Table of contents

We consider a toy model of a vacuum closed Friedman-Robertson-Walker universe. The parametric amplification of vacuum metric fluctuations dynamically induced close to the initial singularity results in production of squeezed gravitons. Then we recall that the longest wavelength gravitons propagating in the closed Friedman-Robertson-Walker background are maintaining the symmetry of Bianchi IX type. As the scale factor goes to zero (and gravitons gain their importance) the complex behavior of the Bianchi IX model (mixmaster dynamics) close to the singularity may be interpreted as a result of interaction between gravity waves. A similar scenario may be expected in a more general inhomogeneous case. Therefore we put foreward an idea that the initial and the final singularities may be fundamentally different. This point of view is analogous to that of Penrose who claims that such a fundamental distinction is an inevitable feature of gravity expressed in overwhelming tendency to produce clumpiness in the universe.

A novel algorithm for a reconstruction of the phase shift profile produced by a transparent object in a coherent wave, from a set of two recorded intensity distributions is presented. Contrary to well known algorithms of in-line holography, the method works under the near-field condition where the size of the first Fresnel zone is much less than the characteristic size of the object's details. Such a condition is typical for an in-line holography experimental setup with the use of coherent high energy x-rays (E > 20 keV) produced by synchrotron radiation sources of the third generation like ESRF. The novel algorithm is fast and insensitive to a partial loss of coherence or weak detector resolution. The method can be applied to x-ray refraction tomography.

Using experimental data from the neutron transmission measurements on enriched ^206,207,208Pb, natural Pb and Bi targets, the potential scattering radii R' and the electric polarizability of the neutron α_n were determined by general least squares fit at fixed neutron-electron bound scattering length values: b_ne = −1.32 × 10⁻³ fm (Garching) and b_ne = −1.59 × 10⁻³ fm (Dubna). The evaluations were performed in two versions: (1) The potential scattering radii R' were taken as fitted parameters; (2) R' values were deduced from optical model calculations. The obtained potential scattering radii values are in the range R' = 9.0 − 10.0 fm. The electric polarizability of the neutron in the first version resulted in α_n = +(0.12 ± 0.44) × 10⁻³ fm³ with the Garching b_ne value and α_n = −(0.97 ± 0.44) × 10⁻³ fm³ with the Dubna b_ne value, but in the second calculation version - in α_n = −(0.14 ± 0.37) × 10⁻³ fm³ with both b_ne values. On the basis of obtained results we give preference to the Garching b_ne value.

We report measurements of cross sections for multielectron capture processes in collision between Ne¹⁰⁺ and Ar at 20 and 190 keV energies. We also present visible photon spectroscopy at 190 keV and coincidence measurements between wavelength selected photons and recoil ions. A theoretical evaluation of the multicapture process cross sections is given in the framework of the molecular classical over the Barrier Model (MCBM). Radiative stabilization and autoionization of the excited captured electrons are estimated in a simple model based on an energy criterion.

Beam-foil spectra of silicon have been recorded in the region 450-1270 Å. Sixty new transitions have been identified as combinations between 2p³3s, 3p and 3d in O-like silicon, Si VII, leading to an almost complete description of the energy level structure in these configurations. The line identifications are supported by isoelectronic comparisons and both ab initio and semi-empirical theoretical calculations.

A method earlier suggested by the author for calculating the contribution of a particular interaction to a particular semiempirical parameter is adopted to calculate the contribution of core polarization to semiempirical values of the hyperfine structure parameters. Core polarization is envisaged as mixing with configurations originated by excitation of electrons from inner s² shells. A contribution of configuration mixing

to the hyperfine structure parameters of the configurations 3d4s, 3d², 3d4p in Sc II spectrum is calculated.

The electric dipole transitions in the nitrogen isoelectronic sequence (Z = 10-30) between the levels of the 1s²2s²2p³, 1s²2s2p⁴ and 1s²2p⁵ configurations are considered. The stationary second-order many-body perturbation theory (MBPT) is used to account for the electron correlations. Non-local potential is used to calculate the radial part of the effective Hamiltonian. Relativistic corrections were included in the Breit-Pauli approximation. The results include energies, wavelengths, and oscillator strengths for all N-like ions in the interval Z = 10-30.

The positive frequency dependent polarizability of atoms α(ω) is discussed in terms of the particle-hole polarization propagator. It is considered in the simplest approximation defined by the Bethe-Salpeter equation which includes a subset of particle-hole interactions to all orders in the Coulomb potential. Its solution is used to show that when the polarizability is formulated in terms of an effective dipole matrix element of the atomic sub-shells, the interaction kernel is symmetric and hence makes the central quantity in the formulation, the polarization function, hermitian.

The self-gravitating instability of an annular fluid jet surrounding a very dense mantle tar cylinder under oscillating periodical oblique electric fields has been developed. The potential and kinetic energies of the system are computed and the characteristic integral differential Mathieu equation is derived by utilizing the Lagrangian energy principle. Some reported works could be recovered as limiting cases. The model is self-gravitationally unstable in axisymmetric mode while it is stable otherwise giving easier experimental observation relative to fluid jets without a mantle. The electrodynamic force has a strong stabilizing influence. Resonance domains appear due to the field periodicity and in some regions the stability conditions depend only on the field frequency. Thence the time-dependent oscillating electric field improves the electrogravitational instability and reduces it to a minimum. However, whatever is the largest electrodynamic stabilizing influence, the self-gravitational instability will never be suppressed because the gravitational instability of sufficiently long waves will persist and this is physically interpreted.

The bifurcation structure of periodically driven current oscillations in the central chamber of a magnetized triple plasma device is investigated experimentally. The target chamber of the triple plasma device is positively biased with respect to the source chamber and the bias voltage mainly drops in a strong double layer formed in the central chamber. At the low potential side of the double layer, a variable negative potential forms that gives rise to a region of negative resistance in the static current-voltage characteristic of the device. In this regime, if a sufficiently high inductance is added to the external circuit, strong nonlinear low-frequency oscillations both in the plasma current and the voltage drop over the plasma occur. These oscillations are interpreted as the periodically repeated exchange between magnetic energy and particle motion in the double layer. The dynamics of the current circuit is described by a van der Pol-type equation where the nonlinearity is given by the derivative of the current-voltage characteristic of the plasma. An additional periodic driver signal, added to the bias voltage, gives rise to a considerably enriched dynamical behaviour as predicted by the theory of driven nonlinear oscillators, including frequency entrainment, quasiperiodicity, periodic pulling and period doubling bifurcations. The experimental observations are well explained by means of the known bifurcation structure of the the periodically driven van der Pol oscillator model.

The stability of the ion temperature gradient (ITG) mode in tokamak geometries is examined analytically for a non-monotonic q-profile [negative magnetic shear, (S)] for all ranges of wavelengths, short, intermediate and long. It is shown that the shear reversal has a weak stabilising influence on the unstable mode [η_i >> η_i^crit, η_i = (d ln T_i/d ln n_i)]. Hence, the best way to stabilise these modes would be to optimise the equilibrium profiles so as to keep η_i < η_i^crit and also S ⩽ 0 in the plasma interior as envisioned by Rewoldt et al (1993).

A high-purity germanium detector was used to determine differential cross sections for coherent scattering of 59.5 keV γ-rays by Fe, Zn and Nb through angles from 55° to 105°. The results were compared with theoretical calculations.

The problem of second sound propagation within the Poiseuille flow regime is considered conformably to the idealized model of an anharmonic dielectric crystal. In the framework of this model the mechanism of heat conduction is purely convective and obeys the variety of Eulerian equation for nonviscous phonon fluids. A set of equations to describe propagation of small perturbations in phonon flux is obtained. For the case of periodic motion the set reduces to wave equations featuring the parametric dependence on phonon fluid velocity. The expression for the phase velocity predicts a drift of reverse temperature wave by heat flux. The feasibility of this result to serve as a ground for experimental verification of wave equation is discussed.

The eddy current technique for the study of the resistivity of cylindrical conductors has been adapted for high precision measurements at the level of a few ppm. By using a mutual inductance bridge at frequencies where the skin depth is less than about one fifth of the radius of the sample, the asymptotic expansions for the complex susceptibility as a function of frequency may be used to obtain both the resistivity and the area of cross-section for samples measured under contactless conditions, and more important here, also their variation with pressure.

Several normal metals and superconductors have been measured at liquid helium temperatures and at pressures of up to 150 bar in order to assess the reliability of the technique. A detailed discussion of these tests is given, and they suggest that it should be practicable to measure the initial bulk modulus of even stiff metals to an accuracy of 0.1% over the temperature range 4-300 K.

The method has been applied to potassium, and to dilute K Rb alloys. The mean value of the initial bulk modulus of potassium at 4.2 K is B_T (4.2 K) = 37.83 ± 0.07 kbar, which is consistent with ultrasonic and bulk compression measurements, but with a ten-fold reduction in the uncertainty: however, this value is inconsistent with the value inferred from measurements of the de Haas-van Alphen effect, at a level of more than five times their combined standard error estimates.

The influence of the addition of a few atomic percents of V on the crystallization temperature, and the magnetic properties of amorphous iron-boron-silicon alloys were investigated using magnetic measurements and Mössbauer spectroscopy. With an increasing V content, the crystallization temperature increases, but the Curie temperature and the magnetic moment of the Fe atom decrease. We have extracted the local random anisotropy from the coercive field. The crystallization of the amorphous Fe₇₄V₆B₁₂Si₈ alloys was studied after vacuum annealing between 600 and 800 K for one hour. An analysis of the Mössbauer spectra along with supporting x-ray diffraction measurements are presented. The crystalline products of these amorphous alloys proceed from bcc-FeSi, t-Fe₃B and o-FeB phases.

Impurities in the vicinity of a weak link, modeled as a ballistic superconducting quantum point contact, fluctuate in time and generate lowfrequency voltage noise. Adopting the RSJ-model, giant fluctuations are found for bias currents (I_B) slightly exceeding the critical current (I_C). This enhanced noise level is caused by switching of a mode-quantized super-current - in the absence of quantization noise is vanishingly small. Minimal noise is always attained at I_B = √2 I_C(T). In the presence of many impurities the noise spectrum is of the form S(ω) ∝ ω^−1+β. The order of magnitude of the exponent β is universally found to be 1/ln (Γ_max/Γ_min) where Γ_max and Γ_min are the maximum and minimum rates of transitions, respectively, of the impurities.

The J-aggregates of quinocyanine dyes (5,6,5'6'-dibenzo-1,1'-diethyl-2,2'-cyanine chloride (Sh) and 1-methyl-1'-octadecyl-2,2'-cyanine perchlorate (S120)) have been fabricated in a Langmuir trough and transferred onto quartz substrate. The formation of the J-aggregates has been studied by methods of conventional absorption and fluorescence time resolved spectroscopy. The mixed J-aggregate of S120 and Sh shows two distinct absorption bands and one fluorescence band intermediate between those of the J-aggregates of the individual component dyes. These results have some anomaly compared with the mixed J-aggregates of quinocyanine dyes and its benzothiazole or benzoselenazole derivative formed in solutions (Scheibe et al., Naturwissenschaften29 474 (1937)) and in Langmuir-Blodgett films (Penner and Mobius, Thin Solid Films132 185 (1985)).