12 research outputs found
SAPPORO: A way to turn your graphics cards into a GRAPE-6
We present Sapporo, a library for performing high-precision gravitational
N-body simulations on NVIDIA Graphical Processing Units (GPUs). Our library
mimics the GRAPE-6 library, and N-body codes currently running on GRAPE-6 can
switch to Sapporo by a simple relinking of the library. The precision of our
library is comparable to that of GRAPE-6, even though internally the GPU
hardware is limited to single precision arithmetics. This limitation is
effectively overcome by emulating double precision for calculating the distance
between particles. The performance loss of this operation is small (< 20%)
compared to the advantage of being able to run at high precision. We tested the
library using several GRAPE-6-enabled N-body codes, in particular with Starlab
and phiGRAPE. We measured peak performance of 800 Gflop/s for running with 10^6
particles on a PC with four commercial G92 architecture GPUs (two GeForce
9800GX2). As a production test, we simulated a 32k Plummer model with equal
mass stars well beyond core collapse. The simulation took 41 days, during which
the mean performance was 113 Gflop/s. The GPU did not show any problems from
running in a production environment for such an extended period of time.Comment: 13 pages, 9 figures, accepted to New Astronom
A pilgrimage to gravity on GPUs
In this short review we present the developments over the last 5 decades that
have led to the use of Graphics Processing Units (GPUs) for astrophysical
simulations. Since the introduction of NVIDIA's Compute Unified Device
Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body
simulations and is so popular these days that almost all papers about high
precision N-body simulations use methods that are accelerated by GPUs. With the
GPU hardware becoming more advanced and being used for more advanced algorithms
like gravitational tree-codes we see a bright future for GPU like hardware in
computational astrophysics.Comment: To appear in: European Physical Journal "Special Topics" : "Computer
Simulations on Graphics Processing Units" . 18 pages, 8 figure
Exploiting the Parallelism Exposed by Partial Evaluation
We describe the key role played by partial evaluation in the Supercomputing Toolkit, a parallel computing system for scientific applications that effectively exploits the vast amount of parallelism exposed by partial evaluation. The Supercomputing Toolkit parallel processor and its associated partial evaluation-based compiler have been used extensively by scientists at MIT, and have made possible recent results in astrophysics showing that the motion of the planets in our solar system is chaotically unstable
Subclustering and Luminous-Dark Matter Segregation in Galaxy Clusters
We have performed a series of N-body experiments on Connection Machine-5 in
order to simulate the formation of galaxy clusters gravitationally dominated by
a massive dark background. In accordance with previous authors we find an
extremely inhomogeneous evolution where subcondensations are continually formed
and merged. The final distribution of galaxies is more centrally condensed than
that of dark matter particles. We have analyzed the origin of this galaxy-dark
matter segregation and also the origin of subclustering leading to this effect.
We have then analysed, analytically and numerically, the dependence of final
segregation on the physical parameters characterizing the model of
protocluster. We also find that such a segregation persists even when inelastic
encounters of dark halos around galaxies are taken into account. We conclude
that this effect cannot be in general avoided in any hierarchical clustering
scenario.Comment: 26 pages plus 13 figures (4 of which, not included, available upon
request to [email protected]), postscript, Preprint OP-9303
Stability of spherical stellar systems II : Numerical results
We have performed a series of high resolution N-body experiments on a
Connection Machine CM-5 in order to study the stability of collisionless
self-gravitating spherical systems. We interpret our results in the framework
of symplectic mechanics, which provides the definition of a new class of
particular perturbations: The preserving perturbations, which are a
generalization of the radial ones. Using models defined by the Ossipkov-Merritt
algorithm, we show that the stability of a spherical anisotropic system is
directly related to the preserving or non-preserving nature of the
perturbations acting on the system. We then generalize our results to all
spherical systems. Since the ``isotropic component'' of the linear variation of
the distribution function cannot be used to predict the stability or
instability of a spherical system, we propose a more useful stability parameter
which is derived from the ``anisotropic'' component of the linear variation.Comment: uuencoded gzip compressed postscript file containing 14 pages,
accepted for publication in MNRA
A Parallelizing Compiler Based on Partial Evaluation
We constructed a parallelizing compiler that utilizes partial evaluation to achieve efficient parallel object code from very high-level data independent source programs. On several important scientific applications, the compiler attains parallel performance equivalent to or better than the best observed results from the manual restructuring of code. This is the first attempt to capitalize on partial evaluation's ability to expose low-level parallelism. New static scheduling techniques are used to utilize the fine-grained parallelism of the computations. The compiler maps the computation graph resulting from partial evaluation onto the Supercomputer Toolkit, an eight VLIW processor parallel computer
Mapping solar system chaos with the Geological Orrery
The Geological Orrery is a network of geological records of orbitally paced climate designed to address the inherent limitations of solutions for planetary orbits beyond 60 million years ago due to the chaotic nature of Solar System motion. We use results from two scientific coring experiments in Early Mesozoic continental strata: the Newark Basin Coring Project and the Colorado Plateau Coring Project. We precisely and accurately resolve the secular fundamental frequencies of precession of perihelion of the inner planets and Jupiter for the Late Triassic and Early Jurassic epochs (223–199 million years ago) using the lacustrine record of orbital pacing tuned only to one frequency (1/405,000 years) as a geological interferometer. Ex- cepting Jupiter’s, these frequencies differ significantly from present values as determined using three independent techniques yielding practically the same results. Estimates for the precession of perihe- lion of the inner planets are robust, reflecting a zircon U–Pb-based age model and internal checks based on the overdetermined origins of the geologically measured frequencies. Furthermore, although not indicative of a correct solution, one numerical solution closely matches the Geological Orrery, with a very low probability of being due to chance. To determine the secular fundamental frequencies of the precession of the nodes of the planets and the important secular resonances with the precession of perihelion, a contemporaneous high-latitude geological archive recording obliquity pacing of climate is needed. These results form a proof of concept of the Geological Orrery and lay out an empirical framework to map the chaotic evo- lution of the Solar System
Causes and Effects of Chaos
Most of the recent literature on chaos and nonlinear dynamics is written either for popular science magazine readers or for advanced mathematicians. This paper gives a broad introduction to this interesting and rapidly growing field at a level that is between the two. The graphical and analytical tools used in the literature are explained and demonstrated, the rudiments of the current theory are outlined and that theory is discussed in the context of several examples: an electronic circuit, a chemical reaction and a system of satellites in the solar system
Librarians and the emerging research library: A case study of complex individual and organizational development.
The purpose of this case study was to increase the knowledge base of how research librarians experience and cope with the turbulence of change within their library system. This research also examined the issues that surround the organizational structures and leadership of transformative change in one research library. A library belonging to the Association of Research Libraries was selected for case study investigation. Seventeen librarians participated in on-site interviews, utilizing a protocol composed of a clustering technique and semi-structured interviewing. Instrumental case studies of each individual were then developed through a collective case method to present the intrinsic case study of the library system as an organization. Data were analyzed primarily through a complex systems theoretical framework while at the same time were grounded in a broad literature base of organizational, leadership, individual change, and library organizational development theories. The findings of the study include: the competing tensions between the physical and virtual environments, the search for professional meaning, coping with the experiences of professional change, the evolution of the organizational structure, and leadership as a shared experience. Analysis of the findings suggest: the emergence of a hypercritical state, the limiting nature of negative feedback, a complex systems framework for professional thinking, coping in the hypercritical organization, the emergence of disorder in the complex system, the blending of self-organizing systems with structural feedback mechanisms, and the complexity of leadership in the new research library