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  • Articles  (4)
  • Articles: DFG German National Licenses  (4)
  • Springer  (4)
  • American Institute of Physics (AIP)
  • 2000-2004
  • 1995-1999  (4)
  • 1990-1994
  • 1960-1964
  • 1998  (4)
  • Geosciences  (2)
  • Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition  (2)
  • Physics  (1)
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  • Articles  (4)
Source
  • Articles: DFG German National Licenses  (4)
Keywords
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  • Springer  (4)
  • American Institute of Physics (AIP)
Years
  • 2000-2004
  • 1995-1999  (4)
  • 1990-1994
  • 1960-1964
Year
Topic
  • Geosciences  (2)
  • Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition  (2)
  • Physics  (1)
  • Biology  (5)
  • Medicine  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Cell-specific density of symbiotic dinoflagellates in tropical anthozoans (1998)
    Springer
    Coral reefs 17 (1998), S. 329-337 
    Details
    ISSN: 1432-0975
    Keywords: Key words Coral ; Sea anemone ; Dinoflagellates ; Symbiosis ; Eutrophication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  Symbiotic dinoflagellates are abundant in the endoderm cells of tropical marine anthozoans, but the cell-specific density (CSD) of symbionts has not yet been investigated. In this study we used mechanical and enzymatic methods of maceration, and staining with substrate-specific fluorochromes, to observe a large number of individual host cells from 33 species of tropical anthozoans collected in Florida, Hawaii and Jamaica or cultured in Monaco. In the majority of species, most of the host cells contained a single algal cell (singlet). Host cells with two or more (up to six) algae were much less abundant. The average CSD for the 33 species was 1.54±0.30 (range 1.11 to 2.19). Singlets arranged in a monolayer can account for the areal density of algae observed in many anthozoans. The dinoflagellates occupy most of the interior of macerated host cells, leaving the host cytoplasm and cell membrane as a thin outer layer, often unresolvable by light microscopy. This spatial arrangement may favor diffusion and transport of CO2, bicarbonate ions, and nutrients from the environment to the algae. The effect of nutrient enrichment on CSD was determined by exposing eleven species to chronically elevated levels of ammonium-N. After four weeks all species exhibited a dramatic increase in algal mitotic index and CSD. The potential consequences of environmentally induced increases in CSD in tropical anthozoans are discussed in terms of the decreased cell-specific photosynthesis (CO2 limitation) and decreased rates of calcification observed in other studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003380050133
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Turbulence and Coherent Organizations in the Atmospheric Boundary Layer: A Radar-Aircraft Experimental Approach (1998)
    Springer
    Boundary layer meteorology 86 (1998), S. 147-179 
    Details
    ISSN: 1573-1472
    Keywords: Turbulence ; Convective boundary layer ; Clear air radar observations ; Coherent organizations ; Radar-aircraft joint observations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The scientific objective of the TRAC experiment (Turbulence Radar Aircraft Cells) was to investigate the respective roles played by small-scale turbulence and coherent structures in the vertical transfer within the atmospheric boundary layer (ABL). Field research held in June 1993 in France was based on coupled aircraft and Doppler radar measurements. The results discussed here are mainly focused on the evaluation of the performance of the radar in the 3D description of the clear air ABL, which was the technical goal of TRAC. During the experiment, the radar was able to provide continuous and coherent echo fields over a range of several tens of kilometres, extending up to about 3 km. Good agreement was obtained in the ABL between the radar-derived turbulent quantities and airborne measurements. As depicted by the reflectivity fields, coherent organizations were found to be a common feature of the eleven ABL cases analyzed. These organizations evolved during the day between a banded structure and a cellular pattern. A very weak correlation was found between the reflectivity field and the atmospheric parameters measured by the aircraft. However, in terms of characteristic scale, the reflectivity field appeared to be strongly related to the water vapour field. The inhomogeneity induced by the coherent circulations questions the representativity of one-dimensional sampling of these 3D fields and suggests the need to adapt the traditional statistical approach of the ABL.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000613232592
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Modelling the influence of assimilate availability on root growth and architecture (1998)
    Springer
    Plant and soil 201 (1998), S. 307-320 
    Details
    ISSN: 1573-5036
    Keywords: apical diameter ; carbon allocation ; Hevea brasiliensis ; root system architecture ; root growth ; rubber tree ; simulation model ; sink strength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A model has been designed to simulate rubber seedling root development as related to assimilate availability. Each root of the system is defined both as an element of a network of axes, characterized by its order, position and connections and as an individual sink competing for assimilates. At each time step, the growth of each root is calculated as a function of its own growth potential and of assimilate availability calculated within the whole plant. The potential elongation rate of a root is estimated by its apical diameter, which reflects the size of the meristem. When a root is initiated, the apical diameter depends on root type, but it varies thereafter according to assimilate availability. Thus, the latter controls both current and potential elongation. The model was able to simulate periodicity in root development as related to shoot growth and to reproduce differences in sensitivity to assimilate availability related to root type. It thereby validated the hypothesis that root growth but also root system architecture depend on assimilate allocation and that apical diameter is a good indicator of root growth potential. Provided that specific calibration is done, this model may be used for other species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004380021699
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Geometrical properties of simulated maize root systems: consequences for length density and intersection density (1998)
    Springer
    Plant and soil 200 (1998), S. 157-167 
    Details
    ISSN: 1573-5036
    Keywords: maize ; model ; root architecture ; root intersection ; root length ; stochastic geometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The spatial distribution of root length density (RLD) is important because it affects water and nutrient uptake. It is difficult to obtain reliable estimates of RLD because root systems are very variable and heterogeneous. We identified systematic trends, clustering, and anisotropy as geometrical properties of root systems, and studied their consequences for the sampling and observation of roots. We determined the degree of clustering by comparing the coefficient of variation of a simulated root system with that of a Boolean model. We also present an alternative theoretical derivation of the relation between RLD and root intersection density (RID) based on the theory of random processes of fibres. We show how systematic trends, clustering and anisotropy affect the theoretical relation between RLD and RID, and the consequences this has for measurement of RID in the field. We simulated the root systems of one hundred maize crops grown for a thermal time of 600 K d, and analysed the distribution of RLD and root intersection density RID on regular grids of locations throughout the simulated root systems. Systematic trends were most important in the surface layers, decreasing with depth. Clustering and anisotropy both increased with depth. Roots at depth had a bimodal distribution of root orientation, causing changes in the ratio of RLD/RID. The close proximity of the emerging lateral roots and the parent axis caused clustering which increased the coefficient of variation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004382531671
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    Paper (German National Licenses)
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