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  • Leydig cells  (2)
  • zirconia  (2)
  • Cyanophyceae  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 105 (1997), S. 60-65 
    ISSN: 1435-1536
    Keywords: SANS ; nanoparticles ; titania ; zirconia ; mixed oxide colloids
    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 local structure of titania/zirconia colloids has been investigated using small-angle neutron scattering (SANS). The colloids were produced by: • hydrolysing a mixture of titanium and zirconium alkoxides, and peptising the resulting hydrolysate with nitric acid (homogeneous); • hydrolysing a titanium alkoxide, and peptising the resulting hydrolysate with aqueous zirconium (IV) nitrate solution (heterogeneous). The final titania/zirconia and metal oxide/nitrate mole ratios were 16.0 and 10.0, respectively. The results of SANS contrast variation experiments are described. The minimum-contrast points for the homogeneous and heterogeneous colloids, determined using either the known analytic form of the scattering at q=0 or the scattering invariant, gave similar results, which differed significantly from the expected value. These differences were attributed to the sorption of nitrate counter-ions and hydroxyl species on the surface of the colloids. In both cases, the scattering at minimum contrast was consistent with a fractal network of uni-dimensional zirconia, with a typical diameter of ∼1.5 nm. The results infer that in the homogeneous colloids, the zirconia is segregated within the matrix of the titania crystallites (on ∼1 nm scale), whereas in the heterogeneous colloids, the zirconia is segregated on the surface of the titania crystallites (on ∼10 nm scale).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 2 (1994), S. 215-220 
    ISSN: 1573-4846
    Keywords: zirconia ; hydrolysis kinetics ; precursor chemistry ; zirconium alkoxides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of zirconia colloids by hydrolysing zirconium n-propoxide in n-propanol has been investigated by simultaneous, multi-angle static and dynamic light scattering, and vibrational spectroscopy, as a function of reactant concentration, water-to-alkoxide mole ratio and temperature. The overall hydrolysis/condensation reaction followed pseudo 2nd-order kinetics at 303 K, with an induction period of 〈1 to 24 hours. The induction period could be substantially reduced by increasing the temperature to 348 K. For hydrolysis with 3.6 moles of water per mole of alkoxide, the apparent activation energy was 24 kJ mol−1. Such a low activation energy implies that hydrolysis occurs readily over the temperature range investigated (303–348 K). During the induction period, processing with stoichiometric, or excess, water produced “oxy-hydroxides”, while “hydrated oxides” formed under water-deficient conditions. The hydrolysis reactions yielded zirconia colloids with equivalent spherical, z-averaged diameters of 〈200 nm. The colloids exhibited fractal dimensions of 3.0, with a low size-polydispersity, inferring the formation of dense, monodispersed spherical particles. SEM observations confirmed these results.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1615-6110
    Keywords: Ascolichens ; Ascomycetes ; Lichenothrix riddlei ; Cyanophyceae ; Scytonema ; Distribution ; anatomy ; fine structure ; Flora of New Zealand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lichenothrix riddlei is reported from two widely separate localities in New Zealand. It was previously known only from the South Eastern states of U.S.A. Light and electron microscopy show its sterile fungal partner to belong to the ascomycetes. Apparently as a consequence of lichenization, the variation in breadth of the trichomes of theScytonema phycobiont is greater than normal. A thin, probably gelatinous layer, covering the fungal cells and the algal sheath in the interstices between them, can be demonstrated by electron microscopy. In the contact region with the algal cells, the otherwise two layered wall of the haustoria is reduced to one layer only. In the fungal protoplast conspicuous stacks of ER-like membranes can be found.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 249 (1987), S. 367-377 
    ISSN: 1432-0878
    Keywords: Ethane dimethanesulphonate ; Leydig cells ; Destruction ; Regeneration ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Ethane dimethanesulphonate (EDS) was used as a specific cytotoxin to eliminate the Leydig cell population of the adult rat testis. Ultrastructural, morphometric and serum gonadotrophin and testosterone analysis was used to study the response of the intertubular tissue of the testis from 1 day to 10 weeks after EDS treatment. In control animals, the testis contained approximately 28 million Leydig cells and 8 million macrophages. Three to seven days after EDS treatment, Leydig cells were absent and serum testosterone was undetectable. Macrophage numbers increased three-fold by 3 days and returned to pretreatment values thereafter. At 2 and 3 weeks post-EDS, foetal-type Leydig cells (∼1–2 million per testis) appeared in proximity to perivascular and peritubular tissues, a feature also observed at 4 weeks when numerous such cells (∼15 million per testis) formed prominent clusters in perivascular and peritubular locations. Between 6 and 10 weeks after EDS treatment, the foetal-type Leydig cells were transformed morphologically into adult-type Leydig cells, they occupied central intertubular positions and their numbers were restored to pretreatment values. Regeneration of Leydig cells was reflected by elevated serum testosterone levels which returned towards the normal range. The results demonstrate the regenerative capacity of the testicular intertubular tissue and indicate a dual site of origin of Leydig cells which initially resemble foetal-type Leydig cells prior to establishing the adult-type Leydig cell population. The morphological pattern of Leydig cell regeneration suggests that in addition to gonadotrophic stimulation, local testicular factors from the seminiferous tubules may stimulate Leydig cell growth.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 243 (1986), S. 405-414 
    ISSN: 1432-0878
    Keywords: Leydig cells ; Ethane dimethanesulphonate ; Ultrastructure ; Destruction ; Gonadotrophins ; Testosterone ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The cytotoxic effects of ethane dimethanesulphonate upon rat Leydig cells were examined ultrastructurally up to 3 days after treatment and related to changes in serum levels of gonadotrophins and testosterone. Six hours after administration of ethane dimethanesulphonate the usual tubulo-vesicular morphology of Leydig-cell smooth endoplasmic reticulum was converted to small vesicles and the Golgi apparatus showed focal hypertrophy into anastomosing tubules. These changes became more marked by 12 h with many Leydig cells exhibiting karyopyknosis and hyperchromatism. Necrotic Leydig cells were often engulfed by macrophages, the latter containing pyknotic fragments of Leydig cells within their cytoplasm. One day after administration, advanced necrosis of Leydig cells occurred, many of which were phagocytosed by macrophages, and on day 3, destruction of Leydig cells was complete resulting in their elimination from the interstitial tissue, which contained only loose connective tissue and macrophages. Structural alterations to the Leydig cells from 6–24 h was reflected by a significant reduction in serum testosterone levels which further declined to the limits of detection accompanying the abolition of Leydig cells on day 3. These changes were paralleled by a significant elevation of serum LH and FSH levels suggesting diminished feedback regulation of pituitary gonadotrophin secretion. The results indicate that ethane dimethanesulphonate is a rapidly acting Leydig cell toxin which may be a useful experimental tool in further studies of spermatogenic function mediated via Sertoli cell-Leydig cell interaction.
    Type of Medium: Electronic Resource
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