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Subject: Konferenzschrift × Start date: 2019 × End date: 2019 ×

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Now showing 1 - 10 of 21
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    Bicrystalline grain boundary junctions of Co-doped and P-doped Ba-122 thin films
    (Milton Park : Taylor & Francis, 2014) Schmidt, S.; Döring, S.; Schmidl, F.; Kurth, F.; Iida, K.; Holzapfel, B.; Kawaguchi, T.; Mori, Y.; Ikuta, H.; Seidel, P.
    We prepared GB junctions of Ba(Fe0.9Co0.1)2As2 thin films on bicrystalline [00 l]-tilt SrTiO3 substrates. The junctions show clear Josephson effects. Electrical characterization shows asymmetric I-V characteristics which can be described within the resistively shunted junction (RSJ) model. A large excess current is observed. Their formal ICRN product is 20.2 μV at 4.2 K, which is decreased to 6.5 μV when taking Iex into account. Fabrication methods to increase this value are discussed. Additionally, measurements on GB junctions of BaFe2(As0.66P0.34)2 thin films on LSAT bicrystalline substrates are shown. Their symmetric RSJ/flux flow-behavior exhibits a formal ICRN product of 45 μV, whereas the excess corrected value is ll μV.
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    Prozessmikrobiologie in landwirtschaftlichen Biogasanlagen : Ermittlung der mikrobiellen Diversität sowie von hauptsächlichen verfahrenstechnischen Einflussfaktoren auf die Mikroflora : Schlussbericht zum Forschungsverbund BIOGAS-BIOCOENOSIS : Laufzeit: 01.11.2011 bis 31.10.2013
    (Hannover : Technische Informationsbibliothek, 2014) Theuerl, Susanne; Klocke, Michael; Maus, Irene; Schlüter, Andreas; Benndorf, Dirk; Kohrs, Fabian; Hitzmann, Bernd; Beltramo, Tetyana
    [no abstract available]
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    Long-term trends in the ionospheric E and F1 regions
    (Göttingen : Copernicus, 2008) Bremer, J.
    Ground based ionosonde measurements are the most essential source of information about long-term variations in the ionospheric E and F1 regions. Data of such observations have been derived at many different ionospheric stations all over the world some for more than 50 years. The standard parameters foE, h'E, and foF1 are used for trend analyses in this paper. Two main problems have to be considered in these analyses. Firstly, the data series have to be homogeneous, i.e. the observations should not be disturbed by artificial steps due to technical reasons or changes in the evaluation algorithm. Secondly, the strong solar and geomagnetic influences upon the ionospheric data have carefully to be removed by an appropriate regression analysis. Otherwise the small trends in the different ionospheric parameters cannot be detected. The trends derived at individual stations differ markedly, however their dependence on geographic or geomagnetic latitude is only small. Nevertheless, the mean global trends estimated from the trends at the different stations show some general behaviour (positive trends in foE and foF1, negative trend in h'E) which can at least qualitatively be explained by an increasing atmospheric greenhouse effect (increase of CO2 content and other greenhouse gases) and decreasing ozone values. The positive foE trend is also in qualitative agreement with rocket mass spectrometer observations of ion densities in the E region. First indications could be found that the changing ozone trend at mid-latitudes (before about 1979, between 1979 until 1995, and after about 1995) modifies the estimated mean foE trend.
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    Cathodoluminescence and TEM investigations of structural and optical properties of AlGaN on epitaxial laterally overgrown AlN/sapphire templates
    (Milton Park : Taylor & Francis, 2013) Zeimer, U.; Mogilatenko, A.; Kueller, V.; Knauer, A.; Weyers, M.
    Surface steps as high as 15 nm on up to 10 μm thick AlN layers grown on patterned AlN/sapphire templates play a major role for the structural and optical properties of AlxGa1−xN layers with x ≥ 0.5 grown subsequently by metalorganic vapour phase epitaxy. The higher the Ga content in these layers is, the stronger is the influence of the surface morphology on their properties. For x = 0.5 not only periodic inhomogeneities in the Al content due to growth of Ga-rich facets are observed by cathodoluminescence, but these facets give rise to additional dislocation formation as discovered by annular dark-field scanning transmission electron microscopy. For AlxGa1−xN layers with x = 0.8 the difference in Al content between facets and surrounding material is much smaller. Therefore, the threading dislocation density (TDD) is only defined by the TDD in the underlying epitaxially laterally overgrown (ELO) AlN layer. This way high quality Al0.8Ga0.2N with a thickness up to 1.5 μm and a TDD ≤ 5x108 cm−2 was obtained.
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    Magnetic tornadoes and chromospheric swirls – Definition and classification
    (Milton Park : Taylor & Francis, 2013) Wedemeyer, Sven; Scullion, Eamon; Steiner, Oskar; de la Cruz Rodriguez, Jaime; Rouppe van der Voort, Luc
    Chromospheric swirls are the observational signatures of rotating magnetic field structures in the solar atmosphere, also known as magnetic tornadoes. Swirls appear as dark rotating features in the core of the spectral line of singly ionized calcium at a wavelength of 854.2 nm. This signature can be very subtle and difficult to detect given the dynamic changes in the solar chromosphere. Important steps towards a systematic and objective detection method are the compilation and characterization of a statistically significant sample of observed and simulated chromospheric swirls. Here, we provide a more exact definition of the chromospheric swirl phenomenon and also present a first morphological classification of swirls with three types: (I) Ring, (II) Split, (III) Spiral. We also discuss the nature of the magnetic field structures connected to tornadoes and the influence of limited spatial resolution on the appearance of their photospheric footpoints.
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    Classification and clustering: models, software and applications
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2009) Mucha, Hans-Joachim; Ritter, Gunter
    We are pleased to present the report on the 30th Fall Meeting of the working group ``Data Analysis and Numerical Classification'' (AG-DANK) of the German Classification Society. The meeting took place at the Weierstrass Institute for Applied Analysis and Stochastics (WIAS), Berlin, from Friday Nov. 14 till Saturday Nov. 15, 2008. Already 12 years ago, WIAS had hosted a traditional Fall Meeting with special focus on classification and multivariate graphics (Mucha and Bock, 1996). This time, the special topics were stability of clustering and classification, mixture decomposition, visualization, and statistical software.
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    Development of the fabrication process and characterization of piezoelectric BaTiO3/epoxy composite used for coated ultrasonic transducer patterns in structural health monitoring
    (Cambridge : arXiv, 2016) Bareiro Ferreira, Oscar; Sridaran Venkat, Ramanan; Adam, Jens; Boller, Christian
    Structural health monitoring (SHM) is based on integrating and/or adapting a sensor system into a structure such that a tolerable damage to occur can be monitored. This requires a network of transducers specifically when this SHM approach is considered as a monitoring system such as based on guided waves. A desirable solution would be to get a transducer network simply ‘printed’ on the structure considered once the network has been designed such as through a simulation approach. In the paper proposed the fabrication process and characterization of a piezoelectric composite to be used as an ultrasonic transducer for damage sensing of structures based on SHM using guided waves is first considered. The composite consists of piezoelectric BaTiO3 particles homogenously distributed in an epoxy resin matrix. A paste with a solid volume fraction of up to 50 vol% was prepared by the direct mechanical mixing of the piezoelectric particles in the epoxy matrix. Due to the ferroelectric properties of BaTiO3 the polarization of the composite is required with a high electric field prior to use. Two electrodes placed on both sides of the samples are required to measure the dielectric and electromechanical properties of the composite in the form of a thick film. The influence of the volume fraction of BaTiO3 on the dialectic properties and piezoelectric transversal constant (d33) of the piezoelectric composite will be shown. Beyond this more materials processing related work performance of those transducers will be demonstrated. This will be done in terms of getting those coated as a transducer pattern/network on a hosting structure after having had the transducer network determined through simulation. Validation of the approach will be done by looking at the transducer network’s performance in terms of detecting guided acoustic waves.
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    Quasi-static and dynamic deformation behaviour of Zr-based bulk metallic glass
    (Milton Park : Taylor & Francis, 2013) Nekouie, V.; Kühn, U.; Roy, A.; Silberschmidt, V.
    Nano- and micro-indentation studies were carried out to characterise a plasticity mechanism through the evolution of localised shear bands that drive material's deformation at sub-micron length scale. Initial deformation of Zr-based bulk metallic glass (BMG) was investigated with nanoindentation tests using a spherical indenter. The indentation cycle reflects an elastic deformation with the yielding load of approx. 3 mN. For designed cycling indentation, hardening and softening phenomena were observed in nano- and micro-indentations, respectively. High-precision dynamic mechanical relaxation measurements were performed using a Dynamic Mechanical Analyzer (DMA), on decreasing frequency from 160 Hz to 0.1 Hz. A mechanical response of the BMG surface to a concentrated impact load was also studied. The obtained results indicated that the studied Zr-based BMG behaved as an elastic-perfectly plastic material at macroscale with discrete plasticity events at smaller length scales.
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    Similarities and differences in polar mesosphere summer echoes observed in the Arctic and Antarctica
    (München : European Geopyhsical Union, 2008) Latteck, R.; Singer, W.; Morris, R.J.; Hocking, W.K.; Murphy, D.J.; Holdsworth, D.A.; Swarnalingam, N.
    Polar Mesosphere Summer Echoes (PMSE) have been observed in the high latitudes of the Northern and Southern Hemisphere for several years using VHF radars located at Andenes/Norway (69° N, 16° E), Resolute Bay/Canada (75° N, 95° W), and Davis/Antarctica (69° S, 78° E). The VHF radars at the three sites were calibrated using the same methods (noise source and delayed transmitting signal) and identical equipment. Volume reflectivity was derived from the calibrated echo power and the characteristics of the seasonal variation of PMSE were estimated at the sites for the years 2004 to 2007. The largest peak volume reflectivity of about 2×10−9 m−1 was observed at Andenes compared with their counterparts at Davis (~4×10−11 m−1) and Resolute Bay (~6×10−12 m−1). The peak of the PMSE height distribution is 85.6 km at Davis which is about 1 km higher than at Andenes. At Resolute Bay the height distribution peaks at about 85 km but only a few layers were found below 84 km. The mean PMSE occurrence rate is 83% at Andenes, 38% at Davis with larger variability and only 18% at Resolute Bay (in late summer). The duration of the PMSE season varies at Andenes from 104 to 113 days and at Davis from 88 to 93 days. In general the PMSE seasons starts about 5 days later at Davis and ends about 10 days earlier compared to Andenes. In all three seasons the PMSE occurrence suddenly drops to a much lower level at Davis about 32 days after solstice whereas the PMSE season decays smoothly at Andenes. The duration of the PMSE season at Andenes and Davis is highly correlated with the presence of equatorward directed winds, the observed differences in PMSE occurrence are related to the mesospheric temperatures at both sites.
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    Emerging pattern of global change in the upper atmosphere and ionosphere
    (München : European Geopyhsical Union, 2008) Laštovička, J.; Akmaev, R.A.; Beig, G.; Bremer, J.; Emmert, J.T.; Jacobi, C.; Jarvis, M.J.; Nedoluha, G.; Portnyagin, Yu. I.
    In the upper atmosphere, greenhouse gases produce a cooling effect, instead of a warming effect. Increases in greenhouse gas concentrations are expected to induce substantial changes in the mesosphere, thermosphere, and ionosphere, including a thermal contraction of these layers. In this article we construct for the first time a pattern of the observed long-term global change in the upper atmosphere, based on trend studies of various parameters. The picture we obtain is qualitative, and contains several gaps and a few discrepancies, but the overall pattern of observed long-term changes throughout the upper atmosphere is consistent with model predictions of the effect of greenhouse gas increases. Together with the large body of lower atmospheric trend research, our synthesis indicates that anthropogenic emissions of greenhouse gases are affecting the atmosphere at nearly all altitudes between ground and space.