Search for the magnetic field of the O7.5 III star xi Persei

Cyclical wind variability is an ubiquitous but as yet unexplained feature among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest representative of this class on the Northern hemisphere. As its prominent cyclical wind properties vary on a rotational time scale (2 or 4 days) the star has been already for a long time a serious magnetic candidate. As the cause of this enigmatic behavior non-radial pulsations and/or a surface magnetic field are suggested. We present a preliminary report on our attempts to detect a magnetic field in this star with high-resolution measurements obtained with the spectropolarimeter Narval at TBL, France during 2 observing runs of 5 nights in 2006 and 5 nights in 2007. Only upper limits could be obtained, even with the longest possible exposure times. If the star hosts a magnetic field, its surface strength should be less than about 300 G. This would still be enough to disturb the stellar wind significantly. From our new data it seems that the amplitude of the known non-radial pulsations has changed within less than a year, which needs further investigation.Comment: 2 pages, 6 figures, contributed poster at IAU Symposium 259 "Cosmic Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain, November 3-7, 200

The evolution of the stellar populations in low surface brightness galaxies

We investigate the star formation history and chemical evolution of low surface brightness (LSB) disk galaxies by modelling their observed spectro-photometric and chemical properties using a galactic chemical and photometric evolution model incorporating a detailed metallicity depen dent set of stellar input data. For a large fraction of the LSB galaxies in our sample, observed properties are best explained by models incorporating an exponentially decreasing global star formation rate (SFR) ending at a present-day gas fraction (M_{gas}/(M_{gas}+M_{stars}) = 0.5 for a galaxy age of 14 Gyr. For some galaxies small amplitude star formation bursts are required to explain the contribution of the young (5-50 Myr old) stellar population to the galaxy integrated luminosity. This suggests that star formation has proceeded in a stochastic manner. The presence of an old stellar population in many late-type LSB galaxies suggests that LSB galaxies roughly follow the same evolutionary history as HSB galaxies, except at a much lower rate. In particular, our results imply that LSB galaxies do not form late, nor have a delayed onset of star formation, but simply evolve slowly.Comment: To be published in A&

Transport of interacting electrons in arrays of quantum dots and diffusive wires

We develop a detailed theoretical investigation of the effect of Coulomb interaction on electron transport in arrays of chaotic quantum dots and diffusive metallic wires. Employing the real time path integral technique we formulate a new Langevin-type of approach which exploits a direct relation between shot noise and interaction effects in mesoscopic conductors. With the aid of this approach we establish a general expression for the Fano factor of 1D quantum dot arrays and derive a complete formula for the interaction correction to the current which embraces all perturbative results previously obtained for various quasi-0D and quasi-1D disordered conductors and extends these results to yet unexplored regimes.Comment: 12 pages, 2 figure

Рецензия на руководство для врачей «Профессиональные заболевания у работников железнодорожного транспорта»

Рецензія на посібник: Профессиональные заболевания у работников железнодорожного транспорта: учебное пособие / С.И. Ткач, А.И. Гоженко, А.Е. Лукьяненко, Е.Я. Николенко. -Одесса: Пальмира,2008. - 168 с

Gap theory of rectification in ballistic three-terminal conductors

We introduce a model for rectification in three-terminal ballistic conductors, where the central connecting node is modeled as a chaotic cavity. For bias voltages comparable to the Fermi energy, a strong nonlinearity is created by the opening of a gap in the transport window. Both noninteracting cavity electrons at arbitrary temperature as well as the hot electron regime are considered. Charging effects are treated within the transmission formalism using a self-consistent analysis. The conductance of the third lead in a voltage probe configuration is varied to also model inelastic effects. We find that the basic transport features are insensitive to all of these changes, indicating that the nonlinearity is robust and well suited to applications such as current rectification in ballistic systems. Our findings are in broad agreement with several recent experiments.Comment: 8 pages, 6 figure

Effects of Local Fields on Electron Beam Voltage Measurement Accuracy

Voltages at various levels have been measured on unpassivated aluminum lines in an integrated circuit (IC) test structure with widths and spacings ranging from 1.5 μm to 8 μm. For the measurements a pulsed electron beam (e-beam) system with 1 keV electrons was used in conjunction with a planar retarding field analyzer. Examination of the results shows that the voltage measurement accuracy is affected by local fields created by the potential differences between neighboring conductors on the IC. They also reveal how these fields and measurement errors are related to the conductor line width and spacing, the supply voltage level and the strength of the extraction field above the circuit