Spatial data occurs in several important and diverse applications in P2P systems, for example, P2P virtual cities, GIS, development planning, etc. For the problem of answering exact queries for spatial region data in the P2P environment, an R¡Vtree based structure probably is a good choice. However, since a peer system is dynamic, the global update characteristics of data insertion/deletion in an R¡Vtree can not work well in a P2P system. Moreover, the problem of overlaps in an R¡Vtree results in large number of the disk accesses (which will be considered as large number of messages in P2P systems). Therefore, a P2PR¡Vtree based indexing method for P2P systems has been proposed which has only local update to the proposed index structure when data insertion/deletion occurs. Although the P2PR¡Vtree can achieve the goal of the local update for data insertion/deletion, the overlapping phenomenon is still hard to solve. Recently, for region data access, an NA¡Vtree has been proposed which outperforms R¡Vtree¡Vlike data structures. Moreover, it does not have the problem of overlaps which may occur in an R¡Vtree. Basically, an NA¡Vtree does not split the spatial space, but it just classifies the spatial data objects by some rules. On the other hand, the Chord system is a well¡Vknown structured P2P system in which the data search is performed by a hash function, instead of flooding used in most of the unstructured P2P system. Since the Chord system is a hash approach, it is easy to deal with data insertion/deletion with only local update. However, the current Chord system can not work well with the region data, since it only works well with a single key value. Therefore, in this thesis, we propose to apply an NA-tree in the Chord system to encode spatial region data in the data key part used in the hash function to data search. That is, we still use one hash function of Chord to assign nodes to peers, and use another hash function to do data assignment by applying an NA¡Vtree to encode the spatial region data to data keys. First, we use three bits to present the first eight children in the NA¡Vtree. Next, we propose two methods to generate the key value of the remaining bits. For our first proposed method, it generates the remaining bits by adding 0¡¦s. This method is simple and applicable to the case that there are few objects in P2P systems. To avoid the case that a peer may own too many objects, the second method takes the central points of regions into consideration. This method is applicable to the case that there are too many objects in the P2P system. Finally, we concatenate the first three and the remaining bits to get the key values of objects. Thus, we combine the NA¡Vtree with the Chord system to solve the overlapping problem which the P2PR¡Vtree can not deal with. In our simulation study, we use six different data distributions to compare our method with the P2PR¡Vtree. From our simulation results, we show that the number of visited peers in our approach is less than that in the P2PR¡Vtree.

With the rapid advances in technologies, strategies for efficiently operating the spatial data are needed. The spatial data consists of points, lines, rectangles, regions, surface, and volumes. In this thesis, we focus on the region data. There are many important and efficient operations for the region data, such as neighbor finding, rotation, and mirroring. The nearest neighbor (NN) finding is frequently used in geographic information system (GIS). We can find the specific point (e.g., a park, a department store, etc.) that is the closest to our position in geographical information systems. In any representation for the region data, it is not instinctive and easy for nearest neighbor finding, since the coordinate information has been lost. Voros, Chen, and Chang have proposed the strategies for the nearest neighbor finding based on the quadtree in eight directions. Chen and Chang have proposed the nearest neighbor finding based on the Peano curves. These strategies for the nearest neighbor finding based on the quadtree and the Peano curve use a looping process, which is time-consuming. On the other hand, in recent years, many researchers have also focused on finding efficient strategies for the rotating and mirroring operations, which is useful when the animation is performed by computers. The boolean function-based encoding is a considerable amount of space-saving with respect to the other binary image representation. The CBLQ representation saves memory space as compared to the other binary image representations that have proposed the strategies of the set operations. However, the processes for obtaining the rotated or mirrored code based on these two representations are time-consuming, since the coordinate information of all pixels has been lost. Therefore, in this thesis, first, for the nearest neighbor finding based on the quadtrees and the Peano curve, we propose the strategy which uses the bitwise and arithmetic operations, and it is more efficient than the strategies based on the looping processes. Next, we propose efficient strategies for rotating and mirroring images based on the boolean function-based encoding and constant bit-length linear quadtrees (CBLQ) representations. From our simulation study, first, we show that our strategies based on the quadtree and the Peano curve require the least CPU-time and our strategy based on the Hilbert curve requires the least total time (the CPU-time + the I/O time) among the strategies for the nearest neighbor finding based on the quadtree and the three space-filling curves. Next, in most of cases, when the black density is no larger than 50%, the CPU-time based on the boolean function-based encoding is less than that based on CBLQ.

Hydrogeochemical studies are generally qualitative in nature. The goal of this study is to investigate the possibility of quantitative interpretation of hydrogeochemistry by considering the chemical characteristics and the isotopic compositions of oxygen, hydrogen, and carbon of the water. This study examines ephemeral stream and well waters from Canada del Oro valley, southern Arizona. By chemical and isotopic considerations, this study finds that the change of chemical composition of the wash water was mainly due to water-rock interaction. The concentrations of dissolved constituents increase between 10 to 50% from upstream to downstream samples, while the evaporation loss of water is less than 3%. By chemical and isotopic considerations of the well waters, this study identifies three recharge waters in the CDO ground-water system. The chemical and water isotopic compositions of the well waters are results of mixing between these three recharge waters and subsequent dissolution of the aquifer. By thermodynamic consideration, albite, kaolinite, montmorillonite, and calcite are the main phases that influence the chemical characteristics of this ground-water system. Simulations with the computer program PHREEQE verifies the above conclusions. The mechanisms that influence the chemical and carbon isotopic compositions of the water are quite different in a system open to a CO2 gas reservoir than in a closed system. Deines, Langmuir, and Harmon (1974) derived a set of chemical-isotopic equations to calculate the carbon isotopic composition of water under open system condition. Wigley, Plummer, and Pearson (1978) formulated a mass transfer equation to calculate the change of carbon isotopic composition of natural water in closed system environment. This study implements these two type of equations as a subroutine--CSOTOP to the computer program PHREEQE. With this PHREEQE-CSOTOP package, the evolution of carbon chemical and isotopic composition of natural water can be conveniently modeled from open to closed system conditions. This study also uses this package to date water samples from the Tucson basin, and finds that choice of reaction path may cause a difference in carbon-14 age of up to a few thousand years. This study concludes that it is possible to rigorously interpret hydrogeochemistry in a quantitative way. With sufficient measurements to define the reaction path, followed by thermodynamic consideration, chemical-isotopic evaluation, and computer modeling, one should be able to achieve this goal.

yes / This paper presents a hybrid system for automatic detection and McIntosh-based classification of sunspot groups on SOHO/MDI white-light images using active-region data extracted from SOHO/MDI magnetogram images. After sunspots are detected from MDI white-light images they are grouped/clustered using MDI magnetogram images. By integrating image-processing and neural network techniques, detected sunspot regions are classified automatically according to the McIntosh classification system. Our results show that the automated grouping and classification of sunspots is possible with a high success rate when compared to the existing manually created catalogues. In addition, our system can detect and classify sunspot groups in their early stages, which are usually missed by human observers. / EPSRC

The importance of agricultural knowledge systems (AKS) especially in rural communities cannot be overemphasized. AKS are important for creation, sharing and enhancing access and usage of agricultural knowledge. They link agricultural research and farms; increase adoption of good agricultural practices; improve the performance of agricultural marketing systems; and enhance effective post-harvest management. Despite the importance of agriculture to the economy and livelihoods of majority of Tanzanians, there is a consensus from scholars that the sector has been performing poorly. This is partially due to limited access to agricultural knowledge resulting into irrational decisions on agricultural activities thus dwarfing the sector. The modified Knowledge Management Processes Model guided the study in investigating how AKS can be strengthened to enhance access and usage of agricultural knowledge among stakeholders. The study adopted a pragmatic paradigm and used mixed method research by applying a survey, key informant interviews, focus group discussions (FGDs) and document reviews. Structured questionnaires were administered to 314 farmers while key informant interviews involved 57 respondents among village executives, councillors, input-suppliers, information providers, buyers, agricultural extension officers and researchers. Moreover, three FGDs involving 24 farmers were conducted. Qualitative data were analysed through classical content and constant comparison analysis, while SPSS software was used to analyse quantitative data. Quantitative and qualitative data were mixed during analysis, interpretation and discussion of results. The study identified farmers, the private sector and the government as major actors, but not working in unison. Most actors used human based systems while few used ICT and paper based systems. Actors needed agricultural knowledge on weather, farm preparation, seeds, crop maintenance, post-harvest practices, agricultural marketing and credits. Most actors shared agricultural knowledge through face-to-face interactions and mobile phones, few through internet. It was concluded that poor linkage among actors limited accessibility of agricultural knowledge. To improve accessibility to agricultural knowledge, a model for strengthening AKS usage is proposed. It is recommended that actors should be linked together and involved in enhancing access and usage of agricultural knowledge. Moreover, the proposed model should be validated before applying it. / Information Science / D. Litt. et Phil (Information Science)