HAL Université de Toulouse, et Toulouse INP
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Ferroelectricity in Single‐Crystalline BaTiO<sub>3</sub> Nanodisks on Silicon
No full textInternational audienceThe miniaturization of ferroelectrics with lateral size reduction is crucial for technological advancement but requires an understanding of the fundamental behavior of ferroelectrics at the nanoscale. While much attention has been focused on vertical scaling of perovskite ferroelectrics with thickness reduction, lateral scaling remains less explored. In this study, ferroelectricity is investigated in 20 nm thick single‐crystalline BaTiO3 nanodisks with a diameter ranging from ≈ 400 down to 100 nm. They are fabricated by Ne ion milling of a 20 nm BaTiO3 film epitaxially grown on SrTiO3‐buffered silicon. The nanodisks are ferroelectric with a Curie temperature in the range 230–270 °C as determined by temperature‐dependent piezoresponse force microscopy. In 100 nm‐diameter nanodisks, the vertical polarization component adopts three distinct patterns in the pristine state, aligning with theoretical predictions. The most prevalent pattern features a uniformly up‐oriented vertical component. The rotational invariance of these domain patterns in the plane suggests a combination of center‐type and flux‐closure domains. Additionally, the up polarization can be switched progressively to down polarization upon application of a pulsed bias of increasing time width. The control of the polarization in nanostructures and of their progressive switching is of particular interest for memory applications
Transport non dissipatif des etats topologiques issus de lignes nodales dans des semi-metaux de Weyl
No full textInternational audienceTopological materials, such as topological insulators or semimetals, usually not only reveal the non-trivial properties of their electronic wavefunctions through the appearance of stable boundary modes, but also through very specific electromagnetic responses. The anisotropic longitudinal magnetoresistance of Weyl semimetals, for instance, carries the signature of the chiral anomaly of Weyl fermions. However for topological nodal line semimetals—materials where the valence and conduction bands cross each other on one-dimensional curves in the three-dimensional Brillouin zone—such a characteristic has been lacking. Here we report the discovery of a peculiar charge transport effect generated by topological nodal lines in trigonal crystals: a dissipationless transverse signal in the presence of coplanar electric and magnetic fields, which we attribute to a Zeeman-induced conversion of topological nodal lines into Weyl nodes under infinitesimally small magnetic fields. We evidence this dissipationless topological response in trigonal PtBi2 persisting up to room temperature, consistent with the presence of extensive topological nodal lines in the band structure of this non-magnetic material. These findings provide a pathway to engineer Weyl nodes by arbitrary small magnetic fields and reveal that bulk topological nodal lines can exhibit non-dissipative transport properties
Constrained Reinforcement Learning for Unstable Point-Feet Bipedal Locomotion Applied to the Bolt Robot
No full textInternational audienceBipedal locomotion is a key challenge in robotics, particularly for robots like Bolt, which have a point-foot design. This study explores the control of such underactuated robots using constrained reinforcement learning, addressing their inherent instability, lack of arms, and limited foot actuation. We present a methodology that leverages Constraints-as-Terminations and domain randomization techniques to enable sim-to-real transfer. Through a series of qualitative and quantitative experiments, we evaluate our approach in terms of balance maintenance, velocity control, and responses to slip and push disturbances. Additionally, we analyze autonomy through metrics like the cost of transport and ground reaction force. Our method advances robust control strategies for point-foot bipedal robots, offering insights into broader locomotion
Spatio-temporal diversity and genetic architecture of pyrantel resistance in Cylicocyclus nassatus, the most abundant horse parasite
No full textInternational audienceCyathostomins are a complex of 50 intestinal parasite species infecting horses and wild equids. The massive administration of modern anthelmintic drugs has increased their relative abundance in horse helminth communities and selected drug-resistant isolates worldwide. Cylicocyclus nassatus is the most prevalent and the most abundant species. The tedious identification and isolation of these worms have hampered studies of their biology that remain largely uncharacterised. Here we have leveraged ultra-low input sequencing protocols to build a reference genome for the most prevalent horse strongyle species. Using this resource, we have established the first estimates of its genetic diversity and population structure on a gradient ranging from Ukraine (close to modern horse domestication area) to North America, while capturing a 19th-century snapshot of C. nassatus diversity in Egypt. Our results support a diverse and lowly structured global population. Modern populations displayed lower nucleotide diversity relative to the old North African isolate. We identified the first genetic candidates upon which pyrantel (an anthelmintic drug used in companion animals) selection likely applied in field populations, highlighting previously suspected genes coding for nicotinic acetylcholine receptor subunits, and identifying new candidates showing differential expression in independently evolved Caenorhabditis elegans lines. These results offer a first resource to widen current knowledge on cyathostomin biology, unravel novel aspects of pyrantel resistance mechanisms and provide candidate genes to track pyrantel resistance in the field
Speckle observations with PISCO in Calern (France):II. Astrometric measurements of visual double stars in 2017-2018 and new or revised orbits for A1913 AB, A1710, COU1394, BU1185, A122, A570, HU577, COU812, HU332, A2095 AB, and A884.
No full textInternational audienceWe present relative astrometric measurements of visual double stars, made in 2017-2018 with the specklecamera PISCO at the 1-m Epsilon telescope of the C2PU facility (Observatoire de la Côte d’Azur, Calernsite). Our observing list contains orbital couples as well as double stars whose motion is still uncertain. From our observations of 1400 multiple stars, we obtained 1376 new measurements with angular separations in the range 0′′ .1 — 8′′ .5, and an average accuracy of 0′′ .008. The mean error on the position angles is 0◦ .50. Most of the position angles were determined without the usual 180◦ ambiguity with the application of the direct vector auto-correlation technique and/or by inspection of the long integration files. We present new and revised orbits for A1913 AB, A1710, COU1394, BU1185, A122, A570, HU577, COU812, HU332, A2095 AB, and A884, partly derived from our PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types
Decision-Epochs Matter: Unveiling Its Impact on the Stability of Scheduling With Randomly Varying Connectivity
No full textInternational audienceA classical result in queuing theory states that in a parallel-queue single-server model, the maximum stability region is unaffected by scheduling decision epochs, and in particular is the same for preemptive and non-preemptive systems. We examine a scenario where queues are randomly connected to the server and show that, unlike the classical case, the maximum stability region strongly depends on the scheduling decision epochs. We compare three settings: decisions can be made anytime (unconstrained), decisions are made only at departures (non-preemptive), and decisions occur when a γ-rate exponential clock rings. We observe a significant reduction in the stability region in the non-preemptive setting compared to the unconstrained one, showing that a non-preemptive scheduler cannot take opportunistically advantage of the random varying connectivity. Also, in the γ-rate clock setting, one can be arbitrarily close to the maximum stability region in the unconstrained setting if we choose γ large enough. In all the settings, we show that the Longest Connected Queue (LCQ) policy achieves maximum stability. From a methodological viewpoint, we introduce a new theoretical tool called "test for fluid limits" (TFL), which offers a method to determine stability on the basis of a simple formal test
STREAM: a system for tracing radiative transfer and energy balance in heterogeneous surfaces
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Structural Analysis of LNMO Cathode Materials using 4D-STEM ACOM and Data Science Techniques
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Derived Foliations
No full textThis is a first version of a book on derived foliations, that are a generalisation of classicalfoliations in the context of derived algebraic geometry. The text starts with the basicdefinitions and constructions, then explore foliated cohomology (with crystalcoefficients), formal and analytic integrability problems, existence of theleaf space, characteristic classes, and two different notions of derivedfoliation in arbitrary characteristics
