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See detailRetrouvailles à vélo avec Dick Annegarn
Demoulin, Laurent ULg

E-print/Working paper (2014)

Le nouveau CD de Dick Annegarn, Vélo va (2014), offre à son auditeur, à travers un bel échantillon de dix chansons, un aperçu des différentes facettes de l’art de l’auteur-compositeur-interprète.

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See detailSome misunderstood or unknown tricks (IX) (LaTeX)
Merciadri, Luca ULg

E-print/Working paper (2014)

We describe here how to display date & time in a standard format, write (draw) dash integrals, number rows in tables, use unhabitual punctuation marks: interrobang and percontation point, draw dependency ... [more ▼]

We describe here how to display date & time in a standard format, write (draw) dash integrals, number rows in tables, use unhabitual punctuation marks: interrobang and percontation point, draw dependency arrows, distinguish between ConTeXt, LuaTeX, teTeX and XeTeX. The last section gives a LaTeX-related crossword puzzle. [less ▲]

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See detailRecueil de réglementation interne des principaux partis allemands, belges et britanniques
Bouhon, Frédéric ULg

E-print/Working paper (2014)

Le présent recueil compile des extraits de la réglementation interne des principaux partis allemands, belges et britanniques. Cette documentation vient principalement appuyer le chapitre 1er de la ... [more ▼]

Le présent recueil compile des extraits de la réglementation interne des principaux partis allemands, belges et britanniques. Cette documentation vient principalement appuyer le chapitre 1er de la deuxième partie de notre étude sur le droit électoral et le principe d’égalité (à paraître en septembre 2014 aux éditions Bruylant) dans laquelle nous avons notamment étudié une partie du droit interne de certaines formations politiques. [less ▲]

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See detailEn attendant Toussaint
Demoulin, Laurent ULg

E-print/Working paper (2014)

Présentation et analyse de deux courtes pièces, Rideau et Ni l'un ni l'autre, écrites par Jean-Philippe Toussaint en 1981, quand il était un jeune auteur inconnu influencé par Samuel Beckett.

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See detailWASP-104b and WASP-106b: two transiting hot Jupiters in 1.75-day and 9.3-day orbits
Smith, A. M. S.; Anderson, D. R.; Armstrong, D. J. et al

E-print/Working paper (2014)

We report the discovery from the WASP survey of two exoplanetary systems, each consisting of a Jupiter-sized planet transiting an 11th magnitude (V) main-sequence star. WASP-104b orbits its star in 1.75 d ... [more ▼]

We report the discovery from the WASP survey of two exoplanetary systems, each consisting of a Jupiter-sized planet transiting an 11th magnitude (V) main-sequence star. WASP-104b orbits its star in 1.75 d, whereas WASP-106b has the fourth-longest orbital period of any planet discovered by means of transits observed from the ground, orbiting every 9.29 d. Each planet is more massive than Jupiter (WASP-104b has a mass of 1.27±0.05 MJup, while WASP-106b has a mass of 1.93±0.08 MJup). Both planets are just slightly larger than Jupiter, with radii of 1.14±0.04 and 1.09±0.04 RJup for WASP-104 and WASP-106 respectively. No significant orbital eccentricity is detected in either system, and while this is not surprising in the case of the short-period WASP-104b, it is interesting in the case of WASP-106b, because many otherwise similar planets are known to have eccentric orbits. [less ▲]

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See detailCeci n’est pas un conseil !
Choffray, Jean-Marie ULg

E-print/Working paper (2014)

La « Grande Récession de 2008 » a un mérite. Un seul ! Elle a rendu public le fait que personne ne savait exactement ce qui s’était passé, ni ce qui se passait. Pourquoi une telle crise de confiance avait ... [more ▼]

La « Grande Récession de 2008 » a un mérite. Un seul ! Elle a rendu public le fait que personne ne savait exactement ce qui s’était passé, ni ce qui se passait. Pourquoi une telle crise de confiance avait-elle vu le jour ? Quelles en seraient les conséquences ? Toutes et tous se sont trompés, y compris les meilleurs. Même celles et ceux qui étaient convaincus d’avoir raison ! Plus que jamais, l’incertitude, la saine et souveraine incertitude, garantit la liberté de l’investisseur... et du professeur ! [less ▲]

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See detailShort Prime Quadratizations of Cubic Negative Monomials
Crama, Yves ULg; Rodriguez Heck, Elisabeth ULg

E-print/Working paper (2014)

Pseudo-Boolean functions naturally model problems in a number of different areas such as computer science, statistics, economics, operations research or computer vision, among others. Pseudo-Boolean ... [more ▼]

Pseudo-Boolean functions naturally model problems in a number of different areas such as computer science, statistics, economics, operations research or computer vision, among others. Pseudo-Boolean optimization (PBO) is NP-hard, even for quadratic polynomial objective functions. However, much progress has been done in finding exact and heuristic algorithms for the quadratic case. Quadratizations are techniques aimed at reducing a general PBO problem to a quadratic polynomial one. Quadratizing single monomials is particularly interesting because it allows quadratizing any pseudo-Boolean function by termwise quadratization. A characterization of short quadratizations for negative monomials has been provided. In this report we present a proof of this characterization for the case of cubic monomials, which requires a different analysis than the case of higher degree. [less ▲]

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See detailOptimization of the service start time for an elementary shortest path problem with time windows
Arda, Yasemin ULg; Crama, Yves ULg; Kucukaydin, Hande ULg

E-print/Working paper (2014)

We investigate an elementary shortest path problem with resource constraints where a single capacitated vehicle, initially located at a depot, must serve a set of customers while respecting their ... [more ▼]

We investigate an elementary shortest path problem with resource constraints where a single capacitated vehicle, initially located at a depot, must serve a set of customers while respecting their individual time windows. When the vehicle visits a customer, it delivers the customer's demand and collects a revenue in return for the delivery. The vehicle can start its trip at any desired time. The transportation cost is a function of both the total distance traveled and the duration of the assigned trip. The objective is to determine the service start time from the depot, the subset of customers to be served, and the trip to be performed so as to minimize the total loss, which is calculated as the di erence between the transportation cost and the revenue collected from the customers. We develop two exact dynamic programming algorithms which can deal with an in nite number of Pareto-optimal states arising from the fact that the starting time and the duration of the trip act like continuous decision variables. We report computational results obtained with these algorithms and with a faster heuristic for the elementary shortest path problem. We also examine the performance of these algorithms when they are used to solve the pricing subproblem arising in the framework of a column generation algorithm for a related vehicle routing problem with time windows. [less ▲]

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See detailColour-magnitude diagrams of transiting Exoplanets - II. A larger sample from photometric distances
Triaud, Amaury H. M. J.; Lanotte, Audrey ULg; Smalley, Barry et al

E-print/Working paper (2014)

Colour-magnitude diagrams form a traditional way of presenting luminous objects in the Universe and compare them to each others. Here, we estimate the photometric distance of 44 transiting exoplanetary ... [more ▼]

Colour-magnitude diagrams form a traditional way of presenting luminous objects in the Universe and compare them to each others. Here, we estimate the photometric distance of 44 transiting exoplanetary systems. Parallaxes for seven systems confirm our methodology. Combining those measurements with fluxes obtained while planets were occulted by their host stars, we compose colour-magnitude diagrams in the near and mid-infrared. When possible, planets are plotted alongside very low-mass stars and field brown dwarfs, who often share similar sizes and equilibrium temperatures. They offer a natural, empirical, comparison sample. We also include directly imaged exoplanets and the expected loci of pure blackbodies. Irradiated planets do not match blackbodies; their emission spectra are not featureless. For a given luminosity, hot Jupiters' daysides show a larger variety in colour than brown dwarfs do and display an increasing diversity in colour with decreasing intrinsic luminosity. The presence of an extra absorbent within the 4.5 $\mu$m band would reconcile outlying hot Jupiters with ultra-cool dwarfs' atmospheres. Measuring the emission of gas giants cooler than 1000 K would disentangle whether planets' atmospheres behave more similarly to brown dwarfs' atmospheres than to blackbodies, whether they are akin to the young directly imaged planets, or if irradiated gas giants form their own sequence. [less ▲]

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See detailEconomic Statistical Design of the VP( X) ̅ Control Charts for Monitoring a Process under Non-normality
Seif, Asghar; Faraz, Alireza ULg; Saniga, Erwin

E-print/Working paper (2014)

Recent studies proved that variable parameters (VP) X ̅ control charts not only detects process mean shifts quicker than the classical X ̅ control chart but also has better economic properties ... [more ▼]

Recent studies proved that variable parameters (VP) X ̅ control charts not only detects process mean shifts quicker than the classical X ̅ control chart but also has better economic properties. Furthermore, like most papers in control chart design, the fundamental assumption is that process data are normally distributed. Nevertheless, process quality variables may not be normal in application. In this paper, we investigate the economic statistical design of the VP X ̅ control chart when the underlying process distribution is non-normal. We illustrate the design procedure and perform a sensitivity analysis on the process and cost parameters based upon the degrees of skewness and kurtosis of the population using an industrial application. [less ▲]

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See detailChina, 1978-2013: from one Plenum to another. Reflections on hopes and constraints for reform in the Xi Jingping era
Florence, Eric ULg

E-print/Working paper (2014)

Why is it so difficult to talk about China in a nuanced and contrasting manner without falling back on superlatives and generalisations? In about thirty years, China’s GDP per capita has multiplied by ... [more ▼]

Why is it so difficult to talk about China in a nuanced and contrasting manner without falling back on superlatives and generalisations? In about thirty years, China’s GDP per capita has multiplied by eight. From a marginal economic power during the Maoist period (1949-1978), China is now ranked tenth in terms of global economic weight. “Wealth and power” (fu qiang) is the expression that embodies China’s quest for modernity since the second half of the 19th century, when China was still under the yoke of the West. This ambition is still at the heart of the “Chinese dream of rejuvenation of the Chinese nation” dear to Xi Jinping, which he set out during the Third Plenum of the 18th Central Committee of the Chinese Communist Party. But focusing only on this vision of “wealth and power” takes us back to one of the most common ways of representing China: reducing the ongoing socio-economic changes and dynamics to a set of numeric values, ultimately reified and homogenised. The increased power and internationalisation of the Chinese economy has prompted a combination of worry and enthusiasm. What does this imply about the paradigm shift in the way we portray this country? Perhaps it is still hard to leave behind the image of a subordinate, poor and voiceless China and consider the Chinese people as, at least, our equals. [less ▲]

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See detailNew Orleans Jazz & Heritage Festival 2014
Sacré, Robert ULg

E-print/Working paper (2014)

Compte rendu du NOLA Jazz & Heritage Festival avril-mai 2014 , avec photos

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See detailThe binary near-Earth asteroid (175706) 1996 FG3 - An observational constraint on its orbital stability
Scheirich, P.; Pravec, P.; Jacobson, S. A. et al

E-print/Working paper (2014)

Using our photometric observations taken between April 1996 and January 2013 and other published data, we derive properties of the binary near-Earth asteroid (175706) 1996 FG3 including new measurements ... [more ▼]

Using our photometric observations taken between April 1996 and January 2013 and other published data, we derive properties of the binary near-Earth asteroid (175706) 1996 FG3 including new measurements constraining evolution of the mutual orbit with potential consequences for the entire binary asteroid population. We also refined previously determined values of parameters of both components, making 1996 FG3 one of the most well understood binary asteroid systems. We determined the orbital vector with a substantially greater accuracy than before and we also placed constraints on a stability of the orbit. Specifically, the ecliptic longitude and latitude of the orbital pole are 266{\deg} and -83{\deg}, respectively, with the mean radius of the uncertainty area of 4{\deg}, and the orbital period is 16.1508 +\- 0.0002 h (all uncertainties correspond to 3sigma). We looked for a quadratic drift of the mean anomaly of the satellite and obtained a value of 0.04 +\- 0.20 deg/yr^2, i.e., consistent with zero. The drift is substantially lower than predicted by the pure binary YORP (BYORP) theory of McMahon and Scheeres (McMahon, J., Scheeres, D. [2010]. Icarus 209, 494-509) and it is consistent with the theory of an equilibrium between BYORP and tidal torques for synchronous binary asteroids as proposed by Jacobson and Scheeres (Jacobson, S.A., Scheeres, D. [2011]. ApJ Letters, 736, L19). Based on the assumption of equilibrium, we derived a ratio of the quality factor and tidal Love number of Q/k = 2.4 x 10^5 uncertain by a factor of five. We also derived a product of the rigidity and quality factor of mu Q = 1.3 x 10^7 Pa using the theory that assumes an elastic response of the asteroid material to the tidal forces. This very low value indicates that the primary of 1996 FG3 is a 'rubble pile', and it also calls for a re-thinking of the tidal energy dissipation in close asteroid binary systems. [less ▲]

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See detailLettre d'information trimestrielle n° 14 du projet DACEFI 2
Meunier, Quentin; Moumbogou, Carl; Boldrini, Sylvie et al

E-print/Working paper (2014)

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See detailSimple connectome inference from partial correlation statistics in calcium imaging
Sutera, Antonio ULg; Joly, Arnaud ULg; François-Lavet, Vincent ULg et al

E-print/Working paper (2014)

In this work, we propose a simple yet effective solution to the problem of connectome inference in calcium imaging data. The proposed algorithm consists of two steps. First, processing the raw signals to ... [more ▼]

In this work, we propose a simple yet effective solution to the problem of connectome inference in calcium imaging data. The proposed algorithm consists of two steps. First, processing the raw signals to detect neural peak activities. Second, inferring the degree of association between neurons from partial correlation statistics. This paper summarises the methodology that led us to win the Connectomics Challenge, proposes a simplified version of our method, and finally compares our results with respect to other inference methods. [less ▲]

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See detailFederico García Lorca en Lieja
Francois, Jeromine ULg

E-print/Working paper (2014)

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See detailThe Macroeconomics of PAYG Pension Schemes in an Aging Society
Artige, Lionel ULg; Cavenaile, Laurent; Pestieau, Pierre ULg

E-print/Working paper (2014)

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See detailSome misunderstood or unknown tricks (VIII) and Turing-completeness (LaTeX)
Merciadri, Luca ULg

E-print/Working paper (2014)

We will begin by exposing new tricks, i.e. how to 1. write ‘closed’ square roots, 2. insert blank pages, 3. ask the reader to turn the page, 4. write bold words in an index, 5. divide a cell by a diagonal ... [more ▼]

We will begin by exposing new tricks, i.e. how to 1. write ‘closed’ square roots, 2. insert blank pages, 3. ask the reader to turn the page, 4. write bold words in an index, 5. divide a cell by a diagonal, 6. draw ‘product integrals,’ 7. understand what happens when \mathcal has a lower-case letter argument. We will then consider an uncommon example of what one can do with LaTeX, in link with its Turing completeness. [less ▲]

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See detailAn Ant Colony System for Responsive Dynamic Vehicle Routing
Schyns, Michael ULg

E-print/Working paper (2014)

We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets ... [more ▼]

We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets (DVRPTWSD). Besides the traditional distance criterion, we address the important case of responsiveness. Responsiveness is defined here as completing a delivery as soon as possible, within the time window, such that the client or the truck may restart its activities. This is crucial for many production or service activities in different fields: express parcel deliveries, taxi services, Just in Time production, express repair services, medical care, petrol station replenishment, etc. We develop an interactive web-based solution to allow dispatchers to take new information into account in real-time. The algorithm and its parametrization were tested on real and artificial instances. We first illustrate our approach with a problem submitted by Liege Airport, the 8th biggest cargo airport in Europe. The goal is to develop a decision system to optimize the journey of the refueling trucks. We then consider some classical VRP benchmarks with extensions for more complex problems. [less ▲]

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See detailHexis
Durand, Pascal ULg

E-print/Working paper (2014)

Définition et discussion du concept d'« Hexis » dans la sociologie de Pierre Bourdieu.

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See detailCapital symbolique
Durand, Pascal ULg

E-print/Working paper (2014)

Présentation et discussion du concept de « Capital symbolique » dans la sociologie de Pierre Bourdieu.

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See detailIllusio
Durand, Pascal ULg

E-print/Working paper (2014)

Définition et discussion du concept d'« Illusio » dans la sociologie de Pierre Bourdieu.

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See detailProtecting Assets Under Non-Parametric Market Conditions
Choffray, Jean-Marie ULg; Pahud de Mortanges, Charles ULg

E-print/Working paper (2014)

Under non-parametric market conditions, investors usually become more concerned about the return of their money than about the return on their money. Protecting assets becomes the surest if not the only ... [more ▼]

Under non-parametric market conditions, investors usually become more concerned about the return of their money than about the return on their money. Protecting assets becomes the surest if not the only path to survival and growth. High frequency trading systems, over leveraged shadow entities, flash crashes, and stealth central bank actions, to name a few, contribute to create a “Rumsfeldian” type of world in which decision makers have to cope not only with “Known knowns” – things they know that they know – but also with “Unknown unknowns” – things they don’t know that they don’t know! The goal of this paper is to explore such a conceptual model of the “Unknown” and to derive from it a concise and coherent set of battle-tested heuristics aimed at designing effective investment strategies to protect assets. [less ▲]

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See detailLes determinants des Price-Earnings ratios en Europe
Lambert, Marie ULg; Lenglois, Julien ULg; Streel, Alexandre ULg et al

E-print/Working paper (2014)

Méthode largement employée en matière d’évaluation d’entreprise, l’analyse dite comparative s’appuie sur une estimation de la valeur des entreprises selon un multiple de leur agrégat financier. Aussi ... [more ▼]

Méthode largement employée en matière d’évaluation d’entreprise, l’analyse dite comparative s’appuie sur une estimation de la valeur des entreprises selon un multiple de leur agrégat financier. Aussi appelée ‘méthode des pairs’, les multiples sont définis sur base d’un échantillon d’entreprises considérées comme comparable en termes de croissance et de risque. Le secteur est généralement retenu en pratique comme critère sous-tendant la croissance et le profil de risque opérationnel de l’entreprise. L’analyse menée dans cet article démontre l’importance des fondamentaux tels que la croissance, le risque et le taux de distribution des bénéfices dans la définition des pairs et donc de la valeur des entreprises. Sur base d’un échantillon des 100 entreprises cotées sur l’EURONEXT, entreprises les plus capitalisées et liquides, l’étude met en évidence un impact différencié de ces déterminants selon les conditions économiques. Les conséquences de notre analyse sont multiples. Premièrement, notre étude témoigne de l’importance des variables telles que le profil de risque et les perspectives croissance pour la sélection des pairs. Notre approche permet par ailleurs d’appréhender la valeur des entreprises sur base de leurs propres fondamentaux, corrigeant ainsi la méthode des multiples ‘sectoriels’ pour les différences qui subsistent au sein des sous-jacents de la valeur. Finalement, cet article nourrit une discussion quant à l’impact de la finance comportementale sur la valorisation de l’entreprise de par l’impact différencié des fondamentaux sur la valeur des entreprises au cours du temps. [less ▲]

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

E-print/Working paper (2014)

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 detailEstimation and approximation in nonlinear dynamic systems using quasilinearization
Frasso, Gianluca ULg; Jaeger, Jonathan ULg; Lambert, Philippe ULg

E-print/Working paper (2014)

Nonlinear (systems of) ordinary differential equations (ODEs) are common tools in the analysis of complex one-dimensional dynamic systems. In this paper we propose a smoothing approach regularized by a ... [more ▼]

Nonlinear (systems of) ordinary differential equations (ODEs) are common tools in the analysis of complex one-dimensional dynamic systems. In this paper we propose a smoothing approach regularized by a quasilinearized ODE-based penalty in order to approximate the state functions and estimate the parameters defining nonlinear differential systems from noisy data. Within the quasilinearized spline based framework, the estimation process reduces to a conditionally linear problem for the optimization of the spline coefficients. Furthermore, standard ODE compliance parameter(s) selection criteria are easily applicable and conditions on the state function(s) can be eventually imposed using soft or hard constraints. The approach is illustrated on real and simulated data. [less ▲]

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See detailTentatives de réflexion sémiotique et psychanalytique au sujet du voile islamique
Demoulin, Laurent ULg

E-print/Working paper (2014)

La sémiotique et la psychanalyse sont peut-être de nature à enrichir le débat sur l'interdiction du voile islamique dans les lieux publics.

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See detailLe Parti Socialiste en 2014: un programme électoral en rupture avec les précédents ?
Piet, Grégory ULg; Dandoy, Régis

E-print/Working paper (2014)

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See detailMultivariate coefficients of variation: comparison and influence functions
Aerts, Stéphanie ULg; Haesbroeck, Gentiane ULg; Ruwet, Christel ULg

E-print/Working paper (2014)

In the univariate setting, coefficients of variation are well known and used to compare the variability of populations characterized by variables expressed in different units or having really different ... [more ▼]

In the univariate setting, coefficients of variation are well known and used to compare the variability of populations characterized by variables expressed in different units or having really different means. When dealing with more than one variable, the use of such a relative dispersion measure is much less common even though several generalizations of the coefficient of variation to the multivariate setting have been introduced in the literature. In this paper, the lack of robustness of the sample versions of the multivariate CV's is illustrated by means of influence functions and a robust counterpart based on the Minimum Covariance Determinant (MCD) estimator is advocated. Then, focusing on two of the considered multivariate CV's, a diagnostic tool based on their influence functions is derived and its efficiency in detecting observations having an unduly large effect on variability is illustrated on a real-life data set. The influence functions are also used to compute asymptotic variances under elliptical distributions, yielding approximate confidence intervals. Finally, simulations are conducted in order to compare the performance of the classical and robust multivariate CV's in a finite sample setting. As expected, when the data are normally distributed, the classical estimator performs better than the robust counterpart based on the MCD estimator, while the reverse is true when the data are contaminated. [less ▲]

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See detailProposition de révisions de l'arrêté n° 018/MEF/SG/DGF/DFCOM du 31 janvier 2013 fixant les procédures d'attribution et de gestion des forêts communautaires
Moumbogou, Carl; Boldrini, Sylvie; Morin, Amélie et al

E-print/Working paper (2014)

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See detailExamining the Effect of Earnings Management on Bid-Ask Spread and Market Liquidity
Sougné, Danielle ULg; Ajina, Aymen ULg

E-print/Working paper (2014)

The main purpose of this paper is to argue the extent that earnings management lowers liquidity. It should increase information asymmetry and impair trading liquidity. Using a sample of French firms from ... [more ▼]

The main purpose of this paper is to argue the extent that earnings management lowers liquidity. It should increase information asymmetry and impair trading liquidity. Using a sample of French firms from 2008 to 2011, we find that firms that manage earnings have wider bid-ask spreads. Our results are robust for both of two well established measures of market liquidity. Therefore the empirical results indicate that firms that exhibit greater earnings management are associated with lower market liquidity. These findings are in line with adverse selection and shed light on the role corporate governance devices can play in the consideration of shareholder interest’s protection, which leads to improved stock market liquidity levels. [less ▲]

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See detailBott type periodicity for the higher octonions
Kreusch, Marie ULg

E-print/Working paper (2014)

We study the series of complex nonassociative algebras $\bbO_n$ and real nonassociative algebras $\bbO_{p,q}$ introduced in~\cite{MGO2011}. These algebras generalize the classical algebras of octonions ... [more ▼]

We study the series of complex nonassociative algebras $\bbO_n$ and real nonassociative algebras $\bbO_{p,q}$ introduced in~\cite{MGO2011}. These algebras generalize the classical algebras of octonions and Clifford algebras. The algebras $\bbO_{n}$ and $\bbO_{p,q}$ with $p+q=n$ have a natural $\Z_2^n$-grading, and they are characterized by cubic forms over the field $\Z_2$. We establish a periodicity for the algebras~$\bbO_{n}$ and $\bbO_{p,q}$ similar to that of the Clifford algebras $\mathrm{Cl}_{n}$ and~$\mathrm{Cl}_{p,q}$. [less ▲]

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See detailHubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
Knutson, Heather A.; Dragomir, Diana; Kreidberg, Laura et al

E-print/Working paper (2014)

Recent results from the Kepler mission indicate that super-Earths (planets with masses between 1-10 times that of the Earth) are the most common kind of planet around nearby Sun-like stars. These planets ... [more ▼]

Recent results from the Kepler mission indicate that super-Earths (planets with masses between 1-10 times that of the Earth) are the most common kind of planet around nearby Sun-like stars. These planets have no direct solar system analogue, and are currently one of the least well-understood classes of extrasolar planets. Many super-Earths have average densities that are consistent with a broad range of bulk compositions, including both water-dominated worlds and rocky planets covered by a thick hydrogen and helium atmosphere. Measurements of the transmission spectra of these planets offer the opportunity to resolve this degeneracy by directly constraining the scale heights and corresponding mean molecular weights of their atmospheres. We present Hubble Space Telescope near-infrared spectroscopy of two transits of the newly discovered transiting super-Earth HD 97658b. We use the Wide Field Camera 3's scanning mode to measure the wavelength-dependent transit depth in thirty individual bandpasses. Our averaged differential transmission spectrum has a median 1 sigma uncertainty of 19 ppm in individual bins, making this the most precise observation of an exoplanetary transmission spectrum obtained with WFC3 to date. Our data are inconsistent with a cloud-free solar metallicity atmosphere at the 17 sigma level. They are a good match for flat models corresponding to either a metal-rich atmosphere or a solar metallicity atmosphere with a cloud or haze layer located at pressures of a mbar or higher. [less ▲]

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See detailLettre d'information trimestrielle n° 13 du projet DACEFI 2
Meunier, Quentin; Moumbogou, Carl; Boldrini, Sylvie et al

E-print/Working paper (2014)

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See detailWASP-20b and WASP-28b: a hot Saturn and a hot Jupiter in near-aligned orbits around solar-type stars
Anderson, D. R.; Collier Cameron, A.; Hellier, C. et al

E-print/Working paper (2014)

We report the discovery of the planets WASP-20b and WASP-28b along with measurements of their sky-projected orbital obliquities. WASP-20b is an inflated, Saturn-mass planet (0.31 $M_{\rm Jup}$; 1.46 $R ... [more ▼]

We report the discovery of the planets WASP-20b and WASP-28b along with measurements of their sky-projected orbital obliquities. WASP-20b is an inflated, Saturn-mass planet (0.31 $M_{\rm Jup}$; 1.46 $R_{\rm Jup}$) in a 4.9-day, near-aligned ($\lambda = 8.1 \pm 3.6^\circ$) orbit around CD-24 102 ($V$=10.7; F9). WASP-28b is an inflated, Jupiter-mass planet (0.91 $M_{\rm Jup}$; 1.21 $R_{\rm Jup}$) in a 3.4-day, near-aligned ($\lambda = 8 \pm 18^\circ$) orbit around a $V$=12, F8 star. As intermediate-mass planets in short orbits around aged, cool stars ($7^{+2}_{-1}$ Gyr for WASP-20 and $5^{+3}_{-2}$ Gyr for WASP-28; both with $T_{\rm eff}$ < 6250 K), their orbital alignment is consistent with the hypothesis that close-in giant planets are scattered into eccentric orbits with random alignments, which are then circularised and aligned with their stars' spins via tidal dissipation. [less ▲]

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See detailEn el laboratorio de la ciencia ficción hispánica: una entrevista
Ceballos Viro, Alvaro ULg

E-print/Working paper (2014)

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See detailLettre d'Information N° 12 projet Dacefi
Meunier, Quentin; Mezui Mba, C.; Boldrini, Sylvie et al

E-print/Working paper (2014)

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See detailExperimental Study and Statistical Modeling of an Injection Scroll Compressor Operating with R407c.
Quoilin, Sylvain ULg

E-print/Working paper (2014)

This working paper describes an experimental study carried out on a refrigeration scroll compressor with and without vapour injection. The test rig designed for that purposed allows evaluating the ... [more ▼]

This working paper describes an experimental study carried out on a refrigeration scroll compressor with and without vapour injection. The test rig designed for that purposed allows evaluating the performance over a wide range of operating conditions, by varying the supply pressure, the injection pressure, the exhaust pressure, the supply superheating and the injection superheating. 97 Steady-state points are measured, with a maximum isentropic efficiency of 64.1% and a maximum consumed electrical power of 13.1 kW. A critical analysis of the experimental results is then carried out to evaluate the quality of the data using a machine learning method. This method based on Gaussian Processes regression, is used to build a statistical operating map of the compressor as a function of the different inputs. This statistical operating map can then be compared to the experimental data points to evaluate their accuracy. [less ▲]

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See detailNonparametric regression with cross-sectional data: an alternative to conditional product-limit estimators
Heuchenne, Cédric ULg; Laurent, Géraldine ULg

E-print/Working paper (2014)

Suppose the random vector (X,Y) satisfies the nonparametric regression model Y=m(X)+varepsilon, where m(x)=E[Y|X=x] and sigma²(x)=Var[varepsilon|X=x] are unknown smooth functions and the error varepsilon ... [more ▼]

Suppose the random vector (X,Y) satisfies the nonparametric regression model Y=m(X)+varepsilon, where m(x)=E[Y|X=x] and sigma²(x)=Var[varepsilon|X=x] are unknown smooth functions and the error varepsilon has zero mean and finite variance conditionally on X=x. The pair (X,Y) is obtained by cross-sectional sampling involving left-truncated and right-censored responses. The considered model is completely nonparametric but the conditional truncation distribution is assumed to be known. The novelty of this work is twofold: first, it extends the results on cross-sectional data to the conditional case and second, it generalizes the length bias results in the conditional case to right censoring and to any truncation distribution. New estimators for m(.) and sigma²(.) are constructed and relevant tools are used to quickly provide the main asymptotic properties for this kind of estimators. Extensive simulations are carried out and show that the new estimators outperform classical nonparametric estimators for left-truncated and right-censored data (when the truncation model is known). Finally, a data set on the mortality of diabetics is analyzed. [less ▲]

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See detailVon Themara nach Belgrad und zurück: Burkhard Spinnens Roman "Nevena"
Dupont, Bruno ULg

E-print/Working paper (2014)

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See detailL’intervention militaire internationale au Kosovo
Pierre, Alexia ULg

E-print/Working paper (2014)

This paper aims first to explore the international armed intervention in Kosovo, formalized through the Allied Force Operation headed by the Nato. A second part is dedicated to the legal aspects of this ... [more ▼]

This paper aims first to explore the international armed intervention in Kosovo, formalized through the Allied Force Operation headed by the Nato. A second part is dedicated to the legal aspects of this intervention regarding the international norms. [less ▲]

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See detailDes royaumes aux nations ? L’Europe barbare aux Ve-VIe siècles
Fialon, Sabine ULg

E-print/Working paper (2014)

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Peer Reviewed
See detailDynamic modelling of reservoir sedimentation in a semi-arid watershed
Adam, Nicolas; Erpicum, Sébastien ULg; Chenaoui, Bakhta et al

E-print/Working paper (2014)

Sedimentation in large reservoirs is a major issue in semi-arid regions characterized by severe seasonal water scarcity. As a contribution to improved sediment management, this study analyses the real ... [more ▼]

Sedimentation in large reservoirs is a major issue in semi-arid regions characterized by severe seasonal water scarcity. As a contribution to improved sediment management, this study analyses the real case of the reservoir of Sidi Yacoub in the north of Algeria. First, a dynamic model of the reservoir was set up and used to estimate hydraulic and sediment inflows, during the period 1990-2010, based on data recorded by the dam operator and measurements at a gauging station located downstream of the reservoir. Second, based on a statistical characterization of inflow and outflow discharges, a projection of future sedimentation was performed until 2030, using the assumption of stationarity of the statistical distributions. Third, the model was used to investigate the influence of possible climate change and to quantify the positive effects of measures to control erosion in the watershed. [less ▲]

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See detailIntentionality as Disposition
Boccaccini, Federico ULg

E-print/Working paper (2014)

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See detailWhat roles for energy cooperatives in the diffusion of distributed generation technologies?
Bauwens, Thomas ULg

E-print/Working paper (2014)

Whereas a centralized model of electricity infrastructure is still dominant today, many scholars advocate the diffusion of distributed generation technologies, implying geographically dispersed and small ... [more ▼]

Whereas a centralized model of electricity infrastructure is still dominant today, many scholars advocate the diffusion of distributed generation technologies, implying geographically dispersed and small-scale generation units located close to consumers. However, there exist various barriers of different natures to a large-scale penetration of these technologies. In this article, we focus on the behavioral and psychological ones, emphasizing the roles that citizens have to play in this issue. More specifically, we explore a specific way of involving citizens in such diffusion, namely energy cooperatives. After presenting the driving forces of the emergence of cooperative firms in the energy sector, we examine the assets of the cooperative ownership structure from the perspectives of behavioral economics and social psychology. Our analysis enables us to build a model of how cooperatives may enhance consumer engagement in the diffusion of distributed generation technologies. This provides a basic theoretical framework for future empirical research. [less ▲]

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See detailIntegrating the weight of history into the alignment framework: the case of distributed generation technologies
Bauwens, Thomas ULg

E-print/Working paper (2014)

Whereas a centralized energy supply system is still dominant today, the energy sector is currently witnessing the development of small-scale and more geographically dispersed generation units, so-called ... [more ▼]

Whereas a centralized energy supply system is still dominant today, the energy sector is currently witnessing the development of small-scale and more geographically dispersed generation units, so-called distributed generation technologies. So-called "alignment framework" proposes a very useful approach to look at this evolution. Yet, we argue in this paper that this framework does not fully take into account the inertia associated with past technological and institutional choices that may hinder future changes. Relying on the concept of socio-technical lock-in, we illustrate this point with the case of the diffusion of distributed generation technologies. Based on this analysis, we propose an adaptation of the alignment framework to integrate these elements. [less ▲]

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See detailParametric conditional variance estimation in location-scale models with censored data
Heuchenne, Cédric ULg; Laurent, Géraldine ULg

E-print/Working paper (2014)

Suppose the random vector (X,Y) satisfies the regression model Y=m(X)+sigma(X)*varepsilon, where m(.)=E(Y|.), sigma²(.)=Var(Y|.) belongs to some parametric class {sigma _theta(.): theta in Theta} and ... [more ▼]

Suppose the random vector (X,Y) satisfies the regression model Y=m(X)+sigma(X)*varepsilon, where m(.)=E(Y|.), sigma²(.)=Var(Y|.) belongs to some parametric class {sigma _theta(.): theta in Theta} and varepsilon is independent of X. The response Y is subject to random right censoring and the covariate X is completely observed. A new estimation procedure is proposed for sigma_theta(.) when m(.) is unknown. It is based on nonlinear least squares estimation extended to conditional variance in the censored case. The consistency and asymptotic normality of the proposed estimator are established. The estimator is studied via simulations and an important application is devoted to fatigue life data analysis. [less ▲]

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See detailThe role of segmentation and investor recognition trough the lens of cross-listing activity
Mouchette, Xavier ULg; Carrieri, Francesca; Muller, Aline ULg

E-print/Working paper (2014)

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See detailLa psychologie morale de Brentano
Boccaccini, Federico ULg

E-print/Working paper (2014)

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Peer Reviewed
See detailStatistically Bundled Shewhart Control Charts for Monitoring Delivery Chains Systems
Foster, Earnest; Faraz, Alireza ULg; Heuchenne, Cédric ULg

E-print/Working paper (2014)

Continuous monitoring of Delivery Time variables by means of control charts in a delivery chain is a very recent application of Statistical Process Control (SPC) to the service sector. The aim of the ... [more ▼]

Continuous monitoring of Delivery Time variables by means of control charts in a delivery chain is a very recent application of Statistical Process Control (SPC) to the service sector. The aim of the proposed method is to provide supply chain decision makers with an easy to be managed tool monitoring the current functioning state of the delivery chain. The implementation of SPC control charts makes it possible to limit over-corrections to false alarm conditions and to maintain at an acceptable level the safety stock, with a consequent reduction of the overall management costs of the delivery chain. An illustrative example shows the proposed control chart implementation in a real delivery chain. [less ▲]

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See detailTowards robust GWAS/GWAI protocol development for epistasis detection in context of real-life datasets
Bessonov, Kyrylo ULg

E-print/Working paper (2014)

The genome-wide association and interaction studies are a common practice these days but the correct application of statistical methods and workflows that consciously select best data processing ... [more ▼]

The genome-wide association and interaction studies are a common practice these days but the correct application of statistical methods and workflows that consciously select best data processing strategies is often missing in many GWA studies. Nevertheless given the multitude of such studies there is little consistency and consensus in data processing workflows and quality control steps. Data selection and filtering is often overlooked or poorly documented. Many times the default settings are blindly used disregarding any adjustments and/or optimizations under the context of specific dataset. In present study we want to bring awareness of paying a closer attention to parameter selection in genome-wide association interaction studies (GWAI). We had tested the impact of LD filtering, selection of epistasis algorithms (BOOST, MB-MDR) and marker selection and prioritization strategies on the final results variability under the context of the Ankylosin Spondolytis (AS) dataset obtained from WTCCC2 [1]. [less ▲]

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See detailHedwig Margrethe Elisabeth von Ranzau
Henneau, Marie-Elisabeth ULg

E-print/Working paper (2014)

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See detailPhysician induced demand for C-sections: does the convenience incentive matter?
Lefevre, Mélanie ULg

E-print/Working paper (2014)

This paper investigates whether physicians induce demand for C-sections in the days preceding leisure periods. I reject that doctors are meaningfully increasing the number of primary cesareans to ... [more ▼]

This paper investigates whether physicians induce demand for C-sections in the days preceding leisure periods. I reject that doctors are meaningfully increasing the number of primary cesareans to accommodate their own preferences for control of deliveries around holiday Mondays. Using a sample of more than 1,300,000 deliveries, I can estimate that the induced demand due to convenience is close to zero. A small signi cant e ect is found for women having had a previous C-section. While I replicate previous results of lower C-section rates on leisure periods, I show that they are due to the way doctors schedule planned cesareans rather than to an induced demand for reason of physicians' convenience. If induced demand occurs, the decision takes place in the labor room and is not planned in advance. [less ▲]

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See detailAn assessment of cross-listed firms’ diversification potential
Mouchette, Xavier ULg; Muller, Aline ULg

E-print/Working paper (2014)

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See detailA Supervised Machine Learning Approach to Variable Branching in Branch-And-Bound
Marcos Alvarez, Alejandro ULg; Louveaux, Quentin ULg; Wehenkel, Louis ULg

E-print/Working paper (2014)

We present in this paper a new approach that uses supervised machine learning techniques to improve the performances of optimization algorithms in the context of mixed-integer programming (MIP). We focus ... [more ▼]

We present in this paper a new approach that uses supervised machine learning techniques to improve the performances of optimization algorithms in the context of mixed-integer programming (MIP). We focus on the branch-and-bound (B&B) algorithm, which is the traditional algorithm used to solve MIP problems. In B&B, variable branching is the key component that most conditions the efficiency of the optimization. Good branching strategies exist but are computationally expensive and usually hinder the optimization rather than improving it. Our approach consists in imitating the decisions taken by a supposedly good branching strategy, strong branching in our case, with a fast approximation. To this end, we develop a set of features describing the state of the ongoing optimization and show how supervised machine learning can be used to approximate the desired branching strategy. The approximated function is created by a supervised machine learning algorithm from a set of observed branching decisions taken by the target strategy. The experiments performed on randomly generated and standard benchmark (MIPLIB) problems show promising results. [less ▲]

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See detailInflated discrete Beta regression models for Likert and discrete rating scale outcomes
Taverne, Cédric; Lambert, Philippe ULg

E-print/Working paper (2014)

Discrete ordinal responses such as Likert scales are regularly proposed in questionnaires and used as dependent variable in modeling. The response distribution for such scales is always discrete, with ... [more ▼]

Discrete ordinal responses such as Likert scales are regularly proposed in questionnaires and used as dependent variable in modeling. The response distribution for such scales is always discrete, with bounded support and often skewed. In addition, one particular level of the scale is frequently inflated as it cumulates respondents who invari- ably choose that particular level (typically the middle or one extreme of the scale) without hesitation with those who chose that alternative but might have selected a neighboring one. The inflated discrete beta regression (IDBR) model addresses those four critical characteristics that have never been taken into account simultaneously by existing models. The mean and the dispersion of rates are jointly regressed on covariates using an underlying beta distribution. The probability that choosers of the inflated level invariably make that choice is also regressed on covariates. Simulation studies used to evaluate the statistical properties of the IDBR model suggest that it produces more precise predictions than competing models. The ability to jointly model the location and dispersion of (the distribution of) an ordinal response, as well as to characterize the profile of subject selecting an ”inflated” alternative are the most relevant features of the IDBR model. It is illustrated with the analysis of the political positioning on a ”left-right” scale of the Belgian respondents in the 2012 European Social Survey. [less ▲]

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See detailEstimation of the error distribution in nonparametric regression with cross-sectional data
Heuchenne, Cédric ULg; Laurent, Géraldine ULg

E-print/Working paper (2014)

In this article, we study the nonparametric regression model Y=m(X)+varepsilon where m(x)=E[Y|X=x] and sigma²(x)=Var[varepsilon|X=x] are unknown smooth functions, and the error varepsilon has zero mean ... [more ▼]

In this article, we study the nonparametric regression model Y=m(X)+varepsilon where m(x)=E[Y|X=x] and sigma²(x)=Var[varepsilon|X=x] are unknown smooth functions, and the error varepsilon has zero mean and finite variance conditionally on X=x. The problem consists in estimating the cumulative distribution function of the error in a nonparametric way when the couple (X,Y) is obtained by cross-sectional sampling while the positive response Y can be right-censored. We propose a new estimator for the error distribution function based on the estimators of m(.) and sigma²(.) described in Heuchenne and Laurent 2014. A bootstrap procedure is developed to solve the critical problem of the smoothing parameter choice. We assess the performance of the proposed estimator through simulations. Finally, a data set based on the mortality of diabetics is analyzed. (Heuchenne Cédric and Laurent Géraldine, Nonparametric regression with cross-sectional data: an alternative to conditional product-limit estimators, 2014) [less ▲]

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See detailSize Matters, Book Value does not! The Fama-French empirical CAPM revisited
Lambert, Marie ULg; Hübner, Georges ULg

E-print/Working paper (2014)

The Fama and French (F&F) factors do not reliably estimate the size and book-to-market effects. Our paper shows that the former has been underestimated in the US market while the latter overestimated. We ... [more ▼]

The Fama and French (F&F) factors do not reliably estimate the size and book-to-market effects. Our paper shows that the former has been underestimated in the US market while the latter overestimated. We do so by replacing F&F’s independent rankings by the conditional ones introduced by Lambert and Hübner (2013), over which we improve the sorting procedure. This new specification better reflects the properties of the individual risk premiums. We emphasize a much stronger size effect than conventionally documented. As a major related outcome, the alternative risk factors deliver less specification errors when used to price passive investment indices [less ▲]

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Peer Reviewed
See detailCan meandering flows in shallow rectangular reservoir be modelled with the 2D shallow water equations?
Peltier, Yann ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

E-print/Working paper (2014)

In this article, the ability of the 2D shallow water equations to model meandering flows in shallow rectangular reservoirs is discussed. Four meandering flows, of various shallowness, were modelled using ... [more ▼]

In this article, the ability of the 2D shallow water equations to model meandering flows in shallow rectangular reservoirs is discussed. Four meandering flows, of various shallowness, were modelled using the academic flow model WOLF 2D, which includes a depth-averaged k- model accounting for the horizontal and vertical turbulent length-scales. The bottom friction was modelled with the Colebrook-White formula and different roughness heights were considered. A Proper Orthogonal Decomposition (POD) was applied to the simulation results to extract the behaviour of the main structures responsible for the meandering flow. The same POD analysis was also performed for the reference experimental flow fields, obtained by Large-Scale Particle Image Velocimetry. The first two POD modes obtained from the numerical simulations assuming a smooth bottom are in good agreement with the experimental modes in terms of energy, as well as temporal and spatial variations, whatever the shallowness. In contrast, the remaining simulated modes are not well rendered. The effect of an increased roughness height in the simulations is finally discussed. It leads to an improved reproduction of the first two modes and of the following modes, except when significant viscous effects govern in the flow. [less ▲]

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See detailAcoustic velocity measurements for evaluating bed stability parameters
Duma, Diana ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

E-print/Working paper (2014)

Assessing the stability of riverbeds is a major issue in many aspects of hydraulic and river engineering. Although the Shields diagram remains the most widely accepted approach, it faces a number of ... [more ▼]

Assessing the stability of riverbeds is a major issue in many aspects of hydraulic and river engineering. Although the Shields diagram remains the most widely accepted approach, it faces a number of shortcomings. In particular, its ability to reflect the influence of turbulence on sediment motion becomes questionable when it is applied under strongly non-uniform flow conditions, which are of high practical relevance in hydraulic engineering. Therefore, new approaches were proposed, which relate the degree of damage of gravel beds to so-called bed stability parameters depending explicitly on the local intensity of flow turbulence. However, these new bed stability parameters are much more demanding in term of detailed description of the flow field and, in all studies so far, they were estimated based only on Laser Doppler Velocimetry or Particle Image Velocimetry. Here, we investigate for the first time the suitability of acoustic velocity measurement techniques to evaluate these bed stability parameters. The experiments focus on smooth-to-rough transitions and a quasi-uniform configuration is used as a reference. Flow velocities were obtained using two complementary devices: an Ultrasonic Velocity Profiler and a 3D Acoustic Doppler Velocimeter. The new experimental results show that relatively robust estimates of the new stability parameters can be obtained from the 3D acoustic measurements. [less ▲]

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See detailThe Airline Container Loading Problem with Pickup and Delivery
Lurkin, Virginie ULg; Schyns, Michael ULg

E-print/Working paper (2013)

The present paper looks into the problem of optimizing the loading of a set of containers and pallets into cargo aircraft serving multiple airports. Due to the pickup and delivery operations occurring at ... [more ▼]

The present paper looks into the problem of optimizing the loading of a set of containers and pallets into cargo aircraft serving multiple airports. Due to the pickup and delivery operations occurring at intermediate airports, this problem is simultaneously a weight and balance problem and a sequencing problem. Our objective is to minimize fuel and handling operations costs. This problem is shown to be NP-hard. We resort to a mixed integer linear program. On the basis of a professional partner's real-world data, TNT Airways, we perform numerical experiments using a standard B&C library. This approach yields better solutions than traditional manual planning, which results in substantial cost savings. [less ▲]

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See detailQue pouvons-nous attendre du sommet européen de décembre 2013 ?
Dumoulin, André ULg

E-print/Working paper (2013)

Hypothèses autour des décisions attendues du sommet UE spécial défense prévu en décembre 2013 avec les différentes écoles de pensée

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See detailQuadratization of symmetric pseudo-Boolean functions
Anthony, Martin; Boros, Endre; Crama, Yves ULg et al

E-print/Working paper (2013)

A pseudo-Boolean function is a real-valued function $f(x)=f(x_1,x_2,\ldots,x_n)$ of $n$ binary variables; that is, a mapping from $\{0,1\}^n$ to ${\bbr}$. For a pseudo-Boolean function $f(x)$ on $\{0,1 ... [more ▼]

A pseudo-Boolean function is a real-valued function $f(x)=f(x_1,x_2,\ldots,x_n)$ of $n$ binary variables; that is, a mapping from $\{0,1\}^n$ to ${\bbr}$. For a pseudo-Boolean function $f(x)$ on $\{0,1\}^n$, we say that $g(x,y)$ is a quadratization of $f$ if $g(x,y)$ is a quadratic polynomial depending on $x$ and on $m$ auxiliary binary variables $y_1,y_2,\ldots,y_m$ such that $f(x)= \min \{ g(x,y) : y \in \{0,1\}^m \} $ for all $x \in \{0,1\}^n$. By means of quadratizations, minimization of $f$ is reduced to minimization (over its extended set of variables) of the quadratic function $g(x,y)$. This is of some practical interest because minimization of quadratic functions has been thoroughly studied for the last few decades, and much progress has been made in solving such problems exactly or heuristically. A related paper initiated a systematic study of the minimum number of auxiliary $y$-variables required in a quadratization of an arbitrary function $f$ (a natural question, since the complexity of minimizing the quadratic function $g(x,y)$ depends, among other factors, on the number of binary variables). In this paper, we determine more precisely the number of auxiliary variables required by quadratizations of \emph{symmetric} pseudo-Boolean functions $f(x)$, those functions whose value depends only on the Hamming weight of the input $x$ (the number of variables equal to 1). [less ▲]

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See detailEstimation and approximation in multidimensional dynamics
Frasso, Gianluca ULg; Jaeger, Jonathan ULg; Lambert, Philippe ULg

E-print/Working paper (2013)

Differential equations (DEs) are commonly used to describe dynamic systems evolving in one (ordinary differential equations or ODEs) or in more than one dimensions (partial differential equations or PDEs ... [more ▼]

Differential equations (DEs) are commonly used to describe dynamic systems evolving in one (ordinary differential equations or ODEs) or in more than one dimensions (partial differential equations or PDEs). In real data applications the parameters involved in the DE models are usually unknown and need to be estimated from the available measurements together with the state function. In this paper, we present frequentist and Bayesian approaches for the joint estimation of the parameters and of the state functions involved in PDEs. We also propose two strategies to include differential (initial and/or boundary) conditions in the estimation procedure. We evaluate the performances of the proposed strategy on simulated and real data applications. [less ▲]

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See detailWhat can we expect from the December 2013 European Summit ?
Dumoulin, André ULg

E-print/Working paper (2013)

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See detailWat kunnen wij verwachten van de Europese top van december 2013 ?
Dumoulin, André ULg

E-print/Working paper (2013)

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See detailSpline approximation to conditional Archimedean copula
Lambert, Philippe ULg

E-print/Working paper (2013)

We propose a flexible copula model to describe changes with a covari- ate in the dependence structure of (conditionally exchangeable) random variables. The starting point is a spline approximation to the ... [more ▼]

We propose a flexible copula model to describe changes with a covari- ate in the dependence structure of (conditionally exchangeable) random variables. The starting point is a spline approximation to the generator of an Archimedean copula. Changes in the dependence structure with a covariate x are modelled by flexible regression of the spline coefficients on x. The performances and properties of the spline estimate of the reference generator and the abilities of these conditional models to approximate conditional copulas are studied through simulations. Inference is made using Bayesian arguments with posterior distributions explored using im- portance sampling or adaptive MCMC algorithms. The modelling strategy is illustrated with two examples. [less ▲]

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See detailMulti-period load assignment problem with stochastic load availability
Crama, Yves ULg; Pironet, Thierry ULg

E-print/Working paper (2013)

In this research, we want to investigate optimization techniques for a generic load assignment problem including a limited fleet of vehicles within a full-truck-load (FTL) multi-period setting including ... [more ▼]

In this research, we want to investigate optimization techniques for a generic load assignment problem including a limited fleet of vehicles within a full-truck-load (FTL) multi-period setting including forecasts on load availability. Several policies are generated from simple heuristics through state of the art approaches such as consensus and restricted expectation algorithms up to the optimization of a subtree of scenarios. Moreover, myopic and a-posteriori deterministic optimizations (including no or fully revealed information) set bounds for policies performance comparisons. Tests are performed for different graphs sizes and sparsity, several distribution laws and number of loads. Performances are compared statistically over paired samples. The robustness of performing policies against a false valuation of the probability distribution is also analyzed. [less ▲]

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Peer Reviewed
See detailUne épaule sur laquelle s'appuyer
Forthomme, Bénédicte ULg

E-print/Working paper (2013)

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See detailCos: A Typical Example of Hellenistic Religion?
Paul, Stéphanie ULg

E-print/Working paper (2013)

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See detailLe samedi 15 août 778
Rolland, Jean-Noël ULg

E-print/Working paper (2013)

Battle of Roncevaux Pass and his historical context. Roncesvalles is famous in History and legend for the defeat of Charlemagne and the death of Roland in 778, during the battle of Roncevaux Pass, when ... [more ▼]

Battle of Roncevaux Pass and his historical context. Roncesvalles is famous in History and legend for the defeat of Charlemagne and the death of Roland in 778, during the battle of Roncevaux Pass, when Charlemagne's rear guard was destroyed by Basque tribes. [less ▲]

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See detailDaniel Kehlmann: Ich und Kaminski
Hackbarth, Sabine ULg; Dupont, Bruno ULg

E-print/Working paper (2013)

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See detailThree irradiated and bloated hot Jupiters: WASP-76b, WASP-82b & WASP-90b
West, R. G.; Almenara, J.-M.; Anderson, D. R. et al

E-print/Working paper (2013)

We report three new transiting hot-Jupiter planets discovered from the WASP surveys combined with radial velocities from OHP/SOPHIE and Euler/CORALIE and photometry from Euler and TRAPPIST. All three ... [more ▼]

We report three new transiting hot-Jupiter planets discovered from the WASP surveys combined with radial velocities from OHP/SOPHIE and Euler/CORALIE and photometry from Euler and TRAPPIST. All three planets are inflated, with radii 1.7-1.8 Rjup. All orbit hot stars, F5-F7, and all three stars have evolved, post-MS radii (1.7-2.2 Rsun). Thus the three planets, with orbits of 1.8-3.9 d, are among the most irradiated planets known. This reinforces the correlation between inflated planets and stellar irradiation. [less ▲]

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See detailThree sub-Jupiter-mass planets: WASP-69b & WASP-84b transit active K dwarfs and WASP-70Ab transits the evolved primary of a G4+K3 binary
Anderson, D. R.; Collier Cameron, A.; Delrez, Laetitia ULg et al

E-print/Working paper (2013)

We report the discovery of the transiting exoplanets WASP-69b, WASP-70Ab and WASP-84b, each of which orbits a bright star (V~10). WASP-69b is a bloated Saturn-mass planet (0.26 M$_{\rm Jup}$, 1.06 R$_{\rm ... [more ▼]

We report the discovery of the transiting exoplanets WASP-69b, WASP-70Ab and WASP-84b, each of which orbits a bright star (V~10). WASP-69b is a bloated Saturn-mass planet (0.26 M$_{\rm Jup}$, 1.06 R$_{\rm Jup}$) in a 3.868-d period around an active mid-K dwarf. We estimate a stellar age of 1 Gyr from both gyrochronological and age-activity relations, though an alternative gyrochronological relation suggests an age of 3 Gyr. ROSAT detected X-rays at a distance of 60$\pm$27 arcsec from WASP-69. If the star is the source then the planet could be undergoing mass-loss at a rate of ~10$^{12}$ g s$^{-1}$. This is 1-2 orders of magnitude higher than the evaporation rate estimated for HD 209458b and HD 189733b, both of which have exhibited anomalously-large Lyman-{\alpha} absorption during transit. WASP-70Ab is a sub-Jupiter-mass planet (0.59 M$_{\rm Jup}$, 1.16R$_{\rm Jup}$) in a 3.713-d orbit around the primary of a spatially-resolved G4+K3 binary, with a separation of 3.3 arcsec ($\geq$800 AU). We exploit the binary nature of the system to construct a H-R diagram, from which we estimate its age to be 9-10 Gyr. WASP-84b is a sub-Jupiter-mass planet (0.69 M$_{\rm Jup}$, 0.94 R$_{\rm Jup}$) in an 8.523-d orbit around an active early-K dwarf. Of the transiting planets discovered from the ground to date, WASP-84b has the third-longest period. From a combination of gyrochronological and age-activity relations we estimate the age of WASP-84 to be ~1 Gyr. For both the active stars WASP-69 and WASP-84 we find a modulation of the radial velocities with a period similar to the photometrically-determined stellar rotation period. We fit the residuals with a low-order harmonic series and subtract the best fit from the RVs prior to deriving the system parameters. In each case the solution is essentially unchanged, with much less than a 1-{\sigma} change to the planetary mass. We found... [less ▲]

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See detailRevealed preference tests of collectively rational consumption behavior: formulations and algorithms
Talla Nobibon, Fabrice; Cherchye, Laurens; Crama, Yves ULg et al

E-print/Working paper (2013)

This paper focuses on revealed preference tests of the collective model of household consumption. We start by showing that the decision problems corresponding to testing collective rationality are {\sc np ... [more ▼]

This paper focuses on revealed preference tests of the collective model of household consumption. We start by showing that the decision problems corresponding to testing collective rationality are {\sc np}-complete. This makes the application of these tests problematic for (increasingly available) large(r) scale data sets. We then present two approaches to overcome this negative result. First, we introduce exact algorithms based on mixed-integer programming ({\sc mip}) formulations of the collective rationality tests, which can be usefully applied to medium sized data sets. Next, we propose simulated annealing heuristics, which allow for efficient testing of the collective model in the case of large data sets. We illustrate our methods by a number of computational experiments based on Dutch labor supply data. [less ▲]

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See detailSearching for Terrestrial Planets Orbiting in the Habitable Zone of Ultra-Cool Stars and Brown Dwarfs
Demory, Brice-Olivier; Seager, Sara; Lissauer, Jack et al

E-print/Working paper (2013)

We propose to use Kepler in 2-wheel mode to conduct a detailed search for Earth-sized planets orbiting ultra-cool stars and brown dwarfs (spectral types from M7 to L3). This population of objects presents ... [more ▼]

We propose to use Kepler in 2-wheel mode to conduct a detailed search for Earth-sized planets orbiting ultra-cool stars and brown dwarfs (spectral types from M7 to L3). This population of objects presents several advantages for exoplanet surveys. First, ultra-cool stars and brown dwarfs are small and thus result in favorable planet-to-star area ratios. Second, because of their low effective temperature, the inner edge of their habitable zone is extremely close (2 to 3 days only). Third, our targets are bright at infrared wavelengths, which will enable detailed follow-up studies. Our program therefore represents a unique opportunity to find a transiting Earth-size exoplanet for which atmospheric features (including biosignatures) could be detected with near-to-come facilities such as JWST. Such exoplanet has not been discovered yet. Kepler in 2-wheel mode provides the required stability and photometric precision to make this survey successful. Our initial target sample includes 60 ultra-cool stars and brown dwarfs from which we expect to detect at least one transiting planet. We propose to monitor each source for 4 days, resulting in a total program duration of ~240 days. [less ▲]

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See detailLettre d'information trimestrielle du projet DACEFI 2 - Retour sur l'attribution des premières forêts communautaires du Gabon
Meunier, Quentin; Moumbogou, Carl; Morin, Amélie et al

E-print/Working paper (2013)

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See detailInvestir Ou Mourir ? Il Faut Choisir…
Choffray, Jean-Marie ULg

E-print/Working paper (2013)

Investir : c’est croire en l’avenir. C’est renoncer en partie au présent pour donner vie au futur. C’est tourner le dos aux « Bouffeurs d’espoir » et à l’illusoire confort du statu quo. Enfin, et surtout ... [more ▼]

Investir : c’est croire en l’avenir. C’est renoncer en partie au présent pour donner vie au futur. C’est tourner le dos aux « Bouffeurs d’espoir » et à l’illusoire confort du statu quo. Enfin, et surtout, c’est oser «Oser » ! La distance séparant le discours public de la performance économique avérée suffit à démontrer l’incompréhension des mécanismes de création de richesse de ceux qui sont censés en avoir la maîtrise et les mettre en œuvre. Il est peu de domaines où les illusions, et autres idées fausses, ont un succès tel qu’elles amènent l’observateur aguerri à s’interroger sur le profit que d’aucuns pourraient en tirer. L’objet de ce document est de partager le fruit d’une réflexion menée sur le thème de l’Investissement, forme proéminente et condition première de l’activité économique, au moment où certains s’interrogent sur son encadrement et cherchent à en limiter la liberté. [less ▲]

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See detailChicago Gospel Festival June 2013
Sacré, Robert ULg

E-print/Working paper (2013)

Compte-rendu avec photos

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See detailPhysician Induced Demand for C-Sections: Does the Convenience Incentive Matter?
Lefevre, Mélanie ULg

E-print/Working paper (2013)

This paper investigates whether physicians induce demand for C-sections in the days preceding leisure periods. I reject that doctors are meaningfully increasing the number of cesareans to accommodate ... [more ▼]

This paper investigates whether physicians induce demand for C-sections in the days preceding leisure periods. I reject that doctors are meaningfully increasing the number of cesareans to accommodate their own preferences for control of deliveries around holiday Mondays. Using a sample of more than 1,300,000 deliveries, I can precisely estimate that the induced demand due to convenience is close to zero. While I replicate previous results of lower C-section rates on leisure periods, I show that they are due to the way doctors schedule planned cesareans rather than to an induced demand for reason of physicians' convenience. [less ▲]

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See detailLes Draps de lit
Demoulin, Laurent ULg

E-print/Working paper (2013)

Les Draps de lit est une pièce de théâtre inédite de Jean-Philippe Toussaint, antérieure à La Salle de bain. Elle est ici éditée avec un apparat critique: variantes et notes critiques.

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See detailLa gouvernance des coopératives en situation de conflit et de post-conflit
Niyungeko, Thadée ULg; Huybrechts, Benjamin ULg

E-print/Working paper (2013)

If governance has become, for many years, as a matter of paramount importance in traditional companies (Berle & Means, 1932), microfinance institutions have also not escaped this need (Rock et al. 1998 ... [more ▼]

If governance has become, for many years, as a matter of paramount importance in traditional companies (Berle & Means, 1932), microfinance institutions have also not escaped this need (Rock et al. 1998), there are about thirty years. Considered essential to address issues related to economic and social development (Wélé, 2009), governance is also emerging as an undeniable factor for to strengthen the financial performance and to increase awareness in microfinance institutions (Rock et al., 1998; Labie, 2001 Helms, 2006). Several authors have contributed to the understanding of corporate governance by using a variety of theoretical approaches (Jensen & Meckling (1976), Fama and Jensen (1983a) for Shareholders approach, Freeman (1984), Donaldson & Preston (1995) Hung (1998) for the stakeholder approach, Meyer and Rowan (1977), Mertens (2010), Muth & Donaldson (1998), Berle & Means (1932); Labie (2005a) for alternative approaches). Applied individually in cooperatives and organizations, these approaches have proved rather one-dimensional and illuminate one aspect of the Boards of Directors (Cornforth, 2004). Hence the need for an approach that integrates the insights of these perspectives has been felt. Thus, a perspective in terms of paradox (Cornforth, 2004) helped to highlight the dilemmas, paradoxes and tensions that boards of directors are facing. Several researchers have used this paradox perspective in different organizations (Demb & Neubauer, 1992 Wood, 1996; Sundaramurthy & Lewis, 2003), but it also did not take long. Criticized for focusing only on the board, this perspective paradox is also alleged to ignore the role of contextual factors. However, as argued by DiMaggio & Powell (1983), Meyer and Rowan (1977), environmental factors play an undeniable role in the way organizations make isomorphic. Rijpens & Adam (2011) also point out that the internal and external factors to the organization involved in the debate on the governance model adopted. Hudon and Seibel (2007) argue that conflicts and disasters seriously affect the socio-economic institutions, public governance, networks and social relations of citizens, including those related to the exchange or transfer of financial resources. This article examines the influence of armed conflict on the cooperatives’ governance. It is built around three fundamental questions. (1) What overlay the systems of cooperatives governance? (2) What is the theoretical model of governance adapted to cooperatives working in conflict situations? (3) How an armed conflict does it influence the cooperatives governance? To answer these questions, this article assumes, first, the confrontation of existing theoretical approaches in the literature on corporate governance in general and cooperatives in particular. It then develops a model of governance adapted to the conflict. Finally, that model will be tested after data collect from a qualitative field study based on the triangulation of information resources and interviews with key players in organizations under study in a country where microfinance institutions have evolved conflict situations. The results will be presented in another article. [less ▲]

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