Monitoring of polycyclic aromatic hydrocarbons in the Lake Baikal basin in the areas of intensive anthropogenic impact     

A. M. Nikanorov  S. A. Reznikov  A. A. Matveev  V. S. Arakelyan 《Russian Meteorology and Hydrology》2012,37(7):477-484

Presented are the results of studying the content of polycyclic aromatic hydrocarbons and benz(a)pyrene in the lake water, in sewage waters of the enterprise, and in the upper 2-cm layer of bottom sediments in the area of the sewage discharge of Baikal Pulp and Paper Mill (BPPM), in bottom sediments in the north of Lake Baikal in the area of the Baikal-Amur Railroad, and in the channel and delta front of the Selenga River. The results were obtained at Hydrochemical Institute in 1981?C1989. The different content of benz[a]pyrene was determined for the first time in bottom sediments (sands and silts) for the bottom area of polygons in the mentioned regions. An intensive pollution exceeding significantly the normalized parameters for the benz[a]pyrene in bottom sediments is registered in the BPPM area only and its content in other areas does not exceed the background values on the whole.  相似文献   

Simulations of the formation of stellar discs in the Galactic Centre via cloud–cloud collisions     

Alexander Hobbs  Sergei Nayakshin 《Monthly notices of the Royal Astronomical Society》2009,394(1):191-206

Young massive stars in the central parsec of our Galaxy are best explained by star formation within at least one, and possibly two, massive self-gravitating gaseous discs. With help of numerical simulations, we here consider whether the observed population of young stars could have originated from a large angle collision of two massive gaseous clouds at   R ≃ 1 pc  from Sgr A*. In all the simulations performed, the post-collision gas flow forms an inner, nearly circular gaseous disc and one or two eccentric outer filaments, consistent with the observations. Furthermore, the radial stellar mass distribution is always very steep,  Σ_*∝ R ⁻²  , again consistent with the observations. All of our simulations produce discs that are warped by between 30° and 60°, in accordance with the most recent observations. The three-dimensional velocity structure of the stellar distribution is sensitive to initial conditions (e.g. the impact parameter of the clouds) and gas cooling details. For example, the runs in which the inner disc is fed intermittently with material possessing fluctuating angular momentum result in multiple stellar discs with different orbital orientations, contradicting the observed data. In all the cases the amount of gas accreted by our inner boundary condition is large, enough to allow Sgr A* to radiate near its Eddington limit over ∼10⁵ yr. This suggests that a refined model would have physically larger clouds (or a cloud and a disc such as the circumnuclear disc) colliding at a distance of a few parsecs rather than 1 pc as in our simulations.  相似文献   

The Fazenda Largo off-craton kimberlites of Piauí State, Brazil     

Felix V. Kaminsky  Sergei M. Sablukov  Ludmila I. Sablukova  Olga D. Zakharchenko 《Journal of South American Earth Sciences》2009,28(3):288-303

In the late 1990s, the Fazenda Largo kimberlite cluster was discovered in the Piauí State of Brazil. As with earlier known kimberlites in this area – Redondão, Santa Filomena-Bom Jesus (Gilbues) and Picos – this cluster is located within the Palaeozoic Parnaiba Sedimentary Basin that separates the São Francisco and the Amazonian Precambrian cratons. Locations of kimberlites are controlled by the ‘Transbrasiliano Lineament’. The Fazenda Largo kimberlites are intensely weathered, almost completely altered rocks with a fine-grained clastic structure, and contain variable amounts of terrigene admixture (quartz sand). These rocks represent near-surface volcano-sedimentary deposits of the crater parts of kimberlite pipes. By petrographic, mineralogical and chemical features, the Fazenda Largo kimberlites are similar to average kimberlite. The composition of the deep-seated material in the Fazenda Largo kimberlites is quite diverse: among mantle microxenoliths are amphibolitised pyrope peridotites, garnetised spinel peridotites, ilmenite peridotites, chromian spinel + chromian diopside + pyrope intergrowths, and large xenoliths of pyrope dunite. High-pressure minerals are predominantly of the ultramafic suite, Cr-association minerals (purplish-red and violet pyrope, chromian spinel, chromian diopside, Cr-pargasite and orthopyroxene). The Ti-association minerals of the ultramafic suite (picroilmenite and orange pyrope), as well as rare grains of orange pyrope-almandine of the eclogite association, are subordinate. Kimberlites from all four pipes contain rare grains of G10 pyrope of the diamond association, but chromian spinel of the diamond association was not encountered. By their tectonic position, by geochemical characteristics, and by the composition of kimberlite indicator minerals, the Fazenda Largo kimberlites, like the others of such type, are unlikely to be economic.  相似文献   

Jom-Bolok Holocene volcanic field in the East Sayan Mts., Siberia,Russia: structure,style of eruptions,magma compositions,and radiocarbon dating   总被引：1，自引：0，他引：1  

Alexei V. Ivanov  Sergei G. Arzhannikov  Elena I. Demonterova  Anastasia V. Arzhannikova  Lyubov A. Orlova 《Bulletin of Volcanology》2011,73(9):1279-1294

Jom-Bolok volcanic field is located in the East Sayan Mts. of Siberia (Russia), a portion of the Asian convergent zone. It is located at the boundary of the Riphean Tuva-Mongolia massif, which was probably reactivated because of the interplay between far-field tectonic stress derived from the India–Asia collision zone and extension in the south-western Baikal rift system. The volcanic field comprises a number of hawaiitic lava flows, of various lengths, which flowed down paleorivers. Flows were fed by fissure eruptions and the largest lava flow field was dated as 7,130?±?140 cal ¹⁴C years BP using a buried organic sample found inside the associated cinder cone. This lava flow field is about 70 km long, ～100 km² in area, and 7.9 km³ in volume. The area and volume of this flow field ranks this eruption highly in the global record of fissure-fed effusive eruptions. This lava flow field makes up 97% of the entire Jom-Bolok volcanic field, a fact which raises a puzzling question: why and/or how did a relatively small-volume volcanic field produce such a large-volume individual eruption? A working hypothesis is that a pond of sublithospheric melt accumulated over a relatively prolonged period. This was then rapidly drained in response of tectonic changes triggered by unloading of ice in the Early Holocene.  相似文献   

Paleomagnetism of Cretaceous units of the Mametchinskiy Peninsula, Kuyul Region, Northeastern Russia: implications for development and evolution of the Northwest Pacific Basin     

William Harbert  Maxim Alexutin  Sergei Sokolov  Kirill Krylov  Vladimir Grigoriev  Alexander Heiphetz  Robert Graham 《Tectonophysics》2001,340(3-4):215-231

The northernmost part of the Kamchatka Peninsula of northeastern Russia, located along the northwestern margin of the Bering Sea, consists of zones of complexly deformed accreted terranes. Progressing from the northwestern Bering Sea inland are the Olyutorskiy, Ukelayat, and Koryak superterranes, which were accreted to the Okhotsk–Chukotsk volcanic–plutonic belt (OChVB) during the Campanian–Maastrichtian (Koryak) to Middle Eocene (Olyutorskiy), respectively. To constrain the accretion paleolatitude of the Koryak superterrane, we paleomagnetically sampled a sedimentary series on the Mametchinskiy Peninsula. At the Mametchinskiy Peninsula, in the northeastern Penzhinskaya Guba (61.45° N, 163.75° E), a gently deformed, well-bedded section of fine-grained Lower to lower Upper Cretaceous turbidites, the Mametchinskaya and Tylakrylskaya Formations are exposed. These strata, which represent the lower part of the sedimentary cover of the terranes in this region and the forearc of OChVB, were sampled at 39 sites (three to seven samples per site). Within the Ainyn terrane, more than 1000 m of section of Cenomanian–Turonian age was sampled at a basal locality (sample groups I and II, sites 1–18, 19–29) and at an upper locality of Valanginian–Barremian age (sample group III, sites 30–39) along the western shore of the Peninsula. Thermal demagnetization and principal component analysis of the demagnetization data show lower-temperature (A) and higher-temperature (B) magnetic components. Although group III samples did not display a coherent A component, the A component of group I and II samples was observed as a single-polarity lower-unblocking temperature component generally removed by 100–400 °C. This component failed the fold test at the 95% confidence level. With respect to direction, the A component is similar to both the present-day field and axial–geocentric dipole directions expected at this site. The B component was observed during thermal demagnetization steps up to 580 °C and was always of downward-directed inclination. Coherence of bedding corrections within each section do not allow statistically meaningful fold tests within groups I, II or III. Assuming the B component represents a Cretaceous magnetization, two overall models are proposed. In the first model (preferred), with the highest clustering of directions (k-value=36.7, N (sites)=36), indicates significant poleward motion of the Ainyn terrane (observed paleolatitude λ_M1=61.0±6.5°; expected North America plate reference site paleolatitude λ_E=74.0±3.5°). In the second model, no significant poleward displacement is implied (λ_M2=72.0±9.6).  相似文献   

Stable Isotope and Lithologic Evidence of Late-Glacial and Holocene Oceanography of the Northwestern Pacific and Its Marginal Seas   总被引：1，自引：0，他引：1  

Sergei A. Gorbarenko 《Quaternary Research》1996,46(3):230-250

Stable isotopes, geochemical, lithological, and micropaleontological results from cores from the far northwest (FNW) Pacific and the Okhotsk and Bering seas are used to reconstruct the regional environment for the last glaciation, the deglacial transition, and the Holocene. δ¹⁸O records of planktonic foraminifera of the region show two “light” shifts during deglacial time, provoked by the freshening of the surface water and climate warming. These north Pacific terminal events (T1ANP and T1BNP) with ages of 12,500 and 9300 yr B.P., respectively, occur almost simultaneously with two episodes of accelerated glacier melting around the North Atlantic. Along with the isotopic shifts, the CaCO₃content in regional sediments increased abruptly (1A and 1B carbonate peaks), probably due to changes of productivity and pore water chemistry of surface sediments. Organic matter and opal concentration increased during the transition (between T1ANP and T1BNP events) in the sediments of the FNW Pacific and the southern part of the Bering Sea and opal content increased in the Holocene in the Bering and Okhotsk Seas. δ¹³C records of cores from the Okhotsk and Bering seas and the FNW Pacific do not contradict the hypothesis of increased intermediate water formation in the region during glaciation. During deglaciation, accumulation of the coarse terrigenous component decreased in sediments of the Bering Sea and the FNW Pacific before the T1ANP event, probably as a result of rising sea level and opening of the Bering Strait.  相似文献   

On the limit-cycle instability in magnetized accretion discs     

Andrea Merloni  Sergei Nayakshin 《Monthly notices of the Royal Astronomical Society》2006,372(2):728-734

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Shapes and sizes of voids in the Lambda cold dark matter universe: excursion set approach     

Sergei Shandarin  Hume A. Feldman  Katrin Heitmann  Salman Habib 《Monthly notices of the Royal Astronomical Society》2006,367(4):1629-1640

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A New Way to Model the Solar Oscillation ℓ−ν Power Spectrum     

Stuart M. Jefferies  Sergei V. Vorontsov 《Solar physics》2004,220(2):347-359

We present a new approach for the precise and accurate forward modeling of the solar oscillation ℓ−ν power spectrum. The approach is designed to provide the basis for a streamlined solar seismic inversion without measurements of the p-mode frequencies. The new strategy represents a paradigm change in how information is extracted from the oscillation spectrum. It also represents a step toward the ideal case of inferring the Sun's properties directly from the raw observations.  相似文献   

Mv Lyr: Transition from Low to High Brightness State     

Elena Pavlenko  Kirill Antoniuk  Sergei Yu. Shugarov  Nataly A. Katysheva  Lenie Muzhdabaeva  Vyacheslav Mikhajlov 《Astrophysics and Space Science》2005,296(1-4):461-464

We present results of multicolour photometry of the nova-like binary MV Lyr in the years 2002–2003, corresponding to the transition of the star from its low (V = 17.8) to high (V = 12.3) brightness state. The transition lasted at most 200 days. During the first ∼50 days MV Lyr brightened at the rate 0.06 mag/day, and during the next ∼150 days at the rate 0.01 mag/day. The brightening was accompanied by a blue shift from 0.45 to 0.05 in V−R, interpreted as an increase of the accretion disk contribution to the total light. During the transition MV Lyr displayed well-known ‘quasi-orbital’ light variations and fast quasi-periodic oscillations with a typical time scale of tens of minutes.  相似文献