Variable-range hopping conduction in LaMnO<Subscript>3 + δ</Subscript>

The temperature dependence of the electrical resistivity ρ(T) for ceramic samples of LaMnO_{3 + δ} (δ = 0.100–0.154) are studied in the temperature range T = 15–350 K, in magnetic fields of 0–10 T, and under hydrostatic pressures P of up to 11 kbar. It is shown that, above the ferromagnet-paramagnet transition temperature of LaMnO_{3 + δ}, the dependence ρ(T) of this compound obeys the Shklovskii-Efros variable-range hopping conduction: ρ(T) = ρ₀(T)exp[(T ₀/T)^1/2], where ρ₀(T) = AT ^9/2 (A is a constant). The density of localized states g(?) near the Fermi level is found to have a Coulomb gap Δ and a rigid gap γ(T). The Coulomb gap Δ assumes values of 0.43, 0.46, and 0.48 eV, and the rigid gap satisfies the relationship γ(T) ≈ γ(T _v)(T/T _v)^1/2, where T _v is the temperature of the onset of variable-range hopping conduction and γ(T _v) = 0.13, 0.16, and 0.17 eV for δ = 0.100, 0.125, and 0.154, respectively. The carrier localization lengths a = 1.7, 1.4, and 1.2 Å are determined for the same values of δ. The effect of hydrostatic pressure on the variable-range hopping conduction in LaMnO_{3 + δ} with δ = 0.154 is analyzed, and the dependences Δ(P) and γ_v(P) are obtained.     

Structure and electrophysical properties of ferrocobaltites <Emphasis Type="Italic">Ln</Emphasis>BaFeCoO<Subscript>5 + δ</Subscript> (<Emphasis Type="Italic">Ln</Emphasis> = Tb,Dy, Ho,Y)

The ferrocobaltites LnBaFeCoO^{5 + δ} (Ln = Tb, Dy, Ho, Y) have been synthesized, and the parameters of their crystal structure have been determined. The thermal expansion, electrical resistivity ρ, and thermopower S of the synthesized compounds have been investigated in air at temperatures in the range from 300 to 1100 K. The compounds have a tetragonal structure (symmetry space group P4/mmm) with the unit cell parameters a = 3.9000 Å and c = 7.5922 Å (Ln = Tb, δ = 0.31), a = 3.8973 Å and c = 7.5679 Å (Ln = Dy, δ = 0.34), a = 3.8970 Å and c = 7.5507 Å (Ln = Ho, δ = 0.28), and a = 3.9029 Å and c = 7.5538 Å (Ln = Y, δ = 0.25). The ferrocobaltites under investigation are p-type semiconductors, and their electrical resistivity ρ and thermopower S decrease in the sequence Tb → Ho → Y → Dy (at room temperature). The linear thermal expansion coefficient of the LnBaFeCoO^{5 + δ} phases in the vicinity of the temperatures ranging from 465 to 535 K increases from (1.15?1.23) × 10^?5 to (1.73?1.93) × 10^?5 K^?1. The parameters of charge transfer in these ferrocobaltites have been determined. It has been found that an increase in the temperature leads to an increase in the excitation energy of charge carriers and a decrease in the activation energy of charge carrier transfer.     

Anomalous temperature dependence of magnetic relaxation in YBa<Subscript>2</Subscript>Cu<Subscript>2</Subscript>O<Subscript>7 − δ</Subscript> oxygen-deficient single crystals

The dependence of the magnetization relaxation rate S = ?d lnM/dlnt on temperature T is measured in YBa₂Cu₃O_{7 ? δ} samples with various oxygen concentrations. It is found that the S(T) curve changes qualitatively when oxygen deficit δ exceeds the threshold value δ_th = 0.37. For δ < δ_th (T _c > 60 K, where T _c is the superconducting transition temperature), function S(T) has the well-known peak at T/T _c = 0.4. For δ > δ_th (at T _c < 51 K), this peak transforms into a plateau and a new sharp peak appears at T/T _c = 0.1. The threshold value δ_th of the oxygen deficit corresponds to the transition of the sample from the disordered state into the ordered state of oxygen vacancies. We consider the change in the shape of the S(T) curve as a macroscopic manifestation of this transition.     

Structure,stability, and thermomechanical properties of Ca-substituted Pr<Subscript>2</Subscript>NiO<Subscript>4 + δ</Subscript>

Ca-substituted layered nickelates with a general Pr_2–x Ca _x NiO_{4 + δ} composition (x = 0–0.7, Δx = 0.1) were prepared in the present work and their structural and physic-chemical properties were investigated in order to select the most optimal materials, which can be used as cathodes for solid oxide fuel cells. With an increase in Ca content in Pr_2–x Ca _x NiO_{4 + δ} the following tendencies were observed: (i) a decrease in the concentration of nonstoichiometric oxygen (δ), (ii) a decrease in the unit cell parameters and volume, (iii) stabilization of the tetragonal structure, (iv) a decrease of the thermal expansion coefficients, and (v) enchancement of thermodynamic stability and compatibility with selected oxygen- and proton-conducting electrolytes. The Pr_1.9Ca_0.1NiO_{4 + δ} material, having highest δ value, departs from the general “properties–composition” dependences ascertained. This indicates that oxygen non-stoichiometry has determining influence on the functional properties of layered nickelates.     

Measurement of polarization angular coefficients in <Emphasis Type="Italic">Z</Emphasis> boson leptonic decays with ATLAS at the LHC

This paper presents the complete set of polarization angular coefficients A _0?7 describing lepton angular distributions in Z boson decay, which were measured at the ATLAS experiment in proton–proton collisions with the energy √s = 8 TeV. Theoretical values for the difference A ₀ ? A ₂ calculated in the fixed-order QCD perturbation theory O(α _s ² ), demonstrate significant deviation from the measured data, which indicates the necessity of taking into account higher order corrections. The evidence of nonzero coefficients A _5,6,7 was obtained for the first time, in accordance with theoretical calculations in O(α _s ² ) approximation. Measurement of the polarization angular coefficients A _i is important for subsequent precision measurement of parameters of the electroweak model at the LHC, such as the sine of Weinberg electroweak mixing angle sin² θ _W and the W boson mass.     

The probabilities of radiative transitions and lifetimes of levels in the spectra of Cu XX,La IV

The probabilities of radiative electric dipole transitions 2p ⁵3p, 2p ⁶–2p ⁵3s, and 2p ⁵3d in the spectrum of neon-like copper Cu XX and 5p ⁵6p, 5p ⁶–5p ⁵6s, 5p ⁵7s, and 5p ⁵5d in the spectrum of xenon-like lanthanum La IV are calculated. The wave functions of the intermediate coupling were found from the wellknown experimental energy levels by the least-squares method (LSM). To transfer to an absolute scale the radial integrals for the transitions calculated in the form of a length on the Hartree–Fock functions have been used. By summing the calculated probabilities of the transitions, the lifetimes of the levels of configurations 2p ⁵3s, 2p ⁵3p, and 2p ⁵3d in the spectrum of Cu XX and levels of configurations 5p ⁵6s, 5p ⁵6p, and 5p ⁵7s in the spectrum of La IV have been obtained.     

Configuration interaction and radiative constants in spectra of argon-like Sc IV-Fe IX ions

The probabilities of the 3p ⁵3d, 3p ⁵4s?3p ⁶, 3p ⁵4p, 3s3p ⁶3d electric dipole transitions and radiative lifetimes of the 3p ⁵3d, 3p ⁵4p, 3p ⁵4s, and 3s3p ⁶3d levels are calculated for the Sc IV–Fe IX isoelectronic sequence.     

Threshold perturbations in current-carrying superconducting bridges with a finite length near the critical temperature

Near the critical temperature of a superconducting transition, the energy of the threshold perturbation δF_thr that transfers a superconducting bridge to a resistive state at a current below the critical current I_c has been determined. It has been shown that δF_thr increases with a decrease in the length of a bridge for short bridges with lengths L < ξ (where ξ is the coherence length) and is saturated for long bridges with L ? ξ. At certain geometrical parameters of banks and bridge, the function δF_thr(L) at the current I → 0 has a minimum at L ~ (2–3)ξ. These results indicate that the effect of fluctuations on Josephson junctions made in the form of short superconducting bridges is reduced and that the effect of fluctuations on bridges with lengths ~(2–3)ξ is enhanced.     

Analysis of the spectrum of the Zn-like Kr VII ion: Highly excited 4<Emphasis Type="Italic">p</Emphasis>4<Emphasis Type="Italic">d</Emphasis> and 4<Emphasis Type="Italic">p</Emphasis>5<Emphasis Type="Italic">s</Emphasis> configurations

The spectrum of the Zn-like Kr VII ion, excited in a capillary discharge and recorded with a high resolution in the wavelength range of 300–1000 Å, was studied. Previously performed identification of the transitions from the levels of the 4s4f, 4s5s, 4s5p, and 4s5d configurations is confirmed and extended, and the energies of these levels are specified. The (4p ²+4s4d)?4p4d and (4p ²+4s5s)?4p5s transitions are identified for the first time, and the energies of all the levels of the 4p4d and 4p5s configurations are determined. The results of the analysis performed are confirmed by semiempirical calculations in terms of the Hartree-Fock method. These results are also shown to conform to the experimental data obtained for lighter ions of the Zn I isoelectronic sequence.     

The effect of impurity on temperature variations in the refractive indices and thickness of TGS crystals

Temperature dependences of optical path difference δΔ_? and the relative changes in thickness δl_?/l of TGS crystals doped with L-valine are studied. Temperature dependences of the relative changes in refractive indices δn_?/(n–1) are calculated. The anisotropy coefficients of refractive indices А_n–1(Т) and linear expansion Аα(Т) are calculated, and a characteristic minimum of these dependences is found near the phase transition temperature.     

Excitation of even levels of erbium atoms without a change in the number of 4<Emphasis Type="Italic">f</Emphasis> electrons

The excitation of even levels of erbium atoms by slow electrons that occurs without a change in the number of electrons in the 4f shell is experimentally studied. The levels investigated belong to the 4f ¹²6s7s, 4f ¹²5d6s, 4f ¹²6s6d configurations. The cross sections measured at an electron energy of 30 eV lie within the range (0.2–18) × 10^?18 cm².     

Exchange Bias in Layered GdBaCo<Subscript>2</Subscript>O<Subscript>5.5</Subscript> Cobaltite

It is established that excess oxygen content δ influences the exchange bias (EB) in layered GdBa-Co₂O_{5 + δ} cobaltite. The EB effect arises in p-type (δ > 0.5) cobaltite and disappears in n-type (δ < 0.5) cobaltite. The main parameters of EB in GdBaCo₂O_5.52(2) polycrystals are determined, including the field and temperature dependences of EB field H _EB , blocking temperature T _B , exchange coupling energy J _i of antiferromagnet–ferromagnet (AFM–FM) interface, and dimensions of FM clusters. The training effect inherent in systems with EB has been studied. The results are explained in terms of exchange interaction between the FM and AFM phases. It is assumed that the EB originates from the coexistence of Co³⁺ and Co⁴⁺ ions that leads to the formation of monodomain FM clusters in the AFM matrix of cobaltite.     

Phenomenology of light- and strange-quark simultaneous production at high energies

This letter presents an extension of EPL116(2017)62001 to light- and strange-quark nonequilibrium chemical phase-space occupancy factors (γ_q,s). The resulting damped trigonometric functionalities relating γ_q,s to the nucleon-nucleon center-of-mass energies (\(\sqrt {{s_{NN}}} \)) looks very similar except different coefficients. The phenomenology of the resulting γ_q,s(\(\sqrt {{s_{NN}}} \)) describes a rapid decrease at \(\sqrt {{s_{NN}}} \) ? 7GeV followed by a faster increase up to ~20 GeV. Then, both γ_q,s become nonsensitive to \(\sqrt {{s_{NN}}} \). Although these differ from γ _s (\(\sqrt {{s_{NN}}} \))obtained at γ _q (\(\sqrt {{s_{NN}}} \))=1, various particle ratios including K⁺/π⁺, K^?/π^?, Λ/π^?, Λ?/π^?, Ξ⁺/π⁺, and Ω/π^?, can well be reproduced, as well. We conclude that γ_q,s(\(\sqrt {{s_{NN}}} \)) should be instead determined from fits of various particle yields and ratios but not merely from fits to the particle ratio K⁺/π⁺.     

Monte Carlo Glauber wounded nucleon model with meson cloud

We study the effect of the nucleon meson cloud on predictions of the Monte Carlo Glauber wounded nucleon model for AA, pA, and pp collisions. From the analysis of the data on the charged multiplicity density in AA collisions we find that the meson–baryon Fock component reduces the required fraction of binary collisions by a factor of ~2 for Au + Au collisions at √s = 0.2 TeV and ~1.5 for Pb + Pb collisions at √s = 2.76 TeV. For central AA collisions, the meson cloud can increase the multiplicity density by ~16–18%. We give predictions for the midrapidity charged multiplicity density in Pb + Pb collisions at √s = 5.02 TeV for the future LHC run 2. We find that the meson cloud has a weak effect on the centrality dependence of the ellipticity ?₂ in AA collisions. For collisions of the deformed uranium nuclei at √s = 0.2 TeV, we find that the meson cloud may improve somewhat agreement with the data on the dependence of the elliptic flow on the charged multiplicity for very small centralities defined via the ZDCs signals. We find that the meson cloud may lead to a noticeable reduction of ?₂ and the size of the fireball in pA and pp collisions.     

Homogeneous nucleation in liquid nitrogen at negative pressures

The kinetics of spontaneous cavitation in liquid nitrogen at positive and negative pressures has been studied in a tension wave formed by a compression pulse reflected from the liquid–vapor interface on a thin platinum wire heated by a current pulse. The limiting tensile stresses (Δp = p_s–p, where p_s is the saturation pressure), the corresponding bubble nucleation frequencies J (10²⁰–10²² s^–1 m^–3), and temperature induced nucleation frequency growth rate G_T = dlnJ/dT have been experimentally determined. At T = 90 K, the limiting tensile stress was Δp = 8.3 MPa, which was 4.9 MPa lower than the value corresponding to the boundary of thermodynamic stability of the liquid phase (spinodal). The measurement results were compared to classical (homogeneous) nucleation theory (CNT) with and without neglect of the dependence of the surface tension of critical bubbles on their dimensions. In the latter case, the properties of new phase nuclei were described in terms of the Van der Waals theory of capillarity. The experimental data agree well with the CNT theory when it takes into account the “size effect.”     

RETRACTED ARTICLE: Density,viscosity and speed of sound of benzaldehyde with benzene at 303.15, 308.15, and 313.15 K

The values of density, viscosity and speed of sound for the binary liquid mixture of Benzaldehyde with Benzene were measured over the entire range of composition at 303.15, 308.15, and 313.15 K. These values are used to calculate the excess molar volume (V ^E), deviation in viscosity (Δη), deviation in speed of sound (ΔU), deviation in isentropic compressibility (Δβ _s ), excess internal pressure (Δπ), excess intermolecular free length (ΔL _f ), excess free volume (V _E ^f ) and excess acoustic impedance (ΔZ). McAllister’s three-body interaction model is used for correlating Kinematic Viscosity of binary mixtures. The excess values were correlated using the Redlich–Kister polynomial equation to obtain their coefficients and standard deviations. The thermophysical properties (density, viscosity, and speed of sound) under the study were fit to the Jouyban–Acree model.     

Measurement of isotope shifts of gadolinium levels by laser-induced fluorescence spectroscopy

The results of isotope shift measurements for the gadolinium atom both in a hollow cathode lamp and in an atomic beam are described. Using laser-induced fluorescence spectroscopy, the measurements were performed for four transitions, which are related to the configurations 4f⁷5d6s²⁹D to 4f⁷5d6s6p⁹D and 4f⁷5d6ss6p⁹FD.     

Magnetic states of iron ions in Bi<Subscript>0.75</Subscript>Si<Subscript>0.25</Subscript>FeO<Subscript>3 − <Emphasis Type="Italic">y</Emphasis></Subscript> perovskites

Hyperfine interactions on ⁵⁷Fe nuclei in cubic perovskite Bi_0.75Sr_0.25FeO_{3 ? y} in the temperature range 87–700 K are studied using Mössbauer spectroscopy. The temperature of the magnetic phase transition (the Neel point T _N ) of bismuth ferrite is T _N = 670(3) K. Below T _N , the experimental spectra demonstrate a partially resolved magnetic hyperfine structure with broadened lines, which is well described by superposition of four sextets. The values of the hyperfine magnetic field B and the isomer shift δ at room temperature initiated that all iron ions are in the trivalent state. Here, three sextets with the equal isomer shifts (δ₁ ≈ δ₂ ≈ δ₃ = 0.38 mm/s correspond to the iron ions in the octahedral oxygen environment; in the fourth sextet, the iron ions are in the square-pyramidal environment (δ₃ = 0.25 mm/s).     

Reactions of initiation of the autoignition of H<Subscript>2</Subscript>–O<Subscript>2</Subscript> mixtures in shock waves

The initiation of the autoignition of hydrogen–oxygen–argon mixtures behind reflected shock waves is studied by absorption and emission spectrophotometry in the temperature range of 960 < T < 1670 K at pressures of ~0.1 MPa. Introduction of Mo(CO)₆ additive in an amount of ~80 ppm made it possible to study the effect of O atoms on the shortening of the ignition delay time of H₂–O₂–Ar mixtures. A kinetic modeling of our own and published experimental data at temperatures of 930 < T < 2500 K and pressures of 0.05 < P < 8.7 MPa enabled to establish how the initiation reactions influence the process of self-ignition and to evaluate the rate constant for one of the initiation reactions: k(H₂ + O₂ → 2OH) = (3 ± 1) × 10¹¹exp(–E _a/RT), cm³ mol^–1 s^–1, where E _a = (40 ± 2) kcal/mol.     

Maslov index for power-law potentials

The Maslov index in the semiclassical Bohr–Sommerfeld quantization rule is calculated for one-dimensional power-law potentials V (x) = ?V ₀/x ^s, x > 0, 0 < s < 2 The result for the potential V(x)=-V ₀/x ^1/2 is compared with the recently reported exact solution. The case of a spherically symmetric power-law potential is also considered.