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Quasi-analytic modal expansion methods for optical modelling of cylindrical nanostructures in GaN LEDsO'Kane, Simon January 2015 (has links)
Gallium nitride (GaN)-based light-emitting diodes (LEDs) with cylindrical nanostructures have been the subject of significant research interest in the past decade, due to the potential of such structures to increase light extraction efficiency and deliver highly directional light emission. Nanorod LEDs, where the light emission is within the nanocylinder, have the additional potential to increase internal quantum efficiency and emit in colours previously thought impractical with GaN-based LEDs. Optical modelling of nanostructured LEDs is usually carried out using finite-difference time-domain methods, which are computationally intensive and do not always provide sufficient insight into the physics underlying the simulation results. This thesis proposes an intuitive, quasi-analytic method based on modal expansion. It is found that it is possible to calculate the far field diffraction patterns of all guided modes supported by a single nanorod, with full consideration of Fabry-Perot effects, in minutes using a standard office desktop computer. Focus is placed on the case of a nanorod of radius 140 nm, for which angular photoluminescence measurements were available to provide a means of validating the model. Consideration of the guided modes alone provides a compelling explanation for gross features in the measured data where none previously existed. It is shown that, using a standard equation from a textbook, it is possible to calculate how much each of the guided and radiation modes of a single nanorod is excited by a Hertzian dipole of known position and orientation with respect to the nanorod geometry. When interference between these modes is considered, it is possible to calculate the total far field angular emission pattern due to that dipole. Comparing these patterns with photoluminescence measurements allows one to infer the locations and orientations of dipole current sources; the results are found to be consistent with those of cathodoluminescence studies.
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Avaliação experimental do crescimento da comunidade fitoplanctônica do reservatório João Leite em diferentes condições de luz e nutrientes / Experimental evaluation of the growth of community phytoplankton reservoir João Leite in different conditions of light and nutrientsPina, Rafaela Wolff de 29 November 2013 (has links)
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Previous issue date: 2013-11-29 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / Human activities of natural resources exploration can have negative impacts on lakes
and reservoirs. The increase in the amount of nitrogen and phosphorus in water
cause deterioration in the water quality and eutrophication. Eutrophication by algae
and cyanobacteria may hinder the use of water for several purposes. João Leite’s
reservoir, located in the state of Goiás, is an important water resource for the public
supply; approximately, 2.300.000 inhabitants are in need of its water. The present
work aimed to study the dynamics of variation of a phytoplankton community in João
Leite’s reservoir by a bioreactors board studies in order to evaluate the population
growth of phytoplankton in different conditions of light and nutrients. The experiments
were performed in nine bioreactors with controlled light conditions (22 μmol de
fótons.m-2 .s-1, 44 μmol de fótons.m-2 .s-1,, 67 μmol de fótons.m-2 .s-1) and nutrients (N /
P = 10) (N / P = 16) and (N / P = 20) and according with a factorial experimental
design with two factors at three levels (3 Meters). The bioreactors were submitted to
a photoperiod of 12/12 hours and kept at a temperature of 25 ± 2 ° C. The natural
water samples were collected in 5 sampling campaigns in the months of April, May,
June and July 2013 from João Leite’s reservoir and monitored for five consecutive
days in the laboratory. The results showed a significant positive correlation between
light and nutrients on the growth of algae and cyanobacteria. A principal component
analysis (PCA) indicated light intensity and nitrate as the factors that most influenced
the increase of phytoplankton density. The paired t-test and Tukey tests showed that
the effect of light, however, was more significant than the effect of nutrients. The
growth of algae and cyanobacteria were modeled as logistic model that adjusted well
to the data with R ² value ranging between 0.80 and 0.99. The laboratory experiment
corroborated the data of seasonal variations in the reservoir, in which occurred as the
increase of algae and cyanobacteria density as was the increase in nitrate
concentration and light intensity. / As atividades humanas de exploração dos recursos naturais podem gerar impactos
negativos em lagos e em reservatórios. O aumento do aporte de nitrogênio e fósforo
nas águas causam a deterioração da qualidade da água e eutrofização. A
eutrofização por algas e cianobactérias pode dificultar o uso compartilhado da água
para diversos fins. O reservatório do João Leite, situado no estado de Goiás, é um
importante recurso hídrico destinado ao abastecimento público de
aproximadamente, 2.300.000 habitantes. O presente trabalho teve como objetivo
estudar a dinâmica da variação da comunidade fitoplanctônica no reservatório do
João Leite por meio de estudo de bancada em biorreatores com a finalidade de
avaliar o crescimento da população de fitoplâncton em diferentes condições de luz e
nutrientes. Os experimentos foram realizados em nove biorreatores com condições
controladas de luz (22 μmol de fótons.m-2 .s-1, 44 μmol de fótons.m-2 .s-1,, 67 μmol de
fótons.m-2 .s-1) e nutrientes (N/P=10), (N/P=16) e (N/P=20) e de acordo com um
planejamento experimental do tipo fatorial com dois fatores em três níveis (3²). Os
biorreatores foram submetidos a um fotoperíodo de 12/12 horas e mantidos a uma
temperatura de 25±2ºC. As amostras de água natural foram coletadas em 5
campanhas amostrais nos meses de Abril, Maio, Junho e Julho de 2013 no
Reservatório do João Leite e monitoradas por 5 dias consecutivos em laboratório.
Os resultados mostraram uma correlação positiva e significativa entre a luz e
nutrientes sobre o crescimento de algas e cianobactérias. Uma análise de
componentes principais (ACP) indicou a intensidade de luz e concentração de nitrato
como os fatores que mais influenciaram o aumento da densidade do fitoplâncton. O
teste t pareado e Tukey mostraram que, todavia o efeito da luz foi mais significativo
do que o efeito dos nutrientes. O crescimento de algas e cianobactérias foram
modelados conforme modelo logístico que se ajustou bem aos dados com o valor de
R² variando entre 0,80 e 0,99. O experimento em laboratório corroborou com os
dados de variação sazonal no reservatório, em que ocorreu aumento da densidade
de algas e cianobactérias à medida que ocorreu o aumento da concentração de
nitrato e intensidade de luz.
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Evaluation of Membrane Aerated Biofilm Reactor and Tertiary Treatment for the Removal of Organic Micropollutants in Municipal WastewaterSanchez Huerta, Claudia 11 1900 (has links)
Occurrence of organic micropollutants (OMPs) in aquatic environment is a worldwide concern. A long list of anthropogenic substances, including pharmaceuticals, hormones, etc., are frequently detected in natural water sources. Wastewater treatment plants are one main source of OMPs pollution, but also a key step to control OMPs dissemination into the environment. This dissertation focuses on the evaluation of Membrane Aerated Biofilm Reactor (MABR) as a sustainable process to treat wastewater polluted by OMPs. Furthermore, application of high intensity pulsed light is proposed as an innovative tertiary treatment to produce reclaimed water of high quality.
In Chapter 1, a literature review was performed to investigate the occurrence and toxicity of 12 selected organic micropollutants (OMPs) in surface and ground water and the limitations of current available biological processes. Among these technologies, systems with enriched nitrifying activity were able to enhance the removal of specific OMPs through cometabolic activities. Thus, I proposed the use of a MABR with enriched nitrifying biomass to treat OMP polluted water.
In Chapter 2, I studied the influence of biofilm thickness on the removal of 13 OMPs via MABR. Results demonstrated OMP removal was dependent on biofilm thickness and bacterial cell density.
MABR demonstrated important efficiencies in the removal of ammonium, COD, acetaminophen and triclosan at early stages of biofilm thickness. However, the removal of nonpolar, hydrophobic 4
OMPs and anionic, acidic OMPs required thicker biofilms, achieving maximum removal at biofilm with 1.02 mm thickness and 2.2 × 106 cell mL-1.
In Chapter 3, the contribution of sorption and biodegradation in the removal of OMPs via MABR was evaluated. At three stages of biofilm thickness studied, biodegradation dominated the removal for most OMPs. Heterotrophs played an important role in OMP biodegradation at all biofilm thickness, while autotrophic nitrifiers enhanced their contribution at thickness beyond 0.58 mm.
Increased removal of pollutants like estrone and ethinyl estradiol were linked to the MABR enrichment with nitrifying bacteria. Sorption was essential for the removal of lipophilic and recalcitrant pollutants like triclosan.
Finally, to provide high quality treated water for reuse, Chapter 4 explores the use of high-intensity pulsed light (HIPL) as post-treatment. The number of pulses and optical energy dose have a significant impact on the OMPs removal. HIPL demonstrated fast kinetics and efficient photodegradation – with significant OMPs removal within milliseconds.
The findings from my Ph.D. dissertation indicate that MABR combined with high-intensity pulse light may be an effective treatment train for the efficient removal OMPs present in municipal wastewaters. This combined treatment process could potentially pave the way to produce high quality reclaimed water for various reuse purposes.
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