213 research outputs found
Challenges for the Parallelization of Loosely Timed SystemC Programs
International audienceSystemC/TLM models are commonly used in the industry to provide an early SoC simulation environment. The open source implementation of the SystemC simulator is sequential. The standard doesn't impose sequential executions, but makes this choice the easiest by imposing coroutine semantics. With the increasing size and complexity of models, and the multiplication of computation cores on recent machines, the parallelization of SystemC simulations is a major research concern. There have been several proposals for SystemC parallelization, but most of them are limited to cycle-accurate models. In this paper we give an overview of the practices in one industrial context. We explain why loosely timed models are the only viable option in this context. We also show that unfortunately, most of the existing approaches for SystemC parallelization can fundamentally not apply to these models. We support this claim with a set of measurements performed on a platform used in production at STMicroelectronics. This paper both surveys existing techniques and identifies unsolved challenges in the parallelization of SystemC/TLM models
New biostratigraphical data for the Burdigalian Montchaibeux Member at the locality Courrendlin-Solé (Canton of Jura, Switzerland)
Geological surveys were carried out in the Miocene deposits at the place known as “En Solé” east of the village Courrendlin (Delémont Basin, Canton of Jura, Switzerland). This resulted in the discovery of new Miocene small mammal assemblages. The association of the rodents Megacricetodon aff. collongensis and Melissiodon sp. allows to biochronostratigraphically correlate for the first time the so- called “Rote Mergel des Mont Chaibeux” representing the lower part of the Montchaibeux Member of the Bois de Raube Formation to the regional M. collongensis–Keramidomys interval zone (MN 4; early Miocene)
Evolution dynamique des amas stellaires jeunes
Comprendre le processus de formation stellaire est un objectif majeur en astronomie. Sur ce sujet les observations ne donnent que très peu d'information, et les modèles numériques sont donc naturellement privilégiés. De tels modèles s'attachent à suivre la dynamique du gaz, sous l'effet de processus physique variés, ce qui nécessite un temps de calcul très important et ne permet pas de modéliser l'évolution au delà de 0.2 Myr environ. Or les résultats observationnels sont essentiellement issus du champ galactique proche, des amas évolués, voire des regions jeunes ou associations d'étoiles, dont l'âge peut varier de 1 Myr à quelques Gyr. Par conséquent, il est nécessaire pour comparer les résultats des modèles aux observations de comprendre ce qu'il se passe durant cet intervalle de temps. La formation stellaire tend à produire des étoiles en groupes, à partir de l'effondrement gravitationnel d'un nuage moléculaire turbulent. A mesure que les étoiles se forment, le gaz est éjecté et l'évolution est dominée par les interactions gravitationnelles. Suivre l'évolution sous l'effet de ces interactions est couramment utilisé afin de contraindre les modèles et de mieux comprendre l'origine des populations stellaires observées. Les étoiles se forment en sous-groupes ou structures hiérarchisées, qui peuvent ensuite fusionner pour donner des amas stellaires proche des amas ouverts, ou au contraire finir en associations distinctes. Dans ma thèse, je me suis intéressé à l'évolution dynamique de petits groupes d'étoiles, jusqu'alors peu étudiés par rapport aux groupes à 1000 ou 10^4 étoiles. J'ai simulé l'évolution de groupes à N < 100, dans le but d'en étudier la dynamique d'un point de vue statistique, grâce notamment au grand nombre de simulations effectuées, et afin d'identifier les signatures observationnelles propres à une situation initiale donnée. A partir d'un grand nombre de configurations initiales (avec N=20, 50, 100, un rayon typique de 0.025 pc à 1 pc) et 500 simulations par configurations, j'ai étudié l'évolution dynamique de groupes composés d'étoiles de même masse ou comprenant un spectre de masse, et sans population de binaire initiale. L'évolution de tels groupes s'est révélée similaire à celle de groupes plus grands, mais avec une phase d'effondrement plus rapide et surtout moins prononcée. Je décris le comportement moyen menant à une lente expansion de l'amas, ainsi qu'une voie d'évolution très différente, apparaissant dans 17% des cas étudiés, où l'amas est complètement dispersé suite à l'éjection d'une binaire centrale serrée. J'ai également recherché dans quelle mesure les données en densité et en vitesse 3D pouvaient permettre d'identifier l'état dynamique initial d'un groupe. L'utilisation de ces seules données suffisait dans certain cas à déterminer la densité initiale, mais elles devraient être complétées par des données concernant la population de binaire. Ce travail pourra être mis en application pour étudier l'origine dynamique d'association ou de groupes stellaires connus. Enfin, j'ai effectué un grand nombre de simulations numériques dans le but de reproduire l'état observé de l'amas eta Chamaeleontis par pure évolution dynamique à partir de conditions initiales standards. Cette association présente des caractéristiques d'amas évolué, telle que son spectre de masse pauvre en objets de faible masse et l'absence de binaires larges. Je montre que ces propriétés ne peuvent pas être reproduites uniquement par la dynamique, et sont donc les traces d'un processus de formation non standard.Understanding the star formation process is a key issue in astronomy. Since direct observation provide only very limited information, this issue is investigated by models. Such models need to take into account complex physical processes while following the gas dynamics, so that simulations need a lot of time to run and do not follow the star formation process for longer than 0.2 Myr. The best known observational results concerns the field population, evolved open clusters or younger clusters or associations, which are between 1 Myr and a few Gyr old. Therefore in order to compare the results from models to known observations, we need to bridge the gap between the two. Star formation appears to produce groups of stars from the collapse of turbulent molecular clouds. As stars form, the gas is progressively ejected from the cluster, and the evolution is dominated by gravitational interactions. Following the dynamical evolution of a group of star using N-Body codes is a standard way used to constraint the models and understand the origin of the different populations. Star formation may produce sub-structure or small groups that merge to form bigger entities, or end up as loose association. In my thesis I focused on the dynamics of small groups, that have not been investigated as thoroughly as 1000 or 10^4 star groups. I performed N-Body simulations of small stellar groups, with N<100, in order to study their dynamics using a statistical approach, made possible by running a large number of simulations, and to find some observational signatures of given initial conditions. This approach enable to take full account of stochastic effects due to dynamical interactions. Using a large number of initial configurations (with N=20, 50, 100, a typical radius from 0.025 pc to 1 pc) and a sample of 500 simulations per configuration, I looked at equal mass groups as well as groups having a mass spectrum, without any binary initially. Such small groups show similar evolution to bigger groups, but with faster and less pronounced collapse phase. I described the average behaviour of slow expansion of the cluster, and an alternative evolution, occurring with 17% probability, that ended in the complete dissolution of the group due to ejection of a central binary. Searching for a way to identify the initial configuration from observational measure, I looked at the complementarity of density and 3D velocity and was able to show that it could be sufficient in some cases to determine the initial density. Further investigations are needed to take into account the information on the binary population and will be used to investigate the formation of known associations or young regions. Finally, I ran a large number of simulations, aiming at reproducing the observed state of the eta Chamaeleontis from standard initial conditions and pure dynamical evolution. This association properties are consistent with a dynamical evolved cluster, namely low-mass object poor and having only tight binaries. I showed that these properties cannot be reproduced with pure dynamical evolution from standard initial mass function and binary population, meaning that its particular features must have been pristine.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF
Arbitrary-order non-linear contribution to self-steepening
Based on the recently published generalized Miller formula, we derive the
spectral dependence of the contribution of arbitrary-order non-linear indices
to the group-velocity index. We show that in the context of laser filamentation
in gases all experimentally-accessible orders (up to the -order
non-linear susceptibility in air and in argon) have
contributions of alternative signs and similar magnitudes. Moreover, we show
both analytically and numerically that the dispersion term of the non-linear
indices must be considered when computing the intensity-dependent group
velocity.Comment: 10 pages, 3 figures (14 panels
Intermittent dislocation flow in viscoplastic deformation
The viscoplastic deformation (creep) of crystalline materials under constant
stress involves the motion of a large number of interacting dislocations.
Analytical methods and sophisticated `dislocation-dynamics' simulations have
proved very effective in the study of dislocation patterning, and have led to
macroscopic constitutive laws of plastic deformation. Yet, a statistical
analysis of the dynamics of an assembly of interacting dislocations has not
hitherto been performed. Here we report acoustic emission measurements on
stressed ice single crystals, the results of which indicate that dislocations
move in a scale-free intermittent fashion. This result is confirmed by
numerical simulations of a model of interacting dislocations that successfully
reproduces the main features of the experiment. We find that dislocations
generate a slowly evolving configuration landscape which coexists with rapid
collective rearrangements. These rearrangements involve a comparatively small
fraction of the dislocations and lead to an intermittent behavior of the net
plastic response. This basic dynamical picture appears to be a generic feature
in the deformation of many other materials. Moreover, it should provide a
framework for discussing fundamental aspects of plasticity, that goes beyond
standard mean-field approaches that see plastic deformation as a smooth laminar
flow
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