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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.
A novel calorimetric technique for the analysis of gas-releasing endothermic dissociation reactions
(2020)
Leadership, leader-follower relationship, and
subordinates’ behaviors during the Covid-19
pandemic
(2021)
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.
Modern portable electronic devices have seen component heat load increasing, while the space available for heat dissipation has decreased. This requires the thermal management system to be optimized to attain the high performance heat sink. Heat sinks plays a major role for dissipating heat in electronic devices. Phase change material (PCM) is used to enhance the heat dissipation in heat sink. This paper reports the results of an experimental investigation of the performance of Pin fin heat sinks filled with phase change materials for thermal management of electronic devices. The experimental set ups are prepared with the graphical programming language with Lab VIEW (Laboratory Virtual Instruments for Engineering Workbench. Three different types of Pin fin Heat sink with and without PCM are investigated based on different operational timings and the temperature is acquired with the help of Data Acquisition Card (DAQ). The results indicated that the inclusion of the PCM could stabilize the temperature for a longer period and reduce the heating rates and peak temperatures of heat sink with increasing the number of fins can enhance the thermal performance of electronic devices.
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.
The boom of information technology development created high demand for skilled labour force in IT occupations. IT professionals install, test, build, repair or maintain hardware and software and can do the job from any location in the world.
Demand for the workforce significantly outstrips the global supply. In a situation of staff shortage employers have to compete on local and global labour markets. The ability of a firm to attract and retain the best talent would become a source of its sustainable competitive advantage.
Aim of the study is to understand what influences perception of employment attractiveness by IT professionals the most. This study intends to expend the existing knowledge about employees´ needs and “psychological contract” concept.
The research was conducted with the participation of 4 IT and 4 HR English-speaking experts who live and work in Austria. In the study the grounded theory approach and the descriptive qualitative methods were applied.
The research findings explain which factors influence the decision of IT professionals to join, stay or leave an employer. The results are discussed in relation to talent attraction and retention practices of Austrian employers.
Signatures of the optical stark effect on entangled photon pairs from resonantly-pumped quantum dots
(2023)
Two-photon resonant excitation of the biexciton-exciton cascade in a quantum dot generates highly polarization-entangled photon pairs in a near-deterministic way. However, the ultimate level of achievable entanglement is still debated. Here, we observe the impact of the laser-induced ac-Stark effect on the quantum dot emission spectra and on entanglement. For increasing pulse-duration-to-lifetime ratios and pump powers, decreasing values of concurrence are recorded. Nonetheless, additional contributions are still required to fully account for the observed below-unity concurrence.