Calculated Diffusion Coefficients Research Articles

Electrochemical investigations of decorated graphite felt electrodes with Nafion/TiO2 nanoparticles for vanadium redox flow battery: Improving electro-catalytic characteristics

The present study aimed to investigate the effect of Nafion/TiO2 nanoparticles as an electrocatalyst on the electrochemical behavior of graphite felt (GF) electrodes in a vanadium redox flow battery. Various electrochemical tests, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV), were conducted to assess the performance of these electrodes at different concentrations of nanoparticles (2-4 g L-1). Additionally, X-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy were employed to analyze the chemical composition, bonding, and morphology of the decorated electrodes, respectively. The CV results revealed several effects of TiO2 nanoparticles on the GF electrode, such as increased peak intensity and shifted peak sites. As the concentration of nanoparticles increased, the peak intensity rose by up to 44%. Moreover, the potentials of the decorated electrodes shifted towards the favorable side compared to the GF electrode, with changes ranging from 18 to 84%. Overall, the optimal concentration of TiO2 nanoparticles (3 g L-1) exhibited excellent electrode performance, characterized by the highest calculated diffusion coefficient, greater reversibility, enhanced electron transfer kinetics, improved stability, lower over-potential, and the lowest activation energy for redox reactions. EIS results demonstrated a significant decrease in polarization resistance (67.2-70.8%) for the decorated electrodes. Furthermore, LSV measurements indicated that the utilization of nano-electrocatalysts effectively inhibited hydrogen evolution at negative potentials.

Diffusion coefficient calculation using the Boltzmann-Matano methodwith a graphical approach for understanding annealed Copper-Zinc couples

This article delves into transport phenomena, essential in science and engineering research, emphasizing Matano's Interface as a key element in diffusion studies. The primary goal is to elucidate a graphical procedure for approaching Matano's Interface within diffusion couples, aiming to calculate diffusion coefficients across various compositions. The comprehensive exploration of the Boltzmann-Matano method, particularly focusing on concentration-dependent diffusion coefficients, is accentuated. Acknowledging the historical context of Ludwig Boltzmann and Matano, the article highlights the practical application of their methodologies, notably in an annealed copper-zinc couple. The graphical determination of the Boltzmann-Matano interface proves crucial in understanding diffusion dynamics. The article successfully integrates theoretical understanding with practical insights, contributing to the broader field of transport phenomena research in science and engineering.

Synergistic effect of ceramic filler in polymer salt complex for improved ion dissociation and migration mechanism

Abstract Use of Ceramic filler is one of the most common approaches to improve the conductivity and stability properties of a solid polymer electrolyte (SPE) cum separator. Among them, active fillers like Garnet have been extensively used to enhance the stability and conductivity of SPE. However, SPE suffers from limited ion migration at room temperature acting as a bottleneck for their application in all solid-state batteries. An extensive study on these fillers' role in ion dissociation and migration can be a stepping stone for advanced SPE. In the present work, an FTIR analysis has primarily been used to identify and evaluate cation coordinate site-cation, and ion pair interactions in a Li6.5La3Zr1.75Te0.25O12 loaded polyethylene oxide-LiCF3SO3 matrix with varying ceramic concentrations. Further, the Trukhan model has been used to calculate diffusion coefficient, mobility, and charge carrier density to interpret relaxation parameters, conductivity, and FTIR results in the SPE samples. Finally, an ion migration model has been proposed based on the results obtained in experimental studies.

A molecular insight into the aggregation of cisplatin in aqueous solutions

Cisplatin (CPT), recognized as a widely used metallodrug, is a prevalent therapeutic agent for the treatment of various cancers. Given the diverse biological conditions in humans, as well as the aquatic environment within cells and the toxicity associated with CPT in cancer treatment, it is imperative to assess and optimize the solvation of CPT under various conditions. In this study, the influence of CPT on the structure of water is explored. In this regard, a systematic molecular dynamics (MD) simulation is employed to investigate the structure and dynamics of CPT in aqueous media, encompassing a range of concentrations from much diluted (0.05 M) to concentrated (5 M). The disruption of water structure by CPT molecules is determined using radial distribution function (RDF), mean-squared displacement (MSD), hydrogen bond number, and combined radial/angular distribution function (CDF). Notably, the CPT aggregates exhibit an impact on the average number of water-water hydrogen bonds. Through calculations of apparent and partial molal volumes of CPT at various concentrations, we observed a sudden and dramatic change in the solution structures up to the critical aggregation concentration of CPT (0.5 molal), a finding corroborated by the calculations of diffusion coefficients. In summary, the self-aggregation of CPT molecules commences at 0.5 molal, leading to increased apparent and partial molal volumes with rising concentration. However, beyond 0.5 molal, the change in volumes becomes less significant, suggesting that while the number of CPT aggregates continues to increase, their size remains relatively constant above this concentration.

Cosmic-Ray Feedback on Bistable Interstellar Medium Turbulence

While cosmic rays (E ≳ 1 GeV) are well coupled to a galaxy’s interstellar medium (ISM) at scales of L > 100 pc, adjusting stratification and driving outflows, their impact on small scales is less clear. Based on calculations of the cosmic-ray diffusion coefficient from observations of the grammage in the Milky Way, cosmic rays have little time to dynamically impact the ISM on those small scales. Using numerical simulations, we explore how more complex cosmic-ray transport could allow cosmic rays to couple to the ISM on small scales. We create a two-zone model of cosmic-ray transport, with the cosmic-ray diffusion coefficient set at the estimated Milky Way value in cold gas but smaller in warm gas. We compare this model to simulations with a constant diffusion coefficient. Quicker diffusion through cold gas allows more cold gas to form compared to a simulation with a constant, small diffusion coefficient. However, slower diffusion in warm gas allows cosmic rays to take energy from the turbulent cascade anisotropically. This cosmic-ray energization comes at the expense of turbulent energy which would otherwise be lost during radiative cooling. Finally, we show our two-zone model is capable of matching observational estimates of the grammage for some transport paths through the simulation.

Experimental investigation of the impact of additives in low clinker cementitious materials on multi-ion transference numbers and diffusion coefficients

In this paper, multi-ion transference numbers were determined throughout the chloride migration testing of low clinker cement-based materials. For this purpose, five cement pastes were studied: pure Portland paste (as a reference) and four other pastes, based on limestone filler, fly ash, slag or silica fume. The transference numbers were calculated from the concentration evolution in the three zones of the migration cell (catholyte, anolyte and sample), considering that: (i) ions moved in the catholyte and anolyte; (ii) ions leached from the sample; (iii) ions were generated from the electrode processes, and (iv) the pore solution of the sample evolved during the test. The chloride transference numbers of pastes with pure Portland cement, limestone filler, fly ash, slag or silica fume are almost zero at the beginning of the migration test but 0.23; 0.18; 0.06; 0.05 and 0.20 at the end of the test, respectively. The ion transference numbers obtained were used for the calculation of diffusion coefficients of chlorides, sodium and potassium using the Nernst-Einstein equation.

Improved efficiency of continuous conversion of alcohols to chlorides in flow microreactors with DESs/HCl via predictive fluid model

The efficient and safe synthesis of chlorides is attractive in pharmaceutical chemicals yet presents challenges. Herein, a novel route has been developed for the conversion of alcohols into the corresponding alkyl chlorides in continuous flow microreactor. Meanwhile, the system utilizes deep eutectic solvents (DESs) hydrochloride solutions (DESs/HCl) as both solvents and catalysts for this reaction. The results suggest that the premixed mode continuous flow microreactor using DESs/HCl can significantly improve the harsh reaction conditions in the synthesis reaction of chlorides. Furthermore, tuning the HCl concentration under 383 K and 30 min conditions significantly increased the yields of n-Butanol chloride and Benzyl chloride to 86 % and 98 %, respectively. This work shows the great application potential of the continuous flow microreactor combined with DESs/HCl to convert alcohols into corresponding alkyl chlorides or aryl chlorides. Besides, the fluid model and HCl absorption kinetics were established based on the calculated diffusion coefficients (DR), Damköhler number (Da), Bodenstein number (Bo), residence time (τ), and experimental results. The flow model of the mixture of DESs/HCl and alcohols in the microreactor was a plug flow, which is beneficial for improving the efficiency of this reaction.

Enhancement of ultrasonic-assisted and agitation-assisted flaxseed oil extractions: Kinetic modeling and optimization

The flaxseed oil extraction process has been investigated and enhanced by applying Ultrasonic-Assisted Extraction (UAE), and Mixer-Assisted Extraction (MAE) methods in this study. Response Surface Methodology (RSM) was also utilized to find the optimal values of the extraction parameters. The optimal conditions for UAE were determined to be 42.7 min extraction time, 0.283 mm particle size, and 2.48 W/mL power intensity, achieving the oil yield of 94.56 %. For MAE, the optimal conditions were 54.5 min extraction time, 0.274 mm particle size, 21.1 °C temperature, and 0.74 W/mL agitation intensity, resulting in the oil yield of 96.73 %. RSM showed high reliability with R2 values above 0.99 for both methods. Gas Chromatography Flame Ionization Detector (GC-FID) analysis revealed that UAE and MAE resulted in higher unsaturated fatty acids concentrations (85.8 % and 86 %, respectively) compared to CPE (78.2 %). Kinetic studies indicated that UAE and MAE are more efficient in extracting unsaturated fatty acids, with MAE showing the highest double bond content. The Kinetic models demonstrated that extraction kinetics were controlled primarily by solid-phase resistance, with the washing coefficients being significantly higher than the diffusion coefficients. The Perez model calculated diffusion coefficients of 8.03 × 10⁻12 m2/s for UAE and 1.41 × 10⁻11 m2/s for MAE, activation energies of 16.44 kJ/mol for UAE and 15.64 kJ/mol for MAE.

Adsorption and dynamics in cylindrical pore: Molecular dynamics and classical density functional theory study

In this work, we investigate the adsorption of single-component and binary neutral fluids in cylindrical pore using molecular dynamics simulations combined with classical density functional theory (cDFT). For the binary case, we also consider scenarios where one component exhibits a non-spherical structure. We investigated the density distribution curves of fluid components in the pore and found that the cDFT calculations without any adjustable parameter yielded results consistent with molecular dynamics simulations. This consistency becomes more pronounced as the temperature increases. At lower temperatures, the theoretical accuracy declines, but it still remains quantitatively reliable. We have developed a method for calculating diffusion coefficient in porous media involving exchange of particles between the exterior and interior of the pores, and applied the method to compute the diffusion coefficients for molecules from outside to inside the pore, as well as within the pore itself. Based on the calculated diffusion coefficients, we can draw several main conclusions: intrapore diffusion along the axial direction always decreases with increasing pore radius; increasing the surface force field strength enhances diffusion in narrow pores while reducing it in wider pores. Moreover, increasing the attraction strength between particles consistently leads to slower diffusion. These findings provide valuable insights into the factors affecting the diffusion process and can be used to optimize porous materials for various applications.

Hydrogen diffusion and hydrogen embrittlement in iron (steel)

This article examines the diffusion of hydrogen (H-diffusion) and the temperature dependences of the diffusion coefficient of hydrogen (DH) in the metal (M)-hydrogen system. The metal used was iron and low-alloy steel. Taking into account experimental data on hydrogen diffusion in the Fe-H and steel-H systems, the main diffusion parameters were calculated and compared. It is shown that the temperature dependences of the hydrogen diffusion coefficient in metal samples in a one-stage reaction under isothermal conditions are described by the Arrhenius equation. For some M-H systems, experimental data show a deviation of the diffusion coefficient from the ideal one calculated using the Arrhenius equation. This discrepancy can be eliminated using the statistical theory of absolute reaction rates. For the temperature range 25–1250 oС, the pre-exponential coefficient and activation energy of hydrogen diffusion in a body-centered cubic (bcc) lattice of iron (α–Fe) were calculated using the Arrhenius equation. These parameters make it possible to describe the dependence of the rate of hydrogen diffusion in a metal on temperature and to predict the behavior of hydrogen diffusion when changing the conditions of the kinetic process (concentration of substances, pressure, structure, composition, etc.). Tabular values of the calculated pre-exponential factor and activation energy of hydrogen diffusion in previously studied iron-based samples are presented. The temperature dependences of the hydrogen diffusion coefficient in a lattice of iron α–Fe can be divided into low-temperature and high-temperature regions. The calculated diffusion parameters of hydrogen in the metal lattice for the low-temperature 25– 800 oC and high-temperature 800–1250 oC regions differ markedly from each other. In addition, these calculated values are significantly influenced by the structure and composition of the metal. We also studied the diffusion of hydrogen in α-iron using ab initio density functional calculations. Molecular dynamics calculations using transition state theory were used. The calculated diffusion coefficient of hydrogen in α-Fe is consistent with previously obtained experimental data. Hydrogen embrittlement (HE) is considered using internal pressure, hydrogen enhanced localized plasticity (HELP) and hydrogen enhanced decohesion embrittlement (HEDE) theories.

Simulation and experimental study of gas-phase diffusion coefficient of selenium dioxide

Improving the removal effect of selenium in wet flue gas desulfurization system is a key way to reduce the emission of selenium pollutants from coal-fired power plants. In order to clarify the removal mechanism of selenium pollutants in the desulfurization tower, it is necessary to obtain accurate selenium gas-phase diffusion coefficient. In this paper, molecular dynamics simulations were used to carry out theoretical calculations of gas-phase diffusion coefficients of SeO2 (the main form of selenium in coal combustion flue gas). The gas-phase diffusion coefficients of SeO2 in the range of 393 K–433 K were measured by a self-developed heavy metal gas diffusion coefficient testing device to verify the accuracy of the molecular dynamics calculations. Furthermore, the calculated gas-phase diffusion coefficients of SeO2 under typical binary and ternary components were obtained by correcting on the basis of Fuller's formula. Finally, a single-droplet absorption model for SeO2 was constructed and experiments were carried out to compare the effect of the gas-phase diffusion coefficient on the accuracy of the model calculations. The error of the model calculations was reduced from 8.09 % to 1.96 % after the correction. In this study, the gas-phase diffusion coefficient of SeO2 in the low-temperature range of coal-fired flue gas was obtained. This study can provide basic data for the development of selenium migration mechanism and control technology.

Validation of quantitative magnetic resonance imaging techniques in head and neck healthy structures involved in the salivary and swallowing function: Accuracy and repeatability

Background and PurposeRadiation-induced damage to the organs at risk (OARs) in head-and-neck cancer (HNC) patient can result in long-term complications. Quantitative magnetic resonance imaging (qMRI) techniques such as diffusion-weighted imaging (DWI), DIXON for fat fraction (FF) estimation and T2 mapping could potentially provide a spatial assessment of such damage. The goal of this study is to validate these qMRI techniques in terms of accuracy in phantoms and repeatability in-vivo across a broad selection of healthy OARs in the HN region. Materials and MethodsScanning was performed at a 3 T diagnostic MRI scanner, including the calculation of apparent diffusion coefficient (ADC) from DWI, FF and T2 maps. Phantoms were scanned to estimate the qMRI techniques bias using Bland-Altman statistics. Twenty-six healthy subjects were scanned twice in a test–retest study to determine repeatability. Repeatability coefficients (RC) were calculated for the parotid, submandibular, sublingual and tubarial salivary glands, oral cavity, pharyngeal constrictor muscle and brainstem. Additionally, a linear mixed-effect model analysis was used to evaluate the effect of subject-specific characteristics on the qMRI values. ResultsBias was 0.009x10-3 mm2/s for ADC, -0.7 % for FF and -7.9 ms for T2. RCs ranged 0.11–0.25x10-3 mm2/s for ADC, 1.2–6.3 % for FF and 2.5–6.3 ms for T2. A significant positive linear relationship between age and the FF and T2 for some of the OARs was found. ConclusionThese qMRI techniques are feasible, accurate and repeatable, which is promising for treatment response monitoring and/or differentiating between healthy and unhealthy tissues due to radiation-induced damage in HNC patients.

Diffusion of curcumin in PLGA-based carriers for drug delivery: a molecular dynamics study

Context:The rapid growth and diversification of drug delivery systems have been significantly supported by advancements in micro- and nano-technologies, alongside the adoption of biodegradable polymeric materials like poly(lactic-co-glycolic acid) (PLGA) as microcarriers. These developments aim to reduce toxicity and enhance target specificity in drug delivery. The use of in silico methods, particularly molecular dynamics (MD) simulations, has emerged as a pivotal tool for predicting the dynamics of species within these systems. This approach aids in investigating drug delivery mechanisms, thereby reducing the costs associated with design and prototyping. In this study, we focus on elucidating the diffusion mechanisms in curcumin-loaded PLGA particles, which are critical for optimizing drug release and efficacy in therapeutic applications.Methods:We utilized MD to explore the diffusion behavior of curcumin in PLGA drug delivery systems. The simulations, executed with GROMACS, modeled curcumin molecules in a representative volume element of PLGA chains and water, referencing molecular structures from the Protein Data Bank and employing the CHARMM force field. We generated PLGA chains of varying lengths using the Polymer Modeler tool and arranged them in a bulk-like environment with Packmol. The simulation protocol included steps for energy minimization, T and p equilibration, and calculation of the isotropic diffusion coefficient from the mean square displacement. The Taguchi method was applied to assess the effects of hydration level, PLGA chain length, and density on diffusion.Results:Our results provide insight into the influence of PLGA chain length, hydration level, and polymer density on the diffusion coefficient of curcumin, offering a mechanistic understanding for the design of efficient drug delivery systems. The sensitivity analysis obtained through the Taguchi method identified hydration level and PLGA density as the most significant input parameters affecting curcumin diffusion, while the effect of PLGA chain length was negligible within the simulated range. We provided a regression equation capable to accurately fit MD results. The regression equation suggests that increases in hydration level and PLGA density result in a decrease in the diffusion coefficient.

Unmodified α-LiFe5O8 as potential anode material of lithium ion battery and the revelation of conversion mechanism

Spinel structured α-LiFe5O8 were prepared via ball milling combined with a straightforward solid-phase method, using Fe2O3 and Li2CO3 as the raw materials. The material maintained a stable capacity of 440 mAh g−1 after 200 cycles at 900 mA g−1 with Coulomb efficiency more than 95 % and also showed facile lithium ion diffusion dynamics. The calculated diffusion coefficient of α-LiFe5O8 ranged around 10−10-10−12 cm2 s−1. Diffusion controlled contribution was dominant over capacitive contribution in the sweeping range 0.1–1.5 mV s−1. A new intercalation-decomposition-conversion mechanism was proposed on the basis that there existed a small pit at the initial stage of the discharge plateau and a significantly low initial discharge plateau voltage was observed compared with the followed discharge cycles. Based on the DFT calculations and the phase diagram of the Li–Fe–O system, we supposed that for the initial discharge of the material, after 1 mol of lithium ion intercalation per unit formula, α-LiFe5O8 decomposed to LiFeO2 and Fe3O4. The followed discharge was the conversion of both LiFeO2 and Fe3O4 to metal Fe and Li2O. Thereafter, the system cycled between Fe2O3 at the fully charged state and metal Fe and Li2O at the fully discharged state.

Using Brownian model to study the effect of temperature on diffusion coefficient

This study employs molecular simulation techniques, particularly the Brownian motion model, to investigate the influence of temperature on diffusion coefficients. Leveraging Einsteins relationship for calculating diffusion coefficients and a one-dimensional random walk model, we systematically explore the impact of simulation direction, particle quantity, and simulation duration on diffusion behavior. The research extends its scope to three-dimensional Brownian motion simulations, offering insights into the stochastic motion of particles in a fluid. The primary objective is to analyze the relationship between temperature and diffusion coefficients. Through rigorous linear regression analysis, a significant and strong linear association is identified, demonstrating that an increase in temperature correlates with an increase in the diffusion coefficient. The research not only contributes to the fundamental understanding of molecular motion but also provides practical recommendations for simulation parameters, especially in resource-constrained computational environments. The study acknowledges certain limitations in the current Brownian motion algorithm and proposes avenues for future research to enhance computational efficiency and precision. This abstract encapsulates the key methodologies, findings, and implications of the research, laying the foundation for a comprehensive exploration of temperature-dependent diffusion coefficients in molecular systems.

Sustainable approach to dye adsorption: hemp-based activated carbon as an effective adsorbent

ABSTRACT In industry, the use of dyes that threaten human health is increasing day by day. RB 19 (Reactive Blue 19, Remazol brilliant blue R), one of the most common dyes that adversely affect natural life, is the subject of this article. In this article, the waste parts of the hemp plant (root, stem and other) were evaluated for use in scientific studies. Hemp wastes were carbonised at 500°C at a heating rate of 10°C/min for 1 hour in the N2 atmosphere. Chemical activation was then carried out with 1:4 potassium hydroxide (KOH) at 800°C under the same conditions. Activated carbon (AC) used as an adsorbent was characterised by elemental analysis (73.3% C, 0.3% H, 0.46% N, 0.02% S and 25.92% O), XRD, SEM, BET and FT-IR analysis. Activated carbon (AC) with 850 μm size, 1858.70 m2/g surface area was obtained by chemical activation of carbonised hemp waste with KOH. SEM images showed that the activated carbon is structurally similar to a honeycomb. Kinetic parameters were analysed with six different equations (Intra Particle Diffusion, Pseudo First, Pseudo Second, Elovich, Avrami, Bangham) and adsorption mechanism with eight different equations (Henry, Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Koble-Corrigan, Flory-Huggins, Harkin-Jura). According to the calculated diffusion coefficient (19.299), it is concluded that diffusion is externally controlled. The Intra-Particle Diffusion constant (75.34) indicated that the outer adsorption layer of activated carbon was thick. When the correlation coefficients of the equations were examined according to the kinetic analysis results, the highest correlation coefficient was observed in the Pseudo-First kinetic model for all temperatures. However, it was determined that it also fits the Bangham and Avrami models. Since Bangham and Avrami models have high regression coefficients (0.96–0.99), it can be said that adsorption also fits these models. Also, the negative Gibbs Free Energy values indicate that adsorption can occur spontaneously and is thermodynamically favourable.

Study of helium diffusion in yttria: A multiscale approach based on the density functional theory and kinetic Monte Carlo, with transmission electron microscopy and thermo-desorption spectroscopy

A known issue for future nuclear reactors is helium accumulation inside the steel structure materials, responsible for structural issues such as embrittlement and cracking. One possible solution is using new types of reinforced steel, such as oxide dispersion strengthened (ODS) steel. It consists of adding oxide nanoparticles to the Fe-based material, especially yttrium oxide (yttria, Y2O3), improving its properties. Therefore, one first step is understanding the helium diffusion inside this system. Very little is known about helium inside yttria, with most studies being theoretical ones. Based on this context, this work proposes a combined theoretical and experimental multiscale approach to investigate helium diffusion inside yttria.The theoretical approach starts with the density functional theory, used to model the atomic yttria cell and determine helium insertion sites. The transitions between the sites were described using the Nudged Elastic Bond (NEB) method. Kinetic Monte Carlo was then employed to obtain the interstitial diffusion coefficient expression for the first time for this material. It showed a limited diffusion at temperatures below 600 K, which may indicate a tendency for He to be blocked in the oxide. Then, the charged vacancies were explored. It showed that the vacancy further reduces helium diffusion. Finally, it was demonstrated that helium spreads across different vacancies and interstitial sites.The experimental part involved implanting helium ions at 50 keV in samples with nanometric or micrometric grains. Then, the specimens were characterised with transmission electron microscopy (TEM) and thermo-desorption spectroscopy (TDS) techniques. TEM did not evidence detectable bubbles even at the highest studied fluence (1 × 1016 cm−2). The TDS highlighted different mechanisms for helium diffusion and the grain size's role, providing a novel model for diffusion coefficient calculation based on interstitial diffusion.

Lower Band Chorus Wave Scattering Causing the Extensive Morningside Diffuse Auroral Precipitation During Active Geomagnetic Conditions: A Detailed Case Study

AbstractThe diffuse aurora is a natural phenomenon observed over the Earth's polar region. Compared with the nightside diffuse aurora, the brightness of the dayside diffuse aurora (0600–1800 magnetic local time (MLT)) is relatively weak, thus requiring more stringent observation conditions. Therefore, the current understanding of what causes the dayside diffuse aurora is still quite limited. Here, we present an intense morningside diffuse aurora (0600–1000 MLT) event observed on 1 January 2016 during the recovery phase of the substorm, using conjugate observations of wave and particle spectrum from the Radiation Belt Storm Probes and auroral emission from the Special Sensor Ultraviolet Spectrographic Imagers on the Air Force Defense Meteorological Satellite Program (DMSP/SSUSI). We perform calculations of diffusion coefficients and simulations of the electron fluxes for this event. Our results show that the chorus waves are the primary contributors to the formation of the morningside diffuse aurora, with precipitated electron energies ranging from a few keV to tens of keV. The lower band chorus shows significant pitch angle scattering efficiency for electrons with energies from 5 to 20 keV. The upper band chorus waves induce acceleration effects on 1–20 keV electrons. We suggest that the upper band chorus waves accelerate low‐energy electrons to higher energies, enabling them to engage in the scattering process of the lower band chorus waves. Our study makes a contribution to recent research on the formation mechanisms of diffuse aurora and deepens our understanding of wave‐particle interactions leading to dayside electron precipitation.

Unraveling the characteristics of adsorption and diffusion of oxygen atoms on the surface of Zr and ZrO2 crystals with point defects from molecular dynamic simulations

Unveiling the characteristics of adsorption and diffusion of oxygen atoms on the surface of zirconium alloys at microscale is significant during the initial stages of zirconium oxide layer formation in PWRs or LWRs. In this work, Adsorption and diffusion of oxygen atoms on the surface of Zr and ZrO2 crystals have been investigated using molecular dynamic simulations. A special focus of this work is on the diffusion coefficient calculation based on our developed unbiased approach. The results show that a weak effect of temperature on the adsorption rate of ZrO2. The greater influence of grain boundary orientation than the concentration of Frenkel defects on the adsorption rate of oxygen atoms. The number of oxygen atoms that diffuse deep into the studied samples after adsorption on the free surface increases with increasing temperature. Moreover, for crystals that have a certain concentration of Frenkel defects in the volume, the diffusion coefficients are greater than for defect-free crystals. The diffusion coefficient of adsorbed oxygen atoms is smaller for crystal system with grain boundary of Zr/Zr. This distinct feature may be solving the experimental puzzle of oxidation rate of zirconium alloys under neutron irradiation.

Development of diffusive gradients in thin-films technique for monitoring polycyclic aromatic hydrocarbons in coastal waters

Addressing the challenge of accurately monitoring polycyclic aromatic hydrocarbons (PAHs) in aquatic systems, this study employed diffusive gradients in thin-films (DGT) technique to achieve methods detection limits as low as 0.02 ng L−1 to 0.05 ng L−1 through in situ preconcentration and determination of time-integrated concentrations. The efficacy of the developed DGT samplers was validated under diverse environmental conditions, demonstrating independence from factors such as pH (5.03–9.01), dissolved organic matter (0–20 mg L−1), and ionic strength (0.0001–0.6 M). Notably, the introduction of a novel theoretical approach to calculate diffusion coefficients based on solvent-accessible volume tailored for PAHs significantly enhanced the method’s applicability, particularly for organic pollutants with low solubility. Field deployments in coastal zones validated the DGT method against traditional grab sampling, with findings advocating a 4 to 7-day optimal deployment duration for balancing sensitivity and mitigating lag time effects. These results provide a sophisticated, efficient solution to the persistent challenge of monitoring hydrophobic organic pollutants in aquatic environments, broadening the scope and applicability of DGT in environmental science and providing a robust tool for researchers.