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On the projective dimension of some deformations of Weyl arrangements
No full textWe show that the logarithmic derivation module of (the cone of) the deformation A of a Weyl arrangement associated with a root system of simply laced type has projective dimension one if the deforming parameter ranges from -j to j+2. In addition, we give an explicit minimal free resolution when the root system is of type A3 and B2. Moreover, in the second case, we determine the jumping lines of maximal jumping order of the associated vector bundle. When the deforming parameter of A (respectively A') ranges from -k to k+j (respectively, from -k' to k'+j), with k different from k' and j at least 3, this allows to distinguish D0(A) from D0(A') shifted by 4(k'-k), even though these modules have the same graded Betti numbers
The Zermelo Navigation Problem on the 2-Sphere of Revolution: An Optimal Control Perspective with Applications to Micromagnetism
No full textInternational audienceThis article presents geometric optimal control techniques for analyzing geodesics in time-optimal Zermelo navigation problems on 2-spheres of revolution. We classify the problem by analyzing the pair , which represents the current (or wind) and the Riemannian metric. Using the maximum principle, the dynamics of geodesics are described by a Hamiltonian vector field on the cotangent bundle . Our primary motivation is the application to micromagnetism, specifically spin magnetization reversal in ferromagnetic ellipsoidal samples. This model depends on four parameters and the amplitude of the applied magnetic field. The problem is formulated as a Zermelo navigation on the 2-sphere, where geodesics are classified as elliptic, hyperbolic, or abnormal. We demonstrate that the transition set , which separates weak and strong current domains, is critical for understanding optimality. A key result shows that abnormal geodesics intersect this set with semi-cubical cusp singularities, a phenomenon we term the Landau–Lifshitz billiard. The analysis of the transition set's connected components is complex and complemented by algebraic geometry and symbolic computations. We further reveal that hyperbolic geodesics lose optimality at their second intersection with the abnormal arc. Our numerical simulations complement this analysis by computing conjugate and cut loci, wavefronts, and accessibility sets, providing new insights into optimal magnetization switching under bounded control
Influence of the starting powder and ball milling on microstructure and mechanical properties of Al0.3CoCrFeNi high entropy alloy, obtained by spark plasma sintering
No full textInternational audienceThis work investigates the effect of ball milling on the microstructure and mechanical properties of Al0.3CoCrFeNi high entropy alloy (HEA), starting from two different powders: pre-alloyed powders obtained by gas atomization and a pure elemental mixture. The powders were densified using spark plasma sintering (SPS). For the atomized powders, ball milling leads to the formation of a heterogeneous core–shell structure that remains after sintering, with grain sizes ranging from 1 to 10 μm in the cores and less than 1 μm in the shells. Slight air contamination during the milling stage promoted the formation of nanometric AlN at grain boundaries within the shells, which inhibited grain coarsening during SPS. Additionally, Al₂O₃ precipitates formed at prior particle boundaries (PPBs). Grain size after sintering is refined from 13 μm to 3.3 μm (without and with 28 h milling of atomized powder), resulting in an increase in hardness (from 182 to 280 HV₂), yield strength (from 370 to 615 MPa), and ultimate tensile strength (from 653 to 770 MPa), accompanied by a loss in ductility (from 54 % to 18 %). However, below 28 h of milling, the strengthening is not as high as would be expected from the Hall-Petch effect. PPBs have been identified as crack initiation sites, leading to lower-than-expected tensile properties. This negative effect of PPBs can be decreased by increasing powder particle size through prolonged milling, thereby reducing PPBs density. In contrast, mechanical activation of elemental powder mixture leads to the formation of an ultrafine-grained microstructure with dispersed nanometric B2 and Al₂O₃ phases. This elaboration route allows a higher mechanical strength (1175 MPa) and hardness (512 HV2), but significantly lower ductility (2 %). The random distribution of minor secondary phases does not lead to PPB-related failure. This study demonstrated the strong influence of starting powders on the milling-induced microstructure, phase formation, and the resulting strengthening mechanisms governing the mechanical behavior of Al0.3CoCrFeNi HEAs
Nutritional regulation of metabolism-dependent and-independent glucosensing in the mammalian taste system
No full textBrief communication ; preproof ref. MOLMET 102280International audienceSummary Dietary glucose is a preferred source of energy, but it remains unknown how the mammalian brain rapidly detects and discriminates this sugar from other sweeteners, and whether this depends on nutritional environment and metabolic need. Our results show that signals generated by metabolism-dependent and -independent actions of oral glucose can each be recruited to guide nutrient choice. Further, glucose (or its non-metabolizable analog) evokes a discernible pattern of neural activity from calorie-matched fructose in the central gustatory system, and this is conditioned by diet. Although the brain responses and corresponding consummatory behaviors do not require sweet taste receptor input, the results indicate that the sweet receptor is important for integrating nutritional states with metabolic pathways in the taste system and ultimately guiding intake towards glucose-yielding substrates
Phenoxy-Amidine (FA) Titanium and Zirconium Complexes: Synthesis, Structure, and Use in Olefin Polymerization
No full textInternational audienceHerein, we report the synthesis of a series of new bis(phenoxy-amidine) dichloro and bis(dimethylamido) Ti and Zr complexes [(FA)2MX2]. In the solid state, all the structures showed a distorted octahedral geometry around the metal center with the same O-trans, N-cis, X-cis configuration. Remarkably, NMR spectroscopic study of (FA)2MX2 complexes in solution shows that all complexes exist only as a C2-symmetric isomer. The direct alkylation of (L4)2TiCl2 and (L4)2ZrCl2 by two equivalents of PhCH2MgCl and/or Me3SiCH2MgCl yielded the corresponding dialkyl complexes without alkylation of the amidine moieties. The (FA)2Ti and Zr complexes are active in ethylene polymerization upon activation by MAO at 25-50 °C in toluene, at 5 bar ethylene pressure, providing linear (ultra) high-molecular-weight PE (Mw up to 2,154,000 g·mol-1 for the soluble fraction), yet with very broad distributions (Mw/Mn = 14-408), testifying an abundant multisite behavior. Complexes with tBu substituents on the ligand aryloxy ring showed better polymerization productivity (up to 230 kgPE·molcat-1·h-1). The (L4)2MX2 complexes, upon activation with MAO, are also slightly active toward styrene (2 to 39 kgPS·molcat-1·h-1 at 25-100 °C) giving polystyrenes with an atactic microstructure and molecular weight characteristics (Đ = 1.77-1.86) indicative of a single-site behavior
Exploring Non-Euclidean Geometry Through Virtual and Real Experiences to Unlock Non-Experts' Intuition
No full textInternational audienceThree-dimensional non-Euclidean geometries are highly abstractmathematical constructs, typically introduced only at advanced levelsof mathematical education due to their conceptual and technicalcomplexity. This paper presents a study exploring whether intuitiveunderstanding of one such geometry – S2 × E, the product of a 2-sphere and a line – can be facilitated through an interactive virtualreality (VR) experience without relying on formal mathematical instruction.We designed an immersive VR environment that allowsusers to explore S2 × E as inhabitants of this space. Participants,who were neither mathematics experts nor students specializing inmathematics, engaged with the system after a short introduction usinga learn-by-doing approach. Results show that participants wereable to infer and articulate key properties of S2 × E without knowledgeprior to the experiment, and that their performance was independentof their educational background or attitude towards mathematics.Our findings demonstrate the potential of VR as a mediumfor conveying abstract geometric concepts through embodied learning,making them accessible to non-expert audiences
Pesticide, des jardins contaminés : le Prosulfocarbe. Interview France TV
No full textInterview France T
Assessing the non-target effects of herbicides on field margin plant communities after controlling for soil, climate, local context and landscape metrics
No full textInternational audienceHighlights: • We used a national dataset of 500 sites monitored yearly from 2013 to 2018. • We analysed the effects of herbicides on plant margin communities. • Herbicides had a negative effect on richness and nature-value species. • Situations of risk for pesticides drift had a negative effect on margin flora.Abstract: Pesticides are often identified as one of the major causes of biodiversity decline in farmlands. However, our knowledge about this relationship has mostly being inferred from small to landscape-scale studies, or from indirect indicators of agricultural practices at large scales. Here, we used a national network of more than 500 sites monitored yearly from 2013 to 2018 in France to assess the non-target effects of herbicides on field margin plant communities. We used hierarchical generalized linear models to investigate the effects of practices on plant species richness, plant species evenness, proportion of nature-value plants, and proportion of grasses in field margins, while controlling for a large number of possible confounding effects. The intensity of herbicide use had a negative effect on plant species richness, and on the proportion of nature-value plants. In the margin of cereal fields, there was a negative effect of dicotyledon herbicides on richness and a negative effect of grass herbicides on species evenness. We also identified, in some specific crops, a negative effect of non-herbicide treatments on margin flora richness and on the proportion of nature-value plants. The presence of surrounding grasslands had a consistent favourable effect on richness and on the proportion of nature-value plants in field margins. Finally, situations of risk for pesticides drift had a negative effect on margin flora. This study confirms that reducing herbicide use represents a robust lever to maintain the floristic diversity of field margins, which could be combined with strategies reducing the risk of pesticide drift
Artificial selection of suppressive or conducive rhizosphere microbiota circumvents the growth-defense trade-off due to a foliar pathogen
No full textInternational audiencePlant-pathogen interactions are influenced by physiological responses and rhizospheric microorganisms, which can create disease-suppressive or disease-conducive soils affecting pathogen dynamics. This study used artificial selection to shape soil microbiota conditioned by Arabidopsis thaliana to either suppress or promote the foliar pathogen Pseudomonas syringae DC3000 (Pst). Over successive iterations, plants were inoculated with Pst, and soils were selected based on plant symptoms: enhanced resistance (suppressive), increased susceptibility (conducive), or no selection (control). A non-inoculated group (non-conditioned) was also included. Disease symptoms, Pst proliferation, and rhizosphere microbiota were monitored each iteration. Selection for suppressive soils reduced disease severity and Pst levels, while conducive soils showed the opposite. Each soil type was enriched in distinct bacterial communities. A growth-defense trade-off was evident in control soils but less so in selected soils. Gene expression analysis revealed that plant hormone homeostasis, especially salicylic acid (SA) and jasmonic acid (JA) played key roles with SA linked to local defense and JA to systemic responses. This work highlights artificial selection as a promising strategy to modulate soil microbiota, influencing plant-pathogen interactions and microbial dynamics