A topological sampling theorem for Robust boundary reconstruction and image segmentation

AbstractExisting theories on shape digitization impose strong constraints on admissible shapes, and require error-free data. Consequently, these theories are not applicable to most real-world situations. In this paper, we propose a new approach that overcomes many of these limitations. It assumes that segmentation algorithms represent the detected boundary by a set of points whose deviation from the true contours is bounded. Given these error bounds, we reconstruct boundary connectivity by means of Delaunay triangulation and α-shapes. We prove that this procedure is guaranteed to result in topologically correct image segmentations under certain realistic conditions. Experiments on real and synthetic images demonstrate the good performance of the new method and confirm the predictions of our theory

Effect of sintering parameters on the mechanical and physical properties of sinter formed materials

Sinter formed materials have been studied in this project. The powders used were stainless steel powders and zinc oxide powders. Three stainless steel powders were studied to evaluate the compressibility, shrinkage and densification during sintering and strength behaviour. The effect of sintering temperature on the high strain rate behaviour of stainless steel powder compacts has been investigated. A dynamic constitutive equation, which describes the material behaviour under dynamic loading, has been established. This equation takes into account the density of the compact. Regarding ceramic powders, the compressibility of four zinc oxide varistor powders have been studied taking into account the particle size, binder content, binder type and lubricant. The green and sintered strength of ceramic compacts have been assessed in relation to the above mentioned parameters. As for sintering, it was required to optimize the temperature profile of the sintering process. To accomplish this, two instruments were developed. The first one was used to monitor and control the weight loss, due to the binder burn out, at a constant rate. The second instrument was developed to monitor and control the shrinkage during sintering. The optimized temperature profile during binder burn out was checked for verification and it has proved reliable. A brief look at the grain growth during sintering was carried out to see the effect of heating rate and soaking time on the grain growth since this is a critical material property influencing the electrical characteristics of zinc oxide varistors

Haptics Rendering and Applications

There has been significant progress in haptic technologies but the incorporation of haptics into virtual environments is still in its infancy. A wide range of the new society's human activities including communication, education, art, entertainment, commerce and science would forever change if we learned how to capture, manipulate and reproduce haptic sensory stimuli that are nearly indistinguishable from reality. For the field to move forward, many commercial and technological barriers need to be overcome. By rendering how objects feel through haptic technology, we communicate information that might reflect a desire to speak a physically- based language that has never been explored before. Due to constant improvement in haptics technology and increasing levels of research into and development of haptics-related algorithms, protocols and devices, there is a belief that haptics technology has a promising future

Micro-mechanical Properties of Niger Delta Sandstone Rock using Advanced Experiments and Multi-scale Modelling

The focus of this investigation is to understand the micromechanical characteristics of the oil-bearing Niger Delta sandstone at different length scales. Initially, the sandstone samples are experimentally characterised to understand their morphological, physical, chemical and mechanical properties at grain scale and bulk scale where applicable. In spite of a significant level of scientific advancements made so far, sensing stress distribution characteristics of opaque and anisotropic materials such as sandstone rock remains as a stiff challenge in a wide range of science and engineering fields including geotechnical, geophysics, petroleum, mining, minerals, advanced materials and particulate science and engineering. Here we present an original framework for simulating and quantifying the strength characteristics of real sandstone samples using combined measurements and modelling strategy. Using photo-stress analysis methodology, first we sense elastic shear stress (or strain) distribution and its components along orthogonal directions on the surface of a V-notch sandstone sample under mechanical loading. Using this and applying a classical grain-scale model, the stiffness ratio of the sandstone is evaluated. This measure is also compared with using ultrasound sensors and a good level of agreement is obtained. Thereafter, the grain-scale stiffness ratio which characterises the signature of material anisotropy is fed as an input in to the discrete element modelling (DEM) of cylindrical sandstone rock samples subjected to uni-axial and tri-axial compression loading. Physical experiments are also conducted to evaluate their load-displacement characteristics and bulk fracture strength of sandstone sample under these loading conditions. A good level of agreement is obtained between the results of simulations and experiments. Taking advantage of the validated DEM simulations, an extensive level of parametric studies are conducted to evaluate the influences of different grain-scale properties on the bulk strength and fracture characteristics of sandstone. Thus the current multi-scale framework can be applied in future to quantify the strength characteristics of such complex and anisotropic materials in a reliable manner

INVESTIGATION OF FLOW AND MICROSTRUCTURE IN RHEOMETRIC AND PROCESSING FLOW CONDITIONS FOR LIQUID CRYSTALLINE PITCH

A fundamental understanding of flow and its influence on the microstructure is required to obtain carbon materials with desired properties. The objective of this research was to investigate the flow and microstructural behavior of a synthetic mesophase pitch (AR-HP) in rheometric and processing flow conditions. In addition, simulation studies were performed to establish a frame work for modeling the flow behavior of this complex material in different flow situations. The steady-shear viscosities obtained from a cone-plate rheometer during increasing rate-sweep experiments exhibited a shear-thinning region (Region I) with a slope of about -0.2 and a plateau (Region II) region. The transient shear stress responses, as measured from cone-plate rheometer, exhibited nonmonotonic behavior as a function of applied strain at all shear rates and temperatures tested. Microstructural study on three orthogonal sections of the sheared samples, reported for the first time, indicates that the local maximum in shear stress was due to yielding of initial microstructure. In addition to high-strain experiments, dynamic experiments were also performed in the linear viscoelastic region. The elastic response was found to be strongly dependent on the microstructure, and a lower slope of 0.8 for the elastic modulus in the low-frequency terminal region was observed as compared to 2 observed for flexible-chain polymers. Relaxation of microstructure was found to be influenced not only by the textural size, but also by layer-plane orientation. The flow-microstructural study was extended to the processing flow conditions by extruding AR-HP mesophase pitch through custom-made dies. Microstructural observations suggest that in the capillary, the orientation of the layer-plane was approximately radial near the wall and the orientation deviated from the radial orientation away from the wall. In the core, no preferred orientation of mesophase layer-planes was observed. Simulation studies were performed using constitutive equations for discotic liquid-crystalline materials in simple shear flow, corresponding with the experimental studies. Two different initial conditions were considered that resemble the experimental results. At steady state, the bulk of the discs were found to be oriented at a flow-aligned angle of -64.1°, which is consistent with the theoretical predictions

Laboratory Studies of Hypervelocity Impacts on Solar System Analogues

Impact cratering and asteroid collisions are major processes throughout the Solar System. Although previous collision-related impact investigations exist (Flynn et al. 2015, Holsapple et al. 2002 and Burchell et al. 1998 are good examples), in the works covering this broad range of investigation, the targets are non-rotating (for the purposes of catastrophic disruption) and different temperature conditions are not considered (for impact cratering). Accordingly, I present experimental processes and data, regarding hypervelocity impact experiments into analogues of (1) rotating asteroids and (2) temperature dependant terrestrial planetary rock. During the course of this work, it was necessary to develop new apparatus and new experimental techniques such as three separate target holders to aid in both catastrophic disruption and heated impact projects, a 3-dimensional model analysis of craters and a completely new, statistically robust, technique to determine a complete crater profile called the KDM method where KDM is Kinnear-Deller-Morris. The main result from this work showed that during an asteroid impact collision where the asteroid is not rotating, the impact energy density for catastrophic disruption is Q*static = 1442 ± 90 J kg-1. However, when the target asteroid was rotating, the condition Q*rotation = 1097 ± 296 J kg-1. The mean value of Q* had thus reduced, but the spread in the data on individual experiments was larger. This leads to two conclusions. The mean value for Q*, based on measurements of many impacts, falls, due to the internal forces acting in the body which are associated with the rotation. This energy term reduction means that the amount of energy to instigate catastrophic disruption is lower and that a rotating asteroid is effectively weaker upon impact than a stationary asteroid. However, the spread in the results indicates that this is not a uniform process, and an individual result for Q* for a rotating or spinning target may be spread over a large range. For the temperature related impacts, as the targets were heated to approximately 1000 K, the target rocks showed an impact dependence more similar to a plastic phase-state than to solidus, due to being held close to temperatures associated with semi-plastic phases. Basalt impact craters displayed this relationship greatest with crater sizes becoming smaller at the higher temperature ranges but larger in the colder brittle solidus temperatures, partly explained in experiments by increased spallation

Drawing from motion capture : developing visual languages of animation

The work presented in this thesis aims to explore novel approaches of combining motion capture with drawing and 3D animation. As the art form of animation matures, possibilities of hybrid techniques become more feasible, and crosses between traditional and digital media provide new opportunities for artistic expression. 3D computer animation is used for its keyframing and rendering advancements, that result in complex pipelines where different areas of technical and artistic specialists contribute to the end result. Motion capture is mostly used for realistic animation, more often than not for live-action filmmaking, as a visual effect. Realistic animated films depend on retargeting techniques, designed to preserve actors performances with a high degree of accuracy. In this thesis, we investigate alternative production methods that do not depend on retargeting, and provide animators with greater options for experimentation and expressivity. As motion capture data is a great source for naturalistic movements, we aim to combine it with interactive methods such as digital sculpting and 3D drawing. As drawing is predominately used in preproduction, in both the case of realistic animation and visual effects, we embed it instead to alternative production methods, where artists can benefit from improvisation and expression, while emerging in a three-dimensional environment. Additionally, we apply these alternative methods for the visual development of animation, where they become relevant for the creation of specific visual languages that can be used to articulate concrete ideas for storytelling in animation

Doctor of Philosophy

dissertationA polytype of wollastonite, 2M-wollastonite, that breaks into acicular particles under external forces is being synthesized through two different processes, namely a Partial Melting and Recrystallization Process (PMR Process) and a Flux Growth Process (FG Process). The PMR Process combines the advantages of the solid state reaction and liquid phase reaction methods by creating a partially melted phase to maintain the original shape of the compacts of raw materials while melted regions form locally within the compacts, providing a favorable environment for the growth of alpha-wollastonite in the first step. The target crystal, 2M-wollastonite, nucleates and grows during the subsequent recrystallization stage. Using this process, effects of additives on the preparation of acicular wollastonite particles were investigated. It was found that B2O3 is one of the melting point depressing additives that can lower the melting point of the raw mixtures significantly in a small amount. Li2O is one of the catalytic additives that promote the formation of acicular wollastonite particles. The FG Process completely melt the raw mixtures in a suitable crucible at temperatures above 1400oC, and then lets the melt solidify under a favorable cooling rate to allow the nucleation and growth of 2M-wollastotnite during this stage. It takes advantage of the heat transfer properties of the melt-crucible-furnace wall (MCF) system; a vertical temperature gradient is achieved to provide sites for the preferable nucleation of 2M-wollatonite crystals at the top melt surface. The solidified products contain nearly pure 2M-wollastonite crystals as the major component and an amorphous glass phase as the minor part. Both the PMR and FG processes yielded high-aspect-ratio (HAR) particles. The crystals grown by the PMR process were small in size but large in number, and they grew randomly in the final products. The crystals grown by the FG process were aligned and they formed cellular and dendritic patterns. Such a growth behavior offers additional benefits for producing HAR wollastonite particles. When the two processes were compared, the FG process surpasses the PMR process in terms of efficiency. Modeling and simulation work was done on the FG process that presented cellular and dendritic growth. Based on experimental studies, an empirical model was proposed that modified the existing models on predicting cellular and dendritic growth on a SiO2-CaO-B2O3-Li2O ceramic alloy under high temperature unsteady-state heat transfer. Using this new model, the growth rate and primary arm spacing were predicted well compared with experimental observations. Besides, the average growth front, solidification volume fraction, and mean aspect ratio were also simulated. The simulation work helped to understand and predict the growth of wollastonite crystals in a significant way

LIPIcs, Volume 258, SoCG 2023, Complete Volume

LIPIcs, Volume 258, SoCG 2023, Complete Volum