Institutskolloquium des IPP 2018

The LHCb detector at the Large Hadron Collider has been optimised for the study of rare decays of heavy flavour particles and the breaking of the symmetry between matter and antimatter. After a general introduction to the experiment, the talk will focus on the most important results obtained so far and their relevance for the search of physics beyond the Standard Model. [mehr]

Neutron stars are born as the endpoint of stellar evolution in core-collapse supernovae. The densities in a neutron star are extremely high, so high that nuclei are squeezed into their constituents, neutrons and protons. Exotic matter can appear in the core, either in the form of hyperons or as a new phase in the form of strange quark matter. The properties of neutron stars are determined by the nuclear equation of state of dense matter, so that the observation of neutron stars and neutron star merger can give a telltale signature of the properties of dense matter under extreme conditions. The present astrophysical data on neutron stars and pulsars, rotation-powered neutron stars, is reviewed. The equation of state of dense matter will be discussed and possible implications for future observations of core-collapse supernovae and neutron star mergers will be outlined. [mehr]

Due to the presence of multiple physical scales and complex nonlinear interactions, the numerical simulation of fusion plasmas often leads to computational problems of huge complexity. A long-standing challenge is then to design numerical methods that are computationally efficient, high order accurate and stable on very long time scales. Fortunately, steady progresses in the theory of structure-preserving discretizations have provided a solid mathematical ground for the development of stable high order numerical schemes. In this lecture I will give a brief review of the compatible Finite Element methods that have been developed in this direction, and I will explain how these tools are now being extended to design stable numerical models for the Vlasov-Maxwell equations. Recent ideas that allow to further improve the computational efficiency of such methods will be presented, along with a novel approach to low-noise particle approximations. [mehr]

Comparing North Korea's achievements in the field of missiles with the programs of other countries, one gets the impression that North Korea is a nation of rocket scientists. The recent glorious successes appear like a deja vu of the early days of North Korea's missile program in the 1980s and 1990s, when the country managed to present a full missile program out of the blue. But a close look from an engineer's perspective reveals some discrepancies in the common narrative, thus allowing for some surprising insights into the current situation of North Korea's missile threat. [mehr]

The European Spallation Source (ESS), which is currently under construction in Lund, Sweden, is designed to push the limits of research with neutrons to new horizons. ESS will open up new scientific opportunities which are complementary to those at X-ray sources. These will include unprecedented in-situ and in-operando experiments which are only possible with neutrons due to their special properties. After a short summary of the design and the specifications of the European Spallation Source an overview of the current status and schedule of the ESS construction project will be given with a strong focus on the instruments and the surrounding scientific infrastructure. The overall goal of ESS is to begin user operation in 2023 and ramp up to 15 instruments by 2026. Selected examples of new scientific opportunities in the field of materials and life science will be discussed. [mehr]

Despite the progress made at the Paris climate talks with respect to reducing emissions of greenhouse gases it is possible that the rate of environmental change may result in extensive negative impacts for humans and natural ecosystems. Clearly, emissions cuts are essential to managing climate risk and reducing climate change. However, given the potential consequences of a high rate of environmental change, it is important to investigate complementary approaches. For example, geoengineering methods aimed at altering earth's radiation budget may offer a fast-acting way of moderating the rate of climate change. However, such geoengineering approaches entail a number of new risks, and cannot replace reducing CO₂ emissions/levels. I will discuss different geoengineering methods, focusing on new approaches to stratospheric solar radiation management, highlighting technical capabilities and risk. I will also briefly discuss questions surrounding the potential implementation of such approaches. [mehr]

The brain routinely discovers sensory clues that predict opportunities or dangers. However, it is unclear how neural learning processes can bridge the typically long delays between sensory clues and behavioral outcomes. Here, I introduce a learning concept, aggregate-label learning, that enables biologically plausible model neurons to solve this temporal credit assignment problem. Aggregate-label learning matches a neuron’s number of output spikes to a feedback signal that is proportional to the number of clues but carries no information about their timing. Aggregate-label learning outperforms stochastic reinforcement learning at identifying predictive clues and is able to solve unsegmented speech-recognition tasks. Furthermore, it allows unsupervised neural networks to discover reoccurring constellations of sensory features even when they are widely dispersed across space and time. [mehr]

Large-scale plasma instabilities with the potential of damaging wall structures or reducing their lifetime are a significant concern for magnetic confinement fusion. Among the most critical are disruptions and edge localized modes. Predicting the behavior of such instabilities and their control for ITER and beyond is a challenging task for which input from experiments, theory, and simulations is needed. This presentation describes non-linear MHD simulations of edge localized modes, disruptions and control strategies. The talk will explain why simulations or large-scale instabilities are needed and show that our simulations have already revealed a lot of aspects about the physics of large-scale instabilities. It will also give some insights into the actual work involved “behind the scenes” and challenges we are facing for the future. [mehr]