TY - JOUR A1 - Bürger, Johanna A1 - Hayne, Paul A1 - Gundlach, Bastian A1 - Läuter, Matthias A1 - Kramer, Tobias A1 - Blum, Jürgen T1 - A Microphysical Thermal Model for the Lunar Regolith: Investigating the Latitudinal Dependence of Regolith Properties JF - Journal of Geophysical Research: Planets N2 - The microphysical structure of the lunar regolith provides information on the geologic history of the Moon. We used remote sensing measurements of thermal emission and a thermophysical model to determine the microphysical properties of the lunar regolith. We expand upon previous investigations by developing a microphysical thermal model, which more directly simulates regolith properties, such as grain size and volume filling factor. The modeled temperatures are matched with surface temperatures measured by the Diviner Lunar Radiometer Experiment on board the Lunar Reconnaissance Orbiter. The maria and highlands are investigated separately and characterized in the model by a difference in albedo and grain density. We find similar regolith temperatures for both terrains, which can be well described by similar volume filling factor profiles and mean grain sizes obtained from returned Apollo samples. We also investigate a significantly lower thermal conductivity for highlands, which formally also gives a very good solution, but in a parameter range that is well outside the Apollo data. We then study the latitudinal dependence of regolith properties up to ±80° latitude. When assuming constant regolith properties, we find that a variation of the solar incidence-dependent albedo can reduce the initially observed latitudinal gradient between model and Diviner measurements significantly. A better match between measurements and model can be achieved by a variation in intrinsic regolith properties with a decrease in bulk density with increasing latitude. We find that a variation in grain size alone cannot explain the Diviner measurements at higher latitudes. Y1 - 2024 U6 - https://doi.org/10.1029/2023JE008152 VL - 129 IS - 3 ER - TY - JOUR A1 - Heller, Eric J. A1 - Fleischmann, Ragnar A1 - Kramer, Tobias T1 - Branched Flow N2 - In many physical situations involving diverse length scales, waves or rays representing them travel through media characterized by spatially smooth, random, modest refractive index variations. "Primary" diffraction (by individual sub-wavelength features) is absent. Eventually the weak refraction leads to imperfect focal "cusps". Much later, a statistical regime characterized by momentum diffusion is manifested. An important intermediate regime is often overlooked, one that is diffusive only in an ensemble sense. Each realization of the ensemble possesses dramatic ray limit structure that guides the waves (in the same sense that ray optics is used to design lens systems). This structure is a universal phenomenon called branched flow. Many important phenomena develop in this intermediate regime. Here we give examples and some of the physics of this emerging field. Y1 - 2019 ER - TY - JOUR A1 - Reimers, Jeffrey R. A1 - Biczysko, Malgorzata A1 - Bruce, Douglas A1 - Coker, David F. A1 - Frankcombe, Terry J. A1 - Hashimoto, Hideki A1 - Hauer, Jürgen A1 - Jankowiak, Ryszard A1 - Kramer, Tobias A1 - Linnanto, Juha A1 - Mamedov, Fikret A1 - Müh, Frank A1 - Rätsep, Margus A1 - Renger, Thomas A1 - Styring, Stenbjörn A1 - Wan, Jian A1 - Wang, Zhuan A1 - Wang-Otomo, Zheng-Yu A1 - Weng, Yu-Xiang A1 - Yang, Chunhong A1 - Zhang, Jian-Ping A1 - Freiberg, Arvi A1 - Krausz, Elmars T1 - Challenges facing an understanding of the nature of low-energy excited states in photosynthesis JF - BBA Bioenergetics N2 - While the majority of the photochemical states and pathways related to the biological capture of solar energy are now well understood and provide paradigms for artificial device design, additional low-energy states have been discovered in many systems with obscure origins and significance. However, as low-energy states are naively expected to be critical to function, these observations pose important challenges. A review of known properties of low energy states covering eight photochemical systems, and options for their interpretation, are presented. A concerted experimental and theoretical research strategy is suggested and outlined, this being aimed at providing a fully comprehensive understanding. Y1 - 2016 U6 - https://doi.org/10.1016/j.bbabio.2016.06.010 VL - 1857 IS - 9 SP - 1627 EP - 1640 ER - TY - JOUR A1 - Kramer, Tobias A1 - Läuter, Matthias A1 - Hviid, Stubbe A1 - Jorda, Laurent A1 - Keller, Horst Uwe A1 - Kührt, Ekkehard T1 - Comet 67P/Churyumov-Gerasimenko rotation changes derived from sublimation induced torques JF - Astronomy & Astrophysics N2 - Context. The change of the rotation period and the orientation of the rotation axis of comet 67P/Churyumov-Gerasimenko (67P/C-G) is deducible from images taken by the scientific imaging instruments on-board the Rosetta mission with high precision. Non gravitational forces are a natural explanation for these data. Aims. We describe observed changes for the orientation of the rotation axis and the rotation period of 67P/C-G. For these changes we give an explanation based on a sublimation model with a best-fit for the surface active fraction (model P). Torque effects of periodically changing gas emissions on the surface are considered. Methods. We solve the equation of state for the angular momentum in the inertial and the body- fixed frames and provide an analytic theory of the rotation changes in terms of Fourier coefficients, generally applicable to periodically forced rigid body dynamics. Results. The torque induced changes of the rotation state constrain the physical properties of the surface, the sublimation rate and the local active fraction of the surface. Conclusions. We determine a distribution of the local surface active fraction in agreement with the rotation properties, period and orientation, of 67P/C-G. The torque movement confirms that the sublimation increases faster than the insolation towards perihelion. The derived relatively uniform activity pattern is discussed in terms of related surface features. Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201834349 VL - 630 SP - A3 ER - TY - CHAP A1 - Läuter, Matthias A1 - Kramer, Tobias A1 - Rubin, Martin A1 - Altwegg, Kathrin T1 - Determination of the ice composition near the surface of comet 67P/Churyumov-Gerasimenko T2 - Europlanet Science Congress N2 - During the apparition of comet 67P/Churyumov-Gerasimenko (67P/C-G) solar irradiation causes varying rates for sublimation of volatile species from the cometary nucleus. Because sublimation processes take place close to the cometary surface, the relative abundance of volatiles in the coma and the ice composition are related to each other. To quantify this relation we assume a model for the expansion of a collisionless gas from the surface into the surrounding space. We use an inverse model approach to relate the in situ measurements of gas densities from the two Rosetta instruments COPS (COmet Pressure Sensor) and DFMS (Double Focusing Mass Spectrometer) at the positions of the spacecraft to the locations of surface gas emissions during the Rosetta mission 2014-2016. We assume the temporally integrated gas emissions to be representative for the ice composition close to the surface. Our analysis shows characteristic differences in the ice compositions between both hemispheres of 67P/C-G. In particular CO2 ice has a reduced abundance on the northern hemisphere. In contrast to the hemispherical differences, the two lobes do not show significant differences in terms of their ice composition. Y1 - 2022 U6 - https://doi.org/10.5194/epsc2022-826 SP - EPSC2022-826 ER - TY - CHAP A1 - Noack, Matthias A1 - Reinefeld, Alexander A1 - Kramer, Tobias A1 - Steinke, Thomas T1 - DM-HEOM: A Portable and Scalable Solver-Framework for the Hierarchical Equations of Motion T2 - 2018 IEEE International Parallel and Distributed Processing Symposium Workshops (IPDPSW), 19th IEEE Int. Workshop on Parallel and Distributed Scientific and Engineering Computing (PDSEC 2018) N2 - Computing the Hierarchical Equations of Motion (HEOM) is by itself a challenging problem, and so is writing portable production code that runs efficiently on a variety of architectures while scaling from PCs to supercomputers. We combined both challenges to push the boundaries of simulating quantum systems, and to evaluate and improve methodologies for scientific software engineering. Our contributions are threefold: We present the first distributed memory implementation of the HEOM method (DM-HEOM), we describe an interdisciplinary development workflow, and we provide guidelines and experiences for designing distributed, performance-portable HPC applications with MPI-3, OpenCL and other state-of-the-art programming models. We evaluated the resulting code on multi- and many-core CPUs as well as GPUs, and demonstrate scalability on a Cray XC40 supercomputer for the PS I molecular light harvesting complex. Y1 - 2018 SN - 978-1-5386-5555-9 U6 - https://doi.org/10.1109/IPDPSW.2018.00149 N1 - Best Paper Award SP - 947 EP - 956 ER - TY - GEN A1 - Kramer, Tobias A1 - Noack, Matthias A1 - Baum, Daniel A1 - Hege, Hans-Christian A1 - Heller, Eric J. T1 - Dust and gas emission from cometary nuclei: the case of comet 67P/Churyumov-Gerasimenko N2 - Comets display with decreasing solar distance an increased emission of gas and dust particles, leading to the formation of the coma and tail. Spacecraft missions provide insight in the temporal and spatial variations of the dust and gas sources located on the cometary nucleus. For the case of comet 67P/Churyumov-Gerasimenko (67P/C-G), the long-term obser- vations from the Rosetta mission point to a homogeneous dust emission across the entire illuminated surface. Despite the homogeneous initial dis- tribution, a collimation in jet-like structures becomes visible. We propose that this observation is linked directly to the complex shape of the nucleus and projects concave topographical features into the dust coma. To test this hypothesis, we put forward a gas-dust description of 67P/C-G, where gravitational and gas forces are accurately determined from the surface mesh and the rotation of the nucleus is fully incorporated. The emerging jet-like structures persist for a wide range of gas-dust interactions and show a dust velocity dependent bending. T3 - ZIB-Report - 17-78 Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-66338 SN - 1438-0064 ER - TY - JOUR A1 - Kramer, Tobias A1 - Noack, Matthias A1 - Baum, Daniel A1 - Hege, Hans-Christian A1 - Heller, Eric J. T1 - Dust and gas emission from cometary nuclei: the case of comet 67P/Churyumov-Gerasimenko JF - Advances in Physics: X N2 - Comets display with decreasing solar distance an increased emission of gas and dust particles, leading to the formation of the coma and tail. Spacecraft missions provide insight in the temporal and spatial variations of the dust and gas sources located on the cometary nucleus. For the case of comet 67P/Churyumov-Gerasimenko (67P/C-G), the long-term obser- vations from the Rosetta mission point to a homogeneous dust emission across the entire illuminated surface. Despite the homogeneous initial dis- tribution, a collimation in jet-like structures becomes visible. We propose that this observation is linked directly to the complex shape of the nucleus and projects concave topographical features into the dust coma. To test this hypothesis, we put forward a gas-dust description of 67P/C-G, where gravitational and gas forces are accurately determined from the surface mesh and the rotation of the nucleus is fully incorporated. The emerging jet-like structures persist for a wide range of gas-dust interactions and show a dust velocity dependent bending. Y1 - 2018 U6 - https://doi.org/10.1080/23746149.2017.1404436 VL - 3 IS - 1 SP - 1404436 ER - TY - JOUR A1 - Kramer, Tobias A1 - Rodríguez, Mirta T1 - Effect of disorder and polarization sequences on two-dimensional spectra of light harvesting complexes JF - Photosynthesis Research N2 - Two-dimensional electronic spectra (2DES) provide unique ways to track the energy transfer dynamics in light-harvesting complexes. The interpretation of the peaks and structures found in experimentally recorded 2DES is often not straightforward, since several processes are imaged simultaneously. The choice of specific pulse polarization sequences helps to disentangle the sometimes convoluted spectra, but brings along other disturbances. We show by detailed theoretical calculations how 2DES of the Fenna-Matthews-Olson complex are affected by rotational and conformational disorder of the chromophores. Y1 - 2020 U6 - https://doi.org/10.1007/s11120-019-00699-6 VL - 144 SP - 147 EP - 154 ER - TY - JOUR A1 - Kramer, Tobias A1 - Noack, Matthias A1 - Reinefeld, Alexander A1 - Rodríguez, Mirta A1 - Zelinskyi, Yaroslav T1 - Efficient calculation of open quantum system dynamics and time-resolved spectroscopy with Distributed Memory HEOM (DM-HEOM) JF - Journal of Computational Chemistry N2 - Time- and frequency resolved optical signals provide insights into the properties of light harvesting molecular complexes, including excitation energies, dipole strengths and orientations, as well as in the exciton energy flow through the complex. The hierarchical equations of motion (HEOM) provide a unifying theory, which allows one to study the combined effects of system-environment dissipation and non-Markovian memory without making restrictive assumptions about weak or strong couplings or separability of vibrational and electronic degrees of freedom. With increasing system size the exact solution of the open quantum system dynamics requires memory and compute resources beyond a single compute node. To overcome this barrier, we developed a scalable variant of HEOM. Our distributed memory HEOM, DM-HEOM, is a universal tool for open quantum system dynamics. It is used to accurately compute all experimentally accessible time- and frequency resolved processes in light harvesting molecular complexes with arbitrary system-environment couplings for a wide range of temperatures and complex sizes. Y1 - 2018 U6 - https://doi.org/doi:10.1002/jcc.25354 VL - 39 IS - 22 SP - 1779 EP - 1794 PB - Wiley Periodicals, Inc. ER -