HAL Université de Toulouse, et Toulouse INP
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Why bumblebees have become model species in apidology: A brief history and perspectives
No full textInternational audienceIn recent years, bumblebees have increasingly been used to study various aspects of bee biology, ecology and evolution. They are now broadly accepted as tractable model species, complementary to the domestic honey bees, for fundamental and applied apidology. Here, we provide a brief history of how bumblebee research developed since their domestication and commercialisation for crop pollination in the 1990s. Bumblebees are large social bees that can be kept and trained in the lab year-round. They are easy to manipulate and track individually in their small colonies. These practical advantages have offered new possibilities for experimental bee research, leading to major breakthroughs in different fields such as cognition, navigation, nutrition, host-parasite interactions, and insect declines. Many of these findings have later been confirmed in honey bees and other pollinators. We discuss some exciting directions for future apidology research based on bumblebees
Self-assembled GaAs quantum dashes for direct alignment of liquid crystals on a III-V semiconductor surface
No full textInternational audienceThe development of tunable photonic devices is strategic for miniaturized optical instrumentation and sensing systems. Exploiting the birefringence variation of liquid crystals (LCs) instead of MEMS actuation in such devices could bring better spectral stability and lower power consumption. However, aligning LCs inside a III-V semiconductor device is tricky. We demonstrate that self-assembled gallium arsenide (GaAs) quantum dashes (QDHs) could serve as direct planar aligners for LC nematic molecules. The alignment quality and birefringence variation of a LC-microcell embedding QDHs are shown to be similar to those of a polymer nanograting-based reference, with the added advantage of better electrical performance
Mackinawite partial oxidation to green rust produces a large, abiotic uranium isotope fractionation
No full textInternational audienceLow-oxygen settings and transition zones between strictly anoxic and oxic conditions may have characterised large expanses of Precambrian continental margins, where oxygen-breathing, complex life emerged and diversified. Accurate reconstructions of oxygen levels in such conditions are therefore required, but current geochemical proxies fail in identifying transitional redox conditions. Uranium isotopes are an emerging palaeoredox proxy, as large isotope fractionations are recorded during the reduction of uranium into anoxic sediments. Their potential application to transitional conditions is, however, unclear, because the redox regulating mineralogy of such environments and the associated isotope fractionations are poorly constrained. Here, we explore the mineralogical transformations occurring during the partial oxidation of mackinawite. We show that green rust, a key mineral of Precambrian oceans, forms as a by-product of mackinawite oxidation, along with uraninite and polysulphide. We also demonstrate that this mechanism records a large abiotic uranium isotope fractionation during its reaction with aqueous iron sulphide
Ingenuity Mars Helicopter Cameras: Description and results
No full textInternational audienceThe Ingenuity Mars Helicopter flew a total of 72 flights on Mars between April 2021 and January 2024 as part of a technology demonstration mission. The goal of Ingenuity was to demonstrate powered flight in the thin atmosphere of Mars by conducting five demonstration flights [1]. After successfully accomplishing the first five flights [2], the helicopter began an operations demonstration mission that included 67 additional flights [3], [4]
Prow & co.: inside the fluvial lenses of Gale's layered sulfate unit
No full textInternational audienceFor three years, the Curiosity rover has been exploring the layered sulfate unit (LSu) of Gale crater, Mars. Not only interesting as a potential record of a monotonic environmental shift towards arid conditions at the Noachian-Hesperian transition, we now know that this interval evidences complex environmental parameters which are characterized by alternating wetter and drier conditions at various timescales [1-3]. Such changes in depositional setting are particularly apparent within the Contigo mbr. of the Mirador fm. There, the LSu strata is dominated by stacked, large-scale cross-stratified aeolian sandstones, tens of meters in thickness, that are punctuated by erosion-resistant, decameter-wide, darker-toned and mostly lens-shaped sandstone bodies that suggest a fluvial deposition [4]. Using image data acquired with Mastcam and ChemCam’s RMI, we detail a wealth of sedimentary structures distributed across these lenses, focusing at the Prow outcrop and neighboring buttes (Fig. 1). We also provide a first assessment of the chemical compositions seen by ChemCam’s LIBS at the Prow
Mode transitions and spoke structures in E×B Penning discharge
No full textInternational audienceTwo-dimensional particle-in-cell simulations in the (radial-azimuthal) plane perpendicular to the axial direction of a cylindrical E×B Penning discharge are presented. The low-pressure discharge is self-consistently supported by plasma ionization from the electron beam injected axially, along the direction of the external magnetic field. It is shown that with the increasing strength of the external magnetic field, the discharge undergoes a sequence of transitions between several azimuthal modes. Azimuthal m > 1 spiral arm structures are excited at low magnetic field values as plasma confinement improves and the radial density profile becomes peaked. With a larger field, spiral arms with m > 1 are replaced by the m = 1 spoke mode, most clearly seen in plasma density. A transition from spiral arms to the spoke regime occurs when the plasma potential in the center changes from weakly positive (or zero) to negative. Further increase in the magnetic field results in a well-developed m = 1 spoke mode with additional small-scale higher-frequency m > 1 structures inside and around the spoke. It is shown that while ionization and collisions affect some characteristics of the observed fluctuations, the basic features of the spoke and m > 1 spiral structure remained similar without ionization. The role of energy conservation in small-scale high-frequency modes and spoke dynamics is discussed. It is demonstrated that in regimes with the m = 1 spoke mode, additional m = 4 harmonics of the ion and electron fluxes to the wall appear due to the square boundary. The frequency of the m = 1 mode is weakly affected by the geometry of the boundary
Pediment formation and subsequent erosion in Gale crater: Clues to the climate history of Mars
No full textInternational audienceEvidence of paleo-rivers, fans, deltas, lakes, and channel networks across Mars has prompted much debate about what climate conditions would permit the formation of these surface water derived features. Pediments, gently sloping erosional surfaces of low relief developed in bedrock, have also been identified on Mars. On Earth, these erosional landforms, often thought to be created by overland flow and shallow channelized runoff, are typically capped by fluvial sediments, and thus in exceptionally arid regions, pediments are interpreted to record past wet periods. Here we document the Greenheugh pediment in Gale crater, exploiting the observational capability of the Curiosity rover. The absence of a fluvial cap suggests that the pediment was likely cut by wind erosion, not fluvial processes. The pediment was then buried by an aeolian deposit (Stimson sandstone) that mantled the lower footslopes of Aeolis Mons (informally known as Mt. Sharp). This burial terminated active wind erosion, preserving the pediment surface (as an angular unconformity). Groundwater was present prior-to, during, and shortly after Stimson deposition, perhaps contributing to lithification and certainly to early diagenesis. Post lithification, wind erosion first cut canyons in the northern most footslopes (north of Vera Rubin ridge). Unlithified gravels were deposited in these canyons, likely due to runoff from Mt. Sharp. Boulder-rich fluvial and debris flow deposits built a > 70 m thick sequence (Gediz Vallis ridge) on the southern Greenheugh pediment. Continued wind erosion left elevated patches of gravel on the northern footslopes, and exposure age dating shows that erosion essentially ceased before 1 Ga (but possibly much earlier). Erosion to the south led to emergence of Vera Rubin ridge, retreat of the Greenheugh pediment, and the formation of Glen Torridon valley. Hence, this footslope environment of Mt. Sharp records climate-driven periods of wind erosion, aeolian deposition (and groundwater activity), surface runoff and sediment deposition, followed by further significant wind erosion that declined to present very slow rates. This likely occurred during the late Hesperian and possibly into the Amazonian
Particle‐Trapping Injection Flux Tubes in Saturn's Magnetosphere and High‐Band Electron Cyclotron Harmonic Waves Therein
No full textInternational audienceAbstract Injection flux tubes, characterized by localized equatorial magnetic field enhancements and concomitant hot plasma populations, contribute to Saturn's magnetospheric convection cycle by transporting magnetic flux radially inward. The sharp magnetic gradients at the flux‐tube edges have been demonstrated to enable the trapping of equatorially mirroring particles, leading to their energy‐dispersionless signatures in spacecraft observations. Here, we present a statistical distinction between flux tubes with and without particle‐trapping features in the electron cyclotron harmonic (ECH) wave properties. The particle‐trapping flux tubes carry stronger ECH waves in the high‐harmonic bands, whereas the other category is usually accompanied only by fundamental‐mode waves. This distinction is largely attributed to the higher content of energetic electrons within the particle‐trapping flux tubes. These results improve our understanding of the association between injection flux tubes and the high‐band ECH waves therein, suggesting a unique role of particle‐trapping flux tubes in Saturnian magnetospheric dynamics
Branching Brownian motion versus Random Energy Model in the supercritical phase: overlap distribution and temperature susceptibility
No full text48 pagesInternational audienceIn comparison with Derrida's REM, we investigate the influence of the so-called decoration processes arising in the limiting extremal processes of numerous log-correlated Gaussian fields. In particular, we focus on the branching Brownian motion and two specific quantities from statistical physics in the vicinity of the critical temperature. The first one is the two-temperature overlap, whose behavior at criticality is smoothened by the decoration process - unlike the one-temperature overlap which is identical - and the second one is the temperature susceptibility, as introduced by Sales and Bouchaud, which is strictly larger in the presence of decorations and diverges, close to the critical temperature, at the same speed as for the REM but with a different multiplicative constant. We also study some general decorated cases in order to highlight the fact that the BBM has a critical behavior in some sense to be made precise
Fragmentations with erasure
No full text19 pages, 1 figureWe study sequences of partitions of the unit interval into subintervals, starting from the trivial partition, in which each partition is obtained from the one before by splitting its subintervals in two, according to a given rule, and then merging pairs of subintervals at the break points of the old partition. The th partition then comprises subintervals with break points, and the empirical distribution of these points reveals a surprisingly rich structure, even when the splitting rule is completely deterministic. We consider both deterministic and randomized splitting rules and study the limiting behavior of the empirical distribution of the break points, from multiple angles