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Lists the review papers in the "Journal of Materials Science" for volumes 36, 37 and 38. "The Relation between the Electron to Atom Ratio and Some Properties of Metallic Systems," by G.P. Tiwari et al; "Durability of Materials in Molten Aluminum Alloys," by M. Yan et al; "Functional Properties of Cement-Matrix Composites," by J.J. Petrovic; "Joints Obtained by Soldering, Adhesion, Autohesion and Fastening Studies by Electrical Resistance Measurement," by D.D.L. Chung; Others.

The 3D reconstruction of porous media plays a key role in many engineering applications. There are two main methods for the reconstruction of porous media: physical experimental methods and numerical reconstruction methods. The former are usually expensive and restricted by the limited size of experimental samples, while the latter are relatively cost-effective but still suffer from a lengthy processing time and unsatisfactory performance. With the vigorous development of deep learning in recent years, applying deep learning methods to 3D reconstruction of porous media has become an important direction. Variational auto-encoder (VAE) is one of the typical deep learning methods with a strong ability of extracting features from training images (TIs), but it has the problem of posterior collapse, meaning the generated data from the decoder are not related to its input data, i.e. the latent space Z. This paper proposes a VAE model (called SE-FBN-VAE) based on squeeze-and-excitation network (SENet) and fixed batch normalization (FBN) for the reconstruction of porous media. SENet is a simple and efficient channel attention mechanism, which improves the sensitivity of the model to channel characteristics. The application of SENet to VAE can further improve its ability of extracting features from TIs. Batch normalization (BN) is a common method for data normalization in neural networks, which reduces the convergence time of the network. In this paper, BN is slightly modified to solve the problem of posterior collapse of VAE. Compared with some other numerical methods, the effectiveness and practicability of the proposed method are demonstrated. [ABSTRACT FROM AUTHOR]

Microbially induced carbonate precipitates (MICPs) through ureolysis-driven calcite precipitation have been investigated as a mean of improving the mechanical properties of soil (cohesion, friction, stiffness, and permeability). To achieve a well-controlled and uniform MICP, it is crucial to obtain a homogeneous distribution of bacterial activity. This paper describes a new and simple method to maximize the retention of bacteria in porous silica sand, where the retained bacteria with their activity are distributed homogeneously. This method is based on a novel in situ biomass flocculation technique induced by the presence of a trace amount of Ca2+ and increased alkalinity of the environment due to the hydrolysis of urea. The method has been tested in both 300 mm and 1000 mm sand columns, in which the retained urease activity, content of the produced CaCO3, and final unconfined compressive strength were homogeneously distributed throughout the entire treated columns. The presented bacterial fixation method could also be potentially used to deliver and fix specific bacteria in a target zone. Overall, this method of improving bacterial fixation in porous media can be used for bio-cementation ground improvement, ensuring the uniform performance of treated soils. [ABSTRACT FROM AUTHOR]

Hip and knee replacement operations mostly utilize the cementing procedure, which determines the biocompatibility relevance of bone cement, a porous material, which is filled with the body fluid after surgery. The paper proposes a computer model of the bone cement mechanical behavior with explicit and implicit analyses of different-size pores, including isolated macropores. The multilevel simulation utilizes the movable cellular automaton method. The mechanical behavior of test samples, both dry and containing the body fluid, is studied under uniaxial compression and four-point bending. Nonlinear porosity dependences are detected for elastic and strength properties of bone cement during compression tests. [ABSTRACT FROM AUTHOR]

This paper explores the performance of pilot-scale constructed wetland osmotic microbial fuel cell (CW-OMFC) in different gravel conditions. The performance was measured in terms of power generation, water flux, chemical oxygen demand (COD) removal, and coulombic efficiency. The CW-OMFC was divided into four sections based on the porosity of the materials. The surface area of materials at Side A, Side B, Side C, and Side D were 2.717 m2.g−1, 0.228 m2.g−1, 0.095 m2.g−1, and 0.072 m2.g−1, respectively. The CW-OMFC achieved maximum water flux, minimum reverse salt flux, high power density, and COD removal efficiency of 6.66 ± 0.5 L.m−2.h−1, 3.33 ± 1.2 g.m−2.h−1, 59.53 ± 10 mW.m−2 and 84.69%, respectively, by using high porous materials. The nutrients (nitrogen, phosphorus, and potassium) uptake by plants from wastewater were 12.17%, 12.01%, and 21.73%, respectively. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to investigate the effects of a slightly perturbed boundary on the MHD flow through a channel filled with a porous medium. We start from a rectangular domain and then perturb the upper part of its boundary by the product of the small parameter ε and an arbitrary smooth function h. Employing asymptotic analysis with respect to ε , we derive the first-order effective model. We can clearly observe the nonlocal effects of the small boundary perturbation with respect to the Hartmann number since the asymptotic approximation is derived in explicit form. Theoretical error analysis is also provided, rigorously justifying our formally derived model. [ABSTRACT FROM AUTHOR]

Seepage equation in fissured porous media is a partial differential equation describing the variation of pressure of a given area over time. In traditional seepage equation, the strength of mass source is supposed to be deterministic. However, the mass source in practice is often affected by noise such as transformation of underground environment and geological activities. To depict the noise, some scholars attempted to employ a technique called Winner process. Unfortunately, it is unreasonable to model the noise in seepage equation with Winner process, since change rate of pressure will be infinite. As a alternative tool in uncertainty theory, Liu process is introduced to model the noise, which can refrain from the problem of infinity. Then this paper deduces the uncertain seepage equation in fissured porous media driven by Liu process. Furthermore, the analytic solution and its inverse uncertainty distribution are derived. Finally, a paradox of stochastic seepage equation in fissured porous media is presented. [ABSTRACT FROM AUTHOR]

Diffusive transport in porous media is a complex process in multi-scaled fractured media modeling. This paper presents a diffusive transport model for non-Dacian flow in a naturally fractured reservoir with triple porosity and permeability. To address the non-Darcian flow behavior associated with fluid transport in fractured porous media, the Darcy/Forcheimer equation was used. A point-diffusive equation was obtained from mass conservation and the Darcy–Forcheimer momentum equation; this is used together with interface conditions to incorporate the microscopic properties of the domain. Subsequently, the resulting equation was spatially smoothed to obtain an effective macroscopic average model. The macroscopic model obtained, unlike the existing models, has a cross-diffusive term for mass transport by induced fluxes and a mass transfer term accounting for mass transfer between the matrix and the surrounding fractures via the interface. The numerical simulation displayed a horizontal-linear flow behavior in the fractured network instead of a radial flow in the matrix. The results further suggest that despite the fractures aiding in fluid transport, they enhance fluid production in the reservoir compared to the matrix. [ABSTRACT FROM AUTHOR]

This paper employs various generalized theories of thermoelasticity to study how a microstretched medium consisting of voids has temperature dependency over it and is affected by relaxation time. It leads to the formation of ruling equations, and the application of normal mode analysis helps to determine various variables such as expressions of displacement components, components of the first moment and micro-rotation as well as couple stress, fields of temperature, components representing variation in volume fraction field and stress, etc. Also, it was made sure that the Lord Shulman theory, the coupled theory, and the Green Lindsay theory, where the prior two contain one relaxation time and the latter contains two relaxation times, have been utilized for result validation by comparing the attained results of thermal changes to these theories. Thus, the graphical illustration of these comparisons helps determine the impact that void parameters and relaxation times create along with conclusions regarding their temperature dependency. Some particular cases of interest are deducted from the present investigation. [ABSTRACT FROM AUTHOR]

Fluid flow through layered materials with different wetting behavior is observed in a wide range of applications in biological, environmental and technical systems. Therefore, it is necessary to understand the occuring transport mechanisms of the fluids at the interface between the layered constituents. Of special interest is the water transport in polymer electrolyte membrane fuel cells. Here, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. This is crucial to choose optimal operating conditions and improve the overall cell performance. Pore-scale modeling of gas diffusion layers (GDLs) and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the hydrophobic porous GDL and the hydrophilic gas distributor, a particular challenge is the combination and interaction of the different material structures and wetting properties at the interface and its influence on the flow. In this paper, a modeling approach is presented which captures the influence of a hydrophilic domain on the flow in a hydrophobic porous domain at the interface between the two domains. A pore-network model is used as the basis of the developed concept which is extended to allow the modeling of mixed-wet interactions at the interface. The functionality of the model is demonstrated using basic example configurations with one and several interface pores and it is applied to a realistic GDL representation in contact with a channel-land structured gas distributor. [ABSTRACT FROM AUTHOR]

In this paper, numerical modeling of concentration propagation using various types of barriers and trees with porosity properties in an idealized urban canyon to protect nearby houses was considered. To solve this problem, a modification of the Reynolds-averaged Navier–Stokes equations is used to take into account the porous medium. To validate the mathematical model and the numerical algorithm, a test problem was solved without taking into account various barriers with a source of pollution. After validation, the main problem was solved, describing the emission process of pollutants between houses using different types of grass barriers and trees with different porosity properties. The numerical simulation data were compared with the calculated values using various types of grass barriers and trees. Taking into account the optimal properties of porous trees in combination with barriers, it was found that height of the barrier itself has a minor role in the spread of pollutants. [ABSTRACT FROM AUTHOR]

The initial boundary value problem of an anisotropic porous medium equation is considered in this paper. The existence of a weak solution is proved by the monotone convergent method. By showing that ∇ u ∈ L ∞ (0 , T ; L loc 2 (Ω)) , according to different boundary value conditions, some stability theorems of weak solutions are obtained. The unusual thing is that the partial boundary value condition is based on a submanifold Σ of ∂ Ω × (0 , T) and, in some special cases, Σ = { (x , t) ∈ ∂ Ω × (0 , T) : ∏ a i (x , t) > 0 } . [ABSTRACT FROM AUTHOR]

In this paper we propose the use of a continuous data assimilation algorithm for miscible flow models in a porous medium. In the absence of initial conditions for the model, observed sparse measurements are used to generate an approximation to the true solution. Under certain assumption of the sparse measurements and their incorporation into the algorithm it can be shown that the resulting approximate solution converges to the true solution at an exponential rate as time progresses. Various numerical examples are considered in order to validate the suitability of the algorithm. [ABSTRACT FROM AUTHOR]

Issues associated with the lack of promptness and accuracy of nondestructive testing (NDT) methods for determining the diffusion coefficient in thin porous materials are studied. Since the calibration of diffusant concentration transducers in a porous material takes a long time, the productivity of research on the diffusion coefficient is low when using conventional methods. The authors examine two methods enabling determination of the diffusion coefficient without the actual static characteristic of the used diffusant concentration transducer. The first method relies on recording the time point that corresponds to the maximum concentration of the diffusant following pulse application. When determining the target coefficient via the second method, it is possible to select two identical values of the transducer output characteristic following the pulse application with the recording of corresponding time points. The specified methods are compared. The errors in determining the target coefficient are studied under comparable conditions using both methods. The paper also analyzes the possibility of reducing the resulting error of Method II by selecting quantities included in the calculation expression. The study results can be useful in the production and use of items made of porous materials. [ABSTRACT FROM AUTHOR]

In this paper, we aim to determine the effective permeability of biporous solids containing fractures in a computational homogenization framework. Precisely, at the local scale, we use the Brinkman law for the porous solids and the Stokes equations within fractures. The resolution of the Brinkman/Stokes coupled equations is performed with the fast Fourier transform iterative scheme on periodic unit cells. The role of the dimensions and orientation of the cracks is investigated. The simulation results are also compared with an analytical formulation based on Mori–Tanaka estimates. The findings indicate that, depending on the considered flow direction, the dimensions and orientation of cracks strongly affect the effective permeability of fractured porous media. Besides, we also determine the macroscopic permeability for a population of fractures with regular and random orientations, dimensions and shapes. The results are then given and discussed. [ABSTRACT FROM AUTHOR]

Porous materials have high specific surface area and complicated morphology, which dramatically amplifies interfacially driven processes leading to complex transport behaviors. Our goal was to encourage submissions that explored integrated approaches for bridging pore- and Darcy-scale processes based on a deeper understanding of interfaces in porous media. [Extracted from the article]

A multiscale model was proposed in a companion paper for assessing the impact of bacterial growth attached to soil particles on the intrinsic permeability of soil. In this paper, this model is used to simulate a column experiment. The simulation conditions are described and the results of the simulation runs are presented. Various possible explanations for the observed reduction in permeability in the column experiment are analyzed using the model and it is concluded that the reduction in the metabolic activity of the attached biomass at the bottom of the column is mainly responsible for the reduction in the intrinsic permeability near the top of the column. Based on the set of parameter values used in the simulations, upper and lower bounds on the reduction in metabolic activity are estimated. [ABSTRACT FROM AUTHOR]

Biocoatings concentrate living, nongrowing microbes in nanoporous adhesive polymer films. Any microbial activity or trait of interest can be intensified and stabilized in biocoatings. These films will dramatically expand the functionality of waterborne coatings. Many microbes contain enzyme systems which are unstable when purified. Therefore, thin polymer coatings of active microbes are a revolutionary approach to stabilize living cells as industrial or environmental biocatalysts. We have demonstrated that some microbes survive polymer film formation embedded in nontoxic adhesive waterborne binders by controlling formulation and drying. Biocoatings can be a single layer of randomly oriented microbes or highly structured multilayer films combining monolayers of different types of microbes on solid, porous, or flexible substrates. They can be formed by drawdown or ink-jet deposition, convective sedimentation assembly, dielectrophoresis, or coated onto or embedded within papers. Controlled drying generates nanoporous microstructure; the pores are filled with a carbohydrate glass which stabilizes the entrapped dehydrated microbes. When the coating is rehydrated, the carbohydrates diffuse out generating nanopores. The activity of biocoatings can be 100s of g L (coating volume) h stabilized for 100-1000s of hours, and therefore, they represent a new approach to process intensification (PI) using thin liquid film bioreactors. A current challenge is that many microbes being engineered as environmental, solar, or carbon recycling biocatalysts do not naturally survive film formation. The mechanisms of dehydration damage that occur during biocoating formulation, ambient drying, and during dry storage have begun to be studied. Critical to preserving microbe viability are minimizing osmotic stress, toxic monomers, biocides, and utilizing polymer chemistries that generate strong wet adhesion with arrested coalescence (nanoporosity). Therefore, controlling desiccation, drying rate/uniformity, and residual moisture are important. Optimization of biocoating activity can be affected at multiple stages-cellular engineering prior to coating (preadaptation), formulation, deposition (film thickness), film formation/drying (generates microstructure), dry storage (minimize metabolic activity), and rehydration. Gene induction (activation) leading to enzyme synthesis following rehydration has been demonstrated. However, little is known about gene regulation in nongrowing microbes. Challenges to optimizing biocoating activity include generating stable film porosity, strong wet adhesion, control of residual water content/form/distribution, and nondestructive measurement of entrapped microbe viability and activity. Indirect methods to measure viability include vital staining, enzyme activity, reporter genes, response to light, confocal fluorescent microscopy, and ATP content. Microbes containing stress-inducible reporter genes can be used to monitor cell stress during formulation, film formation, and drying. Future cellular engineering to optimize biocoatings includes desiccation tolerance, light reactivity (photoefficiency), response to oxidative stress, and cell surface-to-polymer or substrate adhesion. Preservation of microbial activity in waterborne coatings could lead to high intensity biocatalysts for environmental cleaning, gaseous carbon recycling, to produce H or electricity from microbial fuel cells, delivery of probiotics, or for biosolar energy harvesting. [ABSTRACT FROM AUTHOR]

In this paper, a preparation method and characteristics of porous coatings enriched in copper distributed in the whole volume on a ternary Ti-Nb-Zr alloy biomaterial obtained by plasma electrolytic oxidation (PEO) in an electrolyte containing HPO within Cu(NO) at potentials of 180 and 450 V are presented. It has been shown that the PEO potential has impact on the thickness of the coatings, i.e., the higher the potential used, the thicker the coating obtained. Using XPS study, it was shown that copper inside the coating appears as Cu and Cu ions, while titanium, niobium, and zirconium appear as Ti, Nb, and Zr (x ≤ 2), respectively. It was also found that the roughness of PEO coating formed at 450 V is higher than the one obtained at 180 V, and it is well correlated with bigger pores after the PEO treatment. Additionally, in this paper two PEO coating models composed of three sub-layers are presented. The thickness of the outer top porous sub-layer obtained after PEO oxidation at both 180 and 450 V equals to about 2 μm, while the semi-porous as well as transition sub-layers are thicker after PEO processing at 450 V (5 μm) than those obtained at 180 V (4 μm thick). The creation of the top porous and transition compact sub-layer of PEO coating may be explained by switch-on and switch-off of the PEO potential, while the middle and semi-porous sub-layers are most likely formed during the stable voltage conditions of PEO treatment. [ABSTRACT FROM AUTHOR]

Although carbon material are widely used for gas separation and adsorption due to its well-developed pore structure, their prevalent wide pore size distribution and scarcity of active adsorption sites limit its gas adsorption capacity. Therefore, in this paper, a series of N-doped microporous carbon adsorbent materials were prepared via utilizing cheap starch as the carbon source and the synthesized melamine resin as the N-doped modifier with the assistance of hydrothermal conversion and high temperature activation by KOH.BET test showed that MF@Cs was a typical microporous carbon material with a pore size distribution of 0.3–2 nm, and its most accessible pore size was about 0.6 nm,which benefits the adsorption of CO2 and CH4. MF@C–1–750 porous carbon material present prominent pore structure parameters, with a maximum specific surface area of 2415.9 cm2/g, a total pore volume of 1.36 cm2/g, and a maximum ultramicro pore volume of 0.42 cm2/g at 0.3 ~ 1.0 nm. MF@Cs porous carbon materials show high static adsorption capacity for CO2 and CH4, the adsorption capacity of CO2 of MF@C–1–750 is as high as 6.54 mmol/g at 273 K and 100 kPa, which is attributed to the excellent ultramicro pore volume of carbon materials. MF@Cs porous carbon material is expected to play a huge application potential in the separation and enrichment of CO2 in the future, due to its simple preparation and low cost, excellent specific surface area, outstanding ultrafine pore capacity and high adsorption capacity of CO2 gas. [ABSTRACT FROM AUTHOR]

Porous materials have a wide field of application in the biomedical, chemical, pharmaceutical, and automotive industries, among others. In many situations, these materials suffer efforts that can compromise their integrity. To prevent this from happening, a powerful tool, named limit analysis, can be used for the determination of a safe condition of operation for parts made of porous materials. However, there are few studies available that relate the design of parts made of porous material with limit analysis. In this paper, an approach for solving limit analysis problems applied to porous materials is presented. Statical and mixed variational principles are proposed for the limit analysis of porous materials, and a discrete mixed variational principle is presented. Two compaction functions, which relate the relative density to the hydrostatic pressure, are tested: the Helle's and Heckel's expressions. The finite element method is used for the numerical approximation of the discrete limit analysis formulation. Some numerical examples are presented, and the obtained results are close to the numerical and analytical solutions previously published. Among the tested compaction functions, Helle's expression showed the highest compaction. [ABSTRACT FROM AUTHOR]

This paper presents a two-scale topology optimization framework for determining the optimal microstructure in porous material under transient heat conduction and transfer. The new optimization model, which can consider the surface area directly from microstructure topology as the size-dependent term, is introduced to enhance the heat transfer performance. In more detail, a homogenization method capable of considering the size-dependent microscopic heat transfer effect is adopted to express the microscopic material responses. A well-known material interpolation, referred to as the SIMP approach, and the design-dependent linear function are used for interpolating intermediate material properties. The minimal transient heat compliance is chosen as an objective function in this optimization problem. For the sensitivity analysis, a coupled-adjoint variable method is adopted to derive transient sensitivity formulation. The analysis shows that the proposed topology optimization model captures not only the transient heat but also the size effect of the microstructure in a transient heat analysis in porous material. [ABSTRACT FROM AUTHOR]

The effect of a porous layer on thermal convection in a closed rotating square chamber has been studied in this paper. The left border of the chamber is heated up, the right one is cooled, and other walls are thermally insulated. The governing relations with the initial and boundary conditions written employing stream function and vorticity variables are worked out by the finite difference technique. Two approaches are considered and analyzed for setting the heat border conditions at the internal interface between clear liquid and porous material. The first approach assumes that the thermal flux is divided between two phases based on their effective conductivities and temperature gradients. The second model states that both phases at the interface obtain the same thermal flux as the wall. The performed analysis has shown possible differences between these models and the range of governing parameters when these models allow to obtain the similar results. [ABSTRACT FROM AUTHOR]

The paper develops theoretical estimates for the parameters that describe the classical theory of poroelasticity for a fluid-saturated porous medium, with a porous elastic skeleton that can exhibit imperfect grain contacts. The results for the poroelastic properties predicted from the modelling are compared with experimental results available in the literature. [ABSTRACT FROM AUTHOR]

Foams are commonly used as sound absorbers and thermal insulators for many industrial and construction applications. The insulating materials market is currently dominated by inorganic fibres like glass and mineral wool, as well as plastic foams. However, worldwide plastics consumption produces huge amounts of waste, generating concerns about soil, air and especially seawater pollution. Hence, new methods for recycling marine microplastic litter according to cleaner production criteria are being sought. This paper presents a novel, sustainable and eco-friendly foamy material made of microplastic waste, namely polyethylene terephthalate (PET) and polystyrene (PS), incorporated into a bio-based matrix. Samples with different compositions were prepared and then characterized for sound absorption properties. Evidence is presented of very good acoustic performances and of how the acoustic characteristics of the end product can be customized using different microplastic content and type. This allows envisioning many industrial and civil applications for this novel open-cell material. [ABSTRACT FROM AUTHOR]

In magnetic resonance imaging (MRI), this MRI is used for the diagnosis of the brain. The dynamic of these particles occurs under the action of the peristaltic waves generated on the flexible walls of the brain. Studying such fluid flow of a Fractional Second-Grade under this action is therefore useful in treating tissues of cancer. This paper deals with a theoretical investigation of the interaction of heat and mass transfer in the peristaltic flow of a magnetic field fractional second-grade fluid through a tube, under the assumption of low Reynolds number and long-wavelength. The analytical solution to a problem is obtained by using Caputo's definition. The effect of different physical parameters, the material constant, magnetic field, and fractional parameter on the temperature, concentration, axial velocity, pressure gradient, pressure rise, friction forces, and coefficient of heat and mass transfer are discussed with particular emphasis. The computed results are presented in graphical form. It is because the nature of heat and mass transfer coefficient is oscillatory which is following the physical expectation due to the oscillatory nature of the tube wall. It is perceived that with an increase in Hartmann number, the velocity decreases. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem. [ABSTRACT FROM AUTHOR]

This paper continues the study of the use of spline functions for problems involving heat and fluid flow in porous media. Thus, we investigate the numerical solution of the problem of free convection in a square cavity filled with a fluid-saturated porous medium having constant temperatures on the side walls, using a spline collocation method. We present the mathematical model and obtain the governing dimensionless equations together with boundary conditions. Then the problem is solved using cubic spline functions approximations. We analyse the streamlines, isotherms and the numerical results of the local and average Nusselt numbers, for different values of the governing parameters. The results obtained are successfully validated when compared with previously reported results from the open literature. This numerical method has several advantages, such as its speed of convergence and the fact that it is easier to use when the boundary conditions are given for the derivatives of the unknown functions, no extra approximations being necessary. Also, when using cubic spline functions, the discretization process leads to a sparse linear system, which is solvable much more efficiently, thus improving the accuracy of the numerical results and reducing the cost of implementation. The present numerical results can help other researchers in finding approximate solutions of problems in heat transfer arising in many applications in industry. [ABSTRACT FROM AUTHOR]

Porous carbon, derived from biomass, has a high specific surface area and is one of the most attractive electrode materials for supercapacitors. Nonetheless, it is difficult to find a simple and efficient method to process inexpensive raw materials, which is also suitable for large-scale manufacture. This paper proposes a facile and scalable ball-milling combined with KOH chemical activation strategy to prepare the honeycomb-like porous carbon framework with high micropores and small dimensional mesopores from the peony seed shells (PS). Ball-milling technology was used to generate the necessary mechanical force to break the bulk biochar coming from the carbonization of PS into small pieces and increase the accessible surface area for the activation process. In addition, more ordered structures are transformed from sp3-hybridized carbon to sp2-hybridized carbon, which enhances the degree of graphitization for the obtained porous carbon. Furthermore, during the ball-milling and chemical activation process, the incorporation of oxygen atoms into the carbon base of as-prepared materials increases its hydrophilicity which facilitates a better interfacial contact between the hydrated electrolyte ions and the electrode surface in the process of charge and discharge. As a result, an as-fabricated supercapacitor, which is made of this highly porous carbon material, can reach a high specific capacitance (339 F g−1) at a current density of 1 A g−1. The other obtained key parameters for capacitors are also excellent: rate performance (260 F g−1 at 20 A g−1), cycling stability (95.2% capacitance retention after 10,000 cycles at a current density of 1 A g−1). In addition, a high energy density (29.6 Wh kg−1 at 180 W kg−1) can be achieved when the material is used in a 1.6 V Na2SO4 aqueous symmetrical supercapacitor. These results confirm that ball-milling (together with chemical activation) can successfully produce honeycomb-like porous carbon from peony seed shells. The developed electrode material has great potential to be applied in practical high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

This paper presents an improved mathematical model for gasification of a solid porous fuel when hot gases are filtered through it. Gasification modes were studied at a constant pressure drop between the gasifier inlet and outlet and at a constant gas velocity at the gasifier inlet using polymethyl methacrylate as an example. In the case of a constant pressure drop, fuel gasification takes longer and the gas temperature at the outlet increases more slowly than in the case of a constant gas velocity at the inlet under comparable conditions. [ABSTRACT FROM AUTHOR]

This paper examines the controlling of the three dimensional dusty nanofluid flow using the two circular cylinders having different thermal conditions. The cylinders are located in the middle area while the location of the right cylinder is changeable. The 3D (three dimensional) cubic flow domain is filled by a non-Darcy porous medium and a magnetic field in Z-direction is taken place. The non-homogeneous two phase model of the nanofluid is applied while the permeability and thermal conductivity of the porous medium are assumed heterogonous. The current situation is represented by two systems of the equations for the nanofluid and dusty phases. The solutions methodology is depending on the 3D SIMPLE scheme together with the finite volume method. Here, It is focused on the distance between the cylinders δ (0.3 ≤ δ ≤ 0.6) , the Darcy number D a (10 - 2 ≤ D a ≤ 10 - 5) , the dusty parameter α d (0.001 ≤ α d ≤ 0.1) , the average nano-parameter ϕ av (0.01 ≤ ϕ av ≤ 0.03) . The major outcomes indicating to that the flow can be well controlled using the inner isothermal cylinders. Also, the cases of the heterogeneity in X - Y and X - Z directions give the lowest values of Nu av . Both the flow and heat transfer rate are enhanced as δ is increased. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of electrophoretic motion of a polyelectrolyte capsule with a porous arbitrary charged conducting shell in an electrolyte (of the same type as the one inside the capsule's cavity) under the action of an external electric field. The corresponding boundary value problem for the velocity components and pressure in the case of small electrical potentials is analytically solved in quadratures. The solution is analyzed numerically for different values of the specific permeability of the capsule, and the thickness of the porous and the electric double layers. The minimum of electrophoretic velocity dependence on the inverse permeability of the porous layer has been found. It is shown that the electrophoretic mobility decreases upon decrease in the conductivity of the material constituting the porous layer. This means that a dielectric capsule can be used for electrophoresis as well. Moreover, its velocity will be even greater than that of a conducting capsule, all other conditions being equal. [ABSTRACT FROM AUTHOR]

The reconstruction of porous media is significant to some fields such as the study of seepage mechanics and reservoir engineering. Traditional methods have challenges in reconstruction quality due to their insufficient learning ability and suffer from lengthy computational time in large-quantity reconstruction tasks since they cannot reuse the parameters or models established previously. As a branch of deep learning, the variational auto-encoder (VAE) has shown excellent performance in extracting characteristics reflecting the underlying data manifold through a set of possible variables based on a latent model. Fisher information can help to balance the encoder and decoder in information control, used to estimate the variance of maximum likelihood estimate equation. Therefore, this paper proposes a method to reconstruct porous media based on VAE and Fisher information. Firstly, the structural characteristics of porous media are studied by the neural networks of the encoder to obtain the mean and variance of these characteristics. Then, the random sampling is carried out to reconstruct the intermediate results, and the optimization function of the encoder is combined with Fisher information to optimize the network. Finally, the intermediate results are input into the decoder to reconstruct porous media, and the optimization function of the decoder combined with Fisher information optimizes the reconstructed results. This method is evaluated by comparing the variogram, multiple-point connectivity, permeability and porosity of sandstone samples with some other typical reconstruction methods, showing its good reconstruction quality and efficiency. Article Highlights: The reconstruction by our method is better than that of traditional methods. The proposed method can reuse the parameters or models established previously. The proposed method has a faster training speed. [ABSTRACT FROM AUTHOR]

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For material modeling and discovery, synthetic microstructures play a critical role as digital twins. They provide stochastic samples upon which direct numerical simulations can be conducted to populate material databases. A large ensemble of simulation data on synthetic microstructures may provide supplemental data to inform and refine macroscopic material models, which might not be feasible from physical experiments alone. However, synthesizing realistic microstructures with realistic microstructural attributes is highly challenging. Thus, it is often oversimplified via rough approximations that may yield an inaccurate representation of the physical world. Here, we propose a novel deep learning method that can synthesize realistic three-dimensional microstructures with controlled structural properties using the combination of generative adversarial networks (GAN) and actor-critic (AC) reinforcement learning. The GAN-AC combination enables the generation of microstructures that not only resemble the appearances of real specimens but also yield user-defined physical quantities of interest (QoI). Our validation experiments confirm that the properties of synthetic microstructures generated by the GAN-AC framework are within a 5% error margin with respect to the target values. The scientific contribution of this paper resides in the novel design of the GAN-AC microstructure generator and the mathematical and algorithmic foundations therein. The proposed method will have a broad and substantive impact on the materials community by providing lenses for analyzing structure-property-performance linkages and for implementing the notion of 'materials-by-design'. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of gassy sand is rather complex owing to the inherent complex nature of sand and the occluded/dissolved gas. For better understanding of the behaviour of gassy sand under monotonic loading, a numerical model is presented in this paper. By considering the gas–water mixture in gassy sand as a homogenous pore fluid, the theory of two-phase saturated porous media is employed. Based on this theory, the impact of the occluded/dissolved gas is characterized by the relationship between the compressibility of pore fluid and the degree of saturation as well as the pore fluid pressure, derived from Boyle's and Henry's Laws. Then an advanced constitutive model for sand is combined with the porous media theory to capture the complex stress–strain behaviour of sand, using a single set of model parameters. Through the spatial and temporal discretization of the governing equations by the finite element method and the well-known θ-method, the porous model is numerically implemented as a user-defined element subroutine provided by ABAQUS, in which the implicit constitutive integration algorithm is used. Finally, the influences of gas type, degree of saturation, pore fluid pressure level, and physical state (void ratio and stress level) on the behaviour of gassy sand are studied by the numerical model. The model is validated by comparing the simulated results with laboratory test data from literature. [ABSTRACT FROM AUTHOR]

Rock is a multiphase material containing porous structures. It is well known that the porous structures of rocks vary at the microscale, while the properties of rocks are consistent at the macroscale. Therefore, predicting the properties of rock by studying the porous structures of rocks is a good way to prevent engineering disasters. Nevertheless, there have been few studies on this issue. The present paper proposes a cooling–solidification annealing reconstruction algorithm, which can be used to reconstruct a numerical rock model with porous structures to predict its properties quickly. In this algorithm, the system is annealed iteratively with decreasing scale and is constrained in the current scale. Moreover, another grey phase is introduced into the ordinary two-phase reconstruction system to form a new three-phase system. Therefore, the novel algorithm is adept at flexibly modelling complex structures. In particular, by using this algorithm, a simple, local and scale-dependent model can generate very complex porous structures, and the uncertain portions at coarser scales can be annealed directionally by constraining the calculation domain. The numerical results of the reconstructed model are also compared with the experimental results to verify the proposed algorithm. The comparison shows that the novel proposed algorithm can quickly generate a rock model with different porous structures to predict its properties quickly. [ABSTRACT FROM AUTHOR]

In this paper, analytical and numerical studies of species separation in vertical and horizontal porous, cylindrical annular cells were presented. The binary fluid, saturating the porous medium, is a water–ethanol mixture. The thickness e of the horizontal and vertical columns is equal to R o - R i , where R i and R o are, respectively, the internal and the external radii. H is the height of the vertical cell, and the length of the horizontal cell. Constant temperatures, T hot and T cold , were imposed on the inner and outer cylinders. Since an important species separation, in thermogravitational column (TGC), is obtained for e < < H , the same assumption was made for the two configurations. The analytical solution was obtained using the parallel flow approximation for both configurations. The governing equations were solved numerically for 2D and 3D configurations using two different software (Comsol Multiphysics and a spectral collocation method with Gauss–Lobatto–Chebyshev points). Velocity, temperature, mass fraction fields and time to reach steady state were compared for the two configurations. The amount of species separated at the top or the bottom of each cell was also compared for each configuration. [ABSTRACT FROM AUTHOR]

The paper presents the results of studies of porous composite materials based on CaCu3Ti4O12 (CCTO) obtained by ceramic technology. Samples of ceramics based on CCTO demonstrate very high values of relative permittivity (ε > 10000). CCTO material was used both as a binder and as a filler for the production of ceramic composites with a porous permeable structure. For the samples under consideration, there was a several-fold decrease in the value of the dielectric constant and an increase in the electrical resistivity compared with the corresponding parameters of CCTO ceramics. The open porosity of ceramic samples was 30–54%, with an average through-pore size from 10 to 50 microns, depending on the size of filler particles. Thus, the obtained composites are permeable to liquids and gases, which allows them to be used for various applications, for example, sensors of gas compositions. [ABSTRACT FROM AUTHOR]

Borehole sealing is the significant measure for improving coalbed methane (CBM) drainage effect. Based on the technology of using particles to seal the air-leakage fractures around drainage borehole, the deposition and blockage characteristics of particles in the coal (rock) broken zone were experimentally investigated under the gas–solid two phase flow conditions, and the porosity formed by the filled glass beads with different particle sizes (3 mm, 4 mm, 5 mm and 6 mm) in the porous medium zone was used to simulate the broken fractures around boreholes in this paper. The results showed that the particle mass flow rate increased with the inlet air velocity for blockage boundary, and the change trend could be divided into three stages: slow growth stage, rapid growth stage and medium growth stage with the increase of inlet air velocity. Furthermore, the relationship between inlet air velocity and particle loading ratio for blockage boundary in the porous medium displayed a scoop-shaped curve: with increasing inlet air velocity, the particle loading ratio decreased at first and then increased rapidly, subsequently increased slowly, which is different from the existing research. In addition, the effects of conveying pressure and particle size of porous medium on the blockage boundary were also studied. The research work is beneficial to engineering applications of the sealing technology. [ABSTRACT FROM AUTHOR]

This paper discusses the practical aspects of data acquisition and signal processing techniques involved while developing an impedance tube. Microphones, data acquisition systems, set of speakers were carefully selected, calibrated, and assembled as one unit. The raw time signal is acquired through a Virtual Instrument (VI) developed in LabVIEW, and the mathematical equations involved in the process are implemented in MATLAB R 2017a. Important considerations involved in these processes have been thoroughly discussed in the paper. The final results contained outliers that were removed by the application of digital filters. The results obtained from the application of different types of digital filters are shown, discussed, and the best combination of filters has been selected. This combination results in a robust and efficient method with an improved low-frequency response (< 250 Hz) which, in a standard commercial impedance tube, was achieved by altering the microphone spacing. The validation was performed by conducting experiments on a blank tube, melamine foam, glass wool, and comparison were made with the result obtained on the set-up of a leading manufacturer, and with the ones reported in works of literature. They show a good match between them which completes the validation. [ABSTRACT FROM AUTHOR]

In this paper, we consider convergence rates to solutions for the damped system of compressible adiabatic flow through porous media with boundary effect. Compared with the results obtained by Pan, the better convergence rates are obtained in this paper. Our approach is based on the technical time-weighted energy estimates. [ABSTRACT FROM AUTHOR]

The generalized equations of solution motion are given both in porous media and in cavities taking into account the osmotic effect. In certain cases, commonly small relevant corrections play a key role since they are mainly causing the solution motion. Based on the generalized equations, a number of problems have been solved that are of practical value. Owing to the limited volume of this paper, only a simplified example is given. [ABSTRACT FROM AUTHOR]

Many processes in nature (e.g., physical and biogeochemical processes in hyporheic zones, and arterial mass transport) occur near the interface of free-porous media. A firm understanding of these processes needs an accurate prescription of flow dynamics near the interface which (in turn) hinges on an appropriate description of interface conditions along the interface of free-porous media. Although the conditions for the flow dynamics at the interface of free-porous media have received considerable attention, many of these studies were empirical and lacked a firm theoretical underpinning. In this paper, we derive a complete and self-consistent set of conditions for flow dynamics at the interface of free-porous media. We first propose a principle of virtual power by incorporating the virtual power expended at the interface of free-porous media. Then by appealing to the calculus of variations, we obtain a complete set of interface conditions for flows in coupled free-porous media. A noteworthy feature of our approach is that the derived interface conditions apply to a wide variety of porous media models. We also show that the two most popular interface conditions—the Beavers–Joseph condition and the Beavers–Joseph–Saffman condition—are special cases of the approach presented in this paper. The proposed principle of virtual power also provides a minimum power theorem for a class of flows in coupled free-porous media, which has a similar mathematical structure as the ones enjoyed by flows in uncoupled free and porous media. The derived interface conditions are summarized along with a pictorial description of the problem, which pertains to the flow of an incompressible fluid in coupled free-porous media. Ψ is the power expended density along the interface. v free and v por are the velocities in the free and porous regions, respectively. A superposed asterisk on a (vectorial) quantity denotes its tangential component along the interface. v n is the normal component of the velocity at the interface from the free region into the porous region. T free extra and T por extra , respectively, denote the extra Cauchy stresses in the free and porous regions. t free and t por , respectively, denote the tractions on the free and porous sides of the interface with outward normals n ^ free and n ^ por . A unit tangential vector along the interface is denoted by s ^ . [ABSTRACT FROM AUTHOR]

The last decade has seen a strong increase of research into flows in fractured porous media, mainly related to subsurface processes but also in materials science and biological applications, as connected fractures can totally dominate flow patterns. Due to the fractures' characteristics as approximately planar discontinuities with an extreme size-to-width ratio, they challenge standard macroscale mathematical and numerical modeling of flow based on averaging. Thus, over the last decades, various, and also fundamentally different, modeling approaches have been developed. This paper reviews common conceptual models and discretization approaches for flow in fractured porous media, with an emphasis on the dominating effects the fractures have on flow processes. In this context, the paper discusses the tight connection between physical and mathematical modeling and simulation approaches. Extensions and research challenges related to transport, multi-phase flow and fluid-solid interaction are also commented on. [ABSTRACT FROM AUTHOR]

All the time the flow of fluids happens below the surface of the earth. These flow processes can only be imagined, but not be fully visualised on how fluid flow behaviour occurs though the porous medium of the rocks. Hence comes the play of microfluidic micromodels. These are a transparent version of slices (2 dimensional) porous structure of rocks such as sandstone duplicated onto materials such as glass, polymers and silicon wafers. Fluids such as crude oil, surfactant and polymer solutions and gases such as carbon dioxide (CO2) are injected through special pumps into these transparent micromodels. The flow patterns and behaviours hence developed inside the micromodels are studied and analysed. Micromodels have helped in different branches of science such as medicine, genetics, liquid channelling and enhanced oil recovery (EOR). The concern of this paper is to study the flow behaviour and EOR in micromodels. Micromodels can be made to represent a micro version of a partially saturated rock with crude oil. The various chemical EOR processes such as surfactant flooding, polymer flooding, gas flooding injected into crude oil filled micromodels with water saturation is studied. The advancement of front developed between displacing and displaced fluids, the fingering effect, the presence of high permeability streaks is observed. Also the breakthrough of the flood front is analysed from the various experiments reviewed. This review paper is undertaken so as to help researchers find a consolidated and concise literature of the trends and developments in microfluidics especially in EOR. [ABSTRACT FROM AUTHOR]

Hydrogen economy has been suggested as a possible green alternative to produce energy, also in the framework of transport applications. According to the specific transport means, different kinds of materials can be adopted. The choice of the most suitable materials should then be addressed according to a systematic analysis of available data. In this paper, together with the major physical storage technologies typically used for aerospace applications, additional possible candidates are suggested, namely clathrates hydrates and metal-organic frameworks (MOFs). They are chosen according to the specific features that are asked in the aerospace industry, such as high storage capacities, low weight and materials cost, high cyclability and full reversibility. To this scope, a comprehensive database based on a large set of information from literature (containing, for example, details on the synthesis processes, the operating temperatures and pressures, volumetric and gravimetric capacities) has been created, and specific tools have been developed to query the database. Indeed, the selection of the materials has been performed via an alternative database approach where the queries can be managed using a user-friendly tool, and potential materials can be selected based on any pool of desirable properties in quantitative terms. Essential information and characterization on theoretical and experimental data about these performing materials are provided and commented. As an example, in this paper, the case of clathrates hydrates is shown, and their potential impact is explored and characterized in this context, suggesting the most suitable synthesis processes. [ABSTRACT FROM AUTHOR]

The article offers the author's views regarding the insights of Ioan Pop on scaling transformations for boundary layer flow on a permeable stretching surface in a porous medium saturated with a nanofluid. He notes that scaling transformations are not algebraic manipulations, but basic concepts of fluid mechanics and heat transfer. He cites that the rescaled boundary value problem is closely related to the nanofluid model being considered by Pop and M. A. A. Hamad as a pseudo-nanofluid model.

Dufour and Soret effects on flow at a stagnation point in a fluid-saturated porous medium are studied in this paper. A two dimensional stagnation-point flow with suction/injection of a Darcian fluid is considered. By using an appropriate similarity transformation, the boundary layer equations of momentum, energy and concentration are reduced to a set of ordinary differential equations, which are solved numerically using the Keller-box method, which is a very efficient finite differences technique. Nusselt and Sherwood numbers are obtained, together with the velocity, temperature and concentration profiles in the boundary layer. For the large suction case, asymptotic analytical solutions of the problem are obtained, which compare favourably with the numerical solutions. A critical view of the problem is presented finally. [ABSTRACT FROM AUTHOR]

A large number of papers are adopting the Beavers and Joseph (BJ) condition (Beavers and Joseph, J Fluid Mech 30(1):197–207, 1967) for describing the boundary condition between a saturated porous medium and a free fluid, in place of the adherence condition. The aim of the paper is to bring some insight into the domain of validity of the BJ condition. After a short review of some papers on the subject, we point out that the experimental conditions of BJ do not show a good separation of scales. That makes the BJ condition not transposable to different macroscopic situations. When the separation of scales is good, an intrinsic boundary condition is obtained by using the homogenization technique of multiple scale asymptotic expansions. As in the BJ condition and other theoretical works, e.g., Jäger and Mikelić (Transp Porous media, 2009, to appear) we obtain the adherence condition of the free fluid at the first order approximation. However, the corrector to the adherence condition is $${\mathcal{O}(\varepsilon^2)}$$ whereas it is $${\mathcal{O}(\varepsilon)}$$ in the BJ condition, where ε is the separation of scales parameter. [ABSTRACT FROM AUTHOR]

In this article the authors comment on the article "Characteristic Curves for Deep Circular Tunnels in Poroplastic Rock," by Antonio Bobet, which appeared in Volume 43, Issue 2 of the journal in 2009. They criticize the analytical solutions for the short-term and long-term responses of a porous medium with an elasto-plastic behavior. They conclude that the long-term solutions only apply to the exceptional case involving advance drainage and complete pore-pressure relief. They add that the short-term computational results are based on a wrong equation.