M.Sc. (Computer Science) / Modelling the geometry of a 3D plant for use in a virtual environment can be highly laborious, and hence modelling a large collection of variations of the same plant can be a difficult task. Procedural rule-based methods, such as L-Systems, that generate plant geometry indirectly are powerful techniques for the modelling of plants. However such methods often require expert knowledge and skill in order to be used effectively. This dissertation explores a method for the modelling of procedurally generated plants using an evolutionary algorithm. The model is based on gene expression programming, and uses a hybrid of automated and interactive fitness evaluation. In the model, organisms are represented with linear genomes that can be expressed as L-Systems. The L-Systems can in turn be interpreted as geometry for 3D plants. Several automated fitness functions are presented to rate plants based on various topological and geometric attributes. These fitness functions are used in conjunction with user-based, interactive fitness evaluation in order to provide a comparison of different organisms. The model discussed in this dissertation offers advantages over previous approaches to modelling plants with evolutionary algorithms, and allows a user to quickly generate a population of varied plants without requiring knowledge of the underlying L-Systems.

The purpose of this study was to evaluate the importance of time-matching separate cine camera views in three-dimensional motion studies and to develop analytical methods to accomplish the time matching. An image space was calibrated using twenty-four control points and motion picture films at about 60 frames per second were taken of a moving bar, and of a subject putting a shot. Combinations of correctly and incorrectly matched views were compared for their accuracy in determining the positions of six object points. An algorithm was derived which included the timing variable in the least squares solution for the X, Y, and Z coordinates. These "best fit" solutions for the timing and for the coordinate locations were compared with criterion values. Alterations in the timing of views tended to introduce a bias into the coordinate locations. The magnitude of the bias was a function of the velocity of the object points and of the camera positioning. To keep final coordinate errors below 5% required the two views to be matched to within 0.008 seconds. The time matching algorithm was able to match the views to within 0.005 seconds. The corresponding coordinates could vary by an average of 2.4% from the correct ones. It was concluded that the analytical time matching algorithm could produce acceptable results if extreme accuracy was not required. / Education, Faculty of / Curriculum and Pedagogy (EDCP), Department of / Graduate

More and more computer applications are using three-dimensional models for a variety of uses (e.g. CAD, graphics, recognition). A major bottleneck is the acquisition of these models. The easiest method for designing the models is to build them directly from images of the object being modelled. This paper describes the design of a system, MOLASYS (for MOdeL Acquisition SYStem), that allows the user to build object models interactively from underlying images. This would not only be easier for the user, but also more accurate as the models will be built directly satisfying the dimensions, shape, and other constraints present in the images. The object models are constructed by constraining model points and edges to match points in the image objects. The constraints are defined by the user and expressed using a Jacobian matrix of partial derivatives of the errors with respect to a set of camera and model parameters. MOLASYS then uses Newton's method to solve for corrections to the parameters that will reduce the errors specified in the constraints to zero. Thus the user describes how the system will change, and the program determines the best way to accomplish the desired changes. The above techniques, implemented in MOLASYS, have resulted in an intuitive and flexible tool for the interactive creation of three-dimensional models. / Science, Faculty of / Computer Science, Department of / Graduate

In this study, topology optimisation for heat-conducting paths in a three-dimensional domain was investigated. The governing equations for the temperature distribution were solved using the finite volume method, the sensitivities of the objective function (average temperature) were solved using the adjoint method, and finally, the optimal architecture was found with the method of moving asymptotes (MMA) using a self programmed code. A two-dimensional domain was evaluated first as a validation for the code and to compare with other papers before considering a three-dimensional cubic domain. For a partial Dirichlet boundary, it was found that the converged architecture in three dimensions closely resembled the converged architectures from two dimensions, with the main branches extending to the outer corners of the domain. However, the partial Dirichlet boundary condition was not realistic, and to represent a more realistic case, a full Dirichlet boundary was also considered. In order to investigate a full Dirichlet boundary condition, the domain had to be supplied with an initial base for the architecture to allow variation in the sensitivities. It was found that the width and height of this base had a significant effect on the maximum temperature. A height of 0.04 with a base width of 0.24 proved to be the most effective, since this small base gave the MMA enough freedom to generate a tree structure. It was first assumed that this base should be in the centre of the bottom boundary and this was later proved. The results showed again that the maximum temperature decreased with an increase in the conductivity ratio or volume constraint. The architectures were similar to the partial Dirichlet boundary, again with the main branches extending to the outer corners of the domain. The main branches were thinner compared with the partial Dirichlet boundary and fewer secondary branches were observed. It was concluded that a full Dirichlet boundary could be solved using topology optimisation, if the boundary was supplied with an initial base. With the successful implementation of the full Dirichlet boundary with one initial base, multiple bases were investigated. First, two bases were used and it was assumed that the optimal placement for these bases was in the centre of each respective half of the bottom boundary, which was later confirmed. The optimal width and height of 0.24 and 0.04 respectively were again optimal for each specific base. The same procedure was followed for four bases and it was assumed that the optimal placement was in the centre of each respective quadrant of the bottom boundary, which was also later confirmed. The optimal width and height of 0.12 and 0.04 respectively were found for this case. With this established, optimisation runs for different conductivity ratios and volume constraints were completed for two and four bases. It was found that two bases offered increased performance in terms of the maximum temperature compared with one base. An increase in performance was also observed when using four bases compared with two bases. A maximum of 20.4% decrease in the maximum temperature was observed when comparing four bases with one. Keywords: topology, optimisation, conduction, three-dimensional / Dissertation (MSc)--University of Pretoria, 2014. / gm2014 / Mechanical and Aeronautical Engineering / Unrestricted

Indiana University-Purdue University Indianapolis (IUPUI) / Background: The advancement of three-dimensional visualization technology provides exciting new opportunities in medical education, including new methods for teaching complex anatomical relationships and promising tools for the training of postgraduate physicians. Information on how faculty use three-dimensional visualization technology for anatomy education is essential for informed discussions surrounding their effectiveness as a teaching tool and use in the medical curriculum, yet the current literature lacks necessary contextual details on how faculty integrate these technologies into actual medical curricula. Methods: Fifteen medical educators from North American medical schools and teaching hospitals completed semi-structured interviews and discussed how they use three-dimensional visualization technology for teaching in preclinical courses, clinical clerkships, and postgraduate programs. Transcripts were analyzed using the constant comparative method and resulting themes were used to inform the creation of a questionnaire. Results: The resulting themes of analysis were organized according to a curricular framework that describes how faculty use these technologies as an instructional resource and how this use is related to the purposes, content, sequence, instructional processes and evaluation of medical curricula. The results demonstrate how three-dimensional visualization technology is being is implemented in a variety of ways in the curriculum and revealed numerous similarities of use across the levels of medical education. Analyses revealed minimal use of three-dimensional visualization technology for assessment and indicated faculty face significant challenges in designing such assessment. Conclusions: Results suggest continuing assessment of the effectiveness of these technologies as a teaching tool needs to encompass broader aspects of use, such as those described in this study. Additionally, results showing similarities of use across levels suggest that educators and administrators should consider how threedimensional visualization technology can be thoughtfully integrated to address the changing needs of learners as they progress through medical education. Findings also suggest that administrators who want to support the integration of three-dimensional visualization technology into the curriculum need to provide adequate support and training to help faculty overcome time limitations and difficulties designing assessment methods.

The study of three-dimensional percolation paths through materials is important in its contribution to understanding defect sensitive properties of materials. This work shows the importance of grain boundary character in modeling defect sensitive boundaries. Also presented are trends of percolation of sensitized grain boundaries in 304 stainless steel (304SS). Of particular interest is how open paths form in a three-dimensional model created through serial sectioning. Evidence is presented that triple or quadruple points that contain typically two boundaries with special character that intersect the percolation path break up the path. Some grains with no known special qualities (i.e., CSL) have observable special behavior.

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As three-dimensional (3D) imaging and fluorescence techniques become standard in optical microscopy, novel approaches to 3D fluorescence microscopy are emerging. One such approach is based on the incoherent holography technique called optical scanning holography (OSH). The main advantage of OSH-based microscopy is that only a single two-dimensional (2D) scan is required to record 3D information, whereas most current 3D microscopes rely on sectioning techniques. To acquire a 3D representation of an object, current microscopes must physically scan the specimen in a series of 2D sections along the z-axis. In order to record holograms by OSH, the fluorescent specimen is scanned with an optically heterodyned laser field consisting of a Fresnel zone pattern. A unique acousto-optic modulator configuration is employed to generate a suitable heterodyne frequency for excitation of the fluorescent object. The optical response of a solution containing a high concentration of 15 um fluorescent latex beads to this type of excitation field has been recorded. In addition, holograms of the same beads have been recorded and reconstructed. To demonstrate the 3D imaging capability of the technique, the hologram includes beads with longitudinal separation of about 2 mm. A detailed comparison of 3D fluorescence microscopy by OSH and the confocal approach was conducted. Areas for comparison were 3D image acquisition time, resolution limits and photobleaching. The analysis shows that an optimized OSH-based fluorescence microscope can offer improved image acquisition time with equal lateral resolution, but with degraded longitudinal resolution when compared to confocal scanning optical microscopy (CSOM). For the photobleaching investigation, the parameter of concern is the fluence received by the specimen during excitation, which takes into account both the irradiance level and the time of illumination. Both peak and average fluence levels are addressed in the comparison. The analysis shows that during a 3D image acquisition, the OSH system will deliver lower peak fluence but higher average fluence levels to the specimen when compared to CSOM. / Ph. D.

Electron tomography is an invaluable technique with the capability of carrying out thorough 3D structural, chemical and morphological characterization of materials at nanometer scale. Tilting range, increment and reconstruction algorithms are three of the main factors affecting the quality of tomograms. An anisotropic degradation can be observed with restricted tilting range and increment. Therefore, this study was carried out to investigate the accuracy of the reconstruction results of MgO (cube-shape) generated by FBP, SART and SIRT tomographic algorithms under various reconstruction conditions, i.e. tilting range and increment. Examining the experimental data with known morphology permits quantitative determination of the accuracy of the reconstruction results by measuring the distortion of the cube in all directions. Moreover, distortion measurements in all directions reveal the relationship between level of distortion and the alpha tilt angle. / Master of Science