03.12.2020 14:00 Zoom
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Constanca Providencia (University of Coimbra) The interplay between neutron stars and the equation of state I will refer to some results on the implication of neutron star observations on the equation of state, and of the equation of state calibrated to experiments on neutron star properties. The following topics will be discussed: the possible hyperon content and implication on neutron star properties, the formation of light clusters in warm matter, constraining the EoS from the tidal deformability and hybrid stars with large quark cores.
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26.11.2020 14:00 Zoom
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Camilla Hansen (Max Planck Institute for Astronomy, Heidelberg) Linking direct and indirect stellar observation to nuclear reactions Observations of cool, low-mass stars provide the best cosmic traces of current and past nuclear reactions taking place in some of the most extreme environments in the Universe. Spectra of old, low-mass stars provide a multi-dimensional channel in time and space to study the nature, ejecta and nuclear reactions that took place billions of years ago in the first stars. The first stars were massive and exploded as supernovae long ago, however, their chemical finger prints survive in the low-mass stars we can still observe today. Through high-resolution, spectroscopic observations of these old generations of stars, we unveil the physical and chemical properties of the first stars and map the gradual chemical enrichment of the Milky Way. Focussing on the heavy elements, stellar abundances indicate that several formation channels must contribute to their production. Distinct contributions from at least two nuclear processes can be traced indirectly; a slow neutron-capture process associated with asymptotic giant branch stars and a rapid neutron-capture process which is harder to map. Past studies suggested supernovae as formation sites, while recent discoveries challenged this simplistic view. The combination of recent gravitational-wave detections and infrared imaging showed that merger events can create r-process material. However, the spectra provided the first direct detections of newly synthesised r-process material in a neutron star merger. In this talk, I will describe how we observationally can trace the origin of r-process elements in the universe and infer the nature of the first stars despite the fact that these are long gone.
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16:12.2019 14:00 S2|11 10
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Bernhard Mueller (MPI Garching) Simulations of Core-Collapse Supernovae: Understanding the birth properties of compact objects and beyond Core-collapse supernovae, the explosions of massive stars, have remained one of the outstanding challenges in computational astrophysics for decades, and the mechanism by which they explode has long eluded us. However, there is now a growing number of 3D simulations that develop successful explosions driven by neutrino heating in conjunction with violent aspherical fluid motions. One of the main challenges is now to corroborate the simulations by confronting them with observables. Among these observables, the birth properties of compact remnant are within close reach. Recent 3D models already obtain neutron star masses, kicks, birth spin periods within the observed range, and predict interesting and possible testable correlations between these neutron star properties. Furthermore, 3D simulations of partially successful fallback supernovae suggest a pathway for the formation of black holes with substantial kicks, for which there is increasing observational evidence. I will conclude with an outlook on other observables that may help to further unravel the inner workings of the multi-dimensional neutrino-driven engine.
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28.11.2019 15:15 S2|11 10
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Valentin Nesterenko (Dubna) Vortical excitations in nuclei Intrinsic vortical excitations represent a remarkable kind of the nuclear flow which does not contribute to the continuity equation. Despite an impressive effort in the theory and experiment, vortical modes still have many open problems and their direct experimental observation is yet questionable. In the present talk, we discuss the nuclear vorticity for the remarkable example of the isoscalar E1 toroidal mode. This mode is known in hydrodynamics as a Hill's vortex. In nuclei, it is mainly realized as an isoscalar giant toroidal dipole resonance (TDR). We sketch some TDR features (interplay of TDR and pygmy E1 resonance, deformation impact, etc) predicted by self-consistent microscopic models and outline the experimental status of the TDR. As a new route in exploration of the vortical toroidal flow, we propose to consider individual low-energy toroidal states in light nuclei like 24Mg, 20Ne, 16O, 12C, 10Be. The Skyrme QRPA results are compared with AMD+GCM cluster results of Kyoto group. A possible way to identify the toroidal flow in the (e,e') reaction through the interplay of convection and magnetization contributions to transversal form factors is discussed. Besides, we inspect the interplay of E1 toroidal and M2 twist vortical modes.
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18.11.2019 10:00 S2|11 10
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Alexander Bartl (TNG Technology Consulting) Software Engineering Best Practices Modern software engineering relies on a lot of tools and techniques that aim to make the code easier to write, easier to understand and more maintainable. Automated testing and continuous integration reduce the need to manually check intermediate results again and again while increasing ones trust in ones results. Version control systems like Git not only facilitate collaboration on code, but make it easier to track down bugs. Structuring code to be more readable and having other people actually read it has value even for code that is not meant to be shared but you will have to get back to after months or years when that paper is in its third round of reviews or you're finally writing up your thesis. Integrated development environments (IDEs) may seem much clunkier than simple text editors, but their code analysis makes them powerful. While I had heard about a number of these topics back in academia, most of them were not common practice and I didn't really see their value for the code I wrote as a PhD student. Having seen them in action now, I wish I had used them already back at university. A lot of my colleagues share the sentiment. Hence this talk, in which I will give an introduction to these topics and explain how they can help you with your scientific coding.
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