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  • 1
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    Abrupt Amazonian tree mortality [Environmental Sciences] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-04-30
    Description: Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 2
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    Global burned area and biomass burning emissions from small fires (2012)
    Wiley
    Details
    Publication Date: 2012-12-11
    Description: In several biomes, including croplands, wooded savannas, and tropical forests, many small fires occur each year that are well below the detection limit of the current generation of global burned area products derived from moderate resolution surface reflectance imagery. Although these fires often generate thermal anomalies that can be detected by satellites, their contributions to burned area and carbon fluxes have not been systematically quantified across different regions and continents. Here we developed a preliminary method for combining 1-km thermal anomalies (active fires) and 500 m burned area observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) to estimate the influence of these fires. In our approach, we calculated the number of active fires inside and outside of 500 m burn scars derived from reflectance data. We estimated small fire burned area by computing the difference normalized burn ratio (dNBR) for these two sets of active fires and then combining these observations with other information. In a final step, we used the Global Fire Emissions Database version 3 (GFED3) biogeochemical model to estimate the impact of these fires on biomass burning emissions. We found that the spatial distribution of active fires and 500 m burned areas were in close agreement in ecosystems that experience large fires, including savannas across southern Africa and Australia and boreal forests in North America and Eurasia. In other areas, however, we observed many active fires outside of burned area perimeters. Fire radiative power was lower for this class of active fires. Small fires substantially increased burned area in several continental-scale regions, including Equatorial Asia (157%), Central America (143%), and Southeast Asia (90%) during 2001–2010. Globally, accounting for small fires increased total burned area by approximately by 35%, from 345 Mha/yr to 464 Mha/yr. A formal quantification of uncertainties was not possible, but sensitivity analyses of key model parameters caused estimates of global burned area increases from small fires to vary between 24% and 54%. Biomass burning carbon emissions increased by 35% at a global scale when small fires were included in GFED3, from 1.9 Pg C/yr to 2.5 Pg C/yr. The contribution of tropical forest fires to year-to-year variability in carbon fluxes increased because small fires amplified emissions from Central America, South America and Southeast Asia—regions where drought stress and burned area varied considerably from year to year in response to El Nino-Southern Oscillation and other climate modes.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Resolving the structure of ionized helium in the intergalactic medium with the far ultraviolet spectroscopic explorer (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-08-11
    Description: The neutral hydrogen (H I) and ionized helium (He II) absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar HE2347-4342 in the 1000 to 1187 angstrom band at a resolving power of 15,000. We resolve the He II Lyman alpha (Lyalpha) absorption as a discrete forest of absorption lines in the redshift range 2.3 to 2.7. About 50 percent of these features have H I counterparts with column densities N(H I) 〉 10(12.3) per square centimeter that account for most of the observed opacity in He II Lyalpha. The He II to H I column density ratio ranges from 1 to 〉1000, with an average of approximately 80. Ratios of 〈100 are consistent with photoionization of the absorbing gas by a hard ionizing spectrum resulting from the integrated light of quasars, but ratios of 〉100 in many locations indicate additional contributions from starburst galaxies or heavily filtered quasar radiation. The presence of He II Lyalpha absorbers with no H I counterparts indicates that structure is present even in low-density regions, consistent with theoretical predictions of structure formation through gravitational instability.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kriss, G A -- Shull, J M -- Oegerle, W -- Zheng, W -- Davidsen, A F -- Songaila, A -- Tumlinson, J -- Cowie, L L -- Deharveng, J M -- Friedman, S D -- Giroux, M L -- Green, R F -- Hutchings, J B -- Jenkins, E B -- Kruk, J W -- Moos, H W -- Morton, D C -- Sembach, K R -- Tripp, T M -- New York, N.Y. -- Science. 2001 Aug 10;293(5532):1112-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA. gak@stsci.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11498584" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Forecasting fire season severity in South America using sea surface temperature anomalies (2011)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2011-11-15
    Description: Fires in South America cause forest degradation and contribute to carbon emissions associated with land use change. We investigated the relationship between year-to-year changes in fire activity in South America and sea surface temperatures. We found that the Oceanic Nino Index was correlated with interannual fire activity in the eastern Amazon, whereas the Atlantic Multidecadal Oscillation index was more closely linked with fires in the southern and southwestern Amazon. Combining these two climate indices, we developed an empirical model to forecast regional fire season severity with lead times of 3 to 5 months. Our approach may contribute to the development of an early warning system for anticipating the vulnerability of Amazon forests to fires, thus enabling more effective management with benefits for climate and air quality.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chen, Yang -- Randerson, James T -- Morton, Douglas C -- DeFries, Ruth S -- Collatz, G James -- Kasibhatla, Prasad S -- Giglio, Louis -- Jin, Yufang -- Marlier, Miriam E -- New York, N.Y. -- Science. 2011 Nov 11;334(6057):787-91. doi: 10.1126/science.1209472.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth System Science, University of California, Irvine, CA 92697, USA. yang.chen@uci.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22076373" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Amazon forests maintain consistent canopy structure and greenness during the dry season (2014)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2014-02-07
    Description: The seasonality of sunlight and rainfall regulates net primary production in tropical forests. Previous studies have suggested that light is more limiting than water for tropical forest productivity, consistent with greening of Amazon forests during the dry season in satellite data. We evaluated four potential mechanisms for the seasonal green-up phenomenon, including increases in leaf area or leaf reflectance, using a sophisticated radiative transfer model and independent satellite observations from lidar and optical sensors. Here we show that the apparent green up of Amazon forests in optical remote sensing data resulted from seasonal changes in near-infrared reflectance, an artefact of variations in sun-sensor geometry. Correcting this bidirectional reflectance effect eliminated seasonal changes in surface reflectance, consistent with independent lidar observations and model simulations with unchanging canopy properties. The stability of Amazon forest structure and reflectance over seasonal timescales challenges the paradigm of light-limited net primary production in Amazon forests and enhanced forest growth during drought conditions. Correcting optical remote sensing data for artefacts of sun-sensor geometry is essential to isolate the response of global vegetation to seasonal and interannual climate variability.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Morton, Douglas C -- Nagol, Jyoteshwar -- Carabajal, Claudia C -- Rosette, Jacqueline -- Palace, Michael -- Cook, Bruce D -- Vermote, Eric F -- Harding, David J -- North, Peter R J -- England -- Nature. 2014 Feb 13;506(7487):221-4. doi: 10.1038/nature13006. Epub 2014 Feb 5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA. ; 1] University of Maryland, College Park, Department of Geographical Sciences, College Park, Maryland 20742, USA [2] Global Land Cover Facility, College Park, Maryland 20740, USA. ; 1] NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA [2] Sigma Space Corporation, Lantham, Maryland 20706, USA. ; 1] NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA [2] University of Maryland, College Park, Department of Geographical Sciences, College Park, Maryland 20742, USA [3] Swansea University, Department of Geography, Singleton Park, Swansea SA2 8PP, UK. ; Earth System Research Center, University of New Hampshire, Durham, New Hampshire 03824, USA. ; Swansea University, Department of Geography, Singleton Park, Swansea SA2 8PP, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24499816" target="_blank"〉PubMed〈/a〉
    Keywords: Artifacts ; Brazil ; Color ; *Droughts ; Ecosystem ; Fresh Water/analysis ; Models, Biological ; Photosynthesis ; Pigmentation/*physiology ; Plant Leaves/anatomy & histology/growth & development/*physiology ; Rain ; Satellite Imagery ; *Seasons ; *Sunlight ; Trees/anatomy & histology/growth & development/*physiology ; *Tropical Climate
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 6
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    Environment and development. Brazil's Soy Moratorium (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-01-24
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gibbs, H K -- Rausch, L -- Munger, J -- Schelly, I -- Morton, D C -- Noojipady, P -- Soares-Filho, B -- Barreto, P -- Micol, L -- Walker, N F -- New York, N.Y. -- Science. 2015 Jan 23;347(6220):377-8. doi: 10.1126/science.aaa0181.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉University of Wisconsin, Madison, WI 53726, USA. hkgibbs@wisc.edu. ; University of Wisconsin, Madison, WI 53726, USA. ; NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. ; University of Maryland, College Park, MD 20742, USA. National Wildlife Federation, Washington, DC 20006, USA. ; Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270-901, Brazil. ; IMAZON Amazon Institute of People and the Environment, 66.060-162 Belem, Para, Brazil. ; Instituto Centro de Vida, 78045-055 Cuiaba, Mato Grosso, Brazil. ; National Wildlife Federation, Washington, DC 20006, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25613879" target="_blank"〉PubMed〈/a〉
    Keywords: Agriculture/*legislation & jurisprudence ; Brazil ; Conservation of Natural Resources/*legislation & jurisprudence ; *Soybeans
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Morton et al. reply (2016)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2016-03-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Morton, Douglas C -- Nagol, Jyoteshwar -- Carabajal, Claudia C -- Rosette, Jacqueline -- Palace, Michael -- Cook, Bruce D -- Vermote, Eric F -- Harding, David J -- North, Peter R J -- England -- Nature. 2016 Mar 17;531(7594):E6. doi: 10.1038/nature16458.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA. ; University of Maryland, College Park, Department of Geographical Sciences, College Park, Maryland 20742, USA. ; Global Land Cover Facility, College Park, Maryland 20740, USA. ; Sigma Space Corporation, Lanham, Maryland 20706, USA. ; Swansea University, Department of Geography, Singleton Park, Swansea SA2 8PP, UK. ; Earth Systems Research Center, University of New Hampshire, Durham, New Hampshire 03824, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26983545" target="_blank"〉PubMed〈/a〉
    Keywords: *Droughts ; Pigmentation/*physiology ; Plant Leaves/*physiology ; *Seasons ; *Sunlight ; Trees/*physiology ; *Tropical Climate
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 8
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    Global burned area and biomass burning emissions from small fires (2013)
    Wiley
    Details
    Publication Date: 2013-01-10
    Description: [1]  In several biomes, including croplands, wooded savannas, and tropical forests, many small fires occur each year that are well below the detection limit of the current generation of global burned area products derived from moderate resolution surface reflectance imagery. Although these fires often generate thermal anomalies that can be detected by satellites, their contributions to burned area and carbon fluxes have not been systematically quantified across different regions and continents. Here we developed a preliminary method for combining 1-km thermal anomalies (active fires) and 500 m burned area observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) to estimate the influence of these fires. In our approach, we calculated the number of active fires inside and outside of 500 m burn scars derived from reflectance data. We estimated small fire burned area by computing the difference normalized burn ratio (dNBR) for these two sets of active fires and then combining these observations with other information. In a final step, we used the Global Fire Emissions Database version 3 (GFED3) biogeochemical model to estimate the impact of these fires on biomass burning emissions. We found that the spatial distribution of active fires and 500 m burned areas were in close agreement in ecosystems that experience large fires, including savannas across southern Africa and Australia and boreal forests in North America and Eurasia. In other areas, however, we observed many active fires outside of burned area perimeters. Fire radiative power was lower for this class of active fires. Small fires substantially increased burned area in several continental-scale regions, including Equatorial Asia (157%), Central America (143%), and Southeast Asia (90%) during 2001–2010. Globally, accounting for small fires increased total burned area by approximately by 35%, from 345 Mha/yr to 464 Mha/yr. A formal quantification of uncertainties was not possible, but sensitivity analyses of key model parameters caused estimates of global burned area increases from small fires to vary between 24% and 54%. Biomass burning carbon emissions increased by 35% at a global scale when small fires were included in GFED3, from 1.9 Pg C/yr to 2.5 Pg C/yr. The contribution of tropical forest fires to year-to-year variability in carbon fluxes increased because small fires amplified emissions from Central America, South America and Southeast Asia—regions where drought stress and burned area varied considerably from year to year in response to El Nino-Southern Oscillation and other climate modes.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Electronic Resource
    Electronic Resource
    Evidence for space charge in atomic layer epitaxy ZnS:Mn alternating-current thin-film electroluminescent devices (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 296-299 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical and optical measurements of ZnS:Mn alternating-current thin-film electroluminescent (ACTFEL) devices grown by atomic layer epitaxy provide evidence for the existence of space charge within the bulk ZnS layer. Blue luminescence is observed during the falling edge of an applied voltage pulse when the ACTFEL device is operated at low temperature. This blue luminescence is attributed to donor-acceptor pair radiative recombination in which chlorine is identified as the donor and a zinc vacancy as the acceptor. This luminescence identification leads to determination of the origin of space charge as arising from impact ionization of the zinc vacancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353903
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  • 10
    Electronic Resource
    Electronic Resource
    Hot electron luminescence in ZnS alternating-current thin-film electroluminescent devices (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 231-233 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hot electron luminescence experiments are performed on ZnS alternating-current thin-film electroluminescent (ACTFEL) devices in order to determine the extent to which the electron distribution is heated. The luminescence spectrum is found to be broad and essentially featureless up to a high energy cutoff of approximately 3.7 eV, which is determined by optical absorption within the ZnS. This result indicates that under normal operating conditions in a ZnS ACTFEL device, a significant fraction of the electrons transported across the phosphor possess energies equal to or in excess of the ZnS band gap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110350
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