What action logics do family livestock farmers have to maintain their activity over the long term ?

This paper sheds light on what livestock farmers do to "last" over the long term, from their own point of view, through explanation and analysis of their action logics. The authors take the examples of four contrasted case studies carried out in France, Uruguay and Argentina, on a total of 45 family livestock systems. Each study of changes in the livestock systems was carried out using cross?disciplinary approaches (livestock sciences, sociology, management sciences) and resulted in descriptions of types of adaptive paths, that are explanations of adaptive paths taken by family livestock systems in relation with farmers' action logics (logics being defined as particular sets of action principles). This diversity of action logics is cross?analysed in order to patterns to test the hypothesis that production context has an effect - or no effect ? on action logics. The conceptual framework used in the four case studies recognizes the capacity of systems to absorb internal and external disturbances. Some generic styles of logics and action domains emerge from the comparison and are relevant to build up adaptive patterns, such as: to tend towards technical optimization or to diversify, to enlarge production volumes or farm structure (livestock and land), to search for autonomy, to be innovative, to preserve internal flexibility for the technical system. The combination of such domains determines generic adaptive patterns and paths that are taken by family livestock systems, independently of the context. The authors then discuss the different adaptive patterns and how these patterns provide evolution and resilience perspectives for family livestock systems. (Résumé d'auteur

On universal Severi varieties of low genus K3 surfaces

We prove the irreducibility of universal Severi varieties parametrizing irreducible, reduced, nodal hyperplane sections of primitive K3 surfaces of genus g, with 3 \le g \le 11, g \neq 10.Comment: Some minor mistakes in the introductory paragraph 1.1 corrected. To appear in Math.

Newton Method on Riemannian Manifolds: Covariant Alpha-Theory

In this paper we study quantitative aspects of Newton method for finding zeros of mappings f: M_n -> R^n and vector fields X: M_x -> TM_

On the Curvature of the Central Path of Linear Programming Theory

We prove a linear bound on the average total curvature of the central path of linear programming theory in terms on the number of independent variables of the primal problem, and independent on the number of constraints.Comment: 24 pages. This is a fully revised version, and the last section of the paper was rewritten, for clarit

On the locus of Prym curves where the Prym--canonical map is not an embedding

We prove that the locus of Prym curves $(C,\eta)$ of genus $g \geq 5$ for which the Prym-canonical system $|\omega_C(\eta)|$ is base point free but the Prym--canonical map is not an embedding is irreducible and unirational of dimension $2g+1$.Comment: Minor modifications. Final version, accepted for publication in Arkiv f\"or Matemati

Intrinsic pseudo-volume forms for logarithmic pairs

31 pagesInternational audienceWe study an adaptation to the logarithmic case of the Kobayashi-Eisenman pseudo-volume form, or rather an adaptation of its variant defined by Claire Voisin, for which she replaces holomorphic maps by holomorphic K-correspondences. We define an intrinsic logarithmic pseudo-volume form \Phi_{X,D} for every pair (X,D) consisting of a complex manifold X and a normal crossing Weil divisor, the positive part of which is reduced. We then prove that \Phi_{X,D} is generically non-degenerate when X is projective and K_X+D is ample. This result is analogous to the classical Kobayashi-Ochiai theorem. We also show the vanishing of \Phi_{X,D} for a large class of log-K-trivial pairs, which is an important step in the direction of the Kobayashi conjecture about infinitesimal measure hyperbolicity in the logarithmic case