Forme di equilibrio di aggregati gravitazionali: modelli numerici con applicazione agli asteroidi

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Formes d'astéroïdes et formation de satellites : rôle de la réaccumulation gravitationnelle

International audienceAsteroid shapes and satellites: role of gravitational reaccumulation. Following current evidences, it is widely accepted that many asteroids would be "gravitational aggregates", i.e. bodies lacking internal cohesion. They could mainly be originated during the catastrophic disruption of some parent bodies, through the gravitational reaccumulation of the resulting fragments. The same events produced the dynamical families that we observe. In this work we address the problem of the origin of shapes of gravitational aggregates, that could contain signatures of their origin. We use a N-body code to simulate the collapse of a cloud of fragments, with a variety of initial velocity distributions and total angular momentum. The fragments are treated as inhelastic spheres, that rapidly accumulate to form rotating aggregates. The resulting shapes and rotational properties are compared with theoretical predictions. The results show that only a precise category of shapes (flattened spheroids) are created via this mechanism. This may provide interesting constraints on the evolution of asteroid shapes, in particular for those with one or more satellites

Formes d'ast\'ero\"ides et formation de satellites : r\^ole de la r\'eaccumulation gravitationnelle

Asteroid shapes and satellites: role of gravitational reaccumulation. Following current evidences, it is widely accepted that many asteroids would be "gravitational aggregates", i.e. bodies lacking internal cohesion. They could mainly be originated during the catastrophic disruption of some parent bodies, through the gravitational reaccumulation of the resulting fragments. The same events produced the dynamical families that we observe. In this work we address the problem of the origin of shapes of gravitational aggregates, that could contain signatures of their origin. We use a N-body code to simulate the collapse of a cloud of fragments, with a variety of initial velocity distributions and total angular momentum. The fragments are treated as inhelastic spheres, that rapidly accumulate to form rotating aggregates. The resulting shapes and rotational properties are compared with theoretical predictions. The results show that only a precise category of shapes (flattened spheroids) are created via this mechanism. This may provide interesting constraints on the evolution of asteroid shapes, in particular for those with one or more satellites

Numerical N-body approach to binary asteroid formation and evolution

thèse issue d'une co-tutelle Italie (Università di Torino) - France (Université de Nice-Sophia Antipolis)Binary asteroids play a role of primary importance in determining some physical parameters difficult to measure from Earth, such as the mass. By studying the origin of binaries in the general frame of gravitational aggregates, we can use them as natural laboratories for granular system physics in microgravity conditions, thus obtaining valuable information for modeling asteroids in general. A large variety exists as for the range of parameters of the observed binary systems, and many possible origins have been suggested for them (catastrophic shattering of a parent object and re-accumulation as multiple bodies, planetary tidal perturbations, cratering, YORP ...). In this work we explore by numerical N-body simulations the dynamics of gravitational aggregates outside the limits of stability for a single body, looking for the most favorable configurations leading to binary systems formation. First we show how common the formation of binary systems in a catastrophic scenario is, well reproducing the variety in the observed population. As a second step we explore the possibility of a gradual shape deformation of an aggregate towards a binary system by the action of a slow perturbing force leading to a possible fission of the body. Our results provide new insights into the formation of asteroid binaries, as shown by a comparison to observations and existing literature.Les astéroïdes binaires ont un rôle d'importance fondamentale dans la détermination de paramètres astéroïdales difficilement mesurables de la Terre, en particulier la masse. En étudiant l'origine des binaires dans le cadre des agrégats gravitationnels, ils servent ainsi comme laboratoires naturels pour la physique des systèmes granulaires à basse gravité, et ils nous donnent des éléments précieux pour la modélisation globale des astéroïdes. Vue la grande diversité existante de caractéristiques des systèmes binaires observés, nombreuses hypothèses ont été postulées pour leur origine (fragmentation catastrophique d'un corps et ré-accumulation sous forme binaire, influences de marée par les planètes, cratérisation, YORP ...). Dans cette thèse nous explorons, grâce à des simulations numériques à N corps, la dynamique d'un agrégat gravitationnel en dehors du régime de stabilité pour un corps simple, en cherchant les configurations les plus favorables à la formation d'un système binaire. Dans une première partie, nous montrons que dans un scénario catastrophique la formation de systèmes binaires est normale, ces-ci bien reproduisant la variété présente dans la population observée. En suite, nous explorons la possibilité d'une déformation progressive d'un agrégat vers un système binaire sous l'action d'une force perturbante agissant lentement jusqu'à la fission éventuelle du corps. Nos résultats proposent des nouveaux regards dans l'étude de la formation des astéroïdes binaires, comme montré par une comparaison avec les observations et la littérature existante

Approche numérique à N corps à la formation et à évolution des astéroïdes binaires

Binary asteroids play a role of primary importance in determining some physical parameters difficult to measure from Earth, such as the mass. By studying the origin of binaries in the general frame of gravitational aggregates, we can use them as natural laboratories for granular system physics in microgravity conditions, thus obtaining valuable information for modelling asteroids in general. A large variety exists as for the range of parameters of the observed binary systems, and many possible origins have been suggested for them (catastrophic shattering of a parent object and reaccumulation as multiple bodies, planetary tidal perturbations, cratering, YORP ). In this work we explore by numerical N-body simulations the dynamics of gravitational aggregates outside the limits of stability for a single body, looking for the most favourable configurations leading to binary systems formation. First we show how common the formation of binary systems in a catastrophic scenario is, well reproducing the variety in the observed population. As a second step we explore the possibility of a gradual shape deformation of an aggregate towards a binary system by the action of a slow perturbing force leading to a possible fission of the body. Our results provide new insights into the formation of asteroid binaries, as shown by a comparison to observations and existing literature.Les astéroïdes binaires ont un rôle d'importance fondamentale dans la détermination de paramètres astéroïdales difficilement mesurables de la Terre, en particulier la masse. En étudiant l'origine des binaires dans le cadre des agrégats gravitationnels, ils servent ainsi comme laboratoires naturels pour la physique des systèmes granulaires à basse gravité, et ils nous donnent des éléments précieux pour la modélisation globale des astéroïdes. Vue la grande diversité existante de caractéristiques des systèmes binaires observés, nombreuses hypothèses ont été postulées pour leur origine (fragmentation catastrophique d'un corps et réaccumulation sous forme binaire, influences de marée par les planètes, cratérisation, YORP ). Dans cette thèse nous explorons, grâce à des simulations numériques à N corps, la dynamique d'un agrégat gravitationnel en dehors du régime de stabilité pour un corps simple, en cherchant les configurations les plus favorables à la formation d'un système binaire. Dans une première partie, nous montrons que dans un scénario catastrophique la formation de systèmes binaires est normale, ces-ci bien reproduisant la variété présente dans la population observée. En suite, nous explorons la possibilité d'une déformation progressive d'un agrégat vers un système binaire sous l'action d'une force perturbante agissant lentement jusqu'à la fission éventuelle du corps. Nos résultats proposent des nouveaux regards dans l'étude de la formation des astéroïdes binaires, comme montré par une comparaison avec les observations et la littérature existante.NICE-BU Sciences (060882101) / SudocPARIS-Observatoire (751142302) / SudocSudocFranceItalyFRI

Slow coronary flow and stress myocardial perfusion imaging. Different patterns in acute patients

We investigated myocardial perfusion in acute patients with slow coronary flow (SCF) at angiography. Whether impaired myocardial perfusion occurs in acute patients with SCF is unknown.We enrolled 28 consecutive patients with SCF in the epicardial coronary arteries with no evidence of significant stenosis. SCF affected a single coronary artery in 14 patients (group A) and all three coronary vessels in 14 others (group B). Coronary angiography was repeated after dipyridamole infusion and single photon emission computed tomography was performed using dipyridamole as the stress agent. The Thrombolysis in Myocardial Infarction frame count was measured in SCF vessels at baseline and after dipyridamole infusion.Mean Thrombolysis in Myocardial Infarction frame count significantly decreased after dipyridamole in both groups. At baseline, mean values of the single photon emission computed tomography score were 31.5 +/- 1.6 and 25.1 +/- 2.1 in groups A and B, respectively. After dipyridamole, they increased from 31.5 +/- 1.6 to 37.8 +/- 1.4 (P < 0.001) in group A, whereas a further decrease to 15.0 +/- 1.2 (P < 0.005) was observed in group B.An opposite behavior of myocardial perfusion was observed after dipyridamole infusion: a normal response in patients with SCF affecting one single coronary artery versus an ischemic-like response in those with CSF affecting all three coronary arteries

11C choline PET guided salvage radiotherapy with volumetric modulation arc therapy and hypofractionation for recurrent prostate cancer after HIFU failure: preliminary results of tolerability and acute toxicity

The purpose of this work was to evaluate tolerance, feasibility and acute toxicity in patients undergoing salvage radiotherapy after high-intensity focused ultrasound (HIFU) failure. From 2005 to 2011 a total of 15 patients were treated with HIFU as primary radical treatment. Between July 2011 and February 2013, all 15 patients presented biochemical relapse after HIFU and 11C choline PET documenting intrapostatic-only failure. Salvage EBRT was performed with moderate hypofractionation schedule in 28 fractions with volumetric modulation arc therapy (VMAT). Genito-urinary (GU) and rectal and bowel toxicity were scored by common terminology criteria for adverse events version 4 (CTCAE V.4) scale. Biochemical response was assessed by ASTRO Phoenix criteria. Median age of patients was 67 years (range: 53-85). The median Gleason score was 7 (range: 6-9). The median prostate specific antigen (PSA) at the time of biochemical relapse after HIFU was 5.2 ng/mL (range: 2-64.2). Seven of the 15 patients received androgen deprivation therapy (ADT) started after HIFU failure, interrupted before 11C choline PET and radiotherapy. Median prescribed dose was 71.4 Gy (range: 71.4-74.2 Gy) in 28 fractions. No radiation related major upper gastrointestinal (GI), rectal and GU toxicity were experienced. GU, acute grade 1 and grade 2 toxicities were recorded in 7/15 and 4/15 respectively; bowel acute grade 1 and grade 2 toxicities in 4/15 and 1/15; rectal acute grade 1 and grade 2 toxicities in 3/15 and 2/15 respectively. No grade 3 or greater acute or late toxicities occurred. Biochemical control was assessed in 12/15 (80%) patients. With a median follow up of 12 months, three out of 15 patients, with biochemical relapse, showed lymph-nodal recurrence. Our early clinical results and biochemical data confirm the feasibility and show a good tolerance of the 11C choline PET guided salvage radiation therapy after HIFU failure. The findings of low acute toxicity is encouraging, but longer follow-up is needed to assess late toxicity and definitive outcomes