Sharif Digital Repository

Titanium dioxide (TiO2) is a transparent n-type semiconductor with wide band gap which makes it suitable for applications such as solar cells. TiO2 dye-sensitized solar cells (DSSCs) transform the visible light energy to the electrical energy by excitation of absorbed dye. In the present study, TiO2 nanowires and nanoparticles were synthesized by hydrothermal and sol-gel methods, respectively. The effect of TiO2 morphology on photovoltaic performance of the cells was studied by fabrication of single layer DSSCs containing pure nanowires, pure nanoparticles and mixture of nanowires and nanoparticles with various weight ratios. The results revealed that, DSSC made of 10 wt% nanowires and 90... 

In this thesis, a model of predator-prey with a continuous threshold harvesting with refuge and without refuge the prey is formulated; and its dynamics, also, its direct effects on ecosystem such as the stability properties of some periodic solutions and coexistence eqilibria are surveyed. Numerical and theoretical analyses are used to investigate boundedness of solutions, stability of eqilibria, periodic orbits, bifurcations and heteroclinic orbits  

Two phase slug flow often happens in culvert and water tunnels conveying water from dams and weirs. Having complicated hydraulic properties, little is known about different hydraulic properties of this kind of flow, while most of the previous studies deal with other liquids than water and air, mostly dealing with chemical and mechanical engineering problems. In this paper, the results from experimental study of air/water slug flow due to changing in slope of the conduit from horizontal to 2, 3 and 4% are presented. The conduit has rectangular cross section with dimension cm of Plexiglas material and inclined part. Air is added to the system upstream of the conduit using an air discharge.... 

Molten carbonate fuel cell (MCFC) is a kind of high operating temperature fuel cells (600-800℃), tupically used for stationary power plant. These fuel cells have high efficiency (about 50%), but expensive to produce electricity. Hence, fuel cells are integrated into gas turbine cycle to decrease cost and increase efficiency of system. In this work, an integrated pressurized molten carbonate fuel cell is selected. Then, structure of selected process is changed and two new systems have proposed. Then, steady-state and dynamic behaviors of three systems were simulated separately, and their performances were compared. Efficiency increased about 5% in two new structures. Total power of system,... 

Servo control valves including pressure control valves and flow control valves are the main components of the hydraulic system. Since these valves are responsible for controlling the flow or pressure in hydraulic systems, are important. In the present study, we focus on modeling and sensitivity analysis of an electro-servo-hydraulic valve with two stages. The first stage mechanism is the seating type (flapper-nozzle) and the second stage mechanism is the sliding type (spool type). For simulation main components of the servo valve include torque motor, flapper, flow through the nozzle-flapper, flow through the orifice and flow through the valve spool and body separately have been modeled.... 

Flash calculations using equations of state are the basis of compositional simulators and inaccuracy in these calculations leads to errors in some time steps or even complete failure of a simulation. One of the problems of this approach is the use of iterative loops, which leads to a high computational cost. The purpose of this research is to use deep machine learning methods, namely multi-layer perceptrons and convolutional neural networks to solve this problem. At first, we defined two 5-component and 10-component hydrocarbon fluid models and used one of the conventional methods of flash calculations (Modified Successive Substitution method) in order to generate the data required for... 

Cardiovascular disease is one of the most leading causes of death in the world and one of the common methods for treating such diseases is replacing damaged blood vessels with artificial ones. Electrospinning, which is a method of producing polymer fibers, is one of the best and common methods of producing synthetic vessels. The first goal in this study was to create a suitable structure for fiber production; therefore, first, an electrospinning device and environmental chamber were designed and built. Then, the effect of alternative and uniform flow on the diameter and structure of the fibers was investigated using 15% wt. Polycaprolactone solution. The results of this study showed that the... 

BASHTI is a new implant-less ACL reconstruction surgery which has recently been considered for its advantages. This study aimed to investigate the effects of tendon and cannulated drill bit diameter on the BASHTI fixation strength and core bone engaged length (CBEL) in an anterior cruciate ligament (ACL) reconstruction. It is believed that CBEL may affect both bone healing process and fixation strength in this technique. Bovine digital tendons and Sawbones blocks were used to mimic the ACL reconstruction. Tendons were sized to 6, 7, 8, 9, and 10 mm and the hole size for the 6-9 mm tendons was set to 10 mm while for the 10 mm tendon was set to 12 mm. Mechanical strength of the specimens was... 

Security analysis of cryptographic systems against implementation attacks, including active and passive attacks, is an important issue due to the large number of such attacks in the real world. Since 2000’s, cryptographers have begun attempting to model active and passive attacks to implementation of cryptographic algorithms. At first, cryptographers modeled the attackers with ability to exploit leakaged information, leading to leakage-resilient cryptography. Afterwards, cryptographers modeled the attackers with ability to tamper with the cryptographic algorithms which led to tamper-resilient cryptography. Actually, the major proposed cryptographic primitive dealing with tampering is the... 

Todays, the most important thing in the oil and gas fields is how to find the main properteis as porosity and permeability; therefere in this project was tryed to estimate to correct porosity in the reservoir area with using estimated porosity from siesmic attributes. For this study Mishrif reservoir in Sarvak formation was selected and the used data are 3D siesmic and also corrected porosity estimated by analysing siesmic attributes from five wells. For combination sresmic and log data, Simulated Annealing was seleted as a Neural Network optimizer for this project.
 

Dimethyl ether (DME) as a clean fuel is a suitable alternative for diesel fuel. It has a high cetane number and does not contain any sulfur or metal compounds. Furthermore, DME does not form any soot and has a potential to reduce NOx emissions. In addition, it is not corrosive to any metal and not harmful to the human body. Two approaches are currently used for the production of DME from synthesis gas. The first is an indirect two-step process involving methanol synthesis followed by catalytic dehydration of methanol to DME over solid-acid catalysts, while the second method enables direct synthesis of DME using a bifunctional catalyst. At present, indirect synthesis of DME is a more... 

The target of reconnaissance receivers is to detect radio frequencies and pulses present in the environment and extracting their characteristics. To receive the signals in the range of 2 to 18 GHz, different receptors can be used. Each receptor has its specific aplications, advantages and disadvantages. In this project, we proposed a receptor scheme with the following features: 1-simple hardware, 2-ability to detect simultaneous signals, 3-hundred percent probability of intercept (POI), 4-high input bandwidth and 5-rapid threat detection. To have such a receptor, we should move data processing parts of receptor to digital domain as much as possible, and reduce the amount of analog... 

Bashti Bone Plug Technique (BBPT) is a novel implant-less surgical methodology for Anterior Cruciate Ligament (ACL) reconstruction. The technique uses the core bone plug belonging to the patient, cut during tunneling with hole saw drill bit, to fix the ends of the tendon graft. Results show that when fitting the bone plug in this method, a large strike is required for fixation which leads to breaking the bone plug and consequently reducing the effective length of the bone plug inside the tunnel during fixation. Therefore, it was decided to use the sheath which covers the bone plug to overcome said challenges since during fixation with the sheath, Due to the low friction coefficient in these... 

The development and use of design methods for control structures has grown significantly in recent decades. In this study, a systematic plantwide control procedure proposed by Skogestad, has been used. The main idea of suggested method is based on the self-optimizing variables. One of the advantages of this method of designing a control structure is considering the economic optimization of the process in most stages of its implementation. The indirect and direct dimethyl ether synthesis from natural gas feed have been investigated in this study. In this research, indirect and direct dimethyl ether synthesis processes are simulated with Aspen Plus V10 and degree of freedom analysis is done....