Dreidimensionale parallele Lattice Boltzmann Hydrodynamiksimulationen turbulenter Strömungen in interstellaren Dunkelwolken

Die Erforschung der klumpigen und filamentartigen Struktur interstellarer Molek ulwolken ist eines der zentralen Probleme der modernen Astrophysik. Wir wissen bislang wenig uber die physikalischen Prozesse, welche die Strukturierung bewirken, aber es wird vermutet, daß Turbulenz eine wesentliche Rolle spielt. In dieser Dissertation untersuche ich den Beitrag turbulenter Str omungen zur Struktur interstellarer Dunkelwolken. Dazu sind dreidimensionale numerische Hydrodynamiksimulationen notwendig, da die analytische Berechnung der detaillierten turbulenten Raumund Geschwindigkeitsstruktur nicht m oglich ist. Mit der " Lattice Boltzmann Methode" verwende ich ein neuartiges numerisches Verfahren, bei welchem die Boltzmanngleichung in einem diskretisierten Phasenraum gel ost wird. Mesoskopische Teilchenpakete bewegen sich mit festen Geschwindigkeiten auf einem kartesischen Gitter und tauschen bei jedem Zeitschritt nach vorgegebenen Regeln Masse aus. Die Methode ist wegen der haupts achlich ..

elektronisch publiziert. 2 Spatial Targeting of Payments for Environmental Services in Costa Rica: A Site Selection Tool for Increasing Conservation Benefits

Payments for environmental services (PES) have become an increasingly popular market-based instrument to translate external, non-market environmental services into financial incentives for landowners to preserve the ecosystems that provide the services. However, lack of spatial differentiation in the targeting mechanism may lead to potential efficiency losses. Addressing this challenge, a formal site selection tool was constructed, which takes into account three variables that vary in space: environmental services, risks of losing services, and participation costs. Using data from Costa Rica‘s Nicoya Peninsula, the tool‘s potential to increase the financial efficiency of Costa Rica‘s PES program is empirically tested. Results show that, given a fixed budget, efficiency increases radically if per hectare payments are aligned to landowners ‘ heterogeneity in participation costs. Selecting sites based on environmental service potential also moderately increases efficiency. Overall additionality could in the best case be doubled but is generally limited due to low deforestation risks. To take advantage of the efficiency potentials of costaligned payments, cost-effective methods for the determination of participation costs would be necessary. Two possible approaches were tested deriving costs from annual land rents, and regressing easy-to-obtain and difficult-to-manipulate variables as proxies on per hectare returns. None of the approaches appeared t

Erscheinungsjahr: 2010Acknowledgements

First, I would like to express my sincere gratitude to Prof. Thomas Heckelei, who has been an excellent supervisor and gave me the opportunity to work at the Institute o