Interactive Technologies for the Public Sphere Toward a Theory of Critical Creative Technology

Digital media cultural practices continue to address the social, cultural and aesthetic contexts of the global information economy, perhaps better called ecology, by inventing new methods and genres that encourage interactive engagement, collaboration, exploration and learning. The theoretical framework for creative critical technology evolved from the confluence of the arts, human computer interaction, and critical theories of technology. Molding this nascent theoretical framework from these seemingly disparate disciplines was a reflexive process where the influence of each component on each other spiraled into the theory and practice as illustrated through the Constructed Narratives project. Research that evolves from an arts perspective encourages experimental processes of making as a method for defining research principles. The traditional reductionist approach to research requires that all confounding variables are eliminated or silenced using methods of statistics. However, that noise in the data, those confounding variables provide the rich context, media, and processes by which creative practices thrive. As research in the arts gains recognition for its contributions of new knowledge, the traditional reductive practice in search of general principles will be respectfully joined by methodologies for defining living principles that celebrate and build from the confounding variables, the data noise. The movement to develop research methodologies from the noisy edges of human interaction have been explored in the research and practices of ludic design and ambiguity (Gaver, 2003); affective gap (Sengers et al., 2005b; 2006); embodied interaction (Dourish, 2001); the felt life (McCarthy & Wright, 2004); and reflective HCI (Dourish, et al., 2004). The theory of critical creative technology examines the relationships between critical theories of technology, society and aesthetics, information technologies and contemporary practices in interaction design and creative digital media. The theory of critical creative technology is aligned with theories and practices in social navigation (Dourish, 1999) and community-based interactive systems (Stathis, 1999) in the development of smart appliances and network systems that support people in engaging in social activities, promoting communication and enhancing the potential for learning in a community-based environment. The theory of critical creative technology amends these community-based and collaborative design theories by emphasizing methods to facilitate face-to-face dialogical interaction when the exchange of ideas, observations, dreams, concerns, and celebrations may be silenced by societal norms about how to engage others in public spaces. The Constructed Narratives project is an experiment in the design of a critical creative technology that emphasizes the collaborative construction of new knowledge about one's lived world through computer-supported collaborative play (CSCP). To construct is to creatively invent one's world by engaging in creative decision-making, problem solving and acts of negotiation. The metaphor of construction is used to demonstrate how a simple artefact - a building block - can provide an interactive platform to support discourse between collaborating participants. The technical goal for this project was the development of a software and hardware platform for the design of critical creative technology applications that can process a dynamic flow of logistical and profile data from multiple users to be used in applications that facilitate dialogue between people in a real-time playful interactive experience

Development of novel methodologies for utilising low-cost sensors for ambient Particulate Matter measurement

There is increasing concern about the impact of ambient Particulate Matter (PM) exposure on human health. Existing ambient air quality monitoring networks, because of their sparseness, are not able to capture the spatial-temporal variation of ambient PM concentration. Recent studies have shown that although low-cost PM monitors, such as Optical Particles Counters (OPCs), can be utilised for both personal exposure and high-density sensor network applications, these sensors can be subject to several limitations such as relative humidity (RH) interferences, the inability to measure smaller (e.g. ultrafine) particles and the assumption made about the constant aerosol density value used in the conversion from number concentration to mass concentration. Water can condense on aerosol particles resulting, if uncorrected for, in particle size growth and thus overestimation of the measured PM concentration in a manner which depends on both RH and the chemical composition of particles. In contrast, failing to account for particles below the sensors’ size detection limit leads to potentially large underestimations of PM concentrations. To account for changes in the aerosol density values assumed by OPCs, the PM readings calculated from the particle size and concentration measurements require the application of an additional, often empirical, factor. Not accounting for this factor, results in a poor agreement between PM measurements from an OPC and a reference gravimetric instrument. To address these issues, this work describes the development, application and assessment of a three-stage correction process which allows low-cost sensors to provide quantitative PM measurements. The first step is to account for the particle hygroscopic growth under high RH conditions. This led to the development of two correction methodologies: 1) a particle size distribution correction algorithm (based on κ-Köhler theory) which corrects for the particle hygroscopic growth after the measurements, and 2) a prototype particle drying system (consisting of a heated inlet) which dries the particles before measuring their size. Results from field studies across winter and summer are presented to show the feasibility and accuracy of the two methodologies. The application of the correction algorithm resulted in a significant improvement in the determination of the correct particle size and concentration, with the overestimation of PM measurements (calculated in the size range of the low-cost sensor) reduced from a factor of 4.60±0.10 to 1.00±0.10. Similarly, the implementation of the particle drying system provided comparable results with the overestimation of PM measurements reduced from a factor of 1.90±0.20 to 0.90±0.10. However, the performance of the correction algorithm is dependent on the correct assumption of the particle chemical composition as opposed to the application of a heated tube on the sensor inlet which ensures drying of the particles. The second step is to estimate and include the contribution of particles below the low-cost sensor size detection limit in the calculation of PM concentrations. An algorithm to determine the concentration of particles below 300 nm diameter based on the particle size distribution of reference measurements between the low-cost sensor and the reference instrument size detection limits was developed. The application of the estimation algorithm resulted in a reduction for the underestimation of the total PM concentrations from a factor of 0.40±0.10 to a factor of 1.10±0.10. Finally, optical reference instruments try to exploit a semi-empirical correction factor to scale the calculated PM values to match the reference gravimetric methods measurements. This work investigated the possibility of applying a similar correction factor to low-cost sensor measurements. It was shown that, by exploiting the ratio between PM2.5 and PM1 measurements, an equivalent correction factor for low-cost sensors can be derived, thus enabling the Alphasense OPC-N2 PM measurement to be accurate within 25% relative to the certified reference equivalent data. This work shows that, when appropriate corrections are applied, portable low-cost sensor can provide PM measurements which are comparable with readings from reference standard instruments. Finally, a conceptual design to exploit the dependence of PM on RH for chemical composition derivation is also included. Even though the sensor used in this work is the Alphasense OPC-N2, the presented methodologies are generally applicable to all OPC-based PM sensors.Thanks to Alphasense Ltd. for fully funding my PhD programme

Simulation of aluminium extrusion process.

The aim of this thesis is to model the extrusion process conditions for some aluminium alloys using Finite Element Modelling (FEM) program. All the simulations were performed with the implicit finite element code FORGE20 (2-D) and FORGE3® (3-D). In this work only the alloys AA2024, AA2014, Al-1 %Cu and AA6063 where experimental work is available were considered. The FORGE2® program was used to investigate and select an appropriate flow stress constitutive equation to describe the material behaviour to model the process conditions. The extrusion pressure and the temperature rise were predicted and the pressure-displacement trace and the events which take place in the deformed material during the extrusion process were also simulated. The effect of the initial billet temperature on friction, and the extent of the surface zone affected by surface friction and the consequence changes in material flow were investigated. The changes in the subgrain size during quasi-static deformation were predicted. This allows a construction of velocity-displacement profiles which would ensure consistent properties over the length of the extrudate. The FORGE3® program was used to simulate the effect of changing the die geometry on material flow during extrusion for rod, shapes and tube extrusion and the effect of the initial temperature on the deformation zone. The load required, temperature evolution, surface formation of the extrudate and material flow during the process, were also predicted. These included solid sections and the production of tubes using bridge die. Two most commonly used constitutiveflow stress equations,the Zener-Hollomon and the Norton-Hoff were analysed and compared with experimental results. It was found that the Zener-Hollomon relationship provided a better representation of the experimental flow stress under high working conditions than the Norton-Hoff relationship. FEM has been successfully applied to model the deformation patterns in the load/displacement traces and temperature evolution during the extrusion cycle. The effect of the initial billet temperature on the deformation zone pattern and its consequent effect on friction using both numerical simulation and experimental work are presented. A specific function relationship to measure directly interfacial friction under conditions approaching those encountered in the quasi-static deformation process is described. The results revealed that the friction factor increases with increase in initial billet temperature and varies during the extrusion cycle. The dead metal zone (DMZ) is observed to vary in form and has a greater volume at high temperatures. FEM proved to be a very effective and efficient way to design the ram speed profile to control the extrudate properties. The control of the properties of the extrudate under a constant (Z) parameter resulted in a more uniform distribution of the subgrain size across and along the extrudate cross-section. Furthermore, the speed profile under constant Z conditions resulted in an improved extrusion speed and hence greater productivity coupled with better control of the subgrain size and the exit temperature. This new extrusion process is termed iso-Z Extrusion, and is considered an improvement on Iso-Thermal extrusion. The usefulness and the limitation of FEM when modelling complex shapes are discussed. Methods to assess the difficulty of hollow and section shapes are presented. The work also illustrates the essentials of numerical analysis in the comprehension of the thermo-mechanical events occurring during extrusion through bridge and shape dies. Results are presented for velocity distribution in the extrusion chamber, Iso-temperature contours and pressure/displacement traces. It is shown that for most of the shapes investigated, the material making up the extrudate cross-sections originated from virgin material within the billet. The outside surface of the extrudate originates from the material moving along the DMZ and the core of the extrudate from the central deformation zone. When simulating tube extrusion, it is shown that the FE program is able to predict the pressure requirements: the pressure/displacement trace showing a double peak for tube extrusion which is discussed in some detail. The FE program appears to predict all the major characteristics of the flow observed macroscopically

Luminescence dating of heated silex - Potential to improve accuracy and precision and application to Paleolithic sites

Thermoluminescence (TL) dating of heated silex artefacts represents an important chronometric tool for Middle to Upper Paleolithic archeological contexts. Since the firing of these lithics can legitimately be attributed to human agency, this method provides direct age estimates of the occupation of a site. However, in relation to other dating methods, the precision of TL dates is comparatively low, and the often observed “overdispersion” in ages of obviously syndepositional finds indicates additional sources of scatter mainly disregarded so far. This thesis examines potential sources of both imprecision and inaccuracy of age estimates as well as the capability of alternative approaches to overcome or reduce these shortcomings of the TL method applied to heated silex. Besides assessing the influence of spurious luminescence signal contributions from sample carriers on determined dose, focus is set on investigating strength and uniformity of the internal dose rate of silex samples and resulting effects on the age. Being constant over burial time, self-dosing may either decrease the influence of elusive and variable external radiation – in case of homogeneous radioelement distribution within the sample – or introduce systematic errors and enhanced data scatter, if radiation is concentrated in “hot spots”. With α- and β-autoradiography and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), both qualitative and quantitative approaches served to draw a detailed picture on presence and spatial distribution of hot spots and associated impurities in thick sections of over 20 silex specimens. While the low β-activity of most samples is rarely visible on respective autoradiographs, recorded α-tracks revealed zones and spots with strongly increased Th and U concentrations. Comparison of autoradiographs with sample surfaces shows a clear relationship between track density and impurities or filled cracks. These findings are confirmed by LA-ICP-MS: In contrast to the low radioactivity of pure silex, most kinds of impurities are related to strongly increased radiation. If this is not accounted for, micro-dosimetric effects may lead to random and systematic errors in age determination. Additionally, the performance of TL single-aliquot regenerative-dose (SAR) protocols for dating small-sized samples and as a diagnostic tool for non-uniform dose distribution in the samples was tested. For both the blue (~475 nm) and red (~630 nm) TL emission it was found that the degree of adequate sensitivity-correction by test dose monitoring strongly depends on the properties of individual samples. However, laboratory doses could be well reproduced for most specimens. By comparing De distributions from natural dose measurements and dose recovery tests and regarding the value range of sensitivity corrected natural signals (Ln/Tn), assessment of sample homogeneity and SAR dose response behavior is enabled, respectively. Unlike for commonly used TL, few is known about optically stimulated luminescence (OSL) of silex. However, access to specific, optically sensitive trap populations (e.g. slow-components) and more gentle heat treatment in the course of SAR sequences may yield the benefits of increased saturation dose levels (and hence upper dating limits) and reduced systematic errors, respectively. Therefore, fundamental properties such as signal composition and thermal long-term stability of silex OSL were studied and its applicability to heated samples evaluated. First-order fitting of linearly modulated (LM-) OSL curves showed best results for five components in most cases. Pulse annealing experiments and the varying heating rate method, however, attested only the best bleachable component sufficient thermal stability. Successful dose recovery tests and OSL ages in agreement to TL ages of the same samples validate the general applicability of this OSL component for dating. However, since not all silex varieties show an optical signal at all, this approach may be regarded as complementary to TL and reassuring for important samples. In the applied part of this thesis, several sets of heated artefacts from Middle and Upper Paleolithic sites in Portugal, Spain, Romania and Egypt were TL and OSL dated. Gravettian samples from Vale Boi (Portugal) were submitted for dating after termination of the excavation, so that environmental radiation could not be determined accurately. This is very likely the reason for the significant deviation between radiocarbon dates of the same layer and TL ages, because SAR and multiple-aliquot additive-dose (MAAD) ages of the same sample agree and other influencing variables such as the α-efficiency or the moisture content have too little impact on the calculated age as to explain the observed discrepancies. The SAR approach allowed dating the relatively small silex samples from the cave site Las Palomas (Spain). Here, successful dose recovery tests indicated the suitability of the measurement procedure, and in-situ measurements of γ-radiation provided more accurate dose rate information. As a result, TL ages between ~51 and ~84 ka allow a first chronometric assessment of the formerly undated archeological remains. Artefacts from the Aurignacian site Româneşti-Dumbrăviţa I (Romania) proved to be more problematic, as part of them had to be discarded due to poor dose reproducibility. SAR measurements, dose recovery tests and their detailed analyses suggested internal non-uniformities of most samples, so that only rigorous data filtering allowed extraction of reliable age estimates. Due to the luminescence behavior of dated samples, the occupation of the site could, however, not be narrowed down to a range smaller than ~39-45 ka, giving a weighted average age of 40.6 ± 1.5 ka for the Aurignacian find layer. Furthermore, two TL emissions (blue and red) and two protocols (SAR and MAAD) were applied to heated silex from Sodmein Cave (Egypt). Dose recovery tests showed uncorrectable sensitivity changes of the TL signal, rendering the TL SAR sequence inaccurate for these samples. Consequently, age estimates are based on TL MAAD and OSL SAR data; for the smallest sample only a TL SAR maximum age can be given. Coming from different depths of a huge hearth, TL ages of dated samples indicate a large time span to be condensed in the archeological deposits, probably reaching from MIS 5e to MIS 5a

Toward a Model of Intercultural Warrant: A Case of the Korean Decimal Classification\u27s Cross-cultural Adaptation of the Dewey Decimal Classification

I examined the Korean Decimal Classification (KDC)\u27s adaptation of the Dewey Decimal Classification (DDC) by comparing the two systems. This case manifests the sociocultural influences on KOSs in a cross-cultural context. I focused my analysis on the changes resulting from the meeting of the two cultures, answering the main research question: “How does KDC adapt DDC in terms of underlying sociocultural perspectives in a classificatory form?” I took a comparative approach and address the main research question in two phases. In Phase 1, quantities of class numbers were analyzed by edition and discipline. The main class with the most consistently high number of class numbers in DDC was the social sciences, while the main class with the most consistently high number of class numbers in KDC was technology. The two main classes are expected to differ in semantic contents or specificities. In Phase 2, patterns of adaptations were analyzed by examining the class numbers, captions, and hierarchical relations within the developed adaptation taxonomy. Implementing the taxonomy as a coding scheme brings two comparative features of classifications: 1) semantic contents determined by captions and quantity of subordinate numbers; and 2) structural arrangement determined by ranks, the broader category, presence and the order of subordinate numbers. Surveying proper forms of adaptation resulted in the development of an adaptation taxonomy that will serve as a framework to account for the conflicts between and harmonization of multiple social and cultural influences in knowledge structures. This study has ramifications in theoretical and empirical foundations for the development of “intercultural warrant” in KOSs

Wear behavior of glass-ceramic and polymer-infiltrated ceramic materials for dental applications

Dissertação de mestrado integrado em Engenharia Biomédica (área de especialidade em Biomateriais, Reabilitação e Biomecânica)Wear of teeth and restorative materials has been often reported by general dental practitioners and researchers. Wear can occur at tooth-tooth, restoration-tooth, or restoration-restoration contacting surfaces, depending on the properties of the related synthetic and natural materials. All-ceramic restorations are the most popular type of dental restorations due to their optical and mechanical properties. However, the abrasiveness of ceramic materials results in progressive wear of contacting surfaces such as resin composite or tooth enamel. Concerning aaesthetics, strength, and wear, new glass ceramics and composites have been commercially introduced in the field of dentistry. The objective of the present work is to study the tribological behavior of a zirconia-reinforced lithium silicate glass-ceramic and a polymer-infiltrated ceramic. Samples were tested on a reciprocating ball-on-plate tribometer at 30 N applied load, 1 Hz and stroke length of 2 mm. The wear sliding tests were carried out against an alumina ball in artificial saliva at 37 ºC. Additionally, micro-scale abrasion tests were also performed in the presence of abrasive particles to simulate three-body abrasion conditions. The micro-scale abrasion tests were performed at 60 rpm with a normal load of 0.8 N for 600 revolutions of a stainless-steel ball in contact with a suspension of hydrated silica particles. After wear tests, the worn surfaces were inspected by scanning electron microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS). The main wear mechanism found during the tests was abrasion. However, the hybrid ceramic, during the reciprocating tests, presented an unstable adhesive tribo-layer, associated with a delamination process. Congruently, the wear volume obtained during the micro-abrasion tests were higher for the polymer infiltrated ceramic than for the glass-ceramic, 1.44x10-1 mm3, and 9.89x10-2 mm3, respectively. The same happened to the specific wear rate for sliding tests where the hybrid ceramic obtained 5.33x10-5 mm3/N.m and the glass-ceramic 3.17x10-5 mm3/N.m. For all test conditions, zirconia reinforced glass-ceramic, presented higher wear resistance than hybrid ceramic, combined with lower friction coefficient against alumina, which indicates the potential of this reinforced glass-ceramic for application in dental restorations.O desgaste dos dentes e materiais de restauro, tem sido referenciado muitas vezes por médicos dentistas e investigadores. O desgaste pode ocorrer na interação de superfícies em contacto, dente-dente, restauro-dente, ou mesmo restauro-restauro, dependendo das propriedades dos materiais sintéticos e naturais. Os restauros totalmente cerâmicos são o tipo mais popular de restauros dentários, devido às suas propriedades óticas e mecânicas. No entanto, a abrasividade dos materiais cerâmicos resulta no desgaste progressivo das superfícies em contacto como resinas compósitas ou esmalte dentário. Tendo em conta a estética, resistência e desgaste, novos vitrocerâmicos e compósitos têm sido introduzidos no campo da dentária. O objetivo do presente trabalho é o estudo do comportamento tribológico de um vitrocerâmico de silicato de lítio reforçado com zircónia e de uma cerâmica infiltrada com polímero. As amostras foram testadas num tribómetro esfera-placa em deslizamento linear alternativo, com uma carga aplicada de 30 N, 1 Hz e 2 mm de amplitude. Estes testes foram realizados contra uma esfera de alumina em saliva artificial a 37 ºC. Além disso, foram realizados testes de abrasão em micro-escala, na presença de partículas abrasivas para simular condições de abrasão a três corpos. Os testes de micro-abrasão foram realizados a 60 rpm e com uma carga normal fixa de 0,8 N para 600 rotações da esfera em aço, usando uma suspensão de sílica hidratada. Após os testes tribológicos, as superfícies desgastadas foram inspecionadas por microscopia eletrónica de varrimento (SEM) e por espetroscopia de energia dispersiva (EDS). O principal mecanismo de desgaste encontrado durante os ensaios foi a abrasão. Porém, o cerâmico hibrido, apresentou uma tribo-camada adesiva e instável, associada a um processo de delaminação. Congruentemente, o volume de desgaste obtido durante os testes de microabrasão foi maior para o cerâmico infiltrado com polímero do que para o vitrocerâmico, 1,44x10-1 mm3 e 9,89x10-2 mm3, respetivamente. O mesmo aconteceu com a taxa de desgaste específica para testes de deslizamento em que a cerâmica híbrida resultou em 5,33x10-5 mm3/N.m e a vitrocerâmica 3,17x10-5 mm3/N.m. Para todas as condições de teste, o vitrocerâmico reforçado com zircónia apresentou maior resistência ao desgaste do que o cerâmico híbrido, combinando com menor coeficiente de atrito contra a alumina, o que indica o potencial de aplicação deste vitrocerâmico reforçado em restaurações dentárias.This work was supported by the Portuguese Foundation of Science and Technology through the projects: POCI-01-0145-FEDER-006941 and UID/EEA/04436/201

Compaction and its influence on the structural behaviour of high speed railways

Doctoral thesis in Civil EngineeringImportant aspects that govern railway embankments, namely, high–speed railways are, on one hand, the strict requirements during construction (material quality, state parameters and mechanical properties limits) associated with generally relatively short construction time available and, on the other hand, the strict requirements on residual settlements concerning serviceability conditions, which are inherent to mechanical performance of embankment layers during and after construction. Therefore, performance based tests should play an important role through an integrated design process starting from site investigation, design, construction and maintenance. In this context, full scale trials assume great importance to establish a methodology either on the establishment of compaction conditions and on promoting continuous stiffness evaluation, aiming to meet high quality requirements and reduce construction time. This is developed through this study involving advanced laboratory and field investigations of different materials. A laboratory test campaign was performed on two materials, a clayey sand and a crushed aggregate employed in field investigation. Void ratio was fixed for each material and molding water content was varied in order to reproduce in situ state conditions. Strength and stiffness were determined by means of triaxial tests. Focus was given to hydro–mechanical behaviour on the very small and large strain domain of clayey sand due to non negligible fine fraction. Results showed marked influence of molding water content on the hydro–mechanical behaviour of both clayey sand and crushed aggregate, yet being stronger on the former material. Field investigation involved two full scale trials, a railway and a road trial embankments. In the railway trial embankment the same materials studied on the laboratory investigation were employed. Construction of trial layers with different thicknesses (0.22, 0.30, 0.40 and 0.50m) and different moisture contents (2% dry of optimum, optimum and 2% wet of optimum Modified Proctor) were carried out and state conditions and mechanical properties were evaluated for several energy levels. Focus was given to mechanical evaluation through spot and continuous test methods. Moisture content was found to strongly influences mechanical performance, rather than density, thus reflecting suction effect on mechanical properties. Comparison between laboratory and field results proofs results consistency. Further, continuous mechanical evaluation by means of Portancem` etre represents a great improvement on quality control/quality assurance (Qa/Qc) of compacted layers. In road trial embankment another two materials were employed, which laboratory investigation was conducted in the aim of another doctoral thesis. Construction of trial layers with different thicknesses (0.30, 0.40 and 0.50m) but with similar moisture contents were carried out and, likewise to railway trial embankment, state conditions and mechanical properties were evaluated for several energy levels. Moisture content was found have unnoticeable influence on moduli for the range of moisture content verified in situ. Conversely, dry density seems to influence mechanical properties, as long as moisture content does not vary significantly. Comparison between full scale trial and laboratory results yielded small differences. This results along with the ones obtained from railway trial embankment assumes great importance taking into account that design is based on mechanical properties usually determined from laboratory tests. Parallel to this study, an experimental program was carried out on road embankment to monitor, on one hand, layer in–ground vibrations during application of impact loads and vibrating loads and, on the other hand, to monitor roller drum roller during compaction seeking to explore the relationship between loads and underlying material mechanical properties. Accelerometers and strain gauges were buried on the capping layer enabling measurement of dynamic response and total strains. In–ground dynamic response reflect a single modulus, though different moduli obtained from dynamic tests performed at layer surface. Further, vertical drum behaviour was found to be sensitive to changes in underlying material stiffness and to be related with in–ground dynamic response.Os aspectos importantes que governam os aterros ferroviários, nomeadamente linhas férreas de alta velocidade, são, por um lado, os elevados requisitos durante a construção (qualidade dos materiais, limites para as condições de estado e para as propriedades mecânicas) associadas a um tempo de construção reduzido e, por outro lado, os elevados requisitos relativos aos assentamentos residuais durante as condições de serviço, que são inerentes ao comportamento mecânico durante e após a construção. Assim, a avaliação mecânica através de ensaios mecanicistas deverá desempenhar um papel preponderante num processo que integra a prospeção, o projecto, a construção e a manutenção. Neste contexto os aterros experimentais assumem grande importância quer na definição das condições de compactação, quer na promoção do controlo de compactação em contínuo visando atingir os elevados requisitos de qualidade e a redução do tempo de construção. Tal é desenvolvido no presente estudo que envolve a investigação avançada em laboratório e em campo de diferentes materiais. A campanha de laboratório foi realizada sobre dois materiais, uma areia argilosa e um agregado britado, utilizados na investigação de campo. O ´índice de vazios foi fixado para cada material tendo-se feito variar o teor em água de modo a reproduzir as condições de estado em campo. Os parâmetros de resistência e de rigidez foram determinados através de ensaios triaxiais. Foi dado especial enfoque ao comportamento hidro–mecânico no domínio das muito pequenas e grandes deformações da areia argilosa devido à fracção fina não negligenciável. Os resultados obtidos mostram clara influência do teor em àgua no comportamento hidro–mecânico de ambos os materiais, sendo essa influência mais evidente na areia argilosa. O estudo de campo compreendeu dois aterros experimentais, um aterro ferroviário e um aterro rodoviário. Os mesmos materiais estudados em laboratório foram utilizados no aterro ferroviário. Procedeu-se `a construção de camadas experimentais com diferentes espessuras (0.22, 0.30, 0.40 and 0.50m) e diferentes teores em ´agua (2% do lado seco do ótimo, ótimo e 2% do lado húmido do ótimo em relação ao Proctor Modificado) e `a avaliação das condições de estado e do comportamento mecânico para vários n´níveis de energia. Especial enfoque foi dado `a avaliação mecânica através de ensaios pontuais e contínuos. Os resultados mostraram grande influência do teor em água, maior do que a influência da densidade, no comportamento mecânico dos materiais o que reflete o efeito da sucção nas propriedades mecânicas. A comparação entre os resultados de campo e de laboratório confirmou a consistência dos mesmos. Para além disso, concluiu-se que a avaliação mecânica em contínuo por meio da utilização do Portancemètre representa um progresso significativo no controlo/garantia de qualidade das camadas compactadas. O aterro experimental rodoviário envolveu a utilização de dois materiais, cujo estudo laboratorial foi desenvolvido no âmbito de outra tese doutoral. As camadas experimentais foram construídas com diferentes espessuras (0.30, 0.40 and 0.50m), mas com teores em ´agua semelhantes e, assim como para o aterro ferroviário, as condições de estado e o comportamento mecânico foram avaliados para vários n´níveis de energia. Para os teores em ´agua encontrados em campo verificou-se que o teor em ´agua teve pouca influência no módulo das camadas. Pelo contrário, a densidade seca parece influenciar as propriedades mecânicas, desde que não se verifique uma grande variação do teor em água. A comparação dos resultados de campo com os de laboratório mostraram pequenas diferenças. Na linha do concluído para o aterro experimental ferroviário, estes resultados assumem grande importância se se tiver em conta que o projecto tem por base as propriedades mecânicas dos materiais determinadas em laboratório. Paralelamente a este estudo, no aterro rodoviário realizou-se um programa experimental visando, por um lado, a monitorização de vibrações em profundidade durante a aplicação de cargas de impacto e visando, por outro lado, a monitorização do rolo do cilindro procurando explorar a relação entre as cargas aplicadas e as propriedades mecânicas. Acelerómetros e extensómetros foram instalados em profundidade na camada de leito de pavimento permitindo a medição da resposta dinâmica e das extensões totais. A resposta dinâmica em profundidade reflete um único módulo, apesar de diferentes módulos obtidos através dos ensaios dinâmicos realizados à superfície. Para além disso, verificou-se que o comportamento do rolo do cilindro é sensível à mudança de rigidez do material e que está relacionado com a resposta dinâmica em profundidade

An exploration of the diffusion dynamics of Open Source Software (OSS): An Agent-Based Computational Economics (ACE) approach

Despite the rising popularity of Open Source Software (OSS), there is limited understanding of the factors that affect the diffusion of OSS at the organizational level. Review of the literature suggests that previous empirical and analytical studies on this subject matter though valuable in their own respect, either did not address the full spectrum of critical factors in one model or did not investigate the impact of critical factors in enough detail leaving some gaps in the literature. In an effort to bridge these gaps, this dissertation develops a model to a) jointly investigate the effect of critical variables other than price on the diffusion dynamics of OSS, b) investigate the effects of social networks or inter-organizational relationships on the diffusion dynamics of OSS, c) propose a new software price discounting scheme and compare its effectiveness against traditional software price discounting schemes on the diffusion dynamics of OSS. An Agent-Based Computational Economics (ACE) approach is adopted to develop a comprehensive simulation model to investigate the aforementioned research problems. Although, desktop operating system software is used as an exemplar to investigate the diffusion of its open source and proprietary alternatives, the framework proposed in the dissertation is general enough to be applied in the investigation of diffusion of other kinds of software as well