A Systematic Look at the Effects of Radiative Feedback on Disc Galaxy Formation

Galaxy formation models and simulations rely on various feedback mechanisms to reproduce the observed baryonic scaling relations and galaxy morphologies. Although dwarf galaxy and giant elliptical properties can be explained using feedback from supernova and active galactic nuclei, Milky Way-sized galaxies still represent a challenge to current theories of galaxy formation. In this paper, we explore the possible role of feedback from stellar radiation in regulating the main properties of disk galaxies such as our own Milky Way. We have performed a suite of cosmological simulations of the same $\sim10^{12} {\rm M}_{\odot}$ halo selected based on its rather typical mass accretion history. We have implemented radiative feedback from young stars using a crude model of radiative transfer for ultraviolet (UV) and infrared (IR) radiation. However, the model is realistic enough such that the dust opacity plays a direct role in regulating the efficiency of our feedback mechanism. We have explored various models for the dust opacity, assuming different constant dust temperatures, as well as a varying dust temperature model. We find that while strong radiative feedback appears as a viable mechanism to regulate the stellar mass fraction in massive galaxies, it also prevents the formation of discs with reasonable morphologies. In models with strong stellar radiation feedback, stellar discs are systematically too thick while the gas disc morphology is completely destroyed due to the efficient mixing between the feedback-affected gas and its surroundings. At the resolution of our simulation suite, we find it impossible to preserve spiral disc morphology while at the same time expelling enough baryons to satisfy the abundance matching constraints.Comment: accepted to MNRA

Modelling Shear Flows with SPH and Grid Based Methods

Given the importance of shear flows for astrophysical gas dynamics, we study the evolution of the Kelvin-Helmholtz instability (KHI) analytically and numerically. We derive the dispersion relation for the two-dimensional KHI including viscous dissipation. The resulting expression for the growth rate is then used to estimate the intrinsic viscosity of four numerical schemes depending on code-specific as well as on physical parameters. Our set of numerical schemes includes the Tree-SPH code VINE, an alternative SPH formulation developed by Price (2008), and the finite-volume grid codes FLASH and PLUTO. In the first part, we explicitly demonstrate the effect of dissipation-inhibiting mechanisms such as the Balsara viscosity on the evolution of the KHI. With VINE, increasing density contrasts lead to a continuously increasing suppression of the KHI (with complete suppression from a contrast of 6:1 or higher). The alternative SPH formulation including an artificial thermal conductivity reproduces the analytically expected growth rates up to a density contrast of 10:1. The second part addresses the shear flow evolution with FLASH and PLUTO. Both codes result in a consistent non-viscous evolution (in the equal as well as in the different density case) in agreement with the analytical prediction. The viscous evolution studied with FLASH shows minor deviations from the analytical prediction.Comment: 16 pages, 17 figure

Operationalizing multimorbidity and autonomy for health services research in aging populations - the OMAHA study

<p>Abstract</p> <p>Background</p> <p>As part of a Berlin-based research consortium on health in old age, the OMAHA (Operationalizing Multimorbidity and Autonomy for Health Services Research in Aging Populations) study aims to develop a conceptual framework and a set of standardized instruments and indicators for continuous monitoring of multimorbidity and associated health care needs in the population 65 years and older.</p> <p>Methods/Design</p> <p>OMAHA is a longitudinal epidemiological study including a comprehensive assessment at baseline and at 12-month follow-up as well as brief intermediate telephone interviews at 6 and 18 months. In order to evaluate different sampling procedures and modes of data collection, the study is conducted in two different population-based samples of men and women aged 65 years and older. A geographically defined sample was recruited from an age and sex stratified random sample from the register of residents in Berlin-Mitte (Berlin OMAHA study cohort, n = 299) for assessment by face-to-face interview and examination. A larger nationwide sample (German OMAHA study cohort, n = 730) was recruited for assessment by telephone interview among participants in previous German Telephone Health Surveys. In both cohorts, we successfully applied a multi-dimensional set of instruments to assess multimorbidity, functional disability in daily life, autonomy, quality of life (QoL), health care services utilization, personal and social resources as well as socio-demographic and biographical context variables. Response rates considerably varied between the Berlin and German OMAHA study cohorts (22.8% vs. 59.7%), whereas completeness of follow-up at month 12 was comparably high in both cohorts (82.9% vs. 81.2%).</p> <p>Discussion</p> <p>The OMAHA study offers a wide spectrum of data concerning health, functioning, social involvement, psychological well-being, and cognitive capacity in community-dwelling older people in Germany. Results from the study will add to methodological and content-specific discourses on human resources for maintaining quality of life and autonomy throughout old age, even in the face of multiple health complaints.</p

SARS-CoV-2 Transmissibility Within Day Care Centers—Study Protocol of a Prospective Analysis of Outbreaks in Germany

Introduction: Until today, the role of children in the transmission dynamics of SARS-CoV-2 and the development of the COVID-19 pandemic seems to be dynamic and is not finally resolved. The primary aim of this study is to investigate the transmission dynamics of SARS-CoV-2 in child day care centers and connected households as well as transmission-related indicators and clinical symptoms among children and adults. Methods and Analysis: COALA (“Corona outbreak-related examinations in day care centers”) is a day care center- and household-based study with a case-ascertained study design. Based on day care centers with at least one reported case of SARS-CoV-2, we include one- to six-year-old children and staff of the affected group in the day care center as well as their respective households. We visit each child's and adult's household. During the home visit we take from each household member a combined mouth and nose swab as well as a saliva sample for analysis of SARS-CoV-2-RNA by real-time reverse transcription polymerase chain reaction (real-time RT-PCR) and a capillary blood sample for a retrospective assessment of an earlier SARS-CoV-2 infection. Furthermore, information on health status, socio-demographics and COVID-19 protective measures are collected via a short telephone interview in the subsequent days. In the following 12 days, household members (or parents for their children) self-collect the same respiratory samples as described above every 3 days and a stool sample for children once. COVID-19 symptoms are documented daily in a symptom diary. Approximately 35 days after testing the index case, every participant who tested positive for SARS-CoV-2 during the study is re-visited at home for another capillary blood sample and a standardized interview. The analysis includes secondary attack rates, by age of primary case, both in the day care center and in households, as well as viral shedding dynamics, including the beginning of shedding relative to symptom onset and viral clearance. Discussion: The results contribute to a better understanding of the epidemiological and virological transmission-related indicators of SARS-CoV-2 among young children, as compared to adults and the interplay between day care and households.Peer Reviewe

Simulations of the Formation of Tidal Dwarf Galaxies

Wir praesentieren die Ergebisse von numerischen Simulationen der Gezeitenarme in wechselwirkenden Galaxien. Die Entstehung von Zwerggalaxien in diesen Gezeitenarmen wurde mit sehr hoher Aufloesung untersucht. Wir stellen fest, dass in reinen N-body Simulationen keine kollabierten Objekte in den Gezeitenarmen entstehen, waehrend Gas effizient den gravitativen Kollaps in Gezeitenarmen triggert, sofern die Gasscheibe der Vorgaenger Galaxie hinreichend grosse Ausdehnung besitzt. Mittels einer Analysemethode, die der von Beobachtern verwendeten nachempfunden ist, bestimmen wir die kinematischen Eigenschaften des massereichsten kollabierten Objekts in unserer Gas-Simulation. Ausserdem praesentieren wir numerische Projekte, die fuer solch hochaufloesende Simulationen noetig sind. VINE, ein neuer N-body SPH Code fuer astrophysikalische Teilchensimulationen wurde in diesem Zusammenhang entwickelt. Der Code verwendet eine binaere Baumstruktur zur Berechnung von Gravitationskraeften. Er kann in Verbindung mit der Spezialhardware GRAPE verwendet werden und ist fuer Shared Memory Supercomputer parallelisiert worden. Sowohl ein Leapfrog als auch ein Runge-Kutta-Fehlberg Integrator wurden implementiert, die beide ein Schema fuer individuelle Zeitschritte der Teilchen verwenden koennen. Weitere implementierte Merkmale sind z.B. periodische Randbedingungen und kosmologische Expansion. Wir praesentieren detaillierte parallele Zeitmessungen des Codes

Expanding epidemic of recently acquired HCV in HIV-coinfected patients over a period of 10 years

Background &amp; Aims: Ongoing transmission of HCV infections is associated with risk factors such as drug injection, needlestick injuries, and men who have sex with men (MSM). Ways of transmission, the course of acute infection, changes of virologic features, and incidence over time are not well known. Methods: Over a period of 10 years, n = 161 patients with recently acquired HCV infection (RAHC) (median follow-up 6.8 years) were prospectively enrolled. NS5B sequencing was performed to re-evaluate the HCV genotype (GT) and for phylogenetic analyses. Results: Patients with RAHC were mainly male (92.5%), MSM (90.1%), and HIV-coinfected (86.3%). Transmission risk factors for MSM and non-MSM were sexual risk behaviour (100 and 6.3%, respectively), injection drug use (9.7 and 37.5%, respectively), and nasal drug use (15.2 and 0%, respectively). Spontaneous and interferon- or direct-acting antiviral-based clearance rates were 13.6, 84.3 and 93.4%, respectively. Mean RAHC declined from 19.8 in the first to 13.2 in the past five study years. Although the majority of infections was caused by HCV GT1a, the frequency of HCV GT4d and slightly HCV GT3a increased over time. No relevant clustering of HCV isolates was observed in non-MSM. However, 45% of HCV GT1a and 100% of HCV GT4d MSM cases clustered with MSM isolates from other countries. Travel-associated infections were supported by personal data in an MSM subgroup. No international clustering was detected in MSM with HCV GT1b or HCV GT3a. Conclusions: RAHCs were mainly diagnosed in HIV-coinfected MSM patients and were associated with sexual risk behaviour. Spontaneous clearance rates were low, and phylogenetic clusters were observed in the majority of patients. Impact and Implications: We evaluated the occurrence and transmission of recently acquired HCV infections (RAHCs) over a period of 10 years. Our data demonstrate that the presence of RAHC was mainly found in HIV-coinfected MSM, with internationally connected transmission networks being observed in the majority of patients. Spontaneous clearance rates were low, and reinfection rates increased mainly driven by a small subset of MSM patients with high-risk behaviour