巴黎第一大学

This paper analyses the European financial crisis through the lens of sovereign bond liquidity. Using novel data we show that government securities are the prime collateral in the European repo market, which is becoming an essential source of funding for the banking system in the Euro area. We document that repo haircuts on peripheral government bonds sharply increased during the crisis, reducing their liquidity and amplifying the raise in the yields of these securities. We study the systemic impact of a liquidity shock on the business cycle and asset prices through a dynamic stochastic general equilibrium model with liquidity frictions. The model predicts a drop in economic activity, inflation and value of illiquid government bonds. We show that an unconventional policy which consists of purchasing illiquid bonds by issuing liquid bonds can alleviate the contractionary effect of liquidity shock. A Bayesian structural vector autoregressive model for the Irish economy confirms empirically the negative impact of a rise in haircuts on the value of government bonds.

Introduction Towns and cities have expanded all over the world for more than eight thousands years The size of these permanent nodules of resident population ranges today from a few thousands to tens of millions inhabitants. The number of cities in a given territory is always in an inverse geometrical progression of their size (for instance, there are about 23 000 urban agglomerations larger than 10 000 inhabitants in the world, 2000 are larger than 100 000 inhabitants and about 200 above 1 million, after Moriconi-Ebrard, 1993). This persistent scaling behaviour has been questioned for more than one century, giving rise to a large variety of interpretations. Are the scaling effects observed in urban systems produced by the hierarchical organisation of societies? Are they generated by purely random processes, a mere product of laws of large numbers? Are they the possibly involuntary result of some not totally conscious social rules? Are they constrained by physical and/or social rules, according to some optimisation or ordering principles? Are they emergent properties linked with the historical process of urbanisation? Could they disappear after the end of the urban transition? As some of the answers that have been offered to these questions are highly contradictory, one might hope that a clarification could come from modelling and simulation, that can be very helpful tools for selecting among different hypothesis. On a theoretical level, urban theories, as in economics or sociology, could receive a better foundation by considering the geographical concept of “system of cities”. These two research directions might also help improve the policies that are intended to control urban systems, by informing the urban governance at local and regional scales about “spontaneous” trends.

Philosophers of science frequently appeal to “complexity” to justify scientific pluralism—the view that some domains require multiple, perhaps non-integrable, models or explanations. This article argues that such appeals often rely on an unexamined metaphysical interpretation of complexity, according to which complexity is an intrinsic property of the world capable of grounding normative methodological prescriptions. I show that this interpretation is both unjustified and unproductive. Through critical analyses of Mitchell’s integrative pluralism, Waters’s “no-structure” argument, and Longino’s account of human behavior, I show that their supposed metaphysical claims about complex systems are in fact epistemic claims in disguise. Once this is acknowledged, metaphysical complexity cannot sustain the strong methodological conclusions pluralists often draw from it. In place of metaphysical foundations, I propose a pragmatist account of complexity. Drawing on Wittgenstein’s notion of family resemblance and Neurath’s concept of Ballungen, I argue that complexity functions as a flexible, non-essentialist cluster concept whose meaning is stabilized through overlapping similarities and paradigm cases, rather than necessary and sufficient conditions. This view preserves the heuristic and organizational role of complexity in scientific inquiry while avoiding unwarranted ontological commitments. Complexity remains philosophically and scientifically useful not because it designates a natural kind, but because it coordinates diverse investigative strategies and supports context-sensitive forms of pluralism. A genuinely pragmatist pluralism, I conclude, requires abandoning the search for metaphysical grounding in favor of a reflexive, non-foundationalist stance.

This paper focuses on Geodesic Principal Component Analysis (GPCA) on a collection of probability distributions using the Otto-Wasserstein geometry. The goal is to identify geodesic curves in the space of probability measures that best capture the modes of variation of the underlying dataset. We first address the case of a collection of Gaussian distributions, and show how to lift the computations in the space of invertible linear maps. For the more general setting of absolutely continuous probability measures, we leverage a novel approach to parameterizing geodesics in Wasserstein space with neural networks. Finally, we compare to classical tangent PCA through various examples and provide illustrations on real-world datasets.

Previous research based on 2001 and 2011 census data indicated rising levels of residential segregation between socio-economic groups in many large city-regions in Europe as well as globally. Rising segregation is an important societal concern, as place of residence plays a crucial role in shaping access to urban opportunities. Residential isolation can be especially harmful for the most vulnerable groups. Income inequality was identified as the primary driver of this segregation. The current paper extends comparative research on residential segregation in Europe by incorporating the latest 2021 census and register-based data to determine whether segregation levels have continued to rise or have peaked, or whether there are signs of desegregation. It also examines how changes in segregation align with shifts in income inequality and occupational structures. A comparative analysis of 16 European capital city-regions shows a slowdown in the rise of segregation, with some city-regions transitioning from segregation to desegregation. These changes coincide with both a slowdown in the growth of income inequality and increased professionalisation of the workforce. The study suggests that future research should focus on the mechanisms driving residential desegregation in different urban contexts, with particular attention to the diversification of residential patterns among the expanding professional class.