Made available in DSpace on 2014-10-09T12:54:02Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:11Z (GMT). No. of bitstreams: 1 12441.pdf: 10808481 bytes, checksum: d5cd417d1d3b2db950bcbe8c2c2da156 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

A principal limitação do uso de MgO em refratários é a facilidade com que reage com água formando hidróxido de magnésio (Mg(OH)2) que, devido à sua menor densidade, causa tensões destrutivas nesses materiais. Para outras aplicações, no entanto, a reação de hidroxilação do MgO é necessária, como em produção de agentes antichamas, em compósitos poliméricos e na correção de pH de solos. Observações empíricas na literatura demonstraram que diferentes fontes de MgO possuem reatividades e sensibilidades à hidroxilação distintas. Este estudo analisou o impacto de variáveis externas (por exemplo, a liberação de calor que ocorre durante a reação ou o volume das amostras) que ainda não foi completamente compreendido. O impacto auto-catalítico da temperatura reacional e da exotermia da reação foi avaliado. Por meio de medidas de temperatura in situ e de grau de hidroxilação termogravimétrico, também foram estudados os impactos do volume das amostras testadas e da concentração de sólidos nas suspensões, por meio de medidas de temperatura in situ e termogravimetria. Analisou-se também as principais diferenças estruturais entre duas principais fontes de MgO (sínter de MgO e magnésia cáustica): morfologia de partículas, densidade e área superficial específica. Em seguida, os mecanismos de hidroxilação em suspensões aquosas e seus efeitos foram avaliados por meio de testes de hidroxilação seguidos de termogravimetria, difração de raios-X, medidas de condutividade iônica, densidade, área superficial específica e microscopia eletrônica, e relacionado com as características físico-químicas e morfológicas das respectivas fontes de MgO. Pôde-se constatar que diferenças significativas entre a temperatura nominal do meio reacional e no interior da amostra podem afetar a cinética de hidroxilação do material. O volume e a concentração de sólidos variáveis também podem acentuar consideravelmente os efeitos da exotermia e gerar gradientes de hidroxilação. Também se verificou que a morfologia e a quantidade do Mg(OH)2 formado mudam significativamente dependendo do precursor e em função das condições de tempo-temperatura. / The use of MgO in refractories is restrict due to the easy reaction with water forming magnesium hydroxide (Mg(OH)2). Its lower density causes compressive stresses that can crack their structure. On the other hand, for applications such as the production of flame retardant agents for polymer composites and pH correcting of contaminated soil, this reaction is necessary. Empirical observations in the literature have shown that different sources of MgO have district levels of chemical reactiveness. The present study analyzed the main structural differences between the two main sources of MgO (magnesia sinter and caustic magnesia): particle morphology, density and specific surface area. The mechanisms of hydroxylation of these raw materials in aqueous suspensions and their effects were followed by hydroxylation tests, X-ray diffraction, ionic conductivity, density, specific surface area and scanning electron microscopy. They were associated with the physical characteristics morphological, chemical of these MgO sources. The impact of external variables (e.g., heat release during the reaction or the sample volume), that was not yet completely understood, was also evaluated through temperature measurements carried out in situ and hydroxylation degree accessed by thermogravimetry. The effects of samples volume and solid concentration in aqueous suspension were also investigated. The results showed that differences between the ambient temperature and reaction inside sample temperature can affect the kinetics of hydroxylation of the material. The samples volume and solids concentration can also enhance significantly the effects of heat release and generate gradients of hydroxylation. It was also found out that the morphology and the amount of Mg(OH)2 formed can change depending on the precursor and on the time-temperature conditions.

Made available in DSpace on 2014-10-09T12:54:02Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:11Z (GMT). No. of bitstreams: 1 12441.pdf: 10808481 bytes, checksum: d5cd417d1d3b2db950bcbe8c2c2da156 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

M.Tech. (Chemical Engineering) / There are a number of processes for the production of biodiesel. Homogenous catalysed processes are the most popular in large scale production due to short reaction times and less extreme reaction conditions. Despite this, homogenous catalysts have a number of disadvantages which include: high probability of soap formation in the presence of water and free fatty acids; they cannot be re-used since some of the catalyst is consumed during the reaction and the separation of the remaining catalyst from the product is difficult. In contrast, heterogeneous catalysts offer simplified production and purification processes. However, their reaction rates are low due to mass transfer restrictions. This work looked at the unsupported and supported nano-MgO as solid catalyst for soybean oil transesterification reaction. More research is being undertaken to overcome these low reaction rate problems. Nano-MgO was used since it has been considered as a bridge between homogenous and heterogeneous catalysts. It was supported to enable easy separation from the reaction products.

No description available.

Malpighian tubules of A. dorsalis mosquito larvae, studied in vitro, actively transported magnesium at high rates against concentration gradients as large as 16-fold and transepithelial potential gradients of approximately -l5mV. Fluid secretion rates, determined over 90 minute periods, in the presence and absence of cAMP, indicated that A. dorsalis tubules were viable and had secretion rates of the same magnitude as those reported for A. taeniorhynchus tubules. Having characterized the in vitro preparation of Malpighian tubules, the main hypothesis that Mg²⁺ transport is driven predominately by counter transport with Na⁺ was tested. This hypothesis was not supported by kinetic, Na-substitution, or inhibitor studies. Kinetic and Bumetanide studies suggest backflux of K drives J mg; however, this was not consistently found in other studies. / Science, Faculty of / Zoology, Department of / Graduate

Bakgrund: Arytmi innebär en avvikande rytm hos hjärtat, alltså att det uppstått en avvikelse i impulsbildning och/eller impulsfortledning. Det kan inverka negativt på livskvalitén, orsaka följdsjukdomar eller leda till livshotande tillstånd. Utöver den konventionella behandlingen finns det behov av ytterligare alternativ. Magnesium är ett essentiellt mineralämne som är viktigt för hjärtats elektrofysiologi. Det har i tidigare studier visat sig att magnesium har haft effekt på postoperativt uppkomna arytmier och att låga nivåer av magnesium hos en frisk population har ökat risken för utvecklandet av olika arytmier. Magnesiums föreslagna antiarytmiska egenskaper är därför av intresse att studera vidare.  Syfte: Syftet med studien är att studera om magnesium har någon antiarytmisk effekt hos individer med arytmi.  Metod: En litteraturstudie genomfördes avseende relevanta artiklar publicerade i databasen PubMed från år 2000 och framåt. En relevansbedömning och kvalitetsgranskning genomfördes med utgångspunkt från Statens beredning för medicinsk och social utvärderings (SBU) metodbok.  Resultat: Tolv artiklar inkluderades i litteraturstudien varav sju uppvisade en antiarytmisk effekt av magnesium. En antiarytmisk effekt vid förmaksflimmer uppvisades i samtliga studier där det administrerades mer än 4 gram intravenöst magnesium. Eftersom magnesium i olika former har olika biotillgänglighet skulle formen eventuellt också kunna vara en bidragande faktor till effekten men studiematerialet var för litet gällande olika magnesiumformer. Vidare går det inte att särskilja om magnesium har olika effekt på olika arytmier då representationen av respektive arytmi var för liten. Slutsats: Magnesium har en antiarytmisk effekt vid administrering över 4 gram intravenöst. Huruvida detta gäller för fler arytmier än förmaksflimmer framkommer inte av denna litteraturstudie. Det finns ett behov av fler studier för att dels undersöka vilken som är den eventuella optimala formen och dosen av magnesium, dels för att utreda vilka typer av arytmier som verkar mottagliga för magnesium som behandlingsalternativ. / Background: Arrhythmia means a deviating rhythm in the heart, either in impulse formation and/or impulse conduction. It can adversely affect the quality of life, cause sequelae or lead to life-threatening conditions. In addition to the conventional treatment, there is a need for alternatives. Magnesium is an essential mineral that is important for the electrophysiology of the heart. Previous studies have shown that magnesium has had an effect on postoperative arrhythmias and that low levels of magnesium in a healthy population have increased the risk of developing various arrhythmias. The proposed antiarrhythmic properties of magnesium are therefore of interest for further study.  Aim: The aim of the study is to investigate whether magnesium has any antiarrhythmic effect in individuals with arrhythmias.  Methods: A literature study was conducted regarding relevant articles published in the PubMed database from the year 2000 and until today. Relevance assessment and quality review were carried out on the basis of  Swedish Agency for Health Technology Assessment and Assessment of Social Services (SBU) method book.  Results: Twelve articles were included in the literature study, seven of which showed an antiarrhythmic effect. An antiarrhythmic effect in atrial fibrillation was shown in all studies where more than 4 grams of intravenous magnesium was administered. Since magnesium in different forms has different bioavailability, the form could possibly also be a contributing factor to the effect, but the study material was too small for different forms of magnesium. Furthermore, it is not possible to distinguish whether magnesium has different effects on different arrhythmias as the representation of each arrhythmia was too small.  Conclusions: Magnesium has antiarrhythmic effect when administrated in excess of 4 gram intravenously. Whether this applies to more arrhythmias than atrial fibrillation does not emerge from this literature study. There is a need for more studies to investigate the possible optimal form and dose of magnesium, and to investigate which types of arrhythmias seem susceptible to magnesium as a treatment alternative.

Magnesium deficiency in rats is known to precipitate audiogenic seizures. An unknown mineral factor in a diet mixture was found to substantially reduce the seizure occurence in magnesium deficient vii animals. This was corrected when the same mineral mixture was remade. Subsequently the faulty mineral mixture was discarded. This research .. as aimed at determining the mineral factor responsible for the observed changes in seizure occurence, and also aimed at investigating the relationships of serum calcium, magnesium and phosphorus concentrations to seizure susceptibility. Treatments to change the serum concentrations of these minerals included dietary manipulation, subcutaneous injection of calcitonin, of 1 ,25-dihydroxycholecalciferol, of calcium and of phosphorus. Animals fed magnesium deficient, low phosphorus diet and magnesium deficient animals fasted over-night were found to have significantly lower audiogenic seizure susceptibility than all other magnesium deficient animals regardless of treatment. Reduced audiogenic seizure susceptibility was not produced by any of the injections. The reduction in seizure with the magnesium deficient, low phosphorus diet indicates that phosphorus is an important factor in the mechanism of audiogenic seizuring in magnesium deficient rats.

No description available.

No description available.