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Macular Pigment and its Contribution to Visual Performance and Experience
Get PDFIntroduction The carotenoids lutein (L), zeaxanthin (Z) and meso-Z (MZ) accumulate at the macula where they are collectively referred to as macular pigment (MP). Scientific research continues to explore the function(s) of MP in the human retina, with two main hypotheses premised on its putative capacity to (1) protect the retina from (photo)-oxidative damage by means of its optical filtration and/or antioxidant properties, the so-called protective hypothesis and (2) influence the quality of visual performance by means of selective short wavelength light absorption prior to photoreceptor light capture, thereby attenuating the effects of chromatic aberration and light scatter, the so-called acuity, visibility and glare hypotheses. The current epidemic of age-related macular degeneration (AMD) has directed researchers to investigate the protective hypothesis of MP, while there has been a conspicuous lack of work designed to investigate the role of MP in visual performance Objectives This M.Sc. (by Research) thesis has four primary objectives: 1. To present and critically appraise the current literature germane to the contribution of MP, if any, to visual performance and experience 2. To assess whether MP optical density (MPOD) is associated with visual performance (Study One) 3. To investigate whether augmentation of MPOD enhances visual performance in normal subjects (Study Two) 4. To assess whether MPOD is associated with colour discrimination and matching (Study Three) Methods Study One: The Relationship between Macular Pigment and Visual Performance One hundred and forty-two young healthy subjects were recruited. MPOD was assessed by customised heterochromatic flicker photometry (cHFP). Visual performance was assessed by psychophysical tests including best corrected visual acuity (BCVA), mesopic and photopic contrast sensitivity, glare disability, photostress recovery time (PRT). Study Two: The Impact of Macular Pigment Augmentation on Visual Performance in Normal Subjects One hundred and twenty-one normal subjects were recruited. The active (A) group consumed 12mg of L and 1mg of Z daily. MPOD was assessed by cHFP. Visual performance was assessed as BCVA, mesopic and photopic contrast sensitivity, glare disability, photostress, and subjective visual function. Subjects were assessed at baseline; three; six; twelve months (V1, V2, V3 and V4, respectively). Study Three: Macular Pigment: its Associations with Colour Discrimination and Matching One hundred and two normal subjects were recruited. Colour vision was assessed with the Farnsworth-Munsell 100 Hue test (FM100), Moreland match on the Heidelberg Multi Colour (HMC) Anomaloscope, and a customised short wavelength automated perimetry (cSWAP) technique at the foveola and at 1°, 2°, 3°, 4° and 5° of retinal eccentricity. MPOD spatial profile was measured using cHFP. Results Study One: The Relationship between Macular Pigment and Visual Performance We report a positive and statistically significant relationship between BCVA and MPOD across its full spatial profile (r = 0.237 to 0.308, P 0.05). Study Two: The Impact of Macular Pigment Augmentation on Visual Performance in Normal Subjects Central MPOD increased significantly in the A group (P 0.05). This statistically significant increase in MPOD in the A group was not, in general, associated with a corresponding improvement in visual performance (P > 0.05, for all variables), with the exception of a statistically significant time/treatment effect in “daily tasks comparative analysis” (P = 0.03). At V4, we report statistically significant differences in mesopic contrast sensitivity at 20.7 cpd, mesopic contrast sensitivity at 1.5 cpd under high glare conditions, and light/dark adaptation comparative analysis between the lower and the upper MP tertile groups (P < 0.05). Study Three: Macular Pigment: its Associations with Colour Discrimination and Matching Total error scores (TES) and % partial error scores (%PES) on the FM100 were uncorrelated to MPOD. Moreland matches shown a significant long wavelength shift with MPOD at between 1° and 3° (at 1.75°, r = 0.489, P <0.001). Sensitivities on cSWAP using foveal targets were significantly inversely correlated with MPOD at both 1.75° (r = -0.461, P < 0.001) and 3° (r = -0.393, P < 0.001). Partial correlation analysis suggests that none of these findings can be attributed to age effects within the range 18 to 40 years. Conclusions Study One: The Relationship between Macular Pigment and Visual Performance Measures of central visual function, including BCVA and contrast sensitivity, were positively associated with MPOD. Glare disability and photostress recovery were unrelated to MPOD Study Two: The Impact of Macular Pigment Augmentation on Visual Performance in Normal Subjects We report that a significant increase in central MP following L supplementation does not, in general, impact on visual performance in young normal subjects, and our pre-specified hypothesis that MP augmentation would result in improved visual performance and/or comfort by 12 months, in those randomised to the A arm, remains unproven. However, subjects with high MP following L supplementation demonstrate visual benefits with respect to glare disability and mesopic contrast sensitivity. Further study into MP and its relationship with visual performance is warranted to enhance our understanding of this pigment‟s role. However, in order to investigate the impact of MP augmentation on visual performance, the findings of our study suggest that we should direct our attention to, a) subjects with low baseline central MP levels, b) subjects with suboptimal visual performance and c) subjects with symptoms of glare disability Study Three: Macular Pigment: its Associations with Colour Discrimination and Matching Our findings suggest that dietary supplementation to increase MPOD is unlikely to adversely affect hue discrimination. The association of MPOD with cSWAP may be a temporally limited effect to which the visual system normally adapts. We suggest that cSWAP may provide a clinical tool for assessing short-wavelength foveal sensitivit
Mixed state effects in waveguide electro-absorbers based on quantum dots
Get PDFMulti-pulse heterodyne pump-probe measurements are used to investigate the reverse bias dynamics of InAs/GaAs quantum dots in a waveguide structure. Using a femtosecond pulse, we simultaneously populate high energy ground states and low energy excited states and measure the resulting gain and phase dynamics over the bandwidth of the pulse. We identify a similar to 5 ps timescale in the phase dynamics which can be associated with low energy ground states outside the pulse bandwidth and may provide an explanation for the deterioration of monolithic mode locked laser performance at high reverse voltages. (C) 2011 American Institute of Physics. [doi:10.1063/1.3653287
Ultrafast Gain and Refractive Index Dynamics in AlInAs/AlGaAs Quantum Dot Based Semiconductor Optical Amplifiers Operating at 800 nm
Get PDFThe ultrafast gain and refractive index dynamics in AlInAs/AlGaAs quantum dot (QD) based semiconductor optical amplifiers is reported. Measurements in the forward bias regime indicate a complete gain recovery timescale of similar to 5 ps, while the phase dynamics occur over a much longer timescale. At increased pump powers, the impact of nonresonant carriers created by two-photon absorption is visible as an increased injection in both gain and phase dynamics. Reverse-biased measurements reveal a similar behavior to previous measurements on InAs QD devices
Generalized Stirling numbers, exponential Riordan arrays and orthogonal polynomials
Get PDFWe define a generalization of the Stirling numbers of the second kind, which depends on two parameters.
The matrices of integers that result are exponential Riordan arrays. We explore links to orthogonal polynomials by studying the production matrices of these Riordan arrays. Generalized Bell numbers are also defined, again depending on two parameters, and we determine the Hankel transform of these numbers
On the Central Coefficients of Bell Matrices
Get PDFWe use the Lagrange inversion theorem to characterize the central coefficients of matrices in the Bell subgroup of the Riordan group of matrices. We give examples of how by using different means of calculating these coefficients we can deduce the generating functions of interesting sequences
Airtightness of Dwellings in Ireland: Design, Workmanship and Control
Get PDFThe residential sector accounts for 25% of Ireland'
s total energy consumption, of which
60% is used for space heating. As thermal insulatio
n standards increase, building air
tightness is playing an increasing role in both bui
lding energy performance and indoor
environmental quality. This paper reports on the re
sults of air tightness testing carried
out on a small number of dwellings. The paper highl
ights the paucity of dwelling
airtightness data for Ireland. The results are comp
ared to past studies and compliance
with the existing standards. While the number of ho
uses tested is small they are broadly
representative of urban dwellings in Ireland. The s
tudy indicates a misconception that
newer buildings are more airtight than older buildi
ngs. The paper concludes that good
design, attention to detail and rigorous controls t
hroughout construction is vital to
delivering air-tight dwellings
Cultural Tourism Experiences : A Development Framework
Get PDFUnique and memorable experiences are crucial for the long-term sustained differentiation of the tourism sector (ITIC, 2006; Fáilte Ireland, 2007). Much attention has been centred upon indigenous cultural tourism as a panacea for revitalising and enhancing the wider services sector of the national economy. Indeed, evidence suggests that the experience value of tourism products is the overriding factor influencing customers‘ motivation to visit attractions (Brunner Sperdin and Peters, 2009). Prior research indicates a lack of theory relating to the nature of experiences and the experience development process (Fitzsimmons and Fitzsimmons 2000; Morgan, et al., 2009). This study aims to close this extant knowledge gap by enhancing our understanding of the nature of cultural tourism experiences and the process by which they can be developed. To achieve this aim, a critical review of literature in the product, service, experience and tourism arenas generated a conceptual framework for the development of cultural tourism experiences. Through the adoption of a qualitative case study of a best practice cultural tourism organisation, the study was able to explore both the nature of cultural tourism experiences and the manner by which they are developed in practice, leading to a refined framework. The major outcome of the study is an experience framework that defines, identifies and articulates the elements of cultural tourism experiences and offers a pragmatic “how to” framework that provides understanding and guidance of the stages and activities of the experience development process. Notably, the study posits learning as the core activity of cultural tourism and emotional outcomes as the core value delivered. Practitioners must create learning opportunities which reinforce personal values and facilitate a range of emotional outcomes based on an understanding of visitors‘ deeper and emotional needs. This study also highlights the equal importance of three types of interaction that stimulate experiences: experience provider to tourist, tourist to tourist and tourist to context. Hence, cultural tourism organisations need to design and offer activities which encourage visitor interaction and active participation to personally create experiences. From a theoretical standpoint, this research has advanced tourism experience literature by delineating the elements that comprise a cultural tourism experience namely, contextual, interactional and emotional outcomes and enhances understanding of the experience development process. The framework clarifies the true nature of cultural tourism experiences and makes a significant contribution to cultural tourism practice as it offers practitioners a pragmatic and implementable process framework to develop new tourism offerings which are capable of generating unique and memorable experiences. From a theoretical standpoint, this research has shown that cultural tourism experiences are no longer ambiguous and abstract
Policy Based Management for Security in Cloud Computing
Get PDFCloud computing is one of the biggest trends in information technology, with individuals, companies and even governments moving towards their use to save costs and increase flexibility. Cloud infrastructures are typically based on virtualised environments, to allow physical infrastructure to be shared by multiple end users. These infrastructures can be very large and complex, with many end users, making their configuration difficult, error-prone and time-consuming. At the same time, the fact that diverse end users share the same physical infrastructure raises security concerns, and can lead to a significant impact from misconfiguration or being slow to react to attacks. In this paper, we focus on the use of Policy Based Management techniques to manage cloud infrastructure, identifying the requirements, surveying the state-of-the-art, identifying the challenges and proposing potential solutions
A further comparison of different TCP/IP and DTN protocols over the D-STAR Digital Data mode
Get PDFThis work examines the performance of the Digital Smart Technologies for Amateur Radio - Digital Data mode with various IP and non-IP based protocols. A throughput comparison was performed between TCP/IP and two DTN convergence Layers. The experimental results show that the DTN NORM Convergence Layer exhibits better performance than TCP/IP and TCP based convergence layers, and, furthermore appears to be more suited for use on difficult radio links
