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

E-print/Working paper (2015)

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 detailOptimal Enforcement of Competition Policy: The Commitments Procedure under Uncertainty
Gautier, Axel ULg; Petit, Nicolas ULg

E-print/Working paper (2015)

Since the introduction of a commitments procedure in EU antitrust policy (Article 9 of Council Regulation 1/2003), the European Commission has extensively settled cases of alleged anticompetitive ... [more ▼]

Since the introduction of a commitments procedure in EU antitrust policy (Article 9 of Council Regulation 1/2003), the European Commission has extensively settled cases of alleged anticompetitive practices. In this paper, we use a formal model of law enforcement (Bebchuk, 1984; Shavell, 1988) to identify the optimal procedure to resolve cases in a context of uncertainty related to the law (L-uncertainty) and to the facts (F-uncertainty). We show that commitments are suboptimal when L-uncertainty is high. Furthermore, the generalized use of commitments creates an additional risk of under-enforcement when F-uncertainty is significant. [less ▲]

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Peer Reviewed
See detailParty autonomy in international family relationships : a research agenda
Wautelet, Patrick ULg

E-print/Working paper (2015)

In recent years, party autonomy has conquered new grounds in cross-border private relationships. Building on first attempts in national codifications, party autonomy has become one of the leading ... [more ▼]

In recent years, party autonomy has conquered new grounds in cross-border private relationships. Building on first attempts in national codifications, party autonomy has become one of the leading principles used in various EU regulations dealing with cross-border family relationships. It can now be found in successions, in divorce, in maintenance matters. This new trend has been greeted sometimes with enthusiasm, sometimes with skepticism. While these Regulations constrain the choice that parties can make, it cannot be denied that the principle of freedom of choice has been openly embraced by the European legislator. Hence this principle evolved, at least within the EU, from what was until recently a marginal phenomenon to a well-respected solution for cross-border family relationships This (r-)evolution occurred quite fast and has attracted much attention. However, much of the research in this area has adopted a limited perspective, focusing exclusively on the possibilities and limits of choice in one specific instrument or adopting a comprehensive outlook but with a strong positive flavor. While it is true that a number of contributions provide excellent food for thought, the overall impression is that more time and more research is needed to start apprehending the fundamental questions raised by this evolution. At this stage, it may be too early to offer a comprehensive study of all questions raised by party autonomy in private international law. New developments may in fact modify the picture soon and add to the fields conquered by party autonomy. At the same time, the relative novelty of the changes makes it difficult to take full stock of all issues raised by the development of party autonomy. This is why scholars should first attempt to define a research agenda. This paper offers a first scratch by exploring various questions which should figure prominently in such agenda. It is by no means meant to be exhaustive. Rather, an attempt will be made to shed some light on the main questions raised by recent evolution in the hope of being an invitation for further research. [less ▲]

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See detailApproche agroforestière. Synthèse des travaux menés par le projet DACEFI2 en agroforesterie. Document de capitalisation.
Boldrini, Sylvie; Meunier, Quentin; Boukouendji, Basile et al

E-print/Working paper (2015)

Le projet DACEFI-2 a eu pour mission première la promotion de la foresterie communautaire comme outil de développement des communautés rurales. L’approche au Gabon en matière de gestion des terroirs ... [more ▼]

Le projet DACEFI-2 a eu pour mission première la promotion de la foresterie communautaire comme outil de développement des communautés rurales. L’approche au Gabon en matière de gestion des terroirs villageois s’est voulue plus embrassante, promouvant en sus de l’exploitation forestière des activités comme l’agriculture, le maraîchage, la collecte des produits forestiers non ligneux ou encore l’agroforesterie. L’agroforesterie est une thématique qui converge parfaitement avec la gestion raisonnée de la forêt, et idéalement avec les modes d’interaction préexistants des villageois avec celle-ci. Concilier dans un même espace la culture de plantes vivrières et l’accès à des arbres à fort intérêt socio-économique apporte une plus-value notoire aux parcelles cultivées. L’optimisation des techniques culturales permet une meilleure productivité et une incitation à la sédentarisation des cultures, élément important à considérer compte tenu des difficultés d’entretien des parcelles éloignées du village (notamment liées aux dégâts causés par les animaux). Ce recueil compile les travaux réalisés en agroforesterie par les équipes du projet DACEFI-2. Il rappelle la stratégie d’intervention et les différentes activités menées, de la sensibilisation auprès des plus jeunes à la promotion de certains produits forestiers non ligneux à potentiel économique avéré. La promotion de l’arbre, de la récolte de la graine jusqu’à sa plantation en passant par sa mise en pépinière aura également animé toute l’équipe durant ces années d’exercice, afin de faire un peu plus valoir ses multiples intérêts et susciter les efforts de gestion, de conservation et de reboisement. [less ▲]

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See detailImportance et rôle de l’investissement…
Choffray, Jean-Marie ULg

E-print/Working paper (2015)

Quelques observations et réflexions en réponse à une question qui m’est souvent posée sur l’importance et le rôle des investisseurs. Ces « Charognards », particulièrement visés au cours des périodes de ... [more ▼]

Quelques observations et réflexions en réponse à une question qui m’est souvent posée sur l’importance et le rôle des investisseurs. Ces « Charognards », particulièrement visés au cours des périodes de tension géopolitique, de populisme ou de débauche monétaire, semblables à celle que nous vivons aujourd’hui. Ma réponse en peu de mots : les investisseurs sont des défenseurs de la valeur du travail par temps calme et des vigies dans la tempête ! [less ▲]

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See detailEntretien avec Kathryn Batchelor
Oumarou Mal Mazou, Rachid ULg

E-print/Working paper (2015)

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See detailA semiparametric model for Generalized Pareto regression based on a dimension reduction assumption
Hambuckers, julien ULg; Heuchenne, Cédric ULg; Lopez, Olivier

E-print/Working paper (2015)

In this paper, we consider a regression model in which the tail of the conditional distribution of the response can be approximated by a Generalized Pareto distribution. Our model is based on a ... [more ▼]

In this paper, we consider a regression model in which the tail of the conditional distribution of the response can be approximated by a Generalized Pareto distribution. Our model is based on a semiparametric single-index assumption on the conditional tail index; while no further assumption on the conditional scale parameter is made. The underlying dimension reduction assumption allows the procedure to be of prime interest in the case where the dimension of the covariates is high, in which case the purely nonparametric techniques fail while the purely parametric ones are too rough to correctly fit to the data. We derive asymptotic normality of the estimators that we define, and propose an iterative algorithm in order to perform their practical implementation. Our results are supported by some simulations and a practical application on a public database of operational losses. [less ▲]

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See detailA branch-and-price algorithm for 2-period vehicle routing problems
Crama, Yves ULg; Rezaei Sadrabadi, Mahmood ULg; Van Woensel, Tom

E-print/Working paper (2015)

We consider a Vehicle Routing Problem (VRP) with deterministic orders in two periods from a set of stores. Orders in period 1 (2) can be postponed (advanced) to the other period but any diversion from the ... [more ▼]

We consider a Vehicle Routing Problem (VRP) with deterministic orders in two periods from a set of stores. Orders in period 1 (2) can be postponed (advanced) to the other period but any diversion from the initial orders incurs a penalty. From the perspective of a Logistics Service Provider (LSP), such diversions could be beneficial if savings in the routing costs outweigh the penalties. So could they be from a store's view, as the store can set a high enough penalty to compensate the diversion from its own optimal orders. In this paper, we introduce a new model where we seek a better solution for the LSP, compared to solving two independent VRPs with fixed orders, by allowing orders to be fully postponed or advanced. We apply a branch-and-price algorithm to solve this model to optimality. Many cutting-edge techniques are implemented to have an efficient branch-and-price algorithm, and two ideas to possibly improve the upper bound are tested. We draw algorithmic and managerial insights based on our test instances. [less ▲]

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See detailInvesting in the Future
Pahud de Mortanges, Charles ULg

E-print/Working paper (2015)

This paper attempts to address the challenges of how to invest in Synthetic Biology firms, most of which are relatively new start-ups and unprofitable. Valuing an early-stage firm with only a brief ... [more ▼]

This paper attempts to address the challenges of how to invest in Synthetic Biology firms, most of which are relatively new start-ups and unprofitable. Valuing an early-stage firm with only a brief operating history, little or no operating profit (or even revenue), and an immature and untested business model, could be a formidable challenge. We propose a limited number of quantitative, and a larger number of qualitative criteria. An investor may consider these when faced with analyzing a new untried business, but one he/she believes has considerable potential for success in the future. [less ▲]

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See detailTopology on new sequence spaces defined with wavelet leaders
Bastin, Françoise ULg; Esser, Céline ULg; Simons, Laurent ULg

E-print/Working paper (2015)

Using wavelet leaders instead of wavelet coefficients, new sequence spaces of type Sν are defined and endowed with a natural topology. Some classical topological properties are then studied; in particular ... [more ▼]

Using wavelet leaders instead of wavelet coefficients, new sequence spaces of type Sν are defined and endowed with a natural topology. Some classical topological properties are then studied; in particular, a generic result about the asymptotic repartition of the wavelet leaders of a sequence in Lν is obtained. Eventually, comparisons and links with Oscillation spaces are also presented as well as with Sν spaces. [less ▲]

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See detailSequential testing of k-out-of-n systems with imperfect tests
Wenchao, Wei; Coolen, Kris ULg; Talla Nobibon, Fabrice et al

E-print/Working paper (2015)

A k-out-of-n system configuration requires that, for the overall system to be functional, at least k out of the total of n components be working. We consider the problem of sequentially testing the ... [more ▼]

A k-out-of-n system configuration requires that, for the overall system to be functional, at least k out of the total of n components be working. We consider the problem of sequentially testing the components of a k-out-of-n system in order to learn the state of the system, when the tests are costly and when the individual component tests are imperfect, which means that a test can identify a component as working when in reality it is down, and vice versa. Each component is tested at most once. Since tests are imperfect, even when all components are tested the state of the system is not necessarily known with certainty, and so reaching a lower bound on the probability of correctness of the system state is used as a stopping criterion for the inspection. We define different classes of inspection policies and we examine global optimality of each of the classes. We find that a globally optimal policy for diagnosing k-out-of-n systems with imperfect tests can be found in polynomial time when the predictive error probabilities are the same for all the components. Of the three policy classes studied, the dominant policies always contain a global optimum, while elementary policies are compact in representation. The newly introduced class of so-called `interrupted block-walking' policies combines these merits of global optimality and of compactness. [less ▲]

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See detailLacunary wavelet series on Cantor sets
Esser, Céline ULg

E-print/Working paper (2015)

We construct functions with prescribed multifractal spectra which satisfy the leaders profile method.

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See detailTowards generic image classification: an extensive empirical study
Marée, Raphaël ULg; Geurts, Pierre ULg; Wehenkel, Louis ULg

E-print/Working paper (2014)

This paper considers the general problem of image classification without using any prior knowledge about image classes. We study variants of a method based on supervised learning whose common steps are ... [more ▼]

This paper considers the general problem of image classification without using any prior knowledge about image classes. We study variants of a method based on supervised learning whose common steps are the extraction of random subwindows described by raw pixel intensity values and the use of ensemble of extremely randomized trees to directly classify images or to learn image features. The influence of method parameters and variants is thoroughly evaluated so as to provide baselines and guidelines for future studies. Detailed results are provided on 80 publicly available datasets that depict very diverse types of images (more than 3800 image classes and over 1.5 million images). [less ▲]

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See detailDetection of local outliers in spatial multivariate data
Ernst, Marie ULg; Haesbroeck, Gentiane ULg

E-print/Working paper (2014)

Outlier detection techniques in spatial data should allow to identify two types of outliers: global and local ones. Local outliers typically have non-spatial attributes that strongly differ from those ... [more ▼]

Outlier detection techniques in spatial data should allow to identify two types of outliers: global and local ones. Local outliers typically have non-spatial attributes that strongly differ from those observed on their neighbors. Detecting local outliers requires to be able to work locally, on neighborhoods, in order to take into account the spatial dependence between the statistical units under consideration, even though the outlyingness is usually measured on the non-spatial variables. Many procedures have been outlined in the literature, but their number reduces when one wants to deal with multivariate non-spatial attributes. In this paper, focus is on the multivariate context. A review of existing procedures is done. A new approach, based on a two-step improvement of an existing one, is also designed and compared with the benchmarked methods by means of examples and simulations. [less ▲]

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See detailLettre d'information du projet Dacefi-Synthèse & réalisations majeures
Meunier, Quentin; Morin, Amélie; Moumbougou, Carl et al

E-print/Working paper (2014)

Cette dernière lettre d'information du projet présente le bilan de ses réalisations et les avancées importantes du Gabon en termes de foresterie communautaire

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See detailProjet DACEFI 2. Principes fondateurs d'une forêt communautaire au Gabon. Outils de vulgarisation et de sensibilisation.
Meunier, Quentin; Boldrini, Sylvie; Larzillière, Adélaïde et al

E-print/Working paper (2014)

Faisant suite à une première phase (2006-2008), le projet pilote Développement d’Alternatives Communautaires à l’Exploitation Forestière Illégale (DACEFI-2, de 2010 à 2014) s’emploie à tester au Gabon la ... [more ▼]

Faisant suite à une première phase (2006-2008), le projet pilote Développement d’Alternatives Communautaires à l’Exploitation Forestière Illégale (DACEFI-2, de 2010 à 2014) s’emploie à tester au Gabon la mise en oeuvre des premières forêts communautaires. Un de ses objectifs majeurs consiste à tester le concept de foresterie communautaire au sein de plusieurs sites partenaires et de témoigner de l’expérience acquise afin que le Ministère en charge des Forêts adapte le cadre réglementaire. Quatre textes majeurs régissent la foresterie communautaire au Gabon, une loi (n°16/01), un décret d’application (n°1028/PR/MEFEPEPEN) et deux arrêtés (n°018/MEF/SG/DGF/DFC et n°106/MEFEPRN). Ils encadrent le processus de création d’une forêt communautaire. Afin de les rendre accessibles à un plus grand nombre, le projet DACEFI-2 s’est proposé de développer plusieurs supports de vulgarisation à destination des agents des Eaux et Forêts et des villageois. En éditant et en diffusant une série de posters, de films ou encore de bandes dessinées, le projet a contribué à faire connaître dans les provinces de l’Ogooué-Ivindo et du Moyen-Ogooué, l’esprit de ces textes légaux qui visent à favoriser le développement des communautés locales. Ce document de capitalisation présente une compilation des outils développés par les équipes du projet pour mener à bien cette campagne de sensibilisation. Nous abordons la gestion forestière durable par le prisme de la foresterie communautaire en évoquant l’esprit de la loi et les enjeux de la foresterie sociale. Nous proposons également une série de recommandations, basées sur notre expérience au Gabon, afin d’optimiser l’efficacité des communautés engagées dans ce processus. [less ▲]

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See detailCorporate board attributes and conditional accounting conservatism: Evidence from French firms
Boussaid, Nabila ULg; Sougné, Danielle ULg; Hamza, Taher

E-print/Working paper (2014)

In this paper we investigate the relationship between boards of directors’ attributes and conditional accounting conservatism in the French context. Using a pooled regression model to evaluate this ... [more ▼]

In this paper we investigate the relationship between boards of directors’ attributes and conditional accounting conservatism in the French context. Using a pooled regression model to evaluate this relationship for the period 2009-2012, our empirical results can be summarized as follows. Firstly, greater board activity encourages more conservative reporting in financial statements. Secondly, greater board size diminishes conditional accounting conservatism. Lastly, there is a positive relationship between gender diversity and conservatism. To ensure robustness we have calculated our results using alternative measures of accounting conservatism, namely time series and accrual-based measures in addition to asymmetric timeliness of earnings. These findings suggest that boards of directors’ attributes are an important factor in determining the financial reporting quality of French firms. [less ▲]

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See detailLe nouveau cadre d’action en matière de climat et d’énergie à l’horizon 2030
Habran, Maxime ULg

E-print/Working paper (2014)

Cette note a pour but de fournir un éclairage sur le nouveau cadre d'action européen en matière de climat et d'énergie

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See detailL-surface and V-valley for optimal anisotropic 2D smoothing
Frasso, Gianluca ULg; Paul, Eilers

E-print/Working paper (2014)

We present the L-surface as an attractive generalization of the L-curve framework for the selection of the optimal smoothing parameters in two dimensional applications. It preserves the desirable features ... [more ▼]

We present the L-surface as an attractive generalization of the L-curve framework for the selection of the optimal smoothing parameters in two dimensional applications. It preserves the desirable features of its unidimensional analogous. The optimal amount of smoothing is indicated by the pair of parameters located in the point of maximum (Gaussian) curvature. Locate this point on a discrete parametric surface can be not straightforward. We introduce the V-valley as a simplified selection criterion based on distance minimization. [less ▲]

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

E-print/Working paper (2014)

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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See detailRéveillez-vous, le monde vous attend…
Gerkens, Jean-François ULg; Faymonville, Marie-Elisabeth ULg; Destiné, Jacques ULg et al

E-print/Working paper (2014)

Par-delà le brouillard des temps présents, un message d’optimisme, de volontarisme, de foi en l’avenir et en la vie, conduisant à sept principes, ou suggestions d’action, faciles à mettre en œuvre.

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Peer Reviewed
See detailEstimating the out-of-sample predictive ability of trading rules: a robust bootstrap approach
Hambuckers, julien ULg; Heuchenne, Cédric ULg

E-print/Working paper (2014)

In this paper, we estimate the out-of-sample predictive ability of a set of trading rules. Usually, this ability is estimated using a rolling-window sample-splitting scheme, true out-of-sample data being ... [more ▼]

In this paper, we estimate the out-of-sample predictive ability of a set of trading rules. Usually, this ability is estimated using a rolling-window sample-splitting scheme, true out-of-sample data being rarely available. We argue that this method makes a poor use of the available information and creates data mining possibilities. Instead, we introduce an alternative bootstrap approach, based on the .632 bootstrap principle. This method enables to build in-sample and out-of-sample bootstrap data sets that do not overlap and exhibit the same time dependencies. We illustrate our methodology on IBM and Microsoft daily stock prices, where we compare 11 trading rules specifications. For the data sets considered, two different filter rule specifications have the highest out-of-sample mean excess returns. However, all tested rules cannot beat a simple buy-and-hold strategy when trading at a daily frequency. [less ▲]

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See detailEmbargo russe sur les aliments européens : l'Europe doit montrer l'exemple
Habran, Maxime ULg

E-print/Working paper (2014)

Cette note a pour but d’apporter des éclaircissements sur les mesures en matière de politique agricole commune prises par l’Union européenne

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See detailDe la crise à l’entreprise, en passant par toi…
Choffray, Jean-Marie ULg

E-print/Working paper (2014)

De la crise à l’entreprise, en passant par toi… est une invitation à l’action, à la prise de responsabilité, à la création responsable de valeur économique et à la recherche obstinée de croissance ... [more ▼]

De la crise à l’entreprise, en passant par toi… est une invitation à l’action, à la prise de responsabilité, à la création responsable de valeur économique et à la recherche obstinée de croissance rentable. Oui! Notre monde vient d’échapper à un effondrement systémique dont 1929 n’aurait constitué qu’un aimable préambule. Oui ! L’entreprise est le seul acteur social créateur de richesse économique et la seule solution au mal qui se répand. Oui ! Il est extrêmement difficile de changer quoi que ce soit sur terre et d’apprendre à dire « non ! » En cas d’échec, le coût est connu : licenciement, exil, condamnation à mort ! [less ▲]

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See detailLettre d'information trimestrielle n° 15 du projet DACEFI 2
Boldrini, Sylvie; Meunier, Quentin; Moumbogou, Carl et al

E-print/Working paper (2014)

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See detailTowards a system of concept in GP/FM. Part I towards a specific indexation system. working draft
Jamoulle, Marc ULg

E-print/Working paper (2014)

EXECUTIVE SUMMARY Towards a system of concept on general practice / family medicine Part 1 Towards a specific indexation system in GP/FM Status of this document ; preliminary draft, not for diffusion ... [more ▼]

EXECUTIVE SUMMARY Towards a system of concept on general practice / family medicine Part 1 Towards a specific indexation system in GP/FM Status of this document ; preliminary draft, not for diffusion Intended audience : Members of the board of the PhD thesis of Marc Jamoulle, department of general practice, Liege University and experts in the field contacted by the author Background :Thousands of general practitioners/ family doctors are gathering each year in local, national or international congresses. They are exchanging thoughts, researches and methods through thousands of communications in various formats; posters, oral communications, workshops and so on. Although this huge collection of bottom-up knowledge is sometimes available through Internet sites, there is no specific indexation system allowing a real knowledge management of the exposed works. Consequently the information could not be reached, which don’t favor the exchange between researchers. The absence of a common indexation system is also a problem to organize the congresses and the participants have always difficulties to find communications relevant of their interest. The technology of semantic web and Linked data have emerged as a future solution to exchange data distributed in many languages between so many providers, the family physicians, spread around the globe. The considerable development of medical ontologies demonstrates the vitality of this field of discovery. Aim of the thesis; To find the best way to identify the main concepts effectively used by practicing GPs by the development of a system of classification embedded in the International classification of Primary Care aiming at retrieval of clinical and non-clinical issues addressed by the authors in their communications To propose a mapped terminology to this classification systems, in other words an ontology of GP/FM, to participle to a linked data based automatic or semi-automatic indexation of knowledge in GP/FM and its implementation in the realm of the semantic web. Content of the part 1 : the first steps towards a global classification system in GP/FM are related as well as previous experiences and difficulties with usual coding systems. The new information technology tools for information management are concisely described which permit the understanding of their importance in future research networks of knowledge in G/FM A comparison of the coding process and results of 6 congress of GP/FM in several countries and 4 languages has been performed to examine the internal reproducibility of the classifying system proposed. Next steps of the thesis are discussed of which first of them would be the constitution of an International research group. [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 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 detailHalf a century of French organizational sociology: methodological roots, compositionist branches
Dubois, Christophe ULg

E-print/Working paper (2014)

Now that 50 years have gone by since the publication of The Bureaucratic Phenomenon (French title: Le phénomène bureaucratique, 1963) by Michel Crozier, what is the legacy bequeathed by the sociology of ... [more ▼]

Now that 50 years have gone by since the publication of The Bureaucratic Phenomenon (French title: Le phénomène bureaucratique, 1963) by Michel Crozier, what is the legacy bequeathed by the sociology of organizations, in France and elsewhere, to today’s researchers? This contribution considers the premises of this methodology in order to establish two important achievements: the “decomposition” of the notions of organization, State and market; and the distinction of three dimensions of organizations, i.e. their managerial discourse, formal and informal structures. This article ends by considering one contemporary challenge this tradition of research has to face: how to account for the mechanisms of collective action, in order to take part in its composition? [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 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 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 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 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 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 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 means ... [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 coefficients of variation (MCV) is illustrated by means of influence functions and some robust counterparts based either on the Minimum Covariance Determinant (MCD) estimator or on the S estimator are advocated. Then, focusing on two of the considered MCV’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 MCV’s in terms of variability and performance of the corresponding asymptotic confidence intervals in a finite sample setting. As expected, when the data are normally distributed, the classical estimator performs better than the robust counterparts based on the MCD or S estimator, while the reverse is true when the data are contaminated. [less ▲]

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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 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 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 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 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 detailIntentionality as Disposition
Boccaccini, Federico ULg

E-print/Working paper (2014)

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See detailLes portfolio : vers une évaluation plus intégrée et plus cohérente avec la notion complexe de compétence
Poumay, Marianne ULg; Maillart, Christelle ULg

E-print/Working paper (2014)

Ce chapitre prend résolument le parti du témoignage et construit sur l’expérience des auteures. Il choisit quelques référents théoriques, qu’il illustre ensuite par deux expériences ciblées, l’une chez ... [more ▼]

Ce chapitre prend résolument le parti du témoignage et construit sur l’expérience des auteures. Il choisit quelques référents théoriques, qu’il illustre ensuite par deux expériences ciblées, l’une chez les étudiants en logopédie/orthophonie et l’autre chez les étudiants en pédagogie de l’enseignement supérieur, deux programmes de l’Université de Liège. Il conclut sur quelques réflexions et perspectives. [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 detailLa psychologie morale de Brentano
Boccaccini, Federico ULg

E-print/Working paper (2014)

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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 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 detailL'expérience internationale étudiante: un atout pour une carrière internationale?
Robert, Jocelyne ULg; Carrabs, Vincenzo

E-print/Working paper (2014)

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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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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 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 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 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 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 detailVorosweep: a fast generalized crystal growing Voronoi diagram generation algorithm
Mouton, Thibaud; Béchet, Eric ULg

E-print/Working paper (2014)

We propose a new algorithm for generating quickly approximate generalized Voronoi diagrams of point sites associated to arbitrary convex distance metric in the Euclidian plane. This algorithm produces ... [more ▼]

We propose a new algorithm for generating quickly approximate generalized Voronoi diagrams of point sites associated to arbitrary convex distance metric in the Euclidian plane. This algorithm produces connected cells by emulating the growth of crystals starting at the point sites, in order to reduce the complexity of the diagram. The main practical contribution is the Vorosweep package which is the reference implementation of the algorithm. Experimental results and benchmarks are given to demonstrate the versatility of this approach. [less ▲]

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See detailLarge deviation spectra based on wavelet leaders
Bastin, Françoise ULg; Esser, Céline ULg; Jaffard, Stéphane ULg

E-print/Working paper (2014)

We introduce a new multifractal formalism, based on distributions of wavelet leaders, which allows to detect non-concave and decreasing multifractal spectra, and we investigate the properties of the ... [more ▼]

We introduce a new multifractal formalism, based on distributions of wavelet leaders, which allows to detect non-concave and decreasing multifractal spectra, and we investigate the properties of the associated function spaces. [less ▲]

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See detailA multifractal formalism based on the Sν spaces: From theory to practice
Esser, Céline ULg; Kleyntssens, Thomas ULg; Nicolay, Samuel ULg

E-print/Working paper (2014)

We present an implementation of a multifractal formalism based on the Sν spaces and show that it effectively gives the right Hölder spectrum in numerous cases. In particular, it allows to recover non ... [more ▼]

We present an implementation of a multifractal formalism based on the Sν spaces and show that it effectively gives the right Hölder spectrum in numerous cases. In particular, it allows to recover non-concave spectra, where other multifractal formalisms only lead to the concave hull of the spectra. [less ▲]

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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 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 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 detailAn overview of the foundations' sector in Belgium
Mernier, Amélie ULg

E-print/Working paper (2013)

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See detailQuelques considérations sur la présomption de titularité des droits d'auteur dans la loi du 30 juin 1994 relative au droit d'auteur et aux droits voisins.
Kouembeu Tagne, Jean Jacques ULg

E-print/Working paper (2013)

Nous avons choisi d'axer notre raisonnement sur la problématique de la présomption de titularité des droits d’auteur dans la loi du 30 juin 1994 relative au droit d'auteur et aux droits voisins. Que ... [more ▼]

Nous avons choisi d'axer notre raisonnement sur la problématique de la présomption de titularité des droits d’auteur dans la loi du 30 juin 1994 relative au droit d'auteur et aux droits voisins. Que signifie-t-elle ? Quelles sont les conditions nécessaires à sa mise en œuvre ? Comment les démonter ? [less ▲]

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See detailUne leçon de Poker Menteur
Choffray, Jean-Marie ULg

E-print/Working paper (2013)

L’évolution de la situation de la société Exide Technologies (Nasdaq : XIDE) offre à l’investisseur potentiel une superbe leçon de « Poker Menteur ». Dans la mesure où les marchés ne produisent pas ... [more ▼]

L’évolution de la situation de la société Exide Technologies (Nasdaq : XIDE) offre à l’investisseur potentiel une superbe leçon de « Poker Menteur ». Dans la mesure où les marchés ne produisent pas souvent ce type de « Quasi-expérience », j’ai décidé d’en reconstruire l’histoire et d’en suivre le développement. En partageant ces observations, mon objectif est de transformer une décision d’investissement réalisée dans des « Conditions Extrêmes » en une expérience susceptible d’être conceptualisée et transmise à d’autres. De plus, la solution à cette situation exceptionnelle pourrait constituer un cas d’école dans le domaine des partenariats public-privé à susciter dans le cadre de la transition énergétique d’un Etat ou d’une région. Temps réel oblige…, trois révisions de ce document sont prévues, en fin de semaine, dans le mois à venir. [less ▲]

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See detailApproximation Algorithms for Multi-Dimensional Vector Assignment Problems
Dokka, Trivikram; Crama, Yves ULg; Spieksma, Frits C.R.

E-print/Working paper (2013)

We consider a special class of axial multi-dimensional assignment problems called multi-dimensional vector assignment (MVA) problems. An instance of the MVA problem is defined by $m$ disjoint sets, each ... [more ▼]

We consider a special class of axial multi-dimensional assignment problems called multi-dimensional vector assignment (MVA) problems. An instance of the MVA problem is defined by $m$ disjoint sets, each of which contains the same number $n$ of $p$-dimensional vectors with nonnegative integral components, and a cost function defined on vectors. The cost of an $m$-tuple of vectors is defined as the cost of their component-wise maximum. The problem is now to partition the $m$ sets of vectors into $n$ $m$-tuples so that no two vectors from the same set are in the same $m$-tuple and so that the total cost of the $m$-tuples is minimized. The main motivation comes from a yield optimization problem in semi-conductor manufacturing. We consider two classes of polynomial-time heuristics for MVA, namely, hub heuristics and sequential heuristics, and we study their approximation ratio. In particular, we show that when the cost function is monotone and subadditive, hub heuristics, as well as sequential heuristics, have finite approximation ratio for every fixed $m$. Moreover, we establish better approximation ratios for certain variants of hub heuristics and sequential heuristics when the cost function is monotone and submodular, or when it is additive. We provide examples to illustrate the tightness of our analysis. Furthermore, we show that the MVA problem is APX-hard even for the case $m=3$ and for binary input vectors. Finally, we show that the problem can be solved in polynomial time in the special case of binary vectors with fixed dimension $p$. [less ▲]

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See detailLe pape François se trompe-t-il ?
Choffray, Jean-Marie ULg

E-print/Working paper (2013)

La crise de panique généralisée à laquelle nous avons assisté depuis 2007/2008 – pour reprendre l’analyse qu’en fait l’homme le mieux informé du monde, Ben Bernanke –, n’est rien d’autre que le double ... [more ▼]

La crise de panique généralisée à laquelle nous avons assisté depuis 2007/2008 – pour reprendre l’analyse qu’en fait l’homme le mieux informé du monde, Ben Bernanke –, n’est rien d’autre que le double d’une crise de confiance trouvant son origine dans l’accélération de l’information et la difficulté du pouvoir politique à en percevoir et à en accepter les conséquences. [less ▲]

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See detailLes FAQs du tableau de bord - Mythes et réalités du tableau de bord à l'ère de la mondialisation
Van Caillie, Didier ULg

E-print/Working paper (2013)

Ce document synthétise en 8 questions clés l'état de notre expérience en matière de conception et d'implémentation d'un tableau de bord dans une organisation, privée ou publique, grande ou petite. Les 8 ... [more ▼]

Ce document synthétise en 8 questions clés l'état de notre expérience en matière de conception et d'implémentation d'un tableau de bord dans une organisation, privée ou publique, grande ou petite. Les 8 questions abordées sont : 1. Qu’est-ce qu’un tableau de bord ? 2. Quelle est son utilité pour une organisation à l’ère de la mondialisation ? 3. Quels sont les prérequis à l’utilisation d’un tableau de bord ? 4. Faut-il un tableau de bord unique ou plusieurs tableaux de bord ? 5. Quels indicateurs intégrer au tableau de bord ? 6. Quelle forme donner à un tableau de bord ? 7. Quelle forme donner aux indicateurs retenus ? 8. Comment piloter le projet "Conception & implémentation d’un tableau de bord" ? [less ▲]

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See detailLa fin d'une époque...?
Choffray, Jean-Marie ULg

E-print/Working paper (2013)

Il est des moments exceptionnels dans la vie qui rappellent les lignes de fracture de l’histoire. C’est, peut-être, ce que notre monde moderne vit aujourd’hui. Dans ce document, et avant que nous ne ... [more ▼]

Il est des moments exceptionnels dans la vie qui rappellent les lignes de fracture de l’histoire. C’est, peut-être, ce que notre monde moderne vit aujourd’hui. Dans ce document, et avant que nous ne vivions ce qui pourrait être un printemps, ou un automne « chaud », il m’a paru utile de mettre un peu d’ordre dans mes observations sur « L’air du temps. » Pas d’autre ambition pour ce texte, donc, que de chercher à comprendre les événements passés, et de prendre date sur les nuages qui s’amoncellent ! [less ▲]

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Peer Reviewed
See detailRetour au travail après une longue absence...
Mairiaux, Philippe ULg

E-print/Working paper (2013)

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See detailLes nouvelles dispositions légales pour la récupération de bois abandonnés
Meunier, Quentin; Moumbogou, Carl; Vermeulen, Cédric ULg

E-print/Working paper (2013)

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See detailLa superposition des permis forestiers, des permis miniers et des futures forêts communautaires
Morin, Amélie; Moumbogou, Carl; Meunier, Quentin et al

E-print/Working paper (2013)

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See detailImpact of uncertainty in climate forcing on projections of the West Antarctic ice sheet over the 21st and 22nd centuries
Payne, A.J.; Cornford, S.L.; Martin, D.F. et al

E-print/Working paper (2013)

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See detailLettre d’information trimestrielle du projet Développement d’Alternatives Communautaires à l’Exploitation Forestière Illégale
Boldrini, Sylvie; Moumbogou; Meunier, Quentin et al

E-print/Working paper (2013)

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See detailEvolution de la ressource ligneuse et des stocks de carbone
Marien, Jean-Noel; Bisiaux, F.; Boulogne, M. et al

E-print/Working paper (2013)

Entre 2010 et 2012, une étude complexe a été menée pour apporter des éléments qualitatifs et quantitatifs fiables sur l’évolution de la ressource ligneuse sur le bassin d’approvisionnement en bois énergie ... [more ▼]

Entre 2010 et 2012, une étude complexe a été menée pour apporter des éléments qualitatifs et quantitatifs fiables sur l’évolution de la ressource ligneuse sur le bassin d’approvisionnement en bois énergie de Kinshasa. Cette étude pluridisciplinaire (Figure 1) a mobilisé l’analyse d’images satellites, la cartographie, les inventaires forestiers, la dendrométrie, des études sur la carbonisation traditionnelle et la compréhension des dynamiques sociales et économiques des zones d’étude. En plus d’analyser l’évolution de la couverture forestière sur la période de suivi (1984-2012), ce travail a permis de quantifier pour la première fois, sur des bases scientifiques et des méthodologies solides, les stocks de biomasse aérienne et de carbone ainsi que leur évolution. Après calage avec les standards REDD+, ces informations devraient se révéler très utiles dans la perspective des futurs projets REDD+ en Afrique centrale. Cette étude couvre une superficie de 900 000 ha située sur le plateau Batéké et au Bas Congo. La zone d’étude concerne près de 80% de l’approvisionnement total en bois énergie de l’agglomération de Kinshasa (Figure 2). [less ▲]

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See detailProgress Report February 2013
Léonard, Grégoire ULg

E-print/Working paper (2013)

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See detailSocial Security and Economic Integration
Artige, Lionel ULg; Dedry, Antoine ULg; Pestieau, Pierre ULg

E-print/Working paper (2013)

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See detailReforming the Postal Universal Service
Gautier, Axel ULg; Poudou, Jean-Christophe

E-print/Working paper (2013)

The postal sector has undergone dramatic changes over the recent years under the double effect of ongoing liberalization and increased competition with alternative communication channels (e-substitution ... [more ▼]

The postal sector has undergone dramatic changes over the recent years under the double effect of ongoing liberalization and increased competition with alternative communication channels (e-substitution). As a result, the mail volume handled by the historical operator has declined sharply while the latter's ability to match the same standard of universal service may be under threat. Thus, a reform of the postal universal service is on the agenda. This paper examines possible reforming options ranging from keeping universal service within the postal sector to redefining universal service as spanning postal and electronic technologies. [less ▲]

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See detailBrentano’s empiricism and the refutation of a priori knowledge
Boccaccini, Federico ULg

E-print/Working paper (2013)

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See detailSoil apparent conductivity measurements for planning and analysis of agricultural experiments: A case study from Western-Thailand
Rudolph, Sebastian; Wongleecharoen, Chalemchart; Marchant, B. et al

E-print/Working paper (2013)

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See detailEstimation from cross-sectional data under a semiparametric truncation model
de Uña-Álvarez, Jacobo; Heuchenne, Cédric ULg; Laurent, Géraldine ULg

E-print/Working paper (2013)

Cross-sectional sampling is often used when investigating inter-event times, resulting in left-truncated and right-censored data. In this paper we consider a semiparametric truncation model in which the ... [more ▼]

Cross-sectional sampling is often used when investigating inter-event times, resulting in left-truncated and right-censored data. In this paper we consider a semiparametric truncation model in which the truncating variable is assumed to belong to a certain parametric family, while nothing is assumed on lifetime and censoring distributions. The novelty of this work is in the fact that it introduces estimators of this semiparametric model in the presence of censoring. Two alternative methods are considered, based on conditional and full likelihood considerations. Asymptotic representations of the estimators for the lifetime distribution are obtained, and their weak convergence is established. The finite sample performance of the new estimators is explored through simulations, and two real data illustrations are provided. One of the conclusions of our research is that both estimators perform better than Wang's NPMLE when the parametric family for the truncation variable is valid) in the sense of the integrated mean squared error, and that the full likelihood approach is preferable to the conditional likelihood approach for the estimation of the lifetime distribution but not necessarily for the estimation of the truncation distribution. [less ▲]

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See detailLa tolérance est coûteuse. On essaye l'intolérance ?
Jacquemain, Marc ULg

E-print/Working paper (2013)

Le texte a servi à présenter une conférence à des étudiants de bacheliers pédagogiques. Il rappelle, sur un ton informel, mais en essayant d'être rigoureux, la place et l'importance de la tolérance dans ... [more ▼]

Le texte a servi à présenter une conférence à des étudiants de bacheliers pédagogiques. Il rappelle, sur un ton informel, mais en essayant d'être rigoureux, la place et l'importance de la tolérance dans toute conception raisonnable de la vie en société. Il rappelle notamment que si la tolérance n'est pas une vertu "flamboyante", elle constitue un préalable indispensable à d'autres modalités plus exigeantes du vivre ensemble [less ▲]

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