The method of fundamental solutions for solving free boundary saturated seepage problem

The problem of seepage flow through a dam is free boundary problem that is more conveniently solved by a meshless method than a mesh-based method such as finite element method (FEM) and finite difference method (FDM). This paper presents method of fundamental solutions, which is one kind of meshless methods, to solve a dam problem using the fundamental solution to the Laplace's equation. Solutions on free boundary are determined by iteration and cubic spline interpolation. The numerical solutions then are compared with the boundary element method (BEM), FDM and FEM to display the performance of present method.     

Synthesis of potassium niobate (KNbO3) nano-powder by a modified solid-state reaction

Crystalline lead-free piezoelectric potassium niobate (KNbO₃) powders have been synthesized through a modified solid-state reaction method. The thermal behavior of the K₂C₂O₄·H₂O and Nb₂O₅ raw material mixture was investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The X-ray diffraction technique (XRD) was used to investigate the phase formation and purity. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The XRD pattern showed that the monophasic perovskite phase of KNbO₃ could be synthesized successfully at a temperature as low as 550 °C for 240 min, with an average crystallite size of 36 ± 8 nm. The SEM images suggested that the average particle size of the powder obtained was 278 ± 75 nm.     

Solid-state reaction synthesis of sodium niobate (NaNbO<Subscript>3</Subscript>) powder at low temperature

A modified solid-state reaction was applied to produce lead-free piezoelectric sodium niobate (NaNbO₃) powders. The mixture of Na₂C₂O₄ and Nb₂O₅ was identified by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The powders were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The SEM image suggested that the particle size of the powders obtained ranged from 180 to 360 nm. The XRD pattern showed that the pure perovskite phase of NaNbO₃ could be synthesized at the low temperature of 475 °C for 1 h, with an average crystallite size of 31.45 ± 5.28 nm. This temperature was about 300 °C lower than that when using the conventional solid-state method with Na₂CO₃ as reactant, which resulted in a cost-, energy-, and time-saving method.     

Numerical Analysis of Heat–Mass Transport and Pressure Build-Up in 1D Unsaturated Porous Medium Subjected to a Combined Microwave and Vacuum System

This article presents one-dimensional numerical analysis of heat-mass transport and pressure build-up inside an unsaturated porous media under microwave energy at a vacuum pressure condition. The unsaturated porous media is composed of glass beads, water, and air. The absorbed microwave power term is computed based on Lambert's law. The finite difference method together with Newton-Raphson technique is employed to predict the heat, multiphase flow, and pressure build-up. Based on the numerical analysis of the effects of vacuum pressure and types of dielectric materials, it was found that the vacuum pressure had a strong effect on temperature, absorbed microwave power, saturation and pressure build-up distribution, and movement of fluid inside the unsaturated porous media during the microwave drying process.     

Carbonized electrospun polyvinylpyrrolidone/metal hybrid nanofiber composites for electrochemical applications

Electrospinning is a very versatile and efficient method of fabricating nanofibers with the desired properties. Polyvinylpyrrolidone (PVP) in ethanol solution was electrospun into nanofibers and used as a precursor for the preparation of carbon nanofibers. Cobalt chloride was also incorporated with PVP nanofibers to produce carbon nanofiber composites with enhanced electrical conductivity and electrochemical properties. The surface morphology and physical properties of the electrospun nanofibers, carbonized nanofibers, and their composites were observed by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The electrochemical behavior of the carbon nanofiber composites was studied by drop‐casting on a working surface of the screen‐printed carbon electrode and examined by cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that carbon nanofiber composites were decorated with cobalt nanoparticles and enhanced the charge‐transfer efficiency on the electrode surface. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45639.     

Numerical analysis of microwave melting of ice-saturated porous medium filled in a rectangular waveguide with resonator using a combined transfinite interpolation and PDE methods

A numerical study is performed for the melting process of ice-saturated porous medium filled in a rectangular waveguide with a resonator subjected to electromagnetic energy. A microwave system supplies a monochromatic wave in a fundamental mode (TE₁₀ mode) with operating frequency of 2.45 GHz. Focus is placed on establishing a computationally efficient approach for solving moving boundary heat transfer problem in a two-dimensional structured grid. Numerically, preliminary grids are first generated by an algebraic method, based on a transfinite interpolation method, with subsequent refinement using a PDE mapping method. A preliminary case study indicates successful implementation of the numerical procedure. The predicted results from two-dimensional melting model are then validated against available experimental results and subsequently used as a tool for efficient computational prototyping. Based on the numerical results are performed illustrating the influence of resonator and layered configuration, in case of the installed resonator has strongly affected on the microwave power absorbed, temperature distribution, and the melting front during microwave melting process.     

Effects of BiMO3 on dielectric,ferroelectric, and piezoelectric properties of perovskite lead‐free piezoelectric BaTiO3–(Bi0.5Na0.5)TiO3 ceramics

New lead‐free piezoelectric ceramics of 0.9BaTiO₃–(0.1?x)(Bi_0.5Na_0.5)TiO₃–xBiMO₃, M=Al and Ga, where x=0.00‐0.10, were fabricated by the solid‐state reaction technique. The effect of BiMO₃ contents on the perovskite structure, phase transition, and dielectric, ferroelectric, and piezoelectric properties was investigated. X‐ray diffraction patterns showed that the ceramics exhibit a monophasic perovskite phase up to x=0.06, suggesting stabilized perovskite structures with B‐site aliovalent substitutions. Compositional‐dependent phase transitions were observed from tetragonal to pseudo‐cubic phase with increasing BiMO₃ amounts. Al³⁺ ions were found to stabilize the transition temperature of the ceramics, while significantly decreasing transition temperature, and a change in the dielectric peak were found with an increasing amount of Ga³⁺. Regarding Al³⁺ substitution, the remanent polarization (P_r) values were found to decrease slightly with the Al³⁺ amount. With regard to Ga³⁺ substitution, P_r values decreased with the Ga³⁺ amount up to 0.06 and then increased slightly. The ceramics became softer with a higher degree of substitution according to the lower coercive field (E_c), when compared with 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃ ceramics. Ceramics with a lower degree of substitution and tetragonal phase showed butterfly strain loops that correlated with normal ferroelectric behavior.