Sharif Digital Repository

In this thesis, design and development of turbine flow meter for measuring of the volumetric flow rate of open channel and calibration system for it have been developed. This system has been constructed from two main sections, namely: software and hardware sections. The hardware section consists of a turbine, turbine chamber, Tachogenerator, microcontroller, and an ultrasonic sensor for measuring of channel water level. The turbine is located in exposure of water stream, and hence can be rotated in proportional to the water stream in which the value of rotation is measured by the tachogenerator, and then sent to the microcontroller, in order to calculate the velocity of water stream. At the... 

Electrodeposion of Zn-Ni Alloy Nanometer Multilayer has been studied. The investigations show that Multilayer coatings have more corrosion resistance than a Monolayer. The electrodeposition of the multilayer coatings was performed with the single bath technique. The sulfate-borate bath has been used for electrodeposition of the Multilayer coatings. The switching cathode density current has been used for the multilayer coatings in cathode current densities of 20, 30, 40, and 50 mA.cm-2. The number of layers with constant overall thickness of 2 µm was 20, 40, 80, and 100. The composition of layers varied between 5-11% wt Ni with the values of cathode current densities. The Response Surface... 

Content delivery networks play a significant role in improving the quality of internet services by placing the necessary content closer to users on servers. Currently, over half of internet traffic is delivered through these networks to end users. The efficiency of a content delivery network depends on various parameters, including the type of requested content, workload distribution methods, network topology, routing algorithms, caching policies, network server configurations, and resource allocation (shared or dedicated hardware resources). Additionally, the requests made to a content delivery network vary based on the type of service and even the time of day, making optimization a... 

In the present work storage of hydrogen molecules in hybrid nanostructures has been evaluated. Hybrid nanostructures consist of carbon structure bases which have been doped by metal atoms. Carbon structures used in this thesis include graphene and metal organic frameworks (MOFs). Carbon structures have superior properties such as very low density, while metal atoms are considered to enhance the interactions and increase the hydrogen storage capacity. In the first step of the work, Monte Carlo method was applied to model the system. To develop the Monte Carlo method for hydrogen adsorption on graphene sheets, Feynman-Hibbs corrections were added to Lennard-Jones potential. However in the next... 

In a typical rigid robot manipulator, joint angels and velocities are often considered as system states. Joint angels are usually measured by precise Shaft Encoders. However, lack of velocity measurement sensors “Tachometers” and their undesired characteristics in most of existing robotic systems make it difficult to have access to full system states. As full access to the system states in various applications is inevitable, velocity observers can be used to reconstruct or estimate the unmeasured velocity signals. This thesis presents an observer for global estimation of joint velocities in robot manipulators. A non-minimal model of a robotic manipulator is introduced to design an... 

Considering the high growth potential of creative industry as well as the increasing trend of e-business, content-oriented digital business has been the main focus of this research. These enterprises are a subset of the creative industry that are primarily developed in the digital context. After reviewing the literature, it was observed that the keyword "value creation" in this type of business has been less considered by research.On the other hand, in conversations with managers who are active in the industry, a practical vacuum was revealed on how to create value in these firms; Because a comprehensive review of value creation processes in these firms can ultimately lead to more profitable... 

Functionally graded porous structures are very close to the bone tissue. Parameters that are related to the pore size and other parameters that determine mechanical properties, can closely represent properties of bone tissue. These parameters contain the percentage of the porosity and the pore size on the porosity side, and modulus of elasticity and yield stress from mechanical view. Calibrated structures with complex geometries, containing porous material, also can be produced by 3D printing technology. One application of porous structures is in production of dental implant with a cylindrical shape, containing a dense core, surrounded by a porous region. The aim of the present study is to... 

Supercapacitors represent a new class of energy storage devices that have been attracted many researchers in last few years. Graphene with unique properties such as superior electrical conductivity and large specific surface area is one of the most suitable materials in supercapacitor applications. Besides, metal oxides are being used as active compounds in supercapacitors due to their role in redox reactions. In this research, synthesis and characterization of supercapacitor electrodes based on graphene and MnO2 nanostructured materials was studied under different conditions. For this purpose, Graphene oxide (GO) was synthesized by Hummers’ method and then, it was deposited on a nickel foam... 

Hydrogen is emerging as a clean and ideal fuel. However, its dependency on freshwater resources will be a threat to a sustainable environment. Considering the abundance of seawater and the scarcity of freshwater resources, direct electrolysis of seawater to produce hydrogen fuel can be a promising and potential alternative to pure water electrolysis technologies. Seawater contains electrochemically active ions with the nature of competition with the oxidation reaction of water, thus affecting the catalytic activity and, subsequently, the selectivity. From the thermodynamic and kinetic aspect in the electrolysis of seawater, the unfavorable reaction related to the formation of chlorine... 

In this research, Synthesis, characterization and photoelectrochemical application of two dimensional MoS2 and WS2 nanosheets have been carefully investigated. And finally, based on theoritical and experimental analysis results, the mechanisms of the observed photoelectrochemical (PEC) activities were suggested.The ab initio density functional calculations about Mo1-xWxS2 monolayer deposited over a TiO2 (110) substrate revealed a shift in band position of the Mo1-xWxS2 in favor of photoelectrochemical water splitting. Moreover, increase of W concentration in Mo1-xWxS2 could improve the charge separation and increase the effective mass ratio leading to an extension of the electron–hole... 

In this study, thermal and rheological properties of nanofluids of water/carbon nanotubes, water/spherical silica nanoparticles and water/hybrid nanoparticles (hybrid of carbon nanotubes and spherical silica nanoparticles) have been investigated. To do so, carbon nanotubes have been synthesized by CCVD process and spherical silica nanoparticles and hybrid nanoparticles by wet chemical method. After synthesis of nanomaterials, nanofluids have been prepared by using SDBS as a dispersant with the concentration of 1.5 times of concentration of nanomaterials and then thermal conductivity, kinematic viscosity, dynamic viscosity and density of nanofluids have been investigated. As the results show,...