Sharif Digital Repository

This paper presents the results of an analytical study on the dynamic characteristics of the Shaking Table facilities at Sharif University. This 3 degree of freedom shaking table is driven by 3 servo-control hydraulic actuators, and consists of a 12 ton, 4m×4m×0.6m steel deck. The main objective of this investigation is to identify the degree of flexibility of the deck, and its adverse effects in causing errors in the simulation of seismic effects on different structural specimens. Many frame specimens of different weights and configurations are subjected to seismic motions, and their responses are calculated using FE models. Some of these models were designed to account for eccentric... 

An important aspect of corrosion prediction for oil/gas wells and pipelines is to obtain a realistic estimate of the corrosion rate. Corrosion rate prediction involves developing a predictive model that utilizes commonly available operational parameters, existing lab/field data, and theoretical models to obtain realistic assessments of corrosion rates. This study presents a new model to predict corrosion rates by using artificial neural network (ANN) systems. The values of pH, velocity, temperature, and partial pressure of the CO2 are input variables of the network and the rate of corrosion has been set as the network output. Among the 718 data sets, 503 of the data were implemented to find... 

In this article effects of sleepers defect on rail vehicle vibration have been investigated. Two parallel rails of the track have been modeled as Euler-Bernoulli beams on elastic points as rail pads. Also sleepers have been modeled as visco-elastic Euler-Bernoulli beams. It is assumed that, some sleepers under the rail track have been fractured and modeled by two beams. The wheelset has 5 DOF which are longitudinal, vertical and lateral movements plus roll and axial rotations. To determine normal contact force between wheel and rail, relative position of wheel and rail has been determined at each instant. Using the coordinate of each wheel points in rail coordinate system, the penetration of... 

A general method for deriving electromagnetic particle in cell (EMPIC) algorithms has been given by Eastwood [Comput. Phys. Commun. 64, 252 (1991)]. This method devises variation of the action-integral to find discrete governing equations. The most important advantage of this method is automatic inclusion of the time coordinate via the action integral into the computational domain. This inclusion is inevitable because electromagnetic algorithms are based on time evolution of the system from its initial state. The drawback of this method is that it is rather abstract. This causes obscurity of particle-mesh interactions and makes it hard to analyze physical treatments of the computational... 

Quantum dots cellular automata is a new computing method in the nanotechnology that has considerable features such as low power, small dimension and high speed switch. A QCA device stores logic based on the position of individual electrons. The fundamental logic elements in QCA are the majority (Fig.1 (a)) and inverter gates (Fig.1 (b)) that operate based on the Coulomb repulsion between electrons [1]  

Storage tanks are always under different hazards such as corrosion and leaking. In this work we have introduced a computational analysis on storage tanks in which a real-time yet efficient monitoring technique using Fiber Bragg Grating (FBG) sensors for corrosion detection on the bottom plate and vibration monitoring on outer surfaces of storage tanks is proposed. A finite element model for the tank is developed, in which the outer tanks surfaces are considered as plate elements and FBG sensors as beam elements. An array of FBG sensors is utilized to compute the generated strain in the FBGs due to losing thickness in the tank's bottom plate and due to vibration on the outer surfaces in... 

Sensor Localization is a crucial part of many location-dependent applications that is utilized in wireless sensor networks (WSNs). Several approaches, including range-based and range-free, have been proposed to calculate the position of randomly deployed sensor nodes. With specific hardware, the range-based schemes typically achieve high accuracy based on either node-to-node distances or angles. On the other hand, the range-free mechanisms support less positioning accuracy with less expense. The proposed scheme is based on range-free localization, which utilizes the received signal strength (RSS) from the anchor nodes. In this work, genetic fuzzy and neuro-fuzzy methods are used to become... 

This paper presents the scheduling optimisation of cargo trains by hybrid computer simulation (CS) and genetic algorithm. Scheduling cargo trains is based on the timetable of passenger trains that have priority in relation to cargo trains. System modelling is accomplished by Visual SLAM by considering time limitations, queue priority and limited station lines. Time limitations define that a cargo train is permitted to travel from station i to j if scheduled passenger trains have completed the travel from station i to j. Queue priority means that passenger trains have priority over cargo trains. In addition, each station has a limited storage track. In addition, all repair, maintenance,... 

This review aims to propose the integrative implementation of microfluidic devices, biomaterials, and computational methods that can lead to a significant progress in tissue engineering and regenerative medicine researches. Simultaneous implementation of multiple techniques can be very helpful in addressing biological processes. Providing controllable biochemical and biomechanical cues within artificial extracellular matrix similar to in vivo conditions is crucial in tissue engineering and regenerative medicine researches. Microfluidic devices provide precise spatial and temporal control over cell microenvironment. Moreover, generation of accurate and controllable spatial and temporal... 

Electrical impedance tomography (EIT) is a simple, economic and healthy technique to capture images from the internal area of the body. Although EIT is cheaper and smaller than other imaging systems and requires no ionizing radiation, the resolution associated with this technique is intrinsically limited and the image reconstruction algorithms proposed up to now are not efficient enough. In addition to low resolution EIT is an ill-posed inverse problem. Block method in EIT is based on electrical properties of materials and used to enhance image resolution and also to improve the reconstruction algorithm. Recently an inverse solution for EIT based on block method has been developed, however,... 

Optical tweezers provide an accurate measurement technique for evaluating mechanical properties of the living cells and many experimental studies have been done to understand the behavior of cells due to external forces. Numerical studies such as finite element methods have been used in order to simulate mechanical behavior of the Red Blood Cells (RBCs). Recent studies have shown that the particle methods are useful tools to simulate the mechanical behavior of living cells. Since in microscopic scales, using discrete models are preferred than continuum methods, a particle-based method is used to simulate the deformation of RBC which is stretched by optical tweezers. The cytoplasm of RBC is... 

This paper deals with the problem of multi-agent learning of a population of players, engaged in a repeated normal-form game. Assuming boundedly-rational agents, we propose a model of social learning based on trial and error, called "social reinforcement learning". This extension of well-known Q-learning algorithm, allows players within a population to communicate and share their experiences with each other. To illustrate the effectiveness of the proposed learning algorithm, a number of simulations on the benchmark game of "Battle of Sexes" has been carried out. Results show that supplementing communication to the classical form of Q-learning, significantly improves convergence speed towards... 

Electrical impedance tomography is a simple and economic medical imaging technology which permits regional assessment of the electrical properties of organs within the body based on measurements made from electrodes on the surface of the body. Block method is a new solution for electrical impedance tomography used to enhance image resolution and to improve reconstruction algorithm. Image reconstruction by block method is an ill-posed and nonlinear problem also has memory and time consuming process which can be improved by using modified equations. Improving forward solution for block electrical impedance tomography method can make linear equations for image reconstruction algorithm  

Nowadays, a great amount of information is circulated through the Internet. Some of them exclusively belong to a special group of users and require protection and safeguarding against unauthorized access. To this end, a category of systems called HIP (Human Interactive Proof) are designed to distinguish between various groups of users. An important task on the Internet websites is registration. Some hackers write programs to make fake registration that waste the resources of the web sites or even stop them from providing services. Therefore, human users should be distinguished from computer programs. CAPTCHA (Completely Automatic Public Turing Test to Tell Computer and Human Apart) methods... 

Background and objective There are many cells with various phenotypic behaviors in cancer interacting with each other. For example, an apoptotic cell may induce apoptosis in adjacent cells. A living cell can also protect cells from undergoing apoptosis and necrosis. These survival and death signals are propagated through interaction pathways between adjacent cells called gap junctions. The function of these signals depends on the cellular context of the cell receiving them. For instance, a receiver cell experiencing a low level of oxygen may interpret a received survival signal as an apoptosis signal. In this study, we examine the effect of these signals on tumor growth. Methods We make an... 

We have developed a simulation system for nanoscale high-electron mobility transistors, in which the self-consistent solution of Poisson and Schrödinger equations is obtained with the finite element method. We solve the exact set of nonlinear differential equations to obtain electron wave function, electric potential distribution, electron density, Fermi surface energy and current density distribution in the whole body of the device. For more precision, local dependence of carrier mobility on the electric field distribution is considered. We furthermore compare the simulation to a recent experimental measurement and observe perfect agreement. We also propose a novel graded channel design,... 

Almost all of the existing domain adaptation methods assume that all test data belong to a single stationary target distribution. However, in many real world applications, data arrive sequentially and the data distribution is continuously evolving. In this paper, we tackle the problem of adaptation to a continuously evolving target domain that has been recently introduced. We assume that the available data for the source domain are labeled but the examples of the target domain can be unlabeled and arrive sequentially. Moreover, the distribution of the target domain can evolve continuously over time. We propose the Evolving Domain Adaptation (EDA) method that first finds a new feature space... 

Optical computing has emerged as a promising candidate for real-time and parallel continuous data processing. Motivated by recent progresses in metamaterial-based analog computing [Science 343, 160 (2014)], we theoretically investigate the realization of two-dimensional complex mathematical operations using rotated configurations, recently reported in [Opt. Lett. 39, 1278 (2014)]. Breaking the reflection symmetry, such configurations could realize both even and odd Green's functions associated with spatial operators. Based on such an appealing theory and by using the Brewster effect, we demonstrate realization of a firstorder differentiator. Such an efficient wave-based computation method... 

A computational tool is developed to capture the interaction of solid object with two-phase flow. The full two-dimensional Navier–Stokes equations are solved on a regular structured grid to resolve the flow field. The level set and the immersed boundary methods are used to capture the free surface of a fluid and a solid object, respectively. A two-step projection method along with Multi-Processing (OpenMP) is employed to solve the flow equations. The computational tool is verified based on numerical and experimental data with three scenarios: a cylinder falling into a rectangular domain due to gravity, transient vertical oscillation of a cylinder by releasing above its equilibrium position,...