Effective Diffusion Research Articles

Magnetic Field Evolution for Crystallization-driven Dynamos in C/O White Dwarfs

We investigate the evolution of magnetic fields generated by the crystallization-driven dynamo in carbon–oxygen white dwarfs (WDs) with masses ≲1.05 M ⊙. We use scalings for the dynamo to demonstrate that the initial magnetic field strength (B 0) has an upper limit that depends on the initial convection zone size (R out,0) and the WD mass. We solve the induction equation to follow the magnetic field evolution after the dynamo phase ends. We show that the predicted surface magnetic field strength (B surf) differs from B 0 by at least a factor of ∼0.3. This reduction depends on R out,0, where values smaller than half of the star radius give B surf ≲ 0.01 B 0. We implement electrical conductivities that account for the solid phase effect on the ohmic diffusion. We observe that the conductivity increases as the solid core grows, freezing in the magnetic field at a certain point of the evolution and slowing its outward transport. We study the effect of turbulent magnetic diffusivity induced by the convection and find that for a small R out,0, B surf is stronger than the nonturbulent diffusion cases because of the more rapid transport, but still orders of magnitude smaller than B 0. Given these limitations, the crystallization-driven dynamo theory could explain only magnetic C/O WDs with field strengths less than a few megagauss for the mass range 0.45–1.05 M ⊙. Our results also suggest that a buried fossil field must be at least 100 times stronger than observed surface fields if crystallization-driven convection is responsible for its transport to the surface.

A numerical investigation on the conductive drying process for phosphate sludge

Phosphate production generates huge quantities of waste materials that pose both economic and environmental challenges. They are characterized by a high-water content, making disposal a very difficult task. To address this issue, conductive drying emerges as a viable solution to reduce the water content in the phosphate sludge to facilitate handling and specially recycling them as construction materials. This paper presents a simplified numerical model based on Fick's law, depicting heat and mass transfer in porous media to simulate the conductive drying process within the phosphate sludge. To provide more accuracy to the numerical model solution, the experimental data are integrated into the numerical model as boundary conditions, enabling the prediction of temperature profiles, thermal conductivity, and effective moisture diffusivity throughout the conductive drying process. The water evaporation capacity is found between 1.25 and 2.1 kg water/m2.h.These findings could be a tool for designing a suitable dryer for phosphate washing sludge.

Pore-scale binary diffusion behavior of Hydrogen-Cushion gas in saline aquifers for underground hydrogen Storage: Optimization of cushion gas type

Cushion gas is required to prevent hydrogen (H2) trapping and interactions between H2 and brine for underground hydrogen storage (UHS) in saline aquifers. However, selecting an appropriate type of cushion gas is not a straightforward task, as it affects the H2 diffusion characteristic in subsurface porous media, thereby impacting purity, recoverability, etc. In this paper, we developed a modified pore network model (PNM) for binary diffusion that incorporates multi-scale diffusion mechanisms to forecast the H2 effective diffusion coefficient (DH2e) and evaluate the impacts of the cushion gas on DH2e. Additionally, the model accounts for the water-lock effects of residual brine, focusing exclusively on the connected pore-throats occupied by the gas phase, which are identified using the invasion percolation algorithm with trapping. Our key findings are as follows: 1) CO2 and N2 demonstrate superior containment effects on H2 compared to CH4 under the specific conditions of the target aquifer, reducing the H2 contamination caused by binary diffusion; 2) The size and topology of porous media exert minimal impacts on the selection of cushion gas, yet they markedly affect the DH2e; 3) The pressure and temperature conditions of the saline aquifer are critical factors in cushion gas selection, with temperature being the more influential parameter. This study provides valuable insights for the implementation of industry-scale UHS in saline aquifers.

Drying Kinetics of Banana Chips: A Modeling Approach

The primary goal of this research is to identify and evaluate the most suitable thin-layer drying model to effectively interpret the drying characteristics of banana chips and determine moisture diffusivity at different drying temperatures. The study utilized physiologically mature “kapok” bananas from the local market in Jember Regency. A flash dryer with a 4000-watt electric heating system was used, equipped with a blower for air circulation, an exhaust fan to expel water vapor. The bananas were processed into chips with a thickness of 1 mm. A total of 2000 g of banana chips were dried at constant temperature according to treatment conditions (air velocity 3.2 m/s, drying at temperatures of 60, 70, and 80°C). The study found that higher drying temperatures (80°C) achieved the highest initial drying rate (35.9% in 30 min) compared to 60°C (28.0%) and 70°C (22.0%). However, the drying rate gradually decreased at all temperatures. The drying kinetics of banana chips at 60, 70, and 80°C aligned well with the modified Midilli model. Effective moisture diffusivity values for banana chips at 60, 70, and 80°C were 4.947E-9 m²/s, 5.165(10–9) m²/s, and 5.756(10–9) m²/s, respectively, indicating that drying at 80°C was the most effective. The effective moisture diffusivity value showed a strong correlation with air velocity, drying temperature, material thickness, RH, and specific material attributes. Keywords: Banana, Diffusivity, Drying, Thin layer drying, Modified Midilli Model.

Diffusive Phyllosphere Microbiome Potentially Regulates Harm and Defence Interactions Between Stephanitis nashi and Its Crabapple Host.

Pear lace bug (Stephanitis nashi) is a significant herbivorous pest, harbouring a diverse microbiome crucial for crabapple (Malus sp.) host adaptation. However, the mutual influence of S. nashi- and plant-associated microbiomes on plant responses to pest damage remains unclear. This study found that S. nashi damage significantly altered bacterial community structure and reduced bacterial evenness in the crabapple phyllosphere. Notably, bacterial diversity within S. nashi was significantly lower than that in the environment, potentially influenced by insect developmental stage, bacterial diffusion stage and endosymbiont species number and abundance. Extensive bacterial correlation and diffusion effect between S. nashi and adjacent plant environments were observed, evident in a gradual decrease in bacterial diversity and an increase in bacterial acquisition ratio from soil to phyllosphere to S. nashi. Correspondingly, S. nashi significantly impacted the metabolic response of crabapple leaves, altering pathways involved in vitamin, amino acid and lipid metabolism and so forth. Furthermore, association analysis linked these metabolic changes to phyllosphere bacterial alterations, emphasizing the important role of diffusive phyllosphere microbiome in regulating S. nashi-crabapple interactions. This study highlights bacterial diffusion effect between insect and plants and their potential role in regulating insect adaptability and plant defence responses, providing new insights into plant-insect-microbiome interactions.

Extraction method for characterizing microcracks on Si3N4 ceramic bearings rolling element with contour segmentation

AbstractAiming at the fuzzy diffusion characteristics of microcrack regions in Si3N4 ceramic bearing rolling elements, an adaptive region segmentation method is proposed to achieve precise extraction of microcrack features. The fuzzy diffusion effect of the microcrack region is analyzed, and a structural complexity matrix is defined to represent the degree of structural variation in the image. A threshold point is determined through histogram analysis, and the matrix dispersion rate is calculated using a box plot to update the correction factor, optimizing the overlap of noise in the microcrack image. The causes of distortion in the microcrack region are analyzed, and pixel points are assigned based on spatial metrics and LAB color features. The fuzzy boundaries and overlapping regions are segmented using the fuzzy C‐means clustering algorithm. A grid search algorithm is embedded to quantitatively evaluate the optimal combination of hyperparameters, enabling comprehensive extraction of microcrack features in Si3N4 ceramic bearing rolling elements. The optimized image achieves an average peak signal‐to‐noise ratio of 39.3, an information fidelity criterion of 7.9328, and an average extraction accuracy of approximately 0.92, effectively overcoming the impact of the fuzzy diffusion effect on the accuracy of microcrack feature extraction in Si3N4 ceramic bearing rolling elements.

Quantitative assessment of congestion diffusion and cascading effect under rainfall-flood disasters: A case study of Nanjing, China

Urban road networks are frequently disrupted by flooding rainfall-flood disasters, which can cause severe traffic disruptions and leading to traffic congestion due to cascading effect. This paper investigates the reliability issues under rainfall-flood conditions. A coupled model, integrating a rainfall-flood model with an improved cascading failure model, is proposed to assess how rainfall intensities and flooding will influence traffic congestion and bring network instability. Utilizing an improved Nonlinear Load-Capacity model, we quantify the impact of congestion and analyze cascading processes under various rainfall-flood conditions. The case study in Nanjing, China reveal that, when congestion causes network pressure to exceed the traffic percolation threshold, traffic congestion diffusion becomes more pronounced, putting excessive strain on other passable roads. Network cascading failures due to traffic congestion diffusion can lead to excessive focus on the remaining passable roads, resulting in a sharp increase in the average importance. The significance of this work lies in its provision of an effective method for predicting potential network disruptions and cascading failures in advance, thereby enhancing post-disaster road operations.

Functional properties of expanded austenite generated on AISI 316L by plasma nitrocarburizing using different active screen materials

Abstract This study investigates the functional properties of the expanded austenite layers generated on AISI 316L austenitic stainless steel resulting from active screen plasma nitrocarburizing using different active screen materials, i.e. steel or solid carbon. Treatments were conducted at 460 °C for 5 hours in a nitrogen-hydrogen feed gas, whereas for the treatments using a steel active screen, methane was added as carbon precursor. Additionally, the bias plasma conditions applied at the samples were varied between 0 kW and 1.25 kW. Samples were characterized by complementary microstructural and compositional investigations, surface roughness and hardness measurements, pin-on-disk tribological tests as well as potentiodynamic polarization tests in H2SO4 and NaCl electrolytes. The functional properties of the case are discussed based on the contents of nitrogen and carbon in the expanded austenite and on their effective diffusion depths. The results show that the usage of a carbon screen generally produces surfaces with uniform layer thickness, high hardness, improved wear resistance and a delayed tendency to pitting corrosion independent of the bias condition applied to the samples. When applying both screen materials at non-biased condition, the general corrosion resistance is slightly reduced under the conditions used, however, the layers generated using the carbon screen have a wear rate that is 3 times lower. It can be concluded that the carbon screen represents a robust treatment variant for austenitic stainless steels to produce sufficiently thick and wear-resistant surface layers in a short treatment duration, which still have the potential to maintain the corrosion resistance in different environments.

Experimental verification of a common assumption in the use of concentration-dependent interdiffusion coefficient

There has generally been a view that concentration-dependent interdiffusion coefficient, D(C), obtained at any diffusion temperature and time is a material constant and can be reliably used to predict diffusion effects at all other isothermal diffusion times. This notion which is implicitly predicated on the assumption that diffusion-induced stress (DIS) rapidly and completely relaxes once formed and does not influence D(C) is experimentally verified in the present work. The results of the study show that reliably computed D(C) from concentration profile obtained at long diffusion time fails to correctly predict concentration profiles at shorter diffusion periods, due to isothermal variation of the D(C) with time. Accordingly, instead of continuing to assume that D(C) is time-independent and can be reliably used to predict diffusion effects at any isothermal diffusion time, without appropriate experimental support, proper experimental verification of this crucial concept in other alloy systems, as done in the present work, is imperative.

Delivery system for dexamethasone phosphate based on a Zn2+-crosslinked polyelectrolyte complex of diethylaminoethyl chitosan and chondroitin sulfate

Hybrid nano- and microparticles based on metal ion crosslinked biopolymers are promising carriers for the development of drug delivery systems with improved biopharmaceutical properties. In this work, dexamethasone phosphate-containing particles based on chondroitin sulfate and chitosan or diethylaminoethyl chitosan additionally crosslinked with Zn2+ were prepared. Depending on the polycation/polyanion ratio in the system, anionic and cationic polyelectrolyte complexes (PECs) were obtained. The anionic Zn2+-containing and Zn2+-free PECs had sizes of 154 and 180 nm and ζ-potentials of −22.4 and −27.5 mV, respectively. The cationic Zn2+-containing and Zn2+-free PECs had sizes of 242 and 362 nm and ζ-potentials of 22.4 and 24.7 mV, respectively. The presence of Zn2+ in the system significantly prolonged the release of dexamethasone phosphate from the hybrid polyelectrolyte particle. The resulting release profiles of dexamethasone phosphate were in agreement with the Peppas-Sahlin kinetic model, which considers the combined effects of Fickian diffusion and polymer chain relaxation on the drug release rate. It was shown that the prolongation of drug release was mainly due to swelling and relaxation of the Zn2+ crosslinked polymers. The developed particles exhibited good mucoadhesive properties and pronounced anti-inflammatory activity, making them attractive candidates for biomedical applications.

Modeling of adsorption-controlled binary gas transport in ultratight porous media

Organic-rich ultratight porous media such as shales have complicated pore types and sizes, dictating their unique fluid transport and storage mechanisms. This paper introduces a diffusion-based binary gas (CH4 and CO2) transport model in such porous media, incorporating key transport and storage mechanisms. Binary gas mixture within the pore volume is divided into two domains: the free-phase and the sorbed-phase, both of which contribute to gas mass transport. Thermodynamic properties of the free phase are determined using the Peng-Robinson equation of state, while a modified extended Langmuir isotherm describes the sorbed phase. The bulk diffusion, Knudsen diffusion, and viscous diffusion are reconciled to describe binary gas transport in the free phase, while the surface diffusion is considered in the sorbed phase. The mass flux is finally related to the effective diffusion coefficient and the free-phase concentration gradient through coupling all transport mechanisms via the equivalent resister network model. The governing equations are solved numerically using a finite difference approach to simulate co-diffusion and counter-diffusion of a binary gas mixture in two nanoporous media, shale and coal.The results reveal that surface diffusion is more pronounced in coal than in shale due to coal's higher adsorption capacity. In co-diffusion cases, both free-phase and sorbed-phase concentrations decrease over time. However, the decline of sorbed-phase concentrations is slower than that of the free-phase. Moreover, CO2 tends to remain adsorbed within the coal matrix due to its stronger adsorption affinity, unlike CH4, which is more likely to flow out. In counter-diffusion cases, injected CO2 first accumulates near the fracture region and then diffuses further into the matrix. Despite shale's pore volume being twice that of coal, similar amounts of CO2 are injected, which can be attributed to coal's higher CO2 adsorption capacity.

Scaling study of diffusion in dynamic crowded spaces

Abstract We formulate a scaling theory for the long-time diffusive motion
in a space occluded by a high density of moving obstacles in
dimensions 1, 2 and 3. Our tracers diffuse anomalously over many decades in
time, before reaching a diffusive steady state with an effective diffusion
constant D eff, which depends on the obstacle diffusivity and density.
The scaling of D eff, above and below a critical regime,
is characterized by two independent critical
parameters: the conductivity exponent μ, also found in models with frozen
obstacles, and an exponent ψ, which quantifies the effect of obstacle
diffusivity.

Analysis of thermophoretic and Brownian diffusions in hydromagnetic curvilinear flow of Carreau nanofluid with activation energy and heat generation

This study presents a theoretical analysis of the thermophoretic and Brownian diffusion effects on the magnetized flow of Carreau nanofluid over a stretchable curved surface. The investigation includes the impact of heat generation and activation energy, which are incorporated into the energy and concentration equations, respectively. The mathematical model of the boundary layer flow is formulated as a set of nonlinear partial differential equations using curvilinear coordinates. These equations are transformed into ordinary differential equations through the application of appropriate similarity variables. The resulting system is solved numerically by using the shooting method along with the Runge-Kutta technique. The accuracy of the numerical results is further verified by the Keller-box method, a finite difference technique. The obtained results are also checked by giving a comparison table with the published data in the literature. Furthermore, the convergence of the solutions is also checked by a convergent series method known as the homotopy analysis method (HAM). The study examines the influence of several key parameters, including the radius of curvature, Weissenberg number, Prandtl number, Lewis number, Brownian and thermophoretic diffusions parameters, Hartmann number, heat generation parameter, activation energy parameter, temperature difference parameter, chemical reaction parameter, and power law index. The effects of these parameters on momentum, temperature, concentration distributions, mass and heat transfer rates, and as well as the skin friction coefficient are examined through graphs and tables. Graphical observations declare that the velocity field diminishes against the rising values of the Hartmann number and Weissenberg number. However, the velocity profile rises with improved values of the radius of curvature parameter and power law index parameter. It is also noticed that the magnitude of the concentration field rises with growing values of the Brownian parameter, activation energy parameter and Lewis number, whereas it shows a decreasing manner against the enhanced values of the thermophoresis parameter and temperature difference parameter.

Application of TbF3 Nano-powders by sand milling process in preparing high performance grain boundary diffusion Nd-Fe-B magnets

The Electrophoretic deposition grain boundary diffusion (EPD-GBD) technology for sintered Nd-Fe-B magnets has garnered significant attention. In this study, TbF3 nano-powders were synthesized via sand milling (SM) process, and the optimal processes were subsequently explored. Notably, the SM powders exhibit two morphologies: blocky and flocculent. With prolonged SM time, the proportion of larger blocky powders decreases gradually, while the proportion of smaller flocculent powders increases. The morphology and proportion of the powders significantly impact the EPD rate and the effectiveness of GBD. Higher blocky powders proportion improved diffusion, reducing residual Tb layer and enhancing magnet coercivity. Higher flocculent powders proportion caused cracking, poor diffusion, thicker residual layer, and lower coercivity. However, a high EPD rate was achieved with a high proportion of flocculent powders. Considering both EPD rate and diffusion effect, the SM process at 1500 r/min for 30 minutes was identified as the optimal parameter. The TbF3 nano-powders prepared by these conditions exhibited superior advantage in the EPD process and the coercivity of GBD magnets compared to traditional micron-scale TbF3 powders, demonstrating the benefits of the SM process in the EPD and GBD processes of Nd-Fe-B magnets.

Effective diffusion constant of stochastic processes with spatially periodic noise

Effective diffusion constant of stochastic processes with spatially periodic noise

Absorption Measurement in Ultrapure Crystalline Quartz with the Eliminated Influence of Ambient Air Absorption in the Time-Resolved Photothermal Common-Path Interferometry Scheme

We demonstrate measurements of the absorption coefficient α ≈ 2.5 × 10−7 cm−1 in synthetic crystalline quartz at a wavelength of 1071 nm with a signal-to-noise ratio of 10/1 using the Time-resolved photothermal common-path interferometry (TPCI) scheme. It utilized cells filled with flowing argon and eliminated the influence of ambient air absorption. The scheme elements limiting the sensitivity of measurements at the level of ≈7.8 × 10−8 cm−1 were revealed. When these elements are replaced by better ones in terms of their thermal influence, the sensitivity of absorption coefficient measurements in crystalline quartz is ~10−8 cm−1. The calculation of the correction due to these optical elements of the values of the measured absorption coefficients is also described, which makes it possible to achieve the same sensitivity without replacing the elements. The improved scheme confirms the presence of the spatial inhomogeneity of absorption with a minimum coefficient of 2.5 × 10−7 cm−1 in synthetic crystalline quartz. The discrepancy of the absorption coefficient values in different regions of the crystal in the presented series of experiments was 2.5 × 10−7 cm−1 to 4 × 10−6 cm−1. Taking into account the ratio of thermo-optical parameters and the heat diffusion effect, the calculation shows that for quartz glasses the corresponding sensitivity of the absorption coefficient measurements equals ≈1.5 × 10−9 cm−1.

Numerical and experimental investigation of the steam penetration in narrow channels during a dynamic steam sterilization cycle

The most challenging aspect of steam sterilization is the removal of all non-condensable gases (NCGs) from the autoclave. These gases prevent the effective killing of microorganisms, impairing the sterility of medical devices. Special cycles are performed to ensure the penetration of steam, even into the deepest passages. To better understand this process, numerical models were developed to determine the spatial distribution of steam within the chamber, including its penetration into narrow channels. These are the first models that can be used to accurately determine the flow within three-dimensional cavities during a dynamic sterilization cycle. To validate the model, an experiment was designed using direct tunable diode laser absorption spectroscopy at a wavelength of 1364 nm to measure the mole fraction of steam present at the end of an aluminum pipe at a temporal resolution of 1 s. This represents a pioneering application of this technique in the field of steam sterilization. This setup was designed for installation on any autoclave. Both simulation and experimental data exhibit good agreement over the entire pressure range (0.18–3.15 bar). The most interesting observation made during the study was the increase in the steam content at the end of the tube while a vacuum was generated. The numerical results show that the mole fraction of H2O increased from 0.53 to 0.63 over the course of a single vacuum phase. This phenomenon was attributed to a stronger diffusion effect combined with small pressure gradients during low pressures. This finding inspired the idea of taking the diffusion effect more into account when designing sterilization cycles in the future to make them more sustainable and effective. The presented methodologies and models represent an excellent basis for conducting more complex investigations in the future, such as those investigating the influence of condensation effects on steam penetration in cavities.

Can urban agglomeration policies promote regional economic agglomeration? Evidence from the Yangtze River Economic Belt in China

The impact of implementing urban agglomeration policies (UAPs) on regional economic agglomeration is crucial for achieving coordinated regional development. This study examines the effects of UAPs on economic agglomeration in the Yangtze River Economic Belt (YREB) in China using panel data from 108 cities spanning from 2006 to 2020. Various research methodologies, such as spatio-temporal variation analysis, Differences-in-Differences (DID), Propensity Score Matching DID (PSM-DID), and Spatial Autocorrelation DID (SACDID) models, are employed. The results indicate a diffusion effect in economic agglomeration of the YREB, leading to a transition from a multilevel center-periphery structure to a contiguous clustering pattern. UAPs have, however, resulted in the concentration of the regional economy towards central cities. Urban agglomerations exhibit an internal siphon effect and a diffusion effect on their exterior. The combination of these two effects manifests itself as a certain degree of siphon. Specifically, UAPs have caused both siphon and diffusion effects in the middle region of the YREB, with less significant impacts in the eastern and western regions. The siphon effects of central cities are influenced by both geographical distance from other cities and, more importantly, economic disparities between them. During the study period, the UAPs served as the indirect rather than direct factor of regional economic coordination.

Thermosensitive double-membrane neurons and their network dynamics

Abstract Cell membrane of biological neurons has distinct geometric structure, and involvement of diffusive term is suitable to estimate the spatial effect of cell membrane on neural activities. The gradient field diversity between two sides of the cell membrane can be approached by using a double-layer membrane model for the neuron. Therefore, two capacitive variables and diffusive terms are used to investigate the neural activities of cell membrane, and the local kinetics is described by a functional circuit composed of two capacitors. The voltages for the two parallel capacitors describe the inner and outer membrane potentials, and the diffusive effect of ions is considered on the membrane surface. The results reveal that neural activities are relative to the capacitance ratio between the inside and outside of the membrane and diffusive coefficient. High-energy periodic external stimulation induces the target waves to spread uniformly, while low-energy chaotic stimulation results in wave fragmentation. Furthermore, when the capacitance ratio exhibits exponential growth under an adaptive control law, the resulting energy gradient within the network induces stable target waves. That is, energy distribution affects the wave propagation and pattern formation in the neuron. The result indicates that the spatial diffusive effect and capacitance diversity between outer and inner cell membranes are important for selection of firing patterns and signal processing during neural activities. This model is more suitable to estimate neural activities than using generic oscillator-like or map neurons without considering the spatial diffusive effect.

Effects of copper on hydroxyapatite thin films by pulsed laser deposition on silicon

AbstractThis study deals with the effect of Cu on hydroxyapatite (HAp) thin films on silicon substrates prepared by pulsed laser deposition (PLD) technique for Cu concentrations ranging from 0 to 0.8 wt.%. Fourier transform infrared spectroscopy and Raman spectroscopy provide additional evidence of HAp in the films, which exhibit characteristic HAp bands such as the 960 cm−1 phosphate ion band. The X‐ray diffraction patterns confirm the presence of HAp, without copper‐related peaks, suggesting that it is not incorporated into the HAp lattice, which is present as an amorphous phase. X‐ray photoelectron spectroscopy confirms the presence of Cu on the HAp thin films, possibly related to the adsorption of Cu2+ on HAp surfaces through electrostatic or interactions with (PO4)3− groups. Atomic force microscopy shows that the roughness of the films varies depending on the presence or absence of copper ions. Finally, density functional theory and kinetic Monte Carlo simulations explain the effects of atomic diffusion on roughness and HAp clustering. These changes correlate with the contact angle values, indicating the formation of hydrophobic films due to copper inclusions.