Effective Diffusion Research Articles

Role of obstacle softness in the diffusive behavior of active particles.

We numerically investigate the diffusive behavior of active Brownian particles in a two-dimensional confined channel filled with soft obstacles, whose softness is controlled by a parameter K. Here, active particles are subjected to an external bias F. Particle diffusion is influenced by entropic barriers that arise due to variations in the shape of the chosen channel geometry. We observed that the interplay between obstacle softness, entropic barriers, and external bias leads to striking transport characteristics of the active particles. For instance, with increasing F, the non-linear mobility exhibits a non-monotonic behavior, and effective diffusion is greatly enhanced, showing multiple peaks in the presence of soft obstacles. Furthermore, as a function of K and F, particles exhibit various diffusive behaviors, e.g., normal diffusion-where the role of obstacles is insignificant, and subdiffusion or superdiffusion-where the particles are partially trapped by the obstacles, and the particles are ultimately caged by the obstacles. These findings help understand the physical situations wherein active agents diffuse in crowded environments.

Characterization of Guest DNA Transport and Adsorption within Host Porous Protein Crystals.

Nucleic acid transport through protein-based pores is a well-characterized phenomenon due in part to advancements in nanopore sequencing. A less studied area is nucleic acid transport through extended protein-based channels, where the additional surface area and increased contact time allow for the study of prolonged binding interactions. Porous protein crystals composed of "CJ", a putative polyisoprenoid-binding protein from Campylobacter jejuni, represent a favorable, highly ordered material for studying DNA transport and binding/unbinding along protein-based channels. These crystals adopt a hexagonal prism habit and contain a densely packed hexagonal array of 13 nm diameter axial nanopores that run from the top to the bottom of the crystal. After cross-linking, the crystals are easily manipulated for experimentation. An adsorption isotherm between host crystals and guest double-stranded 8 base pair DNA (8mer) revealed a high equilibrium adsorption constant of 206 ± 30 L/g. Fluorescence confocal microscopy tracked the loading of guest DNA into host crystals predominately along the major axial crystal nanopores. Four different computational models based on the finite volume (FV) method were assessed to model the transport process for guest 8mer and 15mer dsDNA loading into empty host crystals in terms of fundamental parameters, such as the intrapore diffusion constant. Fitting the models to the data revealed that the most basic FV model sufficed to describe the observed loading behavior, characterized by a single effective diffusion coefficient. Leveraging Fick's first law, we more directly fit a numerical range for the observed intrapore diffusion coefficient as a function of time, position within the crystal, and relative guest concentration. This new transport analysis strategy was applied to both out-of-equilibrium loading and fluorescence recovery after photobleaching (FRAP) experiments. The intrapore diffusion constants are comparable between 8mer and 15mer dsDNA and were found to be 2 orders of magnitude faster for DNA loading into empty crystals than that observed in FRAP experiments, which averaged (10 ± 4) × 10-11 cm2/s.

Effect of hot air temperature and slice thickness on the drying kinetics and quality of Hami melon (Cantaloupe) slices

The effects of hot air temperature and slice thickness on the drying kinetics and quality of Hami melon slices (HMS) were studied. HMS (3 mm and 5 mm) were carried out in a forced convection drying oven at temperatures ranging from 60 ~ 90 °C. The increase in hot air temperature and the decrease in slice thickness led to shorter drying times and higher drying rates. The drying rate curves indicated that the drying process of HMS did not exhibit a constant drying rate period. In the drying kinetics modeling process, the Explinear model was suited for describing the drying curves with higher accuracy. According to Fick’s second law, the moisture effective diffusion coefficient of 3 mm and 5 mm HMS ranged from 4.72 ~ 15.96 × 10-11m2/s at temperatures of 60, 70, 80, and 90 °C. When the thickness of HMS were 3 mm and 5 mm, the activation energies were 30.13 and 43.75 kJ/mol, respectively. When dried at low temperatures, the color of HMS was closer to fresh Hami melon. With the increase of hot air temperature, the hardness of HMS decreases and the rehydration increases. When the thickness of the HMS decreases, the hardness of the slices decreases and the rehydration increases.

A Numerical Investigation on the Effects of Vaned Diffusers on the Aerodynamic Performance of a Low Pressure-Ratio Methane Centrifugal Compressor

A Numerical Investigation on the Effects of Vaned Diffusers on the Aerodynamic Performance of a Low Pressure-Ratio Methane Centrifugal Compressor

Dynamic heat transfer mechanisms of internal thermal mass: effects of thermal conductivity and diffusivity under varied temperature conditions

The appropriate use of internal thermal mass in buildings can reduce energy consumption while maintaining thermal comfort. A prerequisite for selecting suitable internal thermal mass is to establish its relationship with indoor air temperature and heat exchange. However, there is currently a lack of analytical models to describe this relationship. This study investigates the dynamic heat transfer performance of internal thermal mass under constant indoor air temperature, exponentially declining temperatures, and sinusoidal heating and cooling conditions. The results show that under constant indoor air temperature, materials with lower thermal conductivity (e.g., plywood with 0.17 W/m·°C) generate more thermal waves and experience faster surface temperature rises compared to materials with higher conductivity (e.g., reinforced concrete with 1.74 W/m·°C). In the case of exponentially declining indoor air temperature, heat exchange per unit area decreases with increasing thickness, with plywood (0.02 m) reaching its peak temperature at 6360 s, and reinforced concrete (0.2 m) at 9900 s. For sinusoidal temperature variations, the decrement factor for plywood and reinforced concrete decreases from 0.90 to 0.59 as thickness increases from 0.02 m to 0.06 m, while the time lag increases from 1.45 hours to 3.16 hours. The heat exchange is primarily related to the effective thermal capacity per unit area and the storage coefficient, which are determined by the physical properties of the internal thermal mass. These findings provide a quantitative basis for estimating the impact of internal thermal mass on indoor air temperature and heat exchange in the early stages of building design.

Diffusion Mechanism of Waste Crumb Rubber Composite Modified Asphalt Based on Molecular Dynamics Simulation

Waste crumb rubber composite modified asphalt (CRCMA), composed of base asphalt, waste rubber powder, and several additives (softener, activator, and cross-linking agent), has been shown to effectively improve asphalt properties. The interactions between the components in CRCMA are complex, involving molecular diffusion that significantly impacts its performance. The diffusion behavior in asphalt molecules will affect various properties of asphalt and the reasons for the different properties of asphalt can be explained by studying its diffusion mechanism. Therefore, understanding the diffusion mechanism of CRCMA is essential. The molecular dynamics simulation was employed to analyze the factors influencing the diffusion mechanism, using the diffusion coefficient as a key indicator of molecular mobility. The findings showed that the diffusion coefficient of the asphalt system decreased over time but increased with temperature. The rubber composition type also had a significant impact on diffusion, with butadiene rubber (BR) showing the highest coefficient, followed by natural rubber (NR), crumb rubber (CR), and styrene-butadiene rubber (SBR). The diffusion coefficient was the lowest and the diffusion rate was slowest after adding softeners. The diffusion coefficient increased slightly with the addition of CR, and the diffusion rate was slightly accelerated but not significantly. The diffusion coefficient increased rapidly with adding activator and the diffusion rate increased significantly. With the addition of cross-linking agent, the diffusion coefficient began to decrease and the diffusion rate became slower. The CRCMA microscopic performance tests indicated that the swelling effect of CR limits diffusion, while activators promote degradation and desulfurization of CR due to the large molecule structure getting smaller, enhancing diffusion. The S=O bond in the asphalt system was regenerated and re-crosslinked to create a mesh after adding the cross-linking agent. The small molecule structure was transformed into large one. The molecular diffusion was restricted partly and thus the diffusion rate was slowed down.

Intervalence charge transfer in aluminum oxide and aluminosilicate minerals at elevated temperatures

Abstract Single-crystal optical spectra of corundum (Al2O3) and the Al2SiO5 polymorphs andalusite, kyanite, and sillimanite, containing both Fe2+-Fe3+ and Fe2+-Ti4+ intervalence charge transfer (IVCT) absorption bands were measured at temperatures up to 1000 °C. Upon heating, thermally equilibrated IVCT bands significantly decreased in intensity and recovered fully on cooling. These trends contrast with the behavior of crystal field bands at temperature for Fe, Cr, and V in corundum, kyanite, and spinel. The effects of cation diffusion and aggregation, as well as the redistribution of band intensity at temperature, are also discussed. The loss of absorption intensity in the visible and near-infrared regions of the spectrum of these phases may point to a more general behavior of IVCT in minerals at temperatures within the Earth with implications for radiative conductivity within the Earth.

The aluminum and titanium-doped zinc oxide films with improved blocking effect on copper diffusion

Low-cost transparent conductive oxide films and copper metallization play a crucial role in the advancement of silicon heterojunction technologies (SHJ) to the terawatt level. However, the mechanisms of interfacial diffusion of copper through a zinc-based transparent conductive oxides (TCO) layer into silicon are still not known. In this study, we report that for the aluminum and titanium-doped zinc oxide (ATZO) films prepared by the magnetron sputtering method in the n-Si/110 nm TCOs/50 nm Cu structure, compared with indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO), the blocking effect on copper diffusion can be comparable to that of ITO more than that of AZO. The results show that the measured band gap value of ATZO is 3.64 eV, and in terms of carrier concentration, ATZO has a value of 3.7 × 1020 cm−3, which is much higher than the level of AZO. The sample with an ATZO layer also outperforms AZO in band gap, surface morphology, and conductivity, even after heat treatment up to 600 °C. It is important to note, however, that the high-temperature annealing used in this study may have induced changes in the crystallinity and alloy composition of the TCOs, which are not representative of typical SHJ operating conditions. Further studies with more moderate annealing temperatures are needed to better simulate real-world conditions. Nevertheless, ATZO films show strong potential as effective copper diffusion barriers in low-cost metallized photovoltaic applications, offering performance on par with ITO

Combined ANFIS and numerical methods to reveal the mass transfer mechanism of ultrasound-enhanced extraction of proteins from millet

Millet protein, as a promising plant-based protein substitute source, is an excellent basis for essential amino acids compared to commonly consumed staple grains. Compared with the traditional extraction process, ultrasound has been used to enhance the extraction efficiency of various plant-based proteins. To reveal the mechanism of ultrasound-enhanced extraction of proteins, adaptive neuro-fuzzy inference system (ANFIS) algorithm and numerical simulation based on Fick’s law were applied to illustrate the mass transfer behavior of millet proteins under different ultrasonic conditions including solid–liquid ratios (S/L ratios), pH and acoustic energy density levels (AED). The results showed that AED dominated the changes in effective diffusion coefficient (De), showing a positive correlation relationship (p < 0.05). Specifically, when the AED was 47.07 W/cm2, the De value increased by 95 % compared to that of 23.47 W/cm2. Meanwhile, the ANFIS model successfully predicted protein yields across all investigated parameters, achieving a coefficient of determination (R2) greater than 0.97. This model also elucidated the interactions among four critical factors, among which pH and S/L ratios were the main factors affecting protein yield. Concerning the ultrasonic cavitation bubble dynamics, the bubble collapse efficiency enhanced with an increase in AED, and therefore high AED ultrasound can significantly enhance the cavitation effect. Additionally, the results of the yields and physical properties of millet protein also indicated that in contrast with the traditional extraction methods, the ultrasound impactfully improved extraction yield (by 165 %), and combined with pH condition, it decreased the protein particle size (from 813.55 nm to 299.30 nm) without altering the molecular weight distribution. This study offers a novel perspective on the mechanism underlying ultrasound-enhanced protein extraction, drawing upon principles of ultrasonics and extraction processes. The insights gained can serve as a foundation for the food industry to upscale the extraction process, potentially enhancing efficiency and yield.

Kinetics of thermal and photoinduced diffusion of Ag into thin layers of chalcogenide glasses

This study examines the kinetics of thermal diffusion of silver in Ag-GeSe2 and Ag- As10Ge30S60 thin film structures during prolonged storage in the dark at room temperature, as well as the effects of plasmon-enhanced photostimulated diffusion of silver into As10Ge30S60 films. Ag diffraction gratings with a period of 519 nm were used to excite surface plasmon-polaritons (SPP) at the silver-chalcogenide glass interface. It was found that the thermal diffusion coefficient of silver into GeSe2 is significantly higher than into As10Ge30S60. For Ag– As10Ge30S60, photostimulated silver diffusion coefficients were measured with and without SPP excitation. SPP excitation triples the photostimulated Ag flux into As10Ge30S60. Although photosensitivity decreases over time, the plasmon-stimulated increase in Ag flux remains stable. Additionally, As10Ge30S60 thermally doped with silver shows much higher optical absorption at the probing wavelength compared to the photodoped layer with the same silver concentration. Possible mechanisms of these layers formation are discussed.

Cross-field Diffusion Effects on Particle Transport in a Solar Coronal Flux Rope

Solar energetic particles associated with solar flares and coronal mass ejections (CMEs) are key agents of space weather phenomena, posing severe threats to spacecraft and astronauts. Recent observations by Parker Solar Probe indicate that the magnetic flux ropes of a CME can trap energetic particles and act as barriers, preventing other particles from crossing. In this Letter, we introduce the novel COCONUT+PARADISE model to investigate the confinement of energetic particles within a flux rope and the effects of cross-field diffusion (CFD) on particle transport in the solar corona, particularly in the presence of a CME. Using the global magnetohydrodynamic coronal model COolfluid COroNal UnsTructured (COCONUT), we generate background configurations containing a CME modeled as a Titov–Démoulin flux rope (TDFR). We then utilize the particle transport code PArticle Radiation Asset Directed at Interplanetary Space Exploration (PARADISE) to inject monoenergetic 100 keV protons inside one of the TDFR legs near its footpoint and evolve the particles through the COCONUT backgrounds. To study CFD, we employ two different approaches regarding the perpendicular proton mean free path (MFP): a constant MFP and a Larmor radius-dependent MFP. We contrast these results with those obtained without CFD. While particles remain fully trapped within the TDFR without CFD, we find that even relatively small perpendicular MFP values allow particles on the outer layers to escape. In contrast, the initially interior trapped particles stay largely confined. Finally, we highlight how our model and this Letter's results are relevant for future research on particle acceleration and transport in an extended domain encompassing both the corona and inner heliosphere.

Chemical Reaction and Cross Diffusion Effects on Heat and Mass Transfer Characteristics of Viscoelastic Oil-Based Nanofluid Over a Porous Nonlinear Stretching Surface

The impact of chemical reaction and cross diffusion on heat and mass transport characteristics of viscoelastic flow of Al2O3 and CuO oil-based nanofluids past a porous nonlinear stretching surface has been examined. Similarity transformation was used to transform the governing partial differential equations into coupled nonlinear ordinary differential equations and solved numerically by employing the fourth order Runge-Kutta algorithm with a shooting method. Results for the entrenched parameters controlling the flow dynamics have been tabulated and illustrated graphically. The results foundCuO-oil based nanofluid to exhibit higher mass transfer rate and lower heat transfer rate and skin friction coefficient than Al2O3-oil based nanofluid under the same viscoelastic condition. This indicates that CuO-oil based nanofluid can be used as the working fluid in mechanical dampers.

Investigation of ion irradiation effects on mineral analogues of concrete aggregates

Irradiation can cause prominent damage to reactor concrete aggregates leading to amorphization, strength and modulus decrease, radiation induced volume expansion (RIVE) and micro-cracking, which limits their long-term performance. To develop an improved understanding of irradiation effects in concrete, three mineral analogues of concrete aggregates (limestone, marble and quartzite) were irradiated by 5.5 MeV He ions and 13 MeV Ni ions to surface doses of 0.011 displacements per atom (dpa) and 0.23 dpa, respectively, at room temperature. The two different ion species allow irradiation spectrum effects (ionizing and displacive) to be examined. Irradiation induced cracks were observed in He irradiated limestone and marble, and Ni irradiated quartzite. Full amorphization was observed in Ni irradiated quartzite with 14.3 % RIVE, and ∼25 % hardness and modulus decrease, while almost no change was observed in He irradiated quartzite except 4.35 % RIVE, revealing a possible ionization enhanced diffusion effect for high energy light ions. Furthermore, partial amorphization was observed in Ni irradiated marble and limestone matrix with a 12 % hardness decrease in marble while no amorphization was observed for He irradiation with a 20 % hardness increase in limestone matrix. The role of knock-on damage and irradiation spectrum on amorphization, volumetric expansion and mechanical property changes are discussed. Moreover, the onset and critical doses for amorphization and RIVE in quartz are obtained for ion irradiations at room temperature. The dose dependence of RIVE exhibits a delay compared to the amorphization behavior. The superior irradiation resistance of calcite phase compared to quartz phase implies there could be advantages to using calcareous aggregates and lowering the usage of siliceous aggregates for concrete in nuclear power plants for extended operation beyond 60 years. However, other effects such as corrosion, aging and reactions during severe accidents should also be considered, and further investigations are needed.

Pressure Transient Analysis for Fractured Shale Gas Wells Using Trilinear Flow Model

Shale gas, a low-permeability, unconventional resource, requires horizontal drilling and multi-stage fracturing for commercial production. This study develops a trilinear flow model for fractured horizontal wells in shale gas formations, incorporating key mechanisms such as adsorption, desorption, diffusion, wellbore storage, and skin effects. The model delineates seven distinct flow regimes, providing insights into gas migration processes and the factors controlling production. Sensitivity analyses reveal that desorption plays a critical role under low-pressure and low-production conditions, significantly enhancing gas transfer rates from the matrix to the fracture network and contributing to overall production. Monte Carlo simulations further highlight the variability in pressure responses under different input conditions, offering a comprehensive understanding of the model’s behavior in complex reservoir environments. These findings advance the characterization of shale gas flow dynamics and inform the optimization of production strategies.

Diode Laser Absorption Spectroscopy and DSMC Calculations for the Determination of Species-Specific Diffusion Coefficients of a CO2-N2O Gas Mixture in the Transition Gas Regime

Multicomponent gas mixture diffusion in a microscale confined flow in the transition gas regime at Knudsen numbers (Kn) above 0.1 has potential engineering applications in gas-phase microfluidics. Although the calculation of the diffusion coefficient accounts for the influence of the concentration of other species in a multicomponent gas mixture, the higher rate of gas-wall collision at 0.1 &lt; Kn ≤ 10 introduces additional complications not predicted by conventional calculation methods. Thus, simultaneous measurement of diffusion coefficients for multiple gas species ensures accurate estimation of the diffusion coefficient of a particular species that includes the effect of interactions with other species and wall surface conditions in a multicomponent gas mixture at Kn &gt; 0.1. However, most experimental methods for measuring the diffusion coefficient are not species-specific and therefore cannot directly differentiate between the species diffusing in a gas mixture. Thus, this paper demonstrates a new experiment methodology consisting of a two-bulb diffusion configuration accompanied by a tunable diode laser absorption spectroscopy detection technique for species-specific, in-situ, simultaneous measurement of the effective diffusion coefficient for a CO2-N2O gas mixture in the transition gas regime. The experimental results are compared against direct simulation Monte Carlo calculations and the Bosanquet approximation showing a deviation that has not been reported in the literature before.

Pioneer advantage or late-mover advantage? An examination of the interplay between policy diffusion sequence and policy outcomes

In policy diffusion research, considerable focus has been placed on the mechanisms and motivations underlying diffusion, yet there is a notable dearth of analysis linking the diffusion process with policy outcomes. This prompts an important inquiry: Who fares better in terms of policy outcomes—the pioneer or the late mover? Our study investigates China’s River Chief System policy and classifies cities as either pioneers, followers, or laggards according to their position in the diffusion process. Our quantitative analysis of 142 cities indicates that pioneers achieve the most favorable policy outcomes, while laggards are associated with the least favorable results. Further examination of the political incentives driving pioneer advantage suggests that pioneers are driven by political aspirations, followers are driven by political signaling, and laggards are driven by political pressure. This research deepens understanding of policy diffusion by elucidating the interplay between diffusion sequence and policy outcomes, and offers significant insights for policymakers aiming to formulate effective diffusion strategies.

Mid-entropy ceramic (Y0.3Gd0.3Yb0.4)7(Hf0.5Ta0.5)6O24: A potential novel thermal barrier ceramic prepared by ultrafast high-temperature sintering

To meet the demanding service requirements of aero-engines, a mid-entropy thermal barrier ceramic (Y0.3Gd0.3Yb0.4)7(Hf0.5Ta0.5)6O24 (YGYbHT) was designed and successfully prepared by the ultrafast high-temperature sintering, and its performances were systematically characterized and analyzed. After high-temperature annealing at 1500 °C, it exhibited excellent high-temperature phase stability and an extremely sluggish grain growth rate (13 nm/h). Furthermore, the coefficient of thermal expansion(14.85 × 10−6/K) approximated that of nickel-based superalloy, and the thermal conductivity of 2.27 W m−1 K−1 was obtained. Finally, YGYbHT possessed an elastic modulus (155.9 GPa) inferior to traditional YSZ and high hardness (11.83 GPa). The excellent performances are mainly attributed to the entropy-stabilized effect, lattice distortions resulting from the size disorder, and sluggish diffusion effect within the entropy-stabilized material. In conclusion, YGYbHT has the potential to be further developed to replace traditional YSZ as a next-generation thermal barrier coating material.

Microwave-vacuum drying behavior of rosehips: Experimental investigation and mathematical modeling

In this study, the microwave-vacuum drying of rosehips (Rosa canina) was investigated and the effect of different drying conditions during the microwave vacuum drying process on the drying kinetics of rosehips was determined. For this purpose, microwave vacuum drying experiments were carried out until a moisture content less than 10 % by weight was attained at three power (50, 100, and 150 W) and three pressure (40, 75, and 110 mBar (abs)) levels. The drying times ranged from 75 to 195 min depending on the power level and vacuum degree applied. Seven different mathematical models, which are most commonly used in the literature, were fitted to the experimental data, and among these models, the most suitable model was selected by considering the statistical criteria of the highest regression coefficient (R2), the lowest chi-square (χ2), total squared error (SSE) and root mean square error (RMSE). The drying rate (DR) increased with increasing microwave power levels under all pressure levels. The Midilli model was proposed as the best-fit model for predicting the drying behavior of rosehip plants under all drying process conditions. The effective moisture diffusion (Deff) of rosehips under different drying conditions during the MVD process ranged from 5.81⨮10−8-17.32⨮10−8 m2/s and increased with the increasing microwave power at constant pressure.

Assessing the assumption of non-Reliance of concentration-dependent interdiffusion coefficient on maximum component concentration

It is generally assumed that the concentration dependence of the interdiffusion coefficient is a constant material parameter under isothermal conditions, unaffected by the maximum component concentration. Consequently, it is expected that the interdiffusion coefficient obtained from pure-metal/pure-metal diffusion couples can be used to predict diffusion effects, such as concentration profiles in alloy/pure-metal or alloy/alloy diffusion couples within the same binary alloy system, regardless of the maximum component concentration and vice versa. However, this non-trivial assumption neglects the potential influence of diffusion-induced stress on the concentration-dependent interdiffusion coefficient, D(C). This study assesses this assumption, and the results show that predicted concentration profiles based on this common assumption grossly fail to match experimental data. The findings demonstrate that using a constant D(C), irrespective of the maximum component concentration, in the prediction and analysis of diffusion effects can lead to significant errors.

Cavity self-healing mechanism at the interface of high-Cr ferritic steel/austenitic steel dissimilar diffusion-bonded joint during cyclic phase transformation treatment

In this work, cyclic phase transformation treatment (CPTT) was developed to achieve self-healing of interfacial voids in high-Cr ferritic steel/austenitic steel dissimilar diffusion-bonded joints. The evolution of voids was analyzed based on microstructural characteristics, and mechanical properties of joints were assessed through lap-shear tensile tests. The results indicate that, in contrast to isothermal heat treatment (IHT), CPTT significantly enhances efficiency of cavity healing, leading to substantial improvements in both interface bonded ratio and shear performance of joints. By considering equivalent interfacial internal stress, a kinetic model for cavity healing was proposed, incorporating coupled the interface and surface diffusion, and the power-law creep mechanism. Simulation results demonstrate that diffusion predominates during cavity healing with negligible contribution of plastic flow. The actual cavity healing can be divided into two stages: in initial stage the large penny-shaped cavities become shorter in length with negligible change of height, while in the final stage, nearly circular voids shrinkage with a significant decrease of void size due to the enhanced effect of local surface diffusion. Moreover, it suggests that tensile internal stresses can impede healing or even promote residual void growth. Conversely, normal compressive internal stresses within cavity healing zone induced by the cyclic α↔γ phase transformation during CPTT intensify chemical gradients around void neck. This promotes accelerated atomic diffusion adjacent to void neck region, thereby resulting in a notable reduction in the duration required for complete cavity healing.