Sharif Digital Repository

The globular structure of M2 high speed steel in the rolled - annealed and as cast conditions was investigated in the semisolid state. Metallographic observations resulted in globular austenite particles that were surrounded by a liquid phase. Dissolution of various carbides in the austenite phase at semisolid temperatures led to grain boundary liquation and formation of near-spherical solid grains in a liquid matrix. Therefore, at the semisolid state, the solid particles were free from carbides. MC-type and M6C-type eutectic carbides re-precipitated at the grain boundaries during cooling of the samples from the semisolid temperature. The variation of shape factor versus holding time and... 

Nickel and nickel-manganese alloy modified graphite electrodes (G/Ni and G/NiMn) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were employed. In CV studies, in the presence of methanol NiMn alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency upon the... 

A developed route to form TiO2 self cleaning coatings on polycarbonate substrates is reported. TiO2 coatings on plastics may find widespread application in auto and construction industries if possess desired photocatalytic and mechanical properties. A chemical surface treatment method was used to create hydrophilic groups on the surface. X-ray photoelectron spectroscopy showed the treatment led to the oxidation of surface groups. TiO2 deposition was based on wet coating using an anatase sol of TiO2 nanoparticles of 30 nm size. The sol was synthesized using a sol-gel route. A pre-coat of peroxotitanium complex was employed to improve adhesion and inhibit the substrate degradation. The coating... 

Ternary mesoporous nanocomposites of RGO/Fe3O4-ZnO were prepared successfully via hydrothermal technique. Fe3O4-ZnO core/shell nanoparticles were decorated on the surface of reduced graphene oxide platelet to improve charge separation efficiency and magnetic properties. The phase, microstructure and specific surface area of the prepared samples were determined via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy/selected area electron diffraction (TEM/SAED) and Brunauer–Emmett–Teller (BET) techniques. A vibrating sample magnetometer (VSM) was used for recording the magnetization hysteresis curves. The methylene blue (MB)... 

ZnO/CuO nanofibers, with different CuO concentrations, were fabricated by one-step electrospinning of the polymer precursor and annealing in air. Scanning electron microscopy (SEM) showed smooth and beadless morphology for the synthesized nanofibers, while X-ray diffraction (XRD) analysis revealed formation of hexagonal and monoclinic crystalline structure phases for ZnO and CuO nanofibers, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of CuO on the surface of ZnO nanofibers. For further confirming the formation of chemical bonds, Fourier transform infrared (FT-IR) spectroscopy was employed. The effect of Cu contents in the overall electronic band... 

High performance Fe-Gd-P tri-doped TiO2 nanoparticles (1 at% for each dopant) were successfully synthesized by a modified sol–gel method. Various analytical and spectroscopic techniques were carried out to determine the physicochemical properties of the prepared samples, including XRD, EDX, FESEM, BET, FTIR, XPS, PL, EIS and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activities of prepared samples were evaluated by photo degradation of methyl orange (MO) and 4-chlorophenol (4-CP) as model pollutants under visible light irradiation. Effects of each dopant on different properties of TiO2 nanoparticles were investigated. Results show that Gd and P doping enhances TiO2 surface... 

In this paper, a new visco-hyperelastic constitutive law for describing the rate dependent behavior of foams is proposed. The proposed model was based on a phenomenological Zener model: a hyperelastic equilibrium spring, which describes the steady-state, long-term response, parallel to a Maxwell element, which captures the rate-dependency. A nonlinear viscous damper connected in series to a hyperelastic intermediate spring, controls the rate-dependency of the Maxwell element. Therefore, the stress is the sum of equilibrium stress on the equilibrium spring and overstress on the intermediate spring. In hyperelastic theory stress is not calculated directly as in the case of small-strain, linear... 

Mononuclear nonheme iron containing systems are versatile and vital oxidants of substrate hydroxylation reactions in many biosystems, whereby the rate constant of hydroxylation correlates with the strength of the C-H bond that is broken in the process. The thermodynamic reason behind these correlations, however, has never been established. In this work results of a series of density functional theory calculations of substrate hydroxylation by a mononuclear nonheme iron(IV)-oxo oxidant with a 2 His/ 1Asp structural motif analogous to aketoglutarate dependent dioxygenases are presented. The calculations show that these oxidants are very efficient and able to hydroxylate strong C-H bonds,... 

Therapeutic fragmented antibodies show a poor pharmacokinetic profile that leads to frequent high-dose administration. In the current study, for the first time, a novel proline, alanine, serine (PAS) repeat sequence called PAS#208 was designed to extend the plasma half-life of a nanosized anti-vascular endothelial growth factor-A single-domain antibody. Polyacrylamide gel electrophoresis, circular dichroism, dynamic light scattering, and electrophoretic light scattering were used to assess the physicochemical properties of the newly designed PAS sequence. The effect of PAS#208 on the biologic activity of a single-domain antibody was studied using an in vitro proliferation assay. The... 

A numerical model for the deposition of silicon nitride using silane and ammonia mixture in a radio frequency plasma reactor has been developed. Plasma enhanced chemical vapor deposition process is simulated by combined analysis for the glow discharge, fluid flow and chemical reactions. The main goal is to investigate the effect of variations of the process parameters on the deposition rate, and uniformity of the resulting layer. The approach used is based on the theoretical partial differential equation models, without any empirical approximation of the critical data being used. Owing to the fact that the relevant equations are highly nonlinear, the discretization method is of great... 

A model for prediction of corrosion of mild steel in aqueous solutions containing carbon dioxide is proposed. In this model, formation of protective corrosion product is not yet considered, species concentration at the surface was calculated by using molecular diffusion phenomena and the diffusion equations were solved using the finite difference method. Calculated electrochemical currents at the steel surface may be used to determine the corrosion rate. The model was verified experimentally under atmospheric pressure and the effect of parameters, such as liquid velocity and pH, was investigated. The model can predict the electrochemical reaction rates when they were controlled by diffusion... 

The 1H-13C coupling constants of methyl α- and β-pyranosides of d-glucose and d-galactose have been measured by one-dimensional and two-dimensional 1H-13C heteronuclear zero and double quantum, phase sensitive J-HMBC spectra to determine a complete set of coupling constants (1JCH, 2JCH, 3JCH, 2JHH, and 3JHH) within the exocyclic hydroxymethyl group (CH2OH) for each compound. In parallel with these experimental studies, structure, energy, and potential energy surfaces of the hydroxymethyl group for these compounds were determined employing quantum mechanical calculations at the B3LYP level using the 6-311++G** basis set. Values of the vicinal coupling constants involving 1H and 13C in the... 

To overcome the drawback of poor solar light utilization brought about by the narrow photoresponse range of TiO2, a silver and sulfur co-doped TiO2 was synthesized. Using the prepared catalyst, solar photocatalytic degradation of 2-nitrophenol (2-NP) by a TiO2-based catalyst was studied for the first time. Effects of the co-doping on the structural, optical and morphological properties of the synthesized nanoparticles were investigated by different characterization methods: X-ray diffraction, N2 adsorption-desorption measurements, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, UV-visible diffuse reflectance spectroscopy and Fourier... 

Micro-arc oxidation process was used to synthesize V2O5-TiO2 porous layers for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were also employed to evaluate phase structure and chemical composition of the layers. It was found that the V2O5-TiO2 layers consisted of anatase, rutile, and vanadium pentoxide phases fraction of which varied with the applied voltage and the electrolyte concentration. It was also revealed that pore size and surface roughness increased with the applied voltage and the electrolyte... 

AgxPt100−x (x = 0, 25, 50, 75 and 100) nanoparticles were grown on the surface of magnetic graphene oxide nanosheets (Fe3O4@GO) for the first time. The as-prepared nanocomposites were characterized using various techniques such as Fourier transform infrared spectroscopy, powder X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller surface area analysis, vibrating sample magnetometry and thermogravimetric analysis. The Fe3O4@GO-AgxPt100−x catalysts were applied in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol using sodium borohydride (NaBH4). The synthesized nanocomposites... 

Nickel and nickel-copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV) and chronoamperometry (CA) were employed. The cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution. In CV studies, in the presence of methanol NiCu alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel... 

The simultaneous oxidation performance of benzene, toluene, ethylbenzene, and xylene (BTEX) by nanoscale calcium peroxide particles (nCaO2) activated with ferric ions (Fe(III)) and the mechanism of the enhancement of BTEX degradation by L-cysteine (L-cys) were investigated. The batch experimental results showed that the nCaO2/Fe(III)/L-cys process was effective in the destruction of BTEX in both ultrapure water and actual groundwater. A proper amount of L-cys could enhance BTEX degradation due to the promotion of Fe(II)/Fe(III) redox cycles by the participation of L-cys, but an excessive presence of L-cys would cause inhibition. Adding 1.0 mM L-cys to the nCaO2/Fe(III) system, the... 

This study demonstrated the prolonged benefits of polyvinyl-coated calcium peroxide (PVA@CP) in Fe(II)/nFeS mediated Fenton-like reaction. PVA@CP was prepared by a coating of PVA on calcium peroxide (CP) and synthesized nano-sized iron sulfide (nFeS) was characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) elemental mapping, X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES) and Fourier transmission infrared (FTIR) techniques. Trichloroethylene (TCE) degradation in various oxic environments (H2O2, CP, or... 

This study demonstrated the prolonged benefits of polyvinyl-coated calcium peroxide (PVA@CP) in Fe(II)/nFeS mediated Fenton-like reaction. PVA@CP was prepared by a coating of PVA on calcium peroxide (CP) and synthesized nano-sized iron sulfide (nFeS) was characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) elemental mapping, X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES) and Fourier transmission infrared (FTIR) techniques. Trichloroethylene (TCE) degradation in various oxic environments (H2O2, CP, or...