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The structure of liquid carbon elucidated by in situ X-ray diffraction
No full textInternational audienceCarbon has a central role in biology and organic chemistry, and its solid allotropes provide the basis of much of our modern technology1. However, the liquid form of carbon remains nearly uncharted2, and the structure of liquid carbon and most of its physical properties are essentially unknown3. But liquid carbon is relevant for modelling planetary interiors4,5 and the atmospheres of white dwarfs6, as an intermediate state for the synthesis of advanced carbon materials7,8, inertial confinement fusion implosions9, hypervelocity impact events on carbon materials10 and our general understanding of structured fluids at extreme conditions11. Here we present a precise structure measurement of liquid carbon at pressures of around 1 million atmospheres obtained by in situ X-ray diffraction at an X-ray free-electron laser. Our results show a complex fluid with transient bonding and approximately four nearest neighbours on average, in agreement with quantum molecular dynamics simulations. The obtained data substantiate the understanding of the liquid state of one of the most abundant elements in the universe and can test models of the melting line. The demonstrated experimental abilities open the path to performing similar studies of the structure of liquids composed of light elements at extreme conditions
Caractérisation chimique et physique de Nannoconus, principal bio-producteur planctonique de carbonates dans les mers crétacées : aperçus des processus de biominéralisation
No full textNannoconus (~5-20 µm) is characterized by the heaviest skeleton among the calcareous nannofossils present during the Early Cretaceous (~152-120 Ma), making them the major planktonic bio-calcifier for this time period. The massive production of these bio-calcites upon transfer to the sediments must have significantly changed the marine chemistry, possibly affecting the marine biosphere. The skeleton of Nannoconus is represented by an interlocking arrangement of calcitic units forming a wall around a central canal, with two terminal openings. Neither the mode of growth/construction of this massive and sophisticated skeleton nor its calcification process (intra versus extra-cellular) is known till date. Given the micrometric size of Nannoconus, to understand their skeletal chemistry and micro-structure, a set of high-resolution chemical and physical characterization techniques have been applied on well-preserved isolated Nannoconus of various geological settings and ages. The confocal Raman microspectroscopy applied on isolated Nannoconus, demonstrated that the skeleton was made of low-Mg calcite. The Electron Dispersive Spectroscopy (EDS) and the synchrotron based-X-ray microfluorescence (µ-XRF) applied on Nannoconus showed the presence of Mg, Sr, in the skeletal calcite, with contamination by clay minerals, and of Mn due to post-depositional diagenesis. Based on the fluorescent maps of Mg and Sr of Nannoconus, an upper limit of their skeletal concentration has been proposed, targeting the zones with the least clay contamination. For the physical characterization, synchrotron based Ptychography X-ray computed tomography (PXCT) was applied on various morphologies of Nannoconus. With the help of the obtained resolution (~30-50 nm), the basic unit of the skeleton, defined as lamella; was segmented and used to reconstruct the entire skeleton constraining various parameters. This revealed that the lamellae are organized in two distinct inclinations, one following the other, creating the interlocking arrangement. The repetition of this organization generates a stack of lamellae, defined as a segment. Several such segments combined together forming the entire skeleton. This micro-structural arrangement of Nannoconus if translated into a process of calcification, implies alternatingly calcifying two types of lamellae, one after another in a stack, creating the segments. Such complicated calcification with changing inclinations and stacking of the lamellae, forming the segments must require enough space, suggesting an extra-cellular mode of calcification for Nannoconus. This work has also shown that an individual lamella contains multiple calcite nanocrystals. Based on the description of other studied bio-mineralized microstructures, a similar structural arrangement both at nanometric (lamella) and micrometric (segment) scales can be assumed indicating that the nanocrystals are also arranged with two alternating inclinations in an individual lamella, as observed in the segment. Such micro-structural arrangements are generally caused by the presence of bio-molecule(s) with rotational properties (e.g., amino acids) during biomineralization. The confocal Raman spectra obtained from isolated Nannoconus and the secondary ion Mass spectrometric (SIMS) analysis realized on clusters of Nannoconus pointed to the presence of organic matter within the specimens, possibly indicating to the preserved remains of the bio-molecule(s). Detailed nano-structural arrangement of the crystals associated with bio-molecule(s) in individual lamellae of Nannoconus, could be studied further using finer resolution (~0.05 nm) tool such as Transmission Electron Microscopy (TEM).Le Nannoconus (~5-20 µm) est caractérisé par le squelette le plus lourd parmi les nannofossiles calcaires présents au Crétacé inférieur (~152-120 Ma), ce qui en fait le principal bio-calcaire planctonique de cette période. La production massive de ces bio-calcites lors de leur transfert dans les sédiments a dû modifier de manière significative la chimie marine, affectant éventuellement la biosphère marine. La structure squelettique du Nannoconus est représentée par un arrangement imbriqué d'unités calcitiques formant un mur autour d'un canal central, avec deux ouvertures terminales. Cependant, on ne connaît pas encore le process de croissance/construction de ce squelette massif et sophistiqué, ni son mode de calcification (intra- ou extra-cellulaire). Étant donné la taille micrométrique des Nannoconus, une série de outils de caractérisation chimique et physique à haute résolution a été appliquée sur des Nannoconus isolés et bien conservés de différents environnements géologiques et âges pour comprendre la chimie et la microstructure de leur squelette. La microspectroscopie confocale Raman sur des Nannoconus a démontré que la calcite squelettique est à faiblement magnésienne. La spectroscopie dispersive d'électrons (EDS) et la microfluorescence des rayons X basée sur le synchrotron (µ-XRF) appliquées au Nannoconus ont montré la présence de Mg, Sr, dans la calcite squelettique, avec la contamination des minéraux argileux, et de Mn due à la diagenèse post-dépôt. A partir des cartes de fluorescence du Mg et du Sr des Nannoconus, une limite supérieure de leur concentration dans le squelette a été proposée, focaliser les zones les moins contaminées par l'argile. Pour la caractérisation physique, Ptychographie à base de synchrotron tomographie à rayons X (PXCT) a été appliquée à différentes morphologies de Nannoconus. Avec la résolution obtenue (~30-50 nm), l'unité de base du squelette, définie comme une lamelle ; a été segmentée et utilisée pour reconstruire l'ensemble du squelette en contraignant différents paramètres. Il en ressort que les lamelles sont organisées selon deux inclinations distinctes, l'une à la suite de l'autre, créant ainsi l’arrangement imbriqué. La répétition de cette organisation génère un empilement de lamelles, appelé segment. Plusieurs de ces segments combinés ensemble forment le squelette complet. En termes de processus de calcification, Cet arrangement micro-structurel, implique la calcification alternée de deux types de lamelles, l'une après l'autre dans un empilement, créant les segments. La calcification compliquée avec un changement d'inclination et un empilement des lamelles formant les segments doit nécessiter suffisamment d'espace, ce qui suggère un mode de calcification extracellulaire pour le Nannoconus. Ces travaux ont également montré qu'une lamelle individuelle contient plusieurs nanocristaux de calcite. Sur la base de la description d'autres microstructures bio-minéralisées étudiées, on peut supposer un arrangement structurel similaire à l'échelle nanométrique (lamelle) et micrométrique (segment), ce qui indique que les nanocristaux sont également disposés avec deux inclinations alternées dans une lamelle, comme observé dans le segment. Ces arrangements sont généralement dus à la présence de biomolécules ayant des propriétés de rotation (par exemple, des acides aminés) au cours de la biominéralisation. Les spectres Raman confocaux obtenus à partir de Nannoconus isolés et l'analyse par spectrométrie de masse d'ions secondaires (SIMS) réalisée sur des amas de Nannoconus indiquent la présence de matière organique dans les spécimens, ce qui pourrait indiquer la présence de restes préservés de biomolécule(s). L'arrangement nano-structurel détaillé des cristaux associés aux biomolécules dans les lamelles individuelles du Nannoconus pourrait être étudié plus avant en utilisant un outil à résolution plus fine (~0,05 nm) tel que la microscopie électronique à transmission (MET)
What is the optimal configuration for integrating hyperaccumulating plants with photovoltaic systems to enhance plant development and energy production?
No full textInternational audienceIndustrial brownfield soils are often contaminated with trace metals, and these areas can be remediated by agromining, using hyperaccumulating plants that can accumulate metals in their aerial parts. However, this process is too slow to be profitable in the short term. The installation of photovoltaic (PV) modules could improve profitability during the bioremediation period. Thus, the objective of this study was to determine the optimal trade-off between electricity production and the development of hyperaccumulating plants in a pilot site set up between July and November 2023. The pilot site consisted of opaque monocrystalline and bifacial semi-transparent PV modules, beneath which culture trays of a hyperaccumulating plant, Noccaea caerulescens (Nc), were placed in addition to reference trays exposed to the sun without shade due to the PV modules. Several parameters were assessed, including the plant cover rate in trays, the dry biomass of Nc and the PV module temperatures. Regarding the Nc cover, plants growing in the shade of a PV module were up to 5.5 times more developed than those without shade, and all the indicators measured allowed plant cover to be differentiated according to the intensity of solar radiation. Furthermore, regarding the PV modules, the cover of Nc seemed to reduce the temperature on the back of the PV modules and improved their performance ratio by 18 % in October. Analysis of the relationship between solar radiation and PV module heating, taking into account the Nc cover, highlighted a potential evapotranspiration effect of the plant cover in reducing the temperature of the PV modules. These results highlighted the importance of managing plant cover under PV modules and taking it into account in the thermal modelling of PV modules in variable climatic conditions
Method of contact resistivity measurements at typical operating conditions for silicon heterojunction solar cells
No full textInternational audienceThe electron-hole contact resistivity measurement can be used to quantify and understand the transport mechanisms at the interfaces of a solar cell. In the silicon heterojunction solar cell technology, it has been shown that the electron and hole contact resistivities exhibit temperature and illumination dependences. The dependence on illumination is related to the variation in the charge carriers concentration at the interfaces after photogeneration in crystalline silicon (c-Si) absorber. Typically, contact resistivity is determined by using the Transfer LengthMethod (TLM) in dark conditions, but it is not representative of typical solar cell operating conditions. In this study, we propose a method to accurately determine the temperature and injection level of excess charge carriers in TLM samples under illumination. We have established a procedure to correlate the passivation level of theTLM samples with the conductivity of the c-Si absorber. This method highlighted two conductivity regimes within the electron-hole contact as a function of the injection level, with the low injection levels leading to an increase in the contact resistivity. For example, a hole contact resistivity value of up to 800 mΩ cm2 was obtainedfor the lowest injection levels at 300 K. The contact resistivity values determined at the Maximum Power Point (MPP) were used to model the series resistance, which was compared with the experimental values. The simulated results for the series resistance exhibited a clear trend with the temperature similar to the experimental results
The DUNE Science Program
No full textInternational audienceThe international collaboration designing and constructing the Deep Underground Neutrino Experiment (DUNE) at the Long-Baseline Neutrino Facility (LBNF) has developed a two-phase strategy for the implementation of this leading-edge, large-scale science project. The 2023 report of the US Particle Physics Project Prioritization Panel (P5) reaffirmed this vision and strongly endorsed DUNE Phase I and Phase II, as did the previous European Strategy for Particle Physics. The construction of DUNE Phase I is well underway. DUNE Phase II consists of a third and fourth far detector module, an upgraded near detector complex, and an enhanced > 2 MW beam. The fourth FD module is conceived as a 'Module of Opportunity', aimed at supporting the core DUNE science program while also expanding the physics opportunities with more advanced technologies. The DUNE collaboration is submitting four main contributions to the 2026 Update of the European Strategy for Particle Physics process. This submission to the 'Neutrinos and cosmic messengers', 'BSM physics' and 'Dark matter and dark sector' streams focuses on the physics program of DUNE. Additional inputs related to DUNE detector technologies and R&D, DUNE software and computing, and European contributions to Fermilab accelerator upgrades and facilities for the DUNE experiment, are also being submitted to other streams
Effects of Resistance and Speed on Electromyographic Activity of Thigh and Gluteal Muscles in Elite Athletes throughout Resisted Sprint Running
No full textInternational audiencePurpose: The application of horizontal resistance is key in sprint training to modulate velocity and promote adaptations. However, the interaction between velocity and resistance on muscle excitation remains insufficiently studied. This study assessed the electromyographic (EMG) activity of thigh and gluteal muscles in response to varying velocity and resistance during sprinting. Methods: Thirty-seven elite athletes (27 females and 10 males) performed two trials under three conditions: a 40-meter maximal sprint without resistance and two resisted sprints applied by a robotic device with resistive forces equivalent to 25% and 75% of body mass in a sled condition. EMG activity was recorded from eight muscles in the quadriceps, hamstrings, and gluteal muscle groups for both lower limbs. Generalized mixed models were used to analyze average EMG changes with increasing velocity as a function of resistance. Statistical parametric mapping was used to assess the changes within the stance and swing phases as a function of sprint phase and resistance. Results: Hamstring EMG activity increased with increasing velocity (+17.9% in stance phase without resistance) and decreased as resistance increased, with opposite effects observed in quadriceps muscles. Higher gluteal EMG activity was found during the late swing phase with increasing velocity and decreasing resistance. The biceps femoris long head exhibited the largest EMG increase with velocity (+23% in the stance phase) among hamstrings, while the semitendinosus showed the highest increase with reduced resistance (+27% in the stance phase). Conclusions: External resistance and running speed influence thigh muscle activity differently, even within the same muscle group, likely due to distinct muscle architecture and function. These insights should be considered when designing sprint training programs to target specific muscle groups, avoid muscle overloading, and account for inter-individual differences to optimize performance and reduce injury risk
In Silico Formation of Polyphosphazene Networks Based on Phloroglucinol (Phg) and Hexachlorocyclotriphosphazene (HCCP): Structural and Mechanical Properties as a Function of the Phg:HCCP Ratio
No full textInternational audienceTwenty-four molecular models for polyphosphazene networks were created via an in silico polymerization of phloroglucinol Phg (C6H6O3) and hexachlorocyclotriphosphazene HCCP (N3P3Cl6) mixtures at different Phg:HCCP ratios. A series of monomer mixtures at Phg-to-HCCP stoichiometric ratios ranging from 1:1 to 8:1 were created using molecular dynamics (MD) simulations. Alternating phases of reactions followed by relaxation steps led to the progressive formation of percolating polyphosphazene networks. The actual ratios of Phg to HCCP rings incorporated in the network polymers remained close to those in the mixtures for initial ratios up to 2:1. Above 2:1, there was a gradual divergence toward lower values in the networks as the limits to the number of possible bonds for each monomer started to take effect. The details of the structures were found to be very complex in terms of the probability distributions of links per Phg or HCCP ring. The highest degrees of connectivity and ring packing densities were found in the networks formed from the initial mixtures having Phg-to-HCCP ratios of around 2:1. Mechanical tests were carried out in order to ascertain the resistance of the model polyphosphazene networks to compression/decompression. There again, the networks obtained from the 2:1 initial mixture were found to have the highest Young’s modulus and to display the most elasticity as they recovered their initial shape once the compression was removed. The influence of trapped excess monomers in the percolating networks was only noticeable at the highest mixture ratios. The most resistant Phg-HCCP networks are thus obtained from Phg-to-HCCP mixture ratios of around 2:1, with or without trapped excess monomers
Investigation of Internal Deformations Induced by the State of Lithiation Using 3D Tomography and Strain Gauges Applied to Fast Charging Conditions
No full textInternational audienc
Luminosity measurement for lead-lead collisions at = 5.02 TeV in 2015 and 2018 at CMS
No full textInternational audienceMeasurements of the luminosity delivered to the CMS experiment during the lead-lead data-taking periods in 2015 and 2018 are presented for the first time. The collisions were recorded at a nucleon-nucleon center-of-mass energy of 5.02 TeV; the 2018 data sample is three times larger than the 2015 data sample. Three subdetectors are used: the pixel luminosity telescope, the forward hadron calorimeters, and the fast beam conditions monitor. The absolute luminosity calibration is determined using the van der Meer technique that relies on transverse beam separation scans. The dominant sources of uncertainty are the transverse factorizability of the bunch density profiles and, in 2015, the difference between the results obtained using various detectors. The total uncertainty in the integrated luminosity, including the stability of the calibrated subdetector response over time, amounts to 3.0% for 2015, 1.7% for 2018, and 1.6% for the combined data sample