Large-scale instability in a sheared nonhelical turbulence: formation of vortical structures

We study a large-scale instability in a sheared nonhelical turbulence that causes generation of large-scale vorticity. Three types of the background large-scale flows are considered, i.e., the Couette and Poiseuille flows in a small-scale homogeneous turbulence, and the "log-linear" velocity shear in an inhomogeneous turbulence. It is known that laminar plane Couette flow and antisymmetric mode of laminar plane Poiseuille flow are stable with respect to small perturbations for any Reynolds numbers. We demonstrate that in a small-scale turbulence under certain conditions the large-scale Couette and Poiseuille flows are unstable due to the large-scale instability. This instability causes formation of large-scale vortical structures stretched along the mean sheared velocity. The growth rate of the large-scale instability for the "log-linear" velocity shear is much larger than that for the Couette and Poiseuille background flows. We have found a turbulent analogue of the Tollmien-Schlichting waves in a small-scale sheared turbulence. A mechanism of excitation of turbulent Tollmien-Schlichting waves is associated with a combined effect of the turbulent Reynolds stress-induced generation of perturbations of the mean vorticity and the background sheared motions. These waves can be excited even in a plane Couette flow imposed on a small-scale turbulence when perturbations of mean velocity depend on three spatial coordinates. The energy of these waves is supplied by the small-scale sheared turbulence.Comment: 12 pages, 14 figures, Phys. Rev. E, in pres

Quantum state of an injected TROPO above threshold : purity, Glauber function and photon number distribution

In this paper we investigate several properties of the full signal-idler-pump mode quantum state generated by a triply resonant non-degenerate Optical Parametric Oscillator operating above threshold, with an injected wave on the signal and idler modes in order to lock the phase diffusion process. We determine and discuss the spectral purity of this state, which turns out not to be always equal to 1 even though the three interacting modes have been taken into account at the quantum level. We have seen that the purity is essentially dependent on the weak intensity of the injected light and on an asymmetry of the synchronization. We then derive the expression of its total three-mode Glauber P-function, and calculate the joint signal-idler photon number probability distribution and investigate their dependence on the injection

The Problem of Scheduling for the Linear Section of a Single-Track Railway with Independent Edges Orientations

The paper is devoted to the problem of scheduling for the linear section of a single-track railway: how to organize the ow in both directions in the most efficient way. In this paper, the authors propose an algorithm for scheduling with independent edges orientations, examine the properties of this algorithm and perform the computational experiments

Ion beam sputtering method for progressive reduction of nanostructures dimensions

An ion beam based dry etching method has been developed for progressive reduction of dimensions of prefabricated nanostructures. The method has been successfully applied to aluminum nanowires and aluminum single electron transistors (SET). The method is based on removal of material from the structures when exposed to energetic argon ions and it was shown to be applicable multiple times to the same sample. The electrical measurements and samples imaging in between the sputtering sessions clearly indicated that the dimensions, i.e. cross-section of the nanowires and area of the tunnel junctions in SET, were progressively reduced without noticeable degradation of the sample structure. We were able to reduce the effective diameter of aluminum nanowires from ~65 nm down to ~30 nm, whereas the tunnel junction area has been reduced by 40 %

Entanglement measurement of the quadrature components without the homodyne detection in the spatially multi-mode far-field

We consider the measuring procedure that in principle allows to avoid the homodyne detection for the simultaneous selection of both quadrature components in the far-field. The scheme is based on the use of the coherent sources of the non-classical light. The possibilities of the procedure are illustrated on the basis of the use of pixellised sources, where the phase-locked sub-Poissonian lasers or the degenerate optical parametric oscillator generating above threshold are chosen as the pixels. The theory of the pixellised source of the spatio-temporal squeezed light is elaborated as a part of this investigation.Comment: 11 pages, 5 figures, RevTeX4. Submitted to Phys. Rev.

Nonequilibrium phenomena in multiple normal-superconducting tunnel heterostructures

Using the nonequilibrium theory of superconductivity with the tunnel Hamiltonian, we consider a mesoscopic NISINISIN heterostructure, i.e., a structure consisting of five intermittent normal-metal (N) and superconducting (S) regions separated by insulating tunnel barriers (I). Applying the bias voltage between the outer normal electrodes one can drive the central N island very far from equilibrium. Depending on the resistance ratio of outer and inner tunnel junctions, one can realize either effective electron cooling in the central N island or create highly nonequilibrium energy distributions of electrons in both S and N islands. These distributions exhibit multiple peaks at a distance of integer multiples of the superconducting chemical potential. In the latter case the superconducting gap in the S islands is strongly suppressed as compared to its equilibrium value