Transport Model Research Articles

Fixed Source Sensitivity Calculations for Inertial Confinement Fusion Applications

A numerical code library was developed for the radiation transport code MCNP6.3 to calculate generalized response sensitivity coefficients for fixed source neutron transport problems with applications to inertial confinement fusion (ICF) experiments. The new MCNP6.3 dependency is used to generate a novel time convolution response that represents a neutron time-of-flight (nToF) signal. The traditional suite of macroscopic cross-section sensitivities and constrained fixed source probability distribution sensitivities are available for both the standard and the new response tallies in this library. However, novel sensitivity coefficients for the constrained hyperparameters of analytic fixed source probability distributions are emphasized in this work for their connection to ICF neutron transport models. Particularly, advanced Monte Carlo methods are developed for calculating the sensitivity of a nToF signal to perturbations in an ICF plasma’s ion temperature and burn history as well as perturbations in the target liner mass density and the shape parameters of the nToF detector’s impulse response function. Together, these capabilities form an advanced suite of computational tools that can be used to analyze and extract information from any ICF experimental platform.

Rotating cylinder electrode in reactive CO2 capture: Identifying active C species via transport, VLE models and kinetics

AbstractThis article explores technical challenges and potential methodologies for understanding electrochemical Reactive CO Capture (RCC) mechanisms. RCC offers potential energy cost advantages by directly converting captured CO into fuels and chemicals, unlike traditional carbon capture and utilization (CCU) processes that require sequential capture, concentration, and compression. However, direct conversion of captured CO introduces complexity due to additional equilibrium buffer reactions, making it challenging to identify active species for reduction in electrochemical studies. This article discusses methods to integrate transport, thermodynamics, and kinetics concepts to identify active carbon sources in RCC. Vapor‐Liquid Equilibrium (VLE) and transport models are validated against experimental results obtained in a gastight rotating cylinder electrode reactor and are shown as useful tools for studying RCC in heterogeneous electrocatalysts across different capture agents, solvents, and temperatures. This article establishes an experimental framework for advancing research in electrochemical RCC.

Origin of exponentially large increase in the leakage current in alumina films depending on the ALD synthesis temperature

Amorphous aluminum oxide a-Al2O3 deposited by atomic layer deposition (ALD) is widely used in nonvolatile memory devices. In this paper, the leakage current dependence on the ALD synthesis temperature is investigated by six charge transport models: Schottky effect, thermally assisted tunneling at a contact, Frenkel effect, Hill-Adachi model of overlapping Coulomb potentials, Makram-Ebeid and Lannoo multiphonon isolated trap ionization model, and Nasyrov–Gritsenko model of phonon-assisted tunneling between neighboring traps. It is shown that the leakage current exponentially increases with the ALD synthesis temperature, which is related to the increase in trap concentration.

Modulating electrical response and impedance in Co–Cr substituted M-phase barium hexaferrites: Examining microstructure, grain boundaries, charge transport, and computational modeling

This study explores the influence of Co2+ and Cr3+ doping on the microstructure and electrical properties of Ba-hexagonal ferrite synthesized using the sol-gel method. X-ray diffraction (XRD) confirmed the formation of the anticipated hexagonal M-type crystal structure. Field emission scanning electron microscopy (FESEM) revealed the evolution of grain morphology with increasing doping levels, showcasing the formation of needle-like grains. Electrical characterization using an impedance analyzer investigated dielectric, impedance, electric modulus, and conductivity properties at room temperature. The analysis of the dielectric spectra indicated a decrease in dielectric constant and an increase in loss tangent with increasing dopant concentration. The electric modulus spectra provided evidence for non-Debye relaxation behavior, further supported by observations of relaxation processes at varying frequencies in the conductivity spectra. Additionally, an increase in doping led to a decrease in both relaxation time and AC conductivity. Electrochemical impedance spectroscopy (EIS) measurements yielded complex impedance curves. These curves exhibited good agreement with the values obtained through software-based simulations of grain and grain boundary characteristics. Furthermore, the distribution of grains and grain boundaries observed in FESEM micrographs aligned with the patterns predicted by the EIS software.

Nonpremixed and Premixed FPV Modeling of a Turbulent CH4-H2 Bluff-Body Flame

ABSTRACT In this study, modeling of nonpremixed CH4/H2 bluff-body (HM1) flame was performed using nonpremixed and premixed-based flamelet progress variable (FPV) models. The models were developed in an OpenFOAM flow solver, and the performance of the different variants of the FPV model was evaluated in the prediction of flame structure. The premixed FPV tables were constructed by employing two different interpolation techniques, i.e. linear and cubic spline, to retrieve the reactive scalars outside the flammability range. A generalized progress variable equation was introduced in the flow solver, which can be used for both tabulation approaches. Inside the flammable range, the profiles of the reactive scalars obtained from premixed FPV were found to be similar to those of the nonpremixed FPV. However, there exists disparity in the profiles outside the flammable range, particularly in the fuel-rich side between the nonpremixed and premixed approaches. A modified k-ε model was found to be suitable for modeling the turbulence compared to standard k-ε and k-ω shear stress transport models. The predictions of mean reactive scalars by the premixed FPV model, when combined with the linear interpolation, agree very well with experimental data and with the nonpremixed FPV predictions. However, deviations were observed in the predictions of the mean reactive scalar while using the cubic spline method in premixed FPV. All three approaches exhibit almost similar variations in the predictions of minor species. The results obtained from the present approach depict that the developed solver can be extended for modeling turbulent-chemistry interactions arising in partially premixed turbulent flames.

Modelling approach integrating climate projections for coastal groundwater management

Climate change and excessive groundwater extraction are major contributors to rising groundwater salinization due to seawater intrusion in coastal aquifers. This study aims to define a wide-applicable approach in which hydrological balance, boundary conditions, and irrigation water demand, defined over time considering climate change predictions, can integrated into a numerical model of the groundwater system. The approach was tested in a selected coastal aquifer. The approach spans from the past, used to define steady or almost natural conditions for calibration purposes (1950–2000 in the test), to the future (2100), divided in decade steps. The water balance analysis is based on an inverse hydrogeological water balance approach. The future climate change predictions are used to assess variations in boundary conditions of the groundwater model concerning salinity and sea level, recharge, and inflow from upstream aquifers. The approach considers changes in agricultural activities, groundwater demand, and river stage. The regional model is generated using the MODFLOW code for the groundwater flow model and the SEAWAT code for the salt transport model. The test concerns the Metaponto coastal plain, in which a porous aquifer is at salinization risk due to seawater intrusion. In this way, different influences of climate change and human activities are combined to define a 3d view of groundwater depletion and salinization effects. Quantifying these potential effects or risks, adaptation scenarios with numerical assessments are outlined in this study.

Development of novel osteochondral scaffolds and related in vitro environment with the aid of chemical engineering principles.

In tissue engineering, collaboration among experts from different fields is needed to design appropriate cell scaffolds and the required 3D environment. Osteochondral tissue engineering is particularly challenging due to the necessity to provide scaffolds that imitate structural and compositional differences of two neighboring tissues, articular cartilage and bone, and the required complex biophysical environments to cultivate such scaffolds. This work focuses on two key objectives: first, to develop bilayered osteochondral scaffolds based on gellan gum and bioactive glass, and second, to create a biomimetic environment for scaffold characterization by designing and utilization of novel dual-medium cultivation bioreactor chambers. Basic chemical engineering principles were utilized to aid both aims. First, a simple heat transport model based on one-dimensional conduction was applied as a guideline for bilayered scaffold preparation, leading to the formation of the gelatinous upper part and a macroporous lower part with a thin, well-integrated interfacial zone. Second, a novel cultivation chamber was developed to be used in a dynamic compression bioreactor to provide possibilities for flow of two different media, such as chondrogenic and osteogenic. These chambers were utilized for characterization of the novel scaffolds regarding bioactivity and stability under dynamic compression and fluid perfusion during 14 days, while flow distribution under different conditions was analyzed by a tracer method and residence time distribution analysis.

Quantitative Analysis of Aeolian Sand Provenance: A Comprehensive Analysis in the Otindag Dune Field, Central Inner Mongolia, China

The identification and quantification of aeolian sand contributions are essential for understanding the formation of dune fields and mechanisms of modern surface processes. In the present study, we take aeolian sand in the Otindag dune field (hereafter, often referred to as, simply, Otindag) as the research object. The dune field’s immediate source is quantitatively identified based on heavy minerals and the Conservativeness Index (CI), Consensus Ranking (CR), and the Consistent Tracer Selection (CTS) method. The primary source area of the aeolian sand was found to be from the northwestern, upwind area of the Otindag (59 ± 14%), followed by the Yinshan Mountain (17 ± 10%) and the lake basin (23 ± 12%). The proposed sediment transport model elucidates that sediments from the upwind of the Otindag are directly transported from the northwest to the Otindag, where they are deposited. Materials from the southern Yinshan Mountains are carried by rivers to the southern edge of the Otindag, where they are subsequently transported by wind and ultimately deposited. The lake deposits within the Otindag also contribute to the aeolian sand supply under the influence of wind. This study demonstrates that the fingerprinting techniques of CI, CR, and CTS serve as successful strategies for conducting quantitative provenance research in dune fields.

Capturing Exposure Disparities with Chemical Transport Models: Evaluating the Suitability of Downscaling Using Land Use Regression.

High resolution exposure surfaces are essential to capture disparities in exposure to traffic-related air pollution in urban areas. In this study, we develop an approach to downscale Chemical Transport Model (CTM) simulations to a hyperlocal level (∼100m) in the Greater Toronto Area (GTA) under three scenarios where emissions from cars, trucks and buses are zeroed out, thus capturing the burden of each transportation mode. This proposed approach statistically fuses CTMs with Land-Use Regression using machine learning techniques. With this proposed downscaling approach, changes in air pollutant concentrations under different scenarios are appropriately captured by downscaling factors that are trained to reflect the spatial distribution of emission reductions. Our validation analysis shows that high-resolution models resulted in better performance than coarse models when compared with observations at reference stations. We used this downscaling approach to assess disparities in exposure to nitrogen dioxide (NO2) for populations composed of renters, low-income households, recent immigrants, and visible minorities. Individuals in all four categories were disproportionately exposed to the burden of cars, trucks, and buses. We conducted this analysis at spatial resolutions of 12, 4, 1 km, and 100 m and observed that disparities were significantly underestimated when using coarse spatial resolutions. This reinforces the need for high-spatial resolution exposure surfaces for environmental justice analyses.

A Q-band frequency tunable Doppler backscattering (DBS) system for pedestal and scrape-off layer density fluctuation and flow measurements in the DIII-D tokamak.

We present the design and laboratory tests for a new Q-band frequency tunable Doppler backscattering (DBS) system suitable for probing poloidal wavenumber kñ = 6-8cm-1 density fluctuations and their flow velocities in the pedestal and scape-off layer (SOL) of the DIII-D tokamak. This system will provide new measurements in the increasingly important and under-diagnosed far pedestal and SOL plasma regions. These results are important for experimental transport studies and necessary for the validation of transport models, both of which are important to fusion energy research. The use of a single tunable frequency reduces the complexity and potential failure points as compared to a multichannel system. This new system utilizes a 33-50GHz tunable source and will be integrated into the current V-band DBS in DIII-D using a broadband Q- and V-band multiplexer. A full-scale mockup of the quasi-optical system was used to test and optimize the performance. These tests include beam profile measurements at different distances (and angles) from a paraboloidal focusing and steering mirror. The measurements cover the full frequency range 33-75GHz of the integrated/combined Q-V band DBS system and target a large radial coverage of the low-field side of the plasma from ρ = 1.1 to ρ = 0.5, where ρ is the normalized flux surface radial coordinate.

Critical risks with the permeability dimension to describe the hydrogen crossover phenomenon

Hydrogen crossover in water electrolyzer systems equipped with ion exchange membranes (IEM) poses significant safety risks and reduces overall process efficiency. This communication identifies and addresses two critical errors in current hydrogen crossover literature: inaccurate measurement methods and the inappropriate use of permeability (e.g., barrer) to quantify hydrogen crossover. Accurate evaluation of hydrogen crossover through an IEM can be challenging because it is a two-phase material fully hydrated in liquid water. We propose a standardized protocol for accurately measuring hydrogen crossover in fully hydrated IEMs and emphasize the necessity of using flux (e.g., mole∙m−2∙s−1) instead of permeability (e.g., barrer) dimension. The obtained data reveal that normalizing hydrogen crossover by transmembrane pressure and membrane thickness can result in significant errors, with relative errors reaching up to 25%. When applied to the actual electrolysis operation, using the permeability data to predict hydrogen crossover at a current density of 0.4 A cm−2 results in 47% error, with the actual system reaching the lower explosion limit (LEL) while the predicted value does not. Additionally, hydrogen crossover data provides insights into the internal ion channel morphology of IEMs. This communication article intends to convey the current existing safety hazards to the hydrogen research community with a detailed transport models and validation.

Comparison of transport models in dense plasmas

Comparison of transport models in dense plasmas

Modelling the impacts of climate change on agrochemical fate and transport by water on a catchment scale

The export of agrochemicals and their transformation products (TPs) following their application in the agricultural fields poses a threat to water quality. Future changes in climatic conditions (e.g. extreme weather events such as heavy rainfall or extended dry periods) could alter the degradation and mobility of agrochemicals. In this research, we use an integrated modelling framework to understand the impact of extreme climate events on the fate and transport of the agrochemical S-Metolachlor and two of its TPs (M-OXA, Metolachlor Oxanilic Acid and M-ESA, Metolachlor Ethyl Sulfonic Acid). This is done by coupling climate model outputs to the Zin-AgriTra agrochemical reactive transport model in four simulation scenarios. 1) Reference (2015–2018), 2) Very dry (2038–2041), 3) Very wet (2054–2057) and 4) High temperature (2096–2099) conditions of a selected RCP8.5 based regional climate scenario. The modelling framework is tested on an agricultural catchment, Wulka, in Burgenland, Austria. The model results indicate that 13–14 % of applied S-Metolachlor is retained in the soil, and around 85 % is degraded into TPs in the different scenarios. In very dry and high-temperature scenarios, degradation is higher, and hence, there is less S-Metolachlor in the soil. However, a large share of formed M-OXA and M-ESA are retained in the soil, which is transported via overland and groundwater flow, leading to a build-up effect in M-OXA and M-ESA river concentrations over the years. Though a small share of S-Metolachlor and TPs are transported to rivers, their river export is affected by the intensity and amount of rainfall. The very wet and high-temperature scenarios show higher S-Metolachlor and TP concentrations at the catchment outlet due to higher river discharge. The reference scenario shows higher river peak concentrations associated with higher overland flow caused by measured hourly rainfall compared to disaggregated daily precipitation data in the other scenarios.

The sources and transport model of deep-sea sediment in the Southwest Sub-basin of the South China Sea

The sources and transport model of deep-sea sediment in the Southwest Sub-basin of the South China Sea

Consequential life cycle assessment of bamboo leaf ash generation: A Brazilian context

The potential of biomass growth, such as from bamboo leaves, as a source of electricity provides an optimistic scenario for the sustainable development of new green building materials. To validate robust life cycle inventory (LCI) data for incoming high-quality silica sources for cementitious materials, a consequential life cycle assessment (CLCA) on the bamboo leaves ash (BLA) with a prospective approach was conducted. The LCI data was collected in Southeastern Brazil with a prospective maturity in biomass electricity system. The data was gathered by analyzing the various stages involved in the production of BLA, including bamboo cultivation, leaf collection, cogeneration, raw BLA beneficiation, and its impact on cement and electricity marginal production systems. According to the multifunctionality solution, the environmental impacts results of CLCA were discussed using a sensibility analysis with two attributional life cycle assessment (ALCA) scenarios as allocation and “zero environmental load” (considering BLA as residue). The scenarios demonstrate the potential for sustainable use of BLA, especially for its impact on climate change, including the biogenic carbon category. Also, consequences such as avoiding BLA landfilling and increasing the potential for bamboo agricultural holdings to become energy independent was included in the study conclusion. While these results are positive, the prospect of maturing electricity production requires the development of other high-quality materials, such as sugarcane bagasse ash, sugarcane leaf ash and rice husk ash. However, the positives consequences did not overcome the negative impacts from the transportation of BLA into its system boundaries, once the highway transport model is the manly in the Brazilian context. Hence, this study provides important and reproducible pathways for developing LCI data on other biomass ashes, assisting future studies on green building materials.

A perspective on fluid dynamics and geochemistry coupling in geologic CO2 storage: Key reactions, reactive transport modeling, and upscaling methods

Understanding the complicated fluid dynamics and geochemistry coupling behaviors is the key to enhance CO2 storage efficiency and minimize the risks of leakage and mechanical failure in geologic CO2 storage (GCS) reservoirs. This review paper aims to discuss recent research advances associated with fluid dynamics and geochemistry coupling in GCS systems. Four research areas, i.e., flow-induced enhancement of mineral dissolution and precipitation, advanced imaging techniques based on digital core analysis techniques, advances in reactive transport modeling, and upscaling approaches from pore-scale to reservoir-scale, are covered by this review. Based on a comprehensive discussion on the research advances in the aforementioned research areas, current challenges and future research needs of fluid dynamics and geochemistry coupling in geologic CO2 storage are highlighted. Finally, this review discusses how the research in fluid dynamics and geochemistry coupling can help in developing sustainable geologic CO2 storage strategies that can contribute to achieving carbon neutrality goals.

Enhancing herbicide adsorption in low-fertility soil using sugarcane biochar: Insights from Imazapic dynamics

Biochar amendment has emerged as a potential solution for preventing, remediating, and mitigating agricultural compound pollution. This groundbreaking technique not only improves crucial soil properties like porosity, water retention capacity, cation exchange capacity, and pH, but also intricately impacts the interaction and retention mechanisms of polluting molecules. In this study, we investigate the dynamic of the herbicide Imazapic when subjected to applying pyrolyzed biochars, specifically at temperatures of 300 and 500 °C, within the context of a low-fertility soil characterized as dystrophic Yellow Ultisol (YUd) in a sugarcane cultivation area in Igarassu-PE, Brazil. The biochars were produced from sugarcane bagasse by pyrolysis process in a muffle furnace. In laboratory conditions, with saturated soil columns under steady-state, analyses of the mechanisms involved in interaction and transport and determining hydrodispersive parameters for Imazapic were performed by the two-site nonequilibrium transport model using the CXTFIT 2.0 program. Samples of YUd soil amended with biochar pyrolyzed at 300 °C presented a negligible interaction with Imazapic. However, adding biochar pyrolyzed at 500 °C (BC500) to the soil samples enhanced the adsorption coefficient and improved the interaction with Imazapic. This research points out that biochar produced from agricultural waste biomass, such as sugarcane bagasse specifically pyrolyzed at 500 °C, offers a potential means to adsorb herbicides, reducing their leaching to deeper layers of the amended soils and the risk of groundwater contamination and potential environmental negative impacts.

Giant sediment-wave field and supercritical flows in a distally steepened ramp, Fort Payne Formation (Lower Mississippian), Kentucky–Tennessee, U.S.A.

ABSTRACT Sediment waves are common in confined to unconfined settings on modern marine slopes and basin floors worldwide. Their morphology and stratal patterns show that many of them migrate upslope and upflow, a characteristic thought to record Froude-supercritical flow conditions associated with sediment gravity flows and density cascades. Few sediment waves of this type have been observed in the ancient rock record. This study reports the discovery of a giant (> 20,000 km2) sediment-wave field in Lower Mississippian carbonates and shales of the Fort Payne Formation in Tennessee and Kentucky, U.S.A. Sediment waves are present in the clinothem slopes and basin floor of a distally steepened ramp as seismic-scale bedforms ranging from 100 to 700 m long and 15 to 50 m high. Dominant facies include crinoidal shales, packstones, and rudstones. Many of the beds are sharp-based and graded, indicating sediment-gravity-flow deposition. Upslope-inclined rudstones (backsets) and wavy beds with upflow and downflow laminae are common and indicate supercritical flow conditions. These observations and interpretations are in stark contrast to previous interpretations of crinoidal bioherms and Waulsortian-type mounds. Basin physiography, a cool-water heterozoan carbonate factory and coastal upwelling were key factors in establishing a rapidly prograding ramp characterized by high rates of sediment production and basinward shedding. Sediment gravity flows and density cascades transported crinoidal grains downslope and entrained crinoids that inhabited the slope. Flows frequently reached Fr-supercritical flow conditions that led to the formation of sediment waves similar to those on modern marine slopes. This sediment-wave field is one of the first to be documented in the ancient rock record, and its extent is enormous. The near absence of other reported ancient examples must be due to misinterpretation (mounds, slumps) and the problem of observational scale and resolution. Sediment waves are often larger than outcrops. Lack of recognition of sediment waves in subsurface seismic sections is probably due to misinterpretation and insufficient resolution. Perhaps this study demonstrates the need for revisiting and updating existing facies models of carbonate-sediment transport and depositional processes across slopes and basin floors.

Meridional Flow in the Solar Polar Caps Revealed by Magnetic Field Observation and Simulation

As a large-scale motion on the Sun, the meridional flow plays an important role in determining magnetic structure and strength and solar cycle. However, the meridional flow near the solar poles is still unclear. The Hinode observations show that the magnetic flux density in polar caps decreases from the lower latitudes to the poles. Using a surface flux transport model, we simulate the global radial magnetic field to explore the physical process leading to the observed polar magnetic distribution pattern. For the first time, the high-resolution observations of the polar magnetic fields observed by Hinode are used to directly constrain the simulation. Our simulation reproduces the observed properties of the polar magnetic fields, suggesting the existence of a counter-cell meridional flow in the solar polar caps with a maximum amplitude of about 3 m s−1.

Stochastic Gauss-Newton method for estimating absorption and scattering in optical tomography with the Monte Carlo method for light transport

Image reconstruction in optical tomography in the so-called transport regime, where the diffusion approximation is not valid, requires modeling of light transport using the radiative transfer equation. In this work, we approach this problem by utilizing the Monte Carlo method for light transport. In this work, we propose a methodology for absolute imaging of absorption and scattering in this regime utilizing a Monte Carlo method for light transport. The image reconstruction problem is formulated as a minimization problem that is solved using a stochastic Gauss-Newton method. In the construction of the Jacobian matrix for scattering, a perturbation approximation for Monte Carlo is utilized. The approach is evaluated with numerical simulations using an adaptive approach where the number of photon packets is adjusted during the iterations, and with different fixed numbers of photon packets. The simulations show that the Monte Carlo method for light transport can be utilized in the absolute imaging problem of optical tomography and that the absorption and scattering parameters can be estimated simultaneously with good accuracy.