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

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.

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

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

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

The Effect of ECB Monetary Policies on Interest Rates and Volumes

This paper assesses the transmission of ECB monetary policies, conventional and unconventional, to both interest rates and lending volumes or bond issuance for three types of different economic agents through five different markets: sovereign bonds at 6-month, 5-year and 10-year horizons, loans to non-financial corporations, and housing loans to households, during the financial crisis, and for the four largest economies of the Euro Area. We look at three different unconventional tools: excess liquidity, longer-term refinancing operations and securities held for monetary policy purposes following the decomposition of the ECB’s Weekly Financial Statements. We first identify series of ECB policy shocks at the Euro Area aggregate level by removing the systematic component of each series and controlling for announcement effects. We second include these exogenous shocks in country-specific structural VAR, in which we control for the credit demand side. The main result is that only the pass-through from the ECB rate to interest rates has been effective. Unconventional policies have had uneven effects and primarily on interest rates

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

A novel approach of a fully inkjet printed SnO₂-based gas sensor on a flexible foil

International audienceIn recent years, printed and flexible gas sensors have quickly emerged as an innovative area of great interest because of their lightness and low cost. These flexible sensors can be easily integrated into autonomous systems for many applications such as smart food packaging and premature disease detection. In this paper, a novel approach was applied to manufacture a fully inkjet-printed gas sensor on a flexible polymeric foil. Platinum heater and gold electrodes were printed on the top side of the substrate, separated by a thin insulating layer of printed polyimide. An aqueous sol-gel process was adopted to synthesize nanosized SnO2-based sol that guaranty a crystallization at 350 °C, which is entirely consistent with the polyimide foil. Then, the sol was transformed into a stable ink and inkjet printed over the gold electrodes. The printability of different inks was optimized to ensure flawless ejection of droplets, and the complex physico-chemical interactions between the inks and different interfaces were controlled to get well-defined patterns with high resolution. Finally, electrical measurements of the printed sensor were performed to characterize the response and the sensitivity to different concentrations of ethanol, ammonia and carbon monoxide gases, at working temperature of 300 °C, in dry and wet air