Vol 61, No (2016)

In this paper, mathematical models of compressible viscoelastic Maxwell, Oldroyd, and Kelvin- Voigt uids are derived. A model of rotating viscoelastic barotropic Oldroyd uid is studied. A theorem on strong unique solvability of the corresponding initial-boundary value problem is proved. The spectral problem associated with such a system is studied. Results on the spectrum localization, essential and discrete spectra, and spectrum asymptotics are obtained. In the case where the system is in the weightlessness state and does not rotate, results on multiple completeness and basisness of a special system of elements are proved. In such a case, under condition of su ciently large viscosity, expansion of the solution of the evolution problem with respect to a special system of elements is obtained.

In this paper, explicit integral volume formulas for arbitrary compact hyperbolic octahedra with mm2-symmetry are obtained in terms of dihedral angles. Also we give an algorithm for calculation of volume of such octahedra in spherical space.

In a Banach space E, the Cauchy problem vt(t)+ A(t)v(t)= f (t) (0 >t > 1), v(0) = v0 is considered for a di erential equation with linear strongly positive operator A(t) such that its domain D = D(A(t)) is everywhere dense in E independently o t and A(t) generates an analytic semigroup exp{-sA(t)} (s < 0). Under some natural assumptions on A(t), we establish coercive solvability of the Cauchy problem in the Banach space C0β,γ (E). We prove a stronger estimate of the solution compared to estimates known earlier, using weaker restrictions on f(t) and v0.