Sharif Digital Repository

Thermomechanical processing during hot rolling and subsequent annealing of rolled sheets are one of the procedures for improving the tensile and formability properties of metals and alloys. In this regard temperature and reduction in area are the most important variables governing the behavior of 304 L austenitic stainless steel during the hot rolling process. The aim of this research was to investigate the effect of rolling temperature and subsequent annealing on 304L steel in order to achieve a microstructure with favorable mechanical properties and bimodal grain size. For this purpose, the rolling process at temperatures of -50, 25, 200, 400, 600, 800 and 900 °C using different thickness... 

Nowadays high efficiency and power density are desired for designing a power electronic converter. Technology advances in power semiconductor devices, makes it possible to design converters for operation in higher frequencies to reduce size of the converters. As the frequency is increased, switching losses and temperature is also increased, so designing a converter for high frequency operation needs some tradeoffs. LLC resonant converter as a promising solution for battery chargers has ability to adjust its output voltage during Constant Current and Constant Voltage modes. However, its operation mode would change based on switching frequency change. Therefore, for efficiency-oriented... 

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... 

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 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... 

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 “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 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 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... 

Traffic data plays an essential role in Intelligent Transportation Systems (ITS) and offers numerous advantages, including efficient traffic control and system performance improvement. However, due to the scarcity of data collection systems, missing data in traffic datasets is inevitable. Therefore, traffic data imputation becomes an essential task. Graph Neural Network (GNN) is a type of neural network that operates on graph-structured data and has shown potential in handling traffic network related tasks such as traffic prediction and traffic data imputation. In this paper, we contribute to the body of knowledge with two aspects. First, we focus on traffic data imputation using solely... 

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... 

This research addresses the vehicle routing problem considering heterogeneous fleets, time windows, simultaneous pickup and delivery, and the possibility of split deliveries under real-time traffic conditions. The primary objective of this study is to develop a linear optimization model that can optimally allocate vehicles and routes while taking into account the aforementioned constraints. The branch and bound method is employed in CPLEX software to solve this complex problem. The last-mile delivery, as a significant challenge in the logistics field, is also specifically analyzed. The results indicate that the proposed model is capable of solving the vehicle routing problem efficiently and... 

The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

Design of optimal controllers for nonlinear systems and even for linear systems is one of the most important parts of the control science. In optimal controller design, our aim is to maximize or minimize some kind of cost function associated with that particular problem. Such cost functions are usually combining the overall control effort, system’s energy, or some other important specifications of the system. Explicit solution for linear quadratic controllers exists under some mild conditions such as stabilizability of the system. The solution is in the form of a full state-feedback law. But in practical problems, we may not have access to all of the system state variables. The problem can...