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121.
Mohammad Hosein Bina Mostafa Jamali Morteza Shamanian Hamed Sabet 《The International Journal of Advanced Manufacturing Technology》2014,75(9-12):1371-1379
In this work, the effect of weld current on joining capability of austenitic stainless steel (AISI 304) and ferritic stainless steel (AISI 430) sheets with application of resistance spot welding process was investigated. Macrostructure, microstructure, microhardness, tensile shear strength, and failure mode of welded materials were evaluated for different weld currents. The values of weld current were 2.5, 3.75, and 5 kA. It was found that when the weld current increased, the nugget size and the weld strength were increased. Two distinct failure modes including interfacial and pullout were observed during tensile shear test. Finally, an adequate weld current was obtained. 相似文献
122.
Mohamed Mostafa Saied 《电力部件与系统》2014,42(11):1143-1151
Abstract—This article proposes a new approach to study the frequency response and the transient analysis of power transformer windings. For improved accuracy, the suggested model includes, among other equivalent circuit elements, the mutual magnetic couplings between any winding turn and all others. This implies that the equivalent inductance of any considered turn will be a location-dependent parameter. Accordingly, the winding will be analyzed as a non-uniform transmission line. Through the application of a recursive circuit reduction technique, a closed-form Laplace s-domain analytical expression for the winding's input impedance can be obtained for any neutral treatment. The resulting expression can be used to determine the winding's series and parallel resonance frequencies. The s-domain expression for the input impedance, in connection with the numerical inverse Laplace transform, will be utilized for determination of the winding's time-domain transient response for any input voltage or current time waveform. Accuracy increases with the assumed number of winding sections, which can be even increased to the actual number of turns, limited only by the available computation resources. The results of case studies are in good agreement with those available in the literature using the time-domain solution of the simultaneous differential equations in the state variables. 相似文献
123.
Radial heat transfer in laminar pipe flow is characterized by a wide temperature distribution over the pipe cross‐section. We use a validated Computational Fluid Dynamics (CFD) model to show that the superimposition of a transverse vibration on the steady laminar flow of a Newtonian fluid moving in a pipe with an isothermal wall, generates considerable chaotic flow and radial mixing which result in a large enhancement in wall heat transfer as well as a considerably more uniform radial temperature field. Transverse vibration also causes the temperature profile to develop very rapidly in the axial direction reducing the thermal entrance length by a large factor. These effects are dependent on vibration amplitude and frequency, and fluid viscosity. © 2010 American Institute of Chemical Engineers AIChE J, 2011 相似文献
124.
Mehdi Ranjbar Masoud Salavati-Niasari S. Mostafa Hosseinpour-Mashkani 《Journal of Inorganic and Organometallic Polymers and Materials》2012,22(5):1093-1100
In the present work, ZnAl2O4 nanoparticles have been synthesized with the aid of Zn(OAc)2·2H2O and Al(NO3)3·9H2O as starting reagents in the presence of microwave irradiation. Besides, the effect of preparation parameters such as microwave power and irradiation time on the morphology and particle size of products was studied by SEM images. The as-prepared ZnAl2O4 nanoparticles were characterized extensively by techniques like XRD, TEM, SEM, FT-IR, PL, and EDS. Photoluminescence studies of the ZnAl2O4 nanoparticles displayed quantum confinement behavior with band gap of 3.2 eV. The XRD studies showed that pure orthorhombic ZnAl2O4 nanoparticles have been produced after calcination. 相似文献
125.
Auob Safari Jaber Safdari Hossein Abolghasemi Mostafa Forughi Mahnaz Moghaddam 《Chemical Engineering Research and Design》2012
In this research work, the volumetric overall mass transfer coefficient based on continuous-phase (Koca) and axial dispersion coefficients of phases (Ec, Ed) in a pilot Pulsed Packed Liquid Extraction Column (PPLEC) have been studied using plug flow model (PFM) and axial dispersion model (ADM). Experiments have been carried out using standard systems of water/acetone/toluene and water/acetone/n-butyl–acetate. Values of Koca evaluated by ADM are greater than those of PFM by about 20% indicating that the axial mixing lowers the performance of PPLEC. It was found that the drop-size distribution is the main cause of the axial mixing in PPLEC. Increase in dispersed phase flow rate (Qd), increases all Koca, Ed and Ec and the minimum values of both Ed and Ec and the maximum values of Koca are in pulse intensity ranges of 0.8–1 cm/s. Finally, three empirical correlations are proposed for the prediction of these parameters which are in good agreement with the experimental data. 相似文献
126.
M. Mostafa 《Radiochemistry》2009,51(3):313-320
The radioactivity of 131I as well as of the other radioisotopes, obtained from different nuclear reactions occurring during irradiation of natural
tellurium including different decay branches, at the end of irradiation and after different cooling times was calculated.
The optimum cooling time is 90 h.
Published in Russian in Radiokhimiya, 2009, Vol. 51, No. 3, pp. 275–281.
The text was submitted by the author in English. 相似文献
127.
Polyaniline (PAn) and poly(alkyl substituted anilines) were synthesized in aqueous media by chemical polymerization of alkyl substituted aniline in presence of ammonium peroxydisulphate as an oxidant. The products were investigated in terms of morphology, chemical structure, and mechanism of polymerization with scanning electron microscope (SEM), transmission electron microscopy (TEM), fourier transform infrared (FTIR), and UV–visible spectroscopy (UV–vis), respectively. Results indicated that physicochemical properties of poly(alkyl substituted anilines) depend on substituent groups bonded to N-position. In general, alkyl-substituted PAn have similar chemical and optical properties to parent PAn and it seems that the substituted PAn follow the same polymerization mechanism as reported for PAn. The prepared polymers were then tested for the antibacterial properties against Gram-negative bacteria: Escherichia coli (E. coli). The antibacterial properties were assessed by measuring the zones of inhibition. The antimicrobial results showed clearly that PAn and poly(alkyl substituted anilines) exhibited excellent antibacterial activity against the growth of E. coli microorganism. 相似文献
128.
For SCR of NO the study of Ir/Al2O3 solids shows the importance of the activation procedure under mixtures containing CO (NO–C3H6–CO–O2 or NO–CO–O2). The selective reductant remains C3H6, however. The activation goes with an iridium particles sintering without Ir loss. 相似文献
129.
Hamid Ahmadian Mostafa Nourmohammadi 《International Journal of Machine Tools and Manufacture》2010,50(11):998-1005
In machine dynamics the tool point frequency response functions (FRFs) are employed to predict the stable machining conditions. In this paper, a combined analytical–experimental substructuring procedure is proposed to determine the tool point FRFs for different holder–tool configurations. The method employs the measured spindle-machine FRFs and analytical models of the tool and the holder to predict the tool tip FRFs for different sets of tools and holders mounted on the machine spindle without the need for repeated experimental measurements. Distributed joint interfaces are used to couple the three-component model of the machine. The machine tool tip FRFs with different tool–holder combinations are obtained assuming the clamping conditions at joint interfaces remain unchanged. An experimental case study is provided to demonstrate the applicability of the proposed method in dynamic modeling of machine tool. 相似文献
130.
S Mohammad M Mortazavi Hassan Arabi Gholamhossein Zohuri Saeid Ahmadjo Mehdi Nekoomanesh Mostafa Ahmadi 《Polymer International》2010,59(9):1258-1265
Catalysts have a major role in the polymerization of olefins and exert their influence in three ways: (1) polymerization behaviour, including polymerization activity and kinetics; (2) polymer particle morphology, including bulk density, particle size, particle size distribution and particle shape; and (3) polymer microstructure, including molecular weight regulation, chemical composition distribution and short‐ and long‐chain branching. By tailoring the catalyst structure, such as the creation of a bridge or introducing a substituent on the ligand, metallocene catalysts can play a major role in the achievement of desirable properties. Kinetic profiles of the metallocene catalyst used in this study showed decay‐type behaviour for copolymerization of ethylene/α‐olefins. It was observed that increasing the comonomer ratio in the feedstock affected physical properties such as reducing the melting temperature, crystallinity, density and molecular weight of the copolymers. It was also observed that the heterogeneity of the chemical composition distribution and the physical properties were enhanced as the comonomer molecular weight was increased. In particular, 2‐phenyl substitution on the indenyl ring reduced somewhat the melting point of the copolymers. In addition, the copolymer produced using bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl2) catalyst exhibited a narrower distribution of lamellae (0.3–0.9 nm) than the polymer produced using bisindenylzirconium dichloride catalyst (0.5–3.6 nm). The results obtained indicate that the bis(2‐PhInd)ZrCl2 catalyst showed a good comonomer incorporation ability. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and type of substituent in the catalyst. Copyright © 2010 Society of Chemical Industry 相似文献