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  • 1
    Publication Date: 2004-11-30
    Description: The widespread extinctions of large mammals at the end of the Pleistocene epoch have often been attributed to the depredations of humans; here we present genetic evidence that questions this assumption. We used ancient DNA and Bayesian techniques to reconstruct a detailed genetic history of bison throughout the late Pleistocene and Holocene epochs. Our analyses depict a large diverse population living throughout Beringia until around 37,000 years before the present, when the population's genetic diversity began to decline dramatically. The timing of this decline correlates with environmental changes associated with the onset of the last glacial cycle, whereas archaeological evidence does not support the presence of large populations of humans in Eastern Beringia until more than 15,000 years later.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Shapiro, Beth -- Drummond, Alexei J -- Rambaut, Andrew -- Wilson, Michael C -- Matheus, Paul E -- Sher, Andrei V -- Pybus, Oliver G -- Gilbert, M Thomas P -- Barnes, Ian -- Binladen, Jonas -- Willerslev, Eske -- Hansen, Anders J -- Baryshnikov, Gennady F -- Burns, James A -- Davydov, Sergei -- Driver, Jonathan C -- Froese, Duane G -- Harington, C Richard -- Keddie, Grant -- Kosintsev, Pavel -- Kunz, Michael L -- Martin, Larry D -- Stephenson, Robert O -- Storer, John -- Tedford, Richard -- Zimov, Sergei -- Cooper, Alan -- New York, N.Y. -- Science. 2004 Nov 26;306(5701):1561-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Henry Wellcome Ancient Biomolecules Centre, Oxford University, South Parks Road, Oxford OX13PS, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15567864" target="_blank"〉PubMed〈/a〉
    Keywords: Alaska ; Animals ; Bayes Theorem ; *Bison/classification/genetics ; Canada ; China ; *Climate ; DNA, Mitochondrial/genetics ; Environment ; *Fossils ; Genetic Variation ; Genetics, Population ; Human Activities ; Humans ; North America ; Phylogeny ; Population Dynamics ; Sequence Analysis, DNA ; Time
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2006-01-28
    Description: Directly transmitted parasites often provide substantial information about the temporal and spatial characteristics of host-to-host contact. Here, we demonstrate that a fast-evolving virus (feline immunodeficiency virus, FIV) can reveal details of the contemporary population structure and recent demographic history of its natural wildlife host (Puma concolor) that were not apparent from host genetic data and would be impossible to obtain by other means. We suggest that rapidly evolving pathogens may provide a complementary tool for studying population dynamics of their hosts in "shallow" time.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Biek, Roman -- Drummond, Alexei J -- Poss, Mary -- New York, N.Y. -- Science. 2006 Jan 27;311(5760):538-41.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Wildlife Biology Program, University of Montana, Missoula, MT 59812, USA. rbiek@emory.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16439664" target="_blank"〉PubMed〈/a〉
    Keywords: Alberta/epidemiology ; Animals ; Bayes Theorem ; British Columbia/epidemiology ; Ecosystem ; *Evolution, Molecular ; Genes, env ; Genes, pol ; Geography ; Immunodeficiency Virus, Feline/*classification/*genetics ; Lentivirus Infections/epidemiology/*veterinary/virology ; Microsatellite Repeats ; Molecular Sequence Data ; Montana/epidemiology ; Phylogeny ; Population Dynamics ; *Puma/genetics/virology ; Time Factors ; Wyoming/epidemiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2009-01-24
    Description: Debates about human prehistory often center on the role that population expansions play in shaping biological and cultural diversity. Hypotheses on the origin of the Austronesian settlers of the Pacific are divided between a recent "pulse-pause" expansion from Taiwan and an older "slow-boat" diffusion from Wallacea. We used lexical data and Bayesian phylogenetic methods to construct a phylogeny of 400 languages. In agreement with the pulse-pause scenario, the language trees place the Austronesian origin in Taiwan approximately 5230 years ago and reveal a series of settlement pauses and expansion pulses linked to technological and social innovations. These results are robust to assumptions about the rooting and calibration of the trees and demonstrate the combined power of linguistic scholarship, database technologies, and computational phylogenetic methods for resolving questions about human prehistory.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gray, R D -- Drummond, A J -- Greenhill, S J -- New York, N.Y. -- Science. 2009 Jan 23;323(5913):479-83. doi: 10.1126/science.1166858.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19164742" target="_blank"〉PubMed〈/a〉
    Keywords: Bayes Theorem ; Databases, Factual ; *Emigration and Immigration/history ; History, Ancient ; Humans ; *Language ; Linguistics ; *Oceanic Ancestry Group/history ; Pacific Islands ; Philippines ; Phylogeny ; Polynesia ; Population Dynamics ; Taiwan ; Vocabulary
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
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    Publication Date: 2011-08-18
    Description: Two computer programs have been developed to numerically calculate complex, two-dimensional flow fields in scramjets. The first program is written for inlet analysis whereas the second program is written primarily for combustor analysis. Both programs solve the full two-dimensional Navier-Stokes equations by a well-known explicit, predictor-corrector technique. Turbulence is modeled by an algebraic eddy-viscosity model. The combustor program also includes one or more species conservation equations to calculate mixing and reacting flows. The hydrogen/air chemistry in this program is modeled by a complete reaction model. The combustor program has been recently modified to analyze axisymmetric ramjet dump combustor flow field. Results from these computer programs are presented that predict the flow in several scramjet inlet configurations, two model scramjet engine configurations, and in a dump combustor simulator. Computed results are also compared with available experimental data to allow assessment of the programs.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: APL Computational Methods for Ramjets; p 9-24
    Format: text
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  • 5
    Publication Date: 2013-08-31
    Description: The physical phenomena involved when a supersonic flow undergoes chemical reaction are discussed. Detailed physical models of convective and diffusive mixing, and finite rate chemical reaction in supersonic flow are presented. Numerical algorithms used to solve the equations governing these processes are introduced. Computer programs using these algorithms are used to analyze the structure of the reacting mixing layer. It is concluded that, as in subsonic flow, exothermic heat release in unconfined supersonic flows retards fuel/air mixing. Non mixing is shown to be a potential problem in reducing the efficiency of supersonic as well as subsonic combustion. Techniques for enhancing fuel/air mixing and combustion are described.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: VKI, Gas Turbine Combustion, Volume 1; 95 p
    Format: application/pdf
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  • 6
    Publication Date: 2011-08-19
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 3; 423-439
    Format: text
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  • 7
    Publication Date: 2017-10-02
    Description: A detailed understanding of the scramjet combustor flow field is critical to the achievement of a successful design. Even though the combustor flow field is quite complex, it can be realistically viewed as a collection of spatially developing and reacting supersonic mixing layers that are initially discrete, but that ultimately merge into larger more complex zones. These mixing layers begin downstream of a set of fuel injectors that introduce gaseous hydrogen in both a parallel and transverse direction into a supersonic air stream entering from the engine inlet. The behavior of the initial portion of the combustor flow, in the mixing layers near the fuel injectors, appears to be most critical, since this is where the mechanism for efficient high speed mixing must be established to achieve the required degree of combustion downstream. Because of the structure of the flow field in this initial portion of the combustor, a single supersonic, spatially developing and reacting mixing layer serves as an excellent physical model for the overall flow field. Even though this reacting mixing layer flow is geometrically simple, it can still be made to retain all of the fluid mechanical and chemical complexities present in the actual combustor flow field.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: Sandia National Labs., Summary of Discussions at the Eleventh Meeting of the Sandia Cooperative Group on the Aerothermochemistry of Turbulent Combustion; p 10-20
    Format: application/pdf
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  • 8
    Publication Date: 2019-06-28
    Description: NASA Langley has intensively investigated the components of ramjet and scramjet systems for endoatmospheric, airbreathing hypersonic propulsion; attention is presently given to the optimization of scramjet combustor fuel-air mixing and reaction characteristics. A supersonic, spatially developing and reacting mixing layer has been found to serve as an excellent physical model for the mixing and reaction process. Attention is presently given to techniques that have been applied to the enhancement of the mixing processes and the overall combustion efficiency of the mixing layer. A fuel injector configuration has been computationally designed which significantly increases mixing and reaction rates.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 88-3260
    Format: text
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  • 9
    Publication Date: 2019-06-28
    Description: Pursuant to a NASA-Langley development program for a scramjet HST propulsion system entailing the optimization of the scramjet combustor's fuel-air mixing and reaction characteristics, a numerical study has been conducted of the candidate parallel fuel injectors. Attention is given to a method for flow mixing-process and combustion-efficiency enhancement in which a supersonic circular hydrogen jet coflows with a supersonic air stream. When enhanced by a planar oblique shock, the injector configuration exhibited a substantial degree of induced vorticity in the fuel stream which increased mixing and chemical reaction rates, relative to the unshocked configuration. The resulting heat release was effective in breaking down the stable hydrogen vortex pair that had inhibited more extensive fuel-air mixing.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-1914
    Format: text
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  • 10
    Publication Date: 2019-07-27
    Description: Research has been conducted for a number of years at the NASA Langley Research Center to develop a supersonic combustion ramjet (scramjet) capable of propelling a vehicle at hypersonic speeds in the atmosphere or beyond. Recently, that research has been directed toward the optimization of the scramjet combustor, and in particular the efficiency of fuel-air mixing and reaction in the engine. This paper describes a study of fuel-air mixing and reaction in a supersonic flow field, and discusses several techniques that were applied for enhancing the mixing processes and overal combustion efficiency in the flow. Based on the results of the study, an alternate fuel injector configuration was computationally designed, and that configuration significantly increased the amount of fuel-air mixing and combustion over a given combustor length that was achieved.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: International Symposium on Numerical Methods in Engineering; Sept. 11-15, 1989; Lausanne; Switzerland
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