Transport Studies Research Articles

Numerical simulation and experimental study of microplastic transport under open channel shear flow: Roles of particle physical properties and flow velocities

Microplastic (MP) transport patterns under open channel shear flow remain unclear. This study investigates the transport laws of MPs at various flow velocities, MP densities, sizes and concentrations in the U-shaped experimental flume and the numerical flume based on Lattice Boltzmann Method (LBM). The results indicate that the average horizontal particle velocity and the transport distances of Polyvinyl chloride (PVC) and Polystyrene (PS) particles increase with the average cross-sectional flow velocity, while the average vertical particle velocity decreases with it. The total average particle velocity closely matches the average vertical particle velocity, regardless of the variation in MP size, density and concentration. Formula-based analysis reveals that the acceleration of spherical MP transport mainly depends on the particle size and its consequent relative drag force term (RDFT) under the conditions with a single type of MP particles, but on the particle density and its consequent RDFT and relative gravity term (RGT) in the case concerning different types of MP particles with identical particle sizes. The average horizontal particle velocity maximum of PVC and PS are both strongly correlated with the average flow velocity maximum in the cross-section. This correlation lowers with the MP particle size and concentration, and is independent of MP density. Our findings can provide reference for the prevention and control of MP pollution in rivers.

Electron transport in quasi-ballistic FETs subjected to a magnetic field

We report the study of quasi-ballistic electron transport in short FETs subjected to magnetic field. Spatial distributions of electron concentrations, velocities, Hall currents, and voltages in the short FET channels are determined. The basic properties of current–voltage characteristics of quasi-ballistic FETs in magnetic field are analyzed, among them the kink-like characteristics of the near-ballistic device. Peculiarities of magnetoresistance of such FETs are studied for low and high magnetic fields and different current regimes. For nonlinear current regimes, we revealed significantly larger magnetoresistance for the devices with higher ballisticity. Numerical estimates of studied effects are presented. We suggest that the found results contribute to the physics of short FETs and can be used for developing nanoscale devices for particular applications.

Transport of particles in a model of 2D Rayleigh-Benard convection that conserves energy and vorticity

In contrast with the Lorenz model for 2-dimensional Rayleigh - Bénard system, the model proposed by Howard - Krishnamurti (HK) allows the possibility of a large scale horizontally shear flow making feasible the study of particles transport. However, this model lacks conservation of energy and vorticity in the absence of forcing and dissipation. A model that incorporates conservation of energy and vorticity was proposed by A. Gluhovsky et al (GTA). We perform the linear stability analysis of this later model and study the transport process on this velocity field background and make a comparison with the features of the former model. We found that the basic bifurcation structure is retained by the GTA model and discuss the differences that they indeed have. In regard to the transport processes, the basic features found using the HK velocity field background are also kept by the GTA model. We determine the size of the rather small gap in the Rayleigh number where the transport process shift from being shear flow dominated to a Brownian diffusion process.

Evaluation of Southern African wild edible plants for potential herb-drug interactions through ex vivo p-glycoprotein and in vitro cytochrome P450 3A4 inhibitory effects

BackgroundWild edible plants (WEPs) including herbs provide staple foods as well as income for local communities on the African continent. However, these commonly used plant materials interact with orthodox or conventional drugs through both p-glycoprotein (P-gp) and cytochrome P450 enzymes inhibition. Hence, it is vital to explore the possibility of herb-drug interactions when concomitantly taking conventional drug dosage forms with some of the WEPs. P-gp and CYP3A4 show analogous substrate specificities and work together to establish an intestinal absorption barrier against xenobiotics. This study investigated the ex vivo p-glycoprotein inhibition and the in vitro inhibition of cytochrome P450 3A4 (CYP3A4) isoezyme by selected wild edible plants to identify potential food/herb-drug interactions. Methods: Ethanolic extracts of 30 wild edible plants sourced from Lesotho, Eswatini and the Limpopo province of South Africa were used for the study. Drug transport studies using propranolol, a P-glycoprotein substrate, across porcine intestinal tissue were conducted using intestinal sacs with test solutions in Krebs-Ringer bicarbonate buffer (pH 7.4) under a 95 % O2/5 % CO2 atmosphere. For the in vitro luminescent-based CYP3A4 inhibition assay, both porcine liver and intestinal microsomes were extracted from their respective tissues by homogenization, followed by high-speed centrifugation and standardization before use. ResultsSisymbrium thelungii O. E. Schulz significantly (p < 0.05) inhibited P-gp with an effective apparent permeability coefficient (Papp eff) of (7.53±0.33) × 10–6 cm/s and effective flux (Jeff) of 1.38±0.01 µg/cm2/min which was similar to sodium orthovanadate (positive control), indicating potential for herb/food-drug interaction possibly by absorption enhancement of poorly permeable P-gp substrates by this plant. Additionally, both Rubus cuneifolius Pursh and Hypoxis hirsuta (L.) Coville had significant (p < 0.05) p-glycoprotein inhibitory effects with Papp eff of (6.60±0.52) × 10–6 cm/s and Jeff of 1.11±0.08 µg/cm2/min, and Papp eff of 6.58±0.67 × 10–6 cm/s and Jeff of 1.19±0.12 µg/cm2/min, respectively. Significantly (p < 0.05), Rubus cuneifolius at a concentration of 0.2 mg/mL exhibited the strongest CYP3A4 inhibition in liver microsomes suggesting its potential as a bioavailability enhancer of CYP3A4 substrates. Meanwhile, Wahlengergia androsacea A.DC exhibited the most significant (p < 0.05) CYP3A4 inhibitory effect at the same concentration in intestinal microsomes. ConclusionThe observed inhibitory effects of certain wild edible plants on P-gp-mediated drug efflux and CYP3A4 drug metabolism indicate potential food/herb-drug interactions challenges for clinical practice. The herb/food-drug interactions also present opportunities for discovery of new functional excipients for enhancing the permeability of poorly absorbed orally administered drugs that are substrates of P-gp and CYP3A4.

Photo‐activation of Tolane‐based Synthetic Ion Channel for Transmembrane Chloride Transport

AbstractWhile natural channels respond to external stimuli to regulate ion concentration across cell membranes, creating a synthetic version remains challenging. Here, we present a photo‐responsive uncaging technique within an artificial ion channel system, which activates the ion transport process from a transport‐inactive o‐nitrobenzyl‐based caged system. From the comparative ion transport screening, 1 b emerged as the most active transporter. Interestingly, its bis(o‐nitrobenzyl) derivative, i.e., protransporter 1 b′ was inefficient in transporting ions. Detailed transport studies indicated that compound 1 b is an anion selective transporter with a prominent selectivity towards chloride ions by following the antiport mechanism. Compound 1 b′ did not form an ion channel, but after the o‐nitrobenzyl groups were photocleaved, it released 1 b, forming a transmembrane ion channel. The channel exhibited an average diameter of 6.5±0.2 Å and a permeability ratio of . The geometry‐optimization of protransporter 1 b′ indicated significant non‐planarity, corroborating its inefficient self‐assembly. In contrast, the crystal structure of 1 b demonstrates strong self‐assembly via the formation of an intermolecular H‐bond. Geometry optimization studies revealed the plausible self‐assembled channel model and the interactions between the channel and chloride ion.

Photo-activation of Tolane-based Synthetic Ion Channel for Transmembrane Chloride Transport.

While natural channels respond to external stimuli to regulate ion concentration across cell membranes, creating a synthetic version remains challenging. Here, we present a photo-responsive uncaging technique within an artificial ion channel system, which activates the ion transport process from a transport-inactive o-nitrobenzyl-based caged system. From the comparative ion transport screening, 1 b emerged as the most active transporter. Interestingly, its bis(o-nitrobenzyl) derivative, i.e., protransporter 1 b' was inefficient in transporting ions. Detailed transport studies indicated that compound 1 b is an anion selective transporter with a prominent selectivity towards chloride ions by following the antiport mechanism. Compound 1 b' did not form an ion channel, but after the o-nitrobenzyl groups were photocleaved, it released 1 b, forming a transmembrane ion channel. The channel exhibited an average diameter of 6.5±0.2 Å and a permeability ratio of . The geometry-optimization of protransporter 1 b' indicated significant non-planarity, corroborating its inefficient self-assembly. In contrast, the crystal structure of 1 b demonstrates strong self-assembly via the formation of an intermolecular H-bond. Geometry optimization studies revealed the plausible self-assembled channel model and the interactions between the channel and chloride ion.

The Diffusion Tensor of Protons at 1 au: Comparing Simulation, Observation, and Theory

The natural variation in plasma parameters observed at 1 au can lead to a variation in transport parameters, such as diffusion and drift coefficients, for energetic charged particles of solar and galactic origin. Given the importance of these parameters to particle transport studies, this variation is investigated through test particle simulations over a range of energies in the presence of simulated turbulence with properties corresponding to an ensemble of observed turbulence conditions at Earth. The resulting transport coefficients are then compared with observational estimates from the literature, as well as the predictions of several scattering theories. Parallel and perpendicular mean free paths are shown to vary widely, for the former in agreement with prior observational estimates, but not for the latter. Furthermore, a large disparity between the predictions of theory and the simulation results is noted for the perpendicular mean free path. As such, these results indicate that particle transport studies, particularly predictive ones, need to take into account this natural variation in transport coefficients.

FLEXPART version 11: improved accuracy, efficiency, and flexibility

Abstract. Numerical methods and simulation codes are essential for the advancement of our understanding of complex atmospheric processes. As technology and computer hardware continue to evolve, the development of sophisticated code is vital for accurate and efficient simulations. In this paper, we present the recent advancements made in the FLEXible PARTicle dispersion model (FLEXPART), a Lagrangian particle dispersion model, which has been used in a wide range of atmospheric transport studies over the past 3 decades, extending from tracing radionuclides from the Fukushima nuclear disaster, to inverse modelling of greenhouse gases, and to the study of atmospheric moisture cycles. This version of FLEXPART includes notable improvements in accuracy and computational efficiency. (1) By leveraging the native vertical coordinates of European Centre for Medium Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) instead of interpolating to terrain-following coordinates, we achieved an improvement in trajectory accuracy, leading to a ∼8 %–10 % reduction in conservation errors for quasi-conservative quantities like potential vorticity. (2) The shape of aerosol particles is now accounted for in the gravitational settling and dry-deposition calculation, increasing the simulation accuracy for non-spherical aerosol particles such as microplastic fibres. (3) Wet deposition has been improved by the introduction of a new below-cloud scheme, by a new cloud identification scheme, and by improving the interpolation of precipitation. (4) Functionality from a separate version of FLEXPART, the FLEXPART CTM (chemical transport model), is implemented, which includes linear chemical reactions. Additionally, the incorporation of Open Multi-Processing parallelisation makes the model better suited for handling large input data. Furthermore, we introduced novel methods for the input and output of particle properties and distributions. Users now have the option to run FLEXPART with more flexible particle input data, providing greater adaptability for specific research scenarios (e.g. effective backward simulations corresponding to satellite retrievals). Finally, a new user manual (https://flexpart.img.univie.ac.at/docs/, last access: 11 September 2024) and restructuring of the source code into modules will serve as a basis for further development.

A Study of Heavy Road Freight Transport in Poland in the Context of the Pursuit of Sustainable Road Transport

The efficiency of road freight transport determines—to a significant degree—the total environmental footprint and the amount of greenhouse gases and other pollutants released into the atmosphere by inland transport. The rate of empty or partially empty vehicles is one of the key metrics for improvement of the environmental performance of freight road transportation. This paper presents the characteristics of road freight transport in Poland on the basis of data collected by weigh-in-motion stations. Data aggregation for environmental analysis represents a novel aspect of the work. Indicators describing the degree of loading, the share of empty vehicles in traffic, and the share of vehicles of maximum permissible total weight in traffic were determined for a representative group of heavy goods vehicles. Based on the representative load factor value (LFA), a classification of the road section into four groups was proposed. The results obtained show a clear differentiation of the values of the indicators analyzed for individual groups and their variability in the three-year period covered by the analysis. The aggregation method presented can be used to identify the nature of the distribution of the weight categories of the heavy goods vehicles and provide input information for targeted analyses relating to sustainable road transport management and environmental protection. Finally, the grouped LFA values were linked with indicators of energy consumption (ECI) and on-road emissions (EI).

On the use of isotopic differences of carbon fractions of biomass in plants to study transport flows and source-sink relations under different light conditions

It is shown that the differences in the isotopic composition of carbon in the water-soluble and water-insoluble fractions of plant leaf biomass, as well as phloem, are evolutionarily determined. They associated with metabolic reactions during assimilation and photorespiration and do not depend on the illumination mode and on the spectral ranges of headlights used in illumination. The above isotopic shifts are the cause of isotopic differences in assimilatory and photorespiratory carbon stocks that feed various metabolic processes. Due to the strict temporal and spatial organization of metabolism, carbon fluxes from the funds retain isotopic differences without complete mixing. The differences in the isotopic composition of carbon of the water-soluble fraction of biomass and carbon of phloem juice from carbon of the water-insoluble fraction are small (1–3%), but they are quite stable and easily fixed. The carbon of the water-soluble fraction is very close in isotopic composition to the carbon of the phloem and is noticeably enriched with the isotope 13C relative to the water-insoluble fraction, which makes it possible to use it as a marker in the study of assimilate transport in plants, especially during budding and fruiting. It is shown that the reason for the enrichment of autotrophic organs and tissues with isotope 12C relative to carbon of heterotrophic parts of the plant is the predominant participation in their formation of an isotopically light assimilation fund, whereas an isotopically heavy photorespiratory fund takes part in the formation of heterotrophic organs. It is shown that the manifestation of the formation of two isotopically different funds is the discovered relationship of the carbon isotope composition of leaves with their age.

Electroosmotic base magnetic field study of peristaltic transport in a non‐uniform wavy ciliated channel for Williamson fluid with enhancing nanoparticles

Electroosmotic base magnetic field study of peristaltic transport in a non‐uniform wavy ciliated channel for Williamson fluid with enhancing nanoparticles

Dephasing-assisted transport in a tight-binding chain with a linear potential

An environment interacting with a quantum system can enhance transport through the suppression of quantum effects responsible for localization. In this paper, we study the interplay between bulk dephasing and a linear potential in a boundary-driven tight-binding chain. A linear potential induces Wannier-Stark localization in the absence of noise, while dephasing induces diffusive transport in the absence of a tilt. We derive an approximate expression for the steady-state current as a function of both dephasing and tilt which closely matches the exact solution for a wide range of parameters. From it, we find that the maximum current occurs for a dephasing rate equal to the period of Bloch oscillations in the Wannier-Stark localized system. We also find that the current displays a maximum as a function of the system size, provided that the total potential tilt across the chain remains constant. Our results can be verified in current experimental platforms and represents a step forward in analytical studies of environment-assisted transport.

Self-organized transport in noisy dynamic networks.

We present a numerical study of multicommodity transport in a noisy, nonlinear network. The nonlinearity determines the dynamics of the edge capacities, which can be amplified or suppressed depending on the local current flowing across an edge. We consider network self-organization for three different nonlinear functions: For all three we identify parameter regimes where noise leads to self-organization into more robust topologies, that are not found by the sole noiseless dynamics. Moreover, the interplay between noise and specific functional behavior of the nonlinearity gives rise to different features, such as (i) continuous or discontinuous responses to the demand strength and (ii) either single or multistable solutions. Our study shows the crucial role of the activation function on noise-assisted phenomena.

A 45-year updating wind and wave hindcast over the Oman Sea and the Arabian Sea

This study focuses on developing a comprehensive and reliable wind and wave hindcast for the Oman Sea and Arabian Sea, spanning a significant 45-year period (1979–2024). The objective is to capture the intricate wind and wave climate of the region, characterized by distinct monsoon cycles and occasional tropical cyclones. The availability of extensive wave data over four decades would be an irreplaceable tool for researchers and engineers, enabling improved accuracy in extreme value analysis, sediment transport studies, and wave-induced current simulations. Despite limited field observations, all available measured data within the region were collected, analyzed for configuration of the models and utilized for model calibration and validation. The hindcast data was generated using the Weather Research and Forecasting (WRF) model for winds and WAVEWATCH III (WW3) model for waves, and evaluated against observational and measured wind and wave parameters. A comprehensive statistical analysis of the hindcast model's performance reveals adequate agreement with measured data, as evidenced by root mean square errors (RMSEs) of 1.23 m/s for wind speeds and 0.37 m for significant wave heights in average. These results underscore the model's reliability for research and engineering applications, particularly in the Arabian Sea, with a focus on the northern coastlines of the Oman Sea. The specific model configuration employed in this study holds significant potential for future investigations in the northern Indian Ocean, offering a valuable tool for understanding and predicting climatical conditions in this region.

Spatial Big Data and Analysis Strategies Supporting Geographic Information System for Transportation (GIS-T) in Conceptual Design, Modelling, and Decision-making: A Review

Abstract. Transportation is a key component in urban design for cities’ efficiency and residents’ life quality, and GIS has the capability of handling data management, model design, and scientific decision-making for transportation studies. This article reviews how spatial big data and analysis strategies help GIS-T studies from the phases of conceptual design, modelling, and decision-making. In this research, we firstly summarized categorizes of data objects and relevant information for real-world issues from transportation applications in the conceptual design phase. In the modelling phase, optimization strategies for transport planning and accessibility measures through network data were also summarized. Finally, we reviewed spatial analysis methods in supporting transport decision-making, and how spatial methods take advantage of geography features of transport variables in previous studies. Our research primarily focuses on geography research with transportation topics as applications, and this work can help transport experts to have a better understanding of GIS values for transportation modelling and planning.

Probing half-metallicity in Mn2CoSi/Si(100) thin film structures using electrical transport measurements towards spintronic applications

The structural, magnetic, and electronic transport properties of Mn₂CoSi (MCS) thin film have been studied to explore the possibility of half-metallicity of MCS Heusler alloy (HA) in thin film form. Grazing incidence X-ray diffraction (GIXRD) data indicated the presence of the rhombohedral crystal structure with a space group of R 3‾ (148). Spectrum fitting of X-ray reflectivity (XRR) suggests the deposited film has smooth surface with uniform density. Magnetic analysis reveals the ferrimagnetic nature of the film with a transition temperature well above the room temperature. Electric transport study of MCS thin film indicates the non-metallic behavior (< 250 K) and metallic behavior (> 250 K) in different temperature regimes. The persistence of half-metallicity across the entire temperature range is supported by the presence of T7/2 terms in the resistivity data due to two-magnon scattering. Arrhenius equation fitting of the electrical resistivity data in the non-metallic regime results the activation energy of 4.98 meV. At room temperature, the electrical resistivity is 1.372 mΩ-cm which is consistent with the values reported previously for other well-known half-metallic HAs. The observed results of HA in thin film form seems encouraging to us which could find its applications as a magnetic electrode for future spintronics.

Commissioning of the tracer-encapsulated solid pellet (TESPEL) injection system for Wendelstein 7-X and first results for OP1.2b

Abstract A new tracer-encapsulated solid pellet (TESPEL) injection system was successfully commissioned for the stellarator fusion experiment Wendelstein 7-X (W7-X) during its OP1.2b operational campaign. TESPELs are polystyrene encapsulated solid pellets loaded with tracer impurities that have been employed in other stellarator devices for impurity transport studies. During the OP1.2b campaign approximately 140 pellet injections were performed with a successful delivery rate of 89%, thus this system has proven to be very reliable. Here, the experimental set-up and methodology are described first. In addition, it is outlined how, through the analysis of TESPEL time-of-flight signals and of the temporal evolution of line emissions originating from shell and tracer species as well as comparisons with ablation models, the radial localization of the deposited tracer is determined. This contribution also provides a general overview of the TESPEL injector performance during OP1.2b, discusses the global effects of TESPEL injections on W7-X plasmas and reports on first results in terms of a summary of TESPEL injections, plasma response to TESPELs, the post-deposition evolution of tracer spectral emission lines and soft x-ray emissions.

Evaluation of particle tracking codes for dispersing particles in porous media

Particle tracking (PT) is a popular technique in microscopy, microfluidics and colloidal transport studies, where image analysis is used to reconstruct trajectories from bright spots in a video. The performance of many PT algorithms has been rigorously tested for directed and Brownian motion in open media. However, PT is frequently used to track particles in porous media where complex geometries and viscous flows generate particles with high velocity variability over time. Here, we present an evaluation of four PT algorithms for a simulated dispersion of particles in porous media across a range of particle speeds and densities. Of special note, we introduce a new velocity-based PT linking algorithm (V-TrackMat) that achieves high accuracy relative to the other PT algorithms. Our findings underscore that traditional statistics, which revolve around detection and linking proficiency, fall short in providing a holistic comparison of PT codes because they tend to underpenalize aggressive linking techniques. We further elucidate that all codes analyzed show a decrease in performance due to high speeds, particle densities, and trajectory noise. However, linking algorithms designed to harness velocity data show superior performance, especially in the case of high-speed advective motion. Lastly, we emphasize how PT error can influence transport analysis.

Selective neglect of viral risk: Tokyo’s commuter trains during the COVID-19 pandemic

This article asks why Tokyo’s crowded trains were largely absent from official discourses of viral risk in Japan during the COVID-19 pandemic. While public transport environments were often framed as spaces of contagion in other countries, Japanese public health discourses instead tended to emphasize the viral safety of urban railway transport. Drawing on an analysis of media and expert discourse, auto-ethnographic fieldwork, and repeat interviews with commuters, this article examines the processes through which Tokyo’s urban railway network was extracted from discourses of viral risk. It identifies four factors that contributed to this: (1) dominant definitions of risk spaces in public health messaging, (2) trains’ integral role in the operation of socio-economic life, (3) elusiveness of public transport in the epidemiological data, and (4) a focus on “unruly” passenger conduct. This analysis of the selective treatment of viral risks is tied to a critical engagement with theoretical distinctions between “essential” and “existential” mobilities developed in prior anthropological scholarship on the pandemic. Exploring the discursive framing of pandemic mobility practices on one of the world’s most extensive urban railway networks, the article thus contributes to the anthropological study of mobilities and transport in Japan and beyond.

Interface Dependent Coexistence of Two‐Dimensional Electron and Hole Gases in Mn‐doped InAs/GaSb

AbstractThe interface of common III‐V semiconductors InAs and GaSb can be utilized to realize a two‐dimensional (2D) topological insulator state. The 2D electronic gas at this interface can yield Hall quantization from coexisting electrons and holes. This anomaly is a determining factor in the fundamental origin of the topological state in InAs/GaSb. Here, the coexistence of electrons and holes in InAs/GaSb is tied to the chemical sharpness of the interface. Magnetotransport, in samples of Mn‐doped InAs/GaSb cleaved from wafers grown at a spatially inhomogeneous substrate temperature, is studied. It is reported that the observation of quantum oscillations and a quantized Hall effect whose behavior, exhibiting coexisting electrons and holes, is tuned by this spatial nonuniformity. Through transmission electron microscopy measurements, it is additionally found that samples that host this co‐existence exhibit a chemical intermixing between group III and group V atoms that extends over a larger thickness about the interface. The issue of intermixing at the interface is systematically overlooked in electronic transport studies of topological InAs/GaSb. These findings address this gap in knowledge and shed important light on the origin of the anomalous behavior of quantum oscillations seen in this 2D topological insulator.