Sharif Digital Repository

Collective behavior of active matter is observed for self-propelled particles, such as vibrated disks and active Brownian particles, as well as for cytoskeletal filaments in motile cells. Here, a system of quasi two-dimensional penetrable self-propelled rods inside rigid rings is used to construct a complex self-propelled particle. The rods interact sterically with each other and with a stationary or mobile ring via a separation-shifted Lennard-Jones potential. They either have a sliding attachment to the inside of the ring at one of their ends, or can move freely within the ring confinement. We study the inner structure and dynamics of the mobile self-propelled rings. We find that these... 

A significant segment of system identification literature on civil structures is devoted to response-only identification, simply because lack of measurements of input excitations for civil structures is a fairly common scenario. In recent years, several researchers have successfully adapted a second-order blind identification (SOBI) technique-a method originally developed for "blind source separation" of audio signals-to response-only identification of mechanical and civil structures. However, this development had been confined to fully instrumented classically damped systems. While several approaches have been proposed recently for extending SOBI to non-classically damped systems, they all... 

Generalized frequency division multiplexing (GFDM) is one of the multicarrier modulation candidates proposed for the 5th generation of wireless networks. Among GFDM linear receivers, GFDM MMSE receiver achieves the best error performance for multipath fading channels at the cost of high numerical complexity. Hence, the combination of GFDM match filter (MF) receiver and double-side successive interference cancellation (DSIC) method is used instead. However, there is a significant gap between the error performance of GFDM MMSE and DSIC/MF receivers for the case of employing modern channel coding. Recently, we have proposed a new multicarrier scheme based on GFDM architecture called generalized... 

A new methodology is presented with which the likely impact of accident in one process unit of an industry on other process units can be forecast and assessed. The methodology is based on Monte Carlo Simulation and overcomes the limitations of analytical methods, used hitherto, which were inherently limited in their ability to handle the uncertainty and the complexity associated with domino effect phenomena. The methodology has been validated and its applicability has been demonstrated with two case studies  

Nowadays "as everywhere in the world", so much attention is drawn to performing safety and HSE management rules in Iran. Considering the long life of oil and it's relevant industries in Iran (since 1908, first oil well in Middle East, Masjid Soleyman), many units with more than 50 years old are still in operation. This situation posed special problems in performing safety and HSE regulations that some of them are communal among these units. This paper reveals the result of industrial projects, collecting numerous technical checklists in such units and author's experiences in recent years in Iran, which is aimed to announce some of these major problems and also present solutions for them  

To exert the optimum effect, the chemical exchange process to boron isotope separation was investigated. In this enrichment method the distillation of dimethyl ether-boron trifluoride complex, which was one of the most efficient industrial methods for purification of isotope boron-10, was optimized. In chemical exchange process of boron isotopes separation two chemical reactions occur. The first one is the decomposition reaction that is an endothermic reaction. The second one is the exchange reaction that is a pyrogenic reaction. With increasing temperature, the decomposition reaction is speeded while the exchange reaction is slowed down. Affecting on both decomposition and exchange... 

Forecasting is a challenging problem in highly nonlinear dynamic systems. The main goal in development of forecasting models in complex systems is to produce a model that can accurately behave similar to the main system. In problems such as air pollution forecasting, the presence of uncertainties and nonlinearities affects the model's precision. In this paper, ozone concentration, which is well-known as an index for air pollution is forecasted using neuro-fuzzy models. Causal variables are integrated in the models in order to enhance the model's performance. The results are compared to a fuzzy logic approach to demonstrate reliability and accuracy of the proposed model using real observed... 

In this paper, we propose an improved timing estimation method for orthogonal frequency division multiplexing (OFDM) systems. The proposed preamble-aided method is independent of the preamble structure and is based on taking advantage of the whole products available from a given preamble for its correlation. Capable of having an extended correlation length far beyond those used by the previous methods, the proposed scheme presents an estimator with a remarkable performance in severe noise conditions. Further, we introduce a reduced complexity estimator along with the complexity assessments. We finally evaluate the performance of the proposed method in terms of mean square error (MSE). The... 

Image segmentation is one of the fundamental problems in image processing and computer vision, since it is the first step in many image analysis systems. This paper presents a new perspective to image segmentation, namely, segmenting input images by applying efficient community detection algorithms common in social and complex networks. First, a common segmentation algorithm is used to fragment the image into small initial regions. A weighted network is then constructed. Each initial region is mapped to a vertex, and all these vertices are connected to each other. The similarity between two regions is calculated from colour information. This similarity is then used to assign weights to the... 

The goal of image segmentation is to find regions that represent objects or meaningful parts of objects. In this paper a new method is presented for color image segmentation which involves the ideas used for community detection in social networks. In the proposed method an initial segmentation is applied to partition input image into small homogeneous regions. Then a weighted network is constructed from the regions, and a community detection algorithm is applied to it. The detected communities represent segments of the image. A remarkable feature of the method is the ability to segments the image automatically by optimizing the modularity value in the constructed network. The performance of... 

Flood as a natural disaster causes heavy human and economic losses and social unrests in most areas of the world. As flood control cost and flood damage compensation is a heavy burden over countries' budget, traditional flood design methods are being replaced by more reliable risk-based methods employing comprehensive risk analysis. In this respect, flood damage estimation is an important step in flood control systems design and analysis. In large river basins with complex reservoir systems and various land uses, flood damage estimation is complex, data-intensive, time demanding, and uncertain task requiring an intensive hydrologic and hydraulic analysis. In this study a simple approach is... 

The design of a complex active-RC filter for low-IF Wireless applications is described. Fifth-order complex Butterworth filter is designed using Class-AB operational amplifier architecture. This new structure makes the filter suitable for low power applications with high dynamic range. Simulation results show that the filter provides more than 40 dB image rejection ratio (IIR) and dynamic range of 82dB. The complete filter including on-chip tuning circuit consumes only 4.3mW with 1.8V single supply voltage. © 2007 IEEE  

There has been much research in developing scratch drive actuators (SDAs), but because of their dynamic complexity, these microelectromechanical system-based actuators have not been dynamically analyzed up to now. In this paper, a comprehensive model is presented to describe the dynamic behavior of SDA and its components during stepwise motion. In this model, Hamilton's principle and Newton's method are used to extract dynamic equations of the SDA plate and dynamic equation for the linear motion of SDA. This model presents a good insight into the operating principles of SDA by predicting the variation of different variables, such as bushing angle, contact length, horizontal position, and... 

The chaotic dynamics of roto-translatory motion of a triaxial Kelvin-type gyrostat satellite under gravity gradient perturbations is considered. The Hamiltonian approach is used for modelling of the coupled spin-orbit equations of motion. The complex Hamiltonian of the system is reduced via the extended Deprit canonical transformation using the Serret- Andoyer variables. Therefore, this reduction leads to the derivation of the perturbation form of the Hamiltonian that can be used in the Ricci curvature criterion based on the Riemannian manifold geometry for the analysis of chaos phenomenon. The results obtained from Ricci method as well as the values from the Lyapunov exponent demonstrate... 

In this paper, cavity flow is simulated numerically. Forced convection in different Reynolds numbers between 100 and 5000 is simulated. Different and complex thermal boundary conditions are applied and various parameters are calculated numerically. Up and down walls are in constant temperature and left and right walls are thermal insulation in the first thermal boundary condition. The Left and the down walls are in constant temperature and the temperature of the up and the right walls changes linearly in the second thermal boundary condition. For the third thermal boundary condition, the left and the down walls are in constant temperature and the temperature of the up and the right walls... 

In this paper, cavity flow is simulated numerically. Forced convection in different Reynolds numbers between 100 and 5000 is simulated. Different and complex thermal boundary conditions are applied and various parameters are calculated numerically. Up and down walls are in constant temperature and left and right walls are thermal insulation in the first thermal boundary condition. The Left and the down walls are in constant temperature and the temperature of the up and the right walls changes linearly in the second thermal boundary condition. For the third thermal boundary condition, the left and the down walls are in constant temperature and the temperature of the up and the right walls... 

Cyclic voltammetry and transient time (τ) measurements have been used to characterize the system, while potentiostatic I-t transients have been recorded to obtain the nucleation and growth mechanism. The electrodeposition of nickel, iron and nickel-iron alloys on the platinum was studied by electrochemical techniques in the presence of complexing compounds. The cyclic voltammetry results clearly show that the electrodeposition of nickel, iron and nickel-iron alloys is a diffusion-controlled process with a typical nucleation mechanism. The redox potentials of the Ni and Fe are shifted to more cathodic potentials in the complexing electrolytes. In addition, the current transients reveal that... 

Operational modal analysis based on power spectral density transmissibility (PSDT) functions is a useful tool to identify the modal parameters with low sensitivity to excitations. For pole extraction from the PSDT function, a proper parametric identification method such as the polyreference least squares complex frequency-domain method or poly-Max method can be used. Then, the poles are selected from a stabilization diagram (SD) with overestimating the system model order. Therefore, spurious modes can be identified that must be distinguished and removed from the system poles. To reach this aim, many techniques have been proposed and applied. In this paper, a new algorithm is proposed to... 

Background and objective Image registration is one of the fundamental and essential tasks for medical imaging and remote sensing applications. One of the most common challenges in this area is the presence of complex spatially varying intensity distortion in the images. The widely used similarity metrics, such as MI (Mutual Information), CC (Correlation Coefficient), SSD (Sum of Square Difference), SAD (Sum of Absolute Difference) and CR (Correlation Ratio), are not robust against this kind of distortion because stationarity assumption and the pixel-wise independence cannot be obeyed and captured by these metrics. Methods In this paper, we propose a new intensity-based method for... 

One crucial part of an image registration algorithm is utilization of an appropriate similarity metric. For common similarity metrics such as CC or MI, it is assumed that the intensities of image pixels are independent from each other and stationary. Accepting these assumptions, one will have difficulty doing image registration in the presence of spatially varying intensity distortion. In Myronenko et al. [5] a solution based on minimization of residual complexity is introduced to solve this problem. In this work, the weakness of RC method is investigated for more complex spatially varying intensity distortions and a modification of this method is presented to improve its performance in such...