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Primordial axisymmetric compact objects in General Relativity
No full textInternational audienceThe search for exact solutions describing asymptotically FLRW compact objects in General Relativity (GR) remains a notoriously challenging problem. To a large extent, progress has been restricted to the spherically symmetric sector, with the exception of the Kerr-de Sitter and Thakhurta solutions. In this work, we present two new results that advance the description of axisymmetric compact objects embedded in a cosmological background. We first introduce a new solution-generating technique allowing one to construct non-stationary and axisymmetric solutions of the self-interacting Einstein-Scalar system. Using this method, we present the first exact solution which describes a dynamical axisymmetric black (or white) hole embedded in an expanding or contracting cosmology. We provide a detailed investigation of its properties, and in particular its dynamical trapping (or anti-trapping) horizons. To that end, we use the mean curvature vector (MCV) which stands as a natural generalization of the Kodama vector beyond spherical symmetry. The norm of this vector provides a foliation-independent quantity to locate the trapped/anti-trapped and untrapped regions and characterize the causal nature of a given geometry without specific symmetry requirement. The solution-generating method and the techniques to analyze the new solutions provide new powerful tools to further explore the description and the phenomenology of dynamical compact objects embedded in cosmology, in particular those of primordial black holes
Les contraintes internes contrôlent la dynamique d’enroulement des vrilles chez les plantes grimpantes
No full textInternational audiencePlant tendrils are mechanosensitive and highly motile organs known for touch-induced differential growth. The resulting coiling dynamics under external traction reveal that non-homogeneous internal stress over the tendril cross-section is fundamental to understanding the system. External loading inhibits curvature generation and can fully suppress it above a threshold force. Remarkably, however, the internal differential stress onset persists even under the highest applied traction forces.We develop an autotropic morphoelastic growth (AMG) model, grounded in a bi-strip geometry and Kirchhoff rod theory, which capture these main features. In particular, the AMG model reproduces the observed 1/4 ratio between the generated intrinsic curvature at high force and that at zero force. According to the AMG model, this ratio depends solely on the twist-to-bend ratio, which is a parameter determined by the plant species.Les vrilles des plantes sont des organes mécanosensibles et hautement mobiles, connus pour leur croissance différentielle induite par le contact. La dynamique d’enroulement sous traction externe montre que la présence de contraintes internes non homogènes à travers la section de la vrille est essentielle pour comprendre le système. La charge externe inhibe la génération de courbure et peut même la supprimer complètement au-delà d’une force seuil. Il est toutefois remarquable que l’apparition de contraintes différentielles internes persiste, même sous les forces de traction les plus élevées appliquées.Nous développons un modèle de croissance morphoélastique autotropique (AMG), fondé sur une géométrie de type bi-lame et sur la théorie des tiges de Kirchhoff, qui rend compte de ces caractéristiques principales. En particulier, le modèle AMG reproduit le rapport expérimental de 1/4 entre la courbure intrinsèque générée sous forte traction et celle observée en l’absence de force. Selon le modèle AMG, ce rapport dépend uniquement du rapport torsion–flexion, un paramètre déterminé par l’espèce végétale
A Colonial Lens on the High Ground: Imperial Vantage Points in British India and French Indochinese Hill Stations
No full textInternational audienceThis paper focusses on the photographic production within South Asian and Southeast Asian hill stations, established by the British and the French empires in India and in Vietnam, throughout the 19th century. In both countries, hill stations stem from early colonial developments. These remote colonial enclaves were used for a variety of purposes that evolved through time: sanitary, political, military, leisure and commercial (Kennedy 1996). They can be looked at as spatial and symbolic manifestations of imperialism, designed to expand colonial domination to all the corners of the Empire (Mitchell 2002).In order to settle in the hills, the landscape itself had to be domesticated through urban planning, architecture, roads, institutions catering for the new occupants (Sacareau 2007). Soon enough, photography started to be used as a means to document the places, account for their changes, and promote a certain image of the hill stations to a broader audience. Today, vast collections of photographs taken in the hills are kept in colonial archives, be it at the British Library (UK) for India or at the Archives Nationales d’Outre-Mer (France) for Vietnam.Based on a sample of photographs taken between the 1840’s and the 1940’s, this paper will explore the imperial gaze – and visual discourse – on these hill stations. It will interrogate the aesthetics and meanings of these photographs and address the issue of their circulation within and beyond the empires, in order to understand the ways in which photography was used to imprint its gaze and legitimize to the colonisers’ presence.We will examine the tools used to construct this visuality through the photographs that were taken by the colonial settlers on site, for personal and/or propaganda purposes. These photographs were instrumental in defining new aesthetical and scenic functions for these mountains, whose beauty is closely linked to their domination (Zytnicki and Hazdaghli, 2009). The construction of viewpoints, panoramas and hiking trails, and later cable cars, can be explained as panoptic devices serving the construction of a heterotopia (Foucault, 1984). These high angled photographs exploit a symbolic vantage point and enact the domination of these peripheral mountain spaces (Mirzoeff, 2011). They allow contemplating both nature and its colonial reordering, embracing a vast space appropriated to serve racial recreation (Jennings, 2011). Thus, tourism was a consensual and enduring way to not only in the construct, but also in to glorify and promote the imperial gaze
Du serment doctoral d'intégrité scientifique à un serment personnel : un atelier d'écriture et de réflexion sur la responsabilité et le rôle des scientifiques dans la société
No full textNous présentons un atelier de réflexion sur le serment doctoral d’intégrité scientifique et d’écriture d’un serment personnel, destiné aux doctorantes et doctorants, et plus généralement au personnel de la recherche. L’atelier est proposé depuis 2025 comme formation à l’éthique de la recherche dans quelques écoles doctorales en France. Avec un dispositif original, il permet d’examiner plusieurs aspects de la pratique et des enjeux sociaux-environnementaux de le Recherche : la responsabilité des scientifiques, l’engagement, le rôle des sciences dans l’anthropocène, la place de l’éthique et de l’intégrité dans la pratique du doctorat et des sciences en général
Verified Persistent Catenable Deques
No full textInternational audienceThe simple persistent catenable deques invented by Kaplan, Okasaki, and Tarjan (2000) support insertion and extraction at either end and concatenation. They have mutable internal state and rely on a restricted form of mutation; yet they are persistent, that is, they appear to be immutable. Using Iris, we verify that they are correct in sequential and concurrent usage scenarios. Using Iris with time credits, we verify that, provided concurrent accesses are forbidden, every operation has amortized time complexity O(1). This requires repairing a certain mysterious condition in Kaplan, Okasaki, and Tarjan's description
Seven-Coordinate Lanthanide Bis-Halide Bis-Tetrathiometallate Complexes: A Compelling Platform for Luminescent and Magnetic Properties
No full textInternational audienceTo harness the unique luminescent and magnetic properties of lanthanides, precise control over their coordination sphere is essential, whether to minimize deactivation processes or maximize magnetic anisotropy. The traditional approaches rely on the use of large organic ligands bearing strong atom donors to enforce low coordination numbers of Ln ions. Herein we explored an alternative approach, constraining low coordination numbers via a better control of the primary coordination sphere of the Ln center using fully inorganic sulfur-based ligands, tetrathiotungstates. This strategy led to the preparation of an isostructural series of 13 rare-earth complexes, [NEt(4)](3)[LnCl(2)(MeCN){(μ-S)(2)WS(2)}(2)] (1Ln, Ln = Ce-Yb and Y). The unusually low coordination numbers (CN = 7) observed here in the absence of sterically bulky or rigid chelating ligands was rationalized using buried volume analysis. We highlight the potential of this new ligand set for luminescent and single-molecule magnets applications by investigating the properties of 1Yb and 1Dy complexes, respectively
Metallic trace elements in wild and farmed fish from the Aveiro Region (Portugal)
No full textInternational audienceThis study assessed the concentrations of 11 metallic trace elements (MTEs: As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, Zn) in fish muscle from eight wild and farmed species collected in the Aveiro region of Portugal, an area historically affected by industrial pollution. A total of 66 samples were analyzed by ICP-MS. Mean concentrations (mg/kg ww), arranged in ascending order, were: Ni (0.0001), Cd (0.0015), Co (0.0020), Pb (0.0023), Cr (0.0179), Mn (0.0862), Cu (0.2500), Se (0.2964), Fe (1.9236), As (1.9260, total As), and Zn (3.3701). Significant differences were observed among species and between wild and farmed fish, particularly in Dicentrarchus labrax and Sparus aurata. Although Cd and Pb concentrations remained below current European maximum levels, risk assessment based on safe consumption limits (SCLnc) identified total Se, Cd, and Pb as the most restrictive elements for daily intake, especially in children. For arsenic, only total concentrations were considered, as inorganic As could not be distinguished in this study. No significant non-carcinogenic risks were identified at current national average fish consumption levels; however, the potential cumulative and synergistic effects of multiple metals in chronic exposure warrant further investigation. The Metal Pollution Index (MPI < 1 for all samples) confirmed low overall contamination. These findings underscore the importance of ongoing monitoring of trace elements in fish to ensure food safety and protect vulnerable populations
Austérité sanitaire Face à l’érosion de l’économie fondamentale dans les espaces délaissés
No full textInternational audienceSmall and medium-sized cities have long been sidelined in urban research. However,they have recently come to the forefront of media, political and academic debate. Thenotion of “left-behind places” questions the rise of territorial inequalities that lead tothe marginalisation of territories previously integrated into national dynamics, but alsothe political and social consequences of these developments.The article presents two cities that can be considered as left-behind: Roanne, amedium-sized city of 34,000 inhabitants, and La Grand-Combe, a small town of5,000 inhabitants. In a French context where the withdrawal of the state is perceptiblein a number of spheres of public action, the article is based on the analysis of a keysector of the “fundamental economy”: healthcare. The study of the evolution of thissector allows us to refine the analysis of the austerity policies implemented in France.These policies are characterised less by spectacular cuts in funding than by a slowerosion of the workforce, an unequal distribution of resources and a concentration ofsupply that affects access to care.Longtemps restées à la marge de la recherche urbaine, les villes petites et moyennesse sont récemment imposées dans les débats médiatiques, politiques et académiques.La notion d’« espaces délaissés » permet d’interroger la montée des inégalitésterritoriales qui conduisent à la marginalisation de territoires auparavant intégrés dansles dynamiques nationales, mais aussi les conséquences politiques et sociales de cesévolutions.L’article présente deux villes en déclin : Roanne, une ville moyenne de 34 000 habitantset La Grand-Combe, une petite ville de moins de 5 000 habitants. Dans un contextefrançais où le retrait de l’État est perceptible dans un ensemble de sphères de l’actionpublique, ce texte s’appuie sur l’analyse d’un secteur clé de l’« économiefondamentale » : la santé. L’étude des évolutions de ce secteur permet d’affiner celledes politiques d’austérité mises en oeuvre en France. Celles-ci se caractérisent moinspar des coupes spectaculaires dans les dotations que par une lente érosion deseffectifs, une inégale répartition des ressources, et une concentration de l’offre quiaffecte l’accès aux soins
Bifurcation of gravity-capillary Stokes waves with constant vorticity
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