Coherent production of (K + π 0) pairs on nuclei in a Charged-Kaon beam

The cross section for the coherent production of (K ⁺ π ⁰) pairs that is associated with a chiral anomaly and with diagrams involving intermediate K*(892), ρ, ω, and ?(1020) mesons is calculated for the Coulomb interaction of K ⁺ mesons with nuclei. The number of such events that is expected for the OKA detector at the Institute for High Energy Physics (IHEP, Protvino) is presented.     

On vortex shedding from a hexagonal cylinder

The unsteady wake behind a hexagonal cylinder in cross-flow is investigated numerically. The time-dependent three-dimensional Navier-Stokes equations are solved for three different Reynolds numbers Re and for two different cylinder orientations. The topology of the vortex shedding depends on the orientation and the Strouhal frequency is generally higher in the wake of a face-oriented cylinder than behind a corner-oriented cylinder. For both orientations a higher Strouhal number St is observed when Re is increased from 100 to 500 whereas St is unaffected by a further increase up to Re=1000. The distinct variation of St with the orientation of the hexagonal cylinder relative to the oncoming flow is opposite of earlier findings for square cylinder wakes which exhibited a higher St with corner orientation than with face orientation.     

Fractional dimensional Fock space and Haldane's exclusion statistics: q/p case and t−J model

The discussion of fractional dimensional Hilbert spaces in the context of Haldane exclusion statistics is extended from the case of g = 1/p for the statistical parameter to the case of rational g = q/p with q,p coprime positive integers. The corresponding statistical mechanics for a gas of such particles is constructed. This procedure is used to define the statistical mechanics for particles with irrational g. Applications to strongly correlated systems such as the Hubbard and t−J models are discussed.     

Model calculation of the size dependence of the CESR g shift in a small sodium particle

The size dependence of the CESR g shift is calculated for a model Na cube of side L, employing single orthogonalized standing waves for the conduction electron wave-functions. The principal result of this calculation is that the absolute value of δg(L) decreases with decreasing particle size, in contrast with the predictions made for small L by Kawabata on the basis of a model with diffuse surface scattering boundary conditions.     

Theoretical study of Mn doping effects and O or Zn vacancies on the magnetic properties in wurtzite ZnO

The effects of including the exchange interaction (J) and Hubbard on-site Coulombic interaction (U) on the structural parameters and magnetic moment of Mn-doped ZnO were explored. The calculations were performed with the plane-wave pseudopotential method along with generalized-gradient approximations (GGA). Using the GGA+U + +J method by applying Hubbard corrections U_d to the Zn 3d states and U_p to the O 2p states, the lattice constants were calculated for various reported Hubbard parameters. The difference in the lattice constants between the calculated results and experimental measurements is within 1% for pure ZnO and pure MnO. This study considers three cases: (i) substitution of Mn for Zn, (ii) substitution of Mn for Zn combined with Zn vacancy, and (iii) substitution of Mn for Zn with O vacancy. Results are shown that the system is ferromagnetic (FM) when zinc vacancies are present. For three cases with oxygen vacancies, only one of them is FM. It was also found that the Hubbard U and exchange interaction J improved the calculated results, allowing it to exhibit good agreement properties for Mn-doped ZnO with the experimental data.     

Newtonian versus Langevin dynamics: Example of ϕ4-model with infinite range interactions

The functional integral representation for the generating functional (GF) of the canonically averaged ensemble with an underlying Newtonian dynamics is obtained. It is shown that for this representation the non-linear fluctuation-dissipation theorem (NFDT) has the same form as for the Langevin dynamics case. This GF-representation is used for the investigation of the dynamics of the ϕ⁴-model with infinite range interactions at T > T_c. It is shown that the kinetic equation for the complete correlation function has the same form as for the Langevin dynamics case, which was considered before. All peculiarities of Newtonian dynamics are absorbed by one-particle (2-point and 4-point) correlator and response functions. The analysis of this equation shows that the 1/N-fluctuations (where N is the number of particles) restore the ergodicity of the system with the characteristicsrate τ⁻¹ ∼ μ²/N, where μ is a coupling constant.     

Entanglement dynamics in Coriolis coupled rovibrational states of formaldehyde

The entanglement dynamics of two vibrational modes of a polyatomic molecule coupled by Coriolis interaction to overall molecular rotation is studied in terms of two negativities, N(t) and N_s(t), respectively, defined by the minimum of the eigenvalues and by the sum of the negative eigenvalues of the partial transpose of a density matrix. Various initial states are the products of Dicke states and the products of coherent states of vibrations and rotations. Formaldehyde is taken as an example, and the von Neumann entropy s(t) is simulated for the comparison with both negativities. It is shown that negativity N_s(t) is positively correlated with entropy s(t), and the correlated behavior between negativity N(t) and entropy s(t) strongly depends on initial states. However, these three indicators of entanglement display a dominantly positive correlation for the coherent states with small or large parameters. In addition, for the latter state two quantities N(t) and s(t) are nearly unchanged for a long time. This time can be further increased by the increasing of vibrational quantum number so that molecular information processing and quantum computing is allowed. These results are useful in quantum information theory.     

Oscillator strengths for 3dn4s → 3dn4p transitions in the iron series

The observed oscillator strengths for the 3dⁿ4s → 3dⁿ4p transitions in the iron series show anomalous behaviour for Cr and Mn : the former is exceedingly small whereas the latter is unusually large.Theoretical Hartree-Fock gf-values are reported and a considerable discrepancy with experimental values is noted for Cr. The effect of the interaction of 3dⁿ4p with 3d^n?14s4p is studied using a fixed core, multi-configuration Hartree-Fock approximation. This interaction does not improve significantly the agreement with observed values.     

Superconductivity of Hf-Ta and Ta-W alloys under pressure

Measurements on ten binary alloys of the body-centered cubic part of the 5d-alloy series Hf-Ta and Ta-W yield a linear relationship between the derivatives of the quantityg both with respect to pressure and to valence electron concentration, whereg is defined byT _c ∝ θ exp (?1/g). This result agrees with observations on alloys of the 4d-series, Zr-Nb and Nb-Mo. It is concluded that for these alloys composed from the central part of the 4d and 5d transition series, the interaction responsible for superconductivity is less subject to complications than for other transition metals and is probably governed by the electronic density of states. Data on the variation of the transition temperature with concentration in Hf-Ta alloys are included.     

The isovector monopole state and the escape width of double analog resonances

An irreducible vector operator is used to generate isovector monopole states with welldefined values of T and T_z in N > Z nuclei. Reduced transition strengths are calculated in two different ways and the results seem compatible. The Wigner-Eckart theorem is used to derive expressions for the mixing of the monopole states with the ground state and its analog states. Expressions for the escape widths of the monopole states are also derived. An application is made to double analog resonances, and it is found, contrary to expectations, that the mixing with the T?1 monopole state is unable to account for the observed elastic partial width of these resonances in medium and heavy nuclei. The reason for this is the small escape width of the monopole state.     

Self-focusing of cosh-Gaussian laser beams in a parabolic medium with linear absorption

The authors have investigated self-focusing of cosh-Gaussian laser beams in a parabolic medium with linear absorption. The field distribution in the medium is expressed in terms of beam-width parameter f, decentred parameter b and absorption coefficient k_i. The differential equation for f parameter is established by following Wentzel–Kramers–Brillouin (WKB) and paraxial approximations through parabolic wave equation approach and analytical solution is obtained for the same. The behavior of f parameter with the normalized distance of propagation η is studied at various values of b with different absorption levels in the medium. The results are presented graphically and discussed.     

Dependence of nuclear Z factor on the chemical potential

A simple microscopic formula is derived for the renormalization factor Z of Green’s function on the basis of the self-consistency relation of many-body theory and the Brueckner method. This formula involves the derivative of the Brueckner G matrix with respect to energy. Based on the analysis of the properties of the G matrix for a slab of nuclear matter, the G matrix is approximately replaced by the off-mass-shell T matrix taken for free NN scattering at a negative energy E equal to the doubled chemical potential μ of the nucleus under consideration. The Z factor thus calculated depends strongly on μ and decreases with |μ|. This effect is important for analyzing the properties of atomic nuclei near the drip line, where μ is zero.     

On the problem of high temperature superconductivity

This article is a brief review of the present situation in theoretical investigations of high temperature superconductivity. The main subject is a discussion of the formula for a critical temperature T_c for a homogeneous and isotropic substance with arbitrary permeability ?(q, ω). The problem of the maximum possible value of T_c is discussed. It is concluded that at present there are no grounds to consider that values of T_c ? 100°K to be impossible. The paper ends with some remarks on the exciton mechanism of superconductivity for the case of superconductors with a plane geometry.     

Theoretical study of hyperfine interactions at the Ta site in Hafnia polymorphs

The electric field gradient resulting from Ta substitutional defect in normal monoclinic phase is studied using all-electron ab initio NFP-LMTO method. Hyperfine parameters in Pbca and Pnma phases have also been calculated to determine the usefulness of quadrupolar interactions in the investigation of phase diagrams under hydrostatic pressure. Predictions for hyperfine parameters in high temperature P42nmc and Fm3m phases were also developed. Given the donor behavior of Ta in HfO₂, two charge states, 0 and +1, have been studied for each phase. Although HFI do not vary significantly with charge, it was determined that for a Ta+1 in P21/c phase hyperfine parameters is consistent with experimental results. Quadrupolar interactions for transitions to denser phases show important variations with respect to that of the normal phase: asymmetry parameter for Pbca and the electric field gradient for Pnma both increase substantially. At high temperature phases, drastic decrease in both EFG and asymmetry parameter in P42nmc is observed, while they almost vanish in Fm3m.     

A method for solving reaction and bound-state few-body problems: A > 3

A method for solving the few-body problems is described, which is based on the expansion in a small parameter: ratio of the potential energy to the kinetic energy for the states with the hyperspherical numbers K exceeding some value K ₀. The initial problem is reduced to that with modified dynamics in the subspace with K ≤ K ₀ without expansion in the basis functions at K > K ₀.     

Fast approximate technique for the cumulative wavenumber model to modeling radiative transfer in a mixture of real gas media

In the cumulative wavenumber (CW) model, the total range of the absorption cross-section Cη is subdivided into the supplementary absorption cross-section of gray gases C_j, j=1,…,n, where n is the number of gray gases; and the wavenumber region is subdivided into intervals Δ_i=[η_i−1, η_i], i=1, 2,…,p, where p is the number of intervals. The intersection of the two spectral subdivisions is used to define the modeling of the fractional gray gas D_ij. In the CW model, we solve the radiative transfer equation (RTE) in every subinterval D_ij; then it is necessary to solve n x p times the spectral form of the RTE for complete spectral integration. In this work, the CW model is used with a numerical approximation technique based on additive properties of radiative intensity to reduce the solution of RTE to n new fractional gray gas D_j for complete spectral integration. The CW model was first coupled with the discrete ordinates method and the accuracy of the simplified technique and the algorithm was first examined for one-dimensional homogeneous media; results are compared with line-by-line calculations and it is found that the CW model with the simplified technique is exact for the homogeneous media examined. Also, the fast approach is tested in the diffuse reflecting boundaries case. The CW model is implemented in a bi-dimensional enclosure containing real gases in isothermal cases. Afterwards, this approximate technique is extended to non-isothermal and non-homogeneous cases; the results are compared with line-by-line calculations taken from literature and good agreement was found. The results obtained using the acceleration technique for the CW model agree with the results of original CW model. With this acceleration technique the CPU time decreases p times. Spectral database HITRAN and HITEMP are used to obtain the molecular absorption spectrum of the gases.     

Adhesion of elastic films on mound rough surfaces

In this work, we have investigated the adhesive behaviour of elastic films in contact with solid substrates, which are bounded by mound surface roughness. This type of roughness is described by the rms roughness amplitude w, the average mound separation Λ, and the system correlation length ζ. It is shown that both lateral roughness parameters Λ and ζ strongly influence adhesive characteristics. Indeed, with increasing elastic film modulus E, film adhesion is only possible for sufficiently large mound separations Λ. Moreover, the critical elastic modulus E_c (for which spontaneous film decohesion takes place for E>E_c) is shown to increase fast with increasing mound separation Λ when Λ?ζ, while as a function of the system correlation length ζ it increases relatively fast when ζ?Λ.     

Coloring of a one-dimensional lattice by two independent random walkers

A new type of question in random walk theory is formulated and solved for the particular case of a periodic one-dimensional lattice. A “red” and a “blue” random walker perform simultaneous independent simple random walk. Each site is initially uncolored and takes irreversibly the color, red or blue, of the first walker by which it is visited. We study the resulting coloring of the final state, in which each site is either red or blue, on a ring of L sites. We calculate the probability P(n, L) that site n is red, in the scaling limit L → ∞ with n/L fixed, for walkers initially on diametrically opposite sites. We determine by simulation the number of interfaces (that is, pairs of neighboring red and blue sites), for initial separation a between the walkers. This number is ≈ 2.5 for initially diametrically opposite walkers, and appears to increase logarithmically with L/a.     

The multiloop covariant tadpole operator and amplitudes for the bosonic string

An explicit expression is given for the covariant tadpole operator with an arbitrary number of loops, including the ghost zero mode contribution. Its integrand is recast in geometrical terms and is recognized to give the g-vacuum for the bosonic string recently discussed in the literature. By joining the g-tadpole to an N-reggeon vertex the general orientable dual amplitude with g loops is obtained.