Browsing by Author "Liu, Yang"

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    Data Replication Strategies in Cloud Computing
    (North Dakota State University, 2011) Liu, Yang
    Data replication is a widely used technique in various systems. For example, it can be employed in large-scale distributed file systems to increase data availability and system reliability, or it can be used in many network models (e.g. data grid, Amazon CloudFront) to reduce access latency and network bandwidth consumption, etc. I study a series of problems that related to the data replication method in Hadoop Distributed File System (HDFS) and in Amazon CloudFront service. Data failure, which is caused by hardware failure or malfunction, software error, human error, is the greatest threat to the file storage system. I present a set of schemes to enhance the efficiency of the current data replication strategy in HDFS thereby improving system reliability and performance. I also study the application replication placement problem based on an Original-Front sever model, and I propose a novel strategy which intends to maximize the profit of the application providers.
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    Infiltration and Unsaturated Flow under the Influence of Surface Microtopography: Model Simulations and Experimental Observations
    (North Dakota State University, 2014) Liu, Yang
    Surface microtopography affects fundamental hydrologic processes including infiltration and soil-water percolation at different scales. By means of studying the unsaturated flow, this thesis research is aimed to evaluate the effects of surface microtopography on wetting front moving patterns for rough soil surfaces through both experimental study and HYDRUS modeling. Additional influential factors such as rainfall intensity and soil type are also considered. Laboratory-scale infiltration and unsaturated flow experiments were conducted for different microtopographic surfaces, rainfall intensities, and types of soil; and two- and three-dimensional numerical modeling was conducted under the same conditions. The simulated and observed wetting front distributions were compared in this combined experimental and modeling study. It was found that a uniformly distributed wetting front was eventually achieved although soil surfaces had dissimilar topographic characteristics. However, the timing to reach the uniform flat wetting front varied, depending on surface microtopography, soil hydraulic properties, and boundary conditions.