1,720,984 research outputs found
Cosmologie au-delà du modèle standard avec les mesures précises de la polarisation du fond diffus cosmologique
No full textLa cosmologie a connu des progrès remarquables grâce aux mesures de plus en plus précises de différentes sondes cosmologiques telles que les relevés de galaxies, ou le fond diffus cosmologique, permettant l'émergence du modèle standard ΛCDM. Ce modèle fournit une description précise de la structure à grande échelle de l'Univers et de son évolution. Cependant, les mesures locales de la constante de Hubble, qui quantifie le taux d'expansion de l'Univers aujourd'hui, viennent le remettre en cause. La valeur de la constante de Hubble dérivée de l'observation des supernovae de type IA est en désaccord avec la mesure la plus précise de la constante de Hubble obtenue via le fond diffus cosmologique. Cette thèse explore différentes hypothèses qui ont été proposée pour expliquer la tension. Tout d'abord, la différence pourrait provenir d'effets instrumentaux non modélisés dans l'analyse du CMB. Je présente des méthodes pour quantifier les effets systématiques instrumentaux en étudiant la consistance entre les mesures de température et de polarisation du CMB. La tension de Hubble pourrait également être une indication en faveur de la nécessité d'aller au-delà du modèle standard. J'aborde également cette hypothèse en discutant des contraintes obtenues sur un modèle d'énergie noire primordiale, qui induirait une phase d'expansion accélérée dans l'Univers primordial. Je présente également un statut de l'analyse des spectres en puissance pour la future analyse cosmologique des données provenant du télescope ACT (Atacama Cosmology Telescope) qui devrait fournir des contraintes sur la cosmologie indépendantes de Planck avec une précision similaire.Cosmology has witnessed remarkable progress in recent years with more and more precise observations of different probes, including galaxy surveys and observations of cosmic microwave background, consistently supporting the standard model of cosmology. The ΛCDM model provides an accurate description of the large-scale structure and evolution of the Universe. However, a growing challenge to the ΛCDM model arises from local measurements of the Hubble constant, which quantifies the expansion rate of the Universe at present time. The value of the Hubble constant inferred from type IA supernovae is 5σ discrepant with the most precise determination of the Hubble constant from the CMB. This thesis explores different hypothesis that were proposed to alleviate the tension. First, this difference may have arised from unmodelled instrumental effects in the CMB datasets. I present methods to quantify instrumental systematic effects by studying the consistency of CMB temperature and polarisation. The Hubble tension may also be a hint in favor of physics beyond the standard model. I discuss the constraints obtained from various CMB datasets on the Early Dark Energy scenario, a promising solution that induces a phase of accelerated expansion at early time. Lastly, I present the analysis status of the future data release from the Atacama Cosmology Telescope which will provide constraints on cosmology independent from Planck with a similar precision
Cosmologie au-delà du modèle standard avec les mesures précises de la polarisation du fond diffus cosmologique
No full textCosmology has witnessed remarkable progress in recent years with more and more precise observations of different probes, including galaxy surveys and observations of cosmic microwave background, consistently supporting the standard model of cosmology. The ΛCDM model provides an accurate description of the large-scale structure and evolution of the Universe. However, a growing challenge to the ΛCDM model arises from local measurements of the Hubble constant, which quantifies the expansion rate of the Universe at present time. The value of the Hubble constant inferred from type IA supernovae is 5σ discrepant with the most precise determination of the Hubble constant from the CMB. This thesis explores different hypothesis that were proposed to alleviate the tension. First, this difference may have arised from unmodelled instrumental effects in the CMB datasets. I present methods to quantify instrumental systematic effects by studying the consistency of CMB temperature and polarisation. The Hubble tension may also be a hint in favor of physics beyond the standard model. I discuss the constraints obtained from various CMB datasets on the Early Dark Energy scenario, a promising solution that induces a phase of accelerated expansion at early time. Lastly, I present the analysis status of the future data release from the Atacama Cosmology Telescope which will provide constraints on cosmology independent from Planck with a similar precision.La cosmologie a connu des progrès remarquables grâce aux mesures de plus en plus précises de différentes sondes cosmologiques telles que les relevés de galaxies, ou le fond diffus cosmologique, permettant l'émergence du modèle standard ΛCDM. Ce modèle fournit une description précise de la structure à grande échelle de l'Univers et de son évolution. Cependant, les mesures locales de la constante de Hubble, qui quantifie le taux d'expansion de l'Univers aujourd'hui, viennent le remettre en cause. La valeur de la constante de Hubble dérivée de l'observation des supernovae de type IA est en désaccord avec la mesure la plus précise de la constante de Hubble obtenue via le fond diffus cosmologique. Cette thèse explore différentes hypothèses qui ont été proposée pour expliquer la tension. Tout d'abord, la différence pourrait provenir d'effets instrumentaux non modélisés dans l'analyse du CMB. Je présente des méthodes pour quantifier les effets systématiques instrumentaux en étudiant la consistance entre les mesures de température et de polarisation du CMB. La tension de Hubble pourrait également être une indication en faveur de la nécessité d'aller au-delà du modèle standard. J'aborde également cette hypothèse en discutant des contraintes obtenues sur un modèle d'énergie noire primordiale, qui induirait une phase d'expansion accélérée dans l'Univers primordial. Je présente également un statut de l'analyse des spectres en puissance pour la future analyse cosmologique des données provenant du télescope ACT (Atacama Cosmology Telescope) qui devrait fournir des contraintes sur la cosmologie indépendantes de Planck avec une précision similaire
Cosmologie au-delà du modèle standard avec les mesures précises de la polarisation du fond diffus cosmologique
No full textCosmology has witnessed remarkable progress in recent years with more and more precise observations of different probes, including galaxy surveys and observations of cosmic microwave background, consistently supporting the standard model of cosmology. The ΛCDM model provides an accurate description of the large-scale structure and evolution of the Universe. However, a growing challenge to the ΛCDM model arises from local measurements of the Hubble constant, which quantifies the expansion rate of the Universe at present time. The value of the Hubble constant inferred from type IA supernovae is 5σ discrepant with the most precise determination of the Hubble constant from the CMB. This thesis explores different hypothesis that were proposed to alleviate the tension. First, this difference may have arised from unmodelled instrumental effects in the CMB datasets. I present methods to quantify instrumental systematic effects by studying the consistency of CMB temperature and polarisation. The Hubble tension may also be a hint in favor of physics beyond the standard model. I discuss the constraints obtained from various CMB datasets on the Early Dark Energy scenario, a promising solution that induces a phase of accelerated expansion at early time. Lastly, I present the analysis status of the future data release from the Atacama Cosmology Telescope which will provide constraints on cosmology independent from Planck with a similar precision.La cosmologie a connu des progrès remarquables grâce aux mesures de plus en plus précises de différentes sondes cosmologiques telles que les relevés de galaxies, ou le fond diffus cosmologique, permettant l'émergence du modèle standard ΛCDM. Ce modèle fournit une description précise de la structure à grande échelle de l'Univers et de son évolution. Cependant, les mesures locales de la constante de Hubble, qui quantifie le taux d'expansion de l'Univers aujourd'hui, viennent le remettre en cause. La valeur de la constante de Hubble dérivée de l'observation des supernovae de type IA est en désaccord avec la mesure la plus précise de la constante de Hubble obtenue via le fond diffus cosmologique. Cette thèse explore différentes hypothèses qui ont été proposée pour expliquer la tension. Tout d'abord, la différence pourrait provenir d'effets instrumentaux non modélisés dans l'analyse du CMB. Je présente des méthodes pour quantifier les effets systématiques instrumentaux en étudiant la consistance entre les mesures de température et de polarisation du CMB. La tension de Hubble pourrait également être une indication en faveur de la nécessité d'aller au-delà du modèle standard. J'aborde également cette hypothèse en discutant des contraintes obtenues sur un modèle d'énergie noire primordiale, qui induirait une phase d'expansion accélérée dans l'Univers primordial. Je présente également un statut de l'analyse des spectres en puissance pour la future analyse cosmologique des données provenant du télescope ACT (Atacama Cosmology Telescope) qui devrait fournir des contraintes sur la cosmologie indépendantes de Planck avec une précision similaire
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Two shadows on two backlights: forecasting the Ly- forest CMB Lensing bispectrum from ACT/SO/S4 & DESI
Full text linkWe forecast the sensitivity of future correlations between CMB lensing and
the Lyman- forest power spectrum. This squeezed-limit bispectrum probes
the connection between the Lyman- transmission and the underlying
large-scale matter density field. We recover the measured signal-to-noise (SNR)
ratio obtained with PlanckBOSS, and forecast a SNR of and
for DESI combined with ACT, SO and CMB-S4 respectively. For DESI and
SO/CMB-S4, the correlation should be detectable at SNR in 5 redshift
bins, useful for distinguishing our signal from several contaminants.Indeed,
our forecast is affected by large theoretical uncertainties in the current
modeling of the signal and its contaminants, such as continuum misestimation
bias or damped-Lyman- absorbers. Quantifying these more accurately will
be crucial to enable a reliable cosmological interpretation of this observable
in future measurements. We attempt to enumerate the features required in future
Lyman- forest simulations required to do so.Comment: 15 pages, 9 figures, Comments welcom
Two shadows on two backlights: forecasting the Ly- forest CMB Lensing bispectrum from ACT/SO/S4 & DESI
No full textInternational audienceWe forecast the sensitivity of future correlations between CMB lensing and the Lyman- forest power spectrum. This squeezed-limit bispectrum probes the connection between the Lyman- transmission and the underlying large-scale matter density field. We recover the measured signal-to-noise (SNR) ratio obtained with PlanckBOSS, and forecast a SNR of and for DESI combined with ACT, SO and CMB-S4 respectively. For DESI and SO/CMB-S4, the correlation should be detectable at SNR in 5 redshift bins, useful for distinguishing our signal from several contaminants.Indeed, our forecast is affected by large theoretical uncertainties in the current modeling of the signal and its contaminants, such as continuum misestimation bias or damped-Lyman- absorbers. Quantifying these more accurately will be crucial to enable a reliable cosmological interpretation of this observable in future measurements. We attempt to enumerate the features required in future Lyman- forest simulations required to do so
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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