Risk Aversion and International Environmental Agreements

We introduce uncertainty and risk aversion to the study of international environmental agreements. We consider a simple model with identical agents and linear payoffs. We show that a stable treaty with positive action always exists. While uncertainty lowers the action of signatories, we find that it may increase participation. In addition, uncertainty may generate multiple equilibria. A treaty with low action and low participation may coexist with one with high action and high participation. Overall, and despite risk aversion, the impact of uncertainty on welfare may be positive. A reduction in uncertainty may hurt international cooperation.International Environmental Agreements, Risk Aversion, Uncertainty

Do Peers Affect Student Achievement? Evidence from Canada Using Group Size Variation

We provide the first empirical application of a new approach proposed by Lee (2007) to estimate peer effects in a linear-in-means model. This approach allows to control for group-level unobservables and to solve the reflection problem. We investigate peer effects in student achievement in Mathematics, Science, French and History in Quebec secondary schools. We estimate the model using maximum likelihood and instrumental variables methods. We find evidence of peer effects. The endogenous peer effect is positive, when significant, and some contextual peer effects matter. Using calibrated Monte Carlo simulations, we find that high dispersion in group sizes helps with potential issues of weak identification. Nous présentons une première application empirique d’une nouvelle approche développée par Lee (2007) pour estimer les effets de pairs dans un modèle linéaire-en-moyenne. Cette méthode permet de tenir compte des variables non-observées au niveau du groupe et de solutionner le problème de réflexion. Nous estimons les effets de pairs sur la performance scolaire (mesurée par les résultats aux épreuves du ministère de l’Éducation, du Loisir et du Sport) en Mathématiques, en Science, en Français et en Histoire dans les écoles secondaires du Québec. À cette fin, nous utilisons des méthodes de maximum de vraisemblance et de variables instrumentales. Nos résultats corroborent la présence d’effets de pairs. L’effet de pair endogène est positif, lorsqu’il est significatif. En particulier, une hausse d’un point dans la note moyenne de ses pairs accroît la note de l’élève de 0,5 en Français, de 0,65 en Histoire et 0,83 en Math (514). En outre, certains effets contextuels ont de l’importance. À partir de simulations Monte Carlo, nous trouvons qu’une grande variabilité dans la taille des groupes peut réduire les problèmes d’identification faible.peer effects, student achievement, reflection problem, effets de pairs, performance scolaire, problème de réflexion

Do Peers Affect Student Achievement? Evidence from Canada Using Group Size Variation

We provide the first empirical application of a new approach proposed by Lee (2007) to estimate peer effects in a linear-in-means model. This approach allows to control for group-level unobservables and to solve the reflection problem. We investigate peer effects in student achievement in Mathematics, Science, French and History in Quebec secondary schools. We estimate the model using maximum likelihood and instrumental variables methods. We find evidence of peer effects. The endogenous peer effect is positive, when significant, and some contextual peer effects matter. Using calibrated Monte Carlo simulations, we find that high dispersion in group sizes helps with potential issues of weak identification.reflection problem, student achievement, peer effects

Do Peers Affect Student Achievement? Evidence from Canada Using Group Size Variation

We provide the first empirical application of a new approach proposed by Lee (2007) to estimate peer effects in a linear-in-means model. The approach allows to control for group-level unobservables and to solve the reflection problem, without imposing ad hoc exclusion restrictions or requiring peers to be randomly assigned to groups. We investigate the presence of peer effects in student achievement in mathematics, science, french and history at the end of secondary school in the province of Quebec (Canada). We use an original dataset that covers three fourth of all schools in Quebec and contains test scores to the standardized provincial exam required for graduation. We estimate the model using both maximum likelihood and methods based on instrumental variables. We find evidence of peer effects. The endogenous peer effect is positive, when significant, and some contextual peer effects matter. Issues of weak identification that may be present in our estimates are analyzed using calibrated Monte Carlo simulations. We find that identification is much helped by a high variance in peer group sizes.Peer Effects, Student Achievement, Reflection Problem

Providing global public goods under uncertainty

We study how uncertainty and risk aversion affect international agreements to supply global public goods. We consider a benchmark model with homogeneous countries and linear payoffs. When countries directly contribute to a public good, uncertainty tends to lower signatories' efforts but may increase participation. Despite risk aversion, uncertainty may improve welfare. In contrast, when countries try to reduce a global public bad, uncertainty tends to increase signatories' efforts and decrease participation. In that case, an ex-ante reduction of uncertainty may have a large positive multiplier effect on welfare

Transmission tunnel assistée par défaut dans un détecteur infrarouge à multipuits quantiques

Session AffichesNational audienceOn étudie l'influence d'un défaut profond sur la transmission tunnel dans la zone à multipuits quantiques d'un photo-détecteur infrarouge. Dans le cadre d'un formalisme matriciel, le défaut est assimilé à une singularité de Dirac du potentiel

Miroirs de Bragg et microcavités en silicium poreux : effet de l'oxydation

session orale Ma1 « Composants passifs et Optique intégrée » [Ma1.1]National audienceDes structures verticales que sont des miroirs de Bragg et des microcavités ont été élaborées en silicium poreux et en silice poreuse. La silice poreuse est obtenue en oxydant le silicium poreux. Une étude préliminaire a permis d'étudier l'indice de réfraction des couches en silicium poreux avant et après oxydation, la vitesse de formation de ces couches et l'évolution de la variation de l'épaisseur après oxydation en fonction de la porosité initiale des couches. L'objectif de ce travail est d'anticiper l'évolution de la réponse spectrale de ces dispositifs due à l'oxydation

Active Microwave Circuit With Negative Group Delay

"©2007 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."International audienceIn this letter, we report on the design, simulation and implementation of an active negative group delay circuit that operates at 1 GHz with a group delay and a gain, respectively, around -2 ns and 2 dB. Analytical formulas are proposed to demonstrate that the adopted topology is able to simultaneously achieve negative group delay (NGD) and gain while fulfilling active device constraints. The theoretical and simulated results are both validated by frequency measurements of a two-stage active microwave circuit

Usefulness and pitfalls of MAA SPECT/CT in identifying digestive extrahepatic uptake when planning liver radioembolization

International audiencePURPOSE: Identifying gastroduodenal uptake of (99m)Tc-macroaggregated albumin (MAA), which is associated with an increased risk of ulcer disease, is a crucial part of the therapeutic management of patients undergoing radioembolization for liver tumours. Given this context, the use of MAA single photon emission computed tomography (SPECT)/CT may be essential, but the procedure has still not been thoroughly evaluated. The aim of this retrospective study was to determine the effectiveness of MAA SPECT/CT in identifying digestive extrahepatic uptake, while determining potential diagnostic pitfalls. METHODS: Overall, 139 MAA SPECT/CT scans were performed on 103 patients with different hepatic tumour types. Patients were followed up for at least 6 months according to standard requirements. RESULTS: Digestive, or digestive-like, uptake other than free pertechnetate was identified in 5.7% of cases using planar imaging and in 36.6% of cases using SPECT/CT. Uptake sites identified by SPECT/CT included the gastroduodenal region (3.6%), gall bladder (12.2%), portal vein thrombosis (6.5%), hepatic artery (6.5%), coil embolization site (2.1%) as well as falciform artery (5.0%). For 2.1% of explorations, a coregistration error between SPECT and CT imaging could have led to a false diagnosis by erroneously attributing an uptake site to the stomach or gall bladder, when the uptake actually occurred in the liver. CONCLUSION: SPECT/CT is more efficacious than planar imaging in identifying digestive extrahepatic uptake sites, with extrahepatic uptake observed in one third of scans using the former procedure. However, more than half of the uptake sites in our study were vascular in nature, without therapeutic implications. The risk of coregistration errors must also be kept in mind