Occurrence of grapevine virus A (GVA) and other closteroviruses in Tunisian grapevines affected by leafroll disease

Vorkommen von Grapevine-Virus A (GVA) und anderen Closteroviren in blattrollkranken tunesischen RebenReben, die aus den Hauptweinbaugebieten Tunesiens stammten, wurden auf die Anwesenheit von Closteroviren hin überprüft. Während in keiner der symptomfreien Reben Viruspartikel entdeckt wurden, enthielten alle Reben mit Blattrollsymptomen - außer zweien - Closteroviruspartikel, die durch IEM (immune electron microscopy) in konzentrierten Blattextrakten oder unmittelbar in Rohsaft durch ISEM (immunosorbent electron microscopy) identifiziert wurden. Alle vier derzeit bekannten Closteroviren (GClV-1, GClV-2, GClV-3 und GVA) waren, meistens im Gemisch, in Reben mit Blattrollsymptomen vorhanden. GClV-3 und GVA wurden in 77 bzw. 50 % der geprüften Reben entdeckt. Ein tunesisches Isolat von GVA, das durch Planococcus citri auf krautige Testpflanzen übertragen wurde, unterschied sich in biologischer Hinsicht, aber nicht in den charakteristischen physikalisch-chemischen und serologischen Eigenschaften von zwei italienischen Isolaten desselben Virus

Determination of the evolution of the surface potential of a charging insulator by measuring the intensity of its X-ray characteristic peaks

The charge developed in an insulator by an electron beam has often been studied by following the evolution of the secondary electron emission of the target. However this latter proves to be insufficient when one attempts to correlate it with physical properties of the sample such as its density of traps and their spatial distribution. An important step would be to have access to the time evolution of the surface potential Vs(t). However, this latter quantity is not easy to measure. In this paper, we propose a new method to measure the evolution of the surface potential by relating it to the X-ray emission induced by the electronic bombardment. More exactly, we show that there is a relation between the intensity of the characteristic peaks and the potential existing under the beam impact at a given instant of the charge. After having explained the method, we check its validity both experimentally and also by comparison with Monte Carlo simulations. We then present initial results obtained for amorphous SiO2 targets

Contribution à l'étude des effets de charge sur l'émission X des matériaux isolants non métallisés

International audienceThe presence of charges perturbs the microanalysis-X on insulator samples. Attempt to suppress these effects have been fruitless and a better understanding of the charge phenomenon is the only way to a clear interpretation of the results of a microanalysis-X.From a simulation of the charges implanted by an electron beam on an insulator target, we compute, as a fuction of the integrated dose, the caracteristics of the emitted X-rays, such as the generating function phi(rho z) or the intensity of caracteristic lines. We underline the role of the electric field on the primary beam and on the electron trajectories in the target. These results allow the analysis of experimentally measured X-rays. Our studies on the effects of the diameter of the probe and on the exposure time led us to establish the best conditions for the successful microanalysis-X of an insulator

Charge injection modeling and initial SE yield by two fluxes method; New source term of secondary electron generation by Monte Carlo simulation

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