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Sample records for advection dispersion sorption

  1. Numerical simulation of advective-dispersive multisolute transport with sorption, ion exchange and equilibrium chemistry

    USGS Publications Warehouse

    Lewis, F.M.; Voss, C.I.; Rubin, Jacob

    1986-01-01

    A model was developed that can simulate the effect of certain chemical and sorption reactions simultaneously among solutes involved in advective-dispersive transport through porous media. The model is based on a methodology that utilizes physical-chemical relationships in the development of the basic solute mass-balance equations; however, the form of these equations allows their solution to be obtained by methods that do not depend on the chemical processes. The chemical environment is governed by the condition of local chemical equilibrium, and may be defined either by the linear sorption of a single species and two soluble complexation reactions which also involve that species, or binary ion exchange and one complexation reaction involving a common ion. Partial differential equations that describe solute mass balance entirely in the liquid phase are developed for each tenad (a chemical entity whose total mass is independent of the reaction process) in terms of their total dissolved concentration. These equations are solved numerically in two dimensions through the modification of an existing groundwater flow/transport computer code. (Author 's abstract)

  2. Modeling solute advection coupled with sorption kinetics in heterogeneous formations

    NASA Astrophysics Data System (ADS)

    Selroos, Jan-Olof; Cvetkovic, Vladimir

    1992-05-01

    A method for coupling sorption kinetics and solute advection in particle-tracking models is proposed; this method is efficient for the case where sorption rate coefficients can be assumed constant field scale parameters. A simulation example of reactive solute advection in two-dimensional heterogeneous porous media is presented. The effect of sorption kinetics on solute advection is investigated. Nonequilibrium effects are exhibited as enhanced tailing in the solute breakthrough. Because high variability in the hydraulic conductivity also yields enhanced tailing, the nonequilibrium effect is more pronounced for the case of low variability. Moreover, it may be difficult to distinguish cases of low variability with nonequilibrium sorption from cases of high variability with equilibrium sorption. A comparison of Monte Carlo ensemble results is made with an analytical model for the mass arrival of kinetically sorbing solute in heterogeneous porous media obtained using first-order perturbation. The comparison indicates that the analytical model provides reasonable approximations of the expected solute breakthrough if the variance of the natural logarithm of the hydraulic conductivity is smaller than 1.

  3. Backward fractional advection dispersion model for contaminant source prediction

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Meerschaert, Mark M.; Neupauer, Roseanna M.

    2016-04-01

    The forward Fractional Advection Dispersion Equation (FADE) provides a useful model for non-Fickian transport in heterogeneous porous media. The space FADE captures the long leading tail, skewness, and fast spreading typically seen in concentration profiles from field data. This paper develops the corresponding backward FADE model, to identify source location and release time. The backward method is developed from the theory of inverse problems, and then explained from a stochastic point of view. The resultant backward FADE differs significantly from the traditional backward Advection Dispersion Equation (ADE) because the fractional derivative is not self-adjoint and the probability density function for backward locations is highly skewed. Finally, the method is validated using tracer data from a well-known field experiment, where the peak of the backward FADE curve predicts source release time, while the median or a range of percentiles can be used to determine the most likely source location for the observed plume. The backward ADE cannot reliably identify the source in this application, since the forward ADE does not provide an adequate fit to the concentration data.

  4. Purely Lagrangian Simulation of Advection, Dispersion, Precipitation, and Dissolution

    NASA Astrophysics Data System (ADS)

    Benson, D.; Zhang, Y.; Reeves, D. M.

    2008-05-01

    We extend the advantages of Lagrangian random walk particle tracking (RWPT) methods that have long been used to simulate advection and dispersion in highly heterogeneous media. By formulating dissolution as a random, independent decay process, the classical continuum rate law is recovered. Formulating the random precipitation process requires a consideration of the probability that two nearby particles will coincide in a given time period. This depends on local mixing (as by diffusion) and the total domain particle number density, which are fixed and therefore easy to calculate. The result is that the classical law of mass action for equilibrium reactions can be reproduced in an ensemble sense. The same number of parameters for A+B ⇌ C are needed in a probabilistic versus continuum reaction simulation-- —one each for forward and backward probabilities that correspond to rates. The random nature of the simulations allows for significant disequilibrium in any given region at any time that is independent of the numerical details such as time stepping or particle density. This is exemplified by nearby or intermingled groups of reactants and little or no product--—a result that is often noted in the field that is difficult to reconcile with continuum methods or coarse-grained Eulerian models. Our results support recent results of perturbed advection-dispersion-reaction continuum models (Luo et al., WRR 44, 2008), and suggest that many different kinds of reactions can be easily added to existing RWPT codes.

  5. 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...

  6. Analytical solution for the advection-dispersion transport equation in layered media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The advection-dispersion transport equation with first-order decay was solved analytically for multi-layered media using the classic integral transform technique (CITT). The solution procedure used an associated non-self-adjoint advection-diffusion eigenvalue problem that had the same form and coef...

  7. AN EXACT PEAK CAPTURING AND OSCILLATION-FREE SCHEME TO SOLVE ADVECTION-DISPERSION TRANSPORT EQUATIONS

    EPA Science Inventory

    An exact peak capturing and essentially oscillation-free (EPCOF) algorithm, consisting of advection-dispersion decoupling, backward method of characteristics, forward node tracking, and adaptive local grid refinement, is developed to solve transport equations. This algorithm repr...

  8. Relative effects of advection, sorption and diffusion on transport and tailing of chlorinated solvents

    NASA Astrophysics Data System (ADS)

    Maghrebi, M.; Jankovic, I.; Rabideau, A. J.; Allen-King, R. M.; Weissmann, G. S.

    2011-12-01

    Effects of three key transport mechanisms (advection, diffusion and sorption) on transport and contaminant tailing of chlorinated solvents have been investigated using a numerical model. Thousands of model simulations have been conducted for various combinations of transport parameters that govern three key mechanisms in order to quantify tailing and relative importance of each mechanism. Hydraulic conductivity model contains a single inclusion of constant conductivity K embedded in a homogeneous anisotropic background of conductivity Kh,Kv. The inclusion is shaped as an oblate ellipsoid and subject to uniform flow. The background represents "average" conductivity of a heterogeneous formation while inclusion is used to represent geologic units that are more or less conductive than the background. The ratio of long to short semi-axis of the inclusion (a/b) models the ratio of horizontal to vertical integral scales (Ih/Iv) of different geologic units, where integral scales can be obtained, for example, using indicator variograms. The flow solution for present problem is obtained analytically as a closed form solution with exact expressions for Darcy velocity valid both inside and outside the inclusion. Sorption is modeled as an equilibrium process governed by a linear isotherm. The effects on transport and tailing are accounted for using retardation factors. Sorption heterogeneity is created by allowing different values of retardation factor for the interior (Ri) and the exterior of the inclusion (Rb). Diffusive displacements have been added to retarded advective displacements using random walk method. Peclet number, defined as Pe=U Ih/D (U is the groundwater velocity, D is the molecular diffusion coefficient for chlorinated solvents), is used to quantify the diffusion process. Very large numbers of particles (hundreds of thousands) have been tracked using very small time steps (as small as a/10,000) to provide sufficient resolution to breakthrough curves and to

  9. Curves to determine the relative importance of advection and dispersion for solute and vapor transport

    USGS Publications Warehouse

    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.

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

    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...

  11. A Lagrangian-Eulerian finite element method with adaptive gridding for advection-dispersion problems

    SciTech Connect

    Ijiri, Y.; Karasaki, K.

    1994-02-01

    In the present paper, a Lagrangian-Eulerian finite element method with adaptive gridding for solving advection-dispersion equations is described. The code creates new grid points in the vicinity of sharp fronts at every time step in order to reduce numerical dispersion. The code yields quite accurate solutions for a wide range of mesh Peclet numbers and for mesh Courant numbers well in excess of 1.

  12. Analytical solutions of the one-dimensional advection-dispersion solute transport equation subject to time-dependent boundary conditions

    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...

  13. Construction of the SILAM Eulerian atmospheric dispersion model based on the advection algorithm of Michael Galperin

    NASA Astrophysics Data System (ADS)

    Sofiev, M.; Vira, J.; Kouznetsov, R.; Prank, M.; Soares, J.; Genikhovich, E.

    2015-11-01

    The paper presents the transport module of the System for Integrated modeLling of Atmospheric coMposition SILAM v.5 based on the advection algorithm of Michael Galperin. This advection routine, so far weakly presented in the international literature, is positively defined, stable at any Courant number, and efficient computationally. We present the rigorous description of its original version, along with several updates that improve its monotonicity and shape preservation, allowing for applications to long-living species in conditions of complex atmospheric flows. The scheme is connected with other parts of the model in a way that preserves the sub-grid mass distribution information that is a cornerstone of the advection algorithm. The other parts include the previously developed vertical diffusion algorithm combined with dry deposition, a meteorological pre-processor, and chemical transformation modules. The quality of the advection routine is evaluated using a large set of tests. The original approach has been previously compared with several classic algorithms widely used in operational dispersion models. The basic tests were repeated for the updated scheme and extended with real-wind simulations and demanding global 2-D tests recently suggested in the literature, which allowed one to position the scheme with regard to sophisticated state-of-the-art approaches. The advection scheme performance was fully comparable with other algorithms, with a modest computational cost. This work was the last project of Dr. Sci. Michael Galperin, who passed away on 18 March 2008.

  14. Approximate Solution of Time-Fractional Advection-Dispersion Equation via Fractional Variational Iteration Method

    PubMed Central

    İbiş, Birol

    2014-01-01

    This paper aims to obtain the approximate solution of time-fractional advection-dispersion equation (FADE) involving Jumarie's modification of Riemann-Liouville derivative by the fractional variational iteration method (FVIM). FVIM provides an analytical approximate solution in the form of a convergent series. Some examples are given and the results indicate that the FVIM is of high accuracy, more efficient, and more convenient for solving time FADEs. PMID:24578662

  15. Approximate solution of time-fractional advection-dispersion equation via fractional variational iteration method.

    PubMed

    Ibiş, Birol; Bayram, Mustafa

    2014-01-01

    This paper aims to obtain the approximate solution of time-fractional advection-dispersion equation (FADE) involving Jumarie's modification of Riemann-Liouville derivative by the fractional variational iteration method (FVIM). FVIM provides an analytical approximate solution in the form of a convergent series. Some examples are given and the results indicate that the FVIM is of high accuracy, more efficient, and more convenient for solving time FADEs. PMID:24578662

  16. Passive advection-dispersion in networks of pipes: Effect of connectivity and relationship to permeability

    NASA Astrophysics Data System (ADS)

    Bernabé, Y.; Wang, Y.; Qi, T.; Li, M.

    2016-02-01

    The main purpose of this work is to investigate the relationship between passive advection-dispersion and permeability in porous materials presumed to be statistically homogeneous at scales larger than the pore scale but smaller than the reservoir scale. We simulated fluid flow through pipe network realizations with different pipe radius distributions and different levels of connectivity. The flow simulations used periodic boundary conditions, allowing monitoring of the advective motion of solute particles in a large periodic array of identical network realizations. In order to simulate dispersion, we assumed that the solute particles obeyed Taylor dispersion in individual pipes. When a particle entered a pipe, a residence time consistent with local Taylor dispersion was randomly assigned to it. When exiting the pipe, the particle randomly proceeded into one of the pipes connected to the original one according to probabilities proportional to the outgoing volumetric flow in each pipe. For each simulation we tracked the motion of at least 6000 solute particles. The mean fluid velocity was 10-3 ms-1, and the distance traveled was on the order of 10 m. Macroscopic dispersion was quantified using the method of moments. Despite differences arising from using different types of lattices (simple cubic, body-centered cubic, and face-centered cubic), a number of general observations were made. Longitudinal dispersion was at least 1 order of magnitude greater than transverse dispersion, and both strongly increased with decreasing pore connectivity and/or pore size variability. In conditions of variable hydraulic radius and fixed pore connectivity and pore size variability, the simulated dispersivities increased as power laws of the hydraulic radius and, consequently, of permeability, in agreement with previously published experimental results. Based on these observations, we were able to resolve some of the complexity of the relationship between dispersivity and permeability.

  17. THE INTERPLAY BETWEEN GEOCHEMICAL REACTIONS AND ADVECTION-DISPERSION IN CONTAMINANT TRANSPORT AT A URANIUM MILL TAILINGS SITE

    EPA Science Inventory

    It is well known that the fate and transport of contaminants in the subsurface are controlled by complex processes including advection, dispersion-diffusion, and chemical reactions. However, the interplay between the physical transport processes and chemical reactions, and their...

  18. Dispersion, sorption and photodegradation of petroleum hydrocarbons in dispersant-seawater-sediment systems.

    PubMed

    Zhao, Xiao; Liu, Wen; Fu, Jie; Cai, Zhengqing; O'Reilly, S E; Zhao, Dongye

    2016-08-15

    This work examined effects of model oil dispersants on dispersion, sorption and photodegradation of petroleum hydrocarbons in simulated marine systems. Three dispersants (Corexit 9500A, Corexit 9527A and SPC 1000) were used to prepare dispersed water accommodated oil (DWAO). While higher doses of dispersants dispersed more n-alkanes and PAHs, Corexit 9500A preferentially dispersed C11-C20 n-alkanes, whereas Corexit 9527A was more favorable for smaller alkanes (C10-C16), and SPC 1000 for C12-C28 n-alkanes. Sorption of petroleum hydrocarbons on sediment was proportional to TPH types/fractions in the DWAOs. Addition of 18mg/L of Corexit 9500A increased sediment uptake of 2-3 ring PAHs, while higher dispersant doses reduced the uptake, due to micelle-enhanced solubilization effects. Both dispersed n-alkanes and PAHs were susceptible to photodegradation under simulated sunlight. For PAHs, both photodegradation and photo-facilitated alkylation were concurrently taking place. The information can facilitate sounder assessment of fate and distribution of dispersed oil hydrocarbons in marine systems. PMID:27318763

  19. Permeability generation and resetting of tracers during metamorphic fluid flow: implications for advection-dispersion models

    NASA Astrophysics Data System (ADS)

    Cartwright, Ian

    Advection-dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid-saturated medium. However, whether rocks contain a fluid depends on their reaction history, and whether any initial fluid escapes. The behaviour of different rocks may be illustrated using hypothetical marble compositions. Marbles with diverse chemistries (e.g. calcite + dolomite + quartz) are relatively reactive, and will generally produce a fluid during heating. By contrast, marbles with more restricted chemistries (e.g. calcite + quartz or calcite-only) may not. If the rock is not fluid bearing when fluid infiltration commences, mineralogical reactions may produce a reaction-enhanced permeability in calcite + dolomite + quartz or calcite + quartz, but not in calcite-only marbles. The permeability production controls the pattern of mineralogical, isotopic, and geochemical resetting during fluid flow. Tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection-dispersion models; however, tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction. In the case of very unreactive lithologies (e.g. pure calcite marbles, cherts, and quartzites), the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer. Centimetre-scale layering may lead to the formation of self-perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants. Such layered rocks may show patterns of mineralogical resetting that are not predicted by advection-dispersion models. Patterns of mineralogical and isotopic resetting in marbles from a number of terrains, for example: Chillagoe, Marulan South, Reynolds Range (Australia); Adirondack Mountains, Old Woman Mountains, Notch Peak (USA); and Stephen Cross Quarry (Canada) vary as predicted by these models.

  20. Dynamic typology of hydrothermal systems: competing effects of advection, dispersion and reactivity

    NASA Astrophysics Data System (ADS)

    Dolejs, David

    2016-04-01

    Genetic interpretation hydrothermal systems relies on recognition of (i) hydrothermal fluid source, (ii) fluid migration pathways, and (iii) deposition site identified by hydrothermal alteration and/or mineralization. Frequently, only the last object is of interest or accessible to direct observation, but constraints on the fluid source (volume) and pathways can be obtained from evaluation of the time-integrated fluid flux during hydrothermal event. Successful interpretation of the petrological record, that is, progress of alteration reactions, relies on identification of individual contributions arising from solute advection (to the deposition site), its lateral dispersion, and reaction efficiency. Although these terms are all applicable in a mass-conservation relationship within the framework of the transport theory, they are rarely considered simultaneously and their relative magnitudes evaluated. These phenomena operate on variable length and time scales, and may in turn provide insight into the system dynamics such as flow, diffusion and reaction rates, or continuous vs. episodic behavior of hydrothermal events. In addition, here we demonstrate that they also affect estimate of the net fluid flux, frequently by several orders of magnitude. The extent of alteration and mineralization reactions between the hydrothermal fluid and the host environment is determined by: (i) temperature, pressure or any other gradients across the mineralization site, (ii) magnitude of disequilibrium at inflow to the mineralization site, which is related to physico-chemical gradient between the fluid source and the mineralization site, and (iii) chemical redistribution (dispersion) within the mineralization site. We introduce quantitative mass-transport descriptors - Péclet and Damköhler II numbers - to introduce division into dispersion-dominated, advection-dominated and reaction-constrained systems. Dispersive systems are characterized by lateral solute redistribution, driven by

  1. Advection, dispersion, and filtration of fine particles within emergent vegetation of the Florida Everglades

    USGS Publications Warehouse

    Huang, Y.H.; Saiers, J.E.; Harvey, J.W.; Noe, G.B.; Mylon, S.

    2008-01-01

    The movement of particulate matter within wetland surface waters affects nutrient cycling, contaminant mobility, and the evolution of the wetland landscape. Despite the importance of particle transport in influencing wetland form and function, there are few data sets that illuminate, in a quantitative way, the transport behavior of particulate matter within surface waters containing emergent vegetation. We report observations from experiments on the transport of 1 ??m latex microspheres at a wetland field site located in Water Conservation Area 3A of the Florida Everglades. The experiments involved line source injections of particles inside two 4.8-m-long surface water flumes constructed within a transition zone between an Eleocharis slough and Cladium jamaicense ridge and within a Cladium jamaicense ridge. We compared the measurements of particle transport to calculations of two-dimensional advection-dispersion model that accounted for a linear increase in water velocities with elevation above the ground surface. The results of this analysis revealed that particle spreading by longitudinal and vertical dispersion was substantially greater in the ridge than within the transition zone and that particle capture by aquatic vegetation lowered surface water particle concentrations and, at least for the timescale of our experiments, could be represented as an irreversible, first-order kinetics process. We found generally good agreement between our field-based estimates of particle dispersion and water velocity and estimates determined from published theory, suggesting that the advective-dispersive transport of particulate matter within complex wetland environments can be approximated on the basis of measurable properties of the flow and aquatic vegetation. Copyright 2008 by the American Geophysical Union.

  2. The advective-dispersive equation with spatial fractional derivatives as a model for tracer transport in structured soil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The classical model to describe solute transport in soil is based on the advective-dispersive equation where Fick’s law is used to explain dispersion. From the microscopic point of view this is equivalent to consider that the motion of the particles of solute may be simulated by the Brownian motion....

  3. Probabilistic exposure risk assessment with advective-dispersive well vulnerability criteria

    NASA Astrophysics Data System (ADS)

    Enzenhoefer, Rainer; Nowak, Wolfgang; Helmig, Rainer

    2012-02-01

    Time-related advection-based well-head protection zones are commonly used to manage the contamination risk of drinking water wells. According to current water safety plans advanced risk management schemes are needed to better control and monitor all possible hazards within catchments. The goal of this work is to cast the four advective-dispersive intrinsic well vulnerability criteria by Frind et al. [1] into a framework of probabilistic risk assessment framework. These criteria are: (i) arrival time, (ii) level of peak concentration, (iii) time until first arrival of critical concentrations and (iv) exposure time. Our probabilistic framework yields catchment-wide maps of probabilities to not comply with these criteria. This provides indispensable information for catchment managers to perform probabilistic exposure risk assessment and thus improves the basis for risk-informed well-head management. We resolve heterogeneity with high-resolution Monte Carlo simulations and use a new reverse formulation of temporal moment transport equations to keep computational costs low. Our method is independent of dimensionality and boundary conditions, and can account for arbitrary sources of uncertainty. It can be coupled with any method for conditioning on available data. For simplicity, we demonstrate the concept on a 2D example that includes conditioning on synthetic data.

  4. Solution of the advection-dispersion equation: Continuous load of finite duration

    USGS Publications Warehouse

    Runkel, R.L.

    1996-01-01

    Field studies of solute fate and transport in streams and rivers often involve an. experimental release of solutes at an upstream boundary for a finite period of time. A review of several standard references on surface-water-quality modeling indicates that the analytical solution to the constant-parameter advection-dispersion equation for this type of boundary condition has been generally overlooked. Here an exact analytical solution that considers a continuous load of unite duration is compared to an approximate analytical solution presented elsewhere. Results indicate that the exact analytical solution should be used for verification of numerical solutions and other solute-transport problems wherein a high level of accuracy is required. ?? ASCE.

  5. Bad behavior of Godunov mixed methods for strongly anisotropic advection-dispersion equations

    NASA Astrophysics Data System (ADS)

    Mazzia, Annamaria; Manzini, Gianmarco; Putti, Mario

    2011-09-01

    We study the performance of Godunov mixed methods, which combine a mixed-hybrid finite element solver and a Godunov-like shock-capturing solver, for the numerical treatment of the advection-dispersion equation with strong anisotropic tensor coefficients. It turns out that a mesh locking phenomenon may cause ill-conditioning and reduce the accuracy of the numerical approximation especially on coarse meshes. This problem may be partially alleviated by substituting the mixed-hybrid finite element solver used in the discretization of the dispersive (diffusive) term with a linear Galerkin finite element solver, which does not display such a strong ill conditioning. To illustrate the different mechanisms that come into play, we investigate the spectral properties of such numerical discretizations when applied to a strongly anisotropic diffusive term on a small regular mesh. A thorough comparison of the stiffness matrix eigenvalues reveals that the accuracy loss of the Godunov mixed method is a structural feature of the mixed-hybrid method. In fact, the varied response of the two methods is due to the different way the smallest and largest eigenvalues of the dispersion (diffusion) tensor influence the diagonal and off-diagonal terms of the final stiffness matrix. One and two dimensional test cases support our findings.

  6. Horizontal advection and dispersion in a stratified shelf sea: The role of inertial oscillations

    NASA Astrophysics Data System (ADS)

    Inall, Mark E.; Aleynik, Dmitry; Neil, Clare

    2013-10-01

    The role played by inertial motions in horizontal dispersion within the thermocline of a broad, mid-latitude shelf sea is examined through the analysis of a deliberately released dye tracer. Our analysis is of the horizontal and vertical evolution over 40 h of a dye tracer injected into the seasonally stratified thermocline of the Celtic Sea on the NW European Shelf. The inferred diapycnal diffusivity was 1.3-1.5 × 10-5 m2 s-1, and the radial horizontal diffusivities of the depth integrated dye patch ranged from 1.9 to 4.0 m2 s-1. The inferred vertical diffusivity is in agreement with microstructure based estimates, and the depth integrated horizontal diffusivity is broadly in agreement with previous dye release derived estimates made over similar scales and time periods. Asymmetry in the horizontal evolution of the dye patch was evident. We argue that mean shear dispersion was responsible for lateral elongation of the dye patch, particularly between hours 23 and 35 after release, during which time horizontal diffusivity along the major axis, Ka, exceeded that along the minor axis, Kb, by more than a factor of 10. We further show that along-patch shear was predominantly a result of differential advection between a deep residual flow to the south-east and an oscillating wind-driven surface Ekman layer. In this region of strong low frequency (inertial) shear a time dependent model of shear dispersion (Young et al., 1982) was able to account for the observed rate of horizontal dispersion calculated on the target isopycnal surface.

  7. Diffusion related isotopic fractionation effects with one-dimensional advective-dispersive transport.

    PubMed

    Xu, Bruce S; Lollar, Barbara Sherwood; Passeport, Elodie; Sleep, Brent E

    2016-04-15

    Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining "observable" DRIF based on constraints imposed by the scale of measurements in the field, and on standard limits of detection and analytical uncertainty. Specifically, constraints for the detection of DRIF were determined in terms of the diffusive fractionation factor, the initial concentration of contaminants (C0), the method detection limit (MDL) for isotopic analysis, the transport time, and the ratio of the longitudinal mechanical dispersion coefficient to effective molecular diffusion coefficient (Dmech/Deff). The results allow a determination of field conditions under which DRIF may be an important factor in the use of stable carbon isotope measurements for evaluation of contaminant transport and transformation for one-dimensional advective-dispersive transport. This study demonstrates that for diffusion-dominated transport of BTEX, MTBE, and chlorinated ethenes, DRIF effects are only detectable for the smaller molar mass compounds such as vinyl chloride for C0/MDL ratios of 50 or higher. Much larger C0/MDL ratios, corresponding to higher source concentrations or lower detection limits, are necessary for DRIF to be detectable for the higher molar mass compounds. The distance over which DRIF is observable for VC is small (less than 1m) for a relatively young diffusive plume (<100years), and DRIF will not easily be detected by using the conventional sampling approach with "typical" well spacing (at least several meters). With contaminant transport by advection, mechanical dispersion, and molecular diffusion this study suggests that in field sites where Dmech/Deff is larger than 10, DRIF effects will likely not be

  8. TESTING THE FRACTIONAL ADVECTIVE-DISPERSIVE EQUATION FOR SOLUTE TRANSPORT IN SOIL WITH DATA FROM MISCIBLE DISPLACEMENT EXPERIMENTS

    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...

  9. Simulation of Field-Scale Non-Fickian Plumes With Spatiotemporal Fractional Advection- Dispersion Equations

    NASA Astrophysics Data System (ADS)

    Benson, D. A.; Zhang, Y.

    2006-12-01

    Conservative solute transport through natural media is typically "anomalous" or non-Fickian. The anomalous transport may be characterized by faster than linear growth of the centered second moment, or non-Gaussian leading or trailing edges of a plume emanating from a point source. These characteristics develop because of non-local dependence on either past (time) or far upstream (space) concentrations. Non-local equations developed to describe anomalous dispersion usually focus on constant transport parameters and/or independence of the transport on space dimension. These simplifications have been useful for fitting simple transport processes, such as laboratory column tests or 1-D projections of field data. However, they may be insufficient for real field settings, where direction-dependent depositional processes and nonstationary heterogeneity can occur. We develop a generalized, multi-dimensional, spatiotemporal fractional advection- dispersion equation (fADE) with variable parameters to characterize regional-scale anomalous dispersion processes including trapping in immobile zones and/or super-Fickian rapid transport. A Lagrangian numerical model of the space-time fractional transport equation is developed in which solute particles can disperse in both space and time, depending on the medium heterogeneity properties, such as the connectivity and statistical distributions of high versus low-permeability deposits. In the generalized fADE, the range of the order of fractional time derivative is (0 2], representing a wide range of possible trapping behavior. The extension of the order to the range (1 2] is novel to transport theory. We apply the numerical model in 1-D and 2-D to the MADE site tritium plumes, and results indicate that this method can capture the main behaviors of realistic plumes, including local variations of spreading, direction-dependent scaling rates, and arbitrary rapid transport along preferential flow paths. Since the governing equation

  10. CELL DENSITY AND NON-EQUILIBRIUM SORPTION EFFECTS ON BACTERIAL DISPERSAL IN GROUNDWATER MICROCOSMS

    EPA Science Inventory

    The relative importance of dispersion, physical straining, non-equilibrium sorption, and cell density on the dispersal of bacteria was examined in saturated, flow-dynamic sand columns. The bacterial breakthrough as a was followed by measuring the effluent concentration of 3H-aden...

  11. EVALUATION OF SORPTION MODELS IN THE SIMULATION OF NAPHTHALENE TRANSPORT THROUGH SATURATED SOILS

    EPA Science Inventory

    To show the effect of sorption model selection. he one-dimensional transport of naphthalene in two saturated soils was simulated using numerical models, which included the processes of dispersion, advection and sorption. hree different models describing the sorption process: 1) a...

  12. Use of the time fractional advection dispersion equation for push-pull tests at the Macrodispersion Experiment (MADE) site

    NASA Astrophysics Data System (ADS)

    Dean, A. M.; Benson, D. A.; Major, E.

    2010-12-01

    By adding a fractional-in-time term to the traditional advection dispersion equation, a model is able to simulate a late-time heavy-tailed contaminant breakthrough curve. This heavy-tailed breakthrough curve is observed in data collected during a conservative tracer “push-pull” test at the Macrodispersion Experiment (MADE) site. A time fractional advection dispersion equation (fADE) is able to predict power law tailing of conservative solutes by accounting for solutes transferring between the mobile and relatively immobile phases. Solutes can become trapped in a low permeability zone where the transport is controlled by diffusion instead of advection. It has been observed that the late-time heavy-tailed breakthrough curve may follow a power law due to the movement into these low flow zones. By solving the time fADE in a particle tracking program (SLIM-FAST) the model accounts for mass transfer between various phases and produces the same power law tail as observed in field data. For the implementation of the time fADE, in SLIM-FAST, the particles move based on a random-walk motion but have the ability to transition into a relatively immobile phase after (exponentially) random mobile times. Following a period in the immobile phase, the particle re-enters the mobile phase to be moved by advection and Fickian dispersion. To test the fADE approach, a recent single-well push-pull tracer test at the MADE site is reproduced using a groundwater flow code (ParFlow) and a particle tracking code (SLIM-FAST) using various immobile residence-time distributions.

  13. Brine heterogeneity and dispersed interstitial advective flow underneath the sea of galilee, Israel

    NASA Astrophysics Data System (ADS)

    Weinstein, Y.; Katz, A.; Kastner, M.; Nishri, A.; Jannasch, H.

    2003-04-01

    Saline groundwater from submerged sources is today the main source of salts to the Sea of Galilee, supplying annually 72,000 tons chloride to the lake. MOSQUITO flux-meters were deployed during April to September 2001 at seven shallow Kinneret sites in order to study the dispersed interstitial flow. Each instrument carried 3-5 Osmo-Samplers that continuously sampled pore fluids at various depths in the sediment (0-45 cm). Samples were analyzed for their chemistry and for concentration of Na-fluorescein that was previously injected into the sediment. In general, oncentrations of conservative elements (e.g. Cl, Na, B) increase with depth into the sediment at all sites. However, concentrations vary significantly from one site to another. For instance, in sub-lacustrine brines next to the Tiberias Hot Springs Cl concentration reaches more than 14,500 mg/l at 35 cm below lake floor (not much less than the 18,000 mg/l in the nearby on-shore springs), while at other stations, brines are diluted by meteoric water to less than 1,500 mg/l Cl. Ion ratios in pore water indicate that the shallow parts of Lake Kinneret are underlain by several, separate, brine pockets, that are sometimes located very close to each other and discharge to the same area. Pore water at the east and northwest of the lake have Na/Cl ionic ratios between 0.7 and 0.8, similar to that of the overlying lake water, while at the west and south, ratios are significantly lower (<0.6 and <0.5, respectively), indicating larger degree of evaporation of the original brine end-member. Brines next to Tiberias Hot Springs have significantly higher Br/Cl and lower Mg/Cl ratios than pore water from other sites. Eastern shore sub-lacusrine brines (next to Gofra) are distinguished by their very high Sr/Cl and B/Cl ratios. Advective flow rates were derived from temporal patterns of Na-fluorescein concentration in pore water. Flow rates were between 0 and 80 cm/yr. Annual fluxes through the shallow part of the lake are

  14. Sorption of testosterone on partially-dispersed soil particles of different size fractions: Methodology and implications.

    PubMed

    Qi, Yong; Zhang, Tian C

    2016-04-01

    Sorption of hormones to soil particles of different size fractions (DSFs) has been studied to understand their fate and transport (F/T) in soils. Conventional studies fractionated the soil particles into DSFs by using the high speed stirring method and/or adding surfactants to fully disperse the bulk soil. However, the natural processes (e.g., soil erosion, irrigation) often are relatively mild, and many soil particles may be still in the aggregate form. In this study, a method was developed for conducting the sorption test of a representative hormone (i.e., testosterone) to bulk soils first and then analyzing the results against DSFs. Results indicated the particle size distribution (PSD) of the two representative soils tested with partially-dispersed and fully-dispersed methods was significantly different due to the attachment of clay particles on sand and silt. Testosterone was sorbed mainly by the dominant aggregates even though they might have relatively lower sorption affinity than that of clays. However, the small particles (<2000 nm), even with ∼5% mass of the bulk soil, contributed more than 30% of sorbed testosterone in the "whole" soils. The partially-dispersed soil particles of DSFs should be used to understand the transport of hormone in runoff, because using the fully-dispersed soil particles will overestimate while the whole soil method will underestimate the transport potential. With the methodology developed in this study, the sorption tests will not compromise soil's original properties (e.g., aggregates) or the competition (e.g., sorption) among soil particles, and the contribution of DSFs (particularly the partially-dispersed aggregates) to the sorption of the "whole" soil can be determined. PMID:26826645

  15. Does dispersal control population densities in advection-dominated systems? A fresh look at critical assumptions and a direct test.

    PubMed

    Downes, Barbara J; Lancaster, Jill

    2010-01-01

    1. In advection-dominated systems (both freshwater and marine), population dynamics are usually presumed to be dominated by the effects of migrants dispersing by advection, especially over the small spatial scales at which populations can be studied, but few studies have tested this presumption. We tested the hypothesis that benthic densities are controlled by densities of dispersers for two aquatic insects in upland streams. 2. Our study animals were two species of caddisflies (Hydropsychidae), which become sedentary filter-feeders following settlement onto substrata. Densities of dispersers in the drift (advective dispersal) were quantified using nets placed along the upstream edges of riffles, where the latter abruptly abutted a slower, upstream run. Settlement was estimated at each site using brick pavers, half of which had been fenced to prevent colonization of their top surfaces by walking hydropsychids, thus allowing us to distinguish also the mode of movement during settlement. 3. First through fifth instars of two species, Smicrophylax sp. AV2 and Asmicridea sp. AV1, were abundant and showed disparate results. Drift and settlement were relatively strongly related for Smicrophylax. The best fit lines were shown by second and third instars settling on plain bricks, suggesting that drift played a strong role in settlement, but that some drifters dropped to the bottom and located substrata by walking. Quantile regression suggested that drift sets limits to settlement in this species and that settlement success was highly variable. In contrast, settlement by Asmicridea was poorly related to drift; settlers were mainly individuals re-dispersing within sites. 4. Smicrophylax densities appear to be controlled by dispersal from upstream, but benthic density of Asmicridea is more likely linked to local demography. Our data demonstrate the dangers of assuming that supposedly drift-prone species can all be modelled in the same way. Alternative models emphasizing

  16. The cause of advective slowdown of tracer pebbles in rivers: Implementation of Exner-Based Master Equation for coevolving streamwise and vertical dispersion

    NASA Astrophysics Data System (ADS)

    Pelosi, A.; Schumer, R.; Parker, G.; Ferguson, R. I.

    2016-03-01

    Tracer pebbles are often used to study bed load transport processes in gravel bed rivers. Models have been proposed for their downstream dispersion, and also for vertical dispersion, but not for the combined effects of downstream and vertical movement. Here we use the Exner-Based Master Equation to characterize the transient coevolution of streamwise and vertical advection-diffusion of tracer pebbles under equilibrium transport conditions (no net aggradation or degradation). The coevolution of streamwise and vertical dispersion gives rise to behavior that can differ markedly from that associated with purely streamwise processes with no vertical exchange. One example is streamwise advective slowdown. Particles that are advected downward into zones where the probability of reentrainment becomes asymptotically small are essentially trapped and can no longer participate in streamwise advection. As a result, the mean streamwise velocity of the tracer plume declines in time. Qualitative and quantitative comparisons with two field experiments show encouraging agreement despite the simplified boundary conditions in the model.

  17. Groundwater age, life expectancy and transit time distributions in advective dispersive systems; 2. Reservoir theory for sub-drainage basins

    NASA Astrophysics Data System (ADS)

    Cornaton, F.; Perrochet, P.

    2006-09-01

    Groundwater age and life expectancy probability density functions (pdf) have been defined, and solved in a general three-dimensional context by means of forward and backward advection-dispersion equations [Cornaton F, Perrochet P. Groundwater age, life expectancy and transit time distributions in advective-dispersive systems; 1. Generalized reservoir theory. Adv Water Res (xxxx)]. The discharge and recharge zones transit time pdfs were then derived by applying the reservoir theory (RT) to the global system, thus considering as ensemble the union of all inlet boundaries on one hand, and the union of all outlet boundaries on the other hand. The main advantages in using the RT to calculate the transit time pdf is that the outlet boundary geometry does not represent a computational limiting factor (e.g. outlets of small sizes), since the methodology is based on the integration over the entire domain of each age, or life expectancy, occurrence. In the present paper, we extend the applicability of the RT to sub-drainage basins of groundwater reservoirs by treating the reservoir flow systems as compartments which transfer the water fluxes to a particular discharge zone, and inside which mixing and dispersion processes can take place. Drainage basins are defined by the field of probability of exit at outlet. In this way, we make the RT applicable to each sub-drainage system of an aquifer of arbitrary complexity and configuration. The case of the well-head protection problem is taken as illustrative example, and sensitivity analysis of the effect of pore velocity variations on the simulated ages is carried out.

  18. BEHAVIOR OF SENSITIVITIES IN THE ONE-DIMENSIONAL ADVECTION-DISPERSION EQUATION: IMPLICATIONS FOR PARAMETER ESTIMATION AND SAMPLING DESIGN.

    USGS Publications Warehouse

    Knopman, Debra S.; Voss, Clifford I.

    1987-01-01

    The spatial and temporal variability of sensitivities has a significant impact on parameter estimation and sampling design for studies of solute transport in porous media. Physical insight into the behavior of sensitivities is offered through an analysis of analytically derived sensitivities for the one-dimensional form of the advection-dispersion equation. When parameters are estimated in regression models of one-dimensional transport, the spatial and temporal variability in sensitivities influences variance and covariance of parameter estimates. Several principles account for the observed influence of sensitivities on parameter uncertainty. (1) Information about a physical parameter may be most accurately gained at points in space and time. (2) As the distance of observation points from the upstream boundary increases, maximum sensitivity to velocity during passage of the solute front increases. (3) The frequency of sampling must be 'in phase' with the S shape of the dispersion sensitivity curve to yield the most information on dispersion. (4) The sensitivity to the dispersion coefficient is usually at least an order of magnitude less than the sensitivity to velocity. (5) The assumed probability distribution of random error in observations of solute concentration determines the form of the sensitivities. (6) If variance in random error in observations is large, trends in sensitivities of observation points may be obscured by noise. (7) Designs that minimize the variance of one parameter may not necessarily minimize the variance of other parameters.

  19. Sorption and desorption of atrazine and diuron onto water dispersible soil primary size fractions.

    PubMed

    Wang, Peng; Keller, Arturo A

    2009-03-01

    In this study, a low energy separation method was employed to separate water dispersible clay-, silt-, and sand-sized fractions. The batch equilibrium method was used to conduct atrazine and diuron sorption/desorption experiments with the bulk soils and their size fractions separately. A Freundlich sorption model provided the best fit for all sorption and desorption data. A mass balance calculation, taking into account the pesticide concentration differences in the size fraction and bulk soil, showed that pesticide sorption onto the different size fractions reproduces well the total amount of the pesticide sorbed onto the bulk soils. Due to their higher soil organic carbon content, the clay fractions were much more effective sorbents for the pesticides than the bulk soils, silt, and sand fractions. For all soils, the amount of the pesticide sorbed onto the clay fractions was more than 20% of the total amount of the pesticide sorbed by the bulk soils even though the clay fractions in these soils were only 5.3-14.0% (by weight). The clay fractions had the highest desorption hysteresis among all size fractions and the bulk soils, followed by silt fractions, implying the clay fractions had the strongest bound and least desorbable pesticide molecules. Our results suggest that attention should be paid to the pesticide sorbed to the smallest colloids, the water dispersible fraction, which can be potentially mobilized under field conditions, leading to wide spreading of contamination. PMID:19147172

  20. Solution of the advection-dispersion equation by a finite-volume eulerian-lagrangian local adjoint method

    USGS Publications Warehouse

    Healy, R.W.; Russell, T.F.

    1992-01-01

    A finite-volume Eulerian-Lagrangian local adjoint method for solution of the advection-dispersion equation is developed and discussed. The method is mass conservative and can solve advection-dominated ground-water solute-transport problems accurately and efficiently. An integrated finite-difference approach is used in the method. A key component of the method is that the integral representing the mass-storage term is evaluated numerically at the current time level. Integration points, and the mass associated with these points, are then forward tracked up to the next time level. The number of integration points required to reach a specified level of accuracy is problem dependent and increases as the sharpness of the simulated solute front increases. Integration points are generally equally spaced within each grid cell. For problems involving variable coefficients it has been found to be advantageous to include additional integration points at strategic locations in each well. These locations are determined by backtracking. Forward tracking of boundary fluxes by the method alleviates problems that are encountered in the backtracking approaches of most characteristic methods. A test problem is used to illustrate that the new method offers substantial advantages over other numerical methods for a wide range of problems.

  1. Population densities and density-area relationships in a community with advective dispersal and variable mosaics of resource patches.

    PubMed

    Lancaster, Jill; Downes, Barbara J

    2014-12-01

    Many communities comprise species that select resources that are patchily distributed in an environment that is otherwise unsuitable or suboptimal. Effects of this patchiness can depend on the characteristics of patch arrays and animal movements, and produce non-intuitive outcomes in which population densities are unrelated to resource abundance. Resource mosaics are predicted to have only weak effects, however, where patches are ephemeral or organisms are transported advectively. The running waters of streams and benthic invertebrates epitomize such systems, but empirical tests of resource mosaics are scarce. We sampled 15 common macroinvertebrates inhabiting distinct detritus patches at four sites within a sand-bed stream, where detritus formed a major resource of food and living space. At each site, environmental variables were measured for 100 leaf packs; invertebrates were counted in 50 leaf packs. Sites differed in total abundance of detritus, leaf pack sizes and invertebrate densities. Multivariate analysis indicated that patch size was the dominant environmental variable, but invertebrate densities differed significantly between sites even after accounting for patch size. Leaf specialists showed positive and strong density-area relationships, except where the patch size range was small and patches were aggregated. In contrast, generalist species had weaker and variable responses to patch sizes. Population densities were not associated with total resource abundance, with the highest densities of leaf specialists in sites with the least detritus. Our results demonstrate that patchy resources can affect species even in communities where species are mobile, have advective dispersal, and patches are relatively ephemeral. PMID:25190216

  2. Eulerian-Lagrangian numerical scheme for simulating advection, dispersion, and transient storage in streams and a comparison of numerical methods

    USGS Publications Warehouse

    Cox, T.J.; Runkel, R.L.

    2008-01-01

    Past applications of one-dimensional advection, dispersion, and transient storage zone models have almost exclusively relied on a central differencing, Eulerian numerical approximation to the nonconservative form of the fundamental equation. However, there are scenarios where this approach generates unacceptable error. A new numerical scheme for this type of modeling is presented here that is based on tracking Lagrangian control volumes across a fixed (Eulerian) grid. Numerical tests are used to provide a direct comparison of the new scheme versus nonconservative Eulerian numerical methods, in terms of both accuracy and mass conservation. Key characteristics of systems for which the Lagrangian scheme performs better than the Eulerian scheme include: nonuniform flow fields, steep gradient plume fronts, and pulse and steady point source loadings in advection-dominated systems. A new analytical derivation is presented that provides insight into the loss of mass conservation in the nonconservative Eulerian scheme. This derivation shows that loss of mass conservation in the vicinity of spatial flow changes is directly proportional to the lateral inflow rate and the change in stream concentration due to the inflow. While the nonconservative Eulerian scheme has clearly worked well for past published applications, it is important for users to be aware of the scheme's limitations. ?? 2008 ASCE.

  3. Numerical simulation of advection fog formation on multi-disperse aerosols due to combustion-related pollutants

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Liaw, G. S.

    1980-01-01

    The effects of multi-disperse distribution of the aerosol population are presented. Single component and multi-component aerosol species on the condensation/nucleation processes which affect the reduction in visibility are described. The aerosol population with a high particle concentration provided more favorable conditions for the formation of a denser fog than the aerosol population with a greater particle size distribution when the value of the mass concentration of the aerosols was kept constant. The results were used as numerical predictions of fog formation. Two dimensional observations in horizontal and vertical coordinates, together with time-dependent measurements were needed as initial values for the following physical parameters: (1)wind profiles; (2) temperature profiles; (3) humidity profiles; (4) mass concentration of aerosol particles; (5) particle size distribution of aerosols; and (6) chemical composition of aerosols. Formation and dissipation of advection fog, thus, can be forecasted numerically by introducing initial values obtained from the observations.

  4. Advective-diffusive/dispersive transport of chemically reacting species in hydrothermal systems. Final report, FY83-85

    SciTech Connect

    Lichtner, P.C.; Helgeson, H.C.

    1986-06-20

    A general formulation of multi-phase fluid flow coupled to chemical reactions was developed based on a continuum description of porous media. A preliminary version of the computer code MCCTM was constructed which implemented the general equations for a single phase fluid. The computer code MCCTM incorporates mass transport by advection-diffusion/dispersion in a one-dimensional porous medium coupled to reversible and irreversible, homogeneous and heterogeneous chemical reactions. These reactions include aqueous complexing, oxidation/reduction reactions, ion exchange, and hydrolysis reactions of stoichiometric minerals. The code MCCTM uses a fully implicit finite difference algorithm. The code was tested against analytical calculations. Applications of the code included investigation of the propagation of sharp chemical reaction fronts, metasomatic alteration of microcline at elevated temperatures and pressures, and ion-exchange in a porous column. Finally numerical calculations describing fluid flow in crystalline rock in the presence of a temperature gradient were compared with experimental results for quartzite.

  5. Assessment of transient storage exchange and advection-dispersion mechanisms from concentration signatures along breakthrough curves

    NASA Astrophysics Data System (ADS)

    Zaramella, M.; Marion, A.; Lewandowski, J.; Nützmann, G.

    2016-07-01

    Solute transport in rivers is controlled by surface flow hydrodynamics and by transient storage in dead zones, pockets of vegetation and hyporheic sediments where mass exchange and retention are governed by complex mechanisms. The physics of these processes are generally investigated by optimization of transient storage models (TSMs) to experimental data often yielding inconsistent and equifinal parameter sets. Uncertainty on parameters estimation is found to depend not only on the rates of exchange between the stream and storage zones, the stream-water velocity and the stream reach length according to the experimental Damkohler number (DaI), but also on the relative significance between transient storage and longitudinal dispersion on breakthrough curves (BTCs). An optimization strategy was developed and applied to an experimental dataset obtained from tracer tests in a small lowland river, analyzing BTCs generated through tracer injections under different conditions. The method supplies a tool to estimate model parameters from observed data through the analysis of the relative parameter significance. To analyze model performance a double compartment TSM was optimized by a regular fit procedure based on simple root mean square error minimization and by a fit based on a relative significance analysis of mechanism signatures. As a result consistent longitudinal dispersion and transient storage parameters were obtained when the signature targeted optimization was used.

  6. Large-scale advection and dispersion in the tidal Hudson River derived from a deliberate tracer release experiment

    NASA Astrophysics Data System (ADS)

    Ho, D. T.; Schlosser, P.; Schlosser, P.; Schlosser, P.; Caplow, T.; Garrison, M. R.

    2001-12-01

    In recent years, deliberate tracer release experiments have been used in the ocean, rivers, lakes, and groundwater flow systems to study advection, mixing, air-water gas exchange, and exchanges between subsystems. Here we report results from a recent deliberate tracer release experiment conducted in the tidal Hudson River. On July 25, 2001, ca. 3.3 moles of the inert gas SF6 were injected into the Hudson River near Newburgh, NY at a depth of about 6 m. Subsequently, the SF6 was monitored from a boat (Riverkeeper) by pumping water (from 2 m depth) via a submersed pump mounted on the front of the boat, through a gas extraction unit, followed by measurement using an onboard gas chromatograph. The measurement interval was about 2 minutes and the maximum speed of the boat was about 15 km h-1. This allowed us to obtain detailed surveys of the temporal evolution of the tracer plume for 14 days. Initial results from the experiment show that during July/August 2001, there was virtually no net downward advection of the water body originally tagged with SF6. Instead, we observed rapid mixing of the tracer-tagged water up- and down-river. After one week, the tracer-tagged water could be detected over a stretch of 70 km along the axis of the river channel. At this time, the stretch of river labeled with concentrations >50% of the peak value was about 14 km. After two weeks, the tracer-tagged water had extended to over 90 km, while 28 km had SF6 concentrations >50% of the peak value. Vertical mixing into depressions on the bottom of the river reaching more than 175 feet seemed to be rapid. Dispersion coefficients and vertical turbulent exchange coefficients will be discussed.

  7. Spatial Moment Equations for a Groundwater Plume with Degradation and Rate-Limited Sorption

    EPA Science Inventory

    In this note, we analytically derive the solution for the spatial moments of groundwater solute concentration distributions simulated by a one-dimensional model that assumes advective-dispersive transport with first-order degradation and rate-limited sorption. Sorption kinetics...

  8. Derivation of a Multiparameter Gamma Model for Analyzing the Residence-Time Distribution Function for Nonideal Flow Systems as an Alternative to the Advection-Dispersion Equation

    DOE PAGESBeta

    Embry, Irucka; Roland, Victor; Agbaje, Oluropo; Watson, Valetta; Martin, Marquan; Painter, Roger; Byl, Tom; Sharpe, Lonnie

    2013-01-01

    A new residence-time distribution (RTD) function has been developed and applied to quantitative dye studies as an alternative to the traditional advection-dispersion equation (AdDE). The new method is based on a jointly combined four-parameter gamma probability density function (PDF). The gamma residence-time distribution (RTD) function and its first and second moments are derived from the individual two-parameter gamma distributions of randomly distributed variables, tracer travel distance, and linear velocity, which are based on their relationship with time. The gamma RTD function was used on a steady-state, nonideal system modeled as a plug-flow reactor (PFR) in the laboratory to validate themore » effectiveness of the model. The normalized forms of the gamma RTD and the advection-dispersion equation RTD were compared with the normalized tracer RTD. The normalized gamma RTD had a lower mean-absolute deviation (MAD) (0.16) than the normalized form of the advection-dispersion equation (0.26) when compared to the normalized tracer RTD. The gamma RTD function is tied back to the actual physical site due to its randomly distributed variables. The results validate using the gamma RTD as a suitable alternative to the advection-dispersion equation for quantitative tracer studies of non-ideal flow systems.« less

  9. Real-scale miscible grout injection experiment and performance of advection-dispersion-filtration model

    NASA Astrophysics Data System (ADS)

    Bouchelaghem, F.; Vulliet, L.; Leroy, D.; Laloui, L.; Descoeudres, F.

    2001-10-01

    A model was developed, to describe miscible grout propagation in a saturated deformable porous medium, based on Bear's statistical model with spatial volume averaging. In a previous paper, the model was first successfully confronted to one-dimensional laboratory experiments.In the present paper, the numerical model is used to simulate practical grouting operation in a cylindrical injection model. The cylindrical injection model lends itself to study main flow and propagation character istics for a dispersed suspension-type grout, under axisymmetric conditions close to real scale conditions.Comparison between numerical solutions and experimental results is essential to confirm the validity and accuracy of the proposed model from a phenomenological standpoint. The numerical model performances show that the underlying mathematical model constitutes a realistic predictive model reproducing most prominent features during injection of a suspension-type grout into a deformable porous medium. The basic mechanism by which injected miscible grout permeates a soil mass is discussed in detail. Such a tool leads to quality control criteria for grouting on a theoretical basis, which complements existing criteria acquired through engineering practice.

  10. Mathematical and numerical filtration-advection-dispersion model of miscible grout propagation in saturated porous media

    NASA Astrophysics Data System (ADS)

    Bouchelaghem, F.; Vulliet, L.

    2001-10-01

    The development of a predictive model of behaviour of porous media during injection of miscible grout, taking into account convection, dilution and filtration of grout solution with interstitial water, as well as consolidation aspects, is presented. Model assumptions are reviewed and discussed first. During the establishment of the model, we insist on surface terms and their physical relevance in expressing adsorption effects. Constitutive laws such as Fick's law for diffusive mass transport, hydrodynamic dispersion tensor dealing with miscibility, are modified by taking into account filtration effects. A new surface term appears in mass balance equations as a consequence of filtration. According to the filtration laws used, an initial filtration rate is estimated on the basis of a one-dimensional experimental campaign. The field equations are discretized by using Galerkin finite element and -scheme standard method. For transport equation, Streamline Upwind Petrov Galerkin method is employed to prevent numerical oscillations. Lastly, confrontation of numerical results with laboratory experiments constitutes a first step to validate the model on a realistic basis.

  11. Gas-phase diffusion in porous media: Evaluation of an advective- dispersive formulation and the dusty-gas model including comparison to data for binary mixtures

    SciTech Connect

    Webb, S.W.

    1996-05-01

    Two models for gas-phase diffusion and advection in porous media, the Advective-Dispersive Model (ADM) and the Dusty-Gas Model (DGM), are reviewed. The ADM, which is more widely used, is based on a linear addition of advection calculated by Darcy`s Law and ordinary diffusion using Fick`s Law. Knudsen diffusion is often included through the use of a Klinkenberg factor for advection, while the effect of a porous medium on the diffusion process is through a porosity-tortuosity-gas saturation multiplier. Another, more comprehensive approach for gas-phase transport in porous media has been formulated by Evans and Mason, and is referred to as the Dusty- Gas Model (DGM). This model applies the kinetic theory of gases to the gaseous components and the porous media (or ``dust``) to develop an approach for combined transport due to ordinary and Knudsen diffusion and advection including porous medium effects. While these two models both consider advection and diffusion, the formulations are considerably different, especially for ordinary diffusion. The various components of flow (advection and diffusion) are compared for both models. Results from these two models are compared to isothermal experimental data for He-Ar gas diffusion in a low-permeability graphite. Air-water vapor comparisons have also been performed, although data are not available, for the low-permeability graphite system used for the helium-argon data. Radial and linear air-water heat pipes involving heat, advection, capillary transport, and diffusion under nonisothermal conditions have also been considered.

  12. Advection and dispersion heat transport mechanisms in the quantification of shallow geothermal resources and associated environmental impacts.

    PubMed

    Alcaraz, Mar; García-Gil, Alejandro; Vázquez-Suñé, Enric; Velasco, Violeta

    2016-02-01

    Borehole Heat Exchangers (BHEs) are increasingly being used to exploit shallow geothermal energy. This paper presents a new methodology to provide a response to the need for a regional quantification of the geothermal potential that can be extracted by BHEs and the associated environmental impacts. A set of analytical solutions facilitates accurate calculation of the heat exchange of BHEs with the ground and its environmental impacts. For the first time, advection and dispersion heat transport mechanisms and the temporal evolution from the start of operation of the BHE are taken into account in the regional estimation of shallow geothermal resources. This methodology is integrated in a GIS environment, which facilitates the management of input and output data at a regional scale. An example of the methodology's application is presented for Barcelona, in Spain. As a result of the application, it is possible to show the strengths and improvements of this methodology in the development of potential maps of low temperature geothermal energy as well as maps of environmental impacts. The minimum and maximum energy potential values for the study site are 50 and 1800 W/m(2) for a drilled depth of 100 m, proportionally to Darcy velocity. Regarding to thermal impacts, the higher the groundwater velocity and the energy potential, the higher the size of the thermal plume after 6 months of exploitation, whose length ranges from 10 to 27 m long. A sensitivity analysis was carried out in the calculation of heat exchange rate and its impacts for different scenarios and for a wide range of Darcy velocities. The results of this analysis lead to the conclusion that the consideration of dispersion effects and temporal evolution of the exploitation prevent significant differences up to a factor 2.5 in the heat exchange rate accuracy and up to several orders of magnitude in the impacts generated. PMID:26605833

  13. Modeling the adsorption of Cr(III) from aqueous solution onto Agave lechuguilla biomass: study of the advective and dispersive transport.

    PubMed

    Romero-González, J; Walton, J C; Peralta-Videa, J R; Rodríguez, E; Romero, J; Gardea-Torresdey, J L

    2009-01-15

    The biosorption of Cr(III) onto packed columns of Agave lechuguilla was analyzed using an advective-dispersive (AD) model and its analytical solution. Characteristic parameters such as axial dispersion coefficients, retardation factors, and distribution coefficients were predicted as functions of inlet ion metal concentration, time, flow rate, bed density, cross-sectional column area, and bed length. The root-mean-square-error (RMSE) values 0.122, 0.232, and 0.285 corresponding to the flow rates of 1, 2, and 3 (10(-3))dm3min(-1), respectively, indicated that the AD model provides an excellent approximation of the simulation of lumped breakthrough curves for the adsorption of Cr(III) by lechuguilla biomass. Therefore, the model can be used for design purposes to predict the effect of varying operational conditions. PMID:18462882

  14. Aspects of numerical and representational methods related to the finite-difference simulation of advective and dispersive transport of freshwater in a thin brackish aquifer

    USGS Publications Warehouse

    Merritt, M.L.

    1993-01-01

    The simulation of the transport of injected freshwater in a thin brackish aquifer, overlain and underlain by confining layers containing more saline water, is shown to be influenced by the choice of the finite-difference approximation method, the algorithm for representing vertical advective and dispersive fluxes, and the values assigned to parametric coefficients that specify the degree of vertical dispersion and molecular diffusion that occurs. Computed potable water recovery efficiencies will differ depending upon the choice of algorithm and approximation method, as will dispersion coefficients estimated based on the calibration of simulations to match measured data. A comparison of centered and backward finite-difference approximation methods shows that substantially different transition zones between injected and native waters are depicted by the different methods, and computed recovery efficiencies vary greatly. Standard and experimental algorithms and a variety of values for molecular diffusivity, transverse dispersivity, and vertical scaling factor were compared in simulations of freshwater storage in a thin brackish aquifer. Computed recovery efficiencies vary considerably, and appreciable differences are observed in the distribution of injected freshwater in the various cases tested. The results demonstrate both a qualitatively different description of transport using the experimental algorithms and the interrelated influences of molecular diffusion and transverse dispersion on simulated recovery efficiency. When simulating natural aquifer flow in cross-section, flushing of the aquifer occurred for all tested coefficient choices using both standard and experimental algorithms. ?? 1993.

  15. Scaling the fractional advective-dispersive equation for numerical evaluation of microbial dynamics in confined geometries with sticky boundaries

    SciTech Connect

    Parashar, R.; Cushman, J.H.

    2008-06-20

    Microbial motility is often characterized by 'run and tumble' behavior which consists of bacteria making sequences of runs followed by tumbles (random changes in direction). As a superset of Brownian motion, Levy motion seems to describe such a motility pattern. The Eulerian (Fokker-Planck) equation describing these motions is similar to the classical advection-diffusion equation except that the order of highest derivative is fractional, {alpha} element of (0, 2]. The Lagrangian equation, driven by a Levy measure with drift, is stochastic and employed to numerically explore the dynamics of microbes in a flow cell with sticky boundaries. The Eulerian equation is used to non-dimensionalize parameters. The amount of sorbed time on the boundaries is modeled as a random variable that can vary over a wide range of values. Salient features of first passage time are studied with respect to scaled parameters.

  16. A finite-volume Eulerian-Lagrangian localized adjoint method for solution of the advection-dispersion equation

    USGS Publications Warehouse

    Healy, R.W.; Russell, T.F.

    1993-01-01

    Test results demonstrate that the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) outperforms standard finite-difference methods for solute transport problems that are dominated by advection. FVELLAM systematically conserves mass globally with all types of boundary conditions. Integrated finite differences, instead of finite elements, are used to approximate the governing equation. This approach, in conjunction with a forward tracking scheme, greatly facilitates mass conservation. The mass storage integral is numerically evaluated at the current time level, and quadrature points are then tracked forward in time to the next level. Forward tracking permits straightforward treatment of inflow boundaries, thus avoiding the inherent problem in backtracking of characteristic lines intersecting inflow boundaries. FVELLAM extends previous results by obtaining mass conservation locally on Lagrangian space-time elements. -from Authors

  17. Solution of the advection-dispersion equation in two dimensions by a finite-volume Eulerian-Lagrangian localized adjoint method

    USGS Publications Warehouse

    Healy, R.W.; Russell, T.F.

    1998-01-01

    We extend the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) for solution of the advection-dispersion equation to two dimensions. The method can conserve mass globally and is not limited by restrictions on the size of the grid Peclet or Courant number. Therefore, it is well suited for solution of advection-dominated ground-water solute transport problems. In test problem comparisons with standard finite differences, FVELLAM is able to attain accurate solutions on much coarser space and time grids. On fine grids, the accuracy of the two methods is comparable. A critical aspect of FVELLAM (and all other ELLAMs) is evaluation of the mass storage integral from the preceding time level. In FVELLAM this may be accomplished with either a forward or backtracking approach. The forward tracking approach conserves mass globally and is the preferred approach. The backtracking approach is less computationally intensive, but not globally mass conservative. Boundary terms are systematically represented as integrals in space and time which are evaluated by a common integration scheme in conjunction with forward tracking through time. Unlike the one-dimensional case, local mass conservation cannot be guaranteed, so slight oscillations in concentration can develop, particularly in the vicinity of inflow or outflow boundaries. Published by Elsevier Science Ltd.

  18. HIGH TEMPERATURE SORPTION OF CESIUM AND STRONTIUM ON DISPERSED KAOLINITE POWDERS

    EPA Science Inventory

    Sorption of cesium and strontium on kaolinite powders was investigated as a means to minimize the emissions of these metals during certain high-temperature processes currently being developed to isolate and dispose of radiological and mixed wastes. In this work, nonradioactive aq...

  19. STATISTICAL METHODOLOGY FOR ESTIMATING TRANSPORT PARAMETERS: THEORY AND APPLICATIONS TO ONE-DOMENSIONAL ADVECTIVE-DISPERSIVE SYSTEMS.

    USGS Publications Warehouse

    Wagner, Brian J.; Gorelick, Steven M.

    1986-01-01

    A simulation nonlinear multiple-regression methodology for estimating parameters that characterize the transport of contaminants is developed and demonstrated. Finite difference containment transport simulation is combined with a nonlinear weighted least squares multiple-regression procedure. The technique provides optimal parameter estimates and gives statistics for assessing the reliability of these estimates under certain general assumptions about the distributions of the random measurement errors. Monte Carlo analysis is used to estimate parameter reliability for a hypothetical homogeneous soil column for which concentration data contain large random measurement errors. The value of data collected spatially versus data collected temporally was investigated for estimation of velocity, dispersion coefficient, effective porosity, first-order decay rate, and zero-order production. The use of spatial data gave estimates that were 2-3 times more reliable than estimates based on temporal data for all parameters except velocity. (Estimated author abstract) Refs.

  20. Rain splash of soil grains as a stochastic advection-dispersion process, with implications for desert plant-soil interactions and land-surface evolution

    NASA Astrophysics Data System (ADS)

    Furbish, David Jon; Childs, Elise M.; Haff, Peter K.; Schmeeckle, Mark W.

    2009-09-01

    We formulate soil grain transport by rain splash as a stochastic advection-dispersion process. By taking into account the intermittency of grain motions activated by raindrop impacts, the formulation indicates that gradients in raindrop intensity, and thus grain activity (the volume of grains in motion per unit area) can be as important as gradients in grain concentration and surface slope in effecting transport. This idea is confirmed by rain splash experiments and manifest in topographic roughening via mound growth beneath desert shrubs. The formulation provides a framework for describing transport and dispersal of any soil material moveable by rain splash, including soil grains, soil-borne pathogens and nutrients, seeds, or debitage. As such it shows how classic models of topographic "diffusion" reflect effects of slope-dependent grain drift, not diffusion, and it highlights the role of rain splash in the ecological behavior of desert shrubs as "resource islands." Specifically, the growth of mounds beneath shrub canopies, where differential rain splash initially causes more grains to be splashed inward beneath the protective canopy than outward, involves the "harvesting" of nearby soil material, including nutrients. Mounds thus represent temporary storage of soil derived from areas surrounding the shrubs. As the inward grain flux associated with differential rain splash is sustained over the shrub lifetime, mound material is effectively sequestered from erosional processes that might otherwise move this material downslope. With shrub death and loss of the protective canopy, differential rain splash vanishes and the mound material is dispersed to the surrounding area, again subject to downslope movement.

  1. Actinide and technetium sorption on iron-silicate and dispersed clay colloids

    SciTech Connect

    Shade, J.W.; Ames, L.L.; McGarrah, J.E.

    1984-01-01

    Two different colloidal suspensions, representative of those found in waste package interaction tests, were prepared from iron metal and silica powders or sodium-bentonite at 90/sup 0/C. Aliquots were spiked with /sup 233/U, /sup 235/Np, /sup 237/Pu, or /sup 95m/Tc at pH ranges from 2 to 12, then shaken for 24 hours followed by a 15 A filtration. Zeta potential measurements were made on unspiked samples. Similar sorptive properties were observed for both colloids. At 25/sup 0/C both /sup 233/U and /sup 237/Pu exhibit maximum sorption (50-90%) near pH 6. Sorption drops by about a factor of 5 at pH > 8. Slight sorption of /sup 235/Np occurs at pH 11 and decreases to zero at lower pH values. /sup 95m/Tc does not sorb on Fe-silicates and is only slightly sorbed (10%) on smectites. 11 references, 4 figures, 2 tables.

  2. An upscaled approach for transport in media with extended tailing due to back-diffusion using analytical and numerical solutions of the advection dispersion equation

    NASA Astrophysics Data System (ADS)

    Parker, Jack C.; Kim, Ungtae

    2015-11-01

    The mono-continuum advection-dispersion equation (mADE) is commonly regarded as unsuitable for application to media that exhibit rapid breakthrough and extended tailing associated with diffusion between high and low permeability regions. This paper demonstrates that the mADE can be successfully used to model such conditions if certain issues are addressed. First, since hydrodynamic dispersion, unlike molecular diffusion, cannot occur upstream of the contaminant source, models must be formulated to prevent "back-dispersion." Second, large variations in aquifer permeability will result in differences between volume-weighted average concentration (resident concentration) and flow-weighted average concentration (flux concentration). Water samples taken from wells may be regarded as flux concentrations, while soil samples may be analyzed to determine resident concentrations. While the mADE is usually derived in terms of resident concentration, it is known that a mADE of the same mathematical form may be written in terms of flux concentration. However, when solving the latter, the mathematical transformation of a flux boundary condition applied to the resident mADE becomes a concentration type boundary condition for the flux mADE. Initial conditions must also be consistent with the form of the mADE that is to be solved. Thus, careful attention must be given to the type of concentration data that is available, whether resident or flux concentrations are to be simulated, and to boundary and initial conditions. We present 3-D analytical solutions for resident and flux concentrations, discuss methods of solving numerical models to obtain resident and flux concentrations, and compare results for hypothetical problems. We also present an upscaling method for computing "effective" dispersivities and other mADE model parameters in terms of physically meaningful parameters in a diffusion-limited mobile-immobile model. Application of the latter to previously published studies of

  3. An upscaled approach for transport in media with extended tailing due to back-diffusion using analytical and numerical solutions of the advection dispersion equation.

    PubMed

    Parker, Jack C; Kim, Ungtae

    2015-11-01

    The mono-continuum advection-dispersion equation (mADE) is commonly regarded as unsuitable for application to media that exhibit rapid breakthrough and extended tailing associated with diffusion between high and low permeability regions. This paper demonstrates that the mADE can be successfully used to model such conditions if certain issues are addressed. First, since hydrodynamic dispersion, unlike molecular diffusion, cannot occur upstream of the contaminant source, models must be formulated to prevent "back-dispersion." Second, large variations in aquifer permeability will result in differences between volume-weighted average concentration (resident concentration) and flow-weighted average concentration (flux concentration). Water samples taken from wells may be regarded as flux concentrations, while soil samples may be analyzed to determine resident concentrations. While the mADE is usually derived in terms of resident concentration, it is known that a mADE of the same mathematical form may be written in terms of flux concentration. However, when solving the latter, the mathematical transformation of a flux boundary condition applied to the resident mADE becomes a concentration type boundary condition for the flux mADE. Initial conditions must also be consistent with the form of the mADE that is to be solved. Thus, careful attention must be given to the type of concentration data that is available, whether resident or flux concentrations are to be simulated, and to boundary and initial conditions. We present 3-D analytical solutions for resident and flux concentrations, discuss methods of solving numerical models to obtain resident and flux concentrations, and compare results for hypothetical problems. We also present an upscaling method for computing "effective" dispersivities and other mADE model parameters in terms of physically meaningful parameters in a diffusion-limited mobile-immobile model. Application of the latter to previously published studies of

  4. Sorption of high explosives to water-dispersible clay: influence of organic carbon, aluminosilicate clay, and extractable iron.

    PubMed

    Dontsova, Katerina M; Hayes, Charolett; Pennington, Judith C; Porter, Beth

    2009-01-01

    Explosives in soils can present environmental problems for military installations. Fine, mobile particles represent the most reactive fraction of the soil and, therefore, are expected to adsorb explosives and potentially facilitate their transport. The objective of this study was to determine the relative significance of phyllosilicate clay, organic matter, and two forms of extractable iron in adsorption of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by the colloidal water-dispersible clay (WDC) fraction of the soil. The WDC fraction of two mineral and one organic soil was separated and then treated to remove organic carbon (OC) and several forms of iron (Fe(o), oxalate extractable, and Fe(d), dithionite-citrate extractable). Adsorption coefficients were determined for whole soils, untreated, and treated WDC. For mineral soils, adsorption of TNT and RDX on the WDC was greater than on the whole soil. The presence of OC increased explosives sorption by WDC. When OC was removed, iron interfered with TNT sorption. In the presence of OC, removal of Fe(o) decreased RDX adsorption and increased TNT adsorption indicating different adsorption mechanisms. Organic carbon was a more significant indicator of explosives adsorption by WDC than clays or iron oxides and hydroxides. Therefore, OC is the most likely medium for facilitated transport of TNT and RDX. PMID:19465721

  5. iCFD: Interpreted Computational Fluid Dynamics - Degeneration of CFD to one-dimensional advection-dispersion models using statistical experimental design - The secondary clarifier.

    PubMed

    Guyonvarch, Estelle; Ramin, Elham; Kulahci, Murat; Plósz, Benedek Gy

    2015-10-15

    The present study aims at using statistically designed computational fluid dynamics (CFD) simulations as numerical experiments for the identification of one-dimensional (1-D) advection-dispersion models - computationally light tools, used e.g., as sub-models in systems analysis. The objective is to develop a new 1-D framework, referred to as interpreted CFD (iCFD) models, in which statistical meta-models are used to calculate the pseudo-dispersion coefficient (D) as a function of design and flow boundary conditions. The method - presented in a straightforward and transparent way - is illustrated using the example of a circular secondary settling tank (SST). First, the significant design and flow factors are screened out by applying the statistical method of two-level fractional factorial design of experiments. Second, based on the number of significant factors identified through the factor screening study and system understanding, 50 different sets of design and flow conditions are selected using Latin Hypercube Sampling (LHS). The boundary condition sets are imposed on a 2-D axi-symmetrical CFD simulation model of the SST. In the framework, to degenerate the 2-D model structure, CFD model outputs are approximated by the 1-D model through the calibration of three different model structures for D. Correlation equations for the D parameter then are identified as a function of the selected design and flow boundary conditions (meta-models), and their accuracy is evaluated against D values estimated in each numerical experiment. The evaluation and validation of the iCFD model structure is carried out using scenario simulation results obtained with parameters sampled from the corners of the LHS experimental region. For the studied SST, additional iCFD model development was carried out in terms of (i) assessing different density current sub-models; (ii) implementation of a combined flocculation, hindered, transient and compression settling velocity function; and (iii

  6. CONTAMINANT TRANSPORT IN SEDIMENT UNDER THE INFLUENCE OF ADVECTIVE FLUX

    EPA Science Inventory

    Chemical flux across the sediment/water interface is controlled by a combination of diffusive, dispersive and advective processes. The advective process is a function of submarine groundwater discharge and tidal effects. In areas where surface water interacts with groundwater, ...

  7. Fast strontium transport induced by hydrodynamic dispersion and pH-dependent sorption

    NASA Astrophysics Data System (ADS)

    Prigiobbe, Valentina; Hesse, Marc A.; Bryant, Steven L.

    2012-09-01

    As a fluid carries solutes through a porous material, species that sorb onto the surface of the material travel more slowly than the fluid. Stronger adsorption results in slower solute migration, or increased solute retardation. The adsorption of strontium (Sr2+) onto iron-oxides is strongly pH-dependent and becomes significant at high pH. Radioactive Sr2+ isotopes are, therefore, commonly stored in alkaline solutions to maximize their retardation. Field observations and numerical simulations of the leakage of such solutions into low-pH soils, however, show that even Sr2+ stored in alkaline solutions can migrate without retardation. Migration occurs because hydrodynamic dispersion allows mixing of Sr2+ with the low-pH fluid forming an acidic Sr2+-rich plume which can travel without retardation. Here we report the first experimental observations confirming this dispersion-induced fast Sr2+ transport. We report column-flood experiments where a high-pH solution containing Sr2+ was injected into a low-pH porous medium of iron-oxide-coated beads. We observe both a strongly retarded Sr2+ front and an isolated fast pulse of Sr2+ traveling at the average fluid velocity. This dispersion-induced fast pulse of strontium must be taken into account when considering the safety of radionuclide storage in alkaline solutions.

  8. MT3DMS: A MODULAR THREE-DIMENSIONAL MULTISPECIES TRANSPORT MODEL FOR SIMULATION OF ADVECTION, DISPERSION, AND CHEMICAL REACTIONS OF CONTAMINANTS IN GROUNDWATER SYSTEMS: DOCUMENTATION AND USER'S GUIDE

    EPA Science Inventory

    This manual describes the next generation of the modular three-dimensional transport model, MT3D, with significantly expanded capabilities, including the addition of (a) a third-order total-variation-diminishing (TVD) scheme for solving the advection term that is mass conservativ...

  9. 2,4,6-trinitrotoluene (TNT) transformation/sorption in thin-disk soil columns under anaerobic conditions. Final report

    SciTech Connect

    Olin, T.J.; Myers, T.E.; Townsend, D.M.

    1996-09-01

    The sorption and transformation behavior of 2,4,6-trinitrotoluene (TNT) is important to modeling and remediation efforts at military installations where subsurface contamination exists in connection with munitions production. Processes potentially affecting the fate and transport of TNT in soils and groundwater include biotic and abiotic transformation, sorption, advection, hydrodynamic dispersion, dissolution, diffusion, and facilitated transport by organic and inorganic colloids (McGrath 1995). TNT breakthrough curves may provide indications of the type of processes occurring. The transformation rate of TNT is of particular interest in determining the long-term risk associated with TNT contamination in a soil.

  10. Using a Gas-Phase Tracer Test to Characterize the Impact of Landfill Gas Generation on Advective-Dispersive Transport of VOCs in the Vadose Zone

    PubMed Central

    Monger, Gregg R.; Duncan, Candice Morrison; Brusseau, Mark L.

    2015-01-01

    A gas-phase tracer test (GTT) was conducted at a landfill in Tucson, AZ, to help elucidate the impact of landfill gas generation on the transport and fate of chlorinated aliphatic volatile organic contaminants (VOCs). Sulfur hexafluoride (SF6) was used as the non-reactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well, and analyzed for SF6, CH4, CO2, and VOCs. The travel times determined for SF6 from the tracer test are approximately two to ten times smaller than estimated travel times that incorporate transport by only gas-phase diffusion. In addition, significant concentrations of CH4 and CO2 were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF6 are caused by advective transport associated with landfill gas generation. The rates of transport varied vertically, which is attributed to multiple factors including spatial variability of water content, refuse mass, refuse permeability, and gas generation. PMID:26380532

  11. Application of the method of temporal moments to interpret solute transport with sorption and degradation

    NASA Astrophysics Data System (ADS)

    Pang, Liping; Goltz, Mark; Close, Murray

    2003-01-01

    In this note, we applied the temporal moment solutions of [Das and Kluitenberg, 1996. Soil Sci. Am. J. 60, 1724] for one-dimensional advective-dispersive solute transport with linear equilibrium sorption and first-order degradation for time pulse sources to analyse soil column experimental data. Unlike most other moment solutions, these solutions consider the interplay of degradation and sorption. This permits estimation of a first-order degradation rate constant using the zeroth moment of column breakthrough data, as well as estimation of the retardation factor or sorption distribution coefficient of a degrading solute using the first moment. The method of temporal moment (MOM) formulae was applied to analyse breakthrough data from a laboratory column study of atrazine, hexazinone and rhodamine WT transport in volcanic pumice sand, as well as experimental data from the literature. Transport and degradation parameters obtained using the MOM were compared to parameters obtained by fitting breakthrough data from an advective-dispersive transport model with equilibrium sorption and first-order degradation, using the nonlinear least-square curve-fitting program CXTFIT. The results derived from using the literature data were also compared with estimates reported in the literature using different equilibrium models. The good agreement suggests that the MOM could provide an additional useful means of parameter estimation for transport involving equilibrium sorption and first-order degradation. We found that the MOM fitted breakthrough curves with tailing better than curve fitting. However, the MOM analysis requires complete breakthrough curves and relatively frequent data collection to ensure the accuracy of the moments obtained from the breakthrough data.

  12. Application of the method of temporal moments to interpret solute transport with sorption and degradation.

    PubMed

    Pang, Liping; Goltz, Mark; Close, Murray

    2003-01-01

    In this note, we applied the temporal moment solutions of [Das and Kluitenberg, 1996. Soil Sci. Am. J. 60, 1724] for one-dimensional advective-dispersive solute transport with linear equilibrium sorption and first-order degradation for time pulse sources to analyse soil column experimental data. Unlike most other moment solutions, these solutions consider the interplay of degradation and sorption. This permits estimation of a first-order degradation rate constant using the zeroth moment of column breakthrough data, as well as estimation of the retardation factor or sorption distribution coefficient of a degrading solute using the first moment. The method of temporal moment (MOM) formulae was applied to analyse breakthrough data from a laboratory column study of atrazine, hexazinone and rhodamine WT transport in volcanic pumice sand, as well as experimental data from the literature. Transport and degradation parameters obtained using the MOM were compared to parameters obtained by fitting breakthrough data from an advective-dispersive transport model with equilibrium sorption and first-order degradation, using the nonlinear least-square curve-fitting program CXTFIT. The results derived from using the literature data were also compared with estimates reported in the literature using different equilibrium models. The good agreement suggests that the MOM could provide an additional useful means of parameter estimation for transport involving equilibrium sorption and first-order degradation. We found that the MOM fitted breakthrough curves with tailing better than curve fitting. However, the MOM analysis requires complete breakthrough curves and relatively frequent data collection to ensure the accuracy of the moments obtained from the breakthrough data. PMID:12498577

  13. VAC: Versatile Advection Code

    NASA Astrophysics Data System (ADS)

    Tóth, Gábor; Keppens, Rony

    2012-07-01

    The Versatile Advection Code (VAC) is a freely available general hydrodynamic and magnetohydrodynamic simulation software that works in 1, 2 or 3 dimensions on Cartesian and logically Cartesian grids. VAC runs on any Unix/Linux system with a Fortran 90 (or 77) compiler and Perl interpreter. VAC can run on parallel machines using either the Message Passing Interface (MPI) library or a High Performance Fortran (HPF) compiler.

  14. Dispersal

    USGS Publications Warehouse

    2001-01-01

    The ability of species to migrate and disperse is a trait that has interested ecologists for many years. Now that so many species and ecosystems face major environmental threats from habitat fragmentation and global climate change, the ability of species to adapt to these changes by dispersing, migrating, or moving between patches of habitat can be crucial to ensuring their survival. This book provides a timely and wide-ranging overview of the study of dispersal and incorporates much of the latest research. The causes, mechanisms, and consequences of dispersal at the individual, population, species and community levels are considered. The potential of new techniques and models for studying dispersal, drawn from molecular biology and demography, is also explored. Perspectives and insights are offered from the fields of evolution, conservation biology and genetics. Throughout the book, theoretical approaches are combined with empirical data, and care has been taken to include examples from as wide a range of species as possible.

  15. Concentration through large advection

    NASA Astrophysics Data System (ADS)

    Aleja, D.; López-Gómez, J.

    2014-11-01

    In this paper we extend the elegant results of Chen, Lam and Lou [6, Section 2], where a concentration phenomenon was established as the advection blows up, to a general class of adventive-diffusive generalized logistic equations of degenerate type. Our improvements are really sharp as we allow the carrying capacity of the species to vanish in some subdomain with non-empty interior. The main technical devices used in the derivation of the concentration phenomenon are Proposition 3.2 of Cano-Casanova and López-Gómez [5], Theorem 2.4 of Amann and López-Gómez [1] and the classical Harnack inequality. By the relevance of these results in spatial ecology, complete technical details seem imperative, because the proof of Theorem 2.2 of [6] contains some gaps originated by an “optimistic” use of Proposition 3.2 of [5]. Some of the general assumptions of [6] are substantially relaxed.

  16. LAYER DEPENDENT ADVECTION IN CMAQ

    EPA Science Inventory

    The advection methods used in CMAQ require that the Courant-Friedrichs-Lewy (CFL) condition be satisfied for numerical stability and accuracy. In CMAQ prior to version 4.3, the ADVSTEP algorithm established CFL-safe synchronization and advection timesteps that were uniform throu...

  17. Competitive sorption of cis-DCE and TCE in silica gel as a model porous mineral solid.

    PubMed

    Avila, Manuel Alejandro Salaices; Breiter, Roman

    2008-08-01

    The competitive sorption of 1,2-cis-dichloroethene (cis-DCE) and trichloroethene (TCE) was investigated by means of column experiments using a model porous mineral solid represented by silica gel. The experimental isotherms were obtained by employing a chromatographic method. The competitive sorption isotherms were modelled with the extended Freundlich and extended Langmuir isotherms, using the parameters from single-solute experiments. The breakthrough curves were modelled with the advection-dispersion transport equation coupled with the lumped pore diffusion model. The best results were obtained when the extended Freundlich isotherm was employed. The competitive sorption was revealed with the presence of an overshoot in the breakthrough curve of cis-DCE and a decrease in the degree of sorption of cis-DCE (20%) and TCE (12%). A linear dependency of the overshoot with an increase in the concentration of cis-DCE at a fixed concentration of TCE was observed, between 16% and 20%, and at least at concentrations <6 mg L(-1) in the liquid phase. The displaced molecules of cis-DCE by TCE were accumulated through the column causing its overshoot; thus short columns may hinder its observation. Thermodynamic analysis shows an exothermic adsorption process of -34 to -41 kJ mol(-1), which is enhanced by sorption in micropores. The Gibbs free energy is positive for cis-DCE in the multi-component case, due to its displacement by TCE. PMID:18541287

  18. Dispersion of Natural Arsenic in the Malcantone Watershed, Southern Switzerland: Field Evidence for Repeated Sorption-Desorption and Oxidation-Reduction Processes

    SciTech Connect

    Pfeifer,H.; Gueye-Girardet, A.; Reymond, D.; Schlegel, C.; Temgoua, E.; Hesterberg, D.; Chou, J.

    2004-01-01

    In recent years, elevated arsenic concentrations have been found in waters and soils of many countries, often resulting in a health threat for the local population. Switzerland is not an exception and this paper deals with the release and subsequent fate of arsenic in a 200-km{sup 2} mountainous watershed, characterized by crystalline silicate rocks (gneisses, schists, amphibolites) that contain abundant As-bearing sulfide ore deposits, some of which have been mined for iron and gold in the past. Using analytical methods common for mineralogical, ground water and soil studies (XRD, XRF, XAS-XANES and -EXAFS, electron microprobe, extraction, ICP, AAS with hydride generator, ion chromatography), seven different field situations and related dispersion processes of natural arsenic have been studied: (1) release by rock weathering; (2) transport and deposition by water and ice; (3) release of As to the ground and surface water due to increasing pH; (4) accumulation in humic soil horizons; (5) remobilization by reduction in water-saturated soils and stagnant ground waters; (6) remobilization by using P-rich fertilizers or dung and (7) oxidation, precipitation and dilution in surface waters. Comparison of the results with experimental adsorption studies and speciation diagrams from the literature allows us to reconstruct and identify the typical behavior of arsenic in a natural environment under temperate climatic conditions. The main parameters identified are: (a) once liberated from the primary minerals, sorption processes on Fe-oxy-hydroxides dominate over Al-phases, such as Al-hydroxides or clay minerals and limit the As concentrations in the spring and well waters between 20 and 300 {mu}g/l. (b) Precipitation as secondary minerals is limited to the weathering domain, where the As concentrations are still high and not yet too diluted by rain and soils waters. (c) Although neutral and alkaline pH conditions clearly increase the mobility of As, the main factor to

  19. Experiments in Advective and Turbulent Hyporheic Pumping

    NASA Astrophysics Data System (ADS)

    Mccluskey, A. H.; Grant, S.; Stewardson, M. J.

    2014-12-01

    Hyporheic exchange (HE) is the mixing of stream and subsurface waters beneath the sediment-water interface (SWI). At the patch and reach scales, HE is dominated by periodic upwelling and downwelling zones, induced by pressure variation and processes within the turbulent boundary layer (TBL). This can be caused by (1) the geometry of the stream, imposing a stationary wave at the SWI or (2) by a travelling wave associated with the propagation of turbulent pressure waves generated from the TBL. Case (1) has generally been the favoured model of hyporheic exchange and has been referred to as hyporheic 'pumping' by Elliott and Brooks, and subsequently others. Case (2) can be termed turbulent pumping, and has been proposed as a mechanism to model the combined effects of turbulent dispersion alongside steady-state advection. While this has been represented numerically and analytically, conjecture remains about the physical representation of these combined processes. We present initial results from experiments undertaken to classify the spatial and temporal characteristics of pressure variation at and beneath the SWI, with a periodic sinusoidal geometry of wavelength 0.28m and height 0.02m. As an initial characterisation, the advective flow profile has been examined using time-lapse photography of dyes released across the span of a periodic downwelling zone. These tracer tests confirmed delineation of isolated upwelling and downwelling cells as noted by previous authors in modelling studies. However, their distribution deviates from the typical pumping pattern with increased discharge and stream gradient. Empirical orthogonal function (EOF) analysis of high frequency (250Hz) pressure measurements, sampled at an array along the centroid of the flume underneath one wavelength gave further insight into the spatial distribution of turbulent signatures arising from roughness-generated turbulence. A turbulent frequency of 6-10Hz dominates, however the penetration depth appears to

  20. Radionuclide migration laboratory studies for validation of batch sorption data

    SciTech Connect

    Triay, I.R.; Mitchell, A.J.; Ott, M.A.

    1991-12-31

    Advective and diffusive migration experiments (within the Dynamic Transport Column Experiments and Diffusion Studies of the Yucca Mountain Site Characterization Project) involve utilizing crushed material, intact, and fractured tuff in order to test and improve (if necessary) transport models by experimentally observing the migration of sorbing and non-sorbing radionuclides on a laboratory scale. Performing a validation of the sorption data obtained with batch techniques (within the Batch Sorption Study) is an integral part of the mission of the Dynamic Transport Column Experiments and Diffusion Studies. In this paper the work scope of the radionuclide migration laboratory experiments (as they apply to validation of batch sorption data) is reviewed.

  1. Modeling Np and Pu Transport with a Surface Complexation Model and Spatially Variant Sorption Capacities: Implications for Reactive Transport Modeling and Performance Assessments of Nuclear Waste Disposal Sites

    NASA Astrophysics Data System (ADS)

    Glynn, P. D.

    2002-12-01

    One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciation and sorption reactions on the ground-water transport of Np and Pu, two redox-sensitive elements. Earlier 1D simulations (Reardon, 1981) considered the kinetically-limited dissolution of calcite and its effect on ion-exchange reactions (involving 90Sr, Ca, Na, Mg and K), and documented the spatial variation of a 90Sr partition coefficient under both transient and steady-state chemical conditions. In contrast, the simulations presented here assume local equilibrium for all reactions, and consider sorption on constant potential, rather than constant charge, surfaces. Reardon's (1981) findings documenting the spatial and temporal variability of 90Sr partitioning are reexamined and found partially caused by his assumption of a kinetically-limited reaction. In the present simulations, sorption is assumed the only retardation process controlling Pu and Np transport, and is modeled using a diffuse-double-layer-surface-complexation model. Transport simulations consider the inflow of Np- and Pu-contaminated waters into an initially uncontaminated environment, followed by the cleanup of the resultant contamination with uncontaminated water. Simulations are conducted using different spatial distributions of sorption capacities (with the same total potential sorption capacity, i.e. the same total number of sorption sites, but with different variances and spatial correlation structures). A case with a spatially uniform distribution of sorption capacities was also simulated. Results obtained differ markedly from those that would be obtained in transport simulations using constant Kd, Langmuir, or Freundlich sorption models. When possible, simulation results (breakthrough curves) are fitted to a constant Kd advection-dispersion transport model and compared to each other. Functional differences are often great enough that they prevent a meaningful fit of the simulation results with

  2. Modification of a method-of-characteristics solute-transport model to incorporate decay and equilibrium-controlled sorption or ion exchange

    USGS Publications Warehouse

    Goode, D.J.; Konikow, L.F.

    1989-01-01

    The U.S. Geological Survey computer model of two-dimensional solute transport and dispersion in ground water (Konikow and Bredehoeft, 1978) has been modified to incorporate the following types of chemical reactions: (1) first-order irreversible rate-reaction, such as radioactive decay; (2) reversible equilibrium-controlled sorption with linear, Freundlich, or Langmuir isotherms; and (3) reversible equilibrium-controlled ion exchange for monovalent or divalent ions. Numerical procedures are developed to incorporate these processes in the general solution scheme that uses method-of- characteristics with particle tracking for advection and finite-difference methods for dispersion. The first type of reaction is accounted for by an exponential decay term applied directly to the particle concentration. The second and third types of reactions are incorporated through a retardation factor, which is a function of concentration for nonlinear cases. The model is evaluated and verified by comparison with analytical solutions for linear sorption and decay, and by comparison with other numerical solutions for nonlinear sorption and ion exchange.

  3. Modeling Np and Pu transport with a surface complexation model and spatially variant sorption capacities: implications for reactive transport modeling and performance assessments of nuclear waste disposal sites

    NASA Astrophysics Data System (ADS)

    Glynn, Pierre D.

    2003-04-01

    One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciation and sorption reactions on the ground-water transport of Np and Pu, two redox-sensitive elements. Earlier 1D simulations (Reardon, 1981) considered the kinetically limited dissolution of calcite and its effect on ion-exchange reactions (involving 90Sr, Ca, Na, Mg and K), and documented the spatial variation of a 90Sr partition coefficient under both transient and steady-state chemical conditions. In contrast, the simulations presented here assume local equilibrium for all reactions, and consider sorption on constant potential, rather than constant charge, surfaces. Reardon's (1981) seminal findings on the spatial and temporal variability of partitioning (of 90Sr) are reexamined and found partially caused by his assumption of a kinetically limited reaction. In the present work, sorption is assumed the predominant retardation process controlling Pu and Np transport, and is simulated using a diffuse-double-layer-surface-complexation (DDLSC) model. Transport simulations consider the infiltration of Np- and Pu-contaminated waters into an initially uncontaminated environment, followed by the cleanup of the resultant contamination with uncontaminated water. Simulations are conducted using different spatial distributions of sorption capacities (with the same total potential sorption capacity, but with different variances and spatial correlation structures). Results obtained differ markedly from those that would be obtained in transport simulations using constant Kd, Langmuir or Freundlich sorption models. When possible, simulation results (breakthrough curves) are fitted to a constant Kd advection-dispersion transport model and compared. Functional differences often are great enough that they prevent a meaningful fit of the simulation results with a constant Kd (or even a Langmuir or Freundlich) model, even in the case of Np, a weakly sorbed radionuclide under the simulation

  4. Modeling Np and Pu transport with a surface complexation model and spatially variant sorption capacities: Implications for reactive transport modeling and performance assessments of nuclear waste disposal sites

    USGS Publications Warehouse

    Glynn, P.D.

    2003-01-01

    One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciation and sorption reactions on the ground-water transport of Np and Pu, two redox-sensitive elements. Earlier 1D simulations (Reardon, 1981) considered the kinetically limited dissolution of calcite and its effect on ion-exchange reactions (involving 90Sr, Ca, Na, Mg and K), and documented the spatial variation of a 90Sr partition coefficient under both transient and steady-state chemical conditions. In contrast, the simulations presented here assume local equilibrium for all reactions, and consider sorption on constant potential, rather than constant charge, surfaces. Reardon's (1981) seminal findings on the spatial and temporal variability of partitioning (of 90Sr) are reexamined and found partially caused by his assumption of a kinetically limited reaction. In the present work, sorption is assumed the predominant retardation process controlling Pu and Np transport, and is simulated using a diffuse-double-layer-surface-complexation (DDLSC) model. Transport simulations consider the infiltration of Np- and Pu-contaminated waters into an initially uncontaminated environment, followed by the cleanup of the resultant contamination with uncontaminated water. Simulations are conducted using different spatial distributions of sorption capacities (with the same total potential sorption capacity, but with different variances and spatial correlation structures). Results obtained differ markedly from those that would be obtained in transport simulations using constant Kd, Langmuir or Freundlich sorption models. When possible, simulation results (breakthrough curves) are fitted to a constant K d advection-dispersion transport model and compared. Functional differences often are great enough that they prevent a meaningful fit of the simulation results with a constant K d (or even a Langmuir or Freundlich) model, even in the case of Np, a weakly sorbed radionuclide under the

  5. Super-diffusion versus competitive advection: a simulation

    NASA Astrophysics Data System (ADS)

    Del Moro, D.; Giannattasio, F.; Berrilli, F.; Consolini, G.; Lepreti, F.; Gošić, M.

    2015-04-01

    Context. Magnetic element tracking is often used to study the transport and diffusion of the magnetic field on the solar photosphere. From the analysis of the displacement spectrum of these tracers, it has recently been agreed that a regime of super-diffusivity dominates the solar surface. Quite habitually this result is discussed in the framework of fully developed turbulence. Aims: However, the debate whether the super-diffusivity is generated by a turbulent dispersion process, by the advection due to the convective pattern, or even by another process is still open, as is the question of the amount of diffusivity at the scales relevant to the local dynamo process. Methods: To understand how such peculiar diffusion in the solar atmosphere takes place, we compared the results from two different data sets (ground-based and space-borne) and developed a simulation of passive tracers advection by the deformation of a Voronoi network. Results: The displacement spectra of the magnetic elements obtained by the data sets are consistent in retrieving a super-diffusive regime for the solar photosphere, but the simulation also shows a super-diffusive displacement spectrum: its competitive advection process can reproduce the signature of super-diffusion. Conclusions: Therefore, it is not necessary to hypothesize a totally developed turbulence regime to explain the motion of the magnetic elements on the solar surface.

  6. The nature and role of advection in advection-diffusion equations used for modelling bed load transport

    NASA Astrophysics Data System (ADS)

    Ancey, Christophe; Bohorquez, Patricio; Heyman, Joris

    2016-04-01

    The advection-diffusion equation arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Stochastic models can also be used to derive this equation, with the significant advantage that they provide information on the statistical properties of particle activity. Stochastic models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. We develop an approach based on birth-death Markov processes, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received little attention. We show that particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due to velocity fluctuations), with the important consequence that local measurements depend on both the intrinsic properties of particle displacement and the dimensions of the measurement system.

  7. Regenerative Sorption Refrigerator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.; Wen, Liang-Chi; Bard, Steven

    1991-01-01

    Two-stage sorption refrigerator achieves increased efficiency via regenerative-heating concept in which waste heat from praseodymium/cerium oxide (PCO) chemisorption compressor runs charcoal/krypton (C/Kr) sorption compressor. Waste heat from each PCO sorption compressor used to power surrounding C/Kr sorption compressor. Flows of heat in two compressor modules controlled by gas-gap thermal switches. Has no wearing moving parts other than extremely long life, room-temperature check valves operating about twice per hour. Virtually no measurable vibration, and has potential operating life of at least ten years.

  8. Comparison of neptunium sorption results using batch and column techniques

    SciTech Connect

    Triay, I.R.; Furlano, A.C.; Weaver, S.C.; Chipera, S.J.; Bish, D.L.

    1996-08-01

    We used crushed-rock columns to study the sorption retardation of neptunium by zeolitic, devitrified, and vitric tuffs typical of those at the site of the potential high-level nuclear waste repository at Yucca Mountain, Nevada. We used two sodium bicarbonate waters (groundwater from Well J-13 at the site and water prepared to simulate groundwater from Well UE-25p No. 1) under oxidizing conditions. It was found that values of the sorption distribution coefficient, Kd, obtained from these column experiments under flowing conditions, regardless of the water or the water velocity used, agreed well with those obtained earlier from batch sorption experiments under static conditions. The batch sorption distribution coefficient can be used to predict the arrival time for neptunium eluted through the columns. On the other hand, the elution curves showed dispersivity, which implies that neptunium sorption in these tuffs may be nonlinear, irreversible, or noninstantaneous. As a result, use of a batch sorption distribution coefficient to calculate neptunium transport through Yucca Mountain tuffs would yield conservative values for neptunium release from the site. We also noted that neptunium (present as the anionic neptunyl carbonate complex) never eluted prior to tritiated water, which implies that charge exclusion does not appear to exclude neptunium from the tuff pores. The column experiments corroborated the trends observed in batch sorption experiments: neptunium sorption onto devitrified and vitric tuffs is minimal and sorption onto zeolitic tuffs decreases as the amount of sodium and bicarbonate/carbonate in the water increases.

  9. Surfzone alongshore advective accelerations: observations and modeling

    NASA Astrophysics Data System (ADS)

    Hansen, J.; Raubenheimer, B.; Elgar, S.

    2014-12-01

    The sources, magnitudes, and impacts of non-linear advective accelerations on alongshore surfzone currents are investigated with observations and a numerical model. Previous numerical modeling results have indicated that advective accelerations are an important contribution to the alongshore force balance, and are required to understand spatial variations in alongshore currents (which may result in spatially variable morphological change). However, most prior observational studies have neglected advective accelerations in the alongshore force balance. Using a numerical model (Delft3D) to predict optimal sensor locations, a dense array of 26 colocated current meters and pressure sensors was deployed between the shoreline and 3-m water depth over a 200 by 115 m region near Duck, NC in fall 2013. The array included 7 cross- and 3 alongshore transects. Here, observational and numerical estimates of the dominant forcing terms in the alongshore balance (pressure and radiation-stress gradients) and the advective acceleration terms will be compared with each other. In addition, the numerical model will be used to examine the force balance, including sources of velocity gradients, at a higher spatial resolution than possible with the instrument array. Preliminary numerical results indicate that at O(10-100 m) alongshore scales, bathymetric variations and the ensuing alongshore variations in the wave field and subsequent forcing are the dominant sources of the modeled velocity gradients and advective accelerations. Additional simulations and analysis of the observations will be presented. Funded by NSF and ASDR&E.

  10. Advection fog formation in a polluted atmosphere

    SciTech Connect

    Hung, R.J.; Liaw, G.S.

    1981-01-01

    Large quantities of atmospheric aerosols with composition SO/sub 4//sup 2 -/, NO/sub 3//sup -/ and NH/sub 4//sup +/ have been detected in highly industrialized areas. The major portions of aerosol products are the results of energy related fuel combustion. Both microphysical and macrophysical processes are considered in investigating the time dependent evolution of the saturation spectra of condensation nuclei associated with both polluted and clean atmospheres during the time periods of advection fog formation. The results show that the condensation nuclei associated with a polluted atmosphere provide more favorable conditions than condensation nuclei associated with a clean atmosphere to produce dense advection fog, and that attaining a certain degree of supersaturation is not necessarily required for the formation of advection fog with condensation nuclei associated with a polluted atmosphere for monodisperse distribution.

  11. Antidiffusive velocities for multipass donor cell advection

    SciTech Connect

    Margolin, L.; Smolarkiewicz, P.K.

    1999-01-01

    Multidimensional positive definite advection transport algorithm (MPDATA) is an iterative process for approximating the advection equation, which uses a donor cell approximation to compensate for the truncation error of the originally specified donor cell scheme. This step may be repeated an arbitrary number of times, leading to successfully more accurate solutions to the advection equation. In this paper, the authors show how to sum the successive approximations analytically to find a single antidiffusive velocity that represents the effects of an arbitrary number of passes. The analysis is first done in one dimension to illustrate the method and then is repeated in two dimensions. The existence of cross terms in the truncation analysis of the two-dimensional equations introduces an extra complication into the calculation. The authors discuss the implementation of the antidiffusive velocities and provide some examples of applications, including a third-order accurate scheme.

  12. MAGNETIC ADVECTION DUE TO DIFFUSIVITY GRADIENTS

    NASA Astrophysics Data System (ADS)

    Zita, E. J.

    2009-12-01

    We derive and discuss an important source of advection of magnetic fields in plasmas, for a completely general case. Magnetic diffusivity is proportional to electrical resistivity: where the value this parameter is high, it is well known that magnetic fields can leak (or diffuse) rapidly into (or out) of the plasma. Magnetohydrodynamic lore has it that where gradients, or changes in space, of the value of the diffusivity are high, magnetic fields can have enhanced flow (or advection). We derive this phenomenon rigorously, compare our results to other work in the literature, and discuss its implications, especially for kinematic dynamos. As an extra mathematical bonus, we find that the magnetic advection due to diffusivity gradients can be expressed in terms of a diffusion equation within the induction equation, making its computational implementation especially simple.

  13. Efficient mass transport by optical advection

    NASA Astrophysics Data System (ADS)

    Kajorndejnukul, Veerachart; Sukhov, Sergey; Dogariu, Aristide

    2015-10-01

    Advection is critical for efficient mass transport. For instance, bare diffusion cannot explain the spatial and temporal scales of some of the cellular processes. The regulation of intracellular functions is strongly influenced by the transport of mass at low Reynolds numbers where viscous drag dominates inertia. Mimicking the efficacy and specificity of the cellular machinery has been a long time pursuit and, due to inherent flexibility, optical manipulation is of particular interest. However, optical forces are relatively small and cannot significantly modify diffusion properties. Here we show that the effectiveness of microparticle transport can be dramatically enhanced by recycling the optical energy through an effective optical advection process. We demonstrate theoretically and experimentally that this new advection mechanism permits an efficient control of collective and directional mass transport in colloidal systems. The cooperative long-range interaction between large numbers of particles can be optically manipulated to create complex flow patterns, enabling efficient and tunable transport in microfluidic lab-on-chip platforms.

  14. Kinetics of the sorption of triterpene saponin by hypercrosslinked polystyrene

    NASA Astrophysics Data System (ADS)

    Mironenko, N. V.; Brezhneva, T. A.; Selemenev, V. F.

    2013-03-01

    The kinetics of sorption of triterpene saponin by the polymer sorbent NM-200 is considered. The influence of the surface activity of glycoside on the rate of formation and structure of the adsorption layer on the sorbent's surface is established. The rate-determining step of sorption is found to be diffusion into the sorbent grain. The value of the activation energy demonstrates the determining role of dispersion forces in the interaction between triterpene saponin and the polymer sorbent MN-200.

  15. SEPs Dropout Events Associated with Advected Interplanetary Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Bruno, R.; Trenchi, L.; Telloni, D.; D'Amicis, R.; Marcucci, F.; Zurbuchen, T.; Weberg, M. J.

    2013-05-01

    The intensity profile of energetic particles from impulsive solar flares (SEP) often shows abrupt dropouts affecting all energies simultaneously, without time-dispersion. Part of the community thinks that these modulations are directly related to the presence of magnetic structures with a different magnetic topology advected by the wind, a sort of magnetic flux tubes. During the expansion, following the dynamical interaction between plasma regions travelling at different speed, these structures would be partially tangled up in a sort of spaghetti-like bundle. These flux tubes would be alternatively connected or not connected with the flare site and, consequently, they would be filled or devoid of SEPs. When the observer passes through them, he would observe clear particles dropout signatures. We will report about results from a detailed analysis of SEP events which showed several signatures in the local magnetic field and/or plasma parameters associated with SEP modulations. These findings corroborate the idea of a possible link between these particles events observed at the Earth's orbit and magnetic connection or disconnection of the ambient magnetic field with the flare region at the Sun. We will also discuss the advantages represented by future Solar Orbiter in-situ observations. As a matter of fact, Solar Orbiter, from its orbital vantage point during the quasi corotation phase, will be a priviledged observer of this kind of phenomenon since it will observe the advected structure of the solar wind not yet reprocessed by dynamical interaction due to wind expansion.

  16. 3D Flow Visualization Using Texture Advection

    NASA Technical Reports Server (NTRS)

    Kao, David; Zhang, Bing; Kim, Kwansik; Pang, Alex; Moran, Pat (Technical Monitor)

    2001-01-01

    Texture advection is an effective tool for animating and investigating 2D flows. In this paper, we discuss how this technique can be extended to 3D flows. In particular, we examine the use of 3D and 4D textures on 3D synthetic and computational fluid dynamics flow fields.

  17. Evolution of Advection Upstream Splitting Method Schemes

    NASA Technical Reports Server (NTRS)

    Liou, Meng-Sing

    2010-01-01

    This paper focuses on the evolution of advection upstream splitting method(AUSM) schemes. The main ingredients that have led to the development of modern computational fluid dynamics (CFD) methods have been reviewed, thus the ideas behind AUSM. First and foremost is the concept of upwinding. Second, the use of Riemann problem in constructing the numerical flux in the finite-volume setting. Third, the necessity of including all physical processes, as characterised by the linear (convection) and nonlinear (acoustic) fields. Fourth, the realisation of separating the flux into convection and pressure fluxes. The rest of this review briefly outlines the technical evolution of AUSM and more details can be found in the cited references. Keywords: Computational fluid dynamics methods, hyperbolic systems, advection upstream splitting method, conservation laws, upwinding, CFD

  18. Passive advection in a collisionless plasma

    NASA Astrophysics Data System (ADS)

    Kanekar, Anjor; Schekochihin, Alexander; Hammett, Greg; Dorland, William; Loureiro, Nuno

    2014-10-01

    We consider a simple kinetic model for the evolution of the particle distribution function in a magnetized turbulent plasma that includes both phase mixing (Landau damping) and advection by a stochastic velocity field: a ``kinetic passive scalar'' in the Batchelor regime. The advection due to stochastic velocity field allows for a stochastic version of the plasma echo by coupling the ``phase-mixing'' and the ``un-phase-mixing'' components of the free energy. We have developed a new analytical framework to diagnose the efficiency of such coupling. We have also developed a new GPU code named Gandalf that solves this kinetic model numerically. In this poster, we shall present numerical and analytical results related to this work.

  19. Antidiffusive velocities for multipass donor cell advection

    SciTech Connect

    Margolin, L.G. ); Smolarkiewicz, P.K. )

    1989-12-01

    Smolarkiewicz describes an iterative process for approximating the advection equation. Basically, he uses a donor cell approximation to correct for the truncation error of the originally specified donor cell scheme. This step may be repeated an arbitrary number of times leading to successively more accurate solutions to the advection equation. In this report, we show how to sum the successive approximations analytically to find a single antidiffusive velocity that represents the effects of an arbitrary number of passes. The analysis is first done dimension to illustrate the method. The analysis is then repeated in two dimensions. The existence of cross terms in the truncation analysis of the two-dimensional equations introduces an extra complication into the calculation. We discuss the implementation of our new antidiffusive velocities and provide some examples of applications. 6 refs., 5 figs., 4 tabs.

  20. Distributed Parallel Particle Advection using Work Requesting

    SciTech Connect

    Muller, Cornelius; Camp, David; Hentschel, Bernd; Garth, Christoph

    2013-09-30

    Particle advection is an important vector field visualization technique that is difficult to apply to very large data sets in a distributed setting due to scalability limitations in existing algorithms. In this paper, we report on several experiments using work requesting dynamic scheduling which achieves balanced work distribution on arbitrary problems with minimal communication overhead. We present a corresponding prototype implementation, provide and analyze benchmark results, and compare our results to an existing algorithm.

  1. High Order Semi-Lagrangian Advection Scheme

    NASA Astrophysics Data System (ADS)

    Malaga, Carlos; Mandujano, Francisco; Becerra, Julian

    2014-11-01

    In most fluid phenomena, advection plays an important roll. A numerical scheme capable of making quantitative predictions and simulations must compute correctly the advection terms appearing in the equations governing fluid flow. Here we present a high order forward semi-Lagrangian numerical scheme specifically tailored to compute material derivatives. The scheme relies on the geometrical interpretation of material derivatives to compute the time evolution of fields on grids that deform with the material fluid domain, an interpolating procedure of arbitrary order that preserves the moments of the interpolated distributions, and a nonlinear mapping strategy to perform interpolations between undeformed and deformed grids. Additionally, a discontinuity criterion was implemented to deal with discontinuous fields and shocks. Tests of pure advection, shock formation and nonlinear phenomena are presented to show performance and convergence of the scheme. The high computational cost is considerably reduced when implemented on massively parallel architectures found in graphic cards. The authors acknowledge funding from Fondo Sectorial CONACYT-SENER Grant Number 42536 (DGAJ-SPI-34-170412-217).

  2. Efficient mass transport by optical advection

    PubMed Central

    Kajorndejnukul, Veerachart; Sukhov, Sergey; Dogariu, Aristide

    2015-01-01

    Advection is critical for efficient mass transport. For instance, bare diffusion cannot explain the spatial and temporal scales of some of the cellular processes. The regulation of intracellular functions is strongly influenced by the transport of mass at low Reynolds numbers where viscous drag dominates inertia. Mimicking the efficacy and specificity of the cellular machinery has been a long time pursuit and, due to inherent flexibility, optical manipulation is of particular interest. However, optical forces are relatively small and cannot significantly modify diffusion properties. Here we show that the effectiveness of microparticle transport can be dramatically enhanced by recycling the optical energy through an effective optical advection process. We demonstrate theoretically and experimentally that this new advection mechanism permits an efficient control of collective and directional mass transport in colloidal systems. The cooperative long-range interaction between large numbers of particles can be optically manipulated to create complex flow patterns, enabling efficient and tunable transport in microfluidic lab-on-chip platforms. PMID:26440069

  3. Determination of bacterial and viral transport parameters in a gravel aquifer assuming linear kinetic sorption and desorption

    NASA Astrophysics Data System (ADS)

    Mallén, G.; Maloszewski, P.; Flynn, R.; Rossi, P.; Engel, M.; Seiler, K.-P.

    2005-05-01

    The bacteria Escherichia coli and Pseudomonas putida, and the bacteriophage virus H40/1 are examined both for their transport behaviour relative to inert solute tracers and for their modelability under natural flow conditions in a gravel aquifer. The microbes are attenuated in the following sequence: H40/1≥ P. putida≫ E. coli. The latter is desorbed almost completely within a few days. Breakthrough and recovery curves of the simultaneously injected non-reactive tracers are simulated with the 2D and 1D dispersion equation, in order to ascertain longitudinal dispersivity ( αL) and mean flow time ( T0). Mathematical modelling is difficult due to the aquifer heterogeneity, which results in preferential flow paths between injection and observation wells. Therefore, any attempt of fitting the dispersion model (DM) to the entire inert-tracer breakthrough curve (BTC) fails. Adequate fitting of the model to measured data only succeeds using a DM consisting of a superposition of several BTCs, each representing another set of flow paths. This gives rise to a multimodal, rather than a Gaussian groundwater velocity distribution. Only hydraulic parameters derived from the fastest partial curve, which is fitted to the rising part of the Uranine BTC, are suitable to model microbial breakthroughs. The hydraulic parameters found using 2D and 1D models were nearly identical. Their values were put into an analytical solution of 1D advective-dispersive transport combined with two-site reaction model introduced by Cameron and Klute [Cameron, D.R., Klute, A., 1977. Convective-dispersive solute transport with a combined equilibrium and kinetic adsorption model. Water Resour. Res. 13, 183-189], in order to identify reactive transport parameters (sorption/desorption) and attenuation mechanisms for the microbes migration. This shows that the microbes are almost entirely transported through preferential flow paths, which are represented by the first partial curve. Inert tracers, however

  4. Metal sorption on kaolinite

    SciTech Connect

    Westrich, H.R.; Brady, P.V.; Cygan, R.T.; Nagy, K.L.; Anderson, H.L.

    1997-03-01

    A key issue in performance assessment of low-level radioactive waste sites is predicting the transport and retardation of radionuclides through local soils under a variety of hydrologic and geochemical conditions. Improved transport codes should include a mechanistic model of radionuclide retardation. The authors have been investigating metal sorption (Cs{sup +}, Sr{sup 2+}, and Ba{sup 2+}) on a simple clay mineral (kaolinite) to better understand the geochemical interactions of common soil minerals with contaminated groundwaters. These studies include detailed characterizations of kaolinite surfaces, experimental adsorption measurements, surface complexation modeling, and theoretical simulations of cation sorption. The aluminol edge (010) site has been identified as the most likely site for metal sorption on kaolinite in natural solutions. Relative metal binding strengths decrease from Ba{sup 2+} to Sr{sup 2+} to Cs{sup +}, with some portion sorbed on both kaolinite edges and basal surfaces. Some Cs{sup +} also appears to be irreversibly sorbed on both sites. Molecular dynamics simulations suggest that Cs{sup +} is sorbed at aluminol (010) edge sites as an inner-sphere complex and weakly sorbed as an outer-sphere complex on (001) basal surfaces. These results provide the basis to understand and predict metal sorption onto kaolinite, and a framework to characterize sorption processes on more complex clay minerals.

  5. Study of Sorption Properties of Aluminium Oxides and Hydroxides Powders Obtained by Electro-Impulse Methods

    NASA Astrophysics Data System (ADS)

    Zhuravkov, S. P.; Lobanova, G. L.; Martemiyanov, D. V.; Nadeina, L. V.

    2015-04-01

    Experimental results of physicochemical and sorption properties of material samples obtained by electro-spark dispersion in water and by conductor electric explosion in argon are shown in the paper. Due to comparison of investigated samples sorption activity under static conditions, it was able to determine the most effective samples in the process of extraction of Cu2+ ions from aqueous solutions.

  6. Hydrophobic conjugated microporous polymers for sorption of human serum albumin

    NASA Astrophysics Data System (ADS)

    Zheng, Chunli; Du, Miaomiao; Feng, Shanshan; Sun, Hanxue; Li, An; He, Chi; Zhang, TianCheng; Wang, Qiaorui; Wei, Wei

    2016-02-01

    This paper investigated the sorption of human serum albumin (HSA) from water by three kinds of conjugated microporous polymers (CMPs) with surface hydrophobicity and intrinsic porosity. It was found that the three CMPs captured HSA with fast sorption kinetics and good working capacity. Equilibrium was obtained at 80 min for all the tests, and the maximum sorption quantity (qm) ranged from 0.07 to 0.14 mg/mg. With the increase in the particle external surface area of the CMPs, a greater extent of HSA sorption was achieved. Moreover, promoting the dispersion of CMPs in HSA aqueous solution was also beneficial to the extraction. Attenuated Total Reflection Fourier Transform Infrared spectroscopy verified the interactions between the CMPs and the Nsbnd H, Cdbnd O, and Csbnd N groups of HSA. This paper might provide fundamental guidance for the practical application of CMPs to proteins separation and recovery.

  7. Status Of Sorption Cryogenic Refrigeration

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.

    1988-01-01

    Report reviews sorption refrigeration. Developed for cooling infrared detectors, cryogenic research, and other advanced applications, sorption refrigerators have few moving parts, little vibration, and lifetimes of 10 years or more. Describes types of sorption stages, multistage and hybrid refrigeration systems, power requirements, cooling capacities, and advantages and disadvantages of various stages and systems.

  8. Advection and diffusion in shoreline change prediction

    NASA Astrophysics Data System (ADS)

    Anderson, T. R.; Frazer, L. N.

    2010-12-01

    We added longshore advection and diffusion to the simple cross-shore rate calculation method, as used widely by the USGS and others, to model historic shorelines and to predict future shoreline positions; and applied this to Hawaiian Island beach data. Aerial photographs, sporadically taken throughout the past century, yield usable, albeit limited, historic shoreline data. These photographs provide excellent spatial coverage, but poor temporal resolution, of the shoreline. Due to the sparse historic shoreline data, and the many natural and anthropogenic events influencing coastlines, we constructed a simplistic shoreline change model that can identify long-term behavior of a beach. Our new, two-dimensional model combines the simple rate method to accommodate for cross-shore sediment transport with the classic Pelnard-Considère model for diffusion, as well as a longshore advection speed term. Inverse methods identify cross-shore rate, longshore advection speed, and longshore diffusivity down a sandy coastline. A spatial averaging technique then identifies shoreline segments where one parameter can reasonably account for the cross-shore and longshore transport rates in that area. This produces model results with spatial resolution more appropriate to the temporal spacing of the data. Because changes in historic data can be accounted for by varying degrees of cross-shore and longshore sediment transport - for example, beach erosion can equally be explained by sand moving either off-shore or laterally - we tested several different model scenarios on the data: allowing only cross-shore sediment movement, only longshore movement, and a combination of the two. We used statistical information criteria to determine both the optimal spatial resolution and best-fitting scenario. Finally, we employed a voting method predicting the relaxed shoreline position over time.

  9. Sorption vacuum trap

    NASA Technical Reports Server (NTRS)

    Barrington, A. E.; Caruso, A. J.

    1970-01-01

    Modified sorption trap for use in high vacuum systems contains provisions for online regeneration of sorbent material. Trap is so constructed that it has a number of encapsulated resistance heaters and a valving and pumping device for removing gases from heated sorbing material. Excessive downtime is eliminated with this trap.

  10. Kinetics of sorption of uranium(VI) compounds with zirconium-silica nanosorbents

    NASA Astrophysics Data System (ADS)

    Perlova, O. V.; Sazonova, V. F.; Perlova, N. A.; Yaroshenko, N. A.

    2014-06-01

    The kinetics of sorption of uranium(VI) compounds from sulfate and carbonate solutions using four samples of mesoporous zirconium-silica nanosorbents obtained by bitemplate (solubilization) synthesis was studied. The sorption equilibrium set-in time and the kinetic characteristics of sorption were shown to depend on the sorbent (its composition, specific surface area, dispersity, and pore size), the temperature, and the composition and pH of the solution from which uranium compounds are sorbed. The sorption kinetics was described by a first-order equation. The limiting stage of the process was found to be the external diffusion of uranium-containing particles to the sorbent surface.

  11. Coupled ensemble flow line advection and analysis.

    PubMed

    Guo, Hanqi; Yuan, Xiaoru; Huang, Jian; Zhu, Xiaomin

    2013-12-01

    Ensemble run simulations are becoming increasingly widespread. In this work, we couple particle advection with pathline analysis to visualize and reveal the differences among the flow fields of ensemble runs. Our method first constructs a variation field using a Lagrangian-based distance metric. The variation field characterizes the variation between vector fields of the ensemble runs, by extracting and visualizing the variation of pathlines within ensemble. Parallelism in a MapReduce style is leveraged to handle data processing and computing at scale. Using our prototype system, we demonstrate how scientists can effectively explore and investigate differences within ensemble simulations. PMID:24051840

  12. Advective turbulent transport in the fluid plasma

    NASA Astrophysics Data System (ADS)

    Min, Byung-Hoon; An, Chan-Yong; Kim, Chang-Bae

    2013-10-01

    The Hasegawa-Wakatani model (HWM) has been employed in pedagogical analyses of the physics behind the behavior of the tokamak plasmas. In addition to the geometric simplicity HWM has an appealing feature of sustaining autonomous quasi-steady state, unstable modes providing the power that is being transported by the nonlinear interactions and is eventually dissipated by the collisional damping at small scales. Emergence of the zonal flow out of the turbulence is a main candidate to cause the transition from the low plasma confinement to the high mode. In the study of such LH transition with the HWM, the adiabaticity parameter has been shown to play an important role in forcing the zonal flow that results in the regulation of the drift-wave turbulence. Instead of concentrating on the physics of the feedback loop between the turbulence and the zonal flow the present study focuses on the presence of the advective transport of the energy. Numerical simulations of HWM are performed and the connections between the advective transport and the zonal flow will be presented. This work was supported by the Supercpmputing Center/Korea Institute of Science and Technology Information with supercomputing resources including technical support (KSC-2013-C1-009).

  13. Advection, diffusion and delivery over a network

    PubMed Central

    Heaton, Luke L.M.; López, Eduardo; Maini, Philip K.; Fricker, Mark D.; Jones, Nick S.

    2014-01-01

    Many biological, geophysical and technological systems involve the transport of resource over a network. In this paper we present an algorithm for calculating the exact concentration of resource at any point in space or time, given that the resource in the network is lost or delivered out of the network at a given rate, while being subject to advection and diffusion. We consider the implications of advection, diffusion and delivery for simple models of glucose delivery through a vascular network, and conclude that in certain circumstances, increasing the volume of blood and the number of glucose transporters can actually decrease the total rate of glucose delivery. We also consider the case of empirically determined fungal networks, and analyze the distribution of resource that emerges as such networks grow over time. Fungal growth involves the expansion of fluid filled vessels, which necessarily involves the movement of fluid. In three empirically determined fungal networks we found that the minimum currents consistent with the observed growth would effectively transport resource throughout the network over the time-scale of growth. This suggests that in foraging fungi, the active transport mechanisms observed in the growing tips may not be required for long range transport. PMID:23005783

  14. Waves, advection, and cloud patterns on Venus

    NASA Technical Reports Server (NTRS)

    Schinder, Paul J.; Gierasch, Peter J.; Leroy, Stephen S.; Smith, Michael D.

    1990-01-01

    The stable layers adjacent to the nearly neutral layer within the Venus clouds are found to be capable of supporting vertically trapped, horizontally propagating waves with horizontal wavelengths of about 10 km and speeds of a few meters per second relative to the mean wind in the neutral layer. These waves may possibly be excited by turbulence within the neutral layer. Here, the properties of the waves, and the patterns which they might produce within the visible clouds if excited near the subsolar point are examined. The patterns can be in agreement with many features in images. The waves are capable of transferring momentum latitudinally to help maintain the general atmospheric spin, but at present we are not able to evaluate wave amplitudes. We also examine an alternative possibility that the cloud patterns are produced by advection and shearing by the mean zonal and meridional flow of blobs formed near the equator. It is concluded that advection and shearing by the mean flow is the most likely explanation for the general pattern of small scale striations.

  15. Wind Tunnel Measurement of Turbulent and Advective Scalar Fluxes: A Case Study on Intersection Ventilation

    PubMed Central

    Kukačka, Libor; Nosek, Štĕpán; Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk

    2012-01-01

    The objective of this study is to determine processes of pollution ventilation in the X-shaped street intersection in an idealized symmetric urban area for the changing approach flow direction. A unique experimental setup for simultaneous wind tunnel measurement of the flow velocity and the tracer gas concentration in a high temporal resolution is assembled. Advective horizontal and vertical scalar fluxes are computed from averaged measured velocity and concentration data within the street intersection. Vertical advective and turbulent scalar fluxes are computed from synchronized velocity and concentration signals measured in the plane above the intersection. All the results are obtained for five approach flow directions. The influence of the approach flow on the advective and turbulent fluxes is determined. The contribution of the advective and turbulent flux to the ventilation is discussed. Wind direction with the best dispersive conditions in the area is found. The quadrant analysis is applied to the synchronized signals of velocity and concentration fluctuation to determine events with the dominant contribution to the momentum flux and turbulent scalar flux. PMID:22649290

  16. Sorption of strontium on bentonite

    SciTech Connect

    Ali Khan, S.; Riaz-ur-Rehman; Ali Khan, M.

    1995-12-31

    Sorption of Sr on bentonite was studied using the batch technique. Distribution coefficients (K{sub d}) were determined as a function of contact time, pH, sorbent and sorbate concentration and temperature. The data were interpreted in terms of Freundlich, Langmuir and Dubinin-Radushkevich isotherms. Thermodynamic parameters for the sorption system were determined at three different temperatures. The positive value of the heat of sorption, {Delta}H{degree} = 30.62 kJ/mol at 295 K, shows that the sorption of strontium on bentonite is endothermic. The negative value of the free energy of sorption, {Delta}G{degree} = {minus}10.69 kJ/mol at 298 K, shows the spontaneity of the reaction. {Delta}G{degree} becomes more negative with increasing temperature, which shows that the sorption process is more favorable at higher temperatures. The mean free energy for sorption, E {approximately} 9 kJ/mol, suggests that ion exchange is the predominant mode of sorption in the Sr concentration range studies, i.e., 0.01--0.3 mol/dm{sup 3}. The presence of complementary cations depresses the sorption of strontium on bentonite in the order Ca{sup 2+}>Mg{sup 2+}>K{sup +}>Na{sup +}. Some organic complexing agents and natural ligands also affect the sorption of strontium. The desorption studies with ground water at low strontium loads on bentonite show that about 90% of Sr is irreversibly sorbed on the bentonite.

  17. TECHNETIUM SORPTION MEDIA REVIEW

    SciTech Connect

    DUNCAN JB; KELLY SE; ROBBINS RA; ADAMS RD; THORSON MA; HAASS CC

    2011-08-25

    This report presents information and references to aid in the selection of 99Tc sorption media for feasibility studies regarding the removal of 99Tc from Hanford's low activity waste. The report contains literature search material for sorption media (including ion exchange media) for the most tested media to date, including SuperLig 639, Reillex HPQ, TAM (Kruion), Purolite A520E and A530E, and Dowex 1X8. The U.S. Department of Energy (DOE), Office of River Protection (ORP) is responsible for management and completion of the River Protection Project (RPP) mission, which comprises both the Hanford Site tank farms and the Waste Treatment and Immobilization Plant (WTP). The RPP mission is to store, retrieve and treat Hanford's tank waste; store and dispose of treated wastes; and close the tank farm waste management areas and treatment facilities in a safe, environmentally compliant, cost-effective and energy-effective manner.

  18. BUOYANT ADVECTION OF GASES IN UNSATURATED SOIL

    PubMed Central

    Seely, Gregory E.; Falta, Ronald W.; Hunt, James R.

    2010-01-01

    In unsaturated soil, methane and volatile organic compounds can significantly alter the density of soil gas and induce buoyant gas flow. A series of laboratory experiments was conducted in a two-dimensional, homogeneous sand pack with gas permeabilities ranging from 110 to 3,000 darcy. Pure methane gas was injected horizontally into the sand and steady-state methane profiles were measured. Experimental results are in close agreement with a numerical model that represents the advective and diffusive components of methane transport. Comparison of simulations with and without gravitational acceleration permits identification of conditions where buoyancy dominates methane transport. Significant buoyant flow requires a Rayleigh number greater than 10 and an injected gas velocity sufficient to overcome dilution by molecular diffusion near the source. These criteria allow the extension of laboratory results to idealized field conditions for methane as well as denser-than-air vapors produced by volatilizing nonaqueous phase liquids trapped in unsaturated soil. PMID:20396624

  19. Modelling transport in media with heterogeneous advection properties and mass transfer with a Continuous Time Random Walk approach

    NASA Astrophysics Data System (ADS)

    Comolli, Alessandro; Moussey, Charlie; Dentz, Marco

    2016-04-01

    Transport processes in groundwater systems are strongly affected by the presence of heterogeneity. The heterogeneity leads to non-Fickian features, that manifest themselves in the heavy-tailed breakthrough curves, as well as in the non-linear growth of the mean squared displacement and in the non-Gaussian plumes of solute particles. The causes of non-Fickian transport can be the heterogeneity in the flow fields and the processes of mass exchange between mobile and immobile phases, such as sorption/desorption reactions and diffusive mass transfer. Here, we present a Continuous Time Random Walk (CTRW) model that describes the transport of solutes in d-dimensional systems by taking into account both heterogeneous advection and mobile-immobile mass transfer. In order to account for these processes in the CTRW, the heterogeneities are mapped onto a distribution of transition times, which can be decomposed into advective transition times and trapping times, the latter being treated as a compound Poisson process. While advective transition times are related to the Eulerian flow velocities and, thus, to the conductivity distribution, trapping times depend on the sorption/desorption time scale, in case of reactive problems, or on the distribution of diffusion times in the immobile zones. Since the trapping time scale is typically much larger than the advective time scale, we observe the existence of two temporal regimes. The pre-asymptotic regime is defined by a characteristic time scale at which the properties of transport are fully determined by the heterogeneity of the advective field. On the other hand, in the asymptotic regime both the heterogeneity and the mass exchange processes play a role in conditioning the behaviour of transport. We consider different scenarios to discuss the relative importance of the advective heterogeneity and the mass transfer for the occurrence of non-Fickian transport. For each case we calculate analytically the scalings of the breakthrough

  20. Multi-moment advection scheme in three dimension for Vlasov simulations of magnetized plasma

    SciTech Connect

    Minoshima, Takashi; Matsumoto, Yosuke; Amano, Takanobu

    2013-03-01

    We present an extension of the multi-moment advection scheme [T. Minoshima, Y. Matsumoto, T. Amano, Multi-moment advection scheme for Vlasov simulations, Journal of Computational Physics 230 (2011) 6800–6823] to the three-dimensional case, for full electromagnetic Vlasov simulations of magnetized plasma. The scheme treats not only point values of a profile but also its zeroth to second order piecewise moments as dependent variables, and advances them on the basis of their governing equations. Similar to the two-dimensional scheme, the three-dimensional scheme can accurately solve the solid body rotation problem of a gaussian profile with little numerical dispersion or diffusion. This is a very important property for Vlasov simulations of magnetized plasma. We apply the scheme to electromagnetic Vlasov simulations. Propagation of linear waves and nonlinear evolution of the electron temperature anisotropy instability are successfully simulated with a good accuracy of the energy conservation.

  1. Simulation of the advective methane transport and AOM in Shenhu area, the Northern South China Sea

    NASA Astrophysics Data System (ADS)

    Liu, L.; Wu, N.

    2012-04-01

    Anaerobic Oxidation of Methane (AOM) occurs in the transition zone between the presence of sulfate and methane. This reaction is an important process for methane and the global carbon cycle. Methane gas hydrates bearing sediments were recovered in Shenhu Area, the Northern South China Sea, and methane advective transport was detected in this area as well. A one dimension numerical simulation tool was implemented to study the AOM process combined with the advective methane transport in Shenhu Area according to the local drilling data and geochemical information. The modeled results suggest that local methane flux will be consumed in the sediment column via dissolution, sorption and AOM reaction. A portion of methane will enter water column and possibly atmosphere if the methane flux was one order of magnitude higher than current level. Furthermore, the calculated rates of AOM in Shenhu area range similar to that of gas hydrate mounds in Mexico Golf. However, AOM is ability to consume more methane than that in Golf of Mexico due to the lower permeable sediment associated with a deeper sulfate methane transition layer.

  2. Relative dispersion in the atmosphere

    NASA Astrophysics Data System (ADS)

    LaCasce, Joe; Graff, Lise; Guttu, Sigmund

    2014-05-01

    The relative dispersion of pairs of particles in flows is of central importance when describing environmental dispersion, for example of volcanic ash. Atmospheric relative dispersion was examined previously in two balloon experiments in the Southern Hemisphere (the EOLE and TWERLE experiments). In both cases, the dispersion at scales below 1000 km grew exponentially in time, indicating the kinetic energy spectrum is steep. Subsequent analyses suggested though that the dispersion had a power law dependence on time, implying a shallower kinetic energy spectrum. The results from studies employing synthetic particles advected by reanalysis winds are similarly inconsistent, with indications of exponential growth in some cases and power law growth in others. Here we use a different statistic---the probability density function (PDF) of pair displacements---to study dispersion the dispersion of large numbers of synthetic particles, advected by ERA-Interim reanalysis winds. The particles were deployed in the troposphere and stratosphere, both in the tropics and the extra-tropics. We examine the PDFs for the different deployments and compare them to analytical expressions derived for different turbulent inertial ranges. In line with the earlier balloon experiments, the results indicate exponential growth at the sub-deformation (1000 km) scales. At larger scales, the dispersion is anisotropic (predominantly zonal) and pair motion becomes decorrelated. Structure functions calculated from the wind data are in line with these conclusions.

  3. Analysis of the unconditionally positive finite difference scheme for advection-diffusion-reaction equations with different regimes

    NASA Astrophysics Data System (ADS)

    Appadu, A. R.

    2016-06-01

    An unconditionally positive definite scheme has been derived in [1] to approximate a linear advection-diffusion-reaction equation which models exponential travelling waves and the coefficients of advective, diffusive and reactive terms have been chosen as one. The scheme has been baptised as Unconditionally Positive Finite Difference (UPFD). In this work, we use the UPFD scheme to solve the advection-diffusion-reaction problem in [1] and we also extend our study to three other important regimes involved in this model. The temporal step size is varied while fixing the spatial step size. We compute some errors namely; L1 error, dispersion, dissipation errors. We also study the variation of the modulus of the exact amplification factor, modulus of amplification factor of the scheme and relative phase error, all vs the phase angle for the four different regimes.

  4. Hourly and daily evapotranspiration of alfalfa under regional advection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Regional advection often affects the evapotranspiration rates of irrigated crops in the Southern High Plains. In 1998, during a 10-day period (13-22 June) of unusually strong advection, high evapotranspiration (ET) rates for unstressed, irrigated alfalfa (Medicago sativa) were measured with two prec...

  5. Equilibrium sorption of cobalt, cesium, and strontium on Bandelier Tuff: analysis of alternative mathematical modeling

    SciTech Connect

    Polzer, W.L.; Fuentes, H.R.; Essington, E.H.; Roensch, F.R.

    1985-01-01

    Sorption isotherms are derived from batch equilibrium data for cobalt, cesium and strontium on Bandelier Tuff. Experiments were conducted at an average temperature of 23/sup 0/C and equilibrium was defined at 48 hours. The solute concentrations ranged from 0 to 500 mg/L. The radioactive isotopes /sup 60/Co, /sup 137/Cs, and /sup 85/Sr were used to trace the sorption of the stable solutes. The Linear, Langmuir, Freundlich and a Modified Freundlich isotherm equations are evaluated. The Modified Freundlich isotherm equation is validated as a preferred general mathematical tool for representing the sorption of the three solutes. The empirical constants derived from the Modified Freundlich isotherm equation indicate that under dynamic flow conditions strontium will move most rapidly and cobalt least rapidly. On the other hand, chemical dispersion will be greatest for cesium and least for strontium. Hill Plots of the sorption data suggest that in the region of low saturation sorption of all three solutes is impeded by interactions among sorption sites; cobalt exhibits the greatest effect of interactions and strontium shows only a minimal effect. In the saturation region of 50% or more, sorption of cobalt is enhanced slightly by interactions among sorption sites whereas sorption of cesium and strontium appears to be independent of site interactions. 9 references, 4 figures, 2 tables.

  6. Advection, diffusion, and delivery over a network

    NASA Astrophysics Data System (ADS)

    Heaton, Luke L. M.; López, Eduardo; Maini, Philip K.; Fricker, Mark D.; Jones, Nick S.

    2012-08-01

    Many biological, geophysical, and technological systems involve the transport of a resource over a network. In this paper, we present an efficient method for calculating the exact quantity of the resource in each part of an arbitrary network, where the resource is lost or delivered out of the network at a given rate, while being subject to advection and diffusion. The key conceptual step is to partition the resource into material that does or does not reach a node over a given time step. As an example application, we consider resource allocation within fungal networks, and analyze the spatial distribution of the resource that emerges as such networks grow over time. Fungal growth involves the expansion of fluid filled vessels, and such growth necessarily involves the movement of fluid. We develop a model of delivery in growing fungal networks, and find good empirical agreement between our model and experimental data gathered using radio-labeled tracers. Our results lead us to suggest that in foraging fungi, growth-induced mass flow is sufficient to account for long-distance transport, if the system is well insulated. We conclude that active transport mechanisms may only be required at the very end of the transport pathway, near the growing tips.

  7. Advective Mechanisms in Tree Island Formation

    NASA Astrophysics Data System (ADS)

    Stothoff, S.

    2002-05-01

    Tree islands are important landscape features in the Florida Everglades. Tres islands are formed of peat deposited on the shallow limestone bedrock, and have been stressed as the system has changed in response to anthropogenic activities due to the sensitivity of organic soils to hydrologic cycles. The plume shape aligned with flow direction for typical tree islands is characteristic of advective transport, despite the rather low flow velocities in the system. Hypothesized mechanisms for the plume shape include sediment transport downstream from the head of the island (often anchored by a bedrock rise), or nutrient transport downstream allowing plants to produce more sediments in situ. Understanding mechanisms controlling tree island shape will aid in understanding the response of tree islands to hydrologic management. An integrated system of field, laboratory, and modeling studies is underway, with the first effort aimed at bounding the importance of the simpler sediment transport processes before tackling more-complex nutrient transport processes. The numerical model integrating the field and laboratory efforts is a 3D finite volume model considering water flow in the shallow groundwater/surface-water system together with sediment transport. The model can account for variable vegetative resistance through the flow column, including the important case where a dense mat forms at the surface. Model components specific for this system and associated data requirements are presented.

  8. Vertical barriers with increased sorption capacities

    SciTech Connect

    Bradl, H.B.

    1997-12-31

    Vertical barriers are commonly used for the containment of contaminated areas. Due to the very small permeability of the barrier material which is usually in the order of magnitude of 10-10 m/s or less the advective contaminant transport can be more or less neglected. Nevertheless, there will always be a diffusive contaminant transport through the barrier which is caused by the concentration gradient. Investigations have been made to increase the sorption capacity of the barrier material by adding substances such as organoclays, zeolites, inorganic oxides and fly ashes. The contaminants taken into account where heavy metals (Pb) and for organic contaminants Toluole and Phenantrene. The paper presents results of model calculations and experiments. As a result, barrier materials can be designed {open_quotes}tailor-made{close_quotes} depending on the individual contaminant range of each site (e.g. landfills, gasworks etc.). The parameters relevant for construction such as rheological properties, compressive strength and permeability are not affected by the addition of the sorbents.

  9. Bio-sorption based dispersive liquid-liquid microextraction for the highly efficient enrichment of trace-level bisphenol A from water samples prior to its determination by HPLC.

    PubMed

    Haeri, Seyed Ammar

    2016-08-15

    In this study, biosorption based dispersive liquid liquid microextraction (Bio-DLLME) has been developed as a new method for the extraction of bisphenol A (BPA) from water samples. In this technique, the BPA is extracted into a stable cloudy phase. The colloidal phase is composed of micro-particles made from rhaminolipid biosurfactant and methanol, which dispersed in the water samples and facilitated the breakdown of analyte matrix bonds and provided high extraction yields. Rhaminolipid biosurfactants form a thin molecular interfacial film. This layer is formed between donor and recipient phase. This molecular layer, lowers the interfacial tension between immiscible phases (aqueous solution: colloidal particles) and allow dissimilar phases to mix and interact more easily. So the equilibrium state is achieved quickly and, therefore, the extraction time is very short. The attraction of the proposed method is that the extraction is fast, simple and can be done without toxic organic solvents. Also bioaggregates have several advantages such as higher environmental compatibility and biodegradability. Experimental parameters affecting the extraction efficiency were studied and optimized. Under the optimum conditions, relative recoveries of BPA were in the ranges of 98-103.3%. The calibration plot is linear in the range between 1 and 1000μgL(-1) (R(2)=0.998), and the relative standard deviation (RSD, for n=6) is 3.24%. PMID:27362996

  10. Parallel simulation of particle transport in an advection field applied to volcanic explosive eruptions

    NASA Astrophysics Data System (ADS)

    Künzli, Pierre; Tsunematsu, Kae; Albuquerque, Paul; Falcone, Jean-Luc; Chopard, Bastien; Bonadonna, Costanza

    2016-04-01

    Volcanic ash transport and dispersal models typically describe particle motion via a turbulent velocity field. Particles are advected inside this field from the moment they leave the vent of the volcano until they deposit on the ground. Several techniques exist to simulate particles in an advection field such as finite difference Eulerian, Lagrangian-puff or pure Lagrangian techniques. In this paper, we present a new flexible simulation tool called TETRAS (TEphra TRAnsport Simulator) based on a hybrid Eulerian-Lagrangian model. This scheme offers the advantages of being numerically stable with no numerical diffusion and easily parallelizable. It also allows us to output particle atmospheric concentration or ground mass load at any given time. The model is validated using the advection-diffusion analytical equation. We also obtained a good agreement with field observations of the tephra deposit associated with the 2450 BP Pululagua (Ecuador) and the 1996 Ruapehu (New Zealand) eruptions. As this kind of model can lead to computationally intensive simulations, a parallelization on a distributed memory architecture was developed. A related performance model, taking into account load imbalance, is proposed and its accuracy tested.

  11. Anisotropic Turbulent Advection of a Passive Vector Field: Effects of the Finite Correlation Time

    NASA Astrophysics Data System (ADS)

    Antonov, N. V.; Gulitskiy, N. M.

    2016-02-01

    The turbulent passive advection under the environment (velocity) field with finite correlation time is studied. Inertial-range asymptotic behavior of a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow, is investigated by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and prescribed pair correlation function. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to nontrivial fixed points of the RG equations and depend on the relation between the exponents in the energy energy spectrum ɛ ∝ k⊥1-ξ and the dispersion law ω ∝ k⊥2-η . The corresponding anomalous exponents are associated with the critical dimensions of tensor composite operators built solely of the passive vector field itself. In contrast to the well-known isotropic Kraichnan model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the dependence on the integral turbulence scale L has a logarithmic behavior: instead of power-like corrections to ordinary scaling, determined by naive (canonical) dimensions, the anomalies manifest themselves as polynomials of logarithms of L. Due to the presence of the anisotropy in the model, all multiloop diagrams are equal to zero, thus this result is exact.

  12. Chaotic advection, diffusion, and reactions in open flows

    SciTech Connect

    Tel, Tamas; Karolyi, Gyoergy; Pentek, Aron; Scheuring, Istvan; Toroczkai, Zoltan; Grebogi, Celso; Kadtke, James

    2000-03-01

    We review and generalize recent results on advection of particles in open time-periodic hydrodynamical flows. First, the problem of passive advection is considered, and its fractal and chaotic nature is pointed out. Next, we study the effect of weak molecular diffusion or randomness of the flow. Finally, we investigate the influence of passive advection on chemical or biological activity superimposed on open flows. The nondiffusive approach is shown to carry some features of a weak diffusion, due to the finiteness of the reaction range or reaction velocity. (c) 2000 American Institute of Physics.

  13. Burgers turbulence and passive random advection

    NASA Astrophysics Data System (ADS)

    Boldyrev, Stanislav Anatolievich

    1999-10-01

    , and the diffusivity is neglected. These considerations illustrate that even with simple statistics of the velocity field, the statistics of advected quantities are nontrivial due to nonlinear interactions of different spatial directions. The last Chapter 5 summarizes the results and discusses future directions of research.

  14. Clay with Desiccation Cracks is an Advection Dominated Environment

    NASA Astrophysics Data System (ADS)

    Baram, S.; Kurtzman, D.; Sher, Y.; Ronen, Z.; Dahan, O.

    2012-04-01

    , indicating deep soil evaporation. Daily fluctuation of the air temperature in the desiccation cracks supported thermally induced air convection within the cracks void and could explain the deep soil salinization process. Combination of all the abovementioned observations demonstrated that the formation of desiccation cracks network in dispersive clay sediments generates a bulk advection dominated environment for both air and water flow, and that the reference to clay sediments as "hydrologically safe" should to be reconsidered.

  15. Anomalous scaling of a scalar field advected by turbulence

    SciTech Connect

    Kraichnan, R.H.

    1995-12-31

    Recent work leading to deduction of anomalous scaling exponents for the inertial range of an advected passive field from the equations of motion is reviewed. Implications for other turbulence problems are discussed.

  16. Magnetic helicity transport in the advective gauge family

    SciTech Connect

    Candelaresi, Simon; Brandenburg, Axel; Hubbard, Alexander; Mitra, Dhrubaditya

    2011-01-15

    Magnetic helicity fluxes are investigated in a family of gauges in which the contribution from ideal magnetohydrodynamics takes the form of a purely advective flux. Numerical simulations of magnetohydrodynamic turbulence in this advective gauge family exhibit instabilities triggered by the build-up of unphysical irrotational contributions to the magnetic vector potential. As a remedy, the vector potential is evolved in a numerically well behaved gauge, from which the advective vector potential is obtained by a gauge transformation. In the kinematic regime, the magnetic helicity density evolves similarly to a passive scalar when resistivity is small and turbulent mixing is mild, i.e., when the fluid Reynolds number is not too large. In the dynamical regime, resistive contributions to the magnetic helicity flux in the advective gauge are found to be significant owing to the development of small length scales in the irrotational part of the magnetic vector potential.

  17. Sorption isotherms and isosteric heats of sorption of Malaysian paddy.

    PubMed

    Mousa, Wael; Ghazali, Farinazleen Mohamad; Jinap, S; Ghazali, Hasanah Mohd; Radu, Son

    2014-10-01

    Understanding the water sorption characteristics of cereal is extremely essential for optimizing the drying process and ensuring storage stability. Water relation of rough rice was studied at 20, 30, 40 and 50 °C over relative humidity (RH.) between 0.113 and 0.976 using the gravimetric technique. The isotherms displayed the general sigmoid, Type II pattern and exhibited the phenomenon of hysteresis where it was more pronounced at lower temperatures. The sorption characteristics were temperature dependence where the sorption capacity of the paddy increased as the temperature was decreased at fixed (RH). Among the models assessed for their ability to fit the sorption data, Oswin equation was the best followed by the third order polynomial, GAB, Smith, Chung-Pfost, and Henderson models. The monolayer moisture content was higher for desorption than adsorption and tend to decrease with the increase in temperature. Given the temperature dependence of the sorption isotherms the isosteric heats of sorption were calculated using Claussius-Clapeyron equation. The net isosteric heats decreased as the moisture content was increased and heats of desorption were greater than that of adsorption. PMID:25328208

  18. Sorption of aniline derivatives on carbon fabric

    NASA Astrophysics Data System (ADS)

    Fazylova, G. F.; Valinurova, E. R.; Khamitov, E. M.; Kudasheva, F. Kh.

    2015-06-01

    The statistical adsorption of the chloro- and nitroderivatives of aniline on carbon fabric UVIS-AK was studied. The sorption isotherms of anilines on carbon fabric and coals were constructed at room temperature and a comparative analysis of their sorption activity was performed. The sorption isotherms were linearized in the coordinates of the Langmuir and Dubinin-Radushkevich equations. The main sorption parameters were calculated: the characteristic adsorption energies of anilines, changes in the Gibbs energies, monolayer capacities, and sorption equilibrium constants.

  19. Advection around ventilated U-shaped burrows: A model study

    NASA Astrophysics Data System (ADS)

    Brand, Andreas; Lewandowski, JöRg; Hamann, Enrico; Nützmann, Gunnar

    2013-05-01

    Advective transport in the porous matrix of sediments surrounding burrows formed by fauna such as Chironomus plumosus has been generally neglected. A positron emission tomography study recently revealed that the pumping activity of the midge larvae can indeed induce fluid flow in the sediment. We present a numerical model study which explores the conditions at which advective transport in the sediment becomes relevant. A 0.15 m deep U-shaped burrow with a diameter of 0.002 m within the sediment was represented in a 3-D domain. Fluid flow in the burrow was calculated using the Navier-Stokes equation for incompressible laminar flow in the burrow, and flow in the sediment was described by Darcy's law. Nonreactive and reactive transport scenarios were simulated considering diffusion and advection. The pumping activity of the model larva results in considerable advective flow in the sediment at reasonable high permeabilities with flow velocities of up to 7.0 × 10-6 m s-1 close to the larva for a permeability of 3 × 10-12 m2. At permeabilities below 7 × 10-13 m2 advection is negligible compared to diffusion. Reactive transport simulations using first-order kinetics for oxygen revealed that advective flux into the sediment downstream of the pumping larva enhances sedimentary uptake, while the advective flux into the burrow upstream of the larvae inhibits diffusive sedimentary uptake. Despite the fact that both effects cancel each other with respect to total solute uptake, the advection-induced asymmetry in concentration distribution can lead to a heterogeneous solute and redox distribution in the sediment relevant to complex reaction networks.

  20. Adaptive domain decomposition methods for advection-diffusion problems

    SciTech Connect

    Carlenzoli, C.; Quarteroni, A.

    1995-12-31

    Domain decomposition methods can perform poorly on advection-diffusion equations if diffusion is dominated by advection. Indeed, the hyperpolic part of the equations could affect the behavior of iterative schemes among subdomains slowing down dramatically their rate of convergence. Taking into account the direction of the characteristic lines we introduce suitable adaptive algorithms which are stable with respect to the magnitude of the convective field in the equations and very effective on bear boundary value problems.

  1. Silica Precipitation and Lithium Sorption

    SciTech Connect

    Jay Renew

    2015-09-20

    This file contains silica precipitation and lithium sorption data from the project. The silica removal data is corrected from the previous submission. The previous submission did not take into account the limit of detection of the ICP-MS procedure.

  2. A spatial SIS model in advective heterogeneous environments

    NASA Astrophysics Data System (ADS)

    Cui, Renhao; Lou, Yuan

    2016-09-01

    We study the effects of diffusion and advection for a susceptible-infected-susceptible epidemic reaction-diffusion model in heterogeneous environments. The definition of the basic reproduction number R0 is given. If R0 < 1, the unique disease-free equilibrium (DFE) is globally asymptotically stable. Asymptotic behaviors of R0 for advection rate and mobility of the infected individuals (denoted by dI) are established, and the existence of the endemic equilibrium when R0 > 1 is studied. The effects of diffusion and advection rates on the stability of the DFE are further investigated. Among other things, we find that if the habitat is a low-risk domain, there may exist one critical value for the advection rate, under which the DFE changes its stability at least twice as dI varies from zero to infinity, while the DFE is unstable for any dI when the advection rate is larger than the critical value. These results are in strong contrast with the case of no advection, where the DFE changes its stability at most once as dI varies from zero to infinity.

  3. Can soil drying affect the sorption of pesticides in soil?

    NASA Astrophysics Data System (ADS)

    Chaplain, Véronique; Saint, Philippe; Mamy, Laure; Barriuso, Enrique

    2010-05-01

    The sorption of pesticides in soils mainly controls their further dispersion into the environment. Sorption is usually related to the physico-chemical properties of molecules but it also depends on the hydrophobic features of soils. However, the hydrophobicity of soils changes with wetting and drying cycles and this can be enhanced with climate change. The objective of this study was to measure by using controlled artificial soils the influence of the hydrophobic characteristic of soils on the retention of a model pesticide. Artificial soils consisted in silica particles covered by synthetic cationic polymers. Polymers were characterized by the molar ratio of monomers bearing an alkyl chain of 12C. Two polymers were used, with 20 and 80 % ratios, and the same degree of polymerization. In addition, porous and non-porous particles were used to study the accessibility notion and to measure the influence of diffusion on pesticide sorption kinetics. Lindane was chosen as model molecule because its adsorption is supposed mainly due to hydrophobic interactions. Results on polymers adsorption on silica showed that it was governed by electrostatic interactions, without any dependency of the hydrophobic ratio. Polymers covered the entire surface of porous particles. Kinetic measurements showed that lindane sorption was slowed in porous particles due to the molecular diffusion inside the microporosity. The adsorption of lindane on covered silica particles corresponded to a partition mechanism described by linear isotherms. The slope was determined by the hydrophobic ratio of polymers: the sorption of lindane was highest in the most hydrophobic artificial soil. As a result, modification in soil hydrophobicity, that can happen with climate change, might affect the sorption and the fate of pesticides. However additional experiments are needed to confirm these first results. Such artificial soils should be used as reference materials to compare the reactivity of pesticides, to

  4. Linearity of iodine sorption and sorption capacities for seven soils

    SciTech Connect

    Sheppard, M.I.; Hawkins, J.L.; Smith, P.A.

    1996-11-01

    Iodine, a soluble and prevalent element in spent nuclear fuel and a pivotal element in the assessment of Canada`s nuclear fuel waste disposal option, sorbs to soils rich in organics and hydrous oxides. Biotic factors, such as microbes, enzymes and plant exudates, have been implicated in the retention of I to soils. Anion exchange of I{sup {minus}} or IO{sub 3}{sup {minus}} and chemical or biological oxidation to I{sub 2} followed by reactions with the soil organic matter are possible retention mechanisms. We have carried out sorption and desorption studies across a wide range of soil solution concentrations (10{sup {minus}7} to 10{sup 5} mg I/L, 10{sup {minus}12} to 1 M) for seven soils typical of upland and lowland soils of the Canadian Precambrian Shield. Soil solid-liquid partition values (K{sub d}), required for impact assessments, varied from 60 to 1800 L/kg and were significantly correlated with extractable Al oxide content, and background I and organic matter content. Freundlich isotherm fits show that sorption of I across our intentionally large concentration range is nonlinear; however, sorption of I across our intentionally large concentration range is nonlinear; however, sorption of I at environmental concentrations (<0.1 mg I/L soil solution) is linear and can be described by the K{sub d} model. Sorption of I was not related to peroxidase enzyme activity. Desorption percentages were small implying sorption was not easily reversed, even with a strong electrolyte, KNO{sub 3}. Desorption results and simple correlations of I sorption to soil properties suggest that the oxidation of I{sup {minus}} to I{sub 2} and complexation to organic functional groups or oxides are the major processes for I retention in Shield soils. 52 refs., 2 figs., 2 tabs.

  5. Stochastic interpretation of the advection-diffusion equation and its relevance to bed load transport

    NASA Astrophysics Data System (ADS)

    Ancey, C.; Bohorquez, P.; Heyman, J.

    2015-12-01

    The advection-diffusion equation is one of the most widespread equations in physics. It arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Phenomenological laws are usually sufficient to derive this equation and interpret its terms. Stochastic models can also be used to derive it, with the significant advantage that they provide information on the statistical properties of particle activity. These models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. Among these stochastic models, the most common approach consists of random walk models. For instance, they have been used to model the random displacement of tracers in rivers. Here we explore an alternative approach, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. Birth-death Markov processes are well suited to this objective. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received no attention. We therefore look into the possibility of deriving the advection-diffusion equation (with a source term) within the framework of birth-death Markov processes. We show that in the continuum limit (when the cell size becomes vanishingly small), we can derive an advection-diffusion equation for particle activity. Yet while this derivation is formally valid in the continuum limit, it runs into difficulty in practical applications involving cells or meshes of finite length. Indeed, within our stochastic framework, particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due

  6. Dynamic micro-mapping of CO2 sorption in coal

    SciTech Connect

    Radlinski, Andrzej Pawell; Melnichenko, Yuri B; Cheng, Gang; Mastalerz, Maria

    2009-01-01

    We have applied X-ray and neutron small-angle scattering techniques (SAXS, SANS and USANS) to study the interaction between fluids and porous media in the particular case of sub- and super-critical CO2 sorption in coal. These techniques are demonstrated to give unique, pore-size-specific insights into the kinetics of CO2 sorption in a wide range of coal pores (nano to meso), and to provide data that may be used to determine the density of the sorbed CO2. We observed densification of the adsorbed CO2 by a factor up to five compared to the free fluid at the same (p,T) conditions. Our results indicate that details of CO2 sorption into coal pores differ greatly between different coals and depend on the amount of mineral matter dispersed in the coal matrix: a purely organic matrix absorbs more CO2 per unit volume than one contaminated with mineral matter, but mineral matter markedly accelerates the sorption kinetics.

  7. Iodine sorption by highly weathered soils

    NASA Astrophysics Data System (ADS)

    Bruns, W. A.; Bruns, M. R.; Kaplan, D. I.; Murphy, T.; Roberts, K.; Thompson, A.; Seaman, J. C.

    2009-12-01

    Radioactive iodine (I) isotopes such as I-129 are widely distributed throughout Department of Energy (DOE) and other nuclear sites as a result of past enrichment activities. While natural-abundance I serves an important role in thyroid function in human beings, anthropogenic I can cause thyroid cancer. Predominant I species are anionic and generally assumed to move conservatively through typical negatively-charged subsurface material with the mobile water phase. However, many of the 129I contaminated soils and subsurface materials on the DOE Savannah River Site (SRS) near Aiken, SC, contain significant positive charge, which could retain I-129. A series of batch and column experiments were performed in order to determine sorption of three different I species (iodide, iodate, and an organic I compound, 4-iodaniline) over a range of aqueous concentrations (10^-4 to 10^-8 M) onto surface and subsurface soils from SRS. Total aqueous I in solution after equilibration was measured using ICP-MS and used to calculate the partitioning coefficient (Kd). Kd values for all three species were much higher at lower dissolved I concentrations (i.e., non-linear partitioning), and correlated with CDB-extractable Fe and Al and well as soil organic matter content. For the species and concentrations that exhibited high Kd values (>5), we conducted column experiments to evaluate partitioning under dynamic advective systems, using tritium for comparison as a conservative hydrologic tracer. We tracked pH, EC, and hydraulic head in real-time, and the effluent was collected for I analysis as described above. The results indicate a complex pattern of I movement in the natural environment affected by isotope concentration, speciation, and soil characteristics.

  8. Measurement of clay surface areas by polyvinylpyrrolidone (PVP) sorption and its use for quantifying illite and smectite abundance

    USGS Publications Warehouse

    Blum, A.E.; Eberl, D.D.

    2004-01-01

    A new method has been developed for quantifying smectite abundance by sorbing polyvinylpyrrolidone (PVP) on smectite particles dispersed in aqueous solution. The sorption density of PVP-55K on a wide range of smectites, illites and kaolinites is ???0.99 mg/m2, which corresponds to ???0.72 g of PVP-55K per gram of montmorillonite. Polyvinylpyrrolidone sorption on smectites is independent of layer charge and solution pH. PVP sorption on Si02, Fe 2O3 and ZnO normalized to the BET surface area is similar to the sorption densities on smectites. ??-Al 2O3, amorphous Al(OH)3 and gibbsite have no PVP sorption over a wide range of pH, and sorption of PVP by organics is minimal. The insensitivity of PVP sorption densities to mineral layer charge, solution pH and mineral surface charge indicates that PVP sorption is not localized at charged sites, but is controlled by more broadly distributed sorption mechanisms such as Van der Waals' interactions and/or hydrogen bonding. Smectites have very large surface areas when dispersed as single unit-cell-thick particles (???725 m2/g) and usually dominate the total surface areas of natural samples in which smectites are present. In this case, smectite abundance is directly proportional to PVP sorption. In some cases, however, the accurate quantification of smectite abundance by PVP sorption may require minor corrections for PVP uptake by other phases, principally illite and kaolinite. Quantitative XRD can be combined with PVP uptake measurements to uniquely determine the smectite concentration in such sample. ?? 2004, The Clay Minerals Society.

  9. Modeling of sorption characteristics of backfill materials

    SciTech Connect

    Chitra, S.; Sasidhar, P.; Lal, K.B.; Ahmed, J.

    1998-06-01

    Sorption data analysis was carried out using the Freundlich, Langmuir, and Modified Freundlich isotherms for the uptake of sodium and potassium in an initial concentration range of 10--100 mg/L on backfill materials, viz., bentonite, vermiculite, and soil samples. The soil samples were collected from a shallow land disposal facility at Kalpakkam. The Freundlich isotherm equation is validated as a preferred general mathematical tool for representing the sorption of K{sup +} by all the selected backfill materials. The Modified Freundlich isotherm equation is validated as a preferred mathematical tool for representing the sorption of Na{sup +} by the soil samples. Since a negative sorption was observed for the uptake of Na{sup +} by commercial clay minerals (vermiculite and bentonite clay in the laboratory experiments), sorption analysis could not be carried out using the above-mentioned isotherm equations. Hill plots of the sorption data suggest that in the region of low saturation (10--40 mg/L), sorption of K{sup +} by vermiculite is impeded by interaction among sorption sites. In the region of higher saturation (60--100 mg/L), sorption of K{sup +} by all three backfill materials is enhanced by interaction among sorption sites. The Hill plot of the sorption data for Na{sup +} by soil suggests that irrespective of Na{sup +} concentration, sorption of Na{sup +} at one exchange size enhances sorption at other exchange sites.

  10. Sorption of heavy metals by the soil fungi 'Aspergillus niger' and Mucor rouxii

    SciTech Connect

    Mullen, M.D.; Wolf, D.C.; Beveridge, T.J.; Bailey, G.W.

    1992-01-01

    Sorption of the nitrate salts of cadmium(II), copper(II), lanthanum(III) and silver(I) by two fungi, Aspergillus niger and Mucor rouxii, was evaluated using Freundlich adsorption isotherms and energy dispersive X-ray electron microscopy. The linearized Freundlich isotherm described the metal sorption data well for metal concentrations of 5 microM-1 mM metal. Differences in metal binding were observed among metals, as well as between fungal species. Calculated Freundlich K values indicated that metal binding decreased in the order La(3+) > or = Ag(+) > Cu(2+) > Cd(2+). However, sorption of Ag(+) was greater than that of La(3+) from solutions of 0.1 and 1 mM metal and likely due to precipitation at the cell wall surface. At the 1 mM initial concentration, there were no significant differences between the two fungi in metal sorption, except for Ag(+) binding. At the 5 microM concentration, there was no difference between the fungi in their sorption capacities for the four metals. Electron microscopy-energy dispersive X-ray analysis indicated that silver precipitated onto cells as colloidal silver. The results indicate that Freundlich isotherms may be useful for describing short-term metal sorption by fungal biomass and for comparison with other soil constituents in standardized systems. (Copyright (c) 1992 Pergamon Press plc.)

  11. Advecting Procedural Textures for 2D Flow Animation

    NASA Technical Reports Server (NTRS)

    Kao, David; Pang, Alex; Moran, Pat (Technical Monitor)

    2001-01-01

    This paper proposes the use of specially generated 3D procedural textures for visualizing steady state 2D flow fields. We use the flow field to advect and animate the texture over time. However, using standard texture advection techniques and arbitrary textures will introduce some undesirable effects such as: (a) expanding texture from a critical source point, (b) streaking pattern from the boundary of the flowfield, (c) crowding of advected textures near an attracting spiral or sink, and (d) absent or lack of textures in some regions of the flow. This paper proposes a number of strategies to solve these problems. We demonstrate how the technique works using both synthetic data and computational fluid dynamics data.

  12. Concentration polarization, surface currents, and bulk advection in a microchannel

    NASA Astrophysics Data System (ADS)

    Nielsen, Christoffer P.; Bruus, Henrik

    2014-10-01

    We present a comprehensive analysis of salt transport and overlimiting currents in a microchannel during concentration polarization. We have carried out full numerical simulations of the coupled Poisson-Nernst-Planck-Stokes problem governing the transport and rationalized the behavior of the system. A remarkable outcome of the investigations is the discovery of strong couplings between bulk advection and the surface current; without a surface current, bulk advection is strongly suppressed. The numerical simulations are supplemented by analytical models valid in the long channel limit as well as in the limit of negligible surface charge. By including the effects of diffusion and advection in the diffuse part of the electric double layers, we extend a recently published analytical model of overlimiting current due to surface conduction.

  13. Fast multigrid solution of the advection problem with closed characteristics

    SciTech Connect

    Yavneh, I.; Venner, C.H.; Brandt, A.

    1996-12-31

    The numerical solution of the advection-diffusion problem in the inviscid limit with closed characteristics is studied as a prelude to an efficient high Reynolds-number flow solver. It is demonstrated by a heuristic analysis and numerical calculations that using upstream discretization with downstream relaxation-ordering and appropriate residual weighting in a simple multigrid V cycle produces an efficient solution process. We also derive upstream finite-difference approximations to the advection operator, whose truncation terms approximate {open_quotes}physical{close_quotes} (Laplacian) viscosity, thus avoiding spurious solutions to the homogeneous problem when the artificial diffusivity dominates the physical viscosity.

  14. Hydrodynamic dispersion within porous biofilms.

    PubMed

    Davit, Y; Byrne, H; Osborne, J; Pitt-Francis, J; Gavaghan, D; Quintard, M

    2013-01-01

    Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport. PMID:23410370

  15. Tidal Mixing and Buoyancy Advection: Joint Influences on Lobster Distribution in Coastal Maine

    NASA Astrophysics Data System (ADS)

    Brooks, D. A.

    2004-12-01

    The Eastern Maine Coastal Current (EMCC) flows southwestward from the mouth of the Bay of Fundy to Penobscot Bay on the central Maine coast. Maximum non-tidal surface speeds reach 20-30 cm/s about 20 km offshore during April-May when the outflow from the Saint John River is strongest. Vigorous tides cause strong vertical and horizontal mixing, so that dispersal of neutral particles is influenced both by advection and tidal mixing. To survive, planktonic lobsters carried southwestward in the surface flow must settle to a nearshore cobble substrate. Larvae hatched near the Bay of Fundy can be advected to the central coast in 2-3 weeks, roughly the time needed to reach settlement stage. Over the same period, transverse tidal mixing is sufficient to raise nearshore larval concentrations to about half that offshore in the axis of the EMCC. Both processes may be necessary to explain the observed lobster distribution, which exhibits a distinct maximum in the central coastal region. The seasonal development of the EMCC is also influenced by winds and the larger circulation of the Gulf of Maine. This work is part of a multidisciplinary synthesis study funded by the NOAA Coastal Ocean Program.

  16. Theory of advection-driven long range biotic transport

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We propose a simple mechanistic model to examine the effects of advective flow on the spread of fungal diseases spread by wind-blown spores. The model is defined by a set of two coupled non-linear partial differential equations for spore densities. One equation describes the long-distance advectiv...

  17. Topology preserving advection of implicit interfaces on Cartesian grids

    NASA Astrophysics Data System (ADS)

    Qin, Zhipeng; Delaney, Keegan; Riaz, Amir; Balaras, Elias

    2015-06-01

    Accurate representation of implicit interface topology is important for the numerical computation of two phase flow on Cartesian grids. A new method is proposed for the construction of signed distance function by geometrically projecting interface topology onto the Cartesian grid using a multi-level projection framework. The method involves a stepwise improvement in the approximation to the signed distance function based on pointwise, piecewise and locally smooth reconstructions of the interface. We show that this approach provides accurate representation of the projected interface and its topology on the Cartesian grid, including the distance from the interface and the interface normal and curvature. The projected interface can be in the form of either a connected set of marker particles that evolve with Lagrangian advection, or a discrete set of points associated with an implicit interface that evolves with the advection of a scalar function. The signed distance function obtained with geometric projection is independent of the details of the scaler field, in contrast to the conventional approach where advection and reinitialization cannot be decoupled. As a result, errors introduced by reinitialization do not amplify advection errors, which leads to substantial improvement in both volume conservation and topology representation.

  18. Consistency problem with tracer advection in the Atmospheric Model GAMIL

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Wan, Hui; Wang, Bin; Zhang, Meigen

    2008-03-01

    The radon transport test, which is a widely used test case for atmospheric transport models, is carried out to evaluate the tracer advection schemes in the Grid-Point Atmospheric Model of IAP-LASG (GAMIL). Two of the three available schemes in the model are found to be associated with significant biases in the polar regions and in the upper part of the atmosphere, which implies potentially large errors in the simulation of ozone-like tracers. Theoretical analyses show that inconsistency exists between the advection schemes and the discrete continuity equation in the dynamical core of GAMIL and consequently leads to spurious sources and sinks in the tracer transport equation. The impact of this type of inconsistency is demonstrated by idealized tests and identified as the cause of the aforementioned biases. Other potential effects of this inconsistency are also discussed. Results of this study provide some hints for choosing suitable advection schemes in the GAMIL model. At least for the polar-region-concentrated atmospheric components and the closely correlated chemical species, the Flux-Form Semi-Lagrangian advection scheme produces more reasonable simulations of the large-scale transport processes without significantly increasing the computational expense.

  19. ADVECTION INFLUENCES ON EVAPOTRANSPIRATION OF ALFALFA IN A SEMIARID ENVIRONMENT

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Advective enhancement of crop evapotranspiration (ET) occurs when drier, hotter air is transported into the crop by wind and can be an important factor in the water balance of irrigated crops in a semiarid climate. Thirteen days of moderate to extremely high ET rates of irrigated alfalfa (Medicago ...

  20. The 'optimum' upwind advection on a triangular mesh

    NASA Technical Reports Server (NTRS)

    Roe, P. L.

    1990-01-01

    For advection schemes based on fluctuation splitting, a design criterion of optimizing the time step leads to linear schemes that coincide with those designed for least truncation error. A further stage of optimizing the time step using a nonlinear positivity criterion, leads to considerable further gains in resolution.

  1. Tidal variability of lateral advection in a coastal plain estuary

    NASA Astrophysics Data System (ADS)

    Basdurak, N. B.; Valle-Levinson, A.

    2013-07-01

    Tidal variability of lateral advection of momentum (vuy, where u and v are along-estuary and lateral flows, respectively, and the subindex indicates differentiation with respect to the cross-estuary direction) was investigated in a coastal plain estuary with observations at Hampton Roads, which is the transition between the James River and Chesapeake Bay. Towed current velocity profiles and hydrographic profiles were captured during 9 expeditions in 2004 and 2005, to determine the intratidal and spatial changes in lateral advection of momentum and its contribution to along-channel flow. Curvature effects and lateral density gradients were important in driving lateral circulation and in modifying intratidal lateral advection of momentum. Lateral advection had the same order of magnitude as the baroclinic pressure gradient. Its contribution to the along-channel momentum balance was greatest during or just after peak flood and weakest at the end of ebb. During peak flood and peak ebb, the spatial distribution of vuy was seaward at the southern (left) side near surface and at the northern side (right) near bed (looking up-estuary), and landward in the rest of the channel. During slack periods the vuy structures were mostly landward. Observations were in good agreement with analytical model results during peak ebb and flood, but inconsistent during slack periods. The discrepancies between model results and field measurements can be attributed to bathymetry-density gradient interactions, which enhanced ebb-to-flood asymmetries in the along-channel and lateral flow.

  2. BACTERIAL SORPTION OF HEAVY METALS

    EPA Science Inventory

    Four bacteria, Bacillus cereus, B. subtilis, Escherichia coli, and Pseudomonas aeruginosa, were examined for the ability to remove Ag+, Cd2+, Cu2+, and La3+ from solution by batch equilibration methods. d and Cu sorption over the concentration range 0.001 to 1 mM was described by...

  3. Oil dispersants

    SciTech Connect

    Flaherty, L.M.

    1989-01-01

    This book contains papers presented at a symposium of the American Society for Testing and Materials. The topics covered include: The effect of elastomers on the efficiency of oil spill dispersants; planning for dispersant use; field experience with dispersants for oil spills on land; and measurements on natural dispersion.

  4. Modeling and inverting reactive stream tracers undergoing two-site sorption and decay in the hyporheic zone

    NASA Astrophysics Data System (ADS)

    Liao, Zijie; Lemke, Dennis; Osenbrück, Karsten; Cirpka, Olaf A.

    2013-06-01

    Performing stream-tracer experiments is an accepted technique to assess transport characteristics of streams undergoing hyporheic exchange. Recently, combining conservative and reactive tracers, in which the latter presumably undergoes degradation exclusively within the hyporheic zone, has been suggested to study in-stream transport, hyporheic exchange, and the metabolic activity of the hyporheic zone. The combined quantitative analysis to adequately describe such tests, however, has been missing. In this paper, we present mathematical methods to jointly analyze breakthrough curves of a conservative tracer (fluorescein), a linearly degrading tracer (resazurin), and its daughter compound (resorufin), which are synchronously introduced into the stream as pulses. In-stream transport is described by the one-dimensional advection-dispersion equation, amended with a convolution term to account for transient storage within the hyporheic zone over a distribution of travel times, transformation of the reactive tracer in the hyporheic zone, and two-site sorption of the parent and daughter compounds therein. We use a shape-free approach of describing the hyporheic travel-time distribution, overcoming the difficulty of identifying the best functional parameterization for transient storage. We discuss how this model can be fitted to the breakthrough curves of all three compounds and demonstrate the method by an application to a tracer test in the third-order stream Goldersbach in Southern Germany. The entire river water passes once through the hyporheic zone over a travel distance of about 200 m with mean hyporheic residence times ranging between 16 and 23 min. We also observed a secondary peak in the transfer functions at about 1 h indicating a second hyporheic flow path. We could jointly fit the breakthrough curves of all compounds in three monitoring stations and evaluated the parameter uncertainty of the individual and joint fits by a method based on conditional

  5. SORPTION OF HEAVY METALS BY THE SOIL FUNGI ASPERGILLUS NIGER AND MUCOR ROUXII

    EPA Science Inventory

    Sorption of the nitrate salts of cadmium(II), copper (II), lanthanum(III) and silver (I) by two fungi, Aspergillus niger and Mucor rouxii, was evaluated using Fruendlich adsorption isotherms and energy dispersive X-ray electron microscopy. The linearized Freundlich isotherm descr...

  6. Novel Non-invasive Estimation of Coronary Blood Flow using Contrast Advection in Computed Tomography Angiography

    NASA Astrophysics Data System (ADS)

    Eslami, Parastou; Seo, Jung-Hee; Rahsepar, Amirali; George, Richard; Lardo, Albert; Mittal, Rajat

    2014-11-01

    Coronary computed tomography angiography (CTA) is a promising tool for assessment of coronary stenosis and plaque burden. Recent studies have shown the presence of axial contrast concentration gradients in obstructed arteries, but the mechanism responsible for this phenomenon is not well understood. We use computational fluid dynamics to study intracoronary contrast dispersion and the correlation of concentration gradients with intracoronary blood flow and stenotic severity. Data from our CFD patient-specific simulations reveals that contrast dispersions are generated by intracoronary advection effects, and therefore, encode the coronary flow velocity. This novel method- Transluminal Attenuation Flow Encoding (TAFE) - is used to estimate the flowrate in phantom studies as well as preclinical experiments. Our results indicate a strong correlation between the values estimated from TAFE and the values measured in these experiments. The flow physics of contrast dispersion associated with TAFE will be discussed. This work is funded by grants from Coulter Foundation and Maryland Innovation Initiative. The authors have pending patents in this technology and RM and ACL have other financial interests associated with TAFE.

  7. Effect of organic matter on the sorption activity of heavy loamy soils for volatile organic compounds under low moisture conditions

    NASA Astrophysics Data System (ADS)

    Breus, I. P.; Mishchenko, A. A.; Shinkarev, A. A.; Neklyudov, S. A.; Breus, V. A.

    2014-12-01

    The diverse effect of the organic matter content on the sorption of vapors of aromatic and aliphatic hydrocarbons in soils under low moisture (<10.5%) has been revealed in sorption experiments using profile samples from two virgin heavy loamy dark gray forest soils characterized by relatively stable contents of finely dispersed mineral components. The decrease of the hydrocarbon sorption with increasing the content of organic matter under dry conditions (in the moisture range from 0 to 5-6%) indicates its lower sorption activity than that of the clay components and the blocking of the sorption sites on soil minerals by organic matter. At moisture contents above 5-6%, the effect of the soil composition on the sorption activity changes radically: it increases with increasing the content of organic matter. This is due to the inversion of the ratio between the activities of the soil components because of the hydrophilization of the surface of the mineral soil component. As a result, the sorption of water on the minerals reduces the mineral sorption activity to hydrocarbons to a lower level than the activity of organic matter. The maximum manifestation of the revealed blocking effect has been observed for the low-humus soils and this effect decreased with the accumulation of soil organic matter.

  8. Sorption Characteristics of Organic Powder Sorption Material in Fluidized Bed with a Cooling Pipe

    NASA Astrophysics Data System (ADS)

    Horibe, Akihiko; Husain, Syahrul; Inaba, Hideo; Haruki, Naoto

    The dynamic sorption characteristics of organic sorbent materials have been studied by using fluidized bed with a cooling pipe. The organic powder type sorbent made from a bridged complex of sodium polyacrylate which is one of the sorption polymers is adopted in this study. Sorption rate of water vapor and the variation of temperature in the sorbent bed with time were measured under various conditions. As a result, sorption ratio increases and the completion time for the sorption process decreases by using a cooling pipe. Furthermore, the non-dimensional correlation equations were obtained for water vapor mass transfer under sorption process in terms of relevant non-dimensional parameters.

  9. Mixed refrigerant Joule-Thomson sorption cryocoolers

    NASA Astrophysics Data System (ADS)

    Tzabar, Nir; Grossman, Gershon

    2014-01-01

    Joule-Thomson (JT) sorption cryocooling is the most mature technology for cooling from a normal Room-Temperature (RT) down to temperatures below 100 K in the absence of moving parts. Therefore, high reliability and no vibrations are attainable, in comparison with other cryocoolers. Cooling to 80 - 100 K with JT cryocoolers is often implemented with pure nitrogen. Alternatively, mixed refrigerants have been suggested for reducing the operating pressures to enable closed cycle cryocooling. There is a variety of publications describing nitrogen sorption cryocoolers with different configurations of sorption compressors. In the present research we suggest a novel sorption JT cryocooler that operates with a mixed refrigerant. Merging of sorption cryocooling and a mixed refrigerant enables the use of a simple, single stage compressor for cooling to 80 - 100 K, lower operating temperatures of the sorption cycle, and thus - reduced power consumption. In previous studies we have analyzed sorption compressors for mixed gases and mixed refrigerants for JT cryocoolers, separately. In this paper the option of mixed refrigerant sorption JT cryocoolers is explored. The considerations for developing mixed refrigerants to be driven by sorption compressors and to be utilized with JT cryocoolers are provided. It appears that, unlike with pure nitrogen, mixed refrigerants can be suitable for JT cryocooling with a single stage sorption compressor.

  10. Sorption of perfluoroalkyl substances in sewage sludge.

    PubMed

    Milinovic, Jelena; Lacorte, Silvia; Rigol, Anna; Vidal, Miquel

    2016-05-01

    The sorption behaviour of three perfluoroalkyl substances (PFASs) (perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutanesulfonic acid (PFBS)) was studied in sewage sludge samples. Sorption isotherms were obtained by varying initial concentrations of PFOS, PFOA and PFBS. The maximum values of the sorption solid-liquid distribution coefficients (Kd,max) varied by almost two orders of magnitude among the target PFASs: 140-281 mL g(-1) for PFOS, 30-54 mL g(-1) for PFOA and 9-18 mL g(-1) for PFBS. Freundlich and linear fittings were appropriate for describing the sorption behaviour of PFASs in the sludge samples, and the derived KF and Kd,linear parameters correlated well. The hydrophobicity of the PFASs was the key parameter that influenced their sorption in sewage sludge. Sorption parameters and log(KOW) were correlated, and for PFOS (the most hydrophobic compound), pH and Ca + Mg status of the sludge controlled the variation in the sorption parameter values. Sorption reversibility was also tested from desorption isotherms, which were also linear. Desorption parameters were systematically higher than the corresponding sorption parameters (up to sixfold higher), thus indicating a significant degree of irreversible sorption, which decreased in the sequence PFOS > PFOA > PFBS. PMID:26780052

  11. Modeling Solute Transport in Soil Columns Using Advective-Dispersive Equation with Fractional Spatial Derivatives

    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...

  12. Sorption of non-polar organic compounds by micro-sized plastic particles in aqueous solution.

    PubMed

    Hüffer, Thorsten; Hofmann, Thilo

    2016-07-01

    The presence of microscale polymer particles (i.e., microplastics) in the environment has become a major concern in recent years. Sorption of organic compounds by microplastics may affect the phase distribution within both sediments and aqueous phases. To investigate this process, isotherms were determined for the sorption of seven aliphatic and aromatic organic probe sorbates by four polymers with different physico-chemical properties. Sorption increased in the order polyamide < polyethylene < polyvinylchloride < polystyrene. This order does not reflect the particle sizes of the investigated microplastics within the aqueous dispersions, indicating the influence of additional factors (e.g., π-π-interactions) on the sorption of aromatic compounds by polystyrene. Linear isotherms by polyethylene suggested that sorbate uptake was due to absorption into the bulk polymer. In contrast, non-linear isotherms for sorption by PS, PA, and PVC suggest a predominance of adsorption onto the polymer surface, which is supported by the best fit of these isotherms using the Polanyi-Manes model. A strong relationship between the sorption coefficients of the microplastics and the hydrophobicity of the sorbates suggests that hydrophobic interactions are of major importance. PMID:27086075

  13. Application of the Space-Time Conservation Element and Solution Element Method to One-Dimensional Advection-Diffusion Problems

    NASA Technical Reports Server (NTRS)

    Wang, Xiao-Yen; Chow, Chuen-Yen; Chang, Sin-Chung

    1999-01-01

    Test problems are used to examine the performance of several one-dimensional numerical schemes based on the space-time conservation and solution element (CE/SE) method. Investigated in this paper are the CE/SE schemes constructed previously for solving the linear unsteady advection-diffusion equation and the schemes derived here for solving the nonlinear viscous and inviscid Burgers equations. In comparison with the numerical solutions obtained using several traditional finite-difference schemes with similar accuracy, the CE/SE solutions display much lower numerical dissipation and dispersion errors.

  14. Aerosol particles and the formation of advection fog

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Liaw, G. S.; Vaughan, O. H., Jr.

    1979-01-01

    A study of numerical simulation of the effects of concentration, particle size, mass of nuclei, and chemical composition on the dynamics of warm fog formation, particularly the formation of advection fog, is presented. This formation is associated with the aerosol particle characteristics, and both macrophysical and microphysical processes are considered. In the macrophysical model, the evolution of wind components, water vapor content, liquid water content, and potential temperature under the influences of vertical turbulent diffusion, turbulent momentum, and turbulent energy transfers are taken into account. In the microphysical model, the supersaturation effect is incorporated with the surface tension and hygroscopic material solution. It is shown that the aerosol particles with the higher number density, larger size nuclei, the heavier nuclei mass, and the higher ratio of the Van't Hoff factor to the molecular weight favor the formation of the lower visibility advection fogs with stronger vertical energy transfer during the nucleation and condensation time period.

  15. Spiral defect chaos in an advection-reaction-diffusion system

    NASA Astrophysics Data System (ADS)

    Affan, H.; Friedrich, R.

    2014-06-01

    This paper comprises numerical and theoretical studies of spatiotemporal patterns in advection-reaction-diffusion systems in which the chemical species interact with the hydrodynamic fluid. Due to the interplay between the two, we obtained the spiral defect chaos in the activator-inhibitor-type model. We formulated the generalized Swift-Hohenberg-type model for this system. Then the evolution of fractal boundaries due to the effect of the strong nonlinearity at the interface of the two chemical species is studied numerically. The purpose of the present paper is to point out that spiral defect chaos, observed in model equations of the extended Swift-Hohenberg equation for low Prandtl number convection, may actually be obtained also in certain advection-reaction-diffusion systems.

  16. Phase Segregation of Passive Advective Particles in an Active Medium.

    PubMed

    Das, Amit; Polley, Anirban; Rao, Madan

    2016-02-12

    Localized contractile configurations or asters spontaneously appear and disappear as emergent structures in the collective stochastic dynamics of active polar actomyosin filaments. Passive particles which (un)bind to the active filaments get advected into the asters, forming transient clusters. We study the phase segregation of such passive advective scalars in a medium of dynamic asters, as a function of the aster density and the ratio of the rates of aster remodeling to particle diffusion. The dynamics of coarsening shows a violation of Porod behavior; the growing domains have diffuse interfaces and low interfacial tension. The phase-segregated steady state shows strong macroscopic fluctuations characterized by multiscaling and intermittency, signifying rapid reorganization of macroscopic structures. We expect these unique nonequilibrium features to manifest in the actin-dependent molecular clustering at the cell surface. PMID:26919022

  17. Phase Segregation of Passive Advective Particles in an Active Medium

    NASA Astrophysics Data System (ADS)

    Das, Amit; Polley, Anirban; Rao, Madan

    2016-02-01

    Localized contractile configurations or asters spontaneously appear and disappear as emergent structures in the collective stochastic dynamics of active polar actomyosin filaments. Passive particles which (un)bind to the active filaments get advected into the asters, forming transient clusters. We study the phase segregation of such passive advective scalars in a medium of dynamic asters, as a function of the aster density and the ratio of the rates of aster remodeling to particle diffusion. The dynamics of coarsening shows a violation of Porod behavior; the growing domains have diffuse interfaces and low interfacial tension. The phase-segregated steady state shows strong macroscopic fluctuations characterized by multiscaling and intermittency, signifying rapid reorganization of macroscopic structures. We expect these unique nonequilibrium features to manifest in the actin-dependent molecular clustering at the cell surface.

  18. Indium Sorption to Iron Oxides

    NASA Astrophysics Data System (ADS)

    White, S. J.; Sacco, S. A.; Hemond, H.; Hussain, F. A.; Runkel, R. L.; Walton-Day, K. E.; Kimball, B. A.; Shine, J. P.

    2014-12-01

    Indium is an increasingly important metal in semiconductors and electronics, and its use is growing rapidly as a semiconductive coating (as indium tin oxide) for liquid crystal displays (LCDs) and flat panel displays. It also has uses in important energy technologies such as light emitting diodes (LEDs) and photovoltaic cells. Despite its rapid increase in use, very little is known about the environmental behavior of indium, and concerns are being raised over the potential health effects of this emerging metal contaminant. One source of indium to the environment is acid mine drainage from the mining of lead, zinc, and copper sulfides. In our previous studies of a stream in Colorado influenced by acid mine drainage from lead and zinc mining activities, indium concentrations were found to be 10,000 times those found in uncontaminated rivers. However, the speciation and mobility of indium could not be reliably modeled because sorption constants to environmental sorbents have not been determined. In this study, we generate sorption constants for indium to ferrihydrite in the laboratory over a range of pHs, sorbent to sorbate ratios, and ionic strengths. Ferrihydrite is one of the most important sorbents in natural systems, and sorption to amorphous iron oxides such as ferrihydrite is thought to be one of the main removal mechanisms of metals from the dissolved phase in aqueous environments. Because of its relatively low solubility, we also find that indium hydroxide precipitation can dominate indium's partitioning at micromolar concentrations of indium. This precipitation may be important in describing indium's behavior in our study stream in Colorado, where modeling sorption to iron-oxides does not explain the complete removal of indium from the dissolved phase when the pH of the system is artificially raised to above 8. This study contributes much-needed data about indium's aqueous behavior, in order to better understand its fate, transport, and impacts in the

  19. Lattice Boltzmann method for the fractional advection-diffusion equation

    NASA Astrophysics Data System (ADS)

    Zhou, J. G.; Haygarth, P. M.; Withers, P. J. A.; Macleod, C. J. A.; Falloon, P. D.; Beven, K. J.; Ockenden, M. C.; Forber, K. J.; Hollaway, M. J.; Evans, R.; Collins, A. L.; Hiscock, K. M.; Wearing, C.; Kahana, R.; Villamizar Velez, M. L.

    2016-04-01

    Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β , the fractional order α , and the single relaxation time τ , the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering.

  20. Advective and diffusive cosmic ray transport in galactic haloes

    NASA Astrophysics Data System (ADS)

    Heesen, Volker; Dettmar, Ralf-Jürgen; Krause, Marita; Beck, Rainer; Stein, Yelena

    2016-05-01

    We present 1D cosmic ray transport models, numerically solving equations of pure advection and diffusion for the electrons and calculating synchrotron emission spectra. We find that for exponential halo magnetic field distributions advection leads to approximately exponential radio continuum intensity profiles, whereas diffusion leads to profiles that can be better approximated by a Gaussian function. Accordingly, the vertical radio spectral profiles for advection are approximately linear, whereas for diffusion they are of `parabolic' shape. We compare our models with deep Australia Telescope Compact Array observations of two edge-on galaxies, NGC 7090 and 7462, at λλ 22 and 6 cm. Our result is that the cosmic ray transport in NGC 7090 is advection dominated with V=150^{+80}_{-30} km s^{-1}, and that the one in NGC 7462 is diffusion dominated with D=3.0± 1.0 × 10^{28}E_GeV^{0.5} cm^2 s^{-1}. NGC 7090 has both a thin and thick radio disc with respective magnetic field scale heights of hB1 = 0.8 ± 0.1 kpc and hB2 = 4.7 ± 1.0 kpc. NGC 7462 has only a thick radio disc with hB2 = 3.8 ± 1.0 kpc. In both galaxies, the magnetic field scale heights are significantly smaller than what estimates from energy equipartition would suggest. A non-negligible fraction of cosmic ray electrons can escape from NGC 7090, so that this galaxy is not an electron calorimeter.

  1. Lattice Boltzmann method for the fractional advection-diffusion equation.

    PubMed

    Zhou, J G; Haygarth, P M; Withers, P J A; Macleod, C J A; Falloon, P D; Beven, K J; Ockenden, M C; Forber, K J; Hollaway, M J; Evans, R; Collins, A L; Hiscock, K M; Wearing, C; Kahana, R; Villamizar Velez, M L

    2016-04-01

    Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β, the fractional order α, and the single relaxation time τ, the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering. PMID:27176431

  2. Anomalous diffusion of a tracer advected by wave turbulence

    NASA Astrophysics Data System (ADS)

    Balk, Alexander M.

    2001-02-01

    We consider the advection of a passive tracer when the velocity field is a superposition of random waves. Green's function for the turbulent transport (turbulent diffusion and turbulent drift) is derived. This Green's function is shown to imply sub-diffusive or super-diffusive behavior of the tracer. For the analysis we introduce the statistical near-identity transformation. The results are confirmed by numerical simulations.

  3. Cellwise conservative unsplit advection for the volume of fluid method

    NASA Astrophysics Data System (ADS)

    Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri

    2015-02-01

    We present a cellwise conservative unsplit (CCU) advection scheme for the volume of fluid method (VOF) in 2D. Contrary to other schemes based on explicit calculations of the flux balances, the CCU advection adopts a cellwise approach where the pre-images of the control volumes are traced backwards through the flow map. The donating regions of the fluxes are calculated via the streaklines of the grid intersections, represented as polygonal chains whose vertices are determined by backward tracing of particles injected in the flow at different times. High order accuracy is obtained from the fourth-order Runge-Kutta method, where intermediate velocities along pathlines are determined with quadratic temporal and bicubic spatial interpolations. The volumes of the donating regions are corrected in order to fulfill the discrete continuity of incompressible flows. Consequently, the calculation produces non-overlapping donating regions and pre-images with conforming edges to their neighbors, resulting in the conservativeness and the boundedness (liquid volume fraction inside the interval [ 0 , 1 ]) of the CCU advection scheme. Finally, the update of the liquid volume fractions is computed from the intersections of the pre-image polygons with the reconstructed interfaces. The CCU scheme is tested on several benchmark tests for the VOF advection, together with the standard piecewise linear interface calculation (PLIC). The geometrical errors of the CCU compare favorably with other unsplit VOF-PLIC schemes. Finally, potential improvements of the VOF method with the use of more precise interface representation techniques and the future extension of the CCU scheme to 3D are discussed.

  4. Vertical Structure of Advection-dominated Accretion Flows

    NASA Astrophysics Data System (ADS)

    Zahra Zeraatgari, Fateme; Abbassi, Shahram

    2015-08-01

    We solve the set of hydrodynamic equations for optically thin advection-dominated accretion flows by assuming a radially self-similar spherical coordinate system (r,θ ,φ ). The disk is considered to be in steady state and axisymmetric. We define the boundary conditions at the pole and the equator of the disk and, to avoid singularity at the rotation axis, the disk is taken to be symmetric with respect to this axis. Moreover, only the {τ }rφ component of the viscous stress tensor is assumed, and we have set {v}θ =0. The main purpose of this study is to investigate the variation of dynamical quantities of the flow in the vertical direction by finding an analytical solution. As a consequence, we found that the advection parameter, {f}{adv}, varies along the θ direction and reaches its maximum near the rotation axis. Our results also show that, in terms of the no-outflow solution, thermal equilibrium still exists and consequently advection cooling can balance viscous heating.

  5. Laser speckle contrast imaging is sensitive to advective flux

    NASA Astrophysics Data System (ADS)

    Khaksari, Kosar; Kirkpatrick, Sean J.

    2016-07-01

    Unlike laser Doppler flowmetry, there has yet to be presented a clear description of the physical variables that laser speckle contrast imaging (LSCI) is sensitive to. Herein, we present a theoretical basis for demonstrating that LSCI is sensitive to total flux and, in particular, the summation of diffusive flux and advective flux. We view LSCI from the perspective of mass transport and briefly derive the diffusion with drift equation in terms of an LSCI experiment. This equation reveals the relative sensitivity of LSCI to both diffusive flux and advective flux and, thereby, to both concentration and the ordered velocity of the scattering particles. We demonstrate this dependence through a short series of flow experiments that yield relationships between the calculated speckle contrast and the concentration of the scatterers (manifesting as changes in scattering coefficient), between speckle contrast and the velocity of the scattering fluid, and ultimately between speckle contrast and advective flux. Finally, we argue that the diffusion with drift equation can be used to support both Lorentzian and Gaussian correlation models that relate observed contrast to the movement of the scattering particles and that a weighted linear combination of these two models is likely the most appropriate model for relating speckle contrast to particle motion.

  6. Sorption Energy Maps of Clay Mineral Surfaces

    SciTech Connect

    Cygan, Randall T.; Kirkpatrick, R. James

    1999-07-19

    A molecular-level understanding of mineral-water interactions is critical for the evaluation and prediction of the sorption properties of clay minerals that may be used in various chemical and radioactive waste disposal methods. Molecular models of metal sorption incorporate empirical energy force fields, based on molecular orbital calculations and spectroscopic data, that account for Coulombic, van der Waals attractive, and short-range repulsive energies. The summation of the non-bonded energy terms at equally-spaced grid points surrounding a mineral substrate provides a three dimensional potential energy grid. The energy map can be used to determine the optimal sorption sites of metal ions on the exposed surfaces of the mineral. By using this approach, we have evaluated the crystallographic and compositional control of metal sorption on the surfaces of kaolinite and illite. Estimates of the relative sorption energy and most stable sorption sites are derived based on a rigid ion approximation.

  7. PCB Congener Sorption To Carbonaceous Sediment Components: Macroscopic Comparison And Characterization Of Sorption Kinetics And Mechanism

    EPA Science Inventory

    Sorption of polychlorinated biphenyls (PCBs) to sediment is a key process in determining their mobility, bioavailability, and chemical decomposition in aquatic environments. In order to examine the validity of currently used interpretation approaches for PCBs sorption, comparati...

  8. Distinguishing resuspension and advection signals in a hypertidal estuary

    NASA Astrophysics Data System (ADS)

    Todd, David; Souza, Alex; Jago, Colin

    2015-04-01

    Terrestrial material is supplied to an estuary system by the river, while marine material is supplied by the sea. Whether the estuary acts as a trap or a bypass zone for SPM (suspended particulate matter) depends upon the properties and dynamics of both the estuary, including the tidal and residual behaviour of the currents, and the SPM, including particle sizes and settling velocities and concentration gradients, which together control the dynamics, such as the trapping efficiency, of the estuary. Whether an SPM signal is regarded as being one of resuspension or advection depends upon the area of interest, and therefore distinguishing between resuspension and advection can be complex. Material that is resuspended within the area of study is regarded as resuspension, while that which is resuspended outside, but passes through, the area of interest, is regarded as advection. The results of a measurement campaign undertaken in a hypertidal UK estuary during the pre-spring bloom February-March and post-spring bloom May-June are presented utilising a combination of acoustic and optical instruments, moorings, and CTD stations. A characteristic asymmetric "twin peak" signal is present during both time periods, implying the presence of both resuspension and advection. This is confirmed through the use of harmonic analysis. A seasonal variation in the relative importance of the resuspension and advection components is seen between the two observation periods, with the small (<122µm) and large (>122µm) particles displaying different behaviours and providing a strong indication of the presence of flocculation. Approximate point flux calculations showed a reduction in the horizontal gradient of concentration, and subsequently the flood dominance of sediment transport, between May-June and February-March. This has been attributed to changes in biological activity and atmospheric forcing between the two observational periods. Ebb-dominant concentrations brought about by the

  9. Manganese Nitride Sorption Joule-Thomson Refrigerator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.; Phillips, Wayne M.

    1992-01-01

    Proposed sorption refrigeration system of increased power efficiency combines MnxNy sorption refrigeration stage with systems described in "Regenerative Sorption Refrigerator" (NPO-17630). Measured pressure-vs-composition isotherms for reversible chemisorption of N2 in MnxNy suggest feasibility to incorporate MnxNy chemisorption stage in Joule-Thomson cryogenic system. Discovery represents first known reversible nitrogen chemisorption compression system. Has potential in nitrogen-isotope separation, nitrogen purification, or contamination-free nitrogen compression.

  10. Surface complexation model of uranyl sorption on Georgia kaolinite

    USGS Publications Warehouse

    Payne, T.E.; Davis, J.A.; Lumpkin, G.R.; Chisari, R.; Waite, T.D.

    2004-01-01

    The adsorption of uranyl on standard Georgia kaolinites (KGa-1 and KGa-1B) was studied as a function of pH (3-10), total U (1 and 10 ??mol/l), and mass loading of clay (4 and 40 g/l). The uptake of uranyl in air-equilibrated systems increased with pH and reached a maximum in the near-neutral pH range. At higher pH values, the sorption decreased due to the presence of aqueous uranyl carbonate complexes. One kaolinite sample was examined after the uranyl uptake experiments by transmission electron microscopy (TEM), using energy dispersive X-ray spectroscopy (EDS) to determine the U content. It was found that uranium was preferentially adsorbed by Ti-rich impurity phases (predominantly anatase), which are present in the kaolinite samples. Uranyl sorption on the Georgia kaolinites was simulated with U sorption reactions on both titanol and aluminol sites, using a simple non-electrostatic surface complexation model (SCM). The relative amounts of U-binding >TiOH and >AlOH sites were estimated from the TEM/EDS results. A ternary uranyl carbonate complex on the titanol site improved the fit to the experimental data in the higher pH range. The final model contained only three optimised log K values, and was able to simulate adsorption data across a wide range of experimental conditions. The >TiOH (anatase) sites appear to play an important role in retaining U at low uranyl concentrations. As kaolinite often contains trace TiO2, its presence may need to be taken into account when modelling the results of sorption experiments with radionuclides or trace metals on kaolinite. ?? 2004 Elsevier B.V. All rights reserved.

  11. Spatially varying dispersion to model breakthrough curves.

    PubMed

    Li, Guangquan

    2011-01-01

    Often the water flowing in a karst conduit is a combination of contaminated water entering at a sinkhole and cleaner water released from the limestone matrix. Transport processes in the conduit are controlled by advection, mixing (dilution and dispersion), and retention-release. In this article, a karst transport model considering advection, spatially varying dispersion, and dilution (from matrix seepage) is developed. Two approximate Green's functions are obtained using transformation of variables, respectively, for the initial-value problem and for the boundary-value problem. A numerical example illustrates that mixing associated with strong spatially varying conduit dispersion can cause strong skewness and long tailing in spring breakthrough curves. Comparison of the predicted breakthrough curve against that measured from a dye-tracing experiment between Ames Sink and Indian Spring, Northwest Florida, shows that the conduit dispersivity can be as large as 400 m. Such a large number is believed to imply strong solute interaction between the conduit and the matrix and/or multiple flow paths in a conduit network. It is concluded that Taylor dispersion is not dominant in transport in a karst conduit, and the complicated retention-release process between mobile- and immobile waters may be described by strong spatially varying conduit dispersion. PMID:21143474

  12. Plutonium sorption and desorption behavior on bentonite.

    PubMed

    Begg, James D; Zavarin, Mavrik; Tumey, Scott J; Kersting, Annie B

    2015-03-01

    Understanding plutonium (Pu) sorption to, and desorption from, mineral phases is key to understanding its subsurface transport. In this work we study Pu(IV) sorption to industrial grade FEBEX bentonite over the concentration range 10(-7)-10(-16) M to determine if sorption at typical environmental concentrations (≤10(-12) M) is the same as sorption at Pu concentrations used in most laboratory experiments (10(-7)-10(-11) M). Pu(IV) sorption was broadly linear over the 10(-7)-10(-16) M concentration range during the 120 d experimental period; however, it took up to 100 d to reach sorption equilibrium. At concentrations ≥10(-8) M, sorption was likely affected by additional Pu(IV) precipitation/polymerization reactions. The extent of sorption was similar to that previously reported for Pu(IV) sorption to SWy-1 Na-montmorillonite over a narrower range of Pu concentrations (10(-11)-10(-7) M). Sorption experiments with FEBEX bentonite and Pu(V) were also performed across a concentration range of 10(-11)-10(-7) M and over a 10 month period which allowed us to estimate the slow apparent rates of Pu(V) reduction on a smectite-rich clay. Finally, a flow cell experiment with Pu(IV) loaded on FEBEX bentonite demonstrated continued desorption of Pu over a 12 day flow period. Comparison with a desorption experiment performed with SWy-1 montmorillonite showed a strong similarity and suggested the importance of montorillonite phases in controlling Pu sorption/desorption reactions on FEBEX bentonite. PMID:25574607

  13. Differential patterns of divergence in ocean drifters: Implications for larval flatfish advection and recruitment

    NASA Astrophysics Data System (ADS)

    Wilderbuer, Thomas; Duffy-Anderson, Janet T.; Stabeno, Phyllis; Hermann, Albert

    2016-05-01

    In an effort to better understand the physics of the eastern Bering Sea shelf current as it relates to flatfish advection to favorable near-shore areas, sets of multiple, satellite-tracked, oceanic drifters were released in 2010, 2012 and 2013. The release sites and dates were chosen to coincide with known spawning locations for northern rock sole (Lepidopsetta polyxystra) and known time of larval emergence. The drifters were drogued 5-each at 20 and 40 m in 2010 and 2012, and 4 at 40 m and 2 at 20 m in 2013. The locations of drifters were used to calculate divergence over a 90-day period that corresponds to the larval pelagic duration of Bering Sea shelf northern rock sole. Results indicate that there are alternating periods of positive and negative divergence with an overall trend toward drifter separation after 90 days, roughly the end of the rock sole planktonic larval period. Examination of the drifter behavior at the hourly scale indicates that semi-daily tidal forcing is the primary mechanism of drifter divergence and convergence. Field observations of early-stage northern rock sole larval distributions over the same period indicate that predominant oceanographic advection is northerly over the continental shelf among preflexion stages, though juveniles are predominantly found in nursery areas located ~ 400 km eastward and inshore. Evidence from drifter deployments suggests that behavioral movements during the postflexion and early juvenile larval phases that optimize eastward periodicity of tidal cycles is a viable mechanism to enhance eastward movement of northern rock sole larvae to favorable nursery grounds. A regional ocean modeling system (ROMS) was implemented to track the different rates of dispersion in simulations both with and without tidal forcing, and was used to estimate effective horizontal eddy diffusion in the case of both isobaric (fixed-depth) and Lagrangian (neutrally buoyant) particles. The addition of tidal forcing had a pronounced

  14. Update on Advection-Diffusion Purge Flow Model

    NASA Technical Reports Server (NTRS)

    Brieda, Lubos

    2015-01-01

    Gaseous purge is commonly used in sensitive spacecraft optical or electronic instruments to prevent infiltration of contaminants and/or water vapor. Typically, purge is sized using simplistic zero-dimensional models that do not take into account instrument geometry, surface effects, and the dependence of diffusive flux on the concentration gradient. For this reason, an axisymmetric computational fluid dynamics (CFD) simulation was recently developed to model contaminant infiltration and removal by purge. The solver uses a combined Navier-Stokes and Advection-Diffusion approach. In this talk, we report on updates in the model, namely inclusion of a particulate transport model.

  15. Numerical simulation of life cycles of advection warm fog

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Vaughan, O. H.

    1977-01-01

    The formation, development and dissipation of advection warm fog is investigated. The equations employed in the model include the equation of continuity, momentum and energy for the descriptions of density, wind component and potential temperature, respectively, together with two diffusion equations for the modification of water-vapor mixing ratio and liquid-water mixing ratios. A description of the vertical turbulent transfer of heat, moisture and momentum has been taken into consideration. The turbulent exchange coefficients adopted in the model are based on empirical flux-gradient relations.

  16. Subsurface barrier design alternatives for confinement and controlled advection flow

    SciTech Connect

    Phillips, S.J.; Stewart, W.E.; Alexander, R.G.; Cantrell, K.J.; McLaughlin, T.J.

    1994-02-01

    Various technologies and designs are being considered to serve as subsurface barriers to confine or control contaminant migration from underground waste storage or disposal structures containing radioactive and hazardous wastes. Alternatives including direct-coupled flood and controlled advection designs are described as preconceptual examples. Prototype geotechnical equipment for testing and demonstration of these alternative designs tested at the Hanford Geotechnical Development and Test Facility and the Hanford Small-Tube Lysimeter Facility include mobile high-pressure injectors and pumps, mobile transport and pumping units, vibratory and impact pile drivers, and mobile batching systems. Preliminary laboratory testing of barrier materials and additive sequestering agents have been completed and are described.

  17. Visualizing Vector Fields Using Line Integral Convolution and Dye Advection

    NASA Technical Reports Server (NTRS)

    Shen, Han-Wei; Johnson, Christopher R.; Ma, Kwan-Liu

    1996-01-01

    We present local and global techniques to visualize three-dimensional vector field data. Using the Line Integral Convolution (LIC) method to image the global vector field, our new algorithm allows the user to introduce colored 'dye' into the vector field to highlight local flow features. A fast algorithm is proposed that quickly recomputes the dyed LIC images. In addition, we introduce volume rendering methods that can map the LIC texture on any contour surface and/or translucent region defined by additional scalar quantities, and can follow the advection of colored dye throughout the volume.

  18. Alginate and Algal-Based Beads for the Sorption of Metal Cations: Cu(II) and Pb(II).

    PubMed

    Wang, Shengye; Vincent, Thierry; Faur, Catherine; Guibal, Eric

    2016-01-01

    Alginate and algal-biomass (Laminaria digitata) beads were prepared by homogeneous Ca ionotropic gelation. In addition, glutaraldehyde-crosslinked poly (ethyleneimine) (PEI) was incorporated into algal beads. The three sorbents were characterized by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX): the sorption occurs in the whole mass of the sorbents. Sorption experiments were conducted to evaluate the impact of pH, sorption isotherms, and uptake kinetics. A special attention was paid to the effect of drying (air-drying vs. freeze-drying) on the mass transfer properties. For alginate, freeze drying is required for maintaining the porosity of the hydrogel, while for algal-based sorbents the swelling of the material minimizes the impact of the drying procedure. The maximum sorption capacities observed from experiments were 415, 296 and 218 mg Pb g(-1) and 112, 77 and 67 mg Cu g(-1) for alginate, algal and algal/PEI beads respectively. Though the sorption capacities of algal-beads decreased slightly (compared to alginate beads), the greener and cheaper one-pot synthesis of algal beads makes this sorbent more competitive for environmental applications. PEI in algal beads decreases the sorption properties in the case of the sorption of metal cations under selected experimental conditions. PMID:27598128

  19. Eigensolution analysis of spectral/hp continuous Galerkin approximations to advection-diffusion problems: Insights into spectral vanishing viscosity

    NASA Astrophysics Data System (ADS)

    Moura, R. C.; Sherwin, S. J.; Peiró, J.

    2016-02-01

    This study addresses linear dispersion-diffusion analysis for the spectral/hp continuous Galerkin (CG) formulation in one dimension. First, numerical dispersion and diffusion curves are obtained for the advection-diffusion problem and the role of multiple eigencurves peculiar to spectral/hp methods is discussed. From the eigencurves' behaviour, we observe that CG might feature potentially undesirable non-smooth dispersion/diffusion characteristics for under-resolved simulations of problems strongly dominated by either convection or diffusion. Subsequently, the linear advection equation augmented with spectral vanishing viscosity (SVV) is analysed. Dispersion and diffusion characteristics of CG with SVV-based stabilization are verified to display similar non-smooth features in flow regions where convection is much stronger than dissipation or vice-versa, owing to a dependency of the standard SVV operator on a local Péclet number. First a modification is proposed to the traditional SVV scaling that enforces a globally constant Péclet number so as to avoid the previous issues. In addition, a new SVV kernel function is suggested and shown to provide a more regular behaviour for the eigencurves along with a consistent increase in resolution power for higher-order discretizations, as measured by the extent of the wavenumber range where numerical errors are negligible. The dissipation characteristics of CG with the SVV modifications suggested are then verified to be broadly equivalent to those obtained through upwinding in the discontinuous Galerkin (DG) scheme. Nevertheless, for the kernel function proposed, the full upwind DG scheme is found to have a slightly higher resolution power for the same dissipation levels. These results show that improved CG-SVV characteristics can be pursued via different kernel functions with the aid of optimization algorithms.

  20. Regenerative sorption compressors for cryogenic refrigeration

    NASA Technical Reports Server (NTRS)

    Bard, Steven; Jones, Jack A.

    1990-01-01

    Dramatic efficiency improvements for sorption coolers appear possible with use of compressor heat regeneration techniques. The general theory of sorption compressor heat regeneration is discussed in this paper, and several design concepts are presented. These designs result in long-life, low-vibration cryocoolers that potentially have efficiencies comparable to Stirling refrigerators for 65 to 90 K spacecraft instrument cooling applications.

  1. Sorption of paracetamol onto biomaterials.

    PubMed

    Ferchichi, Maroua; Dhaouadi, Hatem

    2016-01-01

    Pharmaceutical residues released into the environment are posing more and more public health problems. It is worthwhile to study the retention of pharmaceuticals residues by adsorption on solid supports. Batch sorption experiments are intended to identify the adsorption isotherms of the pharmaceutically active ingredient on the biomaterials. The results obtained in this study have shown that the retention possibilities of these compounds by bio-adsorbents (clay and sand) are not significant. The negligible sorption for these media is explained by the low hydrophobicity of paracetamol (Log K(ow) = 0.46). The retention of paracetamol on the dehydrated sewage sludge and on Posidonia oceanica showed a relatively significant adsorption with a maximal quantity of 0.956 mg g(-1) and 1.638 mg g(-1) for the dehydrate sludge and P. oceanica, respectively. On the other hand, the study of paracetamol retention on the powdered activated carbon showed a high adsorption capacity of about 515.27 mg g(-1). Isotherm data show a good fit with Langmuir's model. An infrared analysis is carried out. It shows identical bands before and after adsorption, with some modifications. PMID:27387007

  2. Numerical Modelling of Mesoscale Atmospheric Dispersion.

    NASA Astrophysics Data System (ADS)

    Moran, Michael D.

    Mesoscale atmospheric dispersion is more complicated than smaller-scale dispersion because the mean wind field can no longer be considered steady or horizontally homogeneous over mesoscale time and space scales. Wind shear also plays a more important role on the mesoscale, and horizontal dispersion can be enhanced and even dominated by vertical wind shear through either the simultaneous or delayed interaction of horizontal differential advection and vertical mixing over one or two diurnal periods. The CSU mesoscale atmospheric dispersion modelling system has been used in this study to simulate the transport and diffusion of a perfluorocarbon gas for episodic releases made during two North American mesoscale dispersion field experiments, the 1980 Great Plains tracer experiment and the 1983 Cross-Appalachian Tracer Experiment (CAPTEX). Ground -level and elevated tracer concentrations were measured out to distances of 600 km from the source in the first experiment and 1100 km in the second. The physiography of the two experimental domains was quite different, permitting isolation and examination of the roles of terrain forcing and differential advection in mesoscale atmospheric dispersion. Suites of numerical experiments of increasing complexity were carried out for both case studies. The experiments differed in the realism of their representation of both the synoptic-scale flow and the underlying terrain. The Great Plains nocturnal low-level jet played an important role in the first case while temporal changes in the synoptic -scale flow were very significant in the second case. The contributions of differential advection and mesoscale deformation to mesoscale dispersion dominated those of small-scale turbulent diffusion for both cases, and Pasquill's (1962) delayed-shear-enhancement mechanism for lateral dispersion was found to be particularly important. This study was also the first quantitative evaluation of the CSU mesoscale dispersion modelling system with

  3. Ferrous iron sorption by hydrous metal oxides.

    PubMed

    Nano, Genevieve Villaseñor; Strathmann, Timothy J

    2006-05-15

    Ferrous iron is critical to a number of biogeochemical processes that occur in heterogeneous aquatic environments, including the abiotic reductive transformation of subsurface contaminants. The sorption of Fe(II) to ubiquitous soil minerals, particularly iron-free mineral phases, is not well understood. Colloidal TiO2, gamma-AlOOH, and gamma-Al2O2 were used as model hydrous oxides to investigate Fe(II) sorption to iron-free mineral surfaces. Rapid Fe(II) sorption during the first few hours is followed by a much slower uptake process that continues for extended periods (at least 30 days). For equivalent solution conditions, the extent of Fe(II) sorption decreases in the order TiO2 >gamma-Al2O3 >gamma-AlOOH. Short-term equilibrium sorption data measured over a wide range of conditions (pH, ionic strength, Fe(II)-to-sorbent ratio) are well described by the diffuse double layer model. Fe(II) sorption to TiO2 is best described by a single-site model that considers formation of two surface complexes, SOFe+ and SOFeOH0. For gamma-AlOOH and gamma-Al2O3, sorption data are best described by a two-site model that considers formation of SOFe+ complexes at weak- and strong-binding surface sites. Accurate description of sorption data for higher Fe(II) concentrations at alkaline pH conditions requires the inclusion of a Fe(II) surface precipitation reaction in the model formulation. The presence of common groundwater constituents (calcium, sulfate, bicarbonate, or fulvic acid) had no significant effect on Fe(II) sorption. These results demonstrate that iron-free soil minerals can exert a significant influence on Fe(II) sorption and speciation in heterogeneous aquatic systems. PMID:16337955

  4. Sorption kinetics of hexadecyltrimethylammonium on natural clinoptilolite

    SciTech Connect

    Li, Z.

    1999-09-14

    Sorption kinetics of hexadecyltrimethylammonium (HDTMA) chloride on a natural clinoptilolite was studied in this research. The amount of HDTMA sorbed is a function of the initial HDTMA input and the sorption time. When the initial HDTMA input is less than the external cation-exchange capacity of the clinoptilolite, the HDTMA sorption is fast and equilibrium can be established in 1 h. As the initial HDTMA input is greater than the external cation-exchange capacity of clinoptilolite, which will result in more than a monolayer HDTMA surface coverage, the time for HDTMA sorption to reach equilibrium increases exponentially. The HDTMA sorption maximum on clinoptilolite increases logarithmically with mixing time. The counterion solution concentration data suggest that at the initial stage HDTMA molecules sorb on the zeolite via micelle forms, which is manifested by a decrease in chloride solution concentration with time. When HDTMA solution concentration is depleted to less than its critical micelle concentration, the adsorbed micelles (admicelles) rearrange themselves to a more stable monolayer or bilayer configuration, which is reflected by an increase in counterion solution concentration due to the desorption of chloride from admicelles. The time required for the surface rearrangement increases exponentially as the HDTMA input increases. The data of HDTMA sorption kinetics were fitted to different kinetic models, and the parabolic diffusion model fits the data best for the HDTMA sorption, counterion sorption at the initial stage and counterion desorption at the rearrangement stage. Thus, the sorption of HDTMA on clinoptilolite surfaces is diffusion controlled. The results also indicate that it is incomplete to discuss surfactant sorption without counterion concentration data.

  5. A cryogenic circulating advective multi-pass absorption cell

    NASA Astrophysics Data System (ADS)

    Stockett, M. H.; Lawler, J. E.

    2012-03-01

    A novel absorption cell has been developed to enable a spectroscopic survey of a broad range of polycyclic aromatic hydrocarbons (PAH) under astrophysically relevant conditions and utilizing a synchrotron radiation continuum to test the still controversial hypothesis that these molecules or their ions could be carriers of the diffuse interstellar bands. The cryogenic circulating advective multi-pass absorption cell resembles a wind tunnel; molecules evaporated from a crucible or injected using a custom gas feedthrough are entrained in a laminar flow of cryogenically cooled buffer gas and advected into the path of the synchrotron beam. This system includes a multi-pass optical White cell enabling absorption path lengths of hundreds of meters and a detection sensitivity to molecular densities on the order of 107 cm-3. A capacitively coupled radio frequency dielectric barrier discharge provides ionized and metastable buffer gas atoms for ionizing the candidate molecules via charge exchange and the Penning effect. Stronger than expected clustering of PAH molecules has slowed efforts to record gas phase PAH spectra at cryogenic temperatures, though such clusters may play a role in other interstellar phenomena.

  6. Advection-Based Sparse Data Management for Visualizing Unsteady Flow.

    PubMed

    Guo, Hanqi; Zhang, Jiang; Liu, Richen; Liu, Lu; Yuan, Xiaoru; Huang, Jian; Meng, Xiangfei; Pan, Jingshan

    2014-12-01

    When computing integral curves and integral surfaces for large-scale unsteady flow fields, a major bottleneck is the widening gap between data access demands and the available bandwidth (both I/O and in-memory). In this work, we explore a novel advection-based scheme to manage flow field data for both efficiency and scalability. The key is to first partition flow field into blocklets (e.g. cells or very fine-grained blocks of cells), and then (pre)fetch and manage blocklets on-demand using a parallel key-value store. The benefits are (1) greatly increasing the scale of local-range analysis (e.g. source-destination queries, streak surface generation) that can fit within any given limit of hardware resources; (2) improving memory and I/O bandwidth-efficiencies as well as the scalability of naive task-parallel particle advection. We demonstrate our method using a prototype system that works on workstation and also in supercomputing environments. Results show significantly reduced I/O overhead compared to accessing raw flow data, and also high scalability on a supercomputer for a variety of applications. PMID:26356969

  7. THE ADVECTION OF SUPERGRANULES BY THE SUN'S AXISYMMETRIC FLOWS

    SciTech Connect

    Hathaway, David H.; Williams, Peter E.; Rosa, Kevin Dela; Cuntz, Manfred E-mail: peter.williams@nasa.go

    2010-12-10

    We show that the motions of supergranules are consistent with a model in which they are simply advected by the axisymmetric flows in the Sun's surface shear layer. We produce a 10 day series of simulated Doppler images at a 15 minute cadence that reproduces most spatial and temporal characteristics seen in the SOHO/MDI Doppler data. Our simulated data have a spectrum of cellular flows with just two components-a granule component that peaks at spherical wavenumbers of about 4000 and a supergranule component that peaks at wavenumbers of about 110. We include the advection of these cellular components by the axisymmetric flows-differential rotation and meridional flow-whose variations with latitude and depth (wavenumber) are consistent with observations. We mimic the evolution of the cellular pattern by introducing random variations to the phases of the spectral components at rates that reproduce the levels of cross-correlation as functions of time and latitude. Our simulated data do not include any wave-like characteristics for the supergranules yet can reproduce the rotation characteristics previously attributed to wave-like behavior. We find rotation rates which appear faster than the actual rotation rates and attribute this to projection effects. We find that the measured meridional flow does accurately represent the actual flow and that the observations indicate poleward flow to 65{sup 0}-70{sup 0} latitude with equatorward countercells in the polar regions.

  8. Moisture advection to the Arctic : forecasted, analysed and observed

    NASA Astrophysics Data System (ADS)

    Dufour, Ambroise; Zolina, Olga

    2015-04-01

    Besides its contribution to the Arctic hydrological budget, moisture imports from mid-latitudes are also influential on shorter time scales since water vapour advection tends to occur together with extratropical cyclones. Influx of moisture to the Arctic cause the formation of clouds that have an immediate impact on the surface energy budget especially in winter. In the long run, inaccuracies in the description of cloud cover and phase lead to temperature biases in CMIP5 models. The ECMWF workshop on polar prediction has highlighted moisture advection as one of the problematic physical processes limiting the quality of forecasts. Verifying the accuracy of medium-term forecasts is of interest beyond weather prediction : it points to the ability of models to bring adequate quantities of moisture to the Arctic when they are less constrained by observations than in analyses. In this study, we have compared forecasted moisture flux fields with analyses and observations over the period 2000-2010. ECMWF's ERA-Interim provided the forecasts, extending to ten days. For the analyses, in addition to ERA-Interim, we used the Arctic System Reanalysis whose forecast model is optimized for the polar regions and runs at high resolution (30 km). Finally, the Integrated Global Radiosonde Archive data over the Arctic allowed a validation by observations.

  9. Horizontal advection, diffusion and plankton spectra at the sea surface.

    NASA Astrophysics Data System (ADS)

    Bracco, A.; Clayton, S.; Pasquero, C.

    2009-04-01

    Plankton patchiness is ubiquitous in the oceans, and various physical and biological processes have been proposed as its generating mechanisms. However, a coherent statement on the problem is missing, due to both a small number of suitable observations and to an incomplete understanding of the properties of reactive tracers in turbulent media. Abraham (1998) suggested that horizontal advection may be the dominant process behind the observed distributions of phytoplankton and zooplankton, acting to mix tracers with longer reaction times (Rt) down to smaller scales. Conversely, Mahadevan and Campbell (2002) attributed the relative distributions of sea surface temperature and phytoplankton to small scale upwelling, where tracers with longer Rt are able to homogenize more than those with shorter reaction times. Neither of the above mechanisms can explain simultaneously the (relative) spectral slopes of temperature, phytoplankton and zooplankton. Here, with a simple advection model and a large suite of numerical experiments, we concentrate on some of the physical processes influencing the relative distributions of tracers at the ocean surface, and we investigate: 1) the impact of the spatial scale of tracer supply; 2) the role played by coherent eddies on the distribution of tracers with different Rt; 3) the role of diffusion (so far neglected). We show that diffusion determines the distribution of temperature, regardless of the nature of the forcing. We also find that coherent structures together with differential diffusion of tracers with different Rt impact the tracer distributions. This may help in understanding the highly variable nature of observed plankton spectra.

  10. Toward enhanced subsurface intervention methods using chaotic advection.

    PubMed

    Trefry, Michael G; Lester, Daniel R; Metcalfe, Guy; Ord, Alison; Regenauer-Lieb, Klaus

    2012-01-01

    Many intervention activities in the terrestrial subsurface involve the need to recover/emplace distributions of scalar quantities (e.g. dissolved phase concentrations or heat) from/in volumes of saturated porous media. These scalars can be targeted by pump-and-treat methods or by amendment technologies. Application examples include in-situ leaching for metals, recovery of dissolved contaminant plumes, or utilizing heat energy in geothermal reservoirs. While conventional pumping methods work reasonably well, costs associated with maintaining pumping schedules are high and improvements in efficiency would be welcome. In this paper we discuss how transient switching of the pressure at different wells can intimately control subsurface flow, generating a range of "programmed" flows with various beneficial characteristics. Some programs produce chaotic flows which accelerate mixing, while others create encapsulating flows which can isolate fluid zones for lengthy periods. In a simplified model of an aquifer subject to balanced pumping, chaotic flow topologies have been predicted theoretically and verified experimentally using Hele-Shaw cells. Here, a survey of the key characteristics of chaotic advection is presented. Mathematical methods are used to show how these characteristics may translate into practical situations involving regional flows and heterogeneity. The results are robust to perturbations, and withstand significant aquifer heterogeneity. It is proposed that chaotic advection may form the basis of new efficient technologies for groundwater interventions. PMID:21600670

  11. Chaotic advection in 2D anisotropic porous media

    NASA Astrophysics Data System (ADS)

    Varghese, Stephen; Speetjens, Michel; Trieling, Ruben; Toschi, Federico

    2015-11-01

    Traditional methods for heat recovery from underground geothermal reservoirs employ a static system of injector-producer wells. Recent studies in literature have shown that using a well-devised pumping scheme, through actuation of multiple injector-producer wells, can dramatically enhance production rates due to the increased scalar / heat transport by means of chaotic advection. However the effect of reservoir anisotropy on kinematic mixing and heat transport is unknown and has to be incorporated and studied for practical deployment in the field. As a first step, we numerically investigate the effect of anisotropy (both magnitude and direction) on (chaotic) advection of passive tracers in a time-periodic Darcy flow within a 2D circular domain driven by periodically reoriented diametrically opposite source-sink pairs. Preliminary results indicate that anisotropy has a significant impact on the location, shape and size of coherent structures in the Poincare sections. This implies that the optimal operating parameters (well spacing, time period of well actuation) may vary strongly and must be carefully chosen so as to enhance subsurface transport. This work is part of the research program of the Foundation for Fundamental Research on Matter (FOM), which is part of Netherlands Organisation for Scientific Research (NWO). This research program is co-financed by Shell Global Solutions International B.V.

  12. Multiple anisotropic collisions for advection-diffusion Lattice Boltzmann schemes

    NASA Astrophysics Data System (ADS)

    Ginzburg, Irina

    2013-01-01

    This paper develops a symmetrized framework for the analysis of the anisotropic advection-diffusion Lattice Boltzmann schemes. Two main approaches build the anisotropic diffusion coefficients either from the anisotropic anti-symmetric collision matrix or from the anisotropic symmetric equilibrium distribution. We combine and extend existing approaches for all commonly used velocity sets, prescribe most general equilibrium and build the diffusion and numerical-diffusion forms, then derive and compare solvability conditions, examine available anisotropy and stable velocity magnitudes in the presence of advection. Besides the deterioration of accuracy, the numerical diffusion dictates the stable velocity range. Three techniques are proposed for its elimination: (i) velocity-dependent relaxation entries; (ii) their combination with the coordinate-link equilibrium correction; and (iii) equilibrium correction for all links. Two first techniques are also available for the minimal (coordinate) velocity sets. Even then, the two-relaxation-times model with the isotropic rates often gains in effective stability and accuracy. The key point is that the symmetric collision mode does not modify the modeled diffusion tensor but it controls the effective accuracy and stability, via eigenvalue combinations of the opposite parity eigenmodes. We propose to reduce the eigenvalue spectrum by properly combining different anisotropic collision elements. The stability role of the symmetric, multiple-relaxation-times component, is further investigated with the exact von Neumann stability analysis developed in diffusion-dominant limit.

  13. A cryogenic circulating advective multi-pass absorption cell

    SciTech Connect

    Stockett, M. H.; Lawler, J. E.

    2012-03-15

    A novel absorption cell has been developed to enable a spectroscopic survey of a broad range of polycyclic aromatic hydrocarbons (PAH) under astrophysically relevant conditions and utilizing a synchrotron radiation continuum to test the still controversial hypothesis that these molecules or their ions could be carriers of the diffuse interstellar bands. The cryogenic circulating advective multi-pass absorption cell resembles a wind tunnel; molecules evaporated from a crucible or injected using a custom gas feedthrough are entrained in a laminar flow of cryogenically cooled buffer gas and advected into the path of the synchrotron beam. This system includes a multi-pass optical White cell enabling absorption path lengths of hundreds of meters and a detection sensitivity to molecular densities on the order of 10{sup 7} cm{sup -3}. A capacitively coupled radio frequency dielectric barrier discharge provides ionized and metastable buffer gas atoms for ionizing the candidate molecules via charge exchange and the Penning effect. Stronger than expected clustering of PAH molecules has slowed efforts to record gas phase PAH spectra at cryogenic temperatures, though such clusters may play a role in other interstellar phenomena.

  14. A cryogenic circulating advective multi-pass absorption cell.

    PubMed

    Stockett, M H; Lawler, J E

    2012-03-01

    A novel absorption cell has been developed to enable a spectroscopic survey of a broad range of polycyclic aromatic hydrocarbons (PAH) under astrophysically relevant conditions and utilizing a synchrotron radiation continuum to test the still controversial hypothesis that these molecules or their ions could be carriers of the diffuse interstellar bands. The cryogenic circulating advective multi-pass absorption cell resembles a wind tunnel; molecules evaporated from a crucible or injected using a custom gas feedthrough are entrained in a laminar flow of cryogenically cooled buffer gas and advected into the path of the synchrotron beam. This system includes a multi-pass optical White cell enabling absorption path lengths of hundreds of meters and a detection sensitivity to molecular densities on the order of 10(7) cm(-3). A capacitively coupled radio frequency dielectric barrier discharge provides ionized and metastable buffer gas atoms for ionizing the candidate molecules via charge exchange and the Penning effect. Stronger than expected clustering of PAH molecules has slowed efforts to record gas phase PAH spectra at cryogenic temperatures, though such clusters may play a role in other interstellar phenomena. PMID:22462957

  15. Chaotic Advection, Fluid Spreading, and Groundwater Contaminant Plumes

    NASA Astrophysics Data System (ADS)

    Neupauer, R. M.; Mays, D. C.

    2011-12-01

    In situ remediation of contaminated groundwater requires degradation reactions at the interface between the contaminant plume and an injected treatment solution containing chemical or biological amendments. Therefore a promising approach to accelerate in situ remediation is to elongate the interface between the contaminant plume and treatment solution through fluid spreading. The literature on chaotic advection describes how to accomplish spreading in laminar flows, which lack the turbulent eddies that provide spreading in streams or engineered reactors. A key result from the literature on chaotic advection is that spreading is inherent in the vicinity of certain periodic points, which are points to which fluid particles return in successive iterations of chaotic flows. Specifically, spreading is enhanced near the stable and unstable manifolds associated with hyperbolic periodic points. We investigate the transient flow created with a four-well system in which wells are operated sequentially as either injection wells or extraction wells. In particular, we identify the periodic points and demonstrate that fluid spreading occurs nearby. For appropriately designed injection and extraction sequences, the periodic points are located near the interface between the contaminant plume and treatment solution, leading to elongation of the interface, with expected benefits of enhanced reaction and accelerated remediation.

  16. Positivity-preserving numerical schemes for multidimensional advection

    NASA Technical Reports Server (NTRS)

    Leonard, B. P.; Macvean, M. K.; Lock, A. P.

    1993-01-01

    This report describes the construction of an explicit, single time-step, conservative, finite-volume method for multidimensional advective flow, based on a uniformly third-order polynomial interpolation algorithm (UTOPIA). Particular attention is paid to the problem of flow-to-grid angle-dependent, anisotropic distortion typical of one-dimensional schemes used component-wise. The third-order multidimensional scheme automatically includes certain cross-difference terms that guarantee good isotropy (and stability). However, above first-order, polynomial-based advection schemes do not preserve positivity (the multidimensional analogue of monotonicity). For this reason, a multidimensional generalization of the first author's universal flux-limiter is sought. This is a very challenging problem. A simple flux-limiter can be found; but this introduces strong anisotropic distortion. A more sophisticated technique, limiting part of the flux and then restoring the isotropy-maintaining cross-terms afterwards, gives more satisfactory results. Test cases are confined to two dimensions; three-dimensional extensions are briefly discussed.

  17. OBSERVATION OF MAGNETIC RECONNECTION DRIVEN BY GRANULAR SCALE ADVECTION

    SciTech Connect

    Zeng Zhicheng; Cao Wenda; Ji Haisheng

    2013-06-01

    We report the first evidence of magnetic reconnection driven by advection in a rapidly developing large granule using high spatial resolution observations of a small surge event (base size {approx} 4'' Multiplication-Sign 4'') with the 1.6 m aperture New Solar Telescope at the Big Bear Solar Observatory. The observations were carried out in narrowband (0.5 A) He I 10830 A and broadband (10 A) TiO 7057 A. Since He I 10830 A triplet has a very high excitation level and is optically thin, its filtergrams enable us to investigate the surge from the photosphere through the chromosphere into the lower corona. Simultaneous space data from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory were used in the analysis. It is shown that the surge is spatio-temporally associated with magnetic flux emergence in the rapidly developing large granule. During the development of the granule, its advecting flow ({approx}2 km s{sup -1}) squeezed the magnetic flux into an intergranular lane area, where a magnetic flux concentration was formed and the neighboring flux with opposite magnetic polarity was canceled. During the cancellation, the surge was produced as absorption in He I 10830 A filtergrams while simultaneous EUV brightening occurred at its base. The observations clearly indicate evidence of a finest-scale reconnection process driven by the granule's motion.

  18. An unusual H2 sorption mechanism in PCN-14: insights from molecular simulation.

    PubMed

    Pham, Tony; Forrest, Katherine A; Space, Brian

    2016-08-01

    Simulations of H2 sorption were performed in PCN-14, a metal-organic framework (MOF) that consists of Cu(2+) ions coordinated to 5,5'-(9,10-anthracenediyl)diisophthalate (adip) linkers. This MOF displays an excess H2 uptake of 2.70 wt% at 77 K and 1.0 atm and an initial H2Qst value of 8.6 kJ mol(-1) according to previous experimental measurements. The experimental H2 sorption isotherms and Qst values in PCN-14 were reproduced in simulations using well-known H2 potentials that have been widely used for MOF-H2 theoretical studies. H2 sorption in PCN-14 was dominated by repulsion/dispersion energetics; this allowed the experimental observables to be reproduced by a model that includes only Lennard-Jones parameters. The most energetically favorable H2 sorption site in PCN-14 corresponds to sorption within a small cage that is enclosed by three [Cu2(O2CR)4] units and three adip linkers. The anthracenyl rings of the adip linkers represent the secondary sorption sites within the MOF. In contrast to expectations, sorption of H2 onto the Cu(2+) ions of the copper paddlewheels was not observed within the simulations at low loading. The simulations revealed that the open-metal sites in PCN-14 were occupied at high loading. Control simulations of H2 sorption in PCN-14 for different cases in which the partial positive charge of one of the paddlewheel Cu(2+) ions was increased relative to the other revealed that sorption onto the open-metal sites can be captured if there is a very high positive charge on the metal. Otherwise, the calculated partial charge for the Cu(2+) ions in PCN-14 in this work was not high enough in magnitude to facilitate strong H2-metal interactions in simulation. This study shows the power of using molecular simulations to elucidate an unusual H2 sorption behavior in a MOF. PMID:27426916

  19. Average concentration of soluble salts in leached soils inferred from the convective-dispersive equation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The convective-dispersive, or advective-dispersive, or CDE, equation has long been the model of choice for solute transport in soils. Using the total mass of soluble salts in soil profile to evaluate changes in salinity due to irrigation can be beneficial when the spatial variability of soil salini...

  20. Characterization of lead sorption by the natural and Fe(III)-modified zeolite

    NASA Astrophysics Data System (ADS)

    Kragović, Milan; Daković, Aleksandra; Marković, Marija; Krstić, Jugoslav; Gatta, G. Diego; Rotiroti, Nicola

    2013-10-01

    The influence of contact time, temperature and particle size on lead sorption by the natural and Fe(III)-modified zeolites was investigated. Characterization of the natural and Fe(III)-modified zeolite before and after lead sorption was performed by determination of textural properties, by scanning electron microscopy and X-ray spectroscopy in energy-dispersive mode (SEM-EDS), transmission electron microscopy (TEM) and X-ray powder diffraction (XRPD) analysis. Lead sorption kinetics at 303-333 K, best represented by the pseudo-second order model and activation energy (13.5 and 8.5 kJ/mol for the natural and Fe(III)-modified zeolite respectively) confirmed an activated chemical sorption. Desorption experiments indicated that lead was irreversibly sorbed on both zeolites. XRPD, TEM and SEM results showed that modification of the natural zeolite with Fe(III) ions did not change its crystal structure and iron is mainly located at the zeolite surface, likely in form of amorphous iron oxy-hydroxides. Specific surface area significantly increases after modification of the natural zeolite with Fe(III) ions (from 30.2 for the natural to 52.5 m2/g for Fe(III)-modified zeolite). Characterization of both lead saturated sorbents suggested that besides ion exchange, lead is both chemisorbed and precipitated at their surfaces, and presence of amorphous iron in Fe(III)-modified zeolite favors sorption of lead.

  1. Numerical modelling of mesoscale atmospheric dispersion. (Volumes I and II)

    SciTech Connect

    Moran, M.D.

    1992-01-01

    Mesoscale atmospheric dispersion is more complicated than smaller-scale dispersion because the mean wind field can no longer be considered steady or horizontally homogeneous over mesoscale time and space scales. Wind shear also plays an important role on the mesoscale, and horizontal dispersion can be enhanced and even dominated by vertical wind shear through either the simultaneous or delayed interaction of horizontal differential advection and vertical mixing. The CSU mesoscale atmospheric dispersion modelling system has been used in this study to simulate the transport and diffusion of a perfluorocarbon gas for episodic releases made during two mesoscale dispersion field experiments. The physiography of the two experimental domains was quite different, permitting isolation and examination of the roles of terrain forcing and differential advection in mesoscale atmospheric dispersion. Suites of numerical experiments of increasing complexity were carried out for both case studies. The experiments differed in the realism of their representation of both the synoptic-scale flow and the underlying terrain. The contributions of differential advection and mesoscale deformation to mesoscale dispersion dominated those of small-scale turbulent diffusion for both cases, and Pasquill's (1962) delayed-shear-enhancement mechanism for lateral dispersion was found to be particularly important. This study was also the first quantitative evaluation of the CSU mesoscale dispersion modelling system with episodic mesoscale dispersion field data. The modelling system showed considerable skill in predicting quantitative tracer-cloud characteristics such as peak concentration, maximum cloud width, arrival time, transit time, and crosswind integrated exposure. Model predictions also compared favorably with predictions made by a number of other mesoscale dispersion models for the same two case studies.

  2. Ocular dispersion

    NASA Astrophysics Data System (ADS)

    Hammer, Daniel X.; Noojin, Gary D.; Thomas, Robert J.; Stolarski, David J.; Rockwell, Benjamin A.; Welch, Ashley J.

    1999-06-01

    Spectrally resolved white-light interferometry (SRWLI) was used to measure the wavelength dependence of refractive index (i.e., dispersion) for various ocular components. The accuracy of the technique was assessed by measurement of fused silica and water, the refractive indices of which have been measured at several different wavelengths. The dispersion of bovine and rabbit aqueous and vitreous humor was measured from 400 to 1100 nm. Also, the dispersion was measured from 400 to 700 nm for aqueous and vitreous humor extracted from goat and rhesus monkey eyes. For the humors, the dispersion did not deviate significantly from water. In an additional experiment, the dispersion of aqueous and vitreous humor that had aged up to a month was compared to freshly harvested material. No difference was found between the fresh and aged media. An unsuccessful attempt was also made to use the technique for dispersion measurement of bovine cornea and lens. Future refinement may allow measurement of the dispersion of cornea and lens across the entire visible and near-infrared wavelength band. The principles of white- light interferometry including image analysis, measurement accuracy, and limitations of the technique, are discussed. In addition, alternate techniques and previous measurements of ocular dispersion are reviewed.

  3. Fe2+ sorption onto nontronite (NAu-2)

    SciTech Connect

    Jaisi, Deb P.; Liu, Chongxuan; Dong, Hailiang; Blake, Ruth E.; Fein, Jeremy B.

    2008-11-15

    The sorption of ferrous iron to a clay mineral, nontronite (NAu-2, a ferruginous smectite), was investigated under strictly anoxic conditions as a function of pH (3-10), Fe2+ concentration (0.01-50 mM), equilibration time (1 to 35 days), and ionic strength (0.01 to 0.5 M NaClO4). The surface properties of NAu-2 were independently characterized to determine its fixed charge and amphoteric site properties for the interpretation of Fe2+ sorption. Fe2+ sorption to NAu-2 was strongly dependent on pH and ionic strength, reflecting the coupled effects of Fe2+ sorption through ion exchange and surface complexation reactions. Fe2+ sorption to NAu-2 increased with increasing pH from pH 2.5 to 4.5, reached the first plateau from pH 4.5 to 7.0, increased again with increasing pH from pH 7.0 to 8.5, and reached the maximum (the second plateau) above pH 8.5. The Fe2+ sorption below pH 7.0 increased with decreasing ionic strength. The differences of Fe2+ sorption at different ionic strength, however, diminished with increasing equilibration time. The Fe2+ sorption from pH 4.5 to 7.0 increased with increasing equilibration time up to 35 days and showed stronger kinetic behavior in higher ionic strength solutions. Increasing Fe2+ concentration nonlinearly decreased Fe2+ sorption, resulting from the mass action and site saturation. An equilibrium model that integrated ion exchange, surface complexation and aqueous speciation reactions reasonably well described the Fe2+ sorption data as a function of pH, ionic strength, and Fe2+ concentration measured at 24 hours of equilibration. Model calculations showed that species Fe(OH)+ was required to describe Fe2+ sorption above pH 8.0. Model calculation also implied that the ion exchange reactions was responsible for the kinetic behavior of Fe2+ sorption. Overall, this study demonstrated that Fe2+ sorption to NAu-2 was complexly affected by equilibrium and kinetic processes.

  4. Colloid particle size-dependent dispersivity

    NASA Astrophysics Data System (ADS)

    Chrysikopoulos, C. V.; Katzourakis, V. E.

    2014-12-01

    Laboratory and field studies have demonstrated that dispersion coefficients evaluated by fitting advection-dispersion transport models to nonreactive tracer breakthrough curves do not adequately describe colloid transport under the same flow field conditions. Here an extensive laboratory study was undertaken to assess whether the dispersivity, which traditionally has been considered to be a property of the porous medium, is dependent on colloid particle size and interstitial velocity. A total of 49 colloid transport experiments were performed in columns packed with glass beads under chemically unfavorable colloid attachment conditions. Nine different colloid diameters, and various flow velocities were examined. The breakthrough curves were successfully simulated with a mathematical model describing colloid transport in homogeneous, water saturated porous media. The results demonstrated that the dispersivity is positively correlated with colloid particle size, and increases with increasing velocity.

  5. Sorption of radiocesium by active silica.

    PubMed

    McCulloch, C E; Crawford, R W; Angus, M J; Glasser, F P; Rahman, A A

    1984-05-01

    Cement and cement components have previously been shown to exhibit negligible sorption for cesium. Pyrogenic silica has been examined as an additive to cement materials for its ability to reduce the leachability of cesium and to provide a host material with permanent sorption sites. The incorporation of silica into cement composites can also improve the physical characteristics and strength of these materials as long ages. At neutral pH values, there is significant sorption of cesium by silica, but in high pH regimes, such as occur in cement environments, initial sorption is enhanced but this high level of sorption is followed by a gradual release of Cs. This apparent desorption is due to the consumption of SiO2 by Ca(OH)2 to form products which have little sorption potential for cesium. If, however, sufficient SiO2 is added to the system initially such that an excess remains after satisfying the demands of the Ca(OH)2 reaction, permanent sorption sites for cesium may be created. PMID:6327573

  6. Thermally driven advection for radioxenon transport from an underground nuclear explosion

    NASA Astrophysics Data System (ADS)

    Sun, Yunwei; Carrigan, Charles R.

    2016-05-01

    Barometric pumping is a ubiquitous process resulting in migration of gases in the subsurface that has been studied as the primary mechanism for noble gas transport from an underground nuclear explosion (UNE). However, at early times following a UNE, advection driven by explosion residual heat is relevant to noble gas transport. A rigorous measure is needed for demonstrating how, when, and where advection is important. In this paper three physical processes of uncertain magnitude (oscillatory advection, matrix diffusion, and thermally driven advection) are parameterized by using boundary conditions, system properties, and source term strength. Sobol' sensitivity analysis is conducted to evaluate the importance of all physical processes influencing the xenon signals. This study indicates that thermally driven advection plays a more important role in producing xenon signals than oscillatory advection and matrix diffusion at early times following a UNE, and xenon isotopic ratios are observed to have both time and spatial dependence.

  7. Bacterial sorption of heavy metals.

    PubMed Central

    Mullen, M D; Wolf, D C; Ferris, F G; Beveridge, T J; Flemming, C A; Bailey, G W

    1989-01-01

    Four bacteria, Bacillus cereus, B. subtilis, Escherichia coli, and Pseudomonas aeruginosa, were examined for the ability to remove Ag+, Cd2+, Cu2+, and La3+ from solution by batch equilibration methods. Cd and Cu sorption over the concentration range 0.001 to 1 mM was described by Freundlich isotherms. At 1 mM concentrations of both Cd2+ and Cu2+, P. aeruginosa and B. cereus were the most and least efficient at metal removal, respectively. Freundlich K constants indicated that E. coli was most efficient at Cd2+ removal and B. subtilis removed the most Cu2+. Removal of Ag+ from solution by bacteria was very efficient; an average of 89% of the total Ag+ was removed from the 1 mM solution, while only 12, 29, and 27% of the total Cd2+, Cu2+, and La3+, respectively, were sorbed from 1 mM solutions. Electron microscopy indicated that La3+ accumulated at the cell surface as needlelike, crystalline precipitates. Silver precipitated as discrete colloidal aggregates at the cell surface and occasionally in the cytoplasm. Neither Cd2+ nor Cu2+ provided enough electron scattering to identify the location of sorption. The affinity series for bacterial removal of these metals decreased in the order Ag greater than La greater than Cu greater than Cd. The results indicate that bacterial cells are capable of binding large quantities of different metals. Adsorption equations may be useful for describing bacterium-metal interactions with metals such as Cd and Cu; however, this approach may not be adequate when precipitation of metals occurs. Images PMID:2515800

  8. Sorption of methylxanthines by different sorbents

    NASA Astrophysics Data System (ADS)

    Dmitrienko, S. G.; Andreeva, E. Yu.; Tolmacheva, V. V.; Terent'eva, E. A.

    2013-05-01

    Sorption of caffeine, theophylline, theobromine, diprophylline, and pentoxyphylline on different sorbents (supercross-linked polystyrene, surface-modified copolymer of styrene and divinylbenzene Strata-X, and carbon nanomaterials Taunit and Diasorb-100-C16T) was studied in a static mode in an effort to find new sorbents suitable for sorption isolation and concentration of methylxanthines. The peculiarities of sorption of methylxanthines were explained in relation to the solution acidity, the nature of the sorbates and their concentration, the nature of the solvent, and the structural characteristics of the sorbents.

  9. Mobile scintillometry to study heat advection over heterogeneous surfaces

    NASA Astrophysics Data System (ADS)

    Kleissl, J.

    2007-12-01

    Large Aperture Scintillometer (LAS) receivers measure the structure parameter of the refractive index from intensity fluctuations of the transmitter beam. Due to the spatial averaging over 1-4 km employed by this emerging technique the constraints for long temporal averaging (15-30 min) and associated uncertainties that have to be met by other flux measurement techniques do not apply for LASs. In this paper the constraints for temporal averaging of LASs will be examined as a function of environmental conditions and transect geometry. Moreover, analysis of data from a mobile LAS measurement across a surface gradient from rough and dry to smoother and wet will be presented. In this experiment the LAS was mounted on a pickup truck, allowing for quick redeployment of the transect after meaurement. The potential for the use of LAS to study local advection of heat in riparian or irrigated areas in the semi-arid southwest will be evaluated.

  10. Deconvolved spectra of Two Component Advective Flow including jet

    NASA Astrophysics Data System (ADS)

    Mondal, Santanu; Debnath, Dipak; Chakrabarti, Sandip Kumar

    2016-07-01

    Outflows and winds are produced when the accretion flows have positive specific energy. Two Component Advective Flow (TCAF) model suggests that the centrifugal pressure supported region of the flow outside the black hole horizon, acts as the base of this outflow. We study the spectral properties of the TCAF which includes a jet component. We consider the jet as a conical in shape which also up-scatters the soft photons from the Keplerian disc. We see that due to the presence of jet component, spectrum become harder as the jet itself behaves like an another Compton cloud above the inner hot corona. We also see how the jet spectra depends on the flow rates. This gives the direct link in timing properties of the X-rays in CENBOL component and the radiation emitted in the jet component.

  11. Carbon dioxide degassing by advective flow from Usu volcano, Japan.

    PubMed

    Hernández, P A; Notsu, K; Salazar, J M; Mori, T; Natale, G; Okada, H; Virgili, G; Shimoike, Y; Sato, M; Pérez, N M

    2001-04-01

    Magmatic carbon dioxide (CO2) degassing has been documented before the 31 March 2000 eruption of Usu volcano, Hokkaido, Japan. Six months before the eruption, an increase in CO2 flux was detected on the summit caldera, from 120 (September 1998) to 340 metric tons per day (September 1999), followed by a sudden decrease to 39 metric tons per day in June 2000, 3 months after the eruption. The change in CO2 flux and seismic observations suggests that before the eruption, advective processes controlled gas migration toward the surface. The decrease in flux after the eruption at the summit caldera could be due to a rapid release of CO2 during the eruption from ascending dacitic dikes spreading away from the magma chamber beneath the caldera. PMID:11292867

  12. Unification of some advection schemes in two dimensions

    NASA Technical Reports Server (NTRS)

    Sidilkover, D.; Roe, P. L.

    1995-01-01

    The relationship between two approaches towards construction of genuinely two-dimensional upwind advection schemes is established. One of these approaches is of the control volume type applicable on structured cartesian meshes. It resulted in the compact high resolution schemes capable of maintaining second order accuracy in both homogeneous and inhomogeneous cases. Another one is the fluctuation splitting approach, which is well suited for triangular (and possibly) unstructured meshes. Understanding the relationship between these two approaches allows us to formulate here a new fluctuation splitting high resolution (i.e. possible use of artificial compression, while maintaining positivity property) scheme. This scheme is shown to be linearity preserving in inhomogeneous as well as homogeneous cases.

  13. How Hydrate Saturation Anomalies are Diffusively Constructed and Advectively Smoothed

    NASA Astrophysics Data System (ADS)

    Rempel, A. W.; Irizarry, J. T.; VanderBeek, B. P.; Handwerger, A. L.

    2015-12-01

    The physical processes that control the bulk characteristics of hydrate reservoirs are captured reasonably well by long-established model formulations that are rooted in laboratory-verified phase equilibrium parameterizations and field-based estimates of in situ conditions. More detailed assessments of hydrate distribution, especially involving the occurrence of high-saturation hydrate anomalies have been more difficult to obtain. Spatial variations in sediment properties are of central importance for modifying the phase behavior and promoting focussed fluid flow. However, quantitative predictions of hydrate anomaly development cannot be made rigorously without also addressing the changes in phase behavior and mechanical balances that accompany changes in hydrate saturation level. We demonstrate how pore-scale geometrical controls on hydrate phase stability can be parameterized for incorporation in simulations of hydrate anomaly development along dipping coarse-grained layers embedded in a more fine-grained background that is less amenable to fluid transport. Model simulations demonstrate how hydrate anomaly growth along coarse-layer boundaries is promoted by diffusive gas transport from the adjacent fine-grained matrix, while advective transport favors more distributed growth within the coarse-grained material and so effectively limits the difference between saturation peaks and background levels. Further analysis demonstrates how sediment contacts are unloaded once hydrate saturation reaches sufficient levels to form a load-bearing skeleton that can evolve to produce segregated nodules and lenses. Decomposition of such growth forms poses a significant geohazard that is expected to be particularly sensitive to perturbations induced by gas extraction. The figure illustrates the predicted evolution of hydrate saturation Sh in a coarse-grained dipping layer showing how prominent bounding hydrate anomalies (spikes) supplied by diffusive gas transport at early times

  14. Frictional drag reduction by wavy advection of deformable bubbles

    NASA Astrophysics Data System (ADS)

    Oishi, Yoshihiko; Murai, Yuichi; Tasaka, Yuji; Yasushi, Takeda

    2009-02-01

    Bubbles can reduce frictional drag in wall turbulence, and its effect is expected to use for ships and pipelines to save their power consumptions. A number of basic experiments have been carried out to date for finding out the best condition for enhancing the drag reduction. One issue that remains at present is the difference of the performance between steady and unsteady status in terms of bubble concentration. All the experiments in the past deal with the steady effect, i.e., the drag reduction is evaluated as a function of mean void fraction or given gas flow rate of continuous injection. Despite to this, the actual phenomena highly depend on local interaction between two phases upon unsteady manner. We focus on this point and elucidate the influence of time-fluctuating void fraction on the total response to the drag reduction. This view is in fact important to estimate the persistency of the bubble-based drag reduction in the flow direction since bubbles formulate wavy advection during their migration. Our experiments are designed to measure the above-mentioned effect from laminar, transitional, and turbulent flows in a horizontal channel. For avoiding the contamination effect that worsens the reproducibility of the experiment, Silicone oil is used as carrier fluid. The oil also simulates the high Weber number bubble condition because of low surface tension. The unsteady interaction between the wavy advection of bubbles and the local skin friction, a synchronized system is constructed to connect the high-speed camera with the shear transducer, which can evaluate the interaction at 1000 fps. From the results, we confirm that the drag reduction is provided at Re>3000 in the turbulent flow regime, and also the total drag reduction is enhanced by the presence of the waves.

  15. Multirate Runge-Kutta schemes for advection equations

    NASA Astrophysics Data System (ADS)

    Schlegel, Martin; Knoth, Oswald; Arnold, Martin; Wolke, Ralf

    2009-04-01

    Explicit time integration methods can be employed to simulate a broad spectrum of physical phenomena. The wide range of scales encountered lead to the problem that the fastest cell of the simulation dictates the global time step. Multirate time integration methods can be employed to alter the time step locally so that slower components take longer and fewer time steps, resulting in a moderate to substantial reduction of the computational cost, depending on the scenario to simulate [S. Osher, R. Sanders, Numerical approximations to nonlinear conservation laws with locally varying time and space grids, Math. Comput. 41 (1983) 321-336; H. Tang, G. Warnecke, A class of high resolution schemes for hyperbolic conservation laws and convection-diffusion equations with varying time and pace grids, SIAM J. Sci. Comput. 26 (4) (2005) 1415-1431; E. Constantinescu, A. Sandu, Multirate timestepping methods for hyperbolic conservation laws, SIAM J. Sci. Comput. 33 (3) (2007) 239-278]. In air pollution modeling the advection part is usually integrated explicitly in time, where the time step is constrained by a locally varying Courant-Friedrichs-Lewy (CFL) number. Multirate schemes are a useful tool to decouple different physical regions so that this constraint becomes a local instead of a global restriction. Therefore it is of major interest to apply multirate schemes to the advection equation. We introduce a generic recursive multirate Runge-Kutta scheme that can be easily adapted to an arbitrary number of refinement levels. It preserves the linear invariants of the system and is of third order accuracy when applied to certain explicit Runge-Kutta methods as base method.

  16. Examination of the evolution of radiation and advection fogs. Final report

    SciTech Connect

    Orgill, M.M.

    1993-01-01

    A literature study was done on radiation and advection fog evolution. For radiation fog, six stages of fog evolution have been identified -- (1) precursor, (2) sunset, (3) conditioning, (4) mature, (5) sunrise, and (6) dissipation. The evolution of advection fog models has been in parallel with radiation fog models, but no identified stages in the evolution of advection fog have been proposed: (1) precursor, (2) initiation, (3) mature, and (4) dissipation. Radiation and advection fog models will require greater sophistication in order to study fog spatial and temporal variability. Physical aspects that require further study are discussed.

  17. The role of phase dynamics in a stochastic model of a passively advected scalar

    NASA Astrophysics Data System (ADS)

    Moradi, Sara; Anderson, Johan

    2016-05-01

    Collective synchronous motion of the phases is introduced in a model for the stochastic passive advection-diffusion of a scalar with external forcing. The model for the phase coupling dynamics follows the well known Kuramoto model paradigm of limit-cycle oscillators. The natural frequencies in the Kuramoto model are assumed to obey a given scale dependence through a dispersion relation of the drift-wave form -βk/1 +k2 , where β is a constant representing the typical strength of the gradient. The present aim is to study the importance of collective phase dynamics on the characteristic time evolution of the fluctuation energy and the formation of coherent structures. Our results show that the assumption of a fully stochastic phase state of turbulence is more relevant for high values of β, where we find that the energy spectrum follows a k-7 /2 scaling. Whereas for lower β there is a significant difference between a-synchronised and synchronised phase states, one could expect the formation of coherent modulations in the latter case.

  18. Shear dispersion and turbulence decorrelation by differential rotation

    SciTech Connect

    Garcia, O.E.; Bian, N.H.

    2005-01-01

    The shear enhanced dispersion of a passive scalar field subject to differential rotation is investigated analytically and interpretations are given in terms of turbulence shear decorrelation. Using the method of advected coordinates, the enhanced dispersion caused by steady and oscillatory flows with uniform shear is derived and the well-known turbulence shear decorrelation theory is recovered. The additional role of kinetic energy transfer due to differential advection of vorticity is also pointed out. Finally, the shear enhanced dispersion due to flows with periodic variations in space as well as time is given. It is found that radially alternating flows may significantly reduce the turbulence decorrelation time provided the root mean square flow shear is larger than the flow oscillation frequency. In the opposite limit of fast flow oscillations there is no turbulence decorrelation.

  19. COSOLVENT EFFECTS ON SORPTION ISOTHERM LINEARITY

    EPA Science Inventory

    Sorption-desorption hysteresis, slow desorption kinetics, and other nonideal phenomena have been attributed to the differing sorptive characteristics of the natural organic polymers associated with soils and sediments. In this study, aqueous and mixed solvent systems were used t...

  20. SORPTION OF HYDROPHOBIC POLLUTANTS ON NATURAL SEDIMENTS

    EPA Science Inventory

    The sorption of hydrophobic compounds (aromatic hydrocarbons and chlorinated hydrocarbons) spanning a concentration range in water solubility from 500 parts per trillion (ppt) to 1800 parts per million (ppm) on local (North Georgia) pond and river sediments was investigated. The ...

  1. Advection and Diffusion of Substances in Biological Tissues With Complex Vascular Networks

    PubMed Central

    Beard, Daniel A.; Bassingthwaighte, James B.

    2010-01-01

    For highly diffusive solutes the kinetics of blood–tissue exchange is only poorly represented by a model consisting of sets of independent parallel capillary–tissue units. We constructed a more realistic multicapillary network model conforming statistically to morphometric data. Flows through the tortuous paths in the network were calculated based on constant resistance per unit length throughout the network and the resulting advective intracapillary velocity field was used as a framework for describing the extravascular diffusion of a substance for which there is no barrier or permeability limitation. Simulated impulse responses from the system, analogous to tracer water outflow dilution curves, showed flow-limited behavior over a range of flows from about 2 to 5 ml min−1 g−1, as is observed for water in the heart in vivo. The present model serves as a reference standard against which to evaluate computationally simpler, less physically realistic models. The simulated outflow curves from the network model, like experimental water curves, were matched to outflow curves from the commonly used axially distributed models only by setting the capillary wall permeability–surface area (PS) to a value so artifactually low that it is incompatible with the experimental observations that transport is flow limited. However, simple axially distributed models with appropriately high PSs will fit water outflow dilution curves if axial diffusion coefficients are set at high enough values to account for enhanced dispersion due to the complex geometry of the capillary network. Without incorporating this enhanced dispersion, when applied to experimental curves over a range of flows, the simpler models give a false inference that there is recruitment of capillary surface area with increasing flow. Thus distributed models must account for diffusional as well as permeation processes to provide physiologically appropriate parameter estimates. PMID:10784090

  2. Reversibility of strontium sorption on fracture fillings

    SciTech Connect

    Cui, D.; Eriksen, T.E.

    1995-12-31

    Granite has been chosen by several countries as a major candidate for deep geologic disposal of radioactive waste. The authors have carried out a comparative study of sorption and desorption of strontium in groundwater on separated size and magnetic fractions of fracture fillings from deep granite. Complete reversibility of the sorption process was demonstrated by identical Freundlich isotherms, isotopic exchangeability and pH dependence of the distribution coefficient R{sub d}.

  3. Selective sorption behavior of iodine species on an activated carbon disk and its implication for the speciation analysis

    NASA Astrophysics Data System (ADS)

    Yoon, H.; Lee, J.; An, J.

    2013-12-01

    In recent times, iodate (IO3-) which can be generated under highly oxidized conditions such as the ozonation process in a water treatment plant has been receiving increasing attention due to its high toxicity to human and environment. In this respect, sorption behavior of iodide (I-) and IO3- on an activated carbon (AC) disk as a solid sorbent was investigated for the further development of efficient removal and analytical techniques. To this end, batch sorption tests were performed as a function of pH, sample volume, and initial concentration. Sorption of I- occurred preferentially on the surface of AC disk, regardless of pH levels (i.e., 4, 6, and 8). However, IO3- was quite sensitive to pH levels and the sorption capability of IO3- on the AC disk was much smaller than that of I-. Maximum sorption capacities of I- and IO3- in the different matrices (i.e., deionized water and seawater) were also assessed. In addition, the analytical strategy for the iodine speciation was also introduced. Iodine species were separated and pre-concentrated onto the AC disk based on their selective sorption properties according to the pH levels. Then, the AC disk pre-concentrated was directly analyzed using wavelength dispersive X-ray fluorescence spectrometry. Acknowledgement This research was supported by a grant from the Korea Basic Science Institute (project No. E33300).

  4. Characteristics and oil sorption effectiveness of kapok fibre, sugarcane bagasse and rice husks: oil removal suitability matrix.

    PubMed

    Ali, Norizan; El-Harbawi, Mohanad; Jabal, Ayman Abo; Yin, Chun-Yang

    2012-01-01

    The characteristics and water/oil sorption effectiveness ofkapok fibre, sugarcane bagasse and rice husks have been compared. The three biomass types were subjected to field emission scanning electron microscopy-energy dispersive X-ray spectroscopy and surface tension analyses for liquid-air and oil-water systems were conducted. Both kapok fibre and sugarcane bagasse exhibit excellent oil sorption capabilities for diesel, crude, new engine and used engine oils as their oil sorption capacities all exceed 10 g/g. The synthetic sorbent exhibits oil sorption capacities comparable with sugarcane bagasse, while rice husks exhibit the lowest oil sorption capacities among all the sorbents. Kapok fibre shows overwhelmingly high oil-to-water sorption (O/W) ratios ranging from 19.35 to 201.53 while sugarcane bagasse, rice husks and synthetic sorbent have significantly lower O/W ratios (0.76-2.69). This suggests that kapok fibre is a highly effective oil sorbent even in well-mixed oil-water media. An oil sorbent suitability matrix is proposed to aid stakeholders in evaluating customized oil removal usage of the natural sorbents. PMID:22629620

  5. Analysis of the anomalous scale-dependent behavior of dispersivity using straightforward analytical equations: Flow variance vs. dispersion

    SciTech Connect

    Looney, B.B.; Scott, M.T.

    1988-12-31

    Recent field and laboratory data have confirmed that apparent dispersivity is a function of the flow distance of the measurement. This scale effect is not consistent with classical advection dispersion modeling often used to describe the transport of solutes in saturated porous media. Many investigators attribute this anomalous behavior to the fact that the spreading of solute is actually the result of the heterogeneity of subsurface materials and the wide distribution of flow paths and velocities available in such systems. An analysis using straightforward analytical equations confirms this hypothesis. An analytical equation based on a flow variance approach matches available field data when a variance description of approximately 0.4 is employed. Also, current field data provide a basis for statistical selection of the variance parameter based on the level of concern related to the resulting calculated concentration. While the advection dispersion approach often yielded reasonable predictions, continued development of statistical and stochastic techniques will provide more defendable and mechanistically descriptive models.

  6. Passive advection of a vector field: Anisotropy, finite correlation time, exact solution, and logarithmic corrections to ordinary scaling.

    PubMed

    Antonov, N V; Gulitskiy, N M

    2015-10-01

    In this work we study the generalization of the problem considered in [Phys. Rev. E 91, 013002 (2015)] to the case of finite correlation time of the environment (velocity) field. The model describes a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow. Inertial-range asymptotic behavior is studied by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and preassigned pair correlation function. Due to the presence of distinguished direction n, all the multiloop diagrams in this model vanish, so that the results obtained are exact. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to the two nontrivial fixed points of the RG equations. Their stability depends on the relation between the exponents in the energy spectrum E∝k(⊥)(1-ξ) and the dispersion law ω∝k(⊥)(2-η). In contrast to the well-known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the corrections to ordinary scaling are polynomials of logarithms of the integral turbulence scale L. PMID:26565343

  7. Passive advection of a vector field: Anisotropy, finite correlation time, exact solution, and logarithmic corrections to ordinary scaling

    NASA Astrophysics Data System (ADS)

    Antonov, N. V.; Gulitskiy, N. M.

    2015-10-01

    In this work we study the generalization of the problem considered in [Phys. Rev. E 91, 013002 (2015), 10.1103/PhysRevE.91.013002] to the case of finite correlation time of the environment (velocity) field. The model describes a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow. Inertial-range asymptotic behavior is studied by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and preassigned pair correlation function. Due to the presence of distinguished direction n , all the multiloop diagrams in this model vanish, so that the results obtained are exact. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to the two nontrivial fixed points of the RG equations. Their stability depends on the relation between the exponents in the energy spectrum E ∝k⊥1 -ξ and the dispersion law ω ∝k⊥2 -η . In contrast to the well-known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the corrections to ordinary scaling are polynomials of logarithms of the integral turbulence scale L .

  8. Estimation of soil sorption coefficients using QSARs

    SciTech Connect

    Doucette, W.J.

    1994-12-31

    Sorption coefficients quantitatively describe the extent to which an organic chemical distributes itself between an environmental solid and the aqueous phase that it is contact with at equilibrium. Because of the difficulty and expense associated with measuring sorption coefficients, estimated values are often used in place of site specific, experimental values for fate modeling. Most reported methods for estimating the sorption of organic chemicals onto environmental solids are based on observation that for many organic chemicals, and in particular neutral hydrophobic organics, sorption is directly proportional to the quantity of organic matter associated with the solid. Normalizing soil or sediment specific sorption coefficients to the organic carbon content of the sorbent yields a new ``constant``, Koc, that is considered unique property of the organic chemical being sorbed. Values of Koc are then typically estimated from correlations between Koc and various descriptors of hydrophobicity such as octanol/water partition coefficients (Kow), aqueous solubility (S), molecular connectivity indices (MCIs) and retention times or capacity factors generated by reverse phase high performance liquid chromatography (RP-HPLC). Group contribution methods have also been described. While the so-called ``Koc approach`` for estimating sorption coefficients is most appropriate for neutral, hydrophobic organic chemicals on environmental solids containing a significant amount of organic matter, it has been applied to a wide variety of chemical and soil types. This presentation will focus on a discussion of the Koc approach, its applicability and limitations. A comparison of several widely used methods for estimating Koc will be presented.

  9. Evaluating phenanthrene sorption on various wood chars

    USGS Publications Warehouse

    James, G.; Sabatini, D.A.; Chiou, C.T.; Rutherford, D.; Scott, A.C.; Karapanagioti, H.K.

    2005-01-01

    A certain amount of wood char or soot in a soil or sediment sample may cause the sorption of organic compounds to deviate significantly from the linear partitioning commonly observed with soil organic matter (SOM). Laboratory produced and field wood chars have been obtained and analyzed for their sorption isotherms of a model solute (phenanthrene) from water solution. The uptake capacities and nonlinear sorption effects with the laboratory wood chars are similar to those with the field wood chars. For phenanthrene aqueous concentrations of 1 ??gl-1, the organic carbon-normalized sorption coefficients (log Koc) ranging from 5.0 to 6.4 for field chars and 5.4-7.3 for laboratory wood chars, which is consistent with literature values (5.6-7.1). Data with artificial chars suggest that the variation in sorption potential can be attributed to heating temperature and starting material, and both the quantity and heterogeneity of surface-area impacts the sorption capacity. These results thus help to corroborate and explain the range of log Koc values reported in previous research for aquifer materials containing wood chars. ?? 2004 Elsevier Ltd. All rights reserved.

  10. Secondary mineralization pathways induced by dissimilatory iron reduction of ferrihydrite under advective flow

    NASA Astrophysics Data System (ADS)

    Hansel, Colleen M.; Benner, Shawn G.; Neiss, Jim; Dohnalkova, Alice; Kukkadapu, Ravi K.; Fendorf, Scott

    2003-08-01

    Iron (hydr)oxides not only serve as potent sorbents and repositories for nutrients and contaminants but also provide a terminal electron acceptor for microbial respiration. The microbial reduction of Fe (hydr)oxides and the subsequent secondary solid-phase transformations will, therefore, have a profound influence on the biogeochemical cycling of Fe as well as associated metals. Here we elucidate the pathways and mechanisms of secondary mineralization during dissimilatory iron reduction by a common iron-reducing bacterium, Shewanella putrefaciens (strain CN32), of 2-line ferrihydrite under advective flow conditions. Secondary mineralization of ferrihydrite occurs via a coupled, biotic-abiotic pathway primarily resulting in the production of magnetite and goethite with minor amounts of green rust. Operating mineralization pathways are driven by competing abiotic reactions of bacterially generated ferrous iron with the ferrihydrite surface. Subsequent to the initial sorption of ferrous iron on ferrihydrite, goethite (via dissolution/reprecipitation) and/or magnetite (via solid-state conversion) precipitation ensues resulting in the spatial coupling of both goethite and magnetite with the ferrihydrite surface. The distribution of goethite and magnetite within the column is dictated, in large part, by flow-induced ferrous Fe profiles. While goethite precipitation occurs over a large Fe(II) concentration range, magnetite accumulation is only observed at concentrations exceeding 0.3 mmol/L (equivalent to 0.5 mmol Fe[II]/g ferrihydrite) following 16 d of reaction. Consequently, transport-regulated ferrous Fe profiles result in a progression of magnetite levels downgradient within the column. Declining microbial reduction over time results in lower Fe(II) concentrations and a subsequent shift in magnetite precipitation mechanisms from nucleation to crystal growth. While the initial precipitation rate of goethite exceeds that of magnetite, continued growth is inhibited by

  11. Impact of long-term wastewater irrigation on sorption and transport of atrazine in Mexican agricultural soils.

    PubMed

    Müller, K; Duwig, C; Prado, B; Siebe, C; Hidalgo, C; Etchevers, J

    2012-01-01

    In the Mezquital Valley, Mexico, crops have been irrigated with untreated municipal wastewater for more than a century. Atrazine has been applied to maize and alfalfa grown in the area for weed control for 15 years. Our objectives were to analyse (i) how wastewater irrigation affects the filtering of atrazine, and (ii) if the length of irrigation has a significant impact. We compared atrazine sorption to Phaeozems that have been irrigated with raw wastewater for 35 (P35) and 85 (P85) years with sorption to a non-irrigated (P0) Phaeozem soil under rainfed agriculture. The use of bromide as an inert water tracer in column experiments and the subsequent analysis of the tracers' breakthrough curves allowed the calibration of the hydrodynamic parameters of a two-site non equilibrium convection-dispersion model. The quality of the irrigation water significantly altered the soils' hydrodynamic properties (hydraulic conductivity, dispersivity and the size of pores that are hydraulically active). The impacts on soil chemical properties (total organic carbon content and pH) were not significant, while the sodium adsorption ratio was significantly increased. Sorption and desorption isotherms, determined in batch and column experiments, showed enhanced atrazine sorption and reduced and slower desorption in wastewater-irrigated soils. These effects increased with the length of irrigation. The intensified sorption-desorption hysteresis in wastewater-irrigated soils indicated that the soil organic matter developed in these soils had fewer high-energy, easily accessible sorption sites available, leading to lower and slower atrazine desorption rates. This study leads to the conclusion that wastewater irrigation decreases atrazine mobility in the Mezquital valley Phaeozems by decreasing the hydraulic conductivity and increasing the soil's sorption capacity. PMID:22022786

  12. Thermodynamics of cationic surfactant sorption onto natural clinoptilolite

    SciTech Connect

    Sullivan, E.J.; Bowman, R.S.; Carey, J.W.

    1998-10-15

    Sorption enthalpies of hexadecyltrimethylammonium bromide (HDTMA) as monomers and micelles and tetraethylammonium bromide (TEA) were used with surfactant, counterion, and co-ion sorption isotherms to infer the conformation, sorption mechanism, and relative stability of the sorbed surfactants on natural clinoptilolite. The average value of the sorption enthalpy was {minus}10.38 kJ/mol for monomers, {minus}11.98 kJ/mol for micelles, and +3.03 kJ/mol for TEA. Sorption of monomers produced a lower sorption plateau than equivalent micelle sorption (maxima 145 mmol/kg, 225 mmol/kg). Analysis of the sorption data demonstrated a change in the sorption mechanism at the external cation exchange capacity (ECEC) of clinoptilolite. Sorption data from below and above the ECEC were fit to a simple polynomial model and the Gibbs free energy of sorption ({Delta} G{sub m}{sup 0}) and sorption entropies were calculated. Resultant values of {Delta} G{sub m}{sup 0} were {minus}9.27 and {minus}14.38 kJ/mol for HDTMA monomers and micelles, respectively, for sorption below the ECEC, and {minus}16.11 and {minus}23.10 kJ/mol, respectively, for sorption above the ECEC. The value for TEA was {minus}1.04 kJ/mol, indicating weaker sorption than for HDTMA. Monomer sorption to clinoptilolite exceeded the ECEC, even when the solution concentration was below the critical micelle concentration. Hydrophobic (tail-tail) components of {Delta} G{sub m}{sup 0} were the driving force for sorption of HDTMA, both below and above the ECEC. A significant kinetic effect was observed in the sorption isotherms with a period of rapid sorption followed by slow equilibration requiring 7 days to achieve steady state for HDTMA; TEA equilibration occurred within 24 h.

  13. Herschel flight models sorption coolers

    NASA Astrophysics Data System (ADS)

    Duband, L.; Clerc, L.; Ercolani, E.; Guillemet, L.; Vallcorba, R.

    2008-03-01

    The Herschel and Planck satellites will be jointly launched on an ARIANE 5 in 2008. The Herschel payload consists of three instruments built by international scientific consortia, heterodyne instrument for first (HIFI), photo-conductor array camera and spectrometer (PACS) and spectral and photometric imaging receiver (SPIRE). The spacecraft provides the environment for astronomical observations in the infrared and sub-millimeter wavelength range requiring cryogenic temperatures for the cold focal plane units. The spectral and photometric imaging receiver (SPIRE) will cover the 200-670 μm spectral range using bolometric detectors, as the photo-conductor array camera and spectrometer (PACS) will cover the 60-210 μm spectral range. Both instruments SPIRE and PACS feature detectors operating at 300 mK. This cooling will be effected by two helium sorption coolers developed at the Service des Basses Températures of the Commissariat à l'Energie Atomique (CEA-SBT). These coolers based on an evaporative cooling cycle features no moving parts and can be recycled indefinitely pending the availability of a cold heat sink at temperature below 3 K. Several models were developed in the course of the Herschel program and this paper deals with the design, manufacturing and qualification of the flight model coolers.

  14. Interfacial thermodynamics and kinetics of sorption of diclofenac on prepared high performance flower-like MoS2.

    PubMed

    Zhang, Yalei; Yin, Zengfu; Dai, Chaomeng; Zhou, Xuefei; Chen, Wen

    2016-11-01

    Flower-like MoS2 with numerous wrinkled nanosheets was prepared via a facile hydrothermal method. The surface morphology and microstructure of the obtained materials were characterized using X-ray diffraction data (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Additionally, the compositions of the flower-like MoS2 were further revealed by an energy dispersion spectrometer (EDX) and X-ray photoelectron spectrometry (XPS). The obtained MoS2 was used as an adsorbent to remove diclofenac (DCF, C14H10Cl2NO2Na) from aqueous solutions and presented excellent performance for removing DCF. The sorption kinetics, isotherms and effect of solution pH on the sorption were evaluated in batch sorption experiments. The sorption characteristics of the interactions between DCF and MoS2 in water were analyzed using a pseudo-second-order model, an intraparticle diffusion model and Boyd model to determine the sorption rate-determining steps. It was concluded that the sorption of DCF on MoS2 was fitted better by the pseudo-second-order model and that external diffusion governed the sorption process of DCF onto the MoS2. The interfacial interaction free energies between DCF and MoS2 in the sorption process can be calculated based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO). The flower-like MoS2 presenting excellent performance for removing DCF, could be a better choice of treating DCF-containing wastewaters. PMID:27475708

  15. Effects of thinning on transpiration by riparian buffer trees in response to advection and solar radiation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Advective energy occurring in edge environments may increase tree water use (e.g., latent heat loss, LE > net radiation, Rn). In humid agricultural landscapes, advection-enhanced transpiration in riparian buffers may provide hydrologic regulation and flood control benefits; however, research in humi...

  16. Effects of thinning on transpiration by riparian buffer trees in response to advection and solar radiation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Advective energy occurring in edge environments may increase tree water use. In humid agricultural landscapes, advection-enhanced transpiration in riparian buffers may provide hydrologic regulation; however, research in humid environments is lacking. The objectives of this study were to determine ho...

  17. Competitive sorption of organic contaminants in chalk

    NASA Astrophysics Data System (ADS)

    Graber, E. R.; Borisover, M.

    2003-12-01

    In the Negev desert, Israel, a chemical industrial complex is located over fractured Eocene chalk formations where transfer of water and solutes between fracture voids and matrix pores affects migration of contaminants in the fractures due to diffusion into the chalk matrix. This study tests sorption and sorption competition between contaminants in the chalk matrix to make it possible to evaluate the potential for contaminant attenuation during transport in fractures. Single solute sorption isotherms on chalk matrix material for five common contaminants ( m-xylene, ametryn, 1,2-dichloroethane, phenanthrene, and 2,4,6-tribromophenol) were found to be nonlinear, as confirmed in plots of Kd versus initial solution concentration. Over the studied concentration ranges, m-xylene Kd varied by more than a factor of 100, ametryn Kd by a factor of 4, 1,2-dichloroethane Kd by more than a factor of 3, phenanthrene Kd by about a factor of 2, and 2,4,6-tribromophenol Kd by a factor of 10. It was earlier found that sorption is to the organic matter component of the chalk matrix and not to the mineral phases (Chemosphere 44 (2001) 1121). Nonlinear sorption isotherms indicate that there is at least some finite sorption domain. Bi-solute competition experiments with 2,4,6-tribromophenol as the competitor were designed to explore the nature of the finite sorption domain. All of the isotherms in the bi-solute experiments are more linear than in the single solute experiments, as confirmed by smaller variations in Kd as a function of initial solution concentration. For both m-xylene and ametryn, there is a small nonlinear component or domain that was apparently not susceptible to competition by 2,4,6-tribromophenol. The nonlinear sorption domain(s) is best expressed at low solution concentrations. Inert-solvent-normalized single and bi-solute sorption isotherms demonstrate that ametryn undergoes specific force interactions with the chalk sorbent. The volume percent of phenanthrene

  18. MAST solution of advection problems in irrotational flow fields

    NASA Astrophysics Data System (ADS)

    Aricò, Costanza; Tucciarelli, Tullio

    2007-03-01

    A new numerical-analytical Eulerian procedure is proposed for the solution of convection-dominated problems in the case of existing scalar potential of the flow field. The methodology is based on the conservation inside each computational elements of the 0th and 1st order effective spatial moments of the advected variable. This leads to a set of small ODE systems solved sequentially, one element after the other over all the computational domain, according to a MArching in Space and Time technique. The proposed procedure shows the following advantages: (1) it guarantees the local and global mass balance; (2) it is unconditionally stable with respect to the Courant number, (3) the solution in each cell needs information only from the upstream cells and does not require wider and wider stencils as in most of the recently proposed higher-order methods; (4) it provides a monotone solution. Several 1D and 2D numerical test have been performed and results have been compared with analytical solutions, as well as with results provided by other recent numerical methods.

  19. Sea breezes and advective effects in southwest James Bay

    NASA Technical Reports Server (NTRS)

    Mckendry, Ian; Roulet, Nigel

    1994-01-01

    Observations from a transect extending 100 km inland during the Northern Wetlands Study (NOWES) in 1990 show that the sea breeze develops on approximately 25% of days during summer and may penetrate up to 100 km inland on occasions. The sea breeze exhibits a marked diurnal clockwise rotation as a result of the Coriolis effect along the unobstructed coastline. The marine advective effect is shown to depend on gradient wind direction. With northwesterly upper level flow the sea breeze tends to be northeasterly in direction and is associated with decreased temperatures and vapor pressure deficits (VPD). With southwesterly upper level flow the sea breeze tends to have a southeasterly direction and less effect on temperatures and VPD. This is attributed to shorter residence times of air parcels over water. For two cases, Colorado State University mesoscale model simulations show good agreement with surface wind observations and suggest that under northwesterly gradient flow, Bowen ratios are increased in the onshore flow along western James Bay, while during southwesterly gradient flow these effects are negligible. These results have implications for the interpretation of local climate, ecology, and hydrology as well as land-based and airborne turbulent flux measurements made during NOWES.

  20. Sediment transport in a surface-advected estuarine plume

    NASA Astrophysics Data System (ADS)

    Yao, H. Y.; Leonardi, N.; Li, J. F.; Fagherazzi, S.

    2016-03-01

    The interplay between suspended-sediment transport and plume hydrodynamics in a surface-advected estuarine plume is studied using a three-dimensional numerical model. Our analysis focuses on the formation of a sediment-rich alongshore current and on the effect of sediments on the structure of the recirculating freshwater bulge. We introduce the ratio Y between the traveling time of sediment along the bulge edge and the settling timescale. When Y <1, suspended sediments enter the alongshore coastal current. When Y >1 the sediments are deposited within the bulge. We find that a critical range of settling velocities exist above which no transport in the costal current is allowed. Critical settling-velocity values increase with river discharge. Therefore, low magnitude and long-lasting floods promote sediment sorting in the continental shelf. We further find that, for a given flood duration, intermediate flood magnitudes at the limit between subcritical and supercritical flow maximize the alongshore sediment transport. Similarly, for a fixed input of water and sediments, intermediate discharge durations maximize alongshore sediment transport.

  1. Implementation of two-component advective flow solution in XSPEC

    NASA Astrophysics Data System (ADS)

    Debnath, Dipak; Chakrabarti, Sandip K.; Mondal, Santanu

    2014-05-01

    Spectral and temporal properties of black hole candidates can be explained reasonably well using Chakrabarti-Titarchuk solution of two-component advective flow (TCAF). This model requires two accretion rates, namely the Keplerian disc accretion rate and the halo accretion rate, the latter being composed of a sub-Keplerian, low-angular-momentum flow which may or may not develop a shock. In this solution, the relevant parameter is the relative importance of the halo (which creates the Compton cloud region) rate with respect to the Keplerian disc rate (soft photon source). Though this model has been used earlier to manually fit data of several black hole candidates quite satisfactorily, for the first time, we made it user friendly by implementing it into XSPEC software of Goddard Space Flight Center (GSFC)/NASA. This enables any user to extract physical parameters of the accretion flows, such as two accretion rates, the shock location, the shock strength, etc., for any black hole candidate. We provide some examples of fitting a few cases using this model. Most importantly, unlike any other model, we show that TCAF is capable of predicting timing properties from the spectral fits, since in TCAF, a shock is responsible for deciding spectral slopes as well as quasi-periodic oscillation frequencies. L86

  2. Revisiting the Rossby Haurwitz wave test case with contour advection

    NASA Astrophysics Data System (ADS)

    Smith, Robert K.; Dritschel, David G.

    2006-09-01

    This paper re-examines a basic test case used for spherical shallow-water numerical models, and underscores the need for accurate, high resolution models of atmospheric and ocean dynamics. The Rossby-Haurwitz test case, first proposed by Williamson et al. [D.L. Williamson, J.B. Drake, J.J. Hack, R. Jakob, P.N. Swarztrauber, A standard test set for numerical approximations to the shallow-water equations on the sphere, J. Comput. Phys. (1992) 221-224], has been examined using a wide variety of shallow-water models in previous papers. Here, two contour-advective semi-Lagrangian (CASL) models are considered, and results are compared with previous test results. We go further by modifying this test case in a simple way to initiate a rapid breakdown of the basic wave state. This breakdown is accompanied by the formation of sharp potential vorticity gradients (fronts), placing far greater demands on the numerics than the original test case does. We also go further by examining other dynamical fields besides the height and potential vorticity, to assess how well the models deal with gravity waves. Such waves are sensitive to the presence or not of sharp potential vorticity gradients, as well as to numerical parameter settings. In particular, large time steps (convenient for semi-Lagrangian schemes) can seriously affect gravity waves but can also have an adverse impact on the primary fields of height and velocity. These problems are exacerbated by a poor resolution of potential vorticity gradients.

  3. Dispersion Modeling.

    ERIC Educational Resources Information Center

    Budiansky, Stephen

    1980-01-01

    This article discusses the need for more accurate and complete input data and field verification of the various models of air pollutant dispension. Consideration should be given to changing the form of air quality standards based on enhanced dispersion modeling techniques. (Author/RE)

  4. Kinetic research on the sorption of aqueous lead by synthetic carbonate hydroxyapatite.

    PubMed

    Xu, HuanYan; Yang, Lei; Wang, Peng; Liu, Yu; Peng, MingSheng

    2008-01-01

    The sorption of aqueous lead on carbonate-hydroxyapatite (CHAp) is a complicated non-homogeneous solid/water reaction, which from the kinetic point of view has two stages. In the first stage, the reaction rate is so fast and the kinetic pathway so intricate that further research is required. In the second stage, the reaction rate slows down and the reaction process follows that of a first-order kinetic equation. Experimental results show that the relationship between the reaction rate constant k(1) and temperature T agrees with the Arrhenius equation, and that the activation energy of sorption (E(a)) is 11.93 kJ/mol and the frequency factor (A) is 2.51/s. The reaction rate constant k(1) increases with the Pb(2+) initial concentration and decreasing pH, but with increasing CHAp dosage. X-ray diffraction (XRD), scanning electron microscopy with energy dispersion spectrum (SEM-EDS) and toxicity characteristic leaching procedure (TCLP) tests indicate that the main sorption mechanism is dissolution-precipitation, in conjunction with surface sorption. PMID:17360101

  5. Synthesis of assorted metal ions anchored alginate bentonite biocomposites for Cr(VI) sorption.

    PubMed

    Gopalakannan, Venkatrajan; Periyasamy, Soodamani; Viswanathan, Natrayasamy

    2016-10-20

    Biocomposites were synthesized by dispersing bentonite (Bent) clay in a biopolymer namely alginate (Alg) and cross-linked with bi (Ca(2+)), tri (Ce(3+)) and tetravalent (Zr(4+)) metal ions viz., Ca@AlgBent, Ce@AlgBent and Zr@AlgBent composites respectively. The synthesized biocomposites were characterized by various instrumental techniques like FTIR, SEM and EDAX. Cr(VI) sorption capacities (SCs) of the biocomposites Ca@AlgBent, Ce@AlgBent and Zr@AlgBent were examined by batch process. Various adsorption influencing factors viz., contact time, dosage of the sorbent, pH of the medium, temperature, presence of common co-ions and initial Cr(VI) concentration were studied. Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherm models were adopted to examine the adsorption equilibrium. Kinetics of the sorption process was carried out by pseudo-first-order and pseudo-second-order models. The nature of the sorption process was explained using thermodynamic parameters like ΔS°, ΔG° and ΔH° and a possible mechanism for the sorption of Cr(VI) onto the biocomposites was given. The application of the biocomposites at field conditions was also examined by testing it with industrial water. The regeneration studies were carried to know about the reusability of the biocomposites. PMID:27474660

  6. Sorption of tylosin on clay minerals.

    PubMed

    Zhang, Qian; Yang, Chen; Huang, Weilin; Dang, Zhi; Shu, Xiaohua

    2013-11-01

    The equilibrium sorption of tylosin (TYL) on kaolinite and montmorillonite was measured at different solution pH using batch reactor systems. The results showed that all the sorption isotherms were nonlinear and that the nonlinearity decreased as the solution pH increased for a given clay. At a specific aqueous concentration, the single-point sorption distribution coefficient (KD) of TYL decreased rapidly as the solution pH increased. A speciation-dependent sorption model that accounted for the contributions of the cationic and neutral forms of TYL fit the data well, suggesting that the sorption may be dominated by both ion exchange and hydrophobic interactions. The isotherm data also fit well to a dual mode model that quantifies the contributions of a site-limiting Langmuir component (ion exchange) and a non-specific linear partitioning component (hydrophobic interactions). X-ray diffraction analyses revealed that the interlayers of montmorillonite were expanded due to the uptake of TYL. TYL molecules likely form a monolayer surface coverage. PMID:24007614

  7. [Sorption behaviors of BDE-28 on natural soils].

    PubMed

    Liu, Wen-Xin; Ling, Xi; Chen, Jiang-Lin; Li, Wei-Bo; Dou, Han; Tao, Shu

    2011-03-01

    The sorption kinetics and isotherms of BDE-28 on three natural soils with different soil organic matter fractions (f(oc)) were investigated. The results indicated that a two (fast and slow)-compartment first-order model was more appropriate for describing the sorption kinetic data, compared to a one-compartment first-order model, especially in the initial sorption stage within 25 h. The fast sorption was predominant during the whole sorption process from beginning to the apparent sorption equilibrium; while the contribution of the slow sorption to the total sorption amount gradually increased and then achieved a plateau at 49 h or 55 h. The approaching time to the individual sorption capacity for the fast sorption was much shorter than that for the slow sorption. The contribution of the fast sorption to the increase in the total sorption amount of BDE-28 was prevailing at the beginning of sorption process from 2.5 h to 4.5 h; whereas the fraction of the slow sorption became primary at the subsequent stage of sorption process. The fitting results by the Dubinin-Ashtakhov (DA) model were comparable with those by the Freundlich model in the range of apparent equilibrium concentration studied. As for the Freundlich model, the nonlinear exponent (n) values of BDE-28 for the two samples with lower f(oc) (0.72%) or higher f(oc) (7.90%) approached to 1.0 (1.03 +/- 0.05 and 1.00 +/- 0.05, respectively), suggesting the linear sorption characteristics in the studied range of apparent equilibrium concentrations of BDE-28; while the nonlinear behavior of BDE-28 for the left sample with medium f(oc) (4.42%) was indicated by its n value less than 1.0 (0.89 +/- 0.04). PMID:21634174

  8. Effects of sorption competition on caesium diffusion through compacted argillaceous rock

    NASA Astrophysics Data System (ADS)

    Jakob, Andreas; Pfingsten, Wilfried; Van Loon, Luc

    2009-05-01

    We carried out a small-scale laboratory diffusion experiment on a disk-like sample of Opalinus clay from the Mont Terri underground laboratory (Switzerland) using 134Cs as tracer. A through-diffusion phase was followed by an out-diffusion phase where the tracer taken up by the sample was released again. Since the tracer concentration at both boundaries was monitored, careful mass-balance considerations were feasible. A first analysis of the experimental data was done in the frame of a single-species model accounting only for transport and non-linear sorption of caesium. The model could match the data of the through-diffusion phase, however only, when strongly reducing the sorption data based on batch sorption experiments. Yet, such a procedure was in strong contradiction with sorption measurements performed on dispersed and compacted systems. In addition, predictions concerning tracer out-diffusion and mass-balance considerations clearly revealed the shortcomings of this type of model. In a second attempt we applied a multi-species transport model where now the whole water chemistry and a sorption model for caesium were considered. First, the value for the diffusion coefficient was fixed to the best-fit value of the single-species model. But again, the sorption site densities had to be reduced strongly albeit the reduction factor was smaller. Only when fixing the sorption site densities to those values of the sorption model and letting the effective diffusion coefficient D e free for the adjustment, could through-diffusion data be reasonably well fitted and out-diffusion as well as mass-balances be predicted in a satisfying manner. The main results are: (1) The best-fit could be achieved with a value for D e of 1.8 × 10 -10 m 2 s -1 which is rather high but corroborated by results of a molecular modelling study. (2) If caesium arrives in the Opalinus clay sample potassium and sodium (calcium etc.) ions are released and caesium ions are sorbed. The released cations

  9. Round window membrane intracochlear drug delivery enhanced by induced advection.

    PubMed

    Borkholder, David A; Zhu, Xiaoxia; Frisina, Robert D

    2014-01-28

    Delivery of therapeutic compounds to the inner ear via absorption through the round window membrane (RWM) has advantages over direct intracochlear infusions; specifically, minimizing impact upon functional hearing measures. However, previous reports show that significant basal-to-apical concentration gradients occur, with the potential to impact treatment efficacy. Here we present a new approach to inner ear drug delivery with induced advection aiding distribution of compounds throughout the inner ear in the murine cochlea. Polyimide microtubing was placed near the RWM niche through a bullaostomy into the middle ear cavity allowing directed delivery of compounds to the RWM. We hypothesized that a posterior semicircular canalostomy would induce apical flow from the patent cochlear aqueduct to the canalostomy due to influx of cerebral spinal fluid. To test this hypothesis, young adult CBA/CaJ mice were divided into two groups: bullaostomy approach only (BA) and bullaostomy+canalostomy (B+C). Cochlear function was evaluated by distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) thresholds during and after middle ear infusion of salicylate in artificial perilymph (AP), applied near the RWM. The mice recovered for 1week, and were re-tested. The results demonstrate there was no significant impact on auditory function utilizing the RWM surgical procedure with or without the canalostomy, and DPOAE thresholds were elevated reversibly during the salicylate infusion. Comparing the threshold shifts for both methods, the B+C approach had more of a physiological effect than the BA approach, including at lower frequencies representing more apical cochlear locations. Unlike mouse cochleostomies, there was no deleterious auditory functional impact after 1week recovery from surgery. The B+C approach had more drug efficacy at lower frequencies, underscoring potential benefits for more precise control of delivery of inner ear therapeutic compounds

  10. Round Window Membrane Intracochlear Drug Delivery Enhanced by Induced Advection

    PubMed Central

    Borkholder, David A.; Zhu, Xiaoxia; Frisina, Robert D.

    2014-01-01

    Delivery of therapeutic compounds to the inner ear via absorption through the round window membrane (RWM) has advantages over direct intracochlear infusions; specifically, minimizing impact upon functional hearing measures. However, previous reports show that significant basal-to-apical concentration gradients occur, with the potential to impact treatment efficacy. Here we present a new approach to inner ear drug delivery with induced advection aiding distribution of compounds throughout the inner ear in the murine cochlea. Polyimide microtubing was placed near the RWM niche through a bullaostomy into the middle ear cavity allowing directed delivery of compounds to the RWM. We hypothesized that a posterior semicircular canalostomy would induce apical flow from the patent cochlear aqueduct to the canalostomy due to influx of cerebral spinal fluid. To test this hypothesis, young adult CBA/CaJ mice were divided into two groups: bullaostomy approach only (BA) and bullaostomy + canalostomy (B+C). Cochlear function was evaluated by distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) thresholds during and after middle ear infusion of salicylate in artificial perilymph (AP), applied near the RWM. The mice recovered for 1 week, and were re-tested. The results demonstrate there was no significant impact on auditory function utilizing the RWM surgical procedure with or without the canalostomy, and DPOAE thresholds were elevated reversibly during the salicylate infusion. Comparing the threshold shifts for both methods, the B+C approach had more of a physiological effect than the BA approach, including at lower frequencies representing more apical cochlear locations. Unlike mouse cochleostomies, there was no deleterious auditory functional impact after 1 week recovery from surgery. The B+C approach had more drug efficacy at lower frequencies, underscoring potential benefits for more precise control of delivery of inner ear therapeutic compounds

  11. Evaporation of traffic-generated nanoparticles during advection from source

    NASA Astrophysics Data System (ADS)

    Harrison, Roy M.; Jones, Alan M.; Beddows, David C. S.; Dall'Osto, Manuel; Nikolova, Irina

    2016-01-01

    Earlier work has demonstrated the potential for volatilisation of nanoparticles emitted by road traffic as these are advected downwind from the source of emissions, but there have been few studies and the processes have yet to be elucidated in detail. Using a dataset collected at paired sampling sites located respectively in a street canyon and in a nearby park, an in depth analysis of particle number size distributions has been conducted in order to better understand the size reduction of the semi-volatile nanoparticles. By sorting the size distributions according to wind direction and fitting log normal modes, it can be seen that the mode peaking at around 22 nm at the street canyon site is on average shrinking to 6.2 nm diameter at the park site which indicates a mean shrinkage rate for these particles of 0.13 nm s-1 with temperatures within the range 12-18 °C. The diurnal variation of the shrunken mode in the park reflects the diurnal pattern of particle concentrations at the street canyon site taken as the main source area. An analysis of peak diameter for the smallest mode at the downwind park site shows an inverse relationship to wind speed suggesting that dilution rather than travel time is the main determinant of the particle shrinkage rate. An evaluation of previously collected C10 to C35 n-alkane data from a different urban location shows a good fit to Pankow partitioning theory reflecting the semi-volatility of compounds believed to be representative of the composition of diesel exhaust nanoparticles, hence confirming the feasibility of an evaporative mechanism for particle shrinkage.

  12. Advective hydrogel membrane chromatography for monoclonal antibody purification in bioprocessing.

    PubMed

    Hou, Ying; Brower, Mark; Pollard, David; Kanani, Dharmesh; Jacquemart, Renaud; Kachuik, Bradley; Stout, James

    2015-01-01

    Protein A chromatography is widely employed for the capture and purification of monoclonal antibodies (mAbs). Because of the high cost of protein A resins, there is a significant economic driving force to seek new downstream processing strategies. Membrane chromatography has emerged as a promising alternative to conventional resin based column chromatography. However, to date, the application has been limited to mostly ion exchange flow through (FT) mode. Recently, significant advances in Natrix hydrogel membrane has resulted in increased dynamic binding capacities for proteins, which makes membrane chromatography much more attractive for bind/elute operations. The dominantly advective mass transport property of the hydrogel membrane has also enabled Natrix membrane to be run at faster volumetric flow rates with high dynamic binding capacities. In this work, the potential of using Natrix weak cation exchange membrane as a mAb capture step is assessed. A series of cycle studies was also performed in the pilot scale device (> 30 cycles) with good reproducibility in terms of yield and product purities, suggesting potential for improved manufacturing flexibility and productivity. In addition, anion exchange (AEX) hydrogel membranes were also evaluated with multiple mAb programs in FT mode. Significantly higher binding capacity for impurities (support mAb loads up to 10Kg/L) and 40X faster processing speed were observed compared with traditional AEX column chromatography. A proposed protein A free mAb purification process platform could meet the demand of a downstream purification process with high purity, yield, and throughput. PMID:26018631

  13. Critical time scales for advection-diffusion-reaction processes

    NASA Astrophysics Data System (ADS)

    Ellery, Adam J.; Simpson, Matthew J.; McCue, Scott W.; Baker, Ruth E.

    2012-04-01

    The concept of local accumulation time (LAT) was introduced by Berezhkovskii and co-workers to give a finite measure of the time required for the transient solution of a reaction-diffusion equation to approach the steady-state solution [A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Biophys. J.BIOJAU0006-349510.1016/j.bpj.2010.07.045 99, L59 (2010); A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.051906 83, 051906 (2011)]. Such a measure is referred to as a critical time. Here, we show that LAT is, in fact, identical to the concept of mean action time (MAT) that was first introduced by McNabb [A. McNabb and G. C. Wake, IMA J. Appl. Math.IJAMDM0272-496010.1093/imamat/47.2.193 47, 193 (1991)]. Although McNabb's initial argument was motivated by considering the mean particle lifetime (MPLT) for a linear death process, he applied the ideas to study diffusion. We extend the work of these authors by deriving expressions for the MAT for a general one-dimensional linear advection-diffusion-reaction problem. Using a combination of continuum and discrete approaches, we show that MAT and MPLT are equivalent for certain uniform-to-uniform transitions; these results provide a practical interpretation for MAT by directly linking the stochastic microscopic processes to a meaningful macroscopic time scale. We find that for more general transitions, the equivalence between MAT and MPLT does not hold. Unlike other critical time definitions, we show that it is possible to evaluate the MAT without solving the underlying partial differential equation (pde). This makes MAT a simple and attractive quantity for practical situations. Finally, our work explores the accuracy of certain approximations derived using MAT, showing that useful approximations for nonlinear kinetic processes can be obtained, again without treating the governing pde directly.

  14. Verification of Advective Bar Elements Implemented in the Aria Thermal Response Code.

    SciTech Connect

    Mills, Brantley

    2016-01-01

    A verification effort was undertaken to evaluate the implementation of the new advective bar capability in the Aria thermal response code. Several approaches to the verification process were taken : a mesh refinement study to demonstrate solution convergence in the fluid and the solid, visually examining the mapping of the advective bar element nodes to the surrounding surfaces, and a comparison of solutions produced using the advective bars for simple geometries with solutions from commercial CFD software . The mesh refinement study has shown solution convergence for simple pipe flow in both temperature and velocity . Guidelines were provided to achieve appropriate meshes between the advective bar elements and the surrounding volume. Simulations of pipe flow using advective bars elements in Aria have been compared to simulations using the commercial CFD software ANSYS Fluent (r) and provided comparable solutions in temperature and velocity supporting proper implementation of the new capability. Verification of Advective Bar Elements iv Acknowledgements A special thanks goes to Dean Dobranich for his guidance and expertise through all stages of this effort . His advice and feedback was instrumental to its completion. Thanks also goes to Sam Subia and Tolu Okusanya for helping to plan many of the verification activities performed in this document. Thank you to Sam, Justin Lamb and Victor Brunini for their assistance in resolving issues encountered with running the advective bar element model. Finally, thanks goes to Dean, Sam, and Adam Hetzler for reviewing the document and providing very valuable comments.

  15. Modelling of Thermal Advective Reactive Flow in Hydrothermal Mineral Systems Using an Implicit Time-stepped Finite Element Method.

    NASA Astrophysics Data System (ADS)

    Hornby, P. G.

    2005-12-01

    Understanding chemical and thermal processes taking place in hydrothermal mineral deposition systems could well be a key to unlocking new mineral reserves through improved targeting of exploration efforts. To aid in this understanding it is very helpful to be able to model such processes with sufficient fidelity to test process hypotheses. To gain understanding, it is often sufficient to obtain semi-quantitative results that model the broad aspects of the complex set of thermal and chemical effects taking place in hydrothermal systems. For example, it is often sufficient to gain an understanding of where thermal, geometric and chemical factors converge to precipitate gold (say) without being perfectly precise about how much gold is precipitated. The traditional approach is to use incompressible Darcy flow together with the Boussinesq approximation. From the flow field, the heat equation is used to advect-conduct the heat. The flow field is also used to transport solutes by solving an advection-dispersion-diffusion equation. The reactions in the fluid and between fluid and rock act as source terms for these advection-dispersion equations. Many existing modelling systems that are used for simulating such systems use explicit time marching schemes and finite differences. The disadvantage of this approach is the need to work on rectilinear grids and the number of time steps required by the Courant condition in the solute transport step. The second factor can be particularly significant if the chemical system is complex, requiring (at a minimum) an equilibrium calculation at each grid point at each time step. In the approach we describe, we use finite elements rather than finite differences, and the pressure, heat and advection-dispersion equations are solved implicitly. The general idea is to put unconditional numerical stability of the time integration first, and let accuracy assume a secondary role. It is in this sense that the method is semi-quantiative. However

  16. Sorption Characteristics of Sorption Material Coated on Heat Transfer surface of a Heat Exchanger

    NASA Astrophysics Data System (ADS)

    Inaba, Hideo; Komatsu, Fujio; Horibe, Akihiko; Haruki, Naoto; Machida, Akito

    This paper describes sorption characteristics of organic sorbent coated on heat transfer surface of a plate-fin-tube heat exchanger. The organic sorbent is a bridged complex of soldium polyacrylate. This bridged complex containing the carboxyl group as water vapor adsorption site has a larger adsorption abilities as compared with silica gel. The experiments in which the moist air was passed into the heat exchanger coated with sorption material were conducted under various conditions of air flow rate and the temperature of brine that was the heat transfer fluid to cool the air flow in the dehumidifying process. It is found that the sorption rate of vapor is affected by the air flow rate and the brine temperature. Meanwhile, the attempt of clarifying the sorption mechanism is also conducted. Finally the average mass transfer coefficient of the organic sorbent was non-dimensionalized as a function of Reynolds number and non-dimensional temperature. In addition, it was observed that the factor which affects the sorption rate in the water vapor sorption process of the organic sorbent coated on the heat exchanger shifts from the “adsorption step” to the “sorption step”.

  17. Water-sorption properties of tablet disintegrants.

    PubMed

    Khan, K A; Rhodes, C T

    1975-03-01

    The water-sorption properties of four tablet disintegrants, starch, sodium carboxymethylcellulose, sodium starch glycolate, and a cation-exchange resin, were examined in the form of powders and in compressed tablets prepared from calcium phosphate dibasic dihydrate. Dissolution properties of the tablets compare well to the water-sorption properties. The effect of storage in the presence of water vapor upon tablets containing the various disintegrants was evaluated in terms of tablet hardness and disintegration time. Differences in the effects produced in the various tablet formulations can be related to the differing mechanisms whereby the disintegrants effect tablet rupture. Photomicrographic data support the conclusions drawn from the water-sorption, disintegration, and dissolution studies. Sodium starch glycolate and the cation-exchange resin merit careful consideration by formulators using calcium phosphate dibasic dihydrate or similar direct compression matrixes. PMID:1151632

  18. Sorption of sodium dodecylbenzene sulfonate by montmorillonite.

    PubMed

    Yang, Kun; Zhu, Lizhong; Xing, Baoshan

    2007-01-01

    Sorption of linear alkylbenzene sulfonates by soils and sediments is an important process that may affect their fate, transport, toxicity and their application in remediation of contaminated soil and groundwater. In this study, batch experiments were conducted to elucidate the sorption of a widely used anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), by montmorillonite. It was observed that: (i) SDBS was sorbed significantly by montmorillonite saturated with Ca(2+), but little by Na-saturated montmorillonite; (ii) the amount of SDBS sorbed by Ca(2+)-montmorillonite was enhanced by NaCl; and (iii) no significant intercalation of SDBS into Ca(2+)-montmorillonite was observed by X-ray diffraction (XRD) analysis. These results indicate that the removal of SDBS by Ca(2+)-montmorillonite was primarily attributed to the precipitation between DBS(-) and Ca(2+) in solution which was released from montmorillonite via cation exchange. These results will help us to understand the sorption behavior and environmental effects of anionic surfactants. PMID:16759775

  19. Effect of gaseous ammonia on nicotine sorption

    SciTech Connect

    Webb, A.M.; Singer, B.C.; Nazaroff, W.W.

    2002-06-01

    Nicotine is a major constituent of environmental tobacco smoke. Sorptive interactions of nicotine with indoor surfaces can substantially alter indoor concentrations. The phenomenon is poorly understood, including whether sorption is fully reversible or partially irreversible. They hypothesize that acid-base chemistry on indoor surfaces might contribute to the apparent irreversibility of nicotine sorption under some circumstances. Specifically, they suggest that nicotine may become protonated on surfaces, markedly reducing its vapor pressure. If so, subsequent exposure of the surface to gaseous ammonia, a common base, could raise the surface pH, causing deprotonation and desorption of nicotine from surfaces. A series of experiments was conducted to explore the effect of ammonia on nicotine sorption to and reemission from surfaces. The results indicate that, under some conditions, exposure to gaseous ammonia can substantially increase the rate of desorption of previously sorbed nicotine from common indoor surface materials.

  20. The contiguous domains of Arctic Ocean advection: Trails of life and death

    NASA Astrophysics Data System (ADS)

    Wassmann, P.; Kosobokova, K. N.; Slagstad, D.; Drinkwater, K. F.; Hopcroft, R. R.; Moore, S. E.; Ellingsen, I.; Nelson, R. J.; Carmack, E.; Popova, E.; Berge, J.

    2015-12-01

    The central Arctic Ocean is not isolated, but tightly connected to the northern Pacific and Atlantic Oceans. Advection of nutrient-, detritus- and plankton-rich waters into the Arctic Ocean forms lengthy contiguous domains that connect subarctic with the arctic biota, supporting both primary production and higher trophic level consumers. In turn, the Arctic influences the physical, chemical and biological oceanography of adjacent subarctic waters through southward fluxes. However, exports of biomass out of the Arctic Ocean into both the Pacific and Atlantic Oceans are thought to be far smaller than the northward influx. Thus, Arctic Ocean ecosystems are net biomass beneficiaries through advection. The biotic impact of Atlantic- and Pacific-origin taxa in arctic waters depends on the total supply of allochthonously-produced biomass, their ability to survive as adults and their (unsuccessful) reproduction in the new environment. Thus, advective transport can be thought of as trails of life and death in the Arctic Ocean. Through direct and indirect (mammal stomachs, models) observations this overview presents information about the advection and fate of zooplankton in the Arctic Ocean, now and in the future. The main zooplankton organisms subjected to advection into and inside the Arctic Ocean are (a) oceanic expatriates of boreal Atlantic and Pacific origin, (b) oceanic Arctic residents and (c) neritic Arctic expatriates. As compared to the Pacific gateway the advective supply of zooplankton biomass through the Atlantic gateways is 2-3 times higher. Advection characterises how the main planktonic organisms interact along the contiguous domains and shows how the subarctic production regimes fuel life in the Arctic Ocean. The main differences in the advective regimes through the Pacific and Atlantic gateways are presented. The Arctic Ocean is, at least in some regions, a net heterotrophic ocean that - during the foreseeable global warming trend - will more and more rely

  1. Fog dispersion

    NASA Technical Reports Server (NTRS)

    Frost, W.; Christensen, L. S.; Collins, F. G.; Camp, D. W.

    1980-01-01

    A study of economically viable techniques for dispersing warm fog at commercial airports is presented. Five fog dispersion techniques are examined: evaporation suppression, downwash, mixing, seeding with hygroscopic material, thermal techniques, and charged particle techniques. Thermal techniques, although effective, were found to be too expensive for routine airport operations, and detrimental to the environment. Seeding or helicopter downwash are practical for small-scale or temporary fog clearing, but are probably not useful for airport operations on a routine basis. Considerable disagreement exists on the capability of charged particle techniques, which stems from the fact that different assumptions and parameter values are used in the analytical models. Recommendations resulting from the review of this technique are listed, and include: experimental measurements of the parameters in question; a study to ascertain possible safety hazards, such as increased electrical activity or fuel ignition during refueling operations which could render charged particle techniques impractical; and a study of a single charged particle generator.

  2. Sorption of dodecyltrimethylammonium chloride (DTAC) to agricultural soils.

    PubMed

    Xiang, Lei; Sun, Teng-Fei; Zheng, Mei-Jie; Li, Yan-Wen; Li, Hui; Wong, Ming-Hung; Cai, Quan-Ying; Mo, Ce-Hui

    2016-08-01

    Quaternary ammonium compounds (QACs) used as cationic surfactants are intensively released into environment to be pollutants receiving more and more concerns. Sorption of dodecyltrimethylammonium chloride (DTAC), one of commonly used alkyl QACs, to five types of agricultural soils at low concentrations (1-50mg/L) was investigated using batch experiments. DTAC sorption followed pseudo-second-order kinetics and reached reaction equilibrium within 120min. Both Freundlich model and Langmuir model fitted well with DTAC isotherm data with the latter better. DTAC sorption was spontaneous and favorable, presenting a physical sorption dominated by ion exchanges. Sorption distribution coefficient and sorption affinity demonstrated that soil clay contents acted as a predominant phase of DTAC sorption. DTAC could display a higher mobility and potential accumulation in crops in the soils with lower clay contents and lower pH values. Sorption of DTAC was heavily affected by ions in solution with anion promotion and cation inhibition. PMID:27101455

  3. Comparative sorption, desorption and leaching potential of aminocyclopyrachlor and picloram

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aminocyclopyrachlor and picloram sorption, desorption and leaching potential were investigated in three soils from Minnesota and Hawaii. Aminocyclopyrachlor and picloram sorption fit the Freundlich equation and was independent of concentration for aminocyclopyrachlor (1/n = 1), but not for picloram ...

  4. Horizontal Advection and Mixing of Pollutants in the Urban Atmospheric Environment

    NASA Astrophysics Data System (ADS)

    Magnusson, S. P.; Entekhabi, D.; Britter, R.; Norford, L.; Fernando, H. J.

    2013-12-01

    Although urban air quality and its impacts on the public health have long been studied, the increasing urbanization is raising concerns on how to better control and mitigate these health impacts. A necessary element in predicting exposure levels is fundamental understanding of flow and dispersion in urban canyons. The complex topology of building structures and roads requires the resolution of turbulence phenomena within urban canyons. The use of dense and low porosity construction material can lead to rapid heating in response to direct solar exposure due to large thermal mass. Hence thermal and buoyancy effects may be as important as mechanically-forced or shear-induced flows. In this study, the transport of pollutants within the urban environment, as well as the thermal and advection effects, are investigated. The focus is on the horizontal transport or the advection effects within the urban environment. With increased urbanization and larger and more spread cities, concern about how the upstream air quality situation can affect downstream areas. The study also examines the release and the dispersion of hazardous material. Due to the variety and complexity of urban areas around the world, the urban environment is simplified into adjacent two-dimensional urban street canyons. Pollutants are released inside each canyon. Computational Fluid Dynamics (CFD) simulations are applied to evaluate and quantify the flow rate out of each canyon and also the exchange of pollutants between the canyons. Imagine a row of ten adjacent urban street canyons of aspect ratio 1 with horizontal flow perpendicular to it as shown in the attached figure. C is the concentration of pollutants. The first digit indicates in what canyon the pollutant is released and the second digit indicates the location of that pollutant. For example, C3,4 is the concentration of pollutant released inside canyon 3 measured in canyon 4. The same amount of pollution is released inside the ten street canyons

  5. Radioiodide sorption to sediment minerals

    SciTech Connect

    Kaplan, D.I.; Serne, R.J.; Parker, K.E.; Kutnyakov, I.V.

    1999-07-01

    Laboratory studies were conducted to quantify and understand the processes by which iodide (I{sup {minus}}) sorbs to minerals found in subsurface arid sediments. Little or no I{sup {minus}} sorbed to montmorillonite (K{sub d} = {minus}0.42 {+-} 0.08 mL/g), quartz (K{sub d} = 0.04 {+-} 0.02 mL/g), vermiculite (K{sub d} = 0.56 {+-} 0.21 mL/g), calcite (K{sub d} = 0.04 {+-} 0.01 mL/g), goethite (K{sub d} = 0.10 {+-} 0.03 mL/g), or chlorite (K{sub d} = {minus}0.22 {+-} 0.06 mL/g). A significant amount of I{sup {minus}} sorbed to illite (K{sub d} = 15.14 {+-} 2.84 mL/g). Upon treating the iodide-laden illite with dissolved F{sup {minus}}, Cl{sup {minus}}, Br{sup {minus}}, or {sup 127}I{sup {minus}}, desorption (or isotopic exchange in the case of {sup 127}I) removed, respectively, 43 {+-} 3%, 45 {+-} 0%, 52 {+-} 3, and 83 {+-} 1% of the I{sup {minus}} originally adsorbed to the illite. The fact that such large amounts of I{sup {minus}} could be desorbed suggests that the I{sup {minus}} was weakly adsorbed, and not chemically bonded to a soft metal, such as mercury or silver, that may have existed in the illite structure as trace impurities. Finally, I{sup {minus}} sorption to illite was strongly pH-dependent; the K{sub d} values decreased from 46 to 22 mL/g as the pH values increased from 3.6 to 9.4. Importantly, I{sup {minus}} sorbed to illite even under alkaline conditions. Together, these experiments suggest that illite removed I{sup {minus}} from the aqueous phase predominantly by reversible physical adsorption to the pH-dependent edge sites. Illites may constitute a substantial proportion of the clay-size fraction of many arid sediments and therefore may play an important role in retarding I{sup {minus}} movement in these sediments.

  6. Measurement of advection of CO2 over grasslands in complex terrain in the Alps

    NASA Astrophysics Data System (ADS)

    Zhao, Peng; Hammerle, Albin; Wohlfahrt, Georg

    2015-04-01

    The role of advection is often ignored in the estimation of net ecosystem exchange (NEE) of CO2 in ecosystems. However, some studies reported that more realistic estimates of night-time NEE could be gathered if horizontal and vertical advections are included. While most of previous advection experiments have been conducted in forest ecosystems, grassland ecosystems have a great advantage as measurements of advection can be realised with smaller infrastructure and thus less experimental effort. In a preliminary simplified study, advection showed an important contribution to NEE during night time at a sub-alpine grassland site. This three-year program is focused on the role of advection for NEE of grassland ecosystems in complex terrain in the Alps. We are going to carry out field campaigns at four sites which cover a range of terrain types typical for mountains with varying degrees of complexity, including a valley-bottom site, a steep-slope site, a mixed-terrain site, and an undulating-terrain site. Observations will take place in a notional control volume with a length varying from 50 m to 5 m at each site in order to quantify the effects of horizontal spatial scale on advection estimates. The observations at each site include vertical flux of CO2 measured by eddy-covariance technique, horizontal and vertical advections of CO2 calculated from the measurement of wind components and CO2 gradients, and NEE measured by chambers. Among all, the measurement of the horizontal advection of CO2 needs many efforts because of small-scale variability in sources/sinks of CO2. We are going to use tubes with multiple inlets, which allows sampling at multiple positions across the faces at three heights of the control volume. Thus, we would be able to quantify the contribution of advection to NEE at different grassland sites situated in complex terrain in the Alps, and to quantify the effect of spatial scale of advection measurements with a given experimental setup and accuracy on

  7. Sorption cryogenic refrigeration - Status and future

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.

    1988-01-01

    The operation principles of sorption cryogenic refrigeration are discussed. Sorption refrigerators have virtually no wear-related moving parts, have negligible vibration, and offer extremely long life (at least ten years), making it possible to obtain efficient, long life and low vibration cooling to as low as 7 K for cryogenic sensors. The physisorption and chemisorption systems recommended for various cooling ranges down to 7 K are described in detail. For long-life cooling at 4-5 K temperatures, a hybrid chemisorption-mechanical refrigeration system is recommended.

  8. Structure of chitosan gels mineralized by sorption

    NASA Astrophysics Data System (ADS)

    Modrzejewska, Z.; Skwarczyńska, A.; Douglas, T. E. L.; Biniaś, D.; Maniukiewicz, W.; Sielski, J.

    2015-10-01

    The paper presents the structural studies of mineralized chitosan hydrogels. Hydrogels produced by using sodium beta-glycerophosphate (Na-β-GP) as a neutralizing agent. Mineralization was performed method "post loading", which consisted in sorption to the gels structure Ca ions. In order to obtain - in the structure of gels - compounds similar to the hydroxyapatites present naturally in bone tissue, gels after sorption were modified in: pH 7 buffer and sodium hydrogen phosphate. In order to determine the structural properties of the gels, the following methods were used: infrared spectroscopy with Fourier transformation, FTIR, X-ray diffractometry, XRD, scanning electron microscopy, SEM.

  9. Clumpy Accretion onto Black Holes. I. Clumpy-advection-dominated Accretion Flow Structure and Radiation

    NASA Astrophysics Data System (ADS)

    Wang, Jian-Min; Cheng, Cheng; Li, Yan-Rong

    2012-04-01

    We investigate the dynamics of clumps embedded in and confined by the advection-dominated accretion flows (ADAFs), in which collisions among the clumps are neglected. We start from the collisionless Boltzmann equation and assume that interaction between the clumps and the ADAF is responsible for transporting the angular momentum of clumps outward. The inner edge of the clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong- and weak-coupling cases, in which the averaged properties of clumps follow the ADAF dynamics and are mainly determined by the black hole potential, respectively. We propose the analytical solution of the dynamics of clumps for the two cases. The velocity dispersion of clumps is one magnitude higher than the ADAF for the strong-coupling case. For the weak-coupling case, we find that the mean radial velocity of clumps is linearly proportional to the coefficient of the drag force. We show that the tidally disrupted clumps would lead to an accumulation of the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot ADAF will be efficiently cooled down by photons from the debris disk, giving rise to a collapse of the ADAF, and quench the clumpy accretion. Subsequently, evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF, resulting in an oscillation of the global clumpy-ADAF. Applications of the present model are briefly discussed to X-ray binaries, low ionization nuclear emission regions, and BL Lac objects.

  10. CLUMPY ACCRETION ONTO BLACK HOLES. I. CLUMPY-ADVECTION-DOMINATED ACCRETION FLOW STRUCTURE AND RADIATION

    SciTech Connect

    Wang Jianmin; Cheng Cheng; Li Yanrong

    2012-04-01

    We investigate the dynamics of clumps embedded in and confined by the advection-dominated accretion flows (ADAFs), in which collisions among the clumps are neglected. We start from the collisionless Boltzmann equation and assume that interaction between the clumps and the ADAF is responsible for transporting the angular momentum of clumps outward. The inner edge of the clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong- and weak-coupling cases, in which the averaged properties of clumps follow the ADAF dynamics and are mainly determined by the black hole potential, respectively. We propose the analytical solution of the dynamics of clumps for the two cases. The velocity dispersion of clumps is one magnitude higher than the ADAF for the strong-coupling case. For the weak-coupling case, we find that the mean radial velocity of clumps is linearly proportional to the coefficient of the drag force. We show that the tidally disrupted clumps would lead to an accumulation of the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot ADAF will be efficiently cooled down by photons from the debris disk, giving rise to a collapse of the ADAF, and quench the clumpy accretion. Subsequently, evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF, resulting in an oscillation of the global clumpy-ADAF. Applications of the present model are briefly discussed to X-ray binaries, low ionization nuclear emission regions, and BL Lac objects.

  11. SEBAL-A: A remote sensing ET algorithm that accounts for advection with limited data. Part II: Test for transferability

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Because the Surface Energy Balance Algorithm for Land (SEBAL) tends to underestimate ET under conditions of advection, the model was modified by incorporating an advection component as part of the energy usable for crop evapotranspiration (ET). The modification involved the estimation of advected en...

  12. SORPTION AND REEMISSION OF FORMALDEHYDE BY GYPSUM WALLBOARD

    EPA Science Inventory

    The paper gives results of an analysis of the sorption and desorption of formaldehyde by unpainted wallboard, using a mass transfer model based on the Langmuir sorption isotherm. he sorption and desorption rate constants are determined by short-term experimental data. ong-term so...

  13. Black Hole Event Horizons and Advection-Dominated Accretion

    NASA Technical Reports Server (NTRS)

    McClintock, Jeffrey; Mushotzky, Richard F. (Technical Monitor)

    2001-01-01

    The XMM data on black-hole X-ray novae are only now becoming available and they have so far not been included in any publications. This work is part of a larger project that makes use of both XMM and Chandra data. Our first publication on the Chandra results is the following: "New Evidence for Black Hole Event Horizons from Chandra" by M.R. Garcia, J.E. McClintock, R. Narayan, P. Callanan, D. Barret and S. Murray (2001, ApJ, 553, L47). Therein we present the luminosities of the two black-hole X-ray novae, GRO J0422+22 and 4U1 543-47, which were observed by Chandra. These results are combined with the luminosities of four additional black-hole X-ray novae, which were observed as part of a Chandra GTO program (PI: S. Murray). The very low, but nonzero, quiescent X-ray luminosities of these black hole binaries is very difficult to understand in the context of standard viscous accretion disk theory. The principal result of this work is that X-ray novae that contain black hole primaries are about 100 times fainter that X-ray novae that contain neutron star primaries. This result had been suggested in earlier work, but the present work very firmly establishes this large luminosity difference. The result is remarkable because the black-hole and the neutron-star systems are believed to be similar in many respects. Most importantly, the mass transfer rate from the secondary star is believed to be very comparable for the two kinds of systems for similar orbital periods. The advection-dominated accretion flow (ADAF) model provides a natural framework for understanding the extraordinarily low luminosities of the black hole systems and the hundred-fold greater luminosities of the neutron star systems. The chief feature of an ADAF is that the heat energy in the accreting gas is trapped in the gas and travels with it, rather than being radiated promptly. Thus the accreting gas reaches the central object with a huge amount of thermal energy. If the accretor is a black hole, the

  14. Hydration and sorption characteristics of a polyfunctional weak-base anion exchanger after the sorption of vanillin and ethylvanillin

    NASA Astrophysics Data System (ADS)

    Rodionova, D. O.; Voronyuk, I. V.; Eliseeva, T. V.

    2016-07-01

    Features of the sorption of substituted aromatic aldehydes by a weak-base anion exchanger under equilibrium conditions are investigated using vanillin and ethylvanillin as examples. Analysis of the sorption isotherms of carbonyl compounds at different temperatures allows us to calculate the equilibrium characteristics of their sorption and assess the entropy and enthalpy contributions to the energy of the process. Hydration characteristics of the macroporous weak-base anion exchanger before and after the sorption of aromatic aldehydes are compared.

  15. Dispersive transport of charge carriers in disordered nanostructured materials

    NASA Astrophysics Data System (ADS)

    Sibatov, R. T.; Uchaikin, V. V.

    2015-07-01

    Dispersive transport of charge carriers in disordered nanostructured semiconductors is described in terms of integral diffusion equations nonlocal in time. Transient photocurrent kinetics is analyzed for different situations. Relation to the fractional differential approach is demonstrated. Using this relation provides specifications in interpretation of the time-of-flight data. Joint influence of morphology and energy distribution of localized states is described in frames of the trap-limited advection-diffusion on a comb structure modeling a percolation cluster.

  16. Dispersive processes in models of regional radionuclide migration. Technical memorandum

    SciTech Connect

    Evenson, D.E.; Dettinger, M.D.

    1980-05-01

    Three broad areas of concern in the development of aquifer scale transport models will be local scale diffusion and dispersion processes, regional scale dispersion processes, and numerical problems associated with the advection-dispersion equation. Local scale dispersion processes are fairly well understood and accessible to observation. These processes will generally be dominated in large scale systems by regional processes, or macro-dispersion. Macro-dispersion is primarily the result of large scale heterogeneities in aquifer properties. In addition, the effects of many modeling approximations are often included in the process. Because difficulties arise in parameterization of this large scale phenomenon, parameterization should be based on field measurements made at the same scale as the transport process of interest or else partially circumvented through the application of a probabilistic advection model. Other problems associated with numerical transport models include difficulties with conservation of mass, stability, numerical dissipation, overshoot, flexibility, and efficiency. We recommend the random-walk model formulation for Lawrence Livermore Laboratory's purposes as the most flexible, accurate and relatively efficient modeling approach that overcomes these difficulties.

  17. Sorption of Cu(II) Ions on Chitosan-Zeolite X Composites: Impact of Gelling and Drying Conditions.

    PubMed

    Djelad, Amal; Morsli, Amine; Robitzer, Mike; Bengueddach, Abdelkader; di Renzo, Francesco; Quignard, Françoise

    2016-01-01

    Chitosan-zeolite Na-X composite beads with open porosity and different zeolite contents were prepared by an encapsulation method. Preparation conditions had to be optimised in order to stabilize the zeolite network during the polysaccharide gelling process. Composites and pure reference components were characterized using X-ray diffraction (XRD); scanning electron microscopy (SEM); N₂ adsorption-desorption; and thermogravimetric analysis (TG). Cu(II) sorption was investigated at pH 6. The choice of drying method used for the storage of the adsorbent severely affects the textural properties of the composite and the copper sorption effectiveness. The copper sorption capacity of chitosan hydrogel is about 190 mg·g(-1). More than 70% of this capacity is retained when the polysaccharide is stored as an aerogel after supercrititcal CO₂ drying, but nearly 90% of the capacity is lost after evaporative drying to a xerogel. Textural data and Cu(II) sorption data indicate that the properties of the zeolite-polysaccharide composites are not just the sum of the properties of the individual components. Whereas a chitosan coating impairs the accessibility of the microporosity of the zeolite; the presence of the zeolite improves the stability of the dispersion of chitosan upon supercritical drying and increases the affinity of the composites for Cu(II) cations. Chitosan-zeolite aerogels present Cu(II) sorption properties. PMID:26797593

  18. AN EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION

    EPA Science Inventory

    Many numerical methods use characteristic analysis to accommodate the advective component of transport. Such characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. A generalization of characteri...

  19. Fast Coherent Particle Advection through Time-Varying Unstructured Flow Datasets.

    PubMed

    Chen, Mingcheng; Shadden, Shawn C; Hart, John C

    2016-08-01

    Tracing the paths of collections of particles through a flow field is a key step for many flow visualization and analysis methods. When a flow field is interpolated from the nodes of an unstructured mesh, the process of advecting a particle must first find which cell in the unstructured mesh contains the particle. Since the paths of nearby particles often diverge, the parallelization of particle advection quickly leads to incoherent memory accesses of the unstructured mesh. We have developed a new block advection GPU approach that reorganizes particles into spatially coherent bundles as they follow their advection paths, which greatly improves memory coherence and thus shared-memory GPU performance. This approach works best for flows that meet the CFL criterion on unstructured meshes of uniformly sized elements, small enough to fit at least two timesteps in GPU memory. PMID:26353375

  20. Finite element approximation of large air pollution problems. I. Advection. Technical report, January-March 1995

    SciTech Connect

    Giraldo, F.X.; Neta, B.

    1995-04-21

    An Eulerian and semi-Lagrangian finite element methods for the solution of the two dimensional advection equation were developed. Bilinear rectangular elements were used. Linear stability analysis of the method is given.

  1. Sensitivity of Gcm Inm Ras To The Change of Humidity Advection Scheme

    NASA Astrophysics Data System (ADS)

    Kostrykin, S. V.

    We study the influence of change the numerical scheme used for humidity advection in the GCM INM RAS on the model results. The previously used advection scheme of the second order ­ leap-frog was changed on the semi-lagrangian cip scheme of the third order. It has shown that the last scheme has excelent numerical properties among other common semi-lagrangian schemes dealing with precise advection of sharp gra- dients. The numerical expriments with GCM has shown that the main changes in the humidity and temperature fields has happend near tropopause. More closeness of the model fields obtained with new advection of humidity to the NCAR/NCEP reanalyses fields are shown.

  2. EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION

    EPA Science Inventory

    Many numerical methods use characteristic analysis to accommodate the advective component of transport. uch characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. eneralization of characteristic...

  3. A Quasi-Conservative Adaptive Semi-Lagrangian Advection-Diffusion Scheme

    NASA Astrophysics Data System (ADS)

    Behrens, Joern

    2014-05-01

    Many processes in atmospheric or oceanic tracer transport are conveniently represented by advection-diffusion type equations. Depending on the magnitudes of both components, the mathematical representation and consequently the discretization is a non-trivial problem. We will focus on advection-dominated situations and will introduce a semi-Lagrangian scheme with adaptive mesh refinement for high local resolution. This scheme is well suited for pollutant transport from point sources, or transport processes featuring fine filamentation with corresponding local concentration maxima. In order to achieve stability, accuracy and conservation, we combine an adaptive mesh refinement quasi-conservative semi-Lagrangian scheme, based on an integral formulation of the underlying advective conservation law (Behrens, 2006), with an advection diffusion scheme as described by Spiegelman and Katz (2006). The resulting scheme proves to be conservative and stable, while maintaining high computational efficiency and accuracy.

  4. Comparison of thermal advection measurements by clear-air radar and radiosonde techniques

    SciTech Connect

    Crochet, M.; Rougier, G.; Bazile, G. Meteorologie Nationale, Trappes )

    1990-10-01

    Vertical profiles of the horizontal wind have been measured every 4 min by a clear-air radar (stratospheric-troposphere radar), and vertical profiles of temperature have been obtained every 2 hours by three radiosonde soundings in the same zone in Brittany during the Mesoscale Frontal Dynamics Project FRONTS 87 campaign. Radar thermal advection is deduced from the thermal wind equation using the measured real horizontal wind instead of the geostrophic wind. Radiosonde thermal advection is determined directly from the sounding station data sets of temperature gradients and also approximately from the thermodynamic equation by the temperature tendency. These approximations, applied during a frontal passage, show the same general features and magnitude of the thermal advection, giving a preliminary but encouraging conclusion for a possible real-time utilization of clear-air radars to monitor thermal advection and to identify its characteristic features. 6 refs.

  5. The impact of advection on stratification and chlorophyll variability in the equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Dave, Apurva C.; Lozier, M. Susan

    2015-06-01

    Previously reported global-scale correlations between interannual variability in upper ocean stratification and chlorophyll a (a proxy for phytoplankton biomass) have been shown to be driven by strong associations between the two properties in the central and western equatorial Pacific. Herein, we present evidence that these correlations are not causal but instead result from the advection of heat, salt, and nutrients in the region. Specifically, we demonstrate that stratification and chlorophyll are simultaneously influenced by shifts in the horizontal advective inputs of cold/saline/nutrient-rich waters from upwelling regions to the east and warm/fresh/nutrient-poor waters to the west. We find that horizontal advection contributes substantially to the annual surface layer nutrient budget and, together with vertical advection, significantly impacts interannual variability in chlorophyll. These results highlight the importance of a three-dimensional framework for examining nutrient supply in the upper ocean—a crucial requirement for assessing future marine ecosystem responses to a changing climate.

  6. A suggested approach toward measuring sorption and applying sorption data to repository performance assessment

    SciTech Connect

    Rundberg, R.S.

    1991-11-01

    The sorption of radioisotopes in relation to geologic disposal of radioactive wastes is discussed. Properties of the radioactive materials, rocks, and minerals, and the chemistry involved are described. 51 refs., 12 figs. CBS

  7. Microporous Carbon Disks For Sorption Refrigerators

    NASA Technical Reports Server (NTRS)

    Munukutla, Lakshmi V.; Moore, Mark R.

    1993-01-01

    Slow, carefully controlled pyrolysis found to turn polyvinylidene chloride disks into carbon disks having small pores and large surface areas. Disks exhibit high adsorptivities making them useful in krypton-sorption refrigerators. Carbons made from polyvinylidene chloride have greater adsorptive capacities. Thermal instability controlled and variability of product reduced by careful control of rates of heating, heating times, and rate of final cooling.

  8. SORPTION OF AGED DICAMBA RESIDUES IN SOIL

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effect of aging on dicamba (3,6-dichloro-2-methoxybenzoic acid) and a major metabolite, 3,6-dichlorosalicylic acid (3,6-DCSA) on sorption was determined in an unamended and a carbon-amended sandy loam soil. During the incubation, sequential solvent extraction with 0.01 N CaCl2 and aqueous aceto...

  9. Sorption studies of human keratinized tissues

    NASA Astrophysics Data System (ADS)

    Johnsen, G. K.; Martinsen, Ø. G.; Grimnes, Sverre

    2010-04-01

    Water content is known to be the most important single parameter for keratinized tissue to remain its vital functions. In that sense, a general knowledge of the water binding properties is of great interest, and a reliable measurement setup must be found. Also, revealing the sorption properties of human keratinized tissues is vital towards a calibration of susceptance based skin hydration measurements that already is an important diagnostic tool in clinical dermatology, and we will see that any hysteresis will complicate such a calibration further. In this study we investigated the sorption properties of keratinized tissues such as human epidermal stratum corneum (SC), hair and nail. The study was performed under controlled environmental conditions with a dynamic vapor sorption (DVS) instrument, and the water uptake of the keratinized test samples was measured as the relative humidity in the ambient air was altered step-wisely. In this study, vital and characteristic water sorption properties such as the isotherm, relative water uptake, and hysteresis were investigated and will be discussed.

  10. Sorption of deisopropylatrazine on broiler litter biochars

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biochars have received increasing attention in recent years for a large-scale soil amendment to improve soil fertility, immobilize contaminants, and to serve as a recalcitrant carbon stock. Information is currently lacking in factors controlling the sorption capacity of manure-derived biochars. In...

  11. Enhancement of the bentonite sorption properties.

    PubMed

    Mockovciaková, Annamária; Orolínová, Zuzana; Skvarla, Jirí

    2010-08-15

    The almost monomineral fraction of bentonite rock-montmorillonite was modified by magnetic particles to enhance its sorption properties. The method of clay modification consists in the precipitation of magnetic nanoparticles, often used in preparing of ferrofluids, on the surface of clay. The influence of the synthesis temperature (20 and 85 degrees C) and the weight ratio of bentonite/iron oxides (1:1 and 5:1) on the composite materials properties were investigated. The obtained materials were characterized by the X-ray diffraction method and Mössbauer spectroscopy. Changes in the surface and pore properties of the magnetic composites were studied by the low nitrogen adsorption method and the electrokinetic measurements. The natural bentonite and magnetic composites were used in sorption experiments. The sorption of toxic metals (zinc, cadmium and nickel) from the model solutions was well described by the linearized Langmuir and Freundlich sorption model. The results show that the magnetic bentonite is better sorbent than the unmodified bentonite if the initial concentration of studied metals is very low. PMID:20435410

  12. Sorption of polyphenolics (tannins) to natural soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Tannins enter soil systems via rainfall through the leaf canopy, leaf litter decomposition, and root exudation and decomposition. For tannins released into soils, the relative importance of sorption to soil; chemical reactions with soil minerals; and biological decomposition is unknown. Determinin...

  13. A fully implicit method for 3D quasi-steady state magnetic advection-diffusion.

    SciTech Connect

    Siefert, Christopher; Robinson, Allen Conrad

    2009-09-01

    We describe the implementation of a prototype fully implicit method for solving three-dimensional quasi-steady state magnetic advection-diffusion problems. This method allows us to solve the magnetic advection diffusion equations in an Eulerian frame with a fixed, user-prescribed velocity field. We have verified the correctness of method and implementation on two standard verification problems, the Solberg-White magnetic shear problem and the Perry-Jones-White rotating cylinder problem.

  14. Advection-Induced Spectrotemporal Defects in a Free-Electron Laser

    SciTech Connect

    Bielawski, S.; Szwaj, C.; Bruni, C.; Garzella, D.; Orlandi, G.L.; Couprie, M.E.

    2005-07-15

    We evidence numerically and experimentally that advection can induce spectrotemporal defects in a system presenting a localized structure. Those defects in the spectrum are associated with the breakings induced by the drift of the localized solution. The results are based on simulations and experiments performed on the super-ACO free-electron laser. However, we show that this instability can be generalized using a real Ginzburg-Landau equation with (i) advection and (ii) a finite-size supercritical region.

  15. Spectral approximation to advection-diffusion problems by the fictitious interface method

    NASA Astrophysics Data System (ADS)

    Frati, A.; Pasquarelli, F.; Quarteroni, A.

    1993-08-01

    The algorithmic aspects of the 'fictitious interface' method used in numerical approximations of convection-dominated flows are discussed. The solution algorithm presented alternates the advection-equation solution with that of the advection-diffusion equation within complementary subdomains. For the problems presently considered, spatial discretization is obtained by the spectral collocation method via Legendre-Gaussian modes. Attention is given to the the fictitious interface method's application to the Burgers equation.

  16. Characterization of cellulosic fibers and fabrics by sorption/desorption.

    PubMed

    Siroka, Barbora; Noisternig, Michael; Griesser, Ulrich J; Bechtold, Thomas

    2008-08-11

    Three cellulosic substrates: lyocell (CLY), viscose (CV), and modal (CMD) in the form of fibers and fabrics were subjected to wet/dry or wash/dry treatments. The accessibility of untreated and treated substrates to water and iodine was investigated using dynamic water-vapor sorption, moisture retention, and iodine sorption methods, to study the influence of treatments on sorption-desorption hysteresis, fraction of moisture sorbed as a monomolecular layer, water retention, and iodine sorption. It was found that the sorption properties of untreated and treated substrates differed with sorbate type as well as substrate type and form. PMID:18314097

  17. Modeling Fission Product Sorption in Graphite Structures

    SciTech Connect

    Szlufarska, Izabela; Morgan, Dane; Allen, Todd

    2013-04-08

    The goal of this project is to determine changes in adsorption and desorption of fission products to/from nuclear-grade graphite in response to a changing chemical environment. First, the project team will employ principle calculations and thermodynamic analysis to predict stability of fission products on graphite in the presence of structural defects commonly observed in very high- temperature reactor (VHTR) graphites. Desorption rates will be determined as a function of partial pressure of oxygen and iodine, relative humidity, and temperature. They will then carry out experimental characterization to determine the statistical distribution of structural features. This structural information will yield distributions of binding sites to be used as an input for a sorption model. Sorption isotherms calculated under this project will contribute to understanding of the physical bases of the source terms that are used in higher-level codes that model fission product transport and retention in graphite. The project will include the following tasks: Perform structural characterization of the VHTR graphite to determine crystallographic phases, defect structures and their distribution, volume fraction of coke, and amount of sp2 versus sp3 bonding. This information will be used as guidance for ab initio modeling and as input for sorptivity models; Perform ab initio calculations of binding energies to determine stability of fission products on the different sorption sites present in nuclear graphite microstructures. The project will use density functional theory (DFT) methods to calculate binding energies in vacuum and in oxidizing environments. The team will also calculate stability of iodine complexes with fission products on graphite sorption sites; Model graphite sorption isotherms to quantify concentration of fission products in graphite. The binding energies will be combined with a Langmuir isotherm statistical model to predict the sorbed concentration of fission

  18. Sorption of triazoles to soil and iron minerals.

    PubMed

    Jia, Yu; Aagaard, Per; Breedveld, Gijs D

    2007-02-01

    Triazoles, additives in runway de-icers, are found in soil and groundwater at airport sites. To better understand the fate and transport of benzotriazole (BTA) and methylbenzotriazole (MeBTA) and to assess possible remediation options of contaminated groundwater, sorption to various soils and ferrous sorbents has been studied. In batch experiments, limited non-linear sorption of BTA to mineral subsoil from the Oslo International Airport, Gardermoen was observed. The sorption to soil could be described using a Freundlich isotherm. pH affected sorption of BTA to subsoil, although the effect was not strong. Increased sorption was observed to zerovalent iron (Fe(0)). MeBTA showed similar sorption behaviour as BTA although the sorption coefficient was generally higher. Sorption to Fe(0) seems to be controlled by multi-layer coverage. Our data suggest that sorption of triazoles to Fe(2)O(3) is negligible. However BTA sorption to 2-line and 6-line ferrihydrites showed strong sorption. The results demonstrate that triazoles are highly mobile in the subsurface environment, however zerovalent iron can be an effective medium for groundwater remediation. Without remediation, wide distribution of triazoles in the environment can be expected due to its extensive application and limited degradability. PMID:17123582

  19. Radionuclide sorption on drill core material from the Canadian Shield

    SciTech Connect

    Vandergraat, T.T.; Abry, D.R.

    1982-06-01

    The sorption of four radionuclides, /sup 90/Sr, /sup 137/Cs, /sup 144/Ce, and /sup 237/Pu, on drill core material from two rock formations in the Canadian Shield has been studied as part of the Canadian Nuclear Fuel Waste Management Program. For all four radionuclides, sorption increased with increased mafic mineral content of the rock. Autoradiographic investigations showed enhanced sorption on dark, or mafic, minerals and high sorption on chlorite infilling material in a closed fracture. Desorption was less complete than sorption after the same equilibration time, indicating a degree of irreversible sorption, or slower desorption kinetics. The effect of surface roughness (measured by mercury porosimetry) on sorption was not as great as that of the chemical and mineral composition of the rock.

  20. Sorption kinetics of heavy oil into porous carbons.

    PubMed

    Nishi, Yoko; Iwashita, Norio; Sawada, Yoshihiro; Inagaki, Michio

    2002-12-01

    Sorption kinetics of heavy oil into porous carbons was evaluated by a concept of liquid sorption coefficient obtained from the weight increase of heavy oil with sorption time, which was measured by a wicking test. Exfoliated graphite, carbonized fir fibers and carbon fiber felts were used as porous materials. It was found that the liquid sorption coefficient of fibrous carbons was twice larger than that of exfoliated graphite. Such a difference in the liquid sorption coefficient between the exfoliated graphite and two fibrous carbons was caused by a difference in effective sorption porosity and tortuosity between them. For the exfoliated graphite and carbonized fir fibers, the liquid sorption coefficient and the effective sorption porosity were strongly dependent on their density. The maximum values of both liquid sorption coefficient and effective sorption porosity of the exfoliated graphite were shown at the bulk density around 16 kg/m3. The liquid sorption coefficient of the carbonized fir fibers increased with increasing the density in the range from 6 to 30 kg/m3. When the carbonized fir fibers were densified above 30 kg/m3, the sorption rate was saturated. On the other hand, the sorption kinetics into the carbon fiber felt was almost independent of the bulk density, because the density of the carbon fiber felt is not effective for the pore structure. The effect of bulk density on the sorption kinetics could be supported from an analysis of pore structure of the porous carbons with different densities, which was measured by mercury porosimeter. PMID:12448551

  1. Advective transport observations with MODPATH-OBS--documentation of the MODPATH observation process

    USGS Publications Warehouse

    Hanson, R.T.; Kauffman, L.K.; Hill, M.C.; Dickinson, J.E.; Mehl, S.W.

    2013-01-01

    The MODPATH-OBS computer program described in this report is designed to calculate simulated equivalents for observations related to advective groundwater transport that can be represented in a quantitative way by using simulated particle-tracking data. The simulated equivalents supported by MODPATH-OBS are (1) distance from a source location at a defined time, or proximity to an observed location; (2) time of travel from an initial location to defined locations, areas, or volumes of the simulated system; (3) concentrations used to simulate groundwater age; and (4) percentages of water derived from contributing source areas. Although particle tracking only simulates the advective component of conservative transport, effects of non-conservative processes such as retardation can be approximated through manipulation of the effective-porosity value used to calculate velocity based on the properties of selected conservative tracers. This program can also account for simple decay or production, but it cannot account for diffusion. Dispersion can be represented through direct simulation of subsurface heterogeneity and the use of many particles. MODPATH-OBS acts as a postprocessor to MODPATH, so that the sequence of model runs generally required is MODFLOW, MODPATH, and MODPATH-OBS. The version of MODFLOW and MODPATH that support the version of MODPATH-OBS presented in this report are MODFLOW-2005 or MODFLOW-LGR, and MODPATH-LGR. MODFLOW-LGR is derived from MODFLOW-2005, MODPATH 5, and MODPATH 6 and supports local grid refinement. MODPATH-LGR is derived from MODPATH 5. It supports the forward and backward tracking of particles through locally refined grids and provides the output needed for MODPATH_OBS. For a single grid and no observations, MODPATH-LGR results are equivalent to MODPATH 5. MODPATH-LGR and MODPATH-OBS simulations can use nearly all of the capabilities of MODFLOW-2005 and MODFLOW-LGR; for example, simulations may be steady-state, transient, or a combination

  2. Defluoridation by Bacteriogenic Iron Oxides: Sorption Studies

    NASA Astrophysics Data System (ADS)

    Evans, K.; Ferris, F.

    2009-05-01

    At concentrations above 1 mg/L, fluoride in drinking water can lead to dental and skeletal fluorosis, a disease that causes mottling of the teeth, calcification of ligaments, crippling bone deformities and many other physiological disorders that can, ultimately, lead to death. Conservative estimates are that fluorosis afflicts tens of millions of people worldwide. As there is no treatment for fluorosis, prevention is the only means of controlling the disease. While numerous defluoridation techniques have been explored, no single method has been found to be both effective and inexpensive enough to implement widely. Our research began in India, with a large-scale geochemical study of the groundwater in a fluoride-contaminated region of Orissa. Having developed a better understanding of the geochemical relationships that exist between fluoride and other parameters present in an affected area, as well as the complex relationships that arise among those parameters that can impact the presence of fluoride, we began investigating certain remediation scenarios involving iron oxides. A common approach to remediation involves the partitioning of fluoride from groundwater by sorption onto a variety of materials, one of the most effective of which is iron oxide whose surface area acts as a scavenger for fluoride. In the presence of iron oxidizing bacteria, the oxidation rate of iron has been shown to be ˜6 times greater than in their absence; fluoride should, therefore, be removed from an aqueous environment by bacteriogenic iron oxides (BIOS) much more quickly than by abiotic iron oxides. Most recently, sorption studies have been conducted using both BIOS and synthetic hydrous ferric oxides in order to compare the behavior between biotic and abiotic sorbents. These studies have provided sorption isotherms that allow comparison of fluoride removed by sorption to BIOS versus synthetic iron oxides. Sorption affinity constants have also been determined, which allow for the

  3. Sensitivity of Deep Soil Organic Carbon Age to Sorption, Transport and Microbial Interactions - Insights from a Calibrated Process Model

    NASA Astrophysics Data System (ADS)

    Ahrens, B.; Schrumpf, M.; Reichstein, M.

    2013-12-01

    Subsoil soil organic carbon (SOC) is characterized by conventional radiocarbon ages on the order of centuries to millennia. Most vertically explicit SOC turnover models represent this persistence of deep SOC by one pool that has millennial turnover times. This approach lumps different stabilizing mechanisms such as chemical recalcitrance, sorptive stabilization and energy limitation into a single rate constant. As an alternative, we present a continuous, vertically explicit SOC decomposition model that allows for stabilization via sorption and microbial interactions (COMISSION model). We compare the COMISSION model with the SOC profile of a Haplic Podzol under a Norway spruce forest. In the COMISSION model two pools receive aboveground litter input and vertically distributed root litter input. The readily leachable and soluble fraction of litter input enters a dissolved organic carbon pool (DOC), while the rest enters the residue pool which represents polymeric, non-soluble SOC. The residue pool is depolymerized with extracellular enzymes produced by a microbial pool to enter the DOC pool which represents SOC potentially available for assimilation by microbes. The adsorption/desorption of DOC from/to mineral surfaces controls the availability of carbon in the DOC pool for assimilatory uptake by microbes. The sorption of DOC is modeled with dynamic Langmuir equations. The desorbed part of the DOC pool not only constitutes the substrate for the microbial pool, but is also transported via advection. Interactions of microbes with the residue and DOC pool are modeled with Michaelis-Menten kinetics - this not only allows representing ';priming', but also the retardation of decomposition via energy limitation in the deep soil where substrate is scarce. Further, soil organic matter is recycled within the soil profile through microbial processing - dead microbes either enter the DOC or the residue pool, and thereby also contribute to longer residence times with soil depth

  4. Study of sorption of two sulfonylurea type of herbicides and their additives on soils and soil components.

    PubMed

    Földényi, Rita; Tóth, Zoltán; Samu, Gyöngyi; Érsek, Csaba

    2013-01-01

    The sorption of two sulfonylurea type herbicides (chlorsulfuron: (1-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea; tribenuron methyl: (methyl-2-[N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-3-(methyl-ureido)-sulfonyl]-benzoate) was studied on sand and chernozem soil adsorbents. Experimental results for solutions prepared from the pure ingredients were compared to those prepared from the appropriate formulated commercial products. At small concentrations, the extent of adsorption of the active ingredient was higher than from the formulation containing solutions. Environmental fate and effects of the forming agents are less investigated because they rarely have concentration limits recommended by authorities. In addition to the adsorption of active ingredients, therefore, the sorption behavior of a widely used additive Supragil WP (sodium diisopropyl naphthalene sulphonate) was also studied. This dispersant is an anionic forming agent applied in a lot of pesticide formulations. Using three different soils (sand, brown forest, chernozem) as adsorbents two-step isotherms were obtained. The role of the soil organic matter (OM) was significant in the adsorption mechanism because the adsorbed amounts of the dispersant correlated with the specific surface area as well as with the total organic carbon (TOC) content of the soils. The sorption behavior indicates the operation of hydrophobic interaction mechanism between the soil OM and the dispersant. These results are supported by our further sorption experiments on clays, too. Zeta potential measurements seem to be promising for the interpretation of multi-step isotherms. The application of this technique proved that higher concentrations of the anionic forming agent assisted the peptization of soil organic matter (SOM) resulting in stable colloidal solution dominated by negative charges. Since the pesticides investigated are also anionic at the studied pH (7 and 8.3) the dissolved organics lead to the

  5. Numerical modelling of mesoscale atmospheric dispersion, volumes 1 and 2

    NASA Astrophysics Data System (ADS)

    Moran, Michael D.

    Mesoscale atmospheric dispersion is more complicated than smaller scale dispersion because the mean wind field can no longer be considered steady or horizontally homogeneous over mesoscale time and space scales. Wind shear also plays a more important role on the mesoscale and horizontal dispersion can be enhanced and even dominated by vertical wind shear through either the simultaneous or delayed interaction of horizontal differential advection and vertical mixing over one or two diurnal periods. The CSU mesoscale atmospheric dispersion modeling system was used to simulate the transport and diffusion of a perfluorocarbon gas for episodic releases made during two North American mesoscale dispersion field experiments, the 1980 Great Plains tracer experiment and the 1983 Cross-Appalachian Tracer Experiment (CAPTEX). Ground-level and elevated tracer concentrations were measured out to distances of 600 km from the source in the first experiment and 1100 km in the second. The physiography of the two experimental domains was quite different, permitting isolation and examination of the roles of terrain forcing and differential advection in mesoscale atmospheric dispersion. Suites of numerical experiments of increasing complexity were carried out for both case studies. The experiments differed in the realism of their representation of both the synoptic-scale flow and the underlying terrain. The Great Plains nocturnal low-level jet played an important role in the first case while temporal changes in the synoptic-scale flow were very significant in the second case. The contributions of differential advection and mesoscale deformation to mesoscale dispersion dominated those of small-scale turbulent diffusion for both cases, and Pasquills delayed-shear-enhancement mechanism for lateral dispersion was found to be particularly important. The first quantitative evaluation of the CSU mesoscale dispersion modeling system with episodic mesoscale dispersion field data was presented

  6. Influence of porewater advection on denitrification in carbonate sands: Evidence from repacked sediment column experiments

    NASA Astrophysics Data System (ADS)

    Santos, Isaac R.; Eyre, Bradley D.; Glud, Ronnie N.

    2012-11-01

    Porewater flow enhances mineralization rates in organic-poor permeable sands. Here, a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from Heron Island (Great Barrier Reef). Experimental conditions (flow path length, advection rate, and temperature) were manipulated to represent conditions similar to near shore tropical environments. HgCl2-poisoned controls were used to assess whether reactions were microbially mediated. Overall, significant correlations were found between oxygen consumption and N2 production. The N:O2 slope of 0.114 implied that about 75% of all the nitrogen mineralized was denitrified. A 4-fold increase in sediment column length (from 10 to 40 cm) resulted in an overall increase in oxygen consumption (1.6-fold), TCO2 production (1.8-fold), and denitrification (1.9-fold). Oxic respiration increased quickly until advection reached 80 L m-2 h-1 and then plateaued at higher advection rates. Interestingly, denitrification peaked (up to 336 μmol N2 m-2 h-1) at intermediate advection rates (30-80 L m-2 h-1). We speculate that intermediate advection rates enhance the development of microniches (i.e., steep oxygen gradients) within porous carbonate sands, perhaps providing optimum conditions for denitrification. The denitrification peak fell within the broad range of advection rates (often on scales of 1-100 L m-2 h-1) typically found on continental shelves implying that carbonate sands may play a major, but as yet unquantified, role in oceanic nitrogen budgets.

  7. Shear dispersion in a capillary tube with a porous wall

    NASA Astrophysics Data System (ADS)

    Dejam, Morteza; Hassanzadeh, Hassan; Chen, Zhangxin

    2016-02-01

    An analytical expression is presented for the shear dispersion during solute transport in a coupled system comprised of a capillary tube and a porous medium. The dispersion coefficient is derived in a capillary tube with a porous wall by considering an accurate boundary condition, which is the continuity of concentration and mass flux, at the interface between the capillary tube and porous medium. A comparison of the obtained results with that in a non-coupled system identifies three regimes including: diffusion-dominated, transition, and advection-dominated. The results reveal that it is essential to include the exchange of solute between the capillary tube and porous medium in development of the shear dispersion coefficient for the last two regimes. The resulting equivalent transport equation revealed that due to mass transfer between the capillary tube and the porous medium, the dispersion coefficient is decreased while the effective velocity in the capillary tube increases. However, a larger effective advection term leads to faster breakthrough of a solute and enhances mass delivery to the porous medium as compared with the classical double-porosity model with a non-coupled dispersion coefficient. The obtained results also indicate that the finite porous medium gives faster breakthrough of a solute as compared with the infinite one. These results find applications in solute transport in porous capillaries and membranes.

  8. Shear dispersion in a capillary tube with a porous wall.

    PubMed

    Dejam, Morteza; Hassanzadeh, Hassan; Chen, Zhangxin

    2016-01-01

    An analytical expression is presented for the shear dispersion during solute transport in a coupled system comprised of a capillary tube and a porous medium. The dispersion coefficient is derived in a capillary tube with a porous wall by considering an accurate boundary condition, which is the continuity of concentration and mass flux, at the interface between the capillary tube and porous medium. A comparison of the obtained results with that in a non-coupled system identifies three regimes including: diffusion-dominated, transition, and advection-dominated. The results reveal that it is essential to include the exchange of solute between the capillary tube and porous medium in development of the shear dispersion coefficient for the last two regimes. The resulting equivalent transport equation revealed that due to mass transfer between the capillary tube and the porous medium, the dispersion coefficient is decreased while the effective velocity in the capillary tube increases. However, a larger effective advection term leads to faster breakthrough of a solute and enhances mass delivery to the porous medium as compared with the classical double-porosity model with a non-coupled dispersion coefficient. The obtained results also indicate that the finite porous medium gives faster breakthrough of a solute as compared with the infinite one. These results find applications in solute transport in porous capillaries and membranes. PMID:26845232

  9. Sorption modelling on illite. Part II: Actinide sorption and linear free energy relationships

    NASA Astrophysics Data System (ADS)

    Bradbury, M. H.; Baeyens, B.

    2009-02-01

    Sorption edge data for Ni(II), Co(II), Eu(III) and Sn(IV) [Bradbury M. H. and Baeyens B. (2009) Sorption modelling on illite. Part I: titration measurements and sorption of Ni(II), Co(II), Eu(III) and Sn(IV), Part I] on purified Na-Illite du Puy are available from some previous work, and some new measurements for Am(III), Th(IV), Pa(V) and U(VI) are presented here. All of these sorption edge measurements have been modelled with a 2 site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) sorption model for which the site types, site capacities and protolysis constants were fixed [Bradbury M. H. and Baeyens B. (2009), Part I]. In addition, two further data sets for the sorption of Am(III) and Np(V) on Illite du Puy, obtained from the literature, were also modelled in this work. Thus, surface complexation constants for the strong sites in the 2SPNE SC/CE sorption model for nine metals with valence states from II to VI have been obtained. A linear relationship between the logarithm of strong site metal binding constants, SK x-1, and the logarithm of the corresponding aqueous hydrolysis stability constant, OHK x, extending over nearly 35 orders of magnitude is established here for illite for these nine metals. Such correlations are often termed linear free energy relationships (LFER), and although they are quite common in aqueous phase chemistry, they are much less so in surface chemistry, especially over this large range. The LFER for illite could be described by the equation: logSK=7.9±0.4+(0.83±0.02)logOHKx where, " x" is an integer. A similar relationship has been previously obtained for montmorillonite, thus LFERs relating to the sorption on two of the most important clay minerals present in natural systems have been established. Such an LFER approach is an extremely useful tool for estimating surface complexation constants for metals in a chemically consistent manner. It provides a means of obtaining sorption values for

  10. Sorption kinetics and its effects on retention and leaching.

    PubMed

    de Wilde, Tineke; Mertens, Jan; Spanoghe, Pieter; Ryckeboer, Jaak; Jaeken, Peter; Springael, Dirk

    2008-06-01

    Sorption of pesticides to substrates used in biopurification systems is important as it controls the system's efficiency. Ideally, pesticide sorption should occur fast so that leaching of the pesticide in the biopurification system is minimized. Although modeling of pesticide transport commonly assumes equilibrium, this may not always be true in practice. Sorption kinetics have to be taken into account. This study investigated the batch sorption kinetics of linuron, isoproturon, metalaxyl, isoxaben and lenacil on substrates commonly used in a biopurification system, i.e. cow manure, straw, willow chopping, sandy loam soil, coconut chips, garden waste compost and peat mix. The first-order sorption kinetics model was fitted to the observed pesticide concentrations versus time resulting in an estimated kinetic rate constant alpha. Sorption appeared to be fast for the pesticides linuron and isoxaben, pesticides which were classified as immobile, while less mobile pesticides displayed an overall slower sorption. However, the substrate does not seem to be the main parameter influencing the sorption kinetics. Coconut chips, which is a substrate with a high organic matter content showed slow sorption for most of the pesticides. The effect of different estimated alpha values on the breakthrough of pesticides through a biopurification system was evaluated using the HYDRUS 1D model. Significant differences in leaching behavior were observed as a result of the obtained differences in sorption kinetics. PMID:18413279

  11. Sorption Modeling and Verification for Off-Gas Treatment

    SciTech Connect

    Tavlarides, Lawrence L.; Lin, Ronghong; Nan, Yue; Yiacoumi, Sotira; Tsouris, Costas; Ladshaw, Austin; Sharma, Ketki; Gabitto, Jorge; DePaoli, David

    2015-04-29

    The project has made progress toward developing a comprehensive modeling capability for the capture of target species in off gas evolved during the reprocessing of nuclear fuel. The effort has integrated experimentation, model development, and computer code development for adsorption and absorption processes. For adsorption, a modeling library has been initiated to include (a) equilibrium models for uptake of off-gas components by adsorbents, (b) mass transfer models to describe mass transfer to a particle, diffusion through the pores of the particle and adsorption on the active sites of the particle, and (c) interconnection of these models to fixed bed adsorption modeling which includes advection through the bed. For single-component equilibria, a Generalized Statistical Thermodynamic Adsorption (GSTA) code was developed to represent experimental data from a broad range of isotherm types; this is equivalent to a Langmuir isotherm in the two-parameter case, and was demonstrated for Kr on INL-engineered sorbent HZ PAN, water sorption on molecular sieve A sorbent material (MS3A), and Kr and Xe capture on metal-organic framework (MOF) materials. The GSTA isotherm was extended to multicomponent systems through application of a modified spreading pressure surface activity model and generalized predictive adsorbed solution theory; the result is the capability to estimate multicomponent adsorption equilibria from single-component isotherms. This advance, which enhances the capability to simulate systems related to off-gas treatment, has been demonstrated for a range of real-gas systems in the literature and is ready for testing with data currently being collected for multicomponent systems of interest, including iodine and water on MS3A. A diffusion kinetic model for sorbent pellets involving pore and surface diffusion as well as external mass transfer has been established, and a methodology was developed for determining unknown diffusivity parameters from transient

  12. Chemo-mechanical modification of cottonwood for Pb(2+) removal from aqueous solutions: Sorption mechanisms and potential application as biofilter in drip-irrigation.

    PubMed

    Mosa, Ahmed; El-Ghamry, Ayman; Trüby, Peter; Omar, Mahmoud; Gao, Bin; Elnaggar, Abdelhamid; Li, Yuncong

    2016-10-01

    Using biomass (e.g. crop residues) and its derivatives as biosorbents have been recognized as an eco-friendly technique for wastewater decontamination. In this study, mechanically modified cottonwood was further activated with KOH to improve its sorption of Pb(2+). In addition, its potential as a biofilter to safeguard radish (Raphanus sativus, L.) against Pb-stress was evaluated in a gravity-fed drip irrigation system. Physiochemical properties of the chemo-mechanically activated cottonwood (CMACW) and the mechanically activated cottonwood (MACW) before and after sorption process were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), digital selected-area electron diffraction (SAED) and Fourier transform infrared spectroscopy (FTIR). After activation, several sorption mechanisms (i.e. precipitation, electrostatic outer- and inner-sphere complexation) were responsible for the higher sorption capacity of CMACW as compared with MACW (8.55 vs. 7.28 mg g(-1)). Sorption kinetics and isotherms fitted better with the pseudo-second-order and Langmuir models as compared with the pseudo-first-order and Freundlich models, respectively. In the gravity-fed drip irrigation system, the CMACW biofilter reduced the accumulation of Pb in radish roots and shoots and avoided reaching the toxic limits in some cases. Soil types had a significant effect on Pb(2+) bioavailability because of the difference in sorption ability. Findings from this study showed that CMACW biofilter can be used as a safeguard for wastewater irrigation. PMID:27393935

  13. Effect of natural organic materials on cadmium and neptunium sorption

    SciTech Connect

    Kung, K.S.; Triay, I.R.

    1994-10-01

    In a batch sorption study of the effect of naturally occurring organic materials on the sorption of cadmium and neptunium on oxides and tuff surfaces, the model sorbents were synthetic goethite, boehmite, amorphous silicon oxides, and a crushed tuff material from Yucca Mountain, Nevada. An amino acid, 3-(3,4-dihydroxypheny)-DL-alanine (DOPA), and an aquatic-originated fulvic material, Nordic aquatic fulvic acid (NAFA), were used as model organic chemicals. Sorption isotherm results showed that DOPA sorption followed the order aluminum oxide > iron oxide > silicon oxide and that the amount of DOAP sorption for a given sorbent increased as the solution pH was raised. The sorption of cadmium and neptunium on the iron oxide was about ten times higher than that on the aluminum oxide. The sorption of cadmium and neptunium on natural tuff material was much lower than that on aluminum and iron oxides. The sorption of cadmium on iron and aluminum oxides was found to be influenced by the presence of DOPA, and increasing the amount of DOPA coating resulted in higher cadmium sorption on aluminum oxide. However, for iron oxide, cadmium sorption decreased with increasing DOPA concentration. The presence of the model organic materials DOPA and NAFA did not affect the sorption of neptunium on tuff material or on the iron and aluminum oxides. Spectroscopic results indicate that cadmium complexes strongly with DOPA. Therefore, the effect of the organic material, DOPA, on the cadmium sorption is readily observed. However, neptunium is possibly complexed weakly with organic material. Thus, DOPA and NAFA have little effect on neptunium sorption on all sorbents selected for study.

  14. Residual insecticides and the problem of sorption

    PubMed Central

    Bertagna, P.

    1959-01-01

    Whereas laboratory investigations have elucidated the mechanism of sorption of residual insecticides and demonstrated that their persistency is determined by a number of physico-chemical factors and is therefore theoretically calculable, the variables encountered in the field may produce results in apparent conflict with those theoretically expected. Attempts to enhance persistency through the prevention of sorption, although promising, have so far not been fully successful. It is consequently also necessary to assess the residual effectiveness of insecticides, “effectiveness” here being viewed as a biological effect expressed in terms of the mosquito mortality produced. For this purpose bio-assay tests have been used, but with very variable results, and it is suggested that a study of the bio-assay technique itself is needed. This should be conducted in parallel with chemical determinations of the total amount of insecticide present both on and below the sprayed surface. PMID:13799942

  15. Colloidal Dispersions

    NASA Astrophysics Data System (ADS)

    Russel, W. B.; Saville, D. A.; Schowalter, W. R.

    1992-03-01

    The book covers the physical side of colloid science from the individual forces acting between submicron particles suspended in a liquid through the resulting equilibrium and dynamic properties. The relevant forces include Brownian motion, electrostatic repulsion, dispersion attraction, both attraction and repulsion due to soluble polymer, and viscous forces due to relative motion between the particles and the liquid. The balance among Brownian motion and the interparticle forces decides the questions of stability and phase behavior. Imposition of external fields produces complex effects, i.e. electrokinetic phenomena (electric field), sedimentation (gravitational field), diffusion (concentration/chemical potential gradient), and non-Newtonian rheology (shear field). The treatment aims to impart a sound, quantitative understanding based on fundamental theory and experiments with well-characterized model systems. This broad grasp of the fundamentals lends insight and helps to develop the intuitive sense needed to isolate essential features of technological problems and design critical experiments. Some exposure to fluid mechanics, statistical mechanics, and electricity and magnetism is assumed, but each subject is reintroduced in a self-contained manner.

  16. Advection and resulting CO2 exchange uncertainty in a tall forest in central Germany.

    PubMed

    Kutsch, Werner L; Kolle, Olaf; Rebmann, Corinna; Knohl, Alexander; Ziegler, Waldemar; Schulze, Ernst-Detlef

    2008-09-01

    Potential losses by advection were estimated at Hainich Forest, Thuringia, Germany, where the tower is located at a gentle slope. Three approaches were used: (1) comparing nighttime eddy covariance fluxes to an independent value of total ecosystem respiration by bottom-up modeling of the underlying processes, (2) direct measurements of a horizontal CO2 gradient and horizontal wind speed at 2 m height in order to calculate horizontal advection, and (3) direct measurements of a vertical CO2 gradient and a three-dimensional wind profile in order to calculate vertical advection. In the first approach, nighttime eddy covariance measurements were compared to independent values of total ecosystem respiration by means of bottom-up modeling of the underlying biological processes. Turbulent fluxes and storage term were normalized to the fluxes calculated by the bottom-up model. Below a u(*) threshold of 0.6 m/s the normalized turbulent fluxes decreased with decreasing u(*), but the flux to the storage increased only up to values less than 20% of the modeled flux at low turbulence. Horizontal advection was measured by a horizontal CO2 gradient over a distance of 130 m combined with horizontal wind speed measurements. Horizontal advection occurred at most of the evenings independently of friction velocity above the canopy. Nevertheless, horizontal advection was higher when u(*) was low. The peaks of horizontal advection correlated with changes in temperature. A full mass balance including turbulent fluxes, storage, and horizontal and vertical advection resulted in an increase of spikes and scatter but seemed to generally improve the results from the flux measurements. The comparison of flux data with independent bottom-up modeling results as well as the direct measurements resulted in strong indications that katabatic flows along the hill slope during evening and night reduces the measured apparent ecosystem respiration rate. In addition, anabatic flows may occur during the

  17. Advection of Microphysical Scalars in Terminal Area Simulation System (TASS)

    NASA Technical Reports Server (NTRS)

    Ahmad, Nashat N.; Proctor, Fred H.

    2011-01-01

    The Terminal Area Simulation System (TASS) is a large eddy scale atmospheric flow model with extensive turbulence and microphysics packages. It has been applied successfully in the past to a diverse set of problems ranging from prediction of severe convective events (Proctor et al. 2002), tracking storms and for simulating weapons effects such as the dispersion and fallout of fission debris (Bacon and Sarma 1991), etc. More recently, TASS has been used for predicting the transport and decay of wake vortices behind aircraft (Proctor 2009). An essential part of the TASS model is its comprehensive microphysics package, which relies on the accurate computation of microphysical scalar transport. This paper describes an evaluation of the Leonard scheme implemented in the TASS model for transporting microphysical scalars. The scheme is validated against benchmark cases with exact solutions and compared with two other schemes - a Monotone Upstream-centered Scheme for Conservation Laws (MUSCL)-type scheme after van Leer and LeVeque's high-resolution wave propagation method. Finally, a comparison between the schemes is made against an incident of severe tornadic super-cell convection near Del City, Oklahoma.

  18. Mathematical modeling of non-equilibrium sorption

    NASA Astrophysics Data System (ADS)

    Kaliev, Ibragim A.; Mukhambetzhanov, Saltanbek T.; Sabitova, Gulnara S.; Sakhit, Anghyz E.

    2016-08-01

    We consider the system of equations modeling the process of non-equilibrium sorption. Difference approximation of differential problem by the implicit scheme is formulated. The solution of the difference problem is constructed using the sweep method. Based on the numerical results we can conclude the following: when the relaxation time decreases to 0, then the solution of non-equilibrium problem tends with increasing time to solution of the equilibrium problem.

  19. Fast, Low-Duty-Cycle Sorption Refrigerators

    NASA Technical Reports Server (NTRS)

    Johnson, AL; Jones, Jack A.

    1994-01-01

    Metal hydride/hydrogen-sorption refrigerators developed to provide rapid, intermittent cooling at temperatures between 30 and 10 K. In original application, refrigerators cool infrared detectors aboard spacecraft, exhausting heat to outer space via radiators at 250 K. Modified to cool scientific instrumentation on Earth with some loss of efficiency. Require no power during quick cooldown and low heating power during relatively long recharge periods.

  20. Sorption of strontium on clinoptilolite and heulandite

    SciTech Connect

    Chernyavskaya, N.B.

    1986-05-01

    The author investigates the sorption of strontium on the isostructural zeolites clinoptilolite and heulandite. In the Sr/Na/zeolite/H/sub 2/O system, clinoptilolite manifests selectivity for strontium, and heulandite for sodium. The role of the nature of the exchange ions is discussed. Modification of the clinoptilolite with acid, subsequently obtaining the Na, NH/sub 4/, or N/sub 2/H/sub 4/ form, increases the capacity for strontium by a factor of 2-4.

  1. Modeling of Convective-Stratiform Precipitation Processes: Sensitivity to Partitioning Methods and Numerical Advection Schemes

    NASA Technical Reports Server (NTRS)

    Lang, Steve; Tao, W.-K.; Simpson, J.; Ferrier, B.; Einaudi, Franco (Technical Monitor)

    2001-01-01

    Six different convective-stratiform separation techniques, including a new technique that utilizes the ratio of vertical and terminal velocities, are compared and evaluated using two-dimensional numerical simulations of a tropical [Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE)] and midlatitude continental [Preliminary Regional Experiment for STORM-Central (PRESTORM)] squall line. The simulations are made using two different numerical advection schemes: 4th order and positive definite advection. Comparisons are made in terms of rainfall, cloud coverage, mass fluxes, apparent heating and moistening, mean hydrometeor profiles, CFADs (Contoured Frequency with Altitude Diagrams), microphysics, and latent heating retrieval. Overall, it was found that the different separation techniques produced results that qualitatively agreed. However, the quantitative differences were significant. Observational comparisons were unable to conclusively evaluate the performance of the techniques. Latent heating retrieval was shown to be sensitive to the use of separation technique mainly due to the stratiform region for methods that found very little stratiform rain. The midlatitude PRESTORM simulation was found to be nearly invariant with respect to advection type for most quantities while for TOGA COARE fourth order advection produced numerous shallow convective cores and positive definite advection fewer cells that were both broader and deeper penetrating above the freezing level.

  2. A Novel Electrical Model for Advection-Diffusion-Based Molecular Communication in Nanonetworks.

    PubMed

    Azadi, Mehdi; Abouei, Jamshid

    2016-04-01

    In this paper, we propose an end-to-end electrical model to characterize the communication between two nanomachines via advection-diffusion motion along the conventional pipe medium. For this modeling, we consider three modules consisting of transmitter, advection-diffusion propagation and receiver. The modulation scheme and releasing molecules through the conventional pipe medium from the transmitter nanomachine is represented in the transmitter module. The advection-diffusion propagation of molecules along the flow-induced path is shown in advection-diffusion propagation module, and the demodulation scheme of bounded particles at the receiver nanomachine is characterized in the receiver module. Our objective is to find an electrical model of each module under the zero initial condition which enables us to represent the electrical circuit related to each module. The transmitter and the signal propagation models are built on the basis of the molecular advection-diffusion physics, whereas the receiver model is interpreted by stemming from the theory of the ligand-receptor binding chemical process. In addition, we employ the transfer function of modules to derive the normalized gain and the delay of each module. Supported by numerical results, we analyze the effect of physical parameters of the pipe medium on the total normalized gain and delay of molecular communications. PMID:27046879

  3. Estimation of the advection effects induced by surface heterogeneities in the surface energy budget

    NASA Astrophysics Data System (ADS)

    Cuxart, Joan; Wrenger, Burkhard; Martínez-Villagrasa, Daniel; Reuder, Joachim; Jonassen, Marius O.; Jiménez, Maria A.; Lothon, Marie; Lohou, Fabienne; Hartogensis, Oscar; Dünnermann, Jens; Conangla, Laura; Garai, Anirban

    2016-07-01

    The effect of terrain heterogeneities in one-point measurements is a continuous subject of discussion. Here we focus on the order of magnitude of the advection term in the equation of the evolution of temperature as generated by documented terrain heterogeneities and we estimate its importance as a term in the surface energy budget (SEB), for which the turbulent fluxes are computed using the eddy-correlation method. The heterogeneities are estimated from satellite and model fields for scales near 1 km or broader, while the smaller scales are estimated through direct measurements with remotely piloted aircraft and thermal cameras and also by high-resolution modelling. The variability of the surface temperature fields is not found to decrease clearly with increasing resolution, and consequently the advection term becomes more important as the scales become finer. The advection term provides non-significant values to the SEB at scales larger than a few kilometres. In contrast, surface heterogeneities at the metre scale yield large values of the advection, which are probably only significant in the first centimetres above the ground. The motions that seem to contribute significantly to the advection term in the SEB equation in our case are roughly those around the hectometre scales.

  4. Multicomponent gas sorption Joule-Thomson refrigeration

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor); Petrick, S. Walter (Inventor); Bard, Steven (Inventor)

    1991-01-01

    The present invention relates to a cryogenic Joule-Thomson refrigeration capable of pumping multicomponent gases with a single stage sorption compressor system. Alternative methods of pumping a multicomponent gas with a single stage compressor are disclosed. In a first embodiment, the sorbent geometry is such that a void is defined near the output of the sorption compressor. When the sorbent is cooled, the sorbent primarily adsorbs the higher boiling point gas such that the lower boiling point gas passes through the sorbent to occupy the void. When the sorbent is heated, the higher boiling point gas is desorbed at high temperature and pressure and thereafter propels the lower boiling point gas out of the sorption compressor. A mixing chamber is provided to remix the constituent gases prior to expansion of the gas through a Joule-Thomson valve. Other methods of pumping a multicomponent gas are disclosed. For example, where the sorbent is porous and the low boiling point gas does not adsorb very well, the pores of the sorbent will act as a void space for the lower boiling point gas. Alternatively, a mixed sorbent may be used where a first sorbent component physically adsorbs the high boiling point gas and where the second sorbent component chemically absorbs the low boiling point gas.

  5. Lead sorption-desorption from organic residues.

    PubMed

    Duarte Zaragoza, Victor M; Carrillo, Rogelio; Gutierrez Castorena, Carmen M

    2011-01-01

    Sorption and desorption are mechanisms involved in the reduction of metal mobility and bioavailability in organic materials. Metal release from substrates is controlled by desorption. The capacity of coffee husk and pulp residues, vermicompost and cow manure to adsorb Pb2+ was evaluated. The mechanisms involved in the sorption process were also studied. Organic materials retained high concentrations of lead (up to 36,000 mg L(-1)); however, the mechanisms of sorption varied according to the characteristics of each material: degree of decomposition, pH, cation exchange capacity and percentage of organic matter. Vermicompost and manure removed 98% of the Pb from solution. Lead precipitated in manure and vermicompost, forming lead oxide (PbO) and lead ferrite (PbFe4O7). Adsorption isotherms did not fit to the typical Freundlich and Langmuir equations. Not only specific and non-specific adsorption was observed, but also precipitation and coprecipitation. Lead desorption from vermicompost and cow manure was less than 2%. For remediation of Pb-polluted sites, the application of vermicompost and manure is recommended in places with alkaline soils because Pb precipitation can be induced, whereas coffee pulp residue is recommended for acidic soils where Pb is adsorbed. PMID:21780703

  6. Sorption and degradation of four nitroaromatic herbicides in mono and multi-solute saturated/unsaturated soil batch systems

    NASA Astrophysics Data System (ADS)

    Martins, Jean M.; Mermoud, André

    1998-09-01

    This paper presents a study on sorption and degradation processes involved in the fate of nitroaromatic herbicides in an alluvial sandy loam. Particular attention was given to a competitive sorption process and its impact on herbicide biodegradation through bioavailability modification. The main question addressed was the occurrence of antagonistic or synergistic effects in herbicide mixtures. Approaching the problem by using a herbicide combination, it was demonstrated that the more soluble herbicides strongly decreased the sorption of the more hydrophobic ones on the soil organic fraction. Conversely, ionic strength was shown to increase sorption levels dramatically. These results prove that soil solution chemistry is a relevant factor to be taken into account in pesticide behaviour studies. Herbicide biodegradation was studied with the same approach, and the results revealed that degradation of a particular dinitrophenol is affected by the presence of similar molecules. In well-dispersed soil suspensions where herbicide/micro-organism contact is optimal, toxicity was shown to increase herbicide persistence and to be the controlling factor of biodegradation. Conversely, persistence in repacked unsaturated soil batches was strongly decreased in both mono and multi-solute systems. In such solid batches, the soil structure imposed mass transfer kinetics which modify micro-organism/herbicide contact and decreased toxicity effects. Furthermore, the competitive sorption observed in multi-solute systems was supposed to be responsible for the observed increase of herbicide biodegradation presumably by keeping molecules bioavailable for microbial attack. These results support the assumption that soils are divided into two compartments presenting different capacities in regard to chemical sorption and biodegradation, which could be a basis for explaining chemical aging in soil. This study providing new information on physico-chemical control of pollutant biodegradation in

  7. Manganese oxide-modified biochars: preparation, characterization, and sorption of arsenate and lead.

    PubMed

    Wang, Shengsen; Gao, Bin; Li, Yuncong; Mosa, Ahmed; Zimmerman, Andrew R; Ma, Lena Q; Harris, Willie G; Migliaccio, Kati W

    2015-04-01

    This work explored two modification methods to improve biochar's ability to sorb arsenic (As) and lead (Pb). In one, pine wood feedstock was pyrolyzed in the presence of MnCl2·4H2O (MPB) and in the other it was impregnated with birnessite via precipitation following pyrolysis (BPB). The resulting biochars were characterized using thermogravimetry, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analyses. The dominant crystalline forms of Mn oxides in the MPB and BPB were manganosite and birnessite, respectively. Batch sorption studies were carried out to determine the kinetics and magnitude of As(V) and Pb(II) onto the biochars. As(V) and Pb(II) sorption capacities of MPB (0.59 and 4.91 g/kg) and BPB (0.91 and 47.05 g/kg) were significantly higher than that of the unmodified biochar (0.20 and 2.35 g/kg). BPB showed the highest sorption enhancement because of the strong As(V) and Pb(II) affinity of its birnessite particles. PMID:25625462

  8. Assessing the effect of humic acid redox state on organic pollutant sorption by combined electrochemical reduction and sorption experiments.

    PubMed

    Aeschbacher, Michael; Brunner, Sibyl H; Schwarzenbach, René P; Sander, Michael

    2012-04-01

    Natural Organic Matter (NOM) is a major sorbent for organic pollutants in soils and sediments. While sorption under oxic conditions has been well investigated, possible changes in the sorption capacity of a given NOM induced by reduction have not yet been studied. Reduction of quinones to hydroquinones, the major redox active moieties in NOM, increases the number of H-donor moieties and thus may affect sorption. This work compares the sorption of four nonionic organic pollutants of different polarities (naphthalene, acetophenone, quinoline, and 2-naphthol), and of the organocation paraquat to unreduced and electrochemically reduced Leonardite Humic Acid (LHA). The redox states of reduced and unreduced LHA in all sorption experiments were stable, as demonstrated by a spectrophotometric 2,6-dichlorophenol indophenol reduction assay. The sorption isotherms of the nonionic pollutants were highly linear, while paraquat sorption was strongly concentration dependent. LHA reduction did not result in significant changes in the sorption of all tested compounds, not even of the cationic paraquat at pH 7, 9, and 11. This work provides the first evidence that changes in NOM redox state do not largely affect organic pollutant sorption, suggesting that current sorption models are applicable both to unreduced and to reduced soil and sediment NOM. PMID:22372874

  9. A statistical case against the use of the Langmuir model for describing P sorption data

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sorption of P to soils is often investigated through batch experiments where sorption models are fit to the resultant sorption curve by least-squares regression. One of the most commonly used sorption models is the Langmuir model, a model which was originally developed for the study of gas sorption ...

  10. The influence of clay surface modification with berberine on the sorption of anthocyanins

    NASA Astrophysics Data System (ADS)

    Chulkov, A. N.; Deineka, V. I.; Tikhova, A. A.; Vesentzev, A. I.; Deineka, L. A.

    2012-03-01

    The influence of preliminary sorption of berberine on the sorption of anthocyanins by bentonite clay was studied. The cation exchange sorption mechanism was found to be replaced by hydrophobic sorption of these compounds after clay modification with berberine. The enthalpy of sorption along the initial isotherm part changed from endothermic to exothermic.

  11. Advection of methane in the hydrate zone: model, analysis and examples

    NASA Astrophysics Data System (ADS)

    Peszynska, Malgorzata; Showalter, Ralph E.; Webster, Justin T.

    2015-12-01

    A two-phase two-component model is formulated for the advective-diffusive transport of methane in liquid phase through sediment with the accompanying formation and dissolution of methane hydrate. This free-boundary problem has a unique generalized solution in $L^1$; the proof combines analysis of the stationary semilinear elliptic Dirichlet problem with the nonlinear semigroup theory in Banach space for an m-accretive multi-valued operator. Additional estimates of maximum principle type are obtained, and these permit appropriate maximal extensions of the phase-change relations. An example with pure advection indicates the limitations of these estimates and of the model developed here. We also consider and analyze the coupled pressure equation that determines the advective flux in the transport model.

  12. Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample

    NASA Astrophysics Data System (ADS)

    Ebner, Pirmin Philipp; Schneebeli, Martin; Steinfeld, Aldo

    2016-04-01

    Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray microtomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Cold saturated air at the inlet was blown into the snow samples and warmed up while flowing across the sample with a temperature gradient of around 50 K m-1. Changes of the porous ice structure were observed at mid-height of the snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.

  13. First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems

    NASA Technical Reports Server (NTRS)

    Mazaheri, Alireza; Nishikawa, Hiroaki

    2014-01-01

    A time-dependent extension of the first-order hyperbolic system method for advection-diffusion problems is introduced. Diffusive/viscous terms are written and discretized as a hyperbolic system, which recovers the original equation in the steady state. The resulting scheme offers advantages over traditional schemes: a dramatic simplification in the discretization, high-order accuracy in the solution gradients, and orders-of-magnitude convergence acceleration. The hyperbolic advection-diffusion system is discretized by the second-order upwind residual-distribution scheme in a unified manner, and the system of implicit-residual-equations is solved by Newton's method over every physical time step. The numerical results are presented for linear and nonlinear advection-diffusion problems, demonstrating solutions and gradients produced to the same order of accuracy, with rapid convergence over each physical time step, typically less than five Newton iterations.

  14. Power law breakthrough curve tailing in a fracture: The role of advection

    NASA Astrophysics Data System (ADS)

    Fiori, Aldo; Becker, Matthew W.

    2015-06-01

    We offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock. In this example, we limit the model to a single planar fracture of varying aperture. Flow heterogeneity derives from variable fracture aperture, which implies variable transmissivity (T). The analysis employs a physically based model well-suited to strong heterogeneity and relies only upon advective transport. The purely advective model is able to explain a power-law trend of magnitude -2 to -3 in the breakthrough curve tail; a range that has been found in field tracer experiments. The principle cause of this trend is the comparatively slow transport in zones of small transmissivity (tight aperture). Slow advection occurs when either heterogeneity (variance of lnT) is strong or when the assumed heterogeneity distribution is non-Gaussian. Thus, we link breakthrough tailing to the statistical parameters for the transmissivity field.

  15. Warm-air advection, air mass transformation and fog causes rapid ice melt

    NASA Astrophysics Data System (ADS)

    Tjernström, Michael; Shupe, Matthew D.; Brooks, Ian M.; Persson, P. Ola G.; Prytherch, John; Salisbury, Dominic J.; Sedlar, Joseph; Achtert, Peggy; Brooks, Barbara J.; Johnston, Paul E.; Sotiropoulou, Georgia; Wolfe, Dan

    2015-07-01

    Direct observations during intense warm-air advection over the East Siberian Sea reveal a period of rapid sea-ice melt. A semistationary, high-pressure system north of the Bering Strait forced northward advection of warm, moist air from the continent. Air-mass transformation over melting sea ice formed a strong, surface-based temperature inversion in which dense fog formed. This induced a positive net longwave radiation at the surface while reducing net solar radiation only marginally; the inversion also resulted in downward turbulent heat flux. The sum of these processes enhanced the surface energy flux by an average of ~15 W m-2 for a week. Satellite images before and after the episode show sea-ice concentrations decreasing from > 90% to ~50% over a large area affected by the air-mass transformation. We argue that this rapid melt was triggered by the increased heat flux from the atmosphere due to the warm-air advection.

  16. Proton magnetic relaxation in aromatic polyamides during water vapor sorption

    NASA Astrophysics Data System (ADS)

    Smotrina, T. V.; Chulkova, Yu. S.; Karasev, D. V.; Lebedeva, N. P.; Perepelkin, K. E.; Grebennikov, S. F.

    2009-07-01

    The state of the components in the aromatic polyamide-water system was studied by NMR and sorption. A comparative analysis of spin-lattice and spin-spin relaxation in aromatic para-polyamide ( para-aramid) technical fibers Rusar, Kevlar, and Technora was performed depending on the sorption value. The NMR results correlated with the supramolecular structure of polymers and quasi-chemical equation parameters for water vapor sorption.

  17. Pharmaceuticals' sorptions relative to properties of thirteen different soils.

    PubMed

    Kodešová, Radka; Grabic, Roman; Kočárek, Martin; Klement, Aleš; Golovko, Oksana; Fér, Miroslav; Nikodem, Antonín; Jakšík, Ondřej

    2015-04-01

    Transport of human and veterinary pharmaceuticals in soils and consequent ground-water contamination are influenced by many factors, including compound sorption on soil particles. Here we evaluate the sorption isotherms for 7 pharmaceuticals on 13 soils, described by Freundlich equations, and assess the impact of soil properties on various pharmaceuticals' sorption on soils. Sorption of ionizable pharmaceuticals was, in many cases, highly affected by soil pH. The sorption coefficient of sulfamethoxazole was negatively correlated to soil pH, and thus positively related to hydrolytic acidity and exchangeable acidity. Sorption coefficients for clindamycin and clarithromycin were positively related to soil pH and thus negatively related to hydrolytic acidity and exchangeable acidity, and positively related to base cation saturation. The sorption coefficients for the remaining pharmaceuticals (trimethoprim, metoprolol, atenolol, and carbamazepine) were also positively correlated with the base cation saturation and cation exchange capacity. Positive correlations between sorption coefficients and clay content were found for clindamycin, clarithromycin, atenolol, and metoprolol. Positive correlations between sorption coefficients and organic carbon content were obtained for trimethoprim and carbamazepine. Pedotransfer rules for predicting sorption coefficients of various pharmaceuticals included hydrolytic acidity (sulfamethoxazole), organic carbon content (trimethoprimand carbamazepine), base cation saturation (atenolol and metoprolol), exchangeable acidity and clay content (clindamycin), and soil active pH and clay content (clarithromycin). Pedotransfer rules, predicting the Freundlich sorption coefficients, could be applied for prediction of pharmaceutical mobility in soils with similar soil properties. Predicted sorption coefficients together with pharmaceutical half-lives and other imputes (e.g., soil-hydraulic, geological, hydro-geological, climatic) may be used for

  18. Effect of illite particle shape on cesium sorption

    USGS Publications Warehouse

    Rajec, P.; Sucha, V.; Eberl, D.D.; Srodon, J.; Elsass, F.

    1999-01-01

    Samples containing illite and illite-smectite, having different crystal shapes (plates, "barrels", and filaments), were selected for sorption experiments with cesium. There is a positive correlation between total surface area and Cs-sorption capacity, but no correlation between total surface area and the distribution coefficient, Kd. Generally Kd increases with the edge surface area, although "hairy" (filamentous) illite does not fit this pattern, possibly because elongation of crystals along one axis reduces the number of specific sorption sites.

  19. Altimetric lagrangian advection to reconstruct Pacific Ocean fine scale surface tracer fields

    NASA Astrophysics Data System (ADS)

    Rogé, Marine; Morrow, Rosemary; Dencausse, Guillaume

    2015-04-01

    In past studies, lagrangian stirring of surface tracer fields by altimetric surface geostrophic currents has been performed in different mid to high-latitude regions, showing good results in reconstructing finer-scale tracer patterns. Here we apply the technique to three different regions in the eastern and western tropical Pacific, and in the subtropical southwest Pacific. Initial conditions are derived from weekly gridded temperature and salinity fields, based on hydrographic data and Argo. Validation of the improved fine-scale surface tracer fields is performed using satellite AMSRE SST data, and high-resolution ship thermosalinograph data. We test two kinds of lagrangian advection. The standard one-way advection is shown to introduce an increased tracer bias as the advection time increases. Indeed, since we only use passive stirring, a bias is introduced from the missing physics, such as air-sea fluxes or mixing. A second "backward-forward" advection technique is shown to reduce the seasonal bias, but more data is lost around coasts and islands, a strong handicap in the tropical Pacific with many small islands. In the subtropical Pacific Ocean, the mesoscale temperature and salinity fronts are well represented by the one-way advection over a 10-day advection time, including westward propagating features not apparent in the initial fields. In the tropics, the results are less clear. The validation is hampered by the complex vertical stratification, and the technique is limited by the lack of accurate surface currents for the stirring - the gridded altimetric fields poorly represent the meridional currents, and are not detecting the fast tropical instability waves, nor the wind-driven circulation. We suggest that the passive lateral stirring technique is efficient in regions with moderate the high mesoscale energy and correlated mesoscale surface temperature and surface height. In other regions, more complex dynamical processes may need to be included.

  20. Altimetric Lagrangian advection to reconstruct Pacific Ocean fine-scale surface tracer fields

    NASA Astrophysics Data System (ADS)

    Rogé, Marine; Morrow, Rosemary A.; Dencausse, Guillaume

    2015-09-01

    In past studies, Lagrangian stirring of surface tracer fields by altimetric surface geostrophic currents has been performed in different mid- to high-latitude regions, showing good results in reconstructing finer scale tracer patterns. Here, we explore the pertinence of the technique in the western equatorial Pacific and in the subtropical southwest Pacific. Initial conditions are derived from weekly gridded low-resolution temperature and salinity fields based on in situ hydrographic data. Validation of the reconstructed fine-scale surface tracer fields is performed using satellite AMSRE Sea Surface Temperature data and high-resolution ship thermosalinograph data. We test two kinds of Lagrangian advection. The standard one-way advection leads to an increased error as the advection time increases, due to the missing physics, such as air-sea fluxes or non-geostrophic dynamics. A second "backward-forward" advection technique is explored to reduce this bias in the tracer field, with improved results. In the subtropical southwest Pacific Ocean, the mesoscale temperature and salinity fronts are well represented by both Lagrangian advection techniques over a short 7- to 14-day advection time, including westward-propagating features not apparent in the initial fields. In the tropics, the results are less clear. The validation is hampered by the complex vertical stratification, and the lateral stirring technique is limited by the pertinence of using geostrophic surface current fields in the tropics. We suggest that the passive lateral stirring technique is efficient in regions with moderate to high mesoscale energy, where mesoscale surface tracer and surface height fields are correlated. In other regions, more complex dynamical processes may need to be included.

  1. 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).

  2. Single Component Sorption-Desorption Test Experimental Design Approach Discussions

    SciTech Connect

    Phil WInston

    2011-09-01

    A task was identified within the fission-product-transport work package to develop a path forward for doing testing to determine behavior of volatile fission products behavior and to engage members of the NGNP community to advise and dissent on the approach. The following document is a summary of the discussions and the specific approaches suggested for components of the testing. Included in the summary isare the minutes of the conference call that was held with INL and external interested parties to elicit comments on the approaches brought forward by the INL participants. The conclusion was that an initial non-radioactive, single component test will be useful to establish the limits of currently available chemical detection methods, and to evaluated source-dispersion uniformity. In parallel, development of a real-time low-concentration monitoring method is believed to be useful in detecting rapid dispersion as well as desorption phenomena. Ultimately, the test cycle is expected to progress to the use of radio-traced species, simply because this method will allow the lowest possible detection limits. The consensus of the conference call was that there is no need for an in-core test because the duct and heat exchanger surfaces that will be the sorption target will be outside the main neutron flux and will not be affected by irradiation. Participants in the discussion and contributors to the INL approach were Jeffrey Berg, Pattrick Calderoni, Gary Groenewold, Paul Humrickhouse, Brad Merrill, and Phil Winston. Participants from outside the INL included David Hanson of General Atomics, Todd Allen, Tyler Gerczak, and Izabela Szlufarska of the University of Wisconsin, Gary Was, of the University of Michigan, Sudarshan Loyalka and Tushar Ghosh of the University of Missouri, and Robert Morris of Oak Ridge National Laboratory.

  3. Large-eddy Advection in Evapotranspiration Estimates from an Array of Eddy Covariance Towers

    NASA Astrophysics Data System (ADS)

    Lin, X.; Evett, S. R.; Gowda, P. H.; Colaizzi, P. D.; Aiken, R.

    2014-12-01

    Evapotranspiration was continuously measured by an array of eddy covariance systems and large weighting lysimeter in a sorghum in Bushland, Texas in 2014. The advective divergence from both horizontal and vertical directions were measured through profile measurements above canopy. All storage terms were integrated from the depth of soil heat flux plate to the height of eddy covariance measurement. Therefore, a comparison between the eddy covariance system and large weighing lysimeter was conducted on hourly and daily basis. The results for the discrepancy between eddy covariance towers and the lysimeter will be discussed in terms of advection and storage contributions in time domain and frequency domain.

  4. Sorption of fibronectin to human root surfaces in vitro

    SciTech Connect

    Mendieta, C.; Caravana, C.; Fine, D.H. )

    1990-05-01

    The purpose of this study was to determine the conditions that favor the sorption and retention of human plasma fibronectin to cementum. Rectangular root segments prepared from teeth extracted for orthodontic reasons were mounted on a capillary pipette and immersed in solutions of {sup 125}I fibronectin for assay of cementum sorption under various conditions. Kinetic studies showed sorption to be rapid, with 77% of the maximum fibronectin sorption occurring within 1 minute. Fibronectin sorption was reduced when added in conjunction with serum and was inhibited by monovalent ions (such as sodium), but enhanced in the presence of divalent cations (such as calcium). Exposure of cementum to serum partially blocked subsequent sorption of fibronectin, while cementum bound fibronectin was eluted by subsequent exposure to serum. Treatment of cementum with citric acid pH 1.1 (4 minutes) followed by 5% sodium hypochlorite (5 minutes) caused a significant increase in fibronectin sorption with maximum retention upon subsequent exposure to serum (P less than 0.05). Fibronectin sorption to cementum was: rapid, electrostatic in nature, competitive, reversible, Ca+(+)-facilitated, and maximized by prior treatment of the root with citric acid and sodium hypochlorite. It is concluded that sorption of fibronectin to cementum can be achieved for clinical gain; however, conditions of application can significantly influence both accumulation and subsequent release of root sorbed material.

  5. The sorption of polonium, actinium and protactinium onto geological materials

    SciTech Connect

    Baston, G.M.N.; Berry, J.A.; Brownsword, M.; Heath, T.G.; Ilett, D.J.; McCrohon, R.; Tweed, C.J.; Yui, M.

    1999-07-01

    This paper describes a combined experimental and modeling program of generic sorption studies to increase confidence in the performance assessment for a potential high-level radioactive waste repository in Japan. The sorption of polonium, actinium and protactinium onto geological materials has been investigated. Sorption of these radioelements onto bentonite, tuff and granodiorite from equilibrated de-ionized water was studied under reducing conditions at room temperature. In addition, the sorption of actinium and protactinium was investigated at 60 C. Thermodynamic chemical modeling was carried out to aid interpretation of the results.

  6. Pyrolytic temperatures impact lead sorption mechanisms by bagasse biochars.

    PubMed

    Ding, Wenchuan; Dong, Xiaoling; Ime, Inyang Mandu; Gao, Bin; Ma, Lena Q

    2014-06-01

    The characteristics and mechanisms of Pb sorption by biochars produced from sugarcane bagasse at 250, 400, 500, and 600 °C were examined. The Pb sorption isotherms, kinetics and desorption were investigated. All biochars were effective in Pb sorption and were well described by Langmuir isotherm model and pseudo-second-order kinetic model. The maximum sorption capacity decreased from 21 to 6.1 mg g(-1) as temperature increased from 250 to 600 °C. The Pb sorption was rapid initially, probably controlled by cation exchange and complexation and then slowed down, which might be due to intraparticle diffusions. FTIR data and kinetic models suggested that oxygen functional groups were probably responsible for the high Pb sorption onto low temperature biochars (250 and 400 °C) whereas intraparticle diffusion was mainly responsible for low Pb sorption onto high temperature biochars (500 and 600 °C). Decreased phosphorus concentration indicated that P-induced Pb precipitation was also responsible for Pb sorption. Pyrolysis temperature significantly affected biochar properties and played an important role in Pb sorption capacity and mechanisms by biochars. PMID:24393563

  7. Sorption of radionuclides by cement-based barrier materials

    SciTech Connect

    Li, Kefei Pang, Xiaoyun

    2014-11-15

    This paper investigates the sorption of radionuclide ions, {sup 137}Cs{sup +} and {sup 90}Sr{sup 2+}, by cement-based barrier materials for radioactive waste disposal. A mortar with ternary binder is prepared and powder samples are ground from the hardened material following a predetermined granulometry. After pre-equilibrium with an artificial pore solution, the sorption behaviors of powder samples are investigated through single sorption and blended sorption. The results show that: (1) no systematic difference is observed for single and blended sorptions thus the interaction between {sup 137}Cs{sup +} and {sup 90}Sr{sup 2+} sorptions must be weak; (2) the sorption kinetics is rapid and all characteristic times are less than 1d; (3) the sorption capacity is enhanced by C–A–S–H hydrates and the measured K{sub d} values can be predicted from C–S–H sorption data with Ca/Si ratio equal to Ca/(Si + Al) ratio.

  8. SORPTION OF VOLATILE ORGANIC SOLVENTS FROM AQUEOUS SOLUTION ONTO SUBSURFACE SOLIDS

    EPA Science Inventory

    Sorption isotherms for tetrachloroethene on low-carbon subsurface core samples were linear to equilibrium solution concentrations of 2 mg L−1. Concentrations above this value produced pronounced curvature in the sorption isotherms. Sorption of tetrachloroethene, benzene, trichlor...

  9. Characterization of ‘Aged’ Metolachlor Sorption in Soil Using an Accelerated Solvent Extraction (ASE) Technique

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sorption interactions of pesticides with soil determine pesticide availability for transport and degradation in soil. Thus, knowing and understanding pesticide sorption, particularly in aged soils, is important in determining pesticide fate in soils. Sorption of pesticides is traditionally character...

  10. SEDIMENT-ASSOCIATED REACTIONS OF AROMATIC AMINES: 1. ELUCIDATION OF SORPTION MECHANISMS

    EPA Science Inventory

    Sorption of aromatic amines to sediments and soils can occur by both reversible physical processes and irreversible chemical processes. To elucidate the significance of these sorption pathways, the sorption kinetics of aniline and pyridine were studied in resaturated pond sedimen...

  11. Volcanic aerosol optical properties and phase partitioning behavior after long-range advection characterized by UV-Lidar measurements

    NASA Astrophysics Data System (ADS)

    Miffre, A.; David, G.; Thomas, B.; Rairoux, P.; Fjaeraa, A. M.; Kristiansen, N. I.; Stohl, A.

    2012-03-01

    In this paper, an UV-polarization Lidar is used to study the optical properties of volcanic aerosol in the troposphere. The particles were released by the mid-April 2010 eruption of the Eyjafjallajökull volcano (63.63°N, 19.62°W, Iceland) and passed in the troposphere above Lyon (45.76°N, 4.83°E, France) after advection over 2600 km. The FLEXPART particle dispersion model was applied to simulate the volcanic ash transport from Iceland to South West Europe, at the border of the air traffic closure area. Time-altitude plots of FLEXPART ash concentrations as well as of aerosol backscattering are presented, showing the arrival of volcanic particles in the troposphere above Lyon and their mixing into the planetary boundary layer. The particle UV-backscattering coefficient was typically 4 Mm -1 sr -1 and highly sensitive and accurate particle UV-depolarization measurements were performed, with depolarization ranging from a few to 44%. After few days long-range transport, observed ash particles are still non spherical. The observed variations of the backscattering and depolarization coefficients can be attributed to variations in the volcanic particles content. Ash mass concentrations are then retrieved. Moreover, a partitioning into spherical and non spherical particles is evaluated from number concentration ratios between solid ash particles and spherical hydrated sulfate particles. The microphysical properties of volcanic particles can thus be studied by associating an UV-polarization remote sensing instrument with a numerical volcanic ash dispersion model.

  12. Sorption and cosorption of lead and sulfapyridine on carbon nanotube-modified biochars.

    PubMed

    Inyang, Mandu; Gao, Bin; Zimmerman, Andrew; Zhou, Yanmei; Cao, Xinde

    2015-02-01

    New, sustainable, and low-cost materials that can simultaneously remove a range of wastewater contaminants, such as heavy metals and pharmaceutical residues, are needed. In this work, modified biochars were produced by dip-coating hickory or bagasse biomass in carbon nanotube (CNT) suspensions with or without sodium dodecylbenzenesulfonate (SDBS)-aided dispersion prior to slow pyrolysis in a N2 environment at 600 °C. The sulfapyridine (SPY) and lead (Pb) sorption ability of pristine hickory (HC) and bagasse (BC) biochars and the modified biochars with (HC-SDBS-CNT and BC-SDBS-CNT, respectively) and without (HC-CNT and BC-CNT) SDBS was assessed in laboratory aqueous batch single- and binary-solute system. The greatest removal of SPY and Pb was observed for HC-SDBS-CNT (86 % SPY and 71 % Pb) and BC-SDBS-CNT (56 % SPY and 53 % Pb), whereas HC-CNT, BC-CNT, and the pristine biochars removed far less. This can be attributed to the fact that surfactant could prevent the aggregation of CNTs and thus promote the distribution and stabilization of individual CNT nanoparticle on the biochar surface to adsorb the contaminants. The observation of no significant change in Pb sorption capacities of the surfactant-dispersed CNT-modified biochars in the presence of SPY, or vice versa, was indicative of site-specific sorption interactions and a lack of significant competition for functional groups by the two sorbates. These results suggest that products of hybrid technologies, such as biochars modified with CNTs, can yield multi-sorbents and may hold excellent promise as a sustainable wastewater treatment alternative. PMID:25212810

  13. Arsenic sorption onto laterite iron concretions: temperature effect.

    PubMed

    Partey, Frederick; Norman, David; Ndur, Samuel; Nartey, Robert

    2008-05-15

    We investigated arsenate and arsenite sorption onto laterite iron concretions (LIC) to test its suitability for use in the low-tech treatment of arsenic-bearing drinking water. Batch experiments on crushed LIC from Prestea, Ghana were conducted at a series of temperatures, ionic strengths, and pHs. The point of zero net charge on laterite iron concretion was determined by potentiometric titrations yielding an average pHp(ZNC) around 8.64. Experiments show that sorption capacity for both arsenite and arsenate increase with temperature. The equilibrium sorption capacity for arsenite was larger than that for arsenate over the 25 to 60 degrees C temperature range. A Langmuir model satisfactorily fits the arsenite and arsenate sorption isotherm data. Both arsenite and arsenate sorbed over the pH range of natural waters. Arsenite sorption increases with increasing solution pH to a maximum at pH 7, then decreases with further increase in solution pH. Arsenate sorption, on the other hand, shows little change with increasing solution pH. Increasing solution ionic strength 10-fold results in a slight increase in sorption. Ionic strength experiments show that an inner-sphere sorption mechanism is responsible for As (V) sorption on LIC, while As (III) sorption is by an outer-sphere mechanism. Gibbs free energy (DeltaG degrees) for arsenite and arsenate sorption onto LIC was calculated from Langmuir isotherms; the negative values agree with reaction spontaneity. The positive values of the standard enthalpy (DeltaH degrees) show the endothermic nature of arsenite and arsenate sorption onto LIC. Positive entropy (DeltaS degrees) values suggest the affinity of LIC for the arsenic species in solution. Analysis of the arsenic sorption data suggests that LIC can be used for low-tech natural-materials arsenic water treatment. Laterite iron concretions have a number of advantages for this use over commercial materials, including the ability to remove arsenic from waters with a wide

  14. Sorption of norfloxacin onto humic acid extracted from weathered coal.

    PubMed

    Zhang, Qin; Zhao, Ling; Dong, Yuan-Hua; Huang, Guan-Yi

    2012-07-15

    Norfloxacin (NOR), is an ionizable and polar antimicrobial compound, and it may enter the environment in substantial amounts via the application of manure or sewage as a fertilizer. Sorption of NOR onto humic acid (HA) may affect its environmental fate. In this study, HA extracted from weathered coal was used to investigate the sorption of NOR at different solution chemistry conditions (pH, ionic strength) and temperatures. The sorption of NOR onto HA showed a two-stage sorption process with an equilibration time of 48 h. The sorption kinetic curve fitted well with a pseudo second-order kinetic model. Thermodynamic characteristics demonstrated that the sorption of NOR onto HA was a spontaneous and exothermic process predominated by physical sorption. All sorption isotherms fitted well with the Freundlich and Langmuir models and they were highly nonlinear with values of n between 0.4 and 0.5, suggesting the high heterogeneity of HA. Increasing Ca2+ concentration resulted in a considerable reduction in the K(d) values of NOR, hinting that Ca2+ had probably competed with NOR(+,0) for the cation exchange sites on the surfaces of HA. The sorption reached a maximum at pH 6.0 over the pH range of 2.0-8.0, implying that the primary sorption mechanism was cation exchange interaction between NOR(+,0) species and the negatively charged functional groups of HA. Spectroscopic evidence demonstrated that the piperazinyl moiety of NOR was responsible for sorption onto HA, while the carbonyl group and the aromatic structure of HA participated in adsorbing NOR. PMID:22459013

  15. Sorption of Lincomycin by Manure-Derived Biochars from Water.

    PubMed

    Liu, Cheng-Hua; Chuang, Ya-Hui; Li, Hui; Teppen, Brian J; Boyd, Stephen A; Gonzalez, Javier M; Johnston, Cliff T; Lehmann, Johannes; Zhang, Wei

    2016-03-01

    The presence of antibiotics in agroecosystems raises concerns about the proliferation of antibiotic-resistant bacteria and adverse effects to human health. Soil amendment with biochars pyrolized from manures may be a win-win strategy for novel manure management and antibiotics abatement. In this study, lincomycin sorption by manure-derived biochars was examined using batch sorption experiments. Lincomycin sorption was characterized by two-stage kinetics with fast sorption reaching quasi-equilibrium in the first 2 d, followed by slow sorption over 180 d. The fast sorption was primarily attributed to surface adsorption, whereas the long-term slow sorption was controlled by slow diffusion of lincomycin into biochar pore structures. Two-day sorption experiments were performed to explore effects of biochar particle size, solid/water ratio, solution pH, and ionic strength. Lincomycin sorption to biochars was greater at solution pH 6.0 to 7.5 below the dissociation constant of lincomycin (7.6) than at pH 9.9 to 10.4 above its dissociation constant. The enhanced lincomycin sorption at lower pH likely resulted from electrostatic attraction between the positively charged lincomycin and the negatively charged biochar surfaces. This was corroborated by the observation that lincomycin sorption decreased with increasing ionic strength at lower pH (6.7) but remained constant at higher pH (10). The long-term lincomycin sequestration by biochars was largely due to pore diffusion plausibly independent of solution pH and ionic composition. Therefore, manure-derived biochars had lasting lincomycin sequestration capacity, implying that biochar soil amendment could significantly affect the distribution, transport, and bioavailability of lincomycin in agroecosystems. PMID:27065399

  16. Sorption of Zn(II) in aqueous solutions by scoria.

    PubMed

    Kwon, Jang-Soon; Yun, Seong-Taek; Kim, Soon-Oh; Mayer, Bernhard; Hutcheon, Ian

    2005-09-01

    We conducted kinetic and equilibrium sorption experiments on removal of Zn(II) from aqueous solutions by scoria (a vesicular pyroclastic rock with basaltic composition) from Jeju Island, Korea, in order to examine its potential use as an efficient sorbent. The batch-type kinetic sorption tests under variable conditions indicated that the percentage of Zn(II) removal by scoria increases with decreasing initial Zn(II) concentration, particle size, and sorbate/sorbent ratio. However, the sorption capacity decreases with the decrease of the initial Zn(II) concentration and sorbate/sorbent ratio. Equilibrium sorption tests show that Jeju scoria has a larger capacity and affinity for Zn(II) sorption than commercial powdered activated carbon (PAC); at initial Zn(II) concentrations of more than 10mM, the sorption capacity of Jeju scoria is about 1.5 times higher than that of PAC. The acquired sorption data are better fitted to the Langmuir isotherm than the Freundlich isotherm. Careful examination of ionic concentrations in sorption batches suggests that the sorption behavior is mainly controlled by cation exchange and typically displays characteristics of 'cation sorption'. The Zn(II) removal capacity decreases when solution pH decreases because of the competition with hydrogen ions for sorption sites, while the Zn(II) removal capacity increases under higher pH conditions, likely due to hydroxide precipitation. At an initial Zn(II) concentration of 5.0mM, the removal increases from 70% to 96% with the increase of initial pH from 3.0 to 7.0. We recommend Jeju scoria as an economic and efficient sorbent for Zn(II) in contaminated water. PMID:16054911

  17. Studies of anions sorption on natural zeolites.

    PubMed

    Barczyk, K; Mozgawa, W; Król, M

    2014-12-10

    This work presents results of FT-IR spectroscopic studies of anions-chromate, phosphate and arsenate - sorbed from aqueous solutions (different concentrations of anions) on zeolites. The sorption has been conducted on natural zeolites from different structural groups, i.e. chabazite, mordenite, ferrierite and clinoptilolite. The Na-forms of sorbents were exchanged with hexadecyltrimethylammonium cations (HDTMA(+)) and organo-zeolites were obtained. External cation exchange capacities (ECEC) of organo-zeolites were measured. Their values are 17mmol/100g for chabazite, 4mmol/100g for mordenite and ferrierite and 10mmol/100g for clinoptilolite. The used initial inputs of HDTMA correspond to 100% and 200% ECEC of the minerals. Organo-modificated sorbents were subsequently used for immobilization of mentioned anions. It was proven that aforementioned anions' sorption causes changes in IR spectra of the HDTMA-zeolites. These alterations are dependent on the kind of anions that were sorbed. In all cases, variations are due to bands corresponding to the characteristic Si-O(Si,Al) vibrations (occurring in alumino- and silicooxygen tetrahedra building spatial framework of zeolites). Alkylammonium surfactant vibrations have also been observed. Systematic changes in the spectra connected with the anion concentration in the initial solution have been revealed. The amounts of sorbed CrO4(2-), AsO4(3-) and PO4(3-) ions were calculated from the difference between their concentrations in solutions before (initial concentration) and after (equilibrium concentration) sorption experiments. Concentrations of anions were determined by spectrophotometric method. PMID:25002191

  18. Surface Charge and Ion Sorption Properties of Titanium Dioxide

    NASA Astrophysics Data System (ADS)

    Ridley, M. K.; Machesky, M. L.; Wesolowski, D. J.; Finnegan, M. P.; Palmer, D. A.

    2001-12-01

    The interaction of submicron metal oxide particles with natural aqueous solutions results in the hydroxylation of surface sites, which impart a pH-dependent surface charge. The charged submicron particles influence processes such as nanoparticle assembly and alteration, crystal growth rates and morphologies, colloid flocculation, and contaminant transport. The surface charge and ion sorption properties of metal-oxide particles may be studied by potentiometric titrations, using hydrogen-electrode concentration-cells or traditional glass electrodes and an autotitrator. These techniques have been used to quantify the adsorption of various ions (Na+, Rb+, Ca2+, Sr2+, Cl-) on rutile, at ionic strengths up to 1.0 molality and temperatures to 250° C. The crystalline rutile used in these studies is less than 400 nm in diameter, has a BET surface area of 17 m2/g, and the 110 and 100 faces predominate. The negative surface charge of the rutile was enhanced by increasing temperature, increasing ionic strength, and decreasing the ionic radii of the electrolyte cation. Moreover, the addition of a divalent cation significantly enhances the negative charge of the rutile surface. These data have been rationalized with the MUSIC model of Hiemestra and van Riemsdijk, and a Basic Stern layer description of the electric double layer (EDL). Model fitting of the experimental data provides binding constants for the adsorbed counterions and divalent cations, and capacitance values as well as corresponding electrical potential values of the binding planes. Recently, new studies have been initiated to determine particle size affects on the proton induced surface charge and ion sorption properties of titanium dioxide. In these studies, anatase with a BET surface area of 40 and 100 m2/g (primary particle sizes of 40 and 10 nm, respectively) is being investigated. The complexity of both the experimental and modeling procedures increases with decreasing particle size. For example, the fine

  19. Thermodynamics of imidacloprid sorption in Croatian soils

    NASA Astrophysics Data System (ADS)

    Milin, Čedomila; Broznic, Dalibor

    2015-04-01

    Neonicotinoids are increasingly replacing the organophosphate and methylcarbamate acetylcholinesterase inhibitors which are losing their effectiveness because of selection for resistant pest populations. Imidacloprid is the most important neonicotinoid with low soil persistence, high insecticidal potency and relatively low mammalian toxicity. In Croatia, imidacloprid is most commonly used in olive growing areas, including Istria and Kvarner islands, as an effective means of olive fruit fly infestation control. Sorption-desorption behavior of imidacloprid in six soils collected from five coastal regions in Croatia at 20, 30 and 40°C was investigated using batch equilibrium technique. Isothermal data were applied to Freundlich, Langmuir and Temkin equation, and the thermodynamic parameters ΔH°, ΔG°, ΔS° were calculated. The sorption isotherm curves were of non-linear and may be classified as L-type suggesting a relatively high sorption capacity for imidacloprid. Our results showed that the KFsor values decreased for all the tested soils as the temperature increases, indicating that the temperature strongly influence the sorption. Values of ΔG° were negative (-4.65 to -2.00 kJ/mol) indicating that at all experimental temperatures the interactions of imidacloprid with soils were spontaneous process. The negative and small ΔH° values (-19.79 to -8.89 kJ/mol) were in the range of weak forces, such as H-bonds, consistent with interactions and par¬titioning of the imidacloprid molecules into soil organic matter. The ΔS° values followed the range of -57.12 to -14.51 J/molK, suggesting that imidacloprid molecules lose entropy during transition from the solution phase to soil surface. It was found that imidacloprid desorption from soil was concentration and temperature dependent, i.e. at lower imidacloprid concentrations and temperature, lower desorption percentage occurred. Desorption studies revealed that hysteretic behavior under different temperature

  20. Integrated Heat Switch/Oxide Sorption Compressor

    NASA Technical Reports Server (NTRS)

    Bard, Steven

    1989-01-01

    Thermally-driven, nonmechanical compressor uses container filled with compressed praseodymium cerium oxide powder (PrCeOx) to provide high-pressure flow of oxygen gas for driving closed-cycle Joule-Thomson-expansion refrigeration unit. Integrated heat switch/oxide sorption compressor has no moving parts except check valves, which control flow of oxygen gas between compressor and closed-cycle Joule-Thomson refrigeration system. Oxygen expelled from sorbent at high pressure by evacuating heat-switch gap and turning on heater.

  1. A global spectral element model for poisson equations and advective flow over a sphere

    NASA Astrophysics Data System (ADS)

    Mei, Huan; Wang, Faming; Zeng, Zhong; Qiu, Zhouhua; Yin, Linmao; Li, Liang

    2016-03-01

    A global spherical Fourier-Legendre spectral element method is proposed to solve Poisson equations and advective flow over a sphere. In the meridional direction, Legendre polynomials are used and the region is divided into several elements. In order to avoid coordinate singularities at the north and south poles in the meridional direction, Legendre-Gauss-Radau points are chosen at the elements involving the two poles. Fourier polynomials are applied in the zonal direction for its periodicity, with only one element. Then, the partial differential equations are solved on the longitude-latitude meshes without coordinate transformation between spherical and Cartesian coordinates. For verification of the proposed method, a few Poisson equations and advective flows are tested. Firstly, the method is found to be valid for test cases with smooth solution. The results of the Poisson equations demonstrate that the present method exhibits high accuracy and exponential convergence. Highprecision solutions are also obtained with near negligible numerical diffusion during the time evolution for advective flow with smooth shape. Secondly, the results of advective flow with non-smooth shape and deformational flow are also shown to be reasonable and effective. As a result, the present method is proved to be capable of solving flow through different types of elements, and thereby a desirable method with reliability and high accuracy for solving partial differential equations over a sphere.

  2. 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.

  3. Contributions of advective and diffusive oxygen transport through multilayer composite caps over mine waste.

    PubMed

    Kim, Hong; Benson, Craig H

    2004-07-01

    The relative contributions of four mechanisms of oxygen transport in multilayer composite (MLC) caps placed over oxygen-consuming mine waste were evaluated using numerical and analytical methods. MLC caps are defined here as caps consisting of earthen and geosynthetic (polymeric) components where a composite barrier layer consisting of a geomembrane (1-2 mm thick polymeric sheet) overlying a clay layer is the primary barrier to transport. The transport mechanisms that were considered are gas-phase advective transport, gas-phase diffusive transport, liquid-phase advective transport via infiltrating precipitation and liquid-phase diffusive transport. A numerical model was developed to simulate gas-phase advective-diffusive transport of oxygen through a multilayer cap containing seven layers. This model was also used to simulate oxygen diffusion in the liquid phase. An approximate analytical method was used to compute the advective flux of oxygen in the liquid phase. The numerical model was verified for limiting cases using an analytical solution. Comparisons were also made between model predictions and field data for earthen caps reported by others. Results of the analysis show that the dominant mechanism for oxygen transport through MLC caps is gas-phase diffusion. For the cases that were considered, the gas-phase diffusive flux typically comprises at least 99% of the total oxygen flux. Thus, designers of MLC caps should focus on design elements and features that will limit diffusion of gas-phase oxygen. PMID:15145567

  4. An objective method for computing advective surface velocities from sequential infrared satellite images

    NASA Astrophysics Data System (ADS)

    Emery, W. J.; Thomas, A. C.; Collins, M. J.; Crawford, W. R.; Mackas, D. L.

    1986-11-01

    Using cross correlations between sequential infrared satellite images, an objective technique is developed to compute advective sea surface velocities. Cross correlations are computed in 32 × 32 pixel search (second image) and 22 × 22 template (first image) windows from gradients of sea surface temperature computed from the satellite images. Velocity vectors, computed from sequential images of the British Columbia coastal ocean, generally appear coherent and consistent with the seasonal surface current in the region. During periods of strong wind forcing, as indicated by maps of sea level pressure, the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients; when winds are weaker, the advective velocities correspond better with the infrared temperature patterns, suggesting the increased contribution of the geostrophic current to the surface flow. Velocities determined from coincident, near-surface drogued (5-10 m) buoys, positioned every half hour by internal LORAN-C units in mid-June, show excellent agreement with the image advective velocities. In addition, conductivity, temperature, and depth (CTD) measurements (taken during the buoy tracking) confirm the homogeneity of the upper 10 m, and CTD-derived geostrophic currents are consistent with both buoy and sequential image displacement velocities.

  5. Satellite-advection based solar forecasting: lessons learned and progress towards probabalistic solar forecasting

    NASA Astrophysics Data System (ADS)

    Rogers, M. A.

    2015-12-01

    Using satellite observations from GOES-E and GOES-W platforms in concert with GFS-derived cloud-level winds and a standalone radiative transfer model, an advection-derived forecast for surface GHI over the continental United States, with intercomparison between forecasts for four zones over the CONUS and Central Pacific with SURFRAD results. Primary sources for error in advection-based forecasts, primarily driven by false- or mistimed ramp events are discussed, with identification of error sources quantified along with techniques used to improve advection-based forecasts to approximately 10% MAE for designated surface locations. Development of a blended steering wind product utilizing NWP output combined with satellite-derived winds from AMV techniques to improve 0-1 hour advection forecasts will be discussed. Additionally, the use of two years' of solar forecast observations in the development of a prototype probablistic forecast for ramp events will be shown, with the intent of increasing the use of satellite-derived forecasts for grid operators and optimizing integration of renewable resources into the power grid. Elements of the work were developed under the 'Public-Private-Academic Partnership to Advance Solar Power Forecasting' project spearheaded by the National Center for Atmospheric Research.

  6. DEVELOPMENT AND DEMONSTRATION OF A BIDIRECTIONAL ADVECTIVE FLUX METER FOR SEDIMENT-WATER INTERFACE

    EPA Science Inventory

    A bidirectional advective flux meter for measuring water transport across the sediment-water interface has been successfully developed and field tested. The flow sensor employs a heat-pulse technique combined with a flow collection funnel for the flow measurement. Because the dir...

  7. A Study of the Physical Processes of an Advection Fog Boundary Layer

    NASA Astrophysics Data System (ADS)

    Liu, Duan Yang; Yan, Wen Lian; Yang, Jun; Pu, Mei Juan; Niu, Sheng Jie; Li, Zi Hua

    2016-01-01

    A large quantity of advection fog appeared in the Yangtze River delta region between 1 and 2 December 2009. Here, we detail the fog formation and dissipation processes and the background weather conditions. The fog boundary layer and its formation and dissipation mechanisms have also been analyzed using field data recorded in a northern suburb of Nanjing. The results showed the following: (1) This advection fog was generated by interaction between advection of a north-east cold ground layer and a south-east warm upper layer. The double-inversion structure generated by this interaction between the cold and warm advections and steady south-east vapour transport was the main cause of this long-lasting fog. The double-inversion structure provided good thermal conditions for the thick fog, and the south-east vapour transport was not only conducive to maintaining the thickness of the fog but also sustained its long duration. (2) The fog-top altitude was over 600 m for most of the time, and the fog reduced visibility to less than 100 m for approximately 12 h. (3) The low-level jet near the lower inversion layer also played a role in maintaining the thick fog system by promoting heat, momentum and south-east vapour transport.

  8. MECHANISM OF OUTFLOWS IN ACCRETION SYSTEM: ADVECTIVE COOLING CANNOT BALANCE VISCOUS HEATING?

    SciTech Connect

    Gu, Wei-Min

    2015-01-20

    Based on the no-outflow assumption, we investigate steady-state, axisymmetric, optically thin accretion flows in spherical coordinates. By comparing the vertically integrated advective cooling rate with the viscous heating rate, we find that the former is generally less than 30% of the latter, which indicates that the advective cooling itself cannot balance the viscous heating. As a consequence, for radiatively inefficient flows with low accretion rates such as M-dot ≲10{sup −3} M-dot {sub Edd}, where M-dot {sub Edd} is the Eddington accretion rate, the viscous heating rate will be larger than the sum of the advective cooling rate and the radiative cooling one. Thus, no thermal equilibrium can be established under the no-outflow assumption. We therefore argue that in such cases outflows ought to occur and take away more than 70% of the thermal energy generated by viscous dissipation. Similarly, for optically thick flows with extremely large accretion rates such as M-dot ≳10 M-dot {sub Edd}, outflows should also occur owing to the limited advection and the low efficiency of radiative cooling. Our results may help to understand the mechanism of outflows found in observations and numerical simulations.

  9. ADVECTION, EDGE, AND OASIS EFFECTS ON SPATIAL MOISTURE AND FLUX FIELDS FROM LIDAR

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Relatively narrow forest stands such as the riparian Tamarisk bordering the Rio Grande are subject to dry air advection from the adjacent semi-desert environment. The transport of warm dry air into the canopy has a profound effect upon the spatial properties of the moisture field and associated lat...

  10. Alteration of chaotic advection in blood flow around partial blockage zone: Role of hematocrit concentration

    NASA Astrophysics Data System (ADS)

    Maiti, Soumyabrata; Chaudhury, Kaustav; DasGupta, Debabrata; Chakraborty, Suman

    2013-01-01

    Spatial distributions of particles carried by blood exhibit complex filamentary pattern under the combined effects of geometrical irregularities of the blood vessels and pulsating pumping by the heart. This signifies the existence of so called chaotic advection. In the present article, we argue that the understanding of such pathologically triggered chaotic advection is incomplete without giving due consideration to a major constituent of blood: abundant presence of red blood cells quantified by the hematocrit (HCT) concentration. We show that the hematocrit concentration in blood cells can alter the filamentary structures of the spatial distribution of advected particles in an intriguing manner. Our results reveal that there primarily are two major impacts of HCT concentrations towards dictating the chaotic dynamics of blood flow: changing the zone of influence of chaotic mixing and determining the enhancement of residence time of the advected particles away from the wall. This, in turn, may alter the extent of activation of platelets or other reactive biological entities, bearing immense consequence towards dictating the biophysical mechanisms behind possible life-threatening diseases originating in the circulatory system.

  11. Sorption-desorption of aminocyclopyrachlor in selected Brazilian soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aminocyclopyrachlor sorption and desorption was investigated in 14 soils from Brazil, representing a range of pH, and organic carbon (OC) and clay contents. Sorption kinetics demonstrated that soil-solution equilibrium was attained in a 24-h period. Freundlich equation adequately described behavior ...

  12. Continuous and Periodic Sorption Cryocoolers for 10 K and Below

    NASA Technical Reports Server (NTRS)

    Bard, S.; Wade, L.; Karlmann, P.

    1996-01-01

    A novel system is described for Sorption Cryocooling to 10 K, using hydrogen as refrigerant fluid, sorbent beds of metal hydride powders, and thermal compression and expansion. Current status is summarized of sorption cryocooler development for space applications requiring cooling of infrared and submillimeter sensors to 10 K and below. Several design variations, challenges, and predictions are discussed.

  13. Sorption of humic acids and alpha-endosulfan by clayminerals

    SciTech Connect

    Hengpraprom, S.; Lee, C.M.; Coates, R.T.

    2005-02-18

    Sorption of alpha-endosulfan by kaolinite andmontmorillonite alone and in the presence of sorbed and dissolved humicacid (HA) was investigated (pH 8 and 25oC). Three types of HA, Elliotsoil HA (EHA), Peat HA (PHA), and Summit Hill HA (SHHA), were used torepresent typical humic substances found in soils. For sorption of HA byeither mineral, Freundlich sorption coefficient (Kf) values appeared todecrease in the order of EHA>PHA>SHHA, which followedincreasing polarity (expressed as the O/C atomic ratio) and decreasingpercent-carbon content. For both clays, sorption of alpha-endosulfan bythe HA mineral complex was greater than for sorption by the clay alone.Sorption of alpha-endosulfan by the HA mineral complexes followed thesame order as the Kf of the HAs (EHA>PHA>SHHA). Based on theamount of HA adsorbed by each mineral, organic carbon partitioncoefficients (KOC) were determined for sorption of alpha-endosulfan bytwo of the HA mineral complexes. The value of KOC for alpha-endosulfansorption was greater for kaolinite EHA than kaolinite SHHA. However, theopposite trend was found with the montmorillonite HA complexes.Montmorillonite appeared to sorb alpha-endosulfan and/or HA with higheraffinity than kaolinite, which likely is due to its 2:1 layer structureand higher surface area. Sorption of endosulfan diol, a hydrolysisproduct, by the minerals was much less than the parentpesticide.

  14. Mixed-Gas Sorption Joule-Thomson Refrigerator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.; Petrick, S. Walter; Bard, Steven

    1991-01-01

    Proposed mixed-gas sorption Joule-Thomson refrigerator provides cooling down to temperature of 70 K. Includes only one stage and no mechanical compressor. Simpler, operates without vibrating, and consumes less power in producing same amount of cooling. Same sorption principle of operation applicable in compressor that chemisorbs oxygen or hydrogen from mixture with helium, neon, and/or other nonreactive gases.

  15. Sorption-desorption of indaziflam in selected agricultural soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sorption and desorption of indaziflam in 6 soils from Brazil and 3 soils from the USA, with different physical chemical properties, were investigated using the batch equilibration method. Sorption kinetics demonstrated that soil-solution equilibrium was attained in a 24-h period. The Freundlich equa...

  16. LEAD SORPTION ON RUTHENIUM OXIDE: A MACROSCOPIC AND SPECTROSCOPIC STUDY

    EPA Science Inventory

    The sorption and desorption of Pb on RuO2 xH2O were examined kinetically and thermodynamically via spectroscopic and macroscopic investigations. X-ray absorption spectroscopy (XAS) was employed to determine the sorption mechanism with regard to identity of nearest atomic neighbo...

  17. Status report on SIRS: sorption information retrieval system

    SciTech Connect

    Hostetler, D.D.; Serne, R.J.; Baldwin, A.J.; Petrie, G.M.

    1980-11-01

    Two major uses were identified for the Sorption Information Retrieval System: (1) to aid geochemists in the elucidation of sorption mechanisms; and (2) to aid safety assessment modelers in selection of Kds for any given scenerio. Other benefits such as providing an auditable vehicle for the Kd selection were also discussed.

  18. Nitrate sorption and desorption in biochars from fast pyrolysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Increasing the nitrate (NO3-) sorption capacity of Midwestern US soils has the potential to reduce nitrate leaching to ground water and reduce the extent of the hypoxia zone in the Gulf of Mexico. The objective of this study was to determine the sorption and desorption capacity of non-activated and ...

  19. Spatial variation in sorption and dissipation is herbicide-dependent

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In eroded landforms, soil properties that influence herbicide fate are highly variable with landscape position. Understanding the variation in herbicide sorption and dissipation is essential to characterize weed control efficacy and availability for off-site transport. We evaluated the sorption and/...

  20. Sorption Charecterization of Radonuclides on Clays in Yucca Mountain Alluvium

    SciTech Connect

    M. Ding; P.W. Reimus; S. Chipera; C. Scism

    2006-03-17

    Sorption of {sup 237}Np(V) and {sup 233}U(VI) was measured on clays separated from Yucca Mountain alluvium as a function of solution pH and aqueous actinide concentrations. The results indicate that sorption of U and Np on the separated clay fraction depends strongly on solution pH. Np sorption on clays increases slowly with increasing pH from 3 to 7. Above pH 7, Np sorption on clays increases rapidly up to a pH of about 10. On the other hand, U sorption on clays reaches it maximum at a pH of about 6, with sorption decreasing as pH increases from 6 to 8 and then increasing again as pH increases further from 8 to about 10. The results suggest that a Freundlich isotherm can be used to describe U and Np sorption on clays at pH above 5.5. The results of this study indicate that clay minerals play a very important role in the sorption of U and Np on Yucca Mountain alluvium. Indeed, the clay content of the alluvium is probably considerably more important than water chemistry in predicting the ability of the alluvium to attenuate the transport of these radionuclides.

  1. LEAD SORPTION ON RUTHENIUM OXIDE: A MACROSCOPIC AND SPECTROSCOPIC STUDY

    EPA Science Inventory

    Metal oxide phases play an important role in governing the sorption and desorption mechanisms of metals in water, soils, and sediments. Many researchers have examined the efficiency of Pb sorption on Mn, Fe, Al, Ti, and Si oxide surfaces. Most studies concluded that adsorption ...

  2. Picloram and Aminopyralid Sorption to Soil and Clay Minerals

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aminopyralid sorption data are lacking, and these data are needed to predict off-target transport and plant available herbicide in soil solution. The objective of this research was to determine the sorption of picloram and aminopyralid to five soils and three clay minerals and determine if the pote...

  3. OXYANION SORPTION TO HIGH SURFACE AREA IRON AND ALUMINUM OXIDES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sorption of selected oxyanions (Mo, As, and P) to high surface area iron and aluminum oxides was investigated using in situ Raman and ATR-FTIR spectroscopy, batch sorption methods, electrophoretic mobility measurements, and surface complexation modeling. In situ ATR-FTIR and Raman spectra were coup...

  4. Uranium (VI) sorption onto selected mineral surfaces: Key geochemical parameters

    SciTech Connect

    Pabalan, R.T.; Bertetti, F.P.; Prikryl, J.D.; Turner, D.R.

    1996-10-01

    Batch U(VI) sorption experiments were conducted using quartz, montmorillonite, clinoptilolite, and {alpha}-alumina to determine the key geochemical parameters that influence sorption onto mineral surfaces. The experiments were done at different initial U concentration, pH, M/V, and ionic strength, and at ambient and elevated PCO{sub 2} (10{sup -3.5} and 10{sup -2.0} atm, respectively). The results show that U(VI) sorption on all the minerals studied reaches a maximum at near-neutral pH ({approximately}6.3-6.8) and decreases sharply towards more acidic or alkaline conditions. The pH range where U sorption occurs corresponds to the predominance field of aqueous monomeric U(VI)-hydroxy complexes. Sorption is inhibited at high pH and PCO{sub 2} due to formation of aqueous U(VI)-carbonate complexes. For montmorillonite and clinoptilolite, ion-exchange was suppressed due to the relatively high ionic strength of the solutions. Surface charge properties of the sorbent are inferred to be relatively unimportant factors in U(VI) sorption. Sorption data plotted in terms of K{sub d} show that M/V ratio has little influence on the distribution of U(VI) between the solid and aqueous phases. Modeling of the sorption behavior of U(VI) was performed using a surface complexation approach (Diffuse-Layer Model).

  5. Pesticide sorption on geologic material of varying organic carbon content.

    PubMed

    Bouchard, D C; Wood, A L

    1988-09-01

    Sorption of three pesticides on geologic material ranging in organic carbon content from 0.33 to 6.9 g kg-1 was measured in soil columns using a miscible displacement technique. An octanol-water partitioning model was shown to be inappropriate for predicting sorption of the less hydrophobic pesticides on the low organic carbon materials. PMID:3255290

  6. Effect of Animal Manure on Phosphorus Sorption to Soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In most phosphorus (P) sorption studies P is added as an inorganic salt to a pre-defined background solution such as CaCl2 or KCl; however, in many regions the application of P to agricultural fields is in the form of animal manure. The purpose of this study, therefore, was to compare the sorption b...

  7. Using Weighted Least Squares Regression for Obtaining Langmuir Sorption Constants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    One of the most commonly used models for describing phosphorus (P) sorption to soils is the Langmuir model. To obtain model parameters, the Langmuir model is fit to measured sorption data using least squares regression. Least squares regression is based on several assumptions including normally dist...

  8. Column Chromatography To Obtain Organic Cation Sorption Isotherms.

    PubMed

    Jolin, William C; Sullivan, James; Vasudevan, Dharni; MacKay, Allison A

    2016-08-01

    Column chromatography was evaluated as a method to obtain organic cation sorption isotherms for environmental solids while using the peak skewness to identify the linear range of the sorption isotherm. Custom packed HPLC columns and standard batch sorption techniques were used to intercompare sorption isotherms and solid-water sorption coefficients (Kd) for four organic cations (benzylamine, 2,4-dichlorobenzylamine, phenyltrimethylammonium, oxytetracycline) with two aluminosilicate clay minerals and one soil. A comparison of Freundlich isotherm parameters revealed isotherm linearity or nonlinearity was not significantly different between column chromatography and traditional batch experiments. Importantly, skewness (a metric of eluting peak symmetry) analysis of eluting peaks can establish isotherm linearity, thereby enabling a less labor intensive means to generate the extensive data sets of linear Kd values required for the development of predictive sorption models. Our findings clearly show that column chromatography can reproduce sorption measures from conventional batch experiments with the benefit of lower labor-intensity, faster analysis times, and allow for consistent sorption measures across laboratories with distinct chromatography instrumentation. PMID:27379799

  9. On sorption characteristics of some rare-earth oxyhydrates

    SciTech Connect

    Sukharev, Yu.I.; Lepp, Ya.N.

    1995-12-01

    As demonstrated earlier, gadolinium oxyhydrate possesses a considerable sorption capacity for some non-rare-earth elements, as well as for anions (e.g., for sulfate ions), similar to polymer oxyhydrates such as zirconium oxyhydrate. In this paper, the authors assess the selective sorption properties of gadolinium and yttrium oxyhydrates with respect to the yttrium and gadolinium cations.

  10. Improving estimates of ecosystem metabolism by reducing effects of tidal advection on dissolved oxygen time series-Abstract

    EPA Science Inventory

    Continuous time series of dissolved oxygen (DO) have been used to compute estimates of metabolism in aquatic ecosystems. Central to this open water or "Odum" method is the assumption that the DO time is not strongly affected by advection and that effects due to advection or mixin...

  11. Analytical solution of the advection-diffusion transport equation using a change-of-variable and integral transform technique

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This paper presents a formal exact solution of the linear advection-diffusion transport equation with constant coefficients for both transient and steady-state regimes. A classical mathematical substitution transforms the original advection-diffusion equation into an exclusively diffusive equation. ...

  12. Direct simulation of pore level Fickian dispersion scale for transport through dense cubic packed spheres with vortices

    NASA Astrophysics Data System (ADS)

    Cardenas, M. Bayani

    2009-12-01

    The transition from non-Fickian to Fickian macroscale transport is explicitly demonstrated for an increasing array of three-dimensional pores with vortices in between a lattice of cubic packed spheres by microscale finite element Navier-Stokes flow and transport simulations. Solute residence time distribution begins with a power law for one pore but gradually and eventually transforms to an exponential distribution typical of classic dispersive transport after about ten pores. Parameter fitting of an analytical solution to the 1-D advection-dispersion equation using the simulated breakthrough curves leads to fitted pore velocities within 1% of actual values and an asymptotic fitted dispersion coefficient after a few pores. Therefore, after dozens of pores, bulk transport can be described by the advection-dispersion equation. Persistent vortices in similarly structured porous media subjected to similar grain-scale Reynolds and Peclet numbers may have minimal contribution to anomalous transport observed at larger scales.

  13. Sorption mechanisms of metals to graphene oxide

    NASA Astrophysics Data System (ADS)

    Showalter, Allison R.; Duster, Thomas A.; Szymanowski, Jennifer E. S.; Na, Chongzheng; Fein, Jeremy B.; Bunker, Bruce A.

    2016-05-01

    Environmental toxic metal contamination remediation and prevention is an ongoing issue. Graphene oxide is highly sorptive for many heavy metals over a wide pH range under different ionic strength conditions. We present x-ray absorption fine structure (XAFS) spectroscopy results investigating the binding environment of Pb(II), Cd(II) and U(VI) ions onto multi-layered graphene oxide (MLGO). Analysis indicates that the dominant sorption mechanism of Pb to MLGO changes as a function of pH, with increasing inner sphere contribution as pH increases. In contrast, the sorption mechanism of Cd to MLGO remains constant under the studied pH range. This adsorption mechanism is an electrostatic attraction between the hydrated Cd+2 ion and the MLGO surface. The U(VI), present as the uranyl ion, changes only subtly as a function of pH and is bound to the surface via an inner sphere bond. Knowledge of the binding mechanism for each metal is necessary to help in optimizing environmental remediation or prevention in filtration systems.

  14. Sorption of perfluoroalkyl substances to two types of minerals.

    PubMed

    Hellsing, Maja S; Josefsson, Sarah; Hughes, Arwel V; Ahrens, Lutz

    2016-09-01

    The sorption of perfluoroalkyl substances (PFASs) was investigated for two model soil mineral surfaces, alumina (Al2O3) and silica (SiO2), on molecular level using neutron scattering. The PFASs were selected (i.e. perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorooctane sulfonic acid (PFOS)) to examine the role of hydrophobic chain length and hydrophilic functional group on their sorption behaviour. All four PFASs were found to sorb to alumina surface (positively charged) forming a hydrated layer consisting of 50% PFASs. The PFAS solubility limit, which decrease with chain length, was found to strongly influence the sorption behaviour. The sorbed PFAS layer could easily be removed by gentle rinsing with water, indicating release upon rainfall in the environment. No sorption was observed for PFOA and PFOS at silica surface (negatively charged), showing electrostatic interaction being the driving force in the sorption process. PMID:27323291

  15. BIOPLUME III: NATURAL ATTENTUATION DECISION SUPPORT SYSTEM USER'S MANUAL - VERSION 1.0

    EPA Science Inventory

    The BIOPLUME III program is a two-dimensional, finite difference model for simulating the natural attenuation of organic contaminants in ground water due to the processes of advection, dispersion, sorption, and biodegradation. The model simulates the biodegradation of organic...

  16. MODEL -- BIOPLUME III VERSION 1.0 - SEPTEMBER 1997 (SUBSURFACE PROTECTION AND REMEDIATION DIVISION, NRMRL)

    EPA Science Inventory

    BIOPLUME III is a 2D, finite difference model for simulating the natural attenuation of organic contaminants in groundwater due to the processes of advection, dispersion, sorption, and biodegradation. Biotransformation processes are potentially important in the restoration of aq...

  17. Degradation and sorption of atrazine, hexazinone and procymidone in coastal sand aquifer media.

    PubMed

    Pang, Liping; Close, Murray; Flintoft, Mark

    2005-02-01

    possible explanation for these observations is that ionic atrazine is bound to oppositely charged ionic oxides, and ionic oxides have less effect on the sorption of the non-ionic procymidone. The significant tailing in the pesticide breakthrough curves (BTCs) in comparison with the bromide BTC, together with model-simulated results, suggests that the transport of the pesticides was under chemical non-equilibrium conditions with R values that were less than their equivalent values predicted using the batch equilibrium isothermal data. As a result of non-linear kinetic sorption, retardation factors of the pesticides in groundwater systems would not be constant and will decrease with decreasing pesticide concentrations and increasing flow velocities. Hence, the use of equilibrium isotherm data will probably over-predict the sorption of pesticides in groundwater systems. Rhodamine WT, a commonly used groundwater tracer, was significantly retarded (R = 5.48) and its BTC was much more spread out than the bromide BTC. Therefore, it would not be a good tracer for the indication of groundwater flow velocity and dispersion for the coastal sand aquifer system. In contrast to some aquifer media, the dye tracer was unsuitable as a marker of the appearance of atrazine in a coastal sand aquifer system. PMID:15619714

  18. Two-particle dispersion in weakly turbulent thermal convection

    NASA Astrophysics Data System (ADS)

    Schütz, S.; Bodenschatz, E.

    2016-06-01

    We present results from a numerical study of particle dispersion in the weakly nonlinear regime of Rayleigh–Bénard convection of a fluid with Prandtl number around unity, where bi-stability between ideal straight convection rolls and weak turbulence in the form of spiral defect chaos exists. While Lagrangian pair statistics has become a common tool for studying fully developed turbulent flows at high Reynolds numbers, we show that key characteristics of mass transport can also be found in convection systems that show no or weak turbulence. Specifically, for short times, we find an interval of t 3-scaling of pair dispersion, which we explain quantitatively with the interplay of advection and diffusion. For long times we observe diffusion-like dispersion of particles that becomes independent of the individual particles’ stochastic movements. The spreading rate is found to depend on the degree of spatio-temporal chaos.

  19. Lanthanide sorption on smectitic clays in presence of cement leachates

    NASA Astrophysics Data System (ADS)

    Galunin, Evgeny; Alba, María D.; Santos, Maria J.; Abrão, Taufik; Vidal, Miquel

    2010-02-01

    Due to their potential retention capacity, clay minerals have been proposed for use in the engineered barriers for the storage of high-level radioactive actinides in deep geological waste repositories. However, there is still a lack of data on the sorption of actinides in clays in conditions simulating those of the repositories. The present article examines the sorption of two lanthanides (actinide analogues) in a set of smectitic clays (FEBEX bentonite, MX80 bentonite, hectorite, saponite, Otay montmorillonite, and Texas montmorillonite). Distribution coefficients ( Kd) were determined in two media: water and 0.02 mol L -1 Ca, the latter representing the cement leachates that may modify the chemical composition of the water in contact with the clay. The Kd values of the lanthanides used in the experiments (La and Lu) varied greatly (25-50 000 L kg -1) depending on the ionic medium (higher values in water than in the Ca medium), the initial lanthanide concentration (up to three orders of magnitude decrease inversely with lanthanide concentration), and the examined clay (up to one order of magnitude for the same lanthanide and sorption medium). Freundlich and Langmuir isotherms were used to fit sorption data to allow comparison of the sorption parameters among smectites. The model based on the two-site Langmuir isotherms provided the best fit of the sorption data, confirming the existence of sorption sites with different binding energies. The sites with higher sorption affinity were about 6% of the total sorption capacity in the water medium, and up to 17% in the Ca medium, although in this latter site sorption selectivity was lower. The wide range of Kd values obtained regarding the factors examined indicated that the retention properties of the clays should also be considered when selecting a suitable clay for engineered barriers.

  20. Sorption of roxarsone onto soils with different physicochemical properties.

    PubMed

    Fu, Qing-Long; He, Jian-Zhou; Blaney, Lee; Zhou, Dong-Mei

    2016-09-01

    Elevated roxarsone (ROX) concentrations in soils, caused by land application of ROX-bearing poultry litter, mandate investigation of ROX sorption onto soils. Equilibrium and kinetic studies of ROX sorption onto five soils were carried out to explore the relationship between sorption parameters and soil properties, and to reveal the effects of coexisting humic acid (HA), P(V), As(V), and As(III) on ROX transport. Experimental results indicated that ROX sorption reached equilibrium within 24 h, with pseudo-second order rate constants of 5.74-5.26 × 10(2) g/(mg h); film and intra-particle diffusion were the rate-limiting processes. ROX sorption to soils involved partitioning and adsorption phenomena; however, their relative contributions varied for different soils. The maximum ROX sorption varied with soil type, ranging from 0.59 to 4.12 mg/g. Results from correlation analysis and multiple linear regressions revealed that the maximum sorption capacities, partition coefficients, and desorption percentages were correlated with soil properties, especially iron content, total organic carbon, and dissolved organic carbon. ROX sorption to soils was affected more by soil pH than the initial pH of ROX-containing solutions. Carboxylic and amide functional groups were determined to be responsible for ROX sorption to soils. ROX sorption capacities decreased in the presence of HA, P(V), As(V), and As(III), indicating that ROX mobility in soils was facilitated by dissolved organic matter (DOM) and competing anions. PMID:27281543

  1. Sorption of diclofenac and naproxen onto MWCNT in model wastewater treated by H2O2 and/or UV.

    PubMed

    Czech, Bożena; Oleszczuk, Patryk

    2016-04-01

    The application of oxidation processes such as UV and/or H2O2 will change the physicochemical properties of carbon nanotubes (CNT). It may affect the sorption affinity of CNT to different contaminants and then affect their fate in the environment. In the present study the adsorption of two very common used pharmaceuticals (diclofenac and naproxen) onto CNT treated by UV, H2O2 or UV/H2O2 was investigated. Four different adsorption models (Freundlich, Langmuir, Temkin, Dubinin-Radushkevich) were tested. The best fitting of experimental data was observed for Freundlich or Langmuir model. The significant relationships between Q calculated from Langmuir model with O% and dispersity were observed. Kinetics of diclofenac and naproxen followed mainly pseudo-second order indicating for chemisorption limiting step of adsorption. The data showed that the mechanism of sorption was physical or chemical depending on the type of CNT modification. PMID:26866965

  2. A facile synthesis of Fe3O4-charcoal composite for the sorption of a hazardous dye from aquatic environment.

    PubMed

    Ahmed, Md Juned K; Ahmaruzzaman, M

    2015-11-01

    Herein, we synthesized Fe3O4-charcoal composite using chemical precipitation technique and utilized it for the sorption of methylene blue from aqueous solution. The synthesized composite was characterized by Infra-red spectroscopy, N2 adsorption-desorption isotherm, X-ray diffraction, selected area electron diffraction, transmission electron microscopy, and vibrating sample magnetometer. The composite depicts absorption bands conforming to Fe-O, -OH, CO, and C-O vibrations. The composite was mesoporous in nature with a surface area of 387.30 m(2) g(-1). The observed diffraction planes correspond to face-centered cubic Fe3O4 and disordered graphitic carbon. The spherical Fe3O4 particles (average diameter ∼13.8 nm) were uniformly distributed in the carbon matrix of the charcoal. The saturation and remanent magnetizations demonstrate its potential for magnetic separation and reuse. The composite showed dye sorption capacities of 97.49 mg g(-1) and 90.85 mg g(-1) in batch and fixed-bed system. Pseudo-second order kinetics and Temkin isotherm best represented the sorption data. The sorption process was endothermic, spontaneous, and administered by electrostatic, π-π dispersive interactions, film, and intraparticle diffusion. Microwave irradiations followed by methanol elution regenerated the dye-loaded composite with nearly no loss in sorption capacity. The recovery of energy and potential utilization of bottom ash enhances the prospective of Fe3O4-charcoal composite for industrial applications. PMID:26320009

  3. Normal and Anomalous Dispersion in Fluvial Sediment Transport

    NASA Astrophysics Data System (ADS)

    Bradley, D. N.; Tucker, G. E.

    2005-12-01

    Understanding the rate of motion and pattern of dispersion in fluvial sediment transport is essential for a variety of applications, including predicting the fate and transport of solid-phase contaminants and modeling the cosmogenic-nuclide inheritance of water-borne sediment. In order to create a probabilistic model of sediment particle motion, it is necessary to characterize the statistical properties of fluvial sediment dispersion. In general, two modes of behavior have been observed in advective-diffusive transport systems: normal and anomalous dispersion. Normal dispersion is characterized by a well-defined mean position and spatial variance and the time evolution of particle concentration is described by a simple advection-diffusion equation. In contrast, a transport system that exhibits anomalous dispersion will tend to have a heavy-tailed spatial distribution, a mean position that is different from the peak concentration, and a large variance. The fundamental difference lies in the probability distribution of individual particle velocities. When the distribution is sufficiently heavy-tailed, the resulting dispersion pattern will be anomalous. Anomalous dispersion has been observed in geophysical systems ranging from turbulent flow to transport in heterogeneous porous media. Several lines of evidence from the sediment transport literature suggest that fluvial sediment may undergo anomalous dispersion. Tracer experiments show a preference for right-skewed travel distance distributions, a characteristic of anomalous diffusion. Studies suggest that large inputs of sediment to rivers (such as a landslide) tend to disperse in place rather than translate downstream. In addition, the fact that sediment grains can become trapped in flood plains and bars for long periods of time and then move long distances in rare, short duration events such as floods suggests a potential for anomalous dispersion due to a broad distribution of particle residence times. We develop a

  4. Particulate export vs lateral advection in the Antarctic Polar Front (Southern Pacific Ocean)

    NASA Astrophysics Data System (ADS)

    Tesi, T.; Langone, L.; Ravaioli, M.; Capotondi, L.; Giglio, F.

    2012-04-01

    The overarching goal of our study was to describe and quantify the influence of lateral advection relative to the vertical export in the Antarctic Polar Front (Southern Pacific Ocean). In areas where lateral advection of particulate material is significant, budgets of bioactive elements can be inaccurate if fluxes through the water column and to the seabed are exclusively interpreted as passive sinking of particles. However, detailed information on the influence of lateral advection in the water column in the southern ocean is lacking. With this in mind, our study focused between the twilight zone (i.e. mesopelagic) and the benthic nepheloid layer to understand the relative importance of lateral flux with increasing water depth. Measurements were performed south of the Antarctic Polar Front for 1 year (January 10th 1999-January 3rd 2000) at 900, 1300, 2400, and 3700 m from the sea surface. The study was carried out using a 3.5 km long mooring line instrumented with sediment traps, current meters and sensors of temperature and conductivity. Sediment trap samples were characterized via several parameters including total mass flux, elemental composition (organic carbon, total nitrogen, biogenic silica, and calcium carbonate), concentration of metals (aluminum, iron, barium, and manganese), 210Pb activity, and foraminifera taxonomy. High fluxes of biogenic particles were observed in both summer 1999 and 2000 as a result of seasonal algal blooms associated with sea ice retreat and water column stratification. During no-productive periods, several high energy events occurred and resulted in advecting resuspended biogenic particles from flat-topped summits of the Pacific Antarctic Ridge. Whereas the distance between seabed and uppermost sediment traps was sufficient to avoid lateral advection processes, resuspension was significant in the lowermost sediment traps accounting for ~60 and ~90% of the material caught at 2400 and 3700 m, respectively. Samples collected during

  5. a Mesoscale Atmospheric Dispersion Modeling System for Simulations of Topographically Induced Atmospheric Flow and Air Pollution Dispersion.

    NASA Astrophysics Data System (ADS)

    Boybeyi, Zafer

    A mesoscale atmospheric dispersion modeling system has been developed to investigate mesoscale circulations and associated air pollution dispersion, including effects of terrain topography, large water bodies and urban areas. The system is based on a three-dimensional mesoscale meteorological model coupled with two dispersion models (an Eulerian dispersion model and a Lagrangian particle dispersion model). The mesoscale model is hydrostatic and based on primitive equations formulated in a terrain-following coordinate system with a E-varepsilon turbulence closure scheme. The Eulerian dispersion model is based on numerical solution of the advection-diffusion equation to allow one to simulate releases of non-buoyant pollutants (especially from area and volume sources). The Lagrangian particle dispersion model allows one to simulate releases of buoyant pollutants from arbitrary sources (particularly from point and line sources). The air pollution dispersion models included in the system are driven by the meteorological information provided by the mesoscale model. Mesoscale atmospheric circulations associated with sea and lake breezes have been examined using the mesoscale model. A series of model sensitivity studies were performed to investigate the effects of different environmental parameters on these circulations. It was found that the spatial and temporal variation of the sea and lake breeze convergence zones and the associated convective activities depend to a large extent on the direction and the magnitude of the ambient wind. Dispersion of methyl isocyanate gas from the Bhopal accident was investigated using the mesoscale atmospheric dispersion modeling system. A series of numerical experiments were performed to investigate the possible role of the mesoscale circulations on this industrial gas episode. The temporal and spatial variations of the wind and turbulence fields were simulated with the mesoscale model. The dispersion characteristics of the accidental

  6. Applying dispersive changes to Lagrangian particles in groundwater transport models

    USGS Publications Warehouse

    Konikow, Leonard F.

    2010-01-01

    Method-of-characteristics groundwater transport models require that changes in concentrations computed within an Eulerian framework to account for dispersion be transferred to moving particles used to simulate advective transport. A new algorithm was developed to accomplish this transfer between nodal values and advecting particles more precisely and realistically compared to currently used methods. The new method scales the changes and adjustments of particle concentrations relative to limiting bounds of concentration values determined from the population of adjacent nodal values. The method precludes unrealistic undershoot or overshoot for concentrations of individual particles. In the new method, if dispersion causes cell concentrations to decrease during a time step, those particles in the cell having the highest concentration will decrease the most, and those with the lowest concentration will decrease the least. The converse is true if dispersion is causing concentrations to increase. Furthermore, if the initial concentration on a particle is outside the range of the adjacent nodal values, it will automatically be adjusted in the direction of the acceptable range of values. The new method is inherently mass conservative.

  7. Applying Dispersive Changes to Lagrangian Particles in Groundwater Transport Models

    USGS Publications Warehouse

    Konikow, L.F.

    2010-01-01

    Method-of-characteristics groundwater transport models require that changes in concentrations computed within an Eulerian framework to account for dispersion be transferred to moving particles used to simulate advective transport. A new algorithm was developed to accomplish this transfer between nodal values and advecting particles more precisely and realistically compared to currently used methods. The new method scales the changes and adjustments of particle concentrations relative to limiting bounds of concentration values determined from the population of adjacent nodal values. The method precludes unrealistic undershoot or overshoot for concentrations of individual particles. In the new method, if dispersion causes cell concentrations to decrease during a time step, those particles in the cell having the highest concentration will decrease the most, and those with the lowest concentration will decrease the least. The converse is true if dispersion is causing concentrations to increase. Furthermore, if the initial concentration on a particle is outside the range of the adjacent nodal values, it will automatically be adjusted in the direction of the acceptable range of values. The new method is inherently mass conservative. ?? US Government 2010.

  8. A single expression for solute and heat dispersion in homogeneous porous media

    NASA Astrophysics Data System (ADS)

    van Milligen, Boudewijn Ph.; Bons, Paul D.

    2014-05-01

    A variety of expressions have been proposed for dispersion in homogeneous porous media. These expressions are either for heat (thermal) or solute dispersion, and often only valid for a limited range of flow rates, typically expressed in terms of the Péclet number. We present a single, universal expression for both the heat and solute dispersion coefficient (both transverse and longitudinal) in homogeneous porous media, valid over a wide range of Péclet numbers as long as flow is laminar. The expression covers the complex intermediate regime between diffusion and advection controlled dispersion, where dispersion increases non-linearly with flow velocity. Using numerical simulations of pore channel networks, we show that that the intermediate regime can be regarded as a phase transition between random, diffusive transport at low flow velocity and ordered transport controlled by the geometry of the pore space at high flow velocities. This phase transition explains the first-order behavior in the intermediate regime. A new quantifier, the ratio of the amount of solute in dominantly advective versus dominantly diffusive pore channels, plays the role of "order parameter" of this phase transition. Bons, P.D., van Milligen, B.P., Blum, P. 2013. A general unified expression for solute and heat dispersion in homegeneous porous media. Water Resources Research 49, 1-13. van Milligen, B.Ph., Bons, P.D. 2012. Analytical model for tracer dispersion in porous media. Physical Review E 85.

  9. Molecular Scale Assessment of Methylarsenic Sorption on Aluminum Oxide

    SciTech Connect

    Shimizu, M.; Ginder-Vogel, M; Parikh, S; Sparks, D

    2010-01-01

    Methylated forms of arsenic (As), monomethylarsenate (MMA) and dimethylarsenate (DMA), have historically been used as herbicides and pesticides. Because of their large application to agriculture fields and the toxicity of MMA and DMA, the sorption of methylated As to soil constituents requires investigation. MMA and DMA sorption on amorphous aluminum oxide (AAO) was investigated using both macroscopic batch sorption kinetics and molecular scale extended X-ray absorption fine structure (EXAFS) and Fourier transform infrared (FTIR) spectroscopic techniques. Sorption isotherm studies revealed sorption maxima of 0.183, 0.145, and 0.056 mmol As/mmol Al for arsenate (As{sup V}), MMA, and DMA, respectively. In the sorption kinetics studies, 100% of added As{sup V} was sorbed within 5 min, while 78% and 15% of added MMA and DMA were sorbed, respectively. Desorption experiments, using phosphate as a desorbing agent, resulted in 30% release of absorbed As{sup V}, while 48% and 62% of absorbed MMA and DMA, respectively, were released. FTIR and EXAFS studies revealed that MMA and DMA formed mainly bidentate binuclear complexes with AAO. On the basis of these results, it is proposed that increasing methyl group substitution results in decreased As sorption and increased As desorption on AAO.

  10. Sorption of Pseudomonas putida onto differently structured kaolinite minerals

    NASA Astrophysics Data System (ADS)

    Vasiliadou, I. A.; Papoulis, D.; Chrysikopoulos, C.; Panagiotaras, D.; Karakosta, E.; Fardis, M.; Papavassiliou, G.

    2010-12-01

    The presence of bio-colloids (e.g. bacteria and viruses) in the subsurface could be attributed to the release of particles from septic tanks, broken sewer lines or from artificial recharge with treated municipal wastewater. Bio-colloid transport in the subsurface is significantly affected by sorption onto the solid matrix. Bio-colloid attachment onto mobile or suspended in the aqueous phase soil particles (e.g. clay or other minerals) also may influence their fate and transport in the subsurface. The present study focuses on the investigation of Pseudomonas (Ps.) putida sorption onto well (KGa-1) and poorly (KGa-2) crystallized kaolinite minerals. Batch experiments were carried out to determine the sorption isotherms of Ps. putida onto both types of kaolinite particles. The sorption process of Ps. putida onto KGa-1 and KGa-2 is adequately described by a Langmuir isotherm. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy as well as Nuclear Magnetic Resonance were employed to study the sorption mechanisms of Ps. putida. Experimental results indicated that KGa-2 presented higher affinity and sorption capacity than KGa-1. It was shown that electrostatic interactions and structural disorders can influence the sorption capacity of clay particles.

  11. Evaluation of pyrene sorption-desorption on tropical soils.

    PubMed

    Olu-Owolabi, Bamidele I; Diagboya, Paul N; Adebowale, Kayode O

    2014-05-01

    Sorption-desorption processes control soil-pollutant interactions. These processes determine the extent of pyrene transport in soils. Understanding sorption characteristics of pyrene is necessary in ascertaining its fate in soil. Laboratory batch experiments were conducted to study the sorptions-desorption of pyrene on eight soils from varying tropical agro-ecological zones (AEZs). The results showed that pyrene sorptions equilibria were attained within 720 min. Solution pH had a reciprocal effect on pyrene sorptions. Sorption was exothermic and increased with pyrene concentration in solution. The quantities of pyrene sorbed by each soil as well as the hysteresis were proportional to the percentage organic matter, and to some degree, the clay mineralogy. Sorption isotherms showed distributed reactivity involving several linear and non-linear isotherms. The present investigation showed that pyrene is likely to be more available to biota and reach the aquifer faster in low organic matter soils than those with relatively higher organic matter and more so in warmer climes. PMID:24584002

  12. Role of interlayer hydration in lincomycin sorption by smectite clays.

    PubMed

    Wang, Cuiping; Ding, Yunjie; Teppen, Brian J; Boyd, Stephen A; Song, Cunyi; Li, Hui

    2009-08-15

    Lincomycin, an antibiotic widely administered as a veterinary medicine, is frequently detected in water. Little is known about the soil-water distribution of lincomycin despite the fact that this is a major determinant of its environmental fate and potential for exposure. Cation exchange was found to be the primary mechanism responsible for lincomycin sorption by soil clay minerals. This was evidenced by pH-dependent sorption, and competition with inorganic cations for sorptive sites. As solution pH increased, lincomycin sorption decreased. The extent of reduction was consistent with the decrease in cationic lincomycin species in solution. The presence of Ca2+ in solution diminished lincomycin sorption. Clay interlayer hydration status strongly influenced lincomycin adsorption. Smectites with the charge deficit from isomorphic substitution in tetrahedral layers (i.e., saponite) manifest a less hydrated interlayer environment resulting in greater sorption than that by octahedrally substituted clays (i.e., montmorillonite). Strongly hydrated exchangeable cations resulted in a more hydrated clay interlayer environment reducing sorption in the order of Ca- < K- < Cs-smectite. X-ray diffraction revealed that lincomycin was intercalated in smectite clay interlayers. Sorption capacity was limited by clay surface area rather than by cation exchange capacity. Smectite interlayer hydration was shown to be a major, yet previously unrecognized, factor influencing the cation exchange process of lincomycin on aluminosilicate mineral surfaces. PMID:19746709

  13. Sorption compressor/mechanical expander hybrid refrigeration

    NASA Technical Reports Server (NTRS)

    Jones, J. A.; Britcliffe, M.

    1987-01-01

    Experience with Deep Space Network (DSN) ground-based cryogenic refrigerators has proved the reliability of the basic two-stage Gifford-McMahon helium refrigerator. A very long life cryogenic refrigeration system appears possible by combining this expansion system or a turbo expansion system with a hydride sorption compressor in place of the usual motor driven piston compressor. To test the feasibility of this system, a commercial Gifford-McMahon refrigerator was tested using hydrogen gas as the working fluid. Although no attempt was made to optimize the system for hydrogen operation, the refrigerator developed 1.3 W at 30 K and 6.6 W at 60 K. The results of the test and of theoretical performances of the hybrid compressor coupled to these expansion systems are presented.

  14. Sorption of tin on human teeth.

    PubMed

    Helal, A A; Alian, Gh A; Madbouly, H A

    2002-01-01

    The sorption of tin ions on human teeth from water and other drinks has been studied by the radioactive tracer technique using the isotope 113Sn (T(1/2) = 115.1 d) as a tracer. The tooth holds a minimum amount of tin from coffee and a maximum amount is held from water and from tea with sugar. The same technique was also used to study the desorption of tin already taken up on the teeth. It has been found that sorbed tin is hardly desorbed from the teeth specimens. The high uptake of tin on human teeth from various drinks showed that teeth act as a natural sieve holding trace elements. PMID:11768790

  15. Sorption Behaviour of Armenian Natural Zeolites

    SciTech Connect

    Keheyan, Y.; Khachatryan, S.; Christidis, G.; Moraetis, D.; Gevorkyan, R.; Sarkisyan, H.; Yeritsyan, H.; Nikoghosyan, S.; Sahakyan, A.; Kekelidze, N.; Akhalbedashvili, L.

    2005-07-15

    The sorptive behaviour of radioactive waste on Armenian zeolites, natural, irradiated, chemically treated and heated at high temperatures was studied and their capacity for the separation and enrichment of radionuclides was evaluated.The influence of temperature, acidity, basicity, specific activity, electron and gamma irradiation on sorption have been studied. The chemical analysis of exchanged samples was carried out and the cation exchange capacity was determined. Absorption properties of mono-cationic forms of different clinoptilolite samples were studied depending on type of guest cation and contact time.By means of model experiments the laboratory plant for absorption of metal cations from solutions in dynamic regime was designed and developed. This plant was used for experiments of radioactive waste removal from the Armenian nuclear reactor.

  16. A balancing domain decomposition method by constraints for advection-diffusion problems

    SciTech Connect

    Tu, Xuemin; Li, Jing

    2008-12-10

    The balancing domain decomposition methods by constraints are extended to solving nonsymmetric, positive definite linear systems resulting from the finite element discretization of advection-diffusion equations. A pre-conditioned GMRES iteration is used to solve a Schur complement system of equations for the subdomain interface variables. In the preconditioning step of each iteration, a partially sub-assembled finite element problem is solved. A convergence rate estimate for the GMRES iteration is established, under the condition that the diameters of subdomains are small enough. It is independent of the number of subdomains and grows only slowly with the subdomain problem size. Numerical experiments for several two-dimensional advection-diffusion problems illustrate the fast convergence of the proposed algorithm.

  17. Perturbation analysis of steady and unsteady electrohydrodynamic chaotic advection inside translating drops

    NASA Astrophysics Data System (ADS)

    Wu, Fan; Vainchtein, Dmitri; Ward, Thomas

    2015-08-01

    A drop translating in the presence of an electric field is studied analytically. The flow is a combination of a Hadamard-Rybczynski and a Taylor circulation due to the translation and electric field, respectively. We consider chaotic advection that is generated by (1) tilting and (2) time-dependent modulation of the electric field. For the analysis we consider small perturbations in time and space to what is otherwise an integrable flow. By using a robust analytical technique we find an adiabatic invariant (AI) for the system by averaging the equations of motion. The chaotic advection is due to quasirandom jumps of the AI after crossing the separatrix of the unperturbed flow. We demonstrate that the asymptotic analysis leads to a set of criteria that can be used to optimize stirring in these systems.

  18. Advective-diffusive motion on large scales from small-scale dynamics with an internal symmetry

    NASA Astrophysics Data System (ADS)

    Marino, Raffaele; Aurell, Erik

    2016-06-01

    We consider coupled diffusions in n -dimensional space and on a compact manifold and the resulting effective advective-diffusive motion on large scales in space. The effective drift (advection) and effective diffusion are determined as a solvability conditions in a multiscale analysis. As an example, we consider coupled diffusions in three-dimensional space and on the group manifold SO(3) of proper rotations, generalizing results obtained by H. Brenner [J. Colloid Interface Sci. 80, 548 (1981), 10.1016/0021-9797(81)90214-9]. We show in detail how the analysis can be conveniently carried out using local charts and invariance arguments. As a further example, we consider coupled diffusions in two-dimensional complex space and on the group manifold SU(2). We show that although the local operators may be the same as for SO(3), due to the global nature of the solvability conditions the resulting diffusion will differ and generally be more isotropic.

  19. Reaction-diffusion-advection approach to spatially localized treadmilling aggregates of molecular motors

    NASA Astrophysics Data System (ADS)

    Yochelis, Arik; Bar-On, Tomer; Gov, Nir S.

    2016-04-01

    Unconventional myosins belong to a class of molecular motors that walk processively inside cellular protrusions towards the tips, on top of actin filament. Surprisingly, in addition, they also form retrograde moving self-organized aggregates. The qualitative properties of these aggregates are recapitulated by a mass conserving reaction-diffusion-advection model and admit two distinct families of modes: traveling waves and pulse trains. Unlike the traveling waves that are generated by a linear instability, pulses are nonlinear structures that propagate on top of linearly stable uniform backgrounds. Asymptotic analysis of isolated pulses via a simplified reaction-diffusion-advection variant on large periodic domains, allows to draw qualitative trends for pulse properties, such as the amplitude, width, and propagation speed. The results agree well with numerical integrations and are related to available empirical observations.

  20. Two-dimensional atmospheric transport and chemistry model - Numerical experiments with a new advection algorithm

    NASA Technical Reports Server (NTRS)

    Shia, Run-Lie; Ha, Yuk Lung; Wen, Jun-Shan; Yung, Yuk L.

    1990-01-01

    Extensive testing of the advective scheme proposed by Prather (1986) has been carried out in support of the California Institute of Technology-Jet Propulsion Laboratory two-dimensional model of the middle atmosphere. The original scheme is generalized to include higher-order moments. In addition, it is shown how well the scheme works in the presence of chemistry as well as eddy diffusion. Six types of numerical experiments including simple clock motion and pure advection in two dimensions have been investigated in detail. By comparison with analytic solutions, it is shown that the new algorithm can faithfully preserve concentration profiles, has essentially no numerical diffusion, and is superior to a typical fourth-order finite difference scheme.

  1. On Vortex Genesis. An Heuristic Model of Convection-Advection Linkages

    NASA Astrophysics Data System (ADS)

    Bouali, S.

    2003-04-01

    We connect to a model of convection roll an appropriate feedback loop (i.e., the advection retroaction) which unfolds a wide range of vorticity behavior. The 3D numerical computations display the conservative aerologic flows of waterspouts and tropical cyclones. Moreover, several simulations exhibit the singular topology of the structure of cyclones eventually trapped in period-2 orbit. On the other hand, additional advection linkages provide our dynamical system with an explicative proof of the tornadogenesis. These amendements modify the model. The airflows are now dissipatives and we investigate the kinematics of these short life span phenomena. The extended model leads the trajectories of air pockets to one or more vortices. The downbursts and microbursts described in the Fujita classification are also simulated. Our heuristic dynamical system lays the foundation of an unified modelisation of vortices. Theory and Direct Numerical Simulation of the vortex genesis are associated in a new perspective.

  2. A study of turbulent transport of an advective nature in a fluid plasma

    NASA Astrophysics Data System (ADS)

    Min, Byunghoon; An, Chan-Yong; Kim, Chang-Bae

    2014-08-01

    The advective nature of the electrostatic turbulent flux of plasma energy in Fourier space is studied numerically in a nearly adiabatic state. Such a state is represented by the Hasegawa-Mima equation, which is driven by a noise that may model the destabilization due to the phase mismatch of the plasma density and the electric potential. The noise is assumed to be Gaussian and not to be invariant under reflection along a direction ŝ. The flux density induced by such noise is found to be anisotropic: While it is random along ŝ, it is not along the perpendicular direction ŝ ⊥, and the flux is not diffusive. The renormalized response may be approximated as advective, with the velocity being proportional to ( kρ s )2, in the Fourier space.

  3. DPDC (double-pass donor cell): A second-order monotone scheme for advection

    SciTech Connect

    Beason, C W; Margolin, L G

    1988-09-26

    We are developing a new, second-order, monotone scheme for advection. DPDC (i.e., double-pass donor cell) is based on Smolarkiewicz' simple, positive definite method. Both schemes are multipass methods in which upstream approximations to the truncation error are subtracted from the equations. We describe two significant improvements to Smolarkiewicz' method. First, we use a local gauge transformation to convert the method from being positive definite to the stronger condition of being monotone. Second, we analytically approximate the sum of the corrections of all the passes to use in a single corrective pass. This increases the accuracy of the method, but does not increase the order of accuracy. We compare DPDC with van Leer's method for advection of several different pulses in a constant velocity field. 5 refs., 4 figs.

  4. A traceable physical calibration of the vertical advection-diffusion equation for modeling ocean heat uptake

    NASA Astrophysics Data System (ADS)

    Huber, Markus; Tailleux, Remi; Ferreira, David; Kuhlbrodt, Till; Gregory, Jonathan

    2015-04-01

    The classic vertical advection-diffusion (VAD) balance is a central concept in studying the ocean heat budget, in particular in simple climate models (SCMs). Here we present a new framework to calibrate the parameters of the VAD equation to the vertical ocean heat balance of two fully-coupled climate models that is traceable to the models' circulation as well as to vertical mixing and diffusion processes. Based on temperature diagnostics, we derive an effective vertical velocity w∗ and turbulent diffusivity kν∗ for each individual physical process. In steady state, we find that the residual vertical velocity and diffusivity change sign in middepth, highlighting the different regional contributions of isopycnal and diapycnal diffusion in balancing the models' residual advection and vertical mixing. We quantify the impacts of the time evolution of the effective quantities under a transient 1% CO2 simulation and make the link to the parameters of currently employed SCMs.

  5. Numerical advection algorithms and their role in atmospheric transport and chemistry models

    NASA Technical Reports Server (NTRS)

    Rood, Richard B.

    1987-01-01

    During the last 35 years, well over 100 algorithms for modeling advection processes have been described and tested. This review summarizes the development and improvements that have taken place. The nature of the errors caused by numerical approximation to the advection equation are highlighted. Then the particular devices that have been proposed to remedy these errors are discussed. The extensive literature comparing transport algorithms is reviewed. Although there is no clear cut 'best' algorithm, several conclusions can be made. Spectral and pseudospectral techniques consistently provide the highest degree of accuracy, but expense and difficulties assuring positive mixing ratios are serious drawbacks. Schemes which consider fluid slabs bounded by grid points (volume schemes), rather than the simple specification of constituent values at the grid points, provide accurate positive definite results.

  6. Estimation and correction of advection effects with single and multiple, conventional and Doppler radars

    NASA Technical Reports Server (NTRS)

    Gal-Chen, T.

    1981-01-01

    The laws of fluid motion are invariant under a Gallilean transformation. For a perfect observing system, the data analysis should, therefore, also be invariant under a Gallilean transformation. This invariance is often not preserved in practical observing systems. In this connection, it is often advisable to perform mesoscale analysis in a frame moving with respect to the earth's surface. In the present investigation the velocity of such a frame is referred to as an advection velocity. The investigation is concerned with remaining problems regarding the Gallilean transformation. The establishment of a frame of reference for the achievement of maximum coherence is considered, taking into account the case of given nonsimultaneous observations of scalars or Cartesian vectors. It is found that advection speed can be estimated objectively if a scalar or Cartesian vector can be observed directly and if, in addition, the time and position of each observation is approximately known.

  7. Sasaki's variational optimization analysis of temperature and moisture advection in a severe storm environment

    NASA Technical Reports Server (NTRS)

    Mcfarland, M. J.

    1975-01-01

    Temperature and moisture advection patterns of dry air intrusion were analyzed by a variational optimization method to relate mesoscale advection to a severe thunderstorm environment. The analysis results presented here were obtained from a case study, May 26, 1973, when a tornado squall line developed in Oklahoma in conjunction with a clearly delineated dry air intrusion. Observations from the synoptic upper air network were used for inputs of horizontal wind components, potential temperature, and mixing ratio at each 50 mb increment from 950 to 100 mb. An objective analysis was performed to assign values of the variables to grid points of a 15 x 14 horizontal grid with approximate 125 km grid spacing at each pressure level. After the analysis the data fields were smoothed using a variational formalism.

  8. CDF Solutions of Advection-Reaction equations with uncertain parameters (Invited)

    NASA Astrophysics Data System (ADS)

    Boso, F.; Tartakovsky, D. M.

    2013-12-01

    Flow and transport models are affected by parametric uncertainty. Quantitative forecasting of such processes in natural porous media are especially prone to uncertainty because of the inaccessibility and multi-scale nature of the subsurface. We consider a reduced-complexity stochastic transport system which takes into account advection and nonlinear reactions in advection-reaction equations (AREs) with uncertain (random) velocity and reaction parameters. We derive a deterministic equation that governs the evolution of cumulative distribution function (CDF) of a solution of the underlying ARE. Although requiring closure, this differential equation benefits from uniquely defined boundary and initial conditions and can be solved with classic techniques. Here we analyze the accuracy and robustness of the large-eddy-diffusivity closure by comparison with Monte Carlo simulations for different correlation structures and parameters.

  9. Scyphozoa in the Bornholm Basin (central Baltic Sea) The role of advection

    NASA Astrophysics Data System (ADS)

    Barz, Kristina; Hinrichsen, Hans-Harald; Hirche, Hans-Jürgen

    2006-04-01

    The usual absence of ephyrae and late appearance of medusae of the Scyphozoa Aurelia aurita and Cyanea capillata in the Bornholm Basin (BB; central Baltic Sea) indicate that these species are not strobilating in the region and their presence depends on advection. To study their potential origin we compared drift from historically known strobilation areas derived from a circulation model with spatial distributions observed during 19 cruises in the BB during 2002 and 2003. The model results are in good accordance with the field observations. According to the model results inter-annual differences in the timing of first appearance and life stage at appearance of A. aurita were clearly related to differences in the hydrodynamic regime during the investigation periods. During the stagnation regime in 2002 young medusae occurred first in June in the BB. In contrast, in 2003 fast transport due to several inflow events advected ephyrae released between January and March in the western Baltic already in April to the BB. Although the Gullmar Fjord (western Sweden) is the nearest known strobilation area for C. capillata, the model did not support advection from there in numbers explaining the occurrence of this species in the BB in 2002 and 2003. If the model works adequately in this regions we have to assume that the Gullmar Fjord is not a main source region of C. capillata in the BB, but other strobilation areas in the Kattegat or the North Sea appear more important. Our results imply that advection and inflow events are critical for the occurrence and distribution of early stages of jellyfish in the central Baltic Sea. They demonstrate the potential of circulation models as tools to study the effect of long-range transport on the spatial composition of these organisms.

  10. Shadowing and the role of small diffusivity in the chaotic advection of scalars

    NASA Technical Reports Server (NTRS)

    Klapper, I.

    1992-01-01

    Using techniques from shadowing theory, the solution of the scalar advection-diffusion equation is studied. It is shown that, under certain circumstances, the effect of small scalar diffusivity is to smooth the zero-diffusivity solution by averaging local fine-scaled structure against a Gaussian. The method of study depends on shadowing and thus fails for nonuniformly stretching systems, its failure suggesting the ways in which the effects of asymptotically small molecular diffusion can become nonlocal in chaotic fluid flows.

  11. Carbon dioxide seasonality in dynamically ventilated caves: the role of advective fluxes

    NASA Astrophysics Data System (ADS)

    Lang, Marek; Faimon, Jiří; Godissart, Jean; Ek, Camille

    2016-07-01

    The seasonality in cave CO2 levels was studied based on (1) a new data set from the dynamically ventilated Comblain-au-Pont Cave (Dinant Karst Basin, Belgium), (2) archive data from Moravian Karst caves, and (3) published data from caves worldwide. A simplified dynamic model was proposed for testing the effect of all conceivable CO2 fluxes on cave CO2 levels. Considering generally accepted fluxes, i.e., the direct diffusive flux from soils/epikarst, the indirect flux derived from dripwater degassing, and the input/output fluxes linked to cave ventilation, gives the cave CO2 level maxima of 1.9 × 10-2 mol m-3 (i.e., ˜ 440 ppmv), which only slightly exceed external values. This indicates that an additional input CO2 flux is necessary for reaching usual cave CO2 level maxima. The modeling indicates that the additional flux could be a convective advective CO2 flux from soil/epikarst driven by airflow (cave ventilation) and enhanced soil/epikarstic CO2 concentrations. Such flux reaching up to 170 mol s-1 is capable of providing the cave CO2 level maxima up to 3 × 10-2 mol m-3 (70,000 ppmv). This value corresponds to the maxima known from caves worldwide. Based on cave geometry, three types of dynamic caves were distinguished: (1) the caves with the advective CO2 flux from soil/epikarst at downward airflow ventilation mode, (2) the caves with the advective soil/epikarstic flux at upward airflow ventilation mode, and (3) the caves without any soil/epikarstic advective flux. In addition to CO2 seasonality, the model explains both the short-term and seasonal variations in δ13C in cave air CO2.

  12. Advective transport and decomposition of chain-forming planktonic diatoms in permeable sediments

    NASA Astrophysics Data System (ADS)

    Ehrenhauss, Sandra; Huettel, Markus

    2004-09-01

    In laboratory chamber experiments we demonstrate that permeable sediments (>7×10 -12 m 2) exposed to boundary flows filter chain-forming coastal bloom diatoms ( Skeletonema costatum and Thalassiosira rotula) from the water column, causing rapid transfer of fresh organic particulate matter into sediment layers as deep as 5 cm within 72 h. The penetration depth of the diatoms depends on the permeability of the bed and the length of the chains. Long chains were not transported as deep into the sediment as short chains or single cells. The fast advective transfer of phytoplankton cells into sandy sediments may be an important process facilitating organic matter uptake and preventing resuspension of deposited organic material in high-energy coastal environments. High advective flushing rates in medium- and coarse-grained sandy sediments enhanced the mineralisation of the trapped diatoms (2300 to 3200 μmol C m -2 d -1), stimulated benthic oxygen consumption (2300 to 3000 μmol O 2 m -2 d -1), as well as nitrification (up to 20 μmol NO 3- m -2 d -1), relative to sediment where diffusion dominated the solute exchange. Advective solute exchange rates that increase with increasing permeability prevent the accumulation of Si(OH) 4 near the dissolving frustules and in the pore water, leading to an effective recycling of dissolved silica to the production process in the water column (95 to 101 μmol Si(OH) 4 m -2 d -1). This process may also enhance dissolution rates of the deposited opal in coarse-grained sands by maintaining higher degrees of undersaturation than in fine-grained sediments. Our results suggest that advective filtration of planktonic diatoms into permeable sediments increases mineralisation and recycling of Si(OH) 4 and organic matter in high energetic shelf areas.

  13. POD-Galerkin advection model for convective flow: application to a flapping rectangular supersonic jet

    NASA Astrophysics Data System (ADS)

    Jaunet, V.; Collin, E.; Delville, J.

    2016-05-01

    This article describes a model obtained by applying proper orthogonal decomposition to the advection equation. The resulting set of equations links the POD modes, their temporal and spatial derivatives and the flow convection velocity. It provides a technique to calculate the convection velocity of coherent structures. It follows, from the model, that a priori knowledge of the convection velocity suffices to construct a dynamical model of the flow. This is demonstrated using experimental data.

  14. Selective Sorption of Dissolved Organic Carbon Compounds by Temperate Soils

    SciTech Connect

    Jagadamma, Sindhu; Mayes, Melanie; Phillips, Jana Randolph

    2012-01-01

    Physico-chemical sorption of dissolved organic carbon (DOC) on soil minerals is one of the major processes of organic carbon (OC) stabilization in soils, especially in deeper layers. The attachment of C on soil solids is related to the reactivity of the soil minerals and the chemistry of the sorbate functional groups, but the sorption studies conducted without controlling microbial activity may overestimate the sorption potential of soil. This study was conducted to examine the sorptive characteristics of a diverse functional groups of simple OC compounds (D-glucose, L-alanine, oxalic acid, salicylic acid, and sinapyl alcohol) on temperate climate soil orders (Mollisols, Ultisols and Alfisols) with and without biological degradative processes. Equilibrium batch experiments were conducted using 0-100 mg C L-1 at a solid-solution ratio of 1:60 for 48 hrs and the sorption parameters were calculated by Langmuir model fitting. The amount of added compounds that remained in the solution phase was detected by high performance liquid chromatography (HPLC) and total organic C (TOC) analysis. Soil sterilization was performed by -irradiation technique and experiments were repeated to determine the contribution of microbial degradation to apparent sorption. Overall, Ultisols did not show a marked preference for apparent sorption of any of the model compounds, as indicated by a narrower range of maximum sorption capacity (Smax) of 173-527 mg kg soil-1 across compounds. Mollisols exhibited a strong preference for apparent sorption of oxalic acid (Smax of 5290 mg kg soil-1) and sinapyl alcohol (Smax of 2031 mg kg soil-1) over the other compounds. The propensity for sorption of oxalic acid is mainly attributed to the precipitation of insoluble Ca-oxalate due to the calcareous nature of most Mollisol subsoils and its preference for sinapyl alcohol could be linked to the polymerization of this lignin monomer on 2:2 mineral dominated soils. The reactivity of Alfisols to DOC was in

  15. Role of selective sorption in chemiresistor sensors for organophosphorus detection

    SciTech Connect

    Grate, J.W.; Klusty, M.; Barger, W.R.; Snow, A.W. )

    1990-09-15

    Nickel, palladium, platinum, and copper tetrakis(cumylphenoxy)phthalocyanines were combined with an elastomeric, oligomeric fluoropolyol material in mixed Langmuir-Blodgett films on chemiresistor sensors for organophosphorus vapors. The phthalocyanine carried the electronic current, while the fluoropolyol improved the sorption characteristics of the film. This strategy produced sensors with improved response and recovery times and high sensitivity. Factors influencing the selectivity of the sensor responses were analyzed in terms of two steps: sorption and transduction. Sorption was shown to be the primary determinant of selectivity among the organic vapors tested.

  16. Sorption of lanthanum ions by natural clinoptilolite tuff

    NASA Astrophysics Data System (ADS)

    Dampilova, B. V.; Zonkhoeva, E. L.

    2013-08-01

    The equilibrium and kinetics of sorption of lanthanum ions on natural clinoptilolite tuff are studied. It is demonstrated that sorption of lanthanum ions from diluted solutions occurs in micropores of clinoptilolite, and from concentrated solutions in the mesoporous structure of tuff. The main capacity of zeolite tuff is found in the secondary porous structure. The sorption of lanthanum ions is limited by diffusion in tuff grains. Lanthanum ions are regularly distributed in the tuff phase and interact with the Brønsted centers of large clinoptilolite cavities.

  17. Study of sorption and swelling on block coals

    NASA Astrophysics Data System (ADS)

    Qu, Shijie; Chen, Guoqing; Yang, Jianli; Shen, Wenzhong; Li, Yunmei; Niu, Hongxian; Busch, Andreas

    2013-04-01

    Reducing CO2 emission into atmosphere is very important for the mitigation of global climate change. Many processes have been proposed for this purpose, including CO2 sequestration in un-minable coalbeds and enhance coalbed methane production (CO2-ECBM). Several theoretical studies and worldwide demonstration sites have illustrated the potential of the process.Most of these projects experienced permeability reduction of the coalbed with time, leading to operational difficulties because of the loss of injectability. The permeability reduction is generally considered to be caused by the coal swelling that is induced by gas sorption, because it can narrow or close the cleat of the coalbed. As a result, the migration of injected CO2 in coal pore or cleat becomes more difficult. Therefore, sorption and swelling characterizations are important issues for forecasting the performance of aimed coalbed. In this work, CO2/CH4sorption and swelling isotherms of two Chinese block coals (QS and YQ) were measured simultaneously under different temperature and pressure conditions. It was found that the swelling ratio of coal block by CO2 sorption increased with the increase of the gas sorption amount until it approached to a value of ~3 mmol-gas/g-coal and decreased slightly afterwards for both coals; while the swelling ratio of coal block by CH4 sorption increased with the increase of the gas sorption amount in the entire test region for both coals. By correlating the gas sorption amount and the corresponding swelling ratio, it was found that the swelling ratio of coal block is independent of temperature and coal type when the gas sorption amount is less than ~2mmol/g-coal. The differential profile of the swelling ratio with respect to sorption amount is appeared with a maximum value at ~1 mmol/g-coal for CH4 and at ~1.8 mmol/g-coal for CO2. Based on the theories related to gas sorption and solid surface energy, a mathematical model which correlates sorption and swelling behavior

  18. A Petroleum Vapor Intrusion Model Involving Upward Advective Soil Gas Flow Due to Methane Generation.

    PubMed

    Yao, Yijun; Wu, Yun; Wang, Yue; Verginelli, Iason; Zeng, Tian; Suuberg, Eric M; Jiang, Lin; Wen, Yuezhong; Ma, Jie

    2015-10-01

    At petroleum vapor intrusion (PVI) sites at which there is significant methane generation, upward advective soil gas transport may be observed. To evaluate the health and explosion risks that may exist under such scenarios, a one-dimensional analytical model describing these processes is introduced in this study. This new model accounts for both advective and diffusive transport in soil gas and couples this with a piecewise first-order aerobic biodegradation model, limited by oxygen availability. The predicted results from the new model are shown to be in good agreement with the simulation results obtained from a three-dimensional numerical model. These results suggest that this analytical model is suitable for describing cases involving open ground surface beyond the foundation edge, serving as the primary oxygen source. This new analytical model indicates that the major contribution of upward advection to indoor air concentration could be limited to the increase of soil gas entry rate, since the oxygen in soil might already be depleted owing to the associated high methane source vapor concentration. PMID:26322369

  19. Modulated point-vortex pairs on a rotating sphere: Dynamics and chaotic advection

    NASA Astrophysics Data System (ADS)

    Drótos, Gábor; Tél, Tamás; Kovács, Gergely

    2013-06-01

    The dynamics of modulated point-vortex pairs is investigated on a rotating sphere, where modulation is chosen to reflect the conservation of angular momentum (potential vorticity). For sufficiently close vortices (dipoles) the trajectories of their center-of-mass are shown to correspond to those of a point particle moving freely on a rotating sphere. For finite size vortex pairs, a qualitative similarity to the geodesic dynamics is found. The advection dynamics generated by vortex pairs on a rotating sphere is found to be chaotic. In the short time dynamics we point out a transition from closed to open chaotic advection, which implies that the transport properties of the flow might drastically be altered by changing the initial conditions of the pair on the sphere. Due to spherical topology, for long times, even the open advection patterns are found to gradually cross over to that corresponding to a homogeneous closed mixing. This pattern extends along a zonal band, whereas short term closed mixing remains always bounded to the moving pair.

  20. A Comparative Study of Indoor Radon Contributed by Diffusive and Advective Transport through Intact Concrete

    NASA Astrophysics Data System (ADS)

    Chauhan, R. P.; Kumar, Amit

    The present work is aimed that out of diffusive and advective transport which is dominant process for indoor radon entry under normal room conditions. For this purpose the radon diffusion coefficient and permeability of concrete were measured by specially designed experimental set up. The radon diffusion coefficient of concrete was measured by continuous radon monitor. The measured value was (3.78 ± 0.39)×10-8 m2/s and found independent of the radon gas concentration in source chamber. The radon permeability of concrete varied between 1.85×10-17 to 1.36×10-15 m2 for the bulk pressure difference fewer than 20 Pa to 73.3 kPa. From the measured diffusion coefficient and absolute permeability, the radon flux from the concrete surface having concentrations gradient 12-40 kBq/m3 and typical floor thickness 0.1 m was calculated by the application of Fick and Darcy laws. Using the measured flux attributable to diffusive and advective transport, the indoor radon concentration for a typical Indian model room having dimension (5×6×7) m3 was calculated under average room ventilation (0.63 h-1). The results showed that the contribution of diffusive transport through intact concrete is dominant over the advective transport, as expected from the low values of concrete permeability.

  1. Evaluating two numerical advection schemes in HYCOM for eddy-resolving modelling of the Agulhas Current

    NASA Astrophysics Data System (ADS)

    Backeberg, B. C.; Bertino, L.; Johannessen, J. A.

    2009-06-01

    A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism of the model simulation. The most striking improvement over the standard 2nd order momentum advection scheme, is that the southern Agulhas Current is simulated as a well-defined meandering current, rather than a train of successive eddies. A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. It is found that the transport, and hence this exchange, is sensitive to the occurrences of mesoscale features originating upstream in the Mozambique Channel and southern East Madagascar Current, and that the improved HYCOM simulation is well suited for further studies of these inter-actions.

  2. Evaluating two numerical advection schemes in HYCOM for eddy-resolving modelling of the Agulhas Current

    NASA Astrophysics Data System (ADS)

    Backeberg, B. C.; Bertino, L.; Johannessen, J. A.

    2009-02-01

    A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism of the model simulation. The most striking improvement over the standard 2nd order momentum advection scheme, is that the Southern Agulhas Current is simulated as a well-defined meandering current, rather than a train of successive eddies. A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. It is found that the transport, and hence this exchange, is sensitive to the occurrences of mesoscale features originating upstream in the Mozambique Channel and Southern East Madagascar Current, and that the improved HYCOM simulation is well suited for further studies of these inter-actions.

  3. Advective pore water input of nutrients to the Satilla River Estuary, Georgia, USA

    NASA Astrophysics Data System (ADS)

    Jahnke, R. A.; Alexander, C. R.; Kostka, J. E.

    2003-03-01

    In situ benthic flux measurements, pore water nutrient profiles, water column nutrient distributions, sediment grain size distributions and side-scan sonar observations suggest that advective transport of pore waters may be a major input pathway of nutrients into the Satilla River Estuary (coastal Georgia, USA). In situ benthic chamber incubations demonstrate the occurrence of highly variable, but occasionally very large sea floor fluxes of silicate, phosphate, and ammonium. Locally occurring benthic microbial mineralization of organic matter, as estimated by S 35-sulphate reduction rate measurements, is insufficient to support these large fluxes. We hypothesize that the observed interlayering of permeable, sandy sediments with fine-grained, organic-rich sediments in the estuary provides conduits for advective transport of pore water constituents out of the sediments. Because permeable layers may extend significant distances beneath the salt marsh, the large fluxes observed may be supported by remineralization occurring over large areas adjacent to the estuary. Advective transport may be induced by pressure gradients generated by a variety of processes, including landward recharge by meteoric or rain waters if sand layers extend far enough into the maritime coastal lands. Alternatively, tidal variations across the salt marsh sediment surface may hydraulically pump water through the sediment system. Because these fluxes appear to be concentrated into small layers, this source may be a significant input of nutrients to the estuary even if permeable, sandy layers comprise a very small proportion of the seabed.

  4. Modulated point-vortex pairs on a rotating sphere: dynamics and chaotic advection.

    PubMed

    Drótos, Gábor; Tél, Tamás; Kovács, Gergely

    2013-06-01

    The dynamics of modulated point-vortex pairs is investigated on a rotating sphere, where modulation is chosen to reflect the conservation of angular momentum (potential vorticity). For sufficiently close vortices (dipoles) the trajectories of their center-of-mass are shown to correspond to those of a point particle moving freely on a rotating sphere. For finite size vortex pairs, a qualitative similarity to the geodesic dynamics is found. The advection dynamics generated by vortex pairs on a rotating sphere is found to be chaotic. In the short time dynamics we point out a transition from closed to open chaotic advection, which implies that the transport properties of the flow might drastically be altered by changing the initial conditions of the pair on the sphere. Due to spherical topology, for long times, even the open advection patterns are found to gradually cross over to that corresponding to a homogeneous closed mixing. This pattern extends along a zonal band, whereas short term closed mixing remains always bounded to the moving pair. PMID:23848782

  5. Advection-condensation of water vapor with coherent stirring: a stochastic approach

    NASA Astrophysics Data System (ADS)

    Tsang, Yue-Kin; Vanneste, Jacques; Vallis, Geoffrey

    2015-11-01

    The dynamics of atmospheric water is an essential ingredient of weather and climate. Water vapor, in particular, is an important greenhouse gas whose distribution has a strong impact on climate. To gain insight into the factors controlling the distribution of atmospheric moisture, we study an advection-condensation model in which water vapor is passively advected by a prescribed velocity and condensation acts as a sink that maintains the specific humidity below a prescribed, spatially dependent saturation value. The velocity consists of two parts: a single vortex representing large-scale coherent flow (e.g. the Hadley cell) and a white noise component mimicking small-scale turbulence. Steady-state is achieved in the presence of a moisture source at a boundary. We formulate this model as a set of stochastic differential equations. In the fast advection limit, analytical expression for the water vapor distribution is obtained by matched asymptotics. This allows us to make various predictions including the dependence of total precipitation on the vortex strength. These analytical results are verified by Monte Carlo simulations. This work is supported by the UK EPSRC Grant EP/I028072/1 and the Feasibility Fund from the UK EPSRC Network ReCoVER.

  6. Solving turbulent diffusion flame in cylindrical frame applying an improved advective kinetics scheme

    NASA Astrophysics Data System (ADS)

    Darbandi, Masoud; Ghafourizadeh, Majid

    2015-12-01

    In this work, we derive a few new advective flux approximation expressions, apply them in a hybrid finite-volume-element (FVE) formulation, and solve the turbulent reacting flow governing equations in the cylindrical frame. To derive these advective-kinetic-based expressions, we benefit from the advantages of a physical influence scheme (PIS) basically, extend it to the cylindrical frame suitably, and approximate the required advective flux terms at the cell faces more accurately. The present numerical scheme not only respects the physics of flow correctly but also resolves the pressure-velocity coupling problem automatically. We also suggest a bi-implicit algorithm to solve the set of coupled turbulent reacting flow governing equations, in which the turbulence and chemistry governing equations are solved simultaneously. To evaluate the accuracy of new derived FVE-PIS expressions, we compare the current solutions with other available numerical solutions and experimental data. The comparisons show that the new derived expressions provide some more advantages over the past numerical approaches in solving turbulent diffusion flame in the cylindrical frame. Indeed, the current method and formulations can be used to solve and analyze the turbulent diffusion flames in the cylindrical coordinates very reliably.

  7. Universal limiter for transient interpolation modeling of the advective transport equations: The ULTIMATE conservative difference scheme

    NASA Technical Reports Server (NTRS)

    Leonard, B. P.

    1988-01-01

    A fresh approach is taken to the embarrassingly difficult problem of adequately modeling simple pure advection. An explicit conservative control-volume formation makes use of a universal limiter for transient interpolation modeling of the advective transport equations. This ULTIMATE conservative difference scheme is applied to unsteady, one-dimensional scalar pure advection at constant velocity, using three critical test profiles: an isolated sine-squared wave, a discontinuous step, and a semi-ellipse. The goal, of course, is to devise a single robust scheme which achieves sharp monotonic resolution of the step without corrupting the other profiles. The semi-ellipse is particularly challenging because of its combination of sudden and gradual changes in gradient. The ULTIMATE strategy can be applied to explicit conservation schemes of any order of accuracy. Second-order schemes are unsatisfactory, showing steepening and clipping typical of currently popular so-called high resolution shock-capturing of TVD schemes. The ULTIMATE third-order upwind scheme is highly satisfactory for most flows of practical importance. Higher order methods give predictably better step resolution, although even-order schemes generate a (monotonic) waviness in the difficult semi-ellipse simulation. Little is to be gained above ULTIMATE fifth-order upwinding which gives results close to the ultimate for which one might hope.

  8. A deterministic Lagrangian particle separation-based method for advective-diffusion problems

    NASA Astrophysics Data System (ADS)

    Wong, Ken T. M.; Lee, Joseph H. W.; Choi, K. W.

    2008-12-01

    A simple and robust Lagrangian particle scheme is proposed to solve the advective-diffusion transport problem. The scheme is based on relative diffusion concepts and simulates diffusion by regulating particle separation. This new approach generates a deterministic result and requires far less number of particles than the random walk method. For the advection process, particles are simply moved according to their velocity. The general scheme is mass conservative and is free from numerical diffusion. It can be applied to a wide variety of advective-diffusion problems, but is particularly suited for ecological and water quality modelling when definition of particle attributes (e.g., cell status for modelling algal blooms or red tides) is a necessity. The basic derivation, numerical stability and practical implementation of the NEighborhood Separation Technique (NEST) are presented. The accuracy of the method is demonstrated through a series of test cases which embrace realistic features of coastal environmental transport problems. Two field application examples on the tidal flushing of a fish farm and the dynamics of vertically migrating marine algae are also presented.

  9. The effects of advection solvers on the performance of air quality models

    SciTech Connect

    Tanrikulu, S.; Odman, M.T.

    1996-12-31

    The available numerical solvers for the advection term in the chemical species conservation equation have different properties, and consequently introduce different types of errors. These errors can affect the performance of air quality models and lead to biases in model results. In this study, a large number of advection solvers have been studied and six of them were identified as having potential for use in photochemical models. The identified solvers were evaluated extensively using various numerical tests that are relevant to air quality simulations. Among the solvers evaluated, three of them showed better performance in terms of accuracy and some other characteristics such as conservation of mass and positivity. They are the solvers by Bott, Yuamartino, and Dabdub and Seinfeld. These three solvers were incorporated into the SARMAP Air Quality Model (SAQM) and the August 3-6, 1990 ozone episode in the San Joaquin Valley of California was simulated with each. A model performance analysis was conducted for each simulation using the rich air quality database of the 1990 San Joaquin Valley Air Quality Study. The results of the simulations were compared with each other and the effects of advection solvers on the performance of the model are discussed.

  10. Sulfamethoxazole sorption by sediment fractions in comparison to pyrene and bisphenol A.

    PubMed

    Hou, Juan; Pan, Bo; Niu, Xuekui; Chen, Jianzhong; Xing, Baoshan

    2010-09-01

    The environmental behavior of antibiotics has attracted great research attention. However, their sorption mechanisms in soils/sediments are still unknown. Comparison of the sorption properties between the widely-studied hydrophobic organic contaminants (HOCs) and antibiotics may provide valuable insight to antibiotic sorption mechanisms. Thus, in this study batch experiments for pyrene (PYR), bisphenol A (BPA), and sulfamethoxazole (SMX) sorption were conducted on a sediment sample and its separated fractions. Our results showed the high sorption of PYR on black carbon and organic matter. Although high sorption of SMX was observed for both separated organic fractions (humic acids) and inorganic mineral particles, the original sediment particles showed relatively low sorption. Competitive sorption between SMX and dissolved humic acid on mineral particles was observed in this study. This competitive interaction is a unique process for antibiotic sorption in soils/sediments compared with apolar HOCs and may be one of the important factors controlling the antibiotic sorption. PMID:20609505

  11. Anomalous transport regimes and asymptotic concentration distributions in the presence of advection and diffusion on a comb structure

    NASA Astrophysics Data System (ADS)

    Dvoretskaya, Olga A.; Kondratenko, Peter S.

    2009-04-01

    We study the transport of impurity particles on a comb structure in the presence of advection. The main body concentration and asymptotic concentration distributions are obtained. Seven different transport regimes occur on the comb structure with finite teeth: classical diffusion, advection, quasidiffusion, subdiffusion, slow classical diffusion, and two kinds of slow advection. Quasidiffusion deserves special attention. It is characterized by a linear growth of the mean-square displacement. However, quasidiffusion is an anomalous transport regime. We established that a change in transport regimes in time leads to a change in regimes in space. Concentration tails have a cascade structure, namely, consisting of several parts.

  12. Validating Mechanistic Sorption Model Parameters and Processes for Reactive Transport in Alluvium

    SciTech Connect

    Zavarin, M; Roberts, S K; Rose, T P; Phinney, D L

    2002-05-02

    The laboratory batch and flow-through experiments presented in this report provide a basis for validating the mechanistic surface complexation and ion exchange model we use in our hydrologic source term (HST) simulations. Batch sorption experiments were used to examine the effect of solution composition on sorption. Flow-through experiments provided for an analysis of the transport behavior of sorbing elements and tracers which includes dispersion and fluid accessibility effects. Analysis of downstream flow-through column fluids allowed for evaluation of weakly-sorbing element transport. Secondary Ion Mass Spectrometry (SIMS) analysis of the core after completion of the flow-through experiments permitted the evaluation of transport of strongly sorbing elements. A comparison between these data and model predictions provides additional constraints to our model and improves our confidence in near-field HST model parameters. In general, cesium, strontium, samarium, europium, neptunium, and uranium behavior could be accurately predicted using our mechanistic approach but only after some adjustment was made to the model parameters. The required adjustments included a reduction in strontium affinity for smectite, an increase in cesium affinity for smectite and illite, a reduction in iron oxide and calcite reactive surface area, and a change in clinoptilolite reaction constants to reflect a more recently published set of data. In general, these adjustments are justifiable because they fall within a range consistent with our understanding of the parameter uncertainties. These modeling results suggest that the uncertainty in the sorption model parameters must be accounted for to validate the mechanistic approach. The uncertainties in predicting the sorptive behavior of U-1a and UE-5n alluvium also suggest that these uncertainties must be propagated to nearfield HST and large-scale corrective action unit (CAU) models.

  13. Lectures on Dispersion Theory

    DOE R&D Accomplishments Database

    Salam, A.

    1956-04-01

    Lectures with mathematical analysis are given on Dispersion Theory and Causality and Dispersion Relations for Pion-nucleon Scattering. The appendix includes the S-matrix in terms of Heisenberg Operators. (F. S.)

  14. Electrokinetic induced solute dispersion in porous media; pore network modeling

    NASA Astrophysics Data System (ADS)

    Li, Shuai; Schotting, Ruud; Raoof, Amir

    2013-04-01

    Electrokinetic flow plays an important role in remediation process, separation technique, and chromatography. The solute dispersion is a key parameter to determine transport efficiency. In this study, we present the electrokinetic effects on solute dispersion in porous media at the pore scale, using a pore network model. The analytical solution of the electrokinetic coupling coefficient was obtained to quantity the fluid flow velocity in a cylinder capillary. The effect of electrical double layer on the electrokinetic coupling coefficient was investigated by applying different ionic concentration. By averaging the velocity over cross section within a single pore, the average flux was obtained. Applying such single pore relationships, in the thin electrical double layer limit, to each and every pore within the pore network, potential distribution and the induced fluid flow was calculated for the whole domain. The resulting pore velocities were used to simulate solute transport within the pore network. By averaging the results, we obtained the breakthrough curve (BTC) of the average concentration at the outlet of the pore network. Optimizing the solution of continuum scale advection-dispersion equation to such a BTC, solute dispersion coefficient was estimated. We have compared the dispersion caused by electrokinetic flow and pure pressure driven flow under different Peclet number values. In addition, the effect of microstructure and topological properties of porous media on fluid flow and solute dispersion is presented, mainly based on different pore coordination numbers.

  15. Advective Removal of Intraparticle Uranium from Contaminated Vadose Zone Sediments, Hanford, USA

    SciTech Connect

    Ilton, Eugene S.; Qafoku, Nikolla; Liu, Chongxuan; Moore, D. A.; Zachara, John M.

    2008-03-01

    A column study on U contaminated vadose zone sediments from the Hanford Site, WA, was performed in order to aid the development of a model for predicting U(VI) release rates under a dynamic flow regime and for variable geochemical conditions. The sediments of interest are adjacent to and below tank BX-102, part of the BX tank farm that contained high level liquid radioactive waste. Two sediments, with different U(VI) loadings and intraparticle large fracture vs. smaller fracture ratios, were reacted with three different solutions. The primary reservoir for U(VI) appears to be a micron-sized nanocrystalline Na-U-Si phase, possibly Na-boltwoodite, that nucleated and grew on plagioclase grains that line fractures within sand-sized granitic clasts. The solutions were all calcite saturated and in equilibrium with atmospheric CO2, where one solution was simply DI-water, the second was a synthetic ground water (SGW) with elevated Na, and the third was the same SGW but with both elevated Na and Si. The latter two solutions were employed, in part, to test the effect of saturation state on U(VI) release. For both sediments and all three electrolytes, there was an initial rapid release of U(VI) to the advecting solution followed by a plateau of low U(VI) concentration. U(VI) effluent concentration increased during subsequent stop flow (SF) events. The electrolytes with elevated Na and Si appreciably depressed U(VI) concentrations relative to DI water. The effluent data for both sediments and all three electrolytes was simulated reasonably well by a three domain model (the advecting fluid, fractures, and matrix) that coupled U(VI) dissolution rates, intraparticle U(VI) diffusion, and interparticle advective transport of U(VI); where key transport and dissolution processes had been parameterized in previous batch studies. For the calcite-saturated DI-water, U(VI) concentrations in the effluent remained far below saturation with respect to Na-boltwoodite and release of U(VI) to

  16. Variability of Sub-Canopy Flow, Temperature, and Horizontal Advection in Moderately Complex Terrain

    NASA Astrophysics Data System (ADS)

    Thomas, Christoph K.

    2011-04-01

    We examine the space-time structure of the wind and temperature fields, as well as that of the resulting spatial temperature gradients and horizontal advection of sensible heat, in the sub-canopy of a forest with a dense overstorey in moderately complex terrain. Data were collected from a sensor network consisting of ten stations and subject to orthogonal decomposition using the multiresolution basis set and stochastic analyses including two-point correlations, dimensional structure functions, and various other bulk measures for space and time variability. Despite some similarities, fundamental differences were found in the space-time structure of the motions dominating the variability of the sub-canopy wind and temperature fields. The dominating motions occupy similar spatial, but different temporal, scales. A conceptual space-time diagram was constructed based on the stochastic analysis that includes the important end members of the spatial and temporal scales of the observed motions of both variables. Short-lived and small-scale motions govern the variability of the wind, while the diurnal temperature oscillation driven by the surface radiative transfer is the main determinant of the variability in the temperature signal, which occupies much larger time scales. This scale mismatch renders Taylor's hypothesis for sub-canopy flow invalid and aggravates the computation of meaningful estimates of horizontal advective fluxes without dense spatial information. It may further explain the ambiguous and inconclusive results reported in numerous energy and mass balance and advection studies evaluating the hypothesis that accounting for budget components other than the change in storage term and the vertical turbulent flux improves the budget closure when turbulent diffusion is suppressed in plant canopies. Estimates of spatial temperature gradients and advective fluxes were sensitive to the network geometry and the spatial interpolation method. The assumption of linear

  17. Dispersion y dinamica poblacional

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dispersal behavior of fruit flies is appetitive. Measures of dispersion involve two different parameter: the maximum distance and the standard distance. Standard distance is a parameter that describes the probalility of dispersion and is mathematically equivalent to the standard deviation around ...

  18. Sorption kinetics and mechanism of various oils into kapok assembly.

    PubMed

    Dong, Ting; Wang, Fumei; Xu, Guangbiao

    2015-02-15

    Sorption rates of kapok fibers on different oils, such as diesel, cooking oil, used motor oil, and motor oil, were quantitatively evaluated by using a wicking method. Kapok fibers absorbing different oils exhibited large differences in terms sorption coefficients. Microscopic observations of oil wetting on a single kapok showed that the four oils had varying wettability and adhesiveness to kapok, but that all of them penetrated into kapok lumens quickly because of the fiber's low surface energy, which was 40.64 mN/m, and extreme hydrophobicity, with a water contact angle up to 151°. After treatment with chloroform, there were slight changes in oil absorbencies to kapok, but the sorption coefficients for the four oils increased markedly. SEM demonstrated that chloroform treatments caused the smooth surface of the kapok fibers to become highly roughened, with densely vertical grooves that provided more available surface and a larger driving force for oil sorption through the fiber assembly. PMID:25528222

  19. Sorption and transport of sulfur dioxide in polysulfone

    SciTech Connect

    Pfromm, P.H.; Koros, W.J. . Dept. of Chemical Engineering)

    1993-10-25

    The sorption and transport of sulfur dioxide (SO[sub 2]) in polymers is important in areas such as food packaging, polymer degradation, and sensors and monitoring devices. Another possible application is in pollution control for exhaust gases from power plants. Polysulfone is a polymer that is widely used for commercial gas separations with membranes. The authors have investigated the sorption and transport of SO[sub 2] in a commercially available Bisphenol A polysulfone near room temperature. The results were interpreted using the dual-mode sorption model with partial immobilization. Although similar data on other polymers have been published in the literature, they are not aware of any studies of sorption and transport of SO[sub 2] in polysulfone.

  20. SORPTION ON WASTEWATER SOLIDS: ELIMINATION OF BIOLOGICAL ACTIVITY

    EPA Science Inventory

    Sorption was found to be greatly affected by the biological activity in wastewater solids. wo experimental techniques, cyanide treatment and pasteurization, were developed for eliminating the biological activity during isotherm measurements. oth methods are effective; however, pa...

  1. Lead and cadmium sorption mechanisms on magnetically modified biochars.

    PubMed

    Trakal, Lukáš; Veselská, Veronika; Šafařík, Ivo; Vítková, Martina; Číhalová, Sylva; Komárek, Michael

    2016-03-01

    This paper discusses Cd(II) and Pb(II) sorption efficiency of biochars modified by impregnation with magnetic particles. All selected biochar characteristics were significantly affected after the modification. More specifically, the cation exchange capacity increased after the modification, except for grape stalk biochar. However, the changes in the pH value, PZC, and BET surface after modification process were less pronounced. The metal loading rate was also significantly improved, especially for Cd(II) sorption on/in nut shield and plum stone biochars (10- and 16-times increase, respectively). The results indicated that cation exchange (as a metal sorption mechanism) was strengthened after Fe oxide impregnation, which limited the desorbed amount of tested metals. In contrast, the magnetization of grape stalk biochar reduced Pb(II) sorption in comparison with that of pristine biochar. Magnetic modification is, therefore, more efficient for biochars with well-developed structure and for more mobile metals, such as Cd(II). PMID:26748045

  2. Sorption and desorption of sulfentrazone in Brazilian soils.

    PubMed

    Passos, Ana Beatriz R J; Freitas, Marco Antonio M; Torres, Lívia G; Silva, Antonio A; Queiroz, Maria Eliana L R; Lima, Cláudio F

    2013-01-01

    This study was undertaken to obtain information about the behavior of sulfentrazone in soil by evaluating the sorption and desorption of the herbicide in different Brazilian soils. Batch equilibrium method was used and the samples were analyzed by high performance liquid chromatography. Based on the results obtained from the values of Freundlich constants (Kf), we determined the order of sorption (Haplic Planosol < Red-Yellow Latosol < Red Argisol < Humic Cambisol < Regolitic Neosol) and desorption (Regolitic Neosol < Red Argisol < Humic Cambisol < Haplic Planosol < Red-Yellow Latosol) of sulfentrazone in the soils. The process of pesticide sorption in soils was dependent on the levels of organic matter and clay, while desorption was influenced by the organic matter content and soil pH. Thus, the use of sulfentrazone in soils with low clay content and organic matter (low sorption) increases the probability of contaminating future crops. PMID:23638891

  3. Sorption behavior of mixtures of glycerol and starch.

    PubMed

    Enrione, Javier I; Hill, Sandra E; Mitchell, John R

    2007-04-18

    Glycerol is often added to starches to plasticize the product, but the presence of glycerol may also affect the water content of the samples. To evaluate the effect of glycerol on the sorption properties of starches, waxy maize, rice, and wheat starch were thermomechanically extruded in the presence of glycerol. Sorption isotherms of these extruded samples were ascertained using dynamic vapor sorption (DVS). BET and GAB modeling showed a monolayer (mo) significantly higher for waxy maize than for rice and wheat. Glycerol inclusion changed the model values, indicating reduction in sorption energy at the monolayer and restructuring of the multilayer. An interaction factor (xi) based on weight fraction models was calculated. Differences in xi were obtained when glycerol was added, varying from approximately 0.9 for 5% glycerol to approximately 0.8 for 20% glycerol, supporting the hypothesis of interactions between starch and this polyol. PMID:17362027

  4. SPECTROSCOPIC STUDY OF SORPTION OF NITROGEN HETEROCYCLIC COMPOUNDS ON PHYLLOSILICATES

    EPA Science Inventory

    The present study focused on understanding the sorption characteristics of acridine (AcN)and acridine-9-carboxylic acid (AcNCOOH), two typical nitrogen heterocyclic compounds (NHCs), on well-characterized phyllosilicates (hectorite, saponite, and muscovite). Results presented in...

  5. Dispersion of solutes in porous media

    NASA Astrophysics Data System (ADS)

    Hunt, A. G.; Skinner, T. E.; Ewing, R. P.; Ghanbarian-Alavijeh, B.

    2011-04-01

    A recently introduced theory of solute transport in porous media is tested by comparison with experiment. The solute transport is predicted using an adaptation of the cluster statistics of percolation theory to critical path analysis together with knowledge of how the structure of such percolation clusters affects the time of transport across them. Only the effects of a single scale of medium heterogeneity are incorporated, and a minimal amount of information regarding the structure of the medium is required. This framework is used to find effectively the distributions of solute velocities and travel distances and thus generate arrival time distributions. The comparison with experiment focuses on the dispersivity (the ratio of the second to the first moment of the spatial solute distribution). The predictions of the theory in the absence of diffusion are verified by comparing with over 2200 experiments over length scales from a few microns to 100 km. At larger length scales (centimeters on up) about 95% of the data lie within our predicted bounds. At smaller length scales approximately 99.8% of the data lie where we predict. These comparisons are not trivial as the typical values of the dispersivity increase by ten orders of magnitude over ten orders of magnitude of length scale. Noteworthy is that the classical advection-dispersion (ADE) equation predicts that the dispersivity should be independent of length scale! This agreement with experiment requires rethinking of the relevance of diffusion and multi-scale heterogeneity and would also appear to signal the complete inappropriateness of using the classical ADE or any of its derivatives to model solute transport.

  6. Quantitative modeling of soil sorption for xenobiotic chemicals.

    PubMed Central

    Sabljić, A

    1989-01-01

    Experimentally determining soil sorption behavior of xenobiotic chemicals during the last 10 years has been costly, time-consuming, and very tedious. Since an estimated 100,000 chemicals are currently in common use and new chemicals are registered at a rate of 1000 per year, it is obvious that our human and material resources are insufficient to experimentally obtain their soil sorption data. Much work is being done to find alternative methods that will enable us to accurately and rapidly estimate the soil sorption coefficients of pesticides and other classes of organic pollutants. Empirical models, based on water solubility and n-octanol/water partition coefficients, have been proposed as alternative, accurate methods to estimate soil sorption coefficients. An analysis of the models has shown (a) low precision of water solubility and n-octanol/water partition data, (b) varieties of quantitative models describing the relationship between the soil sorption and above-mentioned properties, and (c) violations of some basic statistical laws when these quantitative models were developed. During the last 5 years considerable efforts were made to develop nonempirical models that are free of errors imminent to all models based on empirical variables. Thus far molecular topology has been shown to be the most successful structural property for describing and predicting soil sorption coefficients. The first-order molecular connectivity index was demonstrated to correlate extremely well with the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and heterosubstituted PAHs, and halogenated phenols. The average difference between predicted and observed soil sorption coefficients is only 0.2 on the logarithmic scale (corresponding to a factor of 1.5). A comparison of the molecular connectivity model with the empirical models described earlier shows that the former is superior in

  7. Oxytetracycline sorption to organic matter by metal-bridging.

    PubMed

    MacKay, Allison A; Canterbury, Brian

    2005-01-01

    The sorption of oxytetracycline to metal-loaded ion exchange resin and to natural organic matter by the formation of ternary complexes between polyvalent metal cations and sorbent- and sorbate ligand groups was investigated. Oxytetracycline (OTC) sorption to Ca- and Cu-loaded Chelex-100 resin increased with increasing metal/sorbate ratio at pH 7.6 (OTC speciation: 55% zwitterion, 45% anion). Greater sorption to Cu- than Ca-loaded resin was observed, consistent with the greater stability constants of Cu with both the resin sites and with OTC. Oxytetracycline sorption to organic matter was measured at pH 5.5 (OTC speciation: 1% cation, 98% zwitterion, 1% anion). No detectable sorption was measured for cellulose or lignin sorbents that contain few metal-complexing ligand groups. Sorption to Aldrich humic acid increased from "clean" < "dirty" (no cation exchange pretreatment) < Al-amended < Fe(III)-amended clean humic acid with K(d) values of 5500, 32000, 48000, and 250000 L kg(-1) C, respectively. Calcium amendments of clean humic acid suggested that a portion of the sorbed OTC was interacting by cation exchange. Oxytetracycline sorption coefficients for all humic acid sorbents were well-correlated with the total sorbed Al-plus-Fe(III) concentrations (r(2) = 0.87, log-log plot), suggesting that sorption by ternary complex formation with humic acid is important. Results of this research indicate that organic matter may be an important sorbent phase in soils and sediments for pharmaceutical compounds that can complex metals by the formation of ternary complexes between organic matter ligand groups and pharmaceutical ligand groups. PMID:16221815

  8. The sorption of quercetin by high-basicity anion exchangers

    NASA Astrophysics Data System (ADS)

    Udalova, N. A.; Karpov, S. I.; Selemenev, V. F.; Sharmar, I. A.

    2009-06-01

    The sorption of quercetin on anionites with various porosities in the OH- and Cl- forms was studied under static conditions. The equilibrium (distribution coefficients K p) and kinetic (effective diffusion coefficients D eff) parameters of quercetin sorption on AV-17-2P and AV-17-6M anionites in the Cl- and OH- forms were calculated. The mechanism of quercetin interactions with the anion exchangers was studied by electron microscopy and IR spectroscopy.

  9. Quantitative modeling of soil sorption for xenobiotic chemicals

    SciTech Connect

    Sabljic, A. )

    1989-11-01

    Experimentally determining soil sorption behavior of xenobiotic chemicals during the last 10 years has been costly, time-consuming, and very tedious. Since an estimated 100,000 chemicals are currently in common use and new chemicals are registered at a rate of 1000 per year, it is obvious that our human and material resources are insufficient to experimentally obtain their soil sorption data. Much work is being done to find alternative methods that will enable us to accurately and rapidly estimate the soil sorption coefficients of pesticides and other classes of organic pollutants. Empirical models, based on water solubility and n-octanol/water partition coefficients, have been proposed as alternative, accurate methods to estimate soil sorption coefficients. An analysis of the models has shown (a) low precision of water solubility and n-octanol/water partition data, (b) varieties of quantitative models describing the relationship between the soil sorption and above-mentioned properties, and (c) violations of some basic statistical laws when these quantitative models were developed. During the last 5 years considerable efforts were made to develop nonempirical models that are free of errors imminent to all models based on empirical variables. Thus far molecular topology has been shown to be the most successful structural property for describing and predicting soil sorption coefficients. The first-order molecular connectivity index was demonstrated to correlate extremely well with the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and heterosubstituted PAHs, and halogenated phenols. The average difference between predicted and observed soil sorption coefficients is only 0.2 on the logarithmic scale (corresponding to a factor of 1.5). 63 references.

  10. Sorption behaviour of nonylphenol and nonylphenol monoethoxylate in soils.

    PubMed

    Milinovic, J; Lacorte, S; Rigol, A; Vidal, M

    2015-11-01

    Sorption behaviour of two alkylphenolic compounds (APCs), nonylphenol (NP) and nonylphenol monoethoxylate (NP1EO), was studied in five soils with contrasting characteristics. Sorption isotherms were obtained by equilibrating the soil samples with 0.01 mol L(-1) CaCl2 solutions containing different initial concentrations of NP or NP1EO. Linear fitting was generally appropriate for describing the sorption behaviour of NP and NP1EO in the soils, with the exception of two cases, for which the Freundlich model was more suitable for describing the sorption pattern of NP1EO. Solid-liquid distribution coefficients derived from sorption isotherms (Kd) varied from 24 to 1059 mL g(-1) for NP and from 51 to 740 mL g(-1) for NP1EO. For most soils, sorption Kd values were higher for NP than for NP1EO due to the higher hydrophobicity of NP. Sorption reversibility of NP and NP1EO was also tested from desorption isotherms. Desorption solid-liquid distribution coefficients (Kd,des), obtained from linear fitting, were between 130 and 1467 mL g(-1) for NP and between 24 and 1285 mL g(-1) for NP1EO. Kd,des values were higher than Kd values, which demonstrated that target compounds were irreversibly sorbed into soils, with the exception of the high desorption yield (45%) of NP1EO in the soil with the lowest content of organic matter. The fraction of soil organic carbon (FOC) was a key parameter that influenced the sorption of NP and NP1EO in soils, with logKOC values of 4.0 and 3.8, respectively. PMID:25595537

  11. Uniform surface complexation approaches to radionuclide sorption modeling

    SciTech Connect

    Turner, D.R.; Pabalan, R.T.; Muller, P.; Bertetti, F.P.

    1995-12-01

    Simplified surface complexation models, based on a uniform set of model parameters have been developed to address complex radionuclide sorption behavior. Existing data have been examined, and interpreted using numerical nonlinear least-squares optimization techniques to determine the necessary binding constants. Simplified modeling approaches have generally proven successful at simulating and predicting radionuclide sorption on (hydr)oxides and aluminosilicates over a wide range of physical and chemical conditions.

  12. Uranium sorption by Pseudomonas biomass immobilized in radiation polymerized polyacrylamide bio-beads.

    PubMed

    D'Souza, S F; Sar, Pinaki; Kazy, Sufia K; Kubal, B S

    2006-01-01

    A Pseudomonas strain identified as a potent biosorbent of uranium (U) and thorium was immobilized in radiation-induced polyacrylamide matrix for its application in radionuclide containing wastewater treatment. The immobilized biomass exhibited a high U sorption of 202 mg g(-1) dry wt. with its optimum at pH 5.0. A good fit of experimental data to the Freundlich model suggested multilayered uranium binding with an affinity distribution among biomass metal binding sites. Scanning electron microscopy revealed a highly porous nature of the radiation-polymerized beads with bacterial cells mostly entrapped on pore walls. Energy dispersive X-ray analysis (EDXA) coupled with SEM ascertained the accumulation of uranium by the immobilized biomass without any physical damage to the cells. A significant (90%) part of biosorbed uranium was recovered using sodium bicarbonate with the immobilized biomass maintaining their U resorption capacity for multiple sorption-desorption cycles. Uranium loading and elution behavior of immobilized biomass evaluated within a continuous up-flow packed bed columnar reactor showed its effectiveness in removing uranium from low concentration (50 mg U L(-1)) followed by its recovery resulting in a 4-5-fold waste volume reduction. The data suggested the suitability of radiation polymerization in obtaining bacterial beads for metal removal and also the potential of Pseudomonas biomass in treatment of radionuclide containing waste streams. PMID:16484078

  13. Insights into the mechanisms of mercury sorption onto aluminum based drinking water treatment residuals.

    PubMed

    Deliz Quiñones, Katherine; Hovsepyan, Anna; Oppong-Anane, Akua; Bonzongo, Jean-Claude J

    2016-04-15

    Several studies have demonstrated the ability of drinking water treatment residuals (WTRs) to efficiently sorb metal cations from aqueous solutions. Reported results have stimulated interest on the potential use of WTRs as sorbent for metal removal from contaminated aqueous effluents as well as in metal immobilization in contaminated soils. However, knowledge on mechanisms of metal sorption by WTRs remains very limited and data on the long-term stability of formed metal-WTR complexes as a function of changing key environmental parameters are lacking. In this study, chemical selective sequential extraction (SSE), scanning electron microscopy combined with X-ray energy dispersive spectrometer (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) were used to gain insight into the different mechanisms of mercury (Hg) binding to aluminum based WTR (Al-WTRs). Results from sorption studies show that a significant portion of Hg becomes incorporated in the operationally defined residual fraction of Al-WTRs, and therefore, not prone to dissolution and mobility. The results of solid phase analyses suggested that Hg immobilization by Al-WTR occurs largely through its binding to oxygen donor atoms of mineral ligands driven by a combination of electrostatic forces and covalent bonding. PMID:26780705

  14. Binary metal sorption by pine bark: Study of equilibria and mechanisms

    SciTech Connect

    Al-Asheh, S.; Duvnjak, Z.

    1998-06-01

    Pine bark was able to sorb cadmium, copper, and nickel ions from aqueous solutions. Binary equilibrium data from the combination of these metals were collected in this work using the sorbent. These data were modeled using three types of binary component equilibrium isotherms, all of which resulted in good fitting of the experimental data, with the Langmuir-Freundlich model resulting in their best representation. In general, the capacity of bark for each metal in the binary system was lower than in the single metal systems. The study also examined the mechanisms of metal biosorption by bark. Scanning electron microscopy (SEM) and energy-dispersive c-ray (EDX) microanalyses revealed that metal ions were sorbed mainly at the cell wall of the bark and only a small amount of ions diffused into the cytoplasm. Both the EDX analysis and the atomic absorption spectrophotometry (AAS) measurements showed that ion exchange was an important mechanism in this sorption process. Electron spin resonance (ESR) tests demonstrated that free radicals from the sorbent also have a significant role in the sorption processes.

  15. Hyperbolic Method for Dispersive PDEs: Same High-Order of Accuracy for Solution, Gradient, and Hessian

    NASA Technical Reports Server (NTRS)

    Mazaheri, Alireza; Ricchiuto, Mario; Nishikawa, Hiroaki

    2016-01-01

    In this paper, we introduce a new hyperbolic first-order system for general dispersive partial differential equations (PDEs). We then extend the proposed system to general advection-diffusion-dispersion PDEs. We apply the fourth-order RD scheme of Ref. 1 to the proposed hyperbolic system, and solve time-dependent dispersive equations, including the classical two-soliton KdV and a dispersive shock case. We demonstrate that the predicted results, including the gradient and Hessian (second derivative), are in a very good agreement with the exact solutions. We then show that the RD scheme applied to the proposed system accurately captures dispersive shocks without numerical oscillations. We also verify that the solution, gradient and Hessian are predicted with equal order of accuracy.

  16. Interaction between chitosan and uranyl ions. Role of physical and physicochemical parameters on the kinetics of sorption

    SciTech Connect

    Piron, E. |; Accominotti, M.; Domard, A.

    1997-03-19

    This work corresponds to the first part of our studies on the interactions between chitosan particles dispersed in water and uranyl ions. The measurements were obtained by ICP, and we considered the role of various physical and physicochemical parameters related to chitosan. We showed that the crystallinity, the particle dimensions, and the swelling in water of chitosan are parameters which are connected together and govern the kinetic laws of metal diffusion and sorption. The molecular mobility of the polymer chains is then essential parameter. 31 refs., 5 figs., 3 tabs.

  17. Water sorption by proteins: milk and whey proteins.

    PubMed

    Kinsella, J E; Fox, P F

    1986-01-01

    The content and physical state of water in foods influence their physical, chemical, quality, safety, and functional behavior. Information concerning the sorption behavior of dairy proteins, in the water activity (Aw) range 0 to 0.9, is collated in this paper. The sorption behavior of proteins in general, the kinetics of absorption, factors affecting water binding, the phenomenon of desorption hysteresis, and the chemical and physical nature of water/protein interactions are reviewed in general terms. This is followed by a discussion of thermodynamic aspects of sorption phenomena and the adequacy of the various equations for describing sorption isotherms of proteins. After a discussion of the methods available for measuring sorption by milk proteins, the sorption behavior of various milk protein preparations, i.e., nonfat dry milk, whey proteins, caseins, and milk powders is summarized. Finally, the water activity of cheese and its relationship to solute mobility and solvent water are discussed. Some of the unique features of protein behavior, i.e., conformational changes, swelling, and solubilization are cited as possible sources of disparities between various reports. PMID:3527564

  18. Sorption and degradation of bisphenol A by aerobic activated sludge.

    PubMed

    Zhao, Junming; Li, Yongmei; Zhang, Chaojie; Zeng, Qingling; Zhou, Qi

    2008-06-30

    Laboratory-scale batch experiments were conducted to investigate the sorption and degradation of bisphenol A (BPA) at microg/L range in an aerobic activated sludge system. The sorption isotherms and thermodynamics indicated that the sorption of BPA on sludge was mainly a physical process in which partitioning played a dominating role. The values of sorption coefficient Koc were between 621 and 736 L/kg in the temperature range of 10-30 degrees C. Both mixed liquor suspended solid (MLSS) and temperature influenced BPA sorption on sludge. The degradation of BPA by acclimated activated sludge could be described by first-order reaction equation with the first-order degradation rate constant of 0.80 h(-1) at 20 degrees C. The decrease of initial COD concentration and the increase of MLSS concentration and temperature enhanced BPA degradation rate. The removal of BPA in the activated sludge system was characterized by a quick sorption on the activated sludge and subsequent biodegradation. PMID:18179868

  19. Factors controlling alkylbenzene sorption to municipal solid waste.

    PubMed

    Wu, B; Taylor, C M; Knappe, D R; Nanny, M A; Barlaz, M A

    2001-11-15

    The sorption of toluene and o-xylene to individual municipal solid waste (MSW) constituents [office paper, newsprint, model food and yard waste, high density polyethylene, and poly(vinyl chloride) (PVC)] was evaluated. Effects of sorbent decomposition and solvent composition on alkylbenzene sorption were studied by evaluating biodegradable sorbents in both fresh and anaerobically decomposed form and by complementing single-solute isotherm tests with experiments conducted in acidogenic and methanogenic leachate. Alkylbenzene sorption to plastics was greaterthan to biopolymer composites, and differences in sorbate/sorbent solubility parameter compatibility explained this observation. Alkylbenzene sorption to biopolymer composites yielded linear isotherms, and sorption capacities [log(Koc/Kow)] decreased linearly with increasing sorbent polarity as expressed by the O-alkyl/alkyl ratio. Leachate composition had little effect on alkylbenzene sorption with one exception; volatile fatty acids in acidogenic leachate appeared to convert PVC from a glassy to a rubbery polymer. The results of this study showed that sorbent organic matter affinity for hydrophobic organic contaminants (HOCs) increases with increasing extent of MSW decomposition because of the recalcitrance of plastics and the preferential degradation of polar biopolymers. Furthermore, the plasticizing effect of volatile fatty acids in acidogenic leachate may enhance the bioavailability of HOCs sorbed to glassy organic matter in MSW or in soils contaminated with acidogenic leachate. PMID:11757618

  20. Surface complexation modeling of americium sorption onto volcanic tuff.

    PubMed

    Ding, M; Kelkar, S; Meijer, A

    2014-10-01

    Results of a surface complexation model (SCM) for americium sorption on volcanic rocks (devitrified and zeolitic tuff) are presented. The model was developed using PHREEQC and based on laboratory data for americium sorption on quartz. Available data for sorption of americium on quartz as a function of pH in dilute groundwater can be modeled with two surface reactions involving an americium sulfate and an americium carbonate complex. It was assumed in applying the model to volcanic rocks from Yucca Mountain, that the surface properties of volcanic rocks can be represented by a quartz surface. Using groundwaters compositionally representative of Yucca Mountain, americium sorption distribution coefficient (Kd, L/Kg) values were calculated as function of pH. These Kd values are close to the experimentally determined Kd values for americium sorption on volcanic rocks, decreasing with increasing pH in the pH range from 7 to 9. The surface complexation constants, derived in this study, allow prediction of sorption of americium in a natural complex system, taking into account the inherent uncertainty associated with geochemical conditions that occur along transport pathways. PMID:24963803