An efficient parallel tree-code for the simulation of self-gravitating systems

We describe a parallel version of our tree-code for the simulation of self-gravitating systems in Astrophysics. It is based on a dynamic and adaptive method for the domain decomposition, which exploits the hierarchical data arrangement used by the tree-code. It shows low computational costs for the parallelization overhead -- less than 4% of the total CPU-time in the tests done -- because the domain decomposition is performed 'on the fly' during the tree setting and the portion of the tree that is local to each processor 'enriches' itself of remote data only when they are actually needed. The performances of an implementation of the parallel code on a Cray T3E are presented and discussed. They exhibit a very good behaviour of the speedup (=15 with 16 processors and 10^5 particles) and a rather low load unbalancing (< 10% using up to 16 processors), achieving a high computation speed in the forces evaluation (>10^4 particles/sec with 8 processors).Comment: 10 pages, 8 figures, LaTeX2e, A&A class file needed (included), submitted to A&A; corrected abstract word wrappin

Parallelization of a Code for the Simulation of Self-gravitating Systems in Astrophysics. Preliminary Speed-up Results

We have preliminary results on the parallelization of a Tree-Code for evaluating gravitational forces in N-body astrophysical systems. For our Cray T3D/CRAFT implementation, we have obtained an encouraging speed-up behavior, which reaches a value of 37 with 64 processor elements (PEs). According to the Amdahl'law, this means that about 99% of the code is actually parallelized. The speed-up tests regarded the evaluation of the forces among N = 130,369 particles distributed scaling the actual distribution of a sample of galaxies seen in the Northern sky hemisphere. Parallelization of the time integration of the trajectories, which has not yet been taken into account, is both easier to implement and not as fundamental.Comment: 14 pages LaTeX + 1 EPS figure + 2 EPS colour figures, epsf.sty and aasms4.sty included; to be published in Science & Supercomputing at CINECA, Report 1997 (Bologna, Italy

Food and locality. Heritagization and commercial use of past

This paper reconstructs the birth and first development of food narratives build around the relationship between food and territory. These developed firstly in France between the 18th and 19th century becoming common throughout Europe since the early 20th century. Focussing on the Italian case within the European context, the paper highlights three main points: the ethnocentric character of the classification of regional cuisines during Fascism; the role of marketing in \u201cinventing\u201d territorial food identities; and the \u201cnostalgic turn\u201d in the commercial promotion of \u201cgenuine\u201d foods. In its final remarks the paper asks for a deconstruction of any essentialisation of the food/territory relationship

Merging of globular clusters within inner galactic regions. II. The Nuclear Star Cluster formation

In this paper we present the results of two detailed N-body simulations of the interaction of a sample of four massive globular clusters in the inner region of a triaxial galaxy. A full merging of the clusters takes place, leading to a slowly evolving cluster which is quite similar to observed Nuclear Clusters. Actually, both the density and the velocity dispersion profiles match qualitatively, and quantitatively after scaling, with observed features of many nucleated galaxies. In the case of dense initial clusters, the merger remnant shows a density profile more concentrated than that of the progenitors, with a central density higher than the sum of the central progenitors central densities. These findings support the idea that a massive Nuclear Cluster may have formed in early phases of the mother galaxy evolution and lead to the formation of a nucleus, which, in many galaxies, has indeed a luminosity profile similar to that of an extended King model. A correlation with galactic nuclear activity is suggested.Comment: 18 pages, 10 figures, 3 tables. Submitted to ApJ, main journa