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  • Structure  (2)
  • 41.80E  (1)
  • 1
    ISSN: 1432-0649
    Schlagwort(e): 41.80E ; 52.25 ; 29.15D
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract First results are presented from an experiment scattering laser light from a relativistic electron beam. The 5 cm diameter continuous electron beam of 28 keV kinetic energy and 2.6 A current presents an electron gas of a density of 8×107 cm−3, from which 20 ns pulses of laser light (490 nm) were scattered at a repetition rate of 15 Hz and an average power of 20 mJ per pulse. The Doppler-shifted wavelength of photons backscattered under 180° was analysed with a Fabry-Perot interferometer. This technique provides, for the first time, a non-destructive measurement of the velocity distribution in an electron beam radially resolved in space. The results presented here comprise the direct measurement of the absolute electron energy and the degree of space-charge compensation in the electron beam. The determination of an upper bound of 10−2 for the ratio of longitudinal to transverse electron temperature implies the first direct measurement of a flattened velocity distribution.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    European journal of pediatrics 128 (1978), S. 247-259 
    ISSN: 1432-1076
    Schlagwort(e): Umbilical artery ; Birth ; Neonatal ; Blood vessel ; Structure ; Closure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The structure of the fully-patent umbilical artery and rearrangement of its structural elements with postnatal closure were examined in 10 centimeter long umbilical cord segments which were double-clamped at different time intervals after delivery. The fully-patent umbilical artery consists of two main layers: an outer layer of circularly arranged smooth muscle cells and an inner layer which shows rather irregularly and loosely arranged cells embedded in abundant metachromatic ground substance. No predominantly longitudinal arrangements of cells and fibers reported by earlier investigators could be identified in the inner layer. Closure of the umbilical arteries is initiated by numerous localized contractions which are mainly formed by muscle cells of the outer circular layer. Ultimate closure of larger segments of the umbilical arteries is also mainly produced by contractions of the outer layer. In contrast, the inner layer (which is rich in ground substance) seems to serve mainly as a plastic tissue which can easily be shifted in an axial direction and then folded into the narrowing lumen to complete closure. Electron microscopy reveals that the cells of this layer represent rather poorly differentiated smooth muscle cells which contain only a few tiny myofilaments and can therefore hardly contribute actively to the process of closure.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 130 (1972), S. 378-388 
    ISSN: 1432-0878
    Schlagwort(e): Arteries ; Children ; Structure ; Pattern of calcification ; Light microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Gross calcifications of the common iliac and internal iliac arteries represent a common finding in newborn children and infants. In both arteries, the calcific deposits regularly appear in certain areas of the arterial luminal surface only, whereas the other parts of the arterial wall remain free of gross lesions even in cases with a pronounced calcification. In the common iliac artery, the lateral wall of the vessel and the adjacent sectors of the anterior and posterior wall represent the predilection site of calcific deposits. In the internal iliac artery, the gross calcifications have been regularly demonstrated in the dorso-medial wall. The predominant localisation of the calcification in these parts of the vessels and its absence in the others depend on the definite structural features of the arterial tube and different affinity for calcium of the individual structural elements. In both iliac arteries, only the primary internal elastic membrane undergoes early calcification. However, unlike the most muscular arteries, this membrane is not developed in the whole arterial circumference of the common iliac and internal iliac arteries, but is absent in large areas of their arterial luminal layer. In these areas, the subendothelial or subintimal elastic layers are formed by the networks of longitudinally arranged elastic fibers or membraneous elastic structures which arise from the elastic networks with the further growth. These elastic elements always stay free of calcific deposits. The structural features found in both iliac arteries may be important for the development of the later pathological changes.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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