Vol 107, No 9 (2018)

The meaningful specific anisotropy in the angle distribution of leptons with respect to the three-momentum of pair is predicted as a feasibility signature of synchrotron-like mechanism resulting from the quarks interacting with a collective confining color field in the heavy ion collisions. The lepton pair production rate and the spectrum of pair invariant mass are presented for this new dilepton source that is apparently not taken into consideration in the available phenomenological estimates.

In this letter, we describe the observation of a magnetic field dependent electronic gap, suggestive of local superconductivity, in the point-contact spectrum of microcrystalline graphite. Magnetic field dependent point-contact spectroscopy has been carried out at a temperature of 1.8 K using an etched aluminum tip. At zero field, a gap structure in the differential conductance is observed, showing a gap of Δ = 4.2 meV. On applying magnetic fields of up to 500 mT, this gap gradually closes, following the theoretical prediction by Ginzburg and Landau for a fully flux-penetrated superconductor. By applying BCS-theory, we infer a critical superconducting temperature of 14 K.

The crystallization of a quantum system of hard spheres has been considered for the case where the effects of Bose and Fermi statistics can be neglected. It has been found that the quantum crystal–liquid equilibrium line almost completely coincides with the classical line except for the range of very low temperatures. Because of this nontrivial conclusion, the efficiency of quantum fluctuations at the melting of matter is questionable.

Neutron diffraction studies of a α → γ structural phase transition (T_c ≈ 911°C) in iron samples at different initial states have been performed. The anomalous disappearance of a diffraction pattern is observed in iron in the region of the α → γ phase transition. At repeated heating processes of an as cast sample, this effect becomes less pronounced and it is absent at the heating of iron powder. The observed effects have been assumingly attributed to the formation of small paracrystalline clusters with a large dispersion of the cell parameters in the process of phase transition. The kinetics of formation of clusters is slowed in as cast samples, which leads to the temporal disappearance of the diffraction pattern. These results make it possible to reconsider the atomic processes in the α → γ phase transition in iron.

A Monte Carlo study of the specific features of the nonequilibrium critical behavior has been performed for the two-dimensional “pure” and structurally disordered Ising models in the course of their evolution from the low-temperature initial state at spin concentrations p = 1.0, 0.9, and 0.8. It is shown for the first time that the pinning of domain walls by structural defects leads to the anomalously strong slowing down in the evolution of the autocorrelation function characterized by the superaging effect with exponents μ = 6.25(5) and μ = 6.75(5) for the model with the spin concentrations p = 0.9 and 0.8, respectively. The pure model exhibits the conventional aging with the exponent μ = 1. It is found that the superaging effects in structurally disordered systems lead to vanishing of the limiting fluctuation−dissipation ratio X^∞, whereas X^∞ = 0.751(24) for the pure model.

It has been demonstrated that a quantum state of a broadband single-photon electromagnetic field can be detected and verified by recording the intensity of superradiance of an atomic ensemble governed by non- Wiener dynamics. Under these conditions, the collective relaxation of atoms in the Dike model into vacuum is completely suppressed and only the interaction of the external field with atoms generates a superradiance pulse proportional to the square of the number of atoms. In the case of a single-photon wave packet in a classical state prepared by weakening a broadband source of a family of independent coherent modes, incoherent emission of the same ensemble occurs with the intensity proportional to the number of atoms.

It has been shown that a correlation mechanism that is based on the exchange interaction and destroys the relation between distribution functions and response (Price relation) occurs in a nonequilibrium Lorentz gas (particles interact only with the thermostat). The physical nature of this phenomenon is that the scattering of particles of the gas in the same state on a single particle of the thermostat creates a flux of correlated pairs, which depends on the form of a nonequilibrium distribution function, making impossible the existence of a universal relation between distribution functions and response.

Soft X-ray absorption spectroscopy has been used to determine the charge state and content of cobalt ions in doped cobaltites CaBaCo₄O₇, Y_0.5Ca_0.5BaCo₄O₇, Y_0.5Ca_0.5BaCo_4–xFe_xO₇, and Y_0.5Ca_0.5BaCo_4–zZn_zO₇. A method has been proposed to determine the relative concentrations of cobalt ions in barium-containing cobaltites from the relative intensities of X-ray absorption Со L₃/Ba M₅ spectra, and the relative contents of both Fe and Zn doping elements and Co²⁺ and Co³⁺ ions have been determined. It has been found that the substitution of iron ions for some cobalt ions (cobaltite Y_0.5Ca_0.5BaCo_4–xFe_xO₇) transforms some Co³⁺ ions to Co²⁺ ions. It has been found that iron ions are in the 3+ charge state and have tetrahedral coordination with oxygen ions. The substitution of divalent zinc ions for some cobalt ions (cobaltite Y_0.5Ca_0.5BaCo_4–zZn_zO₇) increases the concentration of high-spin Co3+ ions. The tetrahedral coordination of the Co²⁺ and Co³⁺ ions has been confirmed.