Particle Diffusion Model Research Articles

Dominant Role of Eurasian Evaporation on the Moisture Sources of the Interannual Variations in Central Asian Summer Precipitation

Abstract The precipitation changes in arid and semiarid central Asia have great impacts on the local fragile ecosystem. The summer precipitation in central Asia shows obvious interannual variations, but the corresponding crucial moisture transporting processes remain unclear. Therefore, this study employs the Lagrangian flexible particle (FLEXPART) diffusion model to achieve this goal. Results show that the moisture of climatological summer precipitation in central Asia is mainly from the local regions, the surrounding western and northern Eurasian regions. The contribution of local evaporation from western central Asia is about 2 times that from eastern central Asia. At the interannual time scale, the moisture variations are mainly influenced by the local regions and western Eurasia, while the local evaporation is mainly from western central Asia. Totally, the Eurasian evaporation plays a dominant role in the interannual variations of central Asian summer precipitation by contributing more than 90% of the total moisture. The moisture transports associated with central Asian summer precipitation interannual variations are impacted by the anomalous cyclones over the western and northeastern parts of central Asia during the wet years, which enhance the moisture convergence and hence increase the summer precipitation in central Asia. The anomalous cyclone over the western part of central Asia is correlated with the changes in the intensity of Eurasian summer subtropical westerly jet (ESSWJ), while the anomalous cyclone over the northeastern part of central Asia is correlated with both ESSWJ and the British–Baikal Corridor pattern teleconnection in association with the polar front jet.

Mechanism Study on the Immobilization of Cu2+/Pb2+ in Aqueous Phase by Mineral Co-Milling-Modified Biochar.

A large number of studies have shown that the modification of biochar can greatly improve its adsorption capacity. This study adopts a one-step ball milling technology without solvent medium, using sawdust biochar (600 °C) and attapulgite/diatomaceous earth to prepare MABC10%/MDBC10% (mass ratio: 10% attapulgite/diatomite +90% biochar coabrasive). Characterization experiments show that attapulgite/diatomite was successfully loaded on biochar and has more C/O functional groups and wider adsorption pore sizes. Adsorption kinetics and isotherm experiments show that the adsorption process of MABC10% and MDBC10% on Cu2+/Pb2+ was mainly multilayer chemical adsorption. The adsorption capacities of MABC10% and MDBC10% for Cu2+ were 40.85 and 65.20 mg·L-1, respectively. The adsorption amounts of Pb2+ were 82.63 and 71.32 mg·L-1, respectively. The particle diffusion model shows that the adsorption process was controlled by both the surface adsorption rate limitation and boundary layer diffusion. The higher acidity in the solution will cause part of the negative charges on the surface of attapulgite/diatomite to be neutralized, thereby hindering its adsorption of Cu2+/Pb2+. The presence of coexisting ions did not significantly affect the adsorption performance. Mechanistic studies have shown that pore diffusion, active sites provided by C/O functional groups, electrostatic interactions, and cation exchange are the main mechanisms of MABC10% adsorption of Cu2+/Pb2+. In summary, MABC10% has a significant adsorption synergistic effect compared to MBC. It was an economical and effective adsorbent, and the higher the pH value of the wastewater, the more significant the adsorption effect.

Urea-modified hazelnut shell biochar (N-HSB) for efficient Cr(VI) removal: Performance and mechanism insights

Composite with a high specific surface area of 224.62 m2 g−1 was prepared by adding urea as a nitrogen source to hazelnut shell biochar (HSB). Nitrogen doping significantly enhanced the ability of biochar for Cr(VI) elimination, achieving twice the removal efficiency of unmodified biochar. The impacts of varying the pH and initial concentrations on Cr(VI) removal by urea-modified biochar (N-HSB) were investigated. The Cr(VI) removal by N-HSB was better described by intra particle diffusion model and pseudo-second order kinetic model under optimal conditions. Furthermore, XPS, FTIR, SEM, and BET analyses were used to verify the pivotal roles of oxygen- and nitrogen-containing functional groups. Electrostatic attraction, redox reaction, and complexation constituted the principal mechanisms facilitating Cr(VI) elimination by N-HSB. This study demonstrated that the modification of biochar with urea as a nitrogen source represented a promising strategy for enhancing the removal capacity of biochar for Cr(VI) in aqueous environments.

Synergistic adsorption of methylene blue using ternary composite of phosphoric acid geopolymer, calcium alginate, and sodium lauryl sulfate.

The removal of dyes from the aquatic ecosystem is necessary being a major threat to life. For enhanced remediation of methylene blue (MB) dye, a new ternary biopolymer-geopolymer-surfactant composite adsorbent is synthesized by combining phosphoric acid geopolymer (PAGP), calcium alginate (Alg), and sodium lauryl sulfate (SLS). During the synthesis of the composites, PAGP and SLS were mixed with the alginate matrix, producing porous hybrid beads. The PAGP-SLS-alginate (PSA) beads prepared were characterized using different analytical tools, i.e., scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FTIR), X-ray diffractometry (XRD), surface area and porosimetery (SAP), and thermogravimetric analysis (TGA). To ascertain the ideal conditions for the adsorption process, a batch reactor procedure was used to investigate the effects of several parameters on MB adsorption, including pH (2, 4, 6, 8, 10), PSA adsorbent dosage (0.06-0.12 g), MB concentration (50-500 mg/L), contact time (15 to 300 min), and temperature (25, 35, and 45 °C). The SEM investigation indicated that ~ 1860 μm-sized PSA beads with 6-8 μm voids are generated. Based on XRD, FTIR, and SAP examinations, the material is amorphous, having numerous functional groups and an average pore size of 6.42 nm. Variation of pH has a little effect on the adsorption process, and the pH of 7.44 was found to be the pHpzc of the PSA beads. According to the findings of the batch study, equilibrium adsorption was obtained in 270-300 min, showing that the adsorption process was moderately slow-moving and effective. The dye adsorption linearly increased with initial dye concentration over concentration range of 50-500 mg/L and reciprocally decreased with rise in temperature. 0.06 g adsorbent dose, 25 °C, pH10, and 270 min were found to be the better conditions for adsorption experiments. Langmuir isotherm fitted well compared to Freundlich, Temkin, and Dubinin-Radushkevich (DR) isotherm models on the experimental data, and the maximum adsorption capacity(qmax) calculated was 1666.6 mg. g-1. Pseudo-second-order (PSO) kinetics model and multi steps (two) intra particle diffusion (IPD) model fitted well on the adsorption kinetics data. The system's entropy, Gibbs free energy, and change in enthalpy were measured and found to be -109.171 J. mol-1. K-1, - 8.198 to - 6.014 kJ. mol-1, and - 40.747 kJ. mol-1. Thermodynamics study revealed that adsorption process is exothermic, energetically favorable and resulting in the decrease in randomness. Chemisorption is found to be the dominant mechanism as confirmed by pH effect, Langmuir isotherm, PSO kinetics, IPD model, and thermodynamics parameters. PSA beads were successfully regenerated using ethanol in a course of 120 min and re-used for five times. To sum up, the PSA adsorbent's impressive adsorption capability of 1666.66 mg/g highlights its potential as a successful solution for methylene blue removal. The results of this study add to the expanding corpus of information on sophisticated adsorption materials and demonstrate PSA's potential for real-world uses in wastewater treatment and environmental clean-up.

Green-synthesized, biochar-supported nZVI from mango kernel residue for aqueous hexavalent chromium removal: Performance, mechanism and regeneration

A biochar-supported green nZVI (G-nZVI@MKB) composite was synthesized using mango kernel waste with “dual identity” as reductant and biomass of biochar. The G-nZVI@MKB with a Fe/C mass ratio of 2.0 (G-nZVI@MKB2) was determined as the most favorable composite for hexavalent chromium (Cr(VI)) removal. Distinct influencing parameters were discussed, and 99.0% of Cr(VI) removal occurred within 360 min under these optimized parameters. Pseudo-second order kinetic model and intra particle diffusion model well depicted Cr(VI) removal process. The XRD, FTIR, SEM and XPS analyses verified the key roles of G-nZVI and functional groups, as well as the primary removal mechanisms involving electrostatic attraction, reduction, and complexation. G-nZVI@MKB2 exhibited a good stability and reusability with only a 16.4% decline in Cr(VI) removal after five cycles. This study offered evidence that mango kernel could be recycled as a beneficial resource to synthesize green nZVI-loaded biochar composite for efficient Cr(VI) elimination from water.

Mechanism insight of sorption of Er(III) and Nd(III) ions onto Aluminium barium tungstate synthesized via streamlined sol–gel technique: Time-transient study

Aluminium barium tungstate powder (ABT) was chemically synthesized via streamlined sol–gel technique and exploited as a sorbent material for sorption of erbium and neodymium ions from aqueous solutions under simulated conditions using batch technique. The pH influence, time and temperature factors have been studied. The sorption of neodymium ions was found to be marginally higher than that of erbium ions and the apparent sorption capacity has a progressive influence with temperature. Thermodynamic parameters such as Gibbs free energy change (ΔG◦), enthalpy change (ΔH◦) and entropy change (ΔS◦) were calculated. The negative ΔG◦ values declines with an increase in temperature value, demonstrating that the sorption reaction for both studied ions was spontaneous and more promising at greater temperature. The positive ΔH◦ values affirm that the nature of the sorption processes is endothermic. The comparison of different time transient models applied to the sorption data was assessed for the pseudo first-order (PFO), the pseudo second-order, (PSO) and homogeneous particle diffusion (HPD) models. The results revealed that both PSO and HPD models were found to best correlate the experimental sorption rate data and a monolayer model was adopted as the best suitable model to explore the sorption mechanism for both studied ions. The attained particle diffusion coefficients and rate constant values were acquired from the graphical illustration of the anticipated models. Activation energy change (Ea) and activation entropy change (ΔS±) were also calculated from the linearized Arrhenius model and indicated that the binding process between the sorbent and the studied ions occurred through chemisorption and the sorption of both ions onto synthetic sorbent took place through associative mechanism.

Congo Red Removal from Polluted Water using NaOH Treated Fallen Leaves of Ficus racemosa

Naoh treated biosorbent Ficus Racemosa Leaf Powder (NaFRLP) was prepared from the fallen leaves of the plant. FT-IR, SEM and BET analysis were done to characterize the biosorbent. The biosorbent was found to be mesoporous with an average pore size 18 nm. Batch adsorption equilibrium studies were conducted for the adsorption of congo red on NaFRLP as a function of adsorbent dosage, agitation speed, dye concentration, temperature and contact time. Batch adsorption studies revealed that with an increase in the time of adsorption, the percentage removal of congo red increases and with an increase in the concentration of dye solution, congo red removal decreases. Initial dye concentration of 100 mgL-1, agitation speed 200 rpm and adsorbent dosage 1gL-1 were the optimum conditions for the effective removal of congo red. The adsorption data well agreed with the Langmuir isotherm as indicated by the higher correlation coefficient (R2=0.962) value. Thermodynamic analysis of the batch adsorption studies indicated that all the processes studied were spontaneous with the congo red adsorption on NaFRLP being endothermic. Intra particle diffusion model was also tested. NaFRLP was found to be an effective adsorbent for the removal of congo red from the polluted water.

Isotherm, kinetic and thermodynamic modelling of liquid phase adsorption of the heavy metal ions Zn(II), Pb(II) and Cr(VI) onto MgFe2O4 nanoparticles

MgFe2O4 nanoparticles are synthesized by sol-gel method and the adsorption characteristics of these nanoparticles on the removal of Zn(II), Pb(II) and Cr(VI) ions from their aqueous solutions are analysed. The samples are characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman Spectroscopy. Batch adsorption studies are carried out to investigate the effect of adsorption parameters such as adsorbent dose, pH, temperature, contact time and initial ion concentration. The feasibility and spontaneity of the adsorption process is checked by thermodynamic analysis. Four adsorption kinetics models viz. Pseudo first-order, Pseudo second-order, Intra particle diffusion and Elovich model and four adsorption isotherm models viz Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Temkin isotherm models are studied and employed to model the adsorption equilibrium data. All the kinetics and isotherm parameters including rate constants and maximum adsorption capacity are determined and compared. The adsorption process best fits the Pseudo-second-order kinetics model and Langmuir adsorption isotherm model. Of the three heavy metal ions studied, the adsorption of Zn(II) ions by MgFe2O4 nanoparticles exhibits the best performance, followed by Pb(II) and Cr(VI) ions respectively. By regenerability study, the extent of reuse of the MgFe2O4 nanoparticles is checked.

Synthesis of Carboxymethylcellulose–Acrylamide–Montmorillonite Composite Hydrogels for Wastewater Purification

The three-dimensional network and ample pore structure of novel hydrogel materials enable outstanding adsorption performance for pollutants such as methylene blue (MB) and Cr6+ ions in wastewater. In order to develop an environmentally friendly hydrogel with high adsorption performance and low cost, a type of carboxymethyl cellulose (CMC) composite hydrogel was synthesised with montmorillonite (MMT) via chain radical polymerization, which gives it great potential for application in the field of wastewater purification. A series of hydrogel samples were characterised through SEM, FTIR and nitrogen porosimetry analysis, indicating the successful intercalation of MMT nanosheets into the hydrogel crosslinking network. The mass ratio of CMC to MMT, the amounts of adsorbent, the initial concentration of wastes, pH, and the adsorption temperature were investigated and optimised for hydrogel adsorption performance. When the initial concentration of MB is 60 mg/L, pH is 7, the dosage of MB is 0.5 g/L, and the adsorption temperature is 30 °C, the hydrogel sample the highest adsorption capability for MB removal, with an adsorption amount of 112.9 mg/g. When the initial concentration of Cr6+ is 10 mg/L with a pH of 7, the highest adsorption capacity of the hydrogel for Cr6+ removal is 1.35 mg/g. The fitting results of the isothermal models, the kinetic models, internal particle diffusion models and the thermodynamics of the experimental data of the adsorbate adsorption process show that the adsorption of MB by hydrogel is a spontaneous segmented process of multi-layer physical and chemical adsorption. Additionally, the adsorption of Cr6+ ions by hydrogel is a spontaneous segmented process of multi-layer physical adsorption.

Nondimensional analysis and application of gas desorption and diffusion driven by density gradient in coal particles.

An in-depth understanding of gas diffusion characteristics in coal is of great value to coalbed methane (CBM) production planning and coal mine safety management. However, the mechanism and model of gas diffusion is still unclear, and some methods for determining diffusion coefficients are not accurate enough. Accordingly, a free gas density gradient (FGDG)-driven coal particle gas desorption and diffusion model was established in this work, and numerical solutions were performed via finite difference method (FDM) and dimensionless method. The variation rules of dimensionless gas pressure, gas content, desorption capacity, and desorption rate were obtained. Finally, the application of the dimensionless method in diffusion modeling and diffusion coefficient inversion was discussed. The results show that the dimensionless method can simplify mathematical equation processing and analyze the common phenomena of desorption and diffusion under different parameters. The gas desorption diffusion in coal particles is from the surface to the inside, and there is obvious desorption hysteresis effect. The larger the dimensionless radius or dimensionless time, the smaller the dimensionless gas pressure, gas content, and dimensionless desorption rate. The dimensionless cumulative gas desorption amount increased rapidly first and then tended to flat with dimensionless time. The simulated curve can be easily converted into the variation curves of several different measured parameters, and the diffusion coefficient can be calculated accurately. The prediction curve of the FGDG diffusion model is in good agreement with the experimentally measured data, which verifies its reasonableness. The research content aims to provide some ideas for modeling gas desorption and diffusion behavior.

Adsorption of metal ions by oceanic manganese nodule and deep-sea sediment: Behaviour, mechanism and evaluation

Deep-sea mining disturbs the sediment on the seabed to form plumose flows, carrying metal ions that are transmitted through the food chain, posing a serious threat to marine ecosystems and human health. In this study, two types of marine raw materials were screened: Oceanic Manganese Nodules (OMN) and Deep-sea Sediments (DSS), and prepared the spherical regenerative adsorption materials OMN@SA, DSS@SA and OMN&DSS@SA using sodium alginate (SA) by sol-gel method. Preliminary investigations on the adsorption effect of metal ions were carried out. OMN@SA exhibited the best adsorption capacity, with the adsorption quantities for Cu2+, Co2+ and Ni2+ reaching 31.12, 21.11 and 16.66 mg/g, respectively. The adsorption behaviour is consistent with the Langmuir, pseudo-second-order kinetics and particle diffusion model, indicating that the adsorption process is mainly spontaneous, monolayer chemical adsorption, and the adsorption rate is mainly controlled by internal particle diffusion. SEM-EDS, XRD, FTIR and XPS analyses suggest that the adsorption mechanism includes surface physical adsorption, ion exchange, functional group complexation, electrostatic attraction and precipitation. The fixed bed column experiment shows that OMN@SA can effectively remove metal ions Cu2+, demonstrating excellent stability, safety and good regenerability. This study paves a new direction for the design of efficient and sustainable materials for heavy metal adsorption. More importantly, as marine primordial materials, OMN and DSS have strong technical and economic feasibility for future use in in-situ fixation of metal ions in seafloor sediments and restoration of the original seabed environment.

Sorption of tartrazine dye from aqueous solution using activated carbon prepared from Cocos nucifera husk

Sorption of Tartrazine dye from aqueous solution using activated carbon prepared from Cocos nucifera (coconut) husk was investigated in this work. The coconut shell was first carbonized at 700°C in a muffle furnace and activated with NaOH for one hour. The activated carbon (AC) was applied to remove tartrazine from aqueous solutions over a concentration range of 50-250 mg/L respectively. Adsorbent features were determined using X-ray fluorescence (XRF), Fourier transformed infrared spectroscopy (FTIR), Scanning electron micrograph (SEM) techniques. Based on this investigation, adsorption of Tartrazine dye is strongly affected by initial solution pH, initial solution concentrations, dosage, and time of contact which favours the removal. Except for temperature which was found to decrease with increase temperature for AC, while adsorption capacity of Tartrazine was found to decrease with increase in adsorbent dosage for AC. The optimum pH for adsorption Tartrazine removal was found to be 3. The experimental data of Tartrazine was found to fit the linearized Langmuir isotherm better than the Freundlich isotherm and D-R model indicating a monolayer adsorption. On effect of initial solution concentration, adsorption capacity of Tartrazine was found to increase with increase in concentration for AC. Kinetic data fitted more into pseudo second order model than first order and intra particle diffusion model, suggesting that chemisorption dominate the rate limiting step. The calculated thermodynamic parameters – Gibbs free energy, enthalpy change and entropy change indicated that adsorption of Tartrazine was endothermic and not spontaneous meaning the chemisorption dominates physisorption.

Oxalic acid-modified activated carbons under hydrothermal condition for the adsorption of the 2-butanone.

Growing volatile organic compound (VOC) emission will cause air pollution and further threaten human health. Activated carbon is widely applied to treatment of VOCs in virtue of lower cost and excellent adsorption ability. In this work, the adsorption capacity of polarity VOCs on activated carbon is improved by oxalic acid (H2C2O4) hydrothermal modification. After 2M H2C2O4 modification, the adsorption capacity of 2-butanone rose from 312.60 to 345.98mg/g, and the time reaching saturation adsorption became shorter. BET results showed that both the specific surface area and total pore volume of 2M H2C2O4-modified activated carbon increased by 3.32% and 3.9%, respectively. Both FTIR and XPS characterization confirmed variation of the surface oxygen-containing functional groups (SOFGs), while quantitative analysis via Boehm titration showed the significant increase of total acidity (61.36%), particularly the carboxyl content increased by 96.28%. The results indicated modification process can not only change the pore structure but also the SOFGs of activated carbons. The dynamic adsorption curves conform to the Bangham kinetics model, indicating that the adsorption of 2-butanone on both activated carbon is controlled by the diffusion in the pore channel. The adsorption data was also modeled by the internal particle diffusion model, and the internal diffusion adsorption stage is the rate-controlling step. The stability before and after adsorption and the cycling performance were studied.

Multiple human activities in coastal benthic ecosystems: Introducing a metric of cumulative exposure

Co-occurring anthropogenic activities influence coastal ecosystems around the world. Notions of ecological exposure are promising indicators to better understand environmental status and enhance ecosystem protection. This study characterized anthropogenic exposure in the context of multiple human activities on coastal benthic ecosystems at a scale of <100 km. Using a particle diffusion model and fishing event data, we developed an exposure index for seven human activities (aquaculture, artificial structures, dredging, fisheries, runoff, sewers and shipping) in a Canadian industrial harbour area. A generally low cumulative exposure was obtained, with the highest values observed directly in front of the city and industrial areas. Derived exposure indices explained a portion of the benthic community structure (R2 = 0.22), suggesting an ecological link between the exposure of species and their vulnerability to human activities. Such tools are relevant in data-poor environments where proxies are required to assess the state of an ecosystem, facilitating the application of ecosystem-based management.

Adsorption and desorption characteristics of flavonoids extracted from hawthorn (Crataegus pinnatifida) on macroporous resin

Abstract In this work, the adsorption and desorption capacities of six resins (HP-20, AB-8, X-5, DM130, HPD100, D4006) for the purification of hawthorn flavonoids were investigated. HP-20 resin was screened out that has the best adsorption capacity, with an adsorption capacity of 24.2 mg/g. Langmuir and Freundlich isotherm model, pseudo first-order and pseudo second-order kinetics and intra particle diffusion model were used to fit the adsorption process. The results indicated that the adsorption process of hawthorn flavonoids by HP-20 was in accordance with the Langmuir isotherm model and pseudo second-order model, and the optimal adsorption temperature was 298 K. The adsorption process was spontaneously exothermic as indicated by thermodynamic parameters. After purification, hawthorn flavonoids showed high acetylcholinesterase inhibitory activities.

Analysis of Performance Degradation in Lithium-Ion Batteries Based on a Lumped Particle Diffusion Model.

The analysis of performance degradation in lithium-ion batteries plays a crucial role in achieving accurate and efficient fault diagnosis as well as safety management. This paper proposes a method for studying the degradation pattern of lithium-ion batteries and establishing the structure-activity relationship between internal and external parameters by employing a lumped particle diffusion model. To simulate real-world operating conditions, a cycle life test was conducted with the constant current-constant voltage (CC-CV) charge mode and the discharge mode under New European Driving Cycle (NEDC) working condition. The test aimed to analyze the variations in the external macroscopic characteristic parameters of the battery. Building upon this analysis, a lumped particle diffusion model was constructed, and the model parameters were identified using the Levenberg-Marquardt (L-M) algorithm. Subsequently, the ohmic, activation, and concentration losses of the battery under different aging conditions were determined, revealing the internal state evolution during the degradation process of lithium-ion batteries. The findings indicate that the lumped particle diffusion model provides a comprehensive explanation of the internal mechanisms contributing to the performance degradation of lithium-ion batteries. Moreover, the proposed method offers a novel perspective for the real-time quantitative analysis of lithium-ion battery performance degradation.

Adsorption kinetics, isotherms and thermodynamics of aromatic amino acids in feather hydrolysate onto modified activated carbon

AbstractThe main objective of this study was to produce low cost activated carbons for the adsorption of aromatic amino acids (AA) from feather hydrolysate. By optimizing the static adsorption conditions (time, pH and concentration) of amino acids, the adsorption amounts of tyrosine and phenylalanine reached 15.2 and 20.1 mg/g, respectively, under optimal conditions. Furthermore, it exhibits excellent reusability as it maintains a removal efficiency of 82.0% and 82.8% for tyrosine and phenylalanine after being reused 4 times. The effects of NaOH modified activated carbon (NA‐AC) on the adsorption capacity of AA in feather hydrolysate at different temperatures (298.15, 308.15, 318.15 K) were investigated, and the static adsorption kinetics curves were plotted. The adsorption isotherm (Langmuir, Freundlich model), kinetics (pseudo‐first‐order‐mode, pseudo‐second‐order‐mode, particle diffusion model) and thermodynamics were studied. The results shown that the adsorption process of AA onto NA‐AC accorded with the pseudo‐second‐order‐mode. The adsorption rate was mainly controlled by the liquid film diffusion and the particle diffusion. The adsorption isotherm accorded with the Langmuir adsorption isothermal model. Adsorption was an endothermic process, and increasing temperature was conducive to adsorption. Gibbs energy ΔG indicated that the adsorption process was spontaneous, and enthalpy △H indicated that the adsorption process was mainly physical adsorption. The proposed adsorption mechanisms provide a theoretical basis for the optimization of AA separation and purification process in feather hydrolysate by NA‐AC, which may further improve the separation and purification efficiency of other amino acids in feather hydrolysate.

Single-Particle Tracking in Poly(Ethylene Glycol) Diacrylate: Probe Size Effect on the Diffusion Behaviors of Nanoparticles in Unentangled Polymer Solutions.

A thorough understanding of the relevant factors governing the transport of nanoparticles in poly(ethylene glycol) diacrylate (PEGDA) is crucial for many applications utilizing this polymer. Here, single-particle tracking (SPT) was used to systematically investigate the role of the probe size (3-200 nm) on the diffusion behaviors of individual fluorescent nanoparticles in semidilute and unentangled PEGDA solutions. The quantitative assessment of the SPT data via the recorded single-particle trajectories and diffusion coefficients (D) not only showed that the observed probe dynamics in PEGDA were temporally and spatially heterogeneous, but more importantly that the measured D were observed to be significantly reduced (vs in solvent) and strongly size-dependent. We explained these results based on a modified multiscale model for particle diffusion, built upon well-established hydrodynamics and obstruction theories. We furthermore showed that the presence of steric interactions and probe confinement effects in highly crowded, unentangled PEGDA microstructures can lead to deviations in the single-particle displacements from the expected Gaussian behavior, as revealed by the van Hove displacement distributions and the associated non-Gaussian parameters. This study has demonstrated the power of SPT methods in offering an advanced characterization of the transport characteristics in complex polymer structures, overcoming challenges posed by traditional characterization techniques.

Toroidal modeling of plasma flow damping and density pump-out by RMP during ELM mitigation in HL-2A

Reduction of both the plasma density and toroidal flow speed, due to application of the predominantly n = 1 (n is the toroidal mode number) resonant magnetic perturbation (RMP) for controlling the edge localized mode in the HL-2A tokamak, is numerically investigated utilizing the quasi-linear initial-value code MARS-Q (Liu et al 2013 Phys. Plasmas 20 042503). Simulation results reveal that the neoclassical toroidal viscosity (NTV) due to three dimensional fields plays the key role in modifying the plasma momentum and particle transport in the HL-2A discharge. By comparing the modeling results with the measured density pump-out in the experiment, the electron NTV particle flux model, in combination with the free-boundary condition for the axisymmetric change of the density at the plasma edge, is found to yield the best agreement in terms of both the pump-out level and the overall time scale. Further sensitivity studies show that the simulated density pump-out level is reasonably robust against variations in the model assumptions, including the particle diffusion model and the non-ambipolar versus ambipolar NTV particle flux. The latter however affects the time scale for reaching the steady state solution. Finally, it is found that the plasma edge-peeling response, the NTV torque, as well as the plasma momentum and particle transport, all are sensitive to the toroidal phase difference between the upper and lower rows of the RMP coil currents in HL-2A, with the 30∘ coil phasing producing the minimal side effects on the plasma.

Simulation of Oil Spills in Inland Rivers

The shipping volume in inland waterways has been rapidly increasing in recent years. However, it is still challenging to trace oil spills caused by maritime accidents. In this study, the oil spill dispersion trajectory in inland rivers was obtained by simulating the trajectory of oil particles under different waterway conditions based on a simulated flow field. Firstly, the flow field was simulated using a volume of fluid (VOF) model and the solution of an open-channel equation. Then, an oil particle diffusion and drift model was established using Python to simulate the diffusion of the oil. Finally, eight oil spill simulation scenarios were conducted with different channel shapes and cross-sections. The results showed that oil spills spread more extensively in a curved channel with a trapezoidal cross-section compared to other channel shapes and cross-sections. The findings of this research could be used to guide inland river environmental protection and oil spill trajectory tracking.