Finding top-k frequent balls in high dimensional spaces.

Liu Zheng.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.Includes bibliographical references (leaves 69-72).Abstracts in English and Chinese.Abstract --- p.iAcknowledgement --- p.iiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Contributions --- p.2Chapter 1.2 --- Dissertation Organization --- p.3Chapter 2 --- Problem Statement and Background Study --- p.4Chapter 2.1 --- Problem Statement --- p.4Chapter 2.2 --- Background Study --- p.6Chapter 2.2.1 --- Overview of Pattern Discovery Methods --- p.7Chapter 2.2.2 --- Applications --- p.9Chapter 3 --- Ball Discovery Algorithms --- p.13Chapter 3.1 --- Brute-force Method for Ball Discovery --- p.13Chapter 3.2 --- Ball Discovery with Small Point Sets --- p.15Chapter 3.2.1 --- Pruning the Search Space Using RP-tree --- p.15Chapter 3.2.2 --- CB-tree - Collection of Balls in a Compact and Complete Form --- p.22Chapter 3.2.3 --- Algorithm of Finding Balls Using RP-tree and CB-tree --- p.31Chapter 3.3 --- Ball Discovery in Large Point Sets --- p.31Chapter 3.3.1 --- Candidate Sets of Balls --- p.31Chapter 3.3.2 --- A Divide-and-Conquer Algorithm --- p.35Chapter 3.4 --- Heuristic Greedy Algorithms for Ball Discovery --- p.37Chapter 3.4.1 --- A Heuristic Greedy Algorithm --- p.37Chapter 3.4.2 --- Another Heuristic Greedy Algorithm --- p.38Chapter 4 --- Evaluations --- p.40Chapter 5 --- Discussion --- p.59Chapter 5.1 --- Order and Index the Points --- p.59Chapter 5.2 --- Incremental Points Update --- p.59Chapter 5.3 --- Smallest Enclosed Ball Algorithm --- p.60Chapter 6 --- Conclusion and Future Research --- p.61Chapter A --- Appendix --- p.63Chapter A.1 --- Fundamental Algorithms --- p.63Chapter A.1.1 --- Computing Smallest Enclosed Ball of a Point Set in Euclidean Space --- p.63Chapter A.1.2 --- Finding All Cliques of an Undirected Graph --- p.65Chapter A.2 --- An Example of a Small Data Set --- p.66Bibliography --- p.6

Groundwater dynamics and arsenic mobilisation in Bangladesh: a national-scale characterisation

Elevated arsenic (As) concentrations in groundwater-fed drinking water supplies in Bangladesh are a major public health problem but the hydrogeological conditions that give rise to the mobilisation and regional-scale distribution of As in shallow groundwater remain unknown. Published hypotheses developed from highly localised case studies are, to date, untested regionally and contradictory. My doctoral thesis makes a novel and substantial contribution to knowledge of the relationship between groundwater dynamics and As mobilisation in the Bengal Basin by (1) characterising national-scale groundwater storage dynamics and recharge processes in the shallow aquifer of Bangladesh and (2) relating statistically static and dynamic hydrogeological factors to the observed variation of As concentrations in groundwater. After constructing a national database of shallow groundwater levels from a network of 1267 monitoring stations, robust statistical techniques are applied to characterise long-term (1985 to 2005) trends and seasonality in groundwater levels, net recharge, and groundwater storage; the latter is supported by analysis of remotely sensed data derived from GRACE (Gravity Recovery and Climate Experiment). These characterisations highlight the critical influence of groundwater abstraction on net recharge to the shallow aquifer. Net annual recharge in Bangladesh has increased in response to intensive abstraction challenging conventional definitions of "safe yield". To examine the national-scale variability in groundwater As concentrations generalised regression models were constructed using geology and hydrological factors. Crucially, these models reveal that areas of increasing groundwater-fed irrigation and net recharge are associated with lower As concentrations. These findings are inconsistent with current hypotheses that contend irrigation-induced recharge mobilises groundwater As in shallow aquifers. Inverse associations between As concentrations and both mean annual recharge and trends in groundwater-fed irrigation suggest that As has been actively flushed from the shallow aquifer as a result of recently increased net recharge induced by intensive irrigation in Bangladesh