50Hz alternating electric fields have been used to enhance the mass transfer of ionic solutes within several food and model food materials under a range of conditions. Using image analysis it has been possible to visualise diffusion and determine concentration profiles within solid structures. It has been shown that in a uniform electric field diffusion can be enhanced by ca. 40% above that of normal diffusion, when an electric field strength of approximately 1500 Ym-l is applied. Modelling of the concentration profiles has demonstrated that the mechanism of enhanced mass transfer is dependent on the material in which the ion is diffusing as well as the process temperature and applied electric field strength. For alginate, a highly charged polymer structure, at low temperature (30°C) using a "Fickian" diffusion model fitted the experimental data well. At elevated temperature (100°C) the concentration profiles gave a poor fit to a "Fickian" diffusion model, however fitted well to a "Type II" diffusion model where the surface region of the material was flooded with dye. Within agar, a less highly charged material, diffusion can be fitted well using a Fickian diffusion model in all cases. Although diffusion is not truly Fickian as concentration dependence was seen. A number of effects were seen, the rate of diffusion into the solid material increased with decreasing molecular weight and increasing ionic charge of the dye molecules in solution (methylene blue, rhodamine 60 and fluorescein), however not to the extent predicted by a true electrophoretic model. Furthermore, enhanced diffusion increased by only 25% when the motion of the ions was along the electric field lines, as opposed to at 90°. The enhanced mass transfer effect has been demonstrated in a distorted electric field, local electric field strengths within the system have been calculated, and the diffusion coefficients obtained are in good agreement with diffusion coefficients in a constant electric field. Finally, enhanced mass transfer has been demonstrated in two species of fish, here changes in the diffusion coefficient demonstrate structural changes to the material.

No description available.

The thesis deals with the numerical modeling of nonreactive and nonlinearly sorbing solutes in groundwater and analysis of the effect of heterogeneity resulting from spatial variation of physical and chemical parameters on the transport of solutes. For this purpose, a hy­brid flux corrected transport (FCT) and central difference method based on operator-split approach is developed for advection-dispersion solute transport equation. The advective transport is solved using the FCT technique, while the dispersive transport is solved using a conventional, fully implicit, finite difference scheme. Three FCT methods are developed and extension to multidimensional cases are discussed. The FCT models developed are anlaysed using test problems possessing analyt­ical solutions for one and two dimensional cases, while analysing advection and dispersion dominated transport situations. Different initial and boundary conditions, which mimic the laboratory and field situations are analysed in order to study numerical dispersion, peak cliping and grid orientation. The developed models are tested to study their relative merits and weaknesses for various grid Peclet and Courant numbers. It is observed from the one dimensional results that all the FCT models perform well for continuous solute sources under varying degrees of Courant number restriction. For sharp solute pulses FCT1 and FCT3 methods fail to simulate the fronts for advection dominated situations even for mod­erate Courant numbers. All the FCT models can be extended to multidimensions using a dimensional-split approach while FCT3 can be made fully multidimensional. It is observed that a dimensional-split approach allows use of higher Courant numbers while tracking the fronts accurately for the cases studied. The capability of the FCT2 model is demonstrated in handling situations where the flow is not aligned along the grid direction. It is observed that FCT2 method is devoid of grid orientation error, which is a common problem for many numerical methods based on Cartesian co-ordinate system. The hybrid FCT2 numerical model which is observed to perform better among the three FCT models is extended to model transport of sorbing solutes. The present study analyses the case of nonlinear sorption with a view to extend the model for any reactive transport situation wherein the chemical reactions are nonlinear in nature. A two step approach is adopted in the present study for coupling the partial differential equation gov­erning the transport and the nonlinear algebraic equation governing the equilibrium sorp­tion. The suitability of explicit-implicit (EI - form) formulation for obtaining accurate solution coupling the transport equation with the nonlinear algebraic equation solved using a Newton-Raphson method is demonstrated. The performance of the numerical model is tested for a range of Peclet numbers for modelling self-sharpening and self-smearing con­centration profiles resulting from nonlinear sorption. It is observed that FCT2 model based on this formulation simulates the fronts quite accurately for both advection and dispersion dominated situations. The delay in the solute mobility and additional dispersion are anal­ysed varying the statistical parameters characterising the heterogeneity namely, correlation scale and variance during the transport of solutes and comparisons are drawn with invariant, cases. The impact of dispersion during the heterogeneous transport is discussed.

Uma área de 9 m x 28 m, localizada às margens do açude Cajueiro, no município de Tuparetama - PE, foi instrumentada com o objetivo de estudar os processos de transferência de água e de solutos. O solo local é heterogêneo, sendo constituído por um solo aluvial de características arenosas a franco arenosas. A área, localizada na região semi-árida e utilizada para o cultivo de vazante, está sujeita a altas taxas de evaporação e aos efeitos cíclicos de subida e rebaixamento do nível d\'água do açude. A caracterização física do solo foi feita com base em ensaios de prospecção e granulometria. A caracterização hidráulica foi realizada com base em um ensaio de drenagem interna realizado no centro da área e as concentrações de sais totais presentes no solo foram obtidas pro meio de ensaios de determinação dos sais solúveis em extratos de saturação. Os parâmetros hidráulicos foram obtidos ajustando-se os dados do ensaio de drenagem interna e de monitoração de campo a diversos modelos analíticos, utilizando-se o programa RETC. Os parâmetros hidrodispersivos foram obtidos ajustando-se os dados da curva de eluição experimental aos modelos CDE e CDE-MIM, utilizando-se o programa CXTFIT 2.0. O programa HYDRUS-2D foi utilizado para simular o fluxo de água e o transporte de solutos num domínio de fluxo bi-dimensional com 28 m de comprimento e 2,0 m de profundidade, incluindo a zona saturada e não saturada. O programa simulou bem o comportamento do fluxo medido no campo através da instrumentação. Os valores simulados de umidade se ajustaram melhor aos valores medidos na estação localizada no centro da área instrumentada. Para as camadas superficiais os valores simulados de umidade foram superestimados o que pode estar associado à variabilidade espacial dos parâmetros hidráulicos ou à influência de fluxo preferencial. A simulação do transporte de solutos, feita em termos de sais totais, permitiu concluir que as altas taxas de evaporação, associadas às concentrações de sais totais presentes no solo, tendem a provocar a salinização das camadas superficiais da área estudada. / An area of 9 m x 28 m, located in the banks of the Cajueiro reservoir, in the municipal district of Tuparetama, Pernambuco, has been instrumented with the objective of studying the processes of water flow and solute transport. The local soil is heterogeneous, being constituted by an alluvial soil of sandy characteristics. The area, located in the semi-arid region and used for the agriculture, is subjected to high evaporation rates and cyclical effects of rising and lowering of the water level in the reservoir. The physical characterization of the soil has been undertaken based on sample extraction and texture analysis. The hydraulic characterization has been based on an internal drainage experiment accomplished in the center of the area and the concentrations of present total salts have been obtained from saturation extracts. The hydraulic parameters have been obtained fitting the internal drainage experiment data and the field data to several analytic models, using the program RETC. The hydrodispersive parameters have been obtained fitting the data of breakthrough curves to the models CDE and CDE-MIM, using the program CXTFIT 2.0. The program HYDRUS-2D have been used to simulate the water flow and solute transport in a two-dimensional domain with 28 m of length and 2,0 m of depth, including the saturated and unsaturated zones. The program has simulated well the behavior of the flow measured in the field. The simulated values of water content agreed better with the measured values in the center of the studied area. For the superficial layers the simulated values of water content have been overestimated, which can be associated to both the spacial variability of the hydraulic parameters and the influence of preferential flow. The simulation of the solutes-transport, in terms of total salts, has shown that the high evaporation rates in association to the salts presents in the soil promote the salinization of the superficial layers of the studied area.

Studies of submillimeter gels composed of covalently cross-linked poly(acrylic acid)-g-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic-PAA) networks are reviewed in light of potential applications of the microgels as drug carriers in oral delivery. The microgels are capable of volumetric transitions in response to environmental stimulae such as pH and temperature. It is shown that the type of Pluronic used in the microgel synthesis changes the structure of the resulting microgels, with the more hydrophobic Pluronic imparting porosity. Microgels based on Pluronic L92 (L92-PAA-EGDMA) possess higher ion-exchange capacity than microgels based on Pluronic F127 (F127-PAA-EGDMA), albeit the former are more hydrophobic. Analogously, more hydrophobic but heterogeneous L92-PAA-EGDMA exhibit superior capacity for equilibrium loading of hydrophobic drugs such as taxol, camptothecin and steroid hormones, as well as higher capacity for weakly basic drugs such as doxorubicin, mitomycin C, and mitoxantrone. / Singapore-MIT Alliance (SMA)

Uma área de 9 m x 28 m, localizada às margens do açude Cajueiro, no município de Tuparetama - PE, foi instrumentada com o objetivo de estudar os processos de transferência de água e de solutos. O solo local é heterogêneo, sendo constituído por um solo aluvial de características arenosas a franco arenosas. A área, localizada na região semi-árida e utilizada para o cultivo de vazante, está sujeita a altas taxas de evaporação e aos efeitos cíclicos de subida e rebaixamento do nível d\'água do açude. A caracterização física do solo foi feita com base em ensaios de prospecção e granulometria. A caracterização hidráulica foi realizada com base em um ensaio de drenagem interna realizado no centro da área e as concentrações de sais totais presentes no solo foram obtidas pro meio de ensaios de determinação dos sais solúveis em extratos de saturação. Os parâmetros hidráulicos foram obtidos ajustando-se os dados do ensaio de drenagem interna e de monitoração de campo a diversos modelos analíticos, utilizando-se o programa RETC. Os parâmetros hidrodispersivos foram obtidos ajustando-se os dados da curva de eluição experimental aos modelos CDE e CDE-MIM, utilizando-se o programa CXTFIT 2.0. O programa HYDRUS-2D foi utilizado para simular o fluxo de água e o transporte de solutos num domínio de fluxo bi-dimensional com 28 m de comprimento e 2,0 m de profundidade, incluindo a zona saturada e não saturada. O programa simulou bem o comportamento do fluxo medido no campo através da instrumentação. Os valores simulados de umidade se ajustaram melhor aos valores medidos na estação localizada no centro da área instrumentada. Para as camadas superficiais os valores simulados de umidade foram superestimados o que pode estar associado à variabilidade espacial dos parâmetros hidráulicos ou à influência de fluxo preferencial. A simulação do transporte de solutos, feita em termos de sais totais, permitiu concluir que as altas taxas de evaporação, associadas às concentrações de sais totais presentes no solo, tendem a provocar a salinização das camadas superficiais da área estudada. / An area of 9 m x 28 m, located in the banks of the Cajueiro reservoir, in the municipal district of Tuparetama, Pernambuco, has been instrumented with the objective of studying the processes of water flow and solute transport. The local soil is heterogeneous, being constituted by an alluvial soil of sandy characteristics. The area, located in the semi-arid region and used for the agriculture, is subjected to high evaporation rates and cyclical effects of rising and lowering of the water level in the reservoir. The physical characterization of the soil has been undertaken based on sample extraction and texture analysis. The hydraulic characterization has been based on an internal drainage experiment accomplished in the center of the area and the concentrations of present total salts have been obtained from saturation extracts. The hydraulic parameters have been obtained fitting the internal drainage experiment data and the field data to several analytic models, using the program RETC. The hydrodispersive parameters have been obtained fitting the data of breakthrough curves to the models CDE and CDE-MIM, using the program CXTFIT 2.0. The program HYDRUS-2D have been used to simulate the water flow and solute transport in a two-dimensional domain with 28 m of length and 2,0 m of depth, including the saturated and unsaturated zones. The program has simulated well the behavior of the flow measured in the field. The simulated values of water content agreed better with the measured values in the center of the studied area. For the superficial layers the simulated values of water content have been overestimated, which can be associated to both the spacial variability of the hydraulic parameters and the influence of preferential flow. The simulation of the solutes-transport, in terms of total salts, has shown that the high evaporation rates in association to the salts presents in the soil promote the salinization of the superficial layers of the studied area.

L'extraction de biomolécules à partir de ressources renouvelables devient l'un des thèmes clés dans les domaines de la biotechnologie, de la cosmétologie et de la pharmacie. Pour minimiser la consommation de solvant organique et augmenter l'efficacité, l'extraction avec des mélanges eau/alcool semble être une approche prometteuse. De plus, des étapes supplémentaires de purification et de concentration sont généralement nécessaires pour enrichir le milieu avec les molécules cibles. La nanofiltration (NF) est une technique de séparation idéale et durable pour de telles opérations car elle est propre, sobre et sûre. Il existe néanmoins peu de littérature concernant la NF dans ces mélanges eau/éthanol. Cette étude vise à mieux comprendre les mécanismes de transfert qui régissent la sélectivité dans ces milieux. Dans un premier temps une étude fondamentale est réalisée sur la NF dans des mélanges eau/ alcool seuls ou en présence de solutés neutres et/ou chargés. Les résultats obtenus montrent que lorsque la teneur en alcool augmente, la membrane gonfle, le rayon des pores augmente mais la résistance intrinsèque reste constante. Les mécanismes de transfert bien connus en milieux aqueux (exclusion stérique, interaction électrostatique, interaction diélectique) et en milieux organiques (interactions hydrophobes, affinité soluté-membrane-solvant) sont tous présents dans des mélanges eau/alcool mais leur intensité relative semble être différente. Différents modèles (Spiegler-Kedem & Film, Hydrodynamique & Film, Solution-Diffusion & Film, Pore-Flow & Film, Steric Electric and Dielectric Exclusion) ont été utilisés pour modéliser les rétentions et estimer les paramètres de transfert. / The extraction of bio-molecules from renewable resources is emerging as one of a key topics in the fields of biotechnology, cosmetology and pharmacy. To minimize the organic solvent consumption, as well as to increase the efficiency, extraction by water/alcohol mixtures appears to be a promising approach. Moreover, additional purification and concentration steps are generally required to enrich the medium with the target molecules. Nanofiltration is a de-facto separation technique for such operations because it is clean, sober and safe. Unfortunately, there is few literature on the transfer of water/ethanol mixtures regarding nanofiltration. This study aims to better understand the transfer mechanisms that govern selectivity in these media. At the first step, a fundamental study is realized on nanofiltration in water/alcohol mixtures alone or with the presence of neutral or charged solutes. The obtained results show that when the alcohol content increases, the membrane is swelling, the pore radius increases but the intrinsic resistance is still constant. The well-known transfer mechanisms in aqueous media (steric exclusion, electric interaction, dielectric interaction) and in organic media (hydrophobic interaction, affinity solute-membrane-solvent) are all present in the water/alcohol mixtures, but relative intensity appears to be different. Different models (Spiegler-Kedem & Film, Hydrodynamics & Film, Solution-Diffusion & Film, Pore-Flow & Film, Electric Steric and Dielectric Exclusion) were used to model the retentions and estimate the transfer parameters.

Uma das caracterÃsticas fisiolÃgicas mais importantes das halÃfitas pertencentes ao gÃnero Atriplex à a enorme habilidade de acumular solutos orgÃnicos e inorgÃnicos com o intuito de se ajustar osmoticamente em condiÃÃes de elevada salinidade e deficiÃncia hÃdrica. Contudo estudos compreensivos sobre a contribuiÃÃo relativa desses solutos inorgÃnicos e orgÃnicos no ajustamento osmÃtico de folhas dessas halÃfitas ainda sÃo poucos explorados na literatura. Esse trabalho pretende pela primeira vez na literatura fazer um estudo detalhado, da participaÃÃo e da contribuiÃÃo relativa da maioria dos solutos orgÃnicos e inorgÃnicos no potencial osmÃtico de folhas de Atriplex nummularia, submetidas a concentraÃÃes crescentes de NaCl, ciclos sucessivos de seca e ao polietileno glicol (PEG). Para responder as questÃes acima mencionadas foram conduzidos trÃs grandes experimentos seqÃenciais. No primeiro experimento, mudas de Atriplex nummularia com quatro meses de idade, foram cultivadas em vasos de argila contendo como substrato areia, sendo irrigadas a cada dois dias com soluÃÃo contendo concentraÃÃes crescentes de NaCl (0, 100, 200, 300 e 400 mmol L-1) durante 120 dias. O experimento foi realizado em condiÃÃes de casa de vegetaÃÃo. No segundo experimento, mudas de A. nummularia, com idade de 18 meses foram transplantadas para recipientes de polietileno contendo 5.0 kg de vermiculita, em condiÃÃes de casa de vegetaÃÃo, onde foram submetidas aos seguintes tratamentos (Controle; seca; NaCl + seca; NaCl) por trÃs ciclos sucessivos de seca-reidrataÃÃo (3 semanas) seguido de uma recuperaÃÃo no final do Ãltimo ciclo (apÃs 48 h). No terceiro experimento, plÃntulas de A.nummularia, com idade de dois meses foram transplantadas para cultivo hidropÃnico em vasos plÃsticos com capacidade para 0,8 em sala de crescimento sob condiÃÃes controladas onde sofrerÃo um prÃ-condicionamento com ou sem NaCl por duas semanas. ApÃs foram submetidas aos seguintes tratamentos (controle; PEG; NaCl; NaCl + PEG). Em conclusÃo, os resultados da presente investigaÃÃo demonstram que as plantas de Atriplex nummularia foram capazes de manter o seu crescimento mesmo em condiÃÃes de alta salinidade, principalmente pela capacidade de manutenÃÃo de seu status hÃdrico. Os resultados tambÃm sugerem que a GB à o maior soluto orgÃnico envolvido com o ajustamento osmÃtico (AO) do citoplasma e que sua acumulaÃÃo parece ser uma resposta adaptativa ao estresse provocado pelo NaCl. Em adiÃÃo, o Ãons salinos Na+ e Cl- contribuÃram para a maioria do AO das folhas submetidas ao NaCl. O impacto relativo do K+ sobre o AO das folhas foi reduzido consideravelmente com o aumento da dose externa de NaCl. Os resultados evidenciam tambÃm que o prÃ-condicionamento com NaCl influenciou positivamente no crescimento de Atriplex nummularia, em condiÃÃes de seca, evidenciado pelo maior acÃmulo de massa seca e melhor status hÃdrico das folhas. Dentre os solutos inorgÃnicos analisados, o Na+ e o Cl- foram os que mais contribuÃram para a osmorregulaÃÃo das folhas em condiÃÃes de deficiÃncia hÃdrica. Enquanto, GB foi o soluto orgÃnico mostrou o maior percentual de contribuiÃÃo para o potencial osmÃtico. Entretanto os resultados mostraram que o prÃ-condicionamento das plÃntulas de Atriplex nummularia com NaCl nÃo foram capazes de atenuar os efeitos induzidos pelo PEG.

No description available.

Coccolithophores are single-celled marine phytoplankton, which produce intricate calcium carbonate platelets or ‘coccoliths’. Emiliania huxleyi is the most abundant and widespread coccolithophore, and is one of the most productive calcifying species on earth, playing a key role in global carbon, carbonate and sulphur cycles. Despite much research into coccolithophore biology, the underlying function of their coccoliths is still unknown. The main aim of the research reported in this thesis was to examine the impact of calcification on metabolism in coccolithophores. Calcification is a significant global process, so it is important to discover what effect it has on the metabolism of cells. The major metabolites each have different costs and benefits to the cell, which will vary depending on the habitat and environmental conditions the cell is in. By comparing the metabolite profiles of different strains, including calcifying, non-calcifying, haploid and diploid cells, differences in metabolite composition and potential patterns related to cell type were investigated. Low molecular weight (LMW) metabolites were characterised using a combination of metabolomic techniques. In agreement with previous research, dimethylsulphoniopropionate (DMSP) was the most abundant compound, followed by mannitol and glycine betaine (GBT). Less abundant sugars, polyols and amino acids were also identified. Environmental factors were manipulated to investigate how the principal metabolites were affected by salinity, different light intensities and nutrient (phosphate and nitrate) limitation. The data revealed a striking difference between haploid and diploid cells of the same strain, with the haploid containing lower concentrations of most of the major metabolites. Thus it is proposed that haploid cells have a different osmoregulatory strategy from the diploid cells. A negative correlation was found between DMSP and mannitol, suggesting that mannitol has a dual function, not only as a major storage compound but also as a principal compatible solute. Untargeted metabolite profiling is becoming a popular tool to investigate phenotypes and varying environmental conditions. LC-ESI-QTOF-MS/MS analyses of a wide range of metabolites showed that it is an effective method to identify differences and similarities between E. huxleyi strains grown in different conditions. Strain and growth phase appear to be the more important factors in differentiating metabolite profiles. Surprisingly there were no obvious metabolite profiling differences between calcifying and non-calcifying cells. Untargeted analysis can, however, be used to identify the compounds that did display differences, and which may be important biomarkers, so warrant further investigation. A range of metabolite profiling techniques highlighted important differences between strains, which will hopefully lead onto further research into the metabolome of E. huxleyi, and the unravelling of important metabolic pathways. There has been little research into the LMW metabolites of E. huxleyi, and especially comparisons between strains. Thus the use of metabolomics is a novel way to investigate the difference between cell types and the possible functions of calcification.