A simple method for the determination of slowly varying refractive index profiles from in situ spectrophotometric measurements

Reliable control of the deposition process of optical films and coatings frequently requires monitoring of the refractive index profile throughout the layer. In the present work a simple in situ approach is proposed which uses a WKBJ matrix representation of the optical transfer function of a single thin film on a substrate. Mathematical expressions are developed which represent the minima and maxima envelopes of the curves transmittance-vs-time and reflectance-vs-time. The refractive index and extinction coefficient depth profiles of different films are calculated from simulated spectra as well as from experimental data obtained during PECVD of silicon-compound films. Variation of the deposition rate with time is also evaluated from the position of the spectra extrema as a function of time. The physical and mathematical limitations of the method are discussed.Comment: 10 pages, 11 figures, REVTeX, to be published in Applied Optic

Building a Structural Model: Parameterization and Structurality

A specific concept of structural model is used as a background for discussing the structurality of its parameterization. Conditions for a structural model to be also causal are examined. Difficulties and pitfalls arising from the parameterization are analyzed. In particular, pitfalls when considering alternative parameterizations of a same model are shown to have lead to ungrounded conclusions in the literature. Discussion of observationally equivalent models related to different economic mechanisms are used to make clear the connection between an economicall meaningful parameterization and an economically meaningful decomposition of a complex model. The design of economic policy is used for drawing some practical implications of the proposed analysis

Causality in Econometric Modeling. From Theory to Structural Causal Modeling

This paper examines different approaches for assessing causality as typically followed in econometrics and proposes a constructive perspective for improving statistical models elaborated in view of causal analysis. Without attempting to be exhaustive, this paper examines some of these approaches. Traditional structural modeling is first discussed. A distinction is then drawn between model-based and design-based approaches. Some more recent developments are examined next, namely history-friendly simulation and information-theory based approaches. Finally, in a constructive perspective, structural causal modeling (SCM) is presented, based on the concepts of mechanism and sub-mechanisms, and of recursive decomposition of the joint distribution of variables. This modeling strategy endeavors at representing the structure of the underlying data generating process. It operationalizes the concept of causation through the ordering and role-function of the variables in each of the intelligible sub-mechanisms

Time and Causality in the Social Sciences

This article deals with the role of time in causal models in the social sciences, in particular in structural causal modeling, in contrast to time-free models. The aim is to underline the importance of time-sensitive causal models. For this purpose, it also refers to the important discussion on time and causality in the philosophy of science, and examines how time is taken into account in demography and in economics as examples of social sciences. Temporal information is useful to the extent that it is placed in a correct causal structure, and thus further corroborating the causal mechanism or generative process explaining the phenomenon under consideration. Despite the fact that the causal ordering of variables is more relevant for explanatory purposes than the temporal order, the former should nevertheless take into account the time-patterns of causes and effects, as these are often episodes rather than single events. For this reason in particular, it is time to put time at the core of our causal models

The issue of control in multivariate systems, A contribution of structural modelling.

This paper builds upon Judea Pearl’s directed acyclic graphs approach to causality and the tradition of structural modelling in economics and social science. The paper re-examines the issue of control in complex systems with multiple causes and outcomes, in a specific perspective of structural modelling. It begins with three-variable saturated and unsaturated models, and then examines more complex systems including models with collider and latent confounder discussed by Pearl. In particular, focusing on the causes of an outcome, the paper proposes two simple rules for selecting the variables to be controlled for when studying the direct effect of a cause on an outcome of interest or the total effect when dealing with multiple causal paths. This paper presents a model building strategy that allows a statistical model to be considered as structural. The challenge for the model builder amounts to developing an explanation through a recursive decomposition of the joint distribution of the variables congruent with background knowledge and stable with respect to specified changes of the environment

M & L Jaargang 30/2

Jozef Verlinden Het poolschip Belgica. [The polar ship Belgica.]Om zijn ambitieuze plan voor een poolexpeditie vorm te geven, gaat Adrien de Gerlache op zoek naar een geschikt expeditieschip. Hoe na diverse proefvaarten de robbenjager Patria wordt omgebouwd tot expeditieschip en omgedoopt tot Belgica, blijkt uit het minutieuze verhaal van Jozef Verlinden. Buiten spraakmakende expedities naar het Arctisch gebied wordt de Belgica ingezet als visboot, plezierschip, visverwerkend bedrijf, kolenponton en munitiedepot, tot het in 1940 wordt lek geschoten en roemloos tot zinken gebracht.Tomas Termote en Nicolas Mouchart Het wrak van de Belgica. [The wreck of the Belgica.]Gedegradeerd tot een munitiedepot maakte een Duitse bommenwerper, tijdens het begin van de Tweede Wereldoorlog, een einde aan wat ooit een glorieus poolschip was. Maar de baai van Brurvik wist slechts gedurende een halve eeuw haar geheim te bewaren. Noorse duikers ontdekten het wrak en België herontdekte haar poolschip. Expedities werden op touw gezet om het wrak te bestuderen en om de mogelijkheden voor een berging na te gaan. Tekst en uitleg door Tomas Termote en Nicolas Mouchart.Hugo Decleir Van Belgica tot Princess Elisabeth station. Belgisch wetenschappelijk onderzoek met betrekking tot Antarctica. [From Belgica to the Princess Elisabeth station. Belgian scientific research on Antarctica.]Van de 16de-eeuwse Vlaamse cartografen, over de Belgica, tot het ultramoderne Princess Elisabeth station. Hugo Decleir schetst een overzicht van maar liefst vijf eeuwen wetenschappelijk onderzoek op en rond de Zuidpool. Na lectuur hiervan kan niemand nog ontkennen dat België een wel erg sterke band heeft met het meest zuidelijke werelddeel.Summar

A study of orientational ordering in a fluid of dipolar Gay-Berne molecules using density-functional theory

Published versio

Self-Rated Health in the Baltic Countries, 1994–1999

Numerous studies have examined the explanations of mortality fluctuations in the former USSR during the last decade of the twentieth century-a time of considerable political and socio-economic changes-but fewer studies have considered the health of these populations during this period. Using individual data from the Norbalt surveys held in 1994 and 1999 in the three Baltic countries, we examine the determinants of self-rated health in the three countries and for the two periods, by way of Bayesian structural equation modelling and directed acyclic graphs. The model takes into account, as possible determinants, alcohol consumption, physical health, psychological distress, education, locus of control, and social support. A major result is the remarkable stability of the model's parameters whatever the country, year, gender, ethnicity, or age-group. Particular attention is given to the role of alcohol consumption and to the association observed between better self-assessed health and higher drinking. © 2010 Springer Science+Business Media B.V