ZHG, Hörsaal 10
MPI für Sonnensystemforschung
Unser leuchtender Stern – den Geheimnissen der Sonne auf der Spur
Kontakt: Universität Göttingen
MPI für Sonnensystemforschung
A semi-Lagrangian method for studying thermochemical convection in the internal liquid layers of planets including the coupling of the thermochemical boundary conditions
Numerous planetary bodies contain internal liquid layers in the form of either partially molten iron cores, buried water oceans or primitive magma oceans. Convection in these layers is usually driven by the combination of two buoyancy sources: a thermal source directly related to the planet’s secular cooling, the release of latent heat and possibly radioactive decay, and a compositional source due to some process of cristallisation or fusion, for example the growth of a solid inner core which releases light elements into the liquid outer core, or the melting/freezing of an ice layer which locally enriches or depletes the adjacent water ocean in salts. The dynamics of fusion/crystallization being dependent on the heat flux distribution, the thermochemical boundary conditions are locally coupled at a melting/crystallizing boundary which may affect the convection in various ways, particularly if heterogeneous conditions are imposed at one boundary. In addition, the thermal and compositional molecular diffusivities usually differ by at least 2 orders of magnitude. This can produce significant differences in the convective dynamics compared to pure thermal or compositional convection due to the potential occurence of double-diffusive phenomena. Traditionally, temperature and composition have been combined into one single variable called codensity under the assumption that turbulence mixes all physical properties at an "eddy-diffusion" rate. This description does not allow for a proper treatment of the coupling of the thermochemical boundary conditions and is probably incorrect inside stably stratified layers in which turbulence is diminished and double-diffusive phenomena can be expected. Temperature and composition should therefore be treated separately in simulations, but the weak diffusivity of the compositional field is technically difficult to handle in current geodynamo codes and requires the use of a semi-Lagrangian description to minimize numerical diffusion. During my PhD, I implemented and tested a semi-Lagrangian ”particle-in-cell” method into a geodynamo code (PARODY, E. Dormy, J. Aubert) to properly describe the compositional field. In this seminar, I will describe the general principles of this method and will discuss its advantages compared to classical field descriptions. I will then show first applications of this new tool to the formation of a chemically stratified layer below the CMB, and to geodynamo simulations.
Kontakt: Ulrich Christensen
Seminarraum Astrophysik (SR 17, F 05.104)
Institut für Astrophysik Göttingen
Seminarraum 11, C3.101
Prof. Licheng Sun
Dep. of Chemistry, KTH Royal Institute of Technology, Stockholm
Artificial Photosynthesis - From water splitting reaction mechanisms to functional devices
Molecular catalysts for water oxidation and hydrogen generation inspired by the active sites of respective OEC in Photosystem II and [FeFe]- or [NiFe]-Hydrogenases have been developed in our group during the past two decades. These molecular catalysts are based on Mn, Ru, Fe, Cu, Ni and Co, with some water oxidation catalysts showing record high turnover frequency (TOF) of >1000 s-1 in pH 1 solutions. With the deep understandings of O-O bond and H-H bond formation mechanisms from the molecular catalysts, we have recently developed a series of nanostructured first row transition metal oxides/hydroxides as efficient electrocatalysts for water oxidation and hydrogen generation with low overpotentials. Photoelectrochemical (PEC) cells have been assembled in our group by immobilizing molecular water oxidation catalyst on dye sensitized n-type semiconductor (such as TiO2) as photoanode, and molecular water reduction catalyst on dye sensitized p-type semiconductor (such as NiO) as photocathode. Light driven total water splitting by using these PEC cells will be demonstrated during the lecture.
Kontakt: F. Meyer/Anorganische Chemie
On Hamiltonian lattice gauge theory
I will discuss the following topics:
- The classical lattice gauge field model and its stratified structure.
- Quantization, field and observable algebras.
- Implementing the stratification on quantum level.
- Dynamics, the thermodynamical limit.
Kontakt: K.-H. Rehren
MPS - E+F
MPI für Sonnensystemforschung
Earth-Life-Science Institute, Tokyo, Japan; Geophysical Laboratory, Washington D.C., USA; Solar System Exploration Division, Greenbelt MD, USA
Carbon - Where is it all hidden?
Kontakt: Urs Mall
Max-Born-Hörsaal (HS2), Friedrich-Hund-Platz 1
Fakultät für Physik
Göttinger Physikalisches Kolloquium
Prof. Dr. Eckehard Schöll
Nonlinear dynamics on complex networks
Kontakt: Prof. Dr. Reiner Kree
SR 3, Institut für Theoretische Physik, A03.101
Dr. Jan Christoph
Max-Planck-Institut für Dynamik und Selbstorganisation
A novel approach to unraveling the mechanisms underlying cardiac fibrillation: the collective dynamics of coupled cardiac electro-elasto-mechanics
The self-organizing, pattern forming processes that underlie life-threatening cardiac fibrillation remain insufficiently understood. This is in large part due to the absence of requisite in-depth imaging techniques, capable of visualizing the complex electrical activation patterns that propagate rapidly through the volume of the cardiac muscle during cardiac fibrillation. Imaging the electrical activity of the heart is considered to be a key element to understanding cardiac function, as electrical activity triggers mechanical contractions of the heart muscle. The electrical activity arises in the multi-cellular cardiac substrate, which consists of billions of electrically excitable cardiac cells, among which diffusive cell-to-cell coupling leads to nonlinear waves of electrochemical excitation. Optical fluorescence imaging or optical mapping techniques are the gold-standard in the field, as they provide high-resolution maps of normal and abnormal electrical activity of the heart. During fibrillation, one can observe vortex or spiral waves rotating on the surface of the heart. However, measurements of intracardiac wave phenomena occuring within deeper tissue layers are challenging, as optical techniques lack the sufficient penetration depths necessary to visualize the phenomena at these deeper levels. As a result, complete in-depth three-dimensional visualizations of the wave patterns evolving within the fibrillating cardiac muscle still evade experimental realization. In my talk, I will show that intracardiac wave phenomena can be reconstructed by imaging and analyzing the contractile deformation mechanics of the cardiac muscle. Combining fluorescence and elastographic imaging, my research has shown that the arrhythmic electromechanical activity of the heart exhibits closely correlated electrical and mechanical dynamics. I observed that during fibrillation, electrical spiral waves can be accompanied by rotational elasto-mechancial patterns, which like fingerprints of vortex activity depict characteristic dynamic properties of fibrillation. More specifically, phase singularities, which can be assigned in optical maping to the core region of an electrical spiral rotor, can also be derived when analyzing mechanical deformation. Emerging as a dynamic feature in cardiac deformation mechanics, phase singularities similarly indicate the core region of a rotational deformation pattern, while both electrical and mechanical rotational patterns co-exist and appear
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