Sharif Digital Repository

Modeling the water flow in cohesive fracture is a fundamental issue in the crack growth simulation of cracked concrete gravity dams and hydraulic fracture problems. Discontinuities in porous materials such as concrete, soil and rock have important role on the mechanical and hydraulic behavior of a multiphase system. The creation and propagation of discontinuities, such as cracks in a multi-physics system, lead to a complex non-linear coupled problem with continuous topological changes in the domain.In this study, a mathematical model is presented for for the analysis of dynamic fracture propagation in the saturated and semi-saturated porous media. The solid behavior incorporates a discrete... 

A Polygonal finite element method without conforming mesh was introduced by the authors for modeling large deformation elastoplastic problems. In this method, the geometry and interfaces of the problem are modeled on a uniform mesh. The boundaries are defined on the uniform background mesh using the level set method. Different polygonal elements will be created at the intersection of the interface and the uniform mesh. Polygonal element shape functions are used for the interpolation. In this paper, the capability of this polygonal finite element approach for modeling large deformational frictionless dynamic contact-impact problems is investigated. Contact interfaces are modeled independent... 

In this thesis, manganese oxide nanoparticles with about 5 nm size were synthesized via solvothermal to maximize surface and active sites for proton relaxation. The synthesized nanoparticles were coated with gentisic acid to acquire suitable colloidal stability and biocompatibility. The nanoparticles showed low cytotoxicity in MTT assay. Electrosteric mechanisim was employed for colloidal stability. This mechanisim doesn’t need high surface charge and thick coat which are vital for particles functionality. Then by cell culture eliminating and adding protamine sulfade, nanoparticles uptake were increased tremendously. In this thesis for first time Prussian blue was utilized for staining... 

Diseases such as cancer lead to extensive conversion in the biological structure of cells. These conversions can overshadow cell function. The dynamics of a cell directly depends on how it interacts with other cells and the extracellular environment. Most of these interactions are associated with the occurrence of mechanical phenomena and are due to forces that the cell has experienced. Cell mechanics manifests itself in the Mechanotransduction, the ability of a cell to sense and respond to external forces. Cancer alters the mechanical properties of the components of the cytoskeleton. Understanding the biomechanical behavior of cells and cytoskeleton can play an important role in early... 

In order to improve performance and optimize design of high pressure combustion devices such as liquid rocket engine, gas turbine engine, and diesel engine there is a need for comprehensive understanding of injection, mixing and combustion in supercritical condition. Under this condition chamber pressure is higher than critical pressure of fuel and oxidizer. The characteristic of supercritical condition, include changing thermophysical properties such as density, CP, and compressibility factor. Therefore under this condition ideal state equation cannot correctly predict the mentioned properties. These characteristics make supercritical combustion different from other combustion regimes.... 

In photocatalitic activity of titana an effective approach to achieve high charge separation efficiency and high level of sensitivity under visible light is coupling it with another semiconductor with smaller band gap and appropriate banding energy structure. achieving all mentioned above, we used bilayer structure and coupled TiO2 with hematite which its small band gap(Eg ~ 2.1 ev) is sensitive to visible light. Bilayer systems of TiO2/Fe2O3 , Fe2O3/TiO2 were fabricated by sol-gel process and variable parameter was upper layer thickness. The layers were deposited on glass substrate via sol-gel process. The upper layers were prepared in different thicknesses in two ways. First, they... 

Recently, quasi 1D (Q1D) structures of materials such as nanowires, nanorods and nanobelts with high surface to volume ratio (A/V) and small grain size devoted an extensive part of researches. This is due to their unique properties and thus various applications in manufacturing of nanometric devices. Niobium pentoxide (Nb2O5) as semiconductor with wide bandgap has been applied in various fields including: electrochromic devices, gas sensors, anti-reflective coatings, capacitors, photocatalysts , field emission and recently; antibacterial systems. In this project , initially niobium thin films was deposited on Si(100) substrate using RF magnetron sputtering method and then niobium oxide... 

In this project, two types of graphene obtained from chemical and chemical vapor deposition (CVD) methods were studied for gas/vapor sensing applications . In chemical method, oxidation and exfoliation of graphite was performed in liquid phase. AFM, XPS, Raman spectroscopy and Uv-visible spectroscopy were indicated that single layers synthesis of graphene oxide (GO) sheets was formed successfully. Reduction of the GO to reduced graphene oxide (RGO) was chemically done by hydrazine as a conventional reducing agent and melatonin as a green alternative. Photocatalytic reduction and hybridization of GO with TiO2 was also studied. TEM, SEM and AFM analyses confirmed nucleation and growth of TiO2... 

Networks and the epidemiology of directly transmitted infectious diseases are fun-damentally linked. The foundations of epidemiology and early epidemiological models were based on population wide random-mixing, but in practice each individual has a finite set of contacts to whom they can pass infection; the ensemble of all such contacts forms a network. Knowledge of the structure of the network allows models to compute the epidemic dynamics at the population scale from the individual-level behaviour of infections.Motivated by the analysis of social networks, we study a model of random net-works that has both a given degree distribution and a tunable clustering coefficient.We consider two... 

Recently, nanotechnology has promised to create and/ or improve therapeutic methods which in turn remain minimum side effects by employing synergistic effects of nanostructures. However, a comprehensive understanding of the interactions between nanostructures and building blocks of the biological systems (cells) is essential to create innovative therapeutic methods and compound and also predict their behavior for upcoming applications. In this thesis for the first time, synergistic effects of graphene-nanobubbles in interactions with bacterial (as the simplest model) cells were investigated. Therefore, at the first step, production of nanobubbles (NBs) in the presence of two-dimensional... 

Graphene is a one layer atom thickness and zero energy gap so for using it in nano electronic and transistors baised on graphene it's energy gap should be opened.one of the methods for opening graphene band gap is creating nano scale boundaries or synthesize graphene nanoribbons. One of the new methods for graphene nanoribbon synthesize is longitudinal opening of carbon nanotube. In this thesis graphene nanoribbons synthesize with this method and analyze with AFM and Raman spectroscopy. Carbon nanotubes also have energy gap and IR absorption recently they used for living cell destruction. In this thesis we synthesize graphene nanoribbons and analyzing their optical absorption and use it for... 

TiO2 is known as a photocatalyst in near UV-Visible light region with better efficiency compared to other semiconductor photocatalysts. Many attempts have been done to increase the efficiency of this photocatalyst. also, application of 2D carbon nanostructures namely graphene for increasing the photocatalytic activity of TiO2 has shown positive results.
In this research, we first synthesized Graphene Oxide (GO) suspension by exfolation of graphite oxide suspension. then we fabricated TiO2 thin films on glass substrates by so-called sol-gel method. finally we fabricate Graphene Oxide/TiO2 nanowalls composite films as a photocatalyst in visible light. X-ray photoelectron spectroscopy...