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We propose a model of intergenerational transmission of education wherein children belong to either highly educated or low-educated families. Children choose the intensity of their social activities while parents decide how much educational effort to exert. Using data on adolescents in the United States, we structurally estimate this model and find that, on average, children's homophily acts as a complement to the educational effort of highly educated parents but as a substitute for the educational effort of low-educated parents. We also perform some counterfactual policy simulations. We find that policies that subsidize kids' socialization efforts can backfire for low-educated students because they tend to increase their interactions with other low-educated students (i.e., homophily), which reduces the education effort of their parents and, thus, their chance of becoming educated. On the contrary, policies that increase heterophily by favoring friendship links between kids from different education backgrounds can be effective in reducing the education gap betweenthem.

Road surface reflection tables ( r-tables) relate scene illuminance to luminance seen by a car driver. They are important for many road lighting tasks accounting for road optical properties, such as new illumination design, new pavement texture or lighting design software, to reduce energy consumption without losses on safety and visibility. This paper aims first at finding a space of basis functions to describe r-tables. From a database of 34 r-tables covering a large variety of pavements, a principal component analysis allows to construct a 33-dimensional space, basis for r-table representations. From that statistical model, a method is exposed to retrieve r-table from a luminance map. The estimated r-table is then used to calculate a reconstructed luminance map. Road lighting quality criteria are also derived and they demonstrate the relevancy of the estimated r-table. Finally the model is tested with noisy input data and it remains stable and reliable, making it applicable with experimental luminance maps.

We present a flexible model of wage dynamics where information about job openings is transmitted through social networks. We show that the individuals' wages dynamic is positively associated across time and that this result holds outside the stationary distribution, and under observed and unobserved heterogeneity. We present an empirical application using the British Household Panel Survey by exploiting direct information about individual's social networks. We find that having more employed friends leads to more job offers, but to slightly lower offered wages. We also find that non-relative friends are more helpful than relatives, and that individuals benefit relatively more from their male friends.

Contrary to the conventional wisdom in the literature on United States foreign policy, there was no consensus within the George W. Bush Administration on the parallel between the reconstruc...

International audience; Optimization of lighting installations should be a priority in order to reduce energy consumption and obtrusive light while providing optimal visibility conditions for road users. For the design of lighting installations, it is assumed that the road has homogeneous photometric characteristics and only one viewing angle is used. There are often significant differences between the design of lighting installations and their actual performance. In order to examine whether these differences are due to the photometry of the road, this study proposes metrics to assess the influence of road heterogeneity and observation angle. These metrics have been used on many measurements conducted on site and in the laboratory for different pavements. A calculation engine has been developed to realize road lighting design with several r-tables in the same calculation or for different observation angles. Thus, this study shows that a root mean squared deviation (RMSD) calculation, including average luminance and uniformities associated with different r-tables, is directly correlated to a normalized root mean squared deviation (NRMSD) calculation between these r-tables. With these proposed metrics it is possible to optimize lighting installation while taking into account different types of urban surfaces and the diversity of users.

We explore the asymptotic properties of strategic models of network formation in very large populations. Specifically, we focus on (undirected) exponential random graph models. We want to recover a set of parameters from the individuals' utility functions using the observation of a single, but large, social network. We show that, under some conditions, a simple logit-based estimator is coherent, consistent and asymptotically normally distributed under a weak version of homophily. The approach is compelling as the computing time is minimal and the estimator can be easily implemented using pre-programmed estimators available in most statistical packages. We provide an application of our method using the Add Health database.

Chaque annee, une part significative des depenses gouvernementales est consacree au sport de niveau professionnel ou amateur. Certains analystes affirment que ces investissements contribuent fortement au succes d’un pays aux Jeux olympiques. Nous presentons une analyse econometrique visant a estimer l’effet causal de l’investissement public dans le sport sur le nombre de medailles remportees par un pays. Nous utilisons des modeles de comptage avec effets fixes et variable instrumentale. Selon les specifications retenues, l’elasticite du nombre de medailles obtenues par un pays lors de Jeux olympiques d’ete par rapport aux investissements publics qu’il a effectues varie entre 0,23 et 0,38.

A large effort has been made over the past 10 years to promote the operational use of probabilistic or ensemble streamflow forecasts. Numerous studies have shown that ensemble forecasts are of higher quality than deterministic ones. Many studies also conclude that decisions based on ensemble rather than deterministic forecasts lead to better decisions in the context of flood mitigation. Hence, it is believed that ensemble forecasts possess a greater economic and social value for both decision makers and the general population. However, the vast majority of, if not all, existing hydro-economic studies rely on a cost–loss ratio framework that assumes a risk-neutral decision maker. To overcome this important flaw, this study borrows from economics and evaluates the economic value of early warning flood systems using the well-known Constant Absolute Risk Aversion (CARA) utility function, which explicitly accounts for the level of risk aversion of the decision maker. This new framework allows for the full exploitation of the information related to a forecasts' uncertainty, making it especially suited for the economic assessment of ensemble or probabilistic forecasts. Rather than comparing deterministic and ensemble forecasts, this study focuses on comparing different types of ensemble forecasts. There are multiple ways of assessing and representing forecast uncertainty. Consequently, there exist many different means of building an ensemble forecasting system for future streamflow. One such possibility is to dress deterministic forecasts using the statistics of past error forecasts. Such dressing methods are popular among operational agencies because of their simplicity and intuitiveness. Another approach is the use of ensemble meteorological forecasts for precipitation and temperature, which are then provided as inputs to one or many hydrological model(s). In this study, three concurrent ensemble streamflow forecasting systems are compared: simple statistically dressed deterministic forecasts, forecasts based on meteorological ensembles, and a variant of the latter that also includes an estimation of state variable uncertainty. This comparison takes place for the Montmorency River, a small flood-prone watershed in southern central Quebec, Canada. The assessment of forecasts is performed for lead times of 1 to 5 days, both in terms of forecasts' quality (relative to the corresponding record of observations) and in terms of economic value, using the new proposed framework based on the CARA utility function. It is found that the economic value of a forecast for a risk-averse decision maker is closely linked to the forecast reliability in predicting the upper tail of the streamflow distribution. Hence, post-processing forecasts to avoid over-forecasting could help improve both the quality and the value of forecasts.

Thermokarst lakes are widespread and diverse across permafrost regions and they are considered significant contributors to global greenhouse gas emissions. Paleoenvironmental reconstructions documenting the inception and development of these ecologically important water bodies are generally limited to Pleistocene-age permafrost deposits (Yedoma) of Siberia, Alaska, and the western Canadian Arctic. Here we present the gradual transition from syngenetic ice-wedge polygon terrains to a thermokarst lake in the Eastern Canadian Arctic. We combine geomorphological surveys with paleolimnological reconstructions from sediment cores in an effort to characterize local landscape evolution from terrestrial to freshwater environment. Located on an ice-rich and organic-rich polygonal terrace, the studied lake is now evolving through active thermokarst, as revealed by subsiding and eroding shores, and was likely created by water pooling within a pre-existing topographic depression. Organic sedimentation in the valley started during the mid-Holocene, as documented by the oldest organic debris found at the base of one sediment core and dated at 4.8 kyr BP. Local sedimentation dynamics were initially controlled by fluctuations in wind activity, local moisture and vegetation growth/accumulation, as shown by alternating loess (silt) and peat layers. Fossil diatom assemblages were likewise influenced by local hydro-climatic conditions and reflect a broad range of substrates available in the past (both terrestrial and aquatic). Such conditions likely prevailed until ~ 2000 BP, when peat accumulation stopped as water ponded the surface of degrading ice-wedge polygons, and the basin progressively developed into a thermokarst lake. Interestingly, this happened in the middle of the Neoglacial cooling period, likely under wetter-than-average conditions. Thereafter, the lake continued to develop as evidenced by the dominance of aquatic (both benthic and planktonic) diatom taxa in organic-rich lacustrine muds. Based on these interpretations, we present a four-stage conceptual model of thermokarst lake development during the late Holocene, including some potential future trajectories. Such a model could be applied to other formerly glaciated syngenetic permafrost landscapes.

I present a model of conformism in social networks that incorporates both peer effects and self-selection. I find that equilibrium behaviors are linked through the Laplacian matrix of the equilibrium network. I show that conformism has positive social value and that social welfare can be bounded by network centrality and connectivity measures. I apply the model using empirical data on high school student participation in extracurricular activities. I find that the local effects of conformism (i.e. endogenous peer effect for a fixed network structure) range from 7.5% to 45%, depending on the number of peers that an individual has. Simulations show that the optimal policies of an inequality-averse policy-maker change in relation to the size of a school. Small schools should encourage shy students to integrate more with other students, while large schools should focus on promoting role models within the school.

I look at the equilibrium effects of homophily in network formation games having positive externalities. I show that very weak preferences for network effects (such as preference for being part of a clique) may result in very high levels of homophily at equilibrium. I present an empirical procedure that allows an evaluation of the role of network effects on the observed level of homophily in the data. I apply my method to the formation of friendship networks in the USA. I show that the focus on a random utility model implies that network effects are small and have a negligible contribution to the observed racial homophily in friendship networks.

We consider a decision maker who is responsible for issuing flood warnings for the population. The population is uncertain about the credibility of the warnings and adjusts its beliefs following false alerts or missed events. We show that low credibility leads the decision maker to issue warnings for lower probabilities of flooding. In practice, those probabilities are provided by hydrological forecasts. We therefore use our model to compare welfare under alternative real-world hydro- logical forecasts. We find that when forecasts include non-realistic extreme scenarios, the economy may remain stuck in a state characterized by many false alerts and poor credibility.

The pedestrian is particularly exposed in the field of accidentology and has been the object of studies in diverse disciplines such as psychology or the safety of transportation. Working from models based on cognitive neurosciences and social cognition, this pilot study has for objective to investigate the perception of the pedestrian by the driver. It combines visual saliency measures taken from the recording of road scenes, with data resulting from the discourse retranscription of 11 drivers viewing these same scenes. To describe and understand the relations between these two types of data, the robust canonical correlation analysis was applied. This method brings to light the links between the overall visual environment and the drivers' verbatim. Although exploratory, these results show the link between the measures of saliency and the elements noticed by the drivers and can be interpreted as illustrating the complementarity of the processes bottom-up and top- down in perception. It can be observed that the pedestrian stands out when the driver is not evolving in a crowded environment and if the interaction with the former takes place in a pedestrian zone or in a courteous manner. Thus the drivers show themselves particularly sensitive to the legitimate/illegitimate character in the driving situation which seems to focus their attention and their feelings. Thus this analysis allows to emphasise on a multidimensional construct of the act of driving, integrating the vision, the social representations and the feelings of the drivers according to the contexts of driving.

I present a behavioural model of network formation with positive network externalities in which individuals have preferences for being part of a clique. The behavioural model leads to an associated supermodular (Topkis, 1979) normal form game. I show that the behavioural model converges to the greatest Nash equilibrium of the associated normal-form game. I propose an approximate Bayesian computation (ABC) framework, using original summary statistics, to make inferences about individuals' preferences, and provide an illustration using data on high school friendships.

In this paper, we model network formation and network interactions under a unified framework. The key feature of our model is to allow individuals to respond to incentives that stem from interaction benefits of certain activities when they choose friends (network links), while capturing homophily in terms of unobserved characteristic variables in network formation and activities. There are two advantages of this modeling approach: first, one can evaluate whether incentives from certain interactions are important factors for friendship formation or not. Second, in addition to homophily effects in terms of unobserved characteristics, inclusion of incentive effects in the network formulation also corrects possible friendship selection bias on activity outcomes under network interactions. A theoretical foundation of this unified model is based on a sub-game perfect equilibrium of a two-stage game. A tractable Bayesian MCMC approach is proposed for the estimation of the model, and we demonstrate its finite sample performance in a simulation study. We apply the model to study empirically American high school students' friendship networks from the Add Health dataset. We consider two activity variables, GPA and smoking frequency, and find a significant incentive effect from GPA, but not from smoking, on friendship formation. These results suggest that the benefit of interactions in academic learning is an important factor for friendship formation, whereas the interaction benefit of smoking is not. On the other hand, from the perspective of network interactions, both GPA and smoking frequency are subject to significant positive interaction (peer) effects.

I propose a simple simulation procedure for large games with multiple equilibria. The simulation procedure is based on a best-response dynamic. The implied equilibrium selection mechanism is intuitive: more stable equilibria are selected with higher probability.

This chapter studies some recent developments and challenges in the empirics of the effects of social networks. The authors focus in particular on researchers’ ability to make policy recommendations based on a standard linear econometric model. The chapter examines the potential compatibility between this type of econometric model and a microeconomic theoretical approach based on fundamentals, such as preferences, technology, and decision processes. The chapter discusses sources of identification for the social multiplier as well as for the identity of the key player. The authors study the possibility of testing endogeneity in network formation. The chapter analyzes the use of proxy variables and their impact for the causal interpretation of peer effect coefficients. This analysis suggests that greater care should be taken in grounding econometric network models to sound and credible theoretical underpinnings.

We provide the first empirical application of a new approach proposed by Lee (2007) to estimate peer effects in a linear-in-means model when individuals interact in groups. Assuming sufficient group size variation, this approach allows to control for correlated effects at the group level and to solve the simultaneity (reflection) problem. We clarify the intuition behind identification of peer effects in the model. We investigate peer effects in student achievement in French, Science, Mathematics and History in secondary schools in the Province of Quebec (Canada). We estimate the model using conditional maximum likelihood and instrumental variables methods. We find some evidence of peer effects. The endogenous peer effect is large and significant in Math but imprecisely estimated in the other subjects. Some contextual peer effects are also significant. In particular, for most subjects, the average age of peers has a negative effect on own test score. Using calibrated Monte Carlo simulations, we find that high dispersion in group sizes helps with potential issues of weak identification.

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.

International audience; Fog conditions are the cause of severe car accidents in European western countries because of the poor induced visibility. Its occurrence and intensity are still very difficult to forecast for weather services. Furthermore, visibility determination relies on expensive instruments and does not ease their dissemination. Lately, it has been demonstrated the benefit of infrared cameras to detect and to identify objects in fog while visibility is too low for eye detection. Over the past years, such cameras have become more cost effective. A research program between IFSTTAR and Cerema studied the possibility to retrieve visibility distance in a fog tunnel during its natural dissipation. The purpose of this work is to retrieve atmospheric visibility with a technique based on the combined use of infrared thermography, Principal Components Analysis (PCA) and Partial Least-Square (PLS) regression applied to infrared images.

An epoxy-based crosslinkable polymer functionalized with nonlinear optical (NLO) photochromic dye known as Red Acid Magly was polarly oriented via thermally-assisted all-optical poling to enhance the photostability of the induced order. During the writing (seeding) process the film was cross-linked by heating with a hot-plate and irradiated simultaneously by the coherent superposition of the 1.06 μm fundamental and 0.532 μm second harmonic beams of a nanosecond pulsed Nd:YAG laser. We demonstrate that crosslinking between the polymer matrix and the pendant chromophore groups induced during the thermally-assisted all-optical poling procedure results in a stable light-induced second order susceptibility.

We study some recent developments and challenges in the empirics of the effects of social networks. We focus in particular on researchers’ ability to make policy recommendations based on a standard linear econometric model. We examine the potential compatibility between this type of econometric model and a microeconomic theoretical approach based on fundamentals, such as preferences, technology and decision processes. We discuss sources of identification for the social multiplier as well as for the identity of the key player. We study the possibility of testing endogeneity in network formation. We analyse the use of proxy variables and their impact for the causal interpretation of the peer effect coefficients. Our analysis suggests that greater care should be taken in grounding econometric network models to sound and credible theoretical underpinnings.

Chaque année, une part significative des dépenses gouvernementales est consacrée au sport de niveau professionnel ou amateur. Certains analystes affirment que ces investissements contribuent fortement au succès d’un pays aux Jeux olympiques (JO). Nous présentons une analyse économétrique du nombre de médailles obtenues aux JO. Nous introduisons l’investissement public en sport comme facteur potentiellement important du nombre de médailles remportées par un pays, en prenant soin de contrôler pour l’hétérogénéité inobservable des pays participants aux JO. Nous présentons, à notre connaissance, la première modélisation du succès olympique utilisant des spécifications de comptage (count data model) en panel estimées à l’aide de variables instrumentales et captant les caractéristiques individuelles et invariantes des nations. Selon les spécifications du modèle retenues, un pays aux caractéristiques moyennes aurait dû accroître son investissement de 72 à 94 millions de dollars, ceteris paribus, afin d’obtenir une médaille supplémentaire aux JO d’été de Londres en 2012.

Fog conditions are the cause of severe car accidents in western countries because of the poor induced visibility. Its forecast and intensity are still very difficult to predict by weather services. Infrared cameras allow to detect and to identify objects in fog while visibility is too low for eye detection. Over the past years, the implementation of cost effective infrared cameras on some vehicles has enabled such detection. On the other hand pattern recognition algorithms based on Canny filters and Hough transformation are a common tool applied to images. Based on these facts, a joint research program between IFSTTAR and Cerema has been developed to study the benefit of infrared images obtained in a fog tunnel during its natural dissipation. Pattern recognition algorithms have been applied, specifically on road signs which shape is usually associated to a specific meaning (circular for a speed limit, triangle for an alert, …). It has been shown that road signs were detected early enough in images, with respect to images in the visible spectrum, to trigger useful alerts for Advanced Driver Assistance Systems.

International audience; An infrared system has been developed to monitor transport infrastructures in a stand-alone configuration. It is based on low cost infrared thermal cameras linked with a calculation unit in order to produce a corrected thermal map of the surveyed structure at a selected time step. With the inline version, the data collected feed simplified radiative models running a GPU. With the offline version, the thermal map can be corrected when data are collected under different atmospheric conditions up to foggy night conditions. A model for radiative transmission prediction is proposed and limitations are addressed. Furthermore, the results obtained by image and signal processing methods with data acquired on the transport infrastructure opened to traffic are presented. Finally, conclusions and perspectives for new implementation and new functionalities are presented and discussed.

We explore the asymptotic properties of pairwise stables networks (Jackson and Wolinsky, 1996). Speci fically, we want to recover a set of parameters from the individuals' utility functions using the observation of a single pairwise stable network. We develop Pseudo Maximum Likelihood estimator and show that it is consistent and asymptotically normally distributed under a very weak version of homophily. The approach is compelling as it provides explicit, easy-to-check conditions on the admissible set of preferences. Moreover, the method is easily implementable using pre-programmed estimators available in most statistical packages. We provide an application of our method using the Add Health database.

De nombreux outils de recherche en matière d'adhérence et de visibilité sont étudiés et développés dans le cadre de l'opération de recherche "Prévisions et alertes de situations météo-routières dégradées" (PALM) de l'IFSTTAR. Des outils doivent, à moyen ou long terme, fournir des aides à la décision aux gestionnaires, ou bien encore des aides à la conduite aux automobilistes. Les résultats portent alors autant sur la détermination de la visibilité à l'aide de caméras, sur la mesure de la quantité résiduelle de fondants routiers, que sur les modèles numériques de prévision météorologique.

The universality of the halo mass function is investigated in the context of dark energy cosmologies. This widely used approximation assumes that the mass function can be expressed as a function of the matter density omega_m and the rms linear density fluctuation sigma only, with no explicit dependence on the properties of dark energy or redshift. In order to test this hypothesis we run a series of 15 high-resolution N-body simulations for different cosmological models. These consists of three LCDM cosmologies best fitting WMAP-1, 3 and 5 years data, and three toy-models characterized by a Ratra-Peebles quintessence potential with different slopes and amounts of dark energy density. These toy models have very different evolutionary histories at the background and linear level, but share the same sigma8 value. For each of these models we measure the mass function from catalogues of halos identified in the simulations using the Friend-of-Friend (FoF) algorithm. We find redshift dependent deviations from a universal behaviour, well above numerical uncertainties and of non-stochastic origin, which are correlated with the linear growth factor of the investigated cosmologies. Using the spherical collapse as guidance, we show that such deviations are caused by the cosmology dependence of the non-linear collapse and virialization process. For practical applications, we provide a fitting formula of the mass function accurate to 5 percents over the all range of investigated cosmologies. We also derive an empirical relation between the FoF linking parameter and the virial overdensity which can account for most of the deviations from an exact universal behavior. Overall these results suggest that the halo mass function contains unique cosmological information since it carries a fossil record of the past cosmic evolution.

We present a model for the effective magnetic properties of metamaterials composed of gyromagnetic inclusions in which electromagnetic retardation is accounted for. The formalism is used to derive the effective permeability tensor of axially magnetized ferromagnetic-metallic wires. The complex size-dependent gyromagnetic response of a single wire subjected to an external dynamic magnetic field is first obtained and expressed compactly in terms of renormalized permeability components. We then incorporate this response into an extended Maxwell-Garnett homogenization procedure to yield the effective permeability tensor of the array. An effective external susceptibility tensor, which includes dipolar interactions explicitly, is further introduced to describe the ferromagnetic resonance response of finite-size arrays placed in microwave resonant cavities. We examine the impact of electromagnetic retardation on the resonance, antiresonance, and linewidth and compare the magnetic response expected for conducting and insulating magnetic wires. The conditions under which arrays of ferromagnetic wires may exhibit a region of negative effective permeability are established and are found to be dependent on both the intrinsic magnetic and size-dependent eddy-current losses, thus providing useful guidelines for the design of magnetic metamaterials. The proposed formalism is sufficiently general to be applied or extended to various systems of interest.

Some recent advances in wire-type micro-structured electric metamaterials and nano-structured magnetic metamaterials are presented. It is shown that both exhibit rich macroscopic properties leading to novel microwave concepts and devices. The micro and nano scales may be combined in multi-scale metamaterials with unprecedented functionalities.

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.

We present a model for the effective permeability tensor of nonsaturated arrays of axially magnetized bistable ferromagnetic wires based on a Maxwell-Garnett formalism generalized to include the case of two oppositely magnetized wire populations. Explicit expressions for the complex diagonal and off-diagonal components of the effective permeability tensor are derived to describe the magnetic response of the array and its dependence upon microwave frequency and external magnetic field. The model accounts for the geometrical parameters and the static magnetic configuration of the array, as well as the shape and intrinsic properties of the wires. We incorporate the effect of the static and dynamic interwire dipolar interactions and obtain explicit expressions for the position and relative amplitude of the two ferromagnetic resonance peaks associated with the effective permeability of nonsaturated arrays. The two absorption peaks arise due to the presence of the up and down wire populations, which are predominantly excited by the right-handed and left-handed circularly polarized magnetic field components of the electromagnetic wave propagating inside the array. Excellent agreement is found between the model and experimental results obtained from $S$-parameter broadband microstrip line measurements. Small discrepancies when the array is magnetically unsaturated or when the peaks are close to each other are discussed and attributed to spatial variations of the local interaction field not accounted for by the present model.