@article{KramerNoackReimersetal., author = {Kramer, Tobias and Noack, Matthias and Reimers, Jeffrey R. and Reinefeld, Alexander and Rodr{\´i}guez, Mirta and Yin, Shiwei}, title = {Energy flow in the Photosystem I supercomplex: comparison of approximative theories with DM-HEOM}, series = {Chemical Physics}, volume = {515}, journal = {Chemical Physics}, publisher = {Elsevier B.V.}, doi = {10.1016/j.chemphys.2018.05.028}, pages = {262 -- 271}, abstract = {We analyze the exciton dynamics in PhotosystemI from Thermosynechococcus elongatus using the distributed memory implementation of the hierarchical equation of motion (DM-HEOM) for the 96 Chlorophylls in the monomeric unit. The exciton-system parameters are taken from a first principles calculation. A comparison of the exact results with Foerster rates and Markovian approximations allows one to validate the exciton transfer times within the complex and to identify deviations from approximative theories. We show the optical absorption, linear, and circular dichroism spectra obtained with DM-HEOM and compare them to experimental results.}, language = {en} } @article{NkenkeZachowBenzetal.2004, author = {Nkenke, Emeka and Zachow, Stefan and Benz, Michaela and Maier, Tobias and Veit, Klaus and Kramer, Manuel and Benz, St. and H{\"a}usler, Gerd and Neukam, Friedrich and Lell, Michael}, title = {Fusion of computed tomography data and optical 3D images of the dentition for streak artefact correction in the simulation of orthognathic surgery}, series = {Journal of Dento-Maxillofacial Radiology}, volume = {33}, journal = {Journal of Dento-Maxillofacial Radiology}, doi = {10.1259/dmfr/27071199}, pages = {226 -- 232}, year = {2004}, language = {en} } @inproceedings{LaeuterKramerRubinetal., author = {L{\"a}uter, Matthias and Kramer, Tobias and Rubin, Martin and Altwegg, Kathrin}, title = {Gas production for 14 species on comet 67P/Churyumov-Gerasimenko from 2014-2016}, series = {Europlanet Science Congress}, volume = {14}, booktitle = {Europlanet Science Congress}, publisher = {Europlanet Science Congress}, doi = {10.5194/epsc2020-319}, pages = {EPSC2020-319}, abstract = {During a two year period between 2014 and 2016 the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) has been probed by the Rosetta spacecraft. Density data for 14 gas species was recorded with the COmet Pressure Sensor (COPS) and the Double Focusing Mass Spectrometer (DFMS) being two sensors of the ROSINA instrument. The combination with an inverse gas model yields emission rates on each of 3996 surface elements of a surface shape for the cometary nucleus. The temporal evolution of gas production, of relative abundances, and peak productions weeks after perihelion are investigated. Solar irradiation and gas production are in a complex relation revealing features differing for gas species, for mission time, and for the hemispheres of the comet. This characterization of gas composition allows one to correlate 67P/C-G to other solar and interstellar comets, their formation conditions and nucleus properties, see [Bodewits D., et al., 2020 Nature Astronomy].}, language = {en} } @inproceedings{LaeuterKramerRubinetal., author = {L{\"a}uter, Matthias and Kramer, Tobias and Rubin, Martin and Altwegg, Kathrin}, title = {Gas production of comet 67P/Churyumov-Gerasimenko reconstructed from DFMS/COPS data}, series = {Europlanet Science Congress}, volume = {12}, booktitle = {Europlanet Science Congress}, publisher = {Europlanet Science Congress}, pages = {EPSC2018-515-1}, abstract = {We reconstruct the temporal evolution of surface emissions for the four major gas species H2O, CO2, CO, and O2 emitted during the 2015 apparition of comet 67P/Churyumov-Gerasimenko (67P/C-G). Measurements from the Double Focusing Mass Spectrometer (DFMS) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the COmet Pressure Sensor (COPS) are used to determine the gas sources on the surface with an inverse gas model for the entire coma. For all species, peak production rates and integrated production rates per orbit are evaluated separately for the northern and the southern hemisphere. Complemented with the total mass production, this allows us to estimate the dust-to-gas ratio of the emitted material.}, language = {en} } @article{KramerNoackBaumetal., author = {Kramer, Tobias and Noack, Matthias and Baum, Daniel and Hege, Hans-Christian and Heller, Eric J.}, title = {Homogeneous dust emission and jet structure near active cometary nuclei: the case of 67P/Churyumov-Gerasimenko}, abstract = {We compute trajectories of dust grains starting from a homogeneous surface activity-profile on a irregularly shaped cometary nucleus. Despite the initially homogeneous dust distribution a collimation in jet-like structures becomes visible. The fine structure is caused by concave topographical features with similar bundles of normal vectors. The model incorporates accurately determined gravitational forces, rotation of the nucleus, and gas-dust interaction. Jet-like dust structures are obtained for a wide range of gas-dust interactions. For the comet 67P/Churyumov-Gerasimenko, we derive the global dust distribution around the nucleus and find several areas of agreement between the homogeneous dust emission model and the Rosetta observation of dust jets, including velocity-dependent bending of trajectories.}, language = {en} } @inproceedings{BuergerHayneGundlachetal., author = {B{\"u}rger, Johanna and Hayne, Paul and Gundlach, Bastian and L{\"a}uter, Matthias and Kramer, Tobias and Blum, J{\"u}rgen}, title = {Investigating the Latitudinal Dependence of Lunar Regolith Properties Using LRO/Diviner Data and a Microphysical Thermal Model}, series = {Bulletin of the AAS}, volume = {55}, booktitle = {Bulletin of the AAS}, number = {8}, abstract = {Regolith is formed through weathering of the local rock by meteorite bombardment, space weathering (Pieters \& Noble, 2016) and thermal erosion (Delbo et al., 2014). In the case of the Moon, the space weathering effects and diurnal temperature variations are reduced towards the poles. The aim of this study is to investigate whether the lunar regolith properties derived from the comparison of regolith temperatures measured by the Diviner radiometer (Paige et al., 2010) on board the Lunar Reconnaissance Orbiter (LRO) with simulated temperatures derived from a microphysical thermal model show a latitudinal dependence. The developed microphysical thermal model expands upon previous models by more directly simulating regolith properties, such as grain radius and volume filling factor.}, language = {en} } @article{HoangGarnierLasueetal., author = {Hoang, Margaux and Garnier, Philippe and Lasue, Jeremie and R{\`e}me, Henri and Capria, Maria Teresa and Altwegg, Kathrin and L{\"a}uter, Matthias and Kramer, Tobias and Rubin, Martin}, title = {Investigating the Rosetta/RTOF observations of comet 67P/Churyumov-Gerasimenko using a comet nucleus model: Influence of dust mantle and trapped CO}, series = {Astronomy \& Astrophysics}, volume = {638}, journal = {Astronomy \& Astrophysics}, doi = {10.1051/0004-6361/201936655}, pages = {A106}, abstract = {Context. Cometary outgassing is induced by the sublimation of ices and the ejection of dust originating from the nucleus. Therefore measuring the composition and dynamics of the cometary gas provides information concerning the interior composition of the body. Nevertheless, the bulk composition differs from the coma composition, and numerical models are required to simulate the main physical processes induced by the illumination of the icy body. Aims. The objectives of this study are to bring new constraints on the interior composition of the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P) by comparing the results of a thermophysical model applied to the nucleus of 67P and the coma measurements made by the Reflectron-type Time-Of-Flight (RTOF) mass spectrometer. This last is one of the three instruments of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), used during the Rosetta mission. Methods. Using a thermophysical model of the comet nucleus, we studied the evolution of the stratigraphy (position of the sublimation and crystallisation fronts), the temperature of the surface and subsurface, and the dynamics and spatial distribution of the volatiles (H2O, CO2 and CO). We compared them with the in situ measurements from ROSINA/RTOF and an inverse coma model. Results. We observed the evolution of the surface and near surface temperature, and the deepening of sublimation fronts. The thickness of the dust layer covering the surface strongly influences the H2O outgassing but not the more volatiles species. The CO outgassing is highly sensitive to the initial CO/H2O ratio, as well as to the presence of trapped CO in the amorphous ice. Conclusions. The study of the influence of the initial parameters on the computed volatile fluxes and the comparison with ROSINA/RTOF measurements provide a range of values for an initial dust mantle thickness and a range of values for the volatile ratio. These imply the presence of trapped CO. Nevertheless, further studies are required to reproduce the strong change of behaviour observed in RTOF measurements between September 2014 and February 2015.}, language = {en} } @inproceedings{BuergerGundlachBlumetal., author = {B{\"u}rger, Johanna and Gundlach, Bastian and Blum, J{\"u}rgen and Hayne, Paul and L{\"a}uter, Matthias and Kramer, Tobias}, title = {Lunar regolith properties derived from LRO/Diviner data and thermophysical modelling}, series = {Europlanet Science Congress}, booktitle = {Europlanet Science Congress}, doi = {10.5194/epsc2022-92}, pages = {EPSC2022-92}, abstract = {The Moon as our nearest celestial object is one of the most important bodies for space resource exploration and planetary science. However, knowledge of the physical properties of the lunar regolith is required for the exploitation of lunar resources and for understanding the Moon's geologic history. This knowledge comes mainly from Apollo in-situ experiments and returned samples, but the global distribution of these properties is still poorly understood. Remote sensing measurements offer the opportunity to derive properties of unsampled areas with the help of models. In our study, a microphysical thermal model for the lunar regolith was developed and the simulated surface temperatures were compared with thermal emission measurements from the Diviner radiometer on board the Lunar Reconnaissance Orbiter (LRO) to derive regolith properties. This work expands upon previous investigations of lunar regolith properties using Diviner data, by more directly simulating physical properties such as particle size and porosity.}, language = {en} } @article{RodriguezKramer, author = {Rodr{\´i}guez, Mirta and Kramer, Tobias}, title = {Machine Learning of Two-Dimensional Spectroscopic Data}, series = {Chemical Physics}, volume = {520}, journal = {Chemical Physics}, doi = {10.1016/j.chemphys.2019.01.002}, pages = {52 -- 60}, abstract = {Two-dimensional electronic spectroscopy has become one of the main experimental tools for analyzing the dynamics of excitonic energy transfer in large molecular complexes. Simplified theoretical models are usually employed to extract model parameters from the experimental spectral data. Here we show that computationally expensive but exact theoretical methods encoded into a neural network can be used to extract model parameters and infer structural information such as dipole orientation from two dimensional electronic spectra (2DES) or reversely, to produce 2DES from model parameters. We propose to use machine learning as a tool to predict unknown parameters in the models underlying recorded spectra and as a way to encode computationally expensive numerical methods into efficient prediction tools. We showcase the use of a trained neural network to efficiently compute disordered averaged spectra and demonstrate that disorder averaging has non-trivial effects for polarization controlled 2DES.}, language = {en} } @inproceedings{KramerLaeuter, author = {Kramer, Tobias and L{\"a}uter, Matthias}, title = {Matching the activity of comet 67P/Churyumov-Gerasimenko with long-term ground-based astrometry}, series = {Europlanet Science Congress}, volume = {15}, booktitle = {Europlanet Science Congress}, publisher = {Europlanet Science Congress}, doi = {10.5194/epsc2021-337}, pages = {EPSC2021-337}, abstract = {50 years of astrometric data for comet 67P/C-G (orbital period about 6.45 years) provides a unique opportunity to benchmark non-gravitational acceleration models to the in situ measurements of the volatile release performed from the Rosetta rendezvous mission (2014-2016). Taken together, the Earth-bound and in-situ data yields lower fit errors and serves as a test-case for our ability to deduce thermophysical quantities of cometary nuclei from the Earth-bound observations.}, language = {en} } @article{KramerRodriguezZelinskyi, author = {Kramer, Tobias and Rodriguez, Mirta and Zelinskyi, Yaroslav}, title = {Modeling of Transient Absorption Spectra in Exciton Charge-Transfer Systems}, series = {Journal of Physical Chemistry B}, volume = {121}, journal = {Journal of Physical Chemistry B}, doi = {10.1021/acs.jpcb.6b09858}, pages = {463 -- 470}, abstract = {Time-resolved spectroscopy provides the main tool for analyzing the dynamics of excitonic energy transfer in light-harvesting complexes. To infer time-scales and effective coupling parameters from experimental data requires to develop numerical exact theoretical models. The finite duration of the laser-molecule interactions and the reorganization process during the exciton migration affect the location and strength of spectroscopic signals. We show that the non-perturbative hierarchical equations of motion (HEOM) method captures these processes in a model exciton system, including the charge transfer state.}, language = {en} } @inproceedings{KramerLaeuter, author = {Kramer, Tobias and L{\"a}uter, Matthias}, title = {Modelling the inner coma of comet 67P/Churyumov-Gerasimenko}, series = {Europlanet Science Congress}, volume = {12}, booktitle = {Europlanet Science Congress}, publisher = {Europlanet Science Congress}, pages = {EPSC2018-115-1}, abstract = {Based on about 1 million of pressure measurements around comet 67P/Churyumov-Gerasimenko we reconstruct the gas emission across the entire nucleus. Dust particles are seeded in the gas model and the resulting dust distribution follows a daily pattern which agrees with observations if a uniform dust release across the entire sunlit surface is assumed.}, language = {en} } @inproceedings{LaeuterKramer, author = {L{\"a}uter, Matthias and Kramer, Tobias}, title = {Non-gravitational acceleration and torque on comet 67P/Churyumov-Gerasimenko}, series = {Bulletin of the AAS}, volume = {55}, booktitle = {Bulletin of the AAS}, number = {8}, abstract = {From August 2014 to September 2016, the ESA operated the Rosetta spacecraft mission alongside with comet 67P/Churyumov-Gerasimenko (67P). The mission provided valuable long-term data on the comet's nucleus, including its volume, mass, tensor of inertia, spatial position of the orbital trajectory, and rotational state.}, language = {en} } @inproceedings{KramerLaeuter, author = {Kramer, Tobias and L{\"a}uter, Matthias}, title = {Non-gravitational force model vs observation: the trajectory and rotation-axis of comet 67P/Churyumov-Gerasimenko}, series = {Europlanet Science Congress}, volume = {14}, booktitle = {Europlanet Science Congress}, publisher = {Europlanet Science Congress}, doi = {10.5194/epsc2020-403}, pages = {EPSC2020-403}, abstract = {The determination of non-gravitational forces based on precise astrometry is one of the main tools to establish the cometary character of interstellar and solar-system objects. The Rosetta mission to comet 67P/C-G provided the unique opportunity to benchmark Earth-bound estimates of non-gravitational forces with in-situ data. We determine the accuracy of the standard Marsden and Sekanina parametrization of non-gravitational forces with respect to the observed dynamics. Additionally we analyse the rotation-axis changes (orientation and period) of 67P/C-G. This comparison provides a reference case for future cometary missions and sublimation models for non-gravitational forces.}, language = {en} } @article{KramerNoack, author = {Kramer, Tobias and Noack, Matthias}, title = {On the origin of inner coma structures observed by Rosetta during a diurnal rotation of comet 67P/Churyumov-Gerasimenko}, series = {The Astrophysical Journal Letters}, volume = {823}, journal = {The Astrophysical Journal Letters}, number = {1}, doi = {10.3847/2041-8205/823/1/L11}, pages = {L11}, abstract = {The Rosetta probe around comet 67P/Churyumov-Gerasimenko (67P) reveals an anisotropic dust distribution of the inner coma with jet-like structures. The physical processes leading to jet formation are under debate, with most models for cometary activity focusing on localized emission sources, such as cliffs or terraced regions. Here we suggest, by correlating high-resolution simulations of the dust environment around 67P with observations, that the anisotropy and the background dust density of 67P originate from dust released across the entire sunlit surface of the nucleus rather than from few isolated sources. We trace back trajectories from coma regions with high local dust density in space to the non-spherical nucleus and identify two mechanisms of jet formation: areas with local concavity in either two dimensions or only one. Pits and craters are examples of the first case; the neck region of the bi-lobed nucleus of 67P is an example of the latter case. The conjunction of multiple sources, in addition to dust released from all other sunlit areas, results in a high correlation coefficient (~0.8) of the predictions with observations during a complete diurnal rotation period of 67P.}, language = {en} } @misc{KramerNoack, author = {Kramer, Tobias and Noack, Matthias}, title = {On the origin of inner coma structures observed by Rosetta during a diurnal rotation of comet 67P/Churyumov-Gerasimenko.}, issn = {1438-0064}, doi = {10.3847/2041-8205/823/1/L11}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-59225}, abstract = {The Rosetta probe around comet 67P/Churyumov-Gerasimenko (67P) reveals an anisotropic dust distribution of the inner coma with jet-like structures. The physical processes leading to jet formation are under debate, with most models for cometary activity focusing on localised emission sources, such as cliffs or terraced regions. Here we suggest, by correlating high-resolution simulations of the dust environment around 67P with observations, that the anisotropy and the background dust density of 67P originate from dust released across the entire sunlit surface of the nucleus rather than from few isolated sources. We trace back trajectories from coma regions with high local dust density in space to the non-spherical nucleus and identify two mechanisms of jet formation: areas with local concavity in either two dimensions or only one. Pits and craters are examples of the first case, the neck region of the bilobed nucleus of 67P for the latter one. The conjunction of multiple sources in addition to dust released from all other sunlit areas results in a high correlation coefficient (∼0.8) of the predictions with observations during a complete diurnal rotation period of 67P.}, language = {en} } @article{KramerLaeuter, author = {Kramer, Tobias and L{\"a}uter, Matthias}, title = {Outgassing induced acceleration of comet 67P/Churyumov-Gerasimenko}, series = {Astronomy \& Astrophysics}, volume = {630}, journal = {Astronomy \& Astrophysics}, doi = {10.1051/0004-6361/201935229}, pages = {A4}, abstract = {Cometary activity affects the orbital motion and rotation state due to sublimation induced forces. The availability of precise rotation-axis orientation and position data from the Rosetta mission allows one to accurately determine the outgassing of comet Churyumov-Gerasimenko/67P (67P). We derive the observed non-gravitational acceleration of 67P directly from the Rosetta spacecraft trajectory. From the non-gravitational acceleration we recover the diurnal outgassing variations and study a possible delay of the sublimation response with respect to the peak solar illumination. This allows us to compare the non-gravitational acceleration of 67P with expectations based on empirical models and common assumptions about the sublimation process. We use an iterative orbit refinement and Fourier decomposition of the diurnal activity to derive the outgassing induced non-gravitational acceleration. The uncertainties of the data reduction are established by a sensitivity analysis of an ensemble of best-fit orbits for comet 67P. We find that the Marsden non-gravitational acceleration parameters reproduce part of the non-gravitational acceleration but need to be augmented by an analysis of the nucleus geometry and surface illumination to draw conclusions about the sublimation process on the surface. The non-gravitational acceleration follows closely the subsolar latitude (seasonal illumination), with a small lag angle with respect to local noon around perihelion. The observed minor changes of the rotation axis do not favor forced precession models for the non-gravitational acceleration. In contrast to the sublimation induced torques, the non-gravitational acceleration does not put strong constraints on localized active areas on the nucleus. We find a close agreement of the orbit deduced non-gravitational acceleration and the water production independently derived from Rosetta in-situ measurement.}, language = {en} } @article{KramerNoack, author = {Kramer, Tobias and Noack, Matthias}, title = {Prevailing Dust-transport Directions on Comet 67P/Churyumov-Gerasimenko}, series = {The Astrophysical Journal Letters}, volume = {813}, journal = {The Astrophysical Journal Letters}, number = {2}, doi = {10.1088/2041-8205/813/2/L33}, pages = {L33}, abstract = {Dust transport and deposition behind larger boulders on the comet 67P/Churyumov-Gerasimenko (67P/C-G) have been observed by the Rosetta mission. We present a mechanism for dust-transport vectors based on a homogeneous surface activity model incorporating in detail the topography of 67P/C-G. The combination of gravitation, gas drag, and Coriolis force leads to specific dust transfer pathways, which for higher dust velocities fuel the near-nucleus coma. By distributing dust sources homogeneously across the whole cometary surface, we derive a global dust-transport map of 67P/C-G. The transport vectors are in agreement with the reported wind-tail directions in the Philae descent area.}, language = {en} } @article{KramerLaeuterRubinetal., author = {Kramer, Tobias and L{\"a}uter, Matthias and Rubin, Martin and Altwegg, Kathrin}, title = {Seasonal changes of the volatile density in the coma and on the surface of comet 67P/Churyumov-Gerasimenko}, series = {Monthly Notices of the Royal Astronomical Society}, volume = {469}, journal = {Monthly Notices of the Royal Astronomical Society}, doi = {10.1093/mnras/stx866}, pages = {S20 -- S28}, abstract = {Starting from several monthly data sets of Rosetta's COmetary Pressure Sensor we reconstruct the gas density in the coma around comet 67P/Churyumov-Gerasimenko. The underlying inverse gas model is constructed by fitting ten thousands of measurements to thousands of potential gas sources distributed across the entire nucleus surface. The ensuing self-consistent solution for the entire coma density and surface activity reproduces the temporal and spatial variations seen in the data for monthly periods with Pearson correlation coefficients of 0.93 and higher. For different seasonal illumination conditions before and after perihelion we observe a systematic shift of gas sources on the nucleus.}, language = {en} } @article{LaeuterKramerRubinetal.2018, author = {L{\"a}uter, Matthias and Kramer, Tobias and Rubin, Martin and Altwegg, Kathrin}, title = {Surface localization of gas sources on comet 67P/Churyumov-Gerasimenko based on DFMS/COPS data}, series = {Monthly Notices of the Royal Astronomical Society}, volume = {483}, journal = {Monthly Notices of the Royal Astronomical Society}, publisher = {Monthly Notices of the Royal Astronomical Society}, doi = {10.1093/mnras/sty3103}, pages = {852 -- 861}, year = {2018}, abstract = {We reconstruct the temporal evolution of the source distribution for the four major gas species H2O, CO2, CO, and O2 on the surface of comet 67P/Churyumov-Gerasimenko during its 2015 apparition. The analysis applies an inverse coma model and fits to data between August 6th 2014 and September 5th 2016 measured with the Double Focusing Mass Spectrometer (DFMS) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the COmet Pressure Sensor (COPS). The spatial distribution of gas sources with their temporal variation allows one to construct surface maps for gas emissions and to evaluate integrated productions rates. For all species peak production rates and integrated productions rates per orbit are evaluated separately for the northern and the southern hemisphere. The nine most active emitting areas on the comet's surface are defined and their correlation to emissions for each of the species is discussed.}, language = {en} } @article{LaeuterKramerRubinetal., author = {L{\"a}uter, Matthias and Kramer, Tobias and Rubin, Martin and Altwegg, Kathrin}, title = {The gas production of 14 species from comet 67P/Churyumov-Gerasimenko based on DFMS/COPS data from 2014-2016}, series = {Monthly Notices of the Royal Astronomical Society}, volume = {498}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, publisher = {Monthly Notices of the Royal Astronomical Society}, doi = {10.1093/mnras/staa2643}, pages = {3995 -- 4004}, abstract = {The coma of comet 67P/Churyumov-Gerasimenko has been probed by the Rosetta spacecraft and shows a variety of different molecules. The ROSINA COmet Pressure Sensor and the Double Focusing Mass Spectrometer provide in-situ densities for many volatile compounds including the 14 gas species H2O, CO2, CO, H2S, O2, C2H6, CH3OH, H2CO, CH4, NH3, HCN, C2H5OH, OCS, and CS2. We fit the observed densities during the entire comet mission between August 2014 and September 2016 to an inverse coma model. We retrieve surface emissions on a cometary shape with 3996 triangular elements for 50 separated time intervals. For each gas we derive systematic error bounds and report the temporal evolution of the production, peak production, and the time-integrated total production. We discuss the production for the two lobes of the nucleus and for the northern and southern hemispheres. Moreover we provide a comparison of the gas production with the seasonal illumination.}, language = {en} } @article{LaeuterKramerRubinetal., author = {L{\"a}uter, Matthias and Kramer, Tobias and Rubin, Martin and Altwegg, Kathrin}, title = {The ice composition close to the surface of comet 67P/Churyumov-Gerasimenko}, series = {ACS Earth and Space Chemistry}, volume = {6}, journal = {ACS Earth and Space Chemistry}, number = {5}, doi = {10.1021/acsearthspacechem.1c00378}, pages = {1189 -- 1203}, abstract = {The relation between ice composition in the nucleus of comet 67P/Churyumov-Gerasimenko on the one hand and relative abundances of volatiles in the coma on the other hand is important for the interpretation of density measurements in the environment of the cometary nucleus. For the 2015 apparition, in situ measurements from the two ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) sensors COPS (COmet Pressure Sensor) and DFMS (Double Focusing Mass Spectrometer) determined gas densities at the spacecraft position for the 14 gas species H2O, CO2, CO, H2S, O2, C2H6, CH3OH, H2CO, CH4, NH3, HCN, C2H5OH, OCS, and CS2. We derive the spatial distribution of the gas emissions on the complex shape of the nucleus separately for 50 subintervals of the two-year mission time. The most active patches of gas emission are identified on the surface. We retrieve the relation between solar irradiation and observed emissions from these patches. The emission rates are compared to a minimal thermophysical model to infer the surface active fraction of H2O and CO2. We obtain characteristic differences in the ice composition close to the surface between the two hemispheres with a reduced abundance of CO2 ice on the northern hemisphere (locations with positive latitude). We do not see significant differences for the ice composition on the two lobes of 67P/C-G.}, language = {en} } @inproceedings{KramerLaeuter, author = {Kramer, Tobias and L{\"a}uter, Matthias}, title = {The near nucleus gas and dust environment around comet 67P/Churyumov-Gerasimenko}, series = {Europlanet Science Congress}, booktitle = {Europlanet Science Congress}, doi = {10.5194/epsc2022-281}, pages = {EPSC2022-281}, abstract = {The Rosetta mission to comet 67P/C-G provided a detailed view of the near nucleus environment of an active Jupiter family comet. The continuous monitoring of the gas pressure with the ROSINA experiment at the location of the Rosetta spacecraft in combination with the images of the dust environment acquired by the OSIRIS cameras allows one to test different hypotheses about the origin of the dust and gas emissions. In addition the orbital elements and the rotation axis and spin rate of the nucleus are affected by the gas release.}, language = {en} } @article{KramerKreisbeckRihaetal., author = {Kramer, Tobias and Kreisbeck, Christoph and Riha, Christian and Chiatti, Olivio and Buchholz, Sven and Wieck, Andreas and Reuter, Dirk and Fischer, Saskia}, title = {Thermal energy and charge currents in multi-terminal nanorings}, series = {AIP Advances}, volume = {6}, journal = {AIP Advances}, doi = {10.1063/1.4953812}, pages = {065306}, abstract = {We study in experiment and theory thermal energy and charge transfer close to the quantum limit in a ballistic nanodevice, consisting of multiply connected one-dimensional electron waveguides. The fabricated device is based on an AlGaAs/GaAs heterostructure and is covered by a global top-gate to steer the thermal energy and charge transfer in the presence of a temperature gradient, which is established by a heating current. The estimate of the heat transfer by means of thermal noise measurements shows the device acting as a switch for charge and thermal energy transfer. The wave-packet simulations are based on the multi-terminal Landauer-B{\"u}ttiker approach and confirm the experimental finding of a mode-dependent redistribution of the thermal energy current, if a scatterer breaks the device symmetry.}, language = {en} } @article{KreisbeckKramerMolina, author = {Kreisbeck, Christoph and Kramer, Tobias and Molina, Rafael}, title = {Time-dependent wave packet simulations of transport through Aharanov-Bohm rings with an embedded quantum dot}, series = {Journal of Physics: Condensed Matter}, volume = {29}, journal = {Journal of Physics: Condensed Matter}, number = {15}, doi = {10.1088/1361-648X/aa605d}, pages = {155301}, abstract = {We have performed time-dependent wave packet simulations of realistic Aharonov-Bohm (AB) devices with a quantum dot embedded in one of the arms of the interferometer. The AB ring can function as a measurement device for the intrinsic transmission phase through the quantum dot, however, care has to be taken in analyzing the influence of scattering processes in the junctions of the interferometer arms. We consider a harmonic quantum dot and show how the Darwin-Fock spectrum emerges as a unique pattern in the interference fringes of the AB oscillations.}, language = {en} } @inproceedings{Kramer, author = {Kramer, Tobias}, title = {Transient capture of electrons in magnetic fields, or: comets in the restricted three-body problem}, series = {Journal of Physics: Conference Series}, volume = {1612}, booktitle = {Journal of Physics: Conference Series}, edition = {Symmetries in Science XVIII}, doi = {10.1088/1742-6596/1612/1/012019}, pages = {012019}, abstract = {The motion of celestial bodies in astronomy is closely related to the orbits of electrons encircling an atomic nucleus. Bohr and Sommerfeld presented a quantization scheme of the classical orbits to analyze the eigenstates of the hydrogen atom. Here we discuss another close connection of classical trajectories and quantum mechanical states: the transient dynamics of objects around a nucleus. In this setup a comet (or an electron) is trapped for a while in the vicinity of parent object (Jupiter or an atomic nucleus), but eventually escapes after many revolutions around the center of attraction.}, language = {en} } @article{KramerRodriguez, author = {Kramer, Tobias and Rodriguez, Mirta}, title = {Two-dimensional electronic spectra of the photosynthetic apparatus of green sulfur bacteria}, series = {Scientific Reports}, volume = {7}, journal = {Scientific Reports}, doi = {10.1038/srep45245}, pages = {45245}, abstract = {Advances in time resolved spectroscopy have provided new insight into the energy transmission in natural photosynthetic complexes. Novel theoretical tools and models are being developed in order to explain the experimental results. We provide a model calculation for the two-dimensional electronic spectra of Cholorobaculum tepidum which correctly describes the main features and transfer time scales found in recent experiments. From our calculation one can infer the coupling of the antenna chlorosome with the environment and the coupling between the chlorosome and the Fenna-Matthews-Olson complex. We show that environment assisted transport between the subunits is the required mechanism to reproduce the experimental two-dimensional electronic spectra.}, language = {en} }