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See detailOn the collapse behaviour of oil reservoir chalk
De Gennaro, Vincenzo; Delage, Pierre; Priol, Grégoire et al

in Geotechnique (2004), 54(6), 415-420

Oil exploitation in North Sea Ekofisk oilfield started in 1971, the reservoir is located in a 150 m thick layer of porous chalk (n = 40-50%) at a 3000 m depth. Enhanced oil recovery procedure by sea water ... [more ▼]

Oil exploitation in North Sea Ekofisk oilfield started in 1971, the reservoir is located in a 150 m thick layer of porous chalk (n = 40-50%) at a 3000 m depth. Enhanced oil recovery procedure by sea water injection (waterflooding) was initiated in 1987. Starting from this date, seabed subsidence due to chalk compaction evolves at a fairly constant rate (i.e. 40 cm/year). Nowadays, the decrease of the seafloor level is of about 10 m. Reservoir management and production strategies are at the origin of the growing interest of petroleum industry in disposing of a comprehensive description of the chalk mechanical behaviour. In this note the subsidence due to waterflooding is interpreted within a framework taken from the mechanics of unsaturated soils. By considering oil as the non-wetting fluid and water as the wetting fluid, chalk compaction is depicted as a collapse phenomenon due to oil-water suction decrease. A series of suction controlled tests in the osmotic oedometer cell are presented. Water weakening effects and chalk compaction (collapse) seem likely to occur through the lost of strength of the inter-granular links existing in the oil saturated sample. The nature of these links includes both capillary and physico-chemical fluids-chalk interactions, and is well characterised by the oil-water suction. [less ▲]

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See detailOn the combination of corpus-based and experimental methodologies in the study of causal, contrastive and metadiscourse connectives in L1 and L2 text comprehension and production
Perrez, Julien ULg; Degand, Liesbeth

in Archer, Dawn; Rayson, Paul; Wilson, Andrew (Eds.) et al Proceedings of the Corpus Linguistics 2003 Conference (2003)

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See detailOn the complementarity of contrastive linguistics and interlanguage studies
Rasier, Laurent ULg; Hiligsmann, Philippe

Conference (2008)

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See detailOn the concept of exposure time
Delhez, Eric ULg

in Continental Shelf Research (2013), 71

The concept of exposure time offers an interesting alternative to the residence time for the quantitative assessment of the water renewal of estuaries and semi-enclosed basins. It can cope with the ... [more ▼]

The concept of exposure time offers an interesting alternative to the residence time for the quantitative assessment of the water renewal of estuaries and semi-enclosed basins. It can cope with the oscillations or meandering of the flow around the boundary of the control domain and is therefore particularly suited for tidal seas and sub-basins with strong mesoscale activity. We show however that the exposure time in a control domain \omega cannot be properly defined if \omega is part of a larger bounded system unless some removal process is taken into account. It is therefore suggested to revise and extend the definition of the exposure time by including a first order decay : ``the exposure time for the rate constant \lambda is the total time spent in a control domain \omega by particles subject to a first order decay with a rate constant $\lambda$, irrespective of their possible excursions in and out the control domain''. The exposure time revised in this way is well-defined in all circumstances provided that the decay rate differs from zero but depends on the rate constant \lambda. Alternatively, in order to diagnose the movement of water masses, the first order decay can be considered only outside the control domain. [less ▲]

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See detailOn the concrete complexity of the successor function
Berthé, Valérie; Frougny, Christiane; Rigo, Michel ULg et al

Conference (2012, September 11)

We consider two kinds of questions about the successor function. The first one is concerned with the estimation of the length of the carry propagation when applying the successor map on the first n ... [more ▼]

We consider two kinds of questions about the successor function. The first one is concerned with the estimation of the length of the carry propagation when applying the successor map on the first n integers (or more generally on the first n elements in a given language). This leads to the notion of amortized (or average) carry propagation when applying the successor function. The second question is a computational issue: estimating the number of operations (in classical terms of Turing machines complexity) required to compute the representations of the first n integers from the first one by applying n times the successor function. This leads to the notion of (amortized) complexity, i.e., the average amount of computations required to obtain the successor of an element. [less ▲]

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See detailOn the constitutive equations of the chalk
Charlier, Robert ULg; Radu, Jean-Pol ULg

in ICONMIG'88 (1988)

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See detailOn the construction of automata from linear arithmetic constraints
Wolper, Pierre ULg; Boigelot, Bernard ULg

in Lecture Notes in Computer Science (2000, March), 1785

This paper presents an overview of algorithms for constructing automata from linear arithmetic constraints. It identifies one case in which the special structure of the automata that are constructed ... [more ▼]

This paper presents an overview of algorithms for constructing automata from linear arithmetic constraints. It identifies one case in which the special structure of the automata that are constructed allows a linear-time determinization procedure to be used. Furthermore, it shows through theoretical analysis and experiments that the special structure of the constructed automata does, in quite a general way, render the usual upper bounds on automata operations vastly overpessimistic. [less ▲]

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See detailOn the construction of the inclusion boundary neighbourhood for markov equivalence classes of bayesian network structures
Auvray, Vincent; Wehenkel, Louis ULg

in Proceedings of Uncertainty in Artificial Intelligence (2002)

The problem of learning Markov equivalence classes of Bayesian network structures may be solved by searching for the maximum of a scoring metric in a space of these classes. This paper deals with the ... [more ▼]

The problem of learning Markov equivalence classes of Bayesian network structures may be solved by searching for the maximum of a scoring metric in a space of these classes. This paper deals with the definition and analysis of one such search space. We use a theoretically motivated neighbourhood, the inclusion boundary, and represent equivalence classes by essential graphs. We show that this search space is connected and that the score of the neighbours can be evaluated incrementally. We devise a practical way of building this neighbourhood for an essential graph that is purely graphical and does not explicitely refer to the underlying independences. We find that its size can be intractable, depending on the complexity of the essential graph of the equivalence class. The emphasis is put on the potential use of this space with greedy hillclimbing search. [less ▲]

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See detailOn the Construction of WiMAX Mesh Tree
Nahle, Salim; Iannone, Luigi,; Donnet, Benoît ULg et al

in IEEE Communications Letters (2007), 11(12),

The IEEE 802.16 protocol, also known as WiMAX, has been designed to support long-range communications with high bitrates, using two operation modes: Point-to-Multi-Point (PMP) and Mesh. In the mesh mode ... [more ▼]

The IEEE 802.16 protocol, also known as WiMAX, has been designed to support long-range communications with high bitrates, using two operation modes: Point-to-Multi-Point (PMP) and Mesh. In the mesh mode, Subscriber Stations (SSs) can directly communicate with each other, thus forming a tree, and can be used to forward other's data packets in a multi-hop fashion. On the contrary, in the PMP mode only one hop communication toward the Base Station (BS) is allowed. In this paper, we investigate the performance of the mesh mode by proposing an algorithm for constructing the WiMAX mesh tree. Our algorithm increases routes' effective throughput by splitting long links into multiple shorter ones. We show through simulations that this approach leads to improving the throughput capacity of WiMAX-based wireless mesh networks. [less ▲]

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See detailOn the convergence of relaxation schemes to couple phasor-mode and electromagnetic transients simulations
Plumier, Frédéric ULg; Geuzaine, Christophe ULg; Van Cutsem, Thierry ULg

in Proceedings of the IEEE PES General Meeting (2014, July)

Hybrid simulations combining phasor-mode and electromagnetic transients models aim at taking advantage of computational speed of the former and accuracy of the latter. For simulation accuracy, a ... [more ▼]

Hybrid simulations combining phasor-mode and electromagnetic transients models aim at taking advantage of computational speed of the former and accuracy of the latter. For simulation accuracy, a relaxation process is used, which consists of iterating between both models. The convergence properties of this relaxation process are investigated. The speed of convergence is assessed when the variables exchanged at the interface between both models are respectively pure voltage/current sources, Norton/Thévenin equivalents, or a combination of them. Iteratively updated Norton/Thévenin equivalents are shown to drastically reduce the number of relaxation iterations. [less ▲]

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See detailOn the Convergence of Social Protection Performance in the European Union
Lefebvre, Mathieu ULg; Coelli, Tim; Pestieau, Pierre ULg

in CESifo Economic Studies (2010), 56(2), 300-322

In this article, we use data on five social inclusion indicators (poverty, inequality, unemployment, <br />education and health) to assess and compare the performance of 15 European <br />welfare states ... [more ▼]

In this article, we use data on five social inclusion indicators (poverty, inequality, unemployment, <br />education and health) to assess and compare the performance of 15 European <br />welfare states (EU15) over a 12-year period from 1995 to 2006. Aggregate measures of <br />performance are obtained using index number methods similar to those employed in the <br />construction of the widely used Human Development Index. These are compared with <br />alternative measures derived from data envelopment analysis methods. The influence of <br />methodology choice and the assumptions made in scaling indicators upon the results <br />obtained is illustrated and discussed. We then analyse the evolution of performance <br />over time, finding evidence of some convergence in performance and no sign of social <br />dumping. [less ▲]

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See detailOn the Convergence of Social Protection Performance in the European Union
Lefebvre, Mathieu ULg

Scientific conference (2010, May)

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See detailOn the correlation between oxygen uptake in plastids of greening etiolated oat leaves and pigment photooxidation
Franck, Fabrice ULg; Schmid, G. H.

in Zeitschrift für Naturforschung. Section C : Biosciences (1985), 40c

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See detailOn the cost and complexity of the successor function
Berthé, Valérie; Frougny, Christiane; Rigo, Michel ULg et al

in Arnoux, P.; Bédaride, N. (Eds.) Proceedings of WORDS 2007 (2007)

For a given numeration system, the successor function maps the representation of an integer n onto the representation of its successor n+1. In a general setting, the successor function maps the n-th word ... [more ▼]

For a given numeration system, the successor function maps the representation of an integer n onto the representation of its successor n+1. In a general setting, the successor function maps the n-th word of a genealogically ordered language L onto the (n+1)-th word of L. We show that, if the ratio of the number of elements of length n + 1 over the number of elements of length n of the language has a limit b> 1, then the amortized cost of the successor function is equal to b/(b − 1). From this, we deduce the value of the amortized cost for several classes of numeration systems (integer base systems, canonical numeration systems associated with a Parry number, abstract numeration systems built on a rational language, and rational base numeration systems). [less ▲]

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See detailOn the coupling of primary production and calcification at the continental margin
Harlay, Jérôme ULg; Chou, Lei; Roevros, Nathalie et al

Poster (2004, March 05)

Until now, little attention has been paid to the processes controlling the production, dissolution and fate of biogenic calcium carbonate in the oceans. It is however well known that net deposition rates ... [more ▼]

Until now, little attention has been paid to the processes controlling the production, dissolution and fate of biogenic calcium carbonate in the oceans. It is however well known that net deposition rates of inorganic carbon to the sediments are comparable to those of organic matter. There remains still large uncertainties concerning the production and redissolution of biogenic carbonate in the marine system and thus about the role of the carbonate pump in response to anthropogenic CO2 perturbations. The understanding of these processes is also a prerequisite to predict the response of marine organisms to global environmental changes. In the framework of the Belgian global change programme, we have developed a project devoted to the study of the inorganic carbon cycle in the Bay of Biscay where coccolithophorid blooms occur frequently. The study focuses on processes associated with the oceanic production and dissolution of calcium carbonate, by combining field investigations, laboratory experiments and modelling efforts. Remote sensing demonstrates a close relationship between vertical mixing along the continental margin and the development of the phytoplankton bloom. We will present here, results of 14C incorporation experiments used to evaluate the rate of production of organic and inorganic particulate carbon, obtained during a coccolithophorid spring bloom in the investigated area. A tentative mass balance of the carbon fluxes for this area will be presented, confirming the importance that the calcium carbonate pump may play in the oceanic system. [less ▲]

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See detailOn the coupling of primary production and calcification during a field experiment in the northeastern Atlantic
Chou, Lei; Harlay, Jérôme ULg; Roevros, Nathalie et al

Poster (2003, April 06)

The role of calcifying phytoplanktonic organisms in ocean carbon biogeochemistry and in climate change has received increasing attention in the marine community. The quantification of the production of ... [more ▼]

The role of calcifying phytoplanktonic organisms in ocean carbon biogeochemistry and in climate change has received increasing attention in the marine community. The quantification of the production of biogenic calcium carbonate and associated organic matter in the photic zone and of their fate during settling is essential for a better assessment of the oceanic carbon cycle. In the framework of the Belgian global change programme, we conducted a field experiment on board the R/V Belgica in Spring 2002 along the Northern Bay of Biscay margin during successive coccolithophorid Emiliania huxleyi (Ehux) blooms. We aim, in particular, at quantifying the role of calcifying phytoplanktonic organisms in sequestering carbon. With near real-time transmission of remote sensing data during the survey, we were able to track the position and evolution of the various coccolithophore blooms along the shelf break. Bio-optical measurements were performed for modelling purpose and for calibration of the recently launched MERIS Sensor. During the field campaign, special attention was paid to the precise determination of the dissolved inorganic carbon chemistry. Primary production and rate of calcification were measured using C14 incorporation experiments and the organic to inorganic particulate carbon ratio quantified. Phytoplankton speciation was determined by microscopic examination, flow cytometry and HPLC pigment analyses. Zooplankton grazing experiments on phytoplankton were also performed. Suspended particles were characterised by their chemical composition and morphology. Th234 was used to quantify particle residence times and particulate organic carbon fluxes in surface waters. The results indicate significant particle export during the sampling period, with particle residence times in the upper 80 m ranging from 15 to 45 days. In this presentation, we will integrate the results obtained from remote sensing, biooptical investigation, water chemistry and process studies to elucidate the coupling of primary production and calcification during Ehux blooms and its importance in the marine biogeochemical cycle of carbon. [less ▲]

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See detailOn the DD-carboxypeptidase enzyme system of Streptomyces strain K15
Leyh-Bouille, Mélina; Nguyen-Distèche, Martine ULg; Ghuysen, Jean-Marie ULg

in European Journal of Biochemistry (1981), 115(3), 579-584

Streptomyces K15 possesses a set of exocellular and cell-bound D-alanyl-D-alanine carboxypeptidases. Four of them have been isolated to the stage where each enzyme preparation contains on single ... [more ▼]

Streptomyces K15 possesses a set of exocellular and cell-bound D-alanyl-D-alanine carboxypeptidases. Four of them have been isolated to the stage where each enzyme preparation contains on single penicillin-binding protein. The exocellular 54000-Mr enzyme is extremely sensitive to benzylpenicillin and performs low transpeptidase activity on the carbonyl-donor/amino-acceptor tetrapeptide ACLLys(Gly)-DAla-DAla. The exocellular 40 000-Mr enzyme and the two lysozyme-releasable 40 000-Mr and 38 000-Mr enzymes are moderately sensitive to benzylpenicillin and have a high propensity to catalyse dimer formation from the aforementioned tetrapeptide monomer. [less ▲]

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See detailOn the decoupling of heavy sneutrinos in low-scale seesaw models
Krauss, Manuel E.; Porod, Werner; Staub, Florian et al

E-print/Working paper (2013)

Detailed reference viewed: 10 (0 ULg)
See detailOn the definition and use of landscape metrics to disentangle landscape complexity.
Bogaert, Jan ULg

in Gibelli, G.; Brancucci, G. (Eds.) Pianificare l’Incertezza. L’Ecologia del Paesaggio nella Gestione dei Sistemi Territoriali. (2006)

Detailed reference viewed: 4 (1 ULg)