The objective of the research is to synthesize the diazonium N-(perfluoroalkyl) benzenesulfonimide (PFSI)zwitterionicpolymers as electrolytes in polymerelectrolyte membrane (PEM) fuel cells. The proposed diazoniumPFSI zwitterionic polymer (I) is expected to enhance the thermal and chemical stability, increase the proton conductivity of electrolytes, and improve the catalyst efficiency for PEM fuel cells. Synthesis of the perfluorobenzoyl peroxide initiator, homopolymerization of perfluoro (3-oxapent-4-ene) sulfonyl fluoride,coupling reaction with4-sulfamonylacetanilide, couplingreaction with 4-nitrobenzene sulfonyl amide, n-deacetylation reaction, and diazotization reactionhave been carried outsuccessfully in the lab. The intermediate chemicals are characterized by GC-MS, IR, NMR, and GPC spectroscopies.

The beginning of this thesis contains an overview of properties of the insulators, and description of insulators that were used for in depth research of surface breakdown in vacuum. Furthermore, this work focuses on mechanisms of an electric breakdown initiation at the interface of the solid insulator and surrounding low pressure gas. Multiple methods for measurements of dielectric strength are examined. The experimental part describes the measurements performed in the vacuum chamber. The results of these measurements are then analysed. In conclusion, used insulators are compared and suggestions for further work are given.

The submitted work is aimed at the unconventional fluoride conversation coating preparation on the AZ31, AZ61, ZE10 and ZE41 magnesium alloys by their immersion in Na[BF4] molten salt. The influence of the preparation parameters (such as temperature and time) on the quality of the fluoride conversion coating is investigated. Methods of light and scanning electron microscopy were used for the evaluation of morphology, chemical composition and thickness of the coating. Short and long-term corrosion tests were executed to analyze the corrosion performance in simulated body fluid solution at 37 ± 2 °C with and without the fluoride conversion coating. The short-term behavior was evaluated by potentiodynamic tests, namely by the linear polarization. Long-term performance was assessed by electrochemical impedance spectroscopy or immersion tests. The coating preparation parameters influence on the character of the formed fluoride conversion coating was defined based on the obtained results. The next part of the thesis deals with the description of the possible mechanism of formation and kinetics of growth of the unconventional fluoride conversion coating on the selected AZ61 magnesium alloy. In this part, further detailed analyses were carried out to investigate the microstructure and chemical composition of the fluoride conversion coating using focused ion beam, transmission electron microscopy and X-ray photoelectron spectroscopy.

Tato diplomová práce zkoumá flexibilní materiál k produkci elektřiny založený na piezoelektrickém polymeru Polyvinylidenfluorid (PVDF). Inkorporací piezoaktivní keramiky lze vlastnosti piezoelektrického polymeru PVDF významně zlepšit a převést na užitečnou elektrickou energii. PVDF byl vytvořen elektrostatickým zvlákňováním do vláken o tloušťce 1,5-0,3 µm a poté studován různými analytickými metodami. Tato práce nabízí popis elektrostatického zvlákňování, přípravu vzorků a teoretický úvod do analytických metod, kterým byly vzorky podrobeny. Morfologie a distribuce nanostrukturované keramiky do polymerní matrice PVDF byla pozorována použitím skenovací elektronové mikroskopie (SEM) a energiově disperzní spektroskopie (EDX). Pro tvorbu fáze a podrobné fázové složení byly vzorky charakterizovány infračervenou spektroskopií s Fourierovou transformací (FTIR). Práce také obsahuje analýzu s použitím Ramanovy spektroskopie, metody používané k identifikaci a porovnání chemických sloučenin. Elektrické vlastnosti byly studovány dielektrickou spektroskopií a je poskytnuta korelace se složením. Jednotlivé komponenty dotovaných vláken jsou charakterizovány a vyhodnocovány v souvislosti s jejich budoucím využitím v senzorech.

Magister Chirurgiae Dentium (MChD) / Background: This study aimed to determine the association between dimensional change and surface roughness (Ra) of Vitremer, Activa and Cention N after immersing them into two different media: acidic and artificial saliva media for the period of a year. Measurements were made at 10 time intervals during the observation period. Methodology: This was a quantitative and qualitative study. For the quantitative part, a total of 60 specimens were tested, 20 specimens for each material. The 20 specimens were further divided into 10 specimens. Ten were immersed in acidic media and the rest in saliva media. A measurement of the weight, height, and Ra was carried out as follows: day 0, day 1, day 2, day 7, day 21, day 28, day 60, day 90, day 180 and day 365. Scanning electron microscopy (SEM) was used to examine the surface of each material qualitatively pre and post immersion in the two media. For fluoride measurements, an additional five samples from each material were left suspended in the de-ionized water by the use of dental floss. The materials were moved to new specimen jars after the completion of day 1, 2, 3, 4, 5, 6, 7, 14, 21 and 28. All the specimen jars had been kept for the fluoride measurements. Results: Non-parametric tests were used to analyze the data. Linear regression analysis was used to measure the association between weight, height or surface roughness (Ra) and immersion time for a year. The result of this test showed that Vitremer had a significant association between the weight (p = 0.000), height (p = 0.007) and Ra (p = 0.001) when it was immersed in acidic media. On the other hand, when Vitremer was immersed in saliva media, only the weight variable showed a significant association (p = 0.002). For Cention N, significant association was found for only Ra when immersed in acidic media (p = 0.000). Finally, for Activa, all the studied associations; the weight, height and Ra in both media were found to be insignificant. For saliva media, there was a significant weight change between the three materials during all 10 periods of time (p = 0.000). In the first six months, Cention N demonstrated a significant increase in weight changes followed by Vitremer, then Activa. Yet, after a year, the difference between Cention N and Vitremer became insignificant and Activa showed the least weight changes. There was not a significant difference between the materials in terms of height and Ra measurements. The fluoride experiment was not successful due to technical issues during pH measurements of the collected solutions. For comparison of the studied parameters between the three materials, the Kruskal-Wallis test was used. In acidic media, there was a significant difference between the materials in term of weight change in 10 periods of time (p = 0.000). In particular, after a two month period, Cention N had the highest weight, followed by Vitremer and then by Activa. The difference between Vitremer and Activa became insignificant throughout the rest of the experimental time frame. All the height measurements between the three materials were found to be insignificant except for day 365 (p = 0.048), where both Activa and Cention N were found to be significantly higher than Vitremer. For the Ra comparison, in the first two weeks, particularly day 1, 7 and 14, Cention N had significantly the lowest Ra among the other materials. As the three materials aged in the acidic media (day 180), Vitremer had significantly the highest Ra values. Cention N showed higher Ra values than Activa; nonetheless this difference was not significant. The SEM images showed loss of some particles in all post-experimental images of the materials in acidic media. Vitremer showed the widest cracks with the loss of fillers. In saliva media, there was also loss of particles but to a lesser extent than in acidic media. Yet, the post-experimental image of Activa in saliva resembled the pre-experimental one. Conclusion: Within the limitations of the study, the best material to resist Ra from prolonged acidic attack was Activa followed by Cention N and then Vitremer. Except for Vitremer, no significant changes in the Ra of the other materials were detected when the three materials were immersed in saliva media in the long term. In acidic media Vitremer tended to lose weight and height faster than Cention N and Activa over a year. Cention N is the best material to resist dimensional change. However, in artificial saliva Vitremer gained water rapidly. Activa did not absorb a lot of water and did not reject a lot of water; Activa demonstrated good dimensional stability and this property may be beneficial when compared to the other two materials tested. The clinical significance of the study: All the materials studied were subjected to dimensional and Ra changes following long-term exposure to acidic substances, but the newer materials (Cention N and Activa) seemed to be more dimensionally stable and resistant to Ra changes than the older, well-known material (Vitremer). This may influence a clinician’s choice of restorative material for use in pediatric dentistry.

The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime. This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown. Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results. The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range. The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach. Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.

The primary prevention of dental caries includes the regular reduction of dental plaque, the adequate nutrition with reduced frequency of sugar intake and the application of topical and/or alimentary fluorides. The caries-protective effect of fluorides is based on the stabilization of demineralization/remineralization processes in the surface of teeth. The alimentary fluoride intake involves its nutritional sources, fluoride supplements when administered and unintentionally swallowed fluoride toothpastes. The fluoride intake, besides its verifiable and significant contribution to the control of cariogenic conditions in the oral cavity, brings some risk in the period of permanent teeth development. That is why the fluoride intake in childhood ought to be well set up and controlled for achieving the maximum benefit in caries reduction and for minimizing the risk for the enamel development. The assessment on fluoride content in its most significant nutritional sources and the model estimates of fluoride intake in preschool children have been conducted with the aim at contributing the solution of the benefit/risk strategy of fluoride caries prevention. The fluoride content was estimated in bottled waters for preschool children, in instant milk formulas, in herbal teas for children and in instant products of...

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Bakgrund: Mineraliseringsstörning på tänder kan antingen vara genetiska eller orsakas av interna och/eller externa faktorer. De olika faktorerna orsakar antingen en lokal eller en generell mineraliseringsstörning på emalj. En av faktorerna är en kemikalisk i form av fluor. Fluoridhalter i vatten som är mellan 1,5 – 3,0 mg/l kan orsaka dental fluoros, vilket gör tänderna ömtåliga och mycket sköra. Det har upptäckts höga fluorhalter, i dricksvatten, även långt över det av WHO rekommenderade, 1,0 mg/l, i flera olika länder, däribland Sydafrika. Syfte: Att studera samband mellan fluoridkoncentration i dricksvatten och dental fluoros i Sydafrika hos barn. Frågeställning: Hur påverkar höga respektive låga fluoridkoncentrationer förekomsten av dental fluoros i Sydafrika? Metod: Databaserna DOSS, MEDLINE samt CINHAL användes för att utföra litteraturstudien. Totalt inkluderades 10 artiklar som sedan kvalitetsgranskades inspirerade Forsberg & Wengström kvalitetsgranskningsmall. Resultat: Barn som bodde i ett lågt fluoridområde med 0,19 mg/l, där var det 49% som hade dental fluoros och 38% hade ingen dental fluoros. På områden med hög fluoridhalt upp till 3,00 mg/l var det 96% av barnen som hade dental fluoros, varav 30% hade grad 5 vilket är svår dental fluoros. Slutsats: Ju högre fluoridkoncentrationer i dricksvatten desto större antal fall av dental fluoros / Background: Teeth mineralization disorder can either be genetic or caused by internal and/or external factors. The various factors cause either a local or a general enamel mineralization disorder. One of the factors is a chemical in the form of fluoride. Fluoride levels in water between 1.5 - 3.0 mg/l can cause dental fluorosis, making teeth delicate and very brittle. High fluorine levels have been detected in drinking water, even well above the WHO recommended 1.0 mg/l, in several different countries, including South Africa. Aim: To study the relationship between fluoride concentration in drinking water and dental fluorosis in South Africa in children. Question: How do high respective low fluoride concentrations affect the incidence of dental fluorosis in South Africa? Method: The DOSS, MEDLINE and CINHAL databases were used to carry out the literature study. A total of 10 articles were included, which were then quality checked inspired by Forsberg & Wengström's quality review template. Results: Children living in a low fluoride range of 0.19 mg/l, where 49% had dental fluorosis and 38% had no dental fluorosis. In areas with high fluoride concentrations up to, 3.00 mg/l, 96% of children had dental fluorosis, of which 30% had grade 5 which is severe dental fluorosis. Conclusion: The higher the fluoride concentrations, the greater the number of dental fluorosis cases.

Die Suche nach alternativen Strahlungsquellen für quecksilberhaltige Lampen ist derzeit ein großes Forschungsgebiet. Während für allgemeine Beleuchtungsanwendungen LEDs einen effizienten Ersatz bieten, sind für Anwendungen die UV-Strahlung benötigen gegenwärtig keine effizienten Alternativen auf dem Markt erhältlich. Einen möglichen Ersatz für die aktuellen Quecksilber-Niederdruck-Entladungslampen könnten Xenon-Excimerentladungslampen bilden. Die Entladungswellenlänge dieser Lampen liegt bei 172 nm, was deutlich energiereicher im Vergleich zu den Quecksilber-Niederdruck-Entladungslampen (254 nm) ist. Um die Xenon-Excimerentladungslampen einem möglichst großen Anwendungsbereich zur Verfügung zu stellen, wird die 172 nm Entladung mit Hilfe von Leuchtstoffen in andere Spektralbereiche konvertiert. An diese Leuchtstoffe werden hohe Anforderungen gestellt, wie zum Beispiel eine hohe Absorptionsstärke, hohe Effizienzen und eine hohe Langzeitstabilität, so dass sie für jede Anwendung entwickelt werden müssen. In der vorliegenden Dissertation wurde trivalentes Praseodym (Pr3+) als Aktivatorion in binären und ternären fluoridischen Wirtsstrukturen untersucht. Mit trivalentem Praseodym ist es möglich, eine breite Palette unterschiedlicher Lumineszenzspektren mit Emissionen im ultravioletten und sichtbaren bis hin zum infraroten Spektralbereich zu realisieren. Sowohl Emissionsspektren mit breiten Emissionsbanden, als auch mit schmalen Emissionslinien sind darstellbar. Die Wirtsstruktur und die damit verbundene kristallographische Position des Pr3+ beeinflussen die Entstehung von Banden- oder Linienemission sowie die genaue energetische Lage der Emission. Die fluoridischen Wirtsmaterialien eignen sich wiederum hervorragend zur Bestimmung der hochenergetischen Zustände des Aktivatorions, da sie unter allen Materialklassen die höchsten Bandlücken besitzen. Die Ergebnisse zeigen, dass in fluoridischen Wirtsstrukturen, bei denen sich das Pr3+ in großen Koordinationspolyedern (KZ > 8) befindet, die Emissionsspektren hauptsächlich durch schmale Emissionslinien dominiert werden. Im Gegenzug besitzen die Emissionsspektren, bei denen sich das Pr3+ in kleinen Koordinationspolyedern (KZ < 8) befindet, breite Emissionsbanden. Die Begründung für diese Ergebnisse ist in dem Zusammenspiel zwischen dem nephelauxetischen Effekt und der Kristallfeldaufspaltung der 5d-Orbitale, auch optische Elektronegativität genannt, zu finden. Erfahrungsgemäß weisen die fluoridischen Wirtsstrukturen nur einen geringen nephelauxetischen Effekt auf. Bei oxidischen Wirtsstrukturen ist dieser Effekt deutlich größer, was ebenfalls in der vorliegenden Untersuchung gezeigt werden konnte.