Un semoir de semis direct sous couvert vegetal à traction animale adapté aux conditions du Sénégal

En Afrique de l'Ouest, la conception et l'adaptation locales de semoirs de semis direct de traction animale faciles d'utilisation et accessibles aux petits producteurs sont un des éléments favorables à l'adoption du semis direct sous couvert végétal (SDCV). C'est dans ce sens que l'équipe de FERT et AFDI Touraine a mis au point un prototype de semoir à traction bovine à 2 rangs pour appuyer les petits producteurs (Vadon et al., 2010). Mais malheureusement, jusqu'à présent, ces semoirs de semis direct introduits et testés au moins une fois dans la sous-région à l'image du semoir brésilien (Fitarelli) (Ashburner, 2004 ; Bozza et Kourouma, 2004 cité par Sissoko et Autfray, 2007) n'ont pas répondu aux attentes des agriculteurs à cause des densités de semis et à des doses d'engrais non régulières et à la maniabilité (Fert et Afditouraine, 2014). Aussi, les tests du prototype de l'AFDI (Agriculteurs Français et Développement International) n'ont pas été concluants à cause de sa lourdeur pour les animaux de trait et qu'aussi les adaptations faites pour son allégement et sa facilitation pour sa fabrication locale par les forgerons n'ont pas donné satisfaction (Sissoko et Autfray, 2007). Suite à ces expériences, des suggestions d'adaptation des semoirs aux conditions locales ont été faites pour le Sud du Mali par Sissoko et Autfray ( 2007) " Il conviendrait également dans une optique d'avoir des semoirs plus simples et moins coûteux, sans épandeur d'engrais qui alourdit le système, de transformer le semoir local pour un semis de coton, du mil et du sorgho, en s'inspirant du semoir Fitarelli : rajout d'un disque à l'avant pour trancher la végétation, d'un soc juste derrière pour ouvrir la raie de semis, transfert du réservoir de semences au milieu, confection de roues plus hautes ". Plus de 200 000 semoirs super éco sont utilisés au Sénégal avec les chevaux et les ânes au Sénégal, et quelques dizaines de milliers au Mali (Bordet et al., 1988), c'est pourquoi les suggestions ci-dessus nous ont amené à proposer d'adapter le super-éco au système de semis direct sous couvert végétal permanent (SDCVP). L'objectif de l'article se limite à la conception locale d'un semoir de semis direct à partir du bâti du super éco. Ce qui signifie, un matériel qui peut facilement être fabriqué par les artisans qui fabriquent aujourd'hui les matériels de traction animale, et qui sera compétitif d'un point de vue prix avec les autres matériels de semis direct à traction animale importés. Les résultats sur les performances au semis en conditions réelles en particulier sur les rendements des cultures, seront les prochaines étapes d'évaluation de ce semoir de semis-direct

Scanning electron microscopy of Conidia of Trichoderma Stromaticum, a biocontrol agent of witches broom disease of cocoa.

Estudos morfológicos de conídios de Trichoderma harzianun, um agente de biocontrole da vassoura-de-bruxa do cacaueiro, foram feitos sob microscopia eletrônica de varredura com emissão de campo. Características da superfície de conídios do fungo mostraram ser rugosas quando observadas em alta maginificação; fato esse impossível de ser visualizado por microscopia ótica. Também foram observados, com freqüência, massas de conídios completamente envolvidos por material mucilaginoso e detalhes de células ramificadas dicotomicamente que formam as pústulas

Toward Equations of Galactic Structure

We find that all classes of galaxies, ranging from disks to spheroids and from dwarf spheroidals to brightest cluster galaxies, lie on a two dimensional surface within the space defined by the logarithms of the half-light radius, r_e, mean surface brightness within r_e, I_e, and internal velocity, V^2 = (1/2)v_c^2 + sigma^2, where v_c is the rotational velocity and sigma is the velocity dispersion. If these quantities are expressed in terms of kpc, L_solar/pc^2, and km/s, then log r_e - log V^2 + log I_e + log Upsilon_e + 0.8 = 0, where we provide a fitting function for Upsilon_e, the mass-to-light ratio within r_e in units of M_solar/L_solar, that depends only on V and I_e. The scatter about this surface for our heterogeneous sample of 1925 galaxies is small (< 0.1 dex) and could be as low as ~ 0.05 dex, or 10%. This small scatter has three possible implications for how gross galactic structure is affected by internal factors, such as stellar orbital structure, and by external factors, such as environment. These factors either 1) play no role beyond generating some of the observed scatter, 2) move galaxies along the surface, or 3) balance each other to maintain this surface as the locus of galactic structure equilibria. We cast the behavior of Upsilon_e in terms of the fraction of baryons converted to stars, eta, and the concentration of those stars within the dark matter halo, xi = R_{200}/r_e. We derive eta = 1.9 x 10^{-5} (L/L^*) Upsilon_* V^{-3} and xi = 1.4 V/r_e. Finally, we present and discuss the distributions of eta and xi for the full range of galaxies. For systems with internal velocities comparable to that of the Milky Way (149 < V < 163 km/s), eta = 0.14 +- 0.05, and xi is, on average, ~ 5 times greater for spheroids than for disks. (Abridged)Comment: submitted to Ap

Airborne Particles in Museums

Presents one in a series of research activities aimed at a better understanding of the origin and fate of air pollution within the built environment

Feed the Future Mali Livestock Technology Scaling Program (FtF-MLTSP) - Participatory assessment of animal health service delivery systems in Mali: Constraints and opportunities

United States Agency for International Developmen

Oscillations in the expression of a self-repressed gene induced by a slow transcriptional dynamics

We revisit the dynamics of a gene repressed by its own protein in the case where the transcription rate does not adapt instantaneously to protein concentration but is a dynamical variable. We derive analytical criteria for the appearance of sustained oscillations and find that they require degradation mechanisms much less nonlinear than for infinitely fast regulation. Deterministic predictions are also compared with stochastic simulations of this minimal genetic oscillator

Oscillations in the expression of a self-repressed gene induced by a slow transcriptional dynamics

We revisit the dynamics of a gene repressed by its own protein in the case where the transcription rate does not adapt instantaneously to protein concentration but is a dynamical variable. We derive analytical criteria for the appearance of sustained oscillations and find that they require degradation mechanisms much less nonlinear than for infinitely fast regulation. Deterministic predictions are also compared with stochastic simulations of this minimal genetic oscillator

Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. II. NGC 3256 Clusters

We present Gemini optical spectroscopy of 23 young star clusters in NGC3256. We find that the cluster ages range are from few Myr to ~150 Myr. All these clusters are relatively massive (2--40)x 10^{5} \msun$ and appear to be of roughly 1.5 \zo metallicity. The majority of the clusters in our sample follow the same rotation curve as the gas and hence were presumably formed in the molecular-gas disk. However, a western subsample of five clusters has velocities that deviate significantly from the gas rotation curve. These clusters may either belong to the second spiral galaxy of the merger or may have formed in tidal-tail gas falling back into the system. We discuss our observations in light of other known cluster populations in merging galaxies, and suggest that NGC 3256 is similar to Arp 220, and hence may become an Ultra-luminous Infrared Galaxy as the merger progresses and the star-formation rate increases. Some of the clusters which appeared as isolated in our ground-based images are clearly resolved into multiple sub-components in the HST-ACS images. The same effect has been observed in the Antennae galaxies, showing that clusters are often not formed in isolation, but instead tend to form in larger groups or cluster complexes.Comment: 20 pages, 10 figures, 3 tables; Accepted Ap

Dynamical Friction in dE Globular Cluster Systems

The dynamical friction timescale for globular clusters to sink to the center of a dwarf elliptical galaxy (dE) is significantly less than a Hubble time if the halos have King-model or isothermal profiles and the globular clusters formed with the same radial density profile as the underlying stellar population. We examine the summed radial distribution of the entire globular cluster systems and the bright globular cluster candidates in 51 Virgo and Fornax Cluster dEs for evidence of dynamical friction processes. We find that the summed distribution of the entire globular cluster population closely follows the exponential profile of the underlying stellar population. However, there is a deficit of bright clusters within the central regions of dEs (excluding the nuclei), perhaps due to the orbital decay of these massive clusters into the dE cores. We also predict the magnitude of each dE's nucleus assuming the nuclei form via dynamical friction. The observed trend of decreasing nuclear luminosity with decreasing dE luminosity is much stronger than predicted if the nuclei formed via simple dynamical friction processes. We find that the bright dE nuclei could have been formed from the merger of orbitally decayed massive clusters, but the faint nuclei are several magnitudes fainter than expected. These faint nuclei are found primarily in M_V > -14 dEs which have high globular cluster specific frequencies and extended globular cluster systems. In these galaxies, supernovae-driven winds, high central dark matter densities, extended dark matter halos, the formation of new star clusters, or tidal interactions may act to prevent dynamical friction from collapsing the entire globular cluster population into a single bright nucleus.Comment: 15 pages, 2 tables, 7 figures; to appear in the Astrophysical Journal, April 20, 200

How the asymmetry of internal potential influences the shape of I-V characteristic of nanochannels

Ion transport in biological and synthetic nanochannels is characterized by such phenomena as ion current fluctuations, rectification, and pumping. Recently, it has been shown that the nanofabricated synthetic pores could be considered as analogous to biological channels with respect to their transport characteristics \cite{Apel, Siwy}. The ion current rectification is analyzed. Ion transport through cylindrical nanopores is described by the Smoluchowski equation. The model is considering the symmetric nanopore with asymmetric charge distribution. In this model, the current rectification in asymmetrically charged nanochannels shows a diode-like shape of $I-V$ characteristic. It is shown that this feature may be induced by the coupling between the degree of asymmetry and the depth of internal electric potential well. The role of concentration gradient is discussed