195,043 research outputs found
Model-driven engineering approach to design and implementation of robot control system
In this paper we apply a model-driven engineering approach to designing
domain-specific solutions for robot control system development. We present a
case study of the complete process, including identification of the domain
meta-model, graphical notation definition and source code generation for
subsumption architecture -- a well-known example of robot control architecture.
Our goal is to show that both the definition of the robot-control architecture
and its supporting tools fits well into the typical workflow of model-driven
engineering development.Comment: Presented at DSLRob 2011 (arXiv:cs/1212.3308
RPPM : Rapid Performance Prediction of Multithreaded workloads on multicore processors
Analytical performance modeling is a useful complement to detailed cycle-level simulation to quickly explore the design space in an early design stage. Mechanistic analytical modeling is particularly interesting as it provides deep insight and does not require expensive offline profiling as empirical modeling. Previous work in mechanistic analytical modeling, unfortunately, is limited to single-threaded applications running on single-core processors.
This work proposes RPPM, a mechanistic analytical performance model for multi-threaded applications on multicore hardware. RPPM collects microarchitecture-independent characteristics of a multi-threaded workload to predict performance on a previously unseen multicore architecture. The profile needs to be collected only once to predict a range of processor architectures. We evaluate RPPM's accuracy against simulation and report a performance prediction error of 11.2% on average (23% max). We demonstrate RPPM's usefulness for conducting design space exploration experiments as well as for analyzing parallel application performance
Analysis, classification and comparison of scheduling techniques for software transactional memories
Transactional Memory (TM) is a practical programming paradigm for developing concurrent applications. Performance is a critical factor for TM implementations, and various studies demonstrated that specialised transaction/thread scheduling support is essential for implementing performance-effective TM systems. After one decade of research, this article reviews the wide variety of scheduling techniques proposed for Software Transactional Memories. Based on peculiarities and differences of the adopted scheduling strategies, we propose a classification of the existing techniques, and we discuss the specific characteristics of each technique. Also, we analyse the results of previous evaluation and comparison studies, and we present the results of a new experimental study encompassing techniques based on different scheduling strategies. Finally, we identify potential strengths and weaknesses of the different techniques, as well as the issues that require to be further investigated
A non-hydrodynamical model for acceleration of line-driven winds in Active Galactic Nuclei
We present a study of the acceleration phase of line-driven winds in AGNs, in
order to examine the physical conditions for the existence of such winds for a
wide variety of initial conditions. We built a simple and fast non-hydrodynamic
model, QWIND, where we assume that a wind is launched from the accretion disc
at supersonic velocities of the order of a few 10^2 km/s and we concentrate on
the subsequent supersonic phase. We show that this model can produce a wind
with terminal velocities of the order of 10^4 km/s. There are three zones in
the wind, only the middle one of which can launch a wind: in the inner zone the
wind is too ionized and so experiences only the Compton radiation force which
is not effective in accelerating gas. This inner failed wind however plays an
important role in shielding the next zone, lowering the ionization parameter
there. In the middle zone the lower ionization of the gas leads to a much
larger radiation force and the gas achieves escape velocity This middle zone is
quite thin (about 100 gravitational radii). The outer, third, zone is shielded
from the UV radiation by the central wind zone and so does not achieve a high
enough acceleration to reach escape velocity. We also describe a simple
analytic approximation of our model, based on neglecting the effects of gravity
during the acceleration phase. This analytic approach is in agreement with the
results of the numerical code, and is a powerful way to check whether a
radiation driven wind can be accelerated with a given set of initial
parameters. Our analytical analysis and the fast QWIND model are in agreement
with more complex hydrodynamical models, and allow an exploration of the
dependence of the wind properties for a wide set of initial parameters: black
hole mass, Eddington ratio, initial density profile, X-ray to UV ratio.Comment: 15 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysic
Warp-X: a new exascale computing platform for beam-plasma simulations
Turning the current experimental plasma accelerator state-of-the-art from a
promising technology into mainstream scientific tools depends critically on
high-performance, high-fidelity modeling of complex processes that develop over
a wide range of space and time scales. As part of the U.S. Department of
Energy's Exascale Computing Project, a team from Lawrence Berkeley National
Laboratory, in collaboration with teams from SLAC National Accelerator
Laboratory and Lawrence Livermore National Laboratory, is developing a new
plasma accelerator simulation tool that will harness the power of future
exascale supercomputers for high-performance modeling of plasma accelerators.
We present the various components of the codes such as the new Particle-In-Cell
Scalable Application Resource (PICSAR) and the redesigned adaptive mesh
refinement library AMReX, which are combined with redesigned elements of the
Warp code, in the new WarpX software. The code structure, status, early
examples of applications and plans are discussed
On the diversity and complexity of absorption line profiles produced by outflows in Active Galactic Nuclei
Understanding the origin of AGN absorption line profiles and their diversity
could help to explain the physical structure of the accretion flow, and also to
assess the impact of accretion on the evolution of the AGN host galaxies. Here
we present our first attempt to systematically address the issue of the origin
of the complexities observed in absorption profiles. Using a simple method, we
compute absorption line profiles against a continuum point source for several
simulations of accretion disk winds. We investigate the geometrical,
ionization, and dynamical effects on the absorption line shapes. We find that
significant complexity and diversity of the absorption line profile shapes can
be produced by the non-monotonic distribution of the wind velocity, density,
and ionization state. Non-monotonic distributions of such quantities are
present even in steady-state, smooth disk winds, and naturally lead to the
formation of multiple and detached absorption troughs. These results
demonstrate that the part of a wind where an absorption line is formed is not
representative of the entire wind. Thus, the information contained in the
absorption line is incomplete if not even insufficient to well estimate gross
properties of the wind such as the total mass and energy fluxes. In addition,
the highly dynamical nature of certain portions of disk winds can have
important effects on the estimates of the wind properties. For example, the
mass outflow rates can be off up to two orders of magnitude with respect to
estimates based on a spherically symmetric, homogeneous, constant velocity
wind.Comment: 10 pages, 10 figures, to appear in Ap
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