Sharif Digital Repository

Alumina nanofluids are one of the most useful nanofluids, especially for increasing the thermal conductivity. Due to importance of porous media in the improvement of heat transfer, this study investigates the transport and retention of gamma alumina/water nanofluid in the water-saturated porous media. For this purpose, alumina nanofluids were introduced to the porous media consisting of water-saturated glass beads possessing various pH values (4, 7 and 10) and different ionic strengths (0.001 M of KCl, CaCl2, AlCl3, K2SO4, CaSO4, Al2(SO4)3, K2CO3 and CaCO3). Then the break through curve of each experiment was drawn and modeled by combining classical filtration theory with... 

Thermal optimization of the vertical continuous casting process is considered in the present study. The goal is to find the optimal distribution of the temperature and interfacial heat transfer coefficients corresponding to the primary and secondary cooling systems, in addition to the pulling speed, such that the solidification along the main axis of strand approaches to the unidirectional solidification mode. Unlike many thermal optimization of phase change problems in which the desirable (target) temperature, temperature gradient, or interface position are assumed to be a priori known, a desirable shape feature of the freezing interface (not its explicit position) is assumed to be known in... 

Chromatographic method development for preparative targets is a time-consuming and subjective process. This can be particularly problematic because of the use of valuable samples for isolation and the large consumption of solvents in preparative scale. These processes could be improved by using statistical computations to save time, solvent and experimental efforts. Thus, contributed by ESI-MS, after applying DryLab software to gain an overview of the most effective parameters in separation of synthesized celecoxib and its co-eluted compounds, design of experiment software that relies on multivariate modeling as a chemometric approach was used to predict the optimized touching-band... 

Considering the quasi-brittle mechanical properties of concrete, wedge-splitting tests are employed and improved in this paper to study the fracture behaviour of concrete. A novel wedge-splitting device is designed by fixing ten springs on the force transmission component. The adaptive spring force can be imposed on top of a concrete specimen to retard the brittle fracture process. With the proposed wedge-splitting test design for notched cuboid specimens, the complete load–strain/CMOD curves of concrete can be generated directly. The fracture toughness and the fracture energy can be calculated easily without numerical fitting using the double-K fracture model. The descending branch of the... 

This research explored the corrosion effect of NaCl solution on the surface quality of AZ31 magnesium alloy. Cubic-shaped specimens were immersed in standard 3.5% NaCl solution for 1, 2, 3, and 4 hours. The size of corrosion pits, fatigue crack propagation area, and surface topology were characterized. Fatigue tests were carried out on pre-corroded AZ31 specimens under different stress amplitudes. The correlation between the corrosion time and the virtual crack size was obtained. The virtual crack size is a new parameter that can relate the corrosion to the fatigue life. A new model was proposed to map the surface topology on the virtual crack size of pre-corroded AZ31 magnesium alloy. The... 

This research explored the corrosion effect of NaCl solution on the surface quality of AZ31 magnesium alloy. Cubic-shaped specimens were immersed in standard 3.5% NaCl solution for 1, 2, 3, and 4 hours. The size of corrosion pits, fatigue crack propagation area, and surface topology were characterized. Fatigue tests were carried out on pre-corroded AZ31 specimens under different stress amplitudes. The correlation between the corrosion time and the virtual crack size was obtained. The virtual crack size is a new parameter that can relate the corrosion to the fatigue life. A new model was proposed to map the surface topology on the virtual crack size of pre-corroded AZ31 magnesium alloy. The... 

In this paper, a method of determining physical dimension of Double Barrier Quantum Well (DBQW) of Resonance Tunneling Diodes (RTDs) is presented by using I-V characteristic governing on them. In this procedure, first we have used performance metrics related to RTDs I-V characteristic such as Peak to Valley Current Ratio (PVCR), peak current density (JP), valley current density (JV) and Voltage Swing (VS), and by some other arbitrary points, we have fitted a curve to the RTD current-voltage equation by MATLAB software. Then we have obtained the physical parameter of I-V equation and adjusted some of them with modification coefficients. Next, by choosing the material of barriers and the well... 

Considering the important role of the ambiguity function (AF) of a signal regarding the performance of a matched filter bank for the detection of targets and the estimation of their ranges and velocities, the thumbtack shape is assumed to be the desirable shape of the AF and the method of least squares for the synthesis of the AF is introduced. Then, an iterative method for the allocation of a proper phase to the desired AF is proposed to obtain better results. This method is then applied to select the proper codes for the synthesis of pulsed orthogonal frequency-division multiplexing signals. It is also shown how this method can reduce sidelobes, almost uniformly, throughout the entire... 

The statistics of isoheight lines in the (2+1) -dimensional Kardar-Parisi-Zhang (KPZ) model is shown to be conformally invariant and equivalent to those of self-avoiding random walks. This leads to a rich variety of exact analytical results for the KPZ dynamics. We present direct evidence that the isoheight lines can be described by the family of conformally invariant curves called Schramm-Loewner evolution (or SLEI) with diffusivity Î=8/3. It is shown that the absence of the nonlinear term in the KPZ equation will change the diffusivity I from 8/3 to 4, indicating that the isoheight lines of the Edwards-Wilkinson surface are also conformally invariant and belong to the universality class of... 

In the present paper, the author has attempted to examine fatigue life of automotive safety components under axial variable amplitude loading conditions. To this end, the time components of stress tensor in the critical area of the knuckle and Liu-Zenner criterion were used to calculate the time history of equivalent stress. Then, the probability distribution function (PDF) of stress was extracted by applying the stress level counting technique. The Fourier curve fitting method was employed in order to formulate the PDF. Subsequently, the fatigue life of the component was estimated using the probabilistic approach. Finally, the results of the higher order of Fourier curve fitting and... 

Drying is a common practice for delaying deterioration, preserving quality, and easier prolonged storage of agricultural products. According to the climatic and geographical conditions of Arsanjan County, Fars, Iran. So far, many studies have been conducted on the design and use of various barriers on absorber plates with the aim of increasing heat exchange and subsequently increasing the efficiency of air heaters and solar dryers. However, the effect of using the metal of the sewing machine bobbin on the performance of these dryers has not been studied yet. Therefore, in this study, for the first time, this metal and also pipes containing PCM (phase change material) were used as a barrier... 

The secondary flow of PTT fluids in rectangular cross-sectional plane of microchannels under combined effects of electroosmotic and pressure driving forces is the subject of the present study. Employing second-order central finite difference method in a very refined grid network, we investigate the effect of electrokinetic and geometric parameters on the pattern, strength and the average of the secondary flow. In this regard, we try to illustrate the deformations of recirculating vortices due to change in the dimensionless Debye–Hückel and zeta potential parameters as well as channel aspect ratio. We demonstrate that, in the presence of thick electric double layers, significant alteration... 

Electrospray ionization is a wide spread technique for producing polymeric microcarriers (MCs) by applying electrostatic force and ionic cross-linker, simultaneously. In this study, fabrication process of gelatin-chitosan MCs and its optimization using the Response Surface Methodology (RSM) is reported. Gelatin/chitosan (G/C) blend ratio, applied voltage and feeding flow rate, their individual and interaction effects on the diameter and mechanical strength of the MCs were investigated. The obtained models for diameter and mechanical strength of MCs have a quadratic relationship with G/C blend ratio, applied voltage and feeding flow rate. Using the desirability curve, optimized G/C blend... 

In the previous researches, several theoretical equations were presented for calculation of buildup factor of the single layer shields. Also, the theoretical equations were offered for the two-layered shield that consist of the known materials. For other possible modes of the multi-layered shield, the buildup factor are usually calculated via experimental or simulated data. The purpose of present study is the extraction of the new theoretical equation for the gamma ray buildup factor of three-layered spherical shield made of water, concrete and iron based on the Monte Carlo calculation. To this end, the gamma ray buildup factor of the three-layered spherical shield is calculated via... 

A novel, simple and rapid spectrophotometric method for the determination of nitrophenol (NP) isomer mixtures based on the catalytic activity of gold nanoparticles is described. Gold nanoparticle (∼13 nm) solution was used to catalyze the reduction of NP isomers to aminophenols with an excess amount of NaBH4. The second-order data were obtained by spectrophotometrically monitoring the reduction process of NP isomers. So, multivariate curve resolution optimized by alternative least squares (MCR-ALS) was used to analyze such data. MCR-ALS, an appropriate second-order method, can exploit the so-called 'second order advantage' (the ability to determine in the presence of uncalibrated... 

This paper describes a methodology to develop the interface between a finite element software and optimization algorithm for optimization of concrete high arch dams. The objective function is the volume of the dam. The numbers of design variables are 31 including the thickness and upstream profile of crown cantilever, thickness of the left and right abutments, radius of curvature of water and air faces left and right by use of polynomial curve fitting and cubic spline function. The constraint conditions are the geometric shape, stress, and the stability against sliding. Initially, a program is developed in MATLAB in order to generate the coordinates of nodes; then, finite element software... 

The purpose of this paper is to determine the optimal shape of double curvature concrete arch dams by using the sensitivity of design objective to design variables. Design sensitivities quantify the relationship between the design variables such as thickness of crown cantilever, left and right abutment thickness, crown cantilever upstream profile, radius of curvature of water and air faces on one hand and the objective function such as the volume of the concrete arch dam on the other hand. For this aim, first a methodology was developed to provide interface between a finite element method and an optimization algorithm for shape optimization of double curvature concrete arch dams. The... 

Different equations of state (EOSs) have been used to obtain analytical expressions for the ideal curves, namely, the Joule-Thomson inversion curve (JTIC), Boyle curve (BC), and Joule inversion curve (JIC). The selected EOSs are the Redlich-Kwong (RK), Soave-Redlich-Kwong (SRK), Deiters, linear isotherm regularity (LIR), modified LIR (MLIR), dense system equation of state (DSEOS), and van der Waals (vdW). Analytical expressions have been obtained for the JTIC and BC only by using the LIR, MLIR, and vdW equations of state. The expression obtained using the LIR is the simplest. The experimental data for the JTIC and the calculated points from the empirical EOSs for the BC are well fitted into... 

Multivariate curve resolution (MCR) and multivariate clustering methods along with other chemometric methods are proposed to improve the analysis of gas chromatography-mass spectrometry (GC-MS) fingerprints of secondary metabolites in citrus fruits peels. In this way, chromatographic problems such as baseline/background contribution, low S/N peaks, asymmetric peaks, retention time shifts, and co-elution (overlapped and embedded peaks) occurred during GC-MS analysis of chromatographic fingerprints are solved using the proposed strategy. In this study, first, informative GC-MS fingerprints of citrus secondary metabolites are generated and then, whole data sets are segmented to some... 

Visibility is an important topic in computer graphics, motion planning, and computational geometry. To deal with the increasing complexity of the scenes considered, some research has been performed in visibility processing in order to accelerate the visibility determination. Two of the most studied such structures are visibility graph and visibility complex. Visibility graph is a fundamental geometric structure which is used in many applications, including illumination and rendering, motion planning, pattern recognition, and sensor networks. While the concept of visibility graph is widely studied for 2D scenes, there is no acceptable equivalence of visibility graph for 3D space. Similarly,...