Sharif Digital Repository

This thesis is concerned with stability and tracking of nonlinear noisy Lipschitz systems over the packet erasure channel with feedback acknowledgment when system and measurement are due to bounded noises. The desired stability and tracking criteria is bounded stability and tracking in probability. Two approaches are adopted to address the desired stability and tracking performance, one is based on the Chebyshev inequality and the other is based on the Binomial distribution. It is illustrated that when the erasure probability is large, the approach based on the Chebyshev inequality provides a better bound for stability and tracking in probability; while, when the erasure probability is... 

Compared to block copolymer, random copolymer polypropylene (PPR) has lower toughness and impact resistance, and this defect creates limitations in the use of this polymer in some applications, including in the pipe industry. Creating a beta crystal structure in random polypropylene with the help of nucleating agent is a well-known method to solve this weakness. Following the previous activities in this group, the current research was defined based on the construction of beta nucleator based on calcium pimalat and its use in pipe-grade random polypropylene. Four methods were used to add germinating agent to polymer in this research. Synthesis of germinating agent and then adding it to the... 

Nowadays, many entities and the relationships between them create different types of networks. Graphs are appropriate tools to model these networks. In a graph, nodes show individuals and edges show the relations between them. One of the most important research problems in the field of network analysis is community detection. In a network, a community is a group of nodes that has a lot of connections to the nodes inside the same group and a few to the ones which are outside. Community detection has many real world applications. Recommending items in recommender systems, detecting spy and terrorist groups and predicting future links between members in a social network are some examples where... 

Application of wind energy and specially wind turbines as a green source of energy is getting more popular and as a result, the knowledge of wind energy has been improved dramatically. The purpose of this research is to determine the flow characteristics in the boundary layer profile over an airfoil which is used in a wind turbine blade. The model is sinusoidally oscillated in pitch. For the present study, the critical cross section of the wind turbine blade has been selected and the boundary layer velocity profiles over its airfoil have been investigated experimentally. Dynamic motion is produced with sinusoidal oscillator and the reduced frequency is varied in the range of 0.054 to 0.1.... 

This thesis studies a multi-product location-routing-inventory problem in which location-allocation, inventory and routing decisions are to be taken in a three-level supply chain including suppliers, depots and customers. Each product for each depot could be supplied by more than one supplier and each supplier has a limited supplying capacity per period. Products are distributed from depots to customers by a homogeneous fleet of vehicles. Backlogging is allowable for each customer on the condition of not exceeding a fraction of customer’s demand. A mixed-integer programming formulation is presented to describe the problem then a new hybrid heuristic algorithm based on the simulated annealing... 

Due to Reduction of fossil fuels resources and the pollution caused by using them, it seems inevitable to shift to using reproducible energies. Among different resource of reproducible energy, fuel cell is one of suitable technologies for investigation and development. Fuel cell is an electrochemical system to convert chemical energy of fuel directly to electrical energy. Each fuel cell has seven part (two Bipolar Plate, two electrode, two catalyst layer and polymeric Membrane). Oxidation occur in anode of fuel cell and created electron enters external circuit and then riches the cathode. The positive ion created in the anode reaches the cathode through the membrane (electrolyte) and... 

Planning as one of the most important management tasks in all organizations is necessary and essential. Strategic planning is at the top of every organization’s decision-making, and it is important and crucial. Universities like other organizations cannot survive or thrive without a clear strategy. This study has done considering the importance of planning in universities and higher education institutions and discussing one of the challenges in this field. This challenge is analyzing the paradox of top-down planning and collective decision-making and the authority of faculty members in universities. It is an exploration research with the qualitative method and according to a case study of... 

Tin sulfide with an energy gap of about 1.1 ev is a semiconductor suitable for applications such as solar cells, lithium-ion batteries, photocatalysts and other semiconductor-based devices. There are several methods for synthesizing this semiconductor at the nanometer scale, among which the solvothermal method is an efficient, controllable and inexpensive method. By precisely controlling the parameters of this process, two-dimensional tin sulfide nanosheets with high purity and desirable morphology can be produced. In this research, tin sulfide has been synthesized by solvothermal / hydrothermal chemical method and its metallurgical properties have been studied. Effect of solvothermal... 

Nowadays, heterogeneous photocatalytic processes have attained a particular importance among the other advanced oxidation processes in purification of organic polluted wastewaters. Titanium oxide is the most popular photocatalyst because of its strong oxidizing abilities for decomposition of organic pollutants, superhydrophilicity, chemical stability, long durability, non-toxic nature, and low cost. Same as other semiconductors, high recombination rate of charge carriers is the main weakness that cause decreases in photocatalytic efficiency. One of the solutions is coupling this material with other semiconductors. Core-shell nanoparticles are the type of these composites that show high... 

Nowadays, in many of industrial processes, it’s necessary to measure acceleration of a moving object. Among the different type of accelerometers, the piezoelectric type are most useful and the most widely used. These sensors come in various configurations.
In the past, analytical and semi-empirical models have been used to design piezoelectric accelerometers. In these methods, based on some assumptions, the accelerometer nonlinear model is replaced with a linear model and the equivalent circuit model has been used to model accelerometer behavior. In these methods, the behavior of accelerometer become different from the expected one.
Recently, with the invention of efficient computing... 

Graphs are powerful tools for modeling real-world data. Data analysis using graphs allows us to study the samples relations and identify rich patterns. Although graph modeling can result in a better understanding of data, it requires having strong methods. Graph neural network models have attracted more attention in recent years. These networks are able to simultaneously analyze data features and their relationships to each other and find node representation in low-dimensional feature space. However, due to the novelty of this field, many challenges are still unexplored.In this study, we intend to examine the challenges in this field by focusing on improving the representation of nodes with... 

Features with sculptured or free-form surfaces appear frequently in computer-aided design of parts common to aerospace, automotive, and die and mold industries. Because of their ability to machine complex features and to achieve good surface finish, ball-end tools are widely used in the finish milling process of sculptured parts. This research has been devoted to the modeling of cutter-workpiece engagement (CWE) boundaries, cutting forces, and stability prediction in ball-end finish milling process of sculptured parts. In the first step, a new analytical model taking into account the effect of surface curvatures was presented for three-axis and five-axis ball-end milling processes. In this... 

There are many linear and nonlinear programming problems with uncertain parameters and variables. These types of linear and nonlinear models are called fuzzy linear and nonlinear programming problems. Solving such problems is important, due to applications and variety of these models. Here, we first review various types of fuzzy linear programming problems based on the models or the solution methods. Next, we revise a method due to Kerre to compare two unipolar LR fuzzy numbers and present some new results on the comparison of LR fuzzy numbers. Then, we solve linear programming problems with unipolar fuzzy numbers by our proposed time varient particle swarm optimization (TV-PSO) algorithm.... 

One of the problems that affects the lifetime and cycle life of lithium ion batteries is the localized corrosion of aluminum current collector (during the storage and charging cycle). Since applying corrosion-resistant coating has always been one of the ways to reduce corrosion of materials in different environments, in the present project, this method has been used to prevent corrosion of aluminum in lithium-ion batteries. For this purpose, the graphene oxide coating, which has desirable anti-corrosion properties, was coated on aluminum by Electrophoretic deposition and doctor blade methods. linear polarization, cyclic voltammetry and electrochemical impedance spectroscopy were performed to... 

In the preceding years, hydroxyapatite (HA)-based coatings and scaffolds have been known as the best biomaterials for dental and orthopedics applications. Biocompatible and bioactive hydroxyapatite-based Coatings on metallic implants is one of the best methods for reaching both suitable mechanical properties and appropriate bioactivity, leading to better osseointegration and osteoblast proliferation. The ultimate goal of this project is characterization as well as mechanical and electrochemical behavior investigation of Hydroxyapatite- Chitosan nanocomposite coating by electrophoretic deposition (EPD) method on Plasma Electrolyte Oxidation (PEO) treated titanium substrates and Magnesium (Mg)... 

Titanium anodes activated by noble metal oxides under the trade name of dimensionally stable anodes (DSAs) are widely used in the electrolytic industry, particularly in chlor – alkali electrolysis. Over 20 years of use, the fundamental aspects of their long – lasting performance are not fully understand and the corrosion mechanisms are still the subject of many investigations. RuO2 – TiO2 coatings on titanium substrate, due to proper electrochemical characteristics and good corrosion resistance, is most applicable as an anode in chlor – alkali systems. In the present investigation, the first layer of Pt – Ir coating is applied via electrodeposition method on the pretreated titanium substrate...