72 research outputs found
Study of morphology of reactive dissolution interface using fractal geometry
No full textJ. Pharm. Sci. ISI Document Delivery No.: VF662 Times Cited: 7 Cited Reference Count: 15 Tromelin, A Gnanou, JC Andres, C Pourcelot, Y Chaillot, BInternational audienceThe determination of reactive fractal dimension was carried out using two forms of the Noyes-Whitney equation, -dQ/dt = K(Q/Q(0))(DR/3) and -d Q/dt = K' R(DR-3) using the Richardson plot on the basis of previous data obtained by dissolution of an orthoboric acid powder. The correlation of the results provided by the two ways of calculation allows proposal of the hypothesis that dissolution begins on a specific population of reactive sites and probably promotes the formation of microporous volumes or cracks
Aerosol deposition and origin in French mountains estimated with soil inventories of 210Pb and artificial radionuclides
No full textRadionuclide inventories were measured in soils from different French mountainous areas: Chaîne des Puys (Massif Central), Eastern Corsica, Jura, Montagne Noire, Savoie, Vosges and Rhine Valley. 210Pb soil inventories were used to estimate long-term (>75 yr) deposition of submicron aerosols. Whereas 210Pb total deposition is explained partly by wet deposition, as demonstrated by increase of 210Pb inventory with annual rainfall; a part of 210Pb in the soils of higher altitude is caused by orographic depositions. Using measurements of radionuclides coming from nuclear aerial weapon tests (137Cs and Pu isotopes), we were able to estimate the origin of aerosols deposited in high-altitude sites and to confirm the importance of occult deposition and feeder–seeder mechanism. Using a simple mass balance model, we estimate that occult deposition and feeder–seeder mechanisms account to more than 50% of total deposition of 210Pb and associated submicron aerosols in French altitude sites
Remarques sur le mécanisme de l’isomérisation prototropique des composés propargyliques en série hétéroatomique
No full textÉtude cinétique de l’isomérisation des thioéthers du type R — S — CH2 — C ≡ CH pourR = (— C2H5, — C6H5, — pCH3O — C6H4,— pCH3 — C6H4, — pCl — C6H4, — pN ≡ C — C6H4).La corrélation de Hammett conduit à une valeur positive et relativement élevée de rho (+ 2,1) compatible avec l’arrachement d’un proton au cours du stade lent de la réaction et l’apparition d’une charge négative importante et localisée à l’état de transition. Discussion d’un schéma réactionnel
Directional C-W Doppler sonography in the diagnosis of basilar artery disease.
No full textUsing directional continuous-wave Doppler sonography of the vertebral arteries, we have investigated 1,540 patients during the past 5 years. On the basis of unilateral and bilateral retrograde brachial angiograms in the same patients (a total of 1,989 angiograms) we have developed sonographic criteria for demonstrating a significant increase in the peripheral resistance of both distal vertebral arteries and/or the basilar artery. All 11 cases of basilar artery stenosis of at least 60% reduction in lumen diameter (as shown by angiography) exhibited an approximately 40% or higher reduction in the sum of the modified Pourcelot indices of both vertebral arteries with respect to age-matched controls. All 3 stenoses of less than 60% reduction in lumen diameter were not detected by sonography. Even a good collateral circulation through rete mirabile anastomoses did not normalize the modified Pourcelot indices. One case of a persistent primitive trigeminal artery with thin-calibered vertebral arteries was also detected by sonography. The high percent of patients with one hypoplastic vertebral artery in the group with basilar artery stenoses indicates an increased risk for atherosclerosis of the basilar and/or distal vertebral artery in these patients. All 14 angiographically verified occlusions of the basilar artery were detected by sonographic criteria independent of the occlusion localization. Thus, we believe that directional continuous-wave Doppler sonography is a reliable technique for detecting basilar artery stenoses of at least 60% reduction in lumen diameter and basilar artery occlusions.</jats:p
Compensatory renal growth in children and adults studied by Doppler sonography
No full textTo identify modifications of kidney morphology and of the time-velocity spectral waveform associated with long-term compensatory hypertrophy, spectral Doppler sonography was performed in 30 children and adults with solitary kidneys 7 years to 28 years following nephrectomy. Doppler signals were obtained from three arterial sites in each kidney. The average renal volume was 207 mL and the mean hypertrophy of the kidneys was 186%. The mean value of pulsatility (PI) and Pourcelot (RI) indexes of solitary hypertrophied kidneys was significantly lower than that of normal paired kidneys or allografts with normal function described in the literature. The PI and RI were found to correlate inversely with the kidney volume and the body surface area (BSA). In spite of a long follow-up time, no patient suffered from renal failure. This study suggests that in the case of solitary kidney, specific ranges of PI and RI should be employed rather than those used with paired kidneys
Characterization and migration of atmospheric REE in soils and surface waters
No full textRainwater and snow collected from three different sites in France (Vosges Mountains, French Alps and Strasbourg) show more or less similar shapes of their REE distribution patterns. Rainwater from Strasbourg is the most REE enriched sample, whereas precipitations from the two mountainous, less polluted catchments are less REE enriched and have concentrations close to seawater. They are all strongly LREE depleted. Different water samples from an Alpine watershed comprising snow, interstitial, puddle and streamwater show similar REE distributions with LREE enrichment (rainwater normalized) but MREE and HREE depletion. In this environment, where water transfer from the soil to the river is very quick due to the low thickness of the soils, it appears that REE in streamwater mainly originate from atmospheric inputs. Different is the behaviour of the REE in the spring- and streamwaters from the Vosges Mountains. These waters of long residence time in the deep soil horizons react with soil and bedrock REE carrying minerals and show especially significant negative Eu anomalies compared to atmospheric inputs. Their Sr and Nd isotopic data suggest that most of the Sr and Nd originate from apatite leaching or dissolution. Soil solutions and soil leachates from the upper soil horizons due to alteration processes strongly depleted in REE carrying minerals, have REE distribution patterns close to those of lichens and throughfall. Throughfall is slightly more enriched especially in light REE than filtered rainwater probably due to leaching of atmospheric particles deposited on the foliage and also to leaf excretion. Data suggest that Sr and Nd isotopes of the soil solutions in the upper soil horizons originate from two different sources: 1) An atmospheric source with fertilizer, dust and seawater components and 2) A source mainly determined by mineral dissolution in the soil. These two different sources are also recognizable in the Sr and Nd isotopic composition of the tree’s throughfall solution. The atmospheric contributions of Sr and Nd to throughfall and soil solution are of 20 to 70 and 20%, respectively. In springwater, however, the atmospheric Sr and REE contribution is not detectable
La localisation spatiale par effet Doppler ultrasonore
No full textThe problem of the two-dimensional (2-D) localization of a target by the ultrasound Doppler effect is theoretically investigated, adopting the case of a system composed of one transmitter and two receivers. Accordingly the relation between the Doppler frequency shift at each receiver and the 2-D localization of the target was established. The range R and the azimuth θ are derived from the maximum likelihood Doppler signal processing. The first stage consisted in performing the localization in air, only at the left or at the right side of the line-of-sight of the system
Uranium oxide and other airborne particles deposited on cypress leaves close to a nuclear facility
No full textInternational audienceEnhanced activity of actinides and some decay products has been reported for the leaves of cypress trees (Chamaecyparis nootkatensis) at the edge of the Malvési uranium-processing facility, southwestern France. The enhanced activity is due to the release of actinides via the smokestacks and from artificial ponds inside the facility. This study was conducted to characterize airborne particulate matter deposited on the leaf surfaces and to investigate whether or not radioactive particles may be identified. Air-dried leaf samples were examined by scanning electron microscopy, in combination with energy-dispersive X-ray spectrometry. The samples were scanned systematically in both secondary and backscattered electron modes. Particles ranging in size from <200 nm to ∼40 μm were found on most portions of the adaxial leaf surface, but they are especially abundant at the boundary between facial and lateral leaves. The majority of the analyzed particles could be attributed to five principal classes carbonates, silicates, sulfates, oxides/hydroxides, and halides. In addition, other types of particles were found, including Fe alloys; scheelite-group phases; phosphates; sulfides; and fly ash spheres. Similar particles were also observed on the surface of a wheat sample used for comparison. Of special interest are U-rich particles, which were observed on the cypress leaves only and which were identified as U oxides, except for one particle, which was a U-oxide-fluoride. These U-rich particles were released into the atmosphere by the nuclear facility prior to their deposition on the leaf surfaces. As most of the U-rich particles are <2.5 μm across, they are respirable. Once inhaled, particles containing alpha-emitting isotopes represent a potentially long-term source of ionizing radiation inside the lungs and thus, pose a threat to the health of people living nearby. © 2012 The Royal Society of Chemistry
Ra and
No full textThe activities of 228Ac and 214Bi in French foodstuffs acquired during the last 15
years allow one to obtain reference values of 228Ra and 226Ra activities which are usable to assess the dose to
the French population due to the intake of these two natural radionuclides. As expected,
because of similar 238U and 232Th activities in French soils (around 40
Bq.kg-1), the
226Ra/228Ra activity ratio in French terrestrial foodstuffs is
close to 1. Most kinds of foodstuffs present similar mean activities: from 0.1 to 0.2
Bq.kg-1 fresh for
cereals, leafy vegetables, root vegetables, eggs and fishes (marine and freshwater). The
activity in fruits is lower, around 0.05 Bq.kg-1, similar to that of meat calculated on the basis of
the numerous grass measurement results. The lowest activities are noticeable for milk:
around 0.015 Bq.L-1. All these values are in good agreement with the data from
various countries, but most often 2 to 3 times higher than the reference values proposed
by UNSCEAR. This study also shows that due to the large variability of foodstuff
activities reported by a large amount of data, it is not possible to distinguish the
activities of samples from regions with a gap of only a factor of 2 between their soil
activities
Direct characterization of young giant exoplanets at high spectral resolution by coupling SPHERE and CRIRES+
No full textThis is the final version. Available on open access from EDP Sciences via the DOI in this recordStudies of atmospheres of directly imaged extrasolar planets with high-resolution spectrographs have shown that their characterization
is predominantly limited by noise on the stellar halo at the location of the studied exoplanet. An instrumental combination of highcontrast imaging and high spectral resolution that suppresses this noise and resolves the spectral lines can therefore yield higher quality
spectra. We study the performance of the proposed HiRISE fiber coupling between the direct imager SPHERE and the spectrograph
CRIRES+ at the Very Large Telescope for spectral characterization of directly imaged planets. Using end-to-end simulations of
HiRISE we determine the signal-to-noise ratio (S/N) of the detection of molecular species for known extrasolar planets in H and K
bands, and compare them to CRIRES+. We investigate the ultimate detection limits of HiRISE as a function of stellar magnitude, and
we quantify the impact of different coronagraphs and of the system transmission. We find that HiRISE largely outperforms CRIRES+
for companions around bright hosts like β Pictoris or 51 Eridani. For an H = 3.5 host, we observe a gain of a factor of up to 36 in
observing time with HiRISE to reach the same S/N on a companion at 200 mas. More generally, HiRISE provides better performance
than CRIRES+ in two-hour integration times between 50–400 mas for hosts with H < 8.5 and between 50–800 mas for H < 7. For
fainter hosts like PDS 70 and HIP 65426, no significant improvements are observed. We find that using no coronagraph yields the
best S/N when characterizing known exoplanets due to higher transmission and fiber-based starlight suppression. We demonstrate
that the overall transmission of the system is in fact the main driver of performance. Finally, we show that HiRISE outperforms the
best detection limits of SPHERE for bright stars, opening major possibilities for the characterization of future planetary companions
detected by other techniquesEuropean Union Horizon 202
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