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  • 1
    Electronic Resource
    Electronic Resource
    The early history of oxygen and ozone in the atmosphere (1978)
    Springer
    Pure and applied geophysics 117 (1978), S. 498-512 
    Details
    ISSN: 1420-9136
    Keywords: History of atmosphere ; Oxygen ; Ozone ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract There may have been three stages in the growth of oxygen in the terrestrial atmosphere. Prior to the origin of photosynthesis the only source of oxygen was photolysis of water vapor followed by escape of hydrogen to space. The rate of this process was probably less than the rate of release of reduced gases (principally hydrogen) from volcanoes, so the oxygen partial pressure was held to negligibly low values by photochemical reactions with an excess of hydrogen. The photosynthetic source of oxygen was probably in operation as long ago as 3.8 billion years. It released oxygen to the ocean. Presumably most of this oxygen was destroyed in the ocean as long as its rate of supply was less than the rate of supply of readily oxidizable material (principally Fe2+) provided by the weathering of rocks. This phase appears to have lasted until about 2 billion years ago, during which period most banded iron formations were deposited. During this period the production of oxygen by algae was limited by competition with photosynthetic bacteria, which preempted the supply of nutrient phosphorus as long as reduced chemicals were available in the environment. Once the photosynthetic oxygen source exceeded the rate of supply of reduced minerals exposed by erosion and weathering, the accumulation of oxygen in the ocean and atmosphere could be controlled only by reaction of oxygen with reduced organic material. This is the stabilization mechanism that operates today. It seems unlikely that oxygen could be consumed at a significant rate by this process until oxygen levels sufficiently high to support respiration had been achieved. I therefore suggest that atmospheric oxygen rose rapidly from essentially zero to approximately its present value (within a factor of 10) when the photosynthetic source of oxygen rose above the weathering source of reduced minerals, probably about 2 billion years ago. The ozone layer and the ultraviolet screen were absent prior to this time and essentially fully developed after this time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876630
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  • 2
    Electronic Resource
    Electronic Resource
    Oxygen and hydrogen in the primitive atmosphere (1978)
    Springer
    Pure and applied geophysics 116 (1978), S. 222-231 
    Details
    ISSN: 1420-9136
    Keywords: Photolysis ; Photosynthesis ; Primitive Atmosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract From time to time there appears in the literature the assertion that photolysis of water vapor could have maintained an appreciable concentration of oxygen in the primitive (prebiological) atmosphere. The implausibility of this assertion is argued in this paper. By itself, photolysis does not provide a source of oxygen because it is usually followed by recombination of the products of photolysis. Only the escape to space (at a much smaller rate) of the hydrogen produced by photolysis of water results in a net source of oxygen. The oxidation state of the primitive atmosphere depended on the relative magnitudes of this net source of oxygen and a volcanic source of hydrogen and other reduced gases. Today the volcanic source of reduced gases is approximately equal to the oxygen source provided by photolysis followed by escape. The oxygen source depends on the mixing ratio of water vapor in the stratosphere, which ultimately determines the rate of escape of hydrogen produced from water vapor. Its magnitude may not have been very different in the past. The volcanic source of hydrogen, on the other hand, is likely to have been much larger when the earth was tectonically young. Hydrogen was therefore released to the primitive atmosphere more rapidly than oxygen, probably. Photochemical reactions with the excess hydrogen maintained oxygen mixing ratios at negligibly small levels. The hydrogen mixing ratio was determined by a balance between the volcanic source (reduced by recombination with oxygen) and escape to space. In time, either because of decline of the volcanic source of hydrogen or because of addition of a biological source of oxygen, the input of oxygen to the atmosphere rose above the input of hydrogen. The oxidation state of the atmosphere changed rapidly. Volcanic hydrogen was now consumed by photochemical reactions with excess oxygen, while the oxygen mixing ratio was determined by a balance between the source (reduced by recombination with volcanic hydrogen) and consumption in reactions with reduced material at the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01636879
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  • 3
    Electronic Resource
    Electronic Resource
    Development of the urostyle during metamorphosis in five species of anurans (1979)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 159 (1979), S. 311-329 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Normal development of the urostyle is described during late stages of metamorphosis in five species of anurans: Xenopus laevis (Daudin), Bufo americanus Holbrook, Pseudacris triseriata (Wied), Hyla chrysoscelis Cope, and Rana pipiens Schreber. The developing urostyle of all five species is composed of essentially the same cartilaginous elements: one pair of basidorsals above the notochord and the subtended hypochord. Among the five species there is variation in such details as the number of spinal nerve foramina and the degree of fusion of the basidorsals; however, both the hypochord and basidorsals are very similar in all five genera examined. Consideration of the literature suggests that contradictory descriptions of the developing urostyle result from (1) varied methods of study (alizarin-staining of whole specimens or serial cross-sections), (2) the variety of species examined, and (3) the particular stage of development of the tadpole described by an investigator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051590303
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  • 4
    Electronic Resource
    Electronic Resource
    A comparative radioautographic study of chondrocytic proliferation in nasal septal cartilage of the 5-day-old rat, rabbit, guinea pig and beagleThis investigation was supported in part by USPHA Program Project Grant DE 00853 from the National Institute of Dental Research, Bethesda, Maryland. (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 154 (1979), S. 437-445 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Growth sites within the cartilaginous nasal septa of four different species of animals (5-day-old rats, rabbits, guinea pigs and beagles) were identified by monitoring cellular proliferation radioautographically. A statistical analysis (MANOVA) was employed. It showed that, of the six combinations compared (rat-beagle, rat-guinea pig, rat-rabbit, beagle-guinea pig, beagle-rabbit, and guinea pig-rabbit), in only one (beagle-guinea pig) was there any similarity in growth pattern. The other five combinations all were significantly different. Since no particular areas emerged, with any consistency, as common growth sites within any of the four kinds of septa, it was concluded that the nasal septum might well play a passive role in midfacial growth, rather than an active role as previously thought.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001540308
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  • 5
    Electronic Resource
    Electronic Resource
    A radioautographic study of chondrocytic proliferation in nasal septal cartilage of the newborn rat This investigation was supported in part by USPHA Program Project Grant DE 00853 from the National Institute of Dental Research, Bethesda, Maryland. (1977)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 150 (1977), S. 559-563 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Growth sites within the newborn cartilaginous nasal septum have been identified by monitoring chondrocytic proliferation radioautographically. Tritiated thymidine was the labeling agent used. The results were tabulated and charted graphically; they showed the overall septum to be relatively active mitotically, yielding an average of 3.54 labeled cells per microscopic field counted. However, certain areas showed greater activity than others, namely the anterior tip (4.51 labeled cells/field), the midportion (3.98 labeled cells/field) and the posterior section of the presphenoidal tail (4.24 labeled cells/field).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001500405
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  • 6
    Electronic Resource
    Electronic Resource
    Somatostatin-containing neurons in the rat brain: Widespread distribution revealed by immunocytochemistry after pretreatment with pronaseAided by USPHS Research Grants HD 10306 and ES01104, by the North Carolina United Community Services, and by the Neurobiology Program, University of North Carolina, Chapel Hill. (1978)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 153 (1978), S. 483-488 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Immunocytochemical staining after controlled proteolytic treatment of the sections with pronase revealed widespread distribution of neuronal cell bodies with somatostatin- like immunoreactivity (SLI) in the rat forebrain. SLI-positive neurons were found in regions of the neocortex, the pyriform cortex, the cingulate cortex, the striatum, the olfactory tract and tubercle, the nucleus accumbens, the septum, and the hypothalamus. These results are consistent with previous radioimmunoassay findings and suggest the presence of large somatostatin-like (possibly precursor) molecules in the neurons stained for SLI after pronase treatment.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001530312
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  • 7
    Electronic Resource
    Electronic Resource
    The effects of various hormones on the surface morphology of testicular cells in culture (1978)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 151 (1978), S. 55-69 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The purpose of this investigation was to study the effects of various hormones on the surface morphology of 20-day-old rat testicular cells in culture. Aggregates containing primarily Sertoli cells and germinal cells were obtained by enzymatic digestion. The surface morphology of the cells composing these aggregates was characterized under various culture conditions using light microscopy and scanning electron microscopy. The cytoplasmic processes of Sertoli cells became highly branched and filamentous after being cultured in the presence of rat, human or ovine FSH. Identical branching and filamentation was observed when Sertoli cells were cultured in rat TSH. Finally, numerous large blebs were observed on the surfaces of germinal cells cultured in the presence of insulin.These results suggest that the branching and filamentation of Sertoli cell cytoplasm observed after FSH stimulation are not specific for that hormone.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001510106
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  • 8
    Electronic Resource
    Electronic Resource
    Stimulation of WI-38 cell cycle transit: Effect of serum concentration and cell density (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 89 (1976), S. 251-257 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Flow microfluorometry has been used to characterize the effects of serum concentration and cell density on the initiation of cell cycle transit of stationary phase (G0) human diploid fibroblasts (strain WI-38). The concentration of serum used to stimulate these cultures had no effect on the time cells began appearing in S (the DNA synthetic period), nor on the synchrony with which they moved around the cell cycle. However, as the serum concentration increased, the fraction of the stationary phase population released from G0 increased. Cell density modulated the ability of serum to stimulate cell cycle traverse. For example, at a cell density of 1.81 × 104 cells/cm2, 78% of the population was sensitive to serum stimulation; whereas, when the density was increased to 7.25 × 104 cells/cm2, only 27% of the population could be stimulated. This effect of cell density on the serum response is not simply the result of changing the ratio of serum concentration to cell density, but appears to reflect a true modulation of the population's sensitivity to serum stimulation. These results are consistent with the interpretation that the primary action of serum is to determine the transition of cells from a non-cycling G0 state to a cycling state and that cell density determines the proportion of the population capable of undergoing this transition.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040890208
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of serum on the growth of balb 3T3 A31 mouse fibroblasts and an SV40-transformed derivative (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 88 (1976), S. 277-286 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effect of serum on the growth properties of non-transformed Balb 3T3 A31 and SV40-transformed Balb 3T3 A31 was studied. The concentration of serum in the growth medium of non-transformed cells had little effect on the initial population doubling time, but did regulate the cell density at which the population became quiescent in G1. The doubling time of transformed cells, however, was increased significantly as the concentration of serum was decreased below 4%. This effect on the growth of transformed cells was seen at serum concentrations so low that non-transformed cells did not complete one population doubling. Flow microfluorometric analysis of these populations indicated that the primary effect of different serum concentrations on the non-transformed cells was to modulate the average residence time in G1; whereas, all the cell cycle phases of the transformed cells were affected by serum. At saturation densities, the non-transformed cells became quiescent in G1, but the transformed cells still traversed the cell cycle and their saturation density appeared to be a balance between cell production and cell death occurring primarily in the G1 phase of the cell cycle.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040880303
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