Sharif Digital Repository

A simple, atom economy and highly efficient green protocol have been developed for synthesis of bis(indolyl)alkane by the reaction of indole derivatives with aldehydes and ketones in the presence of small amount of the heteropoly acids in water. © 2007 Elsevier B.V. All rights reserved  

The effects of relaxation and nanocrystallization on magnetic properties of (Fe0.5Co0.5)73.5Si13.5B 9Nb3Cu1 ribbons have been investigated. Ribbons were melt-spun at wheel speed of 38 m/s and then annealed at different temperatures. The results indicated that the relaxation processes shift the Curie temperature of amorphous phase to the higher temperatures. It was also found that through crystallization phenomena the saturation magnetization increases due to the super-exchange between Fe and Co atoms in the crystalline phase. A slight variation in magnetization was observed at ~700 °lC during heating due to the ordering transition in FeCo system. At early stage of crystalline phase... 

Incorporation of the first gradient of strain, in addition to the strain itself, into the strain energy density of an elastic solid leads to Mindlin's first strain gradient theory, which is useful for examination of size effect as well as other mechanical phenomena at the nano-scale. For isotropic elastic solids, the first strain gradient theory, in addition to the two independent Lamé constants, gives rise to five new material constants which in turn reduce to two material parameters, ℓ1 and ℓ2 with dimension of length. The evaluation of these parameters, however, has posed serious challenges, both experimentally and theoretically. In this work ab initio method is used to compute the... 

In this study, empirical constitutive relations of materials with different crystalline structures through severe plastic deformation are introduced. Here, for each material, an optimized empirical relation is chosen by fitting some empirical relations on the results achieved from a dislocation- based constitutive model. In this work, four modes of empirical relations are fitted on the results of modified Estrin-Toth-Molinari-Brechet constitutive model for four materials with different crystalline structures (Al, Cu, Ta, and Zr). The obtained relations for the materials can be usable in commercial finite element codes  

In this study, a hydrophilic metal-organic framework (MOF) was applied to improve the performance of a cellulosic membrane for forward osmosis (FO) desalination application. The characterization results confirmed that the MOF particles existed within the matrix of the modified membrane. The MOF loading led to adjustment of the membranes in terms of overall porosity, pore inter-connectivity and hydrophilicity. These features caused an improvement in the pure water permeability (72%) and reduce the structural parameter of the modified membrane to 136 μm. The FO water flux of the modified membrane enhanced by about 180% compared to an unmodified membrane, without decreasing its selectivity. FO... 

An oxidative pressure acid leaching process was investigated for the extraction of Ni/Co/Cu/Zn metal values from base metal smelter slags. The process is applicable to smelting furnace dump slags, as well as to mid-stream converter slags. In addition to the economical advantages, extracting the base metal values from the dump slags produces an environmentally benign residue. To produce high level of extraction for the metal values, it is necessary to have the slag in crystalline structure. This, in turn, requires cooling the molten smelter slags sufficiently slowly during solidification. It was shown that if the same slags are quenched in water thereby producing an amorphous structure, the... 

We have studied the phase formation of a CoSi2 layer by solid-state reaction of ternary Co/WxTa(1-x)/Si(1 0 0) systems. The effect of cosputtered WxTa(1-x) nanometric interlayers, with different values of x (0, 0.25, 0.5, 0.75 and 1), on the degree of texturing of a CoSi2 layer and disilicide formation of the refractory metals has been investigated. The annealed samples, in a temperature range of 400-1000 °C, were analysed by x-ray diffraction, sheet resistance measurement, scanning electron microscopy, and energy-dispersive x-ray techniques. Using W0.25Ta0.75 and W interlayers, the best (1 0 0) texture of the CoSi2 layer with a thermal stability in the range of 900-1000 °C was produced. In... 

Analytical analysis of straight single-line defect optical waveguides in two dimensional photonic crystals based on expanding electromagnetic fields in terms of Hermite polynomials is reported. This novel electromagnetic field expression is substituted in Helmholtz equation, a new set of linear ordinary differential equations with variable coefficients are obtained, and by employing differential transfer matrix method; defect modes, i.e. the guided modes propagating in the line defect waveguide, are analytically derived. The validity of the results obtained by applying the proposed approach are confirmed by comparing them to those derived by using finite difference time domain method  

In this work, we propose a combined photochemical-chemical method that enables us to grow CdS nanoparticles with ångström precision. CdS nanoparticles were formed through a photo-induced reaction between CdSO 4 and Na2S2O3. Thioglycerol (C 3H8O2S) was used as the capping agent. Fine tuning of the size was subsequently carried out by controlling the pH of the solution. Optical absorption spectroscopy was mainly used to monitor the process of particle formation, and to measure the bandgap and size. X-ray diffraction spectra confirmed the optical sizes and demonstrated crystalline nanoparticles. In the presence of the capping agent there was a dark growth that was completely dependent on the pH... 

The influence of electron beam irradiation on neat nylon 6 was manifested by formation of molecular branches deduced from increase in melt flow index and intrinsic viscosity. Crosslinking of nylon 6 was carried out using electron beam irradiation in presence of triallyl cyanurate (TAC). The crosslinked samples showed a high level of gel content. At a given dose, increasing the TAC level from 1% to 3% increased the gel content of the samples slightly and correspondingly decreased the percent of water absorption. The melting temperature decreased with increasing the dose and the TAC level. All samples containing TAC showed some decrease in crystallinity under exposure to electron beam. The... 

PVDF/nanoclay nanocomposites were prepared via melt mixing method. The intercalated dispersion of the nanoclay in PVDF matrix was confirmed by XRD. According to FTIR, DSC and XRD results, the presence of nanoclay facilitated transition from α-to-β crystalline phase. Electron beam irradiation decreased the melting point of the nanocomposites. The decrease in melting point of the nanocomposites was about 11 C at 500 kGy. The crystallinity of nanocomposites increased at an irradiation dose of 100 kGy and decreased at higher irradiation doses. The extent of crosslinking of the nanocomposites increased significantly with irradiation up to 300 kGy. The nanoclay intensified the increase in yield... 

Properties of melt processed polyamide 66 (PA66)/multiwalled carbon nanotube composite were first characterized experimentally. The experimental results exhibited the formation of crystalline layer around the nanotubes and a considerable enhancement in mechanical properties by incorporation of multiwalled carbon nanotube up to 1 wt%. Mechanical properties were analyzed in terms of structural parameters using micromechanical models proposed in this study. It was suggested that the mechanical properties were greatly dominated by crystalline layer and nanotube length. It was also deduced that the melt mixing process caused a significant nanotube breakage restricting further enhancement of... 

Simple synthesis of silver doped TiO2 nanostructured layers by micro arc oxidation process is reported for the first time. The layers consisted of anatase and rutile phases whose characteristic XRD-peaks shifted toward lower diffraction angles when compared to the pure micro arc oxidized TiO 2 layers. Silver-doping was confirmed by XPS technique. The anatase phase crystalline size was determined as 27.6 and 21.8 nm for the layers grown under the voltages of 350 and 500 V. Employing a UV-Vis spectrophotometer, a red shift in the absorption edge of the layers was observed when silver was incorporated into the titania lattice  

Crystallographic texture considerably affects the formability of crystalline materials. In this paper, the effects of BCC ideal rolling fibers—including α, ε, η, γ, and ξ fibers—on the sheet formability are numerically studied. The simulations are based on the numerical procedure developed by the authors in [1] in which a rate dependent crystal plasticity model along with the power law hardening are employed in a user material subroutine to model the behavior of crystalline materials. In order to determine FLD—in a M-K type approach—second-order derivative of sheet thickness variations with respect to time is used as necking criterion. The calculated FLDs of the fibers are compared with each... 

A metal-organic framework [Co3(BDC)3(DMF)2(H2O)2] was synthesized and structurally characterized. X-ray single crystal analysis revealed that the framework contains a 2D polymeric chain through coordination of 1,4-benzenedicarboxylic acid linker ligand to cobalt centers. The polymer crystallize in monoclinic P21/n space group with a=13.989(3) Å, b=9.6728(17) Å, c=16.707(3) Å, and Z=2. The polymer features a framework based on the perfect octahedral Co-O6 secondary building units. The catalytic activities of [Co3(BDC)3(DMF)2(H2O)2]n for olefins oxidation was conducted. The heterogeneous catalyst could be facilely separated from the reaction mixture, and reused three times without significant... 

Antibacterial activity of tungsten oxide nanorods/microrods were studied against Escherichia coli bacteria under visible light irradiation and in dark. A two-step annealing process at temperatures up to 390 °C and 400-800 °C was applied to synthesize the tungsten oxide nanorods/microrods on tungsten foils using KOH as a catalyst. Annealing the foils at 400 °C in the presence of catalyst resulted in formation of tungsten oxide nanorods (with diameters of 50-90 nm and crystalline phase of WO3) on surface of tungsten foils. By increasing the annealing temperature up to 800 °C, tungsten oxide microrods with K2W6O19 crystalline phase were formed on the foils. The WO3 nanorods showed a strong... 

Modified versions of the Zener drag equation were obtained by evaluating a non-random distribution of incoherent ceramic particles in a nano-crystalline material. Analytical investigation of particle-boundary correlation indicates that the limiting grain size would be proportional to fV -1/3 for fV larger than 2.96%. The limiting grain size can be obtained by a combination of random and non-random Zener drag pressure in the case of volume fractions smaller than 2.96%  

The molecular-dynamics analysis is presented for 3D compaction simulation of nano-crystalline metals under uniaxial compaction process. The nano-crystalline metals consist of nickel and aluminum nano-particles, which are mixed with specified proportions. The EAM pair-potential is employed to model the formation of nano-particles at different temperatures, number of nano-particles, and mixing ratio of Ni and Al nano-particles to form the component into the shape of a die. The die-walls are modeled using the Lennard-Jones inter-atomic potential between the atoms of nano-particles and die-walls. The forming process is model in uniaxial compression, which is simulated until the full-dense... 

A series of reduced graphene oxide/ZnxCd1-xS (RGO/ZnxCd1-xS) nanocomposites (0 < x < 1) with different ratios of Zn/Cd were synthesized via a facile hydrothermal route under optimized experimental conditions and were carefully characterized by various techniques. Because very little is known about the morphology, specific surface area, and crystal phase effects of RGO/ZnxCd1-xS crystals on their photoresponsivity, field-emission scanning electron microscopy (FE-SEM), BET surface area analysis and X-ray diffraction (XRD) data were studied to investigate their effects on photoactivity. Based on the results, a crystal phase transition from a cubic phase in RGO/Zn0.9Cd0.1S to a hexagonal... 

A low cytotoxic metal–organic framework (MOF) UiO-66 (UiO stands for University of Oslo) and NH2-UiO-66, that showed high cell viability of HFF-2 via 3-(4, 5-dimethylthiazol-2-yl) 2, 5-diphenyl tetrazolium assay, was reported as an effective adsorbent (antidotal) agents. The structure of MOFs was confirmed by Fourier transform infrared, Field emission scanning electron microscopy (FESEM) and X-ray diffraction. Thermal behavior of MOFs was investigated using with thermogravimetric analyzer in nitrogen atmosphere to check the thermal stability. FESEM showed NH2-UiO-66 displayed symmetrical crystals with triangular base pyramid morphology, with the particle size around 100 nm and uniform size...