Volume 104, Nº 4 (2016)

It is theoretically shown that the Coulomb interaction between violations of the Bernal–Fowler rules leads to a temperature-induced stepwise increase in their concentration by 6–7 orders of magnitude. This first-order phase transition is accompanied by commensurable decrease in the relaxation time and can be interpreted as melting of the hydrogen bond network. The new phase with the melted hydrogen lattice and survived oxygen one is unstable in the bulk of ice, and further drastic increase in the concentrations of oxygen interstitials and vacancies accomplishes the ice melting. The fraction of broken hydrogen bonds immediately after the melting is about 0.07 of their total number that implies an essential conservation of oxygen lattice in water.

The temperature dependence of the heat capacity at second-order phase transitions that were previously detected in the [Zn₂(C₈H₄O₄)₂ · C₆H₁₂N₂] metal-organic framework compound has been analyzed. The critical exponents have been obtained. It has been shown that the behavior of the heat capacity below the critical temperature of 60 K, which is attributed to the violation of the mirror symmetry of C₂H₁₂N₆ molecules, is exponential.

The formation of unusual chain structures and clusters of particles with the mixed dipole–quadrupole interaction has been found in smectic nanofilms. Unlike topological dipoles and quadrupoles, the interaction between which leads to the formation of structures with finite interparticle distances, the particles with the mixed interaction touch each other and form stable chains and two-dimensional clusters. The orientation of particles in chains is intermediate between dipole and quadrupole chains. The variation of the interparticle distance and orientation of chains is explained qualitatively on the basis of the calculation of the с-director (field lines) near particles and the mutual arrangement of particles providing the minimum distortion of field lines.

The influence of the magnetic field on the photon emission from the quark–gluon plasma created in AA collisions is studied. It is found that the effect of magnetic field is very small even for very optimistic assumption on the magnitude of the magnetic field for noncentral AA collisions.

The features of the effect of selective reflection from rubidium vapor in a nanocell with the thickness L ≈ λ/2 and L ≈ λ/4, where λ = 795 nm is the wavelength of laser radiation resonant with the Rb D₁ line, are studied. It is shown that, because of the behavior of the nanocell as a low-Q-factor Fabry–Pérot etalon, the sign of the derivative of the selective reflection spectra changes near L ≈ λ/2 from negative at L > λ/2 to positive at L < λ/2. The simplicity of the experimental implementation, large amplitude, and sub-Doppler width (40MHz) of a detected signal at an atomic transition frequency are appropriate for applications in metrology and magnetometry. In particular, selective reflection from the nanocell is a convenient frequency marker of atomic transitions; in this case, the amplitudes of peaks are proportional to the transition probabilities. The remote optical monitoring of a magnetic field with a spatial resolution L = λ/4 ≈ 199 of nm is possible on the basis of the splitting of selective reflection peaks in a strong magnetic field (up to 3 kG). A theoretical model describes well the experimental results.

The anisotropy of reflection spectra is studied for the single crystals of layered EuBaCo_1.9O_5.36 cobaltite within the temperature range of 80–295 K. The results involving the comparison with the magnetic and transport characteristics are analyzed. In the reflection spectra from the (001) and (120) planes measured at T = 295 K (below the temperature corresponding to the transition to the semiconducting state, T_MI = 345 K), a contribution from itinerant charge carriers has been revealed. This contribution is associated with the existence of an inhomogeneous charge state. In the reflection spectrum from the (120) plane, the contribution from itinerant charge carriers holds down to T = 80 K. The difference between the reflection spectra from different planes and different characters of their changes with the temperature are attributed to the anisotropy of the clusters with itinerant charge carriers.

The nonlinear dynamics of the interface between ideal dielectric fluids in the presence of tangential discontinuity of the velocity at the interface and the stabilizing action of the horizontal electric field is examined. It is shown that the regime of motion of the interface where liquids move along the field lines occurs in the state of neutral equilibrium where electrostatic forces suppress Kelvin–Helmholtz instability. The equations of motion of the interface describing this regime can be reduced to an arbitrary number of ordinary differential equations describing the propagation and interaction of structurally stable solitary waves, viz. rational solitons. It is shown that weakly interacting solitary waves recover their shape and velocity after collision, whereas strongly interacting solitary waves can form a wave packet (breather).

The natural strong narrowing of Mössbauer lines on long-lived isomers, which was correctly detected in [Yu. D. Bayukov, A. V. Davydov, Yu. N. Isaev, G. R. Kartashov, M. M. Korotkov, and V. V. Migachev, JETP Lett. 90, 499 (2009)] and consistently explained in [S.V. Karyagin, JETP Lett. 98, 174 (2013)] is additionally studied. It is shown that the chemical shift δ between γ emission and absorption lines appears in experiments with natural strong narrowing in the homogeneous medium of a γ source. This shift was previously thought to be impossible. The theory of the γ-resonance gravitational spectrum is developed with allowance for the shift δ. The shift δ and new linewidth k including this shift are determined; this new linewidth is noticeably smaller than that without the shift δ. It is shown that the lifetimes of isomers in experiments with natural strong narrowing are strongly limited from above by the suppression of the γ resonance by the shift δ. The smallness of δ confirms the recently revealed effect of strong natural suppression of monopole broadening [S. V. Karyagin, JETP Lett. 103, 213 (2016)]. It is shown that the electron density on the Ag nucleus inside grains is lower than that at their periphery by ~10^-14%. To detect thinner effects, experiments of a new type are proposed to exclude systematic errors.