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  • 1
    Electronic Resource
    Electronic Resource
    In situ reflectance anisotropy studies of AlxGa1−xAs layers grown on GaAs(001) by molecular beam epitaxy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3115-3120 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reflectance anisotropy spectroscopy was used to examine the surfaces of AlxGa1−xAs layers grown on GaAs(001) by molecular beam epitaxy, where the Al mole fraction was varied across the whole composition range x=(0.0,0.25,0.50,0.75,1.0). All surfaces were also independently characterized using reflection high-energy electron diffraction, and were found to exhibit a c(4×4) reconstruction. After initial changes in the spectra were observed on depositing very thin layers (≤20 monolayers), in the intermediate thickness range a regime was entered in which strong optical interference effects appeared. These effects are accurately accounted for using a four-media model. For thicker layers (≥8000 monolayers), interference effects were seen to diminish and spectra representative of the surfaces of bulk AlxGa1−xAs were obtained. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358663
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Representative reflectance anisotropy spectra from Al(x)Ga(1−x)As layers (x=0 to 1.0) grown on GaAs(001) by molecular beam epitaxy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1930-1932 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present in this study reflectance anisotropy spectra also termed reflectance difference spectra for the surfaces of thick Al(x)Ga(1−x)As (x=0.0, 0.25, 0.50, 0.75, 1.00) layers grown on GaAs(001) by molecular beam epitaxy (MBE). Layers ≥2 μm thick were grown in order to minimize the interference effects from the buried interface and to obtain spectra representative of bulk Al(x)Ga(1−x)As surfaces. All surfaces were also independently characterized using reflection high energy electron diffraction (RHEED), and found to exhibit a c(4×4) reconstruction. The reflectance anisotropy spectra were qualitatively similar to one another, but showed clear dependence of energy and magnitude upon the mole fraction x. These spectra can serve as reference for determining stochiometries in MBE growth of Al(x)Ga(1−x)As and probably should be useful for future comparison to metalorganic vapor phase epitaxy (MOVPE) Al(x)Ga(1−x)As growth. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113280
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    Paper (German National Licenses)
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  • 3
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    A temperate former West Antarctic ice sheet suggested by an extensive zone of subglacial meltwater channels (2014)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2014-11-04
    Description: Several recent studies predict that the West Antarctic Ice Sheet will become increasingly unstable under warmer conditions. Insights on such change can be assisted through investigations of the subglacial landscape, which contains imprints of former ice-sheet behavior. Here, we present radio-echo sounding data and satellite imagery revealing a series of ancient large sub-parallel subglacial bed channels preserved in the region between the Möller and Foundation Ice Streams, West Antarctica. We suggest that these newly recognized channels were formed by significant meltwater routed along the ice-sheet bed. The volume of water required is likely substantial and can most easily be explained by water generated at the ice surface. The Greenland Ice Sheet today exemplifies how significant seasonal surface melt can be transferred to the bed via englacial routing. For West Antarctica, the Pliocene (2.6–5.3 Ma) represents the most recent sustained period when temperatures could have been high enough to generate surface melt comparable to that of present-day Greenland. We propose, therefore, that a temperate ice sheet covered this location during Pliocene warm periods.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 4
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    Behavioral responses of freshwater calanoid copepods to the presence of ultraviolet radiation: avoidance and attraction (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-23
    Description: Binary choice experiments under natural solar radiation were used to test short-term behavioral responses of freshwater calanoid copepods to ultraviolet radiation (UV). Responses of the nine species from 15 populations spanning North and South America included both UV attraction and UV avoidance, and varied among habitats, species and populations. Copepods from more transparent lakes were more attracted to UV than those from less transparent lakes. When individuals were pre-exposed in the laboratory to photosynthetically active radiation (PAR) in the presence and absence of UV, those pre-exposed to UV spent more time in the high UV environment than those exposed to PAR alone. However, these differences disappeared after 150 min, suggesting that the responses were short term and mediated in part by ambient UV conditions. Copepods represent a large proportion of the biomass of zooplankton in many aquatic ecosystems, and their ability to detect and respond behaviorally to UV may enable them to use this ubiquitous environmental cue to regulate their water column position. The use of UV as a habitat selection cue may permit copepods to exploit optimal food environments or limit overlap with less UV-tolerant competitors, predators or parasites, while minimizing damage resulting from longer term UV exposure.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 5
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    A river runs through it (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-15
    Keywords: Ecology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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