This study investigates the mechanical differences between old and newly produced slatted floors through a four-point bending test. To understand to what extent the actual environment has affected the slatted floors, the carbonation depth and corrosion will be examined. The tests showed no mechanical differences between slatted floors which had been in service for a certain amount of years and newly produces ones. Corrosion could be observed on some of the samples but it was not because of the carbonation process. When comparing the calculations of reinforced and pre-stressed concrete slatted floors, the result showed that the pre-stressed floor could carry up to double the load of what the reinforced slatted floor could. The conclusion of this study is, that the pre-stressed slatted floors will certainly hold for at least thirty years and will most likely hold for many years to come.

Abstract Amorphous Selenium (a-Se) was first commercialized for use as a photoconductor in xerography during the middle of the twentieth century. Since then the hole transport properties of a-Se have been studied extensively, however the study of electron transport remains relatively limited. Flat panel digital X-ray detectors using a-Se as a photoconductor have been developed and are being used in mammographic screening. The charge transport properties of the photoconductor layer will in part determine the performance of the flat panel detector. X-ray absorption causes electron-hole pair generation in the bulk of the photoconductor, requiring both electrons and holes to drift across the sample and be collected. If these carriers are lost in the many localized trapping states as they cross the sample, they will not contribute to the image signal resulting in unnecessary radiation exposure to the patient. Eleven a-Se samples were deposited at the University of Saskatchewan varying in thickness from 13 μm to 501 μm. Pure a-Se was chosen to ensure uniformity across the thickness of the samples, that is, to ensure the composition of the film did not change across the thickness. Time of flight transient photoconductivity experiments (TOF) and interrupted field time of flight (IFTOF) measurements were performed to measure the electron drift mobility and lifetime respectively. The product of electron drift mobility μ and lifetime τ, hence the carrier range (μτ) at a given applied electric field. The electron range is an important parameter as this places limits on the practical thickness of the photoconducting layer in a detector. This study also includes an investigation into the effect of the definition of transit time on the calculated drift mobility and analysis of the dispersive transport properties of a-Se. It was observed that as sample thickness (L) increased, electron drift mobility (μ) decreased. In addition electron lifetime (τ) decreased dramatically in samples thinner than 50 μm. Electron range (μτ) was 2.26 × 〖10〗^(-6) cm^2/V in the 147μm sample and 5.46 × 〖10〗^(-8) cm^2/V in the 13 μm sample, a difference of almost two orders of magnitude. The comparison of the half current method and inflection point methods to calculate the transit time of the same TOF curve, shows that the calculated mobility can vary by as much as 24%. This illustrates clearly that it is important to use the same point on the TOF curve to define the transit time. Charge packet dispersion (spread) in the time domain in pure a-Se samples was proportional to L^m where L is the photoconductor thickness and m ~ 1.3, measured at both 1 V/μm and 4 V/μm.

Given the increase in popularity of Lifetime Value (LTV), the argument is that the topic will assume an increasingly central role in research and marketing. As such, the decision to assess the state of the field in Lifetime Value Modelling, and outline challenges unique to choice researchers in customer relationship management (CRM). As the research has argued, there are an excess of issues and analytical challenges that remain unresolved. The researcher hopes that this thesis inspires new answers and new approaches to resolve LTV. The scope of this project covers the building of a LTV model through multiple regression. This thesis is exclusively focused on modelling tenure. In this regard, there are a variety of benchmark statistical techniques arising from survival analysis, which could be applied, to tenure modelling. Tenure prediction will be looked at using survival analysis and compared with "crossbreed" data mining techniques that use multiple regression in concurrence with statistical techniques. It will be demonstrated how data mining tools complement the statistical models, and show that their mutual usage overcomes many of the shortcomings of each singular tool set, resulting in LTV models that are both accurate and comprehensible. Bank XYZ is used as an example and is based on a real scenario of one of the Banks of South Africa. / Thesis (M.Sc. (Computer Science))--North-West University, Vaal Triangle Campus, 2009.

Adhesive bonding is one of the most attractive joining techniques for any structural application, including high profile examples in the aerospace, automotive, marine construction and electrical industries. Advantages of adhesive bonding include; superior fatigue performance, better stress distribution and higher stiffness than conventional joining techniques. When the design of bonded joints is considered, fatigue is of critical importance in most structural applications. There are two main issues that are of importance; a) in-service damage characterisation during fatigue loading and, b) lifetime prediction under both constant and variable amplitude fatigue loading. If fatigue damage characterisation is considered, there has been some work to characterise damage in-situ using the backface strain (BFS) measurement technique, however, there has been little investigation of the effects of different types of fatigue behaviour under different types of geometry and loading. Regarding fatigue lifetime prediction of bonded joints, most of the work in the literature is concentrated with constant amplitude fatigue, rather than variable amplitude fatigue. Fatigue design of a bonded structure based on constant amplitude fatigue, when the actual loading on the structure is of the variable amplitude fatigue, can result in erroneous lifetime prediction. This is because of load interaction effects caused by changes in load ratio, mean load etc., which can decrease the fatigue life considerably. Therefore, the project aims to a) provide a comprehensive study of the use of BFS measurements to characterise fatigue damage, b) develop novel techniques for predicting lifetime under constant amplitude fatigue and c) provide an insight into various types of load interaction effects. In this project, single lap joints (SLJ) and compound double cantilever beam geometries were used. Compound double cantilever beams were used mainly to determine the critical strain energy release rate and to obtain the relationship between strain energy release rate and fatigue crack growth rate. The fatigue life of SLJs was found to be dominated by crack initiation at lower fatigue loads. At higher fatigue loads, fatigue life was found to consist of three phases; initiation, stable crack propagation and fast crack growth. Using these results, a novel damage progression model was developed, which can be used to predict the remaining life of a bonded structure. A non-linear strength wearout model (NLSWM) was also proposed, based on strength wearout experiments, where a normalised strength wearout curve was found to be independent of the fatigue load applied. In this model, an empirical parameter determined from a small number of experiments, can be used to determine the residual strength and remaining life of a bonded structure. A fracture mechanics approach based on the Paris law was also used to predict the fatigue lifetime under constant amplitude fatigue. This latter method was found to under-predict the fatigue life, especially at lower fatigue loads, which was attributed to the absence of a crack initiation phase in the fracture mechanics based approach. A damage mechanics based approach, in which a damage evolution law was proposed based on plastic strain, was found to predict the fatigue life well at both lower and higher fatigue loads. This model was able to predict both initiation and propagation phases. Based on the same model, a unified fatigue methodology (UFM) was proposed, which can be used to not only predict the fatigue lifetime, but also various other fatigue parameters such as BFS, strength wearout and stiffness wearout. The final part of the project investigated variable amplitude fatigue. In this case, fatigue lifetime was found to decrease, owing to damage and crack growth acceleration in various types of variable amplitude fatigue loading spectra. A number of different strength wearout approaches were proposed to predict fatigue lifetime under variable amplitude fatigue loading. The NLSWM, where no interaction effects were considered was found to over-predict the fatigue life, especially at lower fatigue loads. However, approaches such as the modified cycle mix and normalised cycle mix approaches were found to predict the fatigue life well at all loads and for all types of variable amplitude fatigue spectra. Progressive damage models were also applied to predict fatigue lifetime under variable amplitude fatigue loading. In this case a fracture mechanics based approach was found to under-predict the fatigue life for all types of spectra at lower loads, which was established to the absence of a crack initiation phase in this method. Whereas, a damage mechanics based approach was found to over-predict the fatigue lifetime for all the types of variable amplitude fatigue spectra, however the over- prediction remained mostly within the scatter of the experimental fatigue life data. It was concluded that, the damage mechanics based approach has potential for further modification and should be tested on different types of geometry and spectra.

No description available.

The first part of this thesis deals with the study of mesoscopic fluctuations of the Coulomb drag resistance in double-layer GaAs/AlGaAs heterostructures, both in weak magnetic fields and strong magnetic fields. In the second part, measurements are made in a monolayer graphene structure, specifically of the quantum lifetime, and the mesoscopic resistance fluctuations at quantising magnetic fields.

Le challenge de la consommation d'énergie dans les réseaux de capteurs sans fil constitue un verrou technologique qui reste un problème ouvert encore aujourd'hui. Ces travaux de thèse s'inscrivent dans la problématique de la conservation de l'énergie dans les réseaux de capteurs et s'articulent autour de deux axes. Dans la première partie, nous abordons le dimensionnement des protocoles de découverte de voisinage. Nous proposons deux techniques de dimensionnement de ces protocoles qui visent à optimiser la consommation d'énergie des nœuds capteurs. La première technique, PPM-BM, consiste à dimensionner le protocole de découverte de voisins en fonction du niveau de batterie du nœud. La deuxième approche, ECoND, vise à ajuster la fréquence de découverte de voisins en fonction de la connectivité estimée à chaque instant. Cette technique tire profit des cycles temporels des modèles de mouvement des nœuds. La connectivité est estimée en se basant sur l'historique des rencontres. La découverte de voisins est ajustée en fonction du taux de connectivité estimé. Les résultats enregistrés mettent en évidence l'efficacité de ces deux techniques dans l'optimisation de la consommation d'énergie des nœuds sans affecter les performances de taux de livraison de messages et d'overhead. La deuxième partie de la thèse concerne l'optimisation des performances des réseaux de capteurs en termes de durée de vie. Nous reconsidérons dans cette partie certains protocoles de routage relevant du domaine des réseaux à connectivité intermittente et nous proposons le protocole EXLIOSE qui se base sur la capacité d'énergie résiduelle au niveau des nœuds pour assurer un équilibre énergétique, partager la charge et étendre à la fois la durée de vie des nœuds ainsi que celle du réseau / The challenge of energy consumption in wireless sensor networks is a key issue that remains an open problem. This thesis relates to the problem of energy conservation in sensor networks and is divided into two parts. In the first part, we discuss the design of neighbor discovery protocols. We propose two techniques for modulating these protocols in order to optimize the energy consumption of sensor nodes. The first technique, PPM-BM aims to modulate the neighbor discovery protocol based on the battery level of the node. The second approach ECoND aims to set up the frequency of neighbor discovery based on estimated connectivity. This technique takes advantage of the temporal cycles of nodes' movement patterns. Connectivity is estimated based on encounters' history. A neighbor discovery is set up based on the estimated rate of connectivity. The achieved results demonstrate the effectiveness of these techniques in optimizing the energy consumption of nodes while maintaining acceptable message delivery and overhead rates. In the second part of the thesis, we contribute to the optimization of the performance of sensor networks in terms of network lifetime. We review in this section some routing protocols for networks with intermittent connectivity and we propose EXLIOSE protocol which is based on residual energy to ensure energy-balancing, load sharing and network lifetime extending

Depuis ces dernières années, les composants fortement submicroniques du commerce sont utilisés dans les équipements aéronautiques pour des applications spécifiées pour durer plusieurs décennies. Toutefois, ces composants sont destinés aux marchés de masse que représentent les secteurs de la micro informatique et des télécommunications et ne sont pas spécifiques au marché aéronautique. De ce fait, ces composants sont spécialement conçus pour des besoins dits de haute performance ou de basse consommation et pour lesquels la fiabilité n’est pas un critère prioritaire. Pour satisfaire ces marchés, une nouvelle génération technologique émerge tous les deux ans en imposant à chaque fois, une diminution des dimensions des métallisations BEOL ainsi que des transistors FEOL et/ou l’introduction de nouveaux matériaux. Ces modifications ont conduit à une aggravation des mécanismes de défaillance par usure pour les générations de composants fortement submicroniques, au point de ne plus satisfaire les spécifications en durée de vie des équipements aéronautiques. Cette étude s’attache donc à montrer l’impact que peuvent avoir la réduction des dimensions ainsi que la nature des matériaux, sur la durée de vie des technologies numériques CMOS 500 à 45 nm. Pour cela, les mécanismes de défaillances du circuit intégré ont été modélisés et étudiés au travers de trois applications aéronautiques. En complément, des tests de vieillissement de type HCI et NBTI pratiqués sur une SRAM de génération 90 nm ont permis de valider les prédictions. Enfin, les travaux aboutissent à une méthodologie de sélection de composants fortement submicroniques pour une application spécifique, en fonction de la technologie. / For some years, deep sub micron components have been used in aeronautic equipment for long term applications (generally few decades). However, these components are devoted to mass markets that are basically microcomputers and telecommunications and not especially to aeronautics. Hence, deep sub micron components are manufactured for high performance and low consumption needs and unfortunally, reliability is not the main concern. In order to supply these markets, a new generation of components generally arise every two years, introducing BEOL and FEOL scaling and/or new materials. As a consequence, these improvements have induced a lifetime degradation of devices that can threaten their use for longtime specifications of aeronautic equipement. This study points out the effects of scaling and material improvements on the lifetime degradation of CMOS integrated cicuits between the nodes 500-45 nm. To do so, silicon failure mechanisms have been modelised and investigated on three aeronautic applications. As a complement, some HCI and NBTI lifetests have been performed on 90 nm SRAM in order to validate previous lifetime predictions. Finally, this work leads to a methodology for the selection of deep sub micron components for a specific use, depending on the technology.

Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating's final thermal and mechanical properties, and the service lives of the coatings. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, December 2014. / Industrial units cannot operate without failure forever. When the operation of a unit deviates from industrial standards, it is considered to have failed. The time from the moment a unit enters service until it fails is its lifetime. Within reliability and often in life data analysis in general, lifetime is the event of interest. For highly reliable units, accelerated life testing is required to obtain lifetime data quickly. Accelerated tests where failure is not instantaneous, but the end point of an underlying degradation process are considered. Failure during testing occurs when the performance of the unit falls to some specified threshold value such that the unit fails to meet industrial specifications though it has some residual functionality (degraded failure) or decreases to a critical failure level so that the unit cannot perform its function to any degree (critical failure). This problem formulation satisfies the random signs property, a notable competing risks formulation originally developed in maintenance studies but extended to accelerated testing here. Since degraded and critical failures are linked through the degradation process, the open problem of modelling dependent competing risks is discussed. A copula model is assumed and expert opinion is used to estimate the copula. Observed occurrences of degraded and critical failure times are interpreted as times when the degradation process first crosses failure thresholds and are therefore postulated to be distributed as inverse Gaussian. Based on the estimated copula, a use-level unit lifetime distribution is extrapolated from test data. Reliability metrics from the extrapolated use-level unit lifetime distribution are found to differ slightly with respect to different degrees of stochastic dependence between the risks. Consequently, a degree of dependence between the risks that is believed to be realistic to admit is considered an important factor when estimating the use-level unit lifetime distribution from test data. Keywords: Lifetime; Accelerated testing; Competing risks; Copula; First passage time.