scholarly journals Surrogate Model for Multi-Component Diffusion of Uranium through Opalinus Clay on the Host Rock Scale

2021 ◽  
Vol 11 (2) ◽  
pp. 786 ◽  
Author(s):  
Theresa Hennig ◽  
Michael Kühn
Keyword(s):  
Host Rock ◽  
Effective Diffusion ◽  
Chemical Species ◽  
Side Surface ◽  
Distribution Coefficients ◽  
Opalinus Clay ◽  
Diffuse Double Layer ◽  
Minimum Requirement ◽  
Computationally Intensive ◽  
The One

Multi-component (MC) diffusion simulations enable a process based and more precise approach to calculate transport and sorption compared to the commonly used single-component (SC) models following Fick’s law. The MC approach takes into account the interaction of chemical species in the porewater with the diffuse double layer (DDL) adhering clay mineral surfaces. We studied the shaly, sandy and carbonate-rich facies of the Opalinus Clay. High clay contents dominate diffusion and sorption of uranium. The MC simulations show shorter diffusion lengths than the SC models due to anion exclusion from the DDL. This hampers diffusion of the predominant species CaUO2(CO3)32−. On the one side, species concentrations and ionic strengths of the porewater and on the other side surface charge of the clay minerals control the composition and behaviour of the DDL. For some instances, it amplifies the diffusion of uranium. We developed a workflow to transfer computationally intensive MC simulations to SC models via calibrated effective diffusion and distribution coefficients. Simulations for one million years depict maximum uranium diffusion lengths between 10 m and 35 m. With respect to the minimum requirement of a thickness of 100 m, the Opalinus Clay seems to be a suitable host rock for nuclear waste repositories.

scholarly journals Observation and control of the weak topological insulator state in ZrTe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Peng Zhang ◽  
Ryo Noguchi ◽  
Kenta Kuroda ◽  
Chun Lin ◽  
Kaishu Kawaguchi ◽  
...  
Keyword(s):  
Band Gap ◽  
Topological Insulator ◽  
Spin Current ◽  
Side Surface ◽  
Quantum Spin ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Dirac Semimetal ◽  
Topological States ◽  
The One ◽  
And Control

AbstractA quantum spin Hall (QSH) insulator hosts topological states at the one-dimensional (1D) edge, along which backscattering by nonmagnetic impurities is strictly prohibited. Its 3D analogue, a weak topological insulator (WTI), possesses similar quasi-1D topological states confined at side surfaces. The enhanced confinement could provide a route for dissipationless current and better advantages for applications relative to strong topological insulators (STIs). However, the topological side surface is usually not cleavable and is thus hard to observe. Here, we visualize the topological states of the WTI candidate ZrTe5 by spin and angle-resolved photoemission spectroscopy (ARPES): a quasi-1D band with spin-momentum locking was revealed on the side surface. We further demonstrate that the bulk band gap is controlled by external strain, realizing a more stable WTI state or an ideal Dirac semimetal (DS) state. The highly directional spin-current and the tunable band gap in ZrTe5 will provide an excellent platform for applications.

scholarly journals Diffusion of calcium ions in retinal rods. A theoretical calculation.

1981 ◽  
Vol 77 (4) ◽  
pp. 475-487 ◽  
Author(s):  
S McLaughlin ◽  
J Brown
Keyword(s):  
Diffusion Coefficient ◽  
Adsorption Isotherm ◽  
Calcium Ions ◽  
Outer Segment ◽  
Effective Diffusion ◽  
Langmuir Adsorption Isotherm ◽  
Diffuse Double Layer ◽  
Langmuir Adsorption ◽  
Retinal Rods ◽  
Disk Membrane

The Fick diffusion equation is combined with the Langmuir adsorption isotherm and the relevant equations from the Gouy-Chapman theory of the electrical diffuse double layer to demonstrate that the effective diffusion coefficient of calcium ions, both in the cytoplasm of the rod outer segment and within the aqueous space bounded by the disk membrane, should be reduced by a factor of 10-100 because these ions adsorb to phospholipids present in the disk membrane.

scholarly journals Experimental study of multicomponent diffusion in low permeable sediments

2019 ◽  
Vol 98 ◽  
pp. 10002
Author(s):  
Vladimir Lekhov ◽  
Alexei Lekhov
Keyword(s):  
Diffusion Coefficients ◽  
Average Length ◽  
Effective Diffusion ◽  
Length Distribution ◽  
Large Degree ◽  
Multicomponent Diffusion ◽  
Distribution Coefficients ◽  
Disposal Site ◽  
Special Equipment ◽  
Permeable Sediments

Diffusion coefficients for Na+ and distribution coefficients for Cs+, Ba2+, Ni2+, CO2+, Sr2+ were measured on low permeable samples (3 cm diameter, average length 7 cm) from the deep disposal site Siberian Chemical Combine (SSC) using the end-diffusion technique. The direction of diffusion was perpendicular to bedding. Special equipment for experiment were designed and constructed. Two types of concentration observation were used. For non-sorbing Na+ in time used EC sensors and length distribution of sorbed elements. The synthetic solution used in the experiments was a model of low-activity contaminant of the SSC, and consist NaNO3 (25 g/l) and nitrate compounds: Cs+, Ba2+, Ni2+, Co2+, Sr2+ (100 mg/l each). The measured values of the effective diffusion coefficients De) for Na+ from 7.60×10-7 to 1.51×10-5 m2/day and volumetric dimensionless distribution coefficients (Kdρ) are: Cs+ from 0.21 to 22.1, Ba2+ from 1.1 to 1.45, Ni2+ from 0.3 to 16.4, Co2+ from 1.98 to 24.7, Sr2+ from 1.9 to 14.3. The values of the diffusion coefficient show a large degree of variability. The diffusion coefficients of non-sorbing Na+ measured in this study are in good agreement with pore-scale diffusion simulation on microtomography data.

scholarly journals Adsorption of Selected Pharmaceutical Compounds onto Activated Carbon in Dilute Aqueous Solutions Exemplified by Acetaminophen, Diclofenac, and Sulfamethoxazole

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
E.-E. Chang ◽  
Jan-Chi Wan ◽  
Hyunook Kim ◽  
Chung-Huei Liang ◽  
Yung-Dun Dai ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Effective Diffusion ◽  
Molecular Size ◽  
Adsorption Affinity ◽  
Water Partition Coefficient ◽  
Component Systems ◽  
Dilute Aqueous Solutions ◽  
Multiple Component ◽  
The One ◽  
Selection Of

The adsorption of three pharmaceuticals, namely, acetaminophen, diclofenac, and sulfamethoxazole onto granular activated carbon (GAC), was investigated. To study competitive adsorption, both dynamic and steady-state adsorption experiments were conducted by careful selection of pharmaceuticals with various affinities and molecular size. The effective diffusion coefficient of the adsorbate was increased with decease in particle size of GAC. The adsorption affinity represented as Langmuir was consistent with the ranking of the octanol-water partition coefficient,Kow. The adsorption behavior in binary or tertiary systems could be described by competition adsorption. In the binary system adsorption replacement occurred, under which the adsorbate with the smallerKowwas replaced by the one with largerKow. Results also indicated that portion of the micropores could be occupied only by the small target compound, but not the larger adsorbates. In multiple-component systems the competition adsorption might significantly be affected by the macropores and less by the meso- or micropores.

scholarly journals The effect of temperature on the okra drying process: kinetic study and physical properties of powders

2021 ◽  
pp. 649-660
Author(s):  
Francislaine Suelia dos Santos ◽  
Rossana Maria Feitosa de Figueirêdo ◽  
Alexandre José de Melo Queiroz ◽  
Ana Raquel Carmo de Lima ◽  
Thalis Leandro Bezerra de Lima
Keyword(s):  
Free Energy ◽  
Physical Properties ◽  
Gibbs Free Energy ◽  
Effective Diffusion ◽  
Effective Diffusivity ◽  
Effect Of Temperature ◽  
Drying Temperature ◽  
Drying Kinetic ◽  
Drying Models ◽  
The One

This study aimed to evaluate the effect of drying temperature (50, 60, 70 and 80 °C) on okra dehydration by comparing its powder’s physical properties obtained from a sample produced by a lyophilization process. Ten drying models were adjusted to the experimental data of the drying kinetics. As a result, effective diffusivity and activation energy were determined in addition to thermodynamic parameters: entropy, enthalpy and Gibbs free energy. A physical characterization, as well as the pigments and colorimetry analyses of the aforementioned powders were made, by comparing them with samples produced by lyophilization. The powders were characterized for hygroscopicity, solubility, wettability, apparent and compacted density, fluidity and cohesiveness, pigments, colorimetric, morphological analysis (SEM) and X-ray diffraction. Midilli model was the one that best adjusted to the drying kinetic curves. There was a booster in the effective diffusion coefficient with the increase of temperature. Enthalpy and entropy were reduced with the increase of both drying temperature and Gibbs free energy. The powders presented high luminosity, and the lyophilized powder had higher pigments retention and greater solubility. All powders presented poor fluidity and intermediate cohesiveness, with amorphous, irregular and asymmetric particles. Thus, from the present study it was possible to evaluate the best drying method, the one that should be applied for the drying of okra, considering the costs involved, its quality and the final application of the product, meeting the specific needs of each consumer

scholarly journals Uranium migration through the Swiss Opalinus Clay varies on the metre scale in response to differences of the stability constant of the aqueous, ternary uranyl complex Ca<sub>2</sub>UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>

2021 ◽  
Vol 56 ◽  
pp. 97-105
Author(s):  
Theresa Hennig ◽  
Michael Kühn
Keyword(s):  
Stability Constant ◽  
Host Rock ◽  
Uranyl Complex ◽  
Opalinus Clay ◽  
Double Layers ◽  
Anionic Complex ◽  
Order Of Magnitude ◽  
Uranium Migration ◽  
The Stability ◽  
Exclusion Effect

Abstract. The simulation of uranium migration through the Swiss Opalinus Clay is used as an example to quantify the influence of varying values of a stability constant in the underlying thermodynamic database on the migration lengths for the repository scale. Values for the stability constant of the neutral, ternary uranyl complex Ca2UO2(CO3)3 differ in literature by up to one order of magnitude. Within the studied geochemical system, either the neutral or the anionic complex CaUO2(CO3)32- is the predominant one, depending on the chosen value for the neutral complex. This leads to a changed interaction with the diffuse double layers (DDL) enveloping the clay minerals and thus can potentially influence the diffusive transport of uranium. Hence, two identical scenarios only differing in the value for the stability constant of the Ca2UO2(CO3)3 complex were applied in order to quantify and compare the migration lengths of uranium on the host rock scale (50 m) after a simulation time of one million years. We ran multi-component diffusion simulations for the shaly and sandy facies in the Opalinus Clay. A difference in the stability constant of 1.33 log units changes the migration lengths by 5 to 7 m for the sandy and shaly facies, respectively. The deviation is caused by the anion exclusion effect. However, with a maximum diffusion distance of 22 m, the influence of the stability constant of the Ca2UO2(CO3)3 complex on uranium migration in the Opalinus Clay is negligible on the host rock scale.

VisTHAA

2016 ◽  
pp. 151-177
Author(s):  
Laura Cruz-Reyes ◽  
Mercedes Pérez Villafuerte ◽  
Marcela Quiroz-Castellanos ◽  
Claudia Gómez ◽  
Nelson Rangel Valdez ◽  
...  
Keyword(s):  
Design Theory ◽  
Bin Packing ◽  
Heuristic Algorithms ◽  
Statistical Tests ◽  
Packing Problem ◽  
Point Of View ◽  
Minimum Requirement ◽  
The One ◽  
Standard Sets ◽  
Non Parametric

In this chapter, a scientific tool designed to facilitate fair comparisons of heuristics is introduced. Making a fair comparison of the performance of different algorithms is a general problem for the heuristic community. Most of the works on experimental analysis of heuristic algorithms have been focused on tabular comparisons of experimental results over standard sets of benchmark instances. However, from a statistical point of view, and according to the experimental design theory, a minimum requirement to compare heuristic algorithms is the use of non-parametric tests. Non-parametric tests can be used for comparing algorithms whose results represent average values, in spite of the inexistence of relationships between them, and explicit conditions of normality, among others. The proposed tool, referred to as VisTHAA, incorporates four non-parametric statistical tests to facilitate the comparative analysis of heuristics. As a case study, VisTHAA is applied to analyze the published results for the best state-of-the-art algorithms that solve the one-dimensional Bin Packing Problem.

Numerical Simulation of a Large-Scale Industrial Billet Heating Furnace with Direct Flame Impingement

2021 ◽  
Vol 407 ◽  
pp. 11-21
Author(s):  
Sérgio Cavaleiro Costa ◽  
Isabel Malico ◽  
Rui Pedro Monteiro Lima ◽  
Luís Rato
Keyword(s):  
Large Scale ◽  
Chemical Species ◽  
Heating Furnace ◽  
Finite Volume Scheme ◽  
Gas Temperature ◽  
Energy Audit ◽  
Ansys Fluent ◽  
Dissipation Model ◽  
The One ◽  
Good Agreement

Numerical simulations of a billet heating furnace with direct flame impingement operating in a metallurgical plant were carried out and the results compared to measurements obtained in an industrial environment. The transport equations for mass, momentum, energy and mass of chemical species in reactive flow were computed with the use of ANSYS FLUENT. Turbulence, combustion and radiation were modeled using, respectively, the realizable k-ε model, the finite-rate/eddy-dissipation model and the finite volume scheme. The model was used to simulate the furnace operating under the conditions that occurred during an energy audit carried out at an industrial facility (413 kW firing rate and 80% excess air). The predicted furnace efficiency, 72.5%, is in very good agreement with the one obtained in the energy audit (0.4% difference). The flue gas temperature at the end of the second preheating zone was measured during the energy audit and its value compared to the one predicted. In this case, the agreement between measurements and simulation is not so satisfactory (23% difference). This paper presents the validation of a CFD model of a direct-flame impingement furnace for billet heating in a full-scale industrial situation, which was not previously published, and opens the way for more simulations and detailed studies of the phenomena that occur inside this type of furnace.

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