160 research outputs found
Dissipation and nonlocality in a general expanding braneworld universe
No full text32 pages LATEX with 7 eps figuresInternational audienceWe study the evolution of both scalar and tensor cosmological perturbations in a Randall-Sundrum braneworld having an arbitrary expansion history. We adopt a four dimensional point of view where the degrees of freedom on the brane constitute an open quantum system coupled to an environment composed of the bulk gravitons. Due to the expansion of the universe, the brane degrees of freedom and the bulk degrees of freedom interact as they propagate forward in time. Brane excitations may decay through the emission of bulk gravitons which may escape to future infinity, leading to a sort of dissipation from the four dimensional point of view of an observer on the brane. Bulk gravitons may also be reflected off of the curved bulk and reabsorbed by the brane, thereby transformed into quanta on the brane, leading to a sort of nonlocality from the four dimensional point of view. The dissipation and the nonlocality are encoded into the bulk propagator. We estimate the dissipation rates of the bound state as well as of the matter degrees of freedom at different cosmological epochs and for different sources of matter on the brane
Compton y-parameter map of thermal SZ effect from Planck PR4 data
No full text<p>This dataset hosts the results and processing data from the paper "An improved Compton parameter map of thermal Sunyaev-Zeldovich effect from Planck PR4 data", <a href="https://doi.org/10.1093/mnras/stad3156">https://doi.org/10.1093/mnras/stad3156</a>. Please cite this paper, should you use this data.</p>
<p>Contact: <a href="mailto:[email protected]">[email protected]</a></p>
<p>UPDATED FITS HEADER.</p>
Optimization of a pyrochimical process for strategical metals production : neodymium application
No full textCette thèse s'inscrit dans la continuité du programme européen REE4EU dont l'objectif était d'étudier la mise en œuvre d'une chaîne de recyclage du néodyme contenu dans les aimants permanents. A l'issue de ce programme, l'oxyde de néodyme (Nd2O3) obtenu est converti en Nd métallique par électrolyse à haute température d'un mélange LiF-NdF3-Nd2O3 (procédé de type Hall-Héroult). Dans ce procédé, Nd2O3 est dissout sous la forme d'un oxyfluorure NdOF54- qui est consommé lors de l'oxydation d'une anode en carbone (1), tandis que le composé NdF3 du solvant, qui se présente sous la forme NdF63-, est réduit en néodyme sous la forme de métal liquide (2). 2NdOF54- + C(s)+2F- → 2NdF63- + CO2(g)+ 4e- (1) NdF63- + 3e- → Nd(l) + 6F- (2) La réaction globale du procédé est alors la suivante : Nd2O3 + 3/2 C(s) → 2Nd(l) + 3/2 CO2(g)(3) L'objectif principal a été de développer des outils aidant à la gestion de ce procédé tout en déterminant des conditions opératoires optimales. Pour cela, trois thématiques de recherche ont été étudiés :(I) Développer une méthode de dosage de l'oxyde de néodyme qui soit rapide et in-situ pour gérer les ajouts de Nd2O3 et éviter la formation de boues denses polluant le métal produit. Dans cette étude, il a été montré que la dissolution de Nd2O3 dans LiF-NdF3 conduit à l'apparition d'ion oxyde libre O2-. Une méthode de dosage de O2- par voltammétrie à vague carrée utilisant une électrode de Pt est alors développée dans LiF-NdF3-Nd2O3. Cette méthode de dosage est finalement utilisée afin de déterminer la solubilité de Nd2O3 dans LiF-NdF3 entre 850 et 1050 °C. (II) Etudier l'influence de la teneur en Nd2O3 sur l'oxydation d'une anode en carbone dans LiF-NdF3-Nd2O3 afin d'éviter la production de CFX(g) pouvant engendrer un effet d'anode. En analysant par spectroscopie IR les gaz anodiques produits par électrolyse, il a été montré que lorsque l'apport en élément oxyde à l'électrode ne permettait pas d'assurer seule l'oxydation du carbone, du CF4(g) et du C2F6(g) étaient également produit. L'influence de la teneur en Nd2O3 sur la densité de courant limite de diffusion de l'oxyde de néodyme dissout a alors été déterminée par voltammétrie à l'état stationnaire entre 850 et 1050 °C. (III) Etudier l'influence de la densité de courant cathodique sur la production de Nd liquide pour optimiser le rendement et faciliter la récupération du métal. En utilisant la technique de la chronopotentiométrie inverse, il a été mis en avant une augmentation du rendement faradique avec la densité de courant. Dans les conditions de l'étude, le rendement faradique maximal est de 85%. Il a également été observé que la coalescence du néodyme liquide était favorisée pour des densités de courant cathodique élevées (> 3 A.cm-2) facilitant alors sa récupération. A l'issue de ce travail, l'influence d'un changement d'échelle sur le rendement de production de Nd a été étudié en réalisant une électrolyse visant à produire environ 100 g de métal, avec les paramètres opératoires optimisés (densités de courant anodique et cathodique). Un impact significatif du changement d'échelle sur le procédé a ainsi pu être observé avec la dispersion et la dissolution de particules de Nd métal dans le sel. Les résultats obtenus ont permis de proposer des pistes d'étude pour poursuivre l'optimisation du procédé.This thesis follows previous works realized in the REE4EU European program, dedicated to the deployment of neodymium permanent magnets recycling chain. At the end of this program, neodymium oxide (Nd2O3) is obtained then and converted into Nd metal by electrolysis of a LiF-NdF3-Nd2O3 mixture at high temperature (analog to Hall-Heroult process). In this process, Nd2O3 is solubilized into an oxyfluoride complexe NdOF54- that is consumed by anodic reaction to produce CO2(g) (1), meanwhile NdF3 compound (complexed as NdF63-) is reduced into liquid metal (2). 2NdOF54- + C(s)+2F- → 2NdF63- + CO2(g)+ 4e- (1) NdF63- + 3e- → Nd(l) + 6F- (2) The global reaction of the process is: Nd2O3 + 3/2 C(s) → 2Nd(l) + 3/2 CO2(g)(3) The main objectives were to develop tools and methods that help to operate the process and determine optimized parameters. This works was divided into three problematics: (I) Develop a fast and in-situ Nd2O3 titration method in order to manage Nd2O3 feeding and prevent sludge formation that pollutes the produced metal. In this study, it was observed that Nd2O3 dissolution leads to O2- formation. A titration method of O2- using square wave voltammetry on Pt electrode was then developed in LiF-NdF3-Nd2O3. This method was also used to determine Nd2O3 solubility in LiF-NdF3 in the 850 - 1050 °C temperature range. (II) Investigate the influence of Nd2O3 content on the oxidation of carbon anode in LiF-NdF3-Nd2O3 in order to prevent CFX(g) formation that could lead to an anode effect. IR spectroscopic analysis of anodic gas shows that oxide depletion leads to CF4(g) and C2F6(g) production instead of CO2(g). The influence of Nd2O3 content on the critical current density, above which one CFX(g) are produced, was determined by steady state voltammetry in the 850 - 1050 °C temperature range. (III) Investigate the influence of cathodic current density on neodymium production in order to optimize current efficiency and facilitate metal recovering. The chronopotentiometry with current reversal method allowed to observe a current efficiency increase with current density. In our experiment conditions, maximum that could be obtained is 85%. Moreover, a better liquid neodymium coalescence (and then recovery) was observed for high current density (above 3 A.cm-2). Finally, an electrolysis able to produce 100 g of Nd metal was realized in order to study the scale up influence on Nd production with optimized cathodic current density. Dispersed neodymium particles and neodymium dissolution were observed and impacted the neodymium production. The results permit then to propose new research thematic to improve neodymium process
Relativistic SZ maps and electron gas temperature spectroscopy
No full textWhile third-generation CMB experiments have allowed to release the first maps of Compton-y distortion due to thermal Sunyaev-Zeldovich (SZ) effect, next-generation CMB experiments should allow us to map also the electron gas temperature, Te, across the sky through the detection of relativistic corrections to the thermal SZ effect. We discuss about experimental requirements to break the y-Te degeneracy of the observed SZ intensity, and propose a new component separation approach based on moment expansion to disentangle the y and Te observables of the relativistic SZ effect while mitigating foregrounds. We show how our approach offers a new spectroscopic view of the clusters not only across frequencies but now also across temperatures. We also show how the relativistic electron temperature power spectrum provides a new cosmological observable which may complement the Compton-y map power spectrum to break some of the parameter degeneracies in future cosmological SZ analyses
Mapping the hot baryonic gas across the entire sky with LiteBIRD
No full textTrabajo presentado al Colloque National CMB-France #6, celebrado en l'Institut Henri Poincaré (Paris) del 18 al 19 de diciembre de 2024.Peer reviewe
Optimization of foreground moment deprojection for semi-blind CMB polarization reconstruction
No full textArXiv ePrint: 2402.17579Upcoming Cosmic Microwave Background (CMB) experiments, aimed at measuring primordial CMB polarization B-modes, require exquisite control of instrumental systematics and Galactic foreground contamination. Blind minimum-variance techniques, like the Needlet Internal Linear Combination (NILC), have proven effective in reconstructing the CMB polarization signal and mitigating foregrounds and systematics across diverse sky models without suffering from foreground mismodelling errors. Still, residual foreground contamination from NILC may bias the recovered CMB polarization at large angular scales when confronted with the most complex foreground scenarios. By adding constraints to NILC to deproject statistical moments of the Galactic emission, the Constrained Moment ILC (cMILC) method has been demonstrated to further enhance foreground subtraction, albeit with an associated increase in overall noise variance. Faced with this trade-off between foreground bias reduction and overall variance minimization, there is still no recipe on which moments to deproject and which are better suited for blind variance minimization. To address this, we introduce the optimized cMILC (ocMILC) pipeline, which performs full automated optimization of the required number and set of foreground moments to deproject, pivot parameter values, and deprojection coefficients across the sky and angular scales, depending on the actual sky complexity, available frequency coverage, and experiment sensitivity. The optimal number of moments for deprojection, before paying significant noise penalty, is determined through a data diagnosis inspired by the Generalized NILC (GNILC) method. Validated on B-mode simulations of the PICO space mission concept with four challenging foreground models, ocMILC exhibits lower Galactic foreground contamination compared to NILC and cMILC at all angular scales, with limited noise penalty. This multi-layer optimization enables the ocMILC pipeline to achieve unbiased posteriors of the tensor-to-scalar ratio, regardless of foreground complexity.This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory. AC acknowledges funding support by AASS PhD Program, ASI/LiteBIRD grant n. 2020-9-HH.0 and ASI/LiteBIRD grant CUP: F84I20000230005. AC was also supported by the InDark and LiteBIRD INFN projects. MR thanks the Spanish Agencia Estatal de Investigación (AEI, MICIU) for the financial support provided under the projects with references PID2019-110610RB-C21 and PID2022-139223OB-C2, and acknowledges support from the CSIC programme ‘Ayuda a la Incorporación de Científicos Titulares’ provided under the project 202250I159.Peer reviewe
Exploring cosmic origins with CORE: B-mode component separation
No full textWe demonstrate that, for the baseline design of the CORE satellite mission, the polarized foregrounds can be controlled at the level required to allow the detection of the primordial cosmic microwave background (CMB) B-mode polarization with the desired accuracy at both reionization and recombination scales, for tensor-to-scalar ratio values of r 5× 10-3. We consider detailed sky simulations based on state-of-the-art CMB observations that consist of CMB polarization with τ=0.055 and tensor-to-scalar values ranging from r=10-2 to 10-3, Galactic synchrotron, and thermal dust polarization with variable spectral indices over the sky, polarized anomalous microwave emission, polarized infrared and radio sources, and gravitational lensing effects. Using both parametric and blind approaches, we perform full component separation and likelihood analysis of the simulations, allowing us to quantify both uncertainties and biases on the reconstructed primordial B-modes. Under the assumption of perfect control of lensing effects, CORE would measure an unbiased estimate of r=(5 ± 0.4)× 10-3 after foreground cleaning. In the presence of both gravitational lensing effects and astrophysical foregrounds, the significance of the detection is lowered, with CORE achieving a 4σ-measurement of r=5× 10-3 after foreground cleaning and 60% delensing. For lower tensor-to-scalar ratios (r=10-3) the overall uncertainty on r is dominated by foreground residuals, not by the 40% residual of lensing cosmic variance. Moreover, the residual contribution of unprocessed polarized point-sources can be the dominant foreground contamination to primordial B-modes at this r level, even on relatively large angular scales, ℓ ∼ 50. Finally, we report two sources of potential bias for the detection of the primordial B-modes by future CMB experiments: (i) the use of incorrect foreground models, e.g. a modelling error of Δβs = 0.02 on the synchrotron spectral indices may result in an excess in the recovered reionization peak corresponding to an effective Δ r > 10-3; (ii) the average of the foreground line-of-sight spectral indices by the combined effects of pixelization and beam convolution, which adds an effective curvature to the foreground spectral energy distribution and may cause spectral degeneracies with the CMB in the frequency range probed by the experiment.0info:eu-repo/semantics/publishe
Evolution des perturbations cosmologiques dans les univers branaires
No full textNous étudions l'évolution des perturbations cosmologiques scalaires et tensorielles dans un Univers branaire du type Randall-Sundrum en expansion quelconque. Nous adoptons un point de vue quadridimensionnel, considérant les degrés de liberté localisés sur la brane comme un système quantique ouvert couplé à un environnement composé des gravitons du bulk AdS. À cause de l'expansion non-uniforme de l'Univers, les degrés de liberté branaires et ceux du bulk entrent en interaction, générant une dissipation effective ainsi que de la non-localité du point de vue quadridimensionnel d'un observateur sur la brane. À partir des propagateurs retardés nus de la brane Friedman-Robertson-Walker et du bulk AdS, nous calculons le propagateur effectif de la brane en resommant les effets de rétroaction du bulk à tous les ordres dans le couplage brane-bulk. La dissipation et la non-localité sont codées dans le propagateur effectif de la brane. Nous trouvons les taux de dissipation de diverses perturbations de matière sur la brane et de l'état lié du graviton. Nous calculons aussi explicitement le propagateur retardé covariant du graviton dans AdS en toute dimension. À la fin de la thèse, nous explorons la reconstruction des effets de lentilles gravitationnelles sur le CMB en cosmologie standard. À partir des spectres d'anisotropies observés, nous construisons un estimateur statistique du tenseur de cisaillement directement en espace réel de façon locale. L'approche en espace réel développée ici s'avère utile pour analyser des cartes réalistes du CMB contenant une coupure galactique et d'éventuelles petites excisions excluant les point-sources.We explore the evolution of both scalar and tensor cosmological perturbations in a Randall-Sundrum braneworld having an arbitrary expansion history. We adopt a four dimensional perspective where the degrees of freedom localized on the brane constitute an open quantum system coupled to a large environment composed of the Anti-de Sitter (AdS) bulk gravitons. Due to the non-uniform expansion of the universe, the brane degrees offreedom and the bulk degrees of freedom interact as they propagate forward in time, leading to an effective dissipation as well as a nonlocality from the four dimensional point of view of an observer on the brane. From both the "bare" retarded propagators on the Friedman-Robertson-Walker (FRW) brane and in the AdS bulk, we compute the effective retarded propagator on the brane for the "dressed" brane modes by resumming the bulk backreaction effects at all order in the brane-bulk coupling. Dissipation and nonlocality are encoded into the effective brane propagator. We find the dissipation rate of various matter perturbations on the brane as well as of the graviton bound state. We also compute explicitly the covariant AdS retarded Green function for the graviton in any dimension. At the end of the thesis, we investigate the reconstruction of CMB lensing in standard cosmology. From the observed CMB anisotropies power spectra, we construct a statistical estimator of the shear tensor of the lensing field directly in real space in a local manner. The real space methods developed here are useful for analysing realistic CMB maps containing a galactic cut and possibly numerous small excisions to exclude point sources that cannot be reliably subtracted.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
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