Sharif Digital Repository

At first the killing vector fields will be investigated. Conditions are introduced for the hypersurface of a Riemannian manifold with a killing vector field to be equipped with the same killing vector field. Then 2-killing vector field is studied and its relation with killing vector fields and monotone vector fields is presented. After that conformal vector fields are discussed and conditions are introduced in order that the Riemannian manifold equipped with a conformal vector field, isisometric to n-dimensional sphere with constant curvature. Finally we will present the conditions which conformal vector field is a 2-killing vector field. Then we will present the results in which the... 

In this dissertation, two parts of research has been conducted. First, with the aim of minizing the fluctuations of power output of wind farms and the need for energy storage system, optimization of wind farm (WF) layout has been studied. Deployment of battery energy storage system (BESS) is a viable option to alleviate the inherent power fluctuation of wind farms. In this thesis and based on the power spectrum density (PSD) theorem, it is hown that the WF layout affects not only the total harvested energy but also the level of power fluctuation, which in turn influences required capacity of battery energy storage system (BESS) needed to mitigate the inherent power fluctuation of the wind... 

Due to the advances in wireless communications and electronics over the last few years, the development of networks of low-cost, low-power, and multifunctional sensors has received increasing attention. Most important constraints of this network are energy and bandwidth. Data aggregation is one of the effective approaches for reducing energy consumption in wireless sensor networks. Recent research on data collection reveals that, rather than reporting data through long, multi-hop and error-prone routes to a static sink using tree or cluster network structure, allowing and leveraging sink mobility is more promising for energy efficient data gathering. In this work we proposed an effective... 

With the increasing penetration of renewable energies as distributed generation (DG) in power systems, technical problems arise in both distribution and transmission system level. Voltage rise is the main barrier for connection of DGs in rural areas, while excessive reactive power demand from transmission system is the major concern for Transmission System Operators (TSO). Here, a centralized control scheme based on the Smart Grid is proposed to reduce the impact on the transmission system voltages and improve its stability, while mitigating the voltage rise issue in the distribution network. Reactive power output of DGs, substation capacitors and tap setting of transmission transformer are... 

Caching is the process of storing part of popular contents near the users, which not only results in better traffic balance, but also reduces the delay of content delivery. Due to limited cache capacities and time-varying nature of contents popularity, using a proper replacement policy for cached contents during the heavy traffic hours is necessary. Many of the existing methods have ignored the dynamics of requests. Also, most of the previous works have focused on parameters other than QoS characteristics as the performance metric.We propose a cache updating policy for wireless networks considering dynamic popularity for file requests. Our model is a wireless heterogeneous network consisting...