Taxonomy,location of origin and health status of proboscideans from Western Canada investigated using stable isotope analysis          下载免费PDF全文

Jessica Z. Metcalfe  Fred J. Longstaffe  Christopher N. Jass  Grant D. Zazula  Grant Keddie 《第四纪科学杂志》2016,31(2):126-142

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Correlations between re and PGE concentrations in rocks,ores, and minerals of mafic-ultramafic associations     

F. P. Lesnov  G. N. Anoshin 《Doklady Earth Sciences》2011,437(1):387-392

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Comparison of Joint Shearing Resistance Obtained with the Barton and Choubey Criterion and with Direct Shear Tests     

D. Sow  P. Rivard  L. Peyras  P. Breul  Z. A. Moradian  C. Bacconnet  G. Ballivy 《Rock Mechanics and Rock Engineering》2016,49(8):3357-3361

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Oxygen and Sulfides in Bottom Sediments of the Coastal Sevastopol Region of Crimea     

N. A. Orekhova  S. K. Konovalov 《Oceanology》2018,58(5):679-688

Spatial variations in the distribution and fluxes of dissolved oxygen and sulfide in bottom sediments of Omega and Sevastopol bays have been studied. The results of analysis reveal that the distribution of dissolved oxygen and sulfide in pore water depends mostly on seasonal variations in the oxygen concentration in bottom water, grain size, the organic carbon content in bottom sediments, and, additionally for Sevastopol Bay, the iron content. The oxygen flux at the bottom of Sevastopol Bay is 20 times larger in winter–spring compared to that of Omega Bay. Anaerobic conditions in Sevastopol Bay sediments are observed much closer to the surface, with their subsequent development in bottom water.  相似文献   

Statistical Properties of Ribbon Evolution and Reconnection Electric Fields in Eruptive and Confined Flares     

J. Hinterreiter  A. M. Veronig  J. K. Thalmann  J. Tschernitz  W. Pötzi 《Solar physics》2018,293(3):38

A statistical study of the chromospheric ribbon evolution in H\(\alpha\) two-ribbon flares was performed. The data set consists of 50 confined (62%) and eruptive (38%) flares that occurred from June 2000 to June 2015. The flares were selected homogeneously over the H\(\alpha\) and Geostationary Operational Environmental Satellite (GOES) classes, with an emphasis on including powerful confined flares and weak eruptive flares. H\(\alpha\) filtergrams from the Kanzelhöhe Observatory in combination with Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) magnetograms were used to derive the ribbon separation, the ribbon-separation velocity, the magnetic-field strength, and the reconnection electric field. We find that eruptive flares reveal statistically larger ribbon separation and higher ribbon-separation velocities than confined flares. In addition, the ribbon separation of eruptive flares correlates with the GOES SXR flux, whereas no clear dependence was found for confined flares. The maximum ribbon-separation velocity is not correlated with the GOES flux, but eruptive flares reveal on average a higher ribbon-separation velocity (by ≈?10 km?s^?1). The local reconnection electric field of confined (\(cc=0.50 \pm0.02\)) and eruptive (\(cc=0.77 \pm0.03\)) flares correlates with the GOES flux, indicating that more powerful flares involve stronger reconnection electric fields. In addition, eruptive flares with higher electric-field strengths tend to be accompanied by faster coronal mass ejections.  相似文献   

Fuel optimization for low-thrust Earth–Moon transfer via indirect optimal control     

Daniel Pérez-Palau  Richard Epenoy 《Celestial Mechanics and Dynamical Astronomy》2018,130(2):21

The problem of designing low-energy transfers between the Earth and the Moon has attracted recently a major interest from the scientific community. In this paper, an indirect optimal control approach is used to determine minimum-fuel low-thrust transfers between a low Earth orbit and a Lunar orbit in the Sun–Earth–Moon Bicircular Restricted Four-Body Problem. First, the optimal control problem is formulated and its necessary optimality conditions are derived from Pontryagin’s Maximum Principle. Then, two different solution methods are proposed to overcome the numerical difficulties arising from the huge sensitivity of the problem’s state and costate equations. The first one consists in the use of continuation techniques. The second one is based on a massive exploration of the set of unknown variables appearing in the optimality conditions. The dimension of the search space is reduced by considering adapted variables leading to a reduction of the computational time. The trajectories found are classified in several families according to their shape, transfer duration and fuel expenditure. Finally, an analysis based on the dynamical structure provided by the invariant manifolds of the two underlying Circular Restricted Three-Body Problems, Earth–Moon and Sun–Earth is presented leading to a physical interpretation of the different families of trajectories.  相似文献   

Porosity Distribution Characteristics and Geological Analysis of Brine Storage Medium in the Qaidam Basin,Western China     

Shuya Hu  Changlai Xiao  Xiujuan Liang  Quansheng Zhao  Guangcai Wang  Jianwei Zhang  Juan Feng 《中国地理科学(英文版)》2018,28(4):707-716

Underground brine is an unusual water resource that contains abundant mineral resources. It is distributed widely in the Qaidam Basin, western China, a hyperarid inland basin located in the northern Tibetan Plateau. Pores in the brine storage medium act as storage space and transmission channels of underground brine. Therefore, the porosity of brine storage medium determines its ability to store brine. In this study, Mahai Salt Lake was used as the research area as a modern saline lake located in the north area of the Qaidam Basin. A total of 100 porosity samples were collected from eight sampling points in two profiles of the research area at sampling depths of 1.30–314.78 m. The porosity distribution characteristics and influencing factors in brine storage medium were analysed according to the measured porosity data. Based on analysis of the pore structure characteristics, the brine storage medium contains intercrystalline pores, unlike conventional freshwater storage mediums. Moreover, the primary salt rock is susceptible to dissolution by lighter brine, facilitating the formation of secondary porosity. Due to the formation of secondary pores, a porosity greater than 20% remains even at buried depths greater than 100 m. Based on the geological statistical analysis, due to the geographic location, salt formation time, and depositional environment, the porosity values of Mahai Salt Lake do not exhibit a wider distribution, but also show more extreme values than a nearby salt lake. Based on the porosity characteristics by depth, due to the presence of secondary pores, flooding, stratigraphic static pressure, and other factors, porosity shows fluctuations with increasing depth.  相似文献   

Age,Helium Content and Chemical Composition of Globular Clusters in the M31 Neighborhood and in our Galaxy     

M. E. Sharina  V. V. Shimansky  D. A. Khamidullina 《Astrophysical Bulletin》2018,73(3):318-334

We present the results of determinations of age, helium abundance (Y), metallicity ([Fe/H]), and estimations of abundances of the elements: C, N, O, Mg, Ca, Ti, Cr, Ni, Sr, and Ba of four globular clusters in the neighborhood of the Andromeda galaxy ([SD2009]GC7,Mayall II, Mackey-GC1 (MGC1), and Bol 298 (MGC6)) and of six Galactic clusters. Medium-resolution long-slit integrated-light spectra from the clusters under study were used to determine the parameters.Observations of extra-galactic objects were carried out with the 6-m SAO RAS telescope using the SCORPIO-1 multimode focal reducer. Galactic globular clusters NGC6341 (M92), NGC6838 (M71), and NGC7078 were observed with the CARELEC spectrograph at the 1.93-m telescope of the Haute-Provence Observatory. The integratedlight spectra of Galactic globular clusters NGC104, NGC6121 (M4), and NGC7078 (M15) were taken from the spectral library by Schiavon.We selected the best isochrone for each cluster by comparison of the shapes and intensities of the observed and theoretical Balmer line profiles.  相似文献   

Statistical landslide susceptibility assessment in a dynamic environment: A case study for Lanzhou City,Gansu Province,NW China     

Jewgenij Torizin  Li-chao Wang  Michael Fuchs  Bin Tong  Dirk Balzer  Li-qin Wan  Dirk Kuhn  Ang Li  Liang Chen 《山地科学学报》2018,15(6):1299-1318

This study presents a statistical landslide susceptibility assessment (LSA) in a dynamic environment. The study area is located in the eastern part of Lanzhou, NW China. The Lanzhou area has exhibited rapid urbanization rates over the past decade associated with greening, continuous land use change, and geomorphic reshaping activities. To consider the dynamics of the environment in the LSA, multitemporal data for landslide inventories and the corresponding causal factors were collected. The weights of evidence (WofE) method was used to perform the LSA. Three time stamps, i.e., 2000, 2012, and 2016, were selected to assess the state of landslide susceptibility over time. The results show a clear evolution of the landslide susceptibility patterns that was mainly governed by anthropogenic activities directed toward generating safer building grounds for civil infrastructure. The low and very low susceptibility areas increased by approximately 10% between 2000 and 2016. At the same time, areas of medium, high and very high susceptibility zones decreased proportionally. Based on the results, an approach to design the statistical LSA under dynamic conditions is proposed, the issues and limitations of this approach are also discussed. The study shows that under dynamic conditions, the requirements for data quantity and quality increase significantly. A dynamic environment requires greater effort to estimate the causal relations between the landslides and controlling factors as well as for model validation.  相似文献   

Super-Fast Line-Profile Variability in the Spectra of OBA-Stars: B1-Star <Emphasis Type="Italic">ρ</Emphasis> Leo     

A. F. Kholtygin  A. A. Batrakov  S. N. Fabrika  A. F. Valeev  I. M. Tumanova  O. A. Tsiopa 《Astrophysical Bulletin》2018,73(4):471-477

This study continues our investigation of the super-fast variability of line profiles in the spectra of early-type stars. We have investigated the line-profile variability in spectra of OBA-stars with the SCORPIO multi-mode focal reducer mounted at the 6-m SAO RAS telescope. Regular short-period variations of the H and He lines in the spectra of the B1I star ρ Leo were detected with periods ranging from 2 to 90 minutes, as well as irregular line-profile variations on time intervals less than 1 minute. A possible origin of rapid spectral variations is discussed.  相似文献