Sharif Digital Repository

Using a combined hydrothermal and sol-gel route, TiO 2 -capped ZnO nanoparticles with an average size of 60 nm were prepared. The titania shell was amorphous with a thickness of ∼10 nm. Formation of Zn 2TiO 4 phase at higher calcination temperature was noticed. Effects of Ti/Zn molar ratio and coating time on the thickness of TiO 2 shell and the photoactivity of the particles for decolorization of Methylene Blue (MB) under UV lamp irradiation (3 mW/cm 2) were investigated. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, fourier-transform infrared spectrometry (FTIR), diffuse reflectance spectroscopy (DLS), and atomic absorption spectroscopy.... 

The wide utilization of nanomanipulation as a promising approach in microorganisms, nanoelectromechanical systems, and assembly of nanostructures remarks the importance of nanostructures' motion in electric fields. Here, we study the rotational dynamics of metallic and non-metallic nanowires (NWs) in a static uniform electric field in viscous dielectric liquids. For metallic NWs, it has been theoretically shown that the electric field-induced rotation is practically independent of the geometrical dimensions and the electrical properties of NWs. Our experimental results for suspended silver (Ag) NWs in microscope oil are perfectly in agreement with this model. However, in the case of TiO2... 

We report an approach for collecting, charging, and exceedingly fast motion of silver nanowires (Ag NWs) using an external static electric field. With a proper choice of suspension medium, dispersed Ag NWs can be efficiently driven to align and accumulate vertically on the edges of two parallel gold microelectrodes on a glass substrate surface by dielectrophoresis. Then, at sufficiently high electric fields (> 2.0 × 10 5 V/m), these NWs break at the electrode contact point while carrying some net charge. Afterwards, they immediately accelerate in the field direction and, despite an extremely low Reynolds number for the motion of NWs in viscous liquids, move with high speeds (> 25 mm/s)... 

Influence of two nano-size additives oSubject:A. Suspensions. Subject:C. Electrical conductivity. Subject:Castable. Subject:E. Refractories. Subject:Castables. Subject:Electrical conductivity. Subject:Electrical property. Subject:High alumina. Subject:matrix. Subject:Mechanical strength. Subject:Nano-size. Subject:Polycarboxylate ethers. Subject:Refractory castables. Subject:Working time. Subject:Alumina. Subject:Cement additives. Subject:Electric conductivity. Subject:Ethers. Subject:Suspensions (fluids) Subject:Refractory materials. n electrical properties of suspension matrix of self-flowing low-cement high alumina refractory castable is investigated. For this purpose, castament FS 10 and... 

This paper presents a novel and fast method to distinguish regular and irregular regions in satellite and aerial images. This can be employed in further processing such as detecting man-made or artificial structures, disaster response, road sign detection and etc. In order to achieve this goal, we offer a suitable definition of regular shapes. Using this definition, we propose an appropriate technique to evaluate regularity .In our approach, discrete Fourier transform plays the main role for searching the regularity. We suggest a criterion; called RCNR, which indicates to some extent that the shape is regular. The computed RCNR value should be compared with a pre-assigned threshold value for... 

Closed cell aluminum foams are fabricated by using the casting method. The electromagnetic interference (EMI) shielding effectiveness of foams are investigated in the frequency range of 1.44–5 and 8–12 GHz (X band).The shielding materials are made of Al foam with the addition of different concentrations of SiC (5, 10, 15 wt%). Results show that the Al/SiC composite foams have good shielding effectiveness. EMI shielding effectiveness of samples generally increased with increasing porosity and with the increasing of SiC content. The sample with 15 wt% SiC had shielding effectiveness values of up to 150 dB  

TiO2 layers were grown via pulse type microarc oxidation process under different applied voltages, frequencies, and duty cycles. Surface chemical composition and phase structure of the synthesized layers were studied utilizing X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Furthermore, scanning electron microscope (SEM) and atomic force microscope (AFM) were employed to investigate surface morphology and topography of the layers. It was revealed that the layers had a porous structure with both anatase and rutile phases. The anatase relative content in the layers increased with the applied frequency; meanwhile, it decreased with duty cycle at low applied voltages, but... 

An attempt to synthesize pyrochlore free (x)PMN-(1 - x)PZT ceramics (where x is 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) by a mixed powder method was made. In this work, a sol-gel prepared PZT powder was mixed with the mixture of milled PbO, MgO and Nb2O5, and sintered in a two step sintering process. The produced samples with high PZT content showed low densities due to the low compaction ratio of PZT powder. The dielectric properties of PZT-rich and PMN-rich materials were high (with dielectric constant of about 19,000 and 33,000 for PZT-rich and PMN-rich ceramics, respectively) while the other samples exhibited low dielectric properties. Also, the effect of combining PMN with PZT on Curie... 

In this investigation, the crystalline structure of a nanometric CoSi 2 layer, formed in heat treated Co/W x Ta (1-x) /Si(1 0 0) systems, has been studied by XRD analysis. Careful measurements of the diffraction intensities revealed that temporary formation of a metastable diamond cubic structure of CoSi 2 phase, rather than its usual CaF 2 structure, was occurred. It has been shown that formation of this metastable structure depends on the kind of the applied interlayer in addition to the annealing temperature. Among the studied systems with x = 0, 0.25, 0.5, 0.75 and 1, the second and the last systems resulted in growing a (1 0 0) single-texture CoSi 2 layer with the preferred usual CaF 2... 

Epitaxial formation of CoSi2 nanolayer by solid state reaction of Co-Si in refractory metal intermediate-layer and cap-layer systems was investigated. Thin films of Ta and W, as the refractory metal intermediate or cap layers of the Co film, were deposited on Si(100) substrate and then heat-treated. The both interlayers resulted in formation of epitaxial CoSi 2 with (100) crystallographic orientation at 900°C. However, in the Ta intermediated system, the grown CoSi2 layer was thermally unstable at 1000°C, unlike the W system with a stable silicide layer. We found that use of W cap-layer cannot yield an epitaxial CoSi2 phase. But, a Ta cap-layer resulted in formation of epitaxial CoSi2(100)... 

PTCR thermistors are thermally sensitive resistors that show positive temperature coefficient of resistance and are good candidates for applications as self-regulating heating elements and thermal control switches. For these applications, the current-time behavior of thermistors is of primary importance. In this work, heat transfer models were developed to simulate the electrothermal behavior of BaTiO3 thermistors. Also, using simulated temperature profiles, thermal stress distributions of the specimen were calculated to predict crack formation at different conditions. At high voltages, the effects of thermal conductivity and heat transfer coefficient were negligible. At low voltages, the... 

Electrospinning is a simple and cheap process for forming one-dimensional (1D) nanofibers with controllable size, morphology, and chemistry. Besides these, the ultrahigh surface area with industrialization capability has attracted extensive interest in the research community. On the other hand, a photocatalytic process is a promising method for degrading organic pollutants that cannot be removed by conventional wastewater treatment. This review focuses on the recent progress of electrospun nanofibers for the photocatalytic degradation of water pollutants. The linkage between the electrospinning technique and the photocatalytic process is classified into two main categories: (1) polymeric... 

Van der Waals (vdW) heterostructures of two-dimensional monolayers are a relatively new class of materials with highly tunable band alignment, bandgap energy, and bandgap transition type. In this study, we performed density functional theory calculations to investigate how a vdW heterostructure of heptazine-based graphitic carbon nitride (hg-C3N4) and graphitic zinc oxide (g-ZnO) monolayers is formed (hg-C3N4/g-ZnO). This heterostructure is a potential solar-driven photocatalyst for the water-splitting reaction. Upon the formation of the heterostructure, a type-I indirect bandgap (Eg = 2.08 eV) is created with appropriate conduction band minimum and valence band maximum levels relative to... 

We have studied the intramolecular H-bonds existing in cyclic and open forms of glucose using B3LYP/6-311++G(d,p) level, AIM, and NBO methods. The theoretical results indicated that based on acidity values, (ΔHacid), glucose in the open form is more acidic than cyclic form. The acidity values for open and cyclic glucose (332 and 338 kcal/mol) exhibit significantly lower values (i.e., stronger acid) than the reported acidity values for α-/ß-anomers of D-glucopyranose and simple alcohols. Because their conjugate bases are more stabilized through trifurcated and bifurcated intramolecular H-bonds. AIM analysis showed normal H-bonds in the conjugate bases of open glucose (O-Glc), bifurcated, and... 

In this work, the intramolecular H-bonds in galactose were studied using DFT at the B3LYP/6–311++G (d,p) levels of theory, atoms in molecules (AIM), and natural bond orbital (NBO). AIM and NBO analysis revealed a cooperative network of trifurcated, bifurcated, and normal H-bonds for the conjugate bases of open galactse (O-Gal). While for the conjugate base of the cyclic form of galactose, we identified bifurcated and normal H-bonds, which may highlight a crucial feature of the biological activity of a whole class of natural sugars. The O-H…O bonds are categorized as mostly electrostatic, strong H-bonds and more favorable, whereas for multiple interactions involving C=O…H, C-H…O and C-H…H-C... 

Joining Mg to Al is challenging because of the deterioration of mechanical properties caused by the formation of intermetallic compounds (IMCs) at the Mg/Al interface. This study aims to improve the mechanical properties of welded samples by preventing the fracture location at the Mg/Al interface. Friction stir welding was performed to join Mg to Al at different rotational and travel speeds. The micro structure of the welded samples showed the IMCs layers containing Al12Mg17 (γ) and Al3Mg2 (β) at the welding zone with a thickness (> 3.5