On the present habitats and ecology of Vertigo pseudosubstriata Ložek, 1954 (Mollusca,Gastropoda, Vertiginidea) in Central Asia and its distribution history in Central and Eastern Europe     

Stefan Meng  Pavlo Vasyliev  Ivan Khoptynets  Vitalii Tkach  Andreas Maier 《第四纪科学杂志》2021,36(6):1090-1100

The small terrestrial gastropod Vertigo pseudosubstriata Ložek, 1954 is one of the rarest glacial indicator species in the Pleistocene of Central and Eastern Europe. In all, this species has been found at only about 15 sites in Europe. V. pseudosubstriata was initially described as a fossil in Central Europe and was discovered only later alive in Central Asia. With regard to its modern distribution, 25 habitats with V. pseudosubstriata have been examined in Tien Shan and in the central and southern Altai. These findings seem to capture the contemporary distribution of the species and provide information on the boundaries of its ecological requirements. These data are of great significance for the interpretation of the fossil assemblages. Since the few fossil specimens in Europe date from very different glacial periods in the Elsterian, Saalian Complex and Weichselian, it can be concluded that V. pseudosubstriata apparently immigrated in at least three distinct waves. Most of the Pleistocene specimens in eastern Central Europe and Eastern Europe are reported from archaeological sites of the Upper Middle Weichselian (Gravettian), roughly between 33 and 29 ka cal bp. In this paper, we review all reported modern and fossil occurrences and discuss the species' ecological range.  相似文献   

Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid?          下载免费PDF全文

Pavel P. Povinec  Matthias Laubenstein  A. J. Timothy Jull  Ludovic Ferrière  Franz Brandstätter  Ivan Sýkora  Jozef Masarik  Juraj Beňo  Andrej Kováčik  Dan Topa  Christian Koeberl 《Meteoritics & planetary science》2015,50(2):273-286

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long‐lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of ¹⁴C, ²²Na, ²⁶Al, ⁵⁴Mn, ⁵⁷Co, ⁵⁸Co, and ⁶⁰Co, which indicate that the pre‐atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed ²⁶Al activities of the investigated samples, Monte Carlo simulations, and taking into account the ²⁶Al half‐life (0.717 Myr), the cosmic‐ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, ¹⁴C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of ¹⁴C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic ¹³⁷Cs and primordial ⁴⁰K in some of the Chelyabinsk fragments.  相似文献   

New faint optical spectrophotometric standards: hot white dwarfs from the Sloan Digital Sky Survey     

Carlos Allende Prieto  Ivan Hubeny  J. Allyn Smith 《Monthly notices of the Royal Astronomical Society》2009,396(2):759-771

The spectral energy distributions for pure-hydrogen (DA) hot white dwarfs can be accurately predicted by model atmospheres. This makes it possible to define spectrophotometric calibrators by scaling the theoretical spectral shapes with broad-band photometric observations – a strategy successfully exploited for the spectrographs onboard the Hubble Space Telescope ( HST ) using three primary DA standards. Absolute fluxes for non-DA secondary standards, introduced to increase the density of calibrators in the sky, need to be referred to the primary standards, but a far better solution would be to employ a network of DA stars scattered throughout the sky. We search for blue objects in the sixth data release of the Sloan Digital Sky Survey (SDSS) and fit DA model fluxes to identify suitable candidates. Reddening needs to be considered in the analysis of many of these stars. We propose a list of nine pure-hydrogen white dwarfs with absolute fluxes with estimated uncertainties below 3 per cent, including four objects with estimated errors <2 per cent, as candidates for spectrophotometric standards in the range  14 < g < 18  , and provide model-based fluxes scaled to match the SDSS broad-band fluxes for each. We apply the same method to the three HST DA standards, linking the zero point of their absolute fluxes to ugr magnitudes transformed from photometry obtained with the US Naval Observatory 1-m telescope. For these stars, we estimate uncertainties of <1 per cent in the optical, finding good consistency with the fluxes adopted for HST calibration.  相似文献   

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass <Emphasis Type="Italic">Thalassia testudinum</Emphasis> in Jobos Bay,Puerto Rico     

Ylva S. Olsen  Ivan Valiela 《Estuaries and Coasts》2010,33(3):769-783

We examined the effect of nutrients and grazers on Thalassia testudinum in Jobos Bay, Puerto Rico by fertilizing sediment and manipulating grazer abundances. Bottom-up effects were variable: Added nutrients did not increase seagrass aboveground biomass, but decreased belowground biomass—perhaps as a result of less biomass being allocated to belowground structures in response to greater nutrient supply in porewater. Experimental fencing of 1.5 × 1.5 m plots provided shelter that attracted large aggregations of fish, including seagrass herbivores. Seagrass biomass and shoot density decreased with increasing abundance of herbivorous fish, indicating a significant top-down effect. There were interactions between nutrient supply, provision of shelter, and grazing pressure. Fertilization enhanced seagrass %N; however, %N also increased in unfertilized plots that were fenced, most likely due to uptake of N excreted from the large numbers of fish associated with the fences. Only plots where shelter was provided and fertilizer was applied to sediments exhibited evidence of heavy grazing, reducing both seagrass cover and aboveground biomass. In the unfertilized fenced plots, signs of grazing were fewer despite large abundances of fish and enhanced nutritional quality of seagrass leaves. This suggests the possibility that high nutrient availability in sediments lowered concentrations of chemical defense compounds in the seagrass and that cues other than %N may have been involved in stimulating grazing. This study highlights the complexity of bottom-up and top-down interactions in seagrass systems and the important role of refuge availability in shaping the relative strengths of these controls.  相似文献   

Attenuation of Peak Horizontal and Vertical Acceleration in the Dinarides Area     

Herak  Marijan  Markušić  Snježana  Ivančić  Ines 《Studia Geophysica et Geodaetica》2001,45(4):383-394

Peak acceleration attenuation relations for horizontal and vertical components are presented for the Dinarides region, based on 145 3-component accelerograms related to 46 earthquakes with local magnitudes of 4.5 or greater and with epicentral distances of less than 200 km as recorded on 39 recording sites in the greater Dinarides region. The attenuation functions were obtained by two-stage stratified regression on the local magnitude and epicentral distance as independent variables. The predicted peak acceleration values within the distance range covered by the data are comparable to the ones obtained for stiff-soil or rock sites when selected reference relations are used. The rather large average residuals are caused mostly by the lack of information on local site conditions and by the use of epicentral distance instead of fault distance.  相似文献   

Bestimmung der durchgangszeiten von sternen durch die methode der unterbrechung der gesichtsfeldbelichtung     

Josef Kabeláč  Ivan Synek 《Studia Geophysica et Geodaetica》1964,8(2):120-126

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Quasitrapped protons (E p =1–11 MeV) nearL=4 registered by intercosmos-13 satellite     

Ivan Kimák  Karel Kudela  P. V. Vakulov  Reviewer S. Fischer 《Studia Geophysica et Geodaetica》1982,26(2):207-211

Summary Data obtained from apparatus detecting energetic particles on low altitude polar orbiting satellite Intercosmos-13 show enhancement of quiasitrapped proton flux (E_p=1–11 MeV) near L=4 in comparison with both and lower L. This phenomenon persists during intervals with low level of geomagnetic activity. Possibility of influence of false pulses on the result is discussed.  相似文献   

Concepts for reference frames in geodesy and geodynamics: The reference directions     

Erik W. Grafarend  Ivan I. Mueller  Haim B. Papo  Burghard Richter 《Journal of Geodesy》1979,53(3):195-213

Modern high accuracy measurements of the non-rigid earth are to be referred to four-dimensional, i.e., time- and space-dependent reference frames. Geodynamic phenomena derived from these measurements are to be described in a terrestrial reference frame in which both space- and time-like variations can be monitored. Existing conventional terrestrial reference frames (e.g. CIO, BIH) are no longer suitable for such purposes. The ultimate goal of this study is the establishment of a reference frame, moving with the earth in some average sense, in which the geometric and dynamic behavior of the earth can be monitored, and whose motion with respect to inertial space can also be determined. The study is conducted in several parts. In the first part problems related to reference directions are investigated, while subsequent parts deal with positions, i.e., with reference origins and scale. Only the first part is treated in this paper. The approach is based on the fact that reference directions at an observation point on the earth surface are defined by fundamental vectors (gravity, earth rotation, etc.), both space and time variant. These reference directions are interrelated by angular parameters, also derived from the fundamental vectors. The interrelationships between these space- and time-variant angular parameters are illustrated in a commutative diagram, tower of triads, which makes the derivation of the various relationships convenient. In order to determine the above parameters from observations using least squares techniques, a model tower of triads is also presented to allow the formation of linear observation equations. Although the model tower is also space and time variant, its variations are described by adopted parameters representing our current knowledge of the earth.  相似文献   

Computation of diffracted rays in inhomogeneous media with curved interfaces     

Vlastislav Červený  Ivan Pšenčík  Reviewer J. Vaněk 《Studia Geophysica et Geodaetica》1972,16(4):356-366

Summary A method for computing certain types of diffracted rays and corresponding travel-time curves in laterally inhomogeneous media with slightly curved interfaces is suggested. Numerical examples are presented.Dedicated to Academician Alois Zátopek on His 65th Birthday  相似文献   

The effect of earth orientation errors in baseline determination     

Erricos C. Pavlis  Ivan I. Mueller 《Journal of Geodesy》1983,57(1-4):273-282

The determination of baseline lengths from certain space techniques is based on the derived coordinates of the terminal stations. As such, the estimated baselines are susceptible to systematic errors that affect the relative coordinates. One source of error is in the set of parameters which describes the continuously changing relative orientation of the Conventional Terrestrial (CTS) and Inertial (CIS) Reference frames. Due to these errors, the coordinates of each terminal station may in fact refer to a slightly different coordinate svstem, and, therefore, when used for computing the length between the stations, errors will result. The expected magnitudes of such errors and their possible presence in current solutions are investigated. In conclusion, we find that the present level of accuracy and stability of the available parameters connecting the CTS and CIS (e.g., the ERP series) is unsatisfactory for centimeter level baseline length determinations. The available options are either the use of strictly simultaneous SLR data sets (similar to the VLBI data sets) or the improvement of the parameters connecting the CTS and the CIS. The first long-range step in the latter direction is the support of the IAG/IAU Joint Working Group COTES proposal [CSTG Bulletin, 1982], endorsed by both the IAG and IAU in various resolutions [IAU, 1983; IAG, 1982]. Presented at the Annual Fall Meeting of the American Geophysical Union, San Francisco, December 7–15, 1982, and at the Fifth Annual NASA Geodynamics Program Conference and Crustal Dynamics Project Review, Washington, D.C., January 24–28, 1983.  相似文献