Microwave absorption properties of double‐layer nanocomposites based on polypyrrole/natural rubber

Thin flexible double‐layer microwave absorbers have been fabricated based on polypyrrole (PP)/natural rubber (NR) nanocomposites and their reflection loss characteristics were studied in the range of 8–18 GHz. The PP‐NR matrix was prepared from PP and NR in the ratio of 15:85. The polymers used in this work not only serve as the matrix but also improve the microwave absorption properties. The first layer or impedance matching layer which is comprised of graphite, Fe₃O₄, and TiO₂ nanoparticles in PP‐NR transmits the electromagnetic (EM) wave without reflection. The second layer which is made up of PP‐NR filled with Fe₃O₄ disperses the EM wave energy. The design of a double‐layer nanocomposite is a method to match the wave impedance, enhance wave absorption ability, and broaden the absorption frequencies. In order to achieve high absorption properties, the EM parameters such as permittivity, permeability, and thickness were controlled precisely according to quarter‐wave plate. The morphology, absorption properties, scattering parameters, thermal and wetting characteristics of double‐layer nanocomposites were investigated. The minimum reflection loss (R_L) was ?32 dB at 12.1 GHz and the absorbing bandwidth in which the R_L < ?10 dB was 9 GHz for optimum specimen with 2 mm thickness. For this specimen, the contact angle was equal to 118.7° with water as the liquid. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46565.     

Using adaptive neuro-fuzzy inference system (ANFIS) for proton exchange membrane fuel cell (PEMFC) performance modeling

In this paper, an adaptive neuro-fuzzy inference system (ANFIS) is used for modeling proton exchange membrane fuel cell (PEMFC) performance using some numerically investigated and compared with those to experimental results for training and test data. In this way, current density I (A/cm²) is modeled to the variation of pressure at the cathode side P_C (atm), voltage V (V), membrane thickness (mm), Anode transfer coefficient α_an, relative humidity of inlet fuel RH_a and relative humidity of inlet air RH_c which are defined as input (design) variables. Then, we divided these data into train and test sections to do modeling. We instructed ANFIS network by 80% of numerical-validated data. 20% of primary data which had been considered for testing the appropriateness of the models was entered ANFIS network models and results were compared by three statistical criterions. Considering the results, it is obvious that our proposed modeling by ANFIS is efficient and valid and it can be expanded for more general states.     

Assessment of Factors Affecting the Continuing Performance of Firefighters’ Protective Clothing: A Literature Review

There has been some research into the level of damage and changes to important properties of firefighters’ protective clothing after exposure to conditions such as elevated temperature and ultra violet radiation. However, at this time, the results are not comprehensive enough to develop a standard procedure to estimate the remaining useful life of firefighters’ protective clothing. There is also a need to develop non-destructive techniques to evaluate clothing, for most tests used to evaluate properties of clothing are destructive, and visual cues cannot completely assess the level of deterioration of the properties of thermal protective fabrics. In this paper, major factors that affect the continuing performance of firefighters’ protective clothing and their effects on the service life of the clothing are reviewed. Some non-destructive methods which have been employed in different studies to evaluate the degradation of physical properties of firefighters’ protective clothing are also described, along with statistical and probabilistic methods for estimating the useful life of materials. Suggestions for future research, which will assist fire departments in determining the level of damage to clothing, and estimating its remaining useful life are also discussed.     

Reply to Discussion on “Empirical methods for determining shaft bearing capacity of semi-deep foundations socketed in rocks”

Semi-deep foundations socketed in rocks are considered to be a viable option for the foundations in the presence of heavy loads imposed by high-rise buildings and special structures, due to the low settlement and high bearing capacity. In this study, the unconfined compressive strength (UCS) and rock mass cuttability index (RMCI) have been applied to investigating the shaft bearing capacity. For this purpose, a comprehensive database of 178 full-scale load tests is compiled by adding a data set (n = 72) collected by Arioglu et al. (2007) to the data set (n = 106) presented in Rezazadeh and Eslami (2017). Using the database, the applicability and accuracy of the existing empirical methods are evaluated and new relations are derived between the shaft bearing capacity and UCS/RMCI. Moreover, a general equation in case of unknown rock types is proposed and it is verified by another set of data (series 3 in Rezazadeh and Eslami (2017)). Since rock-socketed shafts are supported by rock mass (not intact rock), a reduction factor for the compressive strength is suggested and verified in which the effect of discontinuities is considered using the modified UCS, based upon RMR and RQD to consider the effect of the rock mass properties.     

On the modeling of a piezoelectrically actuated microsensor for simultaneous measurement of fluids viscosity and density

This paper deals with the analysis of a novel micro–electro-mechanical (MEM) fluid density and viscosity sensor. The proposed sensor consists of a micro-beam and a sensing micro-plate immersed in a fluid. In order to actuate longitudinally the micro-beam and micro-plate, the sensor includes a pair of piezoelectric layers bonded to the upper and lower surfaces of the micro-beam and subjected to an AC voltage. The coupled governing partial differential equations of longitudinal vibration of the micro-beam and fluid field have been derived. The obtained governing differential equations with time varying boundary conditions have been transformed to an enhanced form with homogenous boundary conditions. The enhanced equations have been discretized over the beam and fluid domains using a Galerkin based reduced order model. The dynamic response of the sensing plate for different piezoelectric actuation voltages and different exciting frequencies has been investigated. The effects of viscosity and density of fluids and geometrical parameters of the sensor on the response of the sensing plate have been studied.     

Three-dimensional numerical analysis of proton exchange membrane fuel cell

A full three-dimensional, non-isothermal computational fluid dynamics model of a proton exchange membrane fuel cell (PEMFC) with both the gas distribution flow channels and the membrane electrode assembly (MEA) has been developed. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region are developed and numerically solved using a finite volume based computational fluid dynamics technique. In this research some parameters such as Oxygen consumption and fuel cell performance according to the variation of porosity, thickness of gas diffusion layer, and the effect of the boundary conditions were investigated in more details. Numerical results shown that the higher values of gas diffusion layer porosity improve the mass transport within the cell, and this leads to reduce the mass transport loss. The gas diffusion layer thickness affects the fuel cell mass transport. A thinner gas diffusion layer increases the mass transport, and consequently the performance of the fuel cell. Furthermore, the study of boundary conditions effects showed that by insulating the bipolar surfaces, hydrogen and oxygen consumption at the anode and cathode sides increase; so that the fuel cell performance would be optimized. Finally the numerical results of proposed CFD model are compared with the available experimental data that represent good agreement.     

Floor tile glass-ceramic glaze for improvement of glaze surface properties

Simultaneous improvement of surface hardness and glossiness of floor tile glaze, without changing its firing temperature, was the main purpose of the present paper. Thus, various glazes in the system of CaO–MgO–SiO₂–Al₂O₃–ZrO₂ were prepared and their crystallization behaviors within a fast firing cycle were investigated. With increasing amounts of calcium and magnesium oxides to base glass, the optimum glass-ceramic glaze was obtained. The results showed that with increasing of CaO and MgO part weights in frit, the crystallization peak temperature was gradually decreased and the intensities of diopside and zirconium silicate were increased. The comparison of micro hardness for the optimum glass ceramic glaze derived in this work with a traditional one used in floor tile industries indicates an improvement of 21%. It was found that the glaze hardness not only depend on the amount and type of crystalline phases, but also on the residual glass composition. Furthermore, it was observed that the glaze micro hardness is only slightly affected by thermal expansion mismatch of body and glaze.     

Stability analysis of an electrostatically actuated out of plane MEMS structure

In the present research, stability and static analyses of microelectromechanical systems microstructure were investigated by presenting an out-of-plane structure for a lumped mass. The presented model consists of two stationary electrodes in the same plane along with a flexible electrode above and in the middle of the two electrodes. The nonlinear electrostatic force was valuated via numerical methods implemented in COMSOL software where three-dimensional simulations were performed for different gaps. The obtained numerical results were compared to those of previous research works, indicating a good agreement. Continuing with the research, curves of electrostatic and spring forces were demonstrated for different scenarios, with the intersection points (i.e., equilibrium points) further plotted. Also drawn were plots of deflection versus voltage for different cases and phase and time history curves for different values of applied voltage followed by introducing and explaining pull-in and pull-out snap-through voltages in the system for a specific design. It is worth noting that, at voltages between the pull-in and pull-out snap-through voltages, the system was in bi-stable state. Based on the obtained results, it was observed that the gap between the two electrodes and the applied voltage play significant roles in the number and type of the equilibrium points of the system.

     

ZnAl2O4 Nanoparticles as Efficient and Reusable Heterogeneous Catalyst for the Synthesis of 12-phenyl-8,12-dihydro-8,10-dimethyl-9H-naphtho[1′,2′:5,6] pyrano[2,3-d] pyrimidine-9,11-(10H)-diones Under Microwave Irradiation

A simple and one-pot synthesis of naphthopyranopyrimidines is reported by the three-component condensation reaction of aldehydes, β-naphthol, and 1,3-dimethylbarbituric acid using ZnAl₂O₄ nanoparticles under microwave irradiation. This flexible and nano-catalytic procedure showed good recyclability and provides a clean condensation reaction in a short reaction time.     

Fabrication and characterization of electrospun fibrous nanocomposite scaffolds based on poly(lactide‐co‐glycolide)/poly(vinyl alcohol) blends

Tissue engineering involves the fabrication of three‐dimensional scaffolds to support cellular in‐growth and proliferation. Ideally, the scaffolds should be similar to the native extracellular matrix (ECM). Electrospun polymer nanofibrous scaffolds are appropriate candidates for ECM mimetic materials since they mimic the nanoscale properties of ECM. Electrospun polymer nanocomposites based on poly(lactide‐co‐glycolide) (PLGA)/poly(vinyl alcohol) (PVA) and organically modified montmorillonite (OMMT) were prepared by a solution intercalation technique followed by electrospinning. The morphology of fibrous scaffolds based on these nanocomposites was investigated using scanning electron microscopy. The scaffolds showed highly porous structure within the nanofibres of diameters ranging from 400 to 700 nm. X‐ray diffractometry gave evidence of good dispersion of the OMMT in the blends with exfoliated morphology. Measurements of the water uptake and water contact angle of the fibrous scaffolds indicated significant improvement in the hydrophilicity of the scaffolds. Evaluations of the mechanical properties and unrestricted somatic stem cell culture of the electrospun fibrous nanocomposite scaffolds revealed that the PLGA90/PVA10/1.5% OMMT and PLGA90/PVA10/3% OMMT samples are the most useful from the tissue engineering application viewpoint. Copyright © 2010 Society of Chemical Industry