The occurrence, spatial and temporal distribution, and environmental routes of tetracycline resistance and integrase genes in Crassostrea virginica beds     

Andrei L. Barkovskii  Christen Green  Dorset Hurley 《Marine pollution bulletin》2010,60(12):2215-2224

Rapid spread of antibiotic resistance genes has placed them under consideration as emerging environmental contaminants. The occurrence and distribution of tetracycline resistance genes (TRG) and integrons (INT) have been monitored for 2 years in seven oyster beds located in the Altamaha River (Georgia, USA) estuary. TRG/INT profiles varied both temporally (p < 0.025) and spatially between oysters and their environment (p < 0.005) suggesting shifts in sources of contamination and selection of TRG/INT carriers by oysters. The latter was confirmed via analysis of tet(D) and tet(G) distribution between oysters and their environment. Uncommon class 3 integrons dominated the integrons’ profile in oysters. The frequency of TRG/INT incidents correlated (R² ? 0.9) to (i) dissolved solids, (ii) potential water density, and (iii) turbidity but not to the amount of local precipitation suggesting the watershed as the dominant source of TRG/INT contamination and other than directly rainfall-caused run-offs as its environmental route.  相似文献   

Geoarchaeology of the Kostenki–Borshchevo sites,Don River Valley,Russia     

Vance T. Holliday  John F. Hoffecker  Paul Goldberg  Richard I. Macphail  Steven L. Forman  Mikhail Anikovich  Andrei Sinitsyn 《Geoarchaeology》2007,22(2):181-228

The Kostenki–Borshchevo localities include 26 Upper Paleolithic sites on the first and second terraces along the west bank of the Don River, near Voronezh on the central East European Plain. Geoarchaeological research from 2001 through 2004 focused on sites Kostenki 1, 12, and 14, with additional work at Kostenki 11 and 16, and Borshchevo 5. The strata are grouped into three units (bottom up): Unit 1, > 50 ka, consists of coarse alluvium (representing upper terrace 2 deposits) and colluvium, overlain by fine‐grained sediments. Unit 2 includes archaeological horizons sealed within two sets of thin lenses of silt, carbonate, chalk fragments, and organic‐rich soils (termed the Lower Humic Bed and Upper Humic Bed) dating 50–30 ka. Separating the humic beds is a volcanic ash lens identified as the Campanian Ignimbrite Y5 tephra, dated elsewhere by Ar/Ar to ca. 40 ka. The humic beds appear to result from the complex interplay of soil formation, spring deposition, slope action, and other processes. Several horizons buried in the lower part of Unit 2 contain Upper Paleolithic assemblages. The springs and seeps, which are still present in the area today, emanated from the bedrock valley wall. Their presence may account for the unusually high concentration of Upper Paleolithic sites in this part of the central East European Plain. Unit 3, < 30 ka, contains redeposited loess with a buried soil (Gmelin Soil) overlain by a primary full‐glacial loess with an associated Chernozem (Mollisol), forming the surface of the second terrace. © 2007 Wiley Periodicals, Inc.  相似文献   

A Russian record of a Middle Ordovician meteorite shower: Extraterrestrial chromite at Lynna River,St. Petersburg region     

Anders LINDSKOG  Birger SCHMITZ  Anders CRONHOLM  Andrei DRONOV 《Meteoritics & planetary science》2012,47(8):1274-1290

Abstract– Numerous fossil meteorites and high concentrations of sediment‐dispersed extraterrestrial chromite (EC) grains with ordinary chondritic composition have previously been documented from 467 ± 1.6 Ma Middle Ordovician (Darriwilian) strata. These finds probably reflect a temporarily enhanced influx of L‐chondritic matter, following the disruption of the L‐chondrite parent body in the asteroid belt 470 ± 6 Ma. In this study, a Volkhovian‐Kundan limestone/marl succession at Lynna River, northwestern Russia, has been searched for EC grains (>63 μm). Eight samples, forming two separate sample sets, were collected. Five samples from strata around the Asaphus expansus–A. raniceps trilobite Zone boundary, in the lower‐middle Kundan, yielded a total of 496 EC grains in 65.5 kg of rock (average 7.6 EC grains kg^?1, but up to 10.2 grains kg^?1). These are extremely high concentrations, three orders of magnitude higher than “background” levels in similar condensed sediment from other periods. EC grains are typically about 50 times more abundant than terrestrial chrome spinel in the samples and about as common as terrestrial ilmenite. Three stratigraphically lower lying samples, close to the A. lepidurus–A. expansus trilobite Zone boundary, at the Volkhov‐Kunda boundary, yielded only two EC grains in 38.2 kg of rock (0.05 grains kg^?1). The lack of commonly occurring EC grains in the lower interval probably reflects that these strata formed before the disruption of the L‐chondrite parent body. The great similarity in EC chemical composition between this and other comparable studies indicates that all or most EC grains in these Russian mid‐Ordovician strata share a common source––the L‐chondrite parent body.  相似文献   

Hysteretic models for sliding bearings with varying frictional force   总被引：2，自引：1，他引：1  

Tathagata Ray  Apostolos A. Sarlis  Andrei M. Reinhorn  Michael C. Constantinou 《地震工程与结构动力学》2013,42(15):2341-2360

The friction pendulum system is a sliding seismic isolator with self‐centering capabilities. Under severe earthquakes, the movement may be excessive enough to cause the pendulum to hit the side rim of the isolator, which is provided to restrain the sliding. The biaxial behavior of a single friction pendulum, in which the slider contacts the restrainer, is developed using a smooth hysteretic model with nonlinear kinematic hardening. This model is extended to simulate the biaxial response of double and triple friction pendulums with multiple sliding surfaces. The model of a triple friction pendulum is based on the interaction between four sliding interfaces, which in turn is dependent upon the force and displacement conditions prevailing at these interfaces. Each of these surfaces are modeled as nonlinear biaxial springs suitable for a single friction pendulum, using the yield surface, based on the principles of the classical theory of plasticity, and amended for varying frictional yield force, due to variation in vertical load and/or velocity‐dependent friction coefficient. The participation of the nonlinear springs is governed by stick‐slip conditions, dictated by equilibrium and kinematics. The model can simulate the overall force‐deformation behavior, track the displacements in individual sliding surfaces, and account for the ultimate condition when the sliders are in contact with their restrainers. The results of this model are verified by comparison to theoretical calculations and to experiments. The model has been implemented in programs IDARC2D and 3D‐BASIS, and the analytical results are compared with shake table experimental results. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Nonlinear elastic and inelastic spectra with inherent and supplemental damping     

Tathagata Ray  Andrei M. Reinhorn  Satish Nagarajaiah 《地震工程与结构动力学》2013,42(14):2151-2165

During severe seismic events, structures designed according to current standards yield and develop inelastic deformations. While the acceleration responses are limited by the yielding strength, these structures develop permanent deformations (and possible damage) due to such yielding. Spectra developed for inelastic structures can help in determining the desired yield levels and the associated inelastic deformations. Some structures made of special materials or equipped with innovative structural systems may yield, but can recover the deformation upon unloading and, thus, may avoid permanent deformations. These structures are known as nonlinear elastic. Often the post yielding excursions are very large and may exceed their toughness (or deformability). By introducing damping in form of supplemental devices, it is possible to control such deformations and keep them within acceptable limits. Spectra for such nonlinear elastic structures and inelastic structures are developed herein, by considering both inherent and supplemental damping. The difference between the two types of damping is addressed both theoretically and numerically. Design examples of several simple structures using the newly developed spectra are presented, which illustrate the importance of lower strength and damping in these nonlinear elastic or inelastic systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Quantitative modelling of seismic site amplification in an earthquake-endangered capital city: Bucharest,Romania     

Andrei Bala 《Natural Hazards》2014,72(3):1429-1445

Bucharest, the capital city of Romania, with more than 2 million inhabitants, is considered as a natural disaster hotspot by a recent global study of the World Bank and the Columbia University (Dilley M et al. Natural disaster hotspots: a global risk analysis. International Bank for Reconstruction and Development/The World Bank and Columbia University, Washington, DC in 2005). Therefore, it is classified as the second metropolis in Europe, after Istanbul, subjected to important losses in the case of a destructive Vrancea earthquake with moment magnitude greater than seven. Four major earthquakes with moment magnitudes between 6.9 and 7.7 hit Bucharest in the last 68 years. The most recent destructive earthquake on March 4, 1977, with a moment magnitude of 7.4, caused about 1,500 casualties in the capital alone. All disastrous intermediate-depth earthquakes are generated within a small epicentral area—the Vrancea seismogenic region—about 150 km northeast of Bucharest. Thick unconsolidated sedimentary layers below Bucharest amplify the arriving seismic waves causing severe destruction. Ten 50-m-deep boreholes are drilled in the metropolitan area of Bucharest in order to obtain a unique, homogeneous dataset of seismic, soil-mechanic and elasto-dynamic parameters. Cores for dynamic tests were extracted, and vertical seismic profiles were performed to obtain an updated site amplification model related to earthquakes waves. The boreholes are placed near former or existing seismic station sites to allow a direct comparison and calibration of the borehole data with previous seismological measurements. A database containing geological characteristics for each sedimentary layer, geotechnical parameters measured on rock samples, P- and S wave velocity and density for each sedimentary layer is set up, as a result of previous papers with this subject. Direct data obtained by the geophysical methods in the new boreholes drilled in Bucharest City, as well as from laboratory measurements, are used as input data in the program SHAKE2000. Results are obtained in the form of spectral acceleration response, and peak acceleration in depth is computed for every site in which in situ measurements were performed. The acceleration response spectra correspond to the shear-wave amplifications due to the models of sedimentary layers down to (a) 50 m depth; (b) 70 m depth; and (c) 100 m depth. A comparison of the acceleration response spectra obtained by modelling at surface with a real signal recorded at surface is obtained in three sites, as test sites for the three depths considered, in order to calibrate the results obtained by equivalent linear method of the seismic site response.  相似文献   

Small-scale inviscid accretion discs around black holes     

Andrei M. Beloborodov  Andrei F. Illarionov 《Monthly notices of the Royal Astronomical Society》2001,323(1):167-176

Gas falling quasi-spherically on to a black hole forms an inner accretion disc if its specific angular momentum l exceeds l ∗∼ r _g c , where r _g is the Schwarzschild radius. The standard disc model assumes l ≫ l ∗. We argue that, in many black hole sources, accretion flows have angular momenta just above the threshold for disc formation, l ≳ l ∗, and assess the accretion mechanism in this regime. In a range l ∗< l < l _cr, a small-scale disc forms in which gas spirals fast into the black hole without any help from horizontal viscous stresses. Such an 'inviscid' disc, however, interacts inelastically with the feeding infall. The disc–infall interaction determines the dynamics and luminosity of the accretion flow. The inviscid disc radius can be as large as 14 r _g, and the energy release peaks at 2 r _g. The disc emits a Comptonized X-ray spectrum with a break at ∼100 keV. This accretion regime is likely to take place in wind-fed X-ray binaries and is also possible in active galactic nuclei.  相似文献   

The Late Pleistocene megafauna of the Chulym River basin,southeastern West Siberian Plain: chronology and stable isotope composition     

Yaroslav V. Kuzmin  Andrei V. Shpansky 《第四纪科学杂志》2023,38(1):2-7

New data were obtained for the Chulym River basin in the southeastern part of the West Siberian Plain, one of the understudied parts of Siberia in terms of age and composition of carbon and nitrogen stable isotopes for Late Pleistocene megafauna. The ¹⁴C dates from the Sergeevo outcrop, the most complete section of Late Quaternary deposits in the region, are mostly greater than ~30 550 bp. Other localities yielded ¹⁴C values in the range from >44 500 to ~19 300 bp. The finite date of ~42 270 bp for the Khozarian steppe elephant (Mammuthus trogontherii chosaricus) from Asino is intriguing because previously it was not detected in the Late Pleistocene of Siberia after the last interglacial (Marine Isotope Stage 5e), ~115 000–130 000 years ago. Stable isotope data show both similarities and differences compared to the pre-Last Glacial Maximum megafaunal species in other parts of Siberia.  相似文献