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Helioseismology is a direct and most informative method of studying the structure and dynamics of the Sun. Determining the internal differential rotation of the Sun requires that the frequencies of its eigentones be estimated with a high accuracy, which is possible only on the basis of continuous long-term observations. The longest quasi-continuous series of data have been obtained by the Global Oscillation Network Group (GONG). The parameters of each individual mode of solar acoustic oscillations with low spherical degrees l = 0, 1, 2, 3, 4, 5, 6 are determined by using 1260-day-long series of GONG observations. The mean frequency splitting by rotation for the modes of each radial order n is calculated by using all possible combinations between the eigenfrequencies in multiplets. As a result, it has become possible to statistically estimate the splitting and its measurement errors for the modes of each radial order. The mean splitting for each given degree l = 1-6 is presented under the assumption of its independence of oscillation frequency, which holds for the achieved accuracy. The frequencies and splittings for the modes with low spherical degrees l, together with the MDI group results for higher degrees l, are used to invert the radial profile of solar angular velocity. Using the SOLA method to solve the inverse problem of restoring the rotation profile has yielded solutions sensitive to the deepest stellar interiors. Our results indicate that the solar core rotates faster than the surface, and there may be a local minimum in angular velocity at its boundary. [ABSTRACT FROM AUTHOR]

Fourier analysis of the R. Davis group data has been carried out. A method of signal selection at small signal/noise ratio was suggested and significance levels of individual peaks in the spectrum were determined. The correlation coefficients of neutrino fluxes and some characteristics of solar activity were calculated. The analysis conducted allowed us to reveal three significant peaks in the spectral density of Ar production rate in Cl detector: 113.8, 55.6, and 26.6 months (with a ratio of ∼ 4∶2∶1). The probability of a random origin of these peaks is less than 4%. [ABSTRACT FROM AUTHOR]

The asymptotic properties of the gravity modes of solar models with a mixed core have been investigated. In this model, the Brunt-Väissälä frequency has a strong enhancement in the region of variable chemical composition at the boundary of the mixed core, giving rise to a non-equidistant spectrum of gravity modes periods. An asymptotic expression for the periods is derived, which relates the main feature of the departure from period equidistance to the stratification of the model. Qualitative agreement with the numerical periods of the model is obtained. [ABSTRACT FROM AUTHOR]

We have revealed the periods of good visibility for each individual mode of low spherical degree ℓ using irradiance data from the IPHIR experiment. Their statistical properties and the influence on the resulting line shapes are discussed. The analysis of the temporal change of each mode power by Fourier transform with a running temporal window was performed. The running mean power of p-modes (ℓ=0, n=17–24 and ℓ=1, n=16–23) apparently changes with the rotation of the Sun. There is well visible an anticorrelation of the p-mode power with the mean solar magnetic field and less significant correlation with daily sunspot number. [ABSTRACT FROM AUTHOR]

The asymptotic properties of the gravity modes of solar models with a mixed core have been investigated. Such models have been constructed by Gavryusev and Gavryuseva (1984) to explain the low value of the observed neutrino flux (Cleveland, Davis, and Rowly, 1984). The strong enhancement of the Brunt-Väissälä frequency in the region of variable chemical composition at the boundary of the mixed core gives rise to a nonequidistant spectrum of gravity mode periods (Figure 1), contrary to the case of 'standard' models. These models do not satisfy the helioseismological constraints given by the p-modes. However, the peculiar behavior of the numerically computed periods of the gravity modes is interesting to analyze, in view of observational detection in solar and stellar spectra. [ABSTRACT FROM AUTHOR]

Aging at 20°C: I-0-72 h lowering of the stress reaches 15%; II-72-500 h, initially the relaxation process occurs intensely with the stresses lower by 40% after 48 h of aging after which they monotonically lower according to an exponential function. The lowering of the stress after 500-h aging at 20°C reaches 80%. Aging at 125°C: I-0-24 h, the stress falls by 40%; II-24-500 h, there is an insignificant lowering of the stress. After 500 h of aging at 125°C the stress lowers by 50%. [ABSTRACT FROM AUTHOR]