Growth of R 1 − y Sr y F3 − y crystals with rare earth elements of the cerium subgroup (R = La, Ce, Pr, or Nd; 0 ≤ y ≤ 0.16) and the dependence of their density and optical characteristics on composition

Crystals of the R _{1 ? y} Sr _y F_{3 ? y} phases (R = La, Ce, Pr, or Nd; 0 ≤ y ≤ 0.16) with tysonite (LaF₃) structure are grown by the Bridgman method. A linear dependence of the crystal density on the SrF₂ concentration has been revealed for each series of solid solutions. A scheme of heterovalent isomorphous substitution in the tysonite structure, R ³⁺ + F^1? → M ²⁺ + V _F, with compensation of the difference in the cation charges due to the formation of anion vacancies, is confirmed experimentally. The optical transmission spectra are measured in the wavelength range λ = 2.18–22.22 μm. It is shown that the 50%-transmission edge in the IR range is 10.5 μm for all crystals. The refractive index and the polarizability of crystals decrease with decreasing SrF₂ content according to a linear law. The melting curves of the R _{1 ? y} Sr _y F_{3 ? y} phases studied have a maximum; therefore, these phases can be recommended for use as crystals with a high homogeneity and different optical properties in comparison with the corresponding RF₃ crystals.     

Method of molecular dynamics in mechanics of deformable solids

The basic principles of the method of molecular dynamics are analyzed. Symplectic difference schemes for the numerical solution of molecular dynamics equations are considered. Stability is studied, and the errors in the energy conservation law, which are induced by using these schemes, are estimated. Equations of mechanics of continuous media are derived by means of averaging over the volume of an atomic system. Expressions for the stress tensor are obtained by using the virial principle and the method of averaging over the volume. The principles of construction of EAM and MEAM potentials of atomic interaction in crystals are analyzed. Two problems of fracture of copper-molybdenum composites are solved by the method of molecular dynamics.     

Discriminability of tryptophan containing dipeptides using quantum control

We show that the coherent manipulation of molecular wavepackets in the excited states of trp-containing dipeptides allows efficient discrimination among them. Optimal dynamic discrimination fails, however, for some dipeptide couples. When considering the limited spectral resources at play (3 nm bandwidth at 266 nm), we discuss the concept of discriminability, which appears uncorrelated to both static spectra and relaxation lifetimes.     

Evolution of the spectral characteristics upon annealing of lithium borate glasses containing europium and aluminum

The spectral and structural characteristics of lithium borate glasses containing europium and aluminum have been investigated upon annealing at different temperatures. It has been found that the spectral characteristics of the studied system change nonmonotonically with an increase in the annealing temperature. After annealing at a temperature of 600°C, the luminescence spectra of the glasses exhibit broad structureless bands that are specific for the amorphous phase containing Eu³⁺ ions. Then, after annealing at T = 700°C, narrow lines appear in the wavelength ranges 585–595 and 610–620 nm, which correspond to the luminescence of the Eu(BO₂)₃ and EuAl₃(BO₃)₄ borates. A further increase in the annealing temperature (T = 800–900°C) leads to the disappearance of europium aluminum borate. In the luminescence spectra of these samples, there are narrow bands in the wavelength range λ = 585–595 nm, which are typical of europium metaborate. Finally, at a temperature of 1050°C, these bands disappear and narrow lines appear again in the wavelength range 610–620 nm, which are characteristic of the EuAl₃(BO₃)₄ borate. Thus, the temperature annealing makes it possible to purposely change the spectral characteristics of the studied system in the wavelength range 590–615 nm.     

The Electrical Properties of Emulsions Containing a Magnetic Fluid as the Dispersion Medium

A magnetosensitive emulsion comprising glycerin microdroplets dispersed in a magnetic fluid is studied. Being subjected to a magnetic field, the emulsion exhibits anisotropic light scattering and permittivity. The observed effects are explained by the formation of the chainlike structures of the microdroplets.     

Structure of unilamellar vesicles: Numerical analysis based on small-angle neutron scattering data

The structure of polydispersed populations of unilamellar vesicles is studied by small-angle neutron scattering for three types of lipid systems, namely, single-, two-and four-component vesicular systems. Results of the numerical analysis based on the separated-form-factor model are reported.