Due to the fact that the mechanism of acquisition of phosphorus (P) by roots, is mainly by interception, sufficient P uptake is only ensured by maximal root development ("exploitation"). Pot and field trials were conducted to determine the percentage exploitation of the soil volume by roots. The influence of P on root growth of Zea Mays was also studied. Previously, roots were described in terms of root density (cm cm-2, cm cm-3, gram cm-2 and gram cm-3). In this study roots are described in terms of exploitation which combines length, mass and the rhizosphere. The Gompertz function was used to model exploitation by roots as influenced by P application. P along with nitrogen and potassium, had a highly significant (P < 0.001) effect on root growth in the pot experiments. The root systems' function changed after 14 days from nutrient acquisition to shoot supportive. P had no significant effect on root growth in the field trial. Growth was governed by soil moisture, as dryer positions exhibited higher growth. The high P plot had much less root growth in the subsoil than the low P plot. Gompertz functions revealed subtle differences between different treatments. During the first two weeks (when most P uptake occur) roots exploited at the most 1 % of the top soil volume. This implies that any soil analysis (Bray-1 value), should be divided by ≈ 100 to render the "exploitable" P. When considering the total P uptake of a maize crop (5 kg P ton-I), this means that the crop acquires only ≈ 6% of its P from the "plant available" pool (that is represented by the Bray-1 value). This suggests that roots are indeed able to extract the P from "plant unavailable" pools. Therefore, the term "plant available" is misleading and not descriptive concerning P uptake, and its use should be discontinued. / Dissertation (MSc (Soil Science))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

Kumba Iron Ore, Ltd. is the world‘s fourth largest supplier of sea-borne iron ore and currently operates two mines in South Africa namely: the Sishen mine in the Northern Cape and Thabazimbi mine in Limpopo. The Sishen mine, located at the northern end of the Maremane anticline where the bulk of the hematite ore is buried beneath younger cover lithologies, was our focus area. Here the iron resources are made up by laminated and massive ore bodies that belong to the Asbestos Hills Subgroup. These ore bodies are overlain by conglomerates, shales, flagstone and quartzite. The alkalis, potassium and phosphorous, are common constituents of iron ore, which is known to have a deleterious effect on the manufacturing of iron and steel. Therefore steel making companies charge penalties when purchasing iron ore concentrates with alkali concentrations above predetermined levels. To ensure that the export batches at the Sishen mine stay within set limits, the ores from different batches (with alkali concentration greater and below set limits) are mixed to produce a batch which meet requirements. However this solution will soon become ineffective as the low alkali ore is progressively depleted. Conventional methods used to treat high alkali ores include pyro-and hydrometallurgical methods. These approaches have several limitations such as poor product recovery, involvement of high process and energy cost and an increase in pollution load of water resources. Therefore necessitating research and development of alternative cheap and environment friendly procedures, which could supplement or replace conventional methods to ensure that mining stays economically feasible at the Sishen Iron Ore mine. The application of microorganisms to mining practices is collectively referred to as biohydrometallurgy and includes bioleaching and biooxidation processes. The phrase bioleaching refers to the conversion of an insoluble metal (typically a metal sulfide) into a soluble form (typically a metal sulfate), via microbial activity. When metals are extracted into solution, the process is referred to as bioleaching, whereas if the metal remains in the mineral, it is referred to as biooxidation. The latter term biobeneficiation refers to the selective dissolution of undesired minerals from the ores by direct or indirect action of microbes, thereby enriching the desirable mineral content. Therefore the objective of this study was to determine whether bacteria (naturally occurring on the ore or introduced species) could be used to selectively remove the alkalis from the iron ore mined at Sishen. The species evaluated were able to change the solution pH and/or form biofilms, which is assumed to have affected mineral mobilization. Data obtained during this study suggests that the composition of the ore plays a significant role in its susceptibility to bioleaching. Furthermore we also found that the indigenous cultures were more effective than the introduced species to mobilize the alkalis, which could possibly be ascribed to an adaptation of the microbes present. These preliminary results suggest that bioleaching is an effective alternative cost effective approach to treat iron ore and could possibly be implemented in future into the mining schedule at Sishen. / Dissertation (MSc)--University of Pretoria, 2011. / Microbiology and Plant Pathology / unrestricted

The design, construction and optimization of a low power-high temperature heated ceramic sensor to detect leaking of halogen gases in refrigeration systems are presented. The manufacturing process was done with microelectronic assembly and the Low Temperature Cofire Ceramic (LTCC) technique. Four basic sensor materials were fabricated and tested: Li2SiO3, Na2SiO3, K2SiO3, and CaSiO3. The evaluation of the sensor material, sensor size, operating temperature, bias voltage, electrodes size, firing temperature, gas flow, and sensor life was done. All sensors responded to the gas showing stability and reproducibility. Before exposing the sensor to the gas, the sensor was modeled like a resistor in series and the calculations obtained were in agreement with the experimental values. The sensor response to the gas was divided in surface diffusion and bulk diffusion; both were analyzed showing agreement between the calculations and the experimental values. The sensor with 51.5%CaSiO3 + 48.5%Li2SiO3 shows the best results, including a stable current and response to the gas.

No description available.

Dans cette thèse CIFRE nous avons élaboré une solution originale d’assemblage de cristaux optiques pour applications lasers avec les sociétés Cristal Laser et Oxxius. Nous avons ensuite optimisé notre composition de colle ainsi que le procédé d’encollage des cristaux avec la réalisation d’un robot par nos partenaires industriels. De nombreux tests d’assemblage ont été effectués avec des homo-assemblages de paires de cristaux de SiO2, Quartz, YAG, KTP, LBO, BBO et RTP. Ces homo-assemblages sont ensuite traités thermiquement pour stabiliser notre interface de colle et nos résultats sont satisfaisants. Nous avons également réalisé des hétéro-assemblages avec des paires de cristaux de nature différente parmi les cristaux précédemment étudiés comme YAG/Quartz ou SiO2/KTP. Les résultats que nous obtenons avec ces hétéro-composites semblent indiquer que le différentiel de CTE entre les pièces assemblée limite fortement le bon déroulement des traitements thermiques. Nous avons donc étudié le CTE ainsi que le comportement de notre interface de colle en fonction de la température afin de proposer une composition et un traitement adapté à la réalisation de ces hétéro-composites. / In this CIFRE thesis we elaborate a bonding solution, with Cristal Laser and Oxxius companies, for non-linear optical crystals for laser applications. We had to optimize solution’s composition and the bonding process, this resulted in the creation of a bonding robot by our industrial partners. Numerous homo-assemblies bonding tests has been realized with the following crystal pairs of SiO2, Quartz, YAG, KTP, LBO, BBO and RTP. Those homo-assemblies have been thermally treated to stabilize our bonding solution interface and we obtained relatively good results. We also bonded hetero-assemblies with different crystal pairs like YAG/Quartz or SiO2/KTP. The results we get with these hetero-composites suggest that the difference in CTE between the assembled parts greatly limits the smooth heat treatments. We therefore investigated the CTE and the behavior of our adhesive interface depending on the temperature to provide adapted composition and treatment to the realization of these hetero-composites.

The contractile state of microcirculatory vessels is a major determinant of the blood pressure of the whole systemic circulation. Continuous bi-directional communication exists between the endothelial cells (ECs) and smooth muscle cells (SMCs) that regulates calcium (Ca2+) dynamics in these cells. This study presents theoretical approaches to understand some of the important and currently unresolved microcirculatory phenomena. Agonist induced events at local sites have been shown to spread long distances in the microcirculation. We have developed a multicellular computational model by integrating detailed single EC and SMC models with gap junction and nitric oxide (NO) coupling to understand the mechanisms behind this effect. Simulations suggest that spreading vasodilation mainly occurs through Ca2+ independent passive conduction of hyperpolarization in RMAs. Model predicts a superior role for intercellular diffusion of inositol (1,4,5)-trisphosphate (IP3) than Ca2+ in modulating the spreading response. Endothelial derived signals are initiated even during vasoconstriction of stimulated SMCs by the movement of Ca2+ and/or IP3 into the EC which provide hyperpolarizing feedback to SMCs to counter the ongoing constriction. Myoendothelial projections (MPs) present in the ECs have been recently proposed to play a role in myoendothelial feedback. We have developed two models using compartmental and 2D finite element methods to examine the role of these MPs by adding a sub compartment in the EC to simulate MP with localization of intermediate conductance calcium activated potassium channels (IKCa) and IP3 receptors (IP3R). Both models predicted IP3 mediated high Ca2+ gradients in the MP after SMC stimulation with limited global spread. This Ca2+ transient generated a hyperpolarizing feedback of ~ 2-3mV. Endothelium derived hyperpolarizing factor (EDHF) is the dominant form of endothelial control of SMC constriction in the microcirculation. A number of factors have been proposed for the role of EDHF but no single pathway is agreed upon. We have examined the potential of myoendothelial gap junctions (MEGJs) and potassium (K+) accumulation as EDHF using two models (compartmental and 2D finite element). An extra compartment is added in SMC to simulate micro domains (MD) which have NaKα2 isoform sodium potassium pumps. Simulations predict that MEGJ coupling is much stronger in producing EDHF than alone K+ accumulation. On the contrary, K+ accumulation can alter other important parameters (EC Vm, IKCa current) and inhibit its own release as well as EDHF conduction via MEGJs. The models developed in this study are essential building blocks for future models and provide important insights to the current understanding of myoendothelial feedback and EDHF.

Orientador: Marise Aparecida Rodrigues Pollonio / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-27T16:10:14Z (GMT). No. of bitstreams: 1 Vidal_VitorAndreSilva_M.pdf: 1623174 bytes, checksum: fd05ba4c61253e55cc357bf9bd34bf91 (MD5) Previous issue date: 2015 / Resumo: Com o aumento das informações científicas sobre a relação entre a quantidade e composição de alimentos consumidos na dieta e a saúde, a busca por alimentos mais saudáveis tornou-se relevante nas escolhas dos consumidores. A carne e os produtos cárneos são excelente fonte de oligoelementos, proteínas de alto valor biológico, minerais, vitaminas do grupo B e outros compostos bioativos. Porém, os elevados níveis de ácidos graxos saturados, colesterol, gordura, aditivos e, especialmente sódio tem imposto limites ao seu consumo. Neste contexto, o objetivo deste trabalho foi avaliar a redução do teor de cloreto de sódio (NaCl), principal fonte de sódio e tripolifosfato de sódio (TPFS) em emulsões cárneas de baixo custo (alto teor de carne de frango mecanicamente separada) e em formulações nobres (alto teor de matéria-prima cárnea). O estudo foi dividido em duas etapas. Na primeira, foram elaboradas emulsões cárneas populares (60% de carne de frango mecanicamente separada) contendo sais substitutos (NaCl, KCl e CaCl2) combinados ou isolados com base na força iônica correspondente a 2,5% de NaCl, e formulações com apenas redução de 50% destes sais e TPFS com objetivo de avaliar o efeito sobre as propriedades físico-químicas. Na segunda etapa, foram elaborados 5 tratamentos que apresentaram melhor desempenho na primeira etapa, contendo formulações com blend de sais (NaCl, KCl e CaCl2), e redução de 50% de NaCl e TPFS em emulsões cárneas com alto teor de matéria-prima cárnea. O objetivo da segunda etapa foi igualmente utilizar blends de sais como estratégia para reduzir parcialmente o teor de NaCl e TPFS em emulsões cárneas elaboradas com alto teor de matéria-prima cárnea e verificar o efeito destes nas características físico-químicas a fim de que as matrizes cárneas pudessem ser comparadas. Na primeira e segunda etapa foram determinados: teores de Na, K e Ca, estabilidade de emulsão, pH, avaliação da cor instrumental, Aw, microestrutura e perfil de textura. O KCl foi reportado como o melhor sal substituto ao NaCl, não tendo diferença ou resultando somente em pequenas diferenças em relação aos tratamentos contendo apenas NaCl. O sal substituto CaCl2 causou efeito negativo nas características da matriz cárnea, principalmente na porcentagem de extração das proteínas miofibrilares, ainda que com a mesma força iônica que NaCl. O uso de blend de sais (50% NaCl, 25% KCl e 25% CaCl2) mostrou-se ser uma boa alternativa para redução de sódio. Desta forma, a combinação de sais substitutos (50% NaCl, 25% KCl e 25% CaCl2) e utilização do KCl como sal substituto ao NaCl apresentou-se como uma alternativa para redução de sódio tanto em emulsões cárneas com alto teor de matéria-prima cárnea quanto em emulsão cárnea com alto teor de CMS. No entanto, a redução de fosfato em formulações populares com redução de sódio e adicionada de sais substitutos deve ser melhor investigada para ser implementada / Abstract: The scientific and technological development on food composition and its relationship with food intake and health has led consumer to make healthier food choices. Meat and meat products are excellent source of trace elements, protein with high biological value, minerals, B vitamins and other bioactive compounds. However, their high levels of saturated fatty acids, cholesterol, fat, additives and especially sodium have imposed limits on consumption. In this context, the aim of this study was to evaluate the reduction of sodium chloride (NaCl), the main source of sodium, and sodium tripolyphosphate (STPP) in low-cost meat emulsions (high content of mechanically separated poultry meat) and noble formulations (high content of meat raw material). The study was divided into two stages. First, popular meat emulsions were prepared (60% of mechanically deboned poultry meat) containing salts substitutes (NaCl, KCl and CaCl2) alone or in combination, corresponding to ionic strength of 2.5% NaCl. Then, formulations containing 50% of these salts and STPP were also prepared to evaluate the effect of salt reduction on the physicochemical properties of the processed products. In the second stage, the five treatments with the best performance were prepared, containing blend of salts (NaCl, KCl and CaCl2), and 50% reduction of NaCl and STPP in meat emulsions with high content of meat raw material. The second stage aimed to utilize blends of salts as a strategy to partially reduce NaCl and STPP in meat emulsions containing high content of meat raw material, and to verify its effect on the physicochemical characteristics and compare the meat matrices. In both stages, Na, K and Ca, emulsion stability, pH, instrumental color, aw, microstructure and texture profile were determined. The KCl was reported as the best substitute to NaCl, once little differences were observed in the treatments containing only NaCl. The salt substitute CaCl2 caused a negative effect on the characteristics of the meat matrix especially in the percentage of myofibrillar proteins extracted, despite the similar NaCl ionic strength of all formulations. The use of salt blend (50% NaCl, 25% KCl, and CaCl2 25%) proved to be a good alternative to sodium reduction. Thus, the combination of salt substitutes (50% NaCl, 25% KCl, and 25% CaCl2) and the use of KCl as NaCl substitute may be an alternative to sodium reduction in both emulsions with a high content of meat raw material as with high content of mechanically deboned poultry meat. However, further studies are required on the phosphate reduction in the popular formulations containing low sodium and salt substitutes / Mestrado / Tecnologia de Alimentos / Mestre em Tecnologia de Alimentos

Our previous work in yeast has demonstrated that overexpression of FPR1, and others FKBP immunophilins, conferred tolerance to weak organic acids such as acetic and sorbic acid. FK506 binding proteins (FKBP) where originally identified as the cellular targets of the immunosuppressant drugs rapamycin an FK506. FKBPs are peptidyl-prolyl cis-trans isomerases (PPase EC 5.1.2.8) that catalize the isomerization of peptidyl prolyl bonds between cis and trans configuration. FKBP are ubiquitous proteins that can be found either as a single catalytic proteins or being part of more complex proteins. To assess the implication of FKBP proteins in weak acid tolerance in plants we have generated lines of Arabidopsis thaliana overexpressing two different proteins: yeast FPR1 an Arabidopsis FKBP65 (ROF2). We isolated knock-out mutant rof2 and rof1 from T-DNA mutant seeds collection of Salk institute. Finally we crossed the single mutants to get the double mutant rof1 x rof2. In presence of acetic acid transgenic lines overexpressing any of these genes grew better than wild type plant. On the other hand an AtFKBP65 loss-of-function mutant line showed weak acid sensitivity. We Observed a similar behavior in presence of toxic cations (Norspermidine, Hygromycim B) suggesting a role in K+ transport and we have got the confirmation with the growth al low levels of K+. We excluded the direct participation of plasma membrane ATPase because its activity in rof2 knock out mutant is higher. Furthermore ROF2 overexpression lines show a lower activity than wild-type. With 35S:: ROF2-GFP construction it was possible to see a cytosolic and nuclear cellular distribution that in presence of weak acid condition change: the ROF"-GFP leave the nuclear region. In absence of stress we have observed a gain of apical dominance in 35S::AtFKBP65 mutants and its loss in FKBP65 knock-out line. The roots of AtFKBP65 knock-out mutants have reduced number of lateral roots and exogenous application of IAA was abl / Bissoli, G. (2013). Prolyl isomerases are important determinants of intracellular pH homeostasis in Arabidopsis thaliana [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/27596 / Palancia

There is a general lack of atomic resolution data of mobile regions of membrane proteins embedded in lipid bilayers. As an inherently complex system, few techniques can capture information about the mobile portions of an otherwise immobilized protein. The nature of crystallography and solid-state NMR relies on structural rigidity. Solution-state NMR relies on overall mobility of a protein for resolution. In the middle regime, there are few solutions to study these systems. The inward-rectifying, pH-gated potassium channel KcsA from Streptomyces lividans makes an excellent model for the development of methods to study mobile regions of membrane proteins. Of its 160 residues, more than a third are in extracellular do- mains and are not typically captured by solid-state NMR or crystallographic techniques. These pages present evidence that KcsA’s C-terminus is highly mobile and becomes increasingly dynamic when the protein is at low pH and high K+ concen- tration, where the channel is known to be active. By applying proton-detected, high-resolution magic angle spinning NMR (HR-MAS) to fractionally deuterated KcsA, previously unattainable correlations are collected and new resonance assignments are made, demonstrating the utility of the technique. The lipid environment is well known to regulate the function of KcsA in particular and membrane proteins in general. It is generally assumed that reconstituting KcsA into a synthetic phospholipid membranes provides the protein a well-defined environment. Data is presented here which shows that KcsA co-purifies with phosphoglycerol lipids from the E. coli membrane and that these molecules are 13C enriched in the course of isotopically labeling KcsA. Further, significant hydrolysis of both co- purifying and synthetic lipids occurs under ordinary experimental conditions. These findings demand that routine analysis of samples must include verification of the chemical integrity of lipids. Finally, the feasibility of applying dynamic nuclear polarization-enhanced NMR (DNP) to KcsA is investigated as a means of elucidating information about its termini. Although KcsA is known to enhance poorly by DNP, data presented here show that this is not an intrinsic property of the protein but rather an effect of the matrix in which KcsA is investigated. The use of a 15N-enriched free amino acid dissolved into buffers used for DNP is shown to be a powerful diagnostic internal standard.

Le maintien d'un potentiel de membrane de repos négatif est à la base de l'excitabilité neuronale. Ce potentiel négatif est généré par un courant de fuite de potassium induit par les canaux potassiques à deux domaines pore (K2P). Ils se sont révélés impliqués dans de nombreux mécanismes physiologiques et physiopathologiques tels que la dépression, la neuroprotection contre les ischémies, l'anesthésie, la migraine et la perception de la douleur. L'hétéromultimérisation est un mécanisme couramment utilisé dans la nature pour augmenter la diversité fonctionnelle des complexes protéiques. Par exemple, avec 15 gènes classés en 6 sous-familles, les canaux K2P pourraient générer 120 combinaisons et, en théorie, chacune d’elles possèderait des caractéristiques bien distinctes. Ici, nous avons d’abord étudié la capacité des membres de la même sous-famille K2P (sous-famille TREK) à s’assembler pour former des hétéromères fonctionnels dotés de nouvelles propriétés. En alliant l’optopharmacologie, une technique de précipitation de molécules uniques (SiMPull) et une technique de co-localisation à l’échelle de la molécule unique à la membrane plasmique, nous avons déterminé l’existence ainsi que la stœchiométrie des complexes créés entre TREK1, TREK2 et TRAAK. Nous avons caractérisé fonctionnellement les hétérodimères et avons constaté qu'ils formaient tous des canaux sélectifs au potassium rectifiant vers l'extérieur avec une sensibilité à la tension et aux pH variables. Ayant constaté que l’hétéromérisation est possible dans la même sous-famille, nous nous demandons si cela peut être fait entre membres de familles différentes et quelles pourraient en être les conséquences pathophysiologiques. Nous avons trouvé que TREK1 et TREK2 sont capable d’hétéromériser avec le canal plus distant TRESK, un canal K2P impliqué dans la migraine. Chez l'homme, la mutation TRESK-MT, une délétion de 2 paires de base (F139WfsX24) qui induit la formation de TRESK-MT1, un dominant négatif de TRESK, a été corrélé à la migraine. De manière surprenante, nous avons découvert que cette délétion induit un site alternatif de traduction (fsATI), menant à la formation d’un second fragment de TRESK, TRESK-MT2 qui s’assemble spécifiquement avec TREK1 et TREK2. Cet assemblage induit l’extinction des courants TREK, ce qui va augmenter l’excitabilité des neurones trijumeaux, une composante clé dans l’induction de la migraine, à l’origine du phénotype migraineux observé. Ensemble, ces résultats démontrent que l’hétéromérisation des canaux K2P n’est pas rare et doit être considérée pour comprendre leurs fonctions pathophysiologiques. Enfin, les analyses génétiques des mutations liées à des pathologies devraient désormais prendre en compte les fsATI. / Maintenance of a negative resting membrane potential underlies the basis of neuronal excitability. This negative potential is generated by a potassium leak current mediated by two-pore-domain potassium channels (K2P). Over the years, they have been shown to be involved in many physiological and pathophysiological mechanisms such as depression, neuroprotection, anesthesia, migraine and pain perception. Heteromultimerization is a mechanism commonly used to increase the functional diversity of protein complexes. For example, with 15 genes classified in 6 subfamilies, the K2P channel family can potentially generates 120 combinations and, in theory, each of them would show different functional properties. Here, we first investigated the ability of the members from the same K2P subfamily (TREK subfamily) to assemble and form functional heteromeric channels with novel properties. Using single molecule pulldown (SiMPull) from HEK cell lysates, subunit counting in the plasma membrane of living cells and opto-pharmacology, we show that the TREK channel members TREK1, TREK2, and TRAAK readily co-assemble. We functionally characterized the heterodimers and found that all combinations form outwardly rectifying potassium-selective channels but with variable voltage sensitivity and pH regulation. Having found that heteromerization is possible within the same subfamily we wonder if it can happen between members from different subfamilies with lower sequence homology and what could be the pathophysiological consequences. We found that TREK1 and TREK2 are able to heterodimerize with the distantly-related TRESK, a two-pore-domain K+ channel implicated in migraine. Notably, in humans, TRESK-MT, a 2 bp frameshift mutation (F139WfsX24), which induced the formation of TRESK-MT1 a dominant negative for TRESK, was found to perfectly segregate with typical migraine in a large pedigree. Strikingly, we found that the 2 bp frameshift mutation induced an alternative translation initiation (fsATI) which leads to the translation of a second TRESK fragment, termed TRESK-MT2. We show that by co-assembling with and inhibiting TREK1 and TREK2, TRESK-MT2 increases trigeminal sensory neuron excitability, a key component of migraine induction, leading to a migraine-like phenotype. Together these findings demonstrate that K2P heteromerization is not rare and needs to be considered to understand their pathophysiological functions and that genetic analysis of disease-related mutations should consider fsATI as a distinct class of mutations.