Sharif Digital Repository

Different compositions of TiO2–BaTiO3 nanocomposites are synthesized with various weight ratios for dye-sensitized solar cell (DSSC) applications. TiO2 and BaTiO3 nanoparticles (NPs) are synthesized by sol-gel and solvothermal methods, respectively and are employed as the photoanode electrodes. BaTiO3 NPs have pure cubic perovskite crystal structure with an average size of 20-40 nm, while TiO2 NPs show pure anatase phase with 15-30 nm size. The power conversion efficiency (PCE) enhancement of the cells is first attained by controlling the thickness of the films for light harvesting improvement. The fabricated DSSC composed of pure BaTiO3 NPs with an optimal thickness of 25 μm shows... 

Herein, we report the impact of single- and co-doping of nanoparticle TiO2 films with carbon and nitrogen on the photovoltaic characteristics of their corresponding dye-sensitized solar cell (DSC) devices. Different DSCs with various compositions of the photoanode electrodes are fabricated to study their structural and electronic properties by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), field-emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS). We find that the interstitial nitrogen atoms for single N doping have a greater impact on the band gap energy (Eg) than the substitutional (to Ti) carbon... 

Different structures of dye-sensitized solar cells (DSCs) were fabricated with various compositions and arrangement modes of the photoanodes. The solvothermally grown TiO2 nanoparticles and sol-gel derived spherical TiO2 and BaTiO3 particles were employed as the active and scattering layers of DSCs. TiO2 nanoparticles and spherical particles had pure anatase structure with particle size of 15-30 nm and 200-400 nm, respectively, whereas 300-800 nm BaTiO3 particles showed cubic perovskite structure. The efficiency improvement of mono-layer cells made of TiO2 nanoparticles (i.e., 7.22%) was achieved by light harvesting mechanism. Further enhancement of photovoltaic performance was achieved by... 

Heat generation from Very Large-Scale Integrated (VLSI) circuits increases with the development of high-density integrated circuit technology. One of the efficient techniques is liquid cooling by using a microchannel heat sink. Numerical simulations on the microchannel heat sink in the literature are mainly two dimensional. The purpose of the present study is to develop a three-dimensional procedure to investigate flow and conjugate heat transfer in the microchannel heat sink for electronic packaging applications. A finite volume numerical code with a multigrid technique, based on an additive correction multigrid (AC-MG) scheme, which is a high-performance solver, is developed to solve the... 

Heat generation from very large-scale integrated (VLSI) circuits increases with the advent of high-density integrated circuit technology. One of the promising techniques is liquid cooling by using microchannel heat sink. Numerical works on the microchannel heat sink in the literature are mostly two dimensional. The purpose of the present study is to develop a three-dimensional analysis procedure to investigate flow and conjugate heat transfer in the microchannel-based heat sink for electronic packaging applications. The micro-heat sink model consists of a 10 mm long silicon substrate, with rectangular microchannels, 57 μm wide and 180 μm deep, fabricated along the entire length. A finite... 

Microchannels are at the fore front of today's cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections, namely parallel plate channel, circular duct, rectangular... 

Tungsten Inert Gas (TIG) process and titanium cored wires filled with micro size TiC particles were employed to produce surface composite coatings on commercial pure Ti substrate for wear resistance improvement. Wire drawing process was utilized to produce several cored wires from titanium strips and titanium carbide powders. Subsequently, these cored wires were melted and coated on commercial pure Ti using TIG process. This procedure was repeated at different current intensities and welding travel speeds. Composite coating tracks were found to be affected by TIG heat input. The microstructural studies using optical and scanning electron microscopy supported by X-ray diffraction showed that... 

The stability of a viscoelastic plate strip, subjected to an axial load with the Kelvin–Voigt fractional order constitutive relationship is studied. Based on the classical plate theory, the structural formulation of the plate is obtained by using the Newton’s second law and the aerodynamic force due to the fluid flow is evaluated by piston theory. The Galerkin method is employed to discretize the equation of motion into a set of ordinary differential equations. To determine the stability margin of plate the obtained set of ordinary differential equations are solved using the Laplace transform method. The effects of variation of the governing parameters such as axial force, retardation time,... 

Sol composition and ripening conditions are two important parameters in silica fiber production through the conventional sol-gel process. In the current study, silica nanofibers were successfully obtained via the electrospinning technique, and sol-gel formation occurred during this process. Based on previous reports, with the aim of increasing the selectivity, we used the molecular imprinted methodology to produce a selective medium via sol-gel electrospinning. In this process, sol-gel was formed during electrospinning and then, the backbone polymer was removed by heating. To obtain a thin layer of silica nanofibers, the influencing parameters such as backbone polymer types, imprinting time... 

A cryogel–based semi–interpenetrating polymer network (Cryo–SIPN) was prepared in which conductive polymers such as polyaniline (PANI) and polypyrrole (PPy) were formed within the super porous network of acrylic acid cryogel. For completion of cryo-polymerization, all the constituent solutions were severely mixed and placed into the plastic straws and kept at -20°C and then the synthesized cyrogels were cut into the 1-cm length and freeze dried after washing with water. The Cryo–SIPN polymeric composite was applied in micro solid phase extraction (µSPE) of some selected antibiotic residues from various samples. The µSPE method combined with a high performance liquid... 

We introduce a new robust simulation optimization method in which the probability of occurrence of uncertain parameters is considered. It is assumed that the probability distributions are unknown but historical data are on hand and using φ-divergence functionality the uncertainty region for the uncertain probability vector is defined. We propose two approaches to formulate the robust counterpart problem for the objective function estimated by Kriging. The first method is a minimax problem and the second method is based on the chance constraint definition. To illustrate the methods and assess their performance, numerical experiments are conducted. Results show that the second method obtains... 

In this article, a new algorithm for rather expensive simulation problems is presented, which consists of two phases. In the first phase, as a model-based algorithm, the simulation output is used directly in the optimization stage. In the second phase, the simulation model is replaced by a valid metamodel. In addition, a new optimization algorithm is presented. To evaluate the performance of the proposed algorithm, it is applied to the (s,S) inventory problem as well as to five test functions. Numerical results show that the proposed algorithm leads to better solutions with less computational time than the corresponding metamodel-based algorithm. © 2017 Taylor & Francis Group, LLC  

This paper is an extension of an earlier work on electron correlations in semiconducting GaAs-based quasi-one-dimensional quantum wires. The extension was twofold. First, we developed the Singwi, Tosi, Land, and Sölander (STLS) scheme for multisubband structures. Secondly, we developed the multisubband ladder approximation diagrammatic technique. By using the results obtained for the spin symmetric and spin antisymmetric interpolarization and intrapolarization potentials, we calculate the corresponding electron-electron effective potentials. Our results for a two-subband model show that these effective potentials have an attractive part implying the occurrence of s-wave and p-wave pairings,... 

Solid phase extraction coupled with spectrophotometric detection was applied to trace amounts of Pantoprazole (PP) drug using Cetyltrimethylammonium bromide coated-iron oxide magnetite nanoparticles CTAB@Fe3O4 MNPs. After characterization of the prepared nano-adsorbents, experimental parameters affecting the extraction efficiency of the developed method were optimized. The results obtained showed that this proposed approach is applicable in concentrations ranging from 0.1 to 1.5 μg/ml (R2 = 0.9958) indicating that follows Beer's-Lambert law. The limit of detection and the limit of quantification calculated to be 0.014 and 0.04 μg/ml, respectively. The repeatability of the proposed method was... 

Two different ternary nanocomposites, PPy/CNT/CoFe2O4 and PPy/CNT/NiFe2O4, were synthesized by in situ polymerization method. The resulting composites were characterized using Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. They were evaluated with the aim of investigating microwave absorption properties. The results showed that the value of microwave reflection decreases as that of prepared nanocomposites increases. This happens with increase in the PPy content and polymerization on the surface. © 2018 Académie des sciences  

Platinum extraction from spent reforming catalysts in iodine solutions under atmospheric pressure and at temperatures up to 95°C was previously investigated in our group. In this system, platinum is oxidized from the spent catalyst with tri-iodide. In some of the experiments, it was observed that platinum extraction peaked and then decreased. This indicates that a precipitation reaction slowly occurs that removes the dissolved Pt ions from the solution. Power-law rate equation for the Pt extraction to PtI6 2- and the precipitation of the dissolved platinum to PtI 4(s) was implemented to model the experimental Pt extraction data. The activation energies for the platinum dissolution reaction... 

This paper presents the results of an experimental and analytical study on the improvements gained in the axial compressive behavior of confined concrete. Among several parameters affecting compressive ductility of confined concrete, including confinement mechanical volumetric ratio, shape and size effect, number of confinement layers, strength of plain concrete and ductility of confining material, the latter was found to play the most important role in determining the ultimate strain and post peak behavior of concrete. Axial compressive tests were performed on small-scale circular or square section concrete columns, which were retrofitted either by CFRP jacket or by two types of... 

This paper presents the results of an experimental study on the application of pre-stressed high strength metal strips in retrofit of RC columns. Six 2/3 scale were deliberately designated with insufficient transverse reinforcement details and tested under constant axial and cyclic lateral load reversals. The level of axial load and the pattern of strengthening were parameters of this study. It was observed that the technique has been capable to enhance the lateral behavior of columns significantly, in terms of ductility. Very ductile behavior was obtained. The height-wise variations of lateral strain on confining strips are studied. The analysis of the fiber-based model of tested columns...