TY - GEN A1 - Schimka, Selina A1 - Lomadze, Nino A1 - Rabe, Maren A1 - Kopyshev, Alexey A1 - Lehmann, Maren A1 - von Klitzing, Regine A1 - Rumyantsev, Artem M. A1 - Kramarenko, Elena Yu. A1 - Santer, Svetlana T1 - Photosensitive microgels containing azobenzene surfactants of different charges T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - We report on light sensitive microgel particles that can change their volume reversibly in response to illumination with light of different wavelengths. To make the anionic microgels photosensitive we add surfactants with a positively charged polyamine head group and an azobenzene containing tail. Upon illumination, azobenzene undergoes a reversible photo-isomerization reaction from a trans- to a cis-state accompanied by a change in the hydrophobicity of the surfactant. Depending on the isomerization state, the surfactant molecules are either accommodated within the microgel (trans-state) resulting in its shrinkage or desorbed back into water (cis-isomer) letting the microgel swell. We have studied three surfactants differing in the number of amino groups, so that the number of charges of the surfactant head varies between 1 and 3. We have found experimentally and theoretically that the surfactant concentration needed for microgel compaction increases with decreasing number of charges of the head group. Utilization of polyamine azobenzene containing surfactants for the light triggered remote control of the microgel size opens up a possibility for applications of light responsive microgels as drug carriers in biology and medicine. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 461 KW - ph-responsive microgels KW - co-monomer content KW - drug-delivery KW - photoresponsive surfactants KW - metal nanoparticles KW - swelling behavior KW - temperature KW - particles KW - collapse KW - hydrogels Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413528 SN - 1866-8372 IS - 461 ER - TY - JOUR A1 - Malyar, Ivan V. A1 - Gorin, Dmitry A. A1 - Santer, Svetlana A1 - Stetsyura, Svetlana V. T1 - Photo-assisted adsorption of gold nanoparticles onto a silicon substrate JF - Applied physics letters N2 - We report on a photo-assisted adsorption of gold nanoparticles on a silicon substrate studied using atomic-force microscopy and secondary ion mass-spectrometry. Depending on a silicon conductivity type (n-Si or p-Si), the amount of photo-assisted adsorbed gold nanoparticles either increases (n-Si) or decreases (p-Si) on irradiation. In addition, the impacts of a cationic polyelectrolyte monolayer and adsorption time were also revealed. The polyelectrolyte layer enhances the adsorption of the gold nanoparticles but decreases the influence of light. The results of the photo-assisted adsorption on two types of silicon wafer were explained by electron processes at the substrate/solution interface. This work was supported by the German-Russian Interdisciplinary Science Center (G-RISC) funded by the German Federal Foreign Office via the German Academic Exchange Service (DAAD), Project No. P-2014b-1, and Russian foundation for basic research, Project No. 16-08-00524_a. Y1 - 2017 U6 - https://doi.org/10.1063/1.4979082 SN - 0003-6951 SN - 1077-3118 VL - 110 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Hintsche, Marius A1 - Waljor, Veronika A1 - Grossmann, Robert A1 - Kühn, Marco J. A1 - Thormann, Kai M. A1 - Peruani, Fernando A1 - Beta, Carsten T1 - A polar bundle of flagella can drive bacterial swimming by pushing, pulling, or coiling around the cell body JF - Scientific reports N2 - Bacteria swim in sequences of straight runs that are interrupted by turning events. They drive their swimming locomotion with the help of rotating helical flagella. Depending on the number of flagella and their arrangement across the cell body, different run-and-turn patterns can be observed. Here, we present fluorescence microscopy recordings showing that cells of the soil bacterium Pseudomonas putida that are decorated with a polar tuft of helical flagella, can alternate between two distinct swimming patterns. On the one hand, they can undergo a classical push-pull-push cycle that is well known from monopolarly flagellated bacteria but has not been reported for species with a polar bundle of multiple flagella. Alternatively, upon leaving the pulling mode, they can enter a third slow swimming phase, where they propel themselves with their helical bundle wrapped around the cell body. A theoretical estimate based on a random-walk model shows that the spreading of a population of swimmers is strongly enhanced when cycling through a sequence of pushing, pulling, and wrapped flagellar configurations as compared to the simple push-pull-push pattern. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-16428-9 SN - 2045-2322 VL - 7 PB - Macmillan Publishers Limited, part of Springer Nature CY - London ER - TY - THES A1 - Leonhardt, Helmar T1 - Chemotaxis, shape and adhesion dynamics of amoeboid cells studied by impedance fluctuations in open and confined spaces T1 - Chemotaxis, Formänderung und Adhäsionsdynamik amöboider Zellen gemessen durch Impedanzfluktuation N2 - Die vorliegende Arbeit befasst sich mit elektrischen Impedanzmessungen von ameoboiden Zellen auf Mikroelektroden. Der Modellorganismus Dictyostelium discoideum zeigt unter der Bedingung des Nahrungsentzugs einen Übergang zum kollektiven Verhalten, bei dem sich chemotaktische Zellen zu einem multizellulären Aggregat zusammenschliessen. Wir zeigen wie Impedanzaufnahmen über die Dynamik der Zell-substrat Adhäsion ein präzises Bild der Phasen der Aggregation liefern. Darüberhinaus zeigen wir zum ersten mal systematische Einzelzellmessungen von Wildtyp-Zellen und vier Mutanten, die sich in der Stärke der Substratadh äsion unterscheiden. Wir zeichneten die projizierte Zellfläche durch Zeitverlaufsmikroskopie auf und fanden eine Korrelation zwischen den quasi-periodischen Oszillationen in der Kinetik der projizierten Fläche - der Zellform-Oszillation - und dem Langzeittrend des Impedanzsignals. Amoeboidale Motilität offenbart sich typischerweise durch einen Zyklus von Membranausstülpung, Substratadhäsion, Vorwärtsziehen des Zellkörpers und Einziehen des hinteren Teils der Zelle. Dieser Motilitätszyklus resultiert in quasi-periodischen Oszillationen der projizierten Zellfläche und der Impedanz. In allen gemessenen Zelllinien wurden für diesen Zyklus ähnliche Periodendauern beobachtet trotz der Unterschiede in der Anhaftungsstärke. Wir beobachteten, dass die Stärke der Zell-substrat Anhaftung die Impedanz stark beeinflusst, indem die Abweichungen vom Mittelwert (die Grösse der Fluktuationen) vergrössert sind bei Zellen, die die vom Zytoskelett generierten Kräfte effektiv auf das Substrat übertragen. Zum Beispiel sind bei talA- Zellen, in welchen das Actin verankernde Protein Talin fehlt, die Fluktuationen stark reduziert. Einzelzellkraft-Spektroskopie und Ergebnisse eines Ablösungsassays, bei dem Adhäsionskraft gemessen wird indem Zellen einer Scherspannung ausgesetzt werden, bestätigen, dass die Grösse der Impedanz-fluktuationen ein korrektes Mass für die Stärke der Substratadhäsion ist. Schliesslich haben wir uns auch mit dem Einbau von Zell-substrat-Impedanz-Sensoren in mikro-fluidische Apparaturen befasst. Ein chip-basierter elektrischer Chemotaxis Assay wurde entwickelt, der die Geschwindigkeit chemotaktischer Zellen misst, welche entlang eines chemischen Konzentrationsgradienten über Mikroelektroden wandern. N2 - We present electrical impedance measurements of amoeboid cells on microelectrodes. The model organism Dictyostelium discoideum shows under starvation conditions a transition to collective behavior when chemotactic cells collect in multicellular aggregates. We show how impedance recordings give a precise picture of the stages of aggregation by tracing the dynamics of cell-substrate adhesion. Furthermore, we present for the first time systematic single cell measurements of wild type cells and four mutant strains that differ in their substrate adhesion strength. We recorded the projected cell area by time lapse microscopy and found a correlation between quasi-periodic oscillations in the kinetics of the projected area - the cell shape oscillation - and the long-term trend in the impedance signal. Typically, amoeboid motility advances via a cycle of membrane protrusion, substrate adhesion, traction of the cell body and tail retraction. This motility cycle results in the quasi-periodic oscillations of the projected cell area and the impedance. In all cell lines measured, similar periods were observed for this cycle, despite the differences in attachment strength. We observed that cell-substrate attachment strength strongly affects the impedance in that the deviations from mean (the magnitude of fluctuations) are enhanced in cells that effectively transmit forces, generated by the cytoskeleton, to the substrate. For example, in talA- cells, which lack the actin anchoring protein talin, the fluctuations are strongly reduced. Single cell force spectroscopy and results from a detachment assay, where adhesion is measured by exposing cells to shear stress, confirm that the magnitude of impedance fluctuations is a correct measure for the strength of substrate adhesion. Finally, we also worked on the integration of cell-substrate impedance sensors into microfluidic devices. A chip-based electrical chemotaxis assay is designed which measures the speed of chemotactic cells migrating over microelectrodes along a chemical concentration gradient. KW - ECIS KW - cell-substrate adhesion KW - cell movement KW - electrical chemotaxis assay KW - ECIS KW - Zell-substrat Adhäsion KW - Zell Bewegung KW - elektrischer Chemotaxis Assy Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-405016 ER - TY - THES A1 - Schürmann, Robin Mathis T1 - Interaction of the potential DNA-radiosensitizer 8-bromoadenine with free and plasmonically generated electrons T1 - Wechselwikung des potentiellen DNA-Radiosensibilisators 8-Bromoadenin mit freien und plasmonisch erzeugten Elektronen N2 - In Germany more than 200.000 persons die of cancer every year, which makes it the second most common cause of death. Chemotherapy and radiation therapy are often combined to exploit a supra-additive effect, as some chemotherapeutic agents like halogenated nucleobases sensitize the cancerous tissue to radiation. The radiosensitizing action of certain therapeutic agents can be at least partly assigned to their interaction with secondary low energy electrons (LEEs) that are generated along the track of the ionizing radiation. In the therapy of cancer DNA is an important target, as severe DNA damage like double strand breaks induce the cell death. As there is only a limited number of radiosensitizing agents in clinical practice, which are often strongly cytotoxic, it would be beneficial to get a deeper understanding of the interaction of less toxic potential radiosensitizers with secondary reactive species like LEEs. Beyond that LEEs can be generated by laser illuminated nanoparticles that are applied in photothermal therapy (PTT) of cancer, which is an attempt to treat cancer by an increase of temperature in the cells. However, the application of halogenated nucleobases in PTT has not been taken into account so far. In this thesis the interaction of the potential radiosensitizer 8-bromoadenine (8BrA) with LEEs was studied. In a first step the dissociative electron attachment (DEA) in the gas phase was studied in a crossed electron-molecular beam setup. The main fragmentation pathway was revealed as the cleavage of the C-Br bond. The formation of a stable parent anion was observed for electron energies around 0 eV. Furthermore, DNA origami nanostructures were used as platformed to determine electron induced strand break cross sections of 8BrA sensitized oligonucleotides and the corresponding nonsensitized sequence as a function of the electron energy. In this way the influence of the DEA resonances observed for the free molecules on the DNA strand breaks was examined. As the surrounding medium influences the DEA, pulsed laser illuminated gold nanoparticles (AuNPs) were used as a nanoscale electron source in an aqueous environment. The dissociation of brominated and native nucleobases was tracked with UV-Vis absorption spectroscopy and the generated fragments were identified with surface enhanced Raman scattering (SERS). Beside the electron induced damage, nucleobase analogues are decomposed in the vicinity of the laser illuminatednanoparticles due to the high temperatures. In order to get a deeper understanding of the different dissociation mechanisms, the thermal decomposition of the nucleobases in these systems was studied and the influence of the adsorption kinetics of the molecules was elucidated. In addition to the pulsed laser experiments, a dissociative electron transfer from plasmonically generated ”hot electrons” to 8BrA was observed under low energy continuous wave laser illumination and tracked with SERS. The reaction was studied on AgNPs and AuNPs as a function of the laser intensity and wavelength. On dried samples the dissociation of the molecule was described by fractal like kinetics. In solution, the dissociative electron transfer was observed as well. It turned out that the timescale of the reaction rates were slightly below typical integration times of Raman spectra. In consequence such reactions need to be taken into account in the interpretation of SERS spectra of electrophilic molecules. The findings in this thesis help to understand the interaction of brominated nucleobases with plasmonically generated electrons and free electrons. This might help to evaluate the potential radiosensitizing action of such molecules in cancer radiation therapy and PTT. N2 - Mit deutschlandweit über 200.000 Todesfällen pro Jahr ist Krebs die zweithäufigste Todesursache. In der Krebstherapie werden häufig Strahlenund Chemotherapie kombiniert, da das Krebsgewebe durch die Gabe bestimmter Chemotherapeutika, z.B. halogenierte Nukleinbasen, gegenüber ionisierender Strahlung sensibilisiert wird. Die Wirkung dieser sogenannten Radiosensibilatoren lässt sich zumindest teilweise auf ihre Wechselwirkung mit niederenergetischen Elektronen zurückführen, welche in hoher Zahl entlang der Trajektorie hochenergetischer Teilchen oder Photonen erzeugt werden. In der Krebstherapie ist die DNA ein wichtiger Angriffspunkt, da schwere DNA-Schäden wie Doppelstrangbrüche zum Zelltod führen können. In der klinischen Praxis ist die Anzahl der eingesetzten meist zytotoxischen Radiosensibilisatoren relativ begrenzt. Zur Verbesserung der bestehenden Therapien durch den Einsatz von Medikamenten mit geringeren Nebenwirkungen, ist es notwendig die Wechselwirkungen zwischen potentiellen Radiosensibilisatoren und reaktiven Sekundärteilchen wie niederenergetischen Elektronen besser zu verstehen. Neben der Strahlentherapie werden niederenergetische Elektronen auch durch Laserbestrahlung von plasmonischen Nanopartikeln erzeugt, welche in der Photothermaltherapie (PTT) Anwendung finden. Die mögliche Anwendung von halogenierten Nukleinbasen zur Verbesserung der Photothermaltherapie ist jedoch bisher noch nicht in Erwägung gezogen worden. Im Rahmen dieser kumulativen Dissertation wird die Wechselwirkung des potentiellen Radiosensibilisators 8-Bromoadenin (8BrA) mit niederenergetischen Elektronen untersucht. Unter Verwendung eines gekreuzten Molekül-Elektronenstrahls wurde in einem ersten Schritt die dissoziative Elektronenanlagerung (DEA) an 8BrA untersucht. Dabei zeigte sich, dass der Hauptzerfallskanal in dem Aufbrechen der C-Br Bindung besteht. Darüberhinausgehend wurde bei der Anlagerung von Elektronen mit einer Energie von 0 eV ein stabiles 8BrA Anion beobachtet. Um den Einfluss der DEA-Resonanzen, die für freie Moleküle in der Gasphase beobachtet wurden, auf die elektroneninduzierten DNA-Strangbrüche zu untersuchen wurden DNA- Origami-Nanostrukturen mit Elektronen bestrahlt. Die DNAOrigami-Strukturen wurden sowohl mit 8BrA modifizierten Oligonukleotiden und der nicht modifizierten Kontrollsequenz bestückt und die Strangbruch Wirkungsquerschnitte in Abhängigkeit von der Elektronenenergie bestimmt. DEA-Prozesse hängen stark von dem umgebenden Medium ab. Aus diesem Grund wurden laserbestrahlte Gold-Nanopartikel (AuNPs) als Elektronenquellen auf der Nanoebene verwendet. Der Zerfall von bromierten und unmodifizierten Nukleinbasen wurde mit UV-Vis-Absorptions-Spektroskopie verfolgt, während die Identifizierung der entstandenen Fragmente über Oberflächenverstärkte Ramanstreuung (SERS) erfolgte. Neben dem elektroneninduzierten Schaden, werden die Nukleinbasen in der Umgebung der AuNPs durch die hohen Temperaturen auch thermisch zersetzt. Um diese verschiedenen Prozesse auseinander halten zu können, wurde die thermische Zersetzung auf den laserbestrahlten AuNPs detailliert untersucht und der Einfluss der Adsorptionskinetik herausgearbeitet. Elektroneninduzierte Reaktionen auf Nanopartikeln finden nicht nur bei Bestrahlung mit intensiven Laser-Pulsen statt. Ein dissoziativer Elektronentransfer auf 8BrA, der zum Aufbrechen der C-Br Bindung führt, konnte ebenfalls während der Bestrahlung mit einem kontinuierlichen Laser geringer Intensität mit SERS beobachtet werden. Mit Hilfe von fraktaler Kinetik konnten dabei die Reaktionen auf getrockneten Proben beschrieben werden. Auf diese Art wurde die Reaktion sowohl auf AuNPs als auch auf AgNPs als Funktion der Laserintensität und -Wellenlänge untersucht. Ebenfalls in Lösung konnte das Auftrennen der C-Br Bindung beobachtet werden, wobei die Zeitskalen der Reaktion ein wenig kürzer als die typischen Integrationszeiten bei Ramanmessungen waren. Aus diesem Grund müssen Dissoziative-ElektronenTransfer- Reaktionen bei der Interpretation von SERS Spektren mit in Betracht gezogen werden. Die Ergebnisse dieser kumulativen Doktorarbeit fördern das Verständnis der Wechselwirkungen zwischen bromierten Nukleinbasen mit freien und plasmonisch erzeugten Elektronen. Dies könnte dabei helfen das Potential von 8BrA als möglicher Radiosensibilisator besser beurteilen zu können. KW - DNA damage KW - Radiosensitization KW - dissociative electron attachment KW - nanoparticles KW - plasmonic catalysis KW - DNA-Schädigung KW - dissoziative Elektronen Anlagerung KW - Nanopartikel KW - plasmonische Katalyse Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-407017 ER - TY - JOUR A1 - Smirnov, Lev A. A1 - Osipov, Grigory V. A1 - Pikovskij, Arkadij T1 - Chimera patterns in the Kuramoto-Battogtokh model JF - Journal of physics : A, Mathematical and theoretical N2 - Kuramoto and Battogtokh (2002 Nonlinear Phenom. Complex Syst. 5 380) discovered chimera states represented by stable coexisting synchrony and asynchrony domains in a lattice of coupled oscillators. After a reformulation in terms of a local order parameter, the problem can be reduced to partial differential equations. We find uniformly rotating, spatially periodic chimera patterns as solutions of a reversible ordinary differential equation, and demonstrate a plethora of such states. In the limit of neutral coupling they reduce to analytical solutions in the form of one-and two-point chimera patterns as well as localized chimera solitons. Patterns at weakly attracting coupling are characterized by virtue of a perturbative approach. Stability analysis reveals that only the simplest chimeras with one synchronous region are stable. KW - nonlocal coupled oscillators KW - chimera state KW - coarse-grained order parameter KW - Ott-Antonsen reduction KW - perturbation approach KW - linear stability analysis Y1 - 2017 U6 - https://doi.org/10.1088/1751-8121/aa55f1 SN - 1751-8113 SN - 1751-8121 VL - 50 IS - 8 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Bolotov, Maxim I. A1 - Smirnov, Lev A. A1 - Osipov, Grigory V. A1 - Pikovskij, Arkadij T1 - Breathing chimera in a system of phase oscillators JF - JETP Letters N2 - Chimera states consisting of synchronous and asynchronous domains in a medium of nonlinearly coupled phase oscillators have been considered. Stationary inhomogeneous solutions of the Ott-Antonsen equation for a complex order parameter that correspond to fundamental chimeras have been constructed. The direct numerical simulation has shown that these structures under certain conditions are transformed to oscillatory (breathing) chimera regimes because of the development of instability. Y1 - 2017 U6 - https://doi.org/10.1134/S0021364017180059 SN - 0021-3640 SN - 1090-6487 VL - 106 SP - 393 EP - 399 PB - Pleiades Publ. CY - New York ER - TY - JOUR A1 - Safdari, Hadiseh A1 - Cherstvy, Andrey G. A1 - Chechkin, Aleksei V. A1 - Bodrova, Anna A1 - Metzler, Ralf T1 - Aging underdamped scaled Brownian motion BT - Ensemble- and time-averaged particle displacements, nonergodicity, and the failure of the overdamping approximation JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We investigate both analytically and by computer simulations the ensemble- and time-averaged, nonergodic, and aging properties of massive particles diffusing in a medium with a time dependent diffusivity. We call this stochastic diffusion process the (aging) underdamped scaled Brownian motion (UDSBM). We demonstrate how the mean squared displacement (MSD) and the time-averaged MSD of UDSBM are affected by the inertial term in the Langevin equation, both at short, intermediate, and even long diffusion times. In particular, we quantify the ballistic regime for the MSD and the time-averaged MSD as well as the spread of individual time-averaged MSD trajectories. One of the main effects we observe is that, both for the MSD and the time-averaged MSD, for superdiffusive UDSBM the ballistic regime is much shorter than for ordinary Brownian motion. In contrast, for subdiffusive UDSBM, the ballistic region extends to much longer diffusion times. Therefore, particular care needs to be taken under what conditions the overdamped limit indeed provides a correct description, even in the long time limit. We also analyze to what extent ergodicity in the Boltzmann-Khinchin sense in this nonstationary system is broken, both for subdiffusive and superdiffusive UDSBM. Finally, the limiting case of ultraslow UDSBM is considered, with a mixed logarithmic and power-law dependence of the ensemble-and time-averaged MSDs of the particles. In the limit of strong aging, remarkably, the ordinary UDSBM and the ultraslow UDSBM behave similarly in the short time ballistic limit. The approaches developed here open ways for considering other stochastic processes under physically important conditions when a finite particle mass and aging in the system cannot be neglected. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevE.95.012120 SN - 2470-0045 SN - 2470-0053 VL - 95 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Ramos, Antonio M. T. A1 - Builes-Jaramillo, Alejandro A1 - Poveda, German A1 - Goswami, Bedartha A1 - Macau, Elbert E. N. A1 - Kurths, Jürgen A1 - Marwan, Norbert T1 - Recurrence measure of conditional dependence and applications JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Identifying causal relations from observational data sets has posed great challenges in data-driven causality inference studies. One of the successful approaches to detect direct coupling in the information theory framework is transfer entropy. However, the core of entropy-based tools lies on the probability estimation of the underlying variables. Herewe propose a data-driven approach for causality inference that incorporates recurrence plot features into the framework of information theory. We define it as the recurrence measure of conditional dependence (RMCD), and we present some applications. The RMCD quantifies the causal dependence between two processes based on joint recurrence patterns between the past of the possible driver and present of the potentially driven, excepting the contribution of the contemporaneous past of the driven variable. Finally, it can unveil the time scale of the influence of the sea-surface temperature of the Pacific Ocean on the precipitation in the Amazonia during recent major droughts. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevE.95.052206 SN - 2470-0045 SN - 2470-0053 VL - 95 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Mahata, Khadak Singh A1 - Panday, Arnico Kumar A1 - Rupakheti, Maheswar A1 - Singh, Ashish A1 - Naja, Manish A1 - Lawrence, Mark T1 - Seasonal and diurnal variations in methane and carbon dioxide in the Kathmandu Valley in the foothills of the central Himalayas JF - Atmospheric Chemistry and Physics N2 - The SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley-Atmospheric Brown Clouds) international air pollution measurement campaign was carried out from December 2012 to June 2013 in the Kathmandu Valley and surrounding regions in Nepal. The Kathmandu Valley is a bowl-shaped basin with a severe air pollution problem. This paper reports measurements of two major greenhouse gases (GHGs), methane (CH4) and carbon dioxide (CO2), along with the pollutant CO, that began during the campaign and were extended for 1 year at the SusKat-ABC supersite in Bode, a semi-urban location in the Kathmandu Valley. Simultaneous measurements were also made during 2015 in Bode and a nearby rural site (Chanban) similar to 25 km (aerial distance) to the southwest of Bode on the other side of a tall ridge. The ambient mixing ratios of methane (CH4), carbon dioxide (CO2), water vapor, and carbon monoxide (CO) were measured with a cavity ring-down spectrometer (G2401; Picarro, USA) along with meteorological parameters for 1 year (March 2013-March 2014). These measurements are the first of their kind in the central Himalayan foothills. At Bode, the annual average mixing ratios of CO2 and CH4 were 419.3 (+/- 6.0) ppm and 2.192 (+/- 0.066) ppm, respectively. These values are higher than the levels observed at background sites such as Mauna Loa, USA (CO2: 396.8 +/- 2.0 ppm, CH4: 1.831 +/- 0.110 ppm) and Waliguan, China (CO2: 397.7 +/- 3.6 ppm, CH4: 1.879 +/- 0.009 ppm) during the same period and at other urban and semi-urban sites in the region, such as Ahmedabad and Shadnagar (India). They varied slightly across the seasons at Bode, with seasonal average CH4 mixing ratios of 2.157 (+/- 0.230) ppm in the pre-monsoon season, 2.199 (+/- 0.241) ppm in the monsoon, 2.210 (+/- 0.200) ppm in the post-monsoon, and 2.214 (+/- 0.209) ppm in the winter season. The average CO2 mixing ratios were 426.2 (+/- 25.5) ppm in the pre-monsoon, 413.5 (+/- 24.2) ppm in the monsoon, 417.3 (+/- 23.1) ppm in the postmonsoon, and 421.9 (+/- 20.3) ppm in the winter season. The maximum seasonal mean mixing ratio of CH4 in winter was only 0.057 ppm or 2.6% higher than the seasonal minimum during the pre-monsoon period, while CO2 was 12.8 ppm or 3.1% higher during the pre-monsoon period (seasonal maximum) than during the monsoon (seasonal minimum). On the other hand, the CO mixing ratio at Bode was 191% higher during the winter than during the monsoon season. The enhancement in CO2 mixing ratios during the pre-monsoon season is associated with additional CO2 emissions from forest fires and agro-residue burning in northern South Asia in addition to local emissions in the Kathmandu Valley. Published CO = CO2 ratios of different emission sources in Nepal and India were compared with the observed CO = CO2 ratios in this study. This comparison suggested that the major sources in the Kathmandu Valley were residential cooking and vehicle exhaust in all seasons except winter. In winter, brick kiln emissions were a major source. Simultaneous measurements in Bode and Chanban (15 July-3 October 2015) revealed that the mixing ratios of CO2, CH4, and CO were 3.8, 12, and 64% higher in Bode than Chanban. The Kathmandu Valley thus has significant emissions from local sources, which can also be attributed to its bowl-shaped geography that is conducive to pollution build-up. At Bode, all three gas species (CO2, CH4, and CO) showed strong diurnal patterns in their mixing ratios with a pronounced morning peak (ca. 08:00), a dip in the afternoon, and a gradual increase again through the night until the next morning. CH4 and CO at Chanban, however, did not show any noticeable diurnal variations. These measurements provide the first insights into the diurnal and seasonal variation in key greenhouse gases and air pollutants and their local and regional sources, which is important information for atmospheric research in the region. Y1 - 2017 U6 - https://doi.org/10.5194/acp-17-12573-2017 SN - 1680-7316 SN - 1680-7324 VL - 17 IS - 20 SP - 12573 EP - 12596 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Acero, F. A1 - Aloisio, R. A1 - Amans, J. A1 - Amato, Elena A1 - Antonelli, L. A. A1 - Aramo, C. A1 - Armstrong, T. A1 - Arqueros, F. A1 - Asano, Katsuaki A1 - Ashley, M. A1 - Backes, M. A1 - Balazs, C. A1 - Balzer, A. A1 - Bamba, Aya A1 - Barkov, Maxim A1 - Barrio, J. A. A1 - Benbow, Wystan A1 - Bernloehr, K. A1 - Beshley, V. A1 - Bigongiari, C. A1 - Biland, A. A1 - Bilinsky, A. A1 - Bissaldi, Elisabetta A1 - Biteau, J. A1 - Blanch, O. A1 - Blasi, P. A1 - Blazek, J. A1 - Boisson, C. A1 - Bonanno, G. A1 - Bonardi, A. A1 - Bonavolonta, C. A1 - Bonnoli, G. A1 - Braiding, C. A1 - Brau-Nogue, S. A1 - Bregeon, J. A1 - Brown, A. M. A1 - Bugaev, V. A1 - Bulgarelli, A. A1 - Bulik, T. A1 - Burton, Michael A1 - Burtovoi, A. A1 - Busetto, G. A1 - Bottcher, M. A1 - Cameron, R. A1 - Capalbi, M. A1 - Caproni, Anderson A1 - Caraveo, P. A1 - Carosi, R. A1 - Cascone, E. A1 - Cerruti, M. A1 - Chaty, Sylvain A1 - Chen, A. A1 - Chen, X. A1 - Chernyakova, M. A1 - Chikawa, M. A1 - Chudoba, J. A1 - Cohen-Tanugi, J. A1 - Colafrancesco, S. A1 - Conforti, V. A1 - Contreras, J. L. A1 - Costa, A. A1 - Cotter, G. A1 - Covino, Stefano A1 - Covone, G. A1 - Cumani, P. A1 - Cusumano, G. A1 - Daniel, M. A1 - Dazzi, F. A1 - De Angelis, A. A1 - De Cesare, G. A1 - De Franco, A. A1 - De Frondat, F. A1 - Dal Pino, E. M. de Gouveia A1 - De Lisio, C. A1 - Lopez, R. de los Reyes A1 - De Lotto, B. A1 - de Naurois, M. A1 - De Palma, F. A1 - Del Santo, M. A1 - Delgado, C. A1 - della Volpe, D. A1 - Di Girolamo, T. A1 - Di Giulio, C. A1 - Di Pierro, F. A1 - Di Venere, L. A1 - Doro, M. A1 - Dournaux, J. A1 - Dumas, D. A1 - Dwarkadas, Vikram V. A1 - Diaz, C. A1 - Ebr, J. A1 - Egberts, Kathrin A1 - Einecke, S. A1 - Elsaesser, D. A1 - Eschbach, S. A1 - Falceta-Goncalves, D. A1 - Fasola, G. A1 - Fedorova, E. A1 - Fernandez-Barral, A. A1 - Ferrand, Gilles A1 - Fesquet, M. A1 - Fiandrini, E. A1 - Fiasson, A. A1 - Filipovic, Miroslav D. A1 - Fioretti, V. A1 - Font, L. A1 - Fontaine, Gilles A1 - Franco, F. J. A1 - Freixas Coromina, L. A1 - Fujita, Yutaka A1 - Fukui, Y. A1 - Funk, S. A1 - Forster, A. A1 - Gadola, A. A1 - Lopez, R. Garcia A1 - Garczarczyk, M. A1 - Giglietto, N. A1 - Giordano, F. A1 - Giuliani, A. A1 - Glicenstein, J. A1 - Gnatyk, R. A1 - Goldoni, P. A1 - Grabarczyk, T. A1 - Graciani, R. A1 - Graham, J. A1 - Grandi, P. A1 - Granot, Jonathan A1 - Green, A. J. A1 - Griffiths, S. A1 - Gunji, S. A1 - Hakobyan, H. A1 - Hara, S. A1 - Hassan, T. A1 - Hayashida, M. A1 - Heller, M. A1 - Helo, J. C. A1 - Hinton, J. A1 - Hnatyk, B. A1 - Huet, J. A1 - Huetten, M. A1 - Humensky, T. B. A1 - Hussein, M. A1 - Horandel, J. A1 - Ikeno, Y. A1 - Inada, T. A1 - Inome, Y. A1 - Inoue, S. A1 - Inoue, T. A1 - Inoue, Y. A1 - Ioka, K. A1 - Iori, Maurizio A1 - Jacquemier, J. A1 - Janecek, P. A1 - Jankowsky, D. A1 - Jung, I. A1 - Kaaret, P. A1 - Katagiri, H. A1 - Kimeswenger, S. A1 - Kimura, Shigeo S. A1 - Knodlseder, J. A1 - Koch, B. A1 - Kocot, J. A1 - Kohri, K. A1 - Komin, N. A1 - Konno, Y. A1 - Kosack, K. A1 - Koyama, S. A1 - Kraus, Michaela A1 - Kubo, Hidetoshi A1 - Mezek, G. Kukec A1 - Kushida, J. A1 - La Palombara, N. A1 - Lalik, K. A1 - Lamanna, G. A1 - Landt, H. A1 - Lapington, J. A1 - Laporte, P. A1 - Lee, S. A1 - Lees, J. A1 - Lefaucheur, J. A1 - Lenain, J. -P. A1 - Leto, Giuseppe A1 - Lindfors, E. A1 - Lohse, T. A1 - Lombardi, S. A1 - Longo, F. A1 - Lopez, M. A1 - Lucarelli, F. A1 - Luque-Escamilla, Pedro Luis A1 - Lopez-Coto, R. A1 - Maccarone, M. C. A1 - Maier, G. A1 - Malaguti, G. A1 - Mandat, D. A1 - Maneva, G. A1 - Mangano, S. A1 - Marcowith, Alexandre A1 - Marti, J. A1 - Martinez, M. A1 - Martinez, G. A1 - Masuda, S. A1 - Maurin, G. A1 - Maxted, N. A1 - Melioli, Claudio A1 - Mineo, T. A1 - Mirabal, N. A1 - Mizuno, T. A1 - Moderski, R. A1 - Mohammed, M. A1 - Montaruli, T. A1 - Moralejo, A. A1 - Mori, K. A1 - Morlino, G. A1 - Morselli, A. A1 - Moulin, Emmanuel A1 - Mukherjee, R. A1 - Mundell, C. A1 - Muraishi, H. A1 - Murase, Kohta A1 - Nagataki, Shigehiro A1 - Nagayoshi, T. A1 - Naito, T. A1 - Nakajima, D. A1 - Nakamori, T. A1 - Nemmen, R. A1 - Niemiec, Jacek A1 - Nieto, D. A1 - Nievas-Rosillo, M. A1 - Nikolajuk, M. A1 - Nishijima, K. A1 - Noda, K. A1 - Nogues, L. A1 - Nosek, D. A1 - Novosyadlyj, B. A1 - Nozaki, S. A1 - Ohira, Yutaka A1 - Ohishi, M. A1 - Ohm, S. A1 - Okumura, A. A1 - Ong, R. A. A1 - Orito, R. A1 - Orlati, A. A1 - Ostrowski, M. A1 - Oya, I. A1 - Padovani, Marco A1 - Palacio, J. A1 - Palatka, M. A1 - Paredes, Josep M. A1 - Pavy, S. A1 - Persic, M. A1 - Petrucci, P. A1 - Petruk, Oleh A1 - Pisarski, A. A1 - Pohl, Martin A1 - Porcelli, A. A1 - Prandini, E. A1 - Prast, J. A1 - Principe, G. A1 - Prouza, M. A1 - Pueschel, Elisa A1 - Puelhofer, G. A1 - Quirrenbach, A. A1 - Rameez, M. A1 - Reimer, O. A1 - Renaud, M. A1 - Ribo, M. A1 - Rico, J. A1 - Rizi, V. A1 - Rodriguez, J. A1 - Fernandez, G. Rodriguez A1 - Rodriguez Vazquez, J. J. A1 - Romano, Patrizia A1 - Romeo, G. A1 - Rosado, J. A1 - Rousselle, J. A1 - Rowell, G. A1 - Rudak, B. A1 - Sadeh, I. A1 - Safi-Harb, S. A1 - Saito, T. A1 - Sakaki, N. A1 - Sanchez, D. A1 - Sangiorgi, P. A1 - Sano, H. A1 - Santander, M. A1 - Sarkar, S. A1 - Sawada, M. A1 - Schioppa, E. J. A1 - Schoorlemmer, H. A1 - Schovanek, P. A1 - Schussler, F. A1 - Sergijenko, O. A1 - Servillat, M. A1 - Shalchi, A. A1 - Shellard, R. C. A1 - Siejkowski, H. A1 - Sillanpaa, A. A1 - Simone, D. A1 - Sliusar, V. A1 - Sol, H. A1 - Stanic, S. A1 - Starling, R. A1 - Stawarz, L. A1 - Stefanik, S. A1 - Stephan, M. A1 - Stolarczyk, T. A1 - Szanecki, M. A1 - Szepieniec, T. A1 - Tagliaferri, G. A1 - Tajima, H. A1 - Takahashi, M. A1 - Takeda, J. A1 - Tanaka, M. A1 - Tanaka, S. A1 - Tejedor, L. A. A1 - Telezhinsky, Igor O. A1 - Temnikov, P. A1 - Terada, Y. A1 - Tescaro, D. A1 - Teshima, M. A1 - Testa, V. A1 - Thoudam, S. A1 - Tokanai, F. A1 - Torres, D. F. A1 - Torresi, E. A1 - Tosti, G. A1 - Townsley, C. A1 - Travnicek, P. A1 - Trichard, C. A1 - Trifoglio, M. A1 - Tsujimoto, S. A1 - Vagelli, V. A1 - Vallania, P. A1 - Valore, L. A1 - van Driel, W. A1 - van Eldik, C. A1 - Vandenbroucke, Justin A1 - Vassiliev, V. A1 - Vecchi, M. A1 - Vercellone, Stefano A1 - Vergani, S. A1 - Vigorito, C. A1 - Vorobiov, S. A1 - Vrastil, M. A1 - Vazquez Acosta, M. L. A1 - Wagner, S. J. A1 - Wagner, R. A1 - Wakely, S. P. A1 - Walter, R. A1 - Ward, J. E. A1 - Watson, J. J. A1 - Weinstein, A. A1 - White, M. A1 - White, R. A1 - Wierzcholska, A. A1 - Wilcox, P. A1 - Williams, D. A. A1 - Wischnewski, R. A1 - Wojcik, P. A1 - Yamamoto, T. A1 - Yamamoto, H. A1 - Yamazaki, Ryo A1 - Yanagita, S. A1 - Yang, L. A1 - Yoshida, T. A1 - Yoshida, M. A1 - Yoshiike, S. A1 - Yoshikoshi, T. A1 - Zacharias, M. A1 - Zampieri, L. A1 - Zanin, R. A1 - Zavrtanik, M. A1 - Zavrtanik, D. A1 - Zdziarski, A. A1 - Zech, Alraune A1 - Zechlin, Hannes A1 - Zhdanov, V. A1 - Ziegler, A. A1 - Zorn, J. T1 - Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7-3946 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7-3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti) correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H I emission. We present a series of simulated images of RX J1713.7-3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H I observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator. KW - cosmic rays KW - gamma rays: ISM KW - ISM: individual objects (RX J1713.7-3946, G347.3-0.5) Y1 - 2017 U6 - https://doi.org/10.3847/1538-4357/aa6d67 SN - 0004-637X SN - 1538-4357 VL - 840 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Archambault, S. A1 - Archer, A. A1 - Benbow, Wystan A1 - Bird, Ralph A1 - Bourbeau, E. A1 - Buchovecky, M. A1 - Buckley, J. H. A1 - Bugaev, V. A1 - Cerruti, M. A1 - Connolly, M. P. A1 - Cui, W. A1 - Dwarkadas, Vikram V. A1 - Errando, M. A1 - Falcone, A. A1 - Feng, Q. A1 - Finley, J. P. A1 - Fleischhack, H. A1 - Fortson, L. A1 - Furniss, A. A1 - Griffin, S. A1 - Huetten, M. A1 - Hanna, D. A1 - Holder, J. A1 - Johnson, C. A. A1 - Kaaret, P. A1 - Kar, P. A1 - Kelley-Hoskins, N. A1 - Kertzman, M. A1 - Kieda, D. A1 - Krause, M. A1 - Kumar, S. A1 - Lang, M. J. A1 - Maier, G. A1 - McArthur, S. A1 - McCann, A. A1 - Moriarty, P. A1 - Mukherjee, R. A1 - Nieto, D. A1 - Ong, R. A. A1 - Otte, A. N. A1 - Park, Nahee A1 - Pohl, Martin A1 - Popkow, A. A1 - Pueschel, Elisa A1 - Quinn, J. A1 - Ragan, K. A1 - Reynolds, P. T. A1 - Richards, G. T. A1 - Roache, E. A1 - Sadeh, I. A1 - Santander, M. A1 - Sembroski, G. H. A1 - Shahinyan, K. A1 - Slane, P. A1 - Staszak, D. A1 - Telezhinsky, Igor O. A1 - Trepanier, S. A1 - Tyler, J. A1 - Wakely, S. P. A1 - Weinstein, A. A1 - Weisgarber, T. A1 - Wilcox, P. A1 - Wilhelm, Alina A1 - Williams, D. A. A1 - Zitzer, B. T1 - Gamma-ray Observations of Tycho's Supernova Remnant with VERITAS and Fermi JF - The astrophysical journal : an international review of spectroscopy and astronomical physics KW - material KW - data behind figure Y1 - 2017 U6 - https://doi.org/10.3847/1538-4357/836/1/23 SN - 0004-637X SN - 1538-4357 VL - 836 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Archambault, S. A1 - Archer, A. A1 - Benbow, W. A1 - Bird, Ralph A1 - Bourbeau, E. A1 - Bouvier, A. A1 - Buchovecky, M. A1 - Bugaev, V. A1 - Cardenzana, J. V. A1 - Cerruti, M. A1 - Ciupik, L. A1 - Connolly, M. P. A1 - Cui, W. A1 - Daniel, M. K. A1 - Errando, M. A1 - Falcone, A. A1 - Feng, Q. A1 - Finley, J. P. A1 - Fleischhack, H. A1 - Fortson, L. A1 - Furniss, A. A1 - Gillanders, G. H. A1 - Griffin, S. A1 - Hanna, D. A1 - Hervet, O. A1 - Holder, J. A1 - Hughes, G. A1 - Humensky, T. B. A1 - Hutten, M. A1 - Johnson, C. A. A1 - Kaaret, P. A1 - Kar, P. A1 - Kertzman, M. A1 - Kieda, D. A1 - Krause, M. A1 - Lang, M. J. A1 - Lin, T. T. Y. A1 - Maier, G. A1 - McArthur, S. A1 - Moriarty, P. A1 - Mukherjee, R. A1 - Nieto, D. A1 - Ong, R. A. A1 - Otte, A. N. A1 - Park, N. A1 - Pohl, Martin A1 - Popkow, A. A1 - Pueschel, Elisa A1 - Quinn, J. A1 - Ragan, K. A1 - Reynolds, P. T. A1 - Richards, G. T. A1 - Roache, E. A1 - Rulten, C. A1 - Sadeh, I. A1 - Sembroski, G. H. A1 - Shahinyan, K. A1 - Staszak, D. A1 - Telezhinsky, Igor O. A1 - Trepanier, S. A1 - Wakely, S. P. A1 - Weinstein, A. A1 - Wilcox, P. A1 - Williams, D. A. A1 - Zitzer, B. T1 - Gamma-ray observations under bright moonlight with VERITAS JF - Astroparticle physics N2 - Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > 35%) in two observing modes, firstly by reducing the voltage applied to the PMTs and, secondly, with the addition of ultra-violet (UV) bandpass filters to the cameras. This has allowed observations at up to about 30 times previous NSB levels (around 80% Moon illumination), resulting in 30% more observing time between the two modes over the course of a year. These additional observations have already allowed for the detection of a flare from the 1ES 1727 + 502 and for an observing program targeting a measurement of the cosmic-ray positron fraction. We provide details of these new observing modes and their performance relative to the standard VERITAS observations. (C) 2017 Elsevier B.V. All rights reserved. KW - Instrumentation KW - Moonlight KW - Observing methods KW - VERITAS KW - IACT Y1 - 2017 U6 - https://doi.org/10.1016/j.astropartphys.2017.03.001 SN - 0927-6505 SN - 1873-2852 VL - 91 SP - 34 EP - 43 PB - Elsevier CY - Amsterdam ER - TY - THES A1 - Håkansson, Nils T1 - A Dark Matter line search using 3D-modeling of Cherenkov showers below 10 TeV with VERITAS T1 - Die Suche nach Dunkler Materie mit VERITAS durch Liniensuche und 3D Modellierung von Cherenkov-Schauern unter 10 TeV N2 - Dark matter, DM, has not yet been directly observed, but it has a very solid theoretical basis. There are observations that provide indirect evidence, like galactic rotation curves that show that the galaxies are rotating too fast to keep their constituent parts, and galaxy clusters that bends the light coming from behind-lying galaxies more than expected with respect to the mass that can be calculated from what can be visibly seen. These observations, among many others, can be explained with theories that include DM. The missing piece is to detect something that can exclusively be explained by DM. Direct observation in a particle accelerator is one way and indirect detection using telescopes is another. This thesis is focused on the latter method. The Very Energetic Radiation Imaging Telescope Array System, V ERITAS, is a telescope array that detects Cherenkov radiation. Theory predicts that DM particles annihilate into, e.g., a γγ pair and create a distinctive energy spectrum when detected by such telescopes, e.i., a monoenergetic line at the same energy as the particle mass. This so called ”smoking-gun” signature is sought with a sliding window line search within the sub-range ∼ 0.3 − 10 TeV of the VERITAS energy range, ∼ 0.01 − 30 TeV. Standard analysis within the VERITAS collaboration uses Hillas analysis and look-up tables, acquired by analysing particle simulations, to calculate the energy of the particle causing the Cherenkov shower. In this thesis, an improved analysis method has been used. Modelling each shower as a 3Dgaussian should increase the energy recreation quality. Five dwarf spheroidal galaxies were chosen as targets with a total of ∼ 224 hours of data. The targets were analysed individually and stacked. Particle simulations were based on two simulation packages, CARE and GrISU. Improvements have been made to the energy resolution and bias correction, up to a few percent each, in comparison to standard analysis. Nevertheless, no line with a relevant significance has been detected. The most promising line is at an energy of ∼ 422 GeV with an upper limit cross section of 8.10 · 10^−24 cm^3 s^−1 and a significance of ∼ 2.73 σ, before trials correction and ∼ 1.56 σ after. Upper limit cross sections have also been calculated for the γγ annihilation process and four other outcomes. The limits are in line with current limits using other methods, from ∼ 8.56 · 10^−26 − 6.61 · 10^−23 cm^3s^−1. Future larger telescope arrays, like the upcoming Cherenkov Telescope Array, CTA, will provide better results with the help of this analysis method. N2 - Dunkle Materie, DM, wurde noch nicht direkt beobachtet, aber die Theorie ist sehr solide. Es gibt Beobachtungen, die als indirekte Beweise gelten, z.B. galaktische Rotationskurven, die besagen, dass Galaxien zu schnell rotieren um ohne eine zusätzliche Massenkomponente zusammenhalten zu können, oder elliptische Zwerggalaxien, die massereicher sind als die sichtbare Materie vermuten lässt. Diese Beobachtungen könnten z.B. mit dem Vorhandensein von DM erkärt werden, aber bis jetzt fehlt die Beobachtung eines Phänomens, das ausschließlich durch DM erklärt werden kann. Eine Möglichkeit wäre die Beobachtung einer speziellen Energiesignatur durch Teleskope, welche das Thema der vorliegenden Arbeit ist. Das Very Energetic Radiation Imaging Telescope Array System, VERITAS, ist ein Teleskoparray für Cherenkov-Strahlung. Entsprechend der Theorie sollten Teilchen dunkler Materie annihilieren und z.B. ein γγ Paar bilden. Dieses sollte im Teleskop eine spezielle Energiesignatur hinterlassen, nämlich eine monoenergetische Linie bei einer Energie, die der Teilchenmasse entspricht. Diese ”smoking-gun” Signatur wird mit einer sliding window Liniensuche bei Energien < 10TeV gesucht. In der VERITAS Kollaboration werden standardm¨aßig eine Hillas-Analyse und Nachschlagetabellen aus Teilchensimulationen verwendet, um die Energie des Teilchens zu berechnen, das den Cherenkov-Schauer verursacht hat. Hier wird eine verbesserte Analysemethode verwendet. Dabei wird jeder Schauer als 3D-Gaußkurve modelliert, was die Qualität der Energierekonstruktion erheblich verbessern sollte. Dafur wurden funf elliptische Zwerggalaxien beobachtet und einzeln sowie insgesamt analysiert, insgesamt ~ 224 h Beobachtungszeit. Dabei werden zwei verschiedene Teilchensimulationsprogramme verwendet, CARE und GrISU. In dieser Arbeit wurde die Energieauflösung und die Bias-Korrektur um einige Prozent gegen¨uber der Standardanalyse verbessert. Es wurde jedoch keine signifikante Linie detektiert. Die vielversprechendste Linie befindet sich bei einer Energie von ~ 422GeV und hat einen Querschnitt von 8.10·10^−24 cm^3 s^−1 und ein Signifikanzlevel von ~ 2.73 σ bzw. 1.56σ vor bzw. nach statistischer Korrektur. Außerdem wurden obere Grenzwerte fur verschiedene Annihilierungsprozesse berechnet. Sie stimmen mit anderen aktuellen Grenzwerten überein (~ 8.56 · 10^−26 − 6.61 · 10^−23 cm^3s^−1). Zukünftig werden mehr Beobachtungsdaten und neue Teleskoparrays, wie das Cherenkov Telescope Array, CTA, mit Hilfe dieser Analysemethode bessere Ergebnisse ermöglichen. KW - Dark Matter KW - line search KW - VERITAS KW - 3D-modeling KW - Cherenkov showers KW - Dunkler Materie KW - Line Suche KW - VERITAS KW - 3D Modellierung KW - Cherenkov-Schauern Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-397670 ER - TY - JOUR A1 - Ortiz-Amezcua, Pablo A1 - Guerrero-Rascado, Juan Luis A1 - Jose Granados-Munoz, Maria A1 - Benavent-Oltra, Jose Antonio A1 - Böckmann, Christine A1 - Samaras, Stefanos A1 - Stachlewska, Iwona Sylwia A1 - Janicka, Lucja A1 - Baars, Holger A1 - Bohlmann, Stephanie A1 - Alados-Arboledas, Lucas T1 - Microphysical characterization of long-range transported biomass burning particles from North America at three EARLINET stations JF - Atmospheric Chemistry and Physics N2 - Strong events of long-range transported biomass burning aerosol were detected during July 2013 at three EARLINET (European Aerosol Research Lidar Network) stations, namely Granada (Spain), Leipzig (Germany) and Warsaw (Poland). Satellite observations from MODIS (Moderate Resolution Imaging Spectroradiometer) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) instruments, as well as modeling tools such as HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) and NAAPS (Navy Aerosol Analysis and Prediction System), have been used to estimate the sources and transport paths of those North American forest fire smoke particles. A multiwavelength Raman lidar technique was applied to obtain vertically resolved particle optical properties, and further inversion of those properties with a regularization algorithm allowed for retrieving microphysical information on the studied particles. The results highlight the presence of smoke layers of 1-2 km thickness, located at about 5 km a.s.l. altitude over Granada and Leipzig and around 2.5 km a.s.l. at Warsaw. These layers were intense, as they accounted for more than 30% of the total AOD (aerosol optical depth) in all cases, and presented optical and microphysical features typical for different aging degrees: color ratio of lidar ratios (LR532/LR355) around 2, alpha-related angstrom exponents of less than 1, effective radii of 0.3 mu m and large values of single scattering albedos (SSA), nearly spectrally independent. The intensive microphysical properties were compared with columnar retrievals form co-located AERONET (Aerosol Robotic Network) stations. The intensity of the layers was also characterized in terms of particle volume concentration, and then an experimental relationship between this magnitude and the particle extinction coefficient was established. Y1 - 2017 U6 - https://doi.org/10.5194/acp-17-5931-2017 SN - 1680-7316 SN - 1680-7324 VL - 17 SP - 5931 EP - 5946 PB - Copernicus CY - Göttingen ER - TY - GEN A1 - Pilz, Tobias A1 - Francke, Till A1 - Bronstert, Axel T1 - lumpR 2.0.0: an R package facilitating landscape discretisation for hillslope-based hydrological models N2 - The characteristics of a landscape pose essential factors for hydrological processes. Therefore, an adequate representation of the landscape of a catchment in hydrological models is vital. However, many of such models exist differing, amongst others, in spatial concept and discretisation. The latter constitutes an essential pre-processing step, for which many different algorithms along with numerous software implementations exist. In that context, existing solutions are often model specific, commercial, or depend on commercial back-end software, and allow only a limited or no workflow automation at all. Consequently, a new package for the scientific software and scripting environment R, called lumpR, was developed. lumpR employs an algorithm for hillslope-based landscape discretisation directed to large-scale application via a hierarchical multi-scale approach. The package addresses existing limitations as it is free and open source, easily extendible to other hydrological models, and the workflow can be fully automated. Moreover, it is user-friendly as the direct coupling to a GIS allows for immediate visual inspection and manual adjustment. Sufficient control is furthermore retained via parameter specification and the option to include expert knowledge. Conversely, completely automatic operation also allows for extensive analysis of aspects related to landscape discretisation. In a case study, the application of the package is presented. A sensitivity analysis of the most important discretisation parameters demonstrates its efficient workflow automation. Considering multiple streamflow metrics, the employed model proved reasonably robust to the discretisation parameters. However, parameters determining the sizes of subbasins and hillslopes proved to be more important than the others, including the number of representative hillslopes, the number of attributes employed for the lumping algorithm, and the number of sub-discretisations of the representative hillslopes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 389 Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-402880 ER - TY - JOUR A1 - Matzka, Jürgen A1 - Siddiqui, Tarique Adnan A1 - Lilienkamp, Henning A1 - Stolle, Claudia A1 - Veliz, Oscar T1 - Quantifying solar flux and geomagnetic main field influence on the equatorial ionospheric current system at the geomagnetic observatory Huancayo JF - Journal of Atmospheric and Solar-Terrestrial Physics N2 - In order to analyse the sensitivity of the equatorial ionospheric current system, i.e. the solar quiet current system and the equatorial electrojet, to solar cycle variations and to the secular variation of the geomagnetic main field, we have analysed 51 years (1935-1985) of geomagnetic observatory data from Huancayo, Peru. This period is ideal to analyse the influence of the main field strength on the amplitude of the quiet daily variation, since the main field decreases significantly from 1935 to 1985, while the distance of the magnetic equator to the observatory remains stable. To this end, we digitised some 19 years of hourly mean values of the horizontal component (H), which have not been available digitally at the World Data Centres. Then, the sensitivity of the amplitude Ali of the quiet daily variation to both solar cycle variations (in terms of sunspot numbers and solar flux F10.7) and changes of the geomagnetic main field strength (due to secular variation) was determined. We confirm an increase of Delta H for the decreasing main field in this period, as expected from physics based models (Cnossen, 2016), but with a somewhat smaller rate of 4.4% (5.8% considering one standard error) compared with 6.9% predicted by the physics based model. KW - Magnetic field KW - Equatorial ionosphere KW - Geomagnetic secular variation KW - Solar cycle Y1 - 2017 U6 - https://doi.org/10.1016/j.jastp.2017.04.014 SN - 1364-6826 SN - 1879-1824 VL - 163 SP - 120 EP - 125 PB - Elsevier CY - Oxford ER - TY - THES A1 - Roland, Steffen T1 - Charge carrier recombination and open circuit voltage in organic solar cells T1 - Ladungsträger Rekombination und Leerlaufspannung in organischen Solarzellen BT - from bilayer-model systems to hybrid multi-junctions BT - von Bilayer Modellsystemen zu hybriden Mehrschichtsolarzellen N2 - Tremendous progress in the development of thin film solar cell techniques has been made over the last decade. The field of organic solar cells is constantly developing, new material classes like Perowskite solar cells are emerging and different types of hybrid organic/inorganic material combinations are being investigated for their physical properties and their applicability in thin film electronics. Besides typical single-junction architectures for solar cells, multi-junction concepts are also being investigated as they enable the overcoming of theoretical limitations of a single-junction. In multi-junction devices each sub-cell operates in different wavelength regimes and should exhibit optimized band-gap energies. It is exactly this tunability of the band-gap energy that renders organic solar cell materials interesting candidates for multi-junction applications. Nevertheless, only few attempts have been made to combine inorganic and organic solar cells in series connected multi-junction architectures. Even though a great diversity of organic solar cells exists nowadays, their open circuit voltage is usually low compared to the band-gap of the active layer. Hence, organic low band-gap solar cells in particular show low open circuit voltages and the key factors that determine the voltage losses are not yet fully understood. Besides open circuit voltage losses the recombination of charges in organic solar cells is also a prevailing research topic, especially with respect to the influence of trap states. The exploratory focus of this work is therefore set, on the one hand, on the development of hybrid organic/inorganic multi-junctions and, on the other hand, on gaining a deeper understanding of the open circuit voltage and the recombination processes of organic solar cells. In the first part of this thesis, the development of a hybrid organic/inorganic triple-junction will be discussed which showed at that time (Jan. 2015) a record power conversion efficiency of 11.7%. The inorganic sub-cells of these devices consist of hydrogenated amorphous silicon and were delivered by the Competence Center Thin-Film and Nanotechnology for Photovoltaics in Berlin. Different recombination contacts and organic sub-cells were tested in conjunction with these inorganic sub-cells on the basis of optical modeling predictions for the optimal layer thicknesses to finally reach record efficiencies for this type of solar cells. In the second part, organic model systems will be investigated to gain a better understanding of the fundamental loss mechanisms that limit the open circuit voltage of organic solar cells. First, bilayer systems with different orientation of the donor and acceptor molecules were investigated to study the influence of the donor/acceptor orientation on non-radiative voltage loss. Secondly, three different bulk heterojunction solar cells all comprising the same amount of fluorination and the same polymer backbone in the donor component were examined to study the influence of long range electrostatics on the open circuit voltage. Thirdly, the device performance of two bulk heterojunction solar cells was compared which consisted of the same donor polymer but used different fullerene acceptor molecules. By this means, the influence of changing the energetics of the acceptor component on the open circuit voltage was investigated and a full analysis of the charge carrier dynamics was presented to unravel the reasons for the worse performance of the solar cell with the higher open circuit voltage. In the third part, a new recombination model for organic solar cells will be introduced and its applicability shown for a typical low band-gap cell. This model sheds new light on the recombination process in organic solar cells in a broader context as it re-evaluates the recombination pathway of charge carriers in devices which show the presence of trap states. Thereby it addresses a current research topic and helps to resolve alleged discrepancies which can arise from the interpretation of data derived by different measurement techniques. N2 - In der Photovoltaikforschung spielen neuartige Dünnschichtsolarzellen eine immer größere Rolle. Neben innovativen Design und Anwendungskonzepten sind Material und Kostenreduzierung in der Herstellung die größten Triebfedern für die Entwicklung neuer Technologien. Hier sind neben den vielversprechenden Perowskitsolarzellen insbesondere organische Solarzellen zu nennen, die sich durch ihre chemische Vielseitigkeit, einfache Verarbeitung und stetige Weiterentwicklung in Bezug auf ihre Effizienz auszeichnen. Diese Vielseitigkeit ermöglicht die Herstellung organischer Solarzellen mit unterschiedlicher spektraler Empfindlichkeit, was wiederum Vorteile für den Einsatz in seriengeschaltete Mehrschichtsolarzellen bietet. Diese erlauben es, fundamentale Limitierungen von Einschichtsolarzellsystemen zu überwinden. Der erste Teil dieser Arbeit befasst sich daher mit der Entwicklung einer neuartigen hybriden Multischichtsolarzelle, die sowohl aus anorganischen als auch organischen Subzellen besteht und zum Zeitpunkt ihrer Veröffentlichung einen neuen Effizienzrekord für diese Klasse von Solarzellen aufzeigte. Der zweite Teil der Arbeit befasst sich mit fundamentalen physikalischen Prozessen in organischen Solarzellen, da viele Funktionsmechanismen noch nicht im Detail geklärt sind. An verschiedenen organischen Modellsolarzellsystemen wurde daher unter anderem der Einfluss molekularer Orientierung von Donor- und Akzeptorkomponenten der Solarzelle oder der Einfluss von Fluorinierung des Donors auf die Leerlaufspannung der Solarzelle untersucht. Auf diese Weise konnten neue wichtige Erkenntnisse über den Einfluss von verschiedenen Verlustkanälen und der Energetik auf die Leerlaufspannung gewonnen werden. Der letzte Teil der Arbeit widmet sich der Entwicklung eines neuen Modells, welches den Rekombinationsprozess von Ladungen in einer bestimmten organischen Solarzelle beschreibt. Dieses neue Modell wurde anhand umfangreicher Experimente validiert und ermöglicht es, insbesondere den Einfluss freier und in sogenannten Fallenzuständen gefangener Ladungen auf die Rekombination zu trennen. Damit hat dieses Modell eine weitreichende Bedeutung, zum einen für die Beurteilung von typischen Rekombinationsexperimenten in organischen Solarzellen und zum anderen für die Bewertung des Einflusses von Fallenzuständen auf den Rekombinationsstrom. KW - organic solar cells KW - charge carrier recombination KW - open circuit voltage KW - hybrid multi-junction solar cell KW - organische Solarzellen KW - Ladungsträgerrekombination KW - Leerlaufspannung KW - hybride Mehrschichtsolarzellen Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-397721 ER - TY - JOUR A1 - Jošt, Marko A1 - Albrecht, Steve A1 - Kegelmann, Lukas A1 - Wolff, Christian Michael A1 - Lang, Felix A1 - Lipovšek, Benjamin A1 - Krč, Janez A1 - Korte, Lars A1 - Neher, Dieter A1 - Rech, Bernd A1 - Topič, Marko T1 - Efficient light management by textured nanoimprinted layers for perovskite solar cells JF - ACS photonics N2 - Inorganic-organic perovskites like methylammonium-lead-iodide have proven to be an effective class of 17 materials for fabricating efficient solar cells. To improve their performance, light management techniques using textured surfaces, similar to those used in established solar cell technologies, should be considered. Here, we apply a light management foil created by UV nanoimprint lithography on the glass side of an inverted (p-i-n) perovskite solar cell with 16.3% efficiency. The obtained 1 mA cm(-2) increase in the short-circuit current density translates to a relative improvement in cell performance of 5%, which results in a power conversion efficiency of 17.1%. Optical 3D simulations based on experimentally obtained parameters were used to support the experimental findings. A good match between the simulated and experimental data was obtained, validating the model. Optical simulations reveal that the main improvement in device performance is due to a reduction in total reflection and that relative improvement in the short-circuit current density of up to 10% is possible for large-area devices. Therefore, our results present the potential of light management foils for improving the device performance of perovskite solar cells and pave the way for further use of optical simulations in the field of perovskite solar cells. KW - perovskite solar cells KW - antireflection KW - light management KW - UV nanoimprint lithography KW - optical simulations Y1 - 2017 U6 - https://doi.org/10.1021/acsphotonics.7b00138 SN - 2330-4022 VL - 4 SP - 1232 EP - 1239 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Vandewal, Koen A1 - Benduhn, Johannes A1 - Schellhammer, Karl Sebastian A1 - Vangerven, Tim A1 - Rückert, Janna E. A1 - Piersimoni, Fortunato A1 - Scholz, Reinhard A1 - Zeika, Olaf A1 - Fan, Yeli A1 - Barlow, Stephen A1 - Neher, Dieter A1 - Marder, Seth R. A1 - Manca, Jean A1 - Spoltore, Donato A1 - Cuniberti, Gianaurelio A1 - Ortmann, Frank T1 - Absorption Tails of Donor BT - C-60 Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation JF - Journal of the American Chemical Society N2 - In disordered organic semiconductors, the transfer of a rather localized charge carrier from one site to another triggers a deformation of the molecular structure quantified by the intramolecular relaxation energy. A similar structural relaxation occurs upon population of intermolecular charge-transfer (CT) states formed at organic electron donor (D)-acceptor (A) interfaces. Weak CT absorption bands for D A complexes occur at photon energies below the optical gaps of both the donors and the C-60 acceptor as a result of optical transitions from the neutral ground state to the ionic CT state. In this work, we show that temperature-activated intramolecular vibrations of the ground state play a major role in determining the line shape of such CT absorption bands. This allows us to extract values for the relaxation energy related to the geometry change from neutral to ionic CT complexes. Experimental values for the relaxation energies of 20 D:C-60 CT complexes correlate with values calculated within density functional theory. These results provide an experimental method for determining the polaron relaxation energy in solid-state organic D-A blends and show the importance of a reduced relaxation energy, which we introduce to characterize thermally activated CT processes. Y1 - 2017 U6 - https://doi.org/10.1021/jacs.6b12857 SN - 0002-7863 VL - 139 IS - 4 SP - 1699 EP - 1704 PB - American Chemical Society CY - Washington ER -