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Irradiation origin and stability of CO on trans-Neptunian objects: Laboratory constraints and observational evidence from JWST/DiSCo-TNOs
No full textInternational audienceContext. The James Webb Space Telescope large program DiSCo-TNOs has recently shown that CO2 ice is ubiquitous on 54 mediumsize trans-Neptunian objects (TNOs). TNO surfaces are found to define three main spectral and thus compositional groups that are likely linked to their position before planetary migration. CO ice is observed on the spectral type that is richest in CO2 and on the type that is richer in CH3OH and organics. Considerations on the thermal evolution of TNOs predicted the depletion of hypervolatiles such as CO from their surface layers, however.Aims. We investigate a potential irradiation origin of CO as well as its stability by studying the distribution of CO in two TNO compositional types and compared it with irradiation experiments.Methods. We studied the 4.68 µm band of CO and the 2.70 µm band of CO2 to probe the relation between the two molecules in 33 TNOs. We performed ion irradiation experiments on CO2 and CH3OH ices at 45 and 60 K with 30 keV H+ . We compared the laboratory spectra to TNO observations by focusing on the band areas and positions.Results. We find that the two types of surfaces in which CO is detected are very distinct in terms of their relative abundances and chemical environment. CO that is observed on surfaces that are rich in CO2 are consistent with being produced by CO2 irradiation, specifically, at 45 K. On objects that are rich in CH3OH and complex organics, CO is more likely formed by irradiation of CH3OH. As the CO band areas are only partly related with temperature, the chemical environment plays a major role in the CO retention.Conclusions. We find that the CO that is observed on TNO surfaces is compatible with being a secondary molecule that is entirely formed by late irradiation processes. Its abundance and stability is mostly controlled by the matrix from which it formed
Atoms as Electron Accelerators for New Physics Searches
No full textInternational audienceDue to Heisenberg's uncertainty principle, atomic electrons localized around the nucleus exhibit a characteristic momentum distribution that, in elements with high atomic number, remains significant up to relativistic values. Consequently, in fixed-target experiments, atoms can effectively act as electron accelerators, increasing the centre-of-mass energy in collisions with beam particles. In this work, we leverage this effect to explore its potential for new physics searches. We consider positrons from beams of various energies annihilating with atomic electrons in a W fixed target. We compute the production rates of new vector bosons and pseudoscalar particles as functions of their couplings and masses. We show that the electron-at-rest approximation significantly underestimates the mass reach for producing these new states compared to the results obtained by properly accounting for atomic electron momenta. In particular, we estimate the sensitivity for detecting these new particles using the positron beam at the Beam Test Facility linac at the Laboratori Nazionali di Frascati, the H4 beamline in the CERN North Area, and the proposed Continuous Electron Beam Accelerator Facility of Jefferson Laboratory
Concession minière, conquête coloniale et transformations environnementales. La mine de fer d’Aïn Mokra et son système concessionnaire articulé (1845-fin du xixe siècle)
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« Parcours des études catheriniennes : des éditions italiennes aux traductions françaises »
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Do MPs Make Good Lobbyists? Lessons from a Survey of the French Delegation to the European Parliament
No full textInternational audience"The phenomenon of the revolving door, understood in this study as the reconversion of former members of the European Parliament (MEPs) to jobs linked to lobbying, has been the subject of increasing media and political attention over the last 20 years, although it is not yet easy to objectively weigh its significance or characterise its concrete forms or factors. This analysis attempts to shed light on this using two sources of information: statistical data on post-mandate careers (including lobbying) of a population of elected representatives (the French delegation to the European Parliament), combined with interviews conducted with former MEPs and potential recruiters in consulting firms and large companies. The first observation is that full-time employment as a lobbyist after a term of office is a statistically marginal phenomenon. The qualitative study then goes on to identify a set of explanations relating to the professional boundaries between political institutions and private/commercial organisations, even in a European arena that is reputed to be more blurred and malleable. Nonetheless, the analysis shows that such trajectories do exist, as do various forms of collaboration with interest representation organisations, and identifies which MEPs are more inclined towards this and what skills they bring to bear.
The Social Conditions of ‘Influence’: What Can the Sociology of Interest Representatives Tell Us About Lobbying at the EU Level?
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Tailored 3D microphantoms: an essential tool for quantitative phase tomography analysis of organoids
No full textWe present a novel approach for benchmarking and validating quantitative phase tomography (QPT) systems using three-dimensional microphantoms. These microphantoms, crafted from biological and imaging data, replicate the optical and structural properties of multicellular biological samples. Their fabrication featuring refractive index modulation at sub-micrometer details is enabled by two-photon polymerization. We showcase the effectiveness of our technique via a round-robin test of healthy and tumoral liver organoid phantoms across three different QPT systems. This test reveals sample- and system-dependent errors in measuring dry mass and morphology. Tailored microphantoms establish the gold standard for the optimization of hardware setups, reconstruction strategies and error assessment, paving the way for novel non-invasive, label-free measurements of 3D biological samples
Lecture: Reconfigurable self-assembly of rod-like colloids, the role of chirality and attraction
No full textInternational audienceFilamentous bacteriophages such as fd-like viruses are monodisperse rod-like colloids that have well defined properties of diameter, length, rigidity, charge and chirality. Engineering these viruses leads to a library of colloidal rods, which can be used as building blocks for reconfigurable and hierarchical selfassembly. Their condensation in an aqueous solution with additive polymers, which act as depletants to induce attraction between the rods [1], leads to a myriad of fluid-like micronic structures ranging from isotropic/nematic droplets [2], colloid membranes [3], achiral membrane seeds [1], twisted ribbons [3-4], π-wall [5], pores [4], colloidal skyrmions [4], Möbius anchors [5], scallop membranes [6] to membrane rafts [7] and crystal membranes [8-9]. These structures, and the way that they shape-shift, not only shed light on the role of entropy [10], chiral frustration and topology in soft matter, but also mimic many structures encountered in different fields of science. On the one hand, filamentous phages being an experimental realization of colloidal hard rods, their condensation mediated by depletion interactions constitutes a blueprint for the self-assembly of rod-like particles and provides a fundamental foundation for bio-or material-oriented applications. On the other hand, the chiral properties of the viruses restrict the generalities of some results but vastly broaden the self-assembly possibilities.Figure -Filamentous phages as building blocks for reconfigurable and hierarchical self-assembly. Starting with isotropic suspensions of filamentous phages and depletion interactions, it is possible to drive the system to selfassemble in a myriad of structures. Tuning the depletion interaction leads to the condensation of the virus with increasing density and order. Using the virus chirality, it is possible to turn 2D structures into 3D structures with Gaussian curvature. By mixing different types of rods, the system may phase separately. Optical tweezers and external control over the interactions permits us to navigate continuously in this state diagram and trigger shapeshifting structures.[1] “Filamentous phages as building blocks for reconfigurable and hierarchical self-assembly”. T Gibaud. Journal ofPhysics: Condensed Matter 29, 493003 (2017)[2] “Condensation and dissolution of nematic droplets in dispersions of colloidal rods with thermo–sensitivedepletants.” A. Modlińska, A. M. Alsayed, T. Gibaud. Scientific reports 5, 18432 (2015)[3] “Reconfigurable self-assembly through chiral control of interfacial tension”. T. Gibaud et al. Nature 481, 348(2012)[4] “Force induced formation of twisted chiral ribbons”. A. Balchunas, L. L. Jia, M. J. Zakhary, J Robaszewski, T.Gibaud, Z. Dogic, R. A. Pelcovits, T. R. Powers. Phys. Rev. Lett. 125, 018002 (2020)[5] "Imprintable membranes from incomplete chiral coalescence". M. J. Zakhary, et al. Nature communications 5,3063 (2014)[6] “Achiral symmetry breaking and positive Gaussian modulus lead to scalloped colloidal membranes”. T. Gibaud,et al. Proceedings of the National Academy of Sciences 114, E3376 (2017)[7] “Hierarchical organization of chiral rafts in colloidal membranes”. P. Sharma, A. Ward, T. Gibaud, M. F. Hagan,Z Dogic. Nature 513, 77 (2014)[8] “Direct Liquid to Crystal Transition in a Quasi-Two-Dimensional Colloidal Membrane”. T. Gibaud, D. Constantin.The journal of physical chemistry letters 9, 4302 (2018)[9] “Equation of State of Colloidal Membranes”. A. J. Balchunas, R. A. Cabanas, M. J. Zakhary, T. Gibaud, S. Fraden,P. Sharma, M. F. Hagan, Z. Dogic. Soft Matter 15, 6791 (2019)[10] “Entropic forces stabilize diverse emergent structures in colloidal membranes”, L. Kang, T. Gibaud, Z. Dogic and T. C. Lubensky, Soft Matter 12, 386 (2016)</div
Autophagy machinery as exploited by viruses
No full textInternational audienceViruses adapt and modulate cellular pathways to allow their replication in host cells. The catabolic pathway of macroautophagy, for simplicity referred to as autophagy, is no exception. In this review, we discuss anti-viral functions of both autophagy and select components of the autophagy machinery, and how viruses have evaded them. Some viruses use the membrane remodeling ability of the autophagy machinery to build their replication compartments in the cytosol or efficiently egress from cells in a non-lytic fashion. Some of the autophagy machinery components and their remodeled membranes can even be found in viral particles as envelopes or single membranes around virus packages that protect them during spreading and transmission. Therefore, studies on autophagy regulation by viral infections can reveal functions of the autophagy machinery beyond lysosomal degradation of cytosolic constituents. Furthermore, they can also pinpoint molecular interactions with which the autophagy machinery can most efficiently be manipulated, and this may be relevant to develop effective disease treatments based on autophagy modulation