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  • 2000-2004  (1)
  • 1980-1984  (2)
  • 1940-1944
  • microcinematography  (2)
  • African grasses  (1)
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Erscheinungszeitraum
  • 2000-2004  (1)
  • 1980-1984  (2)
  • 1940-1944
Jahr
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Biological invasions 2 (2000), S. 123-140 
    ISSN: 1573-1464
    Schlagwort(e): African grasses ; ecophysiology ; ecosystem effects ; global change ; invasions ; pasture conversion ; tropical America
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Clearing of natural vegetation for pastures and the deliberate introduction of African grasses constitute significant threats to the biological diversity of the tropics, subtropics, and warm temperate regions of the Americas. African grasses have escaped from cultivated pastures and revegetated rangeland sites and invaded natural areas at alarming rates. Invaded ecosystems tend to be biotically impoverished and differ markedly from adjacent non-invaded areas in structure and function. Effects of pasture creation and invasion by African grasses on ecosystem processes (transformation and flux of energy and matter) are primarily related to loss of woody species and changes in the fire regime. However, the ecophysiological attributes of the African grasses (e.g. high biomass allocation to leaves, high growth rate, and high leaf-level gas exchange rates) also have important consequences. Here we describe the extent of pasture creation with African grasses and their invasive spread in the New World and review ecological effects of these land-cover changes. We highlight a number of comparative ecophysiological studies within the context of mechanisms responsible for invasion by African grasses and resulting ecosystem change.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Gamete Research 4 (1981), S. 83-95 
    ISSN: 0148-7280
    Schlagwort(e): human spermatozoa ; flagellum ; motion ; microcinematography ; kinematics ; Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: A microcinematographic (50 f/s) study was performed on motile human spermatozoa. Eighty percent were found to have a linear trajectory and a pseudo-sinusoidal head displacement pattern. Throughout their progression, the spermatozoa periodically rotated on their longitudinal axis at a frequency equal to that of flagellar wave formation. These waves were found always to begin on the same side of the cell and to propagate in the flattened plane of the head until the moment of rotation. At this time the wave had reached a point near the middle of the flagellum. Beyond this point, the flagellum moves out of the plane of the head. Different variables used to characterize the movement of spermatozoa included the velocity of progression, amplitude and velocity of head displacement, frequency of rotation, wave amplitude, and propagation velocity of the flagellar wave. Among these variables, it was the propagation velocity of the wave that was found to be best correlated with the velocity of spermatozoan progression. This flagellar wave exhibited two stages, one of initiation and one of propagation.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Gamete Research 9 (1984), S. 183-195 
    ISSN: 0148-7280
    Schlagwort(e): flagellar wave ; human spermatozoa ; microcinematography ; Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Microcinematographic analysis (50 frames/sec) of the movement of 57 ejaculated human spermatozoa showed a heterogeneity of the flagellar parameters (velocity of the wave development (Vd), velocity of the wave propagation (Vc), beat frequency) corresponding to that of head trajectories (progressive velocity and amplitude of the lateral head displacement). According to our results the interdoublet sliding velocity might control the progressive velocity of the spermatozoa through the wave propagation velocity. The presence of the principal bend on the proximal part of the flagellum (20 μm) might inhibit the initiation of a new wave. The complex relation existing between Vc and Vd seems to indicate that the two velocities are partly independent of one another.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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