IR spectra and structure of 4-thiobarbituric acid derivatives

On the basis of data from the IR spectra of 4-thiobarbituric acid derivatives, and their deutero analogs, and similarly constructed model compounds, it was established that the investigated substances exist in the thione lactam form and form two types of associates through intermolecular hydrogen bonds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1416–1419, October, 1977.     

Magnetic neutron diffraction under pressures up to 43 GPa. Study of the EuX and GdX compounds

We present some recent results on magnetic neutron studies at pressures above 40 GPa. We used diamond and sapphire anvil pressure cells for low temperature neutron studies and a powder diffractometer specialized for high pressure studies. Focusing systems and low-background conditions allowed us to study samples with volumes as small as 0.001 mm³ in a diamond anvil cell at a pressure of 50 GPa. This technical progress allowed us to obtain new results in studies of “textbook” magnetic insulators EuX (X = S, Se, Te) and GdX (X = As, Sb, Bi). We found new magnetic phases. In the Eu-chalcogenides we observed a strong anion-dependent increase of the ferromagnetic exchange with decreasing lattice constant. In contrast, in the GdX compounds the antiferromagnetic order remains stable up to a pressure of 43 GPa. We show the importance of our results to understand the origin of indirect exchange interactions in magnetic semiconductors with well localized magnetic shells. This revised version was published online in July 2006 with corrections to the Cover Date.     

Homogenization of a convection–diffusion equation in perforated domains with a weak adsorption

The aim of this paper is to study the asymptotic behavior of the solution of a convection–diffusion equation in perforated domains with oscillating velocity and a Robin boundary condition which describes the adsorption on the bord of the obstacles. Without any periodicity assumption, for a large range of perforated media and by mean of variational homogenization, we find the global behavior when the characteristic size ε of the perforations tends to zero. The homogenized model, is a convection–diffusion equation but with an extra term coming from the weak adsorption boundary condition. An example is presented to illustrate the methodology.     

Random oscillations of elastic bodies and the theory of Markov processes

Kiev University. Translated from Prikladnaya Mekhanika, Vol. 27, No. 8, pp. 95–100, August, 1991.     

σ Derivatives of cyclopentadienyldicarbonyliron with five-membered heterocycles

Russian Chemical Bulletin -     

Numerical solution of a boundary-value problem of elasticity theory for a body with an inclusion

We consider the problem of steady-state oscillations of a plane body with an inclusion. A solution algorithm is constructed. Computational experiments are described, which establish the applicability of the proposed procedure for analyzing the effect of defects inside the body on wave fields excited by ultrasonic sources.Kiev University. Translated from Vychislitel'naya i Prikladnaya Matematika, No. 75, pp. 83–87, 1991.     

Investigation of the properties of weakly reflective metamaterials with compensated chirality

The properties of an artificial anisotropic structure formed by microhelices have been numerically simulated by the example of a specially designed sample. The sample contains paired helices with right- and left-handed twisting directions, due to which the metamaterial chirality is compensated for. Helices are characterized by precalculated optimal parameters; as a result, the permittivity and permeability of metamaterial are approximately equal. Therefore, the wave impedance of the structure is close to the impedance of free space in the frequency range near 2 THz and the reflection of normally incident electromagnetic waves is weak. A boundary problem is solved and an analytical expression is obtained for the reflection and transmission coefficients of an electromagnetic wave passing through the structure. The simulated properties of the structure are compared with experimental results.