HAL Université de Toulouse, et Toulouse INP
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Numerical analysis of the impact of water temperature setpoint and energy strategies on indoor pool performance
No full textInternational audienceIndoor swimming pools (ISPs) consume significant amounts of electrical and thermal energy to ensure the heating of water and air, ventilation, and maintaining adequate humidity levels. This is measured in GWh per year for large installations, such as Olympic swimming pools (SPs). In this paper, the problem is initially addressed using a phenomenological approach at steady state of the air-water coupling, based on a real case study. The aim is to identify the key phenomena and the constraints that are the most sensitive, including those related to water and air quality management. A key action lever is found in evaporation, and more specifically, water temperature and the indoor dewpoint temperature, which act as its precursors. In a second step, two different strategies were tested to reduce energy consumption for water heating. It was determined that a strategy which incorporates night setback in conjunction with a precise restart time yields a maximum gain of 4%. The second strategy aims to enhance the energy recovery of thermal solar panels by enabling slight overheating of the pool. Its large volume provides effective energy storage, with estimated energy savings of up to 17% for a 1◦ C overheating. This strategy appears to be a viable option, as it is straightforward to implement. However, the impact of water overheating on the energy consumption of AHU still needs to be analyzed and managed
Evaluating soil communities sensibility to forest structure through the use of eDNA metabarcoding and the Index of Biodiversity Potential
No full textInternational audienceSince the United Nations Conference on Environment and Development and Forests at Rio in 1992, sustainable forest management has included the obligation to preserve biodiversity. However, monitoring the impact on forest management on biodiversity remains difficult due to the complexity, cost and expertise required for taxonomic surveys. The Index of Biodiversity Potential (IBP) has been developed in 2008 to provide forest managers with a rapid habitat assessment tool and has proved to be a valuable tool to reflect above-ground diversity for many taxa. However, most forest diversity lives underground in soil, and the question remains as to whether such an indicator could also reflect changes in below-ground diversity. We sampled 86 forest plots in two distinct regions of South-west France to characterize soil communities through the metabarcoding of eDNA targeting the 18S barcode for eukaryotic taxa. We also assessed the IBP on each plot, as well as several physicochemical parameters. We examined the relationship between IBP —based on ten factors— and its components on the local diversity and composition of communities and compared the responses of distinct phyla within each region. Our results revealed contrasting correlations between the total IBP score, its factors and several phyla.Furthermore, results were different across the two regions studied, suggesting that correlations were partly context dependent. Our results show that structural features typical of mature stands—such as dead wood, habitat trees, and large-diameter trees—also influence the diversity of soil taxa, similarly to aboveground taxa.This supports the complementarity between eDNA metabarcoding and IBP evaluation to target key forest structural traits and their importance for soil biodiversity
Sensitivity of thermal evapotranspiration models to surface and atmospheric drivers across ecosystems and aridity
No full textInternational audienceEvapotranspiration (ET) lies at the core of the energy-water-carbon coupling, particularly under changing climate conditions. Yet, the sensitivity of ET models to key environmental drivers remains insufficiently understood, especially in understanding how thermal-based ET models respond to distinct influences of soil and atmospheric water stress across ecosystems. In this study, we examine the sensitivity of ET to key environmental drivers, including land surface temperature (LST), air temperature (TA), vapor pressure deficit (VPD), downward solar radiation (DSR), and fractional vegetation cover (FVC), using three representative thermal remote sensing (RS) models (STIC, TSEB, and SPARSE) together with global eddy covariance measurements.At the global scale, variance-based sensitivity analysis (Sobol' method) reveals a transition in the dominant driver of ET sensitivity from water-limited to energy-limited regimes: soil dryness (indicated by LST − TA) dominates ET variability up to an aridity index (ratio of precipitation to reference ET) of 0.54 (± 0.06), beyond which DSR becomes the primary driver. Seasonal variability and ET partitioning emphasize the critical role of soil dryness in driving soil evaporation variability, particularly during growing seasons. Furthermore, a water stress test is conducted across four representative sites with varying vegetation cover types. Results show that ET sensitivity to soil dryness nearly doubles during the drought period compared to climatological norms at the grassland site. In contrast, transpiration in forests is more strongly influenced by VPD under moderate drought stress. Analysis indicates that soil dryness generally exerts stronger control on ET than VPD. However, when vegetation cover exceeds 0.49, the influence of VPD anomalies on ET becomes comparable to soil dryness stress.This research advances our understanding of ET dynamics under increasing drought frequency and intensity. It highlights the potential of forthcoming high-resolution thermal-based RS ET products for early drought hazard warnings, climate-resilient decision-making, and sustainable agricultural water management
Existence of monostable fronts for a KPP infinite-difference numerical scheme
No full textInternational audienceWe study the existence of traveling wave solutions for a numerical counterpart of the KPP equation. We obtain the existence of monostable fronts for all super-critical speeds in the regime where the spatial step size is small. The key strategy is to transfer the invertibility of certain linear operators related to the front solutions from the continuous setting to the discrete case we are interested in. We rely on resolvent bounds which are uniform with respect to the step size, a procedure which is also known as spectral convergence. The approach is also able to handle infinite range discretizations with geometrically decaying coefficients that are allowed to have both signs, which prevents the use of the comparison principle
Gas permeability of concrete under compressive creep during drying–wetting cycles
No full textInternational audienceGas permeability is used as an indicator of concrete durability due to its strong correlation with material porosity. However, permeability is typically measured on unloaded specimens or under loading conditions that are not representative of actual structural applications. This experimental investigation aims to enhance the understanding of the impact of mechanical stress on the gas permeability and, by extension, concrete durability, under conditions approaching those of structural applications. For this purpose, a novel experimental setup was designed to measure radial gas flow through hollow concrete specimens under compressive creep loading. The setup was validated by comparing the measured gas permeabilities to those obtained using a Cembureau constant-head permeameter. The impact of two levels of compressive creep on the gas permeability of initially saturated concrete specimens was investigated over a 150-day drying period at 20 °C and 50 % relative humidity. Subsequently, the specimens were immersed in water until constant mass was reached and then dried a second time under identical hygro-mechanical conditions, in order to distinguish the effect of water saturation from that of hygro-mechanical cracking. The results show that sustained loading to 30 % of the concrete compressive strength has no significant impact on gas flow. However, loading concrete to 60 % of its compressive strength leads to a tenfold increase in measured gas permeability, compared to unloaded specimens. Monitoring the mass of the specimens revealed that the studied stress levels do not significantly impact drying kinetics. Therefore, the observed increase in gas permeability is attributed to hygro-mechanical damage
Challenges of operating multiple distributed generators with different primary control strategies in microgrids: Interactions and performance assessment
No full textInternational audienceThis study investigates the effectiveness of hybrid power-sharing control strategies in microgrid systems. It integrates various droop controllers, including conventional droop, universal droop, dVOC, and VSG. The contribution of each controller is evaluated in terms of system stability, efficiency, and adaptability. These assessments consider how different test conditions influence overall system performance. The performance analysis focuses on power sharing during both transient and steady-state conditions. It accounts for DERs connected through complex transmission line impedances and subjected to variable local loads. The study concludes with extensive real-time simulations using the Typhoon HIL 604 platform. These scenarios test different operating conditions to identify the most stable microgrid configuration
Diffusive gradient in thin film for ultra-trace methylmercury measurements in the coastal and open sea
No full textInternational audienceMonomethylmercury (MMHg) is a potent neurotoxin causing neurodevelopmental delays and cardiovascular and immunological issues. Human exposure primarily occurs through seafood consumption due to MMHg bioaccumulation and biomagnification from seawater into marine organisms. Determining MMHg in seawater at ultratrace concentrations poses logistical and analytical challenges. Diffusive Gradient in Thin-film (DGT) samplers represent a promising solution, which captures time-averaged concentrations by preconcentrating in situ MMHg over a defined exposure time. DGT manufactured with 3-mercaptopropyl-functionalized silica (3MFS) in agarose and polyacrylamide gels were tested and compared for the determination of MMHg present in open ocean and coastal waters. Different elution methods using acidic thiourea were tested to reach precise, accurate and quantitative elution of MMHg from the binding gel. We found that polyacrylamide-3MFS binding gels display a higher elution efficiency (94 ± 3 %), precision and better handling compared to agarose-3MFS gels (41 ± 6 %). A unique mooring line installed in the South Western Tropical Pacific Ocean, provided monthly DGT-MMHg concentrations over a year showing potential seasonal differences in MMHg concentrations ranging between 18 and 106 fM. DGT were also deployed in shallow Peruvian coastal waters, exhibiting higher MMHg concentrations (170 ± 97, n = 26) with typical benthopelagic gradients. DGT-MMHg concentrations were in good agreement with discrete water samples analyzed by reference methods using isotope dilution. DGTs offer complementary advantages over oceanographic cruises, notably in situ preconcentration, low blanks, minimal logistical requirements and cost-effectiveness. DGTs represent a valuable tool for studying the marine MMHg cycle for evaluating the implementation of the Minamata Convention
Model-based dependability and performance analysis for satellite systems with collaborative maintenance maneuvers via stochastic games
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Mediterranean alley-cropping agroforestry modifies arthropod temporal dynamics with divergent effects on trophic groups
No full textInternational audienceAgroforestry is promoted as a sustainable agricultural practice that enhances biodiversity and ecosystem services, including natural pest control. However, its effects on arthropod communities, particularly across different trophic groups and seasonal dynamics, remain poorly understood. In this study, we assessed the impact of a Mediterranean alley-cropping agroforestry system on the abundance, diversity, and community composition of eight arthropod trophic groups, in Southern France. Using pan traps and pitfall traps, we sampled arthropods in agroforestry alleys and tree rows at three dates in spring 2023 (April, March and May), comparing them to monocultures and tree plantations. After identification, invertebrate taxa were classified into eight trophic groups based on current ecological knowledge. Agroforestry influenced arthropod abundance and diversity, though responses varied among trophic groups. Community composition, as reflected through a Principal Coordinates Analysis, was primarily structured by phenology rather than habitat type, with pronounced seasonal shifts across most trophic groups. Effect size analysis showed that tree rows supported a higher abundance of certain beneficial arthropods, emphasizing their role in agroforestry system function. Further research on multi-trophic interactions and long-term dynamics is needed to optimize agroforestry as a strategy for ecological intensification
Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering?
No full textInternational audienceBased on observation and data from meteorites and in situ scientific missions, experiments as well as models, the Martian mantle is assumed to share some compositional and mineralogical affinity with the terrestrial mantle. However, there might be subtle differences like the Martian mantle being more ferroan. Yet, we do not have any direct analysis of a Martian mantle rock to confirm this assumption. NASA’s Perseverance rover found olivine-rich boulder-sized float rocks on the upper Jezero fan (Mars). These boulders have an ultramafic composition and their mineralogy is dominantly composed of Fo73±3 olivine with high-Mg orthopyroxene, Cr-rich Ti-Fe oxides and minor plagioclase and high-Ca pyroxene. Microtextural and petrological analysis reveals that these minerals crystallized at equilibrium. In addition, these boulders are different from all the bedrocks analyzed by Perseverance along its traverse which are crustal igneous rocks and sediments. Comparing our data to Martian meteorites and available Mars bulk silicate models (BSM), we discuss that these boulders could represent primitive melts and/or lower crustal material, and we specifically hypothesize that they could be mantle peridotites. We propose that these putative mantle rocks could have been excavated by the succession of impacts from the shallow mantle or lower crust in the Isidis region where Jezero crater is located. These olivine-rich boulders could thereby constitute the first direct analysis of a Martian mantle rock