Browse

DISCOVER

Has File(s)

Search

Current filters:

Search Results

Item hits:
  • Thesis

  • Nonequilibrium transport of heavy metals in soils and its influence on soil remediation

    • Authors: Tsang, Chiu Wa (2006)

  • With increasing concern about soil and groundwater contamination, research on contaminant transport modeling and remediation technology has grown rapidly. Nonequilibrium transport of heavy metals resulting from rate-limited reactions in soils under natural and remediation conditions was investigated with batch, column, and sequential extraction experiments together with transport modeling in this study. Higher pore-water velocity that allowed shorter residence time and lower temperature that reduced the sorption rate resulted in nonequilibrium transport, whereas the reverse promotes equilibrium transport. Diffusion process was probably the rate-limiting step. The disparity of transport behavior was related to both residence time and reaction time. Competition among heavy metal...
  • Thesis

  • Novel estimation methods for unsupervised discovery of latent structure in natural language text

    • Authors: Smith, Noah Ashton (2006)

  • This thesis is about estimating probabilistic models to uncover useful hidden structure in data; specifically, we address the problem of discovering syntactic structure in natural language text. We present three new parameter estimation techniques that generalize the standard approach, maximum likelihood estimation, in different ways. Contrastive estimation maximizes the conditional probability of the observed data given a "neighbor-hood" of implicit negative examples. Skewed deterministic annealing locally maximizes likelihood using a cautious parameter search strategy that starts with an easier optimization problem than likelihood, and iteratively moves to harder problems, culminating in likelihood. Structural annealing is similar, but starts with a heavy bias toward simple syntac...
  • Thesis

  • Numerical modelling of wave-current induced turbidity maximum in the Pearl River estuary

    • Authors: Wang, Chonghao (2006)

  • The dissertation describes a study of the hydrodynamics and sediment transport characteristics as well as the formation and development processes of turbidity maximum in the Pearl River Estuary under the interaction of both wave and current through field data analysis and numerical modelling. Data from a large-scale synchronous hydrographic survey carried out along the main navigational channels are used to study the sediment transport processes in the Pearl River Estuary and subsequently to analyze the formation mechanisms of turbidity maximum. The results show that turbidity maximum widely exists in the Pearl River Estuary and is not only related to the intrusion of salt water, but also to the freshwater runoff from the three western river outlets. Gravitational circulation and t...
  • Thesis

  • Numerical simulation of scour around fixed and sagging pipelines using a two-phase model

    • Authors: Zhao, Zhihe (2006)

  • A key aspect of design and the maintenance of underwater pipelines is the assessment of local scour and its propagation. Scouring around objects placed on a sandy bottom is very complex because it involves two-phase turbulent flows and a myriad of sediment transport modes. This dissertation addresses two principal configurations of scour around pipelines in two parts. First, clear-water scour around a long fixed pipeline placed just above a non-cohesive sandy bed is numerically simulated. Second, live-bed scour around a fixed pipeline and scour below a sagging pipeline are investigated. These two simulations are conducted by using an Eulerian two-phase model that implements Euler-Euler coupled governing equations for fluid and solid phases and a modified k - e turbulence closure for...
  • Thesis

  • On the design and worst-case analysis of certain interactive and approximation algorithms

    • Authors: Mao, Jia (2006)

  • With the speed of current technological changes, computation models are evolving to become more interactive and dynamic. These computation models often differ from traditional ones in that not every piece of the information needed for decision making is available a priori. Efficient algorithm design to solve these problems poses new challenges. In this work we present and study some interactive and dynamic computations and design efficient algorithmic schemes to solve them. Our approach for performance evaluation falls within the framework of worst-case analysis. The worst-case scenarios are analyzed through the incorporation of imaginary adversaries or adversarial input sequences. Worst-case analysis provides safe performance guarantees even when we have little or no prior knowled...
  • Thesis

  • Optimizing communication performance of Web services using differential deserialization of SOAP messages

    • Authors: Abu-Ghazaleh, Nayef Bassam (2006)

  • Web services have recently emerged as a de facto standard for building Grid and distributed computing infrastructures and applications. SOAP, a simple, interoperable, robust, and extensible protocol for the exchange of messages, is the most widely used communication protocol in the Web services model. SOAP’s XML-based message format hinders its performance, thus making it unsuitable in many scientific applications. The deserialization of SOAP messages, which includes processing of XML data and conversion of strings to in-memory data types, is the major performance bottleneck in a SOAP message exchange. The contributions of this dissertation address SOAP’s poor deserialization per¬formance with the design and implementation of differential deserialization (DDS), an optimization tech...
  • Thesis

  • Physical and numerical modelling of the soft soil ground improved by deep cement mixing method

    • Authors: Fang, Zhen (2006)

  • The research described in this thesis focuses on the consolidation behaviour and vertical bearing capacity of soft soil ground improved by Deep Cement Mixing (DCM) method. The soft soil ground modelled in this study may support relatively light structures, reclaimed fills or road embankments. Firstly, an axisymmetric physical model (Model 1) test was carried out to investigate the consolidation behaviour of soft soil ground installed with a single DCM column. The surface settlement, excess pore water pressures at different locations in the soil, and pressures carried by the soil and the DCM column were all measured throughout testing. This model test revealed that the DCM column behaved as a vertical drain partially, which suggests that the DCM column might be regarded as a parti...
  • Thesis

  • Planning and learning for weakly-coupled distributed agents

    • Authors: Guo, Anyuan (2006)

  • Stochastic planning has gained popularity over classical planning in recent years by offering principled ways to model the uncertainty inherent in many real world applications. In particular, Markov decision process (MDP) based approaches are particularly well suited to problems that involve sequential decision making. Partially observable stochastic games (POSGs) are a multi-agent extension of the MDP framework to decentralized decision making. While elegant and expressive, this model has been shown to be intractable. Many real world problems exhibit additional structure that can be leveraged for computational gain. The focus of this thesis is on a class of problems in which the agents are largely independent but may interact by constraining each other’s actions. The best-known s...
  • Thesis

  • Portable language technology: A resource-light approach to morpho-syntactic tagging

    • Authors: Feldman, Anna (2006)

  • Morpho-syntactic tagging is the process of assigning part of speech (POS), case, number, gender, and other morphological information to each word in a corpus. Morpho-syntactic tagging is an important step in natural language processing. Corpora that have been morphologically tagged are very useful both for linguistic research, e.g. finding instances or frequencies of particular constructions in large corpora, and for further computational processing, such as syntactic parsing, speech recognition, stemming, and word-sense disambiguation, among others. Despite the importance of morphological tagging, there are many languages that lack annotated resources. This is almost inevitable because these resources are costly to create. But, as described in this thesis, it is possible to avoid t...
  • Thesis

  • Random geometric graphs: An algorithmic perspective

    • Authors: Avin, Chen (2006)

  • A random geometric graph g(n, r) is a graph resulting from placing n points uniformly at random on the unit square (or on the unit disk) and connecting two points iff their Euclidean distance is at most the radius r(n). Recently, this class of random graphs has gained relevance as a natural model for wireless ad-hoc and sensor networks. Investigating properties of these graphs can unearth properties of the real-life systems they model and allow for the design of efficient algorithms. In this work, we study properties of random geometric graphs motivated by challenges encounter in sensor networks applications. Sensor networks are constructed from a large number of low-cost, low-power sensors equipped with wireless communication and limited processing capabilities. These devices are ...