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See detailHaplotype information combined with iterative pruning PCA (ipPCA) to improve population clustering
Chaichoompu, Kridsadakorn ULg; Fouladi, Ramouna; Wangkumhang, Pongsakorn et al

Scientific conference (2014, April 01)

Single Nucleotide Polymorphisms (SNPs) are commonly used to capture variations between populations. Often genome-wide SNP data are pruned based on linkage disequilibrium (LD) patterns or small subsets of ... [more ▼]

Single Nucleotide Polymorphisms (SNPs) are commonly used to capture variations between populations. Often genome-wide SNP data are pruned based on linkage disequilibrium (LD) patterns or small subsets of SNPs are selected (e.g. PCA-correlated SNPs) to reproduce the genomic structure of the complete data set. Identifying and differentiating between subpopulations using such a reduced set can become challenging, especially when similar geographic regions are involved or when spurious patterns are likely to exist. Although PCA-based methods can resolve structure, they cannot infer ancestry. On the other hand, the structure of haplotypes in unrelated individuals can reveal useful information about genetic ancestry. Notably, haplotype composition and the pattern of LD between markers may vary between larger populations but may also play a role within more confined geographic regions. In addition, iterative pruning principal component analysis (ipPCA) has been shown to be a powerful tool to cluster subpopulations based on SNP profiles. Despite the complexities that are associated with haplotype inference, we argue that added value can be obtained when the LD structure between SNPs is exploited in the search for relevant population strata. In this work, we propose to combine an LD-based novel haplotype encoding scheme with the ipPCA machinery to retrieve fine population substructures. The approach is compared to state-of-the-art methods in the context of population substructure and admixture analysis. [less ▲]

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See detailTheoretical studies of gravitational lensing phenomena: the case of multiply imaged quasars
Wertz, Olivier ULg

Doctoral thesis (2014)

In the early 1960s, gravitational lensing has received a special attention when S. Liebes and S. Refsdal have derived in detail some of the basic equations of the theory. While Liebes (1964) discussed the ... [more ▼]

In the early 1960s, gravitational lensing has received a special attention when S. Liebes and S. Refsdal have derived in detail some of the basic equations of the theory. While Liebes (1964) discussed the probability of detecting these effects and considered several astrophysical applications, Refsdal (1964) derived, inter alia, his famous relation which links the Hubble parameter (H0) to the expected time delays between pairs of lensed images. From that moment, the scientific community fully realized that gravitational lensing effects offer a new way of probing cosmology. However, an important fact has been to accept that the determination of H0 seems to be model dependent, not only on the universe model, but also on the mass distribution of the deflector. The main topic of the present thesis constitutes a straight continuation of this inquiry. We have been sounding parts of the mathematical lensing framework on two fronts. First, considering to first order a very small misalignment between the source, the lens and the observer, we have derived the expressions of the lensed image positions along with their amplification ratios, for the case of power-law axially symmetric mass distributions, the so-called ε-γ family of models (Wertz, Pelgrims & Surdej, 2012). After combining these results, it has allowed us to derive an expression for H0 independently of the model parameters. We have extended this study to the ε-γ family of models with external shear, as well as to the singular isothermal ellipsoid (SIE) models. For both these types of models, we have obtained an expression of H0 which is once again independent, to first order, of the model parameters. Furthermore, even though these families of models remain rigorously distinct, except for the singular isothermal sphere (SIS) and the perfect alignment, the expression of H0 in terms of observable quantities and of the source position takes surprisingly the same simple form. In addition, we have demonstrated the feasibility of analytically constraining to first order the model parameters by only using the astrometric positions of the lensed images. Therefore, for the case of a small misalignment between the source, the deflector and the observer, it is straightforward to determine whether the ε-γ or SIE family of models constitutes a judicious representation of the mass distribution of the deflector. It is conceivable that similar results can be deduced for other families of models. Secondly, we have developed a new analytical approach in order to determine the expression of the deflection angle, hereafter α. Since the latter depends on the deflector mass distribution, there exists no global explicit expression but only an implicit definition of α. Therefore, the analytical methods used to obtain the explicit expression differ for different types of mass distribution. However, using the Fourier transform theory, one may basically express α in terms of the Fourier transform of the surface mass density. Such a method allows us to approach any mass distribution in a unique way. As a first application, we have separately derived the expression of the two components of α for the case of homoeoidal symmetric lenses (Wertz & Surdej, 2013). This original result constitutes a first proof that the Fourier approach constitutes a promising alternative to the complex formalism introduced by Bourassa & Kantowski (1975, corrected by Bray 1984). A particular case of homoeoidal symmetric lenses lies in the non-singular isothermal ellipsoid (NSIE) family of models for which the analytical treatment has been somewhat limited (Kormann & al. 1994). The use of the Fourier approach has made possible to derive a complete analytical treatment of the NSIE, i.e. the expressions of the deflection angle, the deflection potential, and the critical and caustic curves even off the axis (Wertz & Surdej, submitted to MNRAS in february 2014). This original result has allowed us to investigate and better understand this family of models. Furthermore, it is of great interest for mass distribution modeling and to rigorously determine the expected time delays between pairs of lensed images. The previous analytical treatments mainly consisted of parametrical models for the deflector. An alternative way to grasp lenses consists in modeling their mass distribution using non-parametric models. With this aim in mind, we have proceeded as follows: we tessellate the lens plane with squared pixels, and associate to each of them a constant surface mass density. Making use of the Fourier approach, we have derived the expression of the deflection angle for the whole grid. This result contains the main advantage of the non-parametric models, i.e. to model any type of mass distribution without any preconception, and the usefulness of handling quantities which can be described with analytical functions. [less ▲]

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See detailDo Consumers Pay More for What They Value More? The Case of Local Milk-based Dairy Products in Senegal
Lefevre, Mélanie ULg

in Agricultural and Resource Economics Review (2014), 43(1), 158-177

Senegalese consumers prefer milk-based dairy products that are local and fresh to ones produced with imported powder. However, prices for fresh-milk-based and powder-based products are not significantly ... [more ▼]

Senegalese consumers prefer milk-based dairy products that are local and fresh to ones produced with imported powder. However, prices for fresh-milk-based and powder-based products are not significantly different. I address this puzzle by first confirming the preference using choice-based conjoint data to evaluate whether Senegalese consumers will pay a significant positive premium for fresh local products. I then identify price determinants using a unique dataset of milk product characteristics. The results verify the Senegalese preference for fresh local dairy products and show that consumers’ misinformation regarding product composition prevents them from allocating a higher price to local milk-based products. [less ▲]

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See detailIncreasing meltwater discharge from the Nuuk region of the Greenland ice sheet and implications for mass balance (1960-2012)
Van As, D; Andersen, ML; Petersen, D et al

in Journal of Glaciology (2014), 60(220), 314-322

We assess the runoff and surface mass balance (SMB) of the Greenland ice sheet in the Nuuk region (southwest) using output of two regional climate models (RCMs) evaluated by observations. The region ... [more ▼]

We assess the runoff and surface mass balance (SMB) of the Greenland ice sheet in the Nuuk region (southwest) using output of two regional climate models (RCMs) evaluated by observations. The region encompasses six glaciers that drain into Godtha ̊bsfjord. RCM data (1960–2012) are resampled to a high spatial resolution to include the narrow (relative to the native grid spacing) glacier trunks in the ice mask. Comparing RCM gridded results with automatic weather station (AWS) point measurements reveals that locally models can underestimate ablation and overestimate accumulation by up to tens of per cent. However, comparison with lake discharge indicates that modelled regional runoff totals are more accurate. Model results show that melt and runoff in the Nuuk region have doubled over the past two decades. Regional SMB attained negative values in recent high-melt years. Taking into account frontal ablation of the marine-terminating glaciers, the region lost 10–20 km3 w.e. a–1 in 2010–12. If 2010 melting prevails during the remainder of this century, a low-end estimate of sea-level rise of 5 mm is expected by 2100 from this relatively small section (2.6%) of the ice sheet alone. [less ▲]

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See detailLes valeurs et les valorisations des images
Dondero, Maria Giulia ULg

in Biglari, Amir (Ed.) Les valeurs. Aux fondements de la sémiotique (2014)

Cet article vise à explorer la manière dont la sémiotique greimassienne a traité la question des valeurs dans le cadre de l’image, notamment photographique et artistique. Après une relecture critique de ... [more ▼]

Cet article vise à explorer la manière dont la sémiotique greimassienne a traité la question des valeurs dans le cadre de l’image, notamment photographique et artistique. Après une relecture critique de l’ouvrage de Jean-Marie Floch, Les formes de l’empreinte, et de la distinction entre valeurs dans l’image et valorisations des images, ce travail se consacre à l’exposition de nouvelles propositions de la sémiotique des pratiques de Jacques Fontanille en essayant de les lier à des réflexions sur les objets et les pratiques de la photographie artistique (l’utilisation des séries, de l’original, des différents tirages, etc.). Si l’attention est portée surtout sur la photo artistique, ce texte envisage également une comparaison avec les pratiques de l’original et de l’authenticité dans la photo de guerre, la photo de famille et la photo-image pieuse. L’objectif majeur de ce travail est d’étudier les diverses pratiques de valorisation des images photographiques afin de faire éclater la notion ontologique de trace photographique. [less ▲]

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See detailOverview and Benchmarking of Motion Detection Methods
Jodoin, Pierre-Marc; Pierard, Sébastien ULg; Wang, Yi et al

in Bouwmans; Porikli; Hoferlin (Eds.) et al Background Modeling and Foreground Detection for Video Surveillance (2014)

In this chapter, we provide an overview of the most highly cited motion detection meth- ods. We identify the most commonly used background models together with their features, the kind of updating scheme ... [more ▼]

In this chapter, we provide an overview of the most highly cited motion detection meth- ods. We identify the most commonly used background models together with their features, the kind of updating scheme they use, some spatial aggregation models as well as the most widely used post-processing operations. We also provide an overview of datasets used to validate motion detection methods. Please note that this literature review is by no means exhaustive and thus we provide a list of surveys that the reader can rely on for further details. [less ▲]

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See detailIn vitro culture of seal muscle-derived satellite cells
Freichels, Astrid ULg; Baise, Etienne ULg; Jauniaux, Thierry ULg et al

Poster (2014, April)

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See detailEccentric training improves tendon biomechanical properties: a rat model
Kaux, Jean-François ULg; Drion, Pierre ULg; Libertiaux, Vincent et al

in British Journal of Sports Medicine (2014, April), 48(7), 155

Background: Even if eccentric exercises appear favourable in primary prevention of tendons lesions and, especially, in secondary prevention after tendinopathy, the biomechanical changes to the tissue are ... [more ▼]

Background: Even if eccentric exercises appear favourable in primary prevention of tendons lesions and, especially, in secondary prevention after tendinopathy, the biomechanical changes to the tissue are not yet clear. Objective: We aimed to better define the biomechanical changes that affect healthy tendon after eccentric and concentric training. Design: Randomised controlled trial. Participants: Eighteen Sprague-Dawley rats of 2 months. Interventions: The six rats in the control group (U) were not subjected to physical exercise. The 12 remaining rats (6 in each group) ran on a treadmill set at a +15° incline for concentric training (C) or a -15° incline for eccentric training (E), at a speed of 17 m/min for 1 h, three times per week for 5 weeks. Main Outcome Measurements: The tricipital, patellar and Achilles tendons were subsequently removed to perform a traction test until rupture, and a histological analysis was performed. Results: There was a significant improvement in the rupture force of the patellar and tricipital tendons between the U and E groups. The tricipital tendons in the control group presented a significantly smaller cross-section than the E- and C-trained groups, but none between E and C groups. No significant difference was observed for the mechanical stress at rupture per surface unit between the three groups for all three tendons. However, a tendency towards improvement these values was observed between the trained and the U groups for the patellar tendon. Histological studies demonstrated the tendency of the development of a greater number of blood vessels and a larger quantity of collagen in the eccentric group. Conclusions: The mechanical properties of tendons in rats improve after specific training, especially following eccentric training. Our results partly explained how mechanical loading, especially in eccentric mode, could improve the tendon structure. [less ▲]

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See detailEccentric training for elbow hypermobility
Kaux, Jean-François ULg; Delvaux, François ULg; Forthomme, Bénédicte ULg et al

in British Journal of Sports Medicine (2014, April), 48(7), 154

Background: Patients with hypermobility suffer from joints problems and chronic pain is the most frequently reported symptom. Objective: Eccentric muscle strengthening could be very important to protect ... [more ▼]

Background: Patients with hypermobility suffer from joints problems and chronic pain is the most frequently reported symptom. Objective: Eccentric muscle strengthening could be very important to protect hypermobile joints. Design: Case report. Patient: A girl (16 y.o.) affected by an Ehler-Danlos syndrome presented pain in the right elbow and the right wrist after a season of tennis. Interventions: Her training consisted of wrist prono-supination and flexion-extension muscle group reinforcement and proprioceptive training. To protect the wrist against excessive load, the eccentric strengthening exercises of prono-supinator and flexor-extensor muscles of elbow and wrist were undertaken gradually, at increasing speeds within a limited range of motion in flexion and extension, on an isokinetic device after an evaluation. She was also given an orthesis restricting the joint range of motion of the wrist. Main outcome measurements: The evaluation was made by isokinetic evaluation, visual analog scale and MOS-SF36 questionnaire before and after training. Results: The patient rapidly noted a decrease in pain and an increase in the stability of her right arm even when playing tennis. Isokinetic evaluation objectified a significant improvement in maximal torque in flexion-extension muscles of the right elbow. She was also given individualized home exercises. Conclusions: The goal of this eccentric training is to avoid hypermobility by using the muscles as a protective brake in the control of joint positioning. Muscles can be reinforced in eccentric mode with starting position at the maximum length of these muscles when unstreched. The exercises can be carried out safely on an isokinetic device, at slow speed and limited range of joint motion to avoid risk of luxation. Thus, in this case report, the eccentric exercises using an isokinetic device were effective to safely reinforce the muscles as a protective brake for joint hypermobility and prevent pain during practicing tennis. [less ▲]

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See detailProduction de l'habitat et enjeux territoriaux
Dethier, Perrine ULg; Halleux, Jean-Marie ULg

Report (2014)

Le projet de recherche est basé sur le concept de système de production de l'habitat. Un système de production de l'habitat vise à accroître et à améliorer l'offre en logements. Il se structure par les ... [more ▼]

Le projet de recherche est basé sur le concept de système de production de l'habitat. Un système de production de l'habitat vise à accroître et à améliorer l'offre en logements. Il se structure par les interactions entre les modes d'habiter (la demande), les modes de production (l'offre) et les modes de gestion (l'intervention de la puissance publique). Pour le contexte wallon, le système de production actuel est lié à un usage peu parcimonieux de la ressource foncière et à des problèmes importants d’étalement de la périurbanisation. Néanmoins, des signaux avant-coureurs de la mise en place d'un système de production plus vertueux vis-à-vis des principes stratégiques de l'aménagement du territoire semblent se manifester. La recherche I.5. intitulée « Production de l’habitat et enjeux territoriaux » ambitionne d'étudier l'ampleur de ces changements et de comprendre quels sont les processus socioéconomiques qui les instituent. Au final, son objectif est de préciser comment l’intervention de la puissance publique peut s’appuyer sur ces pratiques émergentes en vue de soutenir la transition vers un nouveau système pour la production de l’habitat wallon. Notre ambition est donc d’identifier les conditions qui conduisent à des pratiques plus vertueuses vis-à-vis des principes stratégiques de l’aménagement durable, afin de les renforcer et de les généraliser dès que possible. [less ▲]

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See detailA new methodological approach for error distributions selection in Finance
Hambuckers, julien ULg; Heuchenne, Cédric ULg

Conference (2014, April)

In this article, we propose a robust methodology to select the most appropriate error distribution candidate, in a classical multiplicative heteroscedastic model. In a first step, unlike to the ... [more ▼]

In this article, we propose a robust methodology to select the most appropriate error distribution candidate, in a classical multiplicative heteroscedastic model. In a first step, unlike to the traditional approach, we don't use any GARCH-type estimation of the conditional variance. Instead, we propose to use a recently developed nonparametric procedure (Mercurio and Spokoiny, 2004): the Local Adaptive Volatility Estimation (LAVE). The motivation for using this method is to avoid a possible model misspecification for the conditional variance. In a second step, we suggest a set of estimation and model selection procedures (Berk-Jones tests, kernel density-based selection, censored likelihood score, coverage probability) based on the so-obtained residuals. These methods enable to assess the global fit of a given distribution as well as to focus on its behavior in the tails. Finally, we illustrate our methodology on three time series (UBS stock returns, BOVESPA returns and EUR/USD exchange rates). [less ▲]

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See detailLa discussion à visée démocratique et philosophique au prisme de la critique deleuzienne de la discussion. Analyse d'un verbatim.
Herla, Anne ULg; Jeanmart, Gaëlle

in Diotime. Revue internationale de didactique de la philosophie. (2014, April), 60

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See detailData normalization and supervised learning to assess the condition of patients with multiple sclerosis based on gait analysis
Azrour, Samir ULg; Pierard, Sébastien ULg; Geurts, Pierre ULg et al

Poster (2014, April)

Gait impairment is considered as an important feature of disability in multiple sclerosis but its evaluation in the clinical routine remains limited. In this paper, we assess, by means of supervised ... [more ▼]

Gait impairment is considered as an important feature of disability in multiple sclerosis but its evaluation in the clinical routine remains limited. In this paper, we assess, by means of supervised learning, the condition of patients with multiple sclerosis based on their gait descriptors obtained with a gait analysis system. As the morphological characteristics of individuals influence their gait while being in first approximation independent of the disease level, an original strategy of data normalization with respect to these characteristics is described and applied beforehand in order to obtain more reliable predictions. In addition, we explain how we address the problem of missing data which is a common issue in the field of clinical evaluation. Results show that, based on machine learning combined to the proposed data handling techniques, we can predict a score highly correlated with the condition of patients. [less ▲]

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