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Now showing 1 - 10 of 69
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    Effect of additives on MWCNT dispersion and electrical percolation in polyamide 12 composites
    (Melville, NY : AIP, 2017) Socher, Robert; Krause, Beate; Pötschke, Petra
    The aim of this study was to decrease the electrical percolation threshold of multiwalled carbon nanotubes (MWCNTs) in a polyamide 12 matrix by the use of additives. Different kinds of additives were selected which either interact with the π-system of the MWCNTs (imidazolium based ionic liquid (IL) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)) or improve the MWCNT wettability (cyclic butylene terephthalate, CBT). The composites were melt mixed using a DACA microcompounder. The electrical percolation threshold for PA12/MWCNT without additives, measured on compression molded plates, was found between 2.0 and 2.25 wt%. With all used additives, a significant reduction of the electrical percolation threshold could be achieved. Whereas the addition of IL and CBT resulted in MWCNT percolation at around 1.0 wt%, a slightly higher percolation threshold between 1.0 and 1.5 wt% was found for PTCDA as an additive. Interestingly, the electrical resistivity at higher loadings was decreased by nearly two decades when using CBT and one decade after application of PTCDA, whereas IL did not contribute to lower values in this range. In all cases macrodispersion as assessed by light microscopy was not improved and even worse as compared to non-modified composites. In summary, the results illustrate that these kinds of additives are able to improve the performance of PA12 based MWCNT nanocomposites.
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    Saltwater intrusion under climate change in North-Western Germany - mapping, modelling and management approaches in the projects TOPSOIL and go-CAM
    (Les Ulis : EDP Sciences, 2018) Wiederhold, Helga; Scheer, Wolfgang; Kirsch, Reinhard; Azizur Rahman, M.; Ronczka, Mathias; Szymkiewicz, Adam; Sadurski, A.; Jaworska-Szulc, B.
    Climate change will result in rising sea level and, at least for the North Sea region, in rising groundwater table. This leads to a new balance at the fresh–saline groundwater boundary and a new distribution of saltwater intrusions with strong regional differentiations. These effects are investigated in several research projects funded by the European Union and the German Federal Ministry of Education and Research (BMBF). Objectives and some results from the projects TOPSOIL and go-CAM are presented in this poster.
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    Measurements of particle backscatter, extinction, and lidar ratio at 1064 nm with the rotational raman method in Polly-XT
    (Les Ulis : EDP Sciences, 2018) Engelmann, Ronny; Haarig, Moritz; Baars, Holger; Ansmann, Albert; Kottas, Michael; Marinou, Eleni; Nicolae, D.; Makoto, A.; Vassilis, A.; Balis, D.; Behrendt, A.; Comeron, A.; Gibert, F.; Landulfo, E.; McCormick, M.P.; Senff, C.; Veselovskii, I.; Wandinger, U.
    We replaced a 1064-nm interference filter of a Polly-XT lidar system by a 1058-nm filter to observe pure rotational Raman backscattering from atmospheric Nitrogen and Oxygen. Polly-XT is compact Raman lidar with a Nd:YAG laser (20 Hz, 200 mJ at 1064 nm) and a 30-cm telescope mirror which applies photomultipliers in photoncounting mode. We present the first measured signals at 1058 nm and the derived extinction profile from measurements aboard RV Polarstern and in Leipzig. In combination with another Polly-XT system we could also derive particle backscatter and lidar ratio profiles at 1064 nm.
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    Template-assisted colloidal self-assembly of macroscopic magnetic metasurfaces
    (Cambridge [u.a.] : Soc., 2016) Mayer, Martin; Tebbe, Moritz; Kuttner, Christian; Schnepf, Max J.; König, Tobias A. F.; Fery, Andreas
    We demonstrate a template-assisted colloidal self-assembly approach for magnetic metasurfaces on macroscopic areas. The choice of anisotropic colloidal particle geometry, assembly pattern and metallic film is based on rational design criteria, taking advantage of mirror-charge effects for gold nanorods placed on gold film. Monodisperse gold nanorods prepared utilizing wet-chemistry are arranged with high precision on wrinkled templates to form linear array-type assemblies and subsequently transferred to a thin gold film. Due to the obtained particle-to-film distance of 1.1 nm, the plasmonic mode of the nanorod is able to couple efficiently with the supporting metallic film, giving rise to a magnetic mode in the visible spectrum (721 nm). Conventional UV-vis-NIR measurements in close correlation with electromagnetic simulations provide evidence for the presence of a magnetic resonance on the macroscopic area. The herein presented scalable lithography-free fabrication process paves the road towards colloidal functional metasurfaces with an optical response in the effective magnetic permeability.
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    Influence of graphite and SEBS addition on thermal and electrical conductivity and mechanical properties of polypropylene composites
    (Melville, NY : AIP, 2017) Krause, Beate; Cohnen, A.; Pötschke, Petra; Hickmann, T.; Koppler, D.; Proksch, B.; Kersting, T.; Hopmann, C.
    In this study, composites based on polypropylene (PP) and different graphite fillers were melt mixed using small scale microcompounder Xplore DSM15 as well as lab-scale co-rotating twin screw extruder Coperion ZSK26Mc. The measurements of the electrical and thermal conductivity as well as mechanical properties of the composites were performed on pressed plates. It was found that the addition of graphite powders having different particle size distributions leads to different increases of the thermal conductivity. For synthetic graphite, the PP composites filled with TIMCAL Timrex® KS500 reached the highest value of thermal conductivity of 0.52 W/(m·K) at 10 vol% loading, whereas this composite was not electrical conductive. Furthermore, the influence of a styrene-ethylene-butylene-styrene block copolymer (SEBS) based impact modifier on the mechanical properties of PP filled with 80 wt% of different synthetic graphites was investigated. For that the proportion of SEBS in the PP component was varied systematically. The conductivities were influenced by the type of graphite and the content of impact modifier. The results indicate that the impact strength of the composite containing TIMCAL Timrex® KS300-1250 can be increased by approx. 100 % when replacing 50 wt% of the PP component by SEBS.
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    3b Open-Access-Publikationsfonds
    (Zenodo, 2017) Pampel, Heinz; Tullney, Marco
    Ein Open-Access-Publikationsfonds ist ein Finanzierungs- und Steuerungsinstrument wissenschaftlicher Einrichtungen zur Übernahme von Open-Access-Publikationsgebühren. Dieser Beitrag befasst sich mit Aufbau und Betrieb eines solchen Fonds.
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    Promoting access to and use of seismic data in a large scientific community
    (Les Ulis : EDP Sciences, 2017) Michel, Eric; Belkacem, Kevin; Samadi, Reza; de Assis Peralta, Raphael; Renié, Christian; Abed, Mahfoudh; Lin, Guangyuan; Christensen-Dalsgaard, Jørgen; Houdek, Günter; Handberg, Rasmus; Gizon, Laurent; Burston, Raymond; Nagashima, Kaori; Pallé, Pere; Poretti, Ennio; Rainer, Monica; Mistò, Angelo; Panzera, Maria Rosa; Roth, Markus; Monteiro, Mário J. P. F. G.; Cunha, Margarida S.; Ferreira, João Miguel T. S.
    The growing amount of seismic data available from space missions (SOHO, CoRoT, Kepler, SDO,…) but also from ground-based facilities (GONG, BiSON, ground-based large programmes…), stellar modelling and numerical simulations, creates new scientific perspectives such as characterizing stellar populations in our Galaxy or planetary systems by providing model-independent global properties of stars such as mass, radius, and surface gravity within several percent accuracy, as well as constraints on the age. These applications address a broad scientific community beyond the solar and stellar one and require combining indices elaborated with data from different databases (e.g. seismic archives and ground-based spectroscopic surveys). It is thus a basic requirement to develop a simple and effcient access to these various data resources and dedicated tools. In the framework of the European project SpaceInn (FP7), several data sources have been developed or upgraded. The Seismic Plus Portal has been developed, where synthetic descriptions of the most relevant existing data sources can be found, as well as tools allowing to localize existing data for given objects or period and helping the data query. This project has been developed within the Virtual Observatory (VO) framework. In this paper, we give a review of the various facilities and tools developed within this programme. The SpaceInn project (Exploitation of Space Data for Innovative Helio- and Asteroseismology) has been initiated by the European Helio- and Asteroseismology Network (HELAS).
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    Triple-wavelength lidar observations of the linear depolarization ratio of dried marine particles
    (Les Ulis : EDP Sciences, 2018) Haarig, Moritz; Ansmann, Albert; Baars, Holger; Engelmann, Ronny; Althausen, Dietrich; Bohlmann, Stephanie; Gasteiger, Josef; Farrell, David; Nicolae, D.; Makoto, A.; Vassilis, A.; Balis, D.; Behrendt, A.; Comeron, A.; Gibert, F.; Landulfo, E.; McCormick, M.P.; Senff, C.; Veselovskii, I.; Wandinger, U.
    For aerosol typing with lidar, sea salt particles are usually assumed to be spherical with a consequently low depolarization ratio. Evidence of dried marine particles at the top of the humid marine aerosol layer with a depolarization ratio up to 0.1 has been found at predominately maritime locations on Barbados and in the Southern Atlantic. The depolarization ratio for these probably cubic sea salt particles has been measured at three wavelengths (355, 532 and 1064 nm) simultaneously for the first time and compared to model simulations.
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    Study of mixed phase clouds over west Africa: Ice-crystal corner reflection effects observed with a two-wavelength polarization lidar
    (Les Ulis : EDP Sciences, 2018) Veselovskii, Igor; Goloub, Philippe; Podvin, Thierry; Tanre, Didier; Ansmann, Albert; Korenskiy, Michail; Borovoi, Anatoli; Hu, Qiaoyun; Bovchaliuk, Valentin; Whiteman, David N.; Nicolae, D.; Makoto, A.; Vassilis, A.; Balis, D.; Behrendt, A.; Comeron, A.; Gibert, F.; Landulfo, E.; McCormick, M.P.; Senff, C.; Veselovskii, I.; Wandinger, U.
    Lidar sounding is used for the analysis of possible contribution of the corner reflection (CR) effect to the total backscattering in case of ice crystals. Our study is based on observations of mixed phase clouds performed during the SHADOW campaign in Senegal. Mie-Raman lidar allows measurements at 355 nm and 532 nm at 43 dg. off-zenith angle, so the extinction and backscattering Ångström exponents can be evaluated. In some measurements we observed the positive values of backscattering Ångström exponent, which can be attributed to the corner reflection by horizontally oriented ice plates.
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    Natural streamflow simulation for two largest river basins in Poland: A baseline for identification of flow alterations
    (Göttingen : Copernicus, 2016) Piniewski, Mikołaj; Cudennec, Christophe
    The objective of this study was to apply a previously developed large-scale and high-resolution SWAT model of the Vistula and the Odra basins, calibrated with the focus of natural flow simulation, in order to assess the impact of three different dam reservoirs on streamflow using the Indicators of Hydrologic Alteration (IHA). A tailored spatial calibration approach was designed, in which calibration was focused on a large set of relatively small non-nested sub-catchments with semi-natural flow regime. These were classified into calibration clusters based on the flow statistics similarity. After performing calibration and validation that gave overall positive results, the calibrated parameter values were transferred to the remaining part of the basins using an approach based on hydrological similarity of donor and target catchments. The calibrated model was applied in three case studies with the purpose of assessing the effect of dam reservoirs (Włocławek, Siemianówka and Czorsztyn Reservoirs) on streamflow alteration. Both the assessment based on gauged streamflow (Before-After design) and the one based on simulated natural streamflow showed large alterations in selected flow statistics related to magnitude, duration, high and low flow pulses and rate of change. Some benefits of using a large-scale and high-resolution hydrological model for the assessment of streamflow alteration include: (1) providing an alternative or complementary approach to the classical Before-After designs, (2) isolating the climate variability effect from the dam (or any other source of alteration) effect, (3) providing a practical tool that can be applied at a range of spatial scales over large area such as a country, in a uniform way. Thus, presented approach can be applied for designing more natural flow regimes, which is crucial for river and floodplain ecosystem restoration in the context of the European Union's policy on environmental flows.