The long-awaited discovery of planets in other solar systems shook up the field of astronomy in 1995. While the early years were mainly spent chasing new discoveries and starting to build the zoo of known exoplanets, the focus then shifted to characterizations of the basic physical properties of exoplanets, such as masses, radii, and distributions of their semi-major axes. Now, with dedicated observational facilities and improving theoretical models, we are entering an era of starting to understand how exoplanets form, evolve, and interact with their environment. Not only can we study exoplanetary atmospheres, but also the complex interplay of exoplanets and the behavior of their host stars is beginning to unfold before our telescopes' eyes. I will present the current state of the field and recent progress on the evolution of exoplanet systems, stellar activity, evaporating atmospheres, and potential impacts on the ultimate question of habitability. I will highlight how upcoming missions, some of which I am involved in, will provide new avenues for our understanding of exoplanets.
FIGSS Seminar - Sommersemester 18
With increasing global population and living standards the impact of humanity on the global ecosystem becomes undeniable. In particular the continuing burning of fossil fuels lead to high impending risks for the global climate. To overcome the strong dependence on conventional energy production, power systems have to be transformed to sustainable systems based on energy sources as wind, solar and hydro. However, such are strongly weather-driven and difficult to manage. So, how can we decarbonize power systems in a cost efficient way and guarantee their stability? To partially answer this question, we discuss an approach of linear optimisation of power grids with its main constraints and exemplary demonstrate its application to the German power system.
Real world stimuli are represented in the brain by responses of specific groups of neurons that are active simultaneously. It is however unclear how these neuronal representations change over time with and without learning. We found that neuronal representations of sounds in awake mouse auditory cortex are not stable, even under basal conditions. Auditory cued fear conditioning does both stabilize representations and trigger the formation of new associations, i.e. groups of stimuli mapped onto one neuronal representation. We formulated a set of basic transitions the neuronal representations can undergo to test our hypotheses. Fear conditioning appears to have an opposing effect on inverse transitions. While for example the creation of new associations is increased, we find that the elimination of existing associations is decreased. We conclude that learning consists of both the generation of new associations and the stabilization of associations.
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Orientation preference is a prominent feature of the mammalian visual cortex, but the mechanisms underlying its development remain elusive. Spontaneous cortical activity is thought to play an important role in the maturation of orientation selectivity, yet it is still unclear how spontaneous activity shapes this process.
Here we address this question by combining chronic imaging experiments and computational analyses. We used GCaMP6s to image visually evoked responses with moving grating stimuli and spontaneous activity in ferret primary visual cortex, from four days prior to the natural time of eye-opening (~P30 in ferrets) until about a week after eye-opening. Prior to P30, the eye lids were transiently opened when probing the cortex with grating stimuli. This setup allows us to assess the emergence and refinement of orientation selectivity and its relationship to spontaneous activity during early development.
We found that, already at the earliest time point measured (P26), visual stimuli robustly evoke responses that are modular (i.e., patchy), extend over the whole field of view, and are highly variable across trials. Typically, weak orientation tuning is evident at this stage, but its layout only coarsely resembles the mature organisation. Indeed we observe considerable reorganisation until a near mature layout is reached a few days after eye-opening.
To determine if early spontaneous activity could drive the refinement of orientation preference, we built a correlation-based model of early visual cortex, assuming that locations with positively correlated spontaneous activity become more similar in their tuning at later stages in development, whereas negatively correlated locations become more dissimilar. Using the measured spontaneous correlation structure and layout of orientation preference in the early cortex, our model predicts aspects of the subsequent reorganization of orientation preference towards its mature layout. The model predicts that spontaneous activity and the orientation preference map become increasingly similar in their layout during development and we confirm this prediction with our experimental data. Thus, this correlation-based approach captures the refinement of orientation preference as well as of its relationship to spontaneous activity.
We conclude that early cortical spontaneous activity plays a significant role in driving the refinement of the circuits underlying orientation preference in visual cortex.
The new FIGSS Soft Skill Programm will be presented and dates discussed. The program itself will start in the following winter semester.