All living cell functions require an ongoing supply of energy derived from carbohydrates, lipids and proteins with their own pathways of breakdown. All of them end up in the oxidation of reduced coenzymes, yielding chemically-bound energy in the form of adenosine triphosphate (ATP). One broad definition of energy would be the capability to do work and, therefore, the more work that has to be done, the more energy is needed, which may under extreme conditions put the cell into a state of energy metabolic stress. This complex of problems has been examined in the present thesis, where individuals representing different degrees of training status, have been subjected to various types of stressful work-loads as regards intensity and duration. Meanwhile, the energy turnover has been monitored on different levels as whole body (organism)-, single organ/tissue-, cellular and molecular levels. Combined methodologies have been developed and utilized to examine carefully and in some detail energy expenditure and biochemical variables with study subjects under long-term, (outfield) physically and mentally stressful conditions. When the individuals were in a well-controlled energy balance, a diet rich in saturated fatty acids did not elicit any major metabolic stress signs concerning serum lipoproteins and/or insulin/glucose homeostasis during the test period including high volume and low intensity energy turn over. Only a slight decrease in the Apo-B / Apo-A1 ratio was observed, despite a period of totally sedentary life style among the participants. Mental stress combined with a varying energy balance during off-shore sailing races was shown to cause such an energy metabolic stress situation that development of abdominal obesity and signs of a metabolic syndrome in embryo affected the participants who were young, non-obese men and despite their fairly healthy lifestyle concerning the diet they were on and their physical activity habits. Even well-trained young individuals of both sexes, subjected to exhaustive endurance (high intensity exercise session), developed signs of insulin resistance with a deteriorated intracellular glucose availability leading to a supposed ion pump failure and a disturbed osmoregulation on a cellular level. Hence, they presented themselves as having acquired an energy metabolic stress like condition. In conclusion, an energy metabolic stress syndrome has been described, basically due to impaired fuelling of ion pumps with a cluster of signs and symptoms on single organ/tissue-, cellular and molecular levels manifested by muscular intracellular swelling, tendency towards erythrocyte shrinkage as a consequence of a relative insulin resistance concomitant with ion distribution disturbances (Gardos effect), oxidative stress and osmoregulatory taurine leakage.

Expansive soils occurring in arid and semi-arid climate regions of the world cause serious problems on civil engineering structures. Such soils swell when given an access to water and shrink when they dry out. Several attempts are being made to control the swell-shrink behavior of these soils. Soil stabilization using chemical admixtures is the oldest and most widespread method of ground improvement. In this study, waste limestone dust and waste dolomitic marble dust, by-products of marble industry, were used for stabilization of expansive soils. The expansive soil is prepared in laboratory as a mixture of kaolinite and bentonite. Waste limestone dust and waste dolomitic marble dust were added to the expansive soil with predetermined percentage of stabilizer varying from 0 to 30 percent. Grain size distribution, consistency limits, chemical and mineralogical composition, swelling percentage, and rate of swell were determined for the samples. Swelling percentage decreased and rate of swell increased with increasing stabilizer percentage. Also, samples were cured for 7 days and 28 days before applying swell tests. Curing of samples affects swell percentages and rate of swell in positive way.

Total suction of unsaturated soils is contributed by matric and osmotic suctions. Matric suction arises from capillary actions in the soil structure and varies with changes in moisture content of the soil. Pore fluid osmotic suction is related to the dissolved salt content in soil water (soil water salinity) and increases with pore water salinity. Exposure of clay soils to chemical solutions (example landfill leachate, brine pond solutions) induces osmotic suction difference between soil water and the chemical reservoir. Soil water refers to the aqueous solution residing in soil pores that is chemically composed of H2O molecules and dissolved salt molecules. Osmotic suction difference between soil water and the chemical reservoir is dissipated through the following modes. Salt molecules diffuse from the chemical reservoir to the soil water and H2O molecules from soil water flows to chemical reservoir to equalize salt concentrations in the two chambers. This flow of H2O molecules is called an osmotic flow. During osmotic flow, if the clay particles behave as perfect semi-permeable membranes, only water exchanges between clay voids and the external solution in response to chemical concentration gradients. Clay particles however function as imperfect semi-permeable membranes and transfer dissolved salts in addition to water. The outward flow of H2O molecules from soil water (dilute solution chamber) to chemical reservoir (concentrated solution chamber) causes negative pore fluid pressures to develop within the compacted clay, which then leads to increase in effective stress and the consequent volume decrease is termed as osmotic induced consolidation. Conversely, diffusion of salt molecules from chemical reservoir to soil water in response to chemical concentration gradient reduces the thickness of the diffuse ion layers around the clay particles causing a decrease in the electrical repulsion forces between them. This in turn reduces the separation of the clay particles and, consequently, compresses the clay sample to a lower void ratio; the process being termed as osmotic consolidation. Tests described by researchers show that osmotic consolidation usually has a larger effect than the osmotically induced one. Review of the literature shows that most of the available theoretical and experimental analysis in literature only focuses on the behaviour of clay samples reconstituted from slurries and not on the one of compacted clays. Compacted clays are exposed to osmotic suction gradients under field situations such as landfills and brine ponds where compacted clay liners are in contact with leachate/brine solutions. Examining the impact of osmotic suction dissipation on the swell/compression behaviour of compacted clays forms the focus of the present thesis. Statement of Problem Compacted clays differ from clay samples reconstituted from slurries as they are characterized by both matric suction and osmotic suction. As a result, besides dissipating osmotic suction gradients by diffusion of salt molecules and flow of H2O molecules, compacted clays absorb salt solution in their partly saturated void spaces to dissipate matric suction and in the process may develop swelling strains. However, absorption of salt solution to dissipate matric suction and salt diffusion in response to osmotic suction difference will alter the diffuse double layer (DDL) thickness as the latter is affected by the dissolved salts concentration of soil water; alterations in DDL thickness will in turn affect the swelling behaviour of the compacted clays. The influence of alterations in DDL thickness from dissipation of matric suction and osmotic suction difference on the swelling magnitudes of compacted expansive clays exposed to salt solutions needs to be examined. The direction of salt diffusion in response to dissipation of osmotic suction difference will also impact the swelling behaviour of compacted clays exposed to osmotic suction gradients. Diffusion of salts from external reservoir to soil water (salinization path) in response to osmotic suction gradients will reduce the swell potential of the compacted expansive clay from increased dissolved salts concentration in soil water. Conversely, diffusion of salts from soil water to external reservoir (desalinization path) should facilitate the compacted clay to swell more from reduction in its dissolved salts concentration. The influence of direction of salt diffusion during dissipation of osmotic suction gradient on the swell behaviour of compacted expansive clays needs to be examined. The volumetric response of compacted clays exposed to salt solutions may be different compared with identically compacted specimens wetted with distilled water at same total vertical pressure value. As previously mentioned, exposure of compacted clays to salt solutions, besides destroying capillary bonds will alter the soil water chemistry of the compacted clay specimens from absorption of salt solution to dissipate matric suction and salt diffusion in response to osmotic suction gradients. Alterations in soil water chemistry in turn alter the swell pressures of compacted clay specimens from concomitant changes in electrical repulsion forces. If the modified swell pressure of the compacted specimen exceeds the total vertical pressure, diminished swelling strains result at the macroscopic level. Conversely, the compacted clay will experience compressive strains at the macroscopic level if the total vertical pressure exceeds the modified swell pressure of the compacted specimen. Alterations in the wetting induced volumetric response of compacted clays from modifications in swell pressure upon exposure to salt solutions needs to be examined. Earlier researchers had re-plotted the compressibility data for sodium- montmorillonite clays remolded with sodium chloride solutions using the osmotic suction of the remolding fluids as a stress state variable in a three-dimensional space. Along a plane in which osmotic pressure (π) is constant, the coefficient of volume compressibility (mv) was obtained. Along a plane in which the effective stress [(σ - uw)] is constant, the slope defined the osmotic coefficient of volume compressibility (mπ). The above concept is useful to predict the osmotic consolidation strains of clay specimens upon exposure to salinization paths at constant effective stress. Salt diffusion into soil water in response to osmotic suction gradients may alter the exchangeable cation composition of saturated clay specimens. Alterations in exchangeable cation composition alters the diffuse ion layer thickness of clay particles which in turn may impact the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path. Saturated saline specimens refer to saturated clay specimens that are exposed to salinization (saturated specimens are inundated with salt solution) path. Saturated desalinated specimens are obtained by exposing saturated saline specimens to desalinization (inundated with distilled water) path. Osmotic swelling refers to the swelling strains developed by saturated saline specimens on exposure to desalinization path. These strains result from outward migration of salts in response to osmotic suction gradients. The influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path needs examination. The swelling magnitudes of compacted specimens are influenced by variations in dry density, water content and consolidation pressure. However, the effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path is not known and needs examination. Based on the statement of the problem, the following objectives emerge: • To examine the influence of dissipation of matric suction and osmotic suction difference on the swelling behaviour of compacted expansive clays exposed to osmotic suction gradients (salinization path). • To examine the influence of direction of salt diffusion during dissipation of osmotic suction gradients on the swell behaviour of compacted expansive clays. • To examine alterations in the wetting induced volumetric strain response of compacted clays from modifications in swell pressure upon exposure to salt solutions at range of total vertical pressures. • To predict the osmotic consolidation strains of saturated clay specimens upon exposure to salinization paths at constant effective stress. • To examine the influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path. • To examine, effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path. The organization of the thesis is as follows: After the first introductory chapter, a detailed review of literature is performed towards highlighting the need to examine the influence of dissipation of osmotic suction gradients on the swell-compression behaviour of compacted expansive clays in Chapter 2. Chapter 3 presents a detailed experimental program of the study. Chapter 4 examines the influence of dissipation of matric suction and osmotic suction difference on the swelling behaviour of compacted expansive clays exposed to salinization path. The chapter also examines the influence of direction of salt diffusion durin dissipation of osmotic suction gradients on the swell behaviour of compacted expansive clays. Black cotton soil from Karnataka State was used as the expansive clay specimen to examine these objectives. Inundating compacted expansive clay specimens with (0.1 M to 4 M) sodium chloride solutions at a total vertical pressure of 6.25 kPa in oedometer cells exposed the clay specimens to salinization paths. Measurements of changes in swelling strains, matric suction (measured by filter paper method) and pore water chemistry with time provided insight into the relative influence of matric suction and salt diffusion on the kinetics of swell. Examining the time-axial deformation behaviour of compacted specimens exposed to salinization paths in the post-primary swell region delineated the influence of osmotic suction dissipation on the volume change behaviour of compacted expansive clays. The influence of direction of salt diffusion in response to osmotic suction gradients on the swelling behaviour of compacted expansive clay was examined in the following manner. Salt diffusion from external reservoir to soil water (salinization path) was accomplished by inundating compacted clay specimens with 0.4 M and 4 M sodium chloride solutions in oedometer cells at 6.25 kPa. Salt diffusion from soil water to external reservoir (desalinization path) was accomplished by inundating salt-amended specimens with distilled water in oedometer cells at 6.25 kPa. Salt-amended specimens refer to expansive clay specimens remolded with 0.4 M/4 M sodium chloride solution at desired moisture content and compacted to the design density. Experimental results illustrated that compacted specimens dissipated matric suction by absorption of distilled water and sodium chloride solutions. The initial osmotic suction difference was dissipated by inward diffusion of salts; salt solutions absorbed to dissipate matric suction also contributed to dissipation of osmotic suction difference. The compacted clay specimens swelled on inundation with sodium chloride solutions as dissipation of matric suction and the attendant growth of diffuse ion layer repulsion dominated compacted clay behaviour exposed to salinization paths. However exposure to salinization path reduced swell magnitudes of compacted clay specimens from reductions in diffuse ion layer thickness. The time-swell plots of the compacted clay specimens exposed to salinization path categorized into initial, primary and secondary swell regions. Rates of primary swell were 5 to 21 times larger than rates of secondary swell. Experimental data suggested that primary swell develops relatively rapidly as it is linked to rate of matric suction dissipation. Secondary swell developed more slowly as it is controlled by diffusion of salts and adsorption-desorption reactions. Increase in dissolved salts concentration in soil water during primary swell occurs from salt solution absorbed in response to matric suction and salt diffused in response to osmotic suction difference. Comparatively, increase in dissolved salts concentration in soil water during secondary swell occurs from diffusion of salts in response to osmotic suction gradients. Exposure of salt-amended clays to desalinization path caused outward diffusion of salts to dissipate osmotic suction difference and absorption of distilled water to quench the matric suction of the salt-amended specimens. The salt-amended specimens developed greater swell potentials than compacted specimens inundated with distilled water owing to reduction in dissolved salt concentration of soil water and replacement of native exchangeable calcium and magnesium ions by sodium ions. The time-swell behaviour of salt-amended specimens exposed to desalinization path categorize into four regions: small initial swell region followed by large primary swell and small secondary swell regions and lastly a large tertiary swell region. Complete dissipation of matric suction coincides with end of primary swell and both processes terminate in 120-240 minutes after inundation for salt-amended specimens exposed to desalinization paths. Further, only small fraction (16 to 18 %) of possible salt extrusion occurs at the end of primary swell and bulk of salt extrusion occurs during secondary and tertiary swell. Secondary swell developed at a slower rate than primary swell, as the rate of osmotic suction dissipation during secondary swell was smaller than rate of matric suction dissipation during primary swell. Likewise, tertiary swell developed at similar or faster rate than primary swell, as rate of osmotic suction dissipation during tertiary swell is similar or quicker than rate of matric suction dissipation during primary swell for the salt-amended clays. Analysis of the laboratory results showed that greater magnitude of outward salt diffusion mobilizes larger magnitudes of secondary + tertiary swell in response to dissipation of osmotic suction difference in case of the salt-amended clay specimens. Comparison of swelling behaviour of specimens exposed to salinization and desalinization paths revealed that the direction of salt diffusion impacts their swelling behaviour. Inward salt diffusion during salinization path reduces the swell magnitude of the compacted specimens. Bulk of the swell occurs during primary swell. Outward salt diffusion during desalinization path imparts a larger swell magnitude to the salt-amended specimens in comparison to the compacted specimen inundated with distilled water. Bulk of the swell occurs during secondary + tertiary swell. Dissipation of matric suction was rapid and coincided with the end of primary swell during salinization and desalinization paths. Bulk diffusion of salts during secondary and tertiary swell was a relatively slow process. Chapter 5 examines alterations in the wetting induced volumetric response of compacted clays from modifications in swell pressure upon exposure to salt solutions at range of total vertical pressures (6.25 kPa to 200 kPa). The chapter delineates the manner in which dissipation of matric suction (arising due to unsaturated status of compacted clay) and osmotic suction difference (arising due to chemical concentration gradients between soil water and chemical reservoir) impacts the DDL repulsion pressure/swell pressure and wetting-induced volume change behaviour of compacted expansive clays as a function of total vertical pressures (6.25 kPa to 200 kPa). Alterations in the diffuse double layer repulsion pressure of compacted clays from salt diffusion are calculated based on Gouy- Chapman diffuse double theory. The diffuse double layer repulsion pressures of compacted clays exposed to salinization paths are compared with the oedometer swell pressures. The impact of modifications in swell pressure from salt diffusion on the nature of wetting-induced volumetric strains (swell/compression) experienced by the compacted expansive clay specimens exposed to salinization paths is also examined. The nature of wetting-induced volume change behaviour is analyzed in context of the total vertical pressure to swell pressure ratio of specimens exposed to salinization paths. Salinization experiments are performed in conventional oedometers with the chemical boundary conditions imposed in an “open air” fashion. In the salinization experiments, salt solutions in the oedometer reservoir were in contact with the soil water through wet porous stones. Experimental results revealed that dissipation of initial osmotic suction difference between soil water and oedometer reservoir via salt migration impacted the diffuse double layer repulsion pressure and the wetting-induced volume change behaviour of compacted clays. Osmotic suction varies directly; while, the diffuse double layer thickness inversely varies with dissolved salt concentration of soil water. Consequently, inundation with sodium chloride solutions increase the initial osmotic suction difference at the expense of the diffuse double layer repulsion pressures developed by the compacted clay specimens. Salt diffusion in response to dissipation of osmotic suction difference reduced the theoretical (DDL repulsion pressure) and experimental swell pressures of compacted clays inundated with sodium chloride solutions. The theoretical swell pressures however greatly differed from the experimental swell pressures. The total vertical pressure to modified experimental swell pressure ratio determined the nature of axial strains (swell or compression) experienced by compacted clays on exposure to osmotic suction gradients. When the total vertical pressure to modified swell pressure ratio less than unity, the compacted clay specimens experienced net swelling on inundation with sodium chloride solutions. Conversely, when the total vertical pressure to modified swell pressure ratio exceeded unity, the compacted clay experienced net compression on inundation with sodium chloride solutions. When the total vertical pressure to modified swell pressure ratio was unity, the compacted clay did experience any net axial strains on inundating with sodium chloride solution. The ingress of sodium chloride solutions in response to matric suction saturated the void spaces of the compacted specimens prior to commencement of compression. As a result, compression strains experienced by the compacted specimens on exposure to salt solutions were mainly contributed by osmotic consolidation strains. The amount of salt diffused into soil water had direct bearing on the magnitude of osmotic consolidation strains experienced by the compacted specimens at given total vertical pressure value. The time-rates of primary consolidation are approximately 20 to 100 times quicker than rates of osmotic consolidation. The much slower rates of osmotic consolidation arise, as this process is mainly diffusion controlled in comparison to primary consolidation that is mainly dependent on the soil’s permeability to water flow under load-imposed hydraulic gradients. Primary consolidation strains exceed the osmotic consolidation strains at total vertical pressures of 100 kPa and 200 kPa on exposing the compacted specimen to 1 M sodium chloride solution. The osmotic consolidation strain exceeds the primary consolidation strain on exposing the compacted specimen to 4 M sodium chloride solution at total vertical pressure of 200 kPa. Chapter 6 develops a method to predict the osmotic consolidation strains of saturated clay specimens upon exposure to salinization paths at constant effective stress, examines the influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path and effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path Experimental results illustrated that for a given osmotic suction difference (∆π), larger osmotic consolidation strains are predicted at the lower range of consolidation pressures (25-100 kPa), than at the higher range of consolidation pressures (200-400 kPa) as physico-chemical effects dominated the deformation behaviour at the lower stresses, while; mechanical effects (frictional effects, particle interference) became important at higher range of stresses due to proximity of particles and particle groups. Comparatively, at constant consolidation pressure, the magnitudes of osmotic consolidation strains developed by the saturated clay specimens depend on the magnitude of osmotic suction difference (∆π) imposed on the specimens. The slope of the axial strain versus osmotic suction curve defined the coefficient of osmotic compressibility (mπ). Likewise, slope of the axial strain versus effective stresses plot defined the mv values for the specimens. The mπ values are 10 to 20 times smaller than the mv values indicating that the saturated clay specimens experience smaller osmotic consolidation strains from unit increase in osmotic pressure than consolidation strains from unit increase in consolidation pressure. The predicted osmotic consolidation strains were 1.9 to 2.9 times larger than the experimentally determined values. The experimental values were lower as the saturated clay specimens did not compress sufficiently enough on exposure to salinization at concerned effective stress as the well developed diffuse ion layer of the saturated clay specimen inhibited (osmotic) consolidation of the clay specimen. Ion-exchange reaction has a profound influence on the osmotic swelling developed by the saturated saline specimens and osmotic consolidation strains developed by saturated desalinated specimens upon exposure to osmotic suction gradients. Saturated saline specimens are obtained by salinization of the distilled water aturated specimen with sodium chloride solution at desired vertical stress. During salinization ion exchange occurs between sodium ions of inundating fluid and native divalent exchangeable cations of the clay surface. Upon desalinization in distilled water environment, the saturated saline specimen developed 9.2 % osmotic swelling strain at consolidation pressure of 200 kPa over period of 2560 hours. Comparatively, the unsaturated compacted specimen developed much smaller swelling strain of 0.32 % over period of 26 hours upon inundation with distilled water at consolidation pressure of 200 kPa. The 100-fold larger duration needed by saturated saline specimen to develop larger osmotic swelling strain arose from diffusion controlled outward migration of salts from soil water to distilled water reservoir. The saturated saline specimen exhibited 29-fold larger swell magnitude than the compacted clay specimen at same consolidation pressure as the combined effects of reduction in dissolved salt concentration (from outward diffusion of salts) and enhanced exchangeable sodium concentration increased the diffuse ion layer thickness around clay particles to an extent that the saline specimens swelled by 9 % at 200 kPa. Experimental results also indicated that after ion-exchange equilibrium was established, subjecting saturated saline specimens to cycles of desalinization yielded similar magnitudes of osmotic swelling strains. Likewise saturated desalinated specimen subjected to cycles of salinization yielded similar magnitudes of osmotic consolidation strains. Also the magnitudes of osmotic swelling and osmotic consolidation strains exhibited by the saturated saline and saturated desalinated specimens were of similar magnitudes. Variations in compaction density of the compacted clay specimens had bearing on the osmotic swelling developed by the saturated saline specimens and osmotic consolidation strains developed by the saturated desalinated specimens in response to dissipation of osmotic suction gradients. Desalinization caused the 1.42 Mg/m3series saturated saline specimen to experience 2 fold larger swelling strain than the 1.28 Mg/m3 series saline specimen from outward salt diffusion in response to dissipation of osmotic suction gradient. Similarly, salinization caused the 1.42 Mg/m3 series saturated desalinated specimen to experience 1.46 fold larger osmotic consolidation strain from inward salt diffusion than the 1.28 Mg/m3 desalinated specimen. The much larger swell potential exhibited by the 1.42 Mg/m3saline specimen than the 1.28 Mg/m3 series saline specimen indicates that the influence of compaction dry density persists even after saturation and alterations in exchangeable cation composition of the compacted clay specimens. Experimental results demonstrated that variations in compaction water do not have a bearing on the osmotic swelling and osmotic consolidation strains subsequently developed by the saturated saline and desalinated specimens. Chapter 7 summarizes the main findings of this study.

No description available.

<p>Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network.</p><p>The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering.</p><p>The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent</p><p>The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error.</p><p><b>KEYWORDS:</b>Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling.</p>

An aqueous nanoparticle dispersion is a complex fluid whose mobility in porous media is controlled by four key factors: the conditions necessary for the stability of nanoparticle dispersions, the kinetics of nanoparticle aggregation in an unstable suspension, the rheology of stable or unstable suspensions, and the interactions between the nanoparticles and oil/water interface and mineral surfaces. The challenges in controlling nanoparticle transport come from the variations of pH and ionic strength of brine, the presence of stationary and mobile phases (minerals, oil, water and gas), the geochemical complexity of reservoir rocks, and pore-network. The overall objective of this work is to achieve a better understanding of nanoparticle transport in porous media based on a systematic experimental and theoretical study of above factors. For this purpose, the critical conditions for the aqueous stability of nanoparticles are identified and fit by a theoretical model, which describes the interaction energy between silica nanoparticles. Above critical conditions nanoparticle aggregation becomes significant. A model for the aggregation kinetics is developed and validated by experiments. A mechanistic model for predicting the viscosity of stable and unstable silica nanoparticle dispersions over a wide range of solid volume fraction is developed. This model is based on the concept of effective maximum packing fraction. Adsorption experiments with silica nanoparticles onto quartz, calcite and clay surfaces and interfacial tension measurements provide insightful information on the interaction of the nanoparticles with minerals and decane/water interface. The extent of nanoparticle adsorption on mineral/water and decane/water interfaces is evaluated based on DLVO theory and Gibbs’ equation. Visual observations and analytical methods are used to understand the interaction of nanoparticles with clay. The characterization of nanoparticle behavior in bulk phases is built into an understanding of nanoparticle transport in porous media. In particular, the rheology of nanoparticle dispersions flowing through permeable media is compared with those determined using a rheometer. In the presence of residual oil, the retention of silica nanoparticles at water/oil interface during steady flow is investigated. The results from batch experiments of nanoparticle adsorption are used to explain the flow behavior of these nanoparticles in a glass bead pack at residual oil saturation. / text

Hyaluronic acid (HA) is one of the primary chemical building blocks of the extracellular matrix and thus is an attractive material for biomedical applications. FDA approved HA-based materials are available as dermal fillers, joint viscosupplements, vitreous substitutes, and abdominal adhesion barriers. The engineering of new HA-based materials and applications is an active area of research. Here we develop several new types of HA-based hydrogels with unique and useful properties. To address the challenge of delivering hydrophobic drugs from hydrophilic hydrogel matrices we have grafted HA hydrogels with [Beta]-cyclodextrin to create hydrogels capable of binding poorly water soluble drugs. To create HA hydrogels with unique anisotropic swelling behavior we have developed a dual-crosslinking technique in which a super-swelling chemically crosslinked hydrogel is patterned with low-swelling photocrosslinked domains. When this dual-crosslinked hydrogel is swelled it contorts into a new shape because of differential swelling among photopatterned regions. To address the challenge of creating hydrogel scaffolds with biomimetic branched porosity we have invented a "crystal templating" technique. This technique grows dendritic crystals throughout a biopolymer solution, crosslinks the biopolymer around the crystals, and washes the crystals away to yield a hydrogel with a dendritic macroporous network. Lastly, we invented a method for patterning a substrate with a microarray of hydrogel compartments. A microarray of living cells is obtained when cells are seeded on the hydrogel patterned substrate. This method addresses the need for an inexpensive, simple method for obtaining living cell microarrays that does not require clean room labs and lithographic expertise. Each of these new materials were based on hyaluronic acid hydrogels but the methods are generalizable to hydrogels of other polymers too. In conclusion, the novel methods in this dissertation are a significant contribution to the engineering of HA-based materials. / text

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Biodegradable hydrogels have become very promising materials for a number of biomedical applications, including tissue engineering and drug delivery. For optimal tissue engineering design, the mechanical properties of hydrogels should match those of native tissues as closely as possible because these properties are known to affect the behavior and function of cells seeded in the hydrogels. At the same time, high water-contents, large mesh sizes and well-tuned degradation rates are favorable for the controlled release of growth factors and for adequate transport of nutrients through the hydrogel during tissue regeneration. With these factors in mind, the goal of this research was to develop and investigate the behavior of injectable, biodegradable hydrogels with enhanced stiffness properties that persist even at high degrees of swelling. In order to do this, degradable functionalities were incorporated into photo-crosslinkable poly(ethylene glycol) and poly(acrylic acid) hydrogels, and these two components were used to make a series of double-network hydrogels. Synthesis of the precursor macromers, photopolymerization of the hydrogels, and structural parameters of the hydrogels were analyzed. The composition and the molecular weight between crosslinks (Mc) of the hydrogel components were varied, and the degradation, swelling, thermal and mechanical properties of the hydrogels were characterized over various time scales. These properties were compared to corresponding properties of the component single-network hydrogels.

Uranium-zirconium (U-Zr) alloys comprise a class of metallic nuclear fuel that is regularly considered for application in fast nuclear energy systems. The U-10wt%Zr alloy has been demonstrated to very high burnup without cladding breach in the Experimental Breeder Reactor-II (EBR-II). This was accomplished by successfully accommodating gaseous fission products with low smear density fuel and an enlarged cladding plenum. Fission gas swelling behavior of the fuel has been experimentally revealed to be significantly affected by the temperature gradient within a fuel pin and the multiple phase morphologies that exist across the fuel pin. However, the phase effects on swelling behavior have not been yet fully accounted for in existing fuel performance models which tend to assume the fuel exists as a homogeneous single phase medium across the entire fuel pin. Phase effects on gas bubble nucleation and growth in the alloy were investigated using transmission electron microscopy (TEM). To achieve this end, a comprehensive examination of the alloy system was carried out. This included the fabrication of uranium alloys containing 0.1, 2, 5, 10, 20, 30, 40, and 50 wt% zirconium by melt-casting. These alloys were characterized using electron probe micro-analysis (EPMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Once the alloys were satisfactorily characterized, selected U-Zr alloys were irradiated with 140 keV He^(+) ions at fluences ranging from 1 × 10^(14) to 5 × 10^(16) ions/cm^(2). Metallographic and micro-chemical analysis of the alloys indicated that annealing at 600 °C equilibrates the alloys within 168 h to have stable α-U and δ-UZr_(2) phase morphologies. This was in contrast to some reported data that showed kinetically sluggish δ-UZr_(2) phase formation. Phase transformation temperatures and enthalpies were measured using DSC-TGA for each of the alloys. Measured temperatures from different time annealed alloys have shown consistent matches with most of the features in the current U-Zr phase diagram which further augmented the EPMA observed microstructural equilibrium. Nevertheless, quantitative transformation enthalpy analysis also suggests potential errors in the existing U-Zr binary phase diagram. More specifically, the (β-U, γ2) phase region does not appear to be present in Zr-rich (> 15 wt%) U-Zr alloys and so further investigation may be required. To prepare TEM specimens, characterized U-Zr alloys were mechanically thinned to a thickness of ~150 μm, and then electropolished using a 5% perchloric acid/95% methanol electrolyte. Uranium-rich phase was preferentially thinned in two phase alloys, giving saw-tooth shaped perforated boundaries; the alloy images were very clear and alloy characterization was accomplished. During in-situ heating U-10Zr and U-20Zr alloys up to 810 °C, selected area diffraction (SAD) patterns were observed as the structure evolved up to ~690 °C and the expected α-U → β-U phase transformation at 662 °C was never observed. For the temperature range of the (α-U, γ2) phase region, phase transformation driven diffusion was observed as uranium moved into Zr-rich phase matrix in U-20Zr alloy; this was noted as nonuniform bridging of adjacent phase lamellae in the alloy. From the irradiation tests, nano-scale voids were discovered to be evenly distributed over several micrometers in U-40Zr alloys. For the alloys irradiated at the fluences of 1 × 10^(16) and 5 × 10^(16) ions/cm^(2), estimated void densities were proportional to the irradiation doses, (250 ± 40) and (1460 ± 30) /μm^(2), while void sizes were fairly constant, (6.0 ± 1.5) and (5.2 ± 1.2) nm, respectively. Measured data could be foundational inputs to the further development of a semi-empirical metal fuel performance model.