How to take into account general and contextual knowledge for interactive aiding design: Towards the coupling of CSP and CBR approaches

The goal of this paper is to show how it is possible to support design decisions with two different tools relying on two kinds of knowledge: case-based reasoning operating with contextual knowledge embodied in past cases and constraint filtering that operates with general knowledge formalized using constraints. Our goals are, firstly to make an overview of existing works that analyses the various ways to associate these two kinds of aiding tools essentially in a sequential way. Secondly, we propose an approach that allows us to use them simultaneously in order to assist design decisions with these two kinds of knowledge. The paper is organized as follows. In the first section, we define the goal of the paper and recall the background of case-based reasoning and constraint filtering. In the second section, the industrial problem which led us to consider these two kinds of knowledge is presented. In the third section, an overview of the various possibilities of using these two aiding decision tools in a sequential way is drawn up. In the fourth section, we propose an approach that allows us to use both aiding decision tools in a simultaneous and iterative way according to the availability of knowledge. An example dealing with helicopter maintenance illustrates our proposals

Simulation of 3D interlock composite preforming

The ply to ply interlock fabric preform enables to manufacture, by R.T.M. process, thick composite parts that are resistant to delamination and cracking. Numerical simulation of interlock reinforcement forming allows to determine conditions for feasibility of the process and above all to know the position of fibres in the final composite part. For this forming simulation, specific hexahedral finite elements made of seg- ment yarns are proposed. Position of each yarn segment within the element is taken into account. This avoids determination of a homogenized equivalent continuous law that would be very difficult consider- ing the complexity of the weaving. Transverse properties of fabric are taken into account within a hyp- oelastic constitutive law. A set of 3D interlock fabric forming simulations shows the efficiency of the proposed approach

Aide à la décision exploitant de la connaissance générale et contextuelle : application à la maintenance d’hélicoptère

Les travaux présentés dans cette thèse ont pour objectif de contribuer à l’élaboration d’un outil d’aide à la décision en conception exploitant de la connaissance générale et de la connaissance contextuelle. L’exploitation de la connaissance générale est effectuée à l’aide d’un moteur de filtrage de contraintes et l’exploitation de la connaissance contextuelle repose sur des principes issus du raisonnement à partir de cas et du data-mining. Le résultat principal est basé sur une notion de contrainte dite "contextuelle". L’idée forte revient à paramétrer une contrainte en fonction du contexte dans lequel celle-ci doit être filtrée. Suivant le niveau de confiance caractérisant la connaissance contextuelle, cette contrainte pourra soit être propagée de manière autonome dans le moteur de filtrage soit être utilisée pour fournir une forme de conseil à l’utilisateur du système d’aide. Nous proposons pour identifier le contexte d’emploi de la contrainte d’utiliser le principe de recherche par similarité très largement utilisé dans les travaux portant sur le raisonnement à partir de cas. Afin de compléter ou d’affiner les informations résultant du filtrage de cette contrainte contextuelle, nous utilisons des algorithmes de comptage issus du data-mining pour fournir des fréquences d’apparition caractérisant une forme de confiance dans le résultat. Nos travaux s’inscrivent dans le cadre d’un projet FUI portant sur la maintenance d’hélicoptère. Le but de notre outil est d’estimer au mieux la charge, le cycle, les coûts des activités opérationnelles de maintenance d’un hélicoptère. L’originalité des travaux est de considérer d’une part les connaissances constructeurs (connaissance générale) pour déterminer une première estimation puis de la corriger suivant les conditions d’utilisation effective de l’hélicoptère (connaissance contextuelle)

Geological and Geomorphological study of the original hill at the base of Fourth Dynasty Egyptian monuments. Etude géologique et géomorphologique de la colline originelle à la base des monuments de la quatrième dynastie égyptienne

22 pages; 20 figuresRock foundations of the Kephren and Kheops pyramids are examined in comparison with other Fourth Dynasty monuments: the Sphinx, Queen Kentkawes' mastaba and the Abu Rawash pyramid. This study is based on geological and geomorphological observations, visual observation, and photomontages. Results, correlated with those of former studies, demonstrate the existence of natural hills used as substrata in the construction of the two great pyramids. The minimum volume of these hills can be estimated at 12% and 23% respectively of the volumes of the Kephren and Kheops pyramids. The use of worked rock hills appears to be a characteristic of the construction methods under the Fourth Dynasty.Le substratum rocheux des pyramides de Kheops et Khephren est étudié en comparaison avec celui d'autres monuments de la quatrième dynastie de l'ancienne Egypte : le Sphinx, le mastaba de la reine Kentkawes et la pyramide d'Abu Rawash. Cette étude est basée sur des observations géologiques et géomorphologiques, l'observation visuelle et des photomontages, ainsi que des mesures réalisées sur le terrain. Les résultats, corrélés avec ceux d'études antérieures, démontrent l'existence de collines naturelles utilisées comme assises pour la construction des deux grandes pyramides. Le volume minimum de ces collines peut être estimé par rapport au volume total à 12% pour Khephren et 23% pour Kheops. L'utilisation de collines rocheuses pour asseoir la construction d'un monument apparaît être caractéristique des méthodes de construction utilisées sous la quatrième dynastie

Chandra Detection of X-ray Absorption Associated with a Damped Lyman Alpha System

We have observed three quasars, PKS 1127-145, Q 1331+171 and Q0054+144, with the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray absorption associated with intervening 21-cm and damped Ly$\alpha$ absorbers. For PKS 1127-145, we detect absorption which, if associated with an intervening z_{abs}=0.312 absorber, implies a metallicity of 23% solar. If the absorption is not at z_{abs}=0.312, then the metallicity is still constrained to be less than 23% solar. The advantage of the X-ray measurement is that the derived metallicity is insensitive to ionization, inclusion of an atom in a molecule, or depletion onto grains. The X-ray absorption is mostly due to oxygen, and is consistent with the oxygen abundance of 30% solar derived from optical nebular emission lines in a foreground galaxy at the redshift of the absorber. For Q1331+171 and Q 0054+144, only upper limits were obtained, although the exposure times were intentionally short, since for these two objects we were interested primarily in measuring flux levels to plan for future observations. The imaging results are presented in a companion paper.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical Journa

Metallicity Evolution of Damped Lyman-Alpha Galaxies

We have reanalyzed the existing data on Zinc abundances in damped Ly-alpha (DLA) absorbers to investigate whether their mean metallicity evolves with time. Most models of cosmic chemical evolution predict that the mass- weighted mean interstellar metallicity of galaxies should rise with time from a low value ~ 1/30 solar at z ~ 3 to a nearly solar value at z ~ 0. However, several previous analyses have suggested that there is little or no evolution in the global metallicity of DLAs. We have used a variety of statistical techniques to quantify the global metallicity-redshift relation and its uncertainties, taking into account both measurement and sampling errors. Three new features of our analysis are: (a) an unbinned N(H I)-weighted nonlinear chi-square fit to an exponential relation; (b) survival analysis to treat the large number of limits in the existing data; and (c) a comparison of the data with several models of cosmic chemical evolution based on an unbinned N(H I)-weighted chi-square. We find that a wider range of evolutionary rates is allowed by the present data than claimed in previous studies. The slope of the exponential fit to the N(H I)-weighted mean Zn metallicity vs. redshift relation is -0.20 plus minus 0.11 counting limits as detections and -0.27 plus minus 0.12 counting limits as zeros. Similar results are also obtained if the data are binned in redshift, and if survival analysis is used. These slopes are marginally consistent with no evolution, but are also consistent with the rates predicted by several models of cosmic chemical evolution. Finally, we outline some future measurements necessary to improve the statistics of the global metallicity-redshift relation.Comment: 25 pages, 1 figure, accepted for publication in the Astrophysical Journa

Des études scientifiques pour quel projet professionnel ?

International audienceDepuis plusieurs années les facultés scientifiques doivent faire face à une diminution de leurs effectifs, il est donc légitime de se poser la question des projets professionnels des étudiants arrivant en première année. Les données que nous avons réunies depuis ces 10 dernières années, nous montrent une volonté des étudiants d'obtenir une formation donnant un haut niveau de compétence disciplinaire. En outre, les étudiants universitaires sont demandeurs d'une formation de plus en plus tournée vers une insertion dans le secteur industriel, montrant ainsi un changement profond de leurs aspirations. Si une part importante des étudiants a déjà une idée précise de leur projet, il est étonnant de voir qu'il n'existe pas de corrélation avec l'insertion professionnelle des jeunes diplômés

Dynamical Expansion of Ionization and Dissociation Front around a Massive Star. II. On the Generality of Triggered Star Formation

We analyze the dynamical expansion of the HII region, photodissociation region, and the swept-up shell, solving the UV- and FUV-radiative transfer, the thermal and chemical processes in the time-dependent hydrodynamics code. Following our previous paper, we investigate the time evolutions with various ambient number densities and central stars. Our calculations show that basic evolution is qualitatively similar among our models with different parameters. The molecular gas is finally accumulated in the shell, and the gravitational fragmentation of the shell is generally expected. The quantitative differences among models are well understood with analytic scaling relations. The detailed physical and chemical structure of the shell is mainly determined by the incident FUV flux and the column density of the shell, which also follow the scaling relations. The time of shell-fragmentation, and the mass of the gathered molecular gas are sensitive tothe ambient number density. In the case of the lower number density, the shell-fragmentation occurs over a longer timescale, and the accumulated molecular gas is more massive. The variations with different central stars are more moderate. The time of the shell-fragmentation differs by a factor of several with the various stars of M_* = 12-101 M_sun. According to our numerical results, we conclude that the expanding HII region should be an efficient trigger for star formation in molecular clouds if the mass of the ambient molecular material is large enough.Comment: 49 pages, including 17 figures ; Accepted for publication in Ap

The SOPHIE search for northern extrasolar planets. V. Follow-up of ELODIE candidates: Jupiter-analogs around Sun-like stars

We present radial-velocity measurements obtained in a programs underway to search for extrasolar planets with the spectrograph SOPHIE at the 1.93-m telescope of the Haute-Provence Observatory. Targets were selected from catalogs observed with ELODIE, mounted previously at the telescope, in order to detect long-period planets with an extended database close to 15 years. Two new Jupiter-analog candidates are reported to orbit the bright stars HD150706 and HD222155 in 16.1 and 10.9 yr at 6.7 (+4.0,-1.4) and 5.1(+0.6,-0.7) AU and to have minimum masses of 2.71 (+1.44,-0.66) and 1.90 (+0.67,-0.53) M_Jup, respectively. Using the measurements from ELODIE and SOPHIE, we refine the parameters of the long-period planets HD154345b and HD89307b, and publish the first reliable orbit for HD24040b. This last companion has a minimum mass of 4.01 +/- 0.49 M_Jup orbiting its star in 10.0 yr at 4.92 +/- 0.38 AU. Moreover, the data provide evidence of a third bound object in the HD24040 system. With a surrounding dust debris disk, HD150706 is an active G0 dwarf for which we partially corrected the effect of the stellar spot on the SOPHIE radial-velocities. HD222155 is an inactive G2V star. On the basis of the previous findings of Lovis and collaborators and since no significant correlation between the radial-velocity variations and the activity index are found in the SOPHIE data, these variations are not expected to be only due to stellar magnetic cycles. Finally, we discuss the main properties of this new population of long-period Jupiter-mass planets, which for the moment, consists of fewer than 20 candidates. These stars are preferential targets either for direct-imaging or astrometry follow-up to constrain the system parameters and for higher precision radial-velocity to search for lower mass planets, aiming to find a Solar System twin.Comment: accepted for publication in Astronomy & Astrophysic

A physical upper limit on the HI column density of gas clouds

An intriguing fact about cosmic gas clouds is that they all appear to have neutral (atomic) hydrogen column densities smaller than 10^{22} cm^{-2}. Observations of damped Ly-alpha (DLA) absorption systems further indicate that the maximum N(HI) decreases with increasing metallicity. It is generally assumed that this trend is due to a dust-induced selection bias: DLA systems with high N(HI) and high metallicity contain so much dust that the background QSO becomes too dim to be included in optically selected surveys. Here, it is argued that this explanation may not be viable. Instead, it is proposed that conversion to molecular hydrogen determines the maximum HI column density. Molecular hydrogen forms on the surface of dust grains and is destroyed by photodissociation. Therefore, the molecular fraction correlates with both the dust content and, because of self-shielding, the total hydrogen column density, and anticorrelates with the intensity of the incident UV radiation. It is shown that the first relation can account for the observed anticorrelation between the maximum N(HI) and metallicity.Comment: Accepted for publication in the Astrophysical Journal Letters. 4 pages, 2 figures. Minor change