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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

The Network Lens

Yang, Dingjie January 2010 (has links)
<p>A complex network graphics may be composed of hundreds and thousands of objects, such as nodes and edges. Each object may hold a large number of attributes that might be difficult to explore in the network visualization. Therefore, many visualization tools and approaches have been developed to gain more information from the network graphics. In this paper, we introduce the concept of the Network Lens<em>, </em>a new widget that assists the users to deal with a complex network. The Network Lens is an interactive tool that combines data visualization to a magic lens. With the help of the Network Lens, users can display hidden information of the elements in the network graphics based on their interest. Moreover, the Network Lens supports a series of interactive functions that give the users flexible options to define their own lenses.</p>
202

USE OF INTERFERENCE PASSBAND FILTERS WITH WIDE-ANGLE LENSES FOR MULTISPECTRAL PHOTOGRAPH

McKenney, D. B., Slater, P. N. 10 June 1969 (has links)
QC 351 A7 no. 40 / The aim of this study was to determine to what extent a constant spectral response can be obtained for wide-passband interference filters used with wide -angle lenses. We investigated the possibility of using the curvature of the lens surfaces to reduce the shift in the filter passband for large field angles and found that locating the filter on the proper surface will considerably reduce the shift of the passband. Specifically, we determined the distribution of angles of incidence for full aperture pencils incident at several field angles on the second and fourth surfaces of the 90° Geocon IV, the 90° Paxar, and the 125° Pleogon. We then calculated the spectral transmittance of each lens when a wide passband interference filter was located on its second or fourth surface. We also calculated the degree of polarization introduced. From the cases considered, we found that the tracing of an upper and lower marginal (rim) ray at maximum field angle is sufficient to determine the suitability of a surface, the criterion being that, the smaller the angle of incidence at the surface, the better. In addition, we found that, with the filter on the second surface of the Paxar, spectral transmittance changes with field angle were negligible and the modulation due to polarization was about 1 %.
203

APPLICATION OF ASPHERICS FOR WEIGHT REDUCTION IN SELECTED CATADIOPTRIC LENSES

Buchroeder, Richard A. 07 1900 (has links)
QC 351 A7 no. 69 / The history of modern wide -field, high-speed catadioptric lenses is reviewed. One system comprising only spherical curves and representative of the current art for low-light-level systems is evaluated and used as a baseline design in a weight-reduction study. Five aspheric designs are computed and evaluated. It is found that the use of aspherics will permit weight reduction only in certain instances, i.e., if one element of an all-spherical design can be eliminated or if a fundamentally different configuration that is possible only with aspherics is substituted for the all-spherical configuration. Of these possibilities, the elimination of an element is the best replacement for the baseline design. The case of a highly constrained, purely refractive triplet is studied in some detail. Four designs are computed -from the all-spherical case to the most complex polynomial aspheric. It is found that, if only conic aspherics are employed, significant improvement can be obtained and the problems involved are sensibly the same as those in all-spherical designs. When complex aspherics are applied, the problem becomes surprisingly difficult, and there is some indication that a computer can deal with it better than can a human lens designer.
204

Low-coherence interferometer for contact lens surface metrology

Heideman, Kyle C., Greivenkamp, John E. 29 March 2016 (has links)
Contact lens performance depends on a number of lens properties. Many metrology systems have been developed to measure different aspects of a contact lens, but none test the surface figure in reflection to subwavelength accuracy. Interferometric surface metrology of immersed contact lenses is complicated by the close proximity of the surfaces, low surface reflectivity, and instability of the lens. An interferometer to address these issues was developed and is described here. The accuracy of the system is verified by comparison of glass reference sample measurements against a calibrated commercial interferometer. The described interferometer can accurately reconstruct large surface departures from spherical with reverse raytracing. The system is shown to have residual errors better than 0.05% of the measured surface departure for high slope regions. Measurements made near null are accurate to lambda/20. Spherical, toric, and bifocal soft contact lenses have been measured by this system and show characteristics of contact lenses not seen in transmission testing. The measurements were used to simulate a transmission map that matches an actual transmission test of the contact lens to lambda/18. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
205

Correção da presbiopia pseudofácica através da implantação secundária de diafragma estenopeico no sulco ciliar / Pseudophakic presbyopia correction through secondary implantation of pinhole diaphragm in the ciliary sulcus

Trindade, Claudio Lovaglio Cançado 16 April 2019 (has links)
INTRODUÇÃO: A presbiopia pseudofácica, imposta pela extração do cristalino e implantação de uma lente intraocular monofocal, representa uma relativa limitação da cirurgia de catarata moderna. Diversos métodos para compensação de tal fenômeno já foram descritos. Nesse estudo, avaliamos a eficácia de um implante intraocular estenopeico em promover ampliação da profundidade de foco, e seu impacto no desempenho visual. MÉTODOS: Foram selecionados 10 pacientes hígidos, com boa saúde ocular, previamente submetidos a cirurgia de catarata bilateral com implante de lente intraocular monofocal, os quais apresentavam limitação da acuidade visual para perto. Os pacientes foram submetidos a implantação monocular do diafragma intraocular estenopeico XtraFocus®, no sulco ciliar. As variáveis avaliadas foram acuidade visual, refração subjetiva, sensibilidade ao contraste, amplitude de pseudoacomodação (curva de defocus), estereopsia, campimetria computadorizada, teste de efeito Pulfrich, e avaliação subjetiva do desempenho visual, através da aplicação de questionário. RESULTADOS: Houve significativa melhora da acuidade visual para perto, com 7 pacientes alcançando acuidade visual sem correção para perto de 20/30, no olho operado. Não houve impacto significativo na refração subjetiva, sensibilidade ao contraste e estereopsia. A perimetria computadorizada evidenciou redução de sensibilidade retiniana difusa, no olho operado. A percepção subjetiva do desempenho visual após o tratamento foi favorável, com impacto positivo nas atividades diárias. Não foi observada indução de efeito Pulfrich. CONCLUSÕES: O implante estenopeico estudado foi capaz de promover ampliação da profundidade de foco, com aprimoramento da acuidade visual para perto. O implantação cirúrgica se mostrou segura, sem ocorrência de eventos adversos significativos. Os resultados sugerem que uma maior independência de óculos pode ser alcançada caso a técnica seja aplicada em pacientes portadores de miopia de pequena magnitude. Este achado está em conformidade com trabalhos prévios envolvendo dispositivos estenopeicos. Apesar da limitação à entrada de luz imposta pelo orifício estenopeico, a percepção de luminosidade não é proporcionalmente impactada. Entretanto, em condições de baixa luminosidade, pode haver uma percepção monocular de escuridão / INTRODUCTION: Pseudophakic presbyopia, imposed by crystalline lens extraction and implantation of an artificial monofocal intraocular lens (IOL), represents a relative limitation of modern cataract surgery. Several methods of compensation of this phenomenon have been proposed. In this study, we evaluate the efficacy of a pinhole intraocular implant in promoting depth of focus extension, and its impact in visual performance. METHODS: A selection of 10 healthy patients, with no ocular comorbidity, previously submitted to bilateral cataract surgery and monofocal IOL implantation, presenting with near vision limitation, was carried out. Patients underwent monocular implantation of the XtraFocus® pinhole implant, in the ciliary sulcus. Outcome variables were visual acuity, subjective refraction, contrast sensitivity, amplitude of pseudoaccommodation (defocus curve), stereoacuity, automated perimetry, Pulfrich effect testing and subjective visual performance evaluation with a questionnaire. RESULTS: A significant improvement in near visual acuity was observed, with 7 patients reaching 20/30 uncorrected near visual acuity, in the operated eye. There was no significant impact in subjective refraction, contrast sensitivity and stereoacuity. Automated perimetry revealed a reduction of overall retinal sensitivity, in the operated eye. Subjective assessment of visual performance was favourable, with positive impact in daily activities. Induction of Pulfrich effect was not observed. CONCLUSIONS: The pinhole implant evaluated in this study was able to provide depth of focus extension, and enhance near visual acuity. Surgical implantation was safe, with no occurrence of significant adverse events. Results suggest that a greater level of spectacle independence may be achieved if this approach is combined with low levels of myopia. This finding is in accordance with other studies involving small aperture optics. In spite of the reduction of light entrance caused by the pinhole implant, the overall brightness sensation is not proportionally impaired. However, under low light conditions, a monocular darkening perception can occur
206

Confecção de lentes acrílicas para o ensino de ótica / Development of acrylic for optics education

Cruz, Renato Antonio 23 July 1997 (has links)
A grande carência de material experimental adequado para o ensino de Ótica no Brasil motivou o desenvolvimento de um processo de moldagem de lentes acrílicas, pelo Centro de Divulgação Científica e Cultural. Aproveitando tecnologia já existente na Universidade, o CDCC desenvolveu um processo de moldagem por compressão, relativamente barato, utilizando a placa acrílica comercial como material moldável. O presente trabalho consiste em caracterizar e avaliar esse processo de moldagem de lentes acrílicas. Para tanto, são levantadas as principais características físicas do material moldável. A qualidade ótica da lente moldada é analisada com base em alguns ensaios, tais como medidas de aberrações geométricas e de birrefringência induzida. Os resultados obtidos permitem a determinação dos parâmetros ideais do processo, e demonstram a possibilidade de obtenção de lentes acrílicas de excelente qualidade ótica para o ensino básico, a um custo acessível. / The necessity of experimental optical materials in Brasil for basic learning was the principal motivation for the development of the process to produce acrylic lens in the Centro de Divulgação Científico e Cultural (CDCC). All the process developed use low cost commercial acrylic and a moulding procedure to produce the lens. In this work we characterize the moulding process and the physical properties for the material. The optical quality for the moulding lens was determine measuring: aberrations and the induce birefringence. These results allow us to determine the optimal parameters for the process, and the possibility to production of high quality lens for the basic schools.
207

Influência da ceratometria e profundidade de câmara anterior obtidas por biometria óptica e por sistema Scheimpflug na predição do poder dióptrico de lente intraocular multifocal calculada para emetropia / Influence of keratometry and anterior chamber depth obtained by partial coherence interferometry and Scheimpflug system in the accuracy of intraocular multifocal lens diopter power calculated for emmetropia

Andrade Junior, Newton 26 September 2018 (has links)
Influência da ceratometria e profundidade de câmara anterior obtidas por interferometria de coerência parcial e por sistema Scheimpflug na acurácia do poder dióptrico de lente intraocular multifocal calculada para emetropia [Tese]. São Paulo: Faculdade de Medicina, Universidade de São Paulo; 2018. Objetivo: Verificar se a ceratometria média (K) e a profundidade de câmara anterior (ACD) obtidos por biometria óptica (IOLMaster® 500) e por sistema Scheimpflug (Pentacam® HR) influenciam na predição do cálculo do poder dióptrico de LIO multifocal programada para emetropia. Métodos: Estudo clínico retrospectivo de 198 olhos portadores de catarata senil, tratados com facoemulsificação e implante de LIO multifocal. A diferença entre o valor da ¨LIO ideal¨, previsto pela fórmula biométrica de HAIGIS para emetropia e o poder dióptrico da LIO implantada foi denominada \"desvio teórico da emetropia\" (TDE). Foram testados quatro cenários de cálculo de LIOs, combinando as medidas K e ACD obtidas com os dois dispositivos. Resultados: No trigésimo dia de pós-operatório, o equivalente esférico foi 0 D em 118 dos 198 olhos (60%). O IOL Master® 500 e Pentacam® HR diferiram em relação à média de K (delta 0,09 ± 0,02 D, p < 0,001) e ACD (delta 0,08 ± 0,01 mm; p < 0,001). De acordo com a análise de covariância, o TDE foi 0,17 ± 0,01 D para K e ACD mensurados com IOL Master® 500; 0,27 ± 0,01 D para K e ACD obtidos com Pentacam® HR; 0,15 ± 0,01 D para K gerados com IOL Master® e ACD medidos com Pentacam® HR e 0,28 ± 0,01 D para K mensurado com Pentacam® HR e ACD obtido com IOL Master®. O TDE foi menor quando K foi medido com IOL Master® 500, independente de qual dispositivo foi usado para medir ACD. Conclusões: As predições foram menos confiáveis usando o K gerado pelo Pentacam® HR (diferença média > 0,25D), a despeito de qual equipamento tenha gerado a ACD / Objective: To compare the postoperative refractive predictability of IOL Master® 500 and Pentacam® HR based on K and ACD values in eyes with indication for multifocal IOLs. Methods: Clinical retrospective study of 198 consecutive eyes treated with phacoemulsification and multifocal IOL implantation. The difference between the predicted value and the ideal IOL diopter was termed theoretical deviation from emmetropia (TDE). Using Haigis\' formula, the IOL closest to emmetropia was chosen. Four lens calculation scenarios were tested by combining K and ACD measurements obtained with the two devices. Results: On the 30th postoperative day, the spherical equivalent was 0 D in 118 of the 198 eyes (60%). IOL Master® and Pentacam® HR differed with regard to mean K (delta 0.09 ± 0.02 D; p < 0.001) and ACD (delta 0.08 ± 0.01 mm; p < 0.001). According to the analysis of covariance, TDE was 0.17 ± 0.01 D for K and ACD measured with IOL Master®, 0.27 ± 0.01 D for K and ACD measured with Pentacam HR; 0.15 ± 0.01 D for K measured with IOL Master® and ACD measured with Pentacam® HR, and 0.28 ± 0.01 D for K measured with Pentacam HR and ACD measured with IOL Master®. Mean K was the only statistically significant factor (p < 0.001). Thus, TDE was smaller when K was measured with IOL Master® 500, regardless of which device was used to measure ACD. Conclusion: Predictions were less reliable using the K generated by Pentacam® HR (average difference > 0,25D), regardless of which equipment has generated the ACD
208

Sonoptics : applications of light and sound in the context of biomedicine

Rolfsnes, Hans O. January 2011 (has links)
Ultrasound, applied in combination with microbubbles, has potential as a means to enhance the uptake of therapeutic agents, which could include drugs and nucleic acids, into biological cells. This process is commonly referred to as 'sonoporation', and the enhanced uptake can be caused through the incident ultrasonic pressure fi eld causing radial oscillations (cavitation) in the microbubbles, amongst other possibilities. However, the mechanisms responsible for any resultant increase in cell membrane permeability are not yet fully understood. This project focussed on achieving a more fundamental understanding of these salient processes by building on a platform of previous work within the group. One strand of the project involved a complete characterisation of the performance of a rotating mirror high speed camera (Cordin 550-62) that was previously used by our group [and others] to investigate microbubble cavitation phenomena and interactions with proximal cell membranes. Speci cally, I present herein an investigation into the image formation process with this type of camera, the essence of which stymied previous data interpretations. I demonstrate that an inherent asynchrony in the exposure of pixels within individual image frames leads to a temporal anomaly. This was achieved using low cost, flashing LED lights and resulted in the extraction of an algorithm to correct for the temporal anomaly. In a slightly diff erent context, the delivery of suitable ultrasonic fields is necessary to achieve a uniform treatment across a therapeutic target. This thesis also reports on a study on the design of ultrasonic lenses to alter the focal region of a focussed ultrasound transducer with the aim of producing focal regions that can enable sonoporation of tumours of varying sizes. We show that the use of lenses can be an inexpensive alternative to more complex systems such as phased array transducers. Design modelling and experimental testing of lens prototypes are presented along with preliminary results with tissue mimicking polyacrylamide gel phantoms. The target environment in which the process of sonoporation will be clinically useful (i.e. in the physiological circulation) can be simpli ed as a microfluidic system. One strategy for bubble mediated therapy involves the use of a pro-drug approach, that is, when two otherwise benign ingredients are loaded onto separate microbubble populations, but can become mixed at the anatomical target site by the action of focussed ultrasound whereupon a potent drug is produced. The required mixing can be achieved by the violent coalescence of nearby cavitating bubbles, their reaction product then being released and di ffused into the interiour of nearby cells through sonoporation. A study related to this field is presented here where laser induced thermocapillary flows are shown to cause mixing of the content of a drop in a microfluidic channel in a bid to understand the mixing process at a level that may assist future microbubble engineering strategy. To summarise then, the work presented in this thesis has consolidated earlier unpublished data sets achieved by the group, providing new and exacting experimental evidence and an accurate algorithm that will facilitate post-processing of that earlier data (Chapters 2-3). Moreover, group aspirations to translate earlier in-vitro work on sonoporation towards next phase medical-phantom exposures have been boosted through the provision of a new direction involving acoustic lensing, the experimental data from which was used to completely validate existing models for our own design scenarios (Chapter 4). Finally, previous unpublished observations on microbubble coalescence undertaken by the group suggested a means to implement pro-drug delivery with direct in-situ mixing. Such suggestions were explored within microfluidic contexts using lasers to control and visualise the mixing processes that might arise in such situations (Chapter 5). All of these new insights have served to consolidate the group's previous and as yet unpublished data, opening the way for dissemination with confidence in the integrity of that data, and have also extended group capability and expertise in the areas of MHz-rate high speed framing cameras, the fabrication of acoustic lenses, and with microfluidic mixing.
209

Effects Of Static Vs. Non-static In Vitro Techniques On Lipid Penetration Into Silicone Hydrogel Contact Lenses

January 2014 (has links)
Currently, most contact lenses are made with a silicone hydrogel (Si-Hy) blend that provides softness for comfort as well as high oxygen permeability. Silicone hydrogel lenses have both hydrophilic and hydrophobic areas, and the natural hydrophobicity of the material contributes to biofouling, which is the adsorption of proteins and lipids from the tear film of the eye. Published in vitro investigations into the quantity and spatial distribution of lipids deposited on contact lenses usually involve the use of artificial tear fluid (ATF) that is not changed or replenished over the course of the experiments. Yet, the natural tear film is constantly replenished by the meibomian and lacrimal glands. The intent of this study was to investigate the significance of replenishing the ATF over the study period on lipid absorption profiles and quantities. In part one, fluorescence confocal microscopy was used to observe the penetration profiles of lipids into nine different Si-Hy lenses. In part two, radiolabeling was used to quantify the amount of lipid absorbed by nine different Si-Hy lenses. Using a non-static exposure method was found to allow more absorption of cholesterol than the static method. The non-static method also provided more differentiation between lens types and brands in lipid absorption profiles and amounts than the static method. / acase@tulane.edu
210

Självsanerande ytbeläggning i nanostruktur : Är det möjligt att applicera på elektrooptiska sensorer och till vilken nytta?

Berg, Magnus January 2009 (has links)
<p>Då marina enheter numera deltar i internationella missioner, kommer den nya miljön som enheterna opererar i att påverka bland annat deras sensorer.</p><p>Den här studien avhandlar några av de nu framtagna självsanerande ytbeläggningarna och ger en presentation av hur de fungerar på några marina elektrooptiska sensorers yttersta linser.</p><p>Studien försöker ge svar på ytbeläggningarnas transmittans och hur effektivt de kan sanera bort oönskade saltlager tillsammans med andra nedsmutsande partiklar från sensorlinserna samt den militära nyttan av att använda självsanerande ytbeläggning.</p> / <p>This study deals with now developed self-cleaning coatings and gives a presentation of how they work on some electro-optical sensor lenses used in the navy. The study also examines the coatings transmittance and how efficient they can clean the sensor lenses from undesired salt layers and other soiling particles.</p><p>After the introduction the study presents basic facts of the chosen sensors, nanotechnology, surface wettability and also salts and salinity. Thereafter the study describes current nano-research on self-cleaning coatings and possible results there of, when the coatings are applied on the different sensors.</p><p>In the study I give my opinion of the military benefit of using self-cleaning coatings, which from a general point of view is that there mostly are positive effects using such a coating, in a technical perspective.</p><p>The study ends with conclusions that there are self-cleaning coatings based on TiO<sub>2</sub>-nanoparticles which can transmit within the visual spectra and also can clean undesired soiling particles. But can not confirm that these coatings have the desired effect on salt crystals, or transmit within wavelengths spectrum for IR-detectors and lasers.</p> / ChpT 08-10

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