This thesis examines how computer modelling matters for policy-making by looking at two case studies of European fisheries management. Based on documentary analysis and ethnographic interviews and observations, the main case is located within the European Union (EU) and centred around the flatfish fishery in the North Sea with a supplementary one from outside the EU and focused on the North East Arctic cod fishery in the Barents Sea. As in other much-contested areas of public policy, fisheries officials in the EU and neighbouring countries seek to develop a universalistic and objective ground by which to depoliticise management decisions. In this sense, modelling has long become their preferred approach to produce policy relevant representations of the otherwise hidden dynamics of a fishery. Social constructivists in the field of Science and Technology Studies (STS) studying the modelling used in areas of policy-making such as, for instance, climate change have questioned whether models are the right tools for this job given that the modelling may conceal large uncertainties about their accuracy and relevance to policy-making. Some of these scholars argue for producing ‘good’ models for policy-making, and thus more robust policies, by constructively engaging the non-modellers or non-specialists in the quality assurance of the modelling. ‘Fisheries Studies’ literature suggests, however, that modelling can contribute to policy resilience despite its well-known limitations to produce accurate fish counting. It follows that models are doing something else than providing policy-salient real-looking representations. How may modelling count differently for policy-making in fisheries and beyond? Drawing on the ‘co-production’ of science and social order framework from STS, the thesis puts forward three related arguments. First, that the technologies designed to depoliticise decision-making, including modelling, become spaces for political work by policy-makers, stakeholders and scientists. Second, that the role of computer modelling for policy stems from how representational validity and political usefulness are produced together. Third, that the role of modelling for policy is mediated by virtue of being assessed together with other technologies for depoliticising as part of a whole sociotechnical infrastructure to allow evidence-based decisions. As a distinctive contribution, this thesis thus questions the presumption in many social constructivist accounts that modelling alone becomes central to the policy process and its outcomes. The significance of modelling for policy-making should be understood in terms of its contribution to processes of sociotechnical framing. Narratives that foreground the former and background the latter show an analytical bias that needs turning around.

Nesta tese, nós investigamos os efeitos do reconhecimento individual sobre a formação de grupos. No capítulo 2 nós revisamos o conhecimento sobre as bases evolutivas do comportamento social, e no capítulo 3 nós nos focamos num mecanismo específico, o reconhecimento individual. Nós revisamos as bases do reconhecimento individual para construir um modelo mínimo de como o reconhecimento individual funciona, visando investigar suas consequências para a estrutura social dos animais. O capítulo 4 é construído como uma introdução à modelagem computacional. Utilizando a técnica de modelagem baseada em agentes, no capítulo 5 nós criamos uma população de indivíduos que são capazes de reconhecer uns aos outros e de lembrar as interações passadas. Nós demonstramos que a presença de memória e reconhecimento individual é capaz de afetar dramaticamente o número e tamanho dos grupos formados. Quando não há memória, os indivíduos formam muitos grupos pequenos, sem estrutura definida. Na presença de memória, os indivíduos se agrupam em clusters cerca de uma ordem de grandeza maiores, e consequentemente menos grupos são formados. Nós demonstramos também que a organização interna dos grupos muda: na presença de memória, os grupos apresentam modularidade maior, isto é, há formação de subgrupos dentro do cluster, onde há uma maior frequência de interações entre os indivíduos. Nossos resultados também mostram a influência da densidade para a formação de grupos: quando a densidade é baixa demais, mesmo na presença de reconhecimento individual, as probabilidades de encontro são baixas demais para que os efeitos do reconhecimento sejam percebidos, e o inverso ocorre com densidades altas demais / In this thesis, we investigate the effects of individual recognition on group formation. In chapter 2 we review the current knowledge on the evolutionary basis of social behavior, and in chapter 3 we focus on a specific mechanism, individual recognition. We review the basis of individual recognition to devise a minimal model of how individual recognition works, aiming to investigate its consequences on the social structure of animals. Chapter 4 is structured as an introduction to computational modelling. Using agent-based modelling, in chapter 5 we build a population of individuals which can recognize one another and can remember past interactions. We show that presence of memory and individual recognition can dramatically affect the number and size of groups in the absence of memory, individuals form small, unstructured groups. In the presence of memory, individuals form clusters about an order of magnitude greater in size, and consequently less groups are formed. We also show that the group\'s internal structure changes: with memory, group modularity is higher, that is, subgroups are formed within the cluster, in which frequency of interactions is greater than outside the subgroup. Our results also show that density affects group formation: when density is low, even with individual recognition, encounter probabilities are so low that recognition\'s effects are not visible, and the opposite holds for too high densities

Thesis (Ph. D. (Biochemistry)) -- University of Limpopo, 2004 / The NRF/Royal Society Initiative, and the University of the North Research Development & Administration

There are four big medium density fibreboard (MDF) plants in New Zealand with a total production capacity of close to one million cubic meters per year. A significant quantity of boards (nearly 3% or about 30,000 cubic meters per year) is rejected due to defects such as weak core, low modulus of rupture and elasticity, low internal bonding and delamination. The main cause of these defects, is lack of complete understanding of the inter relationship during the hot-pressing stage between the initial inputs such as temperature, moisture content, platen pressure and its impact on the properties of boards. The best solution is to develop a mathematical model to assist in understanding these relationships and to solve the equations in the model by using advanced software. This will reduce the number of expensive experiments and will enable us to see some of the parameters, which are otherwise difficult to visualise. Several earlier researchers have tried to model hot pressing of wood composites, mostly either for particle board or oriented strand board (OSB), and only a few are for MDF. The type of numerical methods used to solve the model equations and various assumptions, changes from one investigator to the other. The non-availability of source code to convert the mathematical equations into programme, is one of the reasons for this model development. To improve the productivity of MDF plants in New Zealand, there was a need to develop a computer programme which can include all the latest findings and can remove the defects which are present in earlier models. This model attempts a more complete integration than in the previous models of all the components such as heat transfer, moisture movement and vertical density profile formation in a one-dimensional model of hot pressing of MDF. One of the important features added in the heat and mass transfer part of the model is that the equilibrium moisture content (EMC) equation given for solid wood was modified to be applicable for the MDF fibres. In addition, this EMC equation can cover the complete range of hot pressing temperature from 160ºC to 200ºC. The changes in fibre moisture content due to bound water diffusion, which was were earlier neglected, was considered. The resin curing reactions for phenol formaldehyde and urea formaldehyde resins are also incorporated into the model, with the energy and water released during the curing reaction being included in the energy and mass balances. The validation of the heat and mass transfer model was done by comparing the values of core temperature and core pressure from the model and the experiments. The experimental value of core pressure and core temperature is obtained by putting a thermocouple and pressure transducer in the middle of the mat. The experimental core temperature results show qualitative agreement with the predicted results. In the beginning, the core temperatures from both experiment and model overlap each other. In the middle of the press cycle, the experimental core temperature is higher by 10ºC and by the end the difference decreases to 5ºC. The vertical density profile (VDP) is a critical determining factor for the strength and quality of MDF panels. The earlier concept of ratio of modulus of elasticity of the layer to the sum of modulus of elasticity of all the layers in the previous time step, given by Suo and Bowyer (1994), is refined with the latest published findings. The equation given by Carvalho et al. (2001) is used to calculate the MOE of different layers of the mat. The differential equation of a Maxwell element given by Zombori (2001) is used to measure stress, nonlinear strain function and relaxation of fibres. The model gives good agreement of peak and core density at lower platen temperature at 160ºC but with the increase of platen temperature to 198ºC, the rise in peak density is comparatively higher. There is a distinct increase in predicted peak density by 150 kg/m³ in comparison to the experimental result, where the increase is only by 10 kg/m³. There is a large decline (50 kg/m³) in core density in the experimental results in comparison to only a slight decline (13 kg/m³) in the predicted results. The use of Matlab provides a very convenient platform for producing graphical results. The time of computation at present is nearly 20 hrs in a personal computer with Pentium four processor and one GB RAM. The model can predict properties of a pressed board for the standard manufacturing conditions and also the new hot pressing technologies such as the use of steam injection or a cooling zone in the continuous press. A comparative study has been done to show the advantages of using new hot pressing technology. The present model will become an important tool in the hands of wood technologist, process engineers and MDF manufacturing personnel, to better understand the internal processes and to improve production and quality of MDF boards. This theoretical model helped in developing better understanding of internal processes. By using it, we can analyse the impact of platen temperature, moisture content on the core temperature, core pressure and density profile. It gives better insight into the relationship between core pressure and delamination of the board. The model is also able to predict the internal changes in the new hot pressing technologies such as the steam injection pressing and the use of a cooling zone in a continuous press. Using the simulation results, the exact time needed for the complete curing of resin can be calculated and then these results can be applied in the commercial plants. If the pressing time is reduced, then the over all production of both batch press and continuous press will increase. The second part of the project is the development of an empirical model to correlate the physical properties from the MDF board to the mean density. The empirical model is simple and straightforward, and thus can be applied in commercial operation for control and optimization. The empirical model can predict peak density, core density, and modulus of rupture, elasticity and internal bonding within the limits in which those relationships are derived. The model gives good results for thickness ranging from 10 to 13.5 mm and density ranging from 485 kg/m³ to 718 kg/m³.

Nesta tese, nós investigamos os efeitos do reconhecimento individual sobre a formação de grupos. No capítulo 2 nós revisamos o conhecimento sobre as bases evolutivas do comportamento social, e no capítulo 3 nós nos focamos num mecanismo específico, o reconhecimento individual. Nós revisamos as bases do reconhecimento individual para construir um modelo mínimo de como o reconhecimento individual funciona, visando investigar suas consequências para a estrutura social dos animais. O capítulo 4 é construído como uma introdução à modelagem computacional. Utilizando a técnica de modelagem baseada em agentes, no capítulo 5 nós criamos uma população de indivíduos que são capazes de reconhecer uns aos outros e de lembrar as interações passadas. Nós demonstramos que a presença de memória e reconhecimento individual é capaz de afetar dramaticamente o número e tamanho dos grupos formados. Quando não há memória, os indivíduos formam muitos grupos pequenos, sem estrutura definida. Na presença de memória, os indivíduos se agrupam em clusters cerca de uma ordem de grandeza maiores, e consequentemente menos grupos são formados. Nós demonstramos também que a organização interna dos grupos muda: na presença de memória, os grupos apresentam modularidade maior, isto é, há formação de subgrupos dentro do cluster, onde há uma maior frequência de interações entre os indivíduos. Nossos resultados também mostram a influência da densidade para a formação de grupos: quando a densidade é baixa demais, mesmo na presença de reconhecimento individual, as probabilidades de encontro são baixas demais para que os efeitos do reconhecimento sejam percebidos, e o inverso ocorre com densidades altas demais / In this thesis, we investigate the effects of individual recognition on group formation. In chapter 2 we review the current knowledge on the evolutionary basis of social behavior, and in chapter 3 we focus on a specific mechanism, individual recognition. We review the basis of individual recognition to devise a minimal model of how individual recognition works, aiming to investigate its consequences on the social structure of animals. Chapter 4 is structured as an introduction to computational modelling. Using agent-based modelling, in chapter 5 we build a population of individuals which can recognize one another and can remember past interactions. We show that presence of memory and individual recognition can dramatically affect the number and size of groups in the absence of memory, individuals form small, unstructured groups. In the presence of memory, individuals form clusters about an order of magnitude greater in size, and consequently less groups are formed. We also show that the group\'s internal structure changes: with memory, group modularity is higher, that is, subgroups are formed within the cluster, in which frequency of interactions is greater than outside the subgroup. Our results also show that density affects group formation: when density is low, even with individual recognition, encounter probabilities are so low that recognition\'s effects are not visible, and the opposite holds for too high densities

Thesis (MSc.) (Physics) --University of Limpopo, 2007 / Molecular dynamics simulations have been carried out in order to examine the mechanism of diffusion of molecules in amorphous polymer matrix. PDMS model was folded in to a periodic cell, generated by rotational isomeric state (RIS) method at a prescribed temperature and density. Molecular dynamics was used to study transport properties of cyclic PDMS oligomers (hexa-methylcyclotrisiloxane (D3), octa-methylcyclotetrasiloxane (D4) and deca-methylcyclopentasiloxane (D5) using Dreiding and COMPASS force fields. Diffusion coefficients were calculated from the Einstein relation. Only D3 penetrant reached the long time limit from which the Einstein relation is satisfied. Analysis of displacement versus time for all the penetrants in PDMS matrix indicates that the penetrant motion is characterized by relatively long periods interspersed with fairly long and small jumps. Transport of solvent molecules occurs by jumps between individual sections of free volume (cavity/hole) through temporarily open channels. / The National Research Foundation (NRF) and Eskom

Femoroacetabular impingement (FAI) is recognized as a pathomechanical process that leads to hip osteoarthritis (OA). It is hypothesized that mechanical stimuli are prominent at higher range of motions in hips with cam FAI (aspherical femoral head-neck deformity). Adverse loading conditions can impose elevated mechanical stimuli levels at the articulating surfaces and underlying subchondral bone, which plays a predominant mechanical role in early OA. The aim of this research was to determine the levels of mechanical stimuli within the hip, examining the effects of severe cam impingement on the onset of OA, using patient-specific biomechanics data, CT data, and finite element analysis (FEA). Patient-specific hip joint reaction forces were applied to two symptomatic patient models and two control-matched models, segmented from patient-specific CT data. The finite element models were simulated to compare the locations and magnitudes of mechanical stimuli during two quasi-static positions from standing to squatting. Maximum-shear stress (MSS) was analyzed to determine the adverse loading conditions within the joint and strain energy density (SED) was determined to examine its effect on the initiation of bone remodelling. The results revealed that peak mechanical stimuli concentrations were found on the antero-superior acetabulum during the squatting position, underlying to the cartilage. The MSS magnitudes were significantly higher and concentrated for the FAI patients (15.145 ± 1.715 MPa) in comparison with the MSS magnitudes for the control subjects (4.445 ± 0.085 MPa). The FAI group demonstrated a slight increase in peak SED values on the acetabulum from standing (1.005 ± 0.076 kPa) to squatting (1.018 ± 0.082 kPa). Insignificant changes in SED values were noticed for the control subjects. Squatting orients the femoral head into the antero-superior acetabulum, increasing the contact area with the cartilage and labral regions, thus resulting in higher peaks behind the cartilage on the acetabulum. The resultant location of the peak MSS and SED concentrations correspond well with the region of initial cartilage degradation and early OA observed during open surgical dislocation. Due to the relatively low elastic modulus of the articular cartilage, loads are transferred and amplified to the subchondral bone. This further suggests that elevated stimuli levels can provoke stiffening of the underlying subchondral plate, through bone remodelling, and consequently accelerating the onset of cartilage degradation. Since mechanical stimuli results are unique to their patient-specific loading parameters and conditions, it would be difficult to determine a patient-specific threshold to provoke bone remodeling at this stage.

Femoroacetabular impingement (FAI) is recognized as a pathomechanical process that leads to hip osteoarthritis (OA). It is hypothesized that mechanical stimuli are prominent at higher range of motions in hips with cam FAI (aspherical femoral head-neck deformity). Adverse loading conditions can impose elevated mechanical stimuli levels at the articulating surfaces and underlying subchondral bone, which plays a predominant mechanical role in early OA. The aim of this research was to determine the levels of mechanical stimuli within the hip, examining the effects of severe cam impingement on the onset of OA, using patient-specific biomechanics data, CT data, and finite element analysis (FEA). Patient-specific hip joint reaction forces were applied to two symptomatic patient models and two control-matched models, segmented from patient-specific CT data. The finite element models were simulated to compare the locations and magnitudes of mechanical stimuli during two quasi-static positions from standing to squatting. Maximum-shear stress (MSS) was analyzed to determine the adverse loading conditions within the joint and strain energy density (SED) was determined to examine its effect on the initiation of bone remodelling. The results revealed that peak mechanical stimuli concentrations were found on the antero-superior acetabulum during the squatting position, underlying to the cartilage. The MSS magnitudes were significantly higher and concentrated for the FAI patients (15.145 ± 1.715 MPa) in comparison with the MSS magnitudes for the control subjects (4.445 ± 0.085 MPa). The FAI group demonstrated a slight increase in peak SED values on the acetabulum from standing (1.005 ± 0.076 kPa) to squatting (1.018 ± 0.082 kPa). Insignificant changes in SED values were noticed for the control subjects. Squatting orients the femoral head into the antero-superior acetabulum, increasing the contact area with the cartilage and labral regions, thus resulting in higher peaks behind the cartilage on the acetabulum. The resultant location of the peak MSS and SED concentrations correspond well with the region of initial cartilage degradation and early OA observed during open surgical dislocation. Due to the relatively low elastic modulus of the articular cartilage, loads are transferred and amplified to the subchondral bone. This further suggests that elevated stimuli levels can provoke stiffening of the underlying subchondral plate, through bone remodelling, and consequently accelerating the onset of cartilage degradation. Since mechanical stimuli results are unique to their patient-specific loading parameters and conditions, it would be difficult to determine a patient-specific threshold to provoke bone remodeling at this stage.

Femoroacetabular impingement (FAI) is recognized as a pathomechanical process that leads to hip osteoarthritis (OA). It is hypothesized that mechanical stimuli are prominent at higher range of motions in hips with cam FAI (aspherical femoral head-neck deformity). Adverse loading conditions can impose elevated mechanical stimuli levels at the articulating surfaces and underlying subchondral bone, which plays a predominant mechanical role in early OA. The aim of this research was to determine the levels of mechanical stimuli within the hip, examining the effects of severe cam impingement on the onset of OA, using patient-specific biomechanics data, CT data, and finite element analysis (FEA). Patient-specific hip joint reaction forces were applied to two symptomatic patient models and two control-matched models, segmented from patient-specific CT data. The finite element models were simulated to compare the locations and magnitudes of mechanical stimuli during two quasi-static positions from standing to squatting. Maximum-shear stress (MSS) was analyzed to determine the adverse loading conditions within the joint and strain energy density (SED) was determined to examine its effect on the initiation of bone remodelling. The results revealed that peak mechanical stimuli concentrations were found on the antero-superior acetabulum during the squatting position, underlying to the cartilage. The MSS magnitudes were significantly higher and concentrated for the FAI patients (15.145 ± 1.715 MPa) in comparison with the MSS magnitudes for the control subjects (4.445 ± 0.085 MPa). The FAI group demonstrated a slight increase in peak SED values on the acetabulum from standing (1.005 ± 0.076 kPa) to squatting (1.018 ± 0.082 kPa). Insignificant changes in SED values were noticed for the control subjects. Squatting orients the femoral head into the antero-superior acetabulum, increasing the contact area with the cartilage and labral regions, thus resulting in higher peaks behind the cartilage on the acetabulum. The resultant location of the peak MSS and SED concentrations correspond well with the region of initial cartilage degradation and early OA observed during open surgical dislocation. Due to the relatively low elastic modulus of the articular cartilage, loads are transferred and amplified to the subchondral bone. This further suggests that elevated stimuli levels can provoke stiffening of the underlying subchondral plate, through bone remodelling, and consequently accelerating the onset of cartilage degradation. Since mechanical stimuli results are unique to their patient-specific loading parameters and conditions, it would be difficult to determine a patient-specific threshold to provoke bone remodeling at this stage.

This work is focused on laboratory studies of ion chemistry at conditions relevant for astrophysics. The three main outcomes of the thesis are: (1) The experimental study of the reaction rate coefficient of the associative detachment reaction H- + H -> H2 + e-; measurement of the thermal rate coefficient at the temperatures in the range 10-135 K is described. (2) The design of a novel apparatus for detecting the electrons produced in the RF trap and measuring their energy; numerical simulations and preliminary experimental results are presented. (3) The development of a model of the electron cooling in the afterglow plasma and the application of the model in the analysis of the H3+ recombination measurements.