Nonequilibrium spin states and tunnel paramagnetic centers in copper oxide CuO

It is shown that the formation of tunnel paramagnetic centers — triplet spin centers with a strongly different adiabatic potential in different spin states — can form in copper oxides based on CuO clusters. The results of measurements of the magnetization and magnetostriction of CuO single crystals are reported. They attest to the presence of nonequilibrium spin states and confirm the results obtained in the model of tunnel paramagnetic centers. Fiz. Tverd. Tela (St. Petersburg) 39, 474–482 (March 1997)     

Adiabatic Raman polariton in a Bose condensate

The Raman interaction of optical fields with a Bose condensate is studied in the adiabatic regime. A superposition of operators is found — one annihilating an atom in a metastable state and the other annihilating a photon in resonance with a transition from the ground state to an excited state — which is an adiabatic invariant of the problem (Raman polariton). Possible applications for Bose-condensate diagnostics and development of atomic lasers are proposed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 473–477 (10 October 1996)     

Logarithmic singularity in the specific heat in the vicinity of phase transitions in uniaxial ferroelectrics

Using precise vacuum adiabatic calorimetry it is shown that the specific heat of the model ferroelectric crystal TGS does not exhibit the logarithmic singularity predicted by theory above the transition temperature. This discrepancy with the available specific heat data in the literature, obtained by dynamical measurements, is discussed with allowance for the maximum attainable measurement accuracy (0.3%) in the static adiabatic experiment. Fiz. Tverd. Tela (St. Petersburg) 40, 106–108 (January 1998)     

On an adiabatic invariant in the thermodynamics of solids

A thermodynamic invariant in the form of the ratio of a vibrational frequency in an anharmonic solid to the temperature in adiabatic processes is derived. The adiabatic invariance established is used to derive in a simple manner an expression for the temperature change due to elastic adiabatic loading of solids (Kelvin's equation). Fiz. Tverd. Tela (St. Petersburg) 41, 134–136 (January 1999)     

Accumulation of dislocations and thermal strengthening of alloys having an L12 superstructure

This paper discusses the dislocation-accumulation mechanism in alloys having an L1₂ superstructure, which is associated with the formation of Kira-Wilsdorf barriers and the retardation of superdislocations during plastic deformation. A model of the dislocation-accumulation kinetics during plastic deformation is constructed, on the basis of which a mathematical model is formulated for the thermal and deformation strengthening of single crystals of alloys having the L1₂ superstructure. The results of numerical calculations based on the model are compared with the experimentally observed regularities of the deformation and thermal strengthening of single crystals of Ni₃Ge. Fiz. Tverd. Tela (St. Petersburg) 41, 454–460 (March 1999)     

Two-particle correlations from the q-Boson viewpoint

We propose and develop to some extent a novel approach, which allows to effectively describe, for relativistic heavy-ion collisions, the empirically observed deviation from unity of the intercept λ (i.e. the measured value corresponding to zero relative momentum p of two registered identical pions or kaons) of the two-particle correlation function C(p,K). The approach is based on the use of two versions of the so-called q-deformed oscillators and the corresponding picture of ideal gases of q-bosons. By these techniques the intercept λ is put into direct correspondence with the deformation parameter q. For fixed deformation strength, the model predicts particular dependence of the intercept λ on the pion pair mean momentum K. Received: 2 July 1999 / Revised version: 11 November 1999     

Simulation of arbitrary deformations of polycrystals by the method of cellular atomata

A computer model for the deformation of polycrystals is developed, based on the concept of cellular automata. The model is used to investigate a polycrystal by treating it as a multilevel hierarchical system, and to study the peculiarities in the behavior of this system as a function of the material structure, mechanisms of low-level deformation, history of loading and/or deformation at the top hierarchical level, the temperature, and other parameters. Zh. Tekh. Fiz. 68, 130–132 (November 1998)     

Interaction of polarons in two and three dimensions

Two-dimensional and three-dimensional bipolarons of large radius, symmetrized with respect to the coordinate parts of the two-center wave functions, are investigated in the adiabatic approximation with allowance for dynamic interelectronic correlations. The adiabatic potential lines are plotted. It is shown that the quasimolecular configuration appearing in the Hartree-Fock approximation is unstable in both the two-dimensional and the three-dimensional cases. The ground state is a one-center configuration. Estimates are given for the binding energy and the heat of dissociation of a bipolaron. Fiz. Tverd. Tela (St. Petersburg) 39, 441–443 (March 1997)     

Specific heat of LiB3O5 crystals in the temperature interval 80–300 K

The specific heat of LiB₃O₅ crystals is measured by adiabatic calorimetry. The experimental data on the specific heat are used to calculate the change in the thermodynamic functions (the entropy, enthalpy, and Gibbs free energy) and the Debye temperature Θ_D(T) of crystalline LiB₃O₅. Fiz. Tverd. Tela (St. Petersburg) 39, 624–625 (April 1997)     

Calculation of transuranium element synthesis in intensive neutron fluxes under adiabatic conditions

The creation of transuranium isotopes based on intense pulsed nucleosynthesis is considered. The model of multiple neutron captures takes into account the variation of the (n, γ)-cross section resulting from adiabatic expansion of the explosive nucleosynthesis area. The calculated yields of transuranium isotopes obtained under conditions close to a “Par” nuclear explosion, enable us to improve the agreement between the model results and the experimental data within the wide range of atomic mass number A = 248–257, provided the adiabatic conditions are taken into account.     

Activation parameters of stepped deformation of polymers

Creep rates on short deformation base lines before and after a change in temperature and stresses were measured by interferometry to determine the activation energies and activation volumes of the process. It is shown that the activation parameters of polymer creep vary not only at a macroscopic level but also within the micron-size deformation steps. The largest potential barrier corresponds to the lowest rate in a step and plays the role of a “physical node.” The results confirm the supposition that micron-size jumps (steps) of polymer deformation are caused by the nonmonotonic nature of intermolecular interactions in microvolumes of this level. Fiz. Tverd. Tela (St. Petersburg) 40, 1635–1638 (September 1998)     

Propagation of a spatial soliton in a system of tunneling-coupled optical waveguides with a variable coupling coefficient

The problem of the propagation of a spatial soliton in a system of tunneling-coupled optical waveguides is studied. The tunneling coupling coefficient is assumed to be modulated in a transverse direction. The adiabatic dynamics is studied for the case of periodic modulation of the tunneling coupling coefficient. The stationary points for the beam parameters are found. The effective potential is calculated for the center of the beam in the equivalent-particle model. The condition for resonance emission of waves by a soliton is obtained. Zh. Tekh. Fiz. 68, 1–4 (June 1998)     

Deformation of a Virasoro algebra and the integrals of motion of the quantum sine-Gordon equation

A special deformation of a Virasoro algebra such that the screening operator is not deformed (the space where it operates is deformed) is studied. This deformation leads to a 3-index algebra. The residue of the generating function of the generators of this algebra is a generating function of the integrals of motion for the quantum sine-Gordon model. The algebra of generating functions is calculated. Explicit formulas are presented for the first few integrals of motion. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 375–380 (10 March 1996)     

Large-scale flow as an indicator of superplasticity

A model is proposed for superplastic deformation of materials, based on the concept of cooperative grain-boundary slip. The conditions for superplastic deformation are obtained as conditions for coherent shear bands. Analysis of the temperature dependence of the limits of the stress interval for superplastic flow is used as a basis for the introduction of two types of threshold stress that elucidate the cause of the ambiguity in the interpretation of exisiting experimental results. Fiz. Tverd. Tela (St. Petersburg) 39, 2179–2185 (December 1997)     

Disclination mechanism for plastic deformation of nanocrystalline materials

A model is developed for the plastic deformation of nanocrystalline materials in terms of the evolution of a spatial grid of disclinations located at the triple junctions of grains. Plastic deformation takes place as the result of plastic rotation of grains, the mismatch of whose rotations causes the nucleation of partial disclinations at the junctions of intergrain boundaries. It is shown that the distinctive feature of the mechanical behavior of nanocrystals is a deviation from the Hall-Petch law up to a critical grain size D _cr⩽25 nm. Fiz. Tverd. Tela (St. Petersburg) 39, 2023–2028 (November 1997)     

Temperature dependence of the electronic specific heat of superconductors with quantum defects

The electronic specific heat of metals with quantum defects in the superconducting state is examined. The role of the electron-polaron effect, as well as that of the level population factor of two-level states, is analyzed in an adiabatic approach. The cases of intermediate and strong coupling are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 413–418 (March 1998)     

Magnetization curves of DyN clusters

Magnetic properties of isolated Dy_N clusters are studied in a molecular beam performing Stern-Gerlach experiments. The magnetizations μ _z of Dy_N are measured in dependence of the magnetic field strength B = 0-1.6 T and at nozzle temperatures T _n = 18 K and T _n = 300 K. At room temperature the magnetization augments linear with the field following a simple paramagnetic model. At T _n = 18 K the magnetization curves saturate at field strengths B ≥0.8 T. To explain the magnetization process at low temperatures two models are discussed: A model for adiabatic magnetization based on cluster rotation effects and a modified van-Vleck model. Received 30 November 2000     

The influence of elastic stress fields on ionic transport through a 〈superionic crystal〉-〈electrode〉 heterojunction

The appearance of a current in an external circuit has been observed upon elastic deformation of a local region of the superionic crystal RbAg₄I₅. The dependence of the magnitude and sign of the deformation current on the region of application of the local load on the sample is examined, and the temporal characteristics of the processes are investigated. The influence of an elastic deformation on processes taking place at the 〈superionic crystal〉-〈electrode〉 heterojunction is investigated, and a mechanism of generation of the deformation current is proposed. The generation of photostimulated currents upon illumination of a local region of the superionic conductor by light corresponding to intracenter excitation of optically active centers is considered. It is shown that the elastic stress fields arising around photoexcited centers are responsible for the generation of photostimulated currents. Fiz. Tverd. Tela (St. Petersburg) 41, 1766–1771 (October 1999)     

Early Universe in Scalar-Tensor Theory

We consider the flat Robertson–Walker model in scalar-tensor theory proposed by Lau and Prokhovnik. In this model, the field equations are solved by using “gamma-law” form of equation of state p=(γ−1)ρ, where the adiabatic parameter ‘gamma’ (γ) varies continuously as the universe expands. Our aim is to study how the adiabatic parameter γ should vary so that in the course of its evolution the universe goes through a transition from an inflationary to a radiation-dominated phase. A unified one parameter function of γ has been considered to describe the two early phases of evolution of universe. The solutions show the power-law expansion and cosmological constant is found to be positive and decreasing function of cosmic time. The solutions are compatible with the Dirac’s large number hypothesis. The deceleration parameter has been presented in a unified manner in terms of scale factor, which describes the inflation of the model. The nature of singularity and the physical properties have been discussed in details.     

Electric-field effect in a mixed-valence ion pair Cr3+−Cr2+ in a KZnF3 crystal

The influence of an external axial electric field on the absorption spectrum of a Cr³⁺−Cr²⁺ mixed-valence pair center coupled by the double-exchange mechanism in a KZnF₃ crystal is investigated. It is shown experimentally that the Cr³⁺−Cr²⁺ pair has an electric dipole moment. The migration of an electron is accompanied by local lattice strain. At the minima of the adiabatic potential, the intermediate fluorine atom is displaced from the lattice site. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 2, 147–149 (25 July 1998)