Chemistry of the CO dimer at low temperatures

Researchers conducted a series of experiments on the chlorine-catalyzed photodecomposition of O sub 3 both in the gas and in inert solvents such as CF sub 4 and CO sub 2 in the temperature range about 190 to 225 K. The liquid medium was chosen in order to minimize possible surface loss of long-lived ClO dimer, and to aid in the stabilization of transient excited intermediates. The mechanism of dimer formation was as follows: (1) Cl sub 2 + hv yields Cl + Cl; (2) Cl + O sub 3 yields ClO + O sub 2; (3) ClO + ClO yields Cl sub 2 O sub 2. The experiments were done in cooled low temperature cells, with irradiation from an Osram high pressure mercury arc, filtered to remove radiation below 325 nm. Spectral analysis was by means of a Cary Model 2200 UV spectrometer. The principal objectives were: (1) to determine the lifetime of the dimer as a function of temperature; (2) to observe spectral changes in the mixtures which could be attributed to dimer or related products; and (3) to observe chemical or photochemical reactions of the dimer

Les enjeux de la politique rizicole en Guinée

La production de riz est très répandue au Sud du pays, importante dans le Nord-est (Guinée maritime, Guinée forestière), et faible au Nord-Ouest. Le riz pluvial est le système dominant. Le riz importé est moins apprécié que le riz local. 40 % de la production (520 000 t de paddy) est commercialisé sous forme de grain non décortiqué sur les marchés ruraux et de regroupement, dans des échanges interpréfectoraux. Dons les zones de grande production, la consommation de riz en milieu rural est élevée, mais la production de la basse côte est insuffisante pour couvrir les besoins de Conakry et des villes côtières. La relance de la riziculture est fondée sur la modernisation des systèmes de production et l'essor des échanges intérieurs. Les importations ont progressé de 108 000 à 300 000 t en 7 ans. La lettre de politique de développement agricole recommande la mise en valeur des surfaces irrigables, pour augmenter la productivité (de 0,5 - 1,5 t/ha à 2 - 4 t/ha). L'amélioration du secteur rizicole concerne aussi les circuits commerciaux, les accès au crédit. L'enjeu des prochaines années est de structurer une filière de commercialisation des produits vivriers locaux, avec des opérateurs développant des relations contractuelles avec les groupements de producteurs afin de garantir une gestion efficace et pérenne des crédits de commercialisation. (Résumé d'auteur

Scaling of Information in Turbulence

We propose a new perspective on Turbulence using Information Theory. We compute the entropy rate of a turbulent velocity signal and we particularly focus on its dependence on the scale. We first report how the entropy rate is able to describe the distribution of information amongst scales, and how one can use it to isolate the injection, inertial and dissipative ranges, in perfect agreement with the Batchelor model and with a fBM model. In a second stage, we design a conditioning procedure in order to finely probe the asymmetries in the statistics that are responsible for the energy cascade. Our approach is very generic and can be applied to any multiscale complex system.Comment: in Europhysics Letters, 201

An operational solution to acquire multispectral images with standard light cameras : Characterization and acquisition guidelines

In order to develop a low-cost and easy to implement technical solution to map inside-field spatial variability, and to explore its relationship with crop conditions, several experiments were conducted using ultra-light aircraft and Unmanned Aerial Vehicle (UAV) equipped with visible and infrared cameras. The sensors consisted of a ramp of 3 small format digital cameras (EOS 350D, Canon®): one for the visible part of the spectrum, and two modified cameras in order to acquire red edge and near infrared radiations. The images acquisition on the 3 cameras is simultaneous using external triggers and can be activated through the operator remote control on the ground or programmed to be automatically done using an on-board GPS navigation system. On ultra-light aircraft we also add a microbolometer thermal camera to the system. This paper describes the components of this acquisition system and focuses on the geometric and radiometric processing steps necessary for quantitative use of the data. At an altitude of 500 m this system acquires images with a ground resolution of 8 cm for the visible and near infrared bands and 55 cm for the thermal band. Unmanned Aerial Vehicle common altitude stretches over several tenth of meters up to 500 m and is adapted to the survey of fields of several hectares with very high spatial resolution. Ultra-light aircraft offers a range of altitude up to 1 to 2 km and a larger survey capacity with smaller spatial resolution. The spectral sensitivity of the cameras was measured using monospectral emittance sources. We worked both on the raw multispectral images and on the computed jpeg standard output. This allowed us to select the best band (or band combination) to produce red edge and near infrared images. We also developed an algorithm to compensate some radiometric distortion in the acquired images, particularly on vignetting effect. Classical photogrammetric calibration was used in order to measure lens geometry of each camera and evaluate as precisely as possible the coefficients of the lens polynom needed by commercial photogrammetric software. Several sets of images were acquired over experimental fields in temperate zone (on wheat) and tropical zone (on sugarcane). These images were radiometrically and geometrically corrected used the above elements and are stored as georeferenced stackable images in a Geographic Information System. The next step for a quantitative use of the data is to compensate changes due to atmospheric and illumination conditions in the image time series. (Résumé d'auteur

Reply to "Comment on `Quenches in quantum many-body systems: One-dimensional Bose-Hubbard model reexamined' ''

In his Comment [see preceding Comment, Phys. Rev. A 82, 037601 (2010)] on the paper by Roux [Phys. Rev. A 79, 021608(R) (2009)], Rigol argued that the energy distribution after a quench is not related to standard statistical ensembles and cannot explain thermalization. The latter is proposed to stem from what he calls the eigenstate thermalization hypothesis and which boils down to the fact that simple observables are expected to be smooth functions of the energy. In this Reply, we show that there is no contradiction or confusion between the observations and discussions of Roux and the expected thermalization scenario discussed by Rigol. In addition, we emphasize a few other important aspects, in particular the definition of temperature and the equivalence of ensemble, which are much more difficult to show numerically even though we believe they are essential to the discussion of thermalization. These remarks could be of interest to people interested in the interpretation of the data obtained on finite-size systems.Comment: 3 page

The Wide-field High-resolution Infrared TElescope (WHITE)

The Wide-field High-resolution Infrared TElescope (WHITE) will be dedicated in the first years of its life to carrying out a few (well focused in terms of science objectives and time) legacy surveys. WHITE would have an angular resolution of ~0.3'' homogeneous over ~0.7 sq. deg. in the wavelength range 1 - 5 um, which means that we will very efficiently use all the available observational time during night time and day time. Moreover, the deepest observations will be performed by summing up shorter individual frames. We will have a temporal information that can be used to study variable objects. The three key science objectives of WHITE are : 1) A complete survey of the Magellanic Clouds to make a complete census of young stellar objects in the clouds and in the bridge and to study their star formation history and the link with the Milky Way. The interaction of the two clouds with our Galaxy might the closest example of a minor merging event that could be the main driver of galaxy evolution in the last 5 Gyrs. 2) The building of the first sample of dusty supernovae at z<1.2 in the near infrared range (1-5 um) to constrain the equation of state from these obscured objects, study the formation of dust in galaxies and build the first high resolution sample of high redshift galaxies observed in their optical frame 3) A very wide weak lensing survey over that would allow to estimate the equation of state in a way that would favourably compete with space projects.Comment: Invited talk to the 2nd ARENA Conference : "The Astrophysical Science Cases at Dome C" Potsdam 17-21 September, 200

Trouble for MAC

We show that the next-to-leading corrections to the kernel of the gap equation can be large and of opposite sign to the lowest order kernel, in the presence of a gauge boson mass. This calls into question the reliability of the Most Attractive Channel hypothesis.Comment: 8 pages, 1 figure, LaTe

Self-Similar Anisotropic Texture Analysis: the Hyperbolic Wavelet Transform Contribution

Textures in images can often be well modeled using self-similar processes while they may at the same time display anisotropy. The present contribution thus aims at studying jointly selfsimilarity and anisotropy by focusing on a specific classical class of Gaussian anisotropic selfsimilar processes. It will first be shown that accurate joint estimates of the anisotropy and selfsimilarity parameters are performed by replacing the standard 2D-discrete wavelet transform by the hyperbolic wavelet transform, which permits the use of different dilation factors along the horizontal and vertical axis. Defining anisotropy requires a reference direction that needs not a priori match the horizontal and vertical axes according to which the images are digitized, this discrepancy defines a rotation angle. Second, we show that this rotation angle can be jointly estimated. Third, a non parametric bootstrap based procedure is described, that provides confidence interval in addition to the estimates themselves and enables to construct an isotropy test procedure, that can be applied to a single texture image. Fourth, the robustness and versatility of the proposed analysis is illustrated by being applied to a large variety of different isotropic and anisotropic self-similar fields. As an illustration, we show that a true anisotropy built-in self-similarity can be disentangled from an isotropic self-similarity to which an anisotropic trend has been superimposed

Radiometric normalization of multi-temporal visible and near infrared images acquired with light ariborne systems

To study the structure and dynamics of environmental targets, light airborne systems are more and more used as a complement to usual satellite or aerial acquisitions. These systems are composed of small-format digital frame cameras mounted on an ultralight aircraft or an unmanned aerial vehicle. Standard and modified cameras measure the reflected radiation in the visible, the red-edge and near-anfrared bands. The whole system and the geometric and radiometric pre-processing of the images are described in details in the paper "An operational solution to acquire multispectral images with standard light cameras: spectral characterization and acquisition guidelines" submitted for approval to this symposium. This paper deals with the radiometric processing of images time series. Multiple images of the same region captured under different conditions are difficult to compare. This is due to changes in illumination, atmospheric conditions, and flight parameters. Without radiometric normalization, changes between two images are difficult to interpret: they can be linked either to real changes of the surface or to non-scene-dependent changes. In this paper, we propose to compare three methods of radiometric normalization: The invariant targets: - This method consists in uniformly minimizing the effects of non-scene-dependent changes according to a reference date. A given date (image) is chosen as a reference and linear regressions are established, for each of the spectral band between the digital count of invariant points at this date and at all other dates. These linear regressions are then applied to the whole images to normalize them relatively to the reference image. - The spectral indices: ratio-based indices are calculated using the digital counts. This type of indices normalizes by construction the incident radiation. - The calculation of the incident radiation: we use an atmospheric radiative transfer model to calculate the incident radiation at the Top Of the Canopy (TOC) in each spectral band. The model atmospheric inputs come either from meteorological measurements (visibility) or from mean climatic values (water content). The incident radiation values are then used to normalize the digital counts for each acquisition date. In order to evaluate the sensitivity of the model to the accuracy of the atmospheric inputs, a sensitivity analysis will be first performed. The methods will be compared using a time set of airborne multispectral images (blue, green, red, red-edge and near-infrared bands) acquired over agricultural land on Reunion Island. (Texte intégral

Algues Viséennes du sondage de Turnhout (Campine, Belgique)

The article describes twenty-five algae, mostly green algae (dasycladaceans and codiaceans) observed in the Visean carbonates of the Turnhout borehole. Two species are new: Orthriosiphon turnhouti and Atractyliopsis weyanti</i