Relic H ii regions and radiative feedback at high redshifts     

Andrei Mesinger †  Greg L. Bryan  Zoltán Haiman 《Monthly notices of the Royal Astronomical Society》2009,399(3):1650-1662

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Dissociation constants and speciation in aqueous Li₂SO₄ and K₂SO₄ from measurements of electrical conductance to 673 K and 29 MPa     

Andrei V. Sharygin  Robert H. Wood  Victor N. Balashov 《Geochimica et cosmochimica acta》2006,70(20):5169-5182

The electrical conductivities of aqueous solutions of Li₂SO₄ and K₂SO₄ have been measured at 523-673 K at 20-29 MPa in dilute solutions for molalities up to 2 × 10⁻² mol kg⁻¹. These conductivities have been fitted to the conductance equation of Turq, Blum, Bernard, and Kunz with a consensus mixing rule and mean spherical approximation activity coefficients. In the temperature interval 523-653 K, where the dielectric constant, ε, is greater than 14, the electrical conductance data can be fitted by a solution model which includes ion association to form , , and , where M is Li or K. The adjustable parameters of this model are the first and second dissociation constants of the M₂SO₄. For the 673 K and 300 kg m⁻³ state point where the Coulomb interactions are the strongest (dielectric constant, ε = 5), models with more extensive association give good fits to the data. In the case of the Li₂SO₄ model, including the multi-ion associate, , gave an extremely good fit to the conductance data.  相似文献   

Coherent Structures at a Forest Edge: Properties, Coupling and Impact of Secondary Circulations   总被引：1，自引：1，他引：0  

Fabian Eder  Andrei Serafimovich  Thomas Foken 《Boundary-Layer Meteorology》2013,148(2):285-308

Little is known about the influence of coherent structures on the exchange process, mainly in the case of forest edges. Thus, in the framework of the ExchanGE processes in mountainous Regions (EGER) project, measurements of atmospheric turbulence were taken at different heights between a forest and an adjacent clear cutting using sonic anemometers and high-frequency optical gas analyzers. From these turbulence data, dominant coherent structures were extracted using an already existing wavelet methodology, which was developed for homogeneous forest canopies. The aim of this study is to highlight differences in properties of coherent structures between a forest and a clear cutting. Distinct features of coherent exchange at the forest edge are presented and a careful investigation of vertical and horizontal coupling by coherent structures around the surface heterogeneity is made. Within the forest, coherent structures are less frequent but possess larger time scales, indicating that only the largest coherent motions can penetrate through the forest canopy. At the forest edge, there is no crown layer that can hinder the vertical exchange of coherent structures, because these exhibit similar time scales at all heights. In contradiction to that, no improved vertical coupling was detected at the forest edge. This is mainly because the structures captured by the applied routine contribute less to total turbulent fluxes at the edge than within the forest. Thus, coherent structures with time scales between 10 and 40 s are not the dominant exchange mechanism at the forest edge. With respect to the horizontal direction, a consistent picture of coherent transport could be derived: along the forest edge there is mainly good coupling by coherent structures, whereas perpendicular to the forest edge there is mainly decoupling. Finally, it was found that there is a systematic modulation of coherent structures directly at the forest edge: strong ejection motions appear in all time series during the daytime, whereas strong sweeps dominate at night. An effect of wind direction relative to the forest edge is excluded. Consequently, it is hypothesized that this might be an indication of a quasi-stationary secondary circulation above the clear cutting that develops due to differences in surface temperature and roughness. Such circulations might be a relevant turbulent transport mechanism for ecosystem-atmosphere exchange in heterogeneous landscapes.  相似文献   

The instrumentally recorded fall of the Križevci meteorite,Croatia, February 4, 2011          下载免费PDF全文

J. Borovička  P. Spurný  D. Šegon  Ž. Andreić  J. Kac  K. Korlević  J. Atanackov  G. Kladnik  H. Mucke  D. Vida  F. Novoselnik 《Meteoritics & planetary science》2015,50(7):1244-1259

The Kri?evci H6 meteorite was recovered on the basis of fireball data obtained by the cameras of the Croatian Meteor Network. The fireball, which occurred on February 4, 2011, 23:20:40 UT, was also observed by meteor cameras in Slovenia and by the Autonomous Fireball Observatory in Martinsberg, Austria, which belongs to the European Fireball Network. Here, we present detailed data on fireball trajectory, velocity, deceleration, light curve, and orbit. We also modeled the atmospheric fragmentation of the meteoroid on the basis of the light curve and deceleration. The initial mass of the meteoroid was between 25–100 kg, most probably about 50 kg. Severe fragmentation occurred at heights of approximately 60 and 31 km, under dynamic pressures of 0.1 and 3 MPa, respectively. The peak absolute magnitude of ?13.7 was reached during the second severe fragmentation event. The recovered 291 g meteorite was probably the only fragment with a terminal mass exceeding 100 g. The orbit had a low inclination of 0.6 degrees, perihelion distance 0.74 AU, and semimajor axis 1.54 AU. Kri?evci can be ranked among the 10 best documented meteorite falls.  相似文献   

The thermo-tectonic history of the Song-Kul plateau, Kyrgyz Tien Shan: Constraints by apatite and titanite thermochronometry and zircon U/Pb dating     

Johan De Grave  Stijn Glorie  Mikhail M. Buslov  Andrei Izmer  Alena Fournier-Carrie  Vladislav Yu. Batalev  Frank Vanhaecke  Marlina Elburg  Peter Van den haute 《Gondwana Research》2011,20(4):745-763

The Song-Kul Basin sits on a plateau at the Northern and Middle Kyrgyz Tien Shan junction. It is a lacustrine basin, occupied by Lake Song-Kul and predominantly developed on igneous basement. This basement was targeted for a multi-method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present-day morphology. Zircon U/Pb dating by LA-ICP-MS revealed four different magmatic episodes: a Late Cambrian (~ 500 Ma) island arc system, a Late Ordovician (~ 450 Ma) subduction related intrusion, an Early Permian (~ 290 Ma) collisional stage, and a Middle to Late Permian (~ 260 Ma) post-collisional magmatic pulse. Middle to Late Triassic (~ 200–230 Ma) titanite fission-track ages and Late Triassic – Early Jurassic (~ 180–210 Ma) apatite fission-track ages and thermal history modeling indicate the Song-Kul basement was already emplaced in the shallow crust at that time. An exhumed fossil apatite fission-track partial annealing zone is recognized in the bordering Song-Kul mountain ranges. The area experienced only minor post-Early Mesozoic denudation. The igneous basement was slowly brought to apatite (U–Th)/He retention temperatures in the Late Cretaceous–Palaeogene. Miocene to present reactivation of the Tien Shan does not manifestly affect this part of the orogen.  相似文献   

Observed Variations of the Solar Diameter in 1998/2000     

Reis Neto  E.  Andrei  A.H.  Penna  J.L.  Jilinski  E.G.  Puliaev  S.P. 《Solar physics》2003,212(1):7-21

The results from 9112 independent measurements of the solar diameter, made between the years 1998 and 2000, at the Observatório Nacional Rio de Janeiro station, are examined. After the removal of isolated observations and correction of systematic effects, the series of results presents a well-defined normal distribution with standard deviation of 566 milli-arc-seconds (mas). The east and west results, which were taken under quite different atmospheric and instrumental conditions, have been treated separately and the smoothed series correlate at the level of 80%. The solar figure as charted from these data diverges from a perfect sphere by a mid-heliolatitude depletion at the level of 50 mas, and an overall flatness, to the effect of the polar radius being shorter than the equatorial radius by 13±4 mas. Finally, a significant periodic variation around 515 days is found for the observed solar diameter, with amplitude of 60 mas.  相似文献   

Temporal variability in the thermal requirements for vegetation phenology on the Tibetan plateau and its implications for carbon dynamics     

Zhenong Jin  Qianlai Zhuang  Jeffrey S. Dukes  Jin-Sheng He  Andrei P. Sokolov  Min Chen  Tonglin Zhang  Tianxiang Luo 《Climatic change》2016,138(3-4):617-632

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A novel methodology for identifying environmental exposures using GPS data     

Andreea Cetateanu  Bogdan-Alexandru Luca  Andrei Alin Popescu  Angie Page  Ashley Cooper  Andy Jones 《International journal of geographical information science》2016,30(10):1944-1960

Aim: While studies using global positioning systems (GPS) have the potential to refine measures of exposure to the neighbourhood environment in health research, one limitation is that they do not typically identify time spent undertaking journeys in motorised vehicles when contact with the environment is reduced. This paper presents and tests a novel methodology to explore the impact of this concern.

Methods: Using a case study of exposure assessment to food environments, an unsupervised computational algorithm is employed in order to infer two travel modes: motorised and non-motorised, on the basis of which trips were extracted. Additional criteria are imposed in order to improve robustness of the algorithm.

Results: After removing noise in the GPS data and motorised vehicle journeys, 82.43% of the initial GPS points remained. In addition, after comparing a sub-sample of trips classified visually of motorised, non-motorised and mixed mode trips with the algorithm classifications, it was found that there was an agreement of 88%. The measures of exposure to the food environment calculated before and after algorithm classification were strongly correlated.

Conclusion: Identifying non-motorised exposures to the food environment makes little difference to exposure estimates in urban children but might be important for adults or rural populations who spend more time in motorised vehicles.  相似文献   

A framework for modeling uncertainty in regional climate change     

Erwan Monier  Xiang Gao  Jeffery R. Scott  Andrei P. Sokolov  C. Adam Schlosser 《Climatic change》2015,131(1):51-66

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Vegetation and climate history in the Laptev Sea region (Arctic Siberia) during Late Quaternary inferred from pollen records     

Andrei A. Andreev  Lutz Schirrmeister  Pavel E. Tarasov  Andrey Ganopolski  Viktor Brovkin  Christine Siegert  Sebastian Wetterich  Hans-Wolfgang Hubberten 《Quaternary Science Reviews》2011,30(17-18):2182-2199

Paleoenvironmental records from a number of permafrost sections and lacustrine cores from the Laptev Sea region dated by several methods (¹⁴C-AMS, TL, IRSL, OSL and ²³⁰Th/U) were analyzed for pollen and palynomorphs. The records reveal the environmental history for the last ca 200 kyr. For interglacial pollen spectra, quantitative temperature values were estimated using the best modern analogue method. Sparse grass-sedge vegetation indicating arctic desert environmental conditions existed prior to 200 kyr ago. Dense, wet grass-sedge tundra habitats dominated during an interstadial ca 200–190 kyr ago, reflecting warmer and wetter summers than before. Sparser vegetation communities point to much more severe stadial conditions ca 190–130 kyr ago. Open grass and Artemisia communities with shrub stands (Alnus fruticosa, Salix, Betula nana) in more protected and moister places characterized the beginning of the Last Interglacial indicate climate conditions similar to present. Shrub tundra (Alnus fruticosa and Betula nana) dominated during the middle Eemian climatic optimum, when summer temperatures were 4–5 °C higher than today. Early-Weichselian sparse grass-sedge dominated vegetation indicates climate conditions colder and dryer than in the previous interval. Middle Weichselian Interstadial records indicate moister and warmer climate conditions, for example, in the interval 40–32 kyr BP Salix was present within dense, grass-sedge dominated vegetation. Sedge-grass-Artemisia-communities indicate that climate became cooler and drier after 30 kyr BP, and cold, dry conditions characterized the Late Weichselian, ca 26–16 kyr BP, when grass-dominated communities with Caryophyllaceae, Asteraceae, Cichoriaceae, Selaginella rupestris were present. From 16 to 12 kyr BP, grass-sedge communities with Caryophyllaceae, Asteraceae, and Cichoriaceae indicate climate was significantly warmer and moister than during the previous interval. The presence of Salix and Betula reflect temperatures about 4 °C higher than present at about 12–11 kyr BP, during the Allerød interval, but shrubs were absent in the Younger Dryas interval, pointing to a deterioration of climate conditions. Alnus fruticosa, Betula nana, Poaceae, and Cyperaceae dominate early Holocene spectra. Reconstructed absolute temperature values were substantially warmer than present (up to 12 °C). Shrubs gradually disappeared from coastal areas after 7.6 kyr BP when vegetation cover became similar to modern. A comparison of proxy-based paleoenvironmental reconstructions with the simulations performed by an Earth system model of intermediate complexity (CLIMBER-2) show good accordance between the regional paleodata and model simulations, especially for the warmer intervals.  相似文献