A modified Kramers approach to describing the fission of excited atomic nuclei

We present a detailed comparison of the analytical Kramers fission rate (KFR) and the dynamic quasi-stationary rate (QSFR) obtained by numerical simulation. It turns out that for the polynomial potential, the KFR regularly exceeds the QSFR by more than 5%. We obtain KFR corrections that allow us to reduce this disparity to 1%.     

New approach to nonlinear dynamics of fullerenes and fullerites

A new type of nonlinear (anharmonic) excitations—bushes of vibrational modes—in physical systems with point or space symmetry is discussed. All infrared-active and Raman-active bushes for C₆₀ fullerene are found by means of special group-theoretical methods.     

Law describing the approach to saturation of porous anisotropic materials

A law is obtained for the approach to saturation with respect to magnetization for anisotropic magnetic materials with inhomogeneous saturation magnetization. In the calculation, the spin-wave formalism is used. The effect of an inhomogeneous exchange interaction on the approach to saturation is taken into account. The relations obtained are generalizations of the already known Neel and Holstein-Primakov formulas.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 32–38, August, 1979.     

Adiabatic hyperspherical approach to describing low-energy mesic-atom scattering

The adiabatic hyperspherical approach developed previously is used to describe the asymmetric mesic-atom scattering aμ+b → aμ+b, a+bμ (a, b=p, d, t) in the collision-energy range 10^?3≤?≤10² eV. Boundary conditions for J≠0 scattering states are formulated, and partial cross sections for J=0–3 are calculated. Effective numerical codes are developed, and a fast convergence of the adiabatic hyperspherical approach is demonstrated: to achieve a precision of about 1% in the calculated cross sections, it is sufficient to use a basis of not more than ten adiabatic hyperspherical functions. The results that we obtained are compared with the previous ones.     

A renormalization approach to the band structure of superlattices

A k-space renormalization technique for evaluating the band structure of superlattices is examined. The large number of degrees of freedom of a superlattice tight-binding Hamiltonian is first reduced by exploiting the translational symmetry properties in layers perpendicular and parallel to the superlattice axis. The remaining degrees of freedom of the unit supercell are then systematically eliminated by renormalization techniques. Our combination of projective techniques on the one hand and full exploitation of symmetry properties on the other result in a very flexible and efficient algorithm. Some results for a simplified single-site model superlattice are presented as an example of our novel procedure.     

Electronic structure of linear chains of fullerenes

The band structure of linear chains of fullerene molecules is calculated as a function of the intermolecular π-electron overlap integral T, which increases under increasing external pressure. Chains consisting of neutral (C₆₀) and charged (C ₆₀ ⁻ ) molecules are studied. It is shown that there is a sharp transition from a metal (or narrow-gap semiconductor) to an insulator (with band gap ∼1 eV)with increasing T. The proposed model makes it possible to describe the formation of solid-carbon struc-tures, containing chains of covalently bound fullerene molecules, with different pressure-dependent semiconductor properties. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 647–650 (25 April 1997)     

A pure geometric approach to stellar structure

The present work represents a step in dealing with stellar structure using a pure geometric approach. Geometric field theory is used to construct a model for a spherically symmetric configuration. In this case, two solutions have been obtained for the field equations. The first represents an interior solution which may be considered as a pure geometric one in the sense that the tensor describing the material distributions is not a phenomenological object, but a part of the geometric structure used. A general equation of state for a perfect fluid, is obtained from, and not imposed on, the model. The second solution gives rise to Schwarzschild exterior field in its isotropic form. The two solutions are matched, at a certain boundary, to evaluate the constants of integration. The interior solution obtained shows that there are different zones characterizing the configuration: a central radiation dominant zone, a probable convection zone as a physical interpretation of the singularity of the model, and a corona like zone. The model may represent a type of main sequence stars. The present work shows that Einstein’s geometerization scheme can be extended to gain more physical information within material distribution, with some advantages.     

Kinetic approach for describing the fatigue effect in ferroelectrics

A new kinetic approach is proposed for explaining the fatigue effect in ferroelectrics. A self-consistent variation in the area and geometry of the switching region of a sample upon a cyclic switching accompanied by the formation and growth of kinetically frozen domains is considered. It is assumed that fatigue is due to self-organized formation of a spatially inhomogeneous internal bias field due to retardation of bulk screening of the depolarization field. Variations in the switching charge and in the amplitude of switching current, which are calculated with the help of computer simulation of domain kinetics upon cyclic switching, are in good agreement with experimental data obtained for thin lead zirconate-titanate (PZT) thin films.     

Combined dynamical and statistical approach to describing induced fission of heavy nuclei

A combined dynamical and statistical approach to describing induced fission of heavy nuclei is proposed. This approach takes into account the nuclear-dissipation phenomenon and the double-humped structure of the fission barrier. A method that is intended for calculating the angular distribution of fission fragments and which is applicable over a broad range of excitation energies is discussed. The potential of the approach is demonstrated by addressing the problems of self-consistently describing experimental data on fission probabilities for plutonium and americium isotopes, the yields of shape isomers in the α+²³⁸U reaction at alpha-particle energies in the range E _α = 20–32 MeV and the d+^242,240Pu reactions at deuteron energies in the range E _d = 20–30 MeV, fission times in the α + ²³⁸U reaction at alpha-particle energies in the range E _α = 20–32 MeV, and angular distributions of fission fragments in the α + ²³⁸U, ²³⁷Np reactions at alpha-particle energies in the range E _α = 20–100 MeV.     

Theoretical study on structure of boron nitride fullerenes

We propose the parameters of the Stillinger-Weber potential for hexagonal boron nitride (BN) structures. For the reliability of these parameters, the structural property of BN fullerenes is investigated. The stability of BN fullerenes increases with increasing the number of atoms, due to the reduction of the curvature effect of BN fullerenes. The structures of the relative stable fullerenes are B₁₆N₁₆, B₁₈N₁₈, B₂₂N₂₂, B₂₅N₂₅, and B₂₈N₂₈.     

The electronic structure of polymerized fullerenes and dimerized heterofullerenes

\chem{Rb_1C_{60}} and dimerised using electron energy-loss spectroscopy in transmission. From the excitation spectra a reduced density of states is observed for polymerized . This is in contrast to and can be explained by the different type of \squt{doping} and by the different bonding between the fullerene molecules in the two systems. Additional information about the optical properties was obtained from the low energy loss function. Using a Kramers-Kronig analysis, the dielectric function, (), and the optical conductivity, (), have been derived. and the onset of the spectral weight have been compared between the polymer, the dimer and . This onset of spectral weight is found to be at and for o- and for , respectively. Received: 28 October 1996/Accepted: 13 December 1996     

A nonperturbative variational approach to the vacuum structure in quantum chromodynamics

We study the vacuum structure in QCD in a nonperturbative manner using a variational approach with gluon condensates. We show that in Coulomb gauge as the coupling becomes moderately strong, the perturbative vacuum of QCD becomes unstable leading to gluon condensates and a gauge dependent effective mass for the gluons related to the gauge independent value of 〈vac‖G _μν ^a G ^aμν‖vac〉 of Shifmanet al.     

Another way to shape the comprehensive analytical approach describing electromagnetic energy distribution through four-slab-layer structures

Starting from the generalised four-slab layer in electromagnetic theory and photonics, this paper introduces a convenient method and a new proper change of variables in order to obtain the global analytical expressions of the power flows in such multilayer structures for the TE_m and TM_m optical modes. These proper changes of variables and relevant definitions of apt new parameters (Θ, W, Y and ξ) allow us to derive and shape new general analytical formulations and normalizations in terms of power flows. According to such specific parameters, it can be noted that such a comprehensive result brings in an effective criteria form of the classical results ascribed to three-slab problems. Moreover, we have verified with specific cases regarding three-slab problems the validity of our new global frame for analysing power flows. It clearly appears that classical three-slab-waveguide expressions directly stem from our formulation. Naturally, this global four-slab-waveguides approach can be used directly to the analytical calculus of corresponding ratios of power between the different layers, such as the core compared with buffer layers as upper and lower claddings.     

A nuclear structure approach to the nucleon-nucleus optical potential at low energy

An antisymmetrized microscopic calculation of the optical potential for nucleon-⁴⁰Ca elastic scattering is derived. RPA correlations taken into account in the one-particle mass operator are shown to bring a correction to the first-order real potential at low energies and to lead to an imaginary potential. Both are calculated for incident nucleon energies between 10 and 50 MeV. Their general properties are studied in great detail and, after comparison with empirical imaginary potentials, the reliability of such an approach is discussed according to the value of the incident energy.     

Prolongation structure for the reduced Maxwell-Bloch equations describing the two-photon self-induced transparency

The reduced two-phonon Maxwell-Bloch equations are shown to have the nontrivial prolongation structure of Wahlquist and Estabrook. As a result, the associated Lax representation is determined.