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Dissipative Kondo physics in the Anderson Impurity Model with two-body losses
No full textWe study a dissipative version of the Anderson Impurity model, where an interacting impurity is coupled to a fermionic reservoir and exposed to Markovian dissipation in the form of two-body losses. Using a self-consistent hybridization expansion based on the Non-Crossing Approximation (NCA) we compute the dynamics of the impurity, its steady-state and spectral function. We show that the interplay between strong Coulomb repulsion and correlated dissipation gives rise to robust signatures of Kondo physics both at weak and strong losses. These include a strongly suppressed spin relaxation rate, displaying a characteristic Kondo-Zeno crossover and a spectral function where doublon band is quickly destroyed by dissipation while the coherent Kondo peak remains visible for weak losses, then disappears at intermediate values and finally re-emerge as the system enters in the Kondo-Zeno regime. As compared to the case of single particle losses we show that two-body dissipation protects Kondo physics. The picture obtained with NCA is confirmed by numerical simulations of exact dynamics on finite-size chains. We interpret these results using a dissipative Schrieffer-Wolff transformation, which leads to an effective Kondo model with residual impurity-bath losses which are suppressed by strong correlations or strong losses.</div
Residence-colonization trade-off and niche differentiation enable coexistence of Escherichia coli phylogroups in healthy humans
No full textInternational audienceDespite abundant literature on pathogenicity and virulence of the opportunistic pathogen Escherichia coli, much less is known about its ecological and evolutionary dynamics as a commensal. Based on two detailed longitudinal datasets on the gut microbiota of healthy adults followed for months to years in France and the USA, we identified a robust trade-off between the ability to establish in a new host (colonization) and to remain in the host (residence). Major E. coli lineages (phylogroups or subgroups) exhibited similar fitness but diverse strategies, from strong colonisers residing few days in the gut to poor colonisers residing for years. Strains with the largest number of extra-intestinal virulence associated genes and highest pathogenicity also resided for longest in hosts. Furthermore, the residence of a strain was more strongly reduced when it competed with other strains from the same phylogroup than from another phylogroup, suggesting niche differentiation between phylogroups. Based on a discrete-state Markov model developed to describe E. coli dynamics in a host population, we found that the trade-off and niche differentiation acted together as equalizing and stabilizing mechanisms allowing phylogroups to coexist over long periods of time. Our model also predicted that external disturbances may disproportionately affect resident strains, such as the extraintestinal pathogenic ones of subgroup B2.3. Our results call for further studies outside high-income countries, where the prevalence of this phylogroup is much lower. More generally, the trade-off between colonization and persistence could play a role in the diversification of other bacterial species of the microbiome
Persistent, Private, and Mobile Genes: A Model for Gene Dynamics in Evolving Pangenomes
No full textInternational audienceThe pangenome of a species is the set of all genes carried by at least one member of the species. In bacteria, pangenomes can be much larger than the set of genes carried by a single organism. Many questions remain unanswered regarding the evolutionary forces shaping the patterns of the presence/absence of genes in pangenomes of a given species. We introduce a new model for bacterial pangenome evolution along a species phylogeny that explicitly describes the timing of appearance of each gene in the species and accounts for three generic types of gene evolutionary dynamics: persistent genes that are present in the ancestral genome, private genes that are specific to a given clade, and mobile genes that are imported once into the gene pool and then undergo frequent horizontal gene transfers. We call this model the Persistent-Private-Mobile (PPM) model. We develop an algorithm fitting the PPM model and apply it to a dataset of 902 Salmonella enterica genomes. We show that the best fitting model is able to reproduce the global pattern of some multivariate statistics like the gene frequency spectrum and the parsimony vs. frequency plot. Moreover, the gene classification induced by the PPM model allows us to study the position of accessory genes on the chromosome depending on their category, as well as the gene functions that are most present in each category. This work paves the way for a mechanistic understanding of pangenome evolution, and the PPM model developed here could be used for dynamics-aware gene classification
Soigné par le médecin, guéri par le dieu : quand la médecine hippocratique dialogue avec Asclépios
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A Collective Experimental Approach to Sustainable Practices at the Research and Teaching Centre for Environmental Geosciences (CEREGE, Aix-en-Provence, France)
No full textInternational audienceCEREGE is a renowned French Research and Teaching Centre for Environmental Geosciences, employing approximately 220 staff members. In 2019, the carbon footprint of CEREGE’s research-related activities was estimated at around 7 tons of CO2 equivalent per person. This footprint primarily stems from three sources: 1) purchases that are e.g. necessary for various analytical methods, 2) commuting between home and CEREGE’s remote location, and 3) international travel for sampling campaigns and conferences.Since 2019, a group of about a dozen volunteers has been actively implementing awareness-raising initiatives aimed at reducing the environmental impact of CEREGE's research activities. These initiatives include promoting sustainable transportation options, waste sorting, responsible energy consumption, and the effective use of digital technology.In 2023, these small-scale incentive actions evolved into a more collective approach. One notable initiative was the organization of a serious game session, titled “Ma Terre en 180” (Gratiot et al., 2023; https://doi.org/10.1371/journal.pstr.0000049), which aimed to halve the carbon footprint of a fictitious research team. Approximately 100 CEREGE staff members participated in this serious game.The question then arises: how can we effectively achieve this Environmental Transition while maintaining or even enhancing the quality of professional activities and work-life conditions? To address this, the management team of CEREGE, which has been in operation since January 2024, has integrated eco-responsibility as a key policy guideline and established a new eco-responsibility committee within CEREGE’s organizational structure.To formally validate staff approval of the environmental transition project and initiate a collective approach toward more sustainable research practices, a manifesto for CEREGE’s eco-responsibility was adopted through a vote at the beginning of 2024. Since then, the committee has been conducting a participatory process, applying facilitation principles and collective intelligence tools to ensure that all voices are heard and that decisions are widely accepted by the staff.Moreover, small groups are conducting various experiments to test the effectiveness and feasibility of proposed changes in practices. Examples of these experiments include: 1) adjusting laboratory procedures to reduce consumables and waste, and 2) implementing a carbon quota system for travel and purchases within one of the research teams. At the end of 2024, an eco-responsibility charter was approved by CEREGE staff, achieving high participation (79%) and acceptance rates (77%-97%) for each of the ten commitment articles.In this contribution, we will present this collective experimental approach, explore advantages and challenges, and discuss the initial results regarding its effectiveness in reducing the environmental impacts of CEREGE’s activities.
Exploring Livestock Management and Seasonal Rhythms in Early Neolithic Adriatic Communities
No full textInternational audienceThe Adriatic region played a pivotal role in the Neolithization process of the central andwestern Mediterranean, notably marked by the spread of Impressa pottery complex. This"maritime stream" underscores a significant cultural cohesion between the Adriaticcoasts, facilitated by sustained exchanges and shared elements of material culture.Economically, both regions share an emphasis on sheep herding and barley cultivation,although they differ in their use of wild resources, reflecting both local adaptations andcultural preferences. However, knowledge about livestock practices remains limited,particularly regarding animal management and exploitation.This study aims to characterize livestock practices in the Adriatic during the earlyNeolithic, focusing on sheep, the predominant species. By examining mortality profilesfrom sites on both Adriatic coasts, the study seeks to uncover herd demographicmanagement and production orientations. Furthermore, the analysis includes pastoralcalendars from sites such as Tinj and Crno Vrilo (Dalmatia) and Trasano and Rendina(southern Italy), with particular attention to the timing of lambing cycles. This mayprovide insights into potential early practices of autumn lambing deseasoning, a methodstill observed in contemporary Mediterranean contexts.The findings will shed light on the adaptive strategies of these early agropastoralcommunities and their socio-economic organization. This study highlights the Adriatic'scentral role as a cultural and economic nexus in the Mediterranean during the Neolithic,contributing to a broader understanding of the region's impact on the spread anddevelopment of early farming practices
Incorporation of isolated Ag atoms and Au nanoparticles in copper nitride for selective CO electroreduction to multicarbon alcohols
No full textInternational audienceCO electroreduction has recently been explored as an alternative to CO2 electroreduction for multicarbon product formation, because it bypasses the large carbon loss associated with CO2 electroreduction. Although ethylene is generally obtained as the major product, shifting electrolysis towards the production of alcohols is an industrially promising path forward. Here we report a trimetallic-copper-based catalyst, consisting of copper nitride doped with gold nanoparticles and isolated silver atoms, with high selectivity for the formation of C2+ alcohols (Faradic efficiency for ethanol + n-propanol is >70%), within gas-fed flow cells at high current densities. Although active sites are metallic Cu(111) copper atoms derived from copper nitride, gold and silver doping suppresses ethylene formation due to the increased carbophibicity of the catalyst surface, as shown computationally. Overall, these findings open new perspectives regarding the design of catalysts for the production of liquid products from CO
Tunable Josephson voltage source for quantum circuits
No full textInternational audienceNoisy voltage sources can be a limiting factor for both fundamental physics experiments and device applications in quantum information, mesoscopic circuits, magnetometry, and other fields. The best commercial dc voltage sources can be programmed to approximately six digits and have intrinsic noise in the microvolt range. On the other hand, the noise levels in metrological Josephson-junction-based voltage standards is subfemtovolt. Although such voltage standards can be considered “noiseless,” they are generally not designed for continuous tuning of the output voltage nor for supplying current to a load at cryogenic temperatures. We propose a Josephson-effect-based voltage , as opposed to a voltage standard, operating in the 30 − 160 − μ V range, which can supply over 100 nA of current to loads at mK temperatures. We describe the operating principle, the sample design, and the calibration procedure to obtain continuous tunability. We show the current-voltage characteristics of the device, demonstrate how the voltage can be adjusted without dc control connections to room-temperature electronics, and showcase an experiment coupling the source to a mesoscopic load: a small Josephson junction. Finally, we characterize the performance of our source by measuring the voltage noise at the load, 50 pV rms, which is attributed to parasitic resistances in the cabling. This work establishes the use of the Josephson effect for voltage biasing of extremely sensitive quantum devices
Bifunctional Chiral ImPy‐Carbene Ligands. H‐Bonding Controlled Reactivity and Enantioselectivity in Au(I)‐Catalysis
No full textInternational audienceBifunctional chiral N‐heterocyclic carbene ligands have been devised for enantioselective gold(I) catalysis. Based on a single C ‐stereogenic center derived from chiral pool α‐aminoacids and connecting an imidazopyridine core to an arylurea motif, enantioselective gold(I)‐catalyzed cycloisomerization reactions could be achieved. High enantioselectivities were notably observed for substrates presenting a pendant propargyl alcohol on 2‐naphthol and 1,6‐enyne scaffolds. In the latter case, the catalyst shows a high degree of selectivity for the unprecedented 6‐ endo‐dig biscyclization of these substrates to give cyclopropyl‐fused 6‐ring heterocycles with a free OH functionality instead of the previously reported furan‐fused products. This unusual selectivity was investigated by DFT studies, which suggested the dual role of the carbonyl group of the urea moiety: first as an H‐bond acceptor in the catalytic cycle to direct the enantioselectivity and second as a cooperative group in the hydrogen shift leading to deauration