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  • Springer  (168)
  • 1995-1999  (96)
  • 1975-1979  (72)
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  • 1
    Electronic Resource
    Electronic Resource
    Cyclic AMP induces rapid increases in gap junction permeability and changes in the cellular distribution of connexin43 (1995)
    Springer
    The journal of membrane biology 148 (1995), S. 243-253 
    Details
    ISSN: 1432-1424
    Keywords: Gap junction ; Connexin43 (Cx43) ; Cyclic AMP ; Fluorescence recovery after photobleaching ; Junctional communication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The rapid effects of cAMP on gap junction-mediated intercellular communication were examined in several cell types which express different levels of the gap junction protein, connexin43 (Cx43), including immortalized rat hepatocyte and granulosa cells, bovine coronary venular endothelial cells, primary rat myometrial and equine uterine epithelial cells. Functional analysis of changes in junctional communication induced by 8-bromo-cAMP was monitored by a fluorescence recovery after photobleaching assay in subconfluent cultures in the presence or absence of 1.0 mm 1-octanol (an agent which uncouples cells by closing gap junction channels). Communicating cells treated with 1.0 mm 8-bromo-cAMP alone exhibited significant increases in the percent of fluorescence recovery which were detected within 1–3 min depending on cell type, and junctional communication remained significantly elevated for up to 24 hr. Addition of 1.0 mm 8-bromo-cAMP to cultured cells, which were uncoupled with 1.0 mm octanol for 1 min, exhibited partial restoration of gap junctional permeability beginning within 3–5 min. Identical treatments were performed on cultures that were subsequently processed for indirect immunofluorescence to monitor Cx43 distribution. The changes in junctional permeability of cells correlated with changes in the distribution of immunoreactive Cx43. Cells treated for 2 hr with 10 μm monensin exhibited a reduced communication rate which was accompanied by increased vesicular cytoplasmic Cx43 staining and reduced punctate surface staining of junctional plaques. Addition of 1.0 mm 8-bromo-cAMP to these cultures had no effect on the rate of communication or the distribution of Cx43 compared to cultures treated with monensin alone. These data suggest that an effect of cyclic AMP on Cx43 gap junctions is to promote increases in gap junctional permeability by increasing trafficking and/or assembly of Cx43 to plasma membrane gap junctional plaques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235042
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  • 2
    Electronic Resource
    Electronic Resource
    Temperature dependence of the hyperfine parameters of maghemite and al-substituted maghemites (1995)
    Springer
    Physics and chemistry of minerals 22 (1995), S. 178-185 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Synthetic aluminum-substituted maghemite samples, γ-(Al y Fe1-y )2O3 with y=0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by Mössbauer spectroscopy at 8 K and in the range 80 K to 475 K at steps of 25 K. The spectra have been analysed as a superposition of two sextets composed of asymmetrical Lorentzians. The A- and B-site isomer shifts were constrained as: δA=δB-0.12 mm/s. From the temperature dependence of δB it was possible to determine the characteristic Mössbauer temperature and the intrinsic shift. Both quantities clearly increase with increasing Al content, at least up to 10 mole%. The temperature dependence of the A-and B-sites hyperfine fields could be satisfactorily reproduced using the molecular-field theory assuming an antiparallel spin configuration. The exchange integrals were found as: J AB =-25 K; J AA =-18 K and J BB = -3 K. The hyperfine fields show a crossing in the vicinity of 300 K as a result of the relatively strong A-A interaction. The Curie temperature for the non-substituted sample was calculated to be 930 K and decreases to 765 K for the sample with 15 mol% Al. The gradual decrease of the saturation value of the A-site hyperfine field with increasing Al substitution and the constancy of this quantity for the B sites, suggest that the Al cations occupy the B sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202298
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  • 3
    Electronic Resource
    Electronic Resource
    The UG2-Merensky Reef interval of the Bushveld Complex northwest of Pretoria (1996)
    Springer
    Mineralium deposita 31 (1996), S. 386-393 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Northwest of Pretoria, the UG2-Merensky Reef interval overlies a Critical Zone-Lower Zone sequence that contains numerous large blocks of floor material. Nevertheless, individual layers can be correlated with equivalent units at Crocodile River mine, the Rustenburg, Impala, Union, and Amandelbult sections. Concentrations of platinum-group elements in two borehole intersections of the UG2 chromitite are 4 ppm over 1.2 m and 2.4 ppm over 2.2 m. Therefore, bulk PGE levels appear to be only moderately lower than those at Western Platinum mine. This renders models explaining PGE enrichment by upward percolating melt or fluids problematic. The Merensky Reef, although containing sulphides, is only weakly mineralized with PGE (0.6 ppm). The UG2 pyroxenite is separated from the UG2 chromitite by a 15 m noritic layer. The introduction of feldspathic cumulates between two units that elsewhere directly overly each other may be explained by the more evolved composition of resident magma in those parts of the chamber distally located with regard to a major feeder zone at Union Section. It also suggests that the UG2 unit is a multiple rather than a single cyclic unit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189186
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  • 4
    Electronic Resource
    Electronic Resource
    The UG2–Merensky Reef interval of the Bushveld Complex northwest of Pretoria (1996)
    Springer
    Mineralium deposita 31 (1996), S. 386-393 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract.  Northwest of Pretoria, the UG2–Merensky Reef interval overlies a Critical Zone–Lower Zone sequence that contains numerous large blocks of floor material. Nevertheless, individual layers can be correlated with equivalent units at Crocodile River mine, the Rustenburg, Impala, Union, and Amandelbult sections. Concentrations of platinum-group elements in two borehole intersections of the UG2 chromitite are 4 ppm over 1.2 m and 2.4 ppm over 2.2 m. Therefore, bulk PGE levels appear to be only moderately lower than those at Western Platinum mine. This renders models explaining PGE enrichment by upward percolating melt or fluids problematic. The Merensky Reef, although containing sulphides, is only weakly mineralized with PGE (0.6 ppm). The UG2 pyroxenite is separated from the UG2 chromitite by a 15 m noritic layer. The introduction of feldspathic cumulates between two units that elsewhere directly overly each other may be explained by the more evolved composition of resident magma in those parts of the chamber distally located with regard to a major feeder zone at Union Section. It also suggests that the UG2 unit is a multiple rather than a single cyclic unit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050046
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  • 5
    Electronic Resource
    Electronic Resource
    Demographic composition of the feeding population of juvenile loggerhead sea turtles (Caretta caretta) off Charleston, South Carolina: evidence from mitochondrial DNA markers (1995)
    Springer
    Marine biology 123 (1995), S. 869-874 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To determine the origin of juvenile loggerhead turtles (Caretta caretta) that occupy the Charleston Harbor Entrance Channel at Charleston, South Carolina, USA, mitochondrial DNA restriction-fragment length polymorphisms from this feeding population were compared to haplotypes from candidate nesting populations. Previous studies have defined two major nesting populations in the southeastern USA, one corresponding to Florida and the other to Georgia/South Carolina. These nesting populations are distinguished by both unique haplotypes and frequency distributions of common haplotypes. The frequency distribution of haplotypes in the juvenile feeding-ground population was significantly different from both nesting populations, implying that the feeding aggregate is drawn from two or more nesting populations. Assuming that these turtles are derived exclusively from rookeries in the southeastern USA, a maximum likelihood estimator indicates that approximately half are from the Florida rookery and half are from the northern (Georgia/South Carolina) rookery complex. Because 91% of nesting in the southeastern USA occurs in Florida rookeries and 8% in the northern complex, the 50:50 ratio indicates that juvenile turtles from Georgia and South Carolina tend to feed preferentially near their respective rookery locations. Human encroachment on this feeding habitat may pose an especially high risk to the smaller Georgia/South Carolina rookeries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349132
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  • 6
    Electronic Resource
    Electronic Resource
    Genetic composition of a green turtle (Chelonia mydas) feeding ground population: evidence for multiple origins (1998)
    Springer
    Marine biology 130 (1998), S. 345-352 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Migratory marine turtles are extremely difficult to track between their feeding and nesting areas, and the link between juvenile and adult habitats is generally unknown. To assess the composition of a feeding ground (FG) population of juvenile green turtles (Cheloniamydas Linnaeus), mitochondrial DNA control region sequences were examined in 80 post-pelagic individuals (straight carapace length = 31 to 67 cm) sampled in September 1992 from Great Inagua, Bahamas, and compared to those of 194 individuals from nine Atlantic and Mediterranean nesting colonies. Evidence from genetic markers, haplotype frequencies, and maximum likelihood (ML) analyses are concordant in indicating that multiple colonies contribute to the Bahamian FG population. ML analyses suggested that most Bahamian FG juveniles originated in the western (79.5%) and eastern (12.9%) Caribbean regions, and these proportions are roughly comparable to the size of candidate rookeries. These data support a life-cycle model in which individuals become pooled in post-hatchling (pelagic) and juvenile (benthic) habitats as a consequence of ocean currents and movement among FGs. A substantial harvest of immature turtles on their feeding pastures will influence the reproductive success of contributing nesting populations over a wide geographic scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050254
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  • 7
    Electronic Resource
    Electronic Resource
    Population structure of loggerhead turtle (Carettacaretta) nesting colonies in the Atlantic and Mediterranean as inferred from mitochondrial DNA control region sequences (1998)
    Springer
    Marine biology 130 (1998), S. 567-575 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mitochondrial (mt) DNA control region sequences were analyzed for 249 Atlantic and Mediterranean loggerhead turtles (Carettacaretta Linnaeus, 1758) to elucidate nesting population structure and phylogeographic patterns. Ten haplotypes were resolved among individuals sampled between 1987 and 1993, from ten major loggerhead nesting areas in the region. Two distinct phylogenetic lineages were distinguished, separated by an average of 5.1% sequence divergence. Haplotype frequency comparisons between pairs of populations showed significant differentiation between most regional nesting aggregates and revealed six demographically independent groups, corresponding to nesting beaches from: (1) North Carolina, South Carolina, Georgia and northeast Florida, USA; (2) southern Florida, USA; (3) northwest Florida, USA; (4) Quintana Roo, Mexico; (5) Bahia, Brazil; and (6) Peloponnesus Island, Greece. The distribution of mtDNA haplotypes is consistent with a natal homing scenario, in which nesting colonies separated by a few hundred kilometers represent isolated reproductive aggregates. However, a strong exception to this pattern was observed in the first group defined by mtDNA data (North Carolina to northeast Florida), which included samples from four nesting locations spread across thousands of kilometers of coastline. These locations were characterized by a single haplotype in 104 out of 105 samples, providing inadequate resolution of population divisions. In view of the subdivisions observed elsewhere, we attribute the lack of differentiation between North Carolina and northeast Florida to recent colonization of these warm temperate coastlines (after the Wisconsin glaciation) not to ongoing gene flow among spatially distinct nesting locations. The relationships among observed haplotypes suggest a biogeographic scenario defined by climate, natal homing, and rare dispersal events. The redefined relationships among nesting aggregations in the western Atlantic region (southeastern USA and adjacent Mexico) prompt a reconsideration of management strategies for nesting populations and corresponding habitats in this region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050278
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  • 8
    Electronic Resource
    Electronic Resource
    Insect photoperiodism: An hourglass measures photoperiodic time inOstrinia nubilalis (1976)
    Springer
    Journal of comparative physiology 111 (1976), S. 249-259 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The European corn borer (Ostrinia nubilalis) diapauses as a last instar larva. Both induction and termination of diapause are photoperiodically controlled. Larvae enter diapause (Fig. 1) when raised in light cycles containing 12 or 13 h of light per 24 h (LD 12∶12 or LD 13∶11). When placed in LD 16∶8, diapausing larvae undergo pupation and adult development (Fig. 2, 3). Long light cycle (T) experiments demonstrate that the timing mechanism involved in terminating diapause has the properties of an interval timer or hourglass mechanism (Fig. 4). Six inductive 8-h dark phases are necessary for optimal termination (Fig. 5), and they must be coupled with at least 4 h of light per cycle (Fig. 6). The circadian system inOstrinia is probably not involved in any way in this response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00606467
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  • 9
    Electronic Resource
    Electronic Resource
    Surface area of dental enamel, bone, and hydroxyapatite: Chemisorption from solution (1978)
    Springer
    Calcified tissue international 26 (1978), S. 139-142 
    Details
    ISSN: 1432-0827
    Keywords: Chemisorption ; Surface area ; Hydroxyapatite ; Bone ; Enamel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The surface areas of three different samples of hydroxyapatite, samples of deproteinized bone, and samples of whole and deproteinized enamel were determined by adsorption of an adduct (the diglycidyl ether of bisphenol A with N-phenylglycine) from methylene chloride solution. In all cases, the surface areas of these samples agree well with those obtained by the BET (N2) method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02013248
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  • 10
    Electronic Resource
    Electronic Resource
    Combination of two techniques: Amniocentesis and nervous tissue explants. A pilot investigation (1978)
    Springer
    Cellular and molecular life sciences 34 (1978), S. 1143-1144 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Addition of serum derived from amniotic fluid cells (AFS) from Tay Sachs carrier to developing mouse cerebral cortex explants results in excessive accumulation of lipid in neuronal cytoplasm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01922919
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