An immune algorithm for hybrid flow shop scheduling problem with time lags and sequence-dependent setup times

This paper deals with hybrid flow shop scheduling problems considering time lags and sequence-dependent setup times which have wide application in real-world problems. Most of the researches on operations scheduling problems have ignored time lags. A mathematical model is presented which is capable of solving the small size of the considered problem in a reasonable time. Since these problems are strongly NP-hard, a meta-heuristic algorithm based on the immune algorithm is developed. The optimization criterion considered in this paper is the minimization of the makespan. Numerical experiments are used to evaluate the performance and effectiveness of the proposed algorithm. The results of the proposed algorithm are compared with the presented mathematical programming model and a benchmark algorithm. Computational results indicate that the proposed algorithm can produce near-optimal solutions in a short computational time. Moreover, it can be applied easily in real factory conditions and for large-sized problems.     

Guided local buckling (GLB) theory for short braces

According to recent earthquake experiences and experimental results, the local buckling is the most important parameter for limiting the ductility of short braces and prevents earthquake energy absorption in larger drifts. A new theory is introduced to prevent harmful effects of local buckling and use it as an energy absorption device in braced frames. According to this theory oblique stiffeners are provided inside braces section and it is expected to divide lateral drift of the system to smaller deflections inside stiffeners intervals. As much as number of local buckling along braces increases, more energy will be absorbed and the fracture life of the sections increases considerably. This theory is supported by half-scale experimental results and numerical modeling. The obtained results represent uniform and stable energy absorption and reasonable system ductility.     

Mechanical properties of hybrid fiber reinforced lightweight aggregate concrete made with natural pumice

The purpose of this study is to improve the ductility of pumice lightweight aggregate concrete by incorporating hybrid steel and polypropylene fibers. The changes in mechanical properties and also bulk density and workability of pumice lightweight aggregate concrete due to the addition of hybrid steel and polypropylene fibers have been studied. The properties were investigated include bulk density and workability of fresh concrete as well as compressive strength, flexural tensile strength, splitting tensile strength and toughness of hardened concrete. Nine concrete mixtures with different volume fractions of steel and polypropylene fibers were tested. A large increase in compressive and flexural ductility and energy absorption capacity due to the addition of steel fibers was observed. Polypropylene fibers, on the other hand, caused a minor change in mechanical properties of hardened concrete especially in the mixtures made with both steel and polypropylene fibers. These observations provide insight into the benefits of different fiber reinforcement systems to the mechanical performance of pumice lightweight aggregate concrete which is considered to be brittle. These results provide guidance for design of concrete materials with reduced density and enhanced ductility for different applications, including construction of high-rise, earthquake-resistant buildings.     

DIAL–phoswich hybrid system for remote sensing of radioactive plumes in order to evaluate external dose rate

Radioactive pollutants which are released into the atmosphere are known to present a hazard to human health; therefore they must be identified and well protected. Here, an improved remote sensing system is investigated for monitoring radioactive plumes released into the atmosphere from nuclear sites. It is based on the combination of DIAL technique with a phoswich detector array. The DIAL, using a tunable UV/Vis laser, measures the concentration of the radionuclide and the plume distance, whereas the phoswich detects characteristic hard X/γ ray emissions. Here, we have shown the ability of a hybrid system for the prompt identification and quantification of the effluents containing the uranium radionuclide, using the parameters of uranium such as absorption cross-section, absorption spectrum and density.     

Effects of cement size distribution on capillary pore structure of the simulated cement paste

The evolution of tricalcium silicate (C₃S) microstructure during hydration is tri-dimensionally simulated based on an “Integrated Particle Kinetics Model”. The hydration degree, the contact surfaces between the hydrated particles, the hydraulic radius and the capillary pore size distribution of the simulated cement paste at various degrees of hydration are calculated. Three examples of the C₃S microstructure development with different size distributions are presented. The effects of the cement size distribution on pore structure of cement paste are demonstrated and the results are discussed. In these examples, the cement size distribution varies between 3–40, 5–40 and 10–40 μm, respectively.     

Exploring the effects of non-solvent concentration, jet-stretching and hot-drawing on microstructure formation of poly(acrylonitrile) fibers during wet-spinning

The simultaneous effects of non-solvent concentration in the spinning dope, jet-stretching and hot-drawing on porosity, morphology development and mechanical properties of wet-spun poly(acrylonitrile) fibers were studied. Addition of non-solvent to the spinning dope increased dope viscosity, the entanglement density of the polymeric solution and the number of entanglements per chain. Drawability of the as-spun fiber depended on the number of entanglements per polymer chain. Therefore, addition of non-solvent improved or spoiled drawability of the wet-spun fibers based on the concentration of the initial spinning dope. Hot-drawing and jet-stretching did not affect the fraction of nanovoids but shifted their size distribution towards smaller values. However, hot-drawing was more effective in reducing the overall porosity of the fibers in comparison with jet-stretching. Fiber tenacity increased when overall porosity decreased. Finally, strength-diameter correlation showed good agreement with the Griffith’s theory.     

Investigation of the Effect of Tungsten Substitution on Microstructure and Abrasive Wear Performance of In Situ VC-Reinforced High-Manganese Austenitic Steel Matrix Composite

Particulate VC-reinforced high-manganese austenitic steel matrix composites with different vanadium and tungsten contents were synthesized by conventional alloying and casting route. Microstructural characterizations showed that the composites processed by in situ precipitation of the reinforcements were composed of V₈C₇ particulates distributed in an austenitic matrix. It was observed that addition of tungsten to austenite increases work-hardening rate of subsurface layer during pin-on disk wear test. The maximum abrasive wear resistance was achieved at tungsten content equal to 2 wt pct. However, excessive addition of tungsten promoted the formation of W₃C phase and reduced the abrasive wear resistance because of decrease in distribution homogeneity and volume fraction of the reinforcing VC particles.     

Characterization of the Influence of Tool Pin Profile on Microstructural and Mechanical Properties of Friction Stir Welding

In this study, the effect of tool pin profile on mechanical properties, microstructural, material flow, thermal and strain distributions of friction stir welding of AA5083 was investigated. Two different tools with cylindrical and square pin profiles were employed to produce the welds. A numerical model is developed for investigating the effect of tool pin profiles on material flow, thermal and strain distributions based on thermo-mechanically coupled rigid-viscoplastic 3D FEM. Then, optical microscopy was employed to characterize the microstructures features of the weld. Finally, tensile test was carried out to characterize the mechanical properties of the weld. Obtained results showed that square pin profile produced finer grain structure and higher ultimate strength relative to cylindrical one. These results may be related to higher eccentricity, larger stirred zone, and higher temperature in the weld zone of the square pin profile.     

Indicators for evaluation of progress in thermal stabilization reactions of polyacrylonitrile fibers

Using different indices calculated from Fourier Transform Infrared Spectroscopy (FTIR), X‐ray Diffraction (XRD), and Differential Scanning Calorimetry (DSC) spectra, progress in stabilization reactions of three different commercial grade polyacrylonitrile (PAN) fibers is calculated. From each analysis technique quantitative indices are computed which could assess in some particular reactions. Combination of these indices gives further information about the progress of stabilization reactions which cannot be concluded from single indices. The results show that different indices are not fully consistent with each other, depending on the analysis technique and the changes they assess. The advantages and disadvantages of each index are investigated and practical indices are identified which can be used to design the optimum stabilization process. In addition, by combination of some indices it is possible to separate the temperature ranges in which reactions occur in amorphous or crystalline regions. This approach can be used to design appropriate stretching process during stabilization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40343.