Fixed-parameter tractability of Directed Multicut with three terminal pairs parameterized by the size of the cutset: twin-width meets flow-augmentation

We show fixed-parameter tractability of the Directed Multicut problem with three terminal pairs (with a randomized algorithm). This problem, given a directed graph $G$, pairs of vertices (called terminals) $(s_1,t_1)$, $(s_2,t_2)$, and $(s_3,t_3)$, and an integer $k$, asks to find a set of at most $k$ non-terminal vertices in $G$ that intersect all $s_1t_1$-paths, all $s_2t_2$-paths, and all $s_3t_3$-paths. The parameterized complexity of this case has been open since Chitnis, Cygan, Hajiaghayi, and Marx proved fixed-parameter tractability of the 2-terminal-pairs case at SODA 2012, and Pilipczuk and Wahlstr\"{o}m proved the W[1]-hardness of the 4-terminal-pairs case at SODA 2016. On the technical side, we use two recent developments in parameterized algorithms. Using the technique of directed flow-augmentation [Kim, Kratsch, Pilipczuk, Wahlstr\"{o}m, STOC 2022] we cast the problem as a CSP problem with few variables and constraints over a large ordered domain.We observe that this problem can be in turn encoded as an FO model-checking task over a structure consisting of a few 0-1 matrices. We look at this problem through the lenses of twin-width, a recently introduced structural parameter [Bonnet, Kim, Thomass\'{e}, Watrigant, FOCS 2020]: By a recent characterization [Bonnet, Giocanti, Ossona de Mendes, Simon, Thomass\'{e}, Toru\'{n}czyk, STOC 2022] the said FO model-checking task can be done in FPT time if the said matrices have bounded grid rank. To complete the proof, we show an irrelevant vertex rule: If any of the matrices in the said encoding has a large grid minor, a vertex corresponding to the ``middle'' box in the grid minor can be proclaimed irrelevant -- not contained in the sought solution -- and thus reduced

The Nexus of CO2 Emissions, Energy Consumption, Economic Growth, and Trade-Openness in WTO Countries

This paper analyzes the dynamic relationship between CO2 emissions, energy consumption, GDP, and trade-openness from 1971 to 2013, based on the Environmental Kuznets Curve (EKC) hypothesis for 70 WTO countries. Using recently developed secondgeneration panel data methods, the empirical results support the EKC hypothesis for the high-, middle-, and lower-income panels used. Concerning the energy consumption and economic growth nexus, the causality results support the conversion hypothesis for the high-income panel, whereas the neutrality hypothesis holds for the lower- and middle-income panels. Based on the causality results, trade-openness does not positively impact CO2 emissions, GDP leads CO2 emissions, and trade-openness causes energy consumption within any income panel. The net effect of economic growth, however, could help to stabilize future CO2 emissions within any income panel

Vier empirische Aufsätze zu sozio-ökonomischen Aspekten der kohlenstoffarmen Energie-Transformation

This thesis contains four empirical contributions which address socio-economic challenges of the Anthropocene and carbon dioxide emissions as well as critical issues of nuclear power which are of relevance for achieving the transformation towards decentralized, sustainable energy systems. We start analyzing the relationship between economic growth and carbon dioxide emissions, thereby challenging the hypothesized long-term sustainability of further economic acceleration. The empirical results indicate that continued economic growth does not pose a natural solution to reduce carbon dioxide emissions in the long-term as suggested by the Environmental Kuznets Curve (EKC) hypothesis. Next, we provide an assessment of the primary drivers of carbon dioxide emissions and identify the average growth in consumption of goods and services produced rather than population as a stronger determinant. We analyze these issues using datasets comprising countries grouped according to their level of economic development and apply dynamic nonstationary panel time series estimation techniques which account for heterogeneity among countries. We then turn towards democracy and security issues surrounding both the introduction and usage of nuclear energy. We are the first to empirically analyze the impacts of democratic development on the introduction of nuclear power. Using a multinomial logistic regression approach to predict category membership, we find that countries with lower democratic development are more likely to introduce nuclear power. Finally, we provide the first empirical analysis of the determinants of the accumulation of nuclear weapons in seven nuclear arms states. Using econometric techniques for inferring causality in time series data, we identify a significant causal relationship between a state’s nuclear warhead stockpiles and its nuclear energy consumption levels.Die vorliegende Dissertation enthält vier empirische Beiträge, welche sich mit sozioökonomischen Herausforderungen des Anthropozäns und Kohlendioxidemissionen sowie kritischen Fragen der Atomkraft befassen, die für den Übergang zu einem dezentralen, nachhaltigen Energiesystemen von Bedeutung sind. Die Arbeit beginnt mit der Analyse des Zusammenhangs zwischen Wirtschaftswachstum und Kohlendioxidemissionen und hinterfragt die Hypothese der langfristigen Nachhaltigkeit von kontinuierlichem Wirtschaftswachstum. Die empirischen Befunde implizieren, dass anhaltendes Wirtschaftswachstum keine nachhaltige Lösung darstellt, um den Kohlendioxidausstoß langfristig zu reduzieren, wie von der Umwelt-Kuznets-Kurve Hypothese vorgeschlagen. Als nächstes evaluieren wir die Determinanten von Kohlendioxidemissionen und identifizieren das durchschnittliche Wachstum des Konsums der produzierten Güter und Dienstleistungen anstelle von Bevölkerungswachstum als stärksten Bestimmungsfaktor. Zur Analyse dieser Fragestellungen benutzen wir Datensätze, in denen Länder entsprechend ihrem wirtschaftlichen Entwicklungsstand klassifiziert werden. Wir verwenden dynamische ökonometrische Schätzverfahren zur Analyse von nicht-stationären Panel-Zeitreihen Daten, welche die Heterogenität zwischen den Ländern berücksichtigen. Danach fokussieren wir demokratie- und sicherheitsrelevante Fragestellungen, welche sowohl die Einführung als auch die Nutzung von Atomkraft betreffen. Wir testen erstmalig empirisch den Zusammenhang zwischen dem Ausmaß an demokratischer Entwicklung und dem Einstieg in die Atomkraft analysieren. Die empirischen Ergebnisse einer multinomialen logistischen Regressionsanalyse zur Vorhersage von Gruppenzugehörigkeiten zeigen, dass Länder mit einem niedrigeren Ausmaß an demokratischer Entwicklung eher den Einstieg in die Atomkraft durchgeführt haben. Abschließend liefern wir die erste empirische Analyse von Bestimmungsfaktoren für die Anhäufung von Atomwaffen in sieben atomar bewaffneten Staaten. Anhand von ökonometrischen Verfahren zur kausalen Modellierung in Zeitreihendaten identifizieren wir eine signifikante kausale Beziehung zwischen der Anzahl an Atomsprengköpfen eines Staates und seines Atomenergieverbrauchs

The impact of population, affluence, technology, and urbanization on CO2 emissions across income groups

This paper analyzes the impact of urbanization on CO2 emissions within the STIRPAT framework over the period 1971 to 2014 for a panel of 76 countries clustered into income groups. Using dynamic panel estimations techniques, the empirical results robustly show an inverted N-shaped relationship between urbanization and CO2 emissions in the long-term associated with the ecological modernization theory in particular for the lower- and middle-income panel: increasing levels of urbanization tend to reduce CO2 emissions in the long-term. The estimated turning point for the urbanization ratio after which CO2 emissions decline is almost identical and around 54% both for the lower- and middle-income panel. The long-term relationship for CO2 emissions and its relevant impact factors tends to be similar across groups. The impact of population determines CO2 emissions significantly only in the long-term within any panel. Different from previous studies, the results robustly indicate that GDP per capita does impact CO2 emissions greater than population in any panel. This suggests, that it is rather the growth in consumption than the number of people leading CO2 emissions to increase. Energy efficiency reductions most harmfully effect CO2 emissions within the high-income panel in the long- and short-run

Democratic quality and nuclear power: Reviewing the global determinants for the introduction of nuclear energy in 166 countries

This paper analyzes the nature of democratic development in a nation on the process of introducing nuclear power over the period 1960 - 2017 for an unbalanced panel of 166 countries. Given the involved political process of introducing nuclear power and its political importance, as well as proposals to construct new nuclear reactors in currently about 30 countries, this question is both of historic and current interest. We apply a multinomial logistic regression approach that relates the likelihood of a country to introduce nuclear power to its level of democratic quality and nuclear warhead possession. The model results suggest that countries with lower levels of democratic development are more likely to introduce nuclear power. Our results moreover indicate that countries which possess at least one nuclear warhead are more likely to continue to use nuclear power instead of not using nuclear power at all. We discuss these results in the context of the public policy debate on nuclear power, yet beyond energy and environmental issues addressing the neglected political and democratic dimension in connection with nuclear power

Nuclear power, democracy, development, and nuclear warheads: Determinants for introducing nuclear power

This paper analyzes the nature of democratic development in a nation on the process of introducing nuclear power over the period 1960 - 2017 for an unbalanced panel of 171 countries. Given the involved political process of introducing nuclear power and its political importance, as well as the current tendency of about 30 countries to "go nuclear", this question is both of historic and current interest. We apply a multinomial logistic regression approach that relates the likelihood of a country to introduce nuclear power to its level of democratic quality and nuclear warhead possession. The model results suggest that countries with lower levels of democratic development are more likely to introduce nuclear power. Our results moreover indicate that countries which possess at least one nuclear warhead are more likely to continue to use nuclear power instead of not using nuclear power at all. We discuss these results in the context of the public policy debate on nuclear power, yet beyond energy and environmental issues addressing international relations, conflict, and security issues connected to nuclear energy