Modeling of Electromagnetic Systems by Coupling of Subproblems – Application to Thin Shell Finite Element Magnetic Models

Doctoral thesis (2013)

The direct application of the finite element method to realistic electromagnetic problems is challenging, especially when modeling structures with thin conductive and/or magnetic parts. This work presents ... [more ▼]

The direct application of the finite element method to realistic electromagnetic problems is challenging, especially when modeling structures with thin conductive and/or magnetic parts. This work presents a subproblem method for correcting the inaccuracies inherent to classical thin shell models, and to efficiently handle geometrical and material variations in parametric studies. [less ▲]

Primo @ ULg : Implémantation de Primo 4.1 à l'ULg

Conference given outside the academic context (2013)

The presentation of neuroendocrine self in the thymus: a sheer necessity for a peaceful coevolution of the neuroendocrine and adaptive immune systems

Scientific conference (2013, June 17)

Risk communication and food safety policies: the case of the case of risk governance with a grain of NaCl

Conference (2013, June 17)

Statistical analysis of incomplete longitudinal ordinal data - Impact of Multiple Imputation on data distribution

Scientific conference (2013, June 17)

Etude de la sphéroïdisation de la perlite et de la recristallisation de la ferrite sous champ magnétique

Doctoral thesis (2013)

The steel industry is constantly looking for innovations and solutions to improve production processes as well as product properties. However, current technologies result from decades of development and ... [more ▼]

The steel industry is constantly looking for innovations and solutions to improve production processes as well as product properties. However, current technologies result from decades of development and thus have already reached maturity. Therefore, bright innovations have to arise from technological breakthroughs. The objective of those novelties is to induce drastic changes in terms of process or product. Magnetic heat treatment might be a solution to reach both objectives. Indeed, recent researches have shown that magnetic fields can significantly modify the transformation kinetics in steels. This can turn into very positive impacts on the metallurgical processes. However, researches on this topic are in the early stage and a lot of fields have not been studied yet. This work has been carried out in this challenging context. The main objective is to study the effect of magnetic fields on cementite spheroidization and ferrite recrystallization. So far, these two transformations involve long thermal treatments at high temperatures. Thus, a reduction of the processing time or an improvement of the mechanical properties of the steels by using magnetic field processing would be a significant improvement for this kind of thermal treatment. The transformations that are studied imply large microstructure modifications: lamellae breaks into spheroids while ferrite recrystallizes. As a consequence, the developments of dedicated microstructure characterization techniques are concomitant objectives. As it will be shown latter, we decided to develop and optimize image analysis tools. Practically, the completion of this work has required the pursuit of four objectives: Objective 1: develop an image analysis tool dedicated to pearlite spheroidization study, Objective 2: study the effect of magnetic field on cementite spheroidization, Objective 3: develop an image analysis tool dedicated to ferrite recrystallization study, Objective 4: study the effect of magnetic field on ferrite recrystallization. This work is divided in four parts described below. A general introduction constitutes the first part. It contains two chapters. Chapter I focuses on a literature review of the effect of magnetic fields on steels. The first section of this chapter deals with the basics of metallurgy and magnetism required to understand this work. Then, the reader will find a literature review about the effects of homogeneous magnetic fields on steel transformations. As it has been said before, the specificity of this work lies in the fact that the transformations studied were analysed and characterized using image analysis. The Chapter II is dedicated to this technique. The basics of image analysis are summarized in the first section of this chapter. Then, specific sections are dedicated to each step of image analysis: pre-treatment, image segmentation and characterizations. The limits of this technique, as well as its applications are described in the two last sections of this chapter. The second part of this work is divided in three chapters and deals with cementite spheroidization under magnetic field. Chapter III provides a detailed introduction to cementite spheroidization. The first section of this chapter introduces the pearlite as well as its microstructure. Using these concepts, the mechanisms and the kinetic of cementite spheroidization and cementite ripening will be introduced. Finally, the last section of this chapter will focus literature results which indicate that a potential effect of magnetic field on cementite spheroidization might be expected. After this detailed introduction, the tools used to study the cementite spheroidization under magnetic field will be described in Chapter IV. The first section deals with the characterization techniques used to study pearlite spheroidization. Then, the furnace and the heat treatments that have been performed will be described. With these tools, we will describe, in Chapter V, the results that have been achieved about cementite spheroidization under magnetic field. First, we will deeply analyse the effect of temperature and heat treatment duration on cementite spheroidization. This will be the opportunity to study in details the mechanism of cementite spheroidization and spheroids ripening. Microstructure evolutions induced by these two transformations will also be analysed. The effects of magnetic field on cementite spheroidization are described in the last section of this chapter. The analysis of the effect of magnetic field on ferrite recrystallization constitutes the third part of this work. It is divided in three chapters. Chapter VI provides a detailed introduction to ferrite recrystallization. The first section of this chapter deals with the crystalline structure defects induced by the steel forming. The detailed description of the mechanisms and the kinetics of defects elimination by the recovery, primary recrystallization and secondary recrystallization constitute the three next sections of this chapter. The last section of this chapter summarizes the results of different relevant studies on the effects of magnetic fields on these three processes. The chapter VI is followed by a detailed description of the characterization techniques as well as the heat treatment performed to study ferrite recrystallization (Chapter VII). Chapter VIII describes the results that have been obtained about ferrite recrystallization under magnetic field. We will study the effect of temperature and heat treatment duration on ferrite recrystallization. The involved transformations will be studied in detail. Finally, the effect of magnetic field on ferrite recrystallization will be discussed in the last section of this chapter. The general conclusions as well as the prospects of this work will be addressed in the fourth part of this work, respectively in Chapters IX and X. [less ▲]

Modelling the top-height growth and site index of Norway spruce in Southern Belgium

in Forest Ecology & Management (2013), 298

Top-height growth in even-aged stands of Norway spruce (Piceaabies (L.) Karst.) from Southern Belgium was modelled using functions which provide an algebraic solution for site index (SI) calculation. 16 ... [more ▼]

Top-height growth in even-aged stands of Norway spruce (Piceaabies (L.) Karst.) from Southern Belgium was modelled using functions which provide an algebraic solution for site index (SI) calculation. 16 well known growth model formulations were parameterized using a method which accounts for heterogeneous variance and autocorrelation on a dataset composed of stem analysis data completed by measuring the heights of all the branch whorls to allow for accurate height–age estimates. Comparison of the parameterized models showed that the oblique asymptotic function known as the Duplat and Tran-Ha III model was the most efficient on our dataset. Validation of the selected model on permanent sample plot data showed no evidence of bias over the full range of possible age, height, site index and densities encountered in Norway spruce stands of Southern Belgium. The new height growth model described represents a significant improvement over the previous model of Dagnelie et al. (1988), which was found to be unreliable and required the use of an iterative process to estimate SI. [less ▲]

Copper phthalocyanine blue pigments in conservation

Doctoral thesis (2013)

The phthalocyanine family, and more specifically the copper phthalocyanines (CuPcs) are the most important blue and green artists’ pigments from the end of the 20th century. This thesis focuses on the ... [more ▼]

The phthalocyanine family, and more specifically the copper phthalocyanines (CuPcs) are the most important blue and green artists’ pigments from the end of the 20th century. This thesis focuses on the CuPc blue pigments used in the artists’ paint formulations. CuPc blue extensive use as modern artists’ pigment and its implications in conservation science are pointed out. Their discovery, chemical composition, molecular structure and general properties are also reviewed. Additionally, the polymorphism and the influence of the crystal form on the final properties of the phthalo blue pigments are discussed. A methodology using non-destructive techniques and statistical analysis is then presented. This new procedure allows the identification of the CuPc crystal form in paint layers and is suitable for artwork analysis. Some CuPc polymorphs are prone to crystallization defects in presence of aromatic solvents, leading to a reduction of color strength and a shift in hue. Crystallization resistance of the CuPc polymorphs has then been assessed by means of crystallization tests performed on dry pigments and on paint films. Case studies are then presented. La famille Soler by Picasso has been studied by imaging and non-invasive analytical techniques. The successive underlying compositions have been revealed and the pigments used for the different compositions have been characterized. Then micro-samples taken from Delvaux’s paintings and Francis and Lichtenstein’s studio paints have been analyzed to characterize the blue pigments preferred by these artists. The crystal form of the phthalo blue pigments identified from four micro-samples taken from two Léger and Pechstein fake paintings have been investigated as well. Finally, the historic phthalo blue samples from the Getty Conservation Institute Reference Collection have been studied. [less ▲]

Atmospheric and oceanic climate forcing of the exceptional Greenland ice sheet surface melt in summer 2012

in International Journal of Climatology (2013), online

The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these ... [more ▼]

The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these exceptional conditions and also to ask the question of how unusual these anomalies were compared to available records. Our analysis allows us to assess the relative contributions of these two key influences to both the extreme melt event and ongoing climate change. In 2012, as in recent warm summers since 2007, a blocking high pressure feature, associated with negative NAO conditions, was present in the mid-troposphere over Greenland for much of the summer. This circulation pattern advected relatively warm southerly winds over the western flank of the ice sheet, forming a ‘heat dome’ over Greenland that led to the widespread surface melting. Both sea-surface temperature and sea-ice cover anomalies seem to have played a minimal role in this record melt, relative to atmospheric circulation. Two representative coastal climatological station averages and several individual stations in south, west and north-west Greenland set new surface air temperature records for May, June, July and the whole (JJA) summer. The unusually warm summer 2012 conditions extended to the top of the ice sheet at Summit, where our reanalysed (1994–2012) DMI Summit weather station summer (JJA) temperature series set new record high mean and extreme temperatures in 2012; 3-hourly instantaneous 2-m temperatures reached an exceptional value of 2.2°C at Summit on 11 July 2012. These conditions translated into the record observed ice-sheet wide melt during summer 2012. However, 2012 seems not to be climatically representative of future ‘average’ summers projected this century. [less ▲]

"Rends excellente ta place de l'Occident". Pour une approche intégrée de la décoration des tombes thébaines sous le règne d'Amenhotep II

Doctoral thesis (2013)

Sur l’ensemble des règnes de la XVIIIème dynastie égyptienne, il apparaît, jusqu’assez récemment, que celui d’Amenhotep II a suscité un intérêt moindre de la part des chercheurs, ces derniers lui ayant ... [more ▼]

Sur l’ensemble des règnes de la XVIIIème dynastie égyptienne, il apparaît, jusqu’assez récemment, que celui d’Amenhotep II a suscité un intérêt moindre de la part des chercheurs, ces derniers lui ayant préféré, de manière générale, ceux plus longs ou historiquement plus déterminants de Thoutmosis III, d’Amenhotep III ou encore d’Amenhotep IV – Akhenaton, et ce bien que plusieurs travaux fondamentaux aient déjà permis de mettre en évidence une série de traits spécifiques à cette période. Le règne d’Amenhotep II se caractérise en effet par une nouvelle gestion du gouvernement, où le phénomène d’hérédité qui s’installait progressivement dans certaines fonctions est endigué mais où, dans le même temps, les membres de quelques familles puissantes et particulièrement proches du roi se voient confier les plus hautes charges de l’administration. Aussi, pour la réalisation de leurs « demeures d’éternité », véritables cartes de visite de leurs propriétaires et témoins privilégiés des grandes orientations de l’époque, les principaux officiels du règne d’Amenhotep II ont pour la plupart porté leur choix sur la partie supérieure de la colline de Sheikh Abd el-Gourna, site particulièrement prisé pour sa position surélevée comme pour la proximité qu’il entretient avec les temples funéraires royaux. Les tombes de ces dignitaires se distinguent néanmoins de celles de leurs prédécesseurs, par des dimensions colossales, par l’étendue et la complexité des dispositifs intérieurs ainsi que par le choix de représentations et d’inscriptions qui, placées à des endroits stratégiques, soulignent les relations étroites qu’entretenait le propriétaire avec Pharaon. En outre, le traitement même des scènes figurées est également, à ce moment précis, l’objet de modifications considérables ; l’art pictural, qui se voulait depuis ses origines purement conceptuel et d’apparence hiéroglyphique, s’assouplit à divers égards pour prendre une apparence plus « sensuelle », plus « perceptuelle ». Ces transformations, qui s’amplifieront encore durant les règnes suivants, jettent déjà, en quelque sorte, les bases de ce qui deviendra la « révolution » du règne d’Akhenaton. Dans ce contexte, la présente thèse vise, au moyen d’une analyse pluridisciplinaire et « intégrée » de la décoration des chapelles du règne d’Amenhotep II, à caractériser dans une perspective socioculturelle les changements iconographiques et stylistiques qui affectent cette production artistique en pleine mutation. [less ▲]