Chemo-dynamical Evolution of the ISM in Galaxies

Chemo-dynamical models have been introduced in the late eighties and are a generally accepted tool for understanding galaxy evolution. They have been successfully applied to one-dimensional problems, e.g. the evolution of non-rotating galaxies, and two-dimensional problems, e.g. the evolution of disk galaxies. Recently, also three-dimensional chemo-dynamical models have become available. In these models the dynamics of different components, i.e. dark matter, stars and a multi-phase interstellar medium, are treated in a self-consistent way and several processes allow for an exchange of matter, energy and momentum between the components or different gas phases. Some results of chemo-dynamical models and their comparison with observations of chemical abundances or star formation histories will be reviewed.Comment: 10 Pages, 5 Figures, to appear in "From Observations to Self-Consistent Modelling of the ISM in Galaxies", 2003, eds M. Avillez et a

The Evolution and Implications of Entrepreneurship Curriculum at Universities

The notion of entrepreneurship is not a new one. Neither is the idea of entrepreneurship education. However, post-secondary entrepreneurship curriculum has exploded the past thirty five years. A number of reasons have helped to fuel this growth. An argument can be made that entrepreneurs can be made and are not born. Entrepreneurship education is the tool that encourages the transformation process. At the university level, most entrepreneurship curriculum is taught in business schools and colleges. Implications indicate that entrepreneurship education is good not only for students who become entrepreneurs. Entrepreneurship curriculum stimulates creativity and ownership, two traits desired by corporate America

Reconstructing the Arches I: Constraining the Initial Conditions

We have performed a series of N-body simulations to model the Arches cluster. Our aim is to find the best fitting model for the Arches cluster by comparing our simulations with observational data and to constrain the parameters for the initial conditions of the cluster. By neglecting the Galactic potential and stellar evolution, we are able to efficiently search through a large parameter space to determine e.g. the IMF, size, and mass of the cluster. We find, that the cluster's observed present-day mass function can be well explained with an initial Salpeter IMF. The lower mass-limit of the IMF cannot be well constrained from our models. In our best models, the total mass and the virial radius of the cluster are initially (5.1 +/- 0.8) 10^4 Msun and 0.76 +/- 0.12 pc, respectively. The concentration parameter of the initial King model is w0 = 3-5.Comment: 12 pages, 14 Figures, revised and accepted for publication in MNRA

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

Instrumente parlamentarischer Kontrolle der Exekutive in westlichen Demokratien

Der vorliegende Beitrag beschäftigt sich mit der Frage der parlamentarischen Kontrolle der Exekutive in 22 westlichen Demokratien. Ausgehend von der Principal-Agent-Theorie zielt er darauf ab, die Instrumente und Ressourcen zu analysieren, die Parlamenten in westlichen Demokratien zur Kontrolle ihrer Exekutiven zu Verfügung stehen. Zunächst wird erörtert, über welche Mittel Parlamente verfügen, um Informationsungleichgewichte zwischen Parlament und Regierung auszugleichen. Die ständigen Parlamentsausschüsse werden in dieser Diskussion als die wichtigste Ressource zur Erlangung von Informationen und zur Ausübung von Kontrolle gegenüber der Exekutive bezeichnet. Neben den Ausschüssen werden weitere parlamentarische Kontrollstrukturen wie Rechungshöfe und parlamentseigene Informationsdienste sowie Informations- und Fragerechte der Parlamente gegenüber den Exekutiven betrachtet. Nach der theoretischen Diskussion der Kontrollmöglichkeiten werden empirische Informationen präsentiert, die strukturelle, formale und personelle Informationsressourcen der Parlamente charakterisieren. Mithilfe dieser Daten wird versucht, insbesondere die Frage zu beantworten, ob es systematische Zusammenhänge zwischen der politischen Stärke einer Exekutive und den parlamentarischen Ressourcen zur Kontrolle der Exekutive gibt. Ein solcher Zusammenhang kann jedoch nicht gefunden werden. Selbst starke Regierungen sind nicht systematisch in der Lage, die Kontrollfähigkeit ihrer Parlamente zu beeinflussen.This paper deals with the question of parliamentary control of the executives of 22 Western democracies. Based on principal-agent theory, it aims to analyze the instruments of control and the control capacity of parliamentary principals vis-à-vis their governmental agents. In a first step, parliamentary resources are discussed as an important means to bridge the information gap between parliament and the executive. In doing so, the paper focuses on parliamentary committees, their institutional structure, their membership, and their formal powers without neglecting further parliamentary information resources like question times, accounting offices, or scientific and library services. Based on this discussion, data is presented to characterize structural, formal, and personal parliamentary information resources. This presentation is summarized by an empirical mapping of the character and properties of parliamentary control structures in Western democracies. The data is then used to answer questions about systematic relationships between parliamentary control resources and the political strength of the executive. The most important result of this analysis is that there is no systematic relationship between political strength of executives and parliamentary control resources. Even politically strong governments are not able to systematically curtail the control resources of their parliaments

A Hybrid N-Body Code Incorporating Algorithmic Regularization and Post-Newtonian Forces

We describe a novel N-body code designed for simulations of the central regions of galaxies containing massive black holes. The code incorporates Mikkola's 'algorithmic' chain regularization scheme including post-Newtonian terms up to PN2.5 order. Stars moving beyond the chain are advanced using a fourth-order integrator with forces computed on a GRAPE board. Performance tests confirm that the hybrid code achieves better energy conservation, in less elapsed time, than the standard scheme and that it reproduces the orbits of stars tightly bound to the black hole with high precision. The hybrid code is applied to two sample problems: the effect of finite-N gravitational fluctuations on the orbits of the S-stars; and inspiral of an intermediate-mass black hole into the galactic center.Comment: 12 pages, 15 figures, accepted for publication in MNRA

A study of major mergers using a multi-phase ISM code

Galaxy interactions are a common phenomenon in clusters of galaxies. Especially major mergers are of particular importance, because they can change the morphological type of galaxies. They have an impact on the mass function of galaxies and they trigger star formation - the main driver of the Galactic Matter Cycle. Therefore, we conducted a study of major mergers by means of a multi-phase ISM code. This code is based on a TREE-SPH-code combined with a sticky particle method allowing for star formation controlled by the properties of a multi-phase ISM. This is in contrast to the usually implemented Schmidt law depending mainly on the gas density. Previously, this code was used on isolated galaxies. Since our star formation recipe is not restricted to a special type of galaxy, it is interesting to apply it to interacting galaxies, too. Our study on major mergers includes a research of global properties of the interacting system, namely the star formation rate and the star formation efficiency, the evaporation and condensation rates, as well as the mass exchange of distinct components, namely stars, diffuse ISM, and clouds. Investigating these properties provides insight to interrelations between various physical processes. The results indicate that the star formation efficiency as well as the evaporation and condensation rates are influenced by the interaction.Comment: 6 pages, 7 figures, to be published in Astronomische Nachrichten (proceedings of Symposium 6 of the JENAM 2008, Vienna

Calibration of radii and masses of open clusters with a simulation

Context: A recent new approach to apply a simple dynamical mass estimate of tidally limited star clusters is based on the identification of the tidal radius in a King profile with the dynamical Jacobi radius. The application to an unbiased open cluster catalogue yields significantly higher cluster masses compared to the classical methods. Aims: We quantify the bias in the mass determination as function of projection direction and cluster age by analysing a simulated star cluster. Methods: We use direct $N$-body simulations of a star cluster including stellar evolution in an analytic Milky Way potential and apply a best fit to the projected number density of cluster stars. Results: We obtain significantly overestimated star cluster masses which depend strongly on the viewing direction. The overestimation is typically in the range of 10-50 percent and reaches a factor of 3.5 for young clusters. Mass segregation reduces the derived limiting radii systematically.Comment: 9 pages, 10+1 figures, accepted by Astronomy and Astrophysic