Large evanescently-induced Brillouin scattering at the surrounding of a nanofibre

Brillouin scattering has been widely exploited for advanced photonics functionalities such as microwave photonics, signal processing, sensing, lasing, and more recently in micro- and nano-photonic waveguides. So far, all the works have focused on the opto-acoustic interaction driven from the core region of micro- and nano-waveguides. Here we observe, for the first time, an efficient Brillouin scattering generated by an evanescent field nearby a sub-wavelength waveguide embedded in a pressurised gas cell, with a maximum gain coefficient of $18.90 \pm 0.17$ m$^{-1}$W$^{-1}$. This gain is 11 times larger than the highest Brillouin gain obtained in a hollow-core fibre and 79 times larger than in a standard single-mode fibre. The realisation of strong free-space Brillouin scattering from a waveguide benefits from the flexibility of confined light while providing a direct access to the opto-acoustic interaction, as required in free-space optoacoustics such as Brillouin spectroscopy and microscopy. Therefore, our work creates an important bridge between Brillouin scattering in waveguides, Brillouin spectroscopy and microscopy, and opens new avenues in light-sound interactions, optomechanics, sensing, lasing and imaging.Comment: Main manuscript: 8 pages, 6 figures; Supplementary: 5 pages, 3 figure

Toward noninvasive assessment of flap viability with time-resolved diffuse optical tomography: a preclinical test on rats

The noninvasive assessment of flap viability in autologous reconstruction surgery is still an unmet clinical need. To cope with this problem, we developed a proof-of-principle fully automatized setup for fast time-gated diffuse optical tomography exploiting Mellin–Laplace transform to obtain three-dimensional tomographic reconstructions of oxy- and deoxy-hemoglobin concentrations. We applied this method to perform preclinical tests on rats inducing total venous occlusion in the cutaneous abdominal flaps. Notwithstanding the use of just four source-detector couples, we could detect a spatially localized increase of deoxyhemoglobin following the occlusion (up to 550 μM in 54 min). Such capability to image spatio-temporal evolution of blood perfusion is a key issue for the noninvasive monitoring of flap viability

Evaluation of an automatic needle-loading system

The purpose of this paper is to evaluate the dosimetric capabilities and the radiation protection (RP) performance of a new automatic needle-loading system for permanent prostate implants, the Isoloader (Mentor Corp.). The unit has been used in more than 100 clinical cases at our institution. The Isoloader is a computerized workstation that allows automated seed testing by a solid-state CdZnTe radiation detector and loading in surgical needles. The seeds are received in a shielded and ready-to-use cartridge. Radiation protection measurements were done on a cartridge filled with 67 125 I seeds and during dosimetric seed verification and needle loading. The reproducibility of the detector was tested and its accuracy was determined by comparison to specified activities of six calibration seeds and to their measurements in a calibrated well-chamber (WC). Finally, the times required to complete dosimetric verification and needle loading were evaluated. The cartridge was found to be adequately shielded, since no significant amount of radiation was detected around it. Radiation during seed assay wa

Alteration of hypothalamic glucose and lactate sensing in 48h hyperglycemic rats.

International audienceHypothalamic detection of nutrients is involved in the control of energy metabolism and is altered in metabolic disorders. Although hypothalamic detection of blood lactate lowers hepatic glucose production and food intake, it is unknown whether it also modulates insulin secretion. To address this, a lactate injection via the right carotid artery (cephalad) was performed in Wistar rats. This triggered a transient increase in insulin secretion. Rats made hyperglycemic for 48h exhibited prolonged insulin secretion in response to a glucose injection via the carotid artery, but lactate injection induced two types of responses: half of the HG rats showed no difference compared to controls and the other half had markedly decreased insulin secretion. Astroglial monocarboxylates transporters MCT1 and MCT4 isoforms transfer lactate from blood to astrocytes and release lactate to the extracellular space, whilst the neuronal MCT2 isoform permits neuronal lactate uptake. We found that astroglial MCT1 and MCT4, and neuronal MCT2 protein levels in the medio-basal hypothalamus (MBH) were not modified by 48h-hyperglycemia. Together, these results indicate that hypothalamic sensing of circulating lactate triggers insulin secretion. Both glucose and lactate sensing are altered in a model of hyperglycemia, without alteration of MBH MCTs protein levels

Détection cérébrale du glucose, plasticité neuronale et métabolisme énergétique

National audienceEnergy intake is usually well regulated and finely adjusted to energy expenditure. This equilibrium, called energy homeostasis, is dependant in part of the central nervous system which is able to analyse the energy state of the organism by the integration of numerous signals coming from the periphery from which glucose is an important one. This review focuses on the recent advances made on the identification of cellular and molecular mechanisms, phenotype of the neurons, neuronal network and their plasticity involved in glucose sensing. For example, it is now well established that neurons responding to hypo-, hyper-glycemia and even at different concentration changes are present at least in the hypothalamus. Mechanisms involved various actors such as glucose transporters, mitochondria and signals generated by their respiratory activity (ATP, reactive oxygen species) and ion channels. A new area concerns the role of the plasticity of neuronal networks involved in the regulation of the energy metabolism. Altogether, these data should allow to define better and possibly modulate the responses associated with modifications of glycemia and in particular changes observed during various nutritional and/or metabolic pathologies

Spring discharge, transit times and intermittency in an alpine catchment: how geomorphology shapes the spatio-temporal dynamics?

International audienceWe investigate spatial and temporal behaviors of spring discharge, transit times and intermittency of a network of springs located in an alpine catchment (Natural conservation area of the Massif of Saint-Barthélemy, Pyrenees, France). Field observations have revealed unprecedented variability of behaviors across the catchment, with springs involving sustained high discharge rates during baseflow while others showing intermittency of wetting and drying periods. This dynamic is expected to be directly dependent on the volume and transmissivity of the connected aquifer set by specific geomorphological (topography scaling, rockslides, deep seated landslides, detritic sediments) and geological features (lithology, faults). Here we aim at understanding the relative controls of those factors in controlling the observed hydrogeological behaviors across the catchment.We performed two field missions during 2021 high and low flow regimes. More than 20 flowing springs and wetlands have been systematically mapped and sampled for environmental tracer analysis. We found that about 30% of the stream and wetland network contract between high and low flows. The springs responsible for this intermittence are connected to high transmissive shallow aquifers with low storage capacities organized within shallow soils and rockslides. However, perennial springs are influenced by deep groundwater flow paths within the bedrock. The analysis of anthropogenic dissolved gases like CFCs and SF6 revealed an average transit time of the order of 10 years for perennial springs with important variabilities across the catchment. The relatively high residence times is also confirmed by high Helium concentrations. We used the gathered dataset to calibrate a hydrogeological model designed to test the relative controls from specific geomorphological and geological characteristics. By comparing models with different structural settings, we found that topography and aquifer compartmentalization, through the decreasing trend in hydraulic conductivities, are key parameters in setting the spatio-temporal pattern of saturated areas and the distribution of transit times across the catchment. In perspective, we discuss the potential evolution of the extent, discharge magnitude and the transit time of seeping groundwater under changing recharge scenarios

Spring discharge, transit times and intermittency in an alpine catchment: how geomorphology shapes the spatio-temporal dynamics?

International audienceWe investigate spatial and temporal behaviors of spring discharge, transit times and intermittency of a network of springs located in an alpine catchment (Natural conservation area of the Massif of Saint-Barthélemy, Pyrenees, France). Field observations have revealed unprecedented variability of behaviors across the catchment, with springs involving sustained high discharge rates during baseflow while others showing intermittency of wetting and drying periods. This dynamic is expected to be directly dependent on the volume and transmissivity of the connected aquifer set by specific geomorphological (topography scaling, rockslides, deep seated landslides, detritic sediments) and geological features (lithology, faults). Here we aim at understanding the relative controls of those factors in controlling the observed hydrogeological behaviors across the catchment.We performed two field missions during 2021 high and low flow regimes. More than 20 flowing springs and wetlands have been systematically mapped and sampled for environmental tracer analysis. We found that about 30% of the stream and wetland network contract between high and low flows. The springs responsible for this intermittence are connected to high transmissive shallow aquifers with low storage capacities organized within shallow soils and rockslides. However, perennial springs are influenced by deep groundwater flow paths within the bedrock. The analysis of anthropogenic dissolved gases like CFCs and SF6 revealed an average transit time of the order of 10 years for perennial springs with important variabilities across the catchment. The relatively high residence times is also confirmed by high Helium concentrations. We used the gathered dataset to calibrate a hydrogeological model designed to test the relative controls from specific geomorphological and geological characteristics. By comparing models with different structural settings, we found that topography and aquifer compartmentalization, through the decreasing trend in hydraulic conductivities, are key parameters in setting the spatio-temporal pattern of saturated areas and the distribution of transit times across the catchment. In perspective, we discuss the potential evolution of the extent, discharge magnitude and the transit time of seeping groundwater under changing recharge scenarios