Temperature dependence of static and dynamic properties of an anisotropic ferrimagnet

The temperature dependences of the magnetizations of sublattices and the spectra of elementary excitations of an anisotropic ferrimagnet have been investigated. It has been shown that, in the anisotropic ferrimagnet, even a weak single-ion anisotropy induces the quantum spin reduction effect and, as a consequence, changes the behavior of the magnetizations of the sublattices. This gives rise to a new branch of magnetic excitations with the purely longitudinal dynamics of the average value of the spin due to the quantum spin reduction effect.     

Unified theory of static,dynamic, and electronic properties of aluminium

The problem of including the many-electron interactions into a pseudopotential theory of aluminium is re-considered. It is shown that due to the valence-core exchange and correlation, the pseudopotential is necessarily non-linear in the valence-electron charge density. We propose a simple way to account for this non-linear effect. This improved valence-core exchange potential allows to give a unified theory of static, dynamic, and electronic properties of aluminium.     

Calculated properties of superheavy nuclei

Ground-state properties of the heaviest nuclei are analyzed within a macroscopic-microscopic approach. The main attention is paid to such properties as deformation, deformation energy, energy of the first rotational state 2⁺ of a nucleus, and the branching ratio of α decay to this 2⁺ state with respect to the decay to the ground state 0⁺. The analysis concerns the problem of experimental confirmation of theoretically predicted deformed shapes of superheavy nuclei situated in the region around the nucleus ²⁷⁰Hs. A large region of even-even nuclei with proton, Z=82–128, and neutron, N=126–190, numbers is considered.     

Roper resonance—Its static and dynamic properties from single- and double-pion production

In most investigations the Roper resonance is sensed only very indirectly via complex partial wave analyses. We find indications for its excitation in the pp→npπ⁺ reaction, where some resonance-like structure is observed in the invariant nπ⁺ mass spectrum at with a width of 150 MeV. The values fit very favorably to the most recent phase shift results as well as to the observations at BES. In near-threshold two-pion production pp→ppπ⁰π⁰ the Roper excitation and its subsequent decay into Nππ is the only dominant process. There we find its decay into the Nσ channel as the dominating decay process — in favor of a monopole nature of the Roper excitation.     

Calculated ground-state properties of heavy nuclei

Ground-state distortions and single-particle corrections are calculated fornuclei with $\text{Z ≧ 68}\text{and}\text{N ≧ 106}$ by use of the macroscopic-microscopic method as developed by Strutinsky. The microscopic part is calculated primarily by use of the folded Yukawa single-particle potential. Its parameters are redetermined to fit a actinide data. The modified oscillator potential is also used in some of the studies. Two methods for calculating the macroscopic energy are investigated. One is the droplet model of Myers and Swiatecki, and other is a modified liquid-drop model in which the surface-energy term is modified to take into account the finite range of the nuclear force. Single-particle level diagrams for the folded Yukawa potential are also presented. They are plotted as functions of the distortion parameters ?, ?₄ and ?₆. Theoretical and experimental single-particle levels at the ground state for actinide nuclei are also compared.     

Calculated phonon dispersion of infinite-layer compounds and the effects of charge fluctuations

In a first step we use an ab initio rigid-ion model (RIM) to calculate the lattice parameters and the phonon dispersion of the infinite-layer compounds CaCuO₂, SrCuO₂, and BaCuO₂. We find an increase of both the planar and the axial lattice constant when going from CaCuO₂ through SrCuO₂ to BaCuO₂. The rate of increase of the planar lattice constant with respect to the alkaline-earth ionic radius is calculated to be smaller for the replacement of Sr by Ba than for the replacement of Ca by Sr. Both results are in accordance with experimental studies. The phonon dispersion in the RIM exhibits several unstable branches mainly related to axial displacements of the oxygens, indicating the tendency of the crystal to reconstruct in a lower-symmetry structure. The structural stability increases, however, towards BaCuO₂; simultaneously, the maximum phonon frequency decreases. AnA _2u zone-center mode with very large LO-TO-splitting exists in all three compounds (ferroelectric mode). In a second step charge fluctuations (CF) are taken into account at the copper- and oxygen ions, using SrCuO₂ as an example. Due to the vanishing of the ferroelectric split a branch with very steep dispersion forms in the [001] direction in the metallic phase whereas the zone-centerA _2u modes are unchanged in the insulating phase because of the two-dimensional (2D) electronic structure assumed. Characteristic nonlocal electron-phonon-interaction effects are associated with theZ-point Sr-axial-breathing mode: CF of uniform sign within the CuO planes but alternating sign in consecutive planes do occur in the metalic phase. This interplane charge transfer is, on the other hand, suppressed in the insulating phase due to the 2D electronic structure assumed. Instead, large induced site-potential changes emerge in this case.     

Influence of static and dynamic internal actions on elastic nonlinear properties of a granulated unconsolidated medium

We have studied the influence of external static (pressure) and dynamic (caused by an elastic wave with a finite amplitude) actions on the linear and nonlinear elastic properties of a granulated unconsolidated medium, which was simulated by steel spheres with diameters of 2 and 4 mm. We have analyzed the equation of state for such a medium taking into account the presence of weakly and strongly deformed contacts between individual spheres. We have obtained expressions for the elasticity coefficient and second- and third-order nonlinear elastic parameters, and we have experimentally studied the influence of external static pressure on their values. We have measured the dependence of the velocity of elastic waves on external static pressure and the probing signal amplitude. In the studied medium, a number of structural phase transitions were observed, related to rearrangement of the packing of spheres, which were caused by both static and dynamic actions. The structural phase transition was accompanied by an anomalous change in the nonlinear elastic parameters of the medium and the velocity of elastic waves. We have analyzed the results based on the Hertz theory of contact interaction.     

Flow equations for the one-dimensional Kondo lattice model: static and dynamic ground state properties

The one-dimensional Kondo lattice model is investigated by means of Wegner's flow equation method. The renormalization procedure leads to an effective Hamiltonian which describes a free one-dimensional electron gas and a Heisenberg chain. The localised spins of the effective model are coupled by the well-known RKKY interaction. They are treated within a Schwinger boson mean field theory which permits the calculation of static and dynamic correlation functions. In the regime of small interaction strength static expectation values agree well with the expected Luttinger liquid behaviour. The parameter K_ρ of the Luttinger liquid theory is estimated and compared to recent results from density matrix renormalization group studies.     

Effect of mechanical boundary conditions on the dynamic and static properties of a strongly anisotropic ferromagnet

The spectra of coupled magnetoelastic waves in a semi-infinite strongly anisotropic easy-plane ferromagnet with a rigidly fixed face are analyzed for two variants of fixation (in the basal plane and perpendicularly to it). The phase states of the system are determined. Differences in the phase diagrams and elementary excitation spectra depending on the choice of the sample fixation plane are considered. When rotational invariance is taken into account, the nonreciprocity effect for the velocities of sound in a crystal appears. It is shown that the velocity of sound in the sample considerably depends on the symmetry of the imposed mechanical boundary conditions. The phase diagrams of the system under investigation are presented.     

Inequalities among static and dynamic critical-point exponents

The mode-mode coupling theoretical expression for the decay rate of order-parameter fluctuations in simple fluids near the critical point is evaluated with the aid of the recently extended Ornstein-Zernike theory. This gives that ψ?ν for the critical-point exponent ψ which characterize the behavior of the thermal conductivity. Also, the results for sound-wave absorption and dispersion near the gas-liquid critical point need not depend on a single reduced frequency variable since scaling may be violated.     

Fracture of spheroplastic under static and dynamic stressing

The fracture of a composite material, a spheroplastic consisting of a polyester resin matrix and glass microspheres as a filler, is studied experimentally and theoretically under static and dynamic stressing. A shock is generated by a pulsed magnetic field. The fracture type in relation to the shock parameters and material structure is analyzed. A method for testing the dynamic behavior of the material based on the incubation time accumulation is suggested.