The radial structure of galaxy groups and clusters

Simple self-consistent models of galaxy groups and clusters are tested against the results of high-resolution adiabatic gasdynamical simulations. We investigate two models based on the existence of a 'universal' dark matter density profile and two versions of the beta-model. The mass distribution of relaxed clusters can be fitted by phenomenological formulae proposed in the literature. Haloes that have experienced a recent merging event are systematically less concentrated and show steeper profiles than relaxed objects near the centre. The hot X-ray emitting gas is found to be in approximate hydrostatic equilibrium with the dark matter potential, and it is well described by a polytropic equation of state. Analytic formulae for the gas density and temperature can be derived from these premises. Though able to reproduce the X-ray surface brightness, the beta-model is shown to provide a poor description of our numerical clusters. We find strong evidence of a 'universal' temperature profile that decreases by a factor of 2-3 from the centre to the virial radius, whereas baryon fraction and entropy are monotonically increasing functions. Numerical resolution and entropy conservation play a key role in the shapes of the profiles at small radii.Comment: 16 pages, 19 figures, minor changes to match published versio

Proceedings of the ECSCW'95 Workshop on the Role of Version Control in CSCW Applications

The workshop entitled "The Role of Version Control in Computer Supported Cooperative Work Applications" was held on September 10, 1995 in Stockholm, Sweden in conjunction with the ECSCW'95 conference. Version control, the ability to manage relationships between successive instances of artifacts, organize those instances into meaningful structures, and support navigation and other operations on those structures, is an important problem in CSCW applications. It has long been recognized as a critical issue for inherently cooperative tasks such as software engineering, technical documentation, and authoring. The primary challenge for versioning in these areas is to support opportunistic, open-ended design processes requiring the preservation of historical perspectives in the design process, the reuse of previous designs, and the exploitation of alternative designs. The primary goal of this workshop was to bring together a diverse group of individuals interested in examining the role of versioning in Computer Supported Cooperative Work. Participation was encouraged from members of the research community currently investigating the versioning process in CSCW as well as application designers and developers who are familiar with the real-world requirements for versioning in CSCW. Both groups were represented at the workshop resulting in an exchange of ideas and information that helped to familiarize developers with the most recent research results in the area, and to provide researchers with an updated view of the needs and challenges faced by application developers. In preparing for this workshop, the organizers were able to build upon the results of their previous one entitled "The Workshop on Versioning in Hypertext" held in conjunction with the ECHT'94 conference. The following section of this report contains a summary in which the workshop organizers report the major results of the workshop. The summary is followed by a section that contains the position papers that were accepted to the workshop. The position papers provide more detailed information describing recent research efforts of the workshop participants as well as current challenges that are being encountered in the development of CSCW applications. A list of workshop participants is provided at the end of the report. The organizers would like to thank all of the participants for their contributions which were, of course, vital to the success of the workshop. We would also like to thank the ECSCW'95 conference organizers for providing a forum in which this workshop was possible

MCPLOTS: a particle physics resource based on volunteer computing

The mcplots.cern.ch web site (MCPLOTS) provides a simple online repository of plots made with high-energy-physics event generators, comparing them to a wide variety of experimental data. The repository is based on the HEPDATA online database of experimental results and on the RIVET Monte Carlo analysis tool. The repository is continually updated and relies on computing power donated by volunteers, via the LHC@HOME platform.Comment: 30 page

The influence of the distribution of cosmic star formation at different metallicities on the properties of merging double compact objects

Binaries that merge within the local Universe originate from progenitor systems that formed at different times and in various environments. The efficiency of formation of double compact objects is highly sensitive to metallicity of the star formation. Therefore, to confront the theoretical predictions with observational limits resulting from gravitational waves observations one has to account for the formation and evolution of progenitor stars in the chemically evolving Universe. In particular, this requires knowledge of the distribution of cosmic star formation rate at different metallicities and times, probed by redshift (SFR(Z,z)). We investigate the effect of the assumed SFR(Z,z) on the properties of merging double compact objects, in particular on their merger rate densities. Using a set of binary evolution models from Chruslinska et al. (2018) we demonstrate that the reported tension between the merger rates of different types of double compact objects and current observational limits in some cases can be resolved if a SFR(Z,z) closer to that expected based on observations of local star-forming galaxies is used, without the need for changing the assumptions about the evolution of progenitor stars of different masses. This highlights the importance of finding tighter constraints on SFR(Z,z) and understanding the associated uncertainties.Comment: 6 pages, 4 figures, resubmitted to MNRAS after minor revisio