In recent decades, the popularity of freeform shapes in contemporary architecture poses new challenges to digital design. One of them is the process of rationalization, i.e. to make freeform skins or structures affordable to manufacture, which draws the most attention from geometry researchers. In this thesis, we aim to realize this process with simple geometric primitives, circular arcs. We investigate architectural surfaces and structures consisting of circular arcs. Our focus is lying on how to employ them nicely and repetitively in architectural design, in order to decrease the cost in manufacturing. Firstly, we study Darboux cyclides, which are algebraic surfaces of order ≤ 4. We provide a computational tool to identify all families of circles on a given cyclide based on the spherical model of M ̈obius geometry. Practical ways to design cyclide patches that pass through certain inputs are presented. In particular, certain triples of circle families on Darboux cyclides may be suitably arranged as 3-webs. We provide a complete classification of all possible 3-webs of circles on Darboux cyclides. We then investigate the circular arc snakes, which are smooth sequences of circu- lar arcs. We evolve the snakes such that their curvature, as a function of arc length, remains unchanged. The evolution of snakes is utilized to approximate given surfaces by circular arcs or to generated freeform shapes, and it is realized by a 2-step pro- cess. More interestingly, certain 6-arc snake with boundary constraints can produce a smooth self motion, which can be employed to build flexible structures. Another challenging topic is approximating smooth freeform skins with simple panels. We contribute to this problem area by approximating a negatively-curved 5 surface with a smooth union of rational bilinear patches. We provide a proof for vertex consistency of hyperbolic nets using the CAGD approach of the rational B ́ezier form. Moreover, we use Darboux transformations for the generation of smooth sur- faces composed of Darboux cyclide patches. In this way we not only eliminate the restriction to surfaces with negative Gaussian curvature, but, also obtain surfaces consisting of circular arcs.

The act of creating anything, from a novel to a simple meal to a building, requires the combination of many elements. Broadly speaking, these elements are technique, technology, and materiality, the three of which are bought into combination according to the intent of the maker. The effects of the combination of these elements can be very powerful. One need only call to mind the cool, damp weightiness of stepping inside a church whose walls are made of solid stone or to contrast this experience with that of picking up a lightweight rowing shell whose thin wood frame and taut fabric skin combine amazing strength with impossible slenderness. These experiences amaze and move us because the various elements that brought them into being are combined in a harmonious way and one that is aligned with a poetic ambition. This is not to say that all three elements need to be mixed in equal proportions or that there is a hierarchy of importance; it is the mixing that is essential, not the presence of any one element. A specific focus of this thesis is technology and the way that architects use it and are shaped by its use. Many architects have rushed to embrace recent advances in digital design and fabrication tools, forgetting that that the act of making requires the convergence of a number of forces. Focussing too much attention on one will often come at that detriment of another. Through a series of projects, this thesis explores a number of methods of designing and making. The projects undertaken range from a series of hand carved spoons, to sculptural, physical translations of flowing water, through to the full-scale realization of a suspended ceiling for the North House prototype. An effort has been made to work across a variety of scales, and to employ as wide a range of techniques and technologies as possible. These projects have afforded a kind of research through making, one that engages the entire body rather than merely the mind, and which has been supplemented with more traditional means of research. In addition to the role of technology in architectural practice, attention has been paid to the relationship between ways of making and time, and to the way in which certain artists, designers, and architects are able to slow, compress, or even transcend time. A series of brief case studies serves to illustrate how this is possible while also describing a set of values against which the work of this thesis can be calibrated. By its very nature this thesis takes the form of an ongoing project, one in search of a somewhat elusive goal. The path that a powerful and moving project must take is often full of uncertainty. If I am certain of anything however, it is that achieving the proper mixture of elements requires patience, persistence, and a willingness to let a project take on a life of its own.

Patterned arrays of metallic nanostructures are commonly used in photonics, electronics, as well as functional materials and biotechnology because of their unique electronic and optical properties. Although great effort has been devoted to the development of nano-patterning techniques in the past decades, there are still existing challenges for nano-fabrication to achieve fine resolution and complex features over macroscopic areas in a reasonable time period. Herein, we devise two versatile patterning strategies, namely indentation colloidal lithography (ICL) and oblique colloidal lithography (OCL), for the stepwise patterning of planar substrates with numerous complex and unique designs. Those strategies combine colloidal self-assembly, imprint molding in conjunction with capillary force lithography and reactive ion etching, all of which are simple and straightforward. Hexagonal arrays of symmetric and nonconcentric gold features are fabricated on glass substrates with highly controllable geometric parameters. The width, size and asymmetry of each surface structure could be tuned down to the ~10 nm level while the scale of the patterned area could exceed 1 cm^(2). Moreover, our technique also leads to the ability to develop an enormous variety of patterns through stepwise amplification of feature types. In particular, some of the features are fabricated for the first time, including target-triangle, hexagram, hexagram-dot and triangle-dot. Distinctive surface plasmon resonance (SPR) properties, such as higher order surface plasmon modes and Fano resonances are both observed from our patterns, which would be highly desired forthe study of plasmonic coupling. In addition, we have demonstrated a surface orientation dependent Raman selectivity on two nano-structures for the first time. Molecular vibrations with opposite symmetries can be selectively enhanced on different substrates. As a demonstration, this property is applied to the odd-even effect of n-alkanethiol self-assembly monolayers (SAMs) on the gold surface. The alternative alternation of the intensity ratios of two vibration pairs have been shown by surface enhanced Raman spectroscopy (SERS) as a function of the number of carbon atoms. The results obtained exhibit high sensitivity and excellent agreement with previous publications.

No description available.

Photonic cavities are able to confine light to a volume of the order of wavelength of light and this ability can be described in terms of the cavity’s quality factor, which in turn, is proportional to the confinement time in units of optical period. This property of the photonic cavities have been found to be very useful in cavity quantum electrodynamics, for e.g., controlling emission from strongly coupled single photon sources like quantum dots. The smallest possible mode volume attainable by a dielectric cavity, however, poses a limit to the degree of coupling and therefore to the Purcell effect. As metal nanoparticles with plasmonic properties can have mode volumes far below the diffraction limit of light, these can be used to achieve stronger coupling, but the lossy nature of the metals can result in extremely poor quality factors. Hence a hybrid approach, where a high-quality dielectric cavity is combined with a low-quality metal nanoparticle, is being actively pursued. Such structures have been shown to have the potential to preserve the best of both worlds. This thesis describes the design, fabrication and characterization of hybrid plasmonic – photonic nanobeam cavities. Experimentally, we were able to achieve a quality factor of 1200 with the hybrid approach, which suggests that the results are promising for future single photon emission studies. It was found that modeling the behaviour (resonant frequencies, quality factors) of these hybrid cavities with conventional computation methods like FDTD can be tedious, for e.g., a comprehensive study of the electromagnetic fields inside a hybrid photonic nanobeam cavity has been found to take up to 48 hours with FDTD. Hence, we also present an alternate method of analysis using perturbation theory, showing good agreement with FDTD. / Graduate

No description available.

To address the commonly poor short wavelength response of the conventional solar cell structure which consists of a highly doped thin emitter layer on top of a thicker and less doped base, the novel concept of the Buried-Windowed-Emitter is introduced. This new solar cell structure makes use of a high quality semiconductor layer on top of the traditionally made highly doped emitter and greatly enhances the spectral response of the solar cell by giving the superficially generated carriers a higher chance of collection at the junction. In the proposed BWE structure the emitter is windowed in order to electrically connect the top layer to the base for current collection. The efficacy of the proposed novel device is proven by computer aided device simulations using the available device simulation tools such as MEDICI. The results of simulation show that the proposed novel Buried-Windowed-Emitter solar cell will not only improve the short wavelength spectral response of the overall cell as expected, but also will boost the spectral efficiency for all the wavelengths. Another exciting conclusion from the results of the computer simulation of the BWE solar cell is that the minority carrier lifetime in the top layer does not need to be very high for a superb performance and values as low as 1µs can still boost the short circuit current of the cell to values close to the theoretical limit of the photo-current collectable by a silicon solar cell. This is indeed a good news for manufacturability of this device as it should be practically feasible to achieve epitaxial films with minority carrier lifetime in this range. In order to increase the understanding about the rather complex structure of the proposed Buried-Windowed-Emitter solar cell, an analytical circuit level model, similar to the case of the standard solar cell, is developed for the proposed device. The developed analytical model helps to understand the importance of the main design parameters such as the dimensions of the pattern of the windowed emitter. On the path to fabricate the proposed BWE solar cell, great deal of work is done on the development of a low temperature (<300°C) epitaxial silicon technology using the benefits of Plasma Enhanced Chemical Vapor Deposition (PECVD). Highly doped epitaxial silicon layers of up to around 1µm thickness are achieved with sheet resistivity as low as 7Ω/sq which is much lower than what is reposted in the literature in similar deposition conditions. Intrinsic, phosphorous doped n-type and boron doped p-type epitaxial films have been developed on silicon substrates. Measurement of reflection spectra of the deposited epitaxial films is proposed as a fast, non destructive and process-integrate-able method to assess the crystalline quality of the epitaxial films. Effects of higher temperature post deposition annealing have been studied on the develop epitaxial films A full technology is developed for the fabrication of the proposed novel solar cells. Photo-masks are designed to create 10 different architectures for the design of the windowed emitter in the BWE cell. All the steps taken in the successful fabrication of the novel BWE cells are presented in detail and the relevant findings are discussed and proposed as future research topics. Three kinds of cells are fabricated using the developed technology to separately study the effects of partial coverage of the windowed emitter, the optical performance of the developed epitaxial silicon films and the performance and manufacturability of the novel BWE solar cell The results show that the concept of windowed-emitter by itself (even without the top layer) is capable of enhancing the performance of the solar cell when compared to a standard design. It also promises high conversion efficiency for the BWE solar cell in case a high quality top layer can be deposited on top of the windowed emitter. The results further reveal the lower than expected quality of the low temperature epitaxial films despite the indication of their full crystallinity through other analyses. Use of the epitaxial films as the emitter of the solar cell is proposed as a direct and effective method of studying the photovoltaic performance of the low temperature epitaxial films. Further development of the epitaxial technology will lead to feasibility of a BWE solar cell with very high photovoltaic performance.

Research Doctorate - Doctor of Philosophy (PhD) / This comparative study between the old Metal Fabrication and Welding (MF&W) trade course 7792 and the newly introduced MF&W trade course 3449, focuses on the data, discussions and recommendations which are likely to help establish what benefits or deficiencies this major change has had on the knowledge base of the current apprentices from the trade course. This is being accomplished by comparing the results from an exit test undertaken by stage III MF&W (Heavy) 7792 apprentices at the Hunter Institute of TAFE in 2001 and the results from exit tests for stage III MF&W (Heavy) 3449 apprentices in New South Wales (NSW) in 2004. These data are supplemented and complemented by an analysis of phone interviews with teachers of MF&W (Heavy) TAFE NSW conducted in 2005. A comparison of the data collected from the stage III Metal Fabrication and Welding (Heavy) apprentices who completed the exit tests in 2001 with those who completed the exit tests in 2004 at TAFE NSW, showed that there was a decline in exit knowledge in the mean scores of the apprentices. When the results of Institute 1's relating to 2001was compared with the results of 2004, the same pattern occurred, whereby it was shown that there was a decline in exit knowledge. This was due to the employers not understanding and embracing the change, or even favouring the changes. In 2004, there were no significant differences between the results of different NSW Institutes. This indicates that the level of material taught on-the-job and off-the-job did not differ across the State. A majority of the MF&W (Heavy) Teachers in NSW who were interviewed indicated that the course did not meet industry needs. The teachers expressed the opinion that the welding component was reasonable in its outcomes but felt that the fabrication part of the course lacked substance in the drawing interpretation, trade calculations and the computer aided drawing components of the course. They preferred the old method of teaching lock-step delivery over competency based training (CBT) method and overwhelmingly indicated that the CBT method had not improved the learning outcomes of the apprentices since the changes that occurred in 1991. The findings indicate that the on-the-job assessment of the apprentice’s training was largely ineffective due to the reluctance of the employers to participate in the system. The teachers felt that this was due mainly to the fact that the employers ‘tick and flick’ approach (whereby the apprentices are given a pass for the competency without completing it) towards doing the assessments. A large majority of those interviewed indicated that the changes to the trade course that occurred from 2001 to 2004 did not result in any improvements in the knowledge base of the apprentices.

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.

Thèse (de maîtrise)--Université Laval, 2008. / Bibliogr. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.