On Asymptotic Flatness and Lorentz Charges

In this paper we establish two results concerning four-dimensional asymptotically flat spacetimes at spatial infinity. First, we show that the six conserved Lorentz charges are encoded in two unique, distinct, but mutually dual symmetric divergence free tensors that we construct from the equations of motion. Second, we show that integrability of Einstein's equations in the asymptotic expansion is sufficient to establish the equivalence between counter-term charges defined from the variational principle and charges defined by Ashtekar and Hansen. These results clarify earlier constructions of conserved charges in the hyperboloid representation of spatial infinity. In showing this, parity condition on the mass aspect is not needed. Along the way in establishing these results, we prove two lemmae on tensor fields on three dimensional de Sitter spacetime stated by Ashtekar-Hansen and Beig-Schmidt and state and prove three additional lemmae.Comment: 26 pages; no figures; v2: minor changes; v3: clarifications + references + a new lemma added, results unaffecte

Why not a di-NUT? or Gravitational duality and rotating solutions

We study how gravitational duality acts on rotating solutions, using the Kerr-NUT black hole as an example. After properly reconsidering how to take into account both electric (i.e. mass-like) and magnetic (i.e. NUT-like) sources in the equations of general relativity, we propose a set of definitions for the dual Lorentz charges. We then show that the Kerr-NUT solution has non-trivial such charges. Further, we clarify in which respect Kerr's source can be seen as a mass M with a dipole of NUT charges.Comment: 20 pages. v2: minor clarifications in section 4, version to appear in PR

Electric and magnetic aspects of gravitational theories

This thesis deals with the construction of conserved charges for asymptotically flat spacetimes at spatial infinity in four spacetime dimensions in a hopefully pedagogical way. As a first motivation of this work, it highlights the difficulties one encounters when trying to understand the gravitational duality, present at the linearized level, in the full non-linear Einstein's theory or even just in an asymptotic regime of it. In the first part, we restrict the discussion to the Noetherian surface charges, called "electric charges", and study the existence of a larger phase space, than previously known in the literature, where the awkward parity boundary conditions, firstly imposed by T. Regge and C. Teitelboim, are relaxed. In the absence of these parity conditions, we show how the Einstein-Hilbert action is a correct variational principle when it is supplemented by an anomalous counter-term and construct conserved and finite charges associated to the larger asymptotic symmetry group. The second and third parts focus on the magnetic information obtained through gravitational duality. As this duality is only known at the linearized level, asymptotic linearity is implicitly assumed at spatial infinity. In the second part, gravitational duality for the linearized gravity theory is reviewed and ten dual Poincar\'e charges, or topological "magnetic" charges, are constructed \`a la Abbott-Deser. The last part explains how the NUT charge N, gravitational dual of the mass M and present in the BPS bound of the supersymmetric charged Taub-NUT black hole, copes with the N=2 superalgebra. This is achieved through a complexification of the Witten-Nester 2-form.Comment: 220 pages, 3 figure

Can Conformational Changes of Proteins Be Represented in Torsion Angle Space? A Study with Rescaled Ridge Regression

Torsion angles are the natural degrees of freedom of protein structures. The ability to determine torsional variations corresponding to observed changes in Cartesian coordinates is highly valuable, notably to investigate the mechanisms of functional conformational changes or to develop computational models of protein dynamics. This issue is far from trivial in practice since the impact of modifying one torsion angle strongly depends on all other angles, and the compounding effects of small variations in bond lengths and valence angles can completely disrupt a protein fold. We demonstrate that naive strategies, such as directly comparing torsion angles between structures without correcting for variations in bond lengths and valence angles or fitting torsional variations without a proper regularization scheme, fail at producing an adequate representation of conformational changes in internal coordinates. In contrast, rescaled ridge regression, a method recently introduced to regularize multidimensional regressions with correlated explanatory variables, is shown to consistently identify a minimal set of torsion angles variations that closely reproduce changes in Cartesian coordinates. This torsional representation of conformational changes is shown to be robust to the choice of experimental structures. It also provides a better agreement with theoretical models of protein dynamics than the Cartesian representation, regarding notably the predominance of low-frequency normal modes in functional motions and the presence, in predicted equilibrium dynamics, of hints of natural selection for specific functional motions. The software is available at https://github.com/ugobas/tnm.Ministery of Economy, grant BIO2016-79043-P. Research at the CBMSO is facilitated by the Fundacion Ramon Arece

Effective harmonic potentials: insights into the internal cooperativity and sequence-specificity of protein dynamics

The proper biological functioning of proteins often relies on the occurrence of coordinated fluctuations around their native structure, or of wider and sometimes highly elaborated motions. Coarse-grained elastic-network descriptions are known to capture essential aspects of conformational dynamics in proteins, but have so far remained mostly phenomenological, and unable to account for the chemical specificities of amino acids. Here, we propose a method to derive residue- and distance-specific effective harmonic potentials from the statistical analysis of an extensive dataset of NMR conformational ensembles. These potentials constitute dynamical counterparts to the mean-force statistical potentials commonly used for static analyses of protein structures. In the context of the elastic network model, they yield a strongly improved description of the cooperative aspects of residue motions, and give the opportunity to systematically explore the influence of sequence details on protein dynamics.Comment: 10 pages, 5 figures, 1 table ; Supplementary Material (11 pages, 7 figures, 1 table) ; 4 Supplementary tables as plain text file

Incertitude de la mesure de terrain en géomorphologie littorale. Approche statistique et quantification des marges d'erreur

479 p.Un des objectifs de la mesure en géomorphologie littorale est d'étudier de façon diachronique les changements morphosédimentaires d'un environnement côtier. La période d'observation et la fréquence des relevés dépendent du but recherché. On choisira une haute fréquence (relevé hebdomadaire) lorsque la problématique est d'analyser le rôle des épisodes à forte récurrence (tempêtes hivernales) dans la mobilité des formes littorales (Lee et Birkemeir, 1993). À l'inverse, une fréquence beaucoup plus faible sera adoptée (relevé annuel) lorsque l'objectif est de suivre l'évolution d'une côte sur du long terme à très long terme (Levoy, 1998). Le problème qui se pose alors est de savoir si les modifications observées relèvent bien de l'action des agents de forçage météo-marins ou si elles ne sont pas le résultat d'erreurs inhérentes à la mesure. Cette étude se propose de quantifier à partir de traitements statistiques les incertitudes liées à la mesure de terrain effectuée au théodolite (figure 1a et 1b), et auDGPS (figure 1c et 1d). Les données utilisées proviennent de suivis réalisés sur plusieurs plages du Finistère et des Côtes d'Armor effectués dans le cadre de travaux de thèse et/ou de recherches contractuelles. Une partie de ces résultats, ceux qui concernent la mesure au théodolite, a déjà fait l'objet d'une présentation dans le cadre des séminaires de notre UMR LETG - 6554 CNRS (Suanez et al., 2005). Pour cette étude, ces données ont été réactualisées en intégrant notamment le travail sur la mesure DGPS

Astrocyte mediated modulation of blood-brain barrier permeability does not correlate with a loss of tight junction proteins from the cellular contacts

In the central nervous system (CNS) complex endothelial tight junctions (TJs) form a restrictive paracellular diffusion barrier, the blood-brain barrier (BBB). Pathogenic changes within the CNS are frequently accompanied by the loss of BBB properties, resulting in brain edema. In order to investigate whether BBB leakiness can be monitored by a loss of TJ proteins from cellular borders, we used an in vitro BBB model where brain endothelial cells in co-culture with astrocytes form a tight permeability barrier for 3H-inulin and 14C-sucrose. Removal of astrocytes from the co-culture resulted in an increased permeability to small tracers across the brain endothelial cell monolayer and an opening of the TJs to horseradish peroxidase as detected by electron microscopy. Strikingly, opening of the endothelial TJs was not accompanied by any visible change in the molecular composition of endothelial TJs as junctional localization of the TJ-associated proteins claudin-3, claudin-5, occludin, ZO-1 or ZO-2 or the adherens junction-associated proteins β-catenin or p120cas did not change. Thus, opening of BBB TJs is not readily accompanied by the complete loss of the junctional localization of TJ protein

Martin Bertrand, du Maroc à l’Indochine : microhistoire d’un « tirailleur métropolitain » (1943 -1951)

Cadet sans terre d’une famille paysanne des Hautes-Alpes, Martin Bertrand (1915-2008) échappe au séminaire en s’engageant dans la garde républicaine mobile qui le conduira à Casablanca, au Maroc, où il sera stationné dès 1941. Mobilisé en 1943 à la suite du débarquement des Alliés en Afrique du Nord, il est affecté à l’encadrement d’une unité coloniale marocaine. Avec « ses » tirailleurs, il participe à la campagne d’Italie, au débarquement en Provence, à la libération de l’Alsace et à l’occupation de l’Allemagne. Après avoir regagné le Maroc pour quelques années, son bataillon est déployé de 1949 à 1951 à Tourane, en Indochine, où l’administration coloniale française tente de reprendre le contrôle de la région. Durant chacune de ses longues absences, Martin Bertrand écrira quasi quotidiennement à son épouse, Hélène, originaire d’une famille de colons espagnols installés en Algérie. Par l’analyse de cette correspondance, ce mémoire de maîtrise propose d’intégrer l’expérience de Martin Bertrand, sous-officier d’un régiment colonial, au sein d’une histoire impériale plus large; celle d’une France qui mène ses troupes au front de ses dernières guerres coloniales et qui déstabilise, dans ce processus, l’ordre qui régit la fonction et la position de chaque soldat. Ainsi, en faisant parler les mots intimes de Martin Bertrand au prisme du contenu de sources plus officielles, telles que les rapports militaires sur le moral des hommes, ce mémoire rend compte à la fois de la complexité des hiérarchies sociales et raciales qui établissent les rapports entre les sous-officiers français et la troupe « indigène » tout autant qu’il explore les questionnements identitaires plus personnels d’un petit cadre.Deprived of his land inheritance like many youngest-born of peasant descent, Martin Bertrand (1915-2008) eventually fled life as a seminarian in the French High-Alps by enlisting in the Mobile Guard and then being stationed in Casablanca, Morocco in 1941. Following the Anglo–American invasion of French North Africa, he was drafted in 1943 to lead a Moroccan colonial recruit unit. With “his” tirailleurs, he took part in the Italian campaign, the Provence landing, the liberation of Alsace, and the occupation of Germany. After the War, he returned to Morocco only to be deployed 3 years later with the same battalion to Tourane, Indochina where the French colonial administration attempted to retake control of the region. During each one of his long absences, Martin Bertrand wrote almost daily to his wife Hélène, descendent of Spanish settlers established in Algeria. By analyzing these letters, this master’s thesis proposes to integrate Martin Bertrand’s experiences, in his functions as a non-commissioned officer in a colonial regiment, into a broader imperial story where France led her armies through her last colonial wars and destabilized the colonial order under which each soldier was governed. Furthermore, this study compares Martin Bertrand’s private letters with more official sources like troop morale reports which allows for an analysis of the complex social and ethnic hierarchies between French non-commissioned officers and “indigenous” troops. At the same time, it explores the deeper questionings of a military intermediary’s self-identity