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  • 1990-1994  (4)
  • 1900-1904
  • Ovulation  (2)
  • pyroclastic deposits  (2)
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Years
  • 1990-1994  (4)
  • 1900-1904
Year
Keywords
  • 1
    Electronic Resource
    Electronic Resource
    Structural aspects of oocyte maturation in the blue fox (Alopex lagopus) (1990)
    Springer
    Anatomy and embryology 181 (1990), S. 325-331 
    Details
    ISSN: 1432-0568
    Keywords: Oocyte maturation ; Ultrastructure ; Fox ; Ovulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Blood samples were taken weekly from seventeen mature blue fox vixens (average age five years), from late anoestrus until pro-oestrus, and then taken daily. The vixens were sacrificed at various stages of oestrus, and oocytes were collected from ovarian follicles by aspiration, and/or from oviducts by flushing. The structural features of oocyte maturation were related to the time of the luteinizing hormone (LH) peak. On days 1–2 after the LH peak the oocyte nucleus migrated from a central to a peripheral position in the ooplasm and assumed a flattened appearance. The cumulus investment expanded simultaneously and ovulation took place around day 2. On days 2–3 the oocyte nuclear envelope broke down, the nucleoli disappeared, the metaphase of the first meiotic division was reached, the Golgi complexes decreased in size, the perivitelline space enlarged, and all junctional contact between cumulus cell projections and oocyte was disrupted. On days 3–5 the first polar body was extruded, the metaphase of the second meiotic division was reached, and the cumulus cells degenerated. On day 5 the release of cortical granule content was occasionally seen, and from day 6 the oocytes showed signs of degeneration. In a few animals deviant oocyte maturation was noticed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00186904
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Radiocarbon redating of contaminated samples from a tropical volcano: the Mansion ‘Series’ of St Kitts, West Indies (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 326-334 
    Details
    ISSN: 1432-0819
    Keywords: Lesser Antilles ; St Kitts ; Mt Liamuiga radiocarbon dating ; charcoal contamination stratigraphy ; pyroclastic deposits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits, in addition to easy contamination of this wood by root systems and soluble humic material. Because the physical nature of the charcoal varies, some samples are more prone to contamination. Two independent studies of the same volcano, Mt Liamuiga on St Kitts in the Lesser Antilles, sometimes using samples from the same carbonized tree, yielded a systematic difference in radiocarbon ages. An exchange of samples and a re-investigation of three physically distinct types of charcoal yielded the following results. Rare, hard, dense charcoal, lacking contamination, which had yielded a spurious age of 2860 years bp, was redated at 1845±58 years bp. Common soft, friable charcoal with good cellular structure proved to be susceptible to contamination. A field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre-treatment was used, indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets. A previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the Mansion ‘Series’ contradicted ages older than 41000 years bp from common friable charcoal in the lower Mansion ‘Series’. The soft powdery charcoal was re-investigated using a sample collected a few centimeters from the original, although field decontamination of this sample was not possible, more extensive laboratory treatment yielded an age of ca. 43000 years bp, again proving that routine laboratory pretreatments are inadequate. A revised geochronology for the Mansion ‘Series’ is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326459
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Radiocarbon redating of contaminated samples from a tropical volcano: the Mansion 'Series' of St Kitts, West Indies (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 326-334 
    Details
    ISSN: 1432-0819
    Keywords: Key wordsLesser Antilles ; St Kitts ; Mt Liamuiga ; radiocarbon dating ; charcoal contamination ; stratigraphy ; pyroclastic deposits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits, in addition to easy contamination of this wood by root systems and soluble humic material. Because the physical nature of the charcoal varies, some samples are more prone to contamination. Two independent studies of the same volcano, Mt Liamuiga on St Kitts in the Lesser Antilles, sometimes using samples from the same carbonized tree, yielded a systematic difference in radiocarbon ages. An exchange of samples and a re-investigation of three physically distinct types of charcoal yielded the following results. Rare, hard, dense charcoal, lacking contamination, which had yielded a spurious age of 2860 years bp, was redated at 1845±58 years bp. Common soft, friable charcoal with good cellular structure proved to be susceptible to contamination. A field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre-treatment was used, indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets. A previous date of 24 870 years bp obtained from powdery charcoal in a horizon beneath the Mansion 'Series' contradicted ages older than 41 000 years bp from common friable charcoal in the lower Mansion 'Series'. The soft powdery charcoal was re-investigated using a sample collected a few centimeters from the original, although field decontamination of this sample was not possible, more extensive laboratory treatment yielded an age of ca. 43 000 years bp, again proving that routine laboratory pre-treatments are inadequate. A revised geochronology for the Mansion 'Series' is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326459
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Fertilization and early embryonic development in the blue fox (Alopex lagopus) (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 36 (1993), S. 331-337 
    Details
    ISSN: 1040-452X
    Keywords: Ovulation ; Meiotic maturation ; Vixens ; Polar fox ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: A total of 15 blue fox vixens aged 1-6 years were mated, 12 once on the first day of estrus and three a second time 48 hr after the first mating, and were killed 4 hr to 8 days following mating. Ova were collected from the oviducts, evaluated by stereomicroscopy, and studied by transmission (TEM; N = 49, 12 vixens) or scanning (SEM, N = 11, three vixens) electron microscopy. At 0-3 days after ovulation, the ova had not cleaved and were at different stages of meiotic maturation. In about one-half of these ova, representing all stages of meiotic maturation, a decondensing sperm head without nuclear envelope or a small pronucleus with partial nuclear envelope was observed. No clear relationship was found between maternal meiotic stage and the stage of paternal pronucleus formation. Sperm tails were never identified in the ooplasm. Cortical granules were released after sperm penetration at early stages of meiotic maturation. Thus the block against polyspermic penetration was activated during maturation of the oocyte. The first two-cell stage appeared 4 days after ovulation (3 days after mating), the first four-cell stage the following day (day 5), and the first eight-cell stage 6 days after ovulation (5 days after mating). In a single vixen mated late (7 days postovulation) two- to four-cell stages appeared the following day (day 8). This indicates that the time required for the first cleavage division decreases with increasing interval from ovulation to mating. The development of a functional nucleolus with fibrillar centers and fibrillar and granular components at the eight-cell stage indicates activation of embryonic RNA synthesis in fox embryos at the six- to eight-cell stage, suggesting that the embryonic genome is activated at this stage. © 1993 Wiley-Liss, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080360308
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    Paper (German National Licenses)
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