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  • 1
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    2D condensation model for the inner Solar Nebula: an enstatite-rich environment (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-06
    Description: Infrared observations provide the dust composition in the protoplanetary discs surface layers, but cannot probe the dust chemistry in the mid-plane, where planet formation occurs. Meteorites show that dynamics was important in determining the dust distribution in the Solar Nebula and needs to be considered if we are to understand the global chemistry in discs. 1D radial condensation sequences can only simulate one disc layer at a time and cannot describe the global chemistry or the complexity of meteorites. To address these limitations, we compute for the first time the 2D distribution of condensates in the inner Solar Nebula using a thermodynamic equilibrium model, and derive time-scales for vertical settling and radial migration of dust. We find two enstatite-rich zones within 1 au from the young Sun: a band ~0.1 au thick in the upper optically-thin layer of the disc interior to 0.8 au , and in the optically-thick disc mid-plane out to ~0.4 au . The two enstatite-rich zones support recent evidence that Mercury and enstatite chondrites (ECs) shared a bulk material with similar composition. Our results are also consistent with infrared observation of protoplanetary disc which show emission of enstatite-rich dust in the inner surface of discs. The resulting chemistry and dynamics suggests that the formation of the bulk material of ECs occurred in the inner surface layer of the disc, within 0.4 au . We also propose a simple alternative scenario in which gas fractionation and vertical settling of the condensates lead to an enstatite-chondritic bulk material.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Double-Strand Break Repair Assays Determine Pathway Choice and Structure of Gene Conversion Events in Drosophila melanogaster (2014)
    Genetics Society of America (GSA)
    Details
    Publication Date: 2014-03-22
    Description: Double-strand breaks (DSBs) must be accurately and efficiently repaired to maintain genome integrity. Depending on the organism receiving the break, the genomic location of the DSB, and the cell-cycle phase in which it occurs, a DSB can be repaired by homologous recombination (HR), nonhomologous end-joining (NHEJ), or single-strand annealing (SSA). Two novel DSB repair assays were developed to determine the contributions of these repair pathways and to finely resolve repair event structures in Drosophila melanogaster . Rad51-dependent homologous recombination is the preferred DSB repair pathway in mitotically dividing cells, and the pathway choice between HR and SSA occurs after end resection and before Rad51-dependent strand invasion. HR events are associated with long gene conversion tracts and are both bidirectional and unidirectional, consistent with repair via the synthesis-dependent strand annealing pathway. Additionally, HR between diverged sequences is suppressed in Drosophila , similar to levels reported in human cells. Junction analyses of rare NHEJ events reveal that canonical NHEJ is utilized in this system.
    Electronic ISSN: 2160-1836
    Topics: Biology
    Published by Genetics Society of America (GSA)
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  • 3
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    The effect of models of the interstellar media on the central mass distribution of galaxies (2014)
    Oxford University Press
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    Publication Date: 2014-04-14
    Description: We compared the central mass distribution of dwarf and spiral galaxies simulated with three different models of the interstellar medium with increasing complexity: primordial (H+He) cooling, additional cooling via metal lines, and molecular hydrogen ( H 2 ) with shielding of atomic and molecular hydrogen, in addition to metal-line cooling. We followed the evolution of four high-resolution, simulated galaxies with V peak  〈 120 km s –1 to a redshift of zero in a fully cosmological cold dark matter context. The spiral galaxies produced with either primordial cooling or H 2 physics had realistic, rising rotation curves. However, the simulations with metal-line cooling produced spiral galaxies with peaked rotation curves. These differences represent changes to the amount of low-angular-momentum baryons removed by stellar feedback. When there was only primordial cooling, the star-forming gas was hotter and the feedback-heated gas cooled relatively slowly so less energy was required to expel it. When H 2 was included, the accompanying shielding produced large amounts of clumpy, cold gas, and the supernova feedback was more highly concentrated. In contrast to the spiral galaxies, the dwarfs had similarly realistic concentrations and displayed similar behaviour across all models because their low metallicities resulted in smaller differences is the behaviour of the gas.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Inertia Influences Pelagic Sargassum Advection and Distribution (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The effect of inertia (resistance to a change in velocity of buoyant finite‐sized objects) on the advection of pelagic Sargassum, a macroalgae, is a function of the size and density of natural Sargassum rafts. Here, we present observations of Sargassum density and an approach for estimating an effective radius of Sargassum rafts from remote sensing observations. This allows the existing theoretical framework for Lagrangian modeling of inertial effects on spherical particles to be applied to Sargassum. Accounting for inertia yields up to a 20% increase in Sargassum export from the Sargasso Sea southward, and provides a return pathway to the tropics that may be important to maintaining a self‐sustaining population. Resolving inertial effects also leads to increases in retention in the Gulf of Mexico and Caribbean Sea, where Sargassum inundation events are increasingly common. Including inertial effects in models of Sargassum advection could improve predictions of these events.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Conservation conflicts across Africa (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-04-03
    Description: There is increasing evidence that areas of outstanding conservation importance may coincide with dense human settlement or impact. We tested the generality of these findings using 1 degree-resolution data for sub-Saharan Africa. We find that human population density is positively correlated with species richness of birds, mammals, snakes, and amphibians. This association holds for widespread, narrowly endemic, and threatened species and looks set to persist in the face of foreseeable population growth. Our results contradict earlier expectations of low conflict based on the idea that species richness decreases and human impact increases with primary productivity. We find that across Africa, both variables instead exhibit unimodal relationships with productivity. Modifying priority-setting to take account of human density shows that, at this scale, conflicts between conservation and development are not easily avoided, because many densely inhabited grid cells contain species found nowhere else.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Balmford, A -- Moore, J L -- Brooks, T -- Burgess, N -- Hansen, L A -- Williams, P -- Rahbek, C -- New York, N.Y. -- Science. 2001 Mar 30;291(5513):2616-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Conservation Biology Group, Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK. a.balmford@zoo.cam.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11283376" target="_blank"〉PubMed〈/a〉
    Keywords: Africa South of the Sahara ; Amphibians ; Animals ; Birds ; *Conservation of Natural Resources ; *Ecosystem ; Humans ; Mammals ; Population Density ; Population Growth ; Snakes
    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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  • 6
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    The pandas' habitat at Wolong Nature Reserve (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-07-31
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Brooks, T -- Bruner, A G -- Brunner, J -- da Fonseca, G A -- Liu, R -- Sung, W -- Yan, X -- New York, N.Y. -- Science. 2001 Jul 27;293(5530):603-5.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11476086" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; China ; *Conservation of Natural Resources ; *Ecosystem ; *Environment ; *Ursidae
    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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    Environment. Can we defy nature's end? (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-09-22
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pimm, S L -- Ayres, M -- Balmford, A -- Branch, G -- Brandon, K -- Brooks, T -- Bustamante, R -- Costanza, R -- Cowling, R -- Curran, L M -- Dobson, A -- Farber, S -- da Fonseca, G A -- Gascon, C -- Kitching, R -- McNeely, J -- Lovejoy, T -- Mittermeier, R A -- Myers, N -- Patz, J A -- Raffle, B -- Rapport, D -- Raven, P -- Roberts, C -- Rodriguez, J P -- Rylands, A B -- Tucker, C -- Safina, C -- Samper, C -- Stiassny, M L -- Supriatna, J -- Wall, D H -- Wilcove, D -- New York, N.Y. -- Science. 2001 Sep 21;293(5538):2207-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Environmental Research and Conservation, MC 5556, Columbia University, New York, NY 10027, USA. StuartPimm@aol.com〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11567124" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Conservation of Natural Resources/economics ; Costs and Cost Analysis ; *Ecosystem ; *Environment ; Public Policy ; Trees
    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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  • 8
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    Ecology. Caribbean catastrophes (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-11-17
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Brooks, T -- Smith, M L -- New York, N.Y. -- Science. 2001 Nov 16;294(5546):1469-71.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Applied Biodiversity Science, Conservation International, Washington, DC 20036, USA. t.brooks@conservation.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11711658" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Bahamas ; *Birds/genetics/physiology ; Conservation of Natural Resources ; DNA, Mitochondrial/genetics ; Disasters ; *Ecosystem ; *Environment ; *Genetic Variation ; *Lizards/physiology ; Population Density ; Population Dynamics ; West Indies
    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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  • 9
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    A global experiment under way (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-03-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉da Fonseca, Gustavo A B -- Gascon, Claude -- Steininger, Marc K -- Brooks, Thomas -- Mittermeier, Russell A -- Lacher, Thomas E Jr -- New York, N.Y. -- Science. 2002 Mar 8;295(5561):1835.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11890179" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Conservation of Natural Resources ; Data Collection ; Databases, Factual ; *Ecosystem ; *Environment ; Plants ; *Research Design ; *Trees
    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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  • 10
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    The pathways and properties of the Amazon River plume in the tropical North Atlantic ocean (2013)
    Wiley
    Details
    Publication Date: 2013-11-17
    Description: The Amazon River Plume spreads across the tropical North Atlantic creating a barrier to vertical mixing. Here, using a 1/6° HYCOM model and data from three research cruises in May-June 2010, Sept-Oct 2011, and July 2012, we investigate the pathways and properties of the plume. Four plume pathways for export of freshwater from the western tropical North Atlantic are identified. These consist of direct and indirect pathways to the northwest, and eastward pathways toward the subtropical gyre and toward Africa in the North Equatorial Counter Current. Because of the seasonality and co-occurrence of these pathways, plume characteristics are highly variable. Two pathways export water to the Caribbean, however the timescales associated with those direct and indirect pathways (3 vs. 6+ months) differ, leading to different salinity characteristics of the plume water. Models results show that the Amazon river and tropical precipitation have similar magnitude impact on the observed seasonal cycle of freshwater within the western tropical Atlantic and at the 8°N, 38°W PIRATA mooring. Freshwater associated with the Amazon also influences surface salinity in winter as far as Africa in the model. Mean plume salinity leads maximum discharge, highlighting the importance of currents and advection rather than discharge in maintaining plume properties. Plume pathways are tied to the underlying current structure, with the North Equatorial Counter Current jet preventing direct freshwater transport into the southern hemisphere. The plume influences underlying currents as well, generating vertical current shear that leads to enhanced eddy stirring and mixing in the model simulations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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