Modeling water infiltration using physical based models, including the vertical variability of soil and rainfall intensity throughout a precipitation event, allows to estimate the runoff and infiltration measured in uncontrolled environments. In this study, the hypothesis was evaluated that, for natural rainfall conditions, a layered heterogeneous soil profile and at plot scale, the assumption of piston-type flow before and after the ponding allows to simulate satisfactorily the infiltration and runoff rates. Infiltration and runoff were simulated for ten events of rainfall, in plots of soil with heterogeneous profile and using the Green-Ampt model (piston type). The calibration of the model was done with the modification of only two parameters, the final degree of saturation and the initial soil water content, implying changes in other parameters of the model but preserving the physical relations. To evaluate model performance, statistical indexes were calculated by comparing the simulated cumulative runoff (Es) with the measured cumulative runoff (Eo). For seven of the ten events, only the adjustment of the degree of saturation was enough for good performance of the model. For the other three events an adjustment the degree of saturation and the initial soil water contente was necessary. Although some simulations did not reproduce the gradual increase in the measured runoff, the model was able to estimate runoff satisfactorily in all events, especially in those of longer duration. / A modelagem da infiltração de água por meio de modelos de base física, incluindo a variabilidade vertical do solo e da intensidade de chuva ao longo de um evento, permite uma melhor estimativa do escoamento e da infiltração medidos em ambiente não controlado. Neste estudo, foi avaliada a hipótese que, para condições de chuva natural em perfil de solo estratificado e escala de parcela, a presunção de fluxo tipo pistão antes e depois do empoçamento permite simular satisfatoriamente a infiltração e o escoamento superficial. A infiltração e o escoamento superficial foram simulados para dez eventos de precipitação, em parcelas de solo com perfil heterogêneo e usando o modelo Green-Ampt (fluxo tipo pistão). A calibração do modelo foi feita com a modificação de apenas dois parâmetros, o grau de saturação final e o conteúdo de água inicial, os quais implicam modificações nos demais parâmetros do modelo, preservando as relações físicas. Para avaliação do desempenho do modelo, índices estatísticos foram calculados, comparando o escoamento acumulado simulado (Es) com o escoamento acumulado medido (Eo). Para sete dos dez eventos de chuva, o ajuste somente do grau de saturação foi suficiente para que houvesse bom desempenho do modelo. Para os outros três eventos foi necessário ajustar o grau de saturação e o conteúdo inicial de água do solo. Embora algumas simulações não tenham reproduzido o incremento gradual no escoamento medido, o modelo permitiu estimar satisfatoriamente o escoamento em todos os eventos, principalmente nos mais longos.

Cyclooxygenases (COXs) and their main renal product, prostaglandin E2 (PGE2), regulate many physiological renal functions and are involved in the pathogenesis of diabetic kidney disease. The PGE2 receptor EP3 has been repeatedly shown to be upregulated during diabetes. Physiologically, EP3 is best recognized to act as a diuretic by antagonizing arginine-vasopressin (AVP)-mediated water reabsorption. Incidentally, the first renal manifestation of diabetes is polyuria, which may trigger a cascade of events leading to DN. We hypothesize that EP3 contributes to polyuria and kidney dysfunction during diabetes. We injected EP3-/- mice with streptozotocin (STZ) and evaluated their renal function 12-weeks post injection. EP3-/- STZ mice exhibit attenuated polyuria while exhibiting increased urine osmolality suggesting enhanced water reabsorption. Western blots reveal that EP3-/- STZ mice have increased expression of aquaporin-1 and aquaporin-2 as well as reduced urinary AVP excretion compared to STZ mice. However, salt transporters were equivalently increased in STZ and EP3-/- STZ mice. In vitro microperfusion shows that EP3 completely abrogates AVP-mediated water reabsorption in STZ cortical collecting ducts. Furthermore, EP3-/- STZ mice showed blunted renal COX-2 expression as well as reduced renal hypertrophy, glomerular hyperfiltration, and albuminuria. Taken together, the data suggests that EP3 contributes to polyuria during diabetes by inhibiting expression of aquaporins. Additionally, EP3 seems to contribute to renal COX-2 induction during diabetes. The lack of an increase in renal COX-2 protein levels in EP3-/- STZ mice may be protective by preventing further renal damage.

This thesis analyses potential benefits of Danube-Oder-Elbe canal to the states of the central Europe. In order to do that it is necessary to describe the current importance of inland navigation within these states as well as the condition of the waterways. The main bottlenecks on existing infrastructure are the missing locks. The paper also looks into the development of support of the Danube-Oder-Elbe canal from the first reference in 1700 to the year of 2014. The last part of the work deals with the calculation of estimated direct costs and profits of the construction. Besides the direct there are also indirect expenses, which cover not only the necessary repairs and maintenance, but also external costs. External costs of inland water navigation are estimated to be six times lower than those of road transport. This difference could be a significant competitive advantage of the river transportation.

Astrocytes posses a wide range of functions within the brain. In response to ischemic conditions they swell due to increased uptake of osmolytes and they are mainly responsible for cytotoxic edema formation. However, they are also able to regulate their volume by releasing osmolytes together with water via the process of regulatory volume decrease (RVD). The Aquaporin 4 (AQP4) channel and Transient receptor potential vanilloid 4 (TRPV4) channel are suspected to be strongly involved in these processes of astrocytic volume regulation. The goal of the present diploma thesis was to clarify the role of both channels in astrocytic swelling in situ. For our experiments we used a subpopulation of green fluorescent protein-labelled astrocytes from AQP4-deficient (AQP4-/- ), TRPV4-deficient (TRPV4-/- ) and control (Ctrl) mice. Cell volume alterations were induced in acute brain slices by hypoosmotic stress or by oxygen-glucose deprivation (OGD). Data were quantified using fluorescence intensity-based approach in the whole cells and in astrocytic endfeet. Our results indicate, that there is no difference in astrocytic swelling or cell volume recovery between astrocytes from AQP4-/- , TRPV4-/- and control mice when exposed to hypoosmotic stress. On the contrary, volume changes induced by OGD varied...

In polymer electrolyte fuel cells (PEFC) chemical energy, in for example hydrogen, is converted by an electrochemical process into electrical energy. The PEFC has a working temperature generally below 100 °C. Under these conditions water management and transport of oxygen to the cathode are the parameters limiting the performance of the PEFC. The purpose of this thesis was to better understand the complex processes in different parts of the PEFC. The rate-limiting processes in the cathode were studied using pure oxygen while varying oxygen pressure and humidity. Mass-transport limitations in the gas diffusion layer using oxygen diluted in nitrogen or helium was also studied. A large capacitive loop was seen at 1-10 Hz with 5-20 % oxygen. When nitrogen was changed to helium, which has a higher binary diffusion coefficient, the loop decreased and shifted to a higher frequency. Steady-state and electrochemical impedance spectroscopy (EIS) models have been developed that accounts for water transport in the membrane and the influence of water on the anode. Due to water drag, the membrane resistance changes with current density. This gives rise to a low frequency loop in the complex plane plot. The loop appeared at a frequency of around 0.1 Hz and varied with D/Lm2, where D is the water diffusion coefficient and Lm is the membrane thickness. The EIS model for the hydrogen electrode gave three to four semicircles in the complex plane plot when taking the influence of water concentration on the anode conductivity and kinetics into account. The high-frequency semicircle is attributed to the Volmer reaction, the medium-frequency semicircle to the pseudocapacitance resulting from the adsorbed hydrogen, and the low-frequency semicircles to variations in electrode performance with water concentration. These low-frequency semicircles appear in a frequency range overlapping with the low-frequency semicircles from the water transport in the membrane. The effects of current density and membrane thickness were studied experimentally. An expected shift in frequency, when varying the membrane thickness was seen. This shift confirms the theory that the low-frequency loop is connected to the water transport in the membrane. / <p>QC 20121011</p>

No description available.

A steady-state computational model for a proton exchange membrane fuel cell (PEMFC) is presented. The model accounts for species transport, electrochemical kinetics, energy transport, current distribution, water uptake and release within the polymer portion of the catalyst layers, and liquid water production and transport. Both two-dimensional and three-dimensional geometries are modeled. For a given geometry, the governing differential equations are solved over a single computational domain. For the two-dimensional model, the solution domain includes a gas channel, gas diffusion layer, and catalyst layer for both the anode and cathode sides of the cell as well as the solid polymer membrane. For the three-dimensional model the current collectors are also modeled on both the anode and cathode sides of the fuel cell. The model for the catalyst layers is based on an agglomerate geometry, which requires water species to exist in dissolved, gaseous, and liquid forms simultaneously. Data related to catalyst layer morphology that was required by the model was obtained via a physical analysis of both commercially available and in-house membrane electrode assemblies (MEA). Analysis techniques including cyclic voltammetry and electron microscopy were used. The coupled set of partial differential equations is solved sequentially over a single solution domain with the commercial computational fluid dynamics (CFD) solver, CFDesign™ and is readily adaptable with respect to geometry and material property definitions. A fuel cell test stand was designed and built to facilitate experimental validation of the model. The test stand is capable of testing cells up to 50 cm2 under a variety of controlled conditions. Model results for both two and three-dimensional fuel cell geometries are presented. Parametric studies performed with the model are also presented and illustrate how fuel cell performance varies due to changes in parameters associated with the transport of reactants and liquid water produced in the cell. In particular, the transport of oxygen, water within the polymer portions of the catalyst layers and membrane, and liquid water within the porous regions of the cell are shown to have significant impact on cell performance, especially at low cell voltage. Parametric studies also address the sensitivity of the model results to certain physical properties, which illustrates the importance of accurately determining the physical properties of the fuel cell components on which the model is based. The results from the three-dimensional model illustrate the impact of the collector plate shoulders (for a conventional flowfield) on oxygen transport and the distribution of current production within the cell. / Ph. D.

In seawater, drinking is a fundamental part of the osmoregulatory strategy for teleost fish, and presents a unique challenge. The intestine has an established role in osmoregulation, and its ability to effectively absorb fluid from imbibed seawater is crucial to compensating for water losses to the surrounding hyperosmotic environment. Alongside solute-linked water transport (driven by NaCl cotransport), intestinal bicarbonate (HCO3-) secretion also benefits fluid absorption directly (via apical Cl-/HCO3- exchange), and indirectly through the formation of calcium carbonate (CaCO3) thus removing the osmotic influence of Ca2+ within the gut fluid. For the European flounder (Platichthys flesus), elevated luminal Ca2+ has proven to be a specific, potent stimulator of HCO3- secretion both in vitro and in vivo where these actions are presumably modulated by an extracellular Ca2+-sensing receptor (CaR). The focus of this work was to learn more about how intestinal HCO3- secretion is regulated, the role of Ca2+, and more specifically the CaR. To achieve this, in vitro ‘gut sac’ experiments investigated how luminal Ca2+ influenced HCO3- secretion, and associated ion and fluid transport. Contrary to expectation, increasing Ca2+ from 5 to 20 mM did not stimulate HCO3- secretion. In an attempt to elucidate the role of CaCO3 precipitation in fluid absorption, and further explore the physiological implications of HCO3- secretion, the intestine was perfused in vivo with salines containing varying concentrations of Ca2+ (10, 40 and 90 mM). The production and secretion of HCO3-, in addition to CaCO3 formation increased accordingly with Ca2+, and was associated with a dramatic 25 % rise in the fraction of fluid absorbed by the gut. Additional in vitro experiments, utilising the Ussing chamber, helped establish some of the characteristics of intestinal HCO3- secretion by the euryhaline killifish (Fundulus heteroclitus), but was unresponsive to elevated mucosal Ca2+. Further attempts to potentiate the activity of the CaR, and application of the receptor agonists gadolinium (Gd3+) and neomycin, failed to produce responses consistent with the effect of Ca2+ observed previously, either in vitro or in vivo. With no evidence supporting a direct role for an extracellular, intestinal CaR in HCO3- secretion it was argued that secretion would be principally regulated by two factors, the ability of the epithelia to generate high levels of intracellular HCO3- and the rate of CaCO3 formation.

L'objectif de cette étude est d'examiner les écoulements diphasiques liquide/gaz dans les canaux des plaques bipolaires des piles à combustible afin de comprendre et de trouver des solutions au problème d'engorgement. L'influence de la section du canal et du matériau utilisé sur les pertes de charge (PDC) et sur la structure de l'écoulement d'eau liquide est plus particulièrement étudiée dans une expérience hors pile. Les mesures des PDC ont permis de mettre en évidence des séquences de bouchages et de débouchages, la fréquence de ces dernières augmentant avec le débit. Par ailleurs il est montré que le rapport des PDC diphasiques moyennées par les PDC en air sec décroit avec le débit et ceci indépendamment de la dimension du canal et qu'il est d'autant plus faible que le revêtement est hydrophile. Enfin différents régimes d'écoulements diphasiques (stratifié et de gouttes) ont pu être mis en évidence dans les différentes zones du canal et un modèle pour chacun d'eux a été établi, confirmant les résultats expérimentaux / This work focuses on the gas-liquid flows in the cathode plate, with the objective to observe their patterns, to understand their behavior, to estimate the pressure drops (PD) and eventually, to reduce clogging and its possible consequences in term of oxygen starvation downstream. A special emphasis is put on the effect of the channel section (typically between 0.5 and 1 mm²) and on the surface properties of the flow field plate materials. The experiments are performed ex-situ. The PD is measured locally along the channel as well as globally between the inlet and outlet, which put forward the existence of clogging/unclogging sequences. The characteristic frequency of these sequences increases with the air flow rate. The results show that the ratio of PD in two-phase flow to PD in dry flow decreases with the air flow rate while it does not seem to depend on the channel size (within the tested range). Moreover this ratio is lower with hydrophilic coating. Finally two main flow patterns (slug and annular flow) have been observed depending on the distance from the inlet and they have been simulated

Understanding the structure and dynamics of molecularly thin films or the state of water confined to nanoscale dimensions is an active field of research and has wide applications in areas ranging from biology to geology. The issues concern fundamental aspects related to the manner in which a substrate influences the organization of water, origin of forces present when water is confined to nanoscale dimensions, and the influence on the structure and dynamics of water adjacent to a surface. The focus of this thesis lies in examining the thermodynamics and transport properties of interfacial and confined water. As a prelude to studying the structure of water confined between two mica surfaces, we first investigated the structuring of water adjacent to a single mica surface using grand canonical Monte Carlo (GCMC) simulations. The adsorption isotherm reveals three distinct stages as the relative vapor pressure in increased. The derived film thickness, isotherm shape, and heats of adsorption are in excellent agreement with recent experimental data. Our study does not support the 2D ice hypothesis and indicates that beyond the first adsorbed layer water is liquid-like. The characteristics of water confined to nanometer dimensions between two hydrophilic surfaces are investigated to assess the influence of chemical functionality of the hydrophilic surface on the structure of confined water. Our study shows that hydration of potassium ions on the mica surface has a strong influence on the water structure and solvation force response of confined water. In contrast to the disrupted hydrogen bond network observed for water confined between mica surfaces, water between silica surfaces is able to retain its hydrogen bond network displaying bulk-like structural features down to surface separations as small as 0.45 nm. An oscillatory solvation force response is observed only for water confined between silica surfaces. We evaluate and contrast the water density, dipole moment distributions, pair correlation functions and the solvation forces as a function of the surface separation. Recent experimental studies have shown that even for subnanometer confinement, the shear viscosity of water between mica surfaces is only three times larger than the free water viscosity. The dynamics of confined water between mica surfaces is evaluated using molecular dynamics simulations. Our analysis shows that the residence time for water in the contact layer is about two orders of magnitude larger than water in the central bulk-like regions between the surfaces. The K+ ions have a strong influence on the dynamics of confined water, leading to a decoupling in the translation and orientational motions. Our analysis also shows the presence of orientational jump dynamics in the contact layer near the mica surface. We also investigate the influence of confinement on the hydration characteristics of NaCl solutions both as a function of the salt concentration and the surface separation, H between graphite surfaces. A hydration limit is defined as the concentration at which a rapid drop in the hydration number is observed with increasing salt concentration. Despite a high degree of confinement, ions are able to form a quasi two-dimensional hydration shell between the two surfaces. The hydration number, reduces to about 4.15 at a pore width of H =8 A, when compared with the bulk hydration number of 6.25. In many practical situations, surfaces that are separated by an intervening fluid can be dissimilar giving rise to the so called Janus interface. In order to probe the fluid structure in such systems, we studied non-polar fluids confined between two asymmetric surfaces. By varying the degree of asymmetry between the two surfaces a wide variety of adsorption situations are examined using GCMC simulations and a mean field lattice model. The degree of asymmetry is found to influence the presence of frozen phases and can also support co-existing liquid and solid phases.