Infrared light emission from atomic point contacts

Gold atomic point contacts are prototype systems to evidence ballistic electron transport. The typical dimension of the nanojunction being smaller than the electron-phonon interaction length, even at room temperature, electrons transfer their excess energy to the lattice only far from the contact. At the contact however, favored by huge current densities, electron-electron interactions result in a nano hot electron gas acting as a source of photons. Using a home built Mechanically Controlled Break Junction, it is reported here, for the first time, that this hot electron gas also radiates in the infrared range (0.2eV to 1.2eV). Moreover, in agreement with the pioneering work of Tomchuk, we show that this radiation is compatible with a blackbody like spectrum emitted from an electron gas at temperatures of several thousands of Kelvin given by $(kB.Te)^2 = \alpha. I.V$ where $\alpha$, $I$ and $V$ are respectively a fitting parameter, the current flowing and the applied bias.Comment: 13 pages, 5 figure

Complete genomic sequence of Raphanus sativus cryptic virus 4 (RsCV4), a novel alphapartitivirus from radish

The present work reports the discovery and complete genome sequencing of a virus from symptomless radish seedlings, classifiable as a novel member of the genus Alphapartitivirus, family Partitiviridae. Total RNA extracted from germinating seedlings was sequenced using Illumina technology. Bioinformatic analysis of the RNA-seq data revealed two contigs representing the near full-length genomic sequences of two genomic RNAs representing a new virus. Analysis of the genome sequence (excluding the polyA tail, RNA1: 1976 nt and RNA2: 1751 nt, respectively) showed a genomic organization typical of viruses classed within the Partitiviridae, with each genomic RNA encoding a single open reading frame (ORF). Phylogenetic analysis of the RNA dependent RNA polymerase (RNA1 ORF) and of the capsid protein (RNA2 ORF) clearly showed the new virus can be classified within the genus Alphapartitivirus, but sequence divergence establishes it as a new species, for which the name “Raphanus sativus cryptic virus 4” is proposed

Discovery of a probable 4-5 Jupiter-mass exoplanet to HD 95086 by direct-imaging

Direct imaging has just started the inventory of the population of gas giant planets on wide-orbits around young stars in the solar neighborhood. Following this approach, we carried out a deep imaging survey in the near-infrared using VLT/NaCo to search for substellar companions. We report here the discovery in L' (3.8 microns) images of a probable companion orbiting at 56 AU the young (10-17 Myr), dusty, and early-type (A8) star HD 95086. This discovery is based on observations with more than a year-time-lapse. Our first epoch clearly revealed the source at 10 sigma while our second epoch lacked good observing conditions hence yielding a 3 sigma detection. Various tests were thus made to rule out possible artifacts. This recovery is consistent with the signal at the first epoch but requires cleaner confirmation. Nevertheless, our astrometric precision suggests the companion to be comoving with the star, with a 3 sigma confidence level. The planetary nature of the source is reinforced by a non-detection in Ks-band (2.18 microns) images according to its possible extremely red Ks - L' color. Conversely, background contamination is rejected with good confidence level. The luminosity yields a predicted mass of about 4-5MJup (at 10-17 Myr) using "hot-start" evolutionary models, making HD 95086 b the exoplanet with the lowest mass ever imaged around a star.Comment: accepted for publication to APJ

Sex-biased gene expression is repeatedly masculinized in asexual females.

Males and females feature strikingly different phenotypes, despite sharing most of their genome. A resolution of this apparent paradox is through differential gene expression, whereby genes are expressed at different levels in each sex. This resolution, however, is likely to be incomplete, leading to conflict between males and females over the optimal expression of genes. Here we test the hypothesis that gene expression in females is constrained from evolving to its optimum level due to sexually antagonistic selection on males, by examining changes in sex-biased gene expression in five obligate asexual species of stick insect, which do not produce males. We predicted that the transcriptome of asexual females would be feminized as asexual females do not experience any sexual conflict. Contrary to our prediction we find that asexual females feature masculinized gene expression, and hypothesise that this is due to shifts in female optimal gene expression levels following the suppression of sex

SINFONI in the Galactic Center: young stars and IR flares in the central light month

We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the central 30 light days of the Galactic Center [...]. To a limiting magnitude of K~16, 9 of 10 stars in the central 0.4 arcsec, and 13 of 17 stars out to 0.7 arcsec from the central black hole have spectral properties of B0-B9, main sequence stars. [...] all brighter early type stars have normal rotation velocities, similar to solar neighborhood stars. We [...] derive improved 3d stellar orbits for six of these S-stars in the central 0.5 arcsec. Their orientations in space appear random. Their orbital planes are not co-aligned with those of the two disks of massive young stars 1-10 arcsec from SgrA*. We can thus exclude [...] that the S-stars as a group inhabit the inner regions of these disks. They also cannot have been located/formed in these disks [...]. [...] we conclude that the S-stars were most likely brought into the central light month by strong individual scattering events. The updated estimate of distance to the Galactic center from the S2 orbit fit is Ro = 7.62 +/- 0.32 kpc, resulting in a central mass value of 3.61 +/- 0.32 x 10^6 Msun. We happened to catch two smaller flaring events from SgrA* [...]. The 1.7-2.45 mum spectral energy distributions of these flares are fit by a featureless, red power law [...]. The observed spectral slope is in good agreement with synchrotron models in which the infrared emission comes from [...] radiative inefficient accretion flow in the central R~10 Rs region.Comment: 50 pages, 10 figures, 2 tables, submitted to ApJ, February 6th, 2005, abstract abridge

Quantum-well states in ultrathin Ag(111) films deposited onto H-passivated Si(111)-(1x1) surfaces

Ag(111) films were deposited at room temperature onto H-passivated Si(111)-(1x1) substrates, and subsequently annealed at 300 C. An abrupt non-reactive Ag/Si interface is formed, and very uniform non-strained Ag(111) films of 6-12 monolayers have been grown. Angle resolved photoemission spectroscopy has been used to study the valence band electronic properties of these films. Well-defined Ag sp quantum-well states (QWS) have been observed at discrete energies between 0.5-2eV below the Fermi level, and their dispersions have been measured along the GammaK, GammaMM'and GammaL symmetry directions. QWS show a parabolic bidimensional dispersion, with in-plane effective mass of 0.38-0.50mo, along the GammaK and GammaMM' directions, whereas no dispersion has been found along the GammaL direction, indicating the low-dimensional electronic character of these states. The binding energy dependence of the QWS as a function of Ag film thickness has been analyzed in the framework of the phase accumulation model. According to this model, a reflectivity of 70% has been estimated for the Ag-sp states at the Ag/H/Si(111)-(1x1) interface.Comment: 6 pages, 6 figures, submitted to Phys. Rev.

On the flow-level stability of data networks without congestion control: the case of linear networks and upstream trees

In this paper, flow models of networks without congestion control are considered. Users generate data transfers according to some Poisson processes and transmit corresponding packet at a fixed rate equal to their access rate until the entire document is received at the destination; some erasure codes are used to make the transmission robust to packet losses. We study the stability of the stochastic process representing the number of active flows in two particular cases: linear networks and upstream trees. For the case of linear networks, we notably use fluid limits and an interesting phenomenon of "time scale separation" occurs. Bounds on the stability region of linear networks are given. For the case of upstream trees, underlying monotonic properties are used. Finally, the asymptotic stability of those processes is analyzed when the access rate of the users decreases to 0. An appropriate scaling is introduced and used to prove that the stability region of those networks is asymptotically maximized

The LAOG-Planet Imaging Surveys

With the development of high contrast imaging techniques and infrared detectors, vast efforts have been devoted during the past decade to detect and characterize lighter, cooler and closer companions to nearby stars, and ultimately image new planetary systems. Complementary to other observing techniques (radial velocity, transit, micro-lensing, pulsar-timing), this approach has opened a new astrophysical window to study the physical properties and the formation mechanisms of brown dwarfs and planets. I here will briefly present the observing challenge, the different observing techniques, strategies and samples of current exoplanet imaging searches that have been selected in the context of the LAOG-Planet Imaging Surveys. I will finally describe the most recent results that led to the discovery of giant planets probably formed like the ones of our solar system, offering exciting and attractive perspectives for the future generation of deep imaging instruments.Comment: 6 pages, 5 figures, Invited talk of "Exoplanets and disks: their formation and diversity" conference, 9-12 March 200

Observations of Low Frequency Solar Radio Bursts from the Rosse Solar-Terrestrial Observatory

The Rosse Solar-Terrestrial Observatory (RSTO; www.rosseobservatory.ie) was established at Birr Castle, Co. Offaly, Ireland (53 05'38.9", 7 55'12.7") in 2010 to study solar radio bursts and the response of the Earth's ionosphere and geomagnetic field. To date, three Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) spectrometers have been installed, with the capability of observing in the frequency range 10-870 MHz. The receivers are fed simultaneously by biconical and log-periodic antennas. Nominally, frequency spectra in the range 10-400 MHz are obtained with 4 sweeps per second over 600 channels. Here, we describe the RSTO solar radio spectrometer set-up, and present dynamic spectra of a sample of Type II, III and IV radio bursts. In particular, we describe fine-scale structure observed in Type II bursts, including band splitting and rapidly varying herringbone features