This research focuses on the utilization of occlusion culling for the real-time visualization of distributed virtual urban environments. Today&#039 / s graphics hardware renders all the primitives in any order and uses z-buffer to determine which primitives are visible on a per-pixel basis. However, visibility is computed in the last stage of rendering pipeline and every rendered primitive is not visible in the final image. Early culling of the invisible primitives in a complex scene is valuable for efficiency in the conventional rendering pipeline. This may reduce the number of primitives that will be processed in the rest of the pipeline. In this thesis, we propose an efficient visibility estimation method for distributed virtual urban environments. The proposed method is based on occlusion culling to identify and cull the occluded parts of the scene. This not only computes conservative potential visible set (PVS) for each client but also assures the computed PVS to be available at the client on-time and reduces the network traffic by grouping the clients which may see each others dynamically.

Effect of stress-assisted aging on stress induced martensitic transformation in hot-rolled Ni-rich 50.7at. Ni%-Ti alloy has been investigated. Alloys are aged freely and under 20 MPa, 100 MPa, and 200 MPa stress at 400 o C for 90 minutes. Aging procedure affected both stress-induced and thermally induced transformation behavior. Superelasticity behavior is correlated with the multistep transformation in aged Ni-rich NiTi alloys and the aging stress level is found to be effective. Relative to the free aged alloy, the alloy aged under 20 MPa exhibited a slight and the alloy aged under 100 MPa exhibited a considerable reduction, whereas the alloy aged under 200 MPa exhibited an increase in the critical transformation stress. DSC studies have shown that the transformation is multistep for freely aged and aged under 20 MPa alloys, whereas it is single step and two-step for alloys aged under 100 MPa and 200 MPa, respectively, and this has been attributed to the effect of stress on nucleation and growth rates. As a result of the different response mechanisms to the applied stress upon loading during superelasticity testing, the recovered strain amounts varied considerably depending on the aging conditions and the test temperatures.

Oil and natural gas are the most strategic raw materials to meet the expanding energy requirement in today&rsquo / s world. They have great impact on issues such as economy, national security, development, competition, and political consistency. Being a developing country, Turkey&rsquo / s natural gas requirement is increasing rapidly. However, the production is far from covering the demand. Recent assumptions point out that natural gas demand of Turkey will reach 44 billion cubic meters in 2010 with a financial burden of 10 billion $ to the national economy. Therefore Turkey requires meeting natural gas demand by using its own conventional natural gas resources. The geological researches and global data encourage Turkey to drill more exploration wells in offshore side of Western Black Sea .In early 2007, the production will be started in Western Black Sea Region with 1.42 million cubic meter gas per day. Moreover, further exploration and production activities in the region are still continuing in order to increase the production. In this thesis, issues such as importance of the natural gas for Turkey and the world, Turkey&rsquo / s present energy situation and natural gas supply and demand scenarios for Turkey have been investigated. The possible impact of natural gas exploration and production in Black Sea region on Turkey&rsquo / s economy in near future has been emphasized. An extensive literature survey using related printed and unprinted media has been performed in order to collect the necessary data and information.