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  • 1
    Publication Date: 2021-06-14
    Description: In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 2
    Publication Date: 2019-07-17
    Description: The time dependent circulation of the North Brazil Current is studied with three numerical ocean circulation models, which differ by the vertical coordinate used to formulate theprimitive equations. The models are driven with the same surface boundary conditions and their horizontal grid-resolution (isotropic, 1/3° at the equator) is in principle fine enough topermit the generation of mesoscale eddies. Our analysis of the mean seasonal currents concludes that the volume transport of the North Brazil Current (NBC) at the equator isprincipally determined by the strength of the meridional overturning, and suggests that the return path of the global thermohaline circulation is concentrated in the NBC. Models whichsimulate a realistic overturning at 24°N of the order of 16-18 Sv also simulate a realistic NBC transport of nearly 35 Sv comparable to estimates deduced from the most recentobservations. In all models, the major part of this inflow of warm waters from the South Atlantic recirculates in the zonal equatorial current system, but the models also agree on theexistence of a permanent coastal mean flow to the north-west, from the equator into the Carribean Sea, in the form of a continuous current or a succession of eddies. Importantdifferences are found between models in their representation of the eddy field. The reasons invoked are the use of different subgrid-scale parameterisations, and differences instability of the NBC retroflection loop because of differences in the representation of the effect of bottom friction according to the vertical coordinate that is used. Finally, even ifdifferences noticed between models in the details of the seasonal mean circulation and water mass properties could be explained by differences in the eddy field, nonetheless themajor characteristics (mean seasonal currents, volume and heat transports) appears to be at first order driven by the strength of the thermohaline circulation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
    Publication Date: 2019-07-17
    Description: Three different, eddy-permitting numerical models are used to examine the seasonal variation ofmeridional mass and heat flux in the North Atlantic, with a focus on the transport mechanisms inthe subtropics relating to observational studies near 25°N. The models, developed in theDYNAMO project, cover the same horizontal domain, with a locally isotropic grid of 1/3° resolutionin longitude, and are subject to the same monthly-mean atmospheric forcing based on athree-year ECMWF climatology. The models differ in the vertical-coordinate scheme(geopotential, isopycnic, and sigma), implying differences in lateral and diapycnic mixingconcepts, and implementation of bottom topography. As shown in the companion paper ofWillebrand et al. (2001), the model solutions exhibit significant discrepancies in the annual-meanpatterns of meridional mass and heat transport, as well as in the structure of the western boundarycurrent system.Despite these differences in the mean properties, the seasonal anomalies of the meridional fluxesare in remarkable agreement, demonstrating a robust model behavior that is primarily dependenton the external forcing, and independent of choices of numerics and parameterization. The annualrange is smaller than in previous model studies in which wind stress climatologies based on marineobservations were used, both in the equatorial Atlantic (1.4 PW) and in the subtropics (0.4-0.5PW). This is a consequence of a weaker seasonal variation in the zonal wind stresses based onthe ECMWF analysis than those derived from climatologies of marine observations.The similarities in the amplitude and patterns of the meridional transport anomalies betwen thedifferent model realizations provide support for previous model conclusions concerning themechanism of seasonal and intraseasonal heat flux variations: they can be rationalized in terms of atime-varying Ekman transport and their predominantly barotropic compensation at depth. Analysisfor 25°N indicates that the net meridional flow variation at depth is concentrated near the westernboundary, but cannot be inferred from transport measurements in the western boundary currentsystem, because of significant and complex recirculations over the western half of the basin. Themodel results instead suggest that the main requirement for estimating the annual cycle of heatflux through a transoceanic section, and the major source of error in model simulations, is anaccurate knowledge of the wind stress variation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
    Publication Date: 2019-07-17
    Description: A systematic intercomparison of three realistic eddy-permitting models of the North Atlanticcirculation has been performed. The models use different concepts for the discretization of thevertical coordinate, namely geopotential levels, isopycnal layers, terrain-following (sigma)coordinates, respectively. Although these models were integrated under nearly identicalconditions, the resulting large-scale model circulations show substantial differences. The resultsdemonstrate that the large-scale thermohaline circulation is very sensitive to the modelrepresentation of certain localised processes, in particular to the amount and water massproperties of the overflow across the Greenland-Scotland region, to the amount of mixing withina few hundred kilometers south of the sills, and to several other processes at small or sub-gridscales. The different behaviour of the three models can to a large extent be explained as aconsequence of the different model representation of these processes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 13 (1991), S. 157-163 
    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Two approximate formulae to calculate the eigenvalues of pure quadrupole interaction in Mössbauer effect studies have been proposed and the eigenvalue coefficients in the formulae have been given for various excited states and ground states of the nucleus with different spin. All the eigenvalues of pure quadrupole interaction between both excited state and ground state of nucleus with spinI=3/2÷9/2 and the electric-field gradient with different asymmetry parameter (η=0÷1.0) have been calculated by these formulae. The results show that the accuracies in all the calculations are more satisfactory or same in comparison with those obtained by the formula of Shenoy and Dunlap, especially when the asymmetry parameter of electric-field gradient is larger than 0.8 for the nucleus with spinI=5/2.
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Chemical Physics Letters 201 (1993), S. 535-542 
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have identified a third citrate synthase gene in Saccharomyces cerevisiae which we have called CIT3Complementation of a citrate synthase-deficient strain of Escherichia coli by lacZ ::CIT3 gene fusions demonstrated that the CIT3 gene encodes an active citrate synthase. The CIT3 gene seems to be regulated in the same way as CIT1, which encodes the mitochondrial isoform of citrate synthase. Deletion of the CIT3 gene in a Δcit1 background severely reduced growth on the respiratory substrate glycerol, whilst multiple copies of the CIT3 gene in a Δcit1 background significantly improved growth on acetate. In vitro import experiments showed that cit3p is transported into the mitochondria. Taken together, these data show that the CIT3 gene encodes a second mitochondrial isoform of citrate synthase.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 7-9 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Confocal microscopy of single molecules bound on a silica surface is performed with precompressed 27 fs laser pulses. Interferometric autocorrelation using a single molecule is demonstrated. It is also shown that orientational distributions can be directly obtained from one- and two-photon images produced with circularly polarized light. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2923-2925 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial SrBi2Ta2O9 thin films have been grown with (001) and (110) orientations by pulsed laser deposition on (001) LaAlO3–Sr2AlTaO6 and (100) LaSrAlO4 substrates, respectively. Four-circle x-ray diffraction and transmission electron microscopy reveal nearly phase pure epitaxial films. Minimization of surface mesh mismatch between the film and substrate (i.e., choice of appropriate substrate material and orientation) was used to stabilize the desired orientations and achieve epitaxial growth. © 1998 American Institute of Physics.
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