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Exploring the formation of multiple dust-trapping rings in the inner Solar System
No full textInternational audienceContext. Isotopic properties of meteorites provide evidence that multiple dust trap or pressure bumps had to form and persist in the inner Solar System on a timescale of millions of years. The formation of a pressure bump at the outer edge of the gap opened by Jupiter would be effective in blocking particles drifting from the outer to the inner disc. Yet this would not be enough to preserve dust in the inner disc. However, in low-viscosity discs and under specific conditions governing the gas cooling time, it has been shown that massive planets can also open secondary gaps, separated by density bumps, inwards of the main gap. The majority of studies of the process of secondary gap formation have been done in two dimensional equatorial simulations with prescribed disc cooling or by approximating the cooling from the disc photosphere. Recent results have shown that an appropriate computation of the disc cooling by including the treatment of radiation transport is key to determining the formation of secondary gaps.Aims. Our aim is to extend previous studies to three dimensional discs by also including radiative effects. Moreover, we also consider non-ideal magnetohydrodynamic effects in discs with a prescribed cooling time to explore the feedback of the magnetic field on secondary gap formation.Methods. We performed three dimensional hydrodynamical numerical simulations with a self-consistent treatment of radiative effects making use of a flux-limited diffusion approximation. We then extended our study to a similar disc including the magnetic field and non-ideal Ohmic and ambipolar effects.Results. We show that in the hydrodynamical model, a disc with low bulk viscosity (αν = 10−4) and consistent treatment of radiative effects, a Jupiter-mass planet is capable of opening multiple gaps. We also show that multiple gaps and rings are formed by planetary masses close to the pebble isolation mass. In the presence of non-ideal MHD effects, multiple gaps and rings are also formed by a Jupiter-mass planet.Conclusions. A solid Jupiter core in low-viscosity discs blocks particles drifting towards and within the inner disc. The formation of multiple gaps and rings inside the planetary orbit at this stage is crucial to preserving dust reservoirs. Such reservoirs are pushed towards the inner part of the disc during Jupiter runaway growth and they are shown to be persistent after Jupiter’s growth. Multiple dust reservoirs could therefore be present in the inner Solar System since the formation of Jupiter’s solid core when the disc is characterised by low viscosity
A Radical Proposition on the Origins of the Received Mathematical Classic the <i>Gnomon of Zhou</i> (<i>Zhoubi</i> 周髀)
No full textInternational audienceIn 656, the Gnomon of Zhou (Zhoubi 周髀) was canonized as one of the Ten Mathematical Classics (Suanjing shishu 算經十書) that would serve as the basis of contemporary curricula, testing and, later, the study of the history of mathematics in ancient China. Itself purporting to have been transmitted from the beginning of human civilization to the Duke of Zhou 周公 (r. 1042–1036 BCE), most modern scholars follow Qian Baocong (1968) in positing that the text was redacted from earlier materials circa 100 bce. In this paper, I will present linguistic evidence that supports Christopher Cullen (1996) and early Qian Baocong’s (1924, 1932) position that the received Gnomon of Zhou came together much later, in the first or second century CE, at around the same time or later than the Nine Chapters on Mathematical Procedures (Jiuzhang suanshu 九章算術). In addition, I will present evidence connecting its early reception and transmission history to the Far North/Northwest that might explain features of this strange text and its strange position in discussions of cosmology in the Middle Period Chinese capitals further south
Ethnolinguistique – Anthropologie linguistique : histoires et études de cas
No full textInternational audienceÉtude du langage en lien avec ses contextes d’usage, culturels et sociaux, le domaine de l’anthropologie linguistique est particulièrement vaste, tant par la diversité de ses objets que par son approche résolument interdisciplinaire. Le présent ouvrage entreprend de croiser des réflexions d'ordre historique, épistémologique et méthodologique afin de prendre du recul face à la richesse et à la complexité du domaine.Un éclairage historique est apporté par l'exploration des différentes voies suivies par la discipline en France depuis le début du 20e siècle, et par l’analyse du processus même de constitution des savoirs dans la longue durée. À partir de différentes études, l'ouvrage questionne également l’intégration par l’anthropologie linguistique d’approches issues de la pragmatique, et son articulation à des sous-domaines disciplinaires spécifiques, tels l’anthropologie médicale ou les études médiatiques. Enfin, des contributions se consacrent à la performance et à l’analyse ethnopoétique, ouvrant des perspectives complémentaires sur les pratiques langagières
A Moebius inversion formula to discard tangled hyperbolic surfaces
No full textRecent literature on Weil-Petersson random hyperbolic surfaces has met a consistent obstacle: the necessity to condition the model, prohibiting certain rare geometric patterns (which we call tangles), such as short closed geodesics or embedded surfaces of short boundary length. The main result of this article is a Moebius inversion formula, allowing to integrate the indicator function of the set of tangle-free surfaces in a systematic, tractable way. It is inspired by a key step of Friedman's celebrated proof of Alon's conjecture. We further prove that our tangle-free hypothesis significantly reduces the number of local topological types of short geodesics, replacing the exponential proliferation observed on tangled surfaces by a polynomial growth
Deciphering the influence of the [4Fe–4S] cluster of tRNA thiolation enzymes on tRNA binding
No full textInternational audienceIron–sulfur clusters [Fe–S] play crucial roles in diverse biological reactions, often serving as prosthetic groups for enzymes. Specifically, certain tRNA-modifying enzymes utilize these clusters to catalyze the thiolation of specific nucleosides. While the participation of [4Fe–4S] clusters in such catalytic processes is known, their potential influence on tRNA binding remains unexplored. In this study, we examine the impact of the cluster on the affinity for tRNA of TtuI from the archeon Methanococcus maripaludis , an enzyme responsible for the formation of 4-thiouridine at position 8 in tRNAs of archaea and bacteria, as well as Escherichia coli TtcA that catalyzes the biosynthesis of 2-thiocytidine at position 32 in bacterial tRNAs. For this purpose, we compare the change of fluorescence properties of judiciously located tryptophans upon tRNA binding between the apo-enzyme (lacking the cluster) and the holo-enzyme (incorporating a reconstituted cluster). Our results indicate that the presence of the [4Fe–4S] cluster does not alter the affinity of the thiolases for tRNA, thus ruling out any direct involvement of the cluster in tRNA binding and emphasizing the purely catalytic role of the [4Fe–4S] cluster in tRNA thiolation
Letter of Intent: AICE -- 100m Atom Interferometer Experiment at CERN
No full textInternational audienceWe propose an O(100)m Atom Interferometer (AI) experiment -- AICE -- to be installed against a wall of the PX46 access shaft to the LHC. This experiment would probe unexplored ranges of the possible couplings of bosonic ultralight dark matter (ULDM) to atomic constituents and undertake a pioneering search for gravitational waves (GWs) at frequencies intermediate between those to which existing and planned experiments are sensitive, among other fundamental physics studies. A conceptual feasibility study showed that this AI experiment could be isolated from the LHC by installing a shielding wall in the TX46 gallery, and surveyed issues related to the proximity of the LHC machine, finding no technical obstacles. A detailed technical implementation study has shown that the preparatory civil-engineering work, installation of bespoke radiation shielding, deployment of access-control systems and safety alarms, and installation of an elevator platform could be carried out during LS3, allowing installation and operation of the AICE detector to proceed during Run 4 without impacting HL-LHC operation. These studies have established that PX46 is a uniquely promising location for an AI experiment. We foresee that, if the CERN management encourages this Letter of Intent, a significant fraction of the Terrestrial Very Long Baseline Atom Interferometer (TVLBAI) Proto-Collaboration may wish to contribute to AICE
Molecular Modification of Cu-Based Electrodes via Electrografting: Effects of Modifier Structure on CO2 Electroreduction Selectivity
No full textInternational audienceCO2 electroreduction to multicarbon products using Cu-based catalysts is one of the strategies currently developed in order to valorize CO2 and store electricity. Molecular modification of material surfaces has been recently explored in order to tune the reactivity of Cu catalysts and improve their selectivity toward C2+ products, in particular ethylene and ethanol. Here, we compare four classes of precursors of aryl radicals, namely, aryl-iodoniums, -diazoniums, -sulfoniums, and -silicates, which are used for grafting an aromatic layer onto the surface of Cu nanoparticles via electroreduction or electrooxidation. In all cases, the surface modification promotes CO–CO coupling and C2+ product formation, leading to a much higher FEC2+/FECO (FE = Faradaic efficiency) ratio. However, we show that the composition of the layer is more complex and diverse than anticipated and likely explains the unexpectedly large variations in selectivity, even though the Cu catalysts were functionalized with presumably the same aromatic layer derived from the same aryl radical generated by the four different precursors. These classes of precursor salts are thus not interchangeable and provide a much larger scope of Cu surface modifications and Cu catalysts than anticipated to be studied independently
Ecosystem responses of a French Mediterranean mountain lake to climate change and soil dynamics since the last deglaciation as inferred from bioindicators and geochemical proxies
No full textInternational audienceMountain environments in the Mediterranean region are experiencing rapid warming and soil degradation, posing threats to aquatic ecosystem diversity and functioning. Documenting the impact of past climate change and soil evolution on high-altitude lake ecosystems is of high importance to scale modern changes into a long-term context and informing management strategies. Here we present the results of the “Hydro-ALPS” project, reconstructing Lake Petit ecosystem responses (Valdeblore, France, 2200 m a.s.l.) to hydrological changes and chemical soil weathering on the watershed since the lake formation (ca. 14 000 years ago). Our approach is based on measurements of major elemental composition of sediments from a 674 cm-long master core, 14C datings on terrestrial macroremains, diatom identification, and extraction of diatom frustules for geochemical analyses (i.e. measurements of oxygen and silicon isotopes). A total of 96 diatom species have been identified in 115 sediment samples. δ18Odiatom varies from 26.6 to 32 ‰ VSMOW (mean SD of 0.2 ‰) in 43 purified samples, the 17Oexcess varies from -140 to -200 per meg (mean SD of 14 per meg) and δ30Sidiatom ranges from -1.14 to 0.14 ‰ VNBS28 (mean SD of 0.06 ‰). These results indicate several ecosystem shifts since the Late glacial-Holocene transition, ca. 12,000 years ago : major changes occurred at the end of the Younger Dryas (both δ18Odiatom and 17Oexcess values indicative of high snowmelt contribution) followed by rapid ecological shifts at 10,100-9800, 9200-9000, 8100-8000, and 7000-6900 cal yr BP (with alternating dominance of diatoms from the Fragilariaceae e.g., Staurosira pseudoconstruens, Staurosira venter and Gomphonemaceae e.g., Gomphonema elegantissimum), in response to cooling events and intense bedrock weathering during the wet Early Holocene period (low δ30Sidiatom). Vegetation development and soil stabilization during the Middle Holocene led to a dominance of the diatom Staurosirella neopinnata, ending with a shift coinciding with the 4.2 ka climate event, described in a previous study.Our findings suggest that during the Early Holocene, the lake ecosystem had a good resilience to centennial-scale climate oscillations, consistently returning to previous conditions. However, the two phases of major ecological shift that occurred 7000 and 4200 years ago, likely driven by climate associated with long lasting changes in pedogenesis and vegetation dynamics, led to new ecosystem functioning baselines
Speech Repression and Threat Narratives in Politics: Social Goals and Cognitive Foundations
No full textInternational audiencePolitical movements are often bound together by mobilizing narratives about social threat. In devoted activists, this triggers moral motivations to protect the narrative from criticism and nuance. Speech repression phenomena include public shaming on social media, the "deplatforming" and "canceling" of controversial speakers, and the intimidation of dissidents. Speech repression phenomena are most puzzling when the narratives activists try to protect are simplistic and inaccurate, which is often the case in politics. Here, I argue that speech repression derives from at least three main sociocognitive motivations. First, hypersensitive dispositions to detect threat, from hostile outgroups in particular. Second, motivations to try to keep people committed to moral causes and mobilized against dangerous groups by controlling information flows and beliefs. Third, motivations to signal personal devotion to causes and ingroups to gain status. Members of most political groups engage in speech repression, even those ostensibly committed to freedom. Political activists and leaders only need to believe that speech restriction will bring about desired effects to engage in it. While speech repression can derive from sincere convictions, insincere self-censorship and sanctioning are widespread
Paleoriver discharge controlled by precession cycle in the North Africa over the past 240,000 years: relationship to sapropel formation
No full textInternational audienceThe sedimentary sequence of the eastern Mediterranean is often marked by organic-rich layers called sapropels. Sapropel formation was mainly caused by excess freshwater input and the subsequent reduction of ventilation due to an enhanced African monsoon combined with deglacial water input. However, the paleoriver discharge from the North Africa under interglacial and glacial boundary conditions and its impact on the sapropel formation has not been fully clarified yet. We obtained an Nd isotopic composition (εNd) record of the detrital fraction as well as a grain size indicator of a marine sediment core from the eastern side of the Gulf of Sirte to reconstruct the reactivation of Libyan fluvial fossil systems for the past 240,000 years. The εNd record showed a systematic increase from a baseline of -12 to -9 to -8 for sapropels S1 to S9, including the glacial sapropel S6. This εNd shift was synchronous with barium enrichment and depleted planktonic foraminiferal oxygen and carbon isotopic compositions that marked the sapropels. Based on a new εNd map of source regions in North Africa, the higher εNd values can be explained by preferential weathering of volcanic fields and soils and increased river discharge under both interglacial and glacial conditions. The grain size indicator showed an increase in fine river particles relative to coarse atmospheric dust when detrital εNd was higher, supporting this interpretation. These observations are consistent with the available detrital εNd records, suggesting that the higher isotopic signals during sapropel formation are a basin-wide feature in the Gulf of Sirte. The hydrological cycle in the study area was estimated to be more sensitive to precessional forcing than to high-latitude climate conditions, being consistent with previous modelling studies