Comparison between backscattered TerraSAR signals and simulations from the radar backscattering models IEM, Oh, and Dubois

The objective of this paper is to evaluate on bare soils the surface backscattering models IEM, Oh, and Dubois in X-band. This analysis uses a large database of TerraSAR-X images and in situ measurements (soil moisture and surface roughness). Oh's model correctly simulates the radar signal for HH and VV polarizations whereas the simulations performed with the Dubois model show a poor correlation between TerraSAR data and model. The backscattering Integral Equation Model (IEM) model simulates correctly the backscattering coefficient only for rms1.5 cm in using Gaussian function. However, the results are not satisfactory for a use of IEM in the inversion of TerraSAR data. A semi-empirical calibration of IEM was done in X-band. Good agreement was found between the TerraSAR data and the simulations using the calibrated version of the IEM

Analysis of TerraSAR-X data sensitivity to bare soil moisture, roughness, composition and soil crust

Le comportement du signal radar TerraSAR-X en fonction des paramètres du sol (rugosité, humidité, structure) a été analysé sur des données 2009 et 2010. Les résultats montrent que la sensibilité du signal radar à l'humidité est plus importante pour des faibles incidences (25° en comparaison à 50°). Pour des fortes valeurs d'humidité, le signal TerraSAR-X est plus sensible à la rugosité du sol à forte incidence (50°). La forte résolution spatiale des données TerraSAR-X (1 m) permet de détecter la croûte de battance à l'échelle intra parcellaire. / Soils play a key role in shaping the environment and in risk assessment. We characterized the soils of bare agricultural plots using TerraSAR-X (9.5 GHz) data acquired in 2009 and 2010. We analyzed the behavior of the TerraSAR-X signal for two configurations, HH-25° and HH-50°, with regard to several soil conditions: moisture content, surface roughness, soil composition and soil-surface structure (slaking crust).The TerraSAR-X signal was more sensitive to soil moisture at a low (25°) incidence angle than at a high incidence angle (50°). For high soil moisture (N25%), the TerraSAR-X signal was more sensitive to soil roughness at a high incidence angle (50°) than at a low incidence angle (25°). The high spatial resolution of the TerraSAR-X data (1 m) enabled the soil composition and slaking crust to be analyzed at the within-plot scale based on the radar signal. The two loamy-soil categories that composed our training plots did not differ sufficiently in their percentages of sand and clay to be discriminated by the X-band radar signal.However, the spatial distribution of slaking crust could be detected when soil moisture variation is observed between soil crusted and soil without crust. Indeed, areas covered by slaking crust could have greater soil moisture and consequently a greater backscattering signal than soils without crust

Use of reflected GNSS SNR data to retrieve either soil moisture or vegetation height from a wheat crop

This work aims to estimate soil moisture and vegetation height from Global Navigation Satellite System (GNSS) Signal to Noise Ratio (SNR) data using direct and reflected signals by the land surface surrounding a ground-based antenna. Observations are collected from a rainfed wheat field in southwestern France. Surface soil moisture is retrieved based on SNR phases estimated by the Least Square Estimation method, assuming the relative antenna height is constant. It is found that vegetation growth breaks up the constant relative antenna height assumption. A vegetation-height retrieval algorithm is proposed using the SNR-dominant period (the peak period in the average power spectrum derived from a wavelet analysis of SNR). Soil moisture and vegetation height are retrieved at different time periods (before and after vegetation's significant growth in March). The retrievals are compared with two independent reference data sets: in situ observations of soil moisture and vegetation height, and numerical simulations of soil moisture, vegetation height and above-ground dry biomass from the ISBA (interactions between soil, biosphere and atmosphere) land surface model. Results show that changes in soil moisture mainly affect the multipath phase of the SNR data (assuming the relative antenna height is constant) with little change in the dominant period of the SNR data, whereas changes in vegetation height are more likely to modulate the SNR-dominant period. Surface volumetric soil moisture can be estimated (R2  =  0.74, RMSE  =  0.009 m3 m−3) when the wheat is smaller than one wavelength (∼ 19 cm). The quality of the estimates markedly decreases when the vegetation height increases. This is because the reflected GNSS signal is less affected by the soil. When vegetation replaces soil as the dominant reflecting surface, a wavelet analysis provides an accurate estimation of the wheat crop height (R2  =  0.98, RMSE  =  6.2 cm). The latter correlates with modeled above-ground dry biomass of the wheat from stem elongation to ripening. It is found that the vegetation height retrievals are sensitive to changes in plant height of at least one wavelength. A simple smoothing of the retrieved plant height allows an excellent matching to in situ observations, and to modeled above-ground dry biomass

Basal ganglia dysfunction in OCD: subthalamic neuronal activity correlates with symptoms severity and predicts high-frequency stimulation efficacy

Functional and connectivity changes in corticostriatal systems have been reported in the brains of patients with obsessive–compulsive disorder (OCD); however, the relationship between basal ganglia activity and OCD severity has never been adequately established. We recently showed that deep brain stimulation of the subthalamic nucleus (STN), a central basal ganglia nucleus, improves OCD. Here, single-unit subthalamic neuronal activity was analysed in 12 OCD patients, in relation to the severity of obsessions and compulsions and response to STN stimulation, and compared with that obtained in 12 patients with Parkinson's disease (PD). STN neurons in OCD patients had lower discharge frequency than those in PD patients, with a similar proportion of burst-type activity (69 vs 67%). Oscillatory activity was present in 46 and 68% of neurons in OCD and PD patients, respectively, predominantly in the low-frequency band (1–8 Hz). In OCD patients, the bursty and oscillatory subthalamic neuronal activity was mainly located in the associative–limbic part. Both OCD severity and clinical improvement following STN stimulation were related to the STN neuronal activity. In patients with the most severe OCD, STN neurons exhibited bursts with shorter duration and interburst interval, but higher intraburst frequency, and more oscillations in the low-frequency bands. In patients with best clinical outcome with STN stimulation, STN neurons displayed higher mean discharge, burst and intraburst frequencies, and lower interburst interval. These findings are consistent with the hypothesis of a dysfunction in the associative–limbic subdivision of the basal ganglia circuitry in OCD's pathophysiology

The pathophysiology of restricted repetitive behavior

Restricted, repetitive behaviors (RRBs) are heterogeneous ranging from stereotypic body movements to rituals to restricted interests. RRBs are most strongly associated with autism but occur in a number of other clinical disorders as well as in typical development. There does not seem to be a category of RRB that is unique or specific to autism and RRB does not seem to be robustly correlated with specific cognitive, sensory or motor abnormalities in autism. Despite its clinical significance, little is known about the pathophysiology of RRB. Both clinical and animal models studies link repetitive behaviors to genetic mutations and a number of specific genetic syndromes have RRBs as part of the clinical phenotype. Genetic risk factors may interact with experiential factors resulting in the extremes in repetitive behavior phenotypic expression that characterize autism. Few studies of individuals with autism have correlated MRI findings and RRBs and no attempt has been made to associate RRB and post-mortem tissue findings. Available clinical and animal models data indicate functional and structural alterations in cortical-basal ganglia circuitry in the expression of RRB, however. Our own studies point to reduced activity of the indirect basal ganglia pathway being associated with high levels of repetitive behavior in an animal model. These findings, if generalizable, suggest specific therapeutic targets. These, and perhaps other, perturbations to cortical basal ganglia circuitry are mediated by specific molecular mechanisms (e.g., altered gene expression) that result in long-term, experience-dependent neuroadaptations that initiate and maintain repetitive behavior. A great deal more research is needed to uncover such mechanisms. Work in areas such as substance abuse, OCD, Tourette syndrome, Parkinson’s disease, and dementias promise to provide findings critical for identifying neurobiological mechanisms relevant to RRB in autism. Moreover, basic research in areas such as birdsong, habit formation, and procedural learning may provide additional, much needed clues. Understanding the pathophysioloy of repetitive behavior will be critical to identifying novel therapeutic targets and strategies for individuals with autism

Sonochemical activity in ultrasonic reactors under heterogeneous conditions

International audienceDue to its physical and chemical effects, ultrasound is widely used for industrial purposes, especially in heterogeneousmedium. Nevertheless, this heterogeneity can influence the ultrasonic activity. In this study, theeffect of the addition of inert glass beads on the sonochemical activity inside an ultrasonic reactor is investigatedby monitoring the formation rate of triiodide, and the ultrasonic power is measured by calorimetry and byacoustic radiation. It was found that the sonochemical activity strongly depends on the surface area of the glassbeads in the medium: it decreases above a critical area value (around 10-² m²), partly due to wave scattering andattenuation. This result is confirmed for a large range of frequencies (from 20 to 1135 kHz) and glass beadsdiameters (from 8-12 μm to 6 mm). It was also demonstrated that above a given threshold of the surface area,only part of the supplied ultrasonic power is devoted to chemical effects of ultrasound. Finally, the acousticradiation power appears to describe the influence of solids on sonochemical activity, contrary to the calorimetricpower

Modeling and analysis of concentration profiles obtained by in-situ SAXS during cross-flow ultrafiltration of colloids

International audienceConcentration profiles and structural organization of different colloidal suspensions in the vicinity of membrane during ultrasonic-assisted ultrafiltration were previously evidenced from non-destructive, real-time, in-situ SAXS measurements (Jin et al., 2014 [11], Jin et al., 2014 [12]). On the basis of these obtained results, this paper explored by numerical calculation, four key factors of the buildup of concentrated polarization layer in such process (matter accumulation, flow property, permeability and osmotic pressure). Two different kind of systems have been studied: anisotropic Laponite clay particles and soft casein micelle particles. For all the systems and filtration conditions investigated, the results have shown that the level of matter accumulated is directly linked to calculated permeation flux and in accordance with the experimental one. The rheological parameters introduced in the calculations have allowed to deduce the charts of yield stress in the concentrated layers and revealed the important role of suspensions flow properties in the mechanisms of filtration involved near the membrane surface. The measured properties of the accumulated layers have been computed with a recent model based upon permeability and osmotic pressure (Bouchoux et al., 2013 [17]). It has been shown good agreement between modeled and experimental values in permeation flux for all the different systems and filtration explored

Cross flow ultrafiltration of skim milk assisted by ultrasound: multi-scale characterization

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Intensification de l’ultrafiltration tangentielle du lait assistée par ultrasons : De l’échelle nanométrique au procédé

Dans ce travail, il est proposé de combiner in-situ des ondes ultrasonores basse fréquence aux champs de pression et aux effets hydrodynamiques lors de l’ultrafiltration tangentielle du lait. Une nouvelle cellule de filtration tangentielle a été développé afin d’une part, d’appliquer des ultrasons au voisinage de toute la surface membranaire au moyen d’une lame vibrante à 20 kHz, et d’autre part d’observer in-situ l’organisation des colloïdes dans les couches de polarisation par diffusion de rayons X aux petits angles (SAXS) [1–4]. L’observation in-situ des profils de concentration permet d’apporter des informations précieuses sur les modifications des couches concentrées sous ultrasons aux échelles nanométriques. L’objectif est de corréler les performances du procédé de filtration à l’échelle macroscopique (flux de perméat, taux de rétention, caractéristiques rhéologiques...) avec les résultats de ces observations aux échelles des particules (profils de concentration et de structure au voisinage de la membrane)

Caractérisation chimique et physique d’un réacteur combiné 20/500 kHz

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