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  • Springer  (181)
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  • 1
    Electronic Resource
    Electronic Resource
    Membranes during yolk-platelet development in oocytes of the toad Bufo marinus (1987)
    Springer
    Development genes and evolution 196 (1987), S. 367-371 
    Details
    ISSN: 1432-041X
    Keywords: Vitellogenesis ; Bufo marinus oocyte ; Yolk-platelet membrane ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Oocytes of the toad Bufo marinus have been studied by means of thin section and particularly freeze-fracture electron microscopy to characterize the cytoplasmic membranes around the yolk organelle, and the storage of yolk material in precursors and platelets. This appears to be a previously unknown type of yolk-platelet formation. During yolk-organelle development from the primordial precursor to the bi-partite fully grown yolk platelet, numerous lipoid droplets are attached to the periphery of the platelet, indicating an intense uptake of lipids. As is typical for amphibians, the fully grown yolk platelet has a crystalline internum covered by a dense osmiophilic externum, and the whole organelle is enveloped by a plasma membrane that shows no direct connection or fusion with endocytotic vesicles. The yolk membrane exhibits few intramembraneous particles (IMPs) at the core areas and some more where it borders fields of lipoid droplets. Here the IMPs show a net-like arrangement in the furrows between adjacent droplets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00375773
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  • 2
    Electronic Resource
    Electronic Resource
    Yolk organelles and their membranes during vitellogenesis ofXenopus oocytes (1989)
    Springer
    Development genes and evolution 198 (1989), S. 92-102 
    Details
    ISSN: 1432-041X
    Keywords: Vitellogenesis ; Xenopus oocyte ; Yolk-platelet membrane ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The yolk platelets ofXenopus laevis have been studied by thin-section and freeze-fracture electron microscopy to characterize the boundary membrane during yolk formation. Throughout vitellogenesis, large yolk platelets are in close contact with smaller nascent yolk organelles. Two types of primordial yolk platelets (I and II) have been discriminated. After membrane fusion these precursors can be completely incorporated into the main body of existing platelets, numerous yolk crystals then merge and form one uniformly stratified core. Lipid droplets are tightly attached to the membrane at all developmental stages of yolk platelets. A direct connection of endoplasmic reticulum to the membranes of yolk platelets was not observed. On freezeetching replicas, yolk-platelet membranes present fracture faces with intramembranous particles (IMP) of various sizes and a heterogeneous distribution of approximately 200–600 IMP/μm2 at the E face, and 1200–2100 IMP/μm2 at the P face. Again, this presentation of the membrane exhibits neither anastomoses to the endoplasmic reticulum, nor caveolae that exclude the uptake of yolk-containing vesicles into these yolk organelles. Proteinaceous yolk platelets tend to fracture along their periphery through the superficial layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02447744
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental studies on the suitability of human mesothelial cells for seeding vascular prostheses: shear stress resistance in vitro (1996)
    Springer
    Journal of materials science 7 (1996), S. 543-550 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: This investigation forms part of a study on the suitability of human omentum mesothelial cells (HOMES) as an alternative to endothelial cells (EC) for seeding vascular grafts. Isolated HOMES were grown in primary culture and characterized by their morphology (light microscopy and scanning electron microscopy (SEM)), as well as by fluorescence-activated cell sorting (FACS) and immunocytochemistry. The latter two methods showed cells which were positive for smooth muscle-type actin and cytokeratin, but negative for factor VIII-related antigen. HOMES were grown to confluence on glass with or without a fibronectin coating. Controlled shear stress was applied for up to 30 min using a plate and cone rheometer at 20 dynes/cm2. These dynamic culture conditions led to loss of only occasional cells. The most marked alterations seen on SEM were some cell elongation, marked raising of the nucleus and loss of luminal cytoplasmic microvilli. Time-lapse video microscopy revealed that shear stress also increased the spreading capacity of some cells. Similar experiments with venous endothelial cells gave a shearing off of a confluent monolayer. This investigation shows the marked shear-stress resistance of HOMES, a pre-requisite for their use to seed vascular prostheses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122177
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  • 4
    Electronic Resource
    Electronic Resource
    Screening of biomedical polymer biocompatibility in NMRI-mice peritoneal cavity: A comparison between ultra-high-molecular-weight polyethylene (UHMW-PE) and polyethyleneterephthalate (PET) (1997)
    Springer
    Journal of materials science 8 (1997), S. 239-245 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The peritoneal resident cell population is influenced by various inflammatory and immunogenic stimuli. The influence of intraperitoneal application of polyethyleneterephthalate (PET) (group A) and ultra-high-molecular-weight polyethylene (UHMW-PE) (group B) powders on peritoneal cell count and macrophage activity was investigated. Powders were tested to mimic wear particles from solid implant devices as these particles often cause chronic granulomatous inflammation. The results were compared with the inflammatory response following an abdominal midline incision (group C) and untreated animals (group D). On days 1, 7, 14 and 30 peritoneal cells were quantified and the number of active macrophages was assessed. Groups A and C mice showed a significant loss of macrophages in the peritoneal lavage at day 1 but this returned to normal values (group D) on day 7. In contrast, group B animals remained at low peritoneal cell counts but showed the highest number of active macrophages. Only in this latter group was adhesion formation and granulomatous clustering of polymer powder observed. Applying the parameters macrophage count and the number of active macrophages it can be concluded that PET elicits a weaker inflammatory reaction than UHMW-PE in mice peritoneal cavity. Thus this animal model may be used as a screening test for biomedical materials, especially their wear products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018595825048
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  • 5
    Electronic Resource
    Electronic Resource
    New Y-TZP powders for medical grade zirconia (1997)
    Springer
    Journal of materials science 8 (1997), S. 113-118 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract There is interest in using zirconia for biomedical applications as ballheads for total hip prostheses. Two potential types are under discussion:partially stabilized zirconia (PSZ) and tetragonal zirconia polycrystals (TZP)materials. Because of its enhanced material properties, TZP stabilized withyttria is favourable. To eliminate high amounts of natural radioactiveimpurities, the precursors are purified. The kind of precursor and purificationmethod determine the powder impurity level. The disadvantage of Y-TZP is thatthe hydrothermal decomposition reaction method is that it depends very stronglyon the grain size and the distribution of the stabilizing yttria within thezirconia grains. Thermodynamical and kinetic investigations on high puritycoprecipitated and yttria-coated zirconia powders show different behaviours.Y-TZP materials based on yttria-coated zirconia powders show excellentmechanical strength of more than 1000 MPa, a Weibull modulus of up to 20 a!nd a fracture toughness of 9 MPa√m. The material properties of Y-TZP ceramicsbased on coprecipitated powders and prepared under the same conditions are lessattractive. It is expected that materials based on yttria-coated zirconia willshow enhanced properties compared to materials derived from coprecipitatedpowders. Therefore Y-TZP materials derived from yttria-coated powders are veryattractive as medical grade zirconia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018562917779
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  • 6
    Electronic Resource
    Electronic Resource
    Investigations into the mechanical reliability of ceramic femoral heads for hip joints (1994)
    Springer
    Journal of materials science 5 (1994), S. 503-506 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: This paper reports the findings of a finite element analysis applied to the study of ceramic femoral ball heads. The objective of carrying out these analyses was to assess the shape design and loading conditions applied to specific femoral heads and to capture the stress fields developed when they are subjected to idealized test conditions. Two designs were considered, these being the existing Biolox keyhole shape, manufactured by Cerasiv, Medical Products Division and an alternative design with a flat top internal hole. For each of these designs, three load cases and two types of frictional contact were considered. It is shown that the key hole shape with full taper contact conditions together with the higher value of surface friction produce the lowest tensile stress fields in the ball head hence increasing mechanical reliability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00058992
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  • 7
    Electronic Resource
    Electronic Resource
    Oogenese und Sexualität der KäferschneckeLepidochitona cinereus (Mollusca, Polyplacophora) (1974)
    Springer
    Helgoland marine research 26 (1974), S. 42-62 
    Details
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung 1. Die Entwicklung der Oocyten vonLepidochitona cinereus (L.) wurde lichtmikroskopisch untersucht und nach histologischen Merkmalen in fünf Stadien eingeteilt. 2. Während der Reifung wachsen die Oocyten aus dem Keimepithel heraus, bleiben mit ihm zunächst durch einen Gewebsstiel verbunden und lösen sich schließlich völlig. 3. Vor Eintritt in die Hauptphase der Vitellogenese wird die Oberfläche durch Vorwölbungen des Cytoplasma wesentlich vergrößert. Diese Vorwölbungen bilden sich später zurück. 4. Die Oocytenhülle ist mehrschichtig und trägt charakteristische Anhänge. 5. Körpervolumen und Ovarvolumen stehen in direkter Korrelation. Die ♀♀ werden bei einer Länge von etwa 6 mm legereif. 6. Erwachsene ♀♀ legen durchschnittlich 1300, maximal 1800 Eier pro Jahr. Höhepunkte der Eiablage sind im Lister Wattenmeer die Monate Mai-Juni und September-Oktober. 7. Die Geschlechter treten im Verhältnis 1:1 auf. 8. Sexualdimorphismus ließ sich nicht nachweisen.
    Notes: Abstract The development of the oocytes ofLepidochitona cinereus (L.) has been studied by light microscopical techniques. This development comprises 5 stages, which can be characterized by histological features. During development the egg cells protrude gradually from the germ epithelium and, finally, become separated from the epithelium. Preceding main vitellogenesis, the oocyte surface is enlarged by cytoplasmic protrusions, which are later reduced. The oocyte cortex or hull is multilayered and is set with appendages. The volumes of the animal's body and of the ovary are directly correlated. Young females become ripe at a length of 6 mm. Adult females produce about 1300 (maximum 1800) eggs annually. Near List (on the North Frisian Island of Sylt) the main spawning times are from May to June and from September to October. Sex ratio is 1 : 1; sexual dimorphism has not been demonstrable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01613304
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesen und Massenspektren von 3,17β-Dihydroxyandrostan-11,16-dionen und 17β-Hydroxyandrostan-3,11,16-trionen (1976)
    Springer
    Monatshefte für Chemie 107 (1976), S. 459-472 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The syntheses and mass spectra of the four 3,17β-dihydroxyandrostane-11,16-diones and of the two 17β-hydroxyandrostane-3,11,16-triones are described. These compounds decompose in the mass spectrometer in a different way than androstanes containing a carbonyl group in the position 11 or 16: First they eliminate the C-atoms 15 to 17. Then a cleavage of the C-atoms of the ringA plus C-6 follows resulting in key ions which contain the ringC and the C-atom 7. The connection of theA/B-ring system can be deduced by the spectra for all described compounds. The unequivocal determination of the configuration of the 3-hydroxy group is possible only for the 3,17β-dihydroxy-5β-androstan-11,16-diones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00906875
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  • 9
    Electronic Resource
    Electronic Resource
    Buchbesprechungen (1986)
    Springer
    Meteorology and atmospheric physics 36 (1986), S. 213-218 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02278329
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  • 10
    Electronic Resource
    Electronic Resource
    Die Großwasserkraftwerke in Österreich und ihre Auswirkungen auf die Forstwirtschaft (Wildbachverbauung) (1952)
    Springer
    European journal of forest research 71 (1952), S. 88-97 
    Details
    ISSN: 1612-4677
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01821451
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