Sharif Digital Repository

Intrusion detection systems and firewalls for web applications serve as an important defensive layer for detecting attacks. These systems typically employ either signature- based or anomaly-based approaches. Signature-based methods require expert knowl- edge to generate signatures for malicious data and, therefore, cannot be used to detect unknown threats. In contrast, anomaly-based methods can detect unknown threats but generally with lower accuracy and precision. Detecting legitimate strings within packet content is challenging for anomaly-based models because not all legitimate patterns are observed during the training phase. In this research, a machine learning model is proposed to... 

The integration of radar and communication functionalities into a unified Joint Radar-Communication (JRC) system offers enhanced spectral efficiency and reduced hardware complexity. Recognized as a key enabler for next-generation wireless networks, JRC systems require a careful balance between radar and communication demands, where waveform design plays a pivotal role in achieving this equilibrium. Although waveform design has been extensively studied separately in radar and communication domains, the requirements of modern networks necessitate a unified approach that simultaneously addresses the needs of both systems. This thesis advances waveform design methodologies for JRC systems,... 

The annual degradation in power quality causes significant losses to electricity consumers, particularly in sensitive industries. One of the most critical challenges associated with power quality is the voltage sags and swells in the grid. voltage sags and swells in the grid pose a major challenge, potentially damaging equipment and disrupting production, which can increase the costs of the final product. Moreover, the AC nature of grid voltage highlights the importance of developing AC-AC converters to mitigate issues arising from grid voltage sags and swells. The primary goal of the employed converter is to compensate for voltage amplitude, without concern for frequency control. Therefore,... 

This research presents a new harmonic model for compact fluorescent lamps and other nonlinear loads. In recent years, nonlinear loads have gained widespread acceptance due to their characteristics. Although CFLs consume less energy, they draw extremely distorted current waveforms resulting in harmonic losses in distribution networks. The presented harmonic Norton models in this work are simple and accurate models which can consider the impact of supply voltage harmonics as well. The parameters of non linear appliances model are determined based on measurements. The characteristics of the proposed models make it suitable for analyzing the impacts of large number of CFLs or other non-linear... 

Electrical systems are prone to voltage or current unbalance due to unbalance loads or asymmetries in network elements such as untransposed lines. Voltage and current unbalance can cause malfunction or reduction in lifetime of different elements. Voltage unbalance has been studied in a variety of publications, due to its high importance and significant effects. However, current unbalance has not gained much attention despite its undeniable influence on transformers’ and line’s lifetime. Observing high values of current unbalance in LV systems is predictable and inevitable. On the other hand, HV systems must be much more balance due to their different structure and absence of large unbalance... 

Physical properties of $Re_1 Ba_2 Cu_3 O_{7-\delta} (Re123)$ high-temperature cuprate superconductors attract many of physicists due to their high transition temperature (above Nitrogen boiling point), relatively simple synthesizing and high critical current density. Among this family, Nd123 and Sm123 single-crystal compounds have the highest transition temperature and critical current density in the magnetic fields less than 2 Tesla. In addition, due to the near ionic radius of Nd and Sm elements, it is possible to synthesize $Nd_{1-x} Sm_x Ba_2 Cu_3 O_{7-\delta} (0 \leq x \leq 1)$ compounds with no significant dislocation. In order to investigate the effects of such doping on electrical... 

In this dissertation, the application of frequency and space diversities in radar target parameter estimation are investigated. On this basis, multi-frequency signal is used to improve the range resolution, array structure is used to increase the angle estimation accuracy and the merger of the multi-frequency signal and array structure are used to increase the maximum number of targets that can be uniquely identified.Considering the desirable properties of multi-frequency signals such as high bandwidth efficiency, high range resolution achievement without chip length decrease and …, there has been increased interest in the vast area of research on the design of such signals that has... 

Target recognition techniques based on micro Doppler phenomenon are popular because they are applicable even on low resolution radars, in contrast to other techniques such as High Resolution Range Profile (HRRP) which need high resolution in range or angle. Usually, main purpose of such techniques is generating robust features against target initial state, velocity, aspect angle, etc. rather than features which exactly identify a target. Main approaches in the literature are based on time-frequency transforms (TFT) such as spectrogram in order to generate features to classify targets, but in this thesis, we propose a totally different method using Recurrence Plot for generating features... 

In this research with Finite Element Methods in ABAQUS, numerical modeling has done in three-dimensions, which can be used to determine the effect of different factors on the surface settlement. Also, various factors such as geotechnical conditions, tunnel diameter,tunnel depth, the impact of the thickness of the segments and the amount of eccentricity of the structure relative to the longitudinal axis of the tunnel considered in this study. Face Pressure Supports, and Grout Injection Pressures are taken into account, too.Tunnel drilling causes a change in the displacement area and creates a changing zone around the tunnel. In this regard, not only adjacent buildings will be affected by... 

This study aimed to estimate and simulate the phenomenon of buzz in a supersonic air intake and examine the effects of turbulence models on the accuracy and quality of modeling this phenomenon was divided into two parts. In the first part, turbulence models and characteristics of each of them in modeling supersonic flow was studied as well as available researches were investigated to achieve appropriate numerical method for numerical analysis of intakes using turbulence models. In the second part, one axial symmetry intake of the compound density type was taken which designed for Mach number of 2.0 in order to achieve accurate numerical methods and validate it to model intakes flow. With ... 

Proton precession magnetometers are one of the most sensitive scalar magnetic sensors. Their function is based on Zeeman effect and also nuclear magnetic resonance phenomena. In this project we have designed and implemented needed coils, swithching and signal detection circuits. Because of extremely high sensitivity of this sensor to induced noises and also gradient of earth’s magnetic fileld, detection of precession signal needs design of low noise electronic circuits with special EMC considerations. The implemented system in this project contains different blocks, such as switching circuit and its related control unit, amplifier, filter and frequency meter. Using this system, the obtained... 

Effective field theory is a practical method for model building and explaining experimental/observational data. These theories are constructed based on knowing low energy degrees of freedom and symmetries (accidental or fundamental). By construction, these theories are applicable up to a cut-off scale and their predictions beyond that are not reliable. For applications to higher energies a UV completion is needed through which modifications are applied or new heavy degrees of freedom are introduced. In order to complete a theory in a Wilsonian approach, scattering amplitudes must satisfy some constraints. These constraints are derived from basic assumptions like Lorentz invariance,... 

In traditional financial theory, investors aim to maximize returns while minimizing risk by using all available information to make informed choices. However, behavioral finance shows that investors often deviate from fully rational behavior due to cognitive biases. In reality, investor decisions result from a complex interplay of rational and behavioral elements. The disposition effect, a common behavioral bias among investors, refers to the tendency to sell winning stocks too early while holding onto losing stocks for too long. This phenomenon was first examined by Shefrin and Statman (1985), and subsequent research has explored and confirmed its existence among various investor groups.... 

Numerous structures which are involved in seismic soil-pile-structure interaction have been destroyed. Considering complexities which exist in soil-pile interaction problems and lack of precise methods without imperfect bases, it is necessary to use numerical methods for analyzing soil-pile interaction problems. In this research, three-dimensional modeling and studying the effect of changing soil and pile parameters on the behavior of pile under earthquake loading is performed using finite difference software, FLAC3D. The soil in this model has a softening behavior. Real earthquake spectrum has been applied into the model as the acceleration time history at the bedrock level. The results of... 

The current global economy challenges and the importance of maintaining a sustainable development strategy has increasingly bolded the importance of construction productivity measures. This research describes the results of a running research that is to find the most critical factors affecting the productivity of high rise concrete building projects in developing countries. To achieve that, we have conducted Delphi method in two phases. In the first phase we had a brainstorming program with construction experts from owner organizations, construction contractors and designing engineers to identify factors that have influenced productivity in recent concrete building construction projects.50... 

Multi-period Value-at-Risk (VaR) forecasting is important for risk management. Financial institutions especially commercial banks according to Basel Committee regulations for capital adequacy in “Internal Approach”, should forecast their VaR for multi-period horizons (longer than one day). The most conventional approach for forecasting multi-period VaR is scaling one-day forecasted VaR that is called “square root of time rule”; therefore most works in this area have been focused on forecasting one-day VaR. In this study, we review performance of a wide range of different methods in forecasting multi-period VaR. The results of our study show that historical simulation performs weakly in... 

Modern communication and space systems such as satellite communication devices, radars, SAR and radio astronomy interferometers are realized with large antenna arrays since this kind of radiating systems are able to generate radiation patterns with high directivity and resolution. In such a framework, conventional arrays with uniform inter-element spacing could be not satisfactory in terms of costs and dimensions. An interesting alternative is to reduce the array elements obtaining the so called ‘ thinned arrays’. Large thinned arrays have been exploited because of their advantages in terms of weight,consumption, hardware complexity, and cost over the... 

A large number of structures subjected to the seismic loading have been damaged or have experienced failure in different parts such as the pile structure or even in the entire structure due to unanticipated effects of the soil-pile-structure interaction.The complexity of problems regarding the soil-pile-structure interaction is an influencing factor in prediction of the behavior of structure during the earthquakes. In this study, the effect of the interaction on the dynamic response of bridges was investigated using the finite element software ABAQUS. The primary purpose of this study, as previously described, is to study the effects of the soil-structure interaction on a bridge located on a... 

After being introduced in 2009, the first fully homomorphic encryption (FHE) scheme has created significant excitement in academia and industry. Despite rapid advances in the last 6 years, FHE schemes are still not ready for deployment due to an efficiency bottleneck. Here we introduce a hardware/software codesign, in fact a hardware accelerator optimized for a class of reconfigurable logic to bring homomorphic encryption schemes one step closer to deployment in real-life applications. The accelerator we present is connected via a fast PCIe interface to a CPU platform to provide homomorphic evaluation services to any application that needs to support blinde computations. Specifically we... 

In this project design of adaptive neural network controller for uncertain nonlinear systems in the presence of different restrictions has been investigated. After providing introduction and motivation, two general forms of nonlinear systems including strict- feedback and pure- feedback have been introduced. In order to solve the problem caused by each restriction, a solution has been proposed. For the strict- feedback nonlinear systems several restrictions are considered such as, unknown dynamic model, unmeasured state, input saturation, unknown control directions, time delays in states and input. Stability analysis based on the Lyapunov theorem has been established. In addition, two kinds...