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Mathematical Bio-Economics 2.0 for Sustainable Fisheries
No full textInternational audienceReconciling food security, economic development, and biodiversity conservation in the face of global changes is a major challenge. The sustainable uses of marine biodiversity in the context of climate change, invasive species, water pollution, and demographic growth is an example of this bio-economic challenge. There is a need for quantitative methods, models, scenarios, and indicators to support policies addressing this issue. Although bio-economic models for marine resources date back to the 1950s and are still used in fisheries management and policy design, they need major improvements, extensions, and breakthroughs. This paper proposes to design a Mathematical Bio-Economics 2.0 (MBE2) for Sustainable Fisheries to advance the development of bio-economic models and scenarios for the management of fisheries and marine ecosystems confronted with unprecedented global change. These models and scenarios should make both ecological and socioeconomic sense while being well-posed mathematically and numerically. To achieve this, we propose to base the MBE2 framework for Sustainable Fisheries on four research axes regarding the mathematics and modeling of: (i) ecosystem-based fisheries management; (ii) criteria of sustainability; (iii) criteria of resilience; and (iv) governance and strategic interactions. The associated methodology of MBE2 draws mainly on dynamic systems theory, optimal and viable controls of systems, game theory, and stochastic approaches. Our analysis, which is based on these four axes, allows us to identify the main methodological gaps to fill compared to current models for fisheries management. | IntroductionBalancing biodiversity conservation with food security and the preservation of a broader set of ecosystem services (ESs), in a context of ecological transition and climate change, is one of the greatest challenges of the century. The creation and development of the IPBES (International Platform for Biodiversity and Ecosystem Services) at the interface of decision-support and scientific knowledge is in direct line with these concerns.</div
Décarbonation, simplification, compétitivité : cherchez l’intrus
No full textLes régulations environnementales constitueraient un frein à l’économie européenne. Est-ce vrai ? L’exemple du mécanisme d’ajustement carbone aux frontières, grande mesure de politique environnementale de l’UE, fournit un cas d’étude parfait. Derrière les clichés, une vision plus nuancée de la relation entre économie et développement durable
Banks defy gravity in tax havens
No full textInternational audienceAbstract This article examines the international activity of banks. We use a gravity framework and country-by-country reports (CbCR) to predict the turnover of European Union (EU) banks worldwide, including jurisdictions usually considered tax havens. Our results show that: (1) about half of the activity of EU banks in tax havens, which accounts for 17% of their global activity, is not explained by standard gravity factors; (2) abnormal activity is concentrated in only a few tax havens (Luxembourg, Hong Kong, and Singapore); and (3) abnormal activity has been stable since the introduction of CbCR
Combien d'étoiles se forment dans des amas compacts dans la Voie Lactée locale ?
No full textInternational audienceContext. Two main models coexist for the environment in which stars form. The clustered model stipulates that the bulk of star formation occurs within dense embedded clusters, but only a minority of them survive the residual gas expulsion phase caused by massive stellar feedback unbinding the clusters. On the other hand, the hierarchical model predicts that star formation happens at a range of scales and densities, where open clusters (OCs) only emerge from the densest regions. Aims. We aim to exploit a recent catalog of compact OCs, corrected for completeness, to obtain an updated estimation of the surface density star formation rate within OCs (∑ SFR, OC ), which we compare with recent estimates of ∑ SFR to determine which model is more likely. Methods. We have applied two methods. The first one consisted of integrating over the power law that was fit for the mass function of the youngest OCs using a MC sampling. The second one consisted of counting the total compact mass within these youngest OCs within 1 kpc, so that the result could be directly compared with local values of ∑ SFR . Results. We estimated new ∑ SFR, OC values between 736 −176 +159 and 875 −35 +34 M ⊙ Myr −1 kpc −2 , depending on the methodology. These results are significantly higher than previous ∑ SFR, OC estimates, which we attribute to the incompleteness of past catalogs, and are consistent with the majority (≥50%) or even the vast majority (≥80%) of the star formation occurring in initially compact clusters, through comparisons with ∑ SFR from the recent literature. Conclusions. Our new ∑ SFR, OC values are consistent with clustered formation being the most dominant mode of star formation
Entrer dans l’enseignement supérieur privé. Trajectoires et socialisations des bacheliers « à l’heure »
No full textInternational audienc
La libéralisation des marchés agricoles comme consécration des intermédiaires. Le cas du lait
No full textInternational audienceStarting in 1992, the reforms of the European Union’s Common Agricultural Policy led to the liberalization of agricultural markets. This article assesses the impact of these reforms on power relations within agri-food supply chains. It shows that processors took advantage of these reforms to reshape and segment agricultural production. It thus contributes to the socioeconomic literature on market intermediaries, and shows that the power of these actors is dependent on institutional configurations and regulations.Amorcées en 1992, les réformes de la politique agricole commune de l’Union européenne ont conduit à une libéralisation des marchés agricoles. Cet article propose d’en évaluer les conséquences sur les relations de pouvoir au sein des filières agroalimentaires. Il montre que l’échelon de la transformation a tiré parti des réformes pour réorienter et segmenter la production agricole. Il contribue ainsi à la littérature socioéconomique sur les intermédiaires de marché et montre que le pouvoir de ces acteurs est tributaire des configurations institutionnelles et de la réglementation
Questionner la liberté d’installation des médecins : un éclairage sociologique
No full textNational audienc
Unveiling the Role of Randomization in Multiclass Adversarial Classification: Insights from Graph Theory
No full textInternational audienceRandomization as a mean to improve the adversarial robustness of machine learning models has recently attracted significant attention. Unfortunately, much of the theoretical analysis so far has focused on binary classification, providing only limited insights into the more complex multiclass setting. In this paper, we take a step toward closing this gap by drawing inspiration from the field of graph theory. Our analysis focuses on discrete data distributions, allowing us to cast the adversarial risk minimization problems within the wellestablished framework of set packing problems. By doing so, we are able to identify three structural conditions on the support of the data distribution that are necessary for randomization to improve robustness. Furthermore, we are able to construct several data distributions where (contrarily to binary classification) switching from a deterministic to a randomized solution significantly reduces the optimal adversarial risk. These findings highlight the crucial role randomization can play in enhancing robustness to adversarial attacks in multiclass classification
On the Relation between Rectified Flows and Optimal Transport
No full textInternational audienceThis paper investigates the connections between rectified flows, flow matching, and optimal transport. Flow matching is a recent approach to learning generative models by estimating velocity fields that guide transformations from a source to a target distribution. Rectified flow matching aims to straighten the learned transport paths, yielding more direct flows between distributions. Our first contribution is a set of invariance properties of rectified flows and explicit velocity fields. In addition, we also provide explicit constructions and analysis in the Gaussian (not necessarily independent) and Gaussian mixture settings and study the relation to optimal transport. Our second contribution addresses recent claims suggesting that rectified flows, when constrained such that the learned velocity field is a gradient, can yield (asymptotically) solutions to optimal transport problems. We study the existence of solutions for this problem and demonstrate that they only relate to optimal transport under assumptions that are significantly stronger than those previously acknowledged. In particular, we present several counter-examples that invalidate earlier equivalence results in the literature, and we argue that enforcing a gradient constraint on rectified flows is, in general, not a reliable method for computing optimal transport maps
Crises, labour market and informality in Brazil: The Covid-19 shock in the light of past dynamics
No full textIn this article, we show the magnitude of the impact of the Covid-19 crisis on the Brazilian labour market, especially on informal workers who were the main victims. This result calls into question the validity of the standard model, referred to in our work as a 'canonical crisis', which states that the informal economy plays a counter-cyclical role as a shock absorber. A thorough analysis reveals that this mechanism was no longer at work either for the pandemic crisis or for the two previous macroeconomic crises: informal employment recedes in times of crisis. In addition, we shed light on a striking phenomenon: the pandemic triggered an upsurge in the number of discouraged workers. How these individuals excluded from the labour market coped day to day remains under-investigated. Among the shock mitigation strategies, only the emergency transfer programme played a significant compensatory role. The crisis may mark a turning point by showing that informal workersa hitherto politically "invisible" groupbecame a focal point of public policy and were able to influence decisions. The government can no longer hide behind the laissez-faire strategy of relying on the informal sector as a safety valve to limit the socioeconomic impacts of crises