On the Origin of Pulsations of Sub-THz Emission from Solar Flares     

V. V. Zaitsev  A. V. Stepanov  P. Kaufmann 《Solar physics》2014,289(8):3017-3032

We propose a model to explain fast pulsations in sub-THz emission from solar flares. The model is based on the approach of a flaring loop as an equivalent electric circuit and explains the pulse-repetition rate, the high-quality factor, Q≥10³, low modulation depth, pulse synchronism at different frequencies, and the dependence of the pulse-repetition rate on the emission flux, observed by Kaufmann et al. (Astrophys. J. 697, 420, 2009). We solved the nonlinear equation for electric current oscillations using a Van der Pol method and found the steady-state value for the amplitude of the current oscillations. Using the pulse rate variation during the flare on 4 November 2003, we found a decrease of the electric current from 1.7×10¹² A in the flare maximum to 4×10¹⁰ A just after the burst. Our model is consistent with the plasma mechanism of sub-THz emission suggested recently by Zaitsev, Stepanov, and Melnikov (Astron. Lett. 39, 650, 2013).  相似文献   

Ferromanganese carbonate metasediments of the Sob area,Polar Urals: Bedding conditions,composition, and genesis     

A. I. Brusnitsyn  V. N. Kuleshov  E. N. Perova  A. N. Zaitsev 《Lithology and Mineral Resources》2017,52(3):192-213

The paper presents the results of study of ferromanganese carbonate rocks in the Sob area (Polar Urals), which is located between the Rai-Iz massif and the Seida–Labytnangi Railway branch. These rocks represent low-metamorphosed sedimentary rocks confined to the Devonian carbonaceous siliceous and clayey–siliceous shales. In terms of ratio of the major minerals, ferromanganese rocks can be divided into three varieties composed of the following minerals: (1) siderite, rhodochrosite, chamosite, quartz, ± kutnahorite, ± calcite, ± magnetite, ± pyrite, ± clinochlore, ± stilpnomelane; (2) spessartite, rhodochrosite, and quartz, ± hematite, ± chamosite; (3) rhodochrosite, spessartite, pyroxmanite, quartz ± tephroite, ± fridelite, ± clinochlore, ± pyrophanite, ± pyrite. In all varieties, the major concentrators of Mn and Fe are carbonates (rhodochrosite, siderite, kutnahorite, Mn-calcite) and chlorite group minerals (clinochlore, chamosite). The chemical composition of rocks is dominated by Si, Fe, Mn, carbon dioxide, and water (L.O.I.): total SiO₂ + Fe₂O ₃ ^tot + MnO + L.O.I. = 85.6?98.4 wt %. The content of Fe and Mn varies from 9.3 to 55.6 wt % (Fe₂O ₃ ^tot + MnO). The Mn/Fe ratio varies from 0.2 to 55.3. In terms of the aluminum module Al_M = Al/(Al + Mn + Fe), the major portion of studied samples corresponds to metalliferous sediments. The δ¹³C_carb range (–30.4 to–11.9‰ PDB) corresponds to authigenic carbonates formed with carbon dioxide released during the microbial oxidation of organic matter in sediments at the dia- and/or catagenetic stage. Ferromanganese sediments were likely deposited in relatively closed seafloor zones (basin-traps) characterized by periodic stagnation. Fe and Mn could be delivered from various sources: input by diverse hydrothermal solutions, silt waters in the course of diagenesis, river discharges, and others. The diagenetic delivery of metals seems to be most plausible. Mn was concentrated during the stagnation of bottom water in basin-traps. Interruption of stagnation promoted the precipitation of Mn. The presence of organic matter fostered a reductive pattern of postsedimentary transformations of metalliferous sediments. Fe and Mn were accumulated initially in the oxide form. During the diagenesis, manganese and iron oxides reacted with organic matter to make up carbonates. Relative to manganese carbonates, iron carbonates were formed under more reductive settings and higher concentrations of carbon dioxide in the interstitial solution. Crystallization of manganese and iron silicates began already at early stages of lithogenesis and ended during the regional metamorphism of metalliferous sediments.  相似文献   

Experimental Model of the Formation of Nanophase Metallic Iron in the Lunar Regolith     

Sorokin  E. M.  Yakovlev  O. I.  Slyuta  E. N.  Gerasimov  M. V.  Zaitsev  M. A.  Shcherbakov  V. D.  Ryazantsev  K. M.  Krasheninnikov  S. P. 《Doklady Earth Sciences》2020,492(2):431-433

Doklady Earth Sciences - One of the signs of “space weathering” on the Moon, including the effect of the solar wind and micrometeorite bombardment, is the formation of nanophase...  相似文献   

Evaluation of formation pore pressure behind the casing using borehole gravity data     

Yuliy A. Dashevsky  Semen Petrov  Alexandr N. Vasilevskiy  Oleg B. Bocharov  Gleb V. Dyatlov 《Studia Geophysica et Geodaetica》2017,61(1):69-92

Reliable estimates of the fluid pressure in the pore space of rocks are critical for different aspects of petroleum exploration and production including injection operations and scenarios of water flooding. Numerous approaches are available for formation pore pressure evaluation, however, these measurements become a challenge inside a cased borehole, and a list of possible options is short: either the casing is to be perforated, or the production tubing needs to be disconnected to perform the pressure tests. We present a method for through-casing evaluation of formation pore pressure without shutting down production. We suggest equipping an observation well with a borehole gravimeter and acquiring time variations of the vertical component of the gravity field. Changes in gravity occur during gas production and are related to time variations of formation pore pressure. Gravity changes obtained in the observation well are supposed to be inverted for time-dependent formation pore pressure variations beyond the casing. Our results and recommendations are based on numerical modeling of pore pressure spatial distribution during gas field exploitation and relevant changes in borehole gravity. Benchmark models were elaborated in order to consider a dynamic process of pressure changes in time and space under conditions similar to those in the Medvezhye gas field (Russia). Different modeling scenarios are considered for early and late stages of gas field exploitation. The sensitivity analysis was performed to estimate quantitatively a sensitivity of borehole temporal gravity changes to variations in formation pore pressure behind the casing. Based on resolution analysis we justify the possibility to extract the gravity measurements directly related to changes in pore pressure from the total changes in the gravity field due to reservoir exploitation. The impact of pore pressure on the gravity field measured in boreholes during the water flooding is also evaluated, and obtained results are discussed.  相似文献   

Hyperstatic reaction method for calculations of tunnels with horseshoe-shaped cross-section under the impact of earthquakes     

Chi  Thanh Nguyen  Alexandr  Gospodarikov 《地震工程与工程振动(英文版)》2020,19(1):179-188

Tunnels are now an integral part of the infrastructure in major cities around the world. For many reasons, these tunnels have horseshoe-shaped cross-sections with round top and flat bottom. This paper presents some improvements to the use of the Hyperstatic Reaction Method-HRM for analysing tunnels with horseshoe-shaped cross-sections when these tunnels operate under the influence of earthquakes, particularly in cases when the tunnel lining is a continuous lining. The analysis used parameters of a tunnel from the Hanoi metro system, as well as parameters of the strongest earthquake that may occur in the central Hanoi area in the improved HRM and 2 D numerical methods using the ABAQUS software. On the basis of the results obtained, the paper gives conclusions about the HRM methodology when it is used to calculate tunnels that have horseshoe cross-sections operating under the influence of earthquakes.  相似文献   

The Characteristic Sizes of the Sunspots and Pores in Solar Cycle 24     

Tlatov  Andrey  Riehokainen  Alexandr  Tlatova  Kseniya 《Solar physics》2019,294(4):1-10

Recent dedicated Hinode polar region campaigns revealed the presence of concentrated kilogauss patches of the magnetic field in the polar regions of the Sun, which are also shown to be correlated with facular bright points at the photospheric level. In this work, we demonstrate that this spatial intermittency of the magnetic field persists even up to the chromospheric heights. The small-scale bright elements visible in the bright network lanes of the solar network structure as seen in the Ca ii H images are termed network bright points. We use special Hinode campaigns devoted to the observation of polar regions of the Sun to study the polar network bright points during the phase of the last extended solar minimum. We use Ca ii H images of chromosphere observed by the Solar Optical Telescope. For magnetic field information, level-2 data of the spectro-polarimeter is used. We observe a considerable association between the polar network bright points and magnetic field concentrations. The intensity of such bright points is found to be correlated well with the photospheric magnetic field strength underneath with a linear relation existing between them.

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Correcting for Cryoprecipitation in the Calibration of IR Channels of the MSU-MR Radiometer     

Alexanin  A. I.  Gektin  Yu. M.  Diakov  S. E.  Zaitsev  A. A.  Kachur  V. A. 《Izvestiya Atmospheric and Oceanic Physics》2018,54(9):1408-1414

Izvestiya, Atmospheric and Oceanic Physics - The presence of cryoprecipitation, which forms a thin film on the input windows of infrared (IR) detectors and distorts the signal, is a major issue in...  相似文献   

The World’s Largest Fouta Djallon–Mandingo Bauxite Province (West Africa): Part III. The Influence of Geomorphic Factors and the Age of Relief on the Spatial Distribution,Size, and Quality of Bauxite Deposits     

Mamedov  V. I.  Makarova  M. A.  Zaitsev  V. A. 《Geology of Ore Deposits》2022,64(1):15-42

Geology of Ore Deposits - The scheme of geomorphic evolution of the region was substantially refined, compared to the previous understanding, based on the results of geologic and geomorphic...  相似文献