Estimating sharka dispersal function by stochastic spatiotemporal modelling

Plant viral diseases, and especially the ones transmitted by aerial vectors, can cause considerable yield losses. A good knowledge of the distances of spread is key to the understanding of disease dynamics. Exploratory approaches aiming at characterizing the spatiotemporal distribution of diseased plants are often used to get an insight into the distances of spread. A more powerful approach is based on stochastic spatiotemporal modelling in order to estimate the dispersal function of the disease (probability density function describing the probability for an infectious plant to infect a healthy plant at distance d). In this study, we implemented a method for estimating the dispersal function of the sharka disease. Sharka is one of the most serious diseases of stone fruit trees (Prunus sp.). It is caused by Plum pox virus (PPV, genus Potyvirus), transmitted by at least twenty different aphid species in a non persistent manner. Due to the inefficiency of insecticides and the very rare sources of resistance against the virus available in the host species, prophylactic disease control is based on the removal of the diseased trees in the orchards. Thus, a very good knowledge of the dispersal function of sharka is crucial for building epidemiological models and optimizing the strategies of surveillance and control. We adapted the methodology published by Gibson (1997) based on a Markov chain Monte Carlo (MCMC) algorithm in order to estimate sharka dispersal function from the maps of 157 contiguous peach orchards reporting the exact location and the sanitary status (asymptomatic/symptomatic) of each of the trees during six consecutive years. An estimation method based on the Gibbs sampling algorithm was developed taking into account the specificities of the dataset (more than two dates of observation, annual removal of diseased trees). This estimation algorithm was validated on simulated data and was proved to be more powerful and better adapted to large datasets than the one proposed by Gibson. Moreover, the influence of latency on the estimation of the dispersal function was quantified. This methodology was then used to estimate the dispersal function of the disease from a subset of the real dataset. The methods developed in this study are generic enough to be used and adapted for the estimation of dispersal functions of any disease transmitted in a non persistent manner, and even for diseases with similar characteristics. (Texte intégral

NW-oriented features on both sides of the Atlantic Ocean: evidence for a Paleozoic collision that formed the Labrador-Biscay wrench fault zone?

Northwest-oriented features have been recognized for many years as fundamental components of the geology of the northwestern European continental shelves. Similarly oriented lineations and faults have been mapped throughout southwestern Britain, western France and across the English Channel. On land in Europe, similar trends are identified as far east as the Urals. Features of similar orientation, extending over a broad area on the North American continental shelf, have recently been identified from geophysical trends. On land in eastern Canada NW-SE faults have been mapped geologically and detected using geophysical and remote sensing data. A Mercator projection map on which the Atlantic Ocean has been restored to its pre-Mesozoic configuration, i.e. before the initiation of the most recent opening of the North Atlantic Ocean, shows that the features are similarly oriented. Although some of the trends showing this direction may be younger, the geological data from both sides of the Atlantic Ocean suggest that the event that led to the formation of these NW-SE features post-dated the Variscan orogeny and may have been associated with the collision between Gondwana and Laurasia. The geometric patterns of the features interpreted as associated with the collision are consistent with patterns produced by a simple physical sandbox model of indentation with a rigid confinement to the west and a small lateral confinement to the east. This configuration is similar to that expected of Gondwana and Laurasia during the late Paleozoic. Faults considered younger than this collision may represent tectonic rejuvenations associated with the initiation of the opening of the North Atlantic Ocean. RÉSUMÉ L'orientation obscrvée du nord-est vers le sud-est des formations rocheuses est reconnue depuis de nombreuses années comme une caractéristique géologique fondamentale des plateaux continentaux du nord-ouest de l'Europe. Des structures linéaires et des failles d'orientation similaires ont été répertoriées dans tout le sud-ouest de l'Angleterre, dans I'ouest de la France et à travers la Manche. Sur le continent européen, des tendances analogues ont pu fitre observées aussi loin à l'est que dans la chaine de l''Oural. Ces caractérstiques orientées qui recouvrent une vaste région du plateau continental de l'Amerique du Nord ont récemment été observées à partir de tendances géophysiques. Dans l'Est canadien, des failles orientées NO-SE ont été portées sur des cartes géologiques et déectées a l'aid.e de données géophysiques et de télélédétection. Ces caractéristiques observées ont été portées sur une carte a projection de Mercator oò figure l'océan Atlantique dans sa configuration d'origine pendant l'ère pré-mésozoTque, soit avant que ne s'amorce rouverture la plus récente de l'Atlantique Nord. Ces caractéristiques nsproduisent la même orientation lorsqu'elles sont portées ainsi sur la carte. Bien que certaines des tendances qui signalent cette orientation semblent d'apparition plus récente, les données géologiques des deux côtés de l'Atlantique portent à croire que le phénomène qui a mené la création de ces linéations NO-SE est survenu après l'orogenése de varisque et peut fltre relié à l'hypercollision survenue entre la Gondwanie et la Laurasie. Les formes géomètriques de ces linéations interprétées en relation avec la collision sont du même type que eel les produites dans un modèle d'échancrure géologique dans un simple carré de sable, celles-ci présentant un confinement rigide è l'ouest et un petit confinement latéral è Test. Il s'agit d'une configuration semblable à celle qui serait caractéristique de la Gondwanie et de la Laurasie. Les failles jugés plus récentes et issues de cette collision pourraient être attribuables à une régénération tectonique qui a accompagné le début de rouverture de l'Atlantique Nord. Traduit par la rédactio

The Structure of Real Interest Rates in Chile.

This paper describes the structure of real interest rates (the real yield curve) in Chile and shows its evolution through time. It provides a practical tool for the systematic study of the determinants of Chilean yield curves. Empirical estimations are based on transaction and auction data for Central Bank bonds and pension recognition bonds issued by the government, applying the Nelson and Siegel method. Estimation results are used to measure the liquidity premium in the market maker’s bond yield, simulate the evolution of the very short and long-term rates, and analyze issues of Central Bank zero-coupon bonds and the response of domestic interest rates to local and international economic events.

Influence of Phosphoramidites in Copper-Catalyzed Conjugate Borylation Reaction

Copper(I) has become the preferred metal to catalyze the β-boration of α,β-unsaturated carbonyl compounds, and now we demonstrate that easily accessible monodentate chiral ligands, such as phosphoramidites and phosphites, can be convenient alternative ligands to induce asymmetry in the enantioselective version of this reaction, particularly in the β-boration of α,β-unsaturated imines.

Séminaire du département de génétique animale de l'I.N.R.A

International audienc

Méthodes d'estimation des effets directs et maternels en sélection animale

International audienc

Tracking the phase-transition energy in disassembly of hot nuclei

In efforts to determine phase transitions in the disintegration of highly excited heavy nuclei, a popular practice is to parametrise the yields of isotopes as a function of temperature in the form $Y(z)=z^{-\tau}f(z^{\sigma}(T-T_0))$, where $Y(z)$'s are the measured yields and $\tau, \sigma$ and $T_0$ are fitted to the yields. Here $T_0$ would be interpreted as the phase transition temperature. For finite systems such as those obtained in nuclear collisions, this parametrisation is only approximate and hence allows for extraction of $T_0$ in more than one way. In this work we look in detail at how values of $T_0$ differ, depending on methods of extraction. It should be mentioned that for finite systems, this approximate parametrisation works not only at the critical point, but also for first order phase transitions (at least in some models). Thus the approximate fit is no guarantee that one is seeing a critical phenomenon. A different but more conventional search for the nuclear phase transition would look for a maximum in the specific heat as a function of temperature $T_2$. In this case $T_2$ is interpreted as the phase transition temperature. Ideally $T_0$ and $T_2$ would coincide. We invesigate this possibility, both in theory and from the ISiS data, performing both canonical ($T$) and microcanonical ($e=E^*/A$) calculations. Although more than one value of $T_0$ can be extracted from the approximate parmetrisation, the work here points to the best value from among the choices. Several interesting results, seen in theoretical calculations, are borne out in experiment.Comment: Revtex, 10 pages including 8 figures and 2 table

A detailed study of the diastereoselective catalytic hydrogenation of 6-hydroxytetrahydroisoquinoline-(3R)-carboxylic ester intermediates

A key step towards a highly-selective antagonist of ionotropic glutamate receptors entails the diastereoselective arene hydrogenation of an enantiopure tetrahydroisoquinoline. An extensive screen using parallel reactors was conducted and led to the discovery of several Pd/C catalysts giving high yield and improved diastereoselectivity from 75 : 25 to 95 : 5. A detailed kinetic study of the best system was performed and supports the reduction occuring in two-steps.