The response of the azimuthal component of the ionospheric electric field to auroral arc brightening
We have analyzed the response of azimuthal component of the ionospheric electric field to auroral arc activity. We have chosen for analysis three intervals of coordinated EISCAT and TV observations on 18 February, 1993. These intervals include three kinds of arc activity: the appearance of a new auroral arc, the gradual brightening of the existing arc and variations of the arc luminosity. The arcs were mostly east-west aligned. In all cases, the enhancement of arc luminosity is accompanied by a decrease in the westward component of the ionospheric electric field. In contrast, an increase of that component seems to be connected with arc fading. The observed response is assumed to have the same nature as the “short circuit” of an external electric field by the conductor. The possible consequence of this phenomenon is discussed.
Anticipation of the winter wheat growth based on seasonal weather forecasts over France
The aim of this study was to examine the ability of a crop model forced by seasonal weather forecasts to anticipate correctly the agrometeorological variables affecting the growth of winter wheat in France. The method is based on wheat growth simulations over 199 sites in France for the period 1981–2005 driven by seasonal weather forecasts, consisting of 6 month long, 45 member hindcasts starting on 1 February. These simulations were challenging a climatologically based wheat growth forecasting system currently used by ARVALIS − Institut du végétal. Both simulations were evaluated against a reference dataset. The simulations using the seasonal weather forecast present good skills for the dates of occurrence of the main growth stages: the ‘leaf sheaths strongly erect’ stage (also referenced as Zadoks scale Z30), the ‘head visible’ stage (Zadoks scale Z50) and the ‘kernel hard’ stage (Zadoks scale Z91). The simulations forced by the seasonal weather forecasts have lower bias than those forced by the climatological data: respectively −0.2 against 1.4 days for the Z30 stage, 1.1 against 3.2 days for the Z50 stage, 1.3 against 4.2 days for the Z91 stage. It is shown that the seasonal forecasting system provides more hit rates than the climatologically based method does. Thus, for the different events forecasted here, better predictability is found using the seasonal forecasting system. Despite shortcomings highlighted in this study, it is shown that a method based on seasonal weather forecasts could be applied in an operational context over France, in order to improve the method currently used in the agricultural sector.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%