Political Cycles : Issue Ownership and the Opposition Advantage

We propose a two dimensional infinite horizon model of public consumption in which investments are decided by a winner-take-all election. Investments in the two public goods create a linkage across periods. We follow the idea of issue ownership introduced by Petrocik (1996) in considering parties with different specialties. We show that the incumbent party vote share decreases the longer it stays in power. The median voter is generally not indifferent between the two parties and, when she is moderate enough, no party can maintain itself in power for ever. This result holds when the parties' main objective is to win the election and is compatible with a large range of candidates sub-objectives, that may change from one election to the next. Finally, the more parties are specialized and the more public policies have long-term effects, the more political cycles are likely to occur. ...French Abstract : Nous proposons un modèle de consommation publique à horizon infini. Les investissements engagés dans la fourniture de deux biens publics sont déterminés par les élections. Ces investissements créent un lien entre les élections successives. Nous suivons l'idée introduite par Petrocik (1996) selon laquelle les partis "possèdent" certains thèmes, en considérant qu'ils ont des spécialités différentes. Nous montrons que la part des voix du parti au pouvoir décroît entre deux élections. L'électeur médian n'est généralement pas indifférent entre les deux partis et, lorsqu'il est suffisamment modéré, aucun parti ne peut se maintenir indéfiniment au pouvoir. Ce résultat est valide lorsque l'objectif principal des partis est de gagner l'élection et est compatible avec un grand ensemble de sous objectifs, qui peuvent changer d'une élection à l'autre. Finalement, plus les partis sont spécialisés et plus les politiques ont des effets de long terme, plus les cycles politiques sont susceptibles d'apparaître.CYCLES; ALTERNATION; ISSUE OWNERSHIP; PUBLIC GOODS; OPPOSITION

Report of the sensor cooler technology panel

The Sensor Cooler Technology Panel identified three major areas in which technology development must be supported in order to meet the system performance requirements for the Astrotech 21 mission set science objectives. They are: long life vibration free refrigerators; mechanical refrigeration for 2 K to 5 K; and flight testing of emerging prototype refrigerators. A development strategy and schedule were recommended for each of the three areas

Limits of flexural wave absorption by open lossy resonators: reflection and transmission problems

The limits of flexural wave absorption by open lossy resonators are analytically and numerically reported in this work for both the reflection and transmission problems. An experimental validation for the reflection problem is presented. The reflection and transmission of flexural waves in 1D resonant thin beams are analyzed by means of the transfer matrix method. The hypotheses, on which the analytical model relies, are validated by experimental results. The open lossy resonator, consisting of a finite length beam thinner than the main beam, presents both energy leakage due to the aperture of the resonators to the main beam and inherent losses due to the viscoelastic damping. Wave absorption is found to be limited by the balance between the energy leakage and the inherent losses of the open lossy resonator. The perfect compensation of these two elements is known as the critical coupling condition and can be easily tuned by the geometry of the resonator. On the one hand, the scattering in the reflection problem is represented by the reflection coefficient. A single symmetry of the resonance is used to obtain the critical coupling condition. Therefore the perfect absorption can be obtained in this case. On the other hand, the transmission problem is represented by two eigenvalues of the scattering matrix, representing the symmetric and anti-symmetric parts of the full scattering problem. In the geometry analyzed in this work, only one kind of symmetry can be critically coupled, and therefore, the maximal absorption in the transmission problem is limited to 0.5. The results shown in this work pave the way to the design of resonators for efficient flexural wave absorption

Reliable ABC model choice via random forests

Approximate Bayesian computation (ABC) methods provide an elaborate approach to Bayesian inference on complex models, including model choice. Both theoretical arguments and simulation experiments indicate, however, that model posterior probabilities may be poorly evaluated by standard ABC techniques. We propose a novel approach based on a machine learning tool named random forests to conduct selection among the highly complex models covered by ABC algorithms. We thus modify the way Bayesian model selection is both understood and operated, in that we rephrase the inferential goal as a classification problem, first predicting the model that best fits the data with random forests and postponing the approximation of the posterior probability of the predicted MAP for a second stage also relying on random forests. Compared with earlier implementations of ABC model choice, the ABC random forest approach offers several potential improvements: (i) it often has a larger discriminative power among the competing models, (ii) it is more robust against the number and choice of statistics summarizing the data, (iii) the computing effort is drastically reduced (with a gain in computation efficiency of at least fifty), and (iv) it includes an approximation of the posterior probability of the selected model. The call to random forests will undoubtedly extend the range of size of datasets and complexity of models that ABC can handle. We illustrate the power of this novel methodology by analyzing controlled experiments as well as genuine population genetics datasets. The proposed methodologies are implemented in the R package abcrf available on the CRAN.Comment: 39 pages, 15 figures, 6 table

Les ajustements des prix de production en France et dans la zone euro. Une synthèse à partir de données quantitatives et qualitatives.

Les modifications de l’environnement économique constituent pour les entreprises des incitations à modifier leurs prix. On observe toutefois que l’ampleur de ces révisions est assez modérée et que près d’une fois sur deux, ces révisions consistent en une baisse de prix.rigidité des prix, prix de production, fréquence de changement de prix.

Identification dynamique de robots avec un modèle de frottement sec fonction de la charge et de la vitesse

International audienceEn robotique, les pertes dans la chaine d'actionnement articulaire des robots sont généralement prises en compte dans le modèle dynamique par un effort de frottement visqueux proportionnel à la vitesse et par un effort constant de frottement sec. Pourtant, d'après la loi de Coulomb, le frottement sec de glissement varie avec les efforts de contact dans les éléments de transmission. Ainsi, cet effet est à prendre en compte pour les systèmes mécaniques soumis à de fortes variations de charge. Cet article présente un nouveau modèle dynamique dans lequel l'effort de frottement sec est proportionnel à la charge selon un coefficient dépendant de la vitesse. Une nouvelle procédure permet d'identifier ce modèle à partir de mesures faites sur le robot réalisant diverses trajectoires avec différents cas de charge. Une validation expérimentale est réalisée sur un robot industriel