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In recent years, much research has been done on medical laser applications inside the human body, as they are minimally invasive and therefore have fewer side effects and are less expensive than conventional therapies. In order to bring the laser light into the human body, a glass fibre with a diffuser is needed. The goal of this master thesis is the characterization and production of fibre optic diffusers that can be used for the three therapeutic applications: photodynamic therapy, laser-induced thermotherapy and endovenous laser therapy. For this purpose the following goals have to be achieved:
- Optimization of the efficiency and homogeneity of internally structured diffusers
- Examine damage thresholds of the diffusers in the tissue using a crash test
- Achieving a better understanding of the decouple mechanism with a simulation
Using an ultra-short pulse laser, modifications could be introduced into the fibre in this way that the radiation profile is homogeneous and the decoupling efficiency is 68.3 %. It was discovered that the radiation profile depends on the wavelength. Attempts have been made to improve the decoupling efficiency by mirroring the distal end of the fibre. The mirror reflects the remaining light back into the fibre, so that it is also decoupled lateral on the modifications. Vapor-deposited aluminum with physical vapor deposition is a promising approach. However, the adhesion of the coating must be improved or the coating must be protected by a mechanical cover, otherwise it will flake off too quickly.
In a crash test, it was shown that the glass fibre diffusers can withstand 20 W laser power for 300 s without visible change. In an ex vivo test, the coagulation zone in the tissue was examined and it was showed that the diffusers radiate radially homogeneously. Using a ray trace simulation, the course of the light rays in the fibre was examined and the correlation of modification width and length with the decoupling efficiency was investigated. It was discovered that there are helical light rays in the fibre, which cannot be decoupled by modifications in the fibre centre.
Die vorliegende Masterarbeit enthält neue Erkenntnisse in Bezug auf die Frage, ob die Änderung einer Analystenempfehlung für Aktien neue Informationen enthält und ein Anleger eine abnormale Rendite erzielen kann. Darüber hinaus wird untersucht, ob in Phasen des konjunkturellen Abschwungs eine höhere abnormale Rendite im Vergleich zu einem konjunkturellen Aufschwung ausgewiesen wird. Die Ergebnisse zeigen, dass Aktienkurse signifikant positiv auf Kaufempfehlungen und signifikant negativ auf Verkaufsempfehlungen reagieren. Zusätzlich wird belegt, dass eine höhere und zeitlich längere Reaktion auf eine Verkaufsempfehlung gegenüber einer Kaufempfehlung stattfindet. Es wird außerdem festgestellt, dass auch bei isolierter Betrachtung der Konjunkturzyklen (Aufschwung und Abschwung) eine abnormale Rendite erzielt wird. Zudem verzeichnen negative Veränderungen der Analystenempfehlungen eine höhere abnormale Rendite als jene bei positiven Veränderungen.
Diese Arbeit resultiert in einem Leitfaden, der zur verbesserten Wirksamkeit von Lernmaßnahmen in Organisationen beitragen soll. Inbesondere die Verkürzung der Halbwertszeit von Wissen gab Anlass zur vorliegenden Untersuchung. In den Kapiteln zwei und drei wurde das theoretische Fundament durch Bearbeitung der Themen Personal-/Kompetenzentwicklung, allgemeine und individuelle Lerntheorie, sowie Lernbedarfsanalyse, Lerntransfer und Lernevaluation gebildet. Darauf aufbauend wurde mit der Methodik (Kapitel 4) der Experteninterviews der aktuelle Stand definierter Organisationen im Raum Ostschweiz, Westösterreich und Liechtenstein hinsichtlich Lernbedarfsanalyse, Lerntransfer und Lernevaluation erhoben. Diese Ergebnisse wurden in Kapitel 5 mit der Literaturstudie aus Kapitel 2 und 3 verglichen. Der Leitfaden besteht für Lernbedarfsanalyse, Lerntransfer und Lernevaluation aus unterschiedlichen Schritten, die in Tabellenformat dargestellt und beschrieben sind (Kapitel 6). In Kapitel 7 wurden, neben einer Zusammenfassung und einem Fazit, weiterführende Forschungsansätze zur Thematik angeführt.
A novel calorimetric technique for the analysis of gas-releasing endothermic dissociation reactions
(2020)
Real-time measurements of the differences in inhaled and exhaled, unlabeled and fully deuterated acetone concentration levels, at rest and during exercise, have been conducted using proton transfer reaction mass spectrometry. A novel approach to continuously differentiate between the inhaled and exhaled breath acetone concentration signals is used. This leads to unprecedented fine grained data of inhaled and exhaled concentrations. The experimental results obtained are compared with those predicted using a simple three compartment model that theoretically describes the influence of inhaled concentrations on exhaled breath concentrations for volatile organic compounds with high blood:air partition coefficients, and hence is appropriate for acetone. An agreement between the predicted and observed concentrations is obtained. Our results highlight that the influence of the upper airways cannot be neglected for volatiles with high blood:air partition coefficients, i.e. highly water soluble volatiles.
Greater specific energy densities in lithium-ion batteries can be achieved by using three-dimensional (3D) porous current collectors, which allow for greater areal mass loadings of the electroactive material. In this paper, we present the use of embroidered current collectors for the preparation of thick, pouch-type Li-ion batteries. Experiments were performed on LiFePO 4 (LFP) water-based slurries using styrene-butadiene rubber (SBR) as binder and sodium carboxymethyl cellulose (CMC) as thickener, and formulations of different rheological characteristics were investigated. The electrochemical performance (cyclic voltammetry, rate capability) and morphological characteristics of the LFP half-pouch cells (X-ray micro computed tomography and scanning electron microscopy) were compared between the formulations. An optimum electrode formulation was identified, and a mechanism is proposed to explain differences between the formulations. With the optimum electrode formulation, 350 µm casted electrodes with high mechanical stability were achieved. Electrodes exhibited 4–6 times greater areal mass loadings (4–6 mAh cm −2 ) and 50% greater electroactive material weight than with foils. In tests of half- and full-pouch embroidered cells, a 50% capacity utilization at 1C-rate and 11% at 2C-rate were observed, with a full recovery at C/5-rate. The cycling stability was also maintained over 55 cycles.
The present research had compared how Uppsala and Bartlett & Ghoshal (B&G) models explain the internationalization process of the Brazilian pulp producer Fibria.
The Uppsala model describes the developments of capabilities that enable the firm to move towards higher commitments abroad. Despite its sine-qua-non dependence on foreign markets, it is unlikely that Fibria will internationalize its production to another country, given the country-specific advantages that the company has in Brazil. Nevertheless, Fibria set its structure abroad even when the direct exports would suffice to reach the markets without any foreign direct investment.
B&G deals with the aspects of the organizational structure and described the Transnational type as the evolution of the international firm. In their typology, Fibria was a Global and Ethnocentric type, but interestingly, elements of Transnational and Geocentric models were also observed in the company.
Both theories overlap or complement each other in many aspects. However, they could not explain the peculiarities of the internationalization of Fibria. One reason is the lack of country-related elements in these models.
Eventually, comparisons between theories such as those presented enable decision-makers to align the corporate strategy using suitable models, bearing in mind the limitations that each method entails.
Clathrate hydrates, or hydrates for short, are inclusion compounds in which water molecules form a hydrogen-bonded host lattice that accommodates the guest molecules. While vast amounts of hydrates are known to exist in seafloor sediments and in the permafrost on Earth, these occurrences might be dwarfed by the amounts of hydrates occurring in space and on celestial bodies. Since methane is the primary guest molecule in most of the natural occurrences on Earth, hydrates are considered a promising source of energy. Moreover, the ability of one volume of hydrate to store about 170 volumes of gas, make hydrates a promising functional material for various industrial applications. While the static properties of hydrates are reasonably well known, the dynamics of hydrate formation and decomposition are insufficiently understood. For instance, the stochastic period of hydrate nucleation, the memory effect, and the self-preservation phenomenon complicate the development of predictive models of hydrate dynamics. Additionally, the influence of meso- and macroscopic defects as well as the roles of mass and heat transport on different length scales remain to be clarified.
Due to its non-invasive and non-destructive nature and the high spatial resolution of approx. 1µm or even less, micro-computed X-ray attenuation tomography ( µCT ) seems to be the perfect method for the study of the evolving structures of forming or decomposing hydrates on the meso- and macroscopic length scale. However, for the naturally occurring hydrates of low atomic number guests the contrast between hydrate, ice, and liquid water is typically very weak because of similar X-ray attenuation coefficients. So far, good contrast was only restricted to synchrotron beamline experiments which utilize the phase information of monochromatic X-rays.
In this thesis it is shown that with the help of a newly developed sample cell, a contrast between the hydrate and the ice phase sufficiently good for the reliable segmentation of the materials can also be achieved in conventional tube-based µCT. An accurate pressure and temperature management, i.e., the added functionality of the cell, further allows for cross-correlation of structural and thermodynamic data. The capability of this µCT setup is demonstrated in a series of studies on the formation and decomposition of hydrates which yield new insights for the development of a novel route to hydrate synthesis. At last, this thesis points towards possibilities how better models of hydrate formation and decomposition can be developed with the aid of µCT and computer simulations.
Gas hydrates are usually synthesized by bringing together a pressurized gas and liquid or solid water. In both cases, the transport of gas or water to the hydrate growth site is hindered once an initial film of hydrate has grown at the water–gas interface. A seemingly forgotten gas-phase technique overcomes this problem by slowly depositing water vapor on a cold surface in the presence of the pressurized guest gas. Despite being used for the synthesis of low-formation-pressure hydrates, it has not yet been tested for hydrates of CO 2 and CH 4 . Moreover, the potential of the technique for the study of hydrate decomposition has not been recognized yet. We employ two advanced implementations of the condensation technique to form hydrates of CO 2 and CH 4 and demonstrate the applicability of the process for the study of hydrate decomposition and the phenomenon of self-preservation. Our results show that CO 2 and CH 4 hydrate samples deposited on graphite at 261–265 K are almost pure hydrates with an ice fraction of less than 8%. Rapid depressurization experiments with thin deposits (approx. 330 mm thickness) of CO 2 hydrate on an aluminum surface at 265 K yield identical dissociation curves when the deposition is done at identical pressure. However, hydrates deposited at 1 MPa almost completely withstand decomposition after rapid depressurization to 0.1 MPa, while samples deposited at 2 MPa decompose 7 times faster. Therefore, this synthesis technique is not only applicable for the study of hydrate decomposition but can also be used for the controlled deposition of a super-preserved hydrate.
Graphite substrates underwent two methods of creating doped silicon carbide films via carbothermal reduction; the first method being liquid-phase processing, or dip-coating, and the second gas-phase processing, otherwise referred to as the solid-vapour reaction. The dip-coating procedure resulted in flaky coatings, while the solid-vapour reaction resulted in polycrystalline films with columnar growth that displayed promising morphological and electrical properties. The films were tested on their performance as semiconductor diodes, and proved that carbothermal reduction in the gas phase is a promising technique for creating polycrystalline silicon carbide films for the application of light-emitting diodes.