Novel Linear Piezo-resistive Auxetic Meta-Sensors with Low Young's Modulus by a Core–Shell Conceptual Design and Electromechanical Modelling

Production of piezo-resistive auxetic sensors is usually carried out through mixing and coating methods. Although these methods are beneficial, Young's modulus of mixed sensors becomes high because of using a high percentage of sensing elements while the durability of coated sensors gets low due to the separation of sensing elements from the sensor surface. This article presents a new core–shell metamaterial model to address the mentioned problems. The shell and the core are produced of polydimethylsiloxane (PDMS) rubber and a mixture of PDMS/graphite powders (73.45 wt% graphite powders), respectively. A finite element model is developed via COMSOL software to predict the electromechanical behaviors of the created sensor and verified by an experimental study. Scanning electron microscope imaging is conducted to detect the separations of the graphite particles. The main important feature of this meta-sensor is to possess a linear sensitivity due to having zero Poisson's ratio. The advantage of this method is that Young's modulus of the sensor does not decrease (unlike the mixing method), and the sensor-coated particles do not separate from the sensor after a while (unlike the coating method). The introduced model has advantages that promote potential applications such as using sensory gloves to detect, for instance, human hand movements.     

Assessing the Vulnerability of California Water Utilities to Wildfires

Water Resources Management - Wildfires are becoming more frequent and destructive in California, and it is essential to quantify their potential impacts on drinking water utilities. This study aims...     

Analysis for Radiation and Shielding Dose in Plasma Focus Neutron Source Using FLUKA

Monte Carlo simulations have been performed for the attenuation of neutron radiation produced at Plasma focus (PF) devices through various shielding design. At the test site it will be fired with deuterium and tritium (D-T) fusion resulting in a yield of about 10¹³ fusion neutrons of 14 MeV. This poses a radiological hazard to scientists and personnel operating the device. The goal of this paper was to evaluate various shielding options under consideration for the PF operating with D-T fusion. Shields of varying neutrons-shielding effectiveness were investigated using concrete, polyethylene, paraffin and borated materials. The most effective shield, a labyrinth structure, allowed almost 1,176 shots per year while keeping personnel under 20 mSV of dose. The most expensive shield that used, square shield with 100 cm concrete thickness on the walls and Borated paraffin along with borated polyethylene added outside the concrete allowed almost 15,000 shot per year.     

Improved configuration for symmetric and asymmetric multilevel inverters with reduced number of circuit devices

In this paper, a topology developed for multilevel voltage source inverters is proposed. The suggested modular configuration consists of several series-connected units, which can be applied as symmetric and asymmetric inverters. In the asymmetric mode, different solutions are suggested to generate an increased number of output voltage levels. In multilevel inverters, the number of required circuit elements determines the total cost, circuit size, installation area, complexity of control scheme and reliability of the inverters. The comparison study among the proposed inverter by considering all the presented algorithms for it, cascaded H-bridge (CHB) inverter and recently proposed converters, confirms that the proposed inverter uses a reduced number of circuit elements. In order to show the practicability of the proposed converter, a prototype of the proposed structure is implemented and tested. The simulation and experimental results are in good agreement with each other, indicating the effectiveness of the proposed inverter.     

Titania Nanostructures for Dye-sensitized Solar Cells

Nano-Micro Letters - Titania is one kind of important materials, which has been extensively investigated because of its unique electronic and optical properties. Research efforts have largely...     

Investigation of polymerization of benzoxazines and thermal degradation characteristics of polybenzoxazines via direct pyrolysis mass spectrometry

Polymerization of benzoxazines and thermal degradation mechanisms of polybenzoxazines were investigated using the direct pyrolysis mass spectrometry (DP‐MS) technique. The benzoxazine structures were based on phenol and aniline and on bisphenol‐A and methylamine or aniline. Polymerizations of the benzoxazines were carried out by curing them at elevated temperatures without addition of initiator or catalyst. DP‐MS data showed the presence of chains generated by opposing polymerization reaction pathways indicating quite complex structures for the polybenzoxazines under investigation. Thermal decomposition of polybenzoxazines was started by the cleavage of methylamine or aniline linkages. It was determined that polybenzoxazines based on phenol were more stable than the corresponding bisphenol‐A‐based polybenzoxazines, while those based on methylamine were more stable than the corresponding polybenzoxazines incorporating aniline. Thus, it can be concluded that the presence of bulky groups decreased the extent of crosslinking which in return decreased the thermal stability. Copyright © 2012 Society of Chemical Industry     

Inclusion of carbon nanotubes in a hydroxyapatite sol–gel matrix

In this study, the inclusion of multi-walled carbon nanotubes as the second phase in the hydroxyapatite matrix, in order to improve the mechanical strength, has been performed via the sol–gel process. The stability of carbon nanotube sol with the changes of pH and dispersant values (sodium dodecyl sulfate) was evaluated by zeta potential analysis. The results indicated that synthesis of hydroxyapatite particles in the presence of the carbon nanotubes had the best result in homogenization of the carbon nanotube dispersion and faster crystallization of hydroxyapatite. The crystallization of hydroxyapatite phase was investigated with differential scanning calorimetry (DSC) and X-ray diffraction and the microstructure of the obtained composite powder was studied by electron microscopy.     

Synthesis of PMN pyrochlore free ceramics via a modified mixed oxide method

A modified mixed oxide method which is based on a two step reaction sintering process was designed to obtain single phase PMN ceramics. In this regard, pyrochlore phase formation during calcination process at different calcination temperatures was studied to determine the best soaking temperature for the first step in the specified method. In other words, the calcination temperature in which the least pyrochlore phase produced was chosen as the first step soaking temperature. The results showed that by utilizing this new method, single phase PMN ceramics with a high relative density of 98% can be synthesized successfully using conventional mixed oxide starting materials.     

Effect of grain refinement on the microstructure and tensile properties of thin 319 Al castings

The structural examinations and tensile properties of thin-section Al castings (319 Al alloy) have been investigated by applying a pattern with different cross sections (2–12 mm). Al–5Ti–1B and Al–5Zr grain refiners were added to the molten Al alloy to produce different levels of Ti (0.01%, 0.05%, 0.1% and 0.15%) and Zr (0.05%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5%) in the castings. From macrostructural studies, it was found that Al–5Zr is less effective in grain refining of 319 alloy in comparison with Al–5Ti–1B master alloy. The optimum levels of grain refiners were selected for determination of tensile properties. T6 heat treatment was applied for selected specimens before tensile testing. Further structural results also showed that thinner sections are less affected by grain refiners. This observation was found to be in a good agreement with tensile test results, where tensile properties of the base and grain refined alloys did not show considerable differences in thinner sections (<6 mm).