Sharif Digital Repository

The discovery of oil and gas resources in deep waters led to the invention of various platforms adapted to these waters. As the search for oil and gas resources is advanced to deep water, it is impossible to use fixed platforms in these depths. Hence, the idea of using floating platforms that can be used in deep waters has been increasingly considered. An option for the exploration and extraction of offshore oil resources is semi-submersible platforms. Under wave, wind, and current forces, a floating structure moves from its initial location. Types of mooring systems are used to maintain the position of the platform. During the life of a platform, mooring lines may be damaged under... 

Confining nematic liquid crystal between two curved boundary conditions while the nematic molecules have a degenerate planar anchoring leads to complex and beautiful textures of molecular disparagement(defect) in the bulk and on the surfaces. Such the liquid crystal shells are made with double-emulsion techniques in microfluidic devices have provided applications for micro-scale colloidal linkers.In this work, we have numerically minimized the elastic energy in one-constant approximation in present of Fournier’s degenerate surface potential with finite element method. The nematic shell is confined between two spherical surfaces that we have studied the final energies and their related... 

Dye sensitized solar cells are one of the cheap and available technologies that have attracted the attention of many researchers. Many factors such as morphology, microstructure, phase composition and the arrangement of photoanode electrode layers have an effect on the photovoltaic properties of DSSCs. Different approaches have been used to improve the efficiency of this type of cells. Among these approaches, we can mention the use of a mixture of different phases of titanium dioxide and the use of perovskite titanate structures as photoanodes. In the current study, the performance of nickel titanate on light absorption and electron-hole separation in titanium dioxide-based dye-sensitized... 

Studying the interaction of active particles with walls and obstacles has a great importance for practical purposes. Using this knowledge, it is possible to control the motion of active particles in different environments.Experimental evidences show that after encountering with a wall, most of the active particles slide along the wall for some time and then detach in a certain direction, independent of their incoming angle. This special collision is considered to guide, sort or trap active particles.In this dissertation, using Brownian dynamics simulations and theories, we study how different selfpropelled particles and walls influence each other. We explore the behavior of two important... 

The purpose of this study is fabrication and characterization of a mesoporous Perovskite solar cell using Barium Titanate as the mesoporous electron transfer layer. In this study, TiO2 nanoparticles and BaTiO3 oxide perovskites were prepared by sol-gel synthesis method and their pastes were applied to the conductive substrate by spin coating method and applied to electron transfer layer in perovskite solar cells. Then Perovskite solar cells were fabricated with different structures from the electron transfer layer.The results of X-ray diffraction analysis showed that pure Barium Titanate and Titanium dioxide nanoparticles were successfully synthesized with tetragonal and cubic crystal... 

Lipid bilayers are one of nature’s solutions to confine and compartmentalize molecules and microorganisms. Usually, the thickness of the membrane is very small compared to the length scale at which it is studied. Therefore it is convenient to represent it with a 2-dimensional surface that has a stretch, shear, and curvature energy. Triangulated surfaces are the most popular discretization method to study the mechanical behavior of vesicles and fluid membranes since their elastic and bending moduli can be rigorously defined. Fluid membranes pose a particular challenge because they do not have a shear modulus. The dynamic triangulation algorithm is the state-of-the-art method developed to... 

Reconstruction of stochastic dynamical equations from measured timeseries of complex systems plays a crucial role in retrieving dynamic information and studying macroscopic states of such systems. This method which has been pursued for decades is practical in diverse fields like physics, biology, ecology, economics, social science, neuroscience and so on. To obtain stochastic dynamic equation, we have to calculate Kramers-Moyal coefficients from Markovian processes measured time series. We aim to propose new method for deriving these coefficients which is more accurate than two current methods, namely the histogram and kernel methods. In this dissertation, we studied dynamic equations of... 

Perovskite solar cells, with high efficiency operation, have been candidated as a cost-effective and environmentally friendly technology. Despite the great progress, there are some primarily issues remained regarding to the perovskite film and its fabrication methods. A very common perovskite cell structure is FTO/TiO2/CH3NH3PbI3/Spiro-OMeTAD/Au. Although, this structure has some advantages, lack of full surface coverage of perovskite film leads researchers to put much effort on finding other constructions. This surface inhomogeneity reduces the amount of light absorption and therefore efficiency. One way to produce a complete and uniform film is applying mixed-halide composition; such as... 

Analytic hierarchy process (AHP) is a structured technique for organizing and analyzing complex decision. This process is used around the world in a wide variety of decision situation, in fields such as government, business, industry, healthcare, and education. In this method, decision problem first is decomposed into a hierarchy of more easily comprehended sub-problems, each of which can be analyzed independently. Once the hierarchy is built, the decision makers systematically evaluate its various elements by comparing them to one another two at a time, with respect to their impact on an element above them in the hierarchy. In this thesis we will study the hierarchy process and also study a... 

In recommender systems, the available data structure is mostly in the form of a graph; Therefore, during the past years, graph based recommendation methods, especially Graph neural networks, have received a lot of attention. These networks obtain the representation of user nodes and items by aggregating multi-hop neighbors in different ways. Unfortunately, the existing methods are part of the Supervised learning scenario and due to the lack of data in recommender systems, they have faced serious challenges. These challenges reduce the ability to learn to representation nodes and the accuracy of recommendations. Recently, knowledge graph based recommendations have achieved excellent... 

The microstructure, morphology and quality of the perovskite organic-inorganic layer as an absorber layer in perovskite solar cells has a significant role on the efficiency and energy conversion of the device. Different solvent engineering methods have been employed to prepare the perovskite layer with the desired properties and thier reproducibility have been studied. Herein, we applied a two-step solution approach by solvent engineering method, using solvents such as isopropyl alcohol, acetone and thier mixture, for preparation of lead iodide films. Moreover, their metallurgical and photovoltaic properties were investigated. The impact of solvent engineering, using solvents such as... 

In this study, the problem of assortment optimization considering a non-parametric choice model will be introduced. The present study is generally divided into two main parts. The first part deals with modeling customer behavior using the definition of tree models of customer preference behavior. The second part is related to the main problem solving framework in order to get the best product combination in the product classification basket. This research is related to the online seller who intends to sell a certain number of types of products without inventory limit. Customers entering the system, according to their specifications, are provided with the appropriate product classification... 

Polycarbonate (PC) is known as one of the engineering plastics with remarkable mechanical properties, but the application of this polymer is limited due to its high notch sensitivity. Blending polycarbonate with other polymers such as acrylonitrile butadiene styrene (ABS) is a method to resolve this disadvantage. PC/ABS blends are commonly used in automotive industry, electrical and electronic devices. As PC and ABS are not completely miscible, a variety of compatibilizers are used to achieve a suitable microstructure and high engineering properties. Considering crucial applications of PC/ABS blends, different flame retardants are also used to reduce the flammability. These flame retardants... 

In recent years, due to greater attention scientific communities to environment and environmental friendly material, use of natural fibers as reinforcing the polymers has increased significantly. High specific strength, low density, cheap, stiffness and recycled by nature, are including promotional items using natural fibers as reinforcing in the polymer composites. In This study has tried in the first place an appropriate method for producing polypropylene composites reinforced with short jute fibers should be presented and then the physical and mechanical properties of composites will be investigated. Used MAPP and Silane for compatibility took improved between natural jute fibers as a... 

Recently, Polypropylene has been extensively used in a variety of applications in the polymer industry, but its quite low stiffness and toughness limit this polyolefin’s application in the engineering functions; thus, the market of polymer blend and composite manufacturing has grown noticeably in the last few years. In the current project, short Flax fibers are used in order to reinforce the PP matrix. Firstly, Flax fibers were washed with the gentle and harsh condition during the alkalization process, then the optimized alkalization condition was determined through comparison of results from X-ray Diffraction (XRD ), Attenuated Total Reflectance FTIR (ATR-FTIR) and microscopic surface... 

Softening and liquefaction of granular soils due to earthquakes have been a major cause for much destruction in preceding decades. This phenomenon mostly occurs in sandy soils, yet its occurrence has also been reported in gravelly soils in the last three decades. Despite the numerous researches which have investigated the undrained cyclic behavior of gravelly soils during earthquakes, there are still some aspects that need further study.This research investigates the effect of initial static shear stress on undrained cyclic resistance of a well graded, medium dense gravelly soil by conducting a series of cyclic triaxial tests. The 23 performed tests are categorized into 5 groups with... 

We investigate order book events impacts on price movement, using the 31 stocks from the Tehran Stock Exchange. We show that in a low-depth market the mid-price change is explained mainly by a linear relationship with our proposed explanatory variable, modified order flow imbalance that represents the depth-adjusted differences of first level orders volumes in different sides of order book. Our results shows that the bid and ask spread has a negative effect on the power of events to move the price