Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xv, 144 p.; also includes graphics (some col.) Includes bibliographical references (p. 129-144). Available online via OhioLINK's ETD Center

Thesis (Ph.D.)--Drexel University, 2010. / Includes abstract and vita. Includes bibliographical references (leaves 123-125).

Thesis (M.S.)--Oregon Graduate Center, 1985.

M.Phil. (Optometry) / Significant vision impairment caused by uncorrected distance or near vision (at a level defined by The World Health Organization as a disability) affects over 600 million people globally (9% of the world’s population). Over 3.5 billion people (52% of the world’s population) need some form of vision correction to see clearly. By 2020, this number is projected to reach 6.1 billion, 66% of the world’s population. Vision impairment is an important issue affecting the everyday lives of these 3.5 billion people worldwide. Two thirds of those affected live in the less developed world where the majority do not have easy access to eye care, eye examinations and affordable spectacles. Purpose If an ametrope or presbyope pricks a small hole into a leaf, piece of paper or cardboard and looks through it, he or she will usually experience improved acuity providing there is no central cataract or any ocular pathology. Rural communities, who have no access to eye-care or vision specialists, with vision problems, may benefit from looking through a pinhole while looking far and near. Many who are longsighted or presbyopic, may have problems reading their Bibles for example. They may only have candles as a source of light at night. They could improve their vision by looking through a small hole while reading. The purpose of this study is to explore the possibility of such a simple and almost cost free device contributing to solving this need. Method Uncompensated (without the pinhole) near or proximal visual acuities (VAs) were measured and recorded on one eye of 45 presbyopic subjects over the age of 50 years in photopic (250 lux) and then scotopic (20 lux) conditions. There were 36 male and 9 female subjects. Their ages ranged between 50 and 74 years with an average of 59 (SD = ±7.52) years. The ambient room illumination for photopic conditions was measured using a Sekonic Lumi Model 246 light-meter. No visual or pathological conditions or requirements were set for the subjects. The subjects were asked to read the smallest letters on the near chart by moving their head closer ...

Contact lens manufacture requires a high level of accuracy and surface integrity in the range of a few nanometres. Amidst numerous optical manufacturing techniques, single-point diamond turning is widely employed in the making of contact lenses due to its capability of producing optical surfaces of complex shapes and nanometric accuracy. For process optimisation, it is ideal to assess the effects of various conditions and also establish their relationships with the surface finish. Presently, there is little information available on the performance of single point diamond turning when machining contact lens polymers. Therefore, the research work undertaken herewith is aimed at testing known facts in contact lens diamond turning and investigating the performance of ultra-high precision manufacturing of contact lens polymers. Experimental tests were conducted on Roflufocon E, which is a commercially available contact lens polymer and on Precitech Nanoform Ultra-grind 250 precision machining. Tests were performed at varying cutting feeds, speed and depth of cut. Initial experimental tests investigated the influence of process factors affecting surface finish in the UHPM of lenses. The acquired data were statistically analysed using Response Surface Method (RSM) to create a model of the process. Subsequently, a model which uses Runge-Kutta’s fourth order non-linear finite series scheme was developed and adapted to deduce the force occurring at the tool tip. These forces were also statistically analysed and modelled to also predict the effects process factors have on cutting force. Further experimental tests were aimed at establishing the presence of the triboelectric wear phenomena occurring during polymer machining and identifying the most influential process factors. Results indicate that feed rate is a significant factor in the generation of high optical surface quality. In addition, the depth of cut was identified as a significant factor in the generation of low surface roughness in lenses. The influence some of these process factors had was notably linked to triboelectric effects. This tribological effect was generated from the continuous rubbing action of magnetised chips on the cutting tool. This further stresses the presence of high static charging during cutting. Moderately humid cutting conditions presented an adequate means for static charge control and displayed improved surface finishes. In all experimental tests, the feed rate was identified as the most significant factor within the range of cutting parameters employed. Hence, the results validated the fact that feed rate had a high influence in polymer machining. The work also established the relationship on how surface roughness of an optical lens responded to monitoring signals and parameters such as force, feed, speed and depth of cut during machining and it generated models for prediction of surface finishes and appropriate selection of parameters. Furthermore, the study provides a molecular simulation analysis for validating observed conditions occurring at the nanometric scale in polymer machining. This is novel in molecular polymer modelling. The outcome of this research has contributed significantly to the body of knowledge and has provided basic information in the area of precision manufacturing of optical components of high surface integrity such as contact lenses. The application of the research findings presented here cuts across various fields such as medicine, semi-conductors, aerospace, defence, telecom, lasers, instrumentation and life sciences.

This work is concerned with how to extract information encoded in small scales of non-Gaussian fields, with the purpose of learning about cosmology using weak gravitational lensing. We do so by comparing different methods on simulated data sets. The topic is relevant, for upcoming galaxy surveys will map the late evolution of the matter density field, which is non-Gaussian, with an unprecedented level of detail, and any improvement on the analysis techniques will increase the experiments' scientific return. First, we investigate some non-Gaussian observables used in the weak lensing community. We analyze to what extent they are sensitive to the background expansion of the universe, and to what extent to the evolution of the structures responsible for the lensing. We then focus our attention on one such statistic, lensing peaks, and assess the performance of a simple halo-based model that has been proposed to forecast their abundance. We find some shortcomings of that semi-analytic approach, and proceed to review some minimal requirements for numerical simulations used to forecast non-Gaussian statistics, to reduce their computational cost while fulfilling the accuracy and precision required by future experiments. Second, we propose a novel measurement, that of the temperature dipole induced on the cosmic microwave background induced by the rotation of ionized gas around galaxies, as an additional observation to help constrain the distribution of baryonic matter on the smallest scales probed by WL experiments. The uncertainty in this distribution is a major theoretical systematic for future surveys. Third, we show how deep neural networks can be used to map pixel-level data into the cosmological parameters of interest, by-passing the previous compression step of measuring pre-designed statistics. We provide the first (simulation-based) credible contours based on neural networks applied to weak lensing data, and discuss how to interpret these models.

Non-imaging Fresnel lenses have been playing an important role in improving the efficiency of the solar energy systems. Many researchers and scientists have devoted their research to optimize the design of the Fresnel lenses. Before it can contribute to energy efficiency increase, a Fresnel lens with optimized design will first need to be fabricated with the most cost-effective method as well as the best quality fabrication as possible. If targeted in a commercial market, feasibility of mass production with a minimum fabrication time would also be a consideration. To bring the design optimization of a Fresnel lens from a conceptual theory to a real-life increase in energy efficiency, the lens needs to be fabricated, tested, compared, and analyzed. This research thesis is intended to explore the performance of the lenses with optimized design through experimental investigations. The design optimization was achieved by a previous PhD student at UNT. A total of six lenses fabricated with four different methods along with two purchased lenses were tested with two different approaches. Multiple testing routes were conducted within a 10-month period to observe the effects of material decomposition and degradation on the lens performance. The resulting experimental data has provided a solid base for analyzing the performance of the lenses, in particular, the energy conversion efficiency increase of the solar cell by using each lens. The potential cause of the performance variation can be extracted from the comparison and evaluation.

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