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Daniel E Giammar - One of the best experts on this subject based on the ideXlab platform.

  • impacts of Diffusive Transport on carbonate mineral formation from magnesium silicate co2 water reactions
    Environmental Science & Technology, 2014
    Co-Authors: Daniel E Giammar, Fei Wang, B Guo, Andrew J Surface, Catherine A Peters, Mark S Conradi, Sophia E Hayes
    Abstract:

    Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with Transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive Transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, 13C NMR spectroscopy tracked the inorganic carbon Transport and speciation in situ. The data were compared with the output of reactive Transport simulations that accounted for Diffusive Transport processes, aqueous speciation, and the fors...

  • impacts of Diffusive Transport on carbonate mineral formation from magnesium silicate co2 water reactions
    Environmental Science & Technology, 2014
    Co-Authors: Daniel E Giammar, Fei Wang, Andrew J Surface, Catherine A Peters, Mark S Conradi, Sophia E Hayes
    Abstract:

    Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with Transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive Transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, 13C NMR spectroscopy tracked the inorganic carbon Transport and speciation in situ. The data were compared with the output of reactive Transport simulations that accounted for Diffusive Transport processes, aqueous speciation, and the fors...

  • effect of Diffusive Transport limitations on uo2 dissolution
    Water Research, 2012
    Co-Authors: Daniel E Giammar, Jose M Cerrato, Vrajesh Mehta, Zimeng Wang, Yin Wang, Troy J Pepping, Kaiuwe Ulrich, Juan S Lezamapacheco, John R Bargar
    Abstract:

    The effects of Diffusive Transport limitations on the dissolution of UO2 were investigated using an artificial groundwater prepared to simulate the conditions at the Old Rifle aquifer site in Colorado, USA. Controlled batch, continuously-stirred tank (CSTR), and plug flow reactors were used to study UO2 dissolution in the absence and presence of Diffusive limitations exerted by permeable sample cells. The net rate of uranium release following oxidative UO2 dissolution obtained from diffusion-limited batch experiments was ten times lower than that obtained for UO2 dissolution with no permeable sample cells. The release rate of uranium to bulk solution from UO2 contained in permeable sample cells under advective flow conditions was more than 100 times lower than that obtained from CSTR experiments without Diffusive limitations. A 1-dimensional Transport model was developed that could successfully simulate diffusion-limited release of U following oxidative UO2 dissolution with the dominant rate-limiting process being the Transport of U(VI) out of the cells. Scanning electron microscopy, X-ray diffraction, and extended X-ray absorption fine structure spectroscopy (EXAFS) characterization of the UO2 solids recovered from batch experiments suggest that oxidative dissolution was more evident in the absence of Diffusive limitations. Ca-EXAFS spectra indicate the presence of Ca in the reacted UO2 solids with a coordination environment similar to that of a CaeOeSi mineral. The findings from this study advance our overall understanding of the coupling of geochemical and Transport processes that can lead to differences in dissolution rates measured in the field and in laboratory experiments.

Eugenio Onate - One of the best experts on this subject based on the ideXlab platform.

  • derivation of stabilized equations for numerical solution of advective Diffusive Transport and fluid flow problems
    Computer Methods in Applied Mechanics and Engineering, 1998
    Co-Authors: Eugenio Onate
    Abstract:

    Abstract The concept of the so-called ‘artificial or balancing diffusion’ used to stabilize the numerical solution of advective-Diffusive Transport and fluid flow problems is revised in this paper. It is shown that the standard forms of the balancing diffusion terms, usually chosen in a heuristic manner, can be naturally found by introducing higher-order approximations in the derivation of the governing differential equations via standard conservation (or equilibrium) principles. This allows us to reinterpret many stabilization algorithms and concepts used in every-day practice by numerical analysts and also provides an expression for computing the stabilization parameter.

  • a mesh free finite point method for advective Diffusive Transport and fluid flow problems
    Computational Mechanics, 1998
    Co-Authors: Eugenio Onate, Sergio Idelsohn
    Abstract:

    The finite point method (FPM) is a gridless numerical procedure based on the combination of weighted least square interpolations on a cloud of points with point collocation for evaluating the approximation integrals. In the paper, details of a procedure for stabilizing the numerical solution for advective-Diffusive Transport and fluid flow problems using the FPM are given. The method is based on a consistent introduction of the stabilizing terms in the governing differential equations. One example showing the applicability of the FPM is given.

  • a finite point method in computational mechanics applications to convective Transport and fluid flow
    International Journal for Numerical Methods in Engineering, 1996
    Co-Authors: Eugenio Onate, Sergio Idelsohn, O C Zienkiewicz, R L Taylor
    Abstract:

    The paper presents a fully meshless procedure fo solving partial differential equations. The approach termed generically the ‘finite point method’ is based on a weighted least square interpolation of point data and point collocation for evaluating the approximation integrals. Some examples showing the accuracy of the method for solution of adjoint and non-self adjoint equations typical of convective-Diffusive Transport and also to the analysis of compressible fluid mechanics problem are presented.

Thomas A Dewers - One of the best experts on this subject based on the ideXlab platform.

  • dissolution of quartz albite and orthoclase in h2o saturated haplogranitic melt at 800 c and 200 mpa Diffusive Transport properties of granitic melts at crustal anatectic conditions
    Journal of Petrology, 2006
    Co-Authors: Antonio Acostavigil, David London, George B Morgan, Thomas A Dewers
    Abstract:

    We have conducted experiments on dissolution of quartz, albite, orthoclase, and corundum into H2O-saturated haplogranite melt at 800 � C and 200MPa over a duration of 120–1488h with the aim of ascertaining the Diffusive Transport properties of granitic melts at crustal anatectic temperatures. Cylinders of anhydrous starting glass and a single mineral phase (quartz or feldspar) were juxtaposed along flat and polished surfaces inside gold or platinum capsules with � 10 wt % added H2O. Concentration profiles in glass (quenched melt) perpendicular to the mineral–glass interfaces and comparison with relevant phase diagrams suggest that melts at the interface are saturated in the dissolving phases after 384h, and with longer durations the concentration profiles are controlled only by diffusion of components in the melt. The evolution of the concentration profiles with time indicates that uncoupled diffusion in the melt takes place along the following four linearly independent directions in oxide composition space: SiO2 ,N a2O, and K2O axes (Si-, Na-, and K-eigenvectors, respectively), and a direction between the Al2O3, Na2O, and K2O axes (Al-eigenvector), such that the Al/Na molar ratio is equal to that of the bulk melt and the Al/(Na þ K) molar ratio is equal to the equilibrium ASI (¼ mol. Al2O3/[Na2O þ K2O]) of the melt. Experiments in which a glass cylinder was sandwiched between two mineral cylinders—quartz and albite, quartz and K-feldspar, or albite and corundum—tested the validity of the inferred directions of uncoupled diffusion and explored longrange chemical communication in the melt via chemical potential gradients. The application of available solutions to the diffusion equations for the experimental quartz and feldspar dissolution data provides diffusivities along the directions of the Si-eigenvector and Al-eigenvector of � (2� 0–2� 8) · 10 � 15 m 2 /s and � (0� 6–2� 4) · 10 � 14 m 2 /s, respectively. Minimum diffusivities of alkalis [� (3–9) · 10 � 11 m 2 /s] are orders of magnitude greater than the tetrahedral components of the melt. The information provided here determines the rate at which crustal anatexis can occur when sufficient heat is supplied and diffusion is the only mass Transport (mixing) process in the melt. The calculated diffusivities imply that a quartzo-feldspathic source rock with initial grain size of 2–3mm undergoing hydrostatic, H2O-saturated melting at 800 � C (infinite heat supply) could produce 20–30 vol. % of homogeneous melt in less than 1–10 years. Slower diffusion in H2O-undersaturated melts will increase this time frame.

Milos Kojic - One of the best experts on this subject based on the ideXlab platform.

  • correction function for accuracy improvement of the composite smeared finite element for Diffusive Transport in biological tissue systems
    Computer Methods in Applied Mechanics and Engineering, 2018
    Co-Authors: Miljan Milosevic, Vladimir Simic, Bogdan Milicevic, Eugene J Koay, Mauro Ferrari, Arturas Ziemys, Milos Kojic
    Abstract:

    Abstract Modeling of drug Transport within capillaries and tissue remains a challenge, especially in tumors and cancers where the capillary network exhibits extremely irregular geometry. Recently introduced Composite Smeared Finite Element (CSFE) provides a new methodology of modeling complex convective and Diffusive Transport in the capillary–tissue system. The basic idea in the formulation of CSFE is in dividing the FE into capillary and tissue domain, coupled by 1D connectivity elements at each node. Mass Transport in capillaries is smeared into continuous fields of pressure and concentration by introducing the corresponding Darcy and diffusion tensors . Despite theoretically correct foundation, there are still differences in the overall mass Transport to (and from) tissue when comparing smeared model and a true 3D model. The differences arise from the fact that the smeared model cannot take into account the detailed non-uniform pressure and concentration distribution in the vicinity of capillaries. We introduced a field of correction function for diffusivity through the capillary walls of smeared models, in order to have the same mass accumulation in tissue as in case of true 3D models. The parameters of the numerically determined correction function are as follows: ratio of thickness and diameter of capillary wall, ratio of diffusion coefficient in capillary wall and surrounding tissue; and volume fraction of capillaries within tissue domain. Partitioning at the capillary wall–blood interface can also be included. It was shown that the correction function is applicable to complex configurations of capillary networks, providing improved accuracy of our robust smeared models in computer simulations of real Transport problems, such as in tumors or human organs.

  • a multi scale fe model for convective Diffusive drug Transport within tumor and large vascular networks
    Computer Methods in Applied Mechanics and Engineering, 2015
    Co-Authors: Milos Kojic, Miljan Milosevic, Mauro Ferrari, Nikola Kojic, Zbigniew Starosolski, Ketankumar B Ghaghada, Rita E Serda, Ananth Annapragada, Arturas Ziemys
    Abstract:

    Abstract Mass Transport within an organ occurs through networks of blood vessels and surrounding tissue. This convective–Diffusive Transport is a very complex process which spans several different scales, from nano- to micro- to macro-scale. The blood vessel network is usually very intricate and irregular with respect to size and geometry, with mass Transport being directly coupled to the neighboring tissue. Due to such complexity, development of a comprehensive Transport model remains a challenge. The primary focus of this study is on solid tumors which are extremely complex autonomous systems with regard to mass Transport. Additionally, tumors develop various biological barriers which hinder effective delivery of drug molecules into cancer tissue. We introduce a multi-scale tumor Transport model where larger tumor vessels are modeled by simple 1D finite elements, whereas the capillary bed is replaced by equivalent 3D continuum finite elements. The model couples convective–Diffusive Transport within capillaries (fluid domain) and tissue (solid domain). These fluid and solid domains are connected by fictitious 1D elements. The proposed tumor model incorporates the imaged inhomogeneous tumor tissue and blood vessel network—from larger vessels to the smallest capillary bed. The tumor model is also applicable to Transport within organs, such as the mouse brain, which is presented here as an example.

  • Transport phenomena computational models for convective and Diffusive Transport in capillaries and tissue
    2015
    Co-Authors: Miljan Milosevic, Mauro Ferrari, Milos Kojic, Nikola Kojic, Velibor Isailovic, Dejan Petrovic, Nenad Filipovic, Arturas Ziemys
    Abstract:

    A review of computational procedures for convective and Diffusive Transport, developed by the authors, is presented in this chapter. The presented finite element computational framework is directed to Transport within capillaries and tissue. The convective Transport includes modeling of motion of deformable bodies within fluid flow. It is based on a strong coupling concept and remeshing procedure. It was found by the authors that this approach has advantages in reliability and accuracy with respect to others available in literature, although it is not computationally efficient. A hierarchical multiscale model for diffusion couples molecular dynamics and continuum FE method by evaluating equivalent continuum Diffusive parameters; these parameters include commonly used diffusion coefficients, but also parameters which account for physicochemical interactions between diffusing molecules and microstructural solid surfaces. A numerical homogenization is used in this multiscale model. Coupled convective and Diffusive Transport is also considered. A number of typical solved examples illustrate generality, robustness, and accuracy of the presented computational methodology.

N Vilmer - One of the best experts on this subject based on the ideXlab platform.

  • Diffusive Transport of energetic electrons in the solar corona x ray and radio diagnostics
    Astronomy and Astrophysics, 2018
    Co-Authors: Sophie Musset, Eduard P Kontar, N Vilmer
    Abstract:

    Context. Imaging spectroscopy in X-rays with RHESSI provides the possibility to investigate the spatial evolution of X-ray emitting electron distribution and therefore, to study Transport effects on energetic electrons during solar flares. Aims. We study the energy dependence of the scattering mean free path of energetic electrons in the solar corona. Methods. We used imaging spectroscopy with RHESSI to study the evolution of energetic electrons distribution in various parts of the magnetic loop during the 2004 May 21 flare. We compared these observations with the radio observations of the gyrosynchrotron radiation of the same flare and with the predictions of a Diffusive Transport model. Results. X-ray analysis shows a trapping of energetic electrons in the corona and a spectral hardening of the energetic electron distribution between the top of the loop and the footpoints. Coronal trapping of electrons is stronger for radio-emitting electrons than for X-ray-emitting electrons. These observations can be explained by a Diffusive Transport model. Conclusions. We show that the combination of X-ray and radio diagnostics is a powerful tool to study electron Transport in the solar corona in different energy domains. We show that the Diffusive Transport model can explain our observations, and in the range 25–500 keV, the scattering mean free path of electrons decreases with electron energy. We can estimate for the first time the scattering mean free path dependence on energy in the corona.

  • Diffusive Transport of energetic electrons in the solar corona x ray and radio diagnostics
    arXiv: Solar and Stellar Astrophysics, 2017
    Co-Authors: Sophie Musset, Eduard P Kontar, N Vilmer
    Abstract:

    Imaging spectroscopy in X-rays with RHESSI provide the possibility to investigate the spatial evolution of the X-ray emitting electron distribution and therefore to study the Transport effects on energetic electrons during solar flares. We study the energy dependence of the energetic electron scattering mean free path in the solar corona. We use the imaging spectroscopy technique with RHESSI to study the evolution of energetic electrons distribution in different part of the magnetic loop during the 2004 May 21 flare. These observations are compared with the radio observations of the gyrosynchrotron radiation of the same flare by Kuznetsov and Kontar (2015), and with the predictions of the Diffusive Transport model described by Kontar et al. (2014). The X-ray analysis shows a trapping of energetic electrons in the corona and a spectral hardening of the energetic electron distribution between the top of the loop and the footpoints. Coronal trapping of electrons is stronger for the radio-emitting electrons than for the X-ray-emitting electrons. These observations can be explained by the Diffusive Transport model derived by Kontar et al. (2014). We show that the combination of X-ray and radio diagnostics is a powerful tool to study electron Transport in the solar corona in different energy domains. We show that the Diffusive Transport model can explain our observations; and in the range 25-500 keV, the electron scattering mean free path decreases with electron energy. We can estimate for the first time the scattering mean free path dependence on energy in the corona.