Sharif Digital Repository

Steganalysis is the process of discovering existence of hidden data in a file or image. Recent advances in steganographic methods result in their wide use in secure communications applications. Reports of using information hiding by criminals to send messages, and malwares to communicate to servers, emphasizes importance of steganalysis in real time applications. Due to wide use of JPEG images in social media and internet, steganalysis of JPEG images is a highly active research topic in information hiding. Number of steganographic tools available for steganography in JPEG domain, shows importance of steganalysis of this image format. Classic Steganalysis techniques combine feature... 

The main objective of all managers of the economic organizations, manufacturing and industrial companies and service providers is to take steps toward improvement and effective use of different resources like workforce, capital, materials, energy and information. To attain the desired productivity, managers have to observe requirements such as establishment of a working organizational structure, effective implementation methods, safe equipment and tools, balanced working atmosphere and qualified human force as the most important factor. Therefore productivity culture should be publicized throughout the organization, and human force should be considered as the main component of this process.... 

Considering the advantages of optical communications and code division multiple access technique, Optical Code Division Multiple Access Networks (OCDMANs) was introduced. Thence, many researchers have suggested methods for creating Quality of Service (QoS) differentiated classes in OCDMANs. In this thesis, we have comprehensive review on the QoS assignment methods and enhance them by offering new techniques. In physical layer, we concentrate on variable chip rate OCDMANs and in MAC sub-layer, a new algorithm named Adaptive Level Control (ALC) is introduced. Then, we focus on the physical design of OCDMANs. Firstly, we solve the problem of one-class OCDMAN and introduce few simple and... 

In this study, the cooperative inertial navigation systems are used to prevent the error growth of the inertial navigation system in unmanned aerial vehicles that fly in group. Here, the navigation problem is defined for a group of unmanned vehicles, flying with full six degrees of freedom and the objective is to estimate the navigation information of all cooperators. Due to the nonlinear equations, the decentralized extended Kalman filter is used to estimate the states of the system. This means that there is a Kalman filter in each vehicle. The inputs of this filter are the range and the bearing angles between the vehicle and the cooperators, the estimated position of the cooperators and... 

In this study, integrated navigation systems that utilize velocity-matching algorithm and are used in automatic landing of Unmanned Aerial Vehicles (UAV) are investigated. At first, the accuracy of the navigation system in the landing phase is analyzed and the relationship between the accuracy of inertial sensors, flight parameters and the accuracy of the navigation system is derived analytically. Then, by integrating the dynamic model of the UAV and the inertial measurement unit, a new algorithm for navigation of fixed-wing UAVs is presented. The integration mechanism of the proposed algorithm is tightly coupled; hence, it is capable to eliminate the errors of UAV model and inertial system.... 

Consistent growth in volume and dynamic behavior of traffic mandates new requirements for fast and adaptive resource allocation in modern optical networks.Elastic optical networks have been proposed to provide a competitive and scalable solution by creating tunable high-capacity optical communication networks in which network elements are configured according to the actual need to minimize resource usage for the specified service requirements. Resource allocation with quality of service constraints is one of the most challenging problems in elastic optical networks which is conventionally formulated as a complex mixed-integer nonlinear optimization program.In this research work, we focus on... 

The perpuse of this thesis is to design and fabricate a laboratory one degree of freedom stable platform under turbulences by model-based design method. To do this, different parts of the system were first modeled in the Solidworks software and then fabricated with various tools. With proper assembly of electronic and mechanical components, the original body of the system was created. Then, the controller motor with a stable platform which is attached to it was modeled and simulated in MATLAB software. Then, the parameters of the equations were calculated using standard identification tests and TCACS optimization algorithm. One of the challenges of this thesis is the malfunction of the... 

In this research, a cooperative terminal guidance algorithm has been derived for simultaneous multi-interceptor collision with a target. This algorithm is obtained using the combination of model predictive control method and differential game theory. One of the features of this method is the calculation of the optimal guidance command in the form of an explicit relationship. Another feature of this method is its resistance to disturbances due to the use of differential game theory. The first innovation of this research is the use of this hybrid method to create a guidance algorithm, even in the non-cooperative guidance problem. The next innovation is in creating a cooperative terminal... 

Mobile edge computing (MEC) is a promising technology that aims to resolve cloud computing’s issues by deploying computation resources at the edge of mobile network and in the proximity of users. The advantages of MEC include reduced latency, energy consumption, and load on access and mobile core networks, to name but a few. Despite all the aforementioned advantages, the mobility of mobile network users causes the traditional MEC architecture to suffer from several issues, such as decreased efficiency and frequent service interruption. One of the methods to manage users’ mobility is virtual machine (VM) migration, where the VM containing the user’s task is migrated to somewhere closer to... 

Natural language processing has been used in solving the problems of humanities, including linguistics and analysis of religious books, such as the Bible, the Torah, and the Quran. One of the challenges in this field is the analysis of issues using the Quran. The problem in this issue is that a person becomes prejudiced in order to analyze the issues and makes incorrect judgements either inadvertently or intentionally based on his/her intellectual background. The same applies to analysis of issues based on the Quran. The method of analysis in this research is to produce an Arabic text based on the language of the Quran by receiving subjects in Persian. In order to achieve this goal, three... 

Hybrid engines are one of a variety of chemical propulsion systems that have been given special attention in recent years by various industries such as space and defense. The most important reasons for considering this type of system are its high safety, its affordable price compared with liquid fuel propulsion systems, the possibility of switching on and off and changing thrust. This system has a lot of disadvantages as well. This system cannot meet all the needs of different industries due to the low regression rate and, consequently, the limitation of the operating range, thrusts and special impulse. As a result, increasing the fuel regression rate in these engines can greatly expand... 

Optical impairments, as a challenging obstacle in optical communication systems, have been under deep attention of optical engineers in recent years. These impairments can be divided into two categories of linear and nonlinear impairments. Dispersion is a significant linear impairment leads to broadening of the optical signal and interference between transmitted symbols during detection. Nonlinear impairments such as cross-phase modulation (XPM) and self-phase modulation (SPM) also distort the transmitted signal through the fiber, causing interference at the receiver and degrading the system's performance. An appropriate solution for compensating optical fiber impairments is to utilize... 

The performance evaluation involves a process by which the employees are periodically and officially evaluated. Major reasons of performance evaluation include, among others, identification of efficient employees and granting bonuses to them to create stimuli to improve their and other employees' performances. The main objective of performance evaluation constitutes study of people's performances in the organization in order for directors to take proper and required decisions to enhance both quantities and qualities of the employees' works. The performance evaluation is deemed to be a major critical function of the management of human resources to facilitate organizational effectiveness. In... 

One of the proposed methods for enhancing optical networks and increasing their capacity is the use of the band multiplexing concept. This approach leverages additional available bands in optical fibers, enabling a significant boost in network capacity at much lower costs compared to other methods. However, fully utilizing the potential of this concept requires efficient resource allocation strategies to adequately counteract the nonlinear effects in optical fibers caused by increased bandwidth. In this research, we introduce an innovative method that simultaneously considers the physical layer constraints and user quality of service requirements for resource allocation in multi-band optical... 

In this thesis one of the sensorless methods which exploits the existing anisotropies of the rotor is utilized to estimate rotor position. In order to implement this method, first a high frequency voltage is injected in a specific, time-varying direction and then the corresponding current response would be observed in order to estimate the rotor saliency position. The estimation of rotor position would be more precise as the magnetic anisotropy due to rotor saliency increases and as a result the effect of noise and different disturbances in estimation of rotor position would be decresed. The effect of stator resistence is one of these disturbances which is usually neglected as a result of... 

The three-phase Dual Active Bridge DC-DC converter, by virtue of its various advantages, has been widely used in numerous industrial and sensitive applications. However, this converter includes a large number of power switching devices, which are the most fragile components in Power Electronics, and therefore, can pose a threat to appropriateness of the converter for such applications. Accordingly, introducing a fault-tolerant scheme for this converter is necessary, in order to meet the demands of high reliability and service continuity in aforementioned applications. In this thesis, firstly, the converter is studied during normal operation as well as under switch open-circuit fault, and the... 

The Fukushima accident is one of the reasons why the spent fuel pool (SFP) is an important safety element. The large amount of spent fuel inside the spent fuel pool has made it a source of hydrogen and radioactive material in the accident of any disturbance to pool cooling. Although the loss of spent fuel pool cooling system accident has a slow transient, it can lead to disasters if you ignore it. In this project, spent fuel pool of Bushehr Power Plant unit ‘I’ was simulated by Ansys Fluent and the natural circulation of fluids in the absence of cooling system was investigated. The distribution of water temperature in the pool was investigated for the worst possible spent fuel pool loading...