Application of extended quadrature method of moments for simulation of bubbly flow and mass transfer in gas‐liquid stirred tanks

In the present paper, two gas‐liquid stirred tanks, one agitated by a radial impeller and another by an axial impeller, are modelled using the open‐source computational fluid dynamic (CFD) package OpenFOAM (open source field operation and manipulation). The combined effect of the bubble break‐up and coalescence in the tank is considered by a population balance model (PBM) called extended quadrature method of moments (EQMOM). The three‐dimensional simulation is made using a multiple reference frame (MRF), a well‐established method for the modelling of mixers. Dispersed gas and bubble dynamics in the turbulent flow are modelled using the Eulerian‐Eulerian approach (E‐E) with mixture k‐epsilon turbulent model and the modified Tomiyama drag coefficient for the momentum exchange. The model is developed to predict the spatial distribution of gas phase fraction, Sauter mean bubble diameter (), number density function (NDF), dissolved oxygen (DO) evolution, and flow structure. The numerical results are compared with experimental data and a fair agreement is achieved. The results of the axial impeller are discussed based on four impeller rotational speeds with different volumetric mass transfer coefficients.     

A Dual Ring Connectivity Model for VANET Under Heterogeneous Traffic Flow

Vehicular ad-hoc network (VANET) is characterized as a highly dynamic wireless network due to the dynamic connectivity of the network nodes. To achieve better connectivity under such dynamic conditions, an optimal transmission strategy is required to direct the information flow between the nodes. Earlier studies on VANET’s overlook the characteristics of heterogeneity in vehicle types, traffic structure, flow for density estimation, and connectivity observation. In this paper, we have proposed a heterogeneous traffic flow based dual ring connectivity model to enhance both the message disseminations and network connectivity. In our proposed model the availability of different types of vehicles on the road, such as, cars, buses, etc., are introduced in an attempt to propose a new communication structure for moving vehicles in VANETl under cooperative transmission in heterogeneous traffic flow. The model is based on the dual-ring structure that forms the primary and secondary rings of vehicular communication. During message disseminations, Slow speed vehicles (buses) on the secondary ring provide a backup path of communication for high speed vehicles (cars) moving on the primary ring. The Slow speed vehicles act as the intermediate nodes in the aforementioned connectivity model that helps improve the network coverage and end-to-end data delivery. For the evaluation and the implementation of dual-ring model a clustering routing scheme warning energy aware cluster-head is adopted that also caters for the energy optimization. The implemented dual-ring message delivery scheme under the cluster-head based routing technique does show improved network coverage and connectivity dynamics even under the multi-hop communication system.     

Smart films based on bacterial cellulose nanofibers modified by conductive polypyrrole and zinc oxide nanoparticles

In this study, we synthesized novel films based on bacterial cellulose (BC), BC modified by polypyrrole (PPy), and a PPy–zinc oxide nanocomposite (BC–PPy–ZnO). The soft polymerization method at room temperature was used to obtain the BC–PPy and BC–PPy–ZnO films. The Combined D‐Optimal design was used to study the effects of the pyrrole monomer concentration, ZnO concentration, and polymerization time on the morphological, physical, color, and electrical conductivity properties of the films. Fourier transform infrared results reflected that some new interactions occurred between BC and PPy and PPy–ZnO. The X‐ray diffraction analysis showed that the crystalline behavior of the BC fiber was hindered because of the complete coating with the amorphous PPy particles. Scanning electron microscopy results show that the ZnO, PPy, and PPy–ZnO nanoparticles were placed between the BC fibers. PPy decreased the water vapor permittivity and total soluble matter percentage. Electrical conductivity studies of the synthesized BC–PPy–ZnO film showed that the film's electrical resistance was changed in different oxidation–reduction or volatile compounds media, so the results suggest that the BC–PPy–ZnO films could be used in antioxidative food active packaging and smart packaging. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46617.     

Biodegradable polypropylene/thermoplastic starch nanocomposites incorporating halloysite nanotubes

In this work, polypropylene/thermoplastic starch (PP/TPS) with and without halloysite nanotubes (HNTs) was prepared via melt mixing in order to obtain environmentally friendly plastics. PP‐grafted maleic anhydride (PP‐g‐MA) was used to improve the compatibility among the highly incompatible polymers. The mechanical characterization showed a reduction in the tensile properties of the polymer when TPS increased; however, HNT successfully compensated for some of the observed losses. The results from the thermogravimetric analysis (TGA) indicated that HNT is an efficient reinforcement for the thermal stability improvement. TPS caused an increase in the storage modulus (G′) and the complex viscosity (η*) which marks a change in the viscoelastic properties of the system. The scanning electron microscope (SEM) images showed the effective plasticization of starch and better dispersion of TPS in the presence of HNT. Some samples were also buried in the soil to measure their sustainability after their lifetime lapse. The results indicated that TPS improves the biodegradability of the PP/TPS system. PP considerably lowered the moisture uptake of TPS; nevertheless, HNT caused a slight increase in the moisture absorption. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45740.     

Preparation of alumina/polystyrene core-shell composite powder via phase inversion process for indirect selective laser sintering applications

Indirect selective laser sintering (SLS) is one of the promising additive manufacturing (AM) methods that can process conventionally difficult or even impossible materials such as ceramics. In this work, an innovative phase inversion technique is used to fabricate spherical alumina particles coated with a thin layer of polystyrene (PS). Then, indirect SLS is used to fabricate green parts from the 6 wt% PS coated alumina particles via a Nd:YAG laser. The assessed SLS process parameters were the scan speed, laser power, scan spacing, pulse frequency, and pulse width. The characterization of the AL₂O₃/PS core-shell composite particles was described using techniques including SEM (for morphology), FT-IR (for chemical bonding at the interfaces), TGA (for mass loss), and DSC (for glass transition temperature, T_g). 3D green parts were then fabricated using proper process parameters as a proof of the feasibility of using SLS technique for AL₂O₃/PS core-shell composite powder. The results showed that using a Nd:YAG laser with less absorption by alumina and PS provides greater penetration through a powder bed. In addition, the possibility of sound connections among particles in every direction was observed due to the uniformity of the coating process in spite of a minimal amount of binder. In addition, green part density measurements show high values compared to previously reported results.     

Effect of polyethylenimine addition and washing on stability and electrophoretic deposition of Co3O4 nanoparticles

In this work, the parameters of cobalt oxide suspension such as conductivity, zeta potential, particle size, stability, and finally the electrophoretic behavior of particles in the absence and presence of polyethylenimine (PEI) in acetone medium were investigated. Also, the effects of washing on the stability and electrophoretic deposition of Co₃O₄ were studied. Characterization of the obtained layer by optical microscopy revealed that there was no deposition in the suspension without PEI, while a uniform layer was formed in the presence of PEI additive. Scanning electron microscopy (SEM) results confirmed the uniformity of layer obtained in acetone using PEI additive. Moreover, SEM results demonstrated that more porous microstructures were obtained at longer deposition durations. The difference in the porosity of the layers, as indicated by the SEM micrographs, is attributed to increase in the deposition time.     

Modification of electrospun poly(L-lactic acid)/polyethylenimine nanofibrous scaffolds for biomedical application

In this study, modification of poly(L-lactic acid) (PLLA) electrospun nanofibrous scaffolds blending with polyethylenimine (PEI) in different blend ratios was performed. The sample with 85:15 blend ratio revealed most promising results, and was selected for further modification with gelatin. It was found that the presence of PEI could enhanced porosity, mechanical properties, surface/bulk hydrophilicity and also gelatin grafting density about five times with positive effect on cell behavior. The results indicated that the limitations of PLLA electrospun nanofibers for potential application as a functional tissue engineering scaffold (i.e., poor cell adhesion and necrosis of host tissues as a result of providing acidic environment while degradation) could be overcome through blending with PEI and grafting with gelatin.     

A Multiply Connected Belief Network approach for schedule risk analysis of metropolitan construction projects

Metropolitan construction projects may be distinguished from other types of projects due to their specific nature. Issues with regard to purchase of property obstacles, a lack of accurate layout drawings for some underground facilities and, therefore, following probable changes in designs make it vital to have specific studies on risk analysis of such engineering projects. However, conventional methods offered in literature of risk analysis fail to consider the interactional mechanisms of risks and their simultaneous occurrence. This paper exploits the Multiply Connected Belief Network approach in MATLAB environment to analyse the simultaneous occurrence of risk factors on schedule delay of a highway project. The method of inference is through Junction Tree Algorithm due to existence of multiply connections in the developed network of the project. The findings for schedule delay were tested in a different space using Monte Carlo simulation and had satisfactory results.     

Side-Channel Information Characterisation Based on Cascade-Forward Back-Propagation Neural Network

Traditional cryptanalysis assumes that an adversary only has access to input and output pairs, but has no knowledge about internal states of the device. However, the advent of side-channel analysis showed that a cryptographic device can leak critical information. In this circumstance, Machine learning is known as a powerful and promising method of analysing of side-channel information. In this paper, an experimental investigation on a FPGA implementation of elliptic curve cryptography (ECC) was conducted to explore the efficiency of side-channel information characterisation based on machine learning techniques. In this work, machine learning is used in terms of principal component analysis (PCA) for the preprocessing stage and a Cascade-Forward Back-Propagation Neural Network (CFBP) as a multi-class classifier. The experimental results show that CFBP can be a promising approach in characterisation of side-channel information.