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  • 1
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    Faunal responses to oxygen gradients on the Pakistan Margin: A comparison of foraminiferans, acrofauna and megafauna (2009)
    In:  EPIC3Deep sea research II
    Details
    Publication Date: 2019-07-17
    Description: The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (1501300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (1401850 m water depth) across the OMZ during the 2003 intermonsoon (MarchMay) and late/post-monsoon (AugustOctober) seasons. All groups exhibited some drop in abundance in the OMZ core (250500 m water depth; O2: 0.100.13 mL/L=4.465.80 μM) but to differing degrees. Densities of foraminiferans 〉63 μm were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans 〉300 μm were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O2 〈0.140.15 mL/L=6.256.69 μM) but were represented by a huge, ophiuroid-dominated abundance peak at 1000 m (O2 0.150.18 mL/L=6.698.03 μM). Gromiid protists were confined largely to depths below 1150 m (O2 〉0.2 mL/L=8.92 μM). The progressively deeper abundance peaks for foraminiferans (〉63 μm), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were 〉0.13 mL/L(=5.80 μM). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
    Electronic Resource
    Electronic Resource
    Life-history variation in three coexisting cheilostome bryozoan species of the genus Stylopoma in Panamá (1996)
    Springer
    Marine biology 126 (1996), S. 461-469 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Life-history variation was studied in three sympatric species of Stylopoma Levinsen [S. spongites (Pallas), S. projecta Canu and Bassler and Stylopoma n. sp. 15] in Panamá. Bryozoan colonies were collected from 27 reefs along 300 km of the Caribbean coast of Panamá. The distribution and abundance of each species were very patchy, but with broad overlap in occurrence among localities and depths. Nevertheless, species differed considerably in colony size, size at first reproduction and numbers of brooding larvae; implying that interspecific differences in life-history traits may contribute to their coexistence. To examine closely this variation in life-history patterns, we grew, in a common garden experiment, the offspring of the two most common species that were obtained from parent colonies collected from several reefs. There were highly significant differences in growth rates and the timing and extent of sexual reproduction which corresponded well to patterns observed in individuals from the field. Other factors, including size of larvae, extent of secondary zooidal calcification and numbers of avicularia were also correlated with differences in life histories. Despite this additional complexity, however, ecological consequences of trade-offs in life history among modular species such as Stylopoma spp. appear very similar to those among unitary species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354628
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  • 3
    Electronic Resource
    Electronic Resource
    Radiation-Widths of Nuclear Energy-Levels (1954)
    [s.l.] : Nature Publishing Group
    Nature 173 (1954), S. 942-943 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE radiation-widths of levels of low excitation can, if sufficiently narrow (~ 10~6 eV.), be determined directly from the life-time of the state. The vast majority of levels, however, have much greater widths, which are often obtainable from properties of the nuclear reactions in which the levels ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/173942a0
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  • 4
    Electronic Resource
    Electronic Resource
    Pile Production of Radioisotopes by Threshold Reactions (1954)
    [s.l.] : Nature Publishing Group
    Nature 173 (1954), S. 396-396 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A systematic survey of threshold reaction cross-sections for fission neutrons was carried out by Hughes, Spatz and Goldstein2 in 1946. Whereas the original purpose of the measurements was to investigate the shape of the fission neutron spectrum at high energies, the present well-known spectrum3 ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/173396a0
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  • 5
    Electronic Resource
    Electronic Resource
    An instrument for the collection of simultaneous small and wide angle x-ray scattering and stress–strain data during deformation of polymers at high strain rates using synchrotron radiation sources (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4051-4054 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A fully integrated system has been developed which allows the study of the deformation of synthetic polymers by simultaneous small- and wide-angle x-ray scattering (SAXS/WAXS) and stress–strain techniques at synchrotron radiation sources. Two-dimensional x-ray data collection is achieved via two charge coupled device based area detectors which provide video signal outputs. A video extensometer provides sample strain and cross-section data during deformation. All three video signals are processed by a powerful Synoptics i860 processor based video framegrabber, with no loss of data. With this data collection strategy a temporal resolution of 40 ms is possible. In order to study the mechanical yield of the sample, a bridge-type strain gauge is used which reveals the sample loading. An electronic trigger mechanism provides accurate synchronization of the x-ray data, sample video data, sample loading information and controls the onset of deformation. Two experiments are highlighted showing the drawing of polyethylene at an overall rate of (approximate)10 s−1. By analysis of the sample video data it is possible to correlate the SAXS and WAXS data with specific points upon the true stress–strain curve. This novel system is shown to be a useful tool for the investigation of the deformation of polymers at rates that are relevant to industrial processing. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150034
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  • 6
    Electronic Resource
    Electronic Resource
    Neutron Optics (1953)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Nuclear and Particle Science 3 (1953), S. 93-118 
    Details
    ISSN: 0066-4243
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ns.03.120153.000521
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  • 7
    Electronic Resource
    Electronic Resource
    Synchrotron diffraction measurement of residual stresses in friction stir welded 5383-H321 aluminium butt joints and their modification by fatigue cycling (2004)
    PO Box 1354, 9600 Garsington Road, Oxford OX4 2XG, UK. : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 27 (2004), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents two-dimensional information on the residual stresses in 8 mm 5383-H321 aluminium plates joined by double pass (DP) friction stir welding (FSW). It considers the inherent variability in residual stress magnitudes along 0.5 m lengths of weld pass, and their modification under a sequence of applied fatigue loads. This represents one of a planned series of experiments aimed at illuminating the effects of fatigue cycling on residual stress fields. In this particular case, the magnitudes of the bending fatigue loads (R= 0.1) were chosen to correlate with the measured proof strengths of the weld metal (approximately 160 MPa) and the parent plate (approximately 260–270 MPa). In four-point bend S–N tests at R= 0.1 on 40 mm wide FS welded specimens of this alloy and plate thickness, these peak stress levels correspond to lives of around 105 cycles and 107 cycles, respectively. Results from the work indicate that significant variability exists among welded plates in peak compressive stress magnitudes (a range of perhaps −50 MPa to −140 MPa), although peak tensile stresses were relatively low and more consistent (from around 0 to 30 MPa). Fatigue loading accentuates the peak-to-valley stress change and causes an overall translation of the stresses to become more positive. Peak tensile stresses increase several-fold during fatigue cycling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.2004.00736.x
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  • 8
    Electronic Resource
    Electronic Resource
    Synchrotron diffraction investigation of the distribution and influence of residual stresses in fatigue (2004)
    PO Box 1354, 9600 Garsington Road, Oxford OX4 2XG, UK. : Blackwell Publishing Ltd.
    Fatigue & fracture of engineering materials & structures 27 (2004), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents some results obtained from synchrotron diffraction investigations into two somewhat related areas of interest to the fatigue community. Firstly, the influence of fatigue cycling on the distribution and magnitude of residual strains and stresses and, secondly, the residual strains and stresses engendered around a growing fatigue crack. Its main premise is that modern tools such as automated synchrotron strain scanning offer the potential for more complete insight into the distribution of residual strains and stresses and their influence on fatigue performance. The first part of the work was accomplished using friction-stir welded (FSW) and metal-inert gas (MIG) welded specimens. The particular interest in these specimens was obtaining detailed knowledge regarding as-welded variation in residual stresses between specimens, the location of peak values relative to local microstructure and stress concentrations, and of their modification during fatigue cycling. Such information may indicate a route forward to the selection of welding process parameters for optimised fatigue performance. The second part of the work considered an established fatigue crack in a compact tension (CT) specimen and examined the ability of synchrotron diffraction to characterize the stresses associated with the plastic enclave around a fatigue crack. This work is of interest in the context of better knowledge of crack-tip shielding by plasticity-induced closure and its incorporation into life prediction methodologies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.2004.00789.x
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  • 9
    Electronic Resource
    Electronic Resource
    Time-Resolved Simultaneous SAXS/WAXS of the Drawing of Polyethylene at the Daresbury SRS (1996)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 3 (1996), S. 84-90 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A system has been developed which represents a significant advance in the quality and extent of small- and wide-angle X-ray scattering data (SAXS and WAXS) that can be recorded simultaneously with strain data during the drawing and annealing of polymer materials. WAXS data are recorded using a Photonic Science charge-coupled-device area detector and SAXS data using a gas-filled multiwire area detector. Strain data, for the region of the specimen from which the SAXS/WAXS data are collected, are calculated from an accurately synchronized continuously recorded video image of the specimen. The system allows X-ray and video image data to be collected as a series of frames with essentially no `dead-time' between frames. The data are fully two-dimensional and can be collected for a wide range of d spacings. The use of this system to investigate the stress-induced orientation and phase changes during the drawing of a range of grades of commercially available polyethylene is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049596000192
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  • 10
    Electronic Resource
    Electronic Resource
    Tholeiite derivative dyke swarms near Erkowit, Red Sea Hills, Sudan (1977)
    Springer
    International journal of earth sciences 66 (1977), S. 228-237 
    Details
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract Extensive dyke swarms have been identified in basement rocks inland from Suakin with NW, N-S, and E-W trends. Petrographic examination and the results of ten XRF analyses of dykes near Erkowit indicate that they belong to a tholeiitic hornblende microgabbro-microdiorite suite. Eight whole rock K-Ar isotopic analyses suggest two possible periods of emplacement at 616±18 Ma. and 660±19 Ma. ago. These are the first geochemical-geochronological data for Sudanese dykes, and suggest an association with the N.E. African igneous ring-complex province.
    Abstract: Résumé On a compilé de grands ensembles de dykes dans le socle de l'intérieur de Suakin. Ils sont orientés N.O.-S.E., N-S et E-O. Les examens pétrographiques et les résultats de dix analyses par fluorescence X, des dykes dans la région d'Erkowit indiquent leur apparartenance à une suite tholéiitique de microgabbro ou microdiorite à hornblende. Huit analyses isotropiques de la roche totale par la méthode K-Ar suggérent deux possibilités de la période d'emplacement, 616±18 Ma et 660±19 Ma. Ces premiers éléments d'information géochimiques et géochronologiques concernant les dykes soudanais suggérent une association avec la province du ring-complex du N.E. Africain.
    Notes: Zusammenfassung Ausgedehnte Ansammlungen von Gängen in nordwestlichen, nord-südlichen und ostwestlichen Richtungen wurden im Grundgebirge landeinwärts von Suakin festgestellt. Eine petrographische Überprüfung und die Ergebnisse von zehn XRF-Analysen von Gängen in der Nähe von Erkowit deuten auf eine tholeiitische Homblende-Mikrogabbro-Mikrodiorit-Gruppe hin. Acht K/Ar-Isotopenanalysen legen zwei mögliche Entstehungsperioden um 616±18 Millionen Jahre und 660±19 Millionen Jahre nahe. Dies sind die ersten geochemisch-geochronologischen Daten für sudanesische Gänge; sie weisen auf eine Verbindung mit der nordostafrikanischen plutonischen Ringkomplex Region hin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01989574
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