Sharif Digital Repository

Inlet performance has an important role in the operation of air-breathing propulsion systems. In this study, performance of a supersonic axisymmetric mixedcompression inlet in the supercritical operating condition is numerically studied. The effects of free-stream Mach number and engine-face pressure on performance parameters, including mass flow ratio, drag coefficient, total pressure recovery, and flow distortion, are investigated. For this sake, a multi-block density-based finite volume CFD code is developed, and Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras oneequation turbulence model are employed. The code is validated by comparing numerical results against other... 

Darrieus type vertical axis wind turbines have several advantages over other wind turbines for local electricity generation in urban environments. However, the main aerodynamic challenge is the negative impacts of the dynamic stall phenomenon on the turbine performance. This study numerically scrutinizes the effects of plasma actuators on the dynamic stall control and performance improvement of a Darrieus turbine. For this sake, unsteady Reynolds-averaged Navier-Stokes equations are solved using a pressure-based finite volume method. The Suzen-Hoang plasma actuator model is employed to calculate the body forces attributed to the plasma actuator. First, the dynamic stall characteristics of... 

The interaction between a lake and groundwater has important implications to the quantity and quality of water in both environments. Quantification of lake-groundwater interaction (LGI) has been challenging in regions with limited in-situ data. LGI can be quantified by physically-based models, direct measurement of seepage, measurements of conservative chemical or isotopic tracers, and lake water balance. Despite the accuracy of the methods based on hydrochemical or isotopic measurements and analysis, they require extensive field data that are costly to collect in large lakes. Instead, the data required to quantify LGI by the lake water budget method can be obtained via typical ground... 

TiO2 nanofibres were prepared using a templating method with tetraisopropylorthotitanate (TiPT) as a precursor. The preparation comprises liquid phase deposition on cellulose fibres followed by thermal removal of the cellulose template. The obtained TiO2 fibrous substance consists of micron-size fibres with a microstructure of nanofibres. It was demonstrated that nanofibres are basically formed through the aggregation of TiO2 nanoparticles and nanorods into chain structures during the thermal treatment process. The measured surface area of the TiO2 fibres was about 250 m2 g-1. It was shown that the pore size distribution is multi-scale and a fractal morphology was demonstrated with two... 

Application of curved beams in special structures requires a special analysis. In this study, the differential quadrature method (DQM) as a well-known numerical method is utilized in the dynamic analysis of the Euler-Bernoulli curved beam problem with a uniform cross section under a constant moving load. DQ approximation of the required partial derivatives is given by a weighted linear sum of the function values at all grid points. A prismatic semicircular arch with simply supported boundary conditions is assumed. The accuracy of the obtained results is corroborated by employing the Galerkin and finite element methods. Finally, the convergence rate of the DQM and Finite Element Method (FEM)... 

TiO2 deposited on a membrane of Ag fibers was prepared as a photoelectrochemical cell electrode. Ag fibers were made by reduction of Ag complexes on cellulose fibers, followed by burning out the template. TiO 2 photocatalyst layers were grown on the fibers by electrophoretic deposition of TiO2 nanoparticles. Ag fibers could be uniformly deposited. Photocatalytic tests by dye decomposition and electrochemical impedance spectroscopy (EIS) under UV illumination demonstrate that Ag fibers act as a good substrate that provides both high surface area and good separation of photogenerated electron-hole pairs and causes the enhancement of photocatalytic activity in comparison with a thin film of... 

Porous poly-silicon (PPS) is a cheaper alternative to single crystal porous silicon and is a favorable choice for making gas sensors. In this study, porous poly-silicon samples were prepared using different HF concentrations and the structural and gas-sensing properties were studied. The topography of the surface was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The variation of electrical conductivity of the samples in the presence of dry air-diluted acetone, ethanol and methanol showed that for a constant etching current, the sensitivity was highest for samples prepared in 13% HF solution. The structure of the films in the optimum HF... 

Transdermal drug delivery systems have overcome many limitations of other drug administration routes, such as injection pain and first-pass metabolism following oral route, although transdermal drug delivery systems are limited to drugs with low molecular weight. Hence, new emerging technology allowing high molecular weight drug delivery across the skin—known as ‘microneedles’—has been developed, which creates microchannels that facilitate drug delivery. In this report, drug-loaded degradable conic microneedles are modeled to characterize the degradation rate and drug release profile. Since a lot of data are available for polylactic acid-co-glycolic acid (PLGA) degradation in the literature,... 

Titania nanofibers were prepared using a colloidal solution of Titania nanoparticles and a templating method. The preparation comprises impregnation of cellulose fibers in the solution containing Titania nanoparticles followed by thermal removal of the cellulose template. It is evidenced by scanning electron microscopy (SEM) that the residue substance consists of micron size fibers with a microstructure of nanofibers. The pore size distribution of the substance is multi-scale and fractal morphology was demonstrated with two fractal regimes with dimensions of 1.78 and 2.97 for sizes below and above 7.5nm, respectively. The surface area of the Titania fibers was measured about 250m2/g. The... 

Density of surface charges of cellulose fibers and -potential of TiO2 nanoparticles in the solution were measured and controlled by pH. The adsorption and clustering of TiO2 nanoparticles on the surface of cellulose fibers were studied using scanning electron microscopy (SEM) and a scale in different situations of repulsion and attraction between the particles and surface. The experiments show formation of two-dimensional clusters of nanoparticles on the surface. Weight measurement of the adsorbed particles and clusters via the adsorption time results in that there are three stages containing nucleation, two-dimensional growth and saturation for clustering of nanoparticles on the surface.... 

Learning a foreign language encompasses a process of trial and error that can lead to the progression of the learner's interlanguage, meaning that the learners make use of their language knowledge that receives feedback and brings about progress through diagnosis of the problems and being corrected by the teacher. Therefore, there exists a need to analyze the underlying reasons causing the students to remain taciturn with a low willingness to communicate (WTC) during a language class. There has been much work done investigating the role of the learner's stable personal characteristics (traits) along with their situational changes at a specific time (states) that influence the student's... 

Using 3-D scanned data to analyze and extract pore network plays a vital role in investigation of porous media's characteristics. In this paper, a new simple method is developed to detect pores and throats for analyzing the connectivity and permeability of the network. This automated method utilizes some of the common and well-known image processing functions which are widely accessible by researchers and this has led to an easy algorithm implementation. In this method, after polishing and quality control of images, using city-block distance function and watershed segmentation algorithm, pores and throats are detected and 3-D network is produced. This method can also be applied on 2-D images... 

In this paper, we try to recognize and distinguish different groups of arrhythmia using novel features which have been obtained from the heart rate's phase space in recent years. For this purpose, we used Triangular Phase Space Mapping (TPSM) and Parabolic Phase Space Mapping (PPSM). For recognition, we used three groups of 15 subjects using the Physionet database (Arrhythmia, Congestive Heart Failure (CHF), and Atrial Fibrillation (AF)) with Normal Sinus Rhythm (NSR). The obtained features discriminate arrhythmia from NSR by p