@article{ZhuShpritsSpasojevicetal.2019, author = {Zhu, Hui and Shprits, Yuri and Spasojevic, M. and Drozdov, Alexander}, title = {New hiss and chorus waves diffusion coefficient parameterizations from the Van Allen Probes and their effect on long-term relativistic electron radiation-belt VERB simulations}, series = {Journal of Atmospheric and Solar-Terrestrial Physics}, volume = {193}, journal = {Journal of Atmospheric and Solar-Terrestrial Physics}, publisher = {Elsevier}, address = {Oxford}, issn = {1364-6826}, doi = {10.1016/j.jastp.2019.105090}, pages = {13}, year = {2019}, abstract = {New wave frequency and amplitude models for the nightside and dayside chorus waves are built based on measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument onboard the Van Allen Probes. The corresponding 3D diffusion coefficients are systematically obtained. Compared with previous commonly-used (typical) parameterizations, the new parameterizations result in differences in diffusion rates that depend on the energy and pitch angle. Furthermore, one-year 3D diffusive simulations are performed using the Versatile Electron Radiation Belt (VERB) code. Both typical and new wave parameterizations simulation results are in a good agreement with observations at 0.9 MeV. However, the new parameterizations for nightside chorus better reproduce the observed electron fluxes. These parameterizations will be incorporated into future modeling efforts.}, language = {en} } @phdthesis{Kerutt2019, author = {Kerutt, Josephine Victoria}, title = {The high-redshift voyage of Lyman alpha and Lyman continuum emission as told by MUSE}, doi = {10.25932/publishup-47881}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-478816}, school = {Universit{\"a}t Potsdam}, pages = {152}, year = {2019}, abstract = {Most of the matter in the universe consists of hydrogen. The hydrogen in the intergalactic medium (IGM), the matter between the galaxies, underwent a change of its ionisation state at the epoch of reionisation, at a redshift roughly between 6>z>10, or ~10^8 years after the Big Bang. At this time, the mostly neutral hydrogen in the IGM was ionised but the source of the responsible hydrogen ionising emission remains unclear. In this thesis I discuss the most likely candidates for the emission of this ionising radiation, which are a type of galaxy called Lyman alpha emitters (LAEs). As implied by their name, they emit Lyman alpha radiation, produced after a hydrogen atom has been ionised and recombines with a free electron. The ionising radiation itself (also called Lyman continuum emission) which is needed for this process inside the LAEs could also be responsible for ionising the IGM around those galaxies at the epoch of reionisation, given that enough Lyman continuum escapes. Through this mechanism, Lyman alpha and Lyman continuum radiation are closely linked and are both studied to better understand the properties of high redshift galaxies and the reionisation state of the universe. Before I can analyse their Lyman alpha emission lines and the escape of Lyman continuum emission from them, the first step is the detection and correct classification of LAEs in integral field spectroscopic data, specifically taken with the Multi-Unit Spectroscopic Explorer (MUSE). After detecting emission line objects in the MUSE data, the task of classifying them and determining their redshift is performed with the graphical user interface QtClassify, which I developed during the work on this thesis. It uses the strength of the combination of spectroscopic and photometric information that integral field spectroscopy offers to enable the user to quickly identify the nature of the detected emission lines. The reliable classification of LAEs and determination of their redshifts is a crucial first step towards an analysis of their properties. Through radiative transfer processes, the properties of the neutral hydrogen clouds in and around LAEs are imprinted on the shape of the Lyman alpha line. Thus after identifying the LAEs in the MUSE data, I analyse the properties of the Lyman alpha emission line, such as the equivalent width (EW) distribution, the asymmetry and width of the line as well as the double peak fraction. I challenge the common method of displaying EW distributions as histograms without taking the limits of the survey into account and construct a more independent EW distribution function that better reflects the properties of the underlying population of galaxies. I illustrate this by comparing the fraction of high EW objects between the two surveys MUSE-Wide and MUSE-Deep, both consisting of MUSE pointings (each with the size of one square arcminute) of different depths. In the 60 MUSE-Wide fields of one hour exposure time I find a fraction of objects with extreme EWs above EW_0>240A of ~20\%, while in the MUSE-Deep fields (9 fields with an exposure time of 10 hours and one with an exposure time of 31 hours) I find a fraction of only ~1\%, which is due to the differences in the limiting line flux of the surveys. The highest EW I measure is EW_0 = 600.63 +- 110A, which hints at an unusual underlying stellar population, possibly with a very low metallicity. With the knowledge of the redshifts and positions of the LAEs detected in the MUSE-Wide survey, I also look for Lyman continuum emission coming from these galaxies and analyse the connection between Lyman continuum emission and Lyman alpha emission. I use ancillary Hubble Space Telescope (HST) broadband photometry in the bands that contain the Lyman continuum and find six Lyman continuum leaker candidates. To test whether the Lyman continuum emission of LAEs is coming only from those individual objects or the whole population, I select LAEs that are most promising for the detection of Lyman continuum emission, based on their rest-frame UV continuum and Lyman alpha line shape properties. After this selection, I stack the broadband data of the resulting sample and detect a signal in Lyman continuum with a significance of S/N = 5.5, pointing towards a Lyman continuum escape fraction of ~80\%. If the signal is reliable, it strongly favours LAEs as the providers of the hydrogen ionising emission at the epoch of reionisation and beyond.}, language = {en} } @article{VojtaSkinnerMetzler2019, author = {Vojta, Thomas and Skinner, Sarah and Metzler, Ralf}, title = {Probability density of the fractional Langevin equation with reflecting walls}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {100}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {2470-0045}, doi = {10.1103/PhysRevE.100.042142}, pages = {11}, year = {2019}, abstract = {We investigate anomalous diffusion processes governed by the fractional Langevin equation and confined to a finite or semi-infinite interval by reflecting potential barriers. As the random and damping forces in the fractional Langevin equation fulfill the appropriate fluctuation-dissipation relation, the probability density on a finite interval converges for long times towards the expected uniform distribution prescribed by thermal equilibrium. In contrast, on a semi-infinite interval with a reflecting wall at the origin, the probability density shows pronounced deviations from the Gaussian behavior observed for normal diffusion. If the correlations of the random force are persistent (positive), particles accumulate at the reflecting wall while antipersistent (negative) correlations lead to a depletion of particles near the wall. We compare and contrast these results with the strong accumulation and depletion effects recently observed for nonthermal fractional Brownian motion with reflecting walls, and we discuss broader implications.}, language = {en} } @article{Goychuk2019, author = {Goychuk, Igor}, title = {Fractional Hydrodynamic Memory and Superdiffusion in Tilted Washboard Potentials}, series = {Physical review letters}, volume = {123}, journal = {Physical review letters}, number = {18}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.180603}, pages = {6}, year = {2019}, abstract = {Diffusion in tilted washboard potentials can paradoxically exceed free normal diffusion. The effect becomes much stronger in the underdamped case due to inertial effects. What happens upon inclusion of usually neglected fractional hydrodynamics memory effects (Basset-Boussinesq frictional force), which result in a heavy algebraic tail of the velocity autocorrelation function of the potential-free diffusion making it transiently superdiffusive? Will a giant enhancement of diffusion become even stronger, and the transient superdiffusion last even longer? These are the questions that we answer in this Letter based on an accurate numerical investigation. We show that a resonancelike enhancement of normal diffusion becomes indeed much stronger and sharper. Moreover, a long-lasting transient regime of superdiffusion, including Richardson-like diffusion, proportional to t(3) and ballistic supertransport, proportional to t(2), is revealed.}, language = {en} } @article{HaeneBruehwilerEckeretal.2019, author = {Haene, Janick and Bruehwiler, Dominik and Ecker, Achim and Hass, Roland}, title = {Real-time inline monitoring of zeolite synthesis by Photon Density Wave spectroscopy}, series = {Microporous and mesoporous materials : zeolites, clays, carbons and related materials}, volume = {288}, journal = {Microporous and mesoporous materials : zeolites, clays, carbons and related materials}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1387-1811}, doi = {10.1016/j.micromeso.2019.109580}, pages = {6}, year = {2019}, abstract = {The formation process of zeolite A (Linde Type A) was monitored inline at 1.5 L scale by Photon Density Wave (PDW) spectroscopy as novel process analytical technology for highly turbid liquid suspensions. As a result, the reduced scattering coefficient, being a measure for particle number, size, and morphology, provides distinct process information, including the formation of amorphous particles and their transfer into crystalline zeolite structures. The onset and end of the crystallization process can be detected inline and in real-time. Analyses by powder X-ray diffraction and electron microscopy, based on a sampling approach, support the interpretation of the results obtained by PDW spectroscopy. In addition, the influence of the molar water content was investigated, indicating a linear increase of the time needed to reach the end of the zeolite A crystallization with increasing molar water content. Further experiments indicate a strong influence of the silica source on the course of the crystallization. The applicability of PDW spectroscopy under even more demanding chemical and physical conditions was investigated by monitoring the synthesis of zeolite L (Linde Type L).}, language = {en} } @article{JelkenHenkelSanter2019, author = {Jelken, Joachim and Henkel, Carsten and Santer, Svetlana}, title = {Solving an old puzzle: fine structure of diffraction spots from an azo-polymer surface relief grating}, series = {Applied physics : B, Lasers and optics}, volume = {125}, journal = {Applied physics : B, Lasers and optics}, number = {11}, publisher = {Springer}, address = {Heidelberg}, issn = {0946-2171}, doi = {10.1007/s00340-019-7331-8}, pages = {11}, year = {2019}, abstract = {We report on the experimental and theoretical interpretation of the diffraction of a probe beam during inscription of a surface relief grating with an interference pattern into a photo-responsive polymer film. For this, we developed a set-up allowing for the simultaneous recording of the diffraction efficiency (DE), the fine structure of the diffraction spot and the topographical changes, in situ and in real time while the film is irradiated. The time dependence of the DE, as the surface relief deepens, follows a Bessel function exhibiting maxima and minima. The size of the probe beam relative to the inscribed grating (i.e., to the size of the writing beams) matters and has to be considered for the interpretation of the DE signal. It is also at the origin of a fine structure within the diffraction spot where ring-shaped features appear once an irradiation time corresponding to the first maximum of the DE has been exceeded.}, language = {en} } @article{Metzler2019, author = {Metzler, Ralf}, title = {Brownian motion and beyond: first-passage, power spectrum, non-Gaussianity, and anomalous diffusion}, series = {Journal of statistical mechanics: theory and experiment}, volume = {2019}, journal = {Journal of statistical mechanics: theory and experiment}, number = {11}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1742-5468}, doi = {10.1088/1742-5468/ab4988}, pages = {18}, year = {2019}, abstract = {Brownian motion is a ubiquitous physical phenomenon across the sciences. After its discovery by Brown and intensive study since the first half of the 20th century, many different aspects of Brownian motion and stochastic processes in general have been addressed in Statistical Physics. In particular, there now exists a very large range of applications of stochastic processes in various disciplines. Here we provide a summary of some of the recent developments in the field of stochastic processes, highlighting both the experimental findings and theoretical frameworks.}, language = {en} } @article{BohdanNiemiecPohletal.2019, author = {Bohdan, Artem and Niemiec, Jacek and Pohl, Martin and Matsumoto, Yosuke and Amano, Takanobu and Hoshino, Masahiro}, title = {Kinetic Simulations of Nonrelativistic Perpendicular Shocks of Young Supernova Remnants. II. Influence of Shock-surfing Acceleration on Downstream Electron Spectra}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {885}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/1538-4357/ab43cf}, pages = {9}, year = {2019}, abstract = {We explore electron preacceleration at high-Mach-number nonrelativistic perpendicular shocks at, e.g., young supernova remnants, which are a prerequisite of further acceleration to very high energies via diffusive shock acceleration. Using fully kinetic particle-in-cell simulations of shocks and electron dynamics in them, we investigate the influence of shock-surfing acceleration (SSA) at the shock foot on the nonthermal population of electrons downstream of the shock. The SSA is followed by further energization at the shock ramp where the Weibel instability spawns a type of second-order Fermi acceleration. The combination of these two processes leads to the formation of a nonthermal electron population, but the importance of SSA becomes smaller for larger ion-to-electron mass ratios in the simulation. We discuss the resulting electron spectra and the relevance of our results to the physics of systems with real ion-to-electron mass ratios and fully three-dimensional behavior.}, language = {en} } @article{PlatCharlotBruzualetal.2019, author = {Plat, A. and Charlot, S. and Bruzual, G. and Feltre, A. and Vidal-Garcia, A. and Morisset, C. and Chevallard, Jacopo and Todt, Helge Tobias}, title = {Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies}, series = {Monthly notices of the Royal Astronomical Society}, volume = {490}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stz2616}, pages = {978 -- 1009}, year = {2019}, abstract = {We explore the production and escape of ionizing photons in young galaxies by investigating the ultraviolet and optical emission-line properties of models of ionization-bounded and density-bounded H II regions, active-galactic-nucleus (AGN) narrow-line regions, and radiative shocks computed all using the same physically consistent description of element abundances and depletion on to dust grains down to very low metallicities. We compare these models with a reference sample of metal-poor star-forming galaxies and Lyman-continuum (LyC) leakers at various redshifts, which allows the simultaneous exploration of more spectral diagnostics than typically available at once for individual subsamples. We confirm that current single- and binary-star population synthesis models do not produce hard-enough radiation to account for the high-ionization emission of the most metal-poor galaxies. Introducing either an AGN or radiative-shock component brings models into agreement with observations. A published model including X-ray binaries is an attractive alternative to reproduce the observed rise in He II lambda 4686/H beta ratio with decreasing oxygen abundance in metal-poor star-forming galaxies, but not the high observed He II lambda 4686/H beta ratios of galaxies with large EW(H beta). A source of harder ionizing radiation appears to be required in these extreme objects, such as an AGN or radiative-shock component, perhaps linked to an initial-mass-function bias towards massive stars at low metallicity. This would also account for the surprisingly high [O I]/[O III] ratios of confirmed LyC leakers relative to ionization-bounded models. We find no simple by-eye diagnostic of the nature of ionizing sources and the escape of LyC photon, which require proper simultaneous fits of several lines to be discriminated against.}, language = {en} } @article{DierckeDenker2019, author = {Diercke, Andrea and Denker, Carsten}, title = {Chromospheric Synoptic Maps of Polar Crown Filaments}, series = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, volume = {294}, journal = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, number = {11}, publisher = {Springer}, address = {Dordrecht}, issn = {0038-0938}, doi = {10.1007/s11207-019-1538-z}, pages = {17}, year = {2019}, abstract = {Polar crown filaments form above the polarity inversion line between the old magnetic flux of the previous cycle and the new magnetic flux of the current cycle. Studying their appearance and their properties can lead to a better understanding of the solar cycle. We use full-disk data of the Chromospheric Telescope (ChroTel) at the Observatorio del Teide, Tenerife, Spain, which were taken in three different chromospheric absorption lines (H alpha lambda 6563 angstrom, Ca II K lambda 3933 angstrom, and He I lambda 10830 angstrom), and we create synoptic maps. In addition, the spectroscopic He I data allow us to compute Doppler velocities and to create synoptic Doppler maps. ChroTel data cover the rising and decaying phase of Solar Cycle 24 on about 1000 days between 2012 and 2018. Based on these data, we automatically extract polar crown filaments with image-processing tools and study their properties. We compare contrast maps of polar crown filaments with those of quiet-Sun filaments. Furthermore, we present a super-synoptic map summarizing the entire ChroTel database. In summary, we provide statistical properties, i.e. number and location of filaments, area, and tilt angle for both the maximum and the declining phase of Solar Cycle 24. This demonstrates that ChroTel provides a promising data set to study the solar cycle.}, language = {en} } @article{DrozdovAseevEffenbergeretal.2019, author = {Drozdov, Alexander and Aseev, Nikita and Effenberger, Frederic and Turner, Drew L. and Saikin, Anthony and Shprits, Yuri}, title = {Storm Time Depletions of Multi-MeV Radiation Belt Electrons Observed at Different Pitch Angles}, series = {Journal of geophysical research : Space physics}, volume = {124}, journal = {Journal of geophysical research : Space physics}, number = {11}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1029/2019JA027332}, pages = {8943 -- 8953}, year = {2019}, abstract = {During geomagnetic storms, the rapid depletion of the high-energy (several MeV) outer radiation belt electrons is the result of loss to the interplanetary medium through the magnetopause, outward radial diffusion, and loss to the atmosphere due to wave-particle interactions. We have performed a statistical study of 110 storms using pitch angle resolved electron flux measurements from the Van Allen Probes mission and found that inside of the radiation belt (L* = 3 - 5) the number of storms that result in depletion of electrons with equatorial pitch angle alpha(eq) = 30 degrees is higher than number of storms that result in depletion of electrons with equatorial pitch angle alpha(eq) = 75 degrees. We conclude that this result is consistent with electron scattering by whistler and electromagnetic ion cyclotron waves. At the outer edge of the radiation belt (L* >= 5.2) the number of storms that result in depletion is also large (similar to 40-50\%), emphasizing the significance of the magnetopause shadowing effect and outward radial transport.}, language = {en} } @article{TeomyRoichmanShokef2019, author = {Teomy, Eial and Roichman, Yael and Shokef, Yair}, title = {Multiple peaks in the displacement distribution of active random walkers}, series = {Journal of statistical mechanics: theory and experiment}, volume = {2019}, journal = {Journal of statistical mechanics: theory and experiment}, number = {11}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1742-5468}, doi = {10.1088/1742-5468/ab4fde}, pages = {22}, year = {2019}, abstract = {We consider a simple model for active random walk with general temporal correlations, and investigate the shape of the probability distribution function of the displacement during a short time interval. We find that under certain conditions the distribution exhibits multiple peaks and we show analytically and numerically that the existence of these peaks is governed by the walker?s tendency to move forward, while the correlations between the timing of its active motion control the magnitude and shape of the peaks. In particular, we find that in a homogeneous system such peaks can occur only if the persistence is strong enough.}, language = {en} } @article{PowierzaGollwitzerWolgastetal.2019, author = {Powierza, Bartosz and Gollwitzer, Christian and Wolgast, Dagmar and Staude, Andreas and Bruno, Giovanni}, title = {Fully experiment-based evaluation of few digital volume correlation techniques}, series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, volume = {90}, journal = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, number = {11}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.5099572}, pages = {10}, year = {2019}, abstract = {Digital Volume Correlation (DVC) is a powerful set of techniques used to compute the local shifts of 3D images obtained, for instance, in tomographic experiments. It is utilized to analyze the geometric changes of the investigated object as well as to correct the corresponding image misalignments for further analysis. It can therefore be used to evaluate the local density changes of the same regions of the inspected specimens, which might be shifted between measurements. In recent years, various approaches and corresponding pieces of software were introduced. Accuracies for the computed shift vectors of up to about 1 parts per thousand of a single voxel size have been reported. These results, however, were based either on synthetic datasets or on an unrealistic setup. In this work, we propose two simple methods to evaluate the accuracy of DVC-techniques using more realistic input data and apply them to several DVC programs. We test these methods on three materials (tuff, sandstone, and concrete) that show different contrast and structural features. Published under license by AIP Publishing.}, language = {en} } @article{BolotovBolotovSmirnovetal.2019, author = {Bolotov, Dmitry and Bolotov, Maxim I. and Smirnov, Lev A. and Osipov, Grigory V. and Pikovskij, Arkadij}, title = {Twisted States in a System of Nonlinearly Coupled Phase Oscillators}, series = {Regular and chaotic dynamics : international scientific journal}, volume = {24}, journal = {Regular and chaotic dynamics : international scientific journal}, number = {6}, publisher = {Pleiades publishing inc}, address = {Moscow}, issn = {1560-3547}, doi = {10.1134/S1560354719060091}, pages = {717 -- 724}, year = {2019}, abstract = {We study the dynamics of the ring of identical phase oscillators with nonlinear nonlocal coupling. Using the Ott - Antonsen approach, the problem is formulated as a system of partial derivative equations for the local complex order parameter. In this framework, we investigate the existence and stability of twisted states. Both fully coherent and partially coherent stable twisted states were found (the latter ones for the first time for identical oscillators). We show that twisted states can be stable starting from a certain critical value of the medium length, or on a length segment. The analytical results are confirmed with direct numerical simulations in finite ensembles.}, language = {en} } @article{HsuKrekhovTarantolaetal.2019, author = {Hsu, H. F. and Krekhov, Andrey and Tarantola, Marco and Beta, Carsten and Bodenschatz, Eberhardt}, title = {Interplay between myosin II and actin dynamics in chemotactic amoeba}, series = {New journal of physics : the open-access journal for physics}, volume = {21}, journal = {New journal of physics : the open-access journal for physics}, number = {11}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab5822}, pages = {15}, year = {2019}, abstract = {The actin cytoskeleton and its response to external chemical stimuli is fundamental to the mechano-biology of eukaryotic cells and their functions. One of the key players that governs the dynamics of the actin network is the motor protein myosin II. Based on a phase space embedding we have identified from experiments three phases in the cytoskeletal dynamics of starved Dictyostelium discoideum in response to a precisely controlled chemotactic stimulation. In the first two phases the dynamics of actin and myosin II in the cortex is uncoupled, while in the third phase the time scale for the recovery of cortical actin is determined by the myosin II dynamics. We report a theoretical model that captures the experimental observations quantitatively. The model predicts an increase in the optimal response time of actin with decreasing myosin II-actin coupling strength highlighting the role of myosin II in the robust control of cell contraction.}, language = {en} } @article{GoettgensHusserKamannetal.2019, author = {G{\"o}ttgens, Fabian and Husser, Tim-Oliver and Kamann, Sebastian and Dreizler, Stefan and Giesers, Benjamin and Kollatschny, Wolfram and Weilbacher, Peter Michael and Roth, Martin M. and Wendt, Martin}, title = {A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {631}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201936485}, pages = {16}, year = {2019}, abstract = {Aims. Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousand other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra (i.e. spectra that contain emission lines), we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. Methods. To detect emission lines in each spectrum, we modelled the expected shape of an emission line as a Gaussian curve. This template was used for matched filtering on the di fferences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of H alpha emission are checked visually and cross-matched with published catalogues. Results. We find 156 stars with H alpha emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detected H alpha emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.}, language = {en} } @article{PadashChechkinDybiecetal.2019, author = {Padash, Amin and Chechkin, Aleksei V. and Dybiec, Bartlomiej and Pavlyukevich, Ilya and Shokri, Babak and Metzler, Ralf}, title = {First-passage properties of asymmetric Levy flights}, series = {Journal of physics : A, Mathematical and theoretical}, volume = {52}, journal = {Journal of physics : A, Mathematical and theoretical}, number = {45}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1751-8113}, doi = {10.1088/1751-8121/ab493e}, pages = {48}, year = {2019}, abstract = {L{\´e}vy flights are paradigmatic generalised random walk processes, in which the independent stationary increments—the 'jump lengths'—are drawn from an -stable jump length distribution with long-tailed, power-law asymptote. As a result, the variance of L{\´e}vy flights diverges and the trajectory is characterised by occasional extremely long jumps. Such long jumps significantly decrease the probability to revisit previous points of visitation, rendering L{\´e}vy flights efficient search processes in one and two dimensions. To further quantify their precise property as random search strategies we here study the first-passage time properties of L{\´e}vy flights in one-dimensional semi-infinite and bounded domains for symmetric and asymmetric jump length distributions. To obtain the full probability density function of first-passage times for these cases we employ two complementary methods. One approach is based on the space-fractional diffusion equation for the probability density function, from which the survival probability is obtained for different values of the stable index and the skewness (asymmetry) parameter . The other approach is based on the stochastic Langevin equation with -stable driving noise. Both methods have their advantages and disadvantages for explicit calculations and numerical evaluation, and the complementary approach involving both methods will be profitable for concrete applications. We also make use of the Skorokhod theorem for processes with independent increments and demonstrate that the numerical results are in good agreement with the analytical expressions for the probability density function of the first-passage times.}, language = {en} } @article{MaheswaranAgarwalSivakumaretal.2019, author = {Maheswaran, Rathinasamy and Agarwal, Ankit and Sivakumar, Bellie and Marwan, Norbert and Kurths, J{\"u}rgen}, title = {Wavelet analysis of precipitation extremes over India and teleconnections to climate indices}, series = {Stochastic Environmental Research and Risk Assessment}, volume = {33}, journal = {Stochastic Environmental Research and Risk Assessment}, number = {11-12}, publisher = {Springer}, address = {New York}, issn = {1436-3240}, doi = {10.1007/s00477-019-01738-3}, pages = {2053 -- 2069}, year = {2019}, abstract = {Precipitation patterns and extremes are significantly influenced by various climatic factors and large-scale atmospheric circulation patterns. This study uses wavelet coherence analysis to detect significant interannual and interdecadal oscillations in monthly precipitation extremes across India and their teleconnections to three prominent climate indices, namely, Nino 3.4, Pacific Decadal Oscillation, and Indian Ocean Dipole (IOD). Further, partial wavelet coherence analysis is used to estimate the standalone relationship between the climate indices and precipitation after removing the effect of interdependency. The wavelet analysis of monthly precipitation extremes at 30 different locations across India reveals that (a) interannual (2-8 years) and interdecadal (8-32 years) oscillations are statistically significant, and (b) the oscillations vary in both time and space. The results from the partial wavelet coherence analysis reveal that Nino 3.4 and IOD are the significant drivers of Indian precipitation at interannual and interdecadal scales. Intriguingly, the study also confirms that the strength of influence of large-scale atmospheric circulation patterns on Indian precipitation extremes varies with spatial physiography of the region.}, language = {en} } @article{LeQuangPhuongHosseiniKohetal.2019, author = {Le Quang Phuong, and Hosseini, Seyed Mehrdad and Koh, Chang Woo and Woo, Han Young and Shoaee, Safa}, title = {Measuring Competing Recombination Losses in a Significantly Reduced Langevin System by Steady-State Photoinduced Absorption and Photocurrent Spectroscopy}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {123}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {45}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.9b08901}, pages = {27417 -- 27422}, year = {2019}, abstract = {Understanding and disentangling photophysical properties of long-lived photoexcitations in bulk heterojunction (BHJ) solar cells, which contribute mostly to photocurrent, provide essential guidelines to their improvement. However, to construct improved physical models, their rational design relies on reliable measurement techniques for charge recombination. Here, we combine photocurrent and photoinduced absorption spectroscopy (PCPIA) to directly probe the free carrier concentration and investigate loss mechanisms of long-lived excitations in nearly 10\% efficient PPDT2FBT/PC70BM BHJ solar cells under steady-state operational conditions. From the PCPIA data obtained under open- circuit and short-circuit conditions, the absorption cross section and the concentration of photoexcitations are obtained. This material system exhibits an exceptionally low bimolecular recombination rate, about 300 times smaller than the diffusion-controlled electron and hole encounter rate. Furthermore, we observe that the fill factor is limited by losses originating from long-lived photoexcitations undergoing dispersive bimolecular recombination.}, language = {en} } @article{LiuVazdaCruzPolyutovetal.2019, author = {Liu, Ji-Cai and Vaz da Cruz, Vinicius and Polyutov, Sergey and F{\"o}hlisch, Alexander}, title = {Recoil-induced dissociation in hard-x-ray photoionization}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {100}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.053408}, pages = {7}, year = {2019}, abstract = {We predict the recoil-induced molecular dissociation in hard-x-ray photoionization. The recoil effect is caused by electronic and photon momentum exchange with the molecule. We show the strong role of relativistic effects for the studied molecular fragmentation. The recoil-induced fragmentation of the molecule is caused by elongation of the bond due to the vibrational recoil effect and because of the centrifugal force caused by the rotational recoil. The calculations of the x-ray photoelectron spectra of the H-2 and NO molecules show that the predicted effects can be observed in high-energy synchrotrons like SOLEIL, SPring-8, PETRA, and XFEL SACLA. The relativistic effect enhances the recoil momentum transfer and makes it strongly sensitive to the direction of ejection of the fast photoelectron with respect to the photon momentum.}, language = {en} } @article{UeckerdtFrielerLangeetal.2019, author = {Ueckerdt, Falko and Frieler, Katja and Lange, Stefan and Wenz, Leonie and Luderer, Gunnar and Levermann, Anders}, title = {The economically optimal warming limit of the planet}, series = {Earth system dynamics}, volume = {10}, journal = {Earth system dynamics}, number = {4}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {2190-4979}, doi = {10.5194/esd-10-741-2019}, pages = {741 -- 763}, year = {2019}, abstract = {Both climate-change damages and climate-change mitigation will incur economic costs. While the risk of severe damages increases with the level of global warming (Dell et al., 2014; IPCC, 2014b, 2018; Lenton et al., 2008), mitigating costs increase steeply with more stringent warming limits (IPCC, 2014a; Luderer et al., 2013; Rogelj et al., 2015). Here, we show that the global warming limit that minimizes this century's total economic costs of climate change lies between 1.9 and 2 ∘C, if temperature changes continue to impact national economic growth rates as observed in the past and if instantaneous growth effects are neither compensated nor amplified by additional growth effects in the following years. The result is robust across a wide range of normative assumptions on the valuation of future welfare and inequality aversion. We combine estimates of climate-change impacts on economic growth for 186 countries (applying an empirical damage function from Burke et al., 2015) with mitigation costs derived from a state-of-the-art energy-economy-climate model with a wide range of highly resolved mitigation options (Kriegler et al., 2017; Luderer et al., 2013, 2015). Our purely economic assessment, even though it omits non-market damages, provides support for the international Paris Agreement on climate change. The political goal of limiting global warming to "well below 2 degrees" is thus also an economically optimal goal given above assumptions on adaptation and damage persistence.}, language = {en} } @article{LeverRamelowGuehr2019, author = {Lever, Fabiano and Ramelow, Sven and G{\"u}hr, Markus}, title = {Effects of time-energy correlation strength in molecular entangled photon spectroscopy}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {100}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.053844}, pages = {6}, year = {2019}, abstract = {In this paper, we explore the time-energy domain quantum-classical transition comparing a classical pump-probe experiment on a diatomic molecule to its quantum enhanced counterpart, where the pump and probe pulses are substituted by the signal and idler beams of a spontaneous parametric down conversion (SPDC) source. Absorption of biphotons generated with SPDC exploits quantum time-energy entanglement to enhance the overall yield and selectivity of the process, when compared with a classical pump-probe setup, while maintaining femtosecond time resolution. We systematically study the effects of correlation strength on process efficiency and selectivity, comparing the results to classical pump-probe spectra. An excitation scheme to improve the yield based on spectral narrowing of biphotons is shown. The results indicate that the quantum improvements in yield are caused by a more efficient use of the total power available for the process.}, language = {en} } @article{LiuYanZhang2019, author = {Liu, Ruo-Yu and Yan, Huirong and Zhang, Heshou}, title = {Role of Anisotropic Diffusion of Particles}, series = {Physical review letters}, volume = {123}, journal = {Physical review letters}, number = {22}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.221103}, pages = {5}, year = {2019}, abstract = {In this Letter, we propose that the x-ray and the TeV observations in the vicinity of Geminga can be understood in the framework of anisotropic diffusion of injected electrons or positrons. This interpretation only requires the turbulence in the vicinity of Geminga to be sub-Alfvenic with the local mean magnetic field direction approximately aligned with our line of sight towards Geminga, without invoking extreme conditions for the environment, such as an extremely small diffusion coefficient and a weak magnetic field of submicrogauss as suggested in previous literature.}, language = {en} } @article{KniepertPaulkePerdigonToroetal.2019, author = {Kniepert, Juliane and Paulke, Andreas and Perdig{\´o}n-Toro, Lorena and Kurpiers, Jona and Zhang, Huotian and Gao, Feng and Yuan, Jun and Zou, Yingping and Le Corre, Vincent M. and Koster, Lambert Jan Anton and Neher, Dieter}, title = {Reliability of charge carrier recombination data determined with charge extraction methods}, series = {Journal of applied physics}, volume = {126}, journal = {Journal of applied physics}, number = {20}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/1.5129037}, pages = {15}, year = {2019}, abstract = {Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k(2) = 1.7 x 10(-17)m(3) s(-1). BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. Published under license by AIP Publishing.}, language = {en} } @article{PatelNoackVacogneetal.2019, author = {Patel, Dhananjay I. and Noack, Sebastian and Vacogne, Charlotte D. and Schlaad, Helmut and Bahr, Stephan and Dietrich, Paul and Meyer, Michael and Thissen, Andreas and Linford, Matthew R.}, title = {Poly(L-lactic acid), by near-ambient pressure XPS}, series = {Surface Science Spectra}, volume = {26}, journal = {Surface Science Spectra}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1055-5269}, doi = {10.1116/1.5110309}, pages = {8}, year = {2019}, abstract = {Near ambient pressure - x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at 2500Pa or higher. With NAP-XPS, one can analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission we show C 1s, O 1s, and survey NAP-XPS spectra from poly(L-lactic acid). The C 1s and O 1s envelopes were fit with three and two Gaussian-Lorentzian sum functions, respectively. Water vapor (800Pa) was used as the residual gas for charge compensation, which was confirmed by the sharp peak at 535.0 eV in the O 1s narrow scan. The uniqueness plot corresponding to the C 1s fit shows that the fit parameters had statistical significance. C 1s and O 1s spectra of PLLA damaged by exposure to x-rays for ca. 1 hour are also included. Published by the AVS.}, language = {en} } @article{GengelPikovskij2019, author = {Gengel, Erik and Pikovskij, Arkadij}, title = {Phase demodulation with iterative Hilbert transform embeddings}, series = {Signal processing}, volume = {165}, journal = {Signal processing}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0165-1684}, doi = {10.1016/j.sigpro.2019.07.005}, pages = {115 -- 127}, year = {2019}, abstract = {We propose an efficient method for demodulation of phase modulated signals via iterated Hilbert transform embeddings. We show that while a usual approach based on one application of the Hilbert transform provides only an approximation to a proper phase, with iterations the accuracy is essentially improved, up to precision limited mainly by discretization effects. We demonstrate that the method is applicable to arbitrarily complex waveforms, and to modulations fast compared to the basic frequency. Furthermore, we develop a perturbative theory applicable to a simple cosine waveform, showing convergence of the technique.}, language = {en} } @article{RamanVenkatesanGulyakovaFruebingetal.2019, author = {Raman Venkatesan, Thulasinath and Gulyakova, Anna A. and Fr{\"u}bing, Peter and Gerhard, Reimund}, title = {Electrical polarization phenomena, dielectric relaxations and structural transitions in a relaxor-ferroelectric terpolymer investigated with electrical probing techniques}, series = {Materials research express}, volume = {6}, journal = {Materials research express}, number = {12}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2053-1591}, doi = {10.1088/2053-1591/ab5352}, pages = {7}, year = {2019}, abstract = {Dielectric Relaxation Spectroscopy (DRS) and Thermally Stimulated Depolarization Current (TSDC) measurements were employed to study dielectric-relaxation processes, structural transitions and electric-polarization phenomena in poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films. Results from DRS confirm the existence of two separate dispersion regions related to a para-to-ferroelectric phase transition and to the glass transition. The dipolar TSDC peak correlates with the loss peak of the ? relaxation that represents the glass transition. The electric polarization calculated from the dipolar TSDC peak (glass transition) shows a non-linear electric-field dependence and saturates at high electric poling fields. As the observed behaviour is essentially the same as that of the electric polarization obtained from direct polarization-versus-electric-field hysteresis measurements, TSDC experiments are also suitable for studying the polarization in relaxor-ferroelectric polymers. A saturation polarization of 44 mC m(?2) was found for an electric field of 190 MV m(?1).}, language = {en} } @article{RuedigerSchultz2019, author = {R{\"u}diger, G{\"u}nther and Schultz, M.}, title = {Non-diffusive angular momentum transport in rotating z-pinches}, series = {Journal of plasma physics}, volume = {85}, journal = {Journal of plasma physics}, number = {6}, publisher = {Cambridge Univ. Press}, address = {New York}, issn = {0022-3778}, doi = {10.1017/S0022377819000606}, pages = {16}, year = {2019}, abstract = {The stability of conducting Taylor-Couette flows under the presence of toroidal magnetic background fields is considered. For strong enough magnetic amplitudes such magnetohydrodynamic flows are unstable against non-axisymmetric perturbations which may also transport angular momentum. In accordance with the often used diffusion approximation, one expects the angular momentum transport to be vanishing for rigid rotation. In the sense of a non-diffusive Lambda effect, however, even for rigidly rotating z-pinches, an axisymmetric angular momentum flux appears which is directed outward (inward) for large (small) magnetic Mach numbers. The internal rotation in a magnetized rotating tank can thus never be uniform. Those particular rotation laws are used to estimate the value of the instability-induced eddy viscosity for which the non-diffusive Lambda effect and the diffusive shear-induced transport compensate each other. The results provide the Shakura \& Sunyaev viscosity ansatz leading to numerical values linearly growing with the applied magnetic field.}, language = {en} } @article{BerrahSanchezGonzalezJureketal.2019, author = {Berrah, N. and S{\´a}nchez-Gonz{\´a}lez, {\´A}lvaro and Jurek, Zoltan and Obaid, Razib and Xiong, H. and Squibb, R. J. and Osipov, T. and Lutman, A. and Fang, L. and Barillot, T. and Bozek, J. D. and Cryan, J. and Wolf, T. J. A. and Rolles, Daniel and Coffee, R. and Schnorr, Kirsten and Augustin, S. and Fukuzawa, Hironobu and Motomura, K. and Niebuhr, Nina Isabelle and Frasinski, L. J. and Feifel, Raimund and Schulz, Claus-Peter and Toyota, Kenji and Son, Sang-Kil and Ueda, K. and Pfeifer, T. and Marangos, J. P. and Santra, Robin}, title = {Femtosecond-resolved observation of the fragmentation of buckminsterfullerene following X-ray multiphoton ionization}, series = {Nature physics}, volume = {15}, journal = {Nature physics}, number = {12}, publisher = {Nature Publ. Group}, address = {London}, issn = {1745-2473}, doi = {10.1038/s41567-019-0665-7}, pages = {1279 -- 1301}, year = {2019}, abstract = {X-ray free-electron lasers have, over the past decade, opened up the possibility of understanding the ultrafast response of matter to intense X-ray pulses. In earlier research on atoms and small molecules, new aspects of this response were uncovered, such as rapid sequences of inner-shell photoionization and Auger ionization. Here, we studied a larger molecule, buckminsterfullerene (C-60), exposed to 640 eV X-rays, and examined the role of chemical effects, such as chemical bonds and charge transfer, on the fragmentation following multiple ionization of the molecule. To provide time resolution, we performed femtosecond-resolved X-ray pump/X-ray probe measurements, which were accompanied by advanced simulations. The simulations and experiment reveal that despite substantial ionization induced by the ultrashort (20 fs) X-ray pump pulse, the fragmentation of C-60 is considerably delayed. This work uncovers the persistence of the molecular structure of C-60, which hinders fragmentation over a timescale of hundreds of femtoseconds. Furthermore, we demonstrate that a substantial fraction of the ejected fragments are neutral carbon atoms. These findings provide insights into X-ray free-electron laser-induced radiation damage in large molecules, including biomolecules.}, language = {en} } @article{StolterfohtLeCorreFeuersteinetal.2019, author = {Stolterfoht, Martin and Le Corre, Vincent M. and Feuerstein, Markus and Caprioglio, Pietro and Koster, Lambert Jan Anton and Neher, Dieter}, title = {Voltage-Dependent Photoluminescence and How It Correlates with the Fill Factor and Open-Circuit Voltage in Perovskite Solar Cells}, series = {Acs energy letters}, volume = {4}, journal = {Acs energy letters}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {2380-8195}, doi = {10.1021/acsenergylett.9b02262}, pages = {2887 -- 2892}, year = {2019}, abstract = {Optimizing the photoluminescence (PL) yield of a solar cell has long been recognized as a key principle to maximize the power conversion efficiency. While PL measurements are routinely applied to perovskite films and solar cells under open circuit conditions (V-OC), it remains unclear how the emission depends on the applied voltage. Here, we performed PL(V) measurements on perovskite cells with different hole transport layer thicknesses and doping concentrations, resulting in remarkably different fill factors (FFs). The results reveal that PL(V) mirrors the current-voltage (JV) characteristics in the power-generating regime, which highlights an interesting correlation between radiative and nonradiative recombination losses. In particular, high FF devices show a rapid quenching of PL(V) from open-circuit to the maximum power point. We conclude that, while the PL has to be maximized at V-OC at lower biases < V-OC the PL must be rapidly quenched as charges need to be extracted prior to recombination.}, language = {en} } @article{SchroetterBoucheZabletal.2019, author = {Schroetter, Ilane and Bouche, Nicolas F. and Zabl, Johannes and Contini, Thierry and Wendt, Martin and Schaye, Joop and Mitchell, Peter and Muzahid, Sowgat and Marino, Raffaella Anna and Bacon, Roland and Lilly, Simon J. and Richard, Johan and Wisotzki, Lutz}, title = {MusE GAs FLOw andWind (MEGAFLOW)}, series = {Monthly notices of the Royal Astronomical Society}, volume = {490}, journal = {Monthly notices of the Royal Astronomical Society}, number = {3}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stz2822}, pages = {4368 -- 4381}, year = {2019}, abstract = {We present results from our on-going MusE GAs FLOw and Wind (MEGAFLOW) survey, which consists of 22 quasar lines of sight, each observed with the integral field unit MUSE and the UVES spectrograph at the ESO Very Large Telescopes (VLT). The goals of this survey are to study the properties of the circumgalactic medium around z similar to 1 star-forming galaxies. The absorption-line selected survey consists of 79 strong MgII absorbers (with rest-frame equivalent width greater than or similar to 0.3 angstrom) and, currently, 86 associated galaxies within 100 projected kpc of the quasar with stellar masses (M-star) from 109 to 1011 M-circle dot. We find that the cool halo gas traced by MgII is not isotropically distributed around these galaxies from the strong bi-modal distribution in the azimuthal angle of the apparent location of the quasar with respect to the galaxy major axis. This supports a scenario in which outflows are bi-conical in nature and co-exist with a co-planar gaseous structure extending at least up to 60-80 kpc. Assuming that absorbers near the minor axis probe outflows, the current MEGAFLOW sample allowed us to select 26 galaxy-quasar pairs suitable for studying winds. From this sample, using a simple geometrical model, we find that the outflow velocity only exceeds the escape velocity when M-star less than or similar to 4 x 10(9) M-circle dot, implying the cool material is likely to fall back except in the smallest haloes. Finally, we find that the mass loading factor., the ratio between the ejected mass rate and the star formation rate, appears to be roughly constant with respect to the galaxy mass.}, language = {en} } @article{CharpinetBrassardFontaineetal.2019, author = {Charpinet, St{\´e}phane and Brassard, P. and Fontaine, G. and Van Grootel, Valerie and Zong, Weika and Giammichele, N. and Heber, Ulrich and Bogn{\´a}r, Zs{\´o}fia and Geier, Stephan and Green, Elizabeth M. and Hermes, J. J. and Kilkenny, D. and Ostensen, R. H. and Pelisoli, Ingrid Domingos and Silvotti, R. and Telting, J. H. and Vuckovic, Maja and Worters, H. L. and Baran, Andrzej S. and Bell, Keaton J. and Bradley, Paul A. and Debes, J. H. and Kawaler, S. D. and Kolaczek-Szymanski, P. and Murphy, S. J. and Pigulski, A. and Sodor, A. and Uzundag, Murat and Handberg, R. and Kjeldsen, H. and Ricker, G. R. and Vanderspek, R. K.}, title = {TESS first look at evolved compact pulsators Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {632}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201935395}, pages = {23}, year = {2019}, abstract = {Context. The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology. Aims. We present the discovery and detailed asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence. Methods. The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star. Results. The light curve analysis reveals that EC 21494-7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 +/- 0.009x2006;M-circle dot) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (greater than or similar to 2;M-circle dot) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 +/- 0.0010;M-circle dot), radius (0.1694 +/- 0.0081;R-circle dot), and luminosity (8.2 +/- 1.1;L-circle dot). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494-7018 has burnt similar to 43\% (in mass) of its central helium and possesses a relatively large mixed core (M-core;=;0.198 +/- 0.010;M-circle dot), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)(core) = 0.16(-0.05)(+0.13)X(O)core=0.16-0.05+0.13\$ X(mathrm{O})_{mathrm{core}}=0.16_{-0.05}<^>{+0.13} \$) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain C-12(alpha,;gamma)O-16 nuclear reaction rate.}, language = {en} } @article{CoduttiBenteFaivreetal.2019, author = {Codutti, Agnese and Bente, Klaas and Faivre, Damien and Klumpp, Stefan}, title = {Chemotaxis in external fields: Simulations for active magnetic biological matter}, series = {PLoS Computational Biology : a new community journal}, volume = {15}, journal = {PLoS Computational Biology : a new community journal}, number = {12}, publisher = {PLoS}, address = {San Fransisco}, issn = {1553-734X}, doi = {10.1371/journal.pcbi.1007548}, pages = {26}, year = {2019}, abstract = {The movement of microswimmers is often described by active Brownian particle models. Here we introduce a variant of these models with several internal states of the swimmer to describe stochastic strategies for directional swimming such as run and tumble or run and reverse that are used by microorganisms for chemotaxis. The model includes a mechanism to generate a directional bias for chemotaxis and interactions with external fields (e.g., gravity, magnetic field, fluid flow) that impose forces or torques on the swimmer. We show how this modified model can be applied to various scenarios: First, the run and tumble motion of E. coli is used to establish a paradigm for chemotaxis and investigate how it is affected by external forces. Then, we study magneto-aerotaxis in magnetotactic bacteria, which is biased not only by an oxygen gradient towards a preferred concentration, but also by magnetic fields, which exert a torque on an intracellular chain of magnets. We study the competition of magnetic alignment with active reorientation and show that the magnetic orientation can improve chemotaxis and thereby provide an advantage to the bacteria, even at rather large inclination angles of the magnetic field relative to the oxygen gradient, a case reminiscent of what is expected for the bacteria at or close to the equator. The highest gain in chemotactic velocity is obtained for run and tumble with a magnetic field parallel to the gradient, but in general a mechanism for reverse motion is necessary to swim against the magnetic field and a run and reverse strategy is more advantageous in the presence of a magnetic torque. This finding is consistent with observations that the dominant mode of directional changes in magnetotactic bacteria is reversal rather than tumbles. Moreover, it provides guidance for the design of future magnetic biohybrid swimmers. Author summary In this paper, we propose a modified Active Brownian particle model to describe bacterial swimming behavior under the influence of external forces and torques, in particular of a magnetic torque. This type of interaction is particularly important for magnetic biohybrids (i.e. motile bacteria coupled to a synthetic magnetic component) and for magnetotactic bacteria (i.e. bacteria with a natural intracellular magnetic chain), which perform chemotaxis to swim along chemical gradients, but are also directed by an external magnetic field. The model allows us to investigate the benefits and disadvantages of such coupling between two different directionality mechanisms. In particular we show that the magnetic torque can speed chemotaxis up in some conditions, while it can hinder it in other cases. In addition to an understanding of the swimming strategies of naturally magnetotactic organisms, the results may guide the design of future biomedical devices.}, language = {en} } @article{JainWheelerEssetal.2019, author = {Jain, Varun and Wheeler, Joshua J. and Ess, Daniel H. and Noack, Sebastian and Vacogne, Charlotte D. and Schlaad, Helmut and Bahr, Stephan and Dietrich, Paul and Meyer, Michael and Thissen, Andreas and Linford, Matthew R.}, title = {Poly(gamma-benzyl l-glutamate), by near-ambient pressure XPS}, series = {Surface science spectra : SSS : an international journal \& database devoted to archiving spectra from surfaces \& interfaces}, volume = {26}, journal = {Surface science spectra : SSS : an international journal \& database devoted to archiving spectra from surfaces \& interfaces}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1055-5269}, doi = {10.1116/1.5109121}, pages = {10}, year = {2019}, abstract = {Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i. e., at greater than 2500 Pa. In this study, poly(.- benzyl L- glutamate) (PBLG) with a molar mass of 11.3 kg/mol was analyzed by NAP-XPS; here, we show the survey, C 1s, N 1s, and O 1s narrow scans of PBLG. The C 1s peak envelope was fitted in three different ways, to five, six, or seven synthetic peaks. In each fit, there was also a shake-up signal. The O 1s narrow scan was well fit with three peaks: CZO and CvO in a 1:2 ratio from the polymer, and a higher energy signal from water vapor. Hartree-Fock orbital energies of a model monomer served as a guide to an additional fit of the C 1s envelope.}, language = {en} } @article{PetitgirardSpiekermannGlazyrinetal.2019, author = {Petitgirard, Sylvain and Spiekermann, Georg and Glazyrin, Konstantin and Garrevoet, Jan and Murakami, Motohiko}, title = {Density of amorphous GeO2 to 133 GPa with possible pyritelike structure and stiffness at high pressure}, series = {Physical review : B, Condensed matter and materials physics}, volume = {100}, journal = {Physical review : B, Condensed matter and materials physics}, number = {21}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.214104}, pages = {8}, year = {2019}, abstract = {Germanium oxide is a prototype network-forming oxide with pressure-induced structural changes similar to those found in crystals and amorphous silicate oxides at high pressure. Studying density and coordination changes in amorphous GeO2 allows for insight into structural changes in silicate oxides at very high pressure, with implications for the properties of planetary magmas. Here, we report the density of germanium oxide glass up to 133 GPa using the x-ray absorption technique, with very good agreement with previous experimental data at pressure below 40 GPa and recent calculation up to 140 GPa. Our data highlight four distinct compressibility domains, corresponding to changes of the local structure of GeO2. Above 80 GPa, our density data show a compressibility and bulk modulus similar to the counterpart crystal phase, and we propose that a compact distorted sixfold coordination, similar to the structural motif of the pyritelike crystalline GeO2 polymorph, is likely to be stable in that pressure range. Our density data point to a smooth continuous evolution of the average coordination for pressure above 20 GPa with persistent sixfold coordination, without sharp density or density slope discontinuities. These observations are in very good agreement with theoretical calculations and spectroscopic measurements, and our results indicate that glasses and melts may behave similarly to their high-pressure solid counterparts with comparable densities, compressibility, and possibly average coordination.}, language = {en} } @article{KraemerMarwan2019, author = {Kr{\"a}mer, Hauke Kai and Marwan, Norbert}, title = {Border effect corrections for diagonal line based recurrence quantification analysis measures}, series = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, volume = {383}, journal = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, number = {34}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0375-9601}, doi = {10.1016/j.physleta.2019.125977}, pages = {16}, year = {2019}, abstract = {Recurrence Quantification Analysis (RQA) defines a number of quantifiers, which base upon diagonal line structures in the recurrence plot (RP). Due to the finite size of an RP, these lines can be cut by the borders of the RP and, thus, bias the length distribution of diagonal lines and, consequently, the line based RQA measures. In this letter we investigate the impact of the mentioned border effects and of the thickening of diagonal lines in an RP (caused by tangential motion) on the estimation of the diagonal line length distribution, quantified by its entropy. Although a relation to the Lyapunov spectrum is theoretically expected, the mentioned entropy yields contradictory results in many studies. Here we summarize correction schemes for both, the border effects and the tangential motion and systematically compare them to methods from the literature. We show that these corrections lead to the expected behavior of the diagonal line length entropy, in particular meaning zero values in case of a regular motion and positive values for chaotic motion. Moreover, we test these methods under noisy conditions, in order to supply practical tools for applied statistical research.}, language = {en} } @misc{Goychuk2019, author = {Goychuk, Igor}, title = {Comment on "Anomalous Escape Governed by Thermal 1/f Noise" Reply (R. K. Singh)}, series = {Physical review letters}, volume = {123}, journal = {Physical review letters}, number = {23}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.238902}, pages = {1}, year = {2019}, language = {en} } @article{WilligReppertDebetal.2019, author = {Willig, Lisa and Reppert, Alexander von and Deb, Marwan and Ganss, F. and Hellwig, O. and Bargheer, Matias}, title = {Finite-size effects in ultrafast remagnetization dynamics of FePt}, series = {Physical review : B, Condensed matter and materials physics}, volume = {100}, journal = {Physical review : B, Condensed matter and materials physics}, number = {22}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.224408}, pages = {6}, year = {2019}, abstract = {We investigate the ultrafast magnetization dynamics of FePt in the L1(0) phase after an optical heating pulse, as used in heat-assisted magnetic recording. We compare continuous and nano-granular thin films and emphasize the impact of the finite size on the remagnetization dynamics. The remagnetization speeds up significantly with increasing external magnetic field only for the continuous film, where domain-wall motion governs the dynamics. The ultrafast remagnetization dynamics in the continuous film are only dominated by heat transport in the regime of high magnetic fields, whereas the timescale required for cooling is prevalent in the granular film for all magnetic field strengths. These findings highlight the necessary conditions for studying the intrinsic heat transport properties in magnetic materials.}, language = {en} } @article{DebPopovaKeller2019, author = {Deb, Marwan and Popova, Elena and Keller, Niels}, title = {Different magneto-optical response of magnetic sublattices as a function of temperature in ferrimagnetic bismuth iron garnet films}, series = {Physical review : B, Condensed matter and materials physics}, volume = {100}, journal = {Physical review : B, Condensed matter and materials physics}, number = {22}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.224410}, pages = {7}, year = {2019}, abstract = {In this paper we investigate the magneto-optical (MO) and magnetic properties of bismuth iron garnet Bi3Fe5O12 thin films over a wide range of photon energies (1.6-3.5 eV) and temperatures (5-740 K). Depending on the photon energy range, the Faraday rotation (Theta(F)) and ellipticity (epsilon(F)) vary nonmonotonously with temperature. This behavior cannot be explained by a magnetization variation that can only decrease with increasing temperature. Theta(F) and epsilon(F) spectra have therefore been analyzed using a model based on two optical transitions of a diamagnetic nature, representing the tetrahedral and octahedral iron sites. Thus, the contribution of each magnetic sublattice has been extracted from the global macroscopic MO response and investigated as a function of temperature. The magnetic properties of octahedral and tetrahedral sublattices depend differently on temperature, suggesting a different anisotropy due to oxygen coordination. We have demonstrated that this relatively simple macroscopic measurement with a subsequent analysis can grant access to the information on the properties at a microscopic level. These results can advance the fundamental understanding of MO properties in multisublattice magnetic materials.}, language = {en} } @article{RosenblumPikovskij2019, author = {Rosenblum, Michael and Pikovskij, Arkadij}, title = {Nonlinear phase coupling functions: a numerical study}, series = {Philosophical Transactions of the Royal Society of London, Series A : Mathematical, Physical and Engineering Sciences}, volume = {377}, journal = {Philosophical Transactions of the Royal Society of London, Series A : Mathematical, Physical and Engineering Sciences}, number = {2160}, publisher = {Royal Society}, address = {London}, issn = {1364-503X}, doi = {10.1098/rsta.2019.0093}, pages = {12}, year = {2019}, abstract = {Phase reduction is a general tool widely used to describe forced and interacting self-sustained oscillators. Here, we explore the phase coupling functions beyond the usual first-order approximation in the strength of the force. Taking the periodically forced Stuart-Landau oscillator as the paradigmatic model, we determine and numerically analyse the coupling functions up to the fourth order in the force strength. We show that the found nonlinear phase coupling functions can be used for predicting synchronization regions of the forced oscillator.}, language = {en} } @article{FeldmannAryaLomadzeetal.2019, author = {Feldmann, David and Arya, Pooja and Lomadze, Nino and Kopyshev, Alexey and Santer, Svetlana}, title = {Light-driven motion of self-propelled porous Janus particles}, series = {Applied physics letters}, volume = {115}, journal = {Applied physics letters}, number = {26}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.5129238}, pages = {5}, year = {2019}, abstract = {We introduce a versatile mechanism of light-driven self-propelled motion applied to porous Janus-type particles. The mechanism is based on the generation of local light-driven diffusio-osmotic (l-LDDO) flow around each single porous particle subjected to suitable irradiation conditions. The photosensitivity is introduced by a cationic azobenzene containing surfactant, which undergoes a photoisomerization reaction from a more hydrophobic trans-state to a rather hydrophilic cis-state under illumination with light. The negatively charged porous silica particles are dispersed in a corresponding aqueous solution and absorb molecules in their trans-state but expel them in their cis-state. During illumination with blue light triggering both trans-cis and cis-trans isomerization at the same time, the colloids start to move due to the generation of a steady-state diffusive flow of cis-isomers out of and trans-isomers into the particle. This is because a hemi-spherical metal cap partially sealing the colloid breaks the symmetry of the otherwise radially directed local flow around the particle, leading to self-propelled motion. Janus particles exhibit superdiffusive motion with a velocity of similar to 0.5 mu m/s and a persistence length of ca. 50 mu m, confined to microchannels the direction can be maintained up to 300 mu m before rotational diffusion reverts it. Particles forming dimers of different shapes can be made to travel along circular trajectories. The unique feature of this mechanism is that the strength of self-propulsion can be tuned by convenient external optical stimuli (intensity and irradiation wavelength) such that a broad variety of experimental situations can be realized in a spatiotemporal way and in situ.}, language = {en} } @phdthesis{Thiede2019, author = {Thiede, Tobias}, title = {A multiscale analysis of additively manufactured lattice structures}, doi = {10.25932/publishup-47041}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-470418}, school = {Universit{\"a}t Potsdam}, pages = {xi, 97, LIII}, year = {2019}, abstract = {Additive Manufacturing (AM) in terms of laser powder-bed fusion (L-PBF) offers new prospects regarding the design of parts and enables therefore the production of lattice structures. These lattice structures shall be implemented in various industrial applications (e.g. gas turbines) for reasons of material savings or cooling channels. However, internal defects, residual stress, and structural deviations from the nominal geometry are unavoidable. In this work, the structural integrity of lattice structures manufactured by means of L-PBF was non-destructively investigated on a multiscale approach. A workflow for quantitative 3D powder analysis in terms of particle size, particle shape, particle porosity, inter-particle distance and packing density was established. Synchrotron computed tomography (CT) was used to correlate the packing density with the particle size and particle shape. It was also observed that at least about 50\% of the powder porosity was released during production of the struts. Struts are the component of lattice structures and were investigated by means of laboratory CT. The focus was on the influence of the build angle on part porosity and surface quality. The surface topography analysis was advanced by the quantitative characterisation of re-entrant surface features. This characterisation was compared with conventional surface parameters showing their complementary information, but also the need for AM specific surface parameters. The mechanical behaviour of the lattice structure was investigated with in-situ CT under compression and successive digital volume correlation (DVC). The deformation was found to be knot-dominated, and therefore the lattice folds unit cell layer wise. The residual stress was determined experimentally for the first time in such lattice structures. Neutron diffraction was used for the non-destructive 3D stress investigation. The principal stress directions and values were determined in dependence of the number of measured directions. While a significant uni-axial stress state was found in the strut, a more hydrostatic stress state was found in the knot. In both cases, strut and knot, seven directions were at least needed to find reliable principal stress directions.}, language = {en} } @book{Feldmeier2019, author = {Feldmeier, Achim}, title = {Theoretical Fluid Dynamics}, series = {Theoretical and Mathematical Physics}, journal = {Theoretical and Mathematical Physics}, publisher = {Springer}, address = {Cham}, isbn = {978-3-030-31021-9 (online)}, doi = {10.1007/978-3-030-31022-6}, pages = {XVI, 569}, year = {2019}, language = {en} } @article{HofmannZuefleShimizuetal.2019, author = {Hofmann, Alexander J. L. and Z{\"u}fle, Simon and Shimizu, Kohei and Schmid, Markus and Wessels, Vivien and J{\"a}ger, Lars and Altazin, Stephane and Ikegami, Keitaro and Khan, Motiur Rahman and Neher, Dieter and Ishii, Hisao and Ruhstaller, Beat and Br{\"u}tting, Wolfgang}, title = {Dipolar Doping of Organic Semiconductors to Enhance Carrier Injection}, series = {Physical review applied}, volume = {12}, journal = {Physical review applied}, number = {6}, publisher = {American Physical Society}, address = {College Park}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.12.064052}, pages = {11}, year = {2019}, abstract = {If not oriented perfectly isotropically, the strong dipole moment of polar organic semiconductor materials such as tris-(8-hydroxyquinolate)aluminum (Alq3) will lead to the buildup of a giant surface potential (GSP) and thus to a macroscopic dielectric polarization of the organic film. Despite this having been a known fact for years, the implications of such high potentials within an organic layer stack have only been studied recently. In this work, the influence of the GSP on hole injection into organic layers is investigated. Therefore, we apply a concept called dipolar doping to devices consisting of the prototypical organic materials N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) as nonpolar host and Alq3 as dipolar dopant with different mixing ratios to tune the GSP. The mixtures are investigated in single-layer monopolar devices as well as bilayer metal/insulator/semiconductor structures. Characterization is done electrically using current-voltage (I-V) characteristics, impedance spectroscopy, and charge extraction by linearly increasing voltage and time of flight, as well as with ultraviolet photoelectron spectroscopy. We find a maximum in device performance for moderate to low doping concentrations of the polar species in the host. The observed behavior can be described on the basis of the Schottky effect for image-force barrier lowering, if the changes in the interface dipole, the carrier mobility, and the GSP induced by dipolar doping are taken into account.}, language = {en} } @article{PisoniStolterfohtLockingeretal.2019, author = {Pisoni, Stefano and Stolterfoht, Martin and Lockinger, Johannes and Moser, Thierry and Jiang, Yan and Caprioglio, Pietro and Neher, Dieter and Buecheler, Stephan and Tiwari, Ayodhya N.}, title = {On the origin of open-circuit voltage losses in flexible n-i-p perovskite solar cells}, series = {Science and technology of advanced materials : STAM}, volume = {20}, journal = {Science and technology of advanced materials : STAM}, publisher = {Taylor \& Francis}, address = {Abingdon}, issn = {1468-6996}, doi = {10.1080/14686996.2019.1633952}, pages = {786 -- 795}, year = {2019}, abstract = {The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recombination losses. Herein, we performed a systematic voltage loss analysis for a typical low-temperature processed, flexible PSC in n-i-p configuration using vacuum deposited C-60 as electron transport layer (ETL) and two-step hybrid vacuum-solution deposition for CH3NH3PbI3 perovskite absorber. We identified the ETL/absorber interface as a bottleneck in relation to non-radiative recombination losses, the quasi-Fermi level splitting (QFLS) decreases from similar to 1.23 eV for the bare absorber, just similar to 90 meV below the radiative limit, to similar to 1.10 eV when C-60 is used as ETL. To effectively mitigate these voltage losses, we investigated different interfacial modifications via vacuum deposited interlayers (BCP, B4PyMPM, 3TPYMB, and LiF). An improvement in QFLS of similar to 30-40 meV is observed after interlayer deposition and confirmed by comparable improvements in the open-circuit voltage after implementation of these interfacial modifications in flexible PSCs. Further investigations on absorber/hole transport layer (HTL) interface point out the detrimental role of dopants in Spiro-OMeTAD film (widely employed HTL in the community) as recombination centers upon oxidation and light exposure. [GRAPHICS] .}, language = {en} } @phdthesis{Nguyen2019, author = {Nguyen, Quyet Doan}, title = {Electro-acoustical probing of space-charge and dipole-polarization profiles in polymer dielectrics for electret and electrical-insulation applications}, doi = {10.25932/publishup-44562}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-445629}, school = {Universit{\"a}t Potsdam}, pages = {105}, year = {2019}, abstract = {Electrets are dielectrics with quasi-permanent electric charge and/or dipoles, sometimes can be regarded as an electric analogy to a magnet. Since the discovery of the excellent charge retention capacity of poly(tetrafluoro ethylene) and the invention of the electret microphone, electrets have grown out of a scientific curiosity to an important application both in science and technology. The history of electret research goes hand in hand with the quest for new materials with better capacity at charge and/or dipole retention. To be useful, electrets normally have to be charged/poled to render them electro-active. This process involves electric-charge deposition and/or electric dipole orientation within the dielectrics ` surfaces and bulk. Knowledge of the spatial distribution of electric charge and/or dipole polarization after their deposition and subsequent decay is crucial in the task to improve their stability in the dielectrics. Likewise, for dielectrics used in electrical insulation applications, there are also needs for accumulated space-charge and polarization spatial profiling. Traditionally, space-charge accumulation and large dipole polarization within insulating dielectrics is considered undesirable and harmful to the insulating dielectrics as they might cause dielectric loss and could lead to internal electric field distortion and local field enhancement. High local electric field could trigger several aging processes and reduce the insulating dielectrics' lifetime. However, with the advent of high-voltage DC transmission and high-voltage capacitor for energy storage, these are no longer the case. There are some overlapped between the two fields of electrets and electric insulation. While quasi-permanently trapped electric-charge and/or large remanent dipole polarization are the requisites for electret operation, stably trapped electric charge in electric insulation helps reduce electric charge transport and overall reduced electric conductivity. Controlled charge trapping can help in preventing further charge injection and accumulation as well as serving as field grading purpose in insulating dielectrics whereas large dipole polarization can be utilized in energy storage applications. In this thesis, the Piezoelectrically-generated Pressure Steps (PPSs) were employed as a nondestructive method to probe the electric-charge and dipole polarization distribution in a range of thin film (several hundred micron) polymer-based materials, namely polypropylene (PP), low-density polyethylene/magnesium oxide (LDPE/MgO) nanocomposites and poly(vinylidene fluoride-co- trifluoro ethylene) (P(VDF-TrFE)) copolymer. PP film surface-treated with phosphoric acid to introduce surfacial isolated nanostructures serves as example of 2-dimensional nano-composites whereas LDPE/MgO serves as the case of 3-dimensional nano-composites with MgO nano-particles dispersed in LDPE polymer matrix. It is evidenced that the nanoparticles on the surface of acid-treated PP and in the bulk of LDPE/MgO nanocomposites improve charge trapping capacity of the respective material and prevent further charge injection and transport and that the enhanced charge trapping capacity makes PP and LDPE/MgO nanocomposites potential materials for both electret and electrical insulation applications. As for PVDF and VDF-based copolymers, the remanent spatial polarization distribution depends critically on poling method as well as specific parameters used in the respective poling method. In this work, homogeneous polarization poling of P(VDF-TrFE) copolymers with different VDF-contents have been attempted with hysteresis cyclical poling. The behaviour of remanent polarization growth and spatial polarization distribution are reported and discussed. The Piezoelectrically-generated Pressure Steps (PPSs) method has proven as a powerful method for the charge storage and transport characterization of a wide range of polymer material from nonpolar, to polar, to polymer nanocomposites category.}, language = {en} } @article{GrebenkovMetzlerOshanin2019, author = {Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb}, title = {Full distribution of first exit times in the narrow escape problem}, series = {New Journal of Physics}, volume = {21}, journal = {New Journal of Physics}, publisher = {Dt. Physikalische Ges.}, address = {Bad Honnef}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab5de4}, pages = {23}, year = {2019}, abstract = {In the scenario of the narrow escape problem (NEP) a particle diffuses in a finite container and eventually leaves it through a small 'escape window' in the otherwise impermeable boundary, once it arrives to this window and crosses an entropic barrier at the entrance to it. This generic problem is mathematically identical to that of a diffusion-mediated reaction with a partially-reactive site on the container's boundary. Considerable knowledge is available on the dependence of the mean first-reaction time (FRT) on the pertinent parameters. We here go a distinct step further and derive the full FRT distribution for the NEP. We demonstrate that typical FRTs may be orders of magnitude shorter than the mean one, thus resulting in a strong defocusing of characteristic temporal scales. We unveil the geometry-control of the typical times, emphasising the role of the initial distance to the target as a decisive parameter. A crucial finding is the further FRT defocusing due to the barrier, necessitating repeated escape or reaction attempts interspersed with bulk excursions. These results add new perspectives and offer a broad comprehension of various features of the by-now classical NEP that are relevant for numerous biological and technological systems.}, language = {en} } @misc{GrebenkovMetzlerOshanin2019, author = {Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb}, title = {Full distribution of first exit times in the narrow escape problem}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {810}, issn = {1866-8372}, doi = {10.25932/publishup-44288}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-442883}, pages = {24}, year = {2019}, abstract = {In the scenario of the narrow escape problem (NEP) a particle diffuses in a finite container and eventually leaves it through a small 'escape window' in the otherwise impermeable boundary, once it arrives to this window and crosses an entropic barrier at the entrance to it. This generic problem is mathematically identical to that of a diffusion-mediated reaction with a partially-reactive site on the container's boundary. Considerable knowledge is available on the dependence of the mean first-reaction time (FRT) on the pertinent parameters. We here go a distinct step further and derive the full FRT distribution for the NEP. We demonstrate that typical FRTs may be orders of magnitude shorter than the mean one, thus resulting in a strong defocusing of characteristic temporal scales. We unveil the geometry-control of the typical times, emphasising the role of the initial distance to the target as a decisive parameter. A crucial finding is the further FRT defocusing due to the barrier, necessitating repeated escape or reaction attempts interspersed with bulk excursions. These results add new perspectives and offer a broad comprehension of various features of the by-now classical NEP that are relevant for numerous biological and technological systems.}, language = {en} } @phdthesis{Willig2019, author = {Willig, Lisa}, title = {Ultrafast magneto-optical studies of remagnetisation dynamics in transition metals}, doi = {10.25932/publishup-44194}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-441942}, school = {Universit{\"a}t Potsdam}, pages = {XIV, 113, XVII}, year = {2019}, abstract = {Ultrafast magnetisation dynamics have been investigated intensely for two decades. The recovery process after demagnetisation, however, was rarely studied experimentally and discussed in detail. The focus of this work lies on the investigation of the magnetisation on long timescales after laser excitation. It combines two ultrafast time resolved methods to study the relaxation of the magnetic and lattice system after excitation with a high fluence ultrashort laser pulse. The magnetic system is investigated by time resolved measurements of the magneto-optical Kerr effect. The experimental setup has been implemented in the scope of this work. The lattice dynamics were obtained with ultrafast X-ray diffraction. The combination of both techniques leads to a better understanding of the mechanisms involved in magnetisation recovery from a non-equilibrium condition. Three different groups of samples are investigated in this work: Thin Nickel layers capped with nonmagnetic materials, a continuous sample of the ordered L10 phase of Iron Platinum and a sample consisting of Iron Platinum nanoparticles embedded in a carbon matrix. The study of the remagnetisation reveals a general trend for all of the samples: The remagnetisation process can be described by two time dependences. A first exponential recovery that slows down with an increasing amount of energy absorbed in the system until an approximately linear time dependence is observed. This is followed by a second exponential recovery. In case of low fluence excitation, the first recovery is faster than the second. With increasing fluence the first recovery is slowed down and can be described as a linear function. If the pump-induced temperature increase in the sample is sufficiently high, a phase transition to a paramagnetic state is observed. In the remagnetisation process, the transition into the ferromagnetic state is characterised by a distinct transition between the linear and exponential recovery. From the combination of the transient lattice temperature Tp(t) obtained from ultrafast X-ray measurements and magnetisation M(t) gained from magneto-optical measurements we construct the transient magnetisation versus temperature relations M(Tp). If the lattice temperature remains below the Curie temperature the remagnetisation curve M(Tp) is linear and stays below the M(T) curve in equilibrium in the continuous transition metal layers. When the sample is heated above phase transition, the remagnetisation converges towards the static temperature dependence. For the granular Iron Platinum sample the M(Tp) curves for different fluences coincide, i.e. the remagnetisation follows a similar path irrespective of the initial laser-induced temperature jump.}, language = {en} } @phdthesis{Nagel2019, author = {Nagel, Oliver}, title = {Amoeboid cells as a transport system for micro-objects}, doi = {10.25932/publishup-44219}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-442192}, school = {Universit{\"a}t Potsdam}, pages = {x, 84}, year = {2019}, abstract = {Due to advances in science and technology towards smaller and more powerful processing units, the fabrication of micrometer sized machines for different tasks becomes more and more possible. Such micro-robots could revolutionize medical treatment of diseases and shall support to work on other small machines. Nevertheless, scaling down robots and other devices is a challenging task and will probably remain limited in near future. Over the past decade the concept of bio-hybrid systems has proved to be a promising approach in order to advance the further development of micro-robots. Bio-hybrid systems combine biological cells with artificial components, thereby benefiting from the functionality of living biological cells. Cell-driven micro-transport is one of the most prominent applications in the emerging field of these systems. So far, micrometer sized cargo has been successfully transported by means of swimming bacterial cells. The potential of motile adherent cells as transport systems has largely remained unexplored. This thesis concentrates on the social amoeba Dictyostelium discoideum as a potential candidate for an amoeboid bio-hybrid transport system. The use of this model organism comes with several advantages. Due to the unspecific properties of Dictyostelium adhesion, a wide range of different cargo materials can be used for transport. As amoeboid cells exceed bacterial cells in size by one order of magnitude, also the size of an object carried by a single cell can also be much larger for an amoeba. Finally it is possible to guide the cell-driven transport based on the chemotactic behavior of the amoeba. Since cells undergo a developmentally induced chemotactic aggregation, cargo could be assembled in a self-organized manner into a cluster. It is also possible to impose an external chemical gradient to guide the amoeboid transport system to a desired location. To establish Dictyostelium discoideum as a possible candidate for bio-hybrid transport systems, this thesis will first investigate the movement of single cells. Secondly, the interaction of cargo and cells will be studied. Eventually, a conceptional proof will be conducted, that the cheomtactic behavior can be exploited either to transport a cargo self-organized or through an external chemical source.}, language = {en} } @misc{WeberBahrsAlirezaeizanjanietal.2019, author = {Weber, Ariane and Bahrs, Marco and Alirezaeizanjani, Zahra and Zhang, Xingyu and Beta, Carsten and Zaburdaev, Vasily}, title = {Rectification of Bacterial Diffusion in Microfluidic Labyrinths}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {801}, issn = {1866-8372}, doi = {10.25932/publishup-44122}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-441222}, pages = {11}, year = {2019}, abstract = {In nature as well as in the context of infection and medical applications, bacteria often have to move in highly complex environments such as soil or tissues. Previous studies have shown that bacteria strongly interact with their surroundings and are often guided by confinements. Here, we investigate theoretically how the dispersal of swimming bacteria can be augmented by microfluidic environments and validate our theoretical predictions experimentally. We consider a system of bacteria performing the prototypical run-and-tumble motion inside a labyrinth with square lattice geometry. Narrow channels between the square obstacles limit the possibility of bacteria to reorient during tumbling events to an area where channels cross. Thus, by varying the geometry of the lattice it might be possible to control the dispersal of cells. We present a theoretical model quantifying diffusive spreading of a run-and-tumble random walker in a square lattice. Numerical simulations validate our theoretical predictions for the dependence of the diffusion coefficient on the lattice geometry. We show that bacteria moving in square labyrinths exhibit enhanced dispersal as compared to unconfined cells. Importantly, confinement significantly extends the duration of the phase with strongly non-Gaussian diffusion, when the geometry of channels is imprinted in the density profiles of spreading cells. Finally, in good agreement with our theoretical findings, we observe the predicted behaviors in experiments with E. coli bacteria swimming in a square lattice labyrinth created in amicrofluidic device. Altogether, our comprehensive understanding of bacterial dispersal in a simple two-dimensional labyrinth makes the first step toward the analysis of more complex geometries relevant for real world applications.}, language = {en} } @article{WeberBahrsAlirezaeizanjanietal.2019, author = {Weber, Ariane and Bahrs, Marco and Alirezaeizanjani, Zahra and Zhang, Xingyu and Beta, Carsten and Zaburdaev, Vasily}, title = {Rectification of Bacterial Diffusion in Microfluidic Labyrinths}, series = {Frontiers in Physics}, volume = {7}, journal = {Frontiers in Physics}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-424X}, doi = {10.3389/fphy.2019.00148}, pages = {11}, year = {2019}, abstract = {In nature as well as in the context of infection and medical applications, bacteria often have to move in highly complex environments such as soil or tissues. Previous studies have shown that bacteria strongly interact with their surroundings and are often guided by confinements. Here, we investigate theoretically how the dispersal of swimming bacteria can be augmented by microfluidic environments and validate our theoretical predictions experimentally. We consider a system of bacteria performing the prototypical run-and-tumble motion inside a labyrinth with square lattice geometry. Narrow channels between the square obstacles limit the possibility of bacteria to reorient during tumbling events to an area where channels cross. Thus, by varying the geometry of the lattice it might be possible to control the dispersal of cells. We present a theoretical model quantifying diffusive spreading of a run-and-tumble random walker in a square lattice. Numerical simulations validate our theoretical predictions for the dependence of the diffusion coefficient on the lattice geometry. We show that bacteria moving in square labyrinths exhibit enhanced dispersal as compared to unconfined cells. Importantly, confinement significantly extends the duration of the phase with strongly non-Gaussian diffusion, when the geometry of channels is imprinted in the density profiles of spreading cells. Finally, in good agreement with our theoretical findings, we observe the predicted behaviors in experiments with E. coli bacteria swimming in a square lattice labyrinth created in amicrofluidic device. Altogether, our comprehensive understanding of bacterial dispersal in a simple two-dimensional labyrinth makes the first step toward the analysis of more complex geometries relevant for real world applications.}, language = {en} } @article{PalyulinBlackburnLomholtetal.2019, author = {Palyulin, Vladimir V and Blackburn, George and Lomholt, Michael A and Watkins, Nicholas W and Metzler, Ralf and Klages, Rainer and Chechkin, Aleksei V.}, title = {First passage and first hitting times of L{\´e}vy flights and L{\´e}vy walks}, series = {New Journal of Physics}, volume = {21}, journal = {New Journal of Physics}, publisher = {Dt. Physikalische Ges.}, address = {Bad Honnef}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab41bb}, pages = {24}, year = {2019}, abstract = {For both L{\´e}vy flight and L{\´e}vy walk search processes we analyse the full distribution of first-passage and first-hitting (or first-arrival) times. These are, respectively, the times when the particle moves across a point at some given distance from its initial position for the first time, or when it lands at a given point for the first time. For L{\´e}vy motions with their propensity for long relocation events and thus the possibility to jump across a given point in space without actually hitting it ('leapovers'), these two definitions lead to significantly different results. We study the first-passage and first-hitting time distributions as functions of the L{\´e}vy stable index, highlighting the different behaviour for the cases when the first absolute moment of the jump length distribution is finite or infinite. In particular we examine the limits of short and long times. Our results will find their application in the mathematical modelling of random search processes as well as computer algorithms.}, language = {en} } @misc{PalyulinBlackburnLomholtetal.2019, author = {Palyulin, Vladimir V and Blackburn, George and Lomholt, Michael A and Watkins, Nicholas W and Metzler, Ralf and Klages, Rainer and Chechkin, Aleksei V.}, title = {First passage and first hitting times of L{\´e}vy flights and L{\´e}vy walks}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {785}, issn = {1866-8372}, doi = {10.25932/publishup-43983}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-439832}, pages = {25}, year = {2019}, abstract = {For both L{\´e}vy flight and L{\´e}vy walk search processes we analyse the full distribution of first-passage and first-hitting (or first-arrival) times. These are, respectively, the times when the particle moves across a point at some given distance from its initial position for the first time, or when it lands at a given point for the first time. For L{\´e}vy motions with their propensity for long relocation events and thus the possibility to jump across a given point in space without actually hitting it ('leapovers'), these two definitions lead to significantly different results. We study the first-passage and first-hitting time distributions as functions of the L{\´e}vy stable index, highlighting the different behaviour for the cases when the first absolute moment of the jump length distribution is finite or infinite. In particular we examine the limits of short and long times. Our results will find their application in the mathematical modelling of random search processes as well as computer algorithms.}, language = {en} } @misc{KindlerPulkkinenCherstvyetal.2019, author = {Kindler, Oliver and Pulkkinen, Otto and Cherstvy, Andrey G. and Metzler, Ralf}, title = {Burst Statistics in an Early Biofilm Quorum Sensing Mode}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {777}, issn = {1866-8372}, doi = {10.25932/publishup-43909}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-439099}, pages = {21}, year = {2019}, abstract = {Quorum-sensing bacteria in a growing colony of cells send out signalling molecules (so-called "autoinducers") and themselves sense the autoinducer concentration in their vicinity. Once—due to increased local cell density inside a "cluster" of the growing colony—the concentration of autoinducers exceeds a threshold value, cells in this clusters get "induced" into a communal, multi-cell biofilm-forming mode in a cluster-wide burst event. We analyse quantitatively the influence of spatial disorder, the local heterogeneity of the spatial distribution of cells in the colony, and additional physical parameters such as the autoinducer signal range on the induction dynamics of the cell colony. Spatial inhomogeneity with higher local cell concentrations in clusters leads to earlier but more localised induction events, while homogeneous distributions lead to comparatively delayed but more concerted induction of the cell colony, and, thus, a behaviour close to the mean-field dynamics. We quantify the induction dynamics with quantifiers such as the time series of induction events and burst sizes, the grouping into induction families, and the mean autoinducer concentration levels. Consequences for different scenarios of biofilm growth are discussed, providing possible cues for biofilm control in both health care and biotechnology.}, language = {en} } @article{KindlerPulkkinenCherstvyetal.2019, author = {Kindler, Oliver and Pulkkinen, Otto and Cherstvy, Andrey G. and Metzler, Ralf}, title = {Burst Statistics in an Early Biofilm Quorum Sensing Mode}, series = {Scientific Reports}, volume = {9}, journal = {Scientific Reports}, publisher = {Macmillan Publishers Limited part of Springer Nature}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-019-48525-2}, pages = {19}, year = {2019}, abstract = {Quorum-sensing bacteria in a growing colony of cells send out signalling molecules (so-called "autoinducers") and themselves sense the autoinducer concentration in their vicinity. Once—due to increased local cell density inside a "cluster" of the growing colony—the concentration of autoinducers exceeds a threshold value, cells in this clusters get "induced" into a communal, multi-cell biofilm-forming mode in a cluster-wide burst event. We analyse quantitatively the influence of spatial disorder, the local heterogeneity of the spatial distribution of cells in the colony, and additional physical parameters such as the autoinducer signal range on the induction dynamics of the cell colony. Spatial inhomogeneity with higher local cell concentrations in clusters leads to earlier but more localised induction events, while homogeneous distributions lead to comparatively delayed but more concerted induction of the cell colony, and, thus, a behaviour close to the mean-field dynamics. We quantify the induction dynamics with quantifiers such as the time series of induction events and burst sizes, the grouping into induction families, and the mean autoinducer concentration levels. Consequences for different scenarios of biofilm growth are discussed, providing possible cues for biofilm control in both health care and biotechnology.}, language = {en} } @misc{ŚlęzakBurneckiMetzler2019, author = {Ślęzak, Jakub and Burnecki, Krzysztof and Metzler, Ralf}, title = {Random coefficient autoregressive processes describe Brownian yet non-Gaussian diffusion in heterogeneous systems}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {765}, issn = {1866-8372}, doi = {10.25932/publishup-43792}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-437923}, pages = {18}, year = {2019}, abstract = {Many studies on biological and soft matter systems report the joint presence of a linear mean-squared displacement and a non-Gaussian probability density exhibiting, for instance, exponential or stretched-Gaussian tails. This phenomenon is ascribed to the heterogeneity of the medium and is captured by random parameter models such as 'superstatistics' or 'diffusing diffusivity'. Independently, scientists working in the area of time series analysis and statistics have studied a class of discrete-time processes with similar properties, namely, random coefficient autoregressive models. In this work we try to reconcile these two approaches and thus provide a bridge between physical stochastic processes and autoregressive models.Westart from the basic Langevin equation of motion with time-varying damping or diffusion coefficients and establish the link to random coefficient autoregressive processes. By exploring that link we gain access to efficient statistical methods which can help to identify data exhibiting Brownian yet non-Gaussian diffusion.}, language = {en} } @article{ŚlęzakBurneckiMetzler2019, author = {Ślęzak, Jakub and Burnecki, Krzysztof and Metzler, Ralf}, title = {Random coefficient autoregressive processes describe Brownian yet non-Gaussian diffusion in heterogeneous systems}, series = {New Journal of Physics}, volume = {21}, journal = {New Journal of Physics}, publisher = {Deutsche Physikalische Gesellschaft ; IOP, Institute of Physics}, address = {Bad Honnef und London}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab3366}, pages = {18}, year = {2019}, abstract = {Many studies on biological and soft matter systems report the joint presence of a linear mean-squared displacement and a non-Gaussian probability density exhibiting, for instance, exponential or stretched-Gaussian tails. This phenomenon is ascribed to the heterogeneity of the medium and is captured by random parameter models such as 'superstatistics' or 'diffusing diffusivity'. Independently, scientists working in the area of time series analysis and statistics have studied a class of discrete-time processes with similar properties, namely, random coefficient autoregressive models. In this work we try to reconcile these two approaches and thus provide a bridge between physical stochastic processes and autoregressive models.Westart from the basic Langevin equation of motion with time-varying damping or diffusion coefficients and establish the link to random coefficient autoregressive processes. By exploring that link we gain access to efficient statistical methods which can help to identify data exhibiting Brownian yet non-Gaussian diffusion.}, language = {en} } @phdthesis{Thater2019, author = {Thater, Sabine}, title = {The interplay between supermassive black holes and their host galaxies}, doi = {10.25932/publishup-43757}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-437570}, school = {Universit{\"a}t Potsdam}, pages = {iv, 186}, year = {2019}, abstract = {Supermassive black holes reside in the hearts of almost all massive galaxies. Their evolutionary path seems to be strongly linked to the evolution of their host galaxies, as implied by several empirical relations between the black hole mass (M BH ) and different host galaxy properties. The physical driver of this co-evolution is, however, still not understood. More mass measurements over homogeneous samples and a detailed understanding of systematic uncertainties are required to fathom the origin of the scaling relations. In this thesis, I present the mass estimations of supermassive black holes in the nuclei of one late-type and thirteen early-type galaxies. Our SMASHING sample extends from the intermediate to the massive galaxy mass regime and was selected to fill in gaps in number of galaxies along the scaling relations. All galaxies were observed at high spatial resolution, making use of the adaptive-optics mode of integral field unit (IFU) instruments on state-of-the-art telescopes (SINFONI, NIFS, MUSE). I extracted the stellar kinematics from these observations and constructed dynamical Jeans and Schwarzschild models to estimate the mass of the central black holes robustly. My new mass estimates increase the number of early-type galaxies with measured black hole masses by 15\%. The seven measured galaxies with nuclear light deficits ('cores') augment the sample of cored galaxies with measured black holes by 40\%. Next to determining massive black hole masses, evaluating the accuracy of black hole masses is crucial for understanding the intrinsic scatter of the black hole- host galaxy scaling relations. I tested various sources of systematic uncertainty on my derived mass estimates. The M BH estimate of the single late-type galaxy of the sample yielded an upper limit, which I could constrain very robustly. I tested the effects of dust, mass-to-light ratio (M/L) variation, and dark matter on my measured M BH . Based on these tests, the typically assumed constant M/L ratio can be an adequate assumption to account for the small amounts of dark matter in the center of that galaxy. I also tested the effect of a variable M/L variation on the M BH measurement on a second galaxy. By considering stellar M/L variations in the dynamical modeling, the measured M BH decreased by 30\%. In the future, this test should be performed on additional galaxies to learn how an as constant assumed M/L flaws the estimated black hole masses. Based on our upper limit mass measurement, I confirm previous suggestions that resolving the predicted BH sphere-of-influence is not a strict condition to measure black hole masses. Instead, it is only a rough guide for the detection of the black hole if high-quality, and high signal-to-noise IFU data are used for the measurement. About half of our sample consists of massive early-type galaxies which show nuclear surface brightness cores and signs of triaxiality. While these types of galaxies are typically modeled with axisymmetric modeling methods, the effects on M BH are not well studied yet. The massive galaxies of our presented galaxy sample are well suited to test the effect of different stellar dynamical models on the measured black hole mass in evidently triaxial galaxies. I have compared spherical Jeans and axisymmetric Schwarzschild models and will add triaxial Schwarzschild models to this comparison in the future. The constructed Jeans and Schwarzschild models mostly disagree with each other and cannot reproduce many of the triaxial features of the galaxies (e.g., nuclear sub-components, prolate rotation). The consequence of the axisymmetric-triaxial assumption on the accuracy of M BH and its impact on the black hole - host galaxy relation needs to be carefully examined in the future. In the sample of galaxies with published M BH , we find measurements based on different dynamical tracers, requiring different observations, assumptions, and methods. Crucially, different tracers do not always give consistent results. I have used two independent tracers (cold molecular gas and stars) to estimate M BH in a regular galaxy of our sample. While the two estimates are consistent within their errors, the stellar-based measurement is twice as high as the gas-based. Similar trends have also been found in the literature. Therefore, a rigorous test of the systematics associated with the different modeling methods is required in the future. I caution to take the effects of different tracers (and methods) into account when discussing the scaling relations. I conclude this thesis by comparing my galaxy sample with the compilation of galaxies with measured black holes from the literature, also adding six SMASHING galaxies, which were published outside of this thesis. None of the SMASHING galaxies deviates significantly from the literature measurements. Their inclusion to the published early-type galaxies causes a change towards a shallower slope for the M BH - effective velocity dispersion relation, which is mainly driven by the massive galaxies of our sample. More unbiased and homogenous measurements are needed in the future to determine the shape of the relation and understand its physical origin.}, language = {en} } @phdthesis{Wagle2019, author = {Wagle, Swapnil}, title = {Multi scale modeling of SNARE-mimetic peptides for their applications in membrane fusion}, pages = {105}, year = {2019}, language = {en} } @misc{GuggenbergerPagniniVojtaetal.2019, author = {Guggenberger, Tobias and Pagnini, Gianni and Vojta, Thomas and Metzler, Ralf}, title = {Fractional Brownian motion in a finite interval}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {755}, issn = {1866-8372}, doi = {10.25932/publishup-43666}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436665}, pages = {13}, year = {2019}, abstract = {Fractional Brownian motion (FBM) is a Gaussian stochastic process with stationary, long-time correlated increments and is frequently used to model anomalous diffusion processes. We study numerically FBM confined to a finite interval with reflecting boundary conditions. The probability density function of this reflected FBM at long times converges to a stationary distribution showing distinct deviations from the fully flat distribution of amplitude 1/L in an interval of length L found for reflected normal Brownian motion. While for superdiffusion, corresponding to a mean squared displacement (MSD) 〈X² (t)〉 ⋍ tᵅ with 1 < α < 2, the probability density function is lowered in the centre of the interval and rises towards the boundaries, for subdiffusion (0 < α < 1) this behaviour is reversed and the particle density is depleted close to the boundaries. The MSD in these cases at long times converges to a stationary value, which is, remarkably, monotonically increasing with the anomalous diffusion exponent α. Our a priori surprising results may have interesting consequences for the application of FBM for processes such as molecule or tracer diffusion in the confines of living biological cells or organelles, or other viscoelastic environments such as dense liquids in microfluidic chambers.}, language = {en} } @article{GuggenbergerPagniniVojtaetal.2019, author = {Guggenberger, Tobias and Pagnini, Gianni and Vojta, Thomas and Metzler, Ralf}, title = {Fractional Brownian motion in a finite interval}, series = {New Journal of Physics}, volume = {21}, journal = {New Journal of Physics}, publisher = {Deutsche Physikalische Gesellschaft ; IOP, Institute of Physics}, address = {Bad Honnef und London}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab075f}, pages = {13}, year = {2019}, abstract = {Fractional Brownian motion (FBM) is a Gaussian stochastic process with stationary, long-time correlated increments and is frequently used to model anomalous diffusion processes. We study numerically FBM confined to a finite interval with reflecting boundary conditions. The probability density function of this reflected FBM at long times converges to a stationary distribution showing distinct deviations from the fully flat distribution of amplitude 1/L in an interval of length L found for reflected normal Brownian motion. While for superdiffusion, corresponding to a mean squared displacement (MSD) 〈X² (t)〉 ⋍ tᵅ with 1 < α < 2, the probability density function is lowered in the centre of the interval and rises towards the boundaries, for subdiffusion (0 < α < 1) this behaviour is reversed and the particle density is depleted close to the boundaries. The MSD in these cases at long times converges to a stationary value, which is, remarkably, monotonically increasing with the anomalous diffusion exponent α. Our a priori surprising results may have interesting consequences for the application of FBM for processes such as molecule or tracer diffusion in the confines of living biological cells or organelles, or other viscoelastic environments such as dense liquids in microfluidic chambers.}, language = {en} } @misc{SposiniMetzlerOshanin2019, author = {Sposini, Vittoria and Metzler, Ralf and Oshanin, Gleb}, title = {Single-trajectory spectral analysis of scaled Brownian motion}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {753}, issn = {1866-8372}, doi = {10.25932/publishup-43652}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436522}, pages = {16}, year = {2019}, abstract = {Astandard approach to study time-dependent stochastic processes is the power spectral density (PSD), an ensemble-averaged property defined as the Fourier transform of the autocorrelation function of the process in the asymptotic limit of long observation times, T → ∞. In many experimental situations one is able to garner only relatively few stochastic time series of finite T, such that practically neither an ensemble average nor the asymptotic limit T → ∞ can be achieved. To accommodate for a meaningful analysis of such finite-length data we here develop the framework of single-trajectory spectral analysis for one of the standard models of anomalous diffusion, scaled Brownian motion.Wedemonstrate that the frequency dependence of the single-trajectory PSD is exactly the same as for standard Brownian motion, which may lead one to the erroneous conclusion that the observed motion is normal-diffusive. However, a distinctive feature is shown to be provided by the explicit dependence on the measurement time T, and this ageing phenomenon can be used to deduce the anomalous diffusion exponent.Wealso compare our results to the single-trajectory PSD behaviour of another standard anomalous diffusion process, fractional Brownian motion, and work out the commonalities and differences. Our results represent an important step in establishing singletrajectory PSDs as an alternative (or complement) to analyses based on the time-averaged mean squared displacement.}, language = {en} } @article{SposiniMetzlerOshanin2019, author = {Sposini, Vittoria and Metzler, Ralf and Oshanin, Gleb}, title = {Single-trajectory spectral analysis of scaled Brownian motion}, series = {New Journal of Physics}, volume = {21}, journal = {New Journal of Physics}, publisher = {Deutsche Physikalische Gesellschaft ; IOP, Institute of Physics}, address = {Bad Honnef und London}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab2f52}, pages = {16}, year = {2019}, abstract = {Astandard approach to study time-dependent stochastic processes is the power spectral density (PSD), an ensemble-averaged property defined as the Fourier transform of the autocorrelation function of the process in the asymptotic limit of long observation times, T → ∞. In many experimental situations one is able to garner only relatively few stochastic time series of finite T, such that practically neither an ensemble average nor the asymptotic limit T → ∞ can be achieved. To accommodate for a meaningful analysis of such finite-length data we here develop the framework of single-trajectory spectral analysis for one of the standard models of anomalous diffusion, scaled Brownian motion.Wedemonstrate that the frequency dependence of the single-trajectory PSD is exactly the same as for standard Brownian motion, which may lead one to the erroneous conclusion that the observed motion is normal-diffusive. However, a distinctive feature is shown to be provided by the explicit dependence on the measurement time T, and this ageing phenomenon can be used to deduce the anomalous diffusion exponent.Wealso compare our results to the single-trajectory PSD behaviour of another standard anomalous diffusion process, fractional Brownian motion, and work out the commonalities and differences. Our results represent an important step in establishing singletrajectory PSDs as an alternative (or complement) to analyses based on the time-averaged mean squared displacement.}, language = {en} } @misc{JelkenSanter2019, author = {Jelken, Joachim and Santer, Svetlana}, title = {Light induced reversible structuring of photosensitive polymer films}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {750}, issn = {1866-8372}, doi = {10.25932/publishup-43643}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436432}, pages = {20295 -- 20305}, year = {2019}, abstract = {In this paper we report on photoswitchable polymer surfaces with dynamically and reversibly fluctuating topographies. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes to form a surface relief grating. In the simplest case, the film shape mimics the intensity distribution and deforms into a wave like, sinusoidal manner with amplitude that may be as large as the film thickness. This process takes place in the glassy state without photo-induced softening. Here we report on an intriguing discovery regarding the formation of reliefs under special illumination conditions. We have developed a novel setup combining the optical part for creating interference patterns, an AFM for in situ acquisition of topography changes and diffraction efficiency signal measurements. In this way we demonstrate that these gratings can be "set in motion" like water waves or dunes in the desert. We achieve this by applying repetitive polarization changes to the incoming interference pattern. Such light responsive surfaces represent the prerequisite for providing practical applications ranging from conveyer or transport systems for adsorbed liquid objects and colloidal particles to generation of adaptive and dynamic optical devices.}, language = {en} } @article{JelkenSanter2019, author = {Jelken, Joachim and Santer, Svetlana}, title = {Light induced reversible structuring of photosensitive polymer films}, series = {RSC Advances}, volume = {9}, journal = {RSC Advances}, number = {35}, publisher = {RSC Publishing}, address = {London}, issn = {2046-2069}, doi = {10.1039/C9RA02571E}, pages = {20295 -- 20305}, year = {2019}, abstract = {In this paper we report on photoswitchable polymer surfaces with dynamically and reversibly fluctuating topographies. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes to form a surface relief grating. In the simplest case, the film shape mimics the intensity distribution and deforms into a wave like, sinusoidal manner with amplitude that may be as large as the film thickness. This process takes place in the glassy state without photo-induced softening. Here we report on an intriguing discovery regarding the formation of reliefs under special illumination conditions. We have developed a novel setup combining the optical part for creating interference patterns, an AFM for in situ acquisition of topography changes and diffraction efficiency signal measurements. In this way we demonstrate that these gratings can be "set in motion" like water waves or dunes in the desert. We achieve this by applying repetitive polarization changes to the incoming interference pattern. Such light responsive surfaces represent the prerequisite for providing practical applications ranging from conveyer or transport systems for adsorbed liquid objects and colloidal particles to generation of adaptive and dynamic optical devices.}, language = {en} } @phdthesis{Bachmann2019, author = {Bachmann, Felix}, title = {Non-linearity of magnetic micropropellers}, school = {Universit{\"a}t Potsdam}, pages = {120}, year = {2019}, language = {en} } @phdthesis{Ramachandran2019, author = {Ramachandran, Varsha}, title = {Massive star evolution, star formation, and feedback at low metallicity}, doi = {10.25932/publishup-43245}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-432455}, school = {Universit{\"a}t Potsdam}, pages = {291}, year = {2019}, abstract = {The goal of this thesis is to broaden the empirical basis for a better, comprehensive understanding of massive star evolution, star formation and feedback at low metallicity. Low metallicity massive stars are a key to understand the early universe. Quantitative information on metal-poor massive stars was sparse before. The quantitative spectroscopic studies of massive star populations associated with large-scale ISM structures were not performed at low metallicity before, but are important to investigate star-formation histories and feedback in detail. Much of this work relies on spectroscopic observations with VLT-FLAMES of ~500 OB stars in the Magellanic Clouds. When available, the optical spectroscopy was complemented by UV spectra from the HST, IUE, and FUSE archives. The two representative young stellar populations that have been studied are associated with the superbubble N 206 in the Large Magellanic Cloud (LMC) and with the supergiant shell SMC-SGS 1 in the Wing of the Small Magellanic Cloud (SMC), respectively. We performed spectroscopic analyses of the massive stars using the nonLTE Potsdam Wolf-Rayet (PoWR) model atmosphere code. We estimated the stellar, wind, and feedback parameters of the individual massive stars and established their statistical distributions. The mass-loss rates of N206 OB stars are consistent with theoretical expectations for LMC metallicity. The most massive and youngest stars show nitrogen enrichment at their surface and are found to be slower rotators than the rest of the sample. The N 206 complex has undergone star formation episodes since more than 30 Myr, with a current star formation rate higher than average in the LMC. The spatial age distribution of stars across the complex possibly indicates triggered star formation due to the expansion of the superbubble. Three very massive, young Of stars in the region dominate the ionizing and mechanical feedback among hundreds of other OB stars in the sample. The current stellar wind feedback rate from the two WR stars in the complex is comparable to that released by the whole OB sample. We see only a minor fraction of this stellar wind feedback converted into X-ray emission. In this LMC complex, stellar winds and supernovae equally contribute to the total energy feedback, which eventually powered the central superbubble. However, the total energy input accumulated over the time scale of the superbubble significantly exceeds the observed energy content of the complex. The lack of energy along with the morphology of the complex suggests a leakage of hot gas from the superbubble. With a detailed spectroscopic study of massive stars in SMC-SGS 1, we provide the stellar and wind parameters of a large sample of OB stars at low metallicity, including those in the lower mass-range. The stellar rotation velocities show a broad, tentatively bimodal distribution, with Be stars being among the fastest. A few very luminous O stars are found close to the main sequence, while all other, slightly evolved stars obey a strict luminosity limit. Considering additional massive stars in evolved stages, with published parameters and located all over the SMC, essentially confirms this picture. The comparison with single-star evolutionary tracks suggests a dichotomy in the fate of massive stars in the SMC. Only stars with an initial mass below 30 solar masses seem to evolve from the main sequence to the cool side of the HRD to become a red supergiant and to explode as type II-P supernova. In contrast, more massive stars appear to stay always hot and might evolve quasi chemically homogeneously, finally collapsing to relatively massive black holes. However, we find no indication that chemical mixing is correlated with rapid rotation. We measured the key parameters of stellar feedback and established the links between the rates of star formation and supernovae. Our study demonstrates that in metal-poor environments stellar feedback is dominated by core-collapse supernovae in combination with winds and ionizing radiation supplied by a few of the most massive stars. We found indications of the stochastic mode of star formation, where the resulting stellar population is fully capable of producing large-scale structures such as the supergiant shell SMC-SGS 1 in the Wing. The low level of feedback in metal-poor stellar populations allows star formation episodes to persist over long timescales. Our study showcases the importance of quantitative spectroscopy of massive stars with adequate stellar-atmosphere models in order to understand star-formation, evolution, and feedback. The stellar population analyses in the LMC and SMC make us understand that massive stars and their impact can be very different depending on their environment. Obviously, due to their different metallicity, the massive stars in the LMC and the SMC follow different evolutionary paths. Their winds differ significantly, and the key feedback agents are different. As a consequence, the star formation can proceed in different modes.}, language = {en} } @phdthesis{Sablowski2019, author = {Sablowski, Daniel}, title = {Spectroscopic analysis of the benchmark system Alpha Aurigae}, doi = {10.25932/publishup-43239}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-432396}, school = {Universit{\"a}t Potsdam}, pages = {169}, year = {2019}, abstract = {Binaries play an important role in observational and theoretical astrophysics. Since the mass and the chemical composition are key ingredients for stellar evolution, high-resolution spectroscopy is an important and necessary tool to derive those parameters to high confidence in binaries. This involves carefully measured orbital motion by the determination of radial velocity (RV) shifts and sophisticated techniques to derive the abundances of elements within the stellar atmosphere. A technique superior to conventional cross-correlation methods to determine RV shifts in known as spectral disentangling. Hence, a major task of this thesis was the design of a sophisticated software package for this approach. In order to investigate secondary effects, such as flux and line-profile variations, imprinting changes on the spectrum the behavior of spectral disentangling on such variability is a key to understand the derived values, to improve them, and to get information about the variability itself. Therefore, the spectral disentangling code presented in this thesis and available to the community combines multiple advantages: separation of the spectra for detailed chemical analysis, derivation of orbital elements, derivation of individual RVs in order to investigate distorted systems (either by third body interaction or relativistic effects), the suppression of telluric contaminations, the derivation of variability, and the possibility to apply the technique to eclipsing binaries (important for orbital inclination) or in general to systems that undergo flux-variations. This code in combination with the spectral synthesis codes MOOG and SME was used in order to derive the carbon 12C/13C isotope ratio (CIR) of the benchmark binary Capella. The observational result will be set into context with theoretical evolution by the use of MESA models and resolves the discrepancy of theory and observations existing since the first measurement of Capella's CIR in 1976. The spectral disentangling code has been made available to the community and its applicability to completely different behaving systems, Wolf-Rayet stars, have also been investigated and resulted in a published article. Additionally, since this technique relies strongly on data quality, continues development of scientific instruments to achieve best observational data is of great importance in observational astrophysics. That is the reason why there has also been effort in astronomical instrumentation during the work on this thesis.}, language = {en} } @phdthesis{Haase2019, author = {Haase, Nadin}, title = {The nascent peptide chain in the ribosomal exit tunnel}, school = {Universit{\"a}t Potsdam}, pages = {105}, year = {2019}, language = {en} } @phdthesis{Peter2019, author = {Peter, Franziska}, title = {Transition to synchrony in finite Kuramoto ensembles}, doi = {10.25932/publishup-42916}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-429168}, school = {Universit{\"a}t Potsdam}, pages = {vi, 93}, year = {2019}, abstract = {Synchronisation - die Ann{\"a}herung der Rhythmen gekoppelter selbst oszillierender Systeme - ist ein faszinierendes dynamisches Ph{\"a}nomen, das in vielen biologischen, sozialen und technischen Systemen auftritt. Die vorliegende Arbeit befasst sich mit Synchronisation in endlichen Ensembles schwach gekoppelter selbst-erhaltender Oszillatoren mit unterschiedlichen nat{\"u}rlichen Frequenzen. Das Standardmodell f{\"u}r dieses kollektive Ph{\"a}nomen ist das Kuramoto-Modell - unter anderem aufgrund seiner L{\"o}sbarkeit im thermodynamischen Limes unendlich vieler Oszillatoren. {\"A}hnlich einem thermodynamischen Phasen{\"u}bergang zeigt im Fall unendlich vieler Oszillatoren ein Ordnungsparameter den {\"U}bergang von Inkoh{\"a}renz zu einem partiell synchronen Zustand an, in dem ein Teil der Oszillatoren mit einer gemeinsamen Frequenz rotiert. Im endlichen Fall treten Fluktuationen auf. In dieser Arbeit betrachten wir den bisher wenig beachteten Fall von bis zu wenigen hundert Oszillatoren, unter denen vergleichbar starke Fluktuationen auftreten, bei denen aber ein Vergleich zu Frequenzverteilungen im unendlichen Fall m{\"o}glich ist. Zun{\"a}chst definieren wir einen alternativen Ordnungsparameter zur Feststellung einer kollektiven Mode im endlichen Kuramoto-Modell. Dann pr{\"u}fen wir die Abh{\"a}ngigkeit des Synchronisationsgrades und der mittleren Rotationsfrequenz der kollektiven Mode von Eigenschaften der nat{\"u}rlichen Frequenzverteilung f{\"u}r verschiedene Kopplungsst{\"a}rken. Wir stellen dabei zun{\"a}chst numerisch fest, dass der Synchronisationsgrad stark von der Form der Verteilung (gemessen durch die Kurtosis) und die Rotationsfrequenz der kollektiven Mode stark von der Asymmetrie der Verteilung (gemessen durch die Schiefe) der nat{\"u}rlichen Frequenzen abh{\"a}ngt. Beides k{\"o}nnen wir im thermodynamischen Limes analytisch verifizieren. Mit diesen Ergebnissen k{\"o}nnen wir Erkenntnisse anderer Autoren besser verstehen und verallgemeinern. Etwas abseits des roten Fadens dieser Arbeit finden wir außerdem einen analytischen Ausdruck f{\"u}r die Volumenkontraktion im Phasenraum. Der zweite Teil der Arbeit konzentriert sich auf den ordnenden Effekt von Fluktuationen, die durch die Endlichkeit des Systems zustande kommen. Im unendlichen Modell sind die Oszillatoren eindeutig in koh{\"a}rent und inkoh{\"a}rent und damit in geordnet und ungeordnet getrennt. Im endlichen Fall k{\"o}nnen die auftretenden Fluktuationen zus{\"a}tzliche Ordnung unter den asynchronen Oszillatoren erzeugen. Das grundlegende Prinzip, die rauschinduzierte Synchronisation, ist aus einer Reihe von Publikationen bekannt. Unter den gekoppelten Oszillatoren n{\"a}hern sich die Phasen aufgrund der Fluktuationen des Ordnungsparameters an, wie wir einerseits direkt numerisch zeigen und andererseits mit einem Synchronisationsmaß aus der gerichteten Statistik zwischen Paaren passiver Oszillatoren nachweisen. Wir bestimmen die Abh{\"a}ngigkeit dieses Synchronisationsmaßes vom Verh{\"a}ltnis von paarweiser nat{\"u}rlicher Frequenzdifferenz zur Varianz der Fluktuationen. Dabei finden wir eine gute {\"U}bereinstimmung mit einem einfachen analytischen Modell, in welchem wir die deterministischen Fluktuationen des Ordnungsparameters durch weißes Rauschen ersetzen.}, language = {en} } @phdthesis{Kurpiers2019, author = {Kurpiers, Jona}, title = {Probing the pathways of free charge generation and recombination in organic solar cells}, doi = {10.25932/publishup-42909}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-429099}, school = {Universit{\"a}t Potsdam}, pages = {VI, 128, xxi}, year = {2019}, abstract = {Organic semiconductors are a promising class of materials. Their special properties are the particularly good absorption, low weight and easy processing into thin films. Therefore, intense research has been devoted to the realization of thin film organic solar cells (OPVs). Because of the low dielectric constant of organic semiconductors, primary excitations (excitons) are strongly bound and a type II heterojunction needs to be introduced to split these excitations into free charges. Therefore, most organic solar cells consist of at least an electron donor and electron acceptor material. For such donor acceptor systems mainly three states are relevant; the photoexcited exciton on the donor or acceptor material, the charge transfer state at the donor-acceptor interface and the charge separated state of a free electron and hole. The interplay between these states significantly determines the efficiency of organic solar cells. Due to the high absorption and the low charge carrier mobilities, the active layers are usually thin but also, exciton dissociation and free charge formation proceeds rapidely, which makes the study of carrier dynamics highly challenging. Therefore, the focus of this work was first to install new experimental setups for the investigation of the charge carrier dynamics in complete devices with superior sensitivity and time resolution and, second, to apply these methods to prototypical photovoltaic materials to address specific questions in the field of organic and hybrid photovoltaics. Regarding the first goal, a new setup combining transient absorption spectroscopy (TAS) and time delayed collection field (TDCF) was designed and installed in Potsdam. An important part of this work concerned the improvement of the electronic components with respect to time resolution and sensitivity. To this end, a highly sensitive amplifier for driving and detecting the device response in TDCF was developed. This system was then applied to selected organic and hybrid model systems with a particular focus on the understanding of the loss mechanisms that limit the fill factor and short circuit current of organic solar cells. The first model system was a hybrid photovoltaic material comprising inorganic quantum dots decorated with organic ligands. Measurements with TDCF revealed fast free carrier recombination, in part assisted by traps, while bias-assisted charge extraction measurements showed high mobility. The measured parameters then served as input for a successful description of the device performance with an analytical model. With a further improvement of the instrumentation, a second topic was the detailed analysis of non-geminate recombination in a disordered polymer:fullerene blend where an important question was the effect of disorder on the carrier dynamics. The measurements revealed that early time highly mobile charges undergo fast non-geminate recombination at the contacts, causing an apparent field dependence of free charge generation in TDCF experiments if not conducted properly. On the other hand, recombination the later time scale was determined by dispersive recombination in the bulk of the active layer, showing the characteristics of carrier dynamics in an exponential density of state distribution. Importantly, the comparison with steady state recombination data suggested a very weak impact of non-thermalized carriers on the recombination properties of the solar cells under application relevant illumination conditions. Finally, temperature and field dependent studies of free charge generation were performed on three donor-acceptor combinations, with two donor polymers of the same material family blended with two different fullerene acceptor molecules. These particular material combinations were chosen to analyze the influence of the energetic and morphology of the blend on the efficiency of charge generation. To this end, activation energies for photocurrent generation were accurately determined for a wide range of excitation energies. The results prove that the formation of free charge is via thermalized charge transfer states and does not involve hot exciton splitting. Surprisingly, activation energies were of the order of thermal energy at room temperature. This led to the important conclusion that organic solar cells perform well not because of predominate high energy pathways but because the thermalized CT states are weakly bound. In addition, a model is introduced to interconnect the dissociation efficiency of the charge transfer state with its recombination observable with photoluminescence, which rules out a previously proposed two-pool model for free charge formation and recombination. Finally, based on the results, proposals for the further development of organic solar cells are formulated.}, language = {en} } @phdthesis{Kav2019, author = {Kav, Batuhan}, title = {Membrane adhesion mediated via lipid-anchored saccharides}, doi = {10.25932/publishup-42879}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-428790}, school = {Universit{\"a}t Potsdam}, pages = {125}, year = {2019}, abstract = {Membrane adhesion is a fundamental biological process in which membranes are attached to neighboring membranes or surfaces. Membrane adhesion emerges from a complex interplay between the binding of membrane-anchored receptors/ligands and the membrane properties. In this work, we study membrane adhesion mediated by lipid-anchored saccharides using microsecond-long full-atomistic molecular dynamics simulations. Motivated by neutron scattering experiments on membrane adhesion via lipid-anchored saccharides, we investigate the role of LeX, Lac1, and Lac2 saccharides and membrane fluctuations in membrane adhesion. We study the binding of saccharides in three different systems: for saccharides in water, for saccharides anchored to essentially planar membranes at fixed separations, and for saccharides anchored to apposing fluctuating membranes. Our simulations of two saccharides in water indicate that the saccharides engage in weak interactions to form dimers. We find that the binding occurs in a continuum of bound states instead of a certain number of well-defined bound structures, which we term as "diffuse binding". The binding of saccharides anchored to essentially planar membranes strongly depends on separation of the membranes, which is fixed in our simulation system. We show that the binding constants for trans-interactions of two lipid-anchored saccharides monotonically decrease with increasing separation. Saccharides anchored to the same membrane leaflet engage in cis-interactions with binding constants comparable to the trans-binding constants at the smallest membrane separations. The interplay of cis- and trans-binding can be investigated in simulation systems with many lipid-anchored saccharides. For Lac2, our simulation results indicate a positive cooperativity of trans- and cis-binding. In this cooperative binding the trans-binding constant is enhanced by the cis-interactions. For LeX, in contrast, we observe no cooperativity between trans- and cis-binding. In addition, we determine the forces generated by trans-binding of lipid-anchored saccharides in planar membranes from the binding-induced deviations of the lipid-anchors. We find that the forces acting on trans-bound saccharides increase with increasing membrane separation to values of the order of 10 pN. The binding of saccharides anchored to the fluctuating membranes results from an interplay between the binding properties of the lipid-anchored saccharides and membrane fluctuations. Our simulations, which have the same average separation of the membranes as obtained from the neutron scattering experiments, yield a binding constant larger than in planar membranes with the same separation. This result demonstrates that membrane fluctuations play an important role at average membrane separations which are seemingly too large for effective binding. We further show that the probability distribution of the local separation can be well approximated by a Gaussian distribution. We calculate the relative membrane roughness and show that our results are in good agreement with the roughness values reported from the neutron scattering experiments.}, language = {en} } @phdthesis{Solopow2019, author = {Solopow, Sergej}, title = {Wavelength dependent demagnetization dynamics in Co2MnGa Heusler-alloy}, doi = {10.25932/publishup-42786}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427860}, school = {Universit{\"a}t Potsdam}, pages = {91}, year = {2019}, abstract = {In dieser Arbeit haben wir ultraschnelle Entmagnetisierung an einer Heusler-Legierung untersucht. Es handelt sich um ein Halbmetall, das sich in einer ferromagnetischen Phase befindet. Die Besonderheit dieses Materials besteht im Aufbau einer Bandstruktur. Diese bildet Zustandsdichten, in der die Majorit{\"a}tselektronen eine metallische B{\"a}nderbildung aufweisen und die Minorit{\"a}tselektronen eine Bandl{\"u}cke in der N{\"a}he des Fermi-Niveaus aufweisen, das dem Aufbau eines Halbleiters entspricht. Mit Hilfe der Pump-Probe-Experimente haben wir zeitaufgel{\"o}ste Messungen durchgef{\"u}hrt. F{\"u}r das Pumpen wurden ultrakurze Laserpulse mit einer Pulsdauer von 100 fs benutzt. Wir haben dabei zwei verschiedene Wellenl{\"a}ngen mit 400 nm und 1240 nm benutzt, um den Effekt der Prim{\"a}ranregung und der Bandl{\"u}cke in den Minorit{\"a}tszust{\"a}nden zu untersuchen. Dabei wurde zum ersten Mal OPA (Optical Parametrical Amplifier) f{\"u}r die Erzeugung der langwelligen Pulse an der FEMTOSPEX-Beamline getestet und erfolgreich bei den Experimenten verwendet. Wir haben Wellenl{\"a}ngen bedingte Unterschiede in der Entmagnetisierungszeit gemessen. Mit der Erh{\"o}hung der Photonenenergie ist der Prozess der Entmagnetisierung deutlich schneller als bei einer niedrigeren Photonenenergie. Wir verkn{\"u}pften diese Ergebnisse mit der Existenz der Energiel{\"u}cke f{\"u}r Minorit{\"a}tselektronen. Mit Hilfe lokaler Elliot-Yafet-Streuprozesse k{\"o}nnen die beobachteten Zeiten gut erkl{\"a}rt werden. Wir haben in dieser Arbeit auch eine neue Probe-Methode f{\"u}r die Magnetisierung angewandt und somit experimentell deren Effektivit{\"a}t, n{\"a}mlich XMCD in Refletiongeometry, best{\"a}tigen k{\"o}nnen. Statische Experimente liefern somit deutliche Indizien daf{\"u}r, dass eine magnetische von einer rein elektronischen Antwort des Systems getrennt werden kann. Unter der Voraussetzung, dass die Photonenenergie der R{\"o}ntgenstrahlung auf die L3 Kante des entsprechenden Elements eingestellt, ein geeigneter Einfallswinkel gew{\"a}hlt und die zirkulare Polarisation fixiert wird, ist es m{\"o}glich, diese Methode zur Analyse magnetischer und elektronischer Respons anzuwenden.}, language = {en} } @article{SarhanKoopmanSchuetzetal.2019, author = {Sarhan, Radwan Mohamed and Koopman, Wouter-Willem Adriaan and Schuetz, Roman and Schmid, Thomas and Liebig, Ferenc and Koetz, Joachim and Bargheer, Matias}, title = {The importance of plasmonic heating for the plasmondriven photodimerization of 4-nitrothiophenol}, series = {Scientific Reports}, volume = {9}, journal = {Scientific Reports}, publisher = {Macmillan Publishers Limited}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-019-38627-2}, pages = {8}, year = {2019}, abstract = {Metal nanoparticles form potent nanoreactors, driven by the optical generation of energetic electrons and nanoscale heat. The relative influence of these two factors on nanoscale chemistry is strongly debated. This article discusses the temperature dependence of the dimerization of 4-nitrothiophenol (4-NTP) into 4,4′-dimercaptoazobenzene (DMAB) adsorbed on gold nanoflowers by Surface-Enhanced Raman Scattering (SERS). Raman thermometry shows a significant optical heating of the particles. The ratio of the Stokes and the anti-Stokes Raman signal moreover demonstrates that the molecular temperature during the reaction rises beyond the average crystal lattice temperature of the plasmonic particles. The product bands have an even higher temperature than reactant bands, which suggests that the reaction proceeds preferentially at thermal hot spots. In addition, kinetic measurements of the reaction during external heating of the reaction environment yield a considerable rise of the reaction rate with temperature. Despite this significant heating effects, a comparison of SERS spectra recorded after heating the sample by an external heater to spectra recorded after prolonged illumination shows that the reaction is strictly photo-driven. While in both cases the temperature increase is comparable, the dimerization occurs only in the presence of light. Intensity dependent measurements at fixed temperatures confirm this finding.}, language = {en} } @phdthesis{Cecchini2019, author = {Cecchini, Gloria}, title = {Improving network inference by overcoming statistical limitations}, doi = {10.25932/publishup-42670}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426705}, school = {Universit{\"a}t Potsdam}, pages = {124}, year = {2019}, abstract = {A reliable inference of networks from data is of key interest in many scientific fields. Several methods have been suggested in the literature to reliably determine links in a network. These techniques rely on statistical methods, typically controlling the number of false positive links, but not considering false negative links. In this thesis new methodologies to improve network inference are suggested. Initial analyses demonstrate the impact of falsepositive and false negative conclusions about the presence or absence of links on the resulting inferred network. Consequently, revealing the importance of making well-considered choices leads to suggest new approaches to enhance existing network reconstruction methods. A simulation study, presented in Chapter 3, shows that different values to balance false positive and false negative conclusions about links should be used in order to reliably estimate network characteristics. The existence of type I and type II errors in the reconstructed network, also called biased network, is accepted. Consequently, an analytic method that describes the influence of these two errors on the network structure is explored. As a result of this analysis, an analytic formula of the density of the biased vertex degree distribution is found (Chapter 4). In the inverse problem, the vertex degree distribution of the true underlying network is analytically reconstructed, assuming the probabilities of type I and type II errors. Chapters 4-5 show that the method is robust to incorrect estimates of α and β within reasonable limits. In Chapter 6, an iterative procedure to enhance this method is presented in the case of large errors on the estimates of α and β. The investigations presented so far focus on the influence of false positive and false negative links on the network characteristics. In Chapter 7, the analysis is reversed - the study focuses on the influence of network characteristics on the probability of type I and type II errors, in the case of networks of coupled oscillators. The probabilities of α and β are influenced by the shortest path length and the detour degree, respectively. These results have been used to improve the network reconstruction, when the true underlying network is not known a priori, introducing a novel and advanced concept of threshold.}, language = {en} } @phdthesis{Kegelmann2019, author = {Kegelmann, Lukas}, title = {Advancing charge selective contacts for efficient monolithic perovskite-silicon tandem solar cells}, doi = {10.25932/publishup-42642}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426428}, school = {Universit{\"a}t Potsdam}, pages = {v, 155}, year = {2019}, abstract = {Hybrid organic-inorganic perovskites are one of the most promising material classes for photovoltaic energy conversion. In solar cells, the perovskite absorber is sandwiched between n- and p-type contact layers which selectively transport electrons and holes to the cell's cathode and anode, respectively. This thesis aims to advance contact layers in perovskite solar cells and unravel the impact of interface and contact properties on the device performance. Further, the contact materials are applied in monolithic perovskite-silicon heterojunction (SHJ) tandem solar cells, which can overcome the single junction efficiency limits and attract increasing attention. Therefore, all contact layers must be highly transparent to foster light harvesting in the tandem solar cell design. Besides, the SHJ device restricts processing temperatures for the selective contacts to below 200°C. A comparative study of various electron selective contact materials, all processed below 180°C, in n-i-p type perovskite solar cells highlights that selective contacts and their interfaces to the absorber govern the overall device performance. Combining fullerenes and metal-oxides in a TiO2/PC60BM (phenyl-C60-butyric acid methyl ester) double-layer contact allows to merge good charge extraction with minimized interface recombination. The layer sequence thereby achieved high stabilized solar cell performances up to 18.0\% and negligible current-voltage hysteresis, an otherwise pronounced phenomenon in this device design. Double-layer structures are therefore emphasized as a general concept to establish efficient and highly selective contacts. Based on this success, the concept to combine desired properties of different materials is transferred to the p-type contact. Here, a mixture of the small molecule Spiro-OMeTAD [2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluoren] and the doped polymer PEDOT [poly(3,4-ethylenedioxythiophene)] is presented as a novel hole selective contact. PEDOT thereby remarkably suppresses charge recombination at the perovskite surface, allowing an increase of quasi-Fermi level splitting in the absorber. Further, the addition of Spiro-OMeTAD into the PEDOT layer is shown to enhance charge extraction at the interface and allow high efficiencies up to 16.8\%. Finally, the knowledge on contact properties is applied to monolithic perovskite-SHJ tandem solar cells. The main goal is to optimize the top contact stack of doped Spiro-OMeTAD/molybdenum oxide(MoOx)/ITO towards higher transparency by two different routes. First, fine-tuning of the ITO deposition to mitigate chemical reduction of MoOx and increase the transmittance of MoOx/ITO stacks by 25\%. Second, replacing Spiro-OMeTAD with the alternative hole transport materials PEDOT/Spiro-OMeTAD mixtures, CuSCN or PTAA [poly(triaryl amine)]. Experimental results determine layer thickness constrains and validate optical simulations, which subsequently allow to realistically estimate the respective tandem device performances. As a result, PTAA represents the most promising replacement for Spiro-OMeTAD, with a projected increase of the optimum tandem device efficiency for the herein used architecture by 2.9\% relative to 26.5\% absolute. The results also reveal general guidelines for further performance gains of the technology.}, language = {en} } @phdthesis{Eckert2019, author = {Eckert, Sebastian}, title = {Accessing active sites of molecular proton dynamics}, doi = {10.25932/publishup-42587}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-425870}, school = {Universit{\"a}t Potsdam}, pages = {xviii, 193}, year = {2019}, abstract = {The unceasing impact of intense sunlight on earth constitutes a continuous source of energy fueling countless natural processes. On a molecular level, the energy contained in the electromagnetic radiation is transferred through photochemical processes into chemical or thermal energy. In the course of such processes, photo-excitations promote molecules into thermally inaccessible excited states. This induces adaptations of their molecular geometry according to the properties of the excited state. Decay processes towards energetically lower lying states in transient molecular geometries result in the formation of excited state relaxation pathways. The photo-chemical relaxation mechanisms depend on the studied system itself, the interactions with its chemical environment and the character of the involved states. This thesis focuses on systems in which photo-induced deprotonation processes occur at specific atomic sites. To detect these excited-state proton dynamics at the affected atoms, a local probe of molecular electronic structure is required. Therefore, site-selective and orbital-specific K-edge soft X-ray spectroscopy techniques are used here to detect photo-induced proton dynamics in gaseous and liquid sample environments. The protonation of nitrogen (N) sites in organic molecules and the oxygen (O) atom in the water molecule are probed locally through transitions between 1s orbitals and the p-derived molecular valence electronic structure. The used techniques are X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Both yield access to the unoccupied local valence electronic structure, whereas the latter additionally probes occupied states. We apply these probes in optical pump X-ray probe experiments to investigate valence excited-state proton transfer capabilities of aqueous 2-thiopyridone. A characteristic shift of N K-edge X-ray absorption resonances as well as a distinct X-ray emission line are established by us as spectral fingerprints of N deprotonation in the system. We utilize them to identify photo-induced N deprotonation of 2-thiopyridone on femtosecond timescales, in optical pump N K-edge RIXS probe measurements. We further establish excited state proton transfer mechanisms on picosecond and nanosecond timescales along the dominant relaxation pathways of 2-thiopyridone using transient N K-edge XAS. Despite being an excellent probe mechanism for valence excited-state proton dynamics, the K-edge core-excitation itself also disturbs the electronic structure at specific sites of a molecule. The rapid reaction of protons to 1s photo-excitations can yield directional structural distortions within the femtosecond core-excited state lifetime. These directional proton dynamics can change the energetic separation of eigenstates of the system and alter probabilities for radiative decay between them. Both effects yield spectral signatures of the dynamics in RIXS spectra. Using these signatures of RIXS transitions into electronically excited states, we investigate proton dynamics induced by N K-edge excitation in the amino-acid histidine. The minor core-excited state dynamics of histidine in basic and neutral chemical environments allow us to establish XAS and RIXS spectral signatures of different N protonation states at its imidazole N sites. Based on these signatures, we identify an excitation-site-independent N-H dissociation for N K-edge excitation under acidic conditions. Such directional structural deformations, induced by core-excitations, also make proton dynamics in electronic ground states accessible through RIXS transitions into vibrationally excited states. In that context, we interpret high resolution RIXS spectra of the water molecule for three O K-edge resonances based on quantum-chemical wave packet propagation simulations. We show that highly oriented ground state vibrational modes of coupled nuclear motion can be populated through RIXS processes by preparation of core-excited state nuclear wave packets with the same directionality. Based on that, we analytically derive the possibility to extract one-dimensional directional cuts through potential energy surfaces of molecular systems from the corresponding RIXS spectra. We further verify this concept through the extraction of the gas-phase water ground state potential along three coordinates from experimental data in comparison to quantum-chemical simulations of the potential energy surface. This thesis also contains contributions to instrumentation development for investigations of photo-induced molecular dynamics at high brilliance X-ray light sources. We characterize the setup used for the transient valence-excited state XAS measurements of 2-thiopyridone. Therein, a sub-micrometer thin liquid sample environment is established employing in-vacuum flat-jet technology, which enables a transmission experimental geometry. In combination with a MHz-laser system, we achieve a high detection sensitivity for photo-induced X-ray absorption changes. Additionally, we present conceptual improvements for temporal X-ray optical cross-correlation techniques based on transient changes of multilayer optical properties, which are crucial for the realization of femtosecond time-resolved studies at synchrotrons and free-electron lasers.}, language = {en} }