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We present a model for the transport of anisotropic turbulence in an accretion disc. The model uses the Reynolds stress tensor approach in the mean field approximation. To study the role of convection in a protoplanetary disc, we combine the turbulence model with a radiative transfer calculation, and also include convection using the mixing length approximation. We find that the turbulence generated by convection causes the angular momentum of the accretion disc to be directed outwards. We also confirm the conclusions of other authors that turbulent convection is unable to provide the observed disc accretion rates as well as a heat source sufficient for the convection to be self-sustaining. The reasons for the latter are the strong anisotropy of the turbulence together with the low efficiency of the energy transfer from the background velocity shear to the turbulent stress tensor. [ABSTRACT FROM AUTHOR]

Results of three-dimensional gas-dynamical numerical simulations of the structure of matter flows in semi-detached binary systems with various component-mass ratios are considered. The main elements of the flows in the models studied are described. The characteristics of density waves inside the accretion disk for various component-mass ratios are considered. The influence of the precessional density wave on the development of instability in the accretion disks and the characteristics of developing turbulence are analyzed. Values of the Shakura-Syunyaev coefficient α for the simulated systems are calculated. [ABSTRACT FROM AUTHOR]

Accretion disks around young binary stars are subject to strong forces exerted by the system components. Gas-dynamical interactions excite strong non-linear perturbations in the disk, which can give rise to turbulence. This study considers a mechanism for the excitation of turbulence based on the instability of non-linear waves in a rotating flow. It is shown that the spectrum of non-linear perturbations excited in the inner part of the disk leads to turbularization of the flow. Estimates of the Shakura-Syunyaev index, α ∼ 0.01−0.05, are obtained for use in numerical models of accretion disks. [ABSTRACT FROM AUTHOR]

We present a method that can be used to recover the spectrum of turbulence from observations of optically thin emission lines formed in astrophysical discs. Within this method, we analyse how line intensity fluctuations depend on the angular resolution of the instrument, used for the observations. The method allows us to restore the slope of the power spectrum of velocity turbulent pulsations and estimate the upper boundary of the turbulence scale. [ABSTRACT FROM AUTHOR]

We suggest a model for the star-formation function and the dissipation of turbulent energy of the interstellar medium. The star-formation function takes into account the effect of turbularization of the ISM. Applying the derived relations to a hierarchical scenario for the formation of galaxies makes it possible to explain the observed delay of star formation in the Galaxy, which corresponds to a range of stellar ages from 8–9 to 10–12 Gyr. [ABSTRACT FROM AUTHOR]