Sharif Digital Repository

The present work describes sensing application of modified TiO 2 nanotubes having carbon-Pt nanoparticles for simultaneous detection of dopamine and uric acid. The TiO 2 nanotubes electrode was prepared using anodizing method, followed by electrodeposition of Pt nanoparticles onto the tubes. Carbon was deposited by decomposition of polyethylene glycol in a tube furnace to improve the conductivity. The C-Pt-TiO 2 nanotubes modified electrode was characterized by cyclic voltam-metry and differential pulse voltammetry methods. The modified electrode displayed high sensitivity towards the oxidation of dopamine and uric acid in a phosphate buffer solution (pH 7.00). The electro-oxidation currents... 

In this study a novel Pt/Ni nanostructure consisting of nano-bushes and nanocubes was fabricated onto TiO 2 nanotubes. The scanning electron microscopy images showed that a large amount of well-dispersed nano-architectures had uniformly covered all over the surface which made an electrode with high surface area. It was obviously seen that the nanocube structures mainly consists of Ni had been grown on top of each other while the Pt colonies represented bush-like structures. As a non-enzymatic glucose biosensor, the Pt/Ni TiO 2 nanotubes modified electrode exhibited an excellent performance. The proposed biosensor had two linear ranges for detection of glucose from 0 to 0.12 mM (correlation... 

Co/Cu multilayers were deposited in a sulfate solution by controlling the current and potential for the deposition of cobalt and copper layer respectively. The electrochemical behavior of these multilayers was studied by cyclic voltammetry and current transients. In addition, a mathematical analysis was used to characterize the electrodeposition system. Simultaneously, the nucleation and growth mechanisms were monitored by these techniques. In this case, the results clearly showed that electrodeposition of cobalt layers was a kinetically controlled process while the reduction of copper ions was a diffusion-control process. Although nucleation mechanism of the single Co deposit was found as a... 

The cobalt-nickel/copper multilayer films were prepared by electrodeposition process in sulfate solution using a three electrode cell. Cyclic voltammetry and double chronoampermetry techniques were utilized to characterize the multilayer system and to obtain the nucleation and growth mechanism. The cyclic voltammograms determined the reduction potential range of the three components and also clearly emphasized that electrodeposition of cobalt-nickel alloy was controlled by a kinetic process, while copper ions were reduced with diffusion-controlled mechanism. These results were confirmed with those which were extracted from the chronoampermetry curves. In addition, the current transients... 

A simple modified TiO2 nanotubes electrode was fabricated by electrodeposition of Pd, Pt and Au nanoparticles. The TiO2 nanotubes electrode was prepared using the anodizing method, followed by modifying Pd nanoparticles onto the tubes surface, offering a uniform conductive surface for electrodeposition of Pt and Au. The performance of the modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry methods. The Au/Pt/Pd/TiO2 NTs modified electrode represented a high sensitivity towards individual detection of dopamine as well as simultaneous detection of dopamine and uric acid using 0.1 M phosphate buffer solution (pH 7.00) as the base solution. In both case,... 

In general, decomposition methods can facilitate the process of solving sophisticated and heterogonous problems in the area of software development and engineering. These approaches are assisting to decompose problems based on different disciplines, characteristics and functionalities that is results into increasing the computational efficiency (e.g. parallel processing/computing) and accelerate the software changing process, software modifications and error tracking. Essentially, these approaches contribute to the degree of modularity to decompose a complex problem into different sub-problems and to focus on local objectives. There are different approaches that are used to decompose a... 

Progressive conversion/shrinking core (PC-SC) models of constant-size cylinders were exploited to interpret the decarburization reactions of MgO-C-Si bricks heated up under blown air. Chemical adsorption/solid (or pore) diffusion mechanisms governed the reaction rate. With 5% silicon, chemical adsorption vanished at 1000 and 1100°C. The oxidation rate lowered then with temperature. This was due apparently to the blocking of the pore-end gorges by the voluminous compounds (like Forstrite). Arrhenius plots of the specific rates yielded the activation energies of the prevailing steps. Without Si antioxidant, three steps were appreciated having activation energies of 51.65 (for chemical... 

TiO2nanocrystals were prepared by hydrolysis and peptisation of titanium isopropoxide under different pH values. The as-prepared powder of very fine anatase crystallites ranges from 8 nm in acidic solution of pH 3 to 10 nm in basic solution of pH 8. Heat treatment of the powders leads to grain growth and anatase - rutile transformation. Experimental results have shown that the anatase to rutile phase transformation in the heat-treated powders depend not only on primary crystallite size but also the presence of brookite phase. It is observed that in the powders with the same size the presence brookite phase would accelerate the anatase to rutile transformation. Furthermore it has been found... 

This work concerns with experimentally and analytically investigation of free gravity drainage process in porous media under the influence of ultrasonic wave radiation. Glass beads ranges from 70 to 100 mesh sizes were packed and used in the tests. The working fluids consist of distilled water, kerosene and Doroud and Paidar crude oils as wetting and air as non-wetting phase. The measured oil recovery data along with Hagoort (1984) backward methodology were used to determine and to compare the relative permeability of wetting phases in presence and absence of ultrasonic radiation. In addition the relative permeability of non-wetting phases for both cases were calculated from inverse modeling... 

Carbon nanotubes with unique physical and mechanical properties have shown great potential for biological applications, including tissue engineering and mimicking the structure and properties of human bones. In the present work, sol-gel synthesized nanocomposite powder of multi-wall carbon nanotube/hydroxyapatite characterized using field-emission scanning electron microscopy, transmission electron microscope, X-ray diffraction, Fourier transform infra-red spectroscopy and thermal analyses. The results show homogenous dispersion of nanotube in well-crystallized hydroxyapatite ceramic matrix. Scanning electron microscopy and transmission electron microscope observations show the sodium... 

Dental composites of A2 color using Bis-GMA, urethane dimethacrylate and triethyleneglycol dimethycrylate resins (70/20/10), and silica filler (70 wt%, 75 wt%, and 80 wt%), a hybrid of nano- and microsilica particles, are made and subjected to the following tests: Fourier transform infrared spectroscopy (FTIR), particle size analyzer, scanning electron microscope (SEM), and also cytotoxicity. FTIR results show that an increase in filler amount yields to a decrease in degree of conversion. Therefore, there should be a compromise between degree of conversion and the filler amount. SEM images manifest the uniformity of silica particles. It is shown from the cytotoxicity tests that as the... 

Biphase TiO2 nanoparticles have been prepared by sol-gel method. Water/titanium molar ratio (r) has been used to control the hydrolysis and condensation of titanium isopropoxide in solution producing titanium oxide with two different polymorphs. The influence of crystallite size and morphology of prepared TiO2 on the phase transformation of the resultant materials has been investigated. Synthesized powders were characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Different trends can be observed in the phase transformation and particle growth of the prepared titanium oxide nanomaterial. It was concluded that, the rate of particle... 

Kinetics of air oxidation of MgO-C-Al refractory at 600°-1300°C were investigated using the software based on the modifled shrinking core model (KDA). Commercial bricks containing 88.5% MgO, 10% residual carbon, and 1.5% aluminum anti-oxidant were oxidized isothermally with air. Combination of experimental data with model calculations indicated gas diffusion through solid material and pores as a major controlling step. Previously observed chemisorption process was eliminated from the rate-controlling mechanism with addition of aluminum antioxidant. Comprehensive rate equations were devised for MgO-C-Al and MgO-C oxidation reactions. Overall activation energies of Q id (internal diffusion) =... 

Usually, resources are short in supply when earthquakes occur. In such emergency situations, disaster relief organizations must use these scarce resources efficiently to achieve the best possible emergency relief. This paper therefore proposes a multi-objective, multi-mode, multi-commodity, and multi-period stochastic model to manage the logistics of both commodities and injured people in the earthquake response. Also, a robust approach is developed and used to make sure that the distribution plan performs well under the various situations that can follow an earthquake. Afterwards, it proposes a solution methodology according to hierarchical objective functions and uses it to illustrate the... 

In this study, a numerical model of unsteady potential flow around submerged marine propellers has been developed. The boundary element approach in combination with time stepping method to model free wake dynamics has been implemented. An important feature of this method in the simulation of pressure-dominant problems is a proper balance between time and accuracy in the numerical process. Another advantage of time stepping method is that there is no need to define wake geometry before modeling. Due to inherent instability of boundary integral equations, a smoothing function to damp the effect of singularities is imposed to the solution. The main innovative idea of this work is that the... 

In this paper, hydrodynamic simulation of fish-like swimming for two types of aquatic animals including tuna fish and giant danio is presented. We employ an unsteady three-dimensional inviscid boundary element method including time stepping algorithm to capture the wake sheet and flow features around swimming fish in a straight course. At each time step, an unsteady Bernoulli equation was used to find the pressure distribution and thrust generated by the animal. To couple fluid solver with kinematic equations of flexible body, undulating motions of backbone were defined using a prescribed continuous function. Although the flexible motion mechanism controls the fish swimming but no structural...