Non-monotonic temperature evolution of dynamic correlations in glass-forming liquids

The viscosity of glass-forming liquids increases by many orders of magnitude if their temperature is lowered by a mere factor of 2-3 [1,2]. Recent studies suggest that this widespread phenomenon is accompanied by spatially heterogeneous dynamics [3,4], and a growing dynamic correlation length quantifying the extent of correlated particle motion [5-7]. Here we use a novel numerical method to detect and quantify spatial correlations which reveal a surprising non-monotonic temperature evolution of spatial dynamical correlations, accompanied by a second length scale that grows monotonically and has a very different nature. Our results directly unveil a dramatic qualitative change in atomic motions near the mode-coupling crossover temperature [8] which involves no fitting or indirect theoretical interpretation. Our results impose severe new constraints on the theoretical description of the glass transition, and open several research perspectives, in particular for experiments, to confirm and quantify our observations in real materials.Comment: 7 page

Particulate matter exposure during pregnancy is associated with birth weight, but not gestational age, 1962-1992: a cohort study

<p>Abstract</p> <p>Background</p> <p>Exposure to air pollutants is suggested to adversely affect fetal growth, but the evidence remains inconsistent in relation to specific outcomes and exposure windows.</p> <p>Methods</p> <p>Using birth records from the two major maternity hospitals in Newcastle upon Tyne in northern England between 1961 and 1992, we constructed a database of all births to mothers resident within the city. Weekly black smoke exposure levels from routine data recorded at 20 air pollution monitoring stations were obtained and individual exposures were estimated via a two-stage modeling strategy, incorporating temporally and spatially varying covariates. Regression analyses, including 88,679 births, assessed potential associations between exposure to black smoke and birth weight, gestational age and birth weight standardized for gestational age and sex.</p> <p>Results</p> <p>Significant associations were seen between black smoke and both standardized and unstandardized birth weight, but not for gestational age when adjusted for potential confounders. Not all associations were linear. For an increase in whole pregnancy black smoke exposure, from the 1^st(7.4 μg/m³) to the 25^th(17.2 μg/m³), 50^th(33.8 μg/m³), 75^th(108.3 μg/m³), and 90^th(180.8 μg/m³) percentiles, the adjusted estimated decreases in birth weight were 33 g (SE 1.05), 62 g (1.63), 98 g (2.26) and 109 g (2.44) respectively. A significant interaction was observed between socio-economic deprivation and black smoke on both standardized and unstandardized birth weight with increasing effects of black smoke in reducing birth weight seen with increasing socio-economic disadvantage.</p> <p>Conclusions</p> <p>The findings of this study progress the hypothesis that the association between black smoke and birth weight may be mediated through intrauterine growth restriction. The associations between black smoke and birth weight were of the same order of magnitude as those reported for passive smoking. These findings add to the growing evidence of the harmful effects of air pollution on birth outcomes.</p

Développement d'un banc de caractérisation des émissions de particules, lors d'une usure par abrasion : application à un solide plan

L'usure de produits finis (nano-structurés ou non) est susceptible de provoquer l'émission de particules de taille nanométrique ou submicronique. Le risque induit par ce phénomène devient une préoccupation croissante en termes d'enjeux sanitaires et environnementaux (rapport ANSES, 2010). L'émissivité des produits finis peut être étudiée en chambre d'émission, dans des conditions maîtrisées en termes de mécanismes de vieillissement et d'énergie mise en jeu, et de sécurité. L'INERIS mène des travaux sur cette thématique en particulier pour l'étude du vieillissement par abrasion de produits finis et la caractérisation de l'aérosol produit. Cette communication présente un dispositif expérimental qui met en oeuvre d'un abrasimètre Taber linéaire, et les résultats obtenus sur un matériau de construction (une brique). Des études préliminaires ont tout d'abord permis de tester différents types de sollicitation et de quantifier l'énergie apportée. Un lien étroit entre ces paramètres et les caractéristiques de l'aérosol produit (quantité et tailles des particules) a pu être établi . Il a été utilisé la Microscopie Electronique à Transmission (MET) pour caractériser plus finement l'aérosol produit. En effet cette technique permet de compléter les informations temps réel (taille et de nombre de particule) par des informations qualitatives, voire semi-quantitatives, sur la nature chimique et physique et la morphologie des particules émises. Les résultats expérimentaux montrent que l'usure d'une brique génère un aérosol très polydispersé dont la granulométrie se situe essentiellement entre 0,5 µm à 6,7 µm, ce que confirme l'observation des prélèvements d'aérosol en MET. Les particules produites sont amorphes, de forme plutôt compacte, et présentent une morphologie qui évoque un processus d'arrachement par fracturation. Ceci est en accord avec la nature chimique des matériaux constitutifs de la brique (silico-aluminates) et la nature de la sollicitation (usure par abrasif très dur)

New Optical Constants of Titan and Pluto Aerosol Analogs from the Visible to the Infrared and Their Use to Analyze Cassini and New Horizons Observations

International audienceIn planetary atmospheres like those of Titan and Pluto, complex organic solid particles are produced from photolysis and radiolysis processes. These aerosols form haze layers, and also settle to the surface. Their presence can significantly impact the atmospheric and surface spectra obtained by remote-sensing instruments like the Visible Infrared Mapping Spectrometer and Composite Infrared Spectrometer on Cassini and the Ralph instrument on New Horizons. Numerous laboratory experiments have been developed to simulate and investigate the chemistry occurring in Titan's and more recently Pluto's atmosphere, resulting in the formation of these solid particles. Many different analytical diagnostics have been used to characterize laboratory-generated analogs (or tholins) of Titan and Pluto aerosols and provide insight on their formation pathways and physical, chemical, and spectral properties. In particular, the complex refractive indices (n + ik, or optical constants) of a variety of Titan and Pluto tholins have been measured over the years. These optical constants describe how the tholins interact with light (transmission, reflection, absorption, scattering), and are therefore fundamental input parameters to simulate haze particles in radiative transfer models used for the interpretation of observational data. These radiative transfer models can leverage the optical constants of different tholins to explore a wide range of compositions, allowing for improved fits and interpretations of observational data resulting in a better understanding of Titan's and Pluto's atmosphere and surface compositions. Here we present the results of several optical constants studies: 1. The measurements of optical constants of Titan tholins produced from plasma chemistry in N2:CH4-based gas mixtures in the NASA Ames COSmIC Facility from the Visible to the Near Infrared (0.4–1.6 µm) and their use in a new analysis of Cassini VIMS observations[1]. 2. The measurements of optical constants of Pluto tholins produced in N2:CH4:CO gas mixtures in COSmIC from 0.4 to 1.6 µm and their use in a new analysis of New Horizons Ralph observations[2,3]. 3. The preliminary results of a comparative analysis of two Titan tholin samples produced from plasma chemistry in N2:CH4 gas mixtures in two different experimental facilities: the LATMOS PAMPRE experiment and the NASA Ames COSmIC facility, and measured from 0.4 to 300 µ

New Optical Constants of Titan and Pluto Aerosol Analogs from the Visible to the Infrared and Their Use to Analyze Cassini and New Horizons Observations

International audienceIn planetary atmospheres like those of Titan and Pluto, complex organic solid particles are produced from photolysis and radiolysis processes. These aerosols form haze layers, and also settle to the surface. Their presence can significantly impact the atmospheric and surface spectra obtained by remote-sensing instruments like the Visible Infrared Mapping Spectrometer and Composite Infrared Spectrometer on Cassini and the Ralph instrument on New Horizons. Numerous laboratory experiments have been developed to simulate and investigate the chemistry occurring in Titan's and more recently Pluto's atmosphere, resulting in the formation of these solid particles. Many different analytical diagnostics have been used to characterize laboratory-generated analogs (or tholins) of Titan and Pluto aerosols and provide insight on their formation pathways and physical, chemical, and spectral properties. In particular, the complex refractive indices (n + ik, or optical constants) of a variety of Titan and Pluto tholins have been measured over the years. These optical constants describe how the tholins interact with light (transmission, reflection, absorption, scattering), and are therefore fundamental input parameters to simulate haze particles in radiative transfer models used for the interpretation of observational data. These radiative transfer models can leverage the optical constants of different tholins to explore a wide range of compositions, allowing for improved fits and interpretations of observational data resulting in a better understanding of Titan's and Pluto's atmosphere and surface compositions. Here we present the results of several optical constants studies: 1. The measurements of optical constants of Titan tholins produced from plasma chemistry in N2:CH4-based gas mixtures in the NASA Ames COSmIC Facility from the Visible to the Near Infrared (0.4–1.6 µm) and their use in a new analysis of Cassini VIMS observations[1]. 2. The measurements of optical constants of Pluto tholins produced in N2:CH4:CO gas mixtures in COSmIC from 0.4 to 1.6 µm and their use in a new analysis of New Horizons Ralph observations[2,3]. 3. The preliminary results of a comparative analysis of two Titan tholin samples produced from plasma chemistry in N2:CH4 gas mixtures in two different experimental facilities: the LATMOS PAMPRE experiment and the NASA Ames COSmIC facility, and measured from 0.4 to 300 µ

Familial melanoma: Clinical factors associated with germline CDKN2A mutations according to the number of patients affected by melanoma in a family

International audienc

TIC & handicap

Quelles contributions les technologies de l'information et de la communication peuvent-elles apporter à une meilleure insertion des personnes en situation de handicap ? Les articles et témoignages de ce numéro apportent chacun une réponse à cette question

On the New Optical Constants Database (OCdb) and its Importance for the Interpretation of Observational Data

International audienceThe Optical Constants database (ocdb.smce.nasa.gov) came online in February 2023 and provides complex refractive indices of laboratory-generated organic refractory materials and ices relevant to (exo)planetary and astrophysical environments. The goal of the OCdb is to centralize published optical constants data to facilitate both their access by the scientific community and their use to analyze observational data returned by space missions and ground-based observatories. Computational tools are also under development to facilitate scientific use of the available OCdb optical constants data sets. Investigators generating laboratory optical constants are therefore encouraged to contribute their data to OCdb in order to increase the availability of their data and to enhance the scientific effectiveness of the database. Optical constants are critical input parameters in models (e.g., radiative transfer, atmospheric, and reflectance spectral models) that are used to simulate the absorption, reflection, and scattering of light due to solid materials present in planetary and astrophysical environments (planets, their satellites, exoplanets, asteroids, comets, protoplanetary disks, etc.), and are key to the compositional interpretation of observations. We will first present the infrastructure of the OCdb and show how to use and contribute to it. We will introduce the two large NASA projects, namely, the Laboratory Astrophysics Directed Work Package and the NASA Center for Optical Constants, that have been instrumental in (i) developing the OCdb, (ii) generating planetary- and astrophysics-relevant ices and organic refractory materials from gas and ice irradiation in the laboratory, and (iii) determining their optical constants for inclusion in OCdb. We will also present two studies that are making use of these optical constants to interpret observations of Titan's atmosphere and Pluto's surface. These studies show the importance of measuring optical constants of laboratory-generated materials, and their impact on the models used to analyze and interpret astronomical observations. These studies also demonstrate the essential role of such a database and the need for optical constants of a broad range of materials and wavelengths to enable the scientific community and to maximize the scientific return from space missions (e.g., Cassini, New Horizons, SOFIA, JWST)

On the New Optical Constants Database (OCdb) and its Importance for the Interpretation of Observational Data

International audienceThe Optical Constants database (ocdb.smce.nasa.gov) came online in February 2023 and provides complex refractive indices of laboratory-generated organic refractory materials and ices relevant to (exo)planetary and astrophysical environments. The goal of the OCdb is to centralize published optical constants data to facilitate both their access by the scientific community and their use to analyze observational data returned by space missions and ground-based observatories. Computational tools are also under development to facilitate scientific use of the available OCdb optical constants data sets. Investigators generating laboratory optical constants are therefore encouraged to contribute their data to OCdb in order to increase the availability of their data and to enhance the scientific effectiveness of the database. Optical constants are critical input parameters in models (e.g., radiative transfer, atmospheric, and reflectance spectral models) that are used to simulate the absorption, reflection, and scattering of light due to solid materials present in planetary and astrophysical environments (planets, their satellites, exoplanets, asteroids, comets, protoplanetary disks, etc.), and are key to the compositional interpretation of observations. We will first present the infrastructure of the OCdb and show how to use and contribute to it. We will introduce the two large NASA projects, namely, the Laboratory Astrophysics Directed Work Package and the NASA Center for Optical Constants, that have been instrumental in (i) developing the OCdb, (ii) generating planetary- and astrophysics-relevant ices and organic refractory materials from gas and ice irradiation in the laboratory, and (iii) determining their optical constants for inclusion in OCdb. We will also present two studies that are making use of these optical constants to interpret observations of Titan's atmosphere and Pluto's surface. These studies show the importance of measuring optical constants of laboratory-generated materials, and their impact on the models used to analyze and interpret astronomical observations. These studies also demonstrate the essential role of such a database and the need for optical constants of a broad range of materials and wavelengths to enable the scientific community and to maximize the scientific return from space missions (e.g., Cassini, New Horizons, SOFIA, JWST)