[en] Is studied the effect of temperature on the lifetime of the resonant macroscopic quantum tunnelling voltage state. In view of experiments it is considered a merit factor in order to balance between measuring extremely small signals of longer duration or larger signals of shorter duration

[en] It is observed that Hartmann flow sustains wave propagation in its centre region for waves whose phase speed is less than the maximum flow speed. Similar to the previous observations it is found that viscous boundary layers around the critical level and at the wall replace the exponential regions and wave sinks req uired for over-reflection in the inviscid flow. The uniform magnetic field stabilizes the flow for small-wave-number disturbances along the ζ-direction. Over-reflection is confined to a few ranges of phase speeds for which the two boun dary layers are close together rather than widely separated. These ranges corres pond exactly to those for which unstable eigenmodes exist. Over-reflection is associated with a wave phase tilt opposite in direction to the shear

[en] An attempt is made to present a simplified analysis of the thermoelectric power in II-VI semiconductors in the presence of quantization of band states under different physical conditions. The thermopower decreases with increasing electron concentration in different manners, which is a direct consequence of band state quantization. It is plotted the thermopower with various other physical variables and the same power exhibits different types of oscillations in low-dimensional II-Vi structures having quantum confinements in one, two and three dimensions, respectively. The well-known results for parabolic energy bands are also been obtained as special cases of generalized formulations under certain limiting conditions. In addition, the theoretical results are in quantitative agreement with the experimental data

[en] The nonlinear propagation of low-frequency electromagnetic Alfven waves along an external static magnetic field in a weakly collisional compensated semiconductor plasma has been investigated. A new kind of envelope solitons in the magnetoactive semiconductor plasma are found to exist. The behaviour of the solitons is discussed

[en] A quantum-mechanical effect specific of the symmetry of the Cu-O plane in cuprate superconductors is presented. We show that pairs of holes in degenerate states are such that their mutual on-site Coulomb interaction W vanishes identically. A procedure for obtaining such W=0 two-hole states in clusters of any size is outlined. Small clusters also display the effect provided they have the full C_4v symmetry and a Cu atom at the centre. In the many-body problem that arises when degenerate states are at the Fermi level, these holes interact indirectly through their screening clouds. This interaction is analysed by the exact diagonalization of an extended Hubbard Hamiltonian in doped CuO₄ clusters and is shown to be attractive with the literature values of all parameters. Bound states of ¹B₂ symmetry and binding energies of the order of 10 meV are obtained. The hole-hole interaction readily returns strongly repulsive if impurity potentials lower the symmetry. Off-site interactions fit well into the scheme. If the current estimates of the parameters are correct, this correlation effect alone can explain pairing

[en] In this report the authors report new optical data showing that disorder in porous silicon leads to strong carrier localisation. Light emission in PS (porous silicon) is suggested to occur through transitions involving localized states

[en] The converging shock wave is a classical example of self-similarity of the second kind, in which the similarity exponent δ^* is found solving a non-linear eigenvalue problem. Work on this problem has been mostly concerned with the precise calculation of δ^* for various adiabatic exponents γ. The authors present new calculations of δ^*, asymptotic Mach numbers and compression ratios for cylindrical and spherical shocks for many γ values; they present profiles of the physical variables, and find some striking properties of the solutions, previously unnoticed

[en] The authors re-examine the topological approach to the integer quantum Hall effect in its original form where an average of the Kubo-Hall conductivity of a magnetic Bloch band has been considered. For the precise definition of this average it is crucial to make a sharp distinction between the discrete Bloch wave numbers k₁, k₂ and the two continuous integration parameters α₁, α₂. The average over the parameter domain 0 ≤ α_j < 2π, j = 1, 2 of the Hall conductivity of the band is a sum of integrals, each associated with different discrete k₁, k₂. They show how this can be transformed into a single integral over the continuous magnetic Brillouin zone 0 ≤ α_j < 2πn_j, j = 1, 2, n_j = number of unit cells in j-direction, keeping k₁, k₂ fixed. This average prescription for the Hall conductivity of a magnetic Bloch band is exactly the same as the one used for a many-body system in the presence of disorder

[en] A previous investigation by one of us, concerning the self-consistent equilibria of a two-region (plasma + gas) cylindrical Tokamak, is extended to the similar equilibria of a Reversed-Field Pinch, where a significant current density is driven by a dynamo electric field due to turbulence. The previous model has been generalized under the following basic assumptions: a) to the lowest order, the turbulent dynamo electric field ε ^(t) is expressed as a homogeneous function of degree 1 of the magnetic field B, say ε ^(t) = α · B, with α being a 2nd-rank tensor, homogeneous of degree 0 in B, and generally depending on the plasma state; b) ε ^(t) does not appear in the plasma power balance, as if it were produced by a Maxwell demon able to extract the needed power from the plasma internal energy. In particular the authors show that, in the simplest case when both α and the plasma resistivity η are isotropic and constant, the magnetic field turns out force-free with constant abnormality αμ₀ / η for vanishing axial electric field E_z. This case also been solved analytically, for whatever E_z, under circular, besides cylindrical, symmetry

[en] Autoregressions with constant parameters are special cases of a general iterative process which, in this paper, is given explicit form. No restriction is imposed to the process of variation of the random variable which is permitted to suffer both continuous variations and / or discrete jumps. As a consequence, the general autoregression assumes the same form of the iterative solution of an appropriate integral (master) equation. The procedure which leads to this conclusion is simple but not so direct and requires a special expedient that in this paper is discussed in detail