Climate variability, food production shocks, and violent conflict in Sub-Saharan Africa

Earlier research that reports a correlational pattern between climate anomalies and violent conflict routinely refers to drought-induced agricultural shocks and adverse economic spillover effects as a key causal mechanism linking the two phenomena. Comparing half a century of statistics on climate variability, food production, and political violence across Sub-Saharan Africa, this study offers the most precise and theoretically consistent empirical assessment to date of the purported indirect relationship. The analysis reveals a robust link between weather patterns and food production where more rainfall generally is associated with higher yields. However, the second step in the causal model is not supported; agricultural output and violent conflict are only weakly and inconsistently connected, even in the specific contexts where production shocks are believed to have particularly devastating social consequences. Although this null result could, in theory, be fully compatible with recent reports of food price-related riots, it suggests that the wider socioeconomic and political context is much more important than drought and crop failures in explaining violent conflict in contemporary Africa

Productivity beyond density: A critique of management models for reindeer pastoralism in Norway

publishedVersio

Productivity beyond density: A critique of management models for reindeer pastoralism in Norway

publishedVersio

Impact of delayed type hypersensitivity arthritis on development of heart failure by aortic constriction in mice

Aims Patients with rheumatoid arthritis (RA) have increased risk of heart failure (HF). The mechanisms and cardiac prerequisites explaining this association remain unresolved. In this study, we sought to determine the potential cardiac impact of an experimental model of RA in mice subjected to HF by constriction of the ascending aorta. Methods Aorta was constricted via thoracotomy and placement of o-rings with inner diameter 0.55 mm or 0.66 mm, or sham operated. RA-like phenotype was instigated by delayed-type hypersensitivity arthritis (DTHA) two weeks after surgery and re-iterated after additional 18 days. Cardiac magnetic resonance imaging (MRI) was performed before surgery and at successive time points throughout the study. Six weeks after surgery the mice were euthanized, blood and tissue were collected, organ weights were documented, and expression levels of cardiac foetal genes were analysed. In a supplemental study, DTHA-mice were euthanized throughout 14 days after induction of arthritis, and blood was analysed for important markers and mediators of RA (SAP, TNF-α and IL-6). In order to put the latter findings into clinical context, the same molecules were analysed in serum from untreated RA patients and compared to healthy controls. Results Significant elevations of inflammatory markers were found in both patient- and murine blood. Furthermore, the DTHA model appeared clinically relevant when compared to the inflammatory responses observed in three prespecified RA severity disease states. Two distinct trajectories of cardiac dysfunction and HF development were found using the two o-ring sizes. These differences were consistent by both MRI, organ weights and cardiac foetal gene expression levels. Still, no difference within the HF groups, nor within the sham groups, could be found when DTHA was induced. Conclusion DTHA mediated systemic inflammation did not cause, nor modify HF caused by aortic constriction. This indicates other prerequisites for RA-induced cardiac dysfunction

A computational pipeline for quantification of mouse myocardial stiffness parameters

The mouse is an important model for theoretical–experimental cardiac research, and biophysically based whole organ models of the mouse heart are now within reach. However, the passive material properties of mouse myocardium have not been much studied. We present an experimental setup and associated computational pipeline to quantify these stiffness properties. A mouse heart was excised and the left ventricle experimentally inflated from 0 to 1.44 kPa in eleven steps, and the resulting deformation was estimated by echocardiography and speckle tracking. An in silico counterpart to this experiment was built using finite element methods and data on ventricular tissue microstructure from diffusion tensor MRI. This model assumed a hyperelastic, transversely isotropic material law to describe the force–deformation relationship, and was simulated for many parameter scenarios, covering the relevant range of parameter space. To identify well-fitting parameter scenarios, we compared experimental and simulated outcomes across the whole range of pressures, based partly on gross phenotypes (volume, elastic energy, and short- and long-axis diameter), and partly on node positions in the geometrical mesh. This identified a narrow region of experimentally compatible values of the material parameters. Estimation turned out to be more precise when based on changes in gross phenotypes, compared to the prevailing practice of using displacements of the material points. We conclude that the presented experimental setup and computational pipeline is a viable method that deserves wider application.acceptedVersio