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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

A mathematical model of cell cycle heterogeneity for personalizing leukemia chemotherapy

Fuentes Gari, Maria January 2015 (has links)
Acute myeloid leukemia is a type of blood cancer characterized by an excessive build-up of immature blood cells in the bone marrow and blood streams. As a result, healthy stem cells become space- and resource-limited, and do not produce enough functional cells for the body to operate normally. Treatment is required immediately, consisting of intensive chemotherapy. Chemotherapy dosage and schedule are derived from established protocols which do not account for patient-specific and disease-specific heterogeneity. Over- or under- dosage are thus common; a more rational and personalized approach to chemotherapy treatments is required. Specifically, incorporating the effect of chemotherapy in a cell cycle phase-specific manner would be highly beneficial. In this work, we developed a population balance model (PBM) of the cell cycle based on the underlying biology that captures the progress of cells within and between phases. It was validated with three leukemia cell lines separately for the duration of one cell cycle, and in variable mixtures where forward and backward kinetics as well as clonal identification were successfully performed. The model was compared against two other cell cycle models: an existing ODE model and a newly developed DDE model featuring phase durations as delays. The PBM outperformed the other two in recapitulating biological features, and displayed a higher sensitivity to treatment when coupled to an existing pharmacokinetic/pharmacodynamic model of chemotherapy treatment. The PBM was further used in the prediction of clonal evolution during chemotherapy, highlighting the important heterogeneity in treatment response between clones but also the competitive features among them that could be critical in the success of the treatment. Finally, the first steps towards implementing this technology at clinical level were taken by defining converted, measurable data sets. A prototype application, "ChemoApp", was developed at the user interface level for the introduction of this research into clinical practice.
12

Wave behaviour in vertical multiphase flow

Zhao, Yujie January 2014 (has links)
The work described in this thesis was aimed at developing the understanding of two regimes in vertical gas-liquid flow in tubes, namely annular flow and churn flow. In annular flow, there is a continuous gas passage at the centre of the pipe with a film of liquid travelling upwards at the wall. Part of the liquid phase in annular flow may be entrained as droplets in the core gas flow. In churn flow there is also a gas core (which the present work has shown to be continuous) and a liquid film; however, the flow direction of the liquid in this film varies with time. Thus, the liquid flows upwards in large waves on the surface of the film; between the waves, the film may change direction and flow downwards towards the next wave. Such flows are extremely complex and there are aspects of their behaviour which are poorly understood. In the work described in this thesis, several areas have been studied. Disturbance waves are of central importance in annular flows. Such waves are characterised by their large amplitudes relative to the mean film thickness, their high translation velocities relative to the mean film speed, and their circumferential coherence (i.e. their 'ring-like' structure when fully developed). An important part of the present work was concerned with the existence, development and translation of disturbance waves in upwards, gas-liquid annular flows. At very low liquid flow rates, disturbance waves are not formed (and, as other work has shown, the entrainment of droplets from the liquid film is negligible). In the present work, multiple conductance probe units have been employed to study the growth and development of disturbance waves. From the results, it is found that disturbance waves begin to appear and to start to achieve their circumferential coherence from lengths as short as 5-10 pipe diameters downstream of the liquid injection location; this coherence gradually strengthens with increasing distance from the inlet. It is further shown that the spectral content of the entire interfacial wave activity shifts to lower frequencies with increasing axial 3 distance from the inlet, with the peak frequency levelling off after approximately 20 pipe diameters. Interestingly, on the other hand, the frequency of occurrence of the disturbance waves first increases away from the inlet as these waves form, reaches a maximum at a length between 7.5 and 15 pipe diameters depending on the flow conditions, and then decreases again. This trend becomes increasingly evident at higher gas and/or liquid flow-rates. Both wave frequency measures increase monotonically at higher gas and/or liquid flowrates. Important evidence regarding the mechanisms of disturbance waves and the associated droplet entrainment can be obtained by the axial view photography technique. This technique is described in Chapters 3 and 6. The technique was used to visualise the wave characteristics, in particular of the two entrainment mechanisms (bag break up and ligament break up mechanisms) proposed previously by Azzopardi (1983). The axial view photography technique provided visual evidence for the existence of the two mechanisms, although in contrast to Azzopardi's findings, both break up mechanisms were observed to occur simultaneously. The axial view photography technique was also used in the present work to provide further insights into the inception of disturbance waves. It was found that the initiation mechanism for disturbance waves was the occurrence of a disturbance at a given location around the tube periphery. This is consistent with the idea of a link between turbulent burst phenomena and disturbance waves first proposed by Azzopardi and Martin (1986). The initial disturbance links up with similar disturbances to ultimately form the characteristic ring-like structure characteristic of fully developed disturbance waves. In churn flow the present work concentrated on three aspects: The use of axial view photography to explore the continuity of the gas core in churn flow. The development (in collaboration with two other research students - Deng Peng and Masroor Ahmad) of a correlation for entrainment rate and hence entrained fraction in churn flow. Measurements of 4 pressure gradient and holdup in churn flow, from which an average wall shear stress can be deduced. In the first task, it was shown (it is believed for the first time) that there is a continuous path for the gas phase near the tube axis. In churn flow the behaviour of entrained fraction is extremely complex and conventional methods for measuring it are no longer valid. Barbosa etal (2002) studied entrainment in churn flow using iso-kinetic sampling probes and the correlation referred to above was based on this data. The correlation has been widely used in predicting the entrained fraction at the transition between churn and annular flow. Since the direction of flow of the liquid film near the channel wall fluctuates, it is difficult to estimate the instantaneous value of wall shear stress. However, if measurements are made of total pressure gradient and liquid holdup, then the mean value of wall shear stress can be estimated. This procedure was pursued by Govan (1990) who used mechanically operated quick-closing valves to measure holdup. In the current work, a new measurement technique was utilised, namely quick closing pinch valve which offer a great accuracy and are easy to install. Pressure gradient and hold up data were collected over a wide range of gas and liquid flowrate. An averaged wall shear stress was then calculated based on these measurements. At higher liquid mass flow rates, the results were in good qualitative agreement with those of Govan (1990) but (at lower mass fluxes) anomalies occur which need further investigation.
13

Forward osmosis for seawater desalination membrane development and process engineering

Kochanov, Ruslan January 2014 (has links)
Although industrial osmotic processes are often referred to as 'novel', the possibility for osmotic power generation has been suggested as early as the 1970s. Today forward osmosis is attracting significant interest and this interest has resulted in intensive research. Forward osmosis has been suggested as viable separation process, with numerous potential applications - from osmotic drug delivery and concentration of liquid foods to water purification and re-use in space. Particularly interesting is the possibility of seawater desalination by forward osmosis, as the process is claimed to require little or no pre-treatment of the feed water, due to minor membrane fouling. This alone is a significant advantage over reverse osmosis. Within the oil and gas sector, research conducted in the last couple of years shows that low salinity waterflooding can result in enhanced oil recovery, and therefore the industry is searching for new possibilities for off-shore based production of low salinity water. Due to the fact that forward osmosis operates at atmospheric pressure and requires no pressure vessels, the process can be utilized for seawater desalination where low overall equipment weight is required - off-shore oil platforms for example. This thesis is focused on the development of membranes for water desalination by forward osmosis, and estimation of the requirements (approximate membrane area and volume) for seawater desalination by a two-stage membrane based forward osmosis-nanofiltration process.
14

Phase behaviour and physical properties of reservoir fluids under addition of carbon dioxide

Al Ghafri, Saif January 2014 (has links)
The phase behaviour of reservoir fluids under the addition of carbon dioxide (CO2) were studied at elevated pressures and temperatures similar to those encountered in enhanced oil recovery (EOR) and carbon storage processes. The principal focus of the work presented in this thesis is the experimental investigation of the phase behaviour of these CO2 mixtures with hydrocarbon reservoir fluids. For this purpose, a new high-pressure high-temperature apparatus was designed and constructed. The apparatus consisted of a thermostated variable-volume view cell driven by a computer-controlled servo motor system. The maximum operating pressure and temperature were 40 MPa and 473.15 K, respectively. Measurements were then made over a wide range of pressure and temperature conditions for two representative CO2-hydrocarbon systems: (CO2 + n-heptane + methylbenzene) and (CO2 + synthetic crude oil). The vapour-liquid phase behaviour of the former system was studied, under CO2 addition and various molar ratios of n-heptane to methylbenzene, along different isotherms at temperatures between (298 and 473) K and at pressures up to approximately 16 MPa. In the latter, the synthetic oil contained a total of 17 components while solution gas (methane, ethane and propane) was added to obtain live synthetic crudes with gas-oil ratios of either 58 or 160. Phase equilibrium and density measurements were then made for the ‘dead’ oil and the two ‘live’ oils under the addition of CO2. The measurements were carried out at temperatures between (298.15 and 423.15) K and at pressures up to 36 MPa, and included vapour-liquid, liquid-liquid and vapour-liquid-liquid equilibrium conditions. The phase equilibria of (carbon dioxide + n-heptane + water) and (carbon dioxide + methane + water) mixtures were also studied using a high pressure quasi-static analytical apparatus with on-line compositional analysis by gas chromatography. The former system was studied under conditions of three-phase equilibria along five isotherms at temperatures from (323.15 to 413.15) K and at pressures up to the upper critical end point (UCEP). In the latter system, compositions of three coexisting fluid phases have been obtained along eight isotherms at temperatures from (285.15 to 303.5) K and at pressures up to either the UCEP or up to the hydrate formation locus. Compositions of coexisting vapour and liquid phases have been obtained along three isotherms at temperatures from (323.15 to 423.15) K and pressures up to 20 MPa for mixtures containing nearly equal overall mole fractions of CH4 and CO2. The quadruple curve along which hydrate coexists with the three fluid phases was also measured. A detailed study of these ternary mixtures was carried out based on comparison with available ternary data of the type (CO2 + n-alkane + water) and available data for the constituent binary subsystems. In this way, we analyze the observed effects on the solubility when the n-alkane component was changed or a third component was added. The experimental data for the (CO2 + hydrocarbon) systems have been compared with results calculated with two predictive models, PPR78 and PR2SRK, based on Peng-Robinson 78 (PR78) and Soave-Redlich-Kwong (SRK) cubic equations of state (EoS) with group-contribution formula for the binary interaction parameters and with the use of different alpha functions. Careful attention was paid to the critical constants and acentric factor of high molar-mass components. The use of the Boston-Mathias modification of the PR78 and SRK equations was also investigated. The experimental data obtained for the (CO2 + n-heptane + methylbenzene) mixture were also compared with the predictions made using SAFT-Gamma-Mie, a group-contribution version of the Statistical Associating Fluid Theory (SAFT), which was implemented with the generalized Mie potential to represent segment-segment interactions. Detailed assessment of the predictive capability of these models concluded that the agreement between the experimental data and prediction from these methods, while not perfect, is very good, especially on the bubble curve. The results suggest that there is merit in the approach of combining these methods with a group-contribution scheme. Comparison between these approaches concluded that they all have comparable accuracies regarding VLE calculations. The experimental data obtained for the ternary mixtures (CO2 + n-alkane + water) have been compared with the predictions of SAFT for potentials of variable range (SAFT-VR), implemented with the square-well (SW) potential using parameters fitted to experimental pure-component and binary-mixture data. A good performance of the SAFT-VR equation in predicting the phase behaviour at different temperatures was observed even with the use of temperature-independent binary interaction parameters. It was also observed that an accurate prediction of phase behaviour at conditions close to criticality cannot be accomplished by mean-field based theories, such as the models used in this work, that do not incorporate long-range density fluctuations. Density measurements on a variety of brines (both single-salt and mixed) were studied in the present work within the context of CO2 storage processes in saline aquifers. Densities of MgCl2(aq), CaCl2(aq), KI(aq), NaCl(aq), KCl(aq), AlCl3(aq), SrCl2(aq), Na2SO4(aq), NaHCO3(aq) , the mixed salt system [(1 – x) NaCl + xKCl](aq) and the synthetic reservoir brine system [x1NaCl + x2KCl + x3MgCl2 + x4CaCl2 + x5SrCl2 + x6Na2SO4 + x7NaHCO3](aq), where x denotes mole fraction, were studied at temperatures between (283 and 473) K and pressures up to 68.5 MPa. The measurements were performed with a vibrating-tube densimeter calibrated under vacuum and with pure water over the full ranges of pressure and temperature investigated. It was observed that careful attention needs to be paid to the type of calibration method selected. An empirical correlation is reported that represents the density for each brine system as a function of temperature, pressure and molality with absolute average relative deviations (%AAD) of approximately 0.02 %. Comparing the model with a large database of results from the literature suggested that the model is in good agreement with most of the available data. The model can be used to calculate density, apparent molar volume and isothermal compressibility of single component salt solutions over the full ranges of temperature, pressure and molality studied. An ideal mixing rule for the density of a mixed electrolyte solution was tested against our mixed salts data and was found to offer good predictions at all conditions studied with an absolute average relative deviation of 0.05 %. The present work was carried out as part of the Qatar Carbonates and Carbon Storage Research Centre (QCCSRC) program. It covered a wide range of phase behaviour and density measurements at conditions relevant to oil and gas fields’ applications, and explored the predictive capabilities of some available models, in particular predictive cubic EoS, SAFT-VR and SAFT-Gamma-Mie. The research and data collected represents a good step in enabling the direct design and optimisation of CO2-EOR and carbon storage processes. An example is the validation of the predictive models and the determination of the miscibility pressure which is essential for effective recovery of the heavy hydrocarbons. Areas in which the research might be extended, both through further experimental studies and improved modelling, have been identified.
15

Study of oxygen dissolution in molten tin : a novel SOFC anode

Agbede, Oluseye Omotoso January 2014 (has links)
Conventional power plants for the conversion of fossil fuels to electricity have low efficiencies and produce large amount of carbon dioxide, a greenhouse gas, which contribute to climate change. Hence, a molten tin reformer and methane-fuelled SOFC with molten tin anode (Sn(l)-SOFC) for easier CO2 capture and higher power efficiency were investigated. Both systems involved oxygen dissolution in molten tin and methane reaction with the dissolved oxygen, as well as gas bubbling, so oxygen dissolution and methane reaction at bubble | molten tin interface were investigated. Oxygen was separated successfully from a 10%O2-He blend through gas bubbling and dissolution in molten tin which suggests that oxygen may be separated from air in the molten tin reformer by bubbling air through molten tin in the first stage of the periodic process. An LSM-YSZ/LSM double-layered reference electrode and YSZ electrolyte potentiometric oxygen sensor was used to measure the concentration of dissolved oxygen in molten tin; hence, enabling derivation of the solubility limit and Gibbs energy change for the formation of SnO which was in equilibrium with oxygen at the solubility limit. The solubility of oxygen in molten tin in equilibrium with SnO in the temperature range 973-1123 K was ca. 0.019-0.107 atom%. The rate of oxygen dissolution in molten tin when 10%O2-He blend was bubbled through it was controlled by chemical reaction at the bubble | molten tin interface; the mechanism involved a first step of chemisorption to molten tin at the bubble | molten tin interface, forming SnO as the absorbed intermediate. The second step of the mechanism involved the dissociation of SnO to molten tin and oxygen atom incorporated in the molten tin. The rate limiting step was the dissociation of SnO into molten tin and oxygen atom. Likewise, the rate of deoxygenation of molten tin by 10%CH4-He was not limited by the diffusion of oxygen atoms in the molten tin but might be limited by surface reaction at the bubble | molten tin interface. The performance of the molten tin reformer and methane-fuelled Sn(l)-SOFC depends on bubble size and behaviour, so bubbles generated in molten tin were characterized by determining the sizes, shape, velocities, and behaviour under different operating conditions of nozzle diameter, gas flow rates and temperatures. A pressure pulse technique which incorporates a differential pressure transducer was employed successfully in the measurement of frequencies of bubble formation in molten tin at high temperatures in the range 973-1173 K while the bubbles were approximated as oblate spheroids which wobbled. LSM cathodes were deposited on micro-tubular YSZ electrolytes and the microstructures and electrical conductivities characterized by scanning electron microscopy (SEM) and four-point probe resistance measurement, respectively. SEM micrographs showed the densification of LSM cathodes with increased sintering temperature, which resulted in increased electrical conductivities. Potential difference-current density data and impedance spectra were determined for a methane-fuelled SOFC with molten tin anode. A peak power density of about 100 W m-2 at a current density of 222 A m-2 and potential difference of 0.45 V was obtained for the methane-fuelled SOFC with molten tin anode at 850 oC. Impedance spectra showed that ohmic potential losses controlled the reactor performance, with about half of those arising from the inherent difficulty in achieving a low resistance contact at the (Ag wire) Ag wool current collector | LSM cathode interface.
16

Chemical interactions between CO2 acidified aqueous fluids and carbonate minerals

Peng, Cheng January 2015 (has links)
The chemical interactions between carbon dioxide (CO2) acidified aqueous fluids and carbonate minerals were studied at elevated temperature and pressure conditions for the purposes of modelling fluid flow and reactive transport in carbonate reservoir formations. Experimental measurements were made of the rate of dissolution of carbonate mineral samples in acidified brines, with specific focus on the reaction rate in the surface reaction controlled regime. Another key outcome of this study was the experimental measurement of pH for CO2 acidified aqueous systems within the context of the data requirements of the oil and gas industry. Some studies have also conducted on the equilibrium constants of carbonate dissolution reactions. Three novel pieces of experimental apparatus were used to perform the experimental measurements, each designed to accommodate the corrosive CO2-acidified reservoir fluids at high-temperature, high-pressure reservoir conditions. A newly designed and constructed batch dissolution reactor system, consisting of three vessels, implemented the rotating disc technique to study carbonate dissolution process without the impact of mass transfer effects. A newly designed and constructed high-pressure pH measurement system used an electrometric technique to quantify the impacts of dissolved CO2 on the acidity of the aqueous solution. An in-situ Micro-Raman reactor apparatus used Raman spectroscopy to exam the equilibrium concentration of bicarbonate ions. All three systems were fully calibrated and validated before being applied to conduct systemic measurements with variation of temperature, pressure, salinity and minerals. The pH measurements for CO2-saturated water in the pressure range from (0.28 to 15.3) MPa and temperatures from (308.3 to 423.2) K were conducted first. Commercially-available pH and Ag/AgCl electrodes were used together with a high pressure equilibrium vessel operating under conditions of precisely controlled temperature and pressure. The results of the study indicate that pH decreases along an isotherm in proportion to -log10(x), where x is the mole fraction of dissolved CO2. An empirical equation has been developed to represent the present results with an uncertainty of ±0.06 pH units. We also compare our results with a new chemical equilibrium model and find agreement to within 0.1 pH unit. The pH measurements were further extended to a CO2-saturated aqueous NaCl solution. A new strategy is proposed to calibrate the pH electrodes by using the Pitzer model to quantify the salt effects. Measurements were carried out at temperatures between (308 and 373) K and at pressures up to 15.4 MPa for NaCl solutions with concentrations of (1, 3, 5) mol·kg-1. The pH is found to increase with increase of pressure, decrease of temperature and increase of NaCl concentration. An empirical equation correlating pH with CO2 solubility has been proposed with an uncertainty of ±0.08 pH units. Comparisons of the experimental data with two thermodynamic simulation packages using different aqueous electrolyte models suggest that the Pitzer model provides reasonably accurate predictions, although further improvements at higher NaCl concentrations would be desirable. New experimental data have been measured for carbonate mineral dissolution rates in CO2-saturated aqueous system and the dissolution kinetics have been determined using the pH model derived in this study. Calcite dissolution rates in CO2-saturated water at pressures ranging from (6.0 to 13.8) MPa and temperatures from (323 to 373) K were first measured. The rate of calcite dissolution in HCl(aq) at temperatures from (298 to 353) K was also measured. The impact of mineral sample surface morphology was investigated and the results suggest that at far-from-equilibrium conditions, the measured calcite dissolution rate is independent of the dislocation density due to the development of a dynamic steady-state pattern of etch pits. The results also indicate that the calcite dissolution rates under surface-reaction-controlled conditions increase with increase of temperature and CO2 partial pressure. A kinetic model incorporating both pH and the activity of CO2(aq) has been developed to represent the dissolution rates found in this study. We report correlations for the corresponding reaction rate constants based on the Arrhenius equation and the activation energies so determined are in reasonable agreement with the literature. The dissolution rate studies were then carried out for two other carbonate minerals, dolomite and magnesite, using pure mineral crystals. Dissolution experiments were conducted in CO2-saturated water and HCl(aq) systems at similar temperature, pressure and pH conditions compared to the calcite experiments. The results indicate that the dissolution rates of dolomite and magnesite also increase with increase of temperature and CO2 partial pressure. The dissolution kinetics of both minerals can be modelled as a single first-order heterogeneous reaction for both the HCl system and the (CO2 + H2O) system. It was also noticed that dolomite dissolves in a stoichiometric manner, which greatly reduced the complexity in modelling. Finally, the dissolution rate investigations were extended to two different reservoir analogue samples (Limestone and Chalk) to validate the reaction kinetics models proposed in this project for reservoir samples. Significant efforts were made to estimate the true reactive surface area. Good agreement has been observed between the experimentally-measured dissolution rates of the reservoir analogue samples and the data calculated using the reaction kinetics model established in this project. It is concluded that the kinetic models and the associated parameters derived in this project can be incorporated into reservoir simulators to provide more accurate reactive transport simulations for future large scale CCS projects. Finally, Raman spectroscopy was used to probe the chemical equilibrium constants of carbonate dissolution reactions by measuring the equilibrium bicarbonate concentration (HCO3-). The utilisation of a new calibration procedure has enabled in-situ, non-invasive and non-destructive, online quantitative fluid-rock interaction studies for carbonate-CO2-brine systems. Both calcite and magnesite were studied in CO2 acidified H2O and 1 M NaCl systems at three temperatures from (297 to 373) K and pressures of 7 MPa and 15 MPa. Several geochemical simulators using different aqueous electrolyte models were used and were able to achieve various degrees of success in predicting the equilibrium HCO3- concentration in comparison with the experimental values. Overall, the Pitzer model demonstrates the widest applicability and highest accuracies for CO2 acidified aqueous system. The present work was carried out as part of the Qatar Carbonates and Carbon Storage Research Centre (QCCSRC) program. It provided extensive mineral dissolution rates and pH data that can be used to characterise the chemical interactions between CO2-acidified aqueous fluids and carbonate minerals relevant to oil- and gas-field applications. The results of this study should facilitate more rigorous modelling of reactive transport and fluid flow in the design and optimisation of enhanced oil recovery and carbon storage processes. Areas in which the research might be extended, both through further experimental studies and improved modelling, have been identified.
17

Selectivity and deactivation in the single-stage synthesis of dimethyl ether from CO2/CO/H2

Montesano Lopez, Raúl January 2014 (has links)
The selectivity and stability of catalysts for the single-stage production of dimethyl ether from gas mixtures containing CO2, CO and H2 is studied. A Cu/ZnO/Al2O3 catalyst was used for the hydrogenation of carbon oxides while the dehydration of methanol was catalysed by γ-alumina, phosphated γ-alumina or protonic zeolites. The influence that the proximity between the methanol synthesis and the methanol dehydration functions has on the catalytic stability is evaluated for each catalyst pair under different feed compositions. The assessment of the effect of zeolite topology on the deactivation and the by-product formation is also aimed. The intimate contact between Cu/ZnO/Al2O3 and γ-alumina is found to cause fast deactivation on both catalysts during the first hours of the experimental runs. It is shown that the detrimental interaction is more severe under CO-rich conditions than for gas mixtures with high CO2 contents. The addition of phosphorus to the γ-alumina up to the monolayer capacity mediates the loss of activity that occurs in the presence of high CO concentrations. The independent characterisation of the spent catalysts gives insights on the mechanism responsible for the observed loss of activity . Five different zeolite structures were considered to be studied as dehydration catalysts: mordenite, ZMS-5, ferrierite, theta-1 and ZSM-23. It is found that the deactivation of zeolites during the single-stage synthesis of DME is dictated by the deposition of carbon residues which is related to the topology of the solid acid. In the conversion of CO/H2, the hydrocarbon distribution depends on the nature of the entrained organics and it is demonstrated that a careful selection of crystallite size and channel structure of the zeolite allows the conversion and selectivity to be controlled. Under CO2 and H2, ZSM-5 is shown to be considerably more active than γ-alumina and very selective towards dimethyl ether. Experiments using different SiO2 to Al2O3 ratios indicate that the deactivation depends on the acid site density rather than on the acid strength.
18

Analysis of carotid wall mechanics based on ultrasound imaging

Wang, Zhongjie January 2014 (has links)
Stroke is the third biggest killer and the leading cause of severe disability in the UK. The most common type of stroke is known as an ischaemic stroke in which blood vessels in the brain become blocked, most often as a result of rupture of atherosclerotic plaques formed in the carotid arteries, especially at the bifurcation and in the entrance to the internal carotid artery which feeds the cerebral circulation. The carotid arteries can be examined through ultrasound scans, which provide images of the vessel allowing assessment of the severity of carotid disease. In this project, ultrasound images of carotid arteries acquired from patients with varying degrees of carotid disease are analysed and computational models are built to predict the mechanical stresses within carotid arteries with or without atherosclerosis. Ultrasound imaging was chosen owing to its non-invasive nature and wide availability. Work presented in this thesis follows a logical progression. First, image analysis tools are developed and presented in Chapter 3. Based on the processed ultrasound images, finite element models of carotid arteries are constructed and biomechanical analyses of varying degrees of complexity are carried out. In Chapter 4, the carotid artery is assumed as an elastic material, and comparisons are made between 2-D and 3-D models based on idealised geometry. In an attempt to improve the predictive ability of the model and achieve better understanding of disease progression, the viscoelastic behaviour of the carotid vessel wall is taken into account, and detailed analyses of the effect of vessel wall viscosity and hysteresis are presented in Chapter 5. Methods used to derive subject-specific viscoelastic material properties from in vivo pressure-diameter data are also described. Finally, in order to understand the effect of interaction between the viscoelastic vessel wall and blood flow in carotid arteries, fully coupled fluid-structure interaction (FSI) models are developed, and the FSI model as well as its validation are presented in Chapter 6. Work reported in this thesis has shown that by combining ultrasound measurement with computational analysis, it is possible to provide additional information that will aid clinicians in their diagnosis and decision making. Carotid biomechanical analysis can be carried out with subject-specific information, such as viscoelastic wall properties and geometry, derived from in vivo data acquired non-invasively. The ultrasound-image based modelling approach developed in this thesis will also help improve our understanding of the role of vessel wall motion in the development and progression of carotid diseases.
19

Template induced polymorphic selectivity in pharmaceutical crystallisation

Parambil, Jose Varghese January 2015 (has links)
Polymorphism in pharmaceutical drug crystals causes differences in their bioavailability, stability and processability. Hence, identifying different crystal polymorphs of an active ingredient during the early stages of drug development and controlling crystal polymorphism during the manufacturing process are important aspects of pharmaceutical crystallisation. Nucleation and growth of different polymorphs in a crystallising solution are regulated by a delicate balance between thermodynamic and kinetic factors. Crystal nucleation predominantly occurs via heterogeneous nucleation pathway as it is energetically favourable than homogeneous nucleation. Template-induced nucleation approach aims to utilise the advantage of heterogeneous nucleation to induce nucleation of specific crystal polymorphs through interfacial interactions between a preformed solid surface and solute molecules at the nucleation stage. In template-induced crystallisation, templates with specific surface properties that can act as heterogeneous nucleation sites are introduced in contact with the crystallising solution. Specific interactions between the template surface and solute molecules are known to influence nucleation and growth of crystal polymorphs. However, the effects of template surface chemistry and other operating conditions such as temperature and supersaturation on template-induced crystallisation is not clearly understood. Hence, the aim of this study is to probe the combined effects of surface chemistry, crystallisation temperature, supersaturation, and solvent on template-induced crystallisation experimentally and consequent development of a molecular modelling approach to study template-induced nucleation. This could help in establishing template-induced nucleation as a method to achieve preferential nucleation of crystal polymorphs and to support template chemistry as a novel parameter for polymorph screenings. Carbamazepine (CBZ) was selected as the model drug compound and silanised glass vials were chosen as the template surfaces. CBZ crystallisation from ethanol solutions on templates with cyano functional surface groups led to selective nucleation of metastable form II crystals while the control surfaces resulted in concomitant nucleation of both form II and stable form III crystals. On mercapto and fluoro templates, CBZ crystallised preferentially as form III polymorph. These variations in the polymorphic outcome with template chemistry, temperature and supersaturation were mapped on to template-induced polymorphic domain (TiPoD) plots. The analysis of TiPoD plots showed that the template-induced nucleation mechanism was prominent within a narrow range of supersaturation across the temperature range studied. The influence of solvents on template-induced nucleation of CBZ polymorphs was also investigated by constructing TiPoD plots in five different solvents. These studies revealed that the templates were less effective in altering polymorphic outcome in highly polar solvent in comparison with the less polar solvents. Interfacial interactions between the template surface and CBZ crystal polymorphs were calculated through molecular modelling. The simulation results suggest that those templates exhibiting favourable interaction energies with the dominant crystal facets of a specific polymorph preferentially induce nucleation of that crystal form.
20

Macroporous polymer mixers

Tebboth, Michael Peter January 2015 (has links)
Macroporous polymers produced by polymerising the continuous phase of high (or medium) internal phase emulsions (H/MIPEs), commonly known as poly(merised)HIPEs (or polyMIPEs), have been intensively researched over the past two decades. The have been investigated for use in many diverse applications including chromatography, membranes, sorbtion, electrodes, bioengineering and filters amongst others. However this work investigates the use of their intricate internal pore structure for the mixing of fluids passing through polyHIPEs. When producing polyHIPEs (also polyMIPEs) by polymerisation of HIPE and MIPE templates it was found that the pore size could be controlled effectively by varying the energy used to agitate the emulsion template. The gas permeability of polyM/HIPEs increased linearly with increasing mean pore throat diameter for a given porosity. Through both residence time distribution experiments and examination of homogenous micromixing it was shown that the mixing in single-phase liquids increased when passed through a polyHIPE as the mean pore throat diameter decreases. There was no difference in mixing performance observed between polyHIPEs produced from Pickering emulsions compared to those produced from surfactant stabilised emulsions. By performing the liquid-liquid extraction of caffeine from aqueous solution with ethyl acetate within a polyHIPE flow cell it was shown that the overall mass transfer coefficient decreased with smaller mean pore throat diameters suggesting more effective mixing. The porosity of the polyHIPE monolith was not found to affect the overall mass transfer coefficient. It was possible to produce interfacial areas, up to 17,600 m2m-3, between the two immiscible liquid phases within polyHIPEs, comparable to industrial extraction methods such as mixer settlers. Impregnating the polyHIPE flow cells with palladium allowed examining whether it is possible to use them as three phase catalytic reactor for nitroreduction. The gas-liquid mixing within the reactor was found to be insufficient to prevent the reduction being mass transfer limited even in the reactors containing the smallest mean pore throat diameters. Less than 0.2% of the palladium catalyst within the reactor was lost from the polyHIPE pore structure during the nitroreductions reactions for all the polyHIPE reactors tested.

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