Sharif Digital Repository

Nowadays, tissue engineering and stem cells-based therapies have outlined a promising prospect in neural networks regeneration. But it usually requires biocompatible and conductive scaffolds for culturing neural stem cells and directing their differentiation toward the neurons. Graphene due to its unique physical and chemical properties has attracted much interest in tissue engineering. For this purpose, in this study biocompatible graphene oxide foams have been used for neural stem cell culturing. For the first time, graphene oxide foam were fabricated by precipitation of chemically exfoliated graphene oxide sheets in an aqueous suspension onto the PET substrate at ~80 oC under UV... 

The problem studied in this research is the online stochastic bipartite matching. In this problem the vertices of one side of the given graph arrive in an online manner, with respect to a probability distribution. Also the edges of the graph exist according to a given probability distribution and one should perform queries from an oracle to know about the existence of an edge. The given graph shall be weighted or unweighted. The goal here is to find a maximum matching in the graph that is as close to the omniscient optimum as possible, while the number of queries performed per vertex is limited. In the general case of the problem, there are no specific conditions, but in other versions,... 

Unique properties of Gold at nanoscale have made it one of the most popular substances used in nanotechnology. The interaction of Gold and Thiolates is one of the most favorite fields of research. Extensive studies about this interaction have revealed the importance and usage of this system in future technology. Due to difficulties of experimentationat nanoscale, computer simulations arevery important. Although interatomic potentials lead to higher computational speeds, they have deficiencies in precise simulation of some phenomena. Ab-initio methods, such as density functional theory, provide powerful tools to increase the accuracy. In this research, the interaction of gold and thiolates... 

When a crack is subjected to a compression field, it will close and its edges will get into contact with each other. Depending on the direction and magnitude of the loads and also the coefficient of friction, ‘stick’ or ‘slip’ situationsbetween the edges will occur. This type of crack is known as ‘frictional crack.’ In this project, first these cracks are studied analytically and the order of singularity is derived using asymptotic analysis and also the analytical fields are determined for both ‘isotropic’ and ‘orthotropic’ materials. Then, numerical simulations are carried out using extended finite element method which is considered as the most powerful means for analyzing the problems... 

Particulate porous mateials have always been of interest in terms of reducing shock waves effects in different protective applications. Therefore, the physics governing the flow in porous media is especially significant for which different models have been presented by the researchers. The complexities of these media have caused many existing models to be unable to properly predict the behavior of granular media under shock loadings. On the other hand, the complexity of the equations makes the numerical solution of them cumbersome and costly in a way that many researchers do not solve the whole coupled equations and reduce their number. In addition, current high-resolution TVD solutions of... 

Transmission-mode ultrasound computed tomography (USCT) has emerged as a novel, safe, and cost-effective method for quantitative imaging of biological tissues, especially in breast screening. Despite technological advancements, challenges such as reduced accuracy in heterogeneous media, incomplete acoustic field coverage, sensitivity to initial conditions, and phenomena like cycle skipping still limit image quality and reconstruction speed in these systems. In this thesis, aiming to improve the speed and performance of USCT imaging, three reconstruction algorithms have been designed, implemented, and evaluated: a travel-time-based Gauss-Newton method, frequency-domain full waveform inversion... 

Titanium alloy Ti-6Al-4V ELI with high biocompatibility and corrosion resistance, has a lot of applications in biomedical engineering. Disadvantage of this alloy is it’s disability to create a fast and good contact with the host/bone environment, after implanting in the body. Beside that it has low wear resistance. Nowadays to optimize the wear resistance, bioactivity and osteoconduction of surface of implants which are made from this alloy, the surface morphology are optimized in size and distribution. Different surface treatments are used for producing rough and porous surfaces to improve bioactivity along with wear resistance. In this study, surface modification of Ti-6Al-4V ELI was done... 

Commercially pure titanium (CP-Ti) is an important groups of titanium family and because of high strength, low density, high corrosion resistance and biocompatibility, this group of titanium is a suitable choice for application at chemical, petrochemical and medicine industry. Nowadays surgeons have a tendency toward use of CP-Ti instead of Ti-6Al-4V alloy. Moreover, because of body anatomy limitation, use of thick sheets result in high volume and damage soft tissue. Therefore, for sheet thickness reduction, study of the effects of metallurgical and geometrical parameter on fracture behavior of thin sheets is important. In this study, the fracture behavior of CP-Ti thin sheets investigated.... 

Adiabatic logic families are a group of logic circuits which operate based on adiabatic principles to tremendously reduce power consumption. These families have basic difference with common logic families in transistor level structure and there signals are not quadrangular but trapezoidal. Also, in these systems the source lines and clock pulse are the same. Research on Adiabatic families needs theoretical information in reversible computing. So we will start this project with explaining fundamental information in this field. After that some of these logic families are introduced and three important and widely used of them (SCRL-RERL-2LAL) are chosen to simulate. In each of these families... 

Various composite friction materials containing 40 vol.% organic binder (phenolic resin plus styrene-butadiene-rubber (SBR)) with varying phenolic-resin/SBR ratio were prepared. The content of phenolic resin in each composite was indicated by the resin value (RV) index ranging between 0-100%. The composites with RVs greater than 50% form resin-based friction materials in which the primary binder is the phenolic resin. For RVs less than 50%, the composites become the rubber-based materials where the primary binder is the SBR. The analysis of mechanical properties exhibited that the conformability of the composites increases upon incorporation of SBR. The frictional analysis revealed that type... 

In 2002 Baskaran and Jafari published an article that was about a spin-1 collective mode. Similarity between carbon nanotubes and graphene was a motivation for working on this project, in order to find another spin mode by considering random phase approximation as a simple way of finding collective motion of a physical systems. Moreover rolling graphene sheet induce diffrent physical properties as a result of chiral axis . In this project we focus only on achiral nanotubes and at last find two collective modes in this structures  

In this research the effects of addition of clay in phenolic glass fiber reinforced composite has been investigated. Layered clay/phenolic nanocomposite resin systems were first prepared with 0.5, 1.5 and 2.5 wt% of Cloisite Na+ (CN) and Cloisite 30B (CB). After that the suspension was hold in an ultrasonic bath for 30 min in order to enhance nanodispersion of the clay platelet within the resin. The phenolic/clay solution was used to impregnate the glass fabric using the solvent impregnation method. After suspension for 2 days in the room with natural condition, the impregnated fabrics were pre-cured at 135 ˚C in an oven for 3.5 min to obtain B-stage prepregs. Seven layers of prepregs (150... 

Vulcanization is one the most crucial process in elastomer manufacturing products. It has been shown that network structure and curing kinetic are strongly dependent on curing system formulation. In addition reinforcing fillers in elastomers can affect them as well. By commencement of nanofillers in rubber domain, effects of nanofiller presence on rubber behavior have been investigated by reaserchers.
In this Project the effect of different curing system formulations on vulcanization kinetic and network structure of NR/SBR elastomeric matrice filled by nanodiamond is investigated. Different ingredients and nanodiamond were added to matrix by mechanical mixing in two roll mill. The... 

Automotive brake pad is one of the most widely used composites. Commonly, more than 10 components are applied to make these materials and due to the large number of components and interactions between them, choice, explaination of the behavior and optimization of brake friction materials are some industry's challenges. Until now, some methods have been presented to design and optimization of these materials, but due to different complexities, there is lack of practical method that could be used for explaining the tribological behavior, engineering calculation and optimization of brake friction materials. Today, formulation of the current brake pads in the industry has mainly come from trial...