Kondo resonance in a nanotube quantum dot coupled to a normal and a superconducting lead

We report on electrical transport measurements through a carbon nanotube quantum dot coupled to a normal and a superconducting lead. The ratio of Kondo temperature and superconducting gap $T_{K}/\Delta$ is identified to govern the transport properties of the system. In the case of $T_{K}<\Delta$ the conductance resonance splits into two resonances at $\pm \Delta$. For the opposite scenario $T_{K}>\Delta$ the conductance resonance persists, however the conductance is not enhanced compared to the normal state due to a relative asymmetry of the lead-dot couplings. Within this limit the data is in agreement with a simple model of a resonant SN-interface.Comment: 4 pages, 2 figures. submitted to the Proc. Rencontres de Moriond on Quantum Information and Decoherence in Nanosystems 200

Illumination in symbiotic binary stars: Non-LTE photoionization models. II. Wind case

We describe a non-LTE photoionization code to calculate the wind structure and emergent spectrum of a red giant wind illuminated by the hot component of a symbiotic binary system. We consider spherically symmetric winds with several different velocity and temperature laws and derive predicted line fluxes as a function of the red giant mass loss rate, \mdot. Our models generally match observations of the symbiotic stars EG And and AG Peg for \mdot about 10^{-8} \msunyr to 10^{-7} \msunyr. The optically thick cross- section of the red giant wind as viewed from the hot component is a crucial parameter in these models. Winds with cross-sections of 2--3 red giant radii reproduce the observed fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models favor winds with acceleration regions that either lie far from the red giant photosphere or extend for 2--3 red giant radii.Comment: 51 pages, LaTeX including three tables, requires 15 Encapsulated Postscript figures, to appear in Ap

Silicates in D-type symbiotic stars: an ISO overview

We investigate the IR spectral features of a sample of D-type symbiotic stars. Analyzing unexploited ISO-SWS data, deriving the basic observational parameters of dust bands and comparing them with respect to those observed in other astronomical sources, we try to highlight the effect of environment on grain chemistry and physic. We find strong amorphous silicate emission bands at 10 micron and 18 micron in a large fraction of the sample. The analysis of the 10 micron band, along with a direct comparison with several astronomical sources, reveals that silicate dust in symbiotic stars shows features between the characteristic circumstellar environments and the interstellar medium. This indicates an increasing reprocessing of grains in relation to specific symbiotic behavior of the objects. A correlation between the central wavelength of the 10 and 18 micron dust bands is found. By the modeling of IR spectral lines we investigate also dust grains conditions within the shocked nebulae. Both the unusual depletion values and the high sputtering efficiency might be explained by the formation of SiO moleculae, which are known to be a very reliable shock tracer. We conclude that the signature of dust chemical disturbance due to symbiotic activity should be looked for in the outer, circumbinary, expanding shells where the environmental conditions for grain processing might be achieved. Symbiotic stars are thus attractive targets for new mid-infrared and mm observations.Comment: 24 pages, 6 figures, 5 tables - to be published in A

Modeling RR Tel through the Evolution of the Spectra

We investigate the evolution of RR Tel after the outburst by fitting the emission spectra in two epochs. The first one (1978) is characterized by large fluctuations in the light curve and the second one (1993) by the slow fading trend. In the frame of a colliding wind model two shocks are present: the reverse shock propagates in the direction of the white dwarf and the other one expands towards or beyond the giant. The results of our modeling show that in 1993 the expanding shock has overcome the system and is propagating in the nearby ISM. The large fluctuations observed in the 1978 light curve result from line intensity rather than from continuum variation. These variations are explained by fragmentation of matter at the time of head-on collision of the winds from the two stars. A high velocity (500 km/s) wind component is revealed from the fit of the SED of the continuum in the X-ray range in 1978, but is quite unobservable in the line profiles. The geometrical thickness of the emitting clumps is the critical parameter which can explain the short time scale variabilities of the spectrum and the trend of slow line intensity decrease.Comment: 26 pages, LaTeX (including 5 Tables) + 6 PostScript figures. To appear in "The Astrophysical Journal

Multiwavelength evidence for a 15-year periodic activity in the symbiotic nova V1016 Cygni

The ~15.1 years period found in the long-term UBV photoelectric and photographic photometry of the symbiotic nova V1016 Cyg is detected also in the (J-K) colour index and in the UV continuum and emission line fluxes from IUE and HUT spectra. It could be interpreted either as the effect of recurrent enhanced mass loss episodes from the Mira type variable companion to a hot component along its ultra-wide orbit (proposed from recent HST observations) or the true orbital period of the inner, unresolved binary of a triple system. A 410-day delay of the maximum of UV emission lines fluxes with respect to the maximum of continuum was found. The pulsation period of the Mira type variable was improved to 474+/-6 days.Comment: 7 pages, 7 PostScript figures. Accepted for pubblication in A&

Amplitude of Aharonov-Bohm oscillations in mesoscopic metallic rings as a function of the DC bias voltage

We report measurements of the amplitude of the Aharonov-Bohm oscillations in a mesoscopic diffusive gold ring as a function of the DC bias voltage VDC. The amplitude of the h/e oscillations increases with VDC once the Thouless energy Ec and thermal energy are exceeded, and decreases at higher values of VDC. The increase of the amplitude is interpreted in terms of a superposition of the statistically independent contributions of eVDC/Ec energy intervals, whereas its decrease at high VDC could be attributed to enhanced inelastic scattering processes

A simple method for the determination of refractive indices of (rough) transparent solids

Simple methods for the determination of refractive indices of transparent polymers and inorganic and organic solids of irregular geometry or with scratched or corrugated surfaces are rare. A classical procedure is based on the invisibility of a body immersed in a liquid with the same refractive index as that of the body. In order to avoid the laborious procedure connected with the search for a liquid with matching refractive index and to find an approach which is independent of the observation by eye, we describe here a modified immersion method which allows the ready determination of the refractive index of solids. The present method is based on the interpolation of the maximum transmission (nTmax) of a solid immersed in liquids with different, typically non-matching, refractive indices. Illustrations with quartz glass, crown glass and poly(vinylidene fluoride) (PVDF) films showed that nTmax can be determined with a reproducibility of ± 0.003. By comparison with refractive indices determined by ellipsometry, it was concluded that the refractive index of a solid can be determined with the modified immersion method within an accuracy better than ± 0.01 when systematic errors resulting from the fit method are also taken into consideratio

Amplituda Aharonov-Bohmovih oscilacija u mezoskopskim metalnim prstenovima kao funkcija uzbudnog istosmjernog napona

We report measurements of the amplitude of the Aharonov-Bohm oscillations in a mesoscopic diffusive gold ring as a function of the DC bias voltage VDC. The amplitude of the h/e oscillations increases with VDC once the Thouless energy Ec and thermal energy are exceeded, and decreases at higher values of VDC. The increase of the amplitude is interpreted in terms of a superposition of the statistically independent contributions of eVDC/Ec energy intervals, whereas its decrease at high VDC could be attributed to enhanced inelastic scattering processes.Izvješćujemo o mjerenjima amplitude Aharonov-Bohmovih oscilacija u mezoskopskom zlatnom difuznom prstenu kao funkcije pobudnog istosmjernog napona VDC. Kad se premaše Thoulessova energija Ec i termička energija, amplituda h/e oscilacija raste s VDC, a opada pri većim VDC. Porast amplitude interpretiramo kao zbrajanje doprinosa statistički neovisnih energijskih intervala eVDC/Ec, dok njezin pad pri većim VDC pripisujemo procesima neelastičnih raspršenja

Amplituda Aharonov-Bohmovih oscilacija u mezoskopskim metalnim prstenovima kao funkcija uzbudnog istosmjernog napona

We report measurements of the amplitude of the Aharonov-Bohm oscillations in a mesoscopic diffusive gold ring as a function of the DC bias voltage VDC. The amplitude of the h/e oscillations increases with VDC once the Thouless energy Ec and thermal energy are exceeded, and decreases at higher values of VDC. The increase of the amplitude is interpreted in terms of a superposition of the statistically independent contributions of eVDC/Ec energy intervals, whereas its decrease at high VDC could be attributed to enhanced inelastic scattering processes.Izvješćujemo o mjerenjima amplitude Aharonov-Bohmovih oscilacija u mezoskopskom zlatnom difuznom prstenu kao funkcije pobudnog istosmjernog napona VDC. Kad se premaše Thoulessova energija Ec i termička energija, amplituda h/e oscilacija raste s VDC, a opada pri većim VDC. Porast amplitude interpretiramo kao zbrajanje doprinosa statistički neovisnih energijskih intervala eVDC/Ec, dok njezin pad pri većim VDC pripisujemo procesima neelastičnih raspršenja