Modeling the effect of plasma density on the dynamics of the microwave spectrum of solar flaring loops

The energetic electron distribution dynamics and radioemission have been numerically simulated in order to interpret three characteristic types of the frequency spectrum slope dynamics between 17 and 34 GHz in different parts of solar flaring loops observed with the Nobeyama Radioheliograph. In all types, the spectrum slope decreases at the rise phase of microwave burst. The behavior is qualitatively different at the decay phase of the burst: the spectrum slope increases immediately after the burst maximum in the first type; continues decreasing or stabilizes, not reaching zero, in the second type; and continues decreasing to zero and becomes positive in the third type. The parameters at which the calculated dynamics of the frequency spectrum slope in different parts of the magnetic loop most strictly corresponds to the observed dynamics have been found. It has been indicated that the first type of the spectrum slope dynamics is related to an increase and decrease in the radio source optical thickness at the rise and decay phases, respectively. The second type is caused by the flattening of the electron energy spectrum that continues at the decay phase. The third type is related to a gradual flattening process of the electron energy spectrum, combined with a large ratio of the plasma density to the magnetic field strength (n ₀ /B) within a loop, and is explained by the Razin effect.     

Synthetic Doppler tomograms of gas flows in the binary system IP Peg

We have synthesized Doppler tomograms of gas flows in the binary system IP Peg using the results of three-dimensional gas-dynamical computations. Gas-dynamical modeling in combination with Doppler tomography enables identification of the key elements of flows in Doppler maps without solution of an ill-posed inverse problem. A comparison of the synthetic tomograms with observations shows that, in the quiescent state of the system, the most luminous components are (1) the shock wave induced by interaction between the circumbinary envelope and the stream from the Lagrange point L ₁ (the “hot line”) and (2) the gas condensation at the apogee of the quasi-elliptical disk. Both the single spiral shock wave arm in the gas-dynamical solution and the stream from L ₁ contribute little to the luminosity. In the active state of the system, when the stream from L ₁ does not play an appreciable role and the disk dominates, both areas of enhanced luminosity in the observational tomograms are associated with the two arms of the spiral shock wave in the disk.     

Sr isotope chemostratigraphy of Upper Jurassic carbonate rocks in the Demerdzhi Plateau (Crimean Mountains)

The first Sr chemostratigraphic data are obtained for the Upper Jurassic carbonate sections in the Demerdzhi Plateau of the Crimean Mountains. The oncoid, microbial, and organogenic-detrital limestone varieties representing shallow-water marine microfacies of the carbonate platform served as material for these studies. The limestone samples for reconstructing the isotopic parameters of depositional environments were selected using geochemical criteria (Mn/Sr < 0.2, Fe/Sr < 1.6, Mg/Ca < 0.024) and subjected to the preliminary treatment in a 1 N ammonium acetate solution. The ⁸⁷Sr/⁸⁶Sr value in the least altered samples increases up the section from 0.70701 to 0.70710. The obtained ⁸⁷Sr/⁸⁶Sr values are correlated with the Sr isotope properties of belemnite rostrae characterizing the Pectinatites scitulus-Pavlovia rotunda ammonite zone in the zonal scale of the Boreal realm, Hyponoticeras hybonotum-M. ponti/B. peroni Zone in the zonal scale of the Tethyan realm, and lower part of the Dorsoplanites panderi Zone in the zonal scale for the transitional domain of the East European Platform. The Sr chemostratigraphic correlation indicates the early Tithonian age of sediments developed in the eastern part of the Demerdzhi Plateau and restricts the upper boundary of the limestone section redeposited within carbonate breccia of Mount Severnaya Demerdzhi to the terminal early Tithonian. The Sr isotope data are used for calculating the sedimentation rates for limestones. They are estimated to be at least 0.23 m/1000 years, which is an anomalously high value for pre-Quaternary carbonate platforms.     

United classification of cosmic gamma-ray bursts and their counterparts

This paper establishes united classification of gamma-ray bursts and their counterparts on the basis of measured characteristics: photon energy E and emission duration T. We find that the interrelation between these characteristics is such that as the energy increases, the duration decreases (and vice versa). The given interrelation reflects the nature of the phenomenon and forms the E–T diagram, which represents a natural classification of all observed events in the energy range from about 10⁹ to 10⁻⁶ eV and in the corresponding interval of durations from about 10⁻² up to 10⁸ s. The proposed classification results from our findings, which are principal for the theory and practical study of the phenomenon.     

Some Promising Avenues of Carbonate Rocks Investigation

Achievements in the study of modern carbonate sediments and ancient sedimentary carbonate rocks, as well as recent data pose new problems and generate a need for the revision of some seemingly unambiguous concepts. The prevalent role of biogenic and, first of all, microbial sedimentation of carbonate (including dolomitic) material and specific nontraditional settings of carbonate accumulation (intermediate and even high latitudes, deep-water basins) becomes more and more evident. The study of the internal structure of carbonate formations and its relationship with specific features of carbonate material deposition, climate, basin depth, and other factors represent a new important problem. The existing concepts of carbonate accumulation evolution need to be revised both from the standpoint of its factual reflection in sedimentary sequences and explanation.     

Paleoproterozoic Age of Gneiss-Granites of the Mamskaya Zone (Baikal–Patom Belt): Geological Implications

Doklady Earth Sciences - This article presents the results of U–Pb geochronological study of gneiss-granites of the Mamskaya zone. The age estimate of 1874 ± 9 Ma (SIMS method) obtained...     

Diversity of Archaeocyaths and Sr Chemostratigraphy of the Lower Cambrian of West Transbaikalia,Uda–Vitim and Birami–Yanguda Zones

Doklady Earth Sciences - The morphology of archaeocyaths from the Oldynda Formation of the Uda–Vitim lithofacial zone and the Aikta Formation of the Birami–Yanguda Zone of West...     

Interpretation of orbital light curves of U Geminorum

We interpret optical and IR orbital light curves of the dwarf nova U Gem in its quiescent state in the framework of “hot line” and “hot spot” models. The hot-line model provides an adequate fit to the light curves, while the hot-spot model is not fully consistent with the observations. The minimum χ² residuals for the hot-spot and hot-line models are 2203 and 168, respectively.     

Determining the Preliminary Orbit in the Non-Coplanar Case

Solar System Research - An algorithm for finding a solution for determining a preliminary orbit in the noncoplanar case, when the plane of the desired orbit does not coincide with the plane of...     

Sr isotopic characteristic of neoproterozoic carbonate sediments from the southern Yenisei Ridge

This paper presents the first Sr isotopic data for the Late Precambrian carbonate rocks of the southern Yenisei Ridge. Their geochemical study allowed estimation of the degree of secondary alterations and gave the possibility to reveal rocks with a less disturbed Rb-Sr isotopic system. The Sr isotopic data indicated Neoproterozoic sedimentation of the rocks about 1070–750 Ma ago. Sr and C isotopic data showed that carbonate rocks of the Sukhoi Pit, Tungusik, and Shirokino groups are Late Riphean and could be comparable with sedimentary sequences of three Precambrian key sections of the Northern Eurasia: the subsequent Derevnino, Burovaya, and Shorikha formations from the Turukhansk Uplift, the Lakhanda Group from the Uchur-Maya region, and the Karatav Group from the South Urals. All studied carbonate rocks are older than 750 Ma and, according to the International Stratigraphic Chart, accumulated prior to global glaciations in the Cryogenian. This is evident from sedimentological study indicating the absence of tillite horizons in the studied sections. δ¹³C values in the sections vary from +0.4 up to +5.3‰, which testifies to the absence of periods of great cold.