@article{ChechkinKantzMetzler2017, author = {Chechkin, Aleksei V. and Kantz, Holger and Metzler, Ralf}, title = {Ageing effects in ultraslow continuous time random walks}, series = {The European physical journal : B, Condensed matter and complex systems}, volume = {90}, journal = {The European physical journal : B, Condensed matter and complex systems}, publisher = {Springer}, address = {New York}, issn = {1434-6028}, doi = {10.1140/epjb/e2017-80270-9}, pages = {12}, year = {2017}, abstract = {In ageing systems physical observables explicitly depend on the time span elapsing between the original initiation of the system and the actual start of the recording of the particle motion. We here study the signatures of ageing in the framework of ultraslow continuous time random walk processes with super-heavy tailed waiting time densities. We derive the density for the forward or recurrent waiting time of the motion as function of the ageing time, generalise the Montroll-Weiss equation for this process, and analyse the ageing behaviour of the ensemble and time averaged mean squared displacements.}, language = {en} } @article{NikolisBenduhnHolzmuelleretal.2017, author = {Nikolis, Vasileios C. and Benduhn, Johannes and Holzmueller, Felix and Piersimoni, Fortunato and Lau, Matthias and Zeika, Olaf and Neher, Dieter and Koerner, Christian and Spoltore, Donato and Vandewal, Koen}, title = {Reducing Voltage Losses in Cascade Organic Solar Cells while Maintaining High External Quantum Efficiencies}, series = {dvanced energy materials}, volume = {7}, journal = {dvanced energy materials}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.201700855}, pages = {122 -- 136}, year = {2017}, abstract = {High photon energy losses limit the open-circuit voltage (V-OC) and power conversion efficiency of organic solar cells (OSCs). In this work, an optimization route is presented which increases the V-OC by reducing the interfacial area between donor (D) and acceptor (A). This optimization route concerns a cascade device architecture in which the introduction of discontinuous interlayers between alpha-sexithiophene (alpha-6T) (D) and chloroboron subnaphthalocyanine (SubNc) (A) increases the V-OC of an alpha-6T/SubNc/SubPc fullerene-free cascade OSC from 0.98 V to 1.16 V. This increase of 0.18 V is attributed solely to the suppression of nonradiative recombination at the D-A interface. By accurately measuring the optical gap (E-opt) and the energy of the charge-transfer state (E-CT) of the studied OSC, a detailed analysis of the overall voltage losses is performed. E-opt - qV(OC) losses of 0.58 eV, which are among the lowest observed for OSCs, are obtained. Most importantly, for the V-OC-optimized devices, the low-energy (700 nm) external quantum efficiency (EQE) peak remains high at 79\%, despite a minimal driving force for charge separation of less than 10 meV. This work shows that low-voltage losses can be combined with a high EQE in organic photovoltaic devices.}, language = {en} } @article{RichterNuzaFoxetal.2017, author = {Richter, Philipp and Nuza, S. E. and Fox, Andrew J. and Wakker, Bart P. and Lehner, N. and Ben Bekhti, Nadya and Fechner, Cora and Wendt, Martin and Howk, J. Christopher and Muzahid, S. and Ganguly, R. and Charlton, Jane C.}, title = {An HST/COS legacy survey of high-velocity ultraviolet absorption in the}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {607}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201630081}, pages = {90}, year = {2017}, abstract = {Context. The Milky Way is surrounded by large amounts of diffuse gaseous matter that connects the stellar body of our Galaxy with its large-scale Local Group (LG) environment. Aims. To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Methods. Along 270 sightlines we measure metal absorption in the lines of Si II, Si III, C II, and C IV and associated H I 21 cm emission in HVCs in the velocity range vertical bar v(LSR)vertical bar = 100-500 km s(-1). With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the HVC absorption characteristics with that of damped Lyman alpha absorbers (DLAs) and constrained cosmological simulations of the LG (CLUES project).}, language = {en} } @article{SundeGrijsSubramanianetal.2017, author = {Sun, Ning-Chen and de Grijs, Richard and Subramanian, Smitha and Bekki, Kenji and Bell, Cameron P. M. and Cioni, Maria-Rosa L. and Ivanov, Valentin D. and Marconi, Marcella and Oliveira, Joana M. and Piatti, Andres E. and Ripepi, Vincenzo and Rubele, Stefano and Tatton, Ben L. and van Loon, Jacco Th.}, title = {The VMC Survey. XXII. Hierarchical Star Formation in the 30 Doradus-N158-N159-N160 Star-forming Complex}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {849}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/1538-4357/aa911e}, pages = {16}, year = {2017}, abstract = {Star formation is a hierarchical process, forming young stellar structures of star clusters, associations, and complexes over a wide range of scales. The star-forming complex in the bar region of the Large Magellanic Cloud is investigated with upper main-sequence stars observed by the VISTA Survey of the Magellanic Clouds. The upper main-sequence stars exhibit highly nonuniform distributions. Young stellar structures inside the complex are identified from the stellar density map as density enhancements of different significance levels. We find that these structures are hierarchically organized such that larger, lower-density structures contain one or several smaller, higher-density ones. They follow power-law size and mass distributions, as well as a lognormal surface density distribution. All these results support a scenario of hierarchical star formation regulated by turbulence. The temporal evolution of young stellar structures is explored by using subsamples of upper main-sequence stars with different magnitude and age ranges. While the youngest subsample, with a median age of log(tau/yr) = 7.2, contains the most substructure, progressively older ones are less and less substructured. The oldest subsample, with a median age of log(tau/yr) = 8.0, is almost indistinguishable from a uniform distribution on spatial scales of 30-300. pc, suggesting that the young stellar structures are completely dispersed on a timescale of similar to 100. Myr. These results are consistent with the characteristics of the 30. Doradus complex and the entire Large Magellanic Cloud, suggesting no significant environmental effects. We further point out that the fractal dimension may be method dependent for stellar samples with significant age spreads.}, language = {en} } @article{RajuKosmellaFribergetal.2017, author = {Raju, Rajarshi Roy and Kosmella, Sabine and Friberg, Stig E. and Koetz, Joachim}, title = {Pickering Janus emulsions and polyelectrolyte complex-stabilized Janus gels}, series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, volume = {533}, journal = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2017.08.022}, pages = {241 -- 248}, year = {2017}, abstract = {Janus emulsions, containing olive oil (OO) and silicone oil (SiO), were formed in presence of polyelectrolyte complex particles, i.e., gelatin-sodium polyacrylate (NaPAA) complexes. The diameter of completely engulfed Janus droplets can be tuned between 50 and 200 mu m by varying the gelatin/NaPAA complex particle size between 200 and 400 nm. The gelatin/NaPAA complex particles adsorbed at the olive oil interface decrease the interfacial tension and stabilize the resulting completely engulfed Pickering Janus emulsions. Long-term stable Janus gels can be synthesized in presence of gelatin/sodium carboxymethylcellulose (NaCMC) mixtures. In that case Coulombic forces are of relevance with regard to the stabilization of the Janus droplets embedded in a gelatin/NaCMC gel matrix. Janus gels show elastic reological behavior and thixotropic properties.}, language = {en} } @article{VafinRiazantsevaYoon2017, author = {Vafin, Sergei and Riazantseva, M. and Yoon, P. H.}, title = {Kinetic Features in the Ion Flux Spectrum}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {850}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/1538-4357/aa9519}, pages = {7}, year = {2017}, abstract = {An interesting feature of solar wind fluctuations is the occasional presence of a well-pronounced peak near the spectral knee. These peaks are well investigated in the context of magnetic field fluctuations in the magnetosheath and they are typically related to kinetic plasma instabilities. Recently, similar peaks were observed in the spectrum of ion flux fluctuations of the solar wind and magnetosheath. In this paper, we propose a simple analytical model to describe such peaks in the ion flux spectrum based on the linear theory of plasma fluctuations. We compare our predictions with a sample observation in the solar wind. For the given observation, the peak requires similar to 10 minutes to grow up to the observed level that agrees with the quasi-linear relaxation time. Moreover, our model well reproduces the form of the measured peak in the ion flux spectrum. The observed lifetime of the peak is about 50 minutes, which is relatively close to the nonlinear Landau damping time of 30-40 minutes. Overall, our model proposes a plausible scenario explaining the observation.}, language = {en} } @article{IgnaceHoleOskinovaetal.2017, author = {Ignace, R. and Hole, K. T. and Oskinova, Lida and Rotter, J. P.}, title = {An X-Ray Study of Two B plus B Binaries: AH Cep and CW Cep}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {850}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/1538-4357/aa93ea}, pages = {7}, year = {2017}, abstract = {AH Cep and CW Cep are both early B-type binaries with short orbital periods of 1.8. days and 2.7. days, respectively. All four components are B0.5V types. The binaries are also double-lined spectroscopic and eclipsing. Consequently, solutions for orbital and stellar parameters make the pair of binaries ideal targets for a study of the colliding winds between two B. stars. Chandra ACIS-I observations were obtained to determine X-ray luminosities. AH. Cep was detected with an unabsorbed X-ray luminosity at a 90\% confidence interval of (9-33) x 10(30) erg s(-1), or (0.5-1.7) x 10(-7) L-Bol , relative to the combined Bolometric luminosities of the two components. While formally consistent with expectations for embedded wind shocks, or binary wind collision, the near-twin system of CW Cep was a surprising nondetection. For CW Cep, an upper limit was determined with L-X/L-Bol < 10(-8), again for the combined components. One difference between these two systems is that AH Cep is part of a multiple system. The X-rays from AH. Cep may not arise from standard wind shocks nor wind collision, but perhaps instead from magnetism in any one of the four components of the system. The possibility could be tested by searching for cyclic X-ray variability in AH. Cep on the short orbital period of the inner B. stars.}, language = {en} } @article{PuppeHoehnKaczoreketal.2017, author = {Puppe, Daniel and H{\"o}hn, Axel and Kaczorek, Danuta and Wanner, Manfred and Wehrhan, Marc and Sommer, Michael}, title = {How big is the influence of biogenic silicon pools on short-term changes in water-soluble silicon in soils? Implications from a study of a 10-year-old soil-plant system}, series = {Biogeosciences}, volume = {14}, journal = {Biogeosciences}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1726-4170}, doi = {10.5194/bg-14-5239-2017}, pages = {14}, year = {2017}, abstract = {The significance of biogenic silicon (BSi) pools as a key factor for the control of Si fluxes from terrestrial to aquatic ecosystems has been recognized for decades. However, while most research has been focused on phytogenic Si pools, knowledge of other BSi pools is still limited. We hypothesized that different BSi pools influence short-term changes in the water-soluble Si fraction in soils to different extents. To test our hypothesis we took plant (Calamagrostis epigejos, Phragmites australis) and soil samples in an artificial catchment in a post-mining landscape in the state of Brandenburg, Germany. We quantified phytogenic (phytoliths), protistic (diatom frustules and testate amoeba shells) and zoogenic (sponge spicules) Si pools as well as Tironextractable and water-soluble Si fractions in soils at the beginning (t(0)) and after 10 years (t(10)) of ecosystem development. As expected the results of Tiron extraction showed that there are no consistent changes in the amorphous Si pool at Chicken Creek (Huhnerwasser) as early as after 10 years. In contrast to t(0) we found increased water-soluble Si and BSi pools at t(10); thus we concluded that BSi pools are the main driver of short-term changes in water-soluble Si. However, because total BSi represents only small proportions of water-soluble Si at t(0) (< 2 \%) and t(10) (2.8-4.3 \%) we further concluded that smaller (< 5 mu m) and/or fragile phytogenic Si structures have the biggest impact on short-term changes in water-soluble Si. In this context, extracted phytoliths (> 5 mu m) only amounted to about 16\% of total Si con-tents of plant materials of C. epigejos and P. australis at t(10); thus about 84\% of small-scale and/or fragile phytogenic Si is not quantified by the used phytolith extraction method. Analyses of small-scale and fragile phytogenic Si structures are urgently needed in future work as they seem to represent the biggest and most reactive Si pool in soils. Thus they are the most important drivers of Si cycling in terrestrial biogeosystems.}, language = {en} } @article{WendtHusserKamannetal.2017, author = {Wendt, Martin and Husser, Tim-Oliver and Kamann, Sebastian and Monreal-Ibero, Ana and Richter, Philipp and Brinchmann, Jarle and Dreizler, Stefan and Weilbacher, Peter Michael and Wisotzki, Lutz}, title = {Mapping diffuse interstellar bands in the local ISM on small scales via MUSE 3D spectroscopy A pilot study based on globular cluster NGC 6397}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {607}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201629816}, pages = {16}, year = {2017}, abstract = {Context. We map the interstellar medium (ISM) including the diffuse interstellar bands (DIBs) in absorption toward the globular cluster NGC6397 using VLT/MUSE. Assuming the absorbers are located at the rim of the Local Bubble we trace structures on the order of mpc (milliparsec, a few thousand AU). Aims. We aimed to demonstrate the feasibility to map variations of DIBs on small scales with MUSE. The sightlines defined by binned stellar spectra are separated by only a few arcseconds and we probe the absorption within a physically connected region. Methods. This analysis utilized the fitting residuals of individual stellar spectra of NGC6397 member stars and analyzed lines from neutral species and several DIBs in Voronoi-binned composite spectra with high signal-to-noise ratio (S/N). Results. This pilot study demonstrates the power of MUSE for mapping the local ISM on very small scales which provides a new window for ISM observations. We detect small scale variations in Na-I and K-I as well as in several DIBs within few arcseconds, or mpc with regard to the Local Bubble. We verify the suitability of the MUSE 3D spectrograph for such measurements and gain new insights by probing a single physical absorber with multiple sight lines.}, language = {en} } @article{AbdallaAbramowskiAharonianetal.2017, author = {Abdalla, Hassan E. and Abramowski, Attila and Aharonian, Felix A. and Benkhali, Faical Ait and Anguner, Ekrem Oǧuzhan and Arakawa, M. and Arrieta, M. and Aubert, Pierre and Backes, Michael and Balzer, Arnim and Barnard, Michelle and Becherini, Yvonne and Tjus, J. Becker and Berge, David and Bernhard, Sabrina and Bernl{\"o}hr, K. and Blackwell, R. and B{\"o}ttcher, Markus and Boisson, Catherine and Bolmont, J. and Bonnefoy, S. and Bordas, Pol and Bregeon, Johan and Brun, Francois and Brun, Pierre and Bryan, Mark and Buechele, M. and Bulik, Tomasz and Capasso, M. and Caroff, S. and Carosi, A. and Casanova, Sabrina and Cerruti, M. and Chakraborty, N. and Chaves, Ryan C. G. and Chen, Andrew and Chevalier, J. and Colafrancesco, Sergio and Condon, B. and Conrad, Jan and Davids, I. D. and Decock, J. and Deil, C. and Devin, J. and deWilt, P. and Dirson, L. and Djannati-Atai, A. and Donath, A. and Dutson, K. and Dyks, J. and Edwards, T. and Egberts, Kathrin and Emery, G. and Ernenwein, J. -P. and Eschbach, S. and Farnier, C. and Fegan, S. and Fernandes, M. V. and Fiasson, A. and Fontaine, G. and Funk, S. and Fuessling, M. and Gabici, S. and Gallant, Y. A. and Garrigoux, T. and Gate, F. and Giavitto, G. and Giebels, B. and Glawion, D. and Glicenstein, J. F. and Gottschall, D. and Grondin, M. -H. and Hahn, J. and Haupt, M. and Hawkes, J. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hinton, James Anthony and Hofmann, W. and Hoischen, Clemens and Holch, Tim Lukas and Holler, M. and Horns, D. and Ivascenko, A. and Iwasaki, H. and Jacholkowska, A. and Jamrozy, M. and Jankowsky, D. and Jankowsky, F. and Jingo, M. and Jouvin, L. and Jung-Richardt, I. and Kastendieck, M. A. and Katarzynski, K. and Katsuragawa, M. and Katz, U. and Kerszberg, D. and Khangulyan, D. and Khelifi, B. and King, J. and Klepser, S. and Klochkov, D. and Kluzniak, W. and Komin, Nu. and Kosack, K. and Krakau, S. and Kraus, M. and Kruer, P. P. and Laffon, H. and Lamanna, G. and Lau, J. and Lees, J. -P. and Lefaucheur, J. and Lemiere, A. and Lemoine-Goumard, M. and Lenain, J. -P. and Leser, Eva and Lohse, T. and Lorentz, M. and Liu, R. and Lopez-Coto, R. and Lypova, I. and Malyshev, D. and Marandon, V. and Marcowith, Alexandre and Mariaud, C. and Marx, R. and Maurin, G. and Maxted, N. and Mayer, M. and Meintjes, P. J. and Meyer, M. and Mitchell, A. M. W. and Moderski, R. and Mohamed, M. and Mohrmann, L. and Mora, K. and Moulin, Emmanuel and Murach, T. and Nakashima, S. and de Naurois, M. and Ndiyavala, H. and Niederwanger, F. and Niemiec, J. and Oakes, L. and Odaka, H. and Ohm, S. and Ostrowski, M. and Oya, I. and Padovani, M. and Panter, M. and Parsons, R. D. and Pekeur, N. W. and Pelletier, G. and Perennes, C. and Petrucci, P. -O. and Peyaud, B. and Piel, Q. and Pita, S. and Poireau, V. and Poon, H. and Prokhorov, D. and Prokoph, H. and Puehlhofer, G. and Punch, M. and Quirrenbach, A. and Raab, S. and Rauth, R. and Reimer, A. and Reimer, O. and Renaud, M. and de los Reyes, R. and Rieger, F. and Rinchiuso, L. and Romoli, C. and Rowell, G. and Rudak, B. and Rulten, C. B. and Sahakian, V. and Saito, S. and Sanchez, David M. and Santangelo, Andrea and Sasaki, M. and Schlickeiser, R. and Schussler, F. and Schulz, A. and Schwanke, U. and Schwemmer, S. and Seglar-Arroyo, M. and Settimo, M. and Seyffert, A. S. and Shafi, N. and Shilon, I. and Shiningayamwe, K. and Simoni, R. and Sol, H. and Spanier, F. and Spir-Jacob, M. and Stawarz, L. and Steenkamp, R. and Stegmann, Christian and Steppa, Constantin Beverly and Sushch, Iurii and Takahashi, T. and Tavernet, J. -P. and Tavernier, T. and Taylor, A. M. and Terrier, R. and Tibaldo, L. and Tiziani, D. and Tluczykont, M. and Trichard, C. and Tsirou, M. and Tsuji, N. and Tuffs, R. and Uchiyama, Y. and van der Walt, D. J. and van Eldik, C. and van Rensburg, C. and van Soelen, B. and Vasileiadis, G. and Veh, J. and Venter, C. and Viana, A. and Vincent, P. and Vink, J. and Voisin, F. and Voelk, H. J. and Vuillaume, T. and Wadiasingh, Z. and Wagner, S. J. and Wagner, P. and Wagner, R. M. and White, R. and Wierzcholska, A. and Willmann, P. and Woernlein, A. and Wouters, D. and Yang, R. and Zaborov, D. and Zacharias, M. and Zanin, R. and Zdziarski, A. A. and Zech, Alraune and Zefi, F. and Ziegler, A. and Zorn, J. and Zywucka, N.}, title = {TeV Gamma-Ray Observations of the Binary Neutron Star Merger GW170817 with HESS}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {850}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, organization = {HESS Collaboration}, issn = {2041-8205}, doi = {10.3847/2041-8213/aa97d2}, pages = {628 -- 650}, year = {2017}, abstract = {We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3 hr after GW170817. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational-wave event. The first of these regions contained the counterpart SSS17a that has been identified in the optical range several hours after our observations. We can therefore present the first data obtained by a ground-based pointing instrument on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between 270 GeV to 8.55 TeV. No significant gamma-ray emission has been found. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system.}, language = {en} } @article{NishikawaMizunoGomezetal.2017, author = {Nishikawa, Ken-Ichi and Mizuno, Yosuke and Gomez, Jose L. and Dutan, Ioana and Meli, Athina and White, Charley and Niemiec, Jacek and Kobzar, Oleh and Pohl, Martin and Frederiksen, Jacob Trier and Nordlund, Ake and Sol, Helene and Hardee, Philip E. and Hartmann, Dieter H.}, title = {Microscopic Processes in Global Relativistic Jets Containing Helical Magnetic Fields: Dependence on Jet Radius}, series = {Galaxies : open access journal}, volume = {5}, journal = {Galaxies : open access journal}, publisher = {MDPI}, address = {Basel}, issn = {2075-4434}, doi = {10.3390/galaxies5040058}, pages = {7}, year = {2017}, abstract = {In this study, we investigate the interaction of jets with their environment at a microscopic level, which is a key open question in the study of relativistic jets. Using small simulation systems during past research, we initially studied the evolution of both electron-proton and electron-positron relativistic jets containing helical magnetic fields, by focusing on their interactions with an ambient plasma. Here, using larger jet radii, we have performed simulations of global jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities, such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI) and the mushroom instability (MI). We found that the evolution of global jets strongly depends on the size of the jet radius. For example, phase bunching of jet electrons, in particular in the electron-proton jet, is mixed with a larger jet radius as a result of the more complicated structures of magnetic fields with excited kinetic instabilities. In our simulation, these kinetic instabilities led to new types of instabilities in global jets. In the electron-proton jet simulation, a modified recollimation occurred, and jet electrons were strongly perturbed. In the electron-positron jet simulation, mixed kinetic instabilities occurred early, followed by a turbulence-like structure. Simulations using much larger (and longer) systems are required in order to further thoroughly investigate the evolution of global jets containing helical magnetic fields.}, language = {en} } @article{YamazakiStolleMatzkaetal.2017, author = {Yamazaki, Yosuke and Stolle, Claudia and Matzka, J{\"u}rgen and Siddiqui, Tarique Adnan and Luehr, Hermann and Alken, Patrick}, title = {Longitudinal Variation of the Lunar Tide in the Equatorial Electrojet}, series = {Journal of geophysical research : Space physics}, volume = {122}, journal = {Journal of geophysical research : Space physics}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1002/2017JA024601}, pages = {12445 -- 12463}, year = {2017}, abstract = {The atmospheric lunar tide is one known source of ionospheric variability. The subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the equatorial ionosphere. There is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude. We use magnetic field measurements from the CHAMP satellite during July 2000 to September 2010 and from the two Swarm satellites during November 2013 to February 2017 to determine, for the first time, the complete seasonal- longitudinal climatology of the semidiurnal lunar tidal variation in the equatorial electrojet intensity. Significant longitudinal variability is found in the amplitude of the lunar tidal variation, while the longitudinal variability in the phase is small. The amplitude peaks in the Peruvian sector (similar to 285 degrees E) during the Northern Hemisphere winter and equinoxes, and in the Brazilian sector (similar to 325 degrees E) during the Northern Hemisphere summer. There are also local amplitude maxima at similar to 55 degrees E and similar to 120 degrees E. The longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field. Another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides. A tidal spectrum analysis of the semidiurnal lunar tidal variation in the equatorial electrojet reveals the dominance of the westward propagating mode with zonal wave number 2 (SW2), with secondary contributions by westward propagating modes with zonal wave numbers 3 (SW3) and 4 (SW4). Eastward propagating waves are largely absent from the tidal spectrum. Further study will be required for the relative importance of ionospheric conductivities and nonmigrating lunar tides.}, language = {en} } @article{DolmatovaGoldobinPikovskij2017, author = {Dolmatova, Anastasiya V. and Goldobin, Denis S. and Pikovskij, Arkadij}, title = {Synchronization of coupled active rotators by common noise}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {96}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, publisher = {American Physical Society}, address = {College Park}, issn = {2470-0045}, doi = {10.1103/PhysRevE.96.062204}, pages = {E10648 -- E10657}, year = {2017}, abstract = {We study the effect of common noise on coupled active rotators. While such a noise always facilitates synchrony, coupling may be attractive (synchronizing) or repulsive (desynchronizing). We develop an analytical approach based on a transformation to approximate angle-action variables and averaging over fast rotations. For identical rotators, we describe a transition from full to partial synchrony at a critical value of repulsive coupling. For nonidentical rotators, the most nontrivial effect occurs at moderate repulsive coupling, where a juxtaposition of phase locking with frequency repulsion (anti-entrainment) is observed. We show that the frequency repulsion obeys a nontrivial power law.}, language = {en} } @article{KuckeinDierckeGonzalezManriqueetal.2017, author = {Kuckein, Christoph and Diercke, Andrea and Gonz{\´a}lez Manrique, Sergio Javier and Verma, Meetu and Loehner-Boettcher, Johannes and Socas-Navarro, H. and Balthasar, Horst and Sobotka, M. and Denker, Carsten}, title = {Ca II 8542 angstrom brightenings induced by a solar microflare}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {608}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201731319}, pages = {13}, year = {2017}, abstract = {Aims. We study small-scale brightenings in Ca II 8542 angstrom line-core images to determine their nature and effect on localized heating and mass transfer in active regions. Methods. High-resolution two-dimensional spectroscopic observations of a solar active region in the near-infrared Ca II 8542 angstrom line were acquired with the GREGOR Fabry-Perot Interferometer attached to the 1.5-m GREGOR telescope. Inversions of the spectra were carried out using the NICOLE code to infer temperatures and line-of-sight (LOS) velocities. Response functions of the Ca II line were computed for temperature and LOS velocity variations. Filtergrams of the Atmospheric Imaging Assembly (AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI) were coaligned to match the ground-based observations and to follow the Ca II brightenings along all available layers of the atmosphere. Results. We identified three brightenings of sizes up to 2 ' x 2 ' that appeared in the Ca II 8542 angstrom line-core images. Their lifetimes were at least 1.5 min. We found evidence that the brightenings belonged to the footpoints of a microflare (MF). The properties of the observed brightenings disqualified the scenarios of Ellerman bombs or Interface Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some common properties with flaring active-region fibrils or flaring arch filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric and coronal layers according to the AIA channels; and (2) both show flaring arches with lifetimes of about 3.0-3.5 min and lengths of similar to 20 ' next to the brightenings. The inversions revealed heating by 600 K at the footpoint location in the ambient chromosphere during the impulsive phase. Connecting the footpoints, a dark filamentary structure appeared in the Ca II line-core images. Before the start of the MF, the spectra of this structure already indicated average blueshifts, meaning upward motions of the plasma along the LOS. During the impulsive phase, these velocities increased up to -2.2 km s(-1). The structure did not disappear during the observations. Downflows dominated at the footpoints. However, in the upper photosphere, slight upflows occurred during the impulsive phase. Hence, bidirectional flows are present in the footpoints of the MF.}, language = {en} } @article{BozzoBernardiniFerrignoetal.2017, author = {Bozzo, Enrico and Bernardini, F. and Ferrigno, Carlo and Falanga, M. and Romano, Patrizia and Oskinova, Lida}, title = {The accretion environment of supergiant fast X-ray transients probed with XMM-Newton}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {608}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201730398}, pages = {20}, year = {2017}, abstract = {Context. Supergiant fast X-ray (SFXT) transients are a peculiar class of supergiant X-ray binaries characterized by a remarkable variability in the X-ray domain, widely ascribed to accretion from a clumpy stellar wind. Aims. In this paper we performed a systematic and homogeneous analysis of the sufficiently bright X-ray flares observed with XMM-Newton from the supergiant fast X-ray transients to probe spectral variations on timescales as short as a few hundred seconds. Our ultimate goal is to investigate whether SFXT flares and outbursts are triggered by the presence of clumps, and to reveal whether strongly or mildly dense clumps are required. Methods. For all sources, we employ a technique developed by our group already exploited in a number of our previous papers, making use of an adaptive rebinned hardness ratio to optimally select the time intervals for the spectral extraction. A total of twelve observations performed in the direction of five SFXTs are reported, providing the largest sample of events available so far. Results. Using the original results reported here and those obtained with our technique from the analysis of two previously published XMM-Newton observations of IGR J17544-2619 and IGR J18410-0535, we show that both strongly and mildly dense clumps can trigger these events. In the former case, the local absorption column density may increase by a factor of >> 3, while in the latter case, the increase is only a factor of similar to 2-3 (or lower). An increase in the absorption column density is generally recorded during the rise of the flares/outbursts, while a drop follows when the source achieves peak flux. In a few cases, a re-increase of the absorption column density after the flare is also detected, and we discovered one absorption event related to the passage of an unaccreted clump in front of the compact object. Overall, there seems to be no obvious correlation between the dynamic ranges in the X-ray fluxes and absorption column densities in supergiant fast X-ray transients, with an indication that lower densities are recorded at the highest fluxes. Conclusions. The spectral variations measured in all sources are in agreement with the idea that the flares/outbursts are triggered by the presence of dense structures in the wind interacting with the X-rays from the compact object (leading to photoionization). The lack of correlation between the dynamic ranges in the X-ray fluxes and absorption column densities can be explained by the presence of accretion inhibition mechanism(s). Based on the knowledge acquired so far on the SFXTs, we propose a classification of the flares/outbursts from these sources in order to drive future observational investigations. We suggest that the difference between the classes of flares/outbursts is related to the fact that the mechanism(s) inhibiting accretion can be overcome more easily in some sources compared to others. We also investigate the possibility that different stellar wind structures, other than clumps, could provide the means to temporarily overcome the inhibition of accretion in supergiant fast X-ray transients.}, language = {en} } @article{GrinbergHellElMellahetal.2017, author = {Grinberg, Victoria and Hell, Natalie and El Mellah, Ileyk and Neilsen, Joseph and Sander, Andreas Alexander Christoph and Leutenegger, Maurice and F{\"u}rst, Felix and Huenemoerder, David P. and Kretschmar, Peter and Kuehnel, Matthias and Martinez-Nunez, Silvia and Niu, Shu and Pottschmidt, Katja and Schulz, Norbert S. and Wilms, Joern and Nowak, Michael A.}, title = {The clumpy absorber in the high-mass X-ray binary Vela X-1}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {608}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201731843}, pages = {18}, year = {2017}, abstract = {Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase similar to 0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. These features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.}, language = {en} } @article{CaoShpritsNietal.2017, author = {Cao, Xing and Shprits, Yuri and Ni, Binbin and Zhelavskaya, Irina}, title = {Scattering of Ultra-relativistic Electrons in the Van Allen Radiation Belts Accounting for Hot Plasma Effects}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-17739-7}, pages = {7}, year = {2017}, abstract = {Electron flux in the Earth's outer radiation belt is highly variable due to a delicate balance between competing acceleration and loss processes. It has been long recognized that Electromagnetic Ion Cyclotron (EMIC) waves may play a crucial role in the loss of radiation belt electrons. Previous theoretical studies proposed that EMIC waves may account for the loss of the relativistic electron population. However, recent observations showed that while EMIC waves are responsible for the significant loss of ultra-relativistic electrons, the relativistic electron population is almost unaffected. In this study, we provide a theoretical explanation for this discrepancy between previous theoretical studies and recent observations. We demonstrate that EMIC waves mainly contribute to the loss of ultra-relativistic electrons. This study significantly improves the current understanding of the electron dynamics in the Earth's radiation belt and also can help us understand the radiation environments of the exoplanets and outer planets.}, language = {en} } @article{EckertNiskanenJayetal.2017, author = {Eckert, Sebastian and Niskanen, Johannes and Jay, Raphael Martin and Miedema, Piter S. and Fondell, Mattis and Kennedy, Brian and Quevedo, Wilson and Iannuzzi, Marcella and F{\"o}hlisch, Alexander}, title = {Valence orbitals and local bond dynamics around N atoms of histidine under X-ray irradiation}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {19}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c7cp05713j}, pages = {32091 -- 32098}, year = {2017}, abstract = {The valence orbitals of aqueous histidine under basic, neutral and acidic conditions and their X-ray induced transformations have been monitored through N 1s resonant inelastic X-ray scattering. Using density functional ab initio molecular dynamics simulations in the core-hole state within the Z + 1 approximation, core-excitation-induced molecular transformations are quantified. Spectroscopic evidence for a highly directional X-ray-induced local N-H dissociation within the scattering duration is presented for acidic histidine. Our report demonstrates a protonation-state and chemical-environment dependent propensity for a molecular dissociation, which is induced by the absorption of high energy photons. This case study indicates that structural deformations in biomolecules under exposure to ionizing radiation, yielding possible alteration or loss of function, is highly dependent on the physiological state of the molecule upon irradiation.}, language = {en} } @article{SanderPudellHerzogetal.2017, author = {Sander, Mathias and Pudell, Jan-Etienne and Herzog, Marc and Bargheer, Matias and Bauer, R. and Besse, V. and Temnov, V. and Gaal, P.}, title = {Quantitative disentanglement of coherent and incoherent laser-induced surface deformations by time-resolved x-ray reflectivity}, series = {Applied physics letters}, volume = {111}, journal = {Applied physics letters}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.5004522}, pages = {4}, year = {2017}, abstract = {We present time-resolved x-ray reflectivity measurements on laser excited coherent and incoherent surface deformations of thin metallic films. Based on a kinematical diffraction model, we derive the surface amplitude from the diffracted x-ray intensity and resolve transient surface excursions with sub-angstrom spatial precision and 70 ps temporal resolution. The analysis allows for decomposition of the surface amplitude into multiple coherent acoustic modes and a substantial contribution from incoherent phonons which constitute the sample heating. Published by AIP Publishing.}, language = {en} } @article{HofackerNeher2017, author = {Hofacker, Andreas and Neher, Dieter}, title = {Dispersive and steady-state recombination in organic disordered semiconductors}, series = {Physical review : B, Condensed matter and materials physics}, volume = {96}, journal = {Physical review : B, Condensed matter and materials physics}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.96.245204}, pages = {5640 -- 5649}, year = {2017}, abstract = {Charge carrier recombination in organic disordered semiconductors is strongly influenced by the thermalization of charge carriers in the density of states (DOS). Measurements of recombination dynamics, conducted under transient or steady-state conditions, can easily be misinterpreted when a detailed understanding of the interplay of thermalization and recombination is missing. To enable adequate measurement analysis, we solve the multiple-trapping problem for recombining charge carriers and analyze it in the transient and steady excitation paradigm for different DOS distributions. We show that recombination rates measured after pulsed excitation are inherently time dependent since recombination gradually slows down as carriers relax in the DOS. When measuring the recombination order after pulsed excitation, this leads to an apparent high-order recombination at short times. As times goes on, the recombination order approaches an asymptotic value. For the Gaussian and the exponential DOS distributions, this asymptotic value equals the recombination order of the equilibrated system under steady excitation. For a more general DOS distribution, the recombination order can also depend on the carrier density, under both transient and steady-state conditions. We conclude that transient experiments can provide rich information about recombination in and out of equilibrium and the underlying DOS occupation provided that consistent modeling of the system is performed.}, language = {en} } @article{HofackerNeher2017, author = {Hofacker, Andreas and Neher, Dieter}, title = {Dispersive and steady-state recombination in organic disordered semiconductors}, series = {Physical review : B, Condensed matter and materials physics}, volume = {96}, journal = {Physical review : B, Condensed matter and materials physics}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.96.245204}, pages = {11}, year = {2017}, abstract = {Charge carrier recombination in organic disordered semiconductors is strongly influenced by the thermalization of charge carriers in the density of states (DOS). Measurements of recombination dynamics, conducted under transient or steady-state conditions, can easily be misinterpreted when a detailed understanding of the interplay of thermalization and recombination is missing. To enable adequate measurement analysis, we solve the multiple-trapping problem for recombining charge carriers and analyze it in the transient and steady excitation paradigm for different DOS distributions. We show that recombination rates measured after pulsed excitation are inherently time dependent since recombination gradually slows down as carriers relax in the DOS. When measuring the recombination order after pulsed excitation, this leads to an apparent high-order recombination at short times. As times goes on, the recombination order approaches an asymptotic value. For the Gaussian and the exponential DOS distributions, this asymptotic value equals the recombination order of the equilibrated system under steady excitation. For a more general DOS distribution, the recombination order can also depend on the carrier density, under both transient and steady-state conditions. We conclude that transient experiments can provide rich information about recombination in and out of equilibrium and the underlying DOS occupation provided that consistent modeling of the system is performed.}, language = {en} } @phdthesis{Bekeraitė2017, author = {Bekeraitė, Simona}, title = {Distribution functions of rotating galaxies}, doi = {10.25932/publishup-42095}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-420950}, school = {Universit{\"a}t Potsdam}, pages = {V, 91}, year = {2017}, abstract = {The work done during the PhD studies has been focused on measurements of distribution functions of rotating galaxies using integral field spectroscopy observations. Throughout the main body of research presented here we have been using CALIFA (Calar Alto Legacy Integral Field Area) survey stellar velocity fields to obtain robust measurements of circular velocities for rotating galaxies of all morphological types. A crucial part of the work was enabled by well-defined CALIFA sample selection criteria: it enabled reconstructing sample-independent distributions of galaxy properties. In Chapter 2, we measure the distribution in absolute magnitude - circular velocity space for a well-defined sample of 199 rotating CALIFA galaxies using their stellar kinematics. Our aim in this analysis is to avoid subjective selection criteria and to take volume and large-scale structure factors into account. Using stellar velocity fields instead of gas emission line kinematics allows including rapidly rotating early type galaxies. Our initial sample contains 277 galaxies with available stellar velocity fields and growth curve r-band photometry. After rejecting 51 velocity fields that could not be modelled due to the low number of bins, foreground contamination or significant interaction we perform Markov Chain Monte Carlo (MCMC) modelling of the velocity fields, obtaining the rotation curve and kinematic parameters and their realistic uncertainties. We perform an extinction correction and calculate the circular velocity v_circ accounting for pressure support a given galaxy has. The resulting galaxy distribution on the M_r - v_circ plane is then modelled as a mixture of two distinct populations, allowing robust and reproducible rejection of outliers, a significant fraction of which are slow rotators. The selection effects are understood well enough that the incompleteness of the sample can be corrected and the 199 galaxies can be weighted by volume and large-scale structure factors enabling us to fit a volume-corrected Tully-Fisher relation (TFR). More importantly, we also provide the volume-corrected distribution of galaxies in the M_r - v_circ plane, which can be compared with cosmological simulations. The joint distribution of the luminosity and circular velocity space densities, representative over the range of -20 > M_r > -22 mag, can place more stringent constraints on the galaxy formation and evolution scenarios than linear TFR fit parameters or the luminosity function alone. In Chapter 3, we measure one of the marginal distributions of the M_r - v_circ distribution: the circular velocity function of rotating galaxies. The velocity function is a fundamental observable statistic of the galaxy population, being of a similar importance as the luminosity function, but much more difficult to measure. We present the first directly measured circular velocity function that is representative between 60 < v_circ < 320 km s^-1 for galaxies of all morphological types at a given rotation velocity. For the low mass galaxy population 60 < v_circ < 170 km s^-1, we use the HIPASS velocity function. For the massive galaxy population 170 < v_circ < 320 km s^-1, we use stellar circular velocities from CALIFA. The CALIFA velocity function includes homogeneous velocity measurements of both late and early-type rotation-supported galaxies. It has the crucial advantage of not missing gas-poor massive ellipticals that HI surveys are blind to. We show that both velocity functions can be combined in a seamless manner, as their ranges of validity overlap. The resulting observed velocity function is compared to velocity functions derived from cosmological simulations of the z = 0 galaxy population. We find that dark matter-only simulations show a strong mismatch with the observed VF. Hydrodynamic Illustris simulations fare better, but still do not fully reproduce observations. In Chapter 4, we present some other work done during the PhD studies, namely, a method that improves the precision of specific angular measurements by combining simultaneous Markov Chain Monte Carlo modelling of ionised gas 2D velocity fields and HI linewidths. To test the method we use a sample of 25 galaxies from the Sydney-AAO Multi-object Integral field (SAMI) survey that had matching ALFALFA HI linewidths. Such a method allows constraining the rotation curve both in the inner regions of a galaxy and in its outskirts, leading to increased precision of specific angular momentum measurements. It could be used to further constrain the observed relation between galaxy mass, specific angular momentum and morphology (Obreschkow \& Glazebrook 2014). Mathematical and computational methods are presented in the appendices.}, language = {en} } @phdthesis{Kornhuber2017, author = {Kornhuber, Kai}, title = {Rossby wave dynamics and changes in summertime weather extremes}, school = {Universit{\"a}t Potsdam}, pages = {xii, 222}, year = {2017}, abstract = {Extreme weather events like heatwaves and floods severely affect societies with impacts ranging from economic damages to losses in human lifes. Global warming caused by anthropogenic greenhouse gas emissions is expected to increase their frequency and intensity, particularly in the warm season. Next to these thermodynamic changes, climate change might also impact the large scale atmospheric circulation.Such dynamic changes might additionally act on the occurence of extreme weather events, but involved mechanisms are often highly non-linear. Therefore, large uncertainty exists on the exact nature of these changes and the related risks to society. Particularly in the densely populated mid-latitudes weather patterns are governed by the large scale circulation like the jet-streams and storm tracks. Extreme weather in this region is often related to persistent weather systems associated with a strongly meandering jet-stream. Such meanders are called Rossby waves. Under specific conditions they can become slow moving, stretched around the entire hemisphere and generate simultaneaous heat- and rainfall extremes in far-away regions. This thesis aims at enhancing the understanding of synoptic-scale, circumglobal Rossby waves and the associated risks of dynamical changes to society. More specific, the analyses investigate their relation to extreme weather, regions at risk, under which conditions they are generated, and the influence of anthropogenic climate change on those conditions now, in the past and in the future. I find that circumglobal Rossby waves promoted simultaneous occuring weather extremes across the northern hemisphere in several recent summers. Further, I present evidence that they are often linked to quasiresonant-amplification of planetary waves. These events include the 2003 European heatwave and the Moscow heatwave of 2010. This non-linear mechanism acts on the upper level flow through trapping and amplification of stationary synoptic scale waves. I show that this resonance mechanism acts in both hemispheres and is related to extreme weather. A main finding is that circumglobal Rossby waves primarily occur as two specific teleconnection patterns associated with a wave 5 and wave 7 pattern in the northern hemisphere, likely due to the favourable longitudinal distance of prominent mountain ridges here. Furthermore, I identify those regions which are particularly at risk: The central United States, western Europe and the Ukraine/Russian region. Moreover, I present evidence that the wave 7 pattern has and extreme weather in these regions. My results suggest that the increase in frequency can be linked to favourable changes in large scale temperature gradients, which I show to be largely underestimated by model simulations. Using surface temperature fingerprint as proxy for investigating historic and future model ensembles, evidence is presented that anthropogenic warming has likely increased the probability for the occurence of circumglobal Rossby waves. Further it is shown that this might lead to a doubling of such events until the end of the century under a high-emission scenario. Overall, this thesis establishes several atmosphere-dynamical pathways by which changes in large scale temperature gradients might link to persistent boreal summer weather. It highlights the societal risks associated with the increasing occurence of a newly discovered Rossby wave teleconnection pattern, which has the potential to cause simultaneaous heat-extremes in the mid-latitudinal bread-basket regions. In addition, it provides further evidence that the traditional picture by which quasi-stationary Rossby waves occur only in the low wavenumber regime, should be reconsidered.}, language = {en} } @misc{SchimkaLomadzeRabeetal.2017, author = {Schimka, Selina and Lomadze, Nino and Rabe, Maren and Kopyshev, Alexey and Lehmann, Maren and von Klitzing, Regine and Rumyantsev, Artem M. and Kramarenko, Elena Yu. and Santer, Svetlana}, title = {Photosensitive microgels containing azobenzene surfactants of different charges}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {461}, issn = {1866-8372}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-413528}, year = {2017}, abstract = {We report on light sensitive microgel particles that can change their volume reversibly in response to illumination with light of different wavelengths. To make the anionic microgels photosensitive we add surfactants with a positively charged polyamine head group and an azobenzene containing tail. Upon illumination, azobenzene undergoes a reversible photo-isomerization reaction from a trans- to a cis-state accompanied by a change in the hydrophobicity of the surfactant. Depending on the isomerization state, the surfactant molecules are either accommodated within the microgel (trans-state) resulting in its shrinkage or desorbed back into water (cis-isomer) letting the microgel swell. We have studied three surfactants differing in the number of amino groups, so that the number of charges of the surfactant head varies between 1 and 3. We have found experimentally and theoretically that the surfactant concentration needed for microgel compaction increases with decreasing number of charges of the head group. Utilization of polyamine azobenzene containing surfactants for the light triggered remote control of the microgel size opens up a possibility for applications of light responsive microgels as drug carriers in biology and medicine.}, language = {en} } @phdthesis{Feulner2017, author = {Feulner, Georg}, title = {The influence of solar radiation changes on the energy budget of Earth's climate}, school = {Universit{\"a}t Potsdam}, pages = {200}, year = {2017}, language = {en} } @phdthesis{Kretschmer2017, author = {Kretschmer, Marlene}, title = {Disentangling causal pathways of the stratospheric polar vortex}, school = {Universit{\"a}t Potsdam}, pages = {171}, year = {2017}, language = {en} } @phdthesis{Ghaisari2017, author = {Ghaisari, Sara}, title = {Magnetic anisotropy analysis of magnetic nanoparticles in magnetotactic bacteria}, school = {Universit{\"a}t Potsdam}, pages = {115}, year = {2017}, language = {en} } @phdthesis{Schuermann2017, author = {Sch{\"u}rmann, Robin Mathis}, title = {Interaction of the potential DNA-radiosensitizer 8-bromoadenine with free and plasmonically generated electrons}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407017}, school = {Universit{\"a}t Potsdam}, pages = {xi, 120}, year = {2017}, abstract = {In Germany more than 200.000 persons die of cancer every year, which makes it the second most common cause of death. Chemotherapy and radiation therapy are often combined to exploit a supra-additive effect, as some chemotherapeutic agents like halogenated nucleobases sensitize the cancerous tissue to radiation. The radiosensitizing action of certain therapeutic agents can be at least partly assigned to their interaction with secondary low energy electrons (LEEs) that are generated along the track of the ionizing radiation. In the therapy of cancer DNA is an important target, as severe DNA damage like double strand breaks induce the cell death. As there is only a limited number of radiosensitizing agents in clinical practice, which are often strongly cytotoxic, it would be beneficial to get a deeper understanding of the interaction of less toxic potential radiosensitizers with secondary reactive species like LEEs. Beyond that LEEs can be generated by laser illuminated nanoparticles that are applied in photothermal therapy (PTT) of cancer, which is an attempt to treat cancer by an increase of temperature in the cells. However, the application of halogenated nucleobases in PTT has not been taken into account so far. In this thesis the interaction of the potential radiosensitizer 8-bromoadenine (8BrA) with LEEs was studied. In a first step the dissociative electron attachment (DEA) in the gas phase was studied in a crossed electron-molecular beam setup. The main fragmentation pathway was revealed as the cleavage of the C-Br bond. The formation of a stable parent anion was observed for electron energies around 0 eV. Furthermore, DNA origami nanostructures were used as platformed to determine electron induced strand break cross sections of 8BrA sensitized oligonucleotides and the corresponding nonsensitized sequence as a function of the electron energy. In this way the influence of the DEA resonances observed for the free molecules on the DNA strand breaks was examined. As the surrounding medium influences the DEA, pulsed laser illuminated gold nanoparticles (AuNPs) were used as a nanoscale electron source in an aqueous environment. The dissociation of brominated and native nucleobases was tracked with UV-Vis absorption spectroscopy and the generated fragments were identified with surface enhanced Raman scattering (SERS). Beside the electron induced damage, nucleobase analogues are decomposed in the vicinity of the laser illuminatednanoparticles due to the high temperatures. In order to get a deeper understanding of the different dissociation mechanisms, the thermal decomposition of the nucleobases in these systems was studied and the influence of the adsorption kinetics of the molecules was elucidated. In addition to the pulsed laser experiments, a dissociative electron transfer from plasmonically generated "hot electrons" to 8BrA was observed under low energy continuous wave laser illumination and tracked with SERS. The reaction was studied on AgNPs and AuNPs as a function of the laser intensity and wavelength. On dried samples the dissociation of the molecule was described by fractal like kinetics. In solution, the dissociative electron transfer was observed as well. It turned out that the timescale of the reaction rates were slightly below typical integration times of Raman spectra. In consequence such reactions need to be taken into account in the interpretation of SERS spectra of electrophilic molecules. The findings in this thesis help to understand the interaction of brominated nucleobases with plasmonically generated electrons and free electrons. This might help to evaluate the potential radiosensitizing action of such molecules in cancer radiation therapy and PTT.}, language = {en} } @phdthesis{Mitzkus2017, author = {Mitzkus, Martin}, title = {Spectroscopic surface brightness fluctuations}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-406327}, school = {Universit{\"a}t Potsdam}, pages = {ix, 89}, year = {2017}, abstract = {Galaxies evolve on cosmological timescales and to study this evolution we can either study the stellar populations, tracing the star formation and chemical enrichment, or the dynamics, tracing interactions and mergers of galaxies as well as accretion. In the last decades this field has become one of the most active research areas in modern astrophysics and especially the use of integral field spectrographs furthered our understanding. This work is based on data of NGC 5102 obtained with the panoramic integral field spectrograph MUSE. The data are analysed with two separate and complementary approaches: In the first part, standard methods are used to measure the kinematics and than model the gravitational potential using these exceptionally high-quality data. In the second part I develop the new method of surface brightness fluctuation spectroscopy and quantitatively explore its potential to investigate the bright evolved stellar population. Measuring the kinematics of NGC 5102 I discover that this low-luminosity S0 galaxy hosts two counter rotating discs. The more central stellar component co-rotates with the large amount of HI gas. Investigating the populations I find strong central age and metallicity gradients with a younger and more metal rich central population. The spectral resolution of MUSE does not allow to connect these population gradients with the two counter rotating discs. The kinematic measurements are modelled with Jeans anisotropic models to infer the gravitational potential of NGC 5102. Under the self-consistent mass-follows-light assumption none of the Jeans models is able to reproduce the observed kinematics. To my knowledge this is the strongest evidence evidence for a dark matter dominated system obtained with this approach so far. Including a Navarro, Frenk \& White dark matter halo immediately solves the discrepancies. A very robust result is the logarithmic slope of the total matter density. For this low-mass galaxy I find a value of -1.75 +- 0.04, shallower than an isothermal halo and even shallower than published values for more massive galaxies. This confirms a tentative relation between total mass slope and stellar mass of galaxies. The Surface Brightness Fluctuation (SBF) method is a well established distance measure, but due to its sensitive to bright stars also used to study evolved stars in unresolved stellar populations. The wide-field spectrograph MUSE offers the possibility to apply this technique for the first time to spectroscopic data. In this thesis I develop the spectroscopic SBF technique and measure the first SBF spectrum of any galaxy. I discuss the challenges for measuring SBF spectra that rise due to the complexity of integral field spectrographs compared to imaging instruments. Since decades, stellar population models indicate that SBFs in intermediate-to-old stellar systems are dominated by red giant branch and asymptotic giant branch stars. Especially the later carry significant model uncertainties, making these stars a scientifically interesting target. Comparing the NGC 5102 SBF spectrum with stellar spectra I show for the first time that M-type giants cause the fluctuations. Stellar evolution models suggest that also carbon rich thermally pulsating asymptotic giant branch stars should leave a detectable signal in the SBF spectrum. I cannot detect a significant contribution from these stars in the NGC 5102 SBF spectrum. I have written a stellar population synthesis tool that predicts for the first time SBF spectra. I compute two sets of population models: based on observed and on theoretical stellar spectra. In comparing the two models I find that the models based on observed spectra predict weaker molecular features. The comparison with the NGC 5102 spectrum reveals that these models are in better agreement with the data.}, language = {en} } @phdthesis{LeighWojno2017, author = {Leigh Wojno, Jennifer}, title = {Correlations between kinematics, chemistry, and ages of stars in the solar neighbourhood as seen by the RAVE survey}, school = {Universit{\"a}t Potsdam}, pages = {114}, year = {2017}, language = {en} } @phdthesis{Leonhardt2017, author = {Leonhardt, Helmar}, title = {Chemotaxis, shape and adhesion dynamics of amoeboid cells studied by impedance fluctuations in open and confined spaces}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-405016}, school = {Universit{\"a}t Potsdam}, pages = {98}, year = {2017}, abstract = {Die vorliegende Arbeit befasst sich mit elektrischen Impedanzmessungen von ameoboiden Zellen auf Mikroelektroden. Der Modellorganismus Dictyostelium discoideum zeigt unter der Bedingung des Nahrungsentzugs einen {\"U}bergang zum kollektiven Verhalten, bei dem sich chemotaktische Zellen zu einem multizellul{\"a}ren Aggregat zusammenschliessen. Wir zeigen wie Impedanzaufnahmen {\"u}ber die Dynamik der Zell-substrat Adh{\"a}sion ein pr{\"a}zises Bild der Phasen der Aggregation liefern. Dar{\"u}berhinaus zeigen wir zum ersten mal systematische Einzelzellmessungen von Wildtyp-Zellen und vier Mutanten, die sich in der St{\"a}rke der Substratadh {\"a}sion unterscheiden. Wir zeichneten die projizierte Zellfl{\"a}che durch Zeitverlaufsmikroskopie auf und fanden eine Korrelation zwischen den quasi-periodischen Oszillationen in der Kinetik der projizierten Fl{\"a}che - der Zellform-Oszillation - und dem Langzeittrend des Impedanzsignals. Amoeboidale Motilit{\"a}t offenbart sich typischerweise durch einen Zyklus von Membranausst{\"u}lpung, Substratadh{\"a}sion, Vorw{\"a}rtsziehen des Zellk{\"o}rpers und Einziehen des hinteren Teils der Zelle. Dieser Motilit{\"a}tszyklus resultiert in quasi-periodischen Oszillationen der projizierten Zellfl{\"a}che und der Impedanz. In allen gemessenen Zelllinien wurden f{\"u}r diesen Zyklus {\"a}hnliche Periodendauern beobachtet trotz der Unterschiede in der Anhaftungsst{\"a}rke. Wir beobachteten, dass die St{\"a}rke der Zell-substrat Anhaftung die Impedanz stark beeinflusst, indem die Abweichungen vom Mittelwert (die Gr{\"o}sse der Fluktuationen) vergr{\"o}ssert sind bei Zellen, die die vom Zytoskelett generierten Kr{\"a}fte effektiv auf das Substrat {\"u}bertragen. Zum Beispiel sind bei talA- Zellen, in welchen das Actin verankernde Protein Talin fehlt, die Fluktuationen stark reduziert. Einzelzellkraft-Spektroskopie und Ergebnisse eines Abl{\"o}sungsassays, bei dem Adh{\"a}sionskraft gemessen wird indem Zellen einer Scherspannung ausgesetzt werden, best{\"a}tigen, dass die Gr{\"o}sse der Impedanz-fluktuationen ein korrektes Mass f{\"u}r die St{\"a}rke der Substratadh{\"a}sion ist. Schliesslich haben wir uns auch mit dem Einbau von Zell-substrat-Impedanz-Sensoren in mikro-fluidische Apparaturen befasst. Ein chip-basierter elektrischer Chemotaxis Assay wurde entwickelt, der die Geschwindigkeit chemotaktischer Zellen misst, welche entlang eines chemischen Konzentrationsgradienten {\"u}ber Mikroelektroden wandern.}, language = {en} } @phdthesis{Sachse2017, author = {Sachse, Manuel}, title = {Dynamics and distribution of dust ejected from the Galilean moons of Jupiter}, school = {Universit{\"a}t Potsdam}, pages = {105}, year = {2017}, language = {en} } @phdthesis{Paul2017, author = {Paul, Fabian}, title = {Markov state modeling of binding and conformational changes of proteins}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404273}, school = {Universit{\"a}t Potsdam}, pages = {X, 112}, year = {2017}, abstract = {Proteins are molecules that are essential for life and carry out an enormous number of functions in organisms. To this end, they change their conformation and bind to other molecules. However, the interplay between conformational change and binding is not fully understood. In this work, this interplay is investigated with molecular dynamics (MD) simulations of the protein-peptide system Mdm2-PMI and by analysis of data from relaxation experiments. The central task it to uncover the binding mechanism, which is described by the sequence of (partial) binding events and conformational change events including their probabilities. In the simplest case, the binding mechanism is described by a two-step model: binding followed by conformational change or conformational change followed by binding. In the general case, longer sequences with multiple conformational changes and partial binding events are possible as well as parallel pathways that differ in their sequences of events. The theory of Markov state models (MSMs) provides the theoretical framework in which all these cases can be modeled. For this purpose, MSMs are estimated in this work from MD data, and rate equation models, which are related to MSMs, are inferred from experimental relaxation data. The MD simulation and Markov modeling of the PMI-Mdm2 system shows that PMI and Mdm2 can bind via multiple pathways. A main result of this work is a dissociation rate on the order of one event per second, which was calculated using Markov modeling and is in agreement with experiment. So far, dissociation rates and transition rates of this magnitude have only been calculated with methods that speed up transitions by acting with time-dependent, external forces on the binding partners. The simulation technique developed in this work, in contrast, allows the estimation of dissociation rates from the combination of free energy calculation and direct MD simulation of the fast binding process. Two new statistical estimators TRAM and TRAMMBAR are developed to estimate a MSM from the joint data of both simulation types. In addition, a new analysis technique for time-series data from chemical relaxation experiments is developed in this work. It allows to identify one of the above-mentioned two-step mechanisms as the mechanism that underlays the data. The new method is valid for a broader range of concentrations than previous methods and therefore allows to choose the concentrations such that the mechanism can be uniquely identified. It is successfully tested with data for the binding of recoverin to a rhodopsin kinase peptide.}, language = {en} } @phdthesis{ThielemannKuehn2017, author = {Thielemann-K{\"u}hn, Nele}, title = {Optically induced ferro- and antiferromagnetic dynamics in the rare-earth metal dysprosium}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402994}, school = {Universit{\"a}t Potsdam}, pages = {iv, 121}, year = {2017}, abstract = {Approaching physical limits in speed and size of today's magnetic storage and processing technologies demands new concepts for controlling magnetization and moves researches on optically induced magnetic dynamics. Studies on photoinduced magnetization dynamics and their underlying mechanisms have been primarily performed on ferromagnetic metals. Ferromagnetic dynamics bases on transfer of the conserved angular momentum connected with atomic magnetic moments out of the parallel aligned magnetic system into other degrees of freedom. In this thesis the so far rarely studied response of antiferromagnetic order to ultra-short optical laser pulses in a metal is investigated. The experiments were performed at the FemtoSpex slicing facility at the storage ring BESSY II, an unique source for ultra-short elliptically polarized x-ray pulses. Laser-induced changes of the 4f-magnetic order parameter in ferro- and antiferromagnetic dysprosium (Dy), were studied by x-ray methods, which yield directly comparable quantities. The discovered fundamental differences in the temporal and spatial behavior of ferro- and antiferrmagnetic dynamics are assinged to an additional channel for angular momentum transfer, which reduces the antiferromagnetic order by redistributing angular momentum within the non-parallel aligned magnetic system, and hence conserves the zero net magnetization. It is shown that antiferromagnetic dynamics proceeds considerably faster and more energy-efficient than demagnetization in ferromagnets. By probing antiferromagnetic order in time and space, it is found to be affected along the whole sample depth of an in situ grown 73 nm tick Dy film. Interatomic transfer of angular momentum via fast diffusion of laser-excited 5d electrons is held responsible for the out-most long-ranging effect. Ultrafast ferromagnetic dynamics can be expected to base on the same origin, which however leads to demagnetization only in regions close to interfaces caused by super-diffusive spin transport. Dynamics due to local scattering processes of excited but less mobile electrons, occur in both magnetic alignments only in directly excited regions of the sample and on slower pisosecond timescales. The thesis provides fundamental insights into photoinduced magnetic dynamics by directly comparing ferro- and antiferromagnetic dynamics in the same material and by consideration of the laser-induced magnetic depth profile.}, language = {en} } @phdthesis{Lysyakova2017, author = {Lysyakova, Liudmila}, title = {Interaction of azobenzene containing surfactants with plasmonic nanoparticles}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403359}, school = {Universit{\"a}t Potsdam}, pages = {viii, 155}, year = {2017}, abstract = {The goal of this thesis is related to the question how to introduce and combine simultaneously plasmonic and photoswitching properties to different nano-objects. In this thesis I investigate the complexes between noble metal nanoparticles and cationic surfactants containing azobenzene units in their hydrophobic tail, employing absorption spectroscopy, surface zeta-potential, and electron microscopy. In the first part of the thesis, the formation of complexes between negatively charged laser ablated spherical gold nanoparticles and cationic azobenzene surfactants in trans- conformation is explored. It is shown that the constitution of the complexes strongly depends on a surfactant-to-gold molar ratio. At certain molar ratios, particle self-assembly into nanochains and their aggregation have been registered. At higher surfactant concentrations, the surface charge of nanoparticles turned positive, attributed to the formation of the stabilizing double layer of azobenzene surfactants on gold nanoparticle surfaces. These gold-surfactant complexes remained colloidally stable. UV light induced trans-cis isomerization of azobenzene surfactant molecules and thus perturbed the stabilizing surfactant shell, causing nanoparticle aggregation. The results obtained with silver and silicon nanoparticles mimick those for the comprehensively studied gold nanoparticles, corroborating the proposed model of complex formation. In the second part, the interaction between plasmonic metal nanoparticles (Au, Ag, Pd, alloy Au-Ag, Au-Pd), as well as silicon nanoparticles, and cis-isomers of azobenzene containing compounds is addressed. Cis-trans thermal isomerization of azobenzenes was enhanced in the presence of gold, palladium, and alloy gold-palladium nanoparticles. The influence of the surfactant structure and nanoparticle material on the azobenzene isomerization rate is expounded. Gold nanoparticles showed superior catalytic activity for thermal cis-trans isomerization of azobenzenes. In a joint project with theoretical chemists, we demonstrated that the possible physical origin of this phenomenon is the electron transfer between azobenzene moieties and nanoparticle surfaces. In the third part, complexes between gold nanorods and azobenzene surfactants with different tail length were exposed to UV and blue light, inducing trans-cis and cis-trans isomerization of surfactant, respectively. At the same time, the position of longitudinal plasmonic absorption maximum of gold nanorods experienced reversible shift responding to the changes in local dielectric environment. Surface plasmon resonance condition allowed the estimation of the refractive index of azobenzene containing surfactants in solution.}, language = {en} } @misc{HerrmannMetzler2017, author = {Herrmann, Carl J. J. and Metzler, Ralf}, title = {A self-avoiding walk with neural delays as a model of fixational eye movements}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403742}, pages = {17}, year = {2017}, abstract = {Fixational eye movements show scaling behaviour of the positional mean-squared displacement with a characteristic transition from persistence to antipersistence for increasing time-lag. These statistical patterns were found to be mainly shaped by microsaccades (fast, small-amplitude movements). However, our re-analysis of fixational eye-movement data provides evidence that the slow component (physiological drift) of the eyes exhibits scaling behaviour of the mean-squared displacement that varies across human participants. These results suggest that drift is a correlated movement that interacts with microsaccades. Moreover, on the long time scale, the mean-squared displacement of the drift shows oscillations, which is also present in the displacement auto-correlation function. This finding lends support to the presence of time-delayed feedback in the control of drift movements. Based on an earlier non-linear delayed feedback model of fixational eye movements, we propose and discuss different versions of a new model that combines a self-avoiding walk with time delay. As a result, we identify a model that reproduces oscillatory correlation functions, the transition from persistence to antipersistence, and microsaccades.}, language = {en} } @article{HerrmannMetzler2017, author = {Herrmann, Carl J. J. and Metzler, Ralf}, title = {A self-avoiding walk with neural delays as a model of fixational eye movements}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Springer Nature}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-13489-8}, pages = {1 -- 17}, year = {2017}, abstract = {Fixational eye movements show scaling behaviour of the positional mean-squared displacement with a characteristic transition from persistence to antipersistence for increasing time-lag. These statistical patterns were found to be mainly shaped by microsaccades (fast, small-amplitude movements). However, our re-analysis of fixational eye-movement data provides evidence that the slow component (physiological drift) of the eyes exhibits scaling behaviour of the mean-squared displacement that varies across human participants. These results suggest that drift is a correlated movement that interacts with microsaccades. Moreover, on the long time scale, the mean-squared displacement of the drift shows oscillations, which is also present in the displacement auto-correlation function. This finding lends support to the presence of time-delayed feedback in the control of drift movements. Based on an earlier non-linear delayed feedback model of fixational eye movements, we propose and discuss different versions of a new model that combines a self-avoiding walk with time delay. As a result, we identify a model that reproduces oscillatory correlation functions, the transition from persistence to antipersistence, and microsaccades.}, language = {en} } @misc{GrebenkovMetzlerOshanin2017, author = {Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb}, title = {Effects of the target aspect ratio and intrinsic reactivity onto diffusive search in bounded domains}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403726}, pages = {11}, year = {2017}, abstract = {We study the mean first passage time (MFPT) to a reaction event on a specific site in a cylindrical geometry—characteristic, for instance, for bacterial cells, with a concentric inner cylinder representing the nuclear region of the bacterial cell. Asimilar problem emerges in the description of a diffusive search by a transcription factor protein for a specific binding region on a single strand of DNA.We develop a unified theoretical approach to study the underlying boundary value problem which is based on a self-consistent approximation of the mixed boundary condition. Our approach permits us to derive explicit, novel, closed-form expressions for the MFPT valid for a generic setting with an arbitrary relation between the system parameters.Weanalyse this general result in the asymptotic limits appropriate for the above-mentioned biophysical problems. Our investigation reveals the crucial role of the target aspect ratio and of the intrinsic reactivity of the binding region, which were disregarded in previous studies. Theoretical predictions are confirmed by numerical simulations.}, language = {en} } @article{GrebenkovMetzlerOshanin2017, author = {Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb}, title = {Effects of the target aspect ratio and intrinsic reactivity onto diffusive search in bounded domains}, series = {New journal of physics}, volume = {19}, journal = {New journal of physics}, publisher = {IOP}, address = {London}, issn = {1367-2630}, doi = {10.1088/1367-2630/aa8ed9}, pages = {1 -- 11}, year = {2017}, abstract = {Westudy the mean first passage time (MFPT) to a reaction event on a specific site in a cylindrical geometry—characteristic, for instance, for bacterial cells, with a concentric inner cylinder representing the nuclear region of the bacterial cell. Asimilar problem emerges in the description of a diffusive search by a transcription factor protein for a specific binding region on a single strand of DNA.We develop a unified theoretical approach to study the underlying boundary value problem which is based on a self-consistent approximation of the mixed boundary condition. Our approach permits us to derive explicit, novel, closed-form expressions for the MFPT valid for a generic setting with an arbitrary relation between the system parameters.Weanalyse this general result in the asymptotic limits appropriate for the above-mentioned biophysical problems. Our investigation reveals the crucial role of the target aspect ratio and of the intrinsic reactivity of the binding region, which were disregarded in previous studies. Theoretical predictions are confirmed by numerical simulations.}, language = {en} } @phdthesis{CanUcar2017, author = {Can Ucar, Mehmet}, title = {Elastic interactions between antagonistic molecular motors}, school = {Universit{\"a}t Potsdam}, pages = {106}, year = {2017}, language = {en} } @article{LomadzeKopyshevBargheeretal.2017, author = {Lomadze, Nino and Kopyshev, Alexey and Bargheer, Matias and Wollgarten, Markus and Santer, Svetlana}, title = {Mass production of polymer nanowires filled with metal nanoparticles}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Springer Nature}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-08153-0}, year = {2017}, abstract = {Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro- or macroscale elements is hampered by the lack of structural components that have both, nano- and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket.}, language = {en} } @misc{LomadzeKopyshevBargheeretal.2017, author = {Lomadze, Nino and Kopyshev, Alexey and Bargheer, Matias and Wollgarten, Markus and Santer, Svetlana}, title = {Mass production of polymer nanowires filled with metal nanoparticles}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402712}, pages = {10}, year = {2017}, abstract = {Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro- or macroscale elements is hampered by the lack of structural components that have both, nano- and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket.}, language = {en} } @misc{WolfHolzmeierWagneretal.2017, author = {Wolf, Thomas J. A. and Holzmeier, Fabian and Wagner, Isabella and Berrah, Nora and Bostedt, Christoph and Bozek, John and Bucksbaum, Philip H. and Coffee, Ryan and Cryan, James and Farrell, Joe and Feifel, Raimund and Martinez, Todd J. and McFarland, Brian and Mucke, Melanie and Nandi, Saikat and Tarantelli, Francesco and Fischer, Ingo and G{\"u}hr, Markus}, title = {Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402692}, pages = {11}, year = {2017}, abstract = {Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.}, language = {en} } @article{WolfHolzmeierWagneretal.2017, author = {Wolf, Thomas J. A. and Holzmeier, Fabian and Wagner, Isabella and Berrah, Nora and Bostedt, Christoph and Bozek, John and Bucksbaum, Philip H. and Coffee, Ryan and Cryan, James and Farrell, Joe and Feifel, Raimund and Martinez, Todd J. and McFarland, Brian and Mucke, Melanie and Nandi, Saikat and Tarantelli, Francesco and Fischer, Ingo and G{\"u}hr, Markus}, title = {Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra}, series = {Applied Sciences}, volume = {7}, journal = {Applied Sciences}, number = {7}, publisher = {MDPI}, address = {Basel}, issn = {2076-3417}, doi = {10.3390/app7070681}, year = {2017}, abstract = {Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.}, language = {en} } @phdthesis{Ehrig2017, author = {Ehrig, Sebastian}, title = {3D curvature and its role on tissue organization}, school = {Universit{\"a}t Potsdam}, pages = {132}, year = {2017}, abstract = {Shape change is a fundamental process occurring in biological tissues during embryonic development and regeneration of tissues and organs. This process is regulated by cells that are constrained within a complex environment of biochemical and physical cues. The spatial constraint due to geometry has a determining role on tissue mechanics and the spatial distribution of force patterns that, in turn, influences the organization of the tissue structure. An understanding of the underlying principles of tissue organization may have wide consequences for the understanding of healing processes and the development of organs and, as such, is of fundamental interest for the tissue engineering community. This thesis aims to further our understanding of how the collective behaviour of cells is influenced by the 3D geometry of the environment. Previous research studying the role of geometry on tissue growth has mainly focused either on flat surfaces or on substrates where at least one of the principal curvatures is zero. In the present work, tissue growth from MC3T3-E1 pre-osteoblasts was investigated on surfaces of controlled mean curvature. One key aspect of this thesis was the development of substrates of controlled mean curvature and their visualization in 3D. It was demonstrated that substrates of controlled mean curvature suitable for cell culture can be fabricated using liquid polymers and surface tension effects. Using these substrates, it was shown that the mean surface curvature has a strong impact on the rate of tissue growth and on the organization of the tissue structure. It was thereby not only demonstrated that the amount of tissue produced (i.e. growth rates) by the cells depends on the mean curvature of the substrate but also that the tissue surface behaves like a viscous fluid with an equilibrium shape governed by the Laplace-Young-law. It was observed that more tissue was formed on highly concave surfaces compared to flat or convex surfaces. Motivated by these observations, an analytical model was developed, where the rate of tissue growth is a function of the mean curvature, which could successfully describe the growth kinetics. This model was also able to reproduce the growth kinetics of previous experiments where tissues have been cultured in straight-sided prismatic pores. A second part of this thesis focuses on the tissue structure, which influences the mechanical properties of the mature bone tissue. Since the extracellular matrix is produced by the cells, the cell orientation has a strong impact on the direction of the tissue fibres. In addition, it was recently shown that some cell types exhibit collective alignment similar to liquid crystals. Based on this observation, a computational model of self-propelled active particles was developed to explore in an abstract manner how the collective behaviour of cells is influenced by 3D curvature. It was demonstrated that the 3D curvature has a strong impact on the self-organization of active particles and gives, therefore, first insights into the principles of self-organization of cells on curved surfaces.}, language = {en} } @misc{ZaksPikovskij2017, author = {Zaks, Michael A. and Pikovskij, Arkadij}, title = {Chimeras and complex cluster states in arrays of spin-torque oscillators}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402180}, pages = {10}, year = {2017}, abstract = {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.}, language = {en} } @article{ZaksPikovskij2017, author = {Zaks, Michael A. and Pikovskij, Arkadij}, title = {Chimeras and complex cluster states in arrays of spin-torque oscillators}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Macmillan Publishers Limited}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-04918-9}, year = {2017}, abstract = {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.}, language = {en} } @misc{NiebuhrHeuer2017, author = {Niebuhr, Mario and Heuer, Axel}, title = {Phase measurement and far-field reconstruction on externally coupled laser diode arrays}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402140}, pages = {6}, year = {2017}, abstract = {Passive coherent combination of several discrete low power laser diodes is a promising way to overcome the issue of degrading beam quality when scaling single emitters to > 10W output power. Such systems would be an efficient alternative to current high power sources, yet they suffer from fatal coherence loss when operated well above threshold. We present a new way to obtain detailed coherence information for laser diode arrays using a spatial light modulator to help identify the underlying decoherence processes. Reconstruction tests of the emitted far-field distribution are conducted to evaluate the performance of our setup.}, language = {en} } @article{NiebuhrHeuer2017, author = {Niebuhr, Mario and Heuer, Axel}, title = {Phase measurement and far-field reconstruction on externally coupled laser diode arrays}, series = {Optics express}, volume = {25}, journal = {Optics express}, number = {13}, publisher = {Optical Society of America}, address = {Washington, DC}, issn = {1094-4087}, doi = {10.1364/OE.25.014317}, pages = {14317 -- 14322}, year = {2017}, abstract = {Passive coherent combination of several discrete low power laser diodes is a promising way to overcome the issue of degrading beam quality when scaling single emitters to > 10W output power. Such systems would be an efficient alternative to current high power sources, yet they suffer from fatal coherence loss when operated well above threshold. We present a new way to obtain detailed coherence information for laser diode arrays using a spatial light modulator to help identify the underlying decoherence processes. Reconstruction tests of the emitted far-field distribution are conducted to evaluate the performance of our setup.}, language = {en} } @article{SchwarzlGodecMetzler2017, author = {Schwarzl, Maria and Godec, Aljaž and Metzler, Ralf}, title = {Quantifying non-ergodicity of anomalous diffusion with higher order moments}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Macmillan Publishers Limited}, address = {London}, doi = {10.1038/s41598-017-03712-x}, pages = {18}, year = {2017}, abstract = {Anomalous diffusion is being discovered in a fast growing number of systems. The exact nature of this anomalous diffusion provides important information on the physical laws governing the studied system. One of the central properties analysed for finite particle motion time series is the intrinsic variability of the apparent diffusivity, typically quantified by the ergodicity breaking parameter EB. Here we demonstrate that frequently EB is insufficient to provide a meaningful measure for the observed variability of the data. Instead, important additional information is provided by the higher order moments entering by the skewness and kurtosis. We analyse these quantities for three popular anomalous diffusion models. In particular, we find that even for the Gaussian fractional Brownian motion a significant skewness in the results of physical measurements occurs and needs to be taken into account. Interestingly, the kurtosis and skewness may also provide sensitive estimates of the anomalous diffusion exponent underlying the data. We also derive a new result for the EB parameter of fractional Brownian motion valid for the whole range of the anomalous diffusion parameter. Our results are important for the analysis of anomalous diffusion but also provide new insights into the theory of anomalous stochastic processes.}, language = {en} } @misc{SchwarzlGodecMetzler2017, author = {Schwarzl, Maria and Godec, Aljaž and Metzler, Ralf}, title = {Quantifying non-ergodicity of anomalous diffusion with higher order moments}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402109}, pages = {18}, year = {2017}, abstract = {Anomalous diffusion is being discovered in a fast growing number of systems. The exact nature of this anomalous diffusion provides important information on the physical laws governing the studied system. One of the central properties analysed for finite particle motion time series is the intrinsic variability of the apparent diffusivity, typically quantified by the ergodicity breaking parameter EB. Here we demonstrate that frequently EB is insufficient to provide a meaningful measure for the observed variability of the data. Instead, important additional information is provided by the higher order moments entering by the skewness and kurtosis. We analyse these quantities for three popular anomalous diffusion models. In particular, we find that even for the Gaussian fractional Brownian motion a significant skewness in the results of physical measurements occurs and needs to be taken into account. Interestingly, the kurtosis and skewness may also provide sensitive estimates of the anomalous diffusion exponent underlying the data. We also derive a new result for the EB parameter of fractional Brownian motion valid for the whole range of the anomalous diffusion parameter. Our results are important for the analysis of anomalous diffusion but also provide new insights into the theory of anomalous stochastic processes.}, language = {en} } @misc{HempelKoseskaNikoloskietal.2017, author = {Hempel, Sabrina and Koseska, Aneta and Nikoloski, Zoran and Kurths, J{\"u}rgen}, title = {Unraveling gene regulatory networks from time-resolved gene expression data}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400924}, pages = {26}, year = {2017}, abstract = {Background: Inferring regulatory interactions between genes from transcriptomics time-resolved data, yielding reverse engineered gene regulatory networks, is of paramount importance to systems biology and bioinformatics studies. Accurate methods to address this problem can ultimately provide a deeper insight into the complexity, behavior, and functions of the underlying biological systems. However, the large number of interacting genes coupled with short and often noisy time-resolved read-outs of the system renders the reverse engineering a challenging task. Therefore, the development and assessment of methods which are computationally efficient, robust against noise, applicable to short time series data, and preferably capable of reconstructing the directionality of the regulatory interactions remains a pressing research problem with valuable applications. Results: Here we perform the largest systematic analysis of a set of similarity measures and scoring schemes within the scope of the relevance network approach which are commonly used for gene regulatory network reconstruction from time series data. In addition, we define and analyze several novel measures and schemes which are particularly suitable for short transcriptomics time series. We also compare the considered 21 measures and 6 scoring schemes according to their ability to correctly reconstruct such networks from short time series data by calculating summary statistics based on the corresponding specificity and sensitivity. Our results demonstrate that rank and symbol based measures have the highest performance in inferring regulatory interactions. In addition, the proposed scoring scheme by asymmetric weighting has shown to be valuable in reducing the number of false positive interactions. On the other hand, Granger causality as well as information-theoretic measures, frequently used in inference of regulatory networks, show low performance on the short time series analyzed in this study. Conclusions: Our study is intended to serve as a guide for choosing a particular combination of similarity measures and scoring schemes suitable for reconstruction of gene regulatory networks from short time series data. We show that further improvement of algorithms for reverse engineering can be obtained if one considers measures that are rooted in the study of symbolic dynamics or ranks, in contrast to the application of common similarity measures which do not consider the temporal character of the employed data. Moreover, we establish that the asymmetric weighting scoring scheme together with symbol based measures (for low noise level) and rank based measures (for high noise level) are the most suitable choices.}, language = {en} } @misc{LoebnerJelkenYadavallietal.2017, author = {Loebner, Sarah and Jelken, Joachim and Yadavalli, Nataraja Sekhar and Sava, Elena and Hurduc, Nicolae and Santer, Svetlana}, title = {Motion of adsorbed nano-particles on azobenzene containing polymer films}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400423}, pages = {11}, year = {2017}, abstract = {We demonstrate in situ recorded motion of nano-objects adsorbed on a photosensitive polymer film. The motion is induced by a mass transport of the underlying photoresponsive polymer material occurring during irradiation with interference pattern. The polymer film contains azobenzene molecules that undergo reversible photoisomerization reaction from trans- to cis-conformation. Through a multi-scale chain of physico-chemical processes, this finally results in the macro-deformations of the film due to the changing elastic properties of polymer. The topographical deformation of the polymer surface is sensitive to a local distribution of the electrical field vector that allows for the generation of dynamic changes in the surface topography during irradiation with different light interference patterns. Polymer film deformation together with the motion of the adsorbed nano-particles are recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the surface deformation. The particles undergo either translational or rotational motion. The direction of particle motion is towards the topography minima and opposite to the mass transport within the polymer film. The ability to relocate particles by photo-induced dynamic topography fluctuation offers a way for a non-contact simultaneous manipulation of a large number of adsorbed particles just in air at ambient conditions.}, language = {en} } @phdthesis{Guber2017, author = {Guber, Christoph Rudolf}, title = {Dust depletion of Ca and Ti in quasar absorption-line systems}, school = {Universit{\"a}t Potsdam}, pages = {178}, year = {2017}, language = {en} } @phdthesis{KianiAlibagheri2017, author = {Kiani Alibagheri, Bahareh}, title = {On structural properties of magnetosome chains}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-398849}, school = {Universit{\"a}t Potsdam}, pages = {XIV, 117}, year = {2017}, abstract = {Magnetotaktische Bakterien besitzen eine intrazellul{\"a}re Struktur, die Magnetosomenkette genannt wird. Magnetosomenketten enthalten Nanopartikel von Eisenkristallen, die von einer Membran umschlossen und entlang eines Zytoskelettfilaments ausgerichtet sind. Dank der Magnetosomenkette ist es magnetotaktischen Bakterien m{\"o}glich sich in Magnetfeldern auszurichten und entlang magnetischer Feldlinien zu schwimmen. Die ausf{\"u}hrliche Untersuchung der strukturellen Eigenschaften der Magnetosomenkette in magnetotaktischen Bakterien sind von grundlegendem wissenschaftlichen Interesse, weil sie Einblicke in die Anordnung des Zytoskeletts von Bakterien erlauben. In dieser Studie haben wir ein neues theoretisches Modell entwickelt, dass sich dazu eignet, die strukturellen Eigenschaften der Magnetosomenketten in magnetotaktischen Bakterien zu erforschen. Zuerst wenden wir uns der Biegesteifigkeit von Magnetosomenketten zu, die von zwei Faktoren beeinflusst wird: Die magnetische Wechselwirkung der Magnetosomenpartikel und der Biegesteifigkeit des Zytoskelettfilaments auf welchem die Magnetosome verankert sind. Unsere Analyse zeigt, dass sich die lineare Konfiguration von Magnetosomenpartikeln ohne die Stabilisierung durch das Zytoskelett zu einer ring{\"o}rmigen Struktur biegen w{\"u}rde, die kein magnetisches Moment aufweist und daher nicht die Funktion eines Kompass in der zellul{\"a}ren Navigation einnehmen k{\"o}nnte. Wir schlussfolgern, dass das Zytoskelettfilament eine stabilisierende Wirkung auf die lineare Konfiguration hat und eine ringf{\"o}rmige Anordnung verhindert. Wir untersuchen weiter die Gleichgewichtskonfiguration der Magnetosomenpartikel in einer linearen Kette und in einer geschlossenen ringf{\"o}rmigen Struktur. Dabei beobachteten wir ebenfalls, dass f{\"u}r eine stabile lineare Anordnung eine Bindung an ein Zytoskelettfilament notwendig ist. In einem externen magnetischen Feld wird die Stabilit{\"a}t der Magnetosomenketten durch die Dipol-Dipol-Wechselwirkung, {\"u}ber die Steifheit und die Bindungsenergie der Proteinstruktur, die die Partikel des Magnetosomen mit dem Filament verbinden, erreicht. Durch Beobachtungen w{\"a}hrend und nach der Behandlung einer Magnetosomenkette mit einem externen magnetischen Feld, l{\"a}sst sich begr{\"u}nden, dass die Stabilisierung von Magnetosomenketten durch Zytoskelettfilamente {\"u}ber proteinhaltige Bindeglieder und die dynamischen Eigenschaften dieser Strukturen realisiert wird. Abschließend wenden wir unser Modell bei der Untersuchung von ferromagnetischen Resonanz-Spektren von Magnetosomenketten in einzelnen Zellen von magnetotaktischen Bakterien an. Wir erforschen den Effekt der magnetokristallinen Anistropie in ihrer dreifach-Symmetrie, die in ferromagnetischen Ressonanz Spektren beobachtet wurden und die Besonderheit von verschiedenen Spektren, die bei Mutanten dieser Bakterien auftreten.}, language = {en} } @article{CherstvyVinodAghionetal.2017, author = {Cherstvy, Andrey G. and Vinod, Deepak and Aghion, Erez and Chechkin, Aleksei V. and Metzler, Ralf}, title = {Time averaging, ageing and delay analysis of financial time series}, series = {New journal of physics}, volume = {19}, journal = {New journal of physics}, publisher = {IOP}, address = {London}, issn = {1367-2630}, doi = {10.1088/1367-2630/aa7199}, pages = {1 -- 11}, year = {2017}, abstract = {We introduce three strategies for the analysis of financial time series based on time averaged observables. These comprise the time averaged mean squared displacement (MSD) as well as the ageing and delay time methods for varying fractions of the financial time series. We explore these concepts via statistical analysis of historic time series for several Dow Jones Industrial indices for the period from the 1960s to 2015. Remarkably, we discover a simple universal law for the delay time averaged MSD. The observed features of the financial time series dynamics agree well with our analytical results for the time averaged measurables for geometric Brownian motion, underlying the famed Black-Scholes-Merton model. The concepts we promote here are shown to be useful for financial data analysis and enable one to unveil new universal features of stock market dynamics.}, language = {en} } @misc{CherstvyVinodAghionetal.2017, author = {Cherstvy, Andrey G. and Vinod, Deepak and Aghion, Erez and Chechkin, Aleksei V. and Metzler, Ralf}, title = {Time averaging, ageing and delay analysis of financial time series}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400541}, pages = {11}, year = {2017}, abstract = {We introduce three strategies for the analysis of financial time series based on time averaged observables. These comprise the time averaged mean squared displacement (MSD) as well as the ageing and delay time methods for varying fractions of the financial time series. We explore these concepts via statistical analysis of historic time series for several Dow Jones Industrial indices for the period from the 1960s to 2015. Remarkably, we discover a simple universal law for the delay time averaged MSD. The observed features of the financial time series dynamics agree well with our analytical results for the time averaged measurables for geometric Brownian motion, underlying the famed Black-Scholes-Merton model. The concepts we promote here are shown to be useful for financial data analysis and enable one to unveil new universal features of stock market dynamics.}, language = {en} } @phdthesis{Qiu2017, author = {Qiu, Xunlin}, title = {Ferroelectrets: heterogenous polymer electrets with high electromechanical response}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-398425}, school = {Universit{\"a}t Potsdam}, pages = {viii, 172}, year = {2017}, abstract = {Ferroelectrets are internally charged polymer foams or cavity-containing polymer-_lm systems that combine large piezoelectricity with mechanical flexibility and elastic compliance. The term "ferroelectret" was coined based on the fact that it is a space-charge electret that also shows ferroic behavior. In this thesis, comprehensive work on ferroelectrets, and in particular on their preparation, their charging, their piezoelectricity and their applications is reported. For industrial applications, ferroelectrets with well-controlled distributions or even uniform values of cavity size and cavity shape and with good thermal stability of the piezoelectricity are very desirable. Several types of such ferroelectrets are developed using techniques such as straightforward thermal lamination, sandwiching sticky templates with electret films, and screen printing. In particular, uoroethylenepropylene (FEP) _lm systems with tubular-channel openings, prepared by means of the thermal lamination technique, show piezoelectric d33 coefficients of up to 160 pC/N after charging through dielectric barrier discharges (DBDs) . For samples charged at suitable elevated temperatures, the piezoelectricity is stable at temperatures of at least 130°C. These preparation methods are easy to implement at laboratory or industrial scales, and are quite flexible in terms of material selection and cavity geometry design. Due to the uniform and well-controlled cavity structures, samples are also very suitable for fundamental studies on ferroelectrets. Charging of ferroelectrets is achieved via a series of dielectric barrier discharges (DBDs) inside the cavities. In the present work, the DBD charging process is comprehensively studied by means of optical, electrical and electro-acoustic methods. The spectrum of the transient light from the DBDs in cellular polypropylene (PP) ferroelectrets directly confirms the ionization of molecular nitrogen, and allows the determination of the electric field in the discharge. Detection of the light emission reveals not only DBDs under high applied voltage but also back discharges when the applied voltage is reduced to sufficiently low values. Back discharges are triggered by the internally deposited charges, as the breakdown inside the cavities is controlled by the sum of the applied electric field and the electric field of the deposited charges. The remanent effective polarization is determined by the breakdown strength of the gas-filled cavities. These findings form the basis of more efficient charging techniques for ferroelectrets such as charging with high-pressure air, thermal poling and charging assisted by gas exchange. With the proposed charging strategies, the charging efficiency of ferroelectrets can be enhanced significantly. After charging, the cavities can be considered as man-made macroscopic dipoles whose direction can be reversed by switching the polarity of the applied voltage. Polarization-versus-electric-field (P(E)) hysteresis loops in ferroelectrets are observed by means of an electro-acoustic method combined with dielectric resonance spectroscopy. P(E) hysteresis loops in ferrroelectrets are also obtained by more direct measurements using a modified Sawyer-Tower circuit. Hysteresis loops prove the ferroic behavior of ferroelectrets. However, repeated switching of the macroscopic dipoles involves complex physico-chemical processes. The DBD charging process generates a cold plasma with numerous active species and thus modifies the inner polymer surfaces of the cavities. Such treatments strongly affect the chargeability of the cavities. At least for cellular PP ferroelectrets, repeated DBDs in atmospheric conditions lead to considerable fatigue of the effective polarization and of the resulting piezoelectricity. The macroscopic dipoles in ferroelectrets are highly compressible, and hence the piezoelectricity is essentially the primary effect. It is found that the piezoelectric d33 coefficient is proportional to the polarization and the elastic compliance of the sample, providing hints for developing materials with higher piezoelectric sensitivity in the future. Due to their outstanding electromechanical properties, there has been constant interest in the application of ferroelectrets. The antiresonance frequencies (fp) of ferroelectrets are sensitive to the boundary conditions during measurement. A tubular-channel FEP ferroelectret is conformably attached to a self-organized minimum-energy dielectric elastomer actuator (DEA). It turns out that the antiresonance frequency (fp) of the ferroelectret film changes noticeably with the bending angle of the DEA. Therefore, the actuation of DEAs can be used to modulate the fp value of ferroelectrets, but fp can also be exploited for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets opens up various new possibilities for application.}, language = {en} } @phdthesis{Roland2017, author = {Roland, Steffen}, title = {Charge carrier recombination and open circuit voltage in organic solar cells}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-397721}, school = {Universit{\"a}t Potsdam}, pages = {VI, 145}, year = {2017}, abstract = {Tremendous progress in the development of thin film solar cell techniques has been made over the last decade. The field of organic solar cells is constantly developing, new material classes like Perowskite solar cells are emerging and different types of hybrid organic/inorganic material combinations are being investigated for their physical properties and their applicability in thin film electronics. Besides typical single-junction architectures for solar cells, multi-junction concepts are also being investigated as they enable the overcoming of theoretical limitations of a single-junction. In multi-junction devices each sub-cell operates in different wavelength regimes and should exhibit optimized band-gap energies. It is exactly this tunability of the band-gap energy that renders organic solar cell materials interesting candidates for multi-junction applications. Nevertheless, only few attempts have been made to combine inorganic and organic solar cells in series connected multi-junction architectures. Even though a great diversity of organic solar cells exists nowadays, their open circuit voltage is usually low compared to the band-gap of the active layer. Hence, organic low band-gap solar cells in particular show low open circuit voltages and the key factors that determine the voltage losses are not yet fully understood. Besides open circuit voltage losses the recombination of charges in organic solar cells is also a prevailing research topic, especially with respect to the influence of trap states. The exploratory focus of this work is therefore set, on the one hand, on the development of hybrid organic/inorganic multi-junctions and, on the other hand, on gaining a deeper understanding of the open circuit voltage and the recombination processes of organic solar cells. In the first part of this thesis, the development of a hybrid organic/inorganic triple-junction will be discussed which showed at that time (Jan. 2015) a record power conversion efficiency of 11.7\%. The inorganic sub-cells of these devices consist of hydrogenated amorphous silicon and were delivered by the Competence Center Thin-Film and Nanotechnology for Photovoltaics in Berlin. Different recombination contacts and organic sub-cells were tested in conjunction with these inorganic sub-cells on the basis of optical modeling predictions for the optimal layer thicknesses to finally reach record efficiencies for this type of solar cells. In the second part, organic model systems will be investigated to gain a better understanding of the fundamental loss mechanisms that limit the open circuit voltage of organic solar cells. First, bilayer systems with different orientation of the donor and acceptor molecules were investigated to study the influence of the donor/acceptor orientation on non-radiative voltage loss. Secondly, three different bulk heterojunction solar cells all comprising the same amount of fluorination and the same polymer backbone in the donor component were examined to study the influence of long range electrostatics on the open circuit voltage. Thirdly, the device performance of two bulk heterojunction solar cells was compared which consisted of the same donor polymer but used different fullerene acceptor molecules. By this means, the influence of changing the energetics of the acceptor component on the open circuit voltage was investigated and a full analysis of the charge carrier dynamics was presented to unravel the reasons for the worse performance of the solar cell with the higher open circuit voltage. In the third part, a new recombination model for organic solar cells will be introduced and its applicability shown for a typical low band-gap cell. This model sheds new light on the recombination process in organic solar cells in a broader context as it re-evaluates the recombination pathway of charge carriers in devices which show the presence of trap states. Thereby it addresses a current research topic and helps to resolve alleged discrepancies which can arise from the interpretation of data derived by different measurement techniques.}, language = {en} } @phdthesis{Hakansson2017, author = {H{\aa}kansson, Nils}, title = {A Dark Matter line search using 3D-modeling of Cherenkov showers below 10 TeV with VERITAS}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-397670}, school = {Universit{\"a}t Potsdam}, pages = {107, xxxvi}, year = {2017}, abstract = {Dark matter, DM, has not yet been directly observed, but it has a very solid theoretical basis. There are observations that provide indirect evidence, like galactic rotation curves that show that the galaxies are rotating too fast to keep their constituent parts, and galaxy clusters that bends the light coming from behind-lying galaxies more than expected with respect to the mass that can be calculated from what can be visibly seen. These observations, among many others, can be explained with theories that include DM. The missing piece is to detect something that can exclusively be explained by DM. Direct observation in a particle accelerator is one way and indirect detection using telescopes is another. This thesis is focused on the latter method. The Very Energetic Radiation Imaging Telescope Array System, V ERITAS, is a telescope array that detects Cherenkov radiation. Theory predicts that DM particles annihilate into, e.g., a γγ pair and create a distinctive energy spectrum when detected by such telescopes, e.i., a monoenergetic line at the same energy as the particle mass. This so called "smoking-gun" signature is sought with a sliding window line search within the sub-range ∼ 0.3 - 10 TeV of the VERITAS energy range, ∼ 0.01 - 30 TeV. Standard analysis within the VERITAS collaboration uses Hillas analysis and look-up tables, acquired by analysing particle simulations, to calculate the energy of the particle causing the Cherenkov shower. In this thesis, an improved analysis method has been used. Modelling each shower as a 3Dgaussian should increase the energy recreation quality. Five dwarf spheroidal galaxies were chosen as targets with a total of ∼ 224 hours of data. The targets were analysed individually and stacked. Particle simulations were based on two simulation packages, CARE and GrISU. Improvements have been made to the energy resolution and bias correction, up to a few percent each, in comparison to standard analysis. Nevertheless, no line with a relevant significance has been detected. The most promising line is at an energy of ∼ 422 GeV with an upper limit cross section of 8.10 · 10^-24 cm^3 s^-1 and a significance of ∼ 2.73 σ, before trials correction and ∼ 1.56 σ after. Upper limit cross sections have also been calculated for the γγ annihilation process and four other outcomes. The limits are in line with current limits using other methods, from ∼ 8.56 · 10^-26 - 6.61 · 10^-23 cm^3s^-1. Future larger telescope arrays, like the upcoming Cherenkov Telescope Array, CTA, will provide better results with the help of this analysis method.}, language = {en} } @phdthesis{Guidi2017, author = {Guidi, Giovanni}, title = {Connecting simulations and observations in galaxy formation studies}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-396876}, school = {Universit{\"a}t Potsdam}, pages = {141}, year = {2017}, abstract = {Observational and computational extragalactic astrophysics are two fields of research that study a similar subject from different perspectives. Observational extragalactic astrophysics aims, by recovering the spectral energy distribution of galaxies at different wavelengths, to reliably measure their properties at different cosmic times and in a large variety of environments. Analyzing the light collected by the instruments, observers try to disentangle the different processes occurring in galaxies at the scales of galactic physics, as well as the effect of larger scale processes such as mergers and accretion, in order to obtain a consistent picture of galaxy formation and evolution. On the other hand, hydrodynamical simulations of galaxy formation in cosmological context are able to follow the evolution of a galaxy along cosmic time, taking into account both external processes such as mergers, interactions and accretion, and internal mechanisms such as feedback from Supernovae and Active Galactic Nuclei. Due to the great advances in both fields of research, we have nowadays available spectral and photometric information for a large number of galaxies in the Universe at different cosmic times, which has in turn provided important knowledge about the evolution of the Universe; at the same time, we are able to realistically simulate galaxy formation and evolution in large volumes of the Universe, taking into account the most relevant physical processes occurring in galaxies. As these two approaches are intrinsically different in their methodology and in the information they provide, the connection between simulations and observations is still not fully established, although simulations are often used in galaxies' studies to interpret observations and assess the effect of the different processes acting on galaxies on the observable properties, and simulators usually test the physical recipes implemented in their hydrodynamical codes through the comparison with observations. In this dissertation we aim to better connect the observational and computational approaches in the study of galaxy formation and evolution, using the methods and results of one field to test and validate the methods and results of the other. In a first work we study the biases and systematics in the derivation of the galaxy properties in observations. We post-process hydrodynamical cosmological simulations of galaxy formation to calculate the galaxies' Spectral Energy Distributions (SEDs) using different approaches, including radiative transfer techniques. Comparing the direct results of the simulations with the quantities obtained applying observational techniques to these synthetic SEDs, we are able to make an analysis of the biases intrinsic in the observational algorithms, and quantify their accuracy in recovering the galaxies' properties, as well as estimating the uncertainties affecting a comparison between simulations and observations when different approaches to obtain the observables are followed. Our results show that for some quantities such as the stellar ages, metallicities and gas oxygen abundances large differences can appear, depending on the technique applied in the derivation. In a second work we compare a set of fifteen galaxies similar in mass to the Milky Way and with a quiet merger history in the recent past (hence expected to have properties close to spiral galaxies), simulated in a cosmological context, with data from the Sloan Digital Sky Survey (SDSS). We use techniques to obtain the observables as similar as possible to the ones applied in SDSS, with the aim of making an unbiased comparison between our set of hydrodynamical simulations and SDSS observations. We quantify the differences in the physical properties when these are obtained directly from the simulations without post-processing, or mimicking the SDSS observational techniques. We fit linear relations between the values derived directly from the simulations and following SDSS observational procedures, which in most of the cases have relatively high correlation, that can be easily used to more reliably compare simulations with SDSS data. When mimicking SDSS techniques, these simulated galaxies are photometrically similar to galaxies in the SDSS blue sequence/green valley, but have in general older ages, lower SFRs and metallicities compared to the majority of the spirals in the observational dataset. In a third work, we post-process hydrodynamical simulations of galaxies with radiative transfer techniques, to generate synthetic data that mimic the properties of the CALIFA Integral Field Spectroscopy (IFS) survey. We reproduce the main characteristics of the CALIFA observations in terms of field of view and spaxel physical size, data format, point spread functions and detector noise. This 3-dimensional dataset is suited to be analyzed by the same algorithms applied to the CALIFA dataset, and can be used as a tool to test the ability of the observational algorithms in recovering the properties of the CALIFA galaxies. To this purpose, we also generate the resolved maps of the simulations' properties, calculated directly from the hydrodynamical snapshots, or from the simulated spectra prior to the addition of the noise. Our work shows that a reliable connection between the models and the data is of crucial importance both to judge the output of galaxy formation codes and to accurately test the observational algorithms used in the analysis of galaxy surveys' data. A correct interpretation of observations will be particularly important in the future, in light of the several ongoing and planned large galaxy surveys that will provide the community with large datasets of properties of galaxies (often spatially-resolved) at different cosmic times, allowing to study galaxy formation physics at a higher level of detail than ever before. We have shown that neglecting the observational biases in the comparison between simulations and an observational dataset may move the simulations to different regions in the planes of the observables, strongly affecting the assessment of the correctness of the sub-resolution physical models implemented in galaxy formation codes, as well as the interpretation of given observational results using simulations.}, language = {en} } @phdthesis{Anders2017, author = {Anders, Friedrich}, title = {Disentangling the chemodynamical history of the Milky Way disc with asteroseismology and spectroscopy}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-396681}, school = {Universit{\"a}t Potsdam}, pages = {121}, year = {2017}, abstract = {Galaxies are among the most complex systems that can currently be modelled with a computer. A realistic simulation must take into account cosmology and gravitation as well as effects of plasma, nuclear, and particle physics that occur on very different time, length, and energy scales. The Milky Way is the ideal test bench for such simulations, because we can observe millions of its individual stars whose kinematics and chemical composition are records of the evolution of our Galaxy. Thanks to the advent of multi-object spectroscopic surveys, we can systematically study stellar populations in a much larger volume of the Milky Way. While the wealth of new data will certainly revolutionise our picture of the formation and evolution of our Galaxy and galaxies in general, the big-data era of Galactic astronomy also confronts us with new observational, theoretical, and computational challenges. This thesis aims at finding new observational constraints to test Milky-Way models, primarily based on infra-red spectroscopy from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and asteroseismic data from the CoRoT mission. We compare our findings with chemical-evolution models and more sophisticated chemodynamical simulations. In particular we use the new powerful technique of combining asteroseismic and spectroscopic observations that allows us to test the time dimension of such models for the first time. With CoRoT and APOGEE (CoRoGEE) we can infer much more precise ages for distant field red-giant stars, opening up a new window for Galactic archaeology. Another important aspect of this work is the forward-simulation approach that we pursued when interpreting these complex datasets and comparing them to chemodynamical models. The first part of the thesis contains the first chemodynamical study conducted with the APOGEE survey. Our sample comprises more than 20,000 red-giant stars located within 6 kpc from the Sun, and thus greatly enlarges the Galactic volume covered with high-resolution spectroscopic observations. Because APOGEE is much less affected by interstellar dust extinction, the sample covers the disc regions very close to the Galactic plane that are typically avoided by optical surveys. This allows us to investigate the chemo-kinematic properties of the Milky Way's thin disc outside the solar vicinity. We measure, for the first time with high-resolution data, the radial metallicity gradient of the disc as a function of distance from the Galactic plane, demonstrating that the gradient flattens and even changes its sign for mid-plane distances greater than 1 kpc. Furthermore, we detect a gap between the high- and low-[\$\alpha\$/Fe] sequences in the chemical-abundance diagram (associated with the thin and thick disc) that unlike in previous surveys can hardly be explained by selection effects. Using 6D kinematic information, we also present chemical-abundance diagrams cleaned from stars on kinematically hot orbits. The data allow us to confirm without doubt that the scale length of the (chemically-defined) thick disc is significantly shorter than that of the thin disc. In the second part, we present our results of the first combination of asteroseismic and spectroscopic data in the context of Galactic Archaeology. We analyse APOGEE follow-up observations of 606 solar-like oscillating red giants in two CoRoT fields close to the Galactic plane. These stars cover a large radial range of the Galactic disc (4.5 kpc \$\lesssim R_{\rm Gal}\lesssim15\$ kpc) and a large age baseline (0.5 Gyr \$\lesssim \tau\lesssim\$ 13 Gyr), allowing us to study the age- and radius-dependence of the [\$\alpha\$/Fe] vs. [Fe/H] distributions. We find that the age distribution of the high-[\$\alpha\$/Fe] sequence appears to be broader than expected from a monolithically-formed old thick disc that stopped to form stars 10 Gyr ago. In particular, we discover a significant population of apparently young, [\$\alpha\$/Fe]-rich stars in the CoRoGEE data whose existence cannot be explained by standard chemical-evolution models. These peculiar stars are much more abundant in the inner CoRoT field LRc01 than in the outer-disc field LRc01, suggesting that at least part of this population has a chemical-evolution rather than a stellar-evolution origin, possibly due to a peculiar chemical-enrichment history of the inner disc. We also find that strong radial migration is needed to explain the abundance of super-metal-rich stars in the outer disc. Finally, we use the CoRoGEE sample to study the time evolution of the radial metallicity gradient in the thin disc, an observable that has been the subject of observational and theoretical debate for more than 20 years. By dividing the CoRoGEE dataset into six age bins, performing a careful statistical analysis of the radial [Fe/H], [O/H], and [Mg/Fe] distributions, and accounting for the biases introduced by the observation strategy, we obtain reliable gradient measurements. The slope of the radial [Fe/H] gradient of the young red-giant population (\$-0.058\pm0.008\$ [stat.] \$\pm0.003\$ [syst.] dex/kpc) is consistent with recent Cepheid data. For the age range of \$1-4\$ Gyr, the gradient steepens slightly (\$-0.066\pm0.007\pm0.002\$ dex/kpc), before flattening again to reach a value of \$\sim-0.03\$ dex/kpc for stars with ages between 6 and 10 Gyr. This age dependence of the [Fe/H] gradient can be explained by a nearly constant negative [Fe/H] gradient of \$\sim-0.07\$ dex/kpc in the interstellar medium over the past 10 Gyr, together with stellar heating and migration. Radial migration also offers a new explanation for the puzzling observation that intermediate-age open clusters in the solar vicinity (unlike field stars) tend to have higher metallicities than their younger counterparts. We suggest that non-migrating clusters are more likely to be kinematically disrupted, which creates a bias towards high-metallicity migrators from the inner disc and may even steepen the intermediate-age cluster abundance gradient.}, language = {en} } @phdthesis{GonzalezManrique2017, author = {Gonz{\´a}lez Manrique, Sergio Javier}, title = {High-Resolution Observations of Emerging Flux Regions}, school = {Universit{\"a}t Potsdam}, pages = {104}, year = {2017}, language = {en} } @misc{MenzelPuhlmannHeuer2017, author = {Menzel, Ralf and Puhlmann, Dirk and Heuer, Axel}, title = {Complementarity in single photon interference - the role of the mode function and vacuum fields}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395210}, pages = {7}, year = {2017}, abstract = {Background In earlier experiments the role of the vacuum fields could be demonstrated as the source of complementarity with respect to the temporal properties (Heuer et al., Phys. Rev. Lett. 114:053601, 2015). Methods Single photon first order interferences of spatially separated regions from the cone structure of spontaneous parametric down conversion allow for analyzing the role of the mode function in quantum optics regarding the complementarity principle. Results Here the spatial coherence properties of these vacuum fields are demonstrated as the physical reason for complementarity in these single photon quantum optical experiments. These results are directly connected to the mode picture in classical optics. Conclusion The properties of the involved vacuum fields selected via the measurement process are the physical background of the complementarity principle in quantum optics.}, language = {en} } @article{MenzelPuhlmannHeuer2017, author = {Menzel, Ralf and Puhlmann, Dirk and Heuer, Axel}, title = {Complementarity in single photon interference - the role of the mode function and vacuum fields}, series = {Journal of the European Optical Society-Rapid}, volume = {13}, journal = {Journal of the European Optical Society-Rapid}, publisher = {Springer}, issn = {1990-2573}, doi = {10.1186/s41476-017-0036-x}, pages = {7}, year = {2017}, abstract = {Background In earlier experiments the role of the vacuum fields could be demonstrated as the source of complementarity with respect to the temporal properties (Heuer et al., Phys. Rev. Lett. 114:053601, 2015). Methods Single photon first order interferences of spatially separated regions from the cone structure of spontaneous parametric down conversion allow for analyzing the role of the mode function in quantum optics regarding the complementarity principle. Results Here the spatial coherence properties of these vacuum fields are demonstrated as the physical reason for complementarity in these single photon quantum optical experiments. These results are directly connected to the mode picture in classical optics. Conclusion The properties of the involved vacuum fields selected via the measurement process are the physical background of the complementarity principle in quantum optics.}, language = {en} } @phdthesis{Shenar2017, author = {Shenar, Tomer}, title = {Comprehensive analyses of massive binaries and implications on stellar evolution}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-104857}, school = {Universit{\"a}t Potsdam}, pages = {187}, year = {2017}, abstract = {Via their powerful radiation, stellar winds, and supernova explosions, massive stars (Mini \& 8 M☉) bear a tremendous impact on galactic evolution. It became clear in recent decades that the majority of massive stars reside in binary systems. This thesis sets as a goal to quantify the impact of binarity (i.e., the presence of a companion star) on massive stars. For this purpose, massive binary systems in the Local Group, including OB-type binaries, high mass X-ray binaries (HMXBs), and Wolf-Rayet (WR) binaries, were investigated by means of spectral, orbital, and evolutionary analyses. The spectral analyses were performed with the non-local thermodynamic equillibrium (non-LTE) Potsdam Wolf-Rayet (PoWR) model atmosphere code. Thanks to critical updates in the calculation of the hydrostatic layers, the code became a state-of-the-art tool applicable for all types of hot massive stars (Chapter 2). The eclipsing OB-type triple system δ Ori served as an intriguing test-case for the new version of the PoWR code, and provided key insights regarding the formation of X-rays in massive stars (Chapter 3). We further analyzed two prototypical HMXBs, Vela X-1 and IGR J17544-2619, and obtained fundamental conclusions regarding the dichotomy of two basic classes of HMXBs (Chapter 4). We performed an exhaustive analysis of the binary R 145 in the Large Magellanic Cloud (LMC), which was claimed to host the most massive stars known. We were able to disentangle the spectrum of the system, and performed an orbital, polarimetric, and spectral analysis, as well as an analysis of the wind-wind collision region. The true masses of the binary components turned out to be significantly lower than suggested, impacting our understanding of the initial mass function and stellar evolution at low metallicity (Chapter 5). Finally, all known WR binaries in the Small Magellanic Cloud (SMC) were analyzed. Although it was theoretical predicted that virtually all WR stars in the SMC should be formed via mass-transfer in binaries, we find that binarity was not important for the formation of the known WR stars in the SMC, implying a strong discrepancy between theory and observations (Chapter 6).}, language = {en} }