Study of the scientific potential of a three 40 cm Telescopes Interferometer at Dome C

Recent site testing (see: http://www-luan.unice.fr/Concordiastro/indexantartic.html) has shown that Dome C in Antarctica might have a high potential for stellar interferometry if some solutions related to the surface atmospheric layer are found. A demonstrator interferometer could be envisioned in order to fully qualify the site and prepare the future development of a large array. We analyse the performances of a prototype interferometer for Dome C made with 3 telescopes of 40 cm diameter. It assumes classical Michelson recombination. The most recent atmospheric and environmental conditions measured at Dome C are considered (see K. Agabi "First whole atmosphere night-time seeing measurements at Dome C, Antarctica"). We also study the possible science reachable with such a demonstrator. Especially we evaluate that even such small aperture interferometer could allow the detection and low resolution spectroscopy of the most favourable pegaside planets.Comment: 6 pages, 5 figures, conferences SPIE, 0rlando, 200

First result with AMBER+FINITO on the VLTI: The high-precision angular diameter of V3879 Sgr

Our goal is to demonstrate the potential of the interferometric AMBER instrument linked with the Very Large Telescope Interferometer (VLTI) fringe-tracking facility FINITO to derive high-precision stellar diameters. We use commissioning data obtained on the bright single star V3879 Sgr. Locking the interferometric fringes with FINITO allows us to record very low contrast fringes on the AMBER camera. By fitting the amplitude of these fringes, we measure the diameter of the target in three directions simultaneously with an accuracy of 25 micro-arcseconds. We showed that V3879 Sgr has a round photosphere down to a sub-percent level. We quickly reached this level of accuracy because the technique used is independent from absolute calibration (at least for baselines that fully span the visibility null). We briefly discuss the potential biases found at this level of precision. The proposed AMBER+FINITO instrumental setup opens several perspectives for the VLTI in the field of stellar astrophysics, like measuring with high accuracy the oblateness of fast rotating stars or detecting atmospheric starspots

Confining ensemble of dyons

We construct the integration measure over the moduli space of an arbitrary number of N kinds of dyons of the pure SU(N) gauge theory at finite temperatures. The ensemble of dyons governed by the measure is mathematically described by a (supersymmetric) quantum field theory that is exactly solvable and is remarkable for a number of striking features: 1) The free energy has the minimum corresponding to the zero average Polyakov line, as expected in the confining phase; 2)The correlation function of two Polyakov lines exhibits a linear potential between static quarks in any N-ality non-zero representation, with a calculable string tension roughly independent of temperature; 3) The average spatial Wilson loop falls off exponentially with its area and the same string tension; 4) At a critical temperature the ensemble of dyons rearranges and de-confines; 5)The estimated ratio of the critical temperature to the square root of the string tension is in excellent agreement with the lattice data.Comment: 26 pp. Construction of general N-ality = k strings added. The title change

Production of a Fermi gas of atoms in an optical lattice

We prepare a degenerate Fermi gas of potassium atoms by sympathetic cooling with rubidium atoms in a one-dimensional optical lattice. In a tight lattice we observe a change of the density of states of the system, which is a signature of quasi two dimensional confinement. We also find that the dipolar oscillations of the Fermi gas along the tight lattice are almost completely suppressed.Comment: 4 pages, 4 figures, revised versio

Electronic, optical and thermal properties of the hexagonal and fcc Ge2Sb2Te5 chalcogenide from first-principle calculations

We present a comprehensive computational study on the properties of face-centered cubic and hexagonal chalcogenide Ge2Sb2Te5. We calculate the electronic structure using density functional theory (DFT); the obtained density of states (DOS) compares favorably with experiments, also looking suitable for transport analysis. Optical constants including refraction index and absorption coefficient capture major experimental features, aside from an energy shift owed to an underestimate of the band gap that is typical of DFT calculations. We also compute the phonon DOS for the hexagonal phase, obtaining a speed of sound and thermal conductivity in good agreement with the experimental lattice contribution. The calculated heat capacity reaches ~ 1.4 x 106 J/(m3 K) at high temperature, in agreement with experimental data, and provides insight into the low-temperature range (< 150 K), where data are unavailable.Comment: 19 pages, 8 figure