Luminescent solar concentrators for fibre optic daylighting

University of Technology, Sydney. Dept. of Applied Physics.Daylight is an abundant source of energy that, if used effectively for lighting in buildings, can improve quality of life and decrease the demand for electric lighting and air-conditioning, reducing energy consumption and costs. Various daylighting systems are available for daylighting the perimeter zones of buildings. However, it is more difficult to transport daylight to remote rooms. The few systems available for remote room daylighting are expensive or disruptive to the building design and rely heavily on direct sunlight. Luminescent Solar Concentrators (LSC’s) contain fluorescent dyes that absorb both direct and diffuse sunlight without tracking the sun, causing fluorescent emission in a specific wavelength range. LSC’s can potentially be used for daylighting, but the only previously demonstrated system is rather bulky and architecturally intrusive, and its output is yellow-green and difficult to control. A stack of three coloured LSC’s is proposed in this thesis, which produces a good white output of over 1,000 lumens under solar illumination of 100,000 lux. This output is transported to a remote room in narrow flexible polymer light guides. A theoretical model of the three-colour LSC stack was developed, which uses the absorption and emission spectra of the dyes to predict the LSC’s output spectrum and lumens. Studies with this model revealed the importance of highly accurate absorption tails data for good prediction of the stack performance. The model was used to determine the optimum size and dye concentration for each LSC. A simple experimental method was devised for characterising the optical performance of a fixed size LSC. Half of the emitted light is trapped at the end of the light guides, so a ‘light extractor’ is required to enable this light to escape. Ray tracing simulations were carried out for various light extractor designs, from which the optimal light extractor size, shape and configuration were determined for maximum optical gain. With a good light extractor design, a gain of 1.7-1.8 should be achievable, but with the current prototypes, the gain is limited to 1.2-1.3, limiting the output to around 1,100 lumens. The violet collector sheet in the LSC stack was also found to be problematic, so an alternative blue light source is proposed. Hence there is room for improvement in future prototypes

Evolution of plasmonic response in growing silver thin films with pre-percolation non-local conduction and emittance drop

The optical response of growing silver thin films undergoes a transition dominated by three distinct plasmonic modes, two localized and one delocalized. Their admix as a function of added mass is analysed. The onset of the delocalized or Drude mode occurs before the sharp electrical percolation transition so optically the full insulator-metal transition is broadened. A scaling explanation supported by images shows Ag islands only have to link up over 200-300 nm to yield partial delocalization. The localized modes are (i) from silver nano-islands and (ii) a transitional anomalous mode, peaking near the dc critical percolation point, from islands surrounded by network. Growing silver within a multilayer oxide stack is compared with that on glass. The transition in thermal emittance matches that in the delocalized mode. Its broadening enables practical tuning of intermediate emittance by varying mass. © 2011 IOP Publishing Ltd

Metal nanoparticle plasmonics inside reflecting metal films

Oxide coated metal nanoparticles buried within a thin metal layer support a surface plasmon resonance. A local dip occurs in spectral reflectance along with a switching off of the film's plasmonic response. Models are introduced in which these resonances are tunable by altering the ratio of oxide thickness to core particle radius. The optical response of two experimental examples is presented and modeled using effective medium theory. Beyond the resonance zone the doped layer switches back to the plasmonic response of a nanoporous version of the host metal whose effective plasma frequency arises only from the percolating component. © 2010 American Institute of Physics

Metal-in-metal localized surface plasmon resonance

Anomalous strong resonances in silver and gold nanoporous thin films which conduct are found to arise from isolated metal nano-islands separated from the surrounding percolating metal network by a thin loop of insulator. This observed resonant optical response is modelled. The observed peak position is in agreement with the observed average dimensions of the silver core and insulator shell. As the insulating ring thickness shrinks, the resonance moves to longer wavelengths and strengthens. This structure is the Babinet's principle counterpart of dielectric core-metal shell nanoparticles embedded in dielectric. Like for the latter, tuning of resonant absorption is possible, but here the matrix reflects rather than transmits, and tuning to longer wavelengths is more practical. A new class of metal mirror occurring as a single thin layer is identified using the same resonances in dense metal mirrors. Narrow band deep localized dips in reflectance result. © 2010 IOP Publishing Ltd

Absorption tails and extinction in luminescent solar concentrators

Non-ultraviolet (UV) photoexposure of luminescent solar concentrators (LSCs) can produce photoproducts that cause additional extinction at wavelengths somewhat longer than the main dye absorption peak. This photo-induced 'tails' extinction is deleterious to luminous output in collectors of useful lengths. An experimental method that enables the subdivision of tails extinction in an LSC into absorbed and scattered components is described. The relevant theory is outlined, and experimental results are presented for a polymethyl methacrylate (PMMA) LSC containing Lumogen F083 dye. For this sample, tails absorption increased significantly with outdoor exposure, while tails scattering remained constant. Further measurements indicate that LSC luminous output is around five times more sensitive to tails absorption than to fluorescence quenching. This work also indicates that merely checking for dye quenching, as is often done, can be a misleading indicator of long-term LSC output. © 2010 Elsevier B.V. All rights reserved

Extraction of trapped light from luminescent solar concentration

In modern light sources such as Luminescent Solar Concentrators (LSC's) and Light Emitting Diodes (LED's), light is emitted within a light-guiding structure of high refractive index. Some of this light is trapped and will not be able to escape. Similar problems are observed when collecting fluorescent radiation in waveguides (1) and scintillation detectors (2). For lighting applications, this trapped light should be ablet o escape the light-guiding structure. In LED's this is commonly achieved witha special profile in the active zone. However, inLSC's the small light-emitting zone is remote from the large light collector so a different approach must betaken. This paper will focus on the extraction of emitted light from rectangular LSc's and propose a way of extracting a large fraction of the trapped light

Perylene dye photodegradation due to ketones and singlet oxygen

The photodegradation rate of a perylene dye (Lumogen F Yellow 083) in methyl isobutyrate was found to increase with ketone concentration for two different ketones. Of the ketones employed, methyl pyruvate, an impurity in methyl methacrylate, was found to be particularly deleterious to dye stability. In agreement with other published studies, the addition of the anti-oxidant DABCO (1,4-diazabicyclo-[2.2.2] octane) to the dye matrix was found to increase dye stability; however when ketones were present, DABCO lead to increased photodegradation. These results highlight the importance of removing ketone impurities from dye matrices during production of Luminescent Solar Concentrators (LSCs). © 2009 Elsevier Ltd. All rights reserved

Does self-monitoring reduce blood pressure? Meta-analysis with meta-regression of randomized controlled trials

Introduction. Self-monitoring of blood pressure (BP) is an increasingly common part of hypertension management. The objectives of this systematic review were to evaluate the systolic and diastolic BP reduction, and achievement of target BP, associated with self-monitoring. Methods. MEDLINE, Embase, Cochrane database of systematic reviews, database of abstracts of clinical effectiveness, the health technology assessment database, the NHS economic evaluation database, and the TRIP database were searched for studies where the intervention included self-monitoring of BP and the outcome was change in office/ambulatory BP or proportion with controlled BP. Two reviewers independently extracted data. Meta-analysis using a random effects model was combined with meta-regression to investigate heterogeneity in effect sizes. Results. A total of 25 eligible randomized controlled trials (RCTs) (27 comparisons) were identified. Office systolic BP (20 RCTs, 21 comparisons, 5,898 patients) and diastolic BP (23 RCTs, 25 comparisons, 6,038 patients) were significantly reduced in those who self-monitored compared to usual care (weighted mean difference (WMD) systolic −3.82 mmHg (95% confidence interval −5.61 to −2.03), diastolic −1.45 mmHg (−1.95 to −0.94)). Self-monitoring increased the chance of meeting office BP targets (12 RCTs, 13 comparisons, 2,260 patients, relative risk = 1.09 (1.02 to 1.16)). There was significant heterogeneity between studies for all three comparisons, which could be partially accounted for by the use of additional co-interventions. Conclusion. Self-monitoring reduces blood pressure by a small but significant amount. Meta-regression could only account for part of the observed heterogeneity

Colorectal cancer prevention for low-income, sociodemographically-diverse adults in public housing: baseline findings of a randomized controlled trial

Background: This paper presents the study design, intervention components, and baseline data from Open Doors to Health, a study designed to address social contextual factors in colorectal cancer (CRC) prevention for low-income, racial/ethnic minority populations. Methods: A cluster randomized design with 12 housing sites as the primary sampling units was used: 6 sites were assigned to a Peer-led plus Screening Access (PL) condition, and 6 were assigned to Screening Access only (SCR) condition. Study-related outcomes were CRC screening, physical activity (measured as mean steps/day), and multivitamin use. Results: At baseline (unweighted sample size = 1554), two-thirds self-reported that they were current with screening recommendations for CRC (corrected for medical records validation, prevalence was 52%), with half having received a colonoscopy (54%); 96% had health insurance. Mean steps per day was 5648 (se mean = 224), and on average 28% of the sample reported regular multivitamin use. Residents reported high levels of social support [mean = 4.40 (se = .03)] and moderately extensive social networks [mean = 2.66 (se = .02)]. Conclusion: Few studies have conducted community-based studies in public housing communities; these data suggest areas for improvement and future opportunities for intervention development and dissemination. Findings from the randomized trial will determine the effectiveness of the intervention on our health-related outcomes as well as inform future avenues of research

Genetic Enhancement Perspectives and Prospects for Grain Nutrients Density

Diet-induced micronutrient malnutrition continues to be a major challenge globally, especially in the developing world. With the ever-increasing population, it becomes a daunting task to feed millions of mouths with nutritious food. It is time to reorient agricultural systems to produce quality food to supply the calorie and nutrient requirements needed by the human body. Biofortification is the process of improving micronutrients density by genetic means. It is cheaper and sustainable and complements well with the nutrient supplementation and fortification— the short-term strategies that are currently deployed to address the micronutrient malnutrition. Sorghum is one of the important food crops globally, adapted to semi-arid tropics, and there is increased awareness on its nutritional importance. Further, there is great opportunity to improve sorghum for nutritional quality. This chapter deals about the genetic enhancement perspectives and prospects for improving the nutritional quality with main emphasis on grain micronutrient density in sorghum