ORBi Community: Physical, chemical, mathematical & earth Sciences
http://hdl.handle.net/2268/150
The Community's search engineSearch this channelsearch
http://orbi.ulg.ac.be/simple-search
Isolating auroral FUV emission lines using compact, broadband instrumentation
http://hdl.handle.net/2268/171722
Title: Isolating auroral FUV emission lines using compact, broadband instrumentation
<br/>
<br/>Author, co-author: Molyneux, P.M.; Bannister, N.P.; Bunce, E.J.; Grodent, Denis; Clarke, J.T.; Fleury-Frenette, Karl; Gérard, Jean-Claude; Lapington, J.; Nichols, J.D.; Rossi, L.
<br/>
<br/>Abstract: Images of auroral emissions at far ultraviolet (FUV, 122–200 nm) wavelengths are useful tools with which to study magnetospheric-ionospheric coupling, as the scattered sunlight background in this region is low, allowing both dayside and nightside auroras to be imaged simultaneously. The ratio of intensities between certain FUV emission lines or regions can be used to characterise the precipitating particles responsible for auroral emissions, and hence is a useful diagnostic of magnetospheric dynamics. Here, we describe how the addition of simple transmission filters to a compact broadband imager design allows far ultraviolet emission ratios to be deduced while also providing large-scale instantaneous images of the aurora. The low mass and volume of such an instrument would make it well-suited for both small satellite Earth-orbiting missions and larger outer planet missions from which it could be used to characterise the tenuous atmospheres observed at several moons, as well as studying the auroral emissions of the gas giants. We present a study to investigate the accuracy of a technique to allow emission line ratio retrieval, as applied to the OI 130.4 nm and 135.6 nm emissions at Ganymede. The ratio of these emissions provides information about the atmospheric composition, specifically the relative abundances of O and O2. Using modelled FUV spectra representative of Ganymede's atmosphere, based on observations by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), we find that the accuracy of the retrieved ratios is a function of the magnitude of the ratio, with the best measurements corresponding to a ratio of ∼1.3
.Comparison of robust detection techniques for local outliers in multivariate spatial data
http://hdl.handle.net/2268/171721
Title: Comparison of robust detection techniques for local outliers in multivariate spatial data
<br/>
<br/>Author, co-author: Ernst, Marie; Haesbroeck, Gentiane
<br/>
<br/>Abstract: Spatial data are characterized by statistical units, with known geographical positions, on which non spatial attributes are measured. Spatial data may contain two types of atypical observations: global and/or local outliers. The attribute values of a global outlier are outlying with respect to the values taken by the majority of the data points while the attribute values of a local outlier are extreme when compared to those of its neighbors.
Usual outlier detection techniques may be used to find global outliers as the geographical positions of the data is not taken into account in this specific search. The detection of local outliers is more complex, especially when there are more than one non spatial attributes. This talk focuses on local detection with two main objectives.
First, we will shortly review some of the local detection techniques that seem to perform well in practice. Among these, one can find robust ``Mahalanobis-type'' detection techniques and a wheighted PCA approach. We suggest an adaptation to one of these to further develop its local characteristic.
Then, examples and simulations, based on linear model of co-regionalisation with Matern models, are reported and discussed in order to compare in an objective way the different detection techniques.Robust detection techniques for multivariate spatial data
http://hdl.handle.net/2268/171720
Title: Robust detection techniques for multivariate spatial data
<br/>
<br/>Author, co-author: Ernst, Marie; Haesbroeck, Gentiane
<br/>
<br/>Abstract: Spatial data are characterized by statistical units, with known geographical positions, on which non spatial attributes are measured. Two types of atypical observations can be defined: global and/or local outliers. The attribute values of a global outlier are outlying with respect to the values taken by the majority of the data points while the attribute values of a local outlier are extreme when compared to those of its neighbors. Classical outlier detection techniques may be used to find global outliers as the geographical positions of the data is not taken into account in this search. The detection of local outliers is more complex especially when there are more than one non spatial attribute. In this poster, two new procedures for local outliers detection are defined. The first approach is to adapt an existing technique using in particular a regularized estimator of the covariance matrix. The second technique measures outlyingness using depth function.Collapsing and reswelling kinetics of thermoresponsive polymers on surfaces: a matter of confinement and constraints
http://hdl.handle.net/2268/171711
Title: Collapsing and reswelling kinetics of thermoresponsive polymers on surfaces: a matter of confinement and constraints
<br/>
<br/>Author, co-author: Willet, Nicolas; Gabriel, Sabine; Jérôme, Christine; Du Prez, Filip; Duwez, Anne-Sophie
<br/>
<br/>Abstract: We report on the collapsing and reswelling ability of grafted poly(methyl vinyl ether) chains of different molecular architectures. In order to study the influence of constraints and confinement of the chains, the polymer was grafted onto AFM tips, as a model of a curved nano-sized surface, and onto macroscopic silicon substrates for comparison purposes. AFM-based force spectroscopy experiments were performed to characterise at the nanoscale the temperature-dependent collapsing process and the reversibility to the swollen state on both substrates. The reversible character of the thermoresponsive transition and its kinetics were shown to greatly depend on the polymer architecture and the constraints encountered by the chains.Emission Tunable, Cytocompatible, Near-IR-Emitting Ag2S Quantum Dots by Aqueous Decomposition of DMSA
http://hdl.handle.net/2268/171706
Title: Emission Tunable, Cytocompatible, Near-IR-Emitting Ag2S Quantum Dots by Aqueous Decomposition of DMSA
<br/>
<br/>Author, co-author: Hocaoglu, I.; Demir, F.; Birer, O.; Kiraz, A.; Sevrin, Chantal; Grandfils, Christian; Yagci Acar, H.Large-scale structure and dynamics of the magnetotails of Mercury, Earth, Jupiter and Saturn.
http://hdl.handle.net/2268/171702
Title: Large-scale structure and dynamics of the magnetotails of Mercury, Earth, Jupiter and Saturn.
<br/>
<br/>Author, co-author: Jackman; Arridge; Andre; Bagenal; Birn; Freeman; Jia; Kidder; Milan; Radioti, Aikaterini; Slavin; Vogt; Volwerk; WalshMulti-Dimensional Vector Assignment Problems
http://hdl.handle.net/2268/171699
Title: Multi-Dimensional Vector Assignment Problems
<br/>
<br/>Author, co-author: Dokka, Trivikram; Crama, Yves; Spieksma, Frits C.R.
<br/>
<br/>Abstract: We consider a special class of axial multi-dimensional assignment problems called multi-
dimensional vector assignment (MVA) problems. An instance of the MVA problem is
defined by m disjoint sets, each of which contains the same number n of p-dimensional
vectors with nonnegative integral components, and a cost function defined on vectors.
The cost of an m-tuple of vectors is defined as the cost of their component-wise maximum.
The problem is now to partition the m sets of vectors into n m-tuples so that no two
vectors from the same set are in the same m-tuple and so that the sum of the costs of the m-tuples is minimized. The main motivation comes from a yield optimization problem
in semi-conductor manufacturing. We consider a particular class of polynomial-time
heuristics for MVA, namely the sequential heuristics, and we study their approximation
ratio. In particular, we show that when the cost function is monotone and subadditive,
sequential heuristics have a finite approximation ratio for every fixed m. Moreover, we
establish smaller approximation ratios when the cost function is submodular and, for a
specific sequential heuristic, when the cost function is additive. We provide examples to
illustrate the tightness of our analysis. Furthermore, we show that the MVA problem is
APX-hard even for the case m = 3 and for binary input vectors. Finally, we show that
the problem can be solved in polynomial time in the special case of binary vectors with
fixed dimension p.
<br/>
<br/>Commentary: A preliminary version of this paper, entitled "Approximation Algorithms for Multi-Dimensional Vector Assignment Problems", is available as a working paper at http://hdl.handle.net/2268/147977. This working paper contains a number of additional results which are only briefly mentioned in the article published in Discrete Optimization.Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
http://hdl.handle.net/2268/171692
Title: Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
<br/>
<br/>Author, co-author: Abdel-Hafiez, M.; Pereira, P.J.; Kuzmichev, S.A.; Kuzmicheva, T.E.; Pudalov, V.M.; Harnagea, L.; Kordyuk, A.A.; Silhanek, Alejandro; Moshchalkov, V.V.; Shen, B.; Wen, Hai-Hu; Vasiliev, A.N.; Chen, Xiao-Jia
<br/>
<br/>Abstract: Using two experimental techniques, we studied single crystals of the 122-FeAs family with almost the same critical temperature, Tc. We investigated the temperature dependence of the lower critical field Hc1(T) of a Ca0.32Na0.68Fe2As2 (Tc ≈ 34 K) single crystal under static magnetic fields H parallel to the c axis. The temperature dependence of the London penetration depth can be described equally well either by a single anisotropic s-wave-like gap or by a two-gap model, while a d-wave approach cannot be used to fit the London penetration depth data. Intrinsic multiple Andreev reflection effect spectroscopy was used to detect bulk gap values in single crystals of the intimate compound Ba0.65K0.35Fe2As2, with the same Tc. We estimated the range of the large gap value L = 6–8 meV (depending on small variation of Tc) and its a k space anisotropy of about 30%, and the small gap Delta ≈ 1.7 ± 0.3 meV. This clearly indicates that the gap structure of our investigated systems more likely corresponds to a nodeless s-wave two gaps.L'odeur : question de sens ou de chimie
http://hdl.handle.net/2268/171674
Title: L'odeur : question de sens ou de chimie
<br/>
<br/>Author, co-author: Romain, Anne-Claude
<br/>
<br/>Abstract: Afin de mesurer au mieux un paramètre, il faut préalablement connaître son identité.
Concernant la métrologie de la pollution olfactive, toute la difficulté réside dans la
particularité de cette pollution. En effet, bien qu’associée à la pollution de l’air
par les molécules volatiles qui la génèrent, elle en diffère par son effet sensoriel. Il va de soi
que la pollution olfactive n’a de sens que par son odeur. Chaque individu a son propre odorat et dès lors sa propre interprétation de l’odeur. C’est cette subjectivité qui rend cette pollution si délicate à qualifier et à quantifier et qui la distingue de la pollution de l’air. De plus, contrairement à d’autres pollutions sensorielles de type sonore ou visuel, l’élément porteur ’est pas dans ce cas une grandeur physique telle que la longueur d’onde électromagnétique ou la variation de pression mais une grandeur physico-chimique particulière dont la mesure est beaucoup plus complexe.
Un dictionnaire de langue française définit l’odeur comme « une émanation volatile,
caractéristique de certains corps et susceptible de provoquer chez l’homme ou chez
un animal des sensations dues à l’excitation d’organes spécialisés ». Cette définition
de l’odeur met notamment en jeu deux disciplines : la chimie et la physiologie. En
effet un chimiste pourrait présenter l’odeur comme un ensemble de molécules aux
propriétés spécifiques qui inhalées par un individu génère une réaction, il s’intéresserait dès
lors aux odorants alors qu’un physiologiste parlerait plutôt du stimulus induit par ces odorants et des mécanismes qui le provoquent au niveau des organes.
Le traitement de l’information olfactive par le cerveau, la perception olfactive, conduit à plusieurs types de sensation. En effet, l’odeur perçue a trois grandes particularités :
l’intensité, la qualité (ou la nature de l’odeur) et la tonalité hédonique ou affective
(agrément/désagrément). A ces trois dimensions, il faut ajouter le caractère temporel du stimulus, dimension très utilisée dans le cadre de la pollution olfactive.Evaluation of bio-based additives in architectural paints
http://hdl.handle.net/2268/171669
Title: Evaluation of bio-based additives in architectural paints
<br/>
<br/>Author, co-author: Wenkin, M.; Delvaux, M.H.; de Lame, C.; Lourtie, A.; Pirmez, A.; Richel, Aurore; Olive, GillesX-raying the winds of the evolved massive binary HDE228766
http://hdl.handle.net/2268/171665
Title: X-raying the winds of the evolved massive binary HDE228766
<br/>
<br/>Author, co-author: Rauw, Grégor; Mahy, Laurent; Nazé, Yaël; Swings, Jean-PierreX-ray emission from magnetic massive stars
http://hdl.handle.net/2268/171664
Title: X-ray emission from magnetic massive stars
<br/>
<br/>Author, co-author: Nazé, Yaël; Petit, Véronique; Rindbrand, Mélanie; Cohen, David; Owocki, Stan; ud-Doula, Asif; Wade, Gregg; Swings, Jean-PierreLe livre préféré - l'essence meme de la science
http://hdl.handle.net/2268/171663
Title: Le livre préféré - l'essence meme de la science
<br/>
<br/>Author, co-author: Nazé, YaëlUn univers de perles - l'évolution des étoiles
http://hdl.handle.net/2268/171662
Title: Un univers de perles - l'évolution des étoiles
<br/>
<br/>Author, co-author: Nazé, YaëlCacahuète céleste
http://hdl.handle.net/2268/171661
Title: Cacahuète céleste
<br/>
<br/>Author, co-author: Nazé, YaëlApplication of magnetic susceptibility as a paleoclimatic proxy on Paleozoic sedimentary rocks and characterization of the magnetic signal – IGCP-580 projects and events
http://hdl.handle.net/2268/171634
Title: Application of magnetic susceptibility as a paleoclimatic proxy on Paleozoic sedimentary rocks and characterization of the magnetic signal – IGCP-580 projects and events
<br/>
<br/>Author, co-author: Da Silva, Anne-Christine; Whalen, M.T.; Hladil, J.; Koptikova, L.; Chen, D.; Spassov, S.; Boulvain, Frédéric; Devleeschouwer, X.ASSESSMENT OF THE PROPORTIONAL ODDS ASSUMPTION IN LONGITUDINAL STUDIES WITH MISSING ORDINAL OUTCOME DATA
http://hdl.handle.net/2268/171631
Title: ASSESSMENT OF THE PROPORTIONAL ODDS ASSUMPTION IN LONGITUDINAL STUDIES WITH MISSING ORDINAL OUTCOME DATA
<br/>
<br/>Author, co-author: Donneau, Anne-Françoise; Mauer, Murielle; Lambert, Philippe; Lesaffre, EmmanuelSIMULATION-BASED COMPARATIVE PERFORMANCE OF MULTIPLE IMPUTATION METHODS FOR INCOMPLETE LONGITUDINAL ORDINAL DATA
http://hdl.handle.net/2268/171630
Title: SIMULATION-BASED COMPARATIVE PERFORMANCE OF MULTIPLE IMPUTATION METHODS FOR INCOMPLETE LONGITUDINAL ORDINAL DATA
<br/>
<br/>Author, co-author: Donneau, Anne-Françoise; Mauer, Murielle; Lambert, Philippe; Molenberghs, GeertOlympiades mathématiques belges - Recueil de questions - Tome 8 (2011-2014)
http://hdl.handle.net/2268/171618
Title: Olympiades mathématiques belges - Recueil de questions - Tome 8 (2011-2014)
<br/>
<br/>Author, co-author: Dupont, Pascal; Sebille, MichelChemical abundances of fast-rotating OB stars
http://hdl.handle.net/2268/171613
Title: Chemical abundances of fast-rotating OB stars
<br/>
<br/>Author, co-author: Cazorla, Constantin; Morel, Thierry; Nazé, Yaël; Rauw, Grégor
<br/>
<br/>Abstract: Fast rotation in massive stars is predicted to induce mixing in their interior, but recent observations have challenged this concept by revealing a population of fast-rotating stars with normal nitrogen abundances at their surface (Hunter et al. 2009, A&A, 496, 841; Brott et al. 2011, A&A, 530, A116, but see Maeder et al. 2014, A&A, 565, A39). However, as the binary fraction of these stars is unknown, the importance of mass-transfer processes cannot be quantified. As a result, no definitive statements about the ability of single-star evolutionary models including rotation to reproduce these observations can be made. Our work combines for the first time a detailed surface abundance analysis with a radial-velocity monitoring for a sample of bright, fast-rotating Galactic OB stars to put strong constraints on stellar evolutionary and interior models.