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  • 1
    Electronic Resource
    Electronic Resource
    Fraction of H-bonded segments of N-ethylpyrrolidone, oligomeric and polymeric vinylpyrrolidone adsorbed from CHCl3 on silica measured by IR spectrometry (1985)
    Springer
    Colloid & polymer science 263 (1985), S. 372-380 
    Details
    ISSN: 1435-1536
    Keywords: Polymer adsorption ; IR spectrometry ; fraction of adhered segments ; silica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The adsorption of N-ethylpyrrolidone (NEP), oligomeric and polymeric vinylpyrrolidone (OVP, PVP) on silica (Aerosil 200) from CHCl3 solution is investigated by IR spectrometry. The influence of the annealing temperature of the silica on the adsorbed amount and on the fraction of adhered segments was studied. The dependences of the amount adsorbed on solution concentration result for NEP in a Langmuir isotherm for OVP and PVP in high affinity isotherms. The fraction of adhered H-bridged carbonyl groups determined by compensation procedures, the fraction of surface SiOH groups occupied and the multiple interaction quotientQ show different dependences on the amount adsorbed for the measured adsorptives, indicating different interactions of the monomeric segments with the surface groups. This behaviour is explained by comparing the amount adsorbed in saturation with monolayer capacities, surface concentration of SiOH groups and frequency shifts. A splitting of the band of the bound carbonyl groups in a double peak was observed with OVP and PVP, referring to an additional interaction of polymer segments neighboured to specifically bound segments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01410383
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Tracer permeability of rat cortical blood vessels during regional hypothermia (1987)
    Springer
    Acta neuropathologica 73 (1987), S. 349-356 
    Details
    ISSN: 1432-0533
    Keywords: Blood-brain barrier ; Cortex ; Lanthanum tracer ; Potassium ; Ion-selective micro-electrode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Using lanthanum nitrate as a tracer, the permeability of rat cortical blood vessels was investigated during regional hypothermia of the cerebral cortex by electron microscopy. The concentration of K+ ions in the extracellular space of the cortex was determined using an ion-selective micro-electrode. Only at temperatures below about 7°C was an extravasation of tracer observed in a number of cortical capillaries and arterioles, where some of the tight junctions became widened and permeable. In a few cases penetration of the tracer into vacuoles of phagocytosing pericytes or macrophages was found. The extravasation of the tracer could mainly be observed in vessels on and below the cortical surface, less often in deeper cortical parts. At the same degree of hypothermia, the K+ concentration in the extracellular space increased, reaching a maximal value of ca. 6 mmol/l at a depth of about 200 μm. As could be shown in one previous experiment, the K+ concentration reached normal values again after rewarming to 37°C for 15 min, but an extravasation of the tracer was still observed. The role of the endothelial tight junctions and of the astrocytes together with the pericytes (or macrophages) is discussed regarding their importance for the effectiveness of the blood-brain barrier system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00688258
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Pattern of compartmentation in human seminiferous tubules showing dislocation of spermatogonia (1989)
    Springer
    Cell & tissue research 256 (1989), S. 183-190 
    Details
    ISSN: 1432-0878
    Keywords: Testis ; Spermatogonia, dislocation ; Compartmentation, pattern ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The pattern of compartmentation of the seminiferous epithelium was investigated, using a lanthanum tracer technique, in human testicular biopsies of adult infertile men (age 27 to 44 years), where dislocation of spermatogonia from the basal lamina occurred. Spermatogonia type A and B were found in a two-or three-layered arrangement, in aberrant locations throughout the seminiferous epithelium, and in intratubular positions associated with fragments of Sertoli cell cytoplasm. Tracer impregnation was found around spermatogonia in a multilayered arrangement, indicating the extension of the basal compartment in a luminal direction. Single spermatogonia within the second or third layer of the seminiferous epithelium were regularly found to be surrounded by tracer. The junctional complex between the lateral membranes of adjacent Sertoli cells was devoid of tight junctions. Tracer penetration around spermatogonia in a more luminal position was prevented by intact Sertoli cell junctional complexes; tracer was also absent from intraluminal located spermatogonia associated with cytoplasmic fragments of Sertoli cells. The luminal extension of the basal compartment associated with the dislocation of spermatogonia clearly differs from the pattern of compartmentation during the movement of primary spermatocytes within undisturbed epithelium. There is a strong incidence of elevated serum levels of folliclestimulating hormone (〉7 U/l), indicating a suppression of Sertoli cell function; this may be the cause for the dislocation of spermatogonia and the changes of compartmentation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00224733
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    Paper (German National Licenses)
    Fulltext
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