Model-free control algorithms for micro air vehicles with transitioning flight capabilities

Micro air vehicles with transitioning flight capabilities, or simply hybrid micro air vehicles, combine the beneficial features of fixed-wing configurations, in terms of endurance, with vertical take-off and landing capabilities of rotorcrafts to perform five different flight phases during typical missions, such as vertical takeoff, transitioning flight, forward flight, hovering and vertical landing. This promising micro air vehicle class has a wider flight envelope than conventional micro air vehicles, which implies new challenges for both control community and aerodynamic designers. One of the major challenges of hybrid micro air vehicles is the fast variation of aerodynamic forces and moments during the transition flight phase which is difficult to model accurately. To overcome this problem, we propose a flight control architecture that estimates and counteracts in real-time these fast dynamics with an intelligent feedback controller. The proposed flight controller is designed to stabilize the hybrid micro air vehicle attitude as well as its velocity and position during all flight phases. By using model-free control algorithms, the proposed flight control architecture bypasses the need for a precise hybrid micro air vehicle model that is costly and time consuming to obtain. A comprehensive set of flight simulations covering the entire flight envelope of tailsitter micro air vehicles is presented. Finally, real-world flight tests were conducted to compare the model-free control performance to that of the Incremental Nonlinear Dynamic Inversion controller, which has been applied to a variety of aircraft providing effective flight performances

An improved method for Ra isotope (226Ra, 228Ra, 224Ra) measurements by gamma spectrometry in natural waters: application to CO2-rich thermal waters from the French Massif Central

International audienc

Premiers âges U/Th sur la grotte des Demoiselles (Hérault) : évolution karstique et relation paléoclimatique [First U/Th ages from the « Grotte des Demoiselles » (Hérault-France) : karstic evolution and palaeoclimatic relationship]

. The U/Th method has been applied to eight speleothem samples from the Demoiselles Cave (Hérault, France), as a first attempt to decipher the history of this cave and compare it to that of another cave in the same region of southern France (Clamouse Cave). Mass spectrometry (U and Th contents) and a spectrometry [(234U/238U) ratios and (230Th) activities] have been used to date these samples. The U contents of the eight samples are very low, between 0.05 and 0.19 ppm. The samples have very low 232Th contents, and thus appear essentially devoid of detrital contamination. The initial (234U/238U) activity ratios calculated for five samples are constant (within 2σ uncertainties) with a mean value of 1. 14. Such a low ratio is consistent with the rapid infiltration of the seepage water through a thin, strongly fractured limestone cover in shallow oxidizing conditions. The ages determined here are consistent with a growth of speleothems during warm and humid periods, with at least four stages of deposition : the first two are older than 250-300 ky ; the two most recent episodes correspond to the last interglacial period (isotopic sub-stages 5. 1 and 5.5, ca 80 and 120 ky respectively), and to the Holocene. The same sub-stages of the last Interglacial correspond to two main episodes of deposition in the nearby Clamouse Cave. Major deposition certainly took place during the two early stages, whereas the two later stages seem to have only added a final touch to the cave ornamentation. In this respect, the Demoiselles Cave appears different from the Clamouse Cave, where the recent stages are the most developed. This can be attributed to the thicker rock cover above the roof of the Clamouse Cave.Cet article présente les premiers âges U/Th obtenus sur huit échantillons appartenant à quatre concrétions différentes de la Grotte des Demoiselles (Hérault, France). Ces datations ont permis de reconstituer dans ses grandes lignes l'histoire de la grotte, et de la comparer avec une autre grotte de la même région du Sud de la France (grotte de la Clamouse). Les teneurs en U et Th ont été mesurées par spectrométrie de masse, alors que les rapports isotopiques (234U/238U) et les activités (230Th) ont été déterminés par spectométrie α. Les teneurs en U de ces huit échantillons sont très basses, entre 0.05 et 0.19 ppm. Les teneurs en 232Th sont extrêmement faibles, indiquant l'absence d'une contamination détritique. Les rapports initiaux (234U/238U) calculés pour cinq échantillons sont constants (dans la marge d'erreur de 2σ), avec une valeur moyenne de 1.14. Cette valeur basse est à relier à une infiltration rapide des eaux de percolation, au travers d'une couverture calcaire peu épaisse, fracturée, en milieu oxydant. Les âges obtenus montrent que la croissance des concrétions a lieu pendant les périodes climatiques chaudes et humides, avec au moins 4 phases majeures de concrétionnement. Les deux premières sont plus anciennes que 250-300 ka. Les deux plus récentes correspondent au dernier interglaciaire (sous-stades isotopiques chauds 5.1 et 5.5, environ 80 et 120 ka respectivement) et à la période Holocène, en accord avec les résultats obtenus dans la grotte voisine de la Clamouse. La majeure partie du concrétionnement a eu lieu pendant les 2 premières phases (> 250 ka), alors que les 2 suivantes ont seulement légèrement modifié l'ornementation de la grotte. De ce point de vue la Grotte des Demoiselles se distingue de la Clamouse, où la couverture rocheuse est plus épaisse et où la proportion du concrétionnement récent apparaît globalement plus importante.Rihs Sophie, Poidevin Jean Louis, Condomines Michel. Premiers âges U/Th sur la grotte des Demoiselles (Hérault) : évolution karstique et relation paléoclimatique [First U/Th ages from the « Grotte des Demoiselles » (Hérault-France) : karstic evolution and palaeoclimatic relationship]. In: Quaternaire, vol. 10, n°4, 1999. pp. 293-297

Extreme radium deficit in the 1957 AD Mugogo lava (Virunga volcanic field, Africa): its bearing on olivine-melilitite genesis

International audienceWe report here U-series and trace element data for an olivine-melilitite lava flow, erupted in 1957 in the Virunga volcanic field and known as the Mugogo eruption. Petrological and geochemical data show that the Mugogo magma represents a primary mantle melt, derived from a low degree of melting of a metasomatised mantle source. It is highly enriched in very incompatible trace elements (e.g. more than 300-fold compared to primitive mantle for Th), with a distinctly lower enrichment in Rb, Ba and Sr. The high Th/U and low (230Th/232Th) ratios (4.4 and 0.750, respectively, with a (230Th/238U) ratio of 1.09) are close to the values found for the Nyamuragira basanites. But the most striking feature is the very low (226Ra/230Th) ratio of 0.48, the lowest ever measured in a mafic volcanic rock. The most probable origin of this Ra deficit is the presence of phlogopite (having a high Ra partition coefficient) in the lithospheric mantle, either as a residual phase during low-degree isobaric melting (in batch-melting or a diffusion-controlled melting models), or in a phlogopite-bearing upper mantle through which the melt migrates and equilibrates (in an equilibrium porous flow model commonly used to describe adiabatic melting). The disequilibrium pattern (230Th) > (238U) > (210Pb) ≫ (226Ra), reversed compared to the pattern observed in the Oldoinyo Lengai natrocarbonatite, suggests that a carbonatite melt might have been involved to explain the Ra deficit. We thus discuss the possibility of an early separation of a Ra-enriched carbonate melt either from the olivine-melilitite melt or from a carbonated mantle source, followed by the production of a low-degree melt of olivine-melilitite composition, but the lack of available experimental, petrological and geochemical evidences makes this process somewhat speculative at present. Further studies of recent (<5 ky) olivine-melilitites are needed to check whether the large Ra deficit is a general characteristic of this type of magma that can be used to constrain models of its formation

(Ra-228/Ra-226) ratios in hydrothermal carbonates and the origin of radium in CO2-rich waters of the Lodeve Basin (South of France)

International audienceThe present study reports data on CO2-rich geothermal waters and their associated carbonate deposits from the SW part of the Permian Lodève Basin (South of France). Both waters and carbonates are enriched in 226Ra, with activities up to 2.2 Bq/L and 3.5 Bq/g respectively. A series of carbonate samples precipitated around the studied wells since 1990 were dated through the 226Ra-210Pb and 228Ra-228Th methods, and the results are discussed in a new Concordia diagram. While both methods give comparable dates for many samples, Ra-Pb ages are sometimes much older than Ra-Th ages. We propose that these discrepancies result from the adsorption of 222Rn daughter nuclides in such a Rn-rich environment. The (228Ra/226Ra)0 activity ratios calculated at the time of deposition are remarkably constant for about 12 years, suggesting the presence of a steady-state aquifer. The low (228Ra/226Ra)0 ratios (0.348 ± 0.008) are best explained if most of the Ra derives from the Cambrian carbonate series (mainly dolostone) underlying the Permian Basin, which have low Th/U and similar (228Ra/226Ra) ratios. This study suggests that Ra and other alkaline-earth elements do not necessarily originate from the rocks surrounding the deep geothermal reservoir, but rather may be introduced into the CO2-rich water during its transfer towards the surface and interaction with carbonate rocks

Recent mobilization of U-series radionuclides in the Bernardan U deposit (French Massif Central)

Several nuclides of the ;238;U (;234;U, ;230;Th, ;226;Ra, ;210;Pb) and ;235;U (;231;Pa, ;227;Ac) decay series have been measured through gamma spectrometry in the U-bearing episyenites of the Bernardan mine (northwest Massif Central, France), in order to study recent mobilizations in the U-deposit and their time-scales. (;230;Th/;238;U) and (;231;Pa/;235;U) ratios show that U has been little affected during the last 350 ky, especially in the U-rich samples. In contrast, ;226;Ra was subjected to a general redistribution, with a clear tendency for Ra to be lost from the U-rich samples and added to U-poor samples. The highest Ra excesses are present in low-U samples, and are related to adsorption onto iron hydroxides. Ra appears to have been redistributed within the mineralised episyenitic bodies, which seem to remain in ;226;Ra;238;U radioactive equilibrium, a result consistent with the earlier study of Leroy [1984. Episyénitisation dans le gisement d'uranium du Bernardan (Marche): Comparaison avec des gisements similaires du Nord-Ouest du Massif Central français. Miner. Depos. 19, 2635]. As shown by the ;226;Ra and ;210;Pb data, the Ra redistribution was very active between 8 and 0.1 ky, and this might be a consequence of the hydrological changes in groundwater circulation accompanying the Holocene climate warming

Timescales of Magma Chamber Processes and Dating of Young Volcanic Rocks

International audienceThis equation shows that on a plot of ( )λ θ e , the volcanics erupted from this reservoir should define a straight line whose y intercept (at 2 λ θ e = 0, i.e., in the future at θ = -∞) is 1 (radioactive equilibrium, cf. Fig. 3). A linear relationship is also obtained if isotope ratios, like ( 230 Th/ 232 Th) θ , are reported versus 2 λ θ e (see Fig. 11 in Condomines et al. 1988). This latter diagram is similar to the well known isotope evolution diagrams used in Sr or Nd isotope geochemistry, where 87 Sr/ 86 Sr or 143 Nd/ 144 Nd ratios are reported versus time.</p

Temporal radon and radium variations in the Lez karstic spring (South of France)

International audienc

Flank eruptions of Mt Etna during the Greek-Roman and Early Medieval periods: New data from Ra-226-Th-230 dating and archaeomagnetism

International audienceIn this paper, we present new data from 226Ra–230Th dating and archaeomagnetism with the aim of improving the knowledge of the flank eruptions that occurred at Mt Etna during the Greek–Roman and Early Medieval periods, as defined in the new geological map of the volcano. The combination of the two dating techniques demonstrates that three major flank eruptions occurred on the lower north and west flanks during Greek–Roman epochs, producing large scoria cones and extensive lava flows. In particular, the Mt Ruvolo and Mt Minardo events highly impacted the territory of the west flank, notably by damming the Simeto River. The new data of the Millicucco and Due Monti lava flows, on the lower north–east flank, indicate a younger age than their stratigraphic ages quoted in the 2011 geological map, since they occurred around 700 and 500 AD, respectively. None of the large flank eruptions occurring on the lower slopes of Etna during the Early Medieval age are reported in the historical sources. Overall, our paper shows that a comprehensive assessment of eruptions at Mount Etna in the last three millennia can only be achieved through a multidisciplinary approach