TY - JOUR A1 - Schewe, Jacob A1 - Levermann, Anders T1 - Non-linear intensification of Sahel rainfall as a possible dynamic response to future warming JF - Earth system dynamics Y1 - 2017 U6 - https://doi.org/10.5194/esd-8-495-2017 SN - 2190-4979 SN - 2190-4987 VL - 8 SP - 495 EP - 505 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Zaks, Michael A1 - Pikovskij, Arkadij T1 - Chimeras and complex cluster states in arrays of spin-torque oscillators JF - Scientific reports N2 - We consider synchronization properties of arrays of spin-torque nano-oscillators coupled via an RC load. We show that while the fully synchronized state of identical oscillators may be locally stable in some parameter range, this synchrony is not globally attracting. Instead, regimes of different levels of compositional complexity are observed. These include chimera states (a part of the array forms a cluster while other units are desynchronized), clustered chimeras (several clusters plus desynchronized oscillators), cluster state (all oscillators form several clusters), and partial synchronization (no clusters but a nonvanishing mean field). Dynamically, these states are also complex, demonstrating irregular and close to quasiperiodic modulation. Remarkably, when heterogeneity of spin-torque oscillators is taken into account, dynamical complexity even increases: close to the onset of a macroscopic mean field, the dynamics of this field is rather irregular. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-04918-9 SN - 2045-2322 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Gao, Shan A1 - Pohl, Martin A1 - Winter, Walter T1 - On the Direct Correlation between Gamma-Rays and PeV Neutrinos from Blazars JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We study the frequently used assumption in multi-messenger astrophysics that the gamma-ray and neutrino fluxes are directly connected because they are assumed to be produced by the same photohadronic production chain. An interesting candidate source for this test is the flat-spectrum radio quasar PKS B1424-418, which recently called attention to a potential correlation between an IceCube PeV neutrino event and its burst phase. We simulate both the multi-waveband photon and the neutrino emission from this source using a self-consistent radiation model. We demonstrate that a simple hadronic model cannot adequately describe the spectral energy distribution for this source, but a lepto-hadronic model with a subdominant hadronic component can reproduce the multi-waveband photon spectrum observed during various activity phases of the blazar. As a conclusion, up to about 0.3 neutrino events may coincide with the burst, which implies that the leptonic contribution dominates in the relevant energy band. We also demonstrate that the time-wise correlation between the neutrino event and burst phase is weak. KW - galaxies: jets KW - gamma rays: general KW - neutrinos Y1 - 2017 U6 - https://doi.org/10.3847/1538-4357/aa7754 SN - 0004-637X SN - 1538-4357 VL - 843 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Cestnik, Rok A1 - Rosenblum, Michael T1 - Reconstructing networks of pulse-coupled oscillators from spike trains JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We present an approach for reconstructing networks of pulse-coupled neuronlike oscillators from passive observation of pulse trains of all nodes. It is assumed that units are described by their phase response curves and that their phases are instantaneously reset by incoming pulses. Using an iterative procedure, we recover the properties of all nodes, namely their phase response curves and natural frequencies, as well as strengths of all directed connections. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevE.96.012209 SN - 2470-0045 SN - 2470-0053 VL - 96 SP - 3455 EP - 3461 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Ran, Niva A. A1 - Roland, Steffen A1 - Love, John A. A1 - Savikhin, Victoria A1 - Takacs, Christopher J. A1 - Fu, Yao-Tsung A1 - Li, Hong A1 - Coropceanu, Veaceslav A1 - Liu, Xiaofeng A1 - Bredas, Jean-Luc A1 - Bazan, Guillermo C. A1 - Toney, Michael F. A1 - Neher, Dieter A1 - Thuc-Quyen Nguyen, T1 - Impact of interfacial molecular orientation on radiative recombination and charge generation efficiency JF - Nature Communications N2 - A long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics-however, the results have important implications on the operation of all optoelectronic devices with donor/ acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting in larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation. Y1 - 2017 U6 - https://doi.org/10.1038/s41467-017-00107-4 SN - 2041-1723 VL - 8 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Schimka, Selina A1 - Gordievskaya, Yulia D. A1 - Lomadze, Nino A1 - Lehmann, Maren A1 - von Klitzing, Regine A1 - Rumyantsev, Artem M. A1 - Kramarenko, Elena Yu. A1 - Santer, Svetlana T1 - Communication: Light driven remote control of microgels’ size in the presence of photosensitive surfactant: Complete phase diagram JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Here we report on a light triggered remote control of microgel size in the presence of photosensitive surfactant. The hydrophobic tail of the cationic surfactant contains azobenzene group that undergoes a reversible photo-isomerization reaction from a trans-to a cis-state accompanied by a change in the hydrophobicity of the surfactant. We have investigated light assisted behaviour and the complex formation of the microgels with azobenzene containing surfactant over the broad concentrational range starting far below and exceeding several times of the critical micelle concentration (CMC). At small surfactant concentration in solution (far below CMC), the surfactant in the trans-state accommodates within the microgel causing its compaction, while the cis-isomer desorbs out of microgel resulting in its swelling. The process of the microgel size change can be described as swelling on UV irradiation (trans-cis isomerization) and shrinking on irradiation with blue light (cis-trans isomerization). However, at the surfactant concentrations larger than CMC, the opposite behaviour is observed: the microgel swells on blue irradiation and shrinks during exposure to UV light. We explain this behaviour theoretically taking into account isomer dependent micellization of surfactant within the microgels. Published by AIP Publishing. Y1 - 2017 U6 - https://doi.org/10.1063/1.4986143 SN - 0021-9606 SN - 1089-7690 VL - 147 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Koc, Azize A1 - Reinhardt, M. A1 - Reppert, Alexander von A1 - Roessle, Matthias A1 - Leitenberger, Wolfram A1 - Dumesnil, K. A1 - Gaal, Peter A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Ultrafast x-ray diffraction thermometry measures the influence of spin excitations on the heat transport through nanolayers JF - Physical review : B, Condensed matter and materials physics N2 - We investigate the heat transport through a rare earth multilayer system composed of yttrium (Y), dysprosium (Dy), and niobium (Nb) by ultrafast x-ray diffraction. This is an example of a complex heat flow problem on the nanoscale, where several different quasiparticles carry the heat and conserve a nonequilibrium for more than 10 ns. The Bragg peak positions of each layer represent layer-specific thermometers that measure the energy flow through the sample after excitation of the Y top layer with fs-laser pulses. In an experiment-based analytic solution to the nonequilibrium heat transport problem, we derive the individual contributions of the spins and the coupled electron-lattice system to the heat conduction. The full characterization of the spatiotemporal energy flow at different starting temperatures reveals that the spin excitations of antiferromagnetic Dy speed up the heat transport into the Dy layer at low temperatures, whereas the heat transport through this layer and further into the Y and Nb layers underneath is slowed down. The experimental findings are compared to the solution of the heat equation using macroscopic temperature-dependent material parameters without separation of spin and phonon contributions to the heat. We explain why the simulated energy density matches our experiment-based derivation of the heat transport, although the simulated thermoelastic strain in this simulation is not even in qualitative agreement. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevB.96.014306 SN - 2469-9950 SN - 2469-9969 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Wolff, Christian Michael A1 - Zu, Fengshuo A1 - Paulke, Andreas A1 - Perdigón-Toro, Lorena A1 - Koch, Norbert A1 - Neher, Dieter T1 - Reduced Interface-Mediated Recombination for High Open-Circuit Voltages in CH3NH3PbI3 Solar Cells JF - Advanced materials N2 - Perovskite solar cells with all-organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high-temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron-transporting layer of inverted perovskite cells affects the open-circuit voltage (V-OC). It is shown that nonradiative recombination mediated by the electron-transporting layer is the limiting factor for the V-OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH3NH3PbI3 perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V-OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge-blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V-OC and efficiency. KW - electron-transport layers KW - nonradiative recombination KW - open-circuit voltage KW - perovskite solar cells Y1 - 2017 U6 - https://doi.org/10.1002/adma.201700159 SN - 0935-9648 SN - 1521-4095 VL - 29 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Maass, Friedrich A1 - Utecht, Manuel Martin A1 - Stremlau, Stephan A1 - Gille, Marie A1 - Schwarz, Jutta A1 - Hecht, Stefan A1 - Klamroth, Tillmann A1 - Tegeder, Petra T1 - Electronic structure changes during the on-surface synthesis of nitrogen-doped chevron-shaped graphene nanoribbons JF - Physical review : B, Condensed matter and materials physics N2 - Utilizing suitable precursor molecules, a thermally activated and surface-assisted synthesis results in the formation of defect-free graphene nanoribbons (GNRs), which exhibit electronic properties that are not present in extended graphene. Most importantly, they have a band gap in the order of a few electron volts, depending on the nanoribbon width. In this study, we investigate the electronic structure changes during the formation of GNRs, nitrogen-doped (singly and doubly N-doped) as well as non-N-doped chevron-shaped CGNRs on Au(111). Thus we determine the optical gaps of the precursor molecules, the intermediate nonaromatic polymers, and finally the aromatic GNRs, using high-resolution electron energy loss spectroscopy and density functional theory calculations. As expected, we find no influence of N-doping on the size of the optical gaps. The gap of the precursor molecules is around 4.5 eV. Polymerization leads to a reduction of the gap to a value of 3.2 eV due to elongation and thus enhanced delocalization. The CGNRs exhibit a band gap of 2.8 eV, thus the gap is further reduced in the nanoribbons, since they exhibit an extended delocalized pi-electron system. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevB.96.045434 SN - 2469-9950 SN - 2469-9969 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Shin, Jaeoh A1 - Cherstvy, Andrey G. A1 - Kim, Won Kyu A1 - Zaburdaev, Vasily T1 - Elasticity-based polymer sorting in active fluids: a Brownian dynamics study JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - While the dynamics of polymer chains in equilibrium media is well understood by now, the polymer dynamics in active non-equilibrium environments can be very different. Here we study the dynamics of polymers in a viscous medium containing self-propelled particles in two dimensions by using Brownian dynamics simulations. We find that the polymer center of mass exhibits a superdiffusive motion at short to intermediate times and the motion turns normal at long times, but with a greatly enhanced diffusivity. Interestingly, the long time diffusivity shows a non-monotonic behavior as a function of chain length and stiffness. We analyze how the polymer conformation and the accumulation of self-propelled particles, and therefore the directed motion of the polymer, are correlated. At the point of maximal polymer diffusivity, the polymer has preferentially bent conformations maintained by the balance between the chain elasticity and the propelling force generated by the active particles. We also consider the barrier crossing dynamics of actively-driven polymers in a double-well potential. The barrier crossing times are demonstrated to have a peculiar non-monotonic dependence, related to that of the diffusivity. This effect can be potentially utilized for sorting polymers from solutions in in vitro experiments. Y1 - 2017 U6 - https://doi.org/10.1039/c7cp02947k SN - 1463-9076 SN - 1463-9084 VL - 19 SP - 18338 EP - 18347 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Niskanen, Johannes A1 - Sahle, Christoph J. A1 - Gilmore, Keith A1 - Uhlig, Frank A1 - Smiatek, Jens A1 - Föhlisch, Alexander T1 - Disentangling structural information from core-level excitation spectra JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Core-level spectra of liquids can be difficult to interpret due to the presence of a range of local environments. We present computational methods for investigating core-level spectra based on the idea that both local structural parameters and the x-ray spectra behave as functions of the local atomic configuration around the absorbing site. We identify correlations between structural parameters and spectral intensities in defined regions of interest, using the oxygen K-edge excitation spectrum of liquid water as a test case. Our results show that this kind of analysis can find the main structure-spectral relationships of ice, liquid water, and supercritical water. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevE.96.013319 SN - 2470-0045 SN - 2470-0053 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kobzar, Oleh A1 - Niemiec, Jacek A1 - Pohl, Martin A1 - Bohdan, Artem T1 - Spatio-temporal evolution of the non-resonant instability in shock precursors of young supernova remnants JF - Monthly notices of the Royal Astronomical Society N2 - A non-resonant cosmic ray (CR) current-driven instability may operate in the shock precursors of young supernova remnants and be responsible for magnetic-field amplification, plasma heating and turbulence. Earlier simulations demonstrated magnetic-field amplification, and in kinetic studies a reduction of the relative drift between CRs and thermal plasma was observed as backreaction. However, all published simulations used periodic boundary conditions, which do not account for mass conservation in decelerating flows and only allow the temporal development to be studied. Here we report results of fully kinetic particle-in-cell simulations with open boundaries that permit inflow of plasma on one side of the simulation box and outflow at the other end, hence allowing an investigation of both the temporal and the spatial development of the instability. Magnetic-field amplification proceeds as in studies with periodic boundaries and, observed here for the first time, the reduction of relative drifts causes the formation of a shock-like compression structure at which a fraction of the plasma ions are reflected. Turbulent electric field generated by the non-resonant instability inelastically scatters CRs, modifying and anisotropizing their energy distribution. Spatial CR scattering is compatible with Bohm diffusion. Electromagnetic turbulence leads to significant non-adiabatic heating of the background plasma maintaining bulk equipartition between ions and electrons. The highest temperatures are reached at sites of large-amplitude electrostatic fields. Ion spectra show supra-thermal tails resulting from stochastic scattering in the turbulent electric field. Together, these modifications in the plasma flow will affect the properties of the shock and particle acceleration there. KW - acceleration of particles KW - shock waves KW - turbulence KW - methods: numerical KW - cosmic rays KW - ISM: supernova remnants Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx1201 SN - 0035-8711 SN - 1365-2966 VL - 469 SP - 4985 EP - 4998 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Gulyakova, Anna A. A1 - Gorokhovatsky, Yuri A. A1 - frübing, Peter A1 - Gerhard, Reimund T1 - Relaxation Processes Determining the Electret Stability of High-Impact Polystyrene/Titanium-Dioxide Composite Films JF - IEEE transactions on dielectrics and electrical insulation N2 - The influence of relaxation processes on the thermal electret stability of high-impact polystyrene (HIPS) free-standing films filled with titanium dioxide (TiO2) of the rutile modification are investigated by means of a combination of dielectric methods (dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC) and thermally stimulated surface-potential decay (TSSPD)), supplemented by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Films with 2, 4, 6 and 8 vol.% TiO2 are compared to each other and to non-filled samples. Filling HIPS with up to 8 vol.% of TiO2 enhances the elastic modulus below the glass transition and increases the thermal electret stability above the glass transition without significantly increasing the DC conductivity. The improvement of the electret stability is caused by the build-up of an interface polarization which decays only gradually if the glass transition is exceeded. Two kinds of Arrhenius processes are considered in order to explain the decay of the composite-polymer electrets: (1) charge release from chemical traps located at the phenyl rings of the polymer chain with an activation energy of E-a = 1.1 eV after passing the glass transition at about 100 degrees C and (2) charge release from traps formed by the TiO2 particles with E-a = 2.4 eV at temperatures above 130 degrees C. Finally, the activation energies are discussed with respect to their significance. KW - High-impact polystyrene KW - titanium dioxide KW - electret stability KW - dielectric relaxation Y1 - 2017 U6 - https://doi.org/10.1109/TDEI.2017.006587 SN - 1070-9878 SN - 1558-4135 VL - 24 SP - 2541 EP - 2548 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Drozdov, Alexander A1 - Shprits, Yuri A1 - Usanova, Maria E. A1 - Aseev, Nikita A1 - Kellerman, Adam C. A1 - Zhu, H. T1 - EMIC wave parameterization in the long-term VERB code simulation JF - Journal of geophysical research : Space physics N2 - Electromagnetic ion cyclotron (EMIC) waves play an important role in the dynamics of ultrarelativistic electron population in the radiation belts. However, as EMIC waves are very sporadic, developing a parameterization of such wave properties is a challenging task. Currently, there are no dynamic, activity-dependent models of EMIC waves that can be used in the long-term (several months) simulations, which makes the quantitative modeling of the radiation belt dynamics incomplete. In this study, we investigate Kp, Dst, and AE indices, solar wind speed, and dynamic pressure as possible parameters of EMIC wave presence. The EMIC waves are included in the long-term simulations (1year, including different geomagnetic activity) performed with the Versatile Electron Radiation Belt code, and we compare results of the simulation with the Van Allen Probes observations. The comparison shows that modeling with EMIC waves, parameterized by solar wind dynamic pressure, provides a better agreement with the observations among considered parameterizations. The simulation with EMIC waves improves the dynamics of ultrarelativistic fluxes and reproduces the formation of the local minimum in the phase space density profiles. KW - radiation belts KW - VERB code KW - EMIC Y1 - 2017 U6 - https://doi.org/10.1002/2017JA024389 SN - 2169-9380 SN - 2169-9402 VL - 122 SP - 8488 EP - 8501 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Pikovskij, Arkadij T1 - Reconstruction of a scalar voltage-based neural field network from observed time series JF - epl : a letters journal exploring the frontiers of physics Y1 - 2017 U6 - https://doi.org/10.1209/0295-5075/119/30004 SN - 0295-5075 SN - 1286-4854 VL - 119 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Davidsen, Joern A1 - Kwiatek, Grzegorz A1 - Charalampidou, Elli-Maria A1 - Goebel, Thomas H. W. A1 - Stanchits, Sergei A1 - Rueck, Marc A1 - Dresen, Georg T1 - Triggering Processes in Rock Fracture JF - Physical review letters N2 - We study triggering processes in triaxial compression experiments under a constant displacement rate on sandstone and granite samples using spatially located acoustic emission events and their focal mechanisms. We present strong evidence that event-event triggering plays an important role in the presence of large-scale or macrocopic imperfections, while such triggering is basically absent if no significant imperfections are present. In the former case, we recover all established empirical relations of aftershock seismicity including the Gutenberg-Richter relation, a modified version of the Omori-Utsu relation and the productivity relation-despite the fact that the activity is dominated by compaction-type events and triggering cascades have a swarmlike topology. For the Gutenberg-Richter relations, we find that the b value is smaller for triggered events compared to background events. Moreover, we show that triggered acoustic emission events have a focal mechanism much more similar to their associated trigger than expected by chance. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevLett.119.068501 SN - 0031-9007 SN - 1079-7114 VL - 119 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Oskinova, Lidia M. A1 - Huenemoerder, D. P. A1 - Hamann, Wolf-Rainer A1 - Shenar, Tomer A1 - Sander, Andreas Alexander Christoph A1 - Ignace, R. A1 - Todt, Helge Tobias A1 - Hainich, Rainer T1 - On the Binary Nature of Massive Blue Hypergiants: High-resolution X-Ray Spectroscopy Suggests That Cyg OB2 12 is a Colliding Wind Binary JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The blue hypergiant Cyg OB2 12 (B3Ia(+)) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si XIV and Mg XII. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere or in a colliding wind zone between binary components. The observed X-ray spectra are well-fitted by thermal plasma models, with average temperatures in excess of 10 MK. The wind speed in Cyg OB2 12 is not high enough to power such high temperatures, but the collision of two winds in a binary system can be sufficient. We used archival data to investigate the X-ray properties of other blue hypergiants. In general, stars of this class are not detected as X-ray sources. We suggest that our new Chandra observations of Cyg OB2 12 can be best explained if Cyg OB2 12 is a colliding wind binary possessing a late O-type companion. This makes Cyg OB2 12 only the second binary system among the 16 known Galactic hypergiants. This low binary fraction indicates that the blue hypergiants are likely products of massive binary evolution during which they either accreted a significant amount of mass or already merged with their companions. KW - stars: individual (Cyg OB2 12) KW - stars: massive KW - stars: mass-loss KW - stars: winds, outflows KW - supergiants KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.3847/1538-4357/aa7e79 SN - 0004-637X SN - 1538-4357 VL - 845 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Cherstvy, Andrey G. T1 - Shape Morphologies of Icosahedral Two-Component Vesicles JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - What are the features of partitioning of crystalline materials on the surface of a two-component icosahedral vesicle? We model the response of the rigid hardly stretchable crystalline icosahedra upon addition of a softer component on its surface. We demonstrate how the soft phase "invades" the shell regions with the highest elastic energy density around 12 5-fold topological defects. We explore the phase diagram of these inhomogeneous shells as a function of the soft material fraction, shell radius, and elastic moduli of the two phases. The findings are compared with the recent computer simulation findings, and their biological relevance, for example, for the structure of icosahedral viruses, is also discussed. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpcb.7b02440 SN - 1520-6106 VL - 121 SP - 7484 EP - 7491 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Vaz da Cruz, Vinicius A1 - Ertan, Emelie A1 - Couto, Rafael C. A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Dantz, Marcus A1 - Kennedy, Brian A1 - Schmitt, Thorsten A1 - Pietzsch, Annette A1 - Guimaraes, Freddy F. A1 - Ågren, Hans A1 - Odelius, Michael A1 - Föhlisch, Alexander A1 - Kimberg, Victor T1 - A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems. Y1 - 2017 U6 - https://doi.org/10.1039/c7cp01215b SN - 1463-9076 SN - 1463-9084 VL - 19 SP - 19573 EP - 19589 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Feldmann, Johannes A1 - Levermann, Anders T1 - From cyclic ice streaming to Heinrich-like events: the grow-and-surge instability in the Parallel Ice Sheet Model JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - Here we report on a cyclic, physical ice-discharge instability in the Parallel Ice Sheet Model, simulating the flow of a three-dimensional, inherently buttressed ice-sheet-shelf system which periodically surges on a millennial timescale. The thermomechanically coupled model on 1 km horizontal resolution includes an enthalpy-based formulation of the thermodynamics, a nonlinear stress-balance-based sliding law and a very simple subglacial hydrology. The simulated unforced surging is characterized by rapid ice streaming through a bed trough, resulting in abrupt discharge of ice across the grounding line which is eventually calved into the ocean. We visualize the central feedbacks that dominate the subsequent phases of ice buildup, surge and stabilization which emerge from the interaction between ice dynamics, thermodynamics and the subglacial till layer. Results from the variation of surface mass balance and basal roughness suggest that ice sheets of medium thickness may be more susceptible to surging than relatively thin or thick ones for which the surge feedback loop is damped. We also investigate the influence of different basal sliding laws (ranging from purely plastic to nonlinear to linear) on possible surging. The presented mechanisms underlying our simulations of self-maintained, periodic ice growth and destabilization may play a role in large-scale ice-sheet surging, such as the surging of the Laurentide Ice Sheet, which is associated with Heinrich events, and ice-stream shutdown and reactivation, such as observed in the Siple Coast region of West Antarctica. Y1 - 2017 U6 - https://doi.org/10.5194/tc-11-1913-2017 SN - 1994-0416 SN - 1994-0424 VL - 11 SP - 1913 EP - 1932 PB - Copernicus CY - Göttingen ER -