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291.
V. V. Shuvalov V. V. Svettsov N. A. Artem’eva I. A. Trubetskaya O. P. Popova D. O. Glazachev 《Solar System Research》2017,51(1):44-58
Soon after the discovery of asteroid 99942 Apophis, it was classified as a potentially hazardous object with a high probability of an impact on the Earth in 2029. Although subsequent observations have substantially reduced the probability of a collision, it has not been ruled out; moreover, similar-sized asteroids in orbits intersecting the Earth’s orbit may well be discovered in the near future. We conduct a numerical simulation of an atmospheric passage and an impact on the Earth’s surface of a stony cosmic body with a diameter of 300 m and kinetic energy of about 1000 Mt, which roughly corresponds to the parameters of the asteroid Apophis, at atmospheric entry angles of 90° (vertical stroke), 45°, and 30°. The simulation is performed by solving three-dimensional equations of hydrodynamics and radiative transfer equations in the approximations of radiative heat conduction and volume emission. The following hazards are considered: an air shock wave, ejecta from the crater, thermal radiation, and ionospheric disturbances. Our calculations of the overpressure and wind speed on the Earth’s surface show that the zone of destruction of the weakest structures can be as large as 700–1000 km in diameter; a decrease in the flight path angle to the surface leads to a marked increase in the area affected by the shock wave. The ionospheric disturbances are global in nature and continue for hours: at distances of several thousand kilometers at altitudes of more than 100 km, air density disturbances are tens of percent and the vertical and horizontal velocity components reach hundreds of meters per second. The impact of radiation on objects on the Earth’s surface is estimated by solving the equation of radiative transfer along rays passing through a luminous area. In clear weather, the size of the zone where thermal heating may ignite wood can be as large as 200 km, and the zone of individual fire outbreaks associated with the ignition of flammable materials can be twice as large. In the 100-km central area, which is characterized by very strong thermal damage, there is ignition of structures, roofs, clothes, etc. The human hazardous area increases with the decrease in the trajectory angle, and people may experience thermal effects at distances of up to 250–400 km from the crater. 相似文献
292.
Erste Ergebnisse unseres Programms zur Untersuchung von Doppelsternen, die mögliche Mitglieder von offenen Sternhaufen sind, werden vorgestellt. Daneben wurde die Verteilung von spektroskopischen Variablen und Bedeckungsveränderlichen in der weiteren Umgebung des offenen Haufens IC 4665 ermittelt. Desweiteren wird über eine photometrische Studie des Variablen V 378 Oph berichtet. Über dieses Objekt gibt es, den Helligkeitswechsel betreffend, widersprüchliche Daten. Unsere Beobachtungen bestätigen, daß V 378 Oph ein Doppelstern vom Typ ß Lyrae ist. Seine Periode wurde bestimmt und eine mittlere Lichtkurve ermittelt. Es wird auf einige Besonderheiten hingewiesen, die zusätzliche lichtelektrische und photometrische Beobachtungen erfordern. Anschließend wird diskutiert, ob V 378 Oph zu Mel 186 (Cr 359) oder IC 4665 gehört. 相似文献
293.
The interrelation between sudden increases in the solar wind dynamic pressure, auroral proton flashes on the dayside equatorward
of the oval, and geomagnetic pulsations in the Pc1 range is considered on the basis of simultaneous observations of the solar
wind plasma parameters, proton auroras on the IMAGE satellite, and geomagnetic pulsations at the Lovozero Observatory. It
is indicated that proton luminosity flashes were observed in 70% of cases equatorward of the auroral oval during sudden changes
in the solar wind pressure. In this case, flashes of proton auroras were observed in 85% of cases during sudden changes in
the pressure, which were related to interplanetary shocks. Increases in pressure during tangential discontinuities were accompanied
by flashes of proton auroras only in 45% of cases. When the ground station was conjugate to the region occupied by a proton
aurora flash, the appearance or intensification of existent pulsations in the Pc1 range was observed in 96% of cases. When
the ground station was not conjugate to the region of a proton luminosity flash, the response in geomagnetic pulsations was
observed in 32% of events. When a sudden change in the solar wind pressure was not accompanied by a proton luminosity flash,
the response in pulsations in the Pc1 range was hardly observed. 相似文献
294.
The Institute of Biology investigations of morphological diversity of bacteriae with the aid of electronic microscopy are used for the purposes of ecological monitoring. The results obtained allow to recommend this method to be widely applied.It has been demonstrated that for oligotrophic lake Baikal microflora consists mainly from ultra-microscopic cocci. Where the river Selenga inflows into Baikal morphological diversity of bacteriae is much wider. Bacterioplankton of Irkutsk reservoir by morphological characteristics is very similar to one of lake Baikal In meso-eutrophic Bratsh reservoir bacteriuplankton is more morphologically diversified. There are flexibacteriae, vibrios. Caulobacter sp. cells occurring in its water body.In the places of waste waters'' income to river. Angara morphological diversity of bacteriae is high and various forms with projections etc. can be observed. 相似文献
295.
We have recently announced that the General Catalogue of Variable Stars enters the stage of its fifth, purely electronic edition(GCVS 5.1). We have included 1408 variable stars in the constellation Centaurus in this new version, GCVS 5.1. Working on this revision, we applied current possibilities from data mining, suggested new variability types for many variable stars and found new light elements for a large number of periodic variables. This paper describes the work completed during the preparation of GCVS 5.1 for Centaurus and discusses in detail a number of the most astrophysically significant cases. 相似文献
296.
In May, 2007 we sank the remains of a Minke whale (Balaenoptera acutorostrata) in the East Sea, Peter the Great Bay, at 30 m of water near the coast of Big Pelis Island. In the present study we describe the nematode communities in sediments under the implanted whale carcass. Abundance of nematodes increased with the distance from the carcass. Dominant trophic group was non-selective deposit feeders. The highest values of indexes of a specific diversity and evenness were noted in sediments under the whale, while domination index occurred at the highest distance from the whale. The suggestion is made that the cause of low density of nematodes in sediments under the whale is an extreme increase in number of macrofaunal animals, and predation and food competition between macro- and meiofauna. The changes noted in nematode assemblages living in an implanted whale in shallow waters are similar to those in deep-sea assemblages. 相似文献
297.
Physical and biological characteristics of the pelagic system across Fram Strait to Kongsfjorden 总被引:1,自引:1,他引:1
Haakon Hop Stig Falk-Petersen Harald Svendsen Slawek Kwasniewski Vladimir Pavlov Olga Pavlova Janne E. Sreide 《Progress in Oceanography》2006,71(2-4):182
The Fram Strait is very important with regard to heat and mass exchange in the Arctic Ocean, and the large quantities of heat carried north by the West Spitsbergen Current (WSC) influence the climate in the Arctic region as a whole. A large volume of water and ice is transported through Fram Strait, with net water transport of 1.7–3.2 Sv southward in the East Greenland Current and a volume ice flux in the range of 0.06–0.11 Sv. The mean annual ice flux is about 866,000 km2 yr−1. The Kongsfjorden–Krossfjorden fjord system on the coast of Spitsbergen, or at the eastern extreme of Fram Strait, is mainly affected by the northbound transport of water in the WSC. Mixing processes on the shelf result in Transformed Atlantic Water in the fjords, and the advection of Atlantic water also carries boreal fauna into the fjords. The phytoplankton production is about 80 g C m−2 yr−1 in Fram Strait, and has been estimated both below and above this for Kongsfjorden. The zooplankton fauna is diverse, but dominated in terms of biomass by calanoid copepods, particularly Calanus glacialis and C. finmarchicus. Other important copepods include C. hyperboreus, Metridia longa and the smaller, more numerous Pseudocalanus (P. minutus and P. acuspes), Microcalanus (M. pusillus and M. pygmaeus) and Oithona similis. The most important species of other taxa appear to be the amphipods Themisto libellula and T. abyssorum, the euphausiids Thysanoessa inermis and T. longicaudata and the chaetognaths Sagitta elegans and Eukrohnia hamata. A comparison between the open ocean of Fram Strait and the restricted fjord system of Kongsfjorden–Krossfjorden can be made within limitations. The same species tend to dominate, but the Fram Strait zooplankton fauna differs by the presence of meso- and bathypelagic copepods. The seasonal and inter-annual variation in zooplankton is described for Kongsfjorden based on the record during July 1996–2002. The ice macrofauna is much less diverse, consisting of a handful of amphipod species and the polar cod. The ice-associated biomass transport of ice-amphipods was calculated, based on the ice area transport, at about 3.55 × 106 ton wet weight per year or about 4.2 × 105 t C yr−1. This represents a large energy input to the Greenland Sea, but also a drain on the core population residing in the multi-year pack ice (MYI) in the Arctic Ocean. A continuous habitat loss of MYI due to climate warming will likely reduce dramatically the sympagic food source. The pelagic and sympagic food web structures were revealed by stable isotopes. The carbon sources of particulate organic matter (POM), being Ice-POM and Pelagic-POM, revealed different isotopic signals in the organisms of the food web, and also provided information about the sympagic–pelagic and pelagic–benthic couplings. The marine food web and energy pathways were further determined by fatty acid trophic markers, which to a large extent supported the stable isotope picture of the marine food web, although some discrepancies were noted, particularly with regard to predator–prey relationships of ctenophores and pteropods. 相似文献
298.
Laurie Boithias Yves Auda Stéphane Audry Jean-Pierre Bricquet Alounsavath Chanhphengxay Vincent Chaplot Anneke de Rouw Thierry Henry des Tureaux Sylvain Huon Jean-Louis Janeau Keooudone Latsachack Yann Le Troquer Guillaume Lestrelin Jean-Luc Maeght Pierre Marchand Pierre Moreau Andrew Noble Anne Pando-Bahuon Kongkeo Phachomphon Khambai Phanthavong Alain Pierret Olivier Ribolzi Jean Riotte Henri Robain Emma Rochelle-Newall Saysongkham Sayavong Oloth Sengtaheuanghoung Norbert Silvera Nivong Sipaseuth Bounsamay Soulileuth Xaysatith Souliyavongsa Phapvilay Sounyaphong Sengkeo Tasaketh Chanthamousone Thammahacksa Jean-Pierre Thiebaux Christian Valentin Olga Vigiak Marion Viguier Khampaseuth Xayyathip 《水文研究》2021,35(5):e14126
Mountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land-use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long-term impact of the conversion of traditional slash-and-burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro-meteorological and soil loss parameters at both microplot (1 m2) and small catchment (0.6 km2) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land-use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment-scale models focused on hydrology and water quality issues. The dataset may be further used to, for example, assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g., contaminants other than faecal bacteria), and assess the relative impacts of both climate and land-use change on the catchment. 相似文献
299.
Grigory Fedorov Andrei A. Andreev Elena Raschke Volker Wennrich Georg Schwamborn Olga Y. Glushkova Olaf Juschus Anja Zander Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):516-533
Lake El'gygytgyn, located in central Chukotka, Russian Arctic, was the subject of an international drilling project that resulted in the recovery of the longest continuous palaeoclimatic and palaeoenvironmental record for the terrestrial Arctic covering the last 3.6 million years. Here, we present the reconstruction of the lake‐level fluctuations of Lake El'gygytgyn since Marine Isotope Stage (MIS) 7 based on lithological and palynological as well as chronological studies of shallow‐water sediment cores and subaerial lake terraces. Reconstructed lake levels show an abrupt rise during glacial–interglacial terminations (MIS 6/5 and MIS 2/1) and during the MIS 4/3 stadial–interstadial transition. The most prominent lowstands occurred during glacial periods associated with a permanent lake‐ice cover (namely MIS 6, MIS 4 and MIS 2). Major triggering mechanisms of the lake‐level fluctuations at Lake El'gygytgyn are predominantly changes in air temperature and precipitation. Regional summer temperatures control the volume of meltwater supply as well as the duration of the lake‐ice cover (permanent or seasonal). The duration of the lake‐ice cover, in turn, enables or hampers near‐shore sediment transport, thus leading to long‐term lake‐level oscillations on glacial–interglacial time scales by blocking or opening the lake outflow, respectively. During periods of seasonal ice cover the lake level was additionally influenced by changes in precipitation. The discovered mechanism of climatologically driven level fluctuations of Lake El'gygytgyn are probably valid for large hydrologically open lakes in the Arctic in general, thus helping to understand arctic palaeohydrology and providing missing information for climate modelling. 相似文献
300.
The first empirical orthogonal functions (EOF1s) of surface-air temperature fluctuations for Russia and its neighboring states
within the period 1950–2005 are analyzed. The spatial distribution of the EOF1, the first principal components (PC1s) of the
observed air temperature (averaged over the summer, July, December–March, and individual winter months), and their time variations
(including trend parameters, some spectral characteristics, and the quantitative indices of relation to circulation indices
(on the basis of multiple step-by-step regression)) are considered. Significant seasonal differences have been revealed: the
winter air-temperature fluctuations are characterized by a higher (when compared to summer) spatial coherence, especially
in the latitudinal direction. The EOF1 of the winter air temperature (averaged over December–March) describes its fluctuations
for almost all of Russia; in this case, no less than 70% of the PC1 variability is due to variations in several circulation
indices; the main contribution (60%) is made by both the North Atlantic Oscillation (NAO) and Scandinavian (SCAND) indices.
On the whole, over the periods 1951–2005 and 1971–2005, the NAO contribution exceeds the SCAND contribution to the winter
temperature variability; the NAO is associated with a more rapid increase in air temperature in 1968–1997 and with the 1971–2005
trend. In 1951–1970 the main contribution to air temperature fluctuations was made by SCAND; the SCAND contribution exceeds
the NAO contribution in the periods 1951–2005 and 1971–2005. The 1971–2005 and 1968–1997 temperature trends are completely
described by variations in the NAO (70%) and SCAND (30%) indices for January and February. 相似文献