Vol 125, No 2 (2017)

It is shown that, depending on the incident wave frequency and the system geometry, the extraordinary transmission of light through a metal film perforated by an array of subwavelength holes can be described by one of the three mechanisms: the “transparency window” in the metal, excitation of the Fabry–Perot resonance of a collective mode produced by the hybridization of evanescence modes of the holes and surface plasmons, and excitation of a plasmon on the rear boundary of the film. The excitation of a plasmon resonance on the front boundary of the metal film does not make any substantial contribution to the transmission coefficient, although introduces a contribution to the reflection coefficient.

We consider a method for optimizing the tunnel effect for low-energy particles by using coherent correlated states formed under controllable pulsed action on these particles. Typical examples of such actions are the effect of a pulsed magnetic field on charged particles in a gas or plasma. Coherent correlated states are characterized most comprehensively by the correlation coefficient r(t); an increase of this factor elevates the probability of particle tunneling through a high potential barrier by several orders of magnitude without an appreciable increase in their energy. It is shown for the first time that the formation of coherent correlated states, as well as maximal |r(t)|_max and time-averaged 〈|r(t)|〉 amplitudes of the correlation coefficient and the corresponding tunneling probability are characterized by a nonmonotonic (oscillating) dependence on the forming pulse duration and amplitude. This result makes it possible to optimize experiments on the realization of low-energy nuclear fusion and demonstrates the incorrectness of the intuitive idea that the tunneling probability always increases with the amplitude of an external action on a particle. Our conclusions can be used, in particular, for explaining random (unpredictable and low-repeatability) experimental results on optimization of energy release from nuclear reactions occurring under a pulsed action with fluctuations of the amplitude and duration. We also consider physical premises for the observed dependences and obtain optimal relations between the aforementioned parameters, which ensure the formation of an optimal coherent correlated state and optimal low-energy tunneling in various physical systems with allowance for the dephasing action of a random force. The results of theoretical analysis are compared with the data of successful experiments on the generation of neutrons and alpha particles in an electric discharge in air and gaseous deuterium.

A dynamic theory is developed for coherent X-ray radiation generated when a diverging beam of relativistic electrons crosses a periodic layered target. Expressions describing the spectral–angular characteristics of coherent X-ray radiation are obtained and analyzed in the Bragg scattering geometry.

A kinetic model is proposed for ion–molecular processes involving charged particles of a humid air plasma produced by a fast electron beam. The model includes more than 600 processes involving electrons and 41 positive and 14 negative ions, including hydrated ions H₃O⁺ (H₂O)_n and O₂⁻(H₂O)_n with n = 1, 2, …, 12. The energy costs of production of electron–ion pairs and electronic and vibrational (for water molecules, also rotational) excitation of molecules are calculated in nitrogen, oxygen, water vapor, air, and humid air. A method is proposed for calculating the energy costs in mixtures by the calculation data in pure gases. The evolution of the plasma composition is studied by the numerical solution of a system of 56 time-dependent balance equations for the number of charged particles of plasma by the fourth-order Runge–Kutta method. The steady-state composition of plasma is determined by solving nonlinear steady-state balance equations for the ionization rates of humid air from 10 to 10¹⁶ cm^–3/s and the fraction of water molecules from 10^–3% to 1.5%. It is established that, for water vapor content (the ratio of the number density of water molecules to the total number density of air molecules) of 0.015–1.5% in air at atmospheric pressure and room temperature, the main ion species are two types of positive ions H₃O⁺ (H₂O)_n with the number of water molecules n = 5, 6 and three species of negative ions O₂⁻(H₂O)_n with n = 5, 8, 9.

The q-theory formalism aims to describe the thermodynamics and dynamics of the deep quantum vacuum. The thermodynamics leads to an exact cancellation of the quantum-field zero-point-energies in equilibrium, which partly solves the main cosmological constant problem. But, with reversible dynamics, the spatially flat Friedmann–Robertson–Walker universe asymptotically approaches the Minkowski vacuum only if the Big Bang already started out in an initial equilibrium state. Here, we extend q-theory by introducing dissipation from irreversible processes. Neglecting the possible instability of a de-Sitter vacuum, we obtain different scenarios with either a de-Sitter asymptote or collapse to a final singularity. The Minkowski asymptote still requires fine-tuning of the initial conditions. This suggests that, within the q-theory approach, the decay of the de-Sitter vacuum is a necessary condition for the dynamical solution of the cosmological constant problem.

The submonolayer adsorption of Na onto the Cu(110) surface is studied. At small Na coverages (Θ = 0.16–0.25 ML), the substrate surface subjected to missing-row reconstruction (1 × 2) is shown to be most stable dynamically. When the coverage increases to Θ = 0.5 ML, the unreconstructed substrate surface with a c(2 × 2) sodium adlayer becomes dynamically stable. For an analysis, we used data on the equilibrium atomic configuration, the adsorption energy, the phonon spectra, the local density of phonon states, and the polarization of localized vibrational modes. All calculations were performed using the interatomic potentials obtained in terms of the embedded-atom method. The calculated frequencies of localized vibrational modes agree well with the existing experimental data.

The compositions La_0.7Sr_0.3Mn_{1 – x}Co_xO₃ (0.13 ≤ x ≤ 1) are studied by neutron diffraction, magnetometry, and measuring the magnetotransport properties. The substitution of cobalt ions for manganese ions is shown to decrease the magnetization and the Curie temperature from 270 K (x = 0.13) to 140 K (x = 0.33). As the cobalt ion content increases to x = 0.5, the Curie temperature increases to 190 K, the magnetization decreases, and the electrical resistivity increases. At x > 0.5, the temperature of transition into a paramagnetic state decreases to 68 K (x = 0.8) and then again increases to 225 K for the La_0.7Sr_0.3CoO₃ composition. The magnetoresistive effect in the range 0.3 ≤ x ≤ 0.4 reaches 97% and decreases gradually with increasing temperature without anomalies near the Curie point. At x ≤ 0.2, the magnetoresistive effect increases near the Curie temperature. The composition at x = 0.6 is stoichiometric, and no coherent magnetic contribution to neutron scattering is detected. The magnetic properties near x ∼ 0.5 are assumed to be caused by partial ordering of Co³⁺ and Mn⁴⁺ ions, and the Co³⁺ ions can be in both low- and high-spin states. The magnetic interaction between Co³⁺ ions in a high-spin state and Mn⁴⁺ is predominantly ferromagnetic, and the ferromagnetic part of the exchange interactions is close to the ferromagnetic part. These data are used to plot a magnetic La_0.7Sr_0.3Mn_{1 – x}Co_xO₃ phase diagram.

Thin films of (Co₄₁Fe₃₉B₂₀)_x(SiO₂)_{100 – x} nanocomposites and hybrid nanocomposite–semiconductor [(Co₄₁Fe₃₉B₂₀)_x(SiO₂)_{100 – x}/C]₅₀ multilayers are synthesized by ion-beam deposition at various contents x of ferromagnetic metallic Co₄₁Fe₃₉B_2O nanogranules in an SiO₂ matrix and at various carbon layer thicknesses h < 2 nm. Their magnetic and electrical properties, high-frequency magnetic permeability, magnetooptical spectra, and FMR spectra are studied. It is found that both the single-layer nanocomposites and the multilayers with carbon interlayers are superparamagnetic at x < x_per, where x_per is the electric conduction percolation threshold: a hysteresis at room temperature is absent, and the blocking temperature determined in quasi-static measurements does not exceed 20–30 K and weakly depends on the carbon layer thickness. At a carbon layer thickness h = 1.2–1.8 nm, the real and imaginary parts of complex magnetic permeability at 50 MHz and room temperature are substantially higher than those of the nanocomposites without carbon layers: their values are typical of ferromagnets. This dependence points to an exchange interaction between nanogranules in layers through a carbon interlayer. The influence of a conducting layer on the static and dynamic magnetic properties of a system of interacting superparamagnetic particles is discussed.

The hysteresis loops and the micromagnetic structure of a ferromagnetic nanolayer with a randomly oriented local easy magnetization axis and two-dimensional magnetization correlations are studied using a micromagnetic simulation. The properties and the micromagnetic structure of the nanolayer are determined by the competition between the anisotropy and exchange energies and by the dipole–dipole interaction energy. The magnetic microstructure can be described as an ensemble of stochastic magnetic domains and topological magnetization defects. Dipole–dipole interaction suppresses the formation of topological magnetization defects. The topological defects in the magnetic microstructure can cause a sharper change in the coercive force with the crystallite size than that predicted by the random magnetic anisotropy model.

We have analyzed the transport regimes and the asymptotic forms of the impurity concentration in a randomly inhomogeneous fractal medium in the case when an impurity source is surrounded by a weakly permeable degrading barrier. The systematization of transport regimes depends on the relation between the time t₀ of emergence of impurity from the barrier and time t_* corresponding to the beginning of degradation. For t₀ < t_*, degradation processes are immaterial. In the opposite situation, when t₀ > t_*, the results on time intervals t < t_* can be formally reduced to the problem with a stationary barrier. The characteristics of regimes with t_* < t < t₀ depend on the scenario of barrier degradation. For an exponentially fast scenario, the interval t_* < t < t₀ is very narrow, and the transport regime occurring over time intervals t < t_* passes almost jumpwise to the regime of the problem without a barrier. In the slow power-law scenario, the transport over long time interval t_* < t < t₀ occurs in a new regime, which is faster as compared to the problem with a stationary barrier, but slower than in the problem without a barrier. The asymptotic form of the concentration at large distances from the source over time intervals t < t₀ has two steps, while for t > t₀, it has only one step. The more remote step for t < t₀ and the single step for t > t₀ coincide with the asymptotic form in the problem without a barrier.

An analytical expression is obtained for the lateral pressure profile in the hydrophobic part of a lipid bilayer of finite curvature. Calculations are carried out within a microscopic model of a lipid bilayer, according to which the energy of a lipid chain represents the energy of a flexible string of finite thickness and the interaction between lipid chains is considered as a steric (entropic) repulsion. This microscopic model allows one to obtain an expression for the distribution of lateral pressure in membranes with given curvature if one considers the bending of a membrane as a small deviation from a flat conformation and applies perturbation theory in the small parameter L₀J, where L₀ is the hydrophobic thickness of a monolayer and J is the mean curvature of the lipid bilayer. The resulting pressure profile depends on the microscopic parameters of the lipid chain: the bending modulus of the lipid chain, incompressible area per lipid chain, and the thickness of a flat monolayer. The coefficient of entropic repulsion between lipids is calculated self-consistently. The analytical results obtained for the lateral pressure distribution are in qualitative agreement with molecular dynamic simulations.