Concept Of Layer Research Articles

Molecular Simulation of Electrode-Solution Interfaces.

Many key industrial processes, from electricity production, conversion, and storage to electrocatalysis or electrochemistry in general, rely on physical mechanisms occurring at the interface between a metallic electrode and an electrolyte solution, summarized by the concept of an electric double layer, with the accumulation/depletion of electrons on the metal side and of ions on the liquid side. While electrostatic interactions play an essential role in the structure, thermodynamics, dynamics, and reactivity of electrode-electrolyte interfaces, these properties also crucially depend on the nature of the ions and solvent, as well as that of the metal itself. Such interfaces pose many challenges for modeling because they are a place where quantum chemistry meets statistical physics. In the present review, we explore the recent advances in the description and understanding of electrode-electrolyte interfaces with classical molecular simulations, with a focus on planar interfaces and solvent-based liquids, from pure solvent to water-in-salt electrolytes.

A Nonlocal Strain Gradient Approach for Out‐of‐Plane Vibration of Axially Moving Functionally Graded Nanoplates in a Hygrothermal Environment

Vibration analyses on axially moving functionally graded nanoplates exposed to hygrothermal environments are presented. The theoretical model of the nanoplate is described via the Kirchhoff plate theory in conjunction with the concept of the physical neutral layer. By employing the nonlocal strain gradient theory, the governing equation of motion is derived based on Hamilton’s principle. The composite beam function method, as well as the complex modal approach, is utilized to obtain the vibration frequencies of axially moving functionally graded nanoplates. Some benchmark results related to the effects of temperature changing, moisture concentration, axial speed, aspect ratio, nonlocal parameter, and the material characteristic scale parameter on the stiffness of axially moving functionally graded nanoplates are obtained. The results reveal that with increasing the nonlocal parameter, gradient index, temperature changing, moisture concentration, and axial speed, the vibration frequencies decrease. The frequencies increase while increasing the material characteristic scale parameter and aspect ratio. Moreover, there is an interaction between the nonlocal parameter and material characteristic scale parameter, influencing and restricting each other.

Calculation of the three-dimensional turbulent boundary layer in the vessel’s bow and midship area by the integral method

The quality of technical solutions applied in ship design and construction is substantially determined by the validity of viscous flow parameters, especially in the vicinity of thrusters. The influence of shapes on velocity, pressure and turbulence distribution can be assessed by physical experimentation. Along with undeniable advantages, physical modelling has a number of disadvantages: high labour input and cost, limited range of parameters variation (e.g. Reynolds numbers), difficulty in separating the influence of individual factors. Therefore, the development of mathematical models and numerical calculation schemes based on them is extremely relevant. Calculation of friction resistance and calculation of the velocity field in the vicinity of a vessel comes down to the calculation of its boundary layer and trace parameters. Current mathematical models with a planar representation, i.e. working with projections rather than real curves, do not give an accurate description. This has led to the need for a mathematical model that can address all of the required characteristics of a three-dimensional turbulent boundary layer. Both differential and integral methods are used to calculate three-dimensional boundary layers. The model is capable of calculating the characteristics of the spatial boundary layer in the stern and the viscous wake, in the bow and in the middle of the vessel. The model is quite versatile: it has been successfully used both for computing the boundary layer characteristics in the bow and midship area by the integral method based on the thick boundary layer concept, and for computing the turbulent flow in the stern and viscous wake by the differential method based on the partial parabolic concept using the k-ε turbulence model. In this paper we will elaborate on the integral method calculation.

Spatially ensemble of polydopamine-protected-Au nanocrystals on Fe3O4@SiO2@γ-AlOOH microflower for improving catalytic performance

Advanced nanocatalysts integrating with high activity and recyclability is one of the most important issues in heterogeneous catalysis. Magnetic hierarchical nanostructures comprising noble metal nanocrystals confined within a protecting penetrable shell will be favored as an efficient candidate toward robust catalytic reactions. This work reports a proof-of-concept magnetic separable nanocatalyst with the polydopamine (PDA)-confined-Au-nanocrystals assembled on the hierarchical surface of Fe3O4@SiO2@γ-AlOOH microflower (Fe3O4@SiO2@γ-AlOOH@Au/PDA). Because of the high surface area of γ-AlOOH hierarchical nanoarchitectures, the loading capacity and dispersity of Au nanocrystals are both improved. These magnetic microflowers present excellent catalytic efficiency and cycling performance in reduction of 4-nitrophenol to 4-aminophenol, which can be ascribed to the superior structure of catalyst. After 9 cycles, the activity of Fe3O4@SiO2@γ-AlOOH@Au/PDA maintains as high as 97.3% due to the protection of PDA shell. In comparison to the spherical Fe3O4@SiO2@Au/PDA, the as-prepared Fe3O4@SiO2@γ-AlOOH@Au/PDA microflowers exhibit quicker catalytic dynamic. The concept of hierarchical nanostructure and penetrable PDA protective layer will be instructive for fabricating high-performance nanocatalysts.

Sprayable PEDOT:PSS based spectrally selective coating for solar energy harvesting

A novel spectrally selective coating was developed on stainless substrates using commercially available poly(ethylene-3,4-dioxythiophene):poly (styrene sulfonate), (PEDOT:PSS) polymer for solar energy harvesting applications. An intrinsic (i.e., single) absorber layer concept was used to develop this coating. The as-prepared PEDOT:PSS dispersion was applied on substrates with thickness in the range of 0.1–5.8 μm using an automated spray deposition system, and the effect of thickness on the optical properties was studied in detail. The intrinsic properties of PEDOT:PSS resulted in high absorptance and low emittance, this was ascertained using glass, quartz and KBR pellets. With optimization of coating thickness, the reflectance edge shifted towards higher wavelength and near perfect absorption was obtained over a broad wavelength range leading to very high absorptance. The optimized PEDOT:PSS coating (approximately 5.8 μm thick) deposited on stainless steel substrates exhibited absorptance of 0.967 and emittance of 0.36.

Extreme dissipation and intermittency in turbulence at very high Reynolds numbers.

Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation probability density function (PDF) based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers, these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume-weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds numbers, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.

Conflicting Aspects in the Flat Plate Boundary Layer Conventional Solution

The solution of the steady-state isothermal gas flow with zero-pressure gradient over a flat plate is classical and was presented by Blasius in 1908. Despite being reduced to a third-order Ordinary Differential Equation, nobody has solved it using just three boundary conditions. In consequence, the “solutions” (exact or numerical) are not unique, do not satisfy Prandtl’s boundary layer concept, and give rise to imprecise criteria of the boundary layer thickness definition (0.99.U∞, where U∞ is the free stream velocity) and to idealizations such as the displacement thickness, δ∗, and the momentum thickness, δI. Even though η, the similarity parameter, is defined as a function of x, it is surprising that it is seen as a constant, η∞, at the limit of the boundary layer, being valid for the entire plate. It is shown that uncountable “solutions” satisfying the classical equation and its three natural boundary layer conditions can be built. The reduction technique of the Boundary Value Problem, BVP, to an Initial Value Problem, IVP, and the Perturbation Analysis Technique, used as an attempt to incorporate a fourth boundary condition to the differential equation, are discussed. A more general and direct method to deduce the classical Blasius’s flat plate equation is considered, as one of the steps to rectify its solution, and shed light on the origin of the conflicting issues involved.

Effects of Weak Electrolytes on Electric Double Layer Ion Distributions.

Many common experimental systems have electric double layers containing weak electrolytes, including systems with buffers. The pH at the boundary of the diffuse layer is an important parameter for determining the physicochemical state of the system, including surface charge density. We show that the Boltzmann equilibrium relation can be used as an exact solution for weak electrolyte electric double layers. Using these results, we provide a closed-form relation for the maximum pH change in a buffered electric double layer, in terms of the boundary potential. Importantly, our results suggest that equilibrium electric double layer concepts developed for strong electrolytes can be expanded to include weak electrolytes.

A new one-dimensional numerical model for unsteady hydraulics of sediments in rivers

This paper presents the model UMHYSER-1D (Unsteady Model for the HYdraulics of SEdiments in Rivers 1-D), a one-dimensional hydromorphodynamic model capable of representing water surface profiles in a single river or a multiriver network, with different flow regimes considering cohesive or non-cohesive sediment transport. It has both steady and unsteady flow and sediment modules. For steady gradually varied flows, UMHYSER-1D uses the standard step method to solve the energy equation and the “NewC” scheme for the de St Venant equations. For sediment transport, UMHYSER-1D uses two methods: for long-term simulation, the unsteady terms of the sediment transport continuity equation are ignored, and a non-equilibrium sediment transport method is used. For short-term simulation, the convection–diffusion equation, with a source term arising from sediment erosion/deposition is solved using the fractional step method. The equation without the source term is solved with an implicit finite-volume method, then the equation with source term is solved. Internal boundary conditions, such as time-stage tables, rating curves, weirs, bridges, and gates are simulated. Incorporated is the active layer concept, which allows selective erosion, enabling the simulation of bed armoring. Non-cohesive sediment transport equations and cohesive sediment physical processes are applied to calculate the sediment deposition and erosion. Finally, UMHYSER-1D empirically accounts for bed geometry adjustments by using a relationship between erosion width and flow rate, an angle of repose condition for bank stability and three minimization theories. The presented validation and application cases show UMHYSER-1D’s capabilities and predicts its promising role in solving complex, real engineering cases.

Finite element modeling and simulation of the fiber–matrix interface in fiber reinforced metal matrix composites

The properties of fiber–matrix interface in the fiber reinforced metal matrix composites (MMCs) have been investigated in the past with the use of push-out test. The finite element (FE) analysis which is used to model the push-out test helps the composite’s designer in optimizing the interfacial properties. A two dimensional planar FE model is presented for investigating the properties of interface. Cohesive layer concept is used to model the interface with a specified thickness. The initial response of the cohesive element is assumed to be linear elastic. The maximum nominal stress criterion is used to define the damage initiation and the damage evolution is defined in terms of fracture energy. The simulation results show that the cohesive layer behaves almost like the matrix for the linear elastic deformation prior to damage. It is concluded that the values of Young’s modulus and shear modulus for the cohesive layer can be taken equal to that of the matrix material for the finite element simulation of the debonding behavior of these MMCs. Furthermore, it is observed that the shear stress at which damage initiates can be determined by using the cohesive layer concept for the interface. Once a damage initiation criterion is met, material damage occurs in accordance with the defined damage evolution law. The complete failure of the interface takes place when the stress becomes zero. However, the interface behavior needs to be defined in a more sophisticated way so as to model the stepwise debonding and failure evolution once the complete debonding has occurred.

Excitation of Bloch Surface Waves in Zero-Admittance Multilayers for High-Sensitivity Sensor Applications

The growing need for classical as well as quantum optical sensing places increasingly stringent requirements upon the desired characteristics of the engendered fields. Specifically, achieving superior field enhancement plays a critical role in applications ranging from chem-bio sensing, Raman and infrared spectroscopies to ion trapping and qubit control in emerging quantum-information science. Due to their low optical losses and ability to exhibit resonant field enhancements, all dielectric multilayers are emerging as an optical material system not only useful to classical photonics and sensing but also of potential to be integrated with quantum materials and quantum sensing. The recently introduced concept of zero-admittance layers [1] within dielectric multilayer materials, enables the creation and control of resonant fields orders of magnitude larger than the exciting field. Here, invoking the zero-admittance concept, we design, fabricate, and characterize an all-dielectric nonabsorbing stack and demonstrate the engendered huge field enhancement. Describing the fields in terms of Bloch surface waves, we connect the surface field to the semiperiodicity in the dielectric domains of the stack. As a specific application of the resonant field, we propose and demonstrate refractive-index sensing for the detection of trace amounts of an analyte. The results include a quantification of the sensitivity of the device with respect to the profile of the exciting field. The experimental results are shown to be in good agreement with theoretical calculations.

Big Data Platform Configuration Using Machine Learning

By ensuring well-developed complex big data platform architectures, data engineers provide data scientists and analysts infrastructure with computational and storage resources to perform their research. Based on such supports, data scientists are provided an opportunity to focus on their domain problems and design the required intelligent modules (i.e., prepare the data; select, train, and tune the machine-learning modules; and validate the results). However, there are still gaps between system engineering and data scientist/engineering teams. Generally, system engineers have limited knowledge on the application domains and the purposes of an analytical program. On the contrary, both data scientists and engineers are usually unfamiliar with the configuration of a computational system, file system, and database. However, the performance of an application can be affected by a system's configuration, and the data scientists and engineers have little information and knowledge about which of the system's properties can affect the application's performance. As a typical example, for Internet-scale applications that have thousands of computing nodes or billions of Internet of Things devices, even a slight improvement may have an enormous influence on energy management and environmental protection issues. To bridge the gap between system engineering and data scientist/engineering teams, we proposed the concept of a configuration layer based on a big data platform, Hadoop. We built a configuration tuner, BigExplorer, to collect and preprocess data. Furthermore, we also created golden configurations for performance improvement. Based on the processed data, we used a semi-automatic feature engineering technique to provide more features for data engineers and developed the performance model using three different machine learning algorithms (i.e., random forest, gradient boosting machine, and support vector machine). Using the commonly used benchmarks of Word-Count, TeraSort, and Pig workloads, our configuration tuner achieved a significant performance improvement of 28%-51% for different workloads than using the rule-of-thumb configuration.

Friction Layer Analysis of a Surface Acoustic Wave Motor

Abstract This study applied appropriate assumptions to simplify a surface acoustic wave (SAW) motor model, as well as the elastic friction layer concept to analyze the two-dimensional contact problem. The effect of inertial force was factored into the equation of motion for the friction layer; the relationship between external force and the displacement of the friction layer surface was determined via Fourier transform; and the displacement field under different loads was analyzed using numerical methods. Based on the friction theory proposed by Armstrong, the relative velocity of the friction layer between the slider and stator was considered in the relationship between the normal and tangential forces acting on both contact surfaces. Finally, the deformation and the contact forces acting on the friction layer were evaluated by assuming the displacement of the stator substrate.

Wide-angle wideband polarization-insensitive perfect absorber based on uniaxial anisotropic metasurfaces

A wide-angle, wideband, and polarization-insensitive metamaterial (MM) absorber was studied based on the theoretical concept of uniaxial perfect matching layer (UPML) in the terahertz range. The MM absorber was designed as a multi-layered anisotropic array structure consisting of a conductive VIA, a bi-layered slot-FSS, and a split-ring resonator (SRR) separated by porous silica spacers. Each component is optimized to approach the required macroscopic uniaxial property for satisfying the reflection-less boundary condition. The SRRs and VIAs were found to play an important role in maintaining large absorption when the angle of oblique incidence increases under transverse electric (TE) and transverse magnetic (TM) polarization, respectively. The absorption achieves 90% in the frequency regime of 0.9 to 10.5 THz, corresponding to a bandwidth of 168% to the central frequency, and retains such high performance up to 60° oblique incidence for both TE and TM waves.

Sediment transport and bed evolution model for complex river systems.

This work presents the theoretical background, development, and preliminary evaluation of a one-dimensional unsteady sediment transport and bed evolution model for a looped river network. The sediment transport and bed evolution model employs a concept that differentiates sediment particles moving in the form of suspended sediment, and near bed, and bed sediment. Applying the active layer concept, the developed model utilizes the appropriate exchange mechanisms between the suspended sediment and active layer material, which are presented in great detail. The governing transport equations were solved using the split operator approach that resulted in two successive steps. The advection equations were solved using the characteristics method, whereas the diffusion equations were discretized using the Crank-Nicholson scheme. The obtained system was complemented with additional auxiliary equations in order to allow sediment transport and bed evolution simulation at nodes, thus enabling the same in a looped river network. The derived equations were applied to develop an open-channel flow, sediment transport, and bed evolution model that was subjected to a series of preliminary numerical tests.

Boundary layer flow of Maxwell fluid due to torsional motion of cylinder: modeling and simulation

This paper investigates the boundary layer flow of the Maxwell fluid around a stretchable horizontal rotating cylinder under the influence of a transverse magnetic field. The constitutive flow equations for the current physical problem are modeled and analyzed for the first time in the literature. The torsional motion of the cylinder is considered with the constant azimuthal velocity E. The partial differential equations (PDEs) governing the torsional motion of the Maxwell fluid together with energy transport are simplified with the boundary layer concept. The current analysis is valid only for a certain range of the positive Reynolds numbers. However, for very large Reynolds numbers, the flow becomes turbulent. Thus, the governing similarity equations are simplified through suitable transformations for the analysis of the large Reynolds numbers. The numerical simulations for the flow, heat, and mass transport phenomena are carried out in view of the bvp4c scheme in MATLAB. The outcomes reveal that the velocity decays exponentially faster and reduces for higher values of the Reynolds numbers and the flow penetrates shallower into the free stream fluid. It is also noted that the phenomenon of stress relaxation, described by the Deborah number, causes to decline the flow fields and enhance the thermal and solutal energy transport during the fluid motion. The penetration depth decreases for the transport of heat and mass in the fluid with the higher Reynolds numbers. An excellent validation of the numerical results is assured through tabular data with the existing literature.

Embedding sensors using selective laser melting for self-cognitive metal parts

We devised a novel method to embed sensors or integrated circuit (IC) chips into metal components by using a selective laser melting (SLM) process. The concept of a protective layer is introduced to fabricate all parts without damaging the sensors during the laser scanning process. The operation of sensors in the parts is analyzed from a computational analysis on the thermal influence of laser heat. The fabricated metal parts show continuous microstructures including grains and phases between the base part and the new part formed after embedding the sensor despite the intermittent SLM process. The embedded sensor operates properly when compared to bare sensors. Plastic circuit board-based IC components were embedded into an Inconel 718C turbine blade, which accurately distinguished three-dimensional vibration along the X, Y, and Z axes. Our results imply that the proposed process can open new avenues for SLM technology to realize metal components with a self-cognitive ability using integrated sensors.

Создание композиционного материала на основе низкоразмерных углеродных частиц

The article considers the issues of thermal shock resistance of carbon materials. To obtain a composite material, the method of electric arc treatment with a relatively low current value was used. The resulting material and its properties correspond to the concept of a double electric layer at the interface, which is due to the orientation of carbon molecules.

Partition of Unity Finite Element Method applied to exterior problems with Perfectly Matched Layers

The Partition of Unity Finite Element Method (PUFEM) is now a well established and efficient method used in computational acoustics to tackle short-wave problems. This method is an extension of the classical finite element method whereby enrichment functions are used in the approximation basis in order to enhance the convergence of the method whilst maintaining a relatively low number of degrees of freedom. For exterior problems, the computational domain must be artificially truncated and special treatments must be followed in order to avoid or reduce spurious reflections. In recent papers, different Non-Reflecting Boundary Conditions (NRBCs) have been used in conjunction with the PUFEM. An alternative is to use the Perfectly Match Layer (PML) concept which consists in adding a computational sponge layer which prevents reflections from the boundary. In contrast with other NRBCs, the PML is not case specific and can be applied to a variety of configurations. The aim of this work is to show the applicability of PML combined with PUFEM for solving the propagation of acoustic waves in unbounded media. Performances of the PUFEM-PML are shown for different configurations ranging from guided waves in ducts, radiation in free space and half-space problems. In all cases, the method is shown to provide acceptable results for most applications, similar to that of local approximation of NRBCs.

Numerical simulation of the debonding behavior of fiber reinforced metal matrix composites

Finite element analysis (FEA) is performed for investigating the debonding behavior of fiber reinforced metal matrix composites (MMCs). An Axisymmetric cylindrical and three dimensional solid finite element (FE) models without interface are constructed which consist of a stainless spring steel wire as fiber reinforcement and an aluminium alloy as matrix. Numerical simulation is carried out with both the spherical and cylindrical indenters. The simulation results obtained in this work are compared with the experimental findings reported in the past. The initial part of load–displacement curve for cylindrical indenter is linear in nature as compared to the non linear behaviour with the spherical indenter. This shows that the non linearity is because of the shape of the indenter and not due to other reasons such as incorrect modeling. The coefficient of friction does not affect the response regarding the load–displacement curve. A large gap between the experimental and simulation curves for the elastic region is due to stiffness of the experimental setup. The simulation curve shows continuous increase in the value of load which is due to the absence of definition of failure criterion. The axisymmetric FE model presented in this study shows the capability to simulate the debonding behaviour of fiber reinforced MMCs. However, it can be improved further with the implementation of cohesive layer concept for modeling the fiber–matrix interface. In future work, the FEA of the axisymmetric model with interface using the cohesive zone modeling (CZM) for the interface will be carried out.