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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The visual computer 14 (1998), S. 83-94 
    ISSN: 1432-2315
    Keywords: Key words: Volume visualization ; Scientific visualization ; Medical imaging ; Shadow Z-buffer ; Shadow map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Z -buffer technique for fast and efficient shadow generation. Volumetric data contain information about the grid points only. Such data do not provide surface information that could be projected immediately onto the shadow map. To solve this problem, we have implemented two techniques. The first uses a modified adaptive version of the well-known marching cubes algorithm for the special characteristics of medical data sets. The algorithm uses material properties for a precise representation of object boundaries, generating volumetric objects quickly and effectively. There are two representations of the same data set: we use a view-independent approximation to display shadows and the original representation of the volume for object visualization in full precision. The second algorithm uses a ray-tracing approach to create shadow maps. The same routine is used for object rendering, but is restricted to depth-value generation. Semitransparent objects are handled by storing an intensity profile in addition to the depth value.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0878
    Keywords: γ-Glutamyl transpeptidase ; Cerebral capillaries ; Blood-brain barrier ; Cell culture ; Pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Endothelial cells were isolated with high viability (〉93%) from porcine brain capillaries by Percoll gradient centrifugation after purely enzymatic digestion. Primary cultures were grown to confluent cell monolayers and quantitated for the activity of γ-glutamyl transpeptidase. The γ-glutamyl transpeptidase activity starts from a high enzymatic level, decreases with time in culture to about 15% of the initial value, and remains constant at this level after day 10 in culture. The activity progression depends on surface conditions. In the presence of collagen, an exponential decrease starts immediately after seeding, with a time constant of 70±10h. In the absence of collagen, γ-glutamyl transpeptidase activity first decreases on day 1 after plating, recovers to the initial value on day 2 and 3 and afterwards declines exponentially to a low and constant activity level. Ethanol added to the cell culture at a time when low constant activity is reached, reactivates the γ-glutamyl transpeptidase to 30% of the initial value.
    Type of Medium: Electronic Resource
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