Solid oxide fuel cells (SOFCs) offer the advantages of (i) employing less expensive catalysts compared to the expensive Pt catalyst used in proton exchange membrane fuel cells and (ii) directly using hydrocarbon fuels without requiring external fuel reforming due to the high operating temperature. However, the conventional high operating temperatures of 800 - 1000 °C lead to interfacial reactions and thermal expansion mismatch among the components and limitations in the choice of electrode and interconnect materials. These problems have prompted a lowering of the operating temperature to an intermediate range of 500 - 800 °C, but the poor oxygen reduction reaction kinetics of the conventional La[subscript 1-x]Sr[subscript x]MnO₃ perovskite cathode remains a major obstacle for the intermediate temperature SOFC. In this regard, cobalt-containing oxides with perovskite or perovskite-related structures have been widely investigated, but they suffer from large thermal expansion coefficient (TEC) mismatch with the electrolytes. With an aim to lower the TEC and maximize the electrochemical performance, this dissertation focuses on perovskite-related and trigonal RBaCo₄O₇-based oxide cathode materials. First, the effect of M = Fe and Cu in the perovskite-related layered LnBaCo₂₋xMxO₊[delta] (Ln = Nd and Gd) oxides has been investigated. The Fe and Cu substitutions lower the polarization resistance and offer fuel cell performance comparable to that of La[subscript 1-x]Sr[subscript x]CoO₃₋[delta] perovskite due to improved chemical stability with the electrolyte and a better matching of the TEC with those of standard electrolytes. Second, the perovskite-related intergrowth oxides Ln(Sr,Ca)₃Fe₁.₅Co₁.₅O₀ and La₁.₈₅Sr₁.₁₅Cu[subscript 2-x]Co[subscript x]O[subscript 6 +delta] and their composites with gadolinia-doped ceria (GDC) have been investigated. The electrical conductivity, TEC, and catalytic activity increase with increasing Co content. The composite cathodes exhibit enhanced electrochemical performance due to lower TEC and increased triple-phase boundary. Third, RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) oxides with a trigonal structure and tetrahedral-site Con+ ions have been investigated. The chemical instability normally encountered with this class of oxides has been overcome by appropriate cationic substitutions as in (Y₀.₅Ca₀.₅)Ba(Co₂.₅Zn₁.₅)O₇ and (Y₀.₅In₀.₅)BaCo₃ZnO₇. With an ideal matching of TEC with those of standard electrolytes, the RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) + GDC composite cathodes exhibit low polarization resistance and electrochemical performance comparable to that of perovskite oxides. / text

Ένας συναρπαστικός τομέας της σύγχρονης έρευνας είναι αυτός των νάνο-συνθέτων υλικών. Το πεδίο αυτό περιλαμβάνει τη μελέτη πολυφασικών υλικών, στα οποία μία ή περισσότερες από τις χωρικές διαστάσεις κάποιας φάσης βρίσκεται στην περιοχή των νανομέτρων (1 nm = 10-9 m = 10 ). Αυτό που ξεχωρίζει τα νανοσύνθετα από τα άλλα συμβατά σύνθετα υλικά είναι η ικανότητα τους να συνδυάζουν ιδιότητες, οι οποίες είναι απαγορευτικές για τα παραδοσιακά υλικά, αλλά και η μεγάλη λειτουργικότητα που παρουσιάζουν. Η εισαγωγή των νάνο-σύνθετων υλικών και οι πολλές επιστημονικές μελέτες που έγιναν τα τελευταία χρόνια στόχευαν και προσδοκούσαν σε μία δραματική βελτίωση των μηχανικών ιδιοτήτων, πράγμα που πολλές φορές δεν επαληθεύθηκε. Τα νάνο-σύνθετα πολυμερικής μήτρας των οποίων η θερμομηχανική συμπεριφορά μελετήθηκε περισσότερο είναι τα συστήματα που περιέχουν ως εγκλείσματα νάνο-σωλήνες άνθρακα (carbon nanotubes), νάνο-σωματίδια αλούμινας και στρωματικά άλατα πυριτίου (layered silicates). Στις μέρες μας υπάρχει ένα αυξανόμενο ενδιαφέρον για τη μελέτη της διηλεκτρικής συμπεριφοράς και αγωγιμότητας των νάνο-σύνθετων πολυμερικής μήτρας - ανόργανων νάνο-εγκλεισμάτων. Στην παρούσα εργασία εξετάσθηκε η διηλεκτρική απόκριση των συστημάτων: (α) πολυμερικής μήτρας (polyurethane rubber, PU) και νάνο-σωματιδίων αλούμινας (alumina- boehmite), (β) πολυμερικής μήτρας (PU ή Natural Rubber, NR ή PU/NR) με στρωματικά άλατα πυριτίου (layered silicates), με παραμέτρους την περιεκτικότητα σε νανοεγκλείσματα, τη θερμοκρασία και τη συχνότητα του εφαρμοζόμενου πεδίου. Η διηλεκτρική φασματοσκοπία (Broadband Dielectric Spectroscopy) έχει αποδειχθεί ως ένα ισχυρό εργαλείο για την έρευνα της μοριακής κινητικότητας, των αλλαγών φάσεων, τους μηχανισμούς αγωγιμότητας και τα διεπιφανειακά φαινόμενα στα πολυμερή και τα σύνθετα πολυμερικά συστήματα. Η διηλεκτρική απόκριση των νάνο-συνθέτων εξετάστηκε με τη βοήθεια της διηλεκτρικής φασματοσκοπίας (BDS) στο εύρος συχνοτήτων 10-1-10 6 Hz και στο εύρος θερμοκρασιών από -100οC έως +70οC. Από τα πειραματικά αποτελέσματα προκύπτει πως παρατηρούνται διηλεκτρικές χαλαρώσεις που οφείλονται τόσο στην πολυμερική μήτρα, όσο και στην ενισχυτική φάση. Τέσσερις διακριτοί τρόποι χαλάρωσης καταγράφηκαν στα φάσματα των συστημάτων που μελετήθηκαν και αποδίδονται στη διεπιφανειακή πόλωση (IP) μήτρας/εγκλεισμάτων, στην υαλώδη μετάβαση (α-mode) των πολυμερών NR και PU, στην κίνηση πλευρικών πολικών ομάδων (β-mode) των αλυσίδων του PU και σε τοπικές κινήσεις εύκαμπτων τμημάτων των αλυσίδων του PU (γ–mode). Στο σύστημα πολυουρεθάνης (PU)–νάνο-σωματιδίων αλούμινας ερευνήθηκε η επίδραση του μέσου μεγέθους των σωματιδίων στην ηλεκτρική απόκριση των υλικών. Από τα αποτελέσματα φαίνεται πως η μείωση του μέσου μεγέθους των νάνο-εγκλεισμάτων οδηγεί σε αύξηση της διεπιφάνειας και των αντίστοιχων φαινομένων που τη συνοδεύει. Τέλος, από τη θερμοκρασιακή εξάρτηση της θέσεως των κορυφών διηλεκτρικών απωλειών, κάθε διεργασίας, προσδιορίστηκαν οι αντίστοιχες ενέργειες ενεργοποίησης. / The impact of nano-materials and nano-structured materials is well known in our days. Nano-composites consists an exciting modern field of scientific research. Nano-composites are multiphase materials where at least one of the dimensions of the reinforcing phase is in nano-scale. The main difference of nano-composites with compatible composites is their ability to achieve superior performance at a very low concentration of the filler. The majority of the active or potential applications of nano-systems is based on their thermo-mechanical behaviour, flame resistance and electrical properties. Under this point of view nano-composites exhibit properties or functions, which seem to be prohibited for traditional materials. Recently, there is an increased interest in studying the dielectric behaviour of polymer matrix – inorganic nano-filler composites. Polymer matrix nano-composites are expected to be useful in replacing conventional insulating materials providing tailored performance, by simply controlling the type and the concentration of nano-inclusions. In the present study is investigated the dielectric behaviour of composites consisted of a polymer matrix and inorganic nano-filler. Natural rubber (NR) and polyurethane rubber (PU) as well as their blend are used as matrices. Nano-composites were prepared by adding synthetic layered silicates (LS) via the latex compounding route. Further, the dielectric response of polyurethane rubber – alumina particles nano-composites, varying the mean particle diameter, is also examined. The dielectric properties of all systems are studied with parameters the temperature and the frequency of the applied field. Broadband Dielectric Spectroscopy (BDS) has been proved to be a powerful tool for the investigation of molecular mobility, phase changes, conductivity mechanisms and interfacial effects in polymers and complex systems. The dielectric response of nano-composites was examined by means of Broadband Dielectric Spectroscopy (BDS) in the frequency range10-1-106 Hz and temperature interval from -100 o C to +70 o C. Experimental results include relaxation phenomena arising from both the polymeric matrix and the filler. Four distinct relaxation modes were recorded in the spectra of all systems containing PU. They were attributed to interfacial polarization, glass transition (α-relaxation), motion of polar side groups and probably motions of the (CH2)n sequence of the PU chain (β and γ-relaxation). NR is a non polar polymer and thus only its glass/rubber transition is recorded in the low temperature range. Interfacial polarization is present in all composites systems. The dielectric response of polyurethane/boehmite alumina nano-composites was examined with an additional parameter, the size of the mean boehmite particle diameter. In order of ascending relaxation rate the following modes were recorded: interfacial polarization, glass/rubber transition (α-mode), motion of polar side groups (β-mode) and re-arrangements of small parts of the PU chain (γ-mode). The intensity and the position of these relaxations appear to vary with the size of the nano-filler. Finally, the activation energies of all the recorded processes were determined via the loss peak dependence on temperature.

Soft iterative detection and decoding techniques have been shown to be able to achieve near-capacity performance in multiple-antenna systems. To obtain the optimal soft information by marginalization over the entire observation space is intractable; and the current literature is unable to guide us towards the best way to obtain the suboptimal soft information. In this thesis, several existing soft-input soft-output (SISO) detectors, including minimum mean-square error-successive interference cancellation (MMSE-SIC), list sphere decoding (LSD), and Fincke-Pohst maximum-a-posteriori (FPMAP), are examined. Prior research has demonstrated that LSD and FPMAP outperform soft-equalization methods (i.e., MMSE-SIC); however, it is unclear which of the two scheme is superior in terms of performance-complexity trade-off. A comparison is conducted to resolve the matter. In addition, an improved scheme is proposed to modify LSD and FPMAP, providing error performance improvement and a reduction in computational complexity simultaneously. Although list-type detectors such as LSD and FPMAP provide outstanding error performance, issues such as the optimal initial sphere radius, optimal radius update strategy, and their highly variable computational complexity are still unresolved. A new detection scheme is proposed to address the above issues with fixed detection complexity, making the scheme suitable for practical implementation. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-07-08 19:29:17.66

Perfect slice sampling is a method to turn Markov Chain Monte Carlo (MCMC) samplers into exact generators for independent random variates. The originally proposed method is rather slow and thus several improvements have been suggested. However, two of them are erroneous. In this article we give a short introduction to perfect slice sampling, point out incorrect methods, and give a new improved version of the original algorithm. (author's abstract) / Series: Preprint Series / Department of Applied Statistics and Data Processing

This dissertation presents an investigation into two so-called live art works – Ugly girl at the rugby (1998) and Chandelier (2001-2002) – by the contemporary South African artist Steven Cohen (1962-). These works are explored with reference to the manner in which Cohen (as self-declared queer Jewish freak) uses performance art as a form of activism in order to expose practices of marginalisation and suppression (oppression) of non-normative or so-called deviant subject positions in terms of gender, race and ethnicity. The analysis of artworks is guided by the discourse of the carnavalesque and performative conceptualisations of gender with particular emphasis on Cohen’s use of drag as contemporary form of masquerade in order to propose an alternative subject position. The argument is as follows: that Cohen, by setting up an extreme alternative to normative identity constructs, manages to destabilise existing hierarchies that are structured according to binaries as these exist in spaces (such as a rugby stadium and a squatter camp) in the South African context. This destabilising of binary hierarchies gives rise to the argument that the symbolically encoded nature of spaces known for associations of suppression, exclusion and marginalisation are wrought open so that alternative meanings can come into being by activating these spaces as multifaceted and chronotopic constructs. The conclusion is that Cohen contributes profoundly towards the destabilisation of identities and in this way also helps to propose invigorating and fresh views of gender, race and ethnicity in a contemporary South African situation. / Thesis (MA (History of Art))--North-West University, Potchefstroom Campus, 2013.

This dissertation presents an investigation into two so-called live art works – Ugly girl at the rugby (1998) and Chandelier (2001-2002) – by the contemporary South African artist Steven Cohen (1962-). These works are explored with reference to the manner in which Cohen (as self-declared queer Jewish freak) uses performance art as a form of activism in order to expose practices of marginalisation and suppression (oppression) of non-normative or so-called deviant subject positions in terms of gender, race and ethnicity. The analysis of artworks is guided by the discourse of the carnavalesque and performative conceptualisations of gender with particular emphasis on Cohen’s use of drag as contemporary form of masquerade in order to propose an alternative subject position. The argument is as follows: that Cohen, by setting up an extreme alternative to normative identity constructs, manages to destabilise existing hierarchies that are structured according to binaries as these exist in spaces (such as a rugby stadium and a squatter camp) in the South African context. This destabilising of binary hierarchies gives rise to the argument that the symbolically encoded nature of spaces known for associations of suppression, exclusion and marginalisation are wrought open so that alternative meanings can come into being by activating these spaces as multifaceted and chronotopic constructs. The conclusion is that Cohen contributes profoundly towards the destabilisation of identities and in this way also helps to propose invigorating and fresh views of gender, race and ethnicity in a contemporary South African situation. / Thesis (MA (History of Art))--North-West University, Potchefstroom Campus, 2013.

Natural coarse textured soils comprise a significant portion (approximately 20%) of the area to be mined at Suncor, Syncrude (aurora mine), Albian/Shell, and CNRL mines in the Alberta’s oil sands (Macyk, 2006). Although similar in soil textural classifications, the undisturbed areas support a range of ecosite types which exhibit different moisture regimes, suggesting that there are natural mechanisms controlling the plant available water sufficient for forest development. The global objective of this study was to evaluate the potential for textural variability to enhance water storage in coarse textured soil. The observations of the infiltration and drainage behaviour of natural and reclaimed coarse-texture soils in this study have demonstrated that this potential exists and can be applied in reclamation design to achieve the ranges of soil water storage needed to establish different ecosites. Field based infiltration and drainage testing, pit excavation and sampling have been completed on 14 sites (7 natural and 7 reclaimed). Bulk saturated hydraulic conductivity and field capacity were estimated for each of the 14 sites based on the field test results. The observed transient water dynamics give an indication of the effect of layering on these material properties. Laboratory analysis of water content (650 samples), particle size (650 samples), water retention (35 samples), organic carbon (100 samples) as well as calibration of field instrumentation were completed on a large number of samples (approximate values shown in brackets above) across all sites. The laboratory analysis was used to characterize textural variability (mean and standard deviation of the particle diameter) for the layered sites and estimate the soil water retention curve (SWRC) relationships for the range of soil textures encountered at the study sites. Pedotransfer functions (PTFs) were used to investigate if there were significant differences in the residual sum of squares between estimated and measured SWRCs. The measured organic carbon was used to aid in estimating permanent wilting point (WP) used in the calculation of the available water holding capacity (AWHC) of all profiles. An investigation into the calibration of the moisture capacitance probe (MCP) was undertaken as part of a comparison of the measured and simulated volumetric water content (VWC) profiles. Water storage at the cessation of drainage was related to the soil texture and textural variability as measured in the laboratory. Sites with more textural variability generally stored more water for plant use. There appeared to be a limit to what can be considered ‘useful’ textural variability. If adjacent soil layers had too extreme a contrast in texture and therefore hydraulic conductivity, unstable/preferential flow (i.e. bypassing of some of the water and nutrients from plant roots) occurred. The total porosity calculated from field samples was often higher than the maximum measured VWC in each layer which may be indicative of one or more factors that resulted in less than full saturation being attained within the targeted 1 m depth of saturation during the test. Some of these factors include: errors in sampling leading to an overestimate of total porosity; lateral flow along textural interfaces; air entrapment within the rapidly advancing wetting front; unstable/preferential flow as a result of the high contrast in hydraulic conductivity (fine over coarse) between adjacent layers (i.e. Ks Ratio >20) or where tests were conducted on slopes (i.e. funnel flow). This latter case was common at the reclaimed sites. A modelling study of one uniform (SV10) and one layered (NLFH1) natural site was conducted. The models were built by incorporating soil properties of the layers in the various soil profiles as estimated from field and/or laboratory testing. This study offers a comparison between various PTFs and their ability to capture the soil-water storage/dynamics during infiltration and drainage testing. The Arya PTF gave a better estimation of the laboratory measured SWRCs. However, when modeling the measured infiltration and drainage testing for the relatively uniform site SV10, the Arya PTF and Modified Kovacs (MK) PTF performed similarly. The Arya PTF performing slightly better for the infiltration phase and the MK PTF performing slightly better for the drainage phase. Both PTFs gave a reasonable estimation of water storage but the MK PTF gave a better estimation of the water storage with time as compared to the Arya PTF. For the highly layered site NLFH1, neither model performed well. The Arya PTF gave a substantially better estimation of the infiltration phase and gave the better estimation of the magnitude of water storage with time, the MK PTF performed marginally better for the drainage phase and gave a better estimation of the shape of the water storage with time. Generally, the study showed that the replication of the profile water storage requirements for the layered natural ecosites (‘b’ and ‘d’ ecosites) has been achieved and can be achieved by layering (or even mixing) available coarse textured reclamation materials. This study has indicated that replicating the highly uniform ecosites (‘a’ ecosites) is where the bigger challenge lies in reclamation. Reclaiming with a diversity of target ecosites is essential to achieving the pre-disturbance land capability standard that the mine operators are bound by. The temptation may exist to simply condone reclamation that has met or exceeded the pre-exisiting land capability. However, problems with ground water recharge and regional water distribution are likely to arise if large areas of lower functioning ecosites are replaced with higher functioning ecosites.

Understanding the bearing response of the footings on layered soils has always been a challenge for researchers. Due to the limitations of analytical and empirical solutions it had been difficult to understand the true bearing behavior. Some researchers have tried solving this problem by numerical analysis and have found some success. In this study the numerical analysis approach has been applied using a commercial tool FLAC (Fast Lagrangian Analysis of Continua) to study the bearing response of surface footings on layered clays. First, small deformation analyses were taken up to study the undrained bearing response of strip and circular footings resting on a horizontally layered strong over a soft clay foundation, and then over soft over strong clay foundation. In the end application of large strain mode of FLAC was explored to investigate the large deformation behavior of the strip footing resting on the surface of a strong over soft clay foundation. All models were run by applying velocity loading and a elastic-perfectly plastic Tresca yield criterion has been used. The results are compared with published Finite Element Method (FEM) results, and with analytical, empirical and semi-empirical solutions. It was found that bearing capacity results from the present small-strain FLAC analyses agree well with the FEM results. However, these results in most of the cases tend to differ (as much as 49% for certain layered clay foundations) from those predicted with analytical, empirical and semi-empirical solutions, mainly due to the assumptions made in these solutions. Since no such assumptions are made in the present FLAC analyses, the results and the methodology of this thesis can be applied to predict the bearing capacity of the practical problems. Application of the large-strain mode of FLAC to study the large deformation of shallow foundations has pointed out a limitation of FLAC in completing such analyses. However, it is observed from the early trends of these analyses that whereas the small deformation analysis may under estimate the ultimate bearing capacity for certain cases of layered foundations where the upper clay is moderately stiffer than the lower clay layer, it might also over predict the ultimate bearing capacity for other cases when the upper clay is very stiff in comparison to the lower clay layer.

Understanding the bearing response of the footings on layered soils has always been a challenge for researchers. Due to the limitations of analytical and empirical solutions it had been difficult to understand the true bearing behavior. Some researchers have tried solving this problem by numerical analysis and have found some success. In this study the numerical analysis approach has been applied using a commercial tool FLAC (Fast Lagrangian Analysis of Continua) to study the bearing response of surface footings on layered clays. First, small deformation analyses were taken up to study the undrained bearing response of strip and circular footings resting on a horizontally layered strong over a soft clay foundation, and then over soft over strong clay foundation. In the end application of large strain mode of FLAC was explored to investigate the large deformation behavior of the strip footing resting on the surface of a strong over soft clay foundation. All models were run by applying velocity loading and a elastic-perfectly plastic Tresca yield criterion has been used. The results are compared with published Finite Element Method (FEM) results, and with analytical, empirical and semi-empirical solutions. It was found that bearing capacity results from the present small-strain FLAC analyses agree well with the FEM results. However, these results in most of the cases tend to differ (as much as 49% for certain layered clay foundations) from those predicted with analytical, empirical and semi-empirical solutions, mainly due to the assumptions made in these solutions. Since no such assumptions are made in the present FLAC analyses, the results and the methodology of this thesis can be applied to predict the bearing capacity of the practical problems. Application of the large-strain mode of FLAC to study the large deformation of shallow foundations has pointed out a limitation of FLAC in completing such analyses. However, it is observed from the early trends of these analyses that whereas the small deformation analysis may under estimate the ultimate bearing capacity for certain cases of layered foundations where the upper clay is moderately stiffer than the lower clay layer, it might also over predict the ultimate bearing capacity for other cases when the upper clay is very stiff in comparison to the lower clay layer.

This thesis focuses on developing of a distributed, efficient and fault tolerant multiresolutional architecture for sensor networks. For demonstrative purpose, a powerful simulation environment using 3D environment model has been developed. The robot network is composed of autonomous robots capable of working cooperatively equipped with single typed simple sensor. The developed layered control architecture is hybrid including both subsumption and motor schema control strategies. In this proposed control method, behaviors in different or in same layer are coordinated with an evaluator unit that overcomes the difficulties of subsumption based architectures in terms of behavioral coordination. The final coordination between these layers is achieved cooperatively. We performed many simulation experiments to test robot deployment, search and task execution. It is shown that some important parameters such as target reaching time, energy consumption, and communication range can be optimized if an approximate prior information about the environment is known. Robots executes task based on a task allocation algorithm. Market based auction method is used as a task allocation algorithm with completely different robot fitness evaluation method allowing a distributive problem solving. Six non-linear fitness functions are developed to increase the fairness, and fault tolerance of task allocation. These functions have been tested to represent the successes and failures of robots in a compact form. Performance analyses test results have shown that fairness increases two times more in task allocation when these fitness functions are used, compared to the results existing fitness evaluation methods used in the market based auction algorithms. Moreover, fault tolerance is increased by using fitness functions devoted to failure conditions.