(Finite) statistical size effects on compressive strength

The larger structures are, the lower their mechanical strength. Already discussed by Leonardo da Vinci and Edmé Mariotte several centuries ago, size effects on strength remain of crucial importance in modern engineering for the elaboration of safety regulations in structural design or the extrapolation of laboratory results to geophysical field scales. Under tensile loading, statistical size effects are traditionally modeled with a weakest-link approach. One of its prominent results is a prediction of vanishing strength at large scales that can be quantified in the framework of extreme value statistics. Despite a frequent use outside its range of validity, this approach remains the dominant tool in the field of statistical size effects. Here we focus on compressive failure, which concerns a wide range of geophysical and geotechnical situations. We show on historical and recent experimental data that weakest-link predictions are not obeyed. In particular, the mechanical strength saturates at a nonzero value toward large scales. Accounting explicitly for the elastic interactions between defects during the damage process, we build a formal analogy of compressive failure with the depinning transition of an elastic manifold. This critical transition interpretation naturally entails finite-size scaling laws for the mean strength and its associated variability. Theoretical predictions are in remarkable agreement with measurements reported for various materials such as rocks, ice, coal, or concrete. This formalism, which can also be extended to the flowing instability of granular media under multiaxial compression, has important practical consequences for future design rules

Preface: the 2020 edition of the XXIVth ISPRS congress

International audienc

A step-economical multicomponent synthesis of 3D-shaped aza-diketopiperazines and their drug-like chemical space analysis

A rapid and atom economical multicomponent synthesis of complex aza-diketopiperazines (aza-DKPs) driven by Rh(I)-catalyzed hydroformylation of alkenylsemicarbazides is described. Combined with catalytic amounts of acid and the presence of nucleophilic species, this unprecedented multicomponent reaction (MCR) enabled the formation of six bonds and a controlled stereocenter from simple substrates. The efficacy of the strategy was demonstrated with a series of various allyl-substituted semicarbazides and nucleophiles leading to the preparation of 3D-shaped bicyclic aza-DKPs. Moreover, an analysis of their 3D molecular descriptors and “drug-likeness” properties highlights not only their originality in the chemical space of aza-heterocycles but also their great potential for medicinal chemistry

Green Edge ice camp campaigns : understanding the processes controlling the under-ice Arctic phytoplankton spring bloom

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797∘ N, 63.7895∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies

The specific surface area and chemical composition of diamond dust near Barrow, Alaska

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95687/1/jgrd17349.pd

Valeur pronostique de l'index de perméabilité vasculaire pulmonaire et de l'eau pulmonaire extravasculaire mesurés par thermodilution transpulmonaire en unité de réanimation pédiatrique

Le monitorage hémodynamique invasif est un sujet d'actualité en réanimation depuis sa remise en cause récente, du fait de son absence de bénéfice en terme de survie et de sa potentielle morbidité. Les réanimateurs, notamment pédiatres, sont dans l'attente de la technique idéale : fiable, non invasive, simple à utiliser et à mettre en place, disponible quels que soient l'âge et le poids du patient. Dans cette optique, les différentes méthodes de monitorage disponibles sont présentées dans une première partie, en mettant en valeur leurs avantages et leurs inconvénients. Parmi toutes ces techniques, le système PiCCO®, associant thermodilution transpulmonaire et analyse du contour de l'onde de pouls, semble bénéficier, pour la population pédiatrique, du meilleur compromis bénéfice / risque. Le principe et les caractéristiques de cette méthode sont détaillés dans la deuxième partie de ce travail. Outre le débit cardiaque, d'autres variables hémodynamiques sont accessibles par ce système. Dans une étude prospective, présentée en troisième partie de ce travail, nous avons étudié la valeur pronostique de 2 paramètres obtenus par thermodilution transpulmonaire: l'eau pulmonaire extravasculaire (EPEI) et l'index de perméabilité vasculaire pulmonaire (IPVP). 19 patients d'âge pédiatrique ont été inclus. La mortalité globale était de 37%. L'EPEI et I'IPVP n'étaient pas corrélés à la mortalité, ni aux marqueurs de gravité classiques (lactates, PRISM), ni aux paramètres gazométriques ou d'oxygénation. Notre étude démontre cependant que le système PiCCO® est utilisable en routine, au quotidien, dans les services de réanimation pédiatrique, sur l'ensemble de la population pédiatrique.NANCY1-SCD Medecine (545472101) / SudocNANCY1-Bib. numérique (543959902) / SudocSudocFranceF

Interaction of an ultrashort optical pulse with a metallic nanotip: A Green dyadic approach

International audienceWe consider the interaction of an ultrashort optical pulse with a metallic nanotip. In the framework of the Green dyadic method, we calculate the time-dependent electric field in the vicinity of the metallic nano-object. The electric field enhancement at the tip apex, its temporal evolution, and its dependence upon the polarization of the incident electric field are addressed. By comparing the case of tungsten and gold nanotips, we show that significantly larger electric field enhancements can be obtained with the latter and point out different temporal responses. Our description provides the time-dependent spatial distribution of the electric field around metallic nano-objects of arbitrary geometries which is the first step to describe light-matter interaction in recently developed laser-driven femtosecond electron nanosources or recent results in ultrafast nanoplasmonics

Creation of a tramway line for the city of Qom in the Republic of Iran

Ces mémoires constituent un travail à visée pédagogique dans le cadre d’un diplôme universitaire et ne constituent en aucun cas une étude susceptible d’être ré-utilisée dans un cadre commercial ou scientifique. Son contenu n’engage que la responsabilité de ses auteurs.Dans le cadre du Mastère Spécialisé « Systèmes de Transports Ferroviaires et Urbains » de l'École des Ponts ParisTech, les étudiants réalisent un projet de transport dans une ville étrangère. Il s’agit d’une étude de faisabilité, similaire aux études amont en phase d’émergence, que réalisent les grands bureaux d’études comme Systra ou Parsons. Ce travail collaboratif, faisant jouer les complémentarités des savoir-faire, prend la forme d’un mini-mémoire.Les résumés de ces mini-mémoires sont regroupés dans un « Urban and Railway transport studies Yearbook », réalisé par la Direction de la Documentation de l'École des Ponts ParisTech en collaboratoire avec Françoise Manderscheid, responsable du Mastère Spécialisé.The agreement signed on July 14th 2015 is a historical event for Iran, allowing the country to join the international community after the end of penalties. Iran is indeed a promising country with a potential market of 80 million people and a well‐ educated middle-class. President Rohani has even stated that the government’s priority is the country’s economic recovery of. The program unlocking Iranian assets and reopening borders for international trade should thus encourage foreign direct investment, increasing trade and stimulating growth. Sanctions relief increase public expectations of economic improvement and international commitment. The transport field has been neglected for years, in favor of industrial fields such as oil and gas, metals and minerals. The city of Qom has been particularly suffering from alarming problems of pollution, congestion and high road accidents, whereas public transport field is still very limited. Monorail and metro projects have already been launched, but they are still under construction. Our project starts with a diagnosis at a national scale to describe geographic, environmental, institutional, economic and socio‐demographic aspects. Then, we focus on specifics of the city of Qom in order to better understand the local expectations. After making an assessment of transportation modes in Qom, we will analyze the mobility in the city to decide if we need to develop a third urban transport system. This will lead us to identify two main corridors in the city, carriers of flows, allowing us to draw a horizontal alignment for this public transportation line. Afterwards, a study of the transport demand on this axis will help us choose the relevant means of transport. A proposal for a complete tramway system will be given, including a technical feasibility study for Infrastructure and Rolling Stock structural subsystems and an operational feasibility study for Operations and Maintenance functional subsystems. Finally, an economic feasibility study will be submitted, taking into account cost and revenue aspects to assess the socio‐economic and financial profitability of such a project. Lastly we will propose project funding options and conditions necessary to support the launch of the project with regard to redirecting transport policy, in order to make it financially viable

Caractérisation en spectroscopie de photoémission de nanodiamants produits par différents modes de synthèse présentant différentes chimies de surface

International audienc

Milled nanodiamonds overproduce solvated electrons while scavenging hydroxyl radicals under gamma irradiation

International audienceAmong the different nanodiamonds, milled nanodiamonds (MNDs) from high pressure high temperature (HPHT) synthesis exhibit a crystalline quality close to the bulk diamond, making it a serious candidate for quantum or energy-related fields. In this study, MNDs aqueous suspensions with oxidized (MND-Ox) and hydrogenated (MND-H) surface chemistries were irradiated with gamma-rays. Using optimized nanoparticle-compatible methods, we revealed that MNDs in suspension enhance the production of solvated electrons under irradiation, with a higher yield for MND-H. Also, for the first time, a surface chemistry-dependent scavenging effect of hydroxyl radicals was highlighted for this type of nanodiamonds