Performance Ehancement of Congestion Control Algorithm Through Traffic Flow Istinction

, M.Sc. Thesis Sharif University of Technology Peyman, Zakariaei (Author) ; Jahangir, Amir Hossein (Supervisor)

Abstract

Congestion is an important issue in the network environment. To keep stable the perfor-mance of the network, congestion control algorithms have been extensively studied. Queue management method employed by the routers is one of the important issues in the congestion control study. Active Queue Management (AQM) has been proposed for early detection of congestion inside the network. AQM mechanisms control the queue length in a router by dropping arriving packets. The Random Early Detection (RED) is the most popular AQM mechanism used in routers on the Intenet to allow network users to simultaneously achieve high throughput and low average delay. The RED algorithm may cause heavy oscillation of...

A Realistic Urban Mobility Model for Mobile Ad Hoc Network

, M.Sc. Thesis Sharif University of Technology Peyman, Sina (Author) ; Manzuri, Mohammad Taghi (Supervisor)

Abstract

A Mobile Ad hoc NETwork (MANET) is a set of wireless mobile nodes that form a self configured network. MANETs do not have infrastructure and are not currently deployed on large scales. So research in this area is simulation based. Mobility model in a mobile ad hoc network explains the movement pattern of mobile users and is designed to describe the change of their location, velocity and acceleration over time. One of the challenges in this field is the definition of a common mobility model that provides an accurate and realistic movement description of mobile nodes. In this thesis we want to study the mobility pattern of vehicles on Kish Island and compare it with different kinds of...

Calculating Runoff Coefficient of Urmia Lake Basin by Empirical Models and Remot Sensing (RS) Technology

, M.Sc. Thesis Sharif University of Technology Akbari, Mahdi (Author) ; Tajrishy, Masoud (Supervisor) ; Arasteh, Peyman (Co-Advisor)

Abstract

Estimation of runoff in the ungauged basins is a challenge for hydrologists. The main objective of this research is to produce runoff coefficient map using SCS-CN (1972) and Kennessey (1930) as empirical models to for Urmia Lake basin between for 2006-2011.Both SCS-CN and Kennessey methods use slope, land use, and soil permeability data to estimate surface runoff. Accuracy of each model is tested along with the observed runoff using the Root Mean Square Error (RMSE).Urmia Lake basin includes about 400,000 hectares irrigated land, which constitutes around 10 percent of the entire basin area. To exclude the anthropological activities from the estimations, methods were applied only for 28...

Attenuation and Scatter Correction in Whole Body Positron Emission Tomography Images using Neural Networks

, M.Sc. Thesis Sharif University of Technology Adeli, Zahra (Author) ; Hosseini, Abolfazl (Supervisor) ; Sheikhzadeh, Peyman (Co-Supervisor)

Abstract

Objective: Accurate quantification in PET imaging is essential for proper evaluation and requires attenuation and scatter correction. Typically, this correction is performed using CT; however, the propagation of CT image errors to PET, the additional radiation dose in PET/CT, especially in pediatric cases and repeated scans, as well as challenges associated with standalone PET and PET/MRI, highlight the need for alternative approaches. This study investigates the capability of deep learning in jointly correcting attenuation and scatter for PET images with different radiotracers. Methods: Various neural network models, including ResNet, U-Net, and swin UNETR, were trained for direct...

AI planning search time and space reduction technique for the problem of web service composition

, Article 2008 AAAI Workshop, Chicago, IL, 13 July 2008 through 14 July 2008 ; Volume WS-08-10 , 2008 , Pages 173-174 Rahmani, H ; Sharif University of Technology

2008

Abstract

One of challenging problems in the domain of web services is the web service composition (i.e the task of composing web services to create new services, capable of fulfilling a need that no single service can satisfy). In real application, there will be a lot of relevant web services for a simple goal, so the search space for such a problem is huge. In this research statement, we show how by extracting some prior knowledge and using simple heuristics, search space and search time can be reduced significantly

Hydrodynamic Interactions of Artificial Reef using a Laboratory Model

, M.Sc. Thesis Sharif University of Technology Kalantari, Mohammad Saeed (Author) ; Borghei, Mahmoud (Supervisor) ; Aghtouman, Peyman (Supervisor)

Abstract

Resources management is essential duo to sustainable development and marine resources limitations. There are several ways to restore coastal damaged ecosystems, one of the best and most cost effective solution is establishment of artificial reefs. A popular type of artificial reef is named Reef ball, a hollow hemisphere. In some regions these habitats has also been used as submerged breakwater. These structures recover and protect endangered species ecosystem although they provide aesthetic view to a beach. Main application of these structures is to provide a safe environment for marine creature. In this study initially Transmission coefficient variation in two-dimensional model experiments...

Robust optimal control for large-scale systems with state delay

, Article Transactions of the Institute of Measurement and Control ; Vol. 36, Issue. 4 , June , 2014 , pp. 551-558 ; ISSN: 01423312 Rahmani, M ; Sadati, N ; Sharif University of Technology

2014

Abstract

Optimal control of large-scale uncertain dynamic systems with time delays in states is considered in this paper. For this purpose, a two-level strategy is proposed to decompose the large-scale system into several interconnected subsystems at the first level. Then optimal control inputs are obtained by minimization of convex performance indices in presence of uncertainties, in the form of states and interactions feedback. The solution is achieved by bounded data uncertainty problems, where the uncertainties are only needed to be bounded and it is not required to satisfy the so-called 'matching conditions'. At the second level, a simple substitution-type interaction prediction method is used...

Dynamic behavior of pile foundations under cyclic loading in liquefiable soils

, Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 114-126 ; 0266352X (ISSN) Rahmani, A ; Pak, A ; Sharif University of Technology

2012

Abstract

In this paper, a fully coupled three-dimensional dynamic analysis is carried out to investigate the dynamic behavior of pile foundations in liquefied ground. A critical state bounding surface plasticity model is used to model soil skeleton, while a fully coupled (u- P) formulation is employed to analyze soil displacements and pore water pressures. Furthermore, in this study, variation of permeability coefficient during liquefaction is taken into account; the permeability coefficient is related to excess pore water pressure ratio. Results of a centrifuge test on pile foundations are used to demonstrate the capability of the model for reliable analysis of piles under dynamic loading. Then, the...

Two-level optimal load-frequency control for multi-area power systems

, Article International Journal of Electrical Power and Energy Systems ; Volume 53, Issue 1 , December , 2013 , Pages 540-547 ; 01420615 (ISSN) Rahmani, M ; Sadati, N ; Sharif University of Technology

2013

Abstract

In large-scale power systems, classical centralized control approaches may fail due to geographically distribution of information and decentralized controllers result in sub-optimal solution for load-frequency control (LFC) problems. In this paper, a two-level structure is presented to obtain optimal solution for LFC problems and also reduce the computational complexity of centralized controllers. In this approach, an interconnected multi-area power system is decomposed into several sub-systems (areas) at the first-level. Then an optimization problem in each area is solved separately, with respect to its local information and interaction signals coming from other areas. At the second-level,...

Hierarchical optimal robust load-frequency control for power systems

, Article IET Generation, Transmission and Distribution ; Volume 6, Issue 4 , 2012 , Pages 303-312 ; 17518687 (ISSN) Rahmani, M ; Sadati, N ; Sharif University of Technology

2012

Abstract

In this study, a hierarchical optimal robust controller is presented for the power system load-frequency control problem. In this approach, the multi-area power system is first decomposed into several sub-systems (areas). Then by using a two-level control strategy, the overall optimal solution is obtained. At the first level, the optimal control of each area is obtained with respect to local information and also considering interactions coming from other areas. At the second level, by using a coordination strategy, the local controllers will converge to global solution and optimal robust controller is achieved. This approach is applicable to both single-area and multi-area interconnected...

Mechanical properties of uncoated and aluminide-coated rené 80

, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 41, Issue 1 , 2010 , Pages 125-137 ; 10735623 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology

2010

Abstract

Nickel-base superalloys such as René 80 are widely used in manufacturing aircraft turbine blades. They are usually coated in order to increase their wear, oxidation, erosion, and hot corrosion properties against environmental degradation. In this article, the mechanical behavior (tensile and low-cycle fatigue (LCF)) of uncoated and aluminide-coated (CODEP-B) René 80 has been studied at 871 °C and 982 °C. Experimental results show that the tensile properties of coated specimens are relatively lower than those of uncoated ones in the same conditions, but application of coating increases the LCF life of René 80 at T = 871 °C, 982 °C, R = (εmin/εmax) = 0, strain rate of 2 × 10-3 s-1, and Δεt =...

Dynamic economic evaluation of distribution automation systems

, Article 2009 International Conference on Electric Power and Energy Conversion Systems, EPECS 2009 ; 2009 ; 9789948427155 (ISBN) Rahmani, S ; Ehsan, M ; Sharif University of Technology

2009

Abstract

In a deregulated environment of power distribution industry, a comprehensive economic evaluation for the implementation of distribution automation (DA) systems is inevitable. Using the presented methodology in this paper and system dynamics approach, it is efficiently possible to deal with variation of the economic parameters such as the interest rate, inflation rate, energy supply cost, load growth, etc. In this paper, economic short-run and long-run impacts of DA systems are evaluated from utility point of view. Also economic benefits from customers' point of view are analyzed. A practical pricing strategy for maximizing the utility profit is suggested depending on the underlying market...

Isothermal LCF behavior in aluminide diffusion coated Rene 80 near the DBTT

, Article Materials and Design ; Volume 30, Issue 4 , 2009 , Pages 1183-1192 ; 02641275 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology

2009

Abstract

Ni-base superalloys such as René 80 are widely used for aircraft turbine blades manufacture, due to possesses suitable mechanical, oxidation and hot corrosion properties. It is usually coated in order to increase its wear, oxidation, erosion and hot corrosion properties against environmental degradation. One the most important properties of coatings is its DBTT. In this paper the behavior of uncoated and coated (CODEP-B) René 80 has been studied near the DBTT (871 °C), R = (εmin/εmax) = 0 and strain rate of about 2 × 10-3 s-1. Experimental results show that in coated specimens while the total cyclic strain is lower than 1%, coating leaves longer fatigue life, at this condition the nucleation...

Modeling of periodic array of cut-through slits with sinusoidal surface conductivity at the interfaces of an anisotropic medium

, Article IEEE Transactions on Antennas and Propagation ; Volume 66, Issue 10 , 2018 , Pages 5630-5633 ; 0018926X (ISSN) Rahmani, B ; Mehrany, K ; Sharif University of Technology

Institute of Electrical and Electronics Engineers Inc 2018

Abstract

A periodic arrangement of 1-D slits carved in a perfect electric conductor is investigated, and an equivalent model which features sinusoidal surface conductivity on its upper and lower interfaces is derived. Therefore, and in sheer contrast to all the previous attempts that were successful in mimicking only the zeroth-order diffracted waves, it is capable of emulating both specular and nonspecular diffraction orders. The accuracy of the model is verified by the full-wave simulations. The proposed model is used to study the sharp Fano-type extraordinary transmission resonances arising in the structure. The transmission spectrum near these resonances is derived in terms of Fano resonance...

Some clarifications on the relation between bohmian quantum potential and mach’s principle

, Article International Journal of Theoretical Physics ; Volume 56, Issue 10 , 2017 , Pages 3096-3107 ; 00207748 (ISSN) Rahmani, F ; Golshani, M ; Sharif University of Technology

2017

Abstract

Mach’s principle asserts that the inertial mass of a body is related to the distribution of other distant bodies. This means that in the absence of other bodies, a single body has no mass. In this case, talking about motion is not possible, because the detection of motion is possible only relative to other bodies. But in physics we are faced with situations that are not fully Machian. As in the case of general theory of relativity where geodesics exist in the absence of any matter, the motion has meaning. Another example which is the main topic of our discussion, refers to Bohmian quantum mechanics, where the inertial mass of a single particle does not vanish, but is modified. We can call...

Some clarifications about the bohmian geodesic deviation equation and raychaudhuri's equation

, Article International Journal of Modern Physics A ; Volume 33, Issue 3 , 2018 ; 0217751X (ISSN) Rahmani, F ; Golshani, M ; Sharif University of Technology

World Scientific Publishing Co. Pte Ltd 2018

Abstract

One of the important and famous topics in general theory of relativity and gravitation is the problem of geodesic deviation and its related singularity theorems. An interesting subject is the investigation of these concepts when quantum effects are considered. Since the definition of trajectory is not possible in the framework of standard quantum mechanics (SQM), we investigate the problem of geodesic equation and its related topics in the framework of Bohmian quantum mechanics in which the definition of trajectory is possible. We do this in a fixed background and we do not consider the backreaction effects of matter on the space-time metric. © 2018 World Scientific Publishing Company

Influence of aluminide diffusion coating on the tensile properties of the Ni-base superalloy René 80

, Article Surface and Coatings Technology ; Volume 202, Issue 8 , 2008 , Pages 1385-1391 ; 02578972 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology

2008

Abstract

Ni-base superalloy René 80 is widely used in manufacturing aircraft turbine blades. The service temperature of this alloy is in the range of 760-982 °C. Although this alloy possesses suitable mechanical, oxidation and hot corrosion properties, it is coated in order to increase its wear, oxidation, erosion and hot corrosion properties against harmful environmental service conditions. In this paper the influence of applying diffusion coating (CODEP-B) on the tensile properties of René 80 has been studied in the temperature range of 22-982 °C. Experimental results show that the tensile properties of the coated specimens are relatively lower than that of uncoated ones in the same conditions. But...

Low cycle fatigue mechanism of René 80 at high temperature-high strain

, Article Materials Science and Engineering A ; Volume 494, Issue 1-2 , 2008 , Pages 385-390 ; 09215093 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology

2008

Abstract

The low cycle fatigue René 80, a Ni-base superalloy, was studied at temperature of 871 °C, R = (εmin/εmax) = 0 and strain rate of about 2 × 10-3 s-1. The dislocation structure and failure surface observations were evaluated through TEM and SEM. TEM studies showed that at Δεt = 0.8% during the first cycle the dislocations formed a hexagonal network in the γ-phase matrix. When the number of cycles increased, the density of dislocations increased as well. At N = Nf and Δεt = 0.8% the cutting of γ′ precipitates took place. SEM studies at Δεt = 0.8% and N = Nf showed that fatigue crack initiation generally occurred at the surface, where it is depleted of the γ′ phase as a result of oxidation by...

Influence of aluminide diffusion coating on low cycle fatigue properties of René 80

, Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 686-695 ; 09215093 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology

2008

Abstract

Low cycle fatigue is one of the most important phenomena affecting the lifetime of jet engine blades. In this paper, the effect of aluminide diffusion coating (CODEP-B) on low cycle fatigue properties of René 80 has been studied at temperature of 871 °C, R = 0 and strain rate of about 2 × 10-3 s-1. Experimental results show that the applied cyclic strain is lower than 0.8%, the presence of aforesaid coating increases the fatigue lifetime. In coated specimens, while the total cyclic strain is lower than 0.8%, the nucleation of the cracks occurs merely in substrate, but in cyclic strain more than 1%, as a result of simultaneous nucleation of cracks in the coating surface, diffusion layer and...

Developing tough terpolymer hydrogel with outstanding swelling ability by hydrophobic association cross-linking

, Article Polymer ; Volume 254 , 2022 ; 00323861 (ISSN) Rahmani, P ; Shojaei, A ; Sharif University of Technology

Elsevier Ltd 2022

Abstract

Hydrogels with remarkable hydrophilicity and tunable toughness are appealing materials to serve as superabsorbent polymers. However, chemically cross-linked hydrogels often suffer from low toughness regardless of their considerable swelling, restricting their widespread applications. In comparison, the network of physically cross-linked hydrogels can be regulated to meet both a high swelling ratio and considerable toughness. Here, we develop superabsorbent and tough hydrophobic associated hydrogels using terpolymerization of poly acrylic acid (PAA), polyacrylamide (PAM), and lauryl methacrylate (LMA) within the micelles formed by sodium dodecyl sulfate (SDS) surfactant. To this end, various...