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  • 1990-1994  (3)
  • Chemistry  (1)
  • Geostatistics  (1)
  • Pigs  (1)
  • 1
    ISSN: 1432-1939
    Keywords: Filamentous algae ; Geostatistics ; Physella herbivory ; Spatial dependence ; Stream periphyton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We demonstrated the effect of an aquatic herbivore on the spatial arrangement of benthic algal biomass within artificial stream channels. Transects of ceramic tiles were exposed to a gradient of snail (Physella) densities in a 30 d experiment. We observed positive effects of snails on the mean abundance of “overstory” algae (the filamentous chlorophyte Cladophora and associated epiphytes), an important benthic microhabitat in streams. Snails altered several aspects of the spatial arrangement of overstory algae. Snails reduced the strength of downstream gradients in overstory biomass, as well as residual variability around these gradients. Geostatistical analysis revealed that snails also reduced the strength of spatial dependence, and so reduced spatial heterogeneity of the overstory, at small scales (〈40 cm). As a result, organisms inhabiting the overstory might experience a more fragmented habitat landscape at high snail densities. In addition, snails increased the scale of spatial dependence in understory algal biomass (algae remaining on tiles after overstory was removed) from 10 cm to 40 cm. Consumer effects on the spatial arrangement of a microhabitat argue for the inclusion of feedbacks between the biota and the environment in spatially-explicit models.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-2573
    Keywords: Pulmonary artery ; Hemodynamics ; Blood velocity ; Pulsed Doppler ultrasound ; Pigs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The aim of this study was to provide detailed data on velocity profile development in the normal porcine main pulmonary artery and its main branches. Under spontaneous hemodynamic conditions in twelve open-chest 90kg pigs, perivascular pulsed Doppler ultrasound was used for blood velocity measurements in the entire cross-sectional area in three axial locations in the main pulmonary artery and along one diameter in the main branches. Computerized threedimensional visualizations of the spatial and temporal development of velocity profiles were made throughout the heart cycle. The results were similar one and two diameters downstream of the pulmonary valve. In the early systolic acceleration phase, the velocity profile became skewed, with the highest velocities (132.7 ± 19.4cm · sec−1) towards the inferior to right superior vessel wall, and rotated counterclockwise 45°–90° during the late acceleration to early deceleration phase in 9 out of 11 pigs. Maximum retrograde velocities (31.4 ± 14.9cm · sec−1) were observed at the inferior to the right superior vessel wall in the late systolic deceleration phase and in early diastole. During diastole, low retrograde to insignificant antegrade velocities were observed. Immediately upstream of the pulmonary bifurcation, the velocity profile disclosed two peaks at locations corresponding to the two main branches. A confined area with retrograde velocities was seen at the right vessel wall in late systole. Low-scale antegrade velocities were observed throughout diastole in the entire cross-sectional area. In the left main branch, the velocity profiles were found to be somewhat skewed towards the left vessel wall, corresponding to the smaller curvature of the left main branch, while the velocity profile in the right main branch was skewed against the superior vessel wall throughout systole. This study thus disclosed that the blood velocity profiles in the main pulmonary artery system were skewed and that mean velocity varied 26%–50% between measuring points, exhibiting an as yet unexplained rotational phenomenon. The skewed velocity profile in the porcine pulmonary trunk indicates that single-point blood velocity measurements can only serve as a basis for cardiac output estimations when used with considerable caution.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 66 (1994), S. 1180-1181 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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