Techn. Hochsch., Diss., 2005--Aachen.

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abstract: Despite recent strides for awareness, treatment, and control of hypertension, prevalence remains high with estimates suggesting one third of Americans have hypertension. The hypotensive effects of potassium and magnesium have been known and administered in a clinical setting for nearly a century. The purpose of this study was to examine the effectiveness of taking a potassium/magnesium supplement to help reduce blood pressure in individuals with mildly-moderately elevated blood pressure. In this randomized, controlled crossover trial, potassium and magnesium supplementation was explored among healthy adults with mildly elevated blood pressure in Phoenix, Arizona. Subjects (n = 12) were randomly assigned to ingest either the treatment chewy bar (217 mg potassium/day; 70.8 mg magnesium/day) or a placebo chewy bar for four weeks. For the subsequent four weeks, subjects ingested the other corresponding chewy bar. Systolic (SBP), diastolic (DBP), and average blood pressure values were not significantly different between the two groups (p = 0.645, p = 0.464 and p = 0.939, respectively). Baseline mean blood pressure was 121.0/75.7 mm Hg. The 12 subjects (8 females, 4 males) had a mean age of 29.3 years old and a mean BMI of 26.2. After four weeks, the treatment group had a slightly higher SBP (118.3 ± 13.3 mm Hg) than the control group (116.5 ± 17.8 mm Hg); however, DBP was lower in the treatment group (71.7 ± 12.4 mm Hg) than the control group (73.0 ± 10.0 mm Hg). In conclusion, daily supplementation of potassium and magnesium (217.2 mg/day and 70.8 mg/day, respectively) did not significantly lower blood pressure in adults with mildly-moderately elevated blood pressure. / Dissertation/Thesis / Masters Thesis Nutrition 2015

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No presente trabalho comprova-se o efeito prejudicial do oxalato, utilizado para a separação prévia de cálcio e magnésio, na determinação complexométrica deste último com EDTA em águas, usando-se em titulação visual o indicador Negro de Eriocromo T e, em titulação potenciométrica, o sistema indicador Hg/Hg-EDTA. Comprovou-se, também, a viabilidade de se usar como titulante uma solução de EDTA \"tetraneutralizado\", em titulações potenciométricas com medidas de pH através de eletrodo de vidro combinado. Neste caso o ponto final é obtido através da hidrólise da espécie Y4-, após o ponto de equivalência. Assim evidenciou-se a viabilidade de um novo método para a determinação da mistura de cálcio e magnésio, pelo uso EDTA \"tetraneutralizado\" e separação prévia dos dois cátions através da adição de oxalato. A detecção do ponto final nestas titulações com EDTA \"tetraneutralizado\" pode também ser feita visualmente com fenolftaleína. O efeito de volume em titulações potenciométricas em geral, num certo nível de concentração, foi objeto de análises diversas inclusive por cálculo computacional de curvas derivativas. Comprovou-se que quanto menor o volume do titulado maior é o salto potenciométrico obtido, caracterizando-se o que se denominou de \"paradoxo potenciométrico\", pois uma menor massa de substância pode ser titulada com, teoricamente, o mesmo erro relativo que para uma massa maior de substância. / Alternative method for the complexometric determination of magnesium. Influence of volume on potentiometric titrations. Keywords: Potentiometry, Magnesium, EDTA. Present paper has been found the negative effect of oxalate, used to the previous separation of calcium and magnesium in a complexometric determination of this last with EDTA in waters, using at visual titration Eriochrome black T as indicator and at potentiometric titration the indicator system Hg/Hg-EDTA. It has been found, also, the viability in the use as titrant a \"tetraneutralized\" EDTA solution, in potentiometric titration with measurements of pH with the glass electrode. In this case the end point is obtained on basis of hydrolysis of Y4- species, after the equivalent point. So it has been displayed the viability of a new method to the determination of the mixture calcium and magnesium by the use of \"tetraneutralized\" EDTA and previous separation of both cations by addition of oxalate. The end point detection can be visually found, in these titrations with \"tetraneutralized\" EDTA, by using of phenolphthalein. The effect of volume in potentiometric titration in general, at a defined concentration level, was subject of several analysis incluse using the compute calculation of derivative curves. It has been found that as smaller volume of titrated performes a higher potentiometric jump, this effect was called for us \"potentiometric paradox\", since an smaller weight of substance can be titrated, with theoretically, the same relative error that to a greater weight of substance.

Understanding the dynamical bases of the interaction between the plant mineral nutrition and the circadian clock could contribute to improve crop yield and resistance to adverse conditions, such as mineral element deficiencies. Magnesium is an essential element that catalyzes more than six hundred enzymatic reactions and occupies the center of the chlorophyll structure in plants. Physiological targets of magnesium deficiency are generally better described in aerial than in belowground organs. In this thesis, we first characterized the root morphology of the model species Arabidopsis thaliana (Columbia-0) in response to magnesium supply during in vitro culture. The length of primary root and the number and length of lateral roots decreased during magnesium depletion. A local magnesium-rich source does not enhance the root foraging capacity, unlike some other major nutrients. Auxin and abscisic acid emerged as two hormones shaping root morphology in response to magnesium deficiency. Second, we investigated the natural variation of the root morphology response to magnesium supply in Arabidopsis. Thirty-six accessions were screened in vitro. Compared to the reference Columbia-0, some accessions had higher number and length of lateral roots at low magnesium supply. Root or shoot magnesium concentrations did not implicitly correlate with the root morphological traits. However, shoot calcium and root phosphorus concentrations correlated positively with the lateral root number and length, while root iron negatively with the length of primary root. Third, we focused on the interaction between the plant magnesium nutrition and the circadian clock circuit. We tested for a possible involvement of PHYTOCHROME INTERACTING FACTOR 3-LIKE 1 (PIL1) - a clock-associated gene that is down-regulated during magnesium depletion - in morphological and physiological responses, and for a circadian connection of PIL1 in the context of magnesium deficiency. The phenotypes of loss-of-function and overexpression lines did not reveal a major role of PIL1 in the magnesium deficiency symptom manifestation but rather in the plant mineral profile. The expression of PIL1 was apparently not under any circadian control. However, PIL1 seemed to regulate the expressions of some core clock genes (CCA1, LHY and PRR9), which were also targets during magnesium deficiency. In conclusion, PIL1 has a link with the circadian rhythm machinery but it does not emerge as a pivotal regulator of magnesium stress responses. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Le magnésium et ses alliages sont de plus en plus utilisés dans les transports pour leur faible densité (1,7), et on cherche à les utiliser sous la forme corroyée. De structure hexagonale compact, le magnésium est très anisotrope et faiblement ductile à froid. La déformation est contrôlée par l'activation de systèmes de glissement et de maclage, seuls le glissement basal et le maclage de traction sont actifs à froid, alors qu'à chaud sont activés les glissements prismatique et pyramidal <c+a>, et le maclage de compression. Nous avons élaboré des monocristaux de magnésium pur de différentes orientations pour mesurer les contraintes de cission résolues critique (CRSS) des différents systèmes par des essais de compression plane à des températures allant de l'ambiante à 450°C. En parallèle nous avons développé un code de plasticité cristalline pour modéliser la déformation de cristaux contraints, ce programme est basée sur la loi de Schmid et le principe du travail maximum, ce qui permet de prédire les systèmes de déformation activés et la contrainte nécessaire, en fonction des CRSS. Nous avons aussi testé le modèle pour prédire le comportement de l’alliage polycristallin AZ31. / Magnesium and its alloys are increasingly used in the transport industry for their low density (1.7), and ideally could be used after plastic shaping. Due to the hcp structure, magnesium is very anisotropic and exhibits low ductility at room temperature. Strain is controlled by the activation of slip and twinning mechanisms, and only basal slip and tensile twinning operate at RT, whereas at high temperature prismatic and pyramidal <c+a> slip, and compressive twinning are active. Pure magnesium single crystals were produced with different orientations to measure the critical resolved shear stresses (CRSS) of the different deformation mechanisms, by channel-die compression from RT to 450°C. In parallel we developed a crystal plasticity model to simulate the deformation of constrained crystals, this model is based on the Schmid law and the principle of maximum work. The model enables the prediction of activated deformation mechanisms and the stress as a function of the CRSS. We have also used the model to predict the behaviour of a polycrystalline alloy AZ31.

Research has focused extensively on the negative health effects of inadequate Mg intake, but the extent of the problem of deficiency deserves further exploration. The notion that U.S. adults consume an inadequate amount of magnesium, leading to increased risk for chronic diseases such as depression, is plausible. National Health and Nutrition Examination Surveys (NHANES), which are large, cross-sectional, population-based data sets that assess the health and nutritional status of U.S. adults and children, indicate over half the adult population does not consume adequate amounts of magnesium based on the estimated average requirement (EAR) established by the Institute of Medicine. Using 2007 to 2010 NHANES data we found 54% of adults do not meet the EAR, confirming results from earlier surveys. As a result of this finding, a review exploring the factors impacting magnesium consumption over time and the adequacy of current intake in U.S. adults was conducted. Changes in agricultural processes that reduce magnesium levels in crops combined with the increasing consumption of processed foods containing little to no magnesium have led to a decrease in mean daily intake by 200-300 mg per day over the past century. However, population-based studies show a steady and consistent recovery in magnesium intake in U.S. adults over the past several decades. A simple, rapid, accurate test for whole body Mg status is lacking and, although population-based studies have limitations, continued monitoring of Mg consumption is essential to determine whether this positive trend continues. In the meantime, since the health consequences of inadequate magnesium are well established, there are no reported cases of hypermagnesemia from food alone, and magnesium is found in healthy foods adults should consume more often, there are few reasons not to encourage increased magnesium intake. Cross-sectional and prospective trials in other countries report an association between magnesium intake and symptoms of depression. Depression is a chronic disease affecting a significant portion of the U.S. population. Magnesium plays a role in many of the pathways involved in the pathophysiology of depression and is found in several enzymes, hormones, and neurotransmitters. Depression and magnesium are both associated with systemic inflammation. Current treatment options for depression are limited by efficacy, cost, availability, side effects, and acceptability to patients. As a result of the need for additional treatment options, interest in the role of magnesium in modulating depressive symptoms has grown. We used the NHANES 2007-2010 data to examine this relationship in U.S. adults and found a significant association between very low magnesium intake and symptoms of depression (RR=1.16; 95% confidence interval (CI) 1.06, 1.30; P=0.03). Whether inadequate magnesium leads to increased risk for depression or depression results in poor dietary intake is not known. To test whether supplementation with over-the-counter magnesium chloride improves symptoms of depression, an open-label, blocked, randomized, cross-over trial was carried out in outpatient primary care clinics on 126 adults (mean age 52; 38% male) diagnosed with, and currently experiencing, mild-to-moderate symptoms. Consumption of magnesium chloride tablets for 6 weeks resulted in a clinically significant net improvement in depression (Patient Health Questionnaire-9) scores of -6.0 points (95% CI -7.9, -4.2; P<0.001) and net improvement in anxiety (Generalized Anxiety Disorders-7) scores of -4.5 points (95% CI -6.6, -2.4; P<0.001). Effects were observed regardless of age, gender, baseline magnesium levels, baseline severity of depression, or use of antidepressant treatments. It worked quickly, was well tolerated, and is much safer and less expensive than conventional treatments with medication. Magnesium supplements are effective for mild-to-moderate depression and are an additional treatment option for patients suffering from depression.

The influence of microstructure on the corrosion behaviour of magnesium alloys has been investigated using advanced microscopy approaches including optical microscopy, SEM, TEM and SKPFM with a focus on the effect of melt-conditioned twin roll casting (MCTRC) and friction stir welding (FSW) on the resultant microstructure of magnesium alloys.The microstructure characterization revealed that intense shearing, generated through the advanced shear technology, resulted in grain refinement and a uniform distribution of the β-phase and reduced micro-porosity in the MCTRC Mg-Al alloys, of which were attributed to the enhanced heterogeneous nucleation, which resulted in a highly refined grain structure. The TRC Mg-Al alloys displayed a coarse grained microstructure, with a random distribution of grain sizes. Deformation features like twinning, localized shear, microporosity and centre-line segregation were some of the commonly observed defects in the TRC alloys. The general microstructure of the AZ series Mg-Al alloys was composed of α-Mg grains, the β-phase, rosette-shaped Al8Mn5 intermetallic particles and β-precipitates.The MCTRC Mg-Al alloys showed improved corrosion resistance owing to the reduced grain size and the β-phase network acting as a corrosion barrier, thereby retarding the corrosion process. The TRC Mg-Al alloys exhibited higher susceptibility to galvanic corrosion due to the coarse and random distribution of grain sizes, and segregation. The corrosion testing results showed different corrosion morphologies, including filiform-like and spherical channel-like along with overall general corrosion. However, galvanic corrosion, initiating at localized sites due to Al8Mn5 intermetallic particles and the Si/Fe impurities accounted for a major deterioration in the performance of the Mg-Al alloys. The polarization curves revealed no evidence of passivation, suggesting that the alloy surface was continuously attacked. SKPFM results indicated that the micro-constituents, namely Al8Mn5 intermetallic particles and the β-phase exhibited higher nobility relative to the α-Mg matrix, suggesting formation of micro-galvanic couples at localized sites leading to the initiation of galvanic corrosion.The AM60 and AZ91 Mg-Al alloys, subjected to FSW, revealed that the traverse speed had a direct influence on the weld zone microstructure, where the size of the friction stir/weld nugget zone decreased with increase in the traverse speed and the increase in the rate of deformation, led to widening of the friction stir zone, below the shoulder. The weld microstructure displayed a prominent friction stir zone, with an ultrafine grain structure of an average grain size ranging from 2-10 μm. The localized increase in temperatures, in the TMAZ, due to the lower tool rotation rates and traverse speeds, which rise above the eutectic melting point (430°C), showed evidence of partial melting followed by re-solidification of the β-phase and evidence of liquation below the shoulder regions in the TMAZ. The morphology of the β-phase clearly revealed solute segregation, inconsistent with the β-phase observed in the parent alloy microstructure.The polarization curves obtained from the weld zones in the FSW AM60 alloy showed an improved corrosion resistance compared with the parent metal zone. SKPFM results revealed that the α-Mg matrix in the friction stir zone showed higher surface potential values compared with the parent alloy microstructure, due to the dissolution of the β-phase, suggesting higher nobility. However, the polarization behaviour of the AZ91 alloys did not show a significant difference in the corrosion resistance in the weld zones due to the higher volume fraction of the β-phase in the AZ91 alloys. The immersion testing results revealed higher susceptibility to corrosion in the transition zone due to the flash formation and the banded microstructure leading to failure of the weld zone.

Magnesium has the lowest density of any structural metal making it a strong candidate for weight savings in the aerospace and automotive industries. However, strong crystallographic textures combine with anisotropic deformation modes to severely limit formability in wrought magnesium alloys. Recently improved formability has been achieved by the addition of small concentrations of solute rare earth elements which reduce the intensity of recrystallisation textures. Developing a mechanistic understanding of this effect is critical in leading alloy design towards a new class of highly formable wrought magnesium alloys. In this study the static recrystallisation mechanism of rolled magnesium rare earth alloys, which causes the texture weakening, is examined with a particular emphasis on the contrasting texture weakening effects in binary and tertiary magnesium rare earth alloys. In binary magnesium-rare earth alloys the `rare-earth' texture is simply a weakened deformation texture, while recrystallisation of magnesium-zinc-rare earth alloys produces unique `rare-earth' texture components. In the binary alloys weakened recrystallisation textures are attributed to the generation of `off-basal' orientations within regions of high strain localisation during deformation. These orientations recrystallise and subsequently dominate the recrystallised texture. Texture weakening by this mechanism is also thought to be observed in non-rare earth magnesium alloys where dynamic recrystallisation is suppressed by cold rolling. The unique rare-earth texture components in magnesium-zinc-rare earth alloys are found to be determined by the orientation of shear bands in the material. Similarly to texture weakening in the binary alloys, nuclei for these orientations are thought to develop during deformation as a result of strain incompatibilities within shear bands. The mechanism forming these orientations remains unclear, however it is postulated that a complex change in recovery behaviour within shear bands, as a result of rare earth and zinc additions, may be the cause. Retarded dynamic recrystallisation is suggested to be of critical importance in the texture weakening mechanisms of all magnesium alloys, both rare earth and non-rare earth. In rare earth alloys dynamic recrystallisation is suppressed by the segregation of rare earth atoms to grain boundaries. A combination of high resolution TEM and EDX shows rare earth atoms form clusters approximately 2nm in diameter on grain boundaries which are expected to retard dynamic recrystallisation through a solute drag mechanism.