On random topological Markov chains with big images and preimages

We introduce a relative notion of the 'big images and preimages'-property for random topological Markov chains. This then implies that a relative version of the Ruelle-Perron-Frobenius theorem holds with respect to summable and locally Hoelder continuous potentials.Comment: Corrected and extended version of the article published in Stochastics and Dynamics 201

Electrical detection of spin accumulation in a p-type GaAs quantum well

We report on experiments in which a spin-polarized current is injected from a $GaMnAs$ ferromagnetic electrode into a $GaAs$ quantum well through an AlAs barrier. The resulting spin polarization in the GaAs well is detected by measuring how the current, tunneling to a second $GaMnAs$ ferromagnetic electrode, depends on the orientation of its magnetization. Our results can be accounted for the non-relaxed spin splitting of the chemical potential, that is spin accumulation, in the $GaAs$ well. We discuss the conditions on the hole spin relaxation time in GaAs that are required to obtain the large effects we observe.Comment: 4 pages - 2 figues; one added note; some numbers corrected on page

Equilibrium states of the pressure function for products of matrices

Let $\{M_i\}_{i=1}^\ell$ be a non-trivial family of $d\times d$ complex matrices, in the sense that for any $n\in \N$, there exists $i_1... i_n\in \{1,..., \ell\}^n$ such that $M_{i_1}... M_{i_n}\neq {\bf 0}$. Let $P \colon (0,\infty)\to \R$ be the pressure function of $\{M_i\}_{i=1}^\ell$. We show that for each $q>0$, there are at most $d$ ergodic $q$-equilibrium states of $P$, and each of them satisfies certain Gibbs property.Comment: 12 pages. To appear in DCD

Transiting exoplanets from the CoRoT space mission. VIII. CoRoT-7b: the first super-Earth with measured radius

Copyright © The European Southern Observatory (ESO)Aims. We report the discovery of very shallow (ΔF/F ≈ 3.4×10−4), periodic dips in the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion. Methods. We used CoRoT colours information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT light curve to derive parameters of the companion. Results. We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation >0.40'' or triple systems are almost excluded with a 8 × 10−4 risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 59 ± 3 × 10−5 day and a radius of Rp = 1.68 ± 0.09 REarth. Analysis of preliminary radial velocity data yields an upper limit of 21 MEarth for the companion mass, supporting the finding. Conclusions. CoRoT-7b is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, ≈1800–2600 K at the substellar point, and a very low one, ≈50 K, on its dark face assuming no atmosphere, have been derived

ÉTUDE PAR CANALISATION DES DÉFAUTS CRÉÉS DANS GaAs PAR L'IMPLANTATION DE Zn+ DE 1 MeV

Le profil de défauts résultant du bombardement ionique d'un monocristal est d'un grand intérêt pour de nombreuses applications. Nous avons utilisé la méthode de rétrodiffusion à grand angle d'ions He+ de 1,5 MeV canalisés, pour étudier la distribution des centres de diffusion créés par l'implantation à 77 K d'ions Zn+ de 1 MeV dans GaAs. Nous avons analysé les spectres de rétrodiffusion à l'aide des calculs de diffusion plurale de Keil et de Meyer et de l'approximation linéaire de Ziegler. Les résultats de ces mesures peuvent se résumer ainsi : Les calculs de Keil et Meyer vérifiés sur des couches évaporées de Ge, ne donnent pas de très bons résultats dans le cas de nos spectres : les phénomènes de diffusion des ions du faisceau d'analyse ne sont pas les mêmes sur une zone endommagée que sur un film amorphe. Le pic et la largeur de la distribution de défauts sont en bon accord avec les calculs théoriques de Sigmund et Sanders sur le profil d'énergie déposée par les ions dans les solides. Nous montrons qu'il est nécessaire de tenir compte de l'énergie transportée par les atomes déplacés loin de leur position primitive.The depth profile of the lattice disorder resulting from ion bombardment of single crystal is of interest in many applications. Channeling effects on the yield of large angle backscattered 1,5 MeV He+ were used to investigate the scattering centers distributions in 1 MeV zinc implanted gallium arsenide at substrate temperature of 77 K. We have used the plural scattering treatments of Keil and Meyer and the linear scattering approximation of Ziegler to analyse the spectra. The results of the measurements may be summarized as follows : The treatments of Keil and Meyer, verified on evapored layers of Ge, do not work fairly well in our case : the scattering effects of the analyzing beam were not the same on a damaged region and on an amorphous film. The peak and the width of the damage distribution agree with the Sigmund Sanders's theorical calculations of the distribution of energy deposited by ions in solids. The necessity of taking the energy transported by recoils away from their point of origin into account is demonstrated

Competency of Nicotiana tabacum L. stem tissues to dedifferentiate is associated with differential levels of cell cycle gene expression and endogenous cytokinins

International audienc