Covariant theory of particle-vibrational coupling and its effect on the single-particle spectrum

The Relativistic Mean Field (RMF) approach describing the motion of independent particles in effective meson fields is extended by a microscopic theory of particle vibrational coupling. It leads to an energy dependence of the relativistic mass operator in the Dyson equation for the single-particle propagator. This equation is solved in the shell-model of Dirac states. As a result of the dynamics of particle-vibrational coupling we observe a noticeable increase of the level density near the Fermi surface. The shifts of the single-particle levels in the odd nuclei surrounding 208-Pb and the corresponding distributions of the single-particle strength are discussed and compared with experimental data.Comment: 27 pages, 8 figure

Scaling and diffusion of oil spills in the Ocean Surface

The region of the Gulf of Lions at the northwestern Mediterranean Sea has been studied within a ten-year period from December 1996 until November 2006. More than 1000 synthetic aperture radar (SAR) images, which have been acquired by the Second European Remote Sensing Satellite (ERS 1/2) as well as from ENVISAT. We present statistical results of the structure of several features revealed by SAR such as oil spills and tensioactive slicks dynamic. We compare oil splils obtained from the projects Clean Seas,ENVA4/CT/0334, RC2003/005700, ESP2005/07551 and ESA/AO/IP2240. Since natural (caused by plankton, fish, etc.) slicks as well as man-made oil slicks dampen the small-scale surface waves, which are responsible for the radar backscattering from the ocean surface, both types of effects may be confused and give look/alike false oil spill detections. The early SAR images were processed at a resolution of 1 pixel=200m and were provided by the RApid Information Dissemination System (RAIDS) SAR processing facility in West Freugh, UK. Recent ENVISAT images directly from ESA allow a higher resolution of 1 pixel = 26 m, improving the detected turbulent scaling range. The occurrence of marine oil pollution as well as several dynamic features near Barcelona (frames 8-10, 19, 20; 200 SAR images)is itself a random multi-scale process. The use of different multifractal techniques, both using limits to the smallest and largest available scales, show that the scaling laws are very complex and depend strongly on intermittency of the assumed turbulent cascade, the shapes of the multifractal spectra functions are seen to deviate from an homogeneous multifractal and depend both on the initial conditions of the spill or slick, and on the transit time that the spill has been subjected to the local turbulence

Self-consistent calculations of quadrupole moments of the first 2+ states in Sn and Pb isotopes

A method of calculating static moments of excited states and transitions between excited states is formulated for non-magic nuclei within the Green function formalism. For these characteristics, it leads to a noticeable difference from the standard QRPA approach. Quadrupole moments of the first 2+ states in Sn and Pb isotopes are calculated using the self-consistent TFFS based on the Energy Density Functional by Fayans et al. with the set of parameters DF3-a fixed previously. A reasonable agreement with available experimental data is obtained.Comment: 5 pages, 6 figure

Optical Study of GaAs quantum dots embedded into AlGaAs nanowires

We report on the photoluminescence characterization of GaAs quantum dots embedded into AlGaAs nano-wires. Time integrated and time resolved photoluminescence measurements from both an array and a single quantum dot/nano-wire are reported. The influence of the diameter sizes distribution is evidenced in the optical spectroscopy data together with the presence of various crystalline phases in the AlGaAs nanowires.Comment: 5 page, 5 figure

Multifractal observations of eddies, oil spills and natural slicks in the ocean surface

Natural and man-made distributions of tensioactive substance concentrations in the sea surface features exhibit self-similarity at all radar reflectivity levels when illuminated by SAR. This allows the investigation of the traces produced by vortices and other features in the ocean surface. The man-made oil spills besides often presenting some linear axis of the pollutant concentration produced by moving ships also show their artificial production in the sea surface by the reduced range of scales, which widens as time measured in terms of the local eddy diffusivity distorts the shape of the oil spills. Thanks to this, multifractal analysis of the different backscattered intensity levels in SAR imagery can be used to distinguish between natural and man-made sea surface features due to their distinct self-similar properties. The differences are detected using the multifractal box-counting algorithm on different sets of SAR images giving also information on the age of the spills. Different multifractal algorithms are compared presenting the differences in scaling as a function of some physical generating process such as the locality or the spectral energy cascade

Anomalous in-plane magneto-optical anisotropy of self-assembled quantum dots

We report on a complex nontrivial behavior of the optical anisotropy of quantum dots that is induced by a magnetic field in the plane of the sample. We find that the optical axis either rotates in the opposite direction to that of the magnetic field or remains fixed to a given crystalline direction. A theoretical analysis based on the exciton pseudospin Hamiltonian unambiguously demonstrates that these effects are induced by isotropic and anisotropic contributions to the heavy-hole Zeeman term, respectively. The latter is shown to be compensated by a built-in uniaxial anisotropy in a magnetic field B_c = 0.4 T, resulting in an optical response typical for symmetric quantum dots.Comment: 5 pages, 3 figure

Production of nanopowders of oxides by means of fiber and pulse-periodical CO2 lasers

The results of investigation of YSZ, Nd:Y2O3, Al2O3 nanopowder production by laser evaporation of oxide targets in a gas current are reported in present paper. For this purpose we used the pulse-periodical CO2 laser and the continuous fiber ytterbium laser with 550 W and 600 W radiation mean power accordingly. The powders obtained by these lasers, consisted of weakly agglomerated spherical nanopartices (≥ 99 wt%), and ≤ 1 wt% of micron sized particles (drops and target fragments). Nanoparticles from various oxides produced by CO2 laser in atmospheric pressure air had close average sizes (10ч16 nm). The productivity of nanopowder synthesis by CO2 laser from YSZ 1%Nd:Y2O3, 1%Nd:Y2O3, Al2O3, and CeGdO was 23 g/hour, 29 g/hour, 24 g/hour and 80 g/hour, respectively. Unlike CO2 laser the deep melting mode is realized during evaporation of 1%Nd:Y2O3 and Al2O3 targets by fiber laser. The crater depth increases up to 300-1000 μm in this mode. As a result, the target surface became very irregular and productivity of nanopowder synthesis was less, than in the case of CO2 laser. To reduce the effect of deep melting the evaporation of a target has been investigated experimentally and theoretically. As a result of our investigations we have obtained 1%Nd:Y2O3 nanopowder with specific surface of 70 m2/g and productivity of 23 g/hour at air pressure 70 kPa. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Quantum-dot-based optical polarization conversion

We report circular-to-linear and linear-to-circular conversion of optical polarization by semiconductor quantum dots. The polarization conversion occurs under continuous wave excitation in absence of any magnetic field. The effect originates from quantum interference of linearly and circularly polarized photon states, induced by the natural anisotropic shape of the self assembled dots. The behavior can be qualitatively explained in terms of a pseudospin formalism.Comment: 5 pages, 3 figures; a reference adde