Sharif Digital Repository

The purpose of the present study was to investigate the effects of friction stir welding parameters on the fatigue life of friction stir welded sheets of Aluminum 7075 alloy. The welding process was carried out under three different rotational speeds and three different welding speeds and specimens were extracted transversely to be used for rotating-bending fatigue tests. Optical microscope and SEM images were used respectively for studying the microstructure of the weld zone and fractography. It was the indicated that an increase in the welding speed or a decrease in the rotational speed will result in an increase in the fatigue life  

The development of innovation ecosystems has become a global trend. These ecosystems have proven their importance to governments by having a significant impact on the creation of technology companies and the economic growth of the country. In Iran, too, for many years, efforts have been made under various headings to develop the innovation ecosystems. In this dissertation, based on the narrative policy framework, the existing policy narratives of innovation ecosystems development policy in iran between 2013-20 years in the case of startup ecosystem have been analyzed. After analyzing these data, it was found that the three main narratives of catch-up, wealth creation and infiltration, have... 

This study investigates the relationship between U.S. presidential elections (1976–2024) and the energy market, with a focus on the impact of fluctuations in oil supply and gasoline prices on voter behavior and its implications for Iran’s energy policymaking. Employing a data-driven approach, the study utilizes random forest models to assess the importance of various variables in predicting election outcomes, point-biserial correlation analysis to examine the relationships between economic and energy indicators, and game theory modeling to develop optimal energy policy strategies for Iran in response to U.S. actions. Historical data on energy markets, election results, and relevant policies... 

Harmonic distortions are one of the most important power quality issues in power systems. Nowadays, vast peneteration of the power electronic devices and nonlinear loads, which are the harmonic-producing devices in a network, causes increase in harmonic distortion level in distribution systems, which has negative impacts. The high level of harmonic peneteration in power system can lead to increase in losses and reduction of network equipment’s life. So, system operators have to find and improve some solutions to control the harmonic level. In this way, investigation in harmonic contribution of major nonlinear loads and utilities is a criticl task, specially when a harmonic problem occures.... 

The purpose of this research is to monitor the health of structures using the updated finite element model, in which digital images are used to optimize the numerical model. Structural Health Monitoring (SHM) is always an important and significant issue that has attracted the attention of many researchers in recent years. In general, some researches have been conducted in this field using physical sensors that provide discrete data to the system for analysis. Using cameras to monitor the structure makes it possible to extract continuous and integrated data from the structure using digital images, which is a significant advantage compared to physical sensors.In this research, a steel... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

One of the most famous criteria to measure the optimality of the election result in the metric space is the amount of distortion. In this framework, the cost of choosing each candidate is considered equal to the total distance of the community members from that candidate. With this definition, the candidate who has the lowest selection cost among all the candidates is called the optimal candidate. The amount of distortion for an electoral mechanism is equal to the maximum amount of the cost of selecting the selected candidate divided by the cost of selecting the desired candidate. It turns out that no deterministic voting mechanism can guarantee a distortion value better than 3. Various... 

Nowadays, one of the problems of network designers and users is the correctness of network equipment functionality. Since routers play an important role in information transfer between various networks and communicate with each other through a routing protocol, any violation of such protocol can result in the network's failure or defective transfer of data. Thus, being assured of the conformance of the implemented protocol in a router with what has been defined in the protocol's standard is of great significance. To this end, before using or exposing a router, network equipment testers should run protocol conformance tests on it and insure its correct functionality. This brings up the... 

In order to increase the network performance, to discover network security threats, to guarantee the quality of services, to simulate networks and develop new network protocols, network designers and operators need software tools to analyze the network traffic. The first step to do this analysis is network monitoring. This can be done by using various software and hardware tools.
In this research we developed a tool which analyzes the network traffic using appropriate statistical methods. The models which are analyzed in this application are: Poisson, Self-similar and Weibull. This application analyzes the network traffic based on this statistical models and calculates their parameters.... 

The increasing number of road accidents and fatalities have yielded the introduction of several solutions by related industries such as automobile manufacture. Proposed solutions can be classified into two categories: passive, such as airbags, and active such as ABS ad ITS-based technologies. Inter vehicles communication let the communication between vehicles(V2V) or between vehicles and road infrastructure (V2I) by relying on DSRC technology and standards. Intelligent Transportation System (ITS) has three main types of applications namely safety, traffic and commercial. Safety applications are the main goal of vehicular communication, and real time guarantee in safety applications is so... 

In real-time systems, jobs that miss their deadline are considered worthless or ineffective. Nowadays, real-time applications (such as multimedia) that communicate through software-defined networks (SDN) are widely used and will continue to expand in the future. SDN is an emerging network architecture in which control plane is separated from data plane to manage it directly. In this research, we make changes to the controller and the switch used in such network to deliver real time packets or real-time flows (such as video) on time, as much as possible. As missed deadline packets are worthless and they waste bandwidth, dropping them is a solution. Moreover, the controller can drop flows that... 

Network Function Virtualization (NFV) is a new paradigm in computer networks for implementing network functions on general-purpose common-of-the-shelf processors. The revolutionized NFV architecture has shown to be a suitable replacement for hardware middleboxes. NFV is in high demand because of its lower costs, increased flexibility, and more scalability. However, the ever-growing volume of network traffic and increased data transfer speed in computer networks have made achieving high performance the major issue in this area. With thousands of processing cores and high memory bandwidth, Graphical Processing Units (GPUs) are potentially an appropriate solution to accelerate network... 

This research uses systems dynamics modeling to present an integrated assessment of the energy-economic damage caused by climate change in Iran under different climate scenarios. Implementing these policies will cause a change in the use of global oil, followed by a change in the outlook for oil price changes in the future. Due to the high dependence of the country's economy on fossil fuels, oil price changes affect the country's economy. In the first step of this thesis, the system dynamics method examines the prospect of oil price change in climate scenarios. Then, according to the oil supply and production, in different scenarios, the assessment of the future conditions of the oil market... 

Nowadays, the significance of securing data and information is undeniable. Cryptography is being used to provide data security. In addition, cryptanalysis is required to evaluate the effectiveness of cryptography methods, and hence, it is an essential concept for securing data. In general, the cryptography functions shall be designed in a way to impose a high load of time-intensive operations to prevent an adversary from accessing the main data from the encrypted data. As a result, cryptography and cryptanalysis algorithms need high performance computations. So far, a number of methods have been proposed to support the required performance. These methods include: distributed computing and... 

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...