly considering relevant physical phenomena (i.e., elastic and inelastic scattering mechanisms). We first rewrite expressions for the rates of elastic scattering mechanisms, in terms of ab initio properties, such as the band structure, density of states, and polar optical phonon frequency. We then solve the linear BTE to obtain the perturbation to the electron distribution—resulting from the dominant scattering mechanisms—and use this to calculate the overall mobility and Seebeck coefficient. Therefore, we have developed an ab initio model for calculating mobility and Seebeck coefficient using the Boltzmann transport (aMoBT) equation. Using aMoBT, we accurately calculate electrical transport properties of the compound n -type semiconductors, GaAs and InN, over various ranges of temperature and carrier concentration. aMoBT is fully predictive and provides high accuracy when compared to experimental measurements on both GaAs and InN, and vastly outperforms both semiempirical models and the BTE-cRTA. Therefore, we assert that this approach represents a first step towards a fully ab initio carrier transport model that is valid in all compound semiconductors.
Explicit solutions of the radiative transport equation in the P{sub 3} approximation
Liemert, André Kienle, Alwin
2014-11-01
Purpose: Explicit solutions of the monoenergetic radiative transport equation in the P{sub 3} approximation have been derived which can be evaluated with nearly the same computational effort as needed for solving the standard diffusion equation (DE). In detail, the authors considered the important case of a semi-infinite medium which is illuminated by a collimated beam of light. Methods: A combination of the classic spherical harmonics method and the recently developed method of rotated reference frames is used for solving the P{sub 3} equations in closed form. Results: The derived solutions are illustrated and compared to exact solutions of the radiative transport equation obtained via the Monte Carlo (MC) method as well as with other approximated analytical solutions. It is shown that for the considered cases which are relevant for biomedical optics applications, the P{sub 3} approximation is close to the exact solution of the radiative transport equation. Conclusions: The authors derived exact analytical solutions of the P{sub 3} equations under consideration of boundary conditions for defining a semi-infinite medium. The good agreement to Monte Carlo simulations in the investigated domains, for example, in the steady-state and time domains, as well as the short evaluation time needed suggests that the derived equations can replace the often applied solutions of the diffusion equation for the homogeneous semi-infinite medium.
Solute Transport in Eroded and Rehabilitated Prairie Landforms. 1. Nonreactive Solute
Technology Transfer Automated Retrieval System (TEKTRAN)
Cultivated North American prairie landscapes are often affected by soil erosion. Soil-landscape rehabilitation, in which topsoil is moved from areas of net deposition (lower slope) to areas of net soil loss by erosion (upper slope), can increase uniformity in soil properties across the landform and ...
Analytical solutions of a fractional diffusion-advection equation for solar cosmic-ray transport
Litvinenko, Yuri E.; Effenberger, Frederic
2014-12-01
Motivated by recent applications of superdiffusive transport models to shock-accelerated particle distributions in the heliosphere, we analytically solve a one-dimensional fractional diffusion-advection equation for the particle density. We derive an exact Fourier transform solution, simplify it in a weak diffusion approximation, and compare the new solution with previously available analytical results and with a semi-numerical solution based on a Fourier series expansion. We apply the results to the problem of describing the transport of energetic particles, accelerated at a traveling heliospheric shock. Our analysis shows that significant errors may result from assuming an infinite initial distance between the shock and the observer. We argue that the shock travel time should be a parameter of a realistic superdiffusive transport model.
Using a derivative-free optimization method for multiple solutions of inverse transport problems
Armstrong, Jerawan C.; Favorite, Jeffrey A.
2016-01-14
Identifying unknown components of an object that emits radiation is an important problem for national and global security. Radiation signatures measured from an object of interest can be used to infer object parameter values that are not known. This problem is called an inverse transport problem. An inverse transport problem may have multiple solutions and the most widely used approach for its solution is an iterative optimization method. This paper proposes a stochastic derivative-free global optimization algorithm to find multiple solutions of inverse transport problems. The algorithm is an extension of a multilevel single linkage (MLSL) method where a meshmore » adaptive direct search (MADS) algorithm is incorporated into the local phase. Furthermore, numerical test cases using uncollided fluxes of discrete gamma-ray lines are presented to show the performance of this new algorithm.« less
Analytical Solutions of a Fractional Diffusion-advection Equation for Solar Cosmic-Ray Transport
NASA Astrophysics Data System (ADS)
Litvinenko, Yuri E.; Effenberger, Frederic
2014-12-01
Motivated by recent applications of superdiffusive transport models to shock-accelerated particle distributions in the heliosphere, we analytically solve a one-dimensional fractional diffusion-advection equation for the particle density. We derive an exact Fourier transform solution, simplify it in a weak diffusion approximation, and compare the new solution with previously available analytical results and with a semi-numerical solution based on a Fourier series expansion. We apply the results to the problem of describing the transport of energetic particles, accelerated at a traveling heliospheric shock. Our analysis shows that significant errors may result from assuming an infinite initial distance between the shock and the observer. We argue that the shock travel time should be a parameter of a realistic superdiffusive transport model.
Darrah, P. R.; Tlalka, M.; Ashford, A.; Watkinson, S. C.; Fricker, M. D.
2006-01-01
Mycelial fungi have a growth form which is unique among multicellular organisms. The data presented here suggest that they have developed a unique solution to internal solute translocation involving a complex, extended vacuole. In all filamentous fungi examined, this extended vacuole forms an interconnected network, dynamically linked by tubules, which has been hypothesized to act as an internal distribution system. We have tested this hypothesis directly by quantifying solute movement within the organelle by photobleaching a fluorescent vacuolar marker. Predictive simulation models were then used to determine the transport characteristics over extended length scales. This modeling showed that the vacuolar organelle forms a functionally important, bidirectional diffusive transport pathway over distances of millimeters to centimeters. Flux through the pathway is regulated by the dynamic tubular connections involving homotypic fusion and fission. There is also a strongly predicted interaction among vacuolar organization, predicted diffusion transport distances, and the architecture of the branching colony margin. PMID:16835455
Technology Transfer Automated Retrieval System (TEKTRAN)
Transport equations governing the movement of multiple solutes undergoing sequential first-order decay reactions have relevance in analyzing a variety of subsurface contaminant transport problems. In this study, a one-dimensional analytical solution for multi-species transport is obtained for finite...
Nutrition of the intervertebral disc: effect of fluid flow on solute transport
Urban, J.P.; Holm, S.; Maroudas, A.; Nachemson, A.
1982-10-01
Adult dogs were injected intravenously with /sup 35/S-sulphate, and moderately exercised for one to six hours to measure isotope concentrations and profiles throughout the intervertebral discs. The isotope profiles were also observed in control animals that had been under anesthesia between injections and death. In both sets of animals, the profiles were in agreement with those expected for isotope transport by diffusion. This agreement indicates that fluid pumping during movement has an insignificant effect on transport of nutrients into the disc. Small solutes, e.g., O/sub 2/, glucose, and sulphate, are transported into the disc chiefly by diffusion. However, calculations show that because of their low diffusivities, pumping may increase the rate of transport of large solutes into the disc, as it does in articular cartilage.
Rockhold, M L
1993-02-01
A field-scale, unsaturated flow and solute transport experiment at the Las Cruces trench site in New Mexico was simulated as part of a blind'' modeling exercise to demonstrate the ability or inability of uncalibrated models to predict unsaturated flow and solute transport in spatially variable porous media. Simulations were conducted using a recently developed multiphase flow and transport simulator. Uniform and heterogeneous soil models were tested, and data from a previous experiment at the site were used with an inverse procedure to estimate water retention parameters. A spatial moment analysis was used to provide a quantitative basis for comparing the mean observed and simulated flow and transport behavior. The results of this study suggest that defensible predictions of waste migration and fate at low-level waste sites will ultimately require site-specific data for model calibration.
dela Peña, Ike; Gevorkiana, Ruzanna; Shi, Wei-Xing
2015-10-01
The precise mechanisms by which cocaine and amphetamine-like psychostimulants exert their reinforcing effects are not yet fully defined. It is widely believed, however, that these drugs produce their effects by enhancing dopamine neurotransmission in the brain, especially in limbic areas such as the nucleus accumbens, by inducing dopamine transporter-mediated reverse transport and/or blocking dopamine reuptake though the dopamine transporter. Here, we present the evidence that aside from dopamine transporter, non-dopamine transporter-mediated mechanisms also participate in psychostimulant-induced dopamine release and contribute to the behavioral effects of these drugs, such as locomotor activation and reward. Accordingly, psychostimulants could increase norepinephrine release in the prefrontal cortex, the latter then alters the firing pattern of dopamine neurons resulting in changes in action potential-dependent dopamine release. These alterations would further affect the temporal pattern of dopamine release in the nucleus accumbens, thereby modifying information processing in that area. Hence, a synaptic input to a nucleus accumbens neuron may be enhanced or inhibited by dopamine depending on its temporal relationship to dopamine release. Specific temporal patterns of dopamine release may also be required for certain forms of synaptic plasticity in the nucleus accumbens. Together, these effects induced by psychostimulants, mediated through a non-dopamine transporter-mediated mechanism involving norepinephrine and the prefrontal cortex, may also contribute importantly to the reinforcing properties of these drugs. PMID:26209364
NASA Astrophysics Data System (ADS)
Bobo, A. M.; Boufadel, M. C.; Abdollahi Nasab, A.
2009-12-01
We investigated beach hydraulics in a gravel beach on Eleanor Island, Prince William Sound, Alaska that was previously polluted with the Exxon Valdez oil spill in 1989. The beach contains trace amounts of oil such that they don’t affect beach hydraulics. Measurements of water pressure and salinity were analyzed and simulated using the model SUTRA (Saturated-Unsaturated Groundwater Flow and Solute Transport). The results indicated that the beach consists of two layers with contrasting hydraulic properties: an upper layer with a hydraulic conductivity of 10-2 m/s, and a lower layer with a hydraulic conductivity of 10-5 m/s. The presence of the layer of low hydraulic conductivity constrained the fall of the water table resulting in a water table fluctuation that is almost independent of distance from the shoreline. This is unlike previous studies, which occurred in sandy beaches, and where the fluctuation decreased going landward. The water table remained above the layers’ interface, which suggests that the oil did not penetrate the lower layer. This could explain the presence of only tracer amount of oil in the beach. A sudden seaward increase of the slope of the two layers’ interface resulted in water leaving the lower layer near the mid-intertidal zone, and draining to the sea through the upper layer. This created the effect of a hydraulic rupture separating the hydraulics in the seaward portion of the beach from the rest of beach, especially at low tide.
NASA Astrophysics Data System (ADS)
Laine-Kaulio, Hanne; Backnäs, Soile; Karvonen, Tuomo; Koivusalo, Harri; McDonnell, Jeffrey J.
2014-10-01
Preferential flow dominates water movement and solute transport in boreal forest hillslopes. However, only a few model applications to date have accounted for preferential flow at forest sites. Here we present a parallel and coupled simulation of flow and transport processes in the preferential flow domain and soil matrix of a forested hillslope section in Kangaslampi, Finland, using a new, three-dimensional, physically based dual-permeability model. Our aim is to simulate lateral subsurface stormflow and solute transport at the slope during a chloride tracer experiment, and to investigate the role of preferential flow in the tracer transport. The model was able to mimic the observed tracer transport during tracer irrigation, but overestimated the dilution velocity of the tracer plume in the highly conductive soil horizons near the soil surface after changing the irrigation to tracer-free water. According to the model, 140 times more chloride was transported downslope in the preferential flow domain than in the soil matrix during the tracer irrigation. The simulations showed, together with reference simulations with a traditional one pore domain model, that a two pore domain approach was required to simulate the observed flow and transport event. The event was characterized by the transmissivity feedback phenomenon and controlled by preferential flow mechanisms, in particular by lateral by-pass flow. According to our results, accounting for the slow-flow and fast-flow domains of soil, as well as the water and solute exchange between the domains, is essential for a successful simulation of flow and solute transport in preferential flow dominated hillslopes.
NASA Astrophysics Data System (ADS)
Vajda, A.; Tuomenvirta, H.; Jokinen, P.; Luomaranta, A.; Makkonen, L.; Tikanmäki, M.; Groenemeijer, P.; Saarikivi, P.; Michaelides, S.; Papadakis, M.; Tymvios, F.; Athanasatos, S.
2012-04-01
This paper provides the first comprehensive climatology of the adverse and extreme weather events affecting the European transport system by estimating the frequency (or probability) of phenomena for the present climate (1971-2000) and an overview of the projected changes in some of these extremes in the future climate until the 2050s. The research was carried out within the framework of the EWENT Project that addresses the European Union (EU) policies and strategies related to climate change, with a particular focus on extreme weather impacts on the EU transportation system. This project is funded by the Seventh Framework Programme (Transports, call ID FPT7-TPT-2008-RTD-1). The analyzed phenomena are wind, snow, blizzards, heavy precipitation, cold spells and heat waves. In addition, reduced visibility conditions determined by fog and dust events, small-scale phenomena affecting the transport system, such as thunderstorms, lightning, large hail and tornadoes and events damaging infrastructure of the transport system, have been considered. Frequency and probability analysis of past and present ex¬tremes were performed using observational and atmospheric reanalysis data. Future changes in the probability of severe events were assessed based on six regional climate model simulations produced in the FP6 ENSEMBLES project (http://www.ensembles-eu.org/). To facilitate the assessment of impacts and consequences of extreme phenomena on a continental level, the WP2 Deliverable introduces a regionalization of the European extreme phenomena, defining the climate zones with similarities in extreme phenomena. The projected changes as well as large natural variability in weather extremes on the transportation network will have impacts of both signs. The decline of extreme cold and snowfall over most of the continent implies a positive impact on road, rail, inland water and air transportation, e.g., by reducing snow removal. However, even with a general decreasing trend in
Garges, J.A.; Baehr, A.L.
1998-01-01
The relative importance of advection and dispersion for both solute and vapor transport can be determined from type curves or concentration, flux, or cumulative flux. The dimensionless form of the type curves provides a means to directly evaluate the importance of mass transport by advection relative to that of mass transport by diffusion and dispersion. Type curves based on an analytical solution to the advection-dispersion equation are plotted in terms of dimensionless time and Peclet number. Flux and cumulative flux type curves provide additional rationale for transport regime determination in addition to the traditional concentration type curves. The extension of type curves to include vapor transport with phase partitioning in the unsaturated zone is a new development. Type curves for negative Peclet numbers also are presented. A negative Peclet number characterizes a problem in which one direction of flow is toward the contamination source, and thereby diffusion and advection can act in opposite directions. Examples are the diffusion of solutes away from the downgradient edge of a pump-and-treat capture zone, the upward diffusion of vapors through the unsaturated zone with recharge, and the diffusion of solutes through a low hydraulic conductivity cutoff wall with an inward advective gradient.
Sheng, F.; Wang, K.; Zhang, R.; Liu, H.H.
2009-03-15
Preferential flow and solute transport are common processes in the unsaturated soil, in which distributions of soil water content and solute concentrations are often characterized as fractal patterns. An active region model (ARM) was recently proposed to describe the preferential flow and transport patterns. In this study, ARM governing equations were derived to model the preferential soil water flow and solute transport processes. To evaluate the ARM equations, dye infiltration experiments were conducted, in which distributions of soil water content and Cl{sup -} concentration were measured. Predicted results using the ARM and the mobile-immobile region model (MIM) were compared with the measured distributions of soil water content and Cl{sup -} concentration. Although both the ARM and the MIM are two-region models, they are fundamental different in terms of treatments of the flow region. The models were evaluated based on the modeling efficiency (ME). The MIM provided relatively poor prediction results of the preferential flow and transport with negative ME values or positive ME values less than 0.4. On the contrary, predicted distributions of soil water content and Cl- concentration using the ARM agreed reasonably well with the experimental data with ME values higher than 0.8. The results indicated that the ARM successfully captured the macroscopic behavior of preferential flow and solute transport in the unsaturated soil.
NASA Technical Reports Server (NTRS)
Porter, H. S.; Varosi, F.; Mayr, H. G.
1987-01-01
The Neumann iteration method presently used for solving the electron transport equation in which energy, attitude, and pitch angle are independent variables is fast, and can compute numerical point-response-function solutions of the electron transport equation. Because both the inelastic cross sections and angular elastic cross sections of the model are empirically based, the solutions obtained represent a test of compatibility between various sets of cross sections and energy deposition measurements. The use of a numerical quadrature based on analytic phase function forms yields accurate phase function integrals at low computational cost.
Evaluation of unsaturated-zone solute-transport models for studies of agricultural chemicals
Nolan, Bernard T.; Bayless, E. Randall; Green, Christopher T.; Garg, Sheena; Voss, Frank D.; Lampe, David C.; Barbash, Jack E.; Capel, Paul D.; Bekins, Barbara A.
2005-01-01
Of the models tested, RZWQM, HYDRUS2D, VS2DT, GLEAMS and PRZM had graphical user interfaces. Extensive documentation was available for RZWQM, HYDRUS2D, and VS2DT. RZWQM can explicitly simulate water and solute flux in macropores, and both HYDRUS2D and VS2DT can simulate water and solute flux in two dimensions. The version of RZWQM tested had a maximum simulation depth of 3 meters. The complex models simulate the formation, transport, and fate of degradates of up to three to five compounds including the parent, with the exception of VS2DT, which simulates the transport and fate of a single compound.
NASA Astrophysics Data System (ADS)
Wang, Quan; Moerner, W. E.
2014-03-01
In aqueous solution, diffusion generally limits the observation window of a nano-meter sized single molecule to milliseconds and prevents quantitative determination of spectroscopic and transport properties molecule-by-molecule. The anti-Brownian electrokinetic (ABEL) trap is a feedback-based microfluidic device that enables prolonged (multiseconds) observation of single molecules in solution. The amount of information that can be extracted from each molecule in solution is thus boosted by three orders of magnitude. We describe recent advances in extending the ABEL trap to conduct both spectroscopic and transport measurements of single trapped molecules. First, by combining the trap with multi-parameter fluorescence detection, synchronized dynamics in different observables can be visualized in solution. We use single molecules of Atto 633 as an example and show that this popular label switches between different emissive states under common imaging conditions. Next, we show how transport properties of trapped single molecules can be extracted in addition to spectroscopic readouts. Due to their direct sensitivity to molecular size and charge, measured transport coefficients can be used to distinguish different molecular species and trace biomolecular interactions in solution. We demonstrate this new paradigm by monitoring DNA hybridization/melting in real-time.
Liu, H.H.; Mukhopadhyay, S.; Spycher, N.; Kennedy, B.
2011-03-15
Precipitation-dissolution reactions are important for a number of applications such as isotopic tracer transport in the subsurface. Analytical solutions have been developed for tracer transport in both single-fracture and multiple-fracture systems associated with these reactions under transient and steady-state transport conditions. These solutions also take into account advective transport in fractures and molecular diffusion in the rock matrix. For studying distributions of disturbed tracer concentration (the difference between actual concentration and its equilibrium value), effects of precipitation-dissolution reactions are mathematically equivalent to a 'decay' process with a decay constant proportional to the corresponding bulk reaction rate. This important feature significantly simplifies the derivation procedure by taking advantage of the existence of analytical solutions for tracer transport associated with radioactive decay in fractured rock. It is also useful for interpreting tracer breakthrough curves, because the impact of a decay process is relatively easy to analyze. Several illustrative examples are presented, which show that the results are sensitive to fracture spacing, matrix diffusion coefficient (fracture surface area), and bulk reaction rate (or 'decay' constant), indicating that the relevant flow and transport parameters may be estimated by analyzing tracer signals.
Strategic network design of Java Island fuel supply with production-transportation solution
NASA Astrophysics Data System (ADS)
Dianawati, Fauzia; Farizal, -; Surjandari, Isti; Marzuli, Rully
2011-10-01
This study aims to find more efficient supply network, from refineries / imports to fuel terminal, which still uses the Tanker, Tank Trucks or Rail Tank Wagon with an alternative pipeline that are considered more efficient than other transport modes, as well as gaining pipeline transportation network optimization analysis tailored to the capabilities/ capacity of refinery production and capacity of the pipe mode. With the complexity of the number of 3 point sources of supply, 19 destination of terminal, 4 kinds of products and 4 types of transport modes, transport-production model modified by adding multi-modal transport and investment costs of new pipeline. Then coded in Lingo program which adopts Branch & Bound technique and input the processed data in order to obtain an optimal distribution pattern produced the lowest distribution costs. This B&B solution was also compared with SCO solution which is a metaheuristic method. The results of this study lead to the development of new modes of pipeline connections in amount of 4 alternatives, generated from the optimal solution, but still potentially earned savings of about IDR 1 Trillion per year from cost-efficiency of product procurement and transportation costs.
Solutions and reductions for radiative energy transport in laser-heated plasma
Broadbridge, P.; Ivanova, N. M.
2015-01-15
A full symmetry classification is given for models of energy transport in radiant plasma when the mass density is spatially variable and the diffusivity is nonlinear. A systematic search for conservation laws also leads to some potential symmetries and to an integrable nonlinear model. Classical point symmetries, potential symmetries, and nonclassical symmetries are used to effect variable reductions and exact solutions. The simplest time-dependent solution is shown to be stable and relevant to a closed system.
NASA Astrophysics Data System (ADS)
Swanson, Ryan D.; Binley, Andrew; Keating, Kristina; France, Samantha; Osterman, Gordon; Day-Lewis, Frederick D.; Singha, Kamini
2015-02-01
The advection-dispersion equation (ADE) fails to describe commonly observed non-Fickian solute transport in saturated porous media, necessitating the use of other models such as the dual-domain mass-transfer (DDMT) model. DDMT model parameters are commonly calibrated via curve fitting, providing little insight into the relation between effective parameters and physical properties of the medium. There is a clear need for material characterization techniques that can provide insight into the geometry and connectedness of pore spaces related to transport model parameters. Here, we consider proton nuclear magnetic resonance (NMR), direct-current (DC) resistivity, and complex conductivity (CC) measurements for this purpose, and assess these methods using glass beads as a control and two different samples of the zeolite clinoptilolite, a material that demonstrates non-Fickian transport due to intragranular porosity. We estimate DDMT parameters via calibration of a transport model to column-scale solute tracer tests, and compare NMR, DC resistivity, CC results, which reveal that grain size alone does not control transport properties and measured geophysical parameters; rather, volume and arrangement of the pore space play important roles. NMR cannot provide estimates of more-mobile and less-mobile pore volumes in the absence of tracer tests because these estimates depend critically on the selection of a material-dependent and flow-dependent cutoff time. Increased electrical connectedness from DC resistivity measurements are associated with greater mobile pore space determined from transport model calibration. CC was hypothesized to be related to length scales of mass transfer, but the CC response is unrelated to DDMT.
How do hydrodynamic instabilities affect 3D transport in geophysical vortices?
NASA Astrophysics Data System (ADS)
Wang, Peng; Özgökmen, Tamay M.
2015-03-01
Three-dimensional (3D) transport within geophysical vortices (e.g. ocean eddies) is important in understanding processes at a variety of scales, ranging from plankton production to climate variability. 3D transport can be affected by hydrodynamic instabilities of geophysical vortices; however, how the instabilities affecting 3D transport is not clear. Focusing on barotropic, inertial and 3D instabilities, we investigate the joint impacts of instabilities on 3D transport by using analytical methods and direct numerical simulations. We discover for the first time that material can be exchanged through 3D pathways which link a family of vortices generated by the instabilities in a single, initially unstable vortex. We also show that instabilities can increase the magnitude of vertical velocity, mixing rate and vertical material exchange. Besides, we find that instabilities can cause the kinetic energy wavenumber spectrum to have a power-law regime different than the classic regimes of k - 5 / 3 and k-3, and propose a new energy spectrum to interpret the non-classic regime.
Soil water repellency affects production and transport of CO2 and CH4 in soil
NASA Astrophysics Data System (ADS)
Urbanek, Emilia; Qassem, Khalid
2016-04-01
Soil moisture is known to be vital in controlling both the production and transport of C gases in soil. Water availability regulates the decomposition rates of soil organic matter by the microorganisms, while the proportion of water/air filled pores controls the transport of gases within the soil and at the soil-atmosphere interface. Many experimental studies and process models looking at soil C gas fluxes assume that soil water is uniformly distributed and soil is easily wettable. Most soils, however, exhibit some degree of soil water repellency (i.e. hydrophobicity) and do not wet spontaneously when dry or moderately moist. They have restricted infiltration and conductivity of water, which also results in extremely heterogeneous soil water distribution. This is a world-wide occurring phenomenon which is particularly common under permanent vegetation e.g. forest, grass and shrub vegetation. This study investigates the effect of soil water repellency on microbial respiration, CO2 transport within the soil and C gas fluxes between the soil and the atmosphere. The results from the field monitoring and laboratory experiments show that soil water repellency results in non-uniform water distribution in the soil which affects the CO2 and CH4 gas fluxes. The main conclusion from the study is that water repellency not only affects the water relations in the soil, but has also a great impact on greenhouse gas production and transport and therefore should be included as an important parameter during the sites monitoring and modelling of gas fluxes.
Osmosis and solute-solvent drag: fluid transport and fluid exchange in animals and plants.
Hammel, H T; Schlegel, Whitney M
2005-01-01
, (3) the return of interstitial fluid to the vasa recta, (4) return of aqueous humor to the episcleral veins, and (5) flow of phloem from source to sink in higher plants and many more examples of fluid transport and fluid exchange in animal and plant physiology. When a membrane is permeable to water only and when it separates differing aqueous solutions, the flow of water is from the solution with the lower osmotic pressure to the solution with the higher osmotic pressure. PMID:15976460
Water and solute transport in agricultural soils predicted by volumetric clay and silt contents.
Karup, Dan; Moldrup, Per; Paradelo, Marcos; Katuwal, Sheela; Norgaard, Trine; Greve, Mogens H; de Jonge, Lis W
2016-09-01
Solute transport through the soil matrix is non-uniform and greatly affected by soil texture, soil structure, and macropore networks. Attempts have been made in previous studies to use infiltration experiments to identify the degree of preferential flow, but these attempts have often been based on small datasets or data collected from literature with differing initial and boundary conditions. This study examined the relationship between tracer breakthrough characteristics, soil hydraulic properties, and basic soil properties. From six agricultural fields in Denmark, 193 intact surface soil columns 20cm in height and 20cm in diameter were collected. The soils exhibited a wide range in texture, with clay and organic carbon (OC) contents ranging from 0.03 to 0.41 and 0.01 to 0.08kgkg(-1), respectively. All experiments were carried out under the same initial and boundary conditions using tritium as a conservative tracer. The breakthrough characteristics ranged from being near normally distributed to gradually skewed to the right along with an increase in the content of the mineral fines (particles ≤50μm). The results showed that the mineral fines content was strongly correlated to functional soil structure and the derived tracer breakthrough curves (BTCs), whereas the OC content appeared less important for the shape of the BTC. Organic carbon was believed to support the stability of the soil structure rather than the actual formation of macropores causing preferential flow. The arrival times of 5% and up to 50% of the tracer mass were found to be strongly correlated with volumetric fines content. Predicted tracer concentration breakthrough points as a function of time up to 50% of applied tracer mass could be well fitted to an analytical solution to the classical advection-dispersion equation. Both cumulative tracer mass and concentration as a function of time were well predicted from the simple inputs of bulk density, clay and silt contents, and applied tracer mass
Water and solute transport in agricultural soils predicted by volumetric clay and silt contents
NASA Astrophysics Data System (ADS)
Karup, Dan; Moldrup, Per; Paradelo, Marcos; Katuwal, Sheela; Norgaard, Trine; Greve, Mogens H.; de Jonge, Lis W.
2016-09-01
Solute transport through the soil matrix is non-uniform and greatly affected by soil texture, soil structure, and macropore networks. Attempts have been made in previous studies to use infiltration experiments to identify the degree of preferential flow, but these attempts have often been based on small datasets or data collected from literature with differing initial and boundary conditions. This study examined the relationship between tracer breakthrough characteristics, soil hydraulic properties, and basic soil properties. From six agricultural fields in Denmark, 193 intact surface soil columns 20 cm in height and 20 cm in diameter were collected. The soils exhibited a wide range in texture, with clay and organic carbon (OC) contents ranging from 0.03 to 0.41 and 0.01 to 0.08 kg kg- 1, respectively. All experiments were carried out under the same initial and boundary conditions using tritium as a conservative tracer. The breakthrough characteristics ranged from being near normally distributed to gradually skewed to the right along with an increase in the content of the mineral fines (particles ≤ 50 μm). The results showed that the mineral fines content was strongly correlated to functional soil structure and the derived tracer breakthrough curves (BTCs), whereas the OC content appeared less important for the shape of the BTC. Organic carbon was believed to support the stability of the soil structure rather than the actual formation of macropores causing preferential flow. The arrival times of 5% and up to 50% of the tracer mass were found to be strongly correlated with volumetric fines content. Predicted tracer concentration breakthrough points as a function of time up to 50% of applied tracer mass could be well fitted to an analytical solution to the classical advection-dispersion equation. Both cumulative tracer mass and concentration as a function of time were well predicted from the simple inputs of bulk density, clay and silt contents, and applied tracer
Factors affecting body weight loss during commercial long haul transport of cattle in North America.
González, L A; Schwartzkopf-Genswein, K S; Bryan, M; Silasi, R; Brown, F
2012-10-01
The objective of the present study was to identify and quantify several factors affecting shrink in cattle during commercial long-haul transport (≥400 km; n = 6,152 journeys). Surveys were designed and delivered to transport carriers to collect relevant information regarding the characteristics of animals, time of loading, origin and destination, and loaded weight before and after transport. In contrast to fat cattle, feeder cattle exhibited greater shrink (4.9 vs. 7.9 ± 0.2% of BW, respectively; P < 0.01), and experienced longer total transport durations (12.4 vs. 14.9 ± 0.99, respectively; P < 0.01) due to border crossing protocols which require mandatory animal inspection. Shrink was greater (P < 0.001) for feeder cattle loaded at ranches/farms and feed yards compared with those loaded at auction markets. Cattle loaded during the afternoon and evening shrank more than those loaded during the night and morning (P < 0.05). Shrinkage was less in cattle transported by truck drivers having 6 or more years of experience hauling livestock compared with those with 5 yr or less (P < 0.05). Shrink increased with both midpoint ambient temperature (% of BW/°C; P < 0.001) and time on truck (% of BW/h; P < 0.001). Temperature and time on truck had a multiplicative effect on each other because shrink increased most rapidly in cattle transported for both longer durations and at higher ambient temperatures (P < 0.001). The rate of shrink over time (% of BW/h) was greatest in cull cattle, intermediate in calves and feeder cattle, and slowest in fat cattle (P < 0.05) but such differences disappeared when the effects of place of origin, loading time, and experience of truck drivers were included in the model. Cull cattle, calves and feeder cattle appear to be more affected by transport compared with fat cattle going to slaughter because of greater shrink. Several factors should be considered when developing guidelines to reduce cattle transport stress and shrink including type
Modeling variably saturated subsurface solute transport with MODFLOW-UZF and MT3DMS
Morway, Eric D.; Niswonger, Richard G.; Langevin, Christian D.; Bailey, Ryan T.; Healy, Richard W.
2013-01-01
The MT3DMS groundwater solute transport model was modified to simulate solute transport in the unsaturated zone by incorporating the unsaturated-zone flow (UZF1) package developed for MODFLOW. The modified MT3DMS code uses a volume-averaged approach in which Lagrangian-based UZF1 fluid fluxes and storage changes are mapped onto a fixed grid. Referred to as UZF-MT3DMS, the linked model was tested against published benchmarks solved analytically as well as against other published codes, most frequently the U.S. Geological Survey's Variably-Saturated Two-Dimensional Flow and Transport Model. Results from a suite of test cases demonstrate that the modified code accurately simulates solute advection, dispersion, and reaction in the unsaturated zone. Two- and three-dimensional simulations also were investigated to ensure unsaturated-saturated zone interaction was simulated correctly. Because the UZF1 solution is analytical, large-scale flow and transport investigations can be performed free from the computational and data burdens required by numerical solutions to Richards' equation. Results demonstrate that significant simulation runtime savings can be achieved with UZF-MT3DMS, an important development when hundreds or thousands of model runs are required during parameter estimation and uncertainty analysis. Three-dimensional variably saturated flow and transport simulations revealed UZF-MT3DMS to have runtimes that are less than one tenth of the time required by models that rely on Richards' equation. Given its accuracy and efficiency, and the wide-spread use of both MODFLOW and MT3DMS, the added capability of unsaturated-zone transport in this familiar modeling framework stands to benefit a broad user-ship.
Modeling variably saturated subsurface solute transport with MODFLOW-UZF and MT3DMS.
Morway, Eric D; Niswonger, Richard G; Langevin, Christian D; Bailey, Ryan T; Healy, Richard W
2013-03-01
The MT3DMS groundwater solute transport model was modified to simulate solute transport in the unsaturated zone by incorporating the unsaturated-zone flow (UZF1) package developed for MODFLOW. The modified MT3DMS code uses a volume-averaged approach in which Lagrangian-based UZF1 fluid fluxes and storage changes are mapped onto a fixed grid. Referred to as UZF-MT3DMS, the linked model was tested against published benchmarks solved analytically as well as against other published codes, most frequently the U.S. Geological Survey's Variably-Saturated Two-Dimensional Flow and Transport Model. Results from a suite of test cases demonstrate that the modified code accurately simulates solute advection, dispersion, and reaction in the unsaturated zone. Two- and three-dimensional simulations also were investigated to ensure unsaturated-saturated zone interaction was simulated correctly. Because the UZF1 solution is analytical, large-scale flow and transport investigations can be performed free from the computational and data burdens required by numerical solutions to Richards' equation. Results demonstrate that significant simulation runtime savings can be achieved with UZF-MT3DMS, an important development when hundreds or thousands of model runs are required during parameter estimation and uncertainty analysis. Three-dimensional variably saturated flow and transport simulations revealed UZF-MT3DMS to have runtimes that are less than one tenth of the time required by models that rely on Richards' equation. Given its accuracy and efficiency, and the wide-spread use of both MODFLOW and MT3DMS, the added capability of unsaturated-zone transport in this familiar modeling framework stands to benefit a broad user-ship. PMID:22834908
Influence of karst evolution on solute transport evaluated by process-based numerical modelling
NASA Astrophysics Data System (ADS)
Hubinger, Bernhard; Birk, Steffen
2010-05-01
Karst waters are of major interest in water resources management. Because of their inherent properties karst systems show great vulnerability with regard to contaminants. Karst systems include highly permeable solution conduit networks formed by chemical aggressive water embedded in a fissured matrix. Small initial voids are widened and thus act as preferential passages, where flow is rapid and often turbulent. Water discharging at karst spring originates from different pathways with different residence times. Contaminant transport through conduit pathways is very rapid, whereas flow through the fissured porous matrix is much slower. Thus, on the one hand, pollutants may be rapidly transported and reach high concentrations at the karst spring shortly after their release; on the other hand, the existence of slow flow components may cause the pollution to last for long times. In this work, solute transport properties of karst aquifers are investigated using generic conduit networks of hydraulically connected proto-conduits with initially log-normally distributed apertures in the millimetre range and below. Conduit evolution is modelled by coupling flow, transport, and dissolution processes, whereby single conduits are widened up to the metre range. Thus, different stages of karst evolution can be distinguished. The resulting flow systems provide the basis for modelling advective-dispersive transport of non-reactive solutes through the network of more or less widened (proto-)conduits. The general transport characteristics in karst systems as well as the influence of heterogeneities and structures on solute transport are illustrated for cases of direct injection into the conduit systems at different evolutionary stages. The resulting breakthrough curves typically show several distinct, chronologically shifted peaks with long tailings, which appears to be similar to data from field tracer experiments.