A human performance experiment was conducted to investigate pixel parameter requirements for three types of flat-panel display images: an alphanumeric character, an oscilloscope waveform, and a real-world image. Subjects performed similarity judgments between an extremely high-quality image and an image composed of different levels of anti-aliasing and pixel width-plus-pixel separation (pitch). It was found that the effect of pitch had greater influence on perceived image quality for the alphanumeric character and oscilloscope waveform than for the real-world image. The results of this research provide empirical evidence showirg that the pixel pitch requirements for flat-panel systems that are used to display binary, high-contrast images (such as text and waveforms) will be more stringent than for low-contrast pictorial images. The three levels of grey-scale anti-aliasing investigated were found to improve image quality for only the binary, high-contrast images.

A Thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy Johannesburg, 2018 / Two dimensional gravity models and a few magnetic models limited to short profiles in the eastern sections of the BC have been used to propose conflicting geometries for the Rustenburg Layered Suite (RLS), especially between the western and eastern lobes; one school argued for completely separate intrusions, while the other proposed that the outcropping lobes are connected at depth. These competing models suggest different emplacement models. They provide a valuable starting point, but, 2.5D potential field modelling is not well suited to modelling complex three dimensional geology. Also, in previous work the magnetics or only the gravity data were modelled independently. Here I present the first full three dimensional potential field forward modelling of the central and southern Bushveld Complex (BC) which has been used to test the geometry of the Bushveld Complex in areas obscured by younger geological cover. Both gravity and magnetic data have been used to develop a geological model that is consistent with both data sets. Joint 3D modelling of regional gravity and magnetic data combined with published crustal thickness models derived from broadband seismic tomography studies were used to create a 3D model of the central and southeastern sections of the BC, as well as the southern part of the northern lobe. Eight downhole logs with more than 730 000 new density and magnetic susceptibility measurements from the RLS were combined with existing data to determine values for Bushveld Complex lithologies that were used in the model. The 3D model has a complex geometry with thick continuous RLS in most of the western lobe, thinner RLS in the south-eastern lobe, but a disrupted RLS in the eastern lobe. Large domes of Transvaal dolomite or thicker granites and granophyre in the eastern lobe interrupt the continuity of the RLS. The western and eastern lobes are therefore broadly connected, with major disruptions largely in the eastern lobe. However, they are not separate intrusions, but represent a single magma chamber affected by pre-existing and syn-magmatic updoming. The model includes the whole thickness of the crust and requires dense material at the crust mantle boundary. Thus, for the first time, I have imaged the remnants of magma staging chambers. The chambers, constrained by the extent of the diffuse crust-mantle transition as determined from teleseismic data, underlie the whole Bushveld Complex, but is thickest under the northern, south-eastern and western parts of the complex. I propose feeders that correlate with the chambers in the northern lobe near the large gravity high near Polokwane and in the south-eastern lobe. / MT 2019

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No description available.

Chunking is defined as the process of organizing information into multi-item clusters appropriate to solving a particular task. It was hypothesized that dynamic information displays could be formatted to group related items. This formatting would facilitate chunking and, in turn, serve to reduce task difficulty. Two novel display grouping formats were evaluated. In Tight Spatial Proximity, iconic symbols belonging to the same class were rearranged so that they were located proximally on the display. In Chunks-In-Sequence (CIS), symbol classes were presented sequentially, but all members within a symbol class were presented simultaneously. Ten individuals participated in Experiment 1. During a trial, 2 to 25 symbols (e.g., cannon, radar, etc.) were presented briefly on a computer display. Displayed symbols were sampled from a larger symbol set (Le., 64 total symbols) representing eight unique symbol classes (e.g., military, highway signs, etc.). Participants then viewed a prompt and responded "yes" or "no" to indicate whether the probe symbol was a member of a class that had been presented during that trial. Results indicated that grouping formats helped participants chunk symbols into appropriate classes and solve the classification task with reduced error rates and subjective workload. Experiment 2 was similar to Experiment 1, with the exception that participants were tasked to remember each symbol presented during a trial rather than just the symbol class names. This task required forming chunks, storing them in memory, and then parsing the chunks into component items. Results indicated that display grouping formats reduced subjective workload, but not error rates. Considering both experiments, it is concluded that spatially or temporally grouped symbols can be chunked more easily than information displayed in a non-grouped format. However, grouping formats will not help operators parse these information chunks given detailed component recall demands. / Ph. D.

When dot-matrix characters are rotated, as might be the case in a moving map display, their dot-matrix patterns are distorted and their legibility is thus affected. In this experiment, 16 subjects performed a random search task, in which they were asked to look for a target in a random character pattern. The independent variables were the direction (clockwise or counterclockwise) and the angle of stimulus image rotation, and the target character's distance from the center of screen, which was also the center of rotation; the dependent variables were response time and response correctness. Significant effects were found in the angle of rotation, the target character's distance from the center, and the target character. The results indicate that (1) no angle-dependent mechanism is involved in performing this task and the angle of rotation influences recognition mainly through the distortion of dot-matrix patterns, (2) the target character's (radial) distance from the center of screen is the determining factor for search time, while the x and y coordinates of the target contributed to dot-matrix pattern distortion, and (3) the target characters interacted differently with the angle and distance factors to determine the extent of distortion and their legibility. Means to quantify the extent of distortion were discussed and the direction for future research is offered. / Master of Science

Recent interest in three-dimensional (3-D) stereoscopic displays has prompted the need to assess the efficacy of retinal disparity depth cues. Accordingly, this study analyzed performance on two 3-D tasks under three levels of signal-to-clutter ratio as participants viewed three display formats portrayed with or without retinal disparity depth cues. Display formats included a plan view and two types of perspective formats. The two tasks assessed viewer ability to compare inter-object distances and extrapolate object positions given a known vector within a 3-D volume. Results indicate that retinal disparity depth cues reduce the number and magnitude of errors within a course prediction task, but did not affect search times or ratings of viewer confidence. Display format affected search times as follows. In a relative distance task, search times for the perspective format are lower than for either the plan view or enhanced perspective formats. In a course prediction task, search times for the plan view and perspective formats are lower than for the enhanced perspective format. Display format does not affect error rate, error magnitude, or ratings of viewer confidence. No interaction between depth cues and display format was observed. The inclusion of retinal disparity depth cues in a visual display system are suggested when the viewer task involves predictions of object position in a 3-D volume and when reducing the number and magnitude of errors is important. Perspective display formats are suggested when fast search times are important. / Master of Science

Considerable research has centered around the issue of whether stereoscopic (3D) viewing allows improved viewer performance for tasks that involve three-dimensional information. Taken as a whole, such previous research indicates that the potential stereoscopic advantage may be dependent on the nature of the task being examined. This task dependency makes it difficult to predict whether stereoscopic viewing will improve viewer performance for a given untested task. By measuring performance over a variety of component tasks, this research examined the potential task-dependent nature of the stereoscopic advantage. In addition, a method was proposed to employ such component-task data for predicting the stereoscopic advantage within future unknown tasks. A set of 12 component tasks (in six task groups, each with two representative tasks) was developed to represent the various task demands of processing 3D visual information. Participants performed each of the 12 component tasks in both a monoscopic (2D) and a stereoscopic (3D) viewing condition. Performance was measured in terms of viewing time, percent accuracy, and a generic mental effort rating. Results indicate that when certain display guidelines are not violated, stereoscopic display improves or at least maintains the overall level of viewer performance for most tasks. Furthermore, the results clearly indicate that the stereoscopic advantage is dependent on the nature of the task. Although further refinement to the set of component tasks is necessary before the precise nature of the task dependency can be determined, the component task method displays considerable promise for being able to predict the stereoscopic advantage for any number of complex 3D tasks. / Ph. D.

This research focuses on the development of polymer microfabrication technologies for the realization of two major components of a pneumatic tactile display: a microactuator array and a complementary microvalve (control) array. The concept, fabrication, and characterization of a kinematically-stabilized polymeric microbubble actuator (¡°endoskeletal microbubble actuator¡±) were presented. A systematic design and modeling procedure was carried out to generate an optimized geometry of the corrugated diaphragm to satisfy membrane deflection, force, and stability requirements set forth by the tactile display goals. A refreshable Braille cell as a tactile display prototype has been developed based on a 2x3 endoskeletal microbubble array and an array of commercial valves. The prototype can provide both a static display (which meets the displacement and force requirement of a Braille display) and vibratory tactile sensations. Along with the above capabilities, the device was designed to meet the criteria of lightness and compactness to permit portable operation. The design is scalable with respect to the number of tactile actuators while still being simple to fabricate. In order to further reduce the size and cost of the tactile display, a microvalve array can be integrated into the tactile display system to control the pneumatic fluid that actuates the microbubble actuator. A piezoelectrically-driven and hydraulically-amplified polymer microvalve has been designed, fabricated, and tested. An incompressible elastomer was used as a solid hydraulic medium to convert the small axial displacement of a piezoelectric actuator into a large valve head stroke while maintaining a large blocking force. The function of the microvalve as an on-off switch for a pneumatic microbubble tactile actuator was demonstrated. To further reduce the cost of the microvalve, a laterally-stacked multilayer PZT actuator has been fabricated using diced PZT multilayer, high aspect ratio SU-8 photolithography, and molding of electrically conductive polymer composite electrodes.

Thesis: M.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1981 / Includes bibliographical references. / by John Harvey Serocki. / M.S. / M.S. Massachusetts Institute of Technology, Department of Mechanical Engineering