Wear Behavior of Multiwalled Carbon Nanotube/AZ31 Composite Obtained by Friction Stir Processing

Multiwalled carbon nanotubes were homogenously dispersed into a magnesium alloy (AZ31) using friction stir processing. The microstructural features, mechanical behaviors including microhardness, and wear properties were investigated. The results showed a significant improvement in wear resistance in the friction stir-processed AZ31 alloy containing multiwalled carbon nanotubes compared to that of the as-received alloy. This was attributed to its higher microhardness and lower coefficient of friction due to the presence of finer matrix grains and uniform dispersion of multiwalled carbon nanotubes.     

Study the effect of distribution of density of states on the depletion width of organic Schottky contacts

Organic semiconductor to metal Schottky contacts have been widely used in electronic devices and to investigate the properties of organic semiconductors. In designing and characterizing these devices the full depletion approximation is used. The analytical and numerical simulations presented in this paper suggest that this approximation is not generally valid. Simulations of a Schottky contact between regioregular-poly 3 hexylthiophene (rr-P3HT) and aluminum show that this approximation becomes worse as molecular order decreases, with the potential profile increasingly deviating from the expected quadratic function of position. Also the depletion width decreasing well below that predicted using the approximation. In this work the slope of the band tail is used as a measure of disorder.     

Probabilistic stability of uncertain composite plates and stochastic irregularity in their buckling mode shapes: A semi-analytical non-intrusive approach

In this study, the mechanical properties of the composite plate were considered Gaussian random fields and their effects on the buckling load and corresponding mode shapes were studied by developing a semi-analytical non-intrusive approach. The random fields were decomposed by the Karhunen−Loève method. The strains were defined based on the assumptions of the first-order and higher-order shear-deformation theories. Stochastic equations of motion were extracted using Euler–Lagrange equations. The probabilistic response space was obtained by employing the non-intrusive polynomial chaos method. Finally, the effect of spatially varying stochastic properties on the critical load of the plate and the irregularity of buckling mode shapes and their sequences were studied for the first time. Our findings showed that different shear deformation plate theories could significantly influence the reliability of thicker plates under compressive loading. It is suggested that a linear relationship exists between the mechanical properties’ variation coefficient and critical loads’ variation coefficient. Also, in modeling the plate properties as random fields, a significant stochastic irregularity is obtained in buckling mode shapes, which is crucial in practical applications.     

Dynamic analysis of carbon nanotubes under electrostatic actuation using modified couple stress theory

Modified couple stress theory is a size-dependent theorem capturing the micro/nanoscale effects influencing the mechanical behaviors of the micro- and nanostructures. In this paper, it is applied to investigate the nonlinear vibration of carbon nanotubes under step DC voltage. The vibration, natural frequencies and dynamic pull-in characteristics of the carbon nanotubes are studied in detail. Moreover, the effects of various boundary conditions and geometries are scrutinized on the dynamic characteristics. The results reveal that application of this theory leads to the higher values of the natural frequencies and dynamic pull-in voltages.     

Double-walled microspheres loaded with meglumine antimoniate: preparation,characterization and in vitro release study

Objective: The objective of this study was to fabricate double-walled poly(lactide-co-glycolide) (PLGA) microspheres to increase encapsulation efficiency and avoid rapid release of hydrophilic drugs such as meglumine antimoniate.

Methods: In this study, double-walled and one-layered microspheres of PLGA were prepared using the emulsion solvent evaporation technique to better control the release of a hydrophilic drug, meglumine antimoniate (Glucantime®), which is the first choice treatment of cutaneous leishmaniasis. The effect of hydrophobic coating on microspheres' size, morphology, encapsulation efficiency and drug release characteristics was evaluated. Furthermore, the presence of antimony in meglumine antimoniate made it possible to observe the drug distribution within the microspheres' cross section by means of energy dispersive X-ray spectroscopy.

Results: Drug distribution images confirmed accumulation of the drug within the inner core of double-walled microspheres. In addition, these microspheres encapsulated the drug more efficiently up to 87% and demonstrated reduced initial burst and prolonged release compared to one-layered microspheres. These superiorities make double-walled microspheres an optimum candidate for sustained delivery of hydrophilic drugs.

Conclusion: Double-walled microspheres provide some advantages over traditional microspheres overcoming most of their limitations. Double-walled microspheres were found to be more efficient than their corresponding one-layered microspheres in terms of encapsulation efficiencies and release characteristics.     

Optimization of Short Load Forecasting in Electricity Market of Iran Using Artificial Neural Networks

Accurate short-term load forecasting (STLF) is one of the essential requirements for power systems. In this paper, two different seasonal artificial neural networks (ANNs) are designed and compared in terms of model complexity, robustness, and forecasting accuracy. Furthermore, the performance of ANN partitioning is evaluated. The first model is a daily forecasting model which is used for forecasting hourly load of the next day. The second model is composed of 24 sub-networks which are used for forecasting hourly load of the next day. In fact, the second model is partitioning of the first model. Time, temperature, and historical loads are taken as inputs for ANN models. The neural network models are based on feed-forward back propagation which are trained and tested using data from electricity market of Iran during 2003 to 2005. Results show a good correlation between actual data and ANN outcomes. Moreover, it is shown that the first designed model consisting of single ANN is more appropriate than the second model consisting of 24 distinct ANNs. Finally ANN results are compared to conventional regression models. It is observed that in most cases ANN models are superior to regression models in terms of mean absolute percentage error (MAPE).     

Spatially resolved laser-induced breakdown spectroscopy in methane-air diffusion flames

A new setup for spatially resolved laser-induced breakdown spectroscopy (SR-LIBS) is used for the first time to analyze methane-air diffusion flames. Using this configuration, background continuum emission is reduced, signal-to-background noise ratio is increased up to eight times, and spatial resolution is enhanced. The local equivalence ratio is also quantitatively estimated and the width of the secondary combustion region at a specified height above the burner is determined for two different methane flow rates. Furthermore, the threshold energy for spark formation is measured for regions inside and outside the flame. The results show that threshold energy is larger at the secondary combustion region, near the border of the flame, than inside the flame.     

Effect of citric acid content on the structural and magnetic properties of SrFe12O19 thin films

Strontium hexaferrite SrFe₁₂O₁₉ thin films have been synthesized on the Si (100) substrate using spin coating sol-gel process. The influence of different citric acid to metal ions (CA/MN) molar ratios of 0.5, 1 and 1.5 on the formation of SrFe₁₂O₁₉ was investigated. Fourier transform infrared analysis and theoretical calculations were conducted to determine and help control the concentration of metal citrates in solution precursors. X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer techniques were also applied to evaluate the composition, microstructure, crystallite size and magnetic properties of the SrFe₁₂O₁₉ thin films. The results showed that single phase strontium hexaferrite thin films with optimum physical properties can be obtained from the solution with the CA/MN molar ratio of 1 after calcination at 800 °C. The SrFe₁₂O₁₉ thin films synthesized with the CA/MN molar ratio of 1 exhibited crystallite size of 42 nm and isotropically magnetic properties of M_s = 267.5 kA/m (at 795.8 kA/m), M_r = 134 kA/m, and H_c = 341.4 kA/m.