Physikalisches Kolloquium

Programm für das Wintersemester 2020/2021

Tuesdays, 16 Uhr c.t.

Institut für Kernphysik, Remote Seminar
live at Zoom

17.11.20Dieter Ries, University of Mainz
Ultracold Neutrons (UCN) provide a unique tool for fundamental neutron research with long observation times. Once produced e.g. in one of the UCN sources at the TRIGA Mainz research reactor, they can be confined by suitable materials, gravity or strong magnetic fields ultimately only limited by the beta decay lifetime of the free neutron. The τSPECT experiment, which is close to being fully commissioned on-site at JGU, aims for a precision determination of the neutron lifetime, which is currently under scrutiny because different measurement techniques yield incompatible results. Another precision measurement with UCN is the search for a non-vanishing electric dipole moment of the neutron, which would violate CP symmetry. Together with the international nEDM collaboration we have recently published a new upper limit on the neutron EDM and are currently commissioning the next generation experiment "n2EDM" at PSI, Switzerland, which aims to push down the limit by an order of magnitude in the coming years. The current state of and results from the τSPECT, nEDM and n2EDM experiment will be presented.
16:15 Uhr s.t., at Recording of the presentation

24.11.20Bert Koopmans, Eindhoven University of Technology, The Netherlands
Femto-magnetism meets spintronics: Towards integrated magneto-photonics
16:15 Uhr s.t., at Recording of the presentation

01.12.20Eli Zeldov, Department of Condensed Matter Physics, Weizmann Institute of Science, Israel
Energy dissipation is a fundamental process governing the dynamics of classical and quantum systems. Despite its vital importance, direct imaging and microscopy of dissipation in quantum systems is currently mostly inaccessible because the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation. We developed a scanning nanoSQUID that resides at the apex of a sharp pipette acting simultaneously as nanomagnetometer with single spin sensitivity and as nanothermometer providing cryogenic thermal imaging with four orders of magnitude improved thermal sensitivity of below 1 µK [1]. The non-contact non-invasive thermometry enables direct visualization and control of the minute heat generated by electrons scattering off a single atomic defect in graphene [2]. By further combining the scanning nanothermometry with simultaneous scanning gate microscopy we demonstrate independent imaging of work and dissipation and reveal the microscopic mechanisms that conceal the true topological protection in the quantum Hall state in graphene [3]. [1] D. Halbertal, J. Cuppens, M. Ben Shalom, L. Embon, N. Shadmi, Y. Anahory, H. R. Naren, J. Sarkar, A. Uri, Y. Ronen, Y. Myasoedov, L. S. Levitov, E. Joselevich, A. K. Geim, and E. Zeldov, Nature 539, 407 (2016). [2] D. Halbertal, M. Ben Shalom, A. Uri, K. Bagani, A.Y. Meltzer, I. Marcus, Y. Myasoedov, J. Birkbeck, L.S. Levitov, A.K. Geim, and E. Zeldov, Science 358, 1303 (2017). [3] A. Marguerite, J. Birkbeck, A. Aharon-Steinberg, D. Halbertal, K. Bagani, I. Marcus, Y. Myasoedov, A.K. Geim, D.J. Perello, and E. Zeldov, Nature 575, 628 (2019).
16:15 Uhr s.t., at Recording of the presentation

08.12.20Sherry Suyu, TU München
Strong gravitational lenses with measured time delays between the multiple images can be used to determine the Hubble constant (H0) that sets the expansion rate of the Universe. An independent determination of H0 is important to ascertain the possible need of new physics beyond the standard cosmological model, given the tension in current H0 measurements. I will describe techniques for measuring H0 from lensing with a realistic account of systematicuncertainties, and present the latest resultsfrom a program aimed to measure H0 from lensing. Search is underway to find new lenses in imaging surveys. An exciting discovery of the first strongly lensed supernova offered a rare opportunity to perform a true blind test of our modeling techniques. I will show the bright prospects of gravitational lens time delays as an independent and competitive cosmological probe.
16:15 Uhr s.t., at Zoom

15.12.20Baha Balantekin, University of Wisconsin, Madison, USA
Earlier theoretical work on neutrino propagation in dense media, in particular the Mikheyev-Smirnov-Wolfenstein effect describing phase changes in neutrino wave functions resulting from their interaction with the background particles, provided an explanation of the measured distortions of the solar neutrinos. A more complex effect takes place in the denser media inside supernovae and neutron-star mergers, where neutrinos interact not only with the background particles but also among themselves. After reviewing key roles neutrinos play in such environments, this many-neutrino problem and resulting collective neutrino oscillations will be discussed. Implications of correlations between neutrinos in this many-neutrino system for nucleosynthesis and terrestrial detection of supernova neutrinos will be explored.
16:15 Uhr s.t., at Recording of the presentation

12.01.21Zheng-Tian Lu, University of Science and Technology of China
The long-lived noble-gas isotope 81Kr is the ideal tracer for water and ice with ages of 105 - 106 years, a range beyond the reach of 14C. 81Kr-dating, a concept pursued over the past five decades, is finally available to the earth science community at large. This is made possible by the development of the Atom Trap Trace Analysis (ATTA) method, in which individual atoms of the desired isotope are captured and detected. ATTA possesses superior selectivity, and is thus far used to analyze the environmental radioactive isotopes 81Kr, 85Kr, and 39Ar. These three isotopes have extremely low isotopic abundances in the range of 10-17 to 10-11, and cover a wide range of ages and applications. In collaboration with earth scientists, we are dating groundwater and mapping its flow in major aquifers around the world. We are also dating old ice from the deep ice cores of Antarctica, Greenland, and the Tibetan Plateau. For an update on this worldwide effort, please google “ATTA Primer”.
16:15 Uhr s.t., at Recording of the presentation

19.01.21Bernadett Weinzierl, University of Vienna, Austria
Aerosol particles are an important constituent of the global climate system. They not only affect the atmospheric radiation budget through scattering and absorption of solar radiation and through their role as cloud/ice nuclei but also impact air quality and human health. Both natural and human processes contribute to the global aerosol load. Whereas coarse‐mode aerosol (>1 μm diameter) mainly originates from natural aerosol sources, fine mode aerosol is frequently associated with human activities. Although substantial effort has been undertaken in the last decades to improve our knowledge about aerosols and their role in the global climate system, aerosol‐cloud‐radiation interactions still pose the largest uncertainty to estimates and interpretations of the Earth’s changing energy budget (IPCC, 2013). In order to decrease these uncertainties, research is necessary. Thereby, research aircraft like the German Aerospace Center (DLR) Falcon and the NASA DC‐8 provide unique platforms to study the horizontal and vertical distribution of aerosols and their microphysical, chemical and optical properties. In this talk, I will introduce aerosols in general, and discuss their effects on the atmosphere and climate. Furthermore, I will show selected results from airborne field experiments with the DLR research aircraft Falcon and the NASA research aircraft DC8 studying the long‐range transport of mineral dust (SALTRACE project), the global distribution of coarse mode aerosols (ATom project), and aerosol mixtures in the Eastern Mediterranean (A‐LIFE project).
16:15 Uhr s.t., at Zoom

26.01.21Viola Priseman, Max-Planck-Institution , Göttingen, Germany
How can we deal with a pandemic like COVID-19 so that neither health nor society and the economy suffer unnecessarily? We inferred the effectiveness of interventions, and developed effective containment strategies. Interestingly, we have identified a metastable state that not only stabilizes low case numbers, but also significantly reduces the necessary contact reductions and lockdowns. In this talk, we will introduce the underlying models, explore different containment strategies, and discuss recent developments.
16:15 Uhr s.t., at Recording of the presentation

02.02.21Andy Brown, ECMWF, Reading, Great Britain
Accurate weather predictions are of huge value to society, being used to inform actions that save lives and money. They are also a scientific success story, with global 5 day forecasts today being as accurate as 2 days forecasts of 30 years go. This talk will summarize the approach used, recent progress and future research and development priorities. These include further advances in understanding and modelling of multiple components of the Earth system (eg atmopshere, land, ocean and sea-ice), developments in observations and data assimilation methods, and bringing together the physical and computational science communities to take full advantage of new supercomputer architectures and advances in data science.
16:15 Uhr s.t., at Recording of the presentation

09.02.21Michael Feindt, University of Karlsruhe
This talk will review my personal history as elementary particle physics researcher (having started to work with neural networks at CERN in 1993), professor and entrepreneur (founder of Phi-T (2002) and Blue Yonder(2008)). It was always driven by what today is called Machine Learning and Artificial Intelligence, with emphasis on also predicting and taking advantage from knowledge about uncertainty. Today Blue Yonder, specialized on AI/ML and decision automation in the supply chain from Manufacturing to Retail, has more than 3500 large companies worldwide as customers and has delivered more than 1 trillion predictions. Examples from many different areas (physics, insurance, retail, supply chain) and experience gained over many years will show the tremendous value, but also the difficulties in bringing these methods into real life production in large scale international collaborations and companies - often against resistance.
16:15 Uhr s.t., at Recording of the presentation

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Prof. Dr. Matthias Schott
Institut für Physik, ETAP

Prof. Dr. Achim Denig
Institut für Kernphysik