Long-term starspot activity of the eclipsing binaries BH Vir and WY Cnc     

A. V. Kozhevnikova  I. Yu. Alekseev  P. A. Heckert  V. P. Kozhevnikov 《Astronomy Reports》2007,51(11):932-946

We present the results of multicolor photometry of the two spotted, short-period, late-type RS CVn stars BH Vir and WY Cnc. We have derived the parameters of the binaries’ components, and refined their masses, radii, and luminosities. A strong flare of WY Cnc was detected for the first time, and pre-flare variations of the star’s activity studied. Our observations and published data spanning 40 years are analyzed using a zone starspot model. We demonstrate that the spots are always concentrated near the equators and at intermediate latitudes, with maximum spotted areas as large as 29% for BH Vir and 21% for WY Cnc. The temperature differences between spotted regions and the quiet photosphere were 2300 K (BH Vir) and 1800 K (WY Cnc). The detected long-term brightness variations of BH Vir suggest the existence of an activity cycle with a probable period of 22 years. Both stars have starspots concentrated at two active longitudes separated by approximately half of the orbital period during all the studied seasons; these longitudes remained the same (0° and 184°) for BH Vir over 40 years, whereas they migrated in the direction of the stellar rotation at a rate of 3.8°/yr for WY Cnc, suggesting a cycle of 47 years for the migration of the active longitudes.  相似文献   

The age and tectonic setting of volcanic and cherty sequences in the ophiolite complex of the Atbashe Ridge (Southern Tien Shan)     

D. V. Alekseev  V. A. Aristov  K. E. Degtyarev 《Doklady Earth Sciences》2007,413(3):380-383

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On late Maastrichtian-early Danian water masses and lithologic and foraminifer assemblages in different tectonic zones of the Mountainous Crimea     

L. F. Kopaevich  A. S. Alekseev  A. M. Nikishin  V. N. Ben’yamovskii  E. V. Yakovishina  E. A. Sokolova  A. I. Voznesenskii 《Moscow University Geology Bulletin》2007,62(3):164-172

This paper presents data on the structure of reference sections of the Maastrichtian-Danian boundary beds and the assemblages of benthic and planktonic foraminifers enclosed in these rocks. These are based on examination of the reference sections in two different structure-facies zones of the Mountainous Crimea: the Kacha Uplift and Indol-Kuban Trough. The strongly different lithologic and foraminifer assemblages in these sections indicate the presence of completely different water masses in the shelf part of the marine basin with water depths varying from those of the middle-lower sublittoral zone (in the Belbek, Beshkosh, and Chakhmakhly sections in the southwestern part of the Mountainous Crimea) to those of the pelagic environment on the continental slope and at the continental rise (section in Mount Klement’ev in the Indol-Kuban Trough). These assemblages indicate the sedimentation environment in the transition zone between the Kacha shelf and the deep-water Black Sea Basin.  相似文献   

Nature of carbonaceous rocks in shear zones in the Dal’negorsk District,Primorye: Black shales or mantle-related ilmenite-graphite metasomatites?     

V. Yu. Alekseev  V. A. Baskina  I. N. Tomson  A. I. Yakushev 《Doklady Earth Sciences》2007,415(2):829-834

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A Unique Find of Rhenium-bearing Wolframite in Ongonites of the Russian Far East     

Alekseev  V. I.  Marin  Yu. B. 《Doklady Earth Sciences》2018,478(2):250-252

Doklady Earth Sciences - Accessory wolframite with an extraordinarily high rhenium content (2.93–3.52%) in ongonite from the Badzhal area in the Far East is described. The capacity of...  相似文献   

Accessory mineralization of rocks from Late Cretaceous intrusive series with Li–F granites in the Far East     

V. I. Alekseev  Yu. B. Marin 《Geology of Ore Deposits》2015,57(7):537-551

Accessory mineralization of the Late Cretaceous intrusive series in the Far East was investigated on the basis of published data and the author’s original evidence. The composition of accessory minerals from leucogranite, monzonitoid rocks, and Li–F granites has been established. The trend in the evolution of Late Cretaceous granitoids is characterized by an increase in the mineral-forming role of iron and rare elements. Diverse accessory minerals and their typomorphic assemblages have been identified for Li–F granites and ongonites. The regional specificity of accessory mineralization in rare-metal granites consists in the leading role of the minerals W, Ta, Nb, Bi, Y, REE, and As. The uniformity of mineral species and mineral assemblages and the typomorphism and evolution of accessory minerals are inherent to the Far East belt of Li–F granites.  相似文献   

Accessory Cassiterite as an Indicator of Rare Metal Petrogenesis and Mineralization     

Alekseev  V. I.  Marin  Yu. B. 《Geology of Ore Deposits》2022,64(7):397-423

Geology of Ore Deposits - This paper is a scientific overview of studies of accessory cassiterite from rare metal granites, pegmatites, and accompanying greisens in 1990–2021. The earlier and...  相似文献   

The upper Viséan–Serpukhovian in the type area for the Serpukhovian Stage (Moscow Basin,Russia): Part 1. Sequences,disconformities, and biostratigraphic summary     

Pavel B. Kabanov  Alexander S. Alekseev  Nilyufer B. Gibshman  Ruslan R. Gabdullin  Aleksei V. Bershov 《Geological Journal》2016,51(2):163-194

The upper Viséan–Serpukhovian strata in the type region for the Serpukhovian Stage is an epeiric‐sea succession ca. 90 m in thickness. The predominantly Viséan Oka Group (comprising the Aleksin, Mikhailov, and Venev formations) is dominated by photozoan packstones with fluvial siliciclastic wedges developed from the west. The Lower Serpukhovian Zaborie Group is composed of the Tarusa and Gurovo formations. The latter is a new name for the shale‐dominated unit of Steshevian Substage age in the studied area. The Zaborie Group is composed of limestones and marls in its lower (Tarusa and basal Gurovo) part and black smectitic to grey palygorskitic shales in the main part of the Gurovo Formation. The Gurovo Formation is capped by a thin limestone with oncoids and a palygorskitic–calcretic palaeosol. The Upper Serpukhovian is composed of a thin (3–12 m) Protva Limestone heavily karstified during a mid‐Carboniferous lowstand. The succession shows a number of unusual sedimentary features, such as a lack of high‐energy facies, shallow‐subtidal marine sediments penetrated by Stigmaria, the inferred atidal to microtidal regime, and palustrine beds composed of saponitic marls. The succession contains many subaerial disconformities characterized by profiles ranging from undercoal solution horizons to palaeokarsts. Incised fluvial channels are reported at two stratigraphic levels to the west of the study area. The deepest incisions developed from the Kholm Disconformity (top of the Mikhailov Formation). This disconformity also exhibits the deepest palaeokarst profile and represents the major hiatus in the Oka–Zaborie succession. The new sea‐level curve presented herein shows two major cycles separated by the Kholm Unconformity at the Mikhailov/Venev boundary. The Lower Serpukhovian transgression moved the base‐level away from falling below the seafloor so that the section becomes conformable above the Forino Disconformity (lower Tarusa). The maximum deepening is interpreted to occur in the lower dark‐shale part of the Gurovo Formation. The base of the Serpukhovian Stage is defined by FADs of the conodont Lochriea ziegleri and the foraminifer Janischewskina delicata in the middle of the sequence VN2. The Aleksinian–Mikhailovian interval is provisionally correlated with the Asbian (Lower–Middle Warnantian) in Western Europe. Based on FODs of Janischewskina typica and first representatives of Climacammina, the Venevian is correlated with the Brigantian in Western Europe. The Tarusian–Protvian interval contains diverse fusulinid and conodont assemblages, but few forms suitable for international correlation. FADs of the zonal conodont species Adetognathus unicornis and Gnathodus bollandensis at several metres above the Protvian base suggest correlation of the entire Zaborie Group and may be the basal Protvian to the Pendleian. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Arctic sea ice cover in connection with climate change     

G. V. Alekseev  E. I. Aleksandrov  N. I. Glok  N. E. Ivanov  V. M. Smolyanitsky  N. E. Kharlanenkova  A. V. Yulin 《Izvestiya Atmospheric and Oceanic Physics》2015,51(9):889-902

Recently published studies on key issues in the evolution of Arctic sea ice cover are reviewed and attempts to answer disputable questions are made in the research part of the work. It is shown that climate warming, manifested in an increase in the surface air temperature, and reduction in the ice cover develop with a high degree of agreement in summer. Based on this fact, anomalies of the September ice-cover area have been retrieved from 1900. They show a significant decrease in the 1930–1940s, which is almost twice as low as in 2007–2012. The influence of fluctuations in the flow of warm and salty Atlantic water is noted in variations in the winter maximum of the ice-cover area in the Barents Sea. An accelerated positive trend has been ascertained for the air temperature in late autumn–early winter in 1993–2012 due to an increase in the open water area in late summer. Inherent regularities of the ice-cover-area variability made it possible to develop a prediction of the monthly values of sea-ice extent with a head time from 6 months to 2 years. Their strong correlation with summer air temperature is used to estimate the onset of summer ice clearance in the Arctic.  相似文献   

Wolframoixiolite in Lithium–Fluorine Granites of the Arga–Ynnakh–Khaya Pluton,Yakutia     

Alekseev  V. I.  Marin  Yu. B.  Galankina  O. L. 《Geology of Ore Deposits》2020,62(7):629-637

Geology of Ore Deposits - A complex of accessory W-bearing tantalo-niobates (columbite-(Fe), columbite-(Mn), tantalite-(Mn), microlite group minerals, and Ta-bearing rutile) involving...  相似文献