Open positions

Multiscale processes determining the chemical composition and meteorological structure of the extratropical tropopause region

Volkmar Wirth (Uni Mainz), Horst Fischer (MPI-C)

The MPI-C has extensive experience in taking measurements of trace gases in the extratropical tropopause region. Recent analysis has shown an interesting connection between the strength of the cross-tropopause mixing and more generic features of the tropopause such as its altitude and sharpness. Owing to their multiscale nature, the underlying processes are notoriously difficult to isolate and understand.
The Institute for Atmospheric Physics at the University of Mainz provides a hierarchy of models which can be used to simulate the relevant processes. The MPI-C will be involved in a measurement campaing using the new HALO aircraft, which is planned for 2010.
Combining the expertise of both groups, this project aims to guide the
campaign as well as to understand and interpret the measurements.

Multiscale processes responsible for the tracer transport from the atmospheric boundary layer into the free troposphere

Volkmar Wirth (Uni Mainz), Mark Lawrence (MPI-C)

Atmospheric moist convection is a key process which determines the distribution of trace gases on the local, regional and global scale. Current regional-scale models allow the simulation of the evolution of individual clouds. However, the details of the evolution and, especially, the coupling to the turbulent boundary layer are either underrepresented or parameterized. This can influence the triggering of moist convection and the ensuing cumulus dynamics, as well as the
concentration of gases and aerosols in the cloud inflow regions. 
This project shall connect the experience in Large-Eddy-Simulation (LES) at the University of Mainz with the expertise in cloud resolving modeling at the MPI-C. It aims to enhance our understanding on how turbulent processes in the boundary layer influence the effective tracer transport into the free troposphere.

 

Photoelectron microscopy with designed ‚hot spots’

Hans-Joachim Elmers, Gerd Schönhense (Physics, Uni Mainz), Hans-Jürgen Butt, Max Kreiter (MPIP)

Sub-wavelength metal structures may concentrate incident light to volumes with typical length scales far below the classical diffraction limit and simultaneously amplify the field by orders of magnitude. These local fields may trigger the emission of photoelectrons. On metal surfaces with irregular roughness ‚hot spots’ were observed which show high-order non-linear effects at moderate light intensities which are seen otherwise exclusively at very high power. An understanding of these effects requires systematic measurements at designed ‘hot spots’ which is the aim of the project.
The defined ‚hot spots’ will be manufactures by bottom-up assembly of metal colloids using organic molecules as linker with a typical size in the Angstrom range. Such structures and their detailed geometrical and optical characterisation is established at the MPI-P. Photoelectron emission from these structures, induced by femtosecond laser pulses, will be investigated in the Photoelectron-Emission Microscopy laboratory at the physics department.
 

Kinetic and Correlation Energy Functionals in Density (Matrix) Functional Theory.

Volker Bach (Inst. f. Mathematics, FB 08, JoGu), Luigi Delle Site (MPIP, Theory Group)

Density and density matrix functional theory plays a key role as an effective theory for quantum mechanical matter whose microscopic description is far too complex to be handled, due to the many degrees of freedom. The goal of this project is the derivation and, if possible, the mathematical justification of new functionals representing the kinetic energy and the correlation energy of these systems, involving aspects of information theory, sampling methods such as QMC, and representability. (Up to 4 graduate students)

 

Reactive biogenic VOCs emissions and their atmospheric degradation: Development of analytical techniques and their application in field studies 

Thorsten Hoffmann (Analytical Chemsitry, Jogu), Jürgen Kesselmeier (Biology, MPIC), Jonathan Williams (Chemistry, MPIC)

Multiple field studies have suggested that the emission of biogenic VOCs and their chemistry within and above the forest canopy are poorly understood due to inadequate detection and quantification of reactive biogenic emissions. Especially higher molecular weight compounds (> C10), such as sesquiterpenes or even higher molecular weight plant volatiles, are very difficult to measure due to their reactivity and polarity combined with low their volatility. However, recent findings indicate that the release of these compounds might not only be underestimated, but also especially sensitive to environmental changes, i.e. abiotic or biotic stress factors (temperature, drought, insect infestation etc.). At the same time these compounds are known to be highly efficient precursors for secondary organic aerosol (SOA) formation, resulting in potentially important implications for the evaluation of feedback mechanisms between biogeochemical relevant forest ecosystems (e.g. tropical or boreal forests) and future climate. However, the quantitative understanding of these processes requires not only the development of sophisticated measurement techniques for atmospheric key components (i.e. for reactive higher molecular organics in the gas phase (GC/MS) and their particle phase degradation products (LC/MS; AMS)) but also their application in collaborative experimental studies together with biologists and atmospheric chemists.

 

New hybrid simulation methods for hydrodynamic interactions in complex fluids

Friederike Schmid (University, Physics) and Burkhard Dünweg (MPIP)

Two Ph.D. positions (sponsored by the VW foundation).
The goal of the project is to develop new efficient simulation methods for investigating hydrodynamic effects in complex fluids, such as charged macromolecules in concentrated salt (buffer) solutions or the (hydro)dynamics of interfaces in phase‐separating fluids. These methods shall be based on hybrid approaches that combine particle‐based with field‐based representations of complex fluids, and/or energy‐driven dynamics with force‐driven dynamics. Two positions are available. The first student will study electrohydrodynamic phenomena in concentrated salt solutions and develop methods that shall be used, e.g., to study DNA electrophoresis and dielectrophoresis in physiological buffers efficiently. The second student will focus on systematic theoretical investigations concerning the Lattice‐Boltzmann (LB) method for multiphase flows, aiming at developing new multiphase LB models that are fully consistent with both thermodynamics and hydrodynamics.
All newly developed algorithms shall be integrated in the program package ESPResSo or its  uccessor ESPResSo++ and made available to the scientific community. Applicants should have a good degree in Physics, Applied Mathematics, Chemistry, Chemical Engineering, or a closely related discipline. Willingness to work both analytically and numerically is essential. Previous experience in computer simulations is advantageous but not strictly required.

 

Flow Properties of Ordered Colloidal Suspensions in Restricted Geometry

Hans-Jürgen Butt (MPI Polymer Research) and Thomas Palberg (FB08, Physics)

Colloidal suspensions form fluid or crystalline ordered states once the range and strength of interaction between the colloidal particles becomes sufficiently large and long-ranged. Due to the excellent accessibility by optical methods most of their corresponding bulk properties are already well understood. We here aim at a deeper understanding of ordering and dis-ordering processes in such soft matter model systems under extreme mechanical load and conditions far off equilibrium. We therefore plan a comprehensive study of their behaviour under flow through narrow slits and pores. Using microscopy and light scattering the response to different driving fields, the mechanisms of shear induced melting and crystallization and the location of non equilibrium phase boundaries will be addressed. Data interpretation will proceed in close collaboration with theoretical groups at Düsseldorf and Utrecht. For a successful approach the involved PhD-Student should have experience in at least two of the following areas: condensed matter physics, light scattering, optical microscopy, image analysis, physics and chemistry of colloids.
 

Investigation of the structure of the major light-harvesting complex LHCII

Harald Paulsen (FB10, Biology), H.W. Spiess (MPI Polymer Research)

The major light-harvesting complex (LHCII) is a main component of the photosynthetic apparatus in plants and among the most abundant membrane proteins on Earth. Electron-paramagnetic resonance (EPR) will be used to measure the structure and structural dynamics of LHCII in vitro in various functional states. Since LHCII can be assembled in vitro from its recombinant apoprotein, spin labels are site-specifically attached to the protein. Therefore, the protein structure can be characterized by measuring distances between or the water accessibility of labelled protein domains. The structure of LHCII in various functional states will be compared to its known crystal structure, answering the question of whether LHCII exhibits structural changes in some of these functional states. The same approach will be used unravel the folding pathway of the LHCII apoprotein during its spontaneous assembly with pigments in vitro. This will not only help to understand LHCII biogenesis in plants but also yield information about how membrane protein folding is influenced by cofactor binding in a protein containing an exceptional number of cofactors. LHCII biogenesis will be more closely modelled by including the chloroplast signal recognition particle (cpSRP) in the protein folding studies.