Series solution of a nonlinear ODE arising in magnetohydrodynamic by HPM-Padé technique

In this study, we investigate the magnetohydrodynamic (MHD) viscous flow due to a shrinking sheet by employing the homotopy perturbation method (HPM) and Padé approximation. The series solution of the governing nonlinear problem is developed. Generally, the truncated series solution is adequate only in a small region when the exact solution is not reached. We overcame this limitation by using the Padé techniques, which have the advantage in turning the polynomial approximation into a rational function, are applied to the series solution to improve the accuracy and enlarge the convergence domain. Comparison of the present solutions is made with the results obtained by other applied methods and excellent agreement is noted.     

Importance of Magnetoresistivity Properties and Decrement of the Flux Pinning Energy in YBa2Cu3O7−x Bulk Superconductors Doped with Gd Nanoparticles

Magnetoresistivity performance of the polycrystalline YBa₂Cu_3?x Gd _x O_7?x (Y123) superconductors is discussed by the change of the flux pinning mechanism using magnetotransport measurements performed in the magnetic field range from 0 to 7 T. The critical transition temperatures, irreversibility fields (μ ₀ H _irr), upper critical fields (μ ₀ H _c2), penetration depths (λ) and coherence lengths (ξ) of the Y123 materials are deduced from the magnetoresistivity curves. Further, activation (flux pinning) energies belonging to the samples are determined from thermally activated flux creep (TAFC) model. The results obtained display that the flux pinning energies reduce with enhancing the applied magnetic field. This may be attributed to the fact that Gd nanoparticles inserted in the Y123 superconducting core lead to exhibit much weaker flux pinning, lesser crystallinity and connectivity between grains as compared to the pure sample due to the presence of stronger pair-breaking mechanism.     

Microstructure behaviour and influence on thermally grown oxide formation of double‐ceramic‐layer EB‐PVD thermal barrier coatings annealed at 1,300 °C under ambient isothermal conditions

To resist high thermal loads in turbines effectively, turbine blades are protected by thermal barrier coatings in combination with additional air cooling. State‐of‐the‐art yttria stabilised zirconia top coats do not operate at temperatures higher than 1,200 °C. Promising candidates for alternative top coats are pyrochlores, lanthanum zirconate and gadolinium zirconate. But lifetime of pyrochlores is short because of spallation. However, combinations of yttria stabilised zirconia and lanthanum zirconate or gadolinium zirconate as multilayer systems are promising top layers operating at higher temperatures than yttria stabilised zirconia. Such thermal barrier coatings top coats as double‐ceramic‐layer systems consisting of 7 wt.% yttria stabilised zirconia and lanthanum zirconate or gadolinium zirconate were deposited by Electron Beam‐Physical Vapour Deposition. The focus of the work was set on the influence of the coating design and the microstructure variation generated at different rotating speeds on the adhesion and thermally grown oxide behaviour after isothermal oxidation at 1,300 °C. Phase formation of the thermal barrier coatings top coats was obtained using X‐ray diffraction. After isothermal oxidation tests for 50 h at 1,300 °C, both, microstructure change and the formation of the thermally grown oxide were investigated. While the pyrochlore single‐ceramic‐layer are completely spalled off, microstructure of the double‐ceramic‐layer reveals only crack initiation. The thermally grown oxide thickness was determined by means of scanning electron microscopy. A high aluminum and oxygen content in the thermally grown oxide is found using X‐ray spectroscopy. Existence of α‐phase in Al₂O₃ was proved by X‐ray diffraction. After isothermal testing, no phase transformation can be detected regarding the double‐ceramic‐layer coatings.     

Surface Textured Polymer Fibers for Microfluidics

This article introduces surface textured polymer fibers as a new platform for the fabrication of affordable microfluidic devices. Fibers are produced tens of meters‐long at a time and comprise 20 continuous and ordered channels (equilateral triangle grooves with side lengths as small as 30 micrometers) on their surfaces. Extreme anisotropic spreading behavior due to capillary action along the grooves of fibers is observed after surface modification with polydopamine (PDA). These flexible fibers can be fixed on any surface—independent of its material and shape—to form three‐dimensional arrays, which spontaneously spread liquid on predefined paths without the need for external pumps or actuators. Surface textured fibers offer high‐throughput fabrication of complex open microfluidic channel geometries, which is challenging to achieve using current photolithography‐based techniques. Several microfluidic systems are designed and prepared on either planar or 3D surfaces to demonstrate outstanding capability of the fiber arrays in control of fluid flow in both vertical and lateral directions. Surface textured fibers are well suited to the fabrication of flexible, robust, lightweight, and affordable microfluidic devices, which expand the role of microfluidics in a scope of fields including drug discovery, medical diagnostics, and monitoring food and water quality.     

Antimicrobial open‐cell polyurethane foams with quaternary ammonium salts

An hydroxyl‐terminated quaternary ammonium salt polymer (QAP) was added to a foam formulation in various amounts between 1 and 5 wt %. The structures of the produced foams and their QAP content were characterized by Fourier transform infrared and EDXRF analyses. A linear polymer of QAP with a diisocyanate was also synthesized to support our investigations. The morphological changes such as the cell size and the cell structure of the produced foams were observed with scanning electron microscopy. Thermogravimetric analysis and dynamic mechanical analysis analyses were applied to examine the thermal and thermomechanical properties of the produced foams. Relatively low amount of QAP‐added foams showed very similar structural and thermomechanical properties to the unmodified foams. In addition, while the unmodified foams did not show any antimicrobial activity, the QAP‐added foams provided significant inactivation against Staphylococcus aureus, yeast and mold at concentrations of about 10² and 10³ CFU within 5 h of contact time. The results showed that the addition of minute amount of QAP can significantly improve the biocidal performance of the produced foams without deteriorating their structure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45914.     

Determining Rainwater Harvesting Storage Capacity with Particle Swarm Optimization

Water Resources Management - A reduction in the amount of available clean water is a universal problem, and the harvest of rainwater is one of the methods that can solve this issue. In this study,...     

Influence of Surface Finish on Flexural Strength and Microhardness of Indirect Resin Composites and the Effect of Thermal Cycling

This study investigated the effect of surface finish and thermal cycling procedures on flexural strength and surface microhardness of three indirect resin composites, Artglass®, Signum®, and Solidex®. The specimens were prepared in sufficient number and size according to flexural and microhardness test requirements (n = 10). Scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analysis was also used for studying the morphology, dispersion, and elemental compositions of fillers. The EDX results showed that Artglass contained 1.57% aluminium oxide (Al₂O₃), 53.29% silicon dioxide (SiO₂), and 2.62% barium oxide (BaO); Signum had 55.69% silicon dioxide (SiO₂) and Solidex had 44.99% silicon dioxide (SiO₂) of total mass. Artglass appeared to display the best flexural strength values under all the test conditions employed (range: 116.8 ± 32.18 to 147.8 ± 47.97 MPa), and it was followed by Signum (range: 93.7 ± 22.84 to 118.0 ± 33.45 MPa). Thermal cycling did not seem to have affected the flexural strength of Artglass and Signum (p > 0.05); however, it led to a significant decrease, from (110.5 ± 20.69 MPa) to 74.0 ± 13.30 MPa (p < 0.001), in the strength of polished Solidex specimens. While surface microhardness of the three materials increased by polishing (Artglass: 55.7 ± 2.64/74.1 ± 8.63 Vickers Hardness Numbers (VHN); Signum: 44.8 ± 3.12/60.7 ± 4.50 VHN; Solidex: 44.0 ± 2.31/53.4 ± 3.58 VHN for unpolished/polished specimens), thermal cycling had a deleterious effect on this property (p < 0.001).     

Effect of Argon Plasma Pretreatment on Tensile Bond Strength of a Silicone Soft Liner to Denture Base Polymers

This study evaluated the effect of argon plasma treatment on tensile bonding of heat-cured and auto-polymerized acrylic resins prior to the processing of a silicone soft liner. Both types of polymethylmethacrylate (PMMA) resins were treated with argon plasma for 1 min or 10 min (n = 5). A control group, including untreated resin specimens, was also formed. After processing of the soft liner, the specimens were deflasked and stored dry for 24 h, and they were then subjected to tensile bond strength testing. In order to see the plasma effect on the resin surface chemistry, representative specimens were analysed by XPS. Highest tensile bond strengths were observed in the 1-min exposure group for each resin, and 10-min exposure yielded the lowest bond strength likely due to the damaging effect of the plasma treatment. XPS analysis showed that the O/C ratios increased greatly in treated samples and that the binding energy values were not significantly changed.     

Neural network based MOSFET channel length and width decision method for analogue integrated circuits

The channel length and width of a MOSFET are two important parameters selected by the experience of the integrated circuit designer. Since drain current of a transistor is directly adjusted by the aspect ratio, the wrong selection of these parameters changes the circuit characteristics. In this work neural networks are used to decide the most suitable selection of channel length and width of MOSFET. Both p-channel and n-channel transistors are modelled by multi layer perceptron (MLP) neural network and the channel length and width are predicted by MLP. MOSFET level 3 is modelled by MLP, training and test data are obtained from HSPICE design environment with YITAL 1.5μ parameters. Developed network is tested with the current mirror and the differential amplifier circuits. Estimated aspect ratios for each transistor are compared with the HSPICE simulation results.     

Electroinduced dispersion polymerization of acrylonitrile in the presence of poly(acrylic acid) and catalytic amount of CE(IV)

Electroinduced dispersion polymerization of acrylonitrile initiated by Ce(IV) was performed in an electrolytic cell in the presence of poly(acrylic acid) (PAA). Micron‐size polyacrylonitrile (PAN) particles were stabilized with PAA by electrostatic interaction or by a PAA–Ce(III)–PAN ternary complex formation. A PAA–PAN stable polymer was formed in the cathodic compartment, and the reduced initiator was reoxidized in the anode, thus allowing for the continuation of the process. A possible mechanism of polymerization is suggested. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 723–728, 2002; DOI 10.1002/app.10076