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Separation and transition on a cone-cylinder-flare: Experimental campaigns
No full textInternational audienceExperimental campaigns were conducted across three Mach 6 facilities on the hypersonic flow around a cone-cylinder-flare (CCF) geometry as part of the NATO STO Research Task Group AVT-346. Two conventional facilities (AFRL M6LT and ONERA R2Ch) and one quiet tunnel (Purdue BAM6QT) were used to test the same geometry and to study the instabilities in both the boundary layer and the shear layer above the axisymmetric separation bubble. Two nose tip radii (one nominally sharp and one blunt with a 5 mm radius) were tested. For the sharp nose tip case, there was excellent agreement between the measurements of both second-mode and shear-layer instabilities across the conventional facilities. However, the measured spectra for the blunt nose tip case showed more significant differences between the two conventional tunnels, potentially due to an alternate dominant instability mechanism coupled with the variations in the freestream noise spectra. The quiet facility resulted in a flow that remained laminar to much higher freestream unit Reynolds numbers, as well as in instability measurements that had more distinct spectral peaks for the sharp tip case and broadband rises for the blunt one. The instability mechanisms at play in the sharp quiet case were found to be the same as those in the conventional facilities
Nano-Structuration Haute Résolution par Lithographie de Copolymères à Blocs pour des Applications Microélectroniques et de Capteurs
No full textAchieving high-resolution nanostructures at sub-10 nm scale is paramount for technological advancements, especially in the field of microelectronics, where the continuous reduction in transistor size plays a crucial role, but also in other fields like in photonics for the fabrication of metasurfaces or in the field of bio/chemical sensors for example. In this context, the directed self-assembly (DSA) of high-χ block copolymers (BCPs) is a promising nanofabrication technique. A higher value of the Flory-Huggins parameter χ, measuring the chemical incompatibility between the blocks, enables the formation of higher resolution features (sub-10 nm).In this PhD thesis, the focus revolves around investigating the DSA of a high-χ lamellar Si-containing material, polystyrene -block- poly(1,1-dimethylsilacyclobutane) (PS-b-PDMSB) with a 9 nm half pitch, on topographic substrates for BCP lithography (a so-called graphoepitaxy process), with the ultimate goal of addressing applications in microelectronics and surface-enhanced Raman spectroscopy (SERS).To attain a lithography-compatible configuration i.e., long-range ordered out-of-plane lamellae, precise control of the wetting interaction between the BCP and its environment (e.g., substrate’s bottom and sidewalls, as well as polymeric top-coat) is required. In the first part of the work, we evaluated various plasma chemistry treatments on the topographic substrates, composed of spin-on-carbon (SOC) guiding lines and a Si base substrate, to favour this vertical alignment within trenches. Notably, a HBr/O2 plasma-treatment achieves both neutral wetting at the bottom interface and strong PS-affine wetting at the SOC trench sidewalls, effectively guiding vertical BCP lamellae along the trenches. On the other hand, a grafted neutral underlayer is shown to induce isotropic wetting, resulting in a ladder-like structure (perpendicular alignment along the guiding lines). Experimental observations are in good agreement with a free energy configurational model developed to describe the systems. The selective removal of one of the BCP domains, for example by plasma etching, results in open out-of-plane structures that serve as lithographic templates for further applications.Additionally, the potential of these dense sub-10 nm structures for SERS-based sensing is evaluated. Metal deposition on these BCP templates yields various nanoscopic gold line structures, which are evaluated through the detection of grafted thiophenol. In particular, long-range aligned anisotropic patterns exhibit a strong polarization-dependent signal. Finite-different-time-domain simulations (FDTD) are also carried out to explain these nano-plasmonic behaviours.La réalisation de nanostructures à haute résolution à une échelle inférieure à 10 nm est essentielle pour les avancées technologiques, en particulier dans le domaine de la microélectronique, où la réduction continue de la taille des transistors joue un rôle crucial. Cependant, elle est également importante dans d'autres domaines comme la photonique, pour la fabrication de métasurfaces, ou encore dans le domaine des capteurs (bio)chimiques. Dans ce contexte, l'auto-assemblage dirigé (DSA) de copolymères à blocs (BCP) à haut paramètre χ s'avère être une technique de nanofabrication prometteuse. Un paramètre χ élevé, qui mesure l'incompatibilité chimique entre les blocs, permet la formation de motifs à plus haute résolution (inférieure à 10 nm).Cette thèse de doctorat se concentre sur l'étude du DSA d'un matériau lamellaire à haut χ contenant du silicium, le polystyrène-bloc-poly(1,1-diméthylsilacyclobutane) (PS-b-PDMSB), avec une demi-période de 9 nm, sur des substrats topographiques (procédé dit de graphoépitaxie), avec pour objectif ultime de répondre à des applications en microélectronique et en spectroscopie Raman exaltée de surface (SERS).Pour obtenir une configuration compatible avec la lithographie, c'est-à-dire des lamelles orientées verticalement et ordonnées à longue distance, un contrôle précis du mouillage entre le BCP et son environnement (avec le fond et les parois latérales du substrat, ainsi qu’avec la couche supérieure polymère) est nécessaire. Dans la première partie de ce travail, nous avons évalué divers traitements plasma sur les substrats topographiques, composés de lignes directrices en spin-on-carbon (SOC) et d'un substrat de base en silicium, afin de favoriser cet alignement vertical à l'intérieur des tranchées. En particulier, un traitement plasma HBr/O2 permet à la fois d’obtenir un mouillage neutre à l'interface inférieure (substrat silicium) et un mouillage fortement préférentiel pour le PS sur les parois latérales (lignes de SOC), guidant ainsi efficacement les lamelles BCP verticales le long des tranchées. En revanche, une sous-couche neutre greffée induit un mouillage isotrope, aboutissant à une structure en échelle (alignement perpendiculaire aux lignes directrices). Les observations expérimentales sont en bon accord avec un modèle d'énergie libre développé pour décrire les différentes configurations d’organisation du système. De plus, la suppression sélective d’un des domaines du BCP par gravure plasma, donne lieu à des structures ouvertes orientées verticalement servant de masques lithographiques pour des applications ultérieures.Par ailleurs, le potentiel de ces structures denses, avec des dimensions caractéristiques de moins de 10 nm, a été évalué pour des applications de détection basées sur la SERS. Le dépôt de métal sur ces gabarits BCP donne lieu à diverses structures de lignes d’or nanoscopiques, évaluées à travers la détection de thiophénol greffé. En particulier, les motifs anisotropes alignés sur de longues distances présentent un signal fortement dépendant de la polarisation. Des simulations basées sur la méthode des différences finies dans le domaine temporel (FDTD) ont été réalisées pour expliquer ces comportements nano-plasmoniques
CHEX-MATE: exploring the kinematical properties of Planck galaxy clusters
No full textInternational audienceWe analyse the kinematical properties of the CHEX-MATE (Cluster HEritage project with XMM-Newton - Mass Assembly and Thermodynamics at the Endpoint of structure formation) galaxy cluster sample. [...] We derive cluster mass profiles for 75 clusters using the \textsc{MG-MAMPOSSt} procedure, which recovers the gravitational potential and the anisotropy profiles from line-of-sight velocities and projected positions of galaxy members. The standard NFW and the Burkert models with flatter cores than NFW both adequately fit the kinematic data, with only marginal statistical preference for one model over the other. An estimation of the mass bias is performed from the comparison with SZ-X-ray-calibrated mass estimates, resulting in a value of when four evidently disturbed clusters are removed from the sample. We assess the dynamical state of the clusters by inferring the Anderson-Darling coefficient and the fraction of galaxies in substructures (). Except for a few cases, we found relatively low values for , suggesting that CHEX-MATE clusters are not too far from relaxation. Moreover, no significant trends emerge among and the difference between the log-masses estimated by \textsc{MG-MAMPOSSt} and by SZ-X-ray. We study the concentration-mass relation for the sample; despite the large scatter, we observe signs of an increasing trend for large-mass clusters, in agreement with recent theoretical expectations. Finally, the analysis of radial anisotropy profiles of member galaxies - stacked in five bins of mass and redshift - reveals that orbits tend to be isotropic at the center and more radial towards the edge, as already found in previous studies. A slight trend of increasing radial orbits at is observed in clusters with larger velocity dispersio
Fermionic sub-GeV Dark Matter from evaporating Primordial Black Holes at DarkSide-50
No full textInternational audienceWe present a search for boosted dark matter from Primordial Black Holes (PBH) evaporation using the DarkSide-50 ionization-signal-only dataset corresponding to the experiment's () exposure. We focus on evaporation of PBHs with masses in the range [] g producing Dirac fermionic dark matter particles with sub-GeV kinetic energy. These relativistic particles, with energies up to hundreds of MeV, can generate detectable signals for masses below MeV. The absence of a signal enables setting complementary limits to those derived from cosmological observations and direct detection searches for cosmic ray-boosted dark matter
DESI DR1 Ly 1D power spectrum: The optimal estimator measurement
No full textInternational audienceThe one-dimensional power spectrum of Ly forest offers rich insights into cosmological and astrophysical parameters, including constraints on the sum of neutrino masses, warm dark matter models, and the thermal state of the intergalactic medium. We present the measurement of using the optimal quadratic maximum likelihood estimator applied to over 300,000 Ly quasars from Data Release 1 (DR1) of the Dark Energy Spectroscopic Instrument (DESI) survey. This sample represents the largest to date for measurements and is larger than the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) by a factor of 1.7. We conduct a meticulous investigation of instrumental and analysis systematics and quantify their impact on . This includes the development of a cross-exposure estimator that eliminates the need to model the pipeline noise and has strong potential for future measurements. We also present new insights into metal contamination through the 1D correlation function. Using a fitting function we measure the evolution of the Ly forest bias with high precision: . In a companion validation paper, we substantially extend our previous suite of CCD image simulations to quantify the pipeline's exquisite performance accurately. In another companion paper, we present DR1 measurements using the Fast Fourier Transform (FFT) approach to power spectrum estimation. These two measurements are consistent with each other and constitute the most precise measurement to date, while being in good agreement with results from the DESI early data release
The El Niño Southern Oscillation (ENSO) Recharge Oscillator Conceptual Model: Achievements and Future Prospects
No full textInternational audienceAbstract The recharge oscillator (RO) is a simple mathematical model of the El Niño Southern Oscillation (ENSO). In its original form, it is based on two ordinary differential equations that describe the evolution of equatorial Pacific sea surface temperature and oceanic heat content. These equations make use of physical principles that operate in nature: (a) the air‐sea interaction loop known as the Bjerknes feedback, (b) a delayed oceanic feedback arising from the slow oceanic response to winds within the equatorial band, (c) state‐dependent stochastic forcing from fast wind variations known as westerly wind bursts (WWBs), and (d) nonlinearities such as those related to deep atmospheric convection and oceanic advection. These elements can be combined at different levels of RO complexity. The RO reproduces ENSO key properties in observations and climate models: its amplitude, dominant timescale, seasonality, and warm/cold phases amplitude asymmetry. We discuss the RO in the context of timely research questions. First, the RO can be extended to account for ENSO pattern diversity (with events that either peak in the central or eastern Pacific). Second, the core RO hypothesis that ENSO is governed by tropical Pacific dynamics is discussed from the perspective of influences from other basins. Finally, we discuss the RO relevance for studying ENSO response to climate change, and underline that accounting for ENSO diversity, nonlinearities, and better links of RO parameters to the long term mean state are important research avenues. We end by proposing important RO‐based research problems
Nucleation barrier effect on pulsating heat pipe performance
No full textInternational audienceDespite their utility, a comprehensive understanding of the internal flow and heat transfer mechanisms within Pulsating Heat Pipes (PHPs) remains challenging. With the objective of clarifying the role of internal tube surface state on PHP performance, this study aims to evaluate the influence of the nucleation barrier using CASCO (Code Avancé de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in French). Numerical findings show that the nucleation barrier has minimal influence on PHP thermal resistance at high heating powers, whereas at lower heating powers, an increase in the nucleation barrier results in decreased PHP thermal resistance. Experimental data from a horizontal 16-turn copper tube PHP prototype filled with HFE-7100 fluid are compared with simulation performed under zero-gravity conditions
The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
No full textInternational audienceThe standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged
Microstructured growth by liquid phase epitaxy of scintillating Gd3Ga5O12 (GGG) doped with Eu3+
No full textInternational audienceMicrostructuration is useful for improving, tuning, or altering material properties and is used in various fields. It is applied to scintillating screens to enhance light extraction and to combine a high X-ray absorption efficiency of the scintillator with a good spatial resolution of the image. Even though the concept of microstructured scintillators is promising, only a few options have been explored and reported, leaving room for advancement. Here, we present the procedure for growing microstructured GGG:Eu with liquid phase epitaxy onto laser-treated GGG substrates with crystallographic orientations (100) and (111). It was found that the microstructure grows epitaxially on the substrate, maintaining the orientation and that its crystallinity is good and comparable to normal epitaxial films of GGG:Eu. The optical properties were also investigated thoroughly and are comparable to the un-structured epitaxial GGG:Eu films. We believe that these promising results can pave the way for other materials to be grown in a microstructured manner, which can be valuable also outside of scintillation for various fields