Algebraic Topology Metheds on Graph Coloring

, M.Sc. Thesis Sharif University of Technology Pouria Omidi (Author) ; Jafari, Amir (Supervisor)

Abstract

The aim of this thesis is to introduce some algebraic topologies methods and apply them on fining the chromatic number of some famous graphs and also hypergraphs. In the first part, we will use a mixture of two well-known technics, Tucker lemma and Discrete Morse theory to find an upper bound for the chromatic number of s-stable Kneser for some specific vector s. to find the sharper upper bound, we will deviate our strategy and use another approach by finding an edge-labeling and apply some theorems in POSET algebraic topology. In this way, we also find a connection between Young diagrams and the numbers of spheres in the box complex related to Kneser graphs and hypergraph. Actually, we can...

Data Placement and Request Handling for User Aware Cloud Services

, M.Sc. Thesis Sharif University of Technology Derakhshanfar, Pouria (Author) ; Movaghar, Ali (Supervisor)

Abstract

Nowadays surfing on social networks and using user-based services have become an inseparable part of our lives. Data and information kept and maintained regularly for these services have been increasing according to rapid growth of users. ergo Cloud is being used for implementing necessary services. In addition, having a management system for data and user’s requests is essential. In previous studies, replicating data and managing requests were used to improve the performance of the systems. Due to the policies of the services provider, one or more aspects has been dedicated to improve service’s performance. Aspects such as usage of resources, quality of services(QoS), and usage of network...

Study of Tunable Graphene Nano Resonator Vibration

, M.Sc. Thesis Sharif University of Technology Derakhshanfar, Soroush (Author) ; Haddadpour, Hassan (Supervisor)

Abstract

In the present investigation, graphene sheets are simulated as Nano resonators using Kirchhoff plate theory and nonlocal continuum theory. External force and interlayer forces are simulated as harmonic and Winkler-like elastic foundation, respectively. Equations are solved analytically and numerically and corresponding results are presented. Considering a two layer resonator, natural frequencies and oscillation amplitude are investigated by free vibration and forced vibration analysis. Also, the effects of parameters such as small scale, sheets dimensions and inciting frequency on the vibration of the resonator, are displayed

Performance Assessment of PEM Fuel Cell in Extreme Conditions (Sub- Freezing Temperatures)

, M.Sc. Thesis Sharif University of Technology Shirazi, Peimaneh (Author) ; Rajabi Qhahnuyeh, Abbas (Supervisor) ; Ahmadi, Pouria (Supervisor)

Abstract

Fossil fuels provide the most needs of the world's energy, however, continues to lead to two key problems. The first problem is their limitation, and the second problem is the creation of serious environmental issues. Therefore, the need for renewable energy sources is felt more than ever.As an energy source, hydrogen is the lightest, most efficient and cleanest fuel. One of its unique properties is efficiency, the production of electricity by fuel cells through the electrochemical process, has far greater efficiency than of mechanical energy production from fossil fuels in internal combustion engines or energy production in thermal power plants. A fuel cell is a device that converts...