Sharif Digital Repository

The local buckling behavior of perfect/defective and single/multi-walled carbon nanotubes (CNTs) under axial compressive forces has been investigated by the molecular dynamics approach. Effects of different types of defects including vacancy and Stone-Wales (SW) defects and their configurations on CNTs with different chiralities at room temperature are studied. Results show that defects largely reduce the buckling stress and the ratio of immediate reduction in buckling compressive stress of the defective CNT to the perfect one, but have little influence on their compressive elastic modulus. SW defects usually reduce the mechanical properties more than vacancy defects, and zigzag CNTs are... 

In this study, Li2O-TiO2-P2O5-x(Fe2O3) (x = 0, 2.5, 5 and 7.5 weight part) glass and glass-ceramics were synthesized through conventional melt-quenching method and subsequently heat treatment. Glass samples were studied by UV–visible spectroscopy and crystallized samples were characterized by differential thermal analysis, X-ray diffractometry and field emission scanning electron microscopy. Besides, electrical properties were examined according to the electrochemical impedance spectroscopy techniques. Experimental optical spectra of the Fe2O3-doped glasses revealed strong UV absorption band in the range of 330–370 nm, which were attributed to the presence of Fe3+ ions. The major crystalline... 

One of the important parts of each transformer is core. It is made from multilayer silicon steel sheets. Silicon steel has high magnetic permission, high electrical resistance and minimum hysterics loss. In different metal forming process, lubrication is done for reducing friction effects. In this research, effect of 3 different type lubricants, mineral material (castor oil), organic material (glycerol), and semi organic material (paraffin) with and without additive (graphite) is investigated. Also, effect of 2 industrial lubricants (suds and motor oil) is compromised with above lubricants. Results show the best lubricant for second cold rolling of silicon steel is semi organic (paraffin)... 

In this article, free vibration behavior of a rotating nano/microcircular plate constructed from functionally graded magneto-elastic material is simulated with the first-order shear deformation theory. For the sake of comparison, the nonlocal elasticity theory and the modified couple stress theory are employed to implement the small size effect in the natural frequencies behavior of the nano/microcircular plate. The governing equations of motion for functionally graded magneto-elastic material nano/microcircular plates are derived based on Hamilton’s principle; comparing the obtained results with those in the literature, they are in a good agreement. Finally, the governing equations are... 

This review investigated the efficiency and mechanism of per- and polyfluoroalkyl substances (PFASs) removal using advanced oxidation processes. Boron-doped diamond (BDD) electrodes in the electrochemical oxidation process are considered one of the ideal anode materials for the oxidation of PFAS compounds due to their high oxidation power with weak electrode-hydroxyl radical interactions. The degradation of PFAS by the combined process of foam fractionation combined with BDD electrochemical oxidation treatment showed that the overall degradation of long-chain PFAS was 77% against 22% of short-chain PFAS in the leachate water treatment plant. The experimental data revealed that photochemical... 

This review investigated the efficiency and mechanism of per- and polyfluoroalkyl substances (PFASs) removal using advanced oxidation processes. Boron-doped diamond (BDD) electrodes in the electrochemical oxidation process are considered one of the ideal anode materials for the oxidation of PFAS compounds due to their high oxidation power with weak electrode-hydroxyl radical interactions. The degradation of PFAS by the combined process of foam fractionation combined with BDD electrochemical oxidation treatment showed that the overall degradation of long-chain PFAS was 77% against 22% of short-chain PFAS in the leachate water treatment plant. The experimental data revealed that photochemical... 

Two novel heterogeneous hybrid catalysts were successfully synthesized using octa-aminopropyl polyhedral oligomeric silsesquioxane hydrochloride salt (OA-POSS) and ionic liquids, followed by immobilization of Cu and Ag nanoparticles. The obtained hybrid catalysts, Cu@POSS-ILs and Ag@POSS-ILs, were characterized using FT-IR, SEM, EDX, TEM, XRD and TGA. Catalytic studies demonstrated that Cu@POSS-ILs was an excellent catalyst for click reaction in aqueous medium. Furthermore, Ag@POSS-ILs was also exhibited to be an active catalyst for 4-nitrophenol (4-NP) reduction. Simple preparation and easy catalysts recovery and recyclability of Cu@POSS-ILs and Ag@POSS-ILs for at least 3 and 6 runs,... 

In this work, for the first time, we presented a novel design strategy to fabricate a new type of Octa-aminopropyl polyhedral oligomeric silsesquioxane hydrochloride salt (OA-POSS)-based Alg/PAAm DN gels, consisting of PAAm gel as the first chemical network and Alg/OA-POSS gel as the second chemical-physical network. Incorporation of OA-POSS nanoparticles with various feed ratio into the second network not only led to form strong coordination interactions but also in comparison to the other Alg/PAAm gels demonstrated superior mechanical properties. pH, temperature, contact time and salt effects parameters were studied on the swelling and dye removal properties of the synthesized DN hybrid... 

Aluminum matrix in situ nanocomposite was produced by one to six passes friction stir processing (FSP) with pre-placed Fe3O4 nanoparticles (15-20 nm). Microstructure studies showed that solid-state reactions between the aluminum matrix and Fe3O4 particles during the process led to in situ formation of Al3Fe and Al5Fe2 in the stir zone. Initial Fe3O4 as well as Al-Fe intermetallic compounds (IMCs) particles were homogeneously dispersed in a fine grain matrix after six passes of FSP. Hardness and ultimate tensile strength of the composites were increased 64 and 27%, respectively, compared to the base metal. The reasons were studied in the light of reinforcing particles distribution, formation... 

An economic order quantity (EOQ) model with payment in advance is developed to purchase highprice raw materials. A joint policy of replenishments and pre-payments is employed to supply the materials. The rate of demand and lead time are taken to be constant and it is assumed that shortage does not occur in the cycles. The cycle is divided into three parts; the first part is the time between the earlier replenishment-time to the next order-time (to), the second part is the period between to to a payment-time (tk) and the third part is the period between tk to the next replenishment-time. At the start of the second part (to), α% of the purchasing cost is paid. The (1-α)% remaining purchasing... 

The reaction kinetics and chemical equilibrium of the reversible catalytic hydrolysis reaction of a methyl acetate to acetic acid and methanol using a strongly acidic ion exchange resin catalyst named Amberlyst 15 were studied. To investigate the different behavior of Amberlyst 15 in the adsorption of reactants and product species, the equilibrium behavior of binary non-reactive liquid mixtures, consisting of one reactant and one product were studied experimentally. The Langmuir model was used to describe the equilibrium condition, quantitatively. Then the employed model was compared with the more complicated thermodynamic models to describe the equilibrium between the catalytic polymer... 

An efficient, green, novel and rapid vortex-assisted dispersive solid-phase extraction (VADSPE) technique was used for the preconcentration and determination of trace levels of Cu2+ followed by flame atomic absorption spectrometry. Graphene oxide (GO) was synthesized from graphite and then modified by pectic acid (poly-d-galacturonic acid, PA) to synthesize the pectic acid–graphene oxide (PA-GO) nanocomposite. The Fourier transform infrared spectrophotometry, field emission scanning electron microcopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis were used to characterize the synthesized GO-PA nanocomposite. By using VADSPE technique, PA-GO was used as an adsorbent for... 

Poly(2-acrylamido-2-methyl propane sulphonic acid) crosslinked with N,N′-methylene bisacrylamide catalyses efficiently the three component condensation reaction of an aromatic aldehyde, β-ketoester and urea in refluxing ethanol to afford the corresponding dihydropyrimidinones in high yield  

The theory of compressive sampling involves making random linear projections of a signal. Provided signal is sparse in some basis, small number of such measurements preserves the information in the signal, with high probability. Following the success in signal reconstruction, compressive framework has recently proved useful in classification, particularly hypothesis testing. In this paper, conventional random projection scheme is first extended to the image domain and the key notion of concentration of measure is closely studied. Findings are then employed to develop a 2D compressive classifier (2D-CC) for sparse images. Finally, theoretical results are validated within a realistic... 

Spectral manifold learning techniques have recently found extensive applications in machine vision. The common strategy of spectral algorithms for manifold learning is exploiting the local relationships in a symmetric adjacency graph, which is typically constructed using k-nearest neighborhood (k-NN) criterion. In this paper, with our focus on locally linear embedding as a powerful and well-known spectral technique, shortcomings of k-NN for construction of the adjacency graph are first illustrated, and then a new criterion, namely k/K-nearest neighborhood (k/K-NN) is introduced to overcome these drawbacks. The proposed criterion involves finding the sparsest representation of each sample in... 

Foaming and crystallisation behaviours of compacted glass powders based on a diopside glass-ceramic composition were investigated using the sintering route. The foaming agent was 2 wt.% SiC particles. The effect of PbO on the foaming ability of glasses was investigated. The results showed that the addition of PbO not only improved the foaming ability, by improving the wettability of the glass-SiC particles but also increased the crystallisation temperature and widened the temperature interval between the dilatometric softening point and the onset of crystallisation. The glass-SiC wetting angle was decreased from 85°for the lead-free glass, to 55°for the glass that contains 15 wt.% PbO  

The extensive use of photocatalysis to address environmental concerns, energy production, and organic transformations has attracted attention in recent decades. The SnO/CSO photocatalytic materials were fabricated through a single-step hydrothermal method and comprehensively characterized using a muti-technique approach to demonstrate the physicochemical, morphological, and electronic features. According to the photocatalytic experiments, the SnO/CSO could remove >96 % of acid blue 92 (AB92) azo dye under optimum conditions, with rate constant 2.37 × 10−2 min−1. Furthermore, the photocatalyst significantly outperformed commercial TiO2 (P25), in reducing CO2 to CO and CH4 with a production... 

(Chemical Equation Presented) New 2-aryl-4-chloro-3-hydroxy-1H-indole-5,7- dicarbaldehydes were synthesized in three steps from acetophenone derivatives. By oxidation of acetophenones to aryl glyoxals using selenium dioxide and condensation with acetylacetone in the presence of ammonium acetate in water 3-acetyl-5-aryl-4-hydroxy-2-methyl-1H-pyrrols were obtained. 2-Aryl-4-chloro-3-hydroxy-1H-indole-5,7-dicarbaldehydes were synthesized via Vilsmeier-Haack reaction of pyrrole derivatives in moderate yields  

Alcohols have been successfully converted into their corresponding carbonyl compounds using hydrogen peroxide catalyzed by lithium chloride on montmorillonite K10. Clay supported lithium chloride can be recovered after using as catalyst for oxidation of alcohols. The future runs according to this procedure showed no considerable decrease in the reaction yield and catalyst effect  

At room temperature, zirconium oxychloride (ZrOCl2· 8H2O) efficiently catalyzes the direct Mannich-type reaction of a variety of in situ generated aldimines using aldehydes and anilines with ketones in a three-component reaction under solvent-free conditions. The reaction proceeds rapidly and affords the corresponding β-amino ketones in good to high yields with good to excellent stereoselectivities. The catalyst can be recycled for subsequent reactions without any appreciable loss of efficiency. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006