Linear elastic fracture mechanics predicts the propagation distance of frictional slip

When a frictional interface is subject to a localized shear load, it is often (experimentally) observed that local slip events initiate at the stress concentration and propagate over parts of the interface by arresting naturally before reaching the edge. We develop a theoretical model based on linear elastic fracture mechanics to describe the propagation of such precursory slip. The model's prediction of precursor lengths as a function of external load is in good quantitative agreement with laboratory experiments as well as with dynamic simulations, and provides thereby evidence to recognize frictional slip as a fracture phenomenon. We show that predicted precursor lengths depend, within given uncertainty ranges, mainly on the kinetic friction coefficient, and only weakly on other interface and material parameters. By simplifying the fracture mechanics model we also reveal sources for the observed non-linearity in the growth of precursor lengths as a function of the applied force. The discrete nature of precursors as well as the shear tractions caused by frustrated Poisson's expansion are found to be the dominant factors. Finally, we apply our model to a different, symmetric set-up and provide a prediction of the propagation distance of frictional slip for future experiments

Validation of spatial multicriteria decision analysis of the risk of highly avian influenza H5N1 in Thailand and its application in Cambodia

Highly Pathogenic Avian Influenza H5N1 (HPAI) virus is now considered endemic in several Asian countries as well as in Egypt. In Cambodia, the virus has been circulating in poultry population since 2004, with a dramatic effect on farmers' livelihoods. HPAI H5N1 is also a public health threat as 56 human cases (including 39 deaths) have been identified so far in this country. In Thailand, no outbreaks have been recently reported, but surveillance and control are still important to prevent any new HPAI H5N1 incursion. Risk maps may efficiently inform disease surveillance and control systems. However, in countries with a lack of primary care systems, their production can be hampered by lack of reliable disease data. In such situations, knowledge-driven modeling methods including spatial multicriteria decision analysis (MCDA) have been identified as an alternative to classical statistical approaches. However, these methods can appear somehow subjective and poorly connected to real data. Validation of knowledge-driven maps is therefore an essential and challenging task. The present study used MCDA to map HPAI H5N1 risk in domestic poultry in Southeast Asia. In a first step, 3 MCDA models (2 with weights calculated from literature review, and 1 with weights attributed by experts) were built and applied to Thailand, where reliable HPAI H5N1 data exist. In a second step, the best model was applied to Cambodia where the number of poultry cases is under-estimated due to poor reporting by farmers. For each country, the same set of 10 predictors was selected. Predictors included density of farm and free-grazing ducks, backyard chicken density, proportion of rice fields and number of rice crops in a 2- and 5-km radius, wetlands density, altitude, human population density and proximity to major cities. 14 and 11 experts were contacted in Thailand and Cambodia, respectively. They were asked i) to choose a relationship between each selected variable and the risk of HPAI H5N1 and ii) to fill a pairwise comparison matrix, where each variable was compared with the others, relative to its importance, on a scale from 1 (“extremely less important”) to 9 (“extremely more important”).Weights for each variable were computed from this matrix through an Analytical Hierarchy Process. All variables values were standardized on a scale from 0 to 1 before aggregation, which was realized using weighted linear combination (WLC). A sensitivity analysis based on the one-factor-at-a-time method was then performed to assess the robustness of the results with respect to expert choices. The predictive ability of each of the 3 models was quantitatively evaluated in Thailand by calculating the Area Under the Curve (AUC) from ROC analysis, based on actual HPAI H5N1 data. Analysis was implemented using the ArcGIS, IDRISI, and R softwares. Results showed that the expert-based model had an excellent prediction capacity in Thailand (AUC = 0.97, CI 95: 0.96-0.97), which was significantly higher to literature-based models (AUC ranging from 0.74 to 0.77). Applied to Cambodia, the expert-based model pointed out a higher risk of HPAI H5N1 in the surroundings of the Tonl´e Sap Lake, as well as in provinces located in the lower Mekong basin bordering Vietnam. Visual inspection of the map showed that high risk areas were consistent with places where poultry outbreaks have been reported. These two high risk areas could correspond to distinct epidemiological mechanisms, with high densities of free grazing ducks participating to virus maintenance in the lakesides and transboundary poultry movements favoring periodic virus introductions from Vietnam. Results suggest that expert opinion could be used to produce risk maps in countries with limited outbreaks data, and that these maps could be a starting point to define risk-based surveillance programs. (Texte intégral

La désinflation manquante : un phénomène américain uniquement ?

Le comportement de l’inflation aux États-Unis lors de la crise économique de 2008-2009, qui n’a pas suivi les prédictions d’une courbe de Phillips classique, a donné lieu au phénomène de « missing disinflation ». Nous évaluons si ce phénomène a également eu lieu en zone euro. Nous trouvons que l’inflation en zone euro a bien suivi les prédictions d’une courbe de Phillips, mais qu’il existe de fortes divergences intra-européennes, entre d’un côté l’Allemagne et la France, où l’inflation prédite par une courbe de Phillips est proche de l’inflation réalisée, et d’un autre l’Italie, l’Espagne et la Grèce, où dans la période qui précède la crise financière, l’inflation observée n’est pas en ligne avec l’inflation prédite. La crise de 2009 semble avoir réduit partiellement ces déviations

Faraday and Cotton-Mouton Effects of Helium at λ=1064\lambda = 1064 nm

We present measurements of the Faraday and the Cotton-Mouton effects of helium gas at $\lambda =~1064$\,nm. Our apparatus is based on an up-to-date resonant optical cavity coupled to longitudinal and transverse magnetic fields. This cavity increases the signal to be measured by more than a factor of 270\,000 compared to the one acquired after a single path of light in the magnetic field region. We have reached a precision of a few percent both for Faraday effect and Cotton-Mouton effect. Our measurements give for the first time the experimental value of the Faraday effect at $\lambda$=\,1064\,nm. This value is compatible with the theoretical prediction. Concerning Cotton-Mouton effect, our measurement is the second reported experimental value at this wavelength, and the first to agree at better than 1$\sigma$ with theoretical predictions.Comment: Submitted to Phys. Rev.

A spatial zero-inflated modelling approach for assessing the H5N1 surveillance system in Thailand

In Thailand, the major epidemic lasted from July 2004 to May 2005. The H5N1 surveillance system has often been assumed to be very efficient during this epidemic. However, no quantitative assessment of the Thai H5N1 surveillance program has been so far undertaken. Here, we propose to use zero-inflated (ZI) models to analyze unilist capture-recapture surveillance data collected during the 2004 epidemic at subdistrict level, to identify the factors driving the presence/absence of the disease and those influencing the detection process. ZI models use the number of detections of infection in the different sites for estimating the total number of infected sites, including those where infection was never detected. We considered each subdistrict of the country as the epidemiological unit (site), and that each H5N1 outbreak notified during the 2004 epidemic constituted a detection of the disease in the site. Therefore, our count dataset focused on the number of detected outbreaks in each subdistrict. To derive the real number of infected sub-districts, we fitted a ZI Poisson model (ZIP) and a ZI negative binomial model (ZINB) to our dataset. We tested the residuals for spatial autocorrelation, proved it was significant and thus added a spatial autocorrelation term in the model. As expected, the spatial ZINB fitted the data better than the spatial ZIP, suggesting the presence of overdispersion in the counts of detections. Derived from the spatial ZINB model, we were able to estimate the real number of infected subdistricts during the epidemic and the sensitivity of detection at sub-district level. We also identified the most important factors that determine the presence/absence of the disease in subdistricts (density of human population and density of free grazing ducks), and influence the detection process (density of free grazing ducks and density of native chicken). (Texte intégral

Assessing the Interest Rate and Bank Lending Channels of ECB Monetary Policies

This paper assesses the transmission of ECB monetary policies, conventional and unconventional, to both interest rates and lending volumes for the money market, sovereign bonds at 6-month, 5-year and 10-year horizons, loans inferior and superior to 1M€ to non-financial corporations, cash and housing loans to households, and deposits, during the financial crisis and in the four largest economies of the Euro Area. We first identify two series of ECB policy shocks at the euro area aggregated level and then include them in country-specific structural VAR. The main result is that only the pass-through from the ECB rate to interest rates has been really effective, consistently with the existing literature, while the transmission mechanism of the ECB rate to volumes and of quantitative easing (QE) operations to interest rates and volumes has been null or uneven over this sample. One argument to explain the differentiated pass-through of ECB monetary policies is that the successful pass-through from the ECB rate to interest rates, which materialized as a huge decrease in interest rates during the sample period, had a negative effect on the supply side of loans, and offset itself its potential positive effects on lending volumes

Laser induced densification of cerium gadolinium oxide: application to single-chamber solid oxide fuel cells

International audienceIn single-chamber solid oxide fuel cells (SC-SOFC), anode and cathode are placed in a gas chamber where they are exposed to a fuel/air mixture. Similarly to conventional dual-chamber SOFC, the anode and the cathode are separated by an electrolyte. However, as in the SC-SOFC configuration the electrolyte does not play tightness role between compartments, this one can be a porous layer. Nevertheless, it is necessary to have a diffusion barrier to prevent the transportation of hydrogen produced locally at the anode to the cathode that reduces fuel cell performances. This study aims to obtain directly a diffusion barrier through the surface densification of the electrolyte Ce0.9Gd0.1O1.95 (CGO) by a laser treatment. KrF excimer laser and Yb fiber laser irradiations were used at different fluences and number of pulses to modify the density of the electrolyte coating. Microstructural characterizations confirmed the modifications on the surface of the electrolyte for appropriate experimental conditions showing either grain growth or densified but cracked surfaces. Gas permeation and electrical conductivities of the modified electrolyte were evaluated. Finally SC-SOFC performances were improved for the cells presenting grain growth at the electrolyte surface

La désinflation manquante est-elle un phénomène américain uniquement ?

La dynamique de l’inflation après la crise de 2007-2009 est-elle atypique ? Selon Paul Krugman : « si la réaction de l’inflation (ndlr : aux Etats-Unis) avait été la même à la suite de la Grande Récession que lors des précédentes crises économiques, nous aurions dû nous trouver aujourd’hui en pleine déflation… Nous ne le sommes pas. » En effet, après 2009, l’inflation aux Etats-Unis est demeurée étonnamment stable au regard de l’évolution de l’activité réelle. Ce phénomène a été qualifié de « désinflation manquante ». Un tel phénomène s’observe-t-il dans la zone euro ? [Premier paragraphe

Status of the BMV experiment

In this contribution we present the status of the BMV experiment whose goal is to measure the vacuum magnetic birefringence