Electrochemical technique for the determination of fractal dimension of dental surfaces

Fractal dimension of a carious tooth surface was determined using an electrochemical method. The method was based on time-dependent diffusion towards electrode surfaces, which is one of the most useful and reliable methods for the determination of fractal dimension of electrode surfaces. For this purpose, the tooth was covered with a gold layer, which acted as an electrode in electrochemical experiments. It is suggested that the fractal dimension can be used as a quantitative measure of the state of dental surfaces. The method presented demonstrates the power of electrochemical techniques for the determination of fractal dimension of surface of non-conducting objects.     

A new operational vector approach for time-fractional subdiffusion equations of distributed order based on hybrid functions

This research study deals with the numerical solutions of linear and nonlinear time-fractional subdiffusion equations of distributed order. The main aim of our approach is based on the hybrid of block-pulse functions and shifted Legendre polynomials. We produce a novel and exact operational vector for the fractional Riemann–Liouville integral and use it via the Gauss–Legendre quadrature formula and collocation method. Consequently, we reduce the proposed equations to systems of equations. The convergence and error bounds for the new method are investigated. Six problems are tested to confirm the accuracy of the proposed approach. Comparisons between the obtained numerical results and other existing methods are provided. Numerical experiments illustrate the reliability, applicability, and efficiency of the proposed method.     

An efficient mixed methodology for free vibration and buckling analysis of orthotropic rectangular plates

In this paper, a simple and efficient mixed Ritz-differential quadrature (DQ) method is presented for free vibration and buckling analysis of orthotropic rectangular plates. The mixed scheme combines the simplicity of the Ritz method and high accuracy and efficiency of the DQ method. The accuracy of the proposed method is demonstrated by comparing the calculated results with those available in the literature. It is shown that highly accurate results can be obtained using a small number of Ritz terms and DQ sample points. The proposed method is suitable for the problem considered due to its simplicity and potential for further development.     

On the mechanism of microporous carbon supercapacitors

Microporous carbon shows the highest supercapacitor performance among other carbon nanomaterials, and thus, is considered as the most promising candidate for the fabrication of high-performance supercapacitors. However, it has puzzled the researchers as micropores do not have enough space for the formation of the so-called double layer. Several models have been proposed to explain the mechanism of energy storage by microporous supercapacitors. The most common one is that the micropores are initially filled by both anions and cations, and charging/discharging is via ion-exchange through these single row-filled micropores. Although this theory has been supported by several computational calculations, it is discussed here that this model is in disagreement with the experimental facts commonly accepted in the literature.     

Electrical Stimulation of Human Mesenchymal Stem Cells on Conductive Substrates Promotes Neural Priming

Electrical stimulation (ES) within a conductive scaffold is potentially beneficial in encouraging the differentiation of stem cells toward a neuronal phenotype. To improve stem cell-based regenerative therapies, it is essential to use electroconductive scaffolds with appropriate stiffnesses to regulate the amount and location of ES delivery. Herein, biodegradable electroconductive substrates with different stiffnesses are fabricated from chitosan-grafted-polyaniline (CS-g-PANI) copolymers. Human mesenchymal stem cells (hMSCs) cultured on soft conductive scaffolds show a morphological change with significant filopodial elongation after electrically stimulated culture along with upregulation of neuronal markers and downregulation of glial markers. Compared to stiff conductive scaffolds and non-conductive CS scaffolds, soft conductive CS-g-PANI scaffolds promote increased expression of microtubule-associated protein 2 (MAP2) and neurofilament heavy chain (NF-H) after application of ES. At the same time, there is a decrease in the expression of the glial markers glial fibrillary acidic protein (GFAP) and vimentin after ES. Furthermore, the elevation of intracellular calcium [Ca²⁺] during spontaneous, cell-generated Ca²⁺ transients further suggests that electric field stimulation of hMSCs cultured on conductive substrates can promote a neural-like phenotype. The findings suggest that the combination of the soft conductive CS-g-PANI substrate and ES is a promising new tool for enhancing neuronal tissue engineering outcomes.     

Polyaniline-coated cerium oxide nanoparticles as an efficient adsorbent for preconcentration of ultra-trace levels of cadmium (ІІ) followed by electrothermal atomic absorption spectrometry

For the first time, polyaniline-coated cerium oxide nanoparticles were synthesized in alkaline media and applied for preconcentration of ultra-trace levels of cadmium (??) in different real samples followed by electrothermal atomic absorption spectrometry. Cerium oxide nanoparticles were synthesized by a microwave method and modified by polyaniline to produce polyaniline-coated cerium oxide nanoparticles. Fourier-transform infrared spectroscopy and scanning electron microscopy were used to characterize the synthesized adsorbent. To optimize the critical experimental conditions; surface response methodology—Box–Behnken experimental design was used. On the basis of the results, pH 8.4, 10?mg of polyaniline-coated cerium oxide nanoparticles, 14.4?min extraction time, and 4.3?min desorption time were selected as the optimum conditions. Under the optimum conditions the calibration curve of cadmium (??) was linear in the range of 0.02–0.4?ng?mL^?1 with a correlation coefficient of 0.9976. The relative standard deviation based on seven replicate analysis of 0.1?ng?mL^?1 cadmium (??) was 4.2% and limit of detection was 0.005?ng?mL^?1 cadmium (??). The analysis of certified reference material shows very good agreement with the certified value. Finally, the proposed method was applied for the determination of ultra-trace levels of cadmium (??) in different water, rice, and tea samples.