Sharif Digital Repository

Modular Robots are group of robots which are made of small components called modules. The advantage of these robots to others is their ability to change physical configuration. Using of these robots in configuration changing due to environmental conditions is popular. While, reconfiguration is one of the most important features in modular robot, it’s the most important concern too. Path planning problem is one of the important problems in robotics .So far, most of presented path planning methods and algorithms are based on fixed-structure and they had little attention to path planning and configuration changing, simultaneously. In this thesis, the Genetic Algorithm is used to find path and... 

Nowadays, multilevel converters are significantly developed in industrial applications as well as energy transmission systems regarding proper quality of output waveforms and fault tolerant operation ability. Among the different topologies of multilevel converters, modular multilevel converter (MMC) due to its modularity feature it more accepted in high voltage direct current (HVDC) transmission systems. Fast fault detection in power electronics converters is necessary to bypass the defected part in order to prevent failure propagation to other Submodules and to provide continues servicing. On this basis, different researches are reported in literature for MMCs fault tolerant operation. In... 

Nowadays Systems in different fields of research like computer science, biology, social networks, information networks, and economics are modeled as graphs. The graphs which model real world systems have very different topological characteristics than those of classic networks. One of the prominent characteristics of these networks, is that its not practical to describe a general model for their structure and behavior. As a consequence of this complexity in modeling and structure, these networks are called complex networks. One of the most important observations in complex networks is the presence of communities, it means that in such networks one can separate vertices in disjoint sets, such... 

Let E be a semi-stable elliptic curve over Q with conductor N and L(E,s) as its L-function. We say that E is modular if there exists an eigenform of weight 2 and level N over X_0(N) such that L(E,s) equals the L-function of f or L(E,s)=L(f,s). Wilse's method to prove this was by proving that the Galois representations induced by E and f are equivalent. First we will discuss that equivalency of those representations is equivalent to equality of L-functions and after that we will use deformation theory for Galois representations to overlook the main ideas of the proof of the modularity theorem. Wiles using the idea of deformation of Galois representaions proved that under proper conditions... 

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 thesis, we studied the representation of Galois groups and modular forms.Also, we presented the Serre’s conjecture which has been proven in two papers published in 2005 and 2008. Moreover, the main aim of this text is presenting the Fontaine-Mazur and Serre’s conjecture  

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... 

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... 

The present research intends to design a controller for modular reconfigurable manipulator robots. Manipulators are made up of several links and joints. By attachment of links and joints in different ways, one may make a variety of robot configurations in modular reconfigurable manipulators.
To meet modularity and reconfiguration needs, hybrid control architecture was selected which contains a central supervisory section and distributed controllers located on individual modules. Central supervisory section specifies the trajectory of the robot and other control tasks like position control, speed control and etc. are performed by distributed controllers. In hybrid architecture, dynamic... 

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... 

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... 

Modular multilevel converters provide higher output voltage levels than switches rated voltages by switching between cascaded modules. Increasing the number of modules might results in less reliability because of an increase in the number of elements. On the other hand, an increase in the number of modules decreases the semiconductors rated voltage, switches power losses and thermal stresses and consequently a lower switches failure rate is expected. Therefore the optimal number of modules, would minimize the failure rate. To investigate it, in this project, first fundamental elements of converter are designed for a MMC with different number of output levels, to drive a medium voltage medium... 

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... 

Albert proposed the cyclic algebraof the degree 4 in1934. After that more studies were conducted on thecyclic algebras on F in conditions in which L = F(µ )nis an extention of F, for in the Albert’s example it wasmanifest that 2|[F(µ ) : F]. In a paper in the same yearnAlbert proposed a condition for an F-division algebrato be cyclic. In this thesis, a theorem will be proposedin which for the condition (n=1) the Albert’s theoremwill be the result. Moreover, F-division rings of the pndegree are investigated. the required means is modularspectral factorization which was for the ?rst time de?nedin clusters by Merkuryev. Finally a condition will beproposed for the fact that F-division... 

Selection of appropriate thermohydraulic tool for analyzing nuclear reactors is a trade of between accuracy and calculation run-time. Nuclear reactors analyses perform on two levels including system and sub-channel. In this regard or the system codes' one-dimensional approach is selected or the CFD codes for considering the three-dimensional and non-equilibrium phenomenon are employed. In this research a T-H tool for prediction of light-water cooled reactors core is developed. Although this code requires lower CPU and run-time in comparison with CFD codes, in contrast with system codes can report non-equilibrium and three-dimensional phenomenon. This code has a modular implementation based... 

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.... 

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... 

This thesis aims at developing control system of a full converter wind turbine with modular and parallel back-to-back converters. Modular structures and paralleling of power electronic converters are the state-of-the-art methods for increasing their transferable power to the grid. Technological advances in high power wind turbines, especially for the offshore installations, which contain permanent magnet synchronous generators with back-to-back full converters, promote the use of modular structures.
In addition to developing the regular control systems of wind turbines for modular structures, selection of appropriate structures, power sharing between parallel converters and mitigation of... 

One of the main issues of business world is competition and competitiveness, and this cannot be happened unless one company absorb new ideas and innovations. Based on what scholars mentioned, companies should utilize users instead of professionals in order to create new innovations, and this is due to that users have better understanding of what users want. As a result, in the mobile platforms, platform owners need to know how to invoke users to create more innovative apps. In this research we were into finding important matters that increase number of innovation of users. We saw that lead-userness, toolkit support, work method autonomy, knowledge sharing, and modularity have an impact on... 

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....