Terrestrial Planet Formation Constrained by Mars and the Structure of the Asteroid Belt

Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoplanetary disk between 1 and 3 AU. The Grand Tack model invokes a specific migration history of the giant planets to remove most of the mass initially beyond 1 AU and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas-drag, as has been proposed to explain the formation of close-in super Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar System. We performed a series of simulations of terrestrial planet formation and asteroid belt evolution starting from disks of planetesimals and planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Disks with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogs significantly more massive than the real planet. In contrast, a disk with a surface density gradient proportional to $r^{-5.5}$ reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disk profile can simultaneously explain the structure of the terrestrial planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.Comment: Accepted for publication in MNRA

An Efficient OpenMP Runtime System for Hierarchical Arch

Exploiting the full computational power of always deeper hierarchical multiprocessor machines requires a very careful distribution of threads and data among the underlying non-uniform architecture. The emergence of multi-core chips and NUMA machines makes it important to minimize the number of remote memory accesses, to favor cache affinities, and to guarantee fast completion of synchronization steps. By using the BubbleSched platform as a threading backend for the GOMP OpenMP compiler, we are able to easily transpose affinities of thread teams into scheduling hints using abstractions called bubbles. We then propose a scheduling strategy suited to nested OpenMP parallelism. The resulting preliminary performance evaluations show an important improvement of the speedup on a typical NAS OpenMP benchmark application

Systematic off-pump coronary artery revascularization in multivessel disease: Experience of three hundred cases

AbstractObjective: We sought to report our recent experience with off-pump coronary artery revascularization in multivessel disease. Methods: Between October 1996 and December 1998, 300 off-pump beating heart operations were performed at the Montreal Heart Institute by a single surgeon, representing 94% of all procedures undertaken during this same time frame (97% for 1998). This cohort of patients was compared with 1870 patients operated on with cardiopulmonary bypass from 1995 to 1996. Results: Mean age, sex distribution, and preoperative risk factors were comparable for the two groups. On average, 2.92 ± 0.8 and 2.84 ± 0.6 grafts per patient were completed in the beating heart and cardiopulmonary bypass groups, respectively. A majority of patients (70%) had either a triple or quadruple bypass. Coronary anastomoses were achieved with myocardial mechanical stabilization and heart “verticalization.” Ischemic time was shorter in the beating heart group (29.8 ± 0.9 vs 45 ± 0.4 minutes, P < .05). Similarly, the need for transfusion was significantly less in the beating heart group (beating heart operations, 34%; cardiopulmonary bypass, 66%; P < .005). Reduced use of postoperative intra-aortic counterpulsation, as well as a lower rise in creatine kinase MB isoenzyme, was observed in the beating heart group. Operative mortality rates (beating heart operations, 1.3%; cardiopulmonary bypass, 2%) and perioperative myocardial infarction (beating heart operations, 3.6%; cardiopulmonary bypass, 4.2%) were comparable for the two groups. Conclusion: In a majority of patients, off-pump complete coronary artery revascularization is an acceptable alternative to conventional operations, yielding good results given progressive experience, rigorous technique, and adequate coronary artery stabilization. (J Thorac Cardiovasc Surg 2000;119:221-9

EASYPAP: a Framework for Learning Parallel Programming

This paper presents EASYPAP, an easy-to-use programming environment designed to help students to learn parallel programming. EASYPAP features a wide range of 2D computation kernels that the students are invited to parallelize using Pthreads, OpenMP, OpenCL or MPI. Execution of kernels can be interactively visualized, and powerful monitoring tools allow students to observe both the scheduling of computations and the assignment of 2D tiles to threads/processes. By focusing on algorithms and data distribution, students can experiment with diverse code variants and tune multiple parameters, resulting in richer problem exploration and faster progress towards efficient solutions. We present selected lab assignments which illustrate how EASYPAP improves the way students explore parallel programming

Les chrétiens d’Alep dans la fabrication et le commerce des tissus aux XVIIe et XVIIIe siècles

Le spectaculaire progrès de la communauté chrétienne d’Alep à l’époque ottomane est lié au rôle qu’elle joua dans la fabrication et le commerce des tissus, principale activité économique de cette ville. L’extension spatiale du quartier chrétien est parallèle au développement de cet artisanat dans les ateliers (qaysâriyya) du faubourg nord d’Alep. Les chrétiens prirent dans les corporations professionnelles concernées une place importante, correspondant à leur activité, ce qui amena une remarquable (et parfois difficile) coexistence avec les musulmans. Dans le commerce des tissus, les réseaux chrétiens furent fortement impliqués : Arméniens au XVIIe siècle, Alépins au XVIIIe. Quand le schisme dans la communauté orthodoxe (1724) donna naissance à la communauté grecque catholique, la diaspora qui se produisit alors amena le développement en  Égypte d’une communauté particulièrement prospère qui s’assura une place importante dans le commerce international des étoffes du Levant.The spectacular growth of the Christian community in Aleppo, during the Ottoman period, is linked with the part it played in the fabrication and trade of cloth, the main economic activity of that city. The spatial expansion of the Christian quarter is parallel with the development of that craft, in the workshops (qaysâriyya) of the northern suburb of Aleppo. The Christians took, in the professional guilds, an important place corresponding with their activity in that field, which caused a remarkable (and sometimes difficult) coexistence with the Moslems. In the cloth trade, the Christian networks, played an important part. They were mainly Armenian in the XVIIth century, Alepine in the XVIIIth. When the schism in the Greek orthodox church (1724) brought about the birth of a new Greek Catholic community, its diaspora to Egypt was the origin of the development of a very prosperous community which was actively involved in the international trade of Levant cloth

Pouvoir politique, autonomies urbaines et mouvements populaires au Caire au XVIIIe siècle

Partant de l’image largement répandue d’un pouvoir central absolu exercé de manière despotique à l’échelon local dans l’Empire ottoman, face aux représentants duquel les populations seraient restées prisonnières de la passivité, l’auteur s’efforce de nuancer et corriger pareil tableau à travers l’exemple du Caire, à la charnière entre le XVIIIe et le XIXe siècle. Revenant préalablement sur l’époque précédente, André Raymond constate que très tôt existaient des limites à l’autorité des gouverneurs ainsi qu’un contrôle étroit exercé sur celle-ci, grâce à une série de règles et de contre-pouvoirs, lesquels devaient empêcher tout arbitraire. Dans ces conditions, les populations locales étaient loin de se cantonner à l’isolement et à l’attentisme. L’entrée des indigènes dans le corps des ‘ulamâ, l’existence de corporations, de confréries et autres organisations du type des tawâ’if, structures à l’origine de l’encadrement de la vie sociale, conféraient à une partie de la population des moyens d’expression et même, parfois, d’intervention auprès des autorités. Les émeutes, fréquentes à la fin du XVIIIe siècle et dont certaines prenaient les traits de véritables insurrections, constituaient un autre moyen d’expression pour le peuple : plus que des revendications «alimentaires», comme celles qui s’étaient déroulées en des temps antérieurs, elles comportaient une forte dimension politique, en réaction aux abus et à la pression de plus en plus lourds exercés par le pouvoir. Ces mouvements populaires qui s’exprimèrent jusqu’à l’avènement de Muhammad Ali, apparurent comme les premières failles de tout le système politique à l’œuvre dans l’Empire ottoman.Starting from the widespread image of an absolute central power despotically exercised on a local scale in the ottoman empire, in front of representatives which populations would have stayed like prisoners of passivity, the author tries to shade and correct such a painting through the example of Cairo, at the cusp of the 18th and 19th century. First coming back to the former time, André Raymond notes that very early limits were existing to the governors auhority as well as a tight control on it thanks to a set of rules and counter powers which had to prevent any arbitrary. In such conditions the local populations were far from limiting to isolation and wait-and-see policy. The enrollment of natives in the ulamâ corpse, the existence of corporations, of brotherhoods and other organizations like tawâ’if, which were the original structures for framing of social life, were endowing a part of population with expression means and sometimes with intervention next to the authorities. The frequent riots at the end of 18th century and some of them would become real insurrections, were building up another expression mean for the population: more than “food” claimings such as it had taken place in former time, they were made up of a strong political dimension, in reaction against injustice and the bigger and bigger pressure exercised by power. These popular movements which took place until the accession of Muhammad Ali were the sign of the first flaws of the whole political system set up in the ottoman empire

Culture générale: conceptions, attentes et stratégies

La présente recherche a été subventionnée par le ministère de l'Éducation, du Loisir et du Sport dans le cadre du Programme d'aide à la recherche sur l'enseignement et l'apprentissage (PAREA)La recherche ayant été réalisée dans le cadre d'une thèse de doctorat en éducation à l'Université du Québec à Trois-Rivières, le rapport est le texte même de cette thèse. Le titre de la thèse est "Culture générale : conceptions, attentes et pratiques pédagogiques de professeures et professeurs du collégial".Également disponible en version papier.Titre de l'écran-titre (visionné le 26 sept. 2011