A prevalência mundial da hanseníase vem demonstrando redução no número de casos, porém, no Brasil e em alguns países, ela ainda representa um grave problema de saúde pública, podendo levar a incapacidades funcionais graves como a cegueira. O objetivo do estudo foi avaliar a relação entre as alterações do piscar e a superfície ocular em hansenianos. Todos os pacientes estudados foram submetidos à mesma anamnese e avaliação oftalmológica: acuidade visual, ectoscopia, biomicroscopia, avaliação da superfície ocular, teste da graduação da força muscular do orbicular, sensibilidade corneana, distância da margem reflexa, medida da pressão intraocular e mensuração do piscar espontâneo palpebral por meio de um método de imagem por vídeo. Dos 56 pacientes examinados, 69,6% eram do sexo masculino, com média de idade de 55,96 ± 16,63 dp, 46,4% se declararam negros e 28,55% pardos, 71,4% apresentavam a forma multibacilar e 73,2% estavam fora do registro ativo da doença. Desses 56 pacientes, 43 apresentaram significativa simetria interocular no acometimento do nervo facial e do trigêmeo (p=0,11), o que foi corroborado pela alta correlação entre as medidas da amplitude do piscar entre os olhos (r=0,90). Apenas 12,5% apresentaram tempo de ruptura do filme lacrimal menor que 10 segundos e em um paciente este foi menor que 5. Evidenciou-se sofrimento da superfície ocular em cerca de 14% dos olhos. As alterações de sensibilidade foram mais prevalentes, pois 51,8% apresentaram algum grau de diminuição. A média geral da taxa do piscar foi de 17,0 ± 2,6 blink/min. De acordo com o exame de Lissamina, observou-se taxa média de 16,0 ± 2,8 (média±dp) para os pacientes com resultado negativo e 23,2 ± 6,8 para os com resultado positivo (t=0,961; p=0,3407); e em relação à sensibilidade corneana, as taxas médias foram 14,6 ± 3,8 e 19,2 ± 3,6 para os pacientes com resposta imediata e alterada, respectivamente (t=0,875; p=0,3857). De acordo com o tônus muscular, a média das taxas do piscar para os pacientes normais e alterados não foi significativa (t=0,539; p=0,592). Apesar do número e da amplitude dos movimentos serem diferentes, a main sequence demonstrou comportamento linear em todos os casos, sendo a média geral 20,25 ± 6,9 (0,94 ep). As médias da taxa, amplitude e efetividade do piscar em pacientes com função do músculo orbicular do olho normal e naqueles com função alterada não demonstraram diferença estatística, já a média da velocidade máxima do piscar com função normal foi de 115,5 ± 47,2 mm/s, enquanto que naqueles com lagoftalmo foi 67,7 ± 27 (t=2,08; p=0,04) e a média do deslocamento horizontal de 2,1 ± 0,7 mm e 0,9 ± 0,8 mm, respectivamente (t=1,99; p=0,05). Embora os pacientes hansenianos não apresentem taxa de piscar diferente do normal, demonstram tendência à diminuição da velocidade e do deslocamento horizontal quando apresentam alterações da função do músculo orbicular. A maioria dos pacientes apresentou alteração de sensibilidade corneana, porém, sem sinais de sofrimento da superfície ocular, principalmente com a cinemática palpebral preservada. / Global prevalence of leprosy has demonstrated a reduction in the number of cases, however, in Brazil and some countries, it still represents a serious public health problem, often leading to severe functional disabilities such as blindness for example. This study aimed to evaluate the relationship between blink and ocular surface in patients with leprosy. Leprosy patients underwent the same history and ophthalmologic evaluation: visual acuity, ectoscopy, slit lamp examination, evaluation of ocular surface, test the eyelid function and the degree of orbicularis function, corneal sensitivity, margin reflex distance, measured intraocular pressure and measuring eyelid spontaneous blinking through an image video system. 69.6% were male, with a mean age of 55.96 ± 16.63 SD. 46.4% declared themselves as black and brown were 28.55%, 71.4% were multibacillary and 73.2% were out of active disease registry. Between the 56 patients examined, 43 of those had significant interocular symmetry of the involvement of the facial and the trigeminal nerves (p=0.11), which was confirmed by the high correlation between the measurements of amplitude flashing of the eyes (r=0,90). Only 12.5% had TFRL was under 10 seconds and in one patient it was under 5 seconds. It was evidenced suffering from ocular surface in about 14% of the eyes. Sensitivity changes were more prevalent, 51.8% had some degree of impairment. Overall average blink rate was 17.0 ± 2.6 blinks/min. In the lissamine test, we observed an average rate of 16.0 ± 2.8 for patients with negative and 23.2 ± 6.8 for a positive result (t=0.961, p=0.3407). The mean values were 14.6 ± 3.8 (mean ± SD) and 19.2 ± 3.6 for for patients with immediate corneal sensitivity response and altered response, respectively (t=0.875, p=0.3857). According muscle tone, mean blink rates for normals and for injured patients, were not different (t=0.539, p=0.592). Although the number and range of motion are different, the main sequence had a linear behavior in all cases, with an overall mean 20.25 ± 6.9 (p 0.94). The mean blink rate, amplitude and effectiveness in patients with normal orbicularis function and those with altered function, showed no statistical diference, while the mean of maximum velocity blink was, with normal function, 115.5 ± 47.2 mm/s, while those with lagophthalmos was 27 ± 67.7 (t=2.08, p=0.04) and the mean horizontal displacement was 2.1 ± 0.7 mm and 0.9 ±0.8 mm respectively (t=1.99, p=0.05). Although leprosy patients do not have a different flash rate of the normal population, blinking characteristics show a tendency to decrease in speed and horizontal scrolling when they show important changes in orbicularis function. The vast majority of patients had corneal sensitivity changes, but without signs of ocular surface suffering, especially those with eyelid kinematics preserved.

Fluorescence intermittency is a random switching between emitting (on) and non-emitting (off) periods found for many single chromophores such as semiconductor quantum dots and organic molecules. The statistics of the duration of on- and off-periods are commonly determined by thresholding the emission time trace of a single chromophore and appear to be power law distributed. Here we test with the help of simulations if the experimentally determined power law distributions can actually reflect the underlying statistics. We find that with the experimentally limited time resolution real power law statistics with exponents αon/off ≳ 1.6, especially if αon ≠ αoff would not be observed as such in the experimental data after binning and thresholding. Instead, a power law appearance could simply be obtained from the continuous distribution of intermediate intensity levels. This challenges much of the obtained data and the models describing the so-called power law blinking.

Eye-tracking is the process of determining the point where the viewer is looking at. Therefore, an eye tracker is a device that measures eye positions and eye movements. Over the recent few years, eye trackers are being used in research in the area of medical technology, visual system, rehabilitation, and human-computer interaction. This study explores the application of eye-tracking in watching and rendering images on a computer screen. In this research, Eye-tracker 5 developed by Tobii is used which is a popular instrument among other eye trackers. Tobii Eye Tracker 5 includes a software development kit (SDK) enabling the creation of new research projects based on eye-tracking and head movement. This work measured eye-tracking streaming data on the digital images, and post-process the gaze data to observe the gaze pattern of the human eye. This thesis investigated the impact of blinking using subtle gaze direction (SGD) approach, which states that flickering on the computer screen in peripheral vision instead of foveal vision attracts human attention and as the viewer’s foveal vision attracted to that blinking point, flickering was stopped and, subsequently, performed flickering to the next point of interest while the viewer is watching the previous point of interest. The work successfully modeled flickering on the desired locations of an image. Furthermore, rendering to different images is also demonstrated in this work using entirely through eye movement. It is envisaged that eye-gazing-based control technology would have tremendous applications in almost all areas of future technology, particularly in assistive technology.

No description available.

This thesis explores how the carrier dynamics within semiconductor nanocrystals can be directly engineered through specific core-shell design. Emphasis is placed on how material characteristics, such as strain or alloying at a core-shell interface, can influence the exciton energies and the recombination dynamics within semiconductor nanocrystals. This study synthesises type-II heterojunction ZnTe/ZnSe core-shell nanocrystals via a diethyl zinc-free synthesis method, producing small size distributions and quantum yields as high as 12%. It was found that the 7% lattice mismatch between the core and shell materials places limitations on the range of structures in which coherent growth is achieved. By developing compositional and strained atomistic core-shell models a variety of physical and optical properties could be simulated and has led to a clear picture of the core-shell architecture to be built. This characterisation provides evidence that the low bulk modulus ZnTe cores are compressed by the higher bulk modulus smaller lattice constant ZnSe shells. Further studies show how strain is manifested in structures with 'sharp' core-shell interfaces and how intentional alloying the interface can influence the growth and exciton energies. A (2-6)-band effective mass model was able to distinguish between the as-grown 'sharp' and 'alloyed' interfaces which indicated that strain accentuates the redshift of the excitonic state whilst reduced strain within an alloyed interface sees a reduced redshift. Single nanocrystal spectroscopy investigations of brightly emitting single graded alloyed nanocrystals and of a size series of commercially available CdSe/ZnS nanocrystals showed almost no fluorescence intermittency (nearly 'non-blinking'). These investigations also identified trion recombination as the main mechanism within the blinking 'off' state. Ultimately this thesis adds to the growing understanding of how specific core-shell architectures manipulate the electronic structure and develops techniques to identify specific material characteristics and how these characteristics influence the physical and optical properties within semiconductor nanocrystals.

This thesis addresses the observed fluorescence intermittency of single semiconductor nanocrystals, so called Quantum Dots (QDs), which is also referred to as blinking. Despite continuous excitation their fluorescence is randomly interrupted by dark periods that can last over several minutes. Especially the extraction of power law dwell time statistics in bright and dark states indicates very complex underlying processes that are not fully understood to date. Here two approaches are followed to reveal the nature of the blinking mechanism. One addresses the common threshold method for extraction of power law dwell times. Its performance is tested with simulations to a broad range of experimentally determined parameters. Strong deviations are found between input and extracted statistics dependent on input parameters themselves. A comparison with experimental data does not support the assignment of power law statistics for the bright state and indicates the existence of distinct blinking mechanisms. The second approach directly aims at the nature of the dark state, which is mostly attributed to charges in the QD or trap states in its vicinity. A method is developed to detect charging processes on single QDs with their fluorescence. Electrochemistry is combined with confocal microscopy also allowing evaluations of excited state lifetimes and emission spectra. Reduction and oxidation of the QD bands are successfully observed as a quenching of QD fluorescence. Single QD observations identify two independent blinking mechanisms, that are assigned to positive and negative charging. Positive charging is not only observed after hole injection but also the extraction of excited electrons. Three additional quenching mechanisms are identified, two of which are assigned to trap relaxation. Differences between two substrate electrodes demonstrate the importance of the substrate material.

The experimental studies presented in this thesis deal with the photoluminescence intermittency of semiconductor quantum dots in different dielectric environments. Detailed analysis of intermittency statistics from single capped CdSe/ZnS, uncapped CdSe and water dispersed CdSe/ZnS QDs in different matrices provide experimental evidence for the model of photoionization with a charge ejected into the surrounding matrix as the source of PL intermittency phenomenon. The distribution of the dark state lifetimes can be described by a power law over a wide range while that of bright state can be described by a power law at shorter times followed by an exponential decay. The lifetimes of the bright and dark states are influenced by the dielectric properties of the surrounding environment. Our experimental results show that the lifetime of the dark state increases with the dielectric constant of the matrix. This is very clear from the linear correlation between αoff and f (ε). We propose a self-trapping model to explain the increase of dark state lifetimes with the dielectric constant of the matrix. A charge will be more stabilized in a medium with high dielectric constant. An energetically more favourable state for an electron in a high dielectric medium decreases the return probability which eventually increases the duration of the off-time. Moreover, the self-trapping model establishes a general model for distribution of states in a matrix. We like to mention, that in the case of bright states, a qualitative observation is the cross over of the on-time power law behavior to an exponential one. The power law part of the decay is nearly matrix independent while the exponential decay, which limits the maximum on-time, strongly depends on dielectric properties of the environment. The exponential part of the on-time probability decays much faster in a high dielectric medium and there exists a linear relation between the time constant of the exponential decay and f (ε). Theoretical background has been provided for the observed results using the recently published DCET model which correlates PL intermittency of QDs with properties of the environment. This supports our previous conjecture of a general model for matrix controlled blinking process. The disagreement between experimentally observed dependence of αoff and f (ε) for different matrices with that of the static tunnelling model proposed by Verberk is due to the fact that the tunneling model considers only an electron transfer between a QD and spatially distributed trap states in vacuum. These states are already stabilized states. It does not assume any medium in between. Therefore, matrix dependent blinking kinetics can not be explained quantitatively by tunneling model even though tunneling between a QD and spatially distributed trap states gives a power law distribution for the blinking kinetics. DCET is a more general (dynamic) model. The bright and dark state parabolas contain QD, charge and the matrix. Therefore, this model could in principle explain matrix dependent blinking kinetics in a better way, for example, the energy difference between the minima of the bright and dark state parabolas (-ΔG0) is defined by the stabilization energy of the system provided by the matrix. However, due to lack of the relevant intrinsic parameters we did not compare this relationship and dependence qualitatively. / Betrachtet man die Fluoreszenz einzelner Farbstoffmoleküle oder Halbleiternanokristalle bei kontinuierlicher Anregung, so stellt man fest, dass die im Zeitverlauf beobachtete Intensität einer stochastischen Variation unterliegt, d. h. dass das Chromophor zwischen emittierenden und nicht emittierenden Zuständen, auch Hell- und Dunkelzuständen genannt, hin- und herschaltet. Dieses als Blinken bekannte Phänomen ist physikalisch wie auch technologisch herausfordernd, lässt es doch einerseits die Realisierbarkeit einer Reihe von quantenoptischen Anwendungen, so z. B. auf dem Gebiet der Quantenkryptographie, dem Quantum Computing oder der optischen Schaltungstechnik auf Basis einzelner Quantenobjekte, in naher Zukunft möglich erscheinen. Andererseits setzt es gewissen Anwendungen, die auf die permanente Sichtbarkeit des Chromophors aufbauen, Grenzen, so zum Beispiel der Verwendung als Lumineszenzmarker in der medizinischen Diagnostik. Weiterhin ist festzustellen, dass das Blinken kritisch von den äußeren Bedingungen und von den Umgebungsparametern abhängt. Aus diesen und anderen Gründen ist ein fundamentales Verständnis der physikalischen Ursachen und der Wechselwirkungsprozesse unerlässlich. Die Forschung dazu steckt noch in den Kinderschuhen. Basierend auf umfangreiche Messungen der Fluoreszenzzeitreihen einzelner Nanokristalle aus CdSe und CdSe/ZnS in verschiedenen Umgebungen, zeigt diese Dissertation exemplarisch den Einfluss der Dielektrizitätsparameter auf das Blinken. Zur Erklärung des Sachverhalts wird ein so genanntes Self-Trapping-Modell zu Rate gezogen. Demnach kommt es zu einer Ionisation des Quantenobjekts und anschließender Ladungstrennung, woraufhin die abgetrennte Ladung für eine gewisse Zeit in der Umgebung lokalisiert bleibt. Die Dauer der Lokalisierung und damit der emittierenden und nicht emittierenden Perioden hängt von der dielektrischen Funktion des umgebenden Materials ab. Dies ist als direkter Nachweis für den photoinduzierten Ladungstransfer als Ursache des Fluoreszenzblinkens zu deuten. Die Arbeit demonstriert, dass die experimentellen Zeitreihen die charakteristischen Merkmale eines diffusionsgesteuerten Ladungstransferprozesses besitzen und nimmt dabei den gegenwärtigen wissenschaftlichen Diskurs über geeignete theoretische Modelle des Fluoreszenzblinkens auf.

Dissertation (Ph.D.)--University of South Florida, 2007. / Includes vita. Includes bibliographical references (leaves 109-141). Also available online.

This thesis addresses the observed fluorescence intermittency of single semiconductor nanocrystals, so called Quantum Dots (QDs), which is also referred to as blinking. Despite continuous excitation their fluorescence is randomly interrupted by dark periods that can last over several minutes. Especially the extraction of power law dwell time statistics in bright and dark states indicates very complex underlying processes that are not fully understood to date. Here two approaches are followed to reveal the nature of the blinking mechanism. One addresses the common threshold method for extraction of power law dwell times. Its performance is tested with simulations to a broad range of experimentally determined parameters. Strong deviations are found between input and extracted statistics dependent on input parameters themselves. A comparison with experimental data does not support the assignment of power law statistics for the bright state and indicates the existence of distinct blinking mechanisms. The second approach directly aims at the nature of the dark state, which is mostly attributed to charges in the QD or trap states in its vicinity. A method is developed to detect charging processes on single QDs with their fluorescence. Electrochemistry is combined with confocal microscopy also allowing evaluations of excited state lifetimes and emission spectra. Reduction and oxidation of the QD bands are successfully observed as a quenching of QD fluorescence. Single QD observations identify two independent blinking mechanisms, that are assigned to positive and negative charging. Positive charging is not only observed after hole injection but also the extraction of excited electrons. Three additional quenching mechanisms are identified, two of which are assigned to trap relaxation. Differences between two substrate electrodes demonstrate the importance of the substrate material.

The experimental studies presented in this thesis deal with the photoluminescence intermittency of semiconductor quantum dots in different dielectric environments. Detailed analysis of intermittency statistics from single capped CdSe/ZnS, uncapped CdSe and water dispersed CdSe/ZnS QDs in different matrices provide experimental evidence for the model of photoionization with a charge ejected into the surrounding matrix as the source of PL intermittency phenomenon. The distribution of the dark state lifetimes can be described by a power law over a wide range while that of bright state can be described by a power law at shorter times followed by an exponential decay. The lifetimes of the bright and dark states are influenced by the dielectric properties of the surrounding environment. Our experimental results show that the lifetime of the dark state increases with the dielectric constant of the matrix. This is very clear from the linear correlation between αoff and f (ε). We propose a self-trapping model to explain the increase of dark state lifetimes with the dielectric constant of the matrix. A charge will be more stabilized in a medium with high dielectric constant. An energetically more favourable state for an electron in a high dielectric medium decreases the return probability which eventually increases the duration of the off-time. Moreover, the self-trapping model establishes a general model for distribution of states in a matrix. We like to mention, that in the case of bright states, a qualitative observation is the cross over of the on-time power law behavior to an exponential one. The power law part of the decay is nearly matrix independent while the exponential decay, which limits the maximum on-time, strongly depends on dielectric properties of the environment. The exponential part of the on-time probability decays much faster in a high dielectric medium and there exists a linear relation between the time constant of the exponential decay and f (ε). Theoretical background has been provided for the observed results using the recently published DCET model which correlates PL intermittency of QDs with properties of the environment. This supports our previous conjecture of a general model for matrix controlled blinking process. The disagreement between experimentally observed dependence of αoff and f (ε) for different matrices with that of the static tunnelling model proposed by Verberk is due to the fact that the tunneling model considers only an electron transfer between a QD and spatially distributed trap states in vacuum. These states are already stabilized states. It does not assume any medium in between. Therefore, matrix dependent blinking kinetics can not be explained quantitatively by tunneling model even though tunneling between a QD and spatially distributed trap states gives a power law distribution for the blinking kinetics. DCET is a more general (dynamic) model. The bright and dark state parabolas contain QD, charge and the matrix. Therefore, this model could in principle explain matrix dependent blinking kinetics in a better way, for example, the energy difference between the minima of the bright and dark state parabolas (-ΔG0) is defined by the stabilization energy of the system provided by the matrix. However, due to lack of the relevant intrinsic parameters we did not compare this relationship and dependence qualitatively. / Betrachtet man die Fluoreszenz einzelner Farbstoffmoleküle oder Halbleiternanokristalle bei kontinuierlicher Anregung, so stellt man fest, dass die im Zeitverlauf beobachtete Intensität einer stochastischen Variation unterliegt, d. h. dass das Chromophor zwischen emittierenden und nicht emittierenden Zuständen, auch Hell- und Dunkelzuständen genannt, hin- und herschaltet. Dieses als Blinken bekannte Phänomen ist physikalisch wie auch technologisch herausfordernd, lässt es doch einerseits die Realisierbarkeit einer Reihe von quantenoptischen Anwendungen, so z. B. auf dem Gebiet der Quantenkryptographie, dem Quantum Computing oder der optischen Schaltungstechnik auf Basis einzelner Quantenobjekte, in naher Zukunft möglich erscheinen. Andererseits setzt es gewissen Anwendungen, die auf die permanente Sichtbarkeit des Chromophors aufbauen, Grenzen, so zum Beispiel der Verwendung als Lumineszenzmarker in der medizinischen Diagnostik. Weiterhin ist festzustellen, dass das Blinken kritisch von den äußeren Bedingungen und von den Umgebungsparametern abhängt. Aus diesen und anderen Gründen ist ein fundamentales Verständnis der physikalischen Ursachen und der Wechselwirkungsprozesse unerlässlich. Die Forschung dazu steckt noch in den Kinderschuhen. Basierend auf umfangreiche Messungen der Fluoreszenzzeitreihen einzelner Nanokristalle aus CdSe und CdSe/ZnS in verschiedenen Umgebungen, zeigt diese Dissertation exemplarisch den Einfluss der Dielektrizitätsparameter auf das Blinken. Zur Erklärung des Sachverhalts wird ein so genanntes Self-Trapping-Modell zu Rate gezogen. Demnach kommt es zu einer Ionisation des Quantenobjekts und anschließender Ladungstrennung, woraufhin die abgetrennte Ladung für eine gewisse Zeit in der Umgebung lokalisiert bleibt. Die Dauer der Lokalisierung und damit der emittierenden und nicht emittierenden Perioden hängt von der dielektrischen Funktion des umgebenden Materials ab. Dies ist als direkter Nachweis für den photoinduzierten Ladungstransfer als Ursache des Fluoreszenzblinkens zu deuten. Die Arbeit demonstriert, dass die experimentellen Zeitreihen die charakteristischen Merkmale eines diffusionsgesteuerten Ladungstransferprozesses besitzen und nimmt dabei den gegenwärtigen wissenschaftlichen Diskurs über geeignete theoretische Modelle des Fluoreszenzblinkens auf.