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  • 1
    Electronic Resource
    Electronic Resource
    Numerical investigations on strong pattern selecting Eckhaus instabilities in neon glow discharges (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 729-739 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Starting from the hydrodynamic description of the positive column in a neon glow discharge, a numerical approach is used in order to study the nonlinear properties of ionization waves. Within the instability region of the homogeneous equilibrium state, a secondary instability of the Eckhaus type is found. Compared to the classical results, the plasma system shows some peculiarities, e.g., an asymmetric stability band and strong selection of periodic patterns. The dependency of the shape and the width of this band on the discharge parameters is investigated. The spatiotemporal dynamics connected with the transitions from the stability band to the instability region have been studied showing different behavior on the upper and lower border of the stability region. Normally a subcritical Eckhaus instability has been revealed. Moreover, at selected sets of plasma parameters the phenomenon of spatiotemporal intermittency is found. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873859
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Onset of chaotic wave dynamics near the critical point in a glow discharge: Theory and experiment (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 146-150 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conditions for the onset of irregular wave dynamics are derived from a theoretical description of ionization waves in a glow discharge by means of amplitude equations. It is shown that the Benjamin–Feir condition of the cubic Ginzburg–Landau equation is a necessary but not sufficient condition for loss of stability of plane waves in a higher order amplitude equation. The onset conditions are numerically evaluated in the case of a neon discharge. Experimental findings concerning the onset of chaotic wave dynamics near the critical point agree very well with the theoretical predictions. This example reveals physical relevance of higher order nonlinearities close to the critical point. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1332119
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: "Numerical investigations on strong pattern selecting Eckhaus instabilities in neon glow discharges" [Phys. Plasmas 7, 729 (2000)] (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3481-3481 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: © American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874216
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  • 4
    Electronic Resource
    Electronic Resource
    Observation of the spatiotemporal dynamics of ionization wave mode transitions (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 833-835 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental observation of transitions between discrete longitudinal wave modes in a dc neon glow discharge is reported. Experimental findings concerning the pattern selecting instability agree with observations of the Eckhaus instability in fluid systems. This is supported by theoretical considerations of a model equation (Complex Ginzburg–Landau equation) based on a fluid model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873089
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  • 5
    Electronic Resource
    Electronic Resource
    Phase space structure and chaotic scattering in near-integrable systems (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 3 (1993), S. 443-457 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the bifurcation phenomena and the change in phase space structure connected with the transition from regular to chaotic scattering in classical systems with unbounded dynamics. The regular systems discussed in this paper are integrable ones in the sense of Liouville, possessing a degenerated unstable periodic orbit at infinity. By means of a McGehee transformation the degeneracy can be removed and the usual Melnikov method is applied to predict homoclinic crossings of stable and unstable manifolds for the perturbed system. The chosen examples are the perturbed radial Kepler problem and two kinetically coupled Morse oscillators with different potential parameters which model the stretching dynamics in ABC molecules. The calculated subharmonic and homoclinic Melnikov functions can be used to prove the existence of chaotic scattering and of elliptic and hyperbolic periodic orbits, to calculate the width of the main stochastic layer and of the resonances, and to predict the range of initial conditions where singularities in the scattering function are found. In the second example the value of the perturbation parameter at which channel transitions set in is calculated. The theoretical results are supplemented by numerical experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.165951
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  • 6
    Electronic Resource
    Electronic Resource
    Kernresonanzuntersuchungen zur Struktur von Steroidketalen (1969)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 311 (1969), S. 983-992 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Durch Protonenresonanzmessungen an Steroiden mit der Äthylendioxy-Gruppe an den C-Atomen 3, 6, 17 und 20 am Cyclohexanon- und Acetonketal in nichtaromatischen und aromatischen Lösungsmitteln werden spektroskopische Charakteristika der Ketalgruppe erhalten. Die „long-range“-Wirkungen der Ketalgruppe auf die angulären Methylgruppen des Steroids, verursacht durch die magnetische Anisotropie und das elektrische Dipolmoment dieser Gruppe, werden theoretisch in relativ guter Übereinstimmung mit den experimentellen Werten ermittelt. An der polaren Ketalgruppe werden in Benzollösung Anlagerungskomplexe gebildet, wobei das π-Elektronensystem des Benzols mit der partiell positiven Seite der Ketalgruppe in Wechselwirkung tritt. Die Breite des Protonenresonanzbereiches der Ketalgruppe, ebenfalls abhängig vom Lösungsmittel, gibt Auskunft über benachbarte Substituenten.Die chemischen Verschiebungen und Kopplungskonstanten der Ketalprotonen selbst erscheinen nicht geeignet, die Stellung der Ketalgruppe im Steroid eindeutig zu bestimmen.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19693110617
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  • 7
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    Bacterioplankton drawdown of coral mass-spawned organic matter (2018)
    NATURE PUBLISHING GROUP
    In:  EPIC3Isme Journal, NATURE PUBLISHING GROUP, 12(9), pp. 2238-2251, ISSN: 1751-7362
    Details
    Publication Date: 2018-08-25
    Description: Coral reef ecosystems are highly sensitive to microbial activities that result from dissolved organic matter (DOM) enrichment of their surrounding seawater. However, the response to particulate organic matter (POM) enrichment is less studied. In a microcosm experiment, we tested the response of bacterioplankton to a pulse of POM from the mass-spawning of Orbicella franksi coral off the Caribbean coast of Panama. Particulate organic carbon (POC), a proxy measurement for POM, increased by 40-fold in seawater samples collected during spawning; 68% degraded within 66 h. The elevation of multiple hydrolases presumably solubilized the spawn-derived POM into DOM. A carbon budget constructed for the 275 µM of degraded POC showed negligible change to the concentration of dissolved organic carbon (DOC), indicating that the DOM was readily utilized. Fourier transform ion cyclotron resonance mass spectrometry shows that the DOM pool became enriched with heteroatom-containing molecules, a trend that suggests microbial alteration of organic matter. Our sensitivity analysis demonstrates that bacterial carbon demand could have accounted for a large proportion of the POC degradation. Further, using bromodeoxyuridine immunocapture in combination with 454 pyrosequencing of the 16S ribosomal RNA gene, we surmise that actively growing bacterial groups were the primary degraders. We conclude that coral gametes are highly labile to bacteria and that such large capacity for bacterial degradation and alteration of organic matter has implications for coral reef health and coastal marine biogeochemistry.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 8
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    Biogeochemical controls on the bacterial populations in the eastern Atlantic Ocean (2011)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Biogeosciences, COPERNICUS GESELLSCHAFT MBH, 8, pp. 3747-3759, ISSN: 1726-4170
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 9
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    Origin-specific molecular signatures of dissolved organic matter in the Lena Delta (2015)
    Springer
    In:  Biogeochemistry, 125 (1-2). pp. 1-14.
    Details
    Publication Date: 2020-10-21
    Description: Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into the Arctic Ocean. We sampled natural waters of the Lena River, the Buor-Khaya Bay (Laptev Sea), permafrost melt water creeks, ice complex melt water creeks and a lake. The goal of this study was to characterize the molecular DOM composition with respect to different water bodies within the Lena Delta. We aimed at an identification of source-specific DOM molecular markers and their relative contribution to DOM of different origin. The molecular characterization was performed for solid-phase extracted DOM by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Average dissolved organic carbon concentrations in the original samples were 490 ± 75 µmol C L−1 for riverine and bay samples and 399 ± 115 µmol C L−1 for permafrost melt water creeks. Average TDN concentrations were elevated in the permafrost melt waters (19.7 ± 7.1 µmol N L−1) in comparison to the river and the bay (both 13.2 ± 2.6 µmol N L−1). FT-ICR MS and statistical tools demonstrated that the origin of DOM in the Lena Delta was systematically reflected in its molecular composition. Magnitude weighted parameters calculated from MS data (O/Cwa, H/Cwa, C/Nwa) highlighted preliminary sample discrimination. The highest H/Cwa of 1.315 was found for DOM in melt water creeks in comparison to 1.281 for river and 1.230 for the bay samples. In the bay samples we observed a higher fraction of oxygen-rich components which was reflected in an O/Cwa ratio of 0.445 in comparison to 0.425 and 0.427 in the river and creeks, respectively. From the southernmost location to the bay a relative depletion of nitrogenous molecular markers and an enrichment of oxidized DOM components occurred. The highest contribution of nitrogenous components was indicative for creeks reflected in a C/Nwa of 104 in comparison to 143 and 176 in the river and bay, respectively. These observations were studied on a molecular formula level using principal component and indicator value analyses. The results showed systematic differences with respect to water origin and constitute an important basis for a better mechanistic understanding of DOM transformations in the changing Arctic rivers.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1007/s10533-014-0049-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    The role of the ocean in the atmospheric budget of carbonyl sulfide (2016)
    In:  [Talk] In: Workshop on Stratospheric Sulfur and its Role in Climate (SSiRC), 25.-28.04.2016, Potsdam, Germany .
    Details
    Publication Date: 2016-05-02
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
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