published_or_final_version / Architecture / Doctoral / Doctor of Philosophy

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The Game of life is probably the most famous cellular automaton. Life shows all the characteristics of Wolfram's complex Class N cellular automata: long-lived transients, static and propagating local structures, and the ability to support universal computation. We examine in this thesis questions about the geometry and criticality of Life. We find that Life has two different regimes with different dimensionalities. In the small scale regime Life shows a fractal dimensionality with Ds = 0.658 and in the large scale regime D1 = 2.0, suggesting that the objects of Life are randomly distributed. We find that Life differentiates between different spatial directions in the universe. This is surprising because Life's transition rules do not show such a differentiation. We find further that the correlations between alive cells extend farthest in the active period and that they decrease in the glider period, suggesting that Life is sub-critical. Finally, we find a size-distribution of active clusters which does not depend on the lattice size and amount of activity, except for the largest clusters. We suggest that this result also indicates that Life is sub-critical.

Thesis (Ph. D.)--University of Chicago, Dept. of Computer Science, March 1999. / Includes bibliographical references. Also available on the Internet.

It is a time consuming task to generate textures for large 3D terrain surfaces in computer games, flight simulations and computer animations. This work explores the use of cellular automata in the automatic generation of textures for large surfaces. I propose a method for generating textures for 3D terrains using various approaches - in particular, a hybrid approach that integrates the concepts of cellular automata, probabilistic distribution according to height and Wang tiles. I also look at other hybrid combinations using cellular automata to generate textures for 3D terrains. Work for this thesis includes development of a tool called "Texullar" that allows users to generate textures for 3D terrain surfaces by configuring various input parameters and choosing cellular automata rules. I evaluate the effectiveness of the approach by conducting a user survey to compare the results obtained by using different inputs and analyzing the results. The findings show that incorporating concepts of cellular automata in texture generation for terrains can lead to better results than random generation of textures. The analysis also reveals that incorporating height information along with cellular automata yields better results than using cellular automata alone. Results from the user survey indicate that a hybrid approach incorporating height information along with cellular automata and Wang tiles is better than incorporating height information along with cellular automata in the context of texture generation for 3D meshes. The survey did not yield enough evidence to suggest whether the use of Wang tiles in combination with cellular automata and probabilistic distribution according to height results in a higher mean score than the use of only cellular automata and probabilistic distribution. However, this outcome could have been influenced by the fact that the survey respondents did not have information about the parameters used to generate the final image - such as probabilistic distributions, the population configurations and rules of the cellular automata.

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The ability to obtain complex global behaviour from simple local rules makes cellular automata an interesting platform for massively parallel computation. However, manually designing a cellular automaton to perform a given computation can be extremely tedious, and automated design techniques such as genetic programming have their limitations because of the absence of human intuition. In this thesis, we propose elements of a framework whose goal is to make the manual synthesis of cellular automata rules exhibiting desired global characteristics more programmer-friendly, while maintaining the simplicity of local processing elements. We also demonstrate the power of that framework by using it to provide intuitive yet effective solutions to the two-dimensional majority classification problem, the convex hull of disconnected points problem, and various problems pertaining to node placement in wireless sensor networks. / Thesis (Master, Computing) -- Queen's University, 2007-12-05 10:26:09.591

This thesis investigates advanced silicon devices fabricated using phosphorous ion implantation. The novel devices presented are the silicon quantum cellular automata cell and the few-donor device implanted with controlled numbers of phosphorous donors. In addition, the thesis presents novel measurements of a phosphorous implanted silicon double-dot device, a crucial building block of a quantum cellular automata cell. The devices were fabricated using standard lithographic techniques and, in the case of few-donor devices, a new method of controlled single ion implantation using on-chip detector electrodes. The positional accuracy of the implanted ions was achieved using a resist mask defined by electron beam lithography. A series of subsequent process steps has also been developed to repair the substrate implantation damage, define surface control gates, and to define single electron transistors used for readout via the detection of sub-electron charge transfer signals in the device. The device operations were achieved at mK-temperatures using various measurement techniques. In the case of quantum cellular automata cells, the device operation was demonstrated directly by switching the polarization of the cells from one logic state to another and detecting the corresponding change in the electrostatic environment using single-electron transistors. The control gate limits necessary for stable QCA cell operation were also determined, indirectly demonstrating QCA logic state switching. The double-dot device operation was demonstrated using SET detection in both linear and for the first time in non-linear regimes. In addition, source-drain conductance detection of charge states, simultaneous detection using single-electron transistors and source-drain conductance, and source-drain bias spectroscopy measurements of these systems were also achieved. In the case of few-donor implanted devices, isolated charge transfers were detected in both MOS and PIN based devices. The signals corresponded to between 0.01 and 0.05 of a single electron charge, induced on the islands of the SETs. The magnetic field dependence of the charge transfers detected in few-donor implanted devices was also investigated, along with basic phosphorous donor ionization experiments. The devices were also measured using SETs operated in rf mode, yielding consistent results. The work presented in this thesis is a step towards realizing a silicon charge-based quantum computer and other advanced single-electron devices based on phosphorous ion-implantation in silicon.