61 research outputs found
Dynamics in Young Star Clusters: From Planets to Massive Stars
The young star clusters we observe today are the building blocks of a new
generation of stars and planets in our Galaxy and beyond. Despite their
fundamental role we still lack knowledge about the conditions under which star
clusters form and the impact of these often harsh environments on the evolution
of their stellar and substellar members. We demonstrate the vital role
numerical simulations play to uncover both key issues. Using dynamical models
of different star cluster environments we show the variety of effects stellar
interactions potentially have. Moreover, our significantly improved measure of
mass segregation reveals that it can occur rapidly even for star clusters
without substructure. This finding is a critical step to resolve the
controversial debate on mass segregation in young star clusters and provides
strong constraints on their initial conditions.Comment: 8 pages, 4 figures; to appear in the proceedings of "Stellar Clusters
and Associations - A RIA workshop on Gaia", 23-27 May 2011, Granada, Spai
Posttraumatische Störungen bei Patienten mit Erkrankungen aus dem schizophrenen Formenkreis
Background
The findings of international studies suggest high rates of interpersonal violence and posttraumatic stress disorder (PTSD) among patients with schizophrenia spectrum disorders. Only few studies, however, have so far been conducted in the German-speaking countries.
Objectives
The aim of our study was to determine the prevalence of lifetime experiences of interpersonal violence and comorbid PTSD among inpatients in a German university hospital.
Method
In N = 145 consecutively admitted patients with schizophrenia spectrum disorders (67 % male) the structured trauma interview (STI) was used to assess experiences of interpersonal violence and the structured clinical interview for DSM-IV (SCID) to assess comorbid PTSD.
Results
Sexual violence under the age of 16 years was reported by 17 % of the patients (women 27 %, men 12 %). Approximately one third (32 %) reported physical violence by parental figures (women 38 %, men 29 %). At least one form of early violence (sexual or physical) was reported by half of the women (48 %) and one third of the men (34 %). Negative sexual experiences later in life were reported by 17 %, physical violence by 38 % and at least one of these forms by 48 % of the patients. In total two thirds of all patients (66 %) reported experiences of violence during their lifetime. The prevalence of acute PTSD was 12 %. Another 9 % of patients had a subsyndromal PTSD.
Conclusion
The present study confirmed the high rates of experiences of interpersonal violence and comorbid PTSD in a German sample of patients with schizophrenia spectrum disorders. Violence and it’s consequences should therefore be routinely assessed and the full spectrum of trauma-specific therapies should be integrated into the treatment of this group of patients
Parallelization, Special Hardware and Post-Newtonian Dynamics in Direct N - Body Simulations
The formation and evolution of supermassive black hole (SMBH) binaries during and after galaxy mergers is an important ingredient for our understanding of galaxy formation and evolution in a cosmological context, e.g. for predictions of cosmic star formation histories or of SMBH demographics (to predict events that emit gravitational waves). If galaxies merge in the course of their evolution, there should be either many binary or even multiple black holes, or we have to find out what happens to black hole multiples in galactic nuclei, e.g. whether they come sufficiently close to merge resulting from emission of gravitational waves, or whether they eject each other in gravitational slingshot interactions
EvoL: The new Padova T-SPH parallel code for cosmological simulations - I. Basic code: gravity and hydrodynamics
We present EvoL, the new release of the Padova N-body code for cosmological
simulations of galaxy formation and evolution. In this paper, the basic Tree +
SPH code is presented and analysed, together with an overview on the software
architectures. EvoL is a flexible parallel Fortran95 code, specifically
designed for simulations of cosmological structure formation on cluster,
galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive
code, based on the classical Oct-tree and on the Smoothed Particle
Hydrodynamics algorithm. It includes special features such as adaptive
softening lengths with correcting extra-terms, and modern formulations of SPH
and artificial viscosity. It is designed to be run in parallel on multiple CPUs
to optimize the performance and save computational time. We describe the code
in detail, and present the results of a number of standard hydrodynamical
tests.Comment: 33 pages, 49 figures, accepted on A&
Quantified HI Morphology III: Merger Visibility Times from HI in Galaxy Simulations
Major mergers of disk galaxies are thought to be a substantial driver in
galaxy evolution. To trace the fraction and the rate galaxies are in mergers
over cosmic times, several observational techniques, including morphological
selection criteria, have been developed over the last decade. We apply this
morphological selection of mergers to 21 cm radio emission line (HI) column
density images of spiral galaxies in nearby surveys. In this paper, we
investigate how long a 1:1 merger is visible in HI from N-body simulations. We
evaluate the merger visibility times for selection criteria based on four
parameters: Concentration, Asymmetry, M20, and the Gini parameter of second
order moment of the flux distribution (GM). Of three selection criteria used in
the literature, one based on Concentration and M20 works well for the HI
perspective with a merger time scale of 0.4 Gyr. Of the three selection
criteria defined in our previous paper, the GM performs well and cleanly
selects mergers for 0.69 Gyr. The other two criteria (A-M20 and C-M20), select
isolated disks as well, but perform best for face-on, gas-rich disks (T(merger)
~ 1 Gyr). The different visibility scales can be combined with the selected
fractions of galaxies in any large HI survey to obtain merger rates in the
nearby Universe. All-sky surveys such as WALLABY with ASKAP and the Medium Deep
Survey with the APETIF instrument on Westerbork are set to revolutionize our
perspective on neutral hydrogen and will provide an accurate measure of the
merger fraction and rate of the present epoch.Comment: 12 pages, 6 figures, 4 tables, accepted by MNRAS, appendix not
include
A pilgrimage to gravity on GPUs
In this short review we present the developments over the last 5 decades that
have led to the use of Graphics Processing Units (GPUs) for astrophysical
simulations. Since the introduction of NVIDIA's Compute Unified Device
Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body
simulations and is so popular these days that almost all papers about high
precision N-body simulations use methods that are accelerated by GPUs. With the
GPU hardware becoming more advanced and being used for more advanced algorithms
like gravitational tree-codes we see a bright future for GPU like hardware in
computational astrophysics.Comment: To appear in: European Physical Journal "Special Topics" : "Computer
Simulations on Graphics Processing Units" . 18 pages, 8 figure
MaGICC baryon cycle: the enrichment history of simulated disc galaxies
Using cosmological galaxy formation simulations from the MaGICC (Making Galaxies in a Cosmological Context) project, spanning stellar mass from ∼107 to 3 × 1010 M⊙, we trace the baryonic cycle of infalling gas from the virial radius through to its eventual participation in the star formation process. An emphasis is placed upon the temporal history of chemical enrichment during its passage through the corona and circumgalactic medium. We derive the distributions of time between gas crossing the virial radius and being accreted to the star-forming region (which allows for mixing within the corona), as well as the time between gas being accreted to the star-forming region and then ultimately forming stars (which allows for mixing within the disc). Significant numbers of stars are formed from gas that cycles back through the hot halo after first accreting to the star-forming region. Gas entering high-mass galaxies is pre-enriched in low-mass proto-galaxies prior to entering the virial radius of the central progenitor, with only small amounts of primordial gas accreted, even at high redshift (z ∼ 5). After entering the virial radius, significant further enrichment occurs prior to the accretion of the gas to the star-forming region, with gas that is feeding the star-forming region surpassing 0.1 Z⊙ by z = 0. Mixing with halo gas, itself enriched via galactic fountains, is thus crucial in determining the metallicity at which gas is accreted to the disc. The lowest mass simulated galaxy (Mvir ∼ 2 × 1010 M⊙, with M⋆ ∼ 107 M⊙), by contrast, accretes primordial gas through the virial radius and on to the disc, throughout its history. Much like the case for classical analytical solutions to the so-called ‘G-dwarf problem’, overproduction of low-metallicity stars is ameliorated by the interplay between the time of accretion on to the disc and the subsequent involvement in star formation – i.e. due to the inefficiency of star formation. Finally, gas outflow/metal removal rates from star-forming regions as a function of galactic mass are presented
N-body simulations of gravitational dynamics
We describe the astrophysical and numerical basis of N-body simulations, both
of collisional stellar systems (dense star clusters and galactic centres) and
collisionless stellar dynamics (galaxies and large-scale structure). We explain
and discuss the state-of-the-art algorithms used for these quite different
regimes, attempt to give a fair critique, and point out possible directions of
future improvement and development. We briefly touch upon the history of N-body
simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu
Antimicrobial effects of pulsed electromagnetic fields from commercially available water treatment devices – controlled studies under static and flow conditions
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