Exponential growth in computer technology, both in terms of individual CPUs and parallel technologies over the past decades has triggered rapid progress in large scale simulations. However, despite these achievements it has become clear that many conventional state-of-the-art techniques are ill-equipped to tackle problems that inherently involve multiple scales in configuration space. Our difficulty is that conventional ("time driven" or "time stepped") techniques update all parts of simulation space (fields, particles) synchronously, i.e. at time intervals assumed to be the same throughout the global computation domain or at best varying on a sub-domain basis (in adaptive mesh refinement algorithms). Using a serial electrostatic model, it was recently shown that discrete event techniques can lead to more than two orders of magnitude speedup compared to the time-stepped approach. In this research, the focus is on the extension of this technique to parallel architectures, using parallel discrete event simulation. Previous research in parallel discrete event simulations of scientific phenomena has been limited This thesis outlines a technique for converting a time-stepped simulation in the scientific domain into an equivalent parallel discrete event model. As a candidate simulation, an electromagnetic hybrid plasma simulation is considered. The experiments and analysis show the trade-offs on performance by varying the following factors: the simulations model characteristics (e.g. lookahead), applications load balancing, and accuracy of simulation results. The experiments are performed on a high performance cluster, using a conservative synchronization mechanism. Initial performance results are encouraging, demonstrating very good parallel speedup for large-scale model configurations containing tens of thousands of cells. Overheads for inter-processor communication remain a challenge for smaller computations.

Many existing researches on image watermarking for copyright protection need to use original image in retrieving watermark. Though it is more robust, it would cause some problems about the authorization of original image. In this thesis, we propose a method based on DCT domain without using original image. Using the property of concentrating energy in DCT transform, the energies of blocks are used for further processing. In the embedding algorithm, the DC coefficients of blocks are first collected. Then they are divided by some number to get remainders. The values of embedded data are embedded in the relationship between corresponding location of embedded data and other locations by adjusting the remainders in all locations. Some typical watermarking attacks and noise are used to evaluate the robustness of our method. Compared with other competing algorithms, it shows that the survival rate of watermark in our method can be almost the same or even better then those methods which need original image. The error rate of the lowest quality JPEG compression can be adjusted less then 1%, when the length of embedding data is 512 bits. Our proposed method can be further improved by adjusting the values of remainders and the block size. These provide flexibility to satisfy different requirements.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

We encounter granular materials on a daily basis. We walk up a gravel path or we eat our breakfast cereals. When handling granular materials on an industrial scale it is important to do so efficiently, to avoid unnecessary energy losses, wear and tear. To help designing efficient tools for handling these materials engineers uses numerical simulations. This project investigates the difference between the two main approaches to simulation of granular materials, the Smooth- and Non-smooth Discrete Element Methods by implementing the Smooth method into AgX dynamics were the Non-smooth method already is implemented, and then setup and execute a range of experiments to investigate their differences. The investigation shows both advantages and weaknesses for both methods. The result of simulations with smooth discrete element method are more consistent than with the nonsmooth discrete element method with respect to choice of time step and other parameters that can be chosen for the simulation. Smooth discrete element method have problems when it comes to extreme situations. The relative simulation time for system as large as treated by this project (more than1000) can not be shown to depend on the size of the system.

This work describes the research conducted in the quest for designing better software for discrete-event system (DES) control. The think-aloud data from an exploratory observational study of solving DES control problems contributed to the formulation of a list of recommendations on how to design and improve DES software. These observations, together with other relevant research, led to the proposal of a novel approach to DES problem solving, namely, the template design methodology. This methodology does not require the introduction of new control theory; it is rather an reinterpretation of the existing modelling framework. Software supporting this methodology was implemented and subsequently evaluated using twelve subjects. Significant improvements in the speed of problem solving as well as positive evaluations by the subjects were observed. The usability data do not show any drawbacks to applying the methodology. / Thesis (Ph.D, Computing) -- Queen's University, 2009-08-21 17:11:14.991

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The use of Discrete Fracture Networks (DFNs) is becoming increasingly common in geomechanical practice in addition to their continuing role in hydrogeology. These models can serve as useful tools for estimating interconnectedness of fractures, leading to estimates of probable block sizes and shapes for a set of input parameters. However, the development of these models is reliant on assumptions made about collected field data and while constructing the model themselves. The implications of these biases and assumptions are not well documented. This work investigates the variables involved in building a Discrete Fracture Network model in order to provide insight into the decisions and assumptions made during the modeling process. Select assumptions required within the FracMan DFN software pertaining to model selection and construction are evaluated; biases and assumptions relating to field data and how it is collected that may impact the development of DFN input parameters are investigated and limits of the effects of these models on block sizes are determined. The parameters determined to be critical in determining the overall geometry of the fracture network are ranked according to their relative importance in DFN modelling and according to the relative accuracy of each parameter. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2014-05-30 18:00:51.384

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