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  • Life and Medical Sciences  (30,791)
  • ASTROPHYSICS  (16,581)
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  • 1
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    Can comet clouds around neutron stars explain gamma-ray bursts? (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The proposal of Harwit and Salpeter (1973) that gamma-ray bursts are due to impacts of comets onto neutron stars is examined further. It is assumed that most stars are formed with comet clouds similar to the Oort comet cloud which surrounds the sun, and it is suggested that there are at least four mechanisms by wich neutron stars may be formed while retaining their comet clouds: a spherically symmetric supernova explosion in an isolated star, accretion-induced collapse of a white dwarf in a cataclysmic variable with a very low mass secondary, accretion-induced collapse of a white dwarf in a wide binary with a low-mass giant companion, and coalescence of a close binary composed of two white dwarfs. Estimates are given of the cometary impact rates for such systems. It is suggested that if the wide binary scenario is correct, optical bursts may arise from the impact of comets onto the white dwarf remnant of the giant companion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 155-163
    Format: text
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  • 2
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    Flux-limited diffusion in a scattering medium (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A diffusion equation (FDT) is presented with a coefficient that reduces to the appropriate limiting form in the streaming and near thermodynamic limits for a moving fluid in which the dominant source of opacity is Thomson scattering. The present results are compared to those obtained with the corresponding equations for an absorptive medium. It is found that FDT for a scattering medium is accurate to better than less than about 17 percent over the range of optical depths of tau in the range of about 0 to 3.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 374; 732-740
    Format: text
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of the scales of Dermophis and Microcaecilia (Amphibia: Gymnophiona), and a comparison to dermal ossifications of other vertebrates (1990)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 206 (1990), S. 25-43 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The structures of the dermal scales and the cells surrounding the scales in two species of gymnophione amphibians were studied using histochemistry and light, scanning and transmission electron microscopy. Scales are composed of a basal platt of several layers of unmineralized collagenous fibers topped with mineralized squamulae. Squamulae are composed of numerous mineralized globules and mineralized, thick collagen fibers. Mineralization is therefore both spheritic and inotropic. Isolated flattened cells lie on the outer surface of the squamulae and seem to be involved in mineral deposition. Cells that line the basal plate synthesize the collagenous stroma of the plate. Each scale lies in a thin connective tissue pocket, and a large connective tissue pouch includes several scales in each annulus.The similarities of gymnophione scales to elasmoid scales of osteichthyans are largely superficial. Aspects of mineralization and of pocket development differ considerably. There are also similarities, as well as differences, in the gymnophione scales and osteoderms of amphibians and of reptiles. We consider that such dermal structures have arisen many times in diverse lineages of vertebrates, and that these are expressions of properties of dermal collagen to support mineralization by specialized dermal cells. However, we recommend that the term “dermal scale” be used for the mineralized dermal units of osteichthyans and gymnophiones, and “osteoderm” for the dermal structures of frogs and squamates, with the understanding that the terminology recognizes certain convergent attributes of shape and structure, but not of process.
    Additional Material: 36 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1052060104
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  • 4
    Electronic Resource
    Electronic Resource
    Structure of the dermal scales in gymnophiona (Amphibia) (1980)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 165 (1980), S. 41-54 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Histology and cytology of dermal scales of the gymnophionans Ichthyophis kohtaoensis and Hypogeophis rostratus reveal their structure and the nature of their mineralization.Dermal scales are small flat disks set in pockets in the transverse ridges of the skin. Each pocket contains several scales of various sizes. A ring of “hypomineralization” of varying diameter may occur on scales of a particular dermal pocket but bears no relation to the diameter of these scales.Three different layers form the scales and are seen on sections perpendicular to the surface. The cells of the basal layer lie deepest. Each of the two or three more superficial fibrous layers is composed of bundles of fibres that are oriented in parallel. The orientation varies among layers. The striation of the fiber scales has a periodicity comparable to that of the surrounding dermal fibers. Squamulae form a discontinuous layer on the scale surface and are the only mineralized part of the scale. The minerals are deposited both on the collagen fibers passing from the fibrous layers into the squamulae, and in the interfibrillar spaces. Spherical concretions, either isolated or coalescent, reaching up to 1 μm, are found on the surface of the squamulae.The dermal scales of Gymnophiona present some analogies with those of evolved bony fishes. Their characteristics could make them an original model for the study of mineralization.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051650105
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  • 5
    Electronic Resource
    Electronic Resource
    New data on the structure and the growth of the osteoderms in the reptile Anguis fragilis L. (Anguidae, Squamata) (1985)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 186 (1985), S. 327-342 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Light and electron microscopy shows the osteoderms of Anguis fragilis to be small, flat disks located in the dermis along the adult trunk: microradiography established the extent of the mineralization.Each osteoderm coincides exactly with an epidermal fold forming the keratinized scales characteristic of the skin of reptiles.Sections perpendicular to the surface show two mineralized layers differing in histological and histochemical characteristics and in fine structure, although both contain collagen fibrils. The structure of each layer can be related to that of the surrounding dermis.The outer superficial layer located in the loose dermis contains few collagen bundles that form a discontinuous sheet at the upper surface of the osteoderms. This superficial layer appears to be constituted of units separated by furrows and is composed of woven fibered bone.The basal plate comprises stratified lamellae formed of parallel-oriented collagen fibrils; the fibrils of successive lamellae lie at right angles. The densely packed collagen fibrils of the basal plate are distributed similarly to those of the dense dermis within which it lies. This layer exhibits structural and histochemical characteristics of a lamellar bone.The presence of two different layers in the osteoderms of Anguis fragilis may reflect their mode of formation, which consists of the deposit of mineral crystals in the preexisting dermal tissue. This mineralization process, considered as a “metaplastic ossification,” may reflect the potentiality retained by the dermis of reptiles to form mineralized structures.
    Additional Material: 28 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051860309
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  • 6
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    X-ray refelection from photoionized media in active galactic nuclei (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We calculate the spectrum of X-ray radiation and reprocessed by a partly ionized optically thick medium in an active galactic nucleus. We self-consistently calculate the ionization balance and thermal balance in the medium along with the distribution of X-ray intensity with optical depth. In addition to absorption or scattering of the incident X-rays, we also compute the spectrum of X-rays emitted by the material, including lines, edges, and bremsstrahlung. The albedo of the medium depends primarily on the X-ray ionization parameter (ratio of incident flux to gas density, zeta(sub Chi), and secondarily on the UV flux generated by dissipation inside the disk; we locate the critical range of zeta(sub Chi) over which the albedo increases from small to nearly unity. While the continuum reflection is very weak below 10 keV when zeta(sub Chi) is small, significnat fluxes are emitted in atomic lines and edges in this energy range. In the limit of large zeta(sub Chi), the albedo below 10 keV increases, but reflection in this band is never gray: some photoelectric absorption remains up to rather large values of zeta(sub Chi), while at still higher values, inverse Compton scattering amplifies the soft X-ray flux. These features are sufficiently sharp that current and near-future X-ray experiments should permit diagnostic measures of zeta(sub Chi).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 437; 2; p. 597-610
    Format: text
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  • 7
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    COMPTEL neutron response at 17 MeV (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Compton imaging telescope (COMPTEL) instrument of the Gamma Ray Observatory was exposed to 17 MeV d,t neutrons prior to launch. These data were analyzed and compared with Monte Carlo calculations using the MCNP(LANL) code. Energy and angular resolutions are compared and absolute efficiencies are calculated at 0 and 30 degrees incident angle. The COMPTEL neutron responses at 17 MeV and higher energies are needed to understand solar flare neutron data.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center, The Compton Observatory Science Workshop,; p 109-115
    Format: application/pdf
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  • 8
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    Low-energy and medium-energy gamma rays from PSR 0531 + 21 (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are presented from the Crab Pulsar PSR 0531 + 21 for energies of 0.3-30 MeV. For energies of 1-30 MeV, the absolute phase and separation of the first and second pulses 12.9 + or - 0.3 ms, widths of the pulses 2.2 + or - 0.5 ms FWHM, and 1.6 + or - 0.4 ms FWHM, ratio of the counts in the second to the first pulse 0.64 + or - 0.33 and ratio of counts in the interpulse region to the total pulsed counts 0.17 + or - 0.30 are compared to te results vor energies, E greater than 50 MeV and their variations with time. Values from the phase plots for E greater than 0.3 MeV are compared with low-energy gamma rays during 1970 through 1980 from several experiments with energies from about 20 to 360 keV. The above suggest different production mechanisms for low- and high-energy gamma rays with a transition at about 1 MeV. Derived fluxes from 0.3 to 30 MeV confirm a previously derived power law.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 299; L23-L27
    Format: text
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  • 9
    Electronic Resource
    Electronic Resource
    Television microscopy of sporulation and spore germination of Bacillus cereus (1956)
    Philadelphia : Wiley-Blackwell
    Journal of Cellular and Comparative Physiology 48 (1956), S. 301-316 
    Details
    ISSN: 0095-9898
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1030480211
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  • 10
    Electronic Resource
    Electronic Resource
    Artenvielfalt und Evolution (1993)
    Weinheim : Wiley-Blackwell
    Biologie in unserer Zeit 23 (1993), S. 308-315 
    Details
    ISSN: 0045-205X
    Keywords: Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Die uns auf der Erde umgebende Vielfalt an Organismen-Arten ist eine selbst für den naturwissenschaftlichen Laien auffällige Erscheinung. Als ein wesentliches Merkmal der belebten Natur bietet die Artenvielfalt dem Biologen ergiebige Forschungsfelder. Dennoch wurde die Erscheinung der Artenvielfalt lange von der moderne biologischen Wissenschaft, aber auch im biologischen Uniterricht recht stiefmütterlich behandelt. Erst nachdem in den vergengenen Jahren Biologen und in der Folge der öffentlich- Keit der weltweite Artenschwund bewußt geworden ist, wird dem Phänomen der Artenvielfalt eine verstärkte Aufmerksam- Keit zuteil. Das zeigt sich in der schnellen Einbürgerung des dem Angelsächsischen entlethnten Schlagworts „Biodiversität“ oder in der wachsenden Zahl an Symposien und Schriften, die sich mit der biologischen Vielfalt befassen. Genannt seien hier nur Wilson [14], ein Buch, welches das Problem der Bedrohung der Vielfalt in den VOrdergrund stellt, Groombridge [4], eine umfassende, vom„ world conservation monitoring centre“ erarbeitete Darstellung der „globalen Biodiversität“ oder der von Schulze und Mooney [9] herausgegebene Symposiumsband, in dem von ökologischer Seite die Frage nach den Funktionen der biologischen Vielfalt behandelt wird. Auch die Evolutionsbiologie sucht nach dem Ur-sprung und den hinter der Artenvielfalt stehenden Kräften [3].
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/biuz.960230508
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