@misc{YangGuehrVecchioneetal.2016,
  author    = {Yang, Jie and Guehr, Markus and Vecchione, Theodore and Robinson, Matthew Scott and Li, Renkai and Hartmann, Nick and Shen, Xiaozhe and Coffee, Ryan and Corbett, Jeff and Fry, Alan and Gaffney, Kelly and Gorkhover, Tais and Hast, Carsten and Jobe, Keith and Makasyuk, Igor and Reid, Alexander and Robinson, Joseph and Vetter, Sharon and Wang, Fenglin and Weathersby, Stephen and Yoneda, Charles and Wang, Xijie and Centurion, Martin},
  title     = {Femtosecond gas phase electron diffraction with MeV electrons},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394989},
  pages     = {19},
  year      = {2016},
  abstract  = {We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.},
  language  = {en}
}
@misc{TomovPenaRoqueetal.2016,
  author    = {Tomov, Petar and Pena, Rodrigo F. O. and Roque, Antonio C. and Zaks, Michael A.},
  title     = {Mechanisms of self-sustained oscillatory states in hierarchical modular networks with mixtures of electrophysiological cell types},
  series = {Frontiers in computational neuroscience},
  journal   = {Frontiers in computational neuroscience},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407724},
  pages     = {17},
  year      = {2016},
  abstract  = {In a network with a mixture of different electrophysiological types of neurons linked by excitatory and inhibitory connections, temporal evolution leads through repeated epochs of intensive global activity separated by intervals with low activity level. This behavior mimics "up" and "down" states, experimentally observed in cortical tissues in absence of external stimuli. We interpret global dynamical features in terms of individual dynamics of the neurons. In particular, we observe that the crucial role both in interruption and in resumption of global activity is played by distributions of the membrane recovery variable within the network. We also demonstrate that the behavior of neurons is more influenced by their presynaptic environment in the network than by their formal types, assigned in accordance with their response to constant current.},
  language  = {en}
}
@phdthesis{Schulz2016,
  author    = {Schulz, Alexander},
  title     = {Untersuchung der Wechselwirkung synoptisch-skaliger mit orographisch bedingten Prozessen in der arktischen Grenzschicht {\"u}ber Spitzbergen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400058},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vi, 194},
  year      = {2016},
  abstract  = {In der vorliegenden Arbeit wird die planetare Grenzschicht in Ny-{\AA}lesund, Spitzbergen, sowohl bez{\"u}glich kleinskaliger („mikrometeorologischer") Effekte als auch in ihrer Kopplung mit der Synoptik untersucht. Dazu werden verschiedene Beobachtungsdaten aus der S{\"a}ule und in Bodenn{\"a}he zusammengezogen und bewertet. Die so gewonnenen Datens{\"a}tze werden dann zur Validierung eines nicht-hydrostatischen, regionalen Klimamodells genutzt. Weiterhin werden orographisch bedingte Einfl{\"u}sse, die Untergrundbeschaffenheit und die lokale Heterogenit{\"a}t der Unterlage untersucht. Hierzu werden meteorologische Gr{\"o}ßen, wie die Variabilit{\"a}t der Temperatur und insbesondere die j{\"a}hrliche Windverteilung in Bodenn{\"a}he untersucht und es erfolgt ein Vergleich von in-situ gemessenen turbulenten Fl{\"u}ssen von den Eddy-Kovarianz-Messkomplexen bei Ny-{\AA}lesund und im Bayelva-Tal unter demselben Aspekt. Es zeigt sich, dass der Eddy-Kovarianz-Messkomplex im Bayelva-Tal sehr stark durch eine orographisch bedingte Kanalisierung der Str{\"o}mung beeinflusst ist und sich nicht f{\"u}r Vergleiche mit regionalen Klimamodellen mit horizontalen Aufl{\"o}sungen von <1km eignet. Die hohe Bodenfeuchte im Bayelva-Tal f{\"u}hrt zudem zu einem deutlich kleineren Bowen-Verh{\"a}ltnis, als es f{\"u}r diese Region zu erwarten ist. Der Eddy-Kovarianz-Messkomplex bei Ny-{\AA}lesund erweist sich hingegen als geeigneter f{\"u}r solche Modellvergleiche, aufgrund der typischen, k{\"u}stennahen Windverteilung und des repr{\"a}sentativen Footprints. Letzteres wird durch die Bestimmung der Footprint-Klimatologie des Jahres 2013 mit einem aktuellen Footprint-Modell erarbeitet. Weiterhin wird die Auswirkung von (Anti-) Zyklonen {\"u}ber den Archipel auf die zeitliche Variabilit{\"a}t der lokalen Grenzschichteigenschaften untersucht und bewertet. Dazu wird ein Zyklonen-Detektions-Algorithmus auf ERA-Interim-Reanalysedatens{\"a}tze angewendet, wodurch die H{\"a}ufigkeit von nahezu ideal konzentrischen Hoch- und die Tiefdruckgebieten f{\"u}r drei Jahre bestimmt wird. Aus dieser Verteilung werden insgesamt drei interessante Zeitr{\"a}ume zu verschiedenen Jahreszeiten ausgew{\"a}hlt und im Rahmen von Prozessstudien die lokalen bodennahen meteorologischen Messungen, der turbulente Austausch an der Oberfl{\"a}che und die Grenzschichtdynamik in der S{\"a}ule untersucht. Die zeitliche Variabilit{\"a}t der dynamischen Grenzschichtstabilit{\"a}t in der S{\"a}ule wird anhand von zeitlich hoch aufgel{\"o}sten vertikalen Profilen der Bulk-Richardson-Zahl aus Kompositprofilen aus Fernerkundungsinstrumenten (Radiometer, Wind-LIDAR) sowie Mastdaten (BSRN-Mast) untersucht und die Grenzschichth{\"o}he ermittelt. Aus diesen Analysen ergibt sich eine deutliche Abh{\"a}ngigkeit der thermischen Stabilit{\"a}t beim Durchzug von Fronten, eine damit einhergehende erhebliche Abh{\"a}ngigkeit der Grenzschichtdynamik und der Grenzschichth{\"o}he sowie des turbulenten Austauschs von der zeitlichen Variabilit{\"a}t der Windgeschwindigkeit in der S{\"a}ule. Auf Grundlage der Standortanalysen und Prozessstudien erfolgt ein Vergleich der bodennahen Messungen und den Beobachtungen aus der S{\"a}ule, sowohl von den genannten Fernerkundungsinstrumenten als auch von In-situ-Messungen (Radiosonden) f{\"u}r den Zeitraum einer Radiosondierungskampagne mit dem nicht-hydrostatischen, regionalen Klimamodel WRF (ARW). Auf Grundlage der Fragestellung, inwieweit aktuelle Schemata die Grenzschichtcharakteristika in orographisch stark gegliedertem Gel{\"a}nde in der Arktis reproduzieren k{\"o}nnen, werden zwei Grenzschichtparametrisierungsschemata mit verschiedenen Ordnungen der Schließung validiert. Hierzu wird die zeitliche Variabilit{\"a}t der Temperatur, der Feuchte und des Windfeldes in der S{\"a}ule bis 2000m in den Simulationen mit den Beobachtungsdaten vergleichen. Es wird gezeigt, dass durch Modifikation der Initialwertfelder eine sehr gute {\"U}bereinstimmung zwischen den Simulationen und den Beobachtungen bereits bei einer horizontalen Aufl{\"o}sung von 1km erreicht werden kann und die Wahl des Grenzschichtschemas nur untergeordneten Einfluss hat. Hieraus werden Ans{\"a}tze der Weiterentwicklung der Parametrisierungen, aber auch Empfehlungen bez{\"u}glich der Initialwertfelder, wie der Landmaske und der Orographie, vorgeschlagen.},
  language  = {de}
}
@phdthesis{Schroeder2016,
  author    = {Schr{\"o}der, Henning},
  title     = {Ultrafast electron dynamics in Fe(CO)5 and Cr(CO)6},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-94589},
  school      = {Universit{\"a}t Potsdam},
  pages     = {v, 87},
  year      = {2016},
  abstract  = {In this thesis, the two prototype catalysts Fe(CO)₅ and Cr(CO)₆ are investigated with time-resolved photoelectron spectroscopy at a high harmonic setup. In both of these metal carbonyls, a UV photon can induce the dissociation of one or more ligands of the complex. The mechanism of the dissociation has been debated over the last decades. The electronic dynamics of the first dissociation occur on the femtosecond timescale. For the experiment, an existing high harmonic setup was moved to a new location, was extended, and characterized. The modified setup can induce dynamics in gas phase samples with photon energies of 1.55eV, 3.10eV, and 4.65eV. The valence electronic structure of the samples can be probed with photon energies between 20eV and 40eV. The temporal resolution is 111fs to 262fs, depending on the combination of the two photon energies. The electronically excited intermediates of the two complexes, as well as of the reaction product Fe(CO)₄, could be observed with photoelectron spectroscopy in the gas phase for the first time. However, photoelectron spectroscopy gives access only to the final ionic states. Corresponding calculations to simulate these spectra are still in development. The peak energies and their evolution in time with respect to the initiation pump pulse have been determined, these peaks have been assigned based on literature data. The spectra of the two complexes show clear differences. The dynamics have been interpreted with the assumption that the motion of peaks in the spectra relates to the movement of the wave packet in the multidimensional energy landscape. The results largely confirm existing models for the reaction pathways. In both metal carbonyls, this pathway involves a direct excitation of the wave packet to a metal-to-ligand charge transfer state and the subsequent crossing to a dissociative ligand field state. The coupling of the electronic dynamics to the nuclear dynamics could explain the slower dissociation in Fe(CO)₅ as compared to Cr(CO)₆.},
  language  = {en}
}
@misc{SchickEckertPontiusetal.2016,
  author    = {Schick, Daniel and Eckert, Sebastian and Pontius, Niko and Mitzner, Rolf and F{\"o}hlisch, Alexander and Holldack, Karsten and Sorgenfrei, Nomi},
  title     = {Versatile soft X-ray-optical cross-correlator for ultrafast applications},
  series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {1331},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-43696},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436962},
  pages     = {054304-1 -- 054304-8},
  year      = {2016},
  abstract  = {We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50\% total X-ray reflectivity and transient signal changes of more than 20\%. (C) 2016 Author(s).},
  language  = {en}
}
@misc{RaetzelWilkensMenzel2016,
  author    = {R{\"a}tzel, Dennis and Wilkens, Martin and Menzel, Ralf},
  title     = {Gravitational properties of light},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-90553},
  year      = {2016},
  abstract  = {The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources.},
  language  = {en}
}
@misc{ReppertPuddellKocetal.2016,
  author    = {Reppert, Alexander von and Puddell, J. and Koc, A. and Reinhardt, M. and Leitenberger, Wolfram and Dumesnil, K. and Zamponi, Flavio and Bargheer, Matias},
  title     = {Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98710},
  pages     = {11},
  year      = {2016},
  abstract  = {We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the N{\´e}el temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.},
  language  = {en}
}
@misc{PimenovaGoldobinRosenblumetal.2016,
  author    = {Pimenova, Anastasiya V. and Goldobin, Denis S. and Rosenblum, Michael and Pikovskij, Arkadij},
  title     = {Interplay of coupling and common noise at the transition to synchrony in oscillator populations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-103471},
  pages     = {7},
  year      = {2016},
  abstract  = {There are two ways to synchronize oscillators: by coupling and by common forcing, which can be pure noise. By virtue of the Ott-Antonsen ansatz for sine-coupled phase oscillators, we obtain analytically tractable equations for the case where both coupling and common noise are present. While noise always tends to synchronize the phase oscillators, the repulsive coupling can act against synchrony, and we focus on this nontrivial situation. For identical oscillators, the fully synchronous state remains stable for small repulsive coupling; moreover it is an absorbing state which always wins over the asynchronous regime. For oscillators with a distribution of natural frequencies, we report on a counter-intuitive effect of dispersion (instead of usual convergence) of the oscillators frequencies at synchrony; the latter effect disappears if noise vanishes.},
  language  = {en}
}
@misc{PavlenkoSanderMitzscherlingetal.2016,
  author    = {Pavlenko, Elena S. and Sander, Mathias and Mitzscherling, Steffen and Pudell, Jan-Etienne and Zamponi, Flavio and R{\"o}ssle, Matthias and Bojahr, Andre and Bargheer, Matias},
  title     = {Azobenzene - functionalized polyelectrolyte nanolayers as ultrafast optoacoustic transducers},
  volume    = {8},
  doi       = {10.1039/C6NR01448H},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-101996},
  pages     = {13297 -- 13302},
  year      = {2016},
  abstract  = {We introduce azobenzene-functionalized polyelectrolyte multilayers as efficient, inexpensive optoacoustic transducers for hyper-sound strain waves in the GHz range. By picosecond transient reflectivity measurements we study the creation of nanoscale strain waves, their reflection from interfaces, damping by scattering from nanoparticles and propagation in soft and hard adjacent materials like polymer layers, quartz and mica. The amplitude of the generated strain ε ∼ 5 × 10-4 is calibrated by ultrafast X-ray diffraction.},
  language  = {en}
}
@phdthesis{Pavlenko2016,
  author    = {Pavlenko, Elena},
  title     = {Hybrid nanolayer architectures for ultrafast acousto-plasmonics in soft matter},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-99544},
  school      = {Universit{\"a}t Potsdam},
  pages     = {85},
  year      = {2016},
  abstract  = {The goal of the presented work is to explore the interaction between gold nanorods (GNRs) and hyper-sound waves. For the generation of the hyper-sound I have used Azobenzene-containing polymer transducers. Multilayer polymer structures with well-defined thicknesses and smooth interfaces were built via layer-by-layer deposition. Anionic polyelectrolytes with Azobenzene side groups (PAzo) were alternated with cationic polymer PAH, for the creation of transducer films. PSS/PAH multilayer were built for spacer layers, which do not absorb in the visible light range. The properties of the PAzo/PAH film as a transducer are carefully characterized by static and transient optical spectroscopy. The optical and mechanical properties of the transducer are studied on the picosecond time scale. In particular the relative change of the refractive index of the photo-excited and expanded PAH/PAzo is Δn/n = - 2.6*10-4. Calibration of the generated strain is performed by ultrafast X-ray diffraction calibrated the strain in a Mica substrate, into which the hyper-sound is transduced. By simulating the X-ray data with a linear-chain-model the strain in the transducer under the excitation is derived to be Δd/d ~ 5*10-4. Additional to the investigation of the properties of the transducer itself, I have performed a series of experiments to study the penetration of the generated strain into various adjacent materials. By depositing the PAzo/PAH film onto a PAH/PSS structure with gold nanorods incorporated in it, I have shown that nanoscale impurities can be detected via the scattering of hyper-sound. Prior to the investigation of complex structures containing GNRs and the transducer, I have performed several sets of experiments on GNRs deposited on a small buffer of PSS/PAH. The static and transient response of GNRs is investigated for different fluence of the pump beam and for different dielectric environments (GNRs covered by PSS/PAH). A systematic analysis of sample architectures is performed in order to construct a sample with the desired effect of GNRs responding to the hyper-sound strain wave. The observed shift of a feature related to the longitudinal plasmon resonance in the transient reflection spectra is interpreted as the event of GNRs sensing the strain wave. We argue that the shift of the longitudinal plasmon resonance is caused by the viscoelastic deformation of the polymer around the nanoparticle. The deformation is induced by the out of plane difference in strain in the area directly under a particle and next to it. Simulations based on the linear chain model support this assumption. Experimentally this assumption is proven by investigating the same structure, with GNRs embedded in a PSS/PAH polymer layer. The response of GNRs to the hyper-sound wave is also observed for the sample structure with GNRs embedded in PAzo/PAH films. The response of GNRs in this case is explained to be driven by the change of the refractive index of PAzo during the strain propagation.},
  language  = {en}
}