No surviving evolved companions of the progenitor of SN 1006

Type Ia supernovae are thought to occur when a white dwarf made of carbon and oxygen accretes sufficient mass to trigger a thermonuclear explosion(1). The accretion could be slow, from an unevolved (main-sequence) or evolved (subgiant or giant) star(2,3) (the single-degenerate channel), or rapid, as the primary star breaks up a smaller orbiting white dwarf(3,4) (the double-degenerate channel). A companion star will survive the explosion only in the single-degenerate channel(5). Both channels might contribute to the production of type Ia supernovae(6,7), but the relative proportions of their contributions remain a fundamental puzzle in astronomy. Previous searches for remnant companions have revealed one possible case for SN 1572 (refs 8, 9), although that has been questioned(10). More recently, observations have restricted surviving companions to be small, main-sequence stars(11-13), ruling out giant companions but still allowing the single-degenerate channel. Here we report the results of a search for surviving companions of the progenitor of SN 1006 (ref. 14). None of the stars within 4 arc minutes of the apparent site of the explosion is associated with the supernova remnant, and we can firmly exclude all giant and subgiant stars from being companions of the progenitor. In combination with previous results, our findings indicate that fewer than 20 per cent of type Ia supernovae occur through the single-degenerate channel.

Ethnic Violence on Kenya's Periphery: Informal Institutions and Local Resilience in Conflict-Affected Communities

Deadly, inter-ethnic group conflict remains a threat to international security in a world where the majority of armed violence occurs not only within states but in the most ungoverned areas within states. Conflicts that occur between groups living in largely ungoverned areas often become deeply protracted and are difficult to resolve when the state is weak and harsh environmental conditions place human security increasingly under threat. However, even under these conditions, why do some local conflicts between ethnic groups escalate, whereas others do not? To analyze this puzzle, the dissertation employs comparative methods to investigate the conditions under which violence erupts or stops and armed actors choose to preserve peace. The project draws upon qualitative data derived from semi-structured interviews, focus group dialogues, and participant observation of local peace processes during field research conducted in six conflict-affected counties in Northern Kenya. Comparative analysis of fifteen conflict episodes with variable outcomes reveals the conditions under which coalitions of civic associations, including local peace committees, faith-based organizations, and councils of elders, inter alia, enhance informal institutional arrangements that contain escalation. Violence is less likely to escalate in communities where cohesive coalitions provide platforms for threat-monitoring, informal pact making, and enforcement of traditional codes of restitution. However, key scope conditions affect whether or not informal organizational structures are capable of containing escalation. In particular, symbolic acts of violence and the use of indiscriminant force by police and military actors commonly undermine local efforts to contain conflict. The dissertation contributes to the literatures on civil society and peacebuilding, demonstrating the importance of comparing processes of escalation and non-escalation and accounting for interactive effects between modes of state and non-state response to local, inter-ethnic group conflict.

Everyday Indivisibility: How Exclusive Religious Practices Explain Variation in Subnational Violence Outcomes

This project explores the puzzle of religious violence variation. Religious actors initiate conflict at a higher rate than their secular counterparts, last longer, are more deadly, and are less prone to negotiated termination. Yet the legacy of religious peacemakers on the reduction of violence is undeniable. Under what conditions does religion contribute to escalated violence and under what conditions does it contribute to peace? I argue that more intense everyday practices of group members, or high levels of orthopraxy, create dispositional indivisibilities that make violence a natural alternative to bargaining. Subnational armed groups with members whose practices are exclusive and isolating bind together through ritual practice, limit the acceptable decisions of leaders, and have prolonged timeframes, all of which result in higher levels of intensity, intransigence and resolve during violent conflict. The theory challenges both instrumentalist and constructivist understandings of social identity and violence. To support this argument, I construct an original cross-national data-set that employs ethnographic data on micro-level religious practices for 724 subnational armed groups in both civil wars and terror campaigns. Using this data, I build an explanatory “religious practice index” for each observation and examine its relationship with conflict outcomes. Findings suggest that exclusive practice groups fight significantly longer with more intensity and negotiate less. I also apply the practice model to qualitative cases. Fieldwork in the West Bank and Sierra Leone reveals that groups with more exclusive religious practicing membership are principle contributors to violence, whereas those with inclusive practices can contribute to peace. The project concludes with a discussion about several avenues for future research and identifies the practical policy applications to better identify and combat religious extremism.

The many lives of magnetized neutron stars

The magnetic field strength at birth is arguably one of the most important properties to determine the evolutionary path of a neutron star. Objects with very high fields, collectively known as magnetars, are characterized by high X-ray quiescent luminosities, occurrence of outbursts, and, for some of them, sporadic giant flares. While the magnetic field strength is believed to drive their collective behaviour, however, the diversity of their properties, and, especially, the observation of magnetar-like bursts from “low-field” pulsars, has been a theoretical puzzle. In this review, we discuss results of long-term simulations following the coupled evolution of the X-ray luminosity and the timing properties for a large, homogeneous sample of X-ray emitting isolated neutron stars, accounting for a range of initial magnetic field strengths, envelope compositions, and neutron star masses. In addition, by following the evolution of magnetic stresses within the neutron star crust, we can also relate the observed magnetar phenomenology to the physical properties of neutron stars, and in particular to their age and magnetic field strength and topology. The dichotomy of “high-B” field pulsars versus magnetars is naturally explained, and occasional outbursts from old, low B-field neutron stars are predicted. We conclude by speculating on the fate of old magnetars, and by presenting observational diagnostics of the neutron star crustal field topology.

Desarrollo de un videojuego basado en procesamiento de imágenes

El objetivo del proyecto consiste en crear un videojuego cuyos niveles se generen a partir del procesamiento de imágenes que el usuario podrá capturar con la cámara del móvil, o que podrá obtener de la galería de fotos del dispositivo. Se realizará una segmentación de la imagen y se extraerán así los elementos a utilizar en el juego, como por ejemplo zonas por las que poder movernos con un personaje, o bien piezas de un puzzle que debamos volver a construir. El videojuego se implementará con el motor Cocos2d-x.

International Capital Flows and Monetary Policy Spillovers

This dissertation examines the drivers and implications of international capital flows. The overarching motivation is the observation that countries not at the centre of global financial markets are subject to considerable spillovers from centre countries, notably from their monetary policy. I present new empirical evidence on the determinants of the observed patterns of international capital flows and monetary policy spillovers, and study their effect on both financial markets and the real economy. In Chapter 2 I provide evidence on the determinants of a puzzling negative correlation observed between productivity growth and net capital inflows to developing and emerging market economies (EMEs) since 1980. By disaggregating net capital inflows into their gross components, I show that this negative correlation is explained by capital outflows related to purchases of very liquid assets from the fastest growing countries. My results suggest a desire for international portfolio diversification in liquid assets by fast growing countries is driving much of the original puzzle. In the reminder of my dissertation I pivot to study the foreign characteristics that drive international capital flows and monetary policy spillovers, with a particular focus on the role of unconventional monetary policy in the United States (U.S.). In Chapter 3 I show that a significant portion of the heterogeneity in EMEs' asset price adjustment following the quantitative easing operations by the Federal Reserve (the Fed) during 2008-2014 can be explained by the degree of bilateral capital market frictions between these countries and the U.S. This is true even after accounting for capital controls, exchange rate regimes, and domestic monetary policies. Chapter 4, co-authored with Michal Ksawery Popiel, studies unconventional monetary policy in a small open economy, looking specifically at the case of Canada since the global financial crisis. We quantify the effect Canadian unconventional monetary policy shocks had on the real economy, while carefully controlling for and quantifying spillovers from U.S. unconventional monetary policy. Our results indicate that the Bank of Canada's unconventional monetary policy increased Canadian output significantly from 2009-2010, but that spillovers from the Fed's policy were even more important for increasing Canadian output after 2008.

Continental regionalism: Brazil's prominent role in the Americas. CEPS Working Document No. 374, February 2013

Brazil has a dual identity as a Latin American country and one of the BRICS (Brazil, Russia, India, China and South Africa). The regional and global dimensions of Brasilia’s foreign policy have been closely intertwined. Inspired by the idea of development and autonomy in the last ten years, Brazil has assumed a stronger regional leadership role. The result has been the emergence of a South American space, with Mercosur and Unasur as the main integration schemes. For Brazil, regionalism is not only a goal in itself but also an instrument for exerting global influence and for ‘soft-balancing’ the United States. Washington’s lower profile in the region has facilitated Brazil’s rise as a regional and even continental player, with a strong influence on the Latin American puzzle composed of many different pieces or concentric circles.

Explaining Euroskepticism as a function of regional representation. ACES Working Papers No. 3, August 2008

Recent scholarship has suggested that nation-states will gradually fade away in favor of regions and super-regions as the main actors within a European Union characterized by strong regional identities. At the same time, recent developments have shown that citizen support for European integration is essential for any future development of the Union. The puzzle inspiring this paper is the finding that the greatest support for the EU increasingly stems from minority nationalist regions seeking to bypass their central states to achieve their policy goals at the EU level. This paper empirically tests this suggestion, while shedding light on the relationship between the quality of representation of regional interests at the EU level and positive citizen attitudes towards the EU. In particular, it finds two explanations for cross-regional variation in the relationship between Euroskepticism and representation: (1) a cultural explanation, embodied by a difference in the nature and quality of representation between regions that are linguistically distinctive and regions that are not; and (2) an institutional explanation, embodied by a difference in the nature and quality of representation between regions from federal and non-federal member states. The paper uses an eclectic methodological approach, first utilizing multivariate regression analysis, estimating logistic and ordinal logit models that help explain variation in Euroskepticism at the regional level. The results are then complemented by the findings of in-depth elite interviews of regional representatives - more specifically the directors of a selection of the many regional information offices present in Brussels. This paper takes the study of Euroskepticism to a new level, as most previous scholarly work has focused on explanations at the individual or at the member state level. At the same time it strengthens the notion of a growing importance of a "Europe of the regions."

Hegemony Without Stability: The fiscal and political vulnerabilities of monetary union. ACES Cases No. 2011.2

The crisis has forced the Euro area to establish an emergency fund that supports member states experiencing a sovereign debt crisis. The difficulties of coming up with such a fund for Greece and other Euro area members stands in marked contrast to the balance of payments support that non-Euro members like Hungary received, swiftly and quietly. In order to solve this puzzle, we first establish the difference between EU interventions and IMF programs and, second, trace the evolution of crisis management with France and Germany in the lead. The lens of hegemonic stability theory suggests that the Franco-German leadership is too weak to provide stability and the extensive use of conditionality is one symptom of this weakness. Providing incentives for cooperation "after hegemony" (Keohane) is the unresolved issues troubling the monetary union. Its dominant powers must acknowledge that markets perceive monetary union to be already politically more integrated than its lack of fiscal integration suggests.

Zalpha-domains: At the intersection between RNA editing and innate immunity

The involvement of A to I RNA editing in antiviral responses was first indicated by the observation of genomic hyper-mutation for several RNA viruses in the course of persistent infections. However, in only a few cases an antiviral role was ever demonstrated and surprisingly, it turns out that ADARs - the RNA editing enzymes - may have a prominent pro-viral role through the modulation/down-regulation of the interferon response. A key role in this regulatory function of RNA editing is played by ADAR1, an interferon inducible RNA editing enzyme. A distinguishing feature of ADAR1, when compared with other ADARs, is the presence of a Z-DNA binding domain, Zalpha. Since the initial discovery of the specific and high affinity binding of Zalpha to CpG repeats in a left-handed helical conformation, other proteins, all related to the interferon response pathway, were shown to have similar domains throughout the vertebrate lineage. What is the biological function of this domain family remains unclear but a significant body of work provides pieces of a puzzle that points to an important role of Zalpha domains in the recognition of foreign nucleic acids in the cytoplasm by the innate immune system. Here we will provide an overview of our knowledge on ADAR1 function in interferon response with emphasis on Zalpha domains.

Evolution of Outcrossing in Experimental Populations of Caenorhabditis elegans

Caenorhabditis elegans can reproduce exclusively by self-fertilization. Yet, males can be maintained in laboratory populations, a phenomenon that continues to puzzle biologists. In this study we evaluated the role of males in facilitating adaptation to novel environments. For this, we contrasted the evolution of a fitness component exclusive to outcrossing in experimental populations of different mating systems. We introgressed a modifier of outcrossing into a hybrid population derived from several wild isolates to transform the wild-type androdioecious mating system into a dioecious mating system. By genotyping 375 single-nucleotide polymorphisms we show that the two populations had similar standing genetic diversity available for adaptation, despite the occurrence of selection during their derivation. We then performed replicated experimental evolution under the two mating systems from starting conditions of either high or low levels of diversity, under defined environmental conditions of discrete non-overlapping generations, constant density at high population sizes (N = 10(4)), no obvious spatial structure and abundant food resources. During 100 generations measurements of sex ratios and male competitive performance showed: 1) adaptation to the novel environment; 2) directional selection on male frequency under androdioecy; 3) optimal outcrossing rates of 0.5 under androdioecy; 4) the existence of initial inbreeding depression; and finally 5) that the strength of directional selection on male competitive performance does not depend on male frequencies. Taken together, these results suggest that androdioecious males are maintained at intermediate frequencies because outcrossing is adaptive.

How much Entrepreneurial Orientation (EO) is needed for Long-term Success?

According to the STEP research framework, entrepreneurial orientation (EO) is one key element of transgenerational value creation. EO refers to key entrepreneurial processes in a company, i.e. to the methods, practices and decision-making styles managers use to act entrepreneurially. 3 EO consists of five main dimensions and several sub dimensions. However, there is a puzzle. Many studies suggest that the higher EO, the more successful a company is. But this seems not always to be true. Just think of many of the dot.com firms at the end of the 1990s. Firm members could act very autonomously, the companies were very innovative, took high risks, were very proactive and very aggressive in the market. However, most of them were not able to survive for more than a few years. So how entrepreneurial has a firm to be in order to achieve long-term success?