924 research outputs found
Joint inference on the redshift distribution of fast radio burst and on the intergalactic baryon content
No full textFast radio bursts are transient radio pulses of extragalactic origin. Their dispersion measure is indicative of the baryon content in the ionized intergalactic medium between the source and the observer. However, inference using unlocalized fast radio bursts is degenerate to the distribution of redshifts of host galaxies. We perform a joint inference of the intergalactic baryon content and the fast radio burst redshift distribution with the use of Bayesian statistics by comparing the likelihood of different models to reproduce the observed statistics in order to infer the most likely models. In addition to two models of the intergalactic medium, we consider contributions from the local environment of the source, assumed to be a magnetar, as well as a representative ensemble of host and intervening galaxies. Assuming that the missing baryons reside in the ionized intergalactic medium, our results suggest that the redshift distribution of observed fast radio bursts peaks at z less than or similar to 0.6. However, conclusions from different instruments regarding the intergalactic baryon content diverge and thus require additional changes to the observed distribution of host redshifts, beyond those caused by telescope selection effects
Redshift estimates for fast radio bursts and implications on intergalactic magnetic fields
No full textContext: Fast Radio Bursts are transient radio pulses from presumably compact stellar sources of extragalactic origin. With new telescopes detecting multiple events per day, statistical methods are required in order to interpret observations and make inferences regarding astrophysical and cosmological questions.
Purpose: We present a method that uses probability estimates of fast radio burst observables to obtain likelihood estimates for the underlying models.
Method: Considering models for all regions along the line-of-sight, including inter- vening galaxies, we perform Monte-Carlo simulations to estimate the distribution of the dispersion measure, rotation measure and temporal broadening. Using Bayesian statistics, we compare these predictions to observations of Fast Radio Bursts.
Results: By applying Bayes theorem, we obtain lower limits on the redshift of Fast Radio Bursts with extragalactic DM 400 pc cm−3. We find that intervening galaxies cannot account for all highly scattered Fast Radio Bursts in FRBcat, thus requiring a denser and more turbulent environment than a SGR 1935+2154-like mag- netar. We show that a sample of 103 unlocalized Fast Radio Bursts with associated extragalactic RM ≥ 1 rad m−2 can improve current upper limits on the strength of intergalactic magnetic fields
The first metazoa living in permanently anoxic conditions
No full textAbstract Background Several unicellular organisms (prokaryotes and protozoa) can live under permanently anoxic conditions. Although a few metazoans can survive temporarily in the absence of oxygen, it is believed that multi-cellular organisms cannot spend their entire life cycle without free oxygen. Deep seas include some of the most extreme ecosystems on Earth, such as the deep hypersaline anoxic basins of the Mediterranean Sea. These are permanently anoxic systems inhabited by a huge and partly unexplored microbial biodiversity. Results During the last ten years three oceanographic expeditions were conducted to search for the presence of living fauna in the sediments of the deep anoxic hypersaline L'Atalante basin (Mediterranean Sea). We report here that the sediments of the L'Atalante basin are inhabited by three species of the animal phylum Loricifera (Spinoloricus nov. sp., Rugiloricus nov. sp. and Pliciloricus nov. sp.) new to science. Using radioactive tracers, biochemical analyses, quantitative X-ray microanalysis and infrared spectroscopy, scanning and transmission electron microscopy observations on ultra-sections, we provide evidence that these organisms are metabolically active and show specific adaptations to the extreme conditions of the deep basin, such as the lack of mitochondria, and a large number of hydrogenosome-like organelles, associated with endosymbiotic prokaryotes. Conclusions This is the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments. Our findings allow us also to conclude that these metazoans live under anoxic conditions through an obligate anaerobic metabolism that is similar to that demonstrated so far only for unicellular eukaryotes. The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen.</p
Fast radio burst dispersion measures and rotation measures and the origin of intergalactic magnetic fields
No full textWe investigate the possibility of measuring intergalactic magnetic fields using the dispersion measures and rotation measures of fast radio bursts. With Bayesian methods, we produce probability density functions for values of these measures. We distinguish between contributions from the intergalactic medium, the host galaxy, and the local environment of the progenitor. To this end, we use constrained, magnetohydrodynamic simulations of the local Universe to compute lines-of-sight integrals from the position of the Milky Way. In particular, we differentiate between predominantly astrophysical and primordial origins of magnetic fields in the intergalactic medium. We test different possible types of host galaxies and probe different distribution functions of fast radio burst progenitor locations inside the host galaxy. Under the assumption that fast radio bursts are produced by magnetars, we use analytic predictions to account for the contribution of the local environment. We find that less than 100 fast radio bursts from magnetars in stellar-wind environments hosted by starburst dwarf galaxies at redshift z ≳ 0.5 suffice to discriminate between predominantly primordial and astrophysical origins of intergalactic magnetic fields. However, this requires the contribution of the Milky Way to be removed with a precision of ≈1 rad m-2. We show the potential existence of a subset of fast radio bursts whose rotation measures carry information on the strength of the intergalactic magnetic field and its origins
"Da ist es gar nicht so einfach zu sagen, hat der jetzt ES“ – die Konstruktion von Normalität und Abweichung im Förderschwerpunkt emotionale und soziale Entwicklung im Gemeinsamen Unterricht"
No full textSchroeder R. "Da ist es gar nicht so einfach zu sagen, hat der jetzt ES“ – die Konstruktion von Normalität und Abweichung im Förderschwerpunkt emotionale und soziale Entwicklung im Gemeinsamen Unterricht". In: von Stechow E, Hackstein P, Müller K, Esefeld M, Klocke B, eds. Inklusion im Spannungsfeld von Normalität und Diversität. Band 1: Grundfragen der Bildung und Erziehung. Bad Heilbrunn: Klinkhardt; 2019: 157-165
Propagation of ultrahigh energy cosmic rays in extragalactic magnetic fields: a view from cosmological simulations
No full textWe use the crpropa code to simulate the propagation of ultrahigh energy cosmic rays (with energy â¥1018eV and pure proton composition) through extragalactic magnetic fields that have been simulated with the cosmological enzo code. We test both primordial and astrophysical magnetogenesis scenarios in order to investigate the impact of different magnetic field strengths in clusters, filaments and voids on the deflection of cosmic rays propagating across cosmological distances. We also study the effect of different source distributions of cosmic rays around simulated Milky Way-like observers. Our analysis shows that the arrival spectra and anisotropy of events are rather insensitive to the distribution of extragalactic magnetic fields, while they are more affected by the clustering of sources within an ~50 Mpc distance to observers. Finally, we find that in order to reproduce the observed degree of isotropy of cosmic rays at ~EeV energies, the average magnetic fields in cosmic voids must be ~ 0.1 nG, providing limits on the strength of primordial seed fields
Einblicke in Normalitätsvorstellungen von Lehramtsstudierenden - "Die Situation meines Förderkindes habe ich mit meiner eigenen verglichen und Mitleid gespürt"
No full textPieper C, Kottmann B. Einblicke in Normalitätsvorstellungen von Lehramtsstudierenden - "Die Situation meines Förderkindes habe ich mit meiner eigenen verglichen und Mitleid gespürt". In: Esefeld M, Müller K, Hackstein P, von Stechow E, Klocke B, eds. Lehren und Lernen . Inklusion im Spannungsfeld von Normalität und Diversität. Vol 2. Bad Heilbrunn: Klinkhardt; 2019: 75-82
Simulations of extragalactic magnetic fields and of their observables
No full textThe origin of extragalactic magnetic fields is still poorly understood. Based on a dedicated suite of cosmological magneto-hydrodynamical simulations with the ENZO code we have performed a survey of different models that may have caused present-day magnetic fields in galaxies and galaxy clusters. The outcomes of these models differ in cluster outskirts, filaments, sheets and voids and we use these simulations to find observational signatures of magnetogenesis. With these simulations, we predict the signal of extragalactic magnetic fields in radio observations of synchrotron emission from the cosmic web, in Faraday rotation, in the propagation of ultra high energy cosmic rays, in the polarized signal from fast radio bursts at cosmological distance and in spectra of distant blazars. In general, primordial scenarios in which present-day magnetic fields originate from the amplification of weak (⩽nG ) uniform seed fields result in more homogeneous and relatively easier to observe magnetic fields than astrophysical scenarios, in which present-day fields are the product of feedback processes triggered by stars and active galaxies. In the near future the best evidence for the origin of cosmic magnetic fields will most likely come from a combination of synchrotron emission and Faraday rotation observed at the periphery of large-scale structures
Heterogene pädagogische Blicke? Multiprofessionelle Kooperation an inklusiven Ganztagsschulen als Thema in der Lehrer*innenbildung
No full textDemmer C, Hopmann B, Kluge J, Lütje-Klose B. Heterogene pädagogische Blicke? Multiprofessionelle Kooperation an inklusiven Ganztagsschulen als Thema in der Lehrer*innenbildung. In: Esefeld M, Müller K, Hackstein P, von Stechow E, Klocke B, eds. Inklusion im Spannungsfeld von Normalität und Diversität. Band 2: Lehren und Lernen. Bad Heilbrunn: Julius Klinkhardt Verlag; 2019: 47-56
Sperm and egg surface components potentially involved in gamete interactions in Drosophila melanogaster.
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