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Development of nitrogen doped resorcinol-formaldehyde gels for carbon capture
Get PDFResorcinol-Formaldehyde (RF) xerogels are organic materials that have been widely studied due to their industrially relevant characteristics, such as high surface areas, suitable pore size and pore volume on which target species can be adsorbed; additionally, RF gels have significant potential to be tailored to specific applications, including catalysis, thermal insulation, filtration, energy storage, and gas treatment, especially CO2 capture.This research focuses on controlling the chemical and physical properties, on both the macroscopic and microscopic scale, with an investigation into the effect these changes have on the application of these xerogels as carbon capture materials. Xerogel properties have been tailored, within this study, by altering the synthesis procedure with focus on monomer concentrations and catalyst to monomer ratio.Nitrogen has been incorporated into the gel structure in order to enhance the favourable Lewis acid-base interactions with CO2. Melamine (M) is used in order to incorporate Nitrogen (N) into the gel structure; and partially replace the Resorcinol (R) traditionally used, resulting in a Melamine-Resorcinol-Formaldehyde (MRF) gel. Repeatability is crucial to method development and validation was achieved by the preparation of a number of gels using a variety of synthetic conditions and process routes.;There are a number of parameters that can be altered when synthesising a gel, namely, R/C (catalyst) and R/F molar ratios, concentration of M, solids content, solution pH, catalyst, solvent, temperature, time, and agitation. This research aims to tailor the gel structure (pore size and volume, surface area, etc.) to enhance the CO2 adsorption capacity and kinetic performance. It will also be important to obtain a better understanding of the N-CO2 interaction. Amongst all the parameters mentioned above, there are two main aspects influencing the sol-gel chemistry of xerogels synthesised by base catalysed routes, which are the concentration of monomers and catalyst, and the initial pH of the sol. Hence, R/C and R/F molar ratios, and M concentration, were chosen for in depth analysis. These factors were varied and their effect on gel properties characterised, allowing a better understanding of how gel characteristics can be tailored and their impact on gel performance. The remaining parameters were held constant throughout the experiments. RF gels produced were subsequently characterised using volumetric and gravimetric analysis to determine porous structure and quantify CO2 capture capacities and kinetics.The results obtained indicate that the family of materials synthesised in this study offer potential routes for carbon capture materials, through a combination of micropore structure development and incorporation of favourable Lewis acid-base interactions between MRF sorbents surface and CO2 molecules.;This work has demonstrated that CO2 adsorption capacities of MRF xerogels have been enhanced as a consequence of incorporating nitrogen functionalities into their structure. This is important because the amount of sorbent required for a given uptake is reduced, which is a key factor for industrial applications given that volumes of equipment and vessels needed for MRF xerogels reduce in comparison to RF materials.The incorporation of melamine have been found to impact the structure of MRF xerogels similarly as R/C. Increasing the melamine content tend to reduce surface area while pore size and pore volume increase. However, the nitrogen functionalities on the surface of MRF xerogels promote successful interactions with CO2 molecules, resulting in higher capacities. Additionally, it was observed that higher R/F (0.75 and 1.0) results in weaker crosslinking and, consequently, the probabilities of gelation failing are high and, also, pore size becomes a random parameter. On the contrary, low R/F (0.25 and 0.5) offers a better control for pore size.Additionally, a fast kinetics of adsorption and desorption have been observed for MRF materials. Cycling studies have been performed using MRF xerogels, which have demonstrated high stability to cycling and an enhanced working capacity compared to RF sorbents. On another matter, flue gases are a complex mixture of different species, therefore, CO2 selectivity have been tested for MRF sorbents using different binary systems, and results show a significant increase, compared to RF xerogels.Resorcinol-Formaldehyde (RF) xerogels are organic materials that have been widely studied due to their industrially relevant characteristics, such as high surface areas, suitable pore size and pore volume on which target species can be adsorbed; additionally, RF gels have significant potential to be tailored to specific applications, including catalysis, thermal insulation, filtration, energy storage, and gas treatment, especially CO2 capture.This research focuses on controlling the chemical and physical properties, on both the macroscopic and microscopic scale, with an investigation into the effect these changes have on the application of these xerogels as carbon capture materials. Xerogel properties have been tailored, within this study, by altering the synthesis procedure with focus on monomer concentrations and catalyst to monomer ratio.Nitrogen has been incorporated into the gel structure in order to enhance the favourable Lewis acid-base interactions with CO2. Melamine (M) is used in order to incorporate Nitrogen (N) into the gel structure; and partially replace the Resorcinol (R) traditionally used, resulting in a Melamine-Resorcinol-Formaldehyde (MRF) gel. Repeatability is crucial to method development and validation was achieved by the preparation of a number of gels using a variety of synthetic conditions and process routes.;There are a number of parameters that can be altered when synthesising a gel, namely, R/C (catalyst) and R/F molar ratios, concentration of M, solids content, solution pH, catalyst, solvent, temperature, time, and agitation. This research aims to tailor the gel structure (pore size and volume, surface area, etc.) to enhance the CO2 adsorption capacity and kinetic performance. It will also be important to obtain a better understanding of the N-CO2 interaction. Amongst all the parameters mentioned above, there are two main aspects influencing the sol-gel chemistry of xerogels synthesised by base catalysed routes, which are the concentration of monomers and catalyst, and the initial pH of the sol. Hence, R/C and R/F molar ratios, and M concentration, were chosen for in depth analysis. These factors were varied and their effect on gel properties characterised, allowing a better understanding of how gel characteristics can be tailored and their impact on gel performance. The remaining parameters were held constant throughout the experiments. RF gels produced were subsequently characterised using volumetric and gravimetric analysis to determine porous structure and quantify CO2 capture capacities and kinetics.The results obtained indicate that the family of materials synthesised in this study offer potential routes for carbon capture materials, through a combination of micropore structure development and incorporation of favourable Lewis acid-base interactions between MRF sorbents surface and CO2 molecules.;This work has demonstrated that CO2 adsorption capacities of MRF xerogels have been enhanced as a consequence of incorporating nitrogen functionalities into their structure. This is important because the amount of sorbent required for a given uptake is reduced, which is a key factor for industrial applications given that volumes of equipment and vessels needed for MRF xerogels reduce in comparison to RF materials.The incorporation of melamine have been found to impact the structure of MRF xerogels similarly as R/C. Increasing the melamine content tend to reduce surface area while pore size and pore volume increase. However, the nitrogen functionalities on the surface of MRF xerogels promote successful interactions with CO2 molecules, resulting in higher capacities. Additionally, it was observed that higher R/F (0.75 and 1.0) results in weaker crosslinking and, consequently, the probabilities of gelation failing are high and, also, pore size becomes a random parameter. On the contrary, low R/F (0.25 and 0.5) offers a better control for pore size.Additionally, a fast kinetics of adsorption and desorption have been observed for MRF materials. Cycling studies have been performed using MRF xerogels, which have demonstrated high stability to cycling and an enhanced working capacity compared to RF sorbents. On another matter, flue gases are a complex mixture of different species, therefore, CO2 selectivity have been tested for MRF sorbents using different binary systems, and results show a significant increase, compared to RF xerogels
Decentralising active network management through distributed constraint optimisation
Get PDFElectricity networks are becoming more complex due to the introduction of distributed energy sources. The power grid will face fundamental changes in its structure and behaviour. In addition, new technologies will be required in order to maintain the stability of the network. A key enabling technology for the future power networks is autonomous distribution networks which operate in cooperation with distributed grid intelligence and active network management. Local control can be achieved through fast control and communications and needs to be coordinated with the overall system controls. The primary issues for distribution network operation with a high penetration of distributed resources is power flow management as well as voltage control. Active Network Management can be described as the control and management of generation and load in distribution networks. The main concept is to satisfy network limits such as voltage, power and frequency while at the same time increase the connected generation output with the minimum cost. There is a need for coordination between generators to maintain the balance in the network and avoid investment costs.This thesis considers the introduction of Distributed Constraint Optimisation as a way of providing Active Network Management. It is an agent-based coordination method that is able to coordinate generators' output without violation of network constraints. This method, which is drawn from the Artificial Intelligence community and was previously used for smaller problems such as meeting scheduling, is studied and evaluated for use in power systems networks in order to provide solutions in a decentralised way.Case studies consider both DC and AC power flow management and the solution of the economic dispatch problem. DC power flow management under DCOP provides optimal solutions for radial networks while AC power flow management is examined from a theoretical standpoint until the limitations of distributed constrained optimisation software are addressed.Electricity networks are becoming more complex due to the introduction of distributed energy sources. The power grid will face fundamental changes in its structure and behaviour. In addition, new technologies will be required in order to maintain the stability of the network. A key enabling technology for the future power networks is autonomous distribution networks which operate in cooperation with distributed grid intelligence and active network management. Local control can be achieved through fast control and communications and needs to be coordinated with the overall system controls. The primary issues for distribution network operation with a high penetration of distributed resources is power flow management as well as voltage control. Active Network Management can be described as the control and management of generation and load in distribution networks. The main concept is to satisfy network limits such as voltage, power and frequency while at the same time increase the connected generation output with the minimum cost. There is a need for coordination between generators to maintain the balance in the network and avoid investment costs.This thesis considers the introduction of Distributed Constraint Optimisation as a way of providing Active Network Management. It is an agent-based coordination method that is able to coordinate generators' output without violation of network constraints. This method, which is drawn from the Artificial Intelligence community and was previously used for smaller problems such as meeting scheduling, is studied and evaluated for use in power systems networks in order to provide solutions in a decentralised way.Case studies consider both DC and AC power flow management and the solution of the economic dispatch problem. DC power flow management under DCOP provides optimal solutions for radial networks while AC power flow management is examined from a theoretical standpoint until the limitations of distributed constrained optimisation software are addressed
The development of a reactive gait assessment : toward identifying risk for falls in older adults
Get PDFFalls are the leading cause of injuries in older adults. To prevent falls, early identification of individuals at risk is therefore needed. Although gait impairments are among the main risk factors, currently available clinical balance and gait assessments lack sensitivity in identifying risk for falls. Since most falls occur following trips or slips reduced ability to adequately recover from gait perturbations may be indicative of fall risk. The main aim of my industrial doctorate programme was to investigate whether reactive gait assessment can be used to identify risk for falls in older adults;I used innovative technology from the company Motek and developed a mixed-perturbation protocol to challenge the individual's gait pattern and measure the recovery responses in a safe, standardized and objective manner. The initial protocol and outcome measures were based on a literature review. Three subsequent phases of development and evaluation were used to deliver a standardized reactive gait assessment.;Using this assessment I was able to reveal that older adults with a history of falls were more affected by contralateral sway and deceleration perturbation in terms of continuous trunk motion than those without a history of falls, while no differences between fallers and non-fallers were found in clinical and steady state gait measures. This suggests that reactive gait assessment has added value in fall risk identification in older adults.;Therefore, I recommend using the contralateral sway and deceleration perturbations of our developed perturbation protocol and assessing responses by means of continuous trunk motion to further evaluate the use of reactive gait assessment for fall risk identification in older adults. Motek as an industrial company can facilitate this by providing customers with the developed reactive gait assessment and encourage clinically driven research to examine the reproducibility and validity of reactive gait assessment using evidence-based, affordable and easy-to-use technologies.Falls are the leading cause of injuries in older adults. To prevent falls, early identification of individuals at risk is therefore needed. Although gait impairments are among the main risk factors, currently available clinical balance and gait assessments lack sensitivity in identifying risk for falls. Since most falls occur following trips or slips reduced ability to adequately recover from gait perturbations may be indicative of fall risk. The main aim of my industrial doctorate programme was to investigate whether reactive gait assessment can be used to identify risk for falls in older adults;I used innovative technology from the company Motek and developed a mixed-perturbation protocol to challenge the individual's gait pattern and measure the recovery responses in a safe, standardized and objective manner. The initial protocol and outcome measures were based on a literature review. Three subsequent phases of development and evaluation were used to deliver a standardized reactive gait assessment.;Using this assessment I was able to reveal that older adults with a history of falls were more affected by contralateral sway and deceleration perturbation in terms of continuous trunk motion than those without a history of falls, while no differences between fallers and non-fallers were found in clinical and steady state gait measures. This suggests that reactive gait assessment has added value in fall risk identification in older adults.;Therefore, I recommend using the contralateral sway and deceleration perturbations of our developed perturbation protocol and assessing responses by means of continuous trunk motion to further evaluate the use of reactive gait assessment for fall risk identification in older adults. Motek as an industrial company can facilitate this by providing customers with the developed reactive gait assessment and encourage clinically driven research to examine the reproducibility and validity of reactive gait assessment using evidence-based, affordable and easy-to-use technologies
An open-source CFD solver for planetary entry
Get PDFhy2Foam is a newly-coded open-source two-temperature computational fluid dynamics(CFD) solver that aims at (1) giving open-source access to a state-of-the-art hypersonic CFD solver to students and researchers; and (2) providing a foundation for a future hybrid CFD-DSMC (direct simulation Monte Carlo) code within the OpenFOAM framework. Benchmarking has firstly been performed for zero-dimensional test cases and hy2Foam has then been shown to produce results in good agreement with previously published data for a 2D-axisymmetric Mach 11 nitrogen flow over a blunted cone and with the dsmcFoam code for a series of Fourier cases and a 2D Mach 20 cylinder flow for a binary reacting mixture. This latter case scenario provides a useful basis for other codes to compare against. hy2Foam and dsmcFoam capabilities have eventually been utilised to derive and to test a new set of chemical rates based on quantum-kinetic theory and that could be employed for Earth atmospheric re-entry computations.hy2Foam is a newly-coded open-source two-temperature computational fluid dynamics(CFD) solver that aims at (1) giving open-source access to a state-of-the-art hypersonic CFD solver to students and researchers; and (2) providing a foundation for a future hybrid CFD-DSMC (direct simulation Monte Carlo) code within the OpenFOAM framework. Benchmarking has firstly been performed for zero-dimensional test cases and hy2Foam has then been shown to produce results in good agreement with previously published data for a 2D-axisymmetric Mach 11 nitrogen flow over a blunted cone and with the dsmcFoam code for a series of Fourier cases and a 2D Mach 20 cylinder flow for a binary reacting mixture. This latter case scenario provides a useful basis for other codes to compare against. hy2Foam and dsmcFoam capabilities have eventually been utilised to derive and to test a new set of chemical rates based on quantum-kinetic theory and that could be employed for Earth atmospheric re-entry computations
Highlandism : its value to Scotland and how a queen and two aristocratic women promoted the phenomenon in the Victorian age
Get PDFIn 1859 a queen, a duchess and a clan chief's daughter came together in Scotland for the inauguration of a pumping station. Piping water into Glasgow from distant Highland hills was an "engineering marvel." The monarch opened the Loch Katrine Waterworks, a duke's kilted army gave the royal salute - and city and countryside were linked. Victorian engineering skills mixed with tartan nostalgia. In these 'Rob Roy' haunts a progressive age beckoned, but it was one that took with it an invented past...This thesis will examine 'Highlandism', a phenomenon viewed with suspicion because it is a product of the British Empire, the British army, royalty and aristocracy. It will examine its authenticity, analyse its worth and detail the contribution made by three women to this male driven trend. Queen Victoria was a patron, the Duchess of Athole an enabler, and Miss MacGregor an intellect behind this plaid and piping craze.This work will show that Highlandism's intellectual foundations are deeper than thought and that royal and aristocratic roles in its development are more positive than imagined. 'Tartan and shortbread' traditions are accused of impeding cultural and political change. Yet Highlandism has stimulated trade and tourism. It has encouraged a global piping tradition,boosted the Gaelic movement and engendered worldwide emotional support for Scotland.With the "tartan monster" possibly being viewed more kindly, perhaps the "haggis" can sit more comfortably with the "culture".In 1859 a queen, a duchess and a clan chief's daughter came together in Scotland for the inauguration of a pumping station. Piping water into Glasgow from distant Highland hills was an "engineering marvel." The monarch opened the Loch Katrine Waterworks, a duke's kilted army gave the royal salute - and city and countryside were linked. Victorian engineering skills mixed with tartan nostalgia. In these 'Rob Roy' haunts a progressive age beckoned, but it was one that took with it an invented past...This thesis will examine 'Highlandism', a phenomenon viewed with suspicion because it is a product of the British Empire, the British army, royalty and aristocracy. It will examine its authenticity, analyse its worth and detail the contribution made by three women to this male driven trend. Queen Victoria was a patron, the Duchess of Athole an enabler, and Miss MacGregor an intellect behind this plaid and piping craze.This work will show that Highlandism's intellectual foundations are deeper than thought and that royal and aristocratic roles in its development are more positive than imagined. 'Tartan and shortbread' traditions are accused of impeding cultural and political change. Yet Highlandism has stimulated trade and tourism. It has encouraged a global piping tradition,boosted the Gaelic movement and engendered worldwide emotional support for Scotland.With the "tartan monster" possibly being viewed more kindly, perhaps the "haggis" can sit more comfortably with the "culture"
Mitochondrial regulation of vascular smooth muscle cell proliferation and migration in atherogenesis and re-stenosis
Get PDFVascular smooth muscle (VSM) cell proliferation and migration are the hallmark of atherosclerosis and re-stenosis. In this study, we have investigated the role of mitochondrial bioactivity in VSM cell proliferation and migration through the regulation of miRNA expression. We also investigated for the first time the role of mitochondrial bioactivity in determining the content of exosomes released by vascular smooth muscle cells and the biological effect these exosomes have on vascular smooth muscle (VSM) cell proliferation and migration.;VSM cells were isolated from 12-week old male Sprague-Dawley rats. Experiments were undertaken using day zero isolated (contractile phenotype), 21-day cultured (synthetic phenotype) and 21-day mitochondrial incompetent (synthetic phenotype- Rho cell). The effect of balloon angioplasty on rat aorta structural remodelling was also studied. VSM cells were also stimulated using 20 ng/ml PDGF and treated with mitochondrial DRP1 inhibitor MDivi-1 (10 μM).;Inhibition of mitochondrial network formation with the DRP1 inhibitor MDivi-1 (10 μM) inhibited angioplasty-dependent remodelling. This observation was confirmed in VSM cell cultures where MDivi-1 significantly reduced proliferation and migration. Total exosomal release was significantly greater in the 21-day cultured cells when compared with quiesced non-proliferating cells and 21-day cultured Rho cells (520 +/- 10 ng, 480 +/- 20 ng and 420 +/- 10 ng per ml respectively) and total exosomal RNA yield was 70.2 +/- 10.2 ng/ul, 118.7 +/- 2.4 ng/ul and 70.8 +/- 4.7 ng/ul respectively.;Mitochondrial function significantly influenced miRNA and mRNA measured in exosomes. When compared with the hyperproliferative synthetic VSM cell miR-21 expression was reduced by 88 +/- 12.1% and miR-145 expression increased by 73 +/- 19.8%. We also measured a 7-fold decrease and 6.6-fold decrease in mTOR, PI3K and 4EBP1 respectively. A significant increase expression of P53, cdkn2a and ROS scavenging proteins including SOD1 and SOD2 were measured in 21-day cultured Rho cells vs. 21-day hyperproliferative VSM cells.;The expression of cellular miRNA was also seen to be influenced by mitochondrial bioactivity. The expression of miR-21 in cells treated with MDivi-1 was 2 ± 0.2 fold lower than the expression level in the PDGF stimulated cells. The expression level of miR-145 in the MDivi-1 treated cells was 0.5 ± 0.1 fold higher than the expression level in the PDGF stimulated cells.;In this study we have further correlated VSM cell hyperproliferative phenotype with mitochondrial function. Moreover, further demonstrated mitochondrial function/ VSM cell phenotype with exosomal release and cargo that potentially drives the hyperproliferative/ migratory phenotype central to atherosclerosis and re-stenosis.Vascular smooth muscle (VSM) cell proliferation and migration are the hallmark of atherosclerosis and re-stenosis. In this study, we have investigated the role of mitochondrial bioactivity in VSM cell proliferation and migration through the regulation of miRNA expression. We also investigated for the first time the role of mitochondrial bioactivity in determining the content of exosomes released by vascular smooth muscle cells and the biological effect these exosomes have on vascular smooth muscle (VSM) cell proliferation and migration.;VSM cells were isolated from 12-week old male Sprague-Dawley rats. Experiments were undertaken using day zero isolated (contractile phenotype), 21-day cultured (synthetic phenotype) and 21-day mitochondrial incompetent (synthetic phenotype- Rho cell). The effect of balloon angioplasty on rat aorta structural remodelling was also studied. VSM cells were also stimulated using 20 ng/ml PDGF and treated with mitochondrial DRP1 inhibitor MDivi-1 (10 μM).;Inhibition of mitochondrial network formation with the DRP1 inhibitor MDivi-1 (10 μM) inhibited angioplasty-dependent remodelling. This observation was confirmed in VSM cell cultures where MDivi-1 significantly reduced proliferation and migration. Total exosomal release was significantly greater in the 21-day cultured cells when compared with quiesced non-proliferating cells and 21-day cultured Rho cells (520 +/- 10 ng, 480 +/- 20 ng and 420 +/- 10 ng per ml respectively) and total exosomal RNA yield was 70.2 +/- 10.2 ng/ul, 118.7 +/- 2.4 ng/ul and 70.8 +/- 4.7 ng/ul respectively.;Mitochondrial function significantly influenced miRNA and mRNA measured in exosomes. When compared with the hyperproliferative synthetic VSM cell miR-21 expression was reduced by 88 +/- 12.1% and miR-145 expression increased by 73 +/- 19.8%. We also measured a 7-fold decrease and 6.6-fold decrease in mTOR, PI3K and 4EBP1 respectively. A significant increase expression of P53, cdkn2a and ROS scavenging proteins including SOD1 and SOD2 were measured in 21-day cultured Rho cells vs. 21-day hyperproliferative VSM cells.;The expression of cellular miRNA was also seen to be influenced by mitochondrial bioactivity. The expression of miR-21 in cells treated with MDivi-1 was 2 ± 0.2 fold lower than the expression level in the PDGF stimulated cells. The expression level of miR-145 in the MDivi-1 treated cells was 0.5 ± 0.1 fold higher than the expression level in the PDGF stimulated cells.;In this study we have further correlated VSM cell hyperproliferative phenotype with mitochondrial function. Moreover, further demonstrated mitochondrial function/ VSM cell phenotype with exosomal release and cargo that potentially drives the hyperproliferative/ migratory phenotype central to atherosclerosis and re-stenosis
Cracking behaviour of clayey geomaterials
Get PDFCracking is a significant problem in the ceramics industry. It results in a substantial loss of production due to the discarded cracked wares associated. There is an understanding that cracking relates from restrained shrinkage and/or uneven drying. One of the solutions to this is to slow the rate of evaporation so that the wares dry more evenly. Such remedial measures are impractical due to the increase in drying space required. What is therefore required for the ceramics industry is a greater understanding of cracking and methods, which work within their manufacturing limitations, to reduce cracking susceptibility.Despite a number of studies, there is a lack of understanding surrounding the mechanisms of crack initiation. It is clear from experimental evidence that the vast majority of cracking occurs while the soil is still saturated or at the transition from saturated to unsaturated. Many researchers assume that cracking is governed by total stress, i.e. a crack initiates when the tensile stress generated in a soil during drying exceeds the tensile strength of the material.;This research investigates the mechanism of crack initiation using an effective stress based approach. A new tensile testing device utilising high capacity tensiometers to allow for the measurement of (negative) pore-water pressure during testing and, hence, the characterisation of the effective stress state has been developed. The device has been designed to test clays in both saturated and unsaturated states.A series of tensile tests were performed on saturated clay samples prepared using non-de-aired and de-aired water. The results show that for non-de-aired tests, when suction approached the air-entry value, failure occurred at a deviatoric stress lower than the one corresponding to the critical state line derived from triaxial and uniaxial compression tests. For specimens with the slurry de-aired before slip casting the de-airing process realigned the deviator stress at failure recorded in the tensile test with the critical state line derived from uniaxial and triaxial compression tests. It could therefore be speculated that water cavitation is one of the mechanisms that can control rupture of clay when subjected to a (total) tensile stress state. Finally, failure data from tests on unsaturated specimens could be fairly modelled by the Mohr-Coulomb criterion extended to unsaturated states. These tests confirm that tensile failure is associated with failure in shear for both saturated and unsaturated states.;Further validation of the shear failure mechanism is attempted via a numerical study using a simple coupled hydro-mechanical Finite Element Method (FEM) model to simulate the desiccation of a clayey soil to the point of crack initiation. The results of four laboratory desiccation tests of specimens with non-uniform geometry and different hydraulic boundary conditions are presented. These tests were simulated via FEM, and the time and location of cracking compared to test the validity of the model and the failure criterion.A greater understanding of the mechanism of cracking has then be used to test more practical remedial measures that can be used in the manufacture of ceramics to reduce cracking. These measures are based around altering the material mixes used in production process, as to this point the adjustment of the slip material relating to cracking has been done by a process of trial and error without guidance. The results of Finite Element Method simulations suggest creating a material with a more graded grain and pore-size distribution can reduce deviatoric stress development during uneven drying.Cracking is a significant problem in the ceramics industry. It results in a substantial loss of production due to the discarded cracked wares associated. There is an understanding that cracking relates from restrained shrinkage and/or uneven drying. One of the solutions to this is to slow the rate of evaporation so that the wares dry more evenly. Such remedial measures are impractical due to the increase in drying space required. What is therefore required for the ceramics industry is a greater understanding of cracking and methods, which work within their manufacturing limitations, to reduce cracking susceptibility.Despite a number of studies, there is a lack of understanding surrounding the mechanisms of crack initiation. It is clear from experimental evidence that the vast majority of cracking occurs while the soil is still saturated or at the transition from saturated to unsaturated. Many researchers assume that cracking is governed by total stress, i.e. a crack initiates when the tensile stress generated in a soil during drying exceeds the tensile strength of the material.;This research investigates the mechanism of crack initiation using an effective stress based approach. A new tensile testing device utilising high capacity tensiometers to allow for the measurement of (negative) pore-water pressure during testing and, hence, the characterisation of the effective stress state has been developed. The device has been designed to test clays in both saturated and unsaturated states.A series of tensile tests were performed on saturated clay samples prepared using non-de-aired and de-aired water. The results show that for non-de-aired tests, when suction approached the air-entry value, failure occurred at a deviatoric stress lower than the one corresponding to the critical state line derived from triaxial and uniaxial compression tests. For specimens with the slurry de-aired before slip casting the de-airing process realigned the deviator stress at failure recorded in the tensile test with the critical state line derived from uniaxial and triaxial compression tests. It could therefore be speculated that water cavitation is one of the mechanisms that can control rupture of clay when subjected to a (total) tensile stress state. Finally, failure data from tests on unsaturated specimens could be fairly modelled by the Mohr-Coulomb criterion extended to unsaturated states. These tests confirm that tensile failure is associated with failure in shear for both saturated and unsaturated states.;Further validation of the shear failure mechanism is attempted via a numerical study using a simple coupled hydro-mechanical Finite Element Method (FEM) model to simulate the desiccation of a clayey soil to the point of crack initiation. The results of four laboratory desiccation tests of specimens with non-uniform geometry and different hydraulic boundary conditions are presented. These tests were simulated via FEM, and the time and location of cracking compared to test the validity of the model and the failure criterion.A greater understanding of the mechanism of cracking has then be used to test more practical remedial measures that can be used in the manufacture of ceramics to reduce cracking. These measures are based around altering the material mixes used in production process, as to this point the adjustment of the slip material relating to cracking has been done by a process of trial and error without guidance. The results of Finite Element Method simulations suggest creating a material with a more graded grain and pore-size distribution can reduce deviatoric stress development during uneven drying
Stability and dynamics of anti-surfactant solutions
Get PDFWe formulate a fluid-dynamical model describing the behaviour of solutions consisting of a fluid solvent and a dissolved solute, and whose surface tension depends on the concentration of the solute. By considering the surface excess of the dissolved solute, this model can describe the Marangoni-driven flow both of fluids in which there is a surfactant present (which decreases surface tension) and of fluids in which there is an anti-surfactant present (which increases surface tension). By investigating the linear stability of an initially quiescent fluid layer, we predict a novel instability that is possible for anti-surfactant solutions, but not for surfactant solutions, and analyse the conditions for the onset of this instability. We formulate the equations governing the flow of a thin film of surfactant or anti-surfactant solution, and demonstrate the wide range of dynamical behaviour that may be displayed by such solutions. In particular, we perform fully non-linear,unsteady numerical computations, and compare the results obtained with the linear approximation for an initially quiescent thin film subject to both small and large perturbations. We analyse the difference in behaviour between surfactants and anti-surfactants when the thin film is subject to large, local disturbances to either the surface concentration or the bulk concentration. We also obtain analytical solutions to reduced versions of the equations governing the flow of a thin film when the Marangoni effect is dominant. We focus on so-called "perfectly soluble"anti-surfactants for which the surface concentration is identically zero. For problems in which the initial condition is discontinuous, the method of characteristicsis employed to obtain simple-wave solutions. Finally, we derive a general,doubly-infinite family of similarity solutions of the reduced (i.e., Marangoni-only)equations, and investigate two of the most interesting cases in detail.We formulate a fluid-dynamical model describing the behaviour of solutions consisting of a fluid solvent and a dissolved solute, and whose surface tension depends on the concentration of the solute. By considering the surface excess of the dissolved solute, this model can describe the Marangoni-driven flow both of fluids in which there is a surfactant present (which decreases surface tension) and of fluids in which there is an anti-surfactant present (which increases surface tension). By investigating the linear stability of an initially quiescent fluid layer, we predict a novel instability that is possible for anti-surfactant solutions, but not for surfactant solutions, and analyse the conditions for the onset of this instability. We formulate the equations governing the flow of a thin film of surfactant or anti-surfactant solution, and demonstrate the wide range of dynamical behaviour that may be displayed by such solutions. In particular, we perform fully non-linear,unsteady numerical computations, and compare the results obtained with the linear approximation for an initially quiescent thin film subject to both small and large perturbations. We analyse the difference in behaviour between surfactants and anti-surfactants when the thin film is subject to large, local disturbances to either the surface concentration or the bulk concentration. We also obtain analytical solutions to reduced versions of the equations governing the flow of a thin film when the Marangoni effect is dominant. We focus on so-called "perfectly soluble"anti-surfactants for which the surface concentration is identically zero. For problems in which the initial condition is discontinuous, the method of characteristicsis employed to obtain simple-wave solutions. Finally, we derive a general,doubly-infinite family of similarity solutions of the reduced (i.e., Marangoni-only)equations, and investigate two of the most interesting cases in detail
Modelling changes in the growth, maturity, and abundance of fish in Scottish waters
Get PDFThe quantity of fish that may be sustainably harvested from the oceans depends uponhow abundant they are and, less obviously, on their rate of growth, the sizes they can attain and the sizes at which they begin reproducing. This thesis investigates whether fish stocks in Scottish waters have exhibited long term changes in growth rates, maturation scheduling or abundance. The Firth of Clyde was of particular interest, so fish stocks from this region were considered separately in each chapter. Scientific bottom trawl survey data were used to examine changes in growth rates and maturation scheduling. Trends in growth rates were determined by calculating time series of mean lengths-at-age and von Bertalanffy growth parameters. Probabilistic maturation reaction norms were used to investigate trends in maturation. The von Bertalanffy growth parameters and maturation indices were regressed against sea-surface temperature data and abundance indices derived from the survey data to determine whether trends in these variables were responsible for changes in growth and maturation. Demersal fish species were considered in chapters 2 and 3, and pelagic fish species were considered in chapter 4. Long term declines in growth rates and lengths-at-maturation were observed in several species. A length based stock assessment model was developed in chapter 5. Information on the length structure of stocks was provided by survey samples instead of catch-at-length data which is typical for such models, so the model presented here should be widely applicable since many different species are sampled by surveys. Model output was compared with existing results derived from more conventional age based models. The results were encouraging; Bayesian implementations, in particular, returned output very similar to the existing age based models.The quantity of fish that may be sustainably harvested from the oceans depends uponhow abundant they are and, less obviously, on their rate of growth, the sizes they can attain and the sizes at which they begin reproducing. This thesis investigates whether fish stocks in Scottish waters have exhibited long term changes in growth rates, maturation scheduling or abundance. The Firth of Clyde was of particular interest, so fish stocks from this region were considered separately in each chapter. Scientific bottom trawl survey data were used to examine changes in growth rates and maturation scheduling. Trends in growth rates were determined by calculating time series of mean lengths-at-age and von Bertalanffy growth parameters. Probabilistic maturation reaction norms were used to investigate trends in maturation. The von Bertalanffy growth parameters and maturation indices were regressed against sea-surface temperature data and abundance indices derived from the survey data to determine whether trends in these variables were responsible for changes in growth and maturation. Demersal fish species were considered in chapters 2 and 3, and pelagic fish species were considered in chapter 4. Long term declines in growth rates and lengths-at-maturation were observed in several species. A length based stock assessment model was developed in chapter 5. Information on the length structure of stocks was provided by survey samples instead of catch-at-length data which is typical for such models, so the model presented here should be widely applicable since many different species are sampled by surveys. Model output was compared with existing results derived from more conventional age based models. The results were encouraging; Bayesian implementations, in particular, returned output very similar to the existing age based models
Statistical methods of detecting change points for the trend of count data
Get PDFIn epidemiology, controlling infection is a crucial element. Since healthcare associated infections (HAIs) are correlated with increasing costs and mortality rates, effective healthcare interventions are required. Several healthcare interventions have been implemented in Scotland and subsequently Health Protection Scotland (HPS) reported a reduction in HAIs [HPS (2015b, 2016a)].;The aim of this thesis is to use statistical methods and change points analysis to detect the time when the rate of HAIs changed and determine which associated interventions may have impacted such rates.;Change points are estimated from polynomial generalized linear models (GLM) and confidence intervals are constructed using bootstrap and delta methods and the two techniques are compared. Segmented regression is also used to look for change points at times when specific interventions took place. A generalization of segmented regression is known as joinpoint analysis which looks for potential change points at each time point in the data, which allows the change to have occurred at any point over time.;The joinpoint model is adjusted by adding a seasonal effect to account for additional variability in the rates. Confidence intervals for joinpoints are constructed using bootstrap and profile likelihood methods and the two approaches are compared. Change points from the smoother trend of the generalized additive model (GAM) are also estimated and bootstrapping is used to construct confidence intervals.;All methods were found to have similar change points. Segmented regression detects the actual point when an intervention took place. Polynomial GLM, spline GAM and joinpoint analysis models are useful when the impact of an intervention occurs after a period of time. Simulation studies are used to compare polynomial GLM, segmented regression and joinpoint analysis models for detecting change points along with their confidence intervals.In epidemiology, controlling infection is a crucial element. Since healthcare associated infections (HAIs) are correlated with increasing costs and mortality rates, effective healthcare interventions are required. Several healthcare interventions have been implemented in Scotland and subsequently Health Protection Scotland (HPS) reported a reduction in HAIs [HPS (2015b, 2016a)].;The aim of this thesis is to use statistical methods and change points analysis to detect the time when the rate of HAIs changed and determine which associated interventions may have impacted such rates.;Change points are estimated from polynomial generalized linear models (GLM) and confidence intervals are constructed using bootstrap and delta methods and the two techniques are compared. Segmented regression is also used to look for change points at times when specific interventions took place. A generalization of segmented regression is known as joinpoint analysis which looks for potential change points at each time point in the data, which allows the change to have occurred at any point over time.;The joinpoint model is adjusted by adding a seasonal effect to account for additional variability in the rates. Confidence intervals for joinpoints are constructed using bootstrap and profile likelihood methods and the two approaches are compared. Change points from the smoother trend of the generalized additive model (GAM) are also estimated and bootstrapping is used to construct confidence intervals.;All methods were found to have similar change points. Segmented regression detects the actual point when an intervention took place. Polynomial GLM, spline GAM and joinpoint analysis models are useful when the impact of an intervention occurs after a period of time. Simulation studies are used to compare polynomial GLM, segmented regression and joinpoint analysis models for detecting change points along with their confidence intervals
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