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Magmatic volatiles control the sub-plinian basaltic eruptions at Ambae volcano, Vanuatu
No full textco-auteur étrangerInternational audienceThe 2017-2018 eruption of Ambae volcano provided a rare opportunity to monitor gas emissions during a sub-Plinian basaltic eruption. Here we document the gas emissions during this eruption using satellite observation, alongside gas measurements and geochemical analyses. Our results indicate that the volcano released 3.3 teragrams of sulfur dioxide, 7.7 of carbon dioxide, 134 of water vapour, 0.2 of hydrogen sulfide, and 0,001 of dihydrogen, ranking Ambae among the world's top volcanic gas emitters. Despite these substantial emissions, the relatively modest volume of 0.47 cubic kilometer of magma that fueled the eruption indicates a volatile-rich magma source. This enrichment is likely linked to the geodynamic setting, where subduction of the faulted, carbonate-rich D'Entrecasteaux Ridge, coupled with an influx of fertile mantle, fostered the formation of volatile-rich magma. High concentrations of volatiles, can drive substantial gas exsolution, increasing magma buoyancy, resulting in greater magma supply and faster ascent rates. Rapid ascent prevents volatile separation from the melt, resulting in powerful gas surges that drive the transition from effusive to basaltic sub-Plinian eruption phases
Experimental study on flow and burning behaviors of pool fires under ventilation conditions inside an engine compartment
No full textInternational audienceDespite the considerable body of work on pool fires taking place in confined and mechanically ventilated environments, there are still important uncertainties in our comprehension of such phenomena and in our ability to forecast their behavior. In this context, experiments are carried out to investigate the impact of airflow velocity on the flow and thermal characteristics of a heptane pool fire in a full-scale engine compartment of an industrial vehicle. The particle image velocimetry (PIV) technique is employed across several areas of interest to investigate the effect of airflow velocities (0, 1.6, 3.2, and 6.4 m/s) on the flow properties in the flame’s neighborhood. An analysis of these zones can provide a representation of the global average velocity fields, which are not often documented in the existing literature for this type of enclosure. The burning characteristics, such as flame shape, mass loss, heat release rate, total heat flux, temperature profiles, and gaseous species concentrations, are investigated and compared among different ventilation conditions. The PIV results exhibit detailed flow structures around the flame in terms of direction and intensity. Vertical and horizontal velocity components are sensitive to changes in ventilation rate and the exhaust hood’s position. Experimental findings reveal the formation of a large corner vortex at low velocity magnitudes. Thomas’ predictions show reasonable agreement with flame height measurements compared to Heskestad’s correlation. A high ventilation rate can lead to a significant increase in both heat release rate and total heat flux. Increasing ventilation rates results in a more significant temperature decrease in the intermittent zone compared to the continuous flame zone. A high ventilation speed of 6.4 m/s does not decrease O concentration as expected, possibly due to the fan’s blowing effect and the dilution of fresh air with combustion product gases. This study enhances the physical understanding of fire behavior in ventilated engine compartments, leading to improved fire safety measures and the design of effective extinguishing systems
Chemical and mechanical performances of CVD‑silicon oxycarbonitride films for corrosion protection applications: Towards inert coatings in aggressive aqueous media
No full textInternational audienceThis study investigates the alteration behaviour of three CVD amorphous silica thin films deposited at three different deposition temperatures, exhibiting thus different network qualities. The hydrolysis of the networks was elucidated through ERDA hydrogen depth profiles acquired throughout the alteration process. It is worth noting that this hydrolysis is insignificant since a maximum of hydrogen atomic concentration of 10% was recorded during all the study. It was also evinced that the concentration and distribution of hydrogen throughout the depth are influenced by two competing phenomena: hydrolysis and ionic exchange of protons with K + ions coming from the solution. This competition is particularly noticeable in the film deposited at the lowest investigated temperature, where the presence of sufficiently large voids facilitates this exchange. Thickness loss rates were successfully calculated showing remarkably low initial rates ranging from 2.5 to 4.8 nm/day, directly correlated with the initial network quality. A residual rate as low as 0.5 nm/day was recorded, indicating limited hydration and hydrolysis mechanisms leading to the release of H4SiO4, given the higher dissociation energy required for such polymerized networks. These findings represent the first available dataset on dissolution rates of CVD-deposited silica films. It was demonstrated that network dissolution occurs evenly across the entire surface since the measured RMS values post-alteration remain quite low with a maximum of 2 nm. Finally, our study was supported by nanoindentation tests to assess hardness and elasticity, revealing a decrease of 38% and 13%, respectively, which was attributed to the high sensitivity of these two properties to physicochemical changes, particularly on the surface, during alteration. This comprehensive investigation has facilitated the accurate correlation of CVD deposition conditions and, consequently, the network quality of silica films to the chemical and mechanical response to aqueous alteration
The NenuFAR Pulsar Blind Survey (NPBS): I. Survey overview, expectations, and first redetections
No full textInternational audienceThe NenuFAR Pulsar Blind Survey (NPBS) is an all-sky survey, searching for pulsars at radio frequencies below 85 MHz with the NenuFAR radio telescope. Taking into account the turnover at low frequencies in the pulsar spectra and the widening of their emission cone towards low frequencies, we expect approximately 8–20 not already discovered pulsars to be detectable by this survey, most of which are likely to be non-standard pulsars or pulsars in unusual parts of the P − Ṗ diagram (such as, e.g. slow pulsars). According to our simulations, we expect the discovered pulsars to feature spectra with spectral indices ≲ −3.2 and low turnover frequencies <<85 MHz. Conversely, a non-detection would give valuable clues as to the population of pulsars in this region of the parameter space. The current first stage of the survey observes declinations above 39° in the frequency range 39–76 MHz. A frequency-averaged sky coverage of 98% is reached by observing 7692 pointings of about 1.5° of radius in 27 min each. The observing programme started in August 2020, and is expected to be completed during 2024. Approximately a third of the data are currently being processed using a search pipeline based on PRESTO with some adaptations to low frequencies. Because of the high scatter broadening and the coarse time resolution, the NPBS searches for pulsars with periods from 30 ms to 30 s and dispersion measures (DMs) between 1 and 70 pc cm−3. In the processed data, 24 known pulsars have been searched in order to verify the observing setup and the search pipeline. Seven of these pulsars have been detected, with DMs between 5 and 42 pc cm−3. The related candidates have periods between 40 ms to 3.5 s, including candidates corresponding to harmonics. Of the seven, six correspond to the most intense pulsars of the set. The last detection is presumably due to a beneficial effect of the scintillation. Based on the faintest detection, the expected minimum signal-to-noise ratio for detecting a pulsar is 4.8, corresponding to a minimum flux of 6.9 mJy in the coldest regions of the sky
José Chabás et Marie-Madeleine Saby, The Tables of 1322 by John of Lignères. An Edition with Commentary, Turnhout, Brepols publishers n.v., 2022 ; 1 vol., 159 p. (Alfonsine Astronomy, 2). ISBN : 978-2-503-59609-9. Prix : € 65,00.
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Black holes with electroweak hair -- the detailed derivation
No full textInternational audienceWe present a very detailed derivation of solutions describing hairy black holes within the gravity-coupled Weinberg-Salam theory, which were previously reported in \href{https://doi.org/10.1103/PhysRevLett.133.171402}{Phys.Rev.Lett. 133 (2024) 171402}. These black holes support a strong magnetic field that polarizes the electroweak vacuum and creates a condensate of massive fields carrying superconducting currents along the black hole horizon. The currents, in turn, generate a ``corona'' of magnetic vortex segments attached to the horizon at both ends. The condensate and corona together constitute the black hole hair. The extremal solutions approach, in the far field, the magnetic Reissner-Nordström configuration, with a total mass that is {\it lower} than the total charge, , due to the negative Zeeman energy of the condensate. This makes the removal of the hair energetically unfavorable. The maximally hairy black holes exhibit masses comparable to terrestrial values, with approximately 11% of their total mass stored in the hair. Given that these solutions arise within a well-tested theoretical framework, they are likely to have physical relevance
L’impact des niveaux de revendication territoriale régionale sur l’intention d’achat de produits alimentaires : Le rôle médiateur de la valeur perçue
No full textInternational audienceThis research focuses on consumer perceptions of the territorial claims made by a region brand on food product packaging. The aim is to study the impact of territorial claims–weak (simple mention of the place) and strong (label set up by the region to meet demanding specifications)–on purchase intention via perceived value. An experiment involving 186 respondents and manipulating the level of territorial claim (absence vs. weak vs. strong) shows that emotional perceived value mediates the impact of the presence of a territorial claim on purchase intention. However, this positive impact is no greater when the claim is strong. Thus, a weak territorial claim improves levels of perceived value (emotional dimension) and purchase intention just as much as a claim that justifies an accreditation process. However, a strong claim generates higher levels of price and social value than a weak claim.Cette recherche s’intéresse aux perceptions des consommateurs vis-à-vis des revendications territoriales proposées par une marque région sur les packagings de produits alimentaires. Il s’agit d’étudier l’impact des revendications territoriales – faible (simple mention du territoire) et forte (label mis en place par la région répondant à un cahier des charges exigeant) – sur l’intention d’achat via la valeur perçue. Une expérimentation auprès de 186 répondants et manipulant le niveau de revendication territoriale (absence vs. faible vs. forte) montre que la valeur perçue émotionnelle médiatise l’impact de la présence d’une revendication territoriale sur l’intention d’achat. En revanche, cet impact positif n’est pas plus important lorsque la revendication territoriale est forte. Ainsi, une revendication territoriale faible améliore tout autant les niveaux de valeur perçue (dimension émotionnelle) et d’intention d’achat qu’une revendication justifiant d’une démarche d’accréditation. Une revendication forte amène cependant des niveaux de valeur prix et sociale plus importants qu’une revendication faible
Rewriting the Narrative: Local Actor Strategies and Territorial Imaginaries in a Peripheralized Region
No full textInternational audienceThis paper explores the interplay between territorial narratives and development prospects in peripheralized regions, using the case of Mecklenburg-Vorpommern (northeastern Germany). This rural region faces significant demographic, socio-economic, and political challenges, compounded by deeply ingrained negative imaginaries portraying it as empty, declining, and marked by racism. These stigmas not only hinder the region’s development but also perpetuate its marginalization within broader territorial hierarchies. To counter this situation, a network of institutional and non-institutional stakeholders tries to challenge these stigmas and promote a more positive image for the region. The creation of alternative territorial narratives aimed at promoting an attractive image of the territory, nature-oriented and grounded in the past, is at the core of local development strategies.To analyze this process, we draw on the concept of peripheralization, developed within German constructivist frameworks. This concept provides a lens to examine territorial evolution through power dynamics and dependency relationships, highlighting stigmatization as a central mechanism of marginalization. Our research adopts a qualitative methodological framework, combining semi-structured interviews with stakeholders at Land and local levels, participant observation in rural development meetings, and critical analysis of local media and online content. This approach enables us to understand the multi-scalar dynamics of narrative construction and dissemination, as well as the tensions between local aspirations and overarching, often negative imaginaries. First, we show that local stakeholders often emphasize the need for a new narrative in the region. Then, we analyze how locally driven narratives highlight local assets and frequently refer to a distinct local "identity." Finally, we explain how these narratives are often undermined by persistent stigma at different scales
Prequantisation from the path integral viewpoint
No full textSlightly reworded, rearranged and extended version of one originally published in the Proceedings of theInt. Conf. on Diff. Geom. Meths. in Math. Phys., Clausthal’1980, Doebner (ed). Springer Lecture Notesin Math. 905, p.197-206 (1982). Marseille preprint CPT-80-P-1230The quantum mechanically admissible definitions of the factor exp (i/ℏ)S(γ) in the Feynman integral are put in bijection with the prequantisations of Kostant and Souriau. The different allowed expressions of this factor -the inequivalent prequantisations -are classified. The theory is illustrated by the Aharonov-Bohm experiment and by identical particles.</div
Isospin precession in non-Abelian Aharonov-Bohm scattering
No full textThis paper is dedicated to the memory of “Tai” (Tai-Tsun Wu : 1933-2024)International audienceThe concept of pseudoclassical isospin is illustrated by the non-Abelian Aharonov-Bohm effect proposed by Wu and Yang in 1975. The spatial motion is free however the isospin precesses when the enclosed magnetic flux and the incoming particle's isosopin are not parallel. The non-Abelian phase factor of Wu and Yang acts on the isospin as an S-matrix. The scattering becomes side-independent when the enclosed flux is quantized, with an integer. The gauge group is an internal symmetry and generates conserved charges only when the flux is quantized, which then splits into two series: for acts trivially but for the implementation is twisted. The orbital and the internal angular momenta are separately conserved. The double rotational symmetry is broken to when odd. For unquantized flux there are no internal symmetries, the charge is not conserved and protons can be turned into neutrons