Understanding the behavior of charring or decomposing materials exposed to high temperature environments is an essential aspect in rocket design. In particular, the tip of re-entry vehicles and sacrificial rocket nozzle liners are both exposed to extremely high temperatures. This thesis is specifically concerned with better understanding the reaction of sacrificial rocket nozzle liners to these high temperature environments. The sacrificial liners are designed to shield the rocket nozzle from the thermal and chemical effects of the heated exhaust gas that flows through the nozzle. However, in the design process space and weight of the rocket are at a premium. The sacrificial liners need to be designed to be as light and thin as possible, while properly shielding the nozzle from the heated exhaust gases. The sacrificial liner material is initially impermeable in its virgin state; however, as the liner is exposed to the heated exhaust gases, it chars and the liner material begins to decompose. The decomposition of the liner by heating in the absence of oxygen is known as pyrolysis. At high temperatures, the virgin material will decompose into a solid material (charred liner) and a vapor (pyrolysis gas). The pyrolysis process leads to the flow of pyrolysis gases throughout the porous charred liner. As a result, significant pressures can build within the liner. If the pressures within the liner are high enough, mechanically weak portions of the liner may fracture and break off. Fracturing of the liner could expose the nozzle to the heated exhaust gases, thus jeopardizing the structural integrity of the nozzle. Therefore, it is important to understand the pressure distribution within the sacrificial liners that occurs as a result of the pyrolysis process. This work describes the code PorePress, which solves for steady state and transient pressure distributions in 1- and 2-D axisymmetric geometries that represent sacrificial liners. The PorePress code is essentially a 1- and 2-dimensional differential equation solver for mixed, unstructured geometries. Specifically, the code is used for solving a coupled form of the Ideal Gas Law, Conservation of Mass, and Conservation of Momentum Equations, which describe the flow and resulting pressures within liner geometries. The code centers around using Taylor Series expansions to approximate derivatives needed to solve the appropriate differential equations. The derivative approximation process used in PorePress is grid transparent, meaning the same method can be used for any combination of quadrilateral (4-sided) or triangular (3-sided) elements in a mesh, without any changes to the code. Stability issues arise in both the 1- and 2-D PorePress solution processes, as a result of the non-linear nature of the coupled equations, high spatial gradients, and large variations in material properties. In the 1-D case stabilization techniques such as: upwinding, dynamic differencing, under-relaxation, and preconditioning are applied. Meanwhile, in the 2-D case, stabilization techniques such as: inverse weighting and QR factorization of the coefficient matrix, under-relaxation, and preconditioning are applied. The steady state and transient solution processes for both the 1- and 2-D pore pressure solution processes used in PorePress are covered in this thesis, as well as discussion of the resulting pressure distributions. Certain sacrificial liner design considerations that arise as a result of PorePress models for sample liner burns are also covered. / Master of Science

Moisture damage is one of the major causes of deterioration of pavements. An example is the damage caused by flooding. While the effects of pore water pressure in pavement have been studied using finite element modeling, few of the models consider a realistic moving tire and the viscoelastic behavior of the asphalt layer. Consequently, a three-dimensional finite element simulation based on Biot consolidation theory and Schapery's non-linear viscoelasticity model, was developed to accurately simulate and analyze the detrimental effects of saturated layers in asphalt pavements. In addition, a parametric study is conducted to analyze the response of pavements with varying surface and base thickness, base and subgrade permeability, and vehicle speeds under different level of saturation. The results indicate that the effects of pore water pressure be considered in the design of pavements in flood-prone areas and in the proposal of flood management plans. Ultimately, the implementation of a "flood resilient" asphalt pavement could be effective in reducing the cost of road restoration and repair in flood-prone areas. / Master of Science / Moisture damage is one of the major causes of deterioration of pavements. An example is the damage caused by flooding. While the effects of pore water pressure in pavement have been studied using finite element modeling, few of the models have accurately modeled the behavior of the asphalt concrete and have not considered the realistic loading conditions. Consequently, a three-dimensional finite element simulation was developed to accurately simulate and analyze the detrimental effects of saturated layers in asphalt pavements. In addition, a parametric study is conducted to analyze the response of pavements with varying surface and base thickness, base and subgrade permeability, and vehicle speeds under different level of saturation. The results indicate that the effects of pore water pressure be considered in the design of pavements in flood-prone areas and in the proposal of flood management plans. Ultimately, the implementation of a "flood resilient" asphalt pavement could be effective in reducing the cost of road restoration and repair in flood-prone areas.

The diffusion behavior of guest molecules introduced in porous materials has been studied. Diffusion studies in such porous materials may help for elucidating the structural properties, transport mechanism and/or surface barriers of the zeolite structure. The focus of this work is on diffusion in nanoporous materials with complex pore spaces. First a short introduction in the basics of diffusion and the PFG NMR technique (Pulsed Field Gradient Nuclear Magnetic Resonance) is described. In the following two chapters the diffusion in hierarchical pore spaces or, to be more precise, zeolites with generated mesopores, which traverse the microporous bulk phase, are investigated. The hierarchical pore spaces consists in the first case of micro- and mesopores and in the second case of micro-, meso- and macropores. The diffusion behavior in these materials has been investigated revealing diffusion acceleration in the mesoporous samples, as compared to the purely microporous material. In the next chapter the diffusion behavior in glass samples with different porosity and their complementary pore space is investigated. Diffusion with full loaded pore spaces and surface diffusion, where the molecules were only able to diffuse along the pore walls, has been explored. The aim was to find out to what extent the diffusion in two complementary pore spaces is correlated. In the last chapter, the effect of an inorganic binder on the transport in zeolite pellets has been studied. First the diffusion behavior in binderless zeolite beads in comparison with the zeolite powder employed for their production has been explored. The particular interest was to find out up to which extent the diffusion patterns observed with the powder samples could again be recognized in the beads. In a second study the transport characteristics within binderless molecular sieves have been investigated, with the purpose to reveal differences in the diffusion behavior in comparison with their binder-containing counterparts.

Parabutoporin (PP) and opistoporin 1 (OP1) are cation, a-helical antimicrobial peptides isolated from the southern African scorpion species, Parabuthus schlechteri and Opistophthalmus carinatus, respectively. Along with their antimicrobial action against bacteria and fungi, these peptides show pore-forming properties in the membranes of mammalian cells. Pore-formation and ion selectivity in cardiac myocytes were investigated by measuring the whole cell leak current by means of the patch clamp technique. Pore-formation was observed as the induction of leak currents. Ion selectivity of the pores was indicated by the shift of the reversal potential (E,,,) upon substitution of intra (K' with CS' and CI- with aspartate) and extracellular (Na' with NMDG') ions. Results were compared with the effect of gramicidin A used as a positive control for monovalent cation selective pores. PP and OP I induced a fluctuating leak current and indicate non-selectivity of PP and OP1-induced pores. An osmotic protection assay to determine estimated pore size was performed on the cardiac myocytes. PP and OP1-induced pores had an estimate pore size of 1.38-1.78 nm in diameter. The effect of PP and OP1 on the membrane potential (MP) of a neuroblastoma cell line and cardiac myocytes was investigated. TMRM was used to mark the MP fluorescently and a confocal microscope used to record the data digitally. The resting membrane potential (RMP) of the neuroblastoma cells was calculated at -38.3 f 1.9 mV. PP (0.5 uM) and OP1 (0.5-1 uM) depolarized the entire cell uniformly to a MP of -1 1.9 k 3.9 mV and -9.4 k 1.9 mV, respectively. This occurred after 20-30 min of peptide exposure. In the case of the cardiac myocytes depolarization was induced to -39.7 f 8.4 mV and -32.6 f 5.2 mV by 0.5-1 uM PP and 1.5-2.5 uM OPl, respectively. / Thesis (M.Sc. (Physiology))--North-West University, Potchefstroom Campus, 2006.

La maladie d'Alzheimer est la maladie neurodégénérative la plus fréquente dont la prévalence augmente avec l'âge. Elle résulte d'un excès de peptide β-amyloïde (Aβ) capable de s'agréger, de s'insérer dans la membrane plasmique des cellules et de s'organiser en pores perméables au calcium. Cette insertion est modulée par la composition lipidique de la membrane dont le cholestérol. Alors que plusieurs études indiquent que le cholestérol interagit avec le peptide Aβ et module sa toxicité, les mécanismes moléculaires sous-jacents demeurent mal compris.A l'aide d'approches expérimentales multiples nous avons évalué le rôle du cholestérol dans l'insertion du peptide Aβ à la membrane ainsi que dans le processus d'oligomérisation responsable de la formation de pore. Notre étude identifie le domaine 22-35 du peptide Aβ comme domaine d'interaction avec le cholestérol au sein duquel deux acides aminés sont essentiels : la Val24 et la Lys28. Ce petit fragment s'organise en pore dans la membrane plasmique et déclenche une entrée massive de calcium dans les cellules. Cet effet n'est plus observé lorsque les cellules ont moins de cholestérol dans leur membrane ou en présence de zinc, un inhibiteur des pores amyloïdes. Le cholestérol maintient le peptide de façon oblique et en hélice α. Cette orientation favorise l'établissement d'une liaison hydrogène entre l'Asp27 d'un peptide et la Lys28 d'un peptide voisin, qui stabilise le pore. Enfin, notre étude montre que le bexarotène, un composé anti-Alzheimer dont le mécanisme d'action est controversé, prévient l'insertion du peptide dans des membranes et empêche la formation de pores dans la membrane plasmique des cellules nerveuses. / Alzheimer's disease is the most common neurodegenerative disease whose prevalence increases with age. It is the result of excess β-amyloid peptide (Aß), which self-organizes. This peptide is able to insert into the plasma membrane of cells where their organization in calcium permeable pores triggers the early stages of toxicity. This insertion is directly modulated by the lipid composition of the membrane especially cholesterol. Whereas several studies indicate that cholesterol interacts with and modulates Aß toxicity, the underlying molecular mechanisms remain poorly understood.Using computational, physico-chemical and cellular approaches, we evaluated the role of cholesterol in the insertion of the Aß peptide in the membrane and in the oligomerization process responsible for pore formation. Our study identifies the 22-35 fragment of Aβ as a functional cholesterol-binding domain in which two amino acids are essential: Val24 and Lys28. When incubated with SH-SY5Y cells, the minimal Aβ22-35 peptide caused an increase of Ca2+ entry. This effect was no longer observed in cholesterol-depleted cells and was inhibited by zinc, a classical blocker of amyloid channels. Cholesterol specifically induced a tilted alpha-helical topology of Aβ22-35 which appeared to facilitate the oligomerization process through the establishment of a hydrogen bond network involving Asn27 and Lys28. Finally, our study showed that bexarotene, an anti-Alzheimer compound whose mechanism of action is still under debate, competitively inhibited Aβ insertion into cholesterol-containing membranes and prevented calcium-permeable amyloid pore formation in the plasma membrane of neural cells.

Oligonucleotides may become a new class of therapies with the potential of curing many today untreatable diseases. Oligonucleotides becomes increasingly more difficult to separate with an increase in length since the relative difference in retention of these very similar compounds becomes increasingly smaller. Therefore, coelution of impurities formed during synthesis may result in insufficient purity, which is necessary for therapeutic treatments. Oligonucleotides are also relatively large biomolecules, possibly consisting of hundreds of nucleotides. As a result, oligonucleotides may have limited diffusion through the stationary phase pores which affects separation performance. Surprisingly few studies have be published in this research area and a wider knowledge in how this affects separation is needed. In this master thesis, separation of deoxythymidine oligonucleotides with 5-30 mers in length were separated with 60, 100, 200 and 300 Å pore size reversed phase C4 columns. It was concluded that pore size resulted in more restricted diffusion if insufficient pore size was used. Poor peak performance was also observed with too large pore sizes which lead to less efficient separations.

Afin d’améliorer la compréhension des effets des coagulants sur les performances des membranes organiques d'ultrafiltration employées dans la production d’eau potable, une caractérisation structurale complète (surface et volume) de l’échelle microscopique à l’échelle macroscopique des membranes (neuves, après filtration de coagulant et après lavage chimique) est utilisée. En premier lieu, les propriétés structurales des membranes planes neuves PES ont été déterminées en fonction du seuil de coupure. Les caractéristiques de surface (taille de pore et taux de remplissage) déterminées par le MEB et les caractéristiques en volume déterminées par l’ellipsométrie de speckle ont montré une évolution croissante avec le seuil de coupure. L’utilisation du LB et de l’AFM avec différentes fenêtres d’observation a montré que la détermination de la rugosité d'une membrane est bien fonction de l'échelle d’observation. L’AFM a permis de différencier les membranes selon leur seuil de coupure mais aussi selon les méthodes de fabrication. En second lieu, l’impact de la nature des coagulants en polychlorosulfate d'aluminium (PAX-XL 7A et Aqualenc F1) sur les propriétés structurales des membranes en PES 100 kDa a été abordé. L'utilisation du modèle d’Hermia et les analyses multi-échelle de la rugosité de surface ont montré que la filtration de suspensions de cogulants de PAX-XL 7A ou Aqualenc F1 produit un dépôt à la surface dû à l’adsorption et/ou la précipitation des produits d’hydrolyse de coagulants, provoquant une modification importante de la morphologie de surface de la membrane. Cette modification structurale est aussi révélée par des mesures du speckle de l’onde diffusée. Des analyses MEB et AFM ont révélé un changement de l’état de surface de la membrane lavées après colmatage. L’extension des techniques de caractérisation structurale, en particulier l'AFM, à l'étude des fibres creuses en AC et PVDF et leur vieillissement a montré une voie d’exploitation très intéressante. / For the better understanding of the effects of the use of coagulants on the performance of ultrafiltration organic membranes applied in the production of drinking water, a complete structural characterization (surface and bulk) from microscopic scale to macroscopic scale of the membranes (new, after filtration of coagulant and after chemical cleaning) is used. First, the structural properties of new flat-sheet PES membranes were determined as a function of MWCO. The characteristics of surface (pore size and recovery rate) determined by SEM and the features of bulk determined by speckle ellipsometry showed an increasing trend with MWCO. The use of WLI and AFM with different observation scales showed that the determination of the roughness of a membrane significantly depends on the observation scale. The AFM was able to differentiate membranes according to their MWCO as well as to the methods of manufacturing. Second, the impact of the nature of aluminum polychlorosulfate coagulants (PAX-XL 7A and Aqualenc F1) on the structural properties of PES 100 kDa membrane is addressed. The use of Hermia model and the analysis of multi-scale surface roughness showed that the filtration of suspensions of coagulants PAX-XL 7A or Aqualenc F1 produces a deposit on the surface through adsorption and/or precipitation of hydrolysis products of coagulant, causing a significant change in the surface morphology of the membrane. This structural modification is also revealed by the measurements of speckle of the light scattering. SEM and AFM analysis revealed a change in the state of surface of the membrane after cleaning of fouled membranes. An extension of the structural characterization techniques, in particular the AFM to the study of hollow fibers and their aging has shown a very interesting way of analysis.

Determining the distribution of porosity and permeability is one of the main challenges in carbonate petroleum reservoir characterization and requires a thorough understanding of pore type and origin, as well as their spatial distributions. Conventional studies of carbonate reservoirs require interpretation and analysis of cores to understand porosity. This study investigates the use of NMR logs in the determination of pore type and origin. This study is based on the analysis of both thin section petrographic and NMR data from a single well that cored the Lower Cretaceous (Aptian) shelf carbonates belonging to the Shuaiba Formation of the Middle East. Photographs of thin sections were used to determine pore type and origin according to Ahr's genetic classification of carbonate porosity. Descriptive statistics and modeling were used to analyze the NMR T2relaxation time distributions. Descriptive statistical analyses included estimating arithmetic average, standard deviation, skewness, median, mode and 90th percentile. T2modeling was performed by fitting multiple log-normal distributions to the measured T2distribution. Data from thin section petrography and from NMR measurements were then compared using conditional probabilities. As expected, thin section analysis revealed the predominance of mud-supported fabrics and micropores between matrix grains Vugs and dissolved rudistid fragments account for most of the macro porosity. Descriptive statistics showed that the mode and th percentile of the T2distribution had the greatest power to discriminate pores by origin. The first principal component (PC1) of the mode-90th percentile system was then used to compute the probabilities of having each pore origin, knowing that PC1 belongs to a given interval. Results were good, with each origin being predictable within a certain range of PC1. Decomposition of the T2distributions was performed using up to 3 log-normal component distributions. Samples of different pore origin behaved distinctively. Depositional porosity showed no increase in fit quality with increasing number of distributions whereas facies selective and diagenetic porosity did, with diagenetic porosity showing the greatest increase.

This thesis describes a numerical modelling methodology to interpret dynamic fluctuations in pore-pressures to isolate the effects of loading associated with changes in total soil moisture (site water balance) alone. The methodology is required to enhance the data-interpretation and performance-assessment for potential applications of a novel piezometer-based, large-scale, geological weighing lysimeter. This interpretative methodology is based on a method of superimposing computer-based numerical analyses of independent causes of pore-pressure transients to separate the different pore-pressure responses. Finite element coupled load-deformation and seepage numerical models were used to simulate field-observed piezometric responses to water table fluctuations and loading induced by surface water balance (using meteorological data).<p> Transient pore-pressures in a deep clay-till-aquitard arising from variations in the water table within a surface-aquifer were modelled and removed from the measured pore-pressure record (corrected for earth tide and barometric effects) to isolate and identify pore-pressure fluctuations arising from loading associated with site water balance. These estimates were compared to simulated pore-pressure responses to an independently measured water balance using meteorological instrumentation. The simulations and observations of the pore-pressure responses to surface water balance were in good agreement over the dry years of a 9-year period. Some periods of significant differences did occur during wet years in which runoff, which is not accounted for in the current analyses, may have occurred.<p> The identification of pore-pressure response to total soil moisture loading using the developed numerical modelling methodology enhances the potential for the deployment of the piezometer-based geological weighing lysimeter for different applications which include real-time monitoring of site water balance and hydrological events such as precipitation and flooding. Interestingly, the disparity occurring during the wet years even suggests the potential to adapt the method to monitor runoff (net lateral flow).<p> The methodology also demonstrated the capability to accurately estimate in situ elastic and hydraulic parameters. Calibration of the model yielded equivalent properties of the aquitard (hydraulic conductivity, Kv, of 2.1E-5 m/day and specific storage, Ss, of 1.36E-5 /m) for a Skemptons B-bar coefficient of 0.91 for an assumed porosity of 0.26. Sensitivity tests also provided insight into the consolidation and pressure propagation (swelling) behaviour of the aquitard under parametric variations. The parameters obtained are consistent with range of values reported for glacial clay till soil. Therefore, this work also provides a unique case history of a method for determining, large scale, in situ material properties for geo-engineers and scientists to explore by simply using piezometric and meteorological data.

This thesis describes a numerical modelling methodology to interpret dynamic fluctuations in pore-pressures to isolate the effects of loading associated with changes in total soil moisture (site water balance) alone. The methodology is required to enhance the data-interpretation and performance-assessment for potential applications of a novel piezometer-based, large-scale, geological weighing lysimeter. This interpretative methodology is based on a method of superimposing computer-based numerical analyses of independent causes of pore-pressure transients to separate the different pore-pressure responses. Finite element coupled load-deformation and seepage numerical models were used to simulate field-observed piezometric responses to water table fluctuations and loading induced by surface water balance (using meteorological data).<p> Transient pore-pressures in a deep clay-till-aquitard arising from variations in the water table within a surface-aquifer were modelled and removed from the measured pore-pressure record (corrected for earth tide and barometric effects) to isolate and identify pore-pressure fluctuations arising from loading associated with site water balance. These estimates were compared to simulated pore-pressure responses to an independently measured water balance using meteorological instrumentation. The simulations and observations of the pore-pressure responses to surface water balance were in good agreement over the dry years of a 9-year period. Some periods of significant differences did occur during wet years in which runoff, which is not accounted for in the current analyses, may have occurred.<p> The identification of pore-pressure response to total soil moisture loading using the developed numerical modelling methodology enhances the potential for the deployment of the piezometer-based geological weighing lysimeter for different applications which include real-time monitoring of site water balance and hydrological events such as precipitation and flooding. Interestingly, the disparity occurring during the wet years even suggests the potential to adapt the method to monitor runoff (net lateral flow).<p> The methodology also demonstrated the capability to accurately estimate in situ elastic and hydraulic parameters. Calibration of the model yielded equivalent properties of the aquitard (hydraulic conductivity, Kv, of 2.1E-5 m/day and specific storage, Ss, of 1.36E-5 /m) for a Skemptons B-bar coefficient of 0.91 for an assumed porosity of 0.26. Sensitivity tests also provided insight into the consolidation and pressure propagation (swelling) behaviour of the aquitard under parametric variations. The parameters obtained are consistent with range of values reported for glacial clay till soil. Therefore, this work also provides a unique case history of a method for determining, large scale, in situ material properties for geo-engineers and scientists to explore by simply using piezometric and meteorological data.