This thesis is concerned with the design of a novel system for inserting porogen particles within internal structure of the bone scaffold. The proposed system would be integrated with a 3D printing machine to create macro-pores based on the conventional porogen leaching method. The system is capable of inserting porogens on pre-designed locations within the scaffold structure to realize the generation of macro-porosity within scaffolds. Several alternatives for such a porogen insertion mechanism are proposed based on employing a mechanical actuator for opening and closing the path of porogen particles from a porogen reservoir to the build chamber. Another possible design that offers significant advantages over its actuator-based alternatives is a pneumatic-based mechanism that picks up porogens from a porogen reservoir and places them at pre-designed locations. Among all the presented alternatives, the pneumatic-based system is selected by utilizing the value matrix method, and detail design of the different parts of this system is presented. The required pilot test setups for performing the feasibility study of the proposed method have been designed and successfully developed, and the practicality of the designed porogen insertion mechanism is proven through experiment.

This thesis is concerned with the design of a novel system for inserting porogen particles within internal structure of the bone scaffold. The proposed system would be integrated with a 3D printing machine to create macro-pores based on the conventional porogen leaching method. The system is capable of inserting porogens on pre-designed locations within the scaffold structure to realize the generation of macro-porosity within scaffolds. Several alternatives for such a porogen insertion mechanism are proposed based on employing a mechanical actuator for opening and closing the path of porogen particles from a porogen reservoir to the build chamber. Another possible design that offers significant advantages over its actuator-based alternatives is a pneumatic-based mechanism that picks up porogens from a porogen reservoir and places them at pre-designed locations. Among all the presented alternatives, the pneumatic-based system is selected by utilizing the value matrix method, and detail design of the different parts of this system is presented. The required pilot test setups for performing the feasibility study of the proposed method have been designed and successfully developed, and the practicality of the designed porogen insertion mechanism is proven through experiment.

Laser Sintering, a method of additive manufacturing, is used in the production of concept models, functional prototypes, and end-use production parts. As the technology has transitioned from a product development tool to an accepted production technique, functional qualities have become increasingly important. Tension properties reported for popular polyamide sintering materials are comparable to the molded properties with the exception of elongation. Reported strains for laser sintered polyamide are in the 15-30% range with 200-400% strains reported for molding. (CES Edupack n.d.) The primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are studied. Methods to quantify decreased mechanical properties are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture. / text

In an effort to gain a more comprehensive and complete understanding of the thermal behaviors occurring during the selective laser sintering process, external temperature measurements were taken during the build process. To accomplish this, an infrared camera was aimed directly through a viewport on the front of the sinterstation. The temperature was monitored during the heating process which showed slightly non-uniform heating of the part bed surface. Temperatures were also recorded while the laser was sintering each layer and the subsequent cooling of the entire machine following the build. By directly capturing infrared images of the part bed’s surface, it is clearer how the temperature gradients behave and the impact such variables have on part build efficiency. / text

Notwithstanding several years of robust growth, solar energy still only accounts for<1% of total electrical generation in the US. Before solar energy can substantially replace fossil fuels subsidy-free at utility scale, further cost reductions and efficiency improvements are needed in complete generating systems. Flat panel silicon PV modules are by far the most dominant solar technology today, but have little room for improvement in efficiency and are limited by balance of system costs. Concentrated PV (CPV) is an alternate approach with long-term potential for much higher efficiency in sunny climates. In CPV modules, large area optics collect and concentrate direct sunlight onto small multi-junction cells with>40% conversion efficiency. Concentrated Solar Power (CSP) uses mirrors to concentrate sunlight onto thermally absorbing receivers, which generate electricity with convention thermal cycles. In this dissertation, four new optical approaches to CPV and CSP with potential for lower cost are analyzed. Common to each approach is the use of large square glass reflectors, which have very low areal cost (~$35/m^2) and field-proven reliability in the CSP industry. Chapter 2 describes a freeform toroidal lens array used to intercept the low concentration line focus of a parabolic trough to produce multiple high concentration foci (>800X) for multi-junction cells. In Chapter 3, three embodiments of dish mirrors and freeform lenslet arrays are explored, including an off-axis system. In each case, a dish mirror illuminates a freeform lenslet array, which divides sunlight equally to a sparse matrix of multi-junction cells. The off-axis optical system achieves +/-0.45° acceptance angle and averages 1215X geometric concentration over 400 multi-junction cells. Chapter 4 proposes a new architecture for CSP central receivers that achieves extremely high collection efficiency (>70%) with unconventional heliostat field tracking. In Chapter 5, the design and preliminary testing of a spectrum-splitting hybrid PV/thermal generator is discussed. This system has the advantage of 'drop-in' capability in existing CSP trough plants and allows for thermal storage, an important mitigation to the intermittency of the solar resource.

Conventional stereoscopic displays present a pair of stereoscopic images on a single and fixed image plane. In consequence, these displays lack the capability of correctly rendering focus cues (i.e. accommodation and retinal blur) and may induce the discrepancy between accommodation and convergence. A number of visual artifacts associated with incorrect focus cues in stereoscopic displays have been reported, limiting the applicability of these displays for demanding applications and daily usage. Depth-fused multi-focal-plane display was proposed to create a fixed-viewpoint volumetric display capable of rendering correct or nearly-correct focus cues in a stereoscopic display through a small number of discretely placed focal planes. It effectively addresses the negative effects of conventional stereoscopic displays on depth perception accuracy and visual fatigue. In this dissertation, the fundamental design methods and considerations of depth-fused displays were refined and extended based on previous works and a high-resolution optical see-through multi-focal-plane head-mounted display enabled by state-of-the-art freeform optics was developed. The prototype system is capable of rendering nearly-correct focus cues for a large volume of 3D space extending into a depth range from 0 to 3 diopters at flicker-free speed. By incorporating freeform optics, the prototype not only achieves high quality imagery across a large 3D volume for the virtual display path but it also maintains better than 0.5 arcminutes visual resolution of the see-through view. The optical design, implementation and experimental validation of the display are presented and discussed in detail.

In this dissertation fully general conditions are presented to correct linear and quadratic field dependent aberrations that do not use any symmetry. They accurately predict the change in imaging aberrations in the presence of lower order field dependent aberrations. The definitions of the image, object, and coordinate system are completely arbitrary. These conditions are derived using a differential operator on the scalar wavefront function. The relationships are verified using ray trace simulations of a number of systems with varying degrees of complexity. The math is shown to be extendable to provide full expansion of the scalar aberration function about field. These conditions are used to guide the design of imaging systems starting with only paraxial surface patches, then growing freeform surfaces that maintain the analytic conditions satisfied for each point in the pupil. Two methods are proposed for the design of axisymmetric and plane symmetric optical imaging systems. Design examples are presented as a proof of the concept.

No description available.

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 16, 2008) Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 100-118).