Sharif Digital Repository

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... 

This work concerns simultaneous determination of relative permeability, capillary pressure, pore size distribution (PSD), and residual oil saturation data by optimization of well testing data, and introduces a new capillary pressure relationship, based on the Weibull distribution function, for direct determination of the PSD function from capillary pressure parameters. Three consecutive injection, fall off, and production well tests are performed on a predefined synthetic reservoir through simulation, and an optimization algorithm is used to find the parameters of relative permeability and capillary pressure curves as well as the value of residual oil saturation. The PSD function is also... 

Boosting is a general method for improving the accuracy of any given learning algorithm. In this paper, we have proposed the boosting method for face recognition (FR) that improves the linear discriminant analysis (LDA)-based technique. The improvement is achieved by incorporating the regularized LDA (R-LDA) technique into the boosting framework. R-LDA is based on a new regularized Fisher's discriminant criterion, which is particularly robust against the small sample size problem compared to the traditional one used in LDA. The AdaBoost technique is utilized within this framework to generalize a set of simple FR subproblems and their corresponding LDA solutions and combines the results from... 

Cheating is an academically dishonest behavior about which there has been a thrust of research. However, it has not been extensively researched in an Iranian context. Therefore, the current study was conducted with 310 Iranian students. A cheating questionnaire was devised and administered to the participants. Certain demographic variables were investigated. Both descriptive and inferential statistics were employed to analyze the obtained data. The results of the descriptive statistics revealed that cheating was common among participants, and most students did not harbor any negative attitude toward cheating or at least were neutral about it. The most common method of cheating was “letting... 

The brain is one of the vital organs in the body. The main cerebral distribution center of blood flow in the brain is the circle of Willis (CoW). In more than 50% of healthy brains and in more than 80% of dysfunctional ones, at least one artery of the circle of Willis is absent or underdeveloped. These variations reduce the collateral flow availability and increase the risk of stroke and transient ischemic attack in patients with atherosclerosis. Thus it is essential to simulate the circle of Willis and investigate the effects of stenosis. In this work the systemic arteries along with the circle of Willis are simulated using the finite volume method and one-dimensional equations of... 

A one dimensional model of the pulmonary arterial network along with systemic circulation was introduced to quantify the human pulmonary artery hemodynamics. A lumped parameter model of the right ventricle was used as the inlet boundary condition. A time varying elastance related the volume and pressure of the right ventricle was imposed in the model. By using a four element Windkessel model, blood flow rate throughout the right ventricle was in hand. An asymmetric structured tree was chosen as the outlet boundary conditions. Simulation was based on solving one-dimensional equations of conservation of mass and momentum by using finite volume method. Blood flow rate, pressure and velocity... 

Wheel wear is one of the major costs in railway tracks consisting of sharp curves. In this paper, wear behavior of S1002 profiles of wheels in the "Southern Line" of Iran's railway, which consists of a large number of distinct and/or consecutive sharp curves, is studied using the field data measuring technique. Based on wear behavior analysis of all wheels, an optimal wagon maintenance technique called the "first and second limits" is suggested to minimize the wagon's cost per traveled distance. The results show that: 1) A severe wheel flange wear occurs for all wheels in comparison to the wheel tread wear in normal tracks; 2) A wagon's detachment for repair of critical wheels on its four... 

Wheel wear has been a concern in the railway for several decades. Studying the form change of the wheel/rail contacts in particular railways consisting of sharp curves helps to identify the risk of severe or catastrophic wear to minimize maintenance costs in order to be competitive in the transportation business. In this paper, the wheel/rail contact was studied on the particular railways. The experimental measurement of wheel profiles was used as an input to Hertz Contact Theory (HCT). It was found that: 1) for these railways the wheel flange is highly worn; 2) a 5th order polynomial function is appropriate to model the wear behavior of the critical wheel; 3) the minimum and maximum contact... 

A study of the wheel and rail wear phenomenon can provide a chance for the optimal use of wheel profile, which results in cost efficiency, dynamic stability, travel comfort, and safety to prevent the derailment, especially in curves. In this paper, the experimental data are recorded based on the field measurements for worn wheels of a passenger wagon in the "Southern line" of Iran's railway system and are combined with the dynamic simulations to study the effects of severe wheel flange wear on the dynamics of wagon. The results show that the amount of wheel wear (especially the wheel flange) directly impacts the dynamic behavior of the wagon in curves. In addition, based on the history of... 

A study of the wheel and rail wear phenomenon can provide a chance for the optimal use of wheel profile, which results in cost efficiency, dynamic stability, travel comfort, and safety to prevent the derailment, especially in curves. In this paper, the experimental data are recorded based on the field measurements for worn wheels of a passenger wagon in the "Southern line" of Iran's railway system and are combined with the dynamic simulations to study the effects of severe wheel flange wear on the dynamics of wagon. The results show that the amount of wheel wear (especially the wheel flange) directly impacts the dynamic behavior of the wagon in curves. In addition, based on the history of... 

Droplet-based microfluidics technologies hold great attention in a wide range of applications, including chemical analysis, drug screening, and food industries. This work aimed to describe the effects of different physical properties of the two immiscible phases on droplet formation in a flow-focusing microfluidic device and determining proper flow rates to form a droplet within the desired size range. A numerical model was developed to solve the governing equations of two-phase flow and the results were validated with previous experimental results. The results demonstrate different types of droplet formation regimes from dripping to jetting and different production rates of droplets as a... 

Three-dimensional cell culture and the forming multicellular aggregates are superior over traditional monolayer approaches due to better mimicking of in vivo conditions and hence functions of a tissue. A considerable amount of attention has been devoted to devising efficient methods for the rapid formation of uniform-sized multicellular aggregates. Microfluidic technology describes a platform of techniques comprising microchannels to manipulate the small number of reagents with unique properties and capabilities suitable for biological studies. The focus of this review is to highlight recent studies of using microfluidics, especially droplet-based types for the formation, culture, and... 

A coupled cellular automata and finite element model has been proposed to evaluate static recrystallization kinetics during non-isothermal annealing of cold deformed low carbon steels. The effects of various factors including heating rate, annealing temperature, and initial microstructures have been considered in the model to accurately predict the static recrystallization kinetics and the final microstructures. In order to examine the employed algorithm, the predicted results have been compared with the experimental observations and a good agreement was found between the two sets of results  

In this work, softening kinetics after cold rolling has been simulated using a coupled finite element-cellular automata model. Firstly, a two-dimensional rigid plastic finite element analysis has been developed to assess strain field and the stored energy accumulation during cold rolling as well as the initial condition of the mesoscopic model. Then, the cellular automata scheme has been employed to calculate the progress of static recrystallization at a given temperature while a dislocation-base model was simultaneously utilized to consider the effect of recovery on static softening process and final microstructures. The model has been examined on isothermal annealing of cold rolled AA5052... 

Bismuth and its alloys provide a paradigm to realize three dimensional materials whose low-energy effective theory is given by Dirac equation in 3+1 dimensions. We study the quantum transport properties of three dimensional Dirac materials within the framework of Landauer-Büttiker formalism. Charge carriers in normal metal satisfying the Schrödinger equation, can be split into four-component with appropriate matching conditions at the boundary with the three dimensional Dirac material (3DDM). We calculate the conductance and the Fano factor of an interface separating 3DDM from a normal metal, as well as the conductance through a slab of 3DDM. Under certain circumstances the 3DDM appears... 

This paper presents a new scheme to apply artificial neural network (ANN) in prediction of static recrystallization (SRX) kinetics. Firstly, based on empirical data of SRX kinetics, a mathematical model is suggested to construct a neural network. Then, an appropriate neural network is trained on the basis of the first and the second derivatives of recrystallized fraction with respect to time. Finally, a thermo-mechanical finite element analysis is coupled with the proposed ANN to predict static recrystallization kinetics in hot rolling process of AA5083. To verify the model, the predicted results and the experimental data are compared and it is observed that there is a good consistency... 

A thermo-mechanical model has been developed to establish a coupled heat conduction and plastic flow analysis in hot-rolling process. This model is capable of predicting temperature, strain, and strain rate distributions during hot rolling as well as the subsequent static recrystallization fraction and grain size changes after hot deformation. Finite element and neural network models are coupled to assess recrystallization kinetics after hot rolling. A new algorithm has been suggested to create differential data sets to train the neural network. The model is then used to predict histories of various deformation variables and recrystallization kinetics in hot rolling of AA5083. Comparison... 

The twist extrusion process is a rather new route to produce highly strained materials. In this process, severe plastic deformation is applied by large shear strains. In this regard, prediction of materials behaviour and extrusion pressure is of importance to die designers and engineers. In this article, utilizing an admissible velocity field together with the upper bound technique, the required energy for twist extrusion is predicted. The proposed model is capable of considering the effect of various parameters such as die geometry and friction conditions. In addition, the model anticipates the critical die design parameters. To verify the proposed model, the predictions are compared with... 

We suggest that spin-singlet pseudo-scalar s-wave superconducting pairing creates a two dimensional sea of Majorana fermions on the surface of three dimensional Dirac superconductors (3DDS). This pseudo-scalar superconducting order parameter Δ5, in competition with scalar Dirac mass m, leads to a topological phase transition due to band inversion. We find that a perfect Andreev-Klein reflection is guaranteed by presence of anomalous Andreev reflection along with the conventional one. This effect manifests itself in a resonant peak of the differential conductance. Furthermore, Josephson current of the Δ5|m|Δ5 junction in the presence of anomalous Andreev reflection is fractional with 4π... 

Motivated by recent developments in the field of topological superconductors, we show that there is a topological phase transition (TPT) for three dimensional Dirac superconductors (3DDS) in the presence of pseudo-scalar superconducting order parameter which leads to the appearance of a two dimensional Majorana sea (2DMS) on its surface. The perfect Andreev–Klein transmission, resonant peak with robust character in the differential conductance and 4π periodic Josephson current are experimental signatures of 2DMS. © 2018 Elsevier B.V