Sharif Digital Repository

Public-key cryptography is vital to secure digital communication. The classic instances of these cryptosystems are insecure against large-scale quantum computers. As a result, post-quantum cryptography has emerged as a replacement, which includes different categories. Isogeny-based schemes are one of the promising candidates mainly because of their smaller public key length. Due to high computational cost of such schemes, efficient implementations are significantly important. In this thesis, we have presented various solutions at three different abstraction layers. At the lowest layer, which deals with modular arithmetic, two hardware architectures are presented to perform modular... 

The dynamic nature of today’s manufacturing industry, which is caused by the intense global competition and constant technological advancements, requires systems that are easily adaptable with new functions and technologies. In fact, a highly responsive manufacturing system is needed in which, introducing new products, adjusting system capacity with demand fluctuations and integrating new technologies with the existing ones are quickly possible. Reconfigurable Manufacturing systems (RMS) are a relatively new paradigm in industry that enable rapid adjustments of production capacity to changes in product mix and volume through their main characteristics including modularity, scalability and... 

Multilevel converters are the best solution in medium and high voltage applications because of their better output votage quality, redundant structure, less power semiconductor losses and common-mode voltages. Modular multilevel converters (MMCs) have additional advantages such as higher degree of modularity, transformerless operation capability and using a single common DC-bus. All these useful features make MMC the first alternative for HVDC systems. Fault detection, defected cells insulation and post fault operation control are necessary to ensure MMC continouse service. A simple, fast and accurate fault detection method is proposed for MMC semiconductor power switches in this thesis.... 

In Modular Multilevel converter, it is necessary to attain different objectives simultaneously. One of the most effective control methods which can cope with this kind of systems is the Model Predictive Control (MPC). This method predicts the values of control objectives based on different feasible states and determines the optimal one using cost functions. The number of feasible states can increase when the number of switches increases in the converter. This makes the MPC unable to be applied in the MMCs with hundereds of submodules (SMs) in each arm because of its heavy computational burden. In this thesis, a modified model predictive control is proposed to reduce the computational burden.... 

The main purpose of this thesis is to study computational questions related to compact Riemann surfaces (algebraic curves) with main emphasis on the theory of Grothendieck’s dessins d’enfants; where recovering the explicit formula of a Belyi map from the corresponding dessin on a topological surface is important. Some applications such as investigating the modular j-function and also certain classes of modular curves are included in this thesis along with a summary of attempts toward generalizing the Belyi theorem to complex dimension two.First two chapters contain necessary prerequisites on compact Riemann surfaces and a short introduction to the theory of dessins d’enfants and Belyi... 

Complex directed networks are widely used in representing, modeling and summarizing various homo and heterogeneous real networks such as protein-protein interactions, social and twitting networks, brain connectomes, chipsets mapping and marketing. While working on undirected networks in the hope for detecting communities or any other static and dynamic structures, has been on agenda of many physician and computer scientists, dealing with directed ones seems more challengeable for quick advances. Availability of theoretical basis especially symmetric adjacency matrix recommends modeling with undirected graphs but we believe that directed graphs are more general and practical to model real... 

Regarding the analysis of real-world networks, the ability to detect regions of high density or “community” is of great importance in network science. The motivation behind this endeavor comes from many publications confirming that the agglomeration of relations is meaningful on its own. At the same time, there have been some attempts, although less than the unsigned route, toward the detection of community in groups of positive relations (similar to unsigned mode) that have, internally, as few negative ties as possible. As an example, signed Modularity is one of the few algorithms in this route.In this thesis, we first tried to analyze the structure of real networks to find out about the... 

The dynamic nature of today’s manufacturing industry, which is caused by the intense global competition and constant technological advancements, requires systems that are easily adaptable with new functions and technologies. In fact, a highly responsive manufacturing system is needed in which, introducing new products, adjusting system capacity with demand fluctuations and integrating new technologies with the existing ones are quickly possible.Reconfigurable Manufacturing systems (RMS) are a relatively new paradigm in industry that enable rapid adjustments of production capacity to changes in product mix and volume through their main characteristics including modularity, scalability and...