Invar and covar behavior of ferromagnets with allowance for magnetophonon interaction: A thermodynamic simulation

Based on the Landau theory of second-order phase transitions with allowance for interaction between the magnetic subsystem and crystal lattice (magnetophonon interaction, MPI), a consistent thermodynamic model of the invar and covar behavior of ferromagnets with MPI is constructed. Model calculations carried out at real temperatures show that the invar (covar) behavior of ferromagnets results from an optimal relationship between the thermodynamic parameters of the ferromagnetic phase. It is demonstrated that MPI is a fundamentally important factor responsible for the invar and covar effects. With the thermodynamic parameters obeying a certain relationship, the invar behavior of ferromagnets is predicted in a much wider temperature range than in known invars.     

Investigation of thermodynamic properties of cerium dioxide by statistical moment method

The thermodynamic properties of the cerium dioxide (CeO₂) are studied using the statistical moment method, including the anharmonicity effects of thermal lattice vibrations. The free energy, linear thermal expansion coefficient, bulk modulus, specific heats at the constant volume and those at the constant pressure, C_V and C_P, are derived in closed analytic forms in terms of the power moments of the atomic displacements. The temperature dependence of the thermodynamic quantities of cerium dioxide is calculated using three different interatomic potentials. The influence of dipole polarization effects on the thermodynamic properties and thermodynamic stability of cerium dioxide have been studied in detail.     

Semiempirical model potential for the interaction of oxygen with the nickel (001) surface

The interaction energy of an O atom with a Ni cluster has been calculated by use of the extended Hückel theory; from these data a semiempirical model potential for O₂ interacting with the Ni(001) surface is constructed. The results are compared with other theoretical and experimental information on the O/Ni and O₂/Ni systems.     

Ferromagnetoelastic interaction in antiferromagnet with allowance for the effect of dislocations

A ferromagnetoelastic medium with antiferromagnetic ordering is described based on the methods of gauge field theory. The effect of dislocations on the quasiferro-and quasiphonon vibrational modes in a two-sublattice antiferromagnet is investigated. It is shown that this effect increases the energy gap of the quasiferromode near the orientational phase transition.     

Determination of the glueball mass with allowance for the relativistic character of interaction

Nonperturbative corrections to an interaction Hamiltonian that are associated with relativistic motion and a large coupling constant are determined on the basis of an investigation of the asymptotic behavior of the polarization loop for charged scalar particles in an external gauge field. The mass spectrum of a bound state is determined analytically. The mechanism responsible for the emergence of the constituent mass of particles that form a bound state is explained. It is shown that the contribution of the vector potential and the contribution of the potential associated with a nonperturbative character of interaction cancel each other and that the slope of the Regge trajectory is determined in terms of the string tension.     

Optical response of a diatomic system with allowance for the dipole-dipole interaction

The optical response of a diatomic system excited by monochromatic light is studied. On the basis of a semiclassical approach, the effects of rearrangement of the energy spectrum of the system due to the dipole-dipole interaction and the effects related to variations in the orientation of the atomic dipole moments under the action of microscopic fields are jointly taken into account. The strongest response of the system is shown to occur at dimensional resonance frequencies. The number of observed intensity peaks depends on the position of the observation point with respect to the interatomic axis. The frequencies of the dimensional resonances are compared with other characteristic frequencies of the atomic spectrum.     

Nonlinear diffraction in a quantum-dot system with allowance for the Hubbard interaction

The propagation of monochromatic laser radiation in a volume system of quantum dots (QDs) that are tunnel-coupled along one axis is considered. The electron energy spectrum of the QD system is modeled in the tight-binding approximation with allowance for the Coulomb interaction of electrons in the Hubbard model. The electromagnetic field of laser radiation in a QD system is described quasi-classically by Maxwell equations; as applied to this problem, they are reduced to a non-one-dimensional wave equation for the vector potential. As a result of the analysis of the wave equation in the approximation of varying amplitudes and phases, an effective equation describing the electromagnetic field in a QD system is obtained and numerically solved. The influence of the parameters of the system and the amplitude and frequency of the field of incident laser radiation on the character of its propagation is investigated. Nonmonotonic dependences of the factor characterizing the laser beam diffraction spread on the parameters of the electron energy spectrum of the system are obtained.     

Critical properties of a frustrated Heisenberg model on a stacked triangular lattice with allowance for second-nearest neighbor interaction

The critical properties of the three-dimensional antiferromagnetic Heisenberg model are investigated using the Monte Carlo method with allowance for second-nearest neighbor interaction. Pseudo-universal critical behavior of this model is observed for small lattices. A complete set of the main static magnetic and chiral indices is calculated with the use of finite-dimensional scaling theory.     

Description of the thermodynamic properties of a nonmetallic solid (germanium): A self-consistent thermodynamic approach

An algorithm is proposed for constructing a Debye-type self-consistent model of a nonmetallic isotropic solid. Using germanium as an example, it is demonstrated that the thermodynamic quantities can be adequately described over a wide range of temperatures even under significantly simplifying assumptions about the thermodynamic parameters.     

Transmission time and bandwidth in pulse code modulation (application of the statistical thermodynamic formalism)

Employing the statistical thermodynamic formalism developed in an earlier paper, it is possible to determine compact sets of transmission times for the words of PCM (pulse code modulation) messages. In particular, we deal with pulses of zero or unit heights. These compact signals, which lead to shorter message times and eliminate redundancy even when successive words are correlated (Markov source), may, however, require additional bandwidth. We examine two simple cases where autocorrelation functions, and therefore power spectra, can be evaluated. In one case, that of the Markov source, it proves possible to accomplishboth shorter transmission time and narrower bandwidth (half-width of the power spectrum), showing that optimization of transmission times can be very worthwhile. Techniques for deriving autocorrelation functions are discussed at length.     

材料化学分析的物理方法(Ⅱ)

原子核由一定数量的白旋为1／2的质子和中子组成．其总自旋视原子核的构成而各异自旋的原子核象个小磁体．无外加磁场时．原子核的自旋取向是随机分布的．加上一外磁场，则原子核的自旋取向受磁场的约束出现有规则的分布．以1H^1原子核为例．自旋，：1／2，在磁场下分为自旋为1／2和-1／2的两个分量．能量相差     

Dynamic and statistical simulation of the fission of highly excited atomic nuclei with allowance for the relaxation stage

Statistical and combined dynamic-statistical approaches to simulating the fission of excited nuclei are compared. It is shown that in the statistical approach, the complete suppression of the fission pro cess during time τ _s does not result in double consideration of the emission of light particles. The importance of dynamic simulation of fission at the stage of relaxation of fission rate R _f (t) to its quasistationary value is demonstrated.     

Effect of the interaction of distant neighbors on the thermodynamic properties of anharmonic-crystal surfaces

The unsymmetrized self-consistsnt field method is employed to study the effect of the interaction of distant neighbors on the structure and thermodynamic properties of a simple model of an anharmonic crystal with a surface — the semiinfinite linear chain. Expressions are obtained for the relaxation of the end atoms, the amplitudes of their oscillations, and the free surface energy. The dependence of the relaxation on the form of the interatomic potential is studied. It is pointed out that relaxation decaying nonmonotonically into the chain as well as a change in the sign of the relaxation accompanying a change in the temperature are possible.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 10–14, February, 1988.     

The thermodynamic properties of weakly interacting quark-gluon plasma via the one-gluon exchange interaction

The thermodynamic properties of the quark-gluon plasma (QGP), as well as its phase diagram, are calculated as a function of baryon density (chemical potential) and temperature. The QGP is assumed to be composed of the light quarks only, i.e., the up and down quarks, which interact weakly, and the gluons which are treated as they are free. The interaction between quarks is considered in the framework of the one gluon exchange model which is obtained from the Fermi liquid picture. The bag model is used, with fixed bag pressure (B)for the nonperturbative part, and the quantum chromodynamics (QCD) coupling is assumed to be constant, i.e., with no dependence on the temperature or the baryon density. The effect of weakly interacting quarks on the QGP phase diagram are shown and discussed. It is demonstrated that the one-gluon exchange interaction for the massless quarks has considerable effect on the QGP phase diagram and it causes the system to reach to the confined phase at the smaller baryon densities and temperatures. The pressure of excluded volume hadron gas model is also used to find the transition phase diagram. Our results depend on the values of bag pressure and the QCD coupling constant. The latter does not have a dramatic effect on our calculations. Finally, we compare our results with the thermodynamic properties of strange quark matter and the lattice QCD prediction for the QGP transition critical temperature.     

A selfconsistent thermodynamic model of a metal solid (Using aluminum as an example)

The fundamental principles of a selfconsistent thermodynamic approach to a simultaneous calculation of the entire set of basic thermodynamic functions of an elementary nonmagnetic metal, taking into account the thermal phonon anharmonicity and the concomitant Debye temperature θ dependence, are reported. It is shown that given a step-by-step analysis, the Debye temperature includes not only lattice but also electronic parameters, which could be interpreted as an indirect thermodynamic evidence of electron-phonon interaction in metals. The model adequacy, both in terms of its quantitative and qualitative validity, is shown by the example of aluminum. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 19–27, December, 2005.     

Effect of the state of a quantized electromagnetic field on the interaction with an atom with allowance for the continuum

This paper studies the effect of a transition into the continuous spectrum on the “collapse” and “revival” of population oscillations in an atom. It is shown that at large values of the mean number of photons in a radiation field and in conditions of weak ionization the phenomena of collapse and revival can still be observed, but the amplitude of population oscillations decreases exponentially because of the damping of the level. The interaction of a quantized electromagnetic field with a Λ system of an atom when one state is continuous is examined. Expressions are derived for the probability of “survival” of the atom when the quantized field was initially in a state with a given number of photons and when it was in a coherent state. An approximate calculation of the sum in averaging over the photon number distribution in the case of a coherent field leads to expressions for the probabilities of survival of the atom that transform into expressions, as the mean number of photons tends to infinity, corresponding to the case of a field in the representation of a fixed number of photons. The possibility of a stable state existing in a coherent quantized field is examined. It is found that for a Λ system the condition for the existence of a stable state remains valid in the case of a coherent state of the field when the photon number is large. Zh. éksp. Teor. Fiz. 113, 1193–1205 (April 1998)     

On the decay of correlations inSO(n)-symmetric ferromagnets

We prove that for low temperaturesT the spin-spin correlation function of the two-dimensional classicalSO(n)-symmetric Ising ferromagnet decays faster than |x|^–constT providedn2. We also discuss a nearest neighbor continuous spin model, with spins restricted to a finite interval, where we show that the spin-spin correlation function decays exponentially in any number of dimensions.Work supported in part by NSF, Grant PHY76-17191A Sloan Fellow     

Pareto-optimal parametric synthesis of axisymmetric magnetic systems with allowance for nonlinear properties of the ferromagnet

A method of Pareto-optimal synthesis is worked out for axisymmetric magnetic systems containing ferromagnetic elements with nonlinear magnetic properties. The method is based on the simultaneous application of the swarm intelligence paradigm and the evolution optimization with the help of genetic algorithms. Numerical examples of designing the devices for producing uniform and gradient magnetic fields in their working volume are considered.