2 resultados para Pyramids.
em AMS Tesi di Dottorato - Alm@DL - Università di Bologna
Resumo:
Corruption is, in the last two decades, considered as one of the biggest problems within the international community, which harms not only a particular state or society but the whole world. The discussion on corruption in law and economics approach is mainly run under the veil of Public choice theory and principal-agent model. Based on this approach the strong international initiatives taken by the UN, the OECD and the Council of Europe, provided various measures and tools in order to support and guide countries in their combat against corruption. These anti-corruption policies created a repression -prevention-transparency model for corruption combat. Applying this model, countries around the world adopted anti-corruption strategies as part of their legal rules. Nevertheless, the recent researches on the effects of this move show non impressive results. Critics argue that “one size does not fit all” because the institutional setting of countries around the world varies. Among the countries which experience problems of corruption, even though they follow the dominant anti-corruption trends, are transitional, post-socialist countries. To this group belong the countries which are emerging from centrally planned to an open market economy. The socialist past left traces on institutional setting, mentality of the individuals and their interrelation, particularly in the domain of public administration. If the idiosyncrasy of these countries is taken into account the suggestion in this thesis is that in public administration in post-socialist countries, instead of dominant anti-corruption scheme repression-prevention-transparency, corruption combat should be improved through the implementation of a new one, structure-conduct-performance. The implementation of this model is based on three regulatory pyramids: anti-corruption, disciplinary anti-corruption and criminal anti-corruption pyramid. This approach asks public administration itself to engage in corruption combat, leaving criminal justice system as the ultimate weapon, used only for the very harmful misdeeds.
Resumo:
Several MCAO systems are under study to improve the angular resolution of the current and of the future generation large ground-based telescopes (diameters in the 8-40 m range). The subject of this PhD Thesis is embedded in this context. Two MCAO systems, in dierent realization phases, are addressed in this Thesis: NIRVANA, the 'double' MCAO system designed for one of the interferometric instruments of LBT, is in the integration and testing phase; MAORY, the future E-ELT MCAO module, is under preliminary study. These two systems takle the sky coverage problem in two dierent ways. The layer oriented approach of NIRVANA, coupled with multi-pyramids wavefront sensors, takes advantage of the optical co-addition of the signal coming from up to 12 NGS in a annular 2' to 6' technical FoV and up to 8 in the central 2' FoV. Summing the light coming from many natural sources permits to increase the limiting magnitude of the single NGS and to improve considerably the sky coverage. One of the two Wavefront Sensors for the mid- high altitude atmosphere analysis has been integrated and tested as a stand- alone unit in the laboratory at INAF-Osservatorio Astronomico di Bologna and afterwards delivered to the MPIA laboratories in Heidelberg, where was integrated and aligned to the post-focal optical relay of one LINC-NIRVANA arm. A number of tests were performed in order to characterize and optimize the system functionalities and performance. A report about this work is presented in Chapter 2. In the MAORY case, to ensure correction uniformity and sky coverage, the LGS-based approach is the current baseline. However, since the Sodium layer is approximately 10 km thick, the articial reference source looks elongated, especially when observed from the edge of a large aperture. On a 30-40 m class telescope, for instance, the maximum elongation varies between few arcsec and 10 arcsec, depending on the actual telescope diameter, on the Sodium layer properties and on the laser launcher position. The centroiding error in a Shack-Hartmann WFS increases proportionally to the elongation (in a photon noise dominated regime), strongly limiting the performance. To compensate for this effect a straightforward solution is to increase the laser power, i.e. to increase the number of detected photons per subaperture. The scope of Chapter 3 is twofold: an analysis of the performance of three dierent algorithms (Weighted Center of Gravity, Correlation and Quad-cell) for the instantaneous LGS image position measurement in presence of elongated spots and the determination of the required number of photons to achieve a certain average wavefront error over the telescope aperture. An alternative optical solution to the spot elongation problem is proposed in Section 3.4. Starting from the considerations presented in Chapter 3, a first order analysis of the LGS WFS for MAORY (number of subapertures, number of detected photons per subaperture, RON, focal plane sampling, subaperture FoV) is the subject of Chapter 4. An LGS WFS laboratory prototype was designed to reproduce the relevant aspects of an LGS SH WFS for the E-ELT and to evaluate the performance of different centroid algorithms in presence of elongated spots as investigated numerically and analytically in Chapter 3. This prototype permits to simulate realistic Sodium proles. A full testing plan for the prototype is set in Chapter 4.