Theoretical tools for atom laser beam propagation

We present a theoretical model for the propagation of non self-interacting atom laser beams. We start from a general propagation integral equation, and we use the same approximations as in photon optics to derive tools to calculate the atom laser beam propagation. We discuss the approximations that allow to reduce the general equation whether to a Fresnel-Kirchhoff integral calculated by using the stationary phase method, or to the eikonal. Within the paraxial approximation, we also introduce the ABCD matrices formalism and the beam quality factor. As an example, we apply these tools to analyse the recent experiment by Riou et al. [Phys. Rev. Lett. 96, 070404 (2006)]

Coûts environnementaux du développement périurbain : impact des configurations urbaines et des choix résidentiels

[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAM [Axe_IRSTEA]DTAM1-REPRO [Axe_IRSTEA]DTAM-QT1-INEGALITESCe projet de recherche part du constat que la littérature existante sur la durabilité des espaces périurbains n'a pas apporté de réponse sur deux points particuliers. En premier lieu, la question du transport est généralement considérée du seul point de vue du transport de personnes, dans une optique d'équilibre partiel dans laquelle le transport des biens produits et consommés dans la ville n'est pas pris en compte. Or la théorie économique récente, dans le cadre des modèles d'économie géographique, montre que la localisation des ménages est étroitement liée à celle des entreprises, et que les configurations existant à l'équilibre dépendent fortement des interrelations entre ces deux catégories d'agents économiques. En d'autres termes, s'il est indispensable de considérer les choix résidentiels des ménages pour analyser les flux de transport engendrés par ces derniers, il est tout aussi indispensable de tenir compte des conséquences de ces localisations résidentielles sur la localisation des entreprises, et aussi des effets en retour des localisations des entreprises sur la distribution spatiale des ménages. Cette question fait l'objet du premier axe de notre recherche. En second lieu, les travaux existants négligent en général le fait que les espaces périurbains accueillent des ménages de catégories sociales variées qui ont des comportements différents en termes de déplacement. Or, il semble important de proposer une analyse du développement périurbain intégrant la question du choix résidentiel des ménages en fonction de leur catégorie sociale, ceci afin de dresser des pistes d'évolution possible des flux de transport engendrés par les espaces périurbains. C'est ce qui est développé dans le second axe de notre recherche. Enfin, ces analyses portant sur la localisation résidentielle des différentes catégories socio-professionnelles nous amènent aussi à analyser la ségrégation résidentielle dans les zones périurbaines, en lien avec les déterminants des choix de localisation résidentielle des ménages. / This research starts from the premise that the existing literature on the sustainability of suburban areas has not provided answers to two specific points. Firstly, the issue of transport is generally considered from the point of view of the transport of persons, in a partial equilibrium framework in which the transport of goods produced and consumed in the city is not taken into account. But the recent economic theory, with the new economic geography models, shows that the location of households is closely linked to the location of firms, and that the existing equilibrium configurations depend strongly on the interrelationships between these two categories of agent. In other words, it is essential to consider the residential choices of households to analyze the traffic flows they generate, but it is also necessary to take into account the consequences of these residential locations on the location of firms and the feedback effects of corporate locations on the spatial distribution of households. This question is the subject of the first axis of our research. Second, existing studies generally neglect the fact that the suburban areas host various social groups of households that have different behaviors in terms of mobility. However, it seems important to provide an analysis of suburban development incorporating the issue of residential choices of households according to their social class, in order to establish avenues for possible evolution of transport flows generated by the suburban areas. This is what is developed in the second focus of our research. Finally, the residential location of the different socio-professional categories is also analyzed in terms of urban segregation, in relation with the determinants of households’ choices

Bayesian workflow for disease transmission modeling in Stan

This tutorial shows how to build, fit, and criticize disease transmission models in Stan, and should be useful to researchers interested in modeling the SARS-CoV-2 pandemic and other infectious diseases in a Bayesian framework. Bayesian modeling provides a principled way to quantify uncertainty and incorporate both data and prior knowledge into the model estimates. Stan is an expressive probabilistic programming language that abstracts the inference and allows users to focus on the modeling. As a result, Stan code is readable and easily extensible, which makes the modeler's work more transparent. Furthermore, Stan's main inference engine, Hamiltonian Monte Carlo sampling, is amiable to diagnostics, which means the user can verify whether the obtained inference is reliable. In this tutorial, we demonstrate how to formulate, fit, and diagnose a compartmental transmission model in Stan, first with a simple Susceptible-Infected-Recovered (SIR) model, then with a more elaborate transmission model used during the SARS-CoV-2 pandemic. We also cover advanced topics which can further help practitioners fit sophisticated models; notably, how to use simulations to probe the model and priors, and computational techniques to scale-up models based on ordinary differential equations

Direct and indirect effects of the COVID-19 pandemic on mortality in Switzerland

The direct and indirect impact of the COVID-19 pandemic on population-level mortality is of concern to public health but challenging to quantify. Using data for 2011–2019, we applied Bayesian models to predict the expected number of deaths in Switzerland and compared them with laboratory-confirmed COVID-19 deaths from February 2020 to April 2022 (study period). We estimated that COVID-19-related mortality was underestimated by a factor of 0.72 (95% credible interval [CrI]: 0.46–0.78). After accounting for COVID-19 deaths, the observed mortality was −4% (95% CrI: −8 to 0) lower than expected. The deficit in mortality was concentrated in age groups 40–59 (−12%, 95%CrI: −19 to −5) and 60–69 (−8%, 95%CrI: −15 to −2). Although COVID-19 control measures may have negative effects, after subtracting COVID-19 deaths, there were fewer deaths in Switzerland during the pandemic than expected, suggesting that any negative effects of control measures were offset by the positive effects. These results have important implications for the ongoing debate about the appropriateness of COVID-19 control measures

Matter-wave laser Interferometric Gravitation Antenna (MIGA): New perspectives for fundamental physics and geosciences

The MIGA project aims at demonstrating precision measurements of gravity with cold atom sensors in a large scale instrument and at studying the associated applications in geosciences and fundamental physics. The first stage of the project (2013-2018) will consist in building a 300-meter long optical cavity to interrogate atom interferometers and will be based at the low noise underground laboratory LSBB in Rustrel, France. The second stage of the project (2018-2023) will be dedicated to science runs and data analyses in order to probe the spatio-temporal structure of the local gravity field of the LSBB region, a site of high hydrological interest. MIGA will also assess future potential applications of atom interferometry to gravitational wave detection in the frequency band $\sim 0.1-10$ Hz hardly covered by future long baseline optical interferometers. This paper presents the main objectives of the project, the status of the construction of the instrument and the motivation for the applications of MIGA in geosciences. Important results on new atom interferometry techniques developed at SYRTE in the context of MIGA and paving the way to precision gravity measurements are also reported.Comment: Proceedings of the 50th Rencontres de Moriond "100 years after GR", La Thuile (Italy), 21-28 March 2015 - 10 pages, 5 figures, 23 references version2: added references, corrected typo

Nested R^\widehat R: Assessing the convergence of Markov chain Monte Carlo when running many short chains

The growing availability of hardware accelerators such as GPUs has generated interest in Markov chains Monte Carlo (MCMC) workflows which run a large number of chains in parallel. Each chain still needs to forget its initial state but the subsequent sampling phase can be almost arbitrarily short. To determine if the resulting short chains are reliable, we need to assess how close the Markov chains are to convergence to their stationary distribution. The $\widehat R$ statistic is a battle-tested convergence diagnostic but unfortunately can require long chains to work well. We present a nested design to overcome this challenge, and introduce tuning parameters to control the reliability, bias, and variance of convergence diagnostics

Pulmonary-Resident Memory Lymphocytes: Pivotal Orchestrators of Local Immunity Against Respiratory Infections

There is increasing evidence that lung-resident memory T and B cells play a critical role in protecting against respiratory reinfection. With a unique transcriptional and phenotypic profile, resident memory lymphocytes are maintained in a quiescent state, constantly surveying the lung for microbial intruders. Upon reactivation with cognate antigen, these cells provide rapid effector function to enhance immunity and prevent infection. Immunization strategies designed to induce their formation, alongside novel techniques enabling their detection, have the potential to accelerate and transform vaccine development. Despite most data originating from murine studies, this review will discuss recent insights into the generation, maintenance and characterisation of pulmonary resident memory lymphocytes in the context of respiratory infection and vaccination using recent findings from human and non-human primate studies