@article{SchmaelzlinMoralejoRutowskaetal.2014,
  author    = {Schmaelzlin, Elmar and Moralejo, Benito and Rutowska, Monika and Monreal-Ibero, Ana and Sandin, Christer and Tarcea, Nicolae and Popp, Juergen and Roth, Martin M.},
  title     = {Raman imaging with a fiber-coupled multichannel spectrograph},
  series = {Sensors},
  volume    = {14},
  journal   = {Sensors},
  number    = {11},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {1424-8220},
  doi       = {10.3390/s141121968},
  pages     = {21968 -- 21980},
  year      = {2014},
  abstract  = {Until now, spatially resolved Raman Spectroscopy has required to scan a sample under investigation in a time-consuming step-by-step procedure. Here, we present a technique that allows the capture of an entire Raman image with only one single exposure. The Raman scattering arising from the sample was collected with a fiber-coupled high-performance astronomy spectrograph. The probe head consisting of an array of 20 x 20 multimode fibers was linked to the camera port of a microscope. To demonstrate the high potential of this new concept, Raman images of reference samples were recorded. Entire chemical maps were received without the need for a scanning procedure.},
  language  = {en}
}
@phdthesis{Orgis2014,
  author    = {Orgis, Thomas},
  title     = {Unstetige Galerkin-Diskretisierung niedriger Ordnung in einem atmosph{\"a}rischen Multiskalenmodell},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70687},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {Die Dynamik der Atmosph{\"a}re der Erde umfasst einen Bereich von mikrophysikalischer Turbulenz {\"u}ber konvektive Prozesse und Wolkenbildung bis zu planetaren Wellenmustern. F{\"u}r Wettervorhersage und zur Betrachtung des Klimas {\"u}ber Jahrzehnte und Jahrhunderte ist diese Gegenstand der Modellierung mit numerischen Verfahren. Mit voranschreitender Entwicklung der Rechentechnik sind Neuentwicklungen der dynamischen Kerne von Klimamodellen, die mit der feiner werdenden Aufl{\"o}sung auch entsprechende Prozesse aufl{\"o}sen k{\"o}nnen, notwendig. Der dynamische Kern eines Modells besteht in der Umsetzung (Diskretisierung) der grundlegenden dynamischen Gleichungen f{\"u}r die Entwicklung von Masse, Energie und Impuls, so dass sie mit Computern numerisch gel{\"o}st werden k{\"o}nnen. Die vorliegende Arbeit untersucht die Eignung eines unstetigen Galerkin-Verfahrens niedriger Ordnung f{\"u}r atmosph{\"a}rische Anwendungen. Diese Eignung f{\"u}r Gleichungen mit Wirkungen von externen Kr{\"a}ften wie Erdanziehungskraft und Corioliskraft ist aus der Theorie nicht selbstverst{\"a}ndlich. Es werden n{\"o}tige Anpassungen beschrieben, die das Verfahren stabilisieren, ohne sogenannte „slope limiter" einzusetzen. F{\"u}r das unmodifizierte Verfahren wird belegt, dass es nicht geeignet ist, atmosph{\"a}rische Gleichgewichte stabil darzustellen. Das entwickelte stabilisierte Modell reproduziert eine Reihe von Standard-Testf{\"a}llen der atmosph{\"a}rischen Dynamik mit Euler- und Flachwassergleichungen in einem weiten Bereich von r{\"a}umlichen und zeitlichen Skalen. Die L{\"o}sung der thermischen Windgleichung entlang der mit den Isobaren identischen charakteristischen Kurven liefert atmosph{\"a}rische Gleichgewichtszust{\"a}nde mit durch vorgegebenem Grundstrom einstellbarer Neigung zu(barotropen und baroklinen)Instabilit{\"a}ten, die f{\"u}r die Entwicklung von Zyklonen wesentlich sind. Im Gegensatz zu fr{\"u}heren Arbeiten sind diese Zust{\"a}nde direkt im z-System(H{\"o}he in Metern)definiert und m{\"u}ssen nicht aus Druckkoordinaten {\"u}bertragen werden.Mit diesen Zust{\"a}nden, sowohl als Referenzzustand, von dem lediglich die Abweichungen numerisch betrachtet werden, und insbesondere auch als Startzustand, der einer kleinen St{\"o}rung unterliegt, werden verschiedene Studien der Simulation von barotroper und barokliner Instabilit{\"a}t durchgef{\"u}hrt. Hervorzuheben ist dabei die durch die Formulierung von Grundstr{\"o}men mit einstellbarer Baroklinit{\"a}t erm{\"o}glichte simulationsgest{\"u}tzte Studie des Grades der baroklinen Instabilit{\"a}t verschiedener Wellenl{\"a}ngen in Abh{\"a}ngigkeit von statischer Stabilit{\"a}t und vertikalem Windgradient als Entsprechung zu Stabilit{\"a}tskarten aus theoretischen Betrachtungen in der Literatur.},
  language  = {de}
}
@phdthesis{Herenz2014,
  author    = {Herenz, Peter},
  title     = {A study of the absorption characteristics of gaseous galaxy halos in the local Universe},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70513},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {Today, it is well known that galaxies like the Milky Way consist not only of stars but also of gas and dust. The galactic halo, a sphere of gas that surrounds the stellar disk of a galaxy, is especially interesting. It provides a wealth of information about in and outflowing gaseous material towards and away from galaxies and their hierarchical evolution. For the Milky Way, the so-called high-velocity clouds (HVCs), fast moving neutral gas complexes in the halo that can be traced by absorption-line measurements, are believed to play a crucial role in the overall matter cycle in our Galaxy. Over the last decades, the properties of these halo structures and their connection to the local circumgalactic and intergalactic medium (CGM and IGM, respectively) have been investigated in great detail by many different groups. So far it remains unclear, however, to what extent the results of these studies can be transferred to other galaxies in the local Universe. In this thesis, we study the absorption properties of Galactic HVCs and compare the HVC absorption characteristics with those of intervening QSO absorption-line systems at low redshift. The goal of this project is to improve our understanding of the spatial extent and physical conditions of gaseous galaxy halos in the local Universe. In the first part of the thesis we use HST /STIS ultraviolet spectra of more than 40 extragalactic background sources to statistically analyze the absorption properties of the HVCs in the Galactic halo. We determine fundamental absorption line parameters including covering fractions of different weakly/intermediately/highly ionized metals with a particular focus on SiII and MgII. Due to the similarity in the ionization properties of SiII and MgII, we are able to estimate the contribution of HVC-like halo structures to the cross section of intervening strong MgII absorbers at z = 0. Our study implies that only the most massive HVCs would be regarded as strong MgII absorbers, if the Milky Way halo would be seen as a QSO absorption line system from an exterior vantage point. Combining the observed absorption-cross section of Galactic HVCs with the well-known number density of intervening strong MgII absorbers at z = 0, we conclude that the contribution of infalling gas clouds (i.e., HVC analogs) in the halos of Milky Way-type galaxies to the cross section of strong MgII absorbers is 34\%. This result indicates that only about one third of the strong MgII absorption can be associated with HVC analogs around other galaxies, while the majority of the strong MgII systems possibly is related to galaxy outflows and winds. The second part of this thesis focuses on the properties of intervening metal absorbers at low redshift. The analysis of the frequency and physical conditions of intervening metal systems in QSO spectra and their relation to nearby galaxies offers new insights into the typical conditions of gaseous galaxy halos. One major aspect in our study was to regard intervening metal systems as possible HVC analogs. We perform a detailed analysis of absorption line properties and line statistics for 57 metal absorbers along 78 QSO sightlines using newly-obtained ultraviolet spectra obtained with HST /COS. We find clear evidence for bimodal distribution in the HI column density in the absorbers, a trend that we interpret as sign for two different classes of absorption systems (with HVC analogs at the high-column density end). With the help of the strong transitions of SiII λ1260, SiIII λ1206, and CIII λ977 we have set up Cloudy photoionization models to estimate the local ionization conditions, gas densities, and metallicities. We find that the intervening absorption systems studied by us have, on average, similar physical conditions as Galactic HVC absorbers, providing evidence that many of them represent HVC analogs in the vicinity of other galaxies. We therefore determine typical halo sizes for SiII, SiIII, and CIII for L = 0.01L∗ and L = 0.05L∗ galaxies. Based on the covering fractions of the different ions in the Galactic halo, we find that, for example, the typical halo size for SiIII is ∼ 160 kpc for L = 0.05L∗ galaxies. We test the plausibility of this result by searching for known galaxies close to the QSO sightlines and at similar redshifts as the absorbers. We find that more than 34\% of the measured SiIII absorbers have galaxies associated with them, with the majority of the absorbers indeed being at impact parameters ρ ≤160 kpc.},
  language  = {en}
}
@misc{LiuTkachovKomberetal.2014,
  author    = {Liu, W. and Tkachov, R. and Komber, H. and Senkovskyy, V. and Schubert, M. and Wei, Z. and Facchetti, A. and Neher, Dieter and Kiriy, A.},
  title     = {Chain-growth polycondensation of perylene diimide-based copolymers},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98724},
  pages     = {8},
  year      = {2014},
  abstract  = {Herein, we report the chain-growth tin-free room temperature polymerization method to synthesize n-type perylene diimide-dithiophene-based conjugated polymers (PPDIT2s) suitable for solar cell and transistor applications. The palladium/electron-rich tri-tert-butylphosphine catalyst is effective to enable the chain-growth polymerization of anion-radical monomer Br-TPDIT-Br/Zn to PPDIT2 with a molecular weight up to Mw ≈ 50 kg mol-1 and moderate polydispersity. This is the second example of the polymerization of unusual anion-radical aromatic complexes formed in a reaction of active Zn and electron-deficient diimide-based aryl halides. As such, the discovered polymerization method is not a specific reactivity feature of the naphthalene-diimide derivatives but is rather a general polymerization tool. This is an important finding, given the significantly higher maximum external quantum efficiency that can be reached with PDI-based copolymers (32-45\%) in all-polymer solar cells compared to NDI-based materials (15-30\%). Our studies revealed that PPDIT2 synthesized by the new method and the previously published polymer prepared by step-growth Stille polycondensation show similar electron mobility and all-polymer solar cell performance. At the same time, the polymerization reported herein has several technological advantages as it proceeds relatively fast at room temperature and does not involve toxic tin-based compounds. Because several chain-growth polymerization reactions are well-suited for the preparation of well-defined multi-functional polymer architectures, the next target is to explore the utility of the discovered polymerization in the synthesis of end-functionalized polymers and block copolymers. Such materials would be helpful to improve the nanoscale morphology of polymer blends in all-polymer solar cells.},
  language  = {en}
}
@phdthesis{Schmidt2014,
  author    = {Schmidt, Lukas},
  title     = {Aerosols and boundary layer structure over Arctic sea ice based on airborne lidar and dropsonde measurements},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-75076},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 98, xiii},
  year      = {2014},
  abstract  = {The atmosphere over the Arctic Ocean is strongly influenced by the distribution of sea ice and open water. Leads in the sea ice produce strong convective fluxes of sensible and latent heat and release aerosol particles into the atmosphere. They increase the occurrence of clouds and modify the structure and characteristics of the atmospheric boundary layer (ABL) and thereby influence the Arctic climate. In the course of this study aircraft measurements were performed over the western Arctic Ocean as part of the campaign PAMARCMIP 2012 of the Alfred Wegener Institute for Polar and Marine Research (AWI). Backscatter from aerosols and clouds within the lower troposphere and the ABL were measured with the nadir pointing Airborne Mobile Aerosol Lidar (AMALi) and dropsondes were launched to obtain profiles of meteorological variables. Furthermore, in situ measurements of aerosol properties, meteorological variables and turbulence were part of the campaign. The measurements covered a broad range of atmospheric and sea ice conditions. In this thesis, properties of the ABL over Arctic sea ice with a focus on the influence of open leads are studied based on the data from the PAMARCMIP campaign. The height of the ABL is determined by different methods that are applied to dropsonde and AMALi backscatter profiles. ABL heights are compared for different flights representing different conditions of the atmosphere and of sea ice and open water influence. The different criteria for ABL height that are applied show large variation in terms of agreement among each other, depending on the characteristics of the ABL and its history. It is shown that ABL height determination from lidar backscatter by methods commonly used under mid-latitude conditions is applicable to the Arctic ABL only under certain conditions. Aerosol or clouds within the ABL are needed as a tracer for ABL height detection from backscatter. Hence an aerosol source close to the surface is necessary, that is typically found under the present influence of open water and therefore convective conditions. However it is not always possible to distinguish residual layers from the actual ABL. Stable boundary layers are generally difficult to detect. To illustrate the complexity of the Arctic ABL and processes therein, four case studies are analyzed each of which represents a snapshot of the interplay between atmosphere and underlying sea ice or water surface. Influences of leads and open water on the aerosol and clouds within the ABL are identified and discussed. Leads are observed to cause the formation of fog and cloud layers within the ABL by humidity emission. Furthermore they decrease the stability and increase the height of the ABL and consequently facilitate entrainment of air and aerosol layers from the free troposphere.},
  language  = {en}
}
@article{PalyulinAlaNissilaMetzler2014,
  author    = {Palyulin, Vladimir V. and Ala-Nissila, Tapio and Metzler, Ralf},
  title     = {Polymer translocation: the first two decades and the recent diversification},
  series = {Soft matter},
  volume    = {45},
  journal   = {Soft matter},
  number    = {10},
  editor    = {Metzler, Ralf},
  publisher = {the Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1744-683X},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-76266},
  pages     = {9016 -- 9037},
  year      = {2014},
  abstract  = {Probably no other field of statistical physics at the borderline of soft matter and biological physics has caused such a flurry of papers as polymer translocation since the 1994 landmark paper by Bezrukov, Vodyanoy, and Parsegian and the study of Kasianowicz in 1996. Experiments, simulations, and theoretical approaches are still contributing novel insights to date, while no universal consensus on the statistical understanding of polymer translocation has been reached. We here collect the published results, in particular, the famous-infamous debate on the scaling exponents governing the translocation process. We put these results into perspective and discuss where the field is going. In particular, we argue that the phenomenon of polymer translocation is non-universal and highly sensitive to the exact specifications of the models and experiments used towards its analysis.},
  language  = {en}
}
@misc{PalyulinAlaNissilaMetzler2014,
  author    = {Palyulin, Vladimir V. and Ala-Nissila, Tapio and Metzler, Ralf},
  title     = {Polymer translocation: the first two decades and the recent diversification},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-76287},
  pages     = {9016 -- 9037},
  year      = {2014},
  abstract  = {Probably no other field of statistical physics at the borderline of soft matter and biological physics has caused such a flurry of papers as polymer translocation since the 1994 landmark paper by Bezrukov, Vodyanoy, and Parsegian and the study of Kasianowicz in 1996. Experiments, simulations, and theoretical approaches are still contributing novel insights to date, while no universal consensus on the statistical understanding of polymer translocation has been reached. We here collect the published results, in particular, the famous-infamous debate on the scaling exponents governing the translocation process. We put these results into perspective and discuss where the field is going. In particular, we argue that the phenomenon of polymer translocation is non-universal and highly sensitive to the exact specifications of the models and experiments used towards its analysis.},
  language  = {en}
}
@article{JeonChechkinMetzler2014,
  author    = {Jeon, Jae-Hyung and Chechkin, Aleksei V. and Metzler, Ralf},
  title     = {Scaled Brownian motion: a paradoxical process with a time dependent diffusivity for the description of anomalous diffusion},
  series = {Physical chemistry, chemical physics : PCCP},
  volume    = {30},
  journal   = {Physical chemistry, chemical physics : PCCP},
  number    = {16},
  publisher = {The Royal Society of Chemistry},
  address   = {Cambridge},
  doi       = {10.1039/C4CP02019G},
  pages     = {15811 -- 15817},
  year      = {2014},
  abstract  = {Anomalous diffusion is frequently described by scaled Brownian motion (SBM){,} a Gaussian process with a power-law time dependent diffusion coefficient. Its mean squared displacement is ?x2(t)? [similar{,} equals] 2K(t)t with K(t) [similar{,} equals] t[small alpha]-1 for 0 < [small alpha] < 2. SBM may provide a seemingly adequate description in the case of unbounded diffusion{,} for which its probability density function coincides with that of fractional Brownian motion. Here we show that free SBM is weakly non-ergodic but does not exhibit a significant amplitude scatter of the time averaged mean squared displacement. More severely{,} we demonstrate that under confinement{,} the dynamics encoded by SBM is fundamentally different from both fractional Brownian motion and continuous time random walks. SBM is highly non-stationary and cannot provide a physical description for particles in a thermalised stationary system. Our findings have direct impact on the modelling of single particle tracking experiments{,} in particular{,} under confinement inside cellular compartments or when optical tweezers tracking methods are used.},
  language  = {en}
}
@phdthesis{Brem2014,
  author    = {Brem, Patrick},
  title     = {Compact objects in dense astrophysical environments},
  school      = {Universit{\"a}t Potsdam},
  pages     = {173},
  year      = {2014},
  language  = {en}
}
@phdthesis{Goswami2014,
  author    = {Goswami, Bedartha},
  title     = {Uncertainties in climate data analysis},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-78312},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {Scientific inquiry requires that we formulate not only what we know, but also what we do not know and by how much. In climate data analysis, this involves an accurate specification of measured quantities and a consequent analysis that consciously propagates the measurement errors at each step. The dissertation presents a thorough analytical method to quantify errors of measurement inherent in paleoclimate data. An additional focus are the uncertainties in assessing the coupling between different factors that influence the global mean temperature (GMT). Paleoclimate studies critically rely on `proxy variables' that record climatic signals in natural archives. However, such proxy records inherently involve uncertainties in determining the age of the signal. We present a generic Bayesian approach to analytically determine the proxy record along with its associated uncertainty, resulting in a time-ordered sequence of correlated probability distributions rather than a precise time series. We further develop a recurrence based method to detect dynamical events from the proxy probability distributions. The methods are validated with synthetic examples and demonstrated with real-world proxy records. The proxy estimation step reveals the interrelations between proxy variability and uncertainty. The recurrence analysis of the East Asian Summer Monsoon during the last 9000 years confirms the well-known `dry' events at 8200 and 4400 BP, plus an additional significantly dry event at 6900 BP. We also analyze the network of dependencies surrounding GMT. We find an intricate, directed network with multiple links between the different factors at multiple time delays. We further uncover a significant feedback from the GMT to the El Ni{\~n}o Southern Oscillation at quasi-biennial timescales. The analysis highlights the need of a more nuanced formulation of influences between different climatic factors, as well as the limitations in trying to estimate such dependencies.},
  language  = {en}
}
@phdthesis{Conrad2014,
  author    = {Conrad, Claudia},
  title     = {Open cluster groups and complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-77605},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 172},
  year      = {2014},
  abstract  = {It is generally agreed upon that stars typically form in open clusters and stellar associations, but little is known about the structure of the open cluster system. Do open clusters and stellar associations form isolated or do they prefer to form in groups and complexes? Open cluster groups and complexes could verify star forming regions to be larger than expected, which would explain the chemical homogeneity over large areas in the Galactic disk. They would also define an additional level in the hierarchy of star formation and could be used as tracers for the scales of fragmentation in giant molecular clouds? Furthermore, open cluster groups and complexes could affect Galactic dynamics and should be considered in investigations and simulations on the dynamical processes, such as radial migration, disc heating, differential rotation, kinematic resonances, and spiral structure. In the past decade there were a few studies on open cluster pairs (de La Fuente Marcos \& de La Fuente Marcos 2009a,b,c) and on open cluster groups and complexes (Piskunov et al. 2006). The former only considered spatial proximity for the identification of the pairs, while the latter also required tangential velocities to be similar for the members. In this work I used the full set of 6D phase-space information to draw a more detailed picture on these structures. For this purpose I utilised the most homogeneous cluster catalogue available, namely the Catalogue of Open Cluster Data (COCD; Kharchenko et al. 2005a,b), which contains parameters for 650 open clusters and compact associations, as well as for their uniformly selected members. Additional radial velocity (RV) and metallicity ([M/H]) information on the members were obtained from the RAdial Velocity Experiment (RAVE; Steinmetz et al. 2006; Kordopatis et al. 2013) for 110 and 81 clusters, respectively. The RAVE sample was cleaned considering quality parameters and flags provided by RAVE (Matijevič et al. 2012; Kordopatis et al. 2013). To ensure that only real members were included for the mean values, also the cluster membership, as provided by Kharchenko et al. (2005a,b), was considered for the stars cross-matched in RAVE. 6D phase-space information could be derived for 432 out of the 650 COCD objects and I used an adaption of the Friends-of-Friends algorithm, as used in cosmology, to identify potential groupings. The vast majority of the 19 identified groupings were pairs, but I also found four groups of 4-5 members and one complex with 15 members. For the verification of the identified structures, I compared the results to a randomly selected subsample of the catalogue for the Milky Way global survey of Star Clusters (MWSC; Kharchenko et al. 2013), which became available recently, and was used as reference sample. Furthermore, I implemented Monte-Carlo simulations with randomised samples created from two distinguished input distributions for the spatial and velocity parameters. On the one hand, assuming a uniform distribution in the Galactic disc and, on the other hand, assuming the COCD data distributions to be representative for the whole open cluster population. The results suggested that the majority of identified pairs are rather by chance alignments, but the groups and the complex seemed to be genuine. A comparison of my results to the pairs, groups and complexes proposed in the literature yielded a partial overlap, which was most likely because of selection effects and different parameters considered. This is another verification for the existence of such structures. The characteristics of the found groupings favour that members of an open cluster grouping originate from a common giant molecular cloud and formed in a single, but possibly sequential, star formation event. Moreover, the fact that the young open cluster population showed smaller spatial separations between nearest neighbours than the old cluster population indicated that the lifetime of open cluster groupings is most likely comparable to that of the Galactic open cluster population itself. Still even among the old open clusters I could identify groupings, which suggested that the detected structure could be in some cases more long lived as one might think. In this thesis I could only present a pilot study on structures in the Galactic open cluster population, since the data sample used was highly incomplete. For further investigations a far more complete sample would be required. One step in this direction would be to use data from large current surveys, like SDSS, RAVE, Gaia-ESO and VVV, as well as including results from studies on individual clusters. Later the sample can be completed by data from upcoming missions, like Gaia and 4MOST. Future studies using this more complete open cluster sample will reveal the effect of open cluster groupings on star formation theory and their significance for the kinematics, dynamics and evolution of the Milky Way, and thereby of spiral galaxies.},
  language  = {en}
}
@phdthesis{Lange2014,
  author    = {Lange, Ilja},
  title     = {Energetische Struktur von Schichten organischer Halbleiter und ihr fundamentaler Einfluss auf die physikalischen Eigenschaften organischer elektronischer Bauteile},
  school      = {Universit{\"a}t Potsdam},
  pages     = {105},
  year      = {2014},
  language  = {de}
}
@phdthesis{Balzer2014,
  author    = {Balzer, Arnim},
  title     = {Crab flare observations with H.E.S.S. phase II},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-72545},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {The H.E.S.S. array is a third generation Imaging Atmospheric Cherenkov Telescope (IACT) array. It is located in the Khomas Highland in Namibia, and measures very high energy (VHE) gamma-rays. In Phase I, the array started data taking in 2004 with its four identical 13 m telescopes. Since then, H.E.S.S. has emerged as the most successful IACT experiment to date. Among the almost 150 sources of VHE gamma-ray radiation found so far, even the oldest detection, the Crab Nebula, keeps surprising the scientific community with unexplained phenomena such as the recently discovered very energetic flares of high energy gamma-ray radiation. During its most recent flare, which was detected by the Fermi satellite in March 2013, the Crab Nebula was simultaneously observed with the H.E.S.S. array for six nights. The results of the observations will be discussed in detail during the course of this work. During the nights of the flare, the new 24 m × 32 m H.E.S.S. II telescope was still being commissioned, but participated in the data taking for one night. To be able to reconstruct and analyze the data of the H.E.S.S. Phase II array, the algorithms and software used by the H.E.S.S. Phase I array had to be adapted. The most prominent advanced shower reconstruction technique developed by de Naurois and Rolland, the template-based model analysis, compares real shower images taken by the Cherenkov telescope cameras with shower templates obtained using a semi-analytical model. To find the best fitting image, and, therefore, the relevant parameters that describe the air shower best, a pixel-wise log-likelihood fit is done. The adaptation of this advanced shower reconstruction technique to the heterogeneous H.E.S.S. Phase II array for stereo events (i.e. air showers seen by at least two telescopes of any kind), its performance using MonteCarlo simulations as well as its application to real data will be described.},
  language  = {en}
}
@phdthesis{Fischer2014,
  author    = {Fischer, Jost Leonhardt},
  title     = {Nichtlineare Kopplungsmechanismen akustischer Oszillatoren am Beispiel der Synchronisation von Orgelpfeifen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71975},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {In dieser Arbeit werden nichtlineare Kopplungsmechanismen von akustischen Oszillatoren untersucht, die zu Synchronisation f{\"u}hren k{\"o}nnen. Aufbauend auf die Fragestellungen vorangegangener Arbeiten werden mit Hilfe theoretischer und experimenteller Studien sowie mit Hilfe numerischer Simulationen die Elemente der Tonentstehung in der Orgelpfeife und die Mechanismen der gegenseitigen Wechselwirkung von Orgelpfeifen identifiziert. Daraus wird erstmalig ein vollst{\"a}ndig auf den aeroakustischen und fluiddynamischen Grundprinzipien basierendes nichtlinear gekoppeltes Modell selbst-erregter Oszillatoren f{\"u}r die Beschreibung des Verhaltens zweier wechselwirkender Orgelpfeifen entwickelt. Die durchgef{\"u}hrten Modellrechnungen werden mit den experimentellen Befunden verglichen. Es zeigt sich, dass die Tonentstehung und die Kopplungsmechanismen von Orgelpfeifen durch das entwickelte Oszillatormodell in weiten Teilen richtig beschrieben werden. Insbesondere kann damit die Ursache f{\"u}r den nichtlinearen Zusammenhang von Kopplungsst{\"a}rke und Synchronisation des gekoppelten Zwei-Pfeifen Systems, welcher sich in einem nichtlinearen Verlauf der Arnoldzunge darstellt, gekl{\"a}rt werden. Mit den gewonnenen Erkenntnissen wird der Einfluss des Raumes auf die Tonentstehung bei Orgelpfeifen betrachtet. Daf{\"u}r werden numerische Simulationen der Wechselwirkung einer Orgelpfeife mit verschiedenen Raumgeometrien, wie z. B. ebene, konvexe, konkave, und gezahnte Geometrien, exemplarisch untersucht. Auch der Einfluss von Schwellk{\"a}sten auf die Tonentstehung und die Klangbildung der Orgelpfeife wird studiert. In weiteren, neuartigen Synchronisationsexperimenten mit identisch gestimmten Orgelpfeifen, sowie mit Mixturen wird die Synchronisation f{\"u}r verschiedene, horizontale und vertikale Pfeifenabst{\"a}nde in der Ebene der Schallabstrahlung, untersucht. Die dabei erstmalig beobachteten r{\"a}umlich isotropen Unstetigkeiten im Schwingungsverhalten der gekoppelten Pfeifensysteme, deuten auf abstandsabh{\"a}ngige Wechsel zwischen gegen- und gleichphasigen Sychronisationsregimen hin. Abschließend wird die M{\"o}glichkeit dokumentiert, das Ph{\"a}nomen der Synchronisation zweier Orgelpfeifen durch numerische Simulationen, also der Behandlung der kompressiblen Navier-Stokes Gleichungen mit entsprechenden Rand- und Anfangsbedingungen, realit{\"a}tsnah abzubilden. Auch dies stellt ein Novum dar.},
  language  = {de}
}
@phdthesis{Holler2014,
  author    = {Holler, Markus},
  title     = {Photon reconstruction for the H.E.S.S. 28 m telescope and analysis of Crab Nebula and galactic centre observations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-72099},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {In the presented thesis, the most advanced photon reconstruction technique of ground-based γ-ray astronomy is adapted to the H.E.S.S. 28 m telescope. The method is based on a semi-analytical model of electromagnetic particle showers in the atmosphere. The properties of cosmic γ-rays are reconstructed by comparing the camera image of the telescope with the Cherenkov emission that is expected from the shower model. To suppress the dominant background from charged cosmic rays, events are selected based on several criteria. The performance of the analysis is evaluated with simulated events. The method is then applied to two sources that are known to emit γ-rays. The first of these is the Crab Nebula, the standard candle of ground-based γ-ray astronomy. The results of this source confirm the expected performance of the reconstruction method, where the much lower energy threshold compared to H.E.S.S. I is of particular importance. A second analysis is performed on the region around the Galactic Centre. The analysis results emphasise the capabilities of the new telescope to measure γ-rays in an energy range that is interesting for both theoretical and experimental astrophysics. The presented analysis features the lowest energy threshold that has ever been reached in ground-based γ-ray astronomy, opening a new window to the precise measurement of the physical properties of time-variable sources at energies of several tens of GeV.},
  language  = {en}
}
@phdthesis{Goldshteyn2014,
  author    = {Goldshteyn, Jewgenij},
  title     = {Frequency-resolved ultrafast dynamics of phonon polariton wavepackets in the ferroelectric crystals LiNbO₃ and LiTaO₃},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-71623},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {During this work I built a four wave mixing setup for the time-resolved femtosecond spectroscopy of Raman-active lattice modes. This setup enables to study the selective excitation of phonon polaritons. These quasi-particles arise from the coupling of electro-magnetic waves and transverse optical lattice modes, the so-called phonons. The phonon polaritons were investigated in the optically non-linear, ferroelectric crystals LiNbO₃ and LiTaO₃. The direct observation of the frequency shift of the scattered narrow bandwidth probe pulses proofs the role of the Raman interaction during the probe and excitation process of phonon polaritons. I compare this experimental method with the measurement where ultra-short laser pulses are used. The frequency shift remains obscured by the relative broad bandwidth of these laser pulses. In an experiment with narrow bandwidth probe pulses, the Stokes and anti-Stokes intensities are spectrally separated. They are assigned to the corresponding counter-propagating wavepackets of phonon polaritons. Thus, the dynamics of these wavepackets was separately studied. Based on these findings, I develop the mathematical description of the so-called homodyne detection of light for the case of light scattering from counter propagating phonon polaritons. Further, I modified the broad bandwidth of the ultra-short pump pulses using bandpass filters to generate two pump pulses with non-overlapping spectra. This enables the frequency-selective excitation of polariton modes in the sample, which allows me to observe even very weak polariton modes in LiNbO₃ or LiTaO₃ that belong to the higher branches of the dispersion relation of phonon polaritons. The experimentally determined dispersion relation of the phonon polaritons could therefore be extended and compared to theoretical models. In addition, I determined the frequency-dependent damping of phonon polaritons.},
  language  = {en}
}
@phdthesis{Trabant2014,
  author    = {Trabant, Christoph},
  title     = {Ultrafast photoinduced phase transitions in complex materials probed by time-resolved resonant soft x-ray diffraction},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71377},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {In processing and data storage mainly ferromagnetic (FM) materials are being used. Approaching physical limits, new concepts have to be found for faster, smaller switches, for higher data densities and more energy efficiency. Some of the discussed new concepts involve the material classes of correlated oxides and materials with antiferromagnetic coupling. Their applicability depends critically on their switching behavior, i.e., how fast and how energy efficient material properties can be manipulated. This thesis presents investigations of ultrafast non-equilibrium phase transitions on such new materials. In transition metal oxides (TMOs) the coupling of different degrees of freedom and resulting low energy excitation spectrum often result in spectacular changes of macroscopic properties (colossal magneto resistance, superconductivity, metal-to-insulator transitions) often accompanied by nanoscale order of spins, charges, orbital occupation and by lattice distortions, which make these material attractive. Magnetite served as a prototype for functional TMOs showing a metal-to-insulator-transition (MIT) at T = 123 K. By probing the charge and orbital order as well as the structure after an optical excitation we found that the electronic order and the structural distortion, characteristics of the insulating phase in thermal equilibrium, are destroyed within the experimental resolution of 300 fs. The MIT itself occurs on a 1.5 ps timescale. It shows that MITs in functional materials are several thousand times faster than switching processes in semiconductors. Recently ferrimagnetic and antiferromagnetic (AFM) materials have become interesting. It was shown in ferrimagnetic GdFeCo, that the transfer of angular momentum between two opposed FM subsystems with different time constants leads to a switching of the magnetization after laser pulse excitation. In addition it was theoretically predicted that demagnetization dynamics in AFM should occur faster than in FM materials as no net angular momentum has to be transferred out of the spin system. We investigated two different AFM materials in order to learn more about their ultrafast dynamics. In Ho, a metallic AFM below T ≈ 130 K, we found that the AFM Ho can not only be faster but also ten times more energy efficiently destroyed as order in FM comparable metals. In EuTe, an AFM semiconductor below T ≈ 10 K, we compared the loss of magnetization and laser-induced structural distortion in one and the same experiment. Our experiment shows that they are effectively disentangled. An exception is an ultrafast release of lattice dynamics, which we assign to the release of magnetostriction. The results presented here were obtained with time-resolved resonant soft x-ray diffraction at the Femtoslicing source of the Helmholtz-Zentrum Berlin and at the free-electron laser in Stanford (LCLS). In addition the development and setup of a new UHV-diffractometer for these experiments will be reported.},
  language  = {en}
}
@article{FoertigKniepertGlueckeretal.2014,
  author    = {Foertig, Alexander and Kniepert, Juliane and Gluecker, Markus and Brenner, Thomas J. K. and Dyakonov, Vladimir and Neher, Dieter and Deibel, Carsten},
  title     = {Nongeminate and geminate recombination in PTB7: PCBM solar cells},
  series = {Advanced functional materials},
  volume    = {24},
  journal   = {Advanced functional materials},
  number    = {9},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1616-301X},
  doi       = {10.1002/adfm.201302134},
  pages     = {1306 -- 1311},
  year      = {2014},
  language  = {en}
}
@article{RolandSchubertCollinsetal.2014,
  author    = {Roland, Steffen and Schubert, Marcel and Collins, Brian A. and Kurpiers, Jona and Chen, Zhihua and Facchetti, Antonio and Ade, Harald W. and Neher, Dieter},
  title     = {Fullerene-free polymer solar cells with highly reduced bimolecular recombination and field-independent charge carrier generation},
  series = {The journal of physical chemistry letters},
  volume    = {5},
  journal   = {The journal of physical chemistry letters},
  number    = {16},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1948-7185},
  doi       = {10.1021/jz501506z},
  pages     = {2815 -- 2822},
  year      = {2014},
  abstract  = {Photogeneration, recombination, and transport of free charge carriers in all-polymer bulk heterojunction solar cells incorporating poly(3-hexylthiophene) (P3HT) as donor and poly([N,N'-bis(2-octyldodecyl)-naphthelene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as acceptor polymer have been investigated by the use of time delayed collection field (TDCF) and time-of-flight (TOF) measurements. Depending on the preparation procedure used to dry the active layers, these solar cells comprise high fill factors (FFs) of up to 67\%. A strongly reduced bimolecular recombination (BMR), as well as a field-independent free charge carrier generation are observed, features that are common to high performance fullerene-based solar cells. Resonant soft X-ray measurements (R-SoXS) and photoluminescence quenching experiments (PQE) reveal that the BMR is related to domain purity. Our results elucidate the similarities of this polymeric acceptor with the superior recombination properties of fullerene acceptors.},
  language  = {en}
}
@article{SteyrleuthnerDiPietroCollinsetal.2014,
  author    = {Steyrleuthner, Robert and Di Pietro, Riccardo and Collins, Brian A. and Polzer, Frank and Himmelberger, Scott and Schubert, Marcel and Chen, Zhihua and Zhang, Shiming and Salleo, Alberto and Ade, Harald W. and Facchetti, Antonio and Neher, Dieter},
  title     = {The Role of Regioregularity, Crystallinity, and Chain Orientation on Electron Transport in a High-Mobility n-Type Copolymer},
  series = {Journal of the American Chemical Society},
  volume    = {136},
  journal   = {Journal of the American Chemical Society},
  number    = {11},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0002-7863},
  doi       = {10.1021/ja4118736},
  pages     = {4245 -- 4256},
  year      = {2014},
  language  = {en}
}