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排序方式: 共有356条查询结果,搜索用时 15 毫秒
281.
Alexander N. Derkachev Sergey A. Gorbarenko Vera V. Ponomareva Maxim V. Portnyagin Galina I. Malakhova Yanguang Liu 《第四纪科学杂志》2020,35(1-2):362-379
This paper presents the first detailed study of a late Pleistocene marine tephra sequence from the NW Pacific, downwind from the Kamchatka volcanic arc. Sediment core SO201-2-40, located on the Meiji Rise ~400 km offshore the peninsula, includes 25 tephras deposited within the last 215 ka. Volcanic glass from the tephras was characterized using single-shard electron microprobe analysis and laser ablation inductively coupled mass spectrometry. The age of tephras was derived from a new age model based on paleomagnetic and paleoclimate studies. Geochemical correlation of distal tephras to Kamchatkan pyroclastic deposits allowed the identification of tephras from the Karymsky, Gorely, Opala and Shiveluch eruptive centers. Three of these tephras were also correlated to other marine and terrestrial sites and hence are identified as the best markers for the north-west Pacific region. These are an early Holocene tephra from the Karymsky caldera (~8.7 ka) and two tephras falling into the Marine Isotope Stage (MIS) 6 glacial time: an MIS 6.4 tephra from Shiveluch (~141 ka) and the MIS 6.5 Rauchua tephra (~175 ka) from Karymsky. The data presented in this study can be used in paleovolcanological and paleoceanographic reconstructions. 相似文献
282.
SLOBODSKOVA Valentina V. ZHURAVEL Elena V. KUKLA Sergey P. CHELOMIN Victor P. 《中国海洋大学学报(英文版)》2019,(1)
Marine pollution affects all life processes in aquatic organisms. The genotoxic effect of pollution on the mussel Crenomytilus grayanus was assessed. Bivalves were collected from the ‘clean'(Vostochnaya Cove) and polluted(Nakhodka Bay) areas in the Peter the Great Bay. The degree of DNA damage in C. grayanus was determined by alkaline comet assay as mean percentage of DNA in tail, and the genetic damage index was calculated. Our results indicate that almost one-third of DNA in cells of gills and digestive gland of C. grayanus inhabiting the Nakhodka Bay had destructive changes compared to the individuals of this species from the Vostochnaya Cove. This study has shown that chronic pollution of the aquatic environment causes destructive changes to DNA in gill and digestive gland cells of C. grayanus. 相似文献
283.
We simulate the dynamics of slender magnetic flux tubes(MFTs) in the accretion disks of T Tauri stars. The dynamical equations of our model take into account aerodynamic and turbulent drag forces, and the radiative heat exchange between the MFT and ambient gas. The structure of the disk is calculated with the help of our MHD model of the accretion disks. We consider the MFTs formed at distances of 0.027-0.8 au from the star with various initial radii and plasma betas β_0. The simulations show that MFTs with a weak magnetic field(β_0= 10) rise slowly with speeds less than the speed of sound. MFTs with β_0= 1 form an outflowing magnetized corona above the disk. Strongly magnetized MFTs(β_0= 0.1) can cause outflows with velocities 20-50 km s~(-1). The tubes rise periodically over times from several days to several months according to our simulations. We propose that periodically rising MFTs can absorb stellar radiation and contribute to the IR-variability of young stellar objects. 相似文献
284.
Since 2013, round-the-clock monitoring of the sky has been carried out simultaneously in 96 beams using a high-sensitivity radio telescope called the Large Phased Array(LPA) at the frequency110.25 MHz. These observations are made under the program of interplanetary plasma investigation.The same data are used to search for pulsars by means of power spectra. To increase the sensitivity of the pulsar search, 500–600 power spectra corresponding to different days of observations are summed. In the integrated spectra of known pulsars, besides expected improvement in signal-to-noise(S/N) ratio for the frequency harmonics, some features are explored in this paper. We present the 27 strongest pulsars which are in a field with declination 21°-42°. The observable details in the integrated power spectra are connected with the presence of pulsar periods of the second(P_2) and third(P_3) class, which have been identified. Empirical relations for calculating these periods are obtained. The value P_2 is estimated for 26 pulsars, and for 15 sources it is made for the first time. The value P_3 is estimated for 13 pulsars,among them these values are given for five sources for the first time. 相似文献
285.
The Chelyabinsk meteorite: New insights from a comprehensive electron microscopy and Raman spectroscopy study with evidence for graphite in olivine of ordinary chondrites 下载免费PDF全文
David Kaeter Martin A. Ziemann Ute Böttger Iris Weber Lutz Hecht Sergey A. Voropaev Alexander V. Korochantsev Andrey V. Kocherov 《Meteoritics & planetary science》2018,53(3):416-432
We present results of petrographic, mineralogical, and chemical investigations of three Chelyabinsk meteorite fragments. Three distinct lithologies were identified: light S3 LL5, dark S4–S5 LL5 material, and opaque fine-grained former impact melt. Olivine–spinel thermometry revealed an equilibration temperature of 703 ± 23 °C for the light lithology. All plagioclase seems to be secondary, showing neither shock-induced fractures nor sulfide-metal veinlets. Feldspathic glass can be observed showing features of extensive melting and, in the dark lithology, as maskelynite, lacking melt features and retaining grain boundaries of former plagioclase. Olivine of the dark lithology shows planar deformation features. Impact melt is dominated by Mg-rich olivine and resembles whole-rock melt. Melt veins (<2 mm) are connected to narrower veinlets. Melt vein textures are similar to pegmatite textures showing chilled margins, a zone of inward-grown elongated crystals and central vugs, suggesting crystallization from supercooled melt. Sulfide-metal droplets indicate liquid immiscibility of both silicate and sulfide as well as sulfide and metal melts. Impact melting may have been an important factor for differentiation of primitive planetary bodies. Graphite associated with micrometer-sized melt inclusions in primary olivine was detected by Raman mapping. Carbon isotopic studies of graphite could be applied to test a possible presolar origin. 相似文献
286.
Aleskerova Anna Kubryakov Arseny Stanichny Sergey Medvedeva Alessia Plotnikov Evgeniy Mizyuk Artem Verzhevskaia Liudmila 《Ocean Dynamics》2021,71(6):655-677
Ocean Dynamics - Long-term arrays of satellite optical measurements of Landsat-5,7,8 and Sentinel-2 were used to describe the characteristics of submesoscale eddy (SE) dynamics in different parts... 相似文献
287.
Recent spectroscopic data pointing to low heavy-element abundances Z pose a severe problem for solar-structure modeling. The low-Z abundances imply a lower opacity and a relatively shallow convective zone, both of which are in obvious contradiction with the observed helioseismic sound-speed profile. This paper presents a series of solar models with different heavy-element abundances. The SAHA-S equation of state and OPAL opacities properly take into account the respective heavy-element abundances. Diffusion of individual elements is also included in the models. Sound-speed profiles are compared with inversion results and it is shown that the models with low Z are in disagreement with the inversion data. Even combining the effect of diffusion, overshooting and mixing for the sound-speed profile did not lead to a solution of the low-Z problem. Models with varied neon abundance have also been computed. It turned out that a substantial increase of the neon abundance could produce a model in agreement with the sound-speed inversion but the required abundance increase would be unrealistic. The effect of the neon enhancement on the adiabatic exponent profile in the convection zone is also presented. 相似文献
288.
Analysis of climate policy targets under uncertainty 总被引:1,自引:1,他引:0
Mort Webster Andrei P. Sokolov John M. Reilly Chris E. Forest Sergey Paltsev Adam Schlosser Chien Wang David Kicklighter Marcus Sarofim Jerry Melillo Ronald G. Prinn Henry D. Jacoby 《Climatic change》2012,112(3-4):569-583
Although policymaking in response to the climate change threat is essentially a challenge of risk management, most studies of the relation of emissions targets to desired climate outcomes are either deterministic or subject to a limited representation of the underlying uncertainties. Monte Carlo simulation, applied to the MIT Integrated Global System Model (an integrated economic and earth system model of intermediate complexity), is used to analyze the uncertain outcomes that flow from a set of century-scale emissions paths developed originally for a study by the U.S. Climate Change Science Program. The resulting uncertainty in temperature change and other impacts under these targets is used to illustrate three insights not obtainable from deterministic analyses: that the reduction of extreme temperature changes under emissions constraints is greater than the reduction in the median reduction; that the incremental gain from tighter constraints is not linear and depends on the target to be avoided; and that comparing median results across models can greatly understate the uncertainty in any single model. 相似文献
289.
Sergey M. Kudryavtsev Natalia S. Kudryavtseva 《Celestial Mechanics and Dynamical Astronomy》2009,105(4):353-360
An accurate development of the latest JPL’s numerical ephemeris of Pluto, DE421, to compact analytical series is done. Rectangular
barycentric ICRF coordinates of Pluto from DE421 are approximated by compact Fourier series with a maximum error of 1.3 km
over 1900–2050 (the entire time interval covered by the ephemeris). To calculate Pluto positions relative to the Sun, a development
of rectangular heliocentric ICRF coordinates of the Solar System barycenter to Poisson series is additionally made. As a result,
DE421 Pluto heliocentric positions by the new analytical series are represented to an accuracy of better than 5 km over 1900–2050. 相似文献
290.
Christina Neal Olga Girina Sergey Senyukov Alexander Rybin Jeffrey Osiensky Pavel Izbekov Gail Ferguson 《Natural Hazards》2009,51(2):245-262
More than 65 potentially active volcanoes on the Kamchatka Peninsula and the Kurile Islands pose a substantial threat to aircraft on the Northern Pacific (NOPAC), Russian Trans-East (RTE), and Pacific Organized Track System (PACOTS) air routes. The Kamchatka Volcanic Eruption Response Team (KVERT) monitors and reports on volcanic hazards to aviation for Kamchatka and the north Kuriles. KVERT scientists utilize real-time seismic data, daily satellite views of the region, real-time video, and pilot and field reports of activity to track and alert the aviation industry of hazardous activity. Most Kurile Island volcanoes are monitored by the Sakhalin Volcanic Eruption Response Team (SVERT) based in Yuzhno-Sakhalinsk. SVERT uses daily moderate resolution imaging spectroradiometer (MODIS) satellite images to look for volcanic activity along this 1,250-km chain of islands. Neither operation is staffed 24 h per day. In addition, the vast majority of Russian volcanoes are not monitored seismically in real-time. Other challenges include multiple time-zones and language differences that hamper communication among volcanologists and meteorologists in the US, Japan, and Russia who share the responsibility to issue official warnings. Rapid, consistent verification of explosive eruptions and determination of cloud heights remain significant technical challenges. Despite these difficulties, in more than a decade of frequent eruptive activity in Kamchatka and the northern Kuriles, no damaging encounters with volcanic ash from Russian eruptions have been recorded. 相似文献