Application of adaptive neuro-fuzzy technique and regression models to predict the compressive strength of geopolymer composites

This article introduces an adaptive network-based fuzzy inference system (ANFIS) model and two linear and nonlinear regression models to predict the compressive strength of geopolymer composites. Geopolymers are highly complex materials which involve many variables which make modeling its properties very difficult. There is no systematic approach in the mix design for geopolymers. The amounts of silica modulus, Na₂O content, w/b ratios, and curing time have a great influence on the compressive strength. In this study, by developing and comparing parametric linear and nonlinear regressions and ANFIS models, we dealt with predicting the compressive strength of geopolymer composites for possible use in mix-design framework considering the mentioned complexities. ANFIS model developed by generalized bell-shaped membership function was recognized the best approach, and the prediction results of linear and nonlinear regression models as empirical methods showed the weakness of these models comparing ANFIS model.

     

A comprehensive analytical solution of macromolecular transport within an artery

Macromolecule transport within an artery is investigated and a comprehensive analytical solution is presented. The transport within the lumen and the arterial wall are coupled. Arterial wall is modeled as a four-layer porous wall. The layers are all treated as macroscopically homogeneous porous media. The volume-averaged porous media equations are employed to solve for transport through the porous arterial layers. Staverman filtration coefficient is incorporated to account for selective permeability of each porous layer to macromolecules. The problem encompasses complex interfacial transport phenomena involving various porous–porous as well as porous–fluid interfaces. The method of matched asymptotic expansions is employed to solve for the fluid flow field and species concentration distributions. For comparison purposes, the physiological and transport parameters associated with each porous layer are obtained from the literature. The analytical results are in excellent agreement with previous numerical studies. The results presented in this work provide the first comprehensive analytical solution representing arterial transport phenomena.     

A Cell‐Based Distributed‐Coordinated Approach for Network‐Level Signal Timing Optimization

This article develops an efficient methodology to optimize the timing of signalized intersections in urban street networks. Our approach distributes a network‐level mixed‐integer linear program (MILP) to intersection level. This distribution significantly reduces the complexity of the MILP and makes it real‐time and scalable. We create coordination between MILPs to reduce the probability of finding locally optimal solutions. The formulation accounts for oversaturated conditions by using an appropriate objective function and explicit constraints on queue length. We develop a rolling‐horizon solution algorithm and apply it to several case‐study networks under various demand patterns. The objective function of the optimization program is to maximize intersection throughput. The comparison of the obtained solutions to an optimal solution found by a central optimization approach (whenever possible) shows a maximum of 1% gap on a number of performance measures over different conditions.     

Blood and milk neutrophil chemiluminescence and viability in primiparous and pluriparous dairy cows during late pregnancy,around parturition and early lactation

Extensive studies have shown the polymorphonuclear leukocytes (PMN) dysfunction inextricably links to parturition. To investigate the effect of parity on PMN function, phorbol 12-myristate 13-acetate (PMA) stimulated luminol-amplified chemiluminescence (CL) and viability of blood and milk PMN were investigated in primiparous and pluriparous dairy cows during periparturient period. The CL kinetics of blood and milk PMN and hematological profiles were also assessed. Milk PMN CL was always lower than blood PMN CL. Blood and milk PMN CL and milk PMN viability were significantly higher in primiparous cows throughout the study. Blood PMN CL in pluriparous cows showed a sharper decrease. Both in pluriparous and in primiparous cows, minimal blood PMN CL appeared at periparturient day (PPD) 2. After PPD 7, blood PMN CL recovery rate was faster in primiparous cows. Milk PMN CL was minimal at PPD 2 in both groups. Whereas no changes were observed in blood PMN viability, the viability of milk PMN in primiparous cows was substantially higher than in pluriparous cows. The number of circulating eosinophils and immature neutrophils was substantially higher in primiparous cows throughout the study. The CL kinetics of blood PMN at PPD -2 and 2 and of milk PMN at PPD 2 exhibited different responses to PMA, with higher intensity and durability, peaking and subsiding more slowly in primiparous dairy cows. The pronounced reduction in PMN CL and viability in milk PMN of pluriparous cows may be involved in the underlying mechanisms that make these animals more susceptible to periparturient infectious diseases.     

Enhanced ductility and tensile properties of hybrid montmorillonite/cellulose nanowhiskers reinforced polylactic acid nanocomposites

Montmorillonite (MMT)/cellulose nanowhiskers (CNW) reinforced polylactic acid (PLA) hybrid nanocomposites were prepared by solution casting. CNW were isolated from microcrystalline cellulose using a chemical swelling method. An initial study showed that the optimum MMT content, for mechanical properties, in a PLA/MMT nanocomposite is five parts per hundred parts of polymer (phr). Various amounts of CNW were added to the optimum formulation of PLA/MMT to produce PLA/MMT/CNW hybrid nanocomposites. FT-IR analysis indicated the formation of some polar interactions, resulting in enhanced tensile properties of the hybrid nanocomposites. The highest tensile strength for the hybrid nanocomposites was obtained for a 1 phr CNW content. Young’s modulus was also found to increase with an increasing CNW content. Interestingly, the strain to failure (or ductility) of the hybrid nanocomposites increased significantly from ~10 to ~90 % with the addition of 1 phr CNW. This increase in ductility was proposed to be due to the nucleation of crazes and the formation of shear bands in the PLA.     

Computational plasticity of mixed hardening pressure-dependency constitutive equations

In the present study, two semi-implicit schemes, based on the exponential maps method, are derived for integrating the pressure-sensitive constitutive equations. In spite of the fact that the consistent tangent operator is necessary to preserve the quadratic rate for the asymptotic convergence of the Newton-Raphson solution in the finite element analyses, there exists no derivation of this operator for the exponential-based integrations of the pressure-sensitive plasticity in the literature. To fulfill this need, the algorithmic tangent operators are extracted for the new semi-implicit as well as the former exponential-based integrations. Moreover, for the accurate integration presented by Rezaiee-Pajand et al. (Eur J Mech A Solids 30:345–361, 2011), the consistent tangent operator is obtained. Eventually, all the investigations are assessed by a broad range of numerical tests.     

Study of Separation Behavior of Activated and Non-Activated MOF-5 as Filler on MOF-based Mixed-Matrix Membranes in H<Subscript>2</Subscript>/CO<Subscript>2</Subscript> Separation

In this study, cubic and tetragonal structures of MOF-5 (C-MOF-5 and T-MOF-5) were successfully synthesized, characterized and incorporated into cellulose acetate (CA) polymer matrix in the range of 6, 9 and 12 wt % to fabricate mixed matrix membranes (MMMs). The effects of smaller pore size of T-MOF-5 and more ZnO molecules in T-MOF-5, on the H₂ and CO₂ permeation properties of C-MOF-5/CA and T-MOF-5/CA MMMs were investigated. The all novel MMMs were prepared using the solution casting method and characterized by FTIR, TGA and SEM. SEM images as well as results of FTIR and TGA analyses confirmed good adhesion between both MOF-5s and CA matrix. Addition of both C-MOF-5 and T-MOF-5 into the CA improved the gas transport properties of the CA, especially in H2 separation. The H₂/CO₂ selectivity continued the increasing trend at 9 wt % and did not significantly reduce even at 12 wt % due to good adhesion between both MOF-5s and CA. The highest H₂/CO₂ selectivity was obtained at 12 and 9 wt % loading of C-MOF-5 and T-MOF-5, respectively. By changing the filler from C-MOF-5 to T-MOF-5, the increasing and reducing of adsorption site of H₂ and CO₂ (respectively), and also reducing in pore size, caused the appearance of H₂ permeability to not change much but the CO2 permeability to reduce. Accordingly, the H₂/CO₂ selectivity in all T-MOF-5/CA MMMs is higher than that in all C-MOF-5/CA MMMs. According to obtained results, the activated MOFs (i.e., C-MOF-5 in this study) are not always the best choices for separation process.     

Curing behavior,thermal, and mechanical properties of epoxy/polyamic acid based on 4,4′-biphtalic dianhydride and 3,3′-dihydroxybenzidine

Different synthesis routes were studied to obtain 4,4′-biphtalic dianhydride/3,3′-dihydroxybenzidine polyimide precursors (polyamic acids [PAAs]) with different inherent viscosities (IVs) and imidization degrees. The synthesized PAAs were introduced as a thermoplastic modifier into an epoxy (EP) resin. Different loadings of PAA were used to investigate the curing behavior, heat resistance, and mechanical properties. The onset curing temperature of the EP by adding 20 wt% PAA diminished by around 15°C. Thermogravimetric analysis revealed that the initial and 10 wt% weight loss temperature for EP with 5 wt% PAA improved by 13°C and 7.7%, respectively. Further, the results of tensile and plane-strain fracture toughness tests indicated that as the amount of PAA increased, the strength and toughness of EP decreased. These improvements were due to the high heat resistance and mechanical properties of PI precursor introduced into the EP, which formed a three-dimensional structure together. The interlaminar shear strength (ILSS) of the system experienced a reduction; however, after adding 2 phr nanosilica to the system containing PAA with average IV and imidization degree, ILSS showed 4.4% increment.     

A new expression for spherical aerosol drag in slip flow regime

A 3D simulation study for an incompressible slip flow around a spherical aerosol particle was performed. The full Navier–Stokes equations were solved and the velocity jump at the gas–particle interface was treated numerically by imposition of the slip boundary condition. Analytical solution to the Stokesian slip flow past a spherical particle was used as a benchmark for code verification, and excellent agreement was achieved. The simulation results showed that in addition to the Knudsen number, the Reynolds number affects the slip correction factor. Thus, the Cunningham-based slip corrections must be augmented by the inclusion of the effect of Reynolds number for application to Lagrangian tracking of fine particles. A new expression for the slip correction factor as a function of both Knudsen number and Reynolds number was developed. The particle total drag coefficient was also correlated against Re and Kn over the range of gas–particle relative speeds yielding the incompressible slip flow from the Stokesian regime up to the threshold of compressibility. Inclusion of gas slip on the particle surface enhances the accuracy of particle drag force prediction up to 40.9% in the range of 0.01<Kn<0.1 and 0.125<Re<20 compared to the no-slip continuum drag values.