Shallow water model for lakes with friction and penetration

We deduce a shallow water model, describ‐ ing the motion of the fluid in a lake, assuming inflow–outflow effects across the bottom. This model arises from the asymptotic analysis of the 3D dimensional Navier–Stokes equations. We prove the global in time existence result for this model in a bounded domain taking the nonlinear slip/friction boundary conditions to describe the inflows and outflows of the porous coast and the rivers. The solvability is shown in the class of solutions with L_p‐bounded vorticity for any given p∈(1,∞]. Copyright © 2009 John Wiley & Sons, Ltd.     

Data-sparse approximation to the operator-valued functions of elliptic operator

In previous papers the arithmetic of hierarchical matrices has been described, which allows us to compute the inverse, for instance, of finite element stiffness matrices discretising an elliptic operator The required computing time is up to logarithmic factors linear in the dimension of the matrix. In particular, this technique can be used for the computation of the discrete analogue of a resolvent

In the present paper, we consider various operator functions, the operator exponential negative fractional powers , the cosine operator function and, finally, the solution operator of the Lyapunov equation. Using the Dunford-Cauchy representation, we get integrals which can be discretised by a quadrature formula which involves the resolvents mentioned above. We give error estimates which are partly exponentially, partly polynomially decreasing.

     

Defects of colloidal crystals

Reasons for the appearance of defects of various types in crystalline colloidal structures formed during the self-organization of the ensembles of spherical nanoparticles are analyzed using lyosols of metal nanoparticles stabilized with polymers as examples. Quantitative characteristic of the degree of imperfection of colloidal crystals is proposed and the procedures for the minimization of the degree of imperfection are discussed. Order-disorder phase transitions of colloidal crystals are studied.     

Rate of convergence of the method of lines for the nonlinear parabolic integrodifferential equation describing a photon recycling diode

We consider the Dirichlet problem and the mixed boundary-value problem for a nonlinear integro-differential equation of a parabolic type, which provides a mathematical model of the various modes in a photon-recycling semiconductor diode. The existence of the mixed derivative ²u/tx is proved for the solution of these problems. Method-of-lines schemes are constructed. An O(h) rate of convergence bound is established for the equation with nonlinear integral and differential components and an O(h²) bound for the equation with a nonlinear integral part.Kiev University. Translated from Vychislitel'naya i Prikladnaya Matematika, No. 74, pp. 21–31, 1992;     

Influence of the ferromagnetic structure on the speed of propagation of magnetoelastic vibrations

The effect of thermomagnetic treatment temperature on the speed of magnetoelastic vibrations propagating in aFe _81.5 B _13.5 Si ₃ C ₂ metal alloy is investigated. A minimum is found in the plot of the dependence of the speed of magnetoelastic vibrations on the thermomagnetic treatment temperature. No minimum is observed in this dependence for amorphous metal alloys treated without magnetic field. It is found that the dependences of the speed of magnetoelastic vibrations on the external magnetic field differ for samples treated differently. The results obtained are explained based on concepts of reorganization of the domain structure of the samples under study. Irkutsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 46–49, September, 1999.     

Spin correlations and a mesoscopic structure in Ni-Mn-Ga

The mesoscopic structures of the Heusler alloys Ni_49.1Mn_29.4Ga_21.5 and Ni₂MnGa are studied by small-angle polarized neutron scattering in the temperature range 15 < T < 400 K. The characteristic temperatures of phase transformations (ferromagnetic, martensitic, and premartensitic transformations) and the characteristic sizes of mesoscopic inhomogeneities in them have been determined. Differences in the spin dynamics of these phases and magnetic-nuclear interference upon neutron scattering have been revealed. The evolutions of the mesoscopic structures in the nonstoichiometric and stoichiometric alloys are found to be substantially different.