oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2018 ( 1 )

2015 ( 18 )

2014 ( 31 )

2013 ( 42 )

Custom range...

Search Results: 1 - 10 of 530 matches for " Piet Hut "
All listed articles are free for downloading (OA Articles)
Page 1 /530
Display every page Item
Stellar Dynamics of Dense Stellar Systems
Piet Hut
Physics , 1998,
Abstract: Stellar dynamics is almost unreasonably well suited for an implementation in terms of special-purpose hardware. Unlike the case of molecular dynamics, stellar dynamics deals exclusively with a long-range force, gravity, which leads to a computational cost scaling as the square of the number of stars involved. While special tricks can lead to a reduction of this cost from $\sim N^2$ to $\sim N\log N$ in the case of very large particle numbers, such tricks are not suitable for all areas within stellar dynamics. When a stellar system is close to equilibrium, and has a very high density, it still pays to compute all interactions on a star by star basis, even for $N=10^5$. Any $cN\log N$ approach would either gloss over the subtle net effects of near-canceling interactions, driving the evolution of such a system, or would carry a prohibitively large coefficient $c$. This paper presents a brief introduction to the stellar dynamics of dense stellar systems, aimed at researchers using special purpose computers in other branches of physics.
Virtual Laboratories and Virtual Worlds
Piet Hut
Physics , 2007, DOI: 10.1017/S1743921308016153
Abstract: Since we cannot put stars in a laboratory, astrophysicists had to wait till the invention of computers before becoming laboratory scientists. For half a century now, we have been conducting experiments in our virtual laboratories. However, we ourselves have remained behind the keyboard, with the screen of the monitor separating us from the world we are simulating. Recently, 3D on-line technology, developed first for games but now deployed in virtual worlds like Second Life, is beginning to make it possible for astrophysicists to enter their virtual labs themselves, in virtual form as avatars. This has several advantages, from new possibilities to explore the results of the simulations to a shared presence in a virtual lab with remote collaborators on different continents. I will report my experiences with the use of Qwaq Forums, a virtual world developed by a new company (see http://www.qwaq.com)
Blue Stragglers as Tracers of Globular Cluster Evolution
Piet Hut
Physics , 1993,
Abstract: Blue stragglers are natural phenomena in star clusters. They originate through mass transfer in isolated binaries, as well as through encounters between two or more stars, in a complex interplay between stellar dynamics and stellar evolution. While this interplay cannot be modeled quantitatively at present, we will be able to do so in one or two years time. With this prospect, the present paper is written largely as a preview.
The Role of Binaries in the Dynamical Evolution of Globular Clusters
Piet Hut
Physics , 1996,
Abstract: Three important developments are vastly increasing our understanding of the role of binaries in the dynamical evolution of globular clusters. From the observational side, the Hubble Space Telescope has shown us detailed pictures of the densest areas in post-collapse cluster cores. From the computational side, the Grape-4 special-purpose hardware is now allowing us to model small globular clusters on a star-by-star basis, and has already given us the first direct evidence of the occurrence of gravothermal oscillations in such systems. From the theoretical astrophysics side, integrated simulations are now becoming feasible that combine stellar dynamics with stellar evolution and hydrodynamics. Given these three developments, we can expect the current rapid progress in our understanding of globular cluster evolution to continue at an even higher rate during the foreseeable future. In this review an outline is given of the current status of globular cluster simulations, and the expected progress over the next five years.
The Role of Binaries in the Dynamical Evolution of the Core of a Globular Cluster
Piet Hut
Physics , 1996,
Abstract: The size of the core is one of the main diagnostics of the evolutionary state of a globular cluster. Much has been learned over the last few years about the behavior of the core radius during and after core collapse, under a variety of different conditions related to the presence or absence of large numbers of binaries. An overview is presented of the basic physical principles that can be used to estimate the core radius. Four different situations are discussed, and expressions are presented for the ratio $r_c/r_h$ of core radius to half mass radius. The regimes are: deep collapse in the absence of primordial binaries; steady post-collapse evolution after primordial binaries have been burned up; chaotic post-collapse evolution under the same conditions; and post-collapse evolution in the presence of primordial binaries. In addition, modifications to all of these cases are indicated for the more realistic situation where effects of the galactic tidal field are taken into account.
The Starlab Environment for Dense Stellar Systems
Piet Hut
Physics , 2002,
Abstract: Traditionally, a simulation of a dense stellar system required choosing an initial model, running an integrator, and analyzing the output. Almost all of the effort went into writing a clever integrator that could handle binaries, triples and encounters between various multiple systems efficiently. Recently, the scope and complexity of these simulations has increased dramatically, for three reasons: 1) the sheer size of the data sets, measured in Terabytes, make traditional `awking and grepping' of a single output file impractical; 2) the addition of stellar evolution data brings qualitatively new challenges to the data reduction; 3) increased realism of the simulations invites realistic forms of `SOS': Simulations of Observations of Simulations, to be compared directly with observations. We are now witnessing a shift toward the construction of archives as well as tailored forms of visualization including the use of virtual reality simulators and planetarium domes, and a coupling of both with budding efforts in constructing virtual observatories. This review describes these new trends, presenting Starlab as the first example of a full software environment for realistic large-scale simulations of dense stellar systems.
The GRAPE-4, a Teraflops Stellar Dynamics Computer
Piet Hut
Physics , 1997,
Abstract: Recently, special-purpose computers have surpassed general-purpose computers in the speed with which large-scale stellar dynamics simulations can be performed. Speeds up to a Teraflops are now available, for simulations in a variety of fields, such as planetary formation, star cluster dynamics, galactic nuclei, galaxy interactions, galaxy formation, large scale structure, and gravitational lensing. Future speed increases for special-purpose computers will be even more dramatic: a Petaflops version, tentatively named the GRAPE-6, could be built within a few years, whereas general-purpose computers are expected to reach this speed somewhere in the 2010-2015 time frame. Boards with a handful of chips from such a machine could be made available to individual astronomers. Such a board, attached to a fast workstation, will then deliver Teraflops speeds on a desktop, around the year 2000.
Gravitational Thermodynamics
Piet Hut
Physics , 1997,
Abstract: The gravitational N-body problem, for $N>2$, is the oldest unsolved problem in mathematical physics. Some of the most ideal examples that can be found in nature are globular star clusters, with $N \sim 10^6$. In this overview, I discuss six types of fundamental sources of unpredictability, each of which poses a different challenge to attempts to determine the long-term behavior of these systems, governed by a peculiar type of thermodynamics.
Virtual Laboratories
Piet Hut
Physics , 2006, DOI: 10.1143/PTPS.164.38
Abstract: At the frontier of most areas in science, computer simulations play a central role. The traditional division of natural science into experimental and theoretical investigations is now completely outdated. Instead, theory, simulation, and experimentation form three equally essential aspects, each with its own unique flavor and challenges. Yet, education in computational science is still lagging far behind, and the number of text books in this area is minuscule compared to the many text books on theoretical and experimental science. As a result, many researchers still carry out simulations in a haphazard way, without properly setting up the computational equivalent of a well equipped laboratory. The art of creating such a virtual laboratory, while providing proper extensibility and documentation, is still in its infancy. A new approach is described here, Open Knowledge, as an extension of the notion of Open Source software. Besides open source code, manuals, and primers, an open knowledge project provides simulated dialogues between code developers, thus sharing not only the code, but also the motivations behind the code.
Dense Stellar Systems as Laboratories for Fundamental Physics
Piet Hut
Physics , 2006,
Abstract: Galactic nuclei and globular clusters act as laboratories in which nature experiments with normal stars, neutron stars and black holes, through collisions and through the formation of bound states, in the form of binaries. The main difference with the usual Earth-based laboratories is that we cannot control the experiments. Instead, we have no choice but to create virtual laboratories on Earth, in order to simulate all the relevant physics in large-scale computational experiments. This implies a realistic treatment of stellar dynamics, stellar evolution, and stellar hydrodynamics. Each of these three fields has its own legacy codes, workhorses that are routinely used to simulate star clusters, stars, and stellar collisions, respectively. I outline the main steps that need to be taken in order to embed and where needed transform these legacy codes in order to produce a far more modular and robust environment for modeling dense stellar systems. The time is right to do so: within a few years computers will reach the required speed, in the Petaflops range, to follow a star cluster with a million stars for ten billion years, while resolving the internal binary and multiple star motions. By that time simulation software will be the main bottleneck in our ability to analyze dense stellar systems. Only through full-scale simulations will we be able to critically test our understanding of the `microphysics' of stellar collisions and their aftermath, in a direct comparison with observations.
Page 1 /530
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.