AGN observations with a less than 100 GeV threshold using H.E.S.S. II

The recent addition of the 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment's sensitivity towards low energies. The lowest energy threshold is obtained using monoscopic observations with CT5, providing access to gamma-ray energies below 100 GeV. This is particularly beneficial for studies of Active Galactic Nuclei (AGN) with soft spectra and located at redshifts >= 0.5. Stereoscopic measurements with the full array (CT1-5) provide a better background rejection than CT5 Mono, at a cost of a higher threshold. We report on the analysis employing the CT5 data for AGN observations with a < 100 GeV threshold. In particular, the spectra of PKS 2155-304 and PG 1553+113 are presented.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherland

Continuous measurement of nitrate concentration in a highly event-responsive agricultural catchment in south-west of France: is the gain of information useful?

A nitrate sensor has been set up to measure every 10 min the nitrate signal in a stream draining a small agricultural catchment dominated by fertilized crops during a 2-year study period (2006–2008) in the south-west of France. An in situ sampling protocol using automatic sampler to monitor flood events have been used to assume a point-to-point calibration of the sensor values. The nitrate concentration exhibits nonsystematic concentration and dilution effects during flood events. We demonstrate that the calibrated nitrate sensor signal gathered from the outlet is considered to be a continuous signal using the Nyquist–Shannon sampling theorem. The objectives of this study are to quantify the errors generated by a typical infrequent sampling protocol and to design appropriate sampling strategy according to the sampling objectives. Nitrate concentration signal and flow data are numerically sampled to simulate common sampling frequencies. The total fluxes calculated from the simulated samples are compared with the reference value computed on the continuous signal. Uncertainties are increasing as sampling intervals increase; the method that is not using continuous discharge to compute nitrate fluxes bring larger uncertainty. The dispersion and bias computed for each sampling interval are used to evaluate the uncertainty during each hydrological period. High underestimation is made during flood periods when high-concentration period is overlooked. On the contrary, high sampling frequencies (from 3 h to 1 day) lead to a systematic overestimation (bias around 3%): highest concentrations are overweighted by the interpolation of the concentration in such case. The in situ sampling protocol generates less than 1% of load estimation error and sample highest concentration peaks. We consider useful such newly emerging field technologies to assess short-term variations of water quality parameters, to minimize the number of samples to be analysed and to assess the quality state of the stream at any time

Role of the Resonator Geometry on the Pressure Spectrum of Reed Conical Instruments

International audienc

Understanding nitrogen transfer dynamics in a small agricultural catchment: Comparison of a distributed (TNT2) and a semi distributed (SWAT) modeling approaches

The coupling of an hydrological and a crop model is an efficient approach to study the impact of the interactions between agricultural practices and catchment physical characteristics on stream water quality. We analyzed the consequences of using different modeling approaches of the processes controlling the nitrogen (N) dynamics in a small agricultural catchment monitored for 15 years. Two agro-hydrological models were applied: the fully distributed model TNT2 and the semi-distributed SWAT model. Using the same input dataset, the calibration process aimed at reproducing the same annual water and N balance in both models, to compare the spatial and temporal variability of the main N processes. The models simulated different seasonal cycles for soil N. The main processes involved were N mineralization and denitrification. TNT2 simulated marked seasonal variations with a net increase of mineralization in autumn, after a transient immobilization phase due to the burying of the straw with low C:N ratio. SWAT predicted a steady humus mineralization with an increase when straws are buried and a decrease afterwards. Denitrification was mainly occuring in autumn in TNT2 because of the dynamics of N availability in soil and of the climatic and hydrological conditions. SWAT predicts denitrification in winter, when mineral N is available in soil layers. The spatial distribution of these two processes was different as well: less denitrification in bottom land and close to ditches in TNT2, as a result of N transfer dynamics. Both models simulate correctly global trend and inter-annual variability of N losses in small agricultural catchment when a sufficient amount data is available for calibration. However, N processes and their spatial interactions are simulated very differently, in particular soil mineralization and denitrification. The use of such tools for prediction must be considered with care, unless a proper calibration and validation of the different N processes is carried out

Aerogel-based metasurfaces for perfect acoustic energy absorption

International audienceThe unusual viscoelastic properties of silica aerogel plates are efficiently used to design subwavelength perfect sound absorbers. We theoretically, numerically and experimentally report a perfect absorbing metamaterial panel made of periodically arranged resonant building blocks consisting of a slit loaded by a clamped aerogel plate backed by a closed cavity. The impedance matching condition is analyzed using the Argand diagram of the reflection coefficient, i.e., the trajectory of the reflection coefficient as a function of frequency in the complex plane. The lack or excess of losses in the system can be identified via this Argand diagram in order to achieve the impedance matching condition. The universality of this tool can be further exploited to design more complex metasurfaces for perfect sound absorption, thus allowing the rapid design of efficient absorbing metamaterials

Influence of post-exercise hot-water therapy on long-term adaptations to training in elite short-track speed skaters

International audienceThis study aimed to investigate the effects of regular hot water bathing (HWB), undertaken 10 min after the last training session of the day, on chronic adaptations to training in elite athletes. Six short-track (ST) speed skaters completed four weeks of post-training HWB and four weeks of post-training passive recovery (PR) according to a randomized cross-over study. During HWB, participants sat in a jacuzzi (40 °C; 20 min). According to linear mixed models, maximal isometric strength of knee extensor muscles was significantly increased for training with HWB (p 0.05), including aerobic peak power output, the decline rate of jump height during 1 min-continuous maximal countermovement jumps (i.e. anaerobic capacity index), and the force-velocity relationship. Regarding specific tasks on ice, a small effect of training was found on both half-lap time and total time during a 1.5-lap all-out exercise (p = 0.0487; d = 0.23 and p = 0.0332; d = 0.21, respectively) but no additional effect of HWB was observed. In summary, the regular HWB protocol used in this study can induce additional effects on maximal isometric strength without compromising aerobic and anaerobic adaptations or field performance in these athletes

Simulation du fonctionnement hydrodynamique des milieux humides dans les plaines alluviales

International audienceLa modélisation hydrodynamique est peu utilisée afin de simuler le fonctionnement des milieux humides à l’échelle des plaines alluviales et nécessite souvent de nombreuses données d’entrée souvent difficiles à acquérir. On présente ici un outil de simulation, Accept’Hydro, qui est alimenté par quatre données d’entrée : le modèle numérique d’élévation (IGN), les données piézométriques (banque ADES), l’historique des débits rivières (banque HYDRO), et le réseau hydrographie (BD Carthage). Après l’étape de création automatique du maillage non-uniforme, adapté au domaine étudié, le logiciel génère en sortie les hauteurs d’eau et les vitesses d’écoulement dans la rivière et dans la nappe souterraine, au pas de temps journalier. Les données simulées, sur une période de temps minimal de 10 ans, sont traitées afin de cartographier les milieux humides potentiels en bordure de cours d’eau. De plus, cet outil permet d’intégrer des hypothèses sur l’évolution des débits afin de prendre en compte les modifications dues au change ment climatique, et d’en simuler les impacts sur le fonctionnement hydrologique. On présente ici les résultats d’Accept’Hydro sur la plaine alluviale de la Garonne et ses milieux humides pour la période 2004-2013, dans le département du Tarn-et-Garonne. Dans ce secteur, les simulations prévoient une diminution de la superficie des milieux humides pour l’horizon 2030, en partant d’hypothèses de diminution des débits saisonniers

Accept'Hydro: a tool for evaluating potential wetland areas at floodplain scale.

National audienceAlluvial wetlands have the functions of hydrological regulation and water purification, but are also of interest for preventing flooding and improving the water quality of the natural environment that serves as a reserve for drinking water and biodiversity. Delimiting these areas is often difficult because it involves both the physical characteristics (topography, river morphology etc.) and hydrodynamic characteristics of the porous medium (permeability etc.) The proposed tool, Accept'Hydro, includes a hydrodynamic simulation of the river, the alluvial aquifer and their interaction, and produces maps of alluvial wetlands with using hydrological criteria. The tool's primary step consists of selecting the studied area using Google Maps, which automatically triggers the generation of a non-uniform mesh covering this area, as well as all the inputs needed for the hydrodynamic simulation to run. The hydrodynamic model based on the equations of Peyrard et al. (2008) allows water levels and flow rates in the river and the alluvial aquifer to be simulated with a non-uniform mesh (cells from 1 to 200 metres per side), combined with a good performance in CPU calculation time. The software program allows the impacts of climate change (changes in hydrology and temperature) and/or anthropogenic change on the hydrodynamic functioning of wetlands to be assessed, and the impact of infrastructure and hydropower facilities on the river to be tested

Les contaminants métalliques traqués par la spectrométrie atomique dans le bioéthanol

International audienceDans le cadre de la transition énergétique, l'utilisation de biocarburants à base de carbone renouvelable est une des alternatives permettant de limiter l'émission de CO 2 fossile. La diversité des sources potentielles de biomasse requiert en revanche une caractérisation des polluants inorganiques éventuels qui pourraient s'avérer nuisibles. Dans cette optique, une investigation sur les teneurs en contaminants métalliques dans différentes sources de bioéthanol a été menée en collaboration avec l'Université d'Alicante. Nous avons constaté des teneurs systématiquement inférieures au mg/kg sur la totalité des échantillons analysés, lesquels représentent un panel important des bioéthanols utilisés en tant que base de carburant ou base pétrochimique. La source de ces très faibles teneurs a été investiguée en suivant le schéma de fabrication du bioéthanol à partir de betteraves et les résultats montrent que la plupart des métaux présents dans le bioéthanol ont comme source la biomasse de départ. L'étape de distillation est particulièrement efficace pour éliminer ces contaminants : les concentrations sont divisées par 10000. Abstract : As part of the energy transition, the use of renewable biofuels is one of the alternatives to limit the emission of fossil CO 2. Anyhow, the assessment of the environmental benefit provided by the use of biofuels requires a thorough characterization of the inorganic pollutants potentially present in the biomass used as a source of biofuel. With this in mind, an investigation on the levels of metallic contaminants in different bio-ethanol samples was conducted in collaboration with the University of Alicante. The samples chosen were appropriate to be used either as a fuel themselves or blended with fossil fuels. We have found that metallic species were present at concentrations below the mg/kg level in virtually all the bioethanol samples under study. The source of these very low levels of contaminants has been investigated following the bioethanol production scheme from beet and the results show that most of the metals present in bioethanol are also present in the original biomass. From all the procedures required to obtain the biofuel, the distillation of the syrup resulting from the fermentation step is particularly effective in removing these contaminants : Concentrations of metallic species in bioethanol is divided 10,000 times

Seismic motion in urban sites consisting of blocks in welded contact with a soft layer overlying a hard half space: I. Finite set of blocks

We address the problem of the response to a seismic wave of an urban site consisting of $N$ non-identical, non-equispaced blocks overlying a soft layer underlain by a hard substratum. The results of a theoretical analysis, appealing to a space-frequency mode-matching (MM) technique, are compared to those obtained by a space-time finite element (FE) technique. The two methods are shown to give rise to the same prediction of the seismic response for N=1 and N=2 blocks. The mechanism of the interaction between blocks and the ground, as well as that of the mutual interaction between blocks, are studied. It is shown that the presence of a small number of blocks modifies the seismic disturbance in a manner which evokes qualitatively, but not quantitatively, what was observed during the 1985 Michoacan earthquake in Mexico City. Disturbances at a much greater level, induced by a large number of blocks (in fact, a periodic set) are studied in the companion paper.Comment: submitted to Geophys.J.Int