Entropic Multi-Relaxation Models for Simulation of Fluid Turbulence

A recently introduced family of lattice Boltzmann (LB) models (Karlin, B\"osch, Chikatamarla, Phys. Rev. E, 2014) is studied in detail for incompressible two-dimensional flows. A framework for developing LB models based on entropy considerations is laid out extensively. Second order rate of convergence is numerically confirmed and it is demonstrated that these entropy based models recover the Navier-Stokes solution in the hydrodynamic limit. Comparison with the standard Bhatnagar-Gross-Krook (LBGK) and the entropic lattice Boltzmann method (ELBM) demonstrates the superior stability and accuracy for several benchmark flows and a range of grid resolutions and Reynolds numbers. High Reynolds number regimes are investigated through the simulation of two-dimensional turbulence, particularly for under-resolved cases. Compared to resolved LBGK simulations, the presented class of LB models demonstrate excellent performance and capture the turbulence statistics with good accuracy.Comment: To be published in Proceedings of Discrete Simulation of Fluid Dynamics DSFD 201

Energy diplomacy: West Germany, the Soviet Union and the oil crises of the 1970s

This article analyzes West German energy policy and negotiations with the Soviet Union during the Cold War. Archival sources from the West German government show that long-term energy diplomacy became a carefully built link which guaranteed cooperation even during political crises,such as the one in 1980/81. This article argues that energy diplomacy catalyzed Brandt’s Ostpolitik. In particular, natural gas pipelines implied mutual trust within a stable relationship, which led to further collaborations, including cooperation in nuclear power. It points out that, from this perspective, 1973 was not exactly a turning point, and some grandiose plans in the years after the first oil crisis failed. Furthermore the article shows how the second oil crisis in 1979 increased cooperation cooperation between West Germany and the Soviet Union, although this strained West Germany’s relationship with the United States. Archival documents reveal that energy policy matters remained wellcalculated and persistent. Thus, the Soviet Union became a more reliable partner than many Arab countries

Observing Conflict Escalation in World Society: Ukraine's Maidan and Mali's Breakup

How do conflicts escalate? This is one of the major questions in conflict research. To offer further answers, Richard Bösch follows a tripartite agenda: First, he develops a constructivist methodology for the study of conflict escalation embedded in a Luhmannian systems theoretical world society perspective. Bösch argues that conflicts can be observed as social systems and he looks at the process of conflict escalation by analysing communication. Second, this analysis offers two case studies: the Maidan protests in Ukraine 2013-2014 and Mali's crisis 2010-2012. Third, it gives insights on how systems theoretical research can be beneficial for Peace and Conflict Studies

Ecology of fungal denitrifiers in terrestrial ecosystems : global patterns and effects of management in agricultural soils

Denitrification is the dominant source of nitrous oxide (N2O) from terrestrial ecosystems, a potent greenhouse gas and stratospheric ozone-depleting agent. Fungi can perform denitrification and terminate the process with N2O, making them a potentially important source of N2O. This thesis aimed to broaden the understanding of the ecology of this understudied group in the nitrogen cycle by assessing their global abundance and distribution in terrestrial ecosystems and evaluating the effects of soil management practices on their abundance, community composition, and contribution to N2O production in agricultural soils.Fungi carrying the denitrification marker gene nirK were rare and cosmopolitan and compared to prokaryotic denitrifiers, they were most abundant in forests and croplands, although prokaryotes dominated in all biomes. Agricultural management practices affected the abundance and community composition of fungal denitrifiers through changes in the availability of carbon and nitrogen. Long-term fertilization increased their abundance, irrespective of soil type or climate, but did not affect fungal contributions to potential N2O production. Instead, the genetic potential of bacterial denitrifiers was more important. In unfertilized soils, biotic and abiotic controls of N2O production rates were important, but in fertilized soils only abiotic soil properties were involved. Inversion tillage, compared with other types of tillage, led to a reduction of the genetic potential for fungal denitrification relative to that of bacterial denitrifiers and selected for fungi with opportunistic lifestyles. These results highlight that fungal denitrifiers are found across all terrestrial ecosystems, are significantly influenced by soil management but contribute less to N2O emissions than their prokaryotic counterparts