Contention-Aware Dynamic Memory Bandwidth Isolation with Predictability in COTS Multicores: An Avionics Case Study

Airbus is investigating COTS multicore platforms for safety-critical avionics applications, pursuing helicopter-style autonomous and electric aircraft. These aircraft need to be ultra-lightweight for future mobility in the urban city landscape. As a step towards certification, Airbus identified the need for new methods that preserve the ARINC 653 single core schedule of a Helicopter Terrain Awareness and Warning System (HTAWS) application while scheduling additional safety-critical partitions on the other cores. As some partitions in the HTAWS application are memory-intensive, static memory bandwidth throttling may lead to slow down of such partitions or provide only little remaining bandwidth to the other cores. Thus, there is a need for dynamic memory bandwidth isolation. This poses new challenges for scheduling, as execution times and scheduling become interdependent: scheduling requires execution times as input, which depends on memory latencies and contention from memory accesses of other cores - which are determined by scheduling. Furthermore, execution times depend on memory access patterns. In this paper, we propose a method to solve this problem for slot-based time-triggered systems without requiring application source-code modifications using a number of dynamic memory bandwidth levels. It is NoC and DRAM controller contention-aware and based on the existing interference-sensitive WCET computation and the memory bandwidth throttling mechanism. It constructs schedule tables by assigning partitions and dynamic memory bandwidth to each slot on each core, considering worst case memory access patterns. Then at runtime, two servers - for processing time and memory bandwidth - run on each core, jointly controlling the contention between the cores and the amount of memory accesses per slot. As a proof-of-concept, we use a constraint solver to construct tables. Experiments on the P4080 COTS multicore platform, using a research OS from Airbus and EEMBC benchmarks, demonstrate that our proposed method enables preserving existing schedules on a core while scheduling additional safety-critical partitions on other cores, and meets dynamic memory bandwidth isolation requirements

Ökologische Nachhaltigkeit in klein- und mittelständischen Betrieben

ÖKOLOGISCHE NACHHALTIGKEIT IN KLEIN- UND MITTELSTÄNDISCHEN BETRIEBEN Ökologische Nachhaltigkeit in klein- und mittelständischen Betrieben / Högner, Sabine (Rights reserved) ( -

Validation of the network of relationship inventory in female and male adolescents

Friendships and their different qualities have been shown to be important for adolescents\u27 socio-emotional development and psychological adjustment. In empirical research on such friendship qualities, the Network of Relationship Inventory-Relationship Quality Version (NRI-RQV) is a widely used questionnaire. Here, we conduct an extensive validation of a German version of the NRI-RQV, investigating its factor structure, reliability, and concurrent validity, in a sample of N= 679 adolescents aged 13-18 years. Applying multigroup confirmatory factor analysis, we further test whether the factor structure of the friendship quality construct holds across groups of males and females. Results showed that a structure with nine correlated first-order factors fit the data well, indicating nine distinct friendship qualities in males and females. Measurement invariance testing suggested the same underlying friendship quality construct, albeit differences in mean scores per gender. As evidence for concurrent validity, closeness and discordant friendship qualities showed expected correlations with empathy and social problems, respectively, but not with aggressive behavior. Overall, results indicate good psychometric properties for the German version of the NRI-RQV as a measure of friendship qualities in both males and females. (DIPF/Orig.

A comprehensive set of simulations of high-velocity collisions between main sequence stars

We report on a very large set of simulations of collisions between two main sequence (MS) stars. These computations were done with the ``Smoothed Particle Hydrodynamics'' method. Realistic stellar structure models for evolved MS stars were used. In order to sample an extended domain of initial parameters space (masses of the stars, relative velocity and impact parameter), more than 15000 simulations were carried out. We considered stellar masses ranging between 0.1 and 75 Msun and relative velocities up to a few thousands km/s. To limit the computational burden, a resolution of 2000-30000 particles per star was used. The primary goal of this study was to build a complete database from which the result of any collision can be interpolated. This allows us to incorporate the effects of stellar collisions with an unprecedented level of realism into dynamical simulations of galactic nuclei and other dense stellar clusters. We make the data describing the initial condition and outcome (mass and energy loss, angle of deflection) of all our simulations freely available on the Internet. We find that the outcome of collisions depends sensitively on the stellar structure and that, in most cases, using polytropic models is inappropriate. Published fitting formulas for the collision outcomes, established from a limited set of collisions, prove of limited use because they do not allow robust extrapolation to other stellar structures or relative velocities.Comment: 45 pages, 44 figures. Modified to reflect the changes in the published version (MNRAS). PDF version with high-res figures at http://obswww.unige.ch/~freitag/papers/article_collisions.pdf, simulation data at http://obswww.unige.ch/~freitag/MODEST_WG4/FB_Collision_Data/, movies at http://obswww.unige.ch/~freitag/collisions/animations/index.htm

Higher order moment models of dense stellar systems: Applications to the modeling of the stellar velocity distribution function

Dense stellar systems such as globular clusters, galactic nuclei and nuclear star clusters are ideal loci to study stellar dynamics due to the very high densities reached, usually a million times higher than in the solar neighborhood; they are unique laboratories to study processes related to relaxation. There are a number of different techniques to model the global evolution of such a system. In statistical models we assume that relaxation is the result of a large number of two-body gravitational encounters with a net local effect. We present two moment models that are based on the collisional Boltzmann equation. By taking moments of the Boltzmann equation one obtains an infinite set of differential moment equations where the equation for the moment of order $n$ contains moments of order $n+1$. In our models we assume spherical symmetry but we do not require dynamical equilibrium. We truncate the infinite set of moment equations at order $n=4$ for the first model and at order $n=5$ for the second model. The collisional terms on the right-hand side of the moment equations account for two-body relaxation and are computed by means of the Rosenbluth potentials. We complete the set of moment equations with closure relations which constrain the degree of anisotropy of our model by expressing moments of order $n+1$ by moments of order $n$. The accuracy of this approach relies on the number of moments included from the infinite series. Since both models include fourth order moments we can study mechanisms in more detail that increase or decrease the number of high velocity stars. The resulting model allows us to derive a velocity distribution function, with unprecedented accuracy, compared to previous moment models.Comment: Accepted for publication by MNRAS after minor correction

Origin of the S Stars in the Galactic Center

Over the last 15 years, around a hundred very young stars have been observed in the central parsec of our Galaxy. While the presence of young stars forming one or two stellar disks at approx. 0.1 pc from the supermassive black hole (SMBH) can be understood through star formation in accretion disks, the origin of the S stars observed a factor of 10 closer to the SMBH has remained a major puzzle. Here we show the S stars to be a natural consequence of dynamical interaction of two stellar disks at larger radii. Due to precession and Kozai interaction, individual stars achieve extremely high eccentricities at random orientation. Stellar binaries on such eccentric orbits are disrupted due to close passages near the SMBH, leaving behind a single S star on a much tighter orbit. The remaining star may be ejected from the vicinity of the SMBH, thus simultaneously providing an explanation for the observed hypervelocity stars in the Milky Way halo.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letters; final version, minor changes onl

Simulations of the formation of stellar discs in the Galactic centre via cloud-cloud collisions

Young massive stars in the central parsec of our Galaxy are best explained by star formation within at least one, and possibly two, massive self-gravitating gaseous discs. With help of numerical simulations, we here consider whether the observed population of young stars could have originated from a large angle collision of two massive gaseous clouds at R approx. 1 parsec from Sgr A*. In all the simulations performed, the post-collision gas flow forms an inner, nearly circular gaseous disc and one or two eccentric outer filaments, consistent with the observations. Furthermore, the radial stellar mass distribution is always very steep, Sigma proportional to R^-2, again consistent with the observations. All of our simulations produce discs that are warped by between 30 to 60 degrees, in accordance with the most recent observations. The 3D velocity structure of the stellar distribution is sensitive to initial conditions (e.g., the impact parameter of the clouds) and gas cooling details. For example, the runs in which the inner disc is fed intermittently with material possessing fluctuating angular momentum result in multiple stellar discs with different orbital orientations, contradicting the observed data. In all the cases the amount of gas accreted by our inner boundary condition is large, enough to allow Sgr A* to radiate near its Eddington limit over approx. 10^5 years. This suggests that a refined model would have physically larger clouds (or a cloud and a disc such as the circumnuclear disc) colliding at a distance of a few parsecs rather than 1 parsec as in our simulations.Comment: 18 pages, 14 figures. Accepted for publication in MNRAS. Minor additions at referee request. Movies of simulations available at http://www.astro.le.ac.uk/~aph11/movies.htm

Constraining the initial mass function of stars in the Galactic Centre

(abridged) Here we discuss the question whether the extreme circumstances in the centre of the Milky Way may be the reason for a significant variation of the IMF. By means of stellar evolution models using different codes we show that the observed luminosity in the central parsec is too high to be explained by a long-standing top-heavy IMF, considering the limited amount of mass inferred from stellar kinematics in this region. In contrast, continuous star formation over the Galaxy's lifetime following a canonical IMF results in a mass-to-light ratio and a total mass of stellar black holes (SBHs) consistent with the observations. Furthermore, these SBHs migrate towards the centre due to dynamical friction, turning the cusp of visible stars into a core as observed in the Galactic Centre. For the first time here we explain the luminosity and dynamical mass of the central cluster and both the presence and extent of the observed core, since the number of SBHs expected from a canonical IMF is just enough to make up for the missing luminous mass. We conclude that the Galactic Centre is consistent with the canonical IMF and do not suggest a systematic variation as a result of the region's properties such as high density, metallicity, strong tidal field etc.Comment: MNRAS, accepted, 8 pages, 4 figure

Loss cone: past, present and future

The capture and subsequent in--spiral of compact stellar remnants by central massive black holes, is one of the more interesting likely sources of gravitational radiation detectable by LISA. The relevant stellar population includes stellar mass black holes, and possibly intermediate mass black holes, generally on initially eccentric orbits. Predicted detectable rates of capture are highly uncertain, but may be high enough that source confusion is an issue. Foreground events with relatively high signal-to-noise ratio may provide important tests of general relativity. I review the rate estimates in the literature, and the apparent discrepancy between different authors' estimates, and discuss some of the relevant uncertainties and physical processes. The white dwarf mergers rate are uncertain by a factor of few; the neutron star merger rate is completely uncertain and likely to be small; the black hole merger rate is likely to be dominant for detectable mergers and is uncertain by at least two orders of magnitude, largely due to unknown physical conditions and processes. The primary difference in rate estimates is due to different initial conditions and less directly due to different estimates of key physical processes, assumed in different model scenarios for in-spiral and capture.Comment: 7 pages, revtex twocolumn, Special LISA Issue Classical and Quantum Gravity in pres