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Wave dispersion and bifurcation analyses of eikonal gradient-enhanced isotropic damage models
No full textInternational audienc
Innovating Bolometers' Mounting: A Gravity-Based Approach
No full textInternational audienceCryogenic calorimeters, also known as bolometers, are among the leading technologies for searching for rare events. The CUPID experiment is exploiting this technology to deploy a tonne-scale detector to search for neutrinoless double-beta decay of Mo. The CUPID collaboration proposed an innovative approach to assembling bolometers in a stacked configuration, held in position solely by gravity. This gravity-based assembly method is unprecedented in the field of bolometers and offers several advantages, including relaxed mechanical tolerances and simplified construction. To assess and optimize its performance, we constructed a medium-scale prototype hosting 28 LiMoO crystals and 30 Ge light detectors, both operated as cryogenic calorimeters at the Laboratori Nazionali del Gran Sasso (Italy). Despite an unexpected excess of noise in the light detectors, the results of this test proved (i) a thermal stability better than 0.5 mK at 10 mK, (ii) a good energy resolution of LiMoO bolometers, (6.6 2.2) keV FWHM at 2615 keV, and (iii) a LiMoO light yield measured by the closest light detector of 0.36 keV/MeV, sufficient to guarantee the particle identification requested by CUPID
Cohérence quantique, mélange intercanal et dissipation dans les canaux de bords des effets Hall quantiques fractionnaires et entiers
No full textThis thesis focuses on the study of quantum decoherence, inter-channel tunneling, and dissipation in the integer and fractional quantum Hall states, using the platform of two-dimensional gases—notably formed at the interface of the n-doped GaAs/AlGaAs heterostructure used here. Quantum decoherence refers to the loss of quantum behavior of a studied system, which can be induced by coupling to the external environment. Quantum computing relies on the principle of quantum coherence, and understanding the mechanisms leading to decoherence would enhance our grasp of quantum computing theory, and quantum mechanics in general. During this thesis, the initial focus was on understanding the mechanisms by which decoherence occurs in two different situations: in the integer quantum Hall effect and in the fractional quantum Hall effect (2/3). Then, in the final part, the research was dedicated to the fabrication of a single-electron detector, the last missing link in the chain needed to perform operations with flying electronic qubits — qubits not defined by a two-level energy system, but by a system with two spatial positions. Firstly, in the case of the integer quantum Hall effect, the edge channels all propagate in the same direction, determined in this case by the direction of the magnetic field applied perpendicularly to the sample, and can have opposite spins, which does not favor inter-channel tunneling. However, the n-doped GaAs/AlGaAs heterostructure, due to symmetry breaking in the direction perpendicular to the 2D gas, possesses spin-orbit coupling via the Bychkov-Rashba effect. Thus, the spin can be flipped, which is conducive to elastic inter-channel tunneling. Furthermore, the presence of gates in the middle of the sample, such as the quantum point contact—which is associated with an electric field locally depleting the 2D gas beneath its surface—causes a sudden change in direction for the electrons, potentially leading to tunneling at the point of spatial curvature change. The presence of tunneling is then highlighted here by modeling the partition noise produced by a tunneling point and its measurement. Secondly, in the case of the fractional quantum Hall effect at 2/3, the edge channels are counter-propagating, favoring inter-channel tunneling, which occurs frequently, inelastically, and randomly. A very simple model of this effect can be reproduced by introducing "black boxes", the Landauer reservoirs—or equivalently, energy-preserving reservoirs—where inelastic tunneling is allowed within. The model converges to the historical KFP model when enough reservoirs are introduced. When a quantum point contact is introduced, a conductance plateau at 0.5e²/h is predicted and measured during the experiments conducted in this thesis. Additionally, the presence of dissipation is shown and validated. However, Hong-Ou-Mandel type interferometry experiments reveal a non-zero visibility, indicating that the dissipation mechanism does not cause a total loss of coherence. Finally, in addition to the previous experiments, a single-electron detector was conceived to preserve quantum coherence when measuring a flying qubit, allowing it to be reused for subsequent operations, thus paving the way for quantum computing in two-dimensional electron gases under the quantum Hall effect regime. While the detector has been realized and can detect up to several hundred electrons, the technical optimizations needed to detect a single electron could not be completed before the end of the allotted time for this thesis.Cette thèse porte sur l'étude de la décoherence quantique, du tunneling intercanal et de la dissipation dans les états entiers et fractionnaires de l'effet Hall quantique, en utilisant la plateforme des gaz bidimensionnels à deux dimensions — qui se forme notamment à l'interface de l'hétérostructure dopée n GaAs/AlGaAs, utilisée ici. La décohérence quantique traduit la perte du comportement quantique d'un système étudié, ce qui peut notamment être induit par couplage à l'environnement extérieur. L'informatique quantique repose sur le principe de cohérence quantique, et la compréhension des mécanismes donnant lieu à la décohérence permettrait de mieux saisir la théorie de l'informatique quantique, voire la mécanique quantique de manière générale. Lors de cette thèse, il a été question dans un premier temps de comprendre par quels mécanismes la décoherence a lieu, dans deux situations différentes : dans l'effet Hall quantique entier et dans l'effet Hall quantique fractionnaire (2/3). Puis, dans un dernier temps, la recherche a été dévouée à la fabrication d'un détecteur à électron unique, le dernier maillon de la chaîne manquant pour pouvoir réaliser des opérations avec les qubits volants électroniques — des qubits non pas définis par un système à deux niveaux d'énergie, mais par un système à deux positions spatiales.Premièrement, dans le cas de l'effet Hall quantique entier, les canaux de bords se propagent tous dans la même direction, fixée dans le cas présent par le sens du champ magnétique appliqué perpendiculairement à l'échantillon, et peuvent être de spin opposés, ce qui ne favorise pas le tunneling intercanal. Cependant, l'hétérostructure dopée n GaAs/AlGaAs, par brisure de symétrie dans la direction perpendiculaire au gaz 2D, possède un couplage spin-orbite par effet Bychkov-Rashba. Ainsi, le spin peut être renversé ce qui est propice au tunneling intercanal élastique. Par ailleurs, la présence de grilles au milieu de l'échantillon, comme le point de contact quantique — qui est associé à un champ électrique déplétant localement le gaz 2D sous sa surface — provoque un soudain changement de direction chez les électrons, et peut donc ainsi provoquer du tunneling au point de changement de courbure spatiale. La présence de tunneling est alors ici mise en évidence par une modélisation du bruit de partitionnement produit par un point de tunneling, et sa mesure.Secondement, dans le cas de l'effet Hall quantique fractionnaire à 2/3, les canaux de bords sont contre-propageants, favorisant le tunneling intercanal, qui se produit alors de manière fréquente, inélastique et aléatoire. Un modèle très simple de cet effet peut être reproduit en introduisant des “boîtes noires”, les réservoirs de Landauer — ou de manière équivalente, des réservoirs à conservation d'énergie — où le tunneling inélastique est autorisé en son sein. Le modèle converge vers le modèle historique de KFP lorsque suffisamment de réservoirs sont introduits. Et lorsqu'un point de contact quantique est introduit, un plateau de conductance à 0.5e²/h est prédit, et mesuré lors des expériences effectuées lors de cette thèse. Par ailleurs, la présence de dissipation est montrée et validée. Mais des expériences d'interférométrie de type Hong-Ou-Mandel révèlent une visibilité non nulle, le mécanisme de dissipation ne provoque pas de perte de cohérence quasi-totale. Finalement, en plus des expériences précédentes, il a été pensé un détecteur à électron unique préservant la cohérence quantique lors de la mesure d'un qubit volant; permettant à celui-ci d'être réutilisé pour des opérations ultérieures, ouvrant ainsi la voie à l'informatique quantique dans les gaz bidimensionnels d'électrons sous le régime d'effet Hall quantique. Si le détecteur a été réalisé, et peut détecter jusqu'à plusieurs centaines d'électrons, les optimisations techniques lui permettant de détecter l'électron unique n'ont pas pu être terminées avant la fin du temps imparti pour cette thèse
Menu Avril 2025 Du 31 mars au 4 avril Du 7 au 11 avril
No full textInternational audienceBackground Interest in genomic medicine for human health studies and clinical applications is rapidly increasing. Clinical applications require contamination-free samples to avoid misleading results and provide a sound basis for diagnosis. Results Here we present ContaTester, a tool which requires only allele balance information gathered from a VCF file to detect cross-contamination in germline human DNA samples. Based on a regression model of allele balance distribution, ContaTester allows fast checking of contamination levels for single samples or large cohorts (less than two minutes per sample). We demonstrate the efficiency of ContaTester using experimental validations: ContaTester shows similar results to methods requiring alignment data but with a significantly reduced storage footprint and less computation time. Additionally, for contamination levels above 5%, ContaTester can identify contaminants across a cohort, providing important clues for troubleshooting and quality assessment. Conclusions ContaTester estimates contamination levels from VCF files generated from whole genome sequencing normal sample and provides reliable contaminant identification for cohorts or experimental batches
A 4-by-4 high impedance NbSi TES array for high resolution X-ray spectro-imaging
No full textInternational audienceWe conduct an R&D project on high impedance TES detectors aiming to minimise the focal plane power consumption while having high spectral and spatial resolutions. In this article we review the development of 4-by-4 Niobium–Silicon (NbSi) Transition-Edge-Sensor (TES) arrays. The 16 membrane pixels are suspended by thin (5μm thick) Silicon bridges that ensure electrical wiring and a weak thermal link to the heat sink. We fabricate these arrays on Silicon On Insulator (SOI) wafers with different pixel-to-substrate bridge lengths, widths, orientations and numbers to experimentally determine the Silicon heat conduction at 100mK. We also design different NbSi TES meanders to measure the electron–phonon decoupling effect, the various heat capacities (Si, NbSi, absorber) and the slope of the superconducting transitions. These chips will help to better understand and control the physical parameters for future optimised developments. This constitutes, in addition with our 50mK CMOS multiplexing ASIC and our 4K HEMT-SiGe amplifier, a scaled-down prefiguration of an X-ray cryogenic detector chain for astrophysics
A barcode database for insects associated with the spread of the Cocoa Swollen Shoot Virus Disease in Côte d’Ivoire
No full textInternational audienceSwollen Shoot is a viral disease affecting cocoa trees, transmitted by several species of mealybugs (Insecta, Hemiptera, Sternorrhyncha, Pseudococcidae). These insects maintain trophobiotic relationships with a complex and species-rich assemblage of ants protecting them and natural enemies controlling their populations. Here, we provide a curated DNA barcode database to characterise this insect community. Systematic observation of 7,500 cocoa trees was conducted, coupled with the collection of mealybug colonies and associated insect communities (parasitoids, predators and ants). Natural enemies were reared from mealybug colonies collected from 1,430 cocoa trees. Specimens were identified morphologically and sequenced for fragments of the standard DNA barcode region of the COI. We recovered 17 species of mealybugs from the family Pseudococcidae. Amongst these species, eight are new to the Ivorian cocoa orchard: Dysmicoccus neobrevipes Beardsley, Ferrisia dasylirii (Cockerell), Maconellicoccus ugandae (Laing), Paracoccus marginatus Williams & Granara de Willink, Phenacoccus solenopsis Tinsley, Planococcus minor (Maskell), Pseudococcus concavocerarii James and Pseudococcus occiduus De Lotto. Three of these species were identified for the first time in cocoa orchards in Africa: D. neobrevipes, Fe. dasylirii and Ph. solenopsis. A total of 54 ant species were identified and represented the first record of these species associated with mealybug colonies in cocoa in Côte d’Ivoire. Amongst the species associated with the mealybugs, 22 primary parasitoids, eight hyperparasitoids, 11 ladybirds beetles (Coccinellidae), seven gall midges (Cecidomyidae), one predatory lepidopteran species and four spider species were identified. Nine species of mealybugs parasitoids are newly recorded in the African cocoa orchards: Acerophagus aff. dysmicocci, Aloencyrtus sp., Anagyrus kamali, Anagyrus aff. pseudococci, Aenasius advena, Clausenia aff. corrugata, Gyranusoidea aff. tebygi, Zaplatycerus aff. natalensis (Encyrtidae) and Coccophagus pulvinariae (Aphelinidae) and one hyperparasitoid, Pachyneuron muscarum (Pteromalidae). For Côte d’Ivoire in particular, besides the previously mentioned nine parasitoids and one hyperparasitoid, five additional species are recorded for the first time, including four primary parasitoids, Blepyrus insularis (Encyrtidae), Clausenia corrugata (Encyrtidae), Clausenia sp. (Encyrtidae), and Coccidoctonus pseudococci (Encyrtidae) and one hyperparasitoid, Cheiloneurus cyanonotus (Encyrtidae). These results significantly enhance the knowledge of the diversity of the entomofauna associated with Swollen Shoot disease and pave the way for developing control methods based on the natural regulation of its mealybug (Pseudococcidae) vectors
Discovery of a New Phase in Thin Flakes of KV 3 Sb 5 under Pressure
No full textInternational audienceAbstract Results of magnetotransport measurements are reported on KV 3 Sb 5 thin flakes under pressure. The zero‐field electrical resistance reveals an additional anomaly emerging under pressure ( p ), marking a previously unidentified phase boundary T *( p ). Together with the established T CDW ( p ) and T c ( p ), denoting the charge‐density‐wave transition and a superconducting transition, respectively, the temperature‐pressure phase diagram of KV 3 Sb 5 features a rich interplay among multiple phases. The Hall coefficient evolves reasonably smoothly when crossing the T * phase boundary compared with the variation when crossing T CDW , indicating the preservation of the pristine electronic structure. The mobility spectrum analysis provides further insights into distinguishing different phases. Finally, the high‐pressure quantum oscillation studies up to 31 T combined with the density functional theory calculations further demonstrate that the new phase does not reconstruct the Fermi surface, confirming that the translational symmetry of the pristine metallic state is preserved
Hydroxide and fluoride catalyzed bonding interface closure for low-temperature wafer bonding
No full textSpecial Issue on Low Temperature Bonding for 3D Integration 2024 (LTB-3D2024)International audienceSurface deposition of active chemicals prior to wafer bonding was recently shown to enhance the hydrophilic direct bonding energy. Here, we describe the catalytic effect of hydroxide and fluoride ions at the bonding interface, with further insights into the mechanisms at play
STEP: SuperToken and Early-Pruning for efficient semantic segmentation
No full textInternational audienceVision Transformers (ViTs) achieve state-of-the-art accuracy in numerous vision tasks, but their heavy computational and memory requirements pose significant challenges. Minimising token-related computations is critical to alleviating this computational burden. This paper introduces a novel SuperToken and Early-Pruning (STEP) approach that combines patch merging along with an early-pruning mechanism to optimize token handling in ViTs for semantic segmentation. The improved patch merging method is developed to effectively address the diverse complexities of images. It features a dynamic and adaptive system, dCTS, which employs a CNN-based policy network to determine the quantity and size of patch groups that share the same supertoken during inference. With a flexible merging strategy, it handles superpatches of varying sizes: 2×2, 4×4, 8×8, and 16×16. Early in the network, high-confidence tokens are discarded and preserved from subsequent processing stages. This hybrid approach reduces both computational and memory requirements without significantly compromising segmentation accuracy. It is shown through experimental results that, on average, 40%of tokens can be predicted from the 16th layer onwards when using ViT-Large as the backbone. Additionally, a reduction of up to 3× in computational complexity is achieved, with a maximum drop in accuracy of 2.5%
Timelike Compton scattering on a spin-0 target with kinematic twist-4 precision
No full text23 pages, 5 figuresInternational audienceWe calculate the kinematic twist-3 and 4 corrections to the leading order amplitude of timelike Compton scattering (TCS) on a (pseudo-)scalar target, in the recently developed framework based on the conformal operator-product expansion. This allows us to compute the complete set of helicity amplitudes of the process, in particular those that vanish at leading twist. We compare the effects of higher twist contributions to TCS with those in deeply virtual Compton scattering (DVCS). Our estimates, based on a -meson GPD model, indicate that these contributions are sizeable and will play a crucial role in the interpretation of data from current and forthcoming experiments