Conditions and mechanisms of origination of gravitational instability in layered bulk-elastic geomasses

Various geophysical processes which can lead to the origination of gravitational instability of the Rayleigh-Taylor type in layered bulk-elastic geomasses are analyzed. The analysis is based on obtained by the authors general results of theoretical study of two-layer systems of heavy bulk-elastic materials which are arbitrarily stratified over depth and occupy domains of arbitrary shape. Additionally some presented in a number of recent publications erroneous assertions related to considered issues of stability, are criticized.     

Interaction of acoustic oscillations with an active region on the Sun

Based on MDI data, we constructed acoustic maps of the high-degree solar oscillations as they interacted with the active region NOAA 7978 using the acoustic imaging technique. We analyze the reconstructed power maps for the incoming and outgoing oscillations, as well as the phase-shift maps and the envelope-shift maps of wave packets in the frequency range 3.0–5.0 mHz. We perform a cross-correlation analysis of the time series for the acoustic oscillations before and after their interaction with the active region and analyze direct observational data. Our results point to a difference between the phase and envelope shifts. Thus, for example, the phase and group velocities of the oscillations increase as they pass through a sunspot, with the increase in group velocity being more significant. We found a phase-shift difference between the inward and outward propagating oscillations, ~0.4–0.5 min. This difference is interpreted as the effect of subsurface flow from the active region.     

Miocene dislocations during the formation of the Sea of Japan basin: Case study of Tsushima Island

Lower Miocene rocks of the Taishu Group accumulated in the Tsushima pull-apart graben, which downwarped and was filled with sediments at a particularly high rate (about 2700 m/Ma), in the background of northeastern regional shortening. A considerable part of the sedimentary prism is composed of material supplied by landslide blocks from the shallow shelf. Folding and penetration of granite intrusions on Tsushima Island occurred ca. 15 Ma ago, simultaneously with the main phase of opening of the Sea of Japan, in the field of different, northwestern shortening, which had a local character and was related to clockwise rotation of the Southwestern Japan block. These rotations in turn could have been the result of an intensive rifting episode in the Central and Honshu basins of the Sea of Japan, which are located north of Tsushima Island.     

Caledonian formation of gold-bearing sulfide depositions in Early Proterozoic gabbroids in the northern Ladoga region

We have studied Pb isotopic systems of K-feldspar, pyrite, and pyrrhotine from gabbroids and ore of the Velimyaki Early Proterozoic massif in the northern Ladoga region in the southeastern part of the Fennoscandian Shield. The isochronous Pb–Pb age of sulfides has been determined as ～450 Ma, which corresponds to intersection of the regression line with the lead accumulation curve with μ = 10.4–10.8; the model Pb age of sulfides is close to isochronous under the condition that the composition of lead evolved from a geochemical reservoir with an age of 1.9 Ga. The isotopic parameters of the lead in sulfides and K-feldspar indicate their formation in upper crust conditions (μ = ²³⁸U/²⁰⁴Pb > 10). From the obtained data, it follows that the isotopic composition of lead in K-feldspar corresponds to a Proterozoic age (1890 Ma) of magmatic crystallization of the rocks in the massif, and strongly radiogenic lead sulfides testify, with the greatest probability, to the later (Caledonian) formation of sulfide ores.     

Statistical study of the north–south asymmetry of the solar differential rotation based on various solar structures during 1966–1985

The time variation and latitude dependence of the solar rotation are found using observational data on Hα filaments and compact magnetic features with different polarities during solar activity cycles 20 and 21 (1966–1985). Statistical analysis of the observational data shows that there is a north–south asymmetry in the rotation, both for the Hα filaments and for compact magnetic features (structures) with negative and positive polarities. The N-S asymmetry in the differential rotation of the Hα filaments and the compact magnetic features with both polarities shows up quite distinctly in solar activity cycles 20 and 21, but the asymmetry for the compact magnetic features with positive polarity is comparatively lower in cycle 21. The confidence level is lower the compact magnetic features with positive polarity than for the compact magnetic features with negative polarity.     

The bimetric theory of gravitation with a dynamic background metric

We study the bimetric theory of gravitation with background metric _ik. In contrast to the accepted point of view, in which _ik, is a metric given a priori, we assume that _ik is a dynamic variable determined from the condition that the total action of the gravitating system must be an extremum. As a result it turns out that (1) _ik can be described by the Einstein equation in space-time with the metric _ik and (2) the energy-momentum tensor of the graviational field _ik, is the source of _ik. In this sense _ik can be considered a secondary field in relation to g_ik. We determine the conditions for existence of integral covariant conservation laws. Two of the latter have no analogs in the theory with the background metric given a priori.Translated fromAstrofizika, Vol. 37, No. 3, 1994.The author is grateful to the participants in the seminar of the Department of Theoretical Physics at Erevan State University, and also to W. Bleier, K. A. Bronnikov, V. N. Mel'nikov, and G. Yu. Treder for discussions and valuable remarks. The investigations presented in this paper were partly financed by the International Scientific Fund, grant Ph1-262-0902.     

On the problem of lunar time

New achievements in lunar investigations by spacecrafts provide the reasons why some new international scale of special lunar time nowdays is under discussion. However, the introduction of special time scales for other celestial bodies would turn to be a complex affair. To document this point of view it is shown that, both for making precise astrometrical calculations and for creating a lunar calendar, it should be reasonable to make use of the generally accepted scales of terrestrial time; there is no real need to introduce any special lunar time unit. For calendar needs it is suggested to introduce a local scale of time based on count of the lunations and usual mean solar time units being used within the every lunation.     

Second catalogue of X-ray sources

A catalogue of X-ray sources containing 677 objects known as of 1979 September has been compiled. X-ray data collected by means of rockets, balloons, and satellites during 1964–1979 are listed. Optical and radio counterparts are suggested. The existence of the weak X-ray sources population in the Galaxy is indicated. The number of X-ray sources of each type in the Galaxy is estimated.Astrophysics and Space Science review paper.