Stochastic flow-shop scheduling with minimizing the expected number of tardy jobs

In this research, minimizing the expected number of tardy jobs in a dynamic m machine flow-shop scheduling problem, i.e., $ {F_m}\left| {{r_j}\left| {{\text{E}}\left[ {\sum {{U_j}} } \right]} \right.} \right. $ is investigated. It is assumed that the jobs with deterministic processing times and stochastic due dates arrive randomly to the flow-shop cell. The due date of each job is assumed to be normally distributed with known mean and variance. A dynamic method is proposed for this problem by which the m machine stochastic flow-shop problem is decomposed into m stochastic single-machine sub-problems. Then, each sub-problem is solved as an independent stochastic single-machine scheduling problem by a mathematical programming model. Comparison of the proposed method with the most effective rule of thumb for the proposed problem, i.e., shortest processing time first rule shows that the proposed method performs 23.9 % better than the SPT rule on average for industry-size scheduling problems.     

Cobalt/copper-decorated carbon nanofibers as novel non-precious electrocatalyst for methanol electrooxidation

In this study, Co/Cu-decorated carbon nanofibers are introduced as novel electrocatalyst for methanol oxidation. The introduced nanofibers have been prepared based on graphitization of poly(vinyl alcohol) which has high carbon content compared to many polymer precursors for carbon nanofiber synthesis. Typically, calcination in argon atmosphere of electrospun nanofibers composed of cobalt acetate tetrahydrate, copper acetate monohydrate, and poly(vinyl alcohol) leads to form carbon nanofibers decorated by CoCu nanoparticles. The graphitization of the poly(vinyl alcohol) has been enhanced due to presence of cobalt which acts as effective catalyst. The physicochemical characterization affirmed that the metallic nanoparticles are sheathed by thin crystalline graphite layer. Investigation of the electrocatalytic activity of the introduced nanofibers toward methanol oxidation indicates good performance, as the corresponding onset potential was small compared to many reported materials; 310 mV (vs. Ag/AgCl electrode) and a current density of 12 mA/cm² was obtained. Moreover, due to the graphite shield, good stability was observed. Overall, the introduced study opens new avenue for cheap and stable transition metals-based nanostructures as non-precious catalysts for fuel cell applications.     

Cycloadditions of 1-Aza-2-azoniaallene Salts derived from coumarin and camphor

The 1-aza-2-azoniaallene salt 8 prepared from 3-acetyl coumarin via the hydrazone 6 and the (chloroalkyl)azo derivative 7 reacts with nitriles to afford the 3-(3-chromenyl)-1,2,4-triazolium salts 11a–d . With diisopropylcarbodiimide the triazolium salt 13 and with norborene a tricyclic pyrazolium salt 14 are obtained. Concurrent to these cycloadditions the by-product 12 is formed by intramolecular cyclization of the cumulene 8 . Similarly, the intramolecular cyclization product 18 is isolated as the sole product when the 1-aza-2-azoniaallene salt 17a (prepared from the ethyl carbazone of camphor by chlorination and treatment of the product 16a with SbCl₅) was treated with nitriles, carbodiimides or alkenes. In contrast, 1,2,4-triazolium salts 20a–c , 23c , respectively pyrazolium salts 20d–f , and 1,3,4-thiadiazolium salts 23a,b are obtained by reaction of the 1-aza-2-azoniaallene salt 17b with nitriles, respectively alkenes, alkynes, diisopropylcarbodiimide, and isothiocyanates. The constitutions of two of these products ( 20e, 23a ) were secured by X-ray structural analysis.     

Physiochemical characterizations of hydroxyapatite extracted from bovine bones by three different methods: Extraction of biologically desirable HAp

In the present study, subcritical water and alkaline hydrolysis methods are proposed methodologies for extraction of natural hydroxyapatite bioceramic from bovine bone. In these processes, the bovine bones powder were treated by high pressure water at 250 °C for 1 h and 25% (wt) sodium hydroxide at 250 °C for 5 h, respectively. Also the conventional calcination methodology has been utilized as well (T = 850 °C for 1 h). The obtained apatites from the three treatment processes have been characterized by powder X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT IR), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), electron scanning microscopy (SEM), energy dispersive X-ray analysis (EDX) and field emission scanning electron microscopy (FE SEM). FT IR and XRD results affirmed that both the proposed methods and the traditional one can eliminate the collagen and other organic materials present in the bovine bones. The physiochemical characterizations for the obtained apatites have proved that the subcritical water and the alkaline hydrolysis relatively preserve the carbonate content present in the biological apatite, so they yield carbonated hydroxyapatite which is medically preferable. While, the thermal process produces almost hydroxyapatite carbonate-free.     

Microwave Detection of Stress-Induced Fatigue Cracks in Steel and Potential for Crack Opening Determination

Abstract

Fatigue crack detection in metals is an important practical issue in many industries. In this paper the results of detecting fatigue cracks, using the dominant mode approach, employing flange-mounted, open-ended, rectangular waveguides at several microwave frequencies are presented. The goal of this investigation has been to demonstrate the capability of this approach for detecting stress-induced cracks under various static loads. In addition, a correlation between the features of the measured crack characteristic signals and crack opening has been sought. The results show that at all of the investigated frequencies, cracks from being nearly closed to having openings of up to 0.0508 mm are detected effectively. Furthermore, it is found that the interaction of the flange edge with a crack results in features that can be used to enhance crack detection robustness significantly (i.e., increased probability of detection). Several features associated with these measured crack characteristic signals are shown to correlate linearly with crack opening. Such simple correlations may then be used to estimate a crack opening closely after it has been detected using this approach. A complete discussion of the results is also provided in this paper.     

Characterization of the structural,magnetic and magnetocaloric properties of double perovskite La<Subscript>1.95</Subscript>Sr<Subscript>0.05</Subscript>BMnO<Subscript>6</Subscript> (B = Ni and Co)

An exhaustive study of structural, magnetic and magnetocaloric properties on La_1.95Sr_0.05BMnO₆ (B?=?Ni and Co) double perovskite were performed. The samples were prepared by the sol–gel method. The crystallographic structure was studied by the X-ray diffraction patterns and Rietveld refinement which revealed that all samples crystallize in a monoclinic structure with P2₁/n space group. The magnetic behaviors of these double perovskite have been studied in detail. For La_1.95Sr_0.05NiMnO₆, the M(T) curves exhibit double magnetization transition temperature at 68 K and 266 K which can be ascribed to Ni³⁺–O–Mn³⁺ and Ni²⁺–O–Mn⁴⁺ superexchange interaction, respectively. However, unique magnetic transition has been observed for the La_1.95Sr_0.05CoMnO₆ double perovskite at 210 K due to Co²⁺–O–Mn⁴⁺ superexchange interaction. A deep investigation based on the Landau Theory and Arrot analysis confirmed a second order ferromagnetic phase transition for both samples. Besides, the magnetocaloric behaviors of these new samples have been studied by analysis the magnetic entropy change. This latter reached maximum values of 1.01 and 1.35 J/kg/K for La_1.95Sr_0.05NiMnO₆ and La_1.95Sr_0.05CoMnO₆, respectively, under µ₀H?=?5 T. Moreover, the relative cooling power values for La_1.95Sr_0.05NiMnO₆ and La_1.95Sr_0.05CoMnO₆ are found to be 94 J/kg and 116 J/kg, respectively, under µ₀H?=?5 T. Based on the obtained ΔS_M data, we have also described the universal master curve for (ΔS_M/\(\Delta S_{M}^{{\hbox{max} }}\)) versus rescaled temperature to confirm the order magnetic phase transition. Interestingly, all the ΔS_M(T, H) data points are collapsed into a universal curve in the whole temperature range. The significant values of relative cooling power for both samples suggest that they might be an interesting candidate for exploring a new kind of magnetic refrigerants.     

Hierarchical TiO2/ZnO Nanostructure as Novel Non-precious Electrocatalyst for Ethanol Electrooxidation

Metal oxides have a higher chemical stability in comparison to metals,so they can be utilized as electrocatalysts if the activity could be enhanced.Besides the composition,the morphology of the nanostructures has a considerable impact on the electrocatalytic activity.In this work,zinc oxide nano branches-attached titanium dioxide nanofibers were investigated as an economic and stable catalyst for ethanol electrooxidation in the alkaline media.The introduced material has been synthesized by electrospinning process followed by hydrothermal technique.Briefly,electrospinning of colloidal solution consisting of titanium isopropoxide,poly(vinyl acetate) and zinc nanoparticles was performed to produce nanofibers embedding solid nanoparticles.In order to produce TiO_2 nanofibers containing ZnO nanoparticles,the obtained electrospun nanofiber mats were calcined in air at 600 °C.The formed ZnO nanoparticles were exploited as seeds to outgrow ZnO branches around the TiO_2 nanofibers using the hydrothermal technique at sub-critical water conditions in the presence of zinc nitrate and bis-hexamethylene triamine.The morphology of the final product,as well as the electrochemical measurements indicated that zinc nanoparticles content in the original electrospun nanofibers has a significant influence on the electrocatalytic activity as the best performance was observed with the nanofibers synthesized from electrospun solution containing 0.1 g Zn,and the corresponding current density was 37 mA/cm~2.Overall,this study paves a way to titanium dioxide to be exploited to synthesize effective and stable metal oxide-based electrocatalysts.