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21.
The measurement of solar magnetic fields using the Zeeman effect diagnostics has a fundamental 180° ambiguity in the determination of the azimuth angle of the transverse field component. There are several methods that are used in the community and each one has its merits and demerits. Here we present a disambiguation idea that is based on the assumption that most of the magnetic field on the sun is predominantly vertical. While the method is not applicable to penumbra or other features harboring predominantly horizontal fields like the sheared neutral lines, it is useful for regions where fields are predominantly vertical like network and plage areas. The method is tested with the full-disk solar vector magnetograms observed by the SOLIS/VSM instrument. We find that statistically about 60?–?85 % of the pixels in a typical full-disk magnetogram has a field inclination in the range of 0?–?30° with respect to the local solar normal, and thus can be successfully disambiguated by the proposed method. Due to its non-iterative nature, the present method is extremely fast and therefore can be used as a good initial guess for iterative schemes like the non-potential field computation (NPFC) method. Furthermore, the method is insensitive to noisy pixels as it does not depend upon the neighboring pixels or derivatives. 相似文献
22.
Alexei Pozdnoukhov Mikhail Kanevski 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(5):647-660
The algorithmic approach to data modelling has developed rapidly these last years, in particular methods based on data mining
and machine learning have been used in a growing number of applications. These methods follow a data-driven methodology, aiming
at providing the best possible generalization and predictive abilities instead of concentrating on the properties of the data
model. One of the most successful groups of such methods is known as Support Vector algorithms. Following the fruitful developments
in applying Support Vector algorithms to spatial data, this paper introduces a new extension of the traditional support vector
regression (SVR) algorithm. This extension allows for the simultaneous modelling of environmental data at several spatial
scales. The joint influence of environmental processes presenting different patterns at different scales is here learned automatically
from data, providing the optimum mixture of short and large-scale models. The method is adaptive to the spatial scale of the
data. With this advantage, it can provide efficient means to model local anomalies that may typically arise in situations
at an early phase of an environmental emergency. However, the proposed approach still requires some prior knowledge on the
possible existence of such short-scale patterns. This is a possible limitation of the method for its implementation in early
warning systems. The purpose of this paper is to present the multi-scale SVR model and to illustrate its use with an application
to the mapping of Cs137 activity given the measurements taken in the region of Briansk following the Chernobyl accident. 相似文献
23.
High-frequency radars measure projections of surface velocity vectors on the directions of the radar beams. A variational method for reconstruction of the 2d velocity field from such observations is proposed. The interpolation problem is regularized by penalizing high-frequency variability of the surface vorticity and divergence fields. Twin-data experiments are used to assess the method's skill and compare it with two well-known approaches to HFR data processing: conventional local interpolation and more sophisticated non-local scheme known as open-boundary modal analysis (OMA). It is shown that the variational method and OMA have a significant advantage over local interpolation because of their ability to reconstruct the velocity field within the gaps in data coverage, near the coastlines and in the areas covered only by one radar. Compared to OMA, the proposed variational method appears to be more flexible in processing gappy observations and more accurate at noise levels below 30%. 相似文献
24.
Alexei V. Ivanov Sergei V. Rasskazov Gennady D. Feoktistov Huaiyu He Ariel Boven 《地学学报》2005,17(3):203-208
Main part of the Siberian Traps Large Igneous Province was formed in a short time-span at the Permo-Triassic boundary c. 250 Ma. New 40Ar/39Ar dating results for the Usol'skii dolerite sill in south-eastern part of the province indicate its probable emplacement c. 6 Myr after the main Permo-Triassic magmatic phase. Compilation of the published 40Ar/39Ar and U-Pb ages implies that basaltic and related magmatism lasted in total as long as 22–26 Myr. Therefore, similar to other large igneous provinces, magmatism of the Siberian Traps combined voluminous short-lived and less prominent long-lived events. 相似文献
25.
Alexei V. Ivanov Elena I. Demonterova Sergei V. Rasskazov Tatyana A. Yasnygina 《Journal of Earth System Science》2008,117(1):1-21
Siberian Traps Large Igneous Province (STLIP) is one of the most voluminous volcanic provinces on Earth. The dominant erupted
rocks are low-Ti basalts, which make up 80% by volume of the classical Noril’sk lava sequence. In the west Siberian basin
and Maymecha-Kotuy area, the low-Ti basalts make up about 99% and 50% by volume, respectively. Dolerite sills in the Angara-Taseevskaya
Syncline at the southeastern STLIP exhibit trace element patterns and Sr isotope ratios typical of the low-Ti basalts of the
Noril’sk sequence. The most Mg-rich (MgO 9.5–11 wt%) and hence least differentiated dolerites are characterized by trace element
patterns with Ta-Nb depletion, low Ce/Pb and high Sr/Pr. These trace element features are similar to water-saturated, mantle
wedge-derived island arc basalts. These imply an important role of subduction fluid-derived trace elements in the source of
melting beneath the Angara-Taseevskaya Syncline and other regions of the STLIP. Less magnesium rocks (MgO 3.8–6.1 wt%) with
less prominent Ta-Nb depletion, higher Ce/Pb and lower Sr/Pr could be produced via olivine-plagioclase fractionation of primary
high-magnesium melts. 相似文献
26.
The ecological implications of a Yakutian mammoth's last meal 总被引:1,自引:0,他引:1
Bas van Geel Andr Aptroot Claudia Baittinger Hilary H. Birks Ian D. Bull Hugh B. Cross Richard P. Evershed Barbara Gravendeel Erwin J.O. Kompanje Peter Kuperus Dick Mol Klaas G.J. Nierop Jan Peter Pals Alexei N. Tikhonov Guido van Reenen Peter H. van Tienderen 《Quaternary Research》2008,69(3):361-376
Part of a large male woolly mammoth (Mammuthus primigenius) was preserved in permafrost in northern Yakutia. It was radiocarbon dated to ca. 18,500 14C yr BP (ca. 22,500 cal yr BP). Dung from the lower intestine was subjected to a multiproxy array of microscopic, chemical, and molecular techniques to reconstruct the diet, the season of death, and the paleoenvironment. Pollen and plant macro-remains showed that grasses and sedges were the main food, with considerable amounts of dwarf willow twigs and a variety of herbs and mosses. Analyses of 110-bp fragments of the plastid rbcL gene amplified from DNA and of organic compounds supplemented the microscopic identifications. Fruit-bodies of dung-inhabiting Ascomycete fungi which develop after at least one week of exposure to air were found inside the intestine. Therefore the mammoth had eaten dung. It was probably mammoth dung as no bile acids were detected among the fecal biomarkers analysed. The plant assemblage and the presence of the first spring vessels of terminal tree-rings of dwarf willows indicated that the animal died in early spring. The mammoth lived in extensive cold treeless grassland vegetation interspersed with wetter, more productive meadows. The study demonstrated the paleoecological potential of several biochemical analytical techniques. 相似文献
27.
Alexei V. Ivanov Stanislav V. Palesskii Elena I. Demonterova Irina V. Nikolaeva Igor V. Ashchepkov Sergei V. Rasskazov 《地学学报》2008,20(6):504-511
We determined the concentrations of platinum‐group elements (PGE) and rhenium in granular spinel lherzolites entrained as xenoliths in the Late Cenozoic volcanic rocks of the East Sayan within the Sarkhoi palaeo‐arc block of the Tuva‐Mongolian massif. Major element, PGE and rhenium variations in the East Sayan xenoliths can be explained by impregnation of up to 15% of arc‐type melt into initially depleted mantle harzburgite. Such a refertilization process probably took place in the Middle Neoproterozoic, when the Tuva‐Mongolian massif was in a subduction environment. East Sayan xenoliths show close similarities to Vitim xenoliths, whose host basalts erupted within an off‐cratonic crustal block. Both East Sayan and Vitim xenoliths are different from cratonic and circum‐cratonic peridotite xenoliths of worldwide localities. 相似文献
28.
Anastasia V.Arzhannikova Elena I.Demonterova Marc Jolivet Ekaterina A.Mikheeva Alexei V.Ivanov Sergey G.Arzhannikov Valentin B.Khubanov Vadim S.Kamenetsky 《地学前缘(英文版)》2022,13(1):101254
The Late Paleozoic–Early Mesozoic Mongol-Okhotsk Ocean extended between the Siberian and Amur–North China continents.The timing and modalities of the oceanic closure are widely discussed.It is largely accepted that the ocean closed in a scissor-like manner from southwest to northeast(in modern coordinates),though the timing of this process remains uncertain.Recent studies have shown that both western(West Transbaikalia)and eastern(Dzhagda)parts of the ocean closed almost simultaneously at the Early–Middle Jurassic boundary.However,little information on the key central part of the oceanic suture zone is available.We performed U-Pb(LA-ICP-MS)dating of detrital zircon from wellcharacterized stratigraphic sections of the central part of the Mongol-Okhotsk suture zone.These include the initial marine and final continental sequences of the East Transbaikalia Basin,deposited on the northern Argun-Idemeg terrane basement.We provide new stratigraphic ages for the marine and continental deposits.This revised chronostratigraphy allows assigning an age of~165–155 Ma,to the collisionrelated flexure of the northern Argun-Idemeg terrane and the development of a peripheral foreland basin.This collisional process took place 5 to10 million years later than in the western and eastern parts of the ocean.We demonstrate that the northern Argun-Idemeg terrane was the last block to collide with the Siberian continent,challenging the widely supported scissor-like model of closure of the MongolOkhotsk Ocean.Different segments of the ocean closed independently,depending on the initial shape of the paleo continental margins. 相似文献
29.
Ekaterina V. KOROCHANTSEVA Mario TRIELOFF Alexei I. BUIKIN Jens HOPP 《Meteoritics & planetary science》2009,44(2):293-321
Abstract— We report a high‐resolution 40Ar‐39Ar study of mineral separates and whole‐rock samples of olivine‐phyric (Dhofar 019, Sayh al Uhaymir [SaU] 005) and basaltic (Shergotty, Zagami) shergottites. Excess argon is present in all samples. The highest (40Ar/36Ar)trapped ratios are found for argon in pyroxene melt inclusions (?1500), maskelynite (?1200), impact glass (?1800) of Shergotty and impact glass of SaU 005 (?1200). A high (40Ar/36Ar)trapped component‐usually uniquely ascribed to Martian atmosphere‐can also originate from the Martian interior, indicating a heterogeneous Martian mantle composition. As additional explanation of variable high (40Ar/36Ar)trapped ratios in shocked shergottites, we suggest argon implantation from a “transient atmosphere” during impact induced degassing. The best 40Ar‐39Ar age estimate for Dhofar 019 is 642 ± 72 Ma (maskelynite). SaU 005 samples are between 700–900 Ma old. Relatively high 40Ar‐39Ar ages of melt inclusions within Dhofar 019 (1086 ± 252 Ma) and SaU 005 olivine (885 ± 66 Ma) could date entrapment of a magmatic liquid during early olivine crystallization, or reflect unrecognized excess 40Ar components. The youngest 40Ar‐39Ar age of Shergotty separates (maskelynite) is ?370 Ma, that of Zagami is ?200 Ma. The 40Ar‐39Ar chronology of Dhofar 019 and SaU 005 indicate >1 Ga ages. Apparent ages uncorrected for trapped (e.g., Martian atmosphere, mantle) argon components approach 4.5 Ga, but are not caused by inherited 40Ar, because excess 40Ar is supported by 36Artrapped. Young ages obtained by 40Ar‐39Ar and other chronometers argue for primary rather than secondary events. The cosmic ray exposure ages calculated from cosmogenic argon are 15.7 ± 0.7 Ma (Dhofar 019), 1.0–1.6 Ma (SaU 005), 2.1–2.5 Ma (Shergotty) and 2.2–3.0 Ma (Zagami). 相似文献
30.