Diese Arbeit befasst sich mit unterschiedlichen werkstoffwissenschaftlichen Fragestellungen auf dem Gebiet der magnetokalorischen Kühlung. Magnetokalorische Materialien, z.B. (Mn,Fe)2(P,Si)- oder La(Fe,(Co),Si)13-Legierungen, erwärmen sich bzw. kühlen ab, wenn das Material unter adiabatischer Prozessführung und einer Umgebungstemperatur nahe der magnetischen Phasenübergangstemperatur einem externen Magnetfeld ausgesetzt bzw. daraus entfernt wird. Der magnetokalorische Effekt (MKE) von Materialien kann, bei zyklischer Wiederholung von Magnetisierung und Entmagnetisierung, in einer Wärmepumpe genutzt werden, um Wärme von einer Substanz oder einem Raum abzuführen. Ein Wärmetauscher aus magnetokalorischem Material – der magnetokalorische Regenerator – ist, neben einem Magnet- und Pumpensystem, das essenzielle Bauteil in magnetokalorischen Wärmepumpen und Kältemaschinen. Regeneratoren können aus Schichten unterschiedlicher Pulverchargen eines magnetokalorischen Materials bestehen, dass mit einem Polymer gebunden wird. Der Aufbau von konventionellen (Mn,Fe)2(P,Si)-Pulverschüttungen wird in der vorliegenden Arbeit anhand zerstörungsfreier Röntgencomputertomographie überprüft. Neben individuellen Merkmalen einer Pulvercharge, können entlang der Schichtstapelrichtung auftretende Porositätsvariationen zur Detektion von Schichten genutzt werden. Weiterführend werden magnetische Wechselwirkungen der einzelnen Partikel und Schichten in einem (Mn,Fe)2(P,Si)-Regenerator mittels magneto-optischer Bildgebung untersucht. In La(Fe,(Co),Si)13-Legierungen geht der MKE mit einer zusammensetzungsabhängigen Volumenänderung der Elementarzelle einher, die das Material unter Umständen katastrophal versagen lässt. Die Festigkeit der Legierung spielt sowohl für die Langzeitstabilität als auch die Verarbeitung mit Maschinen eine wesentliche Rolle. Im Rahmen der Arbeit wurde eine intermetallische LaFe10,2Si1,8-Legierung auf unterschiedlichen Längenskalen mechanischen Prüfungen unterzogen. Die Festigkeit ist von inneren Defekten (Mikrorisse, Zweitphasen) beeinflusst, weshalb Druckversuche zur Eigenschaftsbestimmung ungeeignet sind. Lokale Härtemessungen hingegen erlauben eine Abschätzung der intrinsischen Festigkeit der magnetokalorischen Hauptphase von 2GPa. Damit lassen sich Experimente zur Langzeitstabilität unter wiederholt induziertem Phasenübergang erklären. Abschließend wird ein Verfahren demonstriert, dass es ermöglicht magnetokalorische Kompositdrähte mit einem La(Fe,(Co),Si)13-Kern und einer rostfreiem Stahlhülle herzustellen. Drahthalbzeuge sind Geometrien, die bisher nicht für den Aufbau von Regeneratoren in Erwägung gezogen wurden, da sie nicht herstellbar waren. Drähte bieten ein hohes Maß an Anordnungsfreiheit und bereichern die Vielfalt möglicher Regeneratorgeometrien. Das Material wird durch die Stahlhülle sowohl vor chemischen Einflüssen geschützt, als auch mechanisch stabilisiert, und mit Kernvolumenanteilen von bis zu ∼ 60 vol% sind die Drähte für den Einsatz in einer Wärmepumpe geeignet.

Hintergrund: Heiserkeit und Halsschmerzen sind häufige Intubationsfolgen. Ziel dieser Arbeit ist das Erfassen deren postoperativer Inzidenz und Intensität unter Betrachtung der gewählten Tubusart. Methodik: Das Votum der Ethikkommission der Universität Leipzig liegt vor. Es wurden in einem Zeitraum von einem halben Jahr im Fachbereich Kinderanästhesie insgesamt 103 Kinder im Alter von 3 – 12 Jahren zu elektiven kinderchirurgischen Eingriffen in Allgemeinanästhesie eingeschlossen. Die Randomisierung erfolgte per Losentscheid. Die Patienten wurden entweder Gruppe I (Tubus ohne Cuff) oder Gruppe II (Tubus mit Cuff) zugeordnet. Die Kinder wurden vom ersten bis zum dritten postoperativen Tag zu Halsbeschwerden befragt und diese als Heiserkeit oder Schluckbeschwerden erfasst. Bei Angabe von Halsschmerzen wurden diese durch die VAS (1 – 10) objektiviert. Ergebnisse: Halsbeschwerden nach Intubation wurden am ersten postoperativen Tag von 21,4 % der 103 Kinder angegeben. Dabei trat Heiserkeit mit 19,4 % häufiger als Schluckbeschwerden mit 5,8 % auf. Halsschmerzen gaben 5,8 % aller intubierten Patienten an. In der Gruppe I (n = 50) wurden am ersten postoperativen Tag keine Halsschmerzen angegeben. Jedoch gaben in der Gruppe II (n = 53) 12 % der Patienten Halsschmerzen (VAS > 3) an (p < 0.05). Am zweiten postoperativen Tag hatten noch 6,8 % aller Patienten Halsbeschwerden. Am dritten postoperativen Tag waren alle Kinder beschwerdefrei. Schlussfolgerungen: Kinder zeigten nach Intubation am ersten postoperativen Tag sehr häufig Halsbeschwerden, die bis zum dritten postoperativen Tag abklangen. Halsschmerzen wurden nur von den Kindern angegeben, bei denen ein Tubus mit Cuff verwendet wurde.:1. Einleitung .................................................................................... 4 2. Methodik ..................................................................................... 4 3. Auswertung und Statistik ............................................................... 7 4. Ergebnisse ................................................................................... 8 4.1. Demografische Daten .......................................................... 8 4.2. Postoperative Halsbeschwerden ........................................... 10 4.3. Vergleich Gruppe I und II ................................................... 12 4.4. Subgruppenanalyse Altersklassen ........................................ 13 4.5. Arztqualifikation ................................................................ 17 4.6. Einflussfaktoren für postoperative Halsbeschwerden ............... 22 5. Diskussion .................................................................................. 23 5.1. Vorbetrachtungen .............................................................. 23 5.2. Die Studie ........................................................................ 24 5.3. Halsbeschwerden .............................................................. 25 5.4. Arztqualifikation ................................................................ 26 5.5. Die Ergebnisse .................................................................. 27 5.6. Ursachen für Halsbeschwerden ............................................ 28 5.7. Der Tubus ........................................................................ 30 6. Fazit .......................................................................................... 34 7. Zusammenfassung ....................................................................... 35 8. Literaturverzeichnis ...................................................................... 39 9. Abkürzungsverzeichnis ................................................................. 43 I Erklärung über eigenständige Abfassung der Arbeit ............................. 44 II Lebenslauf ................................................................................... 45 III Wissenschaftliche Veröffentlichungen und Vorträge ........................... 47

The major challenge associated with renewable-energy systems especially solar, is the supply intermittency. One effective solution is to incorporate thermal energy storage components utilizing phase change materials (PCMs). These materials have the potential to store large amounts of energy in relatively small volumes and within nearly an isothermal storage process. The primary drawback of today’s PCMs is that their low thermal conductivity values critically limit their energy storage applications. Also, this grossly reduces the melting/ solidification rates, thus making the system response time to be too long. So, the application of heat transfer enhancement is very important. To improve the PCM storage performance, an efficient performing containment vessel (triplex-tube) along with applications of various heat transfer enhancement techniques was investigated. The techniques were; (i) dispersion of solid nanoparticles, (ii) incorporation of metal foam with nanoparticle dispersion, and (iii) insertion of longitudinal fins with nanoparticle dispersion. Validated simulation models were developed to examine the effects of implementing these techniques on the PCM phase-change rate during the energy storage and recovery modes. The results are presented with detailed model description, analysis, and conclusions. Results show that the use of nanoparticles with metal foam or fins is more efficient than using nanoparticles alone within the same volume usage. Also, employing metal foam or fins alone results in much better improvement for the same system volume.

Focusing of strong shock waves in a gas-filled thin test section with various forms of the reflector boundary is investigated. The test section is mounted at the end of the horizontal co-axial shock tube. Two different methods to produce shock waves of various forms are implemented. In the first method the reflector boundary of the test section is exchangeable and four different reflectors are used: a circle, a smooth pentagon, a heptagon and an octagon. It is shown that the form of the converging shock wave is influenced both by the shape of the reflector boundary and by the nonlinear dynamic interaction between the shape of the shock and the propagation velocity of the shock front. Further, the reflected outgoing shock wave is affected by the shape of the reflector through the flow ahead of the shock front. In the second method cylindrical obstacles are placed in the test section at various positions and in various patterns, to create disturbances in the flow that will shape the shock wave. It is shown that it is possible to shape the shock wave in a desired way by means of obstacles. The influence of the supports of the inner body of the co-axial shock tube on the form of the shock is also investigated. A square shaped shock wave is observed close to the center of convergence for the circular and octagonal reflector boundaries but not in any other setups. This square-like shape is believed to be caused by the supports for the inner body. The production of light, as a result of shock convergence, has been preliminary investigated. Flashes of light have been observed during the focusing and reflection process. / QC 20101126

This thesis investigates the oxidation chemistry and ignition properties of formic acid (FA). The study reports experimental measurements of ignition delay time (IDT) and CO/CO2 time histories during FA oxidation in a shock tube. The initial concentration of FA was measured with a laser to minimize uncertainties arising from its low vapor pressure and tendency to form dimers. Shock tube experiments were carried out at two pressures, around 1.7 and 3.5 bar, and temperatures ranging from 1194 to 1658 K, with two equivalence ratios, 0.72 and 1.47. The results show a noticeable dependence of IDTs on temperature and pressure, while there was insignificant dependence on equivalence ratio. Six kinetic models for FA oxidation available in the literature were tested against the obtained data to evaluate their accuracy and suggest potential improvements. We found that 4 models performed well in predicting IDTs and CO/CO2 profiles with some overprediction at certain conditions. Sensitivity analysis revealed that the IDTs of FA are governed by unimolecular decomposition, H abstraction, and radical consumption (HOCO) reactions. The concentration of HO2 is higher at low temperatures, which is favorable for the system’s reactivity as it makes IDTs more sensitive to the reaction HOCHO + HO2 = H2O2 + HOCO. CO formation is controlled by two reactions: CO + OH = HOCO and HOCHO (+M) = CO + H2O, while the second reaction is more pronounced at high temperatures. Moreover, the dissociation of HOCO is faster at higher pressures, leading to higher initial CO concentrations. The formation of CO2 is determined by CO + OH = CO2 + H, while at higher temperatures, HOCHO (+M) = CO2 + H2 (+M) becomes more important, resulting in higher initial CO2 concentrations.

No description available.

No description available.

In an effort to free up valuable storage space, an obsolete dual tube furnace facility was repurposed to process legacy and newly generated reaction by-products for reuse and/or evaluation. These materials consist of magnesium oxide and unreacted chemicals including small amounts of uranium. They will be converted to their safest form. The repurposing of the facility was not a simple undertaking as all of the utilities with the exception of electricity were disconnected from the facility and the furnaces were more than 50 years old. A 2-part project consisting of a construction phase and transition to operations phase was initiated to accomplish the task. Because funding was done in a piecemeal fashion, the dynamics of restarting the facility was accomplished using creative project management. Lessons learned will provide invaluable information for future sustainability endeavors that require the renovation of an out-service facility to meet current and future needs.

Laser absorption spectroscopy has been a valuable technique for sensitive, non-intrusive, in-situ detection of gaseous and liquid phase target species. The infrared spectral region is specifically attractive as it provides opportunities for selective sensing of a multitude of species in various applications. This thesis explores techniques for interference-free sensing in the infrared region for environmental, combustion, and petrochemical applications. A mid-infrared laser-based sensor was designed to detect trace amounts of benzene using off-axis cavity-enhanced absorption spectroscopy and a multidimensional linear regression algorithm. This sensor achieved unprecedented detection limits, making it ideal for environmental and occupational pollution monitoring. Moreover, wavelength tuning and deep neural networks were employed to differentiate between the broadband similar-shaped absorbance spectra of benzene, toluene, ethylbenzene, and xylene isomers. Benzene sensing was enhanced by recent advancement in semiconductor laser technology, which enabled access to the long wavelength mid-infrared region through commercial distributed feedback quantum cascade lasers. The strongest benzene absorbance band in the infrared is near 14.84 μm, and thus was probed for sensitive benzene detection. Wavelength tuning with multidimensional linear regression were employed to selectively measure benzene, carbon dioxide, and acetylene. Cepstral analysis and wavelength tuning were used to develop a selective sensor for fugitive methane emissions. The sensor was proved to be insensitive to baseline laser intensity imperfections and spectral interference from other present species. In combustion studies, it is desirable to have a diagnostic technique that can detect multiple species simultaneously with high sensitivity, selectivity, and fast time response to validate and improve chemical kinetic mechanisms. A mid-infrared laser sensor was developed for selective and sensitive benzene, toluene, ethylbenzene, and xylenes detection in high-temperature shock tube experiments using deep neural networks. The laser was tuned near 3.3 μm, and an off-axis cavity-enhanced absorption spectroscopy setup was used to enable trace detection. Finally, a novel near-infrared laser-based sensor was developed for water-cut sensing in oil-water flow. The sensor was shown to be immune to the presence of salt and sand in the flow and to temperature variations over 25-60°C. This technique has significant advantages for well and reservoir management, where highly accurate water-cut measurements are required.

Invasive plants can alter pollination dynamics in invaded communities by disrupting patterns of pollinator visitation, pollen transfer dynamics (conspecific [CP] and heterospecific [HP]), and reproductive success. The direction of invasive effects (competitive, neutral, and facilitative) may be partially determined by spatial scale and species’ floral traits. Here, we investigated pollinator visitation, CP and HP receipt, and pollen tube growth for species in a C. arvense present community and non-present community at two scales. At the community-level, the effect of C. arvense on pollinator visitation varied among species. Floral symmetry seemed to explain this variation. At the floral neighborhood-level, we found competitive effects for pollinator visits and mixed effects on CP deposition. The overall structure of plant-plant HP deposition networks was slightly altered. We observed lower average centrality across shared species in the C. arvense present community suggesting C. arvense had subverted their roles as pollen donors.