A new hybrid simulated annealing-based genetic programming technique to predict the ultimate bearing capacity of piles

Engineering with Computers - The aim of this research is to develop three soft-computing techniques, including adaptive-neuro-fuzzy inference system (ANFIS), genetic-programming (GP) tree-based,...     

Effect of melt filtration on porosity formation in Sr-modified A356 aluminium alloy

A major concern in Sr-modification is the increased tendency for microporosity formation in the alloy. The effects of melt filtration and Sr-modification on porosity content have been investigated. A significant effect of melt filtration on the reduction of porosity in Sr-modified samples is that the inclusion content of Sr- modified melts is higher than that in an unmodified melt. In an attempt to understand the types of inclusions in Sr-modified A356 melts that cause pore formation, samples have been studied by scanning electron microscopy. It was found that the exposure time of the melt in an oxidising atmosphere affects the oxidation behaviour and the inclusion types of Sr-modified melts. In the cases where the melt was not held for a long time in the oxidising atmosphere, Al₂O₃ films and particles played a significant role, while the Sr- containing oxides did not take part in pore formation. At relatively short holding times, the surface oxide layer of a melt of A356 alloy consisted of Al₂O₃ and Al₂O₃.MgO but was found to contain no detectable SrO. However, intermetallic compound Al₂Si₂Sr was found to be present and it is tentatively proposed that it has role in pore formation. When the melt was held for a long time in an oxidising atmosphere, more than 50% of the surface oxide layer consisted of SrO-containing spinels. IJCMR/460     

Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity

In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value.     

Design of very thin wide band absorbers using modified local best particle swarm optimization

A method of using particle swarm optimization (PSO) algorithm to design electromagnetic absorber is presented. To demonstrate effectiveness of the PSO algorithm three different design cases are optimized. To reduce the local minimum traps, a modified local search strategy is employed. Each design problem is optimized using genetic algorithm (GA) and four variants of PSO algorithms, namely global PSO (gbest), local PSO (lbest), comprehensive learning PSO (CLPSO), and modified local PSO (MLPSO). The results clearly show that the MLPSO is a robust, fast, and useful optimization tool for designing absorbers. A seven-layer absorber achieved by this method has reflection coefficient below 18.7 dB from VHF to 20 GHz.     

Precipitation of Sr-rich intermetallic particles and their influence on pore formation in Sr-modified A356 alloy

The nature of enhanced pore formation in Sr-modified A356 Al alloy melts has been investigated, leading to the observation of the precipitation of Sr-rich compounds on the wetted side of oxide films. Scanning electron microscopy of casting surfaces showed that the surface oxide film might be a good possible nucleation site of Sr-rich compounds. The observation of internal pores using secondary electron microscopy and X-ray microanalysis mapping showed precipitation of Sr-rich compounds on the wetted side of the oxide films in most pores. The possibility of Sr-rich intermetallics being nucleated on oxide films was assessed by determining their planar disregistry factor; good matching planes were found between Al₂Si₂Sr intermetallics and γ-Al₂O₃ and spinel oxide films. The crystallographic alignment revealed in scanning electron microscope (SEM) images also corroborates an epitaxial relationship. Mechanisms by which Sr in Al-Si alloys may contribute to the formation of porosity are discussed.     

Influence of modification, solidification conditions and heat treatment on the microstructure and mechanical properties of A356 aluminum alloy

The effects of casting thickness, modification and heat treatment on the microstructure and mechanical properties of A356.2 alloy have been investigated. Experiments were conducted with unmodified, Sr-modified (0.02% Sr) and Sb-modified (0.2% Sb) on both sand cast test bars with various thicknesses (from 3 to 9 mm) and permanent mold cast test bars.The microstructural changes associated with these treatments have been studied by optical metallography, scanning electron microscopy (SEM) and image analysis.The tensile properties of all samples were determined and the relationship between cooling rate, modification and heat treatment has been investigated.The results show that modification has a beneficial effect on microstructure and improves the mechanical properties of the alloy. Modification has a major role in controlling the kinetics of the spheroidisation of silicon particles during heat treatment. Tensile properties improved more with heat treatment than with modification or cooling rate.Antimony is effective on mechanical properties at higher solidification rates, while Strontium is more effective at lower solidification rates.     

Cholinergic dependence of a cortical neuronal mechanism that supports Pavlovian eyeblink conditioning

Mucin glycoproteins play a key role in the normal function of the airway epithelium. We examined the expression of mucin genes, MUC3, 4, 5AC, 5B, 6, 7, and 8 in human fetal tissues to establish the localization and age of onset of expression of each mucin gene during human development. We detected expression of MUC4, 5AC, 5B, and 7 in the mid-trimester airway epithelium but did not detect expression of MUC3, 6, or 8. MUC4 was expressed in the trachea and large airways in the majority of cells in the airway epithelium. Expression of MUC5AC was only seen in individual goblet cells in the trachea, while MUC5B was expressed in the surface epithelium of the trachea at 13 wk but was largely restricted to submucosal glands by 23 wk of gestation.     

Fatigue characterization and modeling of 30CrNiMo8HH under multiaxial loading

Fatigue of 30CrNiMo8HH steel alloy has been studied thoroughly. Uniaxial cyclic tension-compression, cyclic torsion, proportional tension-torsion, and non-proportional tension-torsion at various strain ratios have been considered. Tests were performed at standard laboratory conditions on solid and tubular specimens machined from an actual driveline component. Fractography was conducted on the tested samples to investigate the fatigue mechanisms involved. Under torsion, large numbers of early micro cracks were found to emanate from the sample's surface, with a few propagating into very long longitudinal cracks. In biaxial tests, cracks tend to propagate into the gauge reducing the cross section area. A strain energy density fatigue parameter has been employed for life prediction of the material under uniaxial and biaxial loading. The life prediction method is based on two different cracking mechanisms that agree with the observed cracking mechanisms in torsion and biaxial loading of 30CrNiMo8HH steel alloy studied here. Energy-based properties are obtained and the predicted lives are compared to experimental results. The results obtained agree well with experiments.     

Synthesis and investigation of anchored copper (II) complexes within MCM-41 as selective catalysts for epoxidation of olefins

In the present study, preparation, characterization and catalytic activity of encapsulated copper (II) complexes within MCM-41 were investigated. The mesoporous molecular sieve MCM-41 was synthesized and grafted with 3-(trimethoxysilyl)-1-propanethiol to give a thiol modified material (MCM-41-S). The prepared material successively was reacted with acrylic acid and acrylonitrile to give AA-MCM-41 and AN-MCM-41, respectively. Using hexamethyldisilazane and copper (II) chloride, copper (II) complexes in the cavities of MCM-41 (Cu-AA-MCM-41 and Cu-AN-MCM-41) were prepared. The presence of copper (II) complex on the surfaces of host matrix and the structure of prepared catalyst is investigated by FT-IR, inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (XRD) and BET nitrogen adsorption–desorption methods. The catalytic activities of the catalysts were studied in epoxidation of olefins. The results showed that activities of the prepared catalysts (Cu-AA-MCM-41 and Cu-AN-MCM-41) and their selectivity to corresponding epoxides were more than those of MCM-41. In addition, the synthesized heterogeneous catalysts were truly reusable.     

Taguchi robust design to optimize synthesis of lead oxalate nano-disks

Disk-shaped lead oxalate nanoparticles were synthesized via sol-precipitation in aqueous media without any surfactant, template or catalyst. Significance of reaction conditions such as: lead and oxalate concentrations, flow rate of reagent addition and temperature of reactor on diameter of synthesized lead oxalate disk-shaped particles were investigated and optimized. The participation of the studied variables in the particle size control of lead oxalate was quantitatively evaluated by analysis of variance. The results showed that lead oxalate nano-disks can be synthesized via controlling effective procedure parameters. Under optimum conditions, disk shaped nano-sized lead oxalate particles with two dimensions (95 nm diameter and 35 nm thickness) were synthesized. The structure and morphology of the lead oxalate nano-disks obtained under optimum conditions of synthesis process were characterized by scanning electron microscopy, X-ray diffraction, infrared spectroscopy and thermal analysis techniques. The Thermal analysis of the nanoparticles obtained under optimum conditions indicates that the main thermal degradation of the nano-disks occurs in the temperature range of 310–380 °C; while, submicron particles decomposed exothermally in more wider temperature range of 320–430 °C.