Yes / Sheet specimens of a PLLA-based polymer have been extended at a temperature near to the glass transition in both uniaxial and planar tension, with stress relaxation observed for some time after reaching the final strain. Both axial and transverse stresses were recorded in the planar experiments. In all cases during loading, yielding at small strain was followed by a drop in true stress and then strain hardening. This was followed by stress relaxation at constant strain, during which stress dropped to reach an effectively constant level. Stresses were modelled as steady state and transient components. Steady-state components were identified with the long-term stress in stress relaxation and associated with an elastic component of the model. Transient stresses were modelled using Eyring mechanisms. The greater part of the stress during strain hardening was associated with dissipative Eyring processes. The model was successful in predicting stresses in both uniaxial and planar extension over a limited range of strain rate.

Gaining a quantitative understanding of metabolic behaviour has long been a major scientific goal. Beginning with crude mass balance experiments and progressing through enzyme kinetics, single-pathway models and collaborative efforts such as a community- based yeast reconstruction and onwards to the digital human. The primary goal of this research was to generate a large-scale kinetic metabolic model of yeast metabolism. As a community our ability to produce large-scale dynamic metabolic models has typically been limited by the time and cost involved in obtaining exact measurements of all relevant kinetic parameters. Attempts have been made to bring about a greater understanding by using computational approaches such as flux balance analysis, and also laboratory approaches such as metabolic profiling. Unfortunately these approaches alone do not go far enough to allow for a rich understanding of the metabolic behaviour.Methods were developed that allowed known data such as fluxes, equilibrium constants and metabolite concentrations to be used in first-approximation strategies. These made possible the construction of a thermodynamically consistent model that was reflective of the organism and growth conditions under which the known data were measured. Efforts were made to improve the strategy by developing already known dynamic flux measurement techniques so they were more reflective of the type of data required for constructing the metabolic model. The model constructed, using data from a specific yeast strain in a continuous culture environment, and included 284 reactions. The model showed a reasonable reproduction of system behaviour after perturbations of extracellular glucose above and below the operating conditions, after identification and substitution of just two exact rate laws of reactions that showed high control over the system. The methods developed require little knowledge beyond the stoichiometric matrix in the first instance, and as such, are applicable to any organism that has a reasonably comprehensive network reconstruction available.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In the present study, two-phase natural circulation flow in a multi-parallel channel system was investigated using experimental and numerical modelling. The investigation was carried out under different power excitations and various system operations (open system, closed system and heat pipe mode). The multichannel system was equipped at the upper end with a condenser enclosed within a steam drum, while the lower portion of each channel was heated to heat the system. For the numerical modelling, transient one-dimensional conservation equations were derived from first principle for both single- and two-phase fluids and used to computer program the system’s discretised simulation model. Temperatures and mass flow rates of the fluid responses as a result of different power excitations and operations were obtained for both the experimental and numerical modelling. It was observed from the results that the fluid experiences a start-up transient before accomplishing steady-state conditions. It was further noted that the transient duration varies with power excitations and system operation modes and hence with the stability of the system. A rise in power proved not to necessarily increase the fluid mass flow rate, but invited oscillations with higher amplitudes, depending on the system’s mode of operation. Type I instability and low-quality steam oscillations were witnessed at low power and open system operation mode (system open to the atmosphere). Type II instabilities and flashing instability were observed to be associated with medium and high-power excitations for the open system mode of operation. The fluid flow became more stable and less oscillatory at all power excitations for the closed system operation mode (system not open to the atmosphere). However, a sub-cooling effect was evident at higher power, where the two-phase fluid temperatures oscillated in a sinusoidal manner. However, the mass flow rates oscillated with high amplitudes in the forward direction in some channels and assumed a unidirectional flow in other channels. In general, steady-state conditions were obtained earlier when the system was operated as a closed system. For the heat pipe mode of operation, the system transient response in all channels exhibited a geysering instability followed by flashing-induced boiling. In-phase (flow in channels exhibiting the same behaviour) and out-of-phase (flow in channels exhibiting contradictory conduct) behaviour between adjacent channels were observed at all power excitations and system operation modes. Flow reversal in heated channels of a natural circulation system were proven to exists even under equal power excitations. / AFRIKAANSE OPSOMMING: In hierdie studie is tweefasige natuurlike sirkulasievloei in ’n parallelle multikanaalstelsel ondersoek deur middel van eksperimentele en numeriese modellering. Die ondersoek is onder verskillende kragopwekkings en verskeie stelselwerkings (oop stelsel, toe stelsel en hittepypmodus). Die multikanaalstelsel is aan die bopunt met ’n kondensor binne ’n stoomdrom toegerus, terwyl die laer gedeelte van elke kanaal verhit is om die stelsel te verhit. Vir die numeriese modellering, is oorgangseendimensionele behoundsvergelykings vanaf die eerste beginsel vir beide een- en tweefasige vloeistowwe afgelei en dit is gebruik om die stelsel se gediskretiseerde simulasiemodel vir ’n rekenaar te programmeer. Temperature en massavloeitempo’s van die vloeistofrespons as gevolg van verskillende kragopwekkings en -werkings is vir beide die eksperimentele en die numeriese modellering verkry. Dit is in die resultate waargeneem dat die vloeistof ’n aansitoorgang ervaar voor dit vloeiewewigstoestande bereik. Daar is verder waargeneem dat die duur van die oorgang wissel volgens kragopwekkings en stelselwerkingsmodusse en dus op grond van die stabiliteit van die stelsel. ’n Toename in krag het nie noodwendig die vloeitempo van die vloeistofmassa verhoog nie, maar het aanleiding gegee tot ossillasies met groter amplitudes, afhangende van die stelsel se metode van werking. Tipe I-onstabiliteit en stoom-ossillasies van ’n lae intensiteit is teen lae krag en oop stelselwerkingsmodus waargeneem (stelsel oop aan die atmosfeer). Tipe II-onstabiliteit en flitsingsonstabiliteit (flashing instability) is met medium- en hoë kragopwekkings vir die oop stelsel modus van werking waargeneem. Die vloeistofvloei het meer stabiel en minder ossillerend geraak by alle kragopwekkings in die geslote stelsel van werking (stelsel nie oop na die atmosfeer nie). ’n Subverkoelingseffek was egter teen hoër krag duidelik, waar die tweefasige vloeistof se temperature sinusvormig geossilleer het. Die massavloeitempo’s het egter met hoë amplitudes in die vorentoe rigting in sommige kanale gevloei en eenrigtingvloei in ander kanale vertoon. Oor die algemeen is vloei-ewewigstoestande vroeër verkry toe die stelsel as ’n geslote stelsel bedryf is. Vir die hittepypmodus van werking het die stelsel se oorgangsweergawe in alle kanale ’n geysering onstabiliteit getoon, gevolg deur flitsinggeïnduseerde (flashing induced) kook. Gelykfasige gedrag (vloei in kanale vertoon dieselfde gedrag) en ongelykfasige gedrag (vloei in kanale vertoon teenstrydige gedrag) tussen langsliggende kanale is met al die kragopwekkings en stelselwerkingsmodusse waargeneem. Vloei-omkering in die verhitte kanale van ’n natuurlike sirkulasiestelsel is bewys om selfs onder gelyke kragopwekkings te bestaan.

Discovering a word’s part of speech is an essential step in acquiring the grammar of a language. In this thesis we examine a variety of computational Bayesian models that use linguistic input available to children, in the form of transcribed child directed speech, to learn part of speech categories. Part of speech categories are characterised by contextual (distributional/syntactic) and word-internal (morphological) similarity. In this thesis, we assume language learners will be aware of these types of cues, and investigate exactly how they can make use of them. Firstly, we enrich the context of a standard model (the Bayesian Hidden Markov Model) by adding sentence type to the wider distributional context.We show that children are exposed to a much more diverse set of sentence types than evident in standard corpora used for NLP tasks, and previous work suggests that they are aware of the differences between sentence type as signalled by prosody and pragmatics. Sentence type affects local context distributions, and as such can be informative when relying on local context for categorisation. Adding sentence types to the model improves performance, depending on how it is integrated into our models. We discuss how to incorporate novel features into the model structure we use in a flexible manner, and present a second model type that learns to use sentence type as a distinguishing cue only when it is informative. Secondly, we add a model of morphological segmentation to the part of speech categorisation model, in order to model joint learning of syntactic categories and morphology. These two tasks are closely linked: categorising words into syntactic categories is aided by morphological information, and finding morphological patterns in words is aided by knowing the syntactic categories of those words. In our joint model, we find improved performance vis-a-vis single-task baselines, but the nature of the improvement depends on the morphological typology of the language being modelled. This is the first token-based joint model of unsupervised morphology and part of speech category learning of which we are aware.

The effects of lime treatment on the mechanical properties of soils are usually not accounted for in the design of geotechnical structures. As a result the potential of lime treatment has not been fully exploited. In this thesis, a comprehensive experimental program has been carried out to identity the key features of the mechanical behaviour of structured materials. The chemical modifications arising from lime treatment were quantified using thermal analysis methods. From these results a non-linear chemo-mechanical coupling was established between the concentration of cementitious compounds and the yield stress. Using these results, a new formulation to model the degradation of the structure at yield has been developed and implemented in a constitutive model for structured materials. This new model, developed in the framework of the Modified Cam Clay model, requires a limited number of additional parameters that all have a physical meaning and can all be determined from a single isotropic compression test. The model has proven to be successful in reproducing the key features of structured materials and for the modelling of the mechanical behaviour of lime treated specimens under various stress paths. Due to similarities in behaviour, it is shown that the formulation is also suitable for naturally structured soils. To account for a structured material in the design of geotechnical structures, a fully functional finite element program for elasto-plastic problems was developed including the pre- and post-processing of the results. A thorough validation has confirmed the good implementation of the finite element method and its suitability for the modelling of complex geometries involving structured materials.

This work outlines the design and implementation of an algorithm to simulate two-polarisation bowed string motion, for the purpose of realistic sound synthesis. The algorithm is based on a physical model of a linear string, coupled with a bow, stopping fi ngers, and a rigid, distributed fingerboard. In one polarisation, the normal interaction forces are based on a nonlinear impact model. In the other polarisation, the tangential forces between the string and the bow, fingers, and fingerboard are based on a force-velocity friction curve model, also nonlinear. The linear string model includes accurate time-domain reproduction of frequency-dependent decay times. The equations of motion for the full system are discretised with an energy-balanced finite difference scheme, and integrated in the discrete time domain. Control parameters are dynamically updated, allowing for the simulation of a wide range of bowed string gestures. The playability range of the proposed algorithm is explored, and example synthesised gestures are demonstrated.

Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this thesis, the seismic performance of such slopes in non-liquefiable granular soils has been investigated and an extensive programme of centrifuge testing was conducted to quantify the improvements to seismic slope performance which can be achieved by installing a row of discretely spaced vertical precast concrete piles. This study focussed on permanent movement and dynamic response at different positions within the slope, especially at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge modelling, analytical (sliding-block) and numerical (Finite Element) models. This thesis makes three major contributions. Firstly, an improved sliding-block (‘Newmark’) approach is developed for estimating permanent deformations of unreinforced slopes during preliminary design phases, in which the formulation of the yield acceleration is fully strain-dependent, incorporating the effects of both material hardening/softening and geometric hardening (re-grading). This is supported by the development of numerical (Finite Element) models which can additionally predict the settlement profile at the crest of the slope and also the dynamic ground motions at this point, for detailed seismic design were also developed. It is shown that these new models considerably outperform existing state-of-the art models which do not incorporate the geometric changes for the case of an earthquake on a virgin slope. It is further shown that only the improved models can correctly capture the behaviour under further earthquakes (e.g. strong aftershocks) and therefore can be used to determine the whole-life performance of a slope under a suite of representative ground motions that the slope may see during its design life, and allow improved estimates of the seismic performance of slopes beyond their design life. The finite element models can accurately replicate the settlement profile at the crest (important for highway or rail infrastructure) and quantify the dynamic motions which would be input to supported structures, though these were generally over-predicted. Secondly, the principles of physical modelling have been used to produce realistically damageable model piles using a new model reinforced concrete (both a designed section specifically detailed to carry the bending moments induced by the slipping soil mass and a nominally reinforced section with low moment capacity). This was used to investigate how piles can stabilise slopes under earthquake events and how the permanent deformation and the dynamic response of stabilised slope are strongly influenced by the pile spacing (S/B) especially at the minimum pile spacing (i.e. S/B=3.5). This is consistent with previous suggestions made for the optimal S/B ratio for encouraging soil arching between piles at maximum spacing both under monotonic conditions, and for numerical investigations of the seismic problem. These were supported by further centrifuge tests on conventional ‘elastic’ piles which were instrumented to measure seismic soil-pile interaction. The importance of reinforcement detailing was also highlighted, with the nominally reinforced section yielding early in the earthquake; the damaged piles subsequently only offer a small (though measureable) reduction in seismic slope performance compared to the unreinforced case. It was demonstrated that both permanent deformations at the slope crest (e.g. settlement) and dynamic ground motions at the crest can be significantly reduced as pile spacing reduced. Finally, a coupled P-y and elastic continuum approach for modelling soil-pile interaction has been used to develop a Newmark procedure applicable for pile-reinforced slopes. It was observed that the single pile resistance is mobilising at beginning of the earthquake’s time and it is strongly influenced by pile stiffness properties, pile spacing and the depth of the slip surface. It was observed also that the depth of the slip surface and pile spacing (S/B) play an important role in the determination of the permanent deformation of the slope. The results show great agreement to centrifuge test data in term of the permanent deformation (settlement at the crest of the slope) with slight differences between the measured (centrifuge) and calculated (this procedure) maximum bending moments.

This report aims to covers the conduction of a final thesis project for the University of Skövde in collaboration with J.Design studio (Stockholm). The purpose of this project is applying and evaluating CAD and different tools related to the field of 3D CAD within design and product development phases. This has been achieved by the development of two pieces of furniture from a defined line of products stated by existing clients of J.Design. The initial phase of the project was knowing the design limitations from both clients and their stakeholders. Once these limitations were known, a pre-study phase where 3D CAD modelling was set as the key tool for the research was done. This research identified related tools with CAD that are applied during the development design phase. Starting the development of the two case studies, the user needs’ phase was the first step in the process, followed by a benchmarking study, an ergonomics study, and finally, setting these requirements into a requirement list. Then, the design development phase took place, covering initial sketches until the detailed final solutions. As a final step, the use of the identified tools was evaluated and analysed based on the experience from the two case studies of this thesis project. From this evaluation came the conclusion that these tools need to take part in the design phase in a certain moment depending on the level of development, and as the level of sophistication of the tool increases, the information and detail provided are also higher.

The potential for life to control its environment was first suggested by Lovelock (1972). Charlson et al (1987) proposed a role for marine planktonic ecosystems in global climate regulation via the production and ventilation to the atmosphere of dimethylsulphide (DMS), a by-product of phytoplankton metabolism. Once in the atmosphere DMS contributes to the formation of cloud condensation nuclei, and increases the amount and brightness of cloud. This affects the albedo of the planet, reflecting more incident sunlight back into space, and cooling the earth. In common with many other 'hypotheses' regarding complex adaptive systems, the hypothesis proposed by Charlson et al (1987) is not experimentally testable. The production and ventilation to the atmosphere of DMS is the result of complex interactions between biological, chemical and physical processes. Consequently, increasing use is being made of mathematical models that simulate these processes to advance understanding of it (Archer et al. 2002). This study examines one of the fundamental mechanisms proposed by the Charlson et al (1987) hypothesis, that increasing global temperatures will lead to increased ventilation of DMS from the ocean to the atmosphere. The study develops one-dimensional biogeochemical models of DMS production by upper ocean ecosystems, based on the model proposed by Gabric et al. (1993b). The models are examined to elucidate their fundamental mathematical properties, and are subjected to sensitivity analysis to identify important processes and parameters. These investigations identify a simpler model that can reproduce the predictions of the Gabric et al. (1993b) model. Predictions derived from model simulations forced by climatologies of measured physical data are compared to a global database of measurements of sea surface DMS concentrations, and to observed depth profiles of DMS in the upper ocean. These comparisons confirm that all models are in good qualitative agreement with measured data. The fifteen global climate prediction models currently in use around the globe all predict substantial warming effects from the ventilation of anthropogenic carbon dioxide to the atmosphere. A simplified DMS model is calibrated to climatologies of Antarctic chlorophyll and DMS data and reproduces the data with great precision. The calibrated model is applied in global warming scenarios to 'test' the efficacy of the mechanism proposed by the Charlson et al (1987) hypothesis. This simulation provides evidence that the response predicted by the hypothesis is indeed feasible, and that substantial increases (up to 45%) in the ventilation of DMS to the atmosphere could be possible in some circumstances. The results of the modelling study provide impetus for further examination of field data. If couplings between marine biota and atmosphere are feasible, then they may be operating contemporarily, and may be detectable. Atmospheric DMS is oxidised to form aerosols (Miller et al. 2002) that influence the aerosol optical depth of the atmosphere. Archives of remote sensed ocean chlorophyll a concentration and aerosol optical depth are examined for evidence of the biologically mediated couplings. A clear coupling between aeolian dust and marine phytoplankton is evident from this analysis, suggesting that the deposition of dust from the atmosphere is a major factor controlling phytoplankton growth in many parts of the ocean. A second coupling between marine phytoplankton and atmospheric aerosols is also detected. This coupling is apparently not related to dust and is symmetrical about the equator, despite the substantial differences in the atmospheres and oceans of each hemisphere. It is speculated that this coupling may reflect the influence of the ventilation of DMS produced by marine phytoplankton on the atmosphere. This thesis provides new evidence supporting the important role of marine ecosystems in global climate regulation by the production of DMS. This evidence is principally obtained from a biogeochemical modelling approach, but is supported by analyses of empirical data. The concordance of results obtained from different approaches suggests that the contribution of marine ecosystems to global climate regulation is real, important and currently active.

The opposition between the realists and the anti-realists isas old as Western science. The question as to whether the“furniture of the world”we call the“things”is to be considered real or not hasconsistently been at the forefront in the debates about scienceand philosophy. This urgent interest is motivated by the closeconnection to another question–namely that of scientificobjectivity - an issue that seldom receives proper treatment.Objectivity has rather been taken for granted in thetraditional Newtonian paradigm with its well-known slogan: Thedetached observer is the objective one and the rational mind ofclarity. It was impossible to continue with this dictum, which isresponsible for the cleft between the natural and socialsciences and still presents a ban on human feelings inscientific endeavours, after the findings of quantum mechanicsat the beginning of the 20th century. However the penetratingpower of this important insight has been astonishingly weak andwith the emergence of computer science in the middle of thecentury, Newtonian science’s self-assumed status ofobjectivity has been apprehended as both very doubtful and asevere hindrance in other areas outside the quantum domain ofscientific activity. The efforts of computer modelling andsimulation analysis revealed a pronounced observer-dependencyregarding investigation. For these reasons this thesis will scrutinise the activityof science and the art of modelling–proposing the use ofa 2-step model of modelling (metamodel) to clarify andemphasize the involvement of the observer in the process ofobservation. This approach reveals that the object-orientedapproach (OOA), which has been the prevailing one since thedawn of Western science and is one of the basic tenets of theNewtonian paradigm, makes science unable to describe itsobjects of discourse in an observer-independent manner. Such ascience is at risk to be considered inconsistent, incompleteand non-objective and for that reason unfit for consensualscientific use. The main claim of this thesis is that the object-orientedapproach is responsible for the genesis of Cartesian dualismand other inconsistencies, which are met in present dayscience. Such a claim is not novel however, but I will arguethat when science is dressed up as the Subject-orientedApproach to Knowledge (SOA) a long row of embarrassing andbewildering situations encountered in classical humanconceptualisation will vanish–in a way that, as far as Iknow, has never been explicitly explained before. This approachalso promises a unification of the different disciplines ofsciences so that e.g. the social sciences can be treated on anequal footing with the natural sciences–and thus thisembarrassing gulf of human knowledge can be removed. This is aprofound shift of paradigm in science and the re-orientation ofhuman thinking required is both considerable andtime-consuming. For this reason this thesis is not a systematic presentationof the SOA, but rather tries, in Part 1, to pave the way for anunderstanding of this approach by an introductory discussionabout the means and scope of science and the essential role ofsymbolic modelling in this endeavour–and in particularthe way these activities will be influenced by the anticipatedchange of paradigm. Some historical aspects of this particularSOA are also given as a background and this section iscompleted by a brief survey of the modern trends in scientificmodelling. Part 2 is collection of papers dealing with the principlesof modelling and simulation, and, rather more importantly, asequence of papers reflecting how the ideas of the SOA havedeveloped throughout the years due to the inconsistencies metwith in these and adjacent areas. To my mind they prove -beyond the point of any consensual doubt–that therealist’s position in science cannot be defended anylonger and that the“things of the world”by thescientific community must be considered merely privateallusions. More important however is the insight that the Newtonianparadigm is unable to produce an observer-independentdescription of this world with its conceived things and theonly way out of this embarrassing dilemma seems to be theacceptance of the SOA–with its hitherto strictly bannedfeature of subjectivity. Using this approach, we claim, sciencecan be given a consensual and consistent foundation–andthe price to pay is the loss of scientific ontology. As alreadypointed out this thesis merely hints at the new path to take–instead concentrating on the reasons for the impendingdemise of scientific realism and need of a constructive systemsscience.