Sharif Digital Repository

In this thesis, some of the well-known DOA algorithms namely Bartlett, Capon, Linear prediction, Maximum Entropy, Pisarenko harmonic decomposition, Minimum norm and MUSIC are analyzed and compared with each other in the identical situations using a uniform linear array. Then based on these comparisons, the appropriate algorithm is selected. In the next step since the linear arrays can't estimate both angles of arrival (Azimuth and Elevation) simultaneously, two dimensional (2D) geometries are introduced and are also compared to each other. Then one of them (circular array) is selected for dipole antenna arrays. The performance of the selected array is evaluated using isotropic elements for... 

Ultrafast signal processing in time-domain with high resolution and reconfigura-bility is a challenging task. This paper, for the first time, introduces a time-varying metasurface consisting of graphene microribbon array for implementing time-lens in the terahertz domain. Given that the surface conductivity of graphene is proportional to the Fermi energy level in the THz regime, it is possible to change the phase property of the incident electromagnetic pulse by changing the Fermi level while the Fermi level itself is a function of voltage. Upon this fact, a quadratic temporal phase modulator, namely time-lens has been realized. This phase modulation is applied to the impinging signal in the... 

In today's era, metal nanoparticles play an important role in technologies emerging from different sciences, such as chemistry, physics, optics, material science, due to their unique characteristics. In the development of nanooptics science, it can be said that metal nanoparticles play an important role. The ability of conductive electrons collective oscillation causes surface charge density fluctuations in nanoparticles, this phenomenon is known as surface plasmons. Surface plasmons are surprisingly coupled with light and cause the significant increase in the intensity of optical fields induced in nanoparticles. Therefore, with the presence of localized surface plasmons or plasmon... 

Understanding of the Molecules is the main purpose of the chemistry. Ab-initio molecular dynamics (AIMD) as a branch of the computational chemistry, tries to give us a deep comprehension of the molecule, and its chemical, physical and optical activities. This comprehension, relies on the accuracy of quantum mechanics, in addition to the speed of the classical mechanics. The mixing of the quantum mechanics and the classical mechanics could simulate activities of the atoms in the time-domain, provided the mixing is done with precaution. This, in turn, helps us to forecast the response of a molecule in different situations, and also translating the macroscopic phenomena in a nanoscopic... 

To date, the plasmonic properties of many metallic and semi-conducting materials have been investigated and used in various industries. One of the plasmonic material categories that have always been considered is polycyclic aromatic hydrocarbon or PAH, whose plasmonic resonance energy depends on the charge state of the molecule. In this regard, it is easy to change the plasmonic resonance energy via changing the induced charge, which is a unique feature of the mentioned materials. In addition, plasmonic structures with excitations in the infrared region are able to enhance the vibration intensity of absorbed molecules by increasing the electric field around themselves. Therefore, they have... 

In this research, the problem of locating fire stations and allocating equipment has been studied and a simulation-optimization approach has been presented to solve the problem. The mathematical models of this research were developed based on the idea of the randomness of the covered demand and the maximum expected coverage model. In these models, the issue of non-availability of equipment to cover accidents, the random nature of accidents, various fire incidents and the equipment needed to cover them are considered. Two mathematical models with deterministic and non-deterministic approach with different scenarios for demand are proposed. The non-deterministic model is developed with the aim... 

One of the main concerns of industrial companies’ managers is providing an efficient logistics system. To achieve an efficient logistics system, the fleet planning problem is studied by many researchers in recent years. This problem consists of multiple sub-problems at three levels: operational, tactical, and strategic. These sub-problems are closely related to each other and need to be studied and addressed in an integrated manner. In this research, an attempt is made to provide an integrated framework to solve the vehicle routing problem (operational), outsourcing problem (tactical), and fleet composition problem (strategic). These problems have various uncertainties, including customer... 

Using “Searchable Encryption” enables us to encrypt the data, while preserving the possibility of running search queries. One of the most important applications of the mentioned is in Cloud Storage. As users do not trust the Cloud space, they are not inclined to store their data on the Could. The solution to this problem is of course, Cryptography. However, ordinary Cryptography methods, eliminate the data’s searchability. Hence, we need encryption schemes that code the data while retaining their searchability. So far, various schemes has been proposed that differ in their performance, security level, and usage. In this thesis, we aim to discuss and analyze these methods  

In this thesis, the aim is designing an optical temporal imaging system. In recent years, due to many applications, including the receipt of high-rate data by slow receivers and compensation of dispersion in telecommunication systems, researchers have considered the topic of temporal imaging. This field of research is based on dispersion, electro-optical modulators or time lenses and space-time theory. By modeling dispersion properties as a depth dimension and taking ideas from three-dimensional spatial imaging systems we intended to increase the temporal resolution and depth of focus of the structure. We also present a novel technique for multiplexing and demultiplexing telecommunication... 

In the last decades, due to the growing demand of transferring information with high transmission rates, the complexity and development of telecommunication and optical systems is remarkable. Researchers around the world attempt to explore extraordinary potential of light to process information. In the mid-19th century, scientists discovered a mathematical symmetry between the spatial and temporal optics fields, which originated from the similarity of equations governing the paraxial diffraction of beams and the dispersion of narrow-band pulses known as space– time duality in scientific texts. This new approach provides more advanced and potent methods to temporal processing and... 

One of the most vital aspects of understanding the traffic phenomenon is scrutinizing the traffic transition status, such as the transition from free flow to congestion. The Percolation Theory is a renowned theory focusing on analyzing various network types to detect the critical zones, which are the zones including links that are important to control to improve stability. By calculating the quality indices of network links, the Percolation Theory can simulate the traffic percolation propagation in the network and determine possible critical zones for further analysis. Most studies in this field assume access to data of several traffic parameters for the entire transportation network, such... 

In recent years, optical biomedical imaging techniques show great potential in noninvasive imaging. Although these methods have many advantages over other biomedical imaging methods (such as Computerized Tomography (CT), Magnetic Resonance Imaging (MRI) and etc.), these techniques confront with some problems such as optical scattering, light absorption and etc. For in vivo imaging, the short-wavelength infrared region (SWIR; 1,000–2,000 nm) provides several advantages over the visible and near-infrared regions: general lack of auto-fluorescence, low light absorption by blood and tissue, and reduced scattering. In this thesis we want to analyze the traditional IR imaging techniques and... 

Strain imaging is a non-invasive ultrasound modality for assessing cardiac function in echocardiography systems. In this thesis, we implemented a fully automated strain imaging system containing 5 steps: 1) echocardiographic view recognition, 2) cardiac cycle phase detection, i.e., the events of end-diastole (ED) and end-systole (ES), 3) segmentation of left ventricular (LV) myocardium, 4) motion estimation of this wall and 5) strain calculation. In this work, we propose a novel deep learning-based framework for phase detection of cardiac cycle by the use of echocardiographic images in multibeat videos. Further, by applying the augmentation technique, the model has been able to detect events... 

Resolvers, due to their robust structure, are widely used in automation systems. Among the types of resolvers, the accuracy of the Wound Rotor (WR) resolver in the occurrence of common mechanical errors is higher than other types of resolvers. therefore, in this thesis, an AFWRR is studied to improve the performance. Increasing the number of poles in WR resolvers is a good solution for increasing the accuracy of these electromagnetic position sensors. However, high-speed WR resolvers due to employing fractional slot windings suffer from rich sub-harmonics in the induced voltages. A common solution for suppressing the undesirable sub-harmonics is using multi-layer winding with appropriate... 

Using visual information of an environment is the immediate way of detecting and identifying an unknown environment. These information maybe obtained using straight visibility detecting sensors. One of the formal models of these visual information is the visibility graph which have a vertex for each vertex (corner point) of the environment and two vertices have an edge whenever their corresponding corners see each other. Then, the problem is to characterize such a graph and reconstruct the target environment with equivalent visibility graph. Despite existence of plenty of research results, these are open problems in computational geometry and rigid results exist only for limited special... 

Housing is among the most primary fundamental needs of the household ,which consumes a high Proportion of the household expenditure and therefore it remains An important topic in macro economical analysis. Estimating and determining housing prices in different urban , areas is also important for planning .Estimations are also use in many decision making and process for the urban , regional , public, privet and organizational policy making. Due to the heterogeneity housing prices and the fact that it’s prices are affected by it’s characteristics , in this research housing prices of a few regions in tehran metropoly are assessed by the hedonic price model using macro and micro... 

Linear position sensors are widely used in linear motion-control systems. In this thesis, the design, optimization, performance analysis, and prototyping of a linear variable reluctance, variable air-gap length resolver are discussed. The accurate modelling of the studied sensor needs three-dimensional (3-D) time stepping finite element analysis (TSFEA) that is computationally expensive and unsuitable for co-usage with optimization algorithms. Therefore, the aim of this thesis is to establish an accurate, yet computationally fast, model suitable for optimal design of linear variable reluctance resolvers. The proposed mathematical model is presented based on modified winding function method. ... 

Computerized tomography (CT) imaging is a powerful tool among the existing bio-imaging techniques for capturing bio-images. In a CT scan procedure, linear sensors receive x-ray radiations, passed through the patient’s body and the reconstruction algorithms provide the required image for physicians from the captured data. In spite of its great advantages, due to the use of x-ray radiations and its ionization effect, it will raise the risk of cancer in long times. Therefore, to take benefit from several advantages of CT such as low-cost and high speed, solving this problem is aimed by many physicians and scientists. A new compressed sensing-based algorithm in order to reduce the number of... 

Frequency-scan millimeter-wave imaging systems are of high interest due to their low cost and acceptable performance in many applications such as concealed-weapon-detection. In recent years, the performance of this system in view of imaging time, image quality and cost has been improved via its implementation based on metamaterial apertures. These structures take advantage from the famous theory of single pixel imaging in optics. Through using the compressive sensing principle, the number of required imaging modes for obtaining diffraction limited resolution is reduced which in turn lessens the imaging time and more importantly the required bandwidth. Still, the image quality and resolution...