Propagation of a quasi bi-annual impulse close to the moment of the solar magnetic field polarity changing

Some particular features of solar differential rotation have been recently revealed in Abastumani Astrophysical Observatory: in the northern hemisphere of the Sun a propagation of a quasi bi-annual impulse of the rotation residual from the high latitudes to the equator, during the time interval of 1979–1981, was statistically demonstrated. Japaridze and Gigolashvili (1992) proposed that this event might be related with the change of magnetic polarity in the northern hemisphere of the Sun in 1981.To prove this hypothesis an investigation of the MHD equations in the local system of coordinates has been carried out. A homogeneous equation with partial derivatives in the linear approximation was obtained. Its solution is presented analytically. The disturbance of velocity enhances especially at the moment of reversal of magnetic field polarity.     

Symplectic methods and their application to the motion of small bodies in the Solar System

Symplectic methods have been widely used in Solar System dynamics. This paper discusses both single step and multistep symplectic methods. For single step methods we point out that the modified algorithm (Wisdom et al., 1991, Kinoshita et. al., 1991) can be executed in the mass center coordinate system and in the Jacobian coordinate system. For multistep methods we describe the connections between symmetric and symplectic methods.     

A photometric study of the bright stars in M33

TheUBV photometry of 105 bright stars and theU magnitudes of 36 bright stars in M33 taken by the 2 m RCC telescope of the Rozhen Observatory at the Bulgarian Academy of Sciences were used to obtain colour-magnitude and colour-colour diagrams. A criterion forV, B-V, andU-B is suggested which facilitates the separation of the member stars from the foreground stars. The vast majority of the bright blue stars with strong negativeU-B are M33 members. The existence of objects with an unusual combination of colours (B-V>0.5 and strong negativeU-B) has been confirmed.     

Plasma model of pulsar emission and some observational consequences

Abastumani Astrophysical Observatory; P. N. Lebedev Physics Institute, USSR Academy of Sciences. Translated from Astrofizika, Vol. 34, No. 3, pp. 433–448, May–June, 1991.     

Cosmic-ray tracks and cobalt-60 in near-surface samples of the Jilin chondrite

Abstract— Cosmic-ray track densities (CRTDs) have been measured on several spot samples from two Jilin specimens from the strewn field (VI-21-057 and VI-42-04), along with ⁶⁰Co activity in three and four sections, respectively, of the same specimens. The observed CRTD gradient agrees remarkably well with that predicted by Bhattacharya et al.'s calculations (1973) of CRTD variation as a function of shielding depth, which indicates a negligible contribution from the first 2π-irradiation stage. The shortest distance of each specimen to the preatmospheric surface is 3.6 cm and 6.8 cm, respectively. The distance scale deduced from these measurements allows the determination of the variation of ⁶⁰Co activity with shielding depth, at low depth values, which is found to be much less steep than model predictions. Two slightly different ⁶⁰Co profiles are proposed that correspond to the two specimens studied. The mean preatmospheric radius of the Jilin chondrite is 85 ± 8 cm, the uncertainty reflecting in part the meteoroid surface roughness.     

The regular motion of an axisymmetrical satellite in the field of a triaxial body

This paper investigates the regular motions of an axisymmetrical satellite in the field of Newton's attraction of a triaxial body. Both the orbital and the self rotational motions of the two bodies are taken into consideration. The exact solutions are discussed using Poincaré's method of small parameter. In the decomposition of the force function all the harmonic terms up to the third order are taken into account.The results show the existence of eight solutions. The stability of the new group of solutions is discussed using two methods to get the necessary and sufficient conditions required for the stability of these motions.     

The gravitation theory in bimetric formulation

The gravitation theory is considered in bimetric formulation with a Lagrangian of the most common type and quadratic with respect to the derivativesg _ik/l of the metric tensor. Restrictions on the dimensionless parameters of the theory are found, basing on the comparison with the Newtonian theory and the analysis of corresponding observational data in the vicinity of the solar system. Propagation of the weak gravitation waves is investigated in the outside gravitational field.     

A determination of the parameters of the level surface of lunar gravity

The spectral coefficients of the selenoid have been obtained by inverting the potential series for lunar gravity. The reference value of the lunar level surface has been determined on the base of the mean radius of lunar topography. This enables to evaluate the parameters of the tri-axial reference ellipsoid best fitted to the lunar level surface.     

The evolution of the Gulf of Corinth (Greece): an aftershock study of the 1981 earthquakes

Summary. A preliminary study of the aftershocks of three earthquakes that occurred near to Corinth (Greece) in 1981 is combined with observations of the morphology and faulting to understand the evolution of the Eastern Gulf of Corinth. The well located aftershocks form a zone 60km long and 20km wide. They do not lie on the main fault planes and are mostly located between the north-dipping faulting on which the first two earthquakes occurred and the south-dipping faulting associated with the third event. A cluster of aftershocks also lies in the footwall of the eastern end of the south-dipping fault of the third event.
Morphologically, it is observed that in the evolution of the Eastern Gulf of Corinth, antithetic faulting apparently predates the appearance of the main faulting at the surface. This evolution can be explained by motion on a deep seated, shallow angle, aseismic normal fault. A model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes.