Identifying distributional characteristics in random coefficients panel data models

We study the identification of panel models with linear individual-specific coefficients, when T is fixed. We show identification of the variance of the effects under conditional uncorrelatedness. Identification requires restricted dependence of errors, reflecting a trade-off between heterogeneity and error dynamics. We show identification of the density of individual effects when errors follow an ARMA process under conditional independence. We discuss GMM estimation of moments of effects and errors, and introduce a simple density estimator of a slope effect in a special case. As an application we estimate the effect that a mother smokes during pregnancy on child's birth weight.

Robust priors in nonlinear panel data models

Many approaches to estimation of panel models are based on an average or integrated likelihood that assigns weights to different values of the individual effects. Fixed effects, random effects, and Bayesian approaches all fall in this category. We provide a characterization of the class of weights (or priors) that produce estimators that are first-order unbiased. We show that such bias-reducing weights must depend on the data unless an orthogonal reparameterization or an essentially equivalent condition is available. Two intuitively appealing weighting schemes are discussed. We argue that asymptotically valid confidence intervals can be read from the posterior distribution of the common parameters when N and T grow at the same rate. Finally, we show that random effects estimators are not bias reducing in general and discuss important exceptions. Three examples and some Monte Carlo experiments illustrate the results.

Curvature and confinement effects for flame speed measurements in laminar spherical and cylindrical flames.

This paper discusses methods used to obtain laminar flame speeds in spherical laminar premixed flames. Most recent studies express the laminar flame consumption speed as ρb/ρudR/dt, where R is the flame radius and ρb/ρu is the ratio of the burnt to the fresh gas density (ρb is evaluated at chemical equilibrium and supposed to be constant). This paper investigates the validity of this assumption by reconsidering it in a more general framework. Other formulae are derived and tested on a DNS of cylindrical flames (methane/air and octane/air). Results show that curvature and confinement effects lead to variations of ρb and ρu and to significant errors on the flame speed. Another expression (first proposed by Bradley and Mitcheson in 1976) is derived where no density evaluation is required and only pressure and flame radius evolution are used. It is shown to provide more precise results for the consumption speed than ρb/ρudR/dt because it takes into account curvature and confinement of the flame in the closed bomb

Derivation of Distances with the Tully-Fisher Relation: The Antlia Cluster

The Tully-Fisher relation is a correlation between the luminosity and the HI 21cm line width in spiral galaxies (LLW relation). It is used to derive galaxy distances in the interval 7 to 100 Mpc. Closer, the Cepheids, TRGB and Surface Brightness Fluctuation methods give a better accuracy. Further, the SNIa are luminous objects still available for distance measurement purposes, though with a dramatically lower density grid of measurements on the sky. Galaxies in clusters are all at the same distance from the observer. Thus the distance of the cluster derived from a large number of galaxies (N) has an error reduced according to the square root of N. However, not all galaxies in a cluster are suitable for the LLW measurement. The selection criteria we use are explained hereafter; the important point being to avoid Malmquist bias and to not introduce any systematics in the distance measurement.Comment: Moriond0

Management Tools for RetD Project Portfolios in Complex Organizations – the case of an international pharmaceutical firm

Project Portfolio Management (PPM) is a growing issue in both professional and academic circles. The typology of Cooper et al. (1998) has pictured the variety of PPM formalized approaches into four types (financial, strategic, scoring and “bubble diagram”). While the use of formalized methods by top performers is clearly attested, the choice of a specific approach and the precise benefits and limits of different instruments are still in debate. The present paper formalizes more precise contingency hypotheses between PPM practices and organizational variables such as R&D strategy, the structure and history of a firm's development, partnership policy and learning track in the project domain. Where managerial implications are concerned, the paper puts forward an analytical framework for the adjustment of portfolio instruments to fit specific situations and develops the conclusions of that framework for an international pharmaceutical group, Merck Lipha. The research underlying this paper adopts an interactive and experimental case-based methodology which has been on-going since 1997.Project; portfolios; pharmaceuticals; decision; processes; interactive research

Inertial dynamics of air bubbles crossing a horizontal fluid–fluid interface

The dynamics of isolated air bubbles crossing the horizontal interface separating two Newtonian immiscible liquids initially at rest are studied both experimentally and computationally. High-speed video imaging is used to obtain a detailed evolution of the various interfaces involved in the system. The size of the bubbles and the viscosity contrast between the two liquids are varied by more than one and four orders of magnitude,respectively, making it possible to obtain bubble shapes ranging from spherical to toroidal. A variety of flow regimes isobserved,including that of small bubbles remaining trapped at the fluid–fluid interface in a film-drainage configuration.In most cases, the bubble succeeds in crossing the interface without being stopped near its undisturbed position and, during a certain period of time, tows a significant column of lower fluid which sometimes exhibits a complex dynamics as it lengthens in the upper fluid. Direct numerical simulations of several selected experimental situations are performed with a code employing a volume of-fluid type formulation of the incompressible Navier–Stokes equations. Comparisons between experimental and numerical results confirm the reliability of the computational approach in most situations but also points out the need for improvements to capture some subtle but important physical processes, most notably those related to film drainage. Influence of the physical parameters highlighted by experiments and computations, especially that of the density and viscosity contrasts between the two fluids and of the various interfacial tensions, is discussed and analysed in the light of simple models and available theories

Tension des mots et néologie par télescopage dans la publicité

This paper shows how lexical telescoping in advertising arouses significant tensions on the language. Some of them are discursive, due on the one hand to the blend of two words that dislocates the integrity of the linguistic sign, and on the other hand to different breaks in the production of advertising statements. Other tensions are pragmatic in that lexical telescoping recategorizes our concepts and reference to the world to win the public acceptance in the direction wished by advertisers. In the end, while illustrating the power of infl uence of words, lexical telescoping creates an antilexicon in order to make advertising communication more effective

La rhétorique des figures : entre formalisme et énonciation

Depuis toujours, la rhétorique des figures a oscillé entre deux pôles qu’elle a eu du mal à harmoniser : d’une part, celui du formalisme qui voit en elles des tournures plus ou moins remarquables ; d’autre part, celui de l’énonciation qui les considère comme des points d’ancrage privilégiés de l’engagement de leurs producteurs. En premier lieu, cet article dresse un bilan critique sur ce statut instable des figures. Après avoir mis en évidence la gestion inégale entre structure et expression figurale chez divers théoriciens, cette étude analyse l’apport du Groupe µ dans la constitution d’une rhétorique intégrée qui concilie le donné sémiotique des figures et leur actualisation en discours. En second lieu, dans le prolongement des travaux du Groupe µ et à partir du cas typique de l’oxymore, un plaidoyer est formulé sur la nécessité de voir, dans les figures, des structures discursives modelées par leur prise en charge énonciative. Comme le montre l’oxymore, si les figures sont des schèmes saillants, ceux-ci sont façonnés par les motivations des sujets communicants.The rhetoric of figures has always oscillated between two poles which could hardly be harmonized: On the one hand, the pole of formalism, which considers figures as more or less striking expressions. On the other hand, the pole of enunciation, which considers them as privileged cornerstones of its producers’ point of view. First of all, this article draws up a critical balance sheet of this unstable status of figures. After emphasizing the unequal management of figurative structure and expression by several theorists, this study analyses the contribution of the Groupe µ to the constitution of an integrated rhetoric which reconciles the semiotic content of figures and their realization in speech. Secondly, following the same lines as the studies of the Groupe µ and falling back on the typical case of the oxymoron, we will formulate a plea about the necessity of seeing in the figures discourse structures which are modelled by their enunciative value. As it is illustrated through the oxymoron, if figures are salient schemata, these are shaped by the motivations of the communicating subjects

Lothar Fischer, Helmut Sturm et HP Zimmer : des collectifs engagés à l'enseignement des Beaux-arts en République Fédérale d'Allemagne

International audienceNous présentons les parcours de 4 artistes ouest-allemands issus de l’académie, Lothar Fischer, Helmut Sturm, Hans-Peter Zimmer et Heimrad Prem, aux riches trajectoires artistiques individuelles et collectives ; ils furent les fondateurs du groupe Spur en 1957, l’un des premiers collectifs d’artistes engagés et subversifs à revoir le jour en Allemagne depuis les années 30. 20 ans plus tard, 3 d’entre eux deviennent enseignants des beaux-arts dans différents établissements réputés de République Fédérale d’Allemagne. Nous interrogerons ici la cohérence de l’évolution de leurs théories et pratiques ; nous nous demanderons quelles conséquences leur démarche de création intuitive et expérimentale a pu avoir sur leur pédagogie, et quelle place, quelle forme un tel cadre pouvait laisser à leur engagement pour un changement global de paradigme social