225 research outputs found
NBSymple, a double parallel, symplectic N-body code running on graphic processing units
No full textWe present and discuss the characteristics and performance, both in term of computational speed and precision, of a numerical code which integrates the equation of motions of N 'particles' interacting via Newtonian gravitation and move in an external galactic smooth field. The force evaluation on every particle is done by mean of direct summation of the contribution of all the other system's particles, avoiding truncation error. The time integration is done with second-order and sixth-order symplectic schemes. The code, NBSymple, has been parallelized twice, by mean of the Compute Unified Device Architecture (CUDA) to make the all-pair force evaluation as fast as possible on high-performance Graphic Processing Units NVIDIA TESLA C1060, while the O(N) computations are distributed on various CPUs by mean of OpenMP Application Program. The code works both in single-precision floating point arithmetics or in double precision. The use of single-precision allows the use of the GPU performance at best but, of course, limits the precision of simulation in some critical situations. We find a good compromise in using a software reconstruction of double-precision for those variables that are most critical for the overall precision of the code. The code is available on the web site astrowww.phys.uniroma1.it/dolcetta/nbsymple.html. © 2010 Elsevier B.V. All rights reserved
An instability in triaxial stellar systems
No full textThe radial-orbit instability is a collective phenomenon that has heretofore only been observed in spherical systems. We find that this instability occurs also in triaxial systems, as we checked by performing extensive N-body simulations whose initial conditions were obtained by sampling a self-consistent triaxial model of a cuspy galaxy composed of luminous and dark matter (Capuzzo-Dolcetta et al. 2007). N-body simulations show a time evolution of the galaxy that is not due to the development of chaotic motions but, rather, to the collective instability induced by an excess of radially biased (box) orbits. The instability quickly transforms such model into a more prolate configuration, with 0.64 < b/a < 0.77 and 0.6 < c/a < 0.7 for the dark halo and 0.64 < b/a < 0.77 and 0.59 < c/a < 0.67 for the luminous matter. Stable triaxial, cuspy galaxies with dark matter halo are obtained when the mass contribution of radially biased orbits to the solution is reduced. These results constitute the first evidence of radial orbit instability in triaxial stellar systems. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA
Evolutionary population synthesis and the Magellanic Clouds clusters
No full textSynthetic bolometric luminosities and U, B, V fluxes are computed for models of globular clusters using available stellar evolutionary tracks for two chemical compositions and for a large interval of age. The author presents some results and considerations relative to the study of some characteristics of the Magellanic Clouds globular clusters
Self-gravitating disks in binary systems: an SPH approach. I. Implementation of the code and reliability tests
No full textThe study of the stability of massive gaseous disks around a star in a nonisolated context is a difficult task and becomes even more complicated for disks that are hosted by binary systems. The role of self-gravity is thought to be significant when the ratio of the disk-to-star mass is non-negligible. To solve these problems, we implemented, tested, and applied our own smoothed particle hydrodynamics (SPH) algorithm. The code (named GaSPH) passed various quality tests and shows good performances, and it can therefore be reliably applied to the study of disks around stars when self-gravity needs to be accounted for. We here introduce and describe the algorithm, including some performance and stability tests. This paper is the first part of a series of studies in which self-gravitating disks in binary systems are let evolve in larger environments such as open clusters
A fully parallel, high precision, N-body code running on hybrid computing platforms
No full textWe present a new implementation of the numerical integration of the classical, gravitational, N-body problem based on a high order Hermite's integration scheme with block time steps, with a direct evaluation of the particle-particle forces. The main innovation of this code (called HiGPUs) is its full parallelization, exploiting both OpenMP and MPI in the use of the multicore Central Processing Units as well as either Compute Unified Device Architecture (CUDA) or OpenCL for the hosted Graphic Processing Units. We tested both performance and accuracy of the code using up to 256 GPUs in the supercomputer IBM iDataPlex DX360M3 Linux Infiniband Cluster provided by the Italian supercomputing consortium CINECA, for values of N <= 8 millions. We were able to follow the evolution of a system of 8 million bodies for few crossing times, task previously unreached by direct summation codes. (c) 2012 Elsevier Inc. All rights reserved
A Counterpart to the Radial Orbit Instability in Triaxial Stellar Systems
No full textSelf-consistent solutions for triaxial mass models are highly non-unique. In general, some of these solutions might be dynamically unstable, making them inappropriate as descriptions of steady-state galaxies. Here we demonstrate for the first time the existence in triaxial galaxy models of an instability similar to the radial-orbit instability of spherical models. The instability manifests itself when the number of box orbits, with predominantly radially motions, is sufficiently large. N-body simulations verify that the evolution is due neither to chaotic orbits nor to departures of the model from selfconsistency, but rather to a collective mode. The instability transforms the triaxial model into a more prolate, but still triaxial, configuration. Stable triaxial models are obtained when the mass contribution of radial orbits is reduced. The implications of our results for the shapes of dark-matter halos are discussed
Consequences of triaxiality for gravitational wave recoil of black holes
No full textCoalescing binary black holes experience a "kick" due to anisotropic emission of gravitational waves with an amplitude as great as ∼200 km s -1. We examine the orbital evolution of black holes that have been kicked from the centers of triaxial galaxies. Timescales for orbital decay are generally longer in triaxial galaxies than in equivalent spherical galaxies, since a kicked black hole does not return directly through the dense center where the dynamical friction force is highest. We evaluate this effect by constructing self-consistent triaxial models and integrating the trajectories of massive particles after they are ejected from the center; the dynamical friction force is computed directly from the velocity dispersion tensor of the self-consistent model. We find return times that are several times longer than in a spherical galaxy with the same radial density profile, particularly in galaxy models with dense centers, implying a substantially greater probability of finding an off-center black hole. © 2007. The American Astronomical Society. All rights reserved
Self-consistent Models of Cuspy Triaxial Galaxies with Dark Matter Halos
No full textWe have constructed realistic, self-consistent models of triaxial elliptical galaxies embedded in triaxial dark matter halos. We examined three different models for the shape of the dark matter halo: (1) with the same axis ratios as the luminous matter (0.7:0.86:1), (2) with a more prolate shape (0.5:0.66:1), and (3) with a more oblate shape (0.7:0.93:1). Self-consistent solutions by means of the standard orbital superposition technique introduced by Schwarzschild were found in each of the three cases. The equilibrium velocity distribution is reproduced by a Lorentzian function better than by a Gaussian. Chaotic orbits were found to be important in all of the models, and their presence was shown to imply a possible slow evolution of the shapes of the halos. Our results demonstrate for the first time that triaxial dark matter halos can coexist with triaxial galaxies
Use of mammalian target of rapamycin inhibitor for treating pathologies including neurodegenerative diseases (Alzheimer's disease), neuroinflammatory diseases and tumor diseases with neurological involvement, by intrathecal administration
No full textThe invention relates to the use of inhibitors of the enzyme mTOR kinase (mammalian target of rapamycin) in the treatment of neuro-oncologic diseases, in particular tuberous sclerosis, neurodegenerative diseases, in particular Alzheimer's disease, and neuroinflammatory diseases, in particular multiple sclerosis and primary progressive aphasia, via intrathecal, or preferably intraventricular, administration of said inhibitors
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