Optimization of PEDOT: PSS thin film for organic solar cell application

As a clean and renewable energy source, the development of the organics solar cells is very promising due to the inorganic solar cell inconvenient production process and material shortness. In this work, P3HT: PCBM bulk-heterojunction devices were produced by spin coating organic layers onto ITO coated glass in air, and deposited it with an Au layer as top metal electrode. Inverted devices were fabricated with and without PEDOT:PSS. Then, several attempts have been conducted to improve power conversion efficiency by optimizing different thicknesses of the interlayer between active layer and metal. Power conversion efficiency, short circuit current, open circuit voltage and fill factor were measured on all produced devices. In contrast, the devices with 50 nm thickness of PEDOT: PSS layer showed as better solar cell with 0.0394% efficiency compared to the devices without PEDOT:PSS. As a result, introduction of PEDOT:PSS layer on active layer improves hole collection at the metal / active layer interface

Single station TEC modelling during storm conditions

It has been shown in ionospheric research that modelling total electron content (TEC) during storm conditions is a big challenge. In this study, mathematical equations were developed to estimate TEC over Sutherland (32.38oS, 20.81oE), during storm conditions, using the Empirical Orthogonal Function (EOF) analysis, combined with regression analysis. TEC was derived from GPS observations and a geomagnetic storm was defined for Dst ≤ -50 nT. The inputs for the model were chosen based on the factors that influence TEC variation, such as diurnal, seasonal, solar and geomagnetic activity variation, and these were represented by hour of the day, day number of the year, F10.7 and A index respectively. The EOF model was developed using GPS TEC data from 1999 to 2013 and tested on different storms. For the model validation (interpolation), three storms were chosen in 2000 (solar maximum period) and three others in 2006 (solar minimum period), while for extrapolation six storms including three in 2014 and three in 2015 were chosen. Before building the model, TEC values for the selected 2000 and 2006 storms were removed from the dataset used to construct the model in order to make the model validation independent on data. A comparison of the observed and modelled TEC showed that the EOF model works well for storms with non-significant ionospheric TEC response and storms that occurred during periods of low solar activity. High correlation coefficients between the observed and modelled TEC were obtained showing that the model covers most of the information contained in the observed TEC. Furthermore, it has been shown that the EOF model developed for a specific station may be used to estimate TEC over other locations within a latitudinal and longitudinal coverage of 8.7o and 10.6o respectively. This is an important result as it reduces the data dimensionality problem for computational purposes. It may therefore not be necessary for regional storm-time TEC modelling to compute TEC data for all the closest GPS receiver stations since most of the needed information can be extracted from measurements at one location

Scenedesmus biomass productivity and nutrient removal from wet market wastewater, a bio-kinetic study

The current study aims to investigate the production of microalgae biomass as a function for different wet market wastewater ratios (10, 25, 50, 75 and 100%) and Scenedesmus sp. initial concentrations (104 , 105 , 106 , 107 cells/mL) through the phycoremediation process. The biomass production, total nitrogen (TN), total phosphorus (TP) and total organic compounds (TOC) were determined daily. The pseudo-first order kinetic model was used to measure the potential of Scendesmus sp. in removing nutrients while the Verhulst logistic kinetic model was used to study the growth kinetic. The study revealed that the maximum productivity of Scenedesmus sp. biomass was recorded with 106 cells/mL of the initial concentration in 50% wet market wastewater (98.54 mg/L/day), and the highest removal of TP, TN, and TOC was obtained (85, 90 and 65% respectively). Total protein and lipid contents in the biomass yield produced in the wet market wastewater were more than that in the biomass produced in the BBM (41.7 vs. 37.4 and 23.2 vs. 19.2%, respectively). The results of GC–MS confirmed detection of 44 compounds in the biomass from the wet market wastewater compared to four compounds in the BBM. These compounds have several applications in pharmaceutical and personal care products, chemical industry and antimicrobial activity. These findings indicated the applicability of wet market wastewater as a production medium for microalgae biomass

A Study Of Equatorial Ionopsheric Variability Using Signal Processing Techniques

The dependence of equatorial ionosphere on solar irradiances and geomagnetic activity are studied in this dissertation using signal processing techniques. The statistical time series, digital signal processing and wavelet methods are applied to study the ionospheric variations. The ionospheric data used are the Total Electron Content (TEC) and the critical frequency of the F2 layer (foF2). Solar irradiance data are from recent satellites, the Student Nitric Oxide Explorer (SNOE) satellite and the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite. The Disturbance Storm-Time (Dst) index is used as a proxy of geomagnetic activity in the equatorial region. The results are summarized as follows. (1) In the short-term variations ≤ 27-days, the previous three days solar irradiances have significant correlation with the present day ionospheric data using TEC, which may contribute 18% of the total variations in the TEC. The 3-day delay between solar irradiances and TEC suggests the effects of neutral densities on the ionosphere. The correlations between solar irradiances and TEC are significantly higher than those using the F10.7 flux, a conventional proxy for short wavelength band of solar irradiances. (2) For variations ≤ 27 days, solar soft X-rays show similar or higher correlations with the ionosphere electron densities than the Extreme Ultraviolet (EUV). The correlations between solar irradiances and foF2 decrease from morning (0.5) to the afternoon (0.1). (3) Geomagnetic activity plays an important role in the ionosphere in short-term variations ≤ 10 days. The average correlation between TEC and Dst is 0.4 at 2-3, 3-5, 5-9 and 9-11 day scales, which is higher than those between foF2 and Dst. The correlations between TEC and Dst increase from morning to afternoon. The moderate/quiet geomagnetic activity plays a distinct role in these short-term variations of the ionosphere (~0.3 correlation)

Variation of the plasmaspheric field-aligned electron density and ion composition as a function of geomagnetic storm activity

Thesis (Ph.D.) University of Alaska Fairbanks, 2015Whistler mode (WM) radio sounding is a powerful new method that provides measurement of both field-aligned electron and ion densities from the satellite altitude (<5,000 km) down to 90 km. Using radio sounding data from the Radio Plasma Imager (RPI) onboard the IMAGE (Imager for Magnetosphere-to-Aurora Global Exploration) satellite, this thesis presents a systematic and efficient approach to implement the whistler mode radio sounding method and discusses the uncertainties in the measured plasma parameters. The sounding method is applied to obtain the first measurements of plasmaspheric field-aligned electron density and ion composition as a function of geomagnetic storm activity during the mid-August to September 2005 period. This period included several geomagnetic storms of varying strength that occurred in succession. The plasmapause was located at L~2.4 during the onset and main phases of the storms. The whistler mode sounding results were augmented by measurements from the CHAMP and DMSP satellites, and ground ionosonde stations during the same period. On the day-side, at L~2, as a function of storm activity the following general results were found: (1) The electron density, relative ion concentrations, and O⁺/H⁺ transition height underwent temporal changes as a function of geomagnetic storm activity, and each species had different temporal behavior thus indicating different recovery times. (2) O⁺/=H⁺ transition height increased by ~200-300 km during the onset, main and early recovery phases of the storms. (3) Variation in the electron density below the O⁺=H⁺ transition height was different than that above. (4) Electron density at F2 peak increased during the onset or main phase of storms followed by a decrease in the recovery phase. (5) Electron density above O+=H+ transition height increased either in the onset or on the first day of recovery phase followed by a decrease. (6) αH₊ decreased during the onset, main and/or early recovery phases of storms; αo₊ increased in the early recovery phases of the storms; αHe₊ varied in a complex manner but in general there was an increase in αHe₊ during the onset phases and decrease in αHe₊ during the recovery phases of the storms. (7) When storms occurred in succession in an interval of roughly less than a day, the latter storms had little or no effect on the electron density and/or ion composition. On the night-side, WM sounding data was sparse. In the case of one moderate storm, we found that 3 days after the storm, at L~2.3, electron density at F2 peak and relative ion concentrations (at all altitudes) were comparable to those before the storm, whereas electron density above O⁺=H⁺ transition height decreased. WM sounding results for the day-side and night-side were in agreement with measurements from CHAMP (~350 km) and DMSP (~850 km). Whistler mode sounding results coupled with physics-based models will allow: (a) investigation of the role of thermospheric winds, dynamo electric fields, and storm time electric fields in causing the variations in electron and ion densities and (b) testing of current theories and validating physics-based models of the thermosphere-ionosphere-magnetosphere

Exploiting new GNSS signals to monitor, model and mitigate the ionospheric effects in GNSS

Signals broadcast by the Global Navigation Satellite Systems (GNSS) enable global, autonomous, geo-spatial positioning exploited in the areas such as geodesy, surveying, transportation and agriculture. The propagation of these signals is affected as they propagate through the Earth's upper atmosphere, the ionosphere, due to the ionic and electronic structure of the ionosphere. The ionosphere, a highly dynamic and spatially and temporally variable medium, can be the largest error source in Global Navigation Satellite System (Klobuchar 1991) in the absence of the Selective Availability. Propagation effects due to the ionosphere lead to errors in the range measurements, impact on receiver signal tracking performance and influence the GNSS positioning solution. The range error can vary from 1 to 100m depending on time of day, season, receiver location, conditions of the earth's magnetic field and solar activity (Hofmann-Wellenhof et al. 2001). This thesis focuses on modelling, monitoring and mitigating the ionospheric effects in GNSS within the scope of GNSS modernization, which introduces new signals, satellites and constellations. The ionosphere and its effects on GNSS signals, impact of the ionospheric effects at the receiver end, predicted error bounds of these effects under different solar, geomagnetic and ionospheric conditions, how these effects can be modelled and monitored with current and new (possible with GNSS modernization) correction approaches, degradation in the GNSS positioning solution and mitigation techniques to counter such degradation are investigated in this thesis. Field recorded and simulated data are considered for studying the refractive and diffractive effects of the ionosphere on GNSS signals, signal tracking performance and position solution. Data from mid-to-high latitudes is investigated for the refractive effects, which are due to dispersive nature of the ionosphere. With the use of multi-frequency, multi-constellation receivers, modelling of the refractive effects is discussed through elimination and estimation of these effects on the basis of dual and triple frequency approaches, concentrating on the benefit of the new GNSS signals. Data from the low latitudes is considered for studying the diffractive effects of the ionosphere, scintillation in particular, in GNSS positioning, and possible mitigation techniques to counter them. Scintillation can have a considerable impact on the performance of GNSS positioning by, for instance, increasing the probability of losing phase lock with a signal and reducing the accuracy of pseudoranges and phase measurements. In this sense, the impact of scintillation on signal tracking performance and position solution is discussed, where a novel approach is proposed for assessing the variance of the signal tracking error during scintillation. The proposed approach also contributes to the work related with scintillation mitigation, as discussed in this thesis. The timeliness of this PhD due to the recent and increasingly active period of the next Solar Cycle (predicted to reach a peak around 2013) and to the ongoing GNSS modernization give this research an opportunity to enhance the ionospheric knowledge, expertise and data archive at NGI, which is rewarding not only for this PhD but also for future research in this area

Statistical analysis of the ionospheric response during storm conditions over South Africa using ionosonde and GPS data

Ionospheric storms are an extreme form of space weather phenomena which affect space- and ground-based technological systems. Extreme solar activity may give rise to Coronal Mass Ejections (CME) and solar flares that may result in ionospheric storms. This thesis reports on a statistical analysis of the ionospheric response over the ionosonde stations Grahamstown (33.3◦S, 26.5◦E) and Madimbo (22.4◦S,30.9◦E), South Africa, during geomagnetic storm conditions which occurred during the period 1996 - 2011. Total Electron Content (TEC) derived from Global Positioning System (GPS) data by a dual Frequency receiver and an ionosonde at Grahamstown, was analysed for the storms that occurred during the period 2006 - 2011. A comprehensive analysis of the critical frequency of the F2 layer (foF2) and TEC was done. To identify the geomagnetically disturbed conditions the Disturbance storm time (Dst) index with a storm criteria of Dst ≤ −50 nT was used. The ionospheric disturbances were categorized into three responses, namely single disturbance, double disturbance and not significant (NS) ionospheric storms. Single disturbance ionospheric storms refer to positive (P) and negative (N) ionospheric storms observed separately, while double disturbance storms refer to negative and positive ionospheric storms observed during the same storm period. The statistics show the impact of geomagnetic storms on the ionosphere and indicate that negative ionospheric effects follow the solar cycle. In general, only a few ionospheric storms (0.11%) were observed during solar minimum. Positive ionospheric storms occurred most frequently (47.54%) during the declining phase of solar cycle 23. Seasonally, negative ionospheric storms occurred mostly during the summer (63.24%), while positive ionospheric storms occurred frequently during the winter (53.62%). An important finding is that only negative ionospheric storms were observed during great geomagnetic storm activity (Dst ≤ −350 nT). For periods when both ionosonde and GPS was available, the two data sets indicated similar ionospheric responses. Hence, GPS data can be used to effectively identify the ionospheric response in the absence of ionosonde data

Long-term analysis of ionospheric response during geomagnetic storms in mid, low and equatorial latitudes

Understanding changes in the ionosphere is important for High Frequency (HF) communications and navigation systems. Ionospheric storms are the disturbances in the Earth’s upper atmosphere due to solar activities such as Coronal Mass Ejections (CMEs), Corotating interaction Regions (CIRs) and solar flares. This thesis reports for the first time on an investigation of ionospheric response to great geomagnetic storms (Disturbance storm time, Dst ≤ −350 nT) that occurred during solar cycle 23. The storm periods analysed were 29 March - 02 April 2001, 27 - 31 October 2003, 18 - 23 November 2003 and 06 - 11 November 2004. Global Navigation Satellite System (GNSS), Total Electron Content (TEC) and ionosonde critical frequency of F2 layer (foF2) data over northern hemisphere (European sector) and southern hemisphere (African sector) mid-latitudes were used to study the ionospheric responses within 15E° - 40°E longitude and ±31°- ±46° geomagnetic latitude. Mid-latitude regions within the same longitude sector in both hemispheres were selected in order to assess the contribution of the low latitude changes especially the expansion of Equatorial Ionization Anomaly (EIA) also known as the dayside ionospheric super-fountain effect during these storms. In all storm periods, both negative and positive ionospheric responses were observed in both hemispheres. Negative ionospheric responses were mainly due to changes in neutral composition, while the expansion of the EIA led to pronounced positive ionospheric storm effect at mid-latitudes for some storm periods. In other cases (e.g 29 October 2003), Prompt Penetration Electric Fields (PPEF), EIA expansion and large scale Traveling Ionospheric Disturbances (TIDs) were found to be present during the positive storm effect at mid-latitudes in both hemispheres. An increase in TEC on the 28 October 2003 was because of the large solar flare with previously determined intensity of X45± 5. A further report on statistical analysis of ionospheric storm effects due to Corotating Interaction Region (CIR)- and Coronal Mass Ejection (CME)-driven storms was performed. The storm periods analyzed occurred during the period 2001 - 2015 which covers part of solar cycles 23 and 24. Dst≤ -30 nT and Kp≥ 3 indices were used to identify the storm periods considered. Ionospheric TEC derived from IGS stations that lie within 30°E - 40°E geographic longitude in mid, low and equatorial latitude over the African sector were used. The statistical analysis of ionospheric storm effects were compared over mid, low and equatorial latitudes in the African sector for the first time. Positive ionospheric storm effects were more prevalent during CME-driven and CIR-driven over all stations considered in this study. Negative ionospheric storm effects occurred only during CME-driven storms over mid-latitude stations and were more prevalent in summer. The other interesting finding is that for the stations considered over mid-, low, and equatorial latitudes, negative-positive ionospheric responses were only observed over low and equatorial latitudes. A significant number of cases where the electron density changes remained within the background variability during storm conditions were observed over the low latitude stations compared to other latitude regions

Determination of Ionospheric Current Systems by Measuring the Phase Shift on Amateur Satellite Frequencies

We investigate the possibility of measuring and using the phase delay of radio frequency transmissions in the amateur satellite band as a method to determine the distribution of currents systems in the ionosphere. The amateur satellite transmissions at 7MHz, 14M Hz, and 144M Hz are low enough for Faraday rotation to cause a significant phase delay on the propagating signals in addition to the phase delay produced by the total electron content (TEC) in the ionosphere. The ionosphere in the E and F regions is modeled as an equivalent thin planar shell of collision free cold plasma 100 km in thickness located in an altitude range of 100 � 200 km. The earth\u27s magnetic field is superposed with a weaker magnetic field due to a narrow Gaussian strip of current representing an ionospheric electrojet. The prole of the current system is obtained by numerically optimizing the Appleton-Hartree dispersion relation for rays of simulated radio frequency (RF) signals that propagate through the ionosphere shell. The optimization procedure is performed with a differential evolution algorithm. From the optimization procedure, we obtain the ionosphere total electron content (TEC) and the strength, prole, and orientation of the ionospheric current system

Improvement of ionospheric corrections applied to the European Geostationary Navigation Overlay System (EGNOS) for applications to terrestrial positioning

2012/2013L’attività di Ricerca svolta durante il ‘Corso di Dottorato in Ingegneria Civile e Ambientale ha riguardato l’attività in collaborazione con il Prof. Radicella presso il Telecommunications/ICT for Development Laboratory (T/ICT4D), the Abdus Salam International Centre of Theoretical Physics, Miramare, e il periodo formativo di tre mesi all’estero presso l’EGNOS Project Office (EPO), sede dell’European Space Agency (ESA) a Toulouse (Francia), sotto la supervisione di Dott. Stefan Schlueter dell’ EPO. Il lavoro svolto, che consiste nello studio dell’effetto della ionosfera sul segnale satellitare di EGNOS (European Geostationary Navigation Overlay System e del conseguente degrado del calcolo della posizione plano altimetrica che ne deriva, si intende come un contributo per l’ottimizzazione di uno dei servizi forniti da EGNOS denominato EGNOS Open Service, ovvero del primo servizio reso disponibile agli utenti a partire dal 2009. Le caratteristiche del servizio EGNOS Open Service sono presentate in un documento ufficiale chiamato EGNOS SDD-OS dell’Agenzia Spaziale Europea. Il suo obiettivo principale è di aumentare l’accuratezza nel posizionamento correggendo i differenti errori che influenzano il segnale GPS a singola frequenza: gli errori di orologio e di orbita dei satelliti e gli errori legati al ritardo di propagazione del segnale in ionosfera. Altre tipologie di errori, come quelli legati alla propagazione del segnale in troposfera e gli errori da multipath, essendo dovuti a effetti locali non possono essere corrette dai sistemi SBASs (Satellite Based Augmentation System). Lo scopo del documento è di suggerire le tecniche e linee guida per i produttori di ricevitori satellitari e di mettere in evidenza l’importanza del posizionamento e delle prestazioni temporali attualmente disponibili per utenti equipaggiati con strumentazione in grado di ricevere sia il segnale di trasmissione GPS in modalità Standard Positioning Service, con utilizzo della sola frequenza L1, sia il segnale fornito da EGNOS. L’importanza di questo lavoro risiede nel fatto che l’EGNOS OS, essendo un Open Service, può facilmente essere usato da differenti utenze, in una vasta gamma di settori quali la navigazione stradale, l’agricoltura di precisione e le applicazioni personali su palmari. Il lavoro svolto quest’anno s’inserisce pertanto in uno degli obiettivi proposti dall’EGNOS SDD OS. L’aspetto fondamentale riguarda i dati ionosferici forniti da EGNOS tramite i messaggi navigazionali MT 18 e MT26. E’ ormai noto come la precisione nel calcolo del posizionamento, che si ottiene mediante un sistema GNSS a singola frequenza, sia dipendente da vari fattori tra i quali quello dominante è legato alla propagazione del segnale in ionosfera. Sebbene i sistemi SBAS, (del quale EGNOS è la componente Europea) abbiano consentito di ridurre notevolmente gli effetti legati a quest'ultima tipologia di errore, anch'essi soffrono di una forte riduzione di prestazioni in condizioni di grande variabilità ionosferica, come quelle legate a alle basse latitudini o alla presenza di tempeste geomagnetiche. Per questo motivo è importante valutare a livello quantitativo le prestazioni di EGNOS in termini di range delay e di posizionamento tramite un adeguato confronto dei dati trattati con software dedicati, come quelli utilizzati dalla scrivente durante i mesi trascorsi all’EPO. Il dato principale fornito da EGNOS consiste nella correzione ionosferica in punti ionosferici di griglia (IGPs). A causa della presenza di punti IGP “non monitorati” in alcune zone dell’area di copertura del sistema (ECAC, European Civil Aviation Conference), non e' possibile calcolare in modo appropriato il ritardo ionosferico nei corrispondenti punti ionosferici (IPPs) in accordo con la tecnica di interpolazione prevista nel documento ufficiale dell’EGNOS, RTCA Do 229C-D Minimal Operational Performance Standard for GPS/WAAS. Questo incide ovviamente sulle prestazioni globali del sistema EGNOS che, in condizioni nominali, presenta una disponibilità massima di punti ionosferici di griglia (IGPs) monitorati nelle zone centrali dell’area ECAC. In questo contesto, il lavoro svoltosi all’EPO si è' diviso in 3 fasi principali: 1. Sono state considerate le possibili aree di miglioramento delle prestazioni del sistema; per queste aree sono state proposte diverse soluzioni di implementazione. Ognuna di queste soluzioni è stata scelta con l’obiettivo di migliorare la disponibilità dell’EGNOS OS e allo stesso tempo di soddisfare le richieste di accuratezza specificate nel documento. 2. Una volta identificate le possibili aree di miglioramento e di studio, sono state valutate le prestazioni associate a ciascuna soluzione proposta, usando un prototipo di ricevitore GNSS. L’utilizzo di un ricevitore/software è motivato dal fatto che questo permette grande flessibilità quando si testano le differenti opzioni. 3. Infine, sulla base della valutazione delle prestazioni ottenute, sono state considerate e discusse le soluzioni in ciascuna area analizzata. Nella prima fase della ricerca è stato studiato una strategia di calcolo per ovviare alla mancanza dei dati di EGNOS ed estendere la disponibilità per i dati di griglia, in particolare nella parte sud della zona ECAC: e’ stato effettuato uno studio delle mappe globali, in particolare quelle fornite dall’International GNSS Service (IGS) e dal CODE, dell’Università di Berna, eseguendo un confronto fra i ritardi ionosferici verticali e quelli obliqui (slant). Lo scopo di questa analisi e' stato quello di determinare il ritardo ionosferico e correggerne l'influenza in un settore critico dell'area ECAC, come quello delle regioni meridionali, a causa dell'assenza dei dati di correzione ionosferica EGNOS. L’obiettivo principale di questa fase è stato quello di confrontare il TEC verticale estratto dai dati EGNOS con quello ottenuto utilizzando le mappe globali di CODE in tutta la zona d’interesse, e infine l'utilizzo dei valori di correzione dei punti di griglia del CODE in sostituzione dei valori mancanti nei punti di griglia non monitorati da EGNOS. L’analisi è stata eseguita per gli anni 2012 e 2013 in giorni caratterizzati sia da condizioni di quiete che da condizioni di tempeste geomagnetiche, in un’area di copertura [40°W, 40°E ] in longitudine e [20°N, 60°N] in latitudine, in modo da valutare quantitativamente in che misura le mappe globali riproducano le condizioni regionali descritte dalla griglia di EGNOS in termini di gradiente spaziale di TEC (sia in longitudine che latitudine). Nella seconda fase della ricerca sono stati calcolati i valori di TEC verticale e obliquo e le coordinate dei punti IPP. In seguito sono stati calcolati i diversi contributi agli IPP ( in termini di TEC) con l’algoritmo di interpolazione bilineare a quattro punti. Sono stati considerati i valori del TEC negli IGPs: - di EGNOS - di CODE - di una griglia sintetica ottenuta sostituendo i dati di CODE nei punti di griglia non monitorati da EGNOS. Utilizzando le diverse correzioni ionosferiche sono stati ricalcolati i valori dei relativi pseudoranges da utilizzare per il calcolo della posizione con correzione WADGPS. I nuovi valori pseudorange così calcolati sono stati inseriti all'interno dei files rinex di diverse stazioni di riferimento, operanti nella parte sud dell’area ECAC. Con l'utilizzo di diversi software utilizzati all’EGNOS Project Office, sono stati valutati gli errori di posizionamento per i diversi modelli di TEC assunti al fine di valutare l’attendibilità delle precisioni planimetriche e altimetriche ottenute. Si è' deciso di usare software di posizionamento flessibili per le varie esigenze che simulassero i ricevitori, in modo da poter applicare le varie correzioni in modo sistematico. Lo scopo dell'attivita' di ricerca svolta, è quello di permettere l’estensione della disponibilità dei dati EGNOS nei valori di griglia in caso di condizioni “non monitorate” del sistema, attraverso lo studio degli effetti dell’impatto ionosferico su EGNOS.XXV Ciclo198