Université Libre de Luozi

L’objectif de l’étude était d’analyser l’influence de la dose d’urée et de la fréquence de sarclage sur l’efficience d’utilisation de l’azote (NUE) et le rendement du maïs dans les conditions écologiques de Kolwezi. Pour y arriver, un essai a été établi en split plot comprenant 2 facteurs, la dose d’urée avec quatre modalités (0 ; 200 ; 300 et 400 kg d’urée.ha-1) et la fréquences de sarclage avec trois modalités (0 ; 1 et 2 sarclages). Après la récolte du maïs sec et le pesage, deux types d’échantillons composites ont été constitués par traitement (un échantillon pour les parties végétatives et un autre pour les graines, soit un total de 24 échantillons composites) et amenés au laboratoire pour analyse de la teneur en azote total par la méthode Kjeldahl. Les résultats obtenus ont montré qu’a l’exception de l’efficience de prélèvement, la dose d’urée a eu une influence très positive sur tous les paramètres d’efficience d’utilisation d’azote (prélèvement d’azote, efficience physiologique, efficience de production) ainsi que sur le rendement en grains du maïs. En revanche, la fréquence de sarclage n’a eu aucun effet sur tous les paramètres d’efficience et le rendement du maïs. Cependant, sa combinaison avec la dose d’urée a seulement influencé l’efficience physiologique ; les autres paramètres étant restés similaires. L’apport de la dose de 200 kg d’urée.ha-1 en combinaison avec un seul sarclage se sont révélés des pratiques non seulement productives, mais aussi optimales, rentables et moins polluantes c’est-à-dire recommandables. Cette étude met à la disposition des producteurs de maïs des pratiques culturales appropriées capables d’améliorer significativement le rendement et la marge bénéficiaire tout en limitant les pertes d’azote.

Con il suo ultimo romanzo, Gary Victor, uno degli scrittori haitiani contemporanei piu produttivi e premiati, getta nuovamente uno sguardo disincantato sulla sua patria d’origine. Come in quasi tutta la sua opera, Victor vuole, anche in Masi, mettere in luce alcuni degli aspetti peculiari della vita, della societa, dei costumi della sua terra natale. Come sempre, lo fa con una profonda ironia che emerge chiaramente pagina dopo pagina. Nel libro a essere presa di mira e prima di tutto la figur...

CONTEXT.The first Gaia Data Release (DR1) significantly improved the previously available proper motions for the majority of the Tycho-2 stars. AIMS. We want to detect runaway stars using Gaia DR1 proper motions and compare our results with previous searches. METHODS. Runaway O stars and BA supergiants are detected using a 2-D proper-motion method. The sample is selected using Simbad, spectra from our GOSSS project, literature spectral types, and photometry processed using CHORIZOS. RESULTS. We detect 76 runaway stars, 17 (possibly 19) of them with no prior identification as such, with an estimated detection rate of approximately one half of the real runaway fraction. An age effect appears to be present, with objects of spectral subtype B1 and later having travelled for longer distances than runaways of earlier subtypes. We also tentatively propose that the fraction of runaways is lower among BA supergiants that among O stars but further studies using future Gaia data releases are needed to confirm this. The frequency of fast rotators is high among runaway O stars, which indicates that a significant fraction of them (and possibly a majority) is produced in supernova explosions.

We present the discovery of a variable optical counterpart to the unidentified gamma-ray source 3FGL J0212.1+5320, and argue this is a new compact binary millisecond pulsar (MSP) candidate. We show 3FGL J0212.1+5320 hosts a semi-detached binary with a 0.86955$\pm$0.00015 d orbital period and a F6-type companion star at an estimated distance of D=1.1$\pm$0.2 kpc, with a radial velocity curve semi-amplitude K$_2$=214.1$\pm$5.0 km s$^{-1}$ and a projected rotational velocity of Vsin(i)=73.2$\pm$1.6 km s$^{-1}$. We find a hard X-ray source at the same location with a 0.5$-$10 keV luminosity L$_\mathrm{X}$=2.6$\times$10$^{32}$ (D/1.1 kpc)$^2$ erg s$^{-1}$, which strengthens the MSP identification. Our results imply a mass ratio q=M$_2$/M$_1$=0.26$^{+0.02}_{-0.03}$ if the companion star fills its Roche lobe, and q$\gtrsim$0.26 in any case. This classifies 3FGL J0212.1+5320 as a "redback" binary MSP; if its MSP nature is confirmed, this will be the brightest compact binary MSP in the optical band (r'$\simeq$14.3 mag) and will have the longest orbital period among Galactic field systems (nearly 21 hr). Based on the light curve peak-to-peak amplitude ($\Delta$r=0.19 mag), we further suggest that the orbital inclination is high and the putative pulsar mass is close to canonical (M$_1$$\simeq$1.3$-$1.6 M$_\odot$). Finally, we discuss the lack of heating signatures and asymmetric optical light curves in the context of other redback MSPs.

The X-ray transient IGR J18245-2452 in the globular cluster M28 contains the first neutron star (NS) seen to switch between rotation-powered and accretion-powered pulsations. We analyse its 2013 March-April 25d-long outburst as observed by Swift, which had a peak bolometric luminosity of ~6% of the Eddington limit (L$_{E}$), and give detailed properties of the thermonuclear burst observed on 2013 April 7. We also present a detailed analysis of new and archival Chandra data, which we use to study quiescent emission from IGR J18245-2452 between 2002 and 2013. Together, these observations cover almost five orders of magnitude in X-ray luminosity (L$_X$, 0.5-10 keV). The Swift spectrum softens during the outburst decay (photon index $\Gamma$ from 1.3 above L$_X$/L$_{E}$=10$^{-2}$ to ~2.5 at L$_X$/L$_{E}$=10$^{-4}$), similar to other NS and black hole (BH) transients. At even lower luminosities, deep Chandra observations reveal hard ($\Gamma$=1-1.5), purely non-thermal and highly variable X-ray emission in quiescence. We therefore find evidence for a spectral transition at L$_X$/L$_{E}$~10$^{-4}$, where the X-ray spectral softening observed during the outburst decline turns into hardening as the source goes to quiescence. Furthermore, we find a striking variability pattern in the 2008 Chandra light curves: rapid switches between a high-L$_X$ "active" state (L$_X\simeq$3.9x10$^{33}$ erg/s) and a low-L$_X$ "passive" state (L$_X\simeq$5.6x10$^{32}$ erg/s), with no detectable spectral change. We put our results in the context of low luminosity accretion flows around compact objects and X-ray emission from millisecond radio pulsars. Finally, we discuss possible origins for the observed mode switches in quiescence, and explore a scenario where they are caused by fast transitions between the magnetospheric accretion and pulsar wind shock emission regimes.